Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

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

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

Offline

#602 2020-02-09 01:12:22

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

Offline

#603 2020-02-11 01:32:08

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

Offline

#604 2020-02-13 00:58:47

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

coronavirus.jpg?w=325&ssl=1


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.

Offline

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

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

P90113067_g.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.

Offline

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

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

ruby-stone-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.

Offline

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

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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

insomnia1-300x336.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.

Offline

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

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.

Pink_and_White_Asiatic_Lily_Flower_Vermeer_300.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.

Offline

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

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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.
lotus-flower-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.

Offline

#610 2020-02-25 00:52:52

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

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).

c7c7c6ae-3d4b-45f0-9b01-21e5aaa520ae.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.

Offline

#611 2020-02-27 01:08:57

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

491) Precipitation

Precipitation, all liquid and solid water particles that fall from clouds and reach the ground. These particles include drizzle, rain, snow, snow pellets, ice crystals, and hail.

The essential difference between a precipitation particle and a cloud particle is one of size. An average raindrop has a mass equivalent to about one million cloud droplets. Because of their large size, precipitation particles have significant falling speeds and are able to survive the fall from the cloud to the ground.

The transition from a cloud containing only cloud droplets to one containing a mixture of cloud droplets and precipitation particles involves two basically different steps: the formation of incipient precipitation elements directly from the vapour state and the subsequent growth of those elements through aggregation and collision with cloud droplets. The initial precipitation elements may be either ice crystals or chemical-solution droplets.

Development of precipitation through the growth of ice crystals depends on the fact that cloud droplets can freeze spontaneously at temperatures below about −40 °C, or −40 °F. (The reduction of cloud droplets to temperatures below the normal freezing point is termed supercooling.) Within supercooled clouds, ice crystals may form through sublimation of water vapour on certain atmospheric dust particles known as sublimation nuclei. In natural clouds, ice crystals form at temperatures colder than about −15 °C (+5 °F). The exact temperature of ice crystal formation depends largely on the physical-chemical nature of the sublimation nucleus.

Once ice crystals have formed within a supercooled cloud, they continue to grow as long as their temperature is colder than freezing. The rates of growth depend primarily upon the temperature and degree of vapour saturation of the ambient air. The crystals grow at the expense of the water droplets. In favourable conditions—e.g., in a large, rapidly growing cumulus cloud—an ice crystal will grow to a size of about 0.13 millimetre (0.005 inch) in three to five minutes after formation. At this size, the rate of growth through sublimation slows down, and further growth is largely through aggregation and collision with cloud droplets.

Small solution drops are also important as incipient precipitation particles. The atmosphere contains many small particles of soluble chemical substances. The two most common are sodium chloride swept up from the oceans and sulfate-bearing compounds formed through gaseous reactions in the atmosphere. Such particles, called condensation nuclei, collect water because of their hygroscopic nature and, at relative humidities above about 80 percent, exist as solution droplets. In tropical maritime air masses, the number of condensation nuclei is often very large. Clouds forming in such air may develop a number of large solution droplets long before the tops of the clouds reach temperatures favourable to the formation of ice crystals.

Regardless of whether the initial precipitation particle is an ice crystal or a droplet formed on a condensation nucleus, the bulk of the growth of the precipitation particle is through the mechanisms of collision and coalescence. Because of their larger size, the incipient precipitation elements fall faster than do cloud droplets. As a result, they collide with the droplets lying in their fall path. The rate of growth of a precipitation particle through collision and coalescence is governed by the relative sizes of the particle and the cloud droplets in the fall path that are actually hit by the precipitation particle and the fraction of these droplets that actually coalesce with the particle after collision.

ag3hzkhga1rot1mmh24k


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.

Offline

#612 2020-02-29 00:08:22

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

492) Bushfire Australia 2019-20

Australia faced a devastating start to it’s fire season in late 2019, and things swiftly got worse before rains helped contain many of the worst fires in February 2020. The Verge will update this page with news and analyses.

What’s happened so far?

Dozens of fires erupted in New South Wales, Australia, prompting the government to declare a state of emergency in November 2019. Fires rapidly spread across all states to become some of the most devastating on record. An area about the size of South Korea, roughly 25.5 million acres, has burned. At least 33 people are dead, including at least three volunteer firefighters, and more are missing. Around 3,000 homes have been destroyed or damaged. As blazes intensified in the days leading up to New Year’s Eve, thousands of people who were forced to evacuate sought shelter on beaches across New South Wales and Victoria.

Summer extends from December to February in Australia, with fire season typically peaking in late January or early February. On January 3rd, officials warned that conditions would get worse over the following few days. “It’s going to be a blast furnace,” New South Wales Transport Minister Andrew Constance said to The Sydney Morning Herald. By January 10th, another round of massive evacuations began across the hardest-hit regions of the southeast due to dangerous winds fanning the flames.

The fires in New South Wales, the state most affected, were finally declared “contained” on February 13th. “After what’s been a truly devastating fire season for both fire fighters and residents who’ve suffered through so much this season ... We can really focus on helping people rebuild,” New South Wales Rural Fire Service deputy commissioner Rob Rogers said in a video shared on Twitter. The relief came after torrential rains marked the wettest week in the region in three decades.

In what has been a very traumatic, exhausting and anxious bush fire season so far, for the first time this season all bush and grass fires in NSW are now contained.

It has taken a lot of work by firefighters, emergency services and communities to get to this point.

The smoke became another disaster. On January 1st, Australia’s capital recorded the worst pollution it’s ever seen, with an air quality index 23 times higher than what’s considered “hazardous.” Smoke in the city crept into birthing rooms, stopped MRI machines from working, and triggered respiratory distress in one elderly woman who died soon after she stepped off a plane.

The smoke reached New Zealand, 1,000 miles away, where it has created eerie scenes atop glacier-covered peaks. The plumes were so thick that a NASA satellite snapped pictures of it from space.

More than 1 billion mammals, birds, and reptiles likely lost their lives in the blazes, according to one estimate from the University of Sydney. Around 25,000 koalas were feared dead on Kangaroo Island. Eight thousand koalas, a third of all the koalas in New South Wales, are believed to have perished, and about 30 percent of the koalas’ habitat has also been wiped out. The devastation only adds to existing pressures on Australia’s unique ecosystems. The continent is home to 244 species that are not found anywhere else. The region also has the highest rate of native mammals becoming extinct over the past 200 years. The Department of Agriculture, Water and the Environment published a list on February 11th of the 113 animal species, including the platypus, that most urgently need help following the fires.

“The potential impacts on wildlife are devastating,” Crystal Kolden, an associate professor of fire science at the University of Idaho who studied wildfires in Tasmania in 2018, tells The Verge. “There won’t be a full accounting for how bad it actually is for years.” Some ecosystems, like eucalyptus forests, are prone to fires and will come back. But Kolden points out that Australia is also home to pockets of vegetation, inhabited by species that have managed to survive for millions of years. “These really incredible remnants of, you know, the era of the dinosaurs essentially, [are] not adapted for fire and when it burns, it will be gone.”

During the Golden Globe Awards on January 5th, celebrities, including Joaquin Phoenix, Ellen DeGeneres, Patricia Arquette, and Cate Blanchett, shared their concern about the fires. Australian native Russell Crowe skipped the awards ceremony because of the blazes (his home was damaged by the fires in November), but Jennifer Aniston delivered a message from him after he won Best Actor in a Limited Series or Motion Picture Made for TV. “Make no mistake. The tragedy unfolding in Australia is climate change-based,” his message said.

What does climate change have to do with it?

Firestorms are not new to Australia. It’s typically hot and dry, similar to conditions in California or the Mediterranean. Eucalyptus forests in Australia have a unique relationship to fire; the trees actually depend on fire to release their seeds.

This season’s fires, however, are unprecedented. It’s a much earlier fire season, and the fires have gotten very big, very early, Kolden tells The Verge. Weather conditions feeding the fires are historic. Australia suffered from its hottest day on record on December 18th, reaching a national average temperature of 41.9 degrees Celsius (107.4 degrees Fahrenheit). Last month was Australia’s hottest December, and 2019 was the country’s hottest and driest year on record. Extreme heat and drought create more tinder to fuel fires. The heightened intensity and frequency of wildfires fall in line with scientists’ predictions for a warming world.

“The reality is, this is a function of climate change — this extreme heat, these extreme conditions that are so volatile and are producing the types of intensity and early season burning that we do not normally see in Australia,” Kolden says.

Australia Prime Minister Scott Morrison is facing heat for his own inaction on climate change and defense of coal. Morrison’s administration faced criticism for thwarting global efforts to complete a rulebook for implementing the Paris agreement during a United Nations climate conference in Madrid in December. Morrison also got backlash for taking a vacation to Hawaii — which he ended up cutting short — in the midst of the fires.

“This Is A Function Of Climate Change.“

“I think there is a feeling among environmental scientists and ecologists in Australia that we’ve been frozen out of the debate, certainly out of policymaking. I think it’s now time to bring the scientists back into the tent to look at what is likely to be happening over the next few decades,” Chris, the ecologist at the University of Sydney who estimated the death toll of animals in the flames, told Public Radio International’s The World. “We’re probably looking at what climate change may look like for other parts of the world in the first stages in Australia at the moment,” he said.

Thousands of protesters took to the streets in Sydney, Melbourne, and other cities across Australia on January 10th. Demonstrators called for an end to fossil fuel subsidies and action on climate change, and they shut down some roads while demanding that Prime Minister Morrison leave office.

How are the fires being fought?

Australia relies heavily on volunteer firefighters, especially in the rural bush where much of the fires are burning. Its fire response relies more heavily on community efforts compared to places like the United States that have centralized fire management systems. The current crisis has led to some policy changes. As volunteers missed work to fight local blazes, Morrison announced in December that they would be compensated. To bolster the local forces, the Australian military sent in its own aircraft and vessels and 3,000 army reservists. Help is also coming from abroad: the United States and Canada have sent firefighters to battle the blazes. Malaysia is preparing to send help, too.

“It's Not Humanely Possible.”

Experts told The Verge that under the extreme conditions, there was not much more that firefighters could do until there was enough rainfall to stop the blazes or the fires ran out of fuel and burned themselves out. “It’s not humanly possible to prevent [these fires] or put them out,” Timothy Ingalsbee, executive director of Firefighters United for Safety, Ethics, and Ecology based in Oregon, tells The Verge. “We have put so much of our strategy for living in fire environments all on firefighters, all on suppression, reacting to blazes. And, you know, now we are facing conditions, given climate change in particular, we can’t do that.”

AUSTRALIA-FIRE.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.

Offline

#613 2020-03-02 01:02:00

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

493) Industrial Revolution

Industrial Revolution, in modern history, the process of change from an agrarian and handicraft economy to one dominated by industry and machine manufacturing. This process began in Britain in the 18th century and from there spread to other parts of the world. Although used earlier by French writers, the term Industrial Revolution was first popularized by the English economic historian Arnold Toynbee (1852–83) to describe Britain’s economic development from 1760 to 1840. Since Toynbee’s time the term has been more broadly applied.

The main features involved in the Industrial Revolution were technological, socioeconomic, and cultural. The technological changes included the following: (1) the use of new basic materials, chiefly iron and steel, (2) the use of new energy sources, including both fuels and motive power, such as coal, the steam engine, electricity, petroleum, and the internal-combustion engine, (3) the invention of new machines, such as the spinning jenny and the power loom that permitted increased production with a smaller expenditure of human energy, (4) a new organization of work known as the factory system, which entailed increased division of labour and specialization of function, (5) important developments in transportation and communication, including the steam locomotive, steamship, automobile, airplane, telegraph, and radio, and (6) the increasing application of science to industry. These technological changes made possible a tremendously increased use of natural resources and the mass production of manufactured goods.

There were also many new developments in nonindustrial spheres, including the following: (1) agricultural improvements that made possible the provision of food for a larger nonagricultural population, (2) economic changes that resulted in a wider distribution of wealth, the decline of land as a source of wealth in the face of rising industrial production, and increased international trade, (3) political changes reflecting the shift in economic power, as well as new state policies corresponding to the needs of an industrialized society, (4) sweeping social changes, including the growth of cities, the development of working-class movements, and the emergence of new patterns of authority, and (5) cultural transformations of a broad order. Workers acquired new and distinctive skills, and their relation to their tasks shifted; instead of being craftsmen working with hand tools, they became machine operators, subject to factory discipline. Finally, there was a psychological change: confidence in the ability to use resources and to master nature was heightened.

The First Industrial Revolution

In the period 1760 to 1830 the Industrial Revolution was largely confined to Britain. Aware of their head start, the British forbade the export of machinery, skilled workers, and manufacturing techniques. The British monopoly could not last forever, especially since some Britons saw profitable industrial opportunities abroad, while continental European businessmen sought to lure British know-how to their countries. Two Englishmen, William and John math, brought the Industrial Revolution to Belgium by developing machine shops at Liège (c. 1807), and Belgium became the first country in continental Europe to be transformed economically. Like its British progenitor, the Belgian Industrial Revolution centred in iron, coal, and textiles.

France was more slowly and less thoroughly industrialized than either Britain or Belgium. While Britain was establishing its industrial leadership, France was immersed in its Revolution, and the uncertain political situation discouraged large investments in industrial innovations. By 1848 France had become an industrial power, but, despite great growth under the Second Empire, it remained behind Britain.

Other European countries lagged far behind. Their bourgeoisie lacked the wealth, power, and opportunities of their British, French, and Belgian counterparts. Political conditions in the other nations also hindered industrial expansion. Germany, for example, despite vast resources of coal and iron, did not begin its industrial expansion until after national unity was achieved in 1870. Once begun, Germany’s industrial production grew so rapidly that by the turn of the century that nation was outproducing Britain in steel and had become the world leader in the chemical industries. The rise of U.S. industrial power in the 19th and 20th centuries also far outstripped European efforts. And Japan too joined the Industrial Revolution with striking success.

The eastern European countries were behind early in the 20th century. It was not until the five-year plans that the Soviet Union became a major industrial power, telescoping into a few decades the industrialization that had taken a century and a half in Britain. The mid-20th century witnessed the spread of the Industrial Revolution into hitherto nonindustrialized areas such as China and India.

The Second Industrial Revolution

Despite considerable overlapping with the “old,” there was mounting evidence for a “new” Industrial Revolution in the late 19th and 20th centuries. In terms of basic materials, modern industry began to exploit many natural and synthetic resources not hitherto utilized: lighter metals, new alloys, and synthetic products such as plastics, as well as new energy sources. Combined with these were developments in machines, tools, and computers that gave rise to the automatic factory. Although some segments of industry were almost completely mechanized in the early to mid-19th century, automatic operation, as distinct from the assembly line, first achieved major significance in the second half of the 20th century.

Ownership of the means of production also underwent changes. The oligarchical ownership of the means of production that characterized the Industrial Revolution in the early to mid-19th century gave way to a wider distribution of ownership through purchase of common stocks by individuals and by institutions such as insurance companies. In the first half of the 20th century, many countries of Europe socialized basic sectors of their economies. There was also during that period a change in political theories: instead of the laissez-faire ideas that dominated the economic and social thought of the classical Industrial Revolution, governments generally moved into the social and economic realm to meet the needs of their more complex industrial societies. That trend was reversed in the United States and the United Kingdom beginning in the 1980s.

c5d09081357ae272521ca1e3fa6b80d6.jpeg


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.

Offline

#614 2020-03-04 01:08:34

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

494) Pneumatic device

Pneumatic device, any of various tools and instruments that generate and utilize compressed air. Examples include rock drills, pavement breakers, riveters, forging presses, paint sprayers, blast cleaners, and atomizers.

Compressed-air power is flexible, economic, and safe. An air device creates no spark hazard in an explosive atmosphere and can be used under wet conditions without electric-shock hazard. A relatively small compressor suffices to fill a storage tank for intermittent use, and no return lines are needed. Other characteristics of a compressed-air system are important in meeting special service requirements. It is relatively easy to connect one device (such as a valve or a cylinder and piston) to another by pipe, tubing, or flexible hose. Many actions can be controlled by a simple manipulation of valves. The motion of an actuating piston in a cylinder can be changed quickly and in small steps with practically no shock. An air system can provide great flexibility in speed and motion control. Relief valves are easily arranged to protect a system and avoid damage. Control of operations is simple, efficient, and centralized. In general, air systems have relatively few moving parts, contributing to high reliability and low maintenance costs.

Development Of Pneumatic Devices

The ordinary hand bellows, used by early smelters and blacksmiths for working iron and other metals, was a simple type of air compressor. The air intake consisted of several holes in a piece of wood, covered with flaps that served as valves. A simple check valve in the discharge prevented air from being drawn back into the bellows during the suction stroke. In the time of Hero (probably 1st century AD), a simple jet-type compressor was used to provide air for smelting and forging.

In the 17th century, the German Otto von Guericke experimented on and significantly improved compressors. In 1829 a stage, or compound, compressor, which involved compressing air in successive cylinders, was patented. Cooling by jets of water sprayed into the cylinder during compression was introduced about 1872; later, a better system of cooling by the use of water-jacketed cylinders was developed. In the United States the first compressor used in large-scale work was a four-cylinder unit for the Hoosac Tunnel, at North Adams, Massachusetts, in 1866.

The 20th century witnessed a large increase in the use of compressed air and of compressed-air devices. The introduction of jet engines for military and passenger aircraft stimulated the use and improvement of centrifugal and axial-flow compressors. The further development of automatic machinery, labour-saving devices, and automatic-control systems led to an increase in the use of pneumatics. In the late 1960s there began a significant development of a new class of compressed-air devices: digital-logic pneumatic-control components, which can be used in various power and control systems.

Major Types Of Pneumatic Devices

Air compressors and pneumatic tools constitute the principal classes of pneumatic devices. Other kinds of apparatus that make use of compressed air are paint-spray equipment, pneumatic tubes for conveying materials, and train brake systems.
An air compressor is a power-driven machine for compressing air from some initial intake pressure (usually atmospheric) to a higher pressure. Compressors (as well as other fluid machines) can be classified into two main types, depending on the air or fluid action: (1) the positive-displacement type and (2) the velocity, or dynamic, type.

In the positive-displacement, or static-pressure, type, the characteristic action is a volumetric change or displacement action. Successive volumes of air are confined within a closed space, and the pressure is increased by reducing the volume of the space. In the simple hand tire pump, pressure is developed by moving a piston in a cylinder. The positive-displacement type may be subdivided into reciprocating (back-and-forth straight-line motion) and rotary (motion in a circular path) compressors. In a positive-displacement machine, neglecting leakage, the volume rate of flow (cubic feet per second) through the compressor is essentially constant over a wide range of discharge pressures.

The dynamic type of compressor may be subdivided into the centrifugal type (with flow through a rotating runner or rotor primarily in a radial direction), the axial-flow type (with flow through a runner primarily in a direction parallel to the axis of rotation), and the fluid-jet type.

Pneumatic tools can be separated into two broad categories on the basis of the driving method: rotor and reciprocating piston. Both kinds are known as air motors. A rotating type of compressor, operating in reverse, serves as one type of motor. Compressed air enters the housing, pushes on the vanes, and rotates a central shaft or spindle. A drill, grinding wheel, or other device is fastened to the spindle. A reciprocating-piston compressor, operating in reverse, also functions as a motor. Compressed air enters the cylinder, expands, and forces the piston to move. The return stroke may be actuated by compressed air on the other side of the piston or by spring action. A tool, such as a riveting hammer, may be connected to the reciprocating piston. Pneumatic tools are normally supplied with compressed air at about 90 psig (pounds per square inch gauge).

With compressed air as the power source, tools have been designed that are relatively lightweight, compact, portable, easy to operate, and free from electrical shock and spark hazards. In underwater operations, compressed air prevents water from entering the air motor.

Pneumatic tools can also be divided into two groups according to the type of tools: portable tools and rock drills. Portable pneumatic tools include abrasive devices (e.g., grinders, buffers, and sanders), drills, reamers, tappers, stud setters, screwdrivers, nutsetters, shears, wrenches, and impact tools. They are normally powered by a rotary-vane type of air motor. Operating speeds can be varied by throttling the air to the motor. Air motors do not become hot when overloaded; they will stand repeated stalling and rapid reversals without damage. Grinders feature air motors, which are typical for this class of device.

Portable tools also include chipping hammers and air hoists. Pneumatic chipping hammers contain an air-operated piston that delivers successive blows to a chisel or forming tool at the end of the hammer. The valve type of tool has a separate mechanism to control the airflow to the piston, thus allowing the operator to control the speed and force of the blows. In a compression riveter the compression, or squeezing action, on the rivet is obtained from an air piston connected to a cam, wedge, or toggle. A yoke riveter has an air-operated clamp or vise that holds the work in place; the yoke absorbs the hammering action and thus reduces operator fatigue. Hoists operated by compressed air are employed in operations requiring accurate control of lifting or lowering speeds. In most cases, they are used outdoors and under conditions in which corrosive fumes, explosive gases, or inflammable fluids are present.

There are also various portable specialty tools, such as concrete vibrators, countersinking tools, spikedrivers, paint mixers, air cranking motors, railway roadbed tampers, valve grinders, reciprocating filing machines, and shank grinders.

Rock drills are used for mining and rock excavation. An example of such a pneumatic tool is the hammer drill, or percussion hammer, which is composed of a piston and a drill made of high-carbon steel. The drill is held loosely in a chuck at the end of the cylinder and is struck by rapid blows from the freely moving piston. For downward-sloping holes, some means must be provided for removing drill cuttings, dust, and sludge. A hollow drill is usually used, and water or air is passed through it to remove the cuttings and cool the drill bit. Another kind of rock drill, called the drifter drill, is used for horizontal holes in mining operations and tunnel driving. It is mounted on some type of rig or frame and is mechanically fed into the work. Stoper drills are used primarily on up-hole or overhead drilling because of the automatic-feed characteristics. The usual stoper is a hammer drill with a self-rotating drill bit and an automatic feed by means of an air piston. Large air-operated earth drills, mounted on motor trucks on trailers, are utilized for digging water wells and blast holes for quarry operations. A high-capacity compressor provides air not only to power the drill tool but also to raise the tools in the hole and to remove drill cuttings from the hole. Such machines are used to advantage in areas where surface water supplies are insufficient to provide the drilling fluid needed for standard rotary and cable-tool well-drilling machines.

Hand-operated pneumatic paving breakers usually use solid steel drills and are not equipped for automatic rotation. One type of tool is valve-actuated, another is valveless. Heavy machines of about 80 pounds (36 kg) are used to break concrete pavement, foundations, and boulders. Medium breakers, weighing about 50 to 70 pounds (23 to 32 kg), are employed when breaking light concrete floors, macadam, and frozen ground. Light tools, weighing less than 50 pounds, are used to break floors, paving, and masonry walls. Heavy and medium-weight breakers can be adapted for driving spikes.

Compressed air is a good vehicle for conveying a paint spray. In a spray gun, the paint (e.g., lacquer, enamel, or plastic coating) is atomized and mixed with compressed air. The principle of operation is similar to that of the jet compressor, with the compressed air serving as the motive fluid to draw the paint into the mixing area. Spray painting usually implies covering relatively large surfaces, such as a building. The term airbrush, by contrast, implies a device for developing a fine, small diameter spray of paint, protective coating, or liquid colour. The airbrush can be a pencil-shaped atomizer used for a variety of much more detailed activities such as shading drawings and retouching photographs.

Pneumatic conveyers are used in various applications for handling materials. In a pressure system the outlet of the compressor leads into the inlet of the conveyer system. In a vacuum system the compressor inlet is at the end of the system. The air-pressure difference across the system depends on the material to be handled. In many places, mail is transferred from one site to another by pneumatic transport capsules in tubes. All sorts of materials may be conveyed by pneumatic systems, from ashes and cement to frozen foods, minerals, nuts, and seeds. Pneumatic handling is safe, fast, clean, automatic, and flexible.

Certain recently developed vehicles are supported by a cushion of air. The most successful of these air-cushion vehicles (ACVs) is the British-made Hovercraft. It is used commercially as a passenger- and car-carrying ferry; a number of them ply the English Channel. Experimental “tracked skimmers” (air-cushion trains) are under development in a number of countries, but they are not yet used commercially to any great extent. In the planning of many city transit systems, consideration is being given to air-cushion vehicles capable of speeds up to 300 miles (480 km) per hour. Other specialized forms of air-cushion vehicles have been designed for use over rough terrain—such as that in Arctic regions—and for other uncommon applications.

Brakes on trains and most buses and large trucks are operated by air pressure. A piston rod from an air cylinder exerts force on the braking device. On railroad cars the air-brake system includes a compressor, pneumatic valves, regulators, piping, reservoir, and other accessories. There are levers, cylinders, and other rigging to apply forces to the brake shoe, which bear directly on the rim of the wheel. Various automatic-control safety arrangements assure a definite braking action should some malfunction develop.

2420849.jpeg


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.

Offline

#615 2020-03-06 00:58:05

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

495) Galapagos Islands

Galapagos Islands, Spanish Islas Galápagos, officially Archipiélago de Colón (“Columbus Archipelago”), island group of the eastern Pacific Ocean, administratively a province of Ecuador. The Galapagos consist of 13 major islands (ranging in area from 5.4 to 1,771 square miles [14 to 4,588 square km]), 6 smaller islands, and scores of islets and rocks lying athwart the Equator 600 miles (1,000 km) west of the mainland of Ecuador. Their total land area of 3,093 square miles (8,010 square km) is scattered over 23,000 square miles (59,500 square km) of ocean. The government of Ecuador designated part of the Galapagos a wildlife sanctuary in 1935, and in 1959 the sanctuary became the Galapagos National Park. In 1978 the islands were designated a UNESCO World Heritage site, and in 1986 the Galapagos Marine Resources Reserve was created to protect the surrounding waters. The Charles Darwin Research Station on Santa Cruz (Indefatigable) Island promotes scientific studies and protects the indigenous vegetation and animal life of the Galapagos.

The Galapagos Islands are formed of lava piles and dotted with shield volcanoes, many of which are periodically active. The striking ruggedness of the arid landscape is accentuated by high volcanic mountains, craters, and cliffs. The largest of the islands, Isabela (Albemarle), is approximately 82 miles (132 km) long and constitutes more than half of the total land area of the archipelago; it contains Mount Azul, at 5,541 feet (1,689 metres) the highest point of the Galapagos Islands. The second largest island is Santa Cruz.

The Galapagos Islands were discovered in 1535 by the bishop of Panama, Tomás de Berlanga, whose ship had drifted off course while en route to Peru. He named them Las Encantadas (“The Enchanted”), and in his writings he marveled at the thousands of large galápagos (tortoises) found there. Numerous Spanish voyagers stopped at the islands from the 16th century, and the Galapagos also came to be used by pirates and by whale and seal hunters. The area had been unclaimed for almost 300 years before colonization began on what is now Santa María Island in 1832, when Ecuador took official possession of the archipelago. The islands became internationally famous as a result of their being visited in 1835 by the English naturalist Charles Darwin; their unusual fauna contributed to the groundbreaking theories on natural selection presented in his ‘On the Origin of Species’ (1859).

The climate of the Galapagos Islands is characterized by low rainfall, low humidity, and relatively low air and water temperatures. The islands have thousands of plant and animal species, of which the vast majority are endemic. The archipelago’s arid lowlands are covered by an open cactus forest. A transition zone at higher elevations is covered with a forest in which pisonia (a four o’clock plant) and guava trees dominate, and the moist forest region above the transition zone is dominated by a Scalesia forest with dense underbrush. The treeless upland zone is covered with ferns and grasses.

The archipelago is renowned for its unusual animal life. Its giant tortoises are thought to have some of the longest life spans (up to 150 years) of any creature on Earth. The close affinities of Galapagos animals to the fauna of South and Central America indicate that most of the islands’ species originated there. Because of subsequent evolutionary adaptations, an amazing range of subspecies are found on the islands today. Galapagos finches, for example, have developed a multitude of adaptive types from one common ancestral type; their subspecies now differ mainly in beak shape and size. The swimming marine iguanas, which feed on seaweed and in some places cover the coastal rocks by the hundreds, are unique and endemic. Another species of interest is the flightless cormorant. In addition, penguins and fur seals live on the islands side by side with tropical animals. A geologic study published in 1992 suggested that underwater seamounts near the Galapagos had formed islands between 5,000,000 and 9,000,000 years ago; this helped explain the great amount of endemic speciation, which many biologists believe could not have occurred in a lesser amount of time. The existing Galapagos Islands were formed between 700,000 and 5,000,000 years ago, making them geologically young.

The islands’ human inhabitants, mostly Ecuadorans, live in settlements on San Cristóbal, Santa María, Isabela, and Santa Cruz islands; Baltra has an Ecuadoran military base. Some of the islands are virtually untouched by humans, but many have been altered by the introduction of nonnative plants, the growth of the local human population, and tourist traffic. Tourism, fishing, and agriculture are the main economic activities. Pop. (2001) 18,640; (2010) 25,124.

galis.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.

Offline

#616 2020-03-08 01:15:54

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

496) Philately

Philately, the study of postage stamps, stamped envelopes, postmarks, postcards, and other materials relating to postal delivery. The term philately also denotes the collecting of these items. The term was coined in 1864 by a Frenchman, Georges Herpin, who invented it from the Greek philos, “love,” and ateleia, “that which is tax-free”; the postage stamp permitted the letter to come free of charge to the recipient, rendering it untaxed.

Early Postage Stamps

The first postage stamps for the prepayment of letter postage were issued in England in 1840. They were the brainchild of Rowland Hill, who successfully proposed them in his pamphlet ‘Post Office Reform’ (1837). Postal charges were then determined mainly by the distance traveled (and the weight of the letter), but Hill proved that the main cost of transport was in the handling and sorting of letters rather than in their carriage. Hill further observed that, because most letters went through post unpaid and postage had to be collected from the recipient on delivery, many of them were refused and had to be returned, thus necessitating a two-way trip for no revenue. Hill proposed a radical change: that all postage be prepaid, and that letters be carried any distance within Great Britain for a fixed rate (which he suggested be a penny for each half-ounce).

With the backing of the Exchequer, Hill had two devices made: prepaid envelopes, and, for those wishing to use their own stationery, adhesive postage stamps. The prepaid envelopes were laughed out of existence owing to their ridiculous designs, but the stamps were an immediate success: a one-penny design in black and a two-penny one in blue, both bearing a profile of Queen Victoria, went on sale to the public on May 1, 1840, and were good for use from May 6. The postage stamp was adopted for use by the semiofficial City Despatch Post of New York City in 1842, and the next year the Brazilian empire and the Swiss cantons of Zürich and Geneva also issued stamps. In 1847 the U.S. government issued stamps of 5- and 10-cent value, bearing pictures of Benjamin Franklin and George Washington, respectively. Austria and various German states followed suit in 1850, after which the remaining countries of the world began to issue stamps.

These early stamps were printed on sheets of paper with no provisions for separating them from each other; this required the use of a knife or scissors to secure individual stamps. But in 1848–54 a machine was adapted by the British Post Office to provide stamps with separations in the course of their manufacture, and most stamps are now edged with tiny holes, called perforations, which enable them to be easily separated. Other innovations eventually followed; airmail stamps, used for letters carried especially by air, were first issued by Italy experimentally in 1917, with the first regular issue put out by the United States in 1918. Other types of stamps include special-delivery stamps, postage-due stamps, and semipostal stamps; the latter are sold at a premium over their face value, with the overage going to charity. Commemorative stamps are regular postage stamps issued to honour some event, activity, or person of national importance; unlike other regular postage stamps (known as definitives), they are printed only once and are allowed to go out of circulation as their supply is used up. The first commemorative stamp was issued by New South Wales in 1888, on the 100th anniversary of that Australian colony’s founding.

Stamp Collecting As A Hobby

The issuance of postage stamps was followed soon after by the earliest reference to stamp collecting, an advertisement in ‘The Times’ of London in 1841 placed by “a young lady, being desirous of covering her dressing-room with cancelled postage stamps.” Mere accumulation rapidly progressed to systematic collecting of the various issues of particular countries, and the first lists of stamps were published in 1861 by Oscar Berger-Levrault in Strasbourg and Alfred Potiquet in Paris. In England, Frederick Booty, J.E. Gray, and Mount Brown all issued catalogs in 1862; Brown’s third edition (1866) listed 2,400 varieties, inclusive of what is now termed postal stationery or envelopes, wrappers, and letter sheets, as well as many local issues. The standard modern stamp catalogs (e.g., Yvert and Tellier in France, Michel’s in Germany, E. Stanley Gibbons’ in Great Britain, and Scott or Minkus in the United States) exclude this latter material, and yet the total number of listings, including minor varieties, reached more than 200,000 by the late 20th century.

Books in which to keep stamps were first issued by Justin Lallier in Paris in 1862 and are known as stamp albums. The typical printed stamp album consists of pages bearing the names of countries and designated spaces for the latter’s stamps in order of their date of issue, with illustrations of representative issues. Comprehensive “worldwide” stamp albums can number 30 or more serial volumes and contain spaces for more than 100,000 stamps, though most collectors use smaller, less inclusive albums. Blank albums are loose-leaf folios whose blank pages allow philatelists to arrange stamps according to their own fancy. In arranging a collection, stamps are not pasted directly on the album page but are usually secured to it by hinges—i.e., small rectangles of translucent paper gummed on one side and folded—which are easily affixed and pulled off from stamps without causing damage. Transparent plastic sleeves with adhesive backing may also be used.

In the 1860s a modest collection of 3,000 stamps could contain almost every variety of stamp issued to that time, but a similar collection in the late 20th century would need more than 200,000 stamps. Because of the sheer bulk, not to mention the prohibitive expense, of a general collection embracing the stamps of all nations and all periods, most collectors turn to specialized fields. They may collect only the stamps of one country, for example, or of one continent, one period of time, or of one European colonial empire. Others specialize in collections of certain kinds of stamps; some collect only one issue and study it thoroughly, and others may collect only revenue stamps or postal stationery. Those interested purely in stamp designs and their subject matter may collect art or religion on stamps, or sports, flowers, animals, bridges, and so on; this sort of collecting is called topical, or thematic, and became very popular in the decades from 1945.

Notable Stamps And Collections

Stamps issued between 1840 and 1875 are now among the world’s most valuable ones because of their rarity and historical significance. The unique one-cent British Guiana magenta of 1856, for instance, was sold in 1970 at auction for $280,000. Other stamps acquire rarity (and hence added value) from printers’ errors; a good example is the printing of a 1918 U.S. 24-cent airmail stamp with an airplane pictured upside down.

Many famous stamp collections of the past have been dispersed and absorbed by others, while some have been sold at auction, bringing sums comparable to those of major works of art. One of the most famous was that of Philippe la Renotiere von Ferrari, a wealthy Austrian-Italian nobleman in Paris. When he died in 1917, during World War I, his collection, which he had built up for 40 years and had willed to a Berlin museum, was seized by the French government and sold at auction between 1921 and 1925 for $2 million. Another outstanding collection in Europe—especially rich in British and colonial issues—was formed principally by King George V, a famed philatelist, and passed on to succeeding British monarchs. The Thomas K. Tapling collection, bequeathed to the British Museum, may well be the finest in public hands. The Smithsonian Institution collection at Washington, D.C., stresses U.S. stamps. The postal museums of many European capitals have outstanding collections, such as those at Berlin, The Hague, and Stockholm.

Philatelic Groups And Publications

The first stamp magazine, the short-lived ‘British Monthly Intelligence’ (1862), was followed by the ‘British Monthly Advertiser’ (1862–64). Among the journals founded in the 19th and early 20th centuries and still extant are the ‘American Philatelist’ (founded 1887), published by the American Philatelic Society, and the ‘London Philatelist’ (published by the Royal Philatelic Society) and ‘The Stamp Lover’ (1908) in Britain.

Clubs or societies of collectors are to be found in most cities of the world, with national and international societies to bind them together. Many of the prominent national societies, such as the Royal Philatelic Society of London and the American Philatelic Society, were formed in the 19th century. The International Philatelic Federation was formed in 1926. Many specialist societies have also sprung up, notably since 1945.

imb_philatelystamps.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.

Offline

#617 2020-03-10 00:52:00

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

497) Hebrides

The Hebrides comprise a widespread and diverse archipelago off the west coast of mainland Scotland. There are two main groups: the Inner and Outer Hebrides.

These islands have a long history of occupation dating back to the Mesolithic, and the culture of the residents has been affected by the successive influences of Celtic-, Norse-, and English-speaking peoples. This diversity is reflected in the names given to the islands, which are derived from the languages that have been spoken there in historic and perhaps prehistoric times.

The Hebrides are the source of much of Scottish Gaelic literature and Gaelic music. Today the economy of the islands is dependent on crofting, fishing, tourism, the oil industry, and renewable energy. The Hebrides have lower biodiversity than mainland Scotland, but there is a significant presence of seals and seabirds.

Hebrides, group of islands extending in an arc off the Atlantic (west) coast of Scotland. They are subdivided into two groups—the Inner Hebrides to the east and the Outer Hebrides to the west—which are separated from each other by channels called the Minch and the Little Minch. The Outer Hebrides are administered as the Western Isles council area. The northern Inner Hebrides lie within the Highland council area, and the southern Inner Hebrides are part of Argyll and Bute council area.

The Hebrides comprise more than 40 islands and innumerable barren islets, but only a few of those islands are inhabited. There has been considerable depopulation, especially in the Outer Hebrides during the 20th century, because of a lack of economic opportunities. The chief islands of the crescent-shaped chain of the Outer Hebrides are Lewis and Harris, North Uist, Benbecula, South Uist, and Barra. St. Kilda lies some 40 miles (65 km) northwest of the main chain. The main islands of the Inner Hebrides are Skye, the Small Isles (Canna, Sanday, Rhum, Eigg, and Muck), Tiree, Mull, Colonsay, Jura, Islay, and Coll.

The Hebrides are known for their unique natural features. The Cuillin Hills of Skye—reaching an elevation of 3,309 feet (1,009 metres)—are said to be the most spectacular massif in Britain. The small island of Rhum became a Nature Conservancy Research Centre in 1957, specializing in the study of the local geology, flora, and fauna. The wildlife of the Hebrides is particularly rich and includes red deer, wild goats, Highland cattle and ponies, and, on Soay Island, a primitive wild sheep.

The Hebrides’ Celtic inhabitants of the 1st millennium CE suffered from Viking raids after the 8th century and were eventually placed under Viking sovereignty until 1266. The fusion of Celts and Vikings produced a period of relatively high cultural and material well-being in the 11th and 12th centuries. The cessation of local wars and the increased cultivation of the potato as a food crop were instrumental in the subsequent population increase, which soon reached the limit of the subsistence economy. A period of social unrest ensued, and in the 19th century emigration from the Hebrides to Australia and Canada became common. The immigration of sheep farmers to the islands from the Scottish mainland—they paid high rents for large acreages of ground—caused the eviction of many small tenants, who resettled in coastal townships where they supplemented the produce of their small plots of land by fishing. In the 19th and 20th centuries the United Kingdom assumed a greater role in the islands’ administration. In 1886 an act of Parliament gave the crofters (tenant farmers) security and heritability of tenure. Later fair rents were established by a Crofters Commission.

The economy of the islands centres on crofting (tenant farming), weaving, and fishing . The grassy plains (machair) on the western coasts of some of the islands are the most fertile agricultural areas in the Hebrides, especially when fertilized with seaweed, the common local practice. Cattle raising and dairying are also practiced. Weaving and fishing are concentrated on the rocky infertile eastern coasts of the islands. The best-known textile enterprise is the manufacture of Harris tweed, which traditionally has provided a part-time occupation for the crofters. The manufacture of tweed in the Hebrides is historically of ancient origin. The wool was originally vegetable-dyed, hand-spun, and handwoven in the crofters’ own homes. Today, before in-home weaving takes place, the washing and dyeing of sheared wool as well as its blending and carding into embryonic yarn, along with the spinning and warping processes, occur in factories, to which the woven tweed returns for finishing and stamping. The whole process now takes place on Lewis and Harris. Herring fishing is important at Stornoway on Lewis. Tourism and the oil industry are also important economic engines. Pop. (2001) Lewis and Harris, 19,918; Barra, 1,078; North Uist, 1,320; South Uist, 1,818; Skye, 9,251; Islay, 3,997; Jura, 188; Colonsay, 113; Mull, 2,696; Tiree, 770; Coll, 164; (2011) Lewis and Harris, 21,031; Barra, 1,174; North Uist, 1,312; South Uist, 1,754; Skye, 10,013; Islay, 3,228; Jura, 196; Colonsay, 132; Mull, 2,819; Tiree, 653; Coll, 195.

westernisles-450.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.

Offline

#618 2020-03-12 00:48:23

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

498) Plumbing (Construction)

Plumbing, system of pipes and fixtures installed in a building for the distribution and use of potable (drinkable) water and the removal of waterborne wastes. It is usually distinguished from water and sewage systems that serve a group of buildings or a city.

One of the problems of every civilization in which the population has been centralized in cities and towns has been the development of adequate plumbing systems. In certain parts of Europe the complex aqueducts built by the Romans to supply their cities with potable water can still be seen. However, the early systems built for the disposal of human wastes were less elaborate. Human wastes were often transported from the cities in carts or buckets or else discharged into an open, water-filled system of ditches that led from the city to a lake or stream.

Improvement in plumbing systems was very slow. Virtually no progress was made from the time of the Romans until the 19th century. The relatively primitive sanitation facilities were inadequate for the large, crowded population centres that sprang up during the Industrial Revolution, and outbreaks of typhoid fever and dysentery were often spread by the consumption of water contaminated with human wastes. Eventually these epidemics were curbed by the development of separate, underground water and sewage systems, which eliminated open sewage ditches. In addition, plumbing fixtures were designed to handle potable water and water-borne wastes within buildings.

The term plumbing fixture embraces not only showers, bathtubs, lavatory basins, and toilets but also such devices as washing machines, garbage-disposal units, hot-water heaters, dishwashers, and drinking fountains.

The water-carrying pipes and other materials used in a plumbing system must be strong, noncorrosive, and durable enough to equal or exceed the expected life of the building in which they are installed. Toilets, urinals, and lavatories usually are made of stable porcelain or vitreous china, although they sometimes are made of glazed cast iron, steel, or stainless steel. Ordinary water pipes usually are made of steel, copper, brass, plastic, or other nontoxic material; and the most common materials for sewage pipes are cast iron, steel, copper, and asbestos cement.

Methods of water distribution vary. For towns and cities, municipally or privately owned water companies treat and purify water collected from wells, lakes, rivers, and ponds and distribute it to individual buildings. In rural areas water is commonly obtained directly from individual wells.

In most cities, water is forced through the distribution system by pumps, although, in rare instances, when the source of water is located in mountains or hills above a city, the pressure generated by gravity is sufficient to distribute water throughout the system. In other cases, water is pumped from the collection and purification facilities into elevated storage tanks and then allowed to flow throughout the system by gravity. But in most municipalities water is pumped directly through the system; elevated storage tanks may also be provided to serve as pressure-stabilization devices and as an auxiliary source in the event of pump failure or of a catastrophe, such as fire, that might require more water than the pumps or the water source are able to supply.

The pressure developed in the water-supply system and the friction generated by the water moving through the pipes are the two factors that limit both the height to which water can be distributed and the maximum flow rate available at any point in the system.

A building’s system for waste disposal has two parts: the drainage system and the venting system. The drainage portion comprises pipes leading from various fixture drains to the central main, which is connected to the municipal or private sewage system. The venting system consists of pipes leading from an air inlet (usually on the building’s roof) to various points within the drainage system; it protects the sanitary traps from siphoning or blowing by equalizing the pressure inside and outside the drainage system.

Sanitary fixture traps provide a water seal between the sewer pipes and the rooms in which plumbing fixtures are installed. The most commonly used sanitary trap is a U bend, or dip, installed in the drainpipe adjacent to the outlet of each fixture. A portion of the waste water discharged by the fixture is retained in the U, forming a seal that separates the fixture from the open drainpipes.

plumbing-work-500x500.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.

Offline

#619 2020-03-14 00:46:51

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

499) Root Canal Treatment

What is a Root Canal?

Root canal treatment is designed to eliminate bacteria from the infected root canal, prevent reinfection of the tooth and save the natural tooth. When one
undergoes a root canal, the inflamed or infected pulp is removed and the inside of the tooth is carefully cleaned and disinfected, then filled and sealed.
What happens during root canal treatment? Learn more about this quick, comfortable procedure that can relieve your pain and save your natural tooth.

There’s no need to be worried if your dentist or endodontist prescribes a root canal procedure to treat a damaged or diseased tooth. Millions of teeth are treated and saved this way each year, relieving pain and making teeth healthy again.

Inside your tooth, beneath the white enamel and a hard layer called dentin, is a soft tissue called pulp. This tissue contains blood vessels, nerves and connective tissue, which help grow the root of your tooth during its development. A fully developed tooth can survive without the pulp because the tooth continues to be nourished by the tissues surrounding it.

A modern root canal treatment is nothing like those old sayings! It’s very similar to a routine filling and can usually be completed in one or two appointments, depending on the condition of your tooth and your personal circumstances. Getting a root canal is relatively painless and extremely effective. You’ll be back to smiling, biting and chewing with ease in no time.

Saving the natural tooth with root canal treatment has many advantages:

•    Efficient chewing
•    Normal biting force and sensation
•    Natural appearance
•    Protects other teeth from excessive wear or strain

All About Root Canals

A root canal (also known as an endodontic treatment) is a serious procedure, but one that specialists handle every day. Before engaging in any type of dental work, it’s important to know the facts about root canals.

Does a root canal hurt?

Since patients are given anesthesia, a root canal isn’t more painful than a regular dental procedure, such as a filling or getting a wisdom tooth removed. However, a root canal is generally a bit sore or numb after the procedure, and can even cause mild discomfort for a few days.

How do you know if you need a root canal?

Root canals are needed for a cracked tooth from injury or genetics, a deep cavity, or issues from a previous filling. Patients generally need a root canal when they notice their teeth are sensitive, particularly to hot and cold sensations.

There are a few symptoms that mean you might need a root canal -

•    Severe pain while chewing or biting
•    Pimples on the gums
•    A chipped or cracked tooth
•    Lingering sensitivity to hot or cold, even after the sensation has been removed
•    Swollen or tender gums
•    Deep decay or darkening of the gums

Can I go to school or work after getting a root canal?

Although you will most likely be numb for 2-4 hours following the procedure, most patients are able to return to school or work directly following a root canal. However, it is advised against eating until the numbness is completely gone.

How much does a root canal cost?

The cost varies depending on how complex the problem is and which tooth is affected. Molars are more difficult to treat; the fee is usually more. Most dental insurance policies provide some coverage for endodontic treatment.

Generally, endodontic treatment and restoration of the natural tooth are less expensive than the alternative of having the tooth extracted. An extracted tooth must be replaced with an implant or bridge to restore chewing function and prevent adjacent teeth from shifting. These procedures tend to cost more than endodontic treatment and appropriate restoration.

Overview

Root canal is a treatment to repair and save a badly damaged or infected tooth instead of removing it. The procedure involves removing the damaged area of the tooth (the pulp) and cleaning and disinfecting it, then filling and sealing it. The common causes affecting the pulp are a cracked tooth, a deep cavity, repeated dental treatment to the tooth or trauma to it. The term "root canal" comes from cleaning of the canals inside the tooth's root.

Decades ago, root canal treatments were painful. With dental advances and local anesthetics, most people have little if any pain with a root canal today.

Understanding

Root canal treatment consists of a number of steps that take place over several office visits, depending on the situation. These steps are:

•    The endodontist examines and x-rays the tooth, then local anesthesia is administered to the affected tooth.
•    A dental dam is usually placed over the affected tooth to isolate it and keep it free from saliva.
•    The endodontist makes an opening through the back of a front tooth or the crown of a molar or pre-molar to remove the diseased pulp, called a pulpectomy.
•    Next, the pulp chamber and root canals are cleaned and shaped in preparation for a filling.
•    The endodontist fills the root canal with gutta percha material.

If more than one visit is needed, a temporary filling is placed in the crown opening to protect the tooth between dental visits. The temporary filling is removed and the pulp chamber and root canal are permanently filled with gutta percha into each of the canals and is sealed in place with cement. Sometimes a metal or plastic rod is placed in the canal for structural support. In the final step, a crown is usually placed over the tooth to restore its natural shape and appearance. If the tooth is broken, a post may be required to build it up prior to placing a crown.

Planning

Many people worry that a root canal will be painful, something that was true in the past. Today, with advanced anesthesia options and surgical techniques - a root canal is as comfortable as getting a filling. An infected tooth (pre-root canal), is usually what causes tooth pain, and a root canal is the solution to this problem. In fact, infected tooth pulp can cause a tooth abscess and can destroy the bone surrounding the tooth.

A treated and restored tooth can last a lifetime with proper care. Root canals have a high success rate and are significantly less expensive than the alternative, tooth extraction and replacement with a bridge or implant.

But tooth decay can still occur in treated teeth, so good oral hygiene and regular dental exams are necessary to prevent further problems.

To determine the success or failure of root canal treatment, dentists typically compare new X-rays with those taken prior to treatment. This comparison will show whether bone continues to be lost or is being regenerated.

Sometimes root canals are not successful because an infection develops inside the tooth, or the original infection was not fully removed. In these cases, an apicoectomy, a procedure where the infection and the root tip are removed and a filling placed, is done. Other times a second root canal is recommended.

Infected-tooth-270x300.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.

Offline

#620 2020-03-16 01:04:53

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

500) Tablet computer

Tablet computer, computer that is intermediate in size between a laptop computer and a smartphone. Early tablet computers used either a keyboard or a stylus to input information, but these methods were subsequently displaced by touch screens.

The precursors to the tablet computer were devices such as the Stylator (1957) and the RAND Tablet (1961) that used a stylus for input into a larger computer. In 1968 Alan Kay, a graduate student at the University of Utah, promoted his vision of a small, powerful tablet-style computer that he later called the Dynabook; however, Kay never actually built a Dynabook. The first true tablet computers were Cambridge Research’s Z88 and Linus Technologies’ Write-Top, which were introduced in 1987. The Z88 accepted input through a keyboard that was part of the main tablet unit, while the Write-Top accepted input through a stylus. Weighing 0.9 kg (2 pounds), the Z88 was much more portable than the Write-Top, which weighed 4 kg (9 pounds) because it came with an internal floppy disk drive.

Many other models followed the Z88 and the Write-Top, but tablet computers languished in sales until 2010, when Apple Inc. unveiled the iPad, a touch-screen device with a display that measured 24.6 cm (9.7 inches) diagonally. It was about 1.2 cm (0.5 inch) thick and weighed about 0.7 kg (1.5 pounds). The iPad was operated with the same set of finger gestures that were used on Apple’s iPhone. The touch screen was capable of displaying high-definition video. The iPad also had such applications as iTunes built-in and could run all applications that were available for the iPhone. In partnership with several major publishers, Apple developed for the iPad its own e-book application, iBooks, as well as an iBook store accessible through the Internet.

Other tablet computers such as the Samsung Galaxy Tab, the Motorola Xoom, and the HP TouchPad followed on the heels of the iPad. The tablet computer market exploded from a mere 2 million sold worldwide in 2009 to 20 million in 2010. Smaller devices such as the Apple iPad mini and Amazon Kindle Fire also appeared, as well as “phablets,” devices such as the Samsung Galaxy Note that were midway in size between a small tablet and a smartphone. Sales of tablet computers peaked in 2014 with 233 million sold and declined thereafter, the decline being attributed to consumers not replacing tablets as often as smartphones.

android-tablet.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.

Offline

#621 2020-03-18 00:48:23

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

501) Rose

Rose, (genus Rosa), genus of some 100 species of perennial shrubs in the rose family (Rosaceae). Roses are native primarily to the temperate regions of the Northern Hemisphere. Many roses are cultivated for their beautiful flowers, which range in colour from white through various tones of yellow and pink to dark crimson and maroon, and most have a delightful fragrance, which varies according to the variety and to climatic conditions.

Most rose species are native to Asia, with smaller numbers being native to North America and a few to Europe and northwest Africa. Roses from different regions of the world hybridize readily, giving rise to types that overlap the parental forms, and making it difficult to determine basic species. Fewer than 10 species, mostly native to Asia, were involved in the crossbreeding that ultimately produced today’s many types of garden roses.

Physical Description

Roses are erect, climbing, or trailing shrubs, the stems of which are usually copiously armed with prickles of various shapes and sizes, commonly called thorns. The leaves are alternate and pinnately compound (i.e., feather-formed), usually with oval leaflets that are sharply toothed. The flowers of wild roses usually have five petals, whereas the flowers of cultivated roses are often double (i.e., with multiple sets of petals). Rose flowers’ size ranges from tiny miniatures 1.25 cm (0.5 inch) in diameter to hybrid flowers measuring more than 17.5 cm (7 inches) across. The rose plant’s fleshy, sometimes edible, berrylike “fruit” (actually the floral cup) is known as a hip and usually ranges from red to orange in colour.

Roses can become infected by a number of diseases, most of them caused by fungi. Powdery mildew appears as a grayish white moldlike growth on the surface of young leaves and stems. Black spot fungus appears as conspicuous black spots on leaves and causes them to fall off. Rust is also a common disease of roses. Aphids are a common insect pest on the leaves and young stems.

Major Species And Hybrids

The flowers of the damask rose (Rosa ×damascena) and several other species are the source of attar of roses used in perfumes. Many species, particularly the rugosa rose (R. rugosa), produce edible rose hips, which are a rich source of vitamin C and are sometimes used in preserves.

There are several major classes of garden roses. The best-known and most-popular class of rose is that of the hybrid tea roses, which accounts for the majority of roses grown in greenhouses and gardens and sold in florist shops. Hybrid teas come in the complete range of rose colours and have large symmetrical blossoms. Hybrid teas resulted from the crossbreeding of frequently blooming but fragile tea roses with vigorous hybrid perpetual roses. The hybrid perpetuals achieved great popularity until they were supplanted by the hybrid teas in the early 20th century. Polyantha roses are a class of very hardy roses that produce dense bunches of tiny blossoms. Floribunda roses are hardy hybrids that resulted from crossing hybrid teas with polyanthas. Grandiflora roses are relatively new hybrids resulting from the crossbreeding of hybrid teas and floribunda roses. Grandifloras produce full-blossomed flowers growing on tall hardy bushes. Among the other classes of modern roses are climbing roses, whose slender stems can be trained to ascend trellises; shrub roses, which develop into large bushes; and miniature roses, which are pygmy-sized plants bearing tiny blossoms. Altogether there are thousands of identifiable varieties of roses in those and other classes.

red-rose-320868__340.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.

Offline

#622 2020-03-20 00:52:44

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

502) Kuiper belt

Kuiper belt, also called Edgeworth-Kuiper belt, flat ring of icy small bodies that revolve around the Sun beyond the orbit of the planet Neptune. It was named for the Dutch American astronomer Gerard P. Kuiper and comprises hundreds of millions of objects—presumed to be leftovers from the formation of the outer planets—whose orbits lie close to the plane of the solar system. The Kuiper belt is thought to be the source of most of the observed short-period comets, particularly those that orbit the Sun in less than 20 years, and for the icy Centaur objects, which have orbits in the region of the giant planets. (Some of the Centaurs may represent the transition from Kuiper belt objects [KBOs] to short-period comets.) Although its existence had been assumed for decades, the Kuiper belt remained undetected until the 1990s, when the prerequisite large telescopes and sensitive light detectors became available.

KBOs orbit at a mean distance from the Sun larger than the mean orbital distance of Neptune (about 30 astronomical units [AU]; 4.5 billion km [2.8 billion miles]). The outer edge of the Kuiper belt is more poorly defined but nominally excludes objects that never go closer to the Sun than 47.2 AU (7.1 billion km [4.4 billion miles]), the location of the 2:1 Neptune resonance, where an object makes one orbit for every two of Neptune’s. The Kuiper belt contains the large objects Eris, Pluto, Makemake, Haumea, Quaoar, and many, likely millions, of other smaller bodies.

Discovery Of The Kuiper Belt

The Irish astronomer Kenneth E. Edgeworth speculated in 1943 that the distribution of the solar system’s small bodies was not bounded by the present distance of Pluto. Kuiper developed a stronger case in 1951. Working from an analysis of the mass distribution of bodies needed to accrete into planets during the formation of the solar system, Kuiper demonstrated that a large residual amount of small icy bodies—inactive comet nuclei—must lie beyond Neptune. A year earlier the Dutch astronomer Jan Oort had proposed the existence of a much-more-distant spherical reservoir of icy bodies, now called the Oort cloud, from which comets are continually replenished. This distant source adequately accounted for the origin of long-period comets—those having periods greater than 200 years. Kuiper noted, however, that comets with very short periods (20 years or less), which all orbit in the same direction as all the planets around the Sun and close to the plane of the solar system, require a nearer, more-flattened source. This explanation, clearly restated in 1988 by the American astronomer Martin Duncan and coworkers, became the best argument for the existence of the Kuiper belt until its direct detection.

In 1992 American astronomer David Jewitt and graduate student Jane Luu discovered (15760) 1992 QB1, which was considered the first KBO. The body is about 200–250 km (125–155 miles) in diameter, as estimated from its brightness. It moves in a nearly circular orbit in the plane of the planetary system at a distance from the Sun of about 44 AU (6.6 billion km [4.1 billion miles]). This is outside the orbit of Pluto, which has a mean radius of 39.5 AU (5.9 billion km [3.7 billion miles]). The discovery of 1992 QB1 alerted astronomers to the feasibility of detecting other KBOs, and within 20 years about 1,500 had been discovered.

On the basis of brightness estimates, the sizes of the larger known KBOs approach or exceed that of Pluto’s largest moon, Charon, which has a diameter of 1,208 km (751 miles). One KBO, given the name Eris, appears to be twice that diameter—i.e., only slightly smaller than Pluto itself. Because of their location outside Neptune’s orbit (mean radius 30.1 AU; 4.5 billion km [2.8 billion miles]), they are also called trans-Neptunian objects (TNOs).

Because several KBOs like Eris are nearly as large as Pluto, beginning in the 1990s, astronomers wondered if Pluto should really be considered as a planet or as one of the largest bodies in the Kuiper belt. Evidence mounted that Pluto was a KBO that just happened to have been discovered 62 years before 1992 QB1, and in 2006 the International Astronomical Union voted to classify Pluto and Eris as dwarf planets.

Orbital Subpopulations

KBOs are classified by their semimajor axis (the mean distance from the Sun), their perihelion distance (the closest approach to the Sun), and the inclination of their orbital plane to that formed by the planets of the solar system. Using these parameters, KBOs are often found in three distinct orbital substructures.

•    Resonant objects: KBOs in mean motion resonance (MMR) with Neptune. An estimated 55,000 KBOs larger than 100 km (60 miles) in diameter orbit the Sun in an integer ratio of Neptune orbital periods. For example, Pluto is in the 3:2 Neptune MMR, completing two orbits around the Sun in the time it takes Neptune to complete three. In fact, nearly one-quarter of all MMR objects are in the 3:2 resonance. In recognition of this kinship, these objects have been dubbed Plutinos.
•    Hot classicals: KBOs with inclinations drawn from a wide distribution (about 16°) and with perihelion distances of between 35 and 40 AU (5.2 billion and 6 billion km [3.3 billion and 3.7 billion miles]). The hot classical population consists of approximately 120,000 objects with diameters larger than 100 km. This population is estimated to included 80,000 objects whose mean distance from the Sun exceeds 50 AU (7.5 billion km [4.6 billion miles]) and that are therefore sometimes referred to collectively as the “outer” or “detached” Kuiper belt.
•    Cold classicals: KBOs drawn from a narrow distribution of orbit inclinations (about 2.6°), with mean orbital distances restricted to 42.5–47.2 AU (6.4 billion–7.1 billion km [4 billion–4.4 billion miles]) and perihelion distances smoothly distributed between 38 AU (5.7 billion km [3.5 billion miles]) and 47.2 AU. The cold classical population is approximately 75,000 objects with diameters of 100 km and larger. Within the cold classicals are a small subpopulation called “the kernel” of 25,000 objects with diameters larger than 100 km. The kernel objects have semimajor axes between 43.8 and 44.4 AU (6.55 billion and 6.64 billion km [4.07 billion and 4.13 billion miles]), orbital eccentricities of between 0.03 and 0.08, and a narrow inclination distribution like the rest of the cold classical component.

The above list contains the currently well-defined substructures of the orbital space of the Kuiper belt. These objects are in metastable orbits; that is, their orbits are stable over timescales of 100 million to 1 billion years. However, some will chaotically diffuse out of the stable region. As more KBOs are discovered, additional significant orbital populations are likely to be found.

KBOs that have significant gravitational interactions with Neptune are called “scattering KBOs.” Scattering KBOs are on orbits that are unstable on million-year timescales. These objects are thought to be in transition from being metastable KBOs to becoming Centaur objects and eventually short-period comets. The metastable region that supplies the scattering population is not known, but it may be the hot classicals or perhaps the resonant KBOs. Not all scattering orbits are equally unstable, and understanding how a KBO in a metastable orbit becomes a short-period comet is an area of active research. The estimated population of scattering sources (3,000–15,000 objects larger than 100 km in diameter) is significantly smaller than theoretical expectations.

Because of the small number of detected sources, the estimated numbers of KBOs are still quite uncertain. Particularly uncertain is the number of small (1–10-km) KBOs if this region of the solar system really is the reservoir for short-period comets. For comparison, there are estimated to be 250 asteroids larger than 100 km in diameter and perhaps 1 million larger than 1 km. If the relation between the number of objects and size for KBOs is similar to that of asteroids, that implies a total Kuiper belt population of more than 100 billion sources larger than 1 km in diameter. This extrapolation is derived from the few hundred sources for which precise detection circumstances are available. However, extrapolating from 300 objects to 100 billion is subject to considerable uncertainty.

As noted above, the planet Neptune has a strong gravitational influence over the orbital structure of the Kuiper belt. There are two prevailing models for the formation of structure in the orbital distribution of KBOs. In the “migration” model, Neptune’s mean orbital distance was initially smaller (around 23 AU; 3.4 billion km [2.1 billion miles[) and slowly migrated to its current location of about 30 AU (4.5 billion km [2.8 billion miles]). During this slow orbital growth many KBOs became trapped into orbital resonance with Neptune. However, this model does not produce the hot classical component, and some other process must therefore lead to more-inclined orbits for KBOs.

Alternatively, in the “Nice” model (named after the French city where it was first proposed), the giant planets of the solar system formed in a more-compact configuration than is seen today, and through gravitational interaction Neptune and Uranus were scattered to their current locations. The Nice model provides a reasonable representation of the hot component of the Kuiper belt but is less successful at producing the resonant objects and does not provide for a cold classical component. A complete explanation of the formation of structure in the outer solar system may be some combination of these two scenarios or some completely different model of evolution.

In addition to the nominal members of the Kuiper belt described above, there are some KBOs whose closest approach to the Sun leaves them well outside the influence of Neptune. Sedna, an object whose closest approach is 76.3 AU (11.4 billion km [7.1 billion miles]), is the most extreme example of these distant outliers. These rare objects (only two objects with closest approaches greater than 47.2 AU [7.1 billion km (4.4 billion miles)] and mean Sun distances larger than 200 AU (29.9 billion km (18.6 billion miles)] are currently known) may represent the very outer edge of the Kuiper belt region or the inner edge of an entirely new population of sources. Sedna is sometimes referred to as a member of the inner Oort cloud.

Families, Binaries, And Satellites

The Kuiper belt is likely to contain families of objects—that is, populations of objects that are likely to have been derived from a single parent body. The members of a family would have similar heliocentric orbital parameters and surface properties. Only one such group, the nine-member Haumea family, is currently well established. The Haumea family members have orbital parameters that are much more similar than would be expected from standard family production. Modeling the production of the Haumea family, an important step toward confirming that these groups really do come from a single progenitor object, is an ongoing field of research.

Pairs of near-equal-sized KBOs that are gravitationally bound together are called binary KBOs. Of the known cold classical KBOs, 15 to 20 percent are in binary systems. The Pluto-Charon system is binary but is unusual in the compactness of the system. The production of binary KBOs requires a large initial population of KBOs, many times larger than that currently observed, for capture into binary pairs to have been possible. Alternatively, binary KBOs might result from a turbulence mechanism at work during the formation of planetesimals in the Kuiper belt. The existence of Kuiper belt binaries appears to preclude a major gravitational scattering of sources in this population, as such effects would have disrupted the observed systems.

A few percent of all KBOs are found to have satellites. The term satellite is used instead of binary when there is a large (+10) mass ratio between the primary KBO and the orbiting material. Satellites likely form when two KBOs collide and some of the disrupted material is captured into orbit around large surviving members. The KBO Haumea has at least two such satellites, Hi’iaka and Namaka. The Haumea satellites were likely captured from the debris of the collision that produced the Haumea family of KBOs.

Kuiper-belt-location-300x198.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.

Offline

#623 2020-03-22 01:01:03

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

503) Cape of Good Hope

Cape of Good Hope, rocky promontory at the southern end of Cape Peninsula, Western Cape province, South Africa. It was first sighted by the Portuguese navigator Bartolomeu Dias in 1488 on his return voyage to Portugal after ascertaining the southern limits of the African continent. One historical account says that Dias named it Cape of Storms and that John II of Portugal renamed it Cape of Good Hope (because its discovery was a good omen that India could be reached by sea from Europe); other sources attribute its present name to Dias himself.

Known for the stormy weather and rough seas encountered there, the cape is situated at the convergence of the warm Mozambique-Agulhas current from the Indian Ocean and the cool Benguela current from Antarctic waters. Grass and low shrub vegetation is characteristic of the promontory, which is part of the Cape of Good Hope Nature Reserve (established 1939) that encompasses the southern tip of the peninsula. There is a lighthouse on Cape Point about 1.2 miles (2 km) east of the Cape of Good Hope.

The Cape of Good Hope is a rocky headland on the Atlantic coast of South Africa. It is a common misconception that the Cape of Good Hope is the southern tip of Africa and the dividing point between the Atlantic and Indian Oceans. The true southernmost point is Cape Agulhas, about 200 km (120 mi) southeast. However, when following the coastline from the equator, the Cape of Good Hope marks the psychologically important point where one begins to travel more eastward than southward. Thus the rounding of the cape in 1488 was considered a significant milestone by the Portuguese attempting to establish direct trade relations with India and the Far East.

In 1488, navigator Bartholomew Dias named the Peninsula "Cabo Tormentoso," or the "Cape of Storms." It was later renamed by King John II of Portugal "Cabo da Boa Esperanca"—the Cape of Good Hope, because of the great optimism engendered by opening a sea route to the East.

The term "Cape of Good Hope" was also used to indicate the early Cape Colony commissioned by the Dutch East India Company, and established in 1652 by the merchant Jan van Riebeeck as a re-provisioning station in the vicinity of the Cape Peninsula. Just prior to the formation of the Union of South Africa, the term referred to the entire region that was to become the Cape Province in 1910.

Geography

South Africa is located at the southernmost region of Africa, with a long coastline that stretches more than 1,550 mi (2,500 km) and across two oceans, (the Atlantic and the Indian).

The Cape Peninsula is a generally rocky peninsula that juts out for 75 km (47 mi) into the Atlantic at the southwestern extremity of the continent. At the southern end of the peninsula are the Cape of Good Hope, and about 2.3 kilometers (1.4 mi) to its east is Cape Point. Geologically, the rocks found at the two capes—and indeed over much of the peninsula—are part of the Table Mountain Group, and are formed of the same type of sandstone as those exposed in the faces of Table Mountain itself. Cape Town is about 50 kilometers to the north of the Cape, in Table Bay at the north end of the peninsula. Table Mountain overlooks Cape Town. The peninsula forms the western boundary of False Bay.

The Cape of Good Hope is sometimes given as the meeting point of the Atlantic Ocean and Indian Ocean. However, Cape Agulhas, about 200 km (120 mi) to the southeast, is defined by the International Hydrographic Organization to be the dividing point between the two oceans.

The term Cape of Good Hope has also been used in a wider sense, to indicate the area of the early European colony in the vicinity of the cape.

National park

Both the Cape of Good Hope and Cape Point offer spectacular scenery. The whole of the southernmost portion of the Cape Peninsula is the wild, rugged, scenic and generally unspoiled Table Mountain National Park. The park runs approximately north-south along the range of mountains that make up the mountainous spine of the Cape Peninsula, from Signal Hill in the north, through Lion's Head, Table Mountain, Constantiaberg, Silvermine Nature Reserve, the mountains of the southern Peninsula, and terminates at Cape Point.

The park is not a single contiguous area; the undeveloped mountainous areas which make up most of the park are separated by developed urban areas on shallower terrain. Thus the park is divided into three separate sections. The section that covers the southernmost area of the Cape Peninsula stretches from Cape Point and the Cape of Good Hope in the south, as far north as Scarborough on the Atlantic coast and Simon's Town on the False Bay coast. It was formed from the Cape of Good Hope Nature Reserve.

Plant and animal life

With its diverse habitat, ranging from rocky mountain tops to beaches and open sea, the Cape of Good Hope is home to at least 250 species of birds.

"Bush birds" tend to be rather scarce because of the coarse, scrubby nature of fynbos vegetation. When flowering, however, proteas and ericas attract sunbirds, sugarbirds, and other species in search of nectar. For most of the year, there are more small birds in coastal thicket than in fynbos.

The area offers excellent vantage points for whale watching. The Southern right whale is the species most likely to be seen in False Bay between June and November. Other species are the Humpback whale and Bryde's whale. Seals and Dusky Dolphins or Orca, the Killer Whales may also be seen.

The strategic position of the Cape of Good Hope between two major ocean currents ensures a rich diversity of marine life. There is a difference between the sea life west of Cape Point and that to the east due to the markedly differing sea temperatures.

The Cape of Good Hope is an integral part of the Cape Floristic Kingdom, the smallest but richest of the world's six floral kingdoms. This comprises a treasure trove of 1,100 species of indigenous plants, of which a number are endemic. Two types of fynbos ("fine bush"), coastal fynbos on alkaline sands and inland fynbos on acid soils, are found.

Characteristic fynbos plants include proteas, ericas (heath), and restios (reeds). Some of the most striking and well-known members belong to the Proteacae family, of which up to 24 species occur. These include King Protea, Sugarbush, Tree Pincushion, and Golden Cone Bush.

Many popular horticultural plants such as pelargoniums, freesias, daisies, lilies, and irises also have their origins in fynbos.
       
History

Stone Age hunter-gatherers who used stone tools and fire arrived in the Western Cape area around 100,000 B.C.E. They survived the Ice Age, when water levels were around 120 meters lower than their current levels. Fossils indicate that by 8000 B.C.E., the inhabitants had developed bows and arrows for hunting. Nearly 6,000 years later, a large migration of tribes further inland brought contact with skilled agriculturalists, prompting cape inhabitants to grow crops.

Some speculate that before European explorers reached the Cape of Good Hope, Chinese, Arabian, or Indian explorers/merchants may already have visited it, and kept records of these visits. The Old World maps such as Kangnido and Fra Mauro map made before 1488 may be evidence of this.

The Khoikhoi were originally part of a pastoral culture and language group found across Southern Africa. Originated in the northern area of modern Botswana, the ethnic group steadily migrated south, reaching the Cape approximately 2,000 years ago. Migratory bands of Khoi living around what is today Cape Town intermarried with San peoples. However the two groups remained culturally distinct as the Khoikhoi continued to graze livestock and the San subsisted as hunter-gatherers. The Khoi resided in the Cape area when European explorers and merchants arrived in the fifteenth century. Europeans referred to the Khoikhoi as "Hottentots."

The first circumnavigation of the Cape of Good Hope by Portuguese explorer Bartolomeu Dias occurred in 1488. Along with the accounts of early navigators, the accounts of shipwreck survivors provide the earliest written accounts of Southern Africa. In the two centuries following 1488, a number of small fishing settlements were made along the coast by Portuguese sailors. In 1652, a victualling station was established at the Cape of Good Hope by Jan van Riebeeck on behalf of the Dutch East India Company. For most of the seventeenth and eighteenth centuries, the slowly expanding settlement was a Dutch possession. The Dutch settlers eventually met the southwesterly expanding Xhosa people in the region of the Fish River. A series of wars ensued, mainly caused by conflicting land and livestock interests.

Great Britain seized the Cape of Good Hope area in 1797 seeking to use Cape Town in particular as a stop on the route to Australia and India. The Dutch East India Company declared bankruptcy, and the British annexed the Cape Colony in 1805. The British continued the frontier wars against the Xhosa, pushing the eastern frontier eastward through a line of forts established along the Fish River and consolidating it by encouraging British settlement. Due to pressure from abolitionist societies in Britain, the British Parliament first stopped its global slave trade in 1806, then abolished slavery in all its colonies in 1833.

The area remained under British rule until it was incorporated into the independent Union of South Africa, created from the Cape and Natal colonies, as well as the republics of Orange Free State and Transvaal, on May 31, 1910.

Looking ahead

The Cape Peninsula is a narrow finger of land with beautiful valleys, bays, and beaches. The Cape of Good Hope at its tip is the most southwesterly point of Africa where the cold Beguela current on the west and the warm Agulhus current on the east merge. This allows for a rich diversity of marine life. One of the world's highest sea cliffs at 250 meters (820 ft) above sea level, it provides an excellent vantage point for whale and dolphin watching.

As one of the great capes of the South Atlantic Ocean, the Cape of Good Hope has been of special significance to sailors for many years. It is a major milestone on the clipper route followed by clipper ships to the Far East and Australia, and is still followed by several offshore yacht races.

These features make the Cape one of the most popular tourist attractions in South Africa. In addition, the Cape is encompassed within the Table Mountain National Park, which is in turn part of the larger Cape Floral World Heritage Site (2004). Both National Park and World Heritage Site status provides for conservation measures and environmental protection. Of particular scientific interest are the plant reproductive strategies including the adaptive responses to fire of the flora and the patterns of seed dispersal by insects. The pollination biology and nutrient cycling are other distinctive ecological processes found in the site.

0911ec9da1bd3c8737bed57d1412b8ba.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.

Offline

#624 2020-03-24 01:33:00

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

504) Asthma

Overview

Asthma is a condition in which your airways narrow and swell and produce extra mucus. This can make breathing difficult and trigger coughing, wheezing and shortness of breath.

For some people, asthma is a minor nuisance. For others, it can be a major problem that interferes with daily activities and may lead to a life-threatening asthma attack.
Asthma can't be cured, but its symptoms can be controlled. Because asthma often changes over time, it's important that you work with your doctor to track your signs and symptoms and adjust treatment as needed.

Symptoms

Asthma symptoms vary from person to person. You may have infrequent asthma attacks, have symptoms only at certain times — such as when exercising — or have symptoms all the time.

Asthma signs and symptoms include:

•    Shortness of breath
•    Chest tightness or pain
•    Trouble sleeping caused by shortness of breath, coughing or wheezing
•    A whistling or wheezing sound when exhaling (wheezing is a common sign of asthma in children)
•    Coughing or wheezing attacks that are worsened by a respiratory virus, such as a cold or the flu

Signs that your asthma is probably worsening include:

•    Asthma signs and symptoms that are more frequent and bothersome
•    Increasing difficulty breathing (measurable with a peak flow meter, a device used to check how well your lungs are working)
•    The need to use a quick-relief inhaler more often

For some people, asthma signs and symptoms flare up in certain situations:

•    Exercise-induced asthma, which may be worse when the air is cold and dry
•    Occupational asthma, triggered by workplace irritants such as chemical fumes, gases or dust
•    Allergy-induced asthma, triggered by airborne substances, such as pollen, mold spores, math waste or particles of skin and dried saliva shed by pets (pet dander)

When to see a doctor

Seek emergency treatment

Severe asthma attacks can be life-threatening. Work with your doctor to determine what to do when your signs and symptoms worsen — and when you need emergency treatment. Signs of an asthma emergency include:

•    Rapid worsening of shortness of breath or wheezing
•    No improvement even after using a quick-relief inhaler, such as albuterol
•    Shortness of breath when you are doing minimal physical activity

Contact your doctor

•    If you think you have asthma. If you have frequent coughing or wheezing that lasts more than a few days or any other signs or symptoms of asthma, see your doctor. Treating asthma early may prevent long-term lung damage and help keep the condition from worsening over time.
•    To monitor your asthma after diagnosis. If you know you have asthma, work with your doctor to keep it under control. Good long-term control helps you feel better from day to day and can prevent a life-threatening asthma attack.
•    If your asthma symptoms get worse. Contact your doctor right away if your medication doesn't seem to ease your symptoms or if you need to use your quick-relief inhaler more often. Don't try to solve the problem by taking more medication without consulting your doctor. Overusing asthma medication can cause side effects and may make your asthma worse.
•    To review your treatment. Asthma often changes over time. Meet with your doctor regularly to discuss your symptoms and make any needed treatment adjustments.

Causes

It isn't clear why some people get asthma and others don't, but it's probably due to a combination of environmental and genetic (inherited) factors.

Asthma triggers

Exposure to various irritants and substances that trigger allergies (allergens) can trigger signs and symptoms of asthma. Asthma triggers are different from person to person and can include:

•    Airborne substances, such as pollen, dust mites, mold spores, pet dander or particles of math waste
•    Respiratory infections, such as the common cold
•    Physical activity (exercise-induced asthma)
•    Cold air
•    Air pollutants and irritants, such as smoke
•    Certain medications, including beta blockers, aspirin, ibuprofen (Advil, Motrin IB, others) and naproxen (Aleve)
•    Strong emotions and stress
•    Sulfites and preservatives added to some types of foods and beverages, including shrimp, dried fruit, processed potatoes, beer and wine
•    Gastroesophageal reflux disease (GERD), a condition in which stomach acids back up into your throat

Risk factors

A number of factors are thought to increase your chances of developing asthma. These include:

•    Having a blood relative (such as a parent or sibling) with asthma
•    Having another allergic condition, such as atopic dermatitis or allergic rhinitis (hay fever)
•    Being overweight
•    Being a smoker
•    Exposure to secondhand smoke
•    Exposure to exhaust fumes or other types of pollution
•    Exposure to occupational triggers, such as chemicals used in farming, hairdressing and manufacturing

Complications

Asthma complications include:

•    Signs and symptoms that interfere with sleep, work or recreational activities
•    Sick days from work or school during asthma flare-ups
•    Permanent narrowing of the bronchial tubes (airway remodeling) that affects how well you can breathe
•    Emergency room visits and hospitalizations for severe asthma attacks
•    Side effects from long-term use of some medications used to stabilize severe asthma

Proper treatment makes a big difference in preventing both short-term and long-term complications caused by asthma.

Prevention

While there's no way to prevent asthma, by working together, you and your doctor can design a step-by-step plan for living with your condition and preventing asthma attacks.

•    Follow your asthma action plan. With your doctor and health care team, write a detailed plan for taking medications and managing an asthma attack. Then be sure to follow your plan.
Asthma is an ongoing condition that needs regular monitoring and treatment. Taking control of your treatment can make you feel more in control of your life in general.
•    Get vaccinated for influenza and pneumonia. Staying current with vaccinations can prevent flu and pneumonia from triggering asthma flare-ups.
•    Identify and avoid asthma triggers. A number of outdoor allergens and irritants — ranging from pollen and mold to cold air and air pollution — can trigger asthma attacks. Find out what causes or worsens your asthma, and take steps to avoid those triggers.
•    Monitor your breathing. You may learn to recognize warning signs of an impending attack, such as slight coughing, wheezing or shortness of breath. But because your lung function may decrease before you notice any signs or symptoms, regularly measure and record your peak airflow with a home peak flow meter.
•    Identify and treat attacks early. If you act quickly, you're less likely to have a severe attack. You also won't need as much medication to control your symptoms.
When your peak flow measurements decrease and alert you to an oncoming attack, take your medication as instructed and immediately stop any activity that may have triggered the attack. If your symptoms don't improve, get medical help as directed in your action plan.
•    Take your medication as prescribed. Just because your asthma seems to be improving, don't change anything without first talking to your doctor. It's a good idea to bring your medications with you to each doctor visit, so your doctor can double-check that you're using your medications correctly and taking the right dose.
•    Pay attention to increasing quick-relief inhaler use. If you find yourself relying on your quick-relief inhaler, such as albuterol, your asthma isn't under control. See your doctor about adjusting your treatment.

Diagnosis

Physical exam

To rule out other possible conditions — such as a respiratory infection or chronic obstructive pulmonary disease (COPD) — your doctor will do a physical exam and ask you questions about your signs and symptoms and about any other health problems.

Tests to measure lung function

You may also be given lung (pulmonary) function tests to determine how much air moves in and out as you breathe. These tests may include:

•    Spirometry. This test estimates the narrowing of your bronchial tubes by checking how much air you can exhale after a deep breath and how fast you can breathe out.
•    Peak flow. A peak flow meter is a simple device that measures how hard you can breathe out. Lower than usual peak flow readings are a sign your lungs may not be working as well and that your asthma may be getting worse. Your doctor will give you instructions on how to track and deal with low peak flow readings.
Lung function tests often are done before and after taking a medication called a bronchodilator, such as albuterol, to open your airways. If your lung function improves with use of a bronchodilator, it's likely you have asthma.

Additional tests

Other tests to diagnose asthma include:

•    Methacholine challenge. Methacholine is a known asthma trigger that, when inhaled, will cause mild constriction of your airways. If you react to the methacholine, you likely have asthma. This test may be used even if your initial lung function test is normal.
•    Nitric oxide test. This test, though not widely available, measures the amount of the gas, nitric oxide, that you have in your breath. When your airways are inflamed — a sign of asthma — you may have higher than normal nitric oxide levels.
•    Imaging tests. A chest X-ray and high-resolution computerized tomography (CT) scan of your lungs and nose cavities (sinuses) can identify any structural abnormalities or diseases (such as infection) that can cause or aggravate breathing problems.
•    Allergy testing. This can be performed by a skin test or blood test. Allergy tests can identify allergy to pets, dust, mold and pollen. If important allergy triggers are identified, this can lead to a recommendation for allergen immunotherapy.
•    Sputum eosinophils. This test looks for certain white blood cells (eosinophils) in the mixture of saliva and mucus (sputum) you discharge during coughing. Eosinophils are present when symptoms develop and become visible when stained with a rose-colored dye (eosin).
•    Provocative testing for exercise and cold-induced asthma. In these tests, your doctor measures your airway obstruction before and after you perform vigorous physical activity or take several breaths of cold air.

How asthma is classified

To classify your asthma severity, your doctor considers your answers to questions about symptoms (such as how often you have asthma attacks and how bad they are), along with the results of your physical exam and diagnostic tests.

Determining your asthma severity helps your doctor choose the best treatment. Asthma severity often changes over time, requiring treatment adjustments.


Asthma is classified into four general categories:

Asthma classification    -   Signs and symptoms
Mild intermittent    -   Mild symptoms up to two days a week and up to two nights a month
Mild persistent    -   Symptoms more than twice a week, but no more than once in a single day
Moderate persistent    -   Symptoms once a day and more than one night a week
Severe persistent    -   Symptoms throughout the day on most days and frequently at night

Treatment

Prevention and long-term control are key in stopping asthma attacks before they start. Treatment usually involves learning to recognize your triggers, taking steps to avoid them and tracking your breathing to make sure your daily asthma medications are keeping symptoms under control. In case of an asthma flare-up, you may need to use a quick-relief inhaler, such as albuterol.

Medications

The right medications for you depend on a number of things — your age, symptoms, asthma triggers and what works best to keep your asthma under control.
Preventive, long-term control medications reduce the inflammation in your airways that leads to symptoms. Quick-relief inhalers (bronchodilators) quickly open swollen airways that are limiting breathing. In some cases, allergy medications are necessary.

Long-term asthma control medications, generally taken daily, are the cornerstone of asthma treatment. These medications keep asthma under control on a day-to-day basis and make it less likely you'll have an asthma attack. Types of long-term control medications include:

•    Inhaled corticosteroids. These anti-inflammatory drugs include fluticasone (Flonase, Flovent HFA), budesonide (Pulmicort Flexhaler, Rhinocort), flunisolide (Aerospan HFA), ciclesonide (Alvesco, Omnaris, Zetonna), beclomethasone (Qnasl, Qvar), mometasone (Asmanex) and fluticasone furoate (Arnuity Ellipta).
You may need to use these medications for several days to weeks before they reach their maximum benefit. Unlike oral corticosteroids, these corticosteroid medications have a relatively low risk of side effects and are generally safe for long-term use.
•    Leukotriene modifiers. These oral medications — including montelukast (Singulair), zafirlukast (Accolate) and zileuton (Zyflo) — help relieve asthma symptoms for up to 24 hours.
In rare cases, these medications have been linked to psychological reactions, such as agitation, aggression, hallucinations, depression and suicidal thinking. Seek medical advice right away for any unusual reaction.
•    Long-acting beta agonists. These inhaled medications, which include salmeterol (Serevent) and formoterol (Foradil, Perforomist), open the airways.
Some research shows that they may increase the risk of a severe asthma attack, so take them only in combination with an inhaled corticosteroid. And because these drugs can mask asthma deterioration, don't use them for an acute asthma attack.
•    Combination inhalers. These medications — such as fluticasone-salmeterol (Advair Diskus), budesonide-formoterol (Symbicort) and formoterol-mometasone (Dulera) — contain a long-acting beta agonist along with a corticosteroid. Because these combination inhalers contain long-acting beta agonists, they may increase your risk of having a severe asthma attack.
•    Theophylline. Theophylline (Theo-24, Elixophyllin, others) is a daily pill that helps keep the airways open (bronchodilator) by relaxing the muscles around the airways. It's not used as often now as in past years.
Quick-relief (rescue) medications are used as needed for rapid, short-term symptom relief during an asthma attack — or before exercise if your doctor recommends it.
Types of quick-relief medications include:

•    Short-acting beta agonists. These inhaled, quick-relief bronchodilators act within minutes to rapidly ease symptoms during an asthma attack. They include albuterol (ProAir HFA, Ventolin HFA, others) and levalbuterol (Xopenex).
Short-acting beta agonists can be taken using a portable, hand-held inhaler or a nebulizer — a machine that converts asthma medications to a fine mist — so that they can be inhaled through a face mask or a mouthpiece.
•    Ipratropium (Atrovent). Like other bronchodilators, ipratropium acts quickly to immediately relax your airways, making it easier to breathe. Ipratropium is mostly used for emphysema and chronic bronchitis, but it's sometimes used to treat asthma attacks.
•    Oral and intravenous corticosteroids. These medications — which include prednisone and methylprednisolone — relieve airway inflammation caused by severe asthma. They can cause serious side effects when used long term, so they're used only on a short-term basis to treat severe asthma symptoms.

If you have an asthma flare-up, a quick-relief inhaler can ease your symptoms right away. But if your long-term control medications are working properly, you shouldn't need to use your quick-relief inhaler very often.

Keep a record of how many puffs you use each week. If you need to use your quick-relief inhaler more often than your doctor recommends, see your doctor. You probably need to adjust your long-term control medication.

Allergy medications may help if your asthma is triggered or worsened by allergies.

These include:

•    Allergy shots (immunotherapy). Over time, allergy shots gradually reduce your immune system reaction to specific allergens. You generally receive shots once a week for a few months, then once a month for a period of three to five years.
•    Omalizumab (Xolair). This medication, given as an injection every two to four weeks, is specifically for people who have allergies and severe asthma. It acts by altering the immune system.

Bronchial thermoplasty

This treatment — which isn't widely available nor right for everyone — is used for severe asthma that doesn't improve with inhaled corticosteroids or other long-term asthma medications.

Generally, over the span of three outpatient visits, bronchial thermoplasty heats the insides of the airways in the lungs with an electrode, reducing the smooth muscle inside the airways. This limits the ability of the airways to tighten, making breathing easier and possibly reducing asthma attacks.

Treat by severity for better control: A stepwise approach

Your treatment should be flexible and based on changes in your symptoms, which should be assessed thoroughly each time you see your doctor. Then your doctor can adjust your treatment accordingly.

For example, if your asthma is well-controlled, your doctor may prescribe less medicine. If your asthma isn't well-controlled or is getting worse, your doctor may increase your medication and recommend more-frequent visits.

Asthma action plan
Work with your doctor to create an asthma action plan that outlines in writing when to take certain medications or when to increase or decrease the dose of your medications based on your symptoms. Also include a list of your triggers and the steps you need to take to avoid them.

Your doctor may also recommend tracking your asthma symptoms or using a peak flow meter on a regular basis to monitor how well your treatment is controlling your asthma.

Lifestyle and home remedies

Although many people with asthma rely on medications to prevent and relieve symptoms, you can do several things on your own to maintain your health and lessen the possibility of asthma attacks.

Avoid your triggers

Taking steps to reduce your exposure asthma triggers is a key part of asthma control, including:

•    Use your air conditioner. Air conditioning reduces the amount of airborne pollen from trees, grasses and weeds that finds its way indoors. Air conditioning also lowers indoor humidity and can reduce your exposure to dust mites. If you don't have air conditioning, try to keep your windows closed during pollen season.
•    Decontaminate your decor. Minimize dust that may worsen nighttime symptoms by replacing certain items in your bedroom. For example, encase pillows, mattresses and box springs in dustproof covers. Remove carpeting and install hardwood or linoleum flooring. Use washable curtains and blinds.
•    Maintain optimal humidity. If you live in a damp climate, talk to your doctor about using a dehumidifier.
•    Prevent mold spores. Clean damp areas in the bath, kitchen and around the house to keep mold spores from developing. Get rid of moldy leaves or damp firewood in the yard.
•    Reduce pet dander. If you're allergic to dander, avoid pets with fur or feathers. Having pets regularly bathed or groomed also may reduce the amount of dander in your surroundings.
•    Clean regularly. Clean your home at least once a week. If you're likely to stir up dust, wear a mask or have someone else do the cleaning.
•    Cover your nose and mouth if it's cold out. If your asthma is worsened by cold or dry air, wearing a face mask can help.

Stay healthy

Taking care of yourself can help keep your symptoms under control, including:

•    Get regular exercise. Having asthma doesn't mean you have to be less active. Treatment can prevent asthma attacks and control symptoms during activity.
Regular exercise can strengthen your heart and lungs, which helps relieve asthma symptoms. If you exercise in cold temperatures, wear a face mask to warm the air you breathe.
•    Maintain a healthy weight. Being overweight can worsen asthma symptoms, and it puts you at higher risk of other health problems.
•    Control heartburn and gastroesophageal reflux disease (GERD). It's possible that the acid reflux that causes heartburn may damage lung airways and worsen asthma symptoms. If you have frequent or constant heartburn, talk to your doctor about treatment options. You may need treatment for GERD before your asthma symptoms improve.

Alternative medicine

Certain alternative treatments may help with asthma symptoms. However, keep in mind that these treatments are not a replacement for medical treatment — especially if you have severe asthma. Talk to your doctor before taking any herbs or supplements, as some may interact with medications you take.

While some alternative remedies are used for asthma, in most cases more research is needed to see how well they work and to measure the extent of possible side effects. Alternative asthma treatments include:

•    Breathing exercises. These exercises may reduce the amount of medication you need to keep your asthma symptoms under control.
•    Herbal and natural remedies. A few herbal and natural remedies that may help improve asthma symptoms include black seed, caffeine, choline and pycnogenol.

Coping and support

Asthma can be challenging and stressful. You may sometimes become frustrated, angry or depressed because you need to cut back on your usual activities to avoid environmental triggers. You may also feel limited or embarrassed by the symptoms of the disease and by complicated management routines.

But asthma doesn't have to be a limiting condition. The best way to overcome anxiety and a feeling of helplessness is to understand your condition and take control of your treatment. Here are some suggestions that may help:

•    Pace yourself. Take breaks between tasks and avoid activities that make your symptoms worse.
•    Make a daily to-do list. This may help you avoid feeling overwhelmed. Reward yourself for accomplishing simple goals.
•    Talk to others with your condition. Chat rooms and message boards on the Internet or support groups in your area can connect you with people facing similar challenges and let you know you're not alone.
•    If your child has asthma, be encouraging. Focus attention on the things your child can do, not on the things he or she can't. Involve teachers, school nurses, coaches, friends and relatives in helping your child manage asthma.

Preparing for your appointment

You're likely to start by seeing your family doctor or a general practitioner. However, when you call to set up an appointment, you may be referred to an allergist or a pulmonologist.

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be well-prepared. Here's some information to help you get ready for your appointment, as well as what to expect from your doctor.

What you can do

These steps can help you make the most of your appointment:
•    Write down any symptoms you're having, including any that may seem unrelated to the reason for which you scheduled the appointment.
•    Note when your symptoms bother you most — for example, if your symptoms tend to get worse at certain times of the day, during certain seasons, or when you're exposed to cold air, pollen or other triggers.
•    Write down key personal information, including any major stresses or recent life changes.
•    Make a list of all medications, vitamins and supplements that you're taking.
•    Take a family member or friend along, if possible. Sometimes it can be difficult to recall all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
•    Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out. For asthma, some basic questions to ask your doctor include:

•    Is asthma the most likely cause of my breathing problems?
•    Other than the most likely cause, what are other possible causes for my symptoms?
•    What kinds of tests do I need?
•    Is my condition likely temporary or chronic?
•    What's the best treatment?
•    What are the alternatives to the primary approach that you're suggesting?
•    I have these other health conditions. How can I best manage them together?
•    Are there any restrictions that I need to follow?
•    Should I see a specialist?
•    Is there a generic alternative to the medicine you're prescribing me?
•    Are there any brochures or other printed material that I can take home with me? What websites do you recommend visiting?

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

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

•    What exactly are your symptoms?
•    When did you first notice your symptoms?
•    How severe are your symptoms?
•    Do you have breathing problems most of the time or only at certain times or in certain situations?
•    Do you have allergies, such as atopic dermatitis or hay fever?
•    What, if anything, appears to worsen your symptoms?
•    What, if anything, seems to improve your symptoms?
•    Do allergies or asthma run in your family?
•    Do you have any chronic health problems?

Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, coughing, chest tightness, and shortness of breath. These may occur a few times a day or a few times per week. Depending on the person, asthma symptoms may become worse at night or with exercise.

Asthma is thought to be caused by a combination of genetic and environmental factors. Environmental factors include exposure to air pollution and allergens. Other potential triggers include medications such as aspirin and beta blockers. Diagnosis is usually based on the pattern of symptoms, response to therapy over time, and spirometry lung function testing. Asthma is classified according to the frequency of symptoms, forced expiratory volume in one second (FEV1), and peak expiratory flow rate. It may also be classified as atopic or non-atopic, where atopy refers to a predisposition toward developing a type 1 hypersensitivity reaction.


There is no cure for asthma. Symptoms can be prevented by avoiding triggers, such as allergens and irritants, and by the use of inhaled corticosteroids. Long-acting beta agonists (LABA) or antileukotriene agents may be used in addition to inhaled corticosteroids if asthma symptoms remain uncontrolled. Treatment of rapidly worsening symptoms is usually with an inhaled short-acting beta-2 agonist such as salbutamol and corticosteroids taken by mouth. In very severe cases, intravenous corticosteroids, magnesium sulfate, and hospitalization may be required.

In 2015, 358 million people globally had asthma, up from 183 million in 1990. It caused about 397,100 deaths in 2015, most of which occurred in the developing world. Asthma often begins in childhood, and the rates have increased significantly since the 1960s. Asthma was recognized as early as Ancient Egypt. The word "asthma" is from the Greek  ásthma, which means "panting".

bronchial-tube-asthma550.aspx?width=350&height=245


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.

Offline

#625 2020-03-26 00:55:57

ganesh
Administrator
Registered: 2005-06-28
Posts: 29,981

Re: Miscellany

505) Black hole

Black hole, cosmic body of extremely intense gravity from which nothing, not even light, can escape. A black hole can be formed by the death of a massive star. When such a star has exhausted the internal thermonuclear fuels in its core at the end of its life, the core becomes unstable and gravitationally collapses inward upon itself, and the star’s outer layers are blown away. The crushing weight of constituent matter falling in from all sides compresses the dying star to a point of zero volume and infinite density called the singularity.

Details of the structure of a black hole are calculated from Albert Einstein’s general theory of relativity. The singularity constitutes the centre of a black hole and is hidden by the object’s “surface,” the event horizon. Inside the event horizon the escape velocity (i.e., the velocity required for matter to escape from the gravitational field of a cosmic object) exceeds the speed of light, so that not even rays of light can escape into space. The radius of the event horizon is called the Schwarzschild radius, after the German astronomer Karl Schwarzschild, who in 1916 predicted the existence of collapsed stellar bodies that emit no radiation. The size of the Schwarzschild radius is proportional to the mass of the collapsing star. For a black hole with a mass 10 times as great as that of the Sun, the radius would be 30 km (18.6 miles).

Only the most massive stars—those of more than three solar masses—become black holes at the end of their lives. Stars with a smaller amount of mass evolve into less compressed bodies, either white dwarfs or neutron stars.

Black holes cannot be observed directly on account of both their small size and the fact that they emit no light. They can be “observed,” however, by the effects of their enormous gravitational fields on nearby matter. For example, if a black hole is a member of a binary star system, matter flowing into it from its companion becomes intensely heated and then radiates X-rays copiously before entering the event horizon of the black hole and disappearing forever. One of the component stars of the binary X-ray system Cygnus X-1 is a black hole. Discovered in 1971 in the constellation Cygnus, this binary consists of a blue supergiant and an invisible companion 8.7 times the mass of the Sun that revolve about one another in a period of 5.6 days.

Some black holes apparently have nonstellar origins. Various astronomers have speculated that large volumes of interstellar gas collect and collapse into supermassive black holes at the centres of quasars and galaxies. A mass of gas falling rapidly into a black hole is estimated to give off more than 100 times as much energy as is released by the identical amount of mass through nuclear fusion. Accordingly, the collapse of millions or billions of solar masses of interstellar gas under gravitational force into a large black hole would account for the enormous energy output of quasars and certain galactic systems.

One such supermassive black hole, Sagittarius A*, exists at the centre of the Milky Way Galaxy. In 2005, infrared observations of stars orbiting the position of Sagittarius A* demonstrated the presence of a black hole with a mass equivalent to 4,310,000 Suns. Supermassive black holes have been detected in other galaxies as well. In 2017 the Event Horizon Telescope obtained an image of the supermassive black hole at the centre of the M87 galaxy. That black hole has a mass equal to six and a half billion Suns but is only 38 billion km (24 billion miles) across. It was the first black hole to be imaged directly. The existence of even larger black holes, each with a mass equal to 10 billion Suns, can be inferred from the energetic effects on gas swirling at extremely high velocities around the centre of NGC 3842 and NGC 4889, galaxies near the Milky Way.

The existence of another kind of nonstellar black hole was proposed by the British astrophysicist Stephen Hawking. According to Hawking’s theory, numerous tiny primordial black holes, possibly with a mass equal to or less than that of an asteroid, might have been created during the big bang, a state of extremely high temperatures and density in which the universe is thought to have originated 13.8 billion years ago. These so-called mini black holes, like the more massive variety, lose mass over time through Hawking radiation and disappear. If certain theories of the universe that require extra dimensions are correct, the Large Hadron Collider could produce significant numbers of mini black holes.

57306126_1678196782488087_5054206849805451264_n.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.

Offline

Board footer

Powered by FluxBB