You are not logged in.
2401) Metalloid
Gist
What are Metalloids? Metalloids can be defined as chemical elements whose physical and chemical properties fall in between the metal and non-metal categories. Boron, germanium, silicon, antimony, As, tellurium and pollanium are the seven most widely recognized metalloids.
Summary
A metalloid, in chemistry, an imprecise term used to describe a chemical element that forms a simple substance having properties intermediate between those of a typical metal and a typical nonmetal. The term is normally applied to a group of between six and nine elements (boron, silicon, germanium, As, antimony, tellurium, and possibly bismuth, polonium, astatine) found near the center of the P-block or main block of the periodic table. There is no single property which can be used to unambiguously identify an element as a metalloid. Since most metalloids tend to display semiconducting properties in at least one of their allomorphic modifications, the class might reasonably be extended to also include gray silicon (which, unlike white silicon, is a semiconductor rather than a metal) and the graphite form of carbon (which, unlike the diamond form, is a semimetal rather than an insulator). Chemically, metalloids correspond to atoms having intermediate electronegativities and an ability to display a range of both positive and negative oxidation states in their compounds.
Details
A metalloid is a chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. The word metalloid comes from the Latin metallum ("metal") and the Greek oeides ("resembling in form or appearance"). There is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature.
The six commonly recognised metalloids are boron, silicon, germanium, As, antimony and tellurium. Five elements are less frequently so classified: carbon, aluminium, selenium, polonium and astatine. On a standard periodic table, all eleven elements are in a diagonal region of the p-block extending from boron at the upper left to astatine at lower right. Some periodic tables include a dividing line between metals and nonmetals, and the metalloids may be found close to this line.
Typical metalloids have a metallic appearance, may be brittle and are only fair conductors of electricity. They can form alloys with metals, and many of their other physical properties and chemical properties are intermediate between those of metallic and nonmetallic elements. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.
The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate or hybrid properties, became widespread in 1940–1960. Metalloids are sometimes called semimetals, a practice that has been discouraged,[2] as the term semimetal has a more common usage as a specific kind of electronic band structure of a substance. In this context, only As and antimony are semimetals, and commonly recognised as metalloids.
Definitions:
Judgment-based
A metalloid is an element that possesses a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals, and which is therefore hard to classify as either a metal or a nonmetal. This is a generic definition that draws on metalloid attributes consistently cited in the literature. Difficulty of categorisation is a key attribute. Most elements have a mixture of metallic and nonmetallic properties, and can be classified according to which set of properties is more pronounced. Only the elements at or near the margins, lacking a sufficiently clear preponderance of either metallic or nonmetallic properties, are classified as metalloids.
Boron, silicon, germanium, As, antimony, and tellurium are commonly recognised as metalloids. Depending on the author, one or more from selenium, polonium, or astatine are sometimes added to the list. Boron sometimes is excluded, by itself, or with silicon. Sometimes tellurium is not regarded as a metalloid. The inclusion of antimony, polonium, and astatine as metalloids has been questioned.
Other elements are occasionally classified as metalloids. These elements include hydrogen, beryllium, nitrogen, phosphorus, sulfur, zinc, gallium, tin, iodine, lead, bismuth, and radon. The term metalloid has also been used for elements that exhibit metallic lustre and electrical conductivity, and that are amphoteric, such as As, antimony, vanadium, chromium, molybdenum, tungsten, tin, lead, and aluminium. The p-block metals,[33] and nonmetals (such as carbon or nitrogen) that can form alloys with metals or modify their properties have also occasionally been considered as metalloids.
Criteria-based
The elements commonly recognised as metalloids, and their ionization energies (IE); electronegativities (EN, revised Pauling scale); and electronic band structures (most thermodynamically stable forms under ambient conditions).
No widely accepted definition of a metalloid exists, nor any division of the periodic table into metals, metalloids, and nonmetals; Hawkes questioned the feasibility of establishing a specific definition, noting that anomalies can be found in several attempted constructs. Classifying an element as a metalloid has been described by Sharp[40] as "arbitrary".
The number and identities of metalloids depend on what classification criteria are used. Emsley recognised four metalloids (germanium, As, antimony, and tellurium); James et al. listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, moscovium, and livermorium). On average, seven elements are included in such lists; individual classification arrangements tend to share common ground and vary in the ill-defined margins.
A single quantitative criterion such as electronegativity is commonly used,[46] metalloids having electronegativity values from 1.8 or 1.9 to 2.2. Further examples include packing efficiency (the fraction of volume in a crystal structure occupied by atoms) and the Goldhammer–Herzfeld criterion ratio. The commonly recognised metalloids have packing efficiencies of between 34% and 41%. The Goldhammer–Herzfeld ratio, roughly equal to the cube of the atomic radius divided by the molar volume, is a simple measure of how metallic an element is, the recognised metalloids having ratios from around 0.85 to 1.1 and averaging 1.0. Other authors have relied on, for example, atomic conductance or bulk coordination number.
Jones, writing on the role of classification in science, observed that "[classes] are usually defined by more than two attributes". Masterton and Slowinski used three criteria to describe the six elements commonly recognised as metalloids: metalloids have ionization energies around 200 kcal/mol (837 kJ/mol) and electronegativity values close to 2.0. They also said that metalloids are typically semiconductors, though antimony and As (semimetals from a physics perspective) have electrical conductivities approaching those of metals. Selenium and polonium are suspected as not in this scheme, while astatine's status is uncertain.
In this context, Vernon proposed that a metalloid is a chemical element that, in its standard state, has (a) the electronic band structure of a semiconductor or a semimetal; and (b) an intermediate first ionization potential "(say 750−1,000 kJ/mol)"; and (c) an intermediate electronegativity (1.9–2.2).
Additional Information
The four major properties of metalloids are as follows:
- They are solids
- They have a metallic luster
- They are brittle
- They are semiconductors
What types of properties do metalloids display?
Metalloid element properties include a mixture of properties of both metals and nonmetals. While some characteristics (such as their metallic luster) are similar to metals, others (such as their brittleness) are similar to nonmetals.
Where are the metalloids on the periodic table?
The metalloids are located along a slanted line between the metal elements and nonmetal elements of the periodic table. They span from Group 13 to Group 16, 17, or 18 based on what criteria of classifying metalloid elements is being used.
How many metalloids are on the periodic table?
There are six elements generally accepted to be metalloids. However, based on the classification criteria being used, the exact number may vary, ranging from six to nine elements.
To summarize:
Metalloid is derived from the Latin metallum (“metal”) and the Greek oeides (“resembling in form or appearance”). A metalloid represents a chemical element exhibiting properties that are intermediate between those of metals and nonmetals. Or we can say they are a mixture of metals and nonmetals. Elements classified as metalloids are frequently highlighted in what is known as the “Metalloid Stair Step” because when colored differently from the other elements, this group of elements resembles a staircase.
The six most often recognized examples of metalloids cover boron, silicon, germanium, As, antiimony, and tellurium. And there are five elements, such as carbon, aluminum, selenium, polonium, and astatine are seldom categorized into metalloids. All eleven elements can be found on the standard periodic table. They are located in a diagonal region of the p-block ranging from boron at the upper left to astatine at the lower right. On some periodic tables, metalloids can be found near the dividing line between metals and nonmetals.
Metalloids have a metallic look, yet they are brittle and only electrical conductors with a level of intermediate to good. Chemically, they mainly act like nonmetals. They can combine with metals to make alloys. The majority of their other chemical and physical properties tend to be intermediate. Metalloids are often too brittle to be used in structural applications. However, metalloids and their compounds are always employed in alloys, biological agents, catalysts, flame retardants, glasses, optical storage, optoelectronics, pyrotechnics, semiconductors, and electronics.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2402) Nonmetal
Gist
The 17 nonmetal elements are: hydrogen, helium, carbon, nitrogen, oxygen, fluorine, neon, phosphorus, sulfur, chlorine, argon, selenium, bromine, krypton, iodine, xenon, and radon.
Summary:
What is an example of a nonmetal element?
An example of a nonmetal element is helium. Helium is a noble gas which possesses very nonmetallic characteristics such as high electronegativity and high ionization energy. However, helium is exceptionally nonreactive and is not found in compounds like most metals are found in. Helium is also a gas at room temperature.
What is a nonmetal definition?
The definition of nonmetals is a classification of elements that possess particular chemical and physical properties such as the following:
* High electronegativity.
* High ionization energy.
* Poor conductor of electricity and heat.
* Relatively low boiling point.
* Matte, nonmetallic appearance, and usually brittle as a solid.
What are the nonmetals on the periodic table?
Nonmetals are typically found toward the top right of the periodic table of elements. This excludes hydrogen, which is all the way in the top left of the periodic table. Nonmetals exhibit nonmetallic characteristics and are poor conductors of heat and electricity, and typically have high ionization energy and electronegativity. Nonmetals include the following elements:
Hydrogen
Helium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Silicon
Phosphorous
Sulfur
Chlorine
Argon
Germanium
As
Selenium
Bromine
Krypton
Antimony
Tellurium
Iodine
Xenon
Radon.
Details
In the context of the periodic table a nonmetal is a chemical element that mostly lacks distinctive metallic properties. They range from colorless gases like hydrogen to shiny crystals like iodine. Physically, they are usually lighter (less dense) than elements that form metals and are often poor conductors of heat and electricity. Chemically, nonmetals have relatively high electronegativity or usually attract electrons in a chemical bond with another element, and their oxides tend to be acidic.
Seventeen elements are widely recognized as nonmetals. Additionally, some or all of six borderline elements (metalloids) are sometimes counted as nonmetals.
The two lightest nonmetals, hydrogen and helium, together make up about 98% of the mass of the observable universe. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—make up the bulk of Earth's atmosphere, biosphere, crust and oceans.
Industrial uses of nonmetals include in electronics, energy storage, agriculture, and chemical production.
Most nonmetallic elements were identified in the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, a basic classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then about twenty properties have been suggested as criteria for distinguishing nonmetals from metals.
Definition and applicable elements
Nonmetallic chemical elements are often described as lacking properties common to metals, namely shininess, pliability, good thermal and electrical conductivity, and a general capacity to form basic oxides. There is no widely accepted precise definition; any list of nonmetals is open to debate and revision. The elements included depend on the properties regarded as most representative of nonmetallic or metallic character.
Fourteen elements are almost always recognized as nonmetals:
Hydrogen
Nitrogen
Oxygen
Sulfur
Fluorine
Chlorine
Bromine
Iodine
Helium
Neon
Argon
Krypton
Xenon
Radon
Three more are commonly classed as nonmetals, but some sources list them as "metalloids", a term which refers to elements regarded as intermediate between metals and nonmetals:
Carbon
Phosphorus
Selenium
One or more of the six elements most commonly recognized as metalloids are sometimes instead counted as nonmetals:
Boron
Silicon
Germanium
As
Antimony
Tellurium
About 15–20% of the 118 known elements are thus classified as nonmetals.
Additional Information
A nonmetal, in physics, is a substance having a finite activation energy (band gap) for electron conduction. This means that nonmetals display low (insulators) to moderate (semiconductors) bulk electrical conductivities, which increase with increasing temperature, and are subject to dielectric breakdown at high voltages and temperatures. Like metals, nonmetals may occur in the solid, liquid, or gaseous state. However, unlike metals, nonmetals display a wide range of both mechanical and optical properties, ranging from brittle to plastic and from transparent to opaque.
From a chemical point of view, nonmetals may be divided into two classes: 1) covalent materials, which contain atoms having small sizes, high electronegativities, low valence vacancy to electron ratios, and a pronounced tendency to form negative ions in chemical reactions and negative oxidation states in their compounds; 2) ionic materials, which contain both small and large atoms. Ions may be formed by adding electrons to (small, electronegative atoms) or by extracting electrons from (large, electropositive) atoms. In ionic materials, nonmetals exist either as monatomic anions (e. g., F-in NaF) or as constituents of polyatomic anions (e.g., N and O in the NO3-`s in NaNO3). When in the form of simple elemental substances, about 25 or 22% of the known elements form nonmetals at normal temperatures and pressures, including all of the elements in the S-block of the periodic table and approximately 58% of those in the P-block.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2303) Water wheel
Gist
A waterwheel is also called a turbine. Water-powered grist mill in Tennessee. Three types of waterwheels are tha horizontal waterwheel, overshot vertical waterwheel, and undershot vertical waterwheel. In the horizontal waterwheel, water flows from an aqueduct or pipe from the side of the wheel and onto the wheel.
A waterwheel is a mechanical device for tapping the energy of running or falling water by means of a set of paddles mounted around a wheel. The force of the moving water is exerted against the paddles, and the consequent rotation of the wheel is transmitted to machinery via the shaft of the wheel.
Summary
A waterwheel, is a mechanical device for tapping the energy of running or falling water by means of a set of paddles mounted around a wheel. The force of the moving water is exerted against the paddles, and the consequent rotation of the wheel is transmitted to machinery via the shaft of the wheel. The waterwheel was perhaps the earliest source of mechanical energy to replace that of humans and animals, and it was first exploited for such tasks as raising water, fulling cloth, and grinding grain.
A brief treatment of waterwheels follows.
The combination of waterwheel and transmission linkage, often including gearing, was from the Middle Ages usually designated a mill. Of the three distinct types of water mills, the simplest and probably the earliest was a vertical wheel with paddles on which the force of the stream acted. Next was the horizontal wheel used for driving a millstone through a vertical shaft attached directly to the wheel. Third was the geared mill driven by a vertical waterwheel with a horizontal shaft. This required more knowledge and engineering skill than the first two, but it had much greater potential. Vertical waterwheels were also distinguished by the location of water contact with the wheel: first, the undershot wheel; second, the breast wheel; and third, the overshot wheel. These waterwheels generally used the energy of moving streams, but tidal mills also appeared in the 11th century.
Each type of mill had its particular advantages and disadvantages. Relatively little is known of their development before the Middle Ages, but certain of their characteristics suggest an order of appearance within the context of the complexity of construction and the possibilities for utilization.
The simple vertical wheel required little extra structure, but the force and rate of power takeoff were dependent upon stream characteristics and wheel diameter. Since change of power direction was not involved, this wheel proved most useful in raising water, utilizing, for instance, a string of pots worked by a chain drive.
The horizontal-wheel mill (sometimes called a Norse or Greek mill) also required little auxiliary construction, but it was suited for grinding because the upper millstone was fixed upon the vertical shaft. The mill, however, could only be used where the current flow was suitable for grinding.
The geared vertical-wheel mill was more versatile. Construction was relatively simple if the wheel was of the undershot kind, because the wheel paddles could be simply dipped in the stream flow, whether it was river, tide, or man-built millrace. A millwright could choose his gear ratio to match power utilization with rate of stream flow, and the wheel could be mounted in a bridge arch or on a barge anchored in midstream. Vitruvius described the first geared vertical wheel for which we have good evidence. This mill is also of major significance because it was the first application of gearing to utilize other than muscle power. This mill had an undershot wheel and, unlike the breast or overshot wheels, did not make use of the weight of falling water.
Mills with geared breast and overshot wheels required more auxiliary construction, but they allowed the most generalized exploitation of available water power. A major construction problem was locating a mill where the fall of water would be suited to the desired diameter of the wheel. Either a long millrace from upstream or a dam could be used.
Little is known of the details of geared-mill development between the time of Vitruvius and the 12th century. An outstanding installation was the grain mill at Barbegal, near Arles, France, which had 16 cascaded overshot wheels, each 7 feet (2 metres) in diameter, with wooden gearing. It is estimated that this mill could meet the needs of a population of 80,000.
Even though the highly adaptable, geared mill, with its widely diversified stream-flow conditions, was used in the Roman Empire, historical evidence suggests that its most dramatic industrial consequences occurred during the Middle Ages in Western Europe. After the 13th century the overshot waterwheel appears to have become more common than the undershot wheel.
The geared mill of the Middle Ages was actually a general mechanism for the utilization of power. The power from a horse- or cattle-powered mill was small compared to that from overshot water-wheels, which usually generated two to five horsepower.
Details
A water wheel is a machine for converting the kinetic energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a large wheel (usually constructed from wood or metal), with numerous blades or buckets attached to the outer rim forming the drive mechanism. Water wheels were still in commercial use well into the 20th century, although they are no longer in common use today. Water wheels are used for milling flour in gristmills, grinding wood into pulp for papermaking, hammering wrought iron, machining, ore crushing and pounding fibre for use in the manufacture of cloth.
Some water wheels are fed by water from a mill pond, which is formed when a flowing stream is dammed. A channel for the water flowing to or from a water wheel is called a mill race. The race bringing water from the mill pond to the water wheel is a headrace; the one carrying water after it has left the wheel is commonly referred to as a tailrace.
Waterwheels were used for various purposes from things such as agriculture to metallurgy in ancient civilizations spanning the Hellenistic Greek world, Rome, China and India. Waterwheels saw continued use in the post-classical age, like in medieval Europe and the Islamic Golden Age, but also elsewhere. In the mid- to late 18th century John Smeaton's scientific investigation of the water wheel led to significant increases in efficiency, supplying much-needed power for the Industrial Revolution. [ Water wheels began being displaced by the smaller, less expensive and more efficient turbine, developed by Benoît Fourneyron, beginning with his first model in 1827. Turbines are capable of handling high heads, or elevations, that exceed the capability of practical-sized waterwheels.
The main difficulty of water wheels is their dependence on flowing water, which limits where they can be located. Modern hydroelectric dams can be viewed as the descendants of the water wheel, as they too take advantage of the movement of water downhill.
Types
Water wheels come in two basic designs:
* a horizontal wheel with a vertical axle; or
* a vertical wheel with a horizontal axle.
The latter can be subdivided according to where the water hits the wheel into backshot (pitch-back), overshot, breastshot, undershot, and stream-wheels. The term undershot can refer to any wheel where the water passes under the wheel[9] but it usually implies that the water entry is low on the wheel.
Overshot and backshot water wheels are typically used where the available height difference is more than a couple of meters. Breastshot wheels are more suited to large flows with a moderate head. Undershot and stream wheel use large flows at little or no head.
There is often an associated millpond, a reservoir for storing water and hence energy until it is needed. Larger heads store more gravitational potential energy for the same amount of water so the reservoirs for overshot and backshot wheels tend to be smaller than for breast shot wheels.
Overshot and pitchback water wheels are suitable where there is a small stream with a height difference of more than 2 metres (6.5 ft), often in association with a small reservoir. Breastshot and undershot wheels can be used on rivers or high volume flows with large reservoirs.
Additional Information
Water wheels are found next to areas of moving water such as rivers or canals. They harness the moving water to generate power or electricity; this can be called hydro-power.
There are three different types of water wheel that you could see, this includes:
* overshot
* undershot
* breastshot.
The main difference between the three types is where the water hits the paddles attached to the wheel - either from above, below or the middle.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2304) Amalgam
Gist
An amalgam is an alloy, or a mixture, of mercury with one or more other metals, often used in dentistry for fillings and in gold extraction.
Summary
An amalgam is an alloy of mercury and one or more other metals. Amalgams are crystalline in structure, except for those with a high mercury content, which are liquid. Known since early times, they were mentioned by Pliny the Elder in the 1st century ad. In dentistry, an amalgam of silver and tin, with minor amounts of copper and zinc, is used to fill teeth.
A sodium amalgam is formed during the manufacture of chlorine and sodium hydroxide by the electrolysis of brine in cells wherein a stream of mercury constitutes the negative electrode. Reaction of the amalgam with water produces a solution of sodium hydroxide and regenerates the mercury for reuse.
Fine particles of silver and gold can be recovered by agitating their ores with mercury and allowing the resultant pasty or liquid amalgam to settle. By distillation of the amalgam, the mercury is reclaimed, and the precious metals are isolated as a residue.
Amalgams of silver, gold, and palladium are known in nature. Moschellandsbergite, silver amalgam, is found at Moschellandsberg, Ger.; Sala, Swed.; and Isère, France. Gold amalgam occurs in California, U.S., Colombia, and Borneo.
Details
An amalgam is an alloy of mercury with another metal. It may be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum. Gold-mercury amalgam is used in the extraction of gold from ore, and dental amalgams are made with metals such as silver, copper, indium, tin and zinc.
Important amalgams:
Zinc amalgam
Zinc amalgam finds use in organic synthesis (e.g., for the Clemmensen reduction). It is the reducing agent in the Jones reductor, used in analytical chemistry. Formerly the zinc plates of dry batteries were amalgamated with a small amount of mercury to prevent deterioration in storage. It is a binary solution (liquid-solid) of mercury and zinc.
Potassium amalgam
For the alkali metals, amalgamation is exothermic, and distinct chemical forms can be identified, such as KHg and KHg2. KHg is a gold-coloured compound with a melting point of 178 °C, and KHg2 a silver-coloured compound with a melting point of 278 °C. These amalgams are very sensitive to air and water, but can be worked with under dry nitrogen. The Hg-Hg distance is around 300 picometres, Hg-K around 358 pm.
Phases K5Hg7 and KHg11 are also known; rubidium, strontium and barium undecamercurides are known and isostructural. Sodium amalgam (NaHg2) has a different structure, with the mercury atoms forming hexagonal layers, and the sodium atoms a linear chain which fits into the holes in the hexagonal layers, but the potassium atom is too large for this structure to work in KHg2.
Sodium amalgam
Sodium amalgam is produced as a byproduct of the chloralkali process and used as an important reducing agent in organic and inorganic chemistry. With water, it decomposes into concentrated sodium hydroxide solution, hydrogen and mercury, which can then return to the chloralkali process anew. If absolutely water-free alcohol is used instead of water, an alkoxide of sodium is produced instead of the alkali solution.
Aluminium amalgam
Aluminium can form an amalgam through a reaction with mercury. Aluminium amalgam may be prepared by either grinding aluminium pellets or wire in mercury, or by allowing aluminium wire or foil to react with a solution of mercuric chloride. This amalgam is used as a reagent to reduce compounds, such as the reduction of imines to amines. The aluminium is the ultimate electron donor, and the mercury serves to mediate the electron transfer.[5] The reaction itself and the waste from it contain mercury, so special safety precautions and disposal methods are needed. As an environmentally friendlier alternative, hydrides or other reducing agents can often be used to accomplish the same synthetic result. Another environmentally friendly alternative is an alloy of aluminium and gallium which similarly renders the aluminium more reactive by preventing it from forming an oxide layer.
Tin amalgam
Tin amalgam was used in the middle of the 19th century as a reflective mirror coating.
Other amalgams
A variety of amalgams are known that are of interest mainly in the research context.
Ammonium amalgam is a grey, soft, spongy mass discovered in 1808 by Humphry Davy and Jöns Jakob Berzelius. It decomposes readily at room temperature or in contact with water or alcohol.
* Thallium amalgam has a freezing point of −58 °C, which is lower than that of pure mercury (−38.8 °C) so it has found a use in low temperature thermometers.
* Gold amalgam: Refined gold, when finely ground and brought into contact with mercury where the surfaces of both metals are clean, amalgamates readily and quickly forms alloys ranging from AuHg2 to Au8Hg.
* Lead forms an amalgam when filings are mixed with mercury[citation needed] and is also listed as a naturally occurring alloy called leadamalgam in the Nickel–Strunz classification.
Dental amalgam
Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc. Amalgam is an "excellent and versatile restorative material" and is used in dentistry because it is inexpensive and relatively easy to use and manipulate during placement. It remains soft for a short time so it can be packed to fill any irregular volume, and then forms a hard compound. Amalgam possesses greater longevity when compared to other direct restorative materials, such as composite. However, this difference has decreased with continual development of composite resins.
Amalgam is typically compared to resin-based composites because many applications are similar and many physical properties and costs are comparable.
Dental amalgam has been studied and is generally considered to be safe for humans, though the validity of some studies and their conclusions have been questioned.
In July 2018 the EU, in consideration of the persistent pollution and environmental toxicity of amalgam's mercury, prohibited amalgam for dental treatment of children under 15 years and of pregnant or breastfeeding women.
Use in mining
Mercury has been used in gold and silver mining because of the convenience and the ease with which mercury and the precious metals will amalgamate. In gold placer mining, in which minute specks of gold are washed from sand or gravel deposits, mercury was often used to separate the gold from other heavy minerals.
After all of the practical metal had been taken out from the ore, the mercury was dispensed down a long copper trough, which formed a thin coating of mercury on the exterior. The waste ore was then transferred down the trough, and gold in the waste amalgamated with the mercury. This coating would then be scraped off and refined by evaporation to get rid of the mercury, leaving behind somewhat high-purity gold.
Mercury amalgamation was first used on silver ores with the development of the patio process in Mexico in 1557. There were also additional amalgamation processes that were created for processing silver ores, including pan amalgamation and the Washoe process.
Gold amalgam:
Gold extraction (mining)
Gold amalgam has proved effective where gold fines ("flour gold") would not be extractable from ore using hydro-mechanical methods. Large amounts of mercury were used in placer mining, where deposits composed largely of decomposed granite slurry were separated in long runs of "riffle boxes", with mercury dumped in at the head of the run. The amalgam formed is a heavy dull gray solid mass. The use of mercury in 19th century placer mining in California, now prohibited, has caused extensive pollution problems in riverine and estuarine environments, ongoing to this day. Sometimes substantial slugs of amalgam are found in downstream river and creek bottoms by amateur wet-suited miners seeking gold nuggets with the aid of an engine-powered water vacuum/dredge mounted on a float.
Gold extraction (ore processing)
Where stamp mills were used to crush gold-bearing ore to fines, a part of the extraction process involved the use of mercury-wetted copper plates, over which the crushed fines were washed. A periodic scraping and re-mercurizing of the plate resulted in amalgam for further processing.
Gold extraction (retorting)
Amalgam obtained by either process was then heated in a distillation retort, recovering the mercury for reuse and leaving behind the gold. As this released mercury vapors to the atmosphere, the process could induce adverse health effects and long term pollution.
Today, mercury amalgamation has been replaced by other methods to recuperate gold and silver from ore in developed nations. Hazards of mercurial toxic waste have played a major role in the phasing out of the mercury amalgamation processes. Mercury amalgamation is still regularly used by small-scale gold placer miners (often illegally), particularly in developing countries.
Amalgam probe
Mercury salts are, compared to mercury metal and amalgams, highly toxic due to their solubility in water. The presence of these salts in water can be detected with a probe that uses the readiness of mercury ions to form an amalgam with copper. A nitric acid solution of salts under investigation is applied to a piece of copper foil, and any mercury ions present will leave spots of silvery-coloured amalgam. Silver ions leave similar spots but are easily washed away, making this a means of distinguishing silver from mercury.
Additional Information
Dental amalgam, often referred to as “silver fillings,” has been a dentistry staple for over a century. These iconic silvery-gray restorations have filled cavities, restored damaged teeth, and saved countless smiles. However, dental amalgam has also faced its share of controversies and debates. In this article, we’ll explore the history, composition, benefits, concerns, and alternatives of dental amalgam to provide a comprehensive view of this commonly used dental material.
A Brief History
Dental amalgam’s history can be traced back to the early 19th century when the amalgamation of metals was a well-known concept. In 1819, the French chemist Louis Nicolas Vauquelin introduced the use of silver amalgam in dentistry. The basic idea was to mix powdered silver with mercury, creating a malleable and durable filling material. This revolutionary development allowed dentists to restore teeth with a more reliable and long-lasting solution compared to earlier methods like using tin and gold.
Composition of Dental Amalgam
Traditional dental amalgam is composed of a mixture of several metals, with the primary components being:
* Silver: Silver provides durability and strength to the amalgam filling.
* Tin: Tin aids in amalgam alloy formation and increases its workability.
* Copper: Copper improves resistance to corrosion and tarnishing.
* Mercury: Mercury serves as the binder, allowing the mixture to become pliable for filling cavities.
The Dental Restoration Process
Dental amalgam is renowned for its ease of use and durability. The process of placing a dental amalgam filling typically involves the following steps:
Preparation: The dentist removes decayed or damaged tooth structure, creating a clean cavity to be filled.
Mixing: The amalgam alloy is mixed with mercury, forming a soft, pliable material.
Filling: The mixed amalgam is carefully placed into the prepared cavity and shaped to match the natural contours of the tooth.
Hardening: Over time, the amalgam hardens and becomes a solid, long-lasting filling.
Benefits of Dental Amalgam
Dental amalgam has several advantages that have contributed to its continued use in dentistry:
Durability: Dental amalgam is exceptionally durable and can withstand the forces of biting and chewing over many years.
Cost-Effectiveness: Amalgam fillings are often more affordable than alternative materials, making them accessible to a broader range of patients.
Quick Placement: The placement of dental amalgam fillings is relatively quick and straightforward, making it a convenient option for both patients and dentists.
Versatility: Amalgam can be used in various dental situations, from small cavities to larger restorations.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2305) Islets of Langerhans
Gist
Islets of Langerhans are clusters of endocrine cells within the pancreas responsible for producing and releasing hormones, primarily insulin and glucagon, which regulate blood sugar levels.
A pancreatic cell that produces hormones (e.g., insulin and glucagon) that are secreted into the bloodstream. These hormones help control the level of glucose (sugar) in the blood. Also called endocrine pancreas cell and islet cell.
Summary
Islets of Langerhans are irregularly shaped patches of endocrine tissue located within the pancreas of most vertebrates. They are named for the German physician Paul Langerhans, who first described them in 1869. The normal human pancreas contains about 1 million islets. The islets consist of four major and two minor cell types, of which the major types (alpha, beta, delta, and pancreatic polypeptide [PP] cells) produce important hormones. The two minor types (D1 and enterochromaffin cells) produce hormones and synthesize serotonin, respectively.
The islets of Langerhans contain alpha, beta, and delta cells that produce glucagon, insulin, and somatostatin, respectively. A fourth type of islet cell, the PP (or F) cell, is located at the periphery of the islets and secretes pancreatic polypeptide. These hormones regulate one another's secretion through paracrine cell-cell interactions.
The most common islet cell, the beta cell, produces insulin, the major hormone in the regulation of carbohydrate, fat, and protein metabolism. Insulin is crucial in several metabolic processes: it promotes the uptake and metabolism of glucose by the body’s cells; it prevents release of glucose by the liver; it causes muscle cells to take up amino acids, the basic components of protein; and it inhibits the breakdown and release of fats. The release of insulin from the beta cells can be triggered by growth hormone (somatotropin) or by glucagon, but the most important stimulator of insulin release is glucose; when the blood glucose level increases—as it does after a meal—insulin is released to counter it. The inability of the islet cells to make insulin or the failure to produce amounts sufficient to control blood glucose level are the causes of diabetes mellitus.
The alpha cells of the islets of Langerhans produce an opposing hormone, glucagon, which releases glucose from the liver and fatty acids from fat tissue. In turn, glucose and free fatty acids favor insulin release and inhibit glucagon release. The delta cells produce somatostatin, a strong inhibitor of somatotropin, insulin, and glucagon; its role in metabolic regulation is not yet clear. Somatostatin is also produced by the hypothalamus and functions there to inhibit secretion of growth hormone by the pituitary gland.
The D1 cell, the first of the two minor and rarer cell types, produces a hormone called vasoactive intestinal polypeptide (VIP). VIPs are responsible for increasing blood glucose levels and releasing gastrointestinal fluids that help with digestion. Enterochromaffin cells, the second minor cell type, synthesize serotonin. Serotonin works in synergy with the other hormones released in islets to help with intestinal mobility. However, enterochromaffin cells are known to cause carcinoid syndrome, a rare condition caused by excess production of serotonin.
Details
The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of the pancreas volume and receive 10–15% of its blood flow. The pancreatic islets are arranged in density routes throughout the human pancreas, and are important in the metabolism of glucose.
Structure
There are about 1 million islets distributed throughout the pancreas of a healthy adult human. While islets vary in size, the average diameter is about 0.2 mm. Each islet is separated from the surrounding pancreatic tissue by a thin, fibrous, connective tissue capsule which is continuous with the fibrous connective tissue that is interwoven throughout the rest of the pancreas.
Microanatomy
Hormones produced in the pancreatic islets are secreted directly into the blood flow by (at least) five types of cells. In rat islets, endocrine cell types are distributed as follows:
* Alpha cells producing glucagon (20% of total islet cells)
* Beta cells producing insulin and amylin (≈70%)
* PP cells (gamma cells or F cells) producing pancreatic polypeptide (<5%)
* Delta cells producing somatostatin (<10%)
* Epsilon cells producing ghrelin (<1%)
It has been recognized that the cytoarchitecture of pancreatic islets differs between species. In particular, while rodent islets are characterized by a predominant proportion of insulin-producing beta cells in the core of the cluster and by scarce alpha, delta and PP cells in the periphery, human islets display alpha and beta cells in close relationship with each other throughout the cluster.
The proportion of beta cells in islets varies depending on the species, in humans it is about 40–50%. In addition to endocrine cells, there are stromal cells (fibroblasts), vascular cells (endothelial cells, pericytes), immune cells (granulocytes, lymphocytes, macrophages, dendritic cells,) and neural cells.
A large amount of blood flows through the islets, 5–6 mL/min per 1 g of islet. It is up to 15 times more than in exocrine tissue of the pancreas.
Islets can influence each other through paracrine and autocrine communication, and beta cells are coupled electrically to six to seven other beta cells, but not to other cell types. Pancreatic islets are characterized by rich innervation and vascularization, although there are notable differences between rodent and human islets. Research indicates that the vascular density in human islets is about five times lower than in rodent islets. The vascular network within the islets resembles a glomeruli-like structure, consisting of highly fenestrated endothelial cells positioned closely to each endocrine cell. Consequently, the oxygen tension within pancreatic islets is significantly higher than that in the surrounding exocrine tissue.
Function
The paracrine feedback system of the pancreatic islets has the following structure:
* Glucose/Insulin: activates beta cells and inhibits alpha cells.
* Glycogen/Glucagon: activates alpha cells which activates beta cells and delta cells.
* Somatostatin: inhibits alpha cells and beta cells. Also inhibits the secretion of pancreatic polypeptide.
A large number of G protein-coupled receptors (GPCRs) regulate the secretion of insulin, glucagon, and somatostatin from pancreatic islets, and some of these GPCRs are the targets of drugs used to treat type-2 diabetes (ref GLP-1 receptor agonists, DPPIV inhibitors).
Electrical activity
Electrical activity of pancreatic islets has been studied using patch clamp techniques. It has turned out that the behavior of cells in intact islets differs significantly from the behavior of dispersed cells.
Clinical significance:
Diabetes
The beta cells of the pancreatic islets secrete insulin, and so play a significant role in diabetes. It is thought that they are destroyed by immune assaults.
Because the beta cells in the pancreatic islets are selectively destroyed by an autoimmune process in type 1 diabetes, clinicians and researchers are actively pursuing islet transplantation as a means of restoring physiological beta cell function, which would offer an alternative to a complete pancreas transplant or artificial pancreas. Islet transplantation emerged as a viable option for the treatment of insulin requiring diabetes in the early 1970s with steady progress over the following three decades. Clinical trials as of 2008 have shown that insulin independence and improved metabolic control can be reproducibly obtained after transplantation of cadaveric donor islets into patients with unstable type 1 diabetes. Alternatively, daily insulin injections are an effective treatment for type 1 diabetes patients who are not candidates for islet transplantation.
People with high body mass index (BMI) are unsuitable pancreatic donors due to greater technical complications during transplantation. However, it is possible to isolate a larger number of islets because of their larger pancreas, and therefore they are more suitable donors of islets.
Islet transplantation only involves the transfer of tissue consisting of beta cells that are necessary as a treatment of this disease. It thus represents an advantage over whole pancreas transplantation, which is more technically demanding and poses a risk of, for example, pancreatitis leading to organ loss. Another advantage is that patients do not require general anesthesia.
Islet transplantation for type 1 diabetes (as of 2008) requires potent immunosuppression to prevent host rejection of donor islets.
The islets are transplanted into a portal vein, which is then implanted in the liver. There is a risk of portal venous branch thrombosis and the low value of islet survival a few minutes after transplantation, because the vascular density at this site is after the surgery several months lower than in endogenous islets. Thus, neovascularization is key to islet survival, that is supported, for example, by VEGF produced by islets and vascular endothelial cells. However, intraportal transplantation has some other shortcomings, and so other alternative sites that would provide better microenvironment for islets implantation are being examined. Islet transplant research also focuses on islet encapsulation, CNI-free (calcineurin-inhibitor) immunosuppression, biomarkers of islet damage or islet donor shortage.
An alternative source of beta cells, such insulin-producing cells derived from adult stem cells or progenitor cells would contribute to overcoming the shortage of donor organs for transplantation. The field of regenerative medicine is rapidly evolving and offers great hope for the nearest future. However, type 1 diabetes is the result of the autoimmune destruction of beta cells in the pancreas. Therefore, an effective cure will require a sequential, integrated approach that combines adequate and safe immune interventions with beta cell regenerative approaches. It has also been demonstrated that alpha cells can spontaneously switch fate and transdifferentiate into beta cells in both healthy and diabetic human and mouse pancreatic islets, a possible future source for beta cell regeneration. In fact, it has been found that islet morphology and endocrine differentiation are directly related. Endocrine progenitor cells differentiate by migrating in cohesion and forming bud-like islet precursors, or "peninsulas", in which alpha cells constitute the peninsular outer layer and beta cells form later beneath them. Cryopreservation has shown promise to improve the supply chain of pancreatic islets for better transplantation outcomes.
Research
Cannabinoid receptors are found widely expressed in islets of Langerhans, and several studies have investigated specific distribution and mechanisms of CB1 versus CB2 receptors in relation to pancreatic endocrine functions, where they play an important homeostatic role, as endocannabinoids modulate pancreatic β-cells function, proliferation, and survival, as well as insulin production, secretion, and resistance.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2306) Gorge
Gorge
Gist
A gorge is a narrow valley with steep, rocky walls located between hills or mountains. The term comes from the French word gorge, which means throat or neck. A gorge is often smaller than a canyon, although both words are used to describe deep, narrow valleys with a stream or river running along their bottom.
Summary
A gorge is a very deep crevice between two mountains or hills. Gorges are formed by rivers running through and eroding rock over a very long period of time.
The Latin root of gorge means "throat," leading to both the "narrow passage" meaning and the French gorgier, "to swallow," which influenced the verb version of gorge, "to overeat." You may love to gorge on ice cream, but the stomachache afterward won't be very pleasant. To remember the "canyon" meaning, think of the famous upstate New York bumper sticker, “Ithaca is gorges.” It's a play on gorgeous, meaning beautiful, and the beautiful ravines in the area.
Details
A gorge is a narrow valley with steep, rocky walls located between hills or mountains. The term comes from the French word gorge, which means throat or neck. A gorge is often smaller than a canyon, although both words are used to describe deep, narrow valleys with a stream or river running along their bottom.
A number of natural forces form gorges. The most common is erosion due to streams or rivers. Streams carve through hard layers of rock, breaking down or eroding it. Sediment from the worn-away rock is then carried downstream. Over time, this erosion will form the steep walls of a gorge. The flooding of streams or rivers increases the speed and intensity of this erosion, creating deeper and wider gorges. The deep Talari Gorges in Mali, for instance, were formed by the Senegal River that flows into the Atlantic Ocean on the western coast of Africa.
Geologic uplift also forms gorges. Geologic uplift is the upward movement of the Earth's surface. Geologic uplift is often associated with earthquakes and orogeny, the process of creating mountains. During geologic uplift, rock layers beneath Earth's surface bump against the surface layers. Softer layers of surface rock erode.
Erosion and geologic uplift often work together to create gorges. Parts of streams or rivers can be elevated, along with land, during the process of geologic uplift. As rivers or streams flow across this uplifted surface, waterfalls form. Over time, the power of the waterfall erodes the softer rock layers underneath, causing the original river bed to collapse and create a gorge. Macocha Gorge in the Jihomoravsk region of the Czech Republic was probably formed by the collapse of an underground cave that had been eroded by the Punkva River.
The movement and melting of glaciers can also produce gorges. Glaciers cut deep valleys into the Earth's surface. These rivers of ice can create huge canyons and sharp, steep gorges. As glaciers melt, or retreat, these gorges and canyons are exposed. The Columbia River Gorge, located in the U.S. states of Washington and Oregon, was partially created by glacial retreat during the last Ice Age.
Engineers have purposely flooded gorges in order to create waterways and dams. These dams generate hydroelectricity, or electricity powered by water. The Three Gorges Dam on the Yangtze River in China is probably the most famous example of such a project. Upstream from the dam, the Qutang, Wu, and Xilang gorges were partially submerged in order to create a waterway. The new waterway would allow freight ships to navigate from the East China Sea, part of the Pacific Ocean, to the city of Chongqing, about 2,250 kilometers (1,400 miles) inland. The 26 turbines of the Three Gorges Dam generate approximately 18,000 megawatts of electricity for Shanghai and other cities. However, many people worry about the environmental impacts of the dam and criticize the fact that more than a million Chinese families were forced to move from their homes near the gorges in order to complete the construction.
Many geological discoveries have been made at gorges because gorges often expose layers of rock that go back thousands of years. Olduvai Gorge in Tanzania has layers dating as far back as two million years. The Olduvai Gorge is famous for the fossils and ancient tools found there by scientists Louis, Mary, and Richard Leakey. These remains of ancient animals and plants provide clues about early humans.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2307) Kairba Dam
Gist
Based on the reservoir capacity, the Kariba Dam is considered to be the largest in the world.
Summary
Kariba Dam, concrete arch dam across the Zambezi River at Kariba Gorge, on the border between Zambia and Zimbabwe. Construction of the dam began on Nov. 6, 1956, and was completed in 1959. The structure is 128 metres (420 feet) high with a crest 579 metres (1,899 feet) in length and a volume of 1,032,000 cubic metres (1,350,000 cubic yards). The dam creates Lake Kariba, and it supplies some 6,700,000,000 kilowatt-hours of electricity annually, generated by Kariba North Bank and South Bank companies (Zambia and Zimbabwe, respectively). Its creation required the resettlement of more than 30,000 Batonka tribespeople of Zambia and the evacuation of thousands of wild animals (“Operation Noah”). Some Africans initially opposed construction of the dam, seeing it as a symbol of the unpopular Federation of Rhodesia and Nyasaland, which dissolved into Rhodesia (now Zimbabwe) and Zambia in 1963. Later, however, the dam was accepted because of the inexpensive electric power it furnishes to Zambia’s prosperous copper industry.
Details
The Kariba dam is a double curvature concrete arch dam in the Kariba gorge of the Zambezi river basin between Zambia and Zimbabwe. At 128m tall and 579m long, the structure forms Lake Kariba - extending 280km and holding 185km³ of water.
An arch dam is a concrete dam that curves upstream. Arch dams are designed so that the water pressing against them compresses and strengthens the structure as it pushes into its foundations.
Arch dams are often used in narrow canyons or gorges – such as the Kariba gorge – as the steep walls of stable rock help support the structure.
The project was a joint venture between the former self-governing protectorates of Northern and Southern Rhodesia (now Zambia and Zimbabwe) and Nyasaland (now Malawi). The dam and 6 flood gates were built between 1955 and 1959, with later work adding turbine rooms to generate electricity.
Building the dam and its reservoir forced the resettlement of around 57,000 Tongan people living along the Zambezi in both Northern Rhodesia and Southern Rhodesia.
The scheme supplies 1,626MW of electricity to Zambia and Zimbabwe. Each country has its own power station – one on the north bank and one on the south bank of the dam.
The Kariba dam is jointly operated by Zambia and Zimbabwe through the Zambezi River Authority.
Difference the dam has made
The Kariba dam provides a cheap source of power for both Zambia and Zimbabwe – this has been crucial for the economies of both countries.
Construction of the dam has led to the preservation of wilderness areas in national parks along the lake shore. This has helped grow a tourist industry in the area – boosting the local economy.
Around 57,000 Tongan people were moved from their homes to make way for the dam.
How the work was done
Engineers chose a concrete arch dam for the Kariba scheme. Not only is the curving structure effective in valleys but arch dams need much less construction material. This makes them economical and practical in remote areas such as the Kariba gorge.
Early stages of work saw the project team build roads through rugged country to the north and south banks of the Zambezi river. They also constructed an airstrip and 2 towns as accommodation for the 7,000 workers on the scheme.
Cement came by rail and was then carried the final 140km to the construction site by road.
Engineers used coffer dams for initial work on the scheme. A coffer dam is an enclosure built in or across water. The enclosed area is pumped out allowing a dry environment for construction.
Concrete was transported from a manufacturing plant using ‘blondin’ cables. These were a type of aerial ropeway also used in slate quarries. Working a bit like cable cars, wagons full of concrete were attached to the ropes and the contents tipped out at the dam construction site.
At the time it was completed in 1959, Kariba had the biggest dam wall in the world. Kariba lake – the reservoir created by the scheme – was the biggest artificial lake in the world.
86 workers died during the construction of the dam.
Additional Information
The Kariba Dam is a double curvature concrete arch dam in the Kariba Gorge of the Zambezi river basin between Zambia and Zimbabwe. The dam stands 128 metres (420 ft) tall and 579 metres (1,900 ft) long. The dam forms Lake Kariba, which extends for 280 kilometres (170 mi) and holds 185 cubic kilometres (150,000,000 acre⋅ft) of water.
Construction
The dam was constructed on the orders of the Government of the Federation of Rhodesia and Nyasaland, a 'federal colony' within the British Empire. The double curvature concrete arch dam was designed by Coyne et Bellier and constructed between 1955 and 1959 by Impresit of Italy at a cost of $135,000,000 for the first stage with only the Kariba South power cavern. Final construction and the addition of the Kariba North Power cavern by Mitchell Construction was not completed until 1977, due to largely political problems, for a total cost of $480,000,000. During construction, 86 construction workers lost their lives.
The dam was officially opened by Queen Elizabeth The Queen Mother on 17 May 1960.
Power generation
The Kariba Dam supplies 2,010 megawatts (2,700,000 hp) of electricity to parts of both Zambia (the Copperbelt) and Zimbabwe and generates 6,400 gigawatt-hours (23,000 TJ) per annum. Each country has its own power station on the north and south bank of the dam, respectively. The south station belonging to Zimbabwe has been in operation since 1960 and had six generators of 125 megawatts (168,000 hp) capacity each for a total of 750 megawatts (1,010,000 hp).
On November 11, 2013 it was announced by Zimbabwe's Finance Minister, Patrick Chinamasa that capacity at the Zimbabwean (South) Kariba hydropower station would be increased by 300 megawatts. The cost of upgrading the facility has been supported by a $319m loan from China. The deal is a clear example of Zimbabwe's "Look East" policy, which was adopted after falling out with Western powers. Construction on the Kariba South expansion began in mid-2014 and was initially expected to be complete in 2019.
In March 2018, president Emmerson Mnangagwa commissioned the completed expansion of Kariba South Hydroelectric Power Station. The addition of two new 150 megawatts (200,000 hp) turbines raised capacity at this station to 1,050 megawatts (1,410,000 hp). The expansion work was done by Sinohydro, at a cost of US$533 million. Work started in 2014, and was completed in March 2018.
The north station belonging to Zambia has been in operation since 1976, and has four generators of 150 megawatts (200,000 hp) each for a total of 600 megawatts (800,000 hp); work to expand this capacity by an additional 360 megawatts (480,000 hp) to 960 megawatts (1,290,000 hp) was completed in December 2013. Two additional 180 MW generators were added.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2308) Antibiotics
Gist
Antibiotics are medicines that treat bacterial infections by killing bacteria or stopping their growth. They are not effective against viral infections like the flu or a cold.
Antibiotics are medicines that fight bacterial infections in people and animals. They work by killing the bacteria or by making it hard for the bacteria to grow and multiply. Antibiotics can be taken in different ways: Orally (by mouth).
Antibiotics are medicines that treat bacterial infections by killing bacteria or stopping their growth. They can be taken orally in the form of pills, capsules, or liquids.
The first antibiotic, penicillin, was accidentally discovered in 1928 by Alexander Fleming, a Scottish bacteriologist, who noticed that a mold inhibited bacterial growth on a petri dish.
Summary
Antibiotics work by killing bacteria and preventing them from multiplying. Common antibiotics include gentamicin, cephalexin, ertapenem, erythromycin, ciprofloxacin, and metronidazole.
They include a range of powerful drugs used to treat diseases caused by bacteria.
Antibiotics cannot treat viral infections, such as cold, flu, and most coughs.
Fast facts on antibiotics
* Alexander Fleming discovered penicillin, the first natural antibiotic, in 1928.
* Antibiotics cannot fight viral infections.
* Fleming predicted the rise of antibiotic resistance.
* Antibiotics either kill or slow the growth of bacteria.
* Side effects can include diarrhea, an upset stomach, and nausea.
What are antibiotics?
Antibiotics are powerful medications that treat certain infections and can save lives when used properly. They either stop bacteria from reproducing or destroy them.
Before bacteria can multiply and cause symptoms, the immune system can typically kill them. White blood cells (WBCs) attack harmful bacteria — even if symptoms occur, the immune system can usually cope and fend off the infection.
However, sometimes the number of harmful bacteria is excessive, and the immune system cannot clear them all. Antibiotics are useful in this scenario.
The first antibiotic was penicillin. Penicillin-based antibiotics, such as ampicillin, amoxicillin, and penicillin G, are still available to treat a variety of infections and have been in use for many years.
Several types of modern antibiotics are available, and they are usually only available with a prescription in the United States. Topical antibiotics are available in over-the-counter (OTC) creams and ointments.
How do antibiotics work?
There are different types of antibiotics, which work in their unique way. However, the two main they work include:
* A bactericidal antibiotic, such as penicillin, kills the bacteria. These drugs usually interfere with either the formation of the bacterial cell wall or its cell contents.
* A bacteriostatic stops bacteria from multiplying.
It may take a few hours or days after taking the first dose before people feel better or their symptoms improve.
Why is it important to take antibiotics when needed?
Experts advise using antibiotics only when they are needed. This is to ensure that the bacteria is killed and is unable to multiply and spread to other parts of the body.
Also, antibiotic use can sometimes be associated with side effects and antibiotic resistance.
Details
Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything.
Many mild bacterial infections get better on their own without using antibiotics.
Antibiotics do not work for viral infections such as colds and flu, and most coughs.
Antibiotics are no longer routinely used to treat:
* chest infections
* ear infections in children
* sore throats
When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future.
When antibiotics are needed
Antibiotics may be used to treat bacterial infections that:
* are unlikely to clear up without antibiotics
* could take too long to clear without treatment
* carry a risk of more serious complications
* could infect others
You may still be infectious after starting a course of antibiotics. Depending on the infection and how it's treated, it can take between 48 hours and 14 days to stop being infectious. Ask a GP or pharmacist for advice.
People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis.
How to take antibiotics
Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist.
Antibiotics can come as:
* tablets, capsules or a liquid that you drink – these can be used to treat most types of mild to moderate infections in the body
* creams, lotions, sprays and drops – these are often used to treat skin infections and eye or ear infections
* injections – these can be given as an injection or through a drip directly into the blood or muscle, and are used for more serious infections
Missing a dose of antibiotics
If you forget to take a dose of your antibiotics, check the patient information leaflet that came with your medicine to find out what to do. If you're not sure, speak to a pharmacist or a GP.
In most cases, you can take the dose you missed as soon as you remember and then continue to take your course of antibiotics as normal.
But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
Accidentally taking an extra dose
There's an increased risk of side effects if you take 2 doses closer together than recommended.
Accidentally taking 1 extra dose of your antibiotic is unlikely to cause you any serious harm.
But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick.
If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible.
Side effects of antibiotics
As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare.
The common side effects include:
* being sick
* feeling sick
* bloating and indigestion
* diarrhoea
Some people may have an allergic reaction to antibiotics, especially penicillin and another type of antibiotic called cephalosporins.
In very rare cases, this can lead to a serious allergic reaction (anaphylaxis), which is a medical emergency.
Call 999 or go to A&E now if:
* you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
* you're wheezing
* you get tightness in the chest or throat
* you have trouble breathing or talking
* your mouth, face, lips, tongue or throat start swelling
You could be having a serious allergic reaction and may need immediate treatment in hospital.
Considerations and interactions
Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding.
Tell your healthcare professional if you're pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you.
Only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member.
Some antibiotics do not mix well with other medicines, such as the contraceptive pill and alcohol.
Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP.
Read more about how antibiotics interact with other medicines.
Additional Information
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of such infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the ones which cause the common cold or influenza. Drugs which inhibit growth of viruses are termed antiviral drugs or antivirals. Antibiotics are also not effective against fungi. Drugs which inhibit growth of fungi are called antifungal drugs.
Sometimes, the term antibiotic—literally "opposing life", from the Greek roots anti, "against" and bios, "life"—is broadly used to refer to any substance used against microbes, but in the usual medical usage, antibiotics (such as penicillin) are those produced naturally (by one microorganism fighting another), whereas non-antibiotic antibacterials (such as sulfonamides and antiseptics) are fully synthetic. However, both classes have the same effect of killing or preventing the growth of microorganisms, and both are included in antimicrobial chemotherapy. "Antibacterials" include bactericides, bacteriostatics, antibacterial soaps, and chemical disinfectants, whereas antibiotics are an important class of antibacterials used more specifically in medicine and sometimes in livestock feed.
Antibiotics have been used since ancient times. Many civilizations used topical application of moldy bread, with many references to its beneficial effects arising from ancient Egypt, Nubia, China, Serbia, Greece, and Rome. The first person to directly document the use of molds to treat infections was John Parkinson (1567–1650). Antibiotics revolutionized medicine in the 20th century. Synthetic antibiotic chemotherapy as a science and development of antibacterials began in Germany with Paul Ehrlich in the late 1880s. Alexander Fleming (1881–1955) discovered modern day penicillin in 1928, the widespread use of which proved significantly beneficial during wartime. The first sulfonamide and the first systemically active antibacterial drug, Prontosil, was developed by a research team led by Gerhard Domagk in 1932 or 1933 at the Bayer Laboratories of the IG Farben conglomerate in Germany. However, the effectiveness and easy access to antibiotics have also led to their overuse and some bacteria have evolved resistance to them. Antimicrobial resistance (AMR), a naturally occurring process, is driven largely by the misuse and overuse of antimicrobials. Yet, at the same time, many people around the world do not have access to essential antimicrobials. The World Health Organization has classified AMR as a widespread "serious threat [that] is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country".[ Each year, nearly 5 million deaths are associated with AMR globally. Global deaths attributable to AMR numbered 1.27 million in 2019.
More Information
An antibiotic is a drug that fights bacteria. Antibiotics can also be called antimicrobials, but this is a broader term that includes drugs that fight bacteria or other types of microbes, such as viruses or fungi. Antibiotics do not work against viruses, such as those that cause colds and flu.
Antibiotics work in many different ways. They might kill bacteria, or merely disable them or slow down their multiplication, giving the immune system more time to clear the infection. Many antibiotics stop the bacteria from making proteins, which is essential for survival and multiplication. Others interfere with their ability to copy DNA.
Penicillin, the first antibiotic to be developed as a medicine, blocks the construction of the bacterium’s cell wall. With this important part of its structure weakened, the cell can easily rupture. Daptomycin disrupts the integrity of the cell membrane, allowing ions or small molecules to leak in and out of the cell, which can also be lethal to bacteria.
Some antibiotics, described as narrow-spectrum, are only effective against specific types of bacteria, while broad-spectrum drugs can fight a wide range.
All antibiotics will have some effect on the bacteria that normally live inside our bodies and contribute to our health, the microbiome. As a side effect, they may kill some bacteria that are good for us, and make it easier for other bacteria to take their place.
We have hundreds of antibiotics, but they fall into about 15 major classes. Many are produced naturally by certain microbes to kill others. Most were discovered between 1940 and 1960. The rate at which we have developed new ones has slowed down dramatically.
Some bacteria have evolved resistance to certain antibiotics. Antibiotic-resistant bacteria are becoming more and more common, making infections harder to treat. This problem has been made worse by the overuse of antibiotics, both in medicine and farming.
Doctors often prescribe a course of antibiotics lasting one or two weeks, and tell patients to finish the course even if they feel better. Recent research suggests that shorter courses are just as effective at killing bacteria and are less likely to fuel antibiotic resistance.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2309) Gun powder
Gist
Gunpowder is a granular mixture of: a nitrate, typically potassium nitrate (KNO3), which supplies oxygen for the reaction; charcoal, which provides carbon and other fuel for the reaction, simplified as carbon (C).
Gunpowder is any of several low-explosive mixtures used as propelling charges in guns and as blasting agents in mining. The first such explosive was black powder, which consists of a mixture of saltpetre (potassium nitrate), sulfur, and charcoal.
Summary
Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, charcoal (which is mostly carbon), and potassium nitrate (saltpeter). The sulfur and charcoal act as fuels while the saltpeter is an oxidizer. Gunpowder has been widely used as a propellant in firearms, artillery, rocketry, and pyrotechnics, including use as a blasting agent for explosives in quarrying, mining, building pipelines, tunnels, and roads.
Gunpowder is classified as a low explosive because of its relatively slow decomposition rate, low ignition temperature and consequently low brisance (breaking/shattering). Low explosives deflagrate (i.e., burn at subsonic speeds), whereas high explosives detonate, producing a supersonic shockwave. Ignition of gunpowder packed behind a projectile generates enough pressure to force the shot from the muzzle at high speed, but usually not enough force to rupture the gun barrel. It thus makes a good propellant but is less suitable for shattering rock or fortifications with its low-yield explosive power. Nonetheless, it was widely used to fill fused artillery shells (and used in mining and civil engineering projects) until the second half of the 19th century, when the first high explosives were put into use.
Gunpowder is one of the Four Great Inventions of China. Originally developed by Taoists for medicinal purposes, it was first used for warfare around AD 904. Its use in weapons has declined due to smokeless powder replacing it, whilst its relative inefficiency led to newer alternatives such as dynamite and ammonium nitrate/fuel oil replacing it in industrial applications.
Effect
Gunpowder is a low explosive: it does not detonate, but rather deflagrates (burns quickly). This is an advantage in a propellant device, where one does not desire a shock that would shatter the gun and potentially harm the operator; however, it is a drawback when an explosion is desired. In that case, the propellant (and most importantly, gases produced by its burning) must be confined. Since it contains its own oxidizer and additionally burns faster under pressure, its combustion is capable of bursting containers such as a shell, grenade, or improvised "pipe bomb" or "pressure cooker" casings to form shrapnel.
In quarrying, high explosives are generally preferred for shattering rock. However, because of its low brisance, gunpowder causes fewer fractures and results in more usable stone compared to other explosives, making it useful for blasting slate, which is fragile, or monumental stone such as granite and marble. Gunpowder is well suited for blank rounds, signal flares, burst charges, and rescue-line launches. It is also used in fireworks for lifting shells, in rockets as fuel, and in certain special effects.
Combustion converts less than half the mass of gunpowder to gas; most of it turns into particulate matter. Some of it is ejected, wasting propelling power, fouling the air, and generally being a nuisance (giving away a soldier's position, generating fog that hinders vision, etc.). Some of it ends up as a thick layer of soot inside the barrel, where it also is a nuisance for subsequent shots, and a cause of jamming an automatic weapon. Moreover, this residue is hygroscopic, and with the addition of moisture absorbed from the air forms a corrosive substance. The soot contains potassium oxide or sodium oxide that turns into potassium hydroxide, or sodium hydroxide, which corrodes wrought iron or steel gun barrels. Gunpowder arms therefore require thorough and regular cleaning to remove the residue.
Gunpowder loads can be used in modern firearms as long as they are not gas-operated. The most compatible modern guns are smoothbore-barreled shotguns that are long-recoil operated with chrome-plated essential parts such as barrels and bores. Such guns have minimal fouling and corrosion and are easier to clean.
Details
Gunpowder is any of several low-explosive mixtures used as propelling charges in guns and as blasting agents in mining.
The first such explosive was black powder, which consists of a mixture of saltpetre (potassium nitrate), sulfur, and charcoal. When prepared in roughly the correct proportions (75 percent saltpetre, 15 percent charcoal, and 10 percent sulfur), it burns rapidly when ignited and produces approximately 40 percent gaseous and 60 percent solid products, the latter mostly appearing as whitish smoke. In a confined space such as the breech of a gun, the pent-up gas can be used for propelling a missile such as a bullet or artillery shell. Black powder is relatively insensitive to shock and friction and must be ignited by flame or heat. Though it has largely been supplanted by smokeless powder as a propellant for ammunition in guns, black powder is still widely used for ignition charges, primers, fuses, and blank-fire charges in military ammunition. With varied proportions of ingredients, it is also used in fireworks, time fuses, signals, squibs, and spatting charges for practice bombs.
Black powder is thought to have originated in China, where it was being used in fireworks and signals by the 10th century. Between the 10th and 12th centuries, the Chinese developed the huo qiang (“fire lance”), a short-range proto-gun that channeled the explosive power of gunpowder through a cylinder—initially, a bamboo tube. Upon ignition, projectiles such as arrows or bits of metal would be forcefully ejected, along with an impressive gout of flame. By the late 13th century the Chinese were employing true guns, made of cast brass or iron. Guns began to appear in the West by 1304, when the Arabs produced a bamboo tube reinforced with iron that used a charge of black powder to shoot an arrow. Black powder was adopted for use in firearms in Europe from the 14th century but was not employed for peaceful purposes, such as mining and road building, until the late 17th century. It remained a useful explosive for breaking up coal and rock deposits until the early 20th century, when it was gradually replaced by dynamite for most mining purposes.
The preparation of black powder from solid ingredients requires uniform mixing and blending of the saltpetre, charcoal, and sulfur. The earliest manufacturing processes used hand methods; the ingredients were simply ground together into a powder using a mortar and pestle. Beginning in the 15th century, water-driven crushing devices of wood, called wooden stamps, came into use to grind the ingredients, and power-driven metallic crushing devices replaced the wooden stamp mills in the 19th century.
Because the burning of black powder is a surface phenomenon, a fine granulation burns faster than a coarse one. A fast burning rate is effective ballistically but tends to create excessive pressures in the gun barrel. Thus, black powder in its powdered form burned too rapidly to be a safe propellant in firearms. To remedy this, Europeans in the 15th and 16th centuries began manufacturing powder in large grains of uniform size. The speed of burning could be varied by using a different size of granule. In the 19th century, as elongated projectiles replaced round balls and the rifling of gun tubes was adopted to rotate and stabilize the projectile, black powders were manufactured to burn even more slowly. In the 1850s Thomas J. Rodman of the U.S. Army developed black powder grains so shaped that they provided a progressively greater burning surface as the combustion progressed, with a resulting maximum energy release after the projectile had already begun to travel down the bore of the gun.
Beginning in the 1860s, black powder was gradually supplanted for use in firearms by guncotton and other, more stable forms of nitrocellulose. Unlike black powder, which burns by the chemical reactions of its constituent ingredients, nitrocellulose is an inherently unstable compound that burns by decomposing rapidly, forming hot gases. In contrast to black powder, it produces almost all gas upon combustion, earning itself the appellation smokeless powder. Also unlike black powder, nitrocellulose burns progressively, generating more gas pressure as combustion proceeds. This results in higher muzzle velocities (for the projectile) and less strain exerted on the firearm.
Nitrocellulose is manufactured by nitrating cellulose fibres such as cotton or wood pulp with nitric and sulfuric acids. Early manufacturing techniques often failed to remove all traces of residual acids from the nitrocellulose, which then tended to undergo an unpredictable spontaneous decomposition resulting in explosion. In the 1880s European chemists began adding special stabilizers to neutralize the residual acids and other decomposition agents in nitrocellulose. The resulting stable and reliable product, known as smokeless powder, was widely adopted in all types of guns in the following decades and supplanted black powder as the propellant charge in artillery and small arms ammunition. (Black powder is still used to ignite the main [smokeless] propellant charge in large-bore artillery pieces, however.)
Nitrocellulose propellants produce much less smoke and flash than black powder and deliver much more mechanical work per unit of weight. The other advantages of smokeless powder are its improved stability in storage, its reduced erosive effects on gun bores, and the improved control obtainable over its rate of burning.
Most forms of gunpowder produced today are either single-base (i.e., consisting of nitrocellulose alone) or double-base (consisting of a combination of nitrocellulose and nitroglycerin). Both types are prepared by plasticizing nitrocellulose with suitable solvents, rolling it into thin sheets, and cutting the sheets into small squares called granules or grains, which are then dried. Control of the burning rate is achieved by varying the composition, size, and geometric shape of the propellant grains and sometimes by surface treatment or coating of the grains. Generally, the goal is to produce a propellant that is slowly converted to gas in the initial stages of burning and more rapidly converted as burning progresses.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2310) Tent
Gist
The word “tent” comes from the Latin word tendere meaning “to stretch” – as in a piece of material stretched tautly across a frame. Tents are typically, but not always, thought of as portable shelters and it has been that way for a long time.
Summary
A tent is a portable shelter, consisting of a rigid framework covered by some flexible substance. Tents are used for a wide variety of purposes, including recreation, exploration, military encampment, and public gatherings such as circuses, religious services, theatrical performances, and exhibitions of plants or livestock. Tents have also been the dwelling places of most of the nomadic peoples of the world, from ancient civilizations such as the Assyrian to the 20th-century Bedouins of North Africa and the Middle East. American Indians developed two types of tent, the conical tepee and the arched wickiup, the latter constructed of thin branches or poles covered with bark or animal hides.
The simplest form of tent is an extremely portable type carried by individual soldiers in the field. When erected, it consists of a low pyramid, formed by a short, diagonally set pole at either end supporting two lengths of cloth joined together at the top and pegged into the ground at the bottom. This is a primitive form of the popular pyramidal A-shaped tent. A long-common tent, the conical bell tent, has a single large vertical pole at its centre and is circular at ground level. The tepee (q.v.) is a variant of this design. Other kinds of tent include the wall tent, an A-shaped tent raised to accommodate straight, vertical walls beneath the slope of the pyramid; the Baker tent, which is a rectangular fabric lean-to with an open front protected by a projecting horizontal flap; the umbrella tent, which was originally made with internal supporting arms like an umbrella but which later became widely popular with external framing of hollow aluminum; and the cabin tent, resembling a wall tent with walls four to six feet high. Special tent designs include mountain tents, which are designed compactly for use in conditions of extreme cold and heavy snow, and back-packing tents, which use extremely lightweight synthetic fabrics and lightweight metal poles. “Pop” tents are designed with spring-loaded frames that erect the tent automatically when released; these are usually hemispheric in shape.
Details
A tent is a shelter consisting of sheets of fabric or other material draped over or attached to a frame of poles or a supporting rope. While smaller tents may be free-standing or attached to the ground, large tents are usually anchored using guy ropes tied to stakes or tent pegs. First used as portable homes by nomads, tents are now more often used for recreational camping and as temporary shelters.
Tents range in size from "bivouac" structures, just big enough for one person to sleep in, up to huge circus tents capable of seating thousands of people. Tents for recreational camping fall into two categories. Tents intended to be carried by backpackers are the smallest and lightest type. Small tents may be sufficiently light that they can be carried for long distances on a touring bicycle, a boat, or when backpacking. The second type are larger, heavier tents which are usually carried in a car or other vehicle. Depending on tent size and the experience of the person or people involved, such tents can usually be assembled (pitched) in between 5 and 25 minutes; disassembly (striking) takes a similar length of time. Some very specialised tents have spring-loaded poles and can be pitched in seconds, but take somewhat longer to strike (take down and pack).
Over the past decade, tents have also been increasingly linked with homelessness crises in the United States, Canada, and other regions. Places of multiple homeless people living in tents closely pitched or plotted near each other are often referred to as tent cities.
History
A form of tent called a teepee or tipi, noted for its cone shape and peak smoke hole, was also used by Native American tribes and Aboriginal Canadians of the Plains Indians since ancient times, variously estimated from 10,000 to 4,000 years BC.
Tents were used at least as far back as the early Iron Age. They are mentioned in the Bible; for example, in Genesis 4:20 Jabal is described as "the first to live in tents and raise sheep and goats". The Roman Army used leather tents, copies of which have been used successfully by modern re-enactors. Various styles developed over time, some derived from traditional nomadic tents, such as the yurt.
Most military tents throughout history were of a simple ridge design. The major technological advance was the use of linen or hemp canvas for the canopy versus leather for the Romans. The primary use of tents was still to provide portable shelter for a small number of men in the field.
By World War I larger designs were being deployed in rear areas to provide shelter for support activities and supplies. Four types of tents which can be characterized by their unique shapes are A-Frame tents, Pyramid tents, Hoop tents , and Dome tents. tents tend not to be very spacious, given their ground surface area.
Use
Tents are used as habitation by nomads, recreational campers, soldiers, and disaster victims. Pole marquees, a type of large tent are typically used as overhead shelter for festivals, weddings, backyard parties, corporate events, excavation (construction) covers, and industrial shelters.
Traditional
Tents have traditionally been used by nomadic people all over the world, such as Native Americans, Mongolian, Turkic and Tibetan Nomads, and the Bedouin.
Military
Armies all over the world have long used tents as part of their working life. Tents are preferred by the military for their relatively quick setup and take down times, compared to more traditional shelters. One of the world's largest users of tents is the U.S. Department of Defense. The U.S. DoD has strict rules on tent quality and tent specifications. The most common tent uses for the military are temporary sleeping quarters (barracks); dining facilities (DFACs); field headquarters; morale, welfare, and recreation (MWR) facilities; and security checkpoints. One of the most popular military designs currently fielded is the TEMPER Tent, an acronym for Tent Expandable Modular PERsonnel. The United States Army is beginning to use a more modern tent called the deployable rapid assembly shelter or DRASH, a collapsible tent with provisions for air conditioning and heating.
Recreational
Camping is a popular form of recreation which often involves the use of tents. A tent is economical and practical because of its portability and low environmental impact. These qualities are necessary when used in the wilderness or backcountry.
Emergency
Tents are often used in humanitarian emergencies, such as war, earthquakes and fire. The primary choice of tents in humanitarian emergencies are canvas tents, because a cotton canvas tent allows functional breathability while serving the purpose of temporary shelter. Tents distributed by organisations such as UNHCR are made by various manufacturers, depending on the region where the tents are deployed, as well as depending on the purpose.
At times, however, these temporary shelters become a permanent or semi-permanent home, especially for displaced people living in refugee camps or shanty towns who can not return to their former home and for whom no replacement homes are made available.
Homelessness
Tents have been increasingly used as shelter for homeless people in the U.S., especially California, Oregon, and Washington. Encampments spiked in the mid-to-late 2010s. These tent cities housing many homeless and travelers/vagabonds have also, are also commonly found in major cities in the South, including Austin, Texas, which had passed a restriction on homeless encampments in May 2021.
Protest movements
Tents are also often used as sites and symbols of protest over time. In 1968 Resurrection City saw hundreds of tents set up by anti-poverty campaigners in Washington D.C. In the 1970s and 1980s anti-nuclear peace camps spread across Europe and North America, with the largest women's-only camp to date set up outside the RAF Greenham Common United States airbase in Newbury, England to protest the deployment there of cruise missiles during the Cold War. The 1990s saw environmental protest camps as part of the campaign for the Clayoquot Sound in Canada and the roads protests in the UK. The first No Border Network camp was held in Strasbourg in 2002, becoming the first in a series of international camps that continue to be organised today. Other international camps of the 2000s include summit counter-mobilisations like Horizone at the Gleneagles G8 gathering in 2005 and the start of Camp for Climate Action in 2006. Since September 2011, the tent has been used as a symbol of the Occupy movement,[citation needed] an international protest movement which is primarily directed against economic and social inequality. Occupy protesters use tents to create camps in public places wherein they can form communities of open discussion and democratic action.
General considerations
Generally, the interior of an enclosed tent is about 10 degrees Fahrenheit warmer than the outside environment (not accounting for wind chill), due to the retention of body heat and (to a lesser extent) radiation.
Tent fabric may be made of many materials including cotton (canvas), nylon, felt and polyester. Cotton absorbs water, so it can become very heavy when wet, but the associated swelling tends to block any minute holes so that wet cotton is more waterproof than dry cotton. Cotton tents were often treated with paraffin to enhance water resistance. Nylon and polyester are much lighter than cotton and do not absorb much water; with suitable coatings they can be very waterproof, but they tend to deteriorate over time due to a slow chemical breakdown caused by ultraviolet light. The most common treatments to make fabric waterproof are silicone impregnation or polyurethane coating. Since stitching makes tiny holes in a fabric seams are often sealed or taped to block these holes and maintain waterproofness, though in practice a carefully sewn seam can be waterproof.
Rain resistance is measured and expressed as hydrostatic head in millimetres (mm). This indicates the pressure of water needed to penetrate a fabric. Heavy or wind-driven rain has a higher pressure than light rain. Standing on a groundsheet increases the pressure on any water underneath. Fabric with a hydrostatic head rating of 1000 mm or less is best regarded as shower resistant, with 1500 mm being usually suitable for summer camping. Tents for year-round use generally have at least 2000 mm; expedition tents intended for extreme conditions are often rated at 3000 mm. Where quoted, groundsheets may be rated for 5000 mm or more.
Many tent manufacturers indicate capacity by such phrases as "3 berth" or "2 person". These numbers indicate how many people the manufacturer thinks can use the tent, though these numbers do not always allow for any personal belongings, such as luggage, inflatable mattresses, camp beds, cots, etc., nor do they always allow for people who are of above average height. Checking the quoted sizes of sleeping areas reveals that several manufacturers consider that a width of 150 cm (4.9 ft) is enough for three people; snug is the operative word.[original research?] Experience indicates that camping may be more comfortable if the actual number of occupants is one or even two less than the manufacturer's suggestion, though different manufacturers have different standards for space requirement and there is no accepted standard.
Tent used in areas with biting insects often have their vent and door openings covered with fine-mesh netting.
Tents can be improvised using waterproof fabric, string, and sticks.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2311) Dry ice
Gist
Dry ice is carbon dioxide in its solid form, a dense, snowlike substance that sublimes (passes directly into the vapour without melting) at −78.5 °C (−109.3 °F), used as a refrigerant, especially during shipping of perishable products such as meats or ice cream. In the production of dry ice, advantage is taken of the spontaneous cooling that occurs when compressed, liquefied carbon dioxide at −57 °C (−71 °F) or lower is allowed suddenly to expand to atmospheric pressure: the liquid freezes to a finely divided solid that is compacted into cakes, weighing about 20 kg (45 pounds).
Summary
Dry ice is frozen carbon dioxide. A block of dry ice has a surface temperature of -109.3 degrees Fahrenheit (-78.5 degrees C). Dry ice also has the very nice feature of sublimation — as it breaks down, it turns directly into carbon dioxide gas rather than a liquid. The super-cold temperature and the sublimation feature make dry ice great for refrigeration.
Many people are familiar with liquid nitrogen, which boils at -320 degrees F (-196 degrees C). Liquid nitrogen is fairly messy and difficult to handle. So why is nitrogen a liquid while carbon dioxide is a solid? This difference is caused by the solid-liquid-gas features of nitrogen and carbon dioxide.
We are all familiar with the solid-liquid-gas behavior of water. We know that at sea level, water freezes at 32 degrees F (0 degrees C) and boils at 212 degrees F (100 degrees C). Water behaves differently as you change the pressure, however.
To make dry ice, you start with a high-pressure container full of liquid carbon dioxide. When you release the liquid carbon dioxide from the tank, the expansion of the liquid and the high-speed evaporation of carbon dioxide gas cools the remainder of the liquid down to the freezing point, where it turns directly into a solid.
If you have ever seen a carbon dioxide fire extinguisher in action, you have seen this carbon dioxide snow form in the nozzle. You compress the carbon dioxide snow to create a block of dry ice. Dry ice sublimates at temperatures higher than −109.2 °F so you will need to use it quick or store it at temperatures lower than -109.2 °F as unlike regular ice it turns into a gas rather than a liquid.
Details
Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimes directly from the solid state to the gas state. It is used primarily as a cooling agent, but is also used in fog machines at theatres for dramatic effects. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods (such as ice cream) where mechanical cooling is unavailable.
Dry ice sublimes at 194.7 K (−78.5 °C; −109.2 °F) at Earth atmospheric pressure. This extreme cold makes the solid dangerous to handle without protection from frostbite injury. While generally not very toxic, the outgassing from it can cause hypercapnia (abnormally elevated carbon dioxide levels in the blood) due to buildup in confined locations.
Properties
Dry ice is the solid form of carbon dioxide (CO2), a molecule consisting of a single carbon atom bonded to two oxygen atoms. Dry ice is colorless, odorless, and non-flammable, and can lower the pH of a solution when dissolved in water, forming carbonic acid (H2CO3).
At pressures below 5.13 atm and temperatures below −56.4 °C (216.8 K; −69.5 °F) (the triple point), CO2 changes from a solid to a gas with no intervening liquid form, through a process called sublimation. The opposite process is called deposition, where CO2 changes from the gas to solid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at 194.7 K (−78.5 °C; −109.2 °F).
The density of dry ice increases with decreasing temperature and ranges between about 1.55 and 1.7 g/{cm}^{3} (97 and 106 lb/cu ft) below 195 K (−78 °C; −109 °F). The low temperature and direct sublimation to a gas makes dry ice an effective coolant, since it is colder than water ice and leaves no residue as it changes state. Its enthalpy of sublimation is 571 kJ/kg (25.2 kJ/mol, 136.5 calorie/g).
Dry ice is non-polar, with a dipole moment of zero, so attractive intermolecular van der Waals forces operate. The composition results in low thermal and electrical conductivity.
Additional Information
Dry ice is made by liquefying carbon dioxide and injecting it into a holding tank, where it’s frozen at a temperature of -109° F and compressed into solid ice. Depending on whether it’s created in a pelletizer or a block press, dry ice can then be made into pellets or large blocks.
Unlike regular ice, dry ice doesn’t melt into a liquid as it warms up. Instead, it converts directly back into its gaseous form in a process known as sublimation. At -109° F, dry ice is also significantly colder than the 32° F surface temperature of regular ice.
Dry Ice History
Dry ice was discovered in the early 1900s and first entered commercial production in the 1920s. The name “dry ice” has been used since 1925, when a manufacturer first trademarked it. Commonly found in commercial settings, the compound is versatile and offers benefits to a broad variety of industries.
The food and agriculture sector, for example, uses dry ice to keep food from spoiling during transport. Because of its low temperature, dry ice inhibits bacterial growth and slows decay, which makes the food crisper, fresher, and flavorful for as long as possible.
There are a multitude of other applications in commercial settings. The entertainment industry, for example, uses dry ice to create a smoky effect without an open flame.
Pest control technicians use it to force gophers out of their holes, which lets the technician close the burrows without hurting wildlife. Dry ice can also attract mosquitoes away from people and clean delicate electronics without corrosive chemical solvents.
Dry Ice Safety
Anyone can take advantage of the many benefits of dry ice, but there are several safety techniques to keep in mind:
* Wear heavy gloves before handling dry ice, as it can cause frostbite if it’s touched directly.
* While it’s safe to use dry ice near food, it should never be ingested, as it can cause internal frostbite.
* Only use dry ice in well-ventilated areas and don’t let the concentration of carbon dioxide in the air reach 5% or higher.
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2312) Angiogram
Gist
An angiogram is a medical imaging test that uses X-rays to visualize blood vessels, typically to detect blockages, narrowing, or other abnormalities, by injecting a special dye (contrast) that highlights the blood vessels.
Summary
Angiography, diagnostic imaging procedure in which arteries and veins are examined by using a contrast agent and X-ray technology. Blood vessels cannot be differentiated from the surrounding organs in conventional radiography. It is therefore necessary to inject into the lumen of the vessels a substance that will distinguish them from the surrounding tissues. The contrast medium used is a water-soluble substance containing iodine. On the radiograph, iodine-containing structures cast a denser shadow than do other body tissues. The technique in use today was developed in the early 1950s by Swedish cardiologist Sven-Ivar Seldinger.
In a typical angiography procedure, a needle is used to puncture the main artery in the groin, armpit, or crook of the arm and to place a coiled wire in the artery. The needle is withdrawn, and a small flexible hollow tube (catheter) is passed over the wire and into the artery. The wire is removed, and contrast medium is injected through the catheter. Both the arteries and the structures they supply with blood can then be visualized.
A technique called digital subtraction angiography (DSA) is particularly useful in diagnosing arterial occlusion (blockage). For example, it can be used to identify constriction (stenosis) of the carotid artery or clot formation (thrombosis) in a pulmonary artery. It also can be used to detect renal vascular disease. After contrast material is injected into an artery or vein, a physician produces fluoroscopic images. Using these digitized images, a computer subtracts the image made with contrast material from a postinjection image made without contrast material, producing an image that allows the dye in the arteries to be seen more clearly. In this manner, the images arising from soft tissues, bones, and gas are the same in both the initial and the subsequent image and are thereby eliminated by the subtraction process. The remaining images of blood vessels containing the contrast material are thus more prominent.
All organs of the body can be examined by using various angiography techniques. Radiographic evaluations of diseased arteries supplying the legs, the brain, and the heart are necessary before corrective surgical procedures are undertaken.
Details
An angiogram is a type of diagnostic test to identify blocked or narrowed blood vessels. The cost of the procedure varies based on multiple factors.
Angiograms, also called or arteriograms, can help doctors detect blood vessel abnormalities, including weakened blood vessels, plaque deposits, and blood clots. They can help doctors diagnose conditions affecting the heart, brain, arms, or legs.
This article discusses why doctors use angiograms, how they perform them, and the risks and side effects associated with the procedure.
It also provides tips for people recovering from an angiogram.
The term “angiogram” refers to a number of diagnostic tests that doctors can use to identify blocked or narrow blood vessels.
Doctors can do an angiogram on different parts of the body, such as:
* the heart, during the diagnosis or treatment of some aspects of heart disease
* the brain, to help diagnose a stroke or the risk of a stroke
* the chest or lungs, for example, to detect bleeding
* the kidneys, to look for high pressure in the renal blood vessels
* the reproductive system, during embolization of tubes or fibroids
* after a trauma to the legs, arms, eyes, or any other body part, to diagnose tears, bleeding, and other problems
* the liver, for example, if a person has cancer
Angiograms also help doctors diagnose a range of cardiovascular diseases, including:
* coronary atherosclerosis
* vascular stenosis
* aneurysms
To perform a traditional angiogram, a doctor will:
* insert a long, narrow tube called a catheter into an artery located in the arm, upper thigh, or groin
* inject contrast dye into the catheter
* take X-rays of the blood vessels
The contrast dye makes blood vessels more visible on X-ray images.
Not all angiograms involve X-ray machines, however. Doctors can also perform angiograms using CT scans and MRI scans.
A doctor may order an angiogram if someone:
* shows signs of a blocked or narrow artery, such as abnormal stress test results
* experiences new or unusual chest pain
* has had a stroke, heart attack, or heart failure
* has or may have other problems that could affect the blood vessels
Angiograms are commonly used to detect heart disease. According to the Centers for Disease Control and Prevention (CDC), heart disease accounts for around 1 in every 4 deaths.
Early diagnosis and prompt treatment can lower a person’s risk of dying from heart disease. Doctors use various tests and procedures, such as angiograms, to identify and treat different types of heart disease.
What do doctors use angiograms for?
A doctor can use an angiogram to examine blood vessels and changes that involve the vascular system in almost any part of the body. It can help detect cardiovascular disease, stroke, and other vascular problems.
Doctors use angiogram results to diagnose the following conditions:
* aneurysms, or bulges that develop in weakened artery walls
* atherosclerosis, which occurs when plaque and fatty material collect on the inner walls of the arteries
* pulmonary embolisms, or blood clots in the lungs
* vascular stenosis, which causes abnormal narrowing of the blood vessels that lead to the brain, heart, or legs
* structural problems in the blood vessels or heart that have been present since birth
A doctor may also order an angiogram to:
* evaluate the health of a person’s blood vessels before surgery
* identify blood vessels feeding a tumor
* plan treatments, such as a coronary bypass, stenting, or chemoembolization
* evaluate a stent after placement
Procedure
The following sections discuss what to expect before, during, and after an angiogram.
Preparation
A doctor will explain how to prepare for an angiogram during the appointment before the procedure. In most cases, people will need to avoid eating and drinking anything the night before the procedure.
People should also arrange for someone to drive them home after they leave the hospital.
It’s important for a person to remember to bring the following items:
* a list of current medications and supplements
* a list of all known allergies
* a current driver’s license or another form of identification
* current medical insurance information
After the person signs in, a nurse will lead them to a private room where they can change into a hospital gown.
The nurse will then insert an intravenous (IV) line into a small vein on the person’s hand or wrist. They will also check the person’s vitals, including their:
* weight
* body temperature
* heart rate
* blood pressure
During the procedure
Before the test, a doctor may administer a mild sedative, which will help the person relax. It will not induce unconsciousness.
The doctor will then disinfect and numb the area of the body where they will insert the catheter. They will make a small cut in the skin and insert the catheter into an artery.
Once the catheter is inside the artery, the doctor will carefully guide it to the blood vessel they want to examine. They will inject the contrast dye through the catheter and take X-ray images of the blood vessel. The person may feel a slight burning sensation when the doctor injects the contrast dye.
After the procedure
After taking the X-ray images, the doctor will remove the catheter and apply steady pressure on the area for about 15 minutes. This ensures that there is no internal bleeding.
A nurse will then take the person back to their hospital room or to the cardiac unit. The doctor may return later to discuss the person’s results.
Interpreting the results
Doctors use angiograms to evaluate the flow of blood to the heart, brain, and other organs. An abnormal angiogram result may indicate that a person has one or more blocked arteries.
In these cases, the doctor may choose to treat the blockage during the angiogram.
What are the risks?
Most people have a very low risk of developing major complications after an angiogram. However, this invasive procedure does have some risks, which are mainly associated with the process of inserting a catheter into the heart.
According to the National Heart, Lung, and Blood InstituteTrusted Source, older adults and people with certain medical conditions, such as chronic kidney disease or diabetes, have a higher risk of experiencing complications after an angiogram.
Risks associated with cardiac catheterization and angiograms include:
* allergic reactions to the local anesthetic, contrast dye, or sedative
* bleeding, bruising, or soreness at the insertion site
* blood clots
* injury to an artery or vein
* damage to the walls of the heart
* acute kidney failure
* infection
* irregular heartbeat
* heart attack or stroke, though this is highly unlikely
People who have had an allergic reaction to contrast dye in the past may need to take medication to reduce the risk of having another allergic reaction. People should take this medication at least 24 hours before the angiogram procedure.
To completely eliminate the risk of an allergic reaction, a doctor can choose to use a different method than the traditional angiogram.
Recovery
After an angiogram, a person will need to rest for a while.
Tips that may help during recovery include:
* avoiding driving or operating machinery until any sedative has completely worn off
* drinking plenty of water
* avoiding strenuous physical activity for the few first days
* keeping the wound clean and dry
* avoiding taking baths, using hot tubs, or swimming in pools while the wound heals
People should contact their doctor if they suspect they have an infection. Symptoms of an infection include:
* redness, swelling, or worsening pain near the wound
* drainage or discharge from the wound
* fever
Additional Information
An angiogram is a diagnostic procedure that uses imaging to show your provider how your blood flows through your blood vessels or heart. An injected contrast material makes it easy to see where blood is moving and where blockages are. Your provider can use X-rays or other types of imaging for your angiogram.
Overview:
What is an angiogram?
An angiogram is a diagnostic procedure that uses X-ray images to look for blockages or narrow spots in your blood vessels (arteries or veins). An angiogram test can show how blood circulates in blood vessels at specific locations in your body. Healthcare providers use an angiogram of your heart, neck, kidneys, legs or other areas to locate the source of an artery or vein issue.
Your healthcare provider may want to do an angiogram procedure when you have signs of blocked, damaged or abnormal blood vessels. An angiogram test helps your provider determine the source of the problem and the extent of damage to your blood vessels.
With an angiogram procedure, your provider can diagnose and plan treatment for conditions like:
* Coronary artery disease (blockage or narrowing in the arteries that supply your heart)
* Peripheral artery disease (blockage or narrowing in your leg arteries)
* Blood clots (mass of blood cells)
* Aneurysm (weak artery wall)
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline
2313) Social Media
Gist
Social media encompasses online platforms and applications where individuals and organizations can connect, share information, and engage in conversations, often through text, images, videos, and other content. These platforms facilitate communication and community building in virtual spaces.
Social media is an internet-based form of communication. Social media platforms allow users to have conversations, share information and create web content.
Social media are interactive technologies that facilitate the creation, sharing and aggregation of content (such as ideas, interests, and other forms of expression) amongst virtual communities and networks.
Summary
Social media: social media, a form of mass media communications on the Internet (such as on websites for social networking and microblogging) through which users share information, ideas, personal messages, and other content (such as videos). Social networking and social media are overlapping concepts, but social networking is usually understood as users building communities among themselves while social media is more about using social networking sites and related platforms to build an audience.
The earliest forms of social media appeared almost as soon as technology could support them. E-mail and chat programs debuted in the early 1970s, but persistent communities did not surface until the creation of the discussion group network USENET in 1979. USENET allowed users to post and receive messages within subject areas called newsgroups. USENET and other discussion forums, such as privately hosted bulletin board systems (BBSs), enabled individuals to interact, but each was essentially a closed system. With the release in 1993 of the Mosaic web browser, those systems were joined with an easy-to-use graphical interface. The architecture of the World Wide Web made it possible to navigate from one site to another with a click, and faster Internet connections allowed for more multimedia content than could be found in the text-heavy newsgroups.
The first companies to create social networks based on web technology were Classmates.com and SixDegrees.com. Classmates.com, founded in 1995, used an aggressive pop-up advertising campaign to draw web surfers to its site. It based its social network on the existing connection between members of high-school and college graduating classes, armed service branches, and workplaces. SixDegrees.com was the first true social networking site. It was launched in 1997 with most of the features that would come to characterize such sites: members could create profiles for themselves, maintain lists of friends, and contact one another through the site’s private messaging system. SixDegrees.com claimed to have attracted more than three million users by 2000, but it failed to translate those numbers into revenue and collapsed with countless other dot-coms when the “bubble” burst that year for shares of e-commerce companies.
Nevertheless, social media sites became popular in the early 21st century. Social networks such as Friendster and MySpace emerged that allowed family members, friends, and acquaintances to connect online. Those two sites were eventually supplanted by Facebook, which became one of the world’s most popular social media sites with billions of users worldwide. Other forms of social media emerged for the sharing of specific types of content. For example, YouTube allows users to share videos, and TikTok is specifically designed for the sharing of short videos. LinkedIn emphasizes a user’s professional connections, where users create pages similar in structure to résumés.
Concerns over the possible negative effects of social media are also growing in tandem with the burgeoning technology. For example, some observers suggest that social media sites spur greater schadenfreude—the emotional experience of pleasure in response to another’s misfortune—perhaps as a result of the dehumanization that occurs when interacting through screens on computers and mobile devices. Some studies also suggest a strong tie between heavy social media use and increased depression, anxiety, loneliness, suicidal tendencies, and feelings of inadequacy. During his second tenure as U.S. surgeon general, Vivek Murthy raised concerns about social media’s impact on children and in 2024 he suggested mandated warning labels on social media sites.
Details
Social media refers to websites and applications that focus on communication, community-based input, interaction, content-sharing and collaboration.
Over the past decade, social media has evolved beyond just a tool for connecting with friends and family. It now serves as a platform for news dissemination, entertainment, and even commerce, becoming a significant part of both personal lives and business operations.
People use social media to stay in touch and interact with various communities, follow trends, and stay informed. In the business world, social media serves as a key tool for marketing, product promotion, customer service, and engagement. Businesses use these platforms to communicate with customers and gather feedback.
Today, nearly all business-to-consumer websites have social components, such as comment fields or social sharing buttons, that make engagement easy. Various tools help companies track, measure, and analyze how their brand is perceived across social media platforms.
Mobile applications have significantly expanded the reach of social media, making these platforms accessible anytime, anywhere. Examples of popular platforms include X (formerly Twitter), Facebook, TikTok, Instagram and LinkedIn. Each platform serves its own unique purpose and audience.
What are the business applications of social media?
Businesses use social media to market products, promote their brand and engage with customers. Social platforms facilitate customer feedback and let customers share their positive or negative experiences. This helps businesses react quickly to customer concerns and maintain consumer confidence.
Social media is increasingly being used for crowdsourcing, a practice where companies use social networking platforms to gather ideas, services, or goods from a broader community such as employees, customers, and the public. This can be invaluable for product improvement or development.
Business to business (B2B) applications for social media include the following:
* Social media analytics. Companies gather data from social platforms and blogs to analyze customer sentiment analysis and make business decisions. This data-driven social media analytics approach enables them to adjust strategies in real time.
* Social media marketing (SMM). This increases brand exposure by creating shareable content that spreads organically across networks. SMM often includes social media optimization (SMO), which draws visitors to a website through strategic posts, updates and blogs.
* Social customer relationship management. Businesses use social CRM tools to foster stronger relationships with their audience. A company's social media pages, such as those on Facebook or Instagram, allow followers to connect, which enhances engagement and helps monitor customer sentiment in real-time.
* Recruiting. Social recruiting has become an integral part of many organizations' hiring strategies, leveraging platforms like LinkedIn to reach a broad candidate pool. It allows businesses to quickly identify and engage with potential hires.
* Enterprise social networking. Tools like Slack, Yammer and Microsoft Teams are widely used for internal communication, collaboration and project management, allowing employees to connect and share information. These platforms also enable businesses to gather valuable market research from external social networks.
What are the benefits of social media?
Social media provides several benefits, including the following:
* User visibility. Social platforms let people easily communicate and exchange ideas or content.
* Business and product marketing. Businesses can quickly promote their products or services to a global audience. Many companies now rely on social media to conduct market research and nurture their customer base. In some industries, like entertainment, the content created on social platforms is the product.
* Audience building. Platforms like Instagram, TikTok and YouTube help individuals -- especially entrepreneurs, artists, and creators -- build a following without needing traditional distributors. For instance, a musician can upload their music to a platform, immediately gaining visibility through their network and beyond.
What are the challenges of social media?
Despite its benefits, social media also poses challenges for individuals and businesses:
* Mental health issues. Overuse of social platforms can contribute to mental health concerns like anxiety, depression, and social media addiction. Research shows that constant exposure to curated content can lead to negative self-comparisons and exacerbate feelings of inadequacy.
* Polarization. Social algorithms often create filter bubbles, where users are exposed only to content that aligns with their existing views, leading to increased polarization and limiting exposure to diverse perspectives.
* Disinformation. Social media can be a breeding ground for misinformation and disinformation. The viral nature of these platforms allows false or misleading information to spread quickly, often with malicious intent.
Businesses face similar and unique social media challenges. These include:
* Offensive posts. Employees using enterprise social platforms can sometimes drift into discussions unrelated to work, leading to potentially offensive or divisive conversations.
* Security risks. Traditional data security and retention policies may not cover adequately the features available in collaboration tools, increasing security risks and compliance concerns.
* Productivity issues. The constant influx of social notifications can become a distraction and hamper employee productivity.
What are enterprise social media best practices?
It's essential for businesses to create a clear social media strategy and set measurable goals to build trust, increase brand awareness and engage with customers. Social media best practices include the following:
* Establishing social media policies. Businesses should create policies that guide employee behavior on social platforms, ensuring no legal or reputational risks arise from inappropriate posts.
* Focusing on the right platforms. Companies should prioritize platforms that best serve their audience. For example, LinkedIn and X are well-suited for B2B marketing.
* Creating engaging content. Rich media like videos, images, and infographics tend to perform better on social platforms. It's important to post content that resonates with users and encourages interaction.
* Using analytics tools. Tracking engagement and staying on top of trends helps businesses adjust their strategies and ensure their social media campaigns are successful.
* Promoting authentic conversations. Social media should reflect the brand's voice while remaining professional. Businesses should engage customers and employees, celebrating positive interactions.
* Checking analytics frequently. Consistent monitoring ensures businesses stay ahead of potential issues and can measure the success of campaigns.
What are the different types of social media?
The four main categories of social platforms are:
* Social networks. These focus on connecting individuals with shared interests. Examples include Facebook and LinkedIn.
* Media-sharing networks. These platforms center around sharing visual content like photos or videos. Examples include YouTube, Instagram and TikTok.
* Community-based networks. These encourage in-depth discussions on specific topics. Reddit is an example.
* Review networks. These focus on reviewing products or services. Examples include Yelp and TripAdvisor.
What are examples of social media?
Here are some examples of popular web-based social media platforms:
* Facebook: A widely-used social networking site where users can create profiles, share content, and communicate with friends and family.
* LinkedIn: A platform designed for professional networking where users can connect and share business-related information.
* Pinterest: A social curation platform where users can share and categorize images.
* Reddit: A discussion-based platform where users engage in conversations around specific topics.
* X: A microblogging platform where users post short updates or "tweets."
* Wikipedia: A collaborative platform where users contribute and edit content in an open-source encyclopedia.
Additional Information
Social media are interactive technologies that facilitate the creation, sharing and aggregation of content (such as ideas, interests, and other forms of expression) amongst virtual communities and networks. Common features include:
* Online platforms that enable users to create and share content and participate in social networking.
* User-generated content—such as text posts or comments, digital photos or videos, and data generated through online interactions.
* Service-specific profiles that are designed and maintained by the social media organization.
* Social media helps the development of online social networks by connecting a user's profile with those of other individuals or groups.
The term social in regard to media suggests platforms enable communal activity. Social media can enhance and extend human networks.[6] Users access social media through web-based apps or custom apps on mobile devices. These interactive platforms allow individuals, communities, and organizations to share, co-create, discuss, participate in, and modify user-generated or self-curated content. Social media is used to document memories, learn, and form friendships. They may be used to promote people, companies, products, and ideas.[8] Social media can be used to consume, publish, or share news.
Social media platforms can be categorized based on their primary function. Social networking sites like Facebook, LinkedIn, and Threads focus on building personal and professional connections. Microblogging platforms, such as Twitter (now X) and Mastodon, emphasize short-form content and rapid information sharing. Media sharing networks, including Instagram, TikTok, YouTube, and Snapchat, allow users to share images, videos, and live streams. Discussion and community forums like Reddit, Quora, and Discord facilitate conversations, Q&A, and niche community engagement. Live streaming platforms, such as Twitch, Facebook Live, and YouTube Live, enable real-time audience interaction. Finally, decentralized social media platforms like Mastodon and Bluesky aim to provide social networking without corporate control, offering users more autonomy over their data and interactions.
Popular social media platforms with over 100 million registered users include Twitter, Facebook, WeChat, ShareChat, Instagram, Pinterest, QZone, Weibo, VK, Tumblr, Baidu Tieba, Threads and LinkedIn. Depending on interpretation, other popular platforms that are sometimes referred to as social media services include YouTube, Letterboxd, QQ, Quora, Telegram, WhatsApp, Signal, LINE, Snapchat, Viber, Reddit, Discord, and TikTok. Wikis are examples of collaborative content creation.
Social media outlets differ from old media (e.g. newspapers, TV, and radio broadcasting) in many ways, including quality,[9] reach, frequency, usability, relevancy, and permanence. Social media outlets operate in a dialogic transmission system (many sources to many receivers) while traditional media operate under a monologic transmission model (one source to many receivers). For instance, a newspaper is delivered to many subscribers, and a radio station broadcasts the same programs to a city.
Social media has been criticized for a range of negative impacts on children and teenagers, including exposure to inappropriate content, exploitation by adults, sleep problems, attention problems, feelings of exclusion, and various mental health maladies. Social media has also received criticism as worsening political polarization and undermining democracy. Major news outlets often have strong controls in place to avoid and fix false claims, but social media's unique qualities bring viral content with little to no oversight. "Algorithms that track user engagement to prioritize what is shown tend to favor content that spurs negative emotions like anger and outrage. Overall, most online misinformation originates from a small minority of "superspreaders," but social media amplifies their reach and influence."
It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.
Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.
Offline