Table of contents

The effect of helium gas pressure on the formation of nanotubes in arc-discharge cathodic deposits was investigated by transmission electron microscopy, thermal gravimetric analysis and differential thermal analysis. Compared with the same thermal analysis of and graphite, the results show that the ratio of the nanotubes to nanoparticles in deposits increases with increasing helium gas pressure ranging from 80 to 700 Torr. These results can be regarded as an approach for controlling the ratio of the nanotubes to nanoparticles by controlling helium atmospheric conditions.

We attempt a comprehensive review of all published research in nondestructive evaluation (NDE) performed with the superconducting quantum interference device (SQUID) magnetometer since the first work was reported in the mid-1980s. The SQUID is the most sensitive detector of magnetic flux known. The energy sensitivity of the SQUID may make it the most sensitive detector of any kind. The research on SQUIDs for NDE is based on the promise of that sensitivity and on the various other desirable properties developed for SQUID instrumentation in biomagnetism and other fields. The sensitivity of SQUID instruments down to very low frequencies allows them to function as eddy-current sensors with unparalleled depth resolution, and to image the static magnetization of paramagnetic materials and the flow of near-dc corrosion currents. The wide dynamic range of the SQUID makes it possible to image defects in steel structures and to measure the magnetomechanical behaviour of ferromagnetic materials with high sensitivity. In the last decade SQUID instrumentation designed specifically for NDE has appeared and improved the spatial resolution of most work to roughly 1 mm, with promise of another order of magnitude improvement within the next five years. Algorithms for flaw detection and image deconvolution have begun to flourish. With many talented, industrious people in the field, the future of SQUID NDE looks bright, provided the crucial first niche can be found.

Light-induced metastable defect creation has been studied in amorphous silicon germanium alloy (a-SiGe:H) materials prepared by using helium or hydrogen dilution in plasma enhanced chemical vapour deposition. From the study of comparison of light-induced degradation in electronic properties and defect density of helium-diluted alloy films with those of hydrogen-diluted a-SiGe:H, it has been revealed that not only the optical gap but also the microstructure of alloy films is responsible for light-induced degradation. Since helium-diluted alloy materials have a compact network and improved microstructure, they are more stable than hydrogen-diluted a-SiGe:H with the same optical gap. The temperature dependence of the mobility - lifetime product in the annealed state and the light-soaked state also shows that the creation of light-induced recombination centres in helium-diluted a-SiGe:H is lower than that in hydrogen-diluted alloy films.

Ion implantation is known to be capable of modifying the surface and near-surface chemical and mechanical properties of solids pertaining to hardness, elastic modulus and fracture toughness. In this study polycrystalline alumina was implanted with and ions (110 keV) to a dose of at room temperature. Mechanical properties such as hardness and Young's modulus were determined using an ultra-low load microindentation hardness tester. With the Vickers indentation method, using different loads, the fracture toughness of the implanted layer was determined. The nature of the chemical phases were characterized by x-ray photoelectron spectroscopy (XPS). Implantation caused an increase in the hardness and the fracture toughness with no detectable effect on the Young's modulus. These modifications were attributed to microstructural changes caused by the implantation. The residual stresses were determined by a previously described indentation technique. They were found to be compressive in nature and ranged from 800 to 1800 MPa.

Wave transmission through periodic and periodic layered structures is studied and the `average transmissivity' for an incident beam with a bounded uniform spectrum is defined. Both positive and negative -function and rectangular potentials are analysed. The phenomenon of the `resonant transmission', where the wave number is in a permitted band of the central layer and in a forbidden band of the side layers of a three-layer system, is also treated. Consequences of the results, applied to the construction of band pass filters, are discussed.

The electrical response of polymer-coated acoustic wave sensors depends on changes in the surface mass loading and changes in viscoelastic properties of the coating material. In this paper we consider the acoustic behaviour and the electrical response of a thickness-shear mode resonator on changes in shear parameters of the coating material at its fundamental frequency as well as its third and fifth harmonics. The changes in material properties were induced by temperature changes. Both a glassy and a rubbery polymer were investigated. The complex shear parameter and dynamic glass transition temperature were calculated from impedance measurements.

A thermoelectric generator with zero internal resistance, vanishing heat leakage and negligible production of Thomson heat is considered. It is shown that such a generator behaves as an ideal Carnot engine or an endoreversible Carnot engine depending upon whether the heat transfer mechanism at the junctions is reversible or a finite rate. Furthermore, the optimized power of the generator is found to be greater than that of the endoreversible Carnot engine.

The parameters of a beam of gadolinium atoms produced with focused 11 kV electrons were measured and their values compared with those obtained by Monte Carlo simulations. The net mass flow rate, the velocity and its standard deviation, the angular distribution and the population density of the ground and first four metastable states were measured by weight-loss, time-of-flight, deposition and laser resonance absorption methods.

An atomic beam velocity of with a standard deviation of were obtained for a net flow rate of . The measured angular distributions are fitted by an equation of the form , where a and n are the distribution parameters and the angle with the vertical line. The atomic excitation temperature derived from the state distributions decreases with the flow rate to about 850 K for the highest flow rate.

The simulations computed with the test-particle Monte Carlo (PTMC) code, including an electronic energy relaxation model, are in good agreement with the experimental values.

The centroid drift velocity and the mean electron velocity of electron swarms in gases have different values even under the same electric field when electron-impact ionization and/or electron attachment processes are present. A new evaluation technique for is proposed based on moment equations, in which the quantitative difference between and is described as a function defined in velocity space. values are derived from calculations using a propagator method performed in velocity space without the electron distribution in real space. The effects of ionization and attachment on are quantitatively analysed for and , and the mechanism producing the difference between and is illustrated.

A potential structure is formed by applying external voltage to a non-uniform Ne collision-dominated plasma sustained by the diffusion from two independent glow discharges. The potential is evolved against the diffusion of free electrons, eventually resulting in a double hump in EEDF in the high-potential region. The axial density profile due to the potential structure is predicted using the hydrodynamic equations by assuming kinetic acceleration of electrons by the electric field and their trapping by the high potential.

Experimental and numerical studies on the behaviour of space charge layers (SPLs) and related sheath-like phenomena generated in a double plasma machine (DPM) are reported. A detailed evaluation of the performance of the multidipole source used in this device indicated that, under the conditions best suited for the investigation of these structures, the emitted electron species used to form the sheath structures could contain significant quantities of electrons with a temperature approximately twice that normally assumed for such plasma sources. It is also suggested that a trapped ion population on the low-potential side of the layer region could cause inflection-like distortions as observed in the sheath potential profiles reported here and in the literature. This hypothesis was investigated using a simple one-dimensional Vlasov - Poisson kinetic model and it was found that such anomalies could also be generated with the trapped ion population absent if a high-temperature electron population was present in the plasma on the high-potential side of the layers.

The space charge effect on residual energy of electrons in optical-field-ionized plasmas is studied in detail by a cloud-in-cell simulation. It is found that a moderate space charge field can restrain ponderomotive heating and cause a transfer of a part of the kinetic energy of electrons into potential energy so that the residual energy of electrons can be reduced effectively. The effects of inverse Bremsstrahlung heating, stimulated Raman scattering and radiation on electron temperature are also briefly discussed. Comparison is made between our results and experimental data.

The electrical resistivity of a post-arc channel after current zero was measured along the nozzle axis in a flat-type gas-blast quenching chamber. In the chamber, iron electrodes were intentionally adopted, since Fe spectral lines at wavelengths of 426 and 443 nm have much higher radiation intensities than those of , F or Cu at temperatures below 5000 K. Observation of the two Fe spectral lines permitted determination of temperature T and iron vapour concentration in the post-arc channel up to s after current zero. On the other hand, of gas contaminated with iron vapour was theoretically calculated on the basis of the simplified first Chapman - Enskog approximation. Use of this calculation result made it possible to estimate of the post-arc channel from the measured T and . The estimation result revealed that increased more dramatically at the nozzle throat than at other axial locations, reaching at after current zero. Furthermore, on the basis of the axial distribution of , the concept of `thermal plasma contacts' was developed to interpret behaviour of the post-arc channel.

The measured optical properties of the Orsay polarized electron source, based on the Penning ionization reaction are presented. The upper limit on the beam energy spread is 0.25 eV, corresponding to our experimental resolution. The highest normalized emittance obtained at low current is . The behaviour of these beam characteristics as a function of different relevant parameters is discussed.

The influence of non-locality and anisotropy of the electron distribution function (EDF), as well as of the non-equilibrium ion diffusion, on the behaviour of the discharge in a strongly electronegative gas has been studied using as an example a DC glow discharge at low pressure. In order to take into account the spatial non-uniformity of the EDF, we used the spatially dependent mean electron energy (MEE) method and the particle-in-cell Monte Carlo (PICMC) technique. The results of calculations were compared with the experimental values of the reduced electric field for the DC glow discharge. It has been shown that, for the case of low pressures (high reduced electric fields), the PICMC technique describes the discharge the most adequately. It has also been shown that the EDF is strongly anisotropic at low pressure, in which case the ionization process is supported by electrons moving in only one direction. The non-equilibrium ion diffusion (due to the ion-heating in the axial electric field) has been shown to bring about a significant modification of charged particle radial profiles. As a result, the region of quasi-neutral electron - ion plasma near the tube wall does not exist throughout the range of pressures studied (0.13 - 2.6 Torr).

The in situ corona is a new technology for destroying a variety of hazardous organic contaminants in soils. Laboratory experiments have revealed the basic physical processes involved in the initiation and operation of treatment. This paper also presents a theoretical model for the in situ corona that agrees with laboratory results. In the in situ corona, resistive dry bands are formed and translated through the entire volume of soil to be treated. Within the dry bands, an electrical discharge similar in nature to an ordinary gas-phase corona is maintained, destroying organic compounds. Now that we have established a fundamental understanding of the phenomenon in the laboratory, the process may next be scaled up to large treatment volumes in the field.

The results of a two-dimensional simulation of a cylindrically symmetric positive streamer in atmospheric pressure air between parallel plate electrodes are reported. A hydrodynamic diffusion - drift model was used. The results show that the streamer radius and velocity grow exponentially in time. We have found that the main parameter which governs streamer propagation is the width of the space charge front . It is shown that: (i) the field at the tip of the streamer is equivalent to the field of a charged ball of radius ; and (ii) the streamer velocity is proportional to , as previously predicted by Loeb [1]. The mechanism of streamer propagation is discussed. It is shown that positive streamer advancement occurs due to avalanche multiplication of primary photoelectrons in the narrow layer of the width ahead of the streamer.

The energy delivered by the power supply is calculated. This energy accumulates as electrostatic energy of the space charge envelope around streamer channel. The energy increases exponentially in time and reaches when the streamer radius is about 20 cm.

The crystal structure of four waxes has been investigated by electron crystallography. Two of these waxes, including a refined petroleum product (Gulfwax) and a material from lignite (montan wax), form well ordered crystals and their structure could be solved quantitatively from the observed diffraction patterns. As also found previously for simpler binary n-paraffin solid solutions, the average structure resembles that of a pure paraffin (e.g. n-) but with a Gaussian distribution of atomic occupancies near the chain ends to account for the statistical distribution of chain lengths within a lamella. Two other waxes from living organisms, South African bee honeycomb and the leaves of the Brazilian carnauba palm, are much less ordered, even though they share the same methylene subcell packing of the most crystalline parts of the previous materials. It appears that these waxes cannot fully separate into distinct lamellae, perhaps due to the presence of very long `tie' molecules, and are therefore `frustrated' crystal structures.

The measurement of thermally stimulated depolarization currents (TSDCs), especially in the modification known as the thermal slicing (TS) or fractional polarization (FP) technique, is a useful experimental technique for examining the dielectric properties of a variety of systems, including glasses and polymers. It is generally assumed that the TS technique detects, for each polarizing temperature , only a narrow range of states, and that analysis of the TSDC reveals the activation energy and pre-exponential factor of their relaxation time. This interpretation is shown to be very dubious in many cases, and especially for glasses near the glass transition temperature when the states in the system are expected to change with time and temperature. This paper addresses the question of what information about a system can reliably be deduced from TS experiments.

While CaS:Pb is already well known as an efficient UV/blue emitting photoluminescent phosphor, only preliminary results on its thin film electroluminescence are available. Thin film electroluminescent devices with a CaS:Pb active layer were deposited by electron beam evaporation. It was found that both the activator concentration and the substrate temperature during deposition strongly influence the optical characteristics. X-ray photoelectron spectroscopy was used to determine the composition of the layers, and the spectral characteristics were compared with results from photoluminescence.

A model of two-dimensional grain growth based on growth and shrinkage of two sub-populations of grains is presented. The model allows a natural description of self-similar normal grain growth. Results from numerical solution of the time-dependent model and the time-independent self-similar reduction are given.

With the Gibbs free energy minimization method, we determine the mole fraction of graphite in plasmas formed in the insulator vapours of PMMA, PA6-6, PETP, POM and PE at LTE. By an approximate method, we compare theoretically the proportion of graphite during the quenching of the electric discharge occurring in circuit breakers. In the temperature range 1000 - 5000 K, the composition and thermodynamic properties (specific enthalpy, specific heat capacity and density) of the plasma phase are given. The results are discussed and compared with those obtained without taking the graphite into account.

Figures 5 and 6 and their captions in the above paper were interchanged. The correct text and numbering are shown below.

Figure 5. A comparison between the KrF^* densities using the single-state and two-state models for the upper laser level.

The plots in figures 4 show the temporal evolution of 16 selected discharge species whose densities were at least three orders of magnitude higher than the rest. It was computed that, during the quasi-steady phase, the respective densities for excited-state manifolds of Kr^* and Kr^** decreased by more than an order of magnitude while that of the vibrationally excited KrF^** species remained fairly steady.

Figure 6. Comparisons between the computed (full line) and measured (dotted) discharge waveforms. V, voltage; I, current; and V_d, the computed laser-channel voltage.

The Kr₂^* species was found to contribute to the photon-absorbing species Kr₂F^*. The computed results showed that ECQ of the KrF^*, KrF^** and Kr₂F^* species contributed to the rising atomic density of F. On the other hand, ECQ reduced the He^* metastable species density. The density of He^*₂ was increased mainly the electron - ion recombination excitation, e^-+He₂⁺.

The rates of formation of excited KrF molecules were compared for two separate cases of (i) one-state and (ii) two-state upper laser levels shown in figure 5.