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Analog Computer
An analog computer or analogue computer is a type of computer that uses the continuous variation aspect of physical phenomena such as electrical, mechanical, or hydraulic quantities (''analog signals'') to model the problem being solved. In contrast, digital computers represent varying quantities symbolically and by discrete values of both time and amplitude (digital signals). Analog computers can have a very wide range of complexity. Slide rules and nomograms are the simplest, while naval gunfire control computers and large hybrid digital/analog computers were among the most complicated. Complex mechanisms for process control and protective relays used analog computation to perform control and protective functions. Analog computers were widely used in scientific and industrial applications even after the advent of digital computers, because at the time they were typically much faster, but they started to become obsolete as early as the 1950s and 1960s, although they remaine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Control System
A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial control systems which are used for controlling processes or machines. The control systems are designed via control engineering process. For continuously modulated control, a feedback controller is used to automatically control a process or operation. The control system compares the value or status of the process variable (PV) being controlled with the desired value or setpoint (SP), and applies the difference as a control signal to bring the process variable output of the plant to the same value as the setpoint. For sequential and combinational logic, software logic, such as in a programmable logic controller, is used. Open-loop and closed-loop control There are two common classes of control action: open loop and closed loop. In an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planisphere
In astronomy, a planisphere () is a star chart analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument to assist in learning how to recognize stars and constellations. The astrolabe, an instrument that has its origins in Hellenistic astronomy, is a predecessor of the modern planisphere. The term ''planisphere'' contrasts with ''armillary sphere'', where the celestial sphere is represented by a three-dimensional framework of rings. Description A planisphere consists of a circular star chart attached at its center to an opaque circular overlay that has a clear elliptical window or hole so that only a portion of the sky map will be visible in the window or hole area at any given time. The chart and overlay are mounted so that they are free to rotate about a common axis. The star chart contains the brightest stars, constellations and (possibly) deep- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hellenistic Period
In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in 31 BC and the conquest of Ptolemaic Egypt the following year. The Ancient Greek word ''Hellas'' (, ''Hellás'') was gradually recognized as the name for Greece, from which the word ''Hellenistic'' was derived. "Hellenistic" is distinguished from "Hellenic" in that the latter refers to Greece itself, while the former encompasses all ancient territories under Greek influence, in particular the East after the conquests of Alexander the Great. After the Macedonian invasion of the Achaemenid Empire in 330 BC and its disintegration shortly after, the Hellenistic kingdoms were established throughout south-west Asia ( Seleucid Empire, Kingdom of Pergamon), north-east Africa ( Ptolemaic Kingdom) and South Asia ( Greco-Bactrian Kingdom, Indo-Greek ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crete
Crete ( el, Κρήτη, translit=, Modern: , Ancient: ) is the largest and most populous of the Greek islands, the 88th largest island in the world and the fifth largest island in the Mediterranean Sea, after Sicily, Sardinia, Cyprus, and Corsica. Crete rests about south of the Greek mainland, and about southwest of Anatolia. Crete has an area of and a coastline of 1,046 km (650 mi). It bounds the southern border of the Aegean Sea, with the Sea of Crete (or North Cretan Sea) to the north and the Libyan Sea (or South Cretan Sea) to the south. Crete and a number of islands and islets that surround it constitute the Region of Crete ( el, Περιφέρεια Κρήτης, links=no), which is the southernmost of the 13 top-level administrative units of Greece, and the fifth most populous of Greece's regions. Its capital and largest city is Heraklion, on the north shore of the island. , the region had a population of 636,504. The Dodecanese are located to the no ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kythera
Kythira (, ; el, Κύθηρα, , also transliterated as Cythera, Kythera and Kithira) is an island in Greece lying opposite the south-eastern tip of the Peloponnese peninsula. It is traditionally listed as one of the seven main Ionian Islands, although it is distant from the main group. Administratively, it belongs to the Islands regional unit, which is part of the Attica region, despite its distance from the Saronic Islands, around which the rest of Attica is centered. As a municipality, it includes the island of Antikythera to the south. The island is strategically located between the Greek mainland and Crete, and from ancient times until the mid 19th century was a crossroads of merchants, sailors, and conquerors. As such, it has had a long and varied history and has been influenced by many civilizations and cultures. This is reflected in its architecture (a blend of traditional, Aegean and Venetian elements), as well as the traditions and customs, influenced by centuries o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antikythera
Antikythera or Anticythera ( ) is a Greek island lying on the edge of the Aegean Sea, between Crete and Peloponnese. In antiquity the island was known as (). Since the 2011 local government reform it is part of the municipality of Kythira island. Antikythera may also refer to the Kythira-Antikythira Strait, through which Mediterranean water enters the Sea of Crete. Its land area is , and it lies south-east of Kythira. It is the most distant part of the Attica region from its heart in the Athens metropolitan area. It is lozenge-shaped, NNW to SSE by ENE to WSW. It is notable for being the location of the discovery of the Antikythera mechanism and for the historical Antikythera wreck. Its main settlement and port is Potamós (pop. 34 inhabitants in the 2011 census). The only other settlements are Galanianá (pop. 15), and Charchalianá (pop. 19). Antikythera is periodically visited by the Ablemon Nautical Company ferry ''F/B Ionis'' on its route between Piraeus (Athens) and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antikythera Wreck
The Antikythera wreck ( gr, Ναυάγιο των Αντικυθήρων) is a Roman-era shipwreck dating from the second quarter of the first century BC."''The Antikythera Shipwreck. The Ship, The Treasures, The Mechanism. National Archaeological Museum, April 2012 – April 2013''". Hellenic Ministry of Culture and Tourism; National Archaeological Museum. Editors Nikolaos Kaltsas & Elena Vlachogianni & Polyxeni Bouyia. Athens: Kapon, 2012, . It was discovered by sponge divers off Point Glyphadia on the Greek island of Antikythera in 1900. The wreck yielded numerous statues, coins, and other artifacts dating back to the fourth century BC, as well as the severely corroded remnants of a device many regard as the world's oldest known analog computer, the Antikythera mechanism. These ancient artifacts, works of art, and elements of the ship are now on display at the National Archaeological Museum of Athens. Discovery Around Easter 1900, Captain Dimitrios Kondos and his crew o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Derek J
''Fashion Queens'' is an American fashion-based talk show that aired on Bravo. The series premiered on March 17, 2013, with a three-week trail run. ''Fashion Queens'' is hosted by Bevy Smith, Derek J, and Miss Lawrence. Derek J and Miss Lawrence both made several appearances on ''The Real Housewives of Atlanta''. Following the series' three-week trial run in March 2013, the first season continued on April 14, 2013. The second season premiere on November 3, 2013, which coincided with the sixth season premiere of ''The Real Housewives of Atlanta''. '' Fashion Queens'' was filmed in New York City. In April 2014, Bravo renewed ''Fashion Queens'' for a third season, which premiered on November 9, 2014. On August 8, 2015, host Bevy Smith confirmed that the series had been cancelled. Segments * The Week in Fashion: Latest fashion news * Reading Room: The hosts dissect celebrities' fashion * Right or Ratchet: The hosts decide if celebrities' outfits are Right or Ratchet * Giving Me Wife: ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orrery
An orrery is a mechanical model of the Solar System that illustrates or predicts the relative positions and motions of the planets and moons, usually according to the heliocentric model. It may also represent the relative sizes of these bodies; however, since accurate scaling is often not practical due to the actual large ratio differences, a subdued approximation may be used instead. Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1704, and one was presented to Charles Boyle, 4th Earl of Orrery – hence the name. They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms. History Ancient versions The Antikythera mechanism, discovered in 1901 in a wreck off the Greek island of Antikythera in the Mediterranean Sea, (it now resides in the National Archaeological Museum of Athens) and extensively studied, exhibited the diu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antikythera Mechanism
The Antikythera mechanism ( ) is an Ancient Greece, Ancient Greek hand-powered orrery, described as the oldest example of an analogue computer used to predict astronomy, astronomical positions and eclipses decades in advance. It could also be used to track the four-year cycle of athletic games which was similar to an Olympiad, the cycle of the ancient Olympic Games. This artefact was among wreckage retrieved from a Antikythera wreck, shipwreck off the coast of the Greek island Antikythera in 1901. On 17 May 1902, it was identified as containing a gear by archaeologist Valerios Stais. The device, housed in the remains of a wooden-framed case of (uncertain) overall size , was found as one lump, later separated into three main fragments which are now divided into 82 separate fragments after conservation efforts. Four of these fragments contain gears, while inscriptions are found on many others. The largest gear is approximately in diameter and originally had 223 teeth. In 2008, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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