arXiv subjects

Vyacheslav N. Gorshkov

Publications and source records attributed to Vyacheslav N. Gorshkov.

11 recordsLinked to original sources

arXiv2021

Roughening transition as a driving factor in the formation of self

Based on the Monte Carlo kinetic method, we investigated the formation mechanisms of periodical modulations arising along the length of one-dimensional structures. The evolution of initially cylindrical nanowires/slabs at temperatures lower than their respective melting temperatures can result either in breakup into single nanoclusters or in the formation of stable states with pronounced modulations of cross section. Such configurations, observed in a number of experiments, are excited at wavelengths that are below the critical value for the development of classical Rayleigh instability. We show that the modulation excited in the subcritical mode corresponds to the appearance of roughening transition on the quasi-one-dimensional surface of nanowires/slabs. Since the arise of roughening transition is possible only on certain facets of metals with a given crystal structure, the short-wavelength modulations of one-dimensional systems, as shown in our work, can be realized (i) with the proper orientation of the nanowire/slab axis providing spontaneous appearance of roughening transition on its lateral surface, (ii) by the method of activating the surface diffusion of atoms by external impact (irradiation with an electron beam or contact with a cold plasma), which stimulates roughening transition without significant heating of the nanowire. The results obtained for the cases of BCC and FCC lattices can be used in the controlled synthesis of ordered one-dimensional structures for use in optoelectronics and in ultra-large-scale integrated circuits.

cond-mat.mes-hall↗

arXiv2020

Diversity of anisotropy effects in the breakup of metallic FCC nanowires into ordered nanodroplet chains

We have analyzed the expressed manifestation of the anisotropy of surface energy density in the dynamics of ultrathin nanowires, which break up into disjointed clusters when annealed below their melting temperature. The breakup process is studied for different temperatures and orientations of the nanowire axis relative to its internal crystal structure using the Monte Carlo kinetic method. We have also presented an approximate analytical model of the instability of nanowires. Generally, the interpretation of experimental results refers to the theoretical model developed by Nichols and Mullins, which is based on conceptions about the Rayleigh instability of liquid jets. In both cases, the theories - which do not take into account the anisotropy of surface energy density - predict the breakup of a nanowire/liquid jet with radius r into fragments with an average length Λ=9r. However, the observed value, Λ/r, often deviates from 9 either to lower values or to substantially greater ones (up to 24-30). Our results explain various observed features of the breakup and the significant variations in the values of its parameter Λ/r depending on experimental conditions. In particular, the ambiguous role of exchange by atoms of the surface of a nanowire with the surrounding layer of free atoms formed as a result of their rather intensive sublimation, which occurs in a number of cases, has been investigated. We have shown that this exchange can lead both to a decrease, and to a significant increase, in the parameter Λ/r. The obtained results could be potentially useful in applications such as the development of optical waveguides based on ordered nanoparticles chains.

cond-mat.mes-hall↗

arXiv2020

Restructuring and Breakup of Nanowires with the Diamond Cubic Crystal Structure into Nanoparticles

A kinetic Monte Carlo approach is applied to study physical mechanisms responsible for the breakup of nanowires with the diamond cubic crystal structure into a chain of nanoparticles discovered in preceding experiments on Silicon nanowires. We show that this process is based on the well-known mechanism of roughening transition, which specifically manifests itself in quasi-one-dimensional systems/nanowires with a pronounced anisotropy of the surface energy density. Depending on the temperature and orientation of the nanowire relative to its internal crystal structure, the wavelengths of substantial cross-sectional modulations exceed its initial radius by 4 to 18 times. For certain orientations, a straight nanowire at the initial stage of evolution forms a serpentine/helical structure. The scenarios of the stage of nanowire ruptures into single nanoclusters are also diverse: either each spindle-shaped region of the nanowire transforms into a separate drop (by long-wave surface perturbations), or the adjacent short-scale beads absorb each other due to the Ostwald ripening effect, which can be accompanied by the formation of long-lived many-body dumbbells. The discovered features of the dynamics of quasi-onedimensional systems expand our conceptions of the physical mechanisms involved in the breakup of nanowires (presented by Nichols and Mullins as a classical model for such instabilities) which could be useful in applications based on chains of ordered nanoparticles.

cond-mat.mtrl-sci↗

arXiv2020

Two-Component Axionic Dark Matter Halos

We consider a two-component dark matter halo (DMH) of a galaxy containing ultra-light axions (ULA) of different mass. The DMH is described as a Bose-Einstein condensate (BEC) in its ground state. In the mean-field (MF) limit we have derived the integro-differential equations for the spherically symmetrical wave functions of the two DMH components. We studied numerically the radial distribution of the mass density of ULA and constructed the parameters which could be used to distinguish between the two- and one-component DMH. We also discuss an interesting connection between the BEC MF ground state of a one-component DMH and Hawking temperature and entropy of a corresponding Black Hole, and Unruh temperature.

hep-ph↗

arXiv2012

A Discrete Two-Dimensional Model of a Loaded Cantilever Influenced by Time-Dependent Forces

We developed a discrete two-dimensional model of a cantilever which incorporates the effects of inhomogeneity, the geometry of an attached particle, and the influence of external time-dependent forces. We provide a comparison between the solutions for our discrete model and its continuous limit. The rotational-vibrational mode is studied in detail. The results of numerical simulations demonstrate usefulness of our model for many applications when a cantilever has a complicated geometry and is affected by time-depended and distributed external forces.

math-ph↗

arXiv2011

Radiation Damping for Speeding-up NMR Applications

We demonstrate theoretically and numerically how to control the NMR relaxation rate after application of the standard spin echo technique. Using radiation damping, we return the nuclear magnetization to its equilibrium state during a time interval that is negligible compared to the relaxation time. We obtain an estimate for optimal radiation damping which is consistent with our numerical simulations.

physics.ins-det↗

arXiv2007

Terahertz and Infrared Uncooled Detector Based on a Microcantilever as a Radiation Pressure Sensor

We consider a far infrared (terahertz), room-temperature detector based on a microcantilever sensor of the radiation pressure. This system has a significantly higher sensitivity than existing uncooled detectors in the far infrared (terahertz) spectral region. The significant enhancement of sensitivity is due the combination non-absorption detection method and high quality optical microcavity. Our theoretical analysis of the detector sensitivity and numerical simulations demonstrate that the narrowband heterodyne detector with the band width 30 MHz has a minimal measurable intensity by three orders of magnitude less than conventional uncooled detectors. In the case of the broadband detector, the noise equivalent temperature difference (NETD) is 7.6 mK, which is significantly smaller than for conventional uncooled thermal detectors.

physics.ins-det↗

arXiv2007

Suppression of Intensity Fluctuations in Free Space High-Speed Optical Communication Based on Spectral Encoding of a Partially Coherent Beam

A new concept of a free-space, high-speed (Gbps) optical communication system based on spectral encoding of radiation from a broadband pulsed laser is developed. It is shown that, in combination with the use of partially coherent laser beams and a relatively slow photosensor, scintillations can be suppressed by orders of magnitude for distances of more than 10 km. We also consider the spectral encoding of radiation from a LED as a gigabit rate solution of the "last mile" problem and rapid-deployment systems for disaster recovery.

physics.optics↗

arXiv2006

Numerical simulations on cleaning the neutron trap for measuring the neutron lifetime

We present the results of numerical simulations of the dynamical behavior of trajectories of ultra cold neutrons (UCN) in a magnetic trap. The main goal of our simulations was to optimize the trap parameters in order to minimize the characteristic times for removing from the trap those untrapped neutrons with relatively long escape times (cleaning the trap). Our results demonstrate that, by a proper choice of the trap parameters cleaning times can be reduced to 15 sec, or even less. Many other dynamical characteristics of the neutrons in the trap, including the conservation of the adiabatic invariant which characterizes the orientation of the magnetic moment along the local magnetic field, are also discussed.

nucl-ex↗

arXiv2005

Irreducible Frequent Patterns in Transactional Databases

Irreducible frequent patters (IFPs) are introduced for transactional databases. An IFP is such a frequent pattern (FP),(x1,x2,...xn), the probability of which, P(x1,x2,...xn), cannot be represented as a product of the probabilities of two (or more) other FPs of the smaller lengths. We have developed an algorithm for searching IFPs in transactional databases. We argue that IFPs represent useful tools for characterizing the transactional databases and may have important applications to bio-systems including the immune systems and for improving vaccination strategies. The effectiveness of the IFPs approach has been illustrated in application to a classification problem.

cs.DS↗

arXiv2005

Iterative Algorithm for Finding Frequent Patterns in Transactional Databases

A high-performance algorithm for searching for frequent patterns (FPs) in transactional databases is presented. The search for FPs is carried out by using an iterative sieve algorithm by computing the set of enclosed cycles. In each inner cycle of level FPs composed of elements are generated. The assigned number of enclosed cycles (the parameter of the problem) defines the maximum length of the desired FPs. The efficiency of the algorithm is produced by (i) the extremely simple logical searching scheme, (ii) the avoidance of recursive procedures, and (iii) the usage of only one-dimensional arrays of integers.

cs.DB↗