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.     

Attractive component in the nucleon-nucleon interaction in the skyrme model

The spin- and isospin-independent part of the nucleon-nucleon interaction in the Skyrme model is shown to contain a weak attractive intermediate-range term in addition to the well-known short-range repulsion. The attraction is a consequence of the rotational degree of a skymion in the presence of the field of another one, and can be thought of as an enhancement of the moment of inertia of each skyrmion. While the attractive term is dominant at large distances it is not sufficiently strong for nuclear binding.     

Absorption in the final state in reactions and decays in the medium

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.     

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.     

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.     

On the Energy-loss in the CERENKOV Radiation

The object of this paper is to find the electromagnetic field and the rate of increase of the field energy due to a pair of charged particles soon after their creation. It is shown that in case of the CERENKOV radiation, there is a constant rate of increase of the field energy. The power spectrum is similar to that obtained in the usual formulation, where the particles are assumed to be moving with uniform velocity since infinite past.     

Hydrogen recombination in the early Universe in the presence of a magnetic field

Hydrogen recombination in the earlyUniverse in the presence of amagnetic field is studied. An equation for the recombination temperature in the presence of a magnetic field is obtained. The limiting cases of weak and strong magnetic fields are examined. A critical field above which the system being considered is in the atomic-hydrogen phase at any temperature is shown to exist. The relative shift of the recombination temperature in a magnetic field is estimated, and it is shown that this shift is small.     

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.     

Breakdown of renormalizability in the Kondo problem in the high-temperature expansion of the free energy

It is shown that there are two energy scales in the Kondo problem: T _k and T ₀, one of which (T _k) is exponentially small in the coupling constant g. The second scale T ₀is proportional to the squared coupling constant. Perturbation theory is valid only in the region T? T ₀. The point T ₀ is apparently the crossover from weak to strong coupling. The first indications of the breakdown of the hypothesis of only one energy scale in the Kondo problem appear in fourth order of perturbation theory.     

Representation of the spin in the Dirac equation for the electron

The conventional interpretation of the spin matrices contained in the Dirac equation for the electron is considered to be mostly unintelligible in the operational sense. It is shown that it appears that the interpretation is often illogical. The necessity of a more comprehensible interpretation of the concerned equation is implied.     

Antimatter in the Universe

Summary The evidence for cosmologically significant amounts of antimatter in the Universe is reviewed. There is no compelling evidence, either theoretical or experimental, for a baryon-symmetric Universe. The possibility is not completely ruled out, however. This essay is dedicated to the memory of the late Robert Golden, a pioneer in the search for antimatter in the cosmic radiation. Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Metal-insulator transition in many valley semiconductors in the spirit of the Hubbard model

The metal-insulator transition using different dielectric functions is investigated for a many valley semiconductor system within the effective mass approximation. The critical concentration as well the value of the Mott constant is enhanced when the Hartree-Fock dielectric function is used with the inclusion of exchange and correlation effects. In the absence of localization, the obtained value of Mott constant is critically examined in terms of Hubbard model. The effects of Anderson localization, exchange and correlation in the Hubbard model are included in a simple way. The relationship between the present model and the Mott criterion in terms of Hubbard model is also brought out. The critical concentration is enhanced when a random distribution of impurities is considered. The value of α is fixed demanding the vanishing of the donor binding energy with the donor concentration for several donors in Si and Ge. Results are compared with the existing data available and discussed in the light of existing literature.     

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.     

The Continual Approach in the Yang-Mills Theory in the External Non-Abelian Field

The theory of Yang-Mills field in interaction with matter fields is considered in the presence of external gauge field. A closed expression for the generating functional of the Green functions is obtained, and a detailed analysis of the Green functions of the scalar, spinor, ghost and Yang-Mills fields is performed. The path-integral solution for all these Green functions is obtained, which includes the functional averaging over the classical trajectories in the space of commuting and anticommuting variables, the latter being anociated with the particle spin and isospin. For illustration an arbitrary Abelian-like external field is considered, as well as non-Abelian-like constant external field.     

On the glueball spectrum in the Klebanov-Strassler model

The spectrum of the linearized equations of IIB supergravity above the Klebanov-Strassler background solution is investigated. It is shown that the spectrum of a scalar particle minimally interacting with the background is degenerate with the spectrum of the graviton (traceless spin-2 mode), and this spectrum is studied in detail. The results are generalized to the more general case of the solution that is known in the literature as a baryonic branch.     

套管中模式波的响应特征

在固井质量评价中主要利用套管中模式波的幅度或衰减变化反映水泥的胶结状况,不同测井仪器在套管中激发的模式波的类型不同,研究套管中各模式波的传播特征和影响因素可充分挖掘测量数据的潜在应用价值。CBL和SBT等测井仪器在套管中主要激发拉伸波,类同于平板中的零阶对称Lamb波,水泥环封隔测井仪器的斜入射模式在套管中主要激发套管弯曲波,类同于平板中的零阶反对称Lamb波,垂直入射模式激发套管共振波,类同于平板中的高阶对称Lamb波。该文重点分析了这些模式波的衰减特征及其对微环的响应,套管弯曲波在套后耦合轻质水泥时对微环不敏感,但在套后耦合常规水泥或重水泥时,其衰减明显高于胶结良好的状况;拉伸波对微环的存在最为敏感;套管共振波对微环不敏感。     

Change in the critical exponent of magnetization in maghemite in the temperature range of the structural phase transition

The magnetization of maghemite and magnetite thin films is measured as a function of the temperature and orientation of the film. It is established that the temperature dependence of the spontaneous magnetization deviates from the Bloch law at low temperatures and is adequately described by the linear function M/M _s = 2.2(1-T/T _C) below the Curie temperature T _C. The linear temperature dependence of the magnetization below the Curie temperature is explained by the change in the spin of iron ions in tetrahedral positions due to local deformations of the crystal lattice.     

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     

立体成型中扫描误差的分析

对立体成型技术中广泛使用的振镜扫描系统进行了理论分析,指出了振镜的二维扫描偏转角和平面坐标之间存在着非线性映射关系.提出了一种实用的校正算法,该算法用理论数据与激光束在相应点的实际数据进行比对,制成校正表,按插值算法校正实际的枕形畸变及其它误差.该算法适用于使用振镜实现二维扫描的系统,能对应用这种原理工作的激光成型设备进行现场校正.