Miscellany

Jai Ganesh · 2019-05-30 00:19:10

350) Kidney

Kidney, in vertebrates and some invertebrates, organ that maintains water balance and expels metabolic wastes. Primitive and embryonic kidneys consist of two series of specialized tubules that empty into two collecting ducts, the Wolffian ducts. The more advanced kidney (metanephros) of adult reptiles, birds, and mammals is a paired compact organ whose functional units, called nephrons, filter initial urine from the blood, reabsorb water and nutrients, and secrete wastes, producing the final urine, which is expelled.

Reptilian and avian kidneys are made up of many tiny lobules that, in birds, are combined into three or more lobes. Collecting tubules from each lobule empty into a separate branch of the ureter. Reptiles have relatively few nephrons (from 3,000 to 30,000 in lizards), while birds have a great number (around 200,000 in a fowl, twice as many as in a mammal of comparable size).

Mammalian kidneys have a somewhat granular outer section (the cortex), containing the glomeruli and convoluted tubules, and a smooth, somewhat striated inner section (the medulla), containing the loops of Henle and the collecting tubules. As the ureter enters the kidney it enlarges into a cavity, the renal pelvis; urine passes into this pelvis from the collecting tubules. Nephrons are numerous (20,000 in a mouse).

In humans the kidneys are about 10 centimetres long and are located beneath the diaphragm and behind the peritoneum. Each kidney contains 1,000,000–1,250,000 nephrons that filter the entire five-quart water content of the blood every 45 minutes—an equivalent of 160 quarts a day. Of this, only 1 1/2quarts are excreted; the remainder is reabsorbed by the nephrons.

Damaged kidneys secrete an enzyme called renin that stimulates constriction of the blood vessels. When the damage has been caused initially by high blood pressure, the increase in pressure from the constricted vessels causes more kidney damage.

(Wolffian duct, also called Archinephric Duct, one of a pair of tubes that carry urine from primitive or embryonic kidneys to the exterior or to a primitive bladder. In amphibians the reproductive system encroaches on the Wolffian duct; in some species the duct carries both urine and sperm, but most amphibians develop a separate tube to carry urine from the kidney.

In advanced vertebrates the Wolffian duct develops in conjunction with the embryonic kidneys. The mature kidney drains through the ureter, however, and the Wolffian duct develops into parts of the male reproductive system, such as the epididymis and the vas deferens.)

Jai Ganesh · 2019-06-01 00:39:40

351) Arthritis

Arthritis, inflammation of the joints and its effects. Arthritis is a general term, derived from the Greek words arthro-, meaning “joint,” and -itis, meaning “inflammation.” Arthritis can be a major cause of disability. In the United States, for example, data collected from 2007 to 2009 indicated that 21 million adults were affected by arthritis and experienced limited activity as a result of their condition. Overall, the incidence of arthritis was on the rise in that country, with 67 million adults expected to be diagnosed by 2030. Likewise, each year in the United Kingdom, arthritis and related conditions caused more than 10 million adults to consult their doctors. Although the most common types of arthritis are osteoarthritis and rheumatoid arthritis, a variety of other forms exist, including those secondary to infection and metabolic disturbances.

Osteoarthritis

Osteoarthritis, also known as degenerative joint disease, is the most common form of arthritis, affecting nearly one-third of people over age 65. It is characterized by joint pain and mild inflammation due to deterioration of the articular cartilage that normally cushions joints. Joint pain is gradual in onset, occurring after prolonged activity, and is typically deep and achy in nature. One or multiple joints may be affected, predominantly involving the knee, hips, spine, and fingers.

Approximately 90 percent of individuals experience crepitus (crackling noises) in the affected joint with motion. Muscle weakness and joint laxity or stiffness can occur as people become reluctant to move painful joints. Patients tend to have decreased joint stability and are predisposed to injuries such as meniscal and anterior cruciate ligament tears. Hip arthritis can affect gait, while arthritis of the hands can lead to decreased dexterity. Enlargement of the bony processes surrounding affected joints, called osteophytes (bone spurs), are common.

Joint trauma, increased age, obesity, certain genetic factors and occupations, and hobbies or sports that result in excessive joint stresses can result in the cartilaginous changes leading to osteoarthritis. Damage begins with the development of small cracks in the cartilage that are perpendicular to the joint. Eventually, cartilage erodes and breaks off, facilitating painful bone-on-bone contact. In due course, pathologic bony changes, such as osteophytes and subchondral bone cysts, develop and further restrict joint movement and integrity.

Osteoarthritis may be divided into two types, primary and secondary osteoarthritis. Primary osteoarthritis is age-related, affecting 85 percent of individuals 75–79 years of age. Although the etiology is unknown, primary osteoarthritis is associated with decreased water-retaining capacity in the cartilage, analogous to a dried-up rubber band that can easily fall apart. Secondary osteoarthritis is caused by another condition, such as joint trauma, congenital joint malalignment, obesity, hormonal disorders, and osteonecrosis. Treatment for osteoarthritis is directed toward reducing pain and correcting joint mechanics and may include exercise, weight loss, nonsteroidal anti-inflammatory drugs, steroids, and total joint replacement surgery.

Autoimmune Arthritis

Autoimmune arthritis is characterized by joint inflammation and destruction caused by one’s own immune system. Genetic predisposition and inciting factors, such as an infection or trauma, can trigger the inappropriate immune response. Rheumatoid arthritis, which is an autoimmune disease, is often associated with elevations in the serum level of an autoantibody called rheumatoid factor, whereas the seronegative arthropathies are not.

Rheumatoid arthritis is a progressive inflammatory condition that can lead to decreased mobility and joint deformities. The worldwide prevalence is 0.8 percent, with a 2:1 predilection for women over men. Disease onset, mainly occurring in the third and fourth decades of life, may be acute or slowly progressive with initial symptoms of fatigue, weakness, malaise, weight loss, and mild, diffuse joint pain. Rheumatoid arthritis tends to affect the hips, knees, elbows, ankles, spine, hands, and feet symmetrically. The disease course is characterized by periods of remission, followed by progressive exacerbations in which specific joints become warm, swollen, and painful. Morning stiffness, typically lasting about two hours, is a hallmark feature of rheumatoid arthritis. Patients with rheumatoid arthritis tend to complain of joint pain after prolonged periods of inactivity, whereas osteoarthritis is typically exacerbated with extended activity. Rheumatoid arthritis can be severely debilitating, resulting in a variety of deformities. Some patients experience complete remission, which typically occurs within two years of disease onset.

Although the exact cause is unknown, rheumatoid arthritis results from the inflammation of the tissues surrounding the joint space. The thin lining of the joint space becomes thick and inflamed, taking on the form of a mass with fingerlike projections (pannus), which invades the joint space and surrounding bone. Initially, this results in joint laxity. However, with progression, the bones can actually undergo fusion (ankylosis), limiting motion.

The effect rheumatoid arthritis has on the hands is a defining characteristic. Clinically, it can be distinguished from osteoarthritis based on the distribution of joints affected in the hands. Rheumatoid arthritis tends to affect the more proximal joints, whereas osteoarthritis tends to affect the more distal joints of the hands and fingers. In severe cases, joint laxity and tendon rupture result in a characteristic deformity of the fingers and wrist.

Rheumatoid nodules are thick fibrous nodules that form as a result of excessive tissue inflammation in rheumatoid arthritis. These nodules are typically present over pressure points, such as the elbows, Achilles tendon, and flexor surfaces of the fingers. Destruction of peripheral blood vessels (vasculitis) from the inflammatory process can occur in any organ, leading to renal failure, myocardial infarction (heart attack), and intestinal infarction (death of part of the intestine). In addition, rheumatoid arthritis is also associated with an increased risk of infections, osteoporosis (thinning of bones), and atherosclerosis(hardening of arteries).

Diagnosis of rheumatoid arthritis is based on the presence of several clinical features: rheumatoid nodules, elevated levels of rheumatoid factor, and radiographic changes. Although rheumatoid factor is found in 70 to 80 percent of people with rheumatoid arthritis, it cannot be used alone as a diagnostic tool, because multiple conditions can be associated with elevated levels of rheumatoid factor.

Since no therapy cures rheumatoid arthritis, treatment is directed toward decreasing symptoms of pain and inflammation. Surgical treatment may include total joint replacement, carpal tunnel release (cutting of the carpal ligament), and tendon repair. Hand splints are used to slow the progression of finger and wrist deformations.

The overall life span of individuals with rheumatoid arthritis is typically shortened by 5–10 years and is highly dependent on disease severity. Disease severity and the likelihood of extra-articular manifestations are each directly related to serum rheumatoid factor levels.

Several rheumatoid arthritis variants exist. In Sjögren syndrome the characteristic symptoms include dry eyes, dry mouth, and rheumatoid arthritis. Felty syndrome is associated with splenomegaly (enlarged spleen), neutropenia (depressed white blood cell levels), and rheumatoid arthritis. Juvenile rheumatoid arthritis is the most common form of childhood arthritis. Disease etiology and clinical course typically differ from that of adult-onset rheumatoid arthritis, and sufferers are prone to the development of other rheumatologic diseases, including rheumatoid arthritis.

Spondyloarthropathies

Ankylosing spondylitis, Reiter syndrome, psoriatic arthritis, and arthritis associated with inflammatory bowel disease are a subset of conditions known as spondyloarthropathies. Typically affected are the sacrum and vertebral column, and back pain is the most common presenting symptom. Enthesitis, inflammation at the insertion of a tendon or ligament into bone, is a characteristic feature of spondyloarthropathy. Unlike rheumatoid arthritis, spondyloarthropathies are not associated with elevated levels of serum rheumatoid factor. Spondyloarthropathies occur most frequently in males and in individuals with a genetic variation known as HLA-B27.

Ankylosing spondylitis is the most common type of spondyloarthropathy, affecting 0.1 to 0.2 percent of the population in the United States. In a region of Turkey, prevalence was found to be 0.25 percent, and in the United Kingdom prevalence is estimated to range from 0.1 to 2 percent. In all regions, the condition occurs more frequently in males than in females and typically strikes between ages 15 and 40. Genetic studies have shown that more than 90 percent of all patients with ankylosing spondylitis who are white and of western European descent are HLA-B27 positive.

Ankylosing spondylitis is characterized by arthritis of the spine and sacroiliac joints. Extensive inflammation of the spinal column is present, causing a characteristic “bamboo spine” appearance on radiographs. Arthritis first occurs in the sacroiliac joints and gradually progresses up the vertebral column, leading to spinal deformity and immobility. Typical symptoms include back pain, which lessens with activity, and heel pain due to enthesitis of the plantar fascia and Achilles tendon. Hip and shoulder arthritis may occur early in the course of the disease.

Reiter syndrome, a type of reactive arthritis, is characterized by the combination of urethritis, conjunctivitis, and arthritis. Patients typically develop acute oligoarthritis (two to four joints affected) of the lower extremities within weeks of gastrointestinal infection or of acquiring a sexually transmitted disease. Reiter arthritis is not considered an infectious arthritis, because the joint space is actually free of bacteria. Instead, an infection outside the joint triggers this form of arthritis. Other symptoms can include fever, weight loss, back pain, enthesitis of the heel, and dactylitis (sausage-shaped swelling of the fingers and toes). Most cases resolve within one year; however, 15–30 percent of patients develop chronic, sometimes progressive arthritis. Occurring almost exclusively in men, Reiter syndrome is strongly linked to the HLA-B27gene variant, which is present in 65 to 96 percent of symptomatic individuals.

Psoriasis is an immune-mediated inflammatory skin condition characterized by raised red plaques with an accompanying silvery scale, which can be painful and itchy at times. Though typically seen on the elbow, knees, scalp, and ears, plaques can occur on any surface of the body. About 10 percent of people with psoriasis (possibly as many as 30 percent in some regions of the world) develop a specific type of arthritis known as psoriatic arthritis.

Psoriatic arthritis typically occurs after psoriasis has been present for many years. In some cases, however, arthritis may precede psoriasis; less often, the two conditions appear simultaneously. Estimates on the prevalence of psoriatic arthritis vary according to population. However, overall, it is thought to affect nearly 1 percent of the general population, with a peak age of onset between 30 and 55. Usually less destructive than rheumatoid arthritis, psoriatic arthritis tends to be mild and slowly progressive, though certain forms, such as arthritis mutilans, can be quite severe. Occasionally the onset of symptoms associated with psoriatic arthritis is acute, though more often it is insidious, initially presenting as oligoarthritis with enthesitis. Over time, arthritis begins to affect multiple joints (polyarthritis), especially the hands and feet, resulting in dactylitis. Typically, the polyarticular pattern of psoriatic arthritis affects a different subset of finger joints than rheumatoid arthritis. It is not until years after peripheral arthritis has occurred that psoriatic arthritis may affect the axial joints, causing inflammation of the sacroiliac joint (sacroiliitis) and intervertebral joints (spondylitis).

Arthritis mutilans is a more severe and much less common pattern (seen in fewer than 5 percent of psoriatic arthritis cases) resulting in bone destruction with characteristic telescoping of the fingers or toes. In addition, individuals with psoriatic arthritis necessitate more aggressive treatment if the onset of the condition occurs before age 20, if there is a family history of psoriatic arthritis, if there is extensive skin involvement, or if the patient has the HLA-DR4 genotype.
Crohn disease and ulcerative colitis, two types of inflammatory bowel disease, are complicated by a spondyloarthropathy in as many as 20 percent of patients.

Although arthritis associated with inflammatory bowel disease typically occurs in the lower extremities, up to 20 percent of cases demonstrate symptoms identical to ankylosing spondylitis. Arthritis is usually exacerbated in conjunction with inflammatory bowel disease exacerbations and lasts several weeks thereafter.

Crystalloid Arthritis

Joint inflammation, destruction, and pain can occur as a result of the precipitation of crystals in the joint space. Gout and pseudogout are the two primary types of crystalloid arthritis caused by different types of crystalloid precipitates.

Gout is an extremely painful form of arthritis that is caused by the deposition of needle-shaped monosodium urate crystals in the joint space (urate is a form of uric acid). Initially, gout tends to occur in one joint only, typically the big toe (podagra), though it can also occur in the knees, fingers, elbows, and wrists. Pain, frequently beginning at night, can be so intense that patients are sensitive to even the lightest touch. Urate crystal deposition is associated with the buildup of excess serum uric acid (hyperuricemia), a by-product of everyday metabolism that is filtered by the kidneys and excreted in the urine. Causes of excess uric acid production include leukemia or lymphoma, alcohol ingestion, and chemotherapy. Kidney disease and certain medications, such as diuretics, can depress uric acid excretion, leading to hyperuricemia. Although acute gouty attacks are self-limited when hyperuricemia is left untreated for years, such attacks can recur intermittently, involving multiple joints. Chronic tophaceous gout occurs when, after about 10 years, chalky, pasty deposits of monosodium urate crystals begin to accumulate in the soft tissue, tendons, and cartilage, causing the appearance of large round nodules called tophi. At this disease stage, joint pain becomes a persistent symptom.

Gout is most frequently seen in men in their 40s, due to the fact that men tend to have higher baseline levels of serum uric acid. In the early 21st century the prevalence of gout appeared to be on the rise globally, presumably because of increasing longevity, changing dietary and lifestyle factors, and the increasing incidence of insulin-resistant syndromes.

Pseudogout is caused by rhomboid-shaped calcium pyrophosphate crystals deposition (CPPD) into the joint space, which leads to symptoms that closely resemble gout. Typically occurring in one or two joints, such as the knee, ankles, wrists, or shoulders, pseudogout can last between one day and four weeks and is self-limiting in nature. A major predisposing factor is the presence of elevated levels of pyrophosphatein the synovial fluid. Because pyrophosphate excess can result from cellular injury, pseudogout is often precipitated by trauma, surgery, or severe illness. A deficiency in alkaline phosphatase, the enzyme responsible for breaking down pyrophosphate, is another potential cause of pyrophosphate excess.

Other disorders associated with synovial CPPD include hyperparathyroidism, hypothyroidism, hemochromatosis, and Wilson disease. Unlike gout, pseudogout affects both men and women, with more than half at age 85 and older.

Infectious Arthritis

Infectious arthritides are a set of arthritic conditions caused by exposure to certain microorganisms. In some instances the microorganisms infiltrate the joint space and cause destruction, whereas in others an infection stimulates an inappropriate immune response leading to reactive arthritis. Typically caused by bacterial infections, infectious arthritis may also result from fungal and viral infections.

Septic arthritis usually affects a single large joint, such as the knee. Although a multitude of organisms may cause arthritis, Staphylococcus aureus is the most common pathogen. Neisseria gonorrhoeae, the bacteria that causes gonorrhea, is a common pathogen affecting male-female active young adults.

The most common way by which bacteria enter the joint space is through the circulatory system after a bloodstream infection. Microorganisms may also be introduced into the joint by penetrating trauma or surgery. Factors that increase the risk of septic arthritis include very young or old age (e.g., infants and the elderly), recent surgery or skin infection, preexisting arthritic condition, immunosuppression, chronic renal failure, and the presence of a prosthetic joint.

Postinfectious arthritis is seen after a variety of infections. Certain gastrointestinal infections, urinary tract infections, and upper respiratory tract infections can lead to arthritic symptoms after the infections themselves have resolved. Examples include Reiter syndrome and arthritis associated with rheumatic fever.

335x227_understanding_arthritis_and_inflammation_other.jpg

Jai Ganesh · 2019-06-03 00:58:30

352) Peacock

Peacock, any of three species of resplendent birds of the pheasant family, Phasianidae (order Galliformes). Strictly, the male is a peacock, and the female is a peahen; both are peafowl. The two most-recognizable species of peafowl are the blue, or Indian, peacock (Pavo cristatus), of India and Sri Lanka, and the green, or Javanese, peacock (P. muticus), found from Myanmar (Burma) to Java. The Congo peacock(Afropavo congensis), which inhabits the forested interior of the Democratic Republic of the Congo, was discovered in 1936 after a search that began in 1913 with the finding of a single feather.

Natural History

In both species of Pavo, the male has a 90–130-cm (35–50-inch) body and 150-cm (60-inch) train of tail feathers that are coloured a brilliant metallic green. This train is mainly formed of the bird’s upper tail coverts, which are enormously elongated. Each feather is tipped with an iridescent eyespot that is ringed with blue and bronze. In courtship displays, the math elevates his tail, which lies under the train, thus elevating the train and bringing it forward. At the climax of this display, the tail feathers are vibrated, giving the feathers of the train a shimmering appearance and making a rustling sound.

The blue peacock’s body feathers are mostly metallic blue-green. The green peacock, with a train much like that of the blue, has green and bronze body feathers. Hens of both species are green and brown and are almost as big as the male but lack the train and the head ornament. In the wild, both species live in open lowland forests, flocking by day and roosting high in trees at night. During the breeding season, the male forms a harem of two to five hens, each of which lays four to eight whitish eggs in a depression in the ground. The eggs are incubated by the peahen until they hatch some 28 days later. The chicks have all of their feathers when they emerge from their eggs and are capable of flight roughly one week after hatching. Most blue and green peafowl become sexually mature at age three. However, some male blue peafowl have been known to breed as early as age two.

As an ornamental bird, the peacock is a staple resident of many of the world’s zoos and has long been famous throughout the Old World. Green peacocks in captivity must be kept apart from other fowl, though, because of their aggressive disposition. Blue peacocks, though native to warm humid climates, can survive northern winters. Green peacocks, however, cannot tolerate much cold.

The Congo peacock is the only large phasianid in Africa. The math is mainly blue and green with a short rounded tail. The hen is reddish and green with a brown topknot. The species is smaller than those in genus Pavo, growing to roughly between 64 and 70 cm (25 to 28 inches) in length by adulthood.
Conservation Status

The International Union for Conservation of Nature (IUCN) Red List classifies the blue peafowl as a species of least concern. However, the green peacock, whose population declined significantly during the latter half of the 20th century because of overhunting and the destruction of large parts of its natural habitat, is classified by the IUCN as an endangered species. The IUCN has classified the Congo peafowl, which has also experienced declines because of hunting and habitat loss, as a vulnerable species.

Jai Ganesh · 2019-06-05 00:02:05

353) Lion

Lion, (Panthera leo), large, powerfully built cat (family Felidae) that is second in size only to the tiger. The proverbial “king of beasts,” the lion has been one of the best-known wild animals since earliest times. Lions are most active at night and live in a variety of habitats but prefer grassland, savanna, dense scrub, and open woodland. Historically, they ranged across much of Europe, Asia, and Africa, but now they are found mainly in parts of Africa south of the Sahara. An isolated population of about 650 Asiatic lions constitute a slightly smaller race that lives under strict protection in India’s Gir National Park and Wildlife Sanctuary.

General Characteristics

The lion is a well-muscled cat with a long body, large head, and short legs. Size and appearance vary considerably between the genders. The male’s outstanding characteristic is his mane, which varies between different individuals and populations. It may be entirely lacking; it may fringe the face; or it may be full and shaggy, covering the back of the head, neck, and shoulders and continuing onto the throat and chest to join a fringe along the belly. In some lions the mane and fringe are very dark, almost black, giving the cat a majestic appearance. Manes make males look larger and may serve to intimidate rivals or impress prospective mates. A full-grown male is about 1.8–2.1 metres (6–7 feet) long, excluding the 1-metre tail; he stands about 1.2 metres high at the shoulder and weighs 170–230 kg (370–500 pounds). The female, or lioness, is smaller, with a body length of 1.5 metres, a shoulder height of 0.9–1.1 metres, and a weight of 120–180 kg. The lion’s coat is short and varies in colour from buff yellow, orange-brown, or silvery gray to dark brown, with a tuft on the tail tip that is usually darker than the rest of the coat.

Prides

Lions are unique among cats in that they live in a group, or pride. The members of a pride typically spend the day in several scattered groups that may unite to hunt or share a meal. A pride consists of several generations of lionesses, some of which are related, a smaller number of breeding males, and their cubs. The group may consist of as few as 4 or as many as 37 members, but about 15 is the average size. Each pride has a well-defined territory consisting of a core area that is strictly defended against intruding lions and a fringe area where some overlap is tolerated. Where prey is abundant, a territory area may be as small as 20 square km (8 square miles), but if game is sparse, it may cover up to 400 square km. Some prides have been known to use the same territory for decades, passing the area on between females. Lions proclaim their territory by roaring and by scent marking. Their distinctive roar is generally delivered in the evening before a night’s hunting and again before getting up at dawn. Males also proclaim their presence by urinating on bushes, trees, or simply on the ground, leaving a pungent scent behind. Defecation and rubbing against bushes leave different scent markings.

There are a number of competing evolutionary explanations for why lions form groups. Large body size and high density of their main prey probably make group life more efficient for females in terms of energy expenditure. Groups of females, for example, hunt more effectively and are better able to defend cubs against infanticidal males and their hunting territory against other females. The relative importance of these factors is debated, and it is not clear which was responsible for the establishment of group life and which are secondary benefits.

Hunting

Lions prey on a large variety of animals ranging in size from rodents and baboons to Cape (or African) buffalo and hippopotamuses, but they predominantly hunt medium- to large-sized hoofed animals such as wildebeests, zebras, and antelopes. Prey preferences vary geographically as well as between neighbouring prides. Lions are known to take elephants and giraffes, but only if the individual is young or especially sick. They readily eat any meat they can find, including carrion and fresh kills that they scavenge or forcefully steal from hyenas, cheetahs, or wild dogs. Lionesses living in open savanna do most of the hunting, whereas males typically appropriate their meals from the female’s kills. However, male lions are also adept hunters, and in some areas they hunt frequently. Pride males in scrub or wooded habitat spend less time with the females and hunt most of their own meals. Nomadic males must always secure their own food.

Though a group of hunting lions is potentially nature’s most formidable predatory force on land, a high proportion of their hunts fail. The cats pay no attention to the wind’s direction (which can carry their scent to their prey), and they tire after running short distances. Typically, they stalk prey from nearby cover and then burst forth to run it down in a short, rapid rush. After leaping on the prey, the lion lunges at its neck and bites until the animal has been strangled. Other members of the pride quickly crowd around to feed on the kill, usually fighting for access. Hunts are sometimes conducted in groups, with members of a pride encircling a herd or approaching it from opposite directions, then closing in for a kill in the resulting panic. The cats typically gorge themselves and then rest for several days in its vicinity. An adult male can consume more than 34 kg (75 pounds) of meat at a single meal and rest for a week before resuming the hunt. If prey is abundant, both genders typically spend 21 to 22 hours a day resting, sleeping, or sitting and hunt for only 2 or 3 hours a day.

Reproduction And Life Cycle

Both sexes are polygamous and breed throughout the year, but females are usually restricted to the one or two adult males of their pride. In captivity lions often breed every year, but in the wild they usually breed no more than once in two years. Females are receptive to mating for three or four days within a widely variable reproductive cycle. During this time a pair generally mates every 20–30 minutes, with up to 50 copulations per 24 hours. Such extended copulation not only stimulates ovulation in the female but also secures paternity for the male by excluding other males. The gestation period is about 108 days, and the litter size varies from one to six cubs, two to four being usual.

Newborn cubs are helpless and blind and have a thick coat with dark spots that usually disappear with maturity. Cubs are able to follow their mothers at about three months of age and are weaned by six or seven months. They begin participating in kills by 11 months but probably cannot survive on their own until they are two years old. Although lionesses will nurse cubs other than their own, they are surprisingly inattentive mothers and often leave their cubs alone for up to 24 hours. There is a corresponding high mortality rate (e.g., 86 percent in the Serengeti), but survival rates improve after the age of two. In the wild, mating maturity is reached at three or four years of age. Some female cubs remain within the pride when they attain mating maturity, but others are forced out and join other prides or wander as nomads. Male cubs are expelled from the pride at about three years of age and become nomads until they are old enough to try to take over another pride (after age five). Many adult males remain nomads for life. Mating opportunities for nomad males are rare, and competition between male lions to defend a pride’s territory and mate with the pride females is fierce. Cooperating partnerships of two to four males are more successful at maintaining tenure with a pride than individuals, and larger coalitions father more surviving offspring per male. Small coalitions typically comprise related males, whereas larger groups often include unrelated individuals. If a new cohort of males is able to take over a pride, they will seek to kill young cubs sired by their predecessors. This has the effect of shortening the time before the cubs’ mothers are ready to mate again. Females attempt to prevent this infanticide by hiding or directly defending their cubs; lionesses are generally more successful at protecting older cubs, as they would be leaving the pride sooner. In the wild lions seldom live more than 8 to 10 years, chiefly because of attacks by humans or other lions or the effects of kicks and gorings from intended prey animals. In captivity they may live 25 years or more.

Distribution

During the Pleistocene Epoch (2,600,000 to 11,700 years ago), lions ranged across all of North America and Africa, through most of the Balkans, and across Anatolia and the Middle East into India. Genetic studies suggest that the lion evolved in eastern and southern Africa, diversifying into a number of subspecies—such as the Barbary lion (Panthera leo leo) of North Africa, the cave lion (P. leo spelaea) of Europe, the American lion (P. leo atrox) of North and Central America, and the Asiatic lion (P. leo persica) of the Middle East and India—starting about 124,000 years ago.

Lions disappeared from North America about 10,000 years ago, from the Balkans about 2,000 years ago, and from Palestine during the Crusades. By the 21st century their numbers had dwindled to a few tens of thousands, and those outside national parks are rapidly losing their habitat to agriculture. The International Union for the Conservation of Nature (IUCN) lists the species as vulnerable, and several subspecies have died out. At present the lion’s main stronghold is in sub-Saharan Africa, and the Asiatic lion exists only as a remnant population made up of approximately 500 individuals inhabiting India’s Gir National Park on the Kathiawar Peninsula. However, the Asiatic lion’s close genetic similarity with the now-extinct Barbary lion has raised hopes among conservationists that a restored population of the latter may be established in North Africa.

Conflict with humans, especially herders, outside parks is a major problem, and humans living around parks remain the predominant source of mortality for most populations. In 1994, for example, a variant of canine distemper caused the death of an estimated 1,000 lions at the Serengeti National Park. The apparent source of the virus was domestic dogs living along the periphery of the park. Despite such challenges, lion populations are healthy in many African reserves and at Gir, and they are a major tourist draw. High population densities of lions, however, can be a problem, not only for local ranchers but also for the cheetah and African wild dog—critically endangered carnivores that lose their kills, their cubs, and their lives to lions.

The genus Panthera includes leopards, jaguars, and tigers as well as lions. In captivity, lions have been induced to mate with other big cats. The offspring of a lion and a tigress is called a liger; that of a tiger and a lioness, a tigon; that of a leopard and a lioness, a leopon. The cat known as the mountain lion, however, is a New World member of the genus Puma.

Jai Ganesh · 2019-06-07 01:10:52

354) Petroleum

Petroleum is a naturally occurring liquid found beneath the Earth’s surface that can be refined into fuel. Petroleum is a fossil fuel, meaning that it has been created by the decomposition of organic matter over millions of years. It is formed in sedimentary rock under intense heat and pressure. Petroleum is used as fuel to power vehicles, heating units and machines of all sorts, as well as being converted into plastics and other materials. Because of worldwide reliance on petroleum, the petroleum industry is extremely powerful and is a major influence on world politics and the global economy.

Breaking down Petroleum

Petroleum and the extraction and processing of petroleum drives the world economy and global politics. The modern world owes its existence to petroleum. Some of the largest companies in the world are involved in the extraction and processing of petroleum, with other companies creating products that either require hydrocarbons to operate or are petroleum-based: plastics, fertilizers, automobiles, and airplanes. Asphalt, which is used to pave highways, is made from petroleum. Vehicles that drive on highways are made of materials derived from petroleum and run on fuels refined from petroleum.

Petroleum is most often associated with crude oil and the wells dug into the ground to bring that liquid to the surface. The liquid can vary in color: from relatively transparent to dark brown or black. Heavier oils are often the darkest in color. Petroleum contains various types of hydrocarbons, and natural gas is often found dissolved in the liquid in significant amounts. The hydrocarbons can be processed in refineries into different types of fuels. Hydrocarbon molecules in petroleum include asphalt, paraffin, and naphthene.

Petroleum is comprised of a mixture of various hydrocarbons, and can have different chemical and physical properties depending on where it is found in the world. In general, the more dense the petroleum the more difficult it is to process and the less valuable it is. “Light” crude is the easiest to refine and are generally considered the most valuable, while the viscosity of “heavy” crude makes it more expensive to refine. “Sour” crude contains sulfur and sulfuric compounds, which makes the fuel less valuable.

In the petroleum industry, petroleum companies are divided into upstream, midstream and downstream. Upstream deals with crude oil. Midstream refers to the storage and transport of crude oil and other more refined products. Downstream refers to products for consumers such as gasoline.

Disadvantages of Petroleum

Petroleum use is embedded in modern life, but the extraction process and use of petroleum are toxic for the environment. Underwater drilling causes leaks, extraction from oil sands strips the earth or uses precious water and fracking destroys the water table. Transporting petroleum through pipelines has the potential to destroy the local environment and shipping petroleum risks spills and uses energy.

Global petroleum use has had a negative impact on the environment, as the carbon released into the atmosphere increases temperatures and is associated with global warming. Many products created with petroleum derivatives do not biodegrade quickly, and the overuse of fertilizers can damage water supplies.

petroleum-production-Fotolia_9699464_Subscription_Monthly_L-500x350-500x350.jpg

Jai Ganesh · 2019-06-09 00:16:20

355) Mongoose

Mongoose, any of nearly three dozen species of small bold predatory carnivores found mainly in Africa but also in southern Asia and southern Europe. Mongooses are noted for their audacious attacks on highly venomous snakes such as king cobras. The 33 species belong to 14 genera. The most common and probably best-known are the 10 species of the genus Herpestes, among which are the Egyptian mongoose, or ichneumon (H. ichneumon), of Africa and southern Europe and the Indian gray mongoose (H. edwardsi), made famous as Rikki-tikki-tavi in Rudyard Kipling’s ‘The Jungle Books’ (1894 and 1895). The meerkat(Suricata suricatta) is also a member of the mongoose family. The colloquial term mongoose may also include Malagasy mongooses—a group of five species found on the island of Madagascar that are closely related to fossas, falanoucs, and fanalokas (the Malagasy civet) and which most sources classify within the family Eupleridae.

Mongooses are short-legged animals with pointed noses, small ears, and long furry tails. The claws do not retract, and in most species there are five toes on each foot. The fur is gray to brown and is commonly grizzled or flecked with lighter gray. Markings, when present, include stripes, dark legs, and pale or ringed tails. The adult size varies considerably, with the smallest being the dwarf mongoose (Helogale parvula), which measures 17–24 cm (7–10 inches) with a 15–20-cm (approximately 6–8-inch) tail. The largest mongoose is the white-tailed mongoose (Ichneumia albicauda), whose body length measures 48–71 cm (about 19–28 inches) long with a tail that may extend up to an additional 47 cm (18.5 inches).

Natural History

Mongooses live in burrows and feed on small mammals, birds, reptiles, eggs, and occasionally fruit. A number of mongooses, especially those of the genus Herpestes, will attack and kill venomous snakes. They depend on speed and agility, darting at the head of the snake and cracking the skull with a powerful bite. Mongooses are bitten occasionally; however, they possess a glycoprotein that binds to proteins in snake venom, deactivating them and making them harmless.

A number of species are noted for their peculiar habit of opening eggs as well as other food items with hard shells (crabs, mollusks, and nuts). The animal stands on its hind legs and hits the egg against the ground. Sometimes it carries the egg to a rock and, standing with its back to the rock, throws the egg between its legs and against the rock until the shell is broken. Early reports of this behaviour met with skepticism but have been verified by other observers. The Malagasy narrow-striped mongoose (Mungotictis decemlineata) exhibits the same behaviour but lies on its side and uses all four feet to toss the egg.
Most species are active during the day and are terrestrial, although the marsh mongoose (Atilax paludinosus) and a few others are semiaquatic. Some mongooses live alone or in pairs, but others, such as the banded mongoose (Mungos mungo), dwarf mongooses (genus Helogale), and meerkats, live in large groups. Litters usually consist of two to four young.

Some species, mainly the Javan mongoose (Herpestes javanicus) but also the Indian gray mongoose, were introduced to numerous islands, including Mafia Island (off the coast of East Africa), Mauritius, and those of Croatia, Hawaii, and Fiji. Originally intended to help control rodentsand snakes, these introductions were disastrous, because the mongooses severely depleted the populations of native fauna. Because of their potential destructiveness, importation of all mongooses into the United States is strictly regulated.

Classification

The presence of an anal scent gland and associated sac is one of the most important anatomical features that differentiates mongooses from members of the family Viverridae—the group of small Old World mammals that contains civets, genets, and linsangs—in which they were formerly classified. The classification considers the carnivore families Herpestidae and Eupleridae and their subdivisions. According to most classifications, mongooses span family Herpestidae and the Galidiinids (Malagasy mongooses) of family Eupleridae. The euplerid subfamily Euplerinae—made up of fossas, falanoucs, and fanalokas—is also included; these animals are related to Malagasy mongooses, but they are not considered mongooses.

Jai Ganesh · 2019-06-11 00:28:13

356) Chennai

Chennai, formerly Madras, city, capital of Tamil Nadu state, southern India, on the Coromandel Coast of the Bay of Bengal. Known as the “Gateway to South India,” Chennai is a major administrative and cultural centre. Pop. (2001) city, 4,343,645; urban agglom., 6,560,242.

History

Armenian and Portuguese traders were living in the San Thome area of what is now present-day Chennai before the arrival of the British in 1639. Madras was the shortened name of the fishing village Madraspatnam, where the British East India Company built a fort and factory (trading post) in 1639–40. At that time, the weaving of cotton fabrics was a local industry, and the English invited the weavers and native merchants to settle near the fort. By 1652 the factory of Fort St. George was recognized as a presidency (an administrative unit governed by a president), and between 1668 and 1749 the company expanded its control. About 1801, by which time the last of the local rulers had been shorn of his powers, the English had become masters of southern India, and Madras had become their administrative and commercial capital. The government of Tamil Nadu officially changed the name of the city to Chennai in 1996.

The Contemporary City

Madras developed without a plan from its 17th-century core, formed by Fort St. George and the Indian quarters. To the north and northwest are the industrial areas; the main residential areas are to the west and south, where a number of modern high-rise apartment buildings have been constructed, and the old villages are in the centre. The most distinctive buildings in the city are the seven large temples in the Dravidian style, situated in the city sections of George Town, Mylapore, and Triplicane. The Chepauk Palace (the former residence of the nawab [Mughal ruler] of Karnataka) and the University Senate House, both in the Deccan Muslim style, and the Victoria Technical Institute and the High Court buildings, both in the Indo-Saracenic style, are generally considered the most attractive buildings of the British period.

Chennai and its suburbs have more than 600 Hindu temples. The oldest is the Parthasarathi Temple built in the 8th century by Pallava kings. The Kapaleeswarar Temple (16th century) is dedicated to the Hindu god Shiva. Other places of worship within the city include Luz Church (1547–82), one of the oldest churches in Chennai; St. Mary’s Church (1678–80), the first British church in India; the San Thome Basilica (1898), built over the tomb of the apostle St. Thomas; and Wallajah Mosque (1795), built by the nawab of Karnataka. The Armenian Church of the Holy Virgin Mary (1772), in the George Town section of Chennai, surrounds a courtyard cemetery with Armenian tombstones dating from the mid-17th century. The international headquarters of the Theosophical Society is situated in gardens between the Adyar River and the coast. Of particular interest there is a banyan tree dating from about 1600.

Since the late 1990s, software development and electronics manufacturing have made up the bulk of Chennai’s economy. Numerous technology parks, where many foreign companies have offices, are found throughout the city. Other major industries include the manufacture of automobiles, rubber, fertilizer, leather, iron ore, and cotton textiles. Wheat, machinery, iron and steel, and raw cotton are imported. There is an oil refinery in Chennai. Services, especially finance and tourism, are also significant. Hotels, luxury resorts, restaurants, marinas, and parks line Marina Beach, the coastline abutting Chennai city.

Chennai has numerous educational institutions. Professional education can be obtained in the state medical and veterinary sciences colleges, the colleges of engineering and technology, the Tamil Nadu Isai Kalluri music college, the College of Arts and Crafts, and the teacher-training colleges. The city is the site of the University of Madras (1857), which has several advanced centres of research. The Indian Institute of Technology, the Central Leather Research Institute, and the Regional Laboratories of the Council of Scientific and Industrial Research are other noteworthy scientific institutions. The M.S. Swaminathan Research Foundation focuses on agricultural development in Chennai and Tamil Nadu.

Since the 1980s Chennai has emerged as one of the leading medical centres of the country. This was a result of the proliferation of private specialty hospitals, especially those which provide treatment for cardiac and eye ailments. Among the leading medical facilities in the city are the Apollo Hospital, the Madras Medical Mission’s Institute of Cardiovascular Diseases, the Sri Ramachandra University Hospital, the Heart Institute of Chennai, and the Shankara Nethralaya (“Temple of the Eye”), an eye hospital.
Cultural institutions in Chennai include the Madras Music Academy, devoted to the encouragement of Karnatak music—the music of Karnataka, the historical region between the southern Coromandel Coast of the Bay of Bengal and the Deccan plateau. The Kalakshetra is a centre of dance and music, and the Rasika Ranjini Sabha, in Mylapore, encourages the theatrical arts. The city has training centres for kuchipudi and bharata natyam (Indian classical dance forms). Kalakshetra and Sri Krishna Gana Sabha, a cultural institution, both host annual dance festivals. The suburban town of Kodambakkam, with its numerous film studios, is described as the Hollywood of southern India. Three theatres—the Children’s Theatre, the Annamalai Manram, and the Museum Theatre—are popular. The Chennai Government Museum has exhibitions on the history and physical aspects of Tamil Nadu. There is a small collection of East India Company antiquities in the Fort Museum (within Fort St. George) and a collection of paintings in the National Art Gallery.

Squash, cricket, tennis, and hockey are popular sports in Chennai and its surrounding region. The Madras Cricket Club (1848), located behind the Chepauk Palace, is host to major national sports tournaments. The city has many other clubs and associations including motor sports, chess, and equestrian events. Rowing and yachting have a small but loyal following at the Madras Boat Club (1867) and the Royal Madras Yacht Club (1911). Guindy National Park is a wildlife sanctuary situated in the heart of the city. Other places for recreation in and around Chennai are the Chennai Crocodile Bank, Pulicat Lake (a large saltwater lagoon), a bird sanctuary, and a zoological park.

Chennai is well connected by road, rail, air, and sea. It has an international airport and seaport. Within the city a network of bus services and auto-rickshaws are common modes of transport. The historic town of Mamallapuram with its shore temple, about 37 miles (60 km) south of Chennai, is a popular tourist destination.

Jai Ganesh · 2019-06-12 00:26:25

357) Fire engine

Fire engine, also called fire truck, mobile (nowadays self-propelled) piece of equipment used in firefighting. Early fire engines were hand pumps equipped with reservoirs and were moved to the scene of a fire by human or animal power. For large fires, the reservoir was kept filled by a bucket brigade, but that method was inefficient, and the short range of the stream of water necessitated positioning the apparatus dangerously close to the fire. The introduction of more-powerful pumps and flexible hose solved this problem, and a great advance was made with the introduction of the steam-powered pump in many large cities in the 19th century. Steam-powered fire engines were used in the Chicago Fire of 1871. A steam engine remained in use by the New York City Fire Department as late as 1932.

Horse traction was replaced early in the 20th century by the internal-combustion engine, which also was used to power the pump. The basic automotive hose carrier quickly assumed its modern form; it carries a powerful pump, a large amount of hose (usually about 1,000 feet, or 300 metres), and a water tank for use where a supply of water is not available. Specialized auxiliary vehicles were also soon developed, including water tank trucks for rural areas. The ladder truck (hook and ladder) mounts a ladder that may be capable of rapid extension to 150 feet, often with a large-capacity nozzle built into the top section. The older type of overlength ladder truck is equipped with steerable rear wheels for negotiating city streets. The main ladder is mounted on the truck’s body; when it is to be raised into the air, the hinged main ladder and its sliding extensions are moved into place by a hydraulic pump. The ladder truck carries some 200 feet or more of ladders to be used from the ground. The snorkel truck, introduced by the Chicago Fire Department in 1958, is equipped with a hydraulically operated crane mounted on a turntable, for use in either firefighting or rescue work. The rescue truck carries such specialized equipment as cutting and wrecking tools, gas masks and inhalators, portable lighting and smoke-ejection devices, chemical extinguishers, life nets, shortwave radios, and medical equipment.

How Fire Engines Work

We see fire engines all the time, but have you ever stopped to think about all of the things that these machines do? Fire engines are amazing pieces of equipment that allow firefighters to perform their jobs and get to fire scenes quickly. The important thing to know about a fire engine is that it is a combination of a personnel carrier, tool box and water tanker. All three components are essential to fighting fires.
With different fire departments having varying needs, fire engines come in all shapes, sizes and colors. In this article, we will take a close look at an Emergency One (E-One) pumper/tanker engine and a Pierce ladder truck. We'll also open up all the doors and compartments on these trucks and see what's inside!

Pump It Up

The primary function of any pumper/tanker fire engine is to carry water in a water tank or drag water in from an outside source, such as a fire hydrant, drop tank, swimming pool or lake.

On this pumper/tanker fire engine, the primary water tank is inside the vehicle, it holds 1,000 gallons (3,785 liters) of water and it runs down the center in the rear of the truck. A drop tank is like a big aboveground pool that can hold about 2,000 gallons of water. A 6-inch diameter, hard suction line is used to drag water out of the drop tank or other exterior water source.

Water stored in the engine's tank or sucked through an outside source is then discharged through water lines, or hoses. These lines are connected at points around the truck. We'll look at all the different lines later.

The heart of the pump/tanker is the impeller water pump. On this particular fire engine, the pump is located just behind the jumpseat area, where the firefighters sit. An impeller is a rotor-like device that has curved blades. Driven by its own diesel engine, the impeller spins inside the pump at a high rate. When water comes into the pump, it hits the inner part of the impeller and is slung outward. Water pressure is created by centrifugal force from the spinning action of the impeller. A valve opens to allow water to hit the center of the rotating impeller. This action is described as entering the eye of the impeller, according to Capt. David Price of the Bayleaf Volunteer Fire Department in North Carolina.

You control the hoses using the truck's pump panel on top of the fire engine. The pump panel is a series of levers and switches that controls how much water is flowing and which lines are being discharged. When arriving at a fire scene, the driver will jump out and climb to the top of the truck to begin pump operation. An indicator -- a series of red lights on the pump panel -- lets the operator know how much water is left in the tank.

The first thing the pump operator is going to do is make sure that the valve between the tank and pump is open. An electric switch on the right side of the pump will open that valve, and ensure that water is flowing into the pump. Next, the operator will check to see which lines have been pulled off the fire engine by the firefighters, and the operator will discharge those lines. "Discharge" means that water is allowed to flow out of the pump and into the hose. The lines are color-coded to make it easy for the operator to know which lines to discharge. The color of the line corresponds to a plate below each lever on the pump panel.

Most of the discharging is controlled by a built-in electronic device, called a mastermind. It automatically controls the pump, and runs the pressure up or down. It also has a built-in relief valve, so that if one person suddenly cuts off a line, the pressure from that line doesn't automatically get fed into another line.
This truck also has a foam system, and carries about 20 gallons (76 L) of foam. The foam tank is embedded in the main water tank. Pumper/tankers carry different types of foam. This particular truck carries Class A foam, which can be used to saturate materials inside a structure to keep those materials from re-igniting. Class B foam is used to fight car fires and other fires where flammable liquids might be present.

In the next section, you'll learn more about the various hoses on the fire engine.

Hose It Down

There are many types of hoses on the fire engine, and each has its own specific role in putting out a blaze. Hoses, also called lines, will put out different amounts of water depending on the hose length, diameter and the amount of pressure in the pump.

When responding to a house fire, the firefighters will immediately pull off the crosslay hoses. These lines are located directly below the pump panel. They lay out in the open and are light, so they are easy to get off the fire engine for attacking a fire. Crosslays are 200 feet (61 m) long, have a diameter of 1.5 inches and can gush water at 95 gallons (360 L) per minute. For smaller fires, such as small wood fires or chimney fires, the small booster line is adequate. A booster line is the smallest hose on the truck and has a diameter of about 1 inch.

Located directly above the pump panel is the deluge gun, also called a deck gun or master stream. Just by looking at it, you know why this water cannon carries those names. The deluge gun is used to put a lot of water on large fires. It can put out in excess of 1,000 gallons per minute.

"If we get a big fire, like a house fire that we can't control with handlines, we can darken it down with that," Doug Mchose, of the Bayleaf Volunteer Fire Department, said. "We can use that on it for a couple of minutes to knock it down to where we can get in there."

The truck also has at least three lines called preconnects. These lines are preconnected to the truck in order to save time at the fire scene. There's one preconnect on the driver's side, one on the back and one on the captain's side of the truck. These lines are between 1.5 and 2.5 inches in diameter, and can put out 250 gallons (946 liters) per minute.

A 5-inch-diameter hose is stored on top of the truck. There is a total of 1,000 feet (305 m) of this line, but it is stored in 100-foot sections. This is the line that the firefighters will hook up to fire hydrants. There's also another 2.5-inch line stored on top of the truck.

In one of the compartments on the captain's side of the truck, there are extra sections of hose. There are two extra sections of the 5-inch hose: a 25-foot and a 50-foot section. These two sections are called curb jumpers, because they typically lay on the curb. These sections give firefighters just a little bit more line to connect to a fire hydrant without having to get another 100-foot section down.

Also stored in this compartment is a hose pack. A hose pack is a small, bundled hose that can be taken to the higher levels of a building. It is banded to make it easier to carry up a ladder. A firefighter can just throw it over his or her shoulder and take it up and through a window. Usually, a hose pack is used if the other lines can't reach inside. This hoseline will connect to the hose that runs up the ladder of the ladder truck, which you will learn more about in the next section.

Going Up!

When a fire breaks out in a multi-story building, a ladder truck is used to get firefighters to the higher floors.

The ladder on the truck is raised and lowered using a hydraulic piston rod. As hydraulic fluid enters this piston rod through one of two hoses, the pressure of the fluid will either cause the rod to extend or retract. If the piston rod extends, the ladder will go up. If it retracts, the ladder will come down.

Another set of hydraulic hoses allow the sections of the ladder to telescope up and down. A hydraulic motor is used to rotate the gear that moves the ladder from left to right. While the ladder is in use, four outriggers are extended to stabilize the truck.

On this 105-foot (32-m) ladder truck built by Pierce, the ladder also has a 3-inch pipe that runs the length of the ladder. This is an extra water line that is sometimes used to spray water on fires that are in a high spot, or to spray water down on a fire. This pipe can spray out 1,000 gallons per minute.

The ladder is controlled by a series of joysticks at the base of the ladder. The outriggers are controlled in the back of the truck. Each outrigger has four control levers: two for extending the beam out and two for lowering the leg to the ground. Metal pads are placed under the legs to prevent the force of the truck from cracking asphalt surfaces.

The Ultimate Mobile Toolbox

Firefighters have to take dozens of tools and other equipment when responding to a fire or medical call. All of this equipment is stored in several compartments that line the sides and back of the fire engine.

Let's open up each compartment and see what's inside.

Here is a list of some of the tools found on a fire engine:

• Barrel strainer - This is an attachment put on a hard suction hose when sucking water out of a lake or pond. This tool keeps debris out of the water supply.
• Nozzles - Different nozzles are needed for different situations. Fog nozzles put out more of a strong mist of water. Other nozzles direct water in a solid stream. There's also a piercing nozzlethat can be used to punch through walls and spray areas that can't be reached otherwise.
• Foam inductor - This is a special nozzle used to mix water and foam.
• Haligan tool - This tool looks similar to a crowbar.
• Sheet rock puller - This tool is used to peel back the sheet rock on walls so that water can be sprayed inside the wall.
• Pike poles - These spear-like tools are about 10 to 12 feet long and are thrust into the ceiling to pull sheet rock down.
• EMS equipment - Most fire engines carry a defibrillator, an emergency oxygen tank and a trauma jump kit, which includes all of the first aid equipment needed for emergencies.
• Gated Y - This special hose adapter can be attached to a line to allow two smaller lines to run off of the same water source.
• Spanner wrenches - These unique tools are used to tighten the lines to the fire engine or to a hydrant.
• Hydrant wrench - This is the wrench used to turn the hydrant on.
• Jaws of Life - This extrication equipment is used to free victims from car or building accidents. Read How the 'Jaws of Life' Work to learn more about these hydraulic machines.
• Exhaust fan - This fan is placed in the doorway to drag smoke out of the house. Fire engines may also carry a positive-pressure exhaust fan, which blows air through the house and out the other side.
• Salvage covers - These are used for covering furniture on a lower floor while firefighters attack a fire on a floor above.

In addition, fire engines also carry bolt cutters, a sledge hammer, a fire extinguisher, a water cooler, a 24-foot (7-m) extension ladder and a 16-foot (5-m) roof ladder. Some trucks may also carry chain saws, rappelling rope and backboards, which are used to transport injured people.
As you can see, there are a lot of tools and devices stored on a fire engine, and the design of the fire engine maximizes all possible storage space.

Grab a Seat

The unique design of a fire engine allows it to carry a lot of crew to the fire scene. Up to eight firefighters, including the driver and the captain, can fit onto this E-One fire engine. The cabin of the fire engine is divided into two sections: the front seat, where the driver and captain sit, and the jumpseat area, where the firefighters sit.

As mentioned before, the driver is responsible for controlling the pump panel. For this reason, there are some basic controls on the driver's dashboard that are related to that task. Two red switches near his left hand operate a generator and jet dump. A jet dump essentially discharges all of the water in the tank into a drop tank through a large discharge outlet in the back.

The driver has another switch within reach that activates the automatic tire chains, which are sometimes needed during the winter to drive through ice and snow. Automatic tire chains save the time and hassle of jacking the truck up and putting tire chains on manually. Click here to learn more about automatic tire chains.

The captain sits in the passenger seat next to the driver in the front section of the cab. The front section of the cab has a firecom, which are radio headsets that allow the captain and driver to communicate with the firefighters sitting in the jumpseat area. The captain will often give instructions to the firefighters on the way to the fire scene.

The jumpseat area is like the backseat of your car. This is the area where four to six firefighters sit on the way to the fire. There is one row of four seats that sit back-to-back with the captain and driver. There are also two fold-down seats directly across from the row of four seats. In between the fold-down seats, there several yellow pouches that contain the firefighters' masks.

Air packs are located in the back of the four main seats. By already having the air packs on the truck, all the firefighters have to do is put them on their shoulders. Each air pack has 30 minutes of air.

smpo0623engines01.jpg?w=400

Jai Ganesh · 2019-06-14 00:38:37

358) Duralumin

Duralmin, strong, hard, lightweight alloy of aluminum, widely used in aircraft construction, discovered in 1906 and patented in 1909 by Alfred Wilm, a German metallurgist; it was originally made only at the company Dürener Metallwerke at Düren, Germany. (The name is a contraction of Dürener and aluminum.) The original composition has been varied for particular applications; it may contain about 4 percent copper, 0.5–1 percent manganese, 0.5–1.5 percent magnesium, and, in some formulations, some silicon. After heat treatment and aging, these alloys are comparable to soft steel in strength.

Duralumin alloys are relatively soft, ductile, and workable in the normal state; they may be rolled, forged, extruded, or drawn into a variety of shapes and products. Their light weight and consequent high strength per unit weight compared with steel suit them for aircraft construction. Because aluminum loses corrosion resistance when alloyed, a special laminated sheet form called alclad is used for aircraft construction; it has thin surface layers of pure aluminum covering the strong duralumin core.

Duralumin is an alloy, a trade name given to the earliest types of the age hardenable aluminum alloys. It is an alloy made up of 90% aluminum,4% copper, 1% magnesium and 0.5% to 1% manganese. It is a very hard alloy. These alloys are used in places where hard alloys are required, for example in the vehicle armor that is used in the defense industry. These alloys were the first widely used deformable aluminum alloys.

Duralumin is a hard, but a lightweight alloy of aluminum. It has a typical yield strength of 450 Mpa, and there are certain other variations, that depend on the composition, type and temper.

Duralumin Metal

Duralumin is actually a metal, which us an alloy of aluminum, copper, magnesium and manganese. Duralumin is a special kind of metal, and is made strong by subjecting it to heat treatment. It may be well spun, tempered, riveted, welded or machinated. The duralumin, which is effectively given heat treatment, can be effectively being resistant to corrosion. It can carry heavy loads, and is ductile. It is specially suited for aircraft construction.

When copper is added to the alloy, its strength increases, but then it also makes it susceptible to corrosion. For the duralumin sheet products, the metallurgical bonding of the highly pure metal layer can increase the corrosion resistance. These sheets are called alclad, and are generally used by the aircraft industry.

Duralumin Properties

Duralumin is a strong, light weighted and hard alloy of aluminum. It is also reflective and impermeable. It is a malleable metal, and can be easily shaped. It is a very good conductor of heat and electricity. It is odorless, and reacts with the oxygen that is around, and forms aluminum oxide. It is resistant to corrosion. It has a thin surface, which is made up of a layer of pure aluminum, which is corrosion resistant, and covers the core of the strong duralumin. Generally, Duralumin alloys are soft, ductile and workable when they are in normal state. They can be easily rolled, folded or forged. They can also be drawn into a variety of shapes and forges. It has a high strength, which can be easily lost during wielding. So it can be easily transformed, and hence is used in aircraft construction. It is suited for aircraft construction because of its lightweight and high strength.

Duralumin Uses

Duralumin has the following uses:

• It is used for making wire, bar and rods for the screw machine products. It is used in places where good strength and good machinability are required.
• It is used in heavy-duty forgings, wheels, plates, extrusions, aircraft fittings, space booster tankage and trauck frame, and other suspension components. It finds applications in places where high strength is required, and services at elevated temperatures.
• It is used for making Aircraft structure, truck wheels, screw machine products, rivets and other structural application products.
• It is used as a sheet for the auto body panels.
• It is also used in forgings, in aircraft engine pistons, impellers of the jet engine sand the compressor rings.
• It is also used for making die and hand forgings.

There is a proper method that is used for the conversion of Duralumin into ingots. It has to undergo a high pressure before being converted to ingots. This pressure treatment includes rolling, pressing and so on. It is then converted to plates, sections, sheets, tubes and wires. It is quenched in water at a temperature of about 500 degree Celsius, for about four days. This is called natural aging. Often, it undergoes artificial aging at a temperature of about 190 degree Celsius, This heat treatment ultimately leads to the inculcation of various strengths in duralumin. In fact, the initial period in which metal airplane was constructed with duralumin; it had to go through these processes. Duralumin is also used widely in the surface transportation, aviation and mechanical engineering.

Jai Ganesh · 2019-06-16 00:57:15

359) Piezoelectricity

You've probably used piezoelectricity (pronounced "pee-ay-zo-electricity") quite a few times today. If you've got a quartz watch, piezoelectricity is what helps it keep regular time. If you've been writing a letter or an essay on your computer with the help of voice recognition software, the microphone you spoke into probably used piezoelectricity to turn the sound energy in your voice into electrical signals your computer could interpret. If you're a bit of an audiophile and like listening to music on vinyl, your gramophone would have been using piezoelectricity to "read" the sounds from your LP records. Piezoelectricity (literally, "pressing electricity") is much simpler than it sounds: it just means using crystals to convert mechanical energy into electricity or vice-versa. Let's take a closer look at how it works and why it's so useful!

What is piezoelectricity?

Squeeze certain crystals (such as quartz) and you can make electricity flow through them. The reverse is usually true as well: if you pass electricity through the same crystals, they "squeeze themselves" by vibrating back and forth. That's pretty much piezoelectricity in a nutshell but, for the sake of science, let's have a formal definition:

Piezoelectricity (also called the piezoelectric effect) is the appearance of an electrical potential (a voltage, in other words) across the sides of a crystal when you subject it to mechanical stress (by squeezing it).

In practice, the crystal becomes a kind of tiny battery with a positive charge on one face and a negative charge on the opposite face; current flows if we connect the two faces together to make a circuit. In the reverse piezoelectric effect, a crystal becomes mechanically stressed (deformed in shape) when a voltage is applied across its opposite faces.

What causes piezoelectricity?

Think of a crystal and you probably picture balls (atoms) mounted on bars (the bonds that hold them together), a bit like a climbing frame. Now, by crystals, scientists don't necessarily mean intriguing bits of rock you find in gift shops: a crystal is the scientific name for any solid whose atoms or molecules are arranged in a very orderly way based on endless repetitions of the same basic atomic building block (called the unit cell). So a lump of iron is just as much of a crystal as a piece of quartz. In a crystal, what we have is actually less like a climbing frame (which doesn't necessarily have an orderly, repeating structure) and more like three-dimensional, patterned wallpaper.

In most crystals (such as metals), the unit cell (the basic repeating unit) is symmetrical; in piezoelectric crystals, it isn't. Normally, piezoelectric crystals are electrically neutral: the atoms inside them may not be symmetrically arranged, but their electrical charges are perfectly balanced: a positive charge in one place cancels out a negative charge nearby. However, if you squeeze or stretch a piezoelectric crystal, you deform the structure, pushing some of the atoms closer together or further apart, upsetting the balance of positive and negative, and causing net electrical charges to appear. This effect carries through the whole structure so net positive and negative charges appear on opposite, outer faces of the crystal.

The reverse-piezoelectric effect occurs in the opposite way. Put a voltage across a piezoelectric crystal and you're subjecting the atoms inside it to "electrical pressure." They have to move to rebalance themselves—and that's what causes piezoelectric crystals to deform (slightly change shape) when you put a voltage across them.

What is piezoelectricity used for?

There are all kinds of situations where we need to convert mechanical energy (pressure or movement of some kind) into electrical signals or vice-versa. Often we can do that with a piezoelectric transducer. A transducer is simply a device that converts small amounts of energy from one kind into another (for example, converting light, sound, or mechanical pressure into electrical signals).

In ultrasound equipment, a piezoelectric transducer converts electrical energy into extremely rapid mechanical vibrations—so fast, in fact, that it makes sounds, but ones too high-pitched for our ears to hear. These ultrasound vibrations can be used for scanning, cleaning, and all kinds of other things.

In a microphone, we need to convert sound energy (waves of pressure traveling through the air) into electrical energy—and that's something piezoelectric crystals can help us with. Simply stick the vibrating part of the microphone to a crystal and, as pressure waves from your voice arrive, they'll make the crystal move back and forth, generating corresponding electrical signals. The "needle" in a gramophone (sometimes called a record player) works in the opposite way. As the diamond-tipped needle rides along the spiral groove in your LP, it bumps up and down. These vibrations push and pull on a lightweight piezoelectric crystal, producing electrical signals that your stereo then converts back into audible sounds.

In a quartz clock or watch, the reverse-piezoelectric effect is used to keep time very precisely. Electrical energy from a battery is fed into a crystal to make it oscillate thousands of times a second. The watch then uses an electronic circuit to turn that into slower, once-per-second beats that a tiny motor and some precision gears use to drive the second, minute, and hour hands around the clock-face.

Piezoelectricity is also used, much more crudely, in spark lighters for gas stoves and barbecues. Press a lighter switch and you'll hear a clicking sound and see sparks appear. What you're doing, when you press the switch, is squeezing a piezoelectric crystal, generating a voltage, and making a spark fly across a small gap.
If you've got an inkjet printer sitting on your desk, it's using precision "syringes" to squirt droplets of ink onto the paper. Some inkjets squirt their syringes using electronically controlled piezoelectric crystals, which squeeze their "plungers" in and out; Canon Bubble Jets fire their ink by heating it instead.

Energy harvesting with piezoelectricity?

If you can make a tiny bit of electricity by pressing one piezoelectric crystal once, could you make a significant amount by pressing many crystals over and over again? What if we buried crystals under city streets and pavements to capture energy as cars and people passed by? This idea, which is known as energy harvesting, has caught many people's interest. Inventors have proposed all kinds of ideas for storing energy with hidden piezoelectric devices, from shoes that convert your walking movements into heat to keep your feet warm, and cellphones that charge themselves from your body movements, to roads that power streetlights, contact lenses that capture energy when you blink, and even gadgets that make energy from the pressure of falling rain.

Is energy harvesting a good idea? At first sight, anything that minimizes waste energy and improves efficiency sounds really sensible. If you could use the floor of a grocery store to capture energy from the feet of hurrying shoppers pushing their heavy carts, and use that to power the store's lights or its chiller cabinets, surely that must be a good thing? Sometimes energy harvesting can indeed provide a decent, if rather modest, amount of power.

The trouble is, however, that energy harvesting schemes can be a big distraction from better ideas. Consider, for example, the concept of building streets with piezoelectric "rumble strips" that soak up energy from passing traffic. Cars are extremely inefficient machines and only a small amount (15 percent or so) of the energy in their fuel powers you down the road. Only a fraction of this fraction is available for recovery from the road—and you wouldn't be able to recover all that fraction with 100 percent efficiency. So the amount of energy you could practically recover, and the efficiency gain you would make for the money you spent, would be minuscule. If you really want to save energy from cars, the sensible way to do it is to address the inefficiencies of car transportation much earlier in the process; for example, by designing engines that are more efficient, encouraging people to car share, swapping from gasoline engines to electric cars, and things of that sort.

That's not to say that energy harvesting has no place; it could be really useful for charging mobile devices using energy that would otherwise go to waste. Imagine a cellphone that charged itself automatically every time it jiggled around in your pocket, for example. Even so, when it comes to saving energy, we should always consider the bigger picture and make sure the time and money we invest is producing the best possible results.

Who discovered piezoelectricity?

The piezoelectric effect was discovered in 1880 by two French physicists, brothers Pierre and Paul-Jacques Curie, in crystals of quartz, tourmaline, and Rochelle salt (potassium sodium tartrate). They took the name from the Greek work piezein, which means "to press."

Jai Ganesh · 2019-06-18 01:58:57

360) Owl

Owl, (order Strigiformes), any member of a homogeneous order of primarily nocturnal raptors found nearly worldwide.

The bird of Athena, the Greek goddess of practical reason, is the little owl(Athene noctua). Owls became symbolic of intelligence because it was thought that they presaged events. On the other hand, because of their nocturnal existence and ominous hooting sounds, owls have also been symbols associated with the occult and the otherworldly. Their secretive habits, quiet flight, and haunting calls have made them the objects of superstition and even fear in many parts of the world. In the Middle Ages the little owl was used as a symbol of the “darkness” before the coming of Christ; by further extension it was used to symbolize a nonbeliever who dwells in this darkness. Similarly the barn owl (Tyto alba) was looked upon as a bird of ill omen, and it subsequently became a symbol of disgrace. Scientific study of owls is difficult owing to their silent nighttime activity, with the result that the ecology, behaviour, and taxonomy of many species remain poorly understood.

General Features

The size range of owls is about the same as that of their day-active counterparts, the hawks, with lengths of about 13–70 cm (5–28 inches) and wingspans between 0.3–2.0 metres (1–6.6 feet). Most owl species are at the lower end of the size range. Owls apparently feed only on animals. Rodents are the most common prey; the smaller species, however, eat insects. All owls have the same general appearance, which is characterized by a flat face with a small hooked beak and large, forward-facing eyes. The tail is short and the wings are rounded. Like the diurnal birds of prey (order Falconiformes), they have large feet with sharp talons. Diversity occurs in size, in the presence or absence of “ear” tufts, and in the shape of the plumage around the face.

Owls are found on all continents except Antarctica and on most oceanic islands. Some, such as the barn owl (Tyto alba) and the short-eared owl (Asio flammeus), are among the most widely distributed birds; others, such as the Palau owl (Pyrroglaux podargina) and the Seychelles owl (Otus insularis), are endemic island species with small populations. Owls often attain higher population densities than hawks and have survived better in areas of human activity. Their nocturnal habits and inconspicuous daytime behaviour provide them some protection from shooting. The greatest population densities are attained by small, territorial, insectivorous species, with pairs spaced about 200 metres (660 feet) apart in suitable woodland.

Natural History

Ecology

Owls utilize virtually all habitats, from grassland and tundra to dense woodland and rainforest. The distribution and density of most species seem to be limited by the availability of suitable nesting sites, rather than by the number of potential prey animals. In general the type of prey taken is dictated by the size of the owl and by the relative abundance of potential prey. Owls that hunt over grassland, such as the barn owl and short-eared owl, hunt by sustained flight, dropping into the grass to catch rodents. Many woodland owls secure prey by dropping from perches at the edges of forest openings. The Southeast Asian hawk owl (Ninox scutulata) sallies from a perch to take flying insects. The whiskered owl (Otus trichopsis) takes flying insects in foliage. Fish owls (Ketupa and Scotopelia) are adapted for taking live fish but also eat other animals. Specialized forms of feeding behaviour have been observed in some owls. The elf owl (Micrathene whitneyi), for instance, has been seen hovering before blossoms, where it scares insects into flight with its wings and then catches them with its beak. A bay owl (Phodilus badius) has been documented stationing itself within a cave to catch bats as they issued forth at dusk. A variety of owls may depend on a single prey species when it becomes exceptionally abundant. Prey is generally swallowed whole, and indigestible material, such as feathers, fur, and bones, are regurgitated in the form of a compact pellet.

Behaviour

Sound is important to owls, especially in mating and territorial defense. Camouflage, daytime immobility, and silent flight may combine to make it as difficult for owls to see each other as it is for natural enemies and human observers to see them. Usual owl sounds include snaps of the bill, claps of the wings in flight, and a variety of vocalizations, with pitches, timbres, and rhythms unique to each species. Pitch differs between sexes (the female higher). Although less melodious than the calls of some birds, the vocalizations of many owls are “songs” in the biological sense and can even be musical to the human ear. The song varies from deep hoots in some large species to chirps, whistles, or warblings in many small owls. When nestlings of the burrowing owl (Speotyto cunicularia) are threatened, the young emit a call that resembles the warning buzz of a rattlesnake—a frequent inhabitant of rodent burrows.

In North American screech owls (genus Otus), a duet that seems to reinforce the pair bond starts with a special song by the male. He is eventually answered in kind by the female, often from a distance. After 10 to 15 minutes of antiphonal (answering) singing, during which the two approach each other, the pair switches to a second duet, during which they meet. In the early spring this may be followed by precopulatory calls and posturing, then mating. Other calls of the screech owl include a note uttered by the female to stimulate the young to reveal their location after they have left the nest; a food-soliciting call by the young; and barking calls accompanied by bill-snapping, which indicate that the young are being ejected from the territory. Calls are also used during the adjustment of territorial boundaries. In many smaller species that do not normally sing duets, the male may sing all night from a single perch.

The nocturnal routine of most owls involves peaks of activity at dusk and dawn. The owl leaves its secluded roost about dusk and moves to a perch overlooking the hunting area. There is a brief period of song, followed by about half an hour of foraging, then a longer period of song. Most of the darker hours of the night are spent inactively, with a period of alternating singing and hunting just before dawn.

Posturing by singing owls indicates that they communicate by sight as well as by sound. The male horned owl (Bubo virginiatus) bows deeply with each song and raises the tail over the back. The wood owls (Strixspecies) engage in bowing, bobbing, and dancing, especially when courting. A defense display given by most large owls when threatened or when defending the nest involves increasing apparent body size by spreading the wings halfway and rotating them forward. The body feathers are raised, and the fearsome appearance is enhanced by snapping the bill and rocking the body from side to side. When seeking to avoid attention at its daytime roost (especially when being attacked by small birds), the owl compresses the plumage, elevates the ear tufts, and half closes the eyes. Combined with its barklike colour and pattern of the plumage, the owl looks like a broken branch.

Reproduction and development

Most owls nest in natural cavities in trees or cliffs or in woodpecker holes. The barn owls and the Eurasian little owls (Athene species) frequently use cavities in buildings. Some of the larger owls utilize old hawk or crow nests. Grassland and tundra owls nest on the ground, sometimes on an elevated hummock, and the burrowing owl digs a nest chamber in a rodent burrow. The laughing owl (Sceloglaux albifacies) was a ground-nester endemic to New Zealand that was driven to extinction in the early 1900s by animals introduced to the islands by settlers.

Frequently the nest cavity provides a daytime roost for one or both of the pair during the nonbreeding months. Most owls add no nesting material to the site, but the fur and feathers of accumulated prey remains and regurgitated pellets may provide some cushion for the eggs. When an open nest is used, leaves, grass, or other soft material may be added as a lining. The great gray owl (Strix nebulosa) occasionally constructs its own platform nest in a tree. In desert areas the smaller owls rely primarily on holes made by woodpeckers in large cacti. Intense competition has been observed among nesting birds, including owls, for occupancy of a limited number of nest sites. The invasion of saguaro desert habitats by the European starling (Sturnus vulgaris) has had a serious effect on small owls and other cactus-dwelling birds. The aggressive and abundant starlings occupy cavities before other species have returned from wintering grounds and successfully defend the holes against native species.

Egg laying is timed such that the young become independent of their parents at a time when prey populations are greatest. At northern latitudes, many owls nest in the spring a month or two earlier than hawks, with the result that an incubating owl is frequently covered by several inches of snow. Barn owls have been found nesting in every month of the year, even at the northern edge of their range, but the peak of nesting is in the spring. Owls lay more eggs than most diurnal raptors, with clutches of up to 12 in the snowy owl (Nyctea scandiaca). In years of lemming abundance, snowy owls attain higher nesting densities, nest earlier, lay more eggs, and have higher fledging rates than when lemmings are scarce. The eggs of owls are more spherical than those of any other bird group, the long diameter averaging only about 1.2 times the short diameter. They are typically laid at two-day intervals, but hatching is not synchronized. The result is that the oldest and youngest nestlings of a large brood may be hatched two or three weeks apart. If the prey populations are inadequate for the adult owls to support the entire large brood, the younger nestlings starve, while the more aggressive older ones are able to maintain normal growth rates and are strong at fledging.

While in the nest, young owls grow two successive coats of white natal down. In the smaller species, the down is replaced by the immature juvenal plumage of softer, lacier texture than that of the adult. At this age, about two-thirds of the way to fledging, the young owls may leave the nest and spend the day several metres from it. In the screech owl, the juvenal plumage has fine barring, unlike the streaking of the adult. The first flight feathers, which appear about the same time, are like those of the adult but are more pointed. In the fall, only a few weeks after its acquisition, this plumage is replaced in a complete molt that introduces a plumage identical to that of the adult. In the larger owls (several species of Bubo), the juvenal plumage resembles that of the adult. Exceptions are the spot-bellied eagle owl (B. nipalensis) and the barred eagle owl (B. sumatranus), which are mostly white, with a pattern of black markings different from that of the adult.

Locomotion

Most owls use their feet only for perching and grasping prey. The burrowing owls, however, being terrestrial, can run rapidly over the ground and rarely perch in vegetation. The typical owl perch is a horizontal branch in a tree. The bay owl habitually perches vertically on the trunk of a tree, with the legs reaching sideways, one foot above the other. The body is held in a vertical position as though the owl were perched on a horizontal limb.

The flight of owls is a steady flapping on a straight path, ending in a short upward glide to the perch. Hunting, usually done from a perch, rarely involves extensive flight, requiring only a short burst of speed to surprise the prey on the ground. Forest owls rarely fly above the canopy of the foliage, but the Southeast Asian hawk-owl (genus Ninox) has been observed high in the air, flapping—or, on one occasion, soaring—in circles through swarms of bats, apparently without catching any. A few grassland and tundra owls hunt in sustained flight and have proportionately more wing area than their forest-dwelling relatives. Short-eared owls flap slowly, the large area of the wings causing the light body to bob up and down; they also glide for brief periods with the wings held in a high V over the back.

Form And Function

All owls share the same general body plan. The wings are long and rounded, the tail short. The legs and toes are of medium length and exceptionally strong for the size of the bird. Each toe is provided with a needle-sharp, curved talon. The outer toe points rearward when perching and is normally directed outward or backward in taking prey, providing the maximum possible toe spread.

The head is broad to accommodate the exceptionally large eyes. The eyes are elongated forward, and each is encased in a tube made up of joined bony elements. Virtually immobile, the eye is rigidly encased. Remarkable flexibility of the neck compensates for the fixed position of the eyes; an owl can turn its head more than 180° in either direction and can thus look directly backward. The vision is binocular, and depth perception is often enhanced by moving the head away from the central plane. Various owls have only rods in the retina, resulting in an absence of colour vision but a great increase in visual acuity and light sensitivity. Contrary to popular opinion, owls are not blind in strong light. Their pupils, which operate independently, can be greatly reduced, protecting the sensitive retina and providing better daytime vision than that found in people.

The ears are large and surrounded by a ruff of papery feathers that serves to concentrate the sound. The feathers covering the ear opening are lacy and permeable to sound. A movable flap (operculum) on the front margin of the opening may function as a baffle to focus sounds. Some owls can locate and capture prey in total darkness, relying on their ability to localize the rustle of a mouse in leaves and to fly to that spot. In many owls the relative position of the ear opening is asymmetrical, being above a so-called blind cavity on one side of the head and below it on the other. The asymmetry is thought to be related to the sensitivity of each ear to sounds of various frequencies, providing the owl with the ability to localize sound sources in two planes simultaneously.

The plumage of owls is soft, dense, and loose. A thick layer of down provides northern owls with insulation against cold. The upper surfaces of the flight feathers of most species are provided with a nap that makes the flight perfectly noiseless, allowing the owl to hear prey without interference caused by the sound of flight. Many owls have erectile tufts of feathers (“ears” or “horns”) above the eyes. The tufts serve to break the round outline of the head, adding to the concealment gained from colour and pattern.

Owls vary in colour from white through many shades of tan, gray, brown, or rufous (reddish) to deep brown. A few are solidly coloured, but most are cryptically patterned with streaks, bars, or spots, often resulting in the bird’s being almost invisible against tree bark. This concealing pattern is well exemplified in the small screech owls. The soft brown, rufous, buff, or gray ground colour of each breast feather is adorned by a blackish bar, a shaft streak, or a combination of both, sometimes outlined in white or rufous. In some widespread species, such as the Eurasian scops owl (O. scops) and the screech owl, geographic variation is so great that some divergent races are more different from one another than some species are from one another. In the far north there is only a faint pattern on a whitish background; in humid temperate forests, a bold pattern on a sooty background; in desert areas, a medium-to-fine pattern on pale gray; in arid tropics, a fine pattern on rufous; and in humid tropics, a coarse pattern on fulvous. Size variation is also present, with northern birds weighing about twice as much as their southern counterparts. The horned owl exhibits similar variation. Screech, scops, and whiskered owls may be either gray or rufous; the base colour apparently is determined by a single gene. Such dimorphism in colour is found in only certain populations of each species: the southern in the whiskered owl and the eastern in the North American screech owl and the Eurasian scops owl. In each case, interbreeding between the uniformly coloured monomorphic and sexually distinct dimorphic populations is limited. The red phase of the screech owl may have survival value in the predominantly deciduous forest of eastern North America, blending with the foliage of summer and autumn, in which reds and browns are strongly represented.

Paleontology And Classification

Fossil history

The fossil history of owls dates to the beginning of the Paleocene Epoch65.5 million years ago, after which occurred a major diversification by the Eocene Epoch (55.8 to 33.9 million years ago). Some early owls reached far greater size than their modern descendants. A giant barn owl, about twice the size of the modern Tyto alba, inhabited Puerto Rico during the Pleistocene Epoch (2.6 million to 11,700 years ago). Another large owl, Ornimegalonyx oteroi from the Pleistocene of Cuba, apparently was flightless. Both owls must have exceeded the modern eagle owls in size.

Distinguishing taxonomic features

The owls form a homogeneous group readily distinguished from all other orders by their general body plan, soft plumage, and skeletal peculiarities. To determine relationships within the Strigiformes, taxonomists utilize features of the skull and the sternum, relative specializations of the eye and ear, and the development of the facial disk. Within some genera the taxonomy is very complex, relying on general proportions, behaviour, voice, and even parasites (feather lice).

Critical appraisal

Most current taxonomic problems are concerned with the placement of certain genera within the family and with the specific status of some populations of complex genera, such as Otus. Isolated populations with different voices are increasingly being recognized as separate species.

Nightjars (order Caprimulgiformes) are considered the owls’ closest relatives, though owls were once thought to be nocturnal raptors related to hawks and eagles (order Falconiformes). Fossil owls represent a variety of distinct families, but taxonomists have divided the order into only two families.

Monox D. I-Fly · 2019-06-18 15:45:57

ganesh wrote:

Most owls nest in natural cavities in trees or cliffs or in woodpecker holes.

Ah, the inspiration of the Flatwood Monster...

Jai Ganesh · 2019-06-18 17:15:26

Monox D. I-Fly wrote:

ganesh wrote:
Most owls nest in natural cavities in trees or cliffs or in woodpecker holes.
Ah, the inspiration of the Flatwood Monster...

Interesting!

In West Virginia folklore, the Flatwoods monster, also known as the Braxton County Monster or Phantom of Flatwoods, is an entity reported to have been sighted in the town of Flatwoods in Braxton County, West Virginia, United States, on September 12, 1952, following the appearance of a bright object crossing the night sky. Nearly fifty years later, investigators concluded that the light was a meteor and the creature was a barn owl perched in a tree, with shadows making it appear to be a large humanoid.

Monox D. I-Fly · 2019-06-18 18:55:56

ganesh wrote:

In West Virginia folklore, the Flatwoods monster, also known as the Braxton County Monster or Phantom of Flatwoods, is an entity reported to have been sighted in the town of Flatwoods in Braxton County, West Virginia, United States, on September 12, 1952, following the appearance of a bright object crossing the night sky.

Wait, Flatwood is the name of the place? I thought it was named Flatwood Monster because it was seen in the woods and had a flat face.

Jai Ganesh · 2019-06-19 00:03:39

Monox D. I-Fly wrote:

ganesh wrote:
In West Virginia folklore, the Flatwoods monster, also known as the Braxton County Monster or Phantom of Flatwoods, is an entity reported to have been sighted in the town of Flatwoods in Braxton County, West Virginia, United States, on September 12, 1952, following the appearance of a bright object crossing the night sky.
Wait, Flatwood is the name of the place? I thought it was named Flatwood Monster because it was seen in the woods and had a flat face.

In West Virginia folklore, the Flatwoods monster, also known as the Braxton County Monster or Phantom of Flatwoods, is an entity reported to have been sighted in the town of Flatwoods in Braxton County, West Virginia, United States, on September 12, 1952, following the appearance of a bright object crossing the night sky. Nearly fifty years later, investigators concluded that the light was a meteor and the creature was a barn owl perched in a tree, with shadows making it appear to be a large humanoid.

Jai Ganesh · 2019-06-20 00:34:28

361) Water cycle

Water cycle, also called hydrologic cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle remains essentially constant, its distribution among the various processes is continually changing.

Evaporation, one of the major processes in the cycle, is the transfer of water from the surface of the Earthto the atmosphere. By evaporation, water in the liquid state is transferred to the gaseous, or vapour, state. This transfer occurs when some molecules in a water mass have attained sufficient kinetic energy to eject themselves from the water surface. The main factors affecting evaporation are temperature, humidity, wind speed, and solar radiation. The direct measurement of evaporation, though desirable, is difficult and possible only at point locations. The principal source of water vapour is the oceans, but evaporation also occurs in soils, snow, and ice.

Evaporation from snow and ice, the direct conversion from solid to vapour, is known as sublimation. Transpiration is the evaporation of water through minute pores, or stomata, in the leaves of plants. For practical purposes, transpiration and the evaporation from all water, soils, snow, ice, vegetation, and other surfaces are lumped together and called evapotranspiration, or total evaporation.

Water vapour is the primary form of atmospheric moisture. Although its storage in the atmosphere is comparatively small, water vapour is extremely important in forming the moisture supply for dew, frost, fog, clouds, and precipitation. Practically all water vapour in the atmosphere is confined to the troposphere (the region below 6 to 8 miles [10 to 13 km] altitude).

The transition process from the vapour state to the liquid state is called condensation. Condensation may take place as soon as the air contains more water vapour than it can receive from a free water surface through evaporation at the prevailing temperature. This condition occurs as the consequence of either cooling or the mixing of air masses of different temperatures. By condensation, water vapour in the atmosphere is released to form precipitation.

Precipitation that falls to the Earth is distributed in four main ways: some is returned to the atmosphere by evaporation, some may be intercepted by vegetation and then evaporated from the surface of leaves, some percolates into the soil by infiltration, and the remainder flows directly as surface runoff into the sea. Some of the infiltrated precipitation may later percolate into streams as groundwater runoff. Direct measurement of runoff is made by stream gauges and plotted against time on hydrographs.

Most groundwater is derived from precipitation that has percolated through the soil. Groundwater flow rates, compared with those of surface water, are very slow and variable, ranging from a few millimetres to a few metres a day. Groundwater movement is studied by tracer techniques and remote sensing.

Ice also plays a role in the water cycle. Ice and snow on the Earth’s surface occur in various forms such as frost, sea ice, and glacier ice. When soil moisture freezes, ice also occurs beneath the Earth’s surface, forming permafrost in tundra climates. About 18,000 years ago glaciers and ice caps covered approximately one-third of the Earth’s land surface. Today about 12 percent of the land surface remains covered by ice masses.

Jai Ganesh · 2019-06-22 00:02:46

362) Transformer

Transformer, device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage. Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.

Transformers change voltage through electromagnetic induction; i.e., as the magnetic lines of force (flux lines) build up and collapse with the changes in current passing through the primary coil, current is induced in another coil, called the secondary. The secondary voltage is calculated by multiplying the primary voltage by the ratio of the number of turns in the secondary coil to the number of turns in the primary coil, a quantity called the turns ratio.

Air-core transformers are designed to transfer radio-frequency currents—i.e., the currents used for radio transmission; they consist of two or more coils wound around a solid insulating substance or on an insulating coil form. Iron-core transformers serve analogous functions in the audio-frequency range.

Impedance-matching transformers are used to match the impedance of a source and that of its load, for most efficient transfer of energy. Isolation transformers are usually employed for reasons of safety to isolate a piece of equipment from the source of power.

quality-engineering-bd-power-distribution-transformer.png

Jai Ganesh · 2019-06-24 01:27:40

363) Uninterruptible Power Supply (UPS)

An uninterruptible power supply (UPS) is a device that allows a computer to keep running for at least a short time when the primary power source is lost. UPS devices also provide protection from power surges.

A UPS contains a battery that "kicks in" when the device senses a loss of power from the primary source. If an end user is working on the computer when the UPS notifies of the power loss, they have time to save any data they are working on and exit before the secondary power source (the battery) runs out. When all power runs out, any data in your computer's random access memory (RAM) is erased. When power surges occur, a UPS intercepts the surge so that it does not damage the computer.

UPS in the data center

Every UPS converts incoming AC to DC through a rectifier and converts it back with an inverter. Batteries or flywheels store energy to use in a utility failure. A bypass circuit routes power around the rectifier and inverter, running the IT load on incoming utility or generator power.

While UPS systems are commonly called double-conversion, line-interactive and standby designs, these terms have been used inconsistently and manufacturers implement them differently: At least one system allows any of the three modes. The International Electro Technical Commission (IEC) adopted more technically descriptive terminology in IEC Std. 62040.

Types of UPSs and their core features

Voltage and frequency independent (VFI): Voltage and frequency independent (VFI) UPS systems are called dual or double conversion because incoming AC is rectified to DC to keep batteries charged and drive the inverter. The inverter re-creates steady AC power to run the IT equipment.

When power fails, the batteries drive the inverter, which continues to run the IT load. When power is restored, either from the utility or a generator, the rectifier delivers direct current (DC) to the inverter and simultaneously recharges the batteries. The inverter runs full time. Utility input is completely isolated from the output, and bypass is only used for maintenance safety or if there is an internal electronics failure. Since there is no break in the power delivered to the IT equipment, vacuum fault interrupter (VFI) is generally considered the most robust form of UPS. Most systems synchronize the output frequency with the input, but that's not necessary, so it still qualifies as frequency independent.

Every power conversion incurs a loss, so the wasted energy has historically been considered the price of ultimate reliability.

Voltage independent (VI): Voltage independent (VI), or true line interactive UPSs have a controlled output voltage, but the same output frequency as the input. Frequency independence is rarely a concern with power in developed countries. Utility power feeds directly to the output and IT equipment, and the rectifier keeps the batteries charged. The inverter is paralleled with the output, compensating for voltage dips and acting as an active filter for voltage spikes and harmonics. Rectifier and inverter losses only occur when incoming power fluctuates. Flywheels and motor/generator sets also qualify as VI.

When incoming power fails, or the voltage goes out of range, the bypass quickly disconnects from the input and the battery drives the inverter. When input power is restored, the bypass re-engages the input, re-charges the batteries and keeps output voltage constant. UPS vendors who use paralleled power sources claim no loss of reliability. The result is around 98% energy efficiency.

Voltage and frequency dependent (VFD): Voltage and frequency dependent (VFD), or standby UPS, is operationally similar to VI and is sometimes mistakenly called line interactive. In conventional VFD systems, the inverter is turned off, so it can take as long as 10 to 12 milliseconds (ms) to start creating power. That break can crash servers, making legacy VFD UPSs a bad fit for data centers.

New VFD concepts have the inverter producing power within 2 ms after being activated. The bypass is normally engaged, just as with VI, so equipment operates directly from the utility or generator. Since the inverter isn't working until power fails, there is no voltage control or power consumed, enabling efficiencies as high as 99%. Power failure or voltage outside of range opens the bypass switch, disengaging input from the output; the inverter starts operating from the batteries. The rectifier is only large enough to keep the batteries charged.

Advantages and disadvantages of UPS

Advantages to using uninterruptable power supplies include:

• No delay between switching from the primary power source to the UPS.
• Can better support critical instruments compared to generators.
• Consumers can choose the type and size of UPS, depending on the amount of power they need to supply to a device.
• UPSs are silent.
• Maintenance of UPS systems is cheaper compared to generators.

Disadvantages to using uninterruptable power supplies include:

• The inability to run heavy appliances- because UPSs are run off of batteries.
• If substandard batteries are used, users may end up replacing the batteries often.
• UPSs may need professional installations.

UPS VS. generators, surge protectors, inverters and AVRs

Unlike UPSs, generators do not seamlessly keep devices running once the primary device is lost. However, generators do provide power for a longer period of time compared to UPSs. UPS systems don’t provide power as long because batteries power them.

Surge protectors (suppressors) help prevent surges and high voltage spikes. However, surge protectors do not operate during power outages, or instances were the main power supply is cut from use.

Power inverters are devices that convert DC to AC. Power inverters are typically connected to an exterior DC source and continuously convert the current to AC. Power inverters commonly use one or more batteries to store power. Using power inverters, there is a delay in the transfer of power from a primary power source to a secondary power source when the main power is cut.

Automatic voltage regulators (AVRs) will control input voltages to minimize voltage fluctuations. AVRs are commonly used in both power converters and inverters.

Jai Ganesh · 2019-06-26 00:08:30

364) Underwater Diving

Underwater diving, also called underwater swimming, swimming done underwater either with a minimum of equipment, as in skin diving (free diving), or with a scuba (abbreviation of self-contained underwater-breathing apparatus) or an Aqua-Lung. Competitive underwater diving sports include spearfishing and underwater hockey, sometimes called “octopush.”

Underwater diving is as old as swimming and has been perpetuated into the present by pearl divers and sponge divers. Skin diving requires only a face mask or goggles, a short breathing tube (protruding from the mouth and kept above water), and flippers, or foot fins. A wet suit, a dry suit, or the latter over the former may be used in cold water. Skin diving was first popularized in the 1920s and ’30s in the Mediterranean and off the California coast, notably by the American diver Guy Gilpatric, whose ‘The Compleat Goggler’ (1938) gave great impetus to the sport and aroused the interest of the French naval engineer and diver Jacques Cousteau. The goggles, flippers, snorkel (the name given the air tube from the German submarine air exhaust and intake device that allowed submerged operation), and face mask were all developed into their basic forms in the 1930s.

Attempts to construct diving apparatus go back to the 19th century, but the sport of scuba, or Aqua-Lung, diving dates from 1943, when Cousteau and the French engineer Émile Gagnan developed the first fully automatic compressed-air Aqua-Lung. Cousteau also did important work on the development of underwater cameras and photography and popularized the sport in ‘Le Monde du silence’ (1952; The Silent World), written with Frédéric Dumas, and in other writings and television and film productions. Clubs formed after 1943 as fast as scuba equipment became available; national associations were formed in France, Italy, Great Britain, Canada, and the United States; and in 1959 Cousteau formed, with 15 national organizations (later more than 50), the Confédération Mondiale des Activités Subaquatique (CMAS; World Underwater Federation).

The fish hunted for food and the coral hunted for ornament by primitive divers are still sought by contemporary skin divers and scuba divers. An improved spear gun devised in the 1930s is used for food hunting, and special underwater cameras are widely used for recreational and scientific purposes. In addition, scuba diving has been useful scientifically in oceanography, in the study of fish and other marine organisms, and in the study of water pollution, as well as in the exploration of ships on the ocean floor and for salvage work, in which the earlier diving helmet with air line from on shipboard has been largely replaced.

diving-in-galapagos2.jpg?w=312&ssl=1

Jai Ganesh · 2019-06-28 01:21:15

365) Stonehenge

Stonehenge, prehistoric stone circle monument, cemetery, and archaeological site located on Salisbury Plain, about 8 miles (13 km) north of Salisbury, Wiltshire, England. It was built in six stages between 3000 and 1520 BCE, during the transition from the Neolithic Period (New Stone Age) to the Bronze Age. As a prehistoric stone circle, it is unique because of its artificially shaped sarsen stones (blocks of Cenozoic silcrete), arranged in post-and-lintel formation, and because of the remote origin of its smaller bluestones (igneous and other rocks) from 100–150 miles (160–240 km) away, in South Wales. The name of the monument probably derives from the Saxon stan-hengen, meaning “stone hanging” or “gallows.” Along with more than 350 nearby monuments and henges (ancient earthworks consisting of a circular bank and ditch), Stonehenge was designated a UNESCO World Heritage site in 1986.

Speculation And Excavation

Stonehenge has long been the subject of historical speculation, and ideas about the meaning and significance of the structure continued to develop in the 21st century. English antiquarian John Aubrey in the 17th century and his compatriot archaeologist William Stukeley in the 18th century both believed the structure to be a Druid temple. This idea has been rejected by more-recent scholars, however, as Stonehenge is now understood to have predated by some 2,000 years the Druids recorded by Julius Caesar.

In 1963 American astronomer Gerald Hawkins proposed that Stonehenge had been constructed as a “computer” to predict lunar and solar eclipses; other scientists also attributed astronomical capabilities to the monument. Most of these speculations, too, have been rejected by experts. In 1973 English archaeologist Colin Renfrew hypothesized that Stonehenge was the centre of a confederation of Bronze Age chiefdoms. Other archaeologists, however, have since come to view this part of Salisbury Plain as a point of intersection between adjacent prehistoric territories, serving as a seasonal gathering place during the 4th and 3rd millennia BCE for groups living in the lowlands to the east and west. In 1998 Malagasy archaeologist Ramilisonina proposed that Stonehenge was built as a monument to the ancestral dead, the permanence of its stones representing the eternal afterlife.

In 2008 British archaeologists Tim Darvill and Geoffrey Wainwright suggested—on the basis of the Amesbury Archer, an Early Bronze Age skeleton with a knee injury, excavated 3 miles (5 km) from Stonehenge—that Stonehenge was used in prehistory as a place of healing. However, analysis of human remains from around and within the monument shows no difference from other parts of Britain in terms of the population’s health.

The Stonehenge that is visible today is incomplete, many of its original sarsens and bluestones having been broken up and taken away, probably during Britain’s Roman and medieval periods. The ground within the monument also has been severely disturbed, not only by the removal of the stones but also by digging—to various degrees and ends—since the 16th century, when historian and antiquarian William Camden noted that “ashes and pieces of burnt bone” were found. A large, deep hole was dug within the stone circle in 1620 by George Villiers, 1st duke of Buckingham, who was looking for treasure. A century later Stukeley surveyed Stonehenge and its surrounding monuments, but it was not until 1874–77 that Flinders Petrie made the first accurate plan of the stones. In 1877 Charles Darwin dug two holes in Stonehenge to investigate the earth-moving capabilities of earthworms. The first proper archaeological excavation was conducted in 1901 by William Gowland.

About half of Stonehenge (mostly on its eastern side) was excavated in the 20th century by the archaeologists William Hawley, in 1919–26, and Richard Atkinson, in 1950–78. The results of their work were not fully published until 1995, however, when the chronology of Stonehenge was revised extensively by means of carbon-14 dating. Major investigations in the early 21st century by the research team of the Stonehenge Riverside Project led to further revisions of the context and sequence of Stonehenge. Darvill and Wainwright’s 2008 excavation was smaller but nonetheless important.

Stages Of Stonehenge

Stonehenge was built within an area that was already special to Mesolithic and Neolithic people. About 8000–7000 BCE, early Mesolithic hunter-gatherers dug pits and erected pine posts within 650 feet (200 metres) of Stonehenge’s future location. It was unusual for prehistoric hunter-gatherers to build monuments, and there are no comparable structures from this era in northwestern Europe. Within a 3-mile (5-km) radius of Stonehenge there remain from the Neolithic Period at least 17 long barrows (burial mounds) and two cursus monuments (long enclosures), all dating to the 4th millennium BCE. Between 2200 and 1700 BCE, during the Bronze Age, the Stonehenge-Durrington stretch of the River Avon was at the centre of a concentration of more than 1,000 round barrows on this part of Salisbury Plain.

First stage: 3000–2935 BCE

The oldest part of the Stonehenge monument was built during the period from 3000 to 2935 BCE. It consists of a circular enclosure that is more than 330 feet (100 metres) in diameter, enclosing 56 pits called the Aubrey Holes, named after John Aubrey, who identified them in 1666. The ditch of the enclosure is flanked on the inside by a high bank and on the outside by a low bank, or counterscarp. The diameters of the outer bank, the ditch, the inner bank, and the circle of Aubrey Holes are equivalent to 270, 300, 330, and 360 long feet (a long foot is an ancient unit of measurement equivalent to 1.056 statute feet or 0.32187 metre), respectively. Deposits in the bottom of the ditch included antler picks, which were used to dig the ditch itself, as well as bones of cattle and deer that were already centuries old when they were placed there. The circular enclosure had two entrances: the main access on the northeast and a narrower entrance on the south.

Although it once was believed that the Aubrey Holes served as pits for wooden posts, excavation and archival research by the Stonehenge Riverside Projectrevealed that they probably held Welsh bluestones.

Human cremation burials were found within and around most of the holes, as well as within the encircling ditch and bank. (Of an estimated 150–240 cremation burials at Stonehenge, 64 had been excavated by the first decade of the 21st century.) The great majority of the burials were of adult males, and pieces of unburned human bone were also found scattered around Stonehenge. The area surrounding the Aubrey Holes was used as a place of burial from roughly 3000 to 2300 BCE; it is the largest known cemetery from the 3rd millennium BCE in Britain.

A second, smaller bluestone circle, 30 feet (10 metres) in diameter and known as Bluestonehenge, was built on the bank of the River Avon over 1 mile (1.6 km) from the Aubrey Holes. Found by the Stonehenge Riverside Project in 2009, it consisted of about 25 Welsh bluestones and may have been used for cremating and removing the flesh from the bodies whose remains were buried and scattered at Stonehenge. Bluestonehenge’s stones were later dismantled and presumably brought to Stonehenge.

Most of the surviving 45 original bluestones of Stonehenge are of spotted dolerite (also called diabase) from southwest Wales, specifically the Preseli Mountains. Other stones of rhyolite, rhyolitic tuff, volcanic ash, and dolerite are believed to be from the same region. A source for one of the rhyolites, however, was identified in 2011 as Pont Saeson, north of the Preselis. The Altar Stone (a toppled upright so called because it looked to the 17th-century architect Inigo Jones like an altar at the centre of the monument) and another two sandstonemonoliths likely came from the Brecon Beacons, a cluster of mountains about 60 miles (100 km) east of the Preseli range.
Although most experts consider these Welsh stones to have been brought by human agency, some geologists argue that they might have been carried toward the Salisbury Plain thousands of years earlier by ice-age glaciers. The Heelstone, a large unworked sarsenoutside the northeastern entrance, also may have been erected during the first stage of Stonehenge, if not earlier. In addition, rows of timber-post holes within the northeastern entrance to the circular enclosure are thought to date to this period; the posts that they contained may have served to mark the movement of the moon toward its northern major limit.

Second stage: 2640–2480 BCE

Except for human burials, there is no evidence of activity between Stonehenge’s first and second stages of construction. About 2500 BCE the sarsen stones were brought from the Avebury area of the Marlborough Downs, about 20 miles (32 km) to the north. Outside the northeastern entrance of Stonehenge they were dressed smooth by pounding with sarsen hammers. They were then arranged inside the circle in a horseshoe-shaped setting of five tall trilithons (paired uprights with a lintel)—the central and largest of which is known as the giant trilithon—surrounded by 30 uprights linked by curved lintels to form a circle. The stones appear to have been laid out systematically in units and subunits of the long foot; the circumference of the sarsen circle is 300 long feet. The lintels, weighing some 7 tons each, are held on top of the uprights by mortise-and-tenon (dovetail) joints, and the ends of the curved lintels of the sarsen circle fit together with tongue-and-groove joints. All the joints were created using hammer stones, presumably in imitation of woodwork. Most of the sarsen uprights weigh about 25 tons and are about 18 feet (5.5 metres) high. The uprights of the giant trilithon, however, were 29 feet (9 metres) and 32 feet (10 metres) high, weighing more than 45 tons.

Only one of the giant trilithon’s uprights still stands, reaching a height above ground of about 23 feet (7 metres). Only six lintels (out of a total of 230) sit in place on the sarsen circle, with two more lying on the ground. Three of the five sarsen trilithon lintels are in place, with the other two on the ground. Four of the uprights from the sarsen circle are absent, and one is much shorter than the others. Although it is possible that the sarsen circle was never completed, the existence of a hole for an absent sarsen suggests that this stone and others were reused as construction materials for Roman buildings and medievalchurches in the vicinity.

The bluestones were observed by Atkinson to have been arranged into a double arc, which, for convenience, he called the Q and R Holes. Atkinson’s records suggested that the Q and R Holes predated the sarsen circle and trilithons, but Darvill and Wainwright’s excavation in 2008 cast doubt on this stratigraphic relationship. It is more likely that the bluestone arc was indeed constructed as part of the sarsen circle and trilithon monument, with bluestones brought from the Aubrey Holes. Bluestones may also have been brought to Stonehenge at this time, or slightly later, from Bluestonehenge (where they had been removed by at least 2280 BCE). The bluestones weigh up to 4 tons each, and the taller ones are over 6 feet (2 metres) high. Most of them are unworked natural pillars.

Four upright stones, called the Station Stones, were erected near the Aubrey Hole ring, probably also during the second stage of Stonehenge, if not during the period between the monument’s first and second stages. Only two of the stones—both of sarsen—have survived. The four Station Stones were placed in a rectangular formation, aligned along the same solstitial axis as the great trilithon and the bluestone arc. The two missing Station Stones were partially covered by low mounds known as the South Barrow and the North Barrow. The South Barrow was raised on top of the floor of a 36-by-33-foot (11-by-10-metre) building in the shape of a D that lay immediately to the east of the small southern entrance through Stonehenge’s bank and ditch. From this entrance an undated passageway marked by timber posts led toward the centre of the monument. Other sarsens were erected within the northeastern entrance. Three of them formed a facade across the entrance, of which the sarsen known as the Slaughter Stone is the sole survivor. Beyond them lies the Heelstone, set within a circular ring ditch. From the Slaughter Stone to just past the Heelstone, three evenly spaced stone holes (undated) share the same axis as the timber posts thought to belong to Stonehenge’s first stage.

About the same time the sarsens were erected, two sets of concentric timber circles were built within a large settlement almost 2 miles (3 km) to the northeast of the Stonehenge monument. One of these circles, called the Southern Circle, was set at the centre of an ancient settlement of small houses. The other, the smaller Northern Circle, was built on the north side of the settlement. Nine houses, up to about 18 feet (5.5 metres) square in plan, were excavated in 2004–07 and reckoned to form part of a 42-acre (17-hectare) settlement that may have supported up to 1,000 such dwellings. This seasonally occupied and short-lived community is thought to have been the builders’ camp. By 2460 BCE its ruins were enclosed by the bank and ditch of Britain’s largest henge enclosure, Durrington Walls. Outside its south entrance stood a third concentric timber circle—Woodhenge.

Third stage: 2470–2280 BCE

Radiocarbon dating indicates that the side ditches and banks of a ceremonial avenue almost 2 miles (3 km) long were dug from Stonehenge to the River Avon at some time in the period between 2470 and 2280 BCE. It is possible that the avenue traces the path of the bluestones that were moved from the Aubrey Holes and Bluestonehenge to the Q and R holes during Stonehenge’s second stage of construction. The avenue varies in width from about 60 to 115 feet (18 to 35 metres) and terminates at a small henge at the riverside. This henge, measuring 100 feet (30 metres) in diameter, was built after the bluestones at its centre were removed. About the first 1,600 feet (500 metres) of the avenue from Stonehenge are aligned toward the summer solstice sunrise and the winter solstice sunset. Excavations in 2008 revealed that this stretch of the avenue’s banks was built upon preexisting natural chalk ridges coincidentally sharing this same solstitial alignment. At Durrington Walls a similar avenue about 560 feet (170 metres) long and 100 feet (30 metres) wide had been built about 2500 BCE between the Southern Circle and the River Avon and remained in use for several centuries. The Durrington avenue was aligned toward the summer solstice sunset, while the Southern Circle faced the winter solstice sunrise. This solstitial alignment raises the possibility that Stonehenge and Durrington were built as complementary halves of a single complex, articulated by the River Avon.

Fourth, fifth, and sixth stages: 2280–1520 BCE

The fourth stage of Stonehenge’s construction occurred between 2280 and 2030 BCE. About 2200 BCE the bluestones were rearranged to form a circle and an inner oval. Atkinson thought that this inner oval was subsequently modified in prehistory to form a horseshoe, but this transformation may have been the result of Roman removal of the stones or of later stone-robbing. At some point during Stonehenge’s fifth stage, between 2030 and 1750 BCE, a ring of pits known as the Z Holes was dug outside the sarsen circle. A second ring of pits, called the Y Holes, was dug during the monument’s sixth and final stage of construction, between 1640 and 1520 BCE. As with all radiocarbon dating, the precise dates of such events can only be estimated within many decades, if not centuries.

Stonehenge In The 21st Century

Stonehenge is the world’s most famous stone circle, visited by more than a million people per year. It stands as an icon for all that is mysterious and awe-inspiring about humanity’s prehistoric past. For well over a century, people have gathered at the monument to celebrate the summer solstice. Although banned in 1985 as a result of violent clashes with police, the annual gathering resumed in 2000 and now draws a crowd of more than 30,000. Modern-day Druidic societies have claimed Stonehenge as their own temple, even though the identification of Stonehenge with the original Druids is suspect. The first such society, the Ancient Order of Druids, was formed in 1781; more recently, the number of similar Druidic and other Neo-Pagan groups has risen in tandem with the decline in conventional religious belief.

In 2009 the British government proposed the construction of a new visitor centre at Airman’s Corner, about 1.5 miles (2 km) from the stones, at the edge of the World Heritage site. In 2010, however, core funding for the project was withdrawn as a part of government budget cuts. Two more circles of pits—one at Airman’s Corner and the other just to the northwest of Stonehenge proper—were discovered by geophysical survey in 2009 and 2010. The dates of these circles are unknown, and it remains to be determined whether the pits held posts or stones or were merely circles of holes.

In December 2015, archaeologists announced that they had discovered two quarries in the Preseli Mountains from which the bluestones had been extracted about 140 miles (225 km) from Stonehenge. Recesses in rock at both sites matched the dimensions of the bluestones, and several stones that were similar to the bluestones in size and shape remained at the sites. Discovering the quarries allowed archaeologists to establish (by performing radiocarbon dating of hazelnut shells and charcoal left by the workers at the quarries) that the stones had been quarried approximately 500 years before Stonehenge was erected. The archaeologists speculated that the bluestones may have been part of an earlier monument that was dismantled and its stones reused to build Stonehenge.

Jai Ganesh · 2019-06-30 00:32:28

366) Zambezi River

Zambezi River, also spelled Zambesi, river draining a large portion of south-central Africa. Together with its tributaries, it forms the fourth largest river basin of the continent. The river flows eastward for about 2,200 miles (3,540 kilometres) from its source on the Central African Plateau to empty into the Indian Ocean. With its tributaries, it drains an area of more than 500,000 square miles (1,300,000 square kilometres). The Zambezi (meaning “Great River” in the language of the Tonga people) includes along its course the Victoria Falls, one of the world’s greatest natural wonders, and the Kariba and Cahora Bassa dams, two of Africa’s largest hydroelectric projects. The river either crosses or forms the boundaries of six countries—Angola, Zambia, Namibia, Botswana, Zimbabwe, and Mozambique—and the use of its waters has been the subject of a series of international agreements.

Physical Features

Physiography

The Zambezi rises out of a marshy bog near Kalene Hill, Zambia, about 4,800 feet (1,460 metres) above sea level, and flows some 20 miles before entering Angola, through which it runs for more than 175 miles. In this first section of its course, the river is met by more than a dozen tributaries of varying sizes. Shortly after reentering Zambia, the river flows over the Chavuma Falls and enters a broad region of hummocky, sand-covered floodplains, the largest of which is the Barotse, or Zambezi, Plain. The region is inundated during the summer floods, when it receives fertile alluvial soils. The main tributaries intersecting the river along the plains are the Kabompo River from the east and the larger Lungué-Bungo (Lungwebungo) River from the west.

The Zambezi then enters a stretch of rapids that extends from Ngonye (Sioma) Falls south to the Katima Mulilo Rapids, after which for about 80 miles it forms the border between Zambia to the north and the eastern Caprivi Strip—an extension of Namibia—to the south. In this stretch the river meanders through the broad grasslands of the Sesheke Plain until it is joined by the Cuando (Kwando) River. Near Kazungula, Zambia, the river, after flowing past Botswana territory to the south, turns almost due east and forms the frontier between Zambia and Zimbabwe. From the Cuando confluence to the Victoria Falls, the Zambezi varies considerably in width, from open reaches with sand islands to stretches of rapids through narrow channels separated by numerous rock islands.

The Victoria Falls mark the end of the upper course of the Zambezi, as its waters tumble with a thunderous roar and an enormous cloud of spray. The area around the falls was once covered by a thick layer of lava, which as it cooled formed wide cracks, or joints, that became filled with softer sediments. As the Zambezi cut its present valley it encountered one of these joints, eroded the sediment, and created a trench, eventually forcing a gap at the lower end of the trench that quickly widened into a gorge. The force of the water also created a second gap at the upper end of the trench that gradually diverted the river until the trench itself was left dry. As the river cut backward it repeated the process, scouring eight successive waterfalls in the past half million years.

The Zambezi’s middle course extends about 600 miles from Victoria Falls to the eastern end of Lake Cahora Bassa in Mozambique. It continues to form the boundary between Zambia and Zimbabwe until it crosses the Mozambique border at Luangwa. Below the falls a gorge some 60 miles long has been formed by the trench-scouring process, through which the river descends in a series of rapids. Just upstream of Lake Kariba the river valley widens and is contained by escarpments nearly 2,000 feet high. The middle Zambezi is notable for the two man-made lakes, Kariba and Cahora Bassa (see below), that constitute much of this stretch of the river. Between the two lakes the Zambezi trends northeast for nearly 40 miles before it turns east below the confluence with the Kafue River, the Zambezi’s largest tributary. In this section the river rushes through two rocky, narrow gorges, the first just below the Kariba Dam and the other above the confluence with the Luangwa River.

At the dam at the eastern end of Lake Cahora Bassa, the Zambezi begins its lower course, during which it descends from the Central African Plateau to the coastal plain. At first the hilly country is replaced by flat areas at the head of the Tete Basin, and the river becomes more placid. About 40 miles downstream the river has cut the Lupata Gorge through a range of hills, where it emerges onto the Mozambique Plain and occupies a broad valley that spreads out in places to a width of three to five miles. Near Vila Fontes the river receives its last great tributary, the Shire River, which drains Lake Nyasa (Malaŵi) some 210 miles to the north.

At its mouth the Zambezi splits into a wide, flat, and marshy delta obstructed by sandbars. There are two main channels, each again divided into two. The wider, eastern channel splits into the Muselo River to the north and the main mouth of the Zambezi to the south. The western channel forms both the Inhamissengo River and the smaller Melambe River. North of the main delta the Chinde River separates from the Zambezi’s main stream to form a navigable channel leading to a shallow harbour.

Hydrology

The Zambezi, according to measurements taken at Maramba (formerly Livingstone), Zambia, experiences its maximum flow in March or April. In October or November the discharge diminishes to less than 10 percent of the maximum. The annual average flow reaches about 247,000 cubic feet (7,000 cubic metres) per second. Measurements taken at Kariba Dam reflect the same seasonal pattern; the highest flood recorded there was in March 1958, when the flow reached 565,000 cubic feet per second.

Climate

The Zambezi River lies within the tropics. The upper and middle course of the river is on an upland plateau, and temperatures, modified by altitude, are relatively mild, generally between 64° and 86° F (18° and 30° C). The winter months (May to July) are cool and dry, with temperatures averaging 68° F (20° C). Between August and October there is a considerable rise in average temperatures, particularly in the river valley itself; just before the rains begin in October temperatures there become excessively hot, often reaching 104° F (40° C). The rainy season lasts from November to April. Rain falls in short, intense thundershowers—the rate sometimes reaching 6 inches (150 millimetres) per hour—with skies clearing between downpours. In these months the upper Zambezi receives nearly all its total rainfall, and this accounts for the great variation in the flow of the river throughout the year. In all, the upper and middle Zambezi valley receives 22 to 30 inches of rain per year. Studies have suggested that a microclimate in the area of Lake Kariba has created a rise in precipitation, possibly as a result of a lake breeze blocked by the escarpment that produces thunderstorms.

In the lower course of the river in Mozambique the influence of the summer monsoon increases the levels of precipitation and humidity. Temperatures are also higher—determined more by the latitude and less by altitude—as the river descends from the plateau.

Plant life

The vegetation along the upper and middle course of the Zambezi is predominantly savanna, with deciduous trees, grass, and open woodland. Mopane woodland (Colophospermum mopane) is predominant on the alluvial flats of the low-lying river valleys and is highly susceptible to fire. Grass, when present, is typically short and sparse. Forestland with species of the genus Baikiaea, found extensively on sandy interfluves between drainage channels, is economically the most important vegetation type in Zambia, for it is the source of the valuable Rhodesian teak (Baikiaea plurijuga). Destruction of the Baikiaea forest results in a regression from forest to grassland, a slow process involving intermediate stages of scrub vegetation. The river additionally has a distinct fringing vegetation, mainly riverine forest including ebony (Diospyros mespiliformis) and small shrubs and ferns (e.g., Haemanthus). In the lower course of the Zambezi, dense bush and evergreen forest, with palm trees and patches of mangrove swamp, is the typical vegetation.

Animal life

The tiger fish is one of the few species found both above and below the Victoria Falls. Pike is predominant in the upper course of the river, as are yellowfish and barbel. Bream are now common both above and below the falls. Crocodiles abound in the Zambezi, though they generally avoid stretches of fast-running water. Hippopotamuses are also found in the upper and lower stretches of the Zambezi.

Elephants are common over much of the river’s course, particularly in areas such as the Sesheke Plain and near the Luangwa confluence. Game animals include buffalo, eland, sable, roan, kudu, waterbuck, impala, duiker, bushbuck, reedbuck, bushpig, and warthog. Of the big cats, lions can be found in the Victoria Falls National Park in Zimbabwe and elsewhere along the river’s course; cheetahs, although comparatively rare, can be sighted; and leopards, rarely seen by daylight, are common, both in the plains and the river gorges. Baboons and monkeys abound throughout the region.

The People

The Lozi (Barotse), who dominate much of the upper Zambezi, have taken advantage of the seasonal flooding of the Barotse Plain for centuries and have an agricultural economy that is supplemented by animal husbandry, fishing, and trade. The main groups of the middle Zambezi include the Tonga, Shona, Chewa, and Nsenga peoples, all of whom largely practice subsistence agriculture. In Mozambique the riverine population is varied; many engage in commercial agriculture—the growing of sugarcane and cotton in particular—which was established by the Portuguese.

The Economy

Navigation

Given its numerous natural barriers—sandbars at the mouth, shallowness, and rapids and cataracts—the Zambezi is of little economic significance as a trade route. About 1,620 miles of the river, however, are navigable by shallow-draft steamers. The longest stretch of unbroken water runs from the river deltaabout 400 miles upstream to the Cahora Bassa Dam. Above the dam Lake Cahora Bassa is navigable to its confluence with the Luangwa River, where navigation is interrupted again to the Kariba Dam. Lake Kariba is navigable, but the river again becomes impassable from the end of the lake to the Ngonye Falls, some 250 miles upstream. It is again navigable by shallow-draft boats for the 300 miles between the Ngonye and Chavuma falls and then for another 120 miles above Chavuma.

The river has four major crossing points. The Victoria Falls Bridge, the first from the head of the river, carries rail, road, and foot traffic between Zambia and Zimbabwe. The dam wall at Kariba is heavily used by road traffic, and a road bridge at Chirundu, Zimb., also connects the two countries. The fourth major crossing is the rail and road bridge between Mutarara (Dona Ana) and Vila de Sena, Mozambique. There are also a number of motor ferries crossing the river at various points.

Kariba and Cahora Bassa schemes

The Kariba Dam harnesses the Zambezi at Kariba, Zimb., 300 miles below Victoria Falls. A concrete-arch dam with a maximum height of 420 feet and a crest length of 1,900 feet carries a road connecting the Zambian and Zimbabwean banks of the gorge. Six floodgates permit a discharge of some 335,000 cubic feet of water per second. Both Zambia and Zimbabwe obtain most of their electricity from the Kariba Dam. Lake Kariba covers an area of about 2,000 square miles. The flooded land was previously inhabited by about 51,000 Tonga agriculturalists, who had to be resettled. The lake stretches for 175 miles from the dam to Devil’s Gorge and is 20 miles across at its widest point. Three townships have been built around lakeshore harbours at Kariba and at Siavonga and Sinazongwe, Zambia. Tourist resorts have also been developed along the lakeshore.

Lake Cahora Bassa was formed by a dam across the Zambezi at the head of Cahora Bassa Gorge, about 80 miles northwest of Tete, Mozambique. The dam, 560 feet high and 1,050 feet wide at its crest, impounds the river for 150 miles to the Mozambique–Zambia border, providing hydroelectric power and water for crop irrigation.

Study And Exploration

The first non-Africans to reach the Zambezi were Arab traders, who utilized the river’s lower reaches from the 10th century onward. They were followed in the 16th century by the Portuguese, who hoped to use the river to develop a trade in ivory, gold, and slaves. Until the 19th century, the river, then called the Zanbere, was believed to flow south from a vast inland sea that was also thought to be the origin of the Nile River. Accurate mapping of the Zambezi did not take place until the Scottish missionary and explorer David Livingstone charted most of the river’s course in the 1850s. Searching for a trade route to the East African coast, he traveled from Sesheke, 150 miles above Victoria Falls, to the Indian Ocean. His map of the river remained the most accurate until the 20th century, when further surveys finally traced the Zambezi to its source.

Jai Ganesh · 2019-07-02 00:32:17

367) Cryogenics

Cryogenics, production and application of low-temperature phenomena.

The cryogenic temperature range has been defined as from −150 °C (−238 °F) to absolute zero (−273 °C or −460 °F), the temperature at which molecular motion comes as close as theoretically possible to ceasing completely. Cryogenic temperatures are usually described in the absolute or Kelvin scale, in which absolute zero is written as 0 K, without a degree sign. Conversion from the Celsius to the Kelvin scale can be done by adding 273 to the Celsius scale.

Cryogenic temperatures are considerably lower than those encountered in ordinary physical processes. At these extreme conditions, such properties of materials as strength, thermal conductivity, ductility, and electrical resistance are altered in ways of both theoretical and commercial importance. Because heat is created by the random motion of molecules, materials at cryogenic temperatures are as close to a static and highly ordered state as is possible.

Cryogenics had its beginning in 1877, the year that oxygen was first cooled to the point at which it became a liquid (−183 °C, 90 K). Since then the theoretical development of cryogenics has been connected to the growth in capability of refrigeration systems. In 1895, when it had become possible to reach temperatures as low as 40 K, air was liquefied and separated into its major components; in 1908 helium was liquefied (4.2 K). Three years later the propensity of many supercooled metals to lose all resistance to electricity—the phenomenon known as superconductivity—was discovered. By the 1920s and 1930s temperatures close to absolute zero were reached, and by 1960 laboratories could produce temperatures of 0.000001 K, a millionth of a degree Kelvin above absolute zero.

Temperatures below 3 K are primarily used for laboratory work, particularly research into the properties of helium. Helium liquefies at 4.2 K, becoming what is known as helium I. At 2.19 K, however, it abruptly becomes helium II, a liquid with such low viscosity that it can literally crawl up the side of a glass and flow through microscopic holes too small to permit the passage of ordinary liquids, including helium I. (Helium I and helium II are, of course, chemically identical.) This property is known as superfluidity.

The most important commercial application of cryogenic gas liquefaction techniques is the storage and transportation of liquefied natural gas (LNG), a mixture largely composed of methane, ethane, and other combustible gases. Natural gas is liquefied at 110 K, causing it to contract to 1/600th of its volume at room temperature and making it sufficiently compact for swift transport in specially insulated tankers.

Very low temperatures are also used for preserving food simply and inexpensively. Produce is placed in a sealed tank and sprayed with liquid nitrogen. The nitrogen immediately vaporizes, absorbing the heat content of the produce.

In cryosurgery a low-temperature scalpel or probe can be used to freeze unhealthy tissue. The resulting dead cells are then removed through normal bodily processes. The advantage to this method is that freezing the tissue rather than cutting it produces less bleeding. A scalpel cooled by liquid nitrogen is used in cryosurgery; it has proved successful in removing tonsils, hemorrhoids, warts, cataracts, and some tumours. In addition, thousands of patients have been treated for Parkinson disease by freezing the small areas of the brain believed to be responsible for the problem.

The application of cryogenics has also extended to space vehicles. In 1981 the U.S. space shuttle Columbia was launched with the aid of liquid hydrogen/liquid oxygen propellants.

Of the special properties of materials cooled to extreme temperatures, superconductivity is the most important. Its chief application has been in the construction of superconducting electromagnets for particle accelerators. These large research facilities require such powerful magnetic fields that conventional electromagnets could be melted by the currents required to generate the fields. Liquid helium cools to about 4 K the cable through which the currents flow, allowing much stronger currents to flow without generating heat by resistance.

Cryogenics is the science of producing and studying low-temperature conditions. The word cryogenics comes from the Greek word cryos , meaning "cold," combined with a shortened form of the English verb "to generate." It has come to mean the generation of temperatures well below those of normal human experience. More specifically, a low-temperature environment is termed a cryogenic environment when the temperature range is below the point at which permanent gases begin to liquefy. Permanent gases are elements that normally exist in the gaseous state and were once believed impossible to liquefy. Among others, they include oxygen, nitrogen, hydrogen, and helium.

The origin of cryogenics as a scientific discipline coincided with the discovery by nineteenth-century scientists that the permanent gases can be liquefied at exceedingly low temperatures. Consequently, the term "cryogenic" applies to temperatures from approximately −100°C (−148°F) down to absolute zero (the coldest point a material could reach).

The temperature of any material—solid, liquid, or gas—is a measure of the energy it contains. That energy is due to various forms of motion among the atoms or molecules of which the material is made. A gas that consists of very rapidly moving molecules, for example, has a higher temperature than one with molecules that are moving more slowly.

In 1848, English physicist William Thomson (later known as Lord Kelvin; 1824–1907) pointed out the possibility of having a material in which particles had ceased all forms of motion. The absence of all forms of motion would result in a complete absence of heat and temperature. Thomson defined that condition as absolute zero.

Jai Ganesh · 2019-07-04 00:04:55

368) Very Large Scale Integration

Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions of transistors or devices into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM and other glue logic. VLSI lets IC designers add all of these into one chip.

History

The history of the transistor dates to the 1920s when several inventors attempted devices that were intended to control current in solid-state diodes and convert them into triodes. Success came after World War II, when the use of silicon and germanium crystals as radar detectors led to improvements in fabrication and theory. Scientists who had worked on radar returned to solid-state device development. With the invention of transistors at Bell Labs in 1947, the field of electronics shifted from vacuum tubes to solid-state device.

With the small transistor at their hands, electrical engineers of the 1950s saw the possibilities of constructing far more advanced circuits. However, as the complexity of circuits grew, problems arose.

One problem was the size of the circuit. A complex circuit like a computer was dependent on speed. If the components were large, the wires interconnecting them must be long. The electric signals took time to go through the circuit, thus slowing the computer.

The invention of the integrated circuit by Jack Kilby and Robert Noyce solved this problem by making all the components and the chip out of the same block (monolith) of semiconductor material. The circuits could be made smaller, and the manufacturing process could be automated. This led to the idea of integrating all components on a single-crystal silicon wafer, which led to small-scale integration (SSI) in the early 1960s, medium-scale integration (MSI) in the late 1960s, and then large-scale integration (LSI) as well as VLSI in the 1970s and 1980s, with tens of thousands of transistors on a single chip (later hundreds of thousands, then millions, and now billions i.e. {10}^{9}).

The first semiconductor chips held two transistors each. Subsequent advances added more transistors, and as a consequence, more individual functions or systems were integrated over time. The first integrated circuits held only a few devices, perhaps as many as ten diodes, transistors, resistors and capacitors, making it possible to fabricate one or more logic gates on a single device. Now known retrospectively as small-scale integration (SSI), improvements in technique led to devices with hundreds of logic gates, known as medium-scale integration (MSI). Further improvements led to large-scale integration (LSI), i.e. systems with at least a thousand logic gates. Current technology has moved far past this mark and today's microprocessors have many millions of gates and billions of individual transistors.

At one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like ultra-large-scale integration (ULSI) were used. But the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use.

In 2008, billion-transistor processors became commercially available. This became more commonplace as semiconductor fabrication advanced from the then-current generation of 65 nm processes. Current designs, unlike the earliest devices, use extensive design automation and automated logic synthesis to lay out the transistors, enabling higher levels of complexity in the resulting logic functionality. Certain high-performance logic blocks like the SRAM (static random-access memory) cell, are still designed by hand to ensure the highest efficiency.

Structured design

Structured VLSI design is a modular methodology originated by Carver Mead and Lynn Conway for saving microchip area by minimizing the interconnect fabrics area. This is obtained by repetitive arrangement of rectangular macro blocks which can be interconnected using wiring by abutment. An example is partitioning the layout of an adder into a row of equal bit slices cells. In complex designs this structuring may be achieved by hierarchical nesting.

Structured VLSI design had been popular in the early 1980s, but lost its popularity later because of the advent of placement and routing tools wasting a lot of area by routing, which is tolerated because of the progress of Moore's Law. When introducing the hardware description language KARL in the mid' 1970s, Reiner Hartenstein coined the term "structured VLSI design" (originally as "structured LSI design"), echoing Edsger Dijkstra's structured programming approach by procedure nesting to avoid chaotic spaghetti-structured program.

Difficulties

As microprocessors become more complex due to technology scaling, microprocessor designers have encountered several challenges which force them to think beyond the design plane, and look ahead to post-silicon:
• Process variation – As photolithography techniques get closer to the fundamental laws of optics, achieving high accuracy in doping concentrations and etched wires is becoming more difficult and prone to errors due to variation. Designers now must simulate across multiple fabrication process corners before a chip is certified ready for production, or use system-level techniques for dealing with effects of variation.
• Stricter design rules – Due to lithography and etch issues with scaling, design rules for layout have become increasingly stringent. Designers must keep in mind an ever increasing list of rules when laying out custom circuits. The overhead for custom design is now reaching a tipping point, with many design houses opting to switch to electronic design automation (EDA) tools to automate their design process.
• Timing/design closure – As clock frequencies tend to scale up, designers are finding it more difficult to distribute and maintain low clock skew between these high frequency clocks across the entire chip. This has led to a rising interest in multicore and multiprocessor architectures, since an overall speedup can be obtained even with lower clock frequency by using the computational power of all the cores.
• First-pass success – As die sizes shrink (due to scaling), and wafer sizes go up (due to lower manufacturing costs), the number of dies per wafer increases, and the complexity of making suitable photomasks goes up rapidly. A mask set for a modern technology can cost several million dollars. This non-recurring expense deters the old iterative philosophy involving several "spin-cycles" to find errors in silicon, and encourages first-pass silicon success. Several design philosophies have been developed to aid this new design flow, including design for manufacturing (DFM), design for test (DFT), and Design for X.

Jai Ganesh · 2019-07-06 00:06:12

369) Spring Balance

Spring balance, weighing device that utilizes the relation between the applied load and the deformation of a spring. This relationship is usually linear; i.e., if the load is doubled, the deformation is doubled. In the circular balance shown in the figure, the upper ends of the helical springs are attached to the casing and the lower ends to a crossbar that can move relative to the casing and to which the load hook is attached. The pinion to which the indicating pointer is attached is pivoted in the casing and meshes with the rack, which is pivotally connected to the crossbar and is pressed into contact with the pinion by the rack spring.

When a load is applied, the springs are stretched, and movement of the crossbar with the rack attached rotates the pinion and the load-indicating pointer. The dial is graduated in scale units that depend on the stiffness of the springs: the stiffer springs have larger scale units and higher load capacity.

Spring balances are widely used commercially. Those with high-load capacities are frequently suspended from crane hooks and are known as crane scales. Smaller units for household use are called fish scales.

A spring scale or spring balance or newton meter is a type of mechanical force gauge or weighing scale. It consists of a spring fixed at one end with a hook to attach an object at the other. It works by Hooke's Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position. Therefore, the scale markings on the spring balance are equally spaced. A spring scale cannot measure mass, only weight.

A spring balance can be calibrated for the accurate measurement of mass in the location in which they are used, but many spring balances are marked right on their face "Not Legal for Trade" or words of similar import due to the approximate nature of the theory used to mark the scale. Also, the spring in the scale can permanently stretch with repeated use.

A spring scale will only read correctly in a frame of reference where the acceleration in the spring axis is constant (such as on earth, where the acceleration is due to gravity). This can be shown by taking a spring scale into an elevator, where the weight measured will change as the elevator moves up and down changing velocities.
If two or more spring balances are hung one below the other in series, each of the scales will read approximately the same, the full weight of the body hung on the lower scale. The scale on top would read slightly heavier due to also supporting the weight of the lower scale itself.

Spring balances come in different sizes. Generally, small scales that measure newtons will have a less firm spring (one with a smaller spring constant) than larger ones that measure tens, hundreds or thousands of newtons or even more depending on the scale of newtons used. The largest spring scale ranged in measurement from 5000–8000 newtons.

A spring balance may be labeled in both units of force (poundals, Newtons) and mass (pounds, kilograms/grams). Strictly speaking, only the force values are correctly labeled. In order to infer that the labeled mass values are correct, an object must be hung from the spring balance at rest in an inertial reference frame, interacting with no other objects but the scale itself.

Uses

Main uses of spring balances are to weigh heavy loads such as trucks, storage silos, and material carried on a conveyor belt. They are also common in science education as basic accelerators. They are used when the accuracy afforded by other types of scales can be sacrificed for simplicity, cheapness, and robustness.
A spring balance measures the weight of an object by opposing the force of gravity acting with the force of an extended spring.

History

The first spring balance in Britain was made around 1770 by Richard Salter of Bilston, near Wolverhampton. He and his nephews John & George founded the firm of ‘George Salter & Co.,’ still notable makers of scales and balances, who in 1838 patented the spring balance. They also applied the same spring balance principle to steam locomotive safety valves, replacing the earlier deadweight valves.

Jai Ganesh · 2019-07-08 01:05:05

370) Acid rain

Acid Rain: Causes, Effects and Solutions

Acid rain, or acid deposition, is a broad term that includes any form of precipitation that contains acidic components, such as sulfuric acid or nitric acid, according to the Environmental Protection Agency (EPA).

The precipitation is not necessarily wet or liquid; the definition includes dust, gasses, rain, snow, fog and hail. The type of acid rain that contains water is called wet deposition. Acid rain formed with dust or gasses is called dry deposition.

Causes

The term acid rain was coined in 1852 by Scottish chemist Robert Angus Smith, according to the Royal Society of Chemistry, which calls him the "father of acid rain." Smith decided on the term while examining rainwater chemistry near industrial cities in England and Scotland. He wrote about his findings in 1872 in the book "Air and Rain: The Beginnings of a Chemical Climatology."

In the 1950s, scientists in the United States started studying the phenomenon, and in the 1960s and early 1970s, acid rain became recognized as a regional environmental issue that affected Western Europe and eastern North America.

Though manmade pollutants are currently affecting most acidic precipitation, natural disasters can be a factor as well. For example, volcanoes can cause acid rain by blasting pollutants into the air. These pollutants can be carried around the world in jet streams and turned into acid rain far from the volcano.

After an asteroid supposedly wiped out the dinosaurs 65.5 million years ago, sulfur trioxide was blasted into the air. When it hit the air, it turned into sulfuric acid, generating a downpour of acid rain, according to a paper published in 2014 in the journal Nature Geoscience.

Even before that, over 4 billion years ago, it is suspected that the air may have had 10,000 times as much carbon dioxide as today. Geologists from the University of Wisconsin-Madison backed up this theory be studying rocks and publishing the results in a 2008 issue of the journal Earth and Planetary Science Letters. "At [those levels of carbon dioxide], you would have had vicious acid rain and intense greenhouse [effects]. That is a condition that will dissolve rocks," said study team member John Valley.

Sulfur dioxide (SO2) and nitrogen oxides (NOx) released into the air by fossil-fuel power plants, vehicles and oil refineries are the biggest cause of acid rain today, according to the EPA. Two thirds of sulfur dioxide and one fourth of nitrogen oxide found in the atmosphere come from electric power generators.

A chemical reaction happens when sulfur dioxide and nitrogen oxides mix with water, oxygen and other chemicals in the air. They then become sulfuric and nitric acids that mix with precipitation and fall to the ground. Precipitation is considered acidic when its pH level is about 5.2 or below, according to Encyclopedia Britannica. The normal pH of rain is around 5.6.

Effects

Acid rain affects nearly everything. Plants, soil, trees, buildings and even statues can be transformed by the precipitation.
Acid rain has been found to be very hard on trees. It weakens them by washing away the protective film on leaves, and it stunts growth. A paper released in the online version of the journal of Environmental Science and Technology in 2005 showed evidence of acid rain stunting tree growth.

"By providing the only preserved soil in the world collected before the acid rain era, the Russians helped our international team track tree growth for the first time with changes in soil from acid rain," said Greg Lawrence, a U.S. Geological Survey scientist who headed the effort. "We've known that acid rain acidifies surface waters, but this is the first time we've been able to compare and track tree growth in forests that include soil changes due to acid rain."

Acid rain can also change the composition of soil and bodies of water, making them uninhabitable for local animals and plants. For example, healthy lakes have a pH of 6.5 or higher. As acid rain raises the level of acidity, fish tend to die off. Most fish species can't survive a water pH of below 5. When the pH becomes a 4, the lake is considered dead, according to National Atmospheric Deposition Program.

It can additionally deteriorate limestone and marble buildings and monuments, like gravestones.

Solutions

There are several solutions to stopping manmade acid rain. Regulating the emissions coming from vehicles and buildings is an important step, according to the EPA. This can be done by restricting the use of fossil fuels and focusing on more sustainable energy sources such as solar and wind power.

Also, each person can do their part by reducing their vehicle use. Using public transportation, walking, riding a bike or carpooling is a good start, according to the EPA. People can also reduce their use of electricity, which is widely created with fossil fuels, or switch to a solar plan. Many electricity companies offer solar packages to their customers that require no installation and low costs.

Biology

Acid rain has been a problem around the world and New England. As the biologist of the team, I have studied how acid rainfall effects and damages the ecosystem. When acid rain falls on forests and crops, the acid rain destroys the leaves and small branches and poisons water ways. A way to tell this is happening is when leaves drop off and are brown.

Without the tops of trees, undergrowth will grow, but then die from more exposure to acidic water. Acid rain also dissolves mineral and nutrients in the soil and washes it away before trees and plants can utilize it. The affect on soil depends on how thick the soil is and what the bedrock is made of. Farmers sometimes crush limestone and fertilizer into the soil because it is basic and adds nutrients. When the trees die we burn them and this creates more pollution in the air. When acid rain falls on crops, the crops die and we lose an important food source.

Lakes and aquatic systems are also affected by acid rain. When the rain falls, it lowers the pH value of the water. This causes the inhabitants to die in and around the water. Plankton die first then crawfish and clams. The next warning sign of acidic water is many mature fish and no young fish. This is because fish cannot spawn n high acidic waters. There are also accounts of hundreds of dead fish washing up on shore. When acid rain falls it washes calcium and aluminum from the soil, which kills the trees. These mineral and nutrients in turn kill fish and cause mosses and underwater plants to grow more. Blackfly larvae also flourish. The dangers of low pH levels cause fish to die they contaminate water supplies and we lose another food supply. When water is acidic it is dangerous to drink and bath in.

Overall, humans create pollution and then it bonds with water partials creating acid rain. The acid rain falls on our crops and water sources, preventing us from using them. There are many ways to stop pollution and everyone should take part in them. As you can see acid rain affects New England and it needs to stop.

Chemist

Acid rain has been a problem in many places for many years. Acidic rain is made of sulfur dioxide, nitrogen oxide, nitric acid, and sulfuric acid. This acidic rain is made from gas, exhaust, and factories that burn fossil fuel. To tell how acidic the rain is you have to test its pH level. pH levels measure the acidity of a substance. A pH scale ranges from 0-14 with anything under 7 being acidic and anything over 7 being bitter. The pH level of normal rain is about 5.6. When the pH level is under 5.6 it is considered dangerous.

Economics

Does acid rain affect building materials?

Yes, acid rain does in fact harm building materials. Calcium carbonate that is commonly found in building materials dissolves in weak acids. Even though many metals corrode, stone and paint deteriorate, which lowers the value of the architecture that is built with these building materials.

Does acid rain have an effect on architecture?

Acid rain most diffidently affects architecture. A great example is The Statue of Liberty, which was once copper, because of acid rain it is now green. Much architecture today involves the use of marble and limestone. These two contain calcium carbonate, which dissolves in weak acids, like we discussed in the first paragraph.

What does acid rain do to our roads, highways, and bridges?

Acid rain also does affect roads, highways, and bridges as well. It causes them to corrode and become weaker. This is a big safety hazard. Bridges could even collapse on themselves if they become too weak. Highways and roads will also become dangerous to travel on.

What is the effect of acid rain on things made from metal such as automobiles, trains, buses, and other means of transportation?

The forms of transportation made of metal, and other metal material period, and coated with rust as the effect of acid rain. They also suffer corrosion. The result is both aesthetically unappealing and affects the performance of the car as well, and is also a little bit of a safety hazard considering the fact that you’re now driving a fragile car that could most likely, and very easily fall apart.

What does the effect of acid cost us in terms of money?

Acid rain causes a good amount of money because of the damage it causes, even though the exact amount cannot be pinpointed. The cost of repairing damaged roads, buildings; even our own personal property can be summed up quite a lot though. Protection against the threat itself can also cost quite a bit of money, a perfect example is protecting your car coating, which involves repeatedly washing and drying the car wastes materials and raises bills.

What are the economic consequences of acid rain on fisheries, forestry, and agriculture?

The acid found in acid rain can also contribute to natural damage. Since enzymes can only survive at a certain pH, the sudden increase in acidity will cause them to denature. This will cause important function of organisms to shut down. Thus, businesses that rely on said organisms, such as agriculture, which depends on crops, will lose a considerable amount of crop to acid rain. Thus, the decrease of product will cause the price to go up, which is bad for consumers. The managers of said businesses will also lose profit if the product sale decreases due to the increased price.

Health effects

Most of acid rain’s effects on humans are indirect. Humans are capable of walking or even swim through it. However, the pollutants inside of acid rain can affect people’s health. Most acid rain is not strong enough to affect people’s health. But if the rain is harsh enough, you can inhale smog and it will enter the body and cause lung problems. When acid rain falls on trees, it ruins the leaves making them unable to produce oxygen for us. It can also harm the lakes and rivers it falls in. If they eat fish caught from those bodies of water it can harm humans. It can also affect lead pipes if the acid number is high enough. If you drink from those pipes, it will have the similar affects as inhaling it. Once in Sweden, the water contained enough acid to turn people’s hair green!

Solutions

How can you prevent acid rain?

A lot of acid rain is caused by things humans do. There are ways we can prevent it from getting worse and help it get better. You can cut back on car use. It is very easy to cut back on how often you use your car. You can carpool or use public transportation. Also cut back on the use of vehicles that burn gas and diesel. You could also cut back on use of your electronics. Those solutions are really only up to citizens. Other things we can do are to burn coal more efficiently. This is not relevant for those who don’t burn coal. Power plants release gypsum that contributes to acid rain. Most of the acid in acid rain is caused by us. It is only us who can prevent it.

Math Is Fun Forum

#426 2019-05-30 00:19:10

Re: Miscellany

#427 2019-06-01 00:39:40

Re: Miscellany

#428 2019-06-03 00:58:30

Re: Miscellany

#429 2019-06-05 00:02:05

Re: Miscellany

#430 2019-06-07 01:10:52

Re: Miscellany

#431 2019-06-09 00:16:20

Re: Miscellany

#432 2019-06-11 00:28:13

Re: Miscellany

#433 2019-06-12 00:26:25

Re: Miscellany

#434 2019-06-14 00:38:37

Re: Miscellany

#435 2019-06-16 00:57:15

Re: Miscellany

#436 2019-06-18 01:58:57

Re: Miscellany

#437 2019-06-18 15:45:57

Re: Miscellany

#438 2019-06-18 17:15:26

Re: Miscellany

#439 2019-06-18 18:55:56

Re: Miscellany

#440 2019-06-19 00:03:39

Re: Miscellany

#441 2019-06-20 00:34:28

Re: Miscellany

#442 2019-06-22 00:02:46

Re: Miscellany

#443 2019-06-24 01:27:40

Re: Miscellany

#444 2019-06-26 00:08:30

Re: Miscellany

#445 2019-06-28 01:21:15

Re: Miscellany

#446 2019-06-30 00:32:28

Re: Miscellany

#447 2019-07-02 00:32:17

Re: Miscellany

#448 2019-07-04 00:04:55

Re: Miscellany

#449 2019-07-06 00:06:12

Re: Miscellany

#450 2019-07-08 01:05:05

Re: Miscellany

Board footer