We measured the differences in $R=\frac{{\sigma }_L}{{\sigma }_T}$ and the cross-section ratio $\frac{{\sigma }^A}{{\sigma }^D}$ in deep-inelastic electron scattering from D, Fe, and Au nuclei in the kinematic range $0.2\le x\le 0.5$ and $1\le Q^2\le 5$ ${(\mathrm{G}\mathrm{e}\mathrm{v}/\mathit{c})}^2$. Our results for $R^A-R^D$ are consistent with zero for all $x$ and $Q^2$, indicating that possible contributions to $R$ from nuclear higher-twist effects and spin-0 constituents in nuclei are not different from those in nucleons. The European Muon Collaboration effect is reconfirmed, and the low-$x$ data from all recent experiments, at all $Q^2$, are now in agreement.

A search for nuclear-bound states of the $\eta$ meson has been carried out. Targets of lithium, carbon, oxygen, and aluminum were placed in a ${\pi }^{+}$ beam at 800 MeV/c. A predicted $\eta$ bound state in ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}_{}^{*}{}_{}{}^{}\left(E_x\approx 540 \mathrm{MeV}\right)$ with a width of ≅ 9 MeV was not observed. A bound state of a size ⅓ of the predicted cross section would have been seen in this experiment at a confidence level of $3\sigma \mathrm{}(P>\mathrm{}0.9987\mathrm{})\mathrm{}$.

Projectile fragmentations of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$, and ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ have been measured at 0.79 GeV/nucleon. Production cross sections and momentum distributions of the produced isotopes ($Z\ge 2$) are measured inclusively. Transverse-momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ from the fragmentation of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ show two Gaussian components of different widths. The width of the wide component is consistent with the values observed in the fragmentation of stable nuclei, whereas the other component shows an extremely narrow width reflecting the weak binding of the two outer neutrons in the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ nucleus.

The neutron decay of the giant monopole resonance region between 13 and 15 MeV in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ is analyzed in terms of collective and statistical doorway states. The direct escape widths of the giant monopole resonance populating the lowest five valence hole states of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ are determined, and compared with the results obtained from complex collective states. This comparison discriminates sharply between different model Hamiltonians which predict similar energies and collectivities for the resonance.

We report the application of a new nonoptical detection scheme in laser spectroscopy on ion beams of on-line isotope separators. The method consists of ground-state depopulation by optical pumping in collinear laser-ion-beam interaction, state-selective neutralization, and charge-state-separated fast-atom counting. Strontium isotope-shift measurements are extended into the strongly deformed region of the neutron-rich isotopes up to ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sr}$. The radii are generally well described by the droplet model including empirical deformatins obtained from $B\left(E2\mathrm{}\right)\mathrm{}$ values.

Some recoil corrections of order $\frac{{\mathrm{}\left(\mathrm{Za}\right)\mathrm{}}^6{m}^2}{M}$ are calculated for the Lamb shift of the $n=2\mathrm{}$ state of hydrogen. These arise from double Coulomb, single transverse, and double transverse exchange processes. The complete known expression is presented and numerical results are compared with existing experiments.

A series of stable multichromatic solutions is presented explicitly based on a band model for cw dye lasers. The results explain recent experimental observations of bichromatic operation in cw dye lasers and predict still higher-order multichromatic steady states.

We show by means of a quantum electrodynamic calculation that excess noise is inherent in the process of optical phase conjugation, both in that the state of the field leaving a phase-conjugate mirror can always be described classically (i.e., its phase-space density is positive semidefinite) and in that the fluctuations in the generated field are always greater than those predicted by Poisson statistics. Except in special cases, quantum noise imposes a limitation on the ability of phase conjugation to remove the effects of aberrations.

An approximate but nonlinear inverse solution of the one-dimensional inhomogeneous Helmholtz equation is presented enabling the size and strength of a lossless scattering object to be determined from amplitude data alone. This is achieved by exploitation of the structure of the scattered field in the complex plane. In addition, the analytic signal is recovered since the solution enables the phase to be determined. The inverse solution is illustrated for a case when the approximate solution becomes exact and then demonstrated on experimental data.

We report the first observation of stochastic resonance in an optical device, the bidirectional ring laser. The experiment exploits a new technique to modulate periodically the asymmetry between the two counter-rotating lasing modes. The measurements verify that the addition of injected noise can lead to an improved signal-to-noise ratio (relative to that observed with no externally injected noise).

The first observation of $H$-mode confinement with electron heating as the sole auxiliary heating method has been made in divertor discharges in the DIII-D tokamak. These discharges exhibit the usual characteristics of the $H$ mode, including improved confinement of particles and energy, when electron cyclotron heating is added at a power level above 0.7 MW. The $H$-mode transition is accompanied by the development of an electron temperature pedestal of 0.25 keV and a dramatic steepening of the density gradient near the separatrix.

The free energy of a $D$-dimensional elastic solid embedded in a $d$-dimensional space and subject to an extrinsic bending energy is defined, and the solid's flat phase studied. An $\epsilon =4-D$ expansion about the upper critical dimension $D_{\mathrm{uc}}=4\mathrm{}$ is performed; exponents characterizing the renormalization of the Lamé coefficients $\lambda$ and $\mu$, and the rigidity $k$, are computed to $O\left(\epsilon \right)$; and exact equations connecting these exponents are derived. Near $D=4\mathrm{}$, fluctuations increase the rigidity, and so tend to stabilize the flat phase.

An order-parameter theory of the crumpling transition in $D$-dimensional polymerized membranes embedded in $d$ dimensions is developed. Within mean-field theory, we show how self-avoidance modifies the behavior at the second-order crumpling transition. Fluctuations drive the transition first order to lowest order in $\epsilon =4-D$, for $d<\mathrm{}{d}_c\approx 219$.

We discuss a dynamical transition in the propagation of fronts into an unstable state of a bistable system. In one regime, the front leads to a new form of pattern formation, in which a periodic state consisting of kinks and antikinks emerges whose wavelength diverges at the transition with an exponent frac32;. In the particular model studied, this periodic state is actually weakly unstable.

Extremely strong superstructure reflections have been observed for the first time by transmission electron microscopy for (110) edge-on ${\mathrm{Ga}}_{0.5}$${\mathrm{In}}_{0.5}$P crystals lattice matched to GaAs. Growth was carried out by metal-organic vapor-phase epitaxy. A monolayer superlattice (SL) of (Ga-rich plane) (In-rich plane)... is formed along [¯111] and [1¯11] directions. The substrates are found to be playing a vital role in the SL formation. Band-gap energy reduction (≅80 meV) has been observed for layers with these SL's.

Single-crystal x-ray diffraction measurements have been performed on solid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ from 15.6 to 23.3 GPa at 300 K with synchrotron radiation. The diffraction patterns demonstrate that the structure of the solid is hexagonal close packed over this pressure-temperature range, contrary to both the interpretation of high-pressure optical studies and to theoretical predictions. The solid is more compressible than is indicated by equations of state calculated with recently determined helium pair potentials. The results suggest that a significant revision of current views of the phase diagram and energetics of dense solid helium is in order.

We present an approach for aggregating Penrose tiles to form a defect-free, 2D pentagonal quasicrystal tiling. Contrary to conventional wisdom, defect-free quasiperiodic tilings can be constructed by use of local rules alone. The results provide new insights as to how materials with only short-range atomic interactions can grow large, nearly perfect quasicrystal grains.

The kinetics of spinodal decomposition has been studied by a Monte Carlo renormalization-group method. Using the standard blocking transformation, we numerically renormalize the evolving configurations during phase separation of a two-dimensional kinetic Ising ferromagnet with spin-exchange dynamics. We find that, as the scaling regime is approached, the domain size $R$ grows in time $t$ as $R\sim t^n$, where we obtain $n=0.338\mathrm{}\pm 0.008$. This is consistent with the classical result of Lifshitz and Slyozov for Ostwald ripening, namely $n=\frac{1}{3}$.

We present a theoretical description of a displacive incommensurate reconstruction roughly modeling that of Mo(001). Through a molecular-dynamics study, we obtain a first realistic picture of the low-temperature structure and solitons, of the temperature-dependent static lattice and phase transition properties, and of the crossover from phason to soft ${\Sigma }_1$ phonon across the transition.

Molecular-dynamics simulations of homogeneous crystalline nucleation in systems of 1300 Lennard-Jones particles have been performed as a function of quench depth. The time lag between the time of formation of the critical nucleus and the time of release of latent heat is observed to be a nonmonotonic function of quench depth. The increase of the time lag for deep quenches is interpreted as evidence for critical slowing down and the influence of a "pseudospinodal."