A method is proposed for constructing a closed approximate equation for weakly nonlinear systems exposed to Gaussian noise with the correlation function of an arbitrary form.
Show AbstractThe region of applicability of the modified method of traveling waves in free space behind a chaotic phase screen is investigated. The model of normal fluctuations of the scattered field phase on the screen is considered in the smallangle scattering approximation. A criterion for the applicability of the modified method is obtained, which substantially extends the potentialities of using the ray interpretation of the wave field in free space as compared to the standard definition of the geometrical optics zone.
Show AbstractThe problem of determining the eigenfrequencies of a cylindrical high-permittivity dielectric resonator is reduced to the solution of a transcendental equation of the zeroth approximation and subsequent calculation of corrections.
Show AbstractA model of autoelectronic emission for self-consistent nonlinear problems of heavy-current microwave electronics is discussed. On the basis of modeling of a complete nonstationary system of Maxwell-Vlasov equations it is shown that the injection current has a clearly pronounced pulsed character.
Show AbstractA gyrotron construction is proposed in which the region of formation of a helical electron beam and the region of interaction are made eoincident. The pumping can be performed by magnetic undulators with a nonadiabatic (over the length} switching-on of the field. The question of the attainable efficiency of this type of devices is investigated for various injector voltages.
Show AbstractThe spectral and temporal behavior of pulses propagating in selectively absorbing and amplifying media has been described. Optimization of pulse shape, compensation for dispersional distortions, and some new methods of compression based on dispersion losses are discussed. The evolution of the Gaussian FM pulse in a "parabolic" medium showing a square complex dispersion characteristic has been considered in detail, in particular, in a laser SRS amplifier. General estimates have been obtained for the energy in the "wings" of the pulse or its frequency spectrum.
Show AbstractA theoretical study has been carried out of the spectral characteristics (the wavelength dependence of radiant transmittance) of thin-layer interference filters (the total optical density of the structure is smaller than half a wavelength). Simple analytical expressions have been obtained that enable one to adequately determine the position and depths of all the extrema on the spectral characteristics of these interference filters. The specific features of the structures under consideration and the potentialities for their utilization in applied optics have been studied and discussed. The computer-aided numerical analysis confirmed the theoretical predictions.
Show AbstractAbsorption of the IR radiation by metallic diffraction gratings was studied by using the optoacouatic effect. Narrow peaks that correspond to resonance excitation of surface electromagnetic waves (SEW) were discovered. The dependence of peak widths was investigated as a function of the SEW pathlength and the width of the angular spectrum of radiation. The macroscopic redistribution of radiation intensity was discovered experimentally in the beam specularly reflected from the grating.
Show AbstractThe increase in the intensity of chlorophyll a fluorescence of phytoplankton under conditions of shortage of mineral nutrition was found to have two components. The first component, whose relative contribution to the overall process of fluorescence intensity change makes up 60-75%, is of a recombination origin and is due to a disruption of the electron transport between the intermediate acceptor Pheo and the primary quinone acceptor $Q_A$ in the reaction center of photosystem II (PS II). The second, nonrecombination, component is due either to weakening of the bond between the light-harvesting antenna and the PS II reaction center, or to disruption of the electron transport between the primary donor P680 and Pheo. It is shown that shortage of mineral nutrition results in the formation of certain number of nonreactive PS II reaction centers with disrupted electron transport from $Q_A$ to the secondary quinone acceptor $Q_B$.
Show AbstractThe probability method was used to describe delayed fluorescence of higher plants. The simplest model proposed is based on the notion of a complex of reaction centers in photosystem Il in which exposure to light induces separation of charges. The model includes pigments, donors and acceptors of electrons with a disrupted electron transport chain, with and without consideration for the nonradiative transition. The results obtained show that a multiexponential decay and a nonmonotonic kinetics of delayed fluorescence may arise in the course of back reactions occurring at the initial stages of electron transfer.
Show AbstractIn this paper we have studied the dynamics of stimulated Raman backscattering (SRBS) of the Gaussian pumping pulse in the plane wave approximation and without allowance for local nonstationarity. Three basic dynamic regimes have been revealed: quasistatic, modulation (spiking), and SRBS regime in an unbounded medium. The conditions for realization and the principal characteristics of these regimes have been established.
Show AbstractIllumination-induced variations of dark conductivity in amorphous hydrogenated silicon films ($\alpha$-Si:Н) doped with boron at different concentrations were investigated. Measurements were carried out in the 270 to 470 K temperature range. Three processes leading to conductivity variation were revealed. Two of them cause an increase in conductivity and are related to the film surface. The third process occurs in the bulk. The possible mechanisms of these processes are considered.
Show AbstractThe possibility of using a laser deformograph as a detector of low-frequency GW-bursts in active filtering of seismic interferences under conditions of incomplete a priori information is considered.
Show AbstractIt is shown that the purely vector part of torsion in the first-order perturbation theory with respect to the constant of interaction between the torsional and electromagnetic fields gives no contribution to the effect ·of interaction of polarized photons in the vapor of sodium atoms.
Show AbstractThe stationary nonlinear Langmuir wave is investigated by the method of kinetic equation. The Maxwellian distribution is employed as the initial velocity distribution of electrons. The asymptotic Laplace method is used to find the nonlinear current. In contrast to the "water bag" type distribution, the limitation on the wave field amplitude is removed.
Show AbstractElectroreflectance spectra of $Hg_{1-x}Mn_xTe$ solid solutions were used to determine the coefficients of a polynomial that expresses the dependence of the transition energy $E_1+\Delta_1$ on the concentration parameter $x$. The possibility of local topographic investigations of the composition heterogeneity on the semiconductor surface is demonstrated.
Show AbstractThe process of tsunami wave generation by motions of the sea floor with residual displacement has been investigated by numerical modeling. Fast, medium-velocity, and slow floor oscillations are considered. The role of nonlinear effects is estimated as a function of the magnitude of the sea floor displacement and oscillation duration in the cases of elevation and subsidence of a sea floor section. The experimental data are compared with the results of numerical experiments.
Show AbstractThe pyroelectric coefficient was measured in the 1.5-80 K temperature range and the permittivity in the 1.5-250 K range for PZT-40 ferroelectric ceramics.
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