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#126 2018-05-01 01:11:58

ganesh
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Re: Miscellany

110) Kiwi

Kiwi, any of five species of flightless birds belonging to the genus Apteryx and found in New Zealand. The name is a Maori word referring to the shrill call of the male. Kiwis are grayish brown birds the size of a chicken. They are related to the extinct moas. Kiwis are unusual in many respects: the vestigial wings are hidden within the plumage; the nostrils are at the tip (rather than the base) of the long, flexible bill; the feathers, which have no aftershafts, are soft and hairlike; the legs are stout and muscular; and each of the four toes has a large claw. The eyes are small and inefficient in full daylight, the ear openings are large and well developed, and very long bristles (perhaps tactile) occur at the base of the bill.

Dwelling in forests, kiwis sleep by day in burrows and forage for food—worms, insects and their larvae, and berries—by night. They can run swiftly when required; when trapped they use their claws in defense.

One or two large white eggs—up to 450 g (1 pound) in weight—are laid in a burrow and are incubated by the male for about 80 days. The egg is, relative to the size of the bird, the largest of any living species. The chick hatches fully feathered and with its eyes open; it does not eat for about a week.

Although no longer abundant, kiwis appear to be in no danger of extinction and may even be gradually adapting to semipastoral land.

The genus Apteryx forms the family Apterygidae, order Apterygiformes. Five species of kiwis are recognized: the tokoeka kiwi (A. australis), which includes the Haast tokoeka, Stewart Island tokoeka, Southern Fiordland tokoeka, and the Northern Fiordland tokoeka; the little spotted kiwi (A. oweni); the great spotted kiwi (A. haasti); the Okarito brown kiwi (A. rowi), also called the Rowi kiwi; and the brown kiwi (A. mantelli), also called the North Island brown kiwi.

rowi-kiwi-465-300x213.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#127 2018-05-03 03:53:13

ganesh
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Re: Miscellany

111) Mutation

Mutation, an alteration in the genetic material (the genome) of a cell of a living organism or of a virus that is more or less permanent and that can be transmitted to the cell’s or the virus’s descendants. (The genomes of organisms are all composed of DNA, whereas viral genomes can be of DNA or RNA; see heredity: The physical basis of heredity.) Mutation in the DNA of a body cell of a multicellular organism (somatic mutation) may be transmitted to descendant cells by DNA replication and hence result in a sector or patch of cells having abnormal function, an example being cancer. Mutations in egg or sperm cells (germinal mutations) may result in an individual offspring all of whose cells carry the mutation, which often confers some serious malfunction, as in the case of a human genetic disease such as cystic fibrosis. Mutations result either from accidents during the normal chemical transactions of DNA, often during replication, or from exposure to high-energy electromagnetic radiation (e.g., ultraviolet light or X-rays) or particle radiation or to highly reactive chemicals in the environment. Because mutations are random changes, they are expected to be mostly deleterious, but some may be beneficial in certain environments. In general, mutation is the main source of genetic variation, which is the raw material for evolution by natural selection.

The genome is composed of one to several long molecules of DNA, and mutation can occur potentially anywhere on these molecules at any time. The most serious changes take place in the functional units of DNA, the genes. A mutated form of a gene is called a mutant allele. A gene is typically composed of a regulatory region, which is responsible for turning the gene’s transcription on and off at the appropriate times during development, and a coding region, which carries the genetic code for the structure of a functional molecule, generally a protein. A protein is a chain of usually several hundred amino acids. Cells make 20 common amino acids, and it is the unique number and sequence of these that give a protein its specific function. Each amino acid is encoded by a unique sequence, or codon, of three of the four possible base pairs in the DNA (A–T, T–A, G–C, and C–G, the individual letters referring to the four nitrogenous bases adenine, thymine, guanine, and cytosine). Hence, a mutation that changes DNA sequence can change amino acid sequence and in this way potentially reduce or inactivate a protein’s function. A change in the DNA sequence of a gene’s regulatory region can adversely affect the timing and availability of the gene’s protein and also lead to serious cellular malfunction. On the other hand, many mutations are silent, showing no obvious effect at the functional level. Some silent mutations are in the DNA between genes, or they are of a type that results in no significant amino acid changes.

Mutations are of several types. Changes within genes are called point mutations. The simplest kinds are changes to single base pairs, called base-pair substitutions. Many of these substitute an incorrect amino acid in the corresponding position in the encoded protein, and of these a large proportion result in altered protein function. Some base-pair substitutions produce a stop codon. Normally, when a stop codon occurs at the end of a gene, it stops protein synthesis, but, when it occurs in an abnormal position, it can result in a truncated and nonfunctional protein. Another type of simple change, the deletion or insertion of single base pairs, generally has a profound effect on the protein because the protein’s synthesis, which is carried out by the reading of triplet codons in a linear fashion from one end of the gene to the other, is thrown off. This change leads to a frameshift in reading the gene such that all amino acids are incorrect from the mutation onward. More-complex combinations of base substitutions, insertions, and deletions can also be observed in some mutant genes.

Mutations that span more than one gene are called chromosomal mutations because they affect the structure, function, and inheritance of whole DNA molecules (microscopically visible in a coiled state as chromosomes). Often these chromosome mutations result from one or more coincident breaks in the DNA molecules of the genome (possibly from exposure to energetic radiation), followed in some cases by faulty rejoining. Some outcomes are large-scale deletions, duplications, inversions, and translocations. In a diploid species (a species, such as human beings, that has a double set of chromosomes in the nucleus of each cell), deletions and duplications alter gene balance and often result in abnormality. Inversions and translocations involve no loss or gain and are functionally normal unless a break occurs within a gene. However, at meiosis (the specialized nuclear divisions that take place during the production of gametes—i.e., eggs and sperm), faulty pairing of an inverted or translocated chromosome set with a normal set can result in gametes and hence progeny with duplications and deletions.

Loss or gain of whole chromosomes results in a condition called aneuploidy. One familiar result of aneuploidy is Down syndrome, a chromosomal disorder in which humans are born with an extra chromosome 21 (and hence bear three copies of that chromosome instead of the usual two). Another type of chromosome mutation is the gain or loss of whole chromosome sets. Gain of sets results in polyploidy—that is, the presence of three, four, or more chromosome sets instead of the usual two. Polyploidy has been a significant force in the evolution of new species of plants and animals.

Most genomes contain mobile DNA elements that move from one location to another. The movement of these elements can cause mutation, either because the element arrives in some crucial location, such as within a gene, or because it promotes large-scale chromosome mutations via recombination between pairs of mobile elements in different locations.

At the level of whole populations of organisms, mutation can be viewed as a constantly dripping faucet introducing mutant alleles into the population, a concept described as mutational pressure. The rate of mutation differs for different genes and organisms. In RNA viruses, such as the human immunodeficiency virus (HIV), replication of the genome takes place within the host cell using a mechanism that is prone to error. Hence, mutation rates in such viruses are high. In general, however, the fate of individual mutant alleles is never certain. Most are eliminated by chance. In some cases a mutant allele can increase in frequency by chance, and then individuals expressing the allele can be subject to selection, either positive or negative. Hence, for any one gene the frequency of a mutant allele in a population is determined by a combination of mutational pressure, selection, and chance.

Mutations_chart.jpg


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#128 2018-05-05 00:59:11

ganesh
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Re: Miscellany

112) Vitamin C

Vitamin C, also called ascorbic acid, water-soluble, carbohydrate-like substance that is involved in certain metabolic processes of animals. Although most animals can synthesize vitamin C, it is necessary in the diet of some, including humans and other primates, in order to prevent scurvy, a disease characterized by soreness and stiffness of the joints and lower extremities, rigidity, swollen and bloody gums, and hemorrhages in the tissues of the body. First isolated in 1928, vitamin C was identified as the curative agent for scurvy in 1932.

Vitamin C is essential for the synthesis of collagen, a protein important in the formation of connective tissue and in wound healing. It acts as an antioxidant, protecting against damage by reactive molecules called free radicals. The vitamin also helps in stimulating the immune system. It has been shown in animal trials that vitamin C has some anticarcinogenic activity.

Relatively large amounts of vitamin C are required—for instance, an adult man is said to need about 70 mg (1 mg = 0.001 gram) per day. Citrus fruits and fresh vegetables are the best dietary sources of the vitamin. Because vitamin C is easily destroyed by reactions with oxygen, especially in neutral or alkaline solution or at elevated temperatures, it is difficult to preserve in foods. The vitamin is added to certain fruits to prevent browning.

vitamin-c-benefit-skin-1.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#129 2018-05-07 02:20:14

ganesh
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Re: Miscellany

113) Aspirin

Aspirin, also called acetylsalicylic acid, derivative of salicylic acid that is a mild nonnarcotic analgesic useful in the relief of headache and muscle and joint aches. Aspirin is effective in reducing fever, inflammation, and swelling and thus has been used for treatment of rheumatoid arthritis, rheumatic fever, and mild infection. In these instances, aspirin generally acts on the symptoms of disease and does not modify or shorten the duration of a disease. However, because of its ability to inhibit the production of blood platelet aggregates (which may cut off the blood supply to regions of the heart or brain), it has also been used as an anticoagulant in the treatment of such conditions as unstable angina or following a minor stroke or heart attack.

Aspirin is sometimes used as a preventive agent for certain diseases. For example, daily intake of low-dose aspirin (75–300 mg) can reduce the risk of heart attack or stroke in high-risk individuals. Studies have also found that long-term use of low-dose aspirin can lower the risk of colon cancer in some persons and is associated with a reduced risk of death from several types of cancer, including certain forms of colon cancer as well as lung cancer and esophageal cancer.

Aspirin acts by inhibiting the production of prostaglandins, body chemicals that are necessary for blood clotting and are noted for sensitizing nerve endings to pain. The use of aspirin has been known to cause allergic reaction and gastrointestinal problems in some people. It has also been linked to the development in children (primarily those 2 to 16 years old) of Reye syndrome, an acute disorder of the liver and central nervous system that may follow viral infections such as influenza and chicken pox, and to the development of age-related macular degeneration (a blinding disorder) in some persons who use the drug regularly over many years. Like almost all drugs, aspirin is to be avoided during pregnancy.

media%2F037%2F037442eb-c883-42b6-8f89-2a71eb8019b3%2FphpyuEj0V.png


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#130 2018-05-08 23:23:35

ganesh
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Re: Miscellany

114) Anaconda

Anaconda, (genus Eunectes), either of two species of constricting, water-loving snakes found in tropical South America. The green anaconda (Eunectes murinus), also called the giant anaconda, sucuri, or water kamudi, is an olive-coloured snake with alternating oval-shaped black spots. The yellow, or southern, anaconda (E. notaeus) is much smaller and has pairs of overlapping spots.

Green anacondas live along tropical waters east of the Andes Mountains and on the Caribbean island of Trinidad. The green anaconda is the largest snake in the world. Although anacondas and pythons both have been reliably measured at over 9 metres (30 feet) long, anacondas have been reported to measure over 10 metres (33 feet) and are much more heavily built. Most individuals, however, do not exceed 5 metres (16 feet).

Green anacondas lie in the water (generally at night) to ambush caimans and mammals such as capybara, deer, tapirs, and peccaries that come to drink. An anaconda seizes a large animal by the neck and almost instantly throws its coils around it, killing it by constriction. Anacondas kill smaller prey, such as small turtles and diving birds, with the mouth and sharp backward-pointing teeth alone. Kills made onshore are often dragged into the water, perhaps to avoid attracting jaguars and to ward off biting ants attracted to the carcass. In the wild, green anacondas are not particularly aggressive. In Venezuela, they are captured easily during the day by herpetologists who, in small groups, merely walk up to the snakes and carry them off.

Green anacondas mate in or very near the water. After nine months, a female gives live birth to 14–82 babies, each more than 62 cm (24 inches) in length. The young grow rapidly, attaining almost 3 metres (10 feet) by age three.

Anacondas are members of the boa family (Boidae).

Anaconda-Pitbull-636816.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#131 2018-05-10 01:33:44

ganesh
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Re: Miscellany

115) Periscope

Periscope, optical instrument used in land and sea warfare, submarine navigation, and elsewhere to enable an observer to see his surroundings while remaining under cover, behind armour, or submerged.

A periscope includes two mirrors or reflecting prisms to change the direction of the light coming from the scene observed: the first deflects it down through a vertical tube, the second diverts it horizontally so that the scene can be viewed conveniently. Frequently there is a telescopic optical system that provides magnification, gives as wide an arc of vision as possible, and includes a crossline or reticle pattern to establish the line of sight to the object under observation. There may also be devices for estimating the range and course of the target in military applications and for photographing through the periscope.

The simplest type of periscope consists of a tube at the ends of which are two mirrors, parallel to each other but at 45° to the axis of the tube. This device produces no magnification and does not give a crossline image. The arc of vision is limited by the simple geometry of the tube: the longer or narrower the tube, the smaller the field of view. Periscopes of this type were widely used in World War II in tanks and other armoured vehicles as observation devices for the driver, gunner, and commander. When fitted with a small, auxiliary gunsight telescope, the tank periscope can also be used in pointing and firing the guns. By employing tubes of rectangular cross section, wide, horizontal fields of view can be obtained.

periscope.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#132 2018-05-10 15:53:30

ganesh
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Re: Miscellany

116) Acetic Acid

Acetic acid (CH3COOH), also called ethanoic acid, the most important of the carboxylic acids. A dilute (approximately 5 percent by volume) solution of acetic acid produced by fermentation and oxidation of natural carbohydrates is called vinegar; a salt, ester, or acylal of acetic acid is called acetate. Industrially, acetic acid is used in the preparation of metal acetates, used in some printing processes; vinyl acetate, employed in the production of plastics; cellulose acetate, used in making photographic films and textiles; and volatile organic esters (such as ethyl and butyl acetates), widely used as solvents for resins, paints, and lacquers. Biologically, acetic acid is an important metabolic intermediate, and it occurs naturally in body fluids and in plant juices.

Acetic acid has been prepared on an industrial scale by air oxidation of acetaldehyde, by oxidation of ethanol (ethyl alcohol), and by oxidation of butane and butene. Today acetic acid is manufactured by a process developed by the chemical company Monsanto in the 1960s; it involves a rhodium-iodine catalyzed carbonylation of methanol (methyl alcohol).

Pure acetic acid, often called glacial acetic acid, is a corrosive, colourless liquid (boiling point 117.9 °C [244.2 °F]; melting point 16.6 °C [61.9 °F]) that is completely miscible with water.

acetic%20acid.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#133 2018-05-12 01:03:48

ganesh
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Re: Miscellany

117) Pascal's Law

Pascal’s principle, also called Pascal’s law, in fluid (gas or liquid) mechanics, statement that, in a fluid at rest in a closed container, a pressure change in one part is transmitted without loss to every portion of the fluid and to the walls of the container. The principle was first enunciated by the French scientist Blaise Pascal.

Pressure is equal to the force divided by the area on which it acts. According to Pascal’s principle, in a hydraulic system a pressure exerted on a piston produces an equal increase in pressure on another piston in the system. If the second piston has an area 10 times that of the first, the force on the second piston is 10 times greater, though the pressure is the same as that on the first piston. This effect is exemplified by the hydraulic press, based on Pascal’s principle, which is used in such applications as hydraulic brakes.

Pascal also discovered that the pressure at a point in a fluid at rest is the same in all directions; the pressure would be the same on all planes passing through a specific point. This fact is also known as Pascal’s principle, or Pascal’s law.

variation_depth.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#134 2018-05-14 00:50:46

ganesh
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Re: Miscellany

118) Benzoic Acid

Benzoic acid, a white, crystalline organic compound belonging to the family of carboxylic acids, widely used as a food preservative and in the manufacture of various cosmetics, dyes, plastics, and insect repellents.

First described in the 16th century, benzoic acid exists in many plants; it makes up about 20 percent of gum benzoin, a vegetable resin. It was first prepared synthetically about 1860 from compounds derived from coal tar. It is commercially manufactured by the chemical reaction of toluene (a hydrocarbon obtained from petroleum) with oxygen at temperatures around 200° C (about 400° F) in the presence of cobalt and manganese salts as catalysts. Pure benzoic acid melts at 122° C (252° F) and is very slightly soluble in water.

Among the derivatives of benzoic acid are sodium benzoate, a salt used as a food preservative; benzyl benzoate, an ester used as a miticide; and benzoyl peroxide, used in bleaching flour and in initiating chemical reactions for preparing certain plastics.

benzoic-acid-250x250.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#135 2018-05-16 00:54:28

ganesh
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Re: Miscellany

119) Basil

Basil, (Ocimum basilicum), also called sweet basil, annual herb of the mint family (Lamiaceae), grown for its aromatic leaves. Basil is likely native to India and is widely grown as a kitchen herb. The leaves are used fresh or dried to flavour meats, fish, salads, and sauces; basil tea is a stimulant.

Basil leaves are glossy and oval-shaped, with smooth or slightly toothed edges that typically cup slightly; the leaves are arranged oppositely along the square stems. The small flowers are borne in terminal clusters and range in colour from white to magenta. The plant is extremely frost-sensitive and grows best in warm climates. Basil is susceptible to Fusarium wilt, blight, and downy mildew, especially when grown in humid conditions.

A number of varieties are used in commerce, including the small-leaf common basil, the larger leaf Italian basil, and the large lettuce-leaf basil. Thai basil (O. basilicum var. thyrsiflora) and the related holy basil (O. tenuiflorum) and lemon basil (O. ×citriodorum) are common in Asian cuisine. The dried large-leaf varieties have a fragrant aroma faintly reminiscent of anise and a warm, sweet, aromatic, mildly pungent flavour. The dried leaves of the common basil are less fragrant and more pungent in flavour.

The essential oil content is 0.1 percent, the principal components of which are methyl chavicol and d-linalool.

BasilSweetEO.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#136 2018-05-18 01:25:21

ganesh
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Re: Miscellany

120) Ear bone

Ear bone, also called Auditory Ossicle, any of the three tiny bones in the middle ear of all mammals. These are the malleus, or hammer, the incus, or anvil, and the stapes, or stirrup. Together they form a short chain that crosses the middle ear and transmits vibrations caused by sound waves from the eardrum membrane to the liquid of the inner ear. The malleus resembles a club more than a hammer, whereas the incus looks like a premolar tooth with an extensive root system. The stapes does closely resemble a stirrup. The top or head of the malleus and the body of the incus are held together by a tightly fitting joint and are seated in the attic, or upper portion, of the eardrum cavity. The handle of the malleus adheres to the upper half of the drum membrane. Three small ligaments hold the head of the malleus, and a fourth attaches a projection (called the short process) from the incus to a slight depression in the back wall of the cavity. The long process of the incus is bent near the lower end and carries a small knoblike bone that is jointed loosely to the head of the stapes—the third and smallest of the ossicles. The stapes lies in a horizontal position at right angles with the long process of the incus. There are two openings in the wall of the bony labyrinth and the stapes footplate fits perfectly in one of these openings—an oval-shaped window, where it is held in place by yet another ligament called the annular ligament.

There are two tiny muscles in the middle ear, which serve to alter the tension on the ear bones and thus the intensity (degree of loudness) of sounds. One, the tensor tympani, is attached to the handle of the malleus (itself attached to the eardrum membrane) and by its contraction tends to draw the malleus inward, thus increasing drum membrane tension. The second, called stapedius, tends to pull the footplate of the stapes out of the oval window. This is accomplished by tipping the stirrup, or stapes, backward.

figure%202.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#137 2018-05-20 00:50:39

ganesh
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Re: Miscellany

121) Spirogyra

Spirogyra, (genus Spirogyra), any member of a genus of some 400 species of free-floating green algae (division Chlorophyta) found in freshwater environments around the world. Named for their beautiful spiral chloroplasts, spirogyras are filamentous algae that consist of thin unbranched chains of cylindrical cells. They can form masses that float near the surface of streams and ponds, buoyed by oxygen bubbles released during photosynthesis. They are commonly used in laboratory demonstrations.

Each cell of the filaments features a large central vacuole, within which the nucleus is suspended by fine strands of cytoplasm. The chloroplasts form a spiral around the vacuole and have specialized bodies known as pyrenoids that store starch. The cell wall consists of an inner layer of cellulose and an outer layer of pectin, which is responsible for the slippery texture of the algae.

Spirogyra species can reproduce both sexually and asexually. Asexual, or vegetative, reproduction occurs by simple fragmentation of the filaments. Sexual reproduction occurs by a process known as conjugation, in which cells of two filaments lying side by side are joined by outgrowths called conjugation tubes. This allows the contents of one cell to completely pass into and fuse with the contents of the other. The resulting fused cell (zygote) becomes surrounded by a thick wall and overwinters, while the vegetative filaments die.

spirogyra.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#138 2018-05-22 00:12:36

ganesh
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Re: Miscellany

122) Hooke's Law

Hooke’s law, law of elasticity discovered by the English scientist Robert Hooke in 1660, which states that, for relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load. Elastic behaviour of solids according to Hooke’s law can be explained by the fact that small displacements of their constituent molecules, atoms, or ions from normal positions is also proportional to the force that causes the displacement.

The deforming force may be applied to a solid by stretching, compressing, squeezing, bending, or twisting. Thus, a metal wire exhibits elastic behaviour according to Hooke’s law because the small increase in its length when stretched by an applied force doubles each time the force is doubled. Mathematically, Hooke’s law states that the applied force F equals a constant k times the displacement or change in length x, or F = kx. The value of k depends not only on the kind of elastic material under consideration but also on its dimensions and shape.

At relatively large values of applied force, the deformation of the elastic material is often larger than expected on the basis of Hooke’s law, even though the material remains elastic and returns to its original shape and size after removal of the force. Hooke’s law describes the elastic properties of materials only in the range in which the force and displacement are proportional. Sometimes Hooke’s law is formulated as F = −kx. In this expression F no longer means the applied force but rather means the equal and oppositely directed restoring force that causes elastic materials to return to their original dimensions.

Hooke’s law may also be expressed in terms of stress and strain. Stress is the force on unit areas within a material that develops as a result of the externally applied force. Strain is the relative deformation produced by stress. For relatively small stresses, stress is proportional to strain.

hookes-Law.gif


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#139 2018-05-23 23:45:13

ganesh
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Re: Miscellany

123) Hibiscus

Hibiscus, any of numerous species of herbs, shrubs, and trees constituting the genus Hibiscus, in the family Malvaceae, and native to warm temperate and tropical regions. Several are cultivated as ornamentals for their showy flowers.

The tropical Chinese hibiscus, or China rose (H. rosa-sinensis), which may reach a height of 4.5 metres (15 feet), rarely exceeds 2 metres (6.5 feet) in cultivation. It is grown for its large, somewhat bell-shaped blossoms. Cultivated varieties have red, white, yellow, or orange flowers. The East African hibiscus (H. schizopetalus), a drooping shrub with deeply lobed red petals, is often grown in hanging baskets indoors. Other members of the genus Hibiscus include the fibre plants mahoe and kenaf, okra, musk mallow, rose of Sharon, and many flowering plants known by the common name mallow.

Hibiscus now includes the former genus Abutilon, containing more than 100 species of herbaceous plants and partly woody shrubs native to tropical and warm temperate areas. Several species are used as houseplants and in gardens for their white to deep orange, usually nodding, five-petaled blossoms. H. hybridum, sometimes called Chinese lantern, is planted outdoors in warm regions and grown in greenhouses elsewhere. The trailing abutilon (H. megapotamicum), often grown as a hanging plant, is noted for its nodding, yellowish orange, closed flowers; it has a handsome variegated-leaf variety. H. pictum, a shrub reaching a height of 4.5 metres (15 feet), often called parlor, or flowering, maple, is grown as a houseplant. An important fibre plant in China is H. theophrastii, called China jute; it is a very serious field weed in the United States, where it is called velvetleaf or Indian mallow.

Hibiscus~~element21.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#140 Yesterday 18:08:47

ganesh
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Re: Miscellany

124) Hydrometer

Hydrometer, device for measuring some characteristics of a liquid, such as its density (weight per unit volume) or specific gravity (weight per unit volume compared with water). The device consists essentially of a weighted, sealed, long-necked glass bulb that is immersed in the liquid being measured; the depth of flotation gives an indication of liquid density, and the neck can be calibrated to read density, specific gravity, or some other related characteristic.

In practice, the floating glass bulb is usually inserted into a cylindrical glass tube equipped with a rubber ball at the top end for sucking liquid into the tube. Immersion depth of the bulb is calibrated to read the desired characteristic. A typical instrument is the storage-battery hydrometer, by means of which the specific gravity of the battery liquid can be measured and the condition of the battery determined. Another instrument is the radiator hydrometer, in which the float is calibrated in terms of the freezing point of the radiator solution. Others may be calibrated in terms of “proof” of an alcohol solution or in terms of the percentage of sugar in a sugar solution.

The Baumé hydrometer, named for the French chemist Antoine Baumé, is calibrated to measure specific gravity on evenly spaced scales; one scale is for liquids heavier than water, and the other is for liquids lighter than water.

specific-gravity-hydrometers.png


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#141 Today 00:22:25

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Re: Miscellany

125) Mercury

Mercury (Hg), also called quicksilver, chemical element, liquid metal of Group 12 (IIb, or zinc group) of the periodic table.

Properties, Uses, And Occurrence

Mercury was known in Egypt and also probably in the East as early as 1500 BCE. The name mercury originated in 6th-century alchemy, in which the symbol of the planet was used to represent the metal; the chemical symbol Hg derives from the Latin hydrargyrum, “liquid silver.” Although its toxicity was recognized at an early date, its main application was for medical purposes.

Mercury is the only elemental metal that is liquid at room temperature. (Cesium melts at about 28.5 °C [83 °F], gallium at about 30 °C [86 °F], and rubidium at about 39 °C [102 °F].) Mercury is silvery white, slowly tarnishes in moist air, and freezes into a soft solid like tin or lead at −38.87 °C (−37.97 °F). It boils at 356.9 °C (674 °F).

It alloys with copper, tin, and zinc to form amalgams, or liquid alloys. An amalgam with silver is used as a filling in dentistry. Mercury does not wet glass or cling to it, and this property, coupled with its rapid and uniform volume expansion throughout its liquid range, makes it useful in thermometers. Barometers and manometers utilize its high density and low vapour pressure. Gold and silver dissolve readily in mercury, and in the past this property was used in the extraction of these metals from their ores.

The good electrical conductivity of mercury makes it exceptionally useful in sealed electrical switches and relays. An electrical discharge through mercury vapour contained in a fused silica tube or bulb produces a bluish glow rich in ultraviolet light, a phenomenon exploited in ultraviolet, fluorescent, and high-pressure mercury-vapour lamps. Mercury’s high thermal neutron-capture cross section (360 barns) and good thermal conductivity make it applicable as a shield and coolant in nuclear reactors. Much mercury is utilized in the preparation of pharmaceuticals and agricultural and industrial fungicides.

The use of mercury in the manufacture of chlorine and caustic soda (sodium hydroxide) by electrolysis of brine depends upon the fact that mercury employed as the negative pole, or cathode, dissolves the sodium liberated to form a liquid amalgam. An interesting application, though not of great commercial significance, is the use of mercury vapour instead of steam in some electrical generating plants, the higher boiling point of mercury providing greater efficiency in the heat cycle.

Mercury occurs in Earth’s crust on the average of about 0.08 gram (0.003 ounce) per ton of rock. The principal ore is the red sulfide, cinnabar. Native mercury occurs in isolated drops and occasionally in larger fluid masses, usually with cinnabar, near volcanoes or hot springs. Over two-thirds of the world supply of mercury comes from China, with most of the remainder coming from Kyrgyzstan and Chile; it is often a by-product of gold mining. Cinnabar is mined in shaft or open-pit operations and refined by flotation. Most of the methods of extraction of mercury rely on the volatility of the metal and the fact that cinnabar is readily decomposed by air or by lime to yield the free metal. Because of the toxicity of mercury and the threat of rigid pollution control, attention is being directed toward safer methods of extracting mercury. These generally rely on the fact that cinnabar is readily soluble in solutions of sodium hypochlorite or sulfide, from which the mercury can be recovered by precipitation with zinc or aluminum or by electrolysis.

Extremely rare natural alloys of mercury have also been found: moschellandsbergite (with silver), potarite (with palladium), and gold amalgam. Mercury is extracted from cinnabar by roasting it in air, followed by condensation of the mercury vapour. Mercury is toxic. Poisoning may result from inhalation of the vapour, ingestion of soluble compounds, or absorption of mercury through the skin.

Natural mercury is a mixture of seven stable isotopes: 196Hg (0.15 percent), 198Hg (9.97 percent), 199Hg (16.87 percent), 200Hg (23.10 percent), 201Hg (13.18 percent), 202Hg (29.86 percent), and 204Hg (6.87 percent). As a wavelength standard and for other precise work, isotopically pure mercury consisting of only mercury-198 is prepared by neutron bombardment of natural gold, gold-197.

Principal Compounds

The compounds of mercury are either of +1 or +2 oxidation state. Mercury(II) or mercuric compounds predominate. Mercury does not combine with oxygen to produce mercury(II) oxide, HgO, at a useful rate until heated to the range of 300 to 350 °C (572 to 662 °F). At temperatures of about 400 °C (752 °F) and above, the reaction reverses with the compound decomposing into its elements. Antoine-Laurent Lavoisier and Joseph Priestley used this reaction in their study of oxygen.

There are relatively few mercury(I) or mercurous compounds. The mercury(I) ion, Hg22+, is diatomic and stable. Mercury(I) chloride, Hg2Cl2 (commonly known as calomel), is probably the most important univalent compound. It is used in antiseptic salves. Mercury(II) chloride, HgCl2 (also called bichloride of mercury or corrosive sublimate), is perhaps the commonest bivalent compound. Although extremely toxic, this odourless, colourless substance has a wide variety of applications. In agriculture it is used as a fungicide; in medicine it is sometimes employed as a topical antiseptic in concentrations of one part per 2,000 parts of water; and in the chemical industry it serves as a catalyst in the manufacture of vinyl chloride and as a starting material in the production of other mercury compounds. Mercury(II) oxide, HgO, provides elemental mercury for the preparation of various organic mercury compounds and certain inorganic mercury salts. This red or yellow crystalline solid is also used as an electrode (mixed with graphite) in zinc-mercuric oxide electric cells and in mercury batteries. Mercury(II) sulfide, HgS, is a black or red crystalline solid used chiefly as a pigment in paints, rubber, and plastics.

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