We have used the momentum spectrum of leptons produced in semileptonic $B$-meson decays to set a 90%-confidence-level upper limit on $\frac{\Gamma (b\to \mathrm{ul}\nu )}{\Gamma (b\to \mathrm{cl}\nu )}$ of 4%. We also measure the semileptonic branching fractions of the $B$ meson to be (12.0±0.7±0.5)% for electrons and (10.8±0.6±1.0)% for muons.

The momentum spectrum of the ${\pi }^{+}$ in stopping $K^{+}$ decays was measured by use of a high-resolution magnetic spectrometer to search for a discrete peak due to a neutral boson $X^0$ in a two-body decay $K^{+}\to {\pi }^{+}{X}^0$. An upper bound of the branching ratio $R(K^{+}\to {\pi }^{+}{X}^0)$ is presented for the mass range of $X^0$ from 10 to 300 MeV/${\mathit{c}}^2$.

Observations have been made 1570 m (water equivalent) underground with an 8000-metric-ton water Cherenkov detector. During a live time of 132 days, events consistent with the decay modes $p\to {\mu }^{+}{K}^0$ and $n\to \nu K^0$ were searched for in a fiducial mass of 3300 metric tons. It is concluded that the limit on the lifetime for bound plus free protons divided by the ${\mu }^{+}{K}^0$ branching ratio is $\frac{\tau }{B}>2.6\mathrm{}\times {10}^{31}$ yr. For bound neutrons decaying into $\nu K^0$ the limit is $\frac{\tau }{B}>0.8\mathrm{}\times {10}^{31}$ yr (90% confidence level).

The angular distribution of isolated photon conversion pairs, collected during the proton-synchrotron-Gargamelle $\nu$ and $\overline{\nu }$ Freon experiments, has been examined to determine whether any anomalous small-angle production is present. There is a definite excess of conversion pairs over what is expected from resonantly produced and neutron-induced ${\pi }^0$'s. This excess is in accord with $\nu -(\overline{\nu }-)$ induced coherent ${\pi }^0$ production off nuclei.

Pion single charge exchange to the isobaric analog state of ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ was measured at $T_{\pi }=48\mathrm{}$ MeV over the angular range 0-150°. The angle-integrated cross section at 48 MeV is 0.43 ± 0.07 mb. The most prominent feature in the measured angular distribution is a deep minimum near 0°. The data are compared with optical-model calculations and the effects of various second-order terms in the potential are investigated.

Velocity spectra of evaporation residues deviate characteristically from the mean velocity of complete fusion, indicating that the lost momentum (mass) in incomplete fusion originates perferentially from the lighter partner. By varying the energy in the range 10-25 MeV/u the authors determine the onset of incomplete and the limit to complete fusion, and they discuss dependence on the mass asymmetry in the entrance channel.

Electron-photon coincidences with initially polarized electrons have been measured for the first time. Results for linear and circular polarization components of the 254-nm line (Hg $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ transition) are presented as a function of electron energy for electrons which are scattered inelastically ($6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ excitation) in the forward direction. The analysis of these polarization components allows one to determine the role of spin-dependent interactions during collision as well as to determine the relative phase of the two scattering amplitudes involved.

The $\frac{1}{R}$ perturbation series for ${\mathrm{H}}_2^{+}$ has a complex Borel sum whose imaginary part determines the asymptotics of the perturbed energy coefficients $E^{\mathrm{}\left(N\right)\mathrm{}}$. The full asymptotic expansion for the energy includes complex, exponentially small terms: $\left\{E\right(R)\mathrm{}\sim \Sigma E^{\mathrm{}\left(N\right)\mathrm{}}{\mathrm{}\left(2R\right)\mathrm{}}^{-N}+,e^{-\frac{R}{n}}\Sigma a^{\mathrm{}\left(N\right)\mathrm{}}{\mathrm{}\left(2R\right)\mathrm{}}^{-N}\}\{+e^{-\frac{2R}{n}}[\Sigma d^{\mathrm{}\left(N\right)\mathrm{}}{\mathrm{}\left(2R\right)\mathrm{}}^{-N}+logR\mathrm{terms}]\pm i{e}^{-\frac{2R}{n}}\Sigma c^{\mathrm{}\left(N\right)\mathrm{}}{\mathrm{}\left(2R\right)\mathrm{}}^{-N}+\dots \}$

The explicit imaginary terms cancel the implicit imaginary part of the Borel sum. An exact relation between the double-well gap series, $\exp (-\frac{R}{n})\Sigma a^{\mathrm{}\left(N\right)\mathrm{}}{\mathrm{}\left(2R\right)\mathrm{}}^{-N}$, and the $i\exp (-2\mathrm{}\frac{R}{n})$ series is derived.

The $5p_{\frac{3}{2}}$ and $5p_{\frac{1}{2}}$ one-electron momentum probability distributions in xenon, measured by means of the noncoplanar symmetric ($e$,$2e$) reaction, show clear and direct manifestations of relativistic effects. The momentum densities and branching ratios cannot be described by nonrelativistic wave functions, but they are in very good agreement with those given by Dirac-Fock wave functions.

Using a simple model of a plasma between two boundaries at which temperature is fixed, we investigate the thermal transport in the collisionless limit, relaxing the usual local neutrality assumption. For physically relevant external parameters, an analytical solution is found where the heat flux is reduced with respect to its value when local electroneutrality is assumed.

Energetic trapped particles are shown to have a destabilizing effect on the internal kink mode in tokamaks. The growth rate is near the ideal magnetohydrodynamic value, but the frequency is comparable to the trapped-particle precession frequency. A model for the instability cycle gives stability properties, associated particle losses, and neutron emissivity consistent with the "fishbone" events observed in poloidal divertor experiments.

Spinodal decomposition has been studied for a binary system with medium-range interactions. The results indicate that the classical theory of Cahn and Hilliard, which predicts an exponential growth of the structure factor for small wave vectors, holds for a certain range of composition within the spinodal region for short times after a quench.

The first total-energy calculations of barriers to interstitial migration have been used to study silicon self-interstitial migration. Migration occurs through the low-electron-density path. Relaxation was found to be important in determining the barrier for both ${\mathrm{Si}}^{\mathrm{}\left(0\right)\mathrm{}}$ and ${\mathrm{Si}}^{\mathrm{}(++)\mathrm{}}$. Electron-assisted migration has been demonstrated. ${\mathrm{Si}}^{\mathrm{}(++)\mathrm{}}$ was found to have lower energy at the tetrahedral site while ${\mathrm{Si}}^{\mathrm{}\left(0\right)\mathrm{}}$ has lower energy at the hexagonal site.

A new two-step quench technique has been used to decouple the effects of nucleation and growth in studies of homogeneous nucleation in the system (isobutyric acid) + water in the neighborhood of the upper critical solution temperature. The results demonstrate that the nucleation process is normal, in accord with theories that ascribe anomalous behavior of the cloud-point curve to critical slowing down of the growth of droplets.

The decay rate has been determined for positrons annihilating with electrons while localized in the image-induced potential well at the (110) surface of a clean well-annealed single crystal of Al at 300 K. The lifetime associated with positrons in this surface state was found to be 580 ± 10 psec. This value, which has never before been directly measured, is in disagreement with present theories. Changes in the lifetime spectra were also found from ion sputtering and from exposure of the surface to various amounts of oxygen.

X-ray photoelectron spectra of the valence bands of K${\mathrm{C}}_8$ are presented and compared with spectra for potassium metal and graphite. Potassium spectra show a clear peak at $E_{\mathrm{F}}$ associated with the metallic $4s$ band; K${\mathrm{C}}_8$ shows only a weak, monotonic response near $E_{\mathrm{F}}$ (similar to that of graphite) which is attributable entirely to graphite states. It is concluded that if an $s$- like band exists in K${\mathrm{C}}_8$ it is occupied by less than 0.04 electron/K atom.

The polarization dependence of the differential reflectivity of the Si(111)2×1 single-domain surface has been studied experimentally. A marked anisotropy of the optical peak at 0.45 eV associated with dangling bonds is observed with maximum absorption along $\left[0\mathrm{}\overline{1}1\right]$ directions. The chain model is in good agreement with the experimental result.

The polarization dependence of midgap optical absorption (0.38-0.51 eV) by Si(111)2×1 single-domain surfaces has been measured directly by photothermal displacement spectroscopy. The absorption is strongest when the light is polarized perpendicular to the period-doubling direction of the 2×1 reconstruction and is reduced by at least 95% when the polarization is rotated by 90°. This result supports the $\pi$-bonded chain model of the Si(111)2×1 surface reconstruction.

In a spin-polarized photoemission experiment the escaping polarized electrons interact with a paramagnetic surface layer of variable thickness. From the depolarization of the photoelectrons the exchange constant acting between the photoelectrons and the paramagnetic moments is obtained.

A probability distribution has been proposed recently by one of us as an order parameter for spin-glasses. We show that this probability depends on the particular realization of the couplings even in the thermodynamic limit, and we study its distribution. We also show that the space of states has an ultrametric topology.