An experiment resulting in the first measurement of the isospin-mixing, charge-symmetry-violating component of the $n-p$ interaction has been performed. The experiment determined the difference in the angles of the zero crossing of the neutron and proton analyzing powers $A_n$ and $A_p$ at 477 MeV. In terms of the laboratory scattering angle of the neutron, the measured difference is ${\theta }_{0n}\left(A_n\right)-{\theta }_{0n}\left(A_p\right)=+0.13\mathrm{}° \pm 0.06° (\pm 0.03°)$, where the second error is a worst-case estimate of systematic error. The resulting difference in the analyzing powers at the zero-crossing angle is $A_n-A_p=+0.0037\mathrm{} \pm 0.0017 (\pm 0.0008)$.

We prove the modular invariance and thus the finiteness of the five-point amplitudes in closed superstrings. The complicated algebra necessary is considerably simplified by making use of the results of Frampton, Moxhay, and Ng for the open superstring.

Empirical evidence for an $\mathrm{SO}\mathrm{}\left(8\right)\mathrm{}\supset \mathrm{SO}\mathrm{}\left(7\right)\mathrm{}$ fermion dynamical symmetry in the Pd-Ru region is presented. This symmetry has the remarkable property that it can describe structural variations in a transition region between vibrator and $\gamma$-soft asymmetric rotor.

A time projection chamber with a selenium double-beta decay source as the central electrode has yielded a lower limit of 1.0 × ${10}^{20}$ yr at 68% confidence level for the two-neutrino half-life of ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$. This limit is consistent with the results of geochemical measurements, and disagrees with the shorter half-life predictions of nuclear theory. For the neutrinoless mode we find a corresponding lower limit of 7 × ${10}^{21}$ yr, also at 68% confidence level.

Recent observations of dc-field-induced interferences in autoionization by several groups can be understood by use of the theoretical work on laser-induced autoionization, which also enables one to study the influence of radiative effects, such as recombination.

Multiphoton ionization in xenon has been studied with 1064-nm circularly polarized coherent light, producing electrons with energies up to 15 eV. A strong suppression of the cross section is observed for electrons below 4 eV, but not for linearly polarized light at the same intensity. We show that if the electrons are emitted in single-step, nonresonant coherent processes, rather than stepwise excitation, the centrifugal potential barrier in the atomic Hamiltonian produces this suppression.

H-atom diamagnetism has been studied in the quasi-Landau regime with final magnetic states $|m_l^f=0\mathrm{}〉$, $|m_l^f=+1\mathrm{}〉$, $|m_l^f=0, +2\mathrm{}〉$, selectively excited by resonant two-photon absorption. All spectra exhibit detailed characteristic line structures. For $|m_l^f=+1\mathrm{}〉$ a new quasi-Landau resonance is discovered with a modulation spacing of $0.64\hslash {\omega }_c$ at $E=0\mathrm{}$, while the other final states are modulated with $1.5\hslash {\omega }_c$. The new resonance can be explained theoretically by a quasibound classical trajectory which lies outside the $z=0\mathrm{}$ symmetry plane.

Fractional quantization of the adiabatic pseudorotation in an isolated molecule is reported. This result, concerning the large-amplitude pseudorotation in $2^2{E}^{\prime }{\mathrm{Na}}_3$, constitutes the first direct verification of the adiabatic sign-change theorem, and also presents the most complete picture of the level structure and internuclear dynamics of a metal-atom cluster yet given.

Several triplet Rydberg $f$ states in molecular hydrogen were observed with a resolution of about 50 MHz under stepwise excitation. Extrapolation of the energy intervals to the Rydberg series limit gives a precise value for the ionization energy for ${\mathrm{H}}_2$ relative to the lowest triplet bound state, the ${}_c{}^{}{}_{}{}^{}\mathrm{}\left(2p\right)\mathrm{}{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ state, and an improved value for the ionization potential of the ${\mathrm{H}}_2$ molecule in the ground state. The new value for the ionization potential is in excellent agreement with ab initio calculations and confirms the Lamb shift in the ground state of ${\mathrm{H}}_2$.

It is shown that in the limit of large nuclear charge $Z$, the chemical potential of a neutral atom is given by $\mu \sim Z^{\frac{-1\mathrm{}}{3}}\times \mathrm{periodic}\mathrm{function}\mathrm{of}{Z}^{\frac{1}{3}}$. This expression accounts for the general behavior of the chemical potential of atoms in the periodic table.

Penning ionization can be the major inelastic process in gas-phase collisions of fast metastable-excited atom beams, yet elastic scattering generally obscures detailed examination of this process. Using a coincidence technique, we have now extracted double-differential cross sections for the ionization processes. Our first results for the ${\mathrm{He}}^{*}\left(2^{3}S\right)+\mathrm{Ar}$ interaction give fresh insight into this often-studied system, most notably by revealing saturation of the absorptive (Penning) channel at distances slightly smaller than are accessible in thermal-energy experiments.

Very-low-energy highly charged ions have been produced by use of white and monochromatic x rays from a wiggler line at the Stanford Synchrotron Radiation Laboratory to generate vacancy cascades following inner-shell photoionization. Recoil-ion energies have been determined and are shown to correspond essentially to room temperatures, even for high charge states. Promising applications to study of the interaction of stellar radiation with cold matter, to high-brightness ionsource development, to precision spectroscopy, and to angle-resolved chemical-physics reactive-scattering studies are discussed.

The first interpretation of giant resonance behavior in the inelastic scattering of electrons from heavy ions is reported for the electron-impact double ionization of ${\mathrm{Cs}}^{+}$. A discussion of the partial-wave potentials and phase shifts leading to this phenomenon is presented along with results of several distorted-wave calculations of the cross section. The theoretical cross sections are in good agreement with the results of a crossed-beam measurement.

Flow-visualization experiments are described which study the onset of convection in ethanolwater mixtures. It is shown that the conducting state becomes unstable to oscillatory convection, and the onset Rayleigh number, the frequency of oscillation, the linear growth rate of the instability, and the spatial pattern of the flow are studied as functions of the parameters of the fluid mixtures. This oscillatory fluid motion does not stabilize at a finite amplitude but grows exponentially with time until large-amplitude, overturning convection is triggered.

The orbitron maser is an electromagnetic wave generation device based on an interaction with electrons orbiting around a thin positively charged conducting wire. A linear theory of this device is presented with full consideration given to the treatment of noncircular electron orbits of arbitrary eccentricity. Strong wave growth is found at high harmonics of the orbital frequency provided that the electron orbits are sufficiently eccentric. Thus the generation of short-wavelength radiation (in the millimeter to submillimeter range) is indicated.

The nature of plasma waves which are resonantly excited when two laser beams beat in a rippled-density plasma is explored both theoretically and experimentally. A theoretical model is presented which, for commonly encountered experimental parameters, predicts rapid saturation of the high—phase-velocity beat wave at an amplitude below that expected for relativistic detuning. Results of experimental studies of this process are presented.

Self-similar structures of single-crystalline domains in lipid monolayers at the air-water interface are observed after a stepwise increase of the surface pressure. It is shown that these fractal structures with Hausdorff dimensions of $d\approx 1.5$ anneal because of the influence of edge tension on time scales of minutes. The results can be understood within the framework of diffusion-limited aggregation taking into account constitutional supercooling due to different miscibilities for impurities in solid and in fluid lipid phases.

The local structure of $\mathrm{S}$ implanted in GaAs has been determined by extended x-ray-absorption fine structure by monitoring of the $\mathrm{S}$ $K\alpha$ fluorescence yield. The $\mathrm{S}$ first-neighbor shell shows a significant static broadening compared to the $\mathrm{S}$ second- and third-neighbor shells. This indicates two S configurations of approximately equal population: (1) substitutional $\mathrm{S}$ on an As site and (2) a complex formed by $\mathrm{S}$ on an As site and an As vacancy on the second-neighbor shell with a $\mathrm{S}$-first-neighbor distance relaxation of 0.14 ± 0.04 Å. The two-site configuration explains the disparity between implanted $\mathrm{S}$ concentration and net electrical activity.

We argue that when a short-range spin-glass system is below its lower critical dimension $d_l$, which seems to be the case for isotropic vector spins in three dimensions, then the corresponding Ruderman-Kittel-Kasuya-Yosida (RKKY) system is in a different universality class and at its lower critical dimension. For dimensions greater than $d_l$, the RKKY and short-range systems have the same critical behavior. This appears to apply to Ising spins, and to anisotropic vector-spin models for which we discuss the dependence of $T_c$ on anisotropy.

We calculate the two-particle contribution to the spectral weight function of the electric correlation functions of the eight-vertex model in the scaling limit to first order in the four-spin coupling. Both $T<\mathrm{}{T}_c$ and $T>\mathrm{}{T}_c$ are considered. In both cases the result is remarkably simple. For $T>\mathrm{}{T}_c$, the effect of the emergence of the bound state from the two-particle continuum is seen. The corresponding results for the Ashkin-Teller model and the $\mathrm{XYZ}$ spin chain are also given.