Quantum discreteness effects and flicker fluctuations in tunneling conductivity

An analysis of events in the tunneling junction shows that the interaction of one-electron processes in a many-electron system may be a source of scale-invariant low-frequency fluctuations of conductivity (the interaction consists in that the quantum probability of an electron transition depends on fast random changes in the environment in the course of the transition, including the changes caused by analogous transitions). The theory relates flicker fluctuations in the tunneling conductivity to the discrete character of the spectrum of electron states and explains the nonlinearity of the noise-current characteristic observed in nanocomposites.     

Modulation of the phase difference between polarization modes in single-mode fibers

Mechanisms of polarization modulation in a single-mode fiber that modulate the phase difference between polarization modes without affecting their amplitudes are considered. A coefficient that characterizes the efficiency of cylindrical piezoceramic modulators and is independent of their resonant properties is introduced. Analytical expressions for this coefficient for different modulation mechanisms are derived. The lateral pressure on the fiber is shown to provide the highest efficiency. For isotropic fibers, a modulator with a squeezing covering, which increases significantly its efficiency, is studied. For anisotropic fibers, the most appropriate way of phase difference modulation is longitudinal extension, in which case the birefringence axes do not have to be matched. In most cases, the measured and predicted efficiencies are in good correspondence.     

Analytical investigation into the mechanism of dielectric losses due to interlayer polarization

The theory of dielectric space-charge polarization losses describes well both the model of an inhomogeneous dielectric [1] and the polarization resulting from mosaic blocks of alkali-halide crystals [2]. The Debye frequency dependences ε*(ω) and tan δ(ω) with non-Arrhenius relaxation time are calculated in the first approximation of perturbation theory [3, 4] with the use of a nonlinear system of the Fokker-Planck and Poisson equations for the interlayer polarization with allowance for tunnel transitions of relaxation oscillators. For the Maxwell mechanism of space-charge relaxation, tan δ(ω) also has the Debye form [5]. It should be noted that in studies cited above the electric field was considered uniform, and the nonlinearity of the initial system of equations was not investigated. This paper removes these restrictions and elaborates a theory of relaxation mechanism. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 28–34, November, 2006.     

Atomic configurations in close-packed lennard-jones systems

Conclusions DS provide a convenient means of researching local atomic configurations in disordered systems. On the one hand, a DS is a strictly defined geometrical structure, while on the other hand the shapes of the simplexes directly reflect the atomic disposition.New characteristics T and O have been proposed for DS shape and allow one to distinguish the corresponding configurations reliably. It is evident that a close-packed system of spherical atoms contains considerable proportions of slightly distorted tetrahedral and octahedral configurations. In a disordered close packing of soft spheres, such configurations form distinct classes similar to those occurring in an FCC crystal.Institute of Chemical Kinetics and Combustion, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 28, No. 2, pp. 62–69, March–April, 1987.     

Investigation and reduction of variance of a weighted estimate in numerical statistical simulation

The efficiency of the “value” and “partial value” modeling related to the construction of a modeling distribution for an auxiliary random variable by multiplying the initial density by a value function is investigated. The value function usually corresponds to a solution of the adjoint equation. Conditions under which the value modeling of the initial distribution reduces the variance compared to the direct simulation are obtained. It is proved that the variance of the weighted estimate is bounded in the case of the partial value modeling. This proposition provides a basis for a method for determining whether or not the variance of the weighted estimate is bounded. This method uses the majorizing adjoint equation. Using a practically important problem in transport theory as an example, the asymptotic optimization of the distribution of the mean free path is presented. The application of the proposed method of the investigation of the variance boundedness for the analysis of the classical exponential transformation method of simulating the mean free path of a particle in the one-dimensional and the spherical variants is discussed.     

Magnetic field penetration into half-space for type-II superconductors of the second kind

Equations that simulate the magnetic induction and current density distributions in half-space in view of the power I-V characteristic are derived. The magnetization front velocity is determined for a given mean rate of external magnetic field variation at the boundary of the sample. An integral condition for the electrical resistance (nonlinearly depending on the magnetic field) under which the magnetic flux penetrates into the sample with a finite rate is found. An analytical solution that simulates the power variation of the magnetic field at the boundary is given. The Bean generalized model describing the current density distribution near the critical current is considered. It is shown that solutions like shock waves may arise beyond the applicability domain of the Bean model.     

Hund’s Case (a)-case (b) transition in the singlet-triplet absorption spectrum of pyrazine in a supersonic jet

An analytic expression is derived for calculating the intensities of individual spin-rovibronic lines in the fully resolved gas phase electronic spectrum of a polyatomic molecule, in which one of the zero-order electronic states is a triplet state. The expression is employed to calculate the effect of fine structure splitting on the singlet-triplet absorption spectrum of pyrazine using the parameters available from experiment. A transition from Hund’s coupling Case (a) to Case (b) on going from low J to high J rotational levels is predicted to occur at a moderate resolution of a few hundred MHz. The effect is more pronounced in pyrazine-d ₄ and the pyrazine-argon van der Waals complex owing to their larger mass. Zh. éksp. Teor. Fiz. 114, 63–90 (July 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.