Chaos-controlling technique for suppressing self-modulation in backward-wave tubes

A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space. Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly twofold.     

Lorentz-Covariant Loop Quantum Gravity

We review the Lorentz-covariant approach to loop quantum gravity. This approach solves the Immirzi parameter problem occurring in the standard loop approach based on the SU(2) gauge group. We show that there exists a unique loop quantization preserving all the classical symmetries at the quantum level and that the results obtained with it, such as the area operator spectrum, are independent of the Immirzi parameter. The standard SU(2) approach violates the diffeomorphism invariance and is therefore an incorrect quantization of gravity.     

Quantum Dot and Antidot Infrared Photodetectors: Iterative Methods for Solving the Laplace Equation in Domains with Involved Geometry

We propose iteration methods for solving the Dirichlet problem in domains with involved geometry. Such problems arise in relation to the problem of optimizing quantum dot and antidot infrared detectors. We estimate the deviation of an approximate solution from the exact solution.     

Synthesis and electrical characteristics of polyaniline nanoparticles and their polymeric composite

Monodisperse polyaniline nanoparticles (PAPSSA) were synthesized from an oxidative dispersion polymerization using poly(sodium 4-styrenesulfonate) (PSSA) as both a polymeric stabilizer and a dopant agent due to its acidity. The nanoparticles were being stabilized with two different molecular weight of PSSA. Size effect of PAPSSA particles were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The d.c. electrical conductivity of composite films on the glass substrate was measured by a four-probe method. It was found that the electrical properties of the composite films are affected by the content of nano-sized polyaniline and different molecular weights of stabilizer in the poly(vinyl alcohol) (PVA) matrix.     

Influence of the Interaction between Two Neighboring Periodically Curved Fibers on the Stress Distribution in a Composite Material

A method is developed for a stress analysis in an infinite elastic body containing two neighboring periodically cophasaly curved fibers located along two parallel lines. The stress distribution is studied when the body is loaded at infinity by uniformly distributed normal forces in the fiber direction. The investigation is carried out within the framework of a piecewise homogeneous body model with the use of exact three-dimensional equations of elasticity theory. Numerical results related to the stress distribution considered and the influence of interaction between the fibers on this distribution are given.     

Variety of LaSrMnO structures induced by growth conditions and laser irradiation

Crystallographic phase transitions in perovskite-like LaSrMnO metallic oxides are studied. The transitions are induced when internal stresses generated during film synthesis (at temperatures between 450 and 730°C) vary (decrease or increase) upon subsequent irradiation by a KrF laser emitting in the UV range. As the synthesis temperature T _s grows, the rhombohedral-to-orthorhombic phase transition occurs at 650–670°C. The resistivity is shown to be either temperature-independent, ρ(T)=const, at T<T _crit, or varies and reaches a maximum, ρ(T)=ρ_max, at the Curie temperature T _c. Optical transmission spectra taken at photon energies ℏω=0.5–2.5 eV exhibit both a high (0.8–0.9) and low (0.1–0.3) transmission coefficient t, depending on the synthesis temperature. As follows from X-ray diffraction data, the laser irradiation causes a phase transition only in LaSrMnO films grown at T _s<650°C. Phases of different size scales appear: the long-range-order orthorhombic matrix and mesoscopic-range-order rhombohedral clusters are observed in the films grown at T _s=450–550°C and the rhombohedral matrix with orthorhombic clusters, in the films grown at T _s=550–650°C.     

1,1,3-Trimethyl-3-phenylindan as a Luminescent Additive to a Plastic Scintillator Based on Poly(methyl Methacrylate)

The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied.     

电镀污水净化新工艺--电浮选方法简介

综述了电浮选方法处理电镀污水的基本原理和提高电浮选净水技术的途径。重点介绍了俄罗斯门捷列夫化工大学的电浮选两种新工艺方法。     

Determining Modes for Continuous Data Assimilation in 2D Turbulence

We study the number of determining modes necessary for continuous data assimilation in the two-dimensional incompressible Navier–Stokes equations. Our focus is on how the spatial structure of the body forcing affects the rate of continuous data assimilation and the number of determining modes. We treat this problem analytically by proving a convergence result depending on the H ^–1 norm of f and computationally by considering a family of forcing functions with identical Grashof numbers that are supported on different annuli in Fourier space. The rate of continuous data assimilation and the number of determining modes is shown to depend strongly on the length scales present in the forcing.