共查询到20条相似文献,搜索用时 24 毫秒
1.
N. I. Trushkin V. B. Karal’nik M. E. Grushin G. I. Aponin Yu. S. Akishev 《Laser Physics》2006,16(1):173-182
The development of streamers and sparks in nitrogen at atmospheric pressure in the pin-to-plane electrode configuration is
studied in experiments and theoretical calculations. It is demonstrated that the near-electrode regions play the decisive
role in streamer initiation. At a negative pin voltage, a spark is formed in the absence of fast primary streamers. At a positive
pin voltage, streamer build-up is initiated by the current spots on the anode that result from the development of the ionization
instabilities in the anode region. The calculations show that the formation of the current spot on the anode leads to a redistribution
of the electric field in the vicinity of the anode, so that a single avalanche is transformed into a streamer under the conditions
when the known criterion for streamer breakdown (the Meek-Raether criterion) is not satisfied.
Original Text ? Astro, Ltd., 2006. 相似文献
2.
The magnetoresistance effects in the bi- and trilayer hybrid planar superconductor/ferromagnet (S/F) structures based on Py (permalloy) and Nb near the superconducting transition temperature T C are considered. It has been experimentally shown that the sign of the observed magnetoresistance peaks in the bilayer S/F systems changes from negative to positive at the permalloy layer thickness corresponding to the change in the type of domain walls from Néel to Bloch. For the Néel walls at the ferromagnet coercive fields, the negative magnetoresistance effect, which is due to a decrease in the depairing action of the exchange field E ex, is observed in the S/F bilayers. For the Bloch domain walls, the magnetoresistance of the bilayer S/F structures is determined by the dissipative motion of Abrikosov vortices in the superconducting layer. In the trilayer F/S/F structures, the magnetoresistance is mainly due to the suppression of the superconducting order parameter in the superconducting layer under the action of the accumulation of the spin-polarized carriers near the S/F interfaces. 相似文献
3.
V. L. Ékelekyan 《Russian Physics Journal》1981,24(7):626-630
Solutions of the Bogolyubov-Born-Green-Kirkwood-Ivon equations in the fourth approximation in the temperature are given in a class of generalized functions both for van der Waals and ionic crystals in the case of the so-called taking into account of smoothed correlations. A statistical thermodynamics of strongly anharmonic van der Waals and ionic crystals is constructed. Temperature expansions of the correlative distribution functions and thermodynamic quantities are investigated within the framework of the indicated method. The temperature dependence of cubic order is taken into account in the expression of the isochoric specific heat and the Grüneisen parameter of the listed crystals. It is shown that the temperature expansion for the isochoric specific heat of anharmonic crystals converges well for a value of the reduced temperature 0.33 Tm (Tm is the melting temperature).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 55–59, July, 1981. 相似文献
4.
Kislyakov A. G. Shkelev E. I. Yastrebov I. P. Savelyev D. V. 《Radiophysics and Quantum Electronics》2003,46(11):852-859
We compare the data on the atmospheric radio emission in two ozone lines with resonance frequencies 96,228 and 101,736 MHz, obtained at the N. I. Lobachevsky State University of Nizhny Novgorod in 1996–2001, with the corresponding results of measuring the number of neutrons in the atmosphere, obtained at the Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (Troitsk, Moscow region) using the NM-64 monitor. It is shown that variations in both the optical depth and the intensity ratio of these lines correlate with variations in the number of neutrons. The maximum observed correlation coefficients for the optical-depth decrements of the lines amount to 0.5–0.6, which is about a factor of 1.5 higher than the maximum correlation coefficient for their intensity ratio. We analyze the dependence of the correlation coefficients on the time shift between data series for the ozone line intensity and the number of neutrons in the atmosphere. It is shown that correlation between these data series almost vanishes for a time shift of about 200 h. We discuss the features of the data on the number of neutrons in the atmosphere and the possibility of the solar origin of neutrons. 相似文献
5.
V. I. Nazaruk 《The European Physical Journal A - Hadrons and Nuclei》2007,31(2):177-183
The role of strong absorption of particles in intermediate and final states has been considered. The range of applicability
of phenomenological models of absorption has been studied. This model is nonuniversal. Its applicability depends on the type
of interaction Hamiltonian and matrix element used. We also demonstrate that the violation of the unitarity condition can
produce a qualitative error in the results. The absorption (decay) in the final state does not tend to suppress the total
process probability as well as the probability of the channel corresponding to absorption. This is true for the reactions,
decays and nˉ conversion in the medium. 相似文献
6.
The capacity and the dielectric loss tangent of a Gd x Mn1–xSe (x ≤ 0.2) solid solution have been measured in the frequency range 1–300 kHz without a magnetic field and in a magnetic field of 8 kOe in the temperature range 100–450 K, and the magnetic moment of the solid solution has been measured in a field of 8.6 kOe. The magnetocapacity effect and the change in the magnetocapacity sign have been observed in room temperature in the paramagnetic region. A correlation of the changes in the dielectric permittivity and the magnetic susceptibility with temperature has been revealed. The magnetocapacity is described using the model with orbital electron ordering and the Maxwell–Wagner model. 相似文献
7.
近年来,科研工作者对ZnO纳米材料研究产生了浓厚的兴趣。ZnO是一种具有宽带隙(3.37 eV)和较大的激子束缚能(60 meV)的六方纤锌矿结构半导体材料。它具有优异的光电、压电、压敏及发光等特性,在发光(激光)二极管、传感器、发光器件、紫外探测器等领域都有非常好的应用前景。至今,有很多非常成熟的实验方法(包括静电纺丝、水热法、溶胶-水热法、化学气相沉积法、旋涂法及电化学沉积法等)用来合成ZnO纳米材料,如纳米线、纳米棒、纳米盘及量子点等。氧化锌纳米结构的制备和性质已得到了广泛的研究,ZnO的可见发光机理一直是研究的热点,但很少有人对可见光范围内的光致发光进行总结。光致发光光谱能反映一些重要信息,如表面缺陷和氧空位、半导体材料的表面状态、光诱导电荷转移过程等。有学者认为ZnO的发光机理与其晶体缺陷有关,还有研究者认为其发光机理与氧空位有关等。通过量子限域效应、带边调制、表面修饰方法、缺陷调控方法等方面综述了ZnO可见区发光机理。 相似文献
8.
Yu. N. Khanin E. E. Vdovin M. V. Grigor’ev L. Eaves O. N. Makarovskiĭ M. Henini 《Journal of Experimental and Theoretical Physics》2007,105(1):177-180
A high narrow peak in the interlayer differential tunnel conductance has been observed in heterostructures with two closely located electron layers at low temperatures. Analysis of the experimental results suggests that this peak is due to the interlayer phase coherence, which appears in the system under investigation owing to the Bose condensation of indirect excitons, i.e., pairs of electrons and holes from different layers in the absence of the magnetic field. 相似文献
9.
10.
邵宇飞 《原子与分子物理学报》2016,33(4):736-744
基于晶体的微观结构提出了一种计算晶体宏观弹性应变场的方法,将该方法应用于金属晶体Fe,得到的应变场与连续介质理论预测结果吻合地很好,从而证明了该方法的准确性.以该方法为基础,进一步考虑无限小应变与有限应变的差值,发现应变差值在晶体剧烈变形区域内较强,对金属晶体Cu位错应变场的计算表明这种应变差异可以用来描述位错的运动状态和芯域结构.该方法可为评估晶体缺陷附近应变状态提供依据. 相似文献
11.
A pronounced peak in the thermal expansion coefficient — and thus in the Grüneisen parameter — has been found at the temperature corresponding to the martensitic transformation in TiNi. This finding, together with results of ultrasound wave propagation studies, attests to anomalous lattice-dynamical behaviour in the vicinity of the phase transition. Ultrasonic wave attenuation and velocity data are interpreted on the basis of Akhieser-type, phonon viscosity damping. Results obtained are consistent with the hypothesis that a soft phonon mode plays a dominant role in the lattice properties of TiNi near the transition. 相似文献
12.
邵宇飞 《原子与分子物理学报》2017,34(6)
基于晶体的微观结构提出了一种计算晶体宏观弹性应变场的方法,将该方法应用于金属晶体Fe,得到的应变场与连续介质理论预测结果吻合地很好,从而证明了该方法的准确性.以该方法为基础,进一步考虑无限小应变与有限应变的差值,发现应变差值在晶体剧烈变形区域内较强,对金属晶体Cu位错应变场的计算表明这种应变差异可以用来描述位错的运动状态和芯域结构.该方法可为评估晶体缺陷附近应变状态提供依据. 相似文献
13.
G. K. Chepurnykh V. A. Chernaya O. G. Medvedovskaya 《Physics of the Solid State》2018,60(9):1712-1717
Taking into account the inexhaustible interest in studying the peculiarities of physical properties in the neighborhood of phase transitions and the growth of experimental investigations of cobalt fluoride, we have studied the peculiarities of magnetic susceptibility in the vicinity of the critical field HC at which cobalt fluoride performs the second-order phase transition from the antiferromagnetic phase to the angular phase. It is discovered that in the magnetic field H ‖ C4, the magnetic susceptibility becomes infinite at H → HC. It is shown that as the magnetic field direction deviates from the C4 axis, the magnetic susceptibility in the critical field HC proves to be finite. It is also shown that the change in the magnetic susceptibility with the change in the magnetic field considerably decreases at extremely insignificant deviations of the field H from the C4 axis. Since the calculations are performed in terms of the Landau theory of phase transitions, we pay attention to the similarity and difference between the obtained results and those in the vicinity of the Curie point obtained by using the Landau theory of phase transitions. 相似文献
14.
A possibility for an increase in the signal-to-noise ratio in the laser spectroscopy that is free of Doppler broadening and is based on the saturated absorption is considered. The application of the counter-propagating laser beams in the multimode regime is proposed. The number of atoms that effectively interact with the field, and, hence, the intensity of a narrow resonance in the line shape can be increased due to the interaction of the counterpropagating modes with different frequencies. It is demonstrated that, for the intrinsic photon noise, the signal-to-noise ratio can be increased by a factor of √N, where N is the number of modes. For the remaining noises (fluctuations of the radiation power, noise of photodetector, etc.), the signal-to-noise ratio can be increased by a factor of N. 相似文献
15.
Using a 1/N expansion for X-operators the leading contributions to the linearized equation for the superconducting gap of the t-J model are derived and the gap equation solved numerically on a square lattice. We find a strong instability towards superconductivity only in the d-wave (T 3) channel with T c/│t│ ~ 0:01 where T c is the transition temperature and t the nearest-neighbor hopping integral. The underlying effective interaction consists of an attractive, instantaneous term with the band width, and a retarded term due to charge and spin fluctuations with ~ J, as energy scale. 相似文献
16.
Vladislav Čápek 《Czechoslovak Journal of Physics》1996,46(11):1001-1009
We apply a previous analysis of the dependence of the dynamic time-convolution equations and their solution on the degree of the initial strength of the polaron cloud to the usual zero-bias spin-boson model and standard second order (i.e. Born) approximation (in tunneling, i.e. the standard dilute blip approximation at =1). At temperatureT=0 and for the usual Ohmic type spin-boson coupling, the asymptotic-time-symmetry-breaking phenomenon as a function of the coupling strentghg can be analyzed, in the above Born approximation, in the wholeg- plane. A hardly interpretable conclusion is found that the symmetry breaking in the above approximation appears just at discrete lines in the plane. This implies instability of the phenomenon in the second-order theory with respect to arbitrarily small perturbations of the initial state and complies with exact proofs of absence of the partial symmetry-breaking phenomenon in analogous symmetric models.The author has pleasure in acknowledging fruitful discussions with Dr. P. Chvosta and Prof. M. Wagner. Supports of grants 292/1994 from the Grant agency of Charles University and 202/93/2428 from the Czech Grant Agency are also gratefully acknowledged. 相似文献
17.
We have carried out an investigation of the nature of the 1 ns intermediate component in the positron time annihilation spectra of five polymers (atactic and isotactic polypropylene, polymethylmethacrylate, teflon, and polyethylene), using the magnetic quenching technique at high fields (1.5–3 T), coupled to lifetime spectroscopy. The results indicate that this component comes from the decay of a positron-electron bound system, different from that associated with the longest lifetime component. Therefore, two different Ps-like systems must be considered in the investigated polymers. 相似文献
18.
PENG Huanwu 《理论物理通讯》1999,31(1):13-20
Following Chou's viewpoint that the Cartesian system of space coordinates and timedefines a Minkowskian space-time in which Einstein's field equations and the harmonic conditionare the laws of gravitation (Ref.[1]), we study the effects of an external gravitational fieldin the propagation and in the emission of light respectively from the generalized Maxrwell andDirac equations of the general theory of relativity by geometric optics and quantum mechanics,and get the usual results for the red shift. For the naively homogeneous and isotropic model ofcosmology (the case with k = 0 in the Robertson-Walker scheme) closed form for the relationbetween distance and red shift is obtained, which indicates that a new way of analyzing theobservational data with not too small red shifts is needed. 相似文献
19.
We study the finite dimensional marginals of the Gibbs measure in the Hopfield model at low temperature when the number of patterns, M, is proportional to the volume with a sufficiently small proportionality constant > 0. It is shown that even when a single pattern is selected (by a magnetic field or by conditioning), the marginals do not converge almost surely, but only in law. The corresponding limiting law is constructed explicitly. We fit our result in the recently proposed language of metastates which we discuss some length. As a byproduct, in a certain regime of the parameters and (the inverse temperature), we also give a simple proof of Talagrands recent result that the replica symmetric solution found by Amit, Gutfreund, and Sompolinsky can be rigorously justified. 相似文献
20.
Paul C. Fife 《Journal of statistical physics》1985,39(5-6):687-703
Conclusion It has been pretty well established that the PC system examined in this talk is a realistic model for the spatially distributed BZ reagent under commonly occurring parameter conditions. The analysis of the system is straightforward and provides a clear picture of the mechanism behind the appearance of fronts, trains, solitary pulses, and target patterns, and behind the generation of spirals, under those conditions. In fact, the PC model has been remarkable successful in reflecting observed phenomena (see a discussion of this point in Ref. 34). Spiral-like structures in 3-space have been called scrolls by A. Winfree; their generation can also be easily understood along these same lines, as resulting from local disturbances of plane solitary waves propagating through 3-space. Fully developed spirals can likely be understood in this same PC context as solutions of the free boundary problem presented in Section 7; more mathematical and numerical work should be done on that problem.Very possibly other parameter conditions exist for which similar spatial patterns can be seen in the BZ reagent, but for which the PC framework is not appropriate; and very likely other excitable biological or chemical media, supporting such patterns, may require other models for their understanding. Nevertheless, it appears likely that models having many of the properties of the one studied here will play a significant role in the unraveling of these more complex systems. 相似文献