Relaxation of the photoinduced ir absorption band in $a$-Si: H was studied in the microsecond time domain as a function of cw bias illumination. The decays follow a power law $t^{-\alpha }$ where the dispersion parameter $\alpha$ increases with bias illumination. At low temperatures, $\alpha$ increases linearly with the steady-state carrier density while at high temperatures it saturates at high illumination levels. These results are interpreted as evidence for the bias-controlled tunneling process at low temperatures and multiple trapping process with tail states under the saturation condition at high temperatures.

It is demonstrated that spin dependences in the secondary-electron yields obtained when electron-spin-polarized $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ atoms are deexcited at a magnetized surface provide a means by which to probe surface magnetism. This technique, which is particularly surface specific, has been used to investigate the dependence of Ni(110) surface magnetism on temperature and the presence of controlled adsorbates.

The dissociative chemisorption of oxygen on Si(100) is studied with use of an ab initio multiconfiguration self-consistent-field cluster approach and a self-consistent field pseudopotential slab simulation. The cluster calculations show, for the first time, that the dissociative adsorption of an oxygen molecule is exothermic by ∼ 3 eV thus providing strong support for atomic chemisorption. Furthermore, atomic oxygen in the first-layer bridging positions is found to be modestly more stable than in the on-top configuration; stable adsorption at both sites is possible.

By tuning the $4p$ level of excited ${\mathrm{Zn}}^{*}$ $3d^{9}4s^{2}4p$ impurities through the conduction-band bottom of alkali metals, we show that the rate at which the excited-impurity configuration decays into conduction-band excitations is insensitive to the extent of $4p$ admixture into the host conduction band. However, the optical matrix elements change markedly with the degree of valence mixing.

The consequences of rotational-symmetry breaking in Heisenberg spin-glasses are studied with use of order parameters which are time-dependent SO(3) rotation matrices. A microscopic derivation of the hydrodynamic "triad" theory, including the effect of small magnetic fields and random anisotropies, is presented. In the mean-field limit the finite-time exchange stiffness and macroscopic anisotropy constants vanish near the transition temperature $T_g$ as ${(T_g-T)}^{\mu }$, $\mu =3\mathrm{}$.

It is proved that the contribution of self-dual twisted gauge configurations (torons) to the gluino condensate $〈\lambda \lambda 〉$ in $N=1\mathrm{}$ supersymmetric Yang-Mills theory remains finite in the thermodynamic limit. Using the richer vacuum structure of the theory, defined in a twisted box, the authors explain the constant value of the instanton contribution to the condensate $〈\lambda \lambda \mathrm{}\left(x\right)\mathrm{}\lambda \lambda \mathrm{}\left(y\right)\mathrm{}〉$. The physical picture obtained is consistent with $\mathrm{tr}{\mathrm{}(-1\mathrm{})\mathrm{}}^F$ and the effective-Lagrangian approach.

The possibility that a scalar boson is sometimes emitted in the decay of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(20.1 MeV, $0^{+}$) is examined experimentally. Finding no positive evidence the authors exclude scalars with Higgs-like couplings for $3\lesssim m_{\varphi }\lesssim 14$ MeV/${\mathit{c}}^2$, where the precise range depends upon the model.

The elastic photon-scattering cross section for carbon and calcium has been measured between 20 and 50 MeV. These data are inconsistent with previously reported measurements of the total photoabsorption cross section. No evidence is found for compact $E2\mathrm{}$ strength in either nucleus. A previously reported concentration of $E2\mathrm{}$ strength in carbon in the 24-44-MeV range is not supported by the data.

The transition charge densities to the lowest $J^{\pi }=2^{+},4^{+}$ states in ${}_{}{}^{204,206}{}_{}{}^{}\mathrm{Pb}$ have been determined through inelastic electron scattering. Their shape is insensitive to the microscopic structure of these states, dominantly of neutron character, but it bears striking similarity to that of the low-frequency phonon of the core. This is regarded as strong evidence supporting the view that the "dressing" of these neutron excitations is mediated through core polarization with the lowest-frequency phonon acting as the most important doorway.

Nuclear charges and kinetic energies were measured for fragments resulting from reactions of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ at 15.3-MeV/u incident energy. These data suggest a nonequilibrium division of the available excitation energy between target and projectile for a large range of energy losses. This interpretation is supported by a consistent analysis of more complete data available for the ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ + ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ reaction at 8.5-MeV/u incident energy.

Pion production was studied at $\frac{E_{\mathrm{lab}}}{A}=35\mathrm{}$ MeV in the reactions ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + Al, Ni, $\mathrm{W}\to {\pi }^0+X$. Neutral pions were measured by detecting their two decay $\gamma$ rays in coincidence in an array of ten Pb-glass Cherenkov-detector telescopes. The measured cross sections are much larger than predicted within the framework of independent nucleon-nucleon collisions and indicate that, at this energy, pion production is the result of cooperative action among many nucleons.

It is shown that it is possible to establish a clear correspondence between bands in the $\mathrm{U}\left(\frac{6}{12}\right)$ SU(3) symmetry scheme and the Nilsson orbits stemming from the $2p_{\frac{1}{2}}$, $2p_{\frac{3}{2}}$, and $1f_{\frac{5}{2}}$ shell-model states. The best empirical example of the specific single-particle structure and Coriolis coupling of rotational bands implicit in the symmetry is found in the low-lying states of ${}_{}{}^{185}{}_{}{}^{}\mathrm{W}$.

The authors propose a method for establishing a connection between the interacting-boson model and geometrical models, which is exact for any number of bosons. With this method they show that effective triaxial deformations occur in the interacting-boson model, and confirm the results of a recent phenomenological study.

A symmetry breaking of the ungerade-gerade character through hyperfine perturbation has been directly observed for the first time in a homonuclear diatomic molecule (${}_{}{}^{127}{}_{}{}^{}\mathrm{I}_2^{}{}_{}{}^{}$). An important consequence of this symmetry breaking is the mixing of ortho and para modifications. Evidenced by anomalies in the observed hfs of high-lying rovibrational levels in the $B{0_{\mathrm{u}}}^{+}$ state and extra lines, it is due to a hyperfine perturbation of this state by a 1g state sharing the same dissociation limit. Such a situation should be met in other molecules.

Microwave experiments and simulation calculations for laser parameters are reported of electron heating and microwave (laser) absorption due to parametric instabilities excited in the strongly steepened density profile near the critical surface. An approximate theory is developed that shows that $\frac{T_H}{T_e}$ should be a function of only the variable $\frac{f_{H}I{{\lambda }_0}^2}{T_e}$. The microwave measurements and simulation calculation results agree (±20%) with this theory.

The propagation of ion-acoustic solitons in a plasma with negative ions has been observed. For sufficiently large concentration of negative ions, applied rarefactive (negative) voltage pulses break up into solitons, whereas compressive pulses evolve into wave trains, with exactly the opposite behavior as that for a plasma composed only of positive ions. There is a critical value of the negative-ion concentration for which a finite-amplitude pulse propagates without steepening.

In contrast to one-dimensional solutions, which are always transversely unstable, completely stable spherically symmetric Langmuir solitons exist. The stability theorem is presented and the existence region of stable three-dimensional solitons is discussed.

Ion turbulence generated in a C${\mathrm{O}}_2$-laser-heated plasma has been studied by means of ruby-laser Thomson scattering. The first general measurement of the ion fluctuation spectrum, $S\left(k\right)\mathrm{}$, induced in the plane of the laser electric field has been made and is reported here. High-speed streak measurements of Thomson-scattered light indicate very short-duration (≲3 ns) and very fast-rise-time (∼10 ps) features in the enhanced ion fluctuations.

The phase diagram of a system of hard ellipsoids of revolution was investigated by means of constant-pressure Monte Carlo simulation. Prolate as well as oblate ellipsoids were considered. The results for the isotherms of the system at several different values of the length-to-breadth ratio are presented. Four different phases of the system are identified and a tentative picture of the phase diagram is given.

An expression is given for the interatomic force constants in terms of two-, three-, and four-body contributions within the tight-binding approximation. These contributions, which depend on the induced bond charge, allow a microscopic real-space interpretation of the phonon anomalies in the bcc $3d$ transition metals V, Cr, and Fe. The real-space formalism is complementary to the $\overrightarrow{q}$-space approach of Varma and Weber, but has the advantage of being directly applicable to problems such as defects which lack translational symmetry.