arXiv subjects

V. V. Ryazanov

Publications and source records attributed to V. V. Ryazanov.

At least 37 records · Page 2Linked to original sources

arXiv2024

Percolation, fractals and the critical point in a nuclear reactor

The trajectories of neutrons in the reactor, the points of their fission of uranium nuclei, the points of neutron absorption, fission chains and chain reactions are considered from the standpoint of fractal geometry and percolation theory. In the study of the stationary critical operating mode of a nuclear reactor, models of Cayley trees and Laplacian fractals are used. This approach allows us to obtain the neutron multiplication equation and an expression for the critical size of the reactor. Models of irreversible growth and various fractal dimensions are also considered as applied to the evolution of neutrons in a reactor. Prospects for the development of the proposed approach to describing reactors, primarily the kinetics and processes of neutron transfer, are indicated.

cond-mat.stat-mech↗

arXiv2024

Application of the concept of hierarchical subordination to chain reactions in a nuclear reactor

Based on the theory of hierarchical structures, a correspondence has been established between the dynamics for the number of neutrons obtained from the theory of branching processes, the number of neutrons of the n-th generation, the number of nodes at the n-th level of the hierarchy, the rate of change in the probability of a chain reaction, the type of intensity and strength of the hierarchical connection, the degree reactor criticality, and neutron trajectories in the reactor. A connection has been found between the probabilities of the formation of a certain generation of the number of neutrons and the probability of the occurrence of a self-sustaining chain reaction of nuclear fission. It is shown that the Tsallis and Rényi distributions describing these processes are related by relations of deformed algebra, and under certain conditions can be accompanying with respect to each other.

cond-mat.stat-mech↗

arXiv2024

Relationship between chain reactions in a nuclear reactor and multifractality

A multifractal model of neutron evolution in a reactor is considered. For chain reactions, the dimension of the multifractal carrier, information and correlation dimensions, the entropy of the fractal set, the maximum and minimum values of the dimension, the multifractal spectrum function and other characteristics of multifractal neutron behavior are found. The use of geometric characteristics of a multifractal makes it possible to describe a stochastic system of hierarchically subordinate statistical ensembles, characterized by Cayley trees. A stationary distribution over hierarchical levels is established, which reduces to the Tsallis power law. Some possibilities for using fractal patterns in the theory of nuclear reactors are indicated.

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arXiv2024

Percolation threshold and critical point of a nuclear reactor

Neutrons in a nuclear reactor move along trajectories corresponding to Cayley trees associated with branching random processes. The probability of percolation, the appearance of such a state of the Bethe lattice in which there is at least one continuous path through neighboring conducting nodes through the entire lattice, corresponds to the probability of the occurrence of a self-sustaining fission chain reaction. At a critical value of the last probability, a (conditionally) infinite cluster of neutrons appears. The probability of percolation, depending on the operating time of the reactor and its size, is associated with the criticality of the reactor. The temporal behavior of the neutron multiplication factor is estimated. Particular attention is paid to the early stages of the development of a self-sustaining chain reaction of nuclear fission. The possibilities of determining the boundaries of the critical region are indicated.

cond-mat.stat-mech↗

arXiv2023

Influence of entropy changes on reactor period

The period of a nuclear reactor is usually represented as a deterministic quantity. In this article, the reactor period is described as a random variable. An approach based on the first passage time is used. In this case, the effect of the change in entropy on the value of the period of the reactor is determined. Relations are obtained that describe the effect of entropy on the period of the reactor. Expressions are obtained for the dispersion of the reactor period. This value cannot be found from a deterministic approach. Knowing the effect of total entropy change on the period of the reactor makes it possible to control the behavior of the reactor.

cond-mat.stat-mech↗

arXiv2023

Antiferromagnetic resonances in superconductor-ferromagnet multilayers

In this work, we study magnetization dynamics in superconductor-ferromagnet (S-F) thin-film multilayer. Theoretical considerations supported by the broad-band ferromagnetic resonance spectroscopy reveal development of acoustic and optic resonance modes in S-F multilayers at significantly higher frequencies in comparison to the Kittel mode of individual F-layers. These modes are formed due to antiferromagnetic-like interaction between F-layers via shared circulating superconducting currents in S-layers. The gap between resonance modes is determined by the thickness and superconducting penetration depth in S-layers. Overall, rich spectrum of S-F multilayers and its tunability opens wide prospects for application of these multialyers in magnonics as well as in various superconducting hybrid systems.

cond-mat.supr-con↗

arXiv2022

Application of the first-passage time method to tribological problems

The time until the failure of some node of the system or until the end of some stage of the operation of the tribological system is associated with the change in entropy in the system that occurs during this time. Methods of the first-passage time by a random process of some given level are used. We assume that the first-passage time is equal to the time to failure. A statistical distribution containing the first-passage time is introduced. The thermodynamic parameter associated with the random variable of the first-passage time is expressed in terms of the change in entropy. This parameter is also included in the expression for the time to failure. This approach allows arbitrary reasons for failures to be included in the consideration. The possibilities of the proposed approach are discussed.

cond-mat.stat-mech↗

arXiv2022

First passage time and change of entropy

The first-passage time is proposed as an independent thermodynamic parameter of the statistical distribution that generalizes the Gibbs distribution. The theory does not include the determination of the first passage statistics itself. A random process is set that describes a physical phenomenon. The first passage statistics is determined from this random process. The thermodynamic parameter conjugated to the first-passage time is the same as the Laplace transform parameter of the first-passage time distribution in the partition function. The corresponding partition function is divided into multipliers, one of which is associated with the equilibrium parameters, and the second one - with the parameters of the first-passage time distribution. The thermodynamic parameter conjugated to the first-passage time can be expressed in terms of the deviation of the entropy from the equilibrium value. Thus, all moments of the distribution of the first passage time are expressed in terms of the deviation of the entropy from its equilibrium value and the external forces acting on the system. By changing the thermodynamic forces, it is possible to change the first passage time.

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arXiv2022

Investigation of radiation-enhanced diffusion using first-passage time

The approach the first-passage time (FPT) of a random process to a certain level is applied to the description of radiation-enhanced diffusion. This is an integral approach to describing the problem of radiation-enhanced diffusion, which does not specify the details of the process but takes into account the overall change in entropy during the process. Relationships are obtained to take into account the influence of radiation effects on the diffusion coefficient. The theoretical results obtained are compared with the experimental ones.

cond-mat.stat-mech↗

arXiv2022

Magnetization dynamics in proximity-coupled superconductor-ferromagnet-superconductor multilayers. Part II

In this work, we study magnetization dynamics in superconductor-ferromagnet-superconductor thin-film structures. Results of the broad-band ferromagnetic resonance spectroscopy are reported for a large set of samples with varied thickness of both superconducting and ferromagnetic layers in a wide frequency, field, and temperature ranges. Experimentally the one-dimensional anisotropic action of superconducting torque on magnetization dynamics is established; its dependence on thickness of layers is revealed. It is demonstrated that experimental findings support the recently-proposed mechanism of the superconducting torque formation via the interplay between the superconducting kinetic inductance and magnetization precession at superconductor-ferromagnet interfaces.

cond-mat.supr-con↗

arXiv2021

Approaching to the deep-strong photon-to-magnon coupling

In this work, the ultra-strong photon-to-magnon coupling is demonstrated for on-chip multilayered superconductor/ferromagnet/insulator hybrid thin film structures reaching the coupling strength above 6 GHz, the coupling ratio about 0.6, the single-spin coupling strength about 350 Hz, and cooperativity about 10^4. High characteristics of coupling are achieved owing to a radical suppression of the photon phase velocity in electromagnetic resonator. With achieved coupling the spectrum reveals inapplicability of the Dicke model, and evidences contribution of the diamagnetic A^2 interaction term in the Hamiltonian of the system, which satisfies the Thomas-Reiche-Kuhn sum rule. The contribution of the A^2 term denotes validity of the Hopfield quantum model and manifests observation of a different hybrid polariton quasi-particle, namely, the plasmon-magnon polariton.

cond-mat.supr-con↗

arXiv2020

Ultra-strong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers

The critical step for future quantum industry demands realization of efficient information exchange between different-platform hybrid systems, including photonic and magnonic systems, that can harvest advantages of distinct platforms. The major restraining factor for the progress in certain hybrid systems is the fundamentally weak coupling parameter between the elemental particles. This restriction impedes the entire field of hybrid magnonics by making realization of scalable on-chip hybrid magnonic systems unattainable. In this work, we propose a general flexible approach for realization of on-chip hybrid magnonic systems with unprecedentedly strong coupling parameters. The approach is based on multilayered micro-structures containing superconducting, insulating and ferromagnetic layers with modified both photon phase velocities and magnon eigen-frequencies. Phenomenologically, the enhanced coupling strength is provided by the radically reduced photon mode volume. The microscopic mechanism of the phonon-to-magnon coupling in studied systems evidences formation of the long-range superconducting coherence via thick strong ferromagnetic layers. This coherence is manifested by coherent superconducting screening of microwave fields by the superconductor/ferromagnet/superconductor three-layers in presence of magnetization precession. This discovery offers new opportunities in microwave superconducting spintronics for quantum technologies.

cond-mat.supr-con↗

arXiv2020

Pseudo spin-valve switch based on ferromagnet/superconductor/ferromagnet trilayer microbridge

A noticeable magnetoresistive effect has been observed on ferromagnet/superconductor/ferromagnet (FSF) microbridges based on diluted ferromagnetic PdFe alloy containing as small as 1% magnetic atoms. Microstructuring of the FSF trilayers does not destroy the effect: the most pronounced curves were obtained on the smallest bridges of 6-8 um wide and 10-15 um long. Below the superconducting transition we are able to control the critical current of microbridges by switching between P and AP orientations of magnetizations of PdFe layers. The operation of FSF-bridge as a magnetic switch is demonstrated in several regimes providing significant voltage discrimination between digital states or remarkably low bit error rate.

cond-mat.supr-con↗

arXiv2020

Magnetization dynamics in proximity-coupled superconductor/ferromagnet/superconductor multilayers

In this work, magnetization dynamics is studied in superconductor/ferromagnet/superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in presence of both superconducting layers and of superconducting proximity at both superconductor/ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: it has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27~T in experiment for a sample with 350~nm thick ferromagnetic layer, and about 0.4~T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum.

cond-mat.supr-con↗

arXiv2020

Non-equilibrium thermodynamics with first-passage time of states as independent thermodynamic parameter

Non-equilibrium states of a thermodynamic statistical system are investigated using the thermodynamic parameter of the system lifetime, first-passage time, the time before degeneration of the system under influence of fluctuations. Statistical distributions that describe the behavior of energy and lifetime are used. Entropy and obtained thermodynamic relations are compared with the results of Extended Irreversible thermodynamics, where as an additional parameter selected fluxes. Explicit expressions are obtained for average lifetime and conjugate thermodynamic quantity. It is shown that, when is only one stationary non-equilibrium state and exponential distribution for the lifetime, flows can only reduce the average system lifetime. However, there are possibilities to description of increase the average lifetime of the system. A description of the growth of the average lifetime for one stationary non-equilibrium state is possible when choosing distributions for the lifetime, differing from the limiting exponential distribution.

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arXiv2019

Nonequilibrium thermodynamics with thermodynamic parameter of lifetime of system. II. Possibilities of increase lifetime

The thermodynamics is studied with the thermodynamic parameter of the lifetime, first-passage time, generalizing the equilibrium thermodynamics. Various ways of describing several stationary nonequilibrium states in the system are considered. The possibilities of increasing the lifetime of the system under external influences on it are investigated.

cond-mat.stat-mech↗

arXiv2019

Equation of state and distribution of particle sizes in Gibbs system

In the framework of Gibbs statistical theory, the issue of the distribution of particle sizes forming the statistical system and the moments of this distribution are considered. This task is relevant for a wide variety of applications. The distribution for particle sizes and moments of this quantity are determined from probabilistic considerations. Particle size depends on interactions in the system, on the compressibility factor, on the number of interacting particles, on the volume of the system. The expressions for the intrinsic volume of particles are substituted into the equations of state written using the theory of excluded volume for various expressions of the exclusion factor. The equations of state thus obtained can be considered as a refinement of the equation of state, a transition to a higher level of description.

cond-mat.stat-mech↗

arXiv2019

Nonequilibrium thermodynmics with thermodynamic parameter of lifetime of system. I

To describe the nonequilibrium states of the system, a new thermodynamic parameter - system lifetime - is introduced. Statistical distributions that describe the behavior of energy and lifetime are recorded. Entropy and obtained thermodynamic relations are compared with the results of Extended Irreversible thermodynamics, where as an additional parameter selected fluxes. For the case of thermal conductivity explicit expressions are obtained for average lifetime and conjugate thermodynamic quantity. It is shown that near the equilibrium state, when is only one stationary nonequilibrium state, flows can only reduce the average system lifetime. But there are possibilities to increase the average lifetime of the system.

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