It is shown that at low temperatures, phonon-assisted electron hopping between soliton bound states may be the dominant conduction process in a lightly doped, one-dimensional Peierls system such as polyacetylene. The presence of disorder, as represented by a spatially random distribution of charged dopant molecules, causes the hopping-conduction pathways to be essentially three dimensional. Calculated values of the conductivity, thermopower, and transverse spin diffusion constant compare favorably with experiment.

A new procedure for evaluating a function at infinity from its power series is analyzed. The limit in the procedure is shown to converge to the smallest singularity of the inverse function, which may or may not be the desired value.

The half-shell cross section for charged-particle scattering is discontinuous at the on-shell point. Moreover, its limits for $p\to k^{-}$ and $p\to k^{+}$ not only differ from each other, they also differ from the corresponding on-shell cross section, often by appreciable energy-dependent factors. This has important consequences for the theoretical description of bremsstrahlung and quasifree data.

Recent experimental data for the energy splitting between the $T=T_0$ and $T=T_0-1\mathrm{}$ components of the charge-exchange vector-dipole resonance are discussed within the framework of a simple model.

We have investigated the reactions ${}_{}{}^{194,196,198}{}_{}{}^{}\mathrm{Pt}$($\overrightarrow{t}$, $\alpha$)${}_{}{}^{193,195,197}{}_{}{}^{}\mathrm{Ir}$ and ${}_{}{}^{191,193}{}_{}{}^{}\mathrm{Ir}$($t$,$p$)${}_{}{}^{193,195}{}_{}{}^{}\mathrm{Ir}$. While the ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ single-particle level structure and two-neutron transfer strengths are not inconsistent with the predictions of the dynamical supersymmetry proposed in this region, ${}_{}{}^{195,197}{}_{}{}^{}\mathrm{Ir}$ show no evidence for the supersymmetry structure.

Correlations between two protons produced in the inclusive reaction $\mathrm{Ar}+\mathrm{KCl}\to p+p+X$ at 1.8 GeV/nucleon have been measured for proton rapidities near the beam rapidity $Y_B$ and near $\frac{Y_B}{2}$. Comparison with model calculations suggests that the size of the region of final scattering is 3.5 fm at $Y_B$ and corresponds to that expected for a projectile remnant. The sizes we obtain at $\frac{Y_B}{2}$ (with or without high multiplicity requirements) are smaller (2.4-2.8 fm) and seem inconsistent with a thermalized source containing a large fraction of the available nucleons.

The inclusive reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\pi }^{\pm }$,${\pi }^{\pm }p$) were studied at 245 MeV over a broad kinematic range by coincidence measurement of the outgoing particles. The ${\pi }^{\pm }-p$ angular correlations, proton energy spectra, and the ratio of positive- to negative-pion cross sections are all consistent with those expected from quasifree scattering. For positive pions, quasifree scattering accounts for (30 ± 3)% of the inclusive pion inelastic scattering to backward angles. The rest is attributed to the (${\pi }^{+}$,${\pi }^{+}n$) reaction and to multistep processes.

We report the first precise measurements of the ionization rate ${\Gamma }_I\mathrm{}\left(F\right)\mathrm{}$ in the tunneling regime for resolved $n=30,40\mathrm{}$ Stark substates of hydrogen. Excellent agreement is obtained with nonrelativistic numerical calculations. No effects of wave function mixing induced by relativistic or other interactions were observed. We consider and give an experimental upper limit for the magnitude of the H-D isotopic shift in ${\Gamma }_I\mathrm{}\left(F\right)\mathrm{}$.

The behavior of photoelectron angular distributions in a strongly driven resonant multiphoton ionization process is discussed. It is shown that the angular distribution changes drastically with increasing intensity as a result of the ac Stark shifting of the levels. Moreover, under strong saturation conditions the distribution reaches a limiting form significantly different from the form predicted by perturbation theory. The effects of the laser bandwidth on the angular distribution are also discussed briefly.

We report theoretically and experimentally a new class of multiphoton scattering in the coherent transient regime associated with a resonant two-level system that is excited by two noncollinear laser beams. We find that its excitation, described by the nonperturbative solutions for the optical Bloch equation, gives rise to a detectable photon scattering of up to 27th-order wave-vector coupling in resonant sodium vapor.

High-$\beta$ plasmas, stable to all ideal magnetohydrodynamic modes, have been found by joint optimization of plasma cross sections and current profile shapes. No wall stabilization is used for the external kink. Dee cross sections are considered with varying aspect ratios. The maximum stable $\beta$ varies from 5% at aspect ratio 4 to 10% at aspect ratio 2.5, and the optimum elongation is 1.8. The low-$n$ kink modes are the most limiting.

High-resolution ac calorimetry measurements have been performed on a liquid-crystal material exhibiting a stacked-hexatic-$B$—smectic-$A$ phase transition. The transition appears to be second order with a pronounced, symmetric heat capacity peak and no observable thermal hysteresis. The data can be fitted by a power law divergence with critical exponents $\alpha ={\alpha }^{\prime }=0.64\mathrm{}\pm 0.04$ and a ratio of critical amplitudes $\frac{A}{A^{\prime }}=0.83\mathrm{}$. Measurements have also been carried out on a crystalline-$B$-smectic-$A$ transition which is found to be first order.

The second-sound velocity of three dilute ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures was measured with high precision down to a temperature of 10 mK and in a magnetic field of 93 kOe. For the most dilute sample, which had a molar concentration of 0.001, the maximum spin polarization of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ atoms was estimated to be 36%. The measured relative change in the secondsound velocity was 3%. This is considerably larger than the change predicted recently by Bashkin and Meyerovich. An explanation for this discrepancy is presented.

The metallic (high-pressure) phase of ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$P${\mathrm{F}}_6$ exhibits Shubnikov—de Haas resistance variations at low temperatures. A single frequency of 0.76 MG has been recorded. A large anisotropy in the transverse magnetoresistance is also observed. Our results imply a two-dimensional Fermi surface under pressure, with compensated electron and hole sections oriented along the crystal $c$ axis. Some unusual and physically significant anomalies associated with the oscillations are discussed.

The microwave emission from long Josephson tunnel junctions dc-current biased on zero-field and Fiske steps has been measured. The frequency and power variation on all steps of the narrow-linewidth radiation near the fundamental cavity-mode frequency and the observed transitions between different modes on a given step may be understood in a picture of multifluxon excitations with propagation of different bunched fluxon configurations depending on the current and magnetic field bias.

Helicon resonance and the de Haas-van Alphen effect have been simultaneously investigated in single crystals of potassium. All samples exhibited the well-known linear magnetoresistance and had a magnetoresistivity tensor which did not have cubic symmetry. Even so, there was no evidence from the de Haas-van Alphen effect of a Fermi surface instability. The results are inconsistent with Overhauser's model of a charge-densitywave ground state in potassium.

It is shown by a calculation analogous to that carried out by Wallace and Zia for the pure Ising model that the lower critical dimension of the Ising model in a random field is 3 and not 2 as suggested by domain energy arguments. Further, the critical dimension for the roughening transition is shown to be 5 as compared to 3 for the pure Ising model.

The total-cross-section difference in pure longitudinal spin states for $p-d$ interactions has been measured at momenta from 1.1 to 6 GeV/c. Spin-dependent Glauber-type corrections and other corrections have been made to obtain $\Delta {\sigma }_L\mathrm{}\left(\mathrm{pn}\right)\mathrm{}$ and $\Delta {\sigma }_L\mathrm{}(I=0\mathrm{})\mathrm{}$. These measurements are of fundamental interest and will also help in determining the existence and nature of dibaryon resonances.

We have observed the decay of the $\Upsilon \mathrm{}\left(2S\right)\mathrm{}$ into the $\Upsilon \mathrm{}\left(1S\right)\mathrm{}$, obtaining a branching ratio of 19.1±3.1±2.9% for the mode $\Upsilon \mathrm{}\left(2S\right)\mathrm{}\to {\pi }^{+}{\pi }^{-}+\Upsilon \mathrm{}\left(1S\right)\mathrm{}$. The di-pion mass spectrum peaks at large invariant mass, and the angular distribution of the di-pion system is consistent with $s$-wave production.

The differential cross section for elastic scattering of pions from deuterium has been measured for momenta of 408, 441, 539, and 600 MeV/c. The measurements confirm the energy dependence of a pronounced minimum around 100°, previously observed with lower-precision experiments. Our results are compared to calculations including effects of excitation of dibaryon resonances in the deuteron.