We suggest that a supersymmetry scheme based on the supergroup $\mathrm{U}\left(\frac{6}{4}\right)$ may be useful in describing many properties of nuclei in the Os-Pt region. The bosons and fermions in the fundamental representation of $\mathrm{U}\left(\frac{6}{4}\right)$ are the low-lying collective (bosonic) and single-particle (fermionic) degrees of freedom. Experimental evidence indicates that the scheme applies to several nuclei in the region within ≈ 30%. This appears to be the first observed example of a supersymmetry.

Detailed excitation functions of angle-integrated cross sections for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ elastic scattering and reactions show narrow, highly correlated structures. These resonances have enhanced partial widths for decay into two ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ fragments and are interpreted as having quasimolecular or fission-isomeric nature.

The scattering of protons by helium atoms is studied in a mean-field approximation to the many-body $S$ matrix. The one-body equations governing the electron dynamics for elastic scattering are solved iteratively beginning with the interaction-picture time-dependent Hartree-Fock (TDHF) solution. At a representative proton laboratory energy of 20 keV, the converged $S$-matrix elements are within 10% of the TDHF value. Inclusive single-charge transfer probabilities calculated in the interaction-picture TDHF approximation agree reasonably well with the experimental data.

The third-order susceptibility of ${\mathrm{H}}_2$ has been calculated under coherent anti-Stokes Raman-scattering conditions, with use of wave functions specifically designed for accurate calculations of sum-rule properties. The theoretical values are in good agreement with experiment.

A modified layered-target technique is used to provide spatial information about continuum x-ray emission in the plane of an infinite target irradiated by a short-pulse C${\mathrm{O}}_2$ laser. Hard x-rays are only observed near or within the laser interaction region. Softer x rays are emitted over a large but shallow area of the target surface. These results are used to discuss lateral energy transport mechanisms.

We have studied ortho-${\mathrm{D}}_2$ and para-${\mathrm{H}}_2$ at pressures up to 540 kbar (54 GPa) and $1.1 \mathrm{K}<T<\mathrm{}300\mathrm{} \mathrm{K}$ by means of Raman scattering in a diamond anvil cell. A phase transition in which the molecules which are spherically symmetric at low pressure go into an orientationally ordered state has been observed in $o$-${\mathrm{D}}_2$ at 278±5 kbar. Line broadening of the roton bands for $p\gtrsim 200$ kbar is interpreted as a precursor of this transition.

Light scattered from the driven free surface of the smectic-$A$ phase of octyloxy cyanobiphenyl (8OCB) provides a low-frequency measurement of second sound. This yields an absolute measurement of the smectic elastic constant, $B$. There is no dispersion in either the angular or frequency dependence of $B$ for angles 35°-83° from the normal and for frequencies from 10-100 kHz. Near the smectic-$A$—to—nematic phase transition the smectic elastic constant can be described by $B=(6.03\mathrm{}\pm 0.05)\times {10}^7$ ${(T_{\mathrm{NA}}-T)}^{0.32\pm 0.015}$ dyn/${\mathrm{cm}}^2$.

We report what we believe is the first experimental measurement of biaxiality in a cholesteric phase. This observation is made in a selectively deuterated nematic that was twisted by the addition of a chiral compound. A theoretically predicted biaxial order parameter (measured in terms of an asymmetry in the time-averaged deuterium quadrupole interaction) was found to be ∼${10}^{-3\mathrm{}}$ for a pitch ∼3 μm and to increase both with decreasing pitch and as the isotropic phase is approached.

We study directed percolation in two dimensions. Critical properties, such as the threshold $p_c$ and the correlation length exponent $\nu$, depend on the direction $\varphi$ at which percolation is observed. We observe crossover from $\nu (\varphi =0)$ to $\nu \left(\varphi \ne 0\right)$; similar crossover is found when the probabilities assigned to vertical and horizontal bonds, $p_V$ and $p_H$, become unequal. For the case $p_H=1\mathrm{}$ we solved the problem exactly, obtaining $p_c\left(\varphi \right)={[1+cot(\frac{1}{4}\pi -\varphi \left)\right]}^{-1\mathrm{}}$, $\nu =2\mathrm{}$.

The static structure factor $S\left(\overrightarrow{\mathrm{K}}\right)$ for a two-dimensional harmonic lattice of finite size $L$ is expressed analytically. Although one consequence of finite size is the absence of very-long-wavelength phonons, we find that the explicit introduction of a phonon cutoff has very little effect. The structure factor shows an universal behavior for all $L$, differing only by scale factors: $S\left(\overrightarrow{\mathrm{K}}\right)$ always has the infinite-size form far from a Bragg point, but is always rounded off close to the Bragg point. Implications for the interpretation of experimental results are discussed.

The electronic structures of pure and mixed Fe-Ni metal clusters, as computed with the self-consistent-field $X\alpha$ scattered-wave method, are used as models for the bonding situation in fcc Fe-Ni alloys. The calculations indicate that several anomalous properties of the Invar alloy ${\mathrm{Fe}}_{64}$${\mathrm{Ni}}_{36}$ are a consequence of the presence, at the Fermi level, of strongly antibonding majority-spin orbitals and nonbonding minority-spin orbitals in this concentration range.

The excited states of chemisorbed pyridine on Ag(111) have been determined with use of electron-energy-loss spectroscopy. In addition to weakly perturbed molecular states we observe new excitations above ∼1.4 eV, which we identify as metal-molecule charge-transfer excitations. These new electronic states provide an explanation for several features observed in surface-enhanced Raman scattering.

High-resolution electron-energy-loss spectroscopy has been used to study the vibrational broadening in the ${}_{}{}^1{}_{}{}^{}B_{2\mathrm{u}}^{}{}_{}{}^{}(\pi ,{\pi }^{*})$ excited state of pyrazine adsorbed on Ag(111). Strong lifetime broadening of ~100 mV for the first and ~20 mV for the second pyrazine layers are determined. These lifetimes are in reasonable agreement with those predicted by classical theory.

We report the observation of strongly nonlinear conductivity with a sharp threshold field and a giant dielectric constant in the charge-density-wave state of Ta${\mathrm{S}}_3$. We argue that these properties reflect the dynamical behavior of the charge-density-wave condensate, and compare the observed behavior with the properties of Nb${\mathrm{Se}}_3$.

We present Monte Carlo evidence of a first-order phase transition in four-dimensional SO(3) lattice gauge theory. This result stands in sharp contrast to the known single-phase structure of the corresponding SU(2) theory, and suggests that the $Z_2$ center degrees of freedom may be important to the thermodynamics of the SU(2) gauge system.

By giving an explicit example in one dimension, it is shown that by relaxing a condition on the ranges, at least two potentials can have the same scattering operator in some cases. The two potentials are local and do not support point eigenvalues. The implications for solutions of the Korteweg-de Vries equation are briefly discussed.

We show there is evidence that a method of summing important logarithmic corrections which are significant in the large-$x$ region leads to a superior description of deep-inelastic scattering data (analyzed with use of the evolution equations). Next-to-leading-order calculations can imitate the impact of this summation method, but at high $x$ it appears that there are higher-order and higher-twist corrections which separate those approaches.

We have performed a high-statistics measurement of Bhabha scattering and of the production of hadrons in electron-positron annihilation at PETRA energies ($12 \mathrm{GeV}<~\sqrt{s}<~36.7 \mathrm{GeV}$). Combining the results with measurements of ${\mu }^{+}{\mu }^{-}$ and ${\tau }^{+}{\tau }^{-}$ production enables us to compare our results with electroweak theory. We find ${{sin}^2\theta }_w=0.27\mathrm{}\pm 0.08$. This is in good agreement with the value obtained from neutrino experiments which were carried out in entirely different kinematic regions.

Resonance phenomena observed experimentally in some lighter-heavy-ion collisions at energies well above the Coulomb barrier are discussed in terms of the number of open channels available to direct reactions for the even-even C + C, C + O, and O + O systems. The calculated number of open channels shows a characteristic energy dependence which reflects the surface transparent absorption needed to observe resonant structure. The weak absorption is particularly pronounced in reactions involving ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ nuclei.

We have used a secondary ion recoil source to study electron capture and ionization in collisions of ${\mathrm{Ar}}^{+q}$ with He, Ne, Ar, and Xe at projectile energies between 250 and 660 eV per charge. By analyzing outgoing projectiles and target ions in coincidence we have measured cross sections for ionization of the system with and without simultaneous electron capture, as well as for normal electron capture only. Cross sections for direct ionization (no electron capture) are found to be small, whereas those for ionization accompanied by electron capture are often quite important.