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Karlqvist Gap
The Karlqvist gap or Karlqvist Field is an electromagnetic phenomenon discovered in 1953 by the Swedish engineer Olle Karlqvist (1922-1976), which is important in magnetic storage for computers. (HTML 1 kB) Karlqvist discovered the phenomenon while designing a ferromagnetic surface layer to the magnetic drum memory for the BESK computer. (HTML 3 kB) When designing a magnetic memory store, the ferromagnetic layer must be studied to determine the variation of the magnetic field with permeability, air gap, layer thickness and other influencing factors. The problem is non-linear and extremely difficult to solve. Karlqvist's gap discovery shows that the non-linear problem could be approximated by a linear boundary value for the two-dimensional static field and the one-dimensional transient field. This linear calculation gives a first approximation. Karlqvist published his discovery in the 1954 paper "Calculation of the magnetic field in ferromagnetic layer of a magnetic drum" at KTH ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnetism
In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of atoms and molecules. Electromagnetism can be thought of as a combination of electricity and magnetism, two distinct but closely intertwined phenomena. In essence, electric forces occur between any two charged particles, causing an attraction between particles with opposite charges and repulsion between particles with the same charge, while magnetism is an interaction that occurs exclusively between ''moving'' charged particles. These two effects combine to create electromagnetic fields in the vicinity of charge particles, which can exert influence on other particles via the Lorentz force. At high energy, the weak force and electromagnetic force are unified as a single electroweak force. The electromagnetic force is responsible for many o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Storage
Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more disk read-and-write head, read/write heads. Magnetic storage media, primarily Hard disk drive, hard disks, are widely used to store Data (computing), computer data as well as sound, audio and video signals. In the field of computing, the term ''magnetic storage'' is preferred and in the field of audio and video production, the term ''magnetic recording'' is more commonly used. The distinction is less technical and more a matter of preference. Other examples of magnetic storage media include floppy disks, magnetic tape, and magnetic stripe card, magnetic stripes on credit cards. History Magnetic storage in the form of wire recording—audio recording on a wire—was publicized by Oberlin Smith in the Sept 8, 1888 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferromagnetism
Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials are the familiar metals noticeably attracted to a magnet, a consequence of their large magnetic permeability. Magnetic permeability describes the induced magnetization of a material due to the presence of an ''external'' magnetic field, and it is this temporarily induced magnetization inside a steel plate, for instance, which accounts for its attraction to the permanent magnet. Whether or not that steel plate acquires a permanent magnetization itself, depends not only on the strength of the applied field, but on the so-called coercivity of that material, which varies greatly among ferromagnetic materials. In physics, several different types of material magnetism are distinguished. Ferromagnetism (along with the similar effect ferrimagnetis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drum Memory
Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory. For many early computers, drum memory formed the main working memory of the computer. It was so common that these computers were often referred to as ''drum machines''. Some drums were also used as secondary storage as for example various IBM drum storage drives. Drums were displaced as primary computer memory by magnetic core memory, which offered a better balance of size, speed, cost, reliability and potential for further improvements. Drums in turn were replaced by hard disk drives for secondary storage, which were both less expensive and offered denser storage. The manufacturing of drums ceased in the 1970s. Technical design A drum memory or drum storage unit contained a large metal cylinder, coated on the outside surface with a ferromagnetic recording material. It could be considered the precu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BESK
BESK (''Binär Elektronisk SekvensKalkylator'', Swedish for "Binary Electronic Sequence Calculator") was Sweden's first electronic computer, using vacuum tubes instead of relays. It was developed by ''Matematikmaskinnämnden'' (Swedish Board for Computing Machinery) and for a short time it was the fastest computer in the world. The computer was completed in 1953 and in use until 1966. The technology behind BESK was later continued with the transistorized FACIT EDB and FACIT EDB-3 machines, both software compatible with BESK. Non-compatible machines highly inspired by BESK were SMIL made for the University of Lund, ''SAABs räkneautomat'' SARA, "SAAB's calculating machine", and DASK made in Denmark. BESK was developed by the Swedish Board for Computing Machinery (Matematikmaskinnämnden) a few years after the mechanical relay computer BARK (Binär Aritmetisk Relä-Kalkylator, Swedish for "Binary Arithmetic Relay Calculator"). The team was initially led by Conny Palm, who die ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a nonuniform magnetic field exerts minuscule forces on "nonmagnetic" materials by three other magnetic effects: paramagnetism, diamagnetism, and antiferromagnetism, although these forces are usually so small they can only be detected by laboratory equipment. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, it is described mathematically by a function assigning a vector to each point of space, cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Permeability (electromagnetism)
In electromagnetism, permeability is the measure of magnetization that a material obtains in response to an applied magnetic field. Permeability is typically represented by the (italicized) Greek letter ''μ''. The term was coined by William Thomson, 1st Baron Kelvin in 1872, and used alongside permittivity by Oliver Heaviside in 1885. The reciprocal of permeability is magnetic reluctivity. In SI units, permeability is measured in henries per meter (H/m), or equivalently in newtons per ampere squared (N/A2). The permeability constant ''μ''0, also known as the magnetic constant or the permeability of free space, is the proportionality between magnetic induction and magnetizing force when forming a magnetic field in a classical vacuum. A closely related property of materials is magnetic susceptibility, which is a dimensionless proportionality factor that indicates the degree of magnetization of a material in response to an applied magnetic field. Explanation In the mac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonlinear System
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other scientists because most systems are inherently nonlinear in nature. Nonlinear dynamical systems, describing changes in variables over time, may appear chaotic, unpredictable, or counterintuitive, contrasting with much simpler linear systems. Typically, the behavior of a nonlinear system is described in mathematics by a nonlinear system of equations, which is a set of simultaneous equations in which the unknowns (or the unknown functions in the case of differential equations) appear as variables of a polynomial of degree higher than one or in the argument of a function which is not a polynomial of degree one. In other words, in a nonlinear system of equations, the equation(s) to be solved cannot be written as a linear combination of the un ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boundary Value Problem
In mathematics, in the field of differential equations, a boundary value problem is a differential equation together with a set of additional constraints, called the boundary conditions. A solution to a boundary value problem is a solution to the differential equation which also satisfies the boundary conditions. Boundary value problems arise in several branches of physics as any physical differential equation will have them. Problems involving the wave equation, such as the determination of normal modes, are often stated as boundary value problems. A large class of important boundary value problems are the Sturm–Liouville problems. The analysis of these problems involves the eigenfunctions of a differential operator. To be useful in applications, a boundary value problem should be well posed. This means that given the input to the problem there exists a unique solution, which depends continuously on the input. Much theoretical work in the field of partial differential ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetostatics
Magnetostatics is the study of magnetic fields in systems where the currents are steady (not changing with time). It is the magnetic analogue of electrostatics, where the electric charge, charges are stationary. The magnetization need not be static; the equations of magnetostatics can be used to predict fast Magnetization reversal, magnetic switching events that occur on time scales of nanoseconds or less. Magnetostatics is even a good approximation when the currents are not static – as long as the currents do not alternating current, alternate rapidly. Magnetostatics is widely used in applications of micromagnetics such as models of magnetic storage devices as in computer memory. Applications Magnetostatics as a special case of Maxwell's equations Starting from Maxwell's equations and assuming that charges are either fixed or move as a steady current \mathbf, the equations separate into two equations for the electric field (see electrostatics) and two for the magnetic fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transient Magnetic Field
ECHELON, originally a secret government code name, is a surveillance program (signals intelligence/SIGINT collection and analysis network) operated by the five signatory states to the UKUSA Security Agreement:Given the 5 dialects that use the terms, UKUSA can be pronounced from "You-Q-SA" to "Oo-Coo-SA", AUSCANNZUKUS can be pronounced from "Oz-Can-Zuke-Us" to "Orse-Can-Zoo-Cuss". :From Talk:UKUSA Agreement: "Per documents officially released by both the Government Communications Headquarters and the National Security Agency, this agreement is referred to as the UKUSA Agreement. This name is subsequently used by media sources reporting on the story, as written in new references used for the article. The NSA press release provides a pronunciation guide, indicating that "UKUSA" should not be read as two separate entities.(National Security Agency)" Australia, Canada, New Zealand, the United Kingdom and the United States, also known as the Five Eyes. Created in the late 1960s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
KTH Royal Institute Of Technology
The KTH Royal Institute of Technology ( sv, Kungliga Tekniska högskolan, lit=Royal Institute of Technology), abbreviated KTH, is a public research university in Stockholm, Sweden. KTH conducts research and education in engineering and technology and is Sweden's largest technical university. Currently, KTH consists of five schools with four campuses in and around Stockholm. KTH was established in 1827 as the ''Teknologiska institutet (Institute of Technology)'' and had its roots in the ''Mekaniska skolan (School of Mechanics)'' that was established in 1798 in Stockholm. But the origin of KTH dates back to the predecessor of the ''Mekaniska skolan'', the ''Laboratorium mechanicum'', which was established in 1697 by the Swedish scientist and innovator Christopher Polhem. The Laboratorium mechanicum combined education technology, a laboratory, and an exhibition space for innovations. In 1877 KTH received its current name, Kungliga Tekniska högskolan (KTH Royal Institute of Technol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
