The upper critical field of superconducting polysulfur nitride, (SN)x

A measurement of the temperature and angular dependence of the upper critical magnetic field H_c² in crystals of polymeric (SN)_x is reported. A large anisotropy is observed at all temperatures with H_c²6 = 8.1 ± 0.4 kOe parallel to, and H_c²⊥ = 870 ± 80 Oe perpendicular to, the polymer axis at 0°K. The results are explained in terms of the polymeric crystal structure and fibrous morphology of (SN)_x.     

Hydrogen diffusion and electronic metastability in amorphous silicon

Hydrogen diffusion and its role in the many electronic metastability phenomena in hydrogenated amorphous silicon (a-Si:H) is reviewed. A-Si:H contains about 10 at% hydrogen, most of which is bonded to silicon. The hydrogen diffuses at relatively low temperatures by releasing hydrogen from the Si-H bonds into interstitial sites. The reactions of hydrogen with the silicon dangling bonds and the weak bonds provide a hydrogen-mediated mechanism for electron-structural interactions, which are manifested as electronic metastability. The annealing of light-induced defects, the equilibration of defects and dopants, the stretched exponential relaxation kinetics, and the atomic structure formed during growth, are all attributed to hydrogen diffusion.     

On the sensitivity of transient photodecay measurements as a probe of localised state distributions in amorphous semiconductors

An investigation is reported of the extent to which structure in the density of localised states in amorphous semiconductor films may be detected from photodecay measurements. Transient photocurrents are computed by a Monte Carlo technique, for the case of an exponential tail of states upon which a sharp rectangular feature has been superimposed. It is shown that a ‘rectangular’ component of energy width kT must protrude from the background exponential tail by at least a factor of 5 in density, in order to exert a readily-detectable influence upon the transient photodecay. It is further demonstrated that the presence of deep-lying features in the distribution of localised states may easily modify the transient decay over a wide range of time; underlining the difficulty of interpreting such data.     

Three-dimensional unsteady flow simulations: Alternative strategies for a volume-averaged calculation

This work builds on a SIMPLE-type code to produce two numerical codes of greatly improved speed and accuracy for solution of the Navier–Stokes equations. Both implicit and explicit codes employ an improved QUICK (quadratic upstream interpolation for convective kinematics) scheme to finite difference convective terms for non-uniform grids. The PRIME (update pressure implicit, momentum explicit) algorithm is used as the computational procedure for the implicit code. Use of both the ICCG (incomplete Cholesky decomposition, conjugate gradient) method and the MG (multigrid) technique to enhance solution execution speed is illustrated. While the implicit code is first-order in time, the explicit is second-order accurate. Two- and three-dimensional forced convection and sidewall-heated natural convection flows in a cavity are chosen as test cases. Predictions with the new schemes show substantial computational savings and very good agreement when compared to previous simulations and experimental data.     

Overlarge sets and partial geometries

We extend our earlier work on overlarge sets of Fano planes, obtaining three results of particular interest. We find seven new partial geometries pg(8,7,4) and nine new strongly regular graphs, by means of switching cliques of points with spreads of lines. One of these new strongly regular graphs supports four different partial geometries. Then we give a new construction of the recently discovered eightfold cover of the complete graph K₁₆.Supported by NSERC grant OGP0008651Supported by ARC grant A49130102 and an Australian Senior Research Fellowship     

Bicategories of spans and relations

A new kind of bicategorical limit is used to characterize bicategories of the form Spant($\text{E}$) and Rel($\text{E}$) where in the former case $\text{E}$ is a category with pullbacks and in the latter $\text{E}$ is a regular category. The characterization of Rel($\text{E}$) differs from those in the literature which require involutions on the bicategories.