Directed current in the Holstein system

We propose a mechanism to rectify charge transport in the semiclassical Holstein model. It is shown that localised initial conditions, associated with a polaron solution, in conjunction with a nonreversion symmetric static electron on-site potential constitute minimal prerequisites for the emergence of a directed current in the underlying periodic lattice system. In particular, we demonstrate that for unbiased spatially localised initial conditions, violation of parity prevents the existence of pairs of counter-propagating trajectories, thus allowing for a directed current despite the time-reversibility of the equations of motion. Occurrence of long-range coherent charge transport is demonstrated

Penetrators (penetrating sondes) and new possibilities for study of the planets

The fields of possible use of penetrators in space research are considered. A survey of the condition of development and plans for use of penetrators abroad is presented and an analysis is given of the significance of scientific problems when probing planets

Terrorism as the challenge to the plans of sustainable tourist development in North-Caucasian Federal District

The problem which is considered in this article is the influence of terrorism on the development of North Caucasian Federal district touristic sphere. The author gives an accent on the negative tendencies of the region, urgency of the problem in the context of the world, necessity of a thorough analysis of the problem on the level of state. The methodology of this research includes system approach and structural analysis. There is a special attention to the statistics and social researches, normative documents, mass media materials, scientific articles of the other authors. The results of the following research make to possible to come to conclusion that this problem should be explored more thoroughly.В данной статье рассматривается проблема влияния терроризма на развитие туристского сектора Северо-Кавказского федерального округа. Автор акцентирует внимание на современных негативных тенденциях в регионе, актуальности проблемы в мировом контексте, необходимости более тщательного анализа проблемы на государственном уровне. Методология исследования включает в себя системный подход и структурный анализ. Большое внимание уделяется статистическим данным и социологическим исследованиям, нормативным документам, материалам СМИ, научным статьям других авторов. Результаты исследования позволили сделать вывод о том, что проблема в дальнейшем должна быть изучена более тщательным образом

Second quantization method in the presence of bound states of particles

We develop an approximate second quantization method for describing the many-particle systems in the presence of bound states of particles at low energies (the kinetic energy of particles is small in comparison to the binding energy of compound particles). In this approximation the compound and elementary particles are considered on an equal basis. This means that creation and annihilation operators of compound particles can be introduced. The Hamiltonians, which specify the interactions between compound and elementary particles and between compound particles themselves are found in terms of the interaction amplitudes for elementary particles. The nonrelativistic quantum electrodynamics is developed for systems containing both elementary and compound particles. Some applications of this theory are considered.Comment: 35 page

Level-rank duality via tensor categories

We give a new way to derive branching rules for the conformal embedding (\asl_n)_m\oplus(\asl_m)_n\subset(\asl_{nm})_1. In addition, we show that the category \Cc(\asl_n)_m^0 of degree zero integrable highest weight (\asl_n)_m-representations is braided equivalent to \Cc(\asl_m)_n^0 with the reversed braiding.Comment: 16 pages, to appear in Communications in Mathematical Physics. Version 2 changes: Proof of main theorem made explicit, example 4.11 removed, references update

Theory of a Narrow roton Absorption Line in the Spectrum of a Disk-Shaped SHF Resonator

We calculate the probability of the birth of a circular phonon (c-phonon) in He II by a c-photon of the resonator. It is shown that this probability has sharp maxima at frequencies, where the effective group velocity of the c-phonon is equal to zero; the density of states of c-phonons strongly grows at such frequencies. For He II, these frequencies correspond to a roton and a maxon. From the probability of the c-roton birth, we calculate the roto line width which is found to approximately agree with the experimental one. We conclude that the roton line observed in the super-high-frequency (SHF) absorption spectrum of helium is related to the birth of c-rotons. A possible interpretation of the Stark effect observed for the roton line is also proposed.Comment: 13 pages, 1 figure, v2: journal variant, several minor correction

A Note on Stress-Energy Tensor and Variational Principle for Null Strings

A straightforward application of the variational principle to null strings meets difficulties since string's world-sheets are degenerate. It is known that the variational principle in this case can be formulted with the help of two-vector density on the string world-sheet which plays a role of Lagrange multipliers. It is shown that recently suggested stress-energy tensor of null strings can be derived by variation over the background metric of the action used to describe tensionless limit in the string theory. One of the Lagrange multipliers is related to the energy of the null string.Comment: 4 page