K. Mazuruk

An experimental study of the influence of a rotating magnetic field on Rayleigh–Bénard convection

A destabilizing vertical temperature gradient and a rotating magnetic field have been applied to a cylindrical column of liquid gallium. The convective flows which arise as a function of these parameters are identified. For small magnetic field strengths, a regime of stationary flow is observed. This regime is bounded by critical values of the Rayleigh and magnetic Taylor numbers. As the rotating magnetic field is increased, the critical Rayleigh number can increase by more than a factor of 10. The rotating magnetic field itself induces an instability at a critical value of the magnetic Taylor number independent of the Rayleigh number. The nature of the bifurcations (whether subcritical or supercritical) and the convective flows occurring at the critical Rayleigh numbers are dependent upon the magnetic Taylor number

Thermoconvective instability in a rotating magnetic field

The effect of a rotating magnetic field (RMF) on the stability of a fluid contained in a cylindrical column and heated from below is investigated. The RMF increases the critical Rayleigh number for asymmetric flow modes but does not affect the onset of instability for axisymmetric modes. The critical Rayleigh number is dependent upon the relative penetration of the magnetic field into the cylinder and the Prandtl number of the fluid. Instability first develops in the form of a single asymmetric meridional roll rotating around the axis of the cylinder, driven by the azimuthal component of the magnetic field.

Flow transitions in a rotating magnetic field

Critical Rayleigh numbers have been measured in a liquid metal cylinder of finite height in the presence of a rotating magnetic field. Several different stability regimes were observed, which were determined by the values of the Rayleigh and Hartmann numbers. For weak rotating magnetic fields and small Rayleigh numbers, the experimental observations can be explained by the existence of a single non-axisymmetric meridional roll rotating around the cylinder, driven by the azimuthal component of the magnetic field. The measured dependence of rotational velocity on magnetic field strength is consistent with the existence of laminar flow in this regime.

Determination of donor and acceptor impurity concentrations in n-InP and n-GaAs

The Hall mobility of semiconducting materials is generally computed without accounting for the Hall factor,rH. It is shown that for low magnetic fields this may lead to considerable errors in the calculation of the impurity concentrations,ND andNA, in both n-GaAs and n-InP of reasonable purity. Tables allowing the determination ofND andNA under low magnetic field conditions are computed at room and liquid nitrogen temperatures. They account forrH and for the inelastic nature of collisions with polar optical phonons without assuming Matthiessens rule.

Frequency effects of a rotating magnetic field on fluid flow in vertical cylinders

The body force generated by a rotating magnetic field applied to a cylindrical column of liquid metal of finite height is investigated theoretically. Although an exact analytical formula has not been found, the proposed approach leads to a good approximate solution. It is demonstrated that the force field is significantly affected by the angular frequency of the rotating magnetic field. In the low-frequency limit, only the azimuthal component is present, while in the high frequency regime, a complex force field is induced which is composed of both azimuthal and meridional components. The resulting azimuthal flow in the Stokesian regime has been numerically obtained and a counter-rotating profile has been demonstrated. The calculated results can be used to determine the fluid flow behavior during crystal growth in a weak rotating magnetic field.

Control of melt convection using traveling magnetic fields

Abstract An axisymmetric traveling magnetic wave induces a meridional base flow in a cylindrical zone of an electrically conducting liquid. This remotely induced flow can be conveniently controlled, in magnitude and direction, and can have benefits for crystal growth applications. In particular, it can be used to significantly offset natural convection. Theoretical basics of this new technological method are presented.

Mass flux and partial pressures of ZnSe by physical vapor transport

Abstract Mass fluxes of ZnSe by physical vapor transport (PVT) were measured in the temperature range of 1050–1140°C using an in situ dynamic technique. The starting materials were heat treated by a hydrogen reduction process followed by the dynamic bake-out method. The amount and composition of the residual gas inside the experimental ampoules were measured after the transport experiments using a total-pressure gauge. The total residual gas pressures measured were about one order of magnitude lower than the values reported on similar processed ZnSe ampoules which were not treated with a hydrogen reduction process. As a result of the reduction in the residual gas pressure, the measured fluxes were 3–7 times higher than previously reported and correspond to a growth rate higher than 10 mm/day at 1120°C. The simultaneous measurements of partial pressures of transport species and the mass fluxes were also performed on a ZnSe optical ampoule. The partial pressures of Zn and Se 2 were obtained by measuring the optical densities of the vapor at the wavelengths of 2138, 3405, 3508, 3613, and 3792 A. For the first time, the experimentally obtained mass fluxes were compared with those calculated, without any adjustable parameters, from a one-dimensional diffusion model which uses all the measured parameters (thermal field, partial pressures of transport species, and residual gas) as inputs, and good agreement was observed.

Magnetic microspheres and tissue model studies for therapeutic applications

Abstract: The use of magnetic fluids and magnetic particles in combinatorial hyperthermia therapy for cancer treatment is reviewed. The investigation approach adopted for producing thermoregulating particles and tissue model studies for studying particle retention and heating characteristics is discussed.

Novel oscillating cup viscometer–application to molten HgTe and Hg0.8Cd0.2Te

A novel oscillating‐cup viscometer, employing strain gauges for electronic signal acquisition, was developed, tested with gallium and applied to molten II‐VI compounds. Kinematic viscosity data were obtained for Ga from 60 to 815 °C, for HgTe from 700 to 790 °C, and for Hg0.8Cd0.2Te from 790 to 850 °C.

Phase diagram of HgTe–ZnTe pseudobinary and density, heat capacity, and enthalpy of mixing of Hg1−xZnxTe pseudobinary melts

In this article, the solidus temperatures of the Hg1−xZnxTe pseudobinary phase diagram for several compositions in the low x region were measured by differential thermal analysis and the HgTe–ZnTe pseudobinary phase diagram was constructed. The densities of two HgZnTe melts, x=0.10 and 0.16, were determined by an in situ pycnometric technique in a transparent furnace over, respectively, 110 and 50 °C ranges of temperature. The thermodynamic properties of the melts, such as the heat capacity and enthalpy of mixing, were calculated for temperatures between the liquidus and 1500 °C by assuming an associated solution model for the liquid phase.