Lagrangian structures in time-periodic vortical flows

The Lagrangian trajectories of fluid particles are experimentally studied in an oscillating four-vortex velocity field. The oscillations occur due to a loss of stability of a steady flow and result in a regular reclosure of streamlines between the vortices of the same sign. The Eulerian velocity field is visualized by tracer displacements over a short time period. The obtained data on tracer motions during a number of oscillation periods show that the Lagrangian trajectories form quasi-regular structures. The destruction of these structures is determined by two characteristic time scales: the tracers are redistributed sufficiently fast between the vortices of the same sign and much more slowly transported into the vortices of opposite sign. The observed behavior of the Lagrangian trajectories is quantitatively reproduced in a new numerical experiment with two-dimensional model of the velocity field with a small number of spatial harmonics. A qualitative interpretation of phenomena observed on the basis of the theory of adiabatic chaos in the Hamiltonian systems is given. <br><br> The Lagrangian trajectories are numerically simulated under varying flow parameters. It is shown that the spatial-temporal characteristics of the Lagrangian structures depend on the properties of temporal change in the streamlines topology and on the adiabatic parameter corresponding to the flow. The condition for the occurrence of traps (the regions where the Lagrangian particles reside for a long time) is obtained

Особенности аппаратурного оформления процесса электроформования полимерных нано- и микроволокнистых материалов

In this article the technique of polymer nano- and microfiber materials electrospinning and its implementation are consideredВ работе рассмотрены существующие способы аппаратурного оформления процесса электроформования полимерных нано- и микроволокнистых материалов, отечественных и зарубежных компаний

Электроформование волокнистых материалов на основе полимерных микро- и нановолокон. История, теория, технология, применение.

This article is devoted to rapid development of such field of chemical fibers technology as electrospinning and dealing with history and theoretical ways of process description.В работе рассмотрена активно развивающаяся в настоящее время область технологии химических волокон – процесс элетроформования. Освещается история, теоретические подходы к описанию процесс

Electrospun fibrous materials from polymer micro- and nanofibers. History, theory, technology, application

This article is devoted to rapid development of such field of chemical fibers technology as electrospinning and dealing with history and theoretical ways of process description

Specificity of implementing the electrospinning of polymeric nano- and microfiber materials

In this article the technique of polymer nano- and microfiber materials electrospinning and its implementation are considere

Superparamagnetic blocking of an ensemble of magnetite nanoparticles upon interparticle interactions

We report on the effect of interparticle magnetic interactions in an ensemble of superparamagnetic magnetite particles with an average size of ~8.4 nm dispersed in the diamagnetic matrix on the blocking of this ensemble in external magnetic field. The two limit cases are investigated: the case of strongly interacting particles, when the value of magnetic dipole-dipole interaction between particles is comparable with the energy of other interactions in the ensemble (the interparticle distance is similar to the nanoparticle diameter) and the case of almost noninteracting particles distant from each other by about ten particle diameters. We demonstrate that the experimental dependence of the blocking temperature on external field is described well within the model [1], in which the density of particles in a nonmagnetic medium is taken into account and the correlation value depends on external magnetic field. The model for describing the magnetic properties of a disperse nanoparticle ensemble is proposed, which makes corrections related to the particle size and mean dipole-dipole interaction energy for the anisotropy constant. The surface magnetic anisotropy of Fe3O4 particles and parameters of the interparticle coupling are estimate

Superparamagnetic blocking of an ensemble of magnetite nanoparticles upon interparticle interactions

We report on the effect of interparticle magnetic interactions in an ensemble of superparamagnetic magnetite particles with an average size of ~8.4 nm dispersed in the diamagnetic matrix on the blocking of this ensemble in external magnetic field. The two limit cases are investigated: the case of strongly interacting particles, when the value of magnetic dipole-dipole interaction between particles is comparable with the energy of other interactions in the ensemble (the interparticle distance is similar to the nanoparticle diameter) and the case of almost noninteracting particles distant from each other by about ten particle diameters. We demonstrate that the experimental dependence of the blocking temperature on external field is described well within the model [1], in which the density of particles in a nonmagnetic medium is taken into account and the correlation value depends on external magnetic field. The model for describing the magnetic properties of a disperse nanoparticle ensemble is proposed, which makes corrections related to the particle size and mean dipole-dipole interaction energy for the anisotropy constant. The surface magnetic anisotropy of Fe3O4 particles and parameters of the interparticle coupling are estimate