Miscellany

Jai Ganesh · 2022-08-19 13:50:44

1449) Saw

Summary

A saw is a tool consisting of a tough blade, wire, or chain with a hard toothed edge. It is used to cut through material, very often wood, though sometimes metal or stone. The cut is made by placing the toothed edge against the material and moving it forcefully forth and less vigorously back or continuously forward. This force may be applied by hand, or powered by steam, water, electricity or other power source. An abrasive saw has a powered circular blade designed to cut through metal or ceramic.

Details

A saw is a tool for cutting solid materials to prescribed lengths or shapes. Most saws take the form of a thin metal strip with teeth on one edge or a thin metal disk with teeth on the periphery. Usually the teeth are “set” (bent) to alternate sides so that the kerf (groove) cut by the saw is wider than the thickness of the saw. This prevents binding between the cut surfaces and the sides of the saw. The thin-strip saws are used in a variety of arrangements for both hand and machine operation, while circular, or disk, saws are invariably machine powered.

The hand hacksaw has a U-shaped frame and blades 20 to 30 cm (8 to 12 inches) long, 1.25 cm (0.5 inch) wide, and 0.06 cm (0.025 inch) thick that close the U and are placed under tension by a screw adjustment in the handle. This saw is one of the most common tools in a machine shop and is used for cutting off solid parts held in a vise. Saws of this type are also used by butchers for cutting bones. For cutting curves and other irregular shapes in wood or other materials, the coping, or jeweler’s, saw, which is basically a hacksaw with a deeper U-shaped frame and a much narrower blade, is well-suited.

The power jigsaw, or scroll saw, does mechanically the same irregular cutting as the hand coping saw. The straight, narrow blade is mounted vertically between a pulsating lower shaft and a reciprocating upper shaft, which together move the blade rapidly up and down. Power hacksaws, driven by electric motors, are indispensable in any general-purpose machine shop or tool room; they are most often used for cutting metal. The blade is much wider and thicker and the frame much heavier than those of a hand hacksaw. The frame, carrying the blade, moves back and forth, cutting in one direction only, while a slight feeding pressure or weight automatically presses the saw against the work.

The vertical bandsaw blade is an endless narrow metal strip, with teeth along one edge, that runs around two large motorized pulleys or wheels that are mounted on a frame so that one is directly above the other. The blade passes through the table on which the work is laid. Blades are available with various sizes of teeth, and on most machines the blade speed can be varied to suit the material being cut.

Among the saws that are neither loops nor disks are three of the most common hand saws used by the carpenter: the ripsaw, the crosscut saw, and the backsaw. The first two have roughly triangular blades about 50 cm (20 inches) long, 10 cm (4 inches) wide at the handle, and tapering to about 5 cm (2 inches) at the opposite end. Ripsaws are used for cutting wood with the grain, crosscut saws for cutting across the grain. The main difference between the saws is in the way the teeth are ground. The ripsaw teeth have cutting edges that are at 90° to the blade and act like a row of chisels; the crosscut has knifelike teeth that are set to alternate sides and cut two parallel lines on each side of the kerf, so that the wood in between is broken up. The backsaw is a crosscut saw with a rectangular blade and heavy steel backing along the side opposite the teeth; this keeps the blade perfectly straight. It is usually guided by an attachment that keeps it level at all times and maintains it in the proper direction when making angular cuts.

Among the machines utilizing a rotating steel disk with peripheral teeth, the radial-arm saw is one of the most useful. The motor-driven blade is manually drawn along a horizontally set shaft or pipe, called a radial arm, that is itself supported by a vertical column attached to a heavy base. The motor-blade unit is free to move back and forth along the arm and can be adjusted to different heights by movement of the radial arm on its vertical support. The motor-blade unit can also be pivoted to make angular and ripping cuts. The work is laid on a wooden table on top of the base, and the motor-blade unit is manually moved across it, cutting as it goes. The table saw (or stationary circular saw) consists of a circular saw that can be raised and tilted, protruding through a slot in a horizontal metal table on which the work can be laid and pushed into contact with the saw. This saw is one of the basic machines in any woodworking shop; with blades of sufficient hardness, table saws can also be used for cutting metal bars. For heavy cutting-off operations the circular or cold saw is used extensively in steel plants such as cold-drawing mills or where large quantities of bars and shafts are cut. In operation, the saw carriage is fed slowly into the work.

The portable electric circular saw, with the blade attached to a motor shaft, is probably the most commonly used saw, particularly by home handymen. With the proper blade it can cut almost any material—wood, metals, plastics, fibreglass, cement block, slate, and brick. On wood it can rip, crosscut, and make angle cuts. The sabre saw, which is basically a portable jigsaw, moves up and down and may have a stroke of as much as 2.5 cm (1 inch). It can rip, crosscut, and make angle cuts. The portable chain saw has practically replaced the woodman’s axe and the two-man hand saw for felling trees. It consists of a thin metal frame supporting a steel roller chain carrying saw teeth attached at intervals along its length; the teeth are slightly wider than the chain to prevent binding of the chain body and the material being cut. An electric motor or a small gasoline engine causes the chain sprocket to rotate, drawing the chain around with it at a high rate of speed.

Jai Ganesh · 2022-08-20 14:28:32

1450) Metrology

Summary

Metrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in France when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention. This has evolved into the International System of Units (SI) as a result of a resolution at the 11th General Conference on Weights and Measures (CGPM) in 1960.

Metrology is divided into three basic overlapping activities:

* The definition of units of measurement
* The realisation of these units of measurement in practice
*
Traceability—linking measurements made in practice to the reference standards

These overlapping activities are used in varying degrees by the three basic sub-fields of metrology:

* Scientific or fundamental metrology, concerned with the establishment of units of measurement
* Applied, technical or industrial metrology—the application of measurement to manufacturing and other processes in society
* Legal metrology, covering the regulation and statutory requirements for measuring instruments and methods of measurement

In each country, a national measurement system (NMS) exists as a network of laboratories, calibration facilities and accreditation bodies which implement and maintain its metrology infrastructure. The NMS affects how measurements are made in a country and their recognition by the international community, which has a wide-ranging impact in its society (including economics, energy, environment, health, manufacturing, industry and consumer confidence). The effects of metrology on trade and economy are some of the easiest-observed societal impacts. To facilitate fair trade, there must be an agreed-upon system of measurement.

Details

Metrology is the science of measurement. From three fundamental quantities, length, mass, and time, all other mechanical quantities—e.g., area, volume, acceleration, and power—can be derived. A comprehensive system of practical measurement should include at least three other bases, taking in the measurement of electromagnetic quantities, of temperature, and of intensity of radiation—e.g., light.

Accordingly, the 11th General Conference of Weights and Measures in 1960 adopted six quantities and units as the bases on which was established the International System of Units. Since 1887 many national standards laboratories have been founded to set up and maintain standards of measurement, both for the six basic quantities and for their systematic derivatives. They also do attendant test and verification work for science and industry. Examples are the National Bureau of Standards (NBS) in the United States (now known as the National Institute of Standards and Technology; NIST), the National Physical Laboratory (NPL) in the United Kingdom, and similar bodies in many other countries. The international metric organization created by the Metric Convention of 1875 (amended in 1921) also has a central laboratory, the International Bureau of Weights and Measures, at Sèvres (near Paris). It has duties analogous to those of the national laboratories but is concerned especially with the international coordination of all scientific work relating to the maintenance and improvement of the metric system of units and standards. This organization acts under the authority of the General Conference of Weights and Measures with the aid of an elected executive body, the International Committee of Weights and Measures, which meets every year.

Measuring a quantity means ascertaining its ratio to some other fixed quantity of the same kind, known as the unit of that kind of quantity. A unit is an abstract conception, defined either by reference to some arbitrary material standard or to natural phenomena. For example, the standard of length in the metric system was defined (1889–1960) by the separation of two lines on a particular metal bar, but it is now defined as equal to the distance traveled by light in a vacuum in a certain period of time.

Metre (m), also spelled meter, in measurement, is a fundamental unit of length in the metric system and in the International Systems of Units (SI). It is equal to approximately 39.37 inches in the British Imperial and United States Customary systems. The metre was historically defined by the French Academy of Sciences in 1791 as 1/10,000,000 of the quadrant of the Earth’s circumference running from the North Pole through Paris to the equator. The International Bureau of Weights and Measures in 1889 established the international prototype metre as the distance between two lines on a standard bar of 90 percent platinum and 10 percent iridium. By 1960 advances in the techniques of measuring light waves had made it possible to establish an accurate and easily reproducible standard independent of any physical artifact. In 1960 the metre was thus defined in the SI system as equal to 1,650,763.73 wavelengths of the orange-red line in the spectrum of the krypton-86 atom in a vacuum.

By the 1980s, advances in laser measurement techniques had yielded values for the speed of light in a vacuum of an unprecedented accuracy, and it was decided in 1983 by the General Conference on Weights and Measures that the accepted value for this constant would be exactly 299,792,458 metres per second. The metre is now thus defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.

QM0718-CLMN-CMS-p1FT.jpg?1530899278

Jai Ganesh · 2022-08-21 13:56:49

1451) Mycology

Summary

Mycology is the branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans, including as a source for tinder, traditional medicine, food, and entheogens, as well as their dangers, such as toxicity or infection.

A biologist specializing in mycology is called a mycologist.

Mycology branches into the field of phytopathology, the study of plant diseases, and the two disciplines remain closely related because the vast majority of plant pathogens are fungi.

Mycology is the branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans, including as a source for tinder, traditional medicine, food, and entheogens, as well as their dangers, such as toxicity or infection.

Details

Mycology Definition

Mycology is the study of fungi, their relationships to each other and other organisms, and the unique biochemistry which sets them apart from other groups. Fungi are eukaryotic organism which belong to their own kingdom. Until advances in DNA technology, it was assumed that fungi were an offshoot of the plant kingdom. DNA and biochemical analysis has revealed that fungi are a separate lineage of eukaryotes, distinguished by their unique cell wall made of chitin and glucans which often surrounds multinucleated cells. Mycology is a necessary branch of biology because fungi is considerably different from both plants and animals.

History of Mycology

Until the 1800’s, it was assumed that fungi were simply a different kind of plant. Mushrooms, the reproductive bodies of fungi, were eaten, used as medicine, and used for their hallucinogenic effects since antiquity. Many classic Greek philosophers and naturalists considered fungi, but still assumed they were more related to plants. By the mid-1800’s the microscope was invented, and scientists began to examine the inner workings of fungi. Microscopes revealed that fungi had distinct features, separate from both plants and animal cells. The term mycology was coined in 1836 in a paper by M.J. Berkeley, when fungi were beginning to be recognized as their own unique kingdom.

However, it was not until the advent of modern biochemistry and DNA analysis that it was fully realized how different fungi were. Instead of a cell wall made of cellulose, the wall in fungi is composed of glucans and chitin, molecules found in plants and insects, respectively. Instead of having a single nucleus, like most plants and animals, fungi are often multinucleated and contain special pores allowing the cytoplasm and nucleus to flow freely between various chambers in the fungal organism. DNA analysis revealed a closer relation to animals than plants. As scientists observed fungal lifecycles further, they realize that the majority of most fungi spends its time as a mold or ooze. This multicellular lifeform moves its way through decaying organic material, utilizing the minerals and organic molecules as it goes. Not only was fungi the major decomposing organism in the world, scientist also determined that certain fungi were responsible for events like fermentation and crop diseases.

With this, the field of mycology exploded. Agricultural mycology focuses on utilizing and controlling fungi in commercial crops. Toxicologists study mushroom and fungi for compounds which adversely affect other organisms. Pharmaceutical companies race to extract useful compounds from mushrooms. Careers in mycology are as diverse and complex as the field itself.

Careers in Mycology

Mycology first became an important science in the agricultural industry, and remains so today. A phytopathologist studies plant diseases, especially those which affect crops. Fungi are a major pest for many crops, but also serve symbiotic roles and allow plants to extract nutrients and water from the soil. Mycology is needed to distinguish between beneficial and harmful fungi, as well as to treat crops and prevent future infections. Further, certain types of fungi are used as pesticides, as they are more natural than synthetic pesticides and can kill targeted insects.

However, mycology has expanded well beyond its origins in agriculture. Once it was realized how broad and diverse the fungi kingdom is, the various roles of fungi in society were better understood. For instance, cheese is produced by various fungi. Mycology can classify and understand these organisms, leading to better and more efficiently produced cheese and dairy products. Yeast is also a form of fungi, and understanding the process of fermentation carried out by yeast is a science in itself. Fermentation science degrees can found from the bachelor level up, and graduates can work in the brewing and distilling industries, creating beer, wines and liquor. Yeast is also used in bread making, and microbiologists are required to maintain the cultures to produce enough yeast for bread production.

A specialized field of mycology is mycotoxicology, or the study of the toxins produced by mushrooms. Typically, a mycotoxicologist has a doctorate degree in biochemistry or organic chemistry, or a medical doctorate with concentrations in mycology and toxins. Fungi produce a variety of chemicals which have toxic effects on all kinds of organisms. Humans have eaten mushrooms since the earliest hunter-gatherers, but many mushrooms remain highly toxic. Other compounds found in mushrooms have potentially beneficial properties which could be used in medicine. Many mycotoxicologists work for pharmaceutical companies, trying to develop new drugs based on these compounds.

Mycology contains still more specializations, and is a continually evolving field. As more research is done, fungi are becoming a large and complex kingdom. Research is expanding and focusing on many special areas, including interesting applications for certain fungi. Some of these applications include radiotrophic fungi which appear to grow in the presence of radioactivity and could possibly alleviate radioactive wastes, and fungi which can break down complex organic substances into carbon dioxide. Many of these applications have tremendous commercial value, and researchers are needed at many institutions to explore these aspects of mycology.

Finally, an ethnomycologist is a scientist who studies the historical uses of fungi. Cultures have used mushroom as food, medicine, hallucinogens, and for a variety of other things. Ethnomycologists study these uses and inform the public and front-line researchers about which fungi have known effects and which are benign. Considering the immense size and diversity of fungi, and the relatively unorganized history of the classification of fungi, ethnomycologists provide a critical function in sorting through the dense but helpful information already gathered by past cultures and societies. The field of mycology is continually expanding as these many professions push the boundaries of knowledge and fill in the missing gaps.

Jai Ganesh · 2022-08-22 14:01:00

1452) Pliers

Summary

Pliers are hand-operated tool for holding and gripping small articles or for bending and cutting wire. Slip-joint pliers have grooved jaws, and the pivot hole in one member is elongated so that the member can pivot in either of two positions in order to grasp objects of different size in the most effective way. On some pliers the jaws have a portion that can cut soft wire and nails.

For bending wire and thin metal, round-nose pliers with tapering, conical jaws are used. Diagonal cutting pliers are used for cutting wire and small pins in areas that cannot be reached by larger cutting tools. Because the cutting edges are diagonally offset about 15 degrees, these can cut objects flush with a surface.

Details

Pliers are a hand tool used to hold objects firmly, possibly developed from tongs used to handle hot metal in Bronze Age Europe. They are also useful for bending and physically compressing a wide range of materials. Generally, pliers consist of a pair of metal first-class levers joined at a fulcrum positioned closer to one end of the levers, creating short jaws on one side of the fulcrum, and longer handles on the other side. This arrangement creates a mechanical advantage, allowing the force of the grip strength to be amplified and focused on an object with precision. The jaws can also be used to manipulate objects too small or unwieldy to be manipulated with the fingers.

Diagonal pliers, also called side cutters, are a similarly-shaped tool used for cutting rather than holding, having a pair of stout blades, similar to scissors except that the cutting surfaces meet parallel to each other rather than overlapping. Ordinary (holding/squeezing) pliers may incorporate a small pair of such cutting blades. Pincers are a similar tool with a different type of head used for cutting and pulling, rather than squeezing. Tools designed for safely handling hot objects are usually called tongs. Special tools for making crimp connections in electrical and electronic applications are often called crimping pliers or crimpers; each type of connection uses its own dedicated tool.

There are many kinds of pliers made for various general and specific purposes.

Jai Ganesh · 2022-08-23 14:12:45

1453) Dermatology

Gist

Dermatology is the branch of medicine dealing with the skin. It is a speciality with both medical and surgical aspects. A dermatologist is a specialist medical doctor who manages diseases related to skin, hair, nails, and some cosmetic problems.

Summary

Dermatology is a medical specialty dealing with the diagnosis and treatment of diseases of the skin. Dermatology developed as a subspecialty of internal medicine in the 18th century; it was initially combined with the diagnosis and treatment of venereal diseases, because syphilis was an important possible diagnosis in any skin rash. Modern dermatology emerged in the early 20th century, after the discovery of an effective drug therapy for syphilis.

Because of the ease of observation of cutaneous symptoms, dermatology had early become a separate branch of medicine. Its scientific basis, however, was not established until the mid-19th century by the Austrian physician Ferdinand von Hebra. Hebra emphasized an approach to skin diseases based on the microscopic examination of skin lesions. Following Hebra’s work, dermatologists concentrated chiefly on the description and classification of skin diseases, but a new emphasis on the biochemistry and physiology of these diseases, begun by Stephen Rothman in the 1930s, led to the development of more sophisticated and effective treatments in the latter half of the 20th century. Dermatologists have gained the capacity to control fungal diseases of the skin, to recognize and treat skin cancers at an early stage, to control the life-threatening skin diseases pemphigus and lupus erythematosus, and to alleviate psoriasis.

Details

Dermatology involves the study, research, diagnosis, and management of any health conditions that may affect the skin, fat hair, nails, and membranes. A dermatologist is the health professional who specializes in this area of healthcare.

The skin is the largest organ of the body, which acts as a barrier to protect the internal organs from injury and bacteria. It is also a good indicator of the overall health of the body, making the field of dermatology important in the diagnosis and management of many health conditions.

Dermatologic Conditions
Conditions of the hair, skin, or nails are very common and almost everyone experiences symptoms of one or other dermatologic condition at some point in their life. In fact, approximately one in six of all visits to a general practitioner involves a problem of the skin. Some of the most common dermatologic conditions include:

* Acne: pimples on the skin due to inflammation of the sebaceous glands
* Dermatitis: red, swollen and sore skin caused by irritation or allergy
* Eczema: rough and inflamed skin that is itchy and may bleed
* Psoriasis: itchy, red, scaly patches on the skin
* Fungal infections: infection of the skin or nails caused by a fungus
* Warts: small hard growth on the skin caused by a virus
* Cold sore: inflamed blister near the mouth caused by herpes simplex virus
* Skin cancer: uncontrolled growth of skin cells

Each of these dermatologic conditions has characteristic symptoms and should be managed in a unique manner. Additionally, each case will vary considerably in severity, which will influence the treatment decisions.

Therapies in Dermatology

There are several types of dermatological therapies that may be used in the management of skin conditions. These may include:

* Topical medications
* Systemic medications
* Dermatohistopathology
* Surgery
* Immunotherapy
* Photodynamic therapy
* Phototherapy
* Laser therapy
* Radiotherapy

Each of these therapies has a specific role to play in the management of certain dermatological conditions. Topical agents are the most common type of treatment, and can be applied directly to the affected area for the desired effect. However, other types of therapy are important for other conditions or particular purposes.

Dermatology as a Profession

A dermatologist is a health professional who specializes in the field of dermatology and is involved in the diagnosis and treatment of hair, skin, and nail conditions.

Although the exact education and training requirements vary according to the country of practice, a dermatologist usually needs to complete medical school and residency (minimum of 6 + 3 years) before commencing a specialized training program in the field of dermatology. The specialization in dermatology typically takes at least four years of intensive study, research, and practice in the field. Continued professional development is also required for dermatologist to demonstrate ongoing competency and maintain their registration to practice.

A trained dermatologist may perform skin surgery to prevent or control skin diseases such as skin cancer, to improve aesthetics of the skin or diagnose a condition of the skin. They are also responsible for the treatment decisions of various dermatological conditions with many types of therapies, including topical agents, systemic agents and other therapies.

Jai Ganesh · 2022-08-24 14:01:10

1454) Geology

Summary

Also known as 'geoscience' or 'Earth science', geology is the study of the structure, evolution and dynamics of the Earth and its natural mineral and energy resources. Geology investigates the processes that have shaped the Earth through its 4500 million (approximate!)

Geology (from Ancient Greek 'earth', and 'study of, discourse') is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated Earth system science and planetary science.

Geology describes the structure of the Earth on and beneath its surface, and the processes that have shaped that structure. It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, and also to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.

Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, and numerical modelling. In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, and providing insights into past climate change. Geology is a major academic discipline, and it is central to geological engineering and plays an important role in geotechnical engineering.

Details

Definition of Geology:

Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them. It includes the study of organisms that have inhabited our planet. An important part of geology is the study of how Earth's materials, structures, processes and organisms have changed over time.

What Does a Geologist Do?

Geologists work to understand the history of our planet. The better they can understand Earth’s history, the better they can foresee how events and processes of the past might influence the future. Here are some examples:

* Geologists study Earth processes: Many processes such as landslides, earthquakes, floods, and volcanic eruptions can be hazardous to people. Geologists work to understand these processes well enough to avoid building important structures where they might be damaged. If geologists can prepare maps of areas that have flooded in the past, they can prepare maps of areas that might be flooded in the future. These maps can be used to guide the development of communities and determine where flood protection or flood insurance is needed.

* Geologists study Earth materials: People use Earth materials every day. They use oil that is produced from wells, metals that are produced from mines, and water that has been drawn from streams or from underground. Geologists conduct studies that locate rocks that contain important metals, plan the mines that produce them and the methods used to remove the metals from the rocks. They do similar work to locate and produce oil, natural gas, and groundwater.

* Geologists study Earth history: Today we are concerned about climate change. Many geologists are working to learn about the past climates of Earth and how they have changed across time. This historical geology news information is valuable to understand how our current climate is changing and what the results might be.

Geology as a Career

Geology can be a very interesting and rewarding career. The minimum training required is a four-year college degree in geology. Pre-college students who are interested in becoming geologists should take a full curriculum of college preparatory courses, especially those in math, science, and writing. Courses related to computers, geography and communication are also valuable.

Geologists work in a variety of settings. These include: natural resource companies, environmental consulting companies, government agencies, non-profit organizations, and universities. Many geologists do field work at least part of the time. Others spend their time in laboratories, classrooms or offices. All geologists prepare reports, do calculations and use computers.

Although a bachelor's degree is required for entry-level employment, many geologists earn master's and/or doctorate degrees. The advanced degrees provide a higher level of training, often in a geology specialty area such as paleontology, mineralogy, hydrology, or volcanology. Advanced degrees will often qualify the geologist for supervisory positions, research assignments, or teaching positions at the university level. These are some of the most sought-after jobs in the field of geology.

Employment opportunities for geologists are very good. Most geology graduates with a strong academic background and good grades have no trouble finding employment if they are willing to move to a location where work is available.

Employment Outlook

Over the next several years, the number of geology job openings is expected to exceed the number of students graduating from university geology programs. Starting salaries for geologists have recently ranged from $50,000 to $100,000 per year.

How Can You Become a Geologist?

If you are a pre-college student, you can prepare to become a geologist by doing well in all of your courses. Science courses are especially important, but math, writing, and other disciplines are used by every geologist during every working day.

If you are considering college or graduate school, there are many universities that offer courses or programs in geology. Visit the website of a school that offers a geology degree, get in touch with the geology department, let them know you are interested, and make arrangements to visit the campus. Don't be hesitant. Good schools and professors want to be contacted by interested students.

Jai Ganesh · 2022-08-25 14:38:55

1455) Wrench

Summary

A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning.

In the UK, Ireland, Australia, and New Zealand spanner is the standard term. The most common shapes are called open-ended spanner and ring spanner. The term wrench is generally used for tools that turn non-fastening devices (e.g. tap wrench and pipe wrench), or may be used for a monkey wrench—an adjustable pipe wrench.

In North American English, wrench is the standard term. The most common shapes are called open-end wrench and box-end wrench. In American English, spanner refers to a specialized wrench with a series of pins or tabs around the circumference. (These pins or tabs fit into the holes or notches cut into the object to be turned.) In American commerce, such a wrench may be called a spanner wrench to distinguish it from the British sense of spanner.

Higher quality wrenches are typically made from chromium-vanadium alloy tool steels and are often drop-forged. They are frequently chrome-plated to resist corrosion and for ease of cleaning.

Hinged tools, such as pliers or tongs, are not generally considered wrenches in English, but exceptions are the plumber wrench (pipe wrench in British English) and Mole wrench (sometimes Mole grips in British English).

The word can also be used in slang to describe an unexpected obstacle, for example, "He threw a spanner in the works" (in U.S. English, "monkey wrench").

Details

A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning.

Wrench, also called spanner, is a tool, usually operated by hand, for tightening bolts and nuts. Basically, a wrench consists of a stout lever with a notch at one or both ends for gripping the bolt or nut in such a way that it can be twisted by a pull on the wrench at right angles to the axes of the lever and the bolt or nut. Some wrenches have ends with straight-sided slots that fit over the part being tightened; these tools are known as open-end wrenches and are made in various sizes to fit specific bolt and nut sizes.

Box-end wrenches have ends that enclose the nut and have 6, 8, 12, or 16 points inside the head. A wrench with 12 points is used on either a hexagonal or a square nut; the 8- and 16-point wrenches are used on square members. Because the sides of the box are thin, these wrenches are suitable for turning nuts that are hard to reach with an open-end wrench.

When a nut or a bolt head is in a recess below the surface of a bolted member, a socket wrench must be used; this is essentially a short pipe with a square or hexagonal hole and either an integral or a removable handle. Modern socket wrenches are made in sets, consisting of a number of short sockets with a square hole in one end that fits a removable handle and 8- or 12-point holes in the other end to fit various bolt and nut sizes. There are several types of handles and extensions, such as a T handle, screwdriver-grip handle, and a ratchet handle.

A useful accessory for a socket-wrench set is a handle equipped with a mechanism that measures the amount of torque, or turning effort, exerted by the wrench on the nut or bolt. One type of torque handle has two arms attached to the head, which carries the socket that fits the bolt or nut to be tightened; one arm carries the torque-indicating scale and remains fixed relative to the head, while the other arm carries the handgrip and is bent, relative to the head and the scale, when a bolt is tightened. A pointer on the bent arm indicates the torque on the scale. The purpose of a torque wrench is to make sure that screws and bolts in bolted assemblies are installed with sufficient tightness to prevent loosening during use, without being overtightened.

Wrenches with one fixed and one adjustable parallel jaw can be used on various sizes of bolts and nuts within a limited range. On one type the jaws are at right angles to the handle; this wrench is known as a monkey wrench. On another type, originally called a Crescent wrench, the jaws are almost parallel to the handle. On both types the movable jaw is adjusted by turning a worm that engages a rack of teeth cut into the jaw.

The adjustable pipe, or Stillson, wrench is used to hold or turn pipes or circular bars. This wrench has serrated jaws, one of which is pivoted on the handle to create a strong gripping action on the work.

Recessed-head screws or set screws commonly have a hexagonally shaped recess and require a special wrench, usually referred to as an Allen wrench; it consists of a hexagonal bar of tool steel shaped into the form of an L, either end of which fits into the recess.

Power or impact wrenches are used for tightening or loosening nuts quickly. They are essentially small handheld electric or pneumatic motors that can rotate socket wrenches at high speed. They are equipped with a torque-limiting device that will stop the rotation of the socket wrench when a preset torque is reached. Pneumatic wrenches are commonly used in automobile service stations, where compressed air is available and the sparking of electric motors is a fire hazard.

Jai Ganesh · 2022-08-26 14:36:38

1456) Screwdriver

Summary

A screwdriver is a tool, manual or powered, used for turning screws. A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. This form of the screwdriver has been replaced in many workplaces and homes with a more modern and versatile tool, a power drill, as they are quicker, easier, and can also drill holes. The shaft is usually made of tough steel to resist bending or twisting. The tip may be hardened to resist wear, treated with a dark tip coating for improved visual contrast between tip and screw—or ridged or treated for additional 'grip'. Handles are typically wood, metal, or plastic and usually hexagonal, square, or oval in cross-section to improve grip and prevent the tool from rolling when set down. Some manual screwdrivers have interchangeable tips that fit into a socket on the end of the shaft and are held in mechanically or magnetically. These often have a hollow handle that contains various types and sizes of tips, and a reversible ratchet action that allows multiple full turns without repositioning the tip or the user's hand.

A screwdriver is classified by its tip, which is shaped to fit the driving surfaces—slots, grooves, recesses, etc.—on the corresponding screw head. Proper use requires that the screwdriver's tip engage the head of a screw of the same size and type designation as the screwdriver tip. Screwdriver tips are available in a wide variety of types and sizes. The two most common are the simple 'blade'-type for slotted screws, and Phillips, generically called "cross-recess", "cross-head", or "cross-point".

A wide variety of power screwdrivers ranges from a simple 'stick'-type with batteries, a motor, and a tip holder all inline, to powerful "pistol" type VSR (variable-speed reversible) cordless drills that also function as screwdrivers. This is particularly useful as drilling a pilot hole before driving a screw is a common operation. Special combination drill-driver bits and adapters let an operator rapidly alternate between the two. Variations include impact drivers, which provide two types of 'hammering' force for improved performance in certain situations, and "right-angle" drivers for use in tight spaces. Many options and enhancements, such as built-in bubble levels, high/low gear selection, magnetic screw holders, adjustable-torque clutches, keyless chucks, 'gyroscopic' control, etc., are available.

Details

A hand or machine tool which engages with the head of a screw and allows torque to be applied to turn the screw, thus driving it in or loosening it.

A screwdriver is a tool, usually hand-operated, for turning screws with slotted heads. For screws with one straight diametral slot cut across the head, standard screwdrivers with flat blade tips and in a variety of sizes are used. Special screws with cross-shaped slots in their heads require a special screwdriver with a blade tip that fits the slots. The most common special screw is the Phillips head (Phillips Screw).

The screwdriver shank is made of tough steel, and the tip is hardened to minimize wear. The handle is made of wood, metal, or plastic.

If a screw cannot be reached with a straight-shank screwdriver, an offset screwdriver is used; this tool has no handle but has a shank with a right-angle bend at both ends. One blade tip is in line with the shank, and the other is at right angles to the shank.

Screwdriver bits can be clamped in a brace, an automatic handle that rotates on being pushed toward the screwhead, or a gear reduction drive in a power drill.

Types of Screwdrivers and their uses

A Screwdriver is a simple and common tool used for fitting or removing a screw. The turning moment created by the screwdriver can be done by manual or electrical. A screwdriver is the most common and performs a simple function with a simple design we use ever, but there are several types developed according to the changes that came across. A screwdriver has a plastic or rubber handle and a grip on it and has different types of tips on the end. We need to use an exact screwdriver to work on a screw. This is important because different shapes of the screwdriver transmit different torque and apply a different amount of pressure on it. To withstand turning movement, pressure, and corrosion resistance, the material should stronger and harder so most of them are made with alloy steel.

Types of Screwdrivers and there uses:

Flat Head Screwdriver:

Flat Head screwdriver is the most common type we use ever, this is the simple and widely used compared to anyone, from many years this has been using for fitting or removing purpose, the shape at the tip has a wedge-shaped flat tip. we can find this screwdriver in most of the tool kits.

This type of tool cannot transmit more torque and there is an easy chance in slipping so we need to choose the exact size required to work on a screw. and we think most of the flathead screwdrivers should need a sharp end but it is not true, the sharp end has a higher slipping rate and may damage the top flat grip of a screw or the tip of the tool. this type of tool needs a little flat surface at the end which avoids easy slipping from the screw head.

Phillips Screwdriver:

Phillips type screwdriver has mostly used in the automobile industry which has a cross(X) shape at the tip of the tool, this type of tool used to turn the screw with more torque to achieve a required fit but has a little slipping rate. it has more grip to handle. by using only the required size we can work efficiently.

Square Screwdriver:

This type of screwdriver name itself explains the shape of the tool, this is also called as Robertson screwdriver, it has a square shape at the end of the tool, this type of tool does not slip from screw due to the fixing between tool and screw has clear tolerance. it can transfer more torque and high load can apply on it to turn the nut compared to most of the tools and we can achieve more grip due to the shape.

Pozidriv Screwdriver:

Pozidriv tool is the same as the Phillips tool but this is developed to increase the torque, contact, decreasing the slip rate, etc. In the pozidriv tool, the contact surface area is more and this tool is more stable. there is also a high torque transmission possible with less slipping from work. this tool has a self-centering design to fit in work accurately. this type of tool has different sizes which can choose according to the work.

Hexagonal Screwdriver:

The hexagonal screwdriver is also called as hex. it has six sides the very common types of screws are used in construction. this tool has a hexagonal shape at the tip and it has more grip and possible to transfer more torque and less slipping from work. german company has developed this type of tool and has a patent on it. this tool can be used to work on nuts, bolts most of the nuts and bolts are using this shape for fixing so the hex tool is highly used in nowadays. we should aware of different sizes in this tool only an exact size is used to tighten or loosen because there are various sizes in this shape that may get confused.

Torx Screwdriver:

Torx has a star shape at the tip of the tool and the same shape on the screw.

This type of screws is mostly used in the automobile industry. most of these shaped screws are used in vehicles, electronic devices, etc. due to the increased in Torx screwdrivers, Torx screws are highly used in automobile, construction, electronic goods, etc.

This is more stable and efficient.

Jai Ganesh · 2022-08-27 14:51:16

1457) Vise

Summary

A vise or vice (British English) is a mechanical apparatus used to secure an object to allow work to be performed on it. Vises have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever.

A vise grip is not a vise but a pair of lever-actuated locking pliers.

Details

Vise, also spelled Vice, is a device consisting of two parallel jaws for holding a workpiece; one of the jaws is fixed and the other movable by a screw, a lever, or a cam. When used for holding a workpiece during hand operations, such as filing, hammering, or sawing, the vise may be permanently bolted to a bench. In vises designed to hold metallic workpieces, the active faces of the jaws are hardened steel plates, often removable, with serrations that grip the workpiece; to prevent damage to soft parts, the permanent jaws can be covered with temporary jaws made from sheet copper or leather. Pipe vises have double V-shaped jaws that grip in four places instead of only two. Woodworking vises have smooth jaws, often of wood, and rely on friction alone rather than on serrations.

For holding workpieces on the tables of machine tools, vises with smooth hardened-steel jaws and flat bases are used. These machine vises are portable but may be clamped to the machine table when in use; means may also be provided for swivelling the active part of the vise so that the workpiece can be held in a variety of positions relative to the base. For holding parts that cannot be clamped with flat jaws, special jaws can be provided.

Jai Ganesh · 2022-08-28 15:01:09

1458) Oncology

Summary

Oncology is a branch of medicine that deals with the study, treatment, diagnosis and prevention of cancer. A medical professional who practices oncology is an oncologist. The name's etymological origin is the Greek word (ónkos), meaning "tumor", "volume" or "mass". Oncology is concerned with:

* The diagnosis of any cancer in a person (pathology)
* Therapy (e.g. surgery, chemotherapy, radiotherapy and other modalities)
* Follow-up of cancer patients after successful treatment
* Palliative care of patients with terminal malignancies
* Ethical questions surrounding cancer care
* Screening efforts:
** of populations, or
** of the relatives of patients (in types of cancer that are thought to have a hereditary basis, such as breast cancer).

Details

What is Oncology?

The term oncology literally means a branch of science that deals with tumours and cancers. The word “onco” means bulk, mass, or tumor while “-logy” means study.

What is cancer?

Each of the cells of the body have a tightly regulated system that controls their growth, maturity, reproduction and eventual death. Cancer begins when cells in a part of the body start to grow out of control. There are many kinds of cancer, but they all start because of out-of-control growth of abnormal cells.

How common is cancer?

Today, millions of people are living with cancer or have had cancer. Cancer is the second leading cause of death in the United States. About one-half of all men and one-third of all women in the US will develop cancer during their lifetimes.

How long has cancer existed for?

Some of the earliest evidence of cancer is found among fossilized bone tumors, human mummies in ancient Egypt, and ancient manuscripts. Abnormalities suggestive of the bone cancer called osteosarcoma have been seen in mummies.

Among manuscripts the first known description of cancer is seen in the Edwin Smith Papyrus and is a copy of part of an ancient Egyptian textbook on trauma surgery. It describes 8 cases of tumors or ulcers of the breast that were treated by cauterization with a tool called the fire drill. It dates back to about 3000 BC. The papyrus describes the condition as “incurable”.

Role of an oncologist

Medical professionals who practice oncology are called Cancer specialists or oncologists. These oncologists have several specific roles. They help in diagnosis of the cancer, help in staging the cancer and grading the aggressive nature of the cancer.

Oncology diagnostic tools

The most important diagnostic tool remains the clinical history of the patient. Common symptoms that point towards cancer include fatigue, weight loss, unexplained anemia, fever of unknown origin etc.

Oncology depends on diagnostic tools like biopsy or removal of bits of the tumour tissue and examining it under the microscope. Other diagnostic tools include endoscopy for the gastrointestinal tract, imaging studies like X-rays, CT scanning, MRI scanning, ultrasound and other radiological techniques, Scintigraphy, Single Photon Emission Computed Tomography, Positron emission tomography and nuclear medicine techniques etc.

Common methods include blood tests for biological or tumor markers. Rise of these markers in blood may be indicative of the cancer.

Cancer therapy

Based on the grade and stage of the cancer, oncologists help plan the therapy that is suitable for each of their patients. This could be by surgery, chemotherapy, radiation therapy and other modalities.

Other specialists

Treatment of cancer may involve other specialists as well. This includes a surgeon, a radiation oncologists or a radiotherapist etc. the whole of the cancer therapy however is co-ordinated by the oncologists.

Relapse and remission

Once initial therapy is completed the oncologists is responsible for follow up of the patient to detect relapse and remission. The former means recurrence or return of the cancer while being in remission means remaining cancer-free.

Palliative care

The oncologist is also responsible for palliative or symptomatic care in patients with terminal malignancies. This and other issues of treatment choice have several ethical issues including patient autonomy and choice that the oncologist needs to be concerned about.

Cancer screening

Oncology and cancer research involves screening the general population for cancer and screening the relatives of patients (in types of cancer that are thought to have a hereditary basis. For example, in breast cancer both population screening by regular mammography and familial screening by genetic analysis of the BRCA1 and BRCA2 genes is performed.

Progress in oncology

There is a tremendous amount of research being conducted on all areas of oncology, ranging from cancer cell biology to chemotherapy treatment regimens and optimal palliative care and pain relief. This makes oncology a continuously changing and developing field.

Cancer research is carried out in clinical trials. In the UK, patients are often enrolled in large studies coordinated by Cancer Research UK (CRUK), Medical Research Council (MRC), the European Organisation for Research and Treatment of Cancer (EORTC) or the National Cancer Research Network (NCRN).

cancer---patient-support.ashx?h=208&w=300&la=en

Jai Ganesh · 2022-08-29 14:28:56

1459) Morphology (biology)

Summary

Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features.

This includes aspects of the outward appearance (shape, structure, colour, pattern, size), i.e. external morphology (or eidonomy), as well as the form and structure of the internal parts like bones and organs, i.e. internal morphology (or anatomy). This is in contrast to physiology, which deals primarily with function. Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts.

Details

Morphology, in biology, is the study of the size, shape, and structure of animals, plants, and microorganisms and of the relationships of their constituent parts. The term refers to the general aspects of biological form and arrangement of the parts of a plant or an animal. The term anatomy also refers to the study of biological structure but usually suggests study of the details of either gross or microscopic structure. In practice, however, the two terms are used almost synonymously.

Typically, morphology is contrasted with physiology, which deals with studies of the functions of organisms and their parts; function and structure are so closely interrelated, however, that their separation is somewhat artificial. Morphologists were originally concerned with the bones, muscles, blood vessels, and nerves comprised by the bodies of animals and the roots, stems, leaves, and flower parts comprised by the bodies of higher plants. The development of the light microscope made possible the examination of some structural details of individual tissues and single cells; the development of the electron microscope and of methods for preparing ultrathin sections of tissues created an entirely new aspect of morphology—that involving the detailed structure of cells. Electron microscopy has gradually revealed the amazing complexity of the many structures of the cells of plants and animals. Other physical techniques have permitted biologists to investigate the morphology of complex molecules such as hemoglobin, the gas-carrying protein of blood, and deoxyribonucleic acid (DNA), of which most genes are composed. Thus, morphology encompasses the study of biological structures over a tremendous range of sizes, from the macroscopic to the molecular.

A thorough knowledge of structure (morphology) is of fundamental importance to the physician, to the veterinarian, and to the plant pathologist, all of whom are concerned with the kinds and causes of the structural changes that result from specific diseases.

Historical background

Evidence that prehistoric humans appreciated the form and structure of their contemporary animals has survived in the form of paintings on the walls of caves in France, Spain, and elsewhere. During the early civilizations of China, Egypt, and the Middle East, as humans learned to domesticate certain animals and to cultivate many fruits and grains, they also acquired knowledge about the structures of various plants and animals.

Aristotle was interested in biological form and structure, and his Historia animalium contains excellent descriptions, clearly recognizable in extant species, of the animals of Greece and Asia Minor. He was also interested in developmental morphology and studied the development of chicks before hatching and the breeding methods of sharks and bees. Galen was among the first to dissect animals and to make careful records of his observations of internal structures. His descriptions of the human body, though they remained the unquestioned authority for more than 1,000 years, contained some remarkable errors, for they were based on dissections of pigs and monkeys rather than of humans.

Although it is difficult to pinpoint the emergence of modern morphology as a science, one of the early landmarks was the publication in 1543 of De humani corporis fabrica by Andreas Vesalius, whose careful dissections of human bodies and accurate drawings of his observations revealed many of the inaccuracies in Galen’s earlier descriptions of the human body.

In 1661 an Italian physiologist, Marcello Malpighi, the founder of microscopic anatomy, demonstrated the presence of the small blood vessels called capillaries, which connect arteries and veins. The existence of capillaries had been postulated 30 years earlier by English physician William Harvey, whose classic experiments on the direction of blood flow in arteries and veins indicated that minute connections must exist between them. Between 1668 and 1680, Dutch microscopist Antonie van Leeuwenhoek used the recently invented microscope to describe red blood cells, human sperm cells, bacteria, protozoans, and various other structures.

Cellular components—the nucleus and nucleolus of plant cells and the chromosomes within the nucleus—and the complex sequence of nuclear events (mitosis) that occur during cell division were described by various scientists throughout the 19th century. Organographie der Pflanzen (1898–1901; Organography of Plants, 1900–05), the great work of a German botanist, Karl von Goebel, who was associated with morphology in all its aspects, remains a classic in the field. British surgeon John Hunter and French zoologist Georges Cuvier were early 19th-century pioneers in the study of similar structures in different animals—i.e., comparative morphology. Cuvier in particular was among the first to study the structures of both fossils and living organisms and is credited with founding the science of paleontology. A British biologist, Sir Richard Owen, developed two concepts of basic importance in comparative morphology—homology, which refers to intrinsic structural similarity, and analogy, which refers to superficial functional similarity. Although the concepts antedate the Darwinian view of evolution, the anatomical data on which they were based became, largely as a result of the work of German comparative anatomist Carl Gegenbaur, important evidence in favour of evolutionary change, despite Owen’s steady unwillingness to accept the view of diversification of life from a common origin.

One of the major thrusts in contemporary morphology has been the elucidation of the molecular basis of cellular structure. Techniques such as electron microscopy have revealed the complex details of cell structure, provided a basis for relating structural details to the particular functions of the cell, and shown that certain cellular components occur in a variety of tissues. Studies of the smallest components of cells have clarified the structural basis not only for the contraction of muscle cells but also for the motility of the tail of the sperm cell and the hairlike projections (cilia and flagella) found on protozoans and other cells. Studies involving the structural details of plant cells, although begun somewhat later than those concerned with animal cells, have revealed fascinating facts about such important structures as the chloroplasts, which contain chlorophyll that functions in photosynthesis. Attention has also been focused on the plant tissues composed of cells that retain their power to divide (meristems), particularly at the tips of stems, and their relationship with the new parts to which they give rise. The structural details of bacteria and blue-green algae, which are similar to each other in many respects but markedly different from both higher plants and animals, have been studied in an attempt to determine their origin.

Morphology continues to be of importance in taxonomy because morphological features characteristic of a particular species are used to identify it. As biologists have begun to devote more attention to ecology, the identification of plant and animal species present in an area and perhaps changing in numbers in response to environmental changes has become increasingly significant.

Fundamental concepts:

Homology and analogy

Homologous structures develop from similar embryonic substances and thus have similar basic structural and developmental patterns, reflecting common genetic endowments and evolutionary relationships. In marked contrast, analogous structures are superficially similar and serve similar functions but have quite different structural and developmental patterns. The arm of a human, the wing of a bird, and the pectoral fins of a whale are homologous structures in that all have similar patterns of bones, muscles, nerves, and blood vessels and similar embryonic origins; each, however, has a different function. The wings of birds and those of butterflies, in contrast, are analogous structures—i.e., both allow flight but have no developmental processes in common.

The terms homology and analogy are also applied to the molecular structures of cellular constituents. Because the hemoglobin molecules from different vertebrate species contain remarkably similar sequences of amino acids, they may be termed homologous molecules. In contrast, hemoglobin and hemocyanin, the latter of which is present in crab blood, are described as analogous molecules because they have a similar function (oxygen transport) but differ considerably in molecular structure. Corresponding similarities occur in the structures of other proteins from different species—e.g., cytochrome c and other enzymes (biological catalysts) such as the lactic dehydrogenases in birds and mammals.

Body plan and symmetry

The bodies of most animals and plants are organized according to one of three types of symmetry: spherical, radial, or bilateral. A spherically symmetrical body is similar throughout and can be cut in any plane through the centre to yield two equal halves. A few of the simplest plants and animals are spherically symmetrical—e.g., protozoans such as Radiolaria and Heliozoa. Radially symmetrical bodies, such as those of starfishes and mushrooms, have a distinguishable top and bottom and usually have a cylindrical shape, with the body parts radiating from the central axis. A starfish can be cut into two equal halves by any plane that includes the line, or axis, running through its centre from top to bottom. The anterior, or oral, end usually contains the mouth; a posterior, or aboral, end may have an math. In the bilaterally symmetrical body of higher animals including humans, only a cut from head to foot exactly in the centre divides the body into equivalent halves. An anterior, or head, end and a posterior, or tail, end can be distinguished; and the dorsal, or back, side can be distinguished from the ventral, or belly, side. But because some internal organs of humans are not symmetrical (e.g., the heart), even the right and left halves of the human body are not exactly equivalent. A few organisms—amoebas, slime molds, and certain sponges—with an irregular form, or one that changes as the organism moves, have no plane of symmetry.

Morphological basis of classification

The features that distinguish closely related species of plants and animals are usually superficial differences such as colour, size, and proportion. In contrast, the major divisions, or phyla, of the plant and animal kingdoms are distinguished by characteristics that, though usually not unique to a single division or phylum, occur in unique combinations in each.

One morphological feature useful in classifying animals and in determining their evolutionary relationships is the presence or absence of cellular differentiation—i.e., animals may be either single-celled or composed of many kinds of cells specialized to perform particular functions. Some multicellular animals have only two embryonic cell, or germ, layers: an ectoderm (outer layer) and an endoderm (inner layer), which lines the digestive tract. Other animals have these, in addition to a mesoderm, which lies between the ectoderm and endoderm. Animals may have one of two types of body cavity. The bodies of the Coelenterata (invertebrates such as the jellyfish) and other primitive many-celled animals consist of a double-walled sac surrounding a single cavity with a mouth. Higher animals have two cavities, and their bodies are constructed on a so-called tube-within-a-tube plan. An inner tube, or digestive tract, is lined with endoderm and opens at each end to form the mouth and the math. An outer tube, or body wall, is covered with ectoderm. Between the two tubes a second cavity, or coelom, lies within the mesoderm and is lined by it. Another major distinguishing morphological feature of animal phyla is the presence or absence of segmentation. The members of several phyla have bodies characterized by the presence of a row of segments, or body units, of the same fundamental structure. Segmented animals include the vertebrates, the annelids (invertebrates such as the earthworm), and the arthropods (invertebrates such as insects); in some segmented animals such as humans and most vertebrates, however, the segmental character of the body is obscured. An evolutionary tendency in many animal phyla has been the progressive differentiation of the anterior end to form a head with conspicuous sense organs and an accumulation of nervous tissues, a brain; the tendency is called cephalization. Some morphological structures are found only in one phylum; for example, only the Coelenterata have stinging cells (nematocysts), the Echinodermata (invertebrates such as starfishes) have a peculiar water vascular system, and only the Chordates (e.g., reptiles, birds) have a dorsally located, hollow nerve cord.

Like animals, plants may be either single-celled or composed of many kinds of specialized cells. The bodies of most of the lower plants, such as algae and fungi, comprise the least-differentiated and least-specialized type of plant cells, parenchyma cells. The embryonic tissues of higher plants, unlike those of animals, remain extremely active throughout the life of the plant. In addition, the different types of cells characteristic of the body of higher plants arise from meristems, specific regions in the plant body where cells divide and enlarge. In all but the simplest forms, the plant body is composed of various types of cells associated in more or less definite ways to form systems of units called tissue systems—e.g., the vascular system consisting of conductive tissues. The arrangement of the components of the vascular system is a distinguishing morphological feature of various plant groups. The character and relative extent of the two phases in the life history of a plant—the sexual phase, or gametophyte, and the sporophyte—vary considerably among the plant groups and are useful in distinguishing them.

Areas of study:

Anatomy

The best known aspect of morphology, usually called anatomy, is the study of gross structure, or form, of organs and organisms. It should not be inferred however, that even the human body, which has been extensively studied, has been so completely explored that nothing remains to be discovered. It was found only in 1965, for example, that the nerve to the pineal gland, which lies on the upper surface of the brain of mammals, is a branch from the sympathetic nerves; the sympathetic nerves receive nerve impulses from a small branch of the nerves that transmit impulses from the eye to the brain (optic nerves). Thus the pineal gland responds by a very indirect route to quantitative changes in the environmental lighting and secretes appropriate amounts of the substance it forms, the hormone melatonin.

Detailed comparisons of the morphological features of different animals, called comparative anatomy, provide strong arguments for the evolutionary relationships among different species. In the course of evolution, animals and plants tend to undergo adaptive morphological changes that enable them to survive under certain environmental conditions. As a result, animals only remotely related evolutionarily may come to resemble each other superficially because of common adaptations to similar environments, a phenomenon known as convergent evolution. Structural similarities—streamlined shape, dorsal fins, tail fins, and flipper-like forelimbs and hindlimbs, for example—have evolved in such varied animal groups as the dolphins and porpoises, both of which are mammals; the extinct ichthyosaurs, which were reptiles; and both the bony and cartilaginous fishes. In a like manner, the mole, an insectivore, and the gopher, a rodent, have both evolved shovellike forelimbs, an adaptation for digging.

An opposite phenomenon, divergent evolution, occurs when animals originally closely related adapt to different environments and come to be superficially quite different. Although sea lions and seals, for example, are carnivores and thus closely related to bears, cats, and dogs, their adaptations to an aquatic existence have resulted in morphological characteristics distinct from those of the terrestrial carnivores. In the course of mammalian evolution, many features have changed to permit specific animal groups to adapt to particular environments—e.g., the number and shape of the teeth, the length and number of bones in the limbs, the number and attachment sites of muscles, the thickness and colour of the hair or fur, and the length and shape of the tail.

Careful study of adaptive morphological aspects has permitted inferences about the course of the evolutionary history of various animals and of their successive adaptations to changing environments. The present-day Australian tree-climbing kangaroos, for example, are the descendents of a ground-dwelling marsupial, from whom evolved forms that began to live in trees and eventually developed limbs adapted to tree climbing. But the events may have occurred in the reverse sequence; that is, specialized limbs may have evolved before the animal adopted an arboreal mode of life. In any event, some of the tree-dwelling kangaroos subsequently left the trees, became readapted to life on the ground (i.e., their hindlegs became adapted for leaping), and then went back to the trees but with legs so highly specialized for leaping as to be useless in grasping a tree trunk; consequently, present-day tree kangaroos climb by bracing their feet against a tree trunk, as do bears. Careful comparisons of the feet of the many kinds of living Australian marsupials reveal the stages in this complicated process of adaptation and re-adaptation.

Changes in genes (mutations) constantly occur and may cause a decrease in size and function of an organ. On the other hand, a change in the environment or in the mode of life of a species may make an organ unnecessary for survival. As a result, many plants and animals contain organs or parts of organs that are useless, degenerate, undersized, or lacking some essential part when compared with homologous structures in related organisms. The human body, for instance, has more than 100 such organs—e.g., the appendix, the fused tail vertebrae (coccyx), the wisdom teeth, the muscles that wiggle the ears, and the hair on the body.

The parts of a seed plant include roots, stems, leaves, and reproductive organs in the flowers. The evolution of specialized conducting tissues called xylem and phloem has enabled seed plants to survive on land and to attain large sizes. Roots anchor the plant, enable it to maintain an upright position, and absorb water, minerals, and other nutrients from the soil. The roots of plants such as carrots, beets, and yams serve as sites for food storage. The stem links the roots with the leaves, where photosynthesis occurs, and its xylem and phloem are continuous with those of root and leaf. The stem supports leaves, flowers, and fruits. Each year, the stems of woody plants add a layer of xylem and phloem, the annual ring, the width of which varies with climatic conditions. A leaf consists of a petiole (stalk), by which it is attached to the stem, and a blade, typically broad and flat, that contains bundles, or veins, of xylem and phloem on the undersurface. The flower contains pollen-producing anthers and egg-producing ovules. After fertilization the base of the flower, or ovary, enlarges and forms the fruit, which is a mature ovary containing seeds, or mature ovules. The bodies of ferns and mosses also are composed of roots, stems, and leaves, but those of lower plants such as mushrooms and kelps are much more simple and lack true roots, stems, and leaves.

Histology

A major trend in the evolution of both plants and animals has resulted in the specialization of cells and a division of labour among them. The cells that make up a tree or a human are quite different; each is specialized to carry out certain functions. Although specialization may permit a cell to function efficiently, it also increases the interdependence of body parts; an injury to or the destruction of one part, therefore, may result in death of the whole organism. The study of the structure and arrangement of tissues, defined as groups or layers of cells that together perform certain special functions, is known as histology. Each kind of tissue is composed of cells with characteristic features such as size, shape, and relationship to adjacent cells and may also contain noncellular material—connective tissue fibres or a bony material.

Morphologists usually separate animal tissues into six groups: epithelial, connective, muscular, blood, nervous, and reproductive tissues. The cells of epithelial tissues form a continuous layer or sheet that either covers the surface of the body or lines some cavity within the body, thus protecting the underlying cells from mechanical and chemical injury or from invasion by microorganisms. Epithelial tissues absorb nutrients and water, secrete a wide variety of substances, and may play a role in the reception of sensory stimuli. The connective tissues—bone, cartilage, ligaments, and fibrous connective tissue—support and hold together the other cells of the body. The cells of the connective tissues secrete large quantities of nonliving material (matrix), the characteristics of which largely determine the nature and the function of the specific types of connective tissue; the matrix secreted by fibrous connective tissue cells, for example, is a thick matted network of microscopic fibres surrounding the connective tissue cells. Connective tissue holds skin to muscle, keeps glands in position, makes up the tough outer walls of the blood vessels, and forms a sheath around nerve fibres and muscle cells. Tendons are flexible, cable-like cords of specialized fibrous connective tissue that join muscles to each other or muscle to bone. Ligaments are somewhat elastic cords of specialized fibrous connective tissue that join one bone to another.

Muscular tissues are composed of elongated, cylindrical, or spindle-shaped cells, each of which contains many small fibres called myofibrils. Muscle cells perform mechanical work by contracting—that is, by becoming shorter and thicker. The three types of vertebrate muscles include the cardiac muscle, which is found only in the walls of the heart; smooth muscles, which are found in the walls of the digestive tract and in other internal organs; and skeletal muscles, which make up the bulk of the muscle masses attached to the bones of the body. Skeletal and cardiac muscles have alternating light and dark stripes the relative sizes of which change during the contraction process. Evidence from electron microscopy indicates that two types of filaments occur in muscle; during contraction, one type of filament slides past the other.

Nerve tissue is made of cells, called neurons, which are specialized to conduct nerve impulses. Two or more thin hairlike fibres, called axons and dendrites, extend from the enlarged cell body containing the nucleus. The neurons extending from the spinal cord to the end of an appendage (e.g., arm, leg) may extend to a metre (about three feet) or more in humans and to several metres in an elephant or a whale.

Egg cells in the female and sperm cells in the male are reproductive tissues adapted for the production of offspring. The egg cell is modified by the accumulation of considerable amounts of yolk and other food reserves. The highly specialized spermatozoon contains a tail, the beating of which propels it to the egg.

Blood is composed of red cells, which are specialized for the transport of oxygen and carbon dioxide, and white cells, which engulf bacteria and produce antibodies (proteins formed in response to foreign substances called antigens). Blood also contains platelets, small fragments of cells from the bone marrow that play a key role in initiating the clotting of blood.

The cells of higher plants may be differentiated into meristematic, protective, fundamental, and conductive tissues. Meristematic tissues, which are composed of small thin-walled cells with few or no vacuoles (cavities), differentiate into the other types of plant tissue and are found in the rapidly growing parts of the plant—e.g., at the tips of roots and stems. Protective tissues are composed of thick-walled cells that protect the underlying thin-walled cells from mechanical abrasion and dehydration; examples of protective tissues include the epidermis of leaves and the cork layers of stems and roots. The fundamental tissues that constitute the body of a plant include the soft parts of the leaf, the components of the pith and the cortex of stems, the roots, and the soft parts of flowers and fruits. These tissues function in the production and storage of food. Two types of conductive tissues occur in higher plants: xylem conducts water and dissolved salts, and phloem conducts dissolved organic materials such as sugars. Both types are composed of elongated cells that fuse end to end with other cells to form the sieve tubes through which substances are transported in phloem and xylem vessels.

Cytology

The living material of most organisms is organized into discrete units called cells, and the study of their features is known as cytology. The cellular contents, when viewed through a microscope at low magnification, usually appear to consist of granules or fibrils of dense material, droplets of fatty substances, and fluid-filled vacuoles suspended in a clear, continuous, semifluid substance called cytoplasm. The remarkable structural complexity of the cell is more fully revealed at the higher magnifications attainable with the electron microscope. Structural details of various cellular components, or organelles, as revealed by the technique known as X-ray diffraction analysis, have provided information concerning the relationships between the structures of the cellular components and of the molecules that constitute them. Although most cells have certain features in common, the kinds and amounts of components vary considerably. Cellular components include structures such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi complex, lysosomes, oil droplets, granules, and fibrils. The cell is surrounded by a membrane, and similar membranes surround many cellular components—e.g., the mitochondria.

A small spherical or oval organelle, the nucleus, is typically found near the centre of a cell. The genes within the nucleus control the development of the various traits of the cell by controlling the synthesis of specific proteins. The nuclear components are separated from those of the cytoplasm by the nuclear membrane. The structure of the nucleolus, a spherical body within the nucleus, is extremely variable in most cells. Although more than one nucleolus may occur in a nucleus, each cell of an animal or plant species has a fixed number of nucleoli. The nucleoli apparently play a role in the synthesis of the ribonucleic acid (RNA) constituent of the cellular components called ribosomes, which function in protein synthesis. Adjacent to the nucleus in the cells of animals and certain lower plants are two small, cylindrical bodies, the centrioles, which, during cell division, separate, migrate to opposite sides of the cell, and organize a structure called a spindle between them.

Within the cytoplasm of both plant and animal cells are components called mitochondria, which may be shaped like spheres, rods, or threads. Each mitochondrion is bounded by a double membrane, the outer layer of which forms the smooth outer boundary of the mitochondrion; the inner layer, folded repeatedly into shelflike folds called cristae, contains enzymes that play an essential role in the conversion of the energy of foodstuffs into the energy used for cellular activities. The cells of most plants contain plastids, small bodies involved in the synthesis and storage of foodstuffs. The most important plastids, the chloroplasts, function in trapping the energy of sunlight during photosynthesis. They are disk-shaped structures with a platelike arrangement of tightly stacked membranes.

The cytoplasmic components important in protein synthesis, the ribosomes, are composed of nucleic acid and protein. Clusters of five or more ribosomes, termed polysomes, appear to be the functional unit in protein synthesis.

Lysosomes are membrane-bound structures containing a variety of enzymes that can break down the large molecular constituents of the cell. The membrane surrounding lysosomes presumably prevents the enzymes from digesting the cell contents before the cell dies.

Embryology

The structures and the relationships among the various parts of a mature plant or animal are usually better understood if the successive developmental stages are studied. Thus, morphologists have traditionally been interested in the study of embryos and their developmental patterns—i.e., the science of embryology.

Development typically begins in animals with the cleavage, or division, of the fertilized egg (zygote) to form a hollow ball of cells called the blastula; the blastula then develops into a hollow cuplike body of two layers of cells, the gastrula, from which the embryo ultimately is formed. At one time, the techniques available to embryologists enabled them to study only whole embryos at different developmental stages. The science of experimental embryology began during the first half of the 20th century, when microsurgical techniques became available either for the removal and study of certain structures from tiny embryos or for their transplantation to other regions of the embryo. Advances in understanding the mechanism by which biological information is transferred in DNA and the means by which this information results in the production of specific proteins have led to efforts to describe development in biochemical terms. Although hypotheses regarding the reasons for the appearance of a specific enzyme or some other protein at a specific time during development have been formulated and tested, the biochemical basis of morphogenesis itself—that is, the reason for the development of particular structures—is not fully understood.

The development of the seed plant is basically different from that of an animal. The egg cell of a seed plant is retained within the enlarged lower part, or ovary, of the seed-bearing organ (pistil) of a flower. Two sperm nuclei pass through a structure called a pollen tube to reach the egg. One sperm nucleus unites with the egg nucleus to form the zygote from which the new plant will develop. The second sperm nucleus unites with two nuclei, called polar nuclei, to form a body called a triploid endosperm, the cells of which divide to form a nutritive mass within the seed. The zygote undergoes several cell divisions to form the embryo, which is surrounded by the endosperm. The embryo develops one or two seed leaves, or cotyledons, which may become thick and fleshy with stored foodstuffs. The epicotyl, which consists of a growing point enclosed by a pair of folded miniature leaves, develops above the point of attachment of the seed leaves. Below the seed leaves extends the hypocotyl, the tip, or radicle, of which forms the primary root of the embryonic plant.

The factors involved in initiating and controlling morphogenesis in plants have been studied by growing cells, tissues, and organs derived from plants. Indeed, an entire carrot plant has been grown from one cell of a mature carrot. This provides striking evidence that the cell from the adult plant contains all of the genetic information needed to produce an entire plant, including roots, stems, and leaves. The technique of growing plants from isolated plant parts has been useful in studies involving the characteristics of embryonic growth, the correlated growth of plant parts, and the nature of differentiation and regeneration (the replacement of lost parts).

Methods in morphology:

Chemical techniques

The methods of investigating gross structure depend on careful dissection, or cutting apart, of an organism and on accurate descriptions of the parts. The study of the structure of tissues and cells has been extended by the techniques of autoradiography and histochemistry. In the former, a tissue is supplied with a radioactive substance and allowed to utilize it for an appropriate period of time, after which the tissue is prepared and placed in contact with a special photographic emulsion. Silver grains in the emulsion in contact with radioactive substances darken; thus, the location of the dark spots indicates the position at which the radioactive substance was concentrated in the tissue. Histochemistry involves the differential staining of cells (i.e., using dyes that stain specific structural and molecular components) to reflect the chemical differences of the constituents. By choosing appropriate dyes, the histochemist is able, for example, to determine the acidity or alkalinity of the chemical compounds that make up cell components. In addition, dyes that stain specific molecular constituents such as glycogen, DNA, RNA, and protein also are used. The histochemist is able to locate a specific enzyme in a thin slice of tissue, to provide the specific substance with which the enzyme reacts to form a product, and to add a compound that reacts with the product to form an insoluble coloured compound the location of which is relatively easy to determine. In this way, information has been obtained about the specific location of enzymes within the cell.

Microscopic techniques

Histologists and cytologists utilize microscopic techniques—light microscopy, phase contrast microscopy, interference microscopy, polarization microscopy, fluorescent microscopy, and electron microscopy—to investigate certain aspects of cell structure. Phase contrast microscopy is widely used to study the structure of living cells because, with such apparatus, internal structures can be observed without killing and staining the cell. In addition, motion pictures of dividing cells or moving cells can be made using phase contrast microscopy.

The interference microscope involves passing two separate beams of light through the specimen. With the appropriate instrument, the mass of material per unit area of the specimen can be determined, and contour mapping of small objects is possible.

Crystalline or fibrous elements, both of which are characterized by an orderly or layered molecular structure, are studied with a polarizing microscope; the polarizing microscope has been particularly useful in studying the detailed structure of bone.

In fluorescence microscopy, the images seen are molecules of fluorescent dyes added to cells that attach to specific cellular components. Appropriate filters are required to insure that only the light of longer wavelength contributes to the image. Fluorescent antibodies have been used to locate specific kinds of proteins and other materials in certain cells of a tissue or in certain regions of a cell. The antibodies are prepared by injecting into a rabbit an antigen (e.g., the protein myosin), which stimulates white blood cells called lymphocytes to synthesize antibodies that react specifically with the antigen. After the antibodies are isolated and purified, the fluorescent dye, fluorescein, becomes attached to them by a chemical reaction. If the fluorescent antibodies are spread over a tissue, they attach specifically to the molecules that stimulated their formation (myosin). The fluorescence microscope reveals the sites containing the antigen–antibody complex as bright luminescent areas in a dark background.

In the scanning electron microscope, a moving spot of electrons (negatively charged particles) is used to scan an object and to produce an image similar to that which appears on a television screen. In this manner, photographs with a three-dimensional appearance can be produced. With the transmission electron microscope, a beam of electrons passes through an object, such as a cell, and is focused on the other side onto a fluorescent screen or a photographic plate. The beam of electrons in the scanning electron microscope is focused and then scanned across the specimen. The electrons that leave the specimen, which are not necessarily the same electrons that strike it, are then used to control the beam of a cathode-ray picture tube. Scanning electron microscopes allow photographs to be taken not only of large molecules such as DNA but of very small objects—individual atoms of elements such as uranium or thorium.

Jai Ganesh · 2022-08-30 14:31:34

1460) Philology

Summary

Philology, traditionally, is the study of the history of language, including the historical study of literary texts. It is also called comparative philology when the emphasis is on the comparison of the historical states of different languages. The philological tradition is one of painstaking textual analysis, often related to literary history and using a fairly traditional descriptive framework. It has been largely supplanted by modern linguistics, which studies historical data more selectively as part of the discussion of broader issues in linguistic theory, such as the nature of language change. However, some philologists continue to work outside a linguistics frame of reference, and their influence can be seen in the names of some university departments (e.g., Romance philology) and journals.

Details

Philology is the study of language in oral and written historical sources; it is the intersection of textual criticism, literary criticism, history, and linguistics (with especially strong ties to etymology). Philology is more commonly defined as the study of literary texts as well as oral and written records, the establishment of their authenticity and their original form, and the determination of their meaning. A person who pursues this kind of study is known as a philologist.

In older usage, especially British, philology is more general, covering comparative and historical linguistics.

Classical philology studies classical languages. Classical philology principally originated from the Library of Pergamum and the Library of Alexandria around the fourth century BCE, continued by Greeks and Romans throughout the Roman/Byzantine Empire. It was eventually resumed by European scholars of the Renaissance, where it was soon joined by philologies of other European (Germanic, Celtic), Eurasian (Slavistics, etc.), Asian (Arabic, Persian, Sanskrit, Chinese, etc.), and African (Egyptian, Nubian, etc.) languages. Indo-European studies involve the comparative philology of all Indo-European languages.

Philology, with its focus on historical development (diachronic analysis), is contrasted with linguistics due to Ferdinand de Saussure's insistence on the importance of synchronic analysis. The contrast continued with the emergence of structuralism and Chomskyan linguistics alongside its emphasis on syntax, although research in historical linguistics is often characterized by reliance on philological materials and findings.

Philology is a humanitarian subject which emerged in the period of the Renaissance establishment, and it studies the history of languages and literature. The word “philology” is originated from the Greek word that means “love”, (lógos) that means “language”.

Apart from the historic development of languages, philology also studies their structure, interrelations, as well as their influence on the culture of people. Philology includes a number of independent sciences, e.g. literature studies, ethnography, folklore studies, and linguistics. Let’s have a closer look at a philologist’s profession.

Who are philologists and what do they do?

A philologist is a specialist who studies different languages, their structure, and history. A philologist also deals with the analysis of texts and other literary works. Philologists have a vast sphere of activity.

What does philologist’s job involve?

* To carry out research

A philologist’s job involves studying texts and other works written in different times. A philologist determines various changes in words and the language, as many words have changed their meanings in course of time.

* To collect folklore information

Philologists have to travel a lot, in order to collect the information in the places where they can find the initial form of the language.

* To prepare the material for publication

Philologists always carry out the in-depth analysis of the information they obtained.

* Teaching activity

Most frequently philologists work as teachers of languages or literature. Their skills of delivering information to other people as well as their ability to make people interested in what they say are irreplaceable.

* Editing

Education in the area of philology is one of the advantages of any editor, as it ensures a high level of literacy.

* Compiling dictionaries
* Translations

Qualities every philologist has to possess

Undoubtedly, a philologist’s profession is not suitable for everyone, because such a specialist must have many qualities, such as diligence and love to read, as the work of this specialist involves a long reading, then correction, translation and editing of various texts in any language. A philologist also has to be extremely attentive so not to miss any tiny detail.

In addition, a philologist has to be a good public speaker, as the majority of philologists work as teachers, and this skill is essential for them.

Prospects of this profession:

* To be a philologist is to have a large number of opportunities which will let you find your place in various spheres of activity.
* Being in demand. Philologists have a perfect command of languages; therefore they can occupy any post.
* Knowledge of foreign languages helps find a job abroad

Jai Ganesh · 2022-08-31 14:26:16

1461) Scissors

Summary

Scissors are hand-operated shearing tools. A pair of scissors consists of a pair of metal blades pivoted so that the sharpened edges slide against each other when the handles (bows) opposite to the pivot are closed. Scissors are used for cutting various thin materials, such as paper, cardboard, metal foil, cloth, rope, and wire. A large variety of scissors and shears all exist for specialized purposes. Hair-cutting shears and kitchen shears are functionally equivalent to scissors, but the larger implements tend to be called shears. Hair-cutting shears have specific blade angles ideal for cutting hair. Using the incorrect type of scissors to cut hair will result in increased damage or split ends, or both, by breaking the hair. Kitchen shears, also known as kitchen scissors, are intended for cutting and trimming foods such as meats.

Inexpensive, mass-produced modern scissors are often designed ergonomically with composite thermoplastic and rubber handles.

Details

Scissors are cutting instrument consisting of a pair of opposed metal blades that meet and cut when the handles at their ends are brought together. The term shears sometimes denotes large-size scissors. Modern instruments are of two types: the more usual pivoted blades have a rivet or screw connection between the cutting ends and the handle ends; spring shears have a C-shaped spring connection at the handle ends.

Spring-type scissors probably date from the Bronze Age and were commonly used in Europe until the end of the Middle Ages. Pivoted scissors of bronze and iron were used in ancient Rome and in China, Japan, and Korea. In Europe their domestic use dates from the 16th century, but not until 1761, when Robert Hinchliffe of Sheffield, Eng., first used cast steel in their manufacture, did large-scale production begin. In the 19th century much hand-forged work was produced, with elaborately ornamented handles. By the end of the 19th century, styles were simplified for mechanical-production methods.

The two blades are made to twist or curve slightly toward one another so that they touch in only two places: at the pivot, or joint, and at the spot along the blades where the cutting is taking place. When completely closed, the points of the blades touch. In the case of the finest cutting instruments, the two unfinished metal blanks and the fasteners are coded with an identifying mark so they can be manufactured as a set.

Blanks are usually made from red-hot steel bars that are forged at high speed between the dies of drop hammers, but others also of satisfactory quality may be made from cold-forged blanks. The steel may contain from 0.55 to 1.03 percent carbon, the higher carbon content providing a harder cutting steel for certain applications. Stainless steel is used for surgical scissors. Certain nonferrous alloys that will not produce sparks or interfere with magnetism are employed in making scissors for cutting cordite and magnetic tape. Handle and blade are usually constructed in one piece, but in some cases the handles are electrically welded to the steel blades.

Expert sharpening is required to restore the edge-angle sharpness; each blade is passed smoothly and lightly across a grinding wheel, following the twist of the blade, with an even pressure throughout the stroke to avoid causing ridges or other irregularities.

A special form of shears used for sheet-metal work, called tin shears, or tin snips, is equipped with high-leverage handles to facilitate cutting the metal. Another special form, pruning shears, are designed for trimming shrubs and trees.

Jai Ganesh · 2022-09-01 14:26:40

1462) Wheel and Axle

Summary

The wheel and axle is a simple machine consisting of a wheel attached to a smaller axle so that these two parts rotate together in which a force is transferred from one to the other. The wheel and axle can be viewed as a version of the lever, with a drive force applied tangentially to the perimeter of the wheel and a load force applied to the axle, respectively, that is balanced around the hinge which is the fulcrum.

Details

Wheel and axle is a basic machine component for amplifying force. In its earliest form it was probably used for raising weights or water buckets from wells. Its principle of operation is demonstrated by the large and small gears attached to the same shaft, as shown at A in the illustration. The tendency of a force F applied at the radius R on the large gear to turn the shaft is sufficient to overcome the larger force W at the radius r on the small gear. The force amplification, or mechanical advantage, is equal to the ratio of the two forces (W:F) and also equal to the ratio of the radii of the two gears (R:r).

For raising weights the wheel and axle has large- and small-diameter drums with ropes wrapped around them in place of the gears. The weight being lifted is attached to the rope on the small drum, and the operator pulls the rope on the large drum. In this arrangement the mechanical advantage is the radius of the large drum divided by the radius of the small drum. An increase in the mechanical advantage can be obtained by using a small drum with two diameters, r1 and r2, and a pulley block, P, as shown in sketch B in the illustration. When lifting a weight, the rope winds on the drum D and off the drum d.

A measure of the force amplification available with the system is the velocity ratio, or the ratio of the velocity (VF) with which the operator pulls the rope at F to the velocity at which the weight W is raised (VW). This ratio is equal to twice the radius of the large drum divided by the difference in the radii of drums D and d. Expressed mathematically, the equation is VF/VW = 2R/(r2 - r1). The actual mechanical advantage W/F is less than this velocity ratio, depending on friction. A very large mechanical advantage may be obtained with this arrangement by making the pulleys D and d of nearly equal radius.

Jai Ganesh · 2022-09-02 14:29:26

1463) Horology

Summary

Horology (lit. 'the study of time'; related to Latin horologium; from Ancient Greek 'instrument for telling the hour'; from 'hour, time', interfix -o-, and suffix -logy) is the study of the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. In current usage, horology refers mainly to the study of mechanical time-keeping devices, while chronometry more broadly includes electronic devices that have largely supplanted mechanical clocks for the best accuracy and precision in time-keeping.

People interested in horology are called horologists. That term is used both by people who deal professionally with timekeeping apparatus (watchmakers, clockmakers), as well as aficionados and scholars of horology. Horology and horologists have numerous organizations, both professional associations and more scholarly societies. The largest horological membership organisation globally is the NAWCC, the National Association of Watch and Clock Collectors, which is USA based, but also has local chapters elsewhere.

Details

Watch is a portable timepiece that has a movement driven either by spring or by electricity and that is designed to be worn or carried in the pocket.

Mechanical watches

The first watches appeared shortly after 1500, early examples being made by Peter Henlein, a locksmith in Nürnberg, Ger. The escapement used in the early watches was the same as that used in the early clocks, the verge. Early watches were made notably in Germany and at Blois in France, among other countries, and were generally carried in the hand or worn on a chain around the neck. They usually had only one hand for the hours.

The mainspring, the element that drives the watch, consists of a flat spring-steel band stressed in bending or coiling; when the watch, or other spring-driven mechanism, is wound, the curvature of the spring is increased, and energy is thus stored. This energy is transmitted to the oscillating section of the watch (called the balance) by the wheeltrain and escapement, the motion of the balance itself controlling the release of the escapement and consequently the timing of the watch. A friction drive permits the hand to be set.

One of the main defects of the early watches was the variation in the torque exerted by the mainspring; that is, the force of the mainspring was greater when fully wound than when it was almost run down. Since the timekeeping of a watch fitted with a verge escapement was greatly influenced by the force driving it, this problem was quite serious. Solution of the problem was advanced almost as soon as the mainspring was invented (about 1450) by the application of the fusee, a cone-shaped, grooved pulley used together with a barrel containing the mainspring. With this arrangement, the mainspring was made to rotate a barrel in which it was housed; a length of catgut, later replaced by a chain, was wound on it, the other end being coiled around the fusee. When the mainspring was fully wound, the gut or chain pulled on the smallest radius of the cone-shaped fusee; as the mainspring ran down, the leverage was progressively increased as the gut or chain pulled on a larger radius. With correct proportioning of mainspring and fusee radii, an almost constant torque was maintained as the mainspring unwound.

The going barrel, in which the mainspring barrel drives the wheeltrain directly, is fitted to all modern mechanical watches and has superseded the fusee. With better quality mainsprings, torque variations have been reduced to a minimum, and with a properly adjusted balance and balance spring, good timekeeping is ensured.

Up to about 1580, the mechanisms of German watches were made almost wholly of iron; about this time, brass was introduced.

In the earliest watches a plain wheel, known as the balance, was used to control the rate of going of the mechanism. It was subjected to no consistent restoring force; consequently, its period of oscillation and, hence, the rate of the timekeeper were dependent on the driving force. This explains the great importance of the fusee.

Controlling the oscillations of a balance with a spring was an important step in the history of timekeeping. English physicist Robert Hooke designed a watch with a balance spring in the late 1650s; there appears to be no evidence, however, that the spring was in the form of a spiral, a crucial element that would become widely employed. Dutch scientist Christiaan Huygens was probably the first to design (1674–75) a watch with a spiral balance spring. The balance spring is a delicate ribbon of steel or other suitable spring material, generally wound into a spiral form. The inner end is pinned into a collet (a small collar), which fits friction-tight on the balance staff, while the outer end is held in a stud fixed to the movement. This spring acts on the balance as gravity does on the pendulum. If the balance is displaced to one side, the spring is wound and energy stored in it; this energy is then restored to the balance, causing it to swing nearly the same distance to the other side if the balance is released.

If there were no frictional losses (e.g., air friction, internal friction in the spring material, and friction at the pivots), the balance would swing precisely the same distance to the other side and continue to oscillate indefinitely; because of these losses, however, the oscillations in practice die away. It is the energy stored in the mainspring and fed to the balance through the wheel train and escapement that maintains the oscillations.

The performance of the modern watch depends on the uniformity of the period of oscillation of the balance—i.e., the regularity of its movement. The balance takes the form of a wheel with a heavy rim, while the spring coupled to it provides the restoring torque. The balance possesses inertia, dependent on its mass and configuration. The spring should ideally provide a restoring force directly proportional to the displacement from its unstressed or zero position.

The balance is mounted on a staff with pivots, and, in watches of good quality, these run in jewels. Two jewels are used at each end of the balance staff, one pierced to provide a bearing, the other a flat end stone providing axial location by bearing against the domed end of the pivot. Frictional effects at the pivots influence the performance of the watch in various positions—for example, lying and hanging.

The balance and spring can be brought to time, or “regulated,” by varying either the restoring couple provided by the spring or the moment of inertia of the balance. In the first case (by far the more common), this is generally effected by providing a pair of curb pins mounted on a movable regulator index that lengthen or shorten the balance spring as needed.

In the second instance, screws are provided at opposite points on the rim of the balance; these screws are friction-tight in their holes and thus can be moved in or out so as to adjust the inertia of the balance. In “free-sprung” watches no regulator index is provided, and the only adjusters are the screws on the balance rim.

Many modern mechanical watches use a lever escapement, invented in England about 1755 by Thomas Mudge, that leaves the balance free to oscillate, coupling to it only while delivering the impulse, taken from the mainspring via the wheel train and while being unlocked by the balance. It was developed into its modern form with the club-tooth escape wheel at the beginning of the 19th century but was not universally adopted until the early 20th century. In good-quality watches the club-tooth escape wheel is made of hardened steel, with the acting surfaces ground and polished. An improved form of the lever escapement is characterized by a double-roller safety action in which the intersection between the guard pin and roller, which takes place underneath the roller, is much deeper than in early single-roller watches; thus, any friction caused by jolts encountered in wear causes less constraint on the balance and less endangerment of the timekeeping properties of the watch. By far the most important watch escapement today is the lever escapement; it is used in its jeweled form in watches of moderate to excellent quality, and it is used with steel pallet pins and a simplified fork-and-roller action in cheaper watches (known as pin-pallet watches).

In the wheel train of a modern watch, it is necessary to achieve a step-up ratio of approximately 1 to 4,000 between barrel and escape wheel. This involves four pairs of gears, the ratio per pair commonly being between 6 to 1 and 10 to 1. Because of space considerations, the pinions must have a low number of leaves (teeth), commonly 6 to 12. This entails a number of special gearing problems, aggravated by the fineness of the pitch. Any error in centre distance, form, or concentricity is therefore proportionately more important than in larger gear trains.

The first patent covering the application of jewels in watches was taken out in London in 1704; diamonds and sapphires were used. Synthetic jewels made from fused powdered alumina (aluminum oxide) are now commonly used. Watch jewels are given a very high polish; a uniform outside diameter for the jewel bearings is highly important, because they are pressed into accurately sized holes smaller than the jewels themselves and held there by friction.

The first patent on the self-winding pocket watch was taken out in London in 1780. An English invention patented in 1924, the self-winding wristwatch by Louis Recordon, contains a swinging weight pivoted at the centre of the movement, coupled to the barrel arbor through reduction wheels and gears. A more modern self-winding watch is fitted with a weight or rotor swinging 360 degrees and winding in both directions.

Electric-powered and electronic watches

Electric-powered watches use one of three drive systems: (1) the galvanometer drive, consisting of the conventional balance-hairspring oscillator, kept in motion by the magnetic interaction of a coil and a permanent magnet, (2) the induction drive, in which an electromagnet attracts a balance containing soft magnetic material, or (3) the resonance drive, in which a tiny tuning fork (about 25 mm [1 inch] in length), driven electrically, provides the motive power. Both galvanometer and induction drive types use a mechanical contact, actuated by the balance motion, to provide properly timed electric-drive pulses. Each oscillation of the balance operates a time-indicating gear train by advancing a toothed wheel one tooth. First produced in 1953, the resonance drive type, properly called an electronic watch, is inherently more accurate since it operates at a frequency higher than that customarily used with balance-type watches, and the tuning fork is a fairly stable source of frequency. The higher frequency requires the replacement of a mechanical contact by a transistor. The minute and rapid motion of the tuning fork moves forward an extremely fine-toothed ratchet wheel. There is very little friction in the electronic watch; only tiny amounts of oil are needed. When the battery is too weak to operate the tuning fork, the watch simply stops, without deterioration. Miniature high-energy-density batteries are used as power sources in all three types.

The progressive miniaturization of electronic components in the late 20th century made possible the development of all-electronic watches, in which the necessary transistors, resistors, capacitors, and other elements were all on one or several miniature integrated circuits, or chips. The complex circuitry of such watches enabled them to perform a variety of timekeeping functions and also made possible digital readouts of the time in place of the traditional second, minute, and hour hands.

Jai Ganesh · 2022-09-03 14:25:29

1464) Atmospheric science

Gist

Atmospheric science is the study of the dynamics and chemistry of the layers of gas that surround the Earth, other planets and moons. This encompasses the interactions between various parts of the atmosphere as well as interactions with the oceans and freshwater systems, the biosphere and human activities.

Summary

Atmospheric science is the study of the Earth's atmosphere and its various inner-working physical processes. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climatology is the study of atmospheric changes (both long and short-term) that define average climates and their change over time, due to both natural and anthropogenic climate variability. Aeronomy is the study of the upper layers of the atmosphere, where dissociation and ionization are important. Atmospheric science has been extended to the field of planetary science and the study of the atmospheres of the planets and natural satellites of the Solar System.

Experimental instruments used in atmospheric science include satellites, rocketsondes, radiosondes, weather balloons, radars, and lasers.

The term aerology is sometimes used as an alternative term for the study of Earth's atmosphere; in other definitions, aerology is restricted to the free atmosphere, the region above the planetary boundary layer.

Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.

Details

Atmospheric science is an interdisciplinary field of study that combines the components of physics and chemistry that focus on the structure and dynamics of Earth’s atmosphere. Mathematical tools, such as differential equations and vector analysis, and computer systems are used to evaluate the physical and chemical relations that describe the workings of the atmosphere.

The atmospheric sciences are traditionally divided into three topical areas—meteorology (the study and forecasting of weather), climatology (the study of long-term atmospheric patterns and their influences), and aeronomy (the study of the physics and chemistry of the upper atmosphere). In meteorology, the focus of study concerns day-to-day and hour-to-hour changes in weather within the lower stratosphere and troposphere. Climatology, on the other hand, concentrates more on longer time periods ranging from a single month to millions of years and attempts to describe the interaction of the atmosphere with the oceans, lakes, land, and glaciers. For example, of the three topical areas, climatology would be the best equipped to provide a farmer with the most likely date of the first frost in the autumn. The focus of aeronomy is on the atmosphere from the stratosphere outward. This field also considers the role the atmosphere plays in the propagation of electromagnetic communications, such as shortwave radio transmissions.

Within these three major topical areas, the broad nature of the atmospheric sciences has spawned practitioners who specialize in several distinct subfields. Scientists who investigate the physics associated with atmospheric flow are called dynamic meteorologists or simply dynamicists. When the investigation procedure involves the application of large computer models of atmospheric structure and dynamics, the scientists are called numerical modelers. Scientists and technicians who specifically investigate procedures of weather forecasting are called synoptic meteorologists, while those who investigate the physical mechanisms associated with the growth of cloud droplets and ice crystals and related precipitation processes are called cloud physicists. Researchers who study atmospheric optical effects are referred to as physical meteorologists, while individuals who investigate the dynamics and observations of climate are called climatologists or climate scientists. Paleoclimatologists are researchers who concentrate on ancient climate patterns. Scientists who investigate atmospheric structure and dynamics within the boundary layer (the layer of the atmosphere closest to Earth’s surface) are referred to as boundary layer meteorologists or micrometeorologists.

3-s2.0-B9780124095489053513-f05351-02-9780124095489.jpg

Jai Ganesh · 2022-09-04 14:37:11

1465) Neurology

Summary

Neurology (from Greek: (neuron), "string, nerve" and the suffix -logia, "study of") is a branch of medicine dealing with disorders of the nervous system. Neurology deals with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal cord and the peripheral nerves. Neurological practice relies heavily on the field of neuroscience, the scientific study of the nervous system.

A neurologist is a physician specializing in neurology and trained to investigate, diagnose and treat neurological disorders. Neurologists treat a myriad of neurologic conditions, including stroke, seizures, movement disorders such as Parkinson's disease, autoimmune neurologic disorders such as multiple sclerosis, headache disorders like migraine and dementias such as Alzheimer's disease. Neurologists may also be involved in clinical research, clinical trials, and basic or translational research. While neurology is a nonsurgical specialty, its corresponding surgical specialty is neurosurgery.

Details

Neurology is a medical specialty concerned with the nervous system and its functional or organic disorders. Neurologists diagnose and treat diseases and disorders of the brain, spinal cord, and nerves.

The first scientific studies of nerve function in animals were performed in the early 18th century by English physiologist Stephen Hales and Scottish physiologist Robert Whytt. Knowledge was gained in the late 19th century about the causes of aphasia, epilepsy, and motor problems arising from brain damage. French neurologist Jean-Martin Charcot and English neurologist William Gowers described and classified many diseases of the nervous system. The mapping of the functional areas of the brain through selective electrical stimulation also began in the 19th century. Despite these contributions, however, most knowledge of the brain and nervous functions came from studies in animals and from the microscopic analysis of nerve cells.

The electroencephalograph (EEG), which records electrical brain activity, was invented in the 1920s by Hans Berger. Development of the EEG, analysis of cerebrospinal fluid obtained by lumbar puncture (spinal tap), and development of cerebral angiography allowed neurologists to increase the precision of their diagnoses and develop specific therapies and rehabilitative measures. Further aiding the diagnosis and treatment of brain disorders were the development of computerized axial tomography (CT) scanning in the early 1970s and magnetic resonance imaging (MRI) in the 1980s, both of which yielded detailed, noninvasive views of the inside of the brain. (See brain scanning.) The identification of chemical agents in the central nervous system and the elucidation of their roles in transmitting and blocking nerve impulses have led to the introduction of a wide array of medications that can correct or alleviate various neurological disorders including Parkinson disease, multiple sclerosis, and epilepsy. Neurosurgery, a medical specialty related to neurology, has also benefited from CT scanning and other increasingly precise methods of locating lesions and other abnormalities in nervous tissues.

Additional Information

Neurologists are medical professionals who specialize in diagnosing and treating conditions that affect the nervous system.

A general practice doctor might make a referral to a neurologist if they believe that an individual shows signs of a neurological problem.

Neurological issues encompass a broad range of conditions, including Alzheimer’s disease, diabetic neuropathy, headaches, and nerve damage.

This article discusses the role of a neurologist, including the types of conditions they treat, the procedures they perform, and when a person might visit this specialist.

What do neurologists do?

A neurologist is a medical doctor who specializes in evaluating, diagnosing, and treating diseases that affect the nervous system.

The nervous system has two parts:

* the central nervous system (CNS), which refers to the brain and spinal cord
* the peripheral nervous system (PNS), which includes all of the nerves outside of the CNS

What do neurologists specialize in?

Due to the complex nature of the nervous system, many neurologists focus on treating certain populations of people or people with specific neurological diseases.

After completing 4 years of medical school to become a physician, neurologists must complete a 4-year residency that consists of 1 year of general internal medicine or pediatrics training, followed by 3 years of neurology training. Some neurologists complete further subspecialty training, which is usually 1–3 years.

Examples of subspecialties within the field of neurology include:

* pediatric or child neurology
* neurodevelopmental disabilities
* neuromuscular medicine
* hospice and palliative care neurology
* pain medicine
* headache medicine
* sleep medicine
* vascular neurology
* autonomic disorders
* neuropsychiatry
* brain injury medicine
* neurocritical care
* epilepsy
* movement disorders
* neuro-oncology

What conditions do neurologists treat?

Neurologists treat neurological conditionsTrusted Source, which are problems that affect the brain, spinal cord, and nerves. These conditions include:

* stroke
* epilepsy
* headaches and migraine
* brain tumors
* brain aneurysms
* peripheral neuropathy
* sleep disorders
* neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease
* neuromuscular disorders, such as muscular dystrophy, myasthenia gravis, and amyotrophic lateral sclerosis (ALS)
* multiple sclerosis (MS), an inflammatory neurological disease
* infections of the nervous system, such as encephalitis, meningitis, and HIV

Sometimes neurologists evaluate people in the hospital who have had surgery or a medical problem if they have a new problem, such as a seizure or decreased alertness.

These neurological evaluations may help determine outlook or the likelihood of improving from a severe illness.

What can a neurologist diagnose?

Neurologists can diagnose a range of conditions affecting the nervous systemTrusted Source, such as:

* stroke
* chronic migraine
* meningitis
* epilepsy
* multiple sclerosis
* Parkinson’s disease
* autism
* dementia and Alzheimer’s disease

What procedures do neurologists perform?

Neurologists perform a range of different tests and procedures to diagnose and treat neurological conditions.

Some of these procedures include:

Lumbar puncture

A neurologist can use a lumbar puncture to collect a sample of spinal fluid. They may use this procedure to help diagnose the following conditions:

* meningitis
* encephalitis
* inflammation of the spinal cord
* leukemia
* autoimmune diseases, such as MS
* dementia
* bleeding in the brain

Neurologists can also use a lumbar puncture to treat conditions that affect the spinal cord. They can inject anesthetics, antibiotics, or cancer treatments using a lumbar puncture needle.

Electromyography

A neurologist can use electromyography (EMG) to assess how well a person’s muscles respond to electrical stimulation from motor neurons, which are nerves that control muscle movement.

Usually, a neurologist will also perform a nerve conduction study (NCV) to measure nerve activity by assessing someone’s response to superficial electric stimulation.

During an EMG, a specially trained technician inserts small needles called electrodes into the muscle. These electrodes record the different electrical activity that occurs in muscle tissue during periods of movement and rest.

The EMG machine produces an electromyogram, which is a record of this activity.

Neurologists can use the results of an EMG to diagnose neuromuscular diseases, such as myasthenia gravis and ALS.

Electroencephalogram

Neurologists use electroencephalograms (EEG) to measure and record electrical activity in the brain.

Neurons in the brain communicate with other neurons through electrical impulses, which an EEG can detect. An EEG can also track brain wave patterns.

During an EEG, a technician will place electrodes on the person’s head. These electrodes connect to a computer that converts electrical signals into patterns that the technician can view on a screen or print on a piece of paper.

Neurologists can use EEG results to identify abnormal electrical activity in the brain and diagnose certain conditions, such as:

* epilepsy
* seizures
* brain tumors
* sleeping problems
* coma, or unresponsiveness

Tensilon test

Myasthenia gravis is a rare neuromuscular disease that weakens the muscles in the arms and legs. A neurologist can use a Tensilon test to diagnose myasthenia gravis.

Tensilon is the brand name of a drug called edrophonium, which prevents the breakdown of acetylcholine, a neurotransmitter that stimulates muscle movement.

Myasthenia gravis causes the immune system to attack acetylcholine receptors in the muscles, which causes muscle fatigue and decreased muscle movement.

During a Tensilon test, a neurologist will inject a small amount of Tensilon into the bloodstream. Then, they will ask the person to perform different movements to determine if muscle strength improves.

The neurologist will continue administering doses of Tensilon each time the person feels tired. If the person notices that their strength returns after each Tensilon injection, this indicates that they are likely to have myasthenia gravis.

Other tests

A neurologist can use the following testsTrusted Source to help diagnose neurological disorders:

* laboratory tests, such as blood and urine analyses
* imaging tests, such as ultrasounds and MRI, CT, and PET scans
* genetic testing
* biopsy
* angiography

What does a neurologist do on your first visit?

A neurological examination will involve tests to check muscle strength, memory, eye health and vision, and coordination. The tests are not usually painful but may cause some mild discomfort.

People will not need to prepare anything for their first neurological visit. The appointment may involve the neurologist:

* asking about any symptoms and current or previous medical conditions or medications
* checking for any visible signs of a condition by assessing a person’s posture, walk, ease of movement, and balance
* performing a physical examination to measure pulse and blood pressure and listen to the lungs and heart
* asking about bowel movements and passing of urine, as these can indicate how well the autonomic nervous system is functioning

After this initial examination, a neurologist may then perform several assessments, such as:

* Cranial nerve tests: These test brain nerve function, which can affect the senses. People may need to identify certain scents and identify letters or numbers in an eye test.
* Coordination and motor skills tests: A neurologist may ask people to spin around, move their limbs in a specific way, tap fingers, or write. People may also have a reflex test, such as a tap on their knee to check the response.
* Sensation tests: A neurologist may check how well people respond to stimuli, such as soft fabric or touching containers holding warm or cold water.
* Cognitive ability tests: A neurologist may ask people about their job, the date, and the time of year to check people’s memory. Language and math tests can also test for concentration. Some tests of cognitive skill, such as the mini-mental state examination (MMSE) or the Montreal Cognitive Assessment (MoCA), are not standard, but a neurologist may perform them if a person is showing signs of cognitive impairment during the neurological evaluation.

When to consult a neurologist

A doctor might refer someone to a neurologist if they have symptoms that indicate a neurological condition, such as:

* frequent or severe headaches
* muscle weakness
* confusion
* dizziness
* loss of coordination
* partial or complete paralysis
* sensory changes that affect the sense of touch, vision, smell, or taste.

Neurologists vs. neurosurgeons
Both neurologists and neurosurgeons treat people who have conditions that affect the nervous system. However, neurosurgeons perform surgery, whereas neurologists do not.

Neurosurgeons complete medical school and then neurosurgery residency, which includes 1 year of general surgery internship, followed by 6–8 years of neurosurgery residency.

All neurosurgeons are qualified to operate on the brain and the spine, and some neurosurgeons further specialize in highly technical procedures.

Generally, a person’s general practice doctor will refer them to a neurologist or a neurosurgeon. Sometimes a neurologist may refer to a neurosurgeon if surgery would be beneficial, and sometimes a neurosurgeon will refer to a neurologist if the individual requires neurological management.

Summary

Neurologists diagnose and treat medical conditions that affect the nervous system.

A general practice doctor may refer a person to a neurologist if they show signs of a neurological disorder, such as:

* persistent or severe headaches
* muscle weakness
* confusion
* dizziness
* loss of coordination
* partial or complete paralysis

Neurologists can perform various procedures to help diagnose and treat neurological conditions. However, if a person requires surgery, their neurologist or doctor will refer them to a neurosurgeon.

Jai Ganesh · 2022-09-05 13:57:33

1466) Nyctalopia

Summary

Nyctalopia (from Ancient Greek 'night', 'blind, invisible', and 'eye'), also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition (for example, vitamin A deficiency). It can be described as insufficient adaptation to darkness.

The most common cause of nyctalopia is retinitis pigmentosa, a disorder in which the rod cells in the retina gradually lose their ability to respond to the light. Patients with this genetic condition have progressive nyctalopia and eventually, their daytime vision may also be affected. In X-linked congenital stationary night blindness, from birth the rods either do not work at all, or work very little, but the condition does not get worse.

Another cause of night blindness is a deficiency of retinol, or vitamin A1, found in fish oils, liver and dairy products.

The opposite problem, the inability to see in bright light, is known as hemeralopia and is much rarer.

Since the outer area of the retina is made up of more rods than cones, loss of peripheral vision often results in night blindness. Individuals with night blindness not only see poorly at night but also require extra time for their eyes to adjust from brightly lit areas to dim ones. Contrast vision may also be greatly reduced.

Rods contain a receptor-protein called rhodopsin. When light falls on rhodopsin, it undergoes a series of conformational changes ultimately generating electrical signals which are carried to the brain via the optic nerve. In the absence of light, rhodopsin is regenerated. The body synthesizes rhodopsin from vitamin A, which is why a deficiency in vitamin A causes poor night vision.

Refractive "vision correction" surgery (especially PRK with the complication of "haze") may rarely cause a reduction in best night-time acuity due to the impairment of contrast sensitivity function (CSF) which is induced by intraocular light-scatter resulting from surgical intervention in the natural structural integrity of the cornea.

Details

It is a condition characterized by an abnormal inability to see in dim light or at night, typically caused by vitamin A deficiency.

What’s night blindness?

Night blindness is a type of vision impairment also known as nyctalopia. People with night blindness experience poor vision at night or in dimly lit environments.

Although the term “night blindness” implies that you can’t see at night, this isn’t the case. You may just have more difficulty seeing or driving in darkness.

Some types of night blindness are treatable while other types aren’t. See your doctor to determine the underlying cause of your vision impairment. Once you know the cause of the problem, you can take steps to correct your vision.

What to look for

The sole symptom of night blindness is difficulty seeing in the dark. You’re more likely to experience night blindness when your eyes transition from a bright environment to an area of low light, such as when you leave a sunny sidewalk to enter a dimly lit restaurant.

You’re also likely to experience poor vision when driving due to the intermittent brightness of headlights and streetlights on the road.

What causes night blindness?

A few eye conditions can cause night blindness, including:

* nearsightedness, or blurred vision when looking at faraway objects
* cataracts, or clouding of the eye’s lens
* retinitis pigmentosa, which occurs when dark pigment collects in your retina and creates tunnel vision
* Usher syndrome, a genetic condition that affects both hearing and vision

Older adults have a greater risk of developing cataracts. They’re therefore more likely to have night blindness due to cataracts than children or young adults.

In rare cases in the United States or in other parts of the world where nutritional diets may vary, vitamin A deficiency can also lead to night blindness.

Vitamin A, also called retinol, plays a role in transforming nerve impulses into images in the retina. The retina is a light-sensitive area in the back of your eye.

People who have pancreatic insufficiency, such as individuals with cystic fibrosis, have difficulty absorbing fat and are at a greater risk of having vitamin A deficiency because vitamin A is fat-soluble. This puts them at greater risk for developing night blindness.

People who have high blood glucose (sugar) levels or diabetes also have a higher risk of developing eye diseases, such as cataracts.

What are the treatment options for night blindness?

Your eye doctor will take a detailed medical history and examine your eyes to diagnose night blindness. You may also need to give a blood sample. Blood testing can measure your vitamin A and glucose levels.

Night blindness caused by nearsightedness, cataracts, or vitamin A deficiency is treatable. Corrective lenses, such as eyeglasses or contacts, can improve nearsighted vision both during the day and at night.

Let your doctor know if you still have trouble seeing in dim light even with corrective lenses.

Cataracts

Clouded portions of your eye’s lens are known as cataracts.

Cataracts can be removed through surgery. Your surgeon will replace your cloudy lens with a clear, artificial lens. Your night blindness will improve significantly after surgery if this is the underlying cause.

Vitamin A deficiency

If your vitamin A levels are low, your doctor might recommend vitamin supplements. Take the supplements exactly as directed.

Most people don’t have vitamin A deficiency because they have access to proper nutrition.

Genetic conditions

Genetic conditions that cause night blindness, such as retinitis pigmentosa, aren’t treatable. The gene that causes pigment to build up in the retina doesn’t respond to corrective lenses or surgery.

People who have this form of night blindness should avoid driving at night.

How can I prevent night blindness?

You can’t prevent night blindness that’s the result of birth defects or genetic conditions, such as Usher syndrome. You can, however, properly monitor your blood sugar levels and eat a balanced diet to make night blindness less likely.

Eat foods rich in antioxidants, vitamins, and minerals, which may help prevent cataracts. Also, choose foods that contain high levels of vitamin A to reduce your risk of night blindness.

Certain orange-colored foods are excellent sources of vitamin A, including:

* cantaloupes
* sweet potatoes
* carrots
* pumpkins
* butternut squash
* mangoes

Vitamin A is also in:

* spinach
* collard greens
* milk
* eggs

What’s the long-term outlook?

If you have night blindness, you should take precautions to keep yourself and others safe. Refrain from driving at night as much as possible until the cause of your night blindness is determined and, if possible, treated.

Arrange to do your driving during the day, or secure a ride from a friend, family member, or taxi service if you need to go somewhere at night.

Wearing sunglasses or a brimmed hat can also help reduce glare when you’re in a brightly lit environment, which can ease the transition into a darker environment.

Jai Ganesh · 2022-09-06 14:10:33

1467) Radiobiology

Summary

Radiobiology (also known as radiation biology, and uncommonly as actinobiology) is a field of clinical and basic medical sciences that involves the study of the action of ionizing radiation on living things, especially health effects of radiation. Ionizing radiation is generally harmful and potentially lethal to living things but can have health benefits in radiation therapy for the treatment of cancer and thyrotoxicosis. Its most common impact is the induction of cancer with a latent period of years or decades after exposure. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Controlled doses are used for medical imaging and radiotherapy.

Details

Radiation biology (also known as radiobiology) is a medical science that involves the study of biological effects of ionizing radiation on living tissues. Radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us. It is a part of our natural world that has been here since the birth of our planet. Whether the source of radiation is natural or man-made, whether it is a large dose of radiation or a small dose, there will be some biological effects. In general, ionizing radiation is harmful and potentially lethal to living beings but can have health benefits in medicine, for example, in radiation therapy for the treatment of cancer and thyrotoxicosis. This chapter briefly summarizes the short and long term consequences which may result from exposure to radiation.

Cellular Damage – Radiobiology

All biological damage effects begin with the consequence of radiation interactions with the atoms forming the cells. All living things are composed of one or more cells. Every part of your body consists of cells or was built by them. Although we tend to think of biological effects in terms of the effect of radiation on living cells, in actuality, ionizing radiation, by definition, interacts only with atoms by a process called ionization. For ionizing radiation, the kinetic energy of particles (photons, electrons, etc.) of ionizing radiation is sufficient and the particle can ionize (to form ion by losing electrons) target atoms to form ions. Simply ionizing radiation can knock electrons from an atom.

There are two mechanisms by which radiation ultimately affects cells. These two mechanisms are commonly called:

* Direct effects. Direct effects are caused by radiation, when radiation interacts directly with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell. The probability of the radiation interacting with the DNA molecule is very small since these critical components make up such a small part of the cell.
* Indirect effects. Indirect effects are caused by interaction of radiation usually with water molecules. Each cell, just as is the case for the human body, is mostly water. Ionizing radiation may break the bonds that hold the water molecule together, producing radicals such as hydroxyl OH, superoxide anion O2–and others. These radicals can contribute to the destruction of the cell.

A large number of cells of any particular type is called a tissue. If this tissue forms a specialised functional unit, it is called an organ. The type and number of cells affected is also an important factor. Some cells and organs in the body are more sensitive to ionizing radiation than others.

Sensitivity of various types of cells to ionizing radiation is very high for tissues consisting of cells that divide rapidly like those found in bone marrow, stomach, intestines, male and female reproductive organs, and developing fetuses. This is because dividing cells require correct DNA information in order for the cell’s offspring to survive. A direct interaction of radiation with an active cell could result in the death or mutation of the cell, whereas a direct interaction with the DNA of a dormant cell would have less of an effect.

As a result, living cells can be classified according to their rate of reproduction, which also indicates their relative sensitivity to radiation. As a result, actively reproducing cells are more sensitive to ionizing radiation than cells that make up skin, kidney or liver tissue. The nerve and muscle cells are the slowest to regenerate and are the least sensitive cells.

High-LET and Low-LET Radiation

As was written, each type of radiation interacts with matter in a different way. For example charged particles with high energies can directly ionize atoms. Alpha particles are fairly massive and carry a double positive charge, so they tend to travel only a short distance and do not penetrate very far into tissue if at all. However alpha particles will deposit their energy over a smaller volume (possibly only a few cells if they enter a body) and cause more damage to those few cells.

Beta particles (electrons) are much smaller than alpha particles. They carry a single negative charge. They are more penetrating than alpha particles. They can travel several meters but deposit less energy at any one point along their paths than alpha particles. This means beta particles tend to damage more cells, but with lesser damage to each. On the other hand electrically neutral particles interacts only indirectly, but can also transfer some or all of their energies to the matter.

It would certainly simplify matters if biological effects of radiation were directly proportional to the absorbed dose. Unfortunately, biological effects depend also on the way in which the absorbed dose is distributed along the path of the radiation. Studies have shown that alpha and neutron radiation cause greater biological damage for a given energy deposition per kg of tissue than gamma radiation does. It was discovered, biological effects of any radiation increases with the linear energy transfer (LET). In short, the biological damage from high-LET radiation (alpha particles, protons or neutrons) is much greater than that from low-LET radiation (gamma rays). This is because the living tissue can more easily repair damage from radiation that is spread over a large area than that which is concentrated in a small area. Of course, at very high levels of exposure gamma rays can still cause a great deal of damage to tissues.

Because more biological damage is caused for the same physical dose (i.e., the same energy deposited per unit mass of tissue), one gray of alpha or neutron radiation is more harmful than one gray of gamma radiation. This fact that radiations of different types (and energies) give different biological effects for the same absorbed dose is described in terms of factors known as the relative biological effectiveness (RBE) and the radiation weighting factor (wR).

Acute Dose and Chronic Dose

Biological effects of radiation and their consequences depends strongly on the level of dose rate obtained. In radiobiology, the dose rate is a measure of radiation dose intensity (or strength). Low-level doses are common for everyday life. In the following points there are a few examples of radiation exposure, which can be obtained from various sources.

05 µSv – Sleeping next to someone
09 µSv – Living within 30 miles of a nuclear power plant for a year
1 µSv – Eating one banana
3 µSv – Living within 50 miles of a coal power plant for a year
10 µSv – Average daily dose received from natural background
20 µSv – Chest X-ray

From biological consequences point of view, it is very important to distinguish between doses received over short and extended periods. Therefore, biological effects of radiation are typically divided into two categories.

* Acute Doses. An “acute dose” (short-term high-level dose) is one that occurs over a short and finite period of time, i.e., within a day.
* Chronic Doses. A “chronic dose” (long-term low-level dose) is a dose that continues for an extended period of time, i.e., weeks and months, so that it is better described by a dose rate.

High doses tend to kill cells, while low doses tend to damage or change them. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Acute doses below 250 mGy are unlikely to have any observable effects. Acute doses of about 3 to 5 Gy have a 50% chance of killing a person some weeks after the exposure, if a person receives no medical treatment.

Low doses spread out over long periods of time don’t cause an immediate problem to any body organ. The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years. Moreover, some studies demonstrate, most of human tissues exhibit a more pronounced tolerance to the effects of low-LET radiation in case of a prolonged exposure compared to a one-time exposure to a similar dose.

Deterministic and Stochastic Effects

In radiobiology, most adverse health effects of radiation exposure are usually divided into two broad classes:

* Deterministic effects are threshold health effects, that are related directly to the absorbed radiation dose and the severity of the effect increases as the dose increases.
* Stochastic effects occur by chance, generally occurring without a threshold level of dose. Probability of occurrence of stochastic effects is proportional to the dose but the severity of the effect is independent of the dose received.

Jai Ganesh · 2022-09-07 14:21:27

1468) Hinge

Summary

A hinge is a piece of metal that fastens the edge of a door, window, lid, etc. to something else and allows it to open or close.

Details

A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other translations or rotations being prevented, and thus a hinge has one degree of freedom. Hinges may be made of flexible material or of moving components. In biology, many joints function as hinges, like the elbow joint.

Door hinges:

Barrel hinge

A barrel hinge consists of a sectional barrel (the knuckle) secured by a pivot. A barrel is simply a hollow cylinder. The vast majority of hinges operate on the barrel principle.

Butt hinge / Mortise hinge

Any hinge which is designed to be set into a door frame and/ or door is considered to be a butt hinge or a mortise hinge. A hinge can also be made as a half-mortise, in which case only one half of the hinge is mortised and the other is not. Most mortise hinges are also barrel hinges by virtue of how they pivot (i.e., a pair of leaves secured to each other by knuckles through which runs a pin).

Butterfly/ Parliament (UK) hinge

These are a decorative variety of barrel hinge with leaves somewhat resembling the wings of a butterfly.

Case hinges

Case hinges are similar to a butt hinge however usually more of a decorative nature most commonly used in suitcases, briefcases, and the like.

Concealed hinge

These are used for furniture doors (with or without self-closing feature, and with or without damping systems). They are made of two parts: One part is the hinge cup and the arm, the other part is the mounting plate. Also called "cup hinge", or "Euro hinge", as they were developed in Europe and use metric installation standards. Most such concealed hinges offer the advantage of full in situ adjustability for standoff distance from the cabinet face as well as pitch and roll by means of two screws on each hinge.

Continuous/ Piano hinge

This variety of barrel hinge runs the entire length of a door, panel, box., etc. Continuous hinges are manufactured with or without holes.

Flag hinge

these consist of a single leaf attached (in the male variety) to a pin. When used, the pin is inserted into the other (female) portion of the hinge. This allows the objects to be easily removed (for example, a removable door). They are manufactured in right-hand and left-hand configurations.

H hinge

These barrel hinges are shaped like an H and used on flush-mounted doors. Small H hinges (3–4 in or 76–102 mm) tend to be used for cabinets hinges, while larger hinges (6–7 in or 150–180 mm) are for passage doors or closet doors.

HL hinge

These were common for passage doors, room doors, and closet doors in the 17th, 18th, and even 19th centuries. On taller doors, H hinges were occasionally used in the middle along with the HL hinges.

Pivot hinge

This hinge pivots in openings in the floor and the top of the door frame. Also referred to as a double-acting floor hinge. This type is found in ancient dry stone buildings and rarely in old wooden buildings. These are also called haar-hung doors. They are a low-cost alternative for use with lightweight doors.[2]

Self-closing hinge

This is a spring-loaded hinge with a speed control function. The same as spring hinge, usually use spring to provide force to close the door and provide a mechanical or hydraulic damper to control door close speed. That can prevent door slamming problem while auto closes a door.

Spring hinge

This is a spring-loaded hinge made to provide assistance in the closing or the opening of the hinge leaves. A spring is a component of a hinge, that applies force to secure a hinge closed or keep a hinge opened.

Swing Clear hinge

Swing Clear Door Hinges (aka Offset Door Hinges) are perfect for residential and commercial doors, as they allow doors to swing completely clear of openings. Swing Clear Hinges can easily comply with Fair Housing Act (FHA) code by providing a minimum ADA 32” clearance clearance when using a 34” door slab.

Living hinge

This hinge takes advantage of the flexibility of plastic to create a join between two objects without any knuckles or pins. They are molded as a single piece, never become rusted, do not squeak, and have several other advantages over other hinges, but the plastic makes them more susceptible to breakage.

Other types include:

* Coach hinge
* Counterflap hinge
* Cranked hinge or storm-proof hinge
* Double action non-spring
* Double action spring hinge
* Flush hinge
* Friction hinge
* Lift-off hinge
* Pinge: A hinge with a quick release pin.
* Rising butt hinge
* Security hinge
* Tee hinge

Building access

Since at least medieval times there have been hinges to draw bridges for defensive purposes for fortified buildings. Hinges are used in contemporary architecture where building settlement can be expected over the life of the building. For example, the Dakin Building in Brisbane, California, was designed with its entrance ramp on a large hinge to allow settlement of the building built on piles over bay mud. This device was effective until October 2006, when it was replaced due to damage and excessive ramp slope.

Large structures

Hinges appear in large structures such as elevated freeway and railroad viaducts. These are included to reduce or eliminate the transfer of bending stresses between structural components, typically in an effort to reduce sensitivity to earthquakes. The primary reason for using a hinge, rather than a simpler device such as a slide, is to prevent the separation of adjacent components. When no bending stresses are transmitted across the hinge it is called a zero moment hinge.

Jai Ganesh · 2022-09-08 14:42:31

1469) Cynophobia

Summary

Cynophobia[a] (from the Greek: "dog" and "fear") is the fear of dogs and canines in general. Cynophobia is classified as a specific phobia, under the subtype "animal phobias". According to Timothy O. Rentz of the Laboratory for the Study of Anxiety Disorders at the University of Texas, animal phobias are among the most common of the specific phobias and 36% of patients who seek treatment report being afraid of dogs or afraid of cats. Although ophidiophobia or arachnophobia are more common animal phobias, cynophobia is especially debilitating because of the high prevalence of dogs and the general ignorance of dog owners to the phobia. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) reports that only 12% to 30% of those with a specific phobia will seek treatment.

Details

What Is Cynophobia?

Cynophobia is the fear of dogs. Like all specific phobias, cynophobia is intense, persistent, and irrational. According to a recent diagnostic manual, between 7% and 9% of any community may suffer from a specific phobia.

A phobia goes beyond mild discomfort or situational fear. It is not just fear in response to a particular situation. Instead, specific phobias interfere with daily life and can cause serious physical and emotional distress. You often can manage or treat cynophobia with medication or psychotherapy.

What Are the Symptoms of Cynophobia?

Cynophobia and other phobias related to animals are often diagnosed through the use of questionnaires and clinical interviews. For example, one snake phobia questionnaire presents a set of 12 statements about your reaction to snakes and asks you to agree or disagree with each statement.

In order to diagnose cynophobia, a doctor would evaluate your behavior and emotional responses concerning dogs. Symptoms of phobias may include any of the following:

* Sweating
* Trembling
* Difficulty breathing
* Rapid heartbeat
* Nausea
* Dizziness
* A feeling of danger
* Fear of losing control
* A fear of dying
* A sense of things being unreal
* Excessive avoidance or anxiety

If you regularly have any of these symptoms in relation to dogs, you may want to talk to your doctor or a licensed therapist about it.

At their most serious, specific phobias can lead to other problems. If you start struggling with any of these, contact your doctor for help:

* Social isolation
* Anxiety disorders or depression
* Substance abuse
* Thoughts of killing oneself

What Causes Cynophobia?

Specific phobias often appear in childhood. However, adults can develop them as well. No one knows exactly what makes someone develop a specific phobia. Potential causes include:

* Traumatic experiences: For example, someone may develop a fear of dogs after being attacked by one.
* Family tendencies: Either genetics or environment can play a role in the development of phobias. If someone in your family has a phobia, you are more likely to develop it as well.
* Changes in brain function: Some people appear to develop phobias as a result of neurological disorders or physical trauma.

How to Treat or Manage Cynophobia

Several forms of therapy have helped people with cynophobia. Consult your doctor or a licensed mental health professional to find the right treatment or combination of treatments.

* Exposure therapy. The most common treatment for specific phobias is exposure therapy. This is also called desensitization. In simple terms, persons undergoing exposure therapy practice interacting with the objects that they fear.

To treat cynophobia, some therapists suggest that you gradually increase both the closeness and length of your exposure. You could start by watching programs that feature dogs or watching dogs from a distance. Then, you work up to spending periods of time with dogs in person.

Another form of exposure therapy with some proven success is called active-imaginal exposure. In this style of treatment, you would vividly imagine interacting with dogs and practice using certain techniques to manage your feelings in response.

More recently, many therapists have had success with virtual reality exposure. Both sound and sight elements are combined in a virtual reality experience. This gives the person practice being around dogs in a safe and controlled environment.

* Cognitive-behavioral therapy (CBT). Cognitive-behavioral therapy is also used to treat specific phobias. It generally includes exposure therapy. In addition, it emphasizes learning to retrain the brain and reframe negative experiences.

The goal of cognitive behavioral therapy is to develop a sense of control over your thoughts and emotions. The therapist aims to help you gain confidence in your ability to handle difficult situations.

* Medications. The impact of drugs on specific phobias has been inconsistent. They appear to work best when used with exposure therapy instead of on their own. However, some anti-anxiety medications such as beta-blockers and sedatives can help you treat the physical symptoms of severe attacks.

More recently, researchers have discovered that a steroid called glucocorticoid can successfully decrease the physical symptoms associated with the anxiety connected to specific phobias. This includes the fear of dogs.

Jai Ganesh · 2022-09-09 14:33:22

1470) Door

Summary

A door is a hinged or otherwise movable barrier that allows ingress (entry) into and egress (exit) from an enclosure. The created opening in the wall is a doorway or portal. A door's essential and primary purpose is to provide security by controlling access to the doorway (portal). Conventionally, it is a panel that fits into the doorway of a building, room, or vehicle. Doors are generally made of a material suited to the door's task. They are commonly attached by hinges, but can move by other means, such as slides or counterbalancing.

The door may be able to move in various ways (at angles away from the doorway/portal, by sliding on a plane parallel to the frame, by folding in angles on a parallel plane, or by spinning along an axis at the center of the frame) to allow or prevent ingress or egress. In most cases, a door's interior matches its exterior side. But in other cases (e.g., a vehicle door) the two sides are radically different.

Many doors incorporate locking mechanisms to ensure that only some people can open them (such as with a key). Doors may have devices such as knockers or doorbells by which people outside announce their presence. (In some countries, such as Brazil, it is customary to clap from the sidewalk to announce one's presence.) Apart from providing access into and out of a space, doors may have the secondary functions of ensuring privacy by preventing unwanted attention from outsiders, of separating areas with different functions, of allowing light to pass into and out of a space, of controlling ventilation or air drafts so that interiors may be more effectively heated or cooled, of dampening noise, and of blocking the spread of fire.

Doors can have aesthetic, symbolic, ritualistic purposes. Receiving the key to a door can signify a change in status from outsider to insider. Doors and doorways frequently appear in literature and the arts with metaphorical or allegorical import as a portent of change.

Details

A door is a barrier of wood, stone, metal, glass, paper, leaves, hides, or a combination of materials, installed to swing, fold, slide, or roll in order to close an opening to a room or building. Early doors, used throughout Mesopotamia and the ancient world, were merely hides or textiles. Doors of rigid, permanent materials appeared simultaneously with monumental architecture. Doors for important chambers were often made of stone or bronze.

Stone doors, usually hung on pivots, top and bottom, were often used on tombs. A marble, paneled example, probably from the time of Augustus, was found at Pompeii; a Greek door (c. AD 200) from a tomb at Langaza, Turkey, has been preserved in the museum at Istanbul.

The use of monumental bronze doors is a tradition that has persisted into the 20th century. The portals of Greek temples were often fitted with cast-bronze grills; the Romans characteristically used solid bronze double doors. They were usually supported by pivots fitted into sockets in the threshold and lintel. The earliest large examples are the 24-foot (7.3-metre) double doors of the Roman Pantheon. The Roman paneled design and mounting technique continued in Byzantine and Romanesque architecture. The art of casting doors was preserved in the Eastern Empire, the most notable example being double doors (c. 838) of the Hagia Sophia cathedral in Constantinople (now Istanbul). In the 11th century bronze castings from Constantinople were imported into southern Italy. Bronze doors were introduced into northern Europe, notably in Germany, when Charlemagne installed a Byzantine pair (cast c. 804) for the cathedral at Aachen. The first bronze doors to be cast in one piece in northern Europe were made for the Cathedral of Hildesheim (c. 1015). They were designed with a series of panels in relief, establishing a sculptural tradition of historical narrative that distinguishes Romanesque and, later, bronze doors.

Hollow casting of relief panels was revived in the 12th century in southern Italy, notably by Barisanus of Trani (cathedral doors, 1175), and carried northward by artists such as Bonanno of Pisa. In 14th-century Tuscany the principal examples are the pairs of sculptured, paneled bronze doors on the Florentine Baptistery; the Gothic south doors (1330–36) are by Andrea Pisano, and the north doors (1403–24) by Lorenzo Ghiberti. Ghiberti’s east doors (1425–52) have come to be known as the “Gates of Paradise” (“Porta del Paradiso”). Bronze doors with relief panels by Antonio Filarete were cast for St. Peter’s Basilica, Rome. Bronze doors were not generally used in northwestern Europe until the 18th century. The first monumental bronze doors in the United States were erected in 1863 in the Capitol at Washington, D.C.

The wooden door was doubtless the most common in antiquity. Archaeological and literary evidence indicate its prevalence in Egypt and Mesopotamia. According to Pompeiian murals and surviving fragments, contemporary doors looked much like modern wood-paneled doors; they were constructed of stiles (vertical beams) and rails (horizontal beams) framed together to support panels and occasionally equipped with locks and hinges. This Roman type of door was adopted in Islāmic countries. In China the wooden door usually consisted of two panels, the lower one solid and the upper one a wooden lattice backed with paper. The traditional Japanese shoji was a wood-framed, paper-covered sliding panel.

The typical Western medieval door was of vertical planks backed with horizontals or diagonal bracing. It was strengthened with long iron hinges and studded with nails. In domestic architecture, interior double doors appeared in Italy in the 15th century and then in the rest of Europe and the American colonies. The paneled effect was simplified until, in the 20th century, a single, hollow-core, flush panel door has become most common.

There also are several types of specialized modern doors. The louvered (or blind) door and the screen door have been used primarily in the United States. The Dutch door, a door cut in two near the middle, allowing the upper half to open while the lower half remains closed, descends from a traditional Flemish-Dutch type. The half door, being approximately half height and hung near the centre of the doorway, was especially popular in the 19th-century American West.

Glazed doors, dating from the 17th century, first appeared as window casements extended to the floor. French doors (double glazed) were incorporated into English and American architecture in the late 17th and 18th centuries. At about this time, the French developed the mirrored door.

Other types of 19th- and 20th-century innovations include the revolving door, the folding door, the sliding door inspired by the Japanese shoji, the canopy door (pivoting at the top of the frame), and the rolling door (of tambourlike construction), also opening to the top.

Jai Ganesh · 2022-09-10 13:52:43

1471) Altimeter

Summary

An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. The most common unit for altimeter calibration worldwide is hectopascals (hPa), except for North America (other than Canada) and Japan where inches of mercury (inHg) are used. To obtain an accurate altitude reading in either feet or meters, the local barometric pressure must be calibrated correctly using the barometric formula.

Use in aircraft

In aircraft, an aneroid barometer measures the atmospheric pressure from a static port outside the aircraft. Air pressure decreases with an increase of altitude—approximately 100 hectopascals per 800 meters or one inch of mercury per 1000 feet or 1 hectopascals per 30 feet near sea level.

The aneroid altimeter is calibrated to show the pressure directly as an altitude above mean sea level, in accordance with a mathematical model atmosphere defined by the International Standard Atmosphere (ISA). Older aircraft used a simple aneroid barometer where the needle made less than one revolution around the face from zero to full scale. This design evolved to three-pointer altimeters with a primary needle and one or more secondary needles that show the number of revolutions, similar to a clock face. In other words, each needle points to a different digit of the current altitude measurement. However this design has fallen out of favor due to the risk of misreading in stressful situations. The design evolved further to drum-type altimeters, the final step in analogue instrumentation, where each revolution of a single needle accounted for 1,000 feet (300 metres), with thousand foot increments recorded on a numerical odometer-type drum. To determine altitude, a pilot had first to read the drum to determine the thousands of feet, then look at the needle for the hundreds of feet. Modern analogue altimeters in transport aircraft are typically drum-type. The latest development in clarity is an Electronic flight instrument system with integrated digital altimeter displays. This technology has trickled down from airliners and military planes until it is now standard in many general aviation aircraft.

Modern aircraft use a "sensitive altimeter". On a sensitive altimeter, the sea-level reference pressure can be adjusted with a setting knob. The reference pressure, in inches of mercury in Canada and the United States, and hectopascals (previously millibars) elsewhere, is displayed in the small Kollsman window, on the face of the aircraft altimeter. This is necessary, since sea level reference atmospheric pressure at a given location varies over time with temperature and the movement of pressure systems in the atmosphere.

In aviation terminology, the regional or local air pressure at mean sea level (MSL) is called the QNH or "altimeter setting", and the pressure that will calibrate the altimeter to show the height above ground at a given airfield is called the QFE of the field. An altimeter cannot, however, be adjusted for variations in air temperature. Differences in temperature from the ISA model will accordingly cause errors in indicated altitude.

In aerospace, the mechanical stand-alone altimeters which are based on diaphragm bellows were replaced by integrated measurement systems which are called air data computers (ADC). This module measures altitude, speed of flight and outside temperature to provide more precise output data allowing automatic flight control and flight level division. Multiple altimeters can be used to design a pressure reference system to provide information about the airplane's position angles to further support inertial navigation system calculations.

Details

An altimeter is a device that measures altitude, the distance of a point above sea level. Altimeters are important navigation instruments for aircraft and spacecraft pilots who monitor their height above the Earth's surface.

An Altimeter is an instrument that measures the altitude of the land surface or any object such as an airplane. The two main types are the pressure altimeter, or aneroid barometer, which approximates altitude above sea level by measuring atmospheric pressure, and the radio altimeter, which measures absolute altitude (distance above land or water) based on the time required for a radio wave signal to travel from an airplane, a weather balloon, or a spacecraft to the ground and back.

The pressure altimeter operates on the principle that average atmospheric pressure decreases linearly with altitude. A typical pressure altimeter is illustrated in the figure. The instrument is enclosed in a case that is connected to the outside of the aircraft by an air pressure inlet at the rear of the housing. Two or more aneroid capsules—i.e., thin corrugated metallic bellows from which air has been exhausted—are positioned near the inlet. These capsules expand when the outside air pressure falls (as in climbing) and contract when the outside air pressure rises (as in descending). By a mechanical arrangement of sector gears, pinion, backlash spring, and crankshaft, the expansion or contraction of the aneroid capsules is converted to the movement of pointers on a dial. The graduated scale dial is marked off in metres or feet, and a series of gear-driven pointers similar to the hands of a clock may be used to indicate the altitude in units of hundreds, thousands, or tens of thousands. The barometric scale dial records the air pressure in millibars (mb). Because atmospheric pressure is measured relative to sea level, a pressure altimeter must be adjusted with a barosetting knob in order to compensate for small variations in barometric pressure caused by changes in local weather.

Jai Ganesh · 2022-09-11 14:08:10

1472) Endocrinology

Summary

Endocrinology (from endocrine + -ology) is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the integration of developmental events proliferation, growth, and differentiation, and the psychological or behavioral activities of metabolism, growth and development, tissue function, sleep, digestion, respiration, excretion, mood, stress, lactation, movement, reproduction, and sensory perception caused by hormones. Specializations include behavioral endocrinology and comparative endocrinology.

The endocrine system consists of several glands, all in different parts of the body, that secrete hormones directly into the blood rather than into a duct system. Therefore, endocrine glands are regarded as ductless glands. Hormones have many different functions and modes of action; one hormone may have several effects on different target organs, and, conversely, one target organ may be affected by more than one hormone.

Details:

What is endocrinology?

Endocrinology is the study of hormones. Hormones are essential for our every-day survival. They control our temperature, sleep, mood, stress, growth and more.

An endocrinologist is a doctor that treats diseases related to problems with hormones. A hormone is a chemical messenger that travels from one cell to another. Hormones are released in one part of the body, travel in the blood stream and have an effect on other part of the body. This helps different parts of the human body to communicate with each other. Hormones are secreted by endocrine glands, such as the pituitary, thyroid or adrenal glands. Not all glands are classified as endocrine glands; for example, sweat glands or lymph glands are not endocrine glands.

Hormones are found in all organisms with more than one cell, and so they are found in plants and animals. They influence or control a wide range of physiological activities, such as growth, development, puberty, level of alertness, sugar regulation and appetite, bone growth, etc. You also find that problems with hormones and the way they work contribute to some of the major diseases of mankind; for example, diabetes, thyroid conditions, pituitary conditions, some sexual problems, some neurological problems, appetite and obesity, bone problems, cancer, etc.

There are whole sub-specialities devoted to specific areas where hormones work. For example:

* Paediatric endocrinology, looking at hormones in children
* Thyroid endocrinology, looking at how the thyroid affects metabolism
* Endocrine-disrupting chemicals, where chemicals which mimic the effects of hormones are present in the environment
* Comparative endocrinology, which looks at the way similar hormones work in different species (e.g. from insects, through to fish, birds, mammals, etc)

Sometimes there are specific societies devoted to the study of these subspecialities.

There are numerous textbooks which can give background information on endocrinology.

Additional Information

Endocrinology is a medical discipline dealing with the role of hormones and other biochemical mediators in regulating bodily functions and with the treatment of imbalances of these hormones.

Although some endocrine diseases, such as diabetes mellitus, have been known since antiquity, endocrinology itself is a fairly recent medical field, depending as it does on the recognition that body tissues and organs secrete chemical mediators directly into the bloodstream to produce distant effects.

Friedrich Henle in 1841 was the first to recognize “ductless glands,” glands that secrete their products into the bloodstream and not into specialized ducts. In 1855 Claude Bernard distinguished the products of these ductless glands from other glandular products by the term “internal secretions,” the first suggestion of what was to become the modern hormone concept.

The first endocrine therapy was attempted in 1889 by Charles Brown-Séquard, who used extracts from animal testes to treat male aging; this prompted a vogue in “organotherapies” that soon faded but that led to adrenal and thyroid extracts that were the forerunners of modern cortisone and thyroid hormones. The first hormone to be purified was secretin, which is produced by the small intestine to trigger the release of pancreatic juices; it was discovered in 1902 by Ernest Starling and William Bayliss. Starling applied the term “hormone” to such chemicals in 1905, proposing a chemical regulation of physiological processes operating in conjunction with nervous regulation; this essentially was the beginning of the field of endocrinology.

The early years of the 20th century saw the purification of a number of other hormones, often leading to new therapies for patients affected by hormonal disorders. In 1914 Edward Kendall isolated thyroxine from thyroid extracts; in 1921 Frederick Banting and Charles Best discovered insulin in pancreatic extracts, immediately transforming the treatment of diabetes (that same year Romanian scientist Nicolas C. Paulescu independently reported the presence of a substance called pancrein, which is thought to have been insulin, in pancreatic extracts); and in 1929 Edward Doisy isolated an estrus-producing hormone from the urine of pregnant females.

The availability of nuclear technology after World War II also led to new treatments for endocrine disorders, notably the use of radioactive iodine to treat hyperthyroidism, greatly reducing the need for thyroid surgery. Combining radioactive isotopes with antibodies against hormones, Rosalyn Yalow and S.A. Berson in 1960 discovered the basis for radioimmunoassays, which enable endocrinologists to determine with great precision minute amounts of hormone, permitting the early diagnosis and treatment of endocrine disorders.

Jai Ganesh · 2022-09-12 14:17:43

1473) Scientific Method

Summary

Scientific method is mathematical and experimental technique employed in the sciences. More specifically, it is the technique used in the construction and testing of a scientific hypothesis.

The process of observing, asking questions, and seeking answers through tests and experiments is not unique to any one field of science. In fact, the scientific method is applied broadly in science, across many different fields. Many empirical sciences, especially the social sciences, use mathematical tools borrowed from probability theory and statistics, together with outgrowths of these, such as decision theory, game theory, utility theory, and operations research. Philosophers of science have addressed general methodological problems, such as the nature of scientific explanation and the justification of induction.

The scientific method is critical to the development of scientific theories, which explain empirical (experiential) laws in a scientifically rational manner. In a typical application of the scientific method, a researcher develops a hypothesis, tests it through various means, and then modifies the hypothesis on the basis of the outcome of the tests and experiments. The modified hypothesis is then retested, further modified, and tested again, until it becomes consistent with observed phenomena and testing outcomes. In this way, hypotheses serve as tools by which scientists gather data. From that data and the many different scientific investigations undertaken to explore hypotheses, scientists are able to develop broad general explanations, or scientific theories.

Details

The scientific method is an empirical method of acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries). It involves careful observation, applying rigorous skepticism about what is observed, given that cognitive assumptions can distort how one interprets the observation. It involves formulating hypotheses, via induction, based on such observations; experimental and measurement-based statistical testing of deductions drawn from the hypotheses; and refinement (or elimination) of the hypotheses based on the experimental findings. These are principles of the scientific method, as distinguished from a definitive series of steps applicable to all scientific enterprises.

Although procedures vary from one field of inquiry to another, the underlying process is frequently the same from one field to another. The process in the scientific method involves making conjectures (hypothetical explanations), deriving predictions from the hypotheses as logical consequences, and then carrying out experiments or empirical observations based on those predictions. A hypothesis is a conjecture, based on knowledge obtained while seeking answers to the question. The hypothesis might be very specific, or it might be broad. Scientists then test hypotheses by conducting experiments or studies. A scientific hypothesis must be falsifiable, implying that it is possible to identify a possible outcome of an experiment or observation that conflicts with predictions deduced from the hypothesis; otherwise, the hypothesis cannot be meaningfully tested.

The purpose of an experiment is to determine whether observations agree with or conflict with the expectations deduced from a hypothesis. Experiments can take place anywhere from a garage to a remote mountaintop to CERN's Large Hadron Collider. There are difficulties in a formulaic statement of method, however. Though the scientific method is often presented as a fixed sequence of steps, it represents rather a set of general principles. Not all steps take place in every scientific inquiry (nor to the same degree), and they are not always in the same order.

Math Is Fun Forum

#1476 2022-08-19 13:50:44

Re: Miscellany

#1477 2022-08-20 14:28:32

Re: Miscellany

#1478 2022-08-21 13:56:49

Re: Miscellany

#1479 2022-08-22 14:01:00

Re: Miscellany

#1480 2022-08-23 14:12:45

Re: Miscellany

#1481 2022-08-24 14:01:10

Re: Miscellany

#1482 2022-08-25 14:38:55

Re: Miscellany

#1483 2022-08-26 14:36:38

Re: Miscellany

#1484 2022-08-27 14:51:16

Re: Miscellany

#1485 2022-08-28 15:01:09

Re: Miscellany

#1486 2022-08-29 14:28:56

Re: Miscellany

#1487 2022-08-30 14:31:34

Re: Miscellany

#1488 2022-08-31 14:26:16

Re: Miscellany

#1489 2022-09-01 14:26:40

Re: Miscellany

#1490 2022-09-02 14:29:26

Re: Miscellany

#1491 2022-09-03 14:25:29

Re: Miscellany

#1492 2022-09-04 14:37:11

Re: Miscellany

#1493 2022-09-05 13:57:33

Re: Miscellany

#1494 2022-09-06 14:10:33

Re: Miscellany

#1495 2022-09-07 14:21:27

Re: Miscellany

#1496 2022-09-08 14:42:31

Re: Miscellany

#1497 2022-09-09 14:33:22

Re: Miscellany

#1498 2022-09-10 13:52:43

Re: Miscellany

#1499 2022-09-11 14:08:10

Re: Miscellany

#1500 2022-09-12 14:17:43

Re: Miscellany

Board footer