The thermal properties of hydrogenated amorphous Si at temperatures between 0.1 and 5 K are shown by calorimetry to be dominated by the presence of molecular hydrogen ${\mathrm{H}}_2$ in microvoids. A spontaneous release of heat due to conversion of $o$-${\mathrm{H}}_2$ to $p$-${\mathrm{H}}_2$ is observed from which the concentration (0.5 at.%) and bimolecular conversion rate (0.025 ${\mathrm{h}}^{-1\mathrm{}}$) are obtained. The specific heat is time dependent, varies roughly as $T^2$ between 0.1 and 3 K, and is attributed to a highly broadened orientational ordering transition of ${\mathrm{H}}_2$ in restricted geometry.

By means of a density functional approach, the phase equilibria of a fluid confined between two adsorbing walls, i.e., in a slitlike capillary, have been investigated. The theory provides a microscopic basis for the phenomenon of capillary condensation and, for fluids in narrow slits, predicts a line of critical points marking the end of the lines of coexistence between "liquid" and "gas" phases.

It is demonstrated that the thermal conductivity of self-ion-implanted, amorphized silicon is an order of magnitude less than that of crystalline silicon and is by far the dominant parameter determining the dynamical response of the ion-implanted silicon system to pulsed-laser radiation; the latent heat and melting temperature of amorphous silicon are relatively unimportant. Transmission electron microscopy indicates that bulk nucleation occurs in the highly undercooled liquid phase; a model simulating this effect is presented.

Electronic eigenfunctions are studied on the tight-binding model of disordered systems at dimensionalities $d=1,2,3\mathrm{}$. It is found that the eigenfunctions have a self-similar (fractal) behavior up to length scales roughly equal to the localization length. For $d=3\mathrm{}$, above the mobility edge, the fractal character persists up to length scales about equal to the correlation length $\xi$. The dependence of the fractal dimensionality $D$ on disorder $W$ is presented. The fractal character of the wave function is suggested as a new method for finding mobility edges.

Measurements of the inelastic scattering time, ${\tau }_{\mathrm{in}}$, for diffusive electrons in three-dimensional indium-oxide films are reported. Two distinct regimes for the behavior of ${\tau }_{\mathrm{in}}$ as a function of temperature and disorder can be recognized: For small values of $K_{\mathrm{F}}l$, Coulomb interactions give the dominant contribution to ${\tau }_{\mathrm{in}}$. As $K_{\mathrm{F}}l$ increases, a distinctly different scattering mechanism takes over.

The SU(2) string tension is obtained from measurements of Wilson loops on a $6^4$ bodycentered hypercubic lattice. A crude perturbative determination of $\Lambda$ indicates that the results are consistent with those of the hypercubic lattice. However, the $\chi \mathrm{}\left(2\right)\mathrm{}$ loop ratio is found to follow the asymptotic-freedom curve for a much larger range of $g_0$ than has ever been observed for any hypercubic actions. This strongly indicates that the bodycentered lattice may, for a given amount of computer run time, greatly increase the reliability of nonperturbative calculations.

It is shown that the value of $\frac{〈N〉}{D}$ is related to the increase of the average transverse momentum with increasing multiplicity. In this way, the rise is smaller for total nucleus-nucleus events than for $\overline{p}p$ events; however, this rise is very fast for central nucleus-nucleus collisions because of the large value of $\frac{〈N〉}{D}$ of such collisions. This effect could explain the large value of the average transverse momentum found in cosmic-ray events.

Results are presented from an experiment observing photoproduction of the $D^{*}$ at a mean energy of 105 GeV. Clean signals are seen for the decay $D^{*\pm }\to {\pi }^{\pm }{D}^0$ with the $D^0$ decaying into both $K^{\mp }{\pi }^{\pm }$ and $K^{\mp }{\pi }^{\pm }{\pi }^0$. Analysis of the Dalitz plot for the $K\pi \pi$ mode gives branching fractions for $K^{-}{\rho }^{+}$, $K^{*-}{\pi }^{+}$, and ${\overline{K}}^{*0\mathrm{}}{\pi }^0$ final states.

The universally used "exact" formula for fission-fragment angular distributions is shown to be valid only under restrictive assumptions. The more general expression, which depends crucially on the final fragment spin distributions, predicts dramatically more anisotropic angular distributions for fission from nuclei at high spin. Recent "anomalous" results are analyzed.

A model based on time-dependent quantum mechanics is presented for calculating the crossover from the adiabatic to the sudden regime in core ionization. With reasonable parameters the predictions of this model are in agreement with newly reported experimental results on shakeup as well as with older data on shakeoff.

The photoelectron emission from atomic xenon has been simultaneously resolved with respect to photon energy, photon (circular) polarization, photoelectron emission angle, electron kinetic energy, and spin-polarization components by use of synchrotron radiation of wavelengths between 48 and 90 nm from the new dedicated electron storage ring BESSY. The angular dependence of the spin polarization and the energy dependence of the dynamical spin parameters experimentally obtained show good agreement with theoretical predictions.

Thomson backscattering of C${\mathrm{O}}_2$-laser radiation is used to determine the parallel momentum spread of a 1-kA/${\mathrm{cm}}^2$, 700-kV magnetized electron beam, emitted from a cold cathode in an apertured diode. The beam is found to be suitable for Raman free-electron-laser applications: a normalized momentum spread of (0.6±0.14)% was obtained for the inhomogeneous broadening; it is also found that the use of an undulator will cause an increase of the broadening.

The inelastic He/Ag(111) cross section has been evaluated in the one-phonon distorted-wave Born approximation. The authors use an atom-surface potential made up by a repulsive part derived from a superposition of atomic charges and by the attractive van der Waals interaction. The surface phonon density of states is evaluated within a force-constants parametrization of the bulk dynamics. By changing the surface force constants the authors are able to explain all the salient features appearing in the experimental time-of-flight spectra.

Landau-Ginzburg-Wilson symmetry analyses and Monte Carlo calculations for the classical antiferromagnetic planar ($\mathrm{XY}$) model on a triangular lattice reveal a wealth of interesting critical phenomena. From this simple model arise a zero-field transition to a state of long-range order, a new mechanism for spin disordering, and a critical point associated with a possible new universality class.

A theoretical study of intercalation predicts stage-changing phase transitions to be continuous and to proceed via stage-disordered states. Detailed results are presented for typical donor and acceptor graphite intercalation compounds. Other systems are also discussed. A scaling rule relating stage disorder to domain size, stage, temperature, in-plane density, and charge transfer is proposed. A fundamental limit is set on the period of well staged structures. Experimental implications are discussed.

A Bonse-Hart x-ray interferometer was used to determine the (220) Fourier component of the distribution function of a chemisorbed submonolayer of bromine on a (111) silicon surface. This measurement demonstrates not only the presence of an x-ray interference field above the crystal surface of the analyzer of a Laue-case interferometer, but when coupled with Bragg-case standing-wave measurements also provides the means to determine uniquely the position of surface atoms relative to the bulk lattice.

The incommensurate phase of krypton on graphite is studied by use of the molecular-dynamics simulation technique for systems with graphite substrate dimensions comparable to present-day laboratory capabilities. At low temperature and for all coverages, honeycomb networks of "heavy" domain walls are observed for the first time. With increasing temperature, distortion from the perfect honeycomb structure becomes more prevalent, characterized by significant fluctuations from the symmetry directions, wall thickening, and wall roughening.

With the aid of a special-purpose molecular-dynamics hardware processor the authors have simulated two-dimensional Lennard-Jones systems of 10 864 particles. The asymptotic behavior of the orientational correlation function is found to be in accordance with a first-order melting transition.

A molecular model of field-dependent photogeneration is presented. The model, diffusion on a lattice in a combined Coulomb and external dc field, is solved exactly. The solution for the quantum efficiency $\eta$ has a larger range of applicability than the continuum theory to which it can be compared in the infinite-sink case. It is shown that $\eta$ can vary greatly with small variation of key molecular parameters and that the high-field limit of $\eta$ is controlled by the same molecular properties which determine its field dependence.

Strong polar-angle dependence has been observed in $\mathrm{KVV}$-Auger spectra of adsorbed molecules. These angular effects are caused by the anisotropy of the Auger matrix element and can be explained by simple symmetry arguments. It is shown with the example CO on Ni(100) that molecular Auger spectra can be largely understood with use of nothing but the present angular results and experimental one-electron binding energies. Information about the adsorbate orientation as well as about the screening mechanism can also be obtained.