Table of contents

An electrostatic field intensity distribution, capable of producing a specified path or trajectory of charged particles with given initial and final conditions, is determined. This path represents the geometric locus for the lines of force of the field. Electrodes capable of producing such an electric field are then designed.

This paper dealt with the experimental observation of enhanced four-wave mixing in BSO. The method used involves sinusoidal phase shift in one of the pump beams. Due to this phase shift a sum of frequencies is present in the temporal modulated intensity on the crystal. The method used provides both phase and amplitude information on the photorefractive effect. Expressions for both these parameters are obtained. A mode operation of the phase conjugator has been demonstrated.

Radiation noise power spectra were measured at frequencies from 20 Hz up to 3 kHz in high-frequency inductively coupled plasma (ICP). Aerosol sample radiation excess noise compared to that of argon radiation at frequencies of about 2 kHz and lower was observed. This excess noise is interpreted as a modulation of the radiation intensity by evaporating aerosol droplets. Further understanding and measurements of the noise spectra can be useful in both sample flow and droplet evaporation rate studies and analysis of possible ways to reduce ICP sample radiation or fluorescence detection limits.

It is shown that the blast wave from a pulsed linear arc inherently leaves flows in its wake which propagate as a cylindrical version of a conventional hyrdodynamic 'puff'. These flows are generated by the transition of the initially cylindrical shock wave to an ultimate spherical configuration. Schlieren cinematography of the expanding flows yields results which are in good agreement with a theory based on a single blast wave model of wake flow formation. The results both support a previous hypothesis of Chomiak (1979) on the subject of spark ignition and establish a mechanism which accounts for the observed increase in the rate of combustion when short duration sparks are used.

A method to detect fluctuations of charged particle density, electron temperature, electric field and plasma potential by Langmuir probes is proposed. The fluctuations are detected for ionisation wave packets excited in a helium positive column with a gas pressure of 0.4 Torr. The radical profile of the ionisation wave component is more concentrated near the centre of the tube as compared with that of the steady-state charged particle density. The wave front is slightly convex towards the cathode. The results suggest that the theory of ionisation waves needs some modifications.

The drift velocities of negative ions in gaseous xenon produced by electron attachment to sulphur hexafluoride molecules were measured as a function of xenon pressure and applied electric field strength at 295 K. A reduced mobility of 0.8+or-0.05 cm² bar V^-1 s^-1 was obtained for the negative SF₆ ions.

A Boltzmann equation, in which the generation of secondary electrons through cumulative ionisation and collisions between two metastable atoms (electron-concentration-dependent processes) is taken properly into consideration, is presented for the first time. This equation is applied to an analysis of the steady-state electron swarm parameters in Hg vapour. The ratio of the Townsend first ionisation coefficient to the electric field strength, alpha /E, for E/N values from 50 to 1412 Td is compared with experimental values. The effect of metastable Hg atoms on the swarm parameters is discussed. It is found that secondary electrons generated through collisions between two metastable Hg atoms are much larger than those generated through cumulative ionisation in a low range of electron concentrations such as is given in Townsend discharges.

The steady-state electron swarm parameters in Hg/Ar mixtures are analysed using a Boltzmann equation in which the collision terms providing generation of secondary electrons via metastable Hg and Ar atoms presented in the preceding paper (see Y. Sakai et al., ibid., vol.22, p.276, 1989) are taken into consideration. The ratio of the Townsend first ionisation coefficient to the electric field strength, alpha /SiE, calculated using the present equation for E/N values from 5 to 1412 Td in Ar with various admixtures of Hg vapour (K=ratio of Hg to total gas atom concentrations from 2*10^-4 to 2*10^-2) is in good agreement with the experimental values of Burgmans and Smeets (1983). For E/N below 100 Td and K above 6*10^-3 ionisation collision between two metastable Hg atoms is found to be the dominant process for electron multiplication. The influence of electron concentration on the swarm behaviour is discussed quantitatively.

A recently observed new type of electrohydrodynamic instability in homeotropically aligned nematic samples with high positive dielectric anisotropy and low positive conductivity anisotropy has been studied in greater detail. Some similarities between this instability and thermally induced Rayleigh-Benard instability have been found in the authors' investigations. It is pointed out that the effects of dielectric anisotropy, charge injection due to the thermionic emission process and of the diffusion current have to be taken into account to explain the observed domains of the Felici-Benard type of instability.

Theoretical expressions are derived to enable the temperature increase to be calculated at any point in a rectangular film that is bombarded by an electron beam of constant current density across its circular cross section. The beam may be incident at any point in the film provided that it does not strike the supporting grid bars which are held at constant temperature. The theory applies when the effects of thermal radiation from the film may be neglected and includes the case of low-temperature studies where the radiation input from the surroundings of the film is much greater than the radiation emitted by the film. Sample calculations are given for a copper film 20 nm thick supported on a 200 mesh copper grid. It is important to note that the calculated results give lower limits to the temperature increases because in a practical case a film is not ideally thermally anchored to the grid bars as is assumed in the theory.

The deflection of a circular plate under a non-uniform load has been investigated using eigenfunction expansion. The deflections are obtained completely analytically in the form of an infinite series. Certain examples which have some valid physical significance are examined and the deflections are obtained in terms of Bessel functions.

A study has been performed of the electrical transport properties of an Li₃VO₄:Li₃PO₄:Li₃BO₃ melt. The material is a mixed conductor and has a high electrical conductivity at room temperature ( sigma approximately 2.0*10^-2 Omega ^-1 m^-1). The dominant part in sigma is ionic. The material melts at 1135 K and is not hygroscopic. For these reasons, it qualifies to be used as electrode material in electrochemical devices using Li⁺ ion active superionic solids. The XRD pattern for the material has also been reported.

Monte Carlo simulations have been performed to study the hot-electron transport in SiO₂ subject to a strongly inhomogeneous electric field produced by a hyperboloid needle and plate assembly. The scattering mechanisms caused by both the polar and non-polar electron-phonon interactions including the Umklapp processes are considered. The spatial evolution of the electron energy distribution and the average electron energy are presented. It is shown that the injected electrons could be energetic without running away from the energy distribution near the needle tip and its importance with regard to the local degradation phenomenon prior to tree initiation in dielectrics is pointed out.

Experimental evidence is provided that common industrial organic insulators (phenol-impregnated pressboard, bakelite) may exhibit negative differential resistance. Insulators have been subjected to high non-uniform electric fields with maximum values which varied between 0.2 MV cm^-1 and 1.2 MV cm^-1 and, according to experimental data, the time-averaged I-V characteristics showed a distinct N-type NDR region, followed by an S-type NDR region, for electric fields near the pre-breakdown region. Various impulse voltages have been applied to solid dielectrics and periodic current pulses were received by the anode electrode. The aging region, at about 0.8 MV cm^-1, was associated with successive current pulse formation with typical values of the order of 2 A and frequencies of the order of 1 MHz. During the breakdown (which occurred for applied electric fields of the order of 1.2 MV cm^-1) only two or three current pulses of 20-40 A were observed. An attempt has been made to interpret and correlate the above results with similar phenomena which occur in semiconductors with a negative differential resistance.

The authors report preparation of Y-Ba-Cu-O thin films by laser evaporation with near-infrared radiation. Pulsed radiation of a Nd-YAG laser (wavelength 1.06 mu m) was used for evaporation of material from the surface of a YBa₂Cu₃O₇ ceramic sample. Thin films, deposited on Al₂O₃ single-crystal substrates, became conductive after a heat treatment in oxygen atmosphere. One of their films, with a room-temperature resistivity of 1 m Omega cm, showed onset of superconductivity at 100 K and had T_c values of 94-76 K (90%-10%) for the resistive transition. The films were characterised by RBS analysis, SEM and X-ray diffraction.

Several ferroelectric properties of triglycine sulphate single crystals both pure and with different doping substitutions in the structure have been studied in the vicinity of the critical point T_c. The parameters engaged in the statistical dipolar theory of ferroelectrics are derived, from dielectric constant and hysteresis loop measurements, allowing a distinction between atomic and dipolar polarisation. The numerical values of the parameters obtained in this way for pure and doped crystals are compared. The internal biasing field is estimated using the data of the pyroelectric measurements. The basic pyroelectric material figure of merit is also calculated and its temperature dependence is reported. The temperature dependence of the coercive field has been measured and found to obey a power law E_c=A(T_c-T)^s. The piezoelectric modulus and the electromechanical coupling coefficient have been also measured and their temperature dependence is investigated. The J-E characteristic in both the ferroelectric and the paraelectric phases is examined; variations in the behaviour according to the type of dopant are observed. The effect of polarising pure and doped TGS samples with a DC field of intensity 10² kV m^-1 on measured properties is also examined.

Changes have been measured in the four polarised components of fluorescence for various dye-tagged minerals, pigments and liquid crystals. Using short-duration pulsed electric fields, the electro-fluorescence principle is shown to have potential as the basis for an optical shutter for display devices. Measurements are reported for a range of materials including nematogen liquid crystals with added dye which is the basis of the 'guest-host' arrangement. Data on clay mineral and pigment particles are shown to offer switching contrasts which, in special cases, approach the optimum achievable. Their potential for fast, multicoloured, lambertian display elements is indicated.

The diffuse scattering of light from two interacting dipoles placed near a flat metal surface is analysed. On the basis of a screened-propagator formalism, an exact calculation of the self-consistent field on the dipole sites is presented. The exact result for the so-called Y-polarised case is compared with those obtained in the first- and second-order Born approximations. The contributions associated with direct and indirect field propagation processes are identified and the radiative and non-radiative indirect processes are studied. Finally, the surface-polariton contribution is determined.

Using a dipole model, the transmission efficiency and the energy distribution of photoelectrons emitted into vacuum by transmission-mode negative electron affinity GaAs photocathodes have been calculated. In contrast to a previous result, the calculation shows that the emitted photoelectrons mainly originate from the X₁, rather than Gamma ₁, energy valley. The shape and width of the energy distribution curves calculated coincide well with the experimental result of Phillips et al. in 1984.

Computer simulations have been performed for the close packing of thick fibres with aspect ratios between 1 and 30. Results are presented for a range of fibre orientations including 3D random, in-plane random and aligned. It is shown that a small degree of out-of-plane randomness enhances packing compared with both in-plane and 3D random orientation distributions. Thickness effects are found to be significant in determining the maximum packing fractions for aspect ratios <or approximately=20. Local ordering is also a significant feature in the close packing of fibres which are otherwise random over length scales greater than the fibre length.

Available approaches for modelling the RF plasma torch are not self-consistent in their treatment of electromagnetic fields. A completely two-dimensional approach is proposed in this Letter, including a self-consistent electromagnetic field formulation. Computational results show that although the overall features of the flow and temperature fields remain unchanged, the size and strength of the recirculation vortexes in the flow field are appreciably smaller than those predicted by the previous approach.

Reactions induced by field-generated plasma at liquid/solid interfaces are used to synthesise a metastable form of iron oxide. The resulting chemical and microstructural changes on the surface of iron are studied using conversion electron Mossbauer spectroscopy (CEMS), while information regarding the surface morphology is obtained through scanning electron microscopy (SEM).

It is demonstrated that the presence of runaway electrons in the near-cathode plasma of a vacuum arc has a pronounced effect on the plasma electrical resistivity. At high current densities (about or greater than 10¹¹ A m^-2) the voltage drop in the plasma is found to be several volts as opposed to the values in excess of 100 V based on Spitzer-Harm resistivity calculations.

For original paper see M.E.R. Shanahan, ibid., vol.21, p.981 (1988). The authors re-examine some of the basic equations relating to displacement of a half-space used in the paper by Shanahan, and recast them in a form more suitable for analysis of an axisymmetric droplet, particularly if its radius is small.

This Letter attempts to examine the impact of the chemical interaction of the alumina substrate on the Y-Ba-Cu-O film deposited on it.

Secondary emission of negative ions of gold by sputtering of alloyed targets is studied. The validity of a criterion proposed by Cuomo et al. (1977) is tested in the case of rare earth-gold alloys with various concentrations.