Aarushhh/wikipedia-simple-splitted huggingface dataset:
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.

Series and parallel 
Resistors can be linked in various combinations to help make a circuit:

Series - Where the resistors are linked one after another. 
Parallel - Where the resistors are linked over one another.

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.  
Nowadays the electrical industry in many cases uses so called surface-mount technology based resistors which can be very small.
Calculating resistance 
Series Circuit: Rt=R1+R2+R3+R4...Rn
Parallel Circuit: 1/Rt=1/R1+1/R2+1/R3...1/Rn  
Where R is the resistor's value

Ohm’s Law 
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

Color code 

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.
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.

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

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. You can also use resistors for soldering electronics.
Resistor materials 
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.

References 

Electronic components
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.

Origin and design
The details of the Death Star changed between different models during production of Star Wars Episode IV: A New Hope. 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 Star Wars Episode VI: Return of the Jedi. 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.

Depiction
The first Death Star was shown in its finished form in Star Wars Episode IV: A New Hope. 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.
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. Darth Sidious (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 Sidious down one of the station's reactor core, apparently killing him. However, Sidious 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 on board the Millennium Falcon.
The first Death Star is also dealt with in the Star Wars prequel trilogy. Its schematics are shown in Star Wars Episode II: Attack of the Clones. At the end of Star Wars Episode III: Revenge of the Sith, the Death Star is shown starting to be built.

References

Other websites
 

Star Wars
Science fiction technology
Requirements for degree
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.
Elements of a PhD / DPhil degree
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.
As a requirement for university teaching 
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.

Other websites 
 The Mathematics PhD in the United Kingdom: Notes on its History Contains information/links of more general relevance than mathematics.

Academia
Academic degrees
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)."

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.

Global 200: Terrestrial

Tropical and subtropical moist broadleaf forests
Afrotropic
 Guinean moist forests
 Congolian coastal forests
 Cameroon Highlands forests
 Northeastern Congolian lowland forests
 Central Congolian lowland forests
 Western Congolian moist forests
 Albertine Rift montane forests
 East African Coastal Forests
 Eastern African montane forests
 Madagascar lowlands and subhumid forests
 Seychelles and Mascarene Islands moist forests

Australasia
 Sulawesi moist forests
 Moluccas moist forests
 Southern New Guinea lowland forests
 New Guinea montane forests
 Solomons-Vanuatu-Bismarck moist forests
 Queensland tropical rain forests
 New Caledonia moist forests
 Lord Howe-Norfolk Islands forests
Indomalaya
 South Western Ghats montane rain forests and moist deciduous forests
 Sri Lanka moist forests
 Northern Indochina Subtropical moist forests
 Southeast China-Hainan moist forests
 Taiwan montane forests
 Annamite Range moist forests
 Sumatran Islands lowland and montane forests
 Philippines moist forests
 Palawan moist forests
 Kayah-Karen/Tenasserim moist forests
 Peninsular Malaysian lowland and montane forests
 Borneo lowland and montane forests
 Nansei Shoto Archipelago forests
 Eastern Deccan Plateau moist forests
 Naga-Manipuri-Chin hills moist forests
 Cardamom Mountains moist forests
 Western Java montane forests

Neotropic
 Greater Antillean moist forests
 Talamancan-Isthmian Pacific forests
 Choco-Darien moist forests
 Northern Andean montane forests
 Coastal Venezuela montane forests
 Guianan moist forests
 Napo moist forests
 Rio Negro-Jurua moist forests
 Guayana Highlands moist forests
 Central Andean yungas
 Southwestern Amazonian moist forests
 Atlantic forests
Oceania
 South Pacific Islands forests
 Hawaii moist forests

Tropical and subtropical dry broadleaf forests

Afrotropic
 Madagascar dry deciduous forests

Australasia
 Nusa Tenggara dry forests
 New Caledonia dry forests

Indomalaya
 Indochina dry forests
 Chhota-Nagpur dry forests

Neotropic
 Mexican dry forests
 Tumbesian-Andean valleys dry forests
 Chiquitano dry forests
 Atlantic dry forests

Oceania
 Hawaii dry forests

Tropical and subtropical coniferous forests

Nearctic
 Sierra Madre Oriental and Occidental pine-oak forests

Neotropic
 Greater Antillean pine forests
 Mesoamerican pine-oak forests

Temperate broadleaf and mixed forests

Australasia
 Eastern Australia temperate forests
 Tasmanian temperate rain forests
 New Zealand temperate forests

Indomalaya
 Eastern Himalayan broadleaf and conifer forests
 Western Himalayan temperate forests

Nearctic
 Appalachian and mixed mesophytic forests

Palearctic
 Southwest China temperate forests
 Russian Far East temperate forests
Temperate coniferous forests

Nearctic
 Pacific temperate rain forests
 Klamath-Siskiyou forests
 Sierra Nevada forests
 Southeastern coniferous and broadleaf forests

Neotropic
 Valdivian temperate rain forests-Juan Fernandez Islands

Palearctic
 European-Mediterranean montane mixed forests
 Caucasus-Anatolian-Hycanian temperate forests
 Altai-Sayan montane forests
 Hengduan Shan coniferous forests

Boreal forests/taiga

Nearctic
 Muskwa-Slave Lake boreal forests
 Canadian taiga

Palearctic
 Ural Mountains taiga
 East Siberian taiga;
 Kamchatka taiga and grasslands

Tropical and subtropical grasslands, savannas, and shrublands

Afrotropic
 Horn of Africa acacia savannas
 East African acacia savannas
 Central and Eastern miombo woodlands
 Sudanian savannas

Australasia
 Northern Australia and Trans-Fly savannas

Indomalaya
 Terai-Duar savannas and grasslands

Neotropic
 Llanos savannas
 Cerrado woodlands and savannas

Temperate grasslands, savannas, and shrublands

Nearctic
 Northern prairie
Neotropic
 Patagonian steppe

Palearctic
 Daurian steppe

Flooded grasslands and savannas

Afrotropic
 Sudd-Sahelian flooded grasslands and savannas
 Zambezian flooded savannas

Indomalaya
 Rann of Kutch flooded grasslands

Neotropic
 Everglades flooded grasslands
 Pantanal flooded savannas

Montane grasslands and shrublands

Afrotropic
 Ethiopian Highlands
 Southern Rift montane woodlands
 East African moorlands
 Drakenberg montane shrublands and woodlands

Australasia
 Central Range subalpine grasslands

Indomalaya
 Kinabalu montane shrublands

Neotropic
 Northern Andean paramo
 Central Andean dry puna

Palearctic
 Tibetan Plateau steppe
 Middle Asian montane steppe and woodlands
 Eastern Himalayan alpine meadows

Tundra

Nearctic
 Alaskan North Slope coastal tundra
 Canadian low arctic tundra

Palearctic
 Fenno-Scandia alpine tundra and taiga
 Taimyr and Russian coastal tundra
 Chukote coastal tundra

Mediterranean forests, woodlands, and shrub

Afrotropic
 Fynbos
Afrotropic
 Fynbos

Australasia
 Southwestern Australia forests and scrub
 Southern Australia mallee and woodlands

Nearctic
 California chaparral and woodlands

Neotropic
 Chilean Matorral

Palearctic
 Mediterranean forests, woodlands, and shrub

Deserts and xeric shrublands

Afrotropic
 Namib-Karoo-kaokoveld deserts
 Madagascar spiny thicket
 Socotra Island desert
 Arabian Highland woodlands and shrublands

Australasia
 Carnavon xeric scrub
 Great Sandy-Tanami deserts

Nearctic
 Sonoran-Baja deserts
 Chihuahuan-Tehuacan deserts

Neotropic
 Galapagos Islands scrub
 Atacama-Sechura deserts

Palearctic
 Central Asian deserts

Mangroves

Afrotropic
 Gulf of Guinea mangroves
 East African mangroves
 Madagascar mangroves

Australasia
 New Guinea mangroves

Indomalaya
 Sundarbans mangroves
 Greater Sundas mangroves

Neotropic
 Guianan-Amazon mangroves
 Panama Bight mangroves

Global 200: Freshwater ecoregions

Large rivers
Large rivers

Afrotropic
 Congo River and flooded forests (Angola, Democratic Republic of Congo, Republic of Congo)

Indomalaya
 Mekong River (Cambodia, China, Laos, Myanmar, Thailand, Vietnam)

Nearctic
 Colorado River (Mexico, United States)
 Lower Mississippi River (United States)

Neotropic
 Amazon River and flooded forests (Brazil, Colombia, Peru)
 Orinoco River and flooded forests (Brazil, Colombia, Venezuela)

Palearctic
 Yangtze River and lakes (China)

Large river headwaters

Afrotropic
 Congo basin piedmont rivers and streams (Angola, Cameroon, Central African Republic, Democratic Republic of Congo, Gabon, Republic of Congo, Sudan)

Nearctic
 Mississippi piedmont rivers and streams (United States)

Neotropic
 Upper Amazon rivers and streams (Bolivia, Brazil, Colombia, Ecuador, French Guiana (France), Guyana, Peru, Suriname, Venezuela)
 Upper Paraná rivers and streams (Argentina, Brazil, Paraguay)
 Brazilian Shield Amazonian rivers and streams (Bolivia, Brazil, Paraguay)

Large river deltas
Large river deltas

Afrotropic
 Niger River delta (Nigeria)

Indomalaya
 Indus River Delta (India, Pakistan)

Palearctic
 Volga River Delta (Kazakhstan, Russia)
 Mesopotamian delta and marshes (Iran, Iraq, Kuwait)
 Danube River delta (Bulgaria, Moldova, Romania, Ukraine, Yugoslavia)
 Lena River delta (Russia)

Small rivers

Afrotropic
 Upper Guinea rivers and streams (Côte d'Ivoire, Guinea, Liberia, Sierra Leone)
 Madagascar freshwater (Madagascar)
 Gulf of Guinea rivers and streams (Angola, Cameroon, Democratic Republic of Congo, Equatorial Guinea, Gabon, Nigeria, Republic of Congo)
 Cape rivers and streams (South Africa)

Australasia
 New Guinea rivers and streams (Indonesia, Papua New Guinea)
 New Caledonia rivers and streams (New Caledonia)
 Kimberley rivers and streams (Australia)
 Southwest Australia rivers and streams (Australia)
 Eastern Australia rivers and streams (Australia)
Indomalaya
 Xi Jiang rivers and streams (China, Vietnam)
 Western Ghats Rivers and Streams (India)
 Southwestern Sri Lanka rivers and streams (Sri Lanka)
 Salween River (China, Myanmar, Thailand)
 Sundaland rivers and swamps (Brunei, Malaysia, Indonesia, Singapore)

Nearctic
 Southeastern rivers and streams (United States)
 Pacific Northwest coastal rivers and streams (United States)
 Gulf of Alaska coastal rivers and streams (Canada, United States)

Neotropic
 Guianan freshwater (Brazil, French Guiana, Guyana, Suriname, Venezuela)
 Greater Antillean freshwater (Cuba, Dominican Republic, Haiti, Puerto Rico)

Palearctic
 Balkan rivers and streams (Albania, Bosnia and Herzogovina, Bulgaria, Croatia, Greece, Macedonia, Turkey, Yugoslavia)
 Russian Far East rivers and wetlands (China, Mongolia, Russia)

Large lakes

Afrotropic
 Rift Valley lakes (Burundi, Democratic Republic of Congo, Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Tanzania, Uganda, Zambia)
Neotropic
 High Andean lakes (Argentina, Bolivia, Chile, Peru)

Palearctic
 Lake Baikal (Russia)
 Lake Biwa (Japan)

Small lakes

Afrotropic
 Cameroon crater lakes (Cameroon)

Australasia
 Lakes Kutubu and Sentani (Indonesia, Papua New Guinea)
 Central Sulawesi lakes (Indonesia)

Indomalaya
 Philippines freshwater (Philippines)
 Inle Lake (Myanmar)
 Yunnan lakes and streams (China)

Neotropic
 Mexican highland lakes (Mexico)

Xeric basins

Australasia
 Central Australian freshwater (Australia)

Nearctic
 Chihuahuan freshwater (Mexico, United States)

Palearctic
 Anatolian freshwater (Syria, Turkey)

Global 200 Marine ecoregions

Polar

Antarctic Ocean
 Antarctic Peninsula & Weddell Sea

Arctic Ocean
 Bering Sea (Canada, Russia, United States)
 Barents-Kara Sea (Norway, Russia)

Temperate shelfs and seas
Mediterranean
 Mediterranean Sea (Albania, Algeria, Bosnia and Herzegovina, Croatia, Cyprus, Egypt, France, Greece, Israel, Italy, Lebanon, Libya, Malta, Monaco, Morocco, Serbia & Montenegro, Slovenia, Spain, Syria, Tunisia, Turkey)

North Temperate Atlantic
 Northeast Atlantic Shelf Marine (Belgium, Denmark, Estonia, Finland, France, Germany, Ireland, Latvia, Lithuania, Netherlands, Norway, Poland, Russia, Sweden, United Kingdom)
 Grand Banks (Canada, St. Pierre and Miquelon (France), United States)
 Chesapeake Bay (United States)

North Temperate Indo-Pacific
 Yellow Sea (China, North Korea, South Korea)
 Sea of Okhotsk (Japan, Russia)

Southern Ocean
 Patagonian Southwest Atlantic (Argentina, Brazil, Chile, Uruguay)
 Southern Australian Marine (Australia)
 New Zealand Marine (New Zealand)

Temperate upwelling

North Temperate Indo-Pacific
 California Current (Canada, Mexico, United States)

South Temperate Atlantic
 Benguela Current (Namibia, South Africa)
South Temperate Indo-Pacific
 Humboldt Current (Chile, Ecuador, Peru)
 Agulhas Current (Mozambique, South Africa)

Tropical upwelling

Central Indo-Pacific
 Western Australian Marine (Australia)

Eastern Indo-Pacific
 Panama Bight (Colombia, Ecuador, Panama)
 Gulf of California (Mexico)
 Galápagos Marine (Ecuador)

Eastern Tropical Atlantic
 Canary Current (Canary Islands, Gambia, Guinea-Bissau, Mauritania, Morocco, Senegal, Western Sahara)

Tropical coral

Central Indo-Pacific
 Nansei Shoto (Japan)
 Sulu-Sulawesi Seas (Indonesia, Malaysia, Philippines)
 Bismarck-Solomon Seas (Indonesia, Papua New Guinea, Solomon Islands)
 Banda-Flores Sea (Indonesia)
 New Caledonia Barrier Reef (New Caledonia)
 Great Barrier Reef (Australia)
 Lord Howe-Norfolk Islands Marine (Australia)
 Palau Marine (Palau)
 Andaman Sea (Andaman and Nicobar Islands (India), Indonesia, Malaysia, Myanmar, Thailand)
Eastern Indo-Pacific
 Tahitian Marine (Cook Islands, French Polynesia)
 Hawaiian Marine (Hawaii)
 Rapa Nui (Easter Island)
 Fiji Barrier Reef (Fiji)

Western Indo-Pacific
 Maldives, Chagos, and Lakshadweep atolls (Chagos Archipelago (United Kingdom), India, Maldives, Sri Lanka)
 Red Sea (Djibouti, Egypt, Eritrea, Israel, Jordan, Saudi Arabia, Sudan, Yemen)
 Arabian Sea (Djibouti, Iran, Oman, Pakistan, Qatar, Saudi Arabia, Somalia, United Arab Emirates, Yemen)
 East African Marine (Kenya, Mozambique, Somalia, Tanzania)
 West Madagascar Marine (Comoros, Madagascar, Mayotte and Iles Glorieuses (France), Seychelles)

Western Tropical Atlantic
 Mesoamerican Reef (Belize, Guatemala, Honduras, Mexico)
 Greater Antillean Marine (Bahamas, Cayman Islands, Cuba, Dominican Republic, Haiti, Jamaica, Puerto Rico, Turks and Caicos Islands, United States)
 Southern Caribbean Sea (Aruba, Columbia, Netherlands Antilles, Panama, Trinidad and Tobago, Venezuela)
 Northeast Brazil Shelf Marine (Brazil)
Related pages
 Biodiversity

Other websites 
 Map of the Global 200
 Conservation status map of the global 200
 List of the Global 200

Ecozones
World Wide Fund for Nature's full definition of an ecoregion, which is widely accepted and used, is the following:
A large area of land or water that contains a geographically distinct assemblage of natural communities that(a) share a large majority of their species and ecological dynamics;(b) share similar environmental conditions, and;(c) interact ecologically in ways that are critical for their long-term persistence.--World Wide Fund for Nature - EcoregionsThe Global 200 is the list of ecoregions identified by the World Wide Fund for Nature (WWF) as priorities for conservation.

 Terrestrial 
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).
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.

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.

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

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

 Freshwater 
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.

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.

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

 Sources 
 Brunckhorst, D. 2000. Bioregional planning: resource management beyond the new millennium.'' Harwood Academic Publishers: Sydney, Australia.

Related pages 
Cape flower region
Great Barrier Reef
Other websites 
 World Wide Fund for Nature: ecoregions 
 Sierra club: ecoregions 
 Activist network cultivating Ecoregions/Bioregions
 A National Ecological Framework for Canada 
 Ecoregions of North America 
 Interactive map and images of North American ecoregions at bioimages.vanderbilt.edu
 Map of the ecozones
In physical geography, a wetland is an environment that combines the properties of land and water. Wetlands are a distinct kind of ecosystem.

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. As well, Ramsar Convention is adopted in 1971 for protection of wetland.
Wetland types 
 A bog or muskeg is acidic peat land (peat bog).
 A moor was originally the same as a bog but has come to be associated with this soil type on hill-tops.
 A moss is a raised bog in Scotland
 A fen is a freshwater peat land with chemically basic (which roughly means alkaline) ground water. This means that it contains a moderate or high proportion of hydroxyl ions (pH value greater than 7).
 A carr is a fen which has developed enough to support trees. It is a European term, mainly applied in the north of the UK.
 A fresh-water marsh's main feature is its openness, with only low-growing or "emergent" plants. It may feature grasses, rushes, reeds, typhas, sedges, and other herbaceous plants (possibly with low-growing woody plants) in a context of shallow water. It is an open form of fen. The Fens in eastern England were just such a wetland.
A coastal (salt)-marsh typically has very salty water, either directly from the ocean or a mixture of salt water and fresh water. Salt-marshes may be associated with estuaries and along waterways between coastal barrier islands and the inner coast. The plants in this kind of marsh can range from reeds in mildly brackish (salty) water to especially hardy salt-grasses (salicornia) on otherwise bare marine mud. Many plants in salt-marshes have evolved to live in such salty conditions with special adaptations. Salt-marshes may be converted to human use as pasture (salting) or for salt production (saltern).
A swamp is wetland with more open water surface and deeper water than a marsh. In North America, 'swamp' is used for wetlands dominated by trees and woody bushes rather than grasses and low herbs. This distinction does not necessarily apply in other areas, for instance in Africa where swamps may be dominated by papyrus instead of trees. A swamp may also be described by the dominant plants growing in it. For example: A mangrove swamp or mangal is a salt or brackish water environment dominated by mangrove trees. A paperbark wetland is a fresh or brackish water environment dominated by the Melaleuca tree.
 A dambo is a shallow, grass-covered depression of central and southern Africa. It is waterlogged in the rainy season, and usually forms the headwaters of a stream or river. It is marshy at the edges and at the headwater, but maybe swampy in the centre and downstream.
A bayou or slough are southern United States terms for a swamp with a creek running through it. In an Indian mangrove swamp, it would be called a creek.
 A peat swamp forest is a low-level tropical or subtropical forest wetland. It produces peat, and is sometimes called a blackwater swamp.
 A constructed wetland is man-made to make a piece of land hold more water than it otherwise would naturally. This allows the land to stay wet enough to grow wetland plants and oftentimes hold water as well. Uses include absorbing flash floods (by holding the extra water from the flood), cleaning sewage (which is done by the plants as the dirty water passes over their roots), enhancing wildlife habitat (for example creating new homes for rare birds or other animals) or for some other human reason.
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.

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.

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

Related pages
Fen
Swamp
Ecoregion

Other websites 
 Marshes of the Lowcountry (South Carolina) -- Beaufort County Library 

Wetlands
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.
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.

Gallery

Sources

Other websites

Cities and towns in Buryatia
Capitals of republics of Russia
The pelagic zone is the open sea or ocean that is not near the coast. The name comes from the Greek πέλαγος (pélagos), which might be translated as "open sea".

To make this clear, seas around continents have continental crust beneath them. They are shallow. Seas away from continents can be very deep, and do not have continental shelves beneath them.

Sub-zones 
The pelagic (or open ocean) zone is divided into a number of sub-zones:
Epipelagic (surface to 200m): the illuminated surface zone where there is enough light for photosynthesis. Because of this, plankton, and the food chain which feeds on it, are in this zone. The top predators are fish such as tuna and many sharks.
 Mesopelagic (from 200m to 1000m): the twilight zone.  Although some light penetrates this deep, it is insufficient for photosynthesis. The name comes from Greek μέσον, middle. 
 Bathyal zone (from 1000m to 4000m): by this depth the ocean is almost entirely dark (with only the occasional bioluminescent organism). There are no living plants, and most animals survive by consuming the snow of detritus falling from the zones above, or (like the marine hatchetfish) by preying upon others. Giant squid live at this depth, and here they are hunted by deep-diving sperm whales. From Greek βαθύς (bathys), deep.
Abyssal zone (from 4000m to the ocean floor): no light penetrates to this depth, and some creatures are blind and colourless. Bioluminescence also occurs in this zone. 
 Hadal zone (the deep water in ocean trenches) – the name comes from Hades, the classical Greek underworld. This zone is less well known. Very few species live in the open areas, but many organisms live in hydrothermal vents.
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.

Other features of the deep ocean 
Seamounts
Ocean ridges

Other websites 
 The Deep Sea pages at Oceanlink 

Biological oceanography
Biomes
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. Egg yolks 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.

β-carotene, a provitamin found in foods like carrots can be converted to vitamin A. The efficiency of the conversion depends on genetics and fat consumption.

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.
Hypervitaminosis A 
Too much vitamin A is also dangerous to one's health. It is a condition known as hypervitaminosis. Vitamin A is not soluble in water, and the human body can not get rid of the excess vitamin A easily by 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 A-rich food like liver.

What applies to humans applies to all mammals at least. Some large predators, such as the big cats, seem not to eat their preys' livers. On the other hand, polar bears apparently do so, and they store vitamin A in their liver cells. However, they have long, sometimes very long, periods between kills. In contrast, African big cats kill about every three or four days, and they do seem to avoid eating the preys' livers.

References 

Fat-soluble vitamins
Vitamin D is a hormone. It is a steroid which is made in the body under the right conditions. To make it, the body needs sunlight, which acts on the lower layers of the skin. 

However, if the body does not make enough, it can be found from food sources in tiny amounts.  In fact, many countries add it automatically to certain foods like milk. Supplements can be easily found in most developed countries.

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

What it does
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.

Different kinds
In total, there are 5 different forms, D1 to D5. The most common ones are D2 and D3 (see images).
D3 (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.

D2 (also called ergocalciferol) is produced by fungi. It is similar to D3, but not exactly the same.

Getting enough
D3 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 D3.

Many things can keep the skin from making enough D3. Winter sunlight may be too weak. Melanin, which protects skin from damage, also keeps it from making D3, which is why people with darker skin are more prone to deficiency. Older people are also prone, because aging skin makes less D3, even with enough sunlight. Clothing, glass, sunscreens and sunblocks also shield the skin from getting enough ultraviolet light to make D3.
It is hard to know how much supplemental Vitamin D, if any, is needed. 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 help most adults.

Few foods naturally contain much D3. Fish do, especially oily ones, such as salmon, sardine and mackerel. Many kinds of edible mushrooms contain some D2, like shiitake. Mushrooms grown in full sunlight tend to have more.

References

Other websites 
Benefits and sources of Vitamin D 
Benefits of Vitamin D 
Factsheet on Vitamin D
FDA takes Vitamin D drugs and feeds them to prisoners 

Fat-soluble vitamins
Steroid hormones
In ecology, a biome is a major regional group of distinctive plant and animal
communities best adapted to the region's physical natural environment,
latitude, elevation, and terrain.

A biome is made up of ecoregions or settlements 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.

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.

A fundamental classification of biomes is into:

 Terrestrial (land) biomes and
 Aquatic (water) biomes.
Biomes are often given local names. For example, a temperate grassland or shrubland biome is known commonly as steppe in central Asia, savanna or field in southern Africa, prairie in North America, pampa in South America and outback or scrub in Australia.
Sometimes an entire biome may be targeted for protection, especially under an individual nation's Biodiversity Action Plan.
Terrestrial biomes
Climate is a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are:
 latitude: arctic, boreal, temperate, subtropical, tropical.
 humidity: humid, semi-humid, semi-arid, and arid.
 seasonal variation: rainfall may be distributed evenly throughout the year, or be marked by seasonal variations.
 dry summer, wet winter: most regions of the earth receive most of their rainfall during the summer months; Mediterranean climate regions receive their rainfall during the winter months.
 elevation: increasing elevation causes a distribution of habitat types similar to that of increasing latitude.

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

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

Udvardy system
In 1975, Miklos Udvardy published a system of biogeographic provinces that were divided into 12 terrestrial biomes.
Bailey system
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).
WWF system
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:
Forests ('broadleaf' = Angiosperm trees)
 Tropical and subtropical moist broadleaf forests (tropical and subtropical, humid)
 Tropical and subtropical dry broadleaf forests (tropical and subtropical, semihumid)
 Tropical and subtropical coniferous forests (tropical and subtropical, semihumid)
 Temperate broadleaf and mixed forests (temperate, humid)
 Temperate coniferous forests (temperate, humid to semihumid)
 Boreal forests/taiga (subarctic, humid)
 Mediterranean forests, woodlands, and scrub or sclerophyll forests (temperate warm, semihumid to semiarid with winter rainfall)
Grasslands
Grasslands
 Tropical and subtropical grasslands, savannas, and shrublands (tropical and subtropical, semiarid)
 Temperate grasslands, savannas, and shrublands (temperate, semiarid)
 Flooded grasslands and savannas (temperate to tropical, fresh or brackish water inundated)
 Montane grasslands and shrublands: alpine (above the tree line) or montane (below the tree line, and hence with trees).
 Tundra (Arctic)
 Deserts and xeric shrublands (temperate to tropical, arid)
 Mangrove (subtropical and tropical, salt water inundated)
Aquatic biomes
 continental shelf
 littoral/intertidal zone
 riparian
 pond
 coral reef
 Ecosystem
 Habitat
 kelp forest
 pack ice
 hydrothermal vents
 cold seeps
 benthic zone
 pelagic zone
 neritic zone

Other biomes
The Endolithic biome, consisting entirely of microscopic life in rock pores (small holes in rocks) and cracks, kilometers beneath the surface, has only recently been discovered and does not fit well into most classification schemes.

Related pages 

 Ecozone

Other websites 
 Biomes of the world (Missouri Botanic Garden)
 Biomes Quiz
Vitamin E (which is also called Tocopherol or Tocotrienol, E307, E308,E309) is a vitamin. There are eight forms of it, E1 to E8. It can be found in vegetable oils. Very often it is also added to lotions and creams for the skin. It is supposed to help the healing of the skin, after burns and injuries, and lower the risk of heart disease and cancer.

Some research suggests that vitamin E has anti-aging benefits.

References 

Fat-soluble vitamins
Vitamin K is a vitamin which is soluble in fat. It is probably best known for its role in the coagulation (clotting) of blood. However, it also serves other important functions in the body.

Vitamin K was discovered by a Danish chemist named Henrik Dam. He won the 1943 Nobel Prize in  Physiology or Medicine for discovering its key role in the coagulation of blood. Since that time, Vitamin K's role in other physiologic functions has become known. One of the most important is its role in controlling where calcium goes in the body.

Without Vitamin K, there would be a loss of blood when a person bleeds, which can lead to unconsciousness or even death. Vitamin K can be found in green vegetables, such as spinach, lettuce, broccoli or cabbage.

References

Fat-soluble vitamins
The B vitamin complex (also called B vitamins) are a group of 8 vitamins. They have an important job in the metabolism of cells. Each B vitamin is a cofactor (a coenzyme) for some key metabolic processes or it is a precursor needed to make one.

Originally, people thought they were just different forms of one vitamin (as with Vitamin D, for example). Later it turned out that they are separate vitamins that often can be found together. They are Vitamin B1/Thiamine, Vitamin B2/Riboflavin, Vitamin B3/Vitamin P/Vitamin PP/Niacin,Vitamin B5/Pantothenic acid, Vitamin B6, Vitamin B7/Vitamin H/Biotin, Vitamin B9/Vitamin M/Vitamin B-c/Folate and Vitamin B12. They are required for growth, and proper functioning of nerves and muscles. B vitamins are found in meat, milk, whole grains and fresh vegetables.

Vitamin B deficiencies have been shown to cause the following symptoms:
mental problems
heart palpitations
heart arrhythmias
exhaustion
paranoia, vague fears, fear that something dreadful is about to happen, nervousness, ADD (attention deficiency), inability to concentrate
thoughts of dying
frustration
inability to sleep
restlessness
tingling in hands
tingling fingers and toes
crying spells, inability to cope
soreness all over

Well-known medical syndromes caused by thiamine deficiency are beri-beri, Wernicke–Korsakoff syndrome (WKS), and optic neuropathy.

References
Places with a subarctic climate (also called boreal climate) have long, usually very cold winters, and short, warm summers. It is found on large landmasses, away from oceans, usually at latitudes from 50° to 70°N. Because there are no large landmasses at such latitudes in the Southern Hemisphere, it is only found at high altitudes (heights) in the Andes and the mountains of Australia and New Zealand's South Island. These climates are in groups Dfc, Dwc, Dfd and Dwd in the Köppen climate classification
This type of climate has very big changes in temperature throughout the year. In winter, temperatures can drop to -40 °C (also -40 °F) and in summer, the temperature may go above 30 °C (86 °F). But the summers are short, as there are no more than three months of the year with an average temperature of at least 10 °C (50 °F). However, at least one must have an average temperature of at least 10 °C (50 °F) . In addition, the coldest month must be below 0°C (32°F) The subarctic climate is in between the humid continental climate and the polar climate. The subarctic climate is found in the these places:

 Much of Siberia
 The northern half of Scandinavia (milder winters in coastal areas)
 Most of Alaska
 Much of Canada from about 50°N to the tree line, including:
Southern Labrador
Northern Quebec except for the far north
Far northern Ontario
The northern Prairie Provinces
Most of the Yukon
Most of the Northwest Territories
With 5–7 months in a row where the average temperature is below freezing, all water in the soil and subsoil freezes several feet deep. In the colder parts of this climate, summer warmth is not enough to thaw (unfreeze) more than a few feet on the top of the soil, so there can be permafrost(soil that is frozen forever). When the ice melts in the summer, 2 to 14 ft (0.6 to 4 m) of soil can thaw, depending on the latitude and the type of soil. Some subarctic climates near oceans (such as southern Alaska and the northern edge of Europe), have milder winters and no permafrost, so it is easier to farm there.
Summer is very short; it has about 45 to 100 days at most, and in a lot of places, the temperatures can go below freezing (32 °F or 0 °C) at any time of the year, even in the summer. Vegetation (plants) in a subarctic climate usually has low diversity (only a few different types of plants grow), because only hardy (very tough) species can survive the long winters and make use of the short summers. Trees are mostly evergreen conifers, because few broadleaved (big leaves) trees can survive the very low temperatures in winter. This type of forest is also known as taiga. The word taiga can also be a name for the climate itself. A lot of plants grow in the taiga (even if there are only a few different kinds of plants), so the taiga (boreal) forest is the largest forest biome on the planet, with most of the forests in Russia and Canada.