Table of contents

The saturation magnetostriction constant, λ_s, of as-prepared and current annealed glass-covered Co₅₇Fe_6.1Ni₁₀B_15.9Si₁₁, Co_67.5Fe₄Ni_1.5B₁₄Si₁₂Mo₁, Co_69.1Fe_5.2Ni₁B_14.8Si_9.9 and Co_69.5Fe_3.9Ni₁B_12.8Si_10.8Mo₂ amorphous microwires has been measured by the small angle magnetization rotation method. As-prepared samples exhibit negative λ_s ranging between -0.9×10^-6 and -0.3×10^-6. Current annealing results in a significant change of λ_s, that is, a general tendency to increase towards zero.

Modification of the classical multipin to plate plasmachemical reactor for pollutant decomposition is proposed in this paper. In this modified reactor a mixture of air and pollutant flows through the needles, contrary to the classical reactor where a mixture of air and pollutant flows around the pins or through the channel plus through the hollow needles.

We give the results of comparison of toluene decomposition efficiency for (a) a reactor with the main stream of a mixture through the channel around the needles and a small flow rate through the needles and (b) a modified reactor. It was found that for similar flow rates and similar energy deposition, the decomposition efficiency of toluene was increased more than six times in the modified reactor.

This new modified reactor was also experimentally tested for the decomposition of volatile hydrocarbons from gasoline distillation range. An average efficiency of VOC decomposition of about 25% was reached. However, significant differences in the decomposition of various hydrocarbon types were observed. The best results were obtained for the decomposition of olefins (reaching 90%) and methyl-tert-butyl ether (about 50%). Moreover, the number of carbon atoms in the molecule affects the quality of VOC decomposition.

A Raman luminescence microscope has been used to determine the residual stresses around Vickers diamond indentations in a relatively large, well-polished, R-cut (102) ruby single crystal. The principle of the method is based on the fact that the frequencies of the luminescence R lines of the ruby shift in a systematic manner with applied stress. It is shown that the hydrostatic component of the residual stress around a 25 N Vickers indentation can be as high as about 2 GPa, and that its magnitude decreases as A/r³, where r is the distance from the centre of indentation and A is a constant. These measurements are shown to be in qualitative agreement with the predictions of the current analytical models, although the magnitudes of the measured residual stresses are an order of magnitude smaller than those predicted by theory. Possible reasons for these differences are discussed.

This paper follows previous demonstrations of demagnification by bias in ultra-high resolution proximity x-ray lithography. The demagnification, ×1-×6, is achieved without lenses or mirrors. Two-dimensional proximity corrections, applied to rectangular mask shapes, are simulated. A V-shaped inrigger, cut into the mask, is particularly effective. When a typical range of broadband illumination wavelengths is used, several beneficial effects are observed when the gap is held at the `critical condition'. Maintaining fine resolution, oscillations - due to Fresnel diffraction parallel to the longer dimension of a rectangle - are virtually eliminated, and the image intensity is made uniform by the elimination of bright spots near the ends of a rectangle.

The pattern dependence of alternating wide and narrow stripe structures was demonstrated in the investigation of electromigration mechanisms. Magnesium accumulated in the portion of the stripe near the cathode and gradually decreased toward the anode. A fatal large void appeared at the current change point near the cathode.

The derivation of general modified Reynolds equations for porous squeeze-film curved surfaces is of interest. On the basis of the Brinkman model (BM), considering the continuity of velocities, viscous shear stresses and pressures at the porous medium/fluid interface, two coupled Reynolds equations governing the porous squeeze-film pressure are derived. These general coupled equations can be applied to predict the porous squeeze-film characteristics. An example of one-dimensional porous parallel plates is illustrated to guide the application of these equations. To show the effects of viscous shear stresses of the BM, the results are compared to the slip-flow model (SFM) and the Darcy model (DM). On the whole, the BM predicts quite different squeeze-film characteristics to those derived by the SFM and DM.

We have successfully fabricated ordered, well-crystallized Bi₂S₃ nanowire arrays embedded in the nanochannels of porous anodic aluminium oxide templates by direct current electrodeposition from a dimethylsulfoxide solution containing BiCl₃ and elemental sulfur. X-ray diffraction and selected area electron diffraction investigations demonstrate that the Bi₂S₃ nanowires have an orthorhombic uniform structure. Electromicroscopy results show that the nanowires are quite ordered with diameters of about 40 nm and lengths up to 5 µm. X-ray energy dispersion analysis indicates that the atomic composition of Bi and S is very close to a 2 : 3 stoichiometry. The optical properties of these nanowires were characterized by optical absorption techniques. These studies reveal that the annealed Bi₂S₃ nanowires have an optical band edge (direct) of about 1.56 eV.

Experiments show anomalous energy distributions in electron beams of low energy ({<}50 eV) with a short drift length of about 2 cm. These anomalous distributions are not due to the well known Boersch effect, but appear to be caused by electron interaction with space charge oscillations very close to the thermionically emitting surface. The dependence of the energy distribution on beam current and voltage is examined, and the connection of the space charge oscillations with previously reported anomalies in thermionic electron emission is discussed.

This paper presents a numerical analysis on the electrical breakdown of neon over a pressure range 100-3000 Torr irradiated with 248 nm laser radiation of pulse length 18 ns operated at threshold irradiance varying between {4×10¹¹} and 2×10¹³ W cm^-2. The investigations are based on a previously developed electron cascade model which solves numerically the time dependent Boltzmann equation simultaneously with a set of rate equations describing the rate of change of the excited states population. The result of computations showed a good agreement between the calculated threshold irradiance and the measured ones over the whole range of gas pressure examined experimentally. A study of the effect of loss processes on the breakdown threshold revealed that diffusion losses are pronounced over pressures <1000 Torr. No evidence for recombination losses is observed at pressures up to 3000 Torr. Analysis of the calculated electron energy distribution function and its parameters reflected the importance of photoionization of the excited states as a physical mechanism responsible for the breakdown of neon under the experimental condition used in this work.

The behaviour of a boundary layer containing fast isotropic primary electrons has been investigated using a modified Tonks-Langmuir model for the one-dimensional collisionless plasma, both using the full space-charge description and the quasi-neutral approximation. The plasma solutions are compared directly to those obtained from a fluid model of the same system developed by Schott in 1987 (Phys. Fluids30 1795). In the kinetic ion model a single double-layer structure is observed to form for all primary electron densities, with a two-stage rise in the boundary potential approaching the wall. This single double-layer exists at a point corresponding to the initiation of oscillatory solutions (periodic double layers) in the potential, particle concentrations and space charge in the fluid model. In the quasi-neutral approximation of the kinetic model, for primary to thermal electron densities above a ratio of about 0.3 the sheath-edge potential jumps from a value close to the voltage equivalent of the electron temperature to a value just under the isotropic electron energy. This is in very close agreement with the previously obtained fluid quasi-neutral solutions.

In the presence of an external electric field, ion transport coefficients (ion mobility and diffusion coefficients) are closely related to the ion-neutral interaction potential. A new generalized potential model, coupled to an optimized Monte Carlo technique, has been developed for the determination of the transport coefficients of polyatomic ions in weakly ionized gases. This corresponds to the polyatomic ion-molecule systems which can affect the electrical behaviour of the flue gas discharges used for the non-thermal plasma reactor for pollution control. The ion-molecule interaction has been described by a rigid core potential model which is adapted for both polar and non-polar systems and also symmetric and asymmetric systems. Momentum transfer cross sections are then determined using a semi-classical approach. The corresponding sets of cross sections including the dominant processes in our intermediate ion energy range (elastic and mainly charge transfer in certain cases) are used in the Monte Carlo code to calculate the ion transport coefficients over a wide range of reduced electric field E/N. These ion transport data fit quite well the drift tube measurements available in the literature for the CO₂⁺/CO₂ system, and also for certain weakly polar cases. The case of the H₂O⁺/H₂O system is then considered thus giving in this highly polar system the ion swarm data for the first time in the literature. Finally, we have considered with quite good reliability some asymmetric systems such as CO₂⁺/N₂ and N₂⁺/CO₂ whose ion data are also needed for flue gas discharge modelling.

The initiation and development of a leader is theoretically studied by considering an electrode which is embedded in a cloud of space charge injected by a corona discharge. The focus is on the initiation of upward lightning from a stationary grounded object in a thundercloud electric field. The main results are also applicable to the leader process in long laboratory air gaps at direct voltage. Simple physical models of non-stationary coronae developing in free space near a solitary stressed sphere and of a leader propagating in the space charge cloud of coronae are suggested. It is shown that the electric field redistribution due to the space charge released by the long corona discharge near the top of a high object hinders the initiation and development of an upward leader from the object in a thundercloud electric field. The conditions for the formation of corona streamers that are required to initiate a leader are derived. The criteria are obtained for a leader to be initiated and propagate in the space charge cloud. A hypothesis is proposed that the streamers are never initiated near the top of a high object under thunderstorm conditions if at ground level there is only a slowly-varying electric field of the thundercloud. The streamers may be induced by the fast-rising electric field of distant downward leaders or intracloud discharges.

We study the spatiotemporal instability in nonlinear self-defocusing dispersive media using a modified (3+1)-dimensional nonlinear Schrödinger equation, in which the space-time focusing and self-steepening are considered to describe the spatiotemporal coupling in ultrashort pulsed beam propagation. We find that, in the normal dispersion media, space-time focusing significantly shrinks the instability region by suppressing the growth of the higher frequency components, while in the anomalous dispersion case, in which it is stable in the standard (3+1)-dimensional nonlinear Schrödinger equation, space-time focusing may lead to the appearance of new instability regions. In addition, the main role played by self-steepening is that it reduces the instability gain and, comparatively, it exerts much more influence on the new instability region resulting from space-time focusing. The numerical simulation of propagation of a cw plane wave in a self-defocusing normal dispersion medium is given to show the break up of the pulse and beam into a pulse train and filament.

The choice of an electrodynamic model of a measurement cell is substantiated. The scheme of a dielectrometer for the measurement of the complex permittivity of aqueous solutions at a frequency of 44 GHz is described. Results of the measurements of the 10% saccharose solution in the temperature interval 30-60 °C are adduced.

Nonlinear behaviour of power piezoceramic materials has to be studied under strong electric fields. A bridge designed for measuring it at low frequency is described. It consists basically of a capacitance comparison bridge that can be used in two different modes: balanced and unbalanced. The nonlinear electric displacement is split into dissipative and nondissipative terms. Dielectric constant is computed from the last term and related to the instantaneous field. The behaviour of soft and hard PZT ceramic materials has been tested according to this model. In both materials, the dielectric constant not only depends on the instantaneous value of the field but also on its amplitude. While the dependence of the real and imaginary parts of the dielectric constant in soft ceramics is large and practically linear to the field amplitude, in hard PZT it is low and nearly quadratic. The rate between both parts depends on the type of ceramic. Dielectric constant can be divided into two terms. One term is allied to the irreversible motion of domain walls, while the other is related to reversible motion. Balanced and unbalanced modes have been tested for both materials, and results are coherent. Accuracy and limitations of the method are discussed.

Using the simulated thermoluminescence (TL) glow peaks, it is shown that the level of quasi-equilibrium (QE) during the emission of a glow peak depends on the heating rate (β) used. Any system which may satisfy the QE condition when β is below a certain value during TL stimulation, may turn to the non-QE condition at higher values of β. The level of QE is examined in terms of the two functions called D(T) and q(T). A quantitative limit is suggested on the value of these functions in order to define a system as quasi-equilibrated. At about the turning point of the QE to non-QE condition the glow peaks begin to change their shape. This property is found for the first time and is used as the first ever experimental method to test whether or not the emission of a given glow peak is occurring under the QE condition. Further, at the QE to non-QE turning point the ratio T_R/τ_m appears to be nearly constant with only a weak dependence on the values of τ_m where T_R is the recording time of the glow peak and τ_m is the recombination lifetime of the free carriers during the peak emission. This near constant value of T_R/τ_m together with the measured value of T_R may be used to estimate the τ_m of the systems which show the non-QE condition above a certain heating rate. The value of τ_m being a function of the concentration and the cross section of the TL related traps, one is able to correlate the value of τ_m thus found with the approximate range of these parameters for the given sample. The results are discussed in the perspective of a well known TL phosphor and the plausible range of its concentration and cross section parameters.

The pressure oscillations during different film boiling modes in He II are studied in this paper. In the sub-cooled film boiling state, a flame-shaped vapour bubble can be seen to be quivering on the planar heater accompanied by a little audible noise, and the pressure oscillation, resulting from both vapour bubble oscillation and liquid column oscillation of bulk He II in a cryostat, is detected. In the noisy film boiling state in saturated He II, a big vapour bubble expands and crushes repeatedly on the planar heater accompanied by a loud acoustic noise, and the pressure oscillation is mainly caused by the crushing and formation of the vapour bubble. There are two possibilities for the occurrence of transition boiling. A theoretical analysis of the pressure oscillation was also carried out, which agreed well with the experimental results.

The modelling of the laser heating process gives insight into the laser workpiece interaction and minimizes the experimental cost. In the present study, analytical solution for the laser pulse heating process is considered and the closed form solution for the temperature rise due to time exponentially varying pulse is obtained. In the analysis, evaporation of the surface is taken into account. A Laplace transformation method was used when formulating the closed form solution for the temperature profiles. The effect of pulse parameters on the temperature profiles is examined in detail. It is found that the closed form solution derived from the present study reduces to the previously obtained analytical solution when the surface recession velocity is set to zero in the closed form solution. Moreover, the predictions of numerical simulation and closed form solution are found to be in good agreement.

The martensitic transformation during gas tungsten arc (GTA) welding of steel 42CrMo4 has been studied using the acoustic emission (AE) monitoring technique. Welds were produced under static conditions (spot welding) and under stationary conditions (travelling arc welding). After spot welding, the root mean square (RMS) value of the continuous acoustic emission was measured, revealing a peak that reflects the evolution of martensite formation during cooling of the spot weld. The RMS value was also measured during travelling arc welding at different heat inputs and corrected for the noise of the welding process to obtain the RMS value due to martensite formation. After welding, optical metallography was carried out to quantify the amount of martensite formed during cooling of the weld. An analysis of the results shows that the squared RMS value is proportional to the volume rate of martensite formation during welding, which is consistent with theory and in good agreement with the results obtained in the case of spot welding. The obtained results suggest that AE can be applied as a real time monitoring technique for the detection of martensite formation during steel welding.