Investigation of the equilibrium establishment in the spin system by using dipole magic echo

An experimental and theoretical investigation of the equilibrium establishment in an isolated spin system is performed. The "time-reversion" effects were used at the experiments. Comparison of the description of the experimental results obtained on the basis of reversible equations of mechanics and nonequilibrium thermodynamics is carried out. It is demonstrated that the equations of mechanics do not describe the spin macrosystem transition to the equilibrium. The experimental results correspond to the theory which is based on the nonequilibrium thermodynamics methods and takes into account the quick decay of cross-correlations in the systems. © Springer-Verlag 1999

Local structure of divalent silver complexes in fluorite crystals as seen by EPR method

The analytical expressions for spin-Hamiltonian parameters of Jahn-Teller paramagnetic centres [AgF2F6]6- in fluorite crystals are deduced. Comparison with the experimental EPR data for CdF2, CaF2 and SrF2 yields information about the local structure of centres [AgF2F6]6-. It is found that two Ag2+-F- bonds of the centre (along the 〈111〉 direction) are shorter than the rest six bonds by factor 1.1. Euler angles of six non-axial fluorines are almost the same as those in the undistorted fluorite structure. © Springer-Verlag 1998 Printed in Austria

The self-diffusion of macromolecules in binary blends of poly(ethylene glycol)

The concentration and molecular mass dependencies of the self-diffusion coefficients were obtained for higher molecular mass component in binary blends of the homopolymer poly(ethylene glycol) (PEG) by a nuclear magnetic resonance method with pulsed magnetic field gradient. The shape of the diffusion decay and its dependence on the diffusion observation time in binary PEG blends have been investigated. The experimental results were explained by hypothesizing the existence of cluster formation in polymer melts and polymer blends and the possibility of molecular exchange between clusters. The entanglement time in such systems was evaluated. Copyright © 1999 John Wiley & Sons, Ltd

Prospects of aluminum heat pipes application to solar collectors of water heating systems

В статті наведені результати розробки алюмінієвих теплових труб та їх випробувань, а також опис дослідних зразків плоского и вакуумного сонячних колекторів і результати їх випробувань. Експериментальні дослідження показали, що нові легкі та недорогі теплові труби мають високі теплопередаючі характеристики. Максимальна теплопередаюча спроможність одної теплової труби не менш ніж 210 Вт, а її термічний опір - від 0,02 до 0,07 C°/Вт. Гідравлічний опір теплообмінника сонячного колектора може бути знижено нижче за 100 Па, а їх ККД достатньо висок до 0,72. Проведені дослідження показали перспективність використання алюмінієвих профільних теплових труб в сонячних колекторах водонагрівальних установок.Results on aluminum heat pipes developments and tests as well as the description of flat plate and evacuated tube solar collector experimental prototypes based on aluminum heat pipes and their tests are presented in the article. As it was proved by the experiments, new lightweight and inexpensive heat pipes have high thermal performances. Maximal heat transfer power of one heat pipe is not less than 210 W; and its thermal resistance is very low - from 0.02 to 0.07 C deg/W. Hydraulic resistance of flat plate solar collector and evacuated one, where aluminum profiled heat pipes are used, could be reduced to less than 100 Pa, and their thermal efficiency is rather high (up to 0.72). The prospects of solar collectors based on aluminum heat pipes application to water heating plants become evident due to their study.В статье приводятся результаты разработки алюминиевых тепловых труб и их испытаний, а также описания опытных образцов плоского и вакуумного солнечных коллекторов и результаты их испытаний. Экспериментальные исследования показали, что новые легкие и недорогие тепловые трубы имеют высокие теплопередающие характеристики. Максимальная теплопередающая способность одной тепловой трубы не менее 210 Вт, а ее термическое сопротивление - от 0,02 до 0,07 C°/Вт. Гидравлическое сопротивление теплообменника солнечного коллектора может быть снижено ниже, чем 100 Па, а их КПД достаточно высок до 0,72. Проведенные исследования показали перспективность применения алюминиевых профильных тепловых труб в солнечных коллекторах водонагревательных установок

Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal

A methodology is worked out to retrieve the numerical values of all the main parameters of the six-dimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propa- gation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60 K for the wave propagating along the [110] direction, for both the longitudinal and shear modes, the latter with two polarizations along the [001] and [110] axes, respectively. We show that these anomalies are due to the ultrasound relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the ex- perimental findings is based on the T2g (eg +t2g) JTE problem including the linear and quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states.Comment: 8 pages, 3 figure

Continuum regime motion of a growing droplet in opposing thermo-diffusiophoretic and gravitational fields of a thermal diffusion cloud chamber

A model for the motion of aerosol particles by Stefan flow, thermo-diffusiophoresis and gravity in a continuum regime is described, which considers a phase change on the particle surface. It is tested in a thermal diffusion cloud chamber where a droplet formed by nucleation quickly grows and simultaneously moves upwards due to vertical temperature and concentration gradients. Kinetic coefficients are assumed to be constant. Model predictions of the height where the droplet reverses its motion are in satisfactory agreement with the experimental results of Ždímal et al. ((1996). Colloids Surfaces A, 106, 119). The droplet motion seems to be predicted well at higher gradients and vapor fluxes, but model underestimates droplet motion at lower ones. For those cases also the free-molecule and transition regimes need to be included. Copyright © 2001 Elsevier Science B.V

An atomic force microscopy study of hybrid polymeric membranes: Surface topographical analysis and estimation of pore size distribution

© 2016, Pleiades Publishing, Ltd.The surface morphology of polymeric membranes as organic–inorganic block copolymers has been studied by atomic force microscopy (AFM). These hybrid block copolymers have been obtained by the polyaddition of toluene 2,4-diisocyanate to macroinitiators and the addition of oligomeric polyhedral оctaglycidyl silsesquioxane (Gl-POSS) as a bulky branching agent in a concentration range of 0.1–15 wt %. The AFM study of the morphology made it possible to determine the main roughness parameters and to perform topographical analysis of the surface of the polymers. The pore size distribution was evaluated by histogrammic approximation with the use of the Gauss distribution. The hypothesis of the normalcy of distribution of the experimental sample of pore diameters was confirmed by a combined criterion and Pearson’s chi-square goodness-of-fit test. The effect of the Gl-POSS concentration on the surface morphology and the microstructure of the organic–inorganic polymeric membranes was found to be nonmonotonic over the test concentration range