Differences in the $D^{+}$ and $D^0$ lifetimes may arise either from 6 dominance in the effective nonleptonic Hamiltonian, or from the dominance of a particular $W^{+}$-exchange diagram which behaves like a $D^0-{{\overline{K}}^0}^{*}$ pole. If 6 dominance holds, then the $F^{+}$ will have a relatively short lifetime and a small semileptonic branching ratio, just like the $D^0$; but if $W^{+}$ exchange is dominant, the $F^{+}$ will have a long lifetime and large semileptonic branching ratio, like the $D^{+}$.

The resistance of amorphous W-Re wires between 2 and 20° K has been measured. Wires with a resistance of approximately 10 kΩ show a different temperature dependence from that of wires with a resistance of over 200 kΩ. The latter show a relative increase in resistance as the temperature is decreased or the magnetic field is increased. These wires also show an anomalous dependence of resistance on width and length. These results are discussed in the perspective of Thouless's suggestion of maximum metallic resistance.

Calculations of the electronic states and total energies of various bonding conformations in hydrogenated amorphous Si are presented. Various surprising results emerge, including identification of peaks in photoemission spectra as signatures of nearest-neighbor SiH configurations, a gap increasing with increasing H content while the conduction band remains essentially unchanged, and localized states in the gap arising from various defects whose energies are in sharp contrast to recently proposed simple model estimates.

In two dimensions the frequency of magnetoconductivity oscillations measures the sum of Fermi-surface areas when the Landau levels are sharp. This explains why (100) Si inversion layers with two occupied subbands show only one frequency. It also explains why the frequency observed on (111) surfaces simulates a valley degeneracy of 2, even though six valleys are occupied.

The superconducting properties of thin granular lead films provide evidence for the existence of clusters which mitigate electrostatic charging effects and allow Josephson coupling to remain favorable in samples with normal-state sheet resistance near the maximum metallic resistivity of 30 000 Ω/sq. The disappearance of zero-resistance transitions together with the precipitous onset of temperature broadening in this range is therefore most likely associated with the localization of electronic states.

The reaction $D^0\to s+\overline{d}+\mathrm{gluon}$ is proposed as a source for the difference in the life-times of the charged and neutral $D$ mesons. In a nonrelativistic bound-state model the rate for the reaction is found to depend on the ratio $\frac{f_D}{m_u}$. For reasonable values of this ratio the observed difference in the lifetimes may be accounted for.

From an analysis of 2275 $\overline{\nu }p\to {\mu }^{+}+X^0$ events at an average $Q^2$ of 4.5 Ge${\mathrm{V}}^2$, there are presented the first measurements, up to one undetermined overall normalization constant, of the $x$ dependence of the proton structure functions using antineutrinos, and of the $u$ and $\overline{d}+\overline{s}$ quark distributions. The result for $u\left(x\right)\mathrm{}$ is in good agreement with models based on fits to electron and muon scattering data. With $u\left(x\right)\mathrm{}$ normalized to those models the absolute antiquark momentum distribution $x[\overline{d}x+\overline{s}\mathrm{}(x\left)\right]$ in the proton is determined.

Giant backbending is predicted to occur in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}$ at $J\approx 26\hslash$. The effect is clearly seen to be the result of the crossing of two bands with very different intrinsic structure.

This paper reports calculations of the influence of a reaction time $T>\mathrm{}{10}^{-21\mathrm{}}$ s in deep-inelastic Xe-Pb collisions on the energy spectrum of $\delta$ electrons ejected in the same collision. It is shown that the lifetime of the superheavy composite system causes pronounced oscillations of width $\epsilon =\frac{h}{T}$ in the electron distribution, which survive the inclusion of multistep excitations and the folding with a lifetime distribution function. This effect may serve as an atomic clock for deep-inelastic collisions.

Inclusive double-differential cross sections for neutron production were measured at 337 MeV/nucleon in the reaction $\mathrm{Ne}+\mathrm{U}\to n+X$. Neutrons were detected with energies between ∼ 12 and ∼ 600 MeV at laboratory angles of 30°, 45°, 60°, and 90°. The neutron spectra above ∼ 30 MeV are comparable with the predictions of a "firestreak" calculation. The neutron spectra differ from proton spectra reported for U and Pb.

We investigated the angular distribution of autoionization electrons from the process ${\mathrm{He}}^{+}$ + He→${\mathrm{He}}^{+}$ + ${\mathrm{He}}^{**}$ at 2 keV in coincidence with the scattered ions. In the angular range where electrons ejected from the target and the charge-exchanged projectile have the same laboratory energy we observe a pronounced interference structure. This can be ascribed to an interference of amplitudes for electron emission from target and projectile, respectively.

It is shown that in optical transitions with a bottleneck, a mode-locked cw dye laser may be used to generate and heterodyne detect picosecond photon echoes. These echoes are stimulated from an accumulated grating in the electronic ground state formed by a train of twin excitation pulses of constant phase difference. In the zero-phonon transition of pentacene in naphthalene at 6026.8 Å the bottleneck is identified and these echoes are used to determine the dominant dephasing process.

In C${\mathrm{O}}_2$-laser irradiation of thick microdisk foils, a significant fraction of the absorbed laser energy is found to be coupled to the rear surface. Moreover, $K\alpha$ and fast-ion emission has given, for the first time, direct evidence that the rear surface is subjected to considerable bombardment, by the transport of hot electrons around the target.

The electronic structure and the phonon dispersion curves of EuS, SmS, ${\mathrm{Sm}}_{0.75}$ ${\mathrm{Y}}_{0.25}$ S, and YS are analyzed. A five-parameter model is deduced which describes the phonon dispersion of ${\mathrm{Sm}}_{0.75}$ ${\mathrm{Y}}_{0.25}$ S quite well. Two nearest-neighbor Sm-S forces and three deformabilities are introduced, two of which are attributed to virtual $f-d$ transitions with dipolar- and "breathing"-type symmetry while the third is a quadrupolar-type sulfur deformability. The model suggests a strongly localized form of the microscopic theory.

The phonon dispersion and elastic constants of mixed-valent ${\mathrm{Sm}}_{0.75}$ ${\mathrm{Y}}_{0.25}$ S are calculated. The microscopic model takes into account interactions of localized $4f$ electrons with lattice vibrations and phonon-induced $4f\leftrightarrows 5d$ transitions leading to a breathing of the rare-earth ionic radius. The resulting three-parameter model yields a quantitative overall agreement with quite anomalous experimental dispersion curves. As input data the unrenormalized frequencies are obtained from a second-neighbor Born-von Kármán model.

Measurements of the structure factor $S\mathrm{}\left(k\right)\mathrm{}$ for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at constant density above and below $T_{\lambda }$ are reported. The results show a clear loss of spatial order on cooling through $T_{\lambda }$. Application of the theory of Cummings, Hyland, and Rowlands to the data allows a measurement of the condensate fraction for He II.

By applying the method of Hyland, Rowlands, and Cummings to pair-correlation functions obtained from new high-accuracy neutron-diffraction measurements, the condensate fraction, $n_0$, in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been determined for seven temperatures in the range $1.00<~T<~2.15$ K. The results are very well described by the relation $n_0\mathrm{}\left(T\right)=n_0\mathrm{}\left(0\right)[1-{\left(\frac{T}{T_{\lambda }}\right)}^{\alpha }]$, with $n_0\mathrm{}\left(0\right)=0.133\mathrm{}\pm 0.012$ and $\alpha =6.2\mathrm{}\pm 1.6$.

The zone folding in the acoustic-phonon dispersion curve of GaAs/AlGaAs superlattices is demonstrated using superconducting tunnel junctions as sources and detectors of quasimonochromatic phonons. We present data on selective transmission of high-frequency phonons due to narrow band reflection determined by the superlattice period.

The coefficient of ellipticity of the liquid-vapor interface of liquid argon has been measured to be $\overline{\rho }\times {10}^4=5.7\mathrm{}\pm 0.4$ at 90°K, rising to 8.8±0.6 at 120°K. Assuming a Fermi density profile and isotropy of the dielectric constant in the interface region, this yields a 10%-90% interface thickness $t\left(90\mathrm{}°\mathrm{K}\right)=7.9\mathrm{}\pm 0.5$ Å and $t\left(120\mathrm{}°\mathrm{K}\right)=15.2\mathrm{}\pm 1.0$ Å, averaged over a surface dimension of the wavelength of light. The measurement is compared with predictions, and theoretical uncertainties are emphasised.

An x-ray study of the Cs layers in ${\mathrm{C}}_{24}$Cs is presented. The Cs layer has a uniform 2-d liquidlike structure at 300 K not in registry with the graphite layers. A crossover to 3-d interlayer correlation is observed at 165 K. Single-crystal measurements show that the Cs layers rotate relative to the graphite $〈100〉$ directions. An orientational ordering between two positionally disordered phases occurs at 228 K and a new transition to a mixed registered phase at 50 K is reported.