Pair energies for Si adatoms on the W{110} for several bond lengths were obtained by direct field-ion—microscopy observations. Maximum binding occurred at a distance $\sqrt{2}a$ in the [$1\overline{1}0$] and maximum antibinding at $a$ in the [001]; $a$ is the lattice constant. From the data, the two-dimensional binding energy per adatom in an adlayer can be calculated. The $[\frac{2\sqrt{2}}{\sqrt{3}}\times \frac{4}{\sqrt{3}}]R35.26°$ superstructure has the lowest energy. Our search for a superstructure formation by thermal equilibration of Si adatoms confirmed this prediction.

High-field magnetization studies of the randomly diluted, anisotropic antiferromagnet ${\mathrm{Fe}}_x{\mathrm{Zn}}_{1-x}{\mathrm{F}}_2$ have confirmed the existence of novel single-spin "exchange flips," occurring at fields $H_0=\frac{1}{8}n{H}_E$ ($n=1,\dots ,5\mathrm{}$), as predicted by a classical spin computer simulation. Field direction hysteresis of $\frac{\mathrm{dM}}{d{H}_0}$ is shown to result from "crossover" behavior to states which have no long-range order.

A description of spin-glass dynamics at low temperatures, based on a "harmonic" theory, is presented. The Hamiltonian is approximated by a quadratic form in the spin deviations from a particular local minimum, and diagonalized. The dynamics is governed by the eigenvalue distribution $\rho \left(\lambda \right)$. The validity of this description is supported by computer simulations. These suggest that $\rho \mathrm{}\left(0\right)\mathrm{}\ne 0$ in two and three dimensions, implying a logarithmic decay in time of the spin autocorrelation function at low temperatures.

A new optical system incorporating a fast Ge photodiode has made possible the first measurements at short times of the low-energy side of the photoluminescence spectrum of $a$-${\mathrm{As}}_2$${\mathrm{S}}_3$. Two photoluminescence processes are separated by their dependence on excitation energy, $E_x$. A number of observations suggest that the first step in the high-$E_x$ process is the creation of delocalized excitations. The abrupt onset of this process leads to the intimation that it arises from transitions across the mobility gap.

Using a five-pass interferometric Brillouin spectrometer, we have measured the pressure dependence of longitudinal- and transverse-acoustic velocities and refractive index of solid $n$-${\mathrm{H}}_2$ and $n$-${\mathrm{D}}_2$ at room temperature in a diamond-anvil cell up to 200 kbar. The equations of state have been determined ($55<~P<~200$ kbar: $\rho =0.0734\mathrm{}{P}^{0.334}-0.0214\mathrm{}$ for solid $n$-${\mathrm{H}}_2$, and $\rho =0.148\mathrm{}{P}^{0.334}-0.0627\mathrm{}$ for solid $n$-${\mathrm{D}}_2$, with $P$ in kbar and $\rho$ in g/${\mathrm{cm}}^3$.

Soft—x-ray appearance-potential spectroscopy has been applied to the metallic glass ${\mathrm{Co}}_{58}$${\mathrm{Ni}}_{10}$${\mathrm{Fe}}_5$${\mathrm{B}}_{16}$${\mathrm{Si}}_{11}$. The $L_{\mathrm{III}}$ spectra of the transition metals resemble closely those of pure samples in the region determined by the $d$ partial density of states. Distinct differences occur in the region characteristic of the $s$ partial density of states. This part of the signal is also clearly affected by crystallization for Co and Fe, Ni remaining unchanged. A dramatic change upon crystallization is exhibited by the boron $K$ spectrum.

When a counterflow supercurrent is generated in a superconducting bimetallic loop by a thermoelectric quasiparticle current, the phase difference can only be maintained constant if very large surface currents flow. We show that this implies a magnetic flux associated with the loop of order $\frac{r}{\lambda }$ ($r$ is the radius of arm perpendicular to $\nabla T$ and $\lambda$ is the penetration depth) greater than the simple theory suggests, and that this may be used to méasure the normal current directly.

A broad Lorentzian ESR line in H-doped Ca${\mathrm{V}}_2$${\mathrm{O}}_6$crystals has been observed and assigned to itinerant electrons in $d_{x^2-y^2}$ orbitals. The spin susceptibility and the ESR linewidth vary weakly between 20 and 300 K, whereas the conductivity varies strongly, consistent with Mott's $\exp -{\left(\frac{T_0}{T}\right)}^{\frac{1}{4}}$ variable-range hopping law for random systems. Our observations demonstrate the existence of Fermi statistics in this system of protons and $d$ electrons which may be more clustered than purely random.

Strong evidence is given of electron-hole-pair trapping at a deep center in InP. The observation of this new kind of metastable state, which had been theoretically predicted, is made possible because of the small value of the recombination rate between the two carriers in a wide temperature range. A model in terms of configuration coordinate diagram is proposed to account for this unusual behavior.

It is shown that proper treatment of the nonlocality of the nuclear optical potential resolves much of the apparent discrepancy between previous theoretical calculations and empirical values of the nucleon mean free path.

An odd-even neutron-number dependence of the alignment frequency of the first pair of $i_{\frac{13}{2}}$ quasineutrons in rare-earth nuclei is established. This effect is explained by a reduction of the neutron pairing-correlation parameter ${\Delta }_n$ for odd-$N$ systems as compared to seniority-zero configurations in even-$N$ nuclei.

It is shown that the loss of electron scattering flux through dielectronic recombination can be quite significant for highly charged ions, thus reducing the contribution of autoionizing resonances to scattering cross sections and hence excitation rates. This process is likely to be of importance in analyzing line emission from high-temperature plasmas. Detailed calculations are carried out for ${\mathrm{O}}^{6+}$ and ${\mathrm{Fe}}^{24+}$. Employing the present formulation, the averaged cross sections for dielectronic recombination may also be computed.

We observed well-resolved spectral features in the stepwise ionization of Na in an applied electric field near the zero-field ionization threshold. A 5890-A pulse excites atoms to the $3{}_{}{}^2{}_{}{}^{}P$ state and a~4085-A pulse, swept through threshold ionizes them. Using the method of Luc-Koenig, we calculated the oscillator strength density versus blue laser frequency and compared it with our data. The agreement is excellent. Parabolic quantum numbers have been assigned to the spectrum and the Fano profiles have been analyzed.

We report the first observation of a laser-induced $M1\mathrm{}$ transition in a fast beam. This new method has been applied to a measurement of the $F=\frac{1}{2}-\frac{3}{2}$ and $F=\frac{3}{2}-\frac{5}{2}$ hyperfine components of the $1s2p{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ fine-structure interval in heliumlike fluorine. The results are 953.60(3) and 961.77(3) ${\mathrm{cm}}^{-1\mathrm{}}$, respectively. From these we extract the fine-structure splitting ${\Delta }_{12}=957.88\mathrm{}\left(3\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$.

X-ray images of laser-irradiated solid targets show spicular structures in the blowoff plasma. Higher density is inferred in the structures, which seem to follow the fluid flow from the target. An explanation involving localized fast-electron production is offered.

Electromagnetic radiation is observed when an electron beam is injected into a uniform quiescent magnetoplasma. The emission peaks near the electron plasma frequency ($\omega \gtrsim {\omega }_p\gg {\omega }_c$) and is found to result from the scattering of unstable intense electrostatic plasma waves off self-consistently produced ion acoustic waves with wave vectors ${\mathcal{k}}_i\simeq {\mathcal{k}}_e$. The emission is localized, polarized, and negligible in intensity at $\omega =2\mathrm{}{\omega }_{\mathrm{pe}}$. Space-time growth and $\omega -\mathcal{k}$ properties of the three-wave interaction are presented.

It is observed that with a sufficiently large incident extraordinary wave amplitude, the electrostatic upper hybrid wave resulting from the mode conversion process at the resonant layer can scatter off the lower hybrid wave and penetrate through its original cutoff to a distance proportional to the product of the scale length and the square root of the mass ratio. A substantial number of energetic ions also appear in the resonant region which is well inside the plasma slab as a result of lower hybrid wave excitation.

It is rigorously proved that the continuum limits of Euclidean ${\varphi }_d^4$ lattice fields are free fields in $d>\mathrm{}4\mathrm{}$. An exact geometric characterization of criticality in Ising models is introduced, and used to prove other mean-field features for $d>\mathrm{}4\mathrm{}$ and hyperscaling in $d=2\mathrm{}$.

We report the results of a study of the mechanism of inclusive dimuon production from the reaction $p+p\to {\mu }^{+}{\mu }^{-}+X$ at the CERN intersecting storage rings. The present experiment was done at the center-of-mass energies $\sqrt{s}=62\mathrm{} \mathrm{and} 44$ GeV and in the dimuon pair invariant-mass region $m=3-25\mathrm{}$ GeV. The dependence on the Feynman variable $x$ has been measured. The average transverse momentum is found to increase with $\sqrt{s}$ and with mass and reaches $〈p_T〉\simeq 1.9$ GeV, compatible with predictions from quantum-chromodynamic gluon processes.

Neutrons were measured in coincidence with both fragments of the deep-inelastic collisions of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Kr}$ on ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$ at 11.9 MeV/amu. The velocity and angular distributions of the neutrons cannot be explained by assuming only statistical neutron evaporation from the fully accelerated fragments.