Projectile fragments formed in the interaction of $0.9A$- and $1.8A$-GeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ions with a Cu disk interact with a second Cu disk and the relative yields of products in the two disks are measured by radioactivation techniques as a function of the distance between them. The data at $1.8A$ GeV demand either (1) decay in flight ($t_{\frac{1}{2}}\approx {10}^{-10\mathrm{}}$ s) of some projectile fragments having large cross sections or (2) production of secondaries with unexpectedly large transverse momenta.

A complete characterization of rotational and electronic fine-structure-state distributions of the product OH from photodissociation of ${\mathrm{H}}_2$O in the first absorption band is presented. Vibrationally excited water molecules are prepared in a well-defined rotational state by ir excitation, and photodissociation of this state is studied. The theory is based on numerically exact wave functions for ground-state water; the dissociative wave function is expanded in terms of $\mathrm{OH}\left({}_{}{}^2{}_{}{}^{}\Pi \right)$ wave functions (including electronic structure) and inelastic effects in the excited state are shown to be negligible. The comparison between theory and experiment is quantitative on the basis of six quantum numbers.

Novel vortices with half-integer number of circulation quanta can exist in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ as a result of the discrete combined symmetry which couples the superfluid and magnetic properties of the liquid. We calculate the texture of an isolated pair of half-quantum vortices and predict a peculiar NMR signature which—being distinctly different from that due to other types of vortices—could help to identify these extraordinary objects in an experiment.

The pseudo one-dimensional compound Nb${\mathrm{Te}}_4$ exhibits a lock-in-type phase transition around 50 K. Electron microscopy reveals the occurrence of discommensurations; their evolution as a function of temperature is reported. A microstructure model is proposed in which cooperative dephasing between one-dimensional Nb-string segments generates the discommensurations. An alternative description using concepts currently applied for long-period antiphase-boundary structures provides a valid description for the phenomena observed below room temperature.

We develop a simple local-field-effect theory in order to calculate the polarization near the surface and the surface dielectric response of crystals. We obtain a surface-induced anisotropy in all the optical properties of cubic crystals. A calculation of the reflectance anisotropy of a Ge(110) surface is in good agreement with recent measurements.

Frequency-dependent complex-conductivity measurements are reported in the charge-density-wave states of Ta${\mathrm{S}}_3$ and Nb${\mathrm{Se}}_3$, in the 10—100-GHz spectral region. A Drude-type behavior associated with damped inertial response of the condensate is observed for the first time. The fundamental parameters that characterize the dynamics of the collective mode (damping constant, pinning energy, and effective mass) are obtained. The results for the effective mass and damping are compared with microscopic theories.

Local-density-functional total-energy calculations are reported for both the structural and metallization transitions of BaSe and BaTe. Good agreement with recent experimental results for BaTe confirms the band-overlap mechanism in this and related closed-shell systems. A metallization pressure of about 400 kbar is predicted for BaSe. These calculations represent the first convincing demonstration of the ability of the local-density-functional approximation to predict band-overlap metallization accurately.

We propose a least-squares-fit method to extract real-frequency correlation functions from imaginary-time Monte Carlo data of a many-particle system. We apply it to the density correlation function in a one-dimensional model of spinless fermions. The spectral functions thus obtained reflect accurately the particle-hole and the soliton-antisoliton excitations of the system in the respective limits of noninteracting and strongly coupled fermions. They are in qualitative agreement with the available analytical results.

The temperature-composition phase diagram of the ${\mathrm{Ni}}_{1-x}{\mathrm{Pt}}_x$ system was determined by x-ray diffraction and in situ high-temperature measurements of electrical resistivity. The Curie temperatures were also determined for both disordered and ordered alloys. Our results provide direct experimental evidence for the interplay between atomic ordering and magnetism. The experimental measurements are satisfactorily reproduced by a Hamiltonian, solved in the tetrahedron approximation of the cluster-variation method, that contains magnetic interactions dependent on chemical and short-range order.

Electrical noise at silicon grain boundaries deviates significantly from Lorentzian behavior. The noise shows a $\frac{1}{f}$ dependence over a wide frequency range. We present a new model to explain this behavior quantitatively. Our model is based on generation and recombination of charge carriers at interface states and explicitly takes into account inhomogeneities within the boundary plane. Such inhomogeneities generally cause deviations from Lorentzian spectra. The quantitative analysis allows us to characterize these interface states.

Frequency-dependent conductivity measurements between 4.5 and 35 GHz are reported in the spin-density-wave (SDW) state of the linear-chain organic conductor ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$P${\mathrm{F}}_6$, where TMTSF denotes tetramethyltetraselenafulvalenium. A giant conductivity resonance, implying long relaxation times, is observed at frequencies well below the single-particle gap. The frequency dependence is strongly depressed by small amounts of impurities. Either collective spin-density-wave conduction or excitations of the spin-density-wave mode are responsible for the observed frequency-dependent response.

We report the first Monte Carlo simulation on the critical relaxation of the three-dimensional kinetic Ising model with free surfaces. The surface-layer magnetization is shown to relax as $t^{-\frac{{\beta }_1}{\nu z}}$ at $T=T_c$, while the bulk magnetization relaxes as $t^{-\frac{\beta }{\nu z}}$. The dynamic bulk-to-surface crossover is discussed in view of the dynamic scaling theory.

The strength of the spin-fluctuation spectrum of U${\mathrm{Pt}}_3$ has been found, with neutron scattering, to decrease dramatically with temperature on approach to the superconducting transition. The spin fluctuations are antiferromagnetic. Their thermally activated intensity is consistent with the existence of a gaplike structure in the normal phase and shows that spin fluctuations take part in the formation of the superconducting state.

We report the first observation of spin-polarized photoelectron diffraction in core-level emission from antiferromagnetic KMn${\mathrm{F}}_3$. The Mn $3s$ multiplet splitting provides an internal source of polarized electrons, and spin-polarized photoelectron diffraction effects of up to 17% are seen in the $\frac{{}_{}{}^5{}_{}{}^{}S}{{}_{}{}^7{}_{}{}^{}S}$ intensity ratio. These effects are found to be very sensitive to both emission direction and temperature. Short-range antiferromagnetic order is found to persist up to approximately 3 times the Néel temperature.

Deexcitation of metastable He atoms has been used to probe the existence of a partially occupied $4s$-derived level close to the Fermi level of K atoms adsorbed on a Cu(110) surface, even at very low coverages. The width of this level decreases from about 3 eV at low coverage to 2 eV at high coverage, reflecting the transition from the chemisorbed to the metallic state of the adsorbate.

The Davydov model for a one-dimensional protein, coupling the high-frequency amide-I vibration to longitudinal-acoustic phonons, is investigated by use of finite-temperature molecular dynamics. Soliton dynamics is studied in both equilibrium and nonequilibrium situations. The random thermal motions prevent self-trapping from occurring at temperatures of interest for transport in real proteins.

Any attempt to describe bound states of three or more Dirac particles, or of two or more such particles in the presence of an external potential, must take into account the problem of continuum dissolution: A Hamiltonian which involves only the sum of free Dirac Hamiltonians for the particles plus local interactions will not have normalizable eigenfunctions because of the mixing of positive- and negative-energy states. A simple model is constructed to illustrate the validity of this "folk theorem," first noted by Brown and Ravenhall in 1951.

Although mass scales associated with string tension, compactification of extra dimension, and Newtonian gravity are a priori independent, these scales must be approximately equal to each other in any unified string theory with realistic couplings. Consequently, the compactification cannot be adequately described in terms of ten-dimensional field theory.

The structure of the quark mass matrices in the standard electroweak model is investigated. The commutator of the quark mass matrices is found to provide a convention-independent measure of $\mathrm{CP}$ nonconservation. The question of maximal $\mathrm{CP}$ nonconservation is discussed. The present experimental data indicate that nowhere is $\mathrm{CP}$ nonconservation maximal.

The constants of motion responsible for the spectrum degeneracy of a nonrelativistic spin-½ particle in the field of a dyon are exhibited. In addition to angular momentum, two vector operators are conserved: One generalizes the Runge-Lenz vector while the other has no counterpart for spinless systems. At fixed energy, they satisfy closed commutation relations. An invariance superalgebra including these conserved quantities is discovered when the system is enlarged by the adjunction of a second spin-½ particle.