The surface structure of small metal particles is characterized by use of electron microscopy techniques. It is found that the surface has a very extensive roughness which can be described by means of a fractal dimension. We report a new method to measure the fractal dimension by image-processing techniques, and computer measurements. Different values of the fractal dimension are found for gold, platinum, and palladium particles depending on particle preparation and surface treatment. It is found that the fractal dimension of small metallic particles changes after a methanation reaction.

Using magneto-optical methods, we have measured the pressure dependence of the energy difference between subbands in an InAs-GaSb superlattice associated with the GaSb valence and the InAs conduction bands, respectively. The experimental results allow a determination of the pressure dependence of the energy separation between the InAs conduction band and the GaSb valence band which is found to decrease at a rate of 5.8 meV/kbar. This result shows that both the conduction- and the valence-band offsets are pressure dependent. Therefore these experiments constitute a critical test for different theories of band lineup.

The electronic structure of the superatom, a recently proposed mesoscopic system made of a spherical semiconductor heterostructure, is investigated by a self-consistent local-density-functional calculation. Numerical results on AlGaAs-GaAs superatoms reveal that the atomic-orbital picture can be successfully applied and that the ground-state configuration is stable at $T\sim 1$ K. The electronic level structure, however, is quite distinct from that of ordinary atoms because of the absence of the $\frac{1}{r}$ singularity in the potential.

We introduce a well-defined geometrical parameter, $\Lambda$, related to dynamically connected pore sizes in composite materials. $\Lambda$ describes the effects of an internal boundary layer on a variety of processes including electrical surface conduction, high-frequency viscous damping of acoustic waves, and healing length effects in fourth sound. We argue that $\Lambda$ is also related to the dc permeability to flow of a viscous fluid.

We have developed a self-consistent multi-ion screening formalism which, unlike conventional treatments, explicitly accounts for the fact that free electrons cannot screen a given donor in a multi-ion system as effectively as they can screen the same donor in a single-ion system. In uncompensated, metallic Si:P at low temperatures, employment of the "multi-ion" screening length significantly improves the agreement between theoretical and experimental electron mobilities.

Nonresonant Raman scattering from intercalant vibrational modes in graphite intercalation compounds, measured on the $a$ face, is reported here for the first time. The penetration depth of light with polarization $\mathbf{E}\parallel \mathbf{c}$ is enhanced by 2 orders of magnitude compared with the penetration depth of light with $\mathbf{E}\perp \mathbf{c}$. We have observed in stage-1 C-As${\mathrm{F}}_5$ three lines at 683, 698, and 753 ${\mathrm{cm}}^{-1\mathrm{}}$. They are identified as the breathing modes of the intercalant molecules As${\mathrm{F}}_6^{-}$, As${\mathrm{F}}_3$, and As${\mathrm{F}}_5$, respectively.

The transport and thermal properties of heavy-fermion superconductors are explained in terms of (i) an anisotropic order parameter with a line or lines of nodes and (ii) an effective mean free path which, except for the lowest temperatures, is approximately temperature independent and of a similar magnitude as in the normal state. Such a mean free path is shown to arise in a consistent treatment of impurity scattering close to the unitarity limit.

The tunneling current is measured as a function of voltage, lateral position, and vertical separation between a tungsten probe tip and a Si(111)2 × 1 surface. A rich spectrum is obtained in the ratio of differential to total conductivity, revealing the structure of the surface-state bands. The magnitude of the parallel wave vector for certain surface states is determined from the decay length of the tunneling current. Real-space images of the surface states reveal a phase reversal between those states on either side of the surface-state band gap.

Small-angle neutron-scattering experiments were made on bovine serum albumin (BSA)-lithium dodecyl sulfate (LDS) complexes in buffer solutions. As increasing amounts of LDS are added, the scattering data indicate that BSA molecules are successively transformed into random coil conformations with LDS forming globular micelles randomly decorating the polypeptide backbones. A cross-section formula is developed which successfully fits small-angle neutron-scattering spectra over the entire $Q$ range. The fractal dimension, the micellar size, and the extent of the denatured protein are simultaneously extracted.

We have used a double-contrast-variation method in small-angle neutron scattering to study the structure of a single-phase microemulsion containing equal amounts of oil (decane) and water stabilized with an aerosol OT surfactant. It is determined that the water-internal-droplet structure persists in this concentrated regime. We believe that this is the first observation of a nonvanishing mean curvature of the interfacial surfactant film in microemulsions with an oil-water ratio of unity.

A new channel in ortho-para hydrogen conversion is suggested as a tenative interpretation of large experimental reaction rates. This process occurs in two steps, via a virtually excited electronic state. The first step involves an exchange of electrons between the molecule and a nearby magnetic impurity while the second step is due to the hyperfine contact interaction between the virtually excited electronic spin of the molecule and its nuclear spins. This new process turns out to be more effective than the Wigner one if the exchange interaction exceeds a moderate value.

The preferential adsorption sites, bond lengths, and vibration frequencies for H on the Pd (001) surface are determined by use of the ab initio pseudopotential local-orbital method. From the calculated total energies we derive a coverage-dependent absorption energy in very good agreement with experiment. We establish that at low coverages ($\theta \le 1$), H occupies fourfold hollow sites. At higher coverages ($1<\mathrm{}\theta \le 2$), islands of bridge-bonded H (local coverage $\theta =2\mathrm{}$) are predicted to coexist with regions of H in hollow sites.

Fat fractals (sets with fractal structure, but nonzero measure) are becoming increasingly important in the study of nonlinear dynamical systems. Since fat fractals are not well characterized by their (integer) dimensions, several scaling exponents have been proposed to characterize these sets, and there has been some debate over which exponent is best. We shed light on this issue by examining these exponents and finding relationships between them. Finally, these results lead naturally to quantitative definitions of the notions of sensitivity to parameters and final-state sensitivity.

A renormalization-group analysis of a tunneling atom interacting with a degenerate electron gas is presented. We consider both electronic screening and electron-assisted tunneling. In the case where the latter is strong, it is shown that, because of the spin degeneracy, the low-temperature behavior is dominated by the nontrivial fixed point of the multichannel Kondo model.

The essential ideas of Davydov's theory of molecular solitons are used to develop a variation of the Zwanzig-Nakajima projection technique. The projection operator is time dependent and contains the feedback characteristic of the soliton dynamic. The result is a nonlinear equation of motion for a reduced density matrix. A Markoffian approximation is considered which contributes corrections to the Davydov-type evolution. The approximate equation of motion embodies the correct fluctuation-dissipation relation for this system and recovers the known exact results in the transportless limit.

The experimentally verified relationship $M_W=M_Z{cos\theta }_W$ implies universal low-energy theorems for scattering of longitudinally polarized $W$ and $Z$ bosons provided that the symmetry-breaking sector contains no particles much lighter than 1 TeV.

We calculate the contribution to the muon anomaly induced by new Yukawa couplings involving heavy-matter $E_6$ fields predicted in the framework of superstring theories. We analyze a few models found in the current literature and show that for some of them the effect is on the order of the standard weak contribution. We produce a specific example where the effect could be even larger. Thus, we conclude that an improved ${\mathrm{}(g-2\mathrm{})\mathrm{}}_{\mu }$ experiment should be sensitive to such effects, if they happen to exist.

We have computed the complete set of amplitudes for fermion + fermion into fermion + fermion $+W^{+}+W^{-}$ for all possible fermion types. We use these results to analyze the phenomenology of the $\mathrm{WW}$ scattering sector and to compare to the effective $W$ approximation.

Top-quark $t$ production via $e^{-}{e}^{+}\to \mathrm{tt}$ with one of $t$,$t$ decaying semileptonically and the other decaying into jets is considered for possible observation at the Stanford Linear Collider and the CERN colliders LEP I and II. It is shown that, with proper procedures involving a series of acceptance cuts, $t$ quarks with masses $m_t\lesssim 70$ GeV can be identified, the higher masses ($50\lesssim m_t\lesssim 70$ GeV) being accessible only at LEP II.

The analyzing power in neutron-proton scattering at 25 MeV neutron energy has been measured to an accuracy of typically ± 0.002 for c.m. scattering angles between 50° and 165°. Contrary to the conclusions reached from earlier precision measurements at 16.9 MeV, the contributions to partial waves with $l\ge 3$ are consistent with predictions based on one-pion exchange. The new data are well described by the Paris potential and by a recent global phase-shift analysis.