Using first-principles self-consistent total-energy calculations for unconstrained and epitaxially confined models of Si-C and Si-Ge alloys we study the general classes of stability of ordered phases of semiconductor alloys. The unusual ordering observed in SiGe grown on a Si substrate is explained.

The equilibrium behavior of a system of randomly distributed classical Heisenberg spins coupled via the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction is studied by Monte Carlo simulations. Finite-size scaling analysis of the results strongly indicates a zero-temperature critical point with the correlation length exponent $\nu =0.87\mathrm{}\pm 0.08$. This conclusion is supported by the observed temperature and sample-size dependence of various relaxation times.

A saturation surface photovoltage is found to occur during ultraviolet photoemission at low temperatures ($T\sim 20$ K) on a variety of silicon (111) surfaces. Below ∼ 50 K surface recombination becomes ineffective thereby allowing flat-band conditions to be achieved with mild uv irradiation. Temperature-dependent photoemission thereby provides a simple and direct method for determining band bending and barrier heights. Results for different silicon (111) surfaces and preparation conditions are discussed.

We propose an explanation of the large sound-attenuation peak observed at the lower transition, $T_{c2\mathrm{}}$, in superconducting ${\mathrm{U}}_{1-x}{\mathrm{Th}}_x{\mathrm{Be}}_{13}$. It assumes that the transition is between two different anisotropic superconducting phases, and that the low-temperature phase is tetragonally distorted. The domain-wall energy is very small at $T_{c2\mathrm{}}$ and the attenuation due to the motion of walls is very large. This attenuation depends strongly on direction and polarization, and so the model may be easily tested. The implications for the phase diagram of these alloys are discussed.

We discuss the question of superconductivity and localization in systems with strong spin-orbit scattering. It is argued that most materials in three dimensions undergo superconductor-metal-insulator transitions with increasing disorder. In thin films, only superconductor-insulator transitions occur. In high-$T_c^{\prime }$ three-dimensional materials and thin films, it is possible to have insulating behavior at high temperature and superconducting behavior at low $T$.

Electronic structure calculations based on density-functional theory and the Korringa-Kohn-Rostoker Green's-function method yield a consistent picture of the behavior of local moments of $3d$ impurities in Pd. The calculated local impurity moments are in good agreement with experiments. The giant moments arise from rather extended polarization clouds consisting of very small induced host moments.

We treat the perihelion shift of the planetary motion and the Lamb shift in hydrogen in an arbitrary number of space dimensions. Comparison with experimental data shows that the deviation from dimensionality four of space-time is less than ${10}^{-9\mathrm{}}$ and 3.6 × ${10}^{-11\mathrm{}}$, respectively, on the length scales associated with these phenomena.

Lattice-gauge-theory evaluation of the spin-orbit potentials between heavy quarks yields a longrange component associated with a Lorentz-scalar confining mechanism and a short-range vector component associated with one-gluon exchange.

We have observed decays of the $\Upsilon \mathrm{}\left(1S\right)\mathrm{}$ into hadronic final states containing high-energy photons. These are interpreted as coming from the decay $\Upsilon \mathrm{}\left(1S\right)\mathrm{}\to \gamma +\mathrm{gluon}+\mathrm{gluon}$. We compare the shape of the observed photon energy spectrum with several theoretical predictions and deduce the value of the strong-coupling constant ${\alpha }_s$ and the QCD scale parameter ${\Lambda }_{\overline{\mathrm{MS}}}$ ($\overline{\mathrm{MS}}$ denotes the modified minimal-subtraction scheme) associated with each prediction.

The observed absence of monopole tracks in large, ancient mica crystals enables us to set an upper limit of less than ∼ ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$ on the flux of supermassive monopoles with $0.0004c<V<\mathrm{}0.0015c$ that are stably attached to nuclei. This limit takes into account the fraction of monopoles not initially bound to protons, the fraction that attach with nuclei on their way to the mica, and the measured storage times for tracks with thermal stability similar to that of monopole tracks.

The spontaneous breaking of chiral symmetry in certain gauge models may also imply the spontaneous breaking of an approximate scale symmetry. This breaking will produce the dilaton as a pseudo-Goldstone boson of spontaneously broken scale invariance.

The mean square spin value of the compound nucleus ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cf}$ has been determined from fissionfragment angular distributions for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ reactions. The anisotropy and, hence, the mean square spin values are much larger than expected. Models which reproduce the enhancement observed in the sub-barrier fusion excitation functions fail to account for the spin-distribution observations.

Within the framework of the relativistic Dirac-Brueckner approach, the equation of state of nuclear matter is studied on the basis of a one-boson-exchange interaction. The saturation properties of the ground state and its compressional energy are calculated. The model is extended to nonzero temperature by use of finite-temperature Green's functions for the dressed nucleons. Isotherms in a $P-\rho$ diagram are obtained which show the existence of a liquid-vapor phase equilibrium below a critical temperature of $T_c\simeq 12$ MeV.

Multielectron ionization of Xe is described in terms of multistep processes, driven by a laser field which is screened by the motion of the outer $5p$ shell. In stepwise multiple ionization of the $5p$ shell, screening is successively reduced. The effective, local intensity will therefore increase during the stripping of the outer shell. In the $4d$ inner-shell region the effective intensity is very low. Finally we point out difficulties connected with the tentative identification of recently observed $4d$ Auger spectra.

At ion-beam power densities which are high enough to ionize the target atoms nearly fully, a stage is reached in the interaction process at which the deposition layer becomes optically thin. At this stage, a corona region is formed which can reach sufficiently high temperatures that range lengthening occurs. This phenomenon is demonstrated in a calculation of the interaction of a ${10}^{14}$-W/${\mathrm{cm}}^2$, 1-MV proton beam with an aluminum target.

Plasma potentials have been measured for the first time in neutral-beam-heated tokamak discharges, with a heavy-ion beam probe. Radial profiles of these potentials are presented for coinjection, counterinjection, and balanced injection, and for plasmas having only Ohmic heating. They are found to be very dependent on the direction of rotation with respect to the plasma current. They are also found qualitatively consistent with those inferred from radial momentum balance with use of the measured toroidal rotation velocity.

The transfer of energy from the driving beam to the trailing beam in the plasma wake-field accelerator is studied in computer simulations. We show that with an asymmetric current distribution in the driving bunch, trailing particles can gain energies up to ${(1+k_p^{}{}_{}{}^2{Z}^2)}^{\frac{1}{2}}\Delta \gamma m{c}^2$, where $Z$ is the bunch length and $\Delta \gamma m{c}^2$ the average energy loss of driving electrons. Because of the relative phase slippage and the two-stream instability, the process of energy gain degrades before the driving beam loses all of its energy; however, even for ${\gamma }_i=150\mathrm{}$, $\frac{\Delta \gamma }{{\gamma }_i}\gtrsim 70\%$, with an energy gain ∼ 1 GeV. Transverse effects are briefly discussed.

Suppression of the drift-cyclotron loss-cone instability (DCLC) in an axisymmetric mirror plasma has been observed for frequencies in the vicinity of the bounce frequency of electrostatically trapped thermal electrons. The location and width of the frequency region of suppression is in good agreement with calculations of bounce-resonance Landau damping.

Pattern formation in the electrodeposition of Zn from a thin layer of ZnS${\mathrm{O}}_4$ solution was studied as a function of electrolyte concentration and applied voltage. We found several qualitatively different growth forms in this system. Most strikingly, a transition from dendritic crystals (where crystalline anisotropy dominates) to disordered ramified patterns is found when the electrolyte concentration is reduced. The disordered patterns may be described as fractal below a concentration-dependent cutoff length.

We report an experiment in the Ohmically-limited electrochemical deposition of zinc which explicitly probes the link between microscopic structure and macroscopic morphology in the development of interfacial patterns far from equilibrium. We report a previously unrecognized transition region between diffusion-limited aggregation and dendritic growth; analysis of the microstructure suggests mechanisms for the macroscopic expression of crystalline anisotropy. We also report the discovery of a metastable crystalline form of zinc produced during electrodeposition.