Namibia the Republic of Namibia, is a country in southern Africa. Its western border is the Atlantic Ocean. Although it does not border Zimbabwe, less than 200 metres of the Zambezi River separates the two countries. Namibia gained independence from South Africa on 21 March 1990, following the Namibian War of Independence, its capital and largest city is Windhoek, it is a member state of the United Nations, the Southern African Development Community, the African Union, the Commonwealth of Nations. Namibia, the driest country in Sub-Saharan Africa, was inhabited since early times by the San and Nama peoples. Around the 14th century, immigrating Bantu peoples arrived as part of the Bantu expansion. Since the Bantu groups, the largest being the Ovambo, have dominated the population of the country. In 1878, the Cape of Good Hope a British colony, had annexed the port of Walvis Bay and the offshore Penguin Islands. In 1884 the German Empire established rule over most of the territory as a protectorate.
It began to develop infrastructure and farming and maintained this German colony until 1915, when South African forces defeated its military. In 1920, after the end of World War I, the League of Nations mandated the country to the United Kingdom, under administration by South Africa, it imposed its laws, including racial rules. From 1948, with the National Party elected to power, South Africa applied apartheid to what was known as South West Africa. In the 20th century and demands for political representation by native African political activists seeking independence resulted in the UN assuming direct responsibility over the territory in 1966, but South Africa maintained de facto rule. In 1973 the UN recognised the South West Africa People's Organisation as the official representative of the Namibian people. Following continued guerrilla warfare, South Africa installed an interim administration in Namibia in 1985. Namibia obtained full independence from South Africa in 1990. However, Walvis Bay and the Penguin Islands remained under South African control until 1994.
Namibia has a population of a stable multi-party parliamentary democracy. Agriculture, herding and the mining industry – including mining for gem diamonds, gold and base metals – form the basis of its economy; the large, arid Namib Desert has resulted in Namibia being overall one of the least densely populated countries in the world. The name of the country is derived from the Namib Desert, considered to be the oldest desert in the world; the name Namib itself is of Nama origin and means "vast place". Before its independence in 1990, the area was known first as German South-West Africa as South-West Africa, reflecting the colonial occupation by the Germans and the South Africans; the dry lands of Namibia have been inhabited since early times by San and Nama. Around the 14th century, immigrating Bantu people began to arrive during the Bantu expansion from central Africa. From the late 18th century onward, Oorlam people from Cape Colony crossed the Orange River and moved into the area that today is southern Namibia.
Their encounters with the nomadic Nama tribes were peaceful. They received the missionaries accompanying the Oorlam well, granting them the right to use waterholes and grazing against an annual payment. On their way further north, the Oorlam encountered clans of the Herero at Windhoek and Okahandja, who resisted their encroachment; the Nama-Herero War broke out in 1880, with hostilities ebbing only after the German Empire deployed troops to the contested places and cemented the status quo among the Nama and Herero. The first Europeans to disembark and explore the region were the Portuguese navigators Diogo Cão in 1485 and Bartolomeu Dias in 1486, but the Portuguese did not try to claim the area. Like most of interior Sub-Saharan Africa, Namibia was not extensively explored by Europeans until the 19th century. At that time traders and settlers came principally from Sweden. In the late 19th century, Dorsland Trekkers crossed the area on their way from the Transvaal to Angola; some of them settled in Namibia instead of continuing their journey.
Namibia became a German colony in 1884 under Otto von Bismarck to forestall perceived British encroachment and was known as German South West Africa. The Palgrave Commission by the British governor in Cape Town determined that only the natural deep-water harbor of Walvis Bay was worth occupying and thus annexed it to the Cape province of British South Africa. From 1904 to 1907, the Herero and the Namaqua took up arms against brutal German colonialism. In calculated punitive action by the German occupiers, government officials ordered extinction of the natives in the Herero and Namaqua genocide. In what has been called the "first genocide of the 20th century", the Germans systematically killed 10,000 Nama and 65,000 Herero; the survivors, when released from detention, were subjected to a policy of dispossession, forced labor, racial segregation, and
Granite domes are domical hills composed of granite with bare rock exposed over most of the surface. Domical features such as these are known as bornhardts. Bornhardts can form in any type of plutonic rock but are composed of granite and granitic gneiss; as granitic plutons cool kilometers below the earth’s surface, minerals in the rock crystallize under uniform confining pressure. Erosion brings the rock closer to the pressure from above the rock decreases; these fractures are known as exfoliation joints, or sheet fractures, form in onionlike patterns that are parallel to the land surface. These sheets of rock peel off the exposed surface and in certain conditions develop domical structures. Additional theories on the origin of granite domes involve tectonic uplift. Sheet fractures are arcuate fractures defining slabs of rock, they form in sets parallel to the Earth’s surface but may form in convex-upward or concave-upward sets. There are several possible explanations for the formation of sheet fractures.
The most popular hypothesis is that they are the result of expansion and tangential fracturing consequent on erosional offloading or pressure release. There is evidence that supports this hypothesis when looking at granitic landforms that have sheet fractures. Granite forms deep in the Earth's crust under conditions of lithostatic pressure. In order for the granite to be exposed at the Earth’s surface a considerable thickness of rock must be eroded; this unloading allows the granite to expand radially and sheet fractures form tangentially to the radial stress. This indicates that the shape of the pre-existing land surface determines the geometry of the sheet fractures. One hypothesis is; this is the case with some granite domes but the fracture related exfoliation joints are what controls the steep slopes. Another theory that regards isolated bornhardts is that they remain after long-distance scarp recession. Moisture related weathering is. In the case of granite in a dissected landscape the dry granite high on a slope remains stable and acts as caprock.
Granite below this is more weathered and eroded because it has been exposed to moisture and has weathered. This leads to the steepening of the slope and the collapse of higher slope elements as well as the maintenance of scarps of constant inclination and morphology during backwearing. Bald Rock National Park, Australia Corcovado – Mountain in central Rio de Janeiro, Brazil El Capitan, United States Exfoliating granite Enchanted Rock, United States Fresno Dome, United States Granite Belt, Australia Half Dome, United States Huangshan China Looking Glass Rock, United States Stone Mountain, United States Yosemite National Park – National park in California, United States, United States Granite domes of the Cairngorms
Intertropical Convergence Zone
The Intertropical Convergence Zone, known by sailors as the doldrums or the calms, is the area encircling Earth near the Equator, where the northeast and southeast trade winds converge. The ITCZ was identified from the 1920s to the 1940s as the "Intertropical Front", but after the recognition in the 1940s and the 1950s of the significance of wind field convergence in tropical weather production, the term ITCZ was applied; when it lies near the Equator, it is called the near-equatorial trough. Where the ITCZ is drawn into and merges with a monsoonal circulation, it is sometimes referred to as a monsoon trough, a usage more common in Australia and parts of Asia. In the seamen's speech, the zone is referred to as the doldrums because of its erratic weather patterns with stagnant calms and violent thunderstorms; the ITCZ appears as a band of clouds thunderstorms, that encircle the globe near the Equator. In the Northern Hemisphere, the trade winds move in a southwestward direction from the northeast, while in the Southern Hemisphere, they move northwestward from the southeast.
When the ITCZ is positioned north or south of the Equator, these directions change according to the Coriolis effect imparted by Earth's rotation. For instance, when the ITCZ is situated north of the Equator, the southeast trade wind changes to a southwest wind as it crosses the Equator; the ITCZ is formed by vertical motion appearing as convective activity of thunderstorms driven by solar heating, which draw air in. The ITCZ is a tracer of the ascending branch of the Hadley cell and is wet; the dry descending branch is the horse latitudes. The location of the ITCZ varies with the seasons corresponding with the location of the thermal equator; as the heat capacity of the oceans is greater than air over land, migration is more prominent over land. Over the oceans, where the convergence zone is better defined, the seasonal cycle is more subtle, as the convection is constrained by the distribution of ocean temperatures. Sometimes, a double ITCZ forms, with one located north and another south of the Equator, one of, stronger than the other.
When this occurs, a narrow ridge of high pressure forms between the two convergence zones. The South Pacific convergence zone is a reverse-oriented, or west-northwest to east-southeast aligned, trough extending from the west Pacific warm pool southeastwards towards French Polynesia, it lies just south of the equator during the Southern Hemisphere warm season, but can be more extratropical in nature east of the International Date Line. It is considered the largest and most important piece of the ITCZ, has the least dependence upon heating from a nearby land mass during the summer than any other portion of the monsoon trough; the southern ITCZ in the southeast Pacific and southern Atlantic, known as the SITCZ, occurs during the Southern Hemisphere fall between 3° and 10° south of the equator east of the 140th meridian west longitude during cool or neutral El Niño–Southern Oscillation patterns. When ENSO reaches its warm phase, otherwise known as El Niño, the tongue of lowered sea surface temperatures due to upwelling off the South American continent disappears, which causes this convergence zone to vanish as well.
Variation in the location of the intertropical convergence zone drastically affects rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the intertropical convergence zone can result in severe droughts or flooding in nearby areas. In some cases, the ITCZ may become narrow when it moves away from the equator. There appears to be a 15 to 25-day cycle in thunderstorm activity along the ITCZ, half the wavelength of the Madden–Julian oscillation. Within the ITCZ the average winds are slight, unlike the zones north and south of the equator where the trade winds feed. Early sailors named this belt of calm the doldrums because of the inactivity and stagnation they found themselves in after days of no wind. To find oneself becalmed in this region in a hot and muggy climate could mean death in an era when wind was the only effective way to propel ships across the ocean. Today and competitive sailors attempt to cross the zone as as possible as the erratic weather and wind patterns may cause unexpected delays.
Tropical cyclogenesis depends upon low-level vorticity as one of its six requirements, the ITCZ fills this role as it is a zone of wind change and speed, otherwise known as horizontal wind shear. As the ITCZ migrates to tropical - subtropical latitudes and beyond during the respective hemisphere's summer season, increasing Coriolis force makes the formation of tropical cyclones within this zone more possible. Surges of higher pressure from high latitudes can enhance tropical disturbances along its axis. In the north Atlantic and the northeastern Pacific oceans, tropical waves move along the axis of the ITCZ causing an increase in thunderstorm activity, under weak vertical wind shear, these clusters of thunderstorms can come. Thunderstorms along the Intertropical Convergence Zone played a role in the loss of Air France Flight 447, which left Rio de Janeiro–Galeão International Airport on Sunday, May 31, 2009, at about 7:00 p.m. local time and had been expected to land at Charles de Gaulle Airport near Paris on Monday, June 1, 2009, at 11:15 a.m.
The aircraft crashed with no survivors while flying through a series
Tin is a chemical element with the symbol Sn and atomic number 50. It is a post-transition metal in group 14 of the periodic table of elements, it is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, has two main oxidation states, +2 and the more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons, it has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not oxidize in air; the first tin alloy used on a large scale was bronze, made of 1/8 tin and 7/8 copper, from as early as 3000 BC. After 600 BC, pure metallic tin was produced. Pewter, an alloy of 85–90% tin with the remainder consisting of copper and lead, was used for flatware from the Bronze Age until the 20th century.
In modern times, tin is used in many alloys, most notably tin/lead soft solders, which are 60% or more tin, in the manufacture of transparent, electrically conducting films of indium tin oxide in optoelectronic applications. Another large application for tin is corrosion-resistant tin plating of steel; because of the low toxicity of inorganic tin, tin-plated steel is used for food packaging as tin cans. However, some organotin compounds can be as toxic as cyanide. Tin is a soft, malleable and crystalline silvery-white metal; when a bar of tin is bent, a crackling sound known as the "tin cry" can be heard from the twinning of the crystals. Tin melts at low temperatures of about 232 °C, the lowest in group 14; the melting point is further lowered to 177.3 °C for 11 nm particles. Β-tin, stable at and above room temperature, is malleable. In contrast, α-tin, stable below 13.2 °C, is brittle. Α-tin has a diamond cubic crystal structure, similar to silicon or germanium. Α-tin has no metallic properties at all because its atoms form a covalent structure in which electrons cannot move freely.
It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications. These two allotropes, α-tin and β-tin, are more known as gray tin and white tin, respectively. Two more allotropes, γ and σ, exist at temperatures above 161 pressures above several GPa. In cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as "tin pest". Although the α-β transformation temperature is nominally 13.2 °C, impurities lower the transition temperature well below 0 °C and, on the addition of antimony or bismuth, the transformation might not occur at all, increasing the durability of the tin. Commercial grades of tin resist transformation because of the inhibiting effect of the small amounts of bismuth, antimony and silver present as impurities. Alloying elements such as copper, bismuth and silver increase its hardness. Tin tends rather to form hard, brittle intermetallic phases, which are undesirable, it does not form wide solid solution ranges in other metals in general, few elements have appreciable solid solubility in tin.
Simple eutectic systems, occur with bismuth, lead and zinc. Tin was one of the first superconductors to be studied. Tin can be attacked by acids and alkalis. Tin can be polished and is used as a protective coat for other metals. A protective oxide layer prevents further oxidation, the same that forms on pewter and other tin alloys. Tin helps to accelerate the chemical reaction. Tin has ten stable isotopes, with atomic masses of 112, 114 through 120, 122 and 124, the greatest number of any element. Of these, the most abundant are 120Sn, 118Sn, 116Sn, while the least abundant is 115Sn; the isotopes with mass numbers have no nuclear spin, while those with odd have a spin of +1/2. Tin, with its three common isotopes 116Sn, 118Sn and 120Sn, is among the easiest elements to detect and analyze by NMR spectroscopy, its chemical shifts are referenced against SnMe4; this large number of stable isotopes is thought to be a direct result of the atomic number 50, a "magic number" in nuclear physics. Tin occurs in 29 unstable isotopes, encompassing all the remaining atomic masses from 99 to 137.
Apart from 126Sn, with a half-life of 230,000 years, all the radioisotopes have a half-life of less than a year. The radioactive 100Sn, discovered in 1994, 132Sn are one of the few nuclides with a "doubly magic" nucleus: despite being unstable, having lopsided proton–neutron ratios, they represent endpoints beyond which stability drops off rapidly. Another 30 metastable isomers have been characterized for isotopes between 111 and 131, the most stable being 121mSn with a half-life of 43.9 years. The relative differences in the abundances of tin's stable isotopes can be explained by their different modes of formation in stellar nucleosynthesis. 116Sn through 120Sn inclusive are formed in the s-process in most stars and hence they are the most common isotopes, while 122Sn and 124Sn are only formed in the r-process (rapid neutr
Botswana the Republic of Botswana, is a landlocked country in Southern Africa. The British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966. Since it has maintained a tradition of stable representative republic, with a consistent record of uninterrupted democratic elections and the best perceived corruption ranking in Africa since at least 1998, it is Africa's oldest continuous democracy. Botswana is topographically flat, with up to 70 percent of its territory being the Kalahari Desert, it is bordered by South Africa to the south and southeast, Namibia to the west and north, Zimbabwe to the northeast. Its border with Zambia to the north near Kazungula is poorly defined but is, at most, a few hundred metres long. A mid-sized country of just over 2 million people, Botswana is one of the most sparsely populated countries in the world. Around 10 percent of the population lives in the capital and largest city, Gaborone.
One of the poorest countries in the world—with a GDP per capita of about US$70 per year in the late 1960s—Botswana has since transformed itself into one of the world's fastest-growing economies. The economy is dominated by mining and tourism. Botswana boasts a GDP per capita of about $18,825 per year as of 2015, one of the highest in Africa, its high gross national income gives the country a high standard of living and the highest Human Development Index of continental Sub-Saharan Africa. Botswana is a member of the African Union, the Southern African Development Community, the Commonwealth of Nations, the United Nations; the country has been among the hardest hit by the HIV/AIDS epidemic. Despite the success in programmes to make treatments available to those infected, to educate the populace in general about how to stop the spread of HIV/AIDS, the number of people with AIDS rose from 290,000 in 2005 to 320,000 in 2013; as of 2014, Botswana has the third-highest prevalence rate for HIV/AIDS, with 20% of the population infected.
The country's name means "land of the tswana", referring to the dominant ethnic group in Botswana. The term Batswana was applied to the Tswana, still the case. However, it has come to be used as a demonym for all citizens of Botswana. Many English dictionaries recommend the term Botswanan to refer to people of Botswana. Archaeological digs have shown. Stone tools and fauna remains have shown that all areas of the country were inhabited at least 400,000 years ago. Evidence left by modern humans such as cave paintings are about 73,000 years old; the original inhabitants of southern Africa were the Khoi peoples. Both speak Khoisan languages and hunted and traded over long distances; when cattle were first introduced about 2000 years ago into southern Africa, pastoralism became a major feature of the economy, since the region had large grasslands free of tsetse fly. It is unclear when Bantu-speaking peoples first moved into the country from the north, although AD 600 seems to be a consensus estimate.
In that era, the ancestors of the modern-day Kalanga moved into what is now the north-eastern areas of the country. These proto-Kalanga were connected to states in Zimbabwe as well as to the Mapungubwe state; these states, located outside of current Botswana's borders, appear to have kept massive cattle herds in what is now the Central District—apparently at numbers approaching modern cattle density. This massive cattle-raising complex prospered until 1300 AD or so, seems to have regressed following the collapse of Mapungubwe. During this era, the first Tswana-speaking groups, the Bakgalagadi, moved into the southern areas of the Kalahari. All these various peoples were connected to trade routes that ran via the Limpopo River to the Indian Ocean, trade goods from Asia such as beads made their way to Botswana most in exchange for ivory and rhinoceros horn; the arrival of the ancestors of the Tswana-speakers who came to control the region has yet to be dated precisely. Members of the Bakwena, a chieftaincy under a legendary leader named Kgabo II, made their way into the southern Kalahari by AD 1500, at the latest, his people drove the Bakgalagadi inhabitants west into the desert.
Over the years, several offshoots of the Bakwena moved into adjoining territories. The Bangwaketse occupied areas to the west, while the Bangwato moved northeast into Kalanga areas. Not long afterwards, a Bangwato offshoot known as the Batawana migrated into the Okavango Delta in the 1790s; the first written records relating to modern-day Botswana appear in 1824. What these records show is that the Bangwaketse had become the predominant power in the region. Under the rule of Makaba II, the Bangwaketse kept vast herds of cattle in well-protected desert areas, used their military prowess to raid their neighbors. Other chiefdoms in the area, by this time, had capitals of 10,000 or so and were prosperous; this equilibrium came to end during the Mfecane period, 1823–1843, when a succession of invading peoples from South Africa entered the country. Although the Bangwaketse were able to defeat the invading Bakololo in 1826, over time all the major chiefdoms in Botswana were attacked and impoverished.
The Bakololo and Amandebele raided and took large numbers of cattle and children from the Batswana—most of whom were driven into the desert or sanctuary areas such as hilltops and caves. Only after 1843, when the Amandebele moved into western Zimbabwe, did this threat subside. During th
An interfluve is a narrow and plateau-like or ridge-like landform between two valleys. Whittow, more defines an interfluve as an area of higher ground between two rivers in the same drainage system; these landforms are created by earth flow. They can be former river terraces that are subsequently bisected by fluvial erosion. In cases where there is a deposit of younger sedimentary beds the interfluves have a rounder and less rugged appearance. A consequence of interfluve formation is the so-called "interfluvial landscape." In South Burgenland and in the East Styrian Hills of Austria the majority of the natural region of the Iller-Lech Plateau in Bavarian Swabia and Upper Swabia with the exception of the major river valleys of the Danube and Lech, the Donauried and the Federseeried as well as the Old Drift landscapes south of the natural region. Doab Interamnia
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi