Technical Physics最新文献

The paper is devoted to computational modeling of biophysical processes with factors of heterogeneous adaptation. Plasticity and variability is the basis of evolution in natural biophysical systems. The complex of behavioral and biochemical adaptations allows the ancient populations of the Caspian Sea to efficiently use the limited resources and withstand the competition. During long-term simultaneous evolution in populations of Caspian organisms, a specific adaptation has appeared that is the strategy of survival optimal for physical conditions of the Caspian Sea. Interference in the existing hydrological systems of the region instantaneously deteriorated the advantages of the evolution strategy. An important form of adaptation for the Caspian Sea is the formation of subpopulation reproductively isolated groups that become units of species formation, accumulating the differences because of the reproductive isolation. In the paper we describe the method for analyzing the intrapopulation structure, where the groups with different reproductive behavior arose in the population. This is an aspect of the technical problem of the method for their introduction. A modified method of antigen differentiation developed by Yu.N. Perevaryukha (patent for invention RU 2253970) allowed determining the belonging of animal units to one of the reproductive groups of marine sturgeons by the differences in their antigens in the blood serum. It was shown that biophysical adaptation to long-term life in sweet water reflects in the presence in blood of specific proteins called the antigen markers. Immunochemical technologies immunodiffusion and electrophoresis are applied to study the markers of reproductive groups of Caspian sturgeons. The knowledge about the character of life cycle of groups isolated by their reproductive behavior and optimal temperature is necessary for artificial recovery of the populations. The data on the presence of two reproductive groups in starry sturgeon Acipencer stellatus are used to model the reproductive activity of the population. The information about the degree of intrapopulation differentiation allows improving the hybrid computational structure for the model of biophysical processes requiring the animal unit introduction technology; this structure was earlier proposed by us in Technical Physics. The model scenario explains the low efficiency of artificial release of sturgeon fish in the Caspian Sea. The procedure for reintroduction of sturgeons into the Caspian Sea must take into account the reproductive peculiarities of groups with different behavior. The considered problem is topical not only for populations of the Volga basin, but also for local populations in southern waters of the Caspian Sea of Iran and Azerbaijan.

Singular integral equations in degenerate cases describe many processes in natural science and technology. The theory of these equations has been studied quite well, but as far as the authors know, there are currently no analytical methods for solving them. In this regard, there is a need to construct approximate methods for solving singular integral equations in degenerate cases. The article is devoted to the construction of such methods, which determines its relevance. When constructing approximate methods, iteration–projection methods are used. A spline–collocation method for solving a degenerate singular characteristic equation is constructed. A two-stage approximate method is proposed for solving complete singular integral equations in degenerate cases.

This work is devoted to analysis of stability (in the Lyapunov sense) of solutions to systems of linear parabolic equations with coefficients depending on time and with delay depending on time. The cases of continuous and impulsive perturbations are considered. A method for studying the stability of solutions to systems of linear parabolic equations is as follows. Applying the Fourier transform to the original system of parabolic equations, we arrive at a system of nonstationary ordinary differential equations with delay depending on time, which is defined in the spectral region. First, the stability of the resulting system is studied by the method of frozen coefficients in the metric of space R_n of n-dimensional vectors. Then the resulting statements are extended to space L₂. The application of the Parseval equality allows us to return to the domain of the originals and to obtain sufficient conditions for the stability of solutions to systems of linear parabolic equations. An algorithm is proposed that allows one to obtain sufficient stability conditions for solutions of finite systems of linear parabolic equations with time-dependent coefficients and with time-dependent delays. Sufficient stability conditions are expressed in terms of the logarithmic norms of matrices composed of the coefficients of the system of parabolic equations. The algorithms are obtained in the metric of space L₂. Algorithms for constructing sufficient stability conditions are efficient both in the case continuous and in the case of impulsive perturbations. A method is proposed for constructing sufficient stability conditions for solutions to finite systems of linear parabolic equations with time-dependent coefficients and delays. The method can be used in the study of nonstationary dynamical systems described by systems of linear parabolic equations with delays depending from time.

The influence of temperature on the processes of dissipative electron tunneling through individual Co nanoparticles (NPs) in an HfO₂ film (10 nm thick) on a conductive substrate with a Co sublayer has been experimentally studied by atomic force microscopy (AFM) with a conducting probe. Co NPs were formed by local anodic oxidation of the Co sublayer using an AFM probe with subsequent drift of Co ions to the AFM probe, their reduction, and growth of Co NPs near the contact of the AFM probe tip with the HfO₂ film surface. In the experiment, the tunnel current–voltage characteristics (CVC) of the formed Co NPs were measured when voltage was applied between the AFM probe and the Co sublayer at different temperatures in the range of 20–105°С. The experimental results were interpreted on the basis of the theory of one-dimensional dissipative tunneling for a model double-well oscillatory potential in an external electric field. At one of the voltage polarities on the AFM probe, kinks in I–V characteristics were observed, accompanied by current oscillations through the AFM probe I, which, according to the theory, corresponds to the situation when the initially asymmetric double-well potential becomes symmetrical. The amplitude of the mentioned oscillations ΔI falls slightly non-linearly with increasing temperature. The results of the experiment were compared with the results of calculations of the temperature dependence of the maximum amplitude of oscillations on the field dependence of the probability of 1D dissipative tunneling. The obtained qualitative agreement between the experimental 19 and theoretical temperature dependences indicates that the experimentally observed features of I–V characteristics are associated with the effect of macroscopic quantum tunneling with dissipation. A qualitative agreement was obtained between the experimental and theoretical results that allow us to assume the possibility of experimental observation of the macroscopic dissipative tunneling effects [1] and thereby confirm the hypothesis expressed in the groundbreaking works of A.J. Leggett, A.I. Larkin, Yu.N. Ovchinnikov, and other authors.

At present, much attention is paid to the dielectric engineering of the material of the surrounding matrix and low-dimensional structures, which makes it possible to purposefully change their properties and optimize the characteristics of semiconductor devices. The aim of this work is a theoretical study of the influence of the pair interaction of quantum dots (QDs), as well as their interaction with the surrounding matrix through 2D dissipative tunneling, on the photodielectric effect (PDE) associated with the excitation of an impurity complex A⁺ + e in a QD system in an external electric field. Interaction of an electron with a hole in an impurity complex A⁺ + e in a QD has been considered in the adiabatic approximation. The dispersion equations for a hole in an impurity complex A⁺ + e in the presence of an external electric field and 2D dissipative tunneling for the s- and p-states of an electron in a QD are obtained within the framework of the zero-range potential model in the effective mass approximation. The influence of the electric field on the ground state of an electron in a QD has been taken into account in the second order of the perturbation theory. The probability of 2D dissipative tunneling is calculated in the one-instanton semiclassical approximation. The relative change in dielectric permittivity has been calculated in the dipole approximation. PDE field-dependence curves have been plotted for InSb QDs. It is shown that the PDE field dependence at a certain value of the strength of an external electric field and the parameters of 2D dissipative tunneling has a characteristic kink associated with the effect of 2D bifurcation, when, under the action of an electric field, the double-well oscillatory potential simulating the “QD–surrounding matrix” system is transformed and the tunnel transfer mode changes from synchronous to asynchronous. It has been established that there are irregular oscillations on the PDE curves in the vicinity of the 2D bifurcation point, which are associated with the regime of quantum beats. It is shown that the amplitude of the oscillations increases with increasing phonon mode frequency and temperature, while the break point shifts towards weaker fields. It has been found that an increase in the constant of interaction with the contact medium, as well as with the constant of the pair interaction of QDs, leads to the suppression of the PDE.