Table of contents

A facility has been constructed for studying supersonic flows of hot gases. The facility used an inductively coupled RF plasma torch to increase the stagnation temperature of nitrogen to approximately 4700 K. The gas then flowed through a converging nozzle (4.9 mm diameter throat) and exhausted into a water-cooled test section as an under-expanded, supersonic jet. The high stagnation temperature resulted in the excitation of electronic states and the formation of PPM levels of ions (in particular, N₂⁺) in the jet flow. Emission from the (0,0) bandhead of the N₂⁺ first negative system (B² Sigma _u⁺-X² Sigma _g⁺) at 3914.4 AA was used to locate the boundaries of the jet. The rotationally resolved spectra of the (0,0) band were examined using both radiative emission and laser-induced fluorescence in order to measure rotational temperatures in the flow. A comparison was made between the measured flow field properties and those predicted by a method of characteristics (MOC) solution.

The linear propagation of optical pulses in monomode optical fibres at zero-dispersion wavelength is studied theoretically. From the envelope transmission equation, the root mean square (RMS) pulse width is obtained, and the minimum evolution condition, minimum pulse width and its corresponding distance are given. The case of chirped pulse is discussed in particular detail. It is shown that an arbitrary initial pulse transmitting at a zero-dispersion point has a restoration characteristic, which is entirely a result of the interplay between second-order dispersion and source chirp.

A binary mixture of spherical macromolecules in solution is analysed by a quasi-elastic light-scattering experiment for low intensity levels (less than one photoelectron per coherence time). In this situation, the Laplace transform, Q(s), of the distribution of the time interval between two consecutive photoelectrons has been measured. The results have been compared with those obtained by the measurement of the second-order correlation function g⁽²⁾( tau ), for the same experimental conditions.

Time-resolved and integrated fluorescence spectral of a capacitively coupled longitudinal KrF excimer laser were measured in the UV visible range. Similar investigations were also carried out with a transversally pumped commercial excimer laser with a standard KrF gas fill. Both lasers were found to have very different spectra. The longitudinal laser showed very strong excitation of rare gas ions. Such high ion densities are avoided in transversal discharges by keeping the discharge homogeneous. However, the longitudinal discharge is capacitively self-stabilized so that no breakdown occurs.

An expression for the heat storage coefficient (HSC) of loose multi-phase systems at interstitial gas pressures is developed in terms of the characteristic pressures. To test the validity of the derived expression, experimental measurements of the HSC of loose multi-phase systems have been carried out at both normal and a range of other interstitial gas pressures using a plane heat source. Good agreement has been found between the determined and the predicted values.

This paper presents an approximate solution technique for design and analysis of tilting-pad journal bearings considering the thermal and elastic effects on the performance of the bearing. The method is based on the numerical solution of the Reynolds equation by a finite-element technique using a one-dimensional temperature profile. The pressure, the energy and the elasticity equations are solved simultaneously at each step of iteration and the local viscosity is determined by the exponential relation given by Vogel and Cameron. The performance parameters are evaluated by conventional methods and a small perturbation technique is used to obtain the dynamic coefficients.

The geometry and residual stress fields of different indentations are studied, as well as their influence on fatigue life. Two different elastic/perfectly plastic denting processes are modelled, named 'asperity flattening' where only contact between the bump and the other body takes place and 'full Hertzian contact flattening' where the bump contact is embedded in an elastic Hertzian contact. The resulting deformed geometry (indentation) and the residual stress field is then used in a fatigue life calculation simulating the over-rolling of the indentation. The influence of bumps with different slopes is examined together with the interaction of the residual stress field and the Hertzian contact stress field from the over-rolling. The influence on life is presented as a function of contact size and contact pressure.

This paper presents results from a study of thermal and elastic effects in the tilting pad journal bearing. The analysis considers thermal and elastic distortions of the pad, thermal growth of the bearing components, and cross-film variations of lubricant viscosity. The computer model is verified against steady-state experimental data gathered from a five-shoe bearing. Calculations indicate that significant changes in bearing and pad clearances may occur as a result of pad, shaft and housing distortions. In some cases, this may lead to an operational preload which is substantially different from that called for in the initial design.

The wall-driven MHD flow of a viscous incompressible fluid in an open channel is investigated. A strong magnetic field is applied parallel to the free surface. The problem is treated by means of matched asymptotic expansions. The flow region is divided into various subregions and the leading terms of the different asymptotic expansions are obtained for M to infinity , where M is the Hartmann number. An exact analytical solution of the equations governing the free-surface layer is obtained. The thickness is of order M^-12/, but it is appreciably different from the bottom layer which has the same thickness.

Self-consistent calculations of the parameters of self-sustained MIP and DCP in argon and in model gases in the diffusion-controlled regime have been carried out. The calculated parameters of argon microwave produced plasmas (MIP) and direct current plasmas (DCP) are in satisfactory agreement with experimental data. The use of the proposed invariant group of parameters, namely specific absorbed power P_d, plasma gas pressure p, discharge tube radius R and tube wall temperature T_W, for the comparisons of different types of electrical discharges have been grounded. The results of calculations in argon using different models of discharge and the results of calculations in model gas plasmas are given.

A laser-sustained argon plasma at atmospheric pressure was investigated numerically at low convection velocities. The plasma temperature distributions and power absorption were calculated for a laser power of 2 kW and for four different f number values 1.06-8.4. The results show that the plasma shape and power absorption strongly depend on the focusing geometry. Total absorption increases with f number from 55% to 83.2% of the laser power. On the other hand, the plasma shape and power absorption are not very sensitive to the intensity distribution of the laser beam and size of the focus spot.

The positive ion current collected by cylindrical Langmuir probes has been measured in an RF argon plasma. The current-voltage characteristics were measured using an RF compensation technique whereby the probe was forced to follow the RF fluctuation in the local plasma potential. The I-V curves from probes of different radii and material show an ion current which is always greater than that predicted by the orbital motion theory and that agrees well with the radial motion theory. This is because the ions travel to the probe from a distance which is limited by the vessel geometry or by the collisional mean free path. The role of the possible collisions, ion-ion and ion-neutral, in the ion trajectories is analysed. It is suggested that the criterion for the application of the orbital motion theory should be tested whenever this theory is used for the determination of the charged particle density.

An emission spectroscopic study is reported of the temperature and the electron density distributions in a DC plasma jet at atmospheric and low pressure conditions. A standard DC plasma spraying torch is used with an Ar-H₂ mixture as the plasma gas (17% H₂ by volume) at a power level of 30 kW (current=600 A, voltage=50 V). Results were obtained for chamber pressures of 100 kPa, 52 kPa and 20 kPa. Electron density measurements were carried out by the Stark broadening of the H_beta line and from the continuum recombination of the Ar⁺ and H⁺ ions. The temperature is obtained by using a Boltzmann plot of the neutral argon lines and the absolute intensity measurements of the argon lines. The results confirm that local thermodynamic equilibrium (LTE) conditions prevail throughout most of the temperature field at pressures of 100 and 53 kPa. Important deviations from LTE conditions are noted at a chamber pressure of 20 kPa. The results at the lowest pressure condition (20 kPa) show important axial variations of the electron density which coincide with the observed diamond shock wave in the plasma jet.

Time-resolved mass spectrometry of positive and negative ion species and time-resolved Langmuir probe measurements were carried out in a pulsed hydrogen discharge. Both measurement techniques show a strong increase of the H^- density in the post-discharge. The experimental results are in good agreement with a theoretical model describing the generation of H^- in the post-discharge. In addition, results for the time-resolved temperatures of positive and negative ions were obtained.

The expression 'memory curve' is used for functions showing the dependences of breakdown time delays t_d on the afterglow period tau at various other preset experimental parameters. The time delay values are averages of series of more than 100 measurement cycles each of the electrical breakdown time delays in nitrogen and neon filled diodes at 40 mbar for various preset tau values. It was established that the slopes of curves of t_d against tau , the memory curves, do not depend on the voltage applied to the diode within the range of 15% to 25% above the static breakdown voltage, indicating that these slopes measure the time variation of metastable concentrations C within the diode, i.e. dC/d tau , in the afterglow period.

A self-consistent modelling and simulation technique of RF nonequilibrium plasmas using a Monte Carlo method is presented. Under the condition that the product of the gas pressure and the gap length is small and/or the local electric field changes rapidly, as is commonly the case with RF plasmas, the electron energy distribution shows a nonequilibrium effect against the local electric field. The kinetics of electrons and ions is calculated by a Monte Carlo method which enables the authors to deal fully with the nonequilibrium effect. The electric field in the plasma is self-consistently determined by solving Poisson's equation. With a particle model, the statistical fluctuation tends to be large in the sheath in which the number densities of electrons and ions are low. A scaling technique which enables the authors to diminish the fluctuation, and therefore the instability of the simulation is used. The simulation method is applied to an RF plasma in an He-like model gas and the results suggest that this model can adequately simulate RF plasmas.

A treatment of the positive column with negative ions as the third species of charge carrier, in addition to electrons and positive ions, is given in the three-fluid approximation in the low-pressure limit. The relation to other work is demonstrated in various limiting cases, particularly treatments of the plasma sheath in the fluid and free-fall approximations. Confinement of the negative ions to the centre of the discharge is found for large values of the ratio of electron temperature to negative ion temperature.

A numerical model of a gas-discharge plasma has been studied, where the reduced electric field strength E/N, the molecular concentrations in the excited states and the corresponding electron energy distribution function (EEDF) have been self-consistently calculated for a mixture of helium and a model molecular gas. In particular, the EEDF was calculated including superelastic collisions. The results have been obtained by means of an iterative procedure, which simultaneously solves the Boltzmann equation for the EEDF, the molecular balance equations for the population of molecular states, and the balance equation of the charged particles. These results for different discharge parameters were compared with those of a cold gas approximation and of a model that neglects superelastic collisions. The results were used to calculate the power transfer from the electric field to the electron system, and subsequently, to the molecular gas.

The influence of a magnetic field on electron transport coefficients in mercury vapour has been studied using a Monte-Carlo simulation technique. The ranges of parameters studied are 10<or=E/N<or=1000 Td and O<or=B/N<or=20*10^-19T cm³ (where E is the electric field, B the magnetic field and N the gas number density). Data on ionization coefficients, transverse and perpendicular drift velocities and mean energy are evaluated at various magnetic field strengths. The results are examined in the light of the effective reduced electric field (EREF) concept. It is found that the EREF is a good approximation for the mean energy, collision frequency and ionization coefficient if the appropriate collision frequency which is dependent on E/N and B/N (instead of a constant collision frequency) is used in EREF calculations. As a result, the application of a magnetic field perpendicular to the electric field decreases the transverse drift velocity, mean energy and ionization coefficient. The influence of the magnetic field on the energy distribution function is also studied.

The relaxation rate of N₂(a¹ Pi _g, v'=0-2) singlet metastable state is observed from the emission of a¹ Pi _g-X¹ Sigma _g⁺ bands in a nitrogen time afterglow. The quenching rates k₀=0.91+or-0.05, k₁=1.64+or-0.048 and k₂=2.12+or-0.055 (*10^-11cm³ s^-1) and the radiative lifetime tau ₀=54.2+or-6.5 mu s, tau ₁=55.9+or-6.0 mu s and t₂=54.1+or-5.8 mu s are deduced from the linear part of the dependences of the time decay against pressure.

The generation of products of plasma chemical reactions in a stable regime of DC corona discharges at thin wires is considered. Equations are obtained for reaction rates in positive and negative discharges. It is shown that the relation between the rates of a plasma chemical reaction in positive and negative cases and the character of the rate dependence upon the wire radius are determined by the relation between the reaction energy threshold and the ionization potential of gas molecules. The estimates obtained for the rates of ozone formation in corona discharges in ambient air agree with experiment.

The dynamical response in an active matrix addressed TN-LCD (twisted nematic liquid crystal display) with anisotropic conductivity is simulated. Formulae for the variation of the electrical induction D and the equations of motion are derived. The voltage across the electrodes, the midplane tilt and the optical transmission can be calculated. The model is verified by experimental measurements.

The present work has been carried out to verify experimentally the conclusions of previous theoretical studies into the effects of electromagnetic radiation on the kinetics of the homogeneous condensation of supersaturated steam. The facility included a source of steady-state radiation (CO₂ laser, 1 kW), a thermodiffusion chamber for the generation of supersaturated steam, and a system of diagnostics for measuring the dimensions of the droplets and controlling the parameters of the laser radiation. The experiment showed a stable co-existence of water droplets and supersaturated steam for certain definite values of the parameters of the thermodiffusion chamber. The droplet dimensions were found to be in good agreement with the theory.

The effect of irradiation (UV-visible light) on a nematic liquid crystal doped with a photoactive azobenzene derivative was investigated. The selective irradiation results in either an E implies Z or Z implies E isomerization of the azobenzene unit. The effect of the isomerization is to cause a reversible depression of the liquid crystal to isotropic (LC implies l) phase transition temperature of the doped mixture, which can be monitored optically as an isothermal phase transition. This depression also results in a biphasic liquid crystal+isotropic region which is discussed. The authors investigate the cause and magnitude of the phase depression as a function of the amount of doped 4-butyl-4'-methoxyazobenzene (photoactive unit) in 4-cyano-4'-n-pentylbiphenyl (liquid crystal unit), and as a function of the percentage conversion of E implies Z (caused by isomerization) in the azobenzene. The photostationary state of the doped mixtures achieved by Z implies E isomerization is considered and its effect upon the transition temperature of the mixture and response time of the system is discussed. They discuss the implications of the photostationary state with regards to the reversibility of the photo-induced phase transition and hence potential applications.

Scanning tunnelling microscope (STM) images of low-load (15-50 gf) Vickers diamond pyramid indentations in a (111) surface of a p-doped single crystal of silicon have been obtained. From these, information such as the surface profile around a residual indentation, the lengths of its diagonals, its depth, the angles between its face/pyramid edge and the undisturbed indented surface, and the volume of material within the pile-up region (i.e. above the original indented surface), has been obtained. In some cases, the volume of the piled-up material has been found to be over 80% of the residual indentation. The experimental findings have been discussed in the light of the existing theories of indentation and the process of elastic recovery.

The dielectric properties of suspensions were originally interpreted neglecting any effects due to diffusion. These were later taken into account only in those systems where there is no current flow between the two phases. This was an essential requirement, since it led to known boundary conditions. In this paper, the authors solve the general case of conducting particles suspended in a conducting medium using a new boundary condition which determined the ion flow across the interface. Their results show important differences with respect to the classical solution: while the dielectric increment is usually lower than the Maxwell-Wagner value as expected, it can exceed it in certain cases, and an additional relaxation can appear at low frequencies.

The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone was determined for dilute mixture using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.

A method is proposed for studying and distinguishing between 'external' and 'internal' processes leading to voltage decay in polymeric electrets. The technique of thermally stimulated partial recovery of voltage (TSRV) yields the difference between the remaining internal homocharge and the accumulated compensation charge after exposure to humid atmospheres. A phenomenological model yields two time-dependent functions which describe the voltage decay processes. The application of these methods to FEP-AL-FEP sandwich structures stored at 95% RH and at room temperature allows one to identify two discrete mechanisms leading to voltage decay. The first describes the deposition of compensation charge from the atmosphere which is dominant over the first ten days of exposure. The second describes homocharge decay accelerated by invasive action.

The dispersion of the refractive index of liquid nitrobenzene has been evaluated in the wavelength range 200-700 nm using a Kramers-Kronig analysis of reflectance data. This information is useful for correction of liquid nitrobenzene Raman cross section measurements for local field effects. The results are compared with directly measured refractive index values in the range 434-656 nm and with other published results.

The accuracy of the initial rise (IR) method and the variable heating rate (VHR) method when the frequency factor depends on temperature as T^a (with -2<or=a<or=2) for the case of a general order thermally stimulated luminescence (TSL) peak is discussed. It has been shown previously that for most practical cases the resulting maximum error in the determination of the activation energy E by the IR method and the VHR methods is about 10%. These methods can therefore be considered as independent from the order of kinetics even if the frequency factor is temperature dependent. A crucial point observed is that for a=2 both the IR and VHR methods overestimate E, whereas for a=-2 they underestimate this value.

The interference modulated transmission spectra T( lambda ) at normal incidence for amorphous arsenic sulphide semiconducting films deposited by thermal evaporation were obtained in the spectral region from 300 nm up to 2000 nm. The straightforward analysis proposed by Swanepoel (1983), which is based on the use of the extremes of the interference fringes, has been applied in order to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Thickness measurements made by a surface profiling stylus have also been carried out to cross check the results obtained by the method employing only T( lambda ). In addition, the optical band gap E_g^opt has been determined from the absorption coefficient values using Tauc's procedure, i.e. from the relationship alpha (h nu )=K(h nu -E_g^opt)²/^h nu , where K is a constant. Finally, it is emphasised that accurate results were achieved not only with the above mentioned glass composition As₂S₃, but also in the case of the non-stoichiometric composition As₃₀S₇₀.

The slow-wave structure of a travelling-wave tube (TWT), consisting of a helix supported by a number of dielectric rods in a glass tube envelope, is modelled and theoretically analysed for the attenuation constant, phase propagation constant and interaction impedance of the structure. The expressions for these quantities are then interpreted to obtain the expressions for Pierce's velocity, loss and space-charge parameters in terms of the structure parameters. Also, the use of these expressions is demonstrated by a small-signal gain calculation for a typical satellite communication helix TWT in use. The theoretical gain is compared with the experimental gain reported elsewhere, for the same tube.

The behaviour of zinc oxide varistors subjected to partial discharges in air is studied with respect to their protective coating (glass and epoxy resin). The decomposition of the medium with residual impurities can considerably influence the varistor current-voltage characteristics. Degradation is due to a conducting deposit around the varistors and a physical corrosion of the coating. The conducting deposit is analysed by physico-chemical methods. The authors show the influence of the partial discharge energy, humidity and surrounding gases on the varistor degradation. Moreover they point out a significant modification of the l(U) characteristic in the ohmic region, with a large increase of leakage current following degradation.

High-speed photographs, taken at a framing rate of approximately two million frames per second, of a deflagrating (subsonic burning with respect to the sound velocity in the crystal) single crystal of beta -lead azide are presented. It is shown for the first time that the reaction-generated stress waves, moving ahead of the reaction front, can cause new reaction sites and it is argued that the cause of the reaction is purely frictional heating. The importance of the frictional mechanism in relation to deflagration/detonation transitions in some explosives is also briefly discussed.

Boundary-layer interaction with free-stream flow over an inclined wall has been examined. The nonlinear boundary-layer equations are solved by following the momentum integral technique to determine the film thickness in the entrance flow region, in the fully developed flow region and in the uniform flow region.