Time filter

Source Type

Starkov A.S.,St Petersburg National Research University Of Information Technologies | Starkov I.A.,Brno University of Technology
Journal of Experimental and Theoretical Physics | Year: 2014

It is proposed to use a generalized matrix averaging (GMA) method for calculating the parameters of an effective medium with physical properties equivalent to those of a set of thin multiferroic layers. This approach obviates the need to solve a complex system of magnetoelectroelasticity equations. The required effective characteristics of a system of multiferroic layers are obtained using only operations with matrices, which significantly simplifies calculations and allows multilayer systems to be described. The proposed approach is applicable to thin-layer systems, in which the total thickness is much less than the system length, radius of curvature, and wavelengths of waves that can propagate in the system (long-wave approximation). Using the GMA method, it is also possible to obtain the effective characteristics of a periodic structure with each period comprising a number of thin multiferroic layers. © 2014, Pleiades Publishing, Inc.


Brody D.C.,Brunel University | Brody D.C.,St Petersburg National Research University of Information Technologies
Journal of Physics A: Mathematical and Theoretical | Year: 2016

In recent reports, suggestions have been put forward to the effect that parity and time-reversal (PT) symmetry in quantum mechanics is incompatible with causality. It is shown here, in contrast, that PT-symmetric quantum mechanics is fully consistent with standard quantum mechanics. This follows from the surprising fact that the much-discussed metric operator on Hilbert space is not physically observable. In particular, for closed quantum systems in finite dimensions there is no statistical test that one can perform on the outcomes of measurements to determine whether the Hamiltonian is Hermitian in the conventional sense, or PT-symmetric - the two theories are indistinguishable. Nontrivial physical effects arising as a consequence of PT symmetry are expected to be observed, nevertheless, for open quantum systems with balanced gain and loss. © 2016 IOP Publishing Ltd.


Nemilov S.V.,St Petersburg National Research University Of Information Technologies
Glass Physics and Chemistry | Year: 2013

The main relaxation theories of glass transition (Leontovich-Mandelstam and Volkenstein- Ptitsyn) variously formulate the kinetic criteria of glass transition. Both of the approaches are shown to be equivalent in physical sense and provide a single expression that connects the rate of change of a melt temperature and the structure relaxtion time. The theory characterizes the width of a temperature band δTg in which the glass transition occurs. The values of δTg can either be obtained from the experiment or be accepted to conform to the value of a temperature step under the change of viscosity by an order of magnitude (direct method for finding by the Volkenstein-Ptitsyn theory). Using the Maxwell equation, a new equation for the calculation of the viscosity for viscoelastic relaxation was suggested, which is based on a shear modulus of glass and the cooling rate. The theory was verified basing on the published data for oxide glass. The average difference between the calculated and measured values of lgη upon glass transition comprises 0 ± 0.30. These results correspond to the cooling rate of 3 K/min and log(η, Pa s) = 12.76 ± 0.26 (for all glass considered). It is shown that the most probable cooling rate which provides the viscosity upon glass transition of ∼1012 Pa s is close to 20 K/min (oxide melts). The theory predetermines the dependence of viscosity upon glass transition on the nature of a glass-forming liquid. The disadvantages of other approaches to the problem under consideration are demonstrated. Original Russian Text © S.V. Nemilov, 2013.


Amosova L.P.,St Petersburg National Research University Of Information Technologies
Journal of Optical Technology (A Translation of Opticheskii Zhurnal) | Year: 2013

This review discusses how the main parameters of the deposition regimes of the oxides of semiconductors and metals affect the structure and relief of a precipitated film and analyzes the orientation mechanisms of liquid crystals (LCs) by means of such films. The dependence between the deposition angles, the tilt of the crystallites, and the tilt of the LC director is reported. It is shown that, when the deposition angle of the orienting film is increased relative to the substrate plane, it can be energetically favorable to make a transition either to the planar or the homeotropic orientation of the LC, depending on the film-deposition rate. © 2013 Optical Society of America.


Grebenkov D.S.,CNRS Condensed Matter Physics Laboratory | Grebenkov D.S.,St Petersburg National Research University Of Information Technologies
Journal of Physics A: Mathematical and Theoretical | Year: 2014

We revise the classical problem of characterizing first exit times of a harmonically trapped particle whose motion is described by a one- or multidimensional Ornstein-Uhlenbeck process. We start by recalling the main derivation steps of a propagator using Langevin and Fokker-Planck equations. The mean exit time, the moment-generating function and the survival probability are then expressed through confluent hypergeometric functions and thoroughly analyzed. We also present a rapidly converging series representation of confluent hypergeometric functions that is particularly well suited for numerical computation of eigenvalues and eigenfunctions of the governing Fokker-Planck operator. We discuss several applications of first exit times, such as the detection of time intervals during which motor proteins exert a constant force onto a tracer in optical tweezers single-particle tracking experiments; adhesion bond dissociation under mechanical stress; characterization of active periods of trend-following and mean-reverting strategies in algorithmic trading on stock markets; relation to the distribution of first crossing times of a moving boundary by Brownian motion. Some extensions are described, including diffusion under quadratic double-well potential and anomalous diffusion. © 2015 IOP Publishing Ltd.


Trofimuk A.A.,St Petersburg National Research University Of Information Technologies
Journal of Optical Technology (A Translation of Opticheskii Zhurnal) | Year: 2013

This letter shows how to use Bezier curves in the design of nonimaging reflectors and lenses. The curve is simplified to increase the ray-tracing rate. A program library is created that describes objects on the basis of Bezier curves, using the ZEMAX system. A technique for optimizing and calculating the secondary optics of LEDs is considered. © 2013 Optical Society of America.


Amosova L.P.,St Petersburg National Research University Of Information Technologies
Semiconductors | Year: 2015

Thin indium-tin oxide (ITO) films are deposited onto cold substrates by magnetron-assisted sputtering. The dependences of the structural, electrical, and optical properties of the films on the oxygen content in the atmosphere of sputtering and the growth rate are studied. It is shown that, if the substrate temperature is no higher than the ITO crystallization temperature and the conditions of growth deviate from the optimal relationship between the oxygen pressure and the growth rate, the resistance of the layers can be six or seven orders of magnitude higher than the resistance of conducting amorphous layers and reach hundreds of megaohms. At the same time, the optical properties of insulating layers in the visible spectral region are completely identical to the properties of the conducing amorphous modification. A conceptual model of defects responsible for the insulating properties of amorphous ITO is proposed. © 2015, Pleiades Publishing, Ltd.


Ermolaev V.L.,St Petersburg National Research University of Information Technologies | Sveshnikova E.B.,St Petersburg National Research University of Information Technologies
Russian Chemical Reviews | Year: 2012

The features of co-luminescence (sensitized luminescence) of lanthanide ions and dye molecules inserted in nanoparticles of complexes formed by trivalent metals with b-diketones are discussed. The mechanisms of energy transfer in these nanoparticles that lead to sensitization of Ln3+ ion luminescence and dye molecule fluorescence are considered. It is shown that the process of nanoparticle formation and their morphology in aqueous solutions can be studied by analyzing the mechanism of their co-luminescence and co-fluorescence. Examples of chemical, biological and medicinal applications of nanoparticles containing lanthanide ions and dye molecules with enhanced luminescence brightness are given. The bibliography includes 131 references. © 2012 Russian Academy of Sciences and Turpion Ltd.


Popov I.Y.,St Petersburg National Research University Of Information Technologies | Smirnov P.I.,St Petersburg National Research University Of Information Technologies
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

Branching chain of rings as a quantum graph is considered. We use the transfer matrix method to obtain the spectral equation. The existence of bound states is proved. The discrete spectrum of the Schrödinger operator for the system is described. We find the dependence of the eigenvalues positions on the branching angle. © 2013 Elsevier B.V.


Potapov A.S.,St Petersburg National Research University Of Information Technologies
Journal of Optical Technology (A Translation of Opticheskii Zhurnal) | Year: 2012

This paper analyzes the necessity of using many information representations simultaneously in image-processing and -analysis systems. The difference between Kolmogorov-complexity and algorithmic-probability criteria when solving induction problems and making decisions is investigated. It is shown that making the optimum decisions (for example, in recognition or prediction problems) requires the use of many representations of information, in terms of which alternative descriptions of the images are constructed. A representational algorithmic-probability criterion is derived for determining the optimum set of representations from a given selection of images. © 2012 Optical Society of America.

Loading St Petersburg National Research University Of Information Technologies collaborators
Loading St Petersburg National Research University Of Information Technologies collaborators