Time-of-flight scattering and recoiling spectrometry is applied to structural analysis of hydrogen on a W(211) surface. Experimental data in the form of a recoiling structural contour map are presented and the hydrogen position is determined as 0.58±0.20 Å above the first-layer W plane and confined within a band that is centered above the [11¯ 1¯] troughs. Effective-medium-theory calculations predict a broad probability distribution for the H atom positions above the troughs due to thermally activated vibrational motion.

Using the scanning tunneling microscope, Au adsorbates are found to bond to Ga atoms on the GaAs(110) surface. A characteristic spectrum of band-gap states is observed for the Au adsorbates. Both donor and acceptor states are seen, and they are identified with the first and second electron states of the Au-Ga bond, respectively.

We report the characteristics of tunneling to a GaAs(110) substrate with distinct, nanometer-size Fe clusters, as a function of distance from and size of the clusters. We show that Fe clusters of volumes ∼150 A${\mathrm{̊}}^3$, corresponding to ≃13 atoms, are observed to be nonmetallic with a gap at the Fermi level. Larger clusters with >35 atoms begin to show metallic characteristics. We observe a continuum of cluster-induced gap states in tunneling to the GaAs substrate surrounding the metallic Fe clusters. The decay length of these states has a minimum decay of 3.4 Å at midgap and diverges at the valence- and conduction-band edges.

We report the first observation of the internal photoemission of holes into the valence band of hydrogenated amorphous silicon from metal contacts. This, together with the corresponding photoemission of electrons into the conduction band, is used to directly determine the room-temperature mobility gap of a-Si:H. The effective mobility gap is found to be 1.89±0.03 eV which is 0.16 eV larger than its Tauc optical gap of 1.73 eV. The important implications of the results on the understanding of a-Si:H band structure, electronic properties, and devices are outlined.

High-field magnetization measurements were perform- ed for the quasi-one-dimensional S=1 antiferromagnet Ni(${\mathrm{C}}_2$${\mathrm{H}}_8$${\mathrm{N}}_2$${)}_2$${\mathrm{NO}}_2$(${\mathrm{ClO}}_4$) up to 39 T. Applied magnetic fields parallel and perpendicular to the chain axis induce a transition from a nonmagnetic to a magnetic state at a critical field, ${\mathit{H}}_{\mathit{c}}^{\mathrm{\parallel }}$=9.8 T, and ${\mathit{H}}_{\mathit{c}}^{\mathrm{\perp }}$=13.1 T, indicating clear evidence for the existence of the Haldane gap. The observed gaps are markedly different from those in neutron-scattering experiments.

The breakdown phenomena of resistively shunted two-dimensional Josephson-junction array with a single defect driven by an external current at zero temperature are studied numerically. The nonlinear Josephson relation causes the formation of vortices at the tips of the defect at $i_v$ and thus lowers the current enhancement there. Above a higher critical current $i_c$ the vortices depin from the defect and march across the sample producing a voltage. The critical current $i_c$ is studied versus defect size. Various dynamic properties and the I-V characteristics of the array are explained in the context of the vortex motion. From the observed features the critical behavior of a randomly disordered array is predicted.

Using high-resolution optical hole burning, we have determined the tunneling level structure of protons in hydrogen bonds at liquid-helium temperatures: The tunneling matrix element is J=8.4±0.1 GHz. The strain deformations of the tunneling potential are reflected in characteristic asymmetric inhomogeneous shapes of the spectral lines and can be explained by correlated variations of J and A, the energy asymmetry of the potential.

We present a new method for optimizing the analysis of data from multiple Monte Carlo computer simulations over wide ranges of parameter values. Explicit error estimates allow objective planning of the lengths of runs and the parameter values to be simulated. The method is applicable to simulations in lattice gauge theories, chemistry, and biology, as well as statistical mechanics.

The possibility that both the formation of nontopological solitons in a primordial second-order phase transition and binary systems of soliton stars could generate a stochastic gravitational-wave background is examined. The present contribution in gravitational radiation to the energy density of the Universe from these processes is estimated for a number of different models. The detectability of such contributions from the timing measurements of the milisecond pulsar and spaceborne laser interferometry is briefly discussed and compared to other cosmological and local sources of background gravitational waves.

We propose a space for bosonic and heterotic string field theories in which all classical vacua are included naturally. WE also illustrate how space-time emerges. The existence of a new string symmetry beyond the usual Becchi-Rouet-Stora-Tyutin symmetry is pointed out.

Contrary to common belief, nonlinear σ models for Su(2) and O(3) manifolds in 1+1 dimensions are found to be nonintegrable, in general, in the Liouville sense. However, the required integrability is restored in a particular conformal gauge, compatible only with the nontrivial boundary condition. The source of such peculiarity and its connection with the analytic structure of the Jost function as well as with the dimensional parameter are discussed.

We report the first observation of the decay ${\mathit{D}}_{\mathit{s}}^{+}$→K¯ ${}_{}{}^0{}_{}{}^{}$${\mathit{K}}^{+}$ and a new measurement of the decay ${\mathit{D}}_{\mathit{s}}^{+}$→K¯ (892${)}^0$${\mathit{K}}^{+}$. The data were collected at √s=4.14 GeV with the Mark III detector at the SLAC ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ storage ring at SPEAR. We obtain the relative branching fractions B(${\mathit{D}}^{+}$s→K${\mathrm{¯}}^0$${\mathit{K}}^{+}$/ B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$)=0.92±0.32±0.20 and B(${\mathit{D}}_{\mathit{s}}^{+}$→K${\mathrm{¯}}^{\mathrm{*}0}$${\mathit{K}}^{+}$)/ B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$)=0.84±0.30±0.22, using our new determination of σB(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$). A search for the Cabibbo-suppressed decay ${\mathit{D}}^{+}$s→${\mathit{K}}^0$${\mathrm{\pi }}^{+}$ yields a limit B(${\mathit{D}}_{\mathit{s}}^{+}$→${\mathit{K}}^0$${\mathrm{\pi }}^{+}$)/B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$)<0.21 at the 90% confidence level.

We present evidence for the quenching of Einstein A coefficients in an Ar-ion laser discharge due to the presence of the high-intensity laser flux. The reduction in spontaneous emission intensity when lasing occurs is found to be dependent on the Einstein A coefficient for transitions originating from the same upper level.

Experimental evidence is presented, for the first time, that ${\mathrm{Xe}}_{\mathrm{N}}^{\mathrm{-}}$, N≥1, atoms and clusters have a lifetime of about ${10}^{\mathrm{-}4}$ s or longer. It is discussed whether the negatively charged xenon atoms and small clusters are in the ground or in an electronically excited, metastable state. Ground-state ${\mathrm{Xe}}_{\mathrm{N}}^{\mathrm{-}}$ clusters are stable if N≥6 and probably down to N=2. Structure in the mass spectra correlates well with calculated binding energies.

Calculations of the adiabatic effects for the ${\mathrm{h}}^3$${\mathrm{\Sigma }}_{\mathrm{g}}^{+}$ state of the hydrogen molecule have been performed using an explicitly correlated wave function. It is shown that in contrast to the Born-Oppenheimer results the adiabatic potential-energy curve for the h state is characterized by a double-minimum function. The nature and consequences of this finding are discussed.

The distribution of local Lyapunov exponents is used to analyze power spectra of conservative dynamical systems. It is shown that sharp and broad peaks in the spectra can be related to well defined regions in phase space, associated with algebraic and exponential stretching of distances, respectively.

The nonlinear bistable effect presented by a mechanical string resonator is set in evidence as a hysteresis of the output intensity upon the input one. Interpretation is given through approximating the nonlinear equation of motion of a fixed boundary string.

Significant forces between dielectric objects can be induced by intense optical fields. We discuss the origin of these forces which are very long range and oscillate in sign at the optical wavelength. A consequence is that light waves can serve to bind matter in new organized forms. We experimentally demonstrate the simplest case by observing a series of bound states between two 1.43-μm-diam plastic spheres in water, and discuss the extension to more complex cases.

The dynamics of a single topological defect and the interaction between pairs, including the process of annihilation of defects of opposite topological charge, are studied experimentally and theoretically near the onset of weak turbulence in Williams domains of electroconvecting nematics. The existence of topological defects requires a gauge field theoretical treatment, enriching the commonly used ‘‘amplitude equations.’’ The gauge field carries the interaction which is found to be of finite range in agreement with detailed observations.

We present a vorrex paradigm for interpreting the evolution of shock-accelerated density-stratified interfaces beyond early times. The paradigm is investigated and illustrated through a series of numerical experiments that compare favorably with recent shock tube experiments. Color images of space-time diagrams of the one-space integrated vorticity function highlight primary and secondary features of the emerging vortex structures.