Ordered overlayers of Sm on Cu(001) were studied by low-energy diffraction and x-ray photoelectron spectroscopy. The Sm valence varied linearly from 2 to 2.7 during the formation of the monolayer. We argue that the intermediate valence was homogeneous. The behavior is compared with that of Sm overlayers on Al(001).

The gelation process in a monolayer adsorbed at the oil/water interface has been monitored by measurement of the shear mechanical properties. A clear sol-gel transition has been observed for the first time in a two-dimensional system.

We have studied the growth kinetics of several systems with highly degenerate ground states which were quenched from a high ($T\gg T_c$) to a low temperature ($T\cong 0$). The mean domain size $R$ increases algebraically with time as $R\cong t^n$, where surprisingly the value of $n$ is observed to fall into one of two universality classes for all the models studied. We observe a distinct crossover from one universality class to the other as the spin interaction is varied.

Quantitative measurements have been made of the superfluid mass per unit area for the interfacial superfluid phase present at the boundary wall of low-concentration mixtures of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. We find a rapid jump in the superfluid mass at the transition temperature in agreement with the prediction of the Kosterlitz-Thouless theory of the superfluid transition in a two-dimensional system.

We report on a study of the evolution of the structure factor $S(k,t)\mathrm{}$ of a binary fluid mixture near the consolute critical point after rapid quenches which kept the system in the stable, one-phase region. $S(k,t)\mathrm{}$ always relaxed more slowly than expected on the basis of linear response and, under certain conditions, overshot the equilibrium value. A nonlinear theory without adjustable parameters, based on the Langevin equations for order-parameter fluctuations near the critical point, agreed with the data.

The shear viscosity $\eta$ of the hard-sphere fluid, at volumes of 1.6 and 2 times the close-packed volume, is computed with use of nonequilibrium molecular dynamics. At high shear rate $\dot{\epsilon }$ we observe a phase transition in which the system undergoes two-dimensional ordering in the plane perpendicular to the flow, accompanied by a sharp decrease in $\eta$. For small $\dot{\epsilon }$, no evidence is found for the square-root dependence on $\dot{\epsilon }$ reported by previous investigators.

The importance of higher-order exchange interaction in localized $S$-state systems is discussed. The equation of motion is solved for a one-dimensional antiferromagnet with bilinear and biquadratic exchange coupling. It is shown that the biquadratic exchange interaction usually cannot be derived from the observed spin-wave dispersion, but is susceptible to experimental determination from the excitation spectra of small clusters of magnetic ions as exemplified for $\mathrm{Cs}{\mathrm{Mn}}_x{\mathrm{Mg}}_{1-x}{\mathrm{Br}}_3$ by inelastic neutron scattering.

A method of using the ac Josephson current between two superconducting electrodes to probe the spin fluctuations of a magnetic insulating barrier of a junction is suggested. The dc $I-V$ characteristic of such a junction measured as a function of both the dc bias voltage $V$ and the magnitude of a magnetic field parallel to the plane of the junction is predicted to be proportional to the imaginary part of the frequency- and wave-vector-dependent susceptibility of the magnetic material.

Measurements of the far-infrared absorption coefficient of a novel composite material that can also be studied by transmission electron microscopy permit new bounds to be placed on the anomalous enhancement by well-dispersed small metal particles. Clumped particles are stronger absorbers.

We report the latest results of timing measurements of the binary pulsar PSR 1913+16. Recent high-quality data have enabled us to measure the excess propagation delay of the pulsar signal caused by the gravitational field of the companion star; this result provides strong additional support for the simplest and most straightforward model of the system. The observed rate of orbital period decay is equal to 1.00 ± 0.04 times that expected from gravitational radiation damping.

We construct arbitrary matrix elements of the quantum evolution operator for a wide class of self-adjoint canonical Hamiltonians, including those which are polynomial in the Heisenberg operators, as the limit of well defined path integrals involving Wiener measure on phase space, as the diffusion constant diverges. A related construction achieves a similar result for an arbitrary spin Hamiltonian.

A practical method is presented for calculating many-parameter renormalization-group trajectories for both spin systems and lattice gauge theories from Monte Carlo computer simulations. It provides a direct check on the assumption of short-range renormalized interactions, and preliminary work indicates improvement of the convergence in the calculation of critical exponents.

A local entropy density for a fluid obeying the revised Enskog equation is defined and the entropy balance equation is derived. The source term is nonnegative for arbitrarily strong inhomogeneities.

A Euclidean lattice formulation is presented of the general fourth-order gravitational action involving $R_{\mu \nu }^2$ terms. This lattice theory is bounded and reflection positive. The existence of a positive Hilbert space and Hamiltonian, and hence unitarity, follow then from the standard nonperturbative Osterwalder-Schrader construction.

A real-space renormalization-group method is used to investigate particle motion on percolation lattices in the presence of an external force $\overrightarrow{\mathrm{K}}$. At the percolation threshold $p_c$ the particle position, $〈R〉$, varies as $〈R〉\propto t^{\chi }$, where $\chi <1\mathrm{}$ and $t^{\chi }$ gives the mean square displacement. Near $p_c$, the linear response theory is found to hold only asymptotically under the condition $\gamma \equiv \frac{\mathrm{Kl}}{k_{\mathrm{B}}T}\lesssim {\xi }^{-1\mathrm{}}$ or $\gamma \lesssim {\mathrm{}\left(\mathrm{wt}\right)\mathrm{}}^{-\frac{\chi }{2}}$, where $l$ is a lattice constant, $\xi$ is a coherence length, and $w$ is a transition rate.

We present a new NMR method for the investigation of rotational Brownian motion based on the appearance of dipolar relaxation as the particles rotate. Our experimental results obtained on submicrometer polystyrene spheres in water confirm quantitatively the basic laws of rotational Brownian motion. The effects of hydrodynamic interactions and long-time tails are discussed.

Induced transitions give rise to enhanced probabilities of finding a large number of pions of the same charge. The exact charge distribution with induced emission fully taken into account is solved in a simple model. The enhancements are found to be large. These effects are observable in high-energy heavy-ion collisions, and possibly are responsible for the cosmic-ray Centauro-like events.

At large $N$, the $\eta {\overrightarrow{\phi }}^6$ theory is shown to possess a nontrivial ultraviolet fixed point. A new phase is found where asymptotic scale invariance is spontaneously broken and a dynamical mass is generated through dimensional transmutation. At the tricritical limit, the spontaneous breaking of an exact scale invariance at leading $N$ results in the formation of a massless composite Goldstone mode, the dilaton. We compare these results to standard $\frac{1}{N}$ expansion and emphasize the nonperturbative nature of these phenomena.

We consider the next level of corrections to the $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ charge asymmetry for beam energies presently of interest. If we define these weak single-loop corrections with an on-mass-shell renormalization scheme, only the $Z$-boson self-energy is nonnegligible and that contribution itself can be redefined into the Born term upon change of scheme to an expansion in the Fermi coupling constant. A compact formula for the $\gamma Z$ box diagram is also presented.

Using data on the coherent production of ${\pi }^{+}{\pi }^{+}{\pi }^{-}$ systems in ${\pi }^{+}$ collisions with nuclei, we have extracted an estimate for the radiative partial width of the $A_1$. The rate for ${A_1}^{+}\to {\pi }^{+}\gamma$ is 640±246 keV, which is a factor of about 2-3 below the value expected on the basis of predictions from quark models and from vector dominance ideas.