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Free-space Optical Communication
Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking. "Free space" means air, outer space, vacuum, or something similar. This contrasts with using solids such as optical fiber cable. The technology is useful where the physical connections are impractical due to high costs or other considerations. History Optical communications, in various forms, have been used for thousands of years. The ancient Greeks used a coded alphabetic system of signalling with torches developed by Cleoxenus, Democleitus and Polybius. In the modern era, semaphores and wireless solar telegraphs called heliographs were developed, using coded signals to communicate with their recipients. In 1880, Alexander Graham Bell and his assistant Charles Sumner Tainter created the photophone, at Bell's newly established Volta Laboratory in Washington, DC. Bell consider ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Washington, DC
) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, National Cathedral , image_flag = Flag of the District of Columbia.svg , image_seal = Seal of the District of Columbia.svg , nickname = D.C., The District , image_map = , map_caption = Interactive map of Washington, D.C. , coordinates = , subdivision_type = Country , subdivision_name = , established_title = Residence Act , established_date = 1790 , named_for = George Washington, Christopher Columbus , established_title1 = Organized , established_date1 = 1801 , established_title2 = Consolidated , established_date2 = 1871 , established_title3 = Home Rule Ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atlantic Wall
The Atlantic Wall (german: link=no, Atlantikwall) was an extensive system of coastal defences and fortifications built by Nazi Germany between 1942 and 1944 along the coast of continental Europe and Scandinavia as a defence against an anticipated Allied invasion of Nazi-occupied Europe from the United Kingdom, during World War II. The manning and operation of the Atlantic Wall was administratively overseen by the German Army, with some support from ''Luftwaffe'' ground forces. The ''Kriegsmarine'' (German Navy) maintained a separate coastal defence network, organised into a number of sea defence zones. Hitler ordered the construction of the fortifications in 1942 through his Führer Directive No. 40. More than half a million French workers were drafted to build it. The wall was frequently mentioned in Nazi propaganda, where its size and strength were usually exaggerated. The fortifications included colossal coastal guns, batteries, mortars, and artillery, and thousands o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carl Zeiss AG
Carl Zeiss AG (), branded as ZEISS, is a German manufacturer of optical systems and optoelectronics, founded in Jena, Germany in 1846 by optician Carl Zeiss. Together with Ernst Abbe (joined 1866) and Otto Schott (joined 1884) he laid the foundation for today's multi-national company. The current company emerged from a reunification of Carl Zeiss companies in East and West Germany with a consolidation phase in the 1990s. ZEISS is active in four business segments with approximately equal revenue (Industrial Quality and Research, Medical Technology, Consumer Markets and Semiconductor Manufacturing Technology) in almost 50 countries, has 30 production sites and around 25 development sites worldwide. Carl Zeiss AG is the holding of all subsidiaries within Zeiss Group, of which Carl Zeiss Meditec AG is the only one that is traded at the stock market. Carl Zeiss AG is owned by the foundation Carl-Zeiss-Stiftung. The Zeiss Group has its headquarters in southern Germany, in the sma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fighting occurring throughout Europe, the Middle East, Africa, the Pacific, and parts of Asia. An estimated 9 million soldiers were killed in combat, plus another 23 million wounded, while 5 million civilians died as a result of military action, hunger, and disease. Millions more died in genocides within the Ottoman Empire and in the 1918 influenza pandemic, which was exacerbated by the movement of combatants during the war. Prior to 1914, the European great powers were divided between the Triple Entente (comprising France, Russia, and Britain) and the Triple Alliance (containing Germany, Austria-Hungary, and Italy). Tensions in the Balkans came to a head on 28 June 1914, following the assassination of Archduke Franz Ferdi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trench Warfare
Trench warfare is a type of land warfare using occupied lines largely comprising military trenches, in which troops are well-protected from the enemy's small arms fire and are substantially sheltered from artillery. Trench warfare became archetypically associated with World War I (1914–1918), when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914.. Trench warfare proliferated when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties. The development of armoured ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Germany Blinker Signal Lamp - National World War I Museum - Kansas City, MO - DSC07704
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated between the Baltic and North seas to the north, and the Alps to the south; it covers an area of , with a population of almost 84 million within its 16 constituent states. Germany borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, and France, Luxembourg, Belgium, and the Netherlands to the west. The nation's capital and most populous city is Berlin and its financial centre is Frankfurt; the largest urban area is the Ruhr. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity. A region named Germania was documented before AD 100. In 962, the Kingdom of Germany formed the bulk of the Holy Roman Empire. During the 16th century, northern ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and east. Although it does not border Zimbabwe, less than 200 metres (660 feet) of the Botswanan right bank 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. Namibia is a member state of the United Nations (UN), the Southern African Development Community (SADC), the African Union (AU) and the Commonwealth of Nations. The driest country in sub-Saharan Africa, Namibia has been inhabited since pre-historic times by the San, Damara and Nama people. Around the 14th century, immigrating Bantu peoples arrived as part of the Bantu expansion. Since then, the Bantu groups, the largest being the Ovambo, h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
German South-West Africa
German South West Africa (german: Deutsch-Südwestafrika) was a colony of the German Empire from 1884 until 1915, though Germany did not officially recognise its loss of this territory until the 1919 Treaty of Versailles. With a total area of 835,100 km², it was one and a half times the size of the mainland German Empire in Europe at the time. The colony had a population of around 2,600 Germans. German rule over this territory was punctuated by numerous rebellions by its native African peoples, which culminated in a campaign of German reprisals from 1904 to 1908 known as the Herero and Namaqua genocide. In 1915, during World War I, German South West Africa was invaded by the Western Allies in the form of South African and British forces. After the war its administration was taken over by the Union of South Africa (part of the British Empire) and the territory was administered as South West Africa under a League of Nations mandate. It became independent as Namibia on 21 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Herero And Namaqua Genocide
The Herero and Namaqua genocide or the Herero and Nama genocide was a campaign of ethnic extermination and collective punishment waged by the German Empire against the Herero (Ovaherero) and the Nama in German South West Africa (now Namibia). It was the first genocide of the 20th century, occurring between 1904 and 1908. In January 1904, the Herero people, who were led by Samuel Maharero, and the Nama people, who were led by Captain Hendrik Witbooi, rebelled against German colonial rule. On January 12, they killed more than 100 German settlers in the area of Okahandja, although women, children, missionaries and non-German Europeans were spared. In August, German General Lothar von Trotha defeated the Ovaherero in the Battle of Waterberg and drove them into the desert of Omaheke, where most of them died of dehydration. In October, the Nama people also rebelled against the Germans, only to suffer a similar fate. Between 24,000 and 100,000 Hereros and 10,000 Nama died in the ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nature (journal)
''Nature'' is a British weekly scientific journal founded and based in London, England. As a multidisciplinary publication, ''Nature'' features peer-reviewed research from a variety of academic disciplines, mainly in science and technology. It has core editorial offices across the United States, continental Europe, and Asia under the international scientific publishing company Springer Nature. ''Nature'' was one of the world's most cited scientific journals by the Science Edition of the 2019 '' Journal Citation Reports'' (with an ascribed impact factor of 42.778), making it one of the world's most-read and most prestigious academic journals. , it claimed an online readership of about three million unique readers per month. Founded in autumn 1869, ''Nature'' was first circulated by Norman Lockyer and Alexander Macmillan as a public forum for scientific innovations. The mid-20th century facilitated an editorial expansion for the journal; ''Nature'' redoubled its efforts in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telephone
A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user. The term is derived from el, τῆλε (''tēle'', ''far'') and φωνή (''phōnē'', ''voice''), together meaning ''distant voice''. A common short form of the term is ''phone'', which came into use early in the telephone's history. In 1876, Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice at a second device. This instrument was further developed by many others, and became rapidly indispensable in business, government, and in households. The essential elements of a telephone are a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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