The first observation is reported of an anomalous attenuation and velocity dispersion near a smectic-$A$—smectic-$C$ phase transition in a liquid crystal. The anomaly is found to be strongly anisotropic and dominated by the Landau-Khalatnikov relaxation of the order parameter in contrast with other liquid-crystalline phase transitions.

Scaling of the dynamic structure factor at high momentum transfer is established by using time-ordered perturbation theory. Whereas the scaling function is the longitudinal momentum distribution for systems interacting with smooth two-body potentials, additional terms contribute in the case of strong short-range repulsion. Illustrative results are presented for a hard-sphere Bose gas and the relevance to electron scattering from nuclei and neutron scattering from liquid helium is discussed.

In contrast to the usual structural "lock-in" incommensurate-commensurate transitions—where the amplitude of the modulation wave continues to increase at $T_c$ but the incommensurate part of the average wave vector of the modulation wave vanishes—in ${\left({\mathrm{C}}_3{\mathrm{H}}_7\mathrm{N}{\mathrm{H}}_3\right)}_2$Mn${\mathrm{Cl}}_4$ the amplitude of the incommensurate modulation wave vanishes outside $T_{c1\mathrm{}}$ and $T_{c2\mathrm{}}$ whereas the wave vector is not critical. This reentrant behavior results from a coupling of the incommensurate order parameter to the temperature-dependent interlayer distance.

The real-time dynamics of the Hubbard model is discussed, under the assumption that the electrons are scattered by Markovian exchange field fluctuations and that the local magnetization regresses towards the instantaneous value of the exchange field with the characteristic time of its correlation function. It is proved that, for large $\frac{U}{W}$, the magnetization lifetime on a site is much larger than the electron hopping time.

Current-voltage characteristics of metallic point contacts with Ce and Yb valence fluctuation compounds are presented, from which are extracted the lifetime width of the conduction electrons due to dynamic scattering on valence fluctuations, the interconfigurational excitation energy, and a strong asymmetry of the conduction-electron density of states about the Fermi energy.

Electron tunneling spectra of TmSe, SmS, Sm${\mathrm{B}}_6$, and Ce${\mathrm{Pd}}_3$ have been measured with the GaAs Schottky-barrier probe tunneling method. Antiferromagnetic TmSe shown an energy gap $2\Delta \left(\mathrm{full}\mathrm{width}\mathrm{at}\mathrm{half}\mathrm{maximum}\right)=1.2\mathrm{}$ meV, in situ pressure-transformed metallic SmS exhibits a gap of 1.7 meV, and Sm${\mathrm{B}}_6$ shows a gap of 2.7 meV, which is independent of magnetic field. For Ce${\mathrm{Pd}}_3$ an inelastic excitation is found near ± 14 meV, which is absent in Y${\mathrm{Pd}}_3$.

In the many-body variational approach, accurate results are obtained for the ground-state properties of the isotropic electron-hole liquid. With the increase in hole mass, the system undergoes a transition to a state with ordered heavy particles. In the case of Ge under a large [111] strain, it is predicted that the metallic state is not stable relative to free excitons. The density dependence of e-h correlation obtained here compares favorably with the experimental estimates.

Magnetic susceptibility of ${(\mathrm{N}-\mathrm{methylphenazinium})}_x{\mathrm{}\left(\mathrm{phenazine}\right)\mathrm{}}_{1-x}(\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{y}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{q}\mathrm{u}\mathrm{i}\mathrm{n}\mathrm{o}\mathrm{d}\mathrm{i}\mathrm{m}\mathrm{e}-\mathrm{t}\mathrm{h}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{d}\mathrm{e})$ [${\left(\mathrm{NMP}\right)}_x{\left(\mathrm{Phen}\right)}_{1-x}\left(\mathrm{TCNQ}\right)$] shows the formation of defect states for $0.5\lesssim x\lesssim 0.54$. Diffuse x-ray scattering and $g$-value studies indicate that these defects are solitons formed in the highly correlated quasi-one-dimensional system that occurs near the quarter-filled-band limit. A model for the decrease in the energy gap in the presence of large numbers of solitons is proposed to explain the excess conductivity.

A "spin superlattice" can be formed by periodical doping with paramagnetic ions, so that only the effective $g$ factor of the conduction electrons is affected. An external magnetic field and temperature therefore provide a suitable control for the modulation amplitude of the potential and hence for the resulting minigap.

This paper reports the first observation of photogenerated gap states in polyacetylene, ${\left(\mathrm{CH}\right)}_x$. A transient optical absorption, at photon energies less than the band gap, is produced by photogeneration of electron-hole pairs. The spectrum of this absorption is measured in both cis and trans isomers of ${\left(\mathrm{CH}\right)}_x$. From a comparison of these spectra with similar spectra seen in molecular analogs of ${\left(\mathrm{CH}\right)}_x$, it is concluded that these gap states are intrinsic, self-localized excitations of the semiconductor chain.

Inverse photoemission spectra have been measured on Ni(110) at 9.7-eV photon energy with a spin-polarized electron source. Consistent with band theory, a $d$-band-derived peak is observed just above the Fermi level that corresponds to transitions to minority-spin states only, and which increases in intensity and displays a slight (0.1-eV) energy dispersion as the angle of electron incidence is increased. The inelastic background displays an unexpected nonzero (∼ -5%) polarization.

Nonperturbative multiple-scattering theory is used to study the influence of the first peak in the density correlation function, $s\left(k\right)\mathrm{}$, on the electronic properties of a structurally disordered metal. The present calculations yield a well-defined minimum in the average density of states and a corresponding peak in the electrical resistivity. The position of these structures is directly related to that of the principal peak in $s\left(k\right)\mathrm{}$.

Composites formed from charged particles and vortices in (2+1)-dimensional models, or flux tubes in three-dimensional models, can have any (fractional) angular momentum. The statistics of these objects, like their spin, interpolates continuously between the usual boson and fermion cases. How this works for two-particle quantum mechanics is discussed here.

The directed-site animal problem on the square and triangular lattices is shown to be equivalent to Baxter's hard-square lattice-gas model with anisotropic next-nearest-neighbor interactions at a disorder point. The exact solution of the latter is used to determine the animal numbers as functions of their size in the two cases. Expressions in closed form are proposed for the number of animals on an infinite strip in terms of width and animal size, and for the average transverse extent of animals of a given size.

In connection with a recent measurement performed by Adeva et al. at PETRA, the transverse-momentum behavior of muons in the $e^{+}{e}^{-}\to e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$ process was studied in a simple and transparent way, with use of the double equivalent-photon approximation. The corresponding distribution is expressed in a scale-invariant form, and good agreement is obtained with the experimental data.

It is found that any complete single-photon tree amplitude has a general canonical form which vanishes in certain kinematical zones provided that any derivative couplings are as prescribed by gauge theory. The location of these zones depends only on the external charges and momenta. Their occurrence is based on classical radiation interference that is a generalization of the well-known absence of dipole radiation by colliding particles with the same charge-to-mass ratio. Weak-boson amplitude zeros are explained.

A locally supersymmetric grand unification program is proposed which couples the $N=1\mathrm{}$ supergravity multiplet to an arbitrary grand unified gauge group with any number of left-handed chiral multiplets and a gauge vector multiplet. A specific model is discussed where it is shown that not only do the gravitational interactions eliminate the degeneracy of the vacuum state encountered in global supersymmetry, but simultaneously they can break both supersymmetry and SU(2) ⊗ U(1) down to a residual $\mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}^c\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ symmetry at ∼300 GeV.

The proton momentum distribution of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been determined up to momenta of 310 MeV/c by use of the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}(e, e^{\prime }p)$. The experimental missing-energy resolution, $\delta E_m=1.2\mathrm{}$ MeV, was sufficient to separate the two- and three-body breakup channels. Results for the three-body disintegration have been obtained up to missing-energy values of 80 MeV. The resulting spectral function is compared to the predictions of Faddeev and variational calculations.

The $3s$ radial wave function $R\left(\mathcal{r}\right)$ has been determined by electron scattering from ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$. The shape of $R\left(\mathcal{r}\right)$ in the central region of the nucleus is used to test the validity of the independent-particle shell model at large nuclear density.

The fully self-consistent random-phase-approximation response of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ to the operator $j_J\left(q\mathcal{r}\right)$ is calculated by using the $D1\mathrm{}$ density-dependent effective interaction and studied as a function of the momentum transfer $q$. Corresponding energy-weighted sum rules are evaluated. A striking $q$ dependence is found for low multipoles, and the high-frequency part of the response function is conjectured to be responsible for recently observed resonantlike structures in heavy ion collisions.