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Alfvén Mach Number
The Alfvén Mach number (also known as the Alfvén number, Alfvénic Mach number, and magnetic Mach number; or ) is a dimensionless quantity representing the ratio of the relative velocity of a fluid to the local Alfvén speed. It is used in plasma physics, where it is analogous to the Mach number but based on Alfvén waves rather than sound waves. Alfvén and Mach were physicists who studied shock waves. Along with the sonic Mach number, the Alfvén Mach number is frequently used to characterize shock fronts and turbulence in magnetized plasmas. \mathrm = \frac where * is the Alfvén Mach number, * is the flow velocity, and * is the Alfvén speed. When , the flow is referred to as ''sub-Alfvénic''; and when , the flow is referred to as ''super-Alfvénic''. See also * Plasma parameters * Magnetic Reynolds number * Lundquist number In plasma physics, the Lundquist number (denoted by S) is a dimensionless ratio which compares the timescale of an Alfvén wave crossing to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimensionless Quantity
Dimensionless quantities, or quantities of dimension one, are quantities implicitly defined in a manner that prevents their aggregation into unit of measurement, units of measurement. ISBN 978-92-822-2272-0. Typically expressed as ratios that align with another system, these quantities do not necessitate explicitly defined Unit of measurement, units. For instance, alcohol by volume (ABV) represents a volumetric ratio; its value remains independent of the specific Unit of volume, units of volume used, such as in milliliters per milliliter (mL/mL). The 1, number one is recognized as a dimensionless Base unit of measurement, base quantity. Radians serve as dimensionless units for Angle, angular measurements, derived from the universal ratio of 2π times the radius of a circle being equal to its circumference. Dimensionless quantities play a crucial role serving as parameters in differential equations in various technical disciplines. In calculus, concepts like the unitless ratios ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alfvén Speed
Alfvén may refer to: People * Hannes Alfvén (1908–1995), Swedish plasma physicist and Nobel Prize in Physics laureate * Hugo Alfvén (1872–1960), Swedish composer, conductor, violinist, and painter * Marie Triepcke Krøyer Alfvén (1867–1940), commonly known as Marie Krøyer, Danish painter, wife of Hugo Other * Alfvén wave In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of plasma wave in which ions oscillate in response to a restoring force provided by an Magnetic tension force, effective tension on the magnetic field lines. Definition ..., a type of magnetohydrodynamic wave, named after Hannes Alfvén * 1778 Alfvén, an asteroid discovered in 1960, named after Hannes Alfvén {{disambig, surname ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plasma Physics
Plasma () is a state of matter characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars (including the Sun), but also dominating the rarefied intracluster medium and intergalactic medium. Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field. The presence of charged particles makes plasma electrically conductive, with the dynamics of individual particles and macroscopic plasma motion governed by collective electromagnetic fields and very sensitive to externally applied fields. The response of plasma to electromagnetic fields is used in many modern devices and technologies, such as plasma televisions or plasma etching. Depending on temperature and density, a certain number of neutral particles may also be present, in which case plasma is called partially ioni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mach Number
The Mach number (M or Ma), often only Mach, (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Austrian physicist and philosopher Ernst Mach. \mathrm = \frac, where: * is the local Mach number, * is the local flow velocity with respect to the boundaries (either internal, such as an object immersed in the flow, or external, like a channel), and * is the speed of sound in the medium, which in air varies with the square root of the thermodynamic temperature. By definition, at Mach1, the local flow velocity is equal to the speed of sound. At Mach0.65, is 65% of the speed of sound (subsonic), and, at Mach1.35, is 35% faster than the speed of sound (supersonic). The local speed of sound, and hence the Mach number, depends on the temperature of the surrounding gas. The Mach number is primarily used to determine the approximation with which a flow can be treated as an i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alfvén Wave
In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of plasma wave in which ions oscillate in response to a restoring force provided by an Magnetic tension force, effective tension on the magnetic field lines. Definition An Alfvén wave is a low-frequency (compared to the ion gyrofrequency) travelling oscillation of the ions and magnetic field in a Plasma (physics), plasma. The ion mass density provides the inertia and the magnetic field line tension provides the restoring force. Alfvén waves propagate in the direction of the magnetic field, and the motion of the ions and the perturbation of the magnetic field are transverse to the direction of propagation. However, Alfvén waves existing at oblique incidences will smoothly change into magnetosonic waves when the propagation is perpendicular to the magnetic field. Alfvén waves are Dispersion relation, dispersionless. Alfvén velocity The low-frequency relative permittivity \varepsilon of a magnetized ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hannes Alfvén
Hannes Olof Gösta Alfvén (; 30 May 1908 – 2 April 1995) was a Swedish electrical engineer, plasma physicist and winner of the 1970 Nobel Prize in Physics for his work on magnetohydrodynamics (MHD). He described the class of MHD waves now known as Alfvén waves. He was originally trained as an electrical power engineer and later moved to research and teaching in the fields of plasma physics and electrical engineering. Alfvén made many contributions to plasma physics, including theories describing the behavior of aurorae, the Van Allen radiation belts, the effect of magnetic storms on the Earth's magnetic field, the terrestrial magnetosphere, and the dynamics of plasmas in the Milky Way galaxy. Education Alfvén received his PhD from the University of Uppsala in 1934. His thesis was titled "Investigations of High-frequency Electromagnetic Waves." Early years In 1934, Alfvén taught physics at both the University of Uppsala and the Nobel Institute for Physics (lat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ernst Mach
Ernst Waldfried Josef Wenzel Mach ( ; ; 18 February 1838 – 19 February 1916) was an Austrian physicist and philosopher, who contributed to the understanding of the physics of shock waves. The ratio of the speed of a flow or object to that of sound is named the Mach number in his honour. As a philosopher of science, he was a major influence on logical positivism and American pragmatism. Through his criticism of Isaac Newton's theories of space and time, he foreshadowed Albert Einstein's theory of relativity. Biography Early life Mach was born in Chrlice (), Moravia, Austrian Empire (now part of Brno in the Czech Republic). His father Jan Nepomuk Mach, who had graduated from Charles-Ferdinand University in Prague, acted as tutor to the noble Brethon family in Zlín in eastern Moravia. His grandfather, Wenzl Lanhaus, an administrator of the Chirlitz estate, was also master builder of the streets there. His activities in that field later influenced Ernst Mach's theoretical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shock Wave
In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium, but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium. For the purpose of comparison, in supersonic speed, supersonic flows, additional increased expansion may be achieved through an expansion fan, also known as a Prandtl–Meyer expansion fan. The accompanying expansion wave may approach and eventually collide and recombine with the shock wave, creating a process of destructive interference. The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by Wave interference, constructive interference. Unlike solitons (another kind of nonlinear wave), the energy and speed of a shock wave alone dissipates relatively quickly with distan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sonic Mach Number
The Mach number (M or Ma), often only Mach, (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Austrian physicist and philosopher Ernst Mach. \mathrm = \frac, where: * is the local Mach number, * is the local flow velocity with respect to the boundaries (either internal, such as an object immersed in the flow, or external, like a channel), and * is the speed of sound in the medium, which in air varies with the square root of the thermodynamic temperature. By definition, at Mach1, the local flow velocity is equal to the speed of sound. At Mach0.65, is 65% of the speed of sound (subsonic), and, at Mach1.35, is 35% faster than the speed of sound (supersonic). The local speed of sound, and hence the Mach number, depends on the temperature of the surrounding gas. The Mach number is primarily used to determine the approximation with which a flow can be treated as an i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shock Front
In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium, but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium. For the purpose of comparison, in supersonic flows, additional increased expansion may be achieved through an expansion fan, also known as a Prandtl–Meyer expansion fan. The accompanying expansion wave may approach and eventually collide and recombine with the shock wave, creating a process of destructive interference. The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by constructive interference. Unlike solitons (another kind of nonlinear wave), the energy and speed of a shock wave alone dissipates relatively quickly with distance. When a shock wave passes through ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between those layers. Turbulence is commonly observed in everyday phenomena such as surf, fast flowing rivers, billowing storm clouds, or smoke from a chimney, and most fluid flows occurring in nature or created in engineering applications are turbulent. Turbulence is caused by excessive kinetic energy in parts of a fluid flow, which overcomes the damping effect of the fluid's viscosity. For this reason, turbulence is commonly realized in low viscosity fluids. In general terms, in turbulent flow, unsteady vortices appear of many sizes which interact with each other, consequently drag due to friction effects increases. The onset of turbulence can be predicted by the dimensionless Reynolds number, the ratio of kinetic energy to viscous damping ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Naval Research Laboratory
The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. Located in Washington, DC, it was founded in 1923 and conducts basic scientific research, applied research, technological development and prototyping. The laboratory's specialties include plasma physics, space physics, materials science, and tactical electronic warfare. NRL is one of the first US government scientific R&D laboratories, having opened in 1923 at the instigation of Thomas Edison, and is currently under the Office of Naval Research. As of 2016, NRL was a United States Navy Working Capital Fund, Navy Working Capital Fund activity, which means it is not a line-item in the US Federal Budget. Instead of direct funding from Congress, all costs, including overhead, were recovered through sponsor-funded research projects. NRL's research expenditures were approximately $1 billion per year. Research The Naval Research L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
