Composite S-Brane Solutions On Product Of Ricci-Flat Spaces

A family of generalized $S$-brane solutions with orthogonal intersection rules and $n$ Ricci-flat factor spaces in the theory with several scalar fields and antisymmetric forms is considered. Two subclasses of solutions with power-law and exponential behaviour of scale factors are singled out. These subclasses contain sub-families of solutions with accelerated expansion of certain factor spaces. The solutions depend on charge densities of branes, their dimensions and intersections, dilatonic couplings and the number of dilatonic fields.Comment: To appear in GR

Semiclassical Calculation of Photon-Stimulated Schwinger Pair Creation

We consider the electron-positron pair creation by a photon in an external constant electric field. The presented treatment is based on a purely quasiclassical calculation of the imaginary part of the on-shell photon polarization operator. By using this approach we find the pair production rate for photons with polarization parallel as well as orthogonal to the external electric field in the leading order in the parameter $eE / m ^ 2$, which has been recently found by other methods. For the orthogonal polarization we also find a new contribution to the rate, which is leading in the ratio of the photon energy to the electron mass $\omega/m$. We also reproduce by a purely geometrical calculation the exponential factor in the probability of the stimulated pair creation at arbitrary energy of the photon.Comment: 16 pages, 4 figure

Historical overview of the passification method and its applications to nonlinear and adaptive control problems

The present survey paper provides a historical overview of the method of passification and its applications to nonlinear and adaptive control problems from 1980 to present days

Stochastic current switching in bistable resonant tunneling systems

Current-voltage characteristics of resonant-tunneling structures often exhibit intrinsic bistabilities. In the bistable region of the I-V curve one of the two current states is metastable. The system switches from the metastable state to the stable one at a random moment in time. The mean switching time \tau depends exponentially on the bias measured from the boundary of the bistable region V_{th}. We find full expressions for \tau (including prefactors) as functions of bias, sample geometry, and in-plane conductivity. Our results take universal form upon appropriate renormalization of the threshold voltage V_{th}. We also show that in large samples the switching initiates inside, at the edge, or at a corner of the sample depending on the parameters of the system.Comment: 21 pages, 5 figure

Decay of metastable current states in one-dimensional resonant tunneling devices

Current switching in a double-barrier resonant tunneling structure is studied in the regime where the current-voltage characteristic exhibits intrinsic bistability, so that in a certain range of bias two different steady states of current are possible. Near the upper boundary V_{th} of the bistable region the upper current state is metastable, and because of the shot noise it eventually decays to the stable lower current state. We find the time of this switching process in strip-shaped devices, with the width small compared to the length. As the bias V is tuned away from the boundary value V_{th} of the bistable region, the mean switching time \tau increases exponentially. We show that in long strips \ln\tau \propto (V_{th} -V)^{5/4}, whereas in short strips \ln\tau \propto (V_{th} -V)^{3/2}. The one-dimensional geometry of the problem enables us to obtain analytically exact expressions for both the exponential and the prefactor of \tau. Furthermore, we show that, depending on the parameters of the system, the switching can be initiated either inside the strip, or at its ends.Comment: 12 pages, 5 figures, update to published versio

The activity-based approach to achieving theoretical and practical consensus in pedagogy of N. F. Talyzina

The relevance of the problem under study is based on the necessity to solve the permanent problem of the unity of theory and practice in the content of students’ cognitive activity in the modern conditions. The purpose of the article is to analyze and to generalize the main concepts of pedagogy by N.F. Talyzina for implementation of the activity-based approach as a productive means of achieving theoretical and practical consensus in the process of forming students’ cognitive activity. The lead approach to studying this problem is the activity-based approach which adequately expresses the objective and the essence of our research. The article is based on the concepts of pedagogy by N.F. Talyzina and reveals the conceptual and instrumental components of implementing the activity-based approach as a productive means of achieving theoretical and practical consensus in the process of forming students’ cognitive activity. The materials of the article can be useful in modeling, designing and constructing a pedagogical concept aimed at achieving the balance between theoretical and practical components within the process of carrying out educational activity. © 2016 Chapaev et al

Particle decay in false vacuum

We revisit the problem of decay of a metastable vacuum induced by the presence of a particle. For the bosons of the `master field' the problem is solved in any number of dimensions in terms of the spontaneous decay rate of the false vacuum, while for a fermion we find a closed expression for the decay rate in (1+1) dimensions. It is shown that in the (1+1) dimensional case an infrared problem of one-loop correction to the decay rate of a boson is resolved due to a cancellation between soft modes of the field. We also find the boson decay rate in the `sine-Gordon staircase' model in the limits of strong and weak coupling.Comment: 19 pages, 2 figure