Percolation through voids around toroidal inclusions.

In the case of media comprised of impermeable particles, fluid flows through voids around impenetrable grains. For sufficiently low concentrations of the latter, spaces around grains join to allow transport on macroscopic scales, whereas greater impenetrable inclusion densities disrupt void networks and block macroscopic fluid flow. A critical grain concentration ρ_{c} marks the percolation transition or phase boundary separating these two regimes.

Percolation through Voids around Randomly Oriented Polyhedra and Axially Symmetric Grains.

Porous materials made up of impermeable grains constrain fluid flow to voids around the impenetrable inclusions. A percolation transition marks the boundary between densities of grains permitting bulk transport and concentrations blocking traversal on macroscopic scales. With dynamical infiltration of void spaces using virtual tracer particles, we treat inclusion geometries exactly.

Percolation through voids around overlapping spheres: a dynamically based finite-size scaling analysis.

The percolation threshold for flow or conduction through voids surrounding randomly placed spheres is calculated. With large-scale Monte Carlo simulations, we give a rigorous continuum treatment to the geometry of the impenetrable spheres and the spaces between them. To properly exploit finite-size scaling, we examine multiple systems of differing sizes, with suitable averaging over disorder, and extrapolate to the thermodynamic limit.

Phase diagram of the disordered RKKY model in dilute magnetic semiconductors.

We consider ferromagnetism in spatially randomly located magnetic moments, as in a diluted magnetic semiconductor, coupled via the carrier-mediated indirect exchange RKKY interaction. We obtain, via Monte Carlo calculations, the magnetic phase diagram as a function of the impurity moment density n(i) and the relative carrier concentration n(c)/n(i). As evidenced by the diverging correlation length and magnetic susceptibility, the boundary between ferromagnetic and nonferromagnetic phases constitutes a line of zero temperature critical points which can be viewed as a magnetic percolation transition.

Quasi-two-dimensional diluted magnetic semiconductor systems.

We develop a theory for two-dimensional diluted magnetic semiconductor systems (e.g., Ga(1-x)Mn(x)As layers) where the itinerant carriers mediating the ferromagnetic interaction between the impurity local moments, as well as the local moments themselves, are confined in a two-dimensional layer.

Vortex states of a superconducting film from a magnetic dot array.

Using Ginzburg-Landau theory, we find novel configurations of vortices in superconducting thin films subject to the magnetic field of a magnetic dot array, with dipole moments oriented perpendicular to the film. Sufficiently strong magnets cause the formation of vortex-antivortex pairs. In most cases, the vortices are confined to dot regions, while the antivortices can form a rich variety of lattice states.

Disordered RKKY lattice mean field theory for ferromagnetism in diluted magnetic semiconductors.

We develop a lattice mean field theory for ferromagnetic ordering in diluted magnetic semiconductors by taking into account the spatial fluctuations associated with random disorder in the magnetic impurity locations and the finite mean free path associated with low carrier mobilities. Assuming a carrier-mediated indirect RKKY exchange interaction among the magnetic impurities, we find substantial deviation from the extensively used continuum Zener model Weiss mean field predictions. Our theory allows accurate analytic predictions for Tc and provides simple explanations for a number of observed anomalies, including the non-Brillouin function magnetization curves, the suppressed low-temperature magnetization saturation, and the dependence of Tc on conductivity.

The acceptance of a vitreous carbon alloplastic material, Proplast, in the rabbit eye.

Proplast, a vitreous, carbon-Teflon, fluorocarbon polymer, was tested in rabbits for corneal tolerance and acceptance. Toxicity, vascularization, epithelialization, infection, and extrusion were studied clinically and histologically. Four techniques were used: implantation of irregular-shaped pieces of material in an interlamellar corneal pocket, lamellar graft implantation with one exposed surface, full-thickness corneal implants in a manner similar to penetrating keratoplasty, and full-thickness implants covered by a conjunctival flap.