A new, nonperturbative, feature of chain conformations in strongly ordered polymeric smectics is found. Like the solitary hairpin defects in polymeric nematics, these features arise from the confinement of the chain, in our case spatial confinement by the smectic layers as well as the directional restrictions of the nematic. This liquid-crystalline reduction in chain entropy is resisted by layer hopping. Consequent exponential variation of chain dimensions is given by a simple kink argument, in accord with a systematic analysis.

We present here the first determination of the anisotropy of the surface Debye-Waller factor involved in a surface extended x-ray-absorption fine-structure (SEXAFS) experiment. It is deduced by use of relative temperature-dependent amplitude functions for two different polarizations. The mean square relative displacements of atoms are calculated with an elaborate lattice-dynamical model, treated by a continued-fraction technique. The results are in good agreement which shows the ability of SEXAFS as a valuable tool for the study of surface vibrations.

The polymorphism of both silica and ice is described by a new chemical relationship between the different crystalline structures (cristobalite, etc.). This relationship is given by the set of admissible screw axes of a tetrahedrally coordinated crystal. The various winding numbers correspond to commensurate cylindrical superstructures calculated from a nonlinear model for both oxygen bonds (Si${\mathrm{O}}_2$) and hydrogen bonds (${\mathrm{H}}_2$O). Glass, in this description, is a strongly incommensurate ("chaotic") modification of cristobalite.

We propose that random and incommensurate superlattices be fabricated to study the Anderson localization of their plasma oscillations, which can be measured by Raman scattering. Specific configurations are suggested which, by duality considerations, allow control of the wave functions relative to the mobility edge in the incommensurate case. Localization effects should be easily observable with presently achievable superlattice parameters.

Vacuum-emission and carrier-separation techniques, together with novel metal-oxide-semiconductor structures, have been used to observe the threshold field for the onset of electron heating in silicon dioxide. The magnitude of this electric field is ≅ 1.5-2.0 MV/cm, independent of oxide thickness and composition. This value is consistent with all of the current theoretical calculations. A minimum average electronic energy of ≅ 1.0 eV is shown to be necessary to observe emission of the electrons into vacuum.

Photoemission measurements of Tm metal films (≃ 1000 Å thick) grown on a copper substrate at 13 K reveal a partial surface valence transition to the divalent $4f^{13}$ state. At room temperature, Tm films deposited on smooth substrates remain purely trivalent, whereas deposition on rough substrates yields small divalent components in the photoemission spectrum. This phenomenon is shown to occur for particularly low-coordinated atoms on rough surfaces, in quantitative agreement with thermochemical predictions.

The ac response of large two-dimensional arrays of proximity-effect Josephson junctions to an oscillating driving field has been studied as a function of temperature, applied transverse magnetic field, and frequency. For an integer number of flux quanta per unit cell, a peak in dissipation and a drop in superfluid density are observed near the superconducting transition of the array. These features as well as their frequency dependence provide clear evidence for the vortex-unbinding transition predicted by the Kosterlitz-Thouless theory.

The dynamical screening of hot carriers in semiconductors is studied by inclusion of the electron-electron interaction directly via a molecular-dynamics approach within the more usual ensemble Monte Carlo technique. We find that the intercarrier interaction cannot be treated by a simple screened Coulomb interaction at very high electric fields, but is characterized by a complicated field- and density-dependent screening function. The details of intercarrier forces are illustrated by calculation of the pair correlation function for the nondegenerate carriers.

We report results of large Monte Carlo simulations of an experimentally realizable random-field system: the three-dimensional dilute Ising antiferromagnetic in a field. We find that the correlation time diverges dramatically as $T\to T_c$; the results are consistent with a proposed new type of activated dynamic scaling. The transition appears to be continuous, with effective critical exponents $\eta =0.5\mathrm{}\pm 0.1$ and $\tilde{\eta }=-1.0\mathrm{}\pm 0.3$ for strong fields, away from the weak-field regime where crossover effects distort exponent estimates. These strong-field exponents satisfy recently derived inequalities.

Evidence is presented for the presence of a "shakedown" satellite near threshold in the $\mathrm{C}-\mathrm{KVV}$ Auger spectrum of graphite. Its origin is shown to be an electron in a relatively long-lived valence-core excitonic level (populated as a result of dynamic core-hole screening) which participates in the Auger decay. Modeling of the shakedown contribution considerably improves agreement in the threshold region between the experimental line shape and a simple one-electron model and represents the first report of Auger intensity resulting from this type of excitonic configuration.

Mikheyev and Smirnov have shown that electron neutrinos above a certain minimum energy $E_m$ may all be converted into $\mu$ neutrinos on their way out through the sun. We assume here that this is the reason why Davis and collaborators, in their experiments, find many fewer solar neutrinos than predicted. The minimum energy $E_m$ is found to be about 6 MeV, the mass $m$ of the $\mu$ neutrino must be greater than that of the electron neutrino, $m_2^2-m_1^2=6\mathrm{}\times {10}^{-5\mathrm{}}$ ${\mathrm{eV}}^2$, and there is a very minor restriction on the neutrino mixing angle.

We discuss the scattering of mesons of arbitrary spin and isospin from baryons in models in which the baryon is considered a soliton, or "skyrmion," in an effective Lagrangean of mesons. Model-independent linear relations between partial-wave amplitudes are derived for $\pi N\to \rho N$ and $\pi N\to \omega N$, and, where possible, are compared with experiment.

This paper describes measurements of the semileptonic weak-neutral-current reactions $\nu {}_{\mu }{}^{}{}_{}{}^{}p\to \nu {}_{\mu }{}^{}{}_{}{}^{}p$ and $\overline{\nu }{}_{\mu }{}^{}{}_{}{}^{}p\to \overline{\nu }{}_{\mu }{}^{}{}_{}{}^{}p$ which yield the absolute differential cross sections $\frac{d\sigma \left(\nu {}_{\mu }{}^{}{}_{}{}^{}p\right)}{d{Q}^2}$ and $\frac{d\sigma \left(\overline{\nu }{}_{\mu }{}^{}{}_{}{}^{}p\right)}{d{Q}^2}$. The weak-neutral-current parameter, ${{sin}^2\theta }_{\mathrm{W}}$, is determined to be ${{sin}^2\theta }_{\mathrm{W}}=0.220\mathrm{}\pm 0.016(\mathrm{stat}.\mathrm{}){}_{-0.031\mathrm{}}{}^{+0.023\mathrm{}}{}_{}{}^{}(\mathrm{syst}.\mathrm{})$.

The ($\alpha ,d_{S=0\mathrm{}}$) reaction was studied for the first time with a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ target at $E_{\alpha }=50\mathrm{}$ MeV. Three $T=1\mathrm{}$ states in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, $0^{+}$ at 2.31 MeV, $3^{-}$ at 8.91 MeV, and a level at 12.6 MeV, were selectively excited. The experimental results were well described by exact finite-range distorted-wave calculations.

The $\mathrm{sdg}$ interacting-boson model is applied to ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$. Energy levels and $E2\mathrm{}$ transitions are calculated. This model is shown to solve the problem of anharmonicity regarding the excitation energy of the first $K^{\pi }=4^{+}$ band relative to that of the first $K^{\pi }=2^{+}$ one. The level scheme including the $K^{\pi }=3^{+}$ band is well reproduced and the calculated $B\left(E2\mathrm{}\right)\mathrm{}$'s are consistent with the experimental data.

Photoelectron spectra of the neon valence satellites have been measured in their near-threshold region. Strong resonance enhancement of the satellite cross section is observed as a result of autoionization of doubly excited Rydberg states. The nonresonant cross section of most satellites follows approximately that of the $2_p$ main line as close as 0.5 eV above threshold. The resonant behavior is explained with respect to correlation effects showing the importance of interchannel coupling for the satellite production. The characteristic differences in the satellite threshold behavior are used to distinguish between relaxation effects and other electron correlations.

The energy-level structure for $M_L=0\mathrm{}$ odd Rydberg states of lithium in a uniform magnetic field has been investigated experimentally. The whole structure of a diamagnetic multiplet excited from the ground state by $\pi$-polarized light has been recorded for the first time. Each multiplet is shown to exhibit two different behaviors; this provides an experimental confirmation for the existence of the two limiting approximate symmetries previously predicted for the diamagnetic Hamiltonian of atomic hydrogen. Furthermore, the observed spectra agree with diagonalization calculations.

Photon-echo modulation spectroscopy is extended into a new regime to study coherences between states that are widely separated in frequency compared with the bandwidth of the exciting laser pulses. Time-delayed four-wave mixing (TDFWM) is observed on the Na $D$ doublet by use of 7-nsec pulses of light spectrally peaked at each of the $D$-line transitions. As the two double-frequency, 7-nsec light pulses are delayed with respect to each other a 1.9-psec beating of the integrated TDFWM signal is observed, even for delays greater than the excitation pulse width.

We report here the first experimental observation of $N=3\mathrm{}$ solitonlike pulses generated by a passively mode-locked ring laser at 620 nm. The evolution of the pulse shape is recorded along the soliton period corresponding to about 2400 cavity round trips. Experimental indications of the soliton character of any pulse produced by this type of laser are also obtained. Properties of high-order solitons could offer new possibilities of intracavity pulse compression.

The usual open-loop semiclassical theory of light detection is extended to include closed-loop operation in which there is feedback from the detector to the source. The revised theory takes the form of a self-exciting point process. It admits photocount statistics that are associated with non-classical light in open-loop configurations, e.g., sub-shot-noise spectra and sub-Poisson photocounts. The extended theory is used to explain two recent closed-loop experiments in which sub-Poisson photocount statistics were produced.