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#576 2020-01-05 01:13:45

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

456) Magnet

Magnet, any material capable of attracting iron and producing a magnetic field outside itself. By the end of the 19th century all the known elements and many compounds had been tested for magnetism, and all were found to have some magnetic property. The most common was the property of diamagnetism, the name given to materials exhibiting a weak repulsion by both poles of a magnet. Some materials, such as chromium, showed paramagnetism, being capable of weak induced magnetization when brought near a magnet. This magnetization disappears when the magnet is removed. Only three elements, iron, nickel, and cobalt, showed the property of ferromagnetism (i.e., the capability of remaining permanently magnetized).

Magnetization Process

The quantities now used in characterizing magnetization were defined and named by William Thomson (Lord Kelvin) in 1850. The symbol B denotes the magnitude of magnetic flux density inside a magnetized body, and the symbol H denotes the magnitude of magnetizing force, or magnetic field, producing it. The two are represented by the equation B = μH, in which the Greek letter mu, μ, symbolizes the permeability of the material and is a measure of the intensity of magnetization that can be produced in it by a given magnetic field. The modern units of the International Standard (SI) system for B are teslas (T) or webers per square metre (Wb/m²) and for H are amperes per metre (A/m). The units were formerly called, respectively, gauss and oersted. The units of μ are henrys per metre.

All ferromagnetic materials exhibit the phenomenon of hysteresis, a lag in response to changing forces based on energy losses resulting from internal friction. If B is measured for various values of H and the results are plotted in graphic form, the result is a loop of the type shown in the accompanying figure, called a hysteresis loop. The name describes the situation in which the path followed by the values of B while H is increasing differs from that followed as H is decreasing. With the aid of this diagram, the characteristics needed to describe the performance of a material to be used as a magnet can be defined. Bs is the saturation flux density and is a measure of how strongly the material can be magnetized. Br is the remanent flux density and is the residual, permanent magnetization left after the magnetizing field is removed; this latter is obviously a measure of quality for a permanent magnet. It is usually measured in webers per square metre. In order to demagnetize the specimen from its remanent state, it is necessary to apply a reversed magnetizing field, opposing the magnetization in the specimen. The magnitude of field necessary to reduce the magnetization to zero is Hc, the coercive force, measured in amperes per metre. For a permanent magnet to retain its magnetization without loss over a long period of time, Hc should be as large as possible. The combination of large Br and large Hc will generally be found in a material with a large saturation flux density that requires a large field to magnetize it. Thus, permanent-magnet materials are often characterized by quoting the maximum value of the product of B and H, (BH)max, which the material can achieve. This product (BH)max is a measure of the minimum volume of permanent-magnet material required to produce a required flux density in a given gap and is sometimes referred to as the energy product.

It was suggested in 1907 that a ferromagnetic material is composed of a large number of small volumes called domains, each of which is magnetized to saturation. In 1931 the existence of such domains was first demonstrated by direct experiment. The ferromagnetic body as a whole appears unmagnetized when the directions of the individual domain magnetizations are distributed at random. Each domain is separated from its neighbours by a domain wall. In the wall region, the direction of magnetization turns from that of one domain to that of its neighbour. The process of magnetization, starting from a perfect unmagnetized state, comprises three stages: (1) Low magnetizing field. Reversible movements of the domain walls occur such that domains oriented in the general direction of the magnetizing field grow at the expense of those unfavourably oriented; the walls return to their original position on removal of the magnetizing field, and there is no remanent magnetization. (2) Medium magnetizing field. Larger movements of domain walls occur, many of which are irreversible, and the volume of favourably oriented domains is much increased. On removal of the field, all the walls do not return to their original positions, and there is a remanent magnetization. (3) High magnetizing field. Large movements of domain walls occur such that many are swept out of the specimen completely. The directions of magnetization in the remaining domains gradually rotate, as the field is increased, until the magnetization is everywhere parallel to the field and the material is magnetized to saturation. On removal of the field, domain walls reappear and the domain magnetizations may rotate away from the original field direction. The remanent magnetization has its maximum value.

The values of Br, Hc, and (BH)max will depend on the ease with which domain walls can move through the material and domain magnetization can rotate. Discontinuities or imperfections in the material provide obstacles to domain wall movement. Thus, once the magnetizing field has driven the wall past an obstacle, the wall will not be able to return to its original position unless a reversed field is applied to drive it back again. The effect of these obstacles is, therefore, to increase the remanence. Conversely, in a pure, homogeneous material, in which there are few imperfections, it will be easy to magnetize the material to saturation with relatively low fields, and the remanent magnetization will be small.

Demagnetization and magnetic anisotropy. As far as domain rotation is concerned, there are two important factors to be considered, demagnetization and magnetic anisotropy (exhibition of different magnetic properties when measured along axes in different directions). The first of these concerns the shape of a magnetized specimen. Any magnet generates a magnetic field in the space surrounding it. The direction of the lines of force of this field, defined by the direction of the force exerted by the field on a (hypothetical) single magnetic north pole, is opposite to the direction of field used to magnetize it originally. Thus, every magnet exists in a self-generated field that has a direction such as to tend to demagnetize the specimen. This phenomenon is described by the demagnetizing factor. If the magnetic lines of force can be confined to the magnet and not allowed to escape into the surrounding medium, the demagnetizing effect will be absent. Thus a toroidal (ring-shaped) magnet, magnetized around its perimeter so that all the lines of force are closed loops within the material, will not try to demagnetize itself. For bar magnets, demagnetization can be minimized by keeping them in pairs, laid parallel with north and south poles adjacent and with a soft-iron keeper laid across each end.

The relevance of demagnetization to domain rotation arises from the fact that the demagnetizing field may be looked upon as a store of magnetic energy. Like all natural systems, the magnet, in the absence of constraints, will try to maintain its magnetization in a direction such as to minimize stored energy; i.e., to make the demagnetizing field as small as possible. To rotate the magnetization away from this minimum-energy position requires work to be done to provide the increase in energy stored in the increased demagnetizing field. Thus, if an attempt is made to rotate the magnetization of a domain away from its natural minimum-energy position, the rotation can be said to be hindered in the sense that work must be done by an applied field to promote the rotation against the demagnetizing forces. This phenomenon is often called shape anisotropy because it arises from the domain’s geometry which may, in turn, be determined by the overall shape of the specimen.

Similar minimum-energy considerations are involved in the second mechanism hindering domain rotation, namely magnetocrystalline anisotropy. It was first observed in 1847 that in crystals of magnetic material there appeared to exist preferred directions for the magnetization. This phenomenon has to do with the symmetry of the atomic arrangements in the crystal. For example, in iron, which has a cubic crystalline form, it is easier to magnetize the crystal along the directions of the edges of the cube than in any other direction. Thus the six cube-edge directions are easy directions of magnetization, and the magnetization of the crystal is termed anisotropic.

Magnetic anisotropy can also be induced by strain in a material. The magnetization tends to align itself in accordance with or perpendicular to the direction of the in-built strain. Some magnetic alloys also exhibit the phenomenon of induced magnetic anisotropy. If an external magnetic field is applied to the material while it is annealed at a high temperature, an easy direction for magnetization is found to be induced in a direction coinciding with that of the applied field.

The above description explains why steel makes a better permanent magnet than does soft iron. The carbon in steel causes the precipitation of tiny crystallites of iron carbide in the iron that form what is called a second phase. The phase boundaries between the precipitate particles and the host iron form obstacles to domain wall movement, and thus the coercive force and remanence are raised compared with pure iron.

The best permanent magnet, however, would be one in which the domain walls were all locked permanently in position and the magnetizations of all the domains were aligned parallel to each other. This situation can be visualized as the result of assembling the magnet from a large number of particles having a high value of saturation magnetization, each of which is a single domain, each having a uniaxial anisotropy in the desired direction, and each aligned with its magnetization parallel to all the others.

Powder Magnets

The problem of producing magnets composed of compacted powders is essentially that of controlling particle sizes so that they are small enough to comprise a single domain and yet not so small as to lose their ferromagnetic properties altogether. The advantage of such magnets is that they can readily be molded and machined into desired shapes. The disadvantage of powder magnets is that when single-domain particles are packed together they are subject to strong magnetic interactions that reduce the coercive force and, to a lesser extent, the remanent magnetization. The nature of the interaction is essentially a reduction of a given particle’s demagnetizing field caused by the presence of its neighbours, and the interaction limits the maximum values of Hc and (BH)max that can be achieved. More success has attended the development of magnetic alloys.

High Anisotropy Alloys


The materials described above depend on shape for their large uniaxial anisotropy. Much work has also been done on materials having a large uniaxial magnetocrystalline anisotropy. Of these, the most successful have been cobalt–platinum (CoPt) and manganese–bismuth (MnBi) alloys.

Alnico Alloys

High coercive force will be obtained where domain wall motion can be inhibited. This condition can occur in an alloy in which two phases coexist, especially if one phase is a finely divided precipitate in a matrix of the other. Alloys containing the three elements iron, nickel, and aluminum show just such behaviour; and permanent magnet materials based on this system, with various additives, such as cobalt, copper, or titanium, are generally referred to as Alnico alloys.

Rare-Earth

–cobalt alloys. Isolated atoms of many elements have finite magnetic moments (i.e., the atoms are themselves tiny magnets). When the atoms are brought together in the solid form of the element, however, most interact in such a way that their magnetism cancels out and the solid is not ferromagnetic. Only in iron, nickel, and cobalt, of the common elements, does the cancelling-out process leave an effective net magnetic moment per atom in the vicinity of room temperature and above. Unfortunately, however, it loses its ferromagnetism at temperatures above 16° C (60° F) so that it is not of practical importance. Several of the rare-earth elements show ferromagnetic behaviour at extremely low temperatures, and many of them have large atomic moments. They are not, however, of great practical value.

Barium Ferrites

Barium ferrite, essentially BaO:6Fe2O3, is a variation of the basic magnetic iron-oxide magnetite but has a hexagonal crystalline form. This configuration gives it a very high uniaxial magnetic anisotropy capable of producing high values of Hc. The powdered material can be magnetically aligned and then compacted and sintered. The temperature and duration of the sintering process determines the size of the crystallites and provides a means of tailoring the properties of the magnet. For very small crystallites the coercive force is high and the remanence is in the region of half the saturation flux density. Larger crystallites give higher Br but lower Hc. This material has been widely used in the television industry for focussing magnets for television tubes.

A further development of commercial importance is to bond the powdered ferrite by a synthetic resin or rubber to give either individual moldings or extruded strips, or sheets, that are semiflexible and can be cut with knives. This material has been used as a combination gasket (to make airtight) and magnetic closure for refrigerator doors.

Permeable Materials

A wide range of magnetic devices utilizing magnetic fields, such as motors, generators, transformers, and electromagnets, require magnetic materials with properties quite contrary to those required for good permanent magnets. Such materials must be capable of being magnetized to a high value of flux density in relatively small magnetic fields and then must lose this magnetization completely on removal of the field.

Because iron has the highest value of magnetic moment per atom of the three ferromagnetic metals, it remains the best material for applications where a high-saturation flux density is required. Extensive investigations have been undertaken to determine how to produce iron as free from imperfections as possible, in order to attain the easiest possible domain wall motion. The presence of such elements as carbon, sulfur, oxygen, and nitrogen, even in small amounts, is particularly harmful; and thus sheet materials used in electrical equipment have a total impurity content of less than 0.4 percent.

Important advantages are obtained by alloying iron with a small amount (about 4 percent) of silicon. The added silicon reduces the magnetocrystalline anisotropy of the iron and hence its coercive force and hysteresis loss. Although there is a reduction in the saturation flux density, this loss is outweighed by the other advantages, which include increased electrical resistivity. The latter is important in applications where the magnetic flux alternates because this induces eddy currents in the magnetic material. The lower the resistivity and the higher the frequency of the alternations, the higher are these currents. They produce a loss of energy by causing heating of the material and will be minimized, at a given frequency, by raising the resistivity of the material.

By a suitable manufacturing process, silicon-iron sheet material can be produced with a high degree of preferred orientation of the crystallites. The material then has a preferred direction of magnetization, and in this direction high permeability and low loss are attained. Commercially produced material has about 3.2 percent silicon and is known as cold-reduced, grain-oriented silicon steel.

Alloys of nickel and iron in various proportions are given the general name Permalloy. As the proportion of nickel varies downward, the saturation magnetization increases, reaching a maximum at about 50 percent, falling to zero at 27 percent nickel, then rising again toward the value for pure iron. The magnetocrystalline anisotropy also falls from the value for pure nickel to a very low value in the region of 80 percent nickel, rising only slowly thereafter. Highest value of permeability is at 78.5 percent nickel, which is called Permalloy A. The maximum relative permeability, which can reach a value in the region of 1,000,000 in carefully prepared Permalloy A, makes the alloy useful and superior to iron and silicon iron at low flux densities.

In addition to barium ferrite, which has a hexagonal crystal form, most of the ferrites of the general formula MeO•Fe2O3, in which Me is a metal, are useful magnetically. They have a different crystalline form called spinel after the mineral spinel (MgAl2O4), which crystallizes in the cubic system. All the spinel ferrites are soft magnetic materials; that is, they exhibit low coercive force and narrow hysteresis loops. Furthermore, they all have a high electrical resistivity and high relative permeabilities, thus making them suitable for use in high-frequency electronic equipment. Their saturation magnetization, however, is low compared with the alloys, and this property limits their use in high-field, high-power transformers. They are hard, brittle, ceramic-like materials and are difficult to machine. Nevertheless, they are widely used, most importantly in computer memories.

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

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

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#577 2020-01-07 01:02:27

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

457) Migraine

Migraine, condition characterized by painful recurring headaches, sometimes with nausea and vomiting. Migraine typically recurs over a period lasting 4 to 72 hours and is often incapacitating. The primary type is migraine without aura (formerly called common migraine). This condition is commonly unilateral (affecting one side of the head), with severe throbbing or pulsating headache and nausea, vomiting, and sensitivity to light and sound.

Between 6 and 9 percent of men and about 17–18 percent of women have migraine. Approximately 2 percent of the global population suffers from chronic migraine. Prevalence of the condition peaks about the third or fourth decade of life for women and men.

In 2010 the World Health Organization ranked migraine as the 19th leading cause of medical-related disability in high-income countries. In the United States it was among the leading pain conditions causing missed days of work.

Causes And Symptoms

Migraine usually begins in a person’s teens or early 20s; however, it can start at any age, even early childhood. When migraine begins after age 50, an underlying brain disease may be the cause. The predisposition to migraine is approximately 50 percent genetic. It is believed that the brains of persons with migraine have hyperexcitable neurophysiological responses, with an inability to normally suppress the electrical response to certain visual and auditory stimuli.

Migraine attacks may be triggered by a variety of factors. Stress, changes in weather, menstruation, and too much or too little sleep are the most common triggers. Although certain foods were once commonly thought to trigger migraine attacks, the results of multiple studies have cast doubt on that assertion.

The presentation of migraine symptoms among patients can vary widely. For example, one patient might have mild unilateral headache with nausea and none of the other symptoms, and another might have a severe throbbing bilateral headache without nausea but with light and sound sensitivity. The two headaches are both migraine but have few symptoms in common.

Many migraine sufferers experience a cluster of symptoms, or “prodrome,” hours before the onset of the migraine headache. The prodrome can consist of yawning, fluid retention, pallor, nausea, light sensitivity, or mood changes, including sadness or irritability. Attempts to treat the prodrome and avoid the ensuing migraine have met with limited success; only a small percentage of patients actually benefit from prodrome treatment. Pain and other symptoms of migraine can be exacerbated by physical activities.

Migraine With Aura

About 20 to 30 percent of persons with migraine occasionally experience migraine with aura. Migraine aura is caused by cortical spreading depression, a neuroelectrical process in which abnormal neural activity migrates slowly across the surface of the brain. The pain is caused by inflammation of the trigeminal nerve (the largest of the cranial nerves) in the head; the inflammation extends to the meninges (the membranous coverings) of the brain. The inflammatory process is mediated by neuropeptides, small proteins that facilitate communication between neurons.

The most common migraine aura is visual. A visual migraine aura typically develops over the course of 4 to 5 minutes and then lasts for up to 60 minutes. It has a positive component, with flashing, shimmering lights, and a negative component, with a dark or gray area of diminished vision. This experience generally enlarges over time and migrates across the visual field.

The second most common type of migraine aura is a sensory aura. This usually starts as tingling and numbness in the hand, which then spreads up the arm and jumps to the face. In some cases it may start in the face or elsewhere. Other sensory migraine auras may cause language disturbances, one-sided weakness, or vertigo (pronounced dizziness and the sensation that one’s surroundings are rotating).

Migraine aura is generally followed by a migraine headache. In some cases, however, the aura is concurrent with the headache. In other cases aura may be followed by a tension-type headache or even no headache at all. When aura without headache begins in older individuals and is not completely typical, it resembles a transient ischemic attack, in which a blood vessel supplying a part of the brain is blocked. This is a warning sign of stroke, and the person needs to be evaluated urgently in a hospital.

Migraine is usually an episodic disorder, with attacks occurring several times per year to several times per week, but it may transform or evolve into chronic migraine, which features a continuous, or almost continuous, headache. This evolution from episodic to daily headache may be facilitated by the overuse of prescription or over-the-counter pain-relieving medications.

Research has shown that patients with chronic migraine, with or without aura, are more likely than healthy persons or persons with episodic migraine to have congenital defects of the heart, such as patent foramen ovale or right-to-left shunt. These conditions, known as atrial septal defects, are characterized by a persistent hole in the partition (or septum) between the upper (atrial) chambers of the heart. The pathophysiological relationship between atrial septal defects and migraine is unclear. Septal defects can be repaired surgically.

Treatment

The treatment of migraine is divided into the treatment of individual attacks and the prevention of future attacks. When over-the-counter medications are inadequate, prescription medications, such as dihydroergotamine or a triptan (a medication developed specifically to treat migraine), are prescribed. Butalbital (a barbiturate) and opioid-containing medications (e.g., codeine) should be avoided or severely restricted, because they cause medication-overuse headache, which is difficult to treat. These drugs also may permanently damage the pain system, and they are addictive.

Preventive treatments are indicated for individuals with frequent migraine, which is generally agreed to be more than four headache days per month.
Many preventive treatment options have been discovered by chance. For example, when migraine patients took medications such as certain antihypertensives (drugs that lower blood pressure), antidepressants, seizure medications, or neurotoxins (e.g., Botox) that were prescribed for other indications, they found that their headaches improved. Biofeedback and stress management are relatively effective preventive measures for migraine. Occasionally migraine symptoms are so severe and disabling
that hospitalization is required.

headache-treatment-types-300x180.png


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

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

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#578 2020-01-09 00:46:05

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

458) Emerald

Emerald, grass-green variety of beryl (q.v.) that is highly valued as a gemstone. The name comes indirectly from the Greek smaragdos, a name that seems to have been given to a number of stones having little in common except a green colour; Pliny’s smaragdus undoubtedly included several distinct species. Much confusion has arisen with respect to the “emerald” of the Scriptures: the Hebrew word rendered emerald in the Authorized Version probably meant carbuncle, a garnet.

The ancients appear to have obtained emeralds from Upper Egypt, where it is said to have been worked as early as 2000 BC. Greek miners were working the mines in the time of Alexander the Great, and later the mines yielded their gems to Cleopatra. Remains of extensive workings were discovered about 1817; “Cleopatra’s Mines” are situated in Jabal Sukayt and Jabal Zabārah near the Red Sea coast, east of Aswān. The Egyptian emeralds occur in mica schist and talc schist.

During the Spanish conquest of South America, vast quantities of emeralds were taken from several rich deposits in Colombia. The only South American emeralds now known occur near Bogotá, Colom. The most famous mine is at Muzo, but workings are known also at Coscuez. The emeralds are found in thin veins in a black bituminous limestone containing ammonites of Lower Cretaceous age.

About 1830 emeralds were discovered in the Urals. They have been worked on the River Takovaya, northeast of Sverdlovsk, where they occur in mica or chlorite schist. Emeralds have been found, also in mica schist, in the Habachtal, Austria, in granite in Eidsvold, Norway, and in a pegmatite vein piercing slaty rocks near Emmaville, N.S.W., Australia. Fine crystals have been obtained from Hiddenite, N.C., in the United States.

Many virtues were formerly ascribed to emeralds. When worn, the stone was held to be a preservative against epilepsy, and when held in the mouth it was believed to be a cure for dysentery. It was supposed to assist women at childbirth, to drive away evil spirits, and to preserve the chastity of the wearer. Administered internally, it was reputed to have great medicinal value. Its refreshing green colour was said to be good for the eyesight.

The physical properties of emerald are essentially the same as those of beryl. Its refractive and dispersive powers are not high, so that cut stones display little brilliancy or fire. The magnificent colour that gives extraordinary value to this gem is probably due to small amounts of chromium. The stone loses colour when strongly heated.

Because of emerald’s high value, attempts were long made to manufacture it synthetically. These efforts finally met with success between 1934 and 1937, when a German patent was issued to cover its synthesis. Synthetic emeralds are currently manufactured in the United States by either a molten-flux process or a hydrothermal method; in the latter technique, aquamarine crystals are placed in a water solution at elevated temperature and pressure and used as a seed to produce emeralds. The crystals thus grown appear very similar to natural crystals and rival them in colour and beauty.

emerald-gem-241324b.jpg


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

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

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#579 2020-01-11 00:55:41

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

459) Andromeda Galaxy

The Andromeda Galaxy (M31): Location, Characteristics & Image

The Andromeda galaxy, our Milky Way's closest neighbor, is the most distant object in the sky that you can see with your unaided eye — but only on a clear night from a location with a very dark sky. The galaxy is a beautiful spiral, but one fact you may not be aware of: We’re safe for a few billion years, but Andromeda is headed our way and on a collision course with the Milky Way.

Andromeda's close proximity to Earth — at only 2.5 million light-years away — makes it a convenient target to observe for extrapolations about other spiral galaxies. In recent years, scientists have done detailed studies of black holes, stars and other objects within the galaxy. This included a stunning mosaic of Andromeda galaxy images taken by the Hubble Space Telescope in 2015.

Location, location, location

The visible fuzzy patch of stars stretches about as long as the width of the full moon, and half as wide; only with significant magnification can you tell it stretches six times that length in fullness.

A spiral galaxy like the Milky Way, Andromeda contains a concentrated bulge of matter in the middle, surrounded by a disk of gas, dust, and stars and an immense halo. Though Andromeda contains approximately a trillion stars to the 250 billion in the Milky Way, our galaxy is actually more massive, because it is thought to contain more dark matter.

Collision course

Andromeda and the Milky Way are heading on a collision course that will alter the structure of the two galaxies forever. The galaxies are rushing closer to one another at about 70 miles per second (112 kilometers per second). Astronomers estimate that Andromeda will collide with the Milky Way in 4 billion years, with the merger concluding 6 billion years from now. By that time, the sun will have swollen into a red giant and swallowed up the terrestrial planets, so Earth will have other things to worry about.

Still, the fresh influx of dust should boost star formation in the new "Milkomeda" galaxy, and the Earthless sun may well leave the Milky Way for good. After a messy phase, where arms project crazily from the combined pair, the two should settle into a smooth elliptical galaxy.

Galaxy collisions are a normal part of the universe's evolution. In fact, both Andromeda and the Milky Way bear signs of having already crashed into other galaxies. Andromeda boasts a large ring of dust in its center, giving it an interesting shape. Astronomers believe this dust may have formed when it swallowed an existing galaxy.

Early observational history

In 964, the Persian astronomer Abd al-Rahman al-Sufi described the galaxy as a "small cloud" in his "Book of Fixed Stars," the first known report of our nearest neighbor. When Charles Messier labeled it M31 in 1764, he incorrectly credited the discovery of what was then called a nebula to the German astronomer, Simon Marius, who provided the first telescopic observation of the object. The first photographs of Andromeda were taken in 1887, by Isaac Roberts.

In the 1920s, the distant galaxy became part of the Great Debate between American astronomers Harlow Shapley and Heber Curtis. At the time, astronomers thought the Milky Way composed the whole universe, and the strange patches known as nebulae lay inside of them. Curtis had spotted various novae in Andromeda, and argued instead that it was a separate galaxy.

The discussion wasn't concluded until 1925, when Edwin Hubble identified a special kind of star known as a Cepheid variable — a star whose characteristics allow for precise measurements of distance — within Andromeda. Because Shapley had previously determined that the Milky Way was only 100,000 light-years across, Hubble's calculations revealed that the fuzzy patch was too far away to lie within the Milky Way.

Hubble went on to use his measurements of the Doppler shifts of the galaxies to determine that the universe was expanding. The calculated distance to Andromeda doubled in the 1940s when Walter Baade was the first to observe individual stars in the central region of the galaxy, and found two different types of Cepheid variables. Radio maps of Andromeda followed in the 1950s, after radio emissions were detected by Hanbury Brown and Cyril Hazard at Jodrell Bank Observatory.

Recent Andromeda discoveries

Our understanding of the size of the Andromeda galaxy has grown bigger in recent years. In 2015, observations from the Hubble Space Telescope found that a halo of material surrounding Andromeda is six times larger and 1,000 times more massive than what was previously measured. (At the time, astronomers said the Milky Way may have a halo as well — and perhaps the two galaxies' halos are already starting to merge.) This follows on from revised size estimates in 2005 and 2007, based on observing stars and star motions.

In 2015, scientists released the most detailed photo of Andromeda ever using a mosaic of images from the Hubble Space Telescope. The image included 7,398 exposures taken over 411 pointings of the telescope. The image revealed more than 100 million stars within the galaxy, as well as dust structures and other features. At the time, scientists said the images would help with extrapolating the structure of spiral galaxies that are even farther from Earth, making them more difficult to view in such detail.

Black hole activities within Andromeda also came under scrutiny. In late 2017, scientists unexpectedly found two supermassive black holes closely orbiting each other. At the time, the research team said these black holes were likely the "most tightly coupled" of any supermassive ones known.

A search using NASA's Chandra X-Ray Telescope yielded 26 black hole candidates in Andromeda in 2013, making this the biggest catch of such candidates ever found in another galaxy besides our own Milky Way. Another 40 black holes were tracked down in 2016 using NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), which specializes in X-ray observations.

Scientists tracked down a probable pulsar — a dead star that spins rapidly — in Andromeda in 2017. The X-ray source was first cataloged by NASA's Swift satellite as object Swift J0042.6+4112, and then characterized by NuSTAR. The newer observations found that this object's spectrum of light appears similar to pulsars in the Milky Way.

Other miscellaneous discoveries in Andromeda include tracking star birth and death in infrared wavelengths in 2011; discovering gamma-ray radiation in 2017 that could be an indication of dark matter, a substance that is only known through its effects on "ordinary" matter such as galaxies; and spotting a ring of dwarf galaxies around Andromeda in 2013 — something that could also be present around the Milky Way.

M31-Andromeda-Galaxy.jpg


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

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

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#580 2020-01-12 00:57:53

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

460) Parkinson's disease

Overview

Parkinson's disease is a progressive nervous system disorder that affects movement. Symptoms start gradually, sometimes starting with a barely noticeable tremor in just one hand. Tremors are common, but the disorder also commonly causes stiffness or slowing of movement.

In the early stages of Parkinson's disease, your face may show little or no expression. Your arms may not swing when you walk. Your speech may become soft or slurred. Parkinson's disease symptoms worsen as your condition progresses over time.

Although Parkinson's disease can't be cured, medications might significantly improve your symptoms. Occasionally, your doctor may suggest surgery to regulate certain regions of your brain and improve your symptoms.

Symptoms

Parkinson's disease signs and symptoms can be different for everyone. Early signs may be mild and go unnoticed. Symptoms often begin on one side of your body and usually remain worse on that side, even after symptoms begin to affect both sides.

Parkinson's signs and symptoms may include:

•    Tremor. A tremor, or shaking, usually begins in a limb, often your hand or fingers. You may a rub your thumb and forefinger back-and-forth, known as a pill-rolling tremor. Your hand may tremor when it's at rest.
•    Slowed movement (bradykinesia). Over time, Parkinson's disease may slow your movement, making simple tasks difficult and time-consuming. Your steps may become shorter when you walk. It may be difficult to get out of a chair. You may drag your feet as you try to walk.
•    Rigid muscles. Muscle stiffness may occur in any part of your body. The stiff muscles can be painful and limit your range of motion.
•    Impaired posture and balance. Your posture may become stooped, or you may have balance problems as a result of Parkinson's disease.
•    Loss of automatic movements. You may have a decreased ability to perform unconscious movements, including blinking, smiling or swinging your arms when you walk.
•    Speech changes. You may speak softly, quickly, slur or hesitate before talking. Your speech may be more of a monotone rather than with the usual inflections.
•    Writing changes. It may become hard to write, and your writing may appear small.

When to see a doctor

See your doctor if you have any of the symptoms associated with Parkinson's disease — not only to diagnose your condition but also to rule out other causes for your symptoms.

Causes

In Parkinson's disease, certain nerve cells (neurons) in the brain gradually break down or die. Many of the symptoms are due to a loss of neurons that produce a chemical messenger in your brain called dopamine. When dopamine levels decrease, it causes abnormal brain activity, leading to symptoms of Parkinson's disease.

The cause of Parkinson's disease is unknown, but several factors appear to play a role, including:

•    Your genes. Researchers have identified specific genetic mutations that can cause Parkinson's disease. But these are uncommon except in rare cases with many family members affected by Parkinson's disease.
However, certain gene variations appear to increase the risk of Parkinson's disease but with a relatively small risk of Parkinson's disease for each of these genetic markers.
•    Environmental triggers. Exposure to certain toxins or environmental factors may increase the risk of later Parkinson's disease, but the risk is relatively small.

Researchers have also noted that many changes occur in the brains of people with Parkinson's disease, although it's not clear why these changes occur. These changes include:

•    The presence of Lewy bodies. Clumps of specific substances within brain cells are microscopic markers of Parkinson's disease. These are called Lewy bodies, and researchers believe these Lewy bodies hold an important clue to the cause of Parkinson's disease.
•    Alpha-synuclein is found within Lewy bodies. Although many substances are found within Lewy bodies, scientists believe an important one is the natural and widespread protein called alpha-synuclein (a-synuclein). It's found in all Lewy bodies in a clumped form that cells can't break down. This is currently an important focus among Parkinson's disease researchers.

Risk factors

Risk factors for Parkinson's disease include:

•    Age. Young adults rarely experience Parkinson's disease. It ordinarily begins in middle or late life, and the risk increases with age. People usually develop the disease around age 60 or older.
•    Heredity. Having a close relative with Parkinson's disease increases the chances that you'll develop the disease. However, your risks are still small unless you have many relatives in your family with Parkinson's disease.
•    Gender. Men are more likely to develop Parkinson's disease than are women.
•    Exposure to toxins. Ongoing exposure to herbicides and pesticides may slightly increase your risk of Parkinson's disease.

Complications

Parkinson's disease is often accompanied by these additional problems, which may be treatable:

•    Thinking difficulties. You may experience cognitive problems (dementia) and thinking difficulties. These usually occur in the later stages of Parkinson's disease. Such cognitive problems aren't very responsive to medications.
•    Depression and emotional changes. You may experience depression, sometimes in the very early stages. Receiving treatment for depression can make it easier to handle the other challenges of Parkinson's disease.
You may also experience other emotional changes, such as fear, anxiety or loss of motivation. Doctors may give you medications to treat these symptoms.
•    Swallowing problems. You may develop difficulties with swallowing as your condition progresses. Saliva may accumulate in your mouth due to slowed swallowing, leading to drooling.
•    Chewing and eating problems. Late-stage Parkinson's disease affects the muscles in your mouth, making chewing difficult. This can lead to choking and poor nutrition.
•    Sleep problems and sleep disorders. People with Parkinson's disease often have sleep problems, including waking up frequently throughout the night, waking up early or falling asleep during the day.

People may also experience rapid eye movement sleep behavior disorder, which involves acting out your dreams. Medications may help your sleep problems.

•    Bladder problems. Parkinson's disease may cause bladder problems, including being unable to control urine or having difficulty urinating.
•    Constipation. Many people with Parkinson's disease develop constipation, mainly due to a slower digestive tract.

You may also experience:

•    Blood pressure changes. You may feel dizzy or lightheaded when you stand due to a sudden drop in blood pressure (orthostatic hypotension).
•    Smell dysfunction. You may experience problems with your sense of smell. You may have difficulty identifying certain odors or the difference between odors.
•    Fatigue. Many people with Parkinson's disease lose energy and experience fatigue, especially later in the day. The cause isn't always known.
•    Pain. Some people with Parkinson's disease experience pain, either in specific areas of their bodies or throughout their bodies.
•    Carnal dysfunction. Some people with Parkinson's disease notice a decrease in carnal desire or performance.

Prevention

Because the cause of Parkinson's is unknown, proven ways to prevent the disease also remain a mystery.

Some research has shown that regular aerobic exercise might reduce the risk of Parkinson's disease.

Some other research has shown that people who drink caffeine — which is found in coffee, tea and cola — get Parkinson's disease less often than those who don't drink it.

However, it is still not known whether caffeine actually protects against getting Parkinson's, or is related in some other way. Currently there is not enough evidence to suggest drinking caffeinated beverages to protect against Parkinson's. Green tea is also related to a reduced risk of developing Parkinson's disease.

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

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

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#581 2020-01-14 01:08:36

ganesh
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Posts: 29,596

Re: Miscellany

461) Diamond

Diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.

The hardness, brilliance, and sparkle of diamonds make them unsurpassed as gems. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April. Diamond stones are weighed in carats (1 carat = 200 milligrams) and in points (1 point = 0.01 carat). In addition to gem-quality stones, several varieties of industrial diamonds occur, and synthetic diamonds have been produced on a commercial scale since 1960.

Diamonds are found in three types of deposits: alluvial gravels, glacial tills, and kimberlite pipes. The kimberlite pipes (such as those at Kimberley, South Africa) form from intrusions of magma into the Earth’s crust and deliver diamonds and other rocks and minerals from the mantle. The pipes themselves are often less than 100 million years old. However, the diamonds they carry were formed 1 to 3.3 billion years ago at depths of more than about 75 miles (120 km). Diamonds found in alluvial and glacial gravels must have been released by fluvial or glacial erosion of the kimberlite matrix and then redeposited in rivers or in glacial till.

Diamonds vary from colourless to black, and they may be transparent, translucent, or opaque. Most diamonds used as gems are transparent and colourless or nearly so. Colourless or pale blue stones are most valued, but these are rare; most gem diamonds are tinged with yellow. A “fancy” diamond has a distinct body colour; red, blue, and green are rarest, and orange, violet, yellow, and yellowish green more common. Most industrial diamonds are gray or brown and are translucent or opaque, but better-quality industrial stones grade imperceptibly into poor quality gems. The colour of diamonds may be changed by exposure to intense radiation (as released in a nuclear reactor or by a particle accelerator) or by heat treatment.

A very high refractive power gives the diamond its extraordinary brilliance. A properly cut diamond will return a greater amount of light to the eye of the observer than will a gem of lesser refractive power and will thus appear more brilliant. The high dispersion gives diamonds their fire, which is caused by the separation of white light into the colours of the spectrum as it passes through the stone.

The scratch hardness of diamond is assigned the value of 10 on the Mohs scale of hardness; corundum, the mineral next to diamond in hardness, is rated as 9. Actually, diamond is very much harder than corundum; if the Mohs scale were linear, diamond’s value would be about 42. The hardness of a diamond varies significantly in different directions, causing cutting and polishing of some faces to be easier than others.

In the atomic structure of diamond, as determined by X-ray diffraction techniques, each carbon atom is linked to four equidistant neighbours throughout the crystal. This close-knit, dense, strongly bonded crystal structure yields diamond properties that differ greatly from those of graphite, native carbon’s other form.

Industrial diamond

Industrial diamond, any diamond that is designated for industrial use, principally as a cutting tool or abrasive. In general, industrial diamonds are too badly flawed, irregularly shaped, poorly coloured, or small to be of value as gems, but they are of vital importance in the modern metalworking and mining industries. Their utility stems from the fact that diamond is the hardest natural substance known.

Industrial diamonds can be mined from natural deposits, or they can be produced synthetically. Among the naturally occurring diamonds, three varieties exist: ballas, bort, and carbonado.

Ballas, or shot bort, is composed of concentrically arranged, spherical masses of minute diamond crystals. Ballas is extremely hard, tough, and difficult to cleave. Principal sources are Brazil and South Africa. Brazilian ballas is said to be the harder of the two.

Bort is a gray to black massive diamond, the colour of which is caused by inclusions and impurities. The name is also applied to badly coloured, flawed, or irregularly shaped diamond crystals that are unsuited for gem purposes. Drilling bort is composed of small, round stones averaging 20 to the carat and is used in diamond drill bits. Crushing bort, the lowest grade of diamond, is crushed in steel mortars and graded into abrasive grits of various sizes; 75 percent of the world’s crushing bort comes from Congo (Kinshasa). Its chief use is in the manufacture of grinding wheels for sharpening cemented carbide metal-cutting tools, but it also is used as loose grains suspended in oil or water for lapping and polishing.

Carbonado, known in the trade as carbon, is black opaque diamond. It is as hard as crystallized diamond but less brittle, and, because its structure is slightly porous, it has a lower specific gravity (3.51 to 3.29). Carbonado has no cleavage and therefore is valuable for use in diamond-set tools. It usually occurs in small masses in the diamond-bearing gravels of Bahia, Brazil, and in Borneo, but it is also found in the Central African Republic and in Siberia. Rock-coring drills, widely used in exploring for new mineral deposits, are made by mounting diamonds around the rim of a hollow metal drill crown. Other important applications include saws for cutting rock and other hard materials, lathes and other types of cutting tools, glass cutters, phonograph needles, hardness testers, and wire-drawing dies.

By the early 21st century, Congo (Kinshasa) and Russia led the world in industrial diamond production. Other major producers of industrial diamonds include Australia and Botswana.

Synthetic diamond

Synthetic diamond, man-made diamond that is usually produced by subjecting graphite to very high temperatures and pressures. Synthetic diamond resembles natural diamond in most fundamental properties, retaining the extreme hardness, broad transparency (when pure), high thermal conductivity, and high electrical resistivity for which diamond is highly prized. Because synthesis is an expensive process, large stones of gem quality are rarely made. Instead, most synthetic diamond is produced as grit or small crystals that are used to provide hard coatings for industrial equipment such as grinding wheels, machine tools, wire-drawing dies, quarrying saws, and mining drills. In addition, diamond films can be grown on various materials by subjecting carbon-containing gas to extreme heat, and those layers can be used in cutting tools, windows for optical devices, or substrates for semiconductors.

In 1880 the Scottish chemist James Ballantyne Hannay claimed that he had made diamonds by heating a mixture of paraffin, bone oil, and lithium to red heat in sealed wrought-iron tubes. In 1893 the French chemist Henri Moissan announced he had been successful in making diamonds by placing a crucible containing pure carbon and iron in an electric furnace and subjecting the very hot (about 4,000 °C [7,000 °F]) mixture to great pressure by sudden cooling in a water bath. Neither of those experiments has been repeated successfully.

During the first half of the 20th century, the American physicist Percy Williams Bridgman conducted extensive studies of materials subjected to high pressures. His work led to the synthesis by the General Electric Company, Schenectady, New York, of diamonds in its laboratory in 1955. The stones were made by subjecting graphite to pressures approaching 7 gigapascals (1 million pounds per square inch) and to temperatures above 1,700 °C (3,100 °F) in the presence of a metal catalyst. Tons of diamonds of industrial quality have been made in variations of that process every year since 1960.

In 1961 shock-wave methods, or explosive-shock techniques, were first used to produce diamond powder, and small quantities of the material are still formed that way. Beginning in the 1950s, Russian researchers began to investigate methods for synthesizing diamond by decomposition of carbon-containing gases such as methane at high heat and low pressure. In the 1980s commercially viable versions of this chemical vapour deposition method were developed in Japan.

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

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

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#582 2020-01-16 01:01:05

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

462) Pummelo

Pummelo, (Citrus maxima), also spelled pomelo, also called shaddock, citrus tree of the family Rutaceae, grown for its large sweet fruits. It is native to mainland Southeast Asia and the Malaysian portion of the island of Borneo. It is sometimes called shaddock, a name that is said to have derived from that of a captain who introduced the tree to the West Indies. The fruit is highly prized in Asia, and the rind is sometimes candied or used in marmalade. Pummelo is one of the original citrus species from which most commercial cultivars are derived; the grapefruit (Citrus ×paradisi), for example, is a cross of pummelo and sweet orange (C. ×sinensis).

Pummelo trees reach 6–13 metres (20–43 feet) in height. The oval evergreen leaves have broadly winged petioles (leaf stems) and are downy on the undersurface, as are the young shoots. The flowers are large and white and are succeeded by very large spheroid or almost pear-shaped fruits, which are lemon-yellow to green in colour and have a sweet flavour. The pulp segments are either pallid or pink and shell out easily from the thick rind.

9 Health Benefits of Pomelo (and How to Eat It)

Pomelo is a large Asian citrus fruit that’s closely related to grapefruit.
It’s shaped like a teardrop and has green or yellow flesh and a thick, pale rind. It can grow to the size of a cantaloupe or larger.
Pomelo tastes similar to grapefruit, but it’s sweeter.
It contains several vitamins, minerals, and antioxidants that make it a healthy addition to your diet.

Here are 9 health benefits of pomelo, including how to easily add it to your diet.


1. Highly nutritious

Pomelo contains a variety of vitamins and minerals and is an excellent source of vitamin C.

One peeled pomelo (about 21 ounces or 610 grams) contains:

•    Calories: 231
•    Protein: 5 grams
•    Fat: 0 grams
•    Carbs: 59 grams
•    Fiber: 6 grams
•    Riboflavin: 12.6% of the Daily Value (DV)
•    Thiamine: 17.3% of the DV
•    Vitamin C: 412% of the DV
•    Copper: 32% of the DV
•    Potassium: 28% of the DV

One fruit packs several days’ worth of vitamin C, a powerful immune-boosting antioxidant that helps prevent cellular damage from harmful compounds called free radicals).

Pomelo is also rich in other vitamins and minerals, including potassium, which helps regulate fluid balance and blood pressure).
Furthermore, pomelo contains several other vitamins and minerals in smaller amounts.

Summary : Pomelo is particularly rich in vitamin C and potassium and contains several other vitamins and minerals, as well as protein and fiber.

2. Full of fiber

One pomelo offers 6 grams of fiber. Most people should aim to get at least 25 grams of fiber per day, so the fruit is an excellent way to help you meet your needs).
It’s particularly rich in insoluble fiber, which helps add bulk to your stool and prevent constipation).

Dietary fiber also serves as a food source for the healthy bacteria in your gut).

In addition, fruit fiber, such as that of pomelo, has been associated with improved bone density, long-term weight maintenance, improved gut and brain health, and a decreased risk of some chronic diseases).

Summary : One pomelo packs 6 grams of fiber. Fiber can help add bulk to your stools, feed healthy gut bacteria, and promote overall wellness.

3. May promote weight loss

Pomelo may help you lose weight.

One peeled pomelo (about 21 ounces or 610 grams) contains 230 calories, which is a relatively low number for such a large volume of food.
Eating a lot of low calorie foods can help keep you full on fewer calories.
What’s more, pomelo contains protein and fiber, both of which can help keep you feeling full for longer.
Both protein- and fiber-containing foods help induce feelings of fullness. Thus, you may find it easier to reduce your calorie intake and lose weight by choosing these foods.

Summary : Pomelo fruit is relatively low in calories for its large size and contains protein and fiber — both of which can help you feel full for longer.

4. Rich in antioxidants

Pomelo is full of antioxidants, which can help prevent and reverse cellular damage caused by free radicals.
Free radicals are compounds found in the environment and food. They can cause health problems and chronic disease when they build up in your body in high levels.
Pomelo not only contains over 400% of the DV for vitamin C, a powerful antioxidant, but also packs several other antioxidant compounds.
The main antioxidants in pomelo are naringenin and naringin, both of which are commonly found in citrus fruits.
Additionally, pomelos contain lycopene, an anti-inflammatory antioxidant that’s also present in tomatoes.
Many of the benefits of pomelos, such as their anti-aging and heart-healthy properties, are credited to their high antioxidant content.

Summary : Pomelos contain high levels of antioxidants, including vitamin C, naringenin, naringin, and lycopene, which may offer various health benefits.

5. May boost heart health

Pomelos may boost heart health by reducing levels of cholesterol and triglycerides, two blood fats that have been linked to heart disease.
One 21-day study in rats found that supplementing with concentrated pomelo extract reduced triglyceride levels by up to 21%, total cholesterol by up to 6%, and LDL (bad) cholesterol by up to 41%.
Another study noted that pomelo may reduce these blood fats by preventing the cholesterol in food from being fully absorbed into the body.
However, more research in humans is needed to establish a connection between pomelo fruit and heart health.
Note that you should avoid pomelo if you’re taking statin drugs for high cholesterol.
Like grapefruits, pomelos contain compounds called furanocoumarins, which can affect the metabolism of statins.

Summary : Pomelo extract has been shown to reduce blood fat levels in animal studies, but more research in humans is needed. If you’re taking a statin drug, you should avoid pomelo.

6. May have anti-aging properties

Due to its high antioxidant content, pomelo may exert anti-aging effects.
Antioxidants, including vitamin C, can help prevent skin damage caused by harmful free radicals, helping you maintain a more youthful appearance.
Pomelo may also decrease the formation of advanced glycation end products (AGEs), which are caused by high blood sugar levels.
AGEs can contribute to the aging process by causing skin discoloration, poor circulation, and vision and kidney problems — especially in people with type 2 diabetes.
However, one test-tube study found that pomelo extract significantly decreased the amount of AGEs that were formed after exposure to sugar.
Moreover, essential oil from the peel of pomelo is rich in antioxidants and can decrease melanin production in the skin, potentially helping prevent discoloration and sunspots .

Summary : Pomelo may have anti-aging properties due to its antioxidant content and ability to decrease the formation of AGEs.

7. May be antibacterial and antifungal

Pomelo may also have antibacterial and antifungal properties, though most of the research on these effects has used essential oils made from pomelo peel.
In one test-tube study, pomelo essential oil slowed the growth of bacteria on soft contact lenses.
Another study observed that pomelo essential oil killed Penicillium expansum, a fungus that can produce a harmful neurotoxin, more effectively than orange, lime, or lemon oils.
While the fruit itself may boast some of these antibacterial and antifungal properties, more research is needed.
Because essential oils are highly concentrated, you should not ingest them, and they should be properly diluted before you apply them to your skin.

Summary : Pomelo essential oils are antibacterial and antifungal. However, more research is needed to understand whether the fruit offers these benefits.

8. May fight cancer cells

Pomelo may likewise help kill cancer cells and prevent the spread of cancer.
One study in mice found that pomelo peel extract suppressed tumor growth, boosted the immune system, and killed cancer cells.
A similar study observed that an extract made from pomelo leaves killed skin cancer cells in mice.
In addition, naringenin — one of the main antioxidants in pomelo — has been shown to kill prostate and pancreatic cancer cells, as well as slow the spread of lung cancer in test-tube studies.
Still, more research in humans is needed to fully understand pomelo’s effect on cancer.
Finally, it’s important to remember that pomelo fruit contains much smaller amounts of these potentially cancer-killing compounds than the concentrated forms used in studies.

Summary : Extract from pomelo peels and leaves have been shown to kill cancer cells and prevent the spread of cancer in test-tube studies. However, more research in humans is needed to understand how pomelo fruit affects cancer.

9. Easy to add to your diet

Pomelo is easy to add to your diet.
You may be able to purchase fresh pomelo at a local Asian market, and dried pomelo is available online.
Though dried pomelo is commonly used to make desserts or eaten as candy in some Asian countries, it’s much higher in calories and added sugar than fresh pomelo.
To peel pomelo, cut off an inch (2.5 cm) from the pointed end of the fruit. Then cut several inch-long (2.5 cm-long) notches into the thick rind around its diameter.
Peel the rind off section by section using these notches.
After peeling the skin, you can easily divide the remaining fruit into sections. Like other citrus fruits, pomelo fruit is separated into sections by a thin, white, fibrous membrane — called the pith — that makes it easy to pull apart.
Pomelo can be eaten by itself as a snack or used as a substitute for other citrus fruits in recipes. It also makes an excellent addition to salads.

Summary : Pomelo is easy to peel and can be eaten by itself or used in recipes. Dried pomelo contains more sugar and calories than raw pomelo.

The bottom line

Pomelo is a highly nutritious fruit that’s low in calories and full of vitamins, minerals, and antioxidants.
It also contains fiber and protein, which can help keep you full for longer.
While it boasts many potential benefits, more research in humans is needed to fully understand its health effects.
All in all, pomelo fruit is a healthy, unique addition to your diet.

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

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

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#583 2020-01-17 01:12:33

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

463) Barbie

Barbie, in full Barbara Millicent Roberts, an 11-inch- (29-cm-) tall plastic doll with the figure of an adult woman that was introduced on March 9, 1959, by Mattel, Inc., a southern California toy company. Ruth Handler, who cofounded Mattel with her husband, Elliot, spearheaded the introduction of the doll. Barbie’s physical appearance was modeled on the German Bild Lilli doll, a risqué gag gift for men based upon a cartoon character featured in the West German newspaper Bild Zeitung.

Since the doll’s inception its body has incited controversy. Mothers in a 1958 Mattel-sponsored market study before the doll’s release criticized Barbie for having “too much of a figure.” Mattel circumvented this problem, however, by advertising Barbie directly to children via television. Mattel, in fact, upon sponsoring Walt Disney’s Mickey Mouse Club program in 1955, became the first toy company to broadcast commercials to children.

In response to consumer demand, in 1961 Mattel brought out Barbie’s ultimate “accessory”—her boyfriend, Ken. (The Handlers’ children were named Barbara and Ken.) In 1963 Mattel added Barbie’s best friend, Midge, and in 1964 her little sister, Skipper. By 1968 Barbie had been issued “friend” dolls of colour, but not until 1980 was the Barbie doll itself released in an African American incarnation.

Since the 1970s, Barbie has been criticized for materialism (amassing cars, houses, and clothes) and unrealistic body proportions. In fact, in 1994 researchers in Finland announced that if Barbie were a real woman, she would not have enough body fat to menstruate. Yet many women who played with the doll credit Barbie with providing an alternative to restrictive 1950s gender roles. Unlike baby dolls, Barbie did not teach nurturing. Outfitted with career paraphernalia, the doll was a model for financial self-sufficiency. (Barbie’s résumé includes, among other things, airline pilot, astronaut, doctor, Olympic athlete, and United States presidential candidate.) Nor was the doll defined by relationships of responsibility to men or family. Barbie has no parents or offspring. When in the early 1960s consumers clamoured for a Barbie-scale baby, Mattel did not make Barbie a mother but issued a “Barbie Baby-Sits” playset.

Although Mattel has positioned Barbie as the ultimate American girl, the doll has never been manufactured in the United States, to avoid higher labour costs. Today the doll has come to symbolize consumer capitalism and is as much a global brand as Coca-Cola, with key markets in Europe, Latin America, and Asia. In 2009 Mattel opened a six-floor flagship Barbie store in Shanghai, featuring a spa, a design studio, and a café in addition to a wide offering of Barbie-related products. Barbie never won the approval of authorities in the Muslim world, however. In 1995 Saudi Arabia stopped its sale because it violated the Islamic dress code. Eventually, similar dolls, some complete with hijabs (head coverings), were marketed to Muslim girls.

Mattel registered Barbie as a work of art, but the doll has also inspired works of art, including a 1986 Andy Warhol portrait and photographs by William Wegman and David Levinthal. Novelists, including A.M. Homes and Barbara Kingsolver, have used the doll in fiction. When interpreting Barbie, artists tend to take one of two approaches: idealizing the doll or, more commonly, using the doll to critique ideas associated with it, from exaggerated femininity to profligate consumption.

Barbie is a very popular collectible. Aficionados are interested in both old Barbies and the special edition Barbies that Mattel creates to cater to this market. Although Barbie’s sales since the year 2000 have not risen as steeply as they did in the 1990s, they still amount to more than a billion dollars annually. Every second, Mattel calculates, two Barbies are sold somewhere in the world.

barbie-doll-250x250.jpg


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

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

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#584 2020-01-18 01:03:35

ganesh
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Posts: 29,596

Re: Miscellany

464) Glider

Glider, nonpowered heavier-than-air craft capable of sustained flight. Though many men contributed to the development of the glider, the most famous pioneer was Otto Lilienthal (1848–96) of Germany, who, with his brother Gustav, began experiments in 1867 on the buoyancy and resistance of air. Lilienthal also investigated camber and wing sections and studied ways to increase the stability of the gliders he built, finally incorporating stabilizing tail surfaces. In 1891 he built his first man-carrying craft, with which he could take off by running downhill into the wind.

In 1896 Octave Chanute, French-born American engineer, began designing gliders that were flown by others under his supervision. He discarded Lilienthal’s method of securing control by a fixed rear fin with the horizontal tail parts freely hinging upward, and instead substituted a rudder and articulated (segmented) wings. Chanute’s gliders were so stable that they made 2,000 flights without an accident.

Orville and Wilbur Wright built their most successful early glider in 1902. Following experimentation they decided to use a vertical rudder that was movable in flight. They then added a horizontal elevator and combined their adjustable vertical rudder with a wing-warping mechanism that permitted them to move the trailing edges of the wings up and down. This perfect control made their gliding safe and allowed them to proceed to the powered airplane.

To fly, a glider must be accelerated to flying speed, the speed at which wings generate enough lift to overcome the force of gravity. In most of the early gliders, flying speed was very low; normal practice was to fly into a wind so that the actual acceleration required was not great. Today’s favoured launching techniques are the airplane tow and the automobile tow. The tow rope normally used is about 200 feet (60 metres) long with a steel ring attached at each end, fitting the tow hooks of the towing vehicle and the glider. Gliders are also launched by shock-cord launching, which works on the principle of a slingshot, or by winch tow, which works like a giant fishing reel, with the glider attached to one end like a fish. While hang gliders usually are launched from a high point and descend, sailplane gliders can soar for hours on the lift from thermals and rising air due to rising terrain.

Since 1935, gliders equipped with recording instruments have gained in reputation as tools for aeronautical and meteorological research. Gliders were widely used in World War II to carry troops and goods. They, and sailplanes in particular, have become increasingly popular for recreational purposes and as vehicles for sports competition.

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

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

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#585 2020-01-19 00:56:34

ganesh
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Re: Miscellany

465) Paint

Paint, decorative and protective coating commonly applied to rigid surfaces as a liquid consisting of a pigment suspended in a vehicle, or binder. The vehicle, usually a resin dissolved in a solvent, dries to a tough film, binding the pigment to the surface.

Paint was used for pictorial and decorative purposes in the caves of France and Spain as early as 15,000 BC. The earliest pigments, which were natural ores such as iron oxide, were supplemented by 6000 BC in China by calcined (fired) mixtures of inorganic compounds and organic pigments; vehicles were prepared from gum arabic, egg white, gelatin, and beeswax.

By 1500 BC the Egyptians were using dyes such as indigo and madder to make blue and red pigments. The exploitation of linseed oil (a drying oil useful as a vehicle) and zinc oxide (a white pigment) in the 18th century brought a rapid expansion of the European paint industry. The 20th century saw important developments in paint technology, including the introduction of synthetic polymers as vehicles and of synthetic pigments; a new understanding of the chemistry and physics of paints; and coating materials with greater fire retardancy, corrosion resistance, and heat stability. Most significant was a return to water-based paints in the form of latex paints that combine easy application and cleanup with reduced hazard of fire.

In modern paint manufacture, pigment particles are dispersed in the vehicle by cylindrical mills that tumble heavy metal or ceramic balls through the paint, or by sand grinders that circulate a suspension of sand through the paint at high speed.

The basic white pigments include zinc oxide, zinc sulfide, lithopone, and titanium dioxide. Most black pigments are composed of elemental carbon. Common red pigments include the minerals iron oxide, cadmium, and cuprous oxide and various synthetic organic pigments. Yellow and orange pigments include chromates, molybdates, and cadmium compounds. Blue and green pigments are either inorganic (synthetic ultramarines and iron blues) or organic (phthalocyanines). Extenders or fillers are sometimes added to paint to increase its spreadability and strength.

paint-emit-vocs-1.jpg


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

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

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#586 2020-01-20 01:20:40

ganesh
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Posts: 29,596

Re: Miscellany

466) Sapphire

Sapphire, transparent to translucent, natural or synthetic variety of corundum (q.v. : quod vide (q.v.) which see; aluminum oxide, Al2O3) that has been highly prized as a gemstone since about 800 BC. Its colour is due mainly to the presence of small amounts of iron and titanium and normally ranges from a very pale blue to deep indigo, with the most valued a medium-deep cornflower blue. Colourless, gray, yellow, pale pink, orange, green, violet, and brown varieties of gem corundum also are known as sapphire; red varieties are called ruby. Much sapphire is unevenly coloured; it is also dichroic; that is, the colour of most varieties changes with the direction of view. Alexandrite sapphire appears blue in daylight and reddish or violet in artificial illumination, somewhat like true alexandrite. Careful heating and cooling under various conditions can induce permanent colour changes in sapphire (e.g., from yellow to colourless or greenish blue and from violet to pink). Other colour changes result from exposure to intense radiation. Most sapphire contains abundant microscopic inclusions; reflections from these yield a faint whitish sheen, known as silk. Tiny, regularly arranged mineral inclusions (commonly rutile) and elongate cavities are responsible for the asterism shown by star sapphire.

Sapphire is a primary constituent of many igneous rocks, especially syenites, pegmatites, and various basic (silica-poor) types; it also occurs in schists and metamorphosed carbonate rocks. Most commercial production has come from alluvial gravels and other placer deposits, where the sapphire commonly is associated with ruby and other gem minerals. The best known sources, including some lode deposits, are in Sri Lanka, Myanmar (Burma), Thailand, Australia (Victoria, Queensland, New South Wales), India, Madagascar, Russia, South Africa, and the United States (Montana, North Carolina).

Most transparent sapphire is faceted, generally in the brilliant style. Such gems have considerable sparkle, but they exhibit little fire because of their modest dispersion (separation of light into its component colours). Skillful cutting of unevenly coloured stones yields gems with a uniform appearance derived from only small portions of relatively deep colour. Star sapphire and other nontransparent varieties are cut en cabochon (in convex form, highly polished) rather than faceted. Despite its great hardness, some sapphire is carved or engraved, especially in the Orient.

Synthetic sapphire has been produced commercially since 1902. Clear, sound material is manufactured in the form of carrot-shaped boules and slender rods. Much is consumed by the jewelry trade, but most synthetic material is used for the manufacture of jewel bearings, gauges, dies, phonograph-needle points, thread guides, and other specialized components; some also is used as a high-grade abrasive. Synthetic star sapphire is made with luminous stars that are more regular and distinct than those in most natural stones; the asterism is obtained through controlled exsolution of impurities.

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

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

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#587 2020-01-21 00:55:40

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

467) Amnesia

Amnesia, loss of memory occurring most often as a result of damage to the brain from trauma, stroke, Alzheimer disease, alcohol and drug toxicity, or infection. Amnesia may be anterograde, in which events following the causative trauma or disease are forgotten, or retrograde, in which events preceding the causative event are forgotten.

The condition also may be traced to severe emotional shock, in which case personal memories (e.g., identity) are affected. Such amnesia seems to represent a psychological escape from or denial of memories that might cause anxiety. These memories are not actually lost, since they can generally be recovered through psychotherapy or after the amnesic state has ended.

Occasionally amnesia may last for weeks, months, or even years, during which time the person may begin an entirely new life. Such protracted reactions are called fugue states. When recovered, the person is usually able to remember events that occurred prior to onset, but events of the fugue period are forgotten. Posthypnotic amnesia, the forgetting of most or all events that occur while under hypnosis in response to a suggestion by the hypnotist, has long been regarded as a sign of deep hypnosis.

The common difficulty of remembering childhood experiences is sometimes referred to as childhood amnesia.

Overview

Amnesia refers to the loss of memories, such as facts, information and experiences. Though forgetting your identity is a common plot device in movies and television, that's not generally the case in real-life amnesia.

Instead, people with amnesia — also called amnestic syndrome — usually know who they are. But, they may have trouble learning new information and forming new memories.

Amnesia can be caused by damage to areas of the brain that are vital for memory processing. Unlike a temporary episode of memory loss (transient global amnesia), amnesia can be permanent.

There's no specific treatment for amnesia, but techniques for enhancing memory and psychological support can help people with amnesia and their families cope.

Symptoms

The two main features of amnesia are:

•    Difficulty learning new information following the onset of amnesia (anterograde amnesia)
•    Difficulty remembering past events and previously familiar information (retrograde amnesia)

Most people with amnesia have problems with short-term memory — they can't retain new information. Recent memories are most likely to be lost, while more remote or deeply ingrained memories may be spared. Someone may recall experiences from childhood or know the names of past presidents, but not be able to name the current president, know what month it is or remember what was for breakfast.

Isolated memory loss doesn't affect a person's intelligence, general knowledge, awareness, attention span, judgment, personality or identity. People with amnesia usually can understand written and spoken words and can learn skills such as bike riding or piano playing. They may understand they have a memory disorder.
Amnesia isn't the same as dementia. Dementia often includes memory loss, but it also involves other significant cognitive problems that lead to a decline in daily functioning.

A pattern of forgetfulness is also a common symptom of mild cognitive impairment (MCI), but the memory and other cognitive problems in MCI aren't as severe as those experienced in dementia.

Additional signs and symptoms

Depending on the cause of the amnesia, other signs and symptoms may include:

•    False memories (confabulation), either completely invented or made up of genuine memories misplaced in time
•    Confusion or disorientation

When to see a doctor

Anyone who experiences unexplained memory loss, head injury, confusion or disorientation requires immediate medical attention.

A person with amnesia may not be able to identify his or her location or have the presence of mind to seek medical care. If someone you know has symptoms of amnesia, help the person get medical attention.

Causes

Normal memory function involves many parts of the brain. Any disease or injury that affects the brain can interfere with memory.

Amnesia can result from damage to brain structures that form the limbic system, which controls your emotions and memories. These structures include the thalamus, which lies deep within the center of your brain, and the hippocampal formations, which are situated within the temporal lobes of your brain.

Amnesia caused by brain injury or damage is known as neurological amnesia. Possible causes of neurological amnesia include:

•    Stroke
•    Brain inflammation (encephalitis) as a result of an infection with a virus such as herpes simplex virus, as an autoimmune reaction to cancer somewhere else in the body (paraneoplastic limbic encephalitis), or as an autoimmune reaction in the absence of cancer
•    Lack of adequate oxygen in the brain, for example, from a heart attack, respiratory distress or carbon monoxide poisoning
•    Long-term alcohol abuse leading to thiamin (vitamin B-1) deficiency (Wernicke-Korsakoff syndrome)
•    Tumors in areas of the brain that control memory
•    Degenerative brain diseases, such as Alzheimer's disease and other forms of dementia
•    Seizures
•    Certain medications, such as benzodiazepines or other medications that act as sedatives

Head injuries that cause a concussion, whether from a car accident or sports, can lead to confusion and problems remembering new information. This is especially common in the early stages of recovery. Mild head injuries typically do not cause lasting amnesia, but more-severe head injuries may cause permanent amnesia.
Another rare type of amnesia, called dissociative (psychogenic) amnesia, stems from emotional shock or trauma, such as being the victim of a violent crime. In this disorder, a person may lose personal memories and autobiographical information, but usually only briefly.

Risk factors

The chance of developing amnesia might increase if you've experienced:

•    Brain surgery, head injury or trauma
•    Stroke
•    Alcohol abuse
•    Seizures

Complications

Amnesia varies in severity and scope, but even mild amnesia takes a toll on daily activities and quality of life. The syndrome can cause problems at work, at school and in social settings.

It may not be possible to recover lost memories. Some people with severe memory problems need to live in a supervised situation or extended-care facility.

Prevention

Because damage to the brain can be a root cause of amnesia, it's important to take steps to minimize your chance of a brain injury. For example:

•    Avoid excessive alcohol use.
•    Wear a helmet when bicycling and a seat belt when driving.
•    Treat any infection quickly so that it doesn't have a chance to spread to the brain.
•    Seek immediate medical treatment if you have any symptoms that suggest a stroke or brain aneurysm, such as a severe headache or one-sided numbness or paralysis.

Diagnosis

To diagnose amnesia, a doctor will do a comprehensive evaluation to rule out other possible causes of memory loss, such as Alzheimer's disease, other forms of dementia, depression or a brain tumor.

Medical history

The evaluation starts with a detailed medical history. Because the person with memory loss may not be able to provide thorough information, a family member, friend or another caregiver generally takes part in the interview as well.

The doctor will ask many questions to understand the memory loss. Issues that might be addressed include:

•    Type of memory loss — recent or long term
•    When the memory problems started and how they progressed
•    Triggering factors, such as a head injury, stroke or surgery
•    Family history, especially of neurological disease
•    Drug and alcohol use
•    Other signs and symptoms, such as confusion, language problems, personality changes or impaired ability to care for self
•    History of seizures, headaches, depression or cancer

Physical exam

The physical examination may include a neurological exam to check reflexes, sensory function, balance, and other physiological aspects of the brain and nervous system.

Cognitive tests

The doctor will test the person's thinking, judgment, and recent and long-term memory. He or she will check the person's knowledge of general information — such as the name of the current president — as well as personal information and past events. The doctor may also ask the person to repeat a list of words.

The memory evaluation can help determine the extent of memory loss and provide insights about what kind of help the person may need.

Diagnostic tests

The doctor may order:

•    Imaging tests — including an MRI and CT scan — to check for brain damage or abnormalities
•    Blood tests to check for infection, nutritional deficiencies or other issues
•    An electroencephalogram to check for the presence of seizure activity

More Information

Treatment

Treatment for amnesia focuses on techniques and strategies to help make up for the memory problem, and addressing any underlying diseases causing the amnesia.

Occupational therapy

A person with amnesia may work with an occupational therapist to learn new information to replace what was lost, or to use intact memories as a basis for taking in new information.

Memory training may also include different strategies for organizing information so that it's easier to remember and for improving understanding of extended conversation.

Technological assistance

Many people with amnesia find it helpful to use smart technology, such as a smartphone or a hand-held tablet device. With some training and practice, even people with severe amnesia can use these electronic organizers to help with day-to-day tasks. For example, smartphones can be programmed to remind them about important events or to take medications.

Low-tech memory aids include notebooks, wall calendars, pill minders, and photographs of people and places.

Medications or supplements

No medications are currently available for treating most types of amnesia.

Amnesia caused by Wernicke-Korsakoff syndrome involves a lack of thiamin. Treatment includes replacing this vitamin and providing proper nutrition. Although treatment, which also needs to include alcohol abstinence, can help prevent further damage, most people won't recover all of their lost memory.

Research may one day lead to new treatments for memory disorders. But the complexity of the brain processes involved makes it unlikely that a single medication will be able to resolve memory problems.

Coping and support

Living with amnesia can be frustrating for those with memory loss, and for their family and friends, too. People with more-severe forms of amnesia may require direct assistance from family, friends or professional caregivers.

It can be helpful to talk with others who understand what you're going through, and who may be able to provide advice or tips on living with amnesia. Ask your doctor if he or she knows of a support group in your area for people with amnesia and their loved ones.

If an underlying cause for the amnesia is identified, there are national organizations that can provide additional information or support for the individual and their families.

Preparing for your appointment

You're likely to start by seeing your family doctor or a general practitioner. However, you may then be referred to a doctor who specializes in disorders of the brain and nervous system (neurologist).

It's a good idea to arrive at your appointment well-prepared. Here's some information to help you get ready for your appointment and to know what to expect from your doctor.

What you can do

•    Write down any unusual symptoms as you experience them, including any that may seem unrelated to the reason for which you scheduled the appointment.
•    Write down key personal information, including any major stresses or recent life changes you can recall. Ask family members or friends to help you, to ensure your list is complete.
•    Make a list of all medications, vitamins or supplements you're taking.
•    Ask a family member or friend to come with you. Even in the best circumstances, it can be difficult to remember all of the information provided to you during an appointment. Someone with you can help you remember everything that was said.
•    Bring a notepad and pen or pencil to jot down the points you want to be sure to remember later.
•    Write down questions to ask your doctor.

Preparing a list of questions can help you make the most of your time with your doctor, as well as ensure that you cover everything you want to ask. For amnesia, some basic questions to ask your doctor include:

•    What's the most likely cause of my symptoms?
•    Are there other possible causes for my symptoms?
•    What kinds of tests do I need? Do these tests require any special preparation?
•    Will my memory ever come back?
•    What treatments are available, and which do you recommend?
•    I have other health conditions. How can I best manage them together?
•    Do I need to restrict any activities?
•    Are there any brochures or other printed material that I can take home? What websites do you recommend?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, including:

•    When did you first notice your memory loss?
•    Did you experience any other symptoms at that time?
•    Were you involved in any trauma? For example, a car accident, violent collision in sports or an assault?
•    Did an illness or another event seem to trigger the memory loss?
•    Does anything help improve your memory?
•    What, if anything, appears to worsen your memory loss?
•    Are the memory problems intermittent or constant?
•    Has the memory loss stayed the same or is it getting worse?
•    Did the memory loss come on suddenly or gradually?

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

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

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#588 2020-01-22 03:42:45

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

468) Albedo

Alternative Title: reflection coefficient

Albedo, fraction of light that is reflected by a body or surface. It is commonly used in astronomy to describe the reflective properties of planets, satellites, and asteroids.

Albedo is usually differentiated into two general types: normal albedo and bond albedo. The former, also called normal reflectance, is a measure of a surface’s relative brightness when illuminated and observed vertically. The normal albedo of snow, for example, is nearly 1.0, whereas that of charcoal is about 0.04. Investigators frequently rely on observations of normal albedo to determine the surface compositions of satellites and asteroids. The albedo, diameter, and distance of such objects together determine their brightness. If the asteroids Ceres and Vesta, for example, could be observed at the same distance, Vesta would be the brighter of the two by roughly 10 percent. Though Vesta’s diameter measures less than half that of Ceres, Vesta appears brighter because its albedo is about 0.35, whereas that of Ceres is only 0.09.

Bond albedo, defined as the fraction of the total incident solar radiation reflected by a planet back to space, is a measure of the planet’s energy balance. (It is so named for the American astronomer George P. Bond, who in 1861 published a comparison of the brightness of the Sun, the Moon, and Jupiter.) The value of bond albedo is dependent on the spectrum of the incident radiation because such albedo is defined over the entire range of wavelengths. Earth-orbiting satellites have been used to measure the Earth’s bond albedo. The most recent values obtained are approximately 0.33. The Moon, which has a very tenuous atmosphere and no clouds, has an albedo of 0.12. By contrast, that of Venus, which is covered by dense clouds, is 0.76.

What Is Albedo?

The term albedo refers to the amount of solar energy that gets reflected off of the Earth and lands back in space.

Albedo is part of the energy from the sunlight that casts back into the atmosphere. These rays have a significant effect on our climate. When the albedo rises, the universe reflects light more and consequently, higher levels of radiation are sent back to space so the Earth cools down. Albedo determines the level of heat on the Earth. It is now well known that most of the light from the sun moves up once it hits the Earth. Research has shown that water absorbs light more thereby reflecting less light. If there is more water compared to a hard surface, then there is less solar emission. The Earth, the moon, or any other planet has the ability to transmit albedo.

Albedo

Albedo can be defined as a way of quantifying how much radiation is reflected from the surface. It is a comparison between the reflection radiation from the surface to the amount of radiation that hits it. This term also refers to the quantity of radiation generated by electromagnetic rays which consequently reflects away.

Seasonal Effects on Albedo

Summer

To understand albedo better, we look at two scenarios. One, if you walk barefoot on the black soil during summer, you will feel a lot of heat and can even get burnt because the surface is absorbing and retaining more heat. Another person walking on white soil during the same season will not be burnt. This is basically because white surface tends to reflect more heat and absorb very little of it. Equally, if you touch a black car in summer it will feel much hotter than touching a white car. This is because black absorbs and retains heat while white car surface will reflect back the solar rays.

Winter

During this season, it is generally wet with either water or ice. Water reflects approximately 6% of the light and absorbs the rest. Ice, on the other hand, reflects 50% to 60% of the incoming solar heat, thereby remaining cooler. A snow-covered area reflects a lot of radiation, which is why skiers having a risk of getting sunburns while on the slopes. Albedo diminishes when the snow-covered places start to warm up.

How is Albedo Quantified?

Albedo helps us to know how well a surface reflects solar energy. It is measured on a scale of zero to one (0-1). Surfaces differ in absorbent ability but will always be in the range of between 0-1.
Value “0” - If a score of zero is given, then the conclusion is that the surface is highly receptive to light, meaning that the surface takes in all the light that comes into contact with it. It is characterized by black surfaces.

Value “1” - This score is evidence that the surface does not absorb incoming light. It is characterized by white surfaces.

The albedo of our planet is 0.367, whereas that of the moon stands at 0.12, meaning the moon reflects 12% out of the radiation that falls on it. There are many satellites set up to monitor the planet's albedo by use of sensors which measure the light from the Earth that reflects on the surface of the moon. NASA has set out what is called Terra and Aqua Satellites to assist identify any changes in albedo.

Various Studies

A. Danjon Studies (1928- 1954)

André-Louis Danjon, a French national, conducted studies on Albedo. He used an approach known as “The eyes of a cat”. He used light to make a bio image of the moon, permitting the sight checking of similarity and differences of the degrees of two research specimens of the moon surfaces. Using this approach, he ceased some light from the part with sunlight to correspond with the sunlight of the other side.

The research led to what is known as Danjon scale astrolabe which also led to enhanced accuracy of major visual astrometry. He further came up with a five-point measuring parameter for assessing the visual appearance and brightness of the moon when there is a total eclipse. He used letter “L” to denote high darkness.

L-O: Moon cannot be seen. This is characterized by the total to the medium dimness.
L-1: The details are visible but with some difficulty.
L-2: The shadows at the middle are very dim but the outer edge is a bit bright.
L-3: The umbral shadow has yellow color around it.
L-4: There is a blue looking shiny color around the moon. It has shades of either red or orange. It illuminates a lot of light.

Earth Surface Albedo Variations 1998- 2014

These were the second studies done within a total of sixteen years. During this period, man tried to understand the ratio of earthshine as compared to lunar shine. This was assessed both from the aerial satellites and on the ground for a period of sixteen years. The moon was the focus of the study.

De Pater and Lissauer Table of Albedo

De Peter and Lissauer categorized albedo into two sets namely Geometric and Bond albedo Geometric albedo means the quantity of radiation in comparison to the frequency which the wave's shape repeats itself while Bond albedo highlights the total radiation reflected from an object in comparison to the total incident radiation from the solar planets.

Albedo Drivers

Some of the factors that drive albedo include but are not limited to the following:

1. Change in land use –This refers to the way people do actions that alters the landscape. Examples range from the natural ecosystem to deforestation to subdividing into small-scale farms and setting up of urban cities leaving the ground bare.

2. Greenhouse emissions – Carbon dioxide and other gases emitted affects albedo.

3. Water degradation – The use of water has increased due to agricultural activities.

4. Pollution – Excess high-level nitrogen and phosphorus flow. This leads to pollution of water bodies and the atmosphere.

The Albedo Effect and Warming of the Universe

It was found that the global albedo has recently gone up and on a measuring scale, the watts per square meter is now greater. This is according to research by Anthony Watts.

The universe is gradually getting hotter due to deforestation. Better forest management skills should be embraced to mitigate effects of albedo. Trees reduce radioactive effects of solar reflection. We should also protect our wetlands and snow cover fractions. The loss of the Arctic is of great concern.

Many states are advocating reforestation since trees are darker and have reduced albedo emission rates. If one plants more trees he is remunerated based on a system called carbon credit. The clouds may at times reflect sunlight but can still hold heat thereby warming up the Earth.

Today climate scientists and researchers are concerned that if global warming continues it will make the polar ice caps to melt making the ocean water to absorb more solar light thereby increasing the global warming. It is in this context that all of us should work towards coming up with better models to curb its effect in future.

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

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

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#589 2020-01-23 00:39:57

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

469) Shaanxi province earthquake of 1556

Shaanxi province earthquake of 1556, (Jan. 23, 1556), massive earthquake in Shaanxi province in northern China, believed to be the deadliest earthquake ever recorded.

The earthquake (estimated at magnitude 8) struck Shaanxi and neighbouring Shanxi province to the east early on Jan. 23, 1556, killing or injuring an estimated 830,000 people. This massive death toll is thought to have reduced the population of the two provinces by about 60 percent. Local annals (which date to 1177 BCE) place the epicentre of the earthquake around Huaxian in Shaanxi. These annals, which record 26 other destructive earthquakes in the province, describe the destruction caused by the 1556 earthquake in a level of vivid detail that is unique among these records. Though the quake lasted only seconds, it leveled mountains, altered the path of rivers, caused massive flooding, and ignited fires that burned for days.

The local records indicate that, in addition to inspiring searches for the causes of earthquakes, this particular quake led the people in the region affected to search for ways to minimize the damage caused by such disasters. Many of the casualties in the quake were people who had been crushed by falling buildings. Thus, in the aftermath of the 1556 quake, many of the stone buildings that had been leveled were replaced with buildings made of softer, more earthquake-resistant materials, such as bamboo and wood.

The 1556 Shaanxi earthquake is associated with three major faults, which form the boundaries of the Wei River basin. All 26 of the earthquakes recorded in the annals had epicentres in this basin.

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

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

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#590 2020-01-24 01:15:28

ganesh
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Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

470) Ambulance

An ambulance is a self-propelled vehicle specifically designed to transport critically sick or injured people to a medical facility. Most ambulances are motor vehicles, although helicopters, airplanes, and boats are also used. The interior of an ambulance has room for one or more patients plus several emergency medical personnel. It also contains a variety of supplies and equipment that are used to stabilize the patient's condition while en route.

Background

The earliest ambulances were simple two-wheeled carts used to carry sick or wounded soldiers who were unable to walk by themselves. The word ambulance comes from the Latin word ambulare, meaning to walk or move about. The first ambulances specifically used to transport patients to a medical facility were developed in the late 1700s in France by Dominique-Jean Larrey, surgeon-in-chief in Napoleon's army. Larrey noted that it took almost a full day for wounded soldiers to be carried to field hospitals, and that most of them died in that time "from want of assistance." To render more immediate aid and provide faster transportation, he designed a horse-drawn carriage staffed by a medical officer and assistant with room for several patients on stretchers.

The first military ambulance corps in the United States was organized in 1862 during the Civil War as part of the Union army. The first civilian ambulance service in the United States was organized three years later by the Cincinnati Commercial Hospital. By the turn of the century, most major hospitals had their own private ambulances. The first motorized ambulance went into operation in Chicago in 1899.

In areas where there were no major hospitals, the local undertaker's hearse was often the only vehicle capable of carrying a patient on a stretcher, and many funeral homes also provided an ambulance service. As a result, the design and construction of ambulances and hearses remained closely related for many years.

Most early ambulances were simply intended to transport patients. After the doctor or fire department rescue squad applied first aid, the patient was loaded into the back of the ambulance for a quick ride to the hospital. In some cases, the doctor rode along, but most of the time the patient rode alone and unattended. In the United States that changed dramatically when the federal government passed the Highway Safety Act in 1966. Among its many standards, the new act set requirements for ambulance design and emergency medical care. Ambulances with low-slung, hearse-like bodies were replaced by high-bodied vans to accommodate additional personnel and equipment. Radios were installed. Many ambulances carried advanced equipment like cardiac defibrillators, along with an math of life-saving medicines and drugs.

Today, ambulances come in a wide variety of shapes and sizes. The simplest designs are equipped to provide basic life support, or BLS, while larger, more sophisticated designs are equipped to provide advanced life support, or ALS. Ambulances may be operated by private companies, hospitals, the local fire or police department, or a separate city-run organization.

Raw Materials

Ambulance manufacturers purchase many components from other suppliers rather than fabricate them themselves. These include the vehicle cab and chassis, warning lights and sirens, radios, most electrical system components, the heating and air conditioning components, the oxygen system components, and various body trim pieces like windows, latches, handles, and hinges.

If the ambulance has a separate body, the body framework is usually made of formed or extruded aluminum. The outer walls are painted aluminum sheet, and the interior walls are usually aluminum sheet covered with a vinyl coating or a laminated plastic. The subfloor may be made of plywood or may use an open-cored plastic honeycomb laminated to aluminum sheet. The interior floor covering is usually a seamless, industrial-grade vinyl that extends partially up each side for easy cleaning.

Interior cabinets in the patient compartment are usually made of aluminum with transparent, shatter-resistant plastic panels in the doors. The counter and wall surfaces in the "action area," the area immediately opposite the patient's head and torso in the left-hand forward portion of the ambulance body, are usually covered with a seamless sheet of stainless steel to resist the effects of blood and other body fluids. Interior seating and other upholstered areas have a flame-retardant foam padding with a vinyl covering. Interior grab handles and grab rails are made of stainless steel. Other interior trim pieces may be made of various rubber or plastic materials.

Design

Ambulance designs fall into three categories. Type I ambulances have a modular, or detachable, body built on a truck chassis. The truck cab is connected to the body through a small window, but the occupants of the cab must go outside the vehicle to enter the ambulance body. Type II ambulances use a van with a raised roof. Because of the van construction, the occupants of the cab can easily enter the body from the inside, although the interior space is limited. Type III ambulances have a modular body built on a cut-away van chassis. This design combines the capacity of the larger modular body with the walk-through accessibility of a van.

The federal requirements for ambulances are defined by General Services Administration Standard KKK-A-1822: Federal Specifications for Ambulances. It covers overall construction, electrical systems, emergency warning lights, and many other aspects of ambulance design. Some states have adopted this federal standard, while others have their own design requirements. Because an ambulance is a motor vehicle, the Federal Motor Vehicle Safety Standards (FMVSS) apply to the vehicle portion. Certain Occupational Safety and Health Administration (OSHA) standards regarding blood-borne and airborne pathogens also apply. Within the framework of these standards, manufacturers may specify specific features and materials to provide their products with unique advantages in the marketplace.

The Manufacturing Process

Ambulances are usually manufactured in a modified assembly line process, where the vehicle or body moves from one fixed area of a plant to another, rather than being pulled along an assembly line. Specific parts are brought to each area for installation or assembly. Different manufacturers may use slightly different processes. The following is a typical sequence of operations for the manufacture of a Type I ambulance with a modular body.

Building the body shell

•    1 The structural components of the ambulance body—the supporting struts, braces, and brackets for the floor, sides, and roof—are either bent to shape using standard machine shop tools, or are cut from specially shaped aluminum extrusions that have been purchased from suppliers. The components are held in the proper position with a device called a jig and are welded together to form the body frame-work.
•    2 The exterior skin pieces are fabricated using standard sheet metal shop tools and are fastened to the outside of the framework using either mechanical fasteners or adhesive bonding. The external compartments are fabricated and welded in place. Finally, the external body doors are fabricated and are fastened in place on hinges.
•    3 The outside of the body shell is then cleaned, sanded, and spray painted with a primer. Next, a sealer is applied. This is followed by a base coat of paint, usually white, and then a clear coat of paint to protect the base color and give the surface a shiny appearance. Between each coat, the body is placed in an oven to dry.
Preparing the cab and chassis
•    4 Additional wiring is added to the cab, chassis, and engine electrical system to accommodate the warning lights and sirens and to bring power to the body. Additional switches and controls are added to the dash as required. The heating and air conditioning system may also be modified.
•    5 Holes are drilled in the vehicle frame rails and mounting brackets are installed to support the ambulance body. The frame rails may be cut to the proper length for the body.

Mounting the body

•    6 The painted body shell is lowered onto the chassis mounting brackets and is bolted in place.
•    7 The cab is usually ordered with the same background color as the body, and does not require priming or base/clear painting. Most ambulances are specified with one or more colored stripes that extend along the sides and rear of the cab and body. The areas around the stripes are masked off with paper and tape so that the position of the stripes on the cab and the body match. The stripes are then painted and dried, and the masking removed.
•    8 The front and rear bumpers, which are not painted, are then installed. If the mirrors have been removed to paint the stripes, they are reinstalled.

Finishing the body

•    9 The electrical wiring in the body walls and ceiling is installed from the inside, and foam panels are bonded in place to provide thermal and noise insulation. With the wiring in place, the exterior lights are mounted and connected, and the exterior latches, grab handles, windows, and other trim pieces are installed.
•    10 The oxygen piping and outlets, which are part of the patient life-support system, are installed in the body walls. The vacuum system, which removes blood, saliva, and other body fluids is also installed. If the ambulance body requires an auxiliary heating and air-conditioning system, it is installed at this time.
•    11 With all the systems in place, the interior cabinets are installed and the walls, floors, and ceilings are covered. The electrical power distribution board is installed in a forward compartment of the body and the panel is connected to the cab and chassis electrical wiring. If the ambulance is specified with an inverter, which converts 12 volts direct current from the vehicle batteries into 120 volts alternating current for use with certain medical equipment, it is also installed at this time.
•    12 The seats and upholstery pieces, which are either purchased or assembled in a separate area, are fastened in place. The interior grab handles, containers, and trim pieces are installed as the final step.

Quality Control

The design of ambulances is regulated by several standards, and the manufacturer must take appropriate steps to ensure compliance with those standards. Each system is inspected and tested for proper installation and operation as part of the manufacturing process. In addition, every material, from the aluminum in the body to the foam in the head rests, is certified by the manufacturer to meet the required specifications.

The Future

Many fire departments are finding that approximately 80-90% of their calls are for medical emergencies, while only 10-20% are for fires. In the case of medical emergencies, an ambulance has to be called in addition to the fire engine. Instead of responding to all calls with large pumpers or ladder trucks, some fire departments are starting to use smaller, lower-cost first-response vehicles that combine the equipment and patient transport capabilities of a rescue truck and ambulance with the fire suppression capabilities of a small pumper. These combination vehicles are able to handle a variety of emergency situations, including those involving small fires such as might occur in vehicle accidents. This saves wear on the larger firefighting vehicles, and eliminates the need to dispatch two vehicles to the same incident. In the future, an increase in traffic congestion and an increase in the average age of the population in the United States are expected to increase the number of medical emergency calls. When this happens, it is expected that the single-function ambulance may be replaced by a multi-function combination vehicle in many areas.

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

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

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#591 Yesterday 00:02:24

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

471) Fenugreek

Fenugreek, (Trigonella foenum-graecum), also spelled foenugreek, fragrant herb of the pea family (Fabaceae) and its dried, flavourful seeds. Native to southern Europe and the Mediterranean region, fenugreek is cultivated in central and southeastern Europe, western Asia, India, and northern Africa.

The seeds’ aroma and taste are strong, sweetish, and somewhat bitter, reminiscent of burnt sugar. They are commonly ground and used as a spice and may also be mixed with flour for bread or eaten raw or cooked. The herb is a characteristic ingredient in some curries and chutneys and is used to make imitation maple syrup. It is eaten as a vegetable in some places and is used as fodder in northern Africa. Traditionally considered an aid to digestion, the seeds have been used as an internal emollient for inflammation of the digestive tract and as an external poultice for boils and abscesses; it is sometimes used to promote milk production in lactating women.

The plants are erect, loosely branched, less than 1 metre (3 feet) tall with trifoliate, light green leaves and small white flowers. The slender pods are up to 15 cm (6 inches) long, curved and beaked, and contain yellow-brown seeds—flat rhomboids characterized by a deep furrow, less than 0.5 cm (0.2 inch) long. They contain the alkaloids trigonelline and choline.

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

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

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#592 Today 01:00:20

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,596

Re: Miscellany

472) Nurek Dam

The Nurek Dam (Tajik for Nurek Hydro-electric Station) is an earth-fill embankment dam on the Vakhsh River in Tajikistan. Its primary purpose is hydroelectric power generation and its power station has an installed capacity of 3,015 MW. Construction of the dam began in 1961 and the power station's first generator was commissioned in 1972. The last generator was commissioned in 1979 and the entire project was completed in 1980 when Tajikistan was still a republic within the Soviet Union, becoming the tallest dam in the world at the time. At 300 m (984 ft), it is currently the second tallest man-made dam in the world, after being surpassed by Jinping-I Dam in 2013. The Rogun Dam, also along the Vakhsh in Tajikistan, may exceed it in size when completed.

Construction

The Nurek Dam was constructed by the Soviet Union between the years 1961 and 1980. It is uniquely constructed, with a central core of cement forming an impermeable barrier within a 300 m (980 ft)-high rock and earth fill construction. The volume of the mound is 54 million meter cube. The dam includes nine hydroelectric generating units, the first commissioned in 1972 and the last in 1979. An estimated 5,000 people were resettled from the dam's flooding area.

The dam is located in a deep gorge along the Vakhsh River in western Tajikistan, about 75 km (47 mi) east of the nation's capital of Dushanbe. A town near the dam, also called Nurek, houses engineers and other workers employed at the dam's power plant.

Electricity generation

A total of nine Francis turbine-generators are installed in the Nurek Dam's power station. Originally having a generating capacity of 300 MW each (2,700 MW total), they were redesigned and retrofitted between 1984 and 1988 so now have a capacity of 335 MW each (3,015 MW total). As of 1994, this formed most of the nation's 4.0 gigawatt hydroelectric generating capacity, which was adequate to meet 98% of the nation's electricity needs.

Reservoir

The reservoir formed by the Nurek Dam, known simply as Nurek, is the largest reservoir in Tajikistan with a capacity of 10.5 cubic kilometers. The reservoir is over 70 km (40 mi) in length, and has a surface area of 98 square kilometers (38 sq mi). The reservoir drives the hydroelectric plant located within the dam. Stored water is also used for irrigation of agricultural land. Irrigation water is transported 14 kilometers through the Dangara irrigation tunnel and is used to irrigate about 700 square kilometers (300 sq mi) of farmland. It is suspected that the reservoir may have caused induced seismicity when being impounded.

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

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

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