Theory of condensation of indirect excitons in a trap

We present theoretical studies of condensation of indirect excitons in a trap. Our model quantifies the effect of screening of the trap potential by indirect excitons on exciton condensation. The theoretical studies are applied to a system of indirect excitons in a GaAs/AlGaAs coupled quantum well structure in a diamond-shaped electrostatic trap where exciton condensation was studied in earlier experiments. The estimated condensation temperature of the indirect excitons in the trap reaches hundreds of milliKelvin

Resonance enhancement of neutrino oscillations due to transition magnetic moments

Studying neutrino propagation in static background of dense matter and electromagnetic field [1] we obtained that the resonance enhancement of neutrino oscillations due to transition magnetic moments is possible. In this work we calculate the probabilities of spin-flavor transitions using solutions of the neutrino evolution equation in slowly varying magnetic field within the adiabatic approximation. We find that the resonance behavior of the transition probabilities is strictly connected to the neutrino polarization.Comment: 8 pages, 2 figures, LaTe

Stationary and non-stationary solutions of the evolution equation for neutrino in matter

We study solutions of the equation which describes the evolution of a neutrino propagating in dense homogeneous medium in the framework of the quantum field theory. In the two-flavor model the explicit form of Green function is obtained, and as a consequence the dispersion law for a neutrino in matter is derived. It is shown that there exist both the solutions describing the stationary states and the solutions describing the spin-flavor coherent states of the neutrino. The stationary states may be different from the mass eigenstates, and the wave function of a state with a definite flavor should be constructed as a linear combination of the wave functions of the stationary states with coefficients, which depend on the mixing angle in matter. In the ultra-relativistic limit the wave functions of the spin-flavor coherent states coincide with the solutions of the quasi-classical evolution equation. Quasi-classical approximation of the wave functions of spin-flavor coherent states is used to calculate the probabilities of transitions between neutrino states with definite flavor and helicity.Comment: 11 pages, 6 figures, revised versio

Radiative transitions of high energy neutrino in dense matter

The quantum theory of the ``spin light'' (electromagnetic radiation emitted by a massive neutrino propagating in dense matter due to the weak interaction of a neutrino with background fermions) is developed. In contrast to the Cherenkov radiation, this effect does not disappear even if the medium refractive index is assumed to be equal to unity. The formulas for the transition rate and the total radiation power are obtained. It is found out that radiation of photons is possible only when the sign of the particle helicity is opposite to that of the effective potential describing the interaction of a neutrino (antineutrino) with the background medium. Due to the radiative self-polarization the radiating particle can change its helicity. As a result, the active left-handed polarized neutrino (right-handed polarized antineutrino) converting to the state with inverse helicity can become practically ``sterile''. Since the sign of the effective potential depends on the neutrino flavor and the matter structure, the ``spin light'' can change a ratio of active neutrinos of different flavors. In the ultra relativistic approach, the radiated photons averaged energy is equal to one third of the initial neutrino energy, and two thirds of the energy are carried out by the final ``sterile'' neutrinos. This fact can be important for the understanding of the ``dark matter'' formation mechanism on the early stages of evolution of the Universe.Comment: 7 pages, latex, one misprint in eq. 12 correcte

Educational event as the pedagogical category

The aim of the investigation is to reveal the essence of the educational event as a pedagogical category. The reason to study the issue is the methodological generality of the term that came into pedagogical everyday life, but which semantic content is still not clear enough. Methods. The methods involve a theoretical analysis of the philosophical and pedagogical literature on the study, the categorical analysis, surveys of students and teachers. Results. The concept content of «event» is looked upon in both historical scholarship and pedagogy, «educational event» is analyzed in unity with the «educational situation» and «educational process». The attitude of students and teachers to educational events was clarified through the surveys; emotional and rational responses of the respondents were differentiated and the peculiarities of events organization in the education system were classified. While teachers and students are considered as subjects of educational events, their goals are delineated. Scientific novelty. The author's own definition of is given. Educational event is defined as a specially organized and unique pedagogical fact limited, but not rigidly determined by the educational situation, and capable of changing the educational process going beyond the boundaries of its conformism. The formulation above is the result of analysis how the concepts of «event», «situation» and «process» may interact in pedagogical discourse. Practical significance. The results can be used while designing the educational programs and projects, as well as in the development of academic courses of innovative pedagogy Цель статьи – выявление сущности образовательного события как педагогической категории. Необходимость описанного в публикации исследования обусловлена методологической «туманностью» данного термина, который вошел в широкий педагогический обиход, но не получил достаточно четкого смыслового наполнения. Методы. В работе использовались теоретический анализ философской и педагогической литературы, категориальный анализ, опросы студентов и учителей. Результаты. Сопоставлено содержание понятия «событие» в исторической науке и педагогике; «образовательное событие» рассмотрено в единстве с «образовательной ситуацией» и «образовательным процессом». При помощи опросов выяснено отношение студентов и работающих учителей к образовательным событиям, дифференцированы эмоциональные и рациональные реакции опрошенных, сгруппированы характеристики события в системе образования. Осуществлено разграничение целей педагогов и обучающихся как субъектов образовательных событий. Научная новизна. Предложена авторская дефиниция образовательного события как специально организованного и уникального педагогического факта, ограниченного образовательной ситуацией, но жестко не детерминированного ею и меняющего образовательный процесс выходом за границы его обыденности. Приведенная формулировка – итог анализа взаимосвязи понятий «событие», «ситуация» и «процесс» в педагогическом дискурсе. Практическая значимость. Результаты исследования могут быть востребованы при создании образовательных программ и проектов, а также при разработке вузовских курсов инновационной педагогик

Вплив адсорбції простих молекул на фазовий перехід у діоксиді ванадію

Вплив адсорбції простих молекул на температуру фазового переходу (T = 338–339 K) дослідже- но з використанням моделей поверхні діоксиду ванадію, співвимірних із цими молекулами. Темпера- турні залежності вільної енергії фаз до та після переходу перетинаються за температур 200–216 К, що відомо для наноструктур діоксиду ванадію. Показано, що використання методу теорії функціоналу густини з гібридним функціоналом B3LYP дає результати, майже ідентичні отриманим ab initio.The effect of adsorption of simple molecules on the temperature of phase transiton in vanadium dioxide (T = 338–339 K) has been studied by means of the models of vanadium dioxide surface commensurable with the sizes of the molecules participating in adsorption. Temperature dependences of the free energy of phases before and after the transition intersect at temperatures of 200–216 К, which is known for nanostructure of vanadium dioxide. Calculations by DFT method produce results almost identical to the calculations ab initio

Solitons supported by singular spatial modulation of the Kerr nonlinearity

We introduce a setting based on the one-dimensional (1D) nonlinear Schroedinger equation (NLSE) with the self-focusing (SF) cubic term modulated by a singular function of the coordinate, |x|^{-a}. It may be additionally combined with the uniform self-defocusing (SDF) nonlinear background, and with a similar singular repulsive linear potential. The setting, which can be implemented in optics and BEC, aims to extend the general analysis of the existence and stability of solitons in NLSEs. Results for fundamental solitons are obtained analytically and verified numerically. The solitons feature a quasi-cuspon shape, with the second derivative diverging at the center, and are stable in the entire existence range, which is 0 < a < 1. Dipole (odd) solitons are found too. They are unstable in the infinite domain, but stable in the semi-infinite one. In the presence of the SDF background, there are two subfamilies of fundamental solitons, one stable and one unstable, which exist together above a threshold value of the norm (total power of the soliton). The system which additionally includes the singular repulsive linear potential emulates solitons in a uniform space of the fractional dimension, 0 < D < 1. A two-dimensional extension of the system, based on the quadratic nonlinearity, is formulated too.Comment: Physical Review A, in pres