Measurements of broad-range momentum spectra for ($p, {\pi }^{-}$) reactions on a number of target nuclei with $13<~A<~92$ have revealed a striking and systematic selectivity for one or a few low-lying discrete states in the residual nuclei. It is proposed that the dominant transitions lead to high-spin, stretched (or nearly stretched) two-particle, one-hole states, as favored by a two-nucleon pion production mechanism.

The angular distribution for the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(p, n){}_{}{}^{16}{}_{}{}^{}\mathrm{F}\left(0^{-}\right)$ has been measured at $E_p=35\mathrm{}$ MeV between 0° and 140° (lab), or momentum transfer 0.34-2.0 ${\mathrm{fm}}^{-1\mathrm{}}$. This is the first observation of an isovector $0^{+}$→$0^{-}$ transition, corresponding to a pure longitudinal spin response, at large momentum transfers. Distorted-wave Born-approximation calculations with the M3Y interaction give a reasonable account of the observed cross sections except at $1.4\lesssim q\lesssim 2.0$ ${\mathrm{fm}}^{-1\mathrm{}}$. This discrepancy might be due to the effects of the pion field in nuclei.

Isotopically resolved nuclear fragments ($A_f, Z_f$), $3<~Z_f<~14$, produced by protons in the energy range $80<~E_{\mathrm{inc}}<~350$ GeV incident on krypton and xenon targets have been studied at the Internal Target Laboratory of the Fermi National Accelerator. A power-law dependence, isobaric yield $\propto {A_f}^{-\tau }$, was found to describe the data over a broad range of yields. The particular value of $\tau$ is a signature for the fragment formation mechanism.

Experimental evidence is presented for a new resonant process in ion-atom collisions which is analogous to dielectronic recombination in free-electron-ion collisions. Resonant behavior observed in the yield of projectile $K$ x rays in coincidence with single-electron capture in 70-160-MeV S + Ar collisions is attributed to simultaneous electron capture and $K$-shell excitation. The data indicate that this resonant process is an important mechanism in inner-shell vacancy production in the energy range studied.

Energy-gain spectra and total cross sections have been measured for projectiles of 492-eV ${\mathrm{Ne}}^{+10\mathrm{}}$ and 443-eV ${\mathrm{Ne}}^{+9\mathrm{}}$ capturing electrons from rare-gas targets. For each collision system a single, or at most two, principal quantum numbers on the projectile are found to be populated. The effective electron-transfer probabilities are found to be quite dependent upon the collision system.

In a homeotropic nematic cell, a solitarylike director wave is excited by a mechanical method. Three photographs of the wave propagation process and measured velocity-time dependence curves are presented. By means of the interference patterns of focused polarized light, it was found that the dark lines observed in white-light photographs correspond to a perpendicular alignment state of the director.

Soliton propagation in nematic liquid crystals under shear is shown to be possible and studied theoretically. Calculations including those pertaining to the modulation of monochromatic or white light passing through such a liquid-crystal cell are presented. Recent experiments are interpreted accordingly and are in good agreement with the theory presented here.

The magnetic-field-induced semimetal-semiconductor transition has been observed in Bi under very high magnetic fields parallel to the binary axis. The transition was observed at 88 T as a change of the transmission of the far-infrared radiation at 337-μm wavelength at low temperature. The field position of the transition as well as the positions of absorption peaks arising from the Shubnikov-de Haas effect were analyzed in terms of newly determined band parameters.

The magnetic response of a single crystal of the tetragonal compound Er${\mathrm{Rh}}_4$${\mathrm{B}}_4$ in the $\overline{c}$ (hard) and $\overline{a}$ (easy) directions is presented. Extreme anisotropy is found in the magnetic and superconducting behavior, allowing a natural separation of the bare superconducting properties from those affected by magnetism. Below $T_{c2\mathrm{}}$ the data reconcile the discrepancy between the ferromagnetic moment per erbium atom measured by neutron scattering and by Mössbauer effect.

Specific-heat measurements on the organic solid di-tetramethyltetraselenafulvalenium-perchlorate ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$ Cl${\mathrm{O}}_4$ demonstrate that $T_c$ decreases as much as 22%, when the cooling rate below 40 K is changed from 0.1 K/min (relaxed state) to 10 K/min (quenched state). The phenomenon is fully reversible as indicated by annealing experiments. The parameters of the superconducting state, the specific-heat jump, the entropy, and the upper critical fields ($\parallel c^{*}$) are strongly affected by the quenching process. A possible explanation is that quenching freezes out lattice disorder.

Pseudopotential total-energy calculations show that the $\pi$-bonded chain reconstruction of the Si(111)-(2×1) surface can be reached from the ideally bonded surface without increasing the total energy by more than 0.03 eV/(surface atom). Hence, the chain surface can be formed easily in the cleavage process. The minimum-energy chain geometry is determined, and the corresponding surface-state dispersion is in remarkable agreement with recent angle-resolved photoemission experiments.

By comparison with photoelectron spectra which contain multielectron shakeup satellites, evidence is found for a structure in x-ray absorption near-edge spectra in Mn${\mathrm{Cl}}_2$, Fe${\mathrm{Cl}}_2$, and Co${\mathrm{Cl}}_2$ produced by these same shakeup transitions. The strength of these shakeup satellites in absorption is weaker than in photoemission, as expected because of the different excitation energy of the photoelectrons involved.

Irradiation of the amorphous semiconductor ${\mathrm{As}}_2$${\mathrm{S}}_3$ with band-edge photons opens a metastable gap in the low-energy density of states of atomic tunneling systems. Electric resonance studies at temperatures below 1 K indicate the annihilation of ∼ ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ tunneling centers, close to the density of metastable paramagnetic electronic defects created by low-level optical excitation. These findings link low-energy atomic tunneling systems to localized midgap electronic states.

Subharmonic bifurcations, generalized multistability, and chaotic behavior were found experimentally in a $Q$-switched C${\mathrm{O}}_2$ laser operating at 10.6 μm. Jumps between two strange attractors lead to a low-frequency ($\frac{1}{f}$ type) divergence in the power spectrum. This is the first experimental evidence of these phenomena in a quantum-optical molecular system. A theoretical model is also presented whose results are in good agreement with the experimental data.

A counterexample is given to a recent suggestion that if the inequalities of Clauser and Horne hold, then there exists a hidden-variable model for a spin-½ correlation experiment of the Einstein-Podolsky-Rosen type.

The dynamics of interfaces where the normal component of an interface velocity is proportional to the curvature is studied. The dynamic structure function due to the motion of random interfaces is shown to satisfy a scaling law. The results are compared with Monte Carlo simulations of the kinetics of the order-disorder transition in a quenched system.

Transverse electromagnetic waves possessing finite energy, action, and $\int \overrightarrow{\mathrm{E}}·\overrightarrow{\mathrm{B}}{d}^{4}x$ are obtained in 3 + 1 dimensions as a solution of the source-free Maxwell's equation in vacuum.

Analytic dyon solutions are obtained for $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ grand unified theories broken down to $\mathrm{SU}\left(N_1\right)\otimes \mathrm{SU}\left(N_2\right)\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$. These solutions are regular everywhere including the origin. A few comments about mass, Pontryagin-like index of dyon, and magnetic flux are made in connection with the recent report of a magnetic monopole discovery.

Measurements are presented of the inclusive charged-particle cross sections $s$ $\frac{d\sigma }{\mathrm{dx}}$ for $e^{+}{e}^{-}$ annihilation at center-of-mass energies of 5.2, 6.5, and 29.0 GeV. Significant scale breaking is observed in these cross sections.

The negative-pion multiplicity is measured for central collisions of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ with KCl at eight energies from 0.36 to 1.8 GeV/nucleon and for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ on KCl and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ on Ba${\mathrm{I}}_2$ at 977 and 772 MeV/nucleon, respectively. A systematic discrepancy with a cascade-model calculation which fits proton- and pion-nucleus cross sections but omits potential-energy effects is used to derive the energy going into bulk compression of the system. A value of the incompressibility constant of $K=240\mathrm{}$ MeV is extracted in a parabolic form of the nuclear-matter equation of state.