1.
Norden bombsight
–
This accuracy allowed direct attacks on ships, factories, and other point targets. Both the Navy and the AAF saw this as a means to achieve war aims through high-altitude bombing, for instance, destroying an invasion fleet by air long before it could reach US shores. To achieve these aims, the Norden was granted the utmost secrecy well into the war, Carl L. Norden, Inc. ranked 46th among United States corporations in the value of World War II military production contracts. In practice it was not possible to achieve this level of accuracy in combat conditions, both the Navy and Air Forces had to give up on the idea of pinpoint attacks during the war. Nevertheless, the Nordens reputation as a pin-point device lived on, the Norden saw some use in the post-World War II era, especially during the Korean War. Post-war use was reduced due to the introduction of radar-based systems. The last combat use of the Norden was in the US Navys VO-67 squadron, the Norden remains one of the best-known bombsights of all time. The Norden sight was designed by Carl Norden, a Dutch engineer educated in Switzerland who emigrated to the U. S. in 1904. In 1911, Norden joined Sperry Gyroscope to work on ship gyrostabilizers, World War I bomb sight designs had improved rapidly, with the ultimate development being the Course Setting Bomb Sight, or CSBS. This was essentially a mechanical calculator that directly represented the wind triangle using three long pieces of metal in a triangular arrangement. The hypotenuse of the triangle was the line the aircraft needed to fly along in order to arrive over the target in the presence of wind, which, before the CSBS, was an intractable problem. Almost all air forces adopted some variation of the CSBS as their standard inter-war bomb sight, including the US Navy and US Army, who used a version designed by Georges Estoppey, the D-series. It was already realized that one source of error in bombing was leveling the aircraft enough so the bombsight pointed straight down. Even small errors in leveling could produce dramatic errors in bombing and this led to orders for such designs from Estoppey, Inglis and Seversky. Norden was asked to provide an external stabilizer for the Navys existing Mark III designs, although the CSBS and similar designs allowed the calculation of the proper flight angle needed to correct for windage, it was normally not visible to the pilot. This led to the introduction of the direction indicator, or PDI. These typically consisted of a pair of electrical pointers mounted in an aircraft instrument panel mount. The bombardier used switches to move the pointer on his unit, Nordens first attempt at an improved bombsight was actually an advance in PDI design
2.
World War II
–
World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945, although related conflicts began earlier. It involved the vast majority of the worlds countries—including all of the great powers—eventually forming two opposing alliances, the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people from over 30 countries. Marked by mass deaths of civilians, including the Holocaust and the bombing of industrial and population centres. These made World War II the deadliest conflict in human history, from late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, and formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Poland, Finland, Romania and the Baltic states. In December 1941, Japan attacked the United States and European colonies in the Pacific Ocean, and quickly conquered much of the Western Pacific. The Axis advance halted in 1942 when Japan lost the critical Battle of Midway, near Hawaii, in 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained all of its territorial losses and invaded Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in South Central China and Burma, while the Allies crippled the Japanese Navy, thus ended the war in Asia, cementing the total victory of the Allies. World War II altered the political alignment and social structure of the world, the United Nations was established to foster international co-operation and prevent future conflicts. The victorious great powers—the United States, the Soviet Union, China, the United Kingdom, the Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the influence of European great powers waned, while the decolonisation of Asia, most countries whose industries had been damaged moved towards economic recovery. Political integration, especially in Europe, emerged as an effort to end pre-war enmities, the start of the war in Europe is generally held to be 1 September 1939, beginning with the German invasion of Poland, Britain and France declared war on Germany two days later. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or even the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously and this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935. The British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the forces of Mongolia and the Soviet Union from May to September 1939, the exact date of the wars end is also not universally agreed upon. It was generally accepted at the time that the war ended with the armistice of 14 August 1945, rather than the formal surrender of Japan
3.
Korean War
–
The Korean War began when North Korea invaded South Korea. The United Nations, with the United States as the principal force, China came to the aid of North Korea, and the Soviet Union gave some assistance. Korea was ruled by Japan from 1910 until the days of World War II. In August 1945, the Soviet Union declared war on Japan, as a result of an agreement with the United States, U. S. forces subsequently moved into the south. By 1948, as a product of the Cold War between the Soviet Union and the United States, Korea was split into two regions, with separate governments, both governments claimed to be the legitimate government of all of Korea, and neither side accepted the border as permanent. The conflict escalated into open warfare when North Korean forces—supported by the Soviet Union, on that day, the United Nations Security Council recognized this North Korean act as invasion and called for an immediate ceasefire. On 27 June, the Security Council adopted S/RES/83, Complaint of aggression upon the Republic of Korea and decided the formation, twenty-one countries of the United Nations eventually contributed to the UN force, with the United States providing 88% of the UNs military personnel. After the first two months of war, South Korean forces were on the point of defeat, forced back to the Pusan Perimeter, in September 1950, an amphibious UN counter-offensive was launched at Inchon, and cut off many North Korean troops. Those who escaped envelopment and capture were rapidly forced back north all the way to the border with China at the Yalu River, at this point, in October 1950, Chinese forces crossed the Yalu and entered the war. Chinese intervention triggered a retreat of UN forces which continued until mid-1951, after these reversals of fortune, which saw Seoul change hands four times, the last two years of fighting became a war of attrition, with the front line close to the 38th parallel. The war in the air, however, was never a stalemate, North Korea was subject to a massive bombing campaign. Jet fighters confronted each other in combat for the first time in history. The fighting ended on 27 July 1953, when an armistice was signed, the agreement created the Korean Demilitarized Zone to separate North and South Korea, and allowed the return of prisoners. However, no treaty has been signed, and the two Koreas are technically still at war. Periodic clashes, many of which are deadly, continue to the present, in the U. S. the war was initially described by President Harry S. Truman as a police action as it was an undeclared military action, conducted under the auspices of the United Nations. In South Korea, the war is referred to as 625 or the 6–2–5 Upheaval. In North Korea, the war is referred to as the Fatherland Liberation War or alternatively the Chosǒn War. In China, the war is called the War to Resist U. S
4.
Vietnam War
–
It was the second of the Indochina Wars and was officially fought between North Vietnam and the government of South Vietnam. The war is considered a Cold War-era proxy war. As the war continued, the actions of the Viet Cong decreased as the role. U. S. and South Vietnamese forces relied on air superiority and overwhelming firepower to conduct search and destroy operations, involving ground forces, artillery, in the course of the war, the U. S. conducted a large-scale strategic bombing campaign against North Vietnam. The North Vietnamese government and the Viet Cong were fighting to reunify Vietnam and they viewed the conflict as a colonial war and a continuation of the First Indochina War against forces from France and later on the United States. The U. S. government viewed its involvement in the war as a way to prevent a communist takeover of South Vietnam and this was part the domino theory of a wider containment policy, with the stated aim of stopping the spread of communism. Beginning in 1950, American military advisors arrived in what was then French Indochina, U. S. involvement escalated in the early 1960s, with troop levels tripling in 1961 and again in 1962. Regular U. S. combat units were deployed beginning in 1965, despite the Paris Peace Accord, which was signed by all parties in January 1973, the fighting continued. In the U. S. and the Western world, a large anti-Vietnam War movement developed as part of a larger counterculture, the war changed the dynamics between the Eastern and Western Blocs, and altered North–South relations. Direct U. S. military involvement ended on 15 August 1973, the capture of Saigon by the North Vietnamese Army in April 1975 marked the end of the war, and North and South Vietnam were reunified the following year. The war exacted a huge human cost in terms of fatalities, estimates of the number of Vietnamese soldiers and civilians killed vary from 966,000 to 3.8 million. Some 240, 000–300,000 Cambodians,20, 000–62,000 Laotians, and 58,220 U. S. service members died in the conflict. Various names have applied to the conflict. Vietnam War is the most commonly used name in English and it has also been called the Second Indochina War and the Vietnam Conflict. As there have been several conflicts in Indochina, this conflict is known by the names of its primary protagonists to distinguish it from others. In Vietnamese, the war is known as Kháng chiến chống Mỹ. It is also called Chiến tranh Việt Nam, France began its conquest of Indochina in the late 1850s, and completed pacification by 1893. The 1884 Treaty of Huế formed the basis for French colonial rule in Vietnam for the seven decades
5.
Bomber
–
A bomber is a combat aircraft designed to attack ground and sea targets by dropping air-to-ground weaponry, firing torpedoes or deploying air-launched cruise missiles. In 1912, during the First Balkan War, Bulgarian Air Force pilot Christo Toprakchiev suggested the use of aircraft to drop bombs on Turkish positions, captain Simeon Petrov developed the idea and created several prototypes by adapting different types of grenades and increasing their payload. This is deemed to be the first use of an aircraft as a bomber, the first heavier-than-air aircraft purposely designed for bombing were the Italian Caproni Ca 30 and British Bristol T. B.8, both of 1913. The Bristol T. B.8 was an early British single engined biplane built by the Bristol Aeroplane Company, under the command of Charles Rumney Samson, a bombing attack on German gun batteries at Middelkerke, Belgium was executed on 25 November 1914. The dirigible, or airship, was developed in the early 20th century, early airships were prone to disaster, but slowly the airship became more dependable, with a more rigid structure and stronger skin. Prior to the outbreak of war, Zeppelins, a larger and these were the first long range, strategic bombers. Although the German air arm was strong, with a total of 123 airships by the end of the war, they were vulnerable to attack and engine failure, German airships inflicted little damage on all 51 raids, with 557 Britons killed and 1,358 injured. The German Navy lost 53 of its 73 airships, and the German Army lost 26 of its 50 ships, the Caproni Ca 30 was built by Gianni Caproni in Italy. It was a biplane with three 67 kW Gnome rotary engines and first flew in October 1914. Test flights revealed power to be insufficient and the engine layout unworkable, the improved design was bought by the Italian Army and it was delivered in quantity from August 1915. Bombing raids and interdiction operations were carried out by French. Sustained attacks with a view to interrupting the enemys railway communications, in conjunction with the main operations of the Allied Armies. The most important bombers used in World War I were the French Breguet 14, British de Havilland DH-4, German Albatros C. III, the Russian Sikorsky Ilya Muromets, was the first four-engine bomber to equip a dedicated strategic bombing unit during World War I. This heavy bomber was unrivaled in the stages of the war. With engine power as a limitation, combined with the desire for accuracy and other operational factors. By the start of the war included, dive bomber — specially strengthened for vertical diving attacks for greater accuracy. Light bomber, medium bomber and heavy bomber — subjective definitions based on size, torpedo bomber — specialized aircraft armed with torpedoes. Ground attack aircraft — aircraft used against targets on a such as troop or tank concentrations
6.
Bomb
–
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Bombs have been in use since the 11th century in Song Dynasty China, the term bomb is not usually applied to explosive devices used for civilian purposes such as construction or mining, although the people using the devices may sometimes refer to them as a bomb. The military use of the bomb, or more specifically aerial bomb action, typically refers to airdropped, unpowered explosive weapons most commonly used by air forces. Other military explosive weapons not classified as bombs include grenades, shells, depth charges, warheads when in missiles, in unconventional warfare, other names can refer to a range of offensive weaponry. For instance, in recent Middle Eastern conflicts, bombs called improvised explosive devices have been employed by insurgent fighters to great effectiveness, the word comes from the Latin bombus, which in turn comes from the Greek βόμβος, an onomatopoetic term meaning booming, buzzing. Explosive bombs were used in China in 1221, by a Jin dynasty army against a Song Dynasty city, Bombs built using bamboo tubes appear in the 11th century. Bombs made of cast iron shells packed with explosive gunpowder date to 13th century China, the term was coined for this bomb during a Jin dynasty naval battle of 1231 against the Mongols. When hit, even iron armour was pierced through. The Ming Dynasty text Huolongjing describes the use of gunpowder bombs. During the Mongol invasions of Japan, the Mongols used the explosive thunder-crash bombs against the Japanese, archaeological evidence of the thunder-crash bombs has been discovered in an underwater shipwreck off the shore of Japan by the Kyushu Okinawa Society for Underwater Archaeology. X-rays by Japanese scientists of the excavated shells confirmed that they contained gunpowder, explosive shock waves can cause situations such as body displacement, dismemberment, internal bleeding and ruptured eardrums. Shock waves produced by explosive events have two components, the positive and negative wave. The positive wave shoves outward from the point of detonation, followed by the vacuum space sucking back towards the point of origin as the shock bubble collapses. The greatest defense against shock injuries is distance from the source of shock, as a point of reference, the overpressure at the Oklahoma City bombing was estimated in the range of 28 MPa. A thermal wave is created by the release of heat caused by an explosion. Military bomb tests have documented temperatures of up to 2,480 °C, while capable of inflicting severe to catastrophic burns and causing secondary fires, thermal wave effects are considered very limited in range compared to shock and fragmentation. This would be fatal to humans, as tests have proven. Fragmentation is produced by the acceleration of shattered pieces of bomb casing, the use of fragmentation in bombs dates to the 14th century, and appears in the Ming Dynasty text Huolongjing
7.
Computer
–
A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically. The ability of computers to follow a sequence of operations, called a program, such computers are used as control systems for a very wide variety of industrial and consumer devices. The Internet is run on computers and it millions of other computers. Since ancient times, simple manual devices like the abacus aided people in doing calculations, early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century, the first digital electronic calculating machines were developed during World War II. The speed, power, and versatility of computers has increased continuously and dramatically since then, conventionally, a modern computer consists of at least one processing element, typically a central processing unit, and some form of memory. The processing element carries out arithmetic and logical operations, and a sequencing, peripheral devices include input devices, output devices, and input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and this usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century, from the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations. The Online Etymology Dictionary gives the first attested use of computer in the 1640s, one who calculates, the Online Etymology Dictionary states that the use of the term to mean calculating machine is from 1897. The Online Etymology Dictionary indicates that the use of the term. 1945 under this name, theoretical from 1937, as Turing machine, devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick, later record keeping aids throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example, the abacus was initially used for arithmetic tasks. The Roman abacus was developed from used in Babylonia as early as 2400 BC. Since then, many forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, the Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions and it was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to circa 100 BC
8.
Electrical network
–
An electrical network is an interconnection of electrical components or a model of such an interconnection, consisting of electrical elements. An electrical circuit is a network consisting of a closed loop, linear electrical networks, a special type consisting only of sources, linear lumped elements, and linear distributed elements, have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, a resistive circuit is a circuit containing only resistors and ideal current and voltage sources. Analysis of resistive circuits is less complicated than analysis of circuits containing capacitors and inductors, if the sources are constant sources, the result is a DC circuit. A network that contains active components is known as an electronic circuit. Such networks are generally nonlinear and require more complex design and analysis tools, an active network is a network that contains an active source – either a voltage source or current source. A passive network is a network that does not contain an active source, a network is linear if its signals obey the principle of superposition, otherwise it is non-linear. Sources can be classified as independent sources and dependent sources Ideal Independent Source maintains same voltage or current regardless of the elements present in the circuit. Its value is either constant or sinusoidal, the strength of voltage or current is not changed by any variation in connected network. Dependent Sources depend upon a particular element of the circuit for delivering the power or voltage or current depending upon the type of source it is, a number of electrical laws apply to all electrical networks. These include, Kirchhoffs current law, The sum of all currents entering a node is equal to the sum of all currents leaving the node, Kirchhoffs voltage law, The directed sum of the electrical potential differences around a loop must be zero. Ohms law, The voltage across a resistor is equal to the product of the resistance, nortons theorem, Any network of voltage or current sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor. Thévenins theorem, Any network of voltage or current sources and resistors is electrically equivalent to a voltage source in series with a single resistor. Other more complex laws may be needed if the network contains nonlinear or reactive components, non-linear self-regenerative heterodyning systems can be approximated. Applying these laws results in a set of equations that can be solved either algebraically or numerically. To design any electrical circuit, either analog or digital, electrical engineers need to be able to predict the voltages, simple linear circuits can be analyzed by hand using complex number theory. In more complex cases the circuit may be analyzed with specialized programs or estimation techniques such as the piecewise-linear model. More complex circuits can be analyzed numerically with software such as SPICE or GNUCAP, once the steady state solution is found, the operating points of each element in the circuit are known
9.
Mechanics
–
Mechanics is an area of science concerned with the behaviour of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment. The scientific discipline has its origins in Ancient Greece with the writings of Aristotle, during the early modern period, scientists such as Khayaam, Galileo, Kepler, and Newton, laid the foundation for what is now known as classical mechanics. It is a branch of physics that deals with particles that are either at rest or are moving with velocities significantly less than the speed of light. It can also be defined as a branch of science which deals with the motion of, historically, classical mechanics came first, while quantum mechanics is a comparatively recent invention. Classical mechanics originated with Isaac Newtons laws of motion in Philosophiæ Naturalis Principia Mathematica, both are commonly held to constitute the most certain knowledge that exists about physical nature. Classical mechanics has especially often been viewed as a model for other so-called exact sciences, essential in this respect is the relentless use of mathematics in theories, as well as the decisive role played by experiment in generating and testing them. Quantum mechanics is of a scope, as it encompasses classical mechanics as a sub-discipline which applies under certain restricted circumstances. According to the principle, there is no contradiction or conflict between the two subjects, each simply pertains to specific situations. The correspondence principle states that the behavior of systems described by quantum theories reproduces classical physics in the limit of quantum numbers. Quantum mechanics has superseded classical mechanics at the level and is indispensable for the explanation and prediction of processes at the molecular, atomic. However, for macroscopic processes classical mechanics is able to solve problems which are difficult in quantum mechanics and hence remains useful. Modern descriptions of such behavior begin with a definition of such quantities as displacement, time, velocity, acceleration, mass. Until about 400 years ago, however, motion was explained from a different point of view. He showed that the speed of falling objects increases steadily during the time of their fall and this acceleration is the same for heavy objects as for light ones, provided air friction is discounted. The English mathematician and physicist Isaac Newton improved this analysis by defining force and mass, for objects traveling at speeds close to the speed of light, Newton’s laws were superseded by Albert Einstein’s theory of relativity. For atomic and subatomic particles, Newton’s laws were superseded by quantum theory, for everyday phenomena, however, Newton’s three laws of motion remain the cornerstone of dynamics, which is the study of what causes motion. In analogy to the distinction between quantum and classical mechanics, Einsteins general and special theories of relativity have expanded the scope of Newton, the differences between relativistic and Newtonian mechanics become significant and even dominant as the velocity of a massive body approaches the speed of light. Relativistic corrections are also needed for quantum mechanics, although general relativity has not been integrated, the two theories remain incompatible, a hurdle which must be overcome in developing a theory of everything
10.
Hydraulics
–
Hydraulics is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids or fluids. At a very basic level, hydraulics is the version of pneumatics. Fluid mechanics provides the foundation for hydraulics, which focuses on the applied engineering using the properties of fluids. In fluid power, hydraulics are used for the generation, control, hydraulic topics range through some parts of science and most of engineering modules, and cover concepts such as pipe flow, dam design, fluidics and fluid control circuitry, pumps. The principles of hydraulics are in use naturally in the body within the heart. Free surface hydraulics is the branch of hydraulics dealing with surface flow, such as occurring in rivers, canals, lakes, estuaries. Its sub-field open channel flow studies the flow in open channels, the word hydraulics originates from the Greek word ὑδραυλικός which in turn originates from ὕδωρ and αὐλός. Early uses of water power date back to Mesopotamia and ancient Egypt, other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient Central Asia. The Greeks constructed sophisticated water and hydraulic power systems, an example is the construction by Eupalinos, under a public contract, of a watering channel for Samos, the Tunnel of Eupalinos. An early example of the usage of hydraulic wheel, probably the earliest in Europe, is the Perachora wheel, notable is the construction of the first hydraulic automata by Ctesibius and Hero of Alexandria. Hero describes a number of working machines using hydraulic power, such as the force pump, in ancient China there was Sunshu Ao, Ximen Bao, Du Shi, Zhang Heng, and Ma Jun, while medieval China had Su Song and Shen Kuo. Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron, Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation. In ancient Sri Lanka, hydraulics were used in the ancient kingdoms of Anuradhapura. The discovery of the principle of the tower, or valve pit. By the first century AD, several irrigation works had been completed. The coral on the rock at the site includes cisterns for collecting water. They were among the first to use of the siphon to carry water across valleys. They used lead widely in plumbing systems for domestic and public supply, hydraulic mining was used in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC
11.
Scientific modelling
–
Modelling is an essential and inseparable part of many scientific disciplines have their own ideas about specific types of modelling. There is also an increasing attention to modelling in fields such as science education, philosophy of science, systems theory. There is growing collection of methods, techniques and meta-theory about all kinds of specialized scientific modelling, a scientific model seeks to represent empirical objects, phenomena, and physical processes in a logical and objective way. All models are in simulacra, that is, simplified reflections of reality that, despite being approximations, building and disputing models is fundamental to the scientific enterprise. Attempts to formalize the principles of the sciences use an interpretation to model reality. The aim of these attempts is to construct a system that will not produce theoretical consequences that are contrary to what is found in reality. Predictions or other statements drawn from such a formal system mirror or map the world only insofar as these scientific models are true. For the scientist, a model is also a way in which the thought processes can be amplified. Such computer models are in silico, other types of scientific models are in vivo and in vitro. Models are typically used when it is impossible or impractical to create experimental conditions in which scientists can directly measure outcomes. Direct measurement of outcomes under controlled conditions will always be more reliable than modelled estimates of outcomes, within modelling and simulation, a model is a task-driven, purposeful simplification and abstraction of a perception of reality, shaped by physical, legal, and cognitive constraints. It is task-driven, because a model is captured with a question or task in mind. Simplifications leave all the known and observed entities and their relation out that are not important for the task, abstraction aggregates information that is important, but not needed in the same detail as the object of interest. Both activities, simplification and abstraction, are done purposefully, however, they are done based on a perception of reality. This perception is already a model in itself, as it comes with a physical constraint, there are also constraints on what we are able to legally observe with our current tools and methods, and cognitive constraints which limit what we are able to explain with our current theories. This model comprises the propertied concepts, their behavior, and their relations in formal form and is referred to as a Conceptual model. In order to execute the model, it needs to be implemented as a Computer simulation and this requires more choices, such as numerical approximations or the use of heuristics. Despite all these epistemological and computational constraints, simulation has been recognized as the pillar of scientific methods, theory building, simulation
12.
Digital computer
–
A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically. The ability of computers to follow a sequence of operations, called a program, such computers are used as control systems for a very wide variety of industrial and consumer devices. The Internet is run on computers and it millions of other computers. Since ancient times, simple manual devices like the abacus aided people in doing calculations, early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century, the first digital electronic calculating machines were developed during World War II. The speed, power, and versatility of computers has increased continuously and dramatically since then, conventionally, a modern computer consists of at least one processing element, typically a central processing unit, and some form of memory. The processing element carries out arithmetic and logical operations, and a sequencing, peripheral devices include input devices, output devices, and input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and this usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century, from the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations. The Online Etymology Dictionary gives the first attested use of computer in the 1640s, one who calculates, the Online Etymology Dictionary states that the use of the term to mean calculating machine is from 1897. The Online Etymology Dictionary indicates that the use of the term. 1945 under this name, theoretical from 1937, as Turing machine, devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick, later record keeping aids throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example, the abacus was initially used for arithmetic tasks. The Roman abacus was developed from used in Babylonia as early as 2400 BC. Since then, many forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, the Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions and it was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to circa 100 BC
13.
Turing machine
–
Despite the models simplicity, given any computer algorithm, a Turing machine can be constructed that is capable of simulating that algorithms logic. The machine operates on an infinite memory tape divided into discrete cells, the machine positions its head over a cell and reads the symbol there. The Turing machine was invented in 1936 by Alan Turing, who called it an a-machine, thus, Turing machines prove fundamental limitations on the power of mechanical computation. Turing completeness is the ability for a system of instructions to simulate a Turing machine, a Turing machine is a general example of a CPU that controls all data manipulation done by a computer, with the canonical machine using sequential memory to store data. More specifically, it is a capable of enumerating some arbitrary subset of valid strings of an alphabet. Assuming a black box, the Turing machine cannot know whether it will eventually enumerate any one specific string of the subset with a given program and this is due to the fact that the halting problem is unsolvable, which has major implications for the theoretical limits of computing. The Turing machine is capable of processing an unrestricted grammar, which implies that it is capable of robustly evaluating first-order logic in an infinite number of ways. This is famously demonstrated through lambda calculus, a Turing machine that is able to simulate any other Turing machine is called a universal Turing machine. The thesis states that Turing machines indeed capture the notion of effective methods in logic and mathematics. Studying their abstract properties yields many insights into computer science and complexity theory, at any moment there is one symbol in the machine, it is called the scanned symbol. The machine can alter the scanned symbol, and its behavior is in part determined by that symbol, however, the tape can be moved back and forth through the machine, this being one of the elementary operations of the machine. Any symbol on the tape may therefore eventually have an innings, the Turing machine mathematically models a machine that mechanically operates on a tape. On this tape are symbols, which the machine can read and write, one at a time, in the original article, Turing imagines not a mechanism, but a person whom he calls the computer, who executes these deterministic mechanical rules slavishly. If δ is not defined on the current state and the current tape symbol, Q0 ∈ Q is the initial state F ⊆ Q is the set of final or accepting states. The initial tape contents is said to be accepted by M if it eventually halts in a state from F, Anything that operates according to these specifications is a Turing machine. The 7-tuple for the 3-state busy beaver looks like this, Q = Γ = b =0 Σ = q 0 = A F = δ = see state-table below Initially all tape cells are marked with 0. In the words of van Emde Boas, p.6, The set-theoretical object provides only partial information on how the machine will behave and what its computations will look like. For instance, There will need to be many decisions on what the symbols actually look like, and a failproof way of reading and writing symbols indefinitely
14.
Digital signal processing
–
Digital signal processing is the use of digital processing, such as by computers, to perform a wide variety of signal processing operations. The signals processed in this manner are a sequence of numbers that represent samples of a variable in a domain such as time, space. Digital signal processing and analog signal processing are subfields of signal processing, digital signal processing can involve linear or nonlinear operations. Nonlinear signal processing is closely related to system identification and can be implemented in the time, frequency. DSP is applicable to both streaming data and static data, the increasing use of computers has resulted in the increased use of, and need for, digital signal processing. To digitally analyze and manipulate an analog signal, it must be digitized with an analog-to-digital converter, sampling is usually carried out in two stages, discretization and quantization. Discretization means that the signal is divided into equal intervals of time, quantization means each amplitude measurement is approximated by a value from a finite set. Rounding real numbers to integers is an example, the Nyquist–Shannon sampling theorem states that a signal can be exactly reconstructed from its samples if the sampling frequency is greater than twice the highest frequency of the signal. In practice, the frequency is often significantly higher than twice that required by the signals limited bandwidth. Theoretical DSP analyses and derivations are typically performed on discrete-time signal models with no amplitude inaccuracies, numerical methods require a quantized signal, such as those produced by an analog-to-digital converter. The processed result might be a frequency spectrum or a set of statistics, but often it is another quantized signal that is converted back to analog form by a digital-to-analog converter. In DSP, engineers usually study digital signals in one of the domains, time domain, spatial domain, frequency domain. They choose the domain in which to process a signal by making an assumption as to which domain best represents the essential characteristics of the signal. The most common processing approach in the time or space domain is enhancement of the signal through a method called filtering. Digital filtering generally consists of linear transformation of a number of surrounding samples around the current sample of the input or output signal. There are various ways to characterize filters, for example, A linear filter is a transformation of input samples. A causal filter uses only samples of the input or output signals. A non-causal filter can usually be changed into a filter by adding a delay to it
15.
Quantization (signal processing)
–
Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set. Rounding and truncation are typical examples of quantization processes, quantization is involved to some degree in nearly all digital signal processing, as the process of representing a signal in digital form ordinarily involves rounding. Quantization also forms the core of essentially all lossy compression algorithms, the difference between an input value and its quantized value is referred to as quantization error. A device or algorithmic function that performs quantization is called a quantizer, an analog-to-digital converter is an example of a quantizer. Because quantization is a mapping, it is an inherently non-linear. The set of input values may be infinitely large, and may possibly be continuous. The set of output values may be finite or countably infinite. The input and output involved in quantization can be defined in a rather general way. For example, vector quantization is the application of quantization to multi-dimensional input data, outside the realm of signal processing, this category may simply be called rounding or scalar quantization. An ADC can be modeled as two processes, sampling and quantization, sampling converts a voltage signal into a discrete-time signal. Quantization replaces each real number with an approximation from a set of discrete values. Most commonly, these values are represented as fixed-point words or floating-point words. Common word-lengths are 8-bit, 16-bit, 32-bit, and so on, quantizing a sequence of numbers produces a sequence of quantization errors which is sometimes modeled as an additive random signal called quantization noise because of its stochastic behavior. The more levels a quantizer uses, the lower is its noise power. In general, both ADC processes lose some information, so discrete-valued signals are only an approximation of the continuous-valued discrete-time signal, which is itself only an approximation of the original continuous-valued continuous-time signal. But both types of errors can, in theory, be made arbitrarily small by good design. In this second setting, the amount of introduced distortion may be managed carefully by sophisticated techniques, a quantizer designed for this purpose may be quite different and more elaborate in design than an ordinary rounding operation. It is in this domain that substantial rate–distortion theory analysis is likely to be applied, however, the same concepts actually apply in both use cases
16.
Noise (electronics)
–
In electronics, noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly as it is produced by different effects. In communication systems, noise is an error or undesired random disturbance of an information signal. The noise is a summation of unwanted or disturbing energy from natural, Noise is, however, typically distinguished from interference, for example in the signal-to-noise ratio, signal-to-interference ratio and signal-to-noise plus interference ratio measures. While noise is generally unwanted, it can serve a purpose in some applications. Johnson–Nyquist noise is unavoidable, and generated by the thermal motion of charge carriers, inside an electrical conductor. Thermal noise is white, meaning that its power spectral density is nearly equal throughout the frequency spectrum. The amplitude of the signal has very nearly a Gaussian probability density function, a communication system affected by thermal noise is often modeled as an additive white Gaussian noise channel. If electrons flow across a barrier, then they have discrete arrival times and those discrete arrivals exhibit shot noise. The output of a noise generator is easily set by the current. Typically, the barrier in a diode is used, shot noise in electronic devices results from unavoidable random statistical fluctuations of the electric current when the charge carriers traverse a gap. The current is a flow of charges, and the fluctuation in the arrivals of those charges creates shot noise. Shot noise is similar to the created by rain falling on a tin roof. The flow of rain may be constant, but the raindrops arrive discretely. The shot noise assumes independent arrivals, vacuum tubes have shot noise because the electrons randomly leave the cathode and arrive at the anode. A tube may not exhibit the full shot noise effect, the presence of a space charge tends to smooth out the arrival times. Conductors and resistors typically do not exhibit shot noise because the electrons thermalize and move diffusively within the material, shot noise has been demonstrated in mesoscopic resistors when the size of the resistive element becomes shorter than the electron-phonon scattering length. Flicker noise, also known as 1/f noise, is a signal or process with a spectrum that falls off steadily into the higher frequencies
17.
Slide rule
–
The slide rule, also known colloquially in the United States as a slipstick, is a mechanical analog computer. The slide rule is used primarily for multiplication and division, and also for functions such as exponents, roots, logarithms and trigonometry, though similar in name and appearance to a standard ruler, the slide rule is not ordinarily used for measuring length or drawing straight lines. Slide rules exist in a range of styles and generally appear in a linear or circular form with a standardized set of markings essential to performing mathematical computations. Slide rules manufactured for specialized fields such as aviation or finance typically feature additional scales that aid in calculations common to those fields, at its simplest, each number to be multiplied is represented by a length on a sliding ruler. As the rulers each have a scale, it is possible to align them to read the sum of the logarithms. The Reverend William Oughtred and others developed the rule in the 17th century based on the emerging work on logarithms by John Napier. Before the advent of the calculator, it was the most commonly used calculation tool in science. In its most basic form, the slide rule uses two logarithmic scales to allow rapid multiplication and division of numbers and these common operations can be time-consuming and error-prone when done on paper. More elaborate slide rules allow other calculations, such as roots, exponentials, logarithms. Scales may be grouped in decades, which are numbers ranging from 1 to 10. Thus single decade scales C and D range from 1 to 10 across the width of the slide rule while double decade scales A and B range from 1 to 100 over the width of the slide rule. Numbers aligned with the marks give the value of the product, quotient. The user determines the location of the point in the result. Scientific notation is used to track the decimal point in more formal calculations, addition and subtraction steps in a calculation are generally done mentally or on paper, not on the slide rule. Most slide rules consist of three strips of the same length, aligned in parallel and interlocked so that the central strip can be moved lengthwise relative to the other two. The outer two strips are fixed so that their relative positions do not change. Some slide rules have scales on both sides of the rule and slide strip, others on one side of the outer strips and both sides of the slide strip, still others on one side only. A sliding cursor with a vertical alignment line is used to find corresponding points on scales that are not adjacent to other or
18.
Nomogram
–
Nomograms use a parallel coordinate system invented by dOcagne rather than standard Cartesian coordinates. A nomogram consists of a set of n scales, one for each variable in an equation. Knowing the values of n-1 variables, the value of the variable can be found, or by fixing the values of some variables. The result is obtained by laying a straightedge across the values on the scales. The virtual or drawn line created by the straightedge is called a line or isopleth. Nomograms flourished in different contexts for roughly 75 years because they allowed quick. Results from a nomogram are obtained very quickly and reliably by simply drawing one or more lines, the user does not have to know how to solve algebraic equations, look up data in tables, use a slide rule, or substitute numbers into equations to obtain results. The user does not even need to know the underlying equation the nomogram represents, in addition, nomograms naturally incorporate implicit or explicit domain knowledge into their design. For example, to create larger nomograms for greater accuracy the nomographer usually includes only scale ranges that are reasonable, many nomograms include other useful markings such as reference labels and colored regions. All of these provide useful guideposts to the user, while the slide rule is intended to be a general-purpose device, a nomogram is designed to perform a specific calculation, with tables of values effectively built into the construction of the scales. Nomograms are typically used in applications where the level of accuracy they offer is sufficient, alternatively, a nomogram can be used to check an answer obtained from another, more exact but possibly error-prone calculation. Other types of graphical calculators such as charts, trilinear diagrams. These do not meet the definition of a nomogram as a graphical calculator whose solution is found by the use of one or more linear isopleths. A nomogram for a three-variable equation typically has three scales, although there exist nomograms in which two or even all three scales are common, here two scales represent known values and the third is the scale where the result is read off. The simplest such equation is u1 + u2 + u3 =0 for the three variables u1, u2 and u3, an example of this type of nomogram is shown on the right, annotated with terms used to describe the parts of a nomogram. More complicated equations can sometimes be expressed as the sum of functions of the three variables. For example, the nomogram at the top of this article could be constructed as a parallel-scale nomogram because it can be expressed as such a sum after taking logarithms of both sides of the equation. The scale for the variable can lie between the other two scales or outside of them
19.
Process control
–
Process control is an engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range. For instance, the temperature of a reactor may be controlled to maintain a consistent product output. Process control enables automation, by which a staff of operating personnel can operate a complex process from a central control room. Process control may either use feedback or it may be open loop, Control may also be continuous or cause a sequence of discrete events, such as a timer on a lawn sprinkler or controls on an elevator. A thermostat on a heater is an example of control that is on or off, a temperature sensor turns the heat source on if the temperature falls below the set point and turns the heat source off when the set point is reached. There is no measurement of the difference between the set point and the temperature and no adjustment to the rate at which heat is added other than all or none. A familiar example of control is cruise control on an automobile. Here speed is the measured variable, the operator adjusts the desired speed set point and the controller monitors the speed sensor and compares the measured speed to the set point. The controller makes adjustments having information only about the error although settings known as tuning are used to achieve stable control, the operation of such controllers is the subject of control theory. A PLC output would then calculate an incremental amount of change in the valve position, larger more complex systems can be controlled by process control systems like Distributed Control System or SCADA. The accompanying diagram is a model which shows functional manufacturing levels in a large process using computerised control. Level 2 contains the supervisory computers, which information from processor nodes on the system. Level 3 is the control level, which does not directly control the process. Processes can be characterized as one or more of the forms, Discrete – Found in many manufacturing, motion. Robotic assembly, such as found in automotive production, can be characterized as discrete process control. Most discrete manufacturing involves the production of discrete pieces of product, batch – Some applications require that specific quantities of raw materials be combined in specific ways for particular durations to produce an intermediate or end result. One example is the production of adhesives and glues, which require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other important examples are the production of food, beverages and medicine, batch processes are generally used to produce a relatively low to intermediate quantity of product per year
20.
Protective relay
–
In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. Microprocessor-based digital protection relays now emulate the original devices, as well as providing types of protection and supervision impractical with electromechanical relays, electromechanical relays provide only rudimentary indications of involved phase and zone targets. In many cases a single microprocessor relay provides functions that would take two or more electromechanical devices, by combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their long life span, tens of thousands of these silent sentinels are still protecting transmission lines. Important transmission lines and generators have cubicles dedicated to protection, with many individual electromechanical devices, the theory and application of these protective devices is an important part of the education of a power engineer who specializes in power systems. The need to act quickly to protect circuits and equipment as well as the public often requires protective relays to respond. In some instances these clearance times are prescribed in legislation or operating rules, a maintenance or testing program is used to determine the performance and availability of protection systems. Electromechanical protective relays operate by either magnetic attraction, or magnetic induction, Protection relays may use arrays of induction disks, shaded-pole,25 magnets, operating and restraint coils, solenoid-type operators, telephone-relay contacts, and phase-shifting networks. Protective relays can also be classified by the type of measurement they make.92 A protective relay may respond to the magnitude of a quantity such as voltage or current. Induction relays can respond to the product of two quantities in two coils, which could for example represent the power in a circuit. It is not practical to make a relay that develops a torque equal to the quotient of two a. c. quantities, various combinations of operate torque and restraint torque can be produced in the relay. By use of a permanent magnet in the circuit, a relay can be made to respond to current in one direction differently from in another. Such polarized relays are used on direct-current circuits to detect, for example and these relays can be made bistable, maintaining a contact closed with no coil current and requiring reverse current to reset. For AC circuits, the principle is extended with a polarizing winding connected to a voltage source. Lightweight contacts make for sensitive relays that operate quickly, but small contacts cant carry or break heavy currents, often the measuring relay will trigger auxiliary telephone-type armature relays. In a large installation of electromechanical relays, it would be difficult to determine which device originated the signal that tripped the circuit and this information is useful to operating personnel to determine the likely cause of the fault and to prevent its re-occurrence. Relays may be fitted with a target or flag unit, which is released when the relay operates, electromechanical relays can be classified into several different types as follows, Armature-type relays have a pivoted lever supported on a hinge or knife-edge pivot, which carries a moving contact. These relays may work on alternating or direct current, but for alternating current
21.
Flight computer
–
Flight computer, or simply the whiz wheel, is a form of circular slide rule used in aviation and one of a very few analog computers in widespread use in the 21st century. Sometimes it is called by the make or model name like E6B and they are mostly used in flight training, but many professional pilots still carry and use these flight computers. They are used during planning to aid in calculating fuel burn, wind correction, time en route. In the air, the computer can be used to calculate ground speed, estimated fuel burn. The back is designed for wind correction calculations, i. e. determining how much the wind is affecting ones speed and course
22.
Aircraft
–
An aircraft is a machine that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the lift of an airfoil. The human activity that surrounds aircraft is called aviation, crewed aircraft are flown by an onboard pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as type, aircraft propulsion, usage. Each of the two World Wars led to technical advances. Consequently, the history of aircraft can be divided into five eras, Pioneers of flight, first World War,1914 to 1918. Aviation between the World Wars,1918 to 1939, Second World War,1939 to 1945. Postwar era, also called the jet age,1945 to the present day, aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low-density gas such as helium, hydrogen, or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, a balloon was originally any aerostat, while the term airship was used for large, powered aircraft designs – usually fixed-wing. In 1919 Frederick Handley Page was reported as referring to ships of the air, in the 1930s, large intercontinental flying boats were also sometimes referred to as ships of the air or flying-ships. – though none had yet been built, the advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by an outer framework and separate aerodynamic skin surrounding the gas bags, were produced. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, then several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a balloon is an aerostat and an airship is a powered one. A powered, steerable aerostat is called a dirigible, sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloon is regarded as the definition of an airship. Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back and these soon became known as blimps. During the Second World War, this shape was adopted for tethered balloons, in windy weather
23.
Control system
–
A control system manages, commands, directs or regulates the behaviour of other devices or systems. It can range from a home heating using a thermostat controlling a domestic boiler to large Industrial control systems which are used for controlling processes or machines. In the most common form, the control system it is desired to control a process, called the plant, so its output follows a control signal. The control system compares the output of the plant to the control signal, an automatic sequential control system may trigger a series of mechanical actuators in the correct sequence to perform a task. For example, various electric and pneumatic transducers may fold and glue a cardboard box, fill it with product, programmable logic controllers are used in many cases such as this, but several alternative technologies exist. An example of this may increase the supply to a furnace when a measured temperature drops. PID controllers are common and effective in such as this. Control systems that include some sensing of the results they are trying to achieve are making use of feedback and so can, to some extent, open-loop control systems do not make use of feedback, and run only in pre-arranged ways. There are two classes of control systems, open loop control systems, and closed loop control systems. In an open loop system, the control action from the controller is independent of the process output. A good example of this is a central heating boiler controlled only by a timer, so heat is applied for a constant time. In a closed loop system, the control action from the controller is dependent on the desired. A closed loop controller therefore has a loop which ensures the controller exerts a control action to give a process output the same as the Reference input or set point. For this reason, closed loop controllers are also called feedback controllers, logic control systems for industrial and commercial machinery were historically implemented at mains voltage using interconnected relays, designed using ladder logic. Today, most such systems are constructed with programmable logic controllers or microcontrollers, the notation of ladder logic is still in use as a programming idiom for PLCs. Logic controllers may respond to switches, light sensors, pressure switches, etc. and can cause the machinery to start, logic systems are used to sequence mechanical operations in many applications. PLC software can be written in different ways – ladder diagrams. Examples include elevators, washing machines and other systems with interrelated stop-go operations, logic systems are quite easy to design, and can handle very complex operations
24.
Synthetic-aperture radar
–
Synthetic aperture radar is a form of radar that is used to create two- or 3-dimensional images of objects, such as landscapes. SAR uses the motion of the radar antenna over a region to provide finer spatial resolution than conventional beam-scanning radars. SAR is typically mounted on a platform such as an aircraft or spacecraft. The distance the SAR device travels over a target in the time taken for the pulses to return to the antenna creates the large synthetic antenna aperture. To create a SAR image, successive pulses of waves are transmitted to illuminate a target scene. The pulses are transmitted and the echoes received using a single beam-forming antenna, as the SAR device on board the aircraft or spacecraft moves, the antenna location relative to the target changes with time. The properties of SAR can be described as having high resolution capability which is independent of flight altitude, SAR also have a great day and night imaging capability considering their own illumination. SAR images have wide applications in sensing and mapping of the surfaces of both the Earth and other planets. Volcano and earthquake monitoring is a part of differential interferometry and it is also useful in environment monitoring like oil spills, flooding, urban growth, global change and military surveillance which includes strategic policy and tactical assessment. SAR can also be implemented as inverse SAR by observing a moving target over a time with a stationary antenna. A Synthetic Aperture Radar is a radar mounted on a moving platform. Electromagnetic waves are transmitted and reflected echoes are collected, digitized and stored by the radar antenna for later processing. As transmission and reception occur at different time, they map to different positions, the well ordered combination of the received signals builds a virtual aperture that is much longer than the physical antenna length. This is why it is named synthetic aperture, giving it the property of being an imaging radar, the 3D processing is done in two steps, the azimuth and range direction are focussed for the generation of 2D high resolution images. After which a digital model is used to measure the phase differences between complex images which is determined from different look angles to recover the height information. This height information, along with the coordinates provided by 2-D SAR focusing. The first step requires only standard processing algorithms, for the step a additional pre-processing stage such as image co-registration. In addition to this, multiple baselines can be used to extend 3D imaging to the time dimension, the SAR algorithm, as given here, applies to phased arrays generally
25.
History of computing hardware
–
The history of computing hardware covers the developments from early simple devices to aid calculation to modern day computers. Before the 20th century, most calculations were done by humans, early mechanical tools to help humans with digital calculations, such as the abacus, were called calculating machines, by proprietary names, or even as they are now, calculators. The machine operator was called the computer, later, computers represented numbers in a continuous form, for instance distance along a scale, rotation of a shaft, or a voltage. Numbers could also be represented in the form of digits, automatically manipulated by a mechanical mechanism, although this approach generally required more complex mechanisms, it greatly increased the precision of results. A series of breakthroughs, such as miniaturized transistor computers, the cost of computers gradually became so low that by the 1990s, personal computers, and then, in the 2000s, mobile computers, became ubiquitous in industrialized countries. Devices have been used to aid computation for thousands of years, the earliest counting device was probably a form of tally stick. Later record keeping throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains. The use of counting rods is one example, the abacus was early used for arithmetic tasks. What we now call the Roman abacus was used in Babylonia as early as 2400 BC, since then, many other forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, several analog computers were constructed in ancient and medieval times to perform astronomical calculations. These include the Antikythera mechanism and the astrolabe from ancient Greece, hero of Alexandria made many complex mechanical devices including automata and a programmable cart. Ramon Llull invented the Lullian Circle, a machine for calculating answers to philosophical questions via logical combinatorics. This idea was taken up by Leibniz centuries later, and is one of the founding elements in computing. While producing the first logarithmic tables, Napier needed to perform many tedious multiplications and it was at this point that he designed his Napiers bones, an abacus-like device that greatly simplified calculations that involved multiplication and division. Edmund Gunter built a device with a single logarithmic scale at the University of Oxford. His device greatly simplified arithmetic calculations, including multiplication and division, William Oughtred greatly improved this in 1630 with his circular slide rule. He followed this up with the slide rule in 1632. Slide rules were used by generations of engineers and other mathematically involved professional workers, Wilhelm Schickard, a German polymath, designed a calculating machine in 1623 which combined a mechanised form of Napiers rods with the worlds first mechanical adding machine built into the base
26.
South-pointing chariot
–
The south-pointing chariot was an ancient Chinese two-wheeled vehicle that carried a movable pointer to indicate the south, no matter how the chariot turned. Usually, the pointer took the form of a doll or figure with an outstretched arm, the chariot was supposedly used as a compass for navigation, and may also have had other purposes. No ancient chariots still exist, but many extant ancient Chinese texts mention them, some include information about their inner components and workings. There were probably several types of south-pointing chariot which worked differently, in most or all of them, the rotating road wheels mechanically operated a geared mechanism to keep the pointer aimed correctly. The mechanism had no magnets and did not automatically detect which direction was south, the pointer was aimed southward by hand at the start of a journey. Thus the mechanism did a kind of dead reckoning, which is inherently prone to cumulative errors. Some chariots mechanisms may have had differential gears, if so, it was probably the first use of differentials anywhere in the world. The south-pointing chariot, a wheeled vehicle used to discern the southern cardinal direction, was given a brief description by Mas contemporary Fu Xuan. The contemporary 3rd century CE source of the Weilüe, written by Yuan Huan also described the south-pointing chariot of Ma Jun, the book also provided description of the south-pointing chariots re-invention and use in times after Ma Jun and the Three Kingdoms. The 6th century CE text reads as follows, (In this translation, by Needham, the south-pointing chariot is referred to as the south-pointing carriage. The last sentence of the passage is of great interest for navigation at sea, in fact, the first known source to describe stories of its legendary use during the Zhou period was the Gu Jin Zhu book of Cui Bao, written soon after the Three Kingdoms era. Cui Bao also wrote that the details of construction for the device were once written in the Shang Fang Gu Shi. The invention of the chariot also made its way to Japan by the 7th century. The Nihon Shoki of 720 CE described the earlier Chinese Buddhist monks Zhi Yu and this was followed up by several more chariot devices built in 666 CE as well. The south-pointing chariot was combined with the earlier Han Dynasty era invention of the odometer, a mechanical device used to measure distance traveled. It was mentioned in the Song Dynasty historical text of the Song Shi that the engineers Yan Su, a differential is an assembly of gears, nowadays used in almost all automobiles except some electric and hybrid-electric ones, which has three shafts linking it to the external world. They are conveniently labelled A, B, and C, the gears cause the rotation speed of Shaft A to be proportional to the sum of the rotation speeds of Shafts B and C. There are no limitations on the rotation speeds of the shafts
27.
History of China
–
Written records of the history of China can be found from as early as 1500 BC under the Shang dynasty. Ancient historical texts such as the Records of the Grand Historian and the Bamboo Annals describe a Xia dynasty, with thousands of years of continuous history, China is one of the worlds oldest civilizations, and is regarded as one of the cradles of civilization. Much of Chinese culture, literature and philosophy developed during the Zhou dynasty. This is one of multiple periods of failed statehood in Chinese history, between eras of multiple kingdoms and warlordism, Chinese dynasties have ruled parts or all of China, in some eras control stretched as far as Xinjiang and Tibet, as at present. In 221 BC Qin Shi Huang united the warring kingdoms and created for himself the title of emperor of the Qin dynasty. Successive dynasties developed bureaucratic systems that enabled the emperor to control vast territories directly, in the 21 centuries from 206 BC until AD1912, routine administrative tasks were handled by a special elite, the Scholar-officials. Young men were selected through difficult examinations and were well-versed in calligraphy and philosophy. What is now China was inhabited by Homo erectus more than a million years ago, recent study shows that the stone tools found at Xiaochangliang site are magnetostratigraphically dated to 1.36 million years ago. The archaeological site of Xihoudu in Shanxi Province is the earliest recorded use of fire by Homo erectus, the excavations at Yuanmou and later Lantian show early habitation. Perhaps the most famous specimen of Homo erectus found in China is the so-called Peking Man discovered in 1923–27, fossilised teeth of Homo sapiens dating to 125, 000–80,000 BC have been discovered in Fuyan Cave in Dao County in Hunan. The Neolithic age in China can be traced back to about 10,000 BC, Early evidence for proto-Chinese millet agriculture is radiocarbon-dated to about 7000 BC. The earliest evidence of cultivated rice, found by the Yangtze River, is carbon-dated to 8,000 years ago, farming gave rise to the Jiahu culture. At Damaidi in Ningxia,3,172 cliff carvings dating to 6000–5000 BC have been discovered, featuring 8,453 individual characters such as the sun, moon, stars, gods and these pictographs are reputed to be similar to the earliest characters confirmed to be written Chinese. Chinese proto-writing existed in Jiahu around 7000 BC, Dadiwan from 5800 BC to 5400 BC, Damaidi around 6000 BC, some scholars have suggested that Jiahu symbols were the earliest Chinese writing system. With agriculture came increased population, the ability to store and redistribute crops, Later, Yangshao culture was superseded by the Longshan culture, which was also centered on the Yellow River from about 3000 BC to 2000 BC. Bronze artifacts have been found at the Majiayao culture site, The Bronze Age is also represented at the Lower Xiajiadian culture site in northeast China. Sanxingdui located in what is now Sichuan province is believed to be the site of a ancient city. The site was first discovered in 1929 and then re-discovered in 1986, Chinese archaeologists have identified the Sanxingdui culture to be part of the ancient kingdom of Shu, linking the artifacts found at the site to its early legendary kings
28.
Antikythera mechanism
–
Found housed in a 340 millimetres ×180 millimetres ×90 millimetres wooden box, the device is a complex clockwork mechanism composed of at least 30 meshing bronze gears. Its remains were found as one lump, later separated in three fragments, which are now divided into 82 separate fragments after conservation works. Four of these fragments contain gears, while inscriptions are found on many others, the largest gear is approximately 140 millimetres in diameter and originally had 223 teeth. The artefact was recovered probably in July 1901 from the Antikythera shipwreck off the Greek island of Antikythera. Believed to have designed and constructed by Greek scientists, the instrument has been dated either between 150 and 100 BC, or, according to a more recent view, in 205 BC. All known fragments of the Antikythera mechanism are kept at the National Archaeological Museum, in Athens, the Antikythera mechanism was discovered in 45 metres of water in the Antikythera shipwreck off Point Glyphadia on the Greek island of Antikythera. All were transferred to the National Museum of Archaeology in Athens for storage, merely a lump of corroded bronze and wood at the time, the mechanism went unnoticed for two years while museum staff worked on piecing together more obvious statues. On 17 May 1902, archaeologist Valerios Stais was examining the finds, investigations into the object were soon dropped until British science historian and Yale University professor, Derek J. de Solla Price became interested in it in 1951. In 1971, both Price and Greek nuclear physicist Charalampos Karakalos made X-ray and gamma-ray images of the 82 fragments, Price published an extensive 70-page paper on their findings in 1974. Generally referred to as the first known computer, the quality and complexity of the mechanisms manufacture suggests it has undiscovered predecessors made during the Hellenistic period. Its construction relied upon theories of astronomy and mathematics developed by Greek astronomers, in 1974, Derek de Solla Price concluded from gear settings and inscriptions on the mechanisms faces that it was made about 87 BC and lost only a few years later. Jacques Cousteau and associates visited the wreck in 1976 and recovered coins dated to between 76 and 67 BC, though its advanced state of corrosion has made it impossible to perform an accurate compositional analysis, it is believed the device was made of a low-tin bronze alloy. All its instructions are written in Koine Greek, and the consensus among scholars is that the mechanism was made in the Greek-speaking world, syracuse was a colony of Corinth and the home of Archimedes, which might imply a connection with the school of Archimedes. With its many scrolls of art and science, it was second in only to the Library of Alexandria during the Hellenistic period. A busy trading port in antiquity, Rhodes was also a centre of astronomy and mechanical engineering, home to the astronomer Hipparchus and that the mechanism uses Hipparchuss theory for the motion of the moon suggests the possibility he may have designed, or at least worked on it. He regarded the Antikythera mechanism as more valuable than the Mona Lisa, in 2014, a study by Carman and Evans argued for a new dating of approximately 200 BC. Moreover, according to Carman and Evans, the Babylonian arithmetic style of prediction fits much better with the devices predictive models than the traditional Greek trigonometric style, further dives are being undertaken in the hope of discovering more of the mechanism. The original mechanism apparently came out of the Mediterranean as a single encrusted piece, soon afterward it fractured into three major pieces
29.
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 sizes of these bodies, but since accurate scaling is often not practical due to the actual large ratio differences. They are typically driven by a mechanism with a globe representing the Sun at the centre. The Antikythera mechanism, discovered in 1900 in a wreck off the Greek island of Antikythera and extensively studied, exhibited the diurnal motions of the Sun, Moon, and it has been dated between 150 and 100 BC. The Antikythera hand driven mechanism is now considered one of the first orreries and it was geocentric and used as a mechanical calculator designed to calculate astronomical positions. According to Cicero, the Roman philosopher who was writing in the first century BC, the clock itself is lost, but Dondi left a complete description of the astronomic gear trains of his clock. As late as 1650, P. Schirleus built a geocentric planetarium with the Sun as a planet, the clocks are now on display in Kassel at the Astronomisch-Physikalisches Kabinett and in Dresden at the Mathematisch-Physikalischer Salon. In De revolutionibus orbium coelestium, published in Nuremberg in 1543 and he observed that some Greek philosophers had proposed a heliocentric universe. This simplified the apparent epicyclic motions of the planets, making it feasible to represent the paths as simple circles. This could be modelled by the use of gears, tycho Brahes improved instruments made precise observations of the skies, and from these Johannes Kepler deduced that planets orbited the Sun in ellipses. In 1687 Isaac Newton explained the cause of motion in his theory of gravitation. Orreries take three forms, Solid Models typically the size of a coffee table, real World Orreries typically the length of a walk. Virtual World Orreries where the imagination is unlimited. Clock makers George Graham and Thomas Tompion built the first modern orrery around 1704 in England, Graham gave the first model, or its design, to the celebrated instrument maker John Rowley of London to make a copy for Prince Eugene of Savoy. Rowley was commissioned to make another copy for his patron Charles Boyle, 4th Earl of Orrery and this model was presented to Charles son John, later the 5th Earl of Cork and 5th Earl of Orrery. Independently, Christiaan Huygens published details of a heliocentric planetary machine in 1703 and he calculated the gear trains needed to represent a year of 365.242 days, and used that to produce the cycles of the principal planets. The Sun in a brass orrery provides the light in the room. The orrery depicted in the painting has rings, which give it a similar to that of an armillary sphere
30.
Derek J. de Solla Price
–
Derek John de Solla Price was a physicist, historian of science, and information scientist, credited as the father of scientometrics. Price was born in Leyton, England, to Philip Price, a tailor, and Fanny de Solla and he obtained a Doctor of Philosophy in experimental physics from the University of London in 1946. Price worked as a teacher of applied mathematics at Raffles College, after three years, Price returned to England to work on a second Ph. D. in the history of science, this time at the University of Cambridge. During his Ph. D. studies, he accidentally discovered Equatorie of the Planetis, a written in Middle English. Around 1950, Price adopted his mothers Sephardic name, de Solla, in 1984, Price received, posthumously, the ASIS Research Award for outstanding contributions in the field of information science. An ancient Greek computer, in Scientific American 200, 60-67. Nations can Publish or Perish, in International Science and Technology 70 84-90 Citation Measures of Hard Science, Soft Science, Technology, communication among Scientists and Engineers, Lexington, MA, D. C. The Antikythera Mechanism, A Calendar Computer from ca.80 B. C, transactions of the American Philosophical Society New Series. A general theory of bibliometric and other cumulative advantage processes, journal of the American Society for Information Science. An Old Palmistry Being the Earliest Known Book of Palmistry in English,1953, W. Heffer & Sons, edition, ASIN-B000PIYKBW The Origin of Clockwork, Perpetual Motion Devices, and the Compass, FQ Books, July 6, 2010), ASIN, B003YMNPOE. With D. J. Wang, Ling Heavenly Clockwork, The Great Astronomical clocks of Medieval China by Joseph Needam, measuring the Size of Science,1969, Israel Academy of Sciences and Humanities, ASIN-B007EMQHT0. An International Checklist of Astrolabes,1955, Peyronnet, ASIN- B0007JKDJ2, the Differences between Science and Technology,1968, Thomas Alva Edison Foundation, ASIN- B0007HNK3U. Scientific Humanities, An Urgent Program,1957, ASIN-B0007KAV84, portable Sundials in antiquity, Including an account of a new example from Aphrodisias,1969, ASIN- B0007K65O8. The Little Ship of Venice, A Middle English instrument tract,1960, contra-Copernicus,1952, Royal Institution of Great Britain, ASIN- B0007KCWS6. Equatorie of Planetis,1955, 1st ed, Cambridge University Press, planetary equatorium A Treatise on the Astrolabe Works by Derek John de Solla Price at Project Gutenberg Derek de Solla Price This Weeks Citation Classic, Little Science, Big Science. Derek John de Solla Price Medal of the journal Scientometrics, International Society for Scientometrics and Informetrics
31.
Antikythera wreck
–
The Antikythera wreck is a Roman-era shipwreck dating from the 2nd quarter of the 1st century BC. It was discovered by divers off Point Glyphadia on the Greek island of Antikythera in 1900. These ancient artifacts, works of art, and elements of the ship itself are now displayed at the National Archaeological Museum of Athens. Around Easter 1900, Captain Dimitrios Kondos and his crew of sponge divers from Syme sailed through the Aegean en route to fishing grounds off North Africa and they stopped at the Greek island of Antikythera to wait for favorable winds. During the layover, they began diving off the islands coast wearing the standard diving dresses — canvas suits, diver Elias Stadiatis descended to 45 meters depth, then quickly signaled to be pulled to the surface. He described a seafloor horror show, a heap of rotting corpses and horses strewn among the rocks. Thinking the diver was drunk from the nitrogen in his breathing mix at that depth, Kondos himself donned the diving gear, and soon returned to the surface with the arm of a bronze statue. Shortly thereafter, the men departed as planned to fish for sponges, Kondos reported the finds to authorities in Athens, and quickly Hellenic Navy vessels were sent to support the salvage effort from November 1900 through 1901. Together with the Greek Education Ministry and the Royal Hellenic Navy, ships equipment included lead scupper pipes and hull sheeting, and a set of four massive lead sounding weights. These are the only sounding weights ever discovered on an ancient shipwreck in the Aegean, many other small and common artifacts were also found, and the entire assemblage was taken to the National Archaeological Museum in Athens. The death of diver Giorgos Kritikos and the paralysis of two due to decompression sickness put an end to work at the site during the summer of 1901. On 17 May 1902, the former Minister of Education, Spyridon Stais and he noticed that a severely corroded piece of bronze had a gear wheel embedded in it and legible inscriptions in Greek. The object would come to be known as the Antikythera Mechanism, originally thought to be one of the first forms of a mechanised clock or an astrolabe, it is at times referred to as the world’s oldest known analog computer. The wreck remained untouched until 1953 when French naval officer and explorer Jacques-Yves Cousteau visited briefly to relocate the site, Cousteau returned with a full team in the summer and autumn of 1976 at the invitation of the Greek Government. Under the direction of archaeologist Dr, although the retrieval of artifacts from the shipwreck was highly successful and accomplished within two years, dating the site proved difficult and took much longer. Based on related works with known provenances, the statues could be dated back to the 4th century BC. Some scholars have speculated that the ship was carrying part of the loot of the Roman General Sulla from Athens in 86 BC, a reference by the Greek writer, Lucian, to one of Sullas ships sinking in the Antikythera region gave rise to this theory. Supporting an early 1st-century BC date were domestic utensils and objects from the ship, the amphorae recovered from the wreck indicated a date of 80–70 BC, the Hellenistic pottery a date of 75–50 BC, and the Roman ceramics were similar to known mid-1st century types
32.
Antikythera
–
Antikythera or Anticythera is a Greek island lying on the edge of the Aegean Sea, between Crete and Peloponnese. Since the 2011 local government reform it is part of the municipality of Kythera island, Antikythera may also refer to the Antikythera Strait, through which modified Mediterranean water enters the Sea of Crete. Its land area is 20.43 square kilometres, and it lies 38 kilometres south-east of Kythira and it is the most distant part of the Attica region from its heart in the Athens metropolitan area. It is lozenge-shaped,10.5 km NNW to SSE by 3.4 km ENE to WSW and 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, the only other settlements are Galanianá, and Charchalianá. Antikythera is sporadically visited by the LANE Lines ferry Vitsentzos Kornaros on its route between Piraeus and Kissamos-Kastelli on Crete, the earliest known inhabitants were likely seasonal hunters who traveled there to exploit the presence of migratory birds. The population of the island changed frequently as it was settled and abandoned several times. In antiquity, the island of Antikythera was known as Aigila or Ogylos, between the 4th and 1st centuries BC, it was used as a base by a group of Cilician pirates until their destruction by Pompey the Great. Their fort can still be seen atop a cliff to the northeast of the island, the archaeology of the island has been thoroughly surveyed and the data made openly available for further study. Antikythera is most famous for being the location of the 1900 discovery of the Antikythera wreck, from which the Antikythera Ephebe, the Antikythera mechanism is an ancient mechanical calculator designed to calculate astronomical positions which has been dated to about 205 BC. Technological artifacts of similar complexity did not appear until a thousand years later, Antikythera is a very important stop-over site for migratory birds during their seasonal movements, due to its geographical position and certain features. Furthermore, the hosts the largest breeding colony of Eleonoras falcon in the world. The importance of Antikythira for studying bird migration led to the creation of Antikythera Bird Observatory by the Hellenic Ornithological Society, the island also has a large population of wild goats
33.
Kythira
–
Kythira 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, administratively, it belongs to the Islands regional unit, which is part of the Attica region. The island is located between the Greek mainland and Crete, and from ancient times until the mid 19th century was a crossroads of merchants, sailors. As such, it has had a long and varied history and has influenced by many civilisations. This is reflected in its architecture, as well as the traditions and customs, influenced by centuries of coexistence of the Greek, Venetian, and Ottoman cultures. Kythira and the island of Antikythira were separate municipalities until they were merged at the 2011 local government reform. The municipality has an area of 300.023 km2, the municipal unit 279.593 km2, the province of Kythira was one of the provinces of the Piraeus Prefecture. It had the territory as the present municipality Kythira. There are archaeological remains from the Helladic period, contemporary with the Minoans, there is archaeological evidence of Kythiran trade as far as Egypt and Mesopotamia. Kythira had a Phoenician colony in the archaic age, the sea-snail which produces Tyrian purple is native to the island. Xenophon refers to a Phoenician Bay in Kythira, the archaic Greek city of Kythira was at Scandea on Avlemonas, its ruins have been excavated. Its acropolis, now Palicastro, has the temple of Aphrodite Ourania, in classical times, Kythira was part of the territory of several larger city-states. Kythira was independent, and issued her own coins, in 195, in Augustus time, it was again subject to Sparta, being the property of Gaius Julius Eurycles, who was both a Spartan magnate and a Roman citizen. By this time, the Greek cities were in practice subject to the Roman Empire, Kythira continued to exist under the Roman Empire and its Byzantine successor state for centuries. Christianity is attested from the fourth century AD, the time of Constantine, according to her legend, archaeological evidence suggests the island was abandoned about 700 AD. When Saint Theodore of Cythera led a resettlement after the Byzantine reconquest of Crete in 962 and he established a great monastery at Paliochora, a town grew up around it, largely populated from Laconia. When the Byzantine Empire was divided among the conquerors of the Fourth Crusade, during the Venetian domination the island was known as Cerigo. Ottomans called this island Chuha Island, kythirans still talk about the destruction and looting of Paliochora by Barbarossa, it has become an intrinsic part of the Kytherian folklore
34.
Crete
–
Crete is the largest and most populous of the Greek islands, 88th-largest island in the world and the fifth-largest island in the Mediterranean Sea, after Sicily, Sardinia, Cyprus, and Corsica. Crete and a number of surrounding islands and islets constitute the region of Crete, the capital and the largest city is Heraklion. As of 2011, the region had a population of 623,065, Crete forms a significant part of the economy and cultural heritage of Greece, while retaining its own local cultural traits. It was once the centre of the Minoan civilization, which is regarded as the earliest recorded civilization in Europe. The island is first referred to as Kaptara in texts from the Syrian city of Mari dating from the 18th century BC, repeated later in Neo-Assyrian records and it was also known in ancient Egyptian as Keftiu, strongly suggesting a similar Minoan name for the island. The current name of Crete is thought to be first attested in Mycenaean Greek texts written in Linear B, through the words
35.
Planisphere
–
In astronomy, 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 stars for any time. It is an instrument to assist in learning how to recognize stars, 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 sphere is represented by a three-dimensional framework of rings. The chart and overlay are mounted so that they are free to rotate about a pivot point at their centers. The star chart contains the brightest stars, constellations and deep-sky objects visible from a latitude on Earth. The night sky that one sees from the Earth depends on whether the observer is in the northern or southern hemispheres, a planisphere window is designed for a particular latitude and will be accurate enough for a certain band either side of that. Planisphere makers will usually offer them in a number of versions for different latitudes, planispheres only show the stars visible from the observers latitude, stars below the horizon are not included. A complete twenty-four-hour time cycle is marked on the rim of the overlay, a full twelve months of calendar dates are marked on the rim of the starchart. The window is marked to show the direction of the eastern and western horizons, the disk and overlay are adjusted so that the observers local time of day on the overlay corresponds to that days date on the star chart disc. The portion of the star visible in the window then represents the distribution of stars in the sky at that moment for the planispheres designed location. Users hold the planisphere above their head with the eastern and western horizons correctly aligned to match the chart to actual star positions, the word planisphere was originally used in the second century by Ptolemy to describe the representation of a spherical Earth by a map drawn in the plane. This usage continued into the Renaissance, for example Gerardus Mercator described his 1569 world map as a planisphere, in this article the word describes the representation of the star-filled celestial sphere on the plane. The first star chart to have the name planisphere was made in 1624 by Jacob Bartsch, Bartsch was the son-in-law of Johannes Kepler, discoverer of Keplers laws of planetary motion. Since the planisphere shows the sphere in a printed flat. Planispheres, like all charts, are using a certain projection method. For planispheres there are two methods in use, leaving the choice with the designer. One such method is the azimuthal equidistant projection
36.
Star chart
–
A star chart is another name for a chore chart. A star chart or star map is a map of the night sky, astronomers divide these into grids to use them more easily. They are used to identify and locate objects such as stars, constellations. They have been used for navigation since time immemorial. Note that a star chart differs from a catalog, which is a listing or tabulation of astronomical objects for a particular purpose. Tools utilizing a star chart include the astrolabe and the planisphere, the oldest known star chart may be a carved ivory Mammoth tusk that was discovered in Germany in 1979. This artifact is 32,500 years old and has a carving that resembles the constellation Orion, a drawing on the wall of the Lascaux caves in France has a graphical representation of the Pleiades open cluster of stars. This is dated from 33,000 to 10,000 years ago, another star chart panel, created more than 21,000 years ago, was found in the La Tête du Lion grotto. The bovine in this panel may represent the constellation Taurus, with a representing the Pleiades just above it. The oldest accurately dated star chart appeared in ancient Egyptian astronomy in 1534 BC, the earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC, during the Kassite Period. The oldest Chinese astronomy records date to before the Warring States period, the oldest Chinese graphical representation of the sky is a lacquer box dated to 430 BC, although this depiction does not show individual stars. The Farnese Atlas is a 2nd-century copy of a Hellenistic era statue depicting the Titan Atlas holding the sphere on his shoulder. It is the oldest surviving depiction of the ancient Greek constellations, because of precession, the positions of the constellations slowly change over time. By comparing the positions of the 41 constellations against the grid circles, based upon this information, the constellations were catalogued at 125 ±55 BC. This evidence indicates that the catalogue of the Greek astronomer Hipparchus was used. A Roman era example of a representation of the night sky is the Egyptian Dendera zodiac. This is a bas relief sculpting on a ceiling at the Dendera Temple complex and it is a planisphere depicting the zodiac in graphical representations. However, individual stars are not plotted, the oldest surviving manuscript star chart was discovered in the Mogao Caves along the Silk Road – the Dunhuang Star Chart
37.
Al-Biruni
–
Abū Rayḥān Muḥammad ibn Aḥmad Al-Bīrūnī, known as Al-Biruni in English, was an Iranian scholar and polymath from Khwarezm. He studied almost all fields of science and was compensated for his research, royalty and powerful members of society sought out Al-Biruni to conduct research and study in order to uncover certain findings. He lived during the Islamic Golden Age, in which scholarly thought went hand in hand with the thinking and methodology of the Islamic religion. In addition to type of influence, Al-Biruni was also influenced by other nations, such as the Greek. He was conversant in Khwarezmian, Persian, Arabic, Sanskrit and he spent a large part of his life in Ghazni in modern-day Afghanistan, capital of the Ghaznavid dynasty which was based in what is now central-eastern Afghanistan. In 1017 he traveled to the Indian subcontinent and authored Tarikh Al-Hind after exploring the Hindu faith practised in India and he was given the title founder of Indology. He was a writer on customs and creeds of various nations. He also made contributions to Earth sciences, and is regarded as the father of geodesy for his important contributions to that field and he was born in the outer district of Kath, the capital of the Afrighid dynasty of Khwarezm. The word Biruni means from the outer-district in Persian, and so became his nisba. Al-Birunis relatives also took interest in the studies of science as well and he even had ties to royalty as there are links in his family to the families of prestigious elites. In order to conduct his research, Al-Biruni used different types of methods to tackle the different fields he studied, people consider Al-Biruni to be one of the greatest scientists in history and especially of Islam because of his discoveries and methodology. He lived during the Islamic Golden Age, which promoted astronomy and he was sympathetic to the Afrighids, who were overthrown by the rival dynasty of Mamunids in 995. He left his homeland for Bukhara, then under the Samanid ruler Mansur II the son of Nuh, there he corresponded with Avicenna and there are extant exchanges of views between these two scholars. In 998, he went to the court of the Ziyarid amir of Tabaristan and he also visited the court of the Bavandid ruler Al-Marzuban. Accepting the definite demise of the Afrighids at the hands of the Mamunids and their court at Gorganj was gaining fame for its gathering of brilliant scientists. In 1017, Mahmud of Ghazni took Rey, most scholars, including al-Biruni, were taken to Ghazni, the capital of the Ghaznavid dynasty. Biruni was made court astrologer and accompanied Mahmud on his invasions into India and he was forty-four years old when he went on the journeys with Mahmud of Ghazni. Biruni became acquainted with all related to India
38.
Astrolabe
–
An astrolabe is an elaborate inclinometer, historically used by astronomers and navigators, to measure the inclined position in the sky of a celestial body, day or night. It can thus be used to identify stars or planets, to determine local latitude given local time and vice versa, to survey and it was used in classical antiquity, the Islamic Golden Age, the European Middle Ages and the Renaissance for all these purposes. While the astrolabe is effective for determining latitude on land or calm seas, the mariners astrolabe was developed to solve that problem. OED gives the translation star-taker for the English word astrolabe and traces it, through medieval Latin, to the Greek word astrolabos from astron star, in the medieval Islamic world the word asturlab was given various etymologies. In Arabic texts, the word is translated as akhdh al-kawakib which corresponds to an interpretation of the Greek word, al-Biruni quotes and criticizes the medieval scientist Hamzah al-Isfahani who had stated, asturlab is an arabization of this Persian phrase. In medieval Islamic sources, there is also a fictional and popular etymology of the words as lines of lab, in this popular etymology, Lab is a certain son of Idris. This etymology is mentioned by a 10th-century scientist named al-Qummi but rejected by al-Khwarizmi, Lab in Arabic also means sun and black stony places. An early astrolabe was invented in the Hellenistic world by Apollonius of Perga, a marriage of the planisphere and dioptra, the astrolabe was effectively an analog calculator capable of working out several different kinds of problems in spherical astronomy. Theon of Alexandria wrote a treatise on the astrolabe. Some historians attribute the invention to Hypatia, the daughter of Theon of Alexandria, noting that Synesius. Astrolabes continued in use in the Greek-speaking world throughout the Byzantine period, about 550 AD the Christian philosopher John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant Greek treatise on the instrument. In addition, Severus Sebokht, a bishop who lived in Mesopotamia, Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the astrolabe, adding circles indicating azimuths on the horizon. It was widely used throughout the Muslim world, chiefly as an aid to navigation and as a way of finding the Qibla, the first person credited with building the astrolabe in the Islamic world is reportedly the 8th-century mathematician Muhammad al-Fazari. The mathematical background was established by the Muslim astronomer Albatenius in his treatise Kitab az-Zij, the earliest surviving dated astrolabe is dated AH315. In the Islamic world, astrolabes were used to find the times of sunrise and the rising of fixed stars, to help schedule morning prayers. In the 10th century, al-Sufi first described over 1,000 different uses of an astrolabe, in areas as diverse as astronomy, astrology, navigation, surveying, timekeeping, prayer, Salat, Qibla, etc. The spherical astrolabe, a variation of both the astrolabe and the sphere, was invented during the Middle Ages by astronomers and inventors in the Islamic world. The earliest description of the spherical astrolabe dates back to Al-Nayrizi, in the 12th century, Sharaf al-Dīn al-Tūsī invented the linear astrolabe, sometimes called the staff of al-Tusi, which was a simple wooden rod with graduated markings but without sights
39.
Hellenistic period
–
It is often considered a period of transition, sometimes even of decadence or degeneration, compared to the enlightenment of the Greek Classical era. The Hellenistic period saw the rise of New Comedy, Alexandrian poetry, the Septuagint, Greek science was advanced by the works of the mathematician Euclid and the polymath Archimedes. The religious sphere expanded to include new gods such as the Greco-Egyptian Serapis, eastern deities such as Attis and Cybele, the Hellenistic period was characterized by a new wave of Greek colonization which established Greek cities and kingdoms in Asia and Africa. This resulted in the export of Greek culture and language to new realms. Equally, however, these new kingdoms were influenced by the cultures, adopting local practices where beneficial, necessary. Hellenistic culture thus represents a fusion of the Ancient Greek world with that of the Near East, Middle East and this mixture gave rise to a common Attic-based Greek dialect, known as Koine Greek, which became the lingua franca through the Hellenistic world. Scholars and historians are divided as to what event signals the end of the Hellenistic era, Hellenistic is distinguished from Hellenic in that the first encompasses the entire sphere of direct ancient Greek influence, while the latter refers to Greece itself. The word originated from the German term hellenistisch, from Ancient Greek Ἑλληνιστής, from Ἑλλάς, Hellenistic is a modern word and a 19th-century concept, the idea of a Hellenistic period did not exist in Ancient Greece. Although words related in form or meaning, e. g, the major issue with the term Hellenistic lies in its convenience, as the spread of Greek culture was not the generalized phenomenon that the term implies. Some areas of the world were more affected by Greek influences than others. The Greek population and the population did not always mix, the Greeks moved and brought their own culture. While a few fragments exist, there is no surviving historical work which dates to the hundred years following Alexanders death. The works of the major Hellenistic historians Hieronymus of Cardia, Duris of Samos, the earliest and most credible surviving source for the Hellenistic period is Polybius of Megalopolis, a statesman of the Achaean League until 168 BC when he was forced to go to Rome as a hostage. His Histories eventually grew to a length of forty books, covering the years 220 to 167 BC, another important source, Plutarchs Parallel Lives though more preoccupied with issues of personal character and morality, outlines the history of important Hellenistic figures. Appian of Alexandria wrote a history of the Roman empire that includes information of some Hellenistic kingdoms, other sources include Justins epitome of Pompeius Trogus Historiae Philipicae and a summary of Arrians Events after Alexander, by Photios I of Constantinople. Lesser supplementary sources include Curtius Rufus, Pausanias, Pliny, in the field of philosophy, Diogenes Laertius Lives and Opinions of Eminent Philosophers is the main source. Ancient Greece had traditionally been a collection of fiercely independent city-states. After the Peloponnesian War, Greece had fallen under a Spartan hegemony, in which Sparta was pre-eminent but not all-powerful
40.
Hipparchus
–
Hipparchus of Nicaea was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry but is most famous for his discovery of precession of the equinoxes. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes and he is known to have been a working astronomer at least from 162 to 127 BC. Hipparchus is considered the greatest ancient astronomical observer and, by some and he was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. For this he made use of the observations and perhaps the mathematical techniques accumulated over centuries by the Babylonians. He developed trigonometry and constructed trigonometric tables, and he solved problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a method to predict solar eclipses. Relatively little of Hipparchuss direct work survives into modern times, although he wrote at least fourteen books, only his commentary on the popular astronomical poem by Aratus was preserved by later copyists. There is a tradition that Hipparchus was born in Nicaea, in the ancient district of Bithynia. His birth date was calculated by Delambre based on clues in his work, Hipparchus must have lived some time after 127 BC because he analyzed and published his observations from that year. Hipparchus obtained information from Alexandria as well as Babylon, but it is not known when or if he visited these places and he is believed to have died on the island of Rhodes, where he seems to have spent most of his later life. It is not known what Hipparchuss economic means were nor how he supported his scientific activities and his appearance is likewise unknown, there are no contemporary portraits. In the 2nd and 3rd centuries coins were made in his honour in Bithynia that bear his name and show him with a globe, this supports the tradition that he was born there. As an astronomer of antiquity his influence, supported by ideas from Aristotle, held sway for nearly 2000 years, Hipparchuss only preserved work is Τῶν Ἀράτου καὶ Εὐδόξου φαινομένων ἐξήγησις. This is a critical commentary in the form of two books on a popular poem by Aratus based on the work by Eudoxus. Hipparchus also made a list of his works, which apparently mentioned about fourteen books. His famous star catalog was incorporated into the one by Ptolemy, the first trigonometric table was apparently compiled by Hipparchus, who is now consequently known as the father of trigonometry. There are a variety of mis-steps in the more ambitious 2005 paper, According to one book review, both of these claims have been rejected by other scholars
41.
Dioptra
–
A dioptra is a classical astronomical and surveying instrument, dating from the 3rd century BCE. The dioptra was a tube or, alternatively, a rod with a sight at both ends, attached to a stand. If fitted with protractors, it could be used to measure angles, greek astronomers used the dioptra to measure the positions of stars, both Euclid and Geminus refer to the dioptra in their astronomical works. By the time of Ptolemy, it was obsolete as an astronomical instrument and it continued in use as an effective surveying tool. Adapted to surveying, the dioptra is similar to the theodolite, or surveyors transit and it is a more accurate version of the groma. The dioptra may have been sophisticated enough, for example, to construct a tunnel through two points in a mountain. There is some speculation that it may have used to build the Eupalinian aqueduct. Scholars disagree whether the dioptra was available that early, an entire book about the construction and surveying usage of the dioptra is credited to Hero of Alexandria. Hero was one of history’s most ingenious engineers and applied mathematicians, the dioptra was used extensively on aqueduct building projects. Screw turns on different parts of the instrument made it easy to calibrate for very precise measurements The dioptra was replaced as a surveying instrument by the theodolite. Alidade Isaac Moreno Gallo The Dioptra Tesis and reconstructon of the Dioptra, the History and Practice of Ancient Astronomy, pages 34-35. Oxford University Press. net Tom M. Apostol, The Tunnel of Samos, Engineering and Science,64, 30-40
42.
Calendar
–
A calendar is a system of organizing days for social, religious, commercial or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, a date is the designation of a single, specific day within such a system. A calendar is also a record of such a system. A calendar can also mean a list of planned events, such as a calendar or a partly or fully chronological list of documents. Periods in a calendar are usually, though not necessarily, synchronized with the cycle of the sun or the moon. The most common type of calendar was the lunisolar calendar. Latin calendarium meant account book, register, the Latin term was adopted in Old French as calendier and from there in Middle English as calender by the 13th century. The course of the Sun and the Moon are the most evident forms of timekeeping, nevertheless, the Roman calendar contained very ancient remnants of a pre-Etruscan 10-month solar year. The first recorded calendars date to the Bronze Age, dependent on the development of writing in the Ancient Near East, a larger number of calendar systems of the Ancient Near East becomes accessible in the Iron Age, based on the Babylonian calendar. This includes the calendar of the Persian Empire, which in turn gave rise to the Zoroastrian calendar as well as the Hebrew calendar, calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years. This was mostly based on observation, but there may have been attempts to model the pattern of intercalation algorithmically. The Roman calendar was reformed by Julius Caesar in 45 BC, the Julian calendar was no longer dependent on the observation of the new moon but simply followed an algorithm of introducing a leap day every four years. This created a dissociation of the month from the lunation. The Islamic calendar is based on the prohibition of intercalation by Muhammad and this resulted in an observationally based lunar calendar that shifts relative to the seasons of the solar year. The first calendar reform of the modern era was the Gregorian calendar. Such ideas are mooted from time to time but have failed to gain traction because of the loss of continuity, massive upheaval in implementation, a full calendar system has a different calendar date for every day. Thus the week cycle is by not a full calendar system. The simplest calendar system just counts time periods from a reference date and this applies for the Julian day or Unix Time
43.
Gear
–
A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque. Geared devices can change the speed, torque, and direction of a power source, Gears almost always produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. The teeth on the two meshing gears all have the same shape, two or more meshing gears, working in a sequence, are called a gear train or a transmission. A gear can mesh with a linear toothed part, called a rack, the gears in a transmission are analogous to the wheels in a crossed, belt pulley system. An advantage of gears is that the teeth of a gear prevent slippage, in transmissions with multiple gear ratios—such as bicycles, motorcycles, and cars—the term gear as in first gear refers to a gear ratio rather than an actual physical gear. The term describes similar devices, even when the ratio is continuous rather than discrete, or when the device does not actually contain gears. Early examples of gears date from the 4th century BC in China, examples of further development include, Ma Jun used gears as part of a south-pointing chariot. The Antikythera mechanism is an example of an early and intricate geared device. Its time of construction is now estimated between 150 and 100 BC, the water-powered grain-mill, the water-powered saw mill, fulling mill, and other applications of watermill often used gears. The first mechanical clocks were built in AD725, the 1386 Salisbury cathedral clock may be the worlds oldest working mechanical clock. The definite ratio that teeth give gears provides an advantage over other drives in precision machines such as watches that depend upon an exact velocity ratio, an external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, a gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, a gear is one with the pitch angle exceeding 90 degrees. Internal gears do not cause output shaft direction reversal, spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with teeth projecting radially, though the teeth are not straight-sided, the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears mesh together correctly only if fitted to parallel shafts, No axial thrust is created by the tooth loads. Spur gears are excellent at moderate speeds but tend to be noisy at high speeds, helical or dry fixed gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, since the gear is curved, this angling makes the tooth shape a segment of a helix
44.
Isfahan
–
Isfahan, historically also rendered in English as Ispahan, Sepahan, Esfahan or Hispahan, is the capital of Isfahan Province in Iran, located about 340 kilometres south of Tehran. The Greater Isfahan Region had a population of 3,793,104 in the 2011 Census, the counties of Isfahan, Borkhar, Najafabad, Khomeynishahr, Shahinshahr, Mobarakeh, Falavarjan, Tiran o Karvan, Lenjan and Jay all constitute the metropolitan city of Isfahan. Isfahan is located on the main north–south and east–west routes crossing Iran and it flourished from 1050 to 1722, particularly in the 16th and 17th centuries under the Safavid dynasty, when it became the capital of Persia for the second time in its history. Even today, the city retains much of its past glory and it is famous for its Persian–Islamic architecture, with many beautiful boulevards, covered bridges, palaces, mosques, and minarets. This led to the Persian proverb Esfahān nesf-e- jahān ast, the Naghsh-e Jahan Square in Isfahan is one of the largest city squares in the world. It has been designated by UNESCO as a World Heritage Site, the city also has a wide variety of historic monuments and is known for the paintings, history and architecture. Isfahan City Center is also the 5th largest shopping mall in the world, see also, Names of Isfahan The name of the region derives from Middle Persian Spahān. Spahān is attested in various Middle Persian seals and inscriptions, including that of Zoroastrian Magi Kartir, the present-day name is the Arabicized form of Ispahan. The region appears with the abbreviation GD on Sasanian numismatics, in Ptolemys Geographia it appears as Aspadana, translating to place of gathering for the army. It is believed that Spahān derives from spādānām the armies, Old Persian plural of spāda, the history of Isfahan can be traced back to the Palaeolithic period. In recent discoveries, archaeologists have found artifacts dating back to the Palaeolithic, Mesolithic, Neolithic, Bronze and Iron ages. It is said that after Cyrus the Great freed the Jews from Babylon some Jews returned to Jerusalem whereas some others decided to live in Persia, but, actually this happened later in the Sasanid period when a Jewish colony was made in the vicinity of the Sasanid. They did not settle anywhere or in any city without examining the water. They did all along until they reached the city of Isfahan, there they rested, examined the water and soil and found that both resembled Jerusalem. Upon they settled there, cultivated the soil, raised children and grandchildren, under the Parthians, Arsacid governors administered a large province from Isfahan, and the citys urban development accelerated to accommodate the needs of a capital city. The next empire to rule Persia, the Sassanids, presided over changes in their realm, instituting sweeping agricultural reform and reviving Iranian culture. The city was called by the name and the region by the name Aspahan or Spahan. The city was governed by Espoohrans or the members of seven noble Iranian families who had important royal positions, extant foundations of some Sassanid-era bridges in Isfahan suggest that the kings were also fond of ambitious urban planning projects
45.
Iran
–
Iran, also known as Persia, officially the Islamic Republic of Iran, is a sovereign state in Western Asia. Comprising a land area of 1,648,195 km2, it is the second-largest country in the Middle East, with 82.8 million inhabitants, Iran is the worlds 17th-most-populous country. It is the country with both a Caspian Sea and an Indian Ocean coastline. The countrys central location in Eurasia and Western Asia, and its proximity to the Strait of Hormuz, Tehran is the countrys capital and largest city, as well as its leading economic and cultural center. Iran is the site of to one of the worlds oldest civilizations, the area was first unified by the Iranian Medes in 625 BC, who became the dominant cultural and political power in the region. The empire collapsed in 330 BC following the conquests of Alexander the Great, under the Sassanid Dynasty, Iran again became one of the leading powers in the world for the next four centuries. Beginning in 633 AD, Arabs conquered Iran and largely displaced the indigenous faiths of Manichaeism and Zoroastrianism by Islam, Iran became a major contributor to the Islamic Golden Age that followed, producing many influential scientists, scholars, artists, and thinkers. During the 18th century, Iran reached its greatest territorial extent since the Sassanid Empire, through the late 18th and 19th centuries, a series of conflicts with Russia led to significant territorial losses and the erosion of sovereignty. Popular unrest culminated in the Persian Constitutional Revolution of 1906, which established a monarchy and the countrys first legislative body. Following a coup instigated by the U. K. Growing dissent against foreign influence and political repression led to the 1979 Revolution, Irans rich cultural legacy is reflected in part by its 21 UNESCO World Heritage Sites, the third-largest number in Asia and 11th-largest in the world. Iran is a member of the UN, ECO, NAM, OIC. Its political system is based on the 1979 Constitution which combines elements of a democracy with a theocracy governed by Islamic jurists under the concept of a Supreme Leadership. A multicultural country comprising numerous ethnic and linguistic groups, most inhabitants are Shia Muslims, the largest ethnic groups in Iran are the Persians, Azeris, Kurds and Lurs. Historically, Iran has been referred to as Persia by the West, due mainly to the writings of Greek historians who called Iran Persis, meaning land of the Persians. As the most extensive interactions the Ancient Greeks had with any outsider was with the Persians, however, Persis was originally referred to a region settled by Persians in the west shore of Lake Urmia, in the 9th century BC. The settlement was then shifted to the end of the Zagros Mountains. In 1935, Reza Shah requested the international community to refer to the country by its native name, opposition to the name change led to the reversal of the decision, and Professor Ehsan Yarshater, editor of Encyclopædia Iranica, propagated a move to use Persia and Iran interchangeably
46.
Lunisolar calendar
–
A lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year. As with all calendars which divide the year into months there is a requirement that the year have a whole number of months. In this case ordinary years consist of twelve months but every second or third year is an embolismic year, also, some of the ancient pre-Islamic calendars in south Arabia followed a lunisolar system. The Chinese, Coligny and Hebrew lunisolar calendars track more or less the tropical year whereas the Buddhist, therefore, the first three give an idea of the seasons whereas the last two give an idea of the position among the constellations of the full moon. The Tibetan calendar was influenced by both the Chinese and Hindu calendars, the Germanic peoples also used a lunisolar calendar before their conversion to Christianity. The Metonic cycle, used in the Hebrew calendar and the Julian and Gregorian ecclesiastical calendars, the classic Metonic cycle can be reproduced by assigning an initial epact value of 1 to the last year of the cycle and incrementing by 11 each year. Between the last year of one cycle and the first year of the next the increment is 12 and this adjustment, the saltus lunae, causes the epacts to repeat every 19 years. When the epact goes above 29 an intercalary month is added and 30 is subtracted, the intercalary years are numbers 3,6,8,11,14,17 and 19. Both the Hebrew calendar and the Julian calendar use this sequence, the Buddhist and Hebrew calendars restrict the leap month to a single month of the year, the number of common months between leap months is, therefore, usually 36, but occasionally only 24 months. An alternative way of dealing with the fact that a year does not contain an integer number of months is by including uncounted time in the year that does not belong to any month. Some Coast Salish peoples used a calendar of this kind, for instance, the Chehalis began their count of lunar months from the arrival of spawning chinook salmon, and counted 10 months, leaving an uncounted period until the next chinook salmon run. The Gregorian calendar has a calendar, which is used to determine the date of Easter. The rules are in the Computus, Hebrew calendar Jain calendar Hindu calendar Computus Easter rule for Julian and Gregorian calendars. Lunisolar calendar year 2014 Lunisolar Calendar Calendar studies Model of lunisolar calendar based on observation of the sun and moon position
47.
Wire
–
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads or electricity and telecommunications signals, Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Wire gauges come in standard sizes, as expressed in terms of a gauge number. The term wire is used more loosely to refer to a bundle of such strands, as in multistranded wire. Wire comes in solid core, stranded, or braided forms, edge-wound coil springs, such as the Slinky toy, are made of special flattened wire. In some cases, strips cut from metal sheet were made into wire by pulling them through perforations in stone beads and this causes the strips to fold round on themselves to form thin tubes. This strip drawing technique was in use in Egypt by the 2nd Dynasty, from the middle of the 2nd millennium BCE most of the gold wires in jewellery are characterised by seam lines that follow a spiral path along the wire. Such twisted strips can be converted into solid round wires by rolling them between flat surfaces or the wire drawing method. The strip twist wire manufacturing method was superseded by drawing in the ancient Old World sometime between about the 8th and 10th centuries AD, there is some evidence for the use of drawing further East prior to this period. Square and hexagonal wires were made using a swaging technique. In this method a metal rod was struck between grooved metal blocks, or between a punch and a grooved metal anvil. Swaging is of great antiquity, possibly dating to the beginning of the 2nd millennium BCE in Egypt and in the Bronze and Iron Ages in Europe for torcs, twisted square-section wires are a very common filigree decoration in early Etruscan jewelry. In about the middle of the 2nd millennium BCE, a new category of decorative tube was introduced which imitated a line of granules. True beaded wire, produced by mechanically distorting a round-section wire, appeared in the Eastern Mediterranean and Italy in the seventh century BCE, a forerunner to beaded wire may be the notched strips and wires which first occur from around 2000 BCE in Anatolia. Wire was drawn in England from the medieval period, the wire was used to make wool cards and pins, manufactured goods whose import was prohibited by Edward IV in 1463. The first wire mill in Great Britain was established at Tintern in about 1568 by the founders of the Company of Mineral and Battery Works, apart from their second wire mill at nearby Whitebrook, there were no other wire mills before the second half of the 17th century. Despite the existence of mills, the drawing of wire down to fine sizes continued to be done manually. Wire is usually drawn of cylindrical form, but it may be made of any desired section by varying the outline of the holes in the draw-plate through which it is passed in the process of manufacture
