2009年1月23日星期五

Synthesizer


A synthesizer (or synthesiser) is an electronic instrument capable of producing a variety of sounds by generating and combining signals of different frequencies. A modern digital synthesizer uses a frequency synthesizer microprocessor component to calculate mathematical functions, which generate signals of different frequencies. There are three main types of synthesizers, which differ in operation: analog, digital and software-based. Synthesizers create electrical signals, rather than direct acoustic sounds, which are then amplified through a loudspeaker or set of headphones.

Synthesizers are typically controlled with a piano-style keyboard, in which each key functions as a switch to turn electronic circuits on and off. This has led to the instruments also sometimes being referred to simply as "keyboards". Although keyboards are the most common control interface, other devices such as saxophone-style wind controllers, MIDI-equipped electric guitars, drum pads or computers are used to control synthesizers. Synthesizers can produce a wide range of sounds, which can either imitate other instruments or generate unusual new timbres.

The first electric synthesizer was invented in 1876 by Elisha Gray, who is best known for his development of a telephone prototype. Robert Moog created a revolutionary synthesizer which was used by Wendy Carlos's Switched-On Bach (1968) a popular recording which introduced many musicians to the sound of synthesizers. In the 1970s, the development of miniaturized solid-state components allowed synthesizers to become self-contained, portable instruments, which made them easier to use in live performances. By the early 1980s, companies such as Yamaha began selling compact, modestly priced synthesizers such as the DX7, and MIDI (Musical Instrument Digital Interface) was developed, which made it easier to integrate and synchronize synthesizers with other electronic instruments. In the 1990's complex synthesizers no longer required specialist hardware and began to appear as software for the PC, often as hardware emulators with on-screen knobs and panels.

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Motorized bicycle


A motorized bicycle, sometimes referred to as a light electric vehicle (LEV), is a bicycle with an attached motor used to assist with pedaling. Generally considered to be a vehicle, sometimes as a motor vehicle or a class of hybrid vehicle, motorized bicycles are usually powered by electric motors or small internal combustion engines. Some can be propelled by the motor alone if the rider chooses not to pedal, while in others the motor will only run if the rider pedals.

Some early motorized bicycles were powered by internal combustion engines whereas some utilized electric motors. With lighter batteries and better storage density, the electric motor has recently seen an increase in popularity.

Motorized bicycles are distinguished from motorcycles by being capable of being powered by pedals alone if required. The actual usage of the pedals varies widely according to the type of vehicle. Those known as mopeds mostly have pedals for emergency use or because of legal requirements and these are not normally used. Those known as power-assist bikes have the pedals as the main form of propulsion with the motor used to give a bit of extra speed, especially uphill. Many motorized bicycles are based on standard bicycle frame designs and technologies, although the modifications to the design to support motorization may be extensive.

In countries where there is a strong bicycle culture (notably in Asia), the motorized bicycle is particularly popular; in 1996 Shanghai had 370,000 motorized bicycles and 470,000 other vehicles.

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Montreal Metro

The Montreal Metro is a rubber-tired metro system, and the main form of public transportation in the city of Montreal, Quebec, Canada.

The Metro, operated by the Société de transport de Montréal (STM), was inaugurated on October 14, 1966, during the tenure of Mayor Jean Drapeau. Originally consisting of 26 stations on three separate lines, the Metro now incorporates 68 stations on four lines measuring 65.33 km (40.59 mi) in length, serving the north, east, and centre of the Island of Montreal with connections to Longueuil, via the Yellow Line, and Laval, via the Orange line. The metro system is currently Canada's second longest and second in total annual passenger usage (in both respects to Toronto's subway system), serving 289.1 million riders a year (transfers not included); according to the STM website, the metro system has transported over 6 billion passengers as of 2006, roughly equivalent to the world's population. The Montreal Metro was inspired by the Paris Metro and in turn is also the inspiration for the Lyon Metro, constructed a few years later, which shares the same rubber-wheel car design and Montreal Metro station architecture.

History
Unbuilt projects
1910
The first subway proposal, dated 1910, was for a single line running underneath De Bleury street and Park Avenue from Craig street (now St-Antoine) all the way to Mont-Royal avenue. The line was to run underground from Craig to Pine Avenue.

1944
In 1944, the Montreal Tramways company proposed a 2 line network, running underneath Ste-Catherine street from Cabot Square (Atwater avenue) to Papineau, and a second line under St-Denis (from Jean-Talon to Notre-Dame), then turning westwards under Notre-Dame and St-Jacques all the way to Guy, then turning north and connecting with the other line at Guy street.

1953
The newly formed Montreal Transportation Commission proposed a single line, running under Ste-Catherine Street from Atwater Avenue towards Peel where the line would have turned south, going underneath Dominion Square all the way down to St-Jacques Street, which it followed to St-Denis Street. Then, it would have gone north all the way to Crémazie Boulevard, right by the Youville maintenance shops.


Between 1967 and 1984
Planned extension of Line 2 Orange,
See "Montreal Metro map, with planned extensions" in next section.
Line 3 Red
Planned extensions of Line 5 Blue,
See "Montreal Metro map, with planned extensions" in next section.
Line 6 (Montreal Metro)
Line 7 White

Initial network
Construction began in May 1962 and was engaged before Montreal was chosen as host of the 1967 World's Fair (Expo 67), held in the summer of 1967. Regardless of the fair, the city badly needed a mass transportation system, projects dating back to 1910. The main lines (Green (Line 1), Atwater to Frontenac; and Orange (Line 2), Bonaventure to Henri-Bourassa) were opened gradually starting in October 1966, with the Yellow line (Line 4) (Berri-de-Montigny to Longueuil, on the south shore of the Saint Lawrence River) not opened until April 1967.

A Line 3 was originally intended as a surface metro running in part through the existing railway tracks running under Mount Royal to Cartierville. But then, as negotiations with the Canadian National Railway (CN Rail) for the use of their tracks and tunnel were stalled, Montreal was chosen as host of the Expo 67. Plans and budgets were therefore redirected for the design and construction of a replacement line, Line 4, constructed especially for Expo 67, in place of the never built Line 3, whose tracks are now used for the Deux-Montagnes commuter train. The Montreal Metro nonetheless continues to be numbered as if this proposed line had been constructed as Line 3 of the Metro.

With the awarding of the 1976 Summer Olympics to Montreal, construction began in October 1971 for the extension of Line 1 from Frontenac to Honoré-Beaugrand to service the main Olympic site; the new stations were opened in June 1976.

Later, Line 1 was extended from Atwater to Angrignon (September 1978), while Line 2 was extended from Bonaventure to Place-Saint-Henri (April 1980), Snowdon (September 1981), Côte-Sainte-Catherine and Plamondon (January and June 1982), and Du Collège (January 1984).

Two years later, a new line (Blue (Line 5)) was built from De Castelnau to Saint-Michel (June 1986), with transfers to Line 2 at Jean-Talon, and Line 2 was extended further to Côte-Vertu (November 1986). Line 5 was then extended to Parc (June 1987), Acadie (March 1988), and the existing Snowdon station on Line 2 (January 1988). To this date, the Montreal Metro is Canada's second largest subway system.

The lines, however, were not planned to end where they eventually did in 1990. Line 2 was originally meant to have two or three more stations beyond Côte-Vertu; however, priority funding was given to Line 5. The plans for Deguire/Poirier, Bois-Franc, and Salaberry stations were scrubbed. Line 5 itself was shortened due to funding issues. It was originally been projected to have stops west of Snowdon (Côte Saint-Luc, Cavendish, Montréal-Ouest, Lafleur) and east of Saint-Michel (Pie-IX, Viau, Lacordaire, Langelier, Galeries d'Anjou).

An entire metro line in initial planning was also scrubbed, the so-called Line 7/Pie IX - Saint-Leonard/White Line, also due to the same funding issues. Proposed for the first time by the Bureau des Transports de Montréal (BTM) in September 1983, the original project for a new north-south line (Line 7, the number 6 being reserved for another surface metro line proposed by the Ministère des Transports du Québec (MTQ)) would have had 10 stations (from Pie-IX to Léger), which then got formally proposed by the Communauté urbaine de Montréal (CUM) at the start of 1984, this time having 12 stations (from Pie-IX to Maurice-Duplessis/Langelier).

While a number of proposals for further expansion had been studied over the years, it all came to a stop around 1990, when the Quebec provincial government placed a moratorium on further metro construction. Then, in 2002, construction began on a three-station extension of Line 2 from Henri-Bourassa under the Rivière des Prairies to Montmorency on the island of Laval (northwest of the island of Montreal). This extension was completed and the three new stations were opened on April 28, 2007. Ridership increased by 50,000 a day to 835,000 with the new stations.

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Iron Man


Iron Man is a fictional character, a superhero that appears in comic books published by Marvel Comics. The character first appeared in Tales of Suspense #39 (March 1963), and was created by writer-editor Stan Lee, scripter Larry Lieber, and artists Don Heck and Jack Kirby.

Born Anthony Edward "Tony" Stark, he suffers a severe heart injury during a kidnapping and is forced to build a destructive weapon. He instead creates a power suit to save his life and help him escape. He later decides to use the suit to protect the world as the superhero, Iron Man.He is a wealthy industrialist and genius inventor who created military weapons and whose metal suit is laden with technological devices that enable him to fight crime. Initially, Iron Man was a vehicle for Stan Lee to explore Cold War themes, particularly the role of American technology and business in the fight against communism. Subsequent re-imaginings of Iron Man have gradually removed the Cold War themes, replacing them with more contemporary concerns such as corporate crime and terrorism.

Throughout most of the comic's history, Iron Man has been a member of the superhero team the Avengers and has been featured in several incarnations of his own various comic book series. The character has been adapted for several animated TV shows, as well as for the 2008 live action films Iron Man and a cameo in The Incredible Hulk where he is played by Robert Downey, Jr.


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Geography of the BattleTech universe

Political entities
Capellan March
In the fictional setting of the BattleTech universe, the Capellan March is an administrative subdivision of the Federated Suns. Originally one of five Marches, the Capellan March grew with the disbandment of the Terran March. Also, the Sarna March was disbanded following Operation Guerrero and the subsequent Lyran secession from the Federated Commonwealth. Though most of the Sarna March was either consumed by the Capellan Confederation or became part of the Chaos March, the Achernar PDZ remained in Federated Suns' hands and was added to the Capellan March. The Capellan March has traditionally been the landhold of the Hasek family, whose leader also holds the title of Duke of New Syrtis, the capital world of the Capellan March. The Duke or Duchess of New Syrtis also holds hereditary title to the dual position of director of the Capellan March command (which carries the rank of Field Marshal) and Minister of the Capellan March. This effectively concentrates civilian and military authority for the border march in the hands of one individual, who can then use all the resources at his or her disposal to deal with any military threats. The people of the March have traditionally nurtured a deep hatred of the neighboring Capellan Confederation. Due to the proximity of the Capellan March to the Capellan Confederation, the vast majority of the winners of the Limp Sword decoration are based out of the Capellan March.

For military purposes, the march is divided into two Operations Areas or Combat Theaters, Edgeward and Coreward. Despite the fact that New Syrtis is located in the Edgeward Combat Theater, command is headquartered on Taygeta (giving it the alternate name of the Taygeta OA). The Coreward Combat Theater's HQ has traditionally been on Kathil, however Duke George Hasek moved it to Novaya Zemlya during the FedCom Civil War and seems content to leave it there (but it is still known as the Kathil OA). From there, the Theaters are broken down into over a dozen Polymorphous Defense Zones (PDZs).

Crucis March
In the fictional BattleTech gaming universe, the Crucis March is the central portion of the state known as the Federated Suns. The Crucis March has historically been ruled directly by the Davion family. Its capital, like that of the Federated Suns as a whole, is New Avalon. Unlike the other Marches of the Federated Suns the Crucis March is divided into Combat Regions which line up completely with the Administrative Regions of the Realm, as opposed to the Draconis and Capellan Marches which are divided into PDZs.

Draconis March
In the fictional world of BattleTech, the Draconis March is the region of the Federated Suns which borders the Draconis Combine. The hostility between the people of the Draconis March and their enemies in the Combine is a large part of the culture of the Draconis March. The Draconis March's capital is the world of Robinson. It has historically been ruled by the Sandoval Family. The military honor guard of the Draconis March is the Robinson Rangers (the New Ivaarsen Chaussers are also historically associated with the region). During Simon Davion's Five Princes era, part of the Draconis March was included into the Terran March, including the capital of Robinson.

In the fictional BattleTech universe, the Sarna March was an administrative district of the Federated Commonwealth. The Sarna March was created after the Fourth Succession War out of the worlds the Federated Suns had conquered from the Capellan Confederation in the early 3030s and the worlds of the Tikonov Free Republic. Since Prince Hanse Davion had given the conquered worlds to his wife, Melissa Steiner, as his wedding present to her, the Sarna March was technically a part of the Lyran State Command. As such, the march was named after its capital world, Sarna, in the Lyran fashion.

Sarna March
The Sarna March was divided into two Operations Areas, Sarna and Terra Firma.
Joshua Marik, son of Captain-General Thomas Marik and heir to the Free Worlds League, was being treated at the New Avalon Institute of Science for leukemia in exchange for the Federated Commonwealth's ability to benefit from the League's large industrial base. When Joshua died, Archon-Prince Victor Steiner-Davion did not want to lose that support, so he executed a plan to replace Joshua with a body-double. This plan succeeded initially, but a Capellan spy was able to detect the fraud. This information passed up the chain until Chancellor Sun-Tzu Liao learned of it. Sun-Tzu decided to use this information to convince Thomas Marik to coordinate an assault on the Federated Commonwealth to regain territory they had lost in the Fourth Succession War.

Sun-Tzu had already been busy building up underground terrorist cells in many of the worlds of the Sarna March. In 3057, the Marik-Liao offensive began. The offensive was primarily spearheaded by Capellan terrorists and League mercenaries. Sensing her opportunity to seize power, Katherine Steiner-Davion, Victor's regent in the Lyran State Command, announced that she was enacting a little-known clause in the Federated-Commonwealth Alliance to secede the Lyran half of the realm from the Federated Commonwealth. She sent out a call to all traditionally Lyran units to return to within the nation's pre-Fourth Succession War borders and signed an independent truce with Thomas Marik. She called her "new" nation the Lyran Alliance.

The Sarna March ceased to exist around 3058, after the Lyran secession. Since the Sarna March was a part of the Lyran State, Archon Melissa Steiner had insisted on garrisoning it primarily with Lyran units. The Lyrans had used many JumpShips to return to Lyran space, leaving the remaining Federated Commonwealth units stranded and unable to help. Simultaneously, Capellan guerillas destabilized the planetary governments, but lacked the ability to fully conquer them without Free Worlds League support. This created a no-man's land that was dubbed the Chaos March.

St. Ives Compact
In the fictional BattleTech universe, the St. Ives Compact was a minor Inner Sphere nation.

Genesis
The Compact began life as the St. Ives Mercantile League. That nation merged with four others to form the Capellan Confederation. Owing to its status as one of the five original founding nations, St. Ives became the St. Ives Commonality, one of five such districts within the Confederation.

The Compact was formed in 3029, as a direct result of the Fourth Succession War. Duchess Candace Liao, firstborn of Chancellor Maximillian Liao and his heir, fell in love with Justin Xiang Allard, a Federated Suns spy who had infiltrated the Capellan Confederation's spy agency. Rather than stay in the Capellan Confederation with a double-agent who helped conquer a third of it, she fled her home nation and took the St. Ives Commonality with her.

Given the destruction the Capellan military suffered at the hand of the Federated Suns, they were unable to do anything about the St. Ives secession. To further protect her fledgling nation, Prime Minister Candace allied with the Federated Suns, who provided military protection.

Clan invasion
The 3030s and '40s were an era of peace for St. Ives. Candace and Justin married and had four children, Kai, Cassandra, Kuan-Yin, and Quintus Allard-Liao.

When news of the Clan Invasion reached St. Ives, it was unknown exactly who was attacking. At the time, Kai was a member of the Armed Forces of the Federated Commonwealth and the unit he was in was rotated to the Clan front. The leaders of the Inner Sphere were called to a conference on Outreach to coordinate strategy with the others. There, Jaime Wolf revealed that the Clans were in fact the descendants of the Star League Defense Force that was led into exile by Commanding General Aleksandr Kerensky in 2784. In order to aid their Federated Commonwealth allies, Duchess Candace authorized the 1st St. Ives Lancers to help against the invasion.

After they had returned from Outreach, a Capellan assassin attempted to kill Candace and Justin. The assassin only succeeded in wounding Candance, but he/she was killed before Justin succumbed to his wounds. Candace traveled home to Sian and killed her sister Romano and the father of Romano's children. Rather than assume the throne herself, she allowed Romano's eldest, Sun-Tzu, to become Chancellor.

The Clan Invasion was halted in 3052 by the Truce of Tukayyid, well before Clan troops neared the St. Ives Compact.


Capellan-St. Ives war
In 3060, Chancellor Sun-Tzu determined that the time was right to reclaim St. Ives. Due to poisonous family politicking in the Federated Commonwealth, a new regime under Katherine Steiner-Davion had come to power that was much less sympathetic to St. Ives. Also, Sun-Tzu had been elected First Lord of the Star League and he used that power to its greatest effect.

A Capellan spy had worked her way up in the ranks of the St. Ives military, and, under her authority as a battalion commander, she launched an "unprovoked" assault against the Capellan Confederation. This was actually a plot by Sun-Tzu to make St. Ives appear the aggressor. Sun-Tzu called in SLDF peacekeepers, but some members of the St. Ives military attacked them, believing it to be the next step in a Sun-Tzu plot. This played perfectly into his hands, as it continued to portray St. Ives as the aggressor.

In 3061, at the Second Whitting Conference, the Star League member nations voted to withdraw peacekeepers from St. Ives because they saw that Sun-Tzu was simply using them to supplement his own forces, who were attempting to retake St. Ives. By that point most of the damage had been done, and Sun-Tzu simply replaced the SLDF troops with Capellan forces. Candace decided that defending the entire Compact was impossible, so she decided to defend the "lower," larger half of the crescent-shaped nation and abandoned the capital of St. Ives.

Soon enough, Candace and Sun-Tzu agreed upon a peace that was largely negotiated by Kuan-Yin Allard-Liao and former ComStar Precentor Martial Anastasius Focht. This agreement called for the Allard-Liao family to hold the St. Ives Commonality as their landhold and for St. Ives to have a greater say in military matters than any of the other Commonalities. With those compromises in place, the St. Ives Compact was officially reintegrated into the Capellan Confederation in 3063.


St. Ives Military Command
The SIMC was never large. It consisted of the prestigious St. Ives Lancers, the workhorse St. Ives Armored Cavalry, and St. Ives Janissaries (a unit modeled on the Ceti Hussars). SIMC doctrine was an amalgamation of strategy and tactics from the Capellan Confederation Armed Forces and the Armed Forces of the Federated Commonwealth. The SIMC also maintained the St. Ives Academy of Martial Sciences on St. Ives. The only military academy in the Compact, SIAMS was designed to train officers for the SIMC.

Tharkad
In the fictional BattleTech universe, Tharkad is the capital world of both the Lyran Alliance and at a later period in BattleTech's history, the Federated Commonwealth. Traditionally, the ruling Steiner family lives here.

Thakard was discovered in 2310 by an explorer group from nearby Donegal. Though the rugged mountains and windy, Arctic climate extending over most of its surface made it seem a dreary place for humans, the world also contained major radioactive and gem deposits. When Seth Marsden visited Tharkad in 2311, he found the cold, peaceful solitude to be breathtaking. So taken was he with the long nights and their spectacular aurora borealis that Marsden managed eventually to control and claim it as his own. He then began a program of massive importation of cold weather plants and animals from Terra and other worlds to spread across his new home.

He had soon created a world with large pine forests populated with deer, caribou, wolves, Skye boars, and Tharkan gazelle. In many ways, Tharkad is like the Arctic wilderness of Terra, except that its Arctic regions extend all the way down to the 30th latitude of the planet. There are five major continents and three major island chains on Tharkad. Tharkad City, the capital, is located on Bremen, the largest continent.

When Tharkad became the capital of the Lyran Commonwealth in 2407, space was cleared in the middle of a large forest ten kilometers to the north of Olympia for construction of the Capital city. The large and somberly elegant Royal Palace, Government House, and Royal Court form the three cusps of the Triad, a triangular complex of buildings all devoted to the administration of the Commonwealth. Today, the Triad includes over 300 buildings of all types and styles, whose purposes range from hospitals and houses of worship to apartments for nobles and Representatives from distant worlds and a botanical garden. It is a common saying that there is a building for every populated world in the Commonwealth somewhere in the Triad.

Even the fusion reactor operating deep beneath this modern city to generate power and heat cannot hold back the Tharkan cold. At the first sign of winter snowfall, the people, both rich and poor, begin unpacking clothing designed for the coming Tharkan blizzards and bone-chilling cold. Attending the Royal Court during a Tharkan winter is an unusual experience for those used to visiting courts in warmer climes. The Commonwealth nobility likes to dress in furs during the winter months, more out of necessity than vanity. Women wear long, fur-trimmed gowns, while the men wear fur hats and fur coats crisscrossed with chains of jewelry and precious metals. As people speak in the large and high-ceilinged Throne Room, their breaths sometimes rise in wisps of condensation to create a thin layer of shiny ice on the armor of the two Griffin BattleMechs guarding the Archon.

Set on the crest of nearby Mount Wotan is Asgard, the military headquarters of the Steiner armed forces. It is a fortress with one major tower flanked by four smaller ones. All five towers are heavily armed; below them are hangers for a regiment of 'Mechs, two infantry and tanks, and a Wing of AeroSpace Fighters. Built some 200 feet beneath the base of the mountain, is the headquarters of the Lyran Intelligence Corps. The LIC directs all operations from this hardened bunker, assigning agents to missions and monitoring the current political and military situation throughout the Inner Sphere. The walls of the bunker are two meters thick and reinforced by a charged-steel mesh. In addition to protecting the occupants and equipment against bombardment, the walls also absorb EMP should an attacker resort to nuclear weapons.

There are no roads leading to the Triad, and so all traffic must enter by VTOL craft or by one of the three separate subway systems that link the Triad with Olympia to the south, Asgard to the west, and the rest of Tharkad City five miles to the north.

During the Good Years, the planet underwent a boom in mining and steel manufacture. The Star League also established a military base with major storage facilities on the tropical Tatyana Islands during this era. With the fall of Star League, Tharkad's industries were plunged for a time into deep economic depression. With the need to produce weapons and other military equipment for the Succession Wars, Tharkad's industries revived.

Tharkad is also home to the Nagelring, the oldest and most prestigious military academy in the Commonwealth. Named after a sword used by an ancient German folk-hero, the academy was originally an official Star League academy. When the Steiner house forces took over after the Star League personnel left the Inner Sphere, they were surprised to find that many of the professors and instructors had decided to stay on.

The Nagelring soon began producing trained officers in all fields for the Commonwealth military. a sprawling university on Tharkad's Bremen continent, the academy has an extensive variety of training aids such as Chameleon training 'Mechs and two-seat Jenny Aerospace fighters. The academy also trains DropShip and JumpShip crews.

Located in Olympia, Tharkad University specializes in history. Though history may not seem of the same importance as scientific research, its study is crucial because 90% of the scientific knowledge now being 'discovered' was originally known for hundreds of years before the Succession Wars erased it from human memory. Katherine Steiner, the first Steiner Archon, was an alumna of Tharkad University and her government continues the policy of heavily funding it.

Most widely known of all the various arts colleges throughout the Commonwealth, is the Rewland college of Fine Arts on Tharkad. It was at Rewland that Jamison Henry, the famed-MechWarrior poet, first realized his talent.

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Ilyushin Il-86


The Ilyushin Il-86 is a medium-range wide-body jet airliner. Designed and tested by the Ilyushin design bureau in the 1970s, it was certificated by the Soviet aircraft industry during the 1970s and 1980s, manufactured jointly in the USSR and Poland, and marketed by the USSR. It was the first Soviet wide-body airliner and the world's second four-engined wide-body.

Only 106 Il-86s were built and only three of those were exported. The type was used overwhelmingly by Aeroflot and, after the collapse of the USSR, by successor post-Soviet airlines. Unusually for a Soviet airliner, the Il-86 saw only limited military service, though an airborne command post version did enter service.

The Il-86 typified the priorities and approaches applied to Soviet airliners as distinct from those applied to Western airliners. Emerging during the Brezhnev stagnation, it suffered from engines which were typical of the 1960s and spent a decade in development, failing to enter service for the Moscow Olympics, as had been intended.

In service, the Il-86 gained recognition as a very safe and reliable machine which did what had been asked of it. By 2008, more than half of all Il-86s had been retired.

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Robot Master

In the original Mega Man series, the term "Robot Master" refers to a special kind of robot or android that possesses a very advanced level of artificial intelligence. There are roughly one hundred thirty six Robot Masters. According to series canon, the Robot Master AI system is jointly credited to Dr. Thomas Light and Dr. Albert Wily. Most Robot Masters possess a unique identification code, consisting of a two-letter "series code" followed by one of N, No, or #, then a three-digit "serial number" (except for the Genesis Unit, which uses two digits).

Robot Masters have AIs vastly superior to the smaller, minor robots within the Mega Man universe. This, even more than their generally humanoid appearance (Sniper Joes are also humanoid in appearance, yet obviously inferior to Robot Masters) is what separates Robot Masters from other advanced robots. They often are designed with a particular strength or element in mind, thus allowing them to thrive in specific environments. Robot Masters tend to be programmed with human-like personalities and quirks, advanced enough to fool most people into believing them to think and act of their own accord. However, this is not true, as the Mega Man X series states X as the first robot to truly be able to think for himself. Robot Masters have a certain capability of thought and will--this allows them to be decisive on the battlefield, yet cannot generally operate beyond certain guidelines. There have been some exceptions, but every one of these occurrences has been explained in some way--such as the robot being faulty to begin with or could have malfunctioned due to damage incurred.

Another telling feature of a Robot Master is their special "weapons", which are generally specialized for that robot and his environment.

NOTE: Some of these Robot Masters have NetNavi counterparts in the MegaMan Battle Network series. The ones that have them will be noted.

It must also be noted that the term "Robot Master" is not used in Japan.

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Invention of radio

Within the timeline of radio, several people were involved in the invention of radio and there were many key inventions in what became the modern systems of wireless. Radio development began as "wireless telegraphy". Closely related, radio was developed along with two other key inventions, the telegraph and the telephone. During the early development of wireless technology and long after its wide use, disputes persisted as to who could claim credit for the invention of radio. The matter was important for economic, political and nationalistic reasons.

Physics of wireless signalling
Several different electrical, magnetic, or electromagnetic physical phenomena can be used to transmit signals over a distance without intervening wires. The various methods for wireless signal transmissions include:

Electrical Conduction through the ground, or through water.
Magnetic induction
Capacitive coupling
Electromagnetic waves
All these physical phenomena, as well as more speculative concepts such as conduction through air, have been tested for purposes of communication. Early researchers may not have understood or disclosed which physical effects were responsible for transmitting signals. Early experiments used the existing theories of the movement of charged particles through an electrical conductor. There was no theory of electromagnetic wave propagation to guide experiments before Maxwell's treatise and its verification by Hertz and others.

Capacitive and inductive coupling systems today are used only for short-range special purpose systems. The physical phenomenon used generally today for long-distance wireless communications involves the use of modulation of electromagnetic waves, which is radio.

Radio antennas radiate electromagnetic waves that can reach the receiver either by ground-wave propagation, by refraction from the ionosphere, known as sky-wave propagation, and occasionally by refraction in lower layers of the atmosphere (tropospheric ducting). The ground-wave component is the portion of the radiated electromagnetic wave that propagates close to the earth's surface. It has both direct-wave and ground-reflected components. The direct-wave is limited only by the distance from the transmitter to the horizon plus a distance added by diffraction around the curvature of the earth. The ground-reflected portion of the radiated wave reaches the receiving antenna after being reflected from the earth's surface. A portion of the ground-wave energy radiated by the antenna may also be guided by the earth's surface as a ground-hugging surface wave.


Early theories and experiments
Several scientists speculated that light might be some kind of wave connected with electricity or magnetism. Around 1830 Francesco Zantedeschi suggested a connection between light, electricity, and magnetism . In 1832 Joseph Henry performed experiments detecting electromagnetic effects over a distance of 200 feet and postulated the existence of electromagnetic waves. In 1846 Michael Faraday speculated that light was a wave disturbance in a force field".
Complete theory of electromagnetism
Based on the experimental work of Faraday and other physicists, James Clerk Maxwell developed the theory of electromagnetism that predicted the existence of electromagnetic waves. He did not transmit or receive radio waves.


Innovations and laboratory experiments
Hughes
In 1879, during experiments with his induction balance, David E. Hughes transmitted signals which he attributed to electromagnetic waves. Hughes' contemporaries claimed that the detected effects were due to electromagnetic induction. Hughes used his apparatus to transmit Morse code using a transmitter controlled by clockwork.


Hertz
Heinrich Rudolf Hertz was the experimental physicist who confirmed Maxwell's work in the laboratory. Hertz, though, did not devise a system for actual general use nor describe the application of the technology. From 1886 to 1888 inclusive, in his UHF experiments, he showed that the properties of radio waves were consistent with Maxwell’s electromagnetic theory. He demonstrated that radio radiation had all the properties of waves (now called electromagnetic radiation), and discovered that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation.

Hertz’s setup for a source and detector of radio waves (then called Hertzian waves or Hertz waves in his honor), comprised a primitive radio system capable of transmitting and receiving radio waves through free space.

Hertz used the damped oscillating currents in a dipole antenna, triggered by a high-voltage electrical capacitive spark discharge, as his source of radio waves. His detector in some experiments was another dipole antenna connected to a narrow spark gap. A small spark in this gap signified detection of the radio waves. When he added cylindrical reflectors behind his dipole antennas, Hertz could detect radio waves about 20 metres from the transmitter in his laboratory. He did not try to transmit further because he wanted to prove electromagnetic theory, not to develop wireless communications.

Hertz seemed uninterested in the practical importance of his experiments. He stated that "It's of no use whatsoever ... this is just an experiment that proves Maestro Maxwell was right - we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."

Asked about the ramifications of his discoveries, Hertz replied, "Nothing, I guess." Hertz also stated, "I do not think that the wireless waves I have discovered will have any practical application." Hertz died in 1894, so the art of radio was left to others to implement into a practical form. His discoveries would later be taken up by entrepreneurs looking to make their fortunes.


Tesla
Around July 1891, Nikola Tesla constructed various apparatus that produced between 15,000 to 18,000 cycles per second. Transmission and radiation of radio frequency energy was a feature exhibited in the experiments by Tesla which he proposed might be used for the telecommunication of information.

After 1892, Tesla delivered a widely reported presentation before the Institution of Electrical Engineers of London in which he suggested that messages could be transmitted without wires. Later, a variety of Tesla's radio frequency systems were demonstrated during another widely known lecture, presented to meetings of the National Electric Light Association in St. Louis, Missouri and the Franklin Institute in Philadelphia. According to the IEEE, "the apparatus that he employed contained all the elements of spark and continuous wave that were incorporated into radio transmitters before the advent of the vacuum tube". However, "he almost perversely rejected the notion of transmission by Hertzian waves, which he considered to be wasteful of energy."

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Deus Ex


Deus Ex (abbreviated DX and pronounced as IPA: /ˌdeɪəsˈɛks/, day-uss ex) is a cyberpunk-themed action role-playing game developed by Ion Storm Inc. and published by Eidos Interactive in the year 2000, which combines gameplay elements of first-person shooters with those of role playing games. The game received almost worldwide critical and industry acclaim, including being named "Best PC Game of All Time" in a 2007 poll carried out by UK gaming magazine PC Zone. It was a frequent candidate for and winner of Game of the Year awards, drawing praise for its pioneering designs in player choice and multiple narrative paths.

Set in a dystopian world during the 2050s, the central plot follows rookie United Nations Anti-Terrorist Coalition agent JC Denton, as he sets out to combat terrorist forces, which have become increasingly prevalent in a world slipping ever further into chaos. As the plot unfolds, Denton becomes entangled in a deep and ancient conspiracy, encountering fictional recreations of organizations such as Majestic 12, the Illuminati, and the Hong Kong Triads throughout his journey.

The game was successful commercially and was among the top selling computer role-playing games at the time of its release. First published for personal computers running Windows, Deus Ex was later ported to Macintosh systems, as well the PlayStation 2 game console, the latter under the title Deus Ex: The Conspiracy. Loki Games worked on a Linux version of the game, but the company went out of business before releasing it. A sequel to Deus Ex, titled Deus Ex: Invisible War, was released on December 2, 2003 for both Windows and the Xbox video game console. On November 26, 2007, it was confirmed that Eidos Montreal is developing a second sequel, Deus Ex 3.

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PIC microcontroller


PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1640 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to "Programmable Interface Controller", but shortly thereafter was renamed "Programmable Intelligent Computer".

PICs are popular with developers and hobbyists alike due to their low cost, wide availability, large user base, extensive collection of application notes, availability of low cost or free development tools, and serial programming (and re-programming with flash memory) capability.

Microchip announced on February 2008 the shipment of its six billionth PIC processor.

Core Architecture
The PIC architecture is distinctively minimalist. It is characterized by the following features:

separate code and data spaces (Harvard architecture)
a small number of fixed length instructions
most instructions are single cycle execution (4 clock cycles), with single delay cycles upon branches and skips
a single accumulator (W), the use of which (as source operand) is implied (ie is not encoded in the opcode)
All RAM locations function as registers as both source and/or destination of math and other functions.
a hardware stack for storing return addresses
a fairly small amount of addressable data space (typically 256 bytes), extended through banking
data space mapped CPU, port, and peripheral registers
the program counter is also mapped into the data space and writable (this is used to implement indirect jumps)
Unlike most other CPUs, there is no distinction between "memory" and "register" space because the RAM serves the job of both memory and registers, and the RAM is usually just referred to as the register file or simply as the registers.


Data Space (RAM)
PICs have a set of registers that function as general purpose RAM. Special purpose control registers for on-chip hardware resources are also mapped into the data space. The addressability of memory varies depending on device series, and all PIC devices have some banking mechanism to extend the addressing to additional memory. Later series of devices feature move instructions which can cover the whole addressable space, independent of the selected bank. In earlier devices (i.e., the baseline and mid-range cores), any register move has to be achieved via the accumulator.

To implement indirect addressing, a "file select register" (FSR) and "indirect register" (INDF) are used: A register number is written to the FSR, after which reads from or writes to INDF will actually be to or from the register pointed to by FSR. Later devices extended this concept with post- and pre- increment/decrement for greater efficiency in accessing sequentially stored data. This also allows FSR to be treated almost like a stack pointer.

External data memory is not directly addressable except in some high pin count PIC18 devices.

Code Space
All PICs feature Harvard architecture, so the code space and the data space are separate. PIC code space is generally implemented as EPROM, ROM, or flash ROM.

In general, external code memory is not directly addressable due to the lack of an external memory interface. The exceptions are PIC17 and select high pin count PIC18 devices.


Word Size
The word size of PICs can be a source of confusion. All PICs handle (and address) data in 8-bit chunks, so they should be called 8-bit microcontrollers. However, the unit of addressability of the code space is not generally the same as the data space. For example, PICs in the baseline and mid-range families have program memory addressable in the same wordsize as the instruction width, ie. 12 or 14 bits respectively. In contrast, in the PIC18 series, the program memory is addressed in 8-bit increments (bytes), which differs from the instruction width of 16 bits.

In order to be clear, the program memory capacity is usually stated in number of (single word) instructions, rather than in bytes.


Stacks
PICs have a hardware call stack, which is used to save return addresses. The hardware stack is not software accessible on earlier devices, but this changed with the 18 series devices.

Hardware support for a general purpose parameter stack was lacking in early series, but this greatly improved in the 18 series, making the 18 series architecture more friendly to high level language compilers.


Instruction Set
A PIC's instructions vary in number from about 35 instructions for the low-end PICs to over 80 instructions for the high-end PICs. The instruction set includes instructions to perform a variety of operations on registers directly, the accumulator and a literal constant or the accumulator and a register, as well as for conditional execution, and program branching.

Some operations, such as bit setting and testing, can be performed on any numbered register, but bi-operand arithmetic operations always involve W; writing the result back to either W or the other operand register. To load a constant, it is necessary to load it into W before it can be moved into another register. On the older cores, all register moves needed to pass through W, but this changed on the "high end" cores.

PIC cores have skip instructions which are used for conditional execution and branching. The skip instructions are: 'skip if bit set', and, 'skip if bit not set'. Because cores before PIC18 had only unconditional branch instructions, conditional jumps are implemented by a conditional skip (with the opposite condition) followed by an unconditional branch. Skips are also of utility for conditional execution of any immediate single following instruction.

The PIC architecture has no (or very meager) hardware support for automatically saving processor state when servicing interrupts. The 18 series improved this situation by implementing shadow registers which save several important registers during an interrupt.

In general, PIC instructions fall into 5 classes:

Operation on W with 8-bit immediate ("literal") operand. E.g. movlw (move literal to W), andlw (AND literal with W). One instruction peculiar to the PIC is retlw, load immediate into W and return, which is used with computed branches to produce lookup tables.
Operation with W and indexed register. The result can be written to either the W register (e.g. addwf reg,w). or the selected register (e.g. addwf reg,w).
Bit operations. These take a register number and a bit number, and perform one of 4 actions: set or clear a bit, and test and skip on set/clear. The latter are used to perform conditional branches. The usual ALU status flags are available in a numbered register so operations such as "branch on carry clear" are possible.
Control transfers. Other than the skip instructions previously mentioned, there are only two: goto and call.
A few miscellaneous zero-operand instructions, such as return from subroutine, and sleep to enter low-power mode.

Interrupt Latency
A very useful and unique property of PICs is that their interrupt latency is constant (it's also low: 3 instruction cycles). The delay is constant even though instructions can take one or two instruction cycles: a dead cycle is optionally inserted into the interrupt response sequence to make this true. External interrupts have to be synchronized with the four clock instruction cycle, otherwise there can be a one instruction cycle jitter. Internal interrupts are already synchronized.

The constant interrupt latency allows PICs to achieve interrupt driven low jitter timing sequences. An example of this is a video sync pulse generator. Other microcontrollers can do this in some cases, but it's awkward. The non-interrupt code has to anticipate the interrupt and enter into a sleep state before it arrives. On PICs, there is no need for this.

The three-cycle latency is increased in practice because the PIC does not store its registers when entering the interrupt routine. Typically, 4 instructions are needed to store the W-register, the status register and switch to a specific bank before starting the actual interrupt processing.


Limitations
The PIC architectures have several limitations:

Only a single accumulator
A small instruction set
Operations and registers are not orthogonal; some instructions can address RAM and/or immediate constants, while others can only use the accumulator
Memory must be directly referenced in arithmetic and logic operations, although indirect addressing is available via 2 additional registers
Register-bank switching is required to access the entire RAM of many devices, making position-independent code complex and inefficient
Conditional skip instructions are used instead of conditional branch instructions used by most other architectures
The following limitations have been addressed in the PIC18, but still apply to earlier cores:

Indexed addressing mode is very rudimentary.
Stack:
The hardware call stack is so small that program structure must often be flattened
The hardware call stack is not addressable, so pre-emptive task switching cannot be implemented
Software-implemented stacks are not efficient, so it is difficult to generate reentrant code and support local variables
Program memory is not directly addressable, and thus space-inefficient and/or time-consuming to access. (This is true of most Harvard architecture microcontrollers.)
With paged program memory, there are two page sizes to worry about: one for CALL and GOTO and another for computed GOTO (typically used for table lookups). For example, on PIC16, CALL and GOTO have 11 bits of addressing, so the page size is 2KB. For computed GOTOs, where you add to PCL, the page size is 256 bytes. In both cases, the upper address bits are provided by the PCLATH register. This register must be changed every time control transfers between pages. PCLATH must also be preserved by any interrupt handler.

Compiler development
These properties have made it difficult to develop compilers that target PIC microcontrollers. While several commercial compilers are available, in 2008, Microchip finally released their C compilers, C18, and C30 for their line of 18f 24f and 30/33f processors. By contrast, Atmel's AVR microcontrollers—which are competitive with PIC in terms of hardware capabilities and price, but feature a RISC instruction set—have long been supported by the GNU C Compiler.

Also, because of these properties, PIC assembly language code can be difficult to comprehend. Judicious use of simple macros can make PIC assembly language much more palatable, but at the cost of a reduction in performance. For example, the original Parallax PIC assembler "pasm" has macros which hide W and make the PIC look like a two-address machine. It has macro instructions like "mov b,a" (move the data from address a to address b) and "add b,a" (add data from address a to data in address b). It also hides the skip instructions by providing three operand branch macro instructions such as "cjne a,b,dest" (compare a with b and jump to dest if they are not equal).

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2009年1月21日星期三

Minimoog


The Minimoog is a monophonic analog synthesizer, invented by Bill Hemsath and Robert Moog. Released in 1970 by the original Moog Music, it was among the first widely available, portable and relatively affordable synthesizers.


Design
At its most basic, the Minimoog control panel can be broken up into 3 sections:

The sound generator (the VCO or voltage-controlled oscillator)
The filter (the VCF or voltage-controlled filter)
The amplifier (the VCA or voltage-controlled amplifier)
To produce a sound, the musician would first choose a sound shape to be generated from the VCO. The VCO provides a choice of several switchable waveforms:

triangle wave
sawtooth wave
a combination of the sawtooth and triangle wave/reverse sawtooth or ramp wave in oscillator three
square wave
two different width pulse waves
The sound then travels from the VCO to the VCF (voltage-controlled filter) where it can be shaped and sculpted, adding resonance.

Next, the sound travels to the voltage-controlled amplifer (VCA). The term "amplifier" can be a bit misleading to novices who might be thinking of a stereo amplifier with a single volume knob. In a modern synthesizer, a VCA actually has 4 separate volume knobs that control four different stages of the sound. For example, the first knob - the Attack volume - controls how loud a sound is when the key is first pressed: does it start immediately like a string being plucked? Or does it fade in gradually like a violin being softly bowed? (See the "Sound Basics" section of the general synthesizer article for more information on this.)

Part of the appeal of this instrument over the early modular Moogs was the fact that the Minimoog required no patch cables. While this imposed the signal flow limitation outlined above (VCO -> VCF -> VCA), there are ways to tweak the sound. For example, in reality, the Minimoog has six sound sources. Five of these sound sources pass to a mixer with independent level controls:

Three voltage-controlled oscillators (see above)
A noise generator
An external line input
And the VCF can itself be made to oscillate, thus comprising the Minimoog's sixth sound source.

The voltage-controlled filter (VCF) and voltage-controlled amplifier (VCA) each have their own ADSD envelope generator (or Attack-Decay-Sustain-Decay). Musicians who are familiar with more modern synthesizers might expect the last letter to be R for "Release" (as in ADSR). However, on the Minimoog, the envelopes are ADSD as the Decay setting also sets the time for what's regularly known as Release. In other words, there are 3 knobs to control 4 sections of the sound (most modern synths have 4 knobs, one for each section) -- a "shortcoming" that doesn't seem to diminish the Minimoog's popularity in any way. There is also a switch above the pitch and modulation wheels to engage the final decay stage as well as a switch for engaging the glide circuit.

The VCF is of transistor ladder type, a design patented by Moog music and even defended in court.
The output of the third oscillator and/or the noise generator can also be routed to the control voltage inputs of the filter and/or oscillators. The amount of pitch or filter modulation thus realized is controlled by the modulation wheel, which is the right one of the two plastic disks located to the left of the keyboard. In this way the third oscillator is frequently used as a low-frequency oscillator to control pitch.

The Minimoog can be controlled using its in-built, 44-note keyboard, which is equipped with modulation and pitch-bend wheels or by feeding in an external one-volt-per-octave pitch-control voltage and triggering the envelope generators with an inverted trigger. External pitch control does not pass through the glide circuit, nor is presented to the VCF tracking switches and thus, the external inputs were not designed for external keyboard control. The lowest note played on the keyboard determines the pitch, a condition that is referred to as low-note priority. The envelope generators do not retrigger unless all notes are lifted before the next note is played, an important characteristic which allows phrasing. The modulation and pitch-bending wheels were an innovation that many instrumentalists found to be extremely playable. The pitch-bend wheel is on the left of the modulation wheel. It is normally kept in the centered position. It is not spring-loaded; the player must return it to the centered position to play in tune. There is a delicate detent mechanism to help the player find the center position tactually. In sharp contrast to later synthesizers that also have pitch-bend wheels, there is no deadband near the center of the wheel's travel; the wheel produces minute changes in pitch no matter how slightly it is moved in either direction. The wheel can therefore be used to introduce slight vibrato or nuance, as well as accurate pitch changes. However, Moog later recommended adding a deadband mod and published this mod in their factory service notes. The detent mechanism can be somewhat adjusted in its strength.

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Oberheim Xpander

The Oberheim Xpander was an analog synthesiser launched by Oberheim in 1984 and discontinued in 1988. It was essentially a keyboardless, six-voice version of the Matrix-12. Utilizing Oberheim's Matrix Modulation technology, the Xpander combined analog audio generation (VCOs, VCF and VCAs) with the flexibility of digital controls logic.

The Xpander "Owner's Manual, First Edition" describes the technology as this:

"An analogy to the Matrix Modulation system might be all of those millions of wires that existed on the first modular synthesizers. As cumbersome as all of that wiring was, it alllowed the user to connect any input to any output, resulting in sophistication and flexibility unmatched by any programmable synthesizer...until now."


Architecture

Analog Components
Each of the six voices of the Xpander is completely independent. That is to say, each could be configured to create a different timbre - this is accomplished via the multi-patch mode which will be described below.

Starting at waveform generation, each voice has two voltage controlled oscillators (VCOs). Each of which is capable of generating sawtooth, triangle, pulse or noise waveforms. Furthermore, the "duty cycle" of the pulse width can be modulated as well. Although perhaps better known for subractive synthesis, the Xpander is also capable of frequency modulation (FM) synthesis by modulating VCO 1 with VCO2.

Moving on from the VCOs, the signal then passes through a multi-mode voltage controlled filter (VCF). The available modes on the filter are:

one-, two-, three- and four-pole low pass
one-, two and three-pole high pass
two- and four-pole band pass
two-pole notch
three-pole phase shift
two- and three-pole high pass plus one-pole low pass
two-pole notch plus one-pole low pass
three-pole phase shift plus one-pole low pass
From the filter, there are two sequential voltage controlled amplifiers (VCAs) through which the signal must pass. And finally the audio is delivered to a variety of outputs: mono, stereo and six independent outputs (corresponding to the six voices).


Digital Controls
Of those analog audio components (VCOs, VCF and VCAs), each can be modulated by several different digital controls.

ADSR Envelopes - each voice can have up to five envelope generators. Each envelope is of the standard Attack-Decay-Sustain-Release model (ADSR), with the addition of an initial Delay phase, thus making them DADSR envelopes, to be exact.
Low Frequency Oscillators (LFOs) - each voice can have up to five LFOs applied. Each LFO can have a different waveform: triangle, square, up-saw, down-saw, random or noise. Additionally, a sampling mode is provided, whereby an independent source (e.g. a different LFO) is sampled at a set frequency.
Lag Generator - the lag function is similar to portamento on traditional sythesizers. However, the lag modulation in the Xpander can be applied to any control or audio signal.
Ramp Generators - each voice can have up to four ramp generators. Similar to the attack portion of an ADSR envelope, the ramp generates a linear signal from zero to the user-defined ramp height.
Tracking Generators - there are three tracking generators available for each voice. The tracking generator provides a mapping from a control source (e.g. key range on the keyboard, or volume pedal, or mod wheel) to a modified output, based on the user-defined settings of the generator.

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Geiger–Müller tube

A Geiger-Müller tube (or GM tube) is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation, and typically produce an audible click for each. It was named for Hans Geiger who invented the device in 1908, and Walther Müller who collaborated with Geiger in developing it further in 1928.It is a type of gaseous ionization detector with an operating voltage in the Geiger plateau.

The Geiger counter is sometimes used as a hardware random number generator.

Description and operation
A Geiger-Müller tube consists of a tube filled with a low-pressure (~0.1 Atm) inert gas such as helium, neon or argon, in some cases in a Penning mixture, and an organic vapor or a halogen gas and contains electrodes, between which there is a voltage of several hundred volts, but no current flowing. The walls of the tube are either metal or the inside coated with metal or graphite to form the cathode while the anode is a wire passing up the center of the tube.

When ionizing radiation passes through the tube, some of the gas molecules are ionized, creating positively charged ions, and electrons. The strong electric field created by the tube's electrodes accelerates the ions towards the cathode and the electrons towards the anode. The ion pairs gain sufficient energy to ionize further gas molecules through collisions on the way, creating an avalanche of charged particles.

This results in a short, intense pulse of current which passes (or cascades) from the negative electrode to the positive electrode and is measured or counted.

Most detectors include an audio amplifier that produce an audible click on discharge. The number of pulses per second measures the intensity of the radiation field. Some Geiger counters display an exposure rate (e.g. mR·h), but this does not relate easily to a dose rate as the instrument does not discriminate between radiation at different energy


GM tubes
The usual form of tube is an end-window tube. This type is so-named because the tube has a window at one end through which ionizing radiation can easily penetrate. The other end normally has the electrical connectors. There are two types of end-window tubes: the glass-mantle type and the mica window type. The glass window type will not detect alpha radiation since it is unable to penetrate the glass, but is usually cheaper and will usually detect beta radiation and X-rays. The mica window type will detect alpha radiation but is more fragile.

Most tubes will detect gamma radiation, and usually beta radiation above about 2.5 MeV. Geiger-Müller tubes will not normally detect neutrons since these do not ionise the gas. However, neutron-sensitive tubes can be produced which either have the inside of the tube coated with boron or contain boron trifluoride or helium-3 gas. The neutrons interact with the boron nuclei, producing alpha particles or with the helium-3 nuclei producing hydrogen and tritium ions and electrons. These charged particles then trigger the normal avalanche process.


Quenching
The G.M. tube must produce a single pulse on entry of a single particle. It must not give any spurious pulse and recover quickly to the passive state. But unfortunately the positive Ar ions that eventually strike the cathode become neutral Ar atoms in an excited state by gaining electrons from the cathode. The excited atoms return to the ground state by emitting photons and these photons cause avalanches and hence spurious pulses.

To prevent the current from flowing continuously there are several techniques to stop, or quench the discharge. Quenching is important because a single particle entering the tube is counted by a single discharge, and so it will be unable to detect another particle until the discharge has been stopped, and because the tube is damaged by prolonged discharges.

External quenching uses external electronics to remove the high voltage between the electrodes. Self-quenching or internal-quenching tubes stop the discharge without external assistance, and contain a small amount of a polyatomic organic vapor such as butane or ethanol; or alternatively a halogen such as bromine or chlorine.

If the diatomic gas(quencher) is introduced in the tube, the positive Ar ions, during their slow motion to the cathode, would have multiple collisions with the quencher gas molecules and transfer their charge and some energy to them. Thus neutral Ar atoms would reach the cathode. The quencher gas ions in their turn reach the cathode, gain electrons thereform and move into excited states. But these excited molecules lose their energy not by photon emission but by dissociation into neutral quencher molecules. No spurious pulses are thus produced.


Invention of halogen tubes
The halogen tubes were invented by Sidney H. Liebson in 1947, and are now the most common form, since the discharge mechanism takes advantage of the metastable state of the inert gas atom to ionize the halogen molecule and produces a more efficient discharge which permits it to operate at much lower voltages, typically 400–600 volts instead of 900–1200 volts. It also has a longer life because the halogen ions can recombine whilst the organic vapor cannot and is gradually destroyed by the discharge process (giving the latter a life of around 108 events).



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Car Power Adaptor


12V Car Charger


PDA Travel Charger


Phone Car Charger


mp3 solar charger


12V Battery Chargers


Agu Fuse Holder


anl fuse holder


Universal Travel Charger


dell battery charger


dc car charger


ag13 button battery


dell cpi battery