arXiv subjects

V. O. Kharchenko

Publications and source records attributed to V. O. Kharchenko.

16 recordsLinked to original sources

arXiv2021

Rate theory modeling a vacancy mediated intra-granular fission gas bubbles growth in amorphous $U_3Si_2$

A model for gas bubble behavior in irradiated amorphous $U_3Si_2$ is generalized to take into account local influence of sinks for point defects and gas atoms as far as defect clustering resulting in growth of dislocation loops. A universality of bubble size distribution function and scaling law of bubble size growth is revealed. Temperature dependencies of main quantities governing bubble growth are discussed. Local distribution of bubbles and dislocation loops inside grains is studied in details to illustrate bubble size change in the vicinity of grain boundaries and estimate local swelling. Obtained data are compared with experimental and numerical studies.

cond-mat.stat-mech↗

arXiv2020

Noise induced effects at nano-structured thin films growth during deposition in plasma-condensate devices

We perform a comprehensive study of noise-induced effects in a stochastic model of reaction-diffusion type, describing nano-structured thin films growth at condensation. We introduce an external flux of adsorbate between neighbour monoatomic layers caused by the electrical field presence near substrate in plasma-condensate devices. We take into account that the strength of the electric field fluctuates around its mean value. We discuss a competing influence of the regular and stochastic parts of the external flux onto the dynamics of adsorptive system. It will be shown that the introduced fluctuations induce first-order phase transition in a homogeneous system, govern the pattern formation in a spatially extended system; these parts of the flux control the dynamics of the patterning, spatial order, morphology of the surface, growth law of the mean size of adsorbate islands, type and linear size of surface structures. The influence of the intensity of fluctuations onto scaling and statistical properties of the nano-structured surface is analysed in detail. This study provides an insight into the details of noise induced effects at pattern formation processes in anisotropic adsorptive systems.

cond-mat.mes-hall↗

arXiv2020

Dislocation loops growth and radiation growth in neutron irradiated Zr-Nb alloys: rate theory modelling

A generalized model to study dislocation loops growth in irradiated binary Zr-based alloys is presented. It takes into account temperature effects, efficiencies of loops to absorb point defects dependent on the loop size, an influence of locality of grain boundary sink strength, and concentration of the alloying element. This model is used to describe the dynamics of loop radii growth in zirconium-niobium alloys under neutron irradiation at reactor conditions. A growth of both loop radii and strains is studied at different grain sizes, location from grain boundaries, and concentration of niobium. It is shown that locality of grain boundary sinks results in a non-uniform deformation of the crystal inside the grains. Additionally, an introduction of niobium as an alloying element decreases the loop radii but promotes the growth of local strains inside the grains.

cond-mat.mtrl-sci↗

arXiv2018

Transitions from low-density state towards high-density state in stochastic bistable plasma-condensate systems

In this article we study transitions from low-density states towards high-density states in bistable plasma-condensate systems. We take into account an anisotropy in transference of adatoms between neighbour layers induced by the electric field near substrate. We derive the generalized one-layer model by assuming that the strength of the electric field is subjected to both periodic oscillations and multiplicative fluctuations. By studying the homogeneous system we discuss the corresponding mean passage time. In the limit of weak fluctuations, we show the optimization of the mean passage time with variation in the frequency of periodic driving in the non-adiabatic limit. Noise induced effects corresponding to asynchronization and acceleration in the transition dynamics are studied in detail.

cond-mat.stat-mech↗

arXiv2018

Phase field modelling voids nucleation and growth in binary systems

We present a comprehensive study of voids formation, nucleation and growth in a prototype model of binary alloys subjected to irradiation by using a combined approach based on phase field and rate theories. It is shown that voids formation is caused by interaction of irradiation-produced vacancies through elastic deformation of a lattice and vacancy coupling with composition field of the alloy. Phase diagrams illustrating the formation of states related to solid solution, phase decomposition, and patterning are obtained. Formation of voids from supersaturated ensemble of vacancies is accompanied by composition rearrangement of alloy components. It was found that elastic inhomogeneity leading to the formation of anisotropic precipitates in an initially prepared binary alloy results in the formation of a void super-lattice under irradiation. It was shown that voids nucleate and grow with dose according to diffusion controlled precipitation processes, where universal dynamics of voids growth is revealed. Estimations of main quantitative and statistical characteristics of voids by using material parameters relevant to most of alloys and steels give good agreement with experimental observations.

cond-mat.stat-mech↗

arXiv2014

Universality and self-similar behaviour of non-equilibrium systems with non-Fickian diffusion

Analytical approaches describing non-Fickian diffusion in complex systems are presented. The corresponding methods are applied to the study of statistical properties of pyramidal islands formation with interacting adsorbate at epitaxial growth. Using the generalized kinetic approach we consider universality, scaling dynamics and fractal properties of pyramidal islands growth. In the framework of generalized kinetics, we propose a theoretical model to examine the numerically obtained data for averaged islands size, the number of islands and the corresponding universal distribution over the island size.

cond-mat.mes-hall↗

arXiv2014

Anomalous features of diffusion in corrugated potentials with spatial correlations: faster than normal, and other surprises

Normal diffusion in corrugated potentials with spatially uncorrelated Gaussian energy disorder famously explains the origin of non-Arrhenius $\exp[-σ^2/(k_BT^2)]$ temperature-dependence in disordered systems. Here we show that unbiased diffusion remains asymptotically normal also in the presence of spatial correlations decaying to zero. However, due to a temporal lack of self-averaging transient subdiffusion emerges on mesoscale, and it can readily reach macroscale even for moderately strong disorder fluctuations of $σ\sim 4-5\, k_BT$. Due to its nonergodic origin such subdiffusion exhibits a large scatter in single trajectory averages. However, at odds with intuition, it occurs essentially faster than one expects from the normal diffusion in the absence of correlations. We apply these results to diffusion of regulatory proteins on DNA molecules and predict that such diffusion should be anomalous, but much faster than earlier expected on a typical length of genes for a realistic energy disorder of several room $k_BT$, or merely $0.05-0.075$ eV.

cond-mat.stat-mech↗

arXiv2013

Rocking Subdiffusive Ratchets: Origin, Optimization and Efficiency

We study origin, parameter optimization, and thermodynamic efficiency of isothermal rocking ratchets based on fractional subdiffusion within a generalized non-Markovian Langevin equation approach. A corresponding multi-dimensional Markovian embedding dynamics is realized using a set of auxiliary Brownian particles elastically coupled to the central Brownian particle (see video on the journal web site). We show that anomalous subdiffusive transport emerges due to an interplay of nonlinear response and viscoelastic effects for fractional Brownian motion in periodic potentials with broken space-inversion symmetry and driven by a time-periodic field. The anomalous transport becomes optimal for a subthreshold driving when the driving period matches a characteristic time scale of interwell transitions. It can also be optimized by varying temperature, amplitude of periodic potential and driving strength. The useful work done against a load shows a parabolic dependence on the load strength. It grows sublinearly with time and the corresponding thermodynamic efficiency decays algebraically in time because the energy supplied by the driving field scales with time linearly. However, it compares well with the efficiency of normal diffusion rocking ratchets on an appreciably long time scale.

cond-mat.stat-mech↗

arXiv2013

Properties of spatial arrangement of V-type defects in irradiated materials: 3D-modelling

We consider the dynamics of pattern formation in a system of point defects under sustained irradiation within the framework of the rate theory. In our study we generalize the standard approach taking into account a production of defects by elastic fields and a stochastic production representing internal multiplicative noise. Using 3D-modelling we have shown that with the damage rate growth, a morphology of clusters composed of vacancies changes. The same effect is observed with variation in the multiplicative noise intensity. Stationary patterns are studied by means of correlation analysis.

cond-mat.mtrl-sci↗

arXiv2011

Morphology change of the silicon surface induced by Ar$^+$ ion beam sputtering

Two-level modeling for nanoscale pattern formation on silicon target by Ar$^+$ ion sputtering is presented. Phase diagram illustrating possible nanosize surface patterns is discussed. Scaling characteristics for the structure wavelength dependence versus incoming ion energy are defined. Growth and roughness exponents in different domains of the phase diagram are obtained.

cond-mat.mtrl-sci↗

arXiv2010

Stochastic effects at ripple formation processes in anisotropic systems with multiplicative noise

We study pattern formation processes in anisotropic system governed by the Kuramoto-Sivashinsky equation with multiplicative noise as a generalization of the Bradley-Harper model for ripple formation induced by ion bombardment. For both linear and nonlinear systems we study noise induced effects at ripple formation and discuss scaling behavior of the surface growth and roughness characteristics. It was found that the secondary parameters of the ion beam (beam profile and variations of an incidence angle) can crucially change the topology of patterns and the corresponding dynamics.

cond-mat.stat-mech↗

arXiv2008

Entropy-driven phase transitions with influence of the field-dependent diffusion coefficient

We present a comprehensive study of the phase transitions in the single-field reaction-diffusion stochastic systems with field-dependent mobility of a power-low form and the internal fluctuations. Using variational principles and mean-field theory it was shown that the noise can sustain spatial patterns and leads to disordering phase transitions. We have shown that the phase transitions can be of critical or non-critical character.

cond-mat.stat-mech↗

arXiv2008

Chaos in a generalized Lorenz system

A three-component dynamic system with influence of pumping and nonlinear dissipation describing a quantum cavity electrodynamic device is studied. Different dynamical regimes are investigated in terms of divergent trajectories approaches and fractal statistics. It has been shown, that in such a system stable and unstable dissipative structures type of limit cycles can be formed with variation of pumping and nonlinear dissipation rate. Transitions to chaotic regime and the corresponding chaotic attractor are studied in details.

nlin.CD↗

arXiv2007

Multifractal spectrum of phase space related to generalized thermostatistics

We consider a self-similar phase space with specific fractal dimension $d$ being distributed with spectrum function $f(d)$. Related thermostatistics is shown to be governed by the Tsallis formalism of the non-extensive statistics, where the non-additivity parameter is equal to ${\barτ}(q)\equiv 1/τ(q)>1$, and the multifractal function $τ(q)= qd_q-f(d_q)$ is the specific heat determined with multifractal parameter $q\in [1,\infty)$. In this way, the equipartition law is shown to take place. Optimization of the multifractal spectrum function $f(d)$ derives the relation between the statistical weight and the system complexity. It is shown the statistical weight exponent $τ(q)$ can be modeled by hyperbolic tangent deformed in accordance with both Tsallis and Kaniadakis exponentials to describe arbitrary multifractal phase space explicitly. The spectrum function $f(d)$ is proved to increase monotonically from minimum value $f=-1$ at $d=0$ to maximum one $f=1$ at $d=1$. At the same time, the number of monofractals increases with growth of the phase space volume at small dimensions $d$ and falls down in the limit $d\to 1$.

cond-mat.stat-mech↗

arXiv2007

Self-organization processes in laser system with nonlinear absorber and external force influence

We discuss mechanisms of self-organization processes in two-level solid-state class-B laser system. The model is considered under assumptions of influence of nonlinear absorber and external force, separately. It was found that self-organization occurs through the Hopf bifurcation and results to a stable pulse radiation. Analysis is performed according to the Floquet exponent investigation. It was found that influence of the nonlinear absorber extends the domain of control parameters that manage a stable periodic radiation processes. An external force suppresses self-organization processes. A combined influence of both external force and nonlinear absorber results to more complicated picture of self-organization with two reentrant Hopf bifurcations.

nlin.AO↗

arXiv2006

Multifractal spectrum of the phase space related to generalized thermostatistics

We consider the set of monofractals within a multifractal related to the phase space being the support of a generalized thermostatistics. The statistical weight exponent $τ(q)$ is shown to can be modeled by the hyperbolic tangent deformed in accordance with both Tsallis and Kaniadakis exponentials whose using allows one to describe explicitly arbitrary multifractal phase space. The spectrum function $f(d)$, determining the specific number of monofractals with reduced dimension $d$, is proved to increases monotonically from minimum value $f=-1$ at $d=0$ to maximum $f=1$ at $d=1$. The number of monofractals is shown to increase with growth of the phase space volume at small dimensions $d$ and falls down in the limit $d\to 1$.

cond-mat.stat-mech↗