Table of contents

We have observed a giant Barkhausen effect where magnetization proceeds continuously with field in a second-order instability process. This is contrasted with the typical giant Barkhausen effect in which the magnetization jumps, or moves discontinuously with field in a first-order instability process. This second-order instability process has been found in Fe-rich amorphous wires in two cases: (i) transverse field-annealed long wires and (ii) short as-cast wires. Anomalous losses are found to be very large and are of significant magnitude around 1 Hz.

Thin films of composition Tb_xFe_1-x about 150 mu m thick have been studied using the magneto-optical Kerr effect and have also had their acquisition curves of isothermal remanent magnetization measured using a spinner flux gate magnetometer. Both types of measurement show that, for x<0.23, the easy magnetization direction lies in the plane of the film, whereas samples with a higher Tb content are more easily magnetized at high fields perpendicular to the film. At lower fields the remanence measurements show that samples of higher Tb content are almost isotropic. The remanence measurements also indicate that those samples with an easy plane also exhibit a marked anisotropy within the plane so that a preferred axis is present, presumably as a result of some asymmetry in the deposition process.

Self-fields and forces as well as the local degree of space-charge neutralization in overcompensated electron beams are considered. The radial variation of the local degree of space-charge neutralization is analysed. A novel model which describes the equilibrium potential distribution in overcompensated beams is proposed and a method for computer simulation of the beam propagation is described. Results from numerical experiments which illustrate the propagation of finite emittance overneutralized beams are presented.

Some effects of CO₂ lasers are studied using a numerical model. A small amount of water vapour increases the output power only in the case of nitrogen-rich gas mixtures due to reduction of CO₂ dissociation, but a better way is the use of a higher CO₂:N₂ ratio. In typical waveguide laser gas mixtures, the degree of dissociation has only a small influence on output power, if it is below 70-80%. That is why catalysts cannot increase the laser output power; they are only useful for a longer laser lifetime. Using a zeolitic stabilization method for the CO₂ partial pressure, laser lifetimes up to 60000 h can be achieved. A method of studying the behaviour of the gas discharge of long traversely radiofrequency-excited waveguide lasers on the basis of the numerical model is presented. A further method is developed for determination of the time-averaged reduced effective field strength in such lasers.

A compact model for the description of ultra-short pulse driven recombination X-ray lasers in hydrogen-like ions is established. Initial densities of plasmas produced from fibre targets irradiated by ultra-short pulses have been related to the intensity of pulse drivers, fibre radius and driving pulse duration. The peak gain dependencies upon the driving pulse duration, fibre radius and intensity of driver, as well as the atomic number are calculated. The optimized conditions for maximum gain operation are discussed. The result was also compared with the simulations of MEDUSA; qualitative agreement was observed.

In this paper, a model of a focused beam with circular symmetry is presented. The acoustic field is defined by a Gaussian surface velocity distribution along the emitter immersed in a fluid. The pressure field is described by a Fourier integral representation, and is evaluated asymptotically using a generalized steepest descent procedure. Simple analytical expressions for the acoustic pressure along the axis are obtained, and the variation of the pressure field as a function of distance from the emitter is illustrated.

An Al single crystal with the axial direction of (452) was fatigued in air, at a constant resolved shear stress amplitude (4 MPa), a frequency of 20 Hz and at room temperature. Time-resolved measurements were then carried out on short cracks in persistent slip bands (PSBS) on the top surface, which has the largest slip steps, using the acoustic signal from the crack, when the acoustic lens was scanned over the crack sending convergent acoustic beams down the specimen, was detected and interpreted quantitatively. The signal results from the reflections of a mixed mode surface wave (Rayleigh longitudinal lateral wave) from the crack mouth. At 1.2*10⁶ cycles, two short cracks in the PSB were measured to be 17 and 27 mu m in depth. The angle with the specimen surface was observed to be about 54 degrees , compared with a value of 51 degrees determined by an X-ray method.

The transient thermal conductivity and transient heat capacity of laminated materials are defined to characterize time-varying properties of heat conduction. The transient thermal properties are related to two kinds of time lags defined by dual boundary value problems of unsteady heat conduction. These properties may depend on the sequence of the laminae. For laminated materials constituted of two components, it is shown that the optimal laminate that maximizes or minimizes the transient thermal properties reduces to a symmetric triple laminate structure. The optimal triple laminate structure gives the maximal or minimal value of the time lag under the constraint that the overall thermal properties are constant. These results can be applied to the equivalent problem of permeation through laminated membranes.

Two-phase systems are assumed to contain spherical particles arranged in a three-dimensional cubic array. A general expression for porosity correction has been derived for diverse two-phase systems from experimental results reported in the literature. The correction term is found to be dependent on the ratio of thermal conductivities of the constituent phases of the system and gives better agreement of predicted effective thermal conductivity values with experimental results.

The classical theory of endoreversible thermodynamics gives rise to an optimum efficiency for the power output given by 1-T₂/T₁^1/2 in contrast to the Carnot efficiency 1-T/T₁ used in reversible thermodynamics. It will be shown that many systems show the same efficiency, although a system giving an optimum efficiency involving T₂/T₁^1/3 has been found.

This paper is concerned with the boundary layer flow of a power law non-Newtonian fluid in the presence of a magnetic field B(x) applied perpendicular to the surface and an electric field E(x) perpendicular to B(x) and the direction of the longitudinal velocity in the boundary layer. Approximate analytical solutions are given, and numerical solutions to the resulting nonlinear ordinary differential equation are presented. Important particular cases like boundary layer flow along a wedge, two-dimensional stagnation point flow, flow over a flat plate and flow in a convergent channel have been studied. The combined effects of the magnetic forces gamma and the flow index n on the velocity profiles, the shear stress on the surface tau _w, the displacement thickness delta ₁ and the momentum thickness delta ₂ are studied. It is found that the velocity of the fluid increases with increase of either gamma or n individually, with the other kept constant. Also, it is established that both analytical and numerical solutions must be used together to solve such problems.

The effect of uniform distribution of internal heat generation on the stability of the Benard-Marangoni convection in a horizontal fluid layer with a deformable upper free surface is investigated. The stability analysis in this study is based on the linear stability theory. The eigenvalue equations obtained from the analysis are solved by using the fourth-order Runge-Kutta-Gill method with the shooting technique. The results indicate that the stability of Benard-Marangoni convection is significantly affected by internal heat generation in the fluid layer and by surface tension at the upper free surface. There are two different kinds of instability mode: the thermal mode and the surface tensile mode. At lower values of the Crispation number C, the instability is dominated by the thermal mode. At higher values of C, the system becomes more unstable and creates the surface tensile mode, which is induced by the surface tensile effect. The Crispation number C at the transition between the thermal and the surface tensile modes decreases as the value of internal heat generation increases and that of thermal buoyance decreases. The bond number Bo at the mode transition increases due to the existence of the internal heat generation. In addition, the system becomes more stable when the Biot number Bi of the upper free surface increases.

Distortion in a weakly ionized homogeneous plasma caused by the installation of a mesh-grid is investigated in a wave-free He positive column. The installation causes distortion in the axial as well as the radial direction, the so-called double-sheath. Such a structure decelerates electrons in a phase of weak electric field, while it accelerates them in that of strong electric field, eventually resulting in a double-humped electron energy distribution function (EEDF). The detected axial variation of the EEDF is compared with a solution of the Boltzmann equation including the spatial derivative.

A planar travelling wave tube comprising a planar helix, constituted from a pair of unidirectionally conducting screens, and partially loaded with a high-density plasma, supports plasma surface waves and the conventional helix modes. Under suitable conditions of plasma density, helix pitch angle and separation between plasma and helix, the two modes are strongly coupled. A sheet electron beam propagating close to the plasma surface drives the coupled modes to instability, giving a large growth rate.

Results of application of two-dimensional detection to optical emission spectroscopy diagnosis are given. The analysis was performed on a low-pressure (0.1 Torr) nitrogen plasma discharge produced by a new type of direct current reactor, which produces current amplification effects. The measured spectra are subjected to several treatments including calibration of the luminous intensity and Abel deconvolution, which allow us to construct radial spectra theoretically. A comparison between these spectra and simulated spectra has been carried out in order to evaluate the temperatures of the medium and to obtain their radial distribution. The possibility of obtaining a more accurate evaluation of rotational and vibrational temperatures is discussed.

Radially and temporally resolved Hg-Na mixing ratio and species densities are determined in current modulated metal halide discharges at different pressures. The results show that the constant mixing ratio approximation is invalid radially and temporally and it is not suitable for reliable species density and radiation calculations. Three 50 Hz Hg-NaI vertically operating discharges at 1.5, 3.1 and 6.3 atm Hg pressures are studied. Side-on phase resolved radiation measurements are used to determine the temperature and the sodium ion density assuming local thermal equilibrium. The reliability of the Abel inversion technique for non-monotonic distributions is numerically tested. The Hg-Na ratio and plasma composition are deduced from a chemical equilibrium model using the experimental results as input parameters. It was found that the Hg-Na ratio modulates with the time as the electron density, the ratio of the sodium ion density to the electron density decreases strongly with the electron density and the sodium neutral density increases with the mercury pressure.

A Monte Carte simulation of electrons emitted from the cathode of a CO₂ gas laser discharge is presented. The influence of a perpendicular magnetic field on the electron transport coefficients has been studied. Data on transverse and perpendicular velocities and electron energy distributions are evaluated at various magnetic field types and strengths. Ionization coefficients and excitation coefficients of 27 useful energy levels of CO₂, N₂ and He are obtained at the same time. The result shows that the application of a magnetic field perpendicular to the electric field decreases the transverse drift velocity, the mean energy and thus the ionization coefficient. As a result, the magnetic field leads to a very high perpendicular velocity, which may be responsible for the stability of our discharge experiments (where a perpendicular magnetic field near the cathode is used to stabilize the direct current discharge of a CO₂ gas laser and to gain a higher input power loading). It is also found that the magnetic field distributions, as well as the field strength, had great effects on the electron transport coefficients and the discharge properties.

Nitrogen dioxide (NO₂) has been shown to be decomposed into N₂ and O₂ in low-pressure glow discharges. The basic data needed to understand the decomposition process, such as the electron-impact ionization alpha /p₂₀ and attachment coefficients eta /p₂₀, where p₂₀ is the gas pressure at 20 degrees C, are measured by a steady-state Townsend method for NO₂/air mixtures with the fractional NO₂ partial pressure K and for 50<E/p₂₀<500 V cm^-1 Torr^-1 (152<E/N<1520 Td). The results show that ( alpha - eta )/p₂₀ for K=1 (NO₂) increases almost linearly with increasing E/p₂₀. In NO₂/air mixtures it increases significantly with decreasing K. The limiting E/p₂₀, (E/p₂₀)_lim at which alpha /p₂₀= eta /p₂₀, is around 100 V cm^- Torr^-1 for NO₂ and decreases monotonically to 33 V cm^-1 Torr^-1 for air with decreasing K. The alpha /p₂₀ value for mixtures decreases significantly with increasing K, especially, at low E/p₂₀. The value of eta /p₂₀ increases with increasing K for the whole range of E/p₂₀ values for which the present measurement has been carried out.

The charge-simulation technique is applied to solve the Poissonian field problem, which is governed by Poisson's equation, the equation for current density, and the current continuity condition in transmission line arrangements. These include the coaxial cylinder arrangement, the monopolar line with single and bundle conductors, and the homopolar line with single conductors. The surface charge on the stressed conductor as well as the charge in the space around it are represented by a discrete set of unknown infinite line charges. Satisfying properly chosen boundary conditions at the transmission line conductors results in a system of algebraic equations whose iterative solution evaluates the unknown line charges. Having determined these unknowns, the potential, electric field and volume charge density can be calculated everywhere between the stressed conductor and the ground plane. The I-V characteristic was evaluated for the investigated arrangements and agreed satisfactorily with those reported earlier.

A methane discharge fluid model is developed, and subsequently combined with a simple gas-phase chemical kinetics model. The aim is to provide better understanding of the charged species dynamics, and their interaction with the gas-phase kinetics in a CH₄ plasma. Swarm data are used as input in the fluid model, which predicts the ion and electron densities, electric fields and ionization rates as a function of space and time in the radio-frequency period. Results show that, due to detachment, the negative ion density in CH₄ is of order 10^-2 that of electrons; a capacitive discharge behaviour is observed analogous to that of an electropositive gas. The effects of electrode spacing (2-6 cm), gas pressure (80 mTorr to 1 Torr) and radio-frequency current (2.2-3.4 mA cm^-2 0.06-0.15 W cm^-2) are studied and compared successfully with experimental data. The time-averaged, spatially-resolved electron density and energy, the set of cross sections for CH₂ and CH₃ dissociation, together with an assumption about the form of the electron energy distribution function, are subsequently used as input in a simplified one-dimensional gas-phase kinetic model. The model predicts the CH₂ and CH₃ spatial profiles, which compare well with experimental data.

The duration of transient glow discharge and the energy dissipated in the gap during the glow phase have been measured in nitrogen. These measurements have been made for gaps up to 7 mm at gas pressures of 40-150 Torr by static breakdown. It has been shown that the transition from the glow to the arc starts to develop in the discharge region near the cathode. The dependence of the glow duration on gas pressure is explained assuming that the criterion for the glow-to-arc transition is that the surface density of energy dissipated in the dark space during the glow phase reaches a certain quantity.

The kinetics of the amorphous-to-crystalline transition in Se₇₀Te₃₀ glass has been studied using electrical conductivity as a sensitive parameter characterizing the transformation process. The experimental data were fitted to the well-known Avrami theory of transformation kinetics. A mean value for the growth parameter n=1.51+or-0.03 and effective activation energy of crystal growth E=104.2 KJ mol^-1 have been obtained in the temperature range 360-375 K for the present system.

The phenomenon of diffusion and reaction in solid bilayers under ion bombardment is described by a set of equations like those occurring in non-equilibrium chemical systems. The model takes into account the variations of the properties of the sample during the process and the reaction rates appear as functions of the ion deposition energy in the inhomogeneous sample. A particular case is considered: an Fe/Al bilayer at temperature T=500 K irradiated by Ar⁺ at 100 keV.

The acoustic modulation of the resonance gamma absorption by spherical particles containing a Mossbauer label is studied. To find the Van Hove function the expression for the acoustic displacements of the atom is used, which is obtained in the framework of the elasticity theory, assuming that the particle size is small relative to the sound wavelength. The results are discussed in detail for cases in which the sound frequency is comparable to or much less than the linewidth.

This paper proposes a new model called the randomness-phonon model to derive the Kohlrausch-Williams-Watt (KWW) form of the relaxation function, namely exp(-(t/ tau *)^1-n). In our theory the index n has clear physical meaning. The term (1-n) corresponds to the degree of randomness.

The sensitivity of photoelectric emission of polycrystalline tungsten, produced by 248 nm laser pulses with 450 fs duration, has been measured. A nonlinear increase of photoemission efficiency, as a function of laser peak intensity, was observed, which confirms earlier observations with gold. This nonlinear behaviour is a direct consequence of non-equilibrium between electron gas and lattice temperatures produced at the surface by the sub-picosecond laser pulses. The nonlinear multiphoton photoemission order k was measured and shown to depend only on the laser intensity absorbed by the tungsten surface.

A theoretical treatment is presented for the supralinearity of thermoluminescence glow peaks. The model assumes part of the thermoluminescence trap population as interactive with the thermally disconnected deep traps. These traps produce supralinear growth of the thermoluminescence response. The initial linear part of the response curve is assumed to be produced by the non-interactive part of the thermoluminescence trap population. The treatment enables determination of the relative concentration of deep traps. Resolution of the observed response curve into linear and supralinear parts allows determination of the relative trap populations responsible for producing the linear and supralinear parts of the response. We have also shown the procedure for determining the trap filling constant using the growth profile of the thermoluminescence glow peak of pre-dose sensitized samples. Apart from interpreting the linear and supralinear behaviour of the thermoluminescence response, the treatment provides a quantitative explanation for the pre-dose sensitization effect.

Thermally stimulated current peaks corresponding to saturated (completely filled) and non-saturated (partially filled) non-first-order thermoluminescence with non-constant recombination lifetime are investigated. The variation of peak temperature and peak shape are studied as trap filling continues to increase until saturation. A set of expressions based on the shape of the peak has been derived, which in principle can be used to evaluate activation energy of such thermally stimulated current peaks. The coefficients involved in the expression are presented for certain kinetic orders, namely 1.5, 2.0 and 2.5. The validity of this peak shape method as well as the method of various heating rates have been checked by considering some numerically computed thermally stimulated current peaks.

Oriented SrTiO₃ thin films were grown in situ on p-type Si(100) substrates by radio frequency magnetron sputtering. The orientations of the films were varied by controlling both growth temperature and oxygen-to-argon content ratio in a discharge gas. Deposition at 640 degrees C in 100% argon discharge yielded (111)-oriented SrTiO₃ film. Film with (100) orientation was obtained by addition of oxygen as a discharge gas at lower growth temperature (<620 degrees C). SrTiO₃ thin films were composed of three regions, an external surface layer, a main layer and an interface layer. The films had very sharp interface layers. The films had a fairly dense structure with homogeneous grain and a columnar structure was observed in the cross section morphology.

Small pieces of high-density polyethylene sheet were dipped into acrylonitrile and exposed to ⁶⁰Co gamma -rays for grafting. The grafting tendency of acrylonitrile onto high-density polyethylene was confirmed, initially from observed changes in sample weight with period of exposure and later with an infrared spectrometer, where the absorption bands corresponding to stretching of (i) C identical to N at 2242 cm^-1 (ii) C=N at 1750 and 1630 cm^-1 and (iii) C-N at 1060 cm^-1 were obtained. The degree of grafting was determined, for the first time, by estimating the amount of nitrogen incorporated in the grafted sample using a 14 MeV neutron activation analysis technique. The electrical properties of the grafted sample were also studied, whereby a slight decrease in resistivity was noted.

Techniques developed for state-of-the-art microwave displacement transducers may be incorporated into a gravity gradiometer array suitable for spatial inertial navigation and geodesic research applications. To make such a system attractive for placement into a small satellite, it should be small in size and weight, rugged, and operate at non-cryogenic temperature. One promising technique is based on the modulation of the resonant frequency of a shielded sapphire microwave resonator. In the present experiment, the sapphire resonator operates in a high-order (azimuthal mode number 12) mode near 9.66 GHz. The unloaded quality factor of 1.0*10⁵ indicates that the mode is probably not a pure whispering gallery mode, but rather a hybrid. A sapphire tuning element is coupled to a spring-mass accelerometer, with a mechanical resonance near 16.8 Hz, and perturbs part of the evanescent field of the resonator. The resonant frequency of the mode is an exponential function of the spacing between the resonator and the tuning element. The present experiment yields a maximum Q(df/dx)=3.91*10² MHz mu m^-1 at 310 K. At this level of sensitivity the current accelerometer would require df/f₀<5*10^-10 to resolve mu g acceleration. The residual phase noise characteristics were also determined by measurement of the single side band (SSB) noise power spectral density.