Table of contents

While studying the viscoelastic flow past an infinite plate with suction and constant heat flux between fluid and plate, Raptis and Tzivanidis (1981) gave the solution of a pair of equations for velocity and temperature as functions of distance. They then gave some approximate solutions. This letter shows that the approximations are not justified and presents an exact analytical study.

The electron temperature in high frequency (HF) discharges has been measured by a new diagnostic method using a sonic probe technique. The results are compared with those obtained by the double-probe technique.

Modulation of large amplitude progressive ionisation waves is studied using a slowly-varying-parameter method. Analytical solutions are presented in terms of elliptic integrals which depend upon a parameter c tied to the wave modulation amplitude.

Computational study shows that ion-electron recombination within the boundary layer should be taken into account for calculating correctly the ion saturation current density. The value region of the rate coefficient for the ion-electron recombination is obtained from this study.

Presents results of a theory of thermally stimulated currents (TSC), which takes into account the trap-controlled dispersive carrier transport in amorphous solids. This theory has been applied to reinterpret recent TSC measurements in poly(N-vinylcarbazole). The carrier trapping time distribution function has been determined, which gives a satisfactory description of dependence of TSC peaks on sample thickness.

An effect of the repetition frequency of charging pulses in an insulator in DLTS experiments is included in the expression for currents DLTS.

Studies of TL glow curves on powder and single crystals of TLD-100 give essential the same results. Differences in materials are not the source of the discrepancy between the authors' results and those of Kathuria and Sunta (1982). In the authors' results, from isothermal annealing of the TL, they find no evidence for non-first-order kinetics and conclude that the kinetics, for both single crystals and powders, is first-order.

A superconducting-cavity stabilised oscillator has been constructed which combines active and passive stabilisation of a 9.6 GHz klystron to obtain a phase noise power spectral density between -170 dB Hz^-1 and -180 dB Hz^-1 at 5 kHz from the carrier, which represents about 40 dB improvement over the state-of-the-art. The device has been developed for use as a low noise pump for a superconducting parametric upconverter transducer on a gravitational radiation antenna. An RF modulated reflex klystron is actively locked to a TE₀₁₁ niobium cavity operated at 2K with a loaded Q approximately 10⁸. Power is extracted from the cavity which acts as a high Q filter.

A tunable cwF-centre laser has been used for optogalvanic detection of the helium 4^1,3F-6^1,3G transition at 2.624 mu m. From a fully quantitative analysis, including measurement of the line absorption coefficient, the authors have determined a value for the ionisation efficiency per laser photon absorbed using a steady-state model of the positive column. This value agrees well with the efficiency calculated from the linear steady-state rate equations. Also, n=4 to 6 transitions of helium and hydrogen have been optogalvanically detected in He-H₂ mixtures. Observations for various mixture ratios are used to explain the quenching effect of H₂ on the He lines.

Using a heterodyne technique of considerably greater sensitivity than interferometry, the authors have studied acoustic effects arising from a TEA laser discharge. Initial adiabatic expansion was observed to be followed by a slow (tens of milliseconds) diffusive relaxation process. Shock waves generated in the vicinity of the cathode and also produced by the pre-ionising arc arrays caused perturbations on a time-scale of tens of microseconds. Discharge heating of the gas caused it to expand by almost an order less than the adiabatic expansion or shock tube theories would suggest. The implications of these findings to the design of high repetition rate and frequency stable TEA lasers are discussed.

For pt.I see ibid., vol.14, p.601, (1981). The process of indentation in PMMA by cone indenters is shown to be highly dependent on the cone angle. For blunt cones (greater than 30 degrees semi-angle) a dead zone is formed ahead of the indenter and this acts as the indenter. The formation of this zone is examined for various blunt cones and the resultant zone is similar for all cases. The zone formation is ascribed to frictional forces and such a zone is not formed with sharp indenters. Irrespective of cone angle and dead-zone formation the deformation under the indenter resembles the expansion of a cavity in the material. Observations of the growth and position of the region of anomalous refractive index and the crack path allow assignment of a value to the parameter 'plastic zone radius/cavity radius', c/a, as required by the expanding cavity model. The c/a value determined in this manner is approximately 1.6. Frictional effects on the shank and tip of the indenter make large contributions to the measured indentation pressure, and corrections for these are suggested. If the c/a value of 1.65 is used the pressures predicted by the expanding cavity model of Puttick et al. (1977) correlate well with the corrected experimental results.

Measurements of streaming potential, U, for the flow of a deionised fluid through dielectric cells with annular sections of various gaps and lengths, are used to investigate the relationship between the potential, fluid pressure across the cell Delta P, and geometric configurations. It is shown that the ratio of Delta P/U remains unchanged through regions of significant change in Delta P, but does change gradually as a function of water resistivity at sufficiently small gaps. This latter change appears to be due to an anomalous electrical interaction between boundary layers across the gap.

The vibrational population distribution of the N₂ electronic ground state has been calculated numerically in a steady-state uniform discharge plasma with plasma parameters varying in the range of electron density N_e from 5*10⁹ to 5*10¹¹ cm^-3 electron temperature T_e from 0.3 to 2 eV, gas pressure P from 0.1 to 10 Torr and gas temperature T_g from 300 to 800K. The theoretical vibrational temperature T_v of N₂X¹ Sigma _g⁺ has been obtained from the calculated population distribution function. The results shown that T_v increases with increasing N_e and decreasing P and has a maximum value around T_e approximately=0.8 eV. The variation of T_g does not greatly influence the calculation of T_v. A comparative experiment has also been conducted. The theoretical T_v agrees well with the experimental T_v with a maximum discrepancy of approximately 17%.

Some general features of long plasma columns sustained by various kinds of electromagnetic waves are described. A steady-state discharge can be maintained only by a limited category of waves as defined in the paper. Both the possibility of existence and the axial structure of the produced plasma column depend mainly on the attenuation characteristics of the wave. The expressions for the axial profiles of electron density and wave power are given. A typical illustration of application of the general results obtained is shown. It is concluded that the discharges sustained by travelling waves constitute a distinct class of microwave discharges.

The author has considered the effects of the optically generated hot carriers to explain the decrease in collection efficiency of solar cells at short wavelengths. The diffusion of these hot carriers to a contact or interface before thermalisation is the major factor for reduction of collection efficiency.

In, Zn and H have been doped into the CdS layer of sintered CdS/Cu₂S solar cells, resulting in considerable improvement in short-circuit current, open-circuit voltage, and degradation performance. The effects of vacuum annealing and sintering at reduced pressure are also reported. It appears that the impurity doping reduces the effective space charge density at the interfacial region in the grain boundaries, thereby decreasing the saturation current density and the diode exponential factor of the cells. Of all the impurities tested, hydrogen has proved to be the most beneficial.

Mossbauer spectra of phosphate glasses containing iron were measured with both gamma-ray transmission and conversion Mossbauer spectroscopy (CEMS) methods. The ionic ratio Fe²⁺/Fe³⁺ measured by CEMS depends strongly on the conditions of the glass formation and on the subsequent thermal annealing and oxidation procedure. This ratio is closely connected with the electrical conductivity. It is shown that the CEMS method is suitable for studies of electronic phenomena in subsurface layers in glass.

An attempt has been made to explain the character of the charging and discharging currents in low-density polyethylene in the time range 10-10⁴s at room temperatures in terms of dipole polarisation. The magnitude of these currents as well as their time and voltage dependence are analysed.

An assessment has been made of the usefulness and accuracy of the reflectivity technique for the non-destructive determination of carrier density and mobility in n-type InP. The technique can be used to below 10¹⁶ cm^-3, but the errors in n increase from about +or-10% for n approximately 10¹⁷ cm^-3 and above and +or-20% at 10¹⁶ cm^-3 to +or-40% at 5*10¹⁵ cm^-3. The errors in mobility are about +or-20%, with the optical mobilities slightly lower than the Hall mobilities at room temperature. Due to the importance of polar optical scattering at low temperatures in the optical measurement, the optical mobilities at 77K are up to an order of magnitude lower than the Hall mobilities for samples with low carrier density. For n>or approximately=5*10¹⁷ cm^-3 impurity scattering dominates in the optical measurement and good agreement is again obtained. Due to increasing radiation penetration depth with decreasing carrier density the following minimum layer thicknesses are required for the accuracy quoted above: 1 mu m at n approximately 10¹⁸ cm^-3, 3 mu m at 10¹⁷ cm^-3 and 10 mu m at 10¹⁶ cm^-3. Accurate results are more difficult to obtain for layers grown on conducting substrates unless the carrier density of the layer is about the same or greater than that of the substrate. The potential of the technique has been shown for use as a non-destructive assessment of a buried layer.

Thin films of ZnS with a zinc to sulphur ratio of about 1.13 were prepared by radiofrequency sputtering and were subsequently implanted with Mn ions. Luminescence was observed for Mn concentrations (C) of between 0.1 and 3 at.% after annealing at temperatures (T_A) between 300 and 500 degrees C. The intensity (I) of the total photoluminescent signal can be described empirically as I approximately C exp(E_A/kT_A)-C² exp(-E_B/kT_A) where E_A and E_B represent activation energies of 0.65 and 0.94 eV respectively. The intensity arising from the first term of this equation is ascribed to single Mn ions whereas the quenching described by the second term possibly results from the interaction between pairs of Mn ions.