Table of contents

A general review of conventional magnetic shielding is presented. Several possible definitions of the term 'shielding factor' are given, taking into account the ferromagnetic nature of shielding materials. An alternative treatment of single-layer axial shielding for a cylindrical shield is presented and compared to a previous approximation. A new algorithm for calculating multi-layer axial shielding factors is derived and shown to be an improvement on existing methods when applied to some assemblies, including one reported for the first time.

A directional-total emissometer is described and shown to be capable of yielding directional-total emittances with good accuracies. Such data are presented on glass, aluminium, copper, brass, Nextel-2010 black velvet paint, Solarcoat-50, Maxorb, Cusorb, Skysorb and Solarcoat-100. The results are, on the whole, in good agreement with theory and with earlier experimental work, except for some earlier experimental work on Maxorb and Skysorb, for which materials the data are closer to theoretical expectations.

The authors report the results of a measurement of the Rayleigh scattering cross section of methane, nitrogen and carbon dioxide using a pulsed laser beam. In a similar study Skowronek and Alayli (1979) reported a variation in the cross section with the duration of the laser pulse. In this work the authors have been unable to reproduce Skowronek and Alayli's result and conclude that there is no effect due to the pulse duration. Their measurements agree with the classical cross section within the experimental error (+or-10% to 15%).

The magnetostatic field of a distributed current in a conductor of three-dimensional extent is usually calculated by integration of the Biot-Savart law over the volume of the conductor. It is shown that in the case of constant conductivity, two different formulae exist, which replace the volume integral by a surface integral. The first needs only the electric potential at the surface of the conductor; the computation of the current density is avoided. The second formula needs only the current density at the surface. The theoretical method has been applied to the technical problem of computing the magnetic blast field of switching contacts, which is responsible for arc motion and the dynamic behaviour of low-voltage switches.

An analysis of the strip dielectric waveguide is presented using a plane-wave-spectrum approach. The modes in the guide are viewed as superpositions of plane waves undergoing multiple reflections at the walls of the guides. The modal fields are evaluated at the residues of the integrand, which is a function of the transverse wavenumbers of the plane waves in the dielectric medium of the guide.

The authors present results on how the optical properties of Langmuir-Blodgett (LB) films vary with wavelength. Multi-layers of the LB material 22-tricosenoic acid were formed into waveguides, thus allowing determinations of their dielectric tensor and thickness. They have been able to separate out bulk and surface terms from the attenuation of the various guided modes and thus obtain information on the surface roughness of the LB films concerned. Further, they have shown that films made on aluminium substrates show considerably less loss than those on silver.

Thermal anomalies in the activation energy of the viscous flow for some liquids and solutions have been reported in the literature. Qurashi and Ahsanullah (1961) have claimed that the activation energy of the viscous flow versus temperature curve for water has periodic discontinuities. Their claim is based on the assumed accuracy of their measurements. A critical examination of their data shows that the extrapolation of their differential Beckman thermometer readings from one region of temperature to the other is untenable and therefore the conclusions of Qurashi and Ahsanullah are based on erroneous experimental results.

Measurements of secondary-electron-emission (SEE) yield are reported for samples of clean 5890 PT graphite and for the same material exposed for some months in the JET Tokamak. The samples exposed in the JET Tokamak give substantially higher values than the clean samples. Controlled experiments show that both implantation with H₂⁺ ions and deposition of thin metal films increase the SEE yield. The experimental data have been integrated over a 3D Maxwellian distribution to obtain the values of effective SEE yield expected from a plasma as a function of electron temperature. From these SEE yields, theoretical values of sheath potential and sheath energy transmission factor have been calculated. The implications for ion sputtering and power loss are discussed.

The dislocation image force due to the free surface of a finite width specimen makes the plastic zone at a crack tip larger. The effect of the dislocation image force on the fracture behaviour of materials with different geometrical shapes is discussed. It is found that the ratio V/A as an indication of the brittle behaviour of structural components is reasonable for elastic-plastic fracture.

Concentration-depth profiles of Ag in Si have been measured with the aid of neutron activation analysis combined with serial removal of sections. The Ag diffusion appears to be very fast. In the bulk of dislocation-free Si wafers saturation is achieved after short periods of annealing. From this the authors conclude that interstitial Ag_i is the predominant configuration in Si without dislocations. Equilibrium concentrations of Ag_i are determined for temperatures between 1287 and 1598 K. The results are thermodynamically analysed, taking into account Ag-Si liquidus data. In dislocated Si much higher Ag concentrations are observed, which vary irregularly with the penetration depth. A comparison of the diffusion and solubility of Ag and Au in Si suggests that in Si with dislocations substitutional Ag_s may arise from Ag_i-Ag_s transitions. Finally an estimate of the Ag_i diffusivity is obtained.

An analysis has been made of Angstrom's method for the measurement of the thermal diffusivity of solids when the length of the sample is short and when the end remote from the periodic heat source is thermally isolated. The results of the analysis have been applied to experimental data obtained from a short specimen of Bi_0.5Sb_1.5Te₃.

Recent experiments on high-quality all-refractory Nb-Al₂O₃-Nb SIS tunnel junctions are reported. The authors have developed a highly reliable device processing route which has allowed the separate influences of the original whole-water deposition conditions and subsequent processing on the junction characteristics to be investigated. Results from several hundred devices, whose sizes vary between 4 and 250 mu m², are presented. The post-processing has not been found to affect device characteristics significantly, but the conditions under which the whole-wafer deposition is performed have a strong effect on both the barrier resistance and the device quality. They report the first evidence that the normal-state resistance and critical current of junctions made under identical oxidation conditions are strongly affected by the temperature at which the base layer of niobium is deposited. Devices have been made with critical current densities greater than 1*10⁷ A m^-2 and V_m values in excess of 50 mV. Differences in the resistances of separate devices on the same slide are evidence of statistical variations in the barrier itself.

The dielectric behaviour of bound water in compressed casein pellets has been studied using the thermally stimulated depolarisation currents method over the temperature range from 77 to 300 K and the hydration range from 1 to 24% w/w. Two distinct relaxation regions are obtained: one in the range of T from 100 to 170 K attributed to the reorientation of loosely bound water molecules, and a second one in the range 190-290 K interpreted mainly in terms of water-assisted relaxation of the protein polar groups. The fact that both relaxations are very markedly influenced by the presence of water for hydration contents, h, higher than 9%, strongly suggests that all water molecules sorbed up to this value are irrotationally bound to the protein macromolecules. Comparison with results obtained by other investigators by a variety of methods, as well as calculation of the primary sorption sites at the molecular level, give further support to the above interpretation.

Using the thermal current analysis (TCA) technique, pyroelectric and relaxation currents have been simultaneously measured in a number of commercial corona-poled PVdF films, over the temperature range 0-120 degrees C. A relaxation peak observed at approximately=55 degrees C is attributed to space charge residing at the crystal/amorphous boundaries of beta -crystallites, resulting in partial dipole cancellation. Annealing films at 60 degrees C removes these charges and produces an enhancement of about 10% in pyroelectricity (measured at 25 degrees C), which subsequently decays with a time constant of about 2 h at room temperature. A second relaxation peak is observed at about 80 degrees C and, although its origin is undetermined, pyroelectric measurements suggest that the underlying mechanism may also be responsible for about 10% of the pyroelectric activity possessed by a new sample.

At low Mn concentrations the optical absorption spectra of irradiated CaF₂:Mn may be strongly influenced by the presence of trace rare-earth (RE) impurities. The RE absorption centres are predominantly due to divalent RE ions, either isolated or associated with NN F centres, known as photochromic (PC) centres, and ionised PC centres (i.e. an RE²⁺ ion with a NN anion vacancy). Some of these centres have a low thermal stability and anneal between room temperature and 200 degrees C. During the annealing of the centres noted above, it is observed that the Mn-related absorption peaks increase in intensity. After this increase, the spectrum is then characteristic of Mn-doped crystals. The temperatures over which the Mn-related absorption features disappear increase as the Mn content increases. During this anneal, intense thermoluminescence (TL) is observed. Accordingly, the temperature at which the TL is observed to be most intense shifts to higher values as the Mn content is raised. In samples intentionally doped with Ce (in addition to Mn) the authors find that the Ce 'quenches' very effectively the Mn-related absorption. If the Ce content is high enough, only Ce-related features can be seen in the absorption spectrum. The TL too is dominated by the Ce defects. They conclude that both the sensitivity and the thermal stability of the TL from CaF₂:Mn are significantly affected by the presence of trace quantities (at the 10 p.p.m. level) of rare-earth ions. These data may be relevant to reported batch-to-batch irregularities in the TL properties of this material.

The forces exerted by the gas jet on the molten layer in laser cutting are investigated theoretically by solving the equations of motion of the gas flow. The pressure distribution along the cutting front is found by the method of conformal mapping, while frictional forces are obtained from boundary layer theory. Both the pressure gradient and the frictional force are of the same importance for the melt ejection. For both contributions, simple scaling laws are presented. The cooling rate of the melt due to the gas stream is shown to be negligible.

The treatment of Simons (1987) concerning the effect of particle coagulation on steady-state Brownian diffusion in a fluid, is extended to cover the case of particles with a fractal structure. It is shown that if a particular dimensionless parameter E lies within certain limits then the spatial variation of phi , the volume fraction of particulate material, exhibits a maximum, while if E exceeds the upper limit no steady state can be set up. It is suggested that measurements of phi could be used for the experimental determination of the fractal dimensionality of coagulating clusters.

A method of real-zero conversion is presented in which the amplitude of the oscillation used to convert complex to real zeros is weighted by the signal amplitude. The resulting signal phase is compared with the usual real-zero-converted phase, and the original signal phase. The weighted method of real-zero conversion is shown to be useful for the detection of variations in signal amplitude, and is of interest for the analysis of scattered fields in coherent images such as occur is seismics, synthetic-aperture radar and ultrasonics.

The Townsend first ionisation coefficient alpha and the electron attachment coefficient eta were measured in CCl₂F₂/SF₆ gas mixtures using the steady-state Townsend method over the range 90<or=E/p<or=130 V cm^-1 Torr^-1. The effective ionisation coefficient alpha of CCl₂F₂/SF₆ exhibited a minimum around the mixture ratio of 50/50 indicating strong eta synergism ( eta =- alpha ) in the gas mixture. The limiting E/p values derived from the pre-breakdown ionisation current measurements in CCL₂F₂/SF₆ mixtures were in agreement with the results of static breakdown experiments reported by previous investigators. However, contrary to the Boltzmann equation analysis by Okabe and co-workers (1985), the present study shows that the synergism is caused mainly by the change in alpha /p resulting from gas mixing rather than the change in eta /p.

Considers a MHD generator with liquid zinc. The main interest is that zinc is currently produced by condensation of its vapour so a MHD power plant could use just the same technology as a zinc production unit. Shock wave condensation is discussed in detail but a biphasic subsonic flow is also possible.

Optical lithography of semiconductor microcircuits relies upon the use of chromium-on-glass masks or reticles. Opaque defects in the mask pattern due to excess of chromium can be repaired by the use of focused ion beams and commercial mask repair systems are now available. During the repair process, ions are implanted into the glass substrate of the mask, giving rise to a stain when the mask is inspected or used for lithography.

Phase velocities and power distributions are calculated for surface acoustic waves (SAW) propagating on various kinds of layered structures. It is found that the SAW power existing in the overgrowth becomes large in the case of a large velocity dispersion, and it monotonically increases with increasing overgrowth thickness for most of the layered structures. However, the power first increases, then decreases, for the a-Si:H/(128 degrees rot. Y-X)LiNbO₃ structure. The reason is discussed in relation to the SAW velocity dispersion.

CuInTe₂ films have been deposited on a titanium substrate from acidic as well as from alkaline baths. The as-deposited films were uniform and adhered well to the substrate. Structural and compositional studies showed that the as-deposited films were amorphous or consisted of fine grains and were stoichiometric in composition.

A dispersion equation is derived for flute modes with frequencies between the electron and ion bounce frequencies in a plasma confined to a magnetic quadrupole. Two intermediate-frequency flute modes, which propagate in opposite directions along the quadrupole axis are predicted for the UMIST quadrupole. The possible excitation of a flute mode by self-interaction of a drift mode is considered.