Voronezh State University

About: Voronezh State University is a education organization based out in Voronezh, Russia. It is known for research contribution in the topics: Silicon & Boundary value problem. The organization has 5166 authors who have published 6097 publications receiving 31680 citations. The organization is also known as: VSU & Voronezh University.

Perturbation theory analysis of attosecond photoionization

Abstract: Ionization of an atom by a few-cycle attosecond xuv pulse is analyzed using perturbation theory (PT), keeping terms in the transition amplitude up to second order in the pulse electric field. Within the PT approach, we present an ab initio parametrization of the ionized electron angular distribution (AD) using rotational invariance and symmetry arguments. This parametrization gives analytically the dependence of the AD on the carrier envelope phase (CEP), the polarization of the pulse, and on the ionized electron momentum direction, $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{p}}$. For the general case of an elliptically polarized pulse, we show that interference of the first- and second-order transition amplitudes causes a CEP-dependent asymmetry (with respect to $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{p}}\ensuremath{\rightarrow}\ensuremath{-}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{p}}$) and both elliptic and circular dichroism effects. All of these effects are maximal in the polarization plane and depend not only on the CEP but also on the phase of dynamical atomic parameters that enter our parametrization of the AD. Within the single active electron model of an atom, for an initial $s$ or $p$ state we define all dynamical parameters in terms of radial matrix elements (analytic expressions for which are given for the Coulomb and zero-range potentials). For ionization of the H atom by linearly polarized pulses, our PT results are in excellent agreement with results of numerical solutions of the time-dependent Schr\"odinger equation of Peng et al. [New J. Phys. 10, 025030 (2008)]. Also, our numerical results show that the asymmetries and dichroism effects at low electron energies have a different physical origin from those at high electron energies. Moreover, our results for Gaussian and cosine-squared pulse shapes are in good qualitative agreement. Finally, we show that our analytic formulas may prove useful for determining few-cycle extreme ultraviolet (xuv) pulse characteristics, such as the CEP and the polarization.

A stochastic model of river discharge fluctuations

Abstract: We study the daily riverowuctuations of 30 international rivers. Using the detrendeductu- ation analysis, we study the correlations in the magnitudes of riverow increments (volatilities), and 1nd power-law correlations in volatilities for time scales less than 1 year; these correlations almost disappear for time scales larger than 1 year. Using surrogate data test for nonlinearity, we show that correlations in the magnitudes of riverowuctuations are a measure for nonlinear- ity. We propose a simple nonlinear stochastic model for riverowuctuations that reproduces the main scaling properties of the riverow series as well as the correlations and periodicities in the magnitudes of riverow increments. According to our model, the source of nonlinear- ity observed in the data is an interaction between a long-term correlated process and the river discharge itself. c

Mitochondrial energy-dissipating systems (alternative oxidase, uncoupling proteins, and external NADH dehydrogenase) are involved in development of frost-resistance of winter wheat seedlings

Abstract: Gene expression, protein synthesis, and activities of alternative oxidase (AOX), uncoupling proteins (UCP), adenine nucleotide translocator (ANT), and non-coupled NAD(P)H dehydrogenases (NDex, NDPex, and NDin) were studied in shoots of etiolated winter wheat (Triticum aestivum L.) seedlings after exposure to hardening low positive (2°C for 7 days) and freezing (-2°C for 2 days) temperatures. The cold hardening efficiently increased frost-resistance of the seedlings and decreased the generation of reactive oxygen species (ROS) during further cold shock. Functioning of mitochondrial energy-dissipating systems can represent a mechanism responsible for the decrease in ROS under these conditions. These systems are different in their response to the action of the hardening low positive and freezing temperatures. The functioning of the first system causes induction of AOX and UCP synthesis associated with an increase in electron transfer via AOX in the mitochondrial respiratory chain and also with an increase in the sensitivity of mitochondrial non-phosphorylating respiration to linoleic and palmitic acids. The increase in electron transfer via AOX upon exposure of seedlings to hardening freezing temperature is associated with retention of a high activity of NDex. It seems that NDex but not the NDPex and NDin can play an important role in maintaining the functional state of mitochondria in heterotrophic tissues of plants under the influence of freezing temperatures. The involvement of the mitochondrial energy-dissipating systems and their possible physiological role in the adaptation of winter crops to cold and frost are discussed.

The method of similar operators in the spectral analysis of non-self-adjoint Dirac operators with non-smooth potentials

Abstract: We use the method of similar operators to study the spectral properties of Dirac operators, and obtain results on the asymptotic behaviour of the spectra of Dirac operators and the convergence of spectral expansions.