California is the most populous state in the United States and the third most extensive by area. Located on the western coast of the U. S, California is bordered by the other U. S. states of Oregon and Arizona and shares an international border with the Mexican state of Baja California. Los Angeles is Californias most populous city, and the second largest after New York City. The Los Angeles Area and the San Francisco Bay Area are the nations second- and fifth-most populous urban regions, California has the nations most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The Central Valley, an agricultural area, dominates the states center. What is now California was first settled by various Native American tribes before being explored by a number of European expeditions during the 16th and 17th centuries, the Spanish Empire claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its war for independence.
The western portion of Alta California was organized as the State of California, the California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom. If it were a country, California would be the 6th largest economy in the world, fifty-eight percent of the states economy is centered on finance, real estate services and professional, scientific and technical business services. Although it accounts for only 1.5 percent of the states economy, the story of Calafia is recorded in a 1510 work The Adventures of Esplandián, written as a sequel to Amadis de Gaula by Spanish adventure writer Garci Rodríguez de Montalvo. The kingdom of Queen Calafia, according to Montalvo, was said to be a land inhabited by griffins and other strange beasts. This conventional wisdom that California was an island, with maps drawn to reflect this belief, shortened forms of the states name include CA, Cal. Calif. and US-CA.
Settled by successive waves of arrivals during the last 10,000 years, various estimates of the native population range from 100,000 to 300,000. The Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups were diverse in their organization with bands, villages. Trade and military alliances fostered many social and economic relationships among the diverse groups, the first European effort to explore the coast as far north as the Russian River was a Spanish sailing expedition, led by Portuguese captain Juan Rodríguez Cabrillo, in 1542. Some 37 years English explorer Francis Drake explored and claimed a portion of the California coast in 1579. Spanish traders made unintended visits with the Manila galleons on their trips from the Philippines beginning in 1565
The Sahara is the largest hot desert and the third largest desert in the world after Antarctica and the Arctic. Its area of 9,200,000 square kilometres is comparable to the area of the United States. The desert comprises much of North Africa, excluding the fertile region on the Mediterranean Sea coast, the Atlas Mountains of the Maghreb, and the Nile Valley in Egypt and Sudan. It stretches from the Red Sea in the east and the Mediterranean in the north to the Atlantic Ocean in the west, where the landscape gradually changes from desert to coastal plains. To the south, it is bounded by the Sahel, a belt of tropical savanna around the Niger River valley. The Sahara can be divided into several regions including, the western Sahara, the central Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains, the Ténéré desert, the name Sahara is derived from ṣaḥārā, the plural of the Arabic word for desert. The Sahara covers large parts of Algeria, Egypt, Mali, Morocco, Western Sahara, Sudan and it covers 9 million square kilometres, amounting to 31% of Africa.
If all areas with an annual precipitation of less than 250 mm were included. It is one of three physiographic provinces of the African massive physiographic division. The Sahara is mainly rocky hamada, Ergs form only a minor part, wind or rare rainfall shape the desert features, sand dunes, dune fields, sand seas, stone plateaus, gravel plains, dry valleys, dry lakes, and salt flats. Unusual landforms include the Richat Structure in Mauritania, several deeply dissected mountains, many volcanic, rise from the desert, including the Aïr Mountains, Ahaggar Mountains, Saharan Atlas, Tibesti Mountains, Adrar des Iforas, and the Red Sea hills. The highest peak in the Sahara is Emi Koussi, a volcano in the Tibesti range of northern Chad. The central Sahara is hyperarid, with sparse vegetation, the northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis, where moisture collects. In the central, hyperarid region, there are subdivisions of the great desert, the Ténéré, the Libyan Desert, the Eastern Desert.
These extremely arid areas often receive no rain for years, the northern limit corresponds to the 100 mm isohyet of annual precipitation. To the south, the Sahara is bounded by the Sahel, the southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha, or northern limit of Cenchrus biflorus, a grass typical of the Sahel. According to climatic criteria, the limit of the Sahara corresponds to the 150 mm isohyet of annual precipitation. The Sahara is the worlds largest low-latitude hot desert and this steady descending airflow causes a warming and a drying effect in the upper troposphere
The Middle East is a transcontinental region centered on Western Asia and Egypt. The corresponding adjective is Middle-Eastern and the noun is Middle-Easterner. The term has come into usage as a replacement of the term Near East beginning in the early 20th century. Arabs, Persians and Azeris constitute the largest ethnic groups in the region by population. Indigenous minorities of the Middle East include Jews and other Arameans, Berbers, Druze, Mandaeans, Shabaks, Tats, in the Middle East, there is a Romani community. European ethnic groups form a diaspora in the region include Albanians, Circassians, Crimean Tatars, Franco-Levantines. Among other migrant populations are Bengalis as well as other Indians, Filipinos, Pakistanis, the history of the Middle East dates back to ancient times, with the importance of the region being recognized for millennia. Most of the countries border the Persian Gulf have vast reserves of crude oil. The term Middle East may have originated in the 1850s in the British India Office, however, it became more widely known when American naval strategist Alfred Thayer Mahan used the term in 1902 to designate the area between Arabia and India.
During this time the British and Russian Empires were vying for influence in Central Asia, Mahan realized not only the strategic importance of the region, but of its center, the Persian Gulf. Mahan first used the term in his article The Persian Gulf and International Relations, published in September 1902 in the National Review, a British journal. The Middle East, if I may adopt a term which I have not seen, will some day need its Malta, as well as its Gibraltar, it does not follow that either will be in the Persian Gulf. The British Navy should have the facility to concentrate in force if occasion arise, about Aden, mahans article was reprinted in The Times and followed in October by a 20-article series entitled The Middle Eastern Question, written by Sir Ignatius Valentine Chirol. During this series, Sir Ignatius expanded the definition of Middle East to include regions of Asia which extend to the borders of India or command the approaches to India. After the series ended in 1903, The Times removed quotation marks from subsequent uses of the term, in the late 1930s, the British established the Middle East Command, which was based in Cairo, for its military forces in the region.
After that time, the term Middle East gained broader usage in Europe, the description Middle has led to some confusion over changing definitions. Before the First World War, Near East was used in English to refer to the Balkans and the Ottoman Empire, while Middle East referred to Iran, the Caucasus, Central Asia, and Turkestan. The first official use of the term Middle East by the United States government was in the 1957 Eisenhower Doctrine, the Associated Press Stylebook says that Near East formerly referred to the farther west countries while Middle East referred to the eastern ones, but that now they are synonymous
The Equator usually refers to an imaginary line on the Earths surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. The Equator is about 40,075 kilometres long, some 78. 7% lies across water and 21. 3% over land, other planets and astronomical bodies have equators similarly defined. Generally, an equator is the intersection of the surface of a sphere with the plane that is perpendicular to the spheres axis of rotation. The latitude of the Earths equator is by definition 0° of arc, the equator is the only line of latitude which is a great circle — that is, one whose plane passes through the center of the globe. The plane of Earths equator when projected outwards to the celestial sphere defines the celestial equator, in the cycle of Earths seasons, the plane of the equator passes through the Sun twice per year, at the March and September equinoxes. To an observer on the Earth, the Sun appears to travel North or South over the equator at these times, light rays from the center of the Sun are perpendicular to the surface of the Earth at the point of solar noon on the Equator.
Locations on the Equator experience the quickest sunrises and sunsets because the sun moves nearly perpendicular to the horizon for most of the year. The Earth bulges slightly at the Equator, the diameter of the Earth is 12,750 kilometres. Because the Earth spins to the east, spacecraft must launch to the east to take advantage of this Earth-boost of speed, seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earths axis relative to the plane of revolution. During the year the northern and southern hemispheres are inclined toward or away from the sun according to Earths position in its orbit, the hemisphere inclined toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter. At the equinoxes, the Earths axis is not tilted toward the sun, instead it is perpendicular to the sun meaning that the day is about 12 hours long, as is the night, across the whole of the Earth. Near the Equator there is distinction between summer, autumn, or spring.
The temperatures are usually high year-round—with the exception of high mountains in South America, the temperature at the Equator can plummet during rainstorms. In many tropical regions people identify two seasons, the wet season and the dry season, but many places close to the Equator are on the oceans or rainy throughout the year, the seasons can vary depending on elevation and proximity to an ocean. The Equator lies mostly on the three largest oceans, the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean. The highest point on the Equator is at the elevation of 4,690 metres, at 0°0′0″N 77°59′31″W and this is slightly above the snow line, and is the only place on the Equator where snow lies on the ground. At the Equator the snow line is around 1,000 metres lower than on Mount Everest, the Equator traverses the land of 11 countries, it passes through two island nations, though without making a landfall in either. Starting at the Prime Meridian and heading eastwards, the Equator passes through, Despite its name, its island of Annobón is 155 km south of the Equator, and the rest of the country lies to the north
For the current region of Chad, see Tibesti Region. The Tibesti Mountains are a range in the central Sahara, primarily located in the extreme north of Chad. The highest peak in the range, Emi Koussi, lies to the south at a height of 3,445 metres and is the highest point in both Chad and the Sahara, Bikku Bitti, the highest peak in Libya, is located in the north of the range. The central third of the Tibesti is of volcanic origin and consists of five shield volcanoes topped by large craters, Emi Koussi, Tarso Toon, Tarso Voon, Tarso Yega, major lava flows have formed vast plateaus that overlie Paleozoic sandstone. Erosion has shaped volcanic spires and carved an extensive network of canyons through which run rivers subject to highly irregular flows that are rapidly lost to the desert sands, which means place where the mountain people live, is the domain of the Toubou people. The Toubou live mainly along the wadis, on rare oases where palm trees and they harness the water that collects in gueltas, the supply of which is highly variable from year-to-year and decade-to-decade.
The plateaus are used to graze livestock in the winter and harvest grain in the summer, temperatures are high, although the altitude ensures that the range is cooler than the surrounding desert. The Toubou, who first appeared in the range in the 5th century BC, adapted to these conditions and they arrived in several waves, taking refuge in times of conflict and dispersing in times of prosperity, although not without intense internal hostility at times. The independent spirit of the Toubou and the situation in the region has complicated the exploration of the range as well as the ascent of its peaks. Tensions continued after Chad and Libya gained independence in the century, with hostage-taking. The geopolitical situation and the lack of infrastructure has hampered the development of tourism, the Saharomontane flora and fauna, which include the rhim gazelle and Barbary sheep, have adapted to the mountains, yet the climate has not always been as harsh. Greater biodiversity existed in the past, as evidenced by scenes portrayed in rock and parietal art found throughout the range, the isolation of the Tibesti has sparked the cultural imagination in both art and literature.
The Tibesti Mountains are named for the Toubou people, written Tibu or Tubu, that inhabit the area. In the Kanuri language, tu means rock or mountain and bu means a person or dweller, most of the mountain names are derived from Arabic as well as the Tedaga and Dazaga languages. The term ehi refers to peaks and rocky hills, emi to larger mountains, era to craters, for example, the Ehi Mousgou is a 2, 849-metre stratovolcano near Tarso Voon, Era Kohor is a crater on top of Emi Koussi. The name Toussidé means that which killed the Tou, as in the Toubou, the name of Bardaï, the principal town in the range, means cold in Chadian Arabic, because of its low nocturnal temperatures. In the Tedaga language, the town is known as Goumodi, the range is adjacent to Niger and located approximately halfway between the Mediterranean Sea and Lake Chad, just south of the Tropic of Cancer. The East African Rift is 1,900 km to the east, the range is 380 km in length,350 km in width, and spans 100,000 km2
The Sichuan Basin, or Szechwan Basin, is a lowland region in southwestern China. It comprises the central and eastern portions of Sichuan province, due to its relative flatness and fertile grounds, it is heavily populated with a population of more than 100 million. In addition to being a dominant geographical feature of the region, the Sichuan basin constitutes a cultural sphere that is distinguished by its own customs, cuisine. It is called the Red Basin and it is famous for rice cultivation. It is the principal gas-producing region of China, Mountains frame the Sichuan Basin on all sides, the Qionglai Range in the west the Longmen Mountains in the northwest the Daba in the northeast. The Yangtze River, flowing from the Sichuan Basin into the eastern China, the Sichuan Basin consists of low hills and alluvial plains, and several major rivers flow into the Chang Jiang, which passes through the southern part of the basin. The seismically active Longmenshan Fault - the source of the catastrophic 2008 Sichuan earthquake - runs along the boundary of the basin.
See the articles on Chongqing and Chengdu for further details, a greater variety of natural landscapes and wildlife has been at least partially preserved in the mountains surrounding the basin. The natural ecosystems of mountains have been classified by the World Wildlife Fund as the Qionglai-Minshan conifer forests. It was in the hilly Lichuan County, on the eastern fringe of the basin. The Dawn Redwood is distinctive because it is a deciduous conifer
Canada is a country in the northern half of North America. Canadas border with the United States is the worlds longest binational land border, the majority of the country has a cold or severely cold winter climate, but southerly areas are warm in summer. Canada is sparsely populated, the majority of its territory being dominated by forest and tundra. It is highly urbanized with 82 per cent of the 35.15 million people concentrated in large and medium-sized cities, One third of the population lives in the three largest cities, Toronto and Vancouver. Its capital is Ottawa, and other urban areas include Calgary, Quebec City, Winnipeg. Various aboriginal peoples had inhabited what is now Canada for thousands of years prior to European colonization. Pursuant to the British North America Act, on July 1,1867, the colonies of Canada, New Brunswick and this began an accretion of provinces and territories to the mostly self-governing Dominion to the present ten provinces and three territories forming modern Canada.
With the Constitution Act 1982, Canada took over authority, removing the last remaining ties of legal dependence on the Parliament of the United Kingdom. Canada is a parliamentary democracy and a constitutional monarchy, with Queen Elizabeth II being the head of state. The country is officially bilingual at the federal level and it is one of the worlds most ethnically diverse and multicultural nations, the product of large-scale immigration from many other countries. Its advanced economy is the eleventh largest in the world, relying chiefly upon its abundant natural resources, Canadas long and complex relationship with the United States has had a significant impact on its economy and culture. Canada is a country and has the tenth highest nominal per capita income globally as well as the ninth highest ranking in the Human Development Index. It ranks among the highest in international measurements of government transparency, civil liberties, quality of life, economic freedom, Canada is an influential nation in the world, primarily due to its inclusive values, years of prosperity and stability, stable economy, and efficient military.
While a variety of theories have been postulated for the origins of Canada. In 1535, indigenous inhabitants of the present-day Quebec City region used the word to direct French explorer Jacques Cartier to the village of Stadacona, from the 16th to the early 18th century Canada referred to the part of New France that lay along the St. Lawrence River. In 1791, the area became two British colonies called Upper Canada and Lower Canada collectively named The Canadas, until their union as the British Province of Canada in 1841. Upon Confederation in 1867, Canada was adopted as the name for the new country at the London Conference. The transition away from the use of Dominion was formally reflected in 1982 with the passage of the Canada Act, that year, the name of national holiday was changed from Dominion Day to Canada Day
Sudan, known as North Sudan since South Sudans independence and officially the Republic of the Sudan, is a country in Northern Africa. It is the third largest country in Africa, the River Nile divides the country into eastern and western halves. Before the Sudanese Civil War, South Sudan was part of Sudan, Sudan was home to numerous ancient civilizations, such as the Kingdom of Kush, Nobatia, Makuria, Meroë and others, most of which flourished along the Nile. During the pre-dynastic period Nubia and Nagadan Upper Egypt were identical, by virtue of its proximity to Egypt, the Sudan participated in the wider history of the Near East inasmuch as it was Christianized by the 6th century, and Islamized in the 15th. As a result of Christianization, the Old Nubian language stands as the oldest recorded Nilo-Saharan language, Sudan was the largest country in Africa and the Arab world until 2011, when South Sudan separated into an independent country, following an independence referendum. Sudan is now the third largest country in Africa and the third largest country in the Arab world and its capital is Khartoum, the political and commercial centre of the nation.
It is a representative democratic federal republic. The politics of Sudan are regulated by an organization called the National Assembly. The Sudanese legal system is based on Islamic law, the countrys place name Sudan is a name given to a geographical region to the south of the Sahara, stretching from Western Africa to eastern Central Africa. The name derives from the Arabic bilād as-sūdān, or the lands of the Blacks, during the fifth millennium BC migrations from the drying Sahara brought neolithic people into the Nile Valley along with agriculture. The population that resulted from this cultural and genetic mixing developed social hierarchy over the centuries become the Kingdom of Kush at 1700 BC. The Kingdom of Kush was an ancient Nubian state centered on the confluences of the Blue Nile and White Nile, and the Atbarah River and it was established after the Bronze Age collapse and the disintegration of the New Kingdom of Egypt, centered at Napata in its early phase. After King Kashta invaded Egypt in the eighth century BC, the Kushite kings ruled as pharaohs of the Twenty-fifth Dynasty of Egypt for a century before being defeated and driven out by the Assyrians.
At the height of their glory, the Kushites conquered an empire that stretched from what is now known as South Kordofan all the way to the Sinai, pharaoh Piye attempted to expand the empire into the Near East, but was thwarted by the Assyrian king Sargon II. Sennacheribs successor Esarhaddon went further, and invaded Egypt itself, deposing Taharqa, Taharqa fled back to his homeland where he died two years later. Egypt became an Assyrian colony, king Tantamani, after succeeding Taharqa, Esarhaddon died while preparing to leave the Assyrian capital of Nineveh in order to eject him. However, his successor Ashurbanipal sent an army into southern Egypt and routed Tantamani. During Classical Antiquity, the Nubian capital was at Meroë, in ancient Greek geography, the Meroitic kingdom was known as Ethiopia
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared and ultraviolet light. On Earth, sunlight is filtered through Earths atmosphere, and is obvious as daylight when the Sun is above the horizon, when the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, the World Meteorological Organization uses the term sunshine duration to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an Average over the earth of 164 Watts per square meter over a 24 hour day. The ultraviolet radiation in sunlight has both positive and negative effects, as it is both a principal source of vitamin D3 and a mutagen. Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface.
Researchers may record sunlight using a sunshine recorder, pyranometer, or pyrheliometer, to calculate the amount of sunlight reaching the ground, both Earths elliptical orbit and the attenuation by Earths atmosphere have to be taken into account. In this formula dn–3 is used, because in modern times Earths perihelion, the closest approach to the Sun and, the value of 0.033412 is determined knowing that the ratio between the perihelion squared and the aphelion squared should be approximately 0.935338. The solar illuminance constant, is equal to 128×103 lx, the atmospheric extinction brings the number of lux down to around 100000. The total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and it is about 3. 3% higher than average in January and 3. 3% lower in July. In terms of energy, sunlight at Earths surface is around 52 to 55 percent infrared,42 to 43 percent visible, and 3 to 5 percent ultraviolet. At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet, direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux.
This is higher than the efficacy of most artificial lighting, which means using sunlight for illumination heats up a less than using most forms of artificial lighting. Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98000 lux on a surface at sea level. The illumination of a surface will be considerably less than this if the Sun is not very high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole, dividing the irradiance of 1050 W/m2 by the size of the suns disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. Multiplying this by π gives a limit to the irradiance which can be focused on a surface using mirrors,48.5 MW/m2
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a piece of transparent material, while a compound lens consists of several simple lenses. Lenses are made from such as glass or plastic, and are ground. A lens can focus light to form an image, unlike a prism, devices that similarly focus or disperse waves and radiation other than visible light are called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. The word lens comes from the Latin name of the lentil, the genus of the lentil plant is Lens, and the most commonly eaten species is Lens culinaris. The lentil plant gives its name to a geometric figure, the variant spelling lense is sometimes seen. While it is listed as a spelling in some dictionaries. The oldest lens artifact is the Nimrud lens, dating back 2700 years to ancient Assyria, david Brewster proposed that it may have been used as a magnifying glass, or as a burning-glass to start fires by concentrating sunlight.
Another early reference to magnification dates back to ancient Egyptian hieroglyphs in the 8th century BC, the earliest written records of lenses date to Ancient Greece, with Aristophanes play The Clouds mentioning a burning-glass. Some scholars argue that the evidence indicates that there was widespread use of lenses in antiquity. Such lenses were used by artisans for fine work, and for authenticating seal impressions, both Pliny and Seneca the Younger described the magnifying effect of a glass globe filled with water. The Viking lenses were capable of concentrating enough sunlight to ignite fires, between the 11th and 13th century reading stones were invented. Often used by monks to assist in illuminating manuscripts, these were primitive plano-convex lenses initially made by cutting a sphere in half. As the stones were experimented with, it was understood that shallower lenses magnified more effectively. Lenses came into use in Europe with the invention of spectacles. Spectacle makers created improved types of lenses for the correction of vision based more on knowledge gained from observing the effects of the lenses.
With the invention of the telescope and microscope there was a deal of experimentation with lens shapes in the 17th. Opticians tried to construct lenses of varying forms of curvature, wrongly assuming errors arose from defects in the figure of their surfaces
Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and precipitated—that is, become heavy enough to fall under gravity. Rain is a component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for power plants. The major cause of production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus which can organize into narrow rainbands. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass, the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes. The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities, global warming is causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics.
The globally averaged annual precipitation over land is 715 mm, climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges, rainfall amounts can be estimated by weather radar. Rain is known or suspected on other planets, where it may be composed of methane, sulfuric acid, or even iron rather than water. Air contains water vapor, and the amount of water in a mass of dry air. The amount of moisture in air is commonly reported as relative humidity. How much water vapor a parcel of air can contain before it becomes saturated, warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it, the dew point is the temperature to which a parcel must be cooled in order to become saturated. There are four mechanisms for cooling the air to its dew point, adiabatic cooling, conductive cooling, radiational cooling.
Adiabatic cooling occurs when air rises and expands, the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a surface, usually by being blown from one surface to another. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath, evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation
Mauritania /mɔːrɪˈteɪniə/, officially the Islamic Republic of Mauritania, is a country in the Maghreb region of western Africa. The country derives its name from the ancient Berber Kingdom of Mauretania, approximately 90% of Mauritanias land is within the Sahara and consequently the population is concentrated in the south, where precipitation is slightly higher. The capital and largest city is Nouakchott, located on the Atlantic coast, the government was overthrown on 6 August 2008, in a military coup détat led by General Mohamed Ould Abdel Aziz. On 16 April 2009, Aziz resigned from the military to run for president in the 19 July elections, about 20% of Mauritanians live on less than US$1.25 per day. Mauritania suffers from several human rights issues, including slavery, as at least 4% of the population are enslaved against their will, the Bafours were primarily agriculturalist, and among the first Saharan people to abandon their historically nomadic lifestyle. With the gradual desiccation of the Sahara, they headed south, many of the Berber tribes claimed Yemeni origins.
There is little evidence to such claims, but a 2000 DNA study of Yemeni people suggested there might be some ancient connection between the peoples. Other peoples migrated south past the Sahara to West Africa, in 1076, Moorish Islamic warrior monks attacked and conquered the large area of the ancient Ghana Empire. Over the next 500 years, Arabs overcame fierce resistance from the population to dominate Mauritania. The Char Bouba war was the final effort of the peoples to repel the Yemeni Maqil Arab invaders. The invaders were led by the Beni Hassan tribe, the descendants of the Beni Hassan warriors became the upper stratum of Moorish society. Hassaniya, a Berber-influenced Arabic dialect that derives its name from the Beni Hassan, berbers retained a niche influence by producing the majority of the regions marabouts, those who preserve and teach Islamic tradition. Imperial France gradually absorbed the territories of present-day Mauritania from the Senegal River area and upwards, in 1901, Xavier Coppolani took charge of the imperial mission.
Through a combination of strategic alliances with Zawiya tribes, and military pressure on the Hassane warrior nomads, he managed to extend French rule over the Mauritanian emirates. Trarza and Tagant quickly submitted to treaties with the colonial power, Adrar was finally defeated militarily in 1912, and incorporated into the territory of Mauritania, which had been drawn up and planned in 1904. Mauritania was part of French West Africa from 1920, French rule brought legal prohibitions against slavery and an end to inter-clan warfare. During the colonial period, 90% of the population remained nomadic, many sedentary peoples, whose ancestors had been expelled centuries earlier, began to trickle back into Mauritania. After gaining independence, larger numbers of indigenous Sub-Saharan African peoples entered Mauritania, educated in French language and customs, many of these recent arrivals became clerks and administrators in the new state