On the theory of magnetic field dependence of heat conductivity in dielectric in isotropic model

Phonon polarization in a magnetic field is analyzed in isotropic model. It is shown, that at presence of spin-phonon interaction phonon possess circular polari-zation which causes the appearance of heat flux component perpendicular both to temperature gradient and magnetic field.Comment: 5 pages, 0 figure

Gallium arsenide thermal conductivity and optical phonon relaxation times from first-principles calculations

In this paper, thermal conductivity of crystalline GaAs is calculated using first-principles lattice dynamics. The harmonic and cubic force constants are obtained by fitting them to the force-displacement data from density functional theory calculations. Phonon dispersion is calculated from a dynamical matrix constructed using the harmonic force constants and phonon relaxation times are calculated using Fermi's Golden rule. The calculated GaAs thermal conductivity agrees well with experimental data. Thermal conductivity accumulations as a function of the phonon mean free path and as a function of the wavelength are obtained. Our results predict a significant size effect on the GaAs thermal conductivity in the nanoscale. Relaxation times of optical phonons and their contributions from different scattering channels are also studied. Such information will help the understanding of hot phonon effects in GaAs-based devices.United States. Dept. of Energy. Office of Science (Award DE-SC0001299

Расчет гидродинамики потока в электроциклоне

To analyze the elektrocyclone flow hydrodynamic computer calculation using the finite element method (FEM) is applied. The geometry of the model corresponds to the laboratory  elektrocyclone. k-ε-turbulence model is used for the computation. The system of equations is solved by SIMPLE algorithm. The calculation results give a pattern of the flow velocity distribution and flow lines in different sections. There is conclusion based on the results about elektrocyclone flow hydrodynamic.Для анализа гидродинамики потока в электроциклоне применен компьютерный расчет с использованием метода конечных элементов (МКЭ). Геометрия модели соответствует лабораторному электроциклону. Для расчетов использована k-ε-модель турбулентности. Система уравнений решается с помощью алгоритма SIMPLE. Результаты расчета дают картину распределения скоростей потока и линий тока в различных сечениях. На основании результатов делается вывод о гидродинамике электроциклона. Выявлен факт, что в бункере электроциклона отсутствует вихревое движение, также нет развитого течения в области стенок, а ниже выхлопного отверстия скорость потока близка к 0. Это благоприятно сказывается на эффективности очистки, т. к. выходящий чистый газ не увлекает с собой осевшие частицы. Выводы: 1) гидродинамика электроциклона может быть описана с помощью математической модели и рассчитана с помощью МКЭ; 2) поток в электроциклоне, как и ожидалось, имеет закрученную структуру, угол закрутки зависит от длины активной зоны; 3) конструкция бункера обеспечивает выход очищенного газа без вовлечения в него уловленных частиц

Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range - of over five orders of magnitude - from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.Comment: Review Paper; 37 manuscript pages; 4 figures and 2 boxe

Copper isotope shifts in Pr and La substituted 123 and 124 cuprate superconductors; comparison with oxygen isotope shifts

Copper isotope shifts of T<SUB>c</SUB>have been measured in 123 and 124 cuprate superconductors with partial substitutions by Pr and La to reduce hole concentration. The 123 compositions were Pr<SUB>x</SUB>Y<SUB>1-x</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB> (x=0.2, 0.3, 0.4) and YLa<SUB>0.3</SUB>Ba<SUB>1.7</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB>. The 124 compounds were Pr<SUB>x</SUB>Y<SUB>1&#8722;x</SUB>Ba<SUB>2</SUB>Cu<SUB>4</SUB>O<SUB>8</SUB> (x=0.2, 0.3) and YLa<SUB>0.3</SUB>Ba<SUB>1.7</SUB>Cu<SUB>4</SUB>O<SUB>8</SUB>.Oxygen isotope experiments in materials with these compositions have shown substantial isotope shifts. We find that the Cu isotope shifts are also substantial, but somewhat smaller. Other findings are: (1) the Cu isotope exponent &#945;<SUB>Cu</SUB> is positive, (2) &#945;<SUB>Cu</SUB> increases rapidly as T<SUB>c</SUB> is reduced by substitution, and rises to a substantial fraction of the BCS value, behavior which is similar to that of the oxygen isotope exponent &#945; O, and (3) when T<SUB>c</SUB> is reduced by non-isovalent substitution, both O and Cu isotope shifts increase greatly, but the ratio &#945;<SUB>Cu/&#945;</SUB>O remains 0.75&#177;0.1 in both 123 and 124, regardless of the amount and site of the non-isovalent substitution

Large copper isotope effect in oxygen depleted YBa<SUB>2</SUB>Cu<SUB>3</SUB>Oy: importance of Cu-dominated phonon modes in the pairing mechanism

We have measured the copper isotope effect in YBa2Cu3Oy. We find a large positive copper-isotope exponent (α Cu≈0.37) in the underdoped plateau region (y~6.6). The exponent decreases to zero (or slightly negative) in the optimally doped region (y~6.94). The α Cu in YBa2Cu3O6.6 is similar to the α O (oxygen-isotope exponent) in YBa2-xLaxCu3Oy with the same Tc. These comparable values of α Cu and α O show that phonons which involve Cu motion as well as the (high-frequency) modes of the oxygen in the CuO2 planes are important in the pairing mechanism