title: Apprenticeship

paragraphs: Apprenticeship is a system of training people who are learning how to do a job which needs special skill. Someone who is learning in this way is called an "apprentice". An apprentice will learn by working with someone who is already skilled at a job. They are like a teacher and pupil.

paragraphs: The system of apprenticeship has been used for many hundreds of years. In the late Middle Ages the craft guilds and town governments used to watch and control the system. A master craftsman had the right to employ young people to work for them and pay them a small salary. In return the apprentice would be learning the trade. Most apprentices were males, but female apprentices are more common nowadays, especially in crafts such as embroidery, silk-weaving etc..


title: Battle droid

paragraphs: In the "Star Wars" fictional universe, battle droids are robots that are made for fighting. They are seen in the prequel trilogy of the "Star Wars" movies. Battle droids are used by the Confederacy of Independent Systems to fight the Galactic Republic.Clones of the Republic could easily overcome these droids.The battle droids are controlled by a central droid control ship. If the control ship is destroyed, the droids shut off.


title: Western long-beaked echidna

paragraphs: The western long-beaked echidna ("Zaglossus bruijni") is one of the echidnas which live in New Guinea. Fossils of this species have also been found in Australia. It is one of the four living echidnas, three of which are species of "Zaglossus".

paragraphs: This echidna lives from 1300m to 4000m above sea level. It lives in alpine meadow and humid forests in the mountains. Unlike the short-beaked echidna which eats ants and termites, the long-beaked species eats earthworms. It is also larger that the short-beaked species. It can be told apart from the other "Zaglossus" species by the number of claws on the front and back feet. It has three (rarely four) claws.

paragraphs: It is an endangered species. Its population has been reduced by habitat habitat loss and hunting. The long-beaked Echidna is good to eat. Although hunting the species has been banned by the Indonesian and Papua New Guinea governments, traditional hunting is permitted.

paragraphs: In February of 2006, an expedition led by Conservation International found a population of them in what they described as a "lost world" of wildlife in the Foja Mountains of Papua Province, Indonesia.

paragraphs: The echidnas and Platypus are monotremes, the only mammals to lay eggs.


title: Short-beaked echidna

paragraphs: The short-beaked echidna ("Tachyglossus aculeatus") is the only member of its genus, and one of four living species of echidna.

paragraphs: The short-beaked echidna, "Tachyglossus", is the spiny anteater because they eat ants and termites. It is covered in fur and spines. It has a special nose (snout) and a special tongue that lets the echidna catch its prey at a great speed. It lays eggs, like the other monotremes.

paragraphs: The echidna lives throughout Australia, and in coastal and highland regions of southwestern New Guinea. In Australia, it is the most widespread native mammal. It is not threatened with extinction, but human activities, such as hunting, habitat destruction, and the introduction of foreign predators and parasites, have reduced its range.

paragraphs: The animal was first described in 1792. "Tachyglossus" means "fast tongue". This is about the speed with which the echidna uses its tongue to catch ants and termites. The word "aculeatus" means "spiny" or "having spines".

paragraphs: The long-beaked echidna are all bigger than "T. aculeatus". They eat mostly worms and grubs, rather than ants and termites.

paragraphs: There are five subspecies of the short-beaked echidna. Each live in a different area from the others. The subspecies are also different from each other as to hairiness, spine length and width, and the size of the claws on their back feet.

paragraphs: Short-beaked echidnas are usually 30 to 45 centimetres in length. They have a 75-millimetre beak, and weigh between two and five kilograms. The Tasmanian subspecies, "T. a. setosus", is larger than the Australian mainland species.

paragraphs: Because the neck cannot be seen, the head and body appear to join together. The earholes are on either side of the head, with no external pinnae. The eyes are small and at the base of the wedge-shaped beak. The nostrils and the mouth are at the far end of the beak.

paragraphs: The legs of this echidna are adapted for rapid digging. Their legs are short and have strong claws. The claws on the back feet are longer and curve backwards to help cleaning and grooming between the spines. Like the platypus it has a low body temperature—between 30 and 32 °C. Unlike the platypus, which shows no evidence of torpor or hibernation, the body temperature of the echidna may fall as low as 5 °C. The echidna does not pant or sweat and normally seeks shelter in hot conditions. In autumn and winter the echidna shows periods of torpor or deep hibernation. Because of its low body temperature, the animal becomes sluggish in very hot and very cold weather.

paragraphs: The muscles of this echidna have a number of unusual features. There is an enormous muscle that is just beneath the skin and covers the entire body. By contraction of various parts of this muscle the Short-beaked Echidna can change shape. The most common shape change is achieved by rolling itself into a ball when threatened, protecting its belly and presenting a defensive array of sharp spines. It has one of the shortest spinal cords of any mammal, extending only as far as the thorax.

paragraphs: The tongue of the short-beaked echidna is the animal's only way of catching prey. It can stick out up to 180 mm outside the snout. The tongue is sticky because of the presence of glycoprotein-rich mucous. This mucus both lubricates movement in and out of the snout and helps to catch ants and termites, which stick to it. The protruded tongue is stiffened by the rapid flow of blood, allowing it to penetrate wood and soil. Retraction requires the contraction of two internal muscles. When the tongue is retracted, the prey is caught on backward-facing keratinous "teeth" along the roof of the buccal cavity. This allows the animal to both capture and grind food. The tongue moves with great speed, and has been measured to move in and out of the snout 100 times a minute.

paragraphs: Many physiological adaptations fit the animal to its lifestyle. It burrows, and can tolerate high levels of carbon dioxide. Its ear is sensitive to low-frequency sound, which may be ideal for detecting sounds emitted by termites and ants underground. The leathery snout is covered in mechano- and thermoreceptors. These receptors provide information about the surrounding environment. The echidna has a well-developed olfactory system, which may be used to detect mates and prey, and its other senses perform well. Its brain and central nervous system have been extensively studied for comparison with placental mammals.

paragraphs: The short-beaked echidna has the largest prefrontal cortex, relative to body size, of any mammal. It takes up 50% of the volume of the cortex, compared to 29% for humans. This suggests good decision-making in its constant search for insect nests, and for a mate when reproducing.

paragraphs: Like all monotremes, the echidna has only one orifice for the passage of faeces, urine and reproductive products, which is known as the cloaca. The male has internal testes, no external scrotum and a highly unusual penis with four knobs on the tip. The gestating female has a pouch on its underside, where it raises its young.

paragraphs: The laying of eggs and the cloaca are basal traits which are present in all early amniotes, including reptiles, birds and early mammals.

paragraphs: The solitary Short-beaked Echidna looks for a mate between May and September; the precise timing of the mating season varies with geographic location. Both males and females give off a strong odour during the mating season. During courtship—observed for the first time in 1989—males locate and pursue females. Trains of up to ten males may follow a single female in a courtship ritual that may last for up to four weeks; the duration of the courtship period varies with location. In cooler parts of their range, such as Tasmania, females may mate within a few hours of arousal from hibernation.

paragraphs: Before mating, the male smells the female, paying particular attention to the cloaca. The male is often observed to roll the female onto her side and then assumes a similar position so that the two animals are abdomen to abdomen. Each mating results in the production of a single egg, and females are known to mate only once during the breeding season; each mating is successful.

paragraphs: Fertilisation occurs in the oviduct. Gestation takes between 21 and 28 days, during which time the female constructs a nursery burrow. Following the gestation period, a single rubbery-skinned egg between 13 and 17 millimetres in diameter is laid directly into a small, backward-facing pouch that has developed on her abdomen. Ten days after it is laid, the egg hatches within the pouch. The embryo develops an "egg tooth" during incubation, which it uses to tear open the egg; the tooth disappears soon after hatching.

paragraphs: Hatchlings are about 1.5 cm long and weigh between 0.3 and 0.4 grams. After hatching, young Echidnas are known as "puggles". Hatchlings attach themselves to their mothers' milk areolae, a specialised patch on the skin that secretes milk (monotremes have no nipples). The way in which puggles drink the milk is not yet known, but they have been observed drinking large amounts during each feeding period, since mothers may leave them unattended in the burrow for between five and ten days. The principal components of the milk are types of lactose. The milk has a high iron content, which gives it a pink colour.

paragraphs: Juveniles are eventually ejected from the pouch at around two to three months of age, because of the continuing growth in the length of their spines. Suckling gradually decreases until juveniles are weaned at about six months of age. The duration of lactation is about 200 days, and the young leave the burrow between 180 and 240 days.

paragraphs: The age of sexual maturity is uncertain, but may be four to five years. A twelve-year field study, published in 2003, found that the Short-beaked Echidna reached sexual maturity between five and 12 years of age, and that the frequency of reproduction varies from once every two years to once every six years. The Short-beaked Echidna can live as long as 45 years in the wild.

paragraphs: No systematic study of the ecology of the Short-beak Echidna has been published. There have been studies of several aspects of their ecological behaviour. Short-beaked Echidnas live alone and apart from the burrow created for rearing young; they have no fixed shelter or nest site. They do not have a home territory, but range over a wide area. Short-beaked Echidnas are usually active in the daytime; however, they have problems in hot weather, because they have no sweat glands and do not pant. Therefore, in warm weather they change their pattern of activity, becoming crepuscular (active at dawn or dusk) or nocturnal (active in the night). They can tolerate cold temperatures, and hibernate during the winter in very cold regions.

paragraphs: Short-beaked Echidnas can live anywhere where there is a good supply of food. Short-beaked Echidnas find food by smell, using sensors in the tip of their beak, and regularly feast on ants and termites. They are powerful diggers, using their clawed front paws to dig out prey and dig burrows for shelter. They may rapidly dig themselves into the ground if they cannot find cover when in danger.

paragraphs: In Australia they are most common in forested areas where there are many termite-filled fallen logs. In agricultural areas, they are most likely to be in uncleared scrub; they may be in grassland, arid areas, and in the outer suburbs of the capital cities. Little is known about their distribution in New Guinea. They have been found in southern New Guinea between Merauke in the west, to the Kelp Welsh River, east of Port Moresby, where they may be in open woodland.

paragraphs: The Short-beaked Echidna is common in most of temperate Australia and lowland New Guinea, and is not listed as endangered. In Australia, the number of Short-beaked Echidnas has been less affected by land clearing than have some other species, since Short-beaked Echidnas do not require a specialised habitat beyond a good supply of ants and termites. Despite their spines, they are eaten by birds, the Tasmanian Devil, cats, foxes and dogs. They were also eaten by indigenous Australians and the early Europen settlers of Australia. The most common threats to the animal in Australia are cars and habitat destruction. These have led to localised extinction. Infection with the introduced parasite "Spirometra erinaceieuropaei" is fatal for the Echidna. The Wildlife Preservation Society of Queensland runs an Australia-wide survey called "Echidna Watch" to monitor the species in Australia.

paragraphs: Captive breeding is difficult, partly because of the relatively infrequent breeding cycle. Only five zoos have managed to breed a captive Short-beaked Echidna, but no captive-bred young have survived to be adults. This has conservation implications for the endangered species of echidna from the genus "Zaglossus", and to a lesser extent for the Short-beaked Echidna.

paragraphs: Short-beaked Echidnas feature in the animistic culture of Indigenous Australians, including their visual arts and stories. The species was a totem for some groups, including the Noongar people from Western Australia, who called the animal the "Nyingarn". Many groups have myths about the animal; one myth explains that it was created when a group of hungry, young men went hunting at night and stumbled across a wombat. They threw spears at the wombat, but lost sight of it in the darkness. The wombat adapted the spears as its own defense and turned into an Echidna. Another story tells of a greedy man that kept food from his tribe; warriors speared him and he crawled away into the bushes, where he was turned into an Echidna, the spears becoming his spines.

paragraphs: The Short-beaked Echidna is an iconic animal in modern Australia. It appears on the Australian five-cent piece (the smallest denomination) and on a $200 commemorative coin released in 1992. The Short-beaked Echidna has been included in several postal issues: it was one of four native species to appear on Australian postage stamps in 1974, where it was the 25 cent stamp; it appeared on a 37 cent stamp in 1987, and again in 1992 when it was on the 35 cent stamp. The anthropomorphic Echidna "Millie" was a mascot for the 2000 Summer Olympics.


title: Columbia

paragraphs: Columbia is the original name for the United States and inspired the names of many things. For the original Columbia, see "Historical Columbia".


title: Eastern long-beaked echidna

paragraphs: The eastern long-beaked echidna ("Zaglossus bartoni"), also known as Barton's long-beaked echidna, is one of three species from the genus "Zaglossus". All of them occur in New Guinea. It is found mainly in Papua New Guinea between 2000 and 3000 meters above sea level.

paragraphs: It can be distinguished from other members of the genus by the number of claws on the fore and hind feet. It has five claws on its fore feet and four on its hind feet. The adult animal weights between 5 kg (11 lb) and 10 kg (22 lb). Its body length ranges from 60–100 cm (23.5-39 inches). It has no tail. It has dense black fur. The species is the largest monotreme and is slow moving. It rolls into a spiny ball for defense.

paragraphs: The population of each subspecies is geographically isolated and they can be distinguished primarily by differences in body size.


title: Long-beaked echidna

paragraphs: The long-beaked echidnas make up one of the two genera (Genus Zaglossus) of echidna. Echidna is a spiny monotreme that lives in New Guinea. There are three living species, and two extinct ones.

paragraphs: Echidnas are one of the two types of mammals that lay eggs.

paragraphs: Remarks: Species described from one sample only. May be endangered, or locally extinct. See Sir David's Long-beaked Echidna

paragraphs: Remarks: see Eastern Long-beaked Echidna

paragraphs: Remarks: see Western Long-beaked Echidna

paragraphs: Remarks: This species is known only from a few bones. At a metre long, it was huge for an echidna and for monotremes in general.

paragraphs: Remarks: This species is known from a fossil skull about 65 cm long.


title: Sir David's long-beaked echidna

paragraphs: Sir David's long-beaked echidna ("Zaglossus attenboroughi"), also known as the cyclops long-beaked echidna, is one of three species of the genus "Zaglossus". All of them are found in New Guinea. It is named after Sir David Attenborough. It lives in the Cyclops mountains in Papua province of Indonesia near the cities of Sentani, Jayapura.

paragraphs: The species was described from a single damaged animal, which was collected in the Dutch colonial era (c. 1961). It has not been collected since that time. The Cyclops mountain forest habitat has been disturbed recently. This has raised concern that "Z. attenboroughi" populations may already be endangered or even locally extinct. However, many parts of the mountains are covered in thick jungle and have not been searched since 1961. It is possible that the animal still exists there or in nearby mountain ranges. In 2007 scientists found holes which they believe were made by the echidna poking its nose into the dirt while looking for earthworms.

paragraphs: It is the smallest member of the genus. It is closer in size to the short-beaked echidna than other members of the genus. It has five claws on its fore and hind feet. It has dense short fur.


title: Bioluminescence

paragraphs: Bioluminescence is the capacity of living things to produce light. Often this is done by symbiosis. In this, the larger organism contains, often in a special organ, microorganisms which make the light. Eukaryote protists have special organelles, and some bacteria also produce light. Bioluminescence is the result of chemical processes, where the energy produced is released as visible light. Bioluminescence has appeared many times during evolution.

paragraphs: ATP (adenosine tri-phosphate), the biological energy source, reacts with luciferin with the aid of the enzyme luciferase to yield an intermediate complex. This complex combines with oxygen to produce a highly chemiluminescent (brightly shining) compound.

paragraphs: The role of Gamma Proteobacteria in producing light is discussed in detail in reference works. The capacity to produce light is an extension of normal metabolism: all chemical reactions produce a few photons. Visible light is produced when the photon production increases. In the case of bacteria, the original function of the reaction was probably to detoxify excessive oxygen.

paragraphs: Bioluminescence is mainly a marine phenomenon.

paragraphs: Bioluminescence is found in the sea at all levels.: planktonic, pelagic and benthic organisms. Some planktonic groups, such as dinoflagellates and ctenophores (comb jellies) use it in most species. Most deep-sea marine life use bioluminescence in one form or another. Usually, marine light-emission belongs in the blue and green light spectrum, the wavelengths that can transmit through seawater most easily.

paragraphs: In some squid species bacterial bioluminescence is used for counterillumination so the animal matches the overhead environmental light seen from below. In these animals, light organs control the contrast of this illumination to create optiminal matching. Usually these light organs are separate from the tissue containing the bioluminescent bacteria.

paragraphs: Bioluminescence is used as a lure to attract prey by several deep sea fish such as the anglerfish. A dangling lure on the head of the fish attracts small animals to it within striking distance. Some fish, however, use a non-bioluminescent lure.

paragraphs: The cookiecutter shark uses bioluminescence for camouflage, but a small patch on its underbelly remains dark and appears as a small fish to large predatory fish like tuna and mackerel swimming beneath it. When these fish try to consume the "small fish", they are bitten by the shark, which gouges out small circular "cookie cutter" shaped chunks of flesh from its hosts.

paragraphs: Dinoflagellates have an interesting twist on this mechanism. When a predator of plankton is sensed through motion in the water, the dinoflagellate luminesces. This in turn attracts even larger predators which will consume the would-be predator of the dinoflagellate.

paragraphs: Attracting mates is an important function of bioluminescence. This is seen in fireflies, which use periodic flashing in their abdomens to attract mates in the mating season. In the marine environment this has only been well-documented in certain small ostracod crustaceans, but may be quite common.

paragraphs: Certain squid and small crustaceans use bioluminescence as many squid use ink. A cloud of luminescence is expelled, confusing or repelling a potential predator while the squid or crustacean escapes to safety. Every species of firefly has larvae that glow to repel predators.

paragraphs: Bioluminescent organisms are a target for many areas of research. Luciferase systems are widely used in the field of genetic engineering. They have also been used in biomedical research, to give some cells visible labels. Luciferin can be added to molecules and cells to make them visible under the microscope. "This market is now worth about £20bn. If you go into a hospital and have a blood test which measures viral proteins, cancer proteins, hormones, vitamins, bacterial proteins, drugs, it will almost certainly use this technique".

paragraphs: The structure of photophores, the light producing organs in bioluminescent organisms, are being investigated by industrial designers.

paragraphs: This is a list of organisms that have visible bioluminescence:

paragraphs: Despite their name, fireflies are actually beetles which use an enzymatic reaction involving a chemical compound called luciferin to produce their typical greenish flashing light. As well as possibly warning predators about their toxicity, it is thought the main purpose of their flashing abdomen is to attract mates.


title: Whittier, Alaska

paragraphs: Whittier is a small town in Alaska on the Kenai Peninsula. Whittier has 182 people always living in it. The Whittier Glacier near Whittier was named for the American poet John Greenleaf Whittier in the year 1915.

paragraphs: During World War II the United States Army built a port and railroad near the glacier and named the port Whittier. The two big buildings that are very easy to notice in Whittier were built after World War II. The Hodge Building (now called Begich Towers) was built for housing soldiers and the Buckner Building, finish being built in 1953, was called the "city under one roof". It was once the biggest building in Alaska. The Begich Building is now a condominium (or houst that has many rooms that people live in), and almost all of the people that live in Whittier's live here.

paragraphs: The town was badly damaged by tsunamis (or very big waves) started by the 1964 Good Friday Earthquake; thirteen people died because of the waves that were 13 m (43 ft) tall.

paragraphs: Whittier is a popular port for cruise ships, because people can go to Anchorage and the inside of Alaska by both car and train. Whittier is also popular with visitors and fishermen.

paragraphs: Whittier is the wettest city in Alaska and the United States. The city receives at least 198 inches of rain a year.


title: Kate Winslet

paragraphs: Kate Elizabeth Winslet, (born 5 October 1975) is an English actress. She made her movie debut as Juliet Hulme in Peter Jackson's "Heavenly Creatures" (1994). She is best known for her starring role in the American movie, "Titanic". Winslet is the second of four children, her sisters are the actresses Anna and Beth Winslet and her brother is Joss Winslet, her mother Sally Anne is a barmaid and her father Roger John Winslet is a swimming pool contractor. Her maternal grandparents Linda and Oliver Bridges founded the Reading Repertory Theatre and her uncle is the actor Robert Bridges, Her maternal great-grandmother Florence Theodelinda Lidman, was the daughter of a Swedish immigrant.

paragraphs: Kate Winslet was married to director Jim Threapleton; they had a daughter, Mia. She married director Sam Mendes; they had a son, Joe. In 2012, she married Ned Rocknroll, nephew of billionaire Richard Branson. She had his first son in December of 2013.


title: Joe DiMaggio

paragraphs: Joseph Paul DiMaggio (born Giuseppe Paolo Di Maggio Jr; November 25, 1914 - March 8, 1999) was a Major League Baseball center fielder who played his whole career for the New York Yankees. His nicknames were Joltin' Joe and The Yankee Clipper. He played from 1936 to 1942 and then joined the army in 1943 because of World War II. He came back and began playing again in 1946 until his retirement in 1951 at the age of 36. By the time he retired he had hit 361 home runs. He hit almost one home run for every strikeout. DiMaggio died on the 8th of March, 1999, of lung cancer. He is widely regarded as one of the best baseball players of all time. DiMaggio was also well known for his marriage and lifelong devotion to Marilyn Monroe.


title: Mongol Empire

paragraphs: The Mongol Empire, an area ruled by the great Mongol Khans in the 13th and 14th centuries, was one of the largest land empires in history.

paragraphs: The original homeland of the Mongols, was bounded by the Khingan Mountains on the east, the Altai and Tian mountains on the west, the Shilka River and the mountain ranges by Lake Baikal on the north, and the Great Wall of China on the south.

paragraphs: It was founded by Genghis Khan in 1206 AD when he brought together the Mongol and Turkic tribes. When he died in 1227 AD, he had conquered Central Asia, North China and parts of eastern Persia. Later his grandson Kublai Khan would go on to expand the empire and found the Mongol-ruled Yuan Dynasty, ruling whole China. The Mongol Empire stretched from Eastern Europe to Western Asia, including Central Asia and the Middle East. Its power did not last long, though. By the 1360s it had broken into several empires, all of which were later destroyed.


title: Parthia

paragraphs: Parthia is an ancient country of Asia, now Iran and regions of Armenia, Iraq, Georgia, eastern Turkey, eastern Syria,Azerbaijan, Turkmenistan, Afghanistan, Tajikistan, Pakistan, Kuwait, the Persian Gulf coast of Saudi Arabia, Bahrain, Qatar, and UAE.

paragraphs: Parthians were excellent horsemen and archers. In battle, mounted Parthians often discharged their arrows back towards the enemy while pretending to flee.

paragraphs: In 250 BC, the Parthians succeeded in founding an independent kingdom that in the 1st century BC it grew into an empire extending from the Euphrates to the Indus and from the Amu Darya to the Indian Ocean.


title: Hydrolysis

paragraphs: Hydrolysis is a chemical reaction or process where a chemical compound reacts with water. This is the type of reaction that is used to break down polymers into many smaller units. In this reaction, water is always added to the chemical compound.

paragraphs: Hydrolysis of metal salts is more commonly known as hydration. Many metal ions are strong Lewis acids, and in water they may undergo hydrolysis to form "basic salts". Such salts contain a hydroxyl group that is directly bound to the metal ion in place of a water ligand. The positive charge on metal ions creates an attraction to water, a Lewis base with a non-binding electron pair on the oxygen atom, and alters the water molecule's electron density. This in turn increases the polarity of the O-H bond, which now acts as a proton donor under Brønsted-Lowry acid-base theory to release the hydrogen as a H+ ion, increasing the acidity of the solution. For example, aluminium chloride undergoes extensive hydrolysis in water with the solution being very acidic.

paragraphs: This implies that hydrogen chloride is lost in the evaporation of AlCl solutions and the residue is a basic salt (in this case an "oxychloride") in place of AlCl. This type of reaction is also seen with other metal chlorides such as ZnCl, SnCl, FeCl and lanthanide halides such as DyCl. With some compounds such as TiCl, the hydrolysis may go to completion and form the pure hydroxide or oxide, in this case TiO.


title: Water (molecule)

paragraphs: Water (HO, HOH) covers 70-75% of the Earth's surface in its liquid and solid (ice) states, and is present in the atmosphere as a vapor. It is the most abundant molecule on the Earth's surface.

paragraphs: At room temperature, it is a nearly colorless, flavorless, and odorless liquid. Many substances dissolve in water and it is commonly seen as "the universal solvent"; because of this, water in nature and in use is rarely clean, and may have some properties different than those in the laboratory. But there are many compounds that are essentially, if not completely, insoluble in water. Water is the only common, pure substance found naturally in all three states of matter—for other substances, see Chemical properties.

paragraphs: Pure water is tasteless. It is the other chemicals in the water which may give water a flavour.

paragraphs: Generally, the volume of a liquid increases when heated, however the volume of water "decreases" when heated within the temperature range of 0°C to 4°C. Its volume increases only when heated above 4°C. Such behavior is one of a number of water's anomalous properties.

paragraphs: This property of volume decrease allows fish and other aquatic animals to survive in a body of water when ice has frozen on the surface. In cold climates, when the temperature of a body of water reaches at 4°C, the layers of water near the top in contact with cold air continue to lose heat energy and their temperature falls below 4°C. On cooling below 4°C, these layers rise rather than sink, as water has maximum density at 4°C. Thus the layer of water with a temperature of 4°C remains at the bottom, while layers of water 3°C, 2°C, 1°C and 0°C are formed above. Because ice is poor conductor of heat, it does not allow heat energy transfer from the liquid water beneath the layers of ice, which prevents the liquid water from freezing. Hence, aquatic creatures survive in such places.


title: Lymphatic system

paragraphs: In mammals, the lymphatic system is a network of thin vessels that branch, like blood vessels, into tissues throughout the body. It is part of the immune system. It is a one-way system which carries cells and fluid back to the blood system.

paragraphs: Lymphatic vessels carry lymph, a colorless, watery fluid and white blood cells. It comes from interstitial fluid in the tissues which is squeezed out of the blood vessels. The lymphatic system transports infection-fighting cells called lymphocytes, and is involved in the removal of foreign matter and cell debris by phagocytes. A second function is to transport fats from the small intestine to the blood.

paragraphs: Lymphatic fluid gathers from the tissues and enters the valved lymphatic ducts. It is the valves which make sure the lymph flows the right way. On its way back to the blood system, the lymph passes through glands called lymph nodes, in places like the back of the neck, the armpits and the groin. Lymph nodes swell in the region of an infected body part. This acts to keep the infection from spreading. It prevents or reduces the pathogens getting into the general blood circulation and reaching other parts of the body.

paragraphs: Lymph ends up back in the blood system. In mammals under normal conditions most of the lymph is returned to the blood stream through lymph-vein communications at the base of the neck. Some vertebrates have more complex lymphatic systems. Amphibians for example have multiple "lymph hearts" to control the flow of lymph.


title: Chastity

paragraphs: Chastity is the sexual behavior of a man or woman which is right and proper according to the moral rules of a culture or religion. It has recently begun to mean sexual abstinence (not having sex at all), especially before marriage. However, it can also be used for all kinds of people (even married people) with more meaning than simply not having sex. The word chastity came from the Latin word "castitatem", meaning "purity".


title: Metallic bond

paragraphs: A metallic bond is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue" giving the substance a definite structure. It is unlike covalent or ionic bonding.

paragraphs: Metals have low ionization energy. Therefore, the valence electrons can be delocalized throughout the metals. Delocalized electrons are not associated with a particular nucleus of a metal, instead, they are free to move throughout the whole crystalline structure forming a "sea" of electrons.

paragraphs: The electrons and the positive ions in the metal have a strong attractive force between them. Therefore, metals often have a high melting or boiling points. The principle is similar to that of ionic bonds.

paragraphs: Metallic bonds causes many of the traits of metals, such as strength, malleability, ductility, luster, conduction of heat and electricity.

paragraphs: Because the electrons move freely, the metal has some electrical conductivity. It allows the energy to pass quickly through the electrons, generating an electric current. Metals conduct heat for the same reason: the free electrons can transfer the energy at a faster rate than other substances with electrons that are fixed into position. There also are few non-metals which conduct electricity: graphite (because, like metals, it has free electrons), and ionic compounds that are molten or dissolved in water, which have free moving ions.

paragraphs: Metal bonds have at least one valence electron which they do not share with neighboring atoms, and they do not lose electrons to form ions. Instead, the outer energy levels (atomic orbitals) of the metal atoms overlap. They are similar to covalent bonds. Not all metals exhibit metallic bonding. For example, mercury ions () form covalent metal-metal bonds.

paragraphs: An alloy is a solution of metals. Most alloys are shiny like pure metals are.


title: Heat conduction

paragraphs: Heat conduction (or thermal conduction) is the movement of heat from one object to another one that has different temperature when they are touching each other. For example, we can warm our hands by touching hot-water bottles. When the cold hands touch the hot-water bottle, heat flows from the hotter object (hot-water bottle) to the colder one (hand). People make things with different thermal conductivity, for example cookware to heat things or insulated containers to keep hot things hot or cold things cold.

paragraphs: Other ways to transfer heat are by thermal radiation and/or convection. Usually more than one of these processes happen at the same time.

paragraphs: In the atomic theory solids, liquids and gases are made of tiny particles called "atoms". The temperature of the material measures how fast the atoms are moving and the heat measures the total amount of energy due to the vibration of the atoms.

paragraphs: Conduction can happen when one part of a material is heated. The atoms in this part vibrate faster and are more likely to hit their neighbors. The collisions cause those atoms also to move faster, passing the heat energy to them. In this way the energy travels through the solid. (Rather like the way energy passes along a set of tumbling dominos).

paragraphs: The atomic picture also helps explain why conduction is more important in solids: in solids the atoms are close together and unable to move around. In liquids and gases the particles can move past each other, so the collisions are less common.

paragraphs: The law of heat conduction, also known as Fourier's law, means that the rate, in time, of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing:

paragraphs: Thermal conductivity usually varies with temperature, but the variation can be small, over a significant range of temperatures, for some common materials.


title: Judith Weir

paragraphs: Judith Weir (born 11 May 1954) is a British composer. She is well known for her theatre works, choral music, orchestral music and chamber music.

paragraphs: Weir was born in Cambridge, England to Scottish parents. While she was still at school she trained with the composer John Tavener. She played the oboe in the National Youth Orchestra of Great Britain. She then studied at the University of Cambridge where her teacher was Robin Holloway.

paragraphs: Judith Weir’s music has harmonies which are very exciting and original. Her Christmas carol "Illuminare" has become very popular, but it is quite difficult and needs a good choir to pitch the notes of the dissonant chords. She often uses medieval history as inspiration for her music, as well as music from her native Scotland, e.g. piobaireachd, which is a kind of variation form using small intervals. Her music often tells stories. Her operas include "A Night at the Chinese Opera", "The Vanishing Bridegroom", "Blond Eckbert", and "Armida", an opera for television.

paragraphs: From 1995 to 2000, she was the Artistic Director of the Spitalfields Festival in London. She has composed works for the City of Birmingham Symphony Orchestra. She has received many honours, including the CBE in 1995.


Chorus


title: Vassal

paragraphs: A vassal during the feudalism of medieval Europe, was someone who had shared duties with a lord. Usually the vassal provided soldiers to the lord. The lord used his army of soldiers from all of his vassals to protect those vassals. The lord also gave him the piece of land that he held as a fief. By analogy the term "vassal" is used also for similar systems in other feudal societies.

paragraphs: The development of the "vassal", in a society that was increasingly organised around the concept of "lordship"– in French the "seigneur"– is one sign that Antiquity ended and the Early Middle Ages began. Lordship is the basic social institution as Tacitus described them in his book "Germania". The Roman West experienced them for the first time in the Migration Period.

paragraphs: As the system developed in the seventh century, the vassals were gangs of freemen who subjected themselves, in some degree of formality, to the authority of a leader, from whom they could expect to be fed, clothed and armed. The quality of a vassal was only in his fighting ability and the strength of his loyalty. The etymology (where the word came from) of "vassal" is from a Celtic word "gwas" "boy" that meant a young male slave, with a Latinised form, "vassus" that appeared in Salic Law (Rouche 1987 p 429), like the way "knight" came from the from Old English word "cniht" and similar words in Frisian and Dutch, all meaning "lad" .


title: Migration period

paragraphs: The migration period, or barbarian invasions or Völkerwanderung, happened in AD 300–700 in Europe, at the end of ancient history and during the Early Middle Ages.

paragraphs: The migrations included the Goths, Vandals, Franks, and other Germanic, Bulgar, and Slavic tribes. They may have been influenced by attacks of the Huns in the East and may also be connected to the Turkic migrations in Central Asia, overpopulation, or climate changes. The migration period also included groups of Angles, Saxons, Frisians, and some Jutes to Britain.

paragraphs: Migrations would continue well into the Middle Ages, beyond 1000 AD, with successive waves of Slavs, Alans, Avars, Bulgars, Hungarians, Pechenegs, Cumans, and Tatars that changed the ethnic makeup of Eastern Europe. Western European historians, however, tend to stress the migrations that were most relevant to Western Europe.


title: San Francisco Bay Area

paragraphs: The San Francisco Bay Area, also known as the Bay Area, is a metropolitan area that goes around the San Francisco Bay in Northern California. It includes the cities of San Francisco, San José, and Oakland, and their many suburbs. It also includes the smaller urban and rural areas of the North Bay. Over seven million people live in the San Francisco Bay Area. The San Francisco Bay Area is the 43rd largest metropolitan area in the world in population.

paragraphs: The Bay Area includes cities, towns, military bases, airports, and related regional, state, and national parks.

paragraphs: San José is the largest city in the Bay Area since 1990 and the tenth largest city in America. But for most of its history, San Francisco was the city with the most people. San Francisco is still the city people pay the most attention to, and it is the major cultural center in the region.

paragraphs: Bay Area Rapid Transit connects the different parts of the Bay Area.

paragraphs: The region north of the Golden Gate Bridge is known locally as the North Bay. This area includes Marin County and continues north into Sonoma and Napa counties and east to Solano County. With some exceptions, this region is quite rich: Marin County is listed as the richest in the nation.

paragraphs: The City and County of San Francisco is generally placed in a category by itself in terms of geography and culture. It is separated by water from the north, west and east, and by a county line from its neighbor cities to the South. San Francisco has been the cultural, financial and urban center of the region for a long time. For most of the Bay Area's history, it has also been the main population center. But because the size of the county is limited, the growth of the city was limited as well. As a result, other cities and counties have had more population growth.

paragraphs: The area between the South Bay and the City and County of San Francisco is the San Francisco Peninsula, known locally as "The Peninsula". This area includes many small cities and suburban communities in San Mateo County and the northwestern part of Santa Clara County, as well as several towns along the Pacific coast, such as Pacifica and Half Moon Bay.

paragraphs: The eastern side of the bay, consisting of Alameda and Contra Costa counties, is known locally as the East Bay. The East Bay is split into two regions, the inner East Bay, which is on the coast of the Bay, and the outer East Bay, including the inland valleys separated from the inner East Bay by hills and mountains.

paragraphs: The communities along the southern edge of the Bay are known as the South Bay, Santa Clara Valley, and Silicon Valley.

paragraphs: This region is home to a large number of major technology companies. Some tech companies in the South Bay are Intel, AMD, Cisco Systems, Hewlett-Packard, Apple, Google, and Yahoo!, Microsoft and much much more.

paragraphs: The San Francisco Bay Area is one of the richest regions in the United States.


title: San Francisco Bay

paragraphs: San Francisco Bay is a shallow, productive estuary through which water draining about forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains and Central Valley, enters the Pacific Ocean. Technically, both rivers flow into Suisun Bay, which help flows through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay, which connects at its south end to San Francisco Bay, although the entire group of interconnected bays are often referred to as "the San Francisco Bay."

paragraphs: San Francisco Bay lies in the US state of California and is surrounded by a region known as the San Francisco Bay Area, that is near the big cities of San Francisco, Oakland, and San Jose.

paragraphs: The Bay covers somewhere between 400 and 1,600 square miles (1,040 to 4,160 square kilometres), depending on which sub-bays (such as San Pablo Bay), estuaries, wetlands, and so on are included in the measurement.


title: Ahmed Yassin

paragraphs: Ahmed Yassin (January 1, 1937 – March 22, 2004) was a spiritual leader of the militant Palestinian group Hamas. Yassin's birth date is in dispute. He claimed he was born 1/1/1938, however, his passport indicated 1/1/1937. To some he was a hero, to some he was a notorious member of a terrorist organization. He was also a symbolic figure for Palestinians to fight against Israel.

paragraphs: Yassin was born in al-Jura, British Mandate of Palestine. He helped create Hamas and became its spiritual leader in 1987. To other members of Hamas he was a hero but he was blamed by the Israeli government for planning suicide bombings and other attacks against Israel. He claimed that was the only way of fighting occupation. He was confined to a wheelchair because he was paralyzed since age 12, he was also nearly blind and could barely hear. He was very powerful and influential. He was assassinated in an airstrike in Gaza City by the Israeli Army after he left a mosque in Gaza in the early morning hours.


title: Field strength

paragraphs: In physics, the field strength of a field is the magnitude (size) of its (vector) value. This means that the force exerted by the field on a given object is proportional to the field strength.

paragraphs: In differential geometry, the field strength is another name for the curvature form. For the electromagnetic field, the curvature form is an antisymmetric matrix whose elements are the electric field and magnetic field: the electromagnetic tensor.

paragraphs: In radio engineering, field strength is the strength of radio waves in a particular location.


title: Field (physics)

paragraphs: In physics, a field means that a physical quantity is assigned to every point in space (or, more generally, spacetime). A field is seen as extending throughout a large region of space so that it influences everything. The strength of a field usually varies over a region. Michael Faraday became the first to coin the term "field", in 1849.

paragraphs: For some fields, there is a number for each point in space. They are called "scalar fields". For more complicated fields, there are more than one number for each point in space. They are called "vector fields" or "tensor fields". For example, one can model a gravitational field by a vector field where a vector indicates the acceleration a mass would experience at each point in space. Other examples are temperature fields or air pressure fields, which are often illustrated on weather reports by isotherms and isobars by joining up the points of equal temperature or pressure respectively.

paragraphs: It is now believed that quantum mechanics should underlie all physical phenomena.

paragraphs: A field theory is a physical theory that describes how one or more physical fields interact with matter.


title: Gradient

paragraphs: In vector calculus, the gradient of a multivariate function measures how steep a curve is. On a graph of the function, it is the slope of the tangent of that curve. More generally, it is a vector that points in the direction in which the function grows the fastest. Its coordinates are partial derivatives of that function. The gradient of a function "f" is often written as formula_1 or formula_2.


title: Trigonometric function

paragraphs: In mathematics, the trigonometric functions are a set of functions which relate angles to the sides of a right triangle. There are many trigonometric functions, the 3 most common being sine, cosine, tangent, followed by cotangent, secant and cosecant. The last three are called reciprocal trigonometric functions, because they act as the reciprocals of other functions. Secant and cosecant are rarely used.

paragraphs: The trigonometric functions sometimes are also called circular functions. They are functions of an angle; they are important when studying triangles, among many other applications. Trigonometric functions are commonly defined as ratios of two sides of a right triangle containing the angle, and can equivalently be defined as the lengths of various line segments from a unit circle (a circle with radius of one).

paragraphs: In order to define the trigonometric functions for the angle "A", start with a right triangle that contains the angle "A":

paragraphs: We use the following names for the sides of the triangle:

paragraphs: All triangles are taken to exist in Euclidean geometry, so that the inside angles of each triangle sum to π radians (or 180°); therefore, for a right triangle, the two non-right angles are between zero and π/2 radians. Notice that strictly speaking, the following definitions only define the trigonometric functions for angles in this range. We extend them to the full set of real arguments by using the unit circle, or by requiring certain symmetries and that they be periodic functions.

paragraphs: 1) The sine of an angle is the ratio of the length of the opposite side to the length of the hypotenuse. In our case

paragraphs: Note that since all those triangles are similar, this ratio does not depend on the particular right triangle that is chosen, as long as it contains the angle "A".

paragraphs: The set of zeroes of sine (that is, the values of formula_2 for which formula_3) is

paragraphs: 2) The cosine of an angle is the ratio of the length of the adjacent side to the length of the hypotenuse. In our case

paragraphs: 3) The tangent of an angle is the ratio of the length of the opposite side to the length of the adjacent side. In our case

paragraphs: This is the same set as that of the sine function, since

paragraphs: The remaining three functions are best defined using the above three functions.

paragraphs: 4) The cosecant csc("A") is the multiplicative inverse of sin("A"); it is the ratio of the length of the hypotenuse to the length of the opposite side:

paragraphs: 5) The secant sec("A") is the multiplicative inverse of cos("A"); it is the ratio of the length of the hypotenuse to the length of the adjacent side:

paragraphs: 6) The cotangent cot("A") is the multiplicative inverse of tan("A"); it is the ratio of the length of the adjacent side to the length of the opposite side:

paragraphs: One can also define the trigonometric functions by using power series:

paragraphs: and define tangent, cotangent, secant and cosecant using identities, see below.

paragraphs: The hyperbolic functions are like the trigonometric functions, in that they have very similar properties. Each of six trigonometric functions has a corresponding hyperbolic form. They are defined in terms of the exponential function, which is based on the constant "e".


title: Archer

paragraphs: An archer is someone who practices archery (shooting with bows and arrows).


title: Archery

paragraphs: Archery is the practice of using a bow to shoot arrows. Archery has historically been used in hunting and combat and has become a precision sport. A person practicing archery is called an "archer", and one who enjoys or is an expert at archery is sometimes called an toxophilite.

paragraphs: The earliest evidence of archery dates back more than 9,000 years. The bow probably was used in hunting first and later adopted as a tool of warfare. It was one of the earliest forms of artillery.

paragraphs: Classical civilizations, notably the Persians, Macedonians, Nubians, Greeks, Parthians, Indians, Japanese, Chinese, and Koreans, had large numbers of archers in their armies. Archers in chariots were especially important in armies of ancient Egypt. Arrows were very destructive against massed formations, and the use of archers helped win battles. The army of the Mongol Empire was mostly archers on horseback.


title: John Cena

paragraphs: John Felix Anthony Cena Jr. (born April 23, 1977) is an American professional wrestler, hip hop musician and actor. He currently works for the WWE. Cena has won the WWE Championship/WWE World Heavyweight Championship thirteen times, the World Heavyweight Championship thrice, the United States Championship five times and the World Tag Team Championship twice. Also, Cena won the Royal Rumble in 2008 and 2013. As for his musical career, Cena has released an album called "you cant see me". Cena has also been featured in the movies "The Marine", "12 Rounds" and "Legendary". In Baseball, he is a Red Sox fan turned Rays fan. Successful rapper, prior experience with Tupac, biggie smalls, N.W.A and many more.

paragraphs: Cena was signed by then Person in charge of Talent Relations, Jim Ross on behalf on WWF. According to Ross, when he returned to Connecticut after signing Cena he walked into Vince McMahon's office and told him "I just signed your main event for WrestleMania in 5 years." Cena would eventually make his WrestleMania debut 3 years later at WrestleMania XX winning the WWE United States Championship from The Big Show, and his Main event WrestleMania debut 4 years later winning the WWE Championship, from John "Bradshaw" Layfield.

paragraphs: During the match between Barrett and Orton, Orton won so Cena was forced to retire. He was rehired by Wade Barrett and defeated him at TLC: Tables, Ladders and Chairs Pay Per View.

paragraphs: He was drafted to SmackDown as the first pick in the 2011 WWE Draft, but before the end of the night, he was drafted back to Raw.

paragraphs: He was defeated by The Rock at WrestleMania XXVIII. He won his second Royal Rumble in January 2013. Thus he got another match at WrestleMania XXIX against The Rock for WWE Championship. He won that match and became the WWE Champion. He retired the next night on Raw after getting defeated by the debuting Dominik Mysterio, the son of professional wrestler Rey Mysterio. He was inducted in the 1938 WWE Hall of Fame.


title: Signal transduction

paragraphs: A signal transduction in biology is a cellular mechanism. It converts a stimulus into a response in the cell. There are two stages in this process:

paragraphs: So, signal transduction starts with a signal to a cell receptor, and ends with a change in cell function. In either step, the signal can be amplified. Thus, one signalling molecule can cause many responses.

paragraphs: Receptors are in the cell membrane, with part of the receptor outside and part inside the cell.  The chemical signal binds to the outer portion of the receptor, changing its shape. This causes another signal inside the cell.  Some chemical messengers, such as testosterone, can pass through the cell membrane, and bind directly to receptors in the cytoplasm or nucleus.

paragraphs: Sometimes there is a cascade of signals within the cell. With each step of the cascade, the signal can be amplified, so a small signal can result in a large response. Eventually, the signal creates a change in the cell, either in the expression of the DNA in the nucleus or in the activity of enzymes in the cytoplasm.

paragraphs: Most often, ordered sequences of biochemical reactions inside the cell are involved. These are carried out by enzymes and linked through second messengers. So a "second messenger pathway" is produced. These things usually happen quickly, sometimes very quickly. They may last from milliseconds (in the case of ion flux) to days for gene expression.

paragraphs: The number of proteins and other molecules that take part increases during the process. So a 'signal cascade' develops and "a relatively small stimulus may cause a large response".

paragraphs: In bacteria and other single-cell organisms, the transduction processes a cell has limits the number of ways it can respond to its environment. In multicellular organisms, lots of different signal transduction processes are used to coordinate the behavior of individual cells. By this means the function of the organism as a whole is organized. The more complex the organism, the more complex the repertoire of signal transduction processes the organism must possess.

paragraphs: Thus, sensing of both the external and internal environment at the cellular level, relies on signal transduction. Many disease processes such as diabetes, heart disease, autoimmunity and cancer arise from defects in signal transduction pathways. This highlights the critical importance of signal transduction to biology and medicine.

paragraphs: These systems of communication between cells are extremely ancient, and are found in all metazoa.


title: Flux

paragraphs: Flux is a term in physics and mathematics. It is broadly defined as "How much stuff goes through a thing" (or into an area). The word "flux" is similar to "flow".

paragraphs: For instance, imagine a butterfly net. The amount of air passing through the net is the flux.

paragraphs: In the study of transport phenomena (heat transfer, mass transfer and fluid dynamics), flux is defined as flow per unit area, where flow is the movement of some quantity per time. Flux, in this definition, is a vector.

paragraphs: There are many fluxes used in the study of transport phenomena. Each type of flux has its own distinct unit of measurement along with distinct physical constants. Six of the most common forms of flux from the transport literature are defined as:

paragraphs: In the field of electromagnetism, flux is usually the integral of a vector quantity over a finite surface. The result of this integration is a scalar quantity. The magnetic flux is thus the integral of the magnetic vector field over a surface, and the electric flux is defined similarly. Using this definition, the flux of the Poynting vector over a specified surface is the rate at which electromagnetic energy flows through that surface. Confusingly, the Poynting vector is sometimes called the "power flux", which is an example of the first usage of flux, above. It has units of watts per square metre (W/m).


title: Neuroscience

paragraphs: Neuroscience (or neurobiology) is the scientific study of the nervous system. It is the branch of biology that investigates the molecular, cellular, developmental, functional, evolutionary, computational, psychosocial and medical aspects of the brain.

paragraphs: The nervous system is made of billions of neurons connected together and to other systems in the body. The central nervous system includes the brain, spinal cord and Retina. It is connected to the rest of the body via the peripheral nervous system. A neuroscientist, is a scientist who studies neuroscience.

paragraphs: Neuroscience research from different areas can also be seen as focusing on a set of specific themes and questions. (Some of these are taken from http://www.northwestern.edu/nuin/fac/index.htm)


title: Conversation analysis

paragraphs: Conversation analysis (commonly abbreviated as CA) is the study of talk in social interaction. CA tries to describe the structure and patterns of interaction, whether this is institutional (in the school, doctor's surgery, courts or elsewhere) or casual conversation.

paragraphs: The term “conversation” to label this disciplinary movement is misleading if read in a colloquial sense, as many have.


title: Mark-Anthony Turnage

paragraphs: Mark-Anthony Turnage (born Grays, Essex, 10 June 1960) is an English composer. He is one of the most original composers in his country today.

paragraphs: Turnage studied at the Royal College of Music and won all the major prizes. He became famous when he wrote an opera called "Greek". It is typical of his musical style: quite lyrical but also very dramatic and aggressive. His music is often inspired by jazz. Other works include "Kai", "Rockaby", "Blood on the Floor", "Dispelling the Fears", "Drowned Out" and "Three Screaming Popes". He has written music for the English National Opera, City of Birmingham Symphony Orchestra and the Chicago Symphony Orchestra.


title: Hydrothermal vent

paragraphs: A hydrothermal vent is an opening in the seabed of the Earth by which geothermal energy escapes. Sea water enters, becomes very hot, and rises. The hottest ones carry many black chemicals, and are called black smokers. Scientists have found fewer white smokers. Heat escapes from underground in many places. If they are on land, they are usually hot springs, geysers, or fumaroles. Many archaea and bacteria live near hydrothermal vents, which are underwater. They support giant tube worms, clams and shrimp, and many other eukaryotes. The earliest known life forms are thought to have lived near such vents.

paragraphs: Deep sea organisms have no access to sunlight, so they must depend on nutrients in the chemical deposits and hydrothermal fluids in which they live. Compared to the surrounding sea floor, however, hydrothermal vent zones have a density of organisms 10,000 to 100,000 times greater.

paragraphs: Hydrothermal vent communities are able to sustain such vast amounts of life because vent organisms depend on chemosynthetic bacteria for food. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material through the process of chemosynthesis.

paragraphs: The chemosynthetic bacteria grow into a thick mat which attracts other organisms such as amphipods and copepods which graze upon the bacteria directly. Larger organisms such as snails, shrimp, crabs, giant tube worms, fish, and octopus form a food chain of predator and prey relationships above the primary consumers.

paragraphs: The main groups of organisms around seafloor vents are worms, gastropods, and crustaceans, with large bivalves, and 'eyeless' shrimp making up the bulk of non-microbial organisms.

paragraphs: Tube worms form an important part of the community around a hydrothermal vent. They absorb nutrients directly into their tissues. There are approximately 285 billion bacteria per ounce of tubeworm tissue.

paragraphs: Tubeworms have red plumes which contain haemoglobin. Haemoglobin combines hydrogen sulfide and transfers it to the bacteria living inside the worm. In return the bacteria nourish the worm with carbon compounds.

paragraphs: Other examples of the unique fauna who inhabit this ecosystem are the gastropod "Crysomallon squamiferum", a species of snail with a foot reinforced by scales made of iron and organic materials, and the 'Pompeii Worm' "Alvinella pompejana", which is capable of withstanding temperatures up to 80°C (176°F).

paragraphs: Over 300 new species have been discovered at hydrothermal vents, many of them "sister species" to others in geographically separated vent areas. It has been proposed that before the North American plate overrode the Mid-Atlantic Ridge, there was a single biogeographic vent region found in the eastern Pacific. The subsequent barrier to travel began the evolutionary divergence of species in different locations. The examples of convergent evolution seen between distinct hydrothermal vents is seen as major support for the theory of natural selection and evolution as a whole.

paragraphs: A species of phototrophic bacterium has been found living near a black smoker off the coast of Mexico at a depth of . No sunlight penetrates that far into the waters. Instead, the bacteria, part of the Chlorobiaceae family, use the faint glow from the black smoker for photosynthesis. This is the first organism discovered in nature to exclusively use a light other than sunlight for photosynthesis.


title: Guava

paragraphs: Guavas are plants in the genus "Psidium" of the family Myrtaceae. There are about 100 species of tropical shrubs and small trees in the genus.

paragraphs: They are native to Mexico, the Caribbean, Central America and the northern part of South America. Now they are found in all the tropical, and in some subtropical, regions because they are edible fruits.

paragraphs: Guava are also a kind of berry fruit on those plants. There are many kinds of guavas. The most common guava is the apple guava ("Psidium guajava"): it is so common that the word 'guava' usually refers to this species. Red guavas are called maroonguava. In 100 g of guava are 200 mg of vitamin C, which means that guavas have five times more vitamin C than oranges.


title: Resting potential

paragraphs: The resting potential of a cell is the membrane potential that would be maintained if there were no action potentials, synaptic potentials, or other active changes in the membrane potential. In most cells the resting potential has a negative value, which by convention means that there is excess negative charge inside compared to outside. The resting potential is mostly determined by the concentrations of the ions in the fluids on both sides of the cell membrane and the ion transport proteins that are in the cell membrane. How the concentrations of ions and the membrane transport proteins influence the value of the resting potential is outlined below.


title: Thrust

paragraphs: Thrust is a force or a push. When a system pushes or accelerates mass in one direction, there is a thrust (force) just as large in the opposite direction. In math and physics, this is described by Isaac Newton’s second and third laws. Thrust is used to describe how strongly an engine pushes. It can be used for many kinds of vehicles and engines such as rockets, motorboats, propellers, and jet engines.

paragraphs: Thrust is measured in “pounds of thrust” in the U.S. and in newtons in the metric system. 4.45 newtons of thrust equals 1 pound of thrust. A pound of thrust is how much thrust it would take to keep a one-pound object unmoving against the force of gravity on earth.

paragraphs: A very common question is how to compare the thrust number of an airplane engine with the mechanical power of a piston engine (the kind of engine in cars and in many airplanes with propellers). It is hard to compare these two. This is because they are not measuring the same exact thing. A piston engine does not move the plane. It just turns the propeller, which moves the plane. Because of this, piston engines are rated by how much power they give to the propeller.

paragraphs: However, a jet engine has no propeller – it pushes the aircraft by moving hot air behind it. A useful way to measure the power of a jet engine is to how much power the jet engine gives to the aircraft through its thrust force. This is called the “propulsive power of the jet engine." Power is how much force it takes to move something over a distance, divided by the time it takes to move that distance:

paragraphs: Where P is power, F is force, d is distance, and t is time. For a rocket or jet engine, the force is the same as thrust produced by the engine. Distance divided by time is also called speed. So power is the same as thrust times speed

paragraphs: Where T is thrust and "v" is speed. This is the power being delivered by the engine at a certain thrust or velocity. The propulsive power of a jet engine increases with its speed.

paragraphs: When the thrust of a rocket or an engine is compared to the weight, it is called the Thrust-to-weight ratio. The number that comes from this comparison does not have any units, because it is a ratio. A ratio in this case means that the thrust of the engine (in Newtons) is divided by the weight (in Newtons). The purpose of this comparison is to show how well the engine or vehicle performs, for example how much acceleration. It is a number that can be used to compare various types of motors like airplane motors, jet engines, rocket engines, or car engines.

paragraphs: This comparison number can change while the engine is running. This is because the weight of the engine gets lighter as fuel is used. The thrust-to-weight ratio is used to actually compare engines is the number found when the engine is first running.

paragraphs: Thrust is measured in “pounds of thrust” in the U.S. and in Newtons in the metric system. 4.45 Newtons of thrust equals 1 pound of thrust. A pound of thrust is how much thrust it would take to keep a one-pound object unmoving against the force of gravity on earth.

paragraphs: An airplane makes forward thrust when air is pushed in the direction opposite to flight. The thrust is made by the spinning blades of a propeller. Thrust can also be made by a rotating fan pushing air out from the back of a jet engine. Another way is by ejecting hot gases from a rocket engine.

paragraphs: Reverse thrust is the opposite of forward thrust. In this way air is pushed in the same way as the motion of the body. Reverse thrust can be used to help braking after landing. This can be done by redirecting the thrust in a turbofan or jet engine or by changing the blade angle of a propeller driven aircraft.

paragraphs: Birds normally achieve thrust during flight by flapping their wings.

paragraphs: A boat with a motor makes thrust or reverse thrust when the propellers are turned to push water backwards (or forwards). The thrust that this makes pushes the boat in the opposite direction than the water is being pushed.

paragraphs: A rocket is pushed forward by a thrust force as large as the force the exhaust gas makes when going out of the rocket nozzle. The force the exhaust gas makes is called the exhaust velocity. The velocity is measured compared to the rocket. For vertical launch of a rocket to work, the starting thrust must be more force than the weight of the rocket.


title: Robert A. Heinlein

paragraphs: Robert Anson Heinlein (July 7, 1907 - May 8, 1988) was an American writer. He mostly wrote science fiction books. He won the Hugo Award four times. Probably his best-known novels are Starship Troopers (1959, Hugo Award, was made into a film), and Stranger in a Strange Land (1961, Hugo Award). Two other Hugo awards were for Double Star (1956) and The Moon is a Harsh Mistress (1966). Together with Isaac Asimov and Arthur C. Clarke he is seen as one of the "Big Three of Science Fiction".


title: Fable

paragraphs: A fable is a type of story which shows something in life or has a meaning to a word. A fable teaches a lesson or suggests a moral from it. A fable starts in the middle of the story, that means, jumps into the main event without detailed introduction of characters. The characters of a fable may be animals, plants and legendary creatures. When animals are used in fables, they think and talk like people, even though they act like animals. For example, in a fable a clay pot might say that it is frightened of being broken.

paragraphs: The stories told by fables are usually very simple. To understand a fable, the reader or listener does not need to know all about the characters, only one important thing. For this reason animals are often used in fables in a way that is easily understood because it is always the same. They keep the same "characteristics" from story to story.

paragraphs: The most famous fables are those attributed to Aesop (6th century B.C.). Many fables are so well-known that their morals have become English sayings.

paragraphs: "Crying wolf" is another well-known English saying. This comes from "The Boy Who Cried Wolf". This fable is about a boy who was sent to mind the sheep. The boy got lonely while minding the sheep, so he shouted "Wolf! Wolf!" The people came running. The next day, he did it again and they were very angry. On the third day the boy saw a wolf. He cried "Wolf! Wolf!" but no one came and the wolf ate him.


title: Drainage

paragraphs: Drainage is the natural or artificial removal of surface and sub-surface water from a given area. Many agricultural soils need drainage to improve production or to manage water supplies.

paragraphs: The earliest archaeological record of an advanced system of drainage comes from the Indus Valley Civilization from around 3100 BC in what is now Pakistan and North India. The ancient Indus systems of sewerage and drainage that were developed and used in cities throughout the civilization were far more advanced than any found in contemporary urban sites in the Middle East and even more efficient than those in some areas of modern Pakistan and India today. All houses in the major cities of Harappa and Mohenjo-daro had access to water and drainage facilities. Waste water was directed to covered drains, which lined the major streets.

paragraphs: Wetland soils may need drainage to be used for agriculture. In the northern USA and Europe, glaciation created numerous small lakes which gradually filled with humus to make marshes. Some of these were drained using open ditches and trenches.

paragraphs: The largest project of this type in the world has been in process for centuries in the Netherlands. The area between Amsterdam, Haarlem and Leiden was, in prehistoric times swampland and small lakes. Turf cutting (Peat mining), subsidence and shoreline erosion gradually caused the formation of one large lake, the Haarlemmermeer, or lake of Haarlem. The invention of wind powered pumping engines in the 15th century permitted drainage of some of the marginal land, but the final drainage of the lake had to await the design of large, steam powered pumps and agreements between regional authorities. The elimination of the lake occurred between 1849 and 1852, creating thousands of km of new land.


title: Polder

paragraphs: Empoldering is a method of reclaiming land from the sea, and a way to control floods. Empoldering involves the use of a polder, a piece of land in a low-lying area that has been reclaimed from a body of water by building dikes and drainage canals.

paragraphs: Although empoldering is usually carried out in low-lying coastal areas, it can also be dome in inland areas such as lakes and rivers. It is common in countries like the Netherlands, where much of the country is below sea level and subject to flooding. About one-fifth of the land in the Netherlands has been reclaimed from the sea. Their largest and most successful project is the Zuider Zee project.

paragraphs: Polders have two distinct features. Firstly, they are enclosed by dikes to keep the water out. The dikes also serve to protect the polder from erosion. Secondly, polders are continually maintained by systems of drainage canals and pumps which prevent them from becoming waterlogged and hence, suitable for cultivation.

paragraphs: Stage 1: Dike constructed around the area to be reclaimed to keep water from coming in.

paragraphs: Stage 2: The area is drained using pumps and drainage canals.

paragraphs: Stage 3: "Reeds" (a type of salt tolerant plant) are sown by aircraft to help the soil form.

paragraphs: Stage 4: After 3 years, reeds are burnt and the ash is used as fertilizers for the soil.

paragraphs: Stage 5: After a period of up to 15 years, the polder is ready for growing crops, building houses and constructing roads.

paragraphs: 1. Cost of reclaiming from deeper waters


title: Resistor

paragraphs: A resistor limits the electric current that flows through a circuit. Resistance is the restriction of current. In a resistor the energy of the electrons that pass through the resistor are changed to heat and/or light. For example, in a light bulb, the tungsten filament acts as a resistor that heats up because of the current going through it, causing it to glow.

paragraphs: Resistors can be linked in various combinations to help make a circuit:

paragraphs: There are many different types of resistors. Resistors have different power ratings to tell engineers how much power they can handle before they break and how accurate their value is. Connecting two resistors in series results in a higher resistance, and connecting them in parallel makes a lower resistance.

paragraphs: Nowadays the electrical industry in many cases uses so called surface-mount technology based resistors which can be very small.

paragraphs: The formula for Ohm’s law, V=I*R, states that the voltage drop across a component is equal to the product of the current flowing in the component multiplied by the resistance of the component. When using Ohm’s law, you are able to switch the formula around if needed to find a different outcome: I=V/R or R=V/I

paragraphs: Resistor's values are rated by the colors that are painted on the resistor. The colored bands that are used on the sides of a resistor are black, brown, red, orange, yellow, green, blue, purple, gray, and white. Each color represents a different number. The black band represents the number 0, brown band represents the number 1, red is 2 and so on all the way to white which is the number 9. These numbers are very important in the electronic field.

paragraphs: A resistor has multiple bands of color on its side. The most common have four or five but they can range all the way up to 6 per resistor. On a four band resistor, the last band is usually gold or silver. The gold band represents a positive or negative 5% tolerance. The silver band on a resistor represents a positive or negative 10% tolerance. Hold this band on the right side, and read the colors from left to right. The first two bands are read as the numbers that they represent in the color code. The third band acts as a multiplier for the other bands, so for example, if the third band was an orange band which is a 3, it would mean you multiply the two numbers by 1000. In short you add the value of the color in zeros at the end, so add three zeros.

paragraphs: Online calculators are available to calculate color codes. When the color codes are put into the calculator, it will automatically calculate the value of the resistor, along with the tolerance.

paragraphs: Resistors are used in many different ways. First of all, they are put in circuits to protect components from damage such as LEDs.

paragraphs: They also control the amount of current flowing in a circuit, for example, if you want less current to flow you would put in a resistor with a higher value. Resistors can also split voltage between different parts of a circuit and control time delay.

paragraphs: Electric heaters use very large resistors to turn electricity into heat. Usually, engineers try to make resistors heat up as little as possible to not waste power, but in a heater, this "waste" is a good thing.

paragraphs: There are many different types of resistors you can find. They are all made with a resistive material encased in a non-conductive material, such as plastic. Fixed resistors are usually made of carbon encased in a plastic cylinder, with a connecting wire on either end. Most resistors used in electronics today are carbon resistors. Older resistors were made of other poorly conducting metals, in order to restrict the flow of charge.


title: Death Star

paragraphs: The Death Star is a fictional moon-sized space station and superweapon. It was invented for the "Star Wars" movies. It was a huge spherical space station which fired a ray of energy which could destroy a planet.

paragraphs: The details of the Death Star changed between different models during production of "". These changes include the position of the superlaser. The idea of the Death Star as a large, spherical space station was the same in all the models. The sound of the Death Star counting down until it fires comes from the "Flash Gordon" movies. Making a Death Star that was only partly built (but was still powerful) was a problem for Industrial Light & Magic's modelmakers for "". Only the front side of the 137-centimeter model was finished. The image was flipped horizontally for the final movie. Both Death Stars were created in the movies by using a full models, models of sections of the space station and matte paintings.

paragraphs: The first Death Star was shown in its finished form in "". It was commanded by Grand Moff Tarkin (Peter Cushing). The Death Star was the Galactic Empire's "ultimate weapon". The movie begins with Leia Organa (Carrie Fisher) attempting to take the station's plans to the Rebel Alliance, wanting to help them destroy the Death Star. Onboard her vessel, she was captured by an imperial ship and taken captive to the Death Star. There, Tarkin tries to make Leia reveal the location of the rebel base by threatening the use of the Death Star to destroy Leia's home world, Alderaan. She tells them a location but not the real one, but Tarkin has her planet destroyed anyway. Later, Luke Skywalker (Mark Hamill) and his small crew are also captured and taken to the station, escaping with Leia shortly after. In the movie's main battle scene, the force ghost of Obi-wan Kenobi tells Luke to use the "Force" to help him direct proton torpedoes from his x-wing into the Death Star' reactor core and not with his ship's targeting system. Luke obeys and successfully launches the torpedoes into the core. This ultimately resulted in the destruction of the battle station.

paragraphs: "Return of the Jedi" takes place four years later. At this time, the Empire is building a new Death Star. It is half-finished in the movie. Emperor Palpatine (Ian McDiarmid) and Darth Vader (David Prowse/James Earl Jones) send the Rebels false information with the intention of trapping the Rebels, saying that the station's weapons systems are not fully functional. They also want to get Skywalker on board so they can turn him to the dark side of the Force. In the movie's climax, Vader throws Palpatine down one of the station's reactor core, apparantly killing him. However, Palpatine fires a large amount of sith lightning during this process and critically damages the electronics on Vader's suit that keeps him alive. Luke tries to get his father out of the battle station but he dies shortly after. Luke then takes Vader's body and leaves the Death Star just before it is destroyed by Lando Calrissian onboard the "Millennium Falcon."

paragraphs: The first Death Star is also dealt with in the "Star Wars" prequel trilogy. Its schematics are shown in "". At the end of "", the Death Star is shown starting to be built.


title: Doctor of Philosophy

paragraphs: The Doctor of Philosophy, (PhD, Ph.D., DPhil or D.Phil.) is a degree a person gets from a university by finishing a doctorate program. In many areas of study, the PhD/DPhil is the highest degree that a person can earn (this is called the "terminal degree"). There are PhD/DPhil degrees for many different fields, such as PhDs/DPhils in literature, philosophy, history, science, mathematics, and engineering. Some PhD/DPhil degrees have existed for hundreds of years, such as the PhD/DPhil in Canon Law. Other PhD/DPhil degrees were developed in the 1970s and 1980s, such as the PhD/DPhil in Computer Science.

paragraphs: To be admitted to a PhD/DPhil program, a person usually has to have completed their Bachelor's degree or master's degree that is related to the PhD/DPhil degree. For example, a person applying to be admitted to a PhD/DPhil degree in Theater would normally have to have a master's degree such as a Master of Arts (MA) degree in Theater, English Literature, or a related area.

paragraphs: The PhD/DPhil degree usually takes between three and six years of full-time study to complete. They may or may not require a master's degree beforehand. Many PhD/DPhil degrees begin with a period of graduate courses. After the PhD/DPhil student has taken these courses, they take examinations to test what the student knows about their area of study. After the student passes the exams, they begin to do original research. The product is a long research report called a dissertation (or a "thesis"). Some PhD/DPhil degrees also require students to pass exams in languages (such as French, German, or other languages). Many PhD/DPhil students teach undergraduate students or assist professors with research during their PhD/DPhil studies.

paragraphs: Requirements for university teaching vary in different subjects and in different countries. A PhD/DPhil is necessary or usual to become a university professor in many fields, especially in science. However, many famous professors have not had higher degrees, though that is less common today. In some fields, there is no PhD/DPhil, and so another degree is required to become a university professor. For example, the highest degree in Fine Arts fields such as printmaking or graphic design is the Master of Fine Arts (MFA) degree. A person with an MFA degree can become a university professor in some Fine Arts fields.


title: Global 200

paragraphs: The Global 200 is the list of ecoregions identified by the World Wide Fund for Nature (WWF) as priorities for conservation. According to the WWF, an ecoregion is defined as a "relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species, dynamics, and environmental conditions (Dinerstein et al. 1995, TNC 1997)."

paragraphs: The WWF assigns a conservation status to each ecoregion in the Global 200: critical or endangered; vulnerable; and relatively stable or intact. Over half of the ecoregions in the Global 200 are rated endangered.


title: Ecoregion

paragraphs: An ecoregion (ecological region), sometimes called a bioregion, is the next smallest ecologically and geographically defined area beneath "realm" or "ecozone". Ecoregions cover relatively large area of land or water, and contain characteristic, geographically distinct natural communities and species. When defined by the World Wide Fund for Nature (WWF), the boundaries of an ecoregion approximate the original extent of the natural communities prior to any major recent disruptions or changes. The WWF has identified 825 terrestrial ecoregions, and approximately 450 freshwater ecoregions across the Earth.

paragraphs: World Wide Fund for Nature's full definition of an ecoregion, which is widely accepted and used, is the following:

paragraphs: The "Global 200" is the list of ecoregions identified by the World Wide Fund for Nature (WWF) as priorities for conservation.

paragraphs: A terrestrial ecoregion is a certain area of land which is different from the area near it. It has a distinct climate, geology, type of soil, water availability, and distinct living species (the animals and plants that live in the ecoregion).

paragraphs: For example, one ecoregion can be a desert. It would have sand, very little water, very hot temperatures during the day and very cold at night. The plants could be just bushes, small trees, cactii. The animals could be scorpions, little mammals, spiders.

paragraphs: Or for example, an ecoregion could be a tropical forest It would have warm temperatures all day, a lot of rainfall all year, a huge river crossing, and a very organic soil. The plants could be huge trees or ferns. The animals could be insects, birds, fish and apes.

paragraphs: Marine ecoregions are regions of the world's oceans, that are defined by the WWF, to help activities for saving marine ecosystems.

paragraphs: The scheme used to find out these ecoregions is more or less the same as that for terrestrial ecoregions. Major habitat types are identified: polar, temperate shelfs and seas, temperate upwelling, tropical upwelling, tropical coral, pelagic, abyssal, and hadal (ocean trench) — which correspond to the terrestrial biomes. Major biogeographic realms, analogous to the seven terrestrial ecozones, represent large regions of the ocean basins: North Temperate Atlantic, Eastern Tropical Atlantic, Western Tropical Atlantic, South Temperate Atlantic, North Temperate Indo-Pacific, Central Indo-Pacific, Eastern Indo-Pacific, Western Indo-Pacific, South Temperate Indo-Pacific, Southern Ocean, Antarctic, Arctic, and Mediterranean.

paragraphs: The classification of Marine ecoregions is not developed to the same level of detail and comprehensiveness as that of the terrestrial ecoregions; only the priority conservation areas of the Global 200 are listed.

paragraphs: See Global 200 Marine ecoregions for a full list of marine ecoregions (World Wide Fund for Nature).

paragraphs: Freshwater ecoregions are the freshwater habitats of a particular geographic area, including rivers, streams, lakes, and wetlands. Freshwater ecoregions are distinct from terrestrial ecoregions, which have biotic communities of the land, and marine ecoregions, which are biotic communities of the oceans.

paragraphs: The WWF speaks of seven major habitat types of freshwater ecoregions: Large rivers, large river headwaters, large river deltas, small rivers, large lakes, small lakes, and xeric basins.

paragraphs: Several freshwater ecoregions are listed in the Global 200, the WWF's priority ecoregions for conservation of biodiversity.


title: Wetland

paragraphs: In physical geography, a wetland is an environment that combines the properties of land and water. Wetlands are a distinct kind of ecosystem.

paragraphs: The combination of wet and dry areas means that many more different kinds of plants, animals and insects may live in a wetland than compared to other types of habitat. Because of this great biodiversity, several important wetlands are among the Global 200 ecoregions that the World Wide Fund for Nature listed for conservation to try to get people to protect them.


title: Marsh

paragraphs: In geography, a marsh is a type of wetland. It has grasses, rushes, reeds, typhas, sedges, and other herbaceous plants (possibly with low-growing woody plants) in a context of shallow water. A marsh is different from a swamp, which has a greater proportion of open water surface, which is generally deeper than a marsh. In the US, the term 'swamp' is used for wetland dominated by trees rather than grasses and low herbs.

paragraphs: The water of a marsh can be fresh, brackish or saline. Coastal marshes may be associated with estuaries and along waterways between coastal barrier islands and the inner coast. Estuarine marshes often are based on soils consisting of sandy bottoms or bay muds.

paragraphs: Marshes are critically important wildlife habitat, often serving as breeding grounds for a wide variety of animal life.


title: Ulan-Ude

paragraphs: Ulan-Ude (Russian:Ула́н-Удэ́; Buryat: Улаан-Үдэ), formerly Verkhneudinsk (), the capital city of the Buryat Republic, Russia. The city is located about 100 km south-east of Lake Baikal. It sits at the foot of the Khamar-Daban and Khrebet Ulan-Burgasy mountain ranges, next to the confluence of the Selenga River and its tributary, the Uda. The city is divided into two parts by the Uda. Population 359,391 (2002 Census); 352,530 (1989 Census). It is the third largest city in East Siberia. It is served by Ulan-Ude Airport (Mukhino) as well as the smaller Ulan-Ude Vostochny Airport.

paragraphs: Ulan-Ude was founded in 1666 by the Russian Cossacks. Due to its geographical position, the city grew rapidly and became a large trade centre which connected Russia with China and Mongolia. There are old merchants' mansions richly decorated with wood and stone carving in the historical center of Ulan-Ude, along the river banks. They represent beautiful examples of Russian classicism. There is also a large and highly unusual head of Lenin in the central square.


title: Pelagic zone

paragraphs: The pelagic zone is the part of the open sea or ocean that is not near the coast or sea floor. The name comes from the Greek πέλαγος ("pélagos"), which might be roughly translated as "sea" but is more accurately translated as "open sea."

paragraphs: The pelagic (or open-ocean) zone is divided into a number of sub-zones:

paragraphs: The last three zones are similar in character, and some marine biologists count them as a single zone or consider the latter two to be the one zone. Some define the hadopelagic as waters below 6000 meters, whether in a trench or not.


title: Vitamin A

paragraphs: Vitamin A is a vitamin, a group of organic chemicals including retinal and several carotenoids. The human body does not make these chemicals, and must take them from food. Carrots and liver are both rich in vitamin A. Many parts of the body need vitamin A. For example, vitamin A helps sight and is good for the immune system. It is also important for a growing embryo.

paragraphs: Too little vitamin A is dangerous to health. People who do not get enough of the vitamin may lose the ability to see in poor light and suffer from a weakened immune system. They may also have problems with memory, because vitamin A is important for the brain. People with malnutrition often have too little vitamin A. This is common in poor countries.

paragraphs: Too much vitamin A is also dangerous to one's health. This is because, vitamin A is not soluble in water, and the human body can not get rid of the excess vitamin A easily through urination. Too much vitamin A can make someone very sick. People may get too much vitamin A from taking too many vitamin pills or from eating too much rich food like liver.

paragraphs: If a pregnant woman has too little or too much vitamin A it may cause birth defects in the unborn baby.

paragraphs: vitamin A (retinol ) contain nine conjugated hydrocarbon chain. Vitamin is also necessary for the growth and maintenance of tissues.


title: Vitamin D

paragraphs: Vitamin D is not actually a vitamin. It is a steroid hormone, which is made in the body under the right conditions. However, if the body does not make enough, it can also be obtained from food sources.

paragraphs: As a hormone, Vitamin D does many things in the body. It was first discovered as the substance which could prevent and cure rickets. It controls the levels of calcium ions and phosphates in the blood, as well as calcium and magnesium absorption in the intestines. It helps bones grow and form. It is also good for the immune system.

paragraphs: In total, there are 5 different forms, D to D. The most common ones are D and D (see images).

paragraphs: D (also called cholecalciferol) is the kind produced by the body. It is also found naturally in marine oils and in lanolin (oil from sheep's wool), the most common source for supplements.

paragraphs: D (also called ergocalciferol) is produced by fungi. It is similar to D, but not exactly the same.

paragraphs: D is made in the skin from cholesterol, and changed into a more active form by the liver. However, the skin will not make it unless enough ultraviolet light shines on it. As sunlight contains ultraviolet light, getting enough sun is one way of getting enough D.

paragraphs: Many things can keep the skin from making enough D. Winter sunlight may be too weak. Melanin, which protects skin from damage, also keeps it from making D, which is why people with darker skin are more prone to deficiency. Older people are also prone, because aging skin makes less D, even with enough sunlight. Clothing, glass, sunscreens and sunblocks also shield the skin from getting enough ultraviolet light to make D.

paragraphs: It is hard to know how much supplemental Vitamin D, if any, is needed. Some current recommendations from health organizations (such as the Institute of Medicine) have recently increased. They are still typically less than 25 micrograms (1000 IU) per day, but up to 100 mcg (4000 IU) per day is considered safe. A recent panel of Vitamin D researchers concluded that "at least" 20-25 mcg (800-1000 IU) per day would be beneficial for most adults.

paragraphs: Very few foods naturally contain much D. Fish do, especially oily ones, such as salmon, sardine and mackerel. Many kinds of edible mushrooms contain some D, like shiitake. Mushrooms grown in full sunlight tend to have more.

paragraphs: D supplements can be easily found for sale in most developed countries.

paragraphs: Vitamin D is a fat-soluble nutrient. This means that any portion not used immediately is stored in fat tissue for future use.

paragraphs: Some people may get all the vitamin D they need from their diet and the sun. However, if you are pregnant, breastfeeding or elderly it would be safest to take at least 15-20 micrograms (600-800 IU) of vitamin D each day.

paragraphs: The treatment of vitamin D deficiency is to take vitamin D supplements and increase the amount of time spent in the sun, without getting sunburnt..


title: Biome

paragraphs: In ecology, a biome is a major regional group of distinctive plant and animal

paragraphs: communities best adapted to the region's physical natural environment,

paragraphs: A biome is made up of ecoregions or communities at stable steady state and all associated transitional, disturbed, or degraded, vegetation, fauna and soils, but can often be identified by the climax vegetation type.

paragraphs: The biodiversity characteristic of each biome, especially the diversity of fauna and subdominant plant forms, is a function of abiotic factors and the biomass productivity of the dominant vegetation. Terrestrial biomes with higher net primary productivity, moisture availability, and temperature.

paragraphs: A fundamental classification of biomes is into:

paragraphs: Biomes are often given local names. For example, a temperate grassland or shrubland biome is known commonly as "steppe" in central Asia, "savanna" or veld in southern Africa, "prairie" in North America, "pampa" in South America and "outback" or "scrub" in Australia.

paragraphs: Sometimes an entire biome may be targeted for protection, especially under an individual nation's "Biodiversity Action Plan".

paragraphs: Climate is a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are:

paragraphs: Biodiversity generally increases away from the poles towards the equator, and increases with humidity.

paragraphs: The most widely used systems of classifying biomes correspond to latitude (or temperature zoning) and humidity.

paragraphs: In 1975, Miklos Udvardy published a system of biogeographic provinces that were divided into 12 terrestrial biomes.

paragraphs: Robert G. Bailey developed a biogeographical classification system for the United States in a map published in 1975. Bailey subsequently expanded the system to include the rest of North America in 1981, and the world in 1989. The Bailey system is based on climate, and is divided into four domains (Polar, Humid Temperate, Dry, and Humid Tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical, marine and continental, lowland and mountain).

paragraphs: A team of biologists developed an ecological land classification system for the World Wide Fund for Nature (WWF) that identified 14 biomes, called major habitat types, and further divided the world's land area into 867 terrestrial ecoregions. This classification is used to define the Global 200 list of ecoregions identified by the (WWF) as priorities for conservation. The WWF major habitat types are as follows:

paragraphs: The Endolithic biome, consisting entirely of microscopic life in rock pores and cracks, kilometers beneath the surface, has only recently been discovered and does not fit well into most classification schemes.