Room-temperature x-ray diffuse scattering experiments are reported for hydrogen in solution in vanadium. Uniaxial stress (below the elastic limit) results in transformation of all hydrogen atoms from $1T$ into $4T$ states; each hydrogen is delocalized over four neighboring $T$ sites via tunneling. The diffusion coefficient of the $4T$ hydrogen, $D_{4T}$, is measured from 340 to 200 K under an external $〈111〉$ stress. It is extraordinarily large as compared to the existing data and satisfies the relation $D_{4T}=D_0\exp \left(\frac{-E}{kT}\right)$, where $D_0=1.6\mathrm{}\times {10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$/s and $E=6\mathrm{}$ meV.

A new structural model for the Si(111)7×7 surface called the pyramidal cluster model is proposed on the basis of specialized low-energy ion-scattering experiments.

The viscosity of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ contained in a 45-μm-high chamber has been studied. The slip correction and a clearly defined maximum in the effective viscosity are resolved in this experiment. The magnitude of the slip correction and the position of the maximum in the effective viscosity are found to be in disagreement with recent theoretical work.

A group-theoretical analysis of chlorine nuclear quadrupole resonance data restricts to two the possible space-group symmetries of the low-temperature phase of Pr${\mathrm{Cl}}_3$. Consideration of this result along with experimental information on the interactions and the susceptibilities allows the transition to be identified as a Jahn-Teller Peierls dimerization. It is similar to the spin-Peierls transition but different in that the spins involved are pseudospins associated with the Jahn-Teller coupling.

The relaxation of photoconduction in a polydiacetylene crystal containing a high density of defects is shown to follow the predictions of the theory for field-dependent diffusion in one dimension. At intermediate times and fields an $\exp [-3\mathrm{}{\left(\frac{t}{{\tau }_1}\right)}^{\frac{1}{3}}]$ law is observed merging into an $\exp \left(\frac{-t}{{\tau }_2}\right)$ behavior as $t\to \infty$. The predicted functional change of ${\tau }_2\mathrm{}\left(E\right)\mathrm{}$ at a critical field is recovered.

An experiment is presented which allows the direct observation of the reflection of conduction electrons in a normal metal at a normal-metal-superconductor interface (Andreev reflection). The experimental findings are in agreement with a change of the quasi-particle-excitation branch on reflection (electron-hole transition). The Andreev-reflection probability can be estimated from the experimental results.

The first systematic study of the energy dependence of a core-level shake-up feature is presented. In contrast to expectations the shake-up peak remains nearly unchanged in intensity down to ∼ 15 eV above threshold. The early and abrupt turn-on of the multi-electron satellite found experimentally is well explained by a theory which describes the transition from adiabatic to sudden core-level excitation by a simple exchange-interaction picture.

Self-generated nonlinear oscillations and chaos are found in the conductance of liquid-He-cooled far-infrared photoconductors made from ultrapure Ge. Complex behavior includes a period-doubling cascade to chaotic oscillation with increasing applied electric field, quasiperiodic oscillation, frequency locking, and intermittent switching between modes of oscillation. A rate-equation model is presented which includes impurity impact ionization and space-charge injection.

Angle- and spin-resolved photoemission spectra from Ni(110) have been measured in the temperature range $0.5<~\frac{T}{T_C}<~0.94$. The data cannot be reconciled either with the predictions of local band theory assuming a temperature-independent exchange splitting or with a pure Stoner model. It is concluded that the exchange splitting decreases with increasing temperature and that spin fluctuations strongly influence the photoemission line shapes.

It is shown that in contrast to previous assumptions the real magnetic dipole interaction has to be considered as a possible source of deviations of the dynamical exponent $z$ from $\frac{5}{2}$ as observed recently on Fe and Ni. While the dipolar crossover temperatures agree with experiment, at $T_c$ the dynamic crossover around the dipolar wave vector $q_d$ as predicted by current theories is absent. It is argued that this effect is related to a hitherto overlooked dynamical decoupling between transverse and noncritical longitudinal fluctuations if $q$ exceeds the inverse correlation range $\kappa$.

The correlation function of the phases of a quantum particle in a one-dimensional random potential is defined and calculated analytically and numerically. Away from eigen-states it decays exponentially with the phase correlation length equal to half of the localization length, while for the eigenstates it saturates at nonzero value.

Optical saturation of highly excited states in the conduction band of a semiconductor and the subsequent extremely fast energy relaxation due to carrier-carrier and opticalphonon scattering at room temperature are observed. The corresponding measured life-time for states 160 meV above the band edge in ${\mathrm{Al}}_{0.34}$${\mathrm{Ga}}_{0.66}$ As is in the range of 80 to 30 fs depending upon the photoexcited carrier density.

A new form of the Navier-Stokes equation resulting from a change of variables is presented. The new form has several advantages: It yields a new asymptotic behavior of the flow for long times and vanishingly small viscosity. In addition an interpretation of the new equation in terms of a simple random walk yields immediately not only the Kolmogorov $\frac{2}{3}$-power law but also an intermittency exponent well within the experimental uncertainty.

A model of classical particles in one space dimension with an elementary length and general finite-range interaction with hard core is considered. It is shown that such a model must have a periodic ground state.

A simple model is discussed for a periodically forced oscillator with a constraint which leads to motions with impacts. For "perfectly plastic" impacts the dynamics is represented by a discontinuous map defined on the circle. The map is shown to undergo perioddoubling bifurcations followed by complex sequences of transitions, due to the discontinuities, in which arbitrarily long superstable periodic motions occur.

New limits are reported on right-handed currents, based on precise measurement of the $e^{+}$ spectrum end point in ${\mu }^{+}$ decay. Highly polarized muons from the TRIUMF "surface" beam were stopped in metal foils within a 1.1-T spin-holding longitudinal field or a 70-G spin-precessing transverse field. For the spin-held data, the $V-A$ decay rate vanishes in the beam direction at the end point. Measurement of this rate sets the 90%-confidence limits $\frac{\xi P_{\mu }\delta }{\rho }>0.9959\mathrm{}$ and $M\left(W_R\right)>\mathrm{}380\mathrm{}$ GeV, where $W_R$ is the possible righthanded gauge boson.

A simple argument based on current algebra is given to show how monopoles can lead to baryon decay and other flavor-changing processes.

Evidence is presented for a narrow meson resonance of mass 1970±5±5 MeV produced in continuum $e^{+}{e}^{-}$ annihilations at $\sqrt{s}$ of 10.5 GeV, and decaying into a $\varphi$ and a charged $\pi$.

A useful definition of the topological charge of a lattice gauge-field configuration is given. This definition is used to calculate the topological susceptibility ${\chi }_t=\frac{〈Q^2〉}{V}$ in SU(2) lattice gauge theory by means of a Monte Carlo simulation. ${\chi }_t={(170\mathrm{}\pm 25 \mathrm{MeV})}^4$ is obtained, in good agreement with the current algebra prediction. Other possible uses of this operator are suggested.

Measurements of longitudinal momenta transferred to mass-identified products of the fragmentation of Cu by ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ions give clear evidence for a change in reaction mechanism between 22 and 84 MeV/u. Results at 84 MeV/u are generally consistent with peripheral interactions. However, at 22 MeV/u large momentum transfers observed for near-target products suggest that strongly damped proceses have become important. Limits to momentum transfer of the type reported by Galin et al. are shown to arise in a natural way from this transition.