Table of contents

was deposited by molecular beam epitaxy on GaAs (311)A-oriented substrates. This highly strained epilayer forms a three-dimensional surface below the critical thickness for strain relaxation. The surface observed by atomic force microscopy shows a corrugated nanostructure with a period of 35 nm along the (233) direction. The photoluminescence spectrum of a sample where the nanostructure was covered with a GaAs cap layer shows a strong peak at 1.28 eV up to room temperature. The dependence on temperature of the radiative recombination time constant indicates that excitons are confined in a zero-dimensional potential up to 100 K. The presence of the nanostructure under the GaAs cap layer was confirmed by cross sectional TEM.

Chemical vapour deposition experiments using gas mixtures of hydrocarbons with carbon dioxide can produce films of either diamond or a graphitic, amorphous form of carbon. The boundaries of the diamond growth domain in the triangular C - H - O gas composition diagram appear to be straight lines. It is shown that this is consistent with a simple model of the competition between the deposition of diamond and amorphous carbon phases. Gas phase carbonaceous fragments can attach to the surface of a growing film. Hydrogen in the gas phase etches poorly bound carbonaceous material from the surface, and also assists the incorporation of carbon into the diamond lattice. Oxygen in the gas phase forms carbon monoxide, and oxygen-bearing species also etch carbonaceous material. With these simple ingredients a rate equation approach is developed which also predicts the rate of diamond growth within the diamond domain, and indicates that oxygen can improve the efficiency of the process.

Surface chemical composition and topography of thin films grown by radiofrequency (rf) reactive sputtering on two different substrates (rough and mechanically polished) were investigated by x-ray photoemission spectromicroscopy (XPSM) and atomic force microscopy (AFM). XPSM measurements showed, for both substrates, a homogeneous chemical composition of the films. The only difference was the observation of different charging in different areas of the film grown on rough alumina substrates, due, presumably, to a non-continuous film. AFM showed large topographical variations (several hundred nanometres) for the film grown on a rough alumina substrate, due to structures already present on the substrate. The estimated roughness of the sensor was 20% larger for the film grown on a rough alumina substrate. The response to carbon monoxide was 30% higher for the sensor grown on rough alumina than that on polished alumina, reflecting the larger exposed sensor area.

Uni-axial anisotropy constants and uni-axial anisotropy fields of oriented polycrystalline magnets were obtained from the field-dependence of the magnetization by three methods and from torque measurements. The results from torque measurements are found to be superior to those from the intersections of magnetization curves for fields parallel and perpendicular to the preferred axis, the integral of the perpendicular magnetization and the maximum in the second derivative of the perpendicular magnetization, called the singular point detection (SPD) method. Sintered Sr ferrite magnets can be considered as quasi-single crystals because of their high degree of orientation and their large crystal grain sizes in the range . A value of was obtained by extrapolation to high field of the term determined by Fourier analysis of unsaturated torque curves. This is closer to the result for single crystals than the other methods. The SPD method was used to analyse data recorded in high pulsed fields to determine the large values of for sintered Nd - Dy - Fe - B magnets with various compositions. There is an increase in that is linear in the Dy content.

The use of Mössbauer spectroscopy in the study of rare-earth intermetallic compounds which are potential permanent magnet materials is reviewed. We consider aspects such as site occupation, interstitial modification, intrinsic magnetism and magnet processing and also the possible future role for Mössbauer spectroscopy.

In this paper, fundamental and practical aspects of the hydrogenation, disproportionation, desorption and recombination (HDDR) process in Nd - Fe - B-type alloys are reviewed. Thermodynamic aspects of the process are discussed as well as the microstructural changes throughout the different stages of the process. A detailed study of the disproportionated state is presented with particular reference to the role of the grain boundary phases. The effect of additives such as Co, Ga and Zr on the general hydrogen absorption and desorption behaviour of the matrix phase and their role in the inducement of magnetic anisotropy in the HDDR powder is discussed. Various mechanisms which have been suggested to explain the origin of anisotropy are described. Finally, consideration is given to some of the problems associated with the `scaling-up' of the HDDR process, which appears to be an extremely promising method for the production of bonded or fully dense hot-pressed magnets.

Since its discovery the Mössbauer effect has been a powerful probe of iron in magnetic materials and, together with neutron scattering and magnetic resonance, complements measurements of magnetic susceptibility and magnetization. The magnetic hyperfine splitting of the spectrum gives a measure of the magnetic moment on the iron atoms, and the line intensities enable the orientation of the magnetic moments to be determined. By applying external magnetic fields the local susceptibility of the iron atoms in paramagnets can be determined, and in magnetically ordered crystals magnetic phase changes may be induced and may be used to measure the magnetic anisotropy. In the early days this was used to determine the magnetic structure of crystalline ferromagnets, ferrimagnets and antiferromagnets. More modern applications include the study of amorphous and disordered crystalline materials (speromagnets, spin glasses, cluster glasses), incommensurate spin structures, fine particle magnets (superparamagnets and superferromagnets), magnetic multilayers, high flux density permanent magnet alloys (e.g. ) and high- superconductors.

High-performance magnetic materials are based on outstanding intrinsic magnetic properties and optimized microstructures and alloy compositions. The interactions between these three parameters in general are rather complex and cannot be treated explicitly by the theory of micromagnetism. Instead numerical methods have to be applied in order to determine the characteristic properties of hysteresis loops. Within the framework of computational micromagnetism (nanomagnetism) using the finite-element method the coercive fields of different types of grain ensembles have been determined. In the case of nanocrystalline composites the roles of grain size, exchange and dipolar coupling between grains will be discussed in detail. It is shown that, in sintered magnets, large coercivities require magnetic de-coupling between the grains, whereas regions with exchange coupling reduce the coercive field drastically, but, however, increase the remanence. Nanocrystalline composite materials with remanence enhancement and high coercivities are shown to require soft grains with diameters of twice the wall width of the hard magnetic phase. For an amount of 50% -Fe coercivities of , a remanence of 1.5 T and an energy product of are expected. A quantitative analysis of the numerical results for and the remanence leads to logarithmic dependences on grain size.

Two-phase nanocomposite materials have been prepared by high-energy ball-milling (HEBM) (2:14:1 phase) (u = 0, 0.75, 1.5 or 3.0; y = 0 or 11.6 and z = 0 or 0.5) or (1:12 phase), with excess Fe and then annealing. Magnetic properties of materials containing volume fractions of up to 75% of a magnetically soft Fe phase have been investigated and remanence enhancement observed. Optimum magnetic properties are obtained for materials with a volume fraction of a magnetically soft phase of 37 - 40%; for -Fe powders a remanent magnetic polarization of 1.05 T and intrinsic coercivity of ; and for -Fe powders a remanent magnetic polarization of 0.85 T and intrinsic coercivity of . For Co-containing alloys, evidence was observed for the redistribution of Co in the HEBM process, resulting in a magnetically soft Fe(Co) phase. The magnetic properties of isotropic -Fe and -Fe type magnets, compacted by hot pressing, are reported.

Research on permanent magnet materials since the late 1980s at the University of Manitoba is described in the context of contemporary research elsewhere. The general objectives sought for a material to be useful as a permanent magnet are identified. The research includes atomic substitutions of the super permanent magnet , other potentially useful ternary crystal structures, interstitial solution of carbon or nitrogen atoms and composite materials. Although x-ray diffraction, magnetization and other measurements have been made over a range of temperatures, the use of Mössbauer spectroscopy has been emphasised. For example, the determination of the site occupancy by various substituted atoms has let to an atomic pair model that quantitatively describes the Curie temperatures. Recently, it has been discovered that silicon stabilizes the 2 - 17 structure and permits gas-phase reactions at temperatures of over . Composite materials are discussed in terms of some proposed models.

An interesting extension in the use of magnetic fluids has resulted from the development of magnetic fluid composites obtained by dispersing micrometre-sized non-magnetic particles in a magnetic fluid. The composites possess a yield stress in a magnetic field which can be described at sufficiently high strain rates by the Bingham relation , where is the shear stress perpendicular to the applied field, the extrapolated yield stress, the strain rate and the plastic viscosity. Thus, a composite, particle concentration , in a field 0.036 T with has a yield stress of 26 Pa. The yield stresses obtained experimentally for different and correspond well to values predicted theoretically by Rosensweig using a determination of based on a continuum concept of unsymmetric stress that develops in the deformed but unyielded anisotropic medium.

A collective dipole is written into a section of magnetic recording tape containing metal particles. The section is then rotated in a magnetic field to follow the decay with cycle number n of the dipole moment . The dipole decays as with small values of p < 0.2 in fields near the coercivity. The measurements of changes within each cycle are interpreted in terms of the reversals of a fraction of the particles. Most of those switch twice per cycle, but some depart from the fraction that remain in the sense of the original dipole to join the growing fraction that remain in the opposite sense. These fractions are extracted from the data and followed from cycle to cycle for thousands of cycles. It is suggested that magnetic recording tapes could be used to study self-organized criticality.

The consideration of a simple model, based on the Stoner and Wohlfarth model of magnetic reversal including time-dependence, allows the measurement of the key viscosity parameter to be related to the micromagnetic changes occurring in the material. An aligned system with a log-normal distribution of volumes has been studied and the measured value of at each field related to the mean volume of the particles which are reversing at that field. It is also shown that, when the system is not aligned, there is no longer a simple relationship between and the physical processes occurring. This is because in this instance is a complex average over the ensemble.

A comparative study has been performed concerning the magnetization behaviour of single-phase and two-phase exchange-coupled . Measurements of reversible and irreversible magnetization and magnetic viscosity have been performed on nanocrystalline samples prepared by mechanical alloying and subsequent heat treatment. Measurements of reversible susceptibility show that the large reversible magnetization of the two-phase material may be attributed entirely to the contribution of the soft phase. It is shown that the two-stage reversal process observed during de-magnetization of the two-phase material is associated with the transition from reversible to irreversible magnetization of the exchange-coupled soft phase. Measurements of magnetic viscosity show that no time-dependent changes occur in the soft phase except when associated with reversal of the hard phase.

An investigation of the relationship between reversible and irreversible magnetization has been carried out. Measurements of reversible susceptibility and reversible magnetization, , in Alnico are found to depend on irreversible magnetization, . When evaluated at constant values of applied field, is found to decrease with increasing irreversible magnetization, . In anisotropic Alnico the dependence of on is sufficiently large to cause to decrease with increasing applied field along the magnetization curve at fields near coercivity. The results are evaluated in terms of a phenomenological model which takes and the internal field, , as constitutive variables which determine .

A theoretical formalism for the treatment of thermally activated magnetization reversal in systems exhibiting incoherent reversal is reviewed. Thermal effects are first introduced into the micromagnetic formalism using the Langevin formalism, an approach that has been shown to be effective for studies of thermal activation over small energy barriers. A different approach based on the ridge optimization method is then used to study the relaxation over large energy barriers. The theory is discussed in relation to recent pulsed field measurements on particulate recording media. Potential applications such as comparison with activation volume measurements are also discussed.

The development of a fast pulsed field magnetometer which can produce pulsed magnetic fields of amplitude up to 450 Oe is described in detail. The pulse width can be adjusted from 0.8 ns upwards, with rise times of as little as 105 ps. The system has been used to examine switching speed limitations in materials commonly used in particulate recording media. Measurements of the remanence coercivity as a function of time down to s show that the analysis of magnetization reversal in terms of the high-energy-barrier approximation for the relaxation time is still valid. However, it appears that the limiting factor for this analysis is when the product of the effective measurement time and the attempt frequency approaches unity.

A micromagnetic model for the calculation of magnetization processes in magnetic multilayer systems has been developed using a finite element method. Shell elements which account for the multilayer structure and a magnetic vector potential to treat long-range dipolar interactions are the essential features of the algorithm. Micromagnetic calculations of hysteresis properties and domain structures in Co/Pt multilayer systems show a qualitative agreement with magnetic images obtained from field emission Lorentz microscopy. The nucleation field of Co/Pt multilayers increases with improving texture. Spatial fluctuations of the magneto-crystalline anisotropy energy create barriers for domain wall motion. The pinning field of domains increases with increasing grain size. The domain wall structure depends on he local magnetocrystalline anisotropy. The wall structure changes from a Bloch-type to a Néel-type wall as the local anisotropy constant decreases. The quality of texture and the grain size significantly influence the jaggedness of domains in Co/Pt multilayers. Large grains and strong deviations of the easy directions from the film normal deteriorate the smoothness of domains and increase the transition width.

The magnetization of the intermetallic compound has been measured at low temperatures over a wide range of magnetic field strengths up to ± 5.0 T, using a SQUID magnetometer. It is shown here for the first time to be a type II superconductor having a critical temperature of 3.2 K. The lower and upper critical fields at T = 2.0 K are 6 ± 2 mT and 1.0 ± 0.1 T respectively.

Mechanochemical processing has been used for producing ultrafine magnetic metal powders, including Co and Ni. Uniform particle sizes of 10 - 20 nm were obtained by the chemical reduction of cobalt and nickel chlorides during mechanical milling with Na. The occurrence of combustion during milling was prevented by the addition of excess of NaCl as a diluent. The ultrafine particles were characterized by saturation magnetization values 90 - 95% of their respective bulk values and significantly increased coercivities.

The effect of mechanical milling on the structure and magnetic properties of has been studied. Decomposition during milling was found to occur via a two-stage reaction involving partial disordering and amorphization of the phase, followed by the formation of . Magnetic behaviour was found to depend on the microstructure developed during milling. Exchange spring behaviour was observed in partially amorphized samples. The influence of annealing on the structure and magnetic properties of milled powders was also investigated.

The development of inert gas atomization (IGA) as a primary production route for Nd - Fe - B type magnets has not been commercially successful due to a cooling rate which is much lower than the maximum achievable in melt-spinning (MS). It is further complicated by the fact that powder particles of a range of sizes are produced which solidify at different rates and form significantly different microstructures. The role of the cooling rate is analysed in a general way by processing the same alloy composition by IGA and MS. MS allows a much broader but controlled range of cooling rates to be studied than is possible in IGA. General MS concepts of underquenching and overquenching are applied to IGA to indicate the state of the microstructure. Although the bulk of the IGA powder was formed in an underquenched condition, energy products approaching those obtainable in optimally quenched MS ribbons could be achieved in the finest size fraction () of powder. Changes in susceptibility show the general trend of improvement in hard magnetic property with decreasing scale of the microstructure. Quenchability diagrams show that TiC additions to the base alloy increase the quenchability and may allow future IGA alloys to be produced in an overquenched condition.

The dependence of the threshold coupling strength on the loss parameter and the incident-beam ratio is calculated and shown for a new mutually pumped phase conjugator with a novel photorefractive crystal of copper-doped potassium sodium strontium barium niobate, in which both incoherent beams are incident upon the negative-c face and they travel in geometric paths similar to the outline of two arches. The maximum reflectivity attained is 21%. The tolerances of the output to both incident angles and positions are assessed. A curve fit is also made between the measured results and theoretical calculation.

The time variations of the gap current I(t) and the voltage log[V(t)] determined respectively from Schlumbohm's and Frommhold's experimental procedures for drift velocity measurement are simulated by using the Monte Carlo technique in Ar gas for five cases of the initial electron pulse shapes, such as the Dirac's function, Gaussian distributions with half widths of 10 ns and 20 ns, and Raether's distributions with half widths of 10 ns and 20 ns, under the condition at which ionization is appreciable. The results show that the time variation of the gap current I(t) is affected by the shape and/or the value of the half width of the initial electron pulse, namely, the profiles of I(t) obtained for the five cases of the initial pulses have different profiles. Therefore, the transit time obtained the from the different profiles of I(t) shows different values. However, it is found that the drift velocity calculated from the gradient of a against d plot does not depend on the shape and/or the value of the half width of the initial pulse, since against d plots obtained for five cases of the initial pulses show good linearity and practically the same gradient. Similar to the case of , although the time variation of log[V(t)] and the transit time are affected by the shape and/or the value of the half width of the initial pulse, against d plots show good linearity and practically the same gradient. Therefore, it is concluded that the drift velocity calculated from the gradient of the against d plot does not depend on the shape or the value of the half width of the initial pulse.

A simple model is reported for copper electrode erosion in electric arc heaters as a result of electrode surface fusion by the action of the arc spot. In the analysis we substitute the real arc spot by an intensive moving surface heat source. The time evolution and the distribution of the electrode surface temperature within the arc spot is studied in coordinates coupled with the moving heat source. The electrode erosion is attributed in the model to the unbalance between the heat supply and the heat removal due to the development of an arc spot fusion zone. An erosion effective enthalpy is applied in the analysis, including all physical processes for the material transformation from the solid state into the plasma state under the action of the intensive heat flux. Formulae were obtained that enable one to calculate the electrode erosion as a function of arc velocity, electrode temperature, current, near-electrode thermal volt-equivalent, current density and electrode material properties. We show briefly that the theory agrees reasonably well with experimental results. The present model enables us to reveal the relative significance of the different parameters in the erosion process and to predict the erosion behaviour in copper electrode electric arc heaters.

Diode laser absorption on the - argon transition is used to measure heavy particle temperatures in a 100 MHz argon inductively coupled plasma. Radial profiles of this temperature are obtained from the Gaussian part of the absorption profile with an accuracy of about 500 K, for four different input powers and at two different heights. The integrated profile is used to calculate the 4s level density and to trace the ionizing and recombining plasma parts. The measurements also show that the method of attributing the Lorentzian width only to Stark broadening for calculating electron densities is not correct for this argon transition in atmospheric plasmas. A second broadening process with Lorentzian shape, Van der Waals broadening, has to be taken into account. Under the measured conditions at the hottest positions in the plasma about 50% of the Lorentz component is due to Van der Waals broadening and this increases to almost 100% at the edges of the plasma.

A new experimental technique suitable for real-time measurements has been developed which permits the determination of the spatial distribution of the electron density of a plasma with a time resolution commensurate with the 6 ns duration of a single laser pulse. The accuracy and sensitivity of the electron density measurements allow the application to low-temperature plasma diagnostics. The possibilities of the method were demonstrated by studying a steady state mini-arc argon plasma at atmospheric pressure. The measured electron densities with 2 cm plasma length spanned the range from to on the plasma axis.

The diffusion of dopant atoms to the surface of a refractory cathode doped with a lowering work-function dopant is considered. The variations of the cathode temperature with time and with the coordinate along the cathode length are taken into account. It is shown that, depending on the value of , the work function at the monolayer coverage, there are two possible scenarios of cathode temperature development. At low , the cathode experiences instability which leads to cleaning of the surface from adatoms and to a sharp rise in temperature. At higher , the cathode temperature changes gradually. The cathode service time, as a period of time when the dopant surface concentration falls and the cathode temperature raises, is estimated. It is shown that a properly organized temperature distribution inside the cathode may increase its service life several times.

The results of two-dimensional (2D) numerical simulation of single positive streamer development in atmospheric air in sphere - plane electrode configuration are presented. Correlation of streamer parameters with sphere radius and applied voltage U is revealed. The values of the electric field at the streamer head and in the channel are shown to be almost independent of and U and equal to 150 - 180 and correspondingly. Streamer velocity and radial dimensions linearly increase with U, the coefficient in these linear relations being independent of . Comparison of the results obtained by 2D modelling and in the frame of the commonly used 1D (or quasi-2D) models is made.

This paper deals with a two-temperature, two-dimensional modelling of a mercury high-pressure plasma stabilized by walls. We consider here a plasma composed of neutral particles, singly ionized positive ions and electrons. Both electron and heavy particle energies are supposed to follow Maxwell distribution functions at different temperatures. Moreover, the electrons were supposed to be carried by the heavy particles in their laminar convection movement. Hydrodynamic conservation equations are then solved by using a 2D semi-implicit finite element scheme. After validation the model is used to discuss deviations from thermal equilibrium due to external arc parameters such as arc current and pressure. These deviations are expressed as differences between electron and heavy particle temperatures. Our results confirm quantitatively for the first time the existence of thermal equilibrium deviations in such types of discharge. These deviations could be significant in many cases, especially when current or pressure is relatively low. Furthermore, we show that, in such types of discharge, the hot core is always closer to thermal equilibrium than the outer discharge jacket.

A back-corona discharge has been tested as a plasma source for decomposition of hydrocarbons . A back-corona discharge has hitherto not been applied for these purposes. The results of laboratory experiments show that the back-corona discharge can decomposite hydrocarbons, similarly to a dc or pulsed streamer corona discharge, with similar energy expense and conversion rate. However, the final concentration of after the same residence time of 60 s is lower for back-corona discharges. The back-corona also produces less CO and during the decomposition process.

The ratio of the Townsend first ionization coefficient to the gas density , the mean-arrival-time drift velocity and the product of the longitudinal electron diffusion coefficient and the gas density in tetraethoxysilane (TEOS) vapour have been experimentally determined over a wide range of E/N from 14 to 6000 Td by a double-shutter drift tube technique using an arrival-time spectra (ATS) analysis. The result shows that the present values of are in excellent agreement with those previously measured by the steady-state Townsend method in an E/N range of 450 - 2000 Td. Values of and in the TEOS vapour are reported for the first time in the present paper. It is revealed that takes an almost constant value at 140 Td < E/N < 300 Td but monotonically increases in the other E/N ranges in the present measurement. The ratio of the longitudinal diffusion coefficient to the electron mobility is also deduced. The result shows that the mean electron energy in the TEOS vapour is very low, which suggests that inelastic collisions between electrons and the TEOS molecule occur more frequently even in a low-electron-energy region.

The influence of dilution of silane with Ar, He and on the mechanism of radical generation in radio frequency discharges used for the deposition of a-Si:H has been examined. The density of SiH radicals in the discharge volume and near the deposition surface was examined by laser-induced fluorescence. The observed phenomena were attributed to the enhancement of the contribution of sheath-related electrons under certain dilution conditions. This explanation was confirmed by numerical simulation using Monte Carlo and probabilistic models that permitted the calculation of the total collision cross section of silane.

We introduce an effective-medium theory for the local field and mean dielectric function of a polymer dispersed liquid crystal (PDLC) film consisting of identical spherical liquid crystal droplets dispersed in a polymer matrix. The theory takes account of the tensor nature of the dielectric response of the liquid crystals and the subsequent re-orientation of the liquid crystal tensor inside the PDLC droplets, as well as the presence of other droplets. We present explicit numerical results for droplets with radial and bipolar director boundary conditions as a function of external voltage.

The importance of understanding the variation of shear strength with pressure in the formulation of constitutive models has long been recognized. Previously, this had been deduced by measurements of the offset of the Hugoniot curve for a material from the calculated hydrostat. In recent papers, a direct measurement technique has been suggested in which both principal components of stress are measured using piezoresistive gauges. The reduction of the data collected from transverse stress gauges has attracted some debate and is reviewed here. In particular, the stress and strain states experienced by the gauge must be considered. The hardening of the gauge with longitudinal stress or pressure was investigated. Examples from experiments in metals and ceramics are given. The effect of gauge geometry was assessed and results show that the measured stresses from either gauge were within 0.5% of each other when subjected to identical impact conditions. An investigation was also performed on the effect of insulation thickness around the gauge and again no effect on the measured stress was found.

A scaling formula of critical current density for anisotropic superconductors has been introduced on the basis of anisotropic Ginzburg - Landau theory and the classical Kramer scaling law. The model predicts the functional dependence of the critical current density on magnetic field and angle, and the functional relationship is in good agreement with experiments performed on thin films.

The frequency dependence of the elasto - piezo - dielectric constants of piezoelectric materials is usually neglected. By means of a new procedure of piezoelectric characterization based on the characterization in the overtones of resonant modes we can measure accurately the constants involved in the piezoelectric behaviour of the materials in a wide range of frequencies.

The characterization in the overtones of resonant modes is possible by using an automatic iterative method, described below, that takes account of the number of the overtone to obtain the appropriate solution of the equation system. The proposed procedure has been checked for the radial resonances in materials that exhibit very different behaviour and very good agreement is obtained in all the overtones not overlapped with the thickness extensional mode of resonance.

Using various particle sizes of starting , we investigated the effect of stress on the dielectric - temperature characteristics of cerium-modified barium titanate. Transmission electron microscopy and energy dispersive spectroscopy confirmed three distinct areas: a grain core, a grain shell, and gradient regions. The grain size and volume fractions of the grain core were somewhat proportional to the particle size of starting . The dielectric - temperature characteristics will be explained in terms of three inhomogeneous regions and the internal stress. The dielectric - temperature characteristic of the large grains proved to be a function of variation in the values, whereas that of the small grains was a function of both the values and the internal stress. In particular, the internal stress was found to be proportional to the volume fraction of the cerium-doped region, to depress and shift the calculated dielectric constant versus temperature characteristics.

Lead liquid metal ion sources (LMISs) were operated using a special specimen holder in situ in a 1 MeV TEM. The dynamics of the tip shape have been observed as a function of the ion emission current. At currents there was a jet-like protrusion on the vertex of the Taylor cone. Linear dependences were found for the decrease of the cone half-angle and the increase of the jet length l as functions of increase in ion emission current. Microdroplet emission was observed at the shank of the Taylor cone over time intervals of 0.1 s and more. The diameter of these microdroplets varied between 40 and 340 nm. This work has improved our understanding of the ion and microdroplet emission processes from the Pb LMIS.

Generalized transmission lines whose differential section contains either an additional series capacitance or parallel inductance arise in the analysis of layered structures when the source and the field are decomposed in TE and TM parts. Basic properties of such transmission lines are studied in the time domain. The differential equations for the voltage and current are of the Klein - Gordon form and known solutions are applied to find voltage and current quantities due to sources on the infinite line. As an example, reflection from a capacitive termination is solved in terms of image sources, which for a point source comprises a point source and an exponentially distributed source.

Various topological and metric properties of the cells in the phelogen of the cork oak have been measured in tangential sections of cork by image analysis methods. These include the fractions of cells with i sides (i-cells), the fractions of adjacencies between i- and k-cells and various distributions of cell areas in relation to topology.

This work presents a method to optimize the recovery efficiency of fine paramagnetic particles from a liquid suspension in an axial HGMF cell. The cell has the flow field bounded by a circular cylindrical wall. It has only one ferromagnetic wire mounted outside the flow field, parallel with its axis and in `paramagnetic capture mode'. The optimization criterion was deduced from the analysis of the particles' trajectories inside the magnetic active space. It is based on the relationship between the geometrical and operational parameters for which the filtration efficiency is 100%. The work also presents some experimental data which are in good agreement with theoretical results.

It is shown that in axially non-uniform plasmas forward and backward surface waves convert into each other in the region of a complex turning point. In the absence of dissipation the coefficient of transformation reaches unity. The complex turning point is due to field asymmetry or surrounding dielectric walls or transverse (radial) density inhomogeneity. The calculations are performed for the case of antisymmetric surface waves propagating on a thin, axially non-uniform, plasma layer.

We have grown superconducting thin films of (Y-123) on (PCMO) buffer layers and PCMO overlayers on Y-123 thin films using pulsed laser ablation deposition. For both sets of films below 50 K, the Y-123 layer is superconducting and the zero-field cooled PCMO layer is insulating. The application of a magnetic field of 8 T results in an insulator - metal transition in the PCMO layer. This field-induced conducting state is stable in zero magnetic field at low temperature. The PCMO layer can be returned to an insulating state by annealing above 100 K. This opens the way for the construction of devices incorporating these oxide materials in which the electronic properties of key components such as the substrate or the barrier layer can be switched in a controlled way by the application of a magnetic field.

Unfortunately an error occurred in representing the ground state Stark levels in figure 9. The correct figure is shown below.

Figure 9. Energy level diagrams of the ⁴I_15/2 ground state for ER³⁺ in LiNbO₃ at two slightly different lattice sites. The energies are derived from the luminescence spectra in figure 7.