arXiv subjects

Kirill A. Kazakov

Publications and source records attributed to Kirill A. Kazakov.

At least 19 recordsLinked to original sources

arXiv2021

The fundamental 1/f noise in monolayer graphene

The quantum indeterminacy caused by non-commutativity of observables at different times sets a lower bound on the voltage noise power spectrum in any conducting material. This bound is calculated explicitly in the case of monolayer graphene. It is found that account of graphene pseudospin/valley band structure raises the quantum bound by a factor of 7/2 compared to the case of spinless charge carriers with a conical energy-momentum dispersion. The bound possesses all characteristic properties of 1/f noise, and its dependence on the charge carrier density is congruent to the experimentally observed.

cond-mat.mes-hall↗

arXiv2021

A quantum bound on the 1/f noise in semiconductors with a conical energy-momentum dispersion

The quantum indeterminacy caused by non-commutativity of observables at different times sets a lower bound on the voltage noise power spectrum in any conducting material. This bound is calculated explicitly in the case of semiconductors with a conical energy-momentum dispersion of charge carriers. It possesses all characteristic properties of 1/f noise. Its momentum decomposition is found to be singular at zero particle momentum, a measurable consequence being a sharp peak in the noise magnitude at small charge carrier density. In application to monolayer graphene, this peak becomes M-shaped on account of a continuous transition from the electron to hole conductivity. A comparison with experimental data is made which demonstrates that the calculated power spectrum is close in magnitude and congruent to the observed.

cond-mat.mes-hall↗

arXiv2020

Quantum theory of flicker noise: the 1/f law as a lower bound on the voltage power spectrum

An approach to the problem of 1/f voltage noise observed in all conducting media is developed based on an uncertainty relation for the Fourier-transformed signal. It is shown that the quantum indeterminacy caused by non-commutativity of observables at different times sets a lower bound on the power spectrum of voltage fluctuations. Using the Schwinger-Keldysh method, this bound is calculated explicitly in the case of unpolarized free-like charge carriers, and is found to have a 1/f low-frequency asymptotic. It is demonstrated also that account of the charge carrier interaction with phonons results in a shift of the frequency exponent from unity. A comparison with the experimental data on 1/f noise in InGaAs quantum wells and high-temperature superconductors is made which shows that the observed noise levels are only a few times as high as the bound established.

quant-ph↗

arXiv2020

1/f noise and quantum indeterminacy

An approach to the problem of 1/f voltage noise in conductors is developed based on an uncertainty relation for the Fourier-transformed signal. The quantum indeterminacy caused by non-commutativity of the observables at different times makes the voltage autocovariance ambiguous, but the power spectrum of fluctuations remains well-defined. It is shown that a lower bound on the power spectrum exists, which is related to the antisymmetric part of the voltage correlation function. Using the Schwinger-Keldysh method, this bound is calculated explicitly in the case of unpolarized charge carriers with a parabolic dispersion, and is found to have a 1/f low-frequency asymptotic. A comparison with the 1/f-noise measurements in InGaAs quantum wells is made which shows that the observed noise levels are only a few times higher than the bound established.

quant-ph↗

arXiv2017

Numerical study of strongly-nonlinear regimes of steady premixed flame propagation. The effect of thermal gas expansion and finite-front-thickness effects

Steady propagation of premixed flames in straight channels is studied numerically using the on-shell approach. A first numerical algorithm for solving the system of nonlinear integro-differential on-shell equations is presented. It is based on fixed-point iterations and uses simple (Picard) iterations or the Anderson acceleration method that facilitates separation of different solutions. Using these techniques, we scan the parameter space of the problem so as to study various effects governing formation of curved flames. These include the thermal gas expansion and the finite-front-thickness effects, namely, the flame stretch, curvature, and compression. In particular, the flame compression is demonstrated to have a profound influence on the flame, strongly affecting the dependence of its propagation speed on the channel width b. Specifically, the solutions found exhibit a sharp increase of the flame speed with the channel width. Under a weak flame compression, this increase commences at b/lambda_c = 2 - 3, where lambda_c is the cutoff wavelength, but this ratio becomes significantly larger as the flame compression grows. The results obtained are also used to identify limitations of the analytical approach based on the weak-nonlinearity assumption, and to revise the role of noise in the flame evolution.

physics.flu-dyn↗

arXiv2016

Experimental and theoretical study of metal combustion in oxygen flows

The effects of oxygen flow speed and pressure on the iron and mild steel combustion are investigated experimentally and theoretically. The studied specimens are vertical cylindrical rods subjected to an axial oxygen flow and ignited at the upper end by laser irradiation. Three main stages of the combustion process have been identified experimentally: (1) Induction period, during which the rod is heated until an intensive metal oxidation begins at its upper end; (2) Static combustion, during which a laminar liquid "cap" slowly grows on the upper rod end; and, after the liquid cap detachment from the sample, (3) Dynamic combustion, which is characterized by a rapid metal consumption and turbulent liquid motions. An analytical description of these stages is given. In particular, a model of the dynamic combustion is constructed based on the turbulent oxygen transport through the liquid metal-oxide flow. This model yields a simple expression for the fraction of metal burned in the process, and allows one to calculate the normal propagation speed of the solid metal--liquid interface as a function of the oxygen flow speed and pressure. A comparison of the theory with the experimental results is made.

physics.flu-dyn↗

arXiv2015

Premixed flame propagation in vertical tubes

Analytical treatment of premixed flame propagation in vertical tubes with smooth walls is given. Using the on-shell flame description, equations describing quasi-steady flame with a small but finite front thickness are obtained and solved numerically. It is found that near the limits of inflammability, solutions describing upward flame propagation come in pairs having close propagation speeds, and that the effect of gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a theory of partial flame propagation driven by the gravitational field is developed. A complete explanation is given of the intricate observed behavior of limit flames, including dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction. The role of the finite front-thickness effects is discussed in detail. Also, various mechanisms governing flame acceleration in smooth tubes are identified. Acceleration of methane-air flames in open tubes is shown to be a combined effect of the hydrostatic pressure difference produced by the ambient cold air and the difference of dynamic gas pressure at the tube ends. On the other hand, a strong spontaneous acceleration of the fast methane-oxygen flames at the initial stage of their evolution in open-closed tubes is conditioned by metastability of the quasi-steady propagation regimes. An extensive comparison of the obtained results with the experimental data is made.

physics.flu-dyn↗

arXiv2015

Effect of vorticity flip-over on the premixed flame structure: First experimental observation of type I inflection flames

Premixed flames propagating in horizontal tubes are observed to take on shape convex towards the fresh mixture, which is commonly explained as a buoyancy effect. A recent rigorous analysis has shown, on the contrary, that this process is driven by the balance of vorticity generated by a curved flame front with the baroclinic vorticity, and predicted existence of a regime in which the leading edge of the flame front is concave. We report first experimental realization of this regime. Our experiments on ethane and n-butane mixtures with air show that flames with an inflection point on the front are regularly produced in lean mixtures, provided that a sufficiently weak ignition is used. The observed flame shape perfectly agrees with the theoretically predicted.

physics.flu-dyn↗

arXiv2014

The mean velocity profile of near-wall turbulent flow

The issue of analytical derivation of the mean velocity profile in a near-wall turbulent flow is revisited in the context of a two-dimensional channel flow. An approach based on the use of dispersion relations for the flow velocity is developed. It is shown that for an incompressible flow conserving vorticity, there exists a decomposition of the velocity field into rotational and potential components, such that the restriction of the former to an arbitrary cross-section of the channel is a functional of the vorticity and velocity distributions over that cross-section, while the latter is divergence-free and bounded downstream thereof. By eliminating the unknown potential component with the help of a dispersion relation, a nonlinear integro-differential equation for the flow velocity is obtained. It is then analyzed within an asymptotic expansion in the small ratio v*/U of the friction velocity to the mean flow velocity. Upon statistical averaging in the lowest nontrivial order, this equation relates the mean velocity to the cross-correlation function of the velocity fluctuations. Analysis of the equation reveals existence of two continuous families of solutions, one having the near-wall asymptotic of the form U \sim ln^p (y/y0), where y is the distance to the wall, p>0 is arbitrary, and the other, U \sim y^n, with n>0 also arbitrary except in the limit n \to 0 where it turns out to be a universal function of the Reynolds number, n \sim 1/ln(Re). It is proved, furthermore, that given a mean velocity distribution having either asymptotic, one can always construct a cross-correlation function so as to satisfy the obtained equation. These results are discussed in the light of the existing controversy regarding experimental verification of the law of the wall.

physics.flu-dyn↗

arXiv2014

One more word on the flicker noise in manganites

It is shown that the conclusion of the Comment by C.Barone et al. [J. Appl. Phys. Vol.115, 116101 (2014)] on the paper [J. Appl. Phys. Vol.113, 094901 (2013)] is a result of several flaws including incorrect assumption that the charge carrier mobility in La_2/3Sr_1/3MnO_3 is independent of temperature, and misinterpretation of the quantum theory of flicker noise. An experimental evidence for strong temperature dependence of the carrier mobility in the metallic state of manganites is given, and prospects for explaining the experimental data given in the Comment are discussed.

cond-mat.stat-mech↗

arXiv2013

Analytical study in the mechanism of flame movement in horizontal tubes. II. Flame acceleration in smooth open tubes

The problem of spontaneous acceleration of premixed flames propagating in open horizontal tubes with smooth walls is revisited. It is proved that in long tubes, this process can be considered quasi-steady, and an equation for the flame front position is derived using the on-shell description. Numerical solutions of this equation are found which show that as in the case of uniform flame movement, there are two essentially different regimes of flame propagation. In the type I regime, the flame speed and its acceleration are comparatively low, whereas the type II regime is characterized by significant flame acceleration that rapidly increases as the flame travels along the tube. A detailed comparison of the obtained results with the experimental data on flame acceleration in methane-air mixtures is given. In particular, it is confirmed that flames propagating in near-stoichiometric mixtures and mixtures near the limits of inflammability belong to the types II and I, respectively, whereas flames in transient mixtures undergo transitions between the two regimes during their travel.

physics.flu-dyn↗

arXiv2011

Analytical study in the mechanism of flame movement in horizontal tubes

The problem of premixed flame propagation in wide horizontal tubes is revisited. Employing the on-shell description of flames with arbitrary gas expansion, a nonlinear second-order differential equation for the front position of steady flame is derived. Solutions to this equation, obtained numerically, reveal two distinct physical regimes of laminar flame propagation controlled by the strong baroclinic effect. They differ by the front shape and flame speed, the ratio of the total consumption rates in the two regimes being 1.4 to 1.8, depending on the value of the gas expansion coefficient. Comparison with the existing experimental data on methane-air flames is made, and explanation of the main trends in the observed flame behavior is given. It is shown, in particular, that the faster (slower) regime of combustion is realized in mixtures close to (far from) the stoichiometric composition, with pronounced changeover in between.

physics.flu-dyn↗

arXiv2010

An interpretation of the infrared singularity of the effective electromagnetic field

The problem of infrared divergence of the effective electromagnetic field produced by elementary particles is revisited using the non-equilibrium model of an electron interacting with low-temperature photons. It is argued that the infrared singularity of the effective field can be interpreted as a thermalization of the electron. It is shown that this thermalization is negligible in actual field measurements as it is completely dominated by the usual quantum spreading.

quant-ph↗

arXiv2009

Infrared nullification of the effective electromagnetic field at finite temperature

The problem of infrared divergence of the effective electromagnetic field at finite temperature (T) is revisited. A model of single spatially localized electron interacting with thermal photons is considered in the limit T to 0 using two different regularization schemes. The first is based on the shift i 0 to i varepsilon of the electron propagator pole in the complex energy plane, and is used to explicitly calculate the effective field in the one-loop approximation. We show that the matrix-valued imaginary part of the electron self-energy can be consistently related to the pole shift, and that the presence of the heat bath leads to appearance of an effective varepsilon sim T, thus providing a natural infrared regulator of the theory. We find that the one-loop effective Coulomb field calculated using this varepsilon vanishes. The other scheme combines an infrared momentum cutoff with smearing of the delta-functions in the interaction vertices. We prove that this regularization admits factorization of the infrared contributions in multi-loop diagrams, and sum the corresponding infinite series. The effective electromagnetic field is found to vanish in this case too. An essentially perturbative nature of this result is emphasized and discussed in connection with the long-range expansion of the effective field.

quant-ph↗

arXiv2009

Premixed Flame Propagation in Curved Channels

A theory of flame propagation in curved channels is developed within the framework of the on-shell description of premixed flames. Employing the Green function appropriate to the given channel geometry, an implicit integral representation for the burnt gas velocity is constructed. It is then used to derive an explicit expression for rotational component of the gas velocity near the flame front by successive separation of irrotational contributions. We prove that this separation can be performed in a way consistent with boundary conditions at the channel walls. As a result, the unknown irrotational component can be projected out by applying a dispersion relation, thus leading to a closed system of equations for the on-shell fresh gas velocity and the flame front position. These equations show that in addition to the usual nonlocality associated with potential flows, vorticity produced by a curved flame leads to specific nonlocal spatial and temporal influence of the channel geometry on the flame evolution. To elucidate this influence, three special cases are considered in more detail -- steady flame stabilized by incoming flow in a bottle-shaped channel, quasi-steady flame, and unsteady flame with small gas expansion propagating in a channel with slowly varying width. In the latter case, analytical solutions of the derived equations are obtained in the first post-Sivashinsky approximation using the method of pole decomposition.

physics.flu-dyn↗

arXiv2009

On the Anomalous Flicker Noise Intensity in High-Temperature Superconductors

The problem of anomalously high levels of flicker noise observed in the normal state of the high-temperature superconductors is addressed. It is argued that the anomaly is the result of incorrect normalization of the power spectra according to the Hooge formula. A careful analysis of the available experimental data is given, which shows that the scaling of the spectral power with sample size is essentially different from the inverse proportionality. It is demonstrated that the measured spectra obey the law given by the recently proposed quantum theory of fundamental flicker noise.

cond-mat.supr-con↗

arXiv2009

Stability analysis of confined V-flames. I. Analytical treatment of the high-velocity limit

The problem of linear stability of confined V-flames with arbitrary gas expansion is addressed. Using the on-shell description of flame dynamics, a general equation governing propagation of disturbances of an anchored flame is obtained. This equation is solved analytically for V-flames in high-velocity channel streams. It is demonstrated that dynamics of flame disturbances in this case is controlled by the memory effects associated with vorticity generated by the curved front. The perturbation growth rate spectrum is determined, and explicit analytic expressions for the eigenfunctions are given. It is found that the piecewise linear V-structure is unstable for all values of the gas expansion coefficient.

physics.flu-dyn↗

arXiv2009

Analytical treatment of 2D steady flames anchored in high-velocity streams

The problem of burning of high-velocity gas streams in channels is revisited. Previous treatments of this issue are found to be incomplete. It is shown that despite relative smallness of the transversal gas velocity, it plays crucial role in determining flame structure. In particular, it is necessary in formulating boundary conditions near the flame anchor, and for the proper account of the flame propagation law. Using the on-shell description of steady anchored flames, a consistent solution of the problem is given. Equations for the flame front position and gas-velocity at the front are obtained. It is demonstrated that they reduce to a second-order differential equation for the front position. Numerical solutions of the derived equations are found.

physics.flu-dyn↗