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#2051 2024-02-06 00:05:46

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2053) Vagus Nerve


The vagal nerves carry signals between your brain, heart and digestive system. They’re a key part of your parasympathetic nervous system. Vagus nerve damage can lead to gastroparesis, food not moving into your intestines. Some people with vasovagal syncope faint from low blood pressure. Vagus nerve stimulation (VNS) can treat epilepsy and depression.


Vagus nerve is the longest and most complex of the cranial nerves. The vagus nerve runs from the brain through the face and thorax to the abdomen. It is a mixed nerve that contains parasympathetic fibres. The vagus nerve has two sensory ganglia (masses of nerve tissue that transmit sensory impulses): the superior and the inferior ganglia. The branches of the superior ganglion innervate the skin in the concha of the ear. The inferior ganglion gives off two branches: the pharyngeal nerve and the superior laryngeal nerve. The recurrent laryngeal nerve branches from the vagus in the lower neck and upper thorax to innervate the muscles of the larynx (voice box). The vagus also gives off cardiac, esophageal, and pulmonary branches. In the abdomen the vagus innervates the greater part of the digestive tract and other abdominal viscera.

The vagus nerve has the most extensive distribution of the cranial nerves. Its pharyngeal and laryngeal branches transmit motor impulses to the pharynx and larynx; its cardiac branches act to slow the rate of heartbeat; its bronchial branch acts to constrict the bronchi; and its esophageal branches control involuntary muscles in the esophagus, stomach, gallbladder, pancreas, and small intestine, stimulating peristalsis and gastrointestinal secretions.

Vagus nerve stimulation, in which the nerve is stimulated with pulses of electricity, is sometimes used for patients with epilepsy or depression that is otherwise untreatable; the technique has also been explored for conditions such as Alzheimer disease and migraine.


The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right vagus nerves—but they are typically referred to collectively as a single subsystem. The vagus is the longest nerve of the autonomic nervous system in the human body and comprises both sensory and motor fibers. The sensory fibers originate from neurons of the nodose ganglion, whereas the motor fibers come from neurons of the dorsal motor nucleus of the vagus and the nucleus ambiguus. The vagus was also historically called the pneumogastric nerve.


Upon leaving the medulla oblongata between the olive and the inferior cerebellar peduncle, the vagus nerve extends through the jugular foramen, then passes into the carotid sheath between the internal carotid artery and the internal jugular vein down to the neck, chest, and abdomen, where it contributes to the innervation of the viscera, reaching all the way to the colon. Besides giving some output to various organs, the vagus nerve comprises between 80% and 90% of afferent nerves mostly conveying sensory information about the state of the body's organs to the central nervous system. The right and left vagus nerves descend from the cranial vault through the jugular foramina, penetrating the carotid sheath between the internal and external carotid arteries, then passing posterolateral to the common carotid artery. The cell bodies of visceral afferent fibers of the vagus nerve are located bilaterally in the inferior ganglion of the vagus nerve (nodose ganglia).

The vagus runs parallel to the common carotid artery and internal jugular vein inside the carotid sheath.

The right vagus nerve gives rise to the right recurrent laryngeal nerve, which hooks around the right subclavian artery and ascends into the neck between the trachea and esophagus. The right vagus then crosses anterior to the right subclavian artery, runs posterior to the superior vena cava, descends posterior to the right main bronchus, and contributes to cardiac, pulmonary, and esophageal plexuses. It forms the posterior vagal trunk at the lower part of the esophagus and enters the diaphragm through the esophageal hiatus.

The left vagus nerve enters the thorax between left common carotid artery and left subclavian artery and descends on the aortic arch. It gives rise to the left recurrent laryngeal nerve, which hooks around the aortic arch to the left of the ligamentum arteriosum and ascends between the trachea and esophagus. The left vagus further gives off thoracic cardiac branches, breaks up into the pulmonary plexus, continues into the esophageal plexus, and enters the abdomen as the anterior vagal trunk in the esophageal hiatus of the diaphragm.


* Pharyngeal nerve
* Superior laryngeal nerve
* Aortic nerve
* Superior cervical cardiac branches of vagus nerve
* Inferior cervical cardiac branch
* Recurrent laryngeal nerve
* Thoracic cardiac branches
* Branches to the pulmonary plexus
* Branches to the esophageal plexus
* Anterior vagal trunk
* Posterior vagal trunk


The vagus nerve includes axons which emerge from or converge onto four nuclei of the medulla:

* The dorsal nucleus of vagus nerve – which sends parasympathetic output to the viscera, especially the intestines
* The nucleus ambiguus – which gives rise to the branchial efferent motor fibers of the vagus nerve and preganglionic parasympathetic neurons that innervate the heart
* The solitary nucleus – which receives afferent taste information and primary afferents from visceral organs
* The spinal trigeminal nucleus – which receives information about deep/crude touch, pain, and temperature of the outer ear, the dura of the posterior cranial fossa and the mucosa of the larynx.


The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest.

Additional Information

The vagus nerve is one of 12 cranial nerves in the body. It’s responsible for various bodily functions, including digestion, heart rate, and breathing.

What is the vagus nerve?

There are 12 cranial nerves in the body. They come in pairs and help link the brain with other areas of the body, such as the head, neck, and torso.

Some send sensory information, including details about smells, sights, tastes, and sounds, to the brain. These nerves have sensory functions. Other cranial nerves control the movement of various muscles and the function of certain glands. These are known as motor functions.

While some cranial nerves have either sensory or motor functions, others have both. The vagus nerve is such a nerve. The cranial nerves are classified using Roman numerals based on their location. The vagus nerve is also called cranial nerve X.

What does the vagus nerve affect?

The vagus nerve also called the pneumogastric nerve, is responsible for various internal organ functions, including:

* digestion
* heart rate
* breathing
* cardiovascular activity
* reflex actions, such as coughing, sneezing, swallowing, and vomiting

It plays a role in the autonomic nervous system, which controls actions people do unconsciously, such as breathing and digestion.

It may also form a link between the gut and the brain, playing a role in what scientists call the gut-brain axis. In recent years, experts have been studying the gut-brain axis to look for links between conditions such as obesity and depression.

Vagus nerve anatomy and function

The word “vagus” means wandering in Latin. This is a very appropriate name, as the vagus nerve is the longest cranial nerve. It runs from the brain stem to part of the colon.

The vagus nerve sensory functions are divided into two components:

* Somatic components. These are sensations felt on the skin or in the muscles.
* Visceral components. These are sensations felt in the organs of the body.

Sensory functions of the vagus nerve include:

* providing somatic sensation information for the skin behind the ear, the external part of the ear canal, and certain parts of the throat
* supplying visceral sensation information for the larynx, esophagus, lungs, trachea, heart, and most of the digestive tract
* playing a small role in the sensation of taste near the root of the tongue

Motor functions of the vagus nerve include:

* stimulating muscles in the pharynx, larynx, and the soft palate, which is the fleshy area near the back of the roof of the mouth
* stimulating muscles in the heart, where it helps to lower resting heart rate
* stimulating involuntary contractions in the digestive tract, including the esophagus, stomach, and most of the intestines, which allow food to move through the tract.

Vagus nerve testing

To test the vagus nerve, a doctor may check the gag reflexTrusted Source. During this part of the examination, the doctor may use a soft cotton swab to tickle the back of the throat on both sides. This should cause the person to gag.

If the person does not gag, this may be due to a problem with the vagus nerve, which could indicate a problem with the brainstem function.

Doctors may also assess vagal nerve function when looking at cardiovascular disease, as discussed in recent research. Damage to the vagal nerve can lead to problems with the cardiovascular system.

Measuring heart rate, blood pressure, and cardiovascular response to exercise can provide clues as to how your vagal nerve performs in conjunction with your cardiovascular system, which is known as cardiovagal tone. It can offer clues to your cardiovascular health.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2052 2024-02-07 00:03:02

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2054) Sales Representative


The Sales Representative is responsible for selling products and meeting customer needs while obtaining orders from existing or potential sales outlets. They ensure that the customer is satisfied and adequately taken care of while making a purchase.


A sales representative promotes and sells a company’s products. Read on to learn the skills, education, and overall requirements for a sales representative and how you can start on a path to become one.

A sales representative promotes and sells products to customers on behalf of a company or organization. Someone in this role pitches products to potential customers, presents new ones to existing customers, maintains existing customer accounts, and ensures a smooth sales process and customer satisfaction. Sales representatives generally must meet sales goals and report to their sales director.

Sales representative jobs can be found in many industries, from technology to manufacturing. Many sales reps have flexible schedules, with work-from-home options in some cases. For anyone who enjoys working with others, it’s a great career choice. Sales representative jobs can be lucrative and rewarding for a self-starter who’s motivated and self-confident.

Types of sales representatives

There are two main types of sales representatives: inside sales representatives and outside sales representatives. An inside sales representative typically uses digital communication tools to connect with customers remotely, whereas an outside sales representative may conduct sales in the "field" via face-to-face interactions.

Sales representatives may sell a variety of products depending on the company and industry. Some types of sales representative jobs include:

* Wholesale
* Manufacturing
* Scientific
* Technical
* Medical
* Pharmaceutical 


A sales representative is responsible for promoting and selling products or services on behalf of a company. This role involves building and maintaining relationships with clients, understanding their needs, and effectively communicating how the company's offerings can meet those requirements. Sales representatives play an important role in the overall sales process, from identifying potential customers and generating leads to closing deals and achieving revenue targets.

Sales representatives employ a variety of strategies to attract and retain customers, including cold calling, networking, and conducting product demonstrations. They are adept at understanding market trends, competitor offerings, and industry developments to position their products or services competitively. Exceptional communication and interpersonal skills are essential for sales representatives, as they engage with clients to address inquiries, negotiate terms, and ensure customer satisfaction.

Duties and Responsibilities

The duties and responsibilities of a sales representative are diverse, encompassing various stages of the sales process.

Here is an overview of the key responsibilities associated with this role:

* Prospecting and Lead Generation: Identify and research potential customers or clients. Generate leads through methods such as cold calling, networking, and leveraging online platforms.
* Client Engagement: Initiate contact with potential customers to understand their needs and introduce the company's products or services. Conduct product demonstrations or presentations to showcase features and benefits.
* Relationship Building: Cultivate and maintain positive relationships with existing and potential clients. Address client inquiries, concerns, or objections in a professional and timely manner.
* Sales Presentations: Create and deliver persuasive sales presentations tailored to the needs of the client. Highlight the unique selling points and value proposition of the products or services.
* Negotiation and Closing Deals: Negotiate terms and conditions with clients to reach mutually beneficial agreements. Close sales deals and achieve or exceed sales targets.
* Product Knowledge: Stay well-informed about the features, specifications, and benefits of the products or services being represented. Keep abreast of industry trends, competitor offerings, and market developments.
* Sales Reporting and Documentation: Maintain accurate records of sales activities, including client interactions, sales calls, and deals closed. Prepare regular reports on sales performance for management.
* Customer Follow-Up: Follow up with clients post-sale to ensure satisfaction and address any additional needs. Seek opportunities for upselling or cross-selling additional products or services.
* Market Research: Conduct market research to identify potential opportunities and challenges. Provide feedback to the company regarding customer preferences, market trends, and competitive activities.
* Collaboration with Teams: Collaborate with marketing, product development, and customer support teams to ensure a cohesive and customer-centric approach. Communicate customer feedback and market insights to internal teams.

Types of Sales Representatives

Sales representatives can specialize in various areas based on the products or services they sell, the industries they target, or the stage of the sales process they focus on. Here are some types of sales representatives:

* Inside Sales Representative: Inside sales representatives work remotely or within the company's office and typically communicate with clients through phone calls, emails, or online meetings. They are responsible for prospecting, lead generation, and closing deals without the need for face-to-face interactions.
* Outside Sales Representative: Outside sales representatives, also known as field sales representatives, engage with clients in person. They often travel to meet potential customers, conduct sales presentations, and build relationships on a personal level.
* Advertising Sales Agent: Advertising sales agents sell advertising space or time to businesses and organizations. They pitch advertising solutions and negotiate contracts, aiming to create effective advertising campaigns that meet both the client's objectives and the media outlet's offerings.
* Retail Salesperson: Retail sales representatives work in a retail environment, interacting directly with customers. They assist shoppers, provide product information, and facilitate sales transactions.
* Insurance Sales Agent: Insurance sales agents sell insurance policies to individuals and businesses. They assess the needs of clients, explain coverage options, and help them choose insurance plans that best fit their requirements.
* Pharmaceutical Sales Representative: Pharmaceutical sales representatives specialize in selling pharmaceuticals, medical equipment, or healthcare services. They typically require a strong understanding of medical terminology and industry regulations.
* Real Estate Agent: Real estate sales representatives focus on selling properties, whether residential or commercial. They assist clients in buying, selling, or renting real estate and often work on commission.
* Car Salesperson: These professionals are responsible for selling automobiles to customers. They guide potential buyers through the car-buying process, provide information on vehicle features, and assist with test drives, negotiations, and paperwork to facilitate a successful sale.
* Technical Sales Representative: Technical sales representatives specialize in selling products or services that require a deep understanding of technical specifications. They often work with complex or specialized solutions and collaborate closely with technical teams.
* Business Development Representative (BDR): Business development representatives focus on generating leads and expanding the customer base. Their primary responsibilities include prospecting, qualifying leads, and setting up appointments or demonstrations for the sales team.
* Enterprise Sales Representative: Enterprise sales representatives target large corporations or organizations as clients. They often manage complex sales cycles, negotiate with high-level decision-makers, and handle larger deal sizes.
* Digital Sales Representative: With the growth of online platforms, digital sales representatives specialize in selling digital products, software, or services. They may focus on e-commerce, digital marketing solutions, or software as a service (SaaS).
* Channel Sales Representative: Channel sales representatives work with third-party distributors, resellers, or partners to sell products. They collaborate with channel partners to reach a broader audience and expand market reach.
* Account Executive: Account executives manage and nurture relationships with existing clients. They focus on upselling, cross-selling, and ensuring client satisfaction. Account executives may also be responsible for renewing contracts and securing long-term commitments.

Additional Information

A sales representative’s job is to promote products and services to potential customers, pitch products with a unique selling promotional strategy, and maintain existing customer accounts by ensuring customers' accounts have a proper and smooth sales process.

Who is a sales representative?

A sales representative (sales rep or salesperson) is an individual who is responsible for selling products, services, or solutions on behalf of a company to prospective customers. Their main objective is to build relationships with potential customers, understand their needs and preferences, and then promote and pitch the company’s offerings to meet those needs.

What does a sales representative do?

The responsibilities of sales representatives are:

* Prospecting
* Building relationships
* Product/service presentation
* Needs assessment
* Customized solutions
* Handling objectives
* Negotiations
* Closing deals
* After-sales support
* Sales reporting

Prospecting: Sales representatives spend a significant amount of them identifying potential customers or leads. They use different methods, such as researching online databases, using social media platforms, attending industry events, and networking to find individuals or businesses that might be interested in their company’s products and services.

Building relationships: Sales representatives are relationship builders. They work on establishing trust and rapport with potential customers to create a foundation for future business opportunities.

Product/service presentation: Once they identify potential customers, sales reps need to effectively present the products and services offered by the company. This includes explaining the benefits and unique selling propositions of the product compellingly. Sales reps must be knowledgeable and confident about the products they are selling.

Needs assessment: During the sales process, sales representatives conduct a thorough needs assessment to understand the specific needs of the customer and pain points of the potential customer.

Customized solutions: Based on the needs assessment, sales reps customize their sales pitch and the solutions to suit the individual customer. They emphasize how their offerings can provide value and solve the customer’s challenges.

Handling objectives: Perspective customers may raise objections or concerns during sales. Sales representatives need to be skilled at handling objections diplomatically and providing suitable responses to alleviate customer objections.

Negotiations: Sales reps engage in negotiations to discuss pricing, terms and conditions while keeping the customer’s interest and budget constraints.

Closing deals: A critical part of a sales rep’s role is to close deals successfully, which means encouraging the customer to make a purchase decision throughout the buying journey.

After-sales support: Sales representatives often continue to be involved after the sales is made. They provide post-sales support, and address customer concerns.

Sales reporting: Sales representatives maintain sales activities, leads, and outcomes records. On the basis of the outcomes, reports are prepared and shared with the team and progress is made towards the target.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2053 2024-02-08 00:02:21

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2055) Alkali


In chemistry, an alkali is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0.


Alkali is any of the soluble hydroxides of the alkali metals—i.e., lithium, sodium, potassium, rubidium, and cesium. Alkalies are strong bases that turn litmus paper from red to blue; they react with acids to yield neutral salts; and they are caustic and in concentrated form are corrosive to organic tissues. The term alkali is also applied to the soluble hydroxides of such alkaline-earth metals as calcium, strontium, and barium and also to ammonium hydroxide. The term was originally applied to the ashes of burned sodium- or potassium-bearing plants, from which the oxides of sodium and potassium could be leached.

The manufacture of industrial alkali usually refers to the production of soda ash (Na2CO3; sodium carbonate) and caustic soda (NaOH; sodium hydroxide). Other industrial alkalies include potassium hydroxide, potash, and lye. The production of a vast range of consumer goods depends on the use of alkali at some stage. Soda ash and caustic soda are essential to the production of glass, soap, miscellaneous chemicals, rayon and cellophane, paper and pulp, cleansers and detergents, textiles, water softeners, certain metals (especially aluminum), bicarbonate of soda, and gasoline and other petroleum derivatives.

People have been using alkali for centuries, obtaining it first from the leachings (water solutions) of certain desert earths. In the late 18th century the leaching of wood or seaweed ashes became the chief source of alkali. In 1775 the French Académie des Sciences offered monetary prizes for new methods for manufacturing alkali. The prize for soda ash was awarded to the Frenchman Nicolas Leblanc, who in 1791 patented a process for converting common salt (sodium chloride) into sodium carbonate. The Leblanc process dominated world production until late in the 19th century, but following World War I it was completely supplanted by another salt-conversion process that had been perfected in the 1860s by Ernest Solvay of Belgium. Late in the 19th century, electrolytic methods for the production of caustic soda appeared and grew rapidly in importance.

In the Solvay, or ammonia-soda process (q.v.) of soda ash manufacture, common salt in the form of a strong brine is chemically treated to eliminate calcium and magnesium impurities and is then saturated with recycling ammonia gas in towers. The ammoniated brine is then carbonated using carbon dioxide gas under moderate pressure in a different type of tower. These two processes yield ammonium bicarbonate and sodium chloride, the double decomposition of which gives the desired sodium bicarbonate as well as ammonium chloride. The sodium bicarbonate is then heated to decompose it to the desired sodium carbonate. The ammonia involved in the process is almost completely recovered by treating the ammonium chloride with lime to yield ammonia and calcium chloride. The recovered ammonia is then reused in the processes already described.

The electrolytic production of caustic soda involves the electrolysis of a strong salt brine in an electrolytic cell. (Electrolysis is the breaking down of a compound in solution into its constituents by means of an electric current in order to bring about a chemical change.) The electrolysis of sodium chloride yields chlorine and either sodium hydroxide or metallic sodium. Sodium hydroxide in some cases competes with sodium carbonate for the same applications, and in any case the two are interconvertible by rather simple processes. Sodium chloride can be made into an alkali by either of the two processes, the difference between them being that the ammonia-soda process gives the chlorine in the form of calcium chloride, a compound of small economic value, while the electrolytic processes produce elemental chlorine, which has innumerable uses in the chemical industry. For this reason the ammonia-soda process, having displaced the Leblanc process, has found itself being displaced, the older ammonia-soda plants continuing to operate very efficiently while newly built plants use electrolytic processes.

In a few places in the world there are substantial deposits of the mineral form of soda ash, known as natural alkali. The mineral usually occurs as sodium sesquicarbonate, or trona (Na2CO3·NaHCO3·2H2O). The United States produces much of the world’s natural alkali from vast trona deposits in underground mines in Wyoming and from dry lake beds in California.


In chemistry, an alkali is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline, and less often, alkalescent, is commonly used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.


The word "alkali" is derived from Arabic al qalīy (or alkali), meaning the calcined ashes (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, was mildly basic. After heating this substance with calcium hydroxide (slaked lime), a far more strongly basic substance known as caustic potash (potassium hydroxide) was produced. Caustic potash was traditionally used in conjunction with animal fats to produce soft soaps, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity. Plant potash lent the name to the element potassium, which was first derived from caustic potash, and also gave potassium its chemical symbol K (from the German name Kalium), which ultimately derived from alkali.

Common properties of alkalis and bases

Alkalis are all Arrhenius bases, ones which form hydroxide ions (OH−) when dissolved in water. Common properties of alkaline aqueous solutions include:

* Moderately concentrated solutions (over 10−3 M) have a pH of 10 or greater. This means that they will turn phenolphthalein from colorless to pink.
* Concentrated solutions are caustic (causing chemical burns).
* Alkaline solutions are slippery or soapy to the touch, due to the saponification of the fatty substances on the surface of the skin.
* Alkalis are normally water-soluble, although some like barium carbonate are only soluble when reacting with an acidic aqueous solution.

Difference between alkali and base

The terms "base" and "alkali" are often used interchangeably, particularly outside the context of chemistry and chemical engineering.

There are various, more specific definitions for the concept of an alkali. Alkalis are usually defined as a subset of the bases. One of two subsets is commonly chosen.

* A basic salt of an alkali metal or alkaline earth metal (this includes Mg(OH)2 (magnesium hydroxide) but excludes NH3 (ammonia)).
* Any base that is soluble in water and forms hydroxide ions or the solution of a base in water. (This includes both Mg(OH)2 and NH3, which forms NH4OH.)
* The second subset of bases is also called an "Arrhenius base".

Alkali salts

Alkali salts are soluble hydroxides of alkali metals and alkaline earth metals, of which common examples are:

* Sodium hydroxide (NaOH) – often called "caustic soda"
* Potassium hydroxide (KOH) – commonly called "caustic potash"
* Lye – generic term for either of two previous salts or their mixture
* Calcium hydroxide (Ca(OH)2) – saturated solution known as "limewater"
* Magnesium hydroxide (Mg(OH)2) – an atypical alkali since it has low solubility in water (although the dissolved portion is considered a strong base due to complete dissociation of its ions)

Alkaline soil

Soils with pH values that are higher than 7.3 are usually defined as being alkaline. These soils can occur naturally, due to the presence of alkali salts. Although many plants do prefer slightly basic soil (including vegetables like cabbage and fodder like buffalo grass), most plants prefer a mildly acidic soil (with pHs between 6.0 and 6.8), and alkaline soils can cause problems.

Alkali lakes

In alkali lakes (also called soda lakes), evaporation concentrates the naturally occurring carbonate salts, giving rise to an alkalic and often saline lake.

Examples of alkali lakes:

* Alkali Lake, Lake County, Oregon
* Baldwin Lake, San Bernardino County, California
* Bear Lake on the Utah–Idaho border
* Lake Magadi in Kenya
* Lake Turkana in Kenya
* Mono Lake, near Owens Valley in California
* Redberry Lake, Saskatchewan
* Summer Lake, Lake County, Oregon
* Tramping Lake, Saskatchewan..


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2054 2024-02-09 00:05:12

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2056) Hairdresser


A hairdresser is a person who cuts people's hair and puts it into a style, usually working in a special shop, called a hairdresser's.


Most hairdressers possess a vast range of skills, but some might choose to specialise in particular treatments and styling techniques. Choosing a specific area of expertise could help you stand out from other hairstylists and put you in higher demand as a consequence. Some of the treatments that aren’t usually considered to be standard include the following:

* Specific colouring techniques e.g. balayage
* Artificial hair extensions and weaves
* Chemical relaxing / keratin straightening
* Traditional or modern perms
* Hair extension styling
* Braiding
* Occasion styling e.g. weddings
* Scalp treatment
* Hot oil treatment
* Detox treatment
* Hair glossing

A hairdressing career appeals to many because of its flexible working hours and the ability to work mobile. All you need to provide a service is the right qualifications, some sterile working space, your tools and your creative mind!

However, if you prefer working around a more established routine, a hair salon would typically expect that you work 40 hours per week, between 9am-6pm with a day off during the week to make up for the Saturdays that you’ll most likely be asked to cover. For those who can’t fit in a full-time role around their other commitments, but still appreciate having a regular working pattern that working in a hair salon offers, part-time hours are normally available.

What qualifications do I need to become a hairdresser?

The most desirable UK qualification is an NVQ - National Vocational Qualification. Passing a Level 2 course will help you start out as a Junior Stylist. To be considered a Senior Stylist, alongside your experience, you will require a Level 3 qualification.

Some salons offer accredited training or apprenticeship schemes that help you gain your qualifications while on the job, but you should usually be prepared to continue working for the salon for some years after your training is completed or pay back the entire cost of your studies. Be sure to understand exactly what is required from you before entering any such schemes.

You could also study Hairdressing Level 2 or 3 Diploma at college. The entry requirements for those courses typically include 2 or more GCSEs at grades 9 to 3 (A* to D), or equivalent for a Level 2 course or between 4-5 GCSEs at grades 9 to 4 (A* to C) for a Level 3 Diploma. These courses can usually be combined with other subjects such as beauty therapy, make-up and nails for those who’d like to develop a broader area of expertise.

You may also want to consider taking an accredited short course with a Professional Beauty Direct Accredited Trainer.  Details of approved training schools can be found on our website.  Accredited courses give those who cannot afford to take a year out to attend college the ability to gain recognised qualifications at a faster pace, with the peace of mind of knowing that they will be able to get insurance to work once qualified.

Aside from official qualifications, a good hairdresser will possess additional key skills, which include a willingness to stay on top of industry trends and learn new techniques, awareness of the ever-changing fashion trends, great customer service and social skills and perhaps above all, creativity.


A hairdresser's job is to organise hair into a particular style or "look". They can cut hair, add colour to it or texture it. A hairdresser may be female or male. Qualified staff are usually called "stylists", who are supported by assistants. Most hairdressing businesses are unisex, that is, they serve both sexes, and have both sexes on their staff.

Male hairdressers who simply cut men's hair (and do not serve females) are often called barbers.

Qualifications for hairdressing usually mean a college course, or an apprenticeship under a senior stylist. Some aspects of the job are quite technical (such as hair dying) and require careful teaching.

A hairdresser specializes in cutting, styling, coloring, and treating hair. These professionals work in salons, spas, or freelance settings, catering to clients of various ages, genders, and hair types.

Hairdressers possess expertise in using a wide range of tools and products to achieve desired hairstyles, including scissors, razors, blow dryers, curling irons, and various hair care products. They consult with clients to understand their preferences and recommend suitable hairstyles based on factors such as face shape, hair texture, and lifestyle. Additionally, hairdressers provide hair care advice and recommend products to maintain the health and appearance of clients' hair between appointments.

Duties and Responsibilities

The duties and responsibilities of a hairdresser encompass a wide range of tasks related to hair care, styling, and customer service. Here are some key responsibilities:

* Hair Cutting and Styling: Hairdressers are skilled in cutting and styling hair according to clients' preferences and facial features. They use various techniques, tools, and products to achieve desired looks, whether it's a simple trim, a layered cut, or an intricate hairstyle for a special occasion.
* Hair Coloring and Treatment: Hairdressers perform hair coloring services, including highlights, lowlights, balayage, and full-color treatments. They also provide hair treatments such as deep conditioning, keratin treatments, and scalp massages to improve the health and appearance of clients' hair.
* Consultation: Before performing any service, hairdressers consult with clients to understand their desired hairstyle, hair type, lifestyle, and maintenance preferences. They offer expert advice and recommendations based on their knowledge and expertise.
* Product Recommendation: Hairdressers recommend hair care products, including shampoos, conditioners, styling products, and treatments, to help clients maintain their hairstyle and keep their hair healthy between salon visits.
* Customer Service: Providing excellent customer service is a crucial aspect of a hairdresser's role. They greet clients warmly, listen attentively to their needs, and ensure they feel comfortable and satisfied throughout their salon experience.
* Sanitation and Hygiene: Hairdressers maintain cleanliness and hygiene standards in the salon by sanitizing tools, equipment, and workstations regularly. They adhere to health and safety protocols to ensure the well-being of clients and staff.
* Continuing Education: To stay current with industry trends and techniques, hairdressers participate in ongoing education and training programs. They attend workshops, seminars, and classes to enhance their skills and expand their knowledge.

Types of Hairdressers

There are several types of hairdressers. Each type of hairdresser requires different skills and expertise, and individuals may choose to specialize in a specific area of hairdressing based on their interests and strengths.

* Barbers: Barbers specialize in cutting and styling men's hair and facial hair. They typically work in barbershops, where they offer a range of services including haircuts, beard trims, and shaves, while also providing grooming advice to clients.
* Celebrity Hairdressers: Celebrity hairdressers cater specifically to the hairstyling needs of celebrities, public figures, and high-profile clients. They often travel with their clients to events, photo shoots, and film sets, providing personalized hair care services and helping them achieve their desired looks for various appearances.
* Hair Colorists: A hair colorist focuses on coloring hair using various techniques and products to achieve desired shades and effects. They assess clients' hair color goals, recommend suitable color options, and apply color treatments with precision and expertise, enhancing clients' overall appearance and confidence.
* Hairdressing Educators: Hairdressing educators specialize in teaching aspiring hairdressers the skills and techniques necessary to succeed in the industry. They develop curriculum, conduct hands-on training sessions, and provide guidance and mentorship to students, ensuring they receive comprehensive education and preparation for their careers in hairdressing.

Are you suited to be a hairdresser?

Hairdressers have distinct personalities. They tend to be artistic individuals, which means they’re creative, intuitive, sensitive, articulate, and expressive. They are unstructured, original, nonconforming, and innovative. Some of them are also enterprising, meaning they’re adventurous, ambitious, assertive, extroverted, energetic, enthusiastic, confident, and optimistic.

What is the workplace of a Hairdresser like?

The workplace of a hairdresser can vary depending on factors such as the type of salon, clientele, and geographic location. Generally, hairdressers work in well-equipped salons that provide a comfortable and inviting environment for both clients and staff. These salons may range from small, independently owned establishments to large, upscale chains located in urban areas or shopping centers.

Inside the salon, hairdressers typically have their own workstation equipped with essential tools and equipment such as styling chairs, mirrors, sinks, and a variety of hair care products. The atmosphere is often lively and energetic, with music playing in the background and a buzz of conversation as stylists interact with clients and colleagues. Some salons may offer additional amenities such as refreshments, magazines, or complimentary Wi-Fi to enhance the client experience.

The work schedule of a hairdresser can vary, with many working full-time, including evenings and weekends to accommodate clients' busy schedules. Flexibility in scheduling is common, allowing hairdressers to balance work and personal commitments. Additionally, some hairdressers may choose to work as freelancers, renting booth space in a salon or offering mobile services to clients in their homes or other locations.

Additional Information

Hairdressing is custom of cutting and arranging the hair, practiced by men and women from ancient times to the present. Early records indicate that the ancient Assyrians wore elaborate curly hair styles; by contrast, the ancient Egyptians, men and women alike, shaved their heads and wore wigs. Whether ornate or simple, hairdressing has been employed by very nearly every society. In 400 BC some Greek women dyed their hair; in the Roman period dying and bleaching were common. Japanese women used lacquer (a precursor of modern-day hair spray) to secure their elaborate coiffures. The wig has come in and gone out of vogue throughout history.

Beginning with the crude curling iron used by women of ancient Rome in creating their elaborate hair styles, hairdressing came to be associated with a variety of technological accoutrements, ranging from simple combs and hairpins to hold the hair in place to complex electrical appliances for drying and grooming the hair and chemical processes to tint, wave, curl, straighten, and condition the hair. By the 20th century, hairdressing itself and the manufacture of materials and equipment had become an occupation and practical art of large proportions.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2055 2024-02-10 00:03:32

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2057) Writer


A writer is a person engaged in writing books, articles, stories, etc., especially as an occupation or profession; an author or journalist.


Writing is a form of human communication by means of a set of visible marks that are related, by convention, to some particular structural level of language.

This definition highlights the fact that writing is in principle the representation of language rather than a direct representation of thought and the fact that spoken language has a number of levels of structure, including sentences, words, syllables, and phonemes (the smallest units of speech used to distinguish one word or morpheme from another), any one of which a writing system can “map onto” or represent. Indeed, the history of writing is in part a matter of the discovery and representation of these structural levels of spoken language in the attempt to construct an efficient, general, and economical writing system capable of serving a range of socially valuable functions. Literacy is a matter of competence with a writing system and with the specialized functions that written language serves in a particular society.

Writing as a system of signs

Languages are systems of symbols; writing is a system for symbolizing these symbols. A writing system may be defined as any conventional system of marks or signs that represents the utterances of a language. Writing renders language visible; while speech is ephemeral, writing is concrete and, by comparison, permanent. Both speaking and writing depend upon the underlying structures of language. Consequently, writing cannot ordinarily be read by someone not familiar with the linguistic structure underlying the oral form of the language. Yet writing is not merely the transcription of speech; writing frequently involves the use of special forms of language, such as those involved in literary and scientific works, that would not be produced orally. In any linguistic community the written language is a distinct and special dialect; usually there is more than one written dialect. Scholars account for these facts by suggesting that writing is related directly to language but not necessarily directly to speech. Consequently, spoken and written language may evolve somewhat distinctive forms and functions.

It is the fact that writing is an expression of language rather than simply a way of transcribing speech that gives to writing, and hence to written language and to literacy, its special properties. As long as writing was seen merely as transcription, as it was by such pioneering linguists as Ferdinand de Saussure and Leonard Bloomfield earlier in the 20th century, its conceptual significance was seriously underestimated. Once writing was seen as providing a new medium for linguistic expression, its distinctness from speech was more clearly grasped. Scholars such as Milman Parry, Marshall McLuhan, Eric Havelock, Jack Goody, and Walter Ong were among the first to analyze the conceptual and social implications of using written as opposed to oral forms of communication.

Writing is merely one, albeit the most important, means of communicating by visible signs. Gestures—such as a raised hand for greeting or a wink for intimate agreement—are visible signs, but they are not writing in that they do not transcribe a linguistic form. Pictures, similarly, may represent events but do not represent language and hence are not a form of writing.

But the boundary between pictures and writing becomes less clear when pictures are used conventionally to convey particular meanings. In order to distinguish pictures from pictorial signs, it is necessary to notice that language has two primary levels of structure, which the French linguist André Martinet referred to as the “double articulation” of language: the meaning structures on one hand and the sound patterns on the other. Indeed, linguists define grammar as a system for mapping—establishing a system of relations between—sound and meaning. These levels of structure admit of several subdivisions, any one of which may be captured in a writing system. The basic unit of the meaning system is called a morpheme; one or more morphemes make up a word. Thus, the word boys is composed of two morphemes, boy and plurality. Grammatically related words make up clauses that express larger units of meaning. Still-larger units make up such discourse structures as propositions and less well-defined units of meaning such as prayers, stories, and poems.

The basic linguistic unit of the sound system is called a phoneme; it is a minimal, contrastive sound unit that distinguishes one utterance from another. Phonemes may be further analyzed in terms of a set of underlying distinctive features, features specifying the ways the sound is physically produced by passing breath through the throat and positioning the tongue and lips. Phonemes may be thought of as roughly equivalent to the sound segments known as consonants and vowels, and combinations of these segments make up syllables.

Writing systems can serve to represent any of these levels of sound or any of the levels of meaning, and, indeed, examples of all of these levels of structure have been exploited by some writing system or other. Writing systems consequently fall into two large general classes: those that are based on some aspect of meaning structure, such as a word or a morpheme, and those that are based on some aspect of the sound system, such as the syllable or the phoneme.

The earlier failure to recognize these levels of structure in language led some scholars to believe that some writing systems, so-called ideograms and pictograms, had been invented to express thought directly, bypassing language altogether. The 17th-century German philosopher Gottfried Leibniz set out to invent the perfect writing system, which would reflect systems of thought directly and thereby be readable by all human beings regardless of their mother tongues. It is now known that such a scheme is impossible. Thought is too intimately related to language to be represented independently of it.

More recently there have been attempts to invent forms for communicating explicit messages without assuming a knowledge of any particular language. Such messages are communicated by means of pictorial signs. Thus, the skirted human figure painted on the door to a toilet, the human figure with an upraised hand on the Pioneer spacecraft, the Amerindian drawing of a horse and rider upside down painted on a rock near a precipitous trail, and the visual patterns branded on range cattle are all attempts to use visual marks to communicate without making any appeal to the structure of any particular language.

However, such signs function only because they represent a high level of linguistic structure and because they function to express one of a highly restricted range of meanings already known to the reader and not because they express ideas or thoughts directly. The sign on the toilet door is an elliptical way of writing “women’s washroom,” just as the word “women” had been earlier. The plaque on the spacecraft can be read as a greeting only if the reader already knows how to express a human greeting symbolically. The inverted horse and rider expressed the message that horses and riders should avoid the trail. And the brand can be read as the name of the owner’s ranch.

Such signs therefore express meanings, not thoughts, and they do so by representing meaning structures larger than can be expressed by a single word. They do so by expressing these meanings elliptically. Such signs are readable because the reader has to consider only a restricted set of possible meanings. While such pictorial signs could not be turned into a general writing system, they can be extremely efficient in serving a restricted set of functions.

The differences between such pictorial signs and other forms of writing are sufficiently great for some scholars to maintain that they are not legitimate types of writing. These differences are that pictorial signs are “motivated”—that is, they visually suggest their meanings—and that they express whole propositions rather than single words. Other scholars would include such signs as a form of writing because they are a conventional means for expressing a particular linguistic meaning. However, scholars agree that such a collection of signs could express only an extremely limited set of meanings.

A similar case is the ancient mosaic found at the entrance of a house in Pompeii, depicting a snarling dog on a chain and bearing the inscription “Cave canem” (“Beware of the dog”). Even nonreaders could “read” the message; the picture is therefore a form of writing rather than of picture making. Such pictorial signs, including logotypes, trademarks, and brand names, are so common in modern urban societies that even very young children learn to read them. Such reading ability is described as “environmental” literacy, not associated with books and schooling.

Similarly, number systems have posed a problem for theorists because such symbols as the Arabic numerals 1, 2, 3, etc., which are conventional across many languages, appear to express thought directly without any intermediary linguistic structure. However, it is more useful to think of these numerals as a particular orthography for representing the meaning structure of these numbers rather than their sound structures. The advantages of this orthography are that the orthography permits the user to carry out mathematical operations, such as carrying, borrowing, and the like, and that the same orthography may be assigned different phonological equivalents in different languages using the same number system. Thus, the numeral 2 is named “two” in English, “deux” in French, “zwei” in German, and so on. Yet it represents not a thought but the word, a piece of language.

It is for these reasons that writing is said to be a system for transcribing language, not for representing thought directly. There are of course other systems for representing thought, including such activities as picture making, dance, and mime. These, however, are not representations of ordinary language; rather, they constitute what the American philosopher Nelson Goodman has called the “languages of art.” These “languages,” or semiotic systems, are systems of signs that are used for expressive and representational purposes. Each of these semiotic systems may in turn be represented by a notational system, a system for representing the semiotic system. Thus, writing can be defined formally as a notational system for representing some level or levels of linguistic form.

Writing is so pervasive in everyday life that many people take it to be synonymous with language, and this confusion affects their understanding of language. The word denotes ambiguously both the oral form and the written form, and so people may confuse them. This occurs, for example, when people think that the sounds of language are made up of letters. Even Aristotle used the same word, gramma, to refer to the basic units of both speech and writing. Yet it is important to distinguish them. People may have competence in a language and yet know nothing about its written form. Similarly, writing is so fundamental to a modern, literate society that its significance has often been overestimated. Since the 18th century it has been common to identify literacy with civilization, indeed with all civil virtues. When European countries colonized other regions, they thought it as important to teach “savages” to read and write as to convert them to Christianity. Modern anthropology has helped to revise what now seems a quaint set of priorities by showing not only that there are no genuinely primitive languages but that differing languages mask no unbridgeable differences between human beings. All humans are rational, speak a language of enormous expressive power, and live in, maintain, and transmit to their young a complex social and moral order.

Scholars of literature have in the past half-century amassed compelling evidence to demonstrate that a complex social order and a rich verbal culture can exist in nonliterate societies. The American scholar Milman Parry, writing in the 1920s, showed that the Homeric epic poems, long regarded as models of literary virtuosity, were in fact the product not of a literate but of an oral tradition. These poems were produced by bards who could not write and were delivered in recitals to audiences who could not read. Writing made possible the recording of these poems, not their composition. The hard and fast dividing line that put civilization and literacy on one side and savagery and irrationality on the other has been abandoned. To be unlettered is no longer confused with being ignorant.

Similarly, it was once generally held that all writing systems represent some stage in a progression toward the ideal writing system, the alphabet. The accepted view today is that all writing systems represent relatively optimal solutions to a large and unique set of constraints, including the structure of the language represented, the functions that the system serves, and the balance of advantages to the reader as opposed to the writer. Consequently, while there are important differences between speaking and writing and between various forms of writing, these differences vary in importance and in effect from language to language and from society to society.


A writer is a person who uses written words in different writing styles, genres and techniques to communicate ideas, to inspire feelings and emotions, or to entertain. Writers may develop different forms of writing such as novels, short stories, monographs, travelogues, plays, screenplays, teleplays, songs, and essays as well as reports, educational material, and news articles that may be of interest to the general public. Writers' works are nowadays published across a wide range of media. Skilled writers who are able to use language to express ideas well, often contribute significantly to the cultural content of a society.

The term "writer" is also used elsewhere in the arts and music, such as songwriter or a screenwriter, but also a stand-alone "writer" typically refers to the creation of written language. Some writers work from an oral tradition.

Writers can produce material across a number of genres, fictional or non-fictional. Other writers use multiple media such as graphics or illustration to enhance the communication of their ideas. Another recent demand has been created by civil and government readers for the work of non-fictional technical writers, whose skills create understandable, interpretive documents of a practical or scientific kind. Some writers may use images (drawing, painting, graphics) or multimedia to augment their writing. In rare instances, creative writers are able to communicate their ideas via music as well as words.

As well as producing their own written works, writers often write about how they write (their writing process); why they write (that is, their motivation); and also comment on the work of other writers (criticism). Writers work professionally or non-professionally, that is, for payment or without payment and may be paid either in advance, or on acceptance, or only after their work is published. Payment is only one of the motivations of writers and many are not paid for their work.

The term writer has been used as a synonym of author, although the latter term has a somewhat broader meaning and is used to convey legal responsibility for a piece of writing, even if its composition is anonymous, unknown or collaborative. Author most often refers to the writer of a book.


Writers choose from a range of literary genres to express their ideas. Most writing can be adapted for use in another medium. For example, a writer's work may be read privately or recited or performed in a play or film. Satire for example, may be written as a poem, an essay, a film, a comic play, or a part of journalism. The writer of a letter may include elements of criticism, biography, or journalism.

Many writers work across genres. The genre sets the parameters but all kinds of creative adaptation have been attempted: novel to film; poem to play; history to musical. Writers may begin their career in one genre and change to another. For example, historian William Dalrymple began in the genre of travel literature and also writes as a journalist. Many writers have produced both fiction and non-fiction works and others write in a genre that crosses the two. For example, writers of historical romances, such as Georgette Heyer, create characters and stories set in historical periods. In this genre, the accuracy of the history and the level of factual detail in the work both tend to be debated. Some writers write both creative fiction and serious analysis, sometimes using other names to separate their work. Dorothy Sayers, for example, wrote crime fiction but was also a playwright, essayist, translator, and critic.

Literary and creative:


Poets make maximum use of the language to achieve an emotional and sensory effect as well as a cognitive one. To create these effects, they use rhyme and rhythm and they also apply the properties of words with a range of other techniques such as alliteration and assonance. A common topic is love and its vicissitudes. Shakespeare's best-known love story Romeo and Juliet, for example, written in a variety of poetic forms, has been performed in innumerable theaters and made into at least eight cinematic versions. John Donne is another poet renowned for his love poetry.


A novelist is an author or writer of novels, though often novelists also write in other genres of both fiction and non-fiction. Some novelists are professional novelists, thus make a living writing novels and other fiction, while others aspire to support themselves in this way or write as an avocation. Most novelists struggle to have their debut novel published, but once published they often continue to be published, although very few become literary celebrities, thus gaining prestige or a considerable income from their work.


A satirist uses wit to ridicule the shortcomings of society or individuals, with the intent of revealing stupidity. Usually, the subject of the satire is a contemporary issue such as ineffective political decisions or politicians, although human vices such as greed are also a common and prevalent subject. Philosopher Voltaire wrote a satire about optimism called Candide, which was subsequently turned into an opera, and many well known lyricists wrote for it. There are elements of Absurdism in Candide, just as there are in the work of contemporary satirist Barry Humphries, who writes comic satire for his character Dame Edna Everage to perform on stage.

Satirists use different techniques such as irony, sarcasm, and hyperbole to make their point and they choose from the full range of genres – the satire may be in the form of prose or poetry or dialogue in a film, for example. One of the most well-known satirists is Jonathan Swift who wrote the four-volume work Gulliver's Travels and many other satires, including A Modest Proposal and The Battle of the Books.

Short story writer

A short story writer is a writer of short stories, works of fiction that can be read in a single sitting.

Interpretive and academic:


Biographers write an account of another person's life. Richard Ellmann (1918–1987), for example, was an eminent and award-winning biographer whose work focused on the Irish writers James Joyce, William Butler Yeats, and Oscar Wilde. For the Wilde biography, he won the 1989 Pulitzer Prize for Biography.


Critics consider and assess the extent to which a work succeeds in its purpose. The work under consideration may be literary, theatrical, musical, artistic, or architectural. In assessing the success of a work, the critic takes account of why it was done – for example, why a text was written, for whom, in what style, and under what circumstances. After making such an assessment, critics write and publish their evaluation, adding the value of their scholarship and thinking to substantiate any opinion. The theory of criticism is an area of study in itself: a good critic understands and is able to incorporate the theory behind the work they are evaluating into their assessment. Some critics are already writers in another genre. For example, they might be novelists or essayists. Influential and respected writer/critics include the art critic Charles Baudelaire (1821–1867) and the literary critic James Wood (born 1965), both of whom have books published containing collections of their criticism. Some critics are poor writers and produce only superficial or unsubstantiated work. Hence, while anyone can be an uninformed critic, the notable characteristics of a good critic are understanding, insight, and an ability to write well.

We can claim with at least as much accuracy as a well-known writer claims of his little books, that no newspaper would dare print what we have to say. Are we going to be very cruel and abusive, then? By no means: on the contrary, we are going to be impartial. We have no friends – that is a great thing – and no enemies.


An editor prepares literary material for publication. The material may be the editor's own original work but more commonly, an editor works with the material of one or more other people. There are different types of editor. Copy editors format text to a particular style and/or correct errors in grammar and spelling without changing the text substantively. On the other hand, an editor may suggest or undertake significant changes to a text to improve its readability, sense or structure. This latter type of editor can go so far as to excise some parts of the text, add new parts, or restructure the whole. The work of editors of ancient texts or manuscripts or collections of works results in differing editions. For example, there are many editions of Shakespeare's plays by notable editors who also contribute original introductions to the resulting publication. Editors who work on journals and newspapers have varying levels of responsibility for the text. They may write original material, in particular editorials, select what is to be included from a range of items on offer, format the material, and/or fact check its accuracy.


Encyclopaedists create organised bodies of knowledge. Denis Diderot (1713–1784) is renowned for his contributions to the Encyclopédie. The encyclopaedist Bernardino de Sahagún (1499–1590) was a Franciscan whose Historia general de las cosas de Nueva España is a vast encyclopedia of Mesoamerican civilization, commonly referred to as the Florentine Codex, after the Italian manuscript library which holds the best-preserved copy.


Essayists write essays, which are original pieces of writing of moderate length in which the author makes a case in support of an opinion. They are usually in prose, but some writers have used poetry to present their argument.


A historian is a person who studies and writes about the past and is regarded as an authority on it. The purpose of a historian is to employ historical analysis to create coherent narratives that explain "what happened" and "why or how it happened". Professional historians typically work in colleges and universities, archival centers, government agencies, museums, and as freelance writers and consultants. Edward Gibbon's six-volume History of the Decline and Fall of the Roman Empire influenced the development of historiography.


Writers who create dictionaries are called lexicographers. One of the most famous is Samuel Johnson (1709–1784), whose Dictionary of the English Language was regarded not only as a great personal scholarly achievement but was also a dictionary of such pre-eminence, that would have been referred to by such writers as Jane Austen.


Researchers and scholars who write about their discoveries and ideas sometimes have profound effects on society. Scientists and philosophers are good examples because their new ideas can revolutionise the way people think and how they behave. Three of the best known examples of such a revolutionary effect are Nicolaus Copernicus, who wrote De revolutionibus orbium coelestium (1543); Charles Darwin, who wrote On the Origin of Species (1859); and Sigmund Freud, who wrote The Interpretation of Dreams (1899).

These three highly influential, and initially very controversial, works changed the way people understood their place in the world. Copernicus's heliocentric view of the cosmos displaced humans from their previously accepted place at the center of the universe; Darwin's evolutionary theory placed humans firmly within, as opposed to above, the order of manner; and Freud's ideas about the power of the unconscious mind overcame the belief that humans were consciously in control of all their own actions.


Translators have the task of finding some equivalence in another language to a writer's meaning, intention and style. Translators whose work has had very significant cultural effect include Al-Ḥajjāj ibn Yūsuf ibn Maṭar, who translated Elements from Greek into Arabic and Jean-François Champollion, who deciphered Egyptian hieroglyphs with the result that he could publish the first translation of the Rosetta Stone hieroglyphs in 1822. Difficulties with translation are exacerbated when words or phrases incorporate rhymes, rhythms, or puns; or when they have connotations in one language that are non-existent in another. For example, the title of Le Grand Meaulnes by Alain-Fournier is supposedly untranslatable because "no English adjective will convey all the shades of meaning that can be read into the simple [French] word 'grand' which takes on overtones as the story progresses." Translators have also become a part of events where political figures who speak different languages meet to look into the relations between countries or solve political conflicts. It is highly critical for the translator to deliver the right information as a drastic impact could be caused if any error occurred.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2056 2024-02-11 00:03:29

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2058) Nursery rhymes


There’s a reason why nursery rhyme songs have been with us for centuries. They work like a charm.

The constant repetition in the nursery rhyme songs is perfect for developing brains that are trying to keep a hold of vocabulary and learn to focus. What’s more, the children learn to listen carefully from beginning to end and get introduced to the imaginative world of storytelling.

Even the youngest of babies can enjoy nursery rhymes and you will quickly find that they start to connect with you as you sing with them.


Nursery rhyme is a verse customarily told or sung to small children. The oral tradition of nursery rhymes is ancient, but new verses have steadily entered the stream. A French poem numbering the days of the month, similar to “Thirty days hath September,” was recorded in the 13th century; but such latecomers as “Twinkle, Twinkle, Little Star” (by Ann and Jane Taylor; pub. 1806) and “Mary Had a Little Lamb” (by Sarah Josepha Hale; pub. 1830) seem to be just as firmly established in the repertoire.

Some of the oldest rhymes are probably those accompanying babies’ games, such as “Handy, dandy, prickly, pandy, which hand will you have?” (recorded 1598) and its German equivalent, “Windle, wandle, in welchem Handle, oben oder unt?” The existence of numerous European parallels for “Ladybird, ladybird [or, in the United States, “Ladybug, ladybug”], fly away home” and for the singing game “London Bridge is falling down” and for the riddle-rhyme “Humpty-Dumpty” suggests the possibility that these rhymes come down from very ancient sources, since direct translation is unlikely.

Such relics of the past are exceptional. Most nursery rhymes date from the 16th, 17th, and, most frequently, the 18th centuries. Apparently most were originally composed for adult entertainment. Many were popular ballads and songs. “The frog who would a-wooing go” first appeared in 1580 as A Moste Strange weddinge of the ffrogge and the mowse. “Oh where, oh where, ish mine little dog gone?” was a popular song written in 1864 by the Philadelphia composer Septimus Winner.

Although many ingenious theories have been advanced attributing hidden significance, especially political allusions, to nursery rhymes, there is no reason to suppose they are any more arcane than the popular songs of the day. Some were inspired by personalities of the time, and occasionally these can be identified. Somerset tradition associates “Little Jack Horner” (recorded 1725) with a Thomas Horner of Mells who did well for himself during the dissolution of the monasteries.

The earliest known published collection of nursery rhymes was Tommy Thumb’s (Pretty) Song Book, 2 vol. (London, 1744). It included “Little Tom Tucker,” “Sing a Song of Sixpence,” and “Who Killed math Robin?” The most influential was Mother Goose’s Melody: or Sonnets for the Cradle, published by the firm of John Newbery in 1781. Among its 51 rhymes were “Jack and Jill,” “Ding Dong Bell,” and “Hush-a-bye baby on the tree top.” An edition was reprinted in the United States in 1785 by Isaiah Thomas. Its popularity is attested by the fact that these verses are still commonly called “Mother Goose rhymes” in the United States. See also alphabet rhyme; counting-out rhyme; Mother Goose.


A nursery rhyme is a traditional poem or song for children in Britain and many other countries, but usage of the term dates only from the late 18th/early 19th century. The term Mother Goose rhymes is interchangeable with nursery rhymes.

From the mid-16th century nursery rhymes began to be recorded in English plays, and most popular rhymes date from the 17th and 18th centuries. The first English collections, Tommy Thumb's Song Book and a sequel, Tommy Thumb's Pretty Song Book, were published by Mary Cooper in 1744. Publisher John Newbery's stepson, Thomas Carnan, was the first to use the term Mother Goose for nursery rhymes when he published a compilation of English rhymes, Mother Goose's Melody, or, Sonnets for the Cradle (London, 1780).



The oldest children's songs for which records exist are lullabies, intended to help a child fall asleep. Lullabies can be found in every human culture. The English term lullaby is thought to come from "lu, lu" or "la la" sounds made by mothers or nurses to calm children, and "by by" or "bye bye", either another lulling sound or a term for a good night. Until the modern era, lullabies were usually recorded only incidentally in written sources. The Roman nurses' lullaby, "Lalla, Lalla, Lalla, aut dormi, aut lacta", is recorded in a scholium on Persius and may be the oldest to survive.

Many medieval English verses associated with the birth of Jesus take the form of a lullaby, including "Lullay, my liking, my dere son, my sweting" and may be versions of contemporary lullabies. However, most of those used today date from the 17th century. For example, a well-known lullaby such as "Rock-a-bye Baby", could not be found in records until the late-18th century when it was printed by John Newbery (c. 1765).

Early nursery rhymes

A French poem, similar to "Thirty days hath September", numbering the days of the month, was recorded in the 13th century. From the later Middle Ages, there are records of short children's rhyming songs, often as marginalia. From the mid-16th century, they began to be recorded in English plays. "Pat-a-cake" is one of the oldest surviving English nursery rhymes. The earliest recorded version of the rhyme appears in Thomas d'Urfey's play The Campaigners from 1698. Most nursery rhymes were not written down until the 18th century when the publishing of children's books began to move from polemic and education towards entertainment, but there is evidence for many rhymes existing before this, including "To market, to market" and "math a doodle doo", which date from at least the late 16th century. Nursery rhymes with 17th-century origins include, "Jack Sprat" (1639), "The Grand Old Duke of York" (1642), "Lavender's Blue" (1672) and "Rain Rain Go Away" (1687).

The first English collection, Tommy Thumb's Song Book and a sequel, Tommy Thumb's Pretty Song Book, were published by Mary Cooper in London in 1744, with such songs becoming known as "Tommy Thumb's songs". A copy of the latter is held in the British Library. John Newbery's stepson, Thomas Carnan, was the first to use the term Mother Goose for nursery rhymes when he published a compilation of English rhymes, Mother Goose's Melody, or, Sonnets for the Cradle (London, 1780). These rhymes seem to have come from a variety of sources, including traditional riddles, proverbs, ballads, lines of Mummers' plays, drinking songs, historical events, and, it has been suggested, ancient pagan rituals. One example of a nursery rhyme in the form of a riddle is "As I was going to St Ives", which dates to 1730. About half of the currently recognised "traditional" English rhymes were known by the mid-18th century. More English rhymes were collected by Joseph Ritson in Gammer Gurton's Garland or The Nursery Parnassus (1784), published in London by Joseph Johnson.

19th century

In the early 19th century printed collections of rhymes began to spread to other countries, including Robert Chambers' Popular Rhymes of Scotland (1826) and in the United States, Mother Goose's Melodies (1833). From this period the origins and authors of rhymes are sometimes known—for instance, in "Twinkle, Twinkle, Little Star" which combines the melody of an 18th-century French tune "Ah vous dirai-je, Maman" with a 19th-century English poem by Jane Taylor entitled "The Star" used as lyrics.

Early folk song collectors also often collected (what is now known as) nursery rhymes, including in Scotland Sir Walter Scott and in Germany Clemens Brentano and Achim von Arnim in Des Knaben Wunderhorn (1806–1808). The first, and possibly the most important academic collection to focus in this area was James Halliwell-Phillipps' The Nursery Rhymes of England (1842) and Popular Rhymes and Tales in 1849, in which he divided rhymes into antiquities (historical), fireside stories, game-rhymes, alphabet-rhymes, riddles, nature-rhymes, places and families, proverbs, superstitions, customs, and nursery songs (lullabies). By the time of Sabine Baring-Gould's A Book of Nursery Songs (1895), folklore was an academic study, full of comments and footnotes. A professional anthropologist, Andrew Lang (1844–1912) produced The Nursery Rhyme Book in 1897.

20th century

The early years of the 20th century are notable for the illustrations to children's books including Randolph Caldecott's Hey Diddle Diddle Picture Book (1909) and Arthur Rackham's Mother Goose (1913). The definitive study of English rhymes remains the work of Iona and Peter Opie.

Meanings of nursery rhymes

Many nursery rhymes have been argued to have hidden meanings and origins. John Bellenden Ker Gawler (1764–1842), for example, wrote four volumes arguing that English nursery rhymes were written in "Low Saxon", a hypothetical early form of Dutch. He then "translated" them back into English, revealing in particular a strong tendency to anti-clericalism. Many of the ideas about the links between rhymes and historical persons, or events, can be traced back to Katherine Elwes' book The Real Personages of Mother Goose (1930), in which she linked famous nursery rhyme characters with real people, on little or no evidence. She posited that children's songs were a peculiar form of coded historical narrative, propaganda or covert protest, and did not believe that they were written simply for entertainment.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2057 2024-02-12 00:02:28

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2059) Container Freight Station


A CFS (container freight station) is a warehouse that specializes in the consolidation and deconsolidation of cargo. An LCL (less than container load) shipment will be taken to a CFS at origin to be consolidated into a container with other cargo.


A Container Freight Station refers to a facility that consolidates or de-consolidates freight before preparing such freight for the next leg of its journey. Most CFS will be located close to ports of entry such as airports, ocean container ports and major railway hubs.  In the US, a CFS is designated by its FIRMS code.  A list of CFS and their designated FIRMS codes can be found here.

Most of the time it is a warehouse where goods and products that do not fit into one container are collected, stored and wait for other goods to fill a container before they are shipped to the next destination. As such, the CFS is used with Less than Container Load (LCL) shipping where one shipment is not enough to fill a container.

Once the shipment arrives at the facility, it is consolidated and packaged into a Full Container Load (FCL) shipment, which can then be transported to the next stage. LCL is thus more cost-effective when a client does not have enough goods to fill a container and opts to share the space in a container with those of another shipper, rather than pay for a full container.


As your business grows, you may look to expand your footing beyond your existing customer base and extend your reach to attract potential customers. To access a seamless network of distribution and shipping, it is essential to utilize containerized shipping. Earlier, goods from the smaller shipments would be loaded and sorted only at the time of onboarding. But today, the shipping process has been revolutionized, for smaller and larger shipments alike, with the help of Container Freight Station (CFS).

What is Container Freight Station (CFS)?

A CFS is an area, typically a warehouse near shipping ports or crucial railway hubs. These container freight stations are either owned by private stakeholders or shipping terminals. Their primary function involves the consolidation and de-consolidation of less-than-container load (LCL) cargo. Consolidation includes bringing together multiple LCL shipments to form a full container load (FCL) whereas de-consolidation is the process of segregating the LCL shipments.

Moreover, a Container Freight Station is also utilized as a temporary storage space for goods for import and export.

Why Container Freight Station?

CFS has become an integral part of the shipping business. It has made the import-export business seamless at both, origin and destination points. And so, container freight stations are segregated into origin CFS and destination CFS.

With the exponential increase in the demand for LCL shipments, the stations have become a sought-after facility for import-export. It offers an advantage of a centralized shipment location, in turn contributing immensely to streamline and ease up the entire process.

What Does A CFS Do?

* Chalk out a viable container load plan
* Obtain and consolidate LCL shipments for export
* De-consolidate the container at destination CFS. Then, dispatch the shipment for delivery
* Loading and unloading of containers
* Assign specific marks and seals to the containers for identification purposes
* Arranging and rearranging empty containers from container yards
* Managing transportation of laden containers to corresponding port or terminal
* Keeping an account of containers before & after shipping and sort accordingly
* Regular maintenance and timely servicing of the containers
* Overlooking the customs clearance procedures while ensuring the goods are kept safe until shipped or picked up
* Utilizing free spaces to become a temporary storage facility for cargo

The Import and Export Process at CFS

As the Container Freight Station (CFS) simplifies the shipping process for LCL and FCL cargos, here's how the process works:


* Exporter arrives with goods at CFS along with a shipping bill
* The goods are unloaded and the CFS custodian accounts for receival of the goods
* Customs authorities initiate customs clearance procedures for the goods
* Once the procedure is completed and customs authorities issue a shipping bill with “let export order”
* CFS begins loading the goods into the container
* The container is sealed and marked. CFS dispatches it to port/terminal for export


* As the container arrives, the importer files an import general manifest (IGM) at the port. This consists of details regarding the cargo, exporter, importer
* The container is then forwarded to the destination CFS
* CFS offloads the cargo and sends it for cargo clearance process
* Cargo owner or their clearing agent files bill of entry. Once the cargo clearance and duty payment is done, it is forwarded to the customs authorities
* Customs issues bill of entry with an “out of charge” order
* The CFS custodian then dispatched the cargo to the importer with a gate pass

As the Container Freight Station acts as an extension of the port, it allows the ports to reduce congestion while streamlining the entire process.

How does the CFS charge?

For every activity the Container Freight Station performs, it levies a charge accordingly. Moreover, the charges for 20-foot, 40-foot and 45-foot containers vary and the charges for reefer, hazardous and over-dimensional cargo (ODC) are higher. And so, it is essential the exporters and importers must know about these charges.

If these charges are not taken into consideration, it can lead to shipment delays, a rise in logistics cost and most importantly, it could deteriorate your relations with customs authorities, which could be a bad sign for your business.

Undeniably, with the introduction of CFS, the process of shipping has been optimized. But we believe that it takes a trustworthy container freight station to understand what your needs are and ensure the delivery of the best services. Which is why we at Allcargo, have India's widest ISO-certified CFS network at your service.

With our Container Freight Station network across India, we aim to bring you everything you need in a “one-stop” service. The state-of-the-art services along with our several years of experience are designed to cater to all your shipping requirements. We understand what it takes to ensure seamless delivery of your products and provide you with results that exceed your expectations.

Additional Information

CFS stands for ‘Container Freight Station’; a station or warehouse where a number goods or products are stored to be shipped together in one or more containers.

At a CFS, the goods normally belong to a number of different customers, and the shipment is often done via LCL shipments.

LCL (Less container load) shipments occur when the exporters don’t have enough cargo to fill one container full (an FCL). We’ve put together a guide on Less Container Load Shipments and Full Container Load Shipments here.

CFS Pier to Pier

Another term often appearing on Bills of Lading or Letters of Credit are CFS/CFS pier to pier, referring to cargo which is packed by the carrier into a container along with other goods and accepted and unpacked by a consignee at the destination terminal or port.

CFS Receiving Services

CFS receiving services are a set of services which are provided between receiving cargo from exporters and packing them into containers.

CFS Receiving Services include:

* Moving empty containers from a Container Yard to a Container Freight Station
* Drayage of loaded containers from the Container Freight Station to the Container Yard
* Tallying
* Issuing dock receipt or shipping order
* The physical movement of cargo in or out of a Container Freight Station
* Stuffing, sealing and marking of containers for labelling and identification
* Storage of containers
* Ordinary sorting and stacking of containers pre or post shipment
* Preparing containers internal load plan

How CFS works

Exports will be delivered to the nominated CFS for packing, and imports will be picked up from the nominated CFS after unpacking.

All cargo going to one destination will be consolidated and packed into one container at the Container Freight Station. For example, the CFS might pack ten different LCL shipments going to Singapore but from different customers into a single 40′ container, and then ship this one container.

Bills of lading for LCL shipments will be lines bills of lading and will mention CFS/CFS on the bill. Accordingly, the shipping line has responsibility from the CFS at the port of load until the CFS at the port of discharge.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2058 2024-02-13 00:08:47

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2060) Molecule


A molecule is two or more atoms connected by chemical bonds, which form the smallest unit of a substance that retains the composition and properties of that substance. Molecules form the basis of chemistry. Molecules are noted with the element symbol and a subscript with the number of atoms.


A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions.

A molecule may be homonuclear, that is, it consists of atoms of one chemical element, e.g. two atoms in the oxygen molecule (O2); or it may be heteronuclear, a chemical compound composed of more than one element, e.g. water (two hydrogen atoms and one oxygen atom; H2O). In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. This relaxes the requirement that a molecule contains two or more atoms, since the noble gases are individual atoms. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are typically not considered single molecules.

Concepts similar to molecules have been discussed since ancient times, but modern investigation into the nature of molecules and their bonds began in the 17th century. Refined over time by scientists such as Robert Boyle, Amedeo Avogadro, Jean Perrin, and Linus Pauling, the study of molecules is today known as molecular physics or molecular chemistry.


Molecule is a a group of two or more atoms that form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance.

Characteristics of molecules

The division of a sample of a substance into progressively smaller parts produces no change in either its composition or its chemical properties until parts consisting of single molecules are reached. Further subdivision of the substance leads to still smaller parts that usually differ from the original substance in composition and always differ from it in chemical properties. In this latter stage of fragmentation the chemical bonds that hold the atoms together in the molecule are broken.

A water molecule is made up of two hydrogen atoms and one oxygen atom. A single oxygen atom contains six electrons in its outer shell, which can hold a total of eight electrons. When two hydrogen atoms are bound to an oxygen atom, the outer electron shell of oxygen is filled.

Atoms consist of a single nucleus with a positive charge surrounded by a cloud of negatively charged electrons. When atoms approach one another closely, the electron clouds interact with each other and with the nuclei. If this interaction is such that the total energy of the system is lowered, then the atoms bond together to form a molecule. Thus, from a structural point of view, a molecule consists of an aggregation of atoms held together by valence forces. Diatomic molecules contain two atoms that are chemically bonded. If the two atoms are identical, as in, for example, the oxygen molecule (O2), they compose a homonuclear diatomic molecule, while if the atoms are different, as in the carbon monoxide molecule (CO), they make up a heteronuclear diatomic molecule. Molecules containing more than two atoms are termed polyatomic molecules, e.g., carbon dioxide (CO2) and water (H2O). Polymer molecules may contain many thousands of component atoms.

Molecular bonding

The ratio of the numbers of atoms that can be bonded together to form molecules is fixed; for example, every water molecule contains two atoms of hydrogen and one atom of oxygen. It is this feature that distinguishes chemical compounds from solutions and other mechanical mixtures. Thus hydrogen and oxygen may be present in any arbitrary proportions in mechanical mixtures but when sparked will combine only in definite proportions to form the chemical compound water (H2O). It is possible for the same kinds of atoms to combine in different but definite proportions to form different molecules; for example, two atoms of hydrogen will chemically bond with one atom of oxygen to yield a water molecule, whereas two atoms of hydrogen can chemically bond with two atoms of oxygen to form a molecule of hydrogen peroxide (H2O2). Furthermore, it is possible for atoms to bond together in identical proportions to form different molecules. Such molecules are called isomers and differ only in the arrangement of the atoms within the molecules. For example, ethyl alcohol (CH3CH2OH) and methyl ether (CH3OCH3) both contain one, two, and six atoms of oxygen, carbon, and hydrogen, respectively, but these atoms are bonded in different ways.

Not all substances are made up of distinct molecular units. Sodium chloride (common table salt), for example, consists of sodium ions and chlorine ions arranged in a lattice so that each sodium ion is surrounded by six equidistant chlorine ions and each chlorine ion is surrounded by six equidistant sodium ions. The forces acting between any sodium and any adjacent chlorine ion are equal. Hence, no distinct aggregate identifiable as a molecule of sodium chloride exists. Consequently, in sodium chloride and in all solids of similar type, the concept of the chemical molecule has no significance. Therefore, the formula for such a compound is given as the simplest ratio of the atoms, called a formula unit—in the case of sodium chloride, NaCl.

Ionic bonding in sodium chloride. An atom of sodium (Na) donates one of its electrons to an atom of chlorine (Cl) in a chemical reaction, and the resulting positive ion (Na+) and negative ion (Cl−) form a stable ionic compound (sodium chloride; common table salt) based on this ionic bond.

Molecules are held together by shared electron pairs, or covalent bonds. Such bonds are directional, meaning that the atoms adopt specific positions relative to one another so as to maximize the bond strengths. As a result, each molecule has a definite, fairly rigid structure, or spatial distribution of its atoms. Structural chemistry is concerned with valence, which determines how atoms combine in definite ratios and how this is related to the bond directions and bond lengths. The properties of molecules correlate with their structures; for example, the water molecule is bent structurally and therefore has a dipole moment, whereas the carbon dioxide molecule is linear and has no dipole moment. The elucidation of the manner in which atoms are reorganized in the course of chemical reactions is important. In some molecules the structure may not be rigid; for example, in ethane (H3CCH3) there is virtually free rotation about the carbon-carbon single bond.

Determining molecular structure

The nuclear positions in a molecule are determined either from microwave vibration-rotation spectra or by neutron diffraction. The electron cloud surrounding the nuclei in a molecule can be studied by X-ray diffraction experiments. Further information can be obtained by electron spin resonance or nuclear magnetic resonance techniques. Advances in electron microscopy have enabled visual images of individual molecules and atoms to be produced.

Theoretically the molecular structure is determined by solving the quantum mechanical equation for the motion of the electrons in the field of the nuclei (called the Schrödinger equation). In a molecular structure the bond lengths and bond angles are those for which the molecular energy is the least. The determination of structures by numerical solution of the Schrödinger equation has become a highly developed process entailing use of computers and supercomputers.

Polar and nonpolar molecules

If a molecule has no net electrical charge, its negative charge is equal to its positive charge. The forces experienced by such molecules depend on how the positive and negative charges are arranged in space. If the arrangement is spherically symmetric, the molecule is said to be nonpolar. If there is an excess of positive charge on one end of the molecule and an excess of negative charge on the other, the molecule has a dipole moment (i.e., a measurable tendency to rotate in an electric or magnetic field) and is therefore called polar. When polar molecules are free to rotate, they tend to favour those orientations that lead to attractive forces.

Nonpolar molecules generally are considered lipophilic (lipid-loving), whereas polar chemicals are hydrophilic (water-loving). Lipid-soluble, nonpolar molecules pass readily through a cell membrane because they dissolve in the hydrophobic, nonpolar portion of the lipid bilayer. Although permeable to water (a polar molecule), the nonpolar lipid bilayer of cell membranes is impermeable to many other polar molecules, such as charged ions or those that contain many polar side chains. Polar molecules pass through lipid membranes via specific transport systems.

Molecular weight

The molecular weight of a molecule is the sum of the atomic weights of its component atoms. If a substance has molecular weight M, then M grams of the substance is termed one mole. The number of molecules in one mole is the same for all substances; this number is known as Avogadro’s number (6.022140857 × {10}^{23}). Molecular weights can be determined by mass spectrometry and by techniques based on thermodynamics or kinetic transport phenomena.

Additional Information:

What is a molecule?

A molecule is two or more atoms connected by chemical bonds, which form the smallest unit of a substance that retains the composition and properties of that substance. Molecules form the basis of chemistry. Molecules are noted with the element symbol and a subscript with the number of atoms.

Atoms are the fundamental unit of an element. They consist of a nucleus and surrounding electrons. When an atom has an incomplete electron shell, it is said to have valence electrons. When two or more atoms come together to share outer shell valence electrons, a chemical (covalent) bond is formed, and they enter a lower energy state. When atoms bond, energy is released in an exothermic reaction. If the covalent bond is broken and the molecule is split apart, it requires energy input and is thereby endothermic.

Diatomic molecules are when only two atoms combine. An example of a diatomic molecule is carbon monoxide (CO) made of a single atom of carbon and one of oxygen. If the two atoms are the same element, it is called a homonuclear diatomic molecule, such as oxygen (O2) and nitrogen (N2). Polyatomic molecules have more than two atoms, such as water (H2O) and carbon dioxide (CO2). Larger molecules are called polymers and may be made of thousands of atoms.

Atoms can combine in many different ways as molecules. The same atoms may combine in different proportions to form different molecules. As an example, two hydrogen atoms and one oxygen atom form water (H2O), while two hydrogen atoms and two oxygen atoms form hydrogen peroxide (H2O2). It is also possible for the same elements to combine in the same proportions but in a different physical configuration. The physical structure of the molecule can determine its properties. An example is in water: The two hydrogen atoms being positioned 120 degrees apart creates a slight directional electrical charge giving water its solvent capabilities.

A molecule's molecular weight is the sum of all its constituent atoms' atomic weights. Avogadro's number (6.02214076 × {10}^{23}) is the number of molecules that constitutes the atomic weight of a molecule in grams (g). For example, water is two hydrogen atoms with a weight of 1 g each and one oxygen atom with a weight of 16 g, meaning that one mole of water molecules weighs 18 g.

The word molecule comes from the Latin molecula meaning a unit of mass. This name was to encompass its original meaning of "the smallest unit of a substance that still retains the properties of that substance." In 1873, James Maxwell defined atom and molecule: "An atom is a body which cannot be cut in two; a molecule is the smallest possible portion of a particular substance." Since molecules were named before their true nature was discovered, it led to what is now an inexact and debated definition.

Nonmolecular compounds

Many compounds do not fit the strict definition of a molecule but are common in chemistry and everyday life. Some examples of structures that are not molecular in nature are crystals, minerals and metals.

Noble gases are elements that do not have valence electrons and, therefore, do not need to form covalent bonds to become stable. Some may consider them a molecule composed of only a single atom.

In salts and ionic bonds, there are not conventional covalent bonds, so they are not considered molecules. For example, table salt (sodium chloride) forms a lattice structure held together by ionic bonds. In an ionic bond, the electrons may be shared by many atoms instead of only two as in a covalent bond. These chemical bonds do not result in clear separation of individual molecules. These chemical structures are expressed as the ratios of their constituent elements.

Metals do not use covalent bonds and are not considered molecules. Instead, they form metallic bonds where the free valence electrons are shared between all the various atoms in delocalized electron clouds. The electrons are free to move throughout the entire structure instead of being localized.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2059 2024-02-14 00:06:12

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2061) Atom


An atom is a particle of matter that uniquely defines a chemical element. An atom consists of a central nucleus that is surrounded by one or more negatively charged electrons. The nucleus is positively charged and contains one or more relatively heavy particles known as protons and neutrons.


An Atom is the basic building block of all matter and chemistry. Atoms can combine with other atoms to form molecules but cannot be divided into smaller parts by ordinary chemical processes.

Most of the atom is empty space. The rest consists of three basic types of subatomic particles: protons, neutrons, and electrons. The protons and neutrons form the atom’s central nucleus. (The ordinary hydrogen atom is an exception; it contains one proton but no neutrons.) As their names suggest, protons have a positive electrical charge, while neutrons are electrically neutral—they carry no charge; overall, then, the nucleus has a positive charge. Circling the nucleus is a cloud of electrons, which are negatively charged. Like opposite ends of a magnet that attract one another, the negative electrons are attracted to a positive force, which binds them to the nucleus. The nucleus is small and dense compared with the electrons, which are the lightest charged particles in nature. The electrons circle the nucleus in orbital paths called shells, each of which holds only a certain number of electrons.

An ordinary, neutral atom has an equal number of protons (in the nucleus) and electrons (surrounding the nucleus). Thus the positive and negative charges are balanced. Some atoms, however, lose or gain electrons in chemical reactions or in collisions with other particles. Ordinary atoms that either gain or lose electrons are called ions. If a neutral atom loses an electron, it becomes a positive ion. If it gains an electron, it becomes a negative ion. These basic subatomic particles—protons, neutrons, and electrons—are themselves made up of smaller substances, such as quarks and leptons.

More than 90 types of atoms exist in nature, and each kind of atom forms a different chemical element. Chemical elements are made up of only one type of atom—gold contains only gold atoms, and neon contains only neon atoms--and they are ranked in order of their atomic number (the total number of protons in its nucleus) in a chart called the periodic table. Accordingly, because an atom of iron has 26 protons in its nucleus, its atomic number is 26 and its ranking on the periodic table of chemical elements is 26. Because an ordinary atom has the same number of electrons as protons, an element’s atomic number also tells how many electrons its atoms have, and it is the number and arrangement of the electrons in their orbiting shells that determines how one atom interacts with another. The key shell is the outermost one, called the valence shell. If this outermost shell is complete, or filled with the maximum number of electrons for that shell, the atom is stable, with little or no tendency to interact with other atoms. But atoms with incomplete outer shells seek to fill or to empty such shells by gaining or losing electrons or by sharing electrons with other atoms. This is the basis of an atom’s chemical activity. Atoms that have the same number of electrons in the outer shell have similar chemical properties.


An atom is a particle of matter that uniquely defines a chemical element. An atom consists of a central nucleus that is surrounded by one or more negatively charged electrons. The nucleus is positively charged and contains one or more relatively heavy particles known as protons and neutrons.

Atoms are the basic building blocks of matter. Anything that takes up space and anything with mass is made up of atoms.

What are protons and neutrons?

Protons and neutrons are subatomic particles that make up the center of the atom, or its atomic nucleus.

* A proton is positively charged. The number of protons in the nucleus of an atom is the atomic number for the chemical element. Different elements' atomic numbers are found in the Periodic Table of Elements. For example, sodium has 11 protons, and its atomic number is 11. A proton has a rest mass, denoted mp, of approximately 1.673 x {10}^{-27} kilogram (kg).
* A neutron is electrically neutral and has a rest mass, denoted mn, of approximately 1.675 x {10}^{-27}.

The mass of a proton or neutron increases when the particle attains extreme speed, for example in a cyclotron or linear accelerator.

The structure of an atom

The total mass of an atom, including the protons, neutrons and electrons, is the atomic mass or atomic weight. The atomic mass or weight is measured in atomic mass units.

* Protons and neutrons make up the nucleus of an atom and the electrons orbit.
* Electrons contribute only a tiny part to the mass of the atomic structure, however, they play an important role in the chemical reactions that create molecules. For most purposes, the atomic weight can be thought of as the number of protons plus the number of neutrons. Because the number of neutrons in an atom can vary, there can be several different atomic weights for most elements.

Protons and electrons have equal and opposite charges. Protons have a positive charge and electrons a negative charge. Normally, atoms have equal numbers of protons and electrons, giving them a neutral charge.

An ion is an atom with a different number of electrons than protons and is electrically charged. An ion with extra electrons has a negative charge and is called an anion and an ion deficient in electrons has a positive charge and is called a cation.

Atoms having the same number of protons but different numbers of neutrons represent the same element and are known as isotopes of that element. An isotope for an element is specified by the sum of the number of protons and neutrons. For example, the following are two isotopes of the carbon atom:

* Carbon 12 is the most common, non-radioactive isotope of carbon.
* Carbon 14 is a less common, radioactive carbon isotope.

The only neutral atom with no neutrons is the hydrogen atom. It has one electron and one proton.

History of the atom

According to CERN, which is the European Council for Nuclear Research, atoms were created 13.7 billion years ago in the first few minutes after the Big Bang. The new universe cooled and expanded, creating the conditions for electrons and quarks -- the smaller particles that make up protons and neutrons -- to form. Millionths of a second later, quarks aggregated to form protons and neutrons, which combined to form the nuclei of atoms.

Bohr atom model diagram

Niels Bohr's model of an atom has electrons orbiting the nucleus in shells that surround the nucleus. The K shell can hold two electrons; the M shell can hold eight; and the L shell can hold up to 32 electrons.

The physicist Ernest Rutherford developed an early model of the atom in 1912. He was the first to suggest that atoms are like miniature solar systems, except that instead of gravity acting as the attractive force, opposing electrical charges serve that function. In the Rutherford atom of atomic theory, electrons orbit the nucleus in circular paths.

Another physicist, Niels Bohr, revised Rutherford's atomic model in 1913. The Bohr atom included negatively charged electrons orbiting the nucleus at specific median distances. These distances are represented by spheres, called shells, surrounding the nucleus. Electrons can move from shell to shell. When an electron absorbs enough energy, it moves to a larger, or higher, shell. When it loses a certain amount of energy, it falls to a smaller, lower shell.

The Bohr radius constant is based on Bohr's model of the atom.

Atomic power

A strong nuclear force holds together the protons and neutrons in the nucleus of an atom. That force overcomes the repulsive force between the positively charged particles. Strong nuclear force -- sometimes referred to as strong force or strong interaction -- only works at very close distances. Strong force is the strongest of the four fundamental forces in nature; the other three are gravitational, electromagnetic and weak nuclear forces.

When the bond between particles in the nucleus is broken, a large amount of energy is released. The process of breaking these bonds is known as nuclear fission. Nuclear power plants use fission to split uranium atoms and generate electricity. Uranium is used for fission because its atoms split relatively easily.

Nuclear power is considered a clean energy source because fission does not emit greenhouse gases. It is a possible energy source for IT data centers looking to reduce their carbon footprint.

Additional Information

The atom is the basic particle of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper. Atoms with the same number of protons but a different number of neutrons are called isotopes of the same element.

Atoms are extremely small, typically around 100 picometers across. A human hair is about a million carbon atoms wide. This is smaller than the shortest wavelength of visible light, which means humans cannot see atoms with conventional microscopes. Atoms are so small that accurately predicting their behavior using classical physics is not possible due to quantum effects.

More than 99.94% of an atom's mass is in the nucleus. Protons have a positive electric charge and neutrons have no charge, so the nucleus is positively charged. The electrons are negatively charged, and this opposing charge is what binds them to the nucleus. If the numbers of protons and electrons are equal, as they normally are, then the atom is electrically neutral as a whole. If an atom has more electrons than protons, then it has an overall negative charge, and is called a negative ion (or anion). Conversely, if it has more protons than electrons, it has a positive charge, and is called a positive ion (or cation).

The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force. This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements. This is a form of nuclear decay.

Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals. The ability of atoms to attach and detach from each other is responsible for most of the physical changes observed in nature. Chemistry is the science that studies these changes.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2060 2024-02-15 00:07:52

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2062) Referee


In sports such as American football, association football, basketball, etc., a person who is in charge of making certain that the rules are followed.


In association football, the referee is the person responsible for interpreting and enforcing the Laws of the Game during a match. The referee is the final decision-making authority on all facts connected with play, and is the match official with the authority to start and stop play and impose disciplinary action against players and coaches during a match.

At most levels of play, the referee is assisted by two assistant referees (formerly known as linesmen), who advise the referee on whether the ball leaves the playing area and any infringements of the Laws of the Game occurring outside of the view of the referee. The final decision on any decision of fact rests with the referee, who has authority to overrule an assistant referee. At higher levels of play, the referee may also be assisted by a fourth official who supervises the teams' technical areas and assists the referee with administrative tasks, and, at the very highest levels, additional assistant referees and/or video assistant referees. Referees and other game officials are licensed and trained by its member national organisations.

Powers and duties

* The referee carries a yellow card and a red card, to indicate respectively a caution for misconduct or to send-off a player.
* The coloured cards were introduced by Ken Aston, a former chair of the FIFA Refereeing Committee

The referee's powers and duties are described by Law 5 of the Laws of the Game. The referee:


* enforces the Laws of the Game
* controls the match in cooperation with the other match officials
* acts as timekeeper, keeps a record of the match and provides the appropriate authorities with a match report,  including information on disciplinary action and any other incidents that occurred before, during or after the match
* supervises and/or indicates the restart of play


* allows play to continue when an offence occurs and the non-offending team will benefit from the advantage, and penalises the offence if the anticipated advantage does not ensue at that time or within a few seconds

Disciplinary action

* punishes the more serious offence, in terms of sanction, restart, physical severity and tactical impact, when more than one offence occurs at the same time
* takes disciplinary action against players guilty of cautionable and sending-off offences
* has the authority to take disciplinary action from entering the field of play for the pre-match inspection until leaving the field of play after the match ends (including kicks from the penalty mark). If, before entering the field of play at the start of the match, a player commits a sending-off offence, the referee has the authority to prevent the player taking part in the match (see Law 3.6); the referee will report any other misconduct
* has the power to show yellow or red cards and, where competition rules permit, temporarily dismiss a player, from entering the field of play at the start of the match until after the match has ended, including during the half-time interval, extra time and kicks from the penalty mark
* takes action against team officials who fail to act in a responsible manner and warns or shows a yellow card for a caution or a red card for a sending-off from the field of play and its immediate surrounds, including the technical area; if the offender cannot be identified, the senior coach present in the technical area will receive the sanction. A medical team official who commits a sending-off offence may remain if the team has no other medical person available, and act if a player needs medical attention
* acts on the advice of other match officials regarding incidents that the referee has not seen

As well as other various duties and powers described fully in Law 5 of the Laws of the Game, pursuant to current updates.


Referees and assistant referees are regulated at a national level. FIFA requires that each national organisation establish a referees committee composed of former officials that has authority over refereeing in that territory. FIFA also mandate that referees pass tests to show sufficient physical fitness and knowledge of the Laws of the Game, as well as an annual medical. Generally, referees are required to have greater experience to officiate higher level matches. The most elite officials, those who are permitted to officiate international games, are listed on the FIFA International Referees List.

Kit and equipment

Referees wear a kit distinguishing themselves from the players. Usually this comprises a shirt of a different colour to the players of both teams.

In the early 20th century, referees wore a blazer rather than a shirt similar to that of the players. Traditionally that uniform was almost always all black, unless one of the teams was wearing a very dark shirt in which case the referee would wear another colour (usually red) to distinguish themself from both teams.

At the 1994 World Cup finals, new shirts were introduced that gave officials a choice of burgundy, yellow or white, and at the same time the creation of the Premier League in England saw referees wear green jerseys: both changes were motivated by television considerations. Since then, most referees have worn either yellow or black, but the colours and styles adopted by individual associations vary greatly. For international contests under the supervision of FIFA, Adidas uniforms are worn because Adidas is the current sponsor. FIFA allows referees to wear five colours: black, red, yellow, green and blue. Along with the jersey, referees are required to wear black shorts, black socks (with white stripes in some cases), and black shoes. The badge, which displays the referee's license level and year of validity, is often affixed to the left chest pocket.

All referees carry a whistle, a watch, penalty cards, a data wallet with pen and paper, and a coin for determining which team has the choice of ends or kick-off. Most are encouraged to have more than one of each on them in case they drop a whistle or a pen runs out and so on. Often, referees use two watches so that they can use one to calculate time lost for stoppages for the purposes of added time. At the highest levels, referees wear a full duplex radio with customised headset to communicate between with their assistants, and assistant referees use electronic flags, which send a signal to the referee when a button is pushed. In matches with goal-line technology, referees will have on their person a device to receive the system's alerts.


Referees use a whistle to help them control matches. The whistle is sometimes needed to stop, start or restart play but should not be used for all stoppages, starts or restarts. FIFA's Laws of the Game document gives guidance as to when the whistle should and should not be used. Overuse of the whistle is discouraged since, as stated in the Laws, "A whistle which is used too frequently unnecessarily will have less impact when it is needed." The whistle is an important tool for the referee along with verbal, body and eye communication.

Before the introduction of the whistle, referees indicated their decisions by waving a white handkerchief. The whistles that were first adopted by referees were made by Joseph Hudson at Mills Munitions in Birmingham, England. The Acme Whistle Company (based at Mills Munitions Factory) first began to mass-produce pea whistles in the 1870s for the Metropolitan Police Force. It is frequently stated the referee's whistle was first used in a game between Nottingham Forest and Sheffield Norfolk in 1878; however the last such fixture known to have taken place between the two clubs was in 1874. The Nottingham Forest account book of 1872 apparently recorded the purchase of an "umpire's whistle" and in 1928 an article by R M Ruck about his playing days in the early 1870s referred to the use of a whistle by umpires to indicate an infringement.

The whistle was not mentioned in the Laws of the Game until 1936 when an IFAB Decision was added as footnote (b) to Law 2, stating "A Referee's control over the players for misconduct or ungentlemanly behaviour commences from the time he enters the field of play, but his jurisdiction in connection with the Laws of the Game commences from the time he blows his whistle for the game to start."

In 2007, when IFAB greatly expanded the Laws of the Game, an Additional Instructions section became available, which is a full page of advice on how and when the whistle should be used as a communication and control mechanism by the referee.


Referees in football were first described by Richard Mulcaster in 1581. In this description of "foteball" he advocates the use of a "judge over the parties". In the modern era, referees are first advocated in English public school football games, notably Eton football in 1845. A match report from Rochdale in 1842 shows their use in a football game between the Bodyguards Club and the Fearnought Club.

In the early years of the codified sport it was assumed that disputes could be adequately settled by discussion between gentlemen players who would never deliberately commit a foul. However, as play became more competitive, the need for officials grew. Initially there existed two umpires, one per team, who could be appealed to with the referee (the game's timekeeper) being "referred" to if the umpires could not agree.

The promotion of referees to the dominant position they occupy today, and the reformation of umpires into the linesmen role, occurred as part of a major restructuring of the laws in 1891.

Positioning and responsibilities

The predominant system of positioning and division of responsibility used by football match officials throughout the world is known as the Diagonal system of control (DSC).

The referee has final decision-making authority on all matters. The referee is assisted by two assistant referees who advise the referee. An assistant referee's judgement is enforced only if the referee accepts that judgement, and the referee has the authority to unilaterally overrule an assistant referee. The referee is the only official empowered with starting and stopping play, and meting out disciplinary actions such as cautions or send-offs.

The two assistant referees are instructed by the referee to each patrol half of a single touchline on opposite sides of the field. For example, on a field running north–south, one assistant referee (AR) would run on the eastern touchline from the north goal line to the halfway line, while the other assistant referee would run on the western touchline from the south goal line to the halfway line. In general, the assistant referees' duties would be to indicate (using their flags) when an offside offence has occurred in their half, when a ball has left the pitch, and if a foul has been executed out of the view of the referee (typically in their quadrant of the field). Generally, the ARs will position themselves in line with either the second to last opponent or the ball – whichever is closer to the goal line – to better judge offside infractions. However, the assistant referee will have specific positioning with respect to corner kicks, penalty kicks, and throw-ins.

The referee patrols the length of the field to cover the ground not covered by their two assistants, generally running in a diagonal pattern from the southeast quadrant of the field towards the northwest quadrant; hence the term "diagonal system of control" (DSC). This pattern is not a specific route but a general guideline that should be modified to the style of play, nature of the game, the location of play at a given time, etc. In some cases the referee may even exit the field if it aids in their decision-making ability. The main idea is that the referee and assistants using the DSC should be able to position themselves quickly and easily to observe the important aspects of play (offside, ball in or out of play, goal-scoring opportunities, challenges for the ball) from multiple angles with multiple sets of eyes.

The description above refers to a left diagonal system of control, known as "running a left" or "standard diagonal". If, before the match, the centre referee on this field decides to run from southwest to northeast, then the assistants must position themselves accordingly and the result will be a right diagonal system of control, otherwise referred to as "running a right" or "reverse diagonal".

In many cases in England, referees use more of "curve" based on a line running from the edge of the 18-yard (16 m) box, and when near the centre circle they then curve to a line level with the other 18-yard (16 m) box line. This is similar to the diagonal system, but with the speed of modern football it is easier to keep up with play. This also helps the referee avoid being in a common "passing lane" through the centre circle itself.

In international matches the left-wing diagonal shown above has been universal since the 1960s. It is now predominant across the world. England until recently was an exception to this convention. Until 1974 referees in the Football League were required to run both diagonals during a match, most opting to run from right wing to right wing in the first half before switching to the left-wing diagonal for the second half. The chief reason for this alternation was to avoid linesmen wearing down the same part of the touchline during matches – this was important given the generally lower quality of pitches at the time. However switching diagonal was also justified in terms of allowing officials to patrol different areas of the field during games. From the 1974–75 season English referees were allowed to run the same diagonal throughout the same match. Most initially opted for the right-wing diagonal although over the years the left-wing diagonal became increasingly popular and the preferred choice of most referees by the early 2000s. From 2007–08 the left-wing diagonal has been mandatory in English professional football although some referees at lower levels still use the opposite approach.

Its implementation as a standard practice for referees is attributed to Sir Stanley Rous, former referee and President of FIFA from 1961 to 1974.

Other systems of control

While the Laws of the Game mandate a single referee with assistants as described above, other systems are used experimentally or explicitly by some non-FIFA-affiliated governing organizations.

Dual system (two referees)

The dual system, has two referees with no assistants. The system is used some matches played under the rules of the National Federation of State High School Associations (NFHS) in the United States, and in other youth or amateur matches. Both referees have equal authority, and the decision of one referee is binding on the other. Each referee is primarily responsible for a specific area of the field similar to those of the assistant referees in the diagonal system, except that the referees are allowed and encouraged to move away from the touch line into the field, particularly as play approaches the goal lines. Like the assistant referees in the diagonal system, each referee is responsible for patrolling one touch line and one goal line and determining possession for the restart if the ball goes out of play on either of those two boundaries.

Positioning in the dual system is similar to that used by officials in basketball: each referee is either termed the "lead" or the "trail", depending on the direction of the attack. If the attack is against the goal to the referee's right (when facing the field from their assigned touch line), then that referee is the lead, and the other is the trail. The lead is positioned ahead of the play, even with the second-to-last defender to the extent possible, while the trail is positioned behind the play. Both are responsible for calling fouls and misconduct and determining the restart when the ball goes out of play on one of their assigned boundary lines. Since the lead is in a better position to determine offside, the lead is responsible for calling offside, while the trail provides an extra monitor for fouls and misconduct while the lead's attention is focused on offside. When the attack changes direction, the trail becomes the lead and vice versa.

Double dual system (3 referees)

The double dual system uses three referees, all equipped with whistles, positioned much as in the traditional diagonal system of control mandated by IFAB. Each referee has the same authority for decision making. It is authorized in the United States for college and high school matches although it is rarely used.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2061 2024-02-16 00:03:01

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2063) Stem cell


What are stem cells? Stem cells are the body's raw materials — cells from which all other cells with specialized functions are generated. Under the right conditions in the body or a laboratory, stem cells divide to form more cells called daughter cells.


In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell in a cell lineage. They are found in both embryonic and adult organisms, but they have slightly different properties in each. They are usually distinguished from progenitor cells, which cannot divide indefinitely, and precursor or blast cells, which are usually committed to differentiating into one cell type.

In mammals, roughly 50–150 cells make up the inner cell mass during the blastocyst stage of embryonic development, around days 5–14. These have stem-cell capability. In vivo, they eventually differentiate into all of the body's cell types (making them pluripotent). This process starts with the differentiation into the three germ layers – the ectoderm, mesoderm and endoderm – at the gastrulation stage. However, when they are isolated and cultured in vitro, they can be kept in the stem-cell stage and are known as embryonic stem cells (ESCs).

Adult stem cells are found in a few select locations in the body, known as niches, such as those in the bone marrow or gonads. They exist to replenish rapidly lost cell types and are multipotent or unipotent, meaning they only differentiate into a few cell types or one type of cell. In mammals, they include, among others, hematopoietic stem cells, which replenish blood and immune cells, basal cells, which maintain the skin epithelium, and mesenchymal stem cells, which maintain bone, cartilage, muscle and fat cells. Adult stem cells are a small minority of cells; they are vastly outnumbered by the progenitor cells and terminally differentiated cells that they differentiate into.

Research into stem cells grew out of findings by Canadian biologists Ernest McCulloch, James Till and Andrew J. Becker at the University of Toronto and the Ontario Cancer Institute in the 1960s. As of 2016, the only established medical therapy using stem cells is hematopoietic stem cell transplantation, first performed in 1958 by French oncologist Georges Mathé. Since 1998 however, it has been possible to culture and differentiate human embryonic stem cells (in stem-cell lines). The process of isolating these cells has been controversial, because it typically results in the destruction of the embryo. Sources for isolating ESCs have been restricted in some European countries and Canada, but others such as the UK and China have promoted the research. Somatic cell nuclear transfer is a cloning method that can be used to create a cloned embryo for the use of its embryonic stem cells in stem cell therapy. In 2006, a Japanese team led by Shinya Yamanaka discovered a method to convert mature body cells back into stem cells. These were termed induced pluripotent stem cells (iPSCs).


Stem cell is an undifferentiated cell that can divide to produce some offspring cells that continue as stem cells and some cells that are destined to differentiate (become specialized). Stem cells are an ongoing source of the differentiated cells that make up the tissues and organs of animals and plants. There is great interest in stem cells because they have potential in the development of therapies for replacing defective or damaged cells resulting from a variety of disorders and injuries, such as Parkinson disease, heart disease, and diabetes. There are two major types of stem cells: embryonic stem cells and adult stem cells, which are also called tissue stem cells.

Embryonic stem cells (often referred to as ES cells) are stem cells that are derived from the inner cell mass of a mammalian embryo at a very early stage of development, when it is composed of a hollow sphere of dividing cells (a blastocyst). Embryonic stem cells from human embryos and from embryos of certain other mammalian species can be grown in tissue culture.

Mouse embryonic stem cells

The most-studied embryonic stem cells are mouse embryonic stem cells, which were first reported in 1981. This type of stem cell can be cultured indefinitely in the presence of leukemia inhibitory factor (LIF), a glycoprotein cytokine. If cultured mouse embryonic stem cells are injected into an early mouse embryo at the blastocyst stage, they will become integrated into the embryo and produce cells that differentiate into most or all of the tissue types that subsequently develop. This ability to repopulate mouse embryos is the key defining feature of embryonic stem cells, and because of it they are considered to be pluripotent—that is, able to give rise to any cell type of the adult organism. If the embryonic stem cells are kept in culture in the absence of LIF, they will differentiate into “embryoid bodies,” which somewhat resemble early mouse embryos at the egg-cylinder stage, with embryonic stem cells inside an outer layer of endoderm. If embryonic stem cells are grafted into an adult mouse, they will develop into a type of tumour called a teratoma, which contains a variety of differentiated tissue types.

Mouse embryonic stem cells are widely used to create genetically modified mice. This is done by introducing new genes into embryonic stem cells in tissue culture, selecting the particular genetic variant that is desired, and then inserting the genetically modified cells into mouse embryos. The resulting “chimeric” mice are composed partly of host cells and partly of the donor embryonic stem cells. As long as some of the chimeric mice have germ cells (sperm or eggs) that have been derived from the embryonic stem cells, it is possible to breed a line of mice that have the same genetic constitution as the embryonic stem cells and therefore incorporate the genetic modification that was made in vitro. This method has been used to produce thousands of new genetic lines of mice. In many such genetic lines, individual genes have been ablated in order to study their biological function; in others, genes have been introduced that have the same mutations that are found in various human genetic diseases. These “mouse models” for human disease are used in research to investigate both the pathology of the disease and new methods for therapy.

Human embryonic stem cells

Extensive experience with mouse embryonic stem cells made it possible for scientists to grow human embryonic stem cells from early human embryos, and the first human stem cell line was created in 1998. Human embryonic stem cells are in many respects similar to mouse embryonic stem cells, but they do not require LIF for their maintenance. The human embryonic stem cells form a wide variety of differentiated tissues in vitro, and they form teratomas when grafted into immunosuppressed mice. It is not known whether the cells can colonize all the tissues of a human embryo, but it is presumed from their other properties that they are indeed pluripotent cells, and they therefore are regarded as a possible source of differentiated cells for cell therapy—the replacement of a patient’s defective cell type with healthy cells. Large quantities of cells, such as dopamine-secreting neurons for the treatment of Parkinson disease and insulin-secreting pancreatic beta cells for the treatment of diabetes, could be produced from embryonic stem cells for cell transplantation. Cells for this purpose have previously been obtainable only from sources in very limited supply, such as the pancreatic beta cells obtained from the cadavers of human organ donors.

The use of human embryonic stem cells evokes ethical concerns, because the blastocyst-stage embryos are destroyed in the process of obtaining the stem cells. The embryos from which stem cells have been obtained are produced through in vitro fertilization, and people who consider preimplantation human embryos to be human beings generally believe that such work is morally wrong. Others accept it because they regard the blastocysts to be simply balls of cells, and human cells used in laboratories have not previously been accorded any special moral or legal status. Moreover, it is known that none of the cells of the inner cell mass are exclusively destined to become part of the embryo itself—all of the cells contribute some or all of their cell offspring to the placenta, which also has not been accorded any special legal status. The divergence of views on this issue is illustrated by the fact that the use of human embryonic stem cells is allowed in some countries and prohibited in others.

In 2009 the U.S. Food and Drug Administration approved the first clinical trial designed to test a human embryonic stem cell-based therapy, but the trial was halted in late 2011 because of a lack of funding and a change in lead American biotech company Geron’s business directives. The therapy to be tested was known as GRNOPC1, which consisted of progenitor cells (partially differentiated cells) that, once inside the body, matured into neural cells known as oligodendrocytes. The oligodendrocyte progenitors of GRNOPC1 were derived from human embryonic stem cells. The therapy was designed for the restoration of nerve function in persons suffering from acute spinal cord injury.

Embryonic germ cells

Embryonic germ (EG) cells, derived from primordial germ cells found in the gonadal ridge of a late embryo, have many of the properties of embryonic stem cells. The primordial germ cells in an embryo develop into stem cells that in an adult generate the reproductive gametes (sperm or eggs). In mice and humans it is possible to grow embryonic germ cells in tissue culture with the appropriate growth factors—namely, LIF and another cytokine called fibroblast growth factor.

Adult stem cells

Some tissues in the adult body, such as the epidermis of the skin, the lining of the small intestine, and bone marrow, undergo continuous cellular turnover. They contain stem cells, which persist indefinitely, and a much larger number of “transit amplifying cells,” which arise from the stem cells and divide a finite number of times until they become differentiated. The stem cells exist in niches formed by other cells, which secrete substances that keep the stem cells alive and active. Some types of tissue, such as liver tissue, show minimal cell division or undergo cell division only when injured. In such tissues there is probably no special stem-cell population, and any cell can participate in tissue regeneration when required.

Epithelial stem cells

The epidermis of the skin contains layers of cells called keratinocytes. Only the basal layer, next to the dermis, contains cells that divide. A number of these cells are stem cells, but the majority are transit amplifying cells. The keratinocytes slowly move outward through the epidermis as they mature, and they eventually die and are sloughed off at the surface of the skin. The epithelium of the small intestine forms projections called villi, which are interspersed with small pits called crypts. The dividing cells are located in the crypts, with the stem cells lying near the base of each crypt. Cells are continuously produced in the crypts, migrate onto the villi, and are eventually shed into the lumen of the intestine. As they migrate, they differentiate into the cell types characteristic of the intestinal epithelium.

Bone marrow and hematopoietic stem cells

Bone marrow contains cells called hematopoietic stem cells, which generate all the cell types of the blood and the immune system. Hematopoietic stem cells are also found in small numbers in peripheral blood and in larger numbers in umbilical cord blood. In bone marrow, hematopoietic stem cells are anchored to osteoblasts of the trabecular bone and to blood vessels. They generate progeny that can become lymphocytes, granulocytes, red blood cells, and certain other cell types, depending on the balance of growth factors in their immediate environment.

Work with experimental animals has shown that transplants of hematopoietic stem cells can occasionally colonize other tissues, with the transplanted cells becoming neurons, muscle cells, or epithelia. The degree to which transplanted hematopoietic stem cells are able to colonize other tissues is exceedingly small. Despite this, the use of hematopoietic stem cell transplants is being explored for conditions such as heart disease or autoimmune disorders. It is an especially attractive option for those opposed to the use of embryonic stem cells.

High doses of chemotherapy or radiation destroy not only cancer cells but also bone marrow, which is rich in blood-forming stem cells. In order to replace damaged marrow, stem cells are harvested from either the blood or the bone marrow of the cancer patient before therapy; cells also may be taken from a genetically compatible donor. In order to remove unwanted cells, such as tumour cells, from the sample, it is incubated with antibodies that bind only to stem cells. The fluid that contains the selected cells is reduced in volume and frozen until needed. The fluid is then thawed, diluted, and reinfused into the patient's body. Once in the bloodstream, the stem cells travel to the bone marrow, where they implant themselves and begin producing healthy cells.

Bone marrow transplants (also known as bone marrow grafts) represent a type of stem cell therapy that is in common use. They are used to allow cancer patients to survive otherwise lethal doses of radiation therapy or chemotherapy that destroy the stem cells in bone marrow. For this procedure, the patient’s own marrow is harvested before the cancer treatment and is then reinfused into the body after treatment. The hematopoietic stem cells of the transplant colonize the damaged marrow and eventually repopulate the blood and the immune system with functional cells. Bone marrow transplants are also often carried out between individuals (allograft). In this case the grafted marrow has some beneficial antitumour effect. Risks associated with bone marrow allografts include rejection of the graft by the patient’s immune system and reaction of immune cells of the graft against the patient’s tissues (graft-versus-host disease).

Bone marrow is a source for mesenchymal stem cells (sometimes called marrow stromal cells, or MSCs), which are precursors to non-hematopoietic stem cells that have the potential to differentiate into several different types of cells, including cells that form bone, muscle, and connective tissue. In cell cultures, bone-marrow-derived mesenchymal stem cells demonstrate pluripotency when exposed to substances that influence cell differentiation. Harnessing these pluripotent properties has become highly valuable in the generation of transplantable tissues and organs. In 2008 scientists used mesenchymal stem cells to bioengineer a section of trachea that was transplanted into a woman whose upper airway had been severely damaged by tuberculosis. The stem cells were derived from the woman’s bone marrow, cultured in a laboratory, and used for tissue engineering. In the engineering process, a donor trachea was stripped of its interior and exterior cell linings, leaving behind a trachea “scaffold” of connective tissue. The stem cells derived from the recipient were then used to recolonize the interior of the scaffold, and normal epithelial cells, also isolated from the recipient, were used to recolonize the exterior of the trachea. The use of the recipient’s own cells to populate the trachea scaffold prevented immune rejection and eliminated the need for immunosuppression therapy. The transplant, which was successful, was the first of its kind.

Research has shown that there are also stem cells in the brain. In mammals very few new neurons are formed after birth, but some neurons in the olfactory bulbs and in the hippocampus are continually being formed. These neurons arise from neural stem cells, which can be cultured in vitro in the form of neurospheres—small cell clusters that contain stem cells and some of their progeny. This type of stem cell is being studied for use in cell therapy to treat Parkinson disease and other forms of neurodegeneration or traumatic damage to the central nervous system.

Dolly the sheep was cloned using the process of somatic cell nuclear transfer (SCNT). While SCNT is used for cloning animals, it can also be used to generate embryonic stem cells. Prior to implantation of the fertilized egg into the uterus of the surrogate mother, the inner cell mass of the egg can be removed, and the cells can be grown in culture to form an embryonic stem cell line (generations of cells originating from the same group of parent cells).
Following experiments in animals, including those used to create Dolly the sheep, there has been much discussion about the use of somatic cell nuclear transfer (SCNT) to create pluripotent human cells. In SCNT the nucleus of a somatic cell (a fully differentiated cell, excluding germ cells), which contains the majority of the cell’s DNA (deoxyribonucleic acid), is removed and transferred into an unfertilized egg cell that has had its own nuclear DNA removed. The egg cell is grown in culture until it reaches the blastocyst stage. The inner cell mass is then removed from the egg, and the cells are grown in culture to form an embryonic stem cell line (generations of cells originating from the same group of parent cells). These cells can then be stimulated to differentiate into various types of cells needed for transplantation. Since these cells would be genetically identical to the original donor, they could be used to treat the donor with no problems of immune rejection. Scientists generated human embryonic stem cells successfully from SCNT human embryos for the first time in 2013.

While promising, the generation and use of SCNT-derived embryonic stem cells is controversial for several reasons. One is that SCNT can require more than a dozen eggs before one egg successfully produces embryonic stem cells. Human eggs are in short supply, and there are many legal and ethical problems associated with egg donation. There are also unknown risks involved with transplanting SCNT-derived stem cells into humans, because the mechanism by which the unfertilized egg is able to reprogram the nuclear DNA of a differentiated cell is not entirely understood. In addition, SCNT is commonly used to produce clones of animals (such as Dolly). Although the cloning of humans is currently illegal throughout the world, the egg cell that contains nuclear DNA from an adult cell could in theory be implanted into a woman’s uterus and come to term as an actual cloned human. Thus, there exists strong opposition among some groups to the use of SCNT to generate human embryonic stem cells.

Induced pluripotent stem cells

Due to the ethical and moral issues surrounding the use of embryonic stem cells, scientists have searched for ways to reprogram adult somatic cells. Studies of cell fusion, in which differentiated adult somatic cells grown in culture with embryonic stem cells fuse with the stem cells and acquire embryonic stem-cell-like properties, led to the idea that specific genes could reprogram differentiated adult cells. An advantage of cell fusion is that it relies on existing embryonic stem cells instead of eggs. However, fused cells stimulate an immune response when transplanted into humans, which leads to transplant rejection. As a result, research has become increasingly focused on the genes and proteins capable of reprogramming adult cells to a pluripotent state. In order to make adult cells pluripotent without fusing them to embryonic stem cells, regulatory genes that induce pluripotency must be introduced into the nuclei of adult cells. To do this, adult cells are grown in cell culture, and specific combinations of regulatory genes are inserted into retroviruses (viruses that convert RNA [ribonucleic acid] into DNA), which are then introduced to the culture medium. The retroviruses transport the RNA of the regulatory genes into the nuclei of the adult cells, where the genes are then incorporated into the DNA of the cells. About 1 out of every 10,000 cells acquires embryonic stem cell properties. Although the mechanism is still uncertain, it is clear that some of the genes confer embryonic stem cell properties by means of the regulation of numerous other genes. Adult cells that become reprogrammed in this way are known as induced pluripotent stem cells (iPS).

Similar to embryonic stem cells, induced pluripotent stem cells can be stimulated to differentiate into select types of cells that could in principle be used for disease-specific treatments. In addition, the generation of induced pluripotent stem cells from the adult cells of patients affected by genetic diseases can be used to model the diseases in the laboratory. For example, in 2008 researchers isolated skin cells from a child with an inherited neurological disease called spinal muscular atrophy and then reprogrammed these cells into induced pluripotent stem cells. The reprogrammed cells retained the disease genotype of the adult cells and were stimulated to differentiate into motor neurons that displayed functional insufficiencies associated with spinal muscular atrophy. By recapitulating the disease in the laboratory, scientists were able to study closely the cellular changes that occurred as the disease progressed. Such models promise not only to improve scientists’ understanding of genetic diseases but also to facilitate the development of new therapeutic strategies tailored to each type of genetic disease.

In 2009 scientists successfully generated retinal cells of the human eye by reprogramming adult skin cells. This advance enabled detailed investigation of the embryonic development of retinal cells and opened avenues for the generation of novel therapies for eye diseases. The production of retinal cells from reprogrammed skin cells may be particularly useful in the treatment of retinitis pigmentosa, which is characterized by the progressive degeneration of the retina, eventually leading to night blindness and other complications of vision. Although retinal cells also have been produced from human embryonic stem cells, induced pluripotency represents a less controversial approach. Scientists have also explored the possibility of combining induced pluripotent stem cell technology with gene therapy, which would be of value particularly for patients with genetic disease who would benefit from autologous transplantation.

Researchers have also been able to generate cardiac stem cells for the treatment of certain forms of heart disease through the process of dedifferentiation, in which mature heart cells are stimulated to revert to stem cells. The first attempt at the transplantation of autologous cardiac stem cells was performed in 2009, when doctors isolated heart tissue from a patient, cultured the tissue in a laboratory, stimulated cell dedifferentiation, and then reinfused the cardiac stem cells directly into the patient’s heart. A similar study involving 14 patients who underwent cardiac bypass surgery followed by cardiac stem cell transplantation was reported in 2011. More than three months after stem cell transplantation, the patients experienced a slight but detectable improvement in heart function.

Patient-specific induced pluripotent stem cells and dedifferentiated cells are highly valuable in terms of their therapeutic applications because they are unlikely to be rejected by the immune system. However, before induced pluripotent stem cells can be used to treat human diseases, researchers must find a way to introduce the active reprogramming genes without using retroviruses, which can cause diseases such as leukemia in humans. A possible alternative to the use of retroviruses to transport regulatory genes into the nuclei of adult cells is the use of plasmids, which are less tumourigenic than viruses.

In 2021 multiple research teams, working independently, generated human blastocyst-like structures in vitro. The structures were grown using different types of cell populations, including human embryonic stem cells, iPS cells, and reprogrammed adult skin cells. The breakthrough provided a novel means of studying human embryonic development and the very early stages of pregnancy.

Additional Information

Stem cells are special human cells that are able to develop into many different cell types. This can range from muscle cells to brain cells. In some cases, they can also fix damaged tissues. Researchers believe that stem cell-based therapies may one day be used to treat serious illnesses, such as paralysis and Alzheimer disease.

Types of stem cells

Stem cells are divided into 2 main forms. They are embryonic stem cells and adult stem cells.

Embryonic stem cells. The embryonic stem cells used in research today come from unused embryos. These result from an in vitro fertilization procedure. They are donated to science. These embryonic stem cells are pluripotent. This means that they can turn into more than one type of cell.

Adult stem cells. There are 2 types of adult stem cells. One type comes from fully developed tissues, such as the brain, skin, and bone marrow. There are only small numbers of stem cells in these tissues. They are more likely to generate only certain types of cells. For example, a stem cell that comes from the liver will only make more liver cells.

The second type is induced pluripotent stem cells. These are adult stem cells that have been changed in a lab to be more like embryonic stem cells. Scientists first reported that human stem cells could be changed in this way in 2006. Induced pluripotent stem cells don't seem to be different from embryonic stem cells, but scientists have not yet found one that can develop every kind of cell and tissue.

Stem cells in medicine

The only stem cells now used to treat disease are hematopoietic stem cells. These are the blood cell-forming adult stem cells found in bone marrow. Every type of blood cell in the bone marrow starts as a stem cell. Stem cells are immature cells that are able to make other blood cells that mature and function as needed.

These cells are used in procedures, such as bone marrow transplants. These help people with cancer make new blood cells after their own hematopoietic stem cells have been killed by radiation therapy and chemotherapy. They may also be used to treat people with conditions, such as Fanconi anemia. This is a blood disorder that causes the body's bone marrow to fail.

Stem cells may help your health in the future in many ways and through many new treatments. Researchers think that stem cells will be used to help create new tissue. For example, one day healthcare providers may be able to treat people with chronic heart disease. They can do this by growing healthy heart muscle cells in a lab and transplanting them into damaged hearts. Other treatments could target illnesses such as type 1 diabetes, spinal cord injuries, Alzheimer disease, and rheumatoid arthritis. New medicines could also be tested on cells made from pluripotent stem cells. 

Challenges in stem cell research

Stem cells need much more study before their use can be expanded. Scientists must first learn more about how embryonic stem cells develop. This will help them understand how to control the type of cells created from them. Another challenge is that the embryonic stem cells available today are likely to be rejected by the body. And some people find it morally troubling to use stem cells that come from embryos.

Scientists also face challenges when using adult pluripotent stem cells. These cells are hard to grow in a lab, so researchers are looking into ways to improve the process. These cells are also found in small amounts in the body. There is a greater chance that they could contain DNA problems.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2062 2024-02-17 00:04:54

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2064) Polymath


A polymath is a person of wide knowledge or learning.

A polymath is a person who knows a lot about a lot of subjects. If your friend is not only a brilliant physics student but has also published a poetry collection and won prizes at political debates, you can describe her as a polymath.

You can think of a polymath as a classic "Renaissance man." Imagine Leonardo da Vinci, for example, who was not only an amazing artist, but also an engineer, inventor, mathematician, and much more. When a person's knowledge covers many different areas, he or she is a polymath. The Greek word for it is polymathes, "having learned much," with poly meaning "much," and manthanein meaning "learn."


A polymath is a person with broad knowledge or learning. Renaissance Man and (less commonly) Homo Universalis are related terms to describe a person who is well educated, or who excels, in a wide variety of subjects or fields. It is based on the Humanistic view of human beings as the center of the universe, unlimited in their capacity. The ideal person, therefore, in this view is one who attains all knowledge and develops all their abilities to the greatest extent, abilities which should encompass the full spectrum of human nature.

The ideal of the polymath Renaissance Man is embodied in the Italian Leon Battista Alberti, an accomplished architect, painter, classicist, poet, mathematician, and horseman, and Leonardo da Vinci, renowned in fields as diverse as art, science, invention, music, and writing.

Today, the ever continuing growth of knowledge has led to a situation where it is next to impossible for any single person to attain a complete knowledge and the ideal is now often regarded as a person expert in one field but with a sufficiently broad base to network effectively with experts in other fields. Also, studies of intelligence have revealed that a single, unitary intelligence is not adequate to account for all human intellect. Instead, the idea of multiple intelligences has gained ground, in which there are various types of intelligence, such as linguistic, logical-mathematical, spatial, bodily-kinesthetic, musical, and so forth, with different people displaying differing levels of each type. In this view, the ideal is to develop one's own unique talents and abilities to the fullest, without needing to be an expert in all areas.


A polymath (Greek polymathēs, "having learned much") is defined as a person with encyclopedic, broad, or varied knowledge or learning. It especially means that the person's knowledge is not restricted to one subject area. The term is used rarely enough to be included in dictionaries of obscure words.

Renaissance Man (a term first recorded in written English in the early twentieth century) is a related term to describe a person who is well educated, or who excels, in a wide variety of subjects or fields.

This ideal developed in Renaissance Italy from the notion expressed by one of its most accomplished representatives, Leon Battista Alberti (1404–1472), that “a man can do all things if he will.” It embodied the basic tenets of Renaissance Humanism, which considered man the center of the universe, limitless in his capacities for development, and led to the notion that men should try to embrace all knowledge and develop their own capacities as fully as possible. Thus the gifted men of the Renaissance sought to develop skills in all areas of knowledge, in physical development, in social accomplishments, and in the arts.

Other similar terms are Homo universalis and Uomo Universale, which in Latin and Italian, respectively, translate as "universal person" or "universal man." These expressions derived from the ideal in Renaissance Humanism that it was possible to acquire a universal learning in order to develop one's potential, (covering both the arts and the sciences and without necessarily restricting this learning to the academic fields). Further, the scope of learning was much narrower so gaining a command of the known accumulated knowledge was more feasible than today.

When someone is called a Renaissance Man today, it is meant that he does not just have broad interests or a superficial knowledge of several fields, but rather that his knowledge is profound, and often that he also has proficiency or accomplishments in (at least some of) these fields, and in some cases even at a level comparable to the proficiency or the accomplishments of an expert. The related term Generalist is often used to contrast this general approach to knowledge to that of the specialist.

The term Universal Genius is also used, taking Leonardo da Vinci as a prime example, especially when a Renaissance man has made historical or lasting contributions in at least one of the fields in which he was actively involved and when he had a universality of approach. Despite the existence of this term, a polymath may not necessarily be classed as a genius; and certainly a genius may not display the breadth of knowledge to qualify as a polymath. Albert Einstein and Marie Curie are examples of people widely viewed as geniuses, but who are not generally considered as polymaths.

According to the Oxford English Dictionary, the words "polymath" and polyhistor mean practically the same; "the classical Latin word polyhistor was used exclusively, and the Greek word frequently, of Alexander Polyhistor," but polymathist appeared later, and then polymath. Thus today, regardless of any differentiation they may have had when originally coined, they are often taken to mean the same thing.

In Britain, phrases such as polymath sportsman, sporting polymath, or simply "polymath" are occasionally used in a restricted sense to refer to athletes that have performed at a high level in several very different sports.

Renaissance Ideal Today

The expression "Renaissance man" today commonly implies only intellectual or scholastic proficiency and knowledge and not necessarily the more universal sense of "learning" implied by the Renaissance Humanism. It is important to note, however, that some dictionaries use the term Renaissance man as roughly synonym of "polymath" in the first meaning, to describe someone versatile with many interests or talents, while others recognize a meaning which is restricted to the Renaissance era and more closely related to the Renaissance ideals.

During the Renaissance, the ideal of Renaissance humanism included the acquisition of almost all available important knowledge. At that time, several universal geniuses seem to have come close to that ideal, with actual achievements in multiple fields. With the passage of time however, "universal learning" has begun to appear ever more self-contradictory. For example, a famous dispute between "Jacob Burckhardt (whose Die Kultur der Renaissance in Italien of 1860 established Alberti as the prototype of the Renaissance Man) and Julius von Schlosser (whose Die Kunstliteratur of 1924 expresses discontent with Burckhardt's assessments on several counts)" deals with the issue of whether Alberti was indeed a dilettante or an actual Universal Man; while an 1863 article about rhetoric said, for instance: "an universal genius is not likely to attain to distinction and to eminence in any thing. To achieve her best results, and to produce her most matured fruit, Genius must bend all her energies in one direction; strive for one object; keep her brain and hand upon one desired purpose and aim."

Since it is considered extremely difficult to genuinely acquire an encyclopaedic knowledge, and even more to be proficient in several fields at the level of an expert, not to mention to achieve excellence or recognition in multiple fields, the word polymath may also be used, often ironically, with a potentially negative connotation as well. Under this connotation, by sacrificing depth for breadth, the polymath becomes a "jack of all trades, master of none." For many specialists, in the context of today's hyperspecialization, the ideal of a Renaissance man is judged to be an anachronism, since it is not uncommon that a specialist can barely dominate the accumulated knowledge of more than just one restricted subfield in his whole life. Many fields of interest take years of single-minded devotion to achieve expertise, often requiring starting at an early age.

In addition, today, expertise is often associated with documents, certifications, diplomas, and degrees and a person who has an abundance of these is often perceived as having more education than practical "working" experience. However, true expertise may require practical familiarity that may be inaccessible to someone who has little or no actual experience in the field or who was not born and raised in the relevant culture. In many such cases, it is realistically possible to achieve only knowledge of theory if not practical experience. For example, on a safari, a jungle native will be a more effective guide than an American scientist who may be educated in the theories of jungle survival but did not grow up acquiring his knowledge the hard way.

Today it is generally considered that the specialist's understanding of knowledge is too narrow and that a synthetic comprehension of different fields is unavailable to him. What is much more common today than the universal approach to knowledge from a single polymath is the multidisciplinary approach to knowledge, which derives from several experts in different fields working together to pool their knowledge and abilities.


Most of the historical figures considered polymaths would most likely not be so regarded today based on the level of knowledge that they possessed. Much of their knowledge was basic and purely theoretical. For example, a gentleman educated in various fields such as math, history, literature, art, and science during the eighteenth or nineteenth centuries may be only the equivalent of an average modern person with a secondary school education. In ancient times, an expert on medicine may be the equivalent of knowing basic modern first aid. In contrast to modern times, knowledge was also condensed and comprehensive information on a particular field could often be found in single volumes or texts.

Caution is necessary when interpreting the word "polymath" since there is always ambiguity regarding what the word denotes. Nevertheless, there are a number of scholars who are recognized as polymaths and/or Renaissance men; some examples follow.

Recognized polymaths

The following people have been described as "polymaths" by several sources—fulfilling the primary definition of the term—although there may not be expert consensus that each is a prime example in the secondary meaning, as "renaissance men" and "universal geniuses."

* Abhinavagupta (fl. 975–1025), an Indian philosopher, literary critic, Shaivite, aesthetist, [[music]ian, poet, dramatist, dancer, exegetical theologian, and logician; "the great Kashmiri philosopher and polymath, Abhinavagupta."
* Akbar the Great (1542-1605), an Indian Mughal emperor, "polymath," architect, artisan, artist, armorer, blacksmith, carpenter, construction worker, engineer, military general, inventor, lacemaker, technologist, theologian, and writer.
* Leone Battista Alberti (1404–1472), "often considered the archetype of the Renaissance polymath."
* Al-Kindi (Alkindus) (801–873), an Arab astronomer, geographer, mathematician, meteorologist, musician, philosopher, physician, physicist, scientist, and politician; "he (Al-Kindî) was an omnivorous polymath, studying everything, writing 265 treatises about everything—arithmetic, geometry, astronomy, meteorology, geography, physics, politics, music, medicine, philosophy."
* Aristotle (384–322 B.C.E.)  "Aristotle was an extraordinary polymath…"
* Samuel Taylor Coleridge (1772–1834), poet, critic, and philosopher; "Coleridge was unquestionably a polymath, with a universal knowledge unequalled by any thinker of his day."
* Benjamin Franklin (1706–1790), a leading author, political theorist, politician, printer, scientist, inventor, civic activist, and diplomat. "The ultimate creole intellectual…. A true polymath of the Enlightenment style, he distinguished himself on both sides of the Atlantic by researches in natural sciences as well as politics and literature."
* Geber (Jabir ibn Hayyan) (721–815), an Arab Muslim chemist, alchemist, astrologer, astronomer, engineer, pharmacist, physician, philosopher, and physicist; "Jābir was a polymath who wrote 300 books on philosophy, 1,300 books on mechanical devices and military machinery, and hundreds of books on alchemy."
* Edward Heron-Allen (1861–1943) Not only was Heron-Allen a lawyer by trade, he also wrote, lectured on and created violins, was an expert on the art of chiromancy or palmistry, having read palms and analyzed the handwriting of luminaries of the period. He wrote on musical, literary and scientific subjects ranging from foraminifera, marine zoology, meteorology, as a Persian scholar translated Classics such as the Rubaiyat of Omar Khayyam and The Lament of Baba Tahir, also wrote on local geographic history, archeology, Buddhist philosophy, the cultivation, gourmet appreciation of and culture of the asparagus, as well as a number of novels and short stories of science fiction and horror written under his pseudonymn of "Christopher Blayre." "Heron-Allen is better described as a polymath…"
* Imhotep (fl. 2650–2611 B.C.E.), Egyptian chancellor, physician, and architect; "Imhotep, circa 2650 B.C.E. (who was revered as being at least semi-divine until the Late Period, although some of this reverence may be due to his status as physician and all-round polymath)."
* Mikhail Lomonosov (1711–1765), "Lomonosov was a true polymath—physicist, chemist, natural scientist, poet and linguist…."
* Shen Kuo (1031–1095), a Chinese scientist, statesman, mathematician, astronomer, meteorologist, geologist, zoologist, botanist, pharmacologist, agronomist, ethnographer, encyclopedist, poet, general, diplomat, hydraulic engineer, inventor, academy chancellor, finance minister, and inspector; "Chinese polymath and astronomer who studied medicine, but became renown for his engineering ability."
* Herbert Simon (1916-2001), "Simon is a very distinguished polymath, famous for work in psychology and computer science, philosophy of science, a leader in artificial intelligence, and a Nobel Prize winner in Economics."
* Mary Somerville (1780–1872), "Somerville was the most celebrated woman scientist of her time. A polymath, she wrote on astronomy, mathematics, physics, chemistry, mineralogy, and geology, among other subjects." "Somerville was the most celebrated woman scientist of her time. A polymath, she wrote on astronomy, mathematics, physics, chemistry, mineralogy, and geology, among other subjects…"
* Rabindranath Tagore (1861–1941), an Indian Bengali polymath; "He was a polymath: a poet, fiction writer, dramatist, painter, educator, political thinker, philosopher of science."
* John von Neumann (1903–1957), physicist, mathematician, game theorist, economist, and pioneering computer scientist. "It isn't often that the human race produces a polymath like von Neumann, then sets him to work in the middle of the biggest crisis in human history…" "Other luminaries would follow Einstein to New Jersey, including the dazzling Hungarian polymath, John von Neumann…"
* H. G. Wells (1866–1946); "Fifty years ago, the British polymath and amateur historian was able to compress the history of the world up to 1920 into one volume…"
* Thomas Young (1773–1829), British polymath, scientist, and Egyptologist, after whom Young's modulus, Young's double-slit experiment, the Young-Laplace equation and the Young-Dupré equation were named. He also studied vision and coined the term Indo-European languages.

Renaissance Men

Leonardo da Vinci is regarded in many Western cultures as the archetypal "Renaissance Man".

The following people represent prime examples of "Renaissance Men" and "universal geniuses," so to say "polymaths" in the strictest interpretation of the secondary meaning of the word. The list also includes some of the Hakeem of the Islamic Golden Age (also known as the "Islamic Renaissance"), who are considered equivalent to the Renaissance Men of the European Renaissance era.

Al-Farabi (Alfarabi) (870–950/951), a Turkic or Persian Muslim who was known as The second teacher because he had great influence on science and philosophy for several centuries, and was widely regarded to be second only to Aristotle in knowledge in his time. Farabi made notable contributions to the fields of mathematics, philosophy, medicine and music. As a philosopher and Neo-Platonist, he wrote rich commentary on Aristotle's work. He is also credited for categorizing logic into two separate groups, the first being "idea" and the second being "proof." Farabi wrote books on sociology and a notable book on music titled Kitab al-Musiqa (The Book of Music). He played and invented a varied number of musical instruments and his pure Arabian tone system is still used in Arabic music.
* Ibn Rushd (Averroes) (1126–1198), an Andalusian Arab philosopher, doctor, physician, jurist, lawyer, astronomer, mathematician, and theologan; "Ibn-Rushd, a polymath also known as Averroes;" "Doctor, Philosopher, Renaissance Man."
* Abū Rayhān al-Bīrūnī (973–1048), a Persian scientist, physicist, anthropologist, astronomer, astrologer, encyclopedist, geodesist, geographer, geologist, historian, mathematician, natural historian, pharmacist, physician, philosopher, scholar, teacher, Ash'ari theologian, and traveler; "al-Biruni was a polymath and traveler (to India), making contributions in mathematics, geography and geology, natural history, calendars and astronomy;" "al-Biruni, a scholar in many disciplines - from linguistics to mineralogy - and perhaps medieval Uzbekistan's most universal genius."
* Nicolaus Copernicus (1473–1543); among the great polymaths of the Renaissance, Copernicus was a mathematician, astronomer, physician, classical scholar, translator, Catholic cleric, jurist, governor, military leader, diplomat and economist. Amid his extensive responsibilities, astronomy figured as little more than an avocation—yet it was in that field that he made his mark upon the world.
* Leonardo da Vinci (1452–1519)"The following selection… shows why this famous Renaissance polymath considered painting to be a science…" "In Leonardo Da Vinci, of course, he had as his subject not just an ordinary Italian painter, but the prototype of the universal genius, the 'Renaissance man,' …"; "prodigious polymath…. Painter, sculptor, engineer, astronomer, anatomist, biologist, geologist, physicist, architect, philosopher, actor, singer, musician, humanist."
* Galileo Galilei (1564–1642), "Italian scientist, physicist, and philosopher. Galileo was a true Renaissance man, excelling at many different endeavors, including lute playing and painting."
* Johann Wolfgang von Goethe (1749–1832) "Germany's greatest man of letters—poet, critic, playwright, and novelist—and the last true polymath to walk the earth" "Goethe comes as close to deserving the title of a universal genius as any man who has ever lived." "He was essentially the last great European Renaissance man." His gifts included incalculable contributions to the areas of German literature and the natural sciences. He is credited with discovery of a bone in the human jaw, and proposed a theory of colors. He has a mineral named in his honor, goethite. He molded the aesthetic properties of the Alps to poetry, thus, changing the local belief from "perfectly hideous" and an "unavoidable misery," to grandeur of the finest most brilliant creation.
* Ibn al-Haytham (Alhacen) (965–1039), an Iraqi Arab scientist, physicist, anatomist, physician, psychologist, astronomer, engineer, mathematician, ophthalmologist, philosopher, and Ash'ari theologian; "a devout, brilliant polymath;" "a great man and a universal genius, long neglected even by his own people;" "Ibn al-Haytham provides us with the historical personage of a versatile universal genius."
* Ibn Khaldun (1332–1406), an Arab social scientist, sociologist, historian, historiographer, philosopher of history, demographer, economist, linguist, philosopher, political theorist, military theorist, Islamic scholar, Ash'ari theologian, diplomat and statesman; "a still-influential polymath;" "in any epoch ibn Khaldun (1332-1406) would deserve the accolade Renaissance man, a person of many talents and diverse interests."
* Thomas Jefferson (1743-1826), some sources describe him as "polymath and President," putting "polymath" first, he is also described as "the walking, talking embodiment of the Enlightenment, a polymath whose list of achievements is as long as it is incredibly varied." John F. Kennedy famously commented, addressing a group of Nobel laureates, that it was "the most extraordinary collection of talent, of human knowledge, that has ever been gathered together at the White House—- with the possible exception of when Thomas Jefferson dined alone."
* Gottfried Leibniz (1646–1716); "Leibniz was a polymath who made significant contributions in many areas of physics, logic, history, librarianship, and of course philosophy and theology, while also working on ideal languages, mechanical clocks, mining machinery…" "A universal genius if ever there was one, and an inexhaustible source of original and fertile ideas, Leibniz was all the more interested in logic because it …" "Gottfried Wilhelm Leibniz was maybe the last Universal Genius incessantly active in the fields of theology, philosophy, mathematics, physics, ...." "Leibniz was perhaps the last great Renaissance man who in Bacon's words took all knowledge to be his province."
* Isaac Newton (1643–1727) was an English physicist, mathematician, astronomer, theologian, natural philosopher and alchemist. His treatise Philosophiae Naturalis Principia Mathematica, published in 1687, described universal gravitation and the three laws of motion, laying the groundwork for classical mechanics, which dominated the scientific view of the physical universe for the next three centuries and is the basis for modern engineering. In a 2005 poll of the Royal Society of who had the greatest effect on the history of science, Newton was deemed more influential than Albert Einstein. "When we see Newton as a late Renaissance man, his particular addiction to classical geometry as ancient wisdom and the most reliable way of unveiling the secrets of nature, seems natural."

Additional Information

A polymath (Greek: romanized: polymathēs, lit. 'having learned much'; Latin: homo universalis, lit. 'universal human') is an individual whose knowledge spans a substantial number of subjects, known to draw on complex bodies of knowledge to solve specific problems.

In Western Europe, the first work to use the term polymathy in its title (De Polymathia tractatio: integri operis de studiis veterum) was published in 1603 by Johann von Wowern, a Hamburg philosopher. Von Wowern defined polymathy as "knowledge of various matters, drawn from all kinds of studies ... ranging freely through all the fields of the disciplines, as far as the human mind, with unwearied industry, is able to pursue them". Von Wowern lists erudition, literature, philology, philomathy, and polyhistory as synonyms.

The earliest recorded use of the term in the English language is from 1624, in the second edition of The Anatomy of Melancholy by Robert Burton; the form polymathist is slightly older, first appearing in the Diatribae upon the first part of the late History of Tithes of Richard Montagu in 1621. Use in English of the similar term polyhistor dates from the late 16th century.

Polymaths include the great scholars and thinkers of the Renaissance and Enlightenment, who excelled at several fields in science, technology, engineering, mathematics, and the arts. In the Italian Renaissance, the idea of the polymath was allegedly expressed by Leon Battista Alberti (1404–1472), a polymath himself, in the statement that "a man can do all things if he will". Gottfried Wilhelm Leibniz has often been seen as a polymath. Al-Biruni was also a polymath. Other well-known and celebrated polymaths include Leonardo da Vinci, Hildegard of Bingen, Ibn al-Haytham, Rabindranath Tagore, Mikhail Lomonosov, Johann Wolfgang von Goethe, Alan Turing, Benjamin Franklin, John von Neumann, Omar Khayyam, Charles Sanders Peirce, Henri Poincaré, Isaac Asimov, Nicolaus Copernicus, René Descartes, Aristotle, Frederick II, Holy Roman Emperor, Averroes, Archimedes, George Washington Carver, Hypatia, Blaise Pascal, Africanus Horton, Wang Wei, Isaac Newton, Pierre-Paul Riquet, Leonhard Euler, Émilie du Châtelet, Nikola Tesla, Thomas Edison, Bertrand Russell, Thomas Young, Sequoyah, Thomas Jefferson and Pierre-Simon Laplace.

Embodying a basic tenet of Renaissance humanism that humans are limitless in their capacity for development, the concept led to the notion that people should embrace all knowledge and develop their capacities as fully as possible. This is expressed in the term Renaissance man, often applied to the gifted people of that age who sought to develop their abilities in all areas of accomplishment: intellectual, artistic, social, physical, and spiritual.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2063 2024-02-18 00:05:10

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2065) Umpire


An umpire is a person who watches a game such as tennis or cricket to make sure that the players obey the rules.


An umpire is an official in a variety of sports and competition, responsible for enforcing the rules of the sport, including sportsmanship decisions such as ejection.

The term derives from the Old French nonper, non, "not" and per, "equal": "one who is requested to act as arbiter of a dispute between two people"  (as evidenced in cricket, where dismissal decisions can only be made on appeal). Noumper shows up around 1350 before undergoing a linguistic shift known as false splitting. It was written in 1426–1427 as a noounpier; the n was lost with the a indefinite article becoming an. The earliest version without the n shows up as owmpere, a variant spelling in Middle English, circa 1440. The leading n became permanently attached to the article, changing it to an Oumper around 1475.

The word was applied to the officials of many sports including baseball, association football (where it has been superseded by assistant-referee) and cricket (which still uses it).

Field hockey

An umpire in field hockey is a person with the authority to make decisions on a hockey field in accordance with the laws of the game. Each match is controlled by two such umpires, where it is typical for umpires to aid one another and correct each other when necessary.


In cricket, dismissal decisions can only be made on appeal by the players. Otherwise, on-field decisions, relevant to the rules and scoring and of the game, are handled by two on-field umpires, although an off-field third umpire may help with certain decisions. At the international level, the match referee is an off-field official who makes judgements concerning the reputable conduct of the game and hands out penalties for breaches of the ICC Cricket Code of Conduct.

Baseball and softball

In baseball and softball, there is commonly a head umpire (also known as a plate umpire) who is in charge of calling balls and strikes from behind the plate, who is assisted by one, two, three, or five field umpires who make calls on their specific bases (or with five umpires the bases and the outfield). On any question, the head umpire has the final call.

Football (Australian rules)

An umpire is an official in the sport of Australian rules football. Games are overseen by one to four field umpires, two to four boundary umpires, and two goal umpires.

Lawn bowls

A lawn bowls match is presided over by a bowls umpire or technical official. In games where single players compete, a marker is required to direct play and assist players with questions relating to the position of their bowls.


In the game of Netball the match at hand is Presided over by 2 umpires, typically female, with a comprehensive knowledge of the rules. There are also 2 timekeepers and 2 scorekeepers who inform the umpires, and players of time remaining, and scores.


In a regatta an umpire is the on-the-water official appointed to enforce the rules of racing and to ensure safety. In some cases an umpire may be designated specifically as starter, or otherwise the umpire starts the race from a launch and follows it to its end, ensuring that crews follow their proper course. If no infringements occur, the result is decided by a judge or judges on the waterside who determine the finish order of the crews.


In match race and team racing an "umpire" is an on-the-water referee appointed to directly enforce the Racing Rules of Sailing. An umpire is also used in fleet racing to enforce Racing Rule 42 which limits the use of kinetics to drive the boat rather than the wind. Umpires are rarely present during sailing races as decisions are normally referred to a jury-style protest committee after the race.


In tennis an umpire is an on-court official, while a referee is an off-court official.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2064 2024-02-19 00:05:03

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2066) Spark plug


A spark plug is an electrical device used in an internal combustion engine to produce a spark which ignites the air-fuel mixture in the combustion chamber.


Spark plug is a device that fits into the cylinder head of an internal-combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, to form a spark for igniting the air–fuel mixture. The electrodes must be able to resist high temperatures, and the insulator separating them must withstand high temperatures and also an electric stress up to several thousand volts. Spark-gap length affects the energy of the spark, and the shape of the insulator affects the temperature of operation. When too cool, operation leads to carbonization and short-circuiting of the gap; when too hot, there may be preignition.

(Internal-combustion engine is any of a group of devices in which the reactants of combustion (oxidizer and fuel) and the products of combustion serve as the working fluids of the engine. Such an engine gains its energy from heat released during the combustion of the nonreacted working fluids, the oxidizer-fuel mixture. This process occurs within the engine and is part of the thermodynamic cycle of the device. Useful work generated by an internal-combustion (IC) engine results from the hot gaseous products of combustion acting on moving surfaces of the engine, such as the face of a piston, a turbine blade, or a nozzle.

Internal-combustion engines are the most broadly applied and widely used power-generating devices currently in existence. Examples include gasoline engines, diesel engines, gas-turbine engines, and rocket-propulsion systems.

Internal-combustion engines are divided into two groups: continuous-combustion engines and intermittent-combustion engines. The continuous-combustion engine is characterized by a steady flow of fuel and oxidizer into the engine. A stable flame is maintained within the engine (e.g., jet engine). The intermittent-combustion engine is characterized by periodic ignition of air and fuel and is commonly referred to as a reciprocating engine. Discrete volumes of air and fuel are processed in a cyclic manner. Gasoline piston engines and diesel engines are examples of this second group.

Internal-combustion engines can be delineated in terms of a series of thermodynamic events. In the continuous-combustion engine, the thermodynamic events occur simultaneously as the oxidizer and fuel and the products of combustion flow steadily through the engine. In the intermittent-combustion engine, by contrast, the events occur in succession and are repeated for each full cycle.

Some air taken in by the turbofan (top) goes to the compressor; the rest bypasses the main engine. In turboprop engines (bottom) the hot gases drive a turbine, which powers the compressor and propeller, and provide jet thrust.
With the exception of rockets (both solid rocket motors and liquid-propellant rocket engines), internal-combustion engines ingest air, then either compress the air and introduce fuel into the air or introduce fuel and compress the air-fuel mixture. Then, common to all internal-combustion engines, the air-fuel mixture is burned, work is extracted from the expansion of the hot gaseous products of combustion, and ultimately the products of combustion are released through the exhaust system. Their operation can be contrasted with that of external-combustion engines (e.g., steam engines), in which the working fluid does not chemically react and energy gain is achieved solely through heat transfer to the working fluid by way of a heat exchanger.

The most common internal-combustion engine is the four-stroke, gasoline-powered, homogeneous-charge, spark-ignition engine. This is because of its outstanding performance as a prime mover in the ground transportation industry. Spark-ignition engines also are used in the aeronautics industry; however, aircraft gas turbines have become the prime movers in this sector because of the emphasis of the aeronautics industry on range, speed, and passenger comfort. The domain of internal-combustion engines also includes such exotic devices as supersonic combustion ramjet engines (scramjets), such as those proposed for hypersonic aircraft, and sophisticated rocket engines and motors, such as those used on U.S. space shuttles and other space vehicles.)


A spark plug is an electrical device used in an internal combustion engine to produce a spark which ignites the air-fuel mixture in the combustion chamber. As part of the engine's ignition system, the spark plug receives high-voltage electricity (generated by an ignition coil in modern engines and transmitted via a spark plug wire) which it uses to generate a spark in the small gap between the positive and negative electrodes. The timing of the spark is a key factor in the engine's behaviour, and the spark plug usually operates shortly before the combustion stroke commences.

The spark plug was invented in 1860, however its use only became widespread after the invention of the ignition magneto in 1902. Diesel engines use compression ignition (instead of spark ignition), therefore they do not normally use spark plugs.


The main elements of a spark plug are the shell, insulator, central electrode and side electrode (also known as "ground strap"). The main part of the insulator is typically made from sintered alumina (Al2O3), a hard ceramic material with high dielectric strength. In marine engines, the shell of the spark plug is often a double-dipped, zinc-chromate coated metal.

A spark plug passes through the wall of the combustion chamber, therefore it must also form part of the seal for the high-pressure gases within the combustion chamber.


The central electrode is connected to the terminal through an internal wire. The central electrode setup as the cathode from where the electrons are ejected. This is because the central electrode is usually the hottest part of the plug, and thermionic emission principles mean it is easier to eject electrons from a hotter surface. The sharp tip of the central electrode also increases the electrical field strength, thus increasing the emission of electrons. The side electrode (which is colder and blunter) requires up to 45 percent higher voltage, therefore only wasted spark systems use the side electrode as the cathode.

The side electrode is made from high-nickel steel and is welded or hot forged to the side of the metal shell.

Spark plugs can contain up to four side electrodes surrounding the central electrode. Multiple side electrodes generally provide longer life, as when the spark gap widens due to electric discharge wear, the spark moves to another closer ground electrode. The disadvantage of multiple side electrodes is that a shielding effect can occur for each electrode, leading to a less efficient burn and increased fuel consumption.

Gap size

The distance between the tip of the spark plug and the central electrode is called the "spark plug gap" and is a key factor in the function of a spark plug. Spark plug gaps for car engines are typically 0.6 to 1.8 mm (0.024 to 0.071 in). Modern engines (using solid-state ignition systems and electronic fuel injection) typically use larger gaps than older engines that use breaker point distributors and carburetors.

Smaller plug gap sizes usually are more reliable at producing a spark, however the spark may be too weak to ignite the fuel-air mixture. A larger plug gap size will produce a stronger spark, however the spark might not always be produced (such as at high RPM). Gap adjustment is not recommended for iridium and platinum spark plugs, because there is a risk of damaging a metal disk welded to the electrode.

Wasted spark applications

Wasted spark systems place a greater strain upon spark plugs since they alternately fire electrons in both directions (from the ground electrode to the central electrode, not just from the central electrode to the ground electrode). As a result, vehicles with such a system should have precious metals on both electrodes, not just on the central electrode, in order to increase service replacement intervals since they wear down the metal more quickly in both directions, not just one.

Indexing of plugs

"Indexing" of plugs upon installation involves installing the spark plug so that the open area of the gap (i.e. the side not shrouded by the side electrode), faces the center of the combustion chamber. This is claimed to improve ignition by maximising the exposure of the fuel-air mixture to the spark in every cylinder.

Indexing is accomplished by either:

* Using thin washers to set the amount of thread engaged by the spark plug, thus determining the orientation of the spark plug within the cylinder head. This must be done individually for each plug, as the orientation of the gap with respect to the threads of the shell is usually random.
* Producing spark plugs with a specific orientation of the gap relative to the threads of the shell. These spark plugs and usually designated as such by a suffix to the part number of the spark plug.

Heat range

An important factor for a spark plug is the temperature that the tip is designed to withstand, called the heat range. Typical heat ranges for passenger car engines are usually between 500 and 850 °C (932 and 1,562 °F). A hotter spark plug has more insulation between itself and the cylinder head, causing less heat to be dissipated from the spark plug and therefore the spark plug remaining hotter. Temperatures higher than 450 °C (842 °F) are needed to prevent carbon build-up on the spark plug, while temperatures over 800 °C (1,470 °F) can cause overheating of the plug.

Switching to a higher heat range is sometimes used to compensate for fuel delivery or oil consumption problems, however this increases the risk of pre-ignition.


Belgian-French engineer Étienne Lenoir is generally credited with the invention of the spark plug in 1860, due to its use in the early Lenoir gas engine.

Several patents relating to electrical ignition systems were filed in the late 1890s, including from Serbian engineer Nikola Tesla, British engineer Frederick Richard Simms and German engineer Robert Bosch. The use of high-voltage spark plugs in commercial viable engines was only made possible after 1902 however, due to the invention of magneto-based ignition systems by Bosch engineer Gottlob Honold. Early manufacturers of spark plugs included American company Champion, British company Lodge brothers and London-based KLG (who pioneed the use of mica as an insulator).

During the 1930s, American geologist Helen Blair Bartlett developed an alumina ceramic-based insulator for the spark plug.

Polonium spark plugs were marketed by Firestone from 1940 to 1953. While the amount of radiation from the plugs was minuscule and not a threat to the consumer, the benefits of such plugs quickly diminished after approximately a month because of polonium's short half-life, and because buildup on the conductors would block the radiation that improved engine performance. The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard's prototype radium plug that preceded it, was that the radiation would improve ionization of the fuel in the cylinder and thus allow the plug to fire more quickly and efficiently.

Additional Information:


The spark plug plays an important role in petrol engines. It is responsible for igniting the fuel/air mixture. The quality of this ignition influences several factors which are of great importance for both driving and the environment. They include smooth running, engine performance and efficiency as well as pollutant emissions. If we consider that a spark plug must ignite between 500 and 3,500 times per minute, it becomes clear how great the contribution of modern spark plug technology is to adherence to current emissions standards and the reduction of fuel consumption.


If we consider the basic construction of the spark plug, there have been no profound changes over the past 50 years. As ever, the spark plug comprises a metal core which is housed in a ceramic insulator. This, in turn, is surrounded by a metal casing which has a thread that is screwed in to the cylinder head and normally has a hexagonal section on the top which accommodates the spark plug socket and allows spark plugs to be installed or removed with a spark plug spanner. The main purpose of the construction lies in ensuring that the electrical circuit at high voltage on the spark plug is closed with a spark, which jumps from the middle electrode to the earth electrode.


The connection is designed as an SAE connection or a 4 mm thread. The ignition cable or a rod coil is plugged into the connection. In both cases a high voltage coupled here must be transported to the other end of the spark plug. The ceramic insulator has two tasks. Its primary purpose is insulation, whereby it prevents flashover of the high voltage to the vehicle mass (= minus), and conducts combustion heat to the cylinder head. The wave-shaped leakage current barriers on the outside of the insulator prevent voltage leaking to the vehicle mass. In doing so, they extend the path to be travelled and increase the electrical resistance, thereby ensuring that the energy takes the path of least resistance - the path through the middle electrode. In order to ensure the electromagnetic compatibility (EMC) and thus the fault-free operation of the on-board electronics, a glass melt is used inside the spark plug as interference suppression. The middle electrode of a standard spark plug is comprised mostly of a nickel alloy. The spark must jump from the end of this electrode over to the earth electrode. The metal housing is firmly attached to the cylinder head via a thread and thus plays an important role in heat dissipation, discharging the bulk of the heat generated during combustion via this connection. The seal ring prevents combustion gas from emerging past the spark plug even at high combustion pressures. In so doing, it prevents pressure losses. Moreover, it conducts heat to the cylinder head and evens out the different expansion properties of the cylinder head and spark plug housing. The inner seals create a gas-tight connection between the insulator and the metal housing, providing an assurance of optimum sealing. The earth electrode of a standard spark plug is made of a nickel alloy. It represents the opposite pole of the middle electrode in normal function.


An up-to-date spark plug must be tailored individually to meet the requirements of different engine designs and driving conditions. Therefore, there cannot be one spark plug which will function without any difficulty in all engines. Due to the variations in temperature development in the respective combustion chambers in different engines, spark plugs with different heat ratings are needed. This heat rating is expressed using what is known as the heat rating number. These heat ratings represent an average temperature measured at electrodes and insulators, corresponding to the engine load in each case. Spark plugs require a special temperature window in order to perform at their best. The lower threshold of this window is a spark plug temperature of 450°C, known as the self-cleaning temperature. Starting from this temperature threshold, the carbon particles which have collected on the insulator tip are burned off. spark plug temperature. If the operating temperature continuously lies below this point, electrically conductive carbon particles can collect, forming deposits until the ignition voltage flows over the carbon layer to the vehicle mass instead of forming a spark. At a spark plug temperature of 850°C or higher, the insulator heats up so much that uncontrolled ignitions can occur on its surface known as glow ignitions. Such uncontrolled, abnormal combustion can lead to engine damage.


Heat development varies greatly from engine to engine. For example, turbocharged engines run significantly hotter than engines which are not charged. Therefore, there is a spark plug for each engine which can conduct a precisely defined measure of heat to the cylinder head and ensures that the optimal temperature window is maintained. The heat rating provides information about the thermal endurance of a spark plug. Every spark plug manufacturer has its own way of expressing the heat rating. Nearly 60% of the heat is dissipated via the spark plug case and thread. The seal ring conducts slightly less than 40% to the cylinder head. The small remaining percentage (making up 100%) flows out through the middle electrode. The insulator absorbs the heat in the combustion chamber and conducts it to the interior of the spark plug. Anywhere that it comes into contact with the case, heat is conducted. By increasing or decreasing the size of this contact surface area, it is possible to determine whether the spark plug is conducting more or less heat through the case. The contact surface area is larger for spark plugs with higher thermal endurance. For spark plugs with lower thermal endurance it is smaller.

Environmental protection

Today more than ever before, the protection of the environment is the focus of attention where motoring matters are concerned. Particular attention is being paid to exhaust gases. Standard spark plugs in particular are subject to normal wear. When it jumps from the earth electrode to the middle electrode of the spark plug, every spark removes microscopically tiny particles from the electrodes. As a consequence, the distance between the electrodes gets bigger over many thousands of kilometres travelled and the risk of misfiring increases. Every time a spark plug misfires, valuable petrol is injected but not combusted. As a result, there is a significant increase in environmental pollution due to the increased in consumption per kilometre alone. Furthermore, the unburned fuel in the catalytic converter can ignite explosively, causing damage that will prevent the catalytic converter from rendering hazardous substances like carbon monoxide, nitrogen oxide and hydrocarbons harmless and requiring it to be replaced.


A vehicle is a highly complex technical commodity whose function can only be sustained if all components are in perfect harmony. Regular service is necessary if this state of harmony also is to be maintained for the engine, which is one of the most highly challenged parts of a vehicle. This includes using high-quality spark plugs whose technical properties help the drive to function without problems and thus provide an assurance of long service life.


Spark plugs that are in perfect working order are essential if a vehicle is to operate safely. Spark plugs should therefore be replaced no later than at the end of the replacement interval prescribed by the motor manufacturer. Important: Spark plugs require a precisely measured torque for installation. This necessitates the use of a special tool known as a torque wrench. If the spark plug is not tight enough, pressure will escape from the piston and the spark plug may overheat. There is also a risk that the ceramic spark plug insulator will fracture. This can damage the piston and thus result in engine damage. Conversely, if the torque is set too high, the spark plug might tear off, possibly leading to the cylinder head having to be replaced. Even if this does not happen, a spark plug that has been screwed too tight can overheat during operation, resulting in damage to the engine.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2065 2024-02-20 00:09:05

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2067) Acid


An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid. Acidic substances are usually identified by their sour taste.


Acid is any substance that in water solution tastes sour, changes the colour of certain indicators (e.g., reddens blue litmus paper), reacts with some metals (e.g., iron) to liberate hydrogen, reacts with bases to form salts, and promotes certain chemical reactions (acid catalysis). Examples of acids include the inorganic substances known as the mineral acids—sulfuric, nitric, hydrochloric, and phosphoric acids—and the organic compounds belonging to the carboxylic acid, sulfonic acid, and phenol groups. Such substances contain one or more hydrogen atoms that, in solution, are released as positively charged hydrogen ions.

Broader definitions of an acid, to include substances that exhibit typical acidic behaviour as pure compounds or when dissolved in solvents other than water, are given by the Brønsted–Lowry theory and the Lewis theory. Examples of nonaqueous acids are sulfur trioxide, aluminum chloride, and boron trifluoride.


An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H+.

Aqueous Arrhenius acids have characteristic properties that provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus, meaning 'sour'. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.

Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride that is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF3), whose boron atom has a vacant orbital that can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH3). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H+) into the solution, which then accept electron pairs. Hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form a covalent bond with an electron pair, however, and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid.

Definitions and concepts

Modern definitions are concerned with the fundamental chemical reactions common to all acids.

Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, so the Arrhenius and Brønsted–Lowry definitions are the most relevant.

The Brønsted–Lowry definition is the most widely used definition; unless otherwise specified, acid–base reactions are assumed to involve the transfer of a proton (H+) from an acid to a base.

Hydronium ions are acids according to all three definitions. Although alcohols and amines can be Brønsted–Lowry acids, they can also function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms.

Brønsted–Lowry acids

While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923, chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid–base reactions involve the transfer of a proton. A Brønsted–Lowry acid (or simply Brønsted acid) is a species that donates a proton to a Brønsted–Lowry base. Brønsted–Lowry acid–base theory has several advantages over Arrhenius theory.

Lewis acids

A third, only marginally related concept was proposed in 1923 by Gilbert N. Lewis, which includes reactions with acid–base characteristics that do not involve a proton transfer. A Lewis acid is a species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor. Brønsted acid–base reactions are proton transfer reactions while Lewis acid–base reactions are electron pair transfers. Many Lewis acids are not Brønsted–Lowry acids.

Applications of acids:

In industry

Acids are fundamental reagents in treating almost all processes in modern industry. Sulfuric acid, a diprotic acid, is the most widely used acid in industry, and is also the most-produced industrial chemical in the world. It is mainly used in producing fertilizer, detergent, batteries and dyes, as well as used in processing many products such like removing impurities. According to the statistics data in 2011, the annual production of sulfuric acid was around 200 million tonnes in the world. For example, phosphate minerals react with sulfuric acid to produce phosphoric acid for the production of phosphate fertilizers, and zinc is produced by dissolving zinc oxide into sulfuric acid, purifying the solution and electrowinning.

In the chemical industry, acids react in neutralization reactions to produce salts. For example, nitric acid reacts with ammonia to produce ammonium nitrate, a fertilizer. Additionally, carboxylic acids can be esterified with alcohols, to produce esters.

Acids are often used to remove rust and other corrosion from metals in a process known as pickling. They may be used as an electrolyte in a wet cell battery, such as sulfuric acid in a car battery.

In food

Carbonated water (H2CO3 aqueous solution) is commonly added to soft drinks to make them effervesce.

Tartaric acid is an important component of some commonly used foods like unripened mangoes and tamarind. Natural fruits and vegetables also contain acids. Citric acid is present in oranges, lemon and other citrus fruits. Oxalic acid is present in tomatoes, spinach, and especially in carambola and rhubarb; rhubarb leaves and unripe carambolas are toxic because of high concentrations of oxalic acid. Ascorbic acid (Vitamin C) is an essential vitamin for the human body and is present in such foods as amla (Indian gooseberry), lemon, citrus fruits, and guava.

Many acids can be found in various kinds of food as additives, as they alter their taste and serve as preservatives.
Phosphoric acid, for example, is a component of cola drinks. Acetic acid is used in day-to-day life as vinegar. Citric acid is used as a preservative in sauces and pickles.

Carbonic acid is one of the most common acid additives that are widely added in soft drinks. During the manufacturing process, CO2 is usually pressurized to dissolve in these drinks to generate carbonic acid. Carbonic acid is very unstable and tends to decompose into water and CO2 at room temperature and pressure. Therefore, when bottles or cans of these kinds of soft drinks are opened, the soft drinks fizz and effervesce as CO2 bubbles come out.

Certain acids are used as drugs. Acetylsalicylic acid (Aspirin) is used as a pain killer and for bringing down fevers.

In human bodies

Acids play important roles in the human body. The hydrochloric acid present in the stomach aids digestion by breaking down large and complex food molecules. Amino acids are required for synthesis of proteins required for growth and repair of body tissues. Fatty acids are also required for growth and repair of body tissues. Nucleic acids are important for the manufacturing of DNA and RNA and transmitting of traits to offspring through genes. Carbonic acid is important for maintenance of pH equilibrium in the body.

Human bodies contain a variety of organic and inorganic compounds, among those dicarboxylic acids play an essential role in many biological behaviors. Many of those acids are amino acids, which mainly serve as materials for the synthesis of proteins. Other weak acids serve as buffers with their conjugate bases to keep the body's pH from undergoing large scale changes that would be harmful to cells. The rest of the dicarboxylic acids also participate in the synthesis of various biologically important compounds in human bodies.

Acid catalysis

Acids are used as catalysts in industrial and organic chemistry; for example, sulfuric acid is used in very large quantities in the alkylation process to produce gasoline. Some acids, such as sulfuric, phosphoric, and hydrochloric acids, also effect dehydration and condensation reactions. In biochemistry, many enzymes employ acid catalysis.

Biological occurrence

Many biologically important molecules are acids. Nucleic acids, which contain acidic phosphate groups, include DNA and RNA. Nucleic acids contain the genetic code that determines many of an organism's characteristics, and is passed from parents to offspring. DNA contains the chemical blueprint for the synthesis of proteins, which are made up of amino acid subunits. Cell membranes contain fatty acid esters such as phospholipids.

An α-amino acid has a central carbon (the α or alpha carbon) that is covalently bonded to a carboxyl group (thus they are carboxylic acids), an amino group, a hydrogen atom and a variable group. The variable group, also called the R group or side chain, determines the identity and many of the properties of a specific amino acid. In glycine, the simplest amino acid, the R group is a hydrogen atom, but in all other amino acids it is contains one or more carbon atoms bonded to hydrogens, and may contain other elements such as sulfur, oxygen or nitrogen. With the exception of glycine, naturally occurring amino acids are chiral and almost invariably occur in the L-configuration. Peptidoglycan, found in some bacterial cell walls contains some D-amino acids. At physiological pH, typically around 7, free amino acids exist in a charged form, where the acidic carboxyl group (-COOH) loses a proton (-COO−) and the basic amine group (-NH2) gains a proton (-NH+ 3). The entire molecule has a net neutral charge and is a zwitterion, with the exception of amino acids with basic or acidic side chains. Aspartic acid, for example, possesses one protonated amine and two deprotonated carboxyl groups, for a net charge of −1 at physiological pH.

Fatty acids and fatty acid derivatives are another group of carboxylic acids that play a significant role in biology. These contain long hydrocarbon chains and a carboxylic acid group on one end. The cell membrane of nearly all organisms is primarily made up of a phospholipid bilayer, a micelle of hydrophobic fatty acid esters with polar, hydrophilic phosphate "head" groups. Membranes contain additional components, some of which can participate in acid–base reactions.

In humans and many other animals, hydrochloric acid is a part of the gastric acid secreted within the stomach to help hydrolyze proteins and polysaccharides, as well as converting the inactive pro-enzyme, pepsinogen into the enzyme, pepsin. Some organisms produce acids for defense; for example, ants produce formic acid.

Acid–base equilibrium plays a critical role in regulating mammalian breathing. Oxygen gas (O2) drives cellular respiration, the process by which animals release the chemical potential energy stored in food, producing carbon dioxide (CO2) as a byproduct. Oxygen and carbon dioxide are exchanged in the lungs, and the body responds to changing energy demands by adjusting the rate of ventilation. For example, during periods of exertion the body rapidly breaks down stored carbohydrates and fat, releasing CO2 into the blood stream. In aqueous solutions such as blood CO2 exists in equilibrium with carbonic acid and bicarbonate ion.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2066 2024-02-21 00:02:19

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2068) Structural Engineering


Structural engineering is a subfield of civil engineering focused on the strength, stability, and durability of buildings, bridges, airplanes, and other structures.


Structural engineering — a specialty within the field of civil engineering — focuses on the framework of structures, and on designing those structures to withstand the stresses and pressures of their environment and remain safe, stable and secure throughout their use. In other words, structural engineers make sure that buildings don't fall down and bridges don't collapse.

Structural engineering is among the oldest types of engineering, dating back to the first instance of tree branches being lashed together with vines to make a shelter. Throughout recorded history, people have been designing and building increasingly larger and more sophisticated structures, from primitive huts to the International Space Station.

The names of the earliest practitioners of structural engineering are lost to antiquity. We will never know who designed the Hanging Gardens of Babylon, the Parthenon or the aqueducts of the Roman Empire. Some of the latter-day practitioners in this field are known, although often not as well as the structures they designed. Prominent structural engineers include Gustave Eiffel (Eiffel Tower, Statue of Liberty) and Eero Saarinen (Gateway Arch). However, most designs for famous modern structures such as the Large Hadron Collider and the James Webb Space Telescope are attributed to companies and government organizations.

What does a structural engineer do?

Structural engineers often work alongside civil engineers and architects as part of a construction team. "In a nutshell," according to the Institution of Structural Engineers, "if a structure was a human body, then the architect would be concerned with the body shape and appearance, and the structural engineer would be concerned with the skeleton and sinews."

Structures must be able to deal with the conditions in which they are built. A house in Canada must have a roof that can bear the weight of heavy snow and a stadium in California must be able to withstand earthquakes, for example. When building bridges, designers must take into account the conditions of terrain, wind, water and traffic volume. Structural engineers consider all of these factors and provide technical advice about the project.

"Structural engineers battle gravity, wind, snow and rain every day to provide the world with outstanding structures," Kate Leighton, a structural engineer, said in "Careers in Structural Engineering, a publication of the Institution of Structural Engineers. "They are experts at solving problems, meeting challenges and providing creative solutions."

Structural engineers "design roof framing (beams, rafters, joists, trusses), floor framing (floor decks, joists, beams, trusses, girders), arches, columns, braces, frames, foundations and walls," according to the National Council of Structural Engineers Association. "In bridges, they design the deck — or riding surface, girders or stringers, and piers. The materials they use include steel, concrete, wood, masonry, and aluminum. Engineers design the structure to resist forces from gravity, earthquakes, high winds, water, soil, collisions and blast explosions."


Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and joints' that create the form and shape of human-made structures. Structural engineers also must understand and calculate the stability, strength, rigidity and earthquake-susceptibility of built structures for buildings and nonbuilding structures. The structural designs are integrated with those of other designers such as architects and building services engineer and often supervise the construction of projects by contractors on site. They can also be involved in the design of machinery, medical equipment, and vehicles where structural integrity affects functioning and safety. See glossary of structural engineering.

Structural engineering theory is based upon applied physical laws and empirical knowledge of the structural performance of different materials and geometries. Structural engineering design uses a number of relatively simple structural concepts to build complex structural systems. Structural engineers are responsible for making creative and efficient use of funds, structural elements and materials to achieve these goals.


Structural engineering dates back to 2700 B.C. when the step pyramid for Pharaoh Djoser was built by Imhotep, the first engineer in history known by name. Pyramids were the most common major structures built by ancient civilizations because the structural form of a pyramid is inherently stable and can be almost infinitely scaled (as opposed to most other structural forms, which cannot be linearly increased in size in proportion to increased loads).

The structural stability of the pyramid, whilst primarily gained from its shape, relies also on the strength of the stone from which it is constructed, and its ability to support the weight of the stone above it. The limestone blocks were often taken from a quarry near the building site and have a compressive strength from 30 to 250 MPa (MPa = Pa × {10}^{6}). Therefore, the structural strength of the pyramid stems from the material properties of the stones from which it was built rather than the pyramid's geometry.

Throughout ancient and medieval history most architectural design and construction were carried out by artisans, such as stonemasons and carpenters, rising to the role of master builder. No theory of structures existed, and understanding of how structures stood up was extremely limited, and based almost entirely on empirical evidence of 'what had worked before' and intuition. Knowledge was retained by guilds and seldom supplanted by advances. Structures were repetitive, and increases in scale were incremental.

No record exists of the first calculations of the strength of structural members or the behavior of structural material, but the profession of a structural engineer only really took shape with the Industrial Revolution and the re-invention of concrete. The physical sciences underlying structural engineering began to be understood in the Renaissance and have since developed into computer-based applications pioneered in the 1970s.

Structural failure

The history of structural engineering contains many collapses and failures. Sometimes this is due to obvious negligence, as in the case of the Pétion-Ville school collapse, in which Rev. Fortin Augustin " constructed the building all by himself, saying he didn't need an engineer as he had good knowledge of construction" following a partial collapse of the three-story schoolhouse that sent neighbors fleeing. The final collapse killed 94 people, mostly children.

In other cases structural failures require careful study, and the results of these inquiries have resulted in improved practices and a greater understanding of the science of structural engineering. Some such studies are the result of forensic engineering investigations where the original engineer seems to have done everything in accordance with the state of the profession and acceptable practice yet a failure still eventuated. A famous case of structural knowledge and practice being advanced in this manner can be found in a series of failures involving box girders which collapsed in Australia during the 1970s.


Structural engineering depends upon a detailed knowledge of applied mechanics, materials science, and applied mathematics to understand and predict how structures support and resist self-weight and imposed loads. To apply the knowledge successfully a structural engineer generally requires detailed knowledge of relevant empirical and theoretical design codes, the techniques of structural analysis, as well as some knowledge of the corrosion resistance of the materials and structures, especially when those structures are exposed to the external environment. Since the 1990s, specialist software has become available to aid in the design of structures, with the functionality to assist in the drawing, analyzing and designing of structures with maximum precision; examples include AutoCAD, StaadPro, ETABS, Prokon, Revit Structure, Inducta RCB, etc. Such software may also take into consideration environmental loads, such as earthquakes and winds.


Structural engineers are responsible for engineering design and structural analysis. Entry-level structural engineers may design the individual structural elements of a structure, such as the beams and columns of a building. More experienced engineers may be responsible for the structural design and integrity of an entire system, such as a building.

Structural engineers often specialize in particular types of structures, such as buildings, bridges, pipelines, industrial, tunnels, vehicles, ships, aircraft, and spacecraft. Structural engineers who specialize in buildings often specialize in particular construction materials such as concrete, steel, wood, masonry, alloys, and composites, and may focus on particular types of buildings such as offices, schools, hospitals, residential, and so forth.

Structural engineering has existed since humans first started to construct their structures. It became a more defined and formalized profession with the emergence of architecture as a distinct profession from engineering during the industrial revolution in the late 19th century. Until then, the architect and the structural engineer were usually one and the same thing – the master builder. Only with the development of specialized knowledge of structural theories that emerged during the 19th and early 20th centuries, did the professional structural engineers come into existence.

The role of a structural engineer today involves a significant understanding of both static and dynamic loading and the structures that are available to resist them. The complexity of modern structures often requires a great deal of creativity from the engineer in order to ensure the structures support and resist the loads they are subjected to. A structural engineer will typically have a four or five-year undergraduate degree, followed by a minimum of three years of professional practice before being considered fully qualified. Structural engineers are licensed or accredited by different learned societies and regulatory bodies around the world (for example, the Institution of Structural Engineers in the UK). Depending on the degree course they have studied and/or the jurisdiction they are seeking licensure in, they may be accredited (or licensed) as just structural engineers, or as civil engineers, or as both civil and structural engineers. Another international organisation is IABSE(International Association for Bridge and Structural Engineering). The aim of that association is to exchange knowledge and to advance the practice of structural engineering worldwide in the service of the profession and society.

Additional Information

Structural engineering is a branch of civil engineering that involves the application of the laws of physics, mathematics and empirical knowledge to safely design the ‘bones’ and load bearing elements of man made structures. Modern day structural engineering provides a large and detailed body of knowledge that can accurately predict the performance of different shapes and materials used in structures to resist loads and stresses on structures. The principles of structural engineering were used thousands of years ago when building structures like the pyramids in Egypt or the Acropolis in Greece.

Structural engineers are trained professionals who are responsible for making sure that the structures we use in our daily lives, like bridges and tall buildings, are safe, stable and don’t collapse under applied loads. They do this by applying their technical knowledge to specify different types of construction materials in various shapes and geometries and design structures that can withstand the pressures and stresses of their environment such as gravity loads, storms and earthquakes.

Structural engineers are brought on to a project if an owner is planning on changing the use of a building, introducing more floors to a building, or adding a significant expansion to a building.  It’s very important to understand that introducing alterations to any structural element without consulting a professional engineer may result in serious damage to the structure and in some cases partial or extensive collapse of the building.

Structural engineers are also brought on board if there is damage to a structure due to fire, corrosion, environmental deterioration, impact or wear and tear that could result in a loss of capacity and impose a threat to the public’s safety. When a structural engineer is contacted for an assessment of an existing building, they would visually inspect the structure and determine the structural integrity of the load bearing elements, potential concerns regarding the occupants safety, suggest repair techniques and recommend structural details to restore the structure to its original conditions in order to resist the applied loads.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2067 Yesterday 00:12:39

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2069) Firefighting


Firefighting is the activity of stopping fires burning.


Firefighting is the activity directed at limiting the spread of fire and extinguishing it, particularly as performed by members of organizations (fire services or fire departments) trained for the purpose. When it is possible, firefighters rescue persons endangered by the fire, if necessary, before turning their full attention to putting it out.

Firefighters, skilled in the use of specific equipment, proceed as rapidly as possible to the site of the fire; in most urban areas, fire stations housing a company of firefighters and their equipment occur frequently enough that an alarm receives a response within two or three minutes. Most fire services in towns inhabited by 5,000 persons or more will dispatch an engine company (pumper), a truck company (ladder truck), and a rescue vehicle to the scene. If the fire involves a structure occupied by many persons, two or more companies may respond to the first alarm. The first firefighters arriving will assess the fire to determine the techniques to be used in putting it out, taking into account the construction of the burning building and any fire protection systems within it.

Systematic firefighting involves four steps: protection of currently uninvolved buildings and areas; confinement of the fire; ventilation of the building; and extinguishment of the fire. Pathways by which the fire could spread are closed off, and the leading edge of the flame is controlled by the application of water or other cooling agents. Openings are made to permit the escape of toxic combustion products and hot air; this step (ventilation) must be conducted with keen judgment so as to permit the firefighters access to the fire without causing its intensification or risking a smoke explosion (the result of admitting fresh air to a space in which a high concentration of unburned fuel particles is present in a hot, oxygen-depleted atmosphere).

The final stage of fighting a fire is extinguishment. The firefighting force uses water streams mixed with appropriate extinguishing agents to quench the remaining flames. When this is accomplished, the firefighters initiate salvage of the structure by removing smoke and water from the interior and protecting undamaged materials.


Firefighting is a profession aimed at controlling and extinguishing fire. A person who engages in firefighting is known as a firefighter or fireman. Firefighters typically undergo a high degree of technical training. This involves structural firefighting and wildland firefighting. Specialized training includes aircraft firefighting, shipboard firefighting, aerial firefighting, maritime firefighting, and proximity firefighting.

Firefighting is a dangerous profession due to the toxic environment created by combustible materials, with major risks being smoke, oxygen deficiency, elevated temperatures, poisonous atmospheres, and violent air flows. To combat some of these risks, firefighters carry self-contained breathing apparatus. Additional hazards include falls — a constant peril while navigating unfamiliar layouts or confined spaces amid shifting debris under limited visibility – and structural collapse that can exacerbate the problems encountered in a toxic environment.

The first step in a firefighting operation is reconnaissance to search for the origin of the fire and to identify the specific risks. Fires can be extinguished by water, fuel or oxidant removal, or chemical flame inhibition; though, because fires are classified depending on the elements involved, such as grease, paper, electrical, etcetera, a specific type of fire extinguisher may be required. The classification is based on the type of fires that the extinguisher is more suitable for. In the United States, the types of fire are described by the National Fire Protection Association.


The earliest known firefighters were in the city of Rome. In 60 A.D., emperor Nero established a Corps of Vigils (Vigiles) to protect Rome after a disastrous fire. It consisted of 7,000 people equipped with buckets and axes who fought fires and served as police.

Historic tactics and tools

In the 3rd century B.C., an Alexandrian Greek named Ctesibius made a double force pump called a siphona. As water rose in the chamber, it compressed the air inside, which forced the water to eject in a steady stream through a pipe and nozzle.

In the 16th century, syringes were also used as firefighting tools, the larger ones being mounted on wheels. Another traditional firefighting method that survived was the bucket brigade, involving two lines of people formed between the water source and the fire. Typically, men in one of the lines would pass along the full buckets of water toward the fire while in the other line women and children would pass back the empty buckets to be refilled.

In the 17th century the first "fire engines" were made, notably in Amsterdam.In 1721, the English inventor Richard Newsham made a popular fire engine that was essentially a rectangular box on wheels filled using a bucket brigade to provide a reservoir while hand-powered pumps supplied sufficient water pressure to douse fires at a distance.

Ancient Rome

Ancient Rome did not have municipal firefighters. Instead, private individuals relied on their slaves or supporters to take action. They would not only form bucket brigades or attempt to smother smaller fires, but would also demolish or raze nearby buildings to slow the spread of the fire. However, there is no mention of fires being extinguished, rather they were contained and burned themselves out. Ancient Rome did not have an organized firefighting force until the Vigiles were formed during the reign of Augustus.

The first ever Roman fire brigade was created by Marcus Licinius Crassus. Fires were almost a daily occurrence in Rome, and Crassus took advantage of the fact that Rome had no fire department, by creating his own brigade—500 men strong—which rushed to burning buildings at the first cry of alarm. Upon arriving at the scene, however, the firefighters did nothing while Crassus offered to buy the burning building from the distressed property owner, at a miserable price. If the owner agreed to sell the property, his men would put out the fire; if the owner refused, then they would simply let the structure burn to the ground. After buying many properties this way, he rebuilt them, and often leased the properties to their original owners or new tenants.

United Kingdom

Prior to the Great Fire of London in 1666, some parishes in the UK had begun to organize rudimentary firefighting crews. After the Great Fire, Nicholas Barbon introduced the first fire insurance. In order to reduce insurance costs, Barbon also formed his own fire brigade, and other companies followed suit.

By the start of the 1800s, insured buildings were identified with a badge or mark indicating that they were eligible for a company's firefighting services. It is a common belief that buildings not insured with a particular company were left by its firefighters to burn, unless they happened to be adjacent to an insured building, in which case it was often in the company's interest to prevent the fire from spreading. This is a common misconception. In 1833 fire insurance companies in London merged to form The London Fire Company Establishment.

Steam-powered apparatuses were first introduced in the 1850s, allowing a greater quantity of water to be directed onto a fire; in the early 1930s they were superseded by versions powered by an internal combustion engine.

In World War II the Auxiliary Fire Service, and later the National Fire Service, were established to supplement local fire services. Before 1938, there was no countrywide standard for firefighting terms, procedures, ranks, or equipment (such as hose couplings). In the month of August in 1939 with war looking very possible the Fire Service's act of 1938 came into effect. This unified Great Britain's fire service and prepared them for the German war machine. During the London Blitz, 700 fire men and 20 fire women, as known during the time period died as a result of heavy bombing, 91 of these perished at the same time defending London. By the end of the London Blitz, 327 firefighters had lost their lives.

United States

In January 1608, a fire destroyed many colonists' provisions and lodgings in Jamestown, Virginia. By the mid-1600s, Boston, New Amsterdam (later New York City), and Philadelphia were all plagued by fires, and volunteer fire brigades began to form.

In 1736, Benjamin Franklin founded the Union Fire Company in Philadelphia, which became the standard for volunteer fire organizations. These firefighters had two critical tools: salvage bags and so-called bed keys. Salvage bags were used to quickly collect and save valuables, and bed keys were used to separate the wooden frame of a bed (often the most valuable item in a home at the time) into pieces for safe and rapid removal from the fire.

The first American attempt at fire insurance failed after a large fire in Charlestown, Massachusetts in 1736. Later in 1740, Benjamin Franklin organized the Philadelphia Contributionship to provide fire insurance, which was more successful. The Contributionship adopted "fire marks" to easily identify insured buildings. Firefighting started to become formalized with rules for providing buckets, ladders, and hooks, and with the formation of volunteer companies. A chain of command was also established.

Firefighter duties

A firefighter's goals are to save lives, protect property, and protect the environment. A fire can rapidly spread and endanger many lives, but with modern firefighting techniques, catastrophe can often be avoided. To prevent fires from starting, a firefighter's duties may include public education about fire safety and conducting fire inspections of locations to verify their adherence to local fire codes.

Firefighter skills

Firefighting requires technical proficiency of operational tactics, equipment, and scene awareness. Firefighters must also have, or be able to acquire, knowledge of department organizations, operations, and procedures, and the district or city street system they will have to negotiate in order to perform their duties.

They must meet minimum physical fitness standards and learn various firefighting duties within a reasonable period.

Examples are:

* Building construction
* Fire behavior
* Firefighting PPE
* Fire extinguishers
* Ropes and knots
* Ground ladders
* Forcible entry
* Search and rescue
* Ventilation
* Fire hose and streams
* Fire suppression
* Salvage and overhaul
* Vehicle extrication and technical rescue
* Hazardous materials response

Specialized skills

Specialized areas of operations may require subject-specific training.

Examples are:

* Fire apparatus driver/operator - trained to drive fire apparatus to and from fires and other emergencies, operate fire-apparatus pumps and aerial devices, and maintain apparatus.
* Hazardous materials technician - certified to mitigate hazardous materials emergencies.
* Rescue technician - certified to perform complex technical rescues.
* Airport firefighter - trained in ARFF.
* Wildland firefighter - trained to extinguish fires in outdoor vegetation, including the wildland/urban interface.

Shift hours

Full-time career firefighters typically follow a 24-hour shift schedule, although some fire departments work 8- or 12-hour shifts. Australian firefighters work a 10/14 shift, in which the day shift works ten hours and the night shift works 14 hours. Firefighting personnel are split up into alternating shifts. Usually, the 24-hour shifts are followed by two days off. The shift personnel arrive for roll call at a specified time, ready to complete a regular tour of duty. While on shift, the firefighter remains at the fire station unless relieved or assigned other duties.

Fire wardens

In fire fighting, there are also people designated as fire wardens, also known as chief officers. Their duties vary, some may ensure evacuation of that part of the building for which they are responsible; others may be responsible for fire control in a particular area, direct a crew in the suppression of forest fires, or function as fire patrolmen in a logging area.

The chief officer is in charge of their firefighters during fires or emergencies, and is expected to command and control the overall situation while effectively combating a fire or other emergency. Chief officers must be able to evaluate their firefighters, use sound judgement when deciding when it is time to withdraw firefighters from a fire, and react calmly in emergency situations. The chief officer must direct the activities of a fire department and supervise all firefighting activities, requiring extensive knowledge of city layouts, the location of streets, fire hydrants and fire alarm boxes, and the principal buildings. A chief officer must be familiar with sources of fires, including explosives, hazardous chemicals, and the combustion qualities of materials in buildings, homes, and industrial plants.

In certain jurisdictions, civilians can get certified to be a Fire Warden, and some cities require certain types of buildings, such as high rises, to have a certain number of Fire Wardens. For example, the city of Houston in the United States requires every tenant in a high-rise to have at least one Fire Warden for every 7500 sq. ft. occupied, and a minimum of two Fire Wardens per floor. In this example, their duties include investigating any fire alarms (see if there really is a fire and if so, its nature), ensuring the fire department is contacted, directing the evacuation of the facility, activating or delaying activation of fire suppression equipment such as halon and sprinklers (delayed in case of a false alarm), meeting the fire department and taking them to the location of the alarm or to the fire past any security or locked doors, and, if necessary, fighting the fire until the fire department arrives.

Firefighter safety zone guidelines

The U.S. Forest Service publishes guidelines for the minimum distance a firefighter should be from a flame. As stated in the National Wildfire Coordinating Group's Incident Response Pocket Guide: "A safety zone is an area where a firefighter can survive without a fire shelter" and should be " least four times the maximum continuous flame height." However this figure only takes into account the effects of radiant heat and does not consider topography nor wind.

Safety Zones can be natural features such as rock screes, meadows, and river bars; or human-made features such a parking lots or areas that have been cleared of vegetation through mechanical means.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


#2068 Yesterday 22:50:57

Jai Ganesh
Registered: 2005-06-28
Posts: 45,483

Re: Miscellany

2070) Dentist


Dentistry is the profession concerned with the prevention and treatment of oral disease, including diseases of the teeth and supporting structures and diseases of the soft tissues of the mouth. Dentistry also encompasses the treatment and correction of malformation of the jaws, misalignment of the teeth, and birth anomalies of the oral cavity such as cleft palate. In addition to general practice, dentistry includes many specialties and subspecialties, including orthodontics and dental orthopedics, pediatric dentistry, periodontics, prosthodontics, oral and maxillofacial surgery, oral and maxillofacial pathology, endodontics, public health dentistry, and oral and maxillofacial radiology.


A dentist is a healthcare provider who diagnoses and treats oral health conditions. Taking good care of your teeth and gums can help you reduce your risk for other serious health conditions, like heart disease and stroke. You should visit a dentist regularly for routine exams and cleanings.

What is a dentist?

A dentist — sometimes called a general dentist or family dentist — is a healthcare provider who diagnoses and treats oral health conditions. Dentists help keep your teeth and gums healthy with regular dental check-ups and cleanings. They can also perform a variety of oral health treatments, including dental fillings, crowns and bridges.

Are dentists doctors?

Yes. Dentists are doctors because they undergo extensive medical training. In the United States, a person who wants to become a dentist must receive an undergraduate degree and complete four years of focused training in an accredited dental school.

The extent of training is similar in other countries, as well — even though titles may differ. For example, in the United Kingdom, people refer to dentists as dental surgeons and traditionally use the title Mr., Miss or Mrs., though some may use Dr.

What’s the difference between a DDS and a DMD?

If you live in the U.S., you may see two different titles following a dentist’s name:

DDS: Doctor of Dental Surgery.
DMD: Doctor of Dental Medicine (Doctor of Medicine in Dentistry)

If you see either of these titles, it means that your dentist graduated from an accredited dental school. A DDS and DMD receive the same amount of training and can perform the same dental procedures.

What does a dentist do?

Dentists can treat a wide range of conditions affecting your teeth, gums, jaws and other areas of your mouth. They offer treatments in:

* Preventive dentistry.
* Restorative dentistry.
* Emergency dental care.

Preventive dentistry

Dentists offer preventive dentistry to protect your teeth and gums from disease-causing bacteria, stopping issues before they start. Preventive treatments include:

* Dental exams.
* Dental X-rays.
* Cleanings.
* Sealants.
* Fluoride treatments.

Restorative dentistry

Dentists also perform restorative procedures to repair or replace damaged or missing teeth. Restorative dentistry treatments include:

* Fillings.
* Crowns.
* Bridges.
* Dental implants.


Dentists are trained professionals who help care for the teeth and mouth. Regularly seeing a dentist can help you to maintain a good level of dental health, which may have a direct impact on your overall well-being.

What Does a Dentist Do?

A dentist has many responsibilities, and one of the most important is promoting good dental hygiene. This helps to prevent complications in your mouth or other parts of the body.

A dentist also diagnoses and treats problems of the gums, teeth, and mouth. Dentists use modern technology and equipment like X-ray machines, lasers, drills, brushes, scalpels, and other medical tools when performing dental procedures. They also wear protective equipment like gloves, masks, and safety glasses to prevent the spread of germs or bacteria.

Some common dentistry tasks include:

* Teaching people about dental hygiene
* Filling cavities
* Removing buildup or decay from teeth
* Repairing or removing damaged teeth
* Reviewing X-rays and diagnostics
* Giving anesthesia
* Putting in fillings or sealants
* Checking the growth of teeth and jawbones.

Dentistry requires a team approach, and the dentist is the leader. Working with the dentist are dental assistants, hygienists, and lab technicians. Together, the team ensures that people get quality dental care.

Education and Training

A dentist is a doctor, so they complete a path of study that’s similar to that of a medical doctor. The first step is to complete an undergraduate program in a related field like biology, chemistry, health, or math, and earn a bachelor of science degree. Next is a dental admissions test, which you need to take to apply for dental schools.

The training process includes:

* Completing two years of biomedical science studies, followed by two years of clinical practice
* Earning a doctor of dental surgery (DDS) or doctor of dental medicine (DDM) degree
* Getting a dental license by passing written and practical exams

Dentists may then choose to get certified by taking the National Board Dental Examination. Depending on the area of specialty, dentists may have to complete a postgraduate residency of one to three years.

Dentists can choose to specialize in one of the following areas, each of which requires a postgraduate residency:

* Dental public health
* Endodontics
* Oral and maxillofacial pathology
* Oral and maxillofacial radiology
* Oral and maxillofacial surgery
* Orthodontics and dentofacial orthopedics
* Pediatric dentistry
* Periodontics
* Prosthodontics

Reasons to See a Dentist

There are several reasons to see a dentist, and it’s important to go for a dental checkup every six months.

Preventive Care

First, your dentist will check for any signs of mouth cancer, gum problems, or dental decay. Checking on these things regularly helps to prevent more serious problems down the road.

Your dental hygienist will also clean your teeth to remove plaque and tartar buildup, which are causes of tooth decay and gum disease. Together, your dentist and hygienist can give you some tips on how to best take care of your teeth at home.

Pain or Discomfort

If you’re feeling pain or discomfort in your teeth, mouth, jaws, or gums, it’s time to see a dentist. Pain or swelling in the neck, mouth, or face can be a sign that something isn’t right. Similarly, if you notice your gums are bleeding or if you’re having trouble chewing or swallowing, you should also schedule a dental care visit to see what the causes could be.

Maintenance and Health

If you have already had a dental procedure, it’s important to make sure that everything is still as it should be. If you’re pregnant, actively using tobacco, or dealing with ongoing medical issues, a dentist can help coordinate your health care with your medical doctor.

Additional Information

A dentist, also known as a dental surgeon, is a health care professional who specializes in dentistry, the branch of medicine focused on the teeth, gums, and mouth. The dentist's supporting team aids in providing oral health services. The dental team includes dental assistants, dental hygienists, dental technicians, and sometimes dental therapists.


Middle Ages

In China as well as France, the first people to perform dentistry were barbers. They have been categorized into 2 distinct groups: guild of barbers and lay barbers. The first group, the Guild of Barbers, was created to distinguish more educated and qualified dental surgeons from lay barbers. Guild barbers were trained to do complex surgeries. The second group, the lay barbers, were qualified to perform regular hygienic services such as shaving and tooth extraction as well as basic surgery. However, in 1400, France made decrees prohibiting lay barbers from practicing all types of surgery. In Germany as well as France from 1530 to 1575 publications completely devoted to dentistry were being published. Ambroise Paré, often known as the Father of Surgery, published his own work about the proper maintenance and treatment of teeth. Ambroise Paré was a French barber surgeon who performed dental care for multiple French monarchs. He is often credited with having raised the status of barber surgeons.

Modern dentistry

Pierre Fauchard of France is often referred to as the "father of modern dentistry" because in 1728 he was the first to publish a scientific textbook on the techniques and practices of dentistry. Over time, trained dentists immigrated from Europe to the Americas to practice dentistry, and by 1760, America had its own native born practicing dentists. Newspapers were used at the time to advertise and promote dental services. In America from 1768 to 1770 the first application of dentistry to verify forensic cases was being pioneered; this was called forensic dentistry. With the rise of dentists, there was also the rise of new methods to improve the quality of dentistry. These new methods included the spinning wheel to rotate a drill and chairs made specifically for dental patients.

In the 1840s the world's first dental school and national dental organization were established. Along with the first dental school came the establishment of the Doctor of Dental Surgery degree, often referred to as a DDS degree. In response to the rise in new dentists as well as dentistry techniques, the first dental practice act was established to regulate dentistry. In the United States, the First Dental Practice Act required dentists to pass each specific state medical board exam in order to practice dentistry in that particular state. However, because the dental act was rarely enforced, some dentists did not obey the act. From 1846 to 1855 new dental techniques were being invented such as the use of ester anesthesia for surgery, and the cohesive gold foil method which enabled gold to be applied to a cavity. The American Dental Association was established in 1859 after a meeting with 26 dentists. Around 1867, the first university-associated dental school was established, Harvard Dental School. Lucy Hobbs Taylor was the first woman to earn a dental degree.

In the 1880s, tube toothpaste was created which replaced the original forms of powder or liquid toothpaste. New dental boards, such as the National Association of Dental Examiners, were created to establish standards and uniformity among dentists. In 1887 the first dental laboratory was established; dental laboratories are used to create dentures and crowns that are specific to each patient. In 1895 the dental X-ray was discovered by a German physicist, Wilhelm Röntgen.

In the 20th century, new dental techniques and technology were invented such as the porcelain crowns (1903), Novocain (a local anesthetic) 1905, precision cast fillings (1907), nylon toothbrushes (1938), water fluoridation (1945), fluoride toothpaste (1950), air driven dental tools (1957), lasers (1960), electric toothbrushes (1960), and home tooth bleaching kits (1989) were invented. Inventions such as the air driven dental tools ushered in a new high-speed dentistry.


By nature of their general training, a licensed dentist can carry out most dental treatments such as restorative (dental restorations, crowns, bridges), orthodontics (braces), prosthodontic (dentures, crown/bridge), endodontic (root canal) therapy, periodontal (gum) therapy, and oral surgery (extraction of teeth), as well as performing examinations, taking radiographs (x-rays) and diagnosis. Additionally, dentists can further engage in oral surgery procedures such as dental implant placement. Dentists can also prescribe medications such as antibiotics, fluorides, pain killers, local anesthetics, sedatives/hypnotics and any other medications that serve in the treatment of the various conditions that arise in the head and neck.

All DDS and DMD degree holders are legally qualified to perform a number of more complex procedures such as gingival grafts, bone grafting, sinus lifts, and implants, as well as a range of more invasive oral and maxillofacial surgery procedures, though many choose to pursue residencies or other post-doctoral education to augment their abilities. A few select procedures, such as the administration of General anesthesia, legally require postdoctoral training in the US. While many oral diseases are unique and self-limiting, poor conditions in the oral cavity can lead to poor general health and vice versa; notably, there is a significant link between periodontal and cardiovascular disease. Conditions in the oral cavity may also be indicative of other systemic diseases such as osteoporosis, diabetes, AIDS, and various blood diseases, including malignancies and lymphoma. Dentists can also prescribe medicines.

Several studies have suggested that dentists and dental students are at high risk of burnout. During burnout, dentists experience exhaustion, alienate from work and perform less efficiently. A systemic study identified risk factors associated with this condition such as practitioner's young age, personality type, gender, the status of education, high job strain and/or working hours, and the burden of clinical degrees requisites. The authors of this study concluded that intervention programs at an early stage during the undergraduate level may provide practitioners with a good strategy to prepare for / cope with this condition.


Depending on the country, all dentists are required to register with their national or local health board, regulators, and professional indemnity insurance, in order to practice dentistry. In the UK, dentists are required to register with the General Dental Council. In Australia, it is the Dental Board of Australia, while in the United States, dentists are registered according to the individual state board. The main role of a dental regulator is to protect the public by ensuring only qualified dental practitioners are registered, handle any complaints or misconduct, and develop national guidelines and standards for dental practitioners to follow.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.


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