Role of the near-electrode regions in the formation of the volume discharge heterogeneity in nitrogen in the pin-to-plane configuration

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.     

Change in the Magnetocapacity in the Paramagnetic Region in a Cation-Substituted Manganese Selenide

The capacity and the dielectric loss tangent of a Gd _x Mn_1–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.     

Structure in the temperature dependence of the lifetime of the excited F-center in KCl

Evidence of a temperature-dependent structure in the lifetime of excited F-centers in KCl is reported. The sharp features are revealed when the temperature control of the sample is better than a few hundreth of a degree. For less accurate temperature control, as currently used in lifetime measurements, sharp variations of the lifetime with temperature are averaged, and the structure is not detectable. A theoretical explanation is suggested.     

ZnO可见区发光机理研究进展

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。     

Superconductivity in the t-J model in the large-N limit

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.     

嵌入单量子点Aharonov-Bohm环中的近藤效应

使用单杂质的Ansderson模型, 从理论上研究了一个嵌入单量子点Aharonov-Bohm环系统处在 近藤区时的基态性质, 并用slave-boson平均场方法求解了该模型.结果表明：在零温, 当介 观环内电子平均能级间隔大于近藤关联能时, 系统内仍然存在一个被减弱了的近藤效应；系 统的基态性质依赖于系统的宇称和环的大小；而尺寸效应和近藤屏蔽效应的共存导致了系统 丰富的物理性质.同时, 可以通过测量介观环中的持续电流和杂质磁化率, 达到探测近藤屏 蔽云的目的. 关键词： 持续电流 杂质磁化率 宇称效应 近藤效应 近藤屏蔽云     

An increase in the sensitivity of the saturated absorption method in the multimode regime

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.     

Operators on the fock space,diagonal in the wave-packet formalism and in the mode representation

We establish the conditions that an operator on the Fock space, diagonal in the mode representation, must verify to have a diagonal form in the wave-packet (W. P.) formalism. And we show that, if these conditions are verified, there is only one set of W.P. on which such a given operator is diagonal. The interest of these results lies in the probabilistic interpretation of a diagonal density matrix in the W.P. formalism; indeed a field described by such a density matrix may be considered as a mixture of one particle W.P. In particular our results apply to chaotic density matrices and prove that there is one way only of describing a given chaotic field as a mixture of one particle W.P.     

Metastates in the Hopfield Model in the Replica Symmetric Regime

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.     

Correlation between Variations in the Number of Neutrons in the Atmosphere and in the Intensities of the Atmospheric Ozone Lines

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.     

On the instanton effect in the finite temperature Yang-Mills theory and in the non-linear σ-model

We have considered the effect of instantons at finite temperature on the interquark force and the order parameter of the Yang-Mills theory, finding a sharp change of regime at a temperature close to the one obtained in the Monte Carlo study. We have also considered the problem of the generation of the mass gap in the non linear σ-model in 2 dimensions. This illustrates the role of the instantons, the intrinsic limitations of the approximations made and suggests a physical picture as in the case of Yang-Mills theory.     

Solutions of the BBGKI equations in the fourth approximation in the temperature

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 T_m (T_m is the melting temperature).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 55–59, July, 1981.     

Understanding the patterns in the BZ reagent

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.     

基于微观结构计算晶体宏观弹性应变场

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.     

强非局域非线性介质中光束传输的Ince-Gauss解

利用强非局域非线性介质中傍轴光束传输的线性模型（Snyder-Mitchell模型）讨论了椭圆坐标系下光束传输过程,通过设立Ince多项式对Gauss函数的调制解得到了强非局域非线性介质中光束稳定传输的Ince-Gauss解.当Ince-Gauss光束的入射功率为临界功率时,光束保持孤子形式传输,否则传输光束的束宽呈现周期性波动,即为呼吸子形式.同时还数值模拟了呼吸子的传输过程.Ince-Gauss光在一定条件下可以连续转换为Hermite-Gauss光或Laguerre-Gauss光,图示展现了几个低阶Ince型光孤子及其转换情况. 关键词： 强非局域非线性介质 Ince-Gauss光 Laguerre-Gauss光 Hermite-Gauss光     

基于微观结构计算晶体宏观弹性应变场

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.     

Crossover in the slow decay of dynamic correlations in the lorentz model

The long-time behavior of transport coefficients in a model for spatially heterogeneous media in two and three dimensions is investigated by molecular dynamics simulations. The behavior of the velocity autocorrelation function is rationalized in terms of a competition of the critical relaxation due to the underlying percolation transition and the hydrodynamic power-law anomalies. In two dimensions and in the absence of a diffusive mode, another power-law anomaly due to trapping is found with an exponent -3 instead of -2. Further, the logarithmic divergence of the Burnett coefficient is corroborated in the dilute limit; at finite density, however, it is dominated by stronger divergences.     

Manifestation of the Dynamics of Spin Temperature in EPR in the Absence of Interaction with the Lattice

Within the framework of the concept of spin temperature in electron paramagnetic resonance (EPR) in the absence of the interaction with the lattice, the time dependence for spin temperatures of the Zeeman subsystem and dipole–dipole reservoir is theoretically investigated in both high- and low-temperature approximations. It is shown that the gain can be produced in the system by switching the frequency of the saturating field. The gain in the system as a function of the detuning of the frequency of the saturating field is investigated in a high-temperature approximation. In the presence of a test field in a high-temperature approximation, the possibility of determining the magnitude of a local magnetic field, which is associated with the time of transverse relaxation of the system, is discussed.     

Lattice properties in the vicinity of the martensitic transformation in TiNi

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.     

Instabilities in foam clusters related to the pressures in the bubbles

We reinterpret an instability in a two-dimensional free foam cluster previously discussed by Weaire et al. (Eur. Phys. J. E 7, 123 (2002)) in terms of the excess pressure in the bubbles. We conclude that in a free foam cluster no bubble can have a pressure below that of the surrounding gas. Received: 20 September 2002 / Accepted: 5 May 2003 / Published online: 27 May 2003 RID="a" ID="a"e-mail: fatima.vaz@ist.utl.pt