We resolve the mean square displacement of particles in concentrated suspensions during the first 20 ns of their motion, before hydrodynamic interactions between particles have had time to fully develop. Nevertheless, we find that the concentrated systems exhibit clear deviations from the isolated-particle theory. These deviations are well described by several scaled versions of the isolated particle theory. The measurements also demonstrate a new multiple-scattering photon correlation technique with ultrashort time resolution.

A model Hamiltonian describing an energy-exhange process between an ultrarelativistic particle and a one-dimensional spin array is proposed and solved exactly. Interesting relations with the quantum measurement problem are discussed.

We examine the possible influence of semiclassical effects on the structure of spacetime in the vicintiy of a black-hole Cauchy horizon. While the classical picture is that of a weak mass-inflation singularity (a null singularity characterized by the unbounded increase of the black-hole internal mass function), we suggest that quantum effects may produce either (i) a stronger, spacelike singularity, or (ii) a regular spacetime, in the sense that curvature would nowhere increase beyond Planckian.

A new precision measurement of the branching ratio of the rare pion decay into a positron and a neutrino (π→eν) has been completed. A beam of positive pions was stopped in an active target of plastic scintillator surrounded by a 4π BGO calorimeter. 3×${10}^5$ rare decays and 1.2×${10}^6$ normal pion decays (π→μν) were recorded. The branching ratio was finally calculated from 1.2×${10}^5$ rare decays after various cuts in the time window from 7.5 to 200 ns after pion stop. The errors of the result (1.235±0.005)×${10}^{\mathrm{-}4}$ are 0.28% statistical and 0.29% systematical.

A combination of the maximum hardness (MH) principle, and the local version of the hard and soft acids and bases (HSAB) principle is tested as a tool to describe the stability and reactivity of polyatomic systems. The local HSAB principle describes regional differences in reactivity whereas the MH principle selects the most stable configuration. This approach is tested using ab initio density functional theory techniques. Total-energy calculations fully confirm the validity of both principles.

We report electron energy spectra from ${\mathrm{He}}^{++}$ (100 eV) ions colliding under grazing incidence with partially cesiated W(110). We propose that at low surface work functions (≤2 eV) the formation of Feshbach resonances associated with the doubly excited He states of the configuration (2l2l’) occurs. This is concluded from the variation of the relative population of the doubly excited He states with the surface work function. Furthermore, a peak can be identified in the spectra which appears to be due to the decay of the Feshbach resonances by one-electron emission.

Total-energy and electronic-structure calculations are presented for a recently proposed dodecahedral cluster of eight titanium and twelve carbon atoms. The calculations were done using density-functional theory and a recently developed cluster full-potential linear muffin-tin orbital method which is suited to arbitrary geometries and permits direct evaluation of the forces. As in the ${\mathrm{C}}_{60}$ molecule, the atoms form a spherical grahitelike shell with a threefold coordination at all sites. The C-C and Ti-C bond lenghts are calculated to be of 2.63 and 3.76 bohrs, respectively, and the binding energy is 6.6 eV per atom. The bonding mechanism is quite different from that which stabilizes the graphite crystal or the ${\mathrm{C}}_{60}$ molecule.

The ionization of hydrogen atoms by a microwave field is numerically studied, for the first time in a realistic picture, using a fully three-dimensional quantum approach with complete inclusion of the continuum. This provides first evidence for the persistence of dynamical localization in higher-dimensional systems. Comparison to the one-dimensional dynamics as well as to experimental results is given.

High-gradient acceleration of externally injected 2.1-MeV electrons by a laser beat wave driven relativistic plasma wave has been demonstrated for the first time. Electrons with energies up to the detection limit of 9.1 MeV were detected when such a plasma wave was resonantly excited using a two-frequency laser. This implies a gradient of 0.7 GeV/m, corresponding to a plasma-wave amplitude of more than 8%. The electron signal was below detection threshold without injection or when the laser was operated on a single frequency.

Observations of individual iridium atoms diffusing over Ir(111) planes with an iridium cluster at the center reveal an empty zone, ∼3 nearest-neighbor spacings wide, around the cluster. In this zone adatoms are never seen. Quantitative studies of the probability of atom incorporation at the cluster, compared to the probability of being trapped at the plane edge, suggest that the empty zone comes about because in the vicinity of the cluster, diffusion toward an ascending step is much more rapid than on a flat terrace, so that adatoms are funneled to the cluster.

Ion-beam-induced crystallization in silicon preamorphized by Ge-ion implantation was studied by combined means of Rutherford backscattering and channeling, and positron annihilation. The epitaxial regrowth of amorphous surface layers in a 〈100〉 Si substrate has been studied with irradiation of 400-keV ${\mathrm{Ar}}^{+}$ ions at the temperature of 400 °C. The ion-beam-induced epitaxy was found to result in a drastic increase in the positron lifetime to a maximum value of 400 psec in the recrystallized silicon layer. It is demonstrated that vacancy migration is promoted during the epitaxial recrystallization to form defect complexes like trivacancies and/or quadrivacancies.

We show by an exact renormalization-group approach that a random two-chain interaction for (d+1)-dimensional directed polymers is marginally relevant at d=1. There is a critical point for d>1 separating the weak and strong disorder phases, and the length scale exponent is ν=[2(d-1)${]}^{\mathrm{-}1}$ for d>1. For the mth-order multicritical case involving random m-chain interactions, the disorder is marginally relevant at ${\mathit{d}}_{\mathit{m}}$=1/(m-1). Here also the disorder induces a critical point for d>${\mathit{d}}_{\mathit{m}}$, with an exponent ${\nu }_{\mathit{m}}$=[2d(m-1)-2${]}^{\mathrm{-}1}$. An essential singularity occurs for the length scale right at d=${\mathit{d}}_{\mathit{m}}$.

We propose a systematic perturbative method for calculating the binding energy of threshold bound states—states which exist for arbitrary small coupling. The starting point is a (regularized) free theory. Explicit calculations are performed for quantum mechanics with arbitrary short-range potential in 1D and various (1+1)-dimensional quantum field theories. We check the method by comparing the results with exact formulas available in solvable models.

Here we demonstrate that the phase separation of a binary mixture confined in a capillary is strongly affected by wetting phenomena for all the compositions. Near a symmetric composition, the hydrodynamics unique to a bicontinuous pattern leads to the extremely quick formation of a macroscopic wetting layer. Then this layer configuration becomes unstable because of the Rayleigh-like instability and eventually a stable, bamboolike structure is found. This final structure is determined kinetically, but not thermodynamically. This is characteristic of a one-dimensional system with a conserved order parameter.

We describe a straightforward method for obtaining a precise value for the fractal dimension (self-affine scaling exponent) of a surface, via scanning tunneling microscopy. It is applied to investigate ion-beam erosion of an iron film surface, provoding strong support for the applicability of scaling theory to submicron erosion processes. A self-affine surface with scaling exponent H=0.53±0.02 is observed to develop.

The charge- or spin-density-wave formation in one-dimensional electron systems under an incommensurate potential is shown to be characterized by infinitely many order parameters and infinitely many mean-field solutions with almost degenerate energies. The complexity of the solutions is described by ultrametricity. The observed field-induced spin-density-wave transition of 2D systems is discussed in this context.

We derive the Landau-Büttiker formula for admittance from the linear response theory. The result is applied to a system which displays a resonance, and it is shown that the admittance has an inductive component proportional to the lifetime of the resonance.

The evolution of the Coulomb blockade of conduction through a small 2D electron island of large density of states, realized in a GaAs/Ga(Al)As heterojunction, is studied from the weak tunnel coupling to the Ohmic regime. Cotunneling arising from quantum charge fluctuations is identified, at low voltage, by its dependence on the product of junction conductances, and the current at threshold voltage is well described by a nonperturbative model. Small Coulomb conductance oscillations are found to persist even when both junctions exceed the conductance quantum.

We consider a model of strongly correlated electrons that exhibits superconductivity. It differs from the Hubbard model by nearest-neighbor interactions. We find the ground-state wave function (in one, two, or three dimensions) and show it to be superconducting for attractive and moderately repulsive on-site interaction.

An analytic expression for the polarized neutron reflectivity ${\mathit{R}}^{\pm }$(θ,λ) from a superconductor with penetration depth λ is derived as an exact solution of the 1D Schrödinger equation in the continuum limit. The down-spin solution ${\mathit{R}}^{\mathrm{-}}$(θ,λ) reveals a surprising oscillatory dependence on λ within a narrow angular range immediately above the total reflection angle, and in fact vanishes when λ and H satisfy certain conditions. This exact solution is applicable to other scattering problems with a general exponential dependence in the potential.