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S. I. Vainshtein

Publications and source records attributed to S. I. Vainshtein.

8 recordsLinked to original sources
arXiv2008

Strongly compressible current sheets under gravitation

Many stormy events in astrophysics occur due to the sudden magnetic energy release. This is possible if a magnetic configuration abruptly changes its topology, an event usually referred to as magnetic reconnection. It is known that pure Ohmic decay is inefficient, occurring during cosmological times (due to the huge characteristic scales $L$). It is recognized that the presence of current sheets speeds up the process, but still insufficiently$^{1,2,3,4,5}$. We show that, in highly compressible and substantially gravitational media, the reconnection is fast enough to account for stormy events. Thus, highly compressible situations offer exiting opportunities in explanations of violent events, although full-scale compressible and gravitational simulations proved to be quite challenging.

astro-ph↗
arXiv2005

Transverse velocities, intermittency and asymmetry in fully developed turbulence

Using experimental transverse velocities data for very high Reynolds number turbulence, we suggest a model describing both formation of intermittency and asymmetry of turbulence. The model, called "bump-model" is a modification of ramp-model suggested earlier, S.I. Vainshtein and K.R. Sreenivasan, Phys. Rev. Lett., 73, 3085 (1994). The connection between asymmetry and intermittency makes it possible to study the latter with relatively low moments.

nlin.CD↗
arXiv2004

Structure of the most singular vortices in fully developed turbulence

Using high Reynolds number experimental data, we search for most dissipative, most intense vortices. These structures possess a scaling predicted by log-Poisson model for the dissipation field $ε_r$. These new experimental data suggest that the most intense structures have co-dimension less than 2. The log-Poisson statistics is compared with log-binomial which follows from the random $β$-model.

physics.flu-dyn↗
arXiv2003

Most singular vortex structures in fully developed turbulence

Using high Reynolds number experimental data, we search for most dissipative, most intense structures. These structures possess a scaling predicted by log-Poisson model for the dissipation field $ε_r$. The probability distribution function for the exponents $α$, $ε_r\sim e^{αa}$, has been constructed, and compared with Poisson distribution. These new experimental data suggest that the most intense structures have co-dimension less than 2. The log-Poisson statistics is compared with log-binomial which follows from the random $β$-model.

physics.flu-dyn↗
arXiv2001

Searching for vortex structures in high Reynolds number turbulence

In experimental study of very high Reynolds number turbulence, we found evidences that there are distinguished vortex structures in the intermediate range, that is, between the Kolmogorov and Taylor microscales, where they are indeed expected to be present. These structures are responsible for the intermittency, and, in the same time, they contribute into asymmetry of turbulent statistics, the latter following from the Kolmogorov law.

physics.flu-dyn↗
arXiv2000

Evidence for topological nonequilibrium in magnetic configurations

We use direct numerical simulations to study the evolution, or relaxation, of magnetic configurations to an equilibrium state. We use the full single-fluid equations of motion for a magnetized, non-resistive, but viscous fluid; and a Lagrangian approach is used to obtain exact solutions for the magnetic field. As a result, the topology of the magnetic field remains unchanged, which makes it possible to study the case of topological nonequilibrium. We find two cases for which such nonequilibrium appears, indicating that these configurations may develop singular current sheets.

astro-ph↗
arXiv1999

Rapid dissipation of magnetic fields due to Hall current

We propose a mechanism for the fast dissipation of magnetic fields which is effective in a stratified medium where ion motions can be neglected. In such a medium, the field is frozen into the electrons and Hall currents prevail. Although Hall currents conserve magnetic energy, in the presence of density gradients, they are able to create current sheets which can be the sites for efficient dissipation of magnetic fields. We recover the frequency, $ω_{MH}$, for Hall oscillations modified by the presence of density gradients. We show that these oscillations can lead to the exchange of energy between different components of the field. We calculate the time evolution and show that magnetic fields can dissipate on a timescale of order $1/ω_{MH}$. This mechanism can play an important role for magnetic dissipation in systems with very steep density gradients where the ions are static such as those found in the solid crust of neutron stars.

astro-ph↗