Social factors of distance learning: adopted from the experience of distance learning implementation in Poltava University of Economics and Trade

The implementation of distance learning (DL) involves solving a number of problems including social ones. The main social groups are involved in this process such as institutions’ and departments’ managers; educational, training and IT support staff. It should be mentioned, that in each of these groups there are supporters and opponents of DL and their quantity varies from one university to another. It should also be pointed out, that the number of DL’s supporters rises considerably. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3341

Stability of Driven Josephson Vortex Lattice in Layered Superconductors Revisited

We analytically study stability of sliding lattice of Josephson vortices driven by a transport current in the stack direction in strong in-plane magnetic field. In contrast to recent findings we obtain that there are no diverse configurations of stable vortex lattices, and, hence, the stable sliding vortex lattice can not be selected by boundary conditions. We find that only the triangular (rhombic) lattice can be stable, its stability being limited by a critical velocity value. At higher velocities there are no simple stable lattices with single flux line per unit cell. Oblique sliding lattices are found to be never stable. Instability of such lattices is revealed beyond the linear approximation in perturbations of the lattice.Comment: 11 pages, 2 figures, RevTeX 4, Submitted to Phys. Rev.

Effective action approach and Carlson-Goldman mode in d-wave superconductors

We theoretically investigate the Carlson-Goldman (CG) mode in two-dimensional clean d-wave superconductors using the effective ``phase only'' action formalism. In conventional s-wave superconductors, it is known that the CG mode is observed as a peak in the structure factor of the pair susceptibility $S(\Omega, \mathbf{K})$ only just below the transition temperature T_c and only in dirty systems. On the other hand, our analytical results support the statement by Y.Ohashi and S.Takada, Phys.Rev.B {\bf 62}, 5971 (2000) that in d-wave superconductors the CG mode can exist in clean systems down to the much lower temperatures, $T \approx 0.1 T_c$. We also consider the manifestations of the CG mode in the density-density and current-current correlators and discuss the gauge independence of the obtained results.Comment: 23 pages, RevTeX4, 12 EPS figures; final version to appear in PR

Dynamics of 2D pancake vortices in layered superconductors

The dynamics of 2D pancake vortices in Josephson-coupled superconducting/normal - metal multilayers is considered within the time-dependent Ginzburg-Landau theory. For temperatures close to $T_{c}$ a viscous drag force acting on a moving 2D vortex is shown to depend strongly on the conductivity of normal metal layers. For a tilted vortex line consisting of 2D vortices the equation of viscous motion in the presence of a transport current parallel to the layers is obtained. The specific structure of the vortex line core leads to a new dynamic behavior and to substantial deviations from the Bardeen-Stephen theory. The viscosity coefficient is found to depend essentially on the angle $\gamma$ between the magnetic field ${\bf B}$ and the ${\bf c}$ axis normal to the layers. For field orientations close to the layers the nonlinear effects in the vortex motion appear even for slowly moving vortex lines (when the in-plane transport current is much smaller than the Ginzburg-Landau critical current). In this nonlinear regime the viscosity coefficient depends logarithmically on the vortex velocity $V$.Comment: 15 pages, revtex, no figure