Table of contents

A detailed investigation of the emission frequency spectra of a gallium liquid metal ion source is presented. The spectra are correlated with current oscillograms. The current for which pulses appear superimposed on the d.c. level of current is well predicted by existing theory. The pulses are believed to be the result of droplet emission, and their terminal frequency appears to coincide with the frequency of vibration of the sides of the liquid cone at high currents. Better understanding of the instabilities that develop on the liquid anode can be useful for deposition purposes.

An overview is given of the state of the art in spin electronics. The technical basis is reviewed and simple ideas of giant magnetoresistance discussed. The connection between spin electronics and mesomagnetism is explored. Three-terminal spin-electronic devices are introduced of various types including hot carrier and hybrid spin/semiconductor devices. Spin-tunnel devices are examined and single spin electronics is also treated. The paper concludes with an outlook on future prospects in this field.

Hence you long legg'd spinners, hence. William Shakespeare

In this paper, the magnetic field at the mouth of a crack in ferromagnetic steel is determined by means of a two-dimensional, linear model. The solution is found by employing an analytical method in which one complex variable is transformed into another by means of a mapping function. An approximate boundary condition, based on the fact that the steel permeability is much larger than that of free space, is used. In this way, three representations of a crack are treated: narrow and open cracks and a semi-elliptical indentation. The mapping function transforms these shapes into a half-plane geometry for which the solution is easily obtained. The advantage of this analytical approach is that the results are readily accessible without the need for a large numerical code. Example calculations are compared with each other and with calculations based on a former theory. This work has application in electromagnetic non-destructive evaluations: eddy-current testing, flux leakage measurements and, most directly, magnetic particle inspection.

SrRuO₃ thin films have been grown on MgO substrates using pulsed laser ablation deposition. The orientation of the SrRuO₃ films changes from the [001] or [110] direction normal to the substrate surface to become predominantly [100] as the thickness of the SrRuO₃increases from 50 to 360 nm. This leads to a change in the magnetic response of the SrRuO₃ films and to a dramatic improvement in the superconducting properties of YBa₂Cu₃O_7−δ films grown on top of the SrRuO₃ layer. The domain structures and the surface morphology of SrRuO₃ films grown on MgO change as the thickness of the film increases. The 50 nm thick SrRuO₃ film grown on an MgO substrate nucleates as rectangular islands, 0.5 to 1 μm in diameter. As the thickness increases to 185 nm, oriented grains ∼1 μm in size are observed. We have noted a different microstructure for the SrRuO₃ thin films grown on SrTiO₃ substrates. The 185 nm thick SrRuO₃ film grown on a SrTiO₃ substrate shows a step like growth pattern.

The development of the soft magnetic properties of melt spun Fe_72−xNb_xAl₅Ga₂P₁₁C₆B₄ (x = 0,2) ribbons by furnace annealing (FA) and current annealing (CA) has been studied. A comparison between the magnetic and structural properties of annealed samples obtained by these two annealing techniques is presented. The annealed states were characterized by x-ray diffraction, transmission electron microscopy, and thermomagnetic and hysteresis measurements. For FA samples crystallization starts at 748 K for x = 0 and at 743 K for x = 2, and for CA samples after applying a heating power of 4.7 W cm⁻². Coercivity reaches its lowest values of 1.91 A m⁻¹ for x = 0 and 5.56 A m⁻¹ for x = 2 after FA at 673 K. The corresponding data for the CA samples are 2.14 A m⁻¹ for x = 0 and 5.27 A m⁻¹ for x = 2 after CA at 3.25 W cm⁻². The higher coercivity of the Nb-containing alloy samples seems to be due to the presence of a small amount of niobium carbide crystallites. However, significant differences in the magnetic hardening between FA and CA crystallized samples are observed. Comparing the coercivity of FA and CA samples with similar crystalline volume fraction, the coercivity is about one order lower for CA samples.

Dielectric properties of SrBi₂(V_0.1Nb_0.9)₂O₉ (SBVN) were investigated in a broad range of temperatures (400–1000 K) and frequencies (1 Hz to 10 MHz). Strong dielectric relaxation at the ferroelectric transition temperature was observed. The effect of post-sinter annealing on the frequency dispersion of SBVN and the possible mechanisms for the observed dielectric relaxation are presented. Electron paramagnetic resonance and x-ray photoelectron spectroscopy investigations provide direct evidence for the existence of lower valence state of vanadium (V⁴⁺) in SBVN ceramics.

We report on our observation of the formation of permanent holographic gratings induced in nematic liquid crystals doped with carbon nanotubes by the simultaneous action of both a spatially modulated light and dc electric field. Properties of these irreversible gratings were investigated with a normally incident laser beam of linear polarization. The polarization dependence of the diffraction intensity of the probe reveals the anisotropic nature of the permanent index gratings.

The pulsed Townsend technique has been used to measure the electron drift velocity, the density-normalized effective ionization coefficient, the density-normalized longitudinal diffusion coefficient ND_L, and the `characteristic energy' of electrons D_L/K, in CO₂ and its mixtures with SF₆ over a wide range of the density-reduced field strength E/N, from 100 to 700 Td (1 Townsend = 10⁻¹⁷ V cm²). The SF₆ content in the mixture was varied between 2% and 70%. It was observed that for small concentrations (2–5%) of SF₆ in the mixtures, the electron drift velocity is relatively close to that for pure CO₂. A similar behaviour was observed for the longitudinal diffusion coefficients. In contrast, the influence of SF₆ in the mixture is strongly apparent in the values for the effective ionization coefficients. From the latter parameter, the critical field strength E/N_crit for each SF₆ concentration could be derived, and it was found that its value is smaller than that measured for the SF₆–N₂ mixtures.

The known solutions joining plasma and sheath for the situation where both plasma and sheath are collisional (Blank 1968 Phys. Fluids11 1688–98, Benilov and Franklin 2002 J. Plasma Phys.65 163–73) are examined in the context which produces the Bohm criterion as a necessary condition for collisionless sheath formation. The conditions under which even in a collisional situation the ions might exceed the ion sound speed before reaching the wall are examined for both the constant ion collision frequency model and the constant ion mean free path model. It is concluded that under such conditions the ions remain in collisional equilibrium with the electric field and that there is no such thing as a collisionally modified Bohm criterion.

A novel plasma method and its application for destruction of Freons using a moderate-power (several hundred watts) microwave torch discharge (MTD) in atmospheric-pressure flowing nitrogen are presented. The capability of the MTD to decompose Freons is demonstrated using a chlorofluorocarbon CCl₃F (Freon CFC-11) as an example. The gas flow rate and microwave power (2.45 GHz) delivered to the MTD were 1–3 litre min⁻¹ and 200–400 W, respectively. Concentration of the CFC-11 in the nitrogen was up to 50%. The results show that the decomposition efficiency of CFC-11 is up to 100% with the removal rate of several hundred g h⁻¹ and energy efficiency of about 1 kg kWh⁻¹. This impressive performance, superior to that of other methods, is achieved without generating any significant unwanted by-products. As a result of this investigation, a relatively low-cost prototype system for Freon destruction based on a moderate-power MTD and a scrubber is proposed.

Hydrogenation of silicon materials has great advantages for its photovoltaic properties and is the key to elimination of crystalline defects during basaltic growth of the crystal. It is therefore interesting to characterize the plasma by optical emission spectroscopy methods in order to study hydrogenation of silicon particles during their treatment by an inductive thermal plasma burning in the Ar–H₂ mixture.

Excited states of atomic hydrogen n' = 3–8, which are responsible for silicon hydrogenation, have been detected by the optical emission spectroscopy of the Balmer series lines. These hydrogen lines have been used to determine electronic density on the plasma axis. Furthermore, Ar I lines were used to estimate the electronic temperature by the Boltzmann plot method. The deviation from the local thermodynamic equilibrium of the plasma has also been estimated.

The micro-hollow cathode (MHC) discharge is investigated with respect to the application as an excimer radiation source, emitting in the VUV-region around 151 nm. For reasons of efficiency and to minimize the mean electrical power input the discharge was driven in pulsed mode. In order to analyse the VUV-generation in a MHC, especially the temporal behaviour of the absolute metastable state density of xenon (1s₅) in correlation with the VUV-emission was investigated. In the pulsed discharge a remarkable amount of the radiation is emitted during the temporal afterglow. In this case the excitation conditions support the dominance of ionization processes. The dissociative recombination causes a clearly visible reservoir effect. In the MHC, this effect was evidenced by the measured time dependence of densities and VUV-emission. The 1s₅-density was measured to be on the order of 1×10¹⁸–1.1×10¹⁹ m⁻³.

For any elemental peak obtained by the thermally stimulated depolarization current technique, there is a relationship between the activation energy W, the pre-exponential factor τ₀, the temperature of the maximum current T_m and the heating rate b. This relationship can yield useful information concerning the values and the distribution of the relaxation parameters. Numerical simulations, using concrete experimental data obtained for nylon 11, are used to demonstrate the analysis for organic dielectrics. Lower limits for the incertitude intervals of W and τ₀ represent the natural or minimum incertitude intervals expected for an elemental relaxation process. Taking advantage of the fact that the natural incertitude interval in activation energies is ΔW≅kT_m (k is Boltzmann's constant), the natural incertitude interval for τ₀ is deduced as Δτ₀≅τ₀. For example, assuming T_m = 300 K and Δτ₀ = 0, the interval ΔT_m for two resolved neighbour elemental peaks, in other words the interval in which T_m can have values as W varies in the limits on the natural incertitude interval, increases from 7.1 to 11.9 K as W decreases from 1.05 to 0.59 eV. An experimental thermogram can be decomposed into a limited number of elemental peaks having W and τ₀ distributed in the limits of the natural or minimum incertitude intervals (ΔW≅kT_m and Δτ₀≅τ₀). The distribution function for a relaxation parameter cannot be determined unambiguously for the case when the width of the distribution is comparable with the natural standard deviation for the given conditions. Only one parameter or only one distribution must be avoided considering any analysis as variable.

On the basis of a keyhole photograph obtained experimentally, the keyhole profiles are determined by the method of polynomial fitting. Then the behaviour of the laser beam in the keyhole is analysed by tracing a ray of light using geometrical optics theory; the Fresnel absorption and reflections in the keyhole are systematically studied, and the laser intensities absorbed on the keyhole walls are calculated. By comparing the laser intensity absorbed on the keyhole walls with the heat flux lost there, the mechanism of energy balance on the keyhole walls is discussed.

This paper investigates the phenomenon of lubricated impact dynamics of ellipsoidal bodies upon semi-infinite elastic solids, giving rise to Hertzian contact conditions. The analysis conforms to the numerical predictions and experimental findings of others, when the physics of motion of the lubricant can be described through Newtonian continuum mechanics, with the dominant viscous action embodied in the transient solution of Reynolds' equation. The equivalence of squeeze film action under impacting conditions with that of a converging gap in pure entraining motion is shown. This concept is extended to study the accelerative nature of the lubricant film surface, and its concordance with Reynolds' assumption through use of a relativistic frame of reference and hyperbolic geometry.

When the investigation is extended to the case of ultra-thin film conjunctions of the order of a few to several molecular diameters of the intervening fluid layer, the physics of fluid film motion through impact involves more complex kinetic interactions. These include the effect of structural force of solvation, as well as that of a meniscus force, formed in such narrow conjunctions. The former, through active dispersion, tends to promote a structureless environment, whilst the latter through wetting action encourages the formation of a coherent film. This paper shows the interplay between these competing kinetics.