On the Numerical Calculation of Frustrations in the Ising Model

JETP Letters - A quantitative measure of magnetic frustration is defined as a thermodynamically averaged relative number of excited pair interactions in the Hamiltonian of a system. The Metropolis...     

Traps in the Nanocomposite Layer of Silicon–Silicon Dioxide and Their Effect on the Luminescent Properties

Physics of the Solid State - The traps of charge carriers in thermal films of silicon dioxide and silicon dioxide with a nanocomposite layer consisting of silicon oxide and silicon nanocrystallites...     

Photorefractive properties of a nanocomposite based on a ferroelectric polymer

The photorefractive effect is demonstrated for the first time for the composite consisting of a ferroelectric material (polyvinylidenefluoride-trifluoroethylene) and single-walled carbon nanotubes that serve as nonlinear optical chromophores and, simultaneously, spectral sensitizers for the laser radiation with a wavelength of 1064 nm. It is demonstrated that the internal field in the ferroelectric material makes it possible to measure the photorefractive effect in the absence of the external field.     

The sound velocity, internal friction, and thermal expansion in a single crystal of La0.85Sr0.15MnO3

The results are given of the investigation of the temperature dependence of the sound velocity v, internal friction Q ^?1, and thermal expansion ΔL/L of a single crystal of La_0.85Sr_0.15MnO₃ in the temperature range from 5 to 400 K. Clearly defined singularities of the elastic properties at a temperature of charge ordering T _co≈200 K are revealed. The results of X-ray diffraction studies performed at room temperature are used to determine the orientations and estimate the sizes of twins. The correlation between magnetic and structure inhomogeneities is established. Based on the results of analysis of the temperature dependence of internal friction and thermal expansion, an assumption is made of the presence in a single crystal of La_0.85Sr_0.15MnO₃ of a structural transition in the temperature range from 15 to 60 K that has not been observed previously.     

Investigation of free and bound excitons in strained ZnTe films grown by MBE on GaAs(100) substrates

A study is reported of the reflectance and low-temperature photoluminescence (PL) spectra of ZnTe films grown by molecular-beam epitaxy (MBE) on GaAs substrates [(100) orientation, 3° deflection toward 〈110〉]. It is shown that the strain-induced splitting of the free-exciton energy level (ΔE _ex) does not depend on ZnTe film thickness within the 1–5.7 μm range and is due to biaxial in-plane film tension. The stresses are primarily determined by the difference between the thermal expansion coefficients of the film and the substrate. It is also shown that the residual stresses originating from incomplete relaxation of the film lattice parameter to its equilibrium value at the growth temperature likewise provide a certain contribution. The position of the spectral line of an exciton bound to a neutral acceptor (As) is well approximated in terms of the present models, taking into account the stresses calculated using the value of ΔE _ex.     

Relativistic microwave devices with postacceleration of an electron beam in the interaction space

We analyzed the possibility of improving the efficiency of microwave devices operating with relativistic electron beams in systems with particle postacceleration in the interaction space. The fundamental feature of this approach is the formation of the accelerating-potential profile with the inherent electric field of a high-current electron beam. It is shown that the use of the space-variant beam-potential sag helps raise the estimated efficiencies of relativistic Cherenkov TWT and BWO up to values of about 50%.     

Determination of the Absorbing and Scattering Properties of the Sea Floor in a Shallow Water Environment by the Spectra of Wide-Band Signals

Sound propagation in a shallow sea is considered within the framework of the two-component model of the sea floor. The porosity and the coefficients of absorption and volume scattering are treated as the parameters characterizing the sea floor. These parameters are determined on the basis of the comparison between the experimental and theoretical frequency spectra of a signal received from a wide-band source. A conclusion is made about the relative contributions of different mechanisms of losses (absorption or scattering) in the sea floor at different sound frequencies.     

Automatic computation of the geometrical characteristics of a surface modified by a scanning nanohardness tester

A technique for automatic determination of the contact area of a remnant impression obtained by nanoindentation with regard to a surrounding relief is suggested. An algorithm on which the suggested technique is based and an algorithm to automatically correct scanning defects are described. The hardness values determined by dynamic nanoindentation and by direct measurement of the impression are compared.     

Calculation of the diffusion coefficient in acoustic turbulence

The first (Born) approximation commonly used to calculate the diffusion coefficient D_T of a passive scalar in acoustic turbulence is shown to be insufficient. Even for a small main parameter—the Mach number, M?1—the next approximation gives a larger contribution to D_T than does the first approximation, but negative in sign. We present a procedure for correctly calculating D_T based on the solution of a nonlinear DIA (direct interaction approximation) equation for the mean Green’s function of the problem. We include an additional term in the general formula for D_T that directly describes the compressibility of acoustic turbulence. This term has not been known previously and has been disregarded even in the Born approximation. A positive value was obtained for D_T=CM³u₀/p₀. The spectrum E(x) was assumed to be smooth at distances Δ x～M²?1.