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Adiabatically
Adiabatic (from ''Gr.'' ἀ ''negative'' + διάβασις ''passage; transference'') refers to any process that occurs without heat transfer. This concept is used in many areas of physics and engineering. Notable examples are listed below. Automobiles * Engine braking, a feature of some diesel engines, uses adiabatic expansion to diminish the vehicle's forward momentum. Meteorology * Adiabatic lapse rate, the change in air temperature with changing height, resulting from pressure change. Quantum chemistry * Adiabatic invariant Born–Oppenheimer approximation Thermodynamics * Adiabatic process * Adiabatic ionization * Adiabatic index * Adiabatic accessibility Quantum mechanics * Adiabatic theorem * Adiabatic quantum motor Electronics * Adiabatic circuit * Adiabatic logic Adiabatic circuits are low-power electronic circuits which use " reversible logic" to conserve energy. The term " adiabatic" refers to an ideal thermodynamic process in which no heat or mass is exc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Process
In thermodynamics, an adiabatic process (Greek: ''adiábatos'', "impassable") is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work.. A translation may be founhere. Also a mostly reliabltranslation is to be foundin As a key concept in thermodynamics, the adiabatic process supports the theory that explains the first law of thermodynamics. Some chemical and physical processes occur too rapidly for energy to enter or leave the system as heat, allowing a convenient "adiabatic approximation".Bailyn, M. (1994), pp. 52–53. For example, the adiabatic flame temperature uses this approximation to calculate the upper limit of flame temperature by assuming combustion loses no heat to its surroundings. In meteorology and oceanography, adiabatic cooling produces condensation of moisture or salinity, oversatu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Accessibility
Adiabatic accessibility denotes a certain relation between two equilibrium states of a thermodynamic system (or of different such systems). The concept was coined by Constantin Carathéodory in 1909 ("adiabatische Erreichbarkeit") and taken up 90 years later by Elliott Lieb and J. Yngvason in their axiomatic approach to the foundations of thermodynamics. It was also used by R. Giles in his 1964 monograph.Robin Giles: "Mathematical Foundations of Thermodynamics", Pergamon, Oxford 1964 Description A system in a state ''Y'' is said to be adiabatically accessible from a state ''X'' if ''X'' can be transformed into ''Y'' without the system suffering transfer of energy as heat or transfer of matter. ''X'' may, however, be transformed to ''Y'' by doing work on ''X''. For example, a system consisting of one kilogram of warm water is adiabatically accessible from a system consisting of one kilogram of cool water, since the cool water may be mechanically stirred to warm it. However, the c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Theorem
The adiabatic theorem is a concept in quantum mechanics. Its original form, due to Max Born and Vladimir Fock (1928), was stated as follows: :''A physical system remains in its instantaneous eigenstate if a given perturbation is acting on it slowly enough and if there is a gap between the eigenvalue and the rest of the Hamiltonian's spectrum.'' In simpler terms, a quantum mechanical system subjected to gradually changing external conditions adapts its functional form, but when subjected to rapidly varying conditions there is insufficient time for the functional form to adapt, so the spatial probability density remains unchanged. Diabatic vs. adiabatic processes At some initial time t_0 a quantum-mechanical system has an energy given by the Hamiltonian \hat(t_0); the system is in an eigenstate of \hat(t_0) labelled \psi(x,t_0). Changing conditions modify the Hamiltonian in a continuous manner, resulting in a final Hamiltonian \hat(t_1) at some later time t_1. The system will e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Transfer
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, Convection (heat transfer), thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system. Heat conduction, also called diffusion, is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Engine Braking
Engine braking occurs when the retarding forces within an engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes. The term is often confused with several other types of braking, most notably compression-release braking or "jake braking" which uses a different mechanism. Traffic regulations in many countries require trucks to always drive with an engaged gear, which in turn provides a certain amount of engine braking (viscous losses to the engine oil and air pumped through the engine and friction losses to the cylinder walls and bearings) when no accelerator pedal is applied. Type Gasoline engines The term "engine braking" refers to the braking effect that occurs in gasoline engines when the accelerator pedal is released. This causes fuel injection to cease and the throttle valve to close almost completely, greatly restricting forced airflow from, for example, a turbocharger. The rest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Lapse Rate
The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. ''Lapse rate'' arises from the word ''lapse'', in the sense of a gradual fall. In dry air, the adiabatic lapse rate is 9.8 °C/km (5.4 °F per 1,000 ft). It corresponds to the vertical component of the spatial gradient of temperature. Although this concept is most often applied to the Earth's troposphere, it can be extended to any gravitationally supported parcel of gas. Definition A formal definition from the ''Glossary of Meteorology'' is: :The decrease of an atmospheric variable with height, the variable being temperature unless otherwise specified. Typically, the lapse rate is the negative of the rate of temperature change with altitude change: :\Gamma = -\frac where \Gamma (sometimes L) is the lapse rate given in units of temperature divided by units of altitude, ''T'' is temperature, and ''z'' is altitude. Convection and adiabatic expansion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Born–Oppenheimer Approximation
In quantum chemistry and molecular physics, the Born–Oppenheimer (BO) approximation is the best-known mathematical approximation in molecular dynamics. Specifically, it is the assumption that the wave functions of atomic nuclei and electrons in a molecule can be treated separately, based on the fact that the nuclei are much heavier than the electrons. Due to the larger relative mass of a nucleus compared to an electron, the coordinates of the nuclei in a system are approximated as fixed, while the coordinates of the electrons are dynamic. The approach is named after Max Born and J. Robert Oppenheimer who proposed it in 1927, in the early period of quantum mechanics. The approximation is widely used in quantum chemistry to speed up the computation of molecular wavefunctions and other properties for large molecules. There are cases where the assumption of separable motion no longer holds, which make the approximation lose validity (it is said to "break down"), but even then t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Ionization
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected. Uses Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps. It is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber. The ionizati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Index
In thermal physics and thermodynamics, the heat capacity ratio, also known as the adiabatic index, the ratio of specific heats, or Laplace's coefficient, is the ratio of the heat capacity at constant pressure () to heat capacity at constant volume (). It is sometimes also known as the ''isentropic expansion factor'' and is denoted by ( gamma) for an ideal gasγ first appeared in an article by the French mathematician, engineer, and physicist Siméon Denis Poisson: * On p. 332, Poisson defines γ merely as a small deviation from equilibrium which causes small variations of the equilibrium value of the density ρ. In Poisson's article of 1823 – * γ was expressed as a function of density D (p. 8) or of pressure P (p. 9). Meanwhile, in 1816 the French mathematician and physicist Pierre-Simon Laplace had found that the speed of sound depends on the ratio of the specific heats. * However, he didn't denote the ratio as γ. In 1825, Laplace stated that the speed of sound is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Quantum Motor
An adiabatic quantum motor is a mechanical device, typically nanometric, driven by a flux of quantum particles and able to perform cyclic motions. The adjective “adiabatic” in this context refers to the limit when the dynamics of the mechanical degrees of freedom is slow compared with the dwell time of the particles passing through the device. In this regime, it is commonly assumed that the mechanical degrees of freedom behave classically. This class of devices works essentially as quantum pumps operated in reverse. While in a quantum pump, the periodic movement of some parameters pumps quantum particles from one reservoir to another, in a quantum motor a DC current of particles induces the cyclic motion of the device. One key feature of these motors is that quantum interferences can be used to increase their efficiency by enhancing the reflection coefficient In physics and electrical engineering the reflection coefficient is a parameter that describes how much of a wave is r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Circuit
Adiabatic circuits are low-power electronic circuits which use " reversible logic" to conserve energy. The term " adiabatic" refers to an ideal thermodynamic process in which no heat or mass is exchanged with the surrounding environment, alluding to the ability of the circuits to reduce energy loss as heat. Unlike traditional CMOS circuits, which dissipate energy during switching, adiabatic circuits reduce dissipation by following two key rules: * Never turn on a transistor when there is a voltage potential between the source and drain. * Never turn off a transistor when current is flowing through it. Because of the second law of thermodynamics, it is not possible to completely convert energy into useful work. However, the term "adiabatic logic" is used to describe logic families that could theoretically operate without losses. The term "quasi-adiabatic logic" is used to describe logic that operates with a lower power than static CMOS logic, but which still has some theoreti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adiabatic Logic
Adiabatic circuits are low-power electronic circuits which use " reversible logic" to conserve energy. The term " adiabatic" refers to an ideal thermodynamic process in which no heat or mass is exchanged with the surrounding environment, alluding to the ability of the circuits to reduce energy loss as heat. Unlike traditional CMOS circuits, which dissipate energy during switching, adiabatic circuits reduce dissipation by following two key rules: * Never turn on a transistor when there is a voltage potential between the source and drain. * Never turn off a transistor when current is flowing through it. Because of the second law of thermodynamics, it is not possible to completely convert energy into useful work. However, the term "adiabatic logic" is used to describe logic families that could theoretically operate without losses. The term "quasi-adiabatic logic" is used to describe logic that operates with a lower power than static CMOS logic, but which still has some theoret ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
