Table of contents

A series of measurements of nuclear stimulated desorption was performed for ¹⁰³Ru, using thin ruthenium films irradiated by thermal neutrons. The magnitude, time dependence and electric charge state of the outgoing ¹⁰³Rh flux was investigated. The utilization of monoenergetic electrons accompanying the ¹⁰³Rh decay for thin film thickness measurement is considered.

We present a new set of universally scaled equations describing radiation and electron beam evolution in gyrotron and cyclotron auto-resonance maser devices. Physical interpretation of the scaling parameters and both linear and numerical solutions to the equations are given. A Hamiltonian is given for certain limiting conditions. With further conditions the equations reduce to a form identical to those describing evolution in the Compton regime free electron laser.

A one-dimensional model including Poisson's equation to consider the space-charge for a discharge-excited ArF excimer laser has been developed. Behaviour of the field distortion by the space-charge and its effect on discharge evolution in the cathode sheath region have been studied. It was shown that the electric field near the cathode was extremely distorted due to the positive space-charge and became approximately 300 kV cm^-1 at the period of laser oscillation, though the maximum of the external field was approximately 20 kV cm^-1. This high field may suggest that a local filamentation starts from the cathode by field emission, if a microscopic protuberance is on the cathode surface. The photoelectron emission from the cathode was shown to be essential to moderate the field distortion in the cathode region and to sustain high-power-large-volume discharges. The decrease in the preionization density caused an increase in the electric field in the cathode at the final stage of the discharge, and an increase in the maximum values of the ArF* and electron number densities.

It is pointed out that the electron diffusion driven by collisions between electrons and neutral molecules cannot explain the radial profiles of electron concentrations observed in the fast-axial-flow continuous wave industrial CO₂ laser plasma. Based on the approximations of the k- epsilon turbulence model, a simplified model of the turbulent electron diffusion is developed. Predicted radial profiles of electron concentration in the laser cavity and experimentally observed profiles are shown to be in reasonable agreement if we assume that the electron density at the boundary is equal to about 0.6 of the maximum electron density.

The theory of the ion-ripple laser, which consists of a relativistic electron beam obliquely travelling through an ion ripple, has been extended to include the partial dielectric guiding effects. When the beam electron current i>or=2 kA it is found that coherent radiation of any high frequency may be guided and localized by the partial dielectric waveguide.

Q-switching of Nd:YAG, Nd:YAlO₃, Nd:KGW laser oscillators with a Cr⁴⁺:YAG as saturable absorber is reported. Transverse mode polarized light pulses with energies of 50 mJ and repetition rates 10 Hz are obtained.

A polarimetric technique developed for phase retardation measurements of birefringent crystal plates for any visible wavelength is described. The basic characteristics of the present method are demonstrated by using the Poincare sphere representation. The incident linearly polarized light beam is modulated by a rotating slightly birefringent crystal plate; a linear analyser is adjusted until the amplitude of the doubled frequency component of the output electric signal issued from the photomultiplier vanishes; the same compensator plate is used for the measurements, whatever the visible wavelength.

We present results of field propagation in tapers and X-junctions obtained with the aid of a new propagation technique. This technique uses the spectral domain of the guided and radiation modes and allows a new modal interpretation of the propagation mechanisms. Additionally, we show that this technique can be considered as a rigorous ray optic approach.

A set-up for varying the temperature (5-90 degrees C) of planar optical waveguides useful in sensing applications is described. The principle is to control the temperature of the cover medium (in this case water). The propagation constants of guided modes are measured via a grating coupler. Only that part of the waveguide in the immediate vicinity of the incoming external light beam is heated or cooled. The temperature coefficients of the thickness and refractive index of the waveguide material can be described by simple polynomial expressions.

A relation between the design parameters of an internally and externally irreversible radiative heat engine is presented to find the maximum power and the efficiency at maximum power output. It was found that the ratio of the reservoir temperatures must be less than half of the cycle-irreversibility parameter and the ratio of area of the heat exchangers must be less than 1.0 for optimum thermal efficiency and maximum power output. Increasing the cycle-irreversibility parameter and the heat-transfer area of the cold side improve thermal efficiency and maximum power output.

The effect of thermal resistance, heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot heat engine is investigated using a new cyclic model. The power output and efficiency of the heat engine are adopted as objective functions for heat engine optimization. The optimal performance of the heat engine is analysed systematically. Some significant results are obtained. For example, the maximum power output and maximum efficiency are determined. The efficiency of the heat engine at maximum power output and the power output of the heat engine at maximum efficiency are also calculated. Curves of the power output varying with the efficiency of the heat engine are obtained. These curves can indicate clearly the rational regions of efficiency and power output for an irreversible Carnot heat engine. It is pointed out that all the conclusions concerning a reversible Carnot heat engine, an endoreversible Carnot heat engine only affected by thermal resistance and an irreversible Carnot heat engine with internal irreversibility and/or heat leakage can be deduced from the results in this paper.

Sapphire dielectric resonator (SDR) transducers have been shown to achieve 10^-15 m Hz^-1/2 sensitivity for vibration frequencies above 100 Hz by using an ultrastable sapphire loaded cavity oscillator as the pump source. This paper describes an interferometric transducer configuration which avoids the need for an ultralow noise oscillator, but maintains existing sensitivity. An initial performance of the transducer with the new configuration is presented.

The paper describes various analytical procedures that account for the influence of the geometry of a rigid indenter upon the measured contact compliance of a smooth perfectly elastic half space. The analytical solutions provide a means of interrelating the reaction force, P, and the displacement, h, characteristics in terms of the contact geometry and the reduced elastic modulus E*. The general form is P=gE*hⁿ, where g and n are functions only of the indenter geometry. This relationship is incorporated into a curve-fitting procedure and used to evaluate the influence of the indenter geometry upon the computed modulus of a poly(isobutylene) rubber. The method described provides a viable means of incorporating the imperfections, associated with the geometry of an indenter, into the interpretation of contact compliance data.

Peristaltic pumping by a sinusoidal travelling wave in the walls of a two-dimensional channel filled with a viscous incompressible couple-stress fluid, is investigated theoretically. A perturbation solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio (wave amplitude:channel half width) is small. The results show that the mean axial velocity decreases with increasing couple-stress parameter eta . The phenomenon of reflux (mean flow reversal) is discussed. A reversal of velocity in the neighbourhood of the centre line occurs when the pressure gradient is greater than that of the critical reflux condition. It is found that the critical reflux pressure increases with the couple-stress parameter. Numerical results are reported for various values of the physical parameters of interest.

We present a theoretical investigation of the time-dependence of the electron energy distribution function and the populations in the 3p⁵ 4s levels of argon under the action of a harmonic electric field, assuming the electron density is constant with time. The analysis is based on the solutions to the time-dependent Boltzmann equation and the system of rate balance equations for the populations in the 3p⁵ 4s levels. It is shown that the results of this temporal analysis may be explained in terms of the characteristic relaxation frequencies for electron-neutral momentum transfer, electron energy transfer, and for the relaxation of each 3p⁵ 4s level. The assumption of time-invariance of electron density is discussed and analysed. The present theory covers a very broad range of field frequencies, from the microwave case down to frequencies of approximately=100 KHz.

A method is described that accounts for the imprisonment of resonance radiation in the calculation of the time-dependent distribution of atoms in resonance states and of the radiation escape in a gas-filled enclosure with cylindrical symmetry. Constant line profile, complete redistribution and pure spectral broadening are assumed. This method is based on the substitution of a matrix product for the radiative terms in the rate equation and the introduction of a symmetrical matrix, related in a simple way to the matrix representation of the radiation transfer probability space. Also, a vector proportional to the vector representation of the radiation escape probability space is introduced allowing the escape radiation to be written as a vector product. This vector and the symmetrical matrix depend only on the type of broadening and number N of discrete intervals considered and can be computed a priori. The concept of escape factor is generalized. The results are applied to standard cases.

The thermodynamic properties and the transport coefficients of thermal plasmas formed in SF₆-copper vapour mixtures were calculated as a function of temperature and pressure for molar concentrations of copper between 0 and 10%. The material property that is most affected by the presence of copper is the electrical conductivity for temperatures up to 10000 K. The results given in this paper enabled a data bank to be built up for modelling arcs in SF₆ seeded with copper vapour.

Absolute line intensities of NI up to NV in the VUV region have been measured in an electron cyclotron resonance discharge running in nitrogen and helium-nitrogen mixtures. Using first-order approximation formulae the densities of NI up to NV were determined. For special NII and NIII lines the influence of excitation by inner-shell ionization on density determinations is discussed.

By using the procedure of current detection from individual cathodes 5-7 mu m distant from each other and by scanning electron microscopy, the initiation of new vacuum arc cathode spots has been studied. Ion current bursts of duration 10-50 ns with an amplitude of 0.1-1 A, and inceptive craters on the initially virgin cathode, have been detected just before the spot transition from one cathode to another. The current density estimated over inceptive craters is >10¹¹ A m^-2. The power flux density of the jet from plasma onto the cathode exceeds 10¹² W m^-2 and is sufficient to heat the cathode surface up to the boiling point for a time approximately=1 ns. The mechanism of spot initiation and its motion in a transverse magnetic field is discussed.

We have developed a partial discharge measurement and analysis system using a personal computer, which allows one to obtain reproduced partial discharge pulse data with the phase information in an applied alternating current voltage and the number of cycles. For the CIGRE method II electrode system using 0.1 mm thick polyethylene film, temporal changes of partial discharge characteristics were measured up to breakdown of the sample. The average inception phase theta _inc was proposed as a new statistical partial discharge parameter, which was obtained by making use of the capability of the time-sequential partial discharge data acquisition of our system; theta _inc is defined as the average of theta _inc of the number of cycles in a measurement; theta _inc is a phase at which the first partial discharge pulse occurs in the half cycle after the polarity reversal of the previous partial discharge pulses. The experimental results revealed that the partial discharge pulse occurrence phase distribution ( phi -q-n distribution) exhibited a good correlation with ageing time. It was suggested that theta _inc is a candidate signal for diagnosis of insulation performance of the system from the initial to middle degradation stage. We also discuss the physics of the temporal change of the phi -q-n distribution and theta _inc as the ageing process proceeded.

A device for rapid visualization of electrical and spatial inhomogeneities of a semi-insulating GaAs (p>or=10⁶ Omega cm) is described. This visualizer is a modification of the ionization type photographic system in which a semiconducting plate is placed between transparent plane parallel electrodes in the gas discharge cell. The gas discharge gaps are formed between free surfaces of the semiconductor and electrodes. When a voltage is applied to the electrodes a discharge luminescence glows in the gap under uniform infrared illumination of the semiconductor. The uniformity of glowing over the semiconductor area is determined by electrical homogeneity and infrared absorptivity of the material. The main discharge glow patterns on both sides and after chemical etching are similar, which reflects the fact that the structural defects are continuous within the plate. The observed patterns give information about EL2 centres in the GaAs semiconductor. Technical data of the ionization-type visualizer of electrical inhomogeneities in a semiconducting plate are given.

First we define an optimum discharge corresponding to a minimum energy consumption (optimum discharge), which may not necessarily correspond to the shortest discharge path. The definition results from charge and voltage measurement in a 2.2 m point-to-plane air gap energized by standard and oscillating impulse shapes. The second step is the creation of a macroscopic model and fitting it, to compare actual discharges with the optimum one. The variation of observable discharge parameters such as axial length of the leader channel, velocity of the leader tip, apparent injected charge, time-to-breakdown and applied voltage value just before breakdown are readily simulated using this model, whatever the waveshape. The third step is to validate the model using previous experimental results on several gap spacings: 5, 10 and 17 m (standard impulse shapes) and 2.2 m (oscillating impulse shapes). Two main phases are shown to exist in both experiment and model: an unstable one resulting from the first corona event and, in some cases, a quasi-steady one occurring before the final jump (breakdown cases). For a breakdown case, the U₅₀ value can be deduced from a U₀ value, the withstand level, given by this model. Finally, the well-known U curves for switching impulses are easily reproduced using our modelling work.

The physics of corona charging phenomena is of paramount importance for the development of such electrotechnologies as precipitation of dust, spraying of powders and selective sorting of particulate mixtures. This study focused on the use of corona discharge in electroseparation processes. Crude theoretical evaluations pointed out that the required corona current density and high-voltage level in this application depend on various factors, such as material characteristics, feed rate and configuration of the electrode system. Experiments carried out on a laboratory roll-type electroseparator demonstrated the capability of a new corona electrode design to generate an extended and quasi-uniform corona field. Stable corona discharges were obtained when energizing that electrode at both positive and negative polarities from a reversible non-filtered full-bridge high-voltage rectifier. The voltage-current characteristics of the corona discharge from the new electrode were determined under various operating conditions: (i) without material in the inter-electrode gap; (ii) with a monolayer of a 50% aluminium-50% polyvinyl chloride particulate mixture on the surface of the grounded electrode; (iii) with a similar monolayer of metallic particles (99% aluminium); and (iv) with a layer of insulating particles (99% polyvinyl chloride). In each case, attention was paid to the upper acceptable limit of operating voltage, as well as to some side effects of corona discharges, such as audible noise and ozone generation. The efficacy of corona charging was assessed by electroseparation tests involving two groups of particulate materials: (i) barley grains, impurified with weeds and soil particulates; and (ii) granular mixtures of metals and plastics, yielded by chopping electric wire and cable scrap. Several practical considerations were formulated, based on a critical evaluation of the experimental results.

The main purpose of this paper is to present a physical model of the positive discharge in long air gaps. A large number of previous experimental and theoretical studies led to the identification of the different successive phases of the spark development: formation and propagation of first corona streamers, inception of the conductive stem at the electrode tip, formation and development of second corona (or 'leader corona') from the stem, and, eventually, the propagation of the leader and leader corona system until the final jump preceding the arc onset. Details of the specific modelling of each phase is presented, using the classical equations for conservation of mass, momentum and energy for each particle species. These basic equations are simplified according to the dominant electrostatic, hydrodynamic or thermodynamic processes involved in each step of the spark development. The resulting models for simulation of the corona and leader phases are coupled with an analytical calculation of the electric field due to the electrodes, the leader channel and the space charge injected into the gap. The different phase simulation models are expressed with a homogeneous simplification level and then linked sequentially into a complete model, which performs the step-by-step simulation of all the successive discharges phases until the final jump. The model described here is self-consistent since the only input data are the electrode geometry and the applied potential wave-shape. A good agreement between computed and experimental results has been obtained in various test configurations; the model has been also used to simulate the discharge behaviour with perturbations of the applied potential wave and permits the analysis of the conditions for stable propagation of the positive leader. It is shown that some parameters of practical interest, as the 50% breakdown voltage or the time to breakdown can be derived from the proposed model.

Thermal quenching of thermally stimulated conductivity has been considered theoretically assuming a model with three types of states in the bandgap of a semiconductor. It has been shown that the contribution of minority charge carriers to thermally stimulated conductivity might distort the shape of a peak or even change the number of peaks observed. Our model involves traps for majority and minority charge carriers as well as recombination centres. A set of equations is solved in a quasi-stationary approximation. For weak re-trapping of electrons and holes, an analytical solution has been obtained. Other cases have been analysed numerically. Since the minority charge carrier density may be of the same order of magnitude as the majority charge carrier density, which is observed experimentally as the inversion of polarity in the Hall effect or thermo-electromotive force, the bipolar conductivity should also be revealed in the thermally stimulated conductivity phenomenon, and this paper confirms it. The experimental thermally stimulated conductivity curves observed in single crystals of GaAs have been interpreted using the proposed model. The estimation of trap parameters taking into account the contribution of minority charge carriers has been discussed.

A copolymer of vinylidene fluoride and trifluoroethylene is solution cast onto a p-type silicon wafer to produce an enhancement field-effect transistor structure. Inversion is induced at the silicon surface when the polymer gate is covered with aluminium and suitably biased. The thermal response of the structure is investigated for two different types of perturbations: a linear temperature ramp, and a pressure-step induced temperature pulse causing a corresponding pulse in the drain to source current. The current response has its origin in three distinct but interrelated temperature dependent effects: the change in inversion layer carrier mobility, the intrinsic reorganization of charge in the semiconductor, and the transfer of electrons to or from surface states at the interfaces. A model which takes all three effects into account is presented. The energies, densities and response times of the interface trapping states are deduced from the model, and excellent agreement between theory and results is obtained for different levels of inversion.

The optical constants of vacuum deposited Ge₂₀Se₈₀ thin films of different thicknesses (74-500 nm) were studied in the wavelength range 400-2000 nm. It was found that both the refractive index (n) and the absorption index (k) are independent of the film thickness. Analysis of the experimental data of n revealed the existence of normal dispersion and fits the Cauchy and Sellmeier dispersion formulae. The allowed optical transition was found to be a non-direct transition with an optical gap of E_g^opt=1.78 eV. The width of the band tail E_e was also determined and found to be 0.15 eV. The surface roughness of Ge₂₀Se₈₀ thin films has been found to depend linearly on the film thickness.

For generation of Cu and Pd ions in liquid metal ion sources Cu-Ga, Cu-Ge, Pd-Ge, Pd-Si and Pd-Sn alloys have been tested as source feed materials. The range of coexistence of solid and liquid phases and the eutectic temperature of the investigated alloys were determined by differential thermal analysis. A stable operation of liquid metal ion sources could be obtained with Cu_63.5Ge_36.5 (at.%) and Pd₃₆Ge₆₄ (at.%) alloys. The recorded mass spectrum of a Cu_63.5Ge_36.5 liquid metal ion source has shown a high current of Cu⁺ ions. The high current of Pd⁺ ions in the mass spectrum of the Pd₃₆Ge₆₄ liquid metal ion source shows that this alloy is a suitable source material for Pd ion generation. An investigation of the ion flux ratio, which depends on the total source current, has revealed a maximum intensity of doubly charged ions in the low-current region. The fraction of doubly charged Cu and Pd ions is less than 1%.

Measurements of the space charge density across the width of a plane parallel sample of degassed crosslinked polyethene (XLPE) have been made recently. Repeated at intervals throughout a period of applied high voltage, these measurements provide data on the dynamics of charge injection and space charge development in the sample under the influence of a stepped high DC voltage. In order to analyse these data, a simple model for bipolar charge injection, subsequent transport and trapping has been developed. This model is reported in this paper, and numerical simulations for charge density generated, as a function of position, time and field, are compared to the experimentally obtained profiles.

This paper describes finite element (FE) elastic and elastic/plastic analysis of spherical indentation process of polymers. Our efforts are targeted towards polymers used in dental restorative materials which behave in a brittle manner. A key component of the wear modelling of such materials is an understanding of the stresses encountered by restorative materials during service, when two-body or three-body interactions cause failure on the surface of dental restorations. The primary objective of this paper is to study the distribution of the stresses and the corresponding strain behaviour around the contact area in order to edify crack phenomena. The large-deformation analysis is repeated for various indentor penetration depths. The commercial FE program initially selected for the analyses proved to be incapable of handling the complex large displacement elasto-plastic problem and eventually a second program was implemented to accomplish the tasks. It was shown how, at a certain load, the tensile stresses are sufficient to form a ring crack in the sample surface around the indenter. The same analysis was then used to show the formation of other median cracks in the sample. The results were closely matched and verified with our experimental investigations. This comparison of theoretical and experimental investigations resulted in further study of the unloading process of the micro-indentation. It showed that upon unloading, the resulting residual stresses produced in the material are large enough to cause the Hertzian-like ring cracks.

Intense microwave beams are proposed to be used for cleaning atmospheric chlorofluorocarbon contamination which is destroying the ozone layer of the Earth. It is shown that it may be possible to excite microwave discharges freely localized in the troposphere. The relation between the quantity of the destroyed chlorofluorocarbons and discharge parameters is established, the energy required for destruction is evaluated and possible unfavourable consequences of the accompanying effects (such as nitrogen oxides production) are analysed. The mechanism of dissociative electron attachment which is manifested in a cold decaying plasma of a pulsed microwave discharge is considered to be a principle mechanism causing dissociation of chlorofluorocarbons (CF₂Cl₂, CFCl₃, etc.). The results are presented of a model laboratory experiment in which, under conditions close to those of free space, a study is made of the efficiency of chlorofluorocarbon dissociation under the action of the discharge produced in air by intense microwave radiation. The experimental results do not contradict the conclusions of the analysis of elementary processes causing the destruction of the chlorofluorocarbon component.

Multi-filamentary superconducting wires of Cu₇₀Nb₃₀ and Cu₇₀Nb₂₉Ga₁ have been fabricated by an in situ technique. Doping of Cu₇₀Nb₃₀ with Ga results in a small decrease in the transition temperature T_c. The critical current density J_c, however, increases appreciably. There is also a small increase in the upper critical field H_c2 The pinning force F_p also increases on doping. The maximum (peak) value of F_p is 1.79*10⁴ N cm^-2 for an undoped wire of diameter 0.20 mm and 3.18*10⁴ N cm^-2 for a doped wire of diameter 0.26 mm.

Viscoelastic boundary layer flow over a stretching sheet with power-law surface temperature including frictional heating and internal heat generation or absorption is studied. The non-similar boundary layer equations are solved to obtain the important physical quantities such as the skin friction coefficient and heat transfer coefficient. It is found that the magnitude of the surface velocity gradient increases and the surface temperature gradient decreases with the non-Newtonian parameter for the case in which the difference between the source temperature and that of the ambient fluid remains constant.

Correlations are demonstrated between the production of N, H and NH active species in an Ar-N₂-H₂ microwave flowing post-discharge and the thickness of epsilon and gamma ' layers on a pure iron substrate. The Fe_2-3N, epsilon -layer thickness increases with N atom density when oxide layers are simultaneously removed by H atoms. A maximum has been found in the post-discharge reactivity when the H₂/N₂ density ratio is in the 10^-3-10^-2 range.

Porosity superlattices have been investigated by transmission electron microscopy, photoluminescence and reflectance spectroscopy. The superlattices were formed on p-type doped Si using two different techniques. Firstly, for homogeneously doped substrates we have periodically varied the formation current density and thereby the porosity. Secondly, the current density was kept constant while etching was performed on periodically doped Si layers. For the first type of superlattices the layer thicknesses were determined by transmission electron microscopy. The results are in good agreement with the values calculated from the etching rate and time. For both types of superlattices, reflectance and photoluminescence spectra show strong modulation due to the periodicity of the superlattice.

The radiative recombination probability P of a carrier released from an active TL trap is computed for the case when the TL traps are interactive with the deep traps. It is shown that the value of P remains constant throughout the TL readout heating when the capture coefficients of the recombination centre and the deep trap are equal. When these coefficients are not equal, P undergoes change but its variation with temperature is still insignificant under a wide variety of conditions. A net value P applicable to the area of the glow curve is calculated and compared with the initial (when heating is begun) value of P, which is used in the analytical expression for the area of the glow curve.