Journal of Physics D: Applied Physics

Farrow, R F C; Jones, G R; Williams, G M; Sullivan, P W; Boyle, W J O; Wotherspoon, J T M

doi: 10.1088/0022-3727/12/10/003pmid: N/A

The vaporisation of Hg0.8Cd0.2Te crystals under Knudsen effusion conditions has been investigated by the technique of modulated-beam mass spectrometry. Hg is the only dissociation vapour species detected at temperatures below 200 degrees C. Between 200 degrees C and 450 degrees C both Hg and Te3 was present but Cd was detected only above 450 degrees C. This grossly incongruent vaporisation leads to considerable concentration gradients within the charge crystals which have been observed directly using SEM, EDEX and X-ray diffraction techniques. Crystals heated to 420 degrees C for several hours under Knudsen effusion conditions lose HgTe via the vapour species Hg and Te2 and develop a surface layer of CdTe which, though porous, remains epitaxial. The development of concentration gradients within the charge at lower temperature leads to a diffusion rate limitation of the mercury vapour pressure developed within the Knudsen oven.

Bahaj, A S; Bailey, A G

doi: 10.1088/0022-3727/12/10/001pmid: N/A

When the potential of a small loop of wire is raised by a few volts with respect to a flat counter electrode it is possible to trap a dielectric particle in a position of stable equilibrium. 50 mu m diameter particles of divinyl benzene suspended in water have been studied. The dielectrophoretic response of such particles as a function of the frequency of the applied voltage should enable relaxation processes at the particle-liquid interface to be determined.

Frazier, G A; Glosser, R

doi: 10.1088/0022-3727/12/10/002pmid: N/A

A technique for obtaining pressure-concentration isotherms of the palladium hydrogen system is described. A quartz crystal thickness monitor is used to directly determine the quantity of hydrogen absorbed by an evaporated palladium film. The measured phase diagrams agree with previous measurements on bulk samples. The method can be applied to any metal film-gas system.

Elwakil, S A; Batanoni, E El; Saad, E A

doi: 10.1088/0022-3727/12/10/004pmid: N/A

The iteration technique is used to find the relation between the linear functional and Pade approximants. Two examples are solved as applications: (i) the neutron escape probability and (ii) the reflection and transmission function in radiative transfer and in turn the emergent and transmitted intensities for a finite slab and the emergent intensity for a semi-infinite medium. Numerical calculations are done and compared with the exact results obtained from other techniques. It is found that the Pade approximants converge to the exact results.

Cook, R J; Rosenberg, C B

doi: 10.1088/0022-3727/12/10/005pmid: N/A

A description is given of measurements made at 35 GHz of the complex transmission coefficient for an isotropic and an anisotropic material using a free space microwave bridge. The medium-loss isotropic material exhibited the effects of multiple internal reflections which have been fully accounted for. In the case of the high-loss anisotropic material the complex reflection coefficient was also measured. The measurements were made in a microwave bridge with the sample placed in free space between horns, with a waveguide reference arm. Separate circuits for transmission and reflection are described. The anisotropic material consisted of coated, conducting parallel glass fibres moulded in an epoxy resin disc. Measurements are reported for the electric vector parallel and perpendicular to the fibre direction. Values of the refractive index n and the absorption index K where calculated from the measured complex transmission and reflection coefficients.

Caldwell, J

doi: 10.1088/0022-3727/12/10/006pmid: N/A

The effects of iron on the uniformity of the field produced by a current carrying axisymmetric conductor are considered. Using a perturbation analysis a simple analytic expression is obtained which describes the field close to the axis of symmetry. The accuracy is estimated by comparing the results with those obtained by using finite-difference methods.

Jones, A R

doi: 10.1088/0022-3727/12/10/007pmid: N/A

Scattering and absorption efficiencies are calculated for chains of spheres in the Rayleigh approximation, and compared with individual particles. For aligned chains significant differences are found for the scattering case which arise due to multiple scattering and coherent phase effects. The absorption efficiency is not influenced by the latter, but the changes are found to be of the same proportion as those in the scattering efficiency due to multiple scattering alone. For randomly oriented chains the effects of multiple scattering are small within the range considered.

McQueen, D H

doi: 10.1088/0022-3727/12/10/008pmid: N/A

An acoustical theory of the photoacoustic effect is presented in such a way that expected signal strengths from microphones in gaseous media and from hydrophones in liquid media can be compared. For liquid media it is shown that the sample acoustic impedance is often quite important. Numerical comparisons of hydrophones and microphones indicate that photoacoustic signals from the former can be stronger than from the latter.

Rashed, M I I; Ghazi, M A; Elbanna, H

doi: 10.1088/0022-3727/12/10/009pmid: N/A

The instability of a thin sheet of liquid moving in the same direction as an air stream is studied theoretically. It is found that instability occurs if the Weber number is less than a critical value related to the ratio of the air and liquid stream velocities. Also, the wavelength for maximum instability is found to be inversely proportional to this critical value.

Giles, C R; Clements, R M; Smy, P R

doi: 10.1088/0022-3727/12/10/010pmid: N/A

The transient electrical properties of a planar probe which is immersed in a flowing continuum plasma and in which the flow velocity is parallel to the probe surface are studied theoretically. When the probe is pulsed negatively, the resultant ion current overshoots its final equilibrium value. The time constant for recovery from this overshoot is shown to yield the information about the plasma flow over the probe. When the plasma sheath edge is inside the hydrodynamic boundary layer it is able to directly probe the velocity structure of the hydrodynamic boundary layer. The theory used to describe the probe's electrical properties differs from other thick sheath theories in that both gas compressibility and ion/electron recombination effects are considered.