共查询到20条相似文献,搜索用时 578 毫秒
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为获得高温气冷堆核电站电气设备绝缘设计所需基础数据, 本文设计了一套测量高压氦气绝缘性能的装置. 利用该装置进行了15-20 ℃, 0.1-7 MPa氦气, 间距0.25, 0.35, 0.5 mm平行极板击穿实验. 实验表明: 氦气的绝缘性能远低于空气; 气压越高, 氦气的击穿电压越大, 3.0 MPa氦气的击穿电压与常压空气基本一致; 根据低气压实验数据和巴申定律推导的公式, 在高气压下计算值偏大, 且偏差随着气压和间距乘积的增大不断增大; 提出了可计算0.1-7 MPa氦气击穿电压的简易公式, 同时修正了高气压氦气的巴申公式, 并进行了理论分析. 相似文献
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在时间不变的特殊无限小变换下,研究相对论性变质量非完整可控力学系统的非Noether守恒量——Hojamn守恒量.建立了系统的运动微分方程, 给出了系统在特殊无限小变换下的形式不变性(Mei对称性)的定义和判据以及系统的形式不变性是Lie对称性的充分必要条件.得到了系统形式不变性导致非Noether守恒量的条件和具体形式.举例说明结果的应用.
关键词:
相对论
非完整可控力学系统
变质量
非Noether守恒量 相似文献
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在水体表面波的扰动作用下,水下光场随深度呈现较为明显的波动现象,且水中光合作用会对水下光场波动作出响应,因而此现象引起了广泛的关注。基于太湖梅梁湾观测的水下光场数据,计算了水下光场随深度的变化,并分析了其波动特征。结果表明:表面波引起了水下光场较为明显的波动现象,波动振幅最大的深度基本小于20 cm,远小于海洋中对应的深度;水下光场波动的振幅随深度呈e的负指数衰减,漫射消光系数越大,水下光场的波动衰减得也越快;当深度大于30 cm时,水下光场的扰动现象基本消失。还计算了船舶对水下光场观测的影响,发现直射光未被遮挡的情况下,漫射比例越高,其相对误差越大。 相似文献
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This paper presents a technique for damage detection in structures under unknown periodic excitations using the transient displacement response. The method is capable of identifying the damage parameters without finding the input excitations. We first define the concept of displacement space as a linear space in which each point represents displacements of structure under an excitation and initial condition. Roughly speaking, the method is based on the fact that structural displacements under free and forced vibrations are associated with two parallel subspaces in the displacement space. Considering this novel geometrical viewpoint, an equation called kernel parallelization equation (KPE) is derived for damage detection under unknown periodic excitations and a sensitivity-based algorithm for solving KPE is proposed accordingly. The method is evaluated via three case studies under periodic excitations, which confirm the efficiency of the proposed method. 相似文献
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Using form invariance under special infinitesimal transformations
in which time is not variable, the non-Noether conserved quantity
of the relativistic nonholonomic system with variable mass is studied.
The differential equations of motion of the system are established.
The definition and criterion of the form invariance of
the system under infinitesimal transformations are studied.
The necessary and sufficient condition under which the form
invariance is a Lie symmetry is given. The condition under
which the form invariance can be led to a non-Noether conserved
quantity and the form of the conserved quantity are obtained.
Finally, an example is given to illustrate the application of the result. 相似文献
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The influence on the recombination luminescence spectra of a field applied to the Schottky barrier and a high excitation density
GaN epitaxial films grown by metalorganic chemical-vapor deposition (MOCVD) is investigated. It is discovered that quenching
of the luminescence takes place under a reverse bias, while an increase in its intensity occurs under a forward bias. The
effect observed is attributed to thickness variation of the space-charge layer under the effects of the applied voltage. The
appearance of a new band caused by exciton-exciton collisions is observed under the conditions of a high excitation density.
Fiz. Tverd. Tela (St. Petersburg) 40, 936–937 (May 1998) 相似文献
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It is important to understand the mechanism to integrate visual and other information for the perception of gravitational
vertical under different conditions of gravity, although most of the experiments to investigate the topic reported so far
has been carried out under normal-gravity (1 G) and under micro-gravity produced in short duration of parabolic flight. The
purpose of this research is to investigate human perception of gravitational vertical under hyper-gravity (1.5G and 2G) to
compare that under normal-gravity (1 G). We measured perceived gravitational vertical using a visual probe presented at the
center while manipulating the orientation of visual stimuli (scenery picture) presented in the surround and the magnitude
of gravitational acceleration. The environment of hyper-gravity was produced by centrifugal force of a rotating flight simulator.
The results show that the accuracy of perceived gravitational vertical increased and the precision of it decreased under hyper-gravity
condition relative to those under the normal-gravity condition when no visual stimulus was presented. However, the effect
of the tilt of visual stimuli did not change under different gravity conditions. 相似文献
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Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chlorophenol and pentachlorophenol has been investigated under air or argon atmosphere. The degradation follows first-order kinetics in the initial state with rates in the range 4.5-6.6 microM min-1 under air and 6.0-7.2 microM min-1 under argon at a concentration of 100 microM of chlorophenols. The rate of OH radical formation from water is 19.8 microM min-1 under argon and 14.7 microM min-1 under air in the same sonolysis conditions. The sonolysis of chlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueous sonolysis. This suggests that the main degradation of chlorophenols proceeds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) ions accelerates the degradation. This is probably due to the regeneration of OH radicals from hydrogen peroxide, which would be formed from recombination of OH radicals and which may contribute a little to the degradation. The ability to inhibit bacterial multiplication of pentachlorophenol decreases with ultrasonic irradiation. 相似文献
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J. K. Percus 《Journal of statistical physics》2002,106(1-2):357-368
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Yudi Rosandi Herbert M. Urbassek 《Applied Physics A: Materials Science & Processing》2010,101(3):509-515
The optical properties of blue-violet InGaN light-emitting diodes under normal and reversed polarizations are numerically
studied. The best light-emitting performance under normal and reversed polarization is obtained in a single quantum-well structure
and double quantum-well structure, respectively. The key factors responsible for these phenomena are presumably the carrier
concentration distribution and the amount of carriers in quantum wells. The turn-on voltage of light-emitting diodes under
reversed polarization is lower than that of light-emitting diodes under normal polarization, due mainly to lower potential
heights for electrons and holes in the active region. 相似文献
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Non-Noether symmetrical conserved quantity for nonholonomic Vacco dynamical systems with variable mass 总被引:1,自引:0,他引:1 下载免费PDF全文
Using a form invariance under special infinitesimal transformations in which time is not variable, the non-Noether conserved quantity of the nonholonomic Vacco dynamical system with variable mass is studied. The differential equations of motion of the systems are established. The definition and criterion of the form invariance of the system under special infinitesimal transformations are studied. The necessary and sufficient condition under which the form invariance is a Lie symmetry is given. The Hojman theorem is established. Finally an example is given to illustrate the application of the result. 相似文献
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In this paper an aqueous solution was irradiated with a 1.63MHz ultrasonic wave. It is shown that if stainless steel can passivate under dynamic polarization in this medium, under static polarization, the latter does not show any repassivation behaviour with time. This is attributed to a diminution of the diffusion layer thickness that is developed at the electrode/electrolyte interface, which is associated with a production of H(2) species by sonolysis and which maintains reductive conditions at the interface. The oxide film formed under ultrasonic irradiation for 1h at a passive potential of+0.2V(SCE) shows an early stage of passivation and an increased disordered state, which implies a considerable decrease in the corrosion resistance behaviour of the sample. The polarization resistance of the stainless steel R(p) is divided by a value of 4.5 under ultrasonic conditions. 相似文献
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A closed contour of excitation (Δ-scheme) of a three-level atom in an optically dense medium under the action of two optical fields and a microwave field has been studied. It is found that phase relations between exciting fields in this medium play a determining role. It is established that, under certain conditions, in an optically dense Δ-atom medium exhibits a quasi-periodic dependence of the refractive index on the coordinate. The conditions under which this dependence is most pronounced are determined. 相似文献
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Degradation mechanisms for a-InGaZnO thin-film transistors functioning under simultaneous DC gate and drain biases 下载免费PDF全文
Tianyuan Song 《中国物理 B》2022,31(8):88101-088101
Degradation of a-InGaZnO thin-film transistors working under simultaneous DC gate and drain bias stress is investigated, and the corresponding degradation mechanism is proposed and verified. The maximum degradation occurs under the bias stress condition that makes the electric field and electron concentration relatively high at the same time. Trapping of hot electrons in the etching-stop layer under the extended drain electrode is proven to be the underlying mechanism. The observed degradation phenomena, including distortion in the transfer curve on a logarithmic scale and two-slope dependence on gate bias on a linear scale, current crowding in the output curve, and smaller degradation in transfer curves measured under large drain bias, can all be well explained with the proposed degradation mechanism. 相似文献
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The negativity of the discrete Wigner functions (DWFs) is a measure of non-classicality and is often used to quantify the degree of quantum coherence in a system. The study of Wigner negativity and its evolution under different quantum channels can provide insight into the stability and robustness of quantum states under their interaction with the environment, which is essential for developing practical quantum computing systems. The variation of DWF negativity of qubit, qutrit, and two-qubit systems under the action of (non)-Markovian random telegraph noise (RTN) and amplitude damping (AD) quantum channels is investigated. Different negative quantum states that can be used as a resource for quantum computation and quantum teleportation are constructed. The success of quantum computation and teleportation is estimated for these states under (non)-Markovian evolutions. 相似文献
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Garry Ludwig 《International Journal of Theoretical Physics》1988,27(3):315-333
An extension is presented of the well-known Geroch-Held-Penrose (GHP) formalism, itself an extension of the still better known Newman-Penrose (NP) formalism. The extended formalism given here uses only quantities that transform properly under all diagonal transformations of the spin frame, that is, not only under boost-rotations, but also under conformal rescalings. Full use is made of the formalism's symmetry under all discrete operations, that is, under conjugation, the prime operation, and the (modified) Sachs transformations. Just as the GHP formalism is considerably simpler than the NP formalism in the case where a spacelike surface is singled out in a natural way, so the present formalism leads to further simplification when a conformal spacelike surface can be singled out. This is the case, for example, in considerations of future null infinity. In general situations all three formalisms are on an equal footing. 相似文献
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S.T. Li X.Y. Zhang Q.P. Wang P. Li J. Chang X.L. Zhang Z.H. Cong 《Applied physics. B, Lasers and optics》2007,87(2):221-226
For laser diode end-pumped solid-state lasers, the pump beam can be considered to be a Gaussian distribution or a top-hat
distribution or between them. The rate equations for Q-switched lasers have been treated before, by considering the pump beam
as a Gaussian distribution. This paper deals with the rate equations and the solutions for Q-switched lasers under a top-hat
pump beam distribution. The normalized rate equation is obtained and solved numerically. A group of general curves are given
and the comparison with the results under the Gaussian pump beam distribution and the plane-wave approximation is made. The
results show that the solutions of the rate equations under a top-hat pump beam distribution are different from those under
a Gaussian pump beam distribution, but the difference is very small. The solutions of the rate equations under both situations
can give much more precise theoretical results than those under the plane-wave approximation.
PACS 42.60.Gd; 42.55.Xi; 42.55.Ah 相似文献