arXiv subjects

V. V. Lebedev

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

32 records · Page 2Linked to original sources

arXiv2015

Nonlinear generation of vorticity in thin smectic films

We analyze a solenoidal motion in a vertically vibrated freely suspended thin smectic film. We demonstrate analytically that transverse oscillations of the film generate two-dimensional vortices in the plane of the film owing to hydrodynamic nonlinearity. An explicit expression for the vorticity of the in-plane film motion in terms of the film displacement is obtained. The air around the film is proven to play a crucial role, since it changes the dispersion relation of transverse oscillations and transmits viscous stresses to the film, modifying its bending motion. We propose possible experimental observations enabling to check our predictions.

physics.flu-dyn↗

arXiv2015

Non-linear fluctuation effects in dynamics of freely suspended film

Long-scale dynamic fluctuation phenomena in freely suspended films is analyzed. We consider isotropic films that, say, can be pulled from bulk smectic A liquid crystals. The key feature of such objects is possibility of bending deformations of the film. The bending (also known as flexular) mode turns out to be anomalously weakly attenuated. In the harmonic approximation there is no viscous-like damping of the bending mode, proportional to q^2 (q is the wave vector of the mode), since it is forbidden by the rotational symmetry. Therefore the bending mode is strongly affected by non-linear dynamic fluctuation effects. We calculate the dominant fluctuation contributions to the damping of the bending mode due to its coupling to the in-plane viscous mode, that restores the viscous-like q^2 damping of the bending mode. Our calculations are performed in the framework of the perturbation theory where the coupling of the modes is assumed to be small, then the bending mode damping is relatively weak. We discuss our results in the context of existing experiments and numeric simulations of the freely suspended films and propose possible experimental observations of our predictions.

cond-mat.soft↗

arXiv2014

Comment on "Thermodynamics of quantum crystalline membranes"

B. Amorim et al., (B.Amorim, R.Roldan, E.Cappelluti, A.Fasolino, F.Guinea, M.I.Katsnelson, Phys. Rev. B, v. 89, 224307 (2014)) reported the theoretical investigation of quantum crystalline membranes. In this comment we dismiss validity of their calculations based on a "natural" estimation of the ultra-violet (UV) divergent contributions into correlation functions. We claim that such calculations may not be performed correctly within the long-scale theory.

cond-mat.stat-mech↗

arXiv2014

Landau theory for helical nematic phases

We propose Landau phenomenology for describing the phase transition from the conventional nematic into the conical helical orientationally non-uniform structure recently identified in liquid crystals formed by "banana"-shaped molecules. The mean field predictions are mostly in agreement with experimental data. Based on the analogy with de Gennes model, we argue that fluctuations of the order parameter turn the transition to the first order phase transition rather than continuous one predicted by the mean-field theory. This conclusion is in agreement with experimental observations. We discuss the new Goldstone mode to be observed in the low-temperature phase.

cond-mat.soft↗

arXiv2013

Asymptotic freedom at zero temperature in crystalline membranes

We investigate effects of quantum (zero-temperature) long wavelength fluctuations of free standing crystalline membranes, that are two-dimensional objects embedded into three-dimensional space. The fluctuations produce logarithmic renormalization of elasticity and bending moduli of the membranes. We find one-loop RG-equations to demonstrate that the system is in the "asymptotic freedom" regime that is the quantum fluctuations destabilize the flat membrane phase.

cond-mat.stat-mech↗

arXiv2010

On role of symmetries in Kelvin wave turbulence

E.V. Kozik and B.V. Svistunov (KS) paper "Symmetries and Interaction Coefficients of Kelvin waves", arXiv:1006.1789v1, [cond-mat.other] 9 Jun 2010, contains a comment on paper "Symmetries and Interaction coefficients of Kelvin waves", V. V. Lebedev and V. S. L'vov, arXiv:1005.4575, 25 May 2010. It relies mainly on the KS text "Geometric Symmetries in Superfluid Vortex Dynamics}", arXiv:1006.0506v1 [cond-mat.other] 2 Jun 2010. The main claim of KS is that a symmetry argument prevents linear in wavenumber infrared asymptotics of the interaction vertex and thereby implies locality of the Kelvin wave spectrum previously obtained by these authors. In the present note we reply to their arguments. We conclude that there is neither proof of locality nor any refutation of the possibility of linear asymptotic behavior of interaction vertices in the texts of KS.

cond-mat.other↗

arXiv2007

Nearly spherical vesicles in an external flow

Tank-treading, tumbling and trembling are different types of the vesicle behavior in an external flow. We derive a dynamical equation for nearly spherical vesicles enabling to establish a phase diagram of the system predicting the regimes. The diagram is drawn in terms of two dimensionless parameters depending on the vesicle excess area, fluid viscosities, membrane viscosity and bending modulus, strength of the flow, and ratio of the elongational and rotational components of the flow. The tank-treading to tumbling transition occurs via a saddle-node bifurcation whereas the tank-treading to trembling transition occurs via a Hopf bifurcation. We establish a critical slowing near the merging point of the transition lines.

cond-mat.soft↗

arXiv2007

Dynamics of nearly spherical vesicles in an external flow

We analytically derive an equation describing vesicle evolution in a fluid where some stationary flow is excited regarding that the vesicle shape is close to a sphere. A character of the evolution is governed by two dimensionless parameters, $S$ and $Λ$, depending on the vesicle excess area, viscosity contrast, membrane viscosity, strength of the flow, bending module, and ratio of the elongation and rotation components of the flow. We establish the ``phase diagram'' of the system on the $S-Λ$ plane: we find curves corresponding to the tank-treading to tumbling transition (described by the saddle-node bifurcation) and to the tank-treading to trembling transition (described by the Hopf bifurcation).

cond-mat.soft↗

arXiv2003

Passive Scalar Evolution in Peripheral Region

We consider evolution of a passive scalar (concentration of pollutants or temperature) in a chaotic (turbulent) flow. A universal asymptotic behavior of the passive scalar decay (homogenization) related to peripheral regions (near walls) is established. The passive scalar moments and its pair correlation function in the peripheral region are analyzed. A special case investigated in our paper is the passive scalar decay along a pipe.

nlin.CD↗

arXiv2002

Disclination motion in hexatic and smectic-C films

We present theoretical study of a single disclination motion in a thin free standing hexatic (or smectic-C) film, driven by a large-scale inhomogeneity in the bond (or director) angle. Back-flow effects and own dynamics of the bond angle are included. We find the angle and hydrodynamic velocity distributions around the moving disclination, what allows us to relate the disclination velocity to the angle gradient far from the disclination. Different cases are examined depending on the ratio of the rotational and shear viscosity coefficients.

cond-mat.soft↗

arXiv2002

Base pair dynamic assisted charge transport in DNA

An 1d model with time-dependent random hopping is proposed to describe charge transport in DNA. It admits to investigate both diffusion of electrons and their tunneling between different sites in DNA. The tunneling appears to be strongly temperature-dependent. Observations of a strong (exponential) as well as a weak distance dependence of the charge transfer in DNA can be explained in the framework of our model.

cond-mat.soft↗

arXiv2000

About Probability Tails in Forced Burgers Turbulence

We consider asymptotics of the velocity derivatives probability distribution functions (PDFs) in Burgers' turbulence. We argue that in the forced case the same power laws as in the decaying case are realized for an infinite system.

nlin.CD↗

arXiv2000

Intermittency in Dynamics of Two-Dimensional Vortex-like Defects

We examine high-order dynamical correlations of defects (vortices, disclinations etc) in thin films starting from the Langevin equation for the defect motion. We demonstrate that dynamical correlation functions $F_{2n}$ of vorticity and disclinicity behave as $F_{2n}\sim y^2/r^{4n}$ where $r$ is the characteristic scale and $y$ is the fugacity. As a consequence, below the Berezinskii-Kosterlitz-Thouless transition temperature $F_{2n}$ are characterized by anomalous scaling exponents. The behavior strongly differs from the normal law $F_{2n}\sim F_2^n$ occurring for simultaneous correlation functions, the non-simultaneous correlation functions appear to be much larger. The phenomenon resembles intermittency in turbulence.

cond-mat.stat-mech↗

arXiv1997

Dynamic Fluctuation Phenomena in Double Membrane Films

Dynamics of double membrane films is investigated in the long-wavelength limit including the overdamped squeezing mode. We demonstrate that thermal fluctuations essentially modify the character of the mode due to its nonlinear coupling to the transversal shear hydrodynamic mode. The corresponding Green function acquires as a function of the frequency a cut along the imaginary semi-axis. Fluctuations lead to increasing the attenuation of the squeezing mode it becomes larger than the `bare' value.

cond-mat.soft↗