Fractal aggregates are considered computationally using off-lattice cluster-cluster aggregation models. The aggregates are made of spherical particles of different sizes distributed according to a Gaussian-like distribution characterized by a mean a0 and a standard deviation sigma. The wave-vector-dependent scattered intensity I(q) is computed in order to study the influence of the particle polydispersity on the crossover between the fractal regime and the Porod regime. It is shown that, given a0, the location q(c) of the crossover decreases as sigma increases. The dependence of q(c) on sigma can be understood from the evolution of the shape of the center-to-center interparticle-distance distribution function.

Existing theories of the oscillatory exchange coupling in magnetic metallic multilayers are reconciled within a common approach. It is shown that Ruderman-Kittel-Kasuya-Yosida-type theories and full-confinement quantum-well results are obtained as limiting cases. Numerically useful and model-independent closed-form expressions for the exchange coupling across a nonmagnetic spacer are obtained in terms of the one-electron propagators. The theory can be extended to deal with nonmagnetic alloy spacers and it is argued that the existence of disorder in the spacer may lead to significant reduction of the interlayer coupling.

We present results from low-angle neutron and x-ray scattering experiments on hydrogen and deuterium loaded (001)-oriented single-crystal Mo/V superlattices. The individual Mo and V layer thicknesses in the samples were determined by simulations of the x-ray reflectivity curves. The intensity of the first-order neutron-diffraction peak for the hydrogenated sample is 31% larger than from the dehydrogenated sample. When deuterated, the intensity of the first-order peak is extremely small, only 0.5% of the dedeuterated sample. The distribution of hydrogen in the layers was derived by simulations of the neutron and the x-ray diffraction patterns. The results unambiguously demonstrate that the hydrogen isotopes are exclusively located in the V layers, but at the interfaces there is a region with reduced hydrogen concentration.

We study the response of the interacting electron gas in one-dimension (1D) to a local external potential. In the low-frequency limit the power-law singularities are essentially modified by backscattering effects which, in the case of zero forward scattering, result in the universal critical exponent depending only on the Luttinger-liquid interactions. The results obtained may be used to describe singular responses of the 1D boson chains.

We show that the well-known 0.15-eV donor in bulk GaAs quenches under IR-light illumination and that the quenched (metastable) state has an electronic transition energy about 0.14 eV deeper than the ground state and can be observed by temperature-dependent-resistivity and Hall-effect measurements. The quenched state thermally recovers by an Auger-like process at a rate of r = 2.3X10(-12) nv(n) exp(-0.18/kT). Many of the properties exhibited by this donor are similar to those predicted theoretically for the complex defect As(Ga)-V(As).