Maximum propagation speed and Cherenkov effect in optical phonon transport through periodic molecular chains

Optical phonons serve as the fast and efficient carriers of energy across periodic polymers due to their delocalization, large group velocity because of covalent bonding and large energy quantum compared to that for acoustic phonons, as it was observed in a number of recent measurements in different oligomers. However, this transport is dramatically sensitive to anharmonic interactions, including the unavoidable interaction with acoustic phonons responsible for the transport decoherence, suppressing ballistic transport at long distances. Here we show that this decoherence is substantially suppressed if the group velocity of optical phonons is less than the sound velocity of acoustic phonons; otherwise ballistic transport is substantially suppressed by a Cherenkov's like emission of acoustic phonons. This conclusion is justified considering energy and momentum conservation during phonon absorption or emission and supported by the numerical evaluation of lifetimes of the optical phonons. It is also consistent with the recent experimental investigations of ballistic optical phonon transport in oligomers with minor exception of relatively short oligophenylenes.Comment: 35 pages, 16 figures, to appear in Journal of Chemical Physic

Interference of nonpolarized light in liquid crystal domains on the polymer surface

The interference of the nonpolarized light transmitted through an ensemble of nematic liquid crystal domains formed on the polycarbonate surface has been investigated. A model based on the superposition of the ordinary and extraordinary beams passed through domains with the radial structure has been developed. Expressions for the phase difference and intensity of the interfering beams, which take into account the distribution of the liquid crystal director field, have been derived. The dependences of the optical transmittance of a domain layer on the applied voltage have been calculated with regard to the material and optical constants of a liquid crystal and structural features and averaged morphological parameters of individual domains in the experimental sample. The results of the calculation are consistent with the experimental data, which confirms the validity of the proposed model

Stationary Ovsyannikov Vortex in the Field of Large Gravitating Center

Рассматривается трехмерное течение газа в рамках модели стационарного особого вихря с гра- витацией. Используя методы группового анализа дифференциальных уравнений, можем свести изучение свойств решения к исследованию обыкновенного дифференциального уравнения, заданно- го неявно. Изучены свойства решений этого уравнения, получено описание режимов течения в фазовом пространстве, доказано существование дозвукового и сверхзвукового режимов движения газа в физическом пространстве. Показано, что классификация типов решений и их качествен- ное поведение аналогичны случаю вихря Овсянникова без гравитации (А.А.Черевко, А.П.Чупахин, 2005 г.).The three-dimensional motion of gas within the limits of model of a stationary special vortex with grav- itation is considered. Using methods of the group analysis of the differential equations, it is possible to reduce studying of properties of the decision to research of properties of an implicitly defined ordinary differential equation. The properties of solutions of this equation are studied, a description of modes of a current in the phase space is obtained, the existence of subsonic and supersonic modes of a gas motion in physical space is proved. It is shown that classification of types of decisions and their qualitative be- havior to a similar case of a vortex of Ovsyannikov without gravitation (A.A.Cherevko, A.P.Chupakhin, 2005)

Stationary Ovsyannikov Vortex in the Field of Large Gravitating Center

Рассматривается трехмерное течение газа в рамках модели стационарного особого вихря с гра- витацией. Используя методы группового анализа дифференциальных уравнений, можем свести изучение свойств решения к исследованию обыкновенного дифференциального уравнения, заданно- го неявно. Изучены свойства решений этого уравнения, получено описание режимов течения в фазовом пространстве, доказано существование дозвукового и сверхзвукового режимов движения газа в физическом пространстве. Показано, что классификация типов решений и их качествен- ное поведение аналогичны случаю вихря Овсянникова без гравитации (А.А.Черевко, А.П.Чупахин, 2005 г.).The three-dimensional motion of gas within the limits of model of a stationary special vortex with grav- itation is considered. Using methods of the group analysis of the differential equations, it is possible to reduce studying of properties of the decision to research of properties of an implicitly defined ordinary differential equation. The properties of solutions of this equation are studied, a description of modes of a current in the phase space is obtained, the existence of subsonic and supersonic modes of a gas motion in physical space is proved. It is shown that classification of types of decisions and their qualitative be- havior to a similar case of a vortex of Ovsyannikov without gravitation (A.A.Cherevko, A.P.Chupakhin, 2005)