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Magnetic Levitation Train

Magnetic levitation train

:Maglev can also mean general magnetic levitation. magnetic levitation magnetic levitation Magnetic levitation transport, or maglev, is a radically new form of transportation that suspends, guides and propels vehicles via electro-magnetic energy. Maglev technology is not “train” technology and is not compatible with conventional railroad tracks. Indeed, the science and engineering behind these ultra-safe and highly reliable ground transportation systems rivals the technological challenges once faced by America’s space program. Indeed, some high-speed maglevs (there are low-speed versions, as well) have top speeds comparable to turboprop and jet aircraft (500 – 580 km/h). It should also be emphasized that maglevs are complete transportation systems. The term maglev refers not only to the vehicles, but to the vehicle/guideway interaction; each being a unique design element specifically tailored to the other to create and precisely control magnetic levitation. The various technological approaches to maglev can be very similar or very different, depending upon the manufacturer. Due to the lack of physical contact between the track and the vehicle, the only friction exerted is that between the vehicles and the air. Consequently maglevs can potentially travel at very high speeds with reasonable energy consumption and noise levels. Systems have been proposed that operate at up to 650 km/h (404 mph), which is far faster than is practical with conventional rail transport. The very high maximum speed potential of maglevs make them competitors to airline routes of 1,000 kilometers (600 miles) or less. The world's first commercial application of a high-speed maglev line is the IOS (initial operating segment) demonstration line in Shanghai that transports people 30 km (18.6 miles) to the airport in just 7 minutes 20 seconds (top speed of 431 km/h or 268 mph, average speed 250 km/h or 150 mph). Other maglev applications worldwide are being investigated for feasibility. Recently, futurist American writer, Allan Silliphant, has proposed a fundamental model of urban metro transit that addresses the problem of going from a central point such as a city center, or an airport, to various points on the periphery of a circle around that center. Using Los Angeles, as an example, it can taken 2.5 hours to cross the city by auto. This is true of almost all great world cities. A deeply constructed maglev radial system, below any existing structures or utilites, can be bored out in virgin bedrock or undisturbed sediment. With a depth of 200 to 300 feet it would be possible to go almost anywhere in most metro areas. A transfer point in the middle will reduce the number of trains needed. Non-stop, cross metro tubes could also be constructed, next to the tube terminating in the center hub, avoiding a transfer. Present maglev speeds of even 200 miles per hour will greatly facilitate movement within an urban center. Surface maglev trains, can continue the outbound movement to the next urban center where a similar "hub and spoke" maglev deep tube system can be established. This can save many billions in fossil fuel consumption, especially if very quick access can be provided at the stations to rental cars and timely connection to public transport on the surface.

Technology

Shanghai :See also: Fundamental Technology Elements in the JR-Maglev article. :See also: Technology in the Transrapid article.

Three types of technology

There are three primary types of maglev technology:
- one that relies on superconducting magnets (electrodynamic suspension or EDS),
- one that relies on feedback controlled electromagnets (electromagnetic suspension or EMS),
- and a newer potentially more economical system that uses permanent magnets (Inductrack). Japan and Germany are active in maglev research, producing several different approaches and designs. In one design, the train can be levitated by the repulsive force of like poles or the attractive force of opposite poles of magnets. The train can be propelled by a linear motor on the track or on the train, or both. Massive electrical induction coils are placed along the track in order to produce the magnetic field necessary to propel the train. Unmoving magnetic bearings using purely electromagnets or permanent magnets are unstable because of Earnshaw's theorem; on the other hand diamagnetic and superconducting magnets can support a maglev stably. Conventional maglev systems are stabilized with electromagnets that have electronic stabilization. The weight of the large electromagnet is a major design issue. A very strong magnetic field is required to levitate a massive train, so conventional maglev research is using superconductor research for an efficient electromagnet.

Inductrack

A newer, perhaps less-expensive, system is called "Inductrack". The technique has a load-carrying ability related to the speed of the vehicle, because it depends on currents induced in a passive electromagnetic array by permanent magnets. In the prototype, the permanent magnets are in a cart; horizontally to provide lift, and vertically to provide stability. The array of wire loops is in the track. The magnets and cart are unpowered, except by the speed of the cart. Inductrack was originally developed as a magnetic motor and bearing for a flywheel to store power. With only slight design changes, the bearings were unrolled into a linear track. Inductrack was developed by physicist Richard Post at Lawrence Livermore National Laboratory. Inductrack uses Halbach arrays for stabilization. Halbach arrays are arrangements of permanent magnets that stabilize moving loops of wire without electronic stabilization. Halbach arrays were originally developed for beam guidance of particle accelerators. They also have a magnetic field on the track side only, thus reducing any potential effects on the passengers.

Spacecraft research

Currently, some space agencies, such as NASA, are researching the use of maglev systems to launch spacecraft. In order to do so, the space agency would have to get a maglev-launched spacecraft up to escape velocity, a task that would otherwise require elaborate timing of magnetic pulses (see coilgun) or a very fast, very powerful electric current (see railgun). Maglev-launching could also be used to make conventional launches more efficient: accelerating a craft up to mach 1 before firing the main engines can save 30% of the weight of the launch vehicle (Heller, 1998).

Pros and Cons of different technologies

Each implementation of the magnetic levitation principle for train-type travel involves advantages and disadvantages. Time will tell as to which principle, and whose implementation, wins out commercially. It must be noted, that the Inductrack and the Superconducting EDS are only levitation technologies. In both cases, vehicles need some other technology for propulsion. A linear motor is used for propulsion in Japanese Superconducting EDS MLX01 maglev. Inductrack, should it ever be developed into a commercial transport technology, will have to solve the propulsion problem, as well as the need to deliver the propulsion energy onboard (due to itself being a completely passive technology). A Jet engine or a linear motor are being considered. The German Transrapid electromagnetic maglev uses a linear motor for both levitation and propulsion. Neither Inductrack nor the Superconducting EDS are able to levitate vehicles at a standstill, although Inductrack provides levitation down to a much lower speed. Wheels are required for both systems, whereas EMS systems are wheel-less. The German Transrapid, Japanese HSST (Linimo), and Korean Rotem maglevs levitate at a standstill, with electricity delivered from guideway power rails. If guideway power is lost on the move, the Transrapid is still able to generate levitation down to 10 km/h speed, using the power from onboard batteries. This is not the case with the HSST and Rotem systems.

Existing Maglev Systems

Jet engine]]

Birmingham 1984–1995

The world's first commercial automated system was a low-speed maglev shuttle that ran from the airport terminal of Birmingham International Airport (UK) to the nearby Birmingham International railway station from 1984 to 1995. The length of the track was 600 m, and trains "flew" at an altitude of 15 mm. It was in operation for nearly eleven years, but obsolescence problems with the electronic systems made it unreliable in its later years and it has now been replaced with a cable-drawn system.

Berlin 1989–1991

In Berlin, the M-Bahn was built in the 1980s: a driverless maglev system with a 1.6 km track connecting three U-Bahn (metro) stations. Testing in passenger traffic started in August 1989, and regular operation started in July 1991. Because of traffic changes after the fall of the Berlin Wall, deconstruction of the line began only two months later and was completed in February 1992. The line was replaced by a regular U-Bahn line.

Transrapid

Transrapid, a German maglev company with a test track in Emsland, constructed the first operational high-speed conventional maglev railway in the world, the Shanghai Maglev Train from downtown Shanghai, China to the new Shanghai airport at Pudong. It was inaugurated in 2002. The highest speed achieved on the Shanghai track has been 501 km/h (311 mph), over a track length of 30 km. Transrapid uses EMS technology.

JR-Maglev

Japan has a test track in Yamanashi prefecture where test trains JR-Maglev MLX01 have reached 581 km/h (363 mph), faster than wheeled trains. These trains use superconducting magnets which allow for a larger gap, and repulsive-type "Electro-Dynamic Suspension" (EDS). In comparison Transrapid uses conventional electromagnets and attractive-type "Electro-Magnetic Suspension" (EMS). These "Superconducting Maglev Shinkansen", developed by the Central Japan Railway Co. ("JR Central") and Kawasaki Heavy Industries, are currently the fastest trains in the world, achieving a record speed of 581 km/h on December 2, 2003. If a proposed Chuo Shinkansen is built, connecting Tokyo to Osaka by maglev, this test track would be part of the line.

Linimo, Nagoya East Hill Line

The world's first commercial automated "Urban Maglev" system commenced operation in March 2005 in Japan. This is the nine-station 8.9 km-long Tobu-kyuryo Line Linimo, otherwise known as the Nagoya East Hill Line. The line has a minimum operating radius of 75 m and a maximum gradient of 6%. The linear-motor magnetic-levitated train has a top speed of 100 km/h. The line serves the local community as well as the Expo 2005 fair site. The trains were designed by the Chubu HSST Development Corporation, which also operates a test track in Nagoya. Urban-type maglevs patterned after the HSST have been constructed and demonstrated in Korea, and a Korean commercial version Rotem is now under construction in Daejeon and projected to go into operation by April of 2007.

FTA's UMTD program

In the US, the Federal Transit Administration (FTA) Urban Maglev Technology Demonstration program has funded the design of several low-speed urban maglev demonstration projects. It has assessed HSST for the Maryland Department of Transportation and maglev technology for the Colorado Department of Transportation. The FTA has also funded work by General Atomics at California University of Pennsylvania to demonstrate new maglev designs, the MagneMotion M3 and of the Maglev2000 of Florida superconducting EDS system. Other US urban maglev demonstration projects of note are the LEVX in Washington State and the Massachusetts-based Magplane.

Southwest Jiaotong University, China

On December 31, 2000, the first crewed high-temperature superconducting maglev was tested successfully at Southwest Jiaotong University, Chengdu, China. This system is based on the principle that bulk high-temperature superconductors can be levitated or suspended stably above or below a permanent magnet. The load was over 530 kg and the levitation gap over 20 mm. The system uses liquid nitrogen, which is very cheap, to cool the superconductor.

US patent, 1969

The first patent for a magnetic levitation train propelled by linear motors was US patent 3,470,828, issued in October 1969 to James R. Powell and Gordon T. Danby. The technology underlying it was invented by Eric Laithwaite, and described by him in "Proceedings of the Institution of Electrical Engineers", vol. 112, 1965, pp. 2361-2375, under the title "Electromagnetic Levitation". Laithwaite patented the linear motor in 1948.

Economics

High-speed maglevs can be expensive to build, but are comparable to the capital costs of building a traditional high-speed rail system from scratch, a highway system or a system of airports. More importantly, maglevs are significantly less expensive to operate and maintain (O&M) than traditional high-speed trains, planes or intercity buses. The data coming out of the Shanghai maglev demonstration project indicates that O&M costs are quite low, and are indeed covered by the current relatively low volume of 7,000 passengers per day. Ridership on this Pudong International Airport line is expected to rise dramatically once the line is extended from Longyang Road metro station all the way to Shanghai's downtown train depot. The Shanghai maglev cost US$1.2B to build which means that at 20,000 passengers a day at US$6 per passenger it will take around 30 years to pay off just the capital costs, not accounting for track maintenance, salaries and electricity. This computes to US$60 million per mile. The proposed Chuo Shinkansen line is estimated to cost approximately US$82 billion to build. However, when one considers the cost of airport construction ($70 billion for a new airport) and 8-lane Interstate highway systems that cost around US$50 million per mile, it becomes immediately apparent that maglev's costs are competitive, especially considering that they can handle much higher volumes of passengers per hour than airports or 8-lane highways and do it without introducing any air pollution along their ROW's (right of way). Low-speed maglevs (100 km/h, or 60 mph), such as the Japanese HSST or Korean Rotem, are expected to cost somewhere around US$30 million per mile. Besides offering improved O&M costs over other transit systems, these low-speed maglevs provide ultra-high levels of operational reliability and introduce zero noise or air pollution into dense urban settings. As maglev systems are deployed around the world, experts fully expect construction costs to drop as new construction methods are perfected.

Proposals

Shanghai-Hangzhou

China is considering maglev as a possible technology option for building a planned high-speed rail network to connect major cities, although the cost may make this impractical. Talks with Germany on the possible construction of a second Transrapid maglev rail linking Shanghai to Hangzhou have started. The Shanghai-Hangzhou maglev line would become the first inter-city Maglev rail line in commercial service in the world. The line will be an extension of the only other Maglev line in commercial service, the Shanghai airport Maglev line. The new line would have to be in service no later than 2010.

London-Glasgow

A maglev line has recently been proposed in the United Kingdom from London to Glasgow with several route options through the Midlands and Northeast, and is reported to be under favourable consideration by the government. [http://www.expall.com/ultraspeed.html] [http://www.guardian.co.uk/transport/Story/0,2763,1545279,00.html]

Honolulu

The city of Honolulu, Hawaii is said to be planning a Linimo class urban Maglev for its main mass transit train.

Philadelphia

In Philadelphia a maglev project is being studied that would connect to the city's international airport and urban core, with additional links being added in the planning stages.

San Diego

San Diego is considering a high-speed maglev line to the Imperial County Airport.

Southern California, Las Vegas

High-speed maglev lines between major cities of southern California and Las Vegas are also being studied. This plan was originally supposed to be part of a I-5 or I-15 expansion plan, but the federal government has ruled it must be separated from interstate work projects.

Baltimore-Washington

A 64 km project linking Camden Yard in Baltimore and Baltimore-Washington International (BWI) Airport to Union Station in Washington, D.C.

Pittsburgh

A 75 km project linking Pittsburgh Airport to Pittsburgh and its eastern suburbs.

Vactrain

:see also Swissmetro More exotic proposals include maglev lines through vacuum-filled tunnels (see Vactrain), where the absence of air resistance would allow extremely high speeds, up to 6000-8000 km/h (4000-5000 mph) according to some sources. Theoretically, these tunnels could be built deep enough to pass under oceans or to use gravity to assist the trains' acceleration. This would likely be prohibitively costly without major advances in tunnelling technology. Alternatives such as elevated concrete tubes with partial vacuums have been proposed to reduce these costs. If the trains topped out at around 8000 km/h (5000 mph), the trip between London and New York would take a breathtakingly short 54 minutes, effectively supplanting aircraft as the world's fastest mode of public transportation.

UniModal

UniModal is a proposed personal rapid transit system using Inductrack suspension to achieve average commute speeds of 160 km/h (100 mph) in the city.

References

External links

Transrapid

- [http://www.maglevboard.net The International Maglev Board]
- [http://www.transrapid.de/ Transrapid]
- [http://www.transrapid.de/en/medien/praesentation/1.html Slideshow on the Transrapid]
- [http://home.wangjianshuo.com/archives/20030809_pudong_airport_maglev_in_depth.htm Shanghai Pudong Airport Maglev in depth]
- [http://www.expall.com/ultraspeed.html The UK Ultraspeed Project]
- [http://www.magneetzweefbaan.nl/ Consortium Transrapid Nederland]
- [http://www.bwmaglev.com/ Baltimore-Washington Maglev Project]
- [http://www.calmaglev.org/ California Maglev Project]
- [http://www.magnetbahn-bayern.de/ Magnetbahn-bayern]
- [http://www.bmg-bayern.de/index.php Bmg-bayern]
- [http://faculty.washington.edu/~jbs/itrans/maglevq.htm Maglev Quicklinks]
- [http://www.swissmetro.com/ Swissmetro]

Japanese Maglev

Linear Motor Car

- [http://www.rtri.or.jp/rd/maglev/html/english/mlx01_E.html RTRI MLX01]
- [http://www.rtri.or.jp/rd/maglev/html/english/maglev_introduction_E.html RTRI Maglev R&D]
- [http://www.rtri.or.jp/rd/maglev/html/english/maglev_technology_E.html RTRI Technologies of Maglev] ----
- [http://www.pref.yamanashi.jp/cgi-bin/linear/index.cgi Yamanashi Linear Express Fan Club (in Japanese)]
- [http://mlx01.fc2web.com/ A site with MLX01 video and photo (in Japanese)]
- [http://gvideo.eizou.pref.yamanashi.jp/real/event/Linear2003.ram MLX01 Video] ----
- [http://www.rtri.or.jp/index.html Railway Technical Research Institute (RTRI)]
- [http://www.rtri.or.jp/rd/maglev/html/english/maglev_frame_E.html RTRI Maglev Systems Development Department]
- [http://jr-central.co.jp/english.nsf/index Central Japan Railway Company]
- [http://jr-central.co.jp/eng.nsf/english/chuo_shinkansen Central Japan Railway Company - Chuo Shinkansen]
- [http://jr-central.co.jp/eng.nsf/english/maglev Central Japan Railway Company - Superconducting Maglev]
- [http://linear.jr-central.co.jp/ Central Japan Railway Company - Linear Express]
- [http://www.linear-chuo-exp-cpf.gr.jp/ Linear Chuo Express (in Japanese)]
- [http://www.linear-chuo-exp-cpf.gr.jp/kidsweb/index.html Linear Chuo Express for kids website (in Japanese)]
- [http://www.pref.aichi.jp/kotsu/rinia/index_e.html Linear Chuo Shinkansen Project] ----
- [http://www.pref.yamanashi.jp/cgi-bin/linear/link.cgi Other Japanese Maglev Links]

Linimo

- [http://www.linimo.jp/ Linimo]

Maglev train companies

These websites contain further information provided by companies building maglev trains (alphabetical order).
- [http://www.ga.com/atg/ems.php General Atomics] (USA)
- [http://hsst.jp/ HSST] (Japan)
- [http://www.maglev2000.com/ Maglev2000] (USA)
- [http://www.rotem.co.kr/ Rotem] (Korea)
- [http://www.transrapid.de/ Transrapid International] (Germany)
- [http://www.expall.com/ultraspeed.html Ultraspeed] (UK; uses Transrapid technology)
- [http://www.swissmetro.com/ Swissmetro] (Switzerland)
- [http://www.boeing.com/defense-space/space/maglev/index.html#1 Boeing]

General

- [http://www.fra.dot.gov/us/content/200 Federal Railroad Administration - MAGLEV]
- [http://www.fra.dot.gov/downloads/RRdev/maglev-sep05.pdf Report to Congess: Costs and Benefits of Magnetic Levitation]
- [http://urbanmaglev.org Urban Maglev Interest Group]
- [http://www.maglev.de Maglev in Asia (China, Shanghai), Japan (Yamanashi) and Germany (Munich; TVE)]
- [http://www.llnl.gov/str/Post.html Lawrence Livermore's InducTrack Site]
- UniModal personal rapid transit system
- [http://www.railserve.com/maglev.html Magnetic Levitation for Transportation] Category:Electric railways Category:Electric vehicles Category:Magnetic devices Category:Monorails ja:磁気浮上式鉄道

Magnetic levitation

Magnetic levitation is the process by which an object is suspended above another object with no other support but magnetic fields. The electromagnetic force is used to counteract the effects of the gravitational force. Earnshaw's theorem proved conclusively that it is not possible to levitate using static, macroscopic, "classical" electromagnetic fields. The forces acting on an object in any combination of gravitational, electrostatic, and magnetostatic fields will make the object's position unstable. However, several possibilities exist to make levitation viable, by violating the assumptions of the theorem.

Methods

Diamagnetism

A substance which is diamagnetic repels a magnetic field. Earnshaw's theorem does not apply to diamagnets since they behave in the opposite manner of a typical magnet (relative permeability μ_r < 1). All materials have diamagnetic properties, but the effect is very weak, and usually overcome by the object's paramagnetic or ferromagnetic properties. A material which is predominantly diamagnetic will be repelled by a magnet, although typical objects only feel a very small force. This can be used to levitate light pieces of pyrolytic graphite or bismuth above a moderately strong permanent magnet. As water is predominantly diamagnetic, this property has been used to levitate water droplets and even live animals, such as a grasshopper and a frog. The magnetic fields required for this are very high, however; in the range of 16 teslas, and create significant problems if ferromagnetic materials are nearby. See also: Diamagnetic levitation

Superconductivity

Due to the Meissner effect, a superconductor also expels magnetic fields (μ_r = 0), much better than a diamagnet. Due to this (and flux pinning) the magnet is held at a fixed distance from the superconductor or vice versa. This is the principle in place behind EDS (electrodynamic suspension) magnetic levitation trains.

Feedback control systems

If the position and trajectory of the object to be levitated can be measured, the field of nearby electromagnets (or even the position of permanent magnets) can be continuously adjusted via feedback control systems to keep the levitated object in the desired position. This is the principle in place behind common tabletop levitation demonstrations, which use a beam of light to measure the position of an object. The electromagnet (arranged to pull the ferromagnetic object upwards) is turned off whenever the beam of light is broken by the object, and turned back on when it falls beyond the beam. This is a very simple example, and not very robust. Much more complicated and effective measurement, magnetic, and control systems are possible. This is also the principle upon which EMS (electromagnetic suspension) magnetic levitation trains are based. The train wraps around the track, and is pulled upwards from below.

Oscillating fields

A conductor can be levitated above an electromagnet with a high frequency alternating current flowing through it. This causes any regular conductor to behave like a diamagnet, due to the eddy currents generated in the conductor. Since the eddy currents create their own fields which oppose the magnetic field, the conductive object is repelled from the electromagnet. This effect requires high frequencies and non-ferromagnetic conductive materials like aluminium or copper, as the ferromagnetic ones are attracted to the electromagnet.

Halbach arrays

Another way of stabilizing the repulsive effect is to use fields that move in space, rather than just time. This effect can be demonstrated with a rotating conductive disc and a permanent magnet, which will repel each other. This is the principle of the Inductrack maglev train system, which avoids the problems inherent in both the EMS and EDS systems. It uses only permanent magnets (in a Halbach array) and unpowered conductors to provide levitation. The only restriction is that the train must already be moving at a few km/h (about human walking speed) to levitate. The energy for suspension comes entirely from forward motion, efficiency is good, and no extremely low temperature suspension magnets are required. Halbach arrays are also well-suited to magnetic levitation of gyroscope, motor and generator spindles.

Gyroscopic motion

The reason a permanent magnet suspended above another magnet is unstable is because the levitated magnet will easily overturn and the force will become attractive. If the levitated magnet is rotated, the gyroscopic forces from spinning and precession can prevent the magnet from overturning. This is the principle behind the Levitron toy. See external links for more details.

External links

- [http://my.execpc.com/~rhoadley/maglev.htm How can you magnetically levitate objects?]
- [http://www.levitron.com/physics.html The Physics of the Levitron (gyroscopic)]
- [http://www.physics.ucla.edu/marty/levitron/ Spin stabilized magnetic levitation - A simple theory of gyroscopic stability against flipping proposed by the manufacturer and others is not sufficient to explain the stability]
- [http://www.lauralee.com/physics.htm Frequently Asked Questions About THE LEVITRON]
- [http://sprott.physics.wisc.edu/demobook/chapter5.htm Levitated aluminum ball (oscillating field)]
- [http://www.oz.net/~coilgun/levitation/home.htm Instructions to build an optically-triggered feedback maglev demonstration]
- [http://www.hfml.sci.kun.nl/levitation-movies.html Videos of magnetically levitated objects, including frogs and grasshoppers] Category:Magnetism

Friction

Friction is the force that opposes the relative motion or tendancy of such motion of two surfaces in contact. The classical linear approximation of the force of friction known as Coulomb friction (named for Charles-Augustin de Coulomb) is expressed as: :

F_ = \frac\cdot F_\cdot \mu_ \,

where :

v \,

=velocity of surface :

F_f  \,

= the force of friction :

F_n \,

= the force normal to the contact surface :

\mu_f \,

= the coefficient of friction This very simple, yet incomplete, representation of friction is adequate for the analysis of many physical systems.

Coefficient of Friction

The coefficient of friction (also known as the frictional coefficient or the friction coefficient) is a scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used -- for example, ice on metal has a low coefficient of friction (they slide past each other easily), while rubber on pavement has a high coefficient of friction (they do not slide past each other easily). It is also important to discriminate between sliding (dynamic) friction and static friction. For sliding friction, the force of friction does not vary with the area of contact between the two objects. This means that sliding friction does not depend on the size of the contact area. However, for static friction where there is an element of adhesion, the contact area does matter. For a race car, wide wheels are used to increase the static friction with the road. However, once adhesion is lost, the size of the contact area is no longer relevant. The force of friction is always exerted in a direction that opposes movement. For example, a chair sliding to the right across a floor experiences the force of friction in the left direction. The coefficient of friction is an empirical measurement -- it has to be measured experimentally, and cannot be found through calculations. Rougher surfaces tend to have higher values. Most dry materials in combination give friction coefficient values from 0.3 to 0.6. It is difficult to maintain values outside this range. A value of 0.0 would mean there is no friction at all. Rubber in contact with other surfaces can yield friction coefficients from 1.0 to 2.0. A system with "interlocking teeth" between surfaces may be indistinguishable from friction, if the "teeth" are small, such as the grains on two sheets of sandpaper or even molecular sized "teeth". Saying that rougher surfaces experience more friction sounds safe enough - two pieces of coarse sandpaper will obviously be harder to move relative to each other than two pieces of fine sandpaper. However, if two pieces of flat metal are made progressively smoother, you will reach a point where the resistance to relative movement increases, due to a vacuum between the two surfaces. If you make them very flat and smooth, and remove all surface contaminants in a vacuum, the smooth flat surfaces will actually adhere to each other, making what is called a cold weld. Once you reach a certain degree of mechanical smoothness, the frictional resistance is found to depend on the nature of the molecular forces in the area of contact, so that substances of comparable "smoothness" can have significantly different coefficients of friction.

Types of Friction

Static Friction

Static friction occurs when the two objects are not moving relative to each other (like a desk on the ground). The coefficient of static friction is typically denoted as μ_s. The initial force to get an object moving is often dominated by static friction.
- Rolling friction occurs moving relative to each other and one "rolls" on the other (like a car's wheels on the ground). This is classified under static friction because the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relative to the ground. The coefficient of rolling friction is typically denoted as μ_r.

Kinetic Friction

Kinetic friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μ_k, and is usually less than the coefficient of static friction. Examples of kinetic friction:
- Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction.
- Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction. When an object is pushed along a surface with coefficient of friction μ_k and a perpendicular (normal) force acting on that object directed towards the surface of magnitude N, then the energy loss of the object is given by: :

U = N \mu_k d \,

Where d is the distance travelled by the object whilst in contact with the surface. This equation is identical to Energy Loss = Force x Distance as the frictional force is a non-conservative force. Note, this equation only applies to kinetic friction, not rolling friction. Physical deformation is associated with friction. While this can be beneficial, as in polishing, it is often a problem, as the materials are worn away, and may no longer hold the specified tolerances. The work done by friction can translate into deformation and heat that in the long run may affect the surface's specification and the coefficient of friction itself. Friction can in some cases cause solid materials to melt. Friction may occur between solids, gases and fluids or any combination thereof. See aerodynamics and hydrodynamics.

Reducing Friction

Devices

Devices, such as ball bearings can change sliding friction into the less significant rolling friction.

Techniques

One technique used by railroad engineers is to back up the train to create slack in the linkages between cars. This allows the train to pull forward and only take on the static friction of one car at a time, instead of all cars at once, thus spreading the static frictional force out over time.

Lubricants

A common way to reduce friction is by using a lubricant, such as oil, that is placed between the two surfaces, often dramatically lessening the coefficient of friction. The science of friction and lubrication is called tribology. Superlubricity, a recently-discovered effect, has been observed in graphite: it is the substantial decrease of friction between two sliding objects, approaching zero levels - a very small amount of frictional energy would be dissipated due to electronic and/or atomic vibrations. Lubricants to overcome friction need not always be thin, turbulent fluids or powdery solids such as graphite and talc; acoustic lubrication actually uses sound as a lubricant.

Lubricant technology

AF coatings (anti-friction coatings) have been successfully used for years as an element of heavy-duty lubrication. Typically used for applications where a permanent lubricating film is needed for metal-to-plastic or plastic-to-plastic lubrication, AF coating technology offers an economic solution to a wide range of engineering problems. The usage of AF coatings, such as Molykote® brand or other prominent anti-friction coating brand, is most successful when requirements for wear and corrosion protection and optimal coefficient of friction are properly met. A low, high, or even constant coefficient of friction is achievable, if the appropriate application and type of AF coating is utilized. A firm, completely dry, and non-contaminating lubricating film results once it is properly prepared and applied. The AF coating generally consists of the resin (epoxy, phenolic, and silicone) - a base material, which adheres well to the surface. Solid lubricants such as MoS₂, PTFE, polyamide, polyethylene, and graphite are set in this base material, passing on the anti-friction properties of an AF coating. Water-dilutable AF coatings, coatings low in solvents, as well as non-combustible or electrostactically sprayable AF coatings, are now being offered to help save energy and meet environmental protection regulations. Many products using AF technology offer corrosion protection in excess of normal industrial requirements, while some are unaffected by fuels, solvents, or oils. Application is typically simple: preferably by spraying, dipping, or brushing on thoroughly degreased metal surfaces. The drying and curing times are short (between three minutes for air-drying and sixty minutes for oven cured coatings).

Products of friction

According to the law of conservation of energy, no energy should be lost due to friction. The kinetic energy lost is transformed primarily into heat and/or motion of other objects and fluids. An airplane will heat and accelerate the air as it passes. A submarine will do the same to the water. In some cases, the "other object" to be accelerated may be the Earth. A sliding hockey puck will come to rest due to friction both by changing its energy into heat and accelerating the Earth in its direction of travel (by an immeasurable amount). Since heat and fluid motion quickly dissipate and the change in velocity of the Earth can't be seen, many early philosophers, such as Aristotle, concluded that moving objects lose energy without an opposing force.

References

- Category:Force ko:마찰력 ja:摩擦

Energy

Energy is a measure of being able to do work. This is a fundamental concept pertaining to the ability for action. In physics, it is a quantity that every physical system possesses. This quantity is not absolute but relative to a state of the system known as its reference state or reference level. The energy of a physical system is defined as the amount of mechanical work that the system can produce if it changes its state to its reference state; for example if a liter of water cools down to 0°C or if a car hits a tree and decelerates from 120 km/h to 0 km/h. Energy of an object can be in several forms, potential—due to the position of the object relative to other objects; kinetic—energy because of its motion; chemical—due to chemical bonds between atoms that make up the substance; electrical—due to its charge; thermal—due to its heat; and nuclear—due to the instability of the nuclei of its atoms. In the case where the "object" is an electromagnetic wave or light, then radiant energy can also be defined. One form of energy can be readily transformed into another; for instance, a battery converts chemical energy into electrical energy, which can be converted into thermal energy. Similarly, potential energy is converted into kinetic energy of moving water and turbine in a dam, which in turn transforms into electric energy by generator. The law of conservation of energy states that in a closed system the total amount of energy, corresponding to the sum of a system's constituent energy components, remains constant. This law follows from translational symmetry of time (that is, independence of any physical process on the moment it started). Some works (thus some forms of energy) are not easily measured by the unaided observer. The term 'energy' is also used in a spiritual or non-scientific way that cannot be quantified, to make certain prepositions look like they are more plausible, by imitating the scientific terminology. Usually this has something to do with mystical and/or healing type references such as acupuncture and reiki.

Forms of Energy

Below is a list of different energy forms. Lotka (1956, p. 5) asked an interesting question about what defines an energy form. :"We are equipped with two separate and distinct senses, the one responding to electromagnetic waves ranging from about 4×10^-4 to 8×10^-4 mm., light waves; the other to somewhat longer waves otherwise of the same character, heat waves. Accordingly we have two separate terms in our language light and heat, to denote two phenomena which, objectively considered, are not separated by any line of division, but merge into one another by gradual transition. Here the question might be raised whether an electromagnetic wave of a length of 9×10^-4 mm. is a light wave or a heat wave." That is to ask, if all forms of energy are defined in terms of infinitesimal increments of the wave spectrum, what makes one form of energy different to another?
- Kinetic energy: the energy of moving objects
- Thermal energy: the energy associated with heat
- Sound energy: the energy of compression waves
- Electrical energy: the energy of moving charged particles
- Potential Energy: the energy that an object has due to position; also known as stored energy
- Chemical energy: the stored energy of chemical substances
- Nuclear energy: the stored energy of the atomic nucleus
- Radiant energy: the energy of electromagnetic waves, including light

Units

SI

The SI unit for both energy and work is the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton-metre and, in terms of SI base units:

1\ \mathrm = 1\ \mathrm \left( \frac \right ) ^ 2 = 1\ \frac

An energy unit that is used in particle physics is the electronvolt (eV). One eV is equivalent to 1.60217653×10⁻¹⁹ J. In spectroscopy the unit cm^-1 = 0.0001239 eV is used to represent energy since energy is inversely proportional to wavelength from the equation

E = h \nu = h c/\lambda

. (Note that torque, which is typically expressed in newton-metres, has the same dimension and this is not a simple coincidence: a torque of 1 newton-metre applied on 1 radian requires exactly 1 newton-metre=joule of energy.)

Other units of energy

In cgs units, one erg is 1 g cm² s⁻², equal to 1.0×10⁻⁷ J. Another obsolete metric unit is the litre-atmosphere (101.325 J). The imperial/US units for both energy and work include the foot-pound force (1.3558 J), the British thermal unit (Btu) which has various values in the region of 1055 J, and the horsepower-hour (2.6845 MJ). The energy unit used for everyday electricity, particularly for utility bills, is the kilowatt-hour (kW h), and one kW h is equivalent to 3.6×10⁶ J (3600 kJ or 3.6 MJ; the metric units usually are self-consistent, and this particular one may seem arbitrary; it's not, the metric measurement for time is the second, and there are 3,600 seconds in an hour -- in other words, 1 kW second = 1 kJ, but the kW h is a more convenient unit for everyday use). The calorie is mainly used in nutrition and equals the amount of heat necessary to raise the temperature of one kilogram of water by 1 degree Celsius, at a pressure of 1 atm. This amount of heat depends somewhat on the initial temperature of the water, which results in various different units sharing the name of "calorie" but having slightly different energy values. It is equal to 4.1868 kJ. The calories used for food energy in nutrition are the large calories based on the kilogram rather than the gram, often identified as food calories. These are sometimes called kilocalories with that calorie being the small calorie based on the gram, and as a result the prefixes are generally avoided for the large calories (i.e., 1 kcal is 4.184 kJ, never 4.184 MJ, even if "calories" are also used for the other, larger unit in the same document or the same nutrition label). Food calories are sometimes noted as Calories (1000 calories) or simply abbreviated Cal with the capital C, but that convention is more often found in chemistry or physics textbooks—which do not use these large calories—than it is in real-world applications by those who do use these calories. (This convention is also, of course, useless when the word calorie appears in a location where it would ordinarily be capitalized, as at the beginning of a sentence or in the first column of a nutrition label as a substitute for the quantity being measured, which is energy, when all the other quantities such as "Iron" and "Sugars" are also capitalized.)

Transfer of energy

Work

Main article: mechanical work. Work is a defined as a path integral of force F over distance s: :

W = \int \mathbf \cdot \mathrm\mathbf

The equation above says that the work (

W

) is equal to the integral of the dot product of the force (

\mathbf

) on a body and the infinitesimal of the body's position (

\mathbf

Heat

Main article: Heat. Heat is the common name for thermal energy of an object that is due to the motion of the atoms and molecules that constitute the object. This motion can be translational (motion of molecules or atoms as a whole; vibrational - relative motion of atoms within molecules or rotational motion. It is the form of energy which is usually linked with a change in temperature or in a change in phase of matter. In chemistry, heat is the amount of energy which is absorbed or released when atoms are rearranged between various molecules by a chemical reaction. The relationship between heat and energy is similar to that between work and energy. Heat flows from areas of high temperature to areas of low temperature. All objects (matter) have a certain amount of internal energy that is related to the random motion of their atoms or molecules. This internal energy is directly proportional to the temperature of the object. When two bodies of different temperature come in to thermal contact, they will exchange internal energy until the temperature is equalised. The amount of energy transferred is the amount of heat exchanged. It is a common misconception to confuse heat with internal energy, but there is a difference: the change of the internal energy is the heat that flows from the surroundings into the system plus the work performed by the surroundings on the system. Heat Energy is transferred in three different ways: conduction, convection and/or radiation.

Conservation of energy

The first law of thermodynamics says that the total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. This law is used in all branches of physics, but frequently violated by quantum mechanics (see off shell). Noether's theorem relates the conservation of energy to the time invariance of physical laws. An example of the conversion and conservation of energy is a pendulum. At its highest points the kinetic energy is zero and the potential gravitational energy is at its maximum. At its lowest point the kinetic energy is at its maximum and is equal to the decrease of potential energy. If one unrealistically assumes that there is no friction, the energy will be conserved and the pendulum will continue swinging forever. (In practice, available energy is never perfectly conserved when a system changes state; otherwise, the creation of perpetual motion machines would be possible.) Another example is a chemical explosion in which potential chemical energy is converted to kinetic energy and heat in a very short time.

Types of energy

All forms of energy: thermal, chemical, electrical, radiant, nuclear etc. can be in fact reduced to kinetic energy or potential energy. For example thermal energy is essentially kinetic energy of atoms and molecules; chemical energy can be visualized to be the potential energy of atoms within molecules; electrical energy can be visualized to be the potential and kinetic energy of electrons; similarly nuclear energy is the potential energy of nucleons in atomic nucleii.

Kinetic energy

Main article: Kinetic energy. Kinetic energy is the portion of energy related to the motion. :

E_k = \int \mathbf \cdot \mathrm\mathbf

The equation above says that the kinetic energy (

E_k

) is equal to the integral of the dot product of the velocity (

\mathbf

) of a body and the infinitesimal of the body's momentum (

\mathbf

). For non-relativistic velocities, that is velocities much smaller than the speed of light, we can use the Newtonian approximation :

E_k = \begin \frac \end mv^2

where E_k is kinetic energy m is mass of the body v is velocity of the body At near-light velocities, we use the correct relativistic formula: :

E_k = m c^2 (\gamma - 1) = \gamma m c^2 - m c^2 \;\!

\gamma = \frac

where v is the velocity of the body m is its rest mass c is the speed of light in a vacuum, which is approximately 300,000 kilometers per second

\gamma m c^2 \,

is the total energy of the body

m c^2 \,

is again the rest mass energy. See also, E=mc². In the form of a Taylor series, the relativistic formula for can be written as: :

E_k = \frac mv^2 - \frac \frac  + \cdots

Hence, the second and higher terms in the series correspond with the "inaccuracy" of the Newtonian approximation for kinetic energy in relation to the relativistic formula. However, the phrase "conservation of energy" is often confusing to a non scientist. This is so, because of the common usage of the terms "save energy" or conserve energy" used in campaigns for conservation of energy resources like electricity or fossil fuels.

Potential energy

Main article: Potential energy. In contrast to kinetic energy, which is the energy of a system due to its motion, or the internal motion of its particles, the potential energy of a system is the energy associated with the spatial configuration of its components and their interaction with each other. Any number of particles which exert forces on each other automatically constitute a system with potential energy. Such forces, for example, may arise from electrostatic interaction (see Coulomb's law), or gravity. In an isolated system consisting of two stationary objects that exert a force

f(x)

on each other and lay on the x-axis, their potential energy is most generally defined as :

E_p = -\int f(x) \, dx

where the force between the objects varies only with distance

x

and is integrated along the line connecting the two objects. To further illustrate the relationship between force and potential energy, consider the same system of two objects situated along the x-axis. If the potential energy due to one of the objects at any point

x

U(x)

, then the force on the that object

x

is :

f(x) = -\frac

This mathematical relationship demonstrates the direct connection between force and potential energy: the force between two objects is in the direction of decreasing potential energy, and the magnitude of the force is proportional to the extent to which potential energy decreases. A large force is associated with a large decrease in potential energy, while a small force is associated with a small decrease in potential energy. Notice how, in this case, the force on an object depends entirely on its potential energy. These two relationships – the definition of potential energy based on force, and the dependence of force on potential energy – show how the concepts of force and potential energy are intimately linked: if two objects do not exert forces on each other, there is no potential energy between them. If two objects do exert forces on each other, then potential energy naturally arises in the system as part of the system's total energy. Since potential energy arises from forces, any change in the system's spatial configuration will either increase or decrease the system's potential energy as the objects are repositioned. When a system moves to a lower potential energy state, energy is either released in some form or converted into another form of energy, such as kinetic energy. The potential energy can be "stored" as gravitational energy, elastic energy, chemical energy, rest mass energy or electrical energy, but arises in all cases from the spatial positioning and interaction of objects within a system. Unlike kinetic energy, which exists in any moving body, potential energy exists in any body which is interacting with another object. For example a mass released above the Earth initially has potential energy resulting from the gravitational attraction of the Earth, which is transferred to kinetic energy as the gravitational force acts on the object and its potential energy is decreased as it falls. Equation: :

E_p = mgh \;

where m is the mass, h is the height and g is the value of acceleration due to gravity at the Earth's surface (see gee).

Internal energy

Main article: Internal energy. Internal energy is the kinetic energy associated with the motion of molecules, and the potential energy associated with the rotational, vibrational and electric energy of atoms within molecules. Internal energy, like energy, is a quantifiable state function of a system.

History

In the past, energy was discussed in terms of easily observable effects it has on the properties of objects or changes in state of various systems. Basically, if something changed, some sort of energy was involved in that change. As it was realized that energy could be stored in objects, the concept of energy came to embrace the idea of the potential for change as well as change itself. Such effects (both potential and realized) come in many different forms; examples are the electrical energy stored in a battery, the chemical energy stored in a piece of food, the thermal energy of a water heater, or the kinetic energy of a moving train. To simply say energy is "change or the potential for change", however, misses many important examples of energy as it exists in the physical world. The concept of energy and work are relatively new additions to the physicist’s toolbox. Neither Galileo nor Newton made any contributions to the theoretical model of energy, and it was not until the middle of the 19th century that these concepts were introduced. The development of steam engines required engineers to develop concepts and formulas that would allow them to describe the mechanical and thermal efficiencies of their systems. Engineers such as Sadi Carnot and James Prescott Joule, mathematicians such as Émile Claperyon and Hermann von Helmholtz , and amateurs such as Julius Robert von Mayer all contibuted to the notions that the ability to perform certain tasks, called work, was somehow related to the amount of energy in the system. The nature of energy was elusive, however, and it was argued for some years whether energy was a substance (the caloric) or merely a physical quantity, such as momentum. William Thomson (Lord Kelvin) amalgamated all of these laws into his laws of thermodynamics, which aided in the rapid development of energetic descriptions of chemical processes by Rudolf Clausius, Josiah Willard Gibbs, Walther Nernst. In addition, this allowed Ludwig Boltzmann to describe entropy in mathematical terms, and to discuss, along with Jožef Stefan, the laws of radiant energy. For further information, see the Timeline of thermodynamics.

Energy and Economy

Main articles: energy development, energy policy The way in which humans use energy is one of the defining characteristics of an economy. The progression from animal power to steam power, then the internal combustion engine and electricity, are key elements in the development of modern civilization. Future energy development, for example of renewable energy, may be key to avoiding the effects of global warming.

Notes

This definition is one of the most common; e.g. [http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_6.html Glossary at the NASA homepage]

External links

- [http://www.unitconversion.org/unit_converter/energy.html Online Energy and Work Converter] - convert between various units of energy and work, such as joule, erg, gigawatt-hour, newton meter, calorie, Btu, and so on
- [http://www.unitconversion.org/unit_converter/energy-v.html Interactive Energy and Work Conversion Table] - convert selected unit to all other units of energy and work
- [http://jumk.de/calc/energy.shtml Conversions of energy units]
- [http://www.physicsweb.org/article/world/15/7/2 What does energy really mean? From Physics World]
- [http://www.energy.ca.gov/glossary/ Glossary of Energy Terms]
- [http://www.iea.org International Energy Agency IEA - OECD] Category:Introductory physics Category:Fundamental physics concepts Category:Physical quantity ko:에너지 ms:Tenaga ja:エネルギー simple:Energy th:พลังงาน

JR-Maglev

] JR-Maglev, MLX01 (X means Experimental), is a magnetic levitation train system developed by the Japan Railway Technical Reasearch Institute (association of Japan Railway Group), composed of maximum 5 cars to run on the Yamanashi Maglev Test Line. On December 2, 2003, a three-car train set attained a maximum speed of 581 km/h in a manned vehicle run.

Fundamental Technology Elements

:See also: Technology in the Magnetic levitation train article. Magnetic levitation trains consist of a levitation system, a guide system, and a driving system.

Levitation

JR-Maglev Levitation system is offered by a Electrodynamic Suspension System (or EDS). Moving magnetic fields create a reactive force which is produced in a conducter by its magnetic field effect. The force holds up the train. The maglev-trains have Superconductivity Magnetic Coils, and the guide ways have levitation coils. When the trains run at high speed, Levitation Coils on guide way get rebounding forces by the Superconductivity Magnetic Coils of the trains. EDS has advance that is larger gaps than EMS, But EDS need supported wheels which are employed in low speeded running.Because EDS can't get large force in lower speeded(150km/h or less in JR-Maglev).

Guide

Levitation coils which are located on the guide way generate guide force.

Driving

JR-Maglev is driven by a Liner Synchronous Motor (which called LSM) System. This system needs to suply power to the coils at guide-way.

Experimental lines in Yamanashi Prefecture

magnetic field] Yamanashi Experiment Lines are facilities that currently have a practical use. It includes about 18.4km of rail (including 16.0km of tunnels).

History

- 1962 – Initial technology research was started.
- 1977 – Miyazaki Prefecture began applying the technology to rail transport.
- 1979 – Experimental train reached a speed of 517km/h (with no passengers).
- 1987 – Reached a speed of 400.8km/h with passengers.
- 1997 – The experiment run was started at Yamanachi tracks (MLX01) on April. In December, it reached a speed of 531km/h with passengers.
- 2003 – Reached a speed of 581km/h with passengers (its record).

External links

Transrapid

Transrapid is a German monorail system using magnetic levitation. Based on a patent from 1934, planning of an actual Transrapid system started in 1969. The test facility for the system in Emsland, Germany was completed in 1987, and in 1989 a Transrapid train reached a record-breaking speed of 436 kilometers per hour. Today the speed-record has exceeded 500 km/h (310 mph). The system is developed and marketed by Siemens AG and ThyssenKrupp.

Economic and environmental consideration

The Transrapid is said to be more energy efficient than a standard train and considerably less noisy. This is chiefly due to the absence of friction between train and track. (However, for high-speed trains in general, most energy is consumed to overcome aerodynamic drag, as it scales, other than the wheels' friction, with the cube of the velocity.) It is also capable of climbing significantly steeper tracks, rendering it especially suitable for mountainous regions. It is possible to flexibly adapt its guideway to the landscape and to have it tightly follow existing roads, railroad tracks, and power lines. Therefore, no significant interventions in the environment are necessary and pristine landscape is protected. Furthermore, the original use of the landscape under the guideway is still possible (farming or grazing for example). However, track building costs are higher than for conventional high-speed trains.

Technology

:See also: Technology in the Magnetic levitation train article. The synchronous longstator linear motor of the Transrapid maglev system is used both for propulsion and braking. It functions like a rotating electric motor whose stator is cut open and stretched along under the guideway. Inside the motor windings, alternating current generates a magnetic traveling field which moves the vehicle without contact. The support magnets in the vehicle function as the excitation portion (rotor). The respective magnetic traveling field works in only one direction, and therefore makes moving train collisions less likely, as more than one train on the track section would travel in the same direction. The superspeed maglev system has no wheels, axles, transmissions, or pantographs. It does not roll; it hovers. Electronic systems guarantee that the clearance remains constant (nominally 10 mm). To hover, the Transrapid requires less power than its air conditioning equipment. The levitation system and all onboard electronics are supplied by the power recovered from harmonic oscillations of magnetic field of the track's linear stator (Those oscillations being parasitic cannot be used for propulsion anyway). In case of power failure of the track's propulsion system Transrapid car uses on-board backup batteries that can supply power to the levitation system.

Transportation system for Germany

The Transrapid originated as one of the competing concepts for new land-based high speed public transportation for Germany. Another competing concept was the InterCity Express (ICE). The ICE "won" in that it was adopted nationwide in Germany. It is argued that the ICE won out in part because of its ability to run on conventional tracks and railway stations (albeit on lines not specifically designed or augmented for high-speed operation, the original ICE trains could not run faster than any other train. However special ICE units (dubbed ICE-T for InterCity Express Triebzug) were built incorporating "tilting" cars like the Italian Pendolino trains that allow for faster operation on older lines). Nevertheless, the Transrapid was seen as the next step beyond the ICE and a major asset for possible export and consequently development was not scrapped at this point, but continued as well. However, in the 1990s, intense political discussions about the Transrapid started in Germany. Though technically superior to normal railroad systems, the transrapid was considered too expensive, as the companies developing it relied on federal subsidies. The controversy mostly raged over the question whether public money should be invested in construction of a track for commercial use. Plans for a track from Berlin to Hamburg were canceled because legislators were not convinced that the project would ever become profitable in competition to the existing (very old and slow) conventional railway line and hence were unwilling to invest the money in times of tight budgets - in spite of the alleged importance of having a working Transrapid system in Germany in order to ease marketing of the system abroad. Some even got as far as arguing that the Transrapid was generally unsuitable for Germany itself because of Germany's many larger and relatively close cities (with the resulting many stops at short intervalls, the time needed to repeatedly accelerate to operation speed and to decelerate before stations becomes a limiting factor in average travel speed for high-speed transportation systems) and that a demonstration line would be better situated in a country where distances between cities are far larger than in Germany.

Construction costs

Building a maglev track is less costly than a comparatively HSR line. The non-contact technology uses factory manufactured girders. To construct a maglev track is approx. 20 to 50 % less expensive in terms of construction. However, the vehicles cost much more than conventional high-speed trains bringing overall project costs ahead of HSR track projects. In comparison, maglev technology might have equal or slightly higher costs by giving commuters much better time saving benefits. Thus, maglev technology gives a favorable ratio of travel time to infrastructure costs. However, due to its high costs, passenger comfort may be compromised as interior seating takes on more of a commercial jet-aircraft configuration than a typical passenger train one.

Maintenance costs

While maglev costs more in terms of the overall project expenses, it saves in maintenance efforts and costs as well as energy consumption. Even though there is no long-time experience drawn from any commercial application, simulations and first data obtained from the Shanghai project prove the assumptions.

Transrapid in China

HSR The only success so far was in the year 2000, when the Chinese government ordered a Transrapid track to be built connecting Shanghai to its Pu Dong airport. It was inaugurated in 2002. Regular daily trips started in March 2004. However, low passenger numbers, due to the remoteness of the terminal station from the city center and high ticket costs, hampered the line. During the first week, the average number of riders per train was only 73 people out of a maximum seating capacity of 440 passengers. One-way trip prices have recently dropped to 50 Renminbi ($6 USD). Nevertheless, the Shanghai Project was designed as a demonstration line, primarily to demonstrate the state-of-the-art technology and capabilities of the German maglev system. A high tilt compared with a relatively high speed of 430 km/h (267 mph) and leaving passengers in the outskirts of Pudong shows that the Chinese authorities were more interested in the technology transfer than commercial success. However, in terms of safety, reliability, availability, and functionality the Transrapid maglev system has demonstrated the readiness of Transrapid for commercial applications worldwide. The Transrapid manufacturers had high hopes of obtaining a subsequent order from China for a track connecting Shanghai with Beijing. Hence, it was considered a serious drawback when in 2004 it is said that China considered to choose the Japanese high-speed train Shinkansen, to the disappointment of Siemens, which had hoped to sell at least the ICE which is manufactured by them as the Transrapid system partly is. Public disapproval of the idea shifted the decision further into the future. In November 2004 talks began about extending the track from Shanghai to Hangzhou, 180 km away. A maglev would shorten the travel time to less than a fifth of its current value, from 2½ hours to 27 minutes.

New projects for Germany

A Transrapid connection of the Bavarian capital Munich to its international airport is now being planned. It would reduce the current connection time via S-Bahn (German city railroad system) from about 40 minutes to 10 minutes.

New project in the UK

The Transrapid is also being [http://www.guardian.co.uk/uk_news/story/0,3604,1500038,00.html considered] by the UK government as a 435 km/h (270 mph) link between London and Glasgow.

External links

- [http://www.transrapid.de/ Transrapid homepage]
- [http://www.maglevboard.net/ The International Maglev Board]
- [http://www.transrapid.de/download/standard_english_042005.pps Slideshow on the Transrapid]
- [http://www.deutsches-museum-bonn.de/ German Museum Bonn The Transrapid is one of the exhibits]
- [http://home.wangjianshuo.com/archives/20030809_pudong_airport_maglev_in_depth.htm Transrapid Pictures at Shanghai Pudong Airport]
- [http://www.magnetbahn-bayern.de Information about the Munich Transrapid connection]
- [http://www.maglev.de Transrapid - Maglev in Asia (China, Shanghai), Japan (Yamanashi) and Germany (Munich; TVE)] Category:Rail transport Category:Siemens products ja:トランスラピッド

Superconductivity

underneath) demonstrates the Meissner effect.]] Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect). In conventional superconductors, superconductivity is caused by a force of attraction between certain conduction electrons arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase composed of correlated pairs of electrons. There also exists a class of materials, known as unconventional superconductors, that exhibit superconductivity but whose physical properties contradict the theory of conventional superconductors. In particular, the so-called high-temperature superconductors superconduct at temperatures much higher than should be possible according to the conventional theory (though still far below room temperature.) There is currently no complete theory of high-temperature superconductivity. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys, some heavily-doped semiconductors, and certain ceramic compounds containing planes of copper and oxygen atoms. The latter class of compounds, known as the cuprates, are high-temperature superconductors. Superconductivity does not occur in noble metals like gold and silver, nor in most ferromagnetic metals, though a number of materials displaying both superconductivity and ferromagnetism have been discovered in recent years. Superconductivity is an essentially quantum mechanical phenomenon, and cannot be understood simply as the idealization of "perfect conductivity" in classical physics.

Elementary properties of superconductors

Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature at which superconductivity is destroyed. On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present. The existence of these "universal" properties imply that superconductivity is a thermodynamic phase, and thus possess certain distinguishing properties which are largely independent of microscopic details.

Zero electrical resistance

The simplest method to measure the electrical resistance of a superconductor is to place the sample in an electrical circuit, in series with a voltage (potential difference) source V (such as a battery), and measure the resulting current. If the resistance of the remaining circuit elements (such as the leads connecting the sample to the rest of the circuit, and the source's internal resistance) is R, the current passing through the sample is V/R. According to Ohm's law, this means that the resistance of the superconducting sample is zero. Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years, and theoretical estimates for the lifetime of persistent current exceed the lifetime of the universe. In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat (which is essentially the vibrational kinetic energy of the lattice ions.) As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance. The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons, instead consisting of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice (given by kT, where k is Boltzmann's constant and T is the temperature), the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation. In a class of superconductors known as type II superconductors (including all known high-temperature superconductors), an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electrical current is applied in conjunction with a strong magnetic field (which may be caused by the electrical current). This is due to the motion of vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortice can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero.

Superconducting phase transition

superfluid In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature T_c. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from less than 1K to around 20K. Solid mercury, for example, has a critical temperature of 4.2K. As of 2001, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB₂), although this material displays enough exotic properties that there is doubt about classifying it as a "conventional" superconductor. Cuprate superconductors can have much higher critical temperatures: YBa₂Cu₃O₇, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. (Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high T_c.) The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as e^−α/T for some constant α. (This exponential behavior is one of the pieces of evidence for the existence of the energy gap.) The order of the superconducting phase transition is still a matter of debate. It had long been thought that the transition is second-order, meaning there is no latent heat. However, recent calculations have suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field.

Meissner effect

When a superconductor is placed in a weak external magnetic field H, the field penetrates the superconductor for only a short distance λ, called the penetration depth, after which it decays rapidly to zero. This is called the Meissner effect, and is a defining characteristic of superconductivity. For most superconductors, the penetration depth is on the order of 100 nm. The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electrical current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from this because a superconductor expels all magnetic fields, not just those that are changing. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law. The Meissner effect was explained by London and London, who showed that the electromagnetic free energy in a superconductor is minimized provided :

\nabla^2\mathbf = \lambda^ \mathbf\,

where :H is the magnetic field and λ is the penetration depth. This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface. decays exponentially The Meissner effect breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value H_c. Depending on the geometry of the sample, one may obtain an intermediate state consisting of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value H_c1 leads to a mixed state in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electrical current as long as the current is not too large. At a second critical field strength H_c2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called fluxons because the flux carried by these vortices is quantized. Most pure elemental superconductors (except niobium, technetium, vanadium and carbon nanotubes) are Type I, while almost all impure and compound superconductors are Type II.

Theories of superconductivity

Since the discovery of superconductivity, great efforts have been devoted to finding out how and why it works. During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957). Generalizations of these theories form the basis for understanding the closely related phenomenon of superfluidity, but the extent to which similar generalizations can be applied to unconventional superconductors as well is still controversial.

History of superconductivity

Main article : History of superconductivity Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistivity of solid mercury at cryogenic temperatures using the recently-discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistivity abruptly disappeared. For this discovery, he was awarded the Nobel Prize in Physics in 1913. In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. The next important step in understanding superconductivity occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. In 1935, F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current. In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Landau and Ginzburg. This theory, which combined Landau's theory of second-order phase transitions with a Scrödinger-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau having died in 1968.) Also in 1950, Maxwell and Reynolds et. al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element. This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity. The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper, and Schrieffer. This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. The BCS theory was set on a firmer footing in 1958, when Bogoliubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian. In 1959, Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature. In 1962, the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse. In the same year, Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator. This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum h/e, and thus (coupled with the quantum Hall resistivity) for Planck's constant h. Josephson was awarded the Nobel Prize for this work in 1973. Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. In that year, Bednorz and Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987). It was shortly found by Paul C. W. Chu of the University of Houston and M.K. Wu at the University of Alabama in Huntsville [http://64.233.161.104/search?q=cache:Ld0r1qeeJNgJ:www.the-scientist.com/yr1988/jul/letters_p14_880711.html+Huntsville++%22paul+chu%22&hl=en] that replacing the lanthanum with yttrium, i.e. making YBCO, raised the critical temperature to 92 K, which was important because liquid nitrogen could then be used as a refrigerant (at atmospheric pressure, the boiling point of nitrogen is 77 K.) This is important commercially because liquid nitrogen can be produced cheaply on-site with no raw materials, and is not prone to some of the problems (solid air plugs, etc) of helium in piping. Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics.

Technological applications of superconductivity

There have been many technological innovations based on superconductivity. Superconductors are used to make the most powerful electromagnets known to man, including those used in MRI machines and the beam-steering magnets used in particle accelerators. Another application is for magnetic separation where weakly magnetic particles are extracted from a background of less or non-magnetic particles (used in a large scale in pigment industries). Superconductors are also used to make SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. Superconductors have also been used to make digital circuits (e.g. based on the Rapid Single Flux Quantum technology) and microwave filters for mobile phone base stations. Many promising applications of superconductivity have been stalled by the impracticality of maintaining large systems (e.g. long stretches of cable) at cryogenic temperatures. These problems may soon be alleviated with the continued development of high temperature superconductors, as these can be cooled by using liquid nitrogen rather than liquid helium (which is much more expensive and difficult to handle) or by using cryocoolers. However, the currently known high-temperature superconductors are brittle ceramics which are not easily turned into wires or other useful shapes. Promising future applications include high-performance transformers, power storage devices, electric power transmission, electric motors (e.g. for vehicle propulsion), magnetic levitation devices, and Fault Current Controllers.

Superconductors in science fiction

Superconductivity has long been a staple of science fiction. One of the first mentions of the phenomenon occurred in Robert A. Heinlein's novel Beyond This Horizon (1942). Notably, the use of a fictional room temperature superconductor was a major plot point in the Ringworld novels by Larry Niven, first published in 1970. Superconductivity is a popular device in science fiction due to the simplicity of the underlying concept - zero electrical resistance - and the rich technological possibilities. For example, superconducting magnets could be used to generate the powerful magnetic fields used by Bussard ramjets, a type of spacecraft commonly encountered in science fiction. The most troublesome property of real superconductors, the need for cryogenic cooling, is often circumvented by postulating the existence of room temperature superconductors. Many stories attribute additional properties to their fictional superconductors, ranging from infinite heat conductivity in Niven's novels (real superconductors conduct heat poorly, though superfluid helium has immense but finite heat conductivity) to providing power to an interstellar travel device in the

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