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#601 2020-02-08 00:56:40

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

481) Streetcar

Streetcar, also called tram or trolley, vehicle that runs on track laid in the streets, operated usually in single units and usually driven by electric motor.

Early streetcars were either horse-drawn or depended for power on storage batteries that were expensive and inefficient. In 1834 Thomas Davenport, a blacksmith from Brandon, Vermont, U.S., built a small battery-powered electric motor and used it to operate a small car on a short section of track. In 1860 an American, G.F. Train, opened three lines in London and one line in Birkenhead. The system was called tramways in Britain and was established at Salford in 1862 and Liverpool in 1865. The invention of the dynamo (generator) led to the application of transmitted power by means of overhead electrified wires to streetcar lines, which subsequently proliferated in Britain, Europe, and the United States.

The cable car, the invention of Andrew Hallidie, was introduced in San Francisco on Sacramento and Clay streets in 1873. The cars were drawn by an endless cable running in a slot between the rails and passing over a steam-driven shaft in the powerhouse. The system was well-adapted for operation on steep hills and reached its most extensive use in San Francisco and Seattle. The cars operated more smoothly than did early electric cars, but they could run only at a constant speed; breaking or jamming of the cable tied up all the cars on the line. Beginning about 1900, most cable trackage was replaced by electric cars; but the Seattle lines lasted until the 1930s, and a portion of the San Francisco system continued in operation in the 21st century.

During the 1890s and the first two decades of the 1900s, conventional electric tramlines replaced horsecar lines in Europe and the United States and made their appearance in the larger cities of Asia, Africa, and South America. In the United States, electric streetcars replaced horse-drawn cars at a particularly rapid rate from 1902 to 1917. The motors and cars were gradually improved: the tiny four-wheeled cars were replaced by heavy eight-wheeled cars that had much greater carrying capacity, and wooden car bodies were replaced by steel ones. The possession of a streetcar line became essential for a growing town or small city, and the larger city streetcar systems extended their lines farther and farther out into the suburbs. The development of streetcars in Europe was equally rapid and continued over a longer period. Many European cities constructed highly efficient streetcar systems, and the electric car became the chief means of urban transport.

British trams usually were double-deck cars operated by two men, one of whom collected the fare; rates were charged according to a zone system. European streetcars were similar to the British, but single-deck cars were common. Power was supplied from overhead wires through a bent piece called a bow or by a collapsible and adjustable frame called a pantograph, in contrast to the universal use of the single trolley pole in the United States. In Britain a conduit system was sometimes used in place of the overhead wires. It consisted of an underground conduit with a continuous slot that contained two conductor rails from which the tram’s contacts collected power.

During the World War I period, streetcar enterprises encountered financial difficulties; as wage and materials costs rose, the companies were squeezed by the fixed fares set almost universally by the municipal franchises. Finally, government action permitted fare raises; but by then the use of automobiles had spread, and many cities shifted to motor-bus systems of public transportation. The direct operating expenses of the bus, per mile, were greater than those of streetcars, but the heavy expenses of track construction and maintenance ultimately rendered streetcars uneconomical. In the United States streetcars began to be supplanted by automobiles and buses in the 1930s, and this trend accelerated during the ’40s and ’50s. In Britain the substitution of buses for trams was hastened during the 1930s by the development of improved double-deck buses, and by the early ’50s there were no trams left running in London. The last major British tram system was that of Glasgow, which employed relatively modern double-deck cars. Paris closed the last of its streetcar lines in the 1930s, and in other parts of France and in Italy many cities shifted to bus operation.

Nevertheless, there are still many major streetcar systems in operation, with many cities building new systems beginning in the late 20th century. Streetcar systems are largely municipal, with private bus competition not permitted. In the 1980s some cities in the United States began adopting light rail transit; the trackage for this modern electric trolley system was less expensive to construct than that for elevated or underground metropolitan train systems. Light rail systems were constructed in such American cities as San Diego, Sacramento, and San Jose, California; Portland, Oregon; and Buffalo, New York. In the early 21st century, increased traffic congestion and the need to revive downtown areas led to increased interest in the streetcar, with new systems being built in some American cities, such as Houston, Texas; Tampa, Florida; and Washington, D.C.

M-PortlandRedWaterfrontStreetcar-viaRNL.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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#602 2020-02-09 01:12:22

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

482) Kalahari Desert

Kalahari Desert, large basinlike plain of the interior plateau of Southern Africa. It occupies almost all of Botswana, the eastern third of Namibia, and the northernmost part of Northern Cape province in South Africa. In the southwest it merges with the Namib, the coastal desert of Namibia. The Kalahari’s longest north–south extent is roughly 1,000 miles (1,600 kilometres), and its greatest east–west distance is about 600 miles; its area has been estimated at some 360,000 square miles (930,000 square kilometres).

Physical Features

Physiography and geology

The Kalahari Desert is a featureless, gently undulating, sand-covered plain, which everywhere is 3,000 feet (900 metres) or more above sea level. Bedrock is exposed only in the low but vertical-walled hills, called kopjes, that rarely but conspicuously rise above the general surface. Aside from the kopjes, three surfaces characterize virtually all of the Kalahari: sand sheets, longitudinal dunes, and vleis (pans).

The sand sheets appear to have been formed during the Pleistocene Epoch (about 2,588,000 to 11,700 years ago), and they have been fixed in place since then. In some areas they appear to have been of fluvial origin, the result of sheet flooding in times of much greater precipitation, but by far the greater part of them were wind-formed. The sheets occupy the eastern part of the Kalahari. Their surface elevation varies only slightly, with relief measured in tens of feet per mile. The depth of the sand there generally exceeds 200 feet. In many areas the sand is red, the result of a thin layer of iron oxide that coats the grains of sand.

The entire western Kalahari Desert is characterized by long chains of dunes, oriented roughly to the north or northwest. The dunes measure at least 1 mile in length, several hundred feet in width, and 20 to 200 feet in height. Each dune is separated from its neighbour by a broad parallel depression locally called a straat (“street,” or “lane”), because each constitutes the easy way to travel.

Vleis, or pans, are the terminal features of desert drainage systems, the “dry lakes” at the end of ephemeral streams. Many are remnant features from an earlier period of greater precipitation. Very little water ever flowed to the sea from the Kalahari. Rather, each stream ended its course in a slightly lower depression from which there was no outlet. There, as the stream dried up, the fine silt particles carried in suspension by the sluggish stream were deposited along with soluble calcium minerals and salts precipitated out of the evaporating water. The results are pans—flat surfaces devoid of vegetation that are gleaming white when dry, hardened by the cementing action of the soluble minerals, and, on occasion, covered by a shallow layer of standing water. Where the salt content is low, pans may become covered with grasses after a rain.

Drainage

In the southern and central parts of the Kalahari Desert, surface water is found only in small, widely scattered waterholes, and surface drainage is nonexistent. Nearly all of the rain that falls disappears immediately into the deep sand. Some is absorbed by the underlying rock strata; some is drawn to the surface by capillary action and evaporated into the air; and some, lifted from the depths by tree roots, is transpired from leaf surfaces. A small amount, landing on nonsandy surfaces, may flow short distances into pans, but this occurs only immediately after the infrequent rains. In some parts of the central and southern Kalahari, extensive ancient drainage systems have been detected—some on the ground and others by way of aerial photographs. None of these operate today, even in the wettest of years.

In the northern Kalahari an extraordinary drainage system prevails. During the summer heavy rains fall on the uplands of central Angola, far to the northwest of the Kalahari. Large amounts of runoff water feed a number of south-flowing streams, which merge to form the Okavango and Cuando (Kwando) rivers. The Okavango flows to the southeast and into the northernmost portion of the Kalahari, eventually breaking up into a number of distributary channels and feeding the vast area of swamps in northern Botswana. After an abnormally wet rainy season in Angola, excess water fills the swamps and overflows, filling Lake Ngami farther to the south, and flows eastward through the Boteti River into Lake Xau and the Makgadikgadi Pans. Similarly, the Cuando River flows south from Angola and partly into a northeastern extension of the same swamps. Thus is created the paradoxical situation of an area with an extensive excess of water in a region chronically short of water.

Soils

Soils in the Kalahari Desert are largely based on sand, are reddish in color, and are low in organic material. Chemically, they are relatively alkaline, and they are extremely dry. In and near the pans, the soils tend to be highly calcareous or saline, and frequently they are toxic to most vegetation.

Climate

Traditionally, an area was classed as desert if it received less than 10 inches (250 millimetres) of rain annually. A more accurate definition of a desert is a region in which the potential evaporation rate is twice as great as the precipitation. Both of these criteria are applicable to the southwestern half of the Kalahari. The northeastern portion, however, receives much more rainfall and, climatically, cannot qualify as a desert; and yet, it is totally lacking in surface water. Rain drains instantly through the deep sands of the area, which creates a situation of edaphic drought (i.e., soil completely devoid of moisture).

Moisture-bearing air is derived from the Indian Ocean, and precipitation is greatest in the northeast (with a mean annual precipitation of more than 20 inches) and declines toward the southwest (less than 5 inches on the southern fringe of the Kalahari). Precipitation, however, is highly variable. Most of the rain comes as summer thunderstorms, with great variation from place to place and from year to year. Winters are extremely dry: humidity is very low, and no rain falls for six to eight months.

Great ranges in both diurnal and seasonal temperatures are the rule, the result of the Kalahari’s relatively high altitude and predominantly clear, dry air (allowing strong insolational heating in daytime and great radiational heat loss at night). As a result, shade temperatures often reach 110–115 °F (43–46 °C) on summer days but drop to 70–80 °F (21–27 °C) on the same nights; temperatures on winter nights commonly drop to freezing and may go as low as 10 °F (−12 °C).

Plant life

The presence of a deep sand cover over most of the area greatly affects the vegetation that grows there. Shallow-rooted plants cannot survive on a perennial basis, although annuals that grow very rapidly after a good rain may be able to sow seeds that will endure until the next good rainy season. Trees with roots deep enough to reach permanently moist sand levels do well.

The southwestern Kalahari Desert, with its very low precipitation, has few trees or large bushes—only scattered xerophytic (drought-tolerant) shrubs and short grasses. The central Kalahari, with more rain, has scattered trees (several species of Acacia) and some shrubs and grasses. The northern Kalahari does not have the appearance of a desert at all. It has open woodlands, palm trees growing among thorn brush, and forests of both evergreen and deciduous trees that grow to heights of 50 feet and yield some species suitable for timber; one of the largest and most unusual of these trees is the baobab. The Okavango Swamp supports a dense growth of reeds, papyrus, pond lilies, and other water-loving plants.

Animal life

The animal life of the Kalahari Desert is also richer and more varied in the north than in the south. Yet even in the arid south, many individuals of several species stay for long periods of the year despite the absence of surface water. The principal species found in the south are springbok, gnu (wildebeest), and hartebeest—all of which occasionally are present in great herds—gemsbok (oryx), eland, and many smaller nongregarious species, such as kudu (in areas of denser brush), steenbok, and duiker.

The northern Kalahari supports a considerable population of giraffes, zebras, elephants, buffalo, and antelopes (roan, sable, tsessebe, and impala); predators such as lions, cheetahs, leopards, wild hunting dogs, and foxes; other large and medium-sized mammals, such as jackals, hyenas, warthogs, baboons, badgers, anteaters, ant bears, hare, and porcupines; and numerous small rodents, several types of snakes and lizards, and a wealth of birdlife.

People And Economy

The Kalahari Desert is inhabited primarily by Bantu speakers and Khoisan-speaking San, with a small number of Europeans.

Bantu-speaking peoples

The Bantu-speaking peoples—the Tswana, the Kgalagadi, and the Herero—are relative newcomers to the Kalahari. In the late 18th century the Tswana spread west from the Limpopo basin into the northern and eastern Kalahari; the Kgalagadi moved north and west into the southern and western Kalahari; and the Herero refugees from the German-Herero conflict of 1904–07 in German South West Africa (now Namibia) fled east into the western and northern Kalahari at the beginning of the 20th century.

Those in the remoter parts of the Kalahari who are unaffected by mining or other industry live in villages of between 200 and 5,000 people. Housing is mostly of the traditional type: single-roomed huts with mud walls and thatched roofs. Water is the limiting factor, confining settlement to places situated near wells or boreholes with potable water.

Cattle, the basis of the economy, are kept on the outskirts of villages, or at distances of up to 50 miles away. Wells and boreholes are owned by local government councils, syndicates of cattle owners, or private individuals; year-round cattle grazing is limited to their vicinity. In summers of above-average rains, however, pastoralists may trek with their stock to remote pastures, where for a short time water may occur in pools. Cattle and goats feed upon a small range of the available vegetation. Since effective pasture management is little practiced, the grazing of these animals is highly destructive. Pasture loss and subsequent desertification are serious threats to the ecology of the Kalahari Desert. Cattle are prized beyond their economic value, as their ownership is a measure of social status and personal worth. Thus, the desire to possess more cattle puts an increasing load on diminishing pasture, leaving it no chance for recovery. The traditional dangers to livestock—drought, disease, internal parasites, and wild predators—have diminished markedly as more boreholes have been sunk, veterinary care improved, and indigenous fauna have grown scarcer. In addition, wealthier cattle owners have improved their herds by introducing better stock and practicing scientific breeding.

Goats furnish most of the meat and milk for home consumption, and nearly all households cultivate crops of corn (maize), sorghum, and pumpkins. Because of the threat of drought, more crops fail than are successful. Wild food plants and the meat of game animals are important components of diet in the smaller and more remote villages. All villages have trading stores or are visited by hawkers who sell foodstuffs and other commodities.

All but the smallest villages have state-run primary schools, which are attended by the great majority of children, although few proceed to secondary education. State-run health clinics and hospitals in the larger villages supplement the services of herbalists and diviners.

Riding horses and donkeys are the usual means of local travel. Trucks belonging to traders or to the mine labour recruiting agency are used for longer journeys.
Large diamond deposits were discovered in Botswana soon after the country’s independence, and the opening of the diamond mine at Orapa in 1971 marked the beginning of the development of mining activities in scattered locations of the Kalahari. In addition, tourism and the sale of handicrafts have become economically important.

San

The San—or Basarwa, as they are called in much of the region—are now either clients of Bantu-speaking pastoralists and work at cattle posts in return for support or they are employees of cattle ranches or are dependents of such employees. Few San still follow their traditional pattern of hunting and gathering. Many have been resettled—often, against their will—by the government of Botswana from their traditional homes in the Central Kalahari Game Reserve to new villages built outside the reserve.
Although all San traditionally were hunter-gatherers, there were significant cultural and social differences between groups. For example, a number of groups had long-standing clientships with Bantu-speaking stockowners, while other groups lived—until the 1970s—solely as autonomous foragers. Of these latter peoples, the Kung (!Kung), !xong, and G/wi tribes (the “! ” and “/” representing click sounds) were intensively studied. While each group was distinct, the G/wi of the Central Kalahari Game Reserve can be considered an example of the traditional San hunter-gatherer way of life.

The G/wi lived together in bands, each consisting of 5 to 16 households linked by bonds of kinship and friendship. Each band had a recognized territory of 300 to 400 square miles, selected for its resources of food plants (the main part of the diet), wet-season water holes (used during the six to eight weeks when sufficient rainwater gathered in pools), trees (for shade, shelter, firewood, and wood for making artifacts), and areas of grazing to attract and sustain herds of game animals. Subsistence was based on a number of species of edible plants, of which eight were staples in their various seasons. This diet was supplemented by the meat of antelopes and other herbivorous mammals, by tortoises and other reptiles, and by the flesh and eggs of all but raptorial and scavenging birds. Plant-gathering was mostly done by women ranging within five miles of the camp, while men hunted over a much larger area. The main hunting weapon was a light bow shooting flimsy, unfletched, poisoned arrows. The range of these bows was only about 75 feet, and great skill was needed to stalk the quarry within this distance. Antelope leather provided material for clothing, which included cloaks that also served as blankets and carrying bags.

From November to some time between late June and early August—a period when there is sufficient food—the band lived as one community, moving from camp to camp every three or four weeks as the local supply of food plants became exhausted. Blighting frosts depleted the available food plants in winter (May to September), and the band would then split into its constituent households, each retreating to a separate part of the territory. Early-fruiting plants increased the food supply just before the approach of the wet season, allowing the band to reunite at a joint campsite. During dry seasons, shelters were little more than open windbreaks made of branches and grass. In rainy periods, domed structures of branches were thatched and made rainproof.

Europeans

Europeans first entered the Kalahari early in the 19th century as travelers, missionaries, ivory hunters, and traders. The only European settlement was in the Ghanzi District, where a number of families were allowed ranching blocks in the 1890s. Until the 1960s they led a life of isolation and poverty, but since then they have been able to gain ownership of the land and improve their living conditions. Most other whites in the Kalahari are government employees or are engaged in private enterprise.

Transportation

Because of its sparsely populated expanse, the Kalahari is served by infrequent roads and tracks, the majority of which are passable only by trucks or four-wheel drive vehicles. Maintained roads connect administrative centres, major habitations, and marginal farming areas in the south, southwest, and northwest. Constructed roads now link eastern Botswana with the Okavango Swamp and with mining developments south of the Makgadikgadi Pans.

Study And Exploration

The Kalahari Desert’s lack of surface water and deep sands constituted a major obstacle to early travelers. The Scottish missionary and explorer David Livingstone, with assistance from local peoples, traversed the Kalahari in 1849 with great effort by utilizing local waterholes. In 1878–79 a party of Boers in the Dorsland (“Thirstland”) Trek crossed the Kalahari from the Transvaal to central Angola by a circuitous route, losing along the way about 250 people and 9,000 cattle, largely from thirst. The introduction of motor vehicles in the 20th century greatly improved transport into the Kalahari, but even as late as the 1950s large areas were virtually inaccessible and were never visited by outsiders. By the mid-1970s, however, vehicle mobility had improved to such a degree that the whole of the Kalahari had been opened to study, hunting, and tourist expeditions, and interest in the desert continued into the 21st century.

Kalahari-Dessert-Landscape-300x225.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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#603 2020-02-11 01:32:08

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

483) Fuzzy logic

Fuzzy logic, in mathematics, a form of logic based on the concept of a fuzzy set. Membership in fuzzy sets is expressed in degrees of truth—i.e., as a continuum of values ranging from 0 to 1. In a narrow sense, the term fuzzy logic refers to a system of approximate reasoning, but its widest meaning is usually identified with a mathematical theory of classes with unclear, or “fuzzy,” boundaries. Control systems based on fuzzy logic are used in many consumer electronic devices in order to make fine adjustments to changes in the environment. Fuzzy logic concepts and techniques have also been profitably used in linguistics, the behavioral sciences, the diagnosis of certain diseases, and even stock market analysis.

Fuzzy Sets

Most concepts used in everyday language, such as “high temperature,” “round face,” or “aquatic animal,” are not clearly defined. In 1965 Lotfi Zadeh, an engineering professor at the University of California at Berkeley, proposed a mathematical definition of those classes that lack precisely defined criteria of membership. Zadeh called them fuzzy sets. Membership in a fuzzy set may be indicated by any number from 0 to 1, representing a range from “definitely not in the set” through “partially in the set” to “completely in the set.” For example, at age 45 a man is neither very young nor very old. This makes it difficult in traditional logic (see laws of thought) to say whether or not he belongs to the set of “old persons.” Clearly he is “sort of” old, a qualitative assessment that can be quantified by assigning a value, or degree of membership, between 0 and 1—say 0.30—for his inclusion in a fuzzy set of old persons.

Fuzzy sets are a generalization of ordinary sets, and they may be combined by operations similar to set union, intersection, and complement. However, some properties of ordinary set operations are no longer valid for fuzzy sets. For instance, the intersection of a fuzzy subset and its complement may be nonempty. In a logic based on fuzzy sets, the principle of the excluded middle is therefore invalid.

Fuzziness as defined by Zadeh is nonstatistical in nature—it represents vagueness due to human intuition, not uncertainty in the probabilistic sense. Membership in a fuzzy set is usually represented graphically. Membership functions are determined by both theoretical and empirical methods that depend on the particular application, and they may include the use of learning and optimization techniques such as neural networks or genetic algorithms.

Fuzzy Control

In technical applications, fuzzy control refers to programs or algorithms using fuzzy logic to allow machines to make decisions based on the practical knowledge of a human operator. The fundamental problem of automatic control is that of determining the appropriate response of the system, or production plant, for any given set of conditions. Conventional control techniques are based on explicit mathematical descriptions of the system, typically a set of differential equations involving a small number of variables. Fuzzy control, on the other hand, does not require an exact theoretical model but only the empirical knowledge of an experienced operator. This knowledge is then expressed as a set of linguistic rules of the form “if [present conditions], then [action to be taken].” For example, “if temperature is low and image density is high, then electric charge should be medium” is one of nine heuristic rules governing the smooth operation of a photocopier. The ambiguous terms—low temperature and high density—are represented as fuzzy sets, and the various linguistic rules are represented as mathematical relations between these sets. The control strategy can then be encoded as an algorithm or computer program. During the operation of the machine, sensors measure the current values of the input variables (temperature and image density, in this case), and a computer or electronic chip then determines the appropriate values of the action variables (e.g., electric charge).

E.H. Mamdani, while a lecturer at Queen Mary College, London, working in the design of learning systems, is credited with implementing the first fuzzy logic controller in the early 1970s. Mamdani and his student Seto Assilian wrote down 24 heuristic rules for controlling the operation of a small steam engine and boiler combination. They then used fuzzy sets to translate these linguistic rules into an algorithm that successfully controlled the system, thus demonstrating the power of the new approach.

Japan’s Fuzzy Boom

Commercial applications of fuzzy logic began to appear in the early 1980s, particularly in Japan, which soon became the centre of academic and industrial research on fuzzy systems. For example, fuzzy logic has been used in the control of cement manufacture and water purification processes, and a fuzzy controller designed by engineers from Hitachi, Ltd., was used to operate the automatic subway trains of the Japanese city of Sendai. Throughout the decade, Japanese consumers were offered scores of goods featuring fuzzy logic components. These included television sets that adjusted volume and contrast depending on noise level and lighting conditions; “smart” washing machines that selected the optimal washing cycle on the basis of quantity and quality of dirt and load size; fuzzy microwave ovens and rice cookers that adjusted for humidity; and video cameras with fuzzy chips that properly adjusted focus and lighting with several objects in the picture. For marketing purposes, the term fuzzy was presented as synonymous with “efficient operation requiring minimal human intervention.”

The Japanese frenzy for fuzzy products eventually subsided, but fuzzy logic is still very much present, if less conspicuously, in a number of consumer products. The automatic transmissions of certain automobiles, for instance, contain a fuzzy component that senses driving style and engine load so as to select the best gear.

Nonengineering Applications

Practical applications of fuzzy logic are not restricted to engineering and related fields. In medicine, expert systems using fuzzy inference can help doctors diagnose diabetes and prostate cancer. Management science, stock market analysis, information retrieval, linguistics, and behavioral sciences are just a few of the other domains where fuzzy logic concepts and techniques have been profitably used.

The late 1990s witnessed the development of hybrid systems, which combine the advantages of two or more computing techniques. So-called neuro-fuzzy systems integrate fuzzy logic and artificial neural networks, enabling a certain form of learning. Systems with neuro-fuzzy components may be found in fields such as stock market prediction, intelligent information systems, and data mining.

fuzzy-logic-427x300.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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#604 2020-02-13 00:58:47

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

484) Coronavirus

Coronavirus, any virus belonging to the family Coronaviridae. Coronaviruses have enveloped virions (virus particles) that measure approximately 120 nm (1 nm = {10}^{-9} metre) in diameter. Club-shaped glycoprotein spikes in the envelope give the viruses a crownlike, or coronal, appearance. The nucleocapsid, made up of a protein shell known as a capsid and containing the viral nucleic acids, is helical or tubular. The coronavirus genome consists of a single strand of positive-sense RNA (ribonucleic acid).

Coronaviridae is generally considered to contain two genera, “Coronavirus” and “Torovirus”, which differ in nucleocapsid morphology, the former being helical and the latter being tubular. Coronaviruses are important agents of gastrointestinal disease in humans, poultry, and bovines. In humans, a species known as SARS coronavirus (or Severe acute respiratory syndrome coronavirus) causes a highly contagious respiratory disease that is characterized by symptoms of fever, cough, and muscle ache, often with progressive difficulty in breathing. The virus emerged in humans in 2002; it likely jumped to humans from an animal reservoir, believed to be horseshoe bats. The ability of SARS coronavirus to jump to humans undoubtedly required genetic changes in the virus. These changes are suspected to have occurred in the palm civet, since the SARS virus present in horseshoe bats is unable to infect humans directly.

In 2012 another coronavirus capable of causing a severe acute respiratory illness later known as Middle East respiratory syndrome (MERS) was discovered in humans. The first case was found in Saudi Arabia, and others were reported within the following year in France, Germany, Jordan, Qatar, Tunisia, the United Arab Emirates, and the United Kingdom. All confirmed cases were directly or indirectly linked to the Middle East, and nearly two-thirds had ended in death. The novel MERS coronavirus was similar to other coronaviruses known to have originated in bats and was thought to be passed from bats to other animals before being transmitted to humans. Camels were identified as one possible reservoir for the MERS virus.

In late 2019 a virus apparently closely related to SARS coronavirus emerged in Wuhan, China. The Wuhan coronavirus caused an illness similar to SARS, characterized primarily by fever and respiratory symptoms. The virus was likewise highly contagious. By early 2020 it had spread throughout regions of China and had reached the United States and Europe, having been carried by travelers from affected regions.

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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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#605 2020-02-15 01:08:06

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

485) Liquefied petroleum gas and other gases

Liquefied petroleum gas (LPG)

Alternative Titles: LP gas, LPG, NGL, gas condensate, liquified petroleum gas, natural gas liquid, natural gasoline

Liquefied petroleum gas (LPG), also called LP gas, any of several liquid mixtures of the volatile hydrocarbons propene, propane, butene, and butane. It was used as early as 1860 for a portable fuel source, and its production and consumption for both domestic and industrial use have expanded ever since. A typical commercial mixture may also contain ethane and ethylene, as well as a volatile mercaptan, an odorant added as a safety precaution.

Liquefied petroleum gas (LPG) is recovered from “wet” natural gas (gas with condensable heavy petroleum compounds) by absorption. The recovered product has a low boiling point and must be distilled to remove the lighter fractions and then be treated to remove hydrogen sulfide, carbon dioxide, and water. The finished product is transported by pipeline and by specially built seagoing tankers. Transportation by truck, rail, and barge has also developed, particularly in the United States.

LPG reaches the domestic consumer in cylinders under relatively low pressures. The largest part of the LPG produced is used in central heating systems, and the next largest as raw material for chemical plants. LPG commonly is used as fuel for gas barbecue grills and gas cooktops and ovens, for gas fireplaces, and in portable heaters. In Europe, LPG water heaters are common. It is also used as an engine fuel and for backup generators. Unlike diesel, LPG can be stored nearly indefinitely without degradation.

Liquefied natural gas

Liquefied natural gas (LNG), natural gas (primarily methane) that has been liquefied for ease of storing and transporting. Liquefied natural gas (LNG) is 600 times smaller than natural gas when the latter is in its gaseous form, and it can be easily shipped overseas. LNG is produced by cooling natural gas below its boiling point, −162 °C (−259 °F), and is stored in double-walled cryogenic containers at or slightly above atmospheric pressure. It can be converted back to its gaseous form by simply raising the temperature.

LNG is more practical than liquefied petroleum gas or other liquid gases, particularly for use in large volumes, because it has the same chemical composition as natural gas. This fact and the growing demand for natural gas have stimulated LNG production. Moreover, LNG technology has made it possible to utilize natural gas from remote areas of the world where it previously had no commercial use and was flared (burned). Special tankers, known as LNG carriers and outfitted with supercooled cryogenic tanks, transport LNG from such countries as Qatar, Australia, Indonesia, and Algeria to markets in China, Europe, and Japan. In the early 21st century, with the expansion of natural gas pipelines in the United States, the country became a net exporter of LNG, whereas it previously had been an important importer of the product. LNG is usually reverted to its gaseous state (regasified) at the import terminals in the receiving countries, where it can then be injected into natural gas pipelines to be moved to power plants and distribution companies for various industrial uses.

Wet gas

Wet gas, natural gas that contains an appreciable proportion of hydrocarbon compounds heavier than methane (e.g., ethane, propane, and butane). The mixture may be gaseous or both liquid and gaseous in the reservoir; the heavier hydrocarbons are condensable when brought to the surface and are frequently separated as natural gas liquids (NGLs). Alternatively, the propane and other lighter compounds may be marketed as liquefied petroleum gas (LPG), and heavier hydrocarbons may be made into gasoline (petrol).

Wet gases usually are characterized by the volume or weight of the condensables contained in a given volume of total gas produced. This figure, computed for volumes at 15 °C (59 °F) and 750 mm of mercury, is usually expressed either in gallons per 1,000 cubic feet or in grams per cubic metre. In the United States, for a gas to be classified as wet, it must contain more than 0.1 gallon of condensables per 1,000 cubic feet of gas.

Dry gas

Dry gas, natural gas that consists of little more than methane, producing little condensable heavier hydrocarbon compounds such as propane and butane when brought to the surface. In the United States, dry gases are defined as those that contain less than 0.1 gallon of condensables per 1,000 cubic feet of produced gas.

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

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#606 2020-02-17 00:47:50

ganesh
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Posts: 29,764

Re: Miscellany

486) Ruby

Ruby, gemstone composed of transparent red corundum (q.v.), a mineral form of aluminum oxide, Al2O3. Its colour varies from deep cochineal to pale rose red, in some cases with a tinge of purple; the most valued is a pigeon-blood red. The red colour arises from the replacement of a small number of aluminum atoms by chromium atoms (1 in 5,000). High refractivity is characteristic; when cut and polished, ruby is a brilliant stone, but, because it has weak dispersion, it lacks fire. On exposure to high temperature, ruby becomes green but regains its original colour upon cooling. When subjected to radiant discharge, ruby phosphoresces with a vivid red glow.

Ruby is a mineral of very limited distribution. Its best known localities are in north-central Myanmar (Burma), northeast of Mandalay, where the gemstone occurs in bands of crystalline limestone associated with granitic and gneissic rocks. Rubies have been found at several localities in Thailand, in gravels with sapphires and spinels; they are generally of dark colour, often inclining to a deep reddish brown. Rubies found in the gem gravels of Sri Lanka are not usually of such good colour as the Myanmar stones.

The stone is sometimes called oriental ruby to distinguish it from other red gems. Thus Cape rubies, Australian rubies, and Arizona rubies are fine garnets; Siberian ruby is rubellite, red tourmaline; and balas ruby is ruby spinel. Although the word ruby is used in the English translation of the Old Testament, it is improbable that ruby was known to the ancient Hebrews.

Rubies have been produced artificially with much success. At one time it was the practice to fuse together small fragments of the natural stone. This method gave way to the flame-fusion (Verneuil) process of forming artificial ruby from purified ammonia alum and small amounts of chrome alum. Synthetic ruby containing 2.5 percent chromic oxide has the prized pigeon-blood red colour. Synthetic rubies possess the physical characteristics of natural corundum but may generally be distinguished by microscopic bubbles and striae.

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

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#607 2020-02-19 00:40:30

ganesh
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Re: Miscellany

487) Insomnia

Overview

Insomnia is a common sleep disorder that can make it hard to fall asleep, hard to stay asleep, or cause you to wake up too early and not be able to get back to sleep. You may still feel tired when you wake up. Insomnia can sap not only your energy level and mood but also your health, work performance and quality of life.

How much sleep is enough varies from person to person, but most adults need seven to eight hours a night.

At some point, many adults experience short-term (acute) insomnia, which lasts for days or weeks. It's usually the result of stress or a traumatic event. But some people have long-term (chronic) insomnia that lasts for a month or more. Insomnia may be the primary problem, or it may be associated with other medical conditions or medications.

You don't have to put up with sleepless nights. Simple changes in your daily habits can often help.

Symptoms

Insomnia symptoms may include:

•    Difficulty falling asleep at night
•    Waking up during the night
•    Waking up too early
•    Not feeling well-rested after a night's sleep
•    Daytime tiredness or sleepiness
•    Irritability, depression or anxiety
•    Difficulty paying attention, focusing on tasks or remembering
•    Increased errors or accidents
•    Ongoing worries about sleep

When to see a doctor

If insomnia makes it hard for you to function during the day, see your doctor to identify the cause of your sleep problem and how it can be treated. If your doctor thinks you could have a sleep disorder, you might be referred to a sleep center for special testing.

Causes

Insomnia may be the primary problem, or it may be associated with other conditions.

Chronic insomnia is usually a result of stress, life events or habits that disrupt sleep. Treating the underlying cause can resolve the insomnia, but sometimes it can last for years.

Common causes of chronic insomnia include:

•    Stress. Concerns about work, school, health, finances or family can keep your mind active at night, making it difficult to sleep. Stressful life events or trauma — such as the death or illness of a loved one, divorce, or a job loss — also may lead to insomnia.
•    Travel or work schedule. Your circadian rhythms act as an internal clock, guiding such things as your sleep-wake cycle, metabolism and body temperature. Disrupting your body's circadian rhythms can lead to insomnia. Causes include jet lag from traveling across multiple time zones, working a late or early shift, or frequently changing shifts.
•    Poor sleep habits. Poor sleep habits include an irregular bedtime schedule, naps, stimulating activities before bed, an uncomfortable sleep environment, and using your bed for work, eating or watching TV. Computers, TVs, video games, smartphones or other screens just before bed can interfere with your sleep cycle.
•    Eating too much late in the evening. Having a light snack before bedtime is OK, but eating too much may cause you to feel physically uncomfortable while lying down. Many people also experience heartburn, a backflow of acid and food from the stomach into the esophagus after eating, which may keep you awake.

Chronic insomnia may also be associated with medical conditions or the use of certain drugs. Treating the medical condition may help improve sleep, but the insomnia may persist after the medical condition improves.

Additional common causes of insomnia include:

•    Mental health disorders. Anxiety disorders, such as post-traumatic stress disorder, may disrupt your sleep. Awakening too early can be a sign of depression. Insomnia often occurs with other mental health disorders as well.
•    Medications. Many prescription drugs can interfere with sleep, such as certain antidepressants and medications for asthma or blood pressure. Many over-the-counter medications — such as some pain medications, allergy and cold medications, and weight-loss products — contain caffeine and other stimulants that can disrupt sleep.
•    Medical conditions. Examples of conditions linked with insomnia include chronic pain, cancer, diabetes, heart disease, asthma, gastroesophageal reflux disease (GERD), overactive thyroid, Parkinson's disease and Alzheimer's disease.
•    Sleep-related disorders. Sleep apnea causes you to stop breathing periodically throughout the night, interrupting your sleep. Restless legs syndrome causes unpleasant sensations in your legs and an almost irresistible desire to move them, which may prevent you from falling asleep.
•    Caffeine, nicotine and alcohol. Coffee, tea, cola and other caffeinated drinks are stimulants. Drinking them in the late afternoon or evening can keep you from falling asleep at night. Nicotine in tobacco products is another stimulant that can interfere with sleep. Alcohol may help you fall asleep, but it prevents deeper stages of sleep and often causes awakening in the middle of the night.

Insomnia and aging

Insomnia becomes more common with age. As you get older, you may experience:

•    Changes in sleep patterns. Sleep often becomes less restful as you age, so noise or other changes in your environment are more likely to wake you. With age, your internal clock often advances, so you get tired earlier in the evening and wake up earlier in the morning. But older people generally still need the same amount of sleep as younger people do.
•    Changes in activity. You may be less physically or socially active. A lack of activity can interfere with a good night's sleep. Also, the less active you are, the more likely you may be to take a daily nap, which can interfere with sleep at night.
•    Changes in health. Chronic pain from conditions such as arthritis or back problems as well as depression or anxiety can interfere with sleep. Issues that increase the need to urinate during the night ―such as prostate or bladder problems ― can disrupt sleep. Sleep apnea and restless legs syndrome become more common with age.
•    More medications. Older people typically use more prescription drugs than younger people do, which increases the chance of insomnia associated with medications.

Insomnia in children and teens

Sleep problems may be a concern for children and teenagers as well. However, some children and teens simply have trouble getting to sleep or resist a regular bedtime because their internal clocks are more delayed. They want to go to bed later and sleep later in the morning.

Risk factors

Nearly everyone has an occasional sleepless night. But your risk of insomnia is greater if:

•    You're a woman. Hormonal shifts during the menstrual cycle and in menopause may play a role. During menopause, night sweats and hot flashes often disrupt sleep. Insomnia is also common with pregnancy.
•    You're over age 60. Because of changes in sleep patterns and health, insomnia increases with age.
•    You have a mental health disorder or physical health condition. Many issues that impact your mental or physical health can disrupt sleep.
•    You're under a lot of stress. Stressful times and events can cause temporary insomnia. And major or long-lasting stress can lead to chronic insomnia.
•    You don't have a regular schedule. For example, changing shifts at work or traveling can disrupt your sleep-wake cycle.

Complications

Sleep is as important to your health as a healthy diet and regular physical activity. Whatever your reason for sleep loss, insomnia can affect you both mentally and physically. People with insomnia report a lower quality of life compared with people who are sleeping well.

Complications of insomnia may include:

•    Lower performance on the job or at school
•    Slowed reaction time while driving and a higher risk of accidents
•    Mental health disorders, such as depression, an anxiety disorder or substance abuse
•    Increased risk and severity of long-term diseases or conditions, such as high blood pressure and heart 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. 

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#608 2020-02-21 00:32:48

ganesh
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Re: Miscellany

488) Lily

Lily, the common name applied to herbaceous flowering plants belonging to the genus Lilium of the family Liliaceae. The genus contains between 80 and 100 species, native to the temperate areas of the Northern Hemisphere. Lilies are prized as ornamental plants, and they have been extensively hybridized.

The word lily is also used in the common names of many plants of other genera that resemble true lilies. These include the day lily (Hemerocallis) and various species of the family Amaryllidaceae.

The true lilies are erect perennial plants with leafy stems, scaly bulbs, usually narrow leaves, and solitary or clustered flowers. The flowers consist of six petallike segments, which may form the shape of a trumpet, with a more or less elongated tube, as in the Madonna lily (Lilium candidum) and Easter lily (L. longiflorum). Alternatively, the segments may be reflexed (curved back) to form a turban shape, as in the Turk’s cap lily (L. martagon); or they may be less strongly reflexed and form an open cup or bowl shape, as in L. umbellatum and L. auratum. The flowers of some species are quite fragrant, and they occur in a wide variety of colours. Plants of most species range in height from 30 to 120 cm (1–4 feet); plants of certain species, however, exceed 2.5 m (8 feet) in height.

Lilies are among the oldest cultivated plants. In Asia Minor, during the 2nd millennium BC, the bulb of the Madonna lily was cultivated for use in a medicinal ointment; the ancients raised the bulbs of this species for food. The Greeks and Romans grew it for ornamental and medicinal purposes. During the Middle Ages the Madonna lily was associated with the Virgin Mary as a symbol of purity; it is often included in paintings of her. In East Asia various species of lily were grown as food and ornamental plants from an early date.

Lilies are usually raised from bulbs, but they can be grown from seed. Different species vary in the amount of sunlight they require. Most prefer a porous, loamy soil, and good drainage is essential. Most species bloom in July or August. The flowering periods of certain species begin in late spring; others bloom in late summer or early autumn.

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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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#609 2020-02-23 00:54:06

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

489) Lotus

Lotus, any of several different plants. The lotus of the Greeks was the species Ziziphus lotus of the buckthorn family (Rhamnaceae), a bush native to southern Europe. It has large fruits containing a mealy substance that can be used for making bread and fermented drinks. In ancient times the fruits were an article of food among the poor, and a wine made from the fruit was thought to produce contentment and forgetfulness.

The Egyptian lotus is a white water lily, Nymphaea lotus (family Nymphaeaceae). The blue lotus (N. caerulea) was the dominant lotus in Egyptian art. The sacred lotus of the Hindus is an aquatic plant (Nelumbo nucifera) with white or delicate pink flowers; the lotus of eastern North America is Nelumbo pentapetala, a similar plant with yellow blossoms (see Nelumbonaceae). The lotus tree, known to the Romans as the Libyan lotus, was probably Celtis australis, the nettle tree of southern Europe, a member of the elm family (Cannabaceae) with fruits like small cherries, first red and then black at maturity.

Lotus is the Latin name for a genus of the pea family (Fabaceae), containing about 100 species distributed in temperate regions of Europe, Asia, Africa, and North America. It is represented in Great Britain, for example, by L. corniculatus, bird’s-foot trefoil, a low-growing ground cover with clusters of small bright yellow flowers that are often streaked with crimson. In North America 20 or more species of Lotus occur and are called such common names as deervetch and deerclover. They are grazed by animals.

The lotus, in the water-lily form, is a persistent ornament in architecture. A well-known example is its use in decorating the capitals of columns, a practice dating from ancient Egyptian times. The lotus is also the basis of the Assyrian sacred tree and the Phoenician stela capitals, which were the antecedent of the Ionic order of architectural design.

In addition to artistic uses, the lotus has, since ancient times, symbolized fertility and related ideas, including birth, purity, rebirth of the dead, and, in astrology, the rising sun.
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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#610 Yesterday 00:52:52

ganesh
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Registered: 2005-06-28
Posts: 29,764

Re: Miscellany

490) Pelican

Pelican, any of seven or eight species of water birds in the genus Pelecanus constituting the family Pelecanidae (order Pelecaniformes), distinguished by their large elastic throat pouches. Pelicans inhabit lakes, rivers, and seacoasts in many parts of the world. With some species reaching a length of 180 cm (70 inches), having a wingspan of 3 metres (10 feet), and weighing up to 13 kg (30 pounds), they are among the largest of living birds.

Pelicans eat fish, which they catch by using the extensible throat pouch as a dip-net. The pouch is not used to store the fish, which are swallowed immediately. One species, the brown pelican (Pelecanus occidentalis), captures fish by a spectacular plunge from the air, but other species swim in formation, driving small schools of fish into shoal water where they are scooped up by the birds.

Pelicans lay one to four bluish white eggs in a stick nest, and the young hatch in about a month. The young live on regurgitated food obtained by thrusting their bills down the parent’s gullet. The young mature at three to four years. Though ungainly on land, pelicans are impressive in flight. They usually travel in small flocks, soaring overhead and often beating their wings in unison. Males and females are similar in appearance, but males are larger.

The best-known pelicans are the two species called white pelicans: P. erythrorhynchos of the New World, the North American white pelican, and P. onocrotalus of the Old World, the European white pelican. Between 1970 and late 2009, the smaller, 107–137-cm brown pelican was listed as endangered by the U.S. Fish and Wildlife Service. Though the brown pelican once bred in enormous colonies along New World coasts, its population declined drastically in North America during the period 1940–70 as a result of use of DDT and related pesticides. The birds’ breeding improved after DDT was banned. The best-known pelicans are the two species called white pelicans: P. erythrorhynchos of the New World, the North American white pelican, and P. onocrotalus of the Old World, the European white pelican. Between 1970 and late 2009, the smaller, 107–137-cm brown pelican was listed as endangered by the U.S. Fish and Wildlife Service. Though the brown pelican once bred in enormous colonies along New World coasts, its population declined drastically in North America during the period 1940–70 as a result of use of DDT and related pesticides. The birds’ breeding improved after DDT was banned.

(DDT, abbreviation of dichlorodiphenyltrichloroethane, also called 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, a synthetic insecticide belonging to the family of organic halogen compounds, highly toxic toward a wide variety of insects as a contact poison that apparently exerts its effect by disorganizing the nervous system.)

Pelicans usually breed in colonies on islands; there may be many small colonies on a single island. The gregarious North American white pelican breeds on islands in lakes in north-central and western North America; all pairs in any colony at any given time are in the same stage of the reproductive cycle. It is migratory, as are some other species. The brown pelican breeds along the tropical and subtropical shores of both the Atlantic and Pacific coasts.

Pelicans were once thought to be more closely related to cormorants, darters, frigate birds, and gannets and boobies, which were placed in the order Pelecaniformes with them. However, more recent genetic analysis suggests that the aforementioned seabirds may be more accurately grouped in their own order (Suliformes). A suggested revision of the order Pelecaniformes places pelicans with herons and egrets (family Ardeidae) and ibises and spoonbills (family Threskiornithidae) along with the hammerhead (Scopus umbretta) and the shoebill (Balaeniceps rex).

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

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