A Simulation study of the cooling of an isolated metal sphere in aqueous media (quenching)

A quantitative study is carried of a metal cooling process in aqueous and water-polymer cooling liquids. In the study, an original spherical hot probe with a heat-insulated stem is used to simulate the cooling conditions of the operating part of the probe and to correspond to the cooling conditions of an isolated sphere. It has been shown that in this case the process consists of distinct consecutive stages, each of which can be studied separately in a quantitative way. The cooling process in all stages is described with a simple exponential relationship containing two parameters. One of these is the effective temperature of the cooling medium; the other is a time constant of the cooling process uniquely related to the heat dissipation coefficient. In the film boiling stage the effective temperature can be much lower than the nominal temperature; moreover, for cooling in cold water it is found to be lower than the absolute temperature, which indicates the dominant contribution of convection to the heat dissipation. The effective temperature of the medium is a monotonously increasing function of the nominal temperature and rises with rising liquid viscosity. Dependence of the cooling process time constant on the liquid temperature is influenced by two competing processes affecting convection, namely, by variations with temperature of the density and viscosity of a liquid. The effect of diminishing density becomes prevalent at temperatures of the liquid above ≈80°C.     

Orientational contribution to the piezoelectric constants of BaTiO3 ceramic in ferroelectric phases with various symmetries

A self-consistent method based on the interaction of a piezoelectric sphere with a piezoelectric medium that has anisotropic elastic and dielectric properties is used to calculate the components of the tensor piezoelectric modulus of BaTiO₃ ceramic in all three ferroelectric modifications. A comparison of the calculated and measured piezoelectric moduli shows that at least 60–70% of the piezoelectric effect in BaTiO₃ ceramic is caused by domain boundary movement throughout the entire ferroelectric region. Fiz. Tverd. Tela (St. Petersburg) 41, 1080–1083 (June 1999)     

A General Solution of the Problem of Elastic-Wave Scattering by a Plane Crack

Doklady Physics - The 3D problem of elastic-wave scattering by cracks in a homogeneous isotropic medium is considered. Using the method of Green’s function and specially introduced auxiliary...     

Mechanical and conducting properties of polypropylene fibers filled with carbon nanotubes with functionalized surface

A procedure for functionalization of the surface of multiwall carbon nanotubes, based on treatment of the nanofiller with a strong oxidant and 1-hexadecylamine and aimed to improve the compatibility of nanotubes with a polypropylene matrix, was examined. Variation of the mechanical and electrical properties of the composite fiber based on polypropylene in relation to the concentration of the modified nanotubes was studied.     

Switching effects in composite films based on the conjugated polymer polyfluorene and ZnO nanoparticles

The S- and N-shaped current—voltage characteristics have been studied for composite films of the conjugated polymer polyfluorene and ZnO nanoparticles deposited onto Al and In₂O₃/SnO₂ electrodes with and without an intermediate sublayer of the conducting polymer PEDT/PSS. The differences in the current— voltage characteristics of the systems (the N- and S-types, respectively) are interpreted using the electro-thermal switching model, which takes into account the structural and electric properties of PEDT/PSS. The switching provides both alignment of polymer molecules and tunneling of charge carriers, which leads to an increase in conductivity. The current flow in this structure causes an increase in temperature of conducting channels; when the temperature reaches certain levels, the conductivity of the channels decreases because the alignment of polymer molecules is upset, which creates an N-shaped form of the current—voltage characteristics.     

Experiment for search for sterile neutrino at SM-3 reactor

In connection with the question of possible existence of sterile neutrino the laboratory on the basis of SM-3 reactor was created to search for oscillations of reactor antineutrino. A prototype of a neutrino detector with scintillator volume of 400 l can be moved at the distance of 6–11 m from the reactor core. The measurements of background conditions have been made. It is shown that the main experimental problem is associated with cosmic radiation background. Test measurements of dependence of a reactor antineutrino flux on the distance from a reactor core have been made. The prospects of search for oscillations of reactor antineutrino at short distances are discussed.     

Peculiarities of cellulose nitrate combustion in ballasted systems

Russian Chemical Bulletin - The dependence of the combustion parameters of cellulose nitrate (nitrocellulose, NC) mixtures with magnesium oxide on the content of the energetic component was studied...     

Continued fraction method in inverse problem of photothermal diagnostics

Received: 1 July 1996/Accepted: 16 October 1996