Positive and negative Knight shifts of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ lines have been observed in NMR magic-angle-sample-spinning experiments on the organic conductor (fluoranthenyl) ${}_2{}^{}{}_{}{}^{}\mathrm{Sb}$${\mathrm{F}}_6$ at room temperature. Knight-shift values (in parts per million) of 61, 42, 40, and -45 were obtained for different carbon positions; correspondingly short spin-lattice relaxation times of 75, 100, 115, and 580 ms were observed. The relevance of these data for one-dimensional conduction is discussed.

We discuss a smoothing-out procedure that deforms a family of locally inhomogeneous and anisotropic spatially closed cosmological models into closed Friedmann-Robertson-Walker universes. This gives a precise content to the averaging hypothesis tacitly assumed in cosmology by providing explicitly the correction terms to the physical sources induced on smoothing out the space-time geometry. The consequences of such terms on the dynamics of the Universe are discussed.

The results of microcanonical simulation of an Ising model defined on a truncated, lattice-embedded, fractal, Sierpinsky carpet of dimension ∼ 1.86 are presented. Estimates for a variety of exponents give, via hyperscaling at criticality and via the behavior of the spin-spin correlation away from criticality, consistently, a dimension ∼ 1.66±0.10.

The diffusion-limited-aggregation model is generalized in order to take into account the surface effects playing an essential role during most of the growth processes. With variation of a parameter of the model the geometry of the clusters generated in the Monte Carlo simulations gradually changes from the randomly branched diffusion-limited-aggregation clusters into compact, nearly regular, snowflakelike patterns. The deposition of particles along a line results in patterns similar to those observed in the experiments on directional solidification.

We show that supersymmetric quantum mechanics may be used to interrelate the spectra of different atoms and ions. This supersymmetry is broken by electron-electron interactions.

The present limit on the mass of the tau neutrino ($m_{{\nu }_{\tau }}<143\mathrm{}$ MeV), obtained from tau decay, may be lowered significantly from a study of the pion spectrum in $K^{+}\to {\pi }^{+}\nu \bar{\nu }$. We show that if $m_{{\nu }_{\tau }}\gtrsim 50$ MeV then the pion spectrum differs significantly from its value when all neutrinos are massless. Our results are also applicable to any new massive neutrino with $50\lesssim m_{{\nu }_h}\lesssim 150$ MeV.

A relativistic generalization of the Heisenberg commutation relations is suggested which is different from the conventional ones used for the intrinsic coordinates and momenta in the relativistic oscillator model and the relativistic string. This new quantum relativistic oscillator model is determined by the requirement that it gives a unified description of relativistic vibrations and rotations and contracts in the nonrelativistic limit $c^{-1\mathrm{}}\to 0$ into the usual nonrelativistic harmonic oscillator.

The relative cross section for the process $\mathrm{Ca}\left(4s5p{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\right)+\mathrm{He}\to \mathrm{Ca}\left(4s5p{}_{}{}^3{}_{}{}^{}P_j^{}{}_{}{}^{}\right)+\mathrm{He}+\Delta E=177\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ is determined as a function of initial alignment of the $\mathrm{Ca}\left(4s5p{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\right)$ state. The experiment is carried out with pulsed laser excitation in a crossed beam. An initial ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ state aligned perpendicular to the relative collision velocity vector produces 50% more ${}_{}{}^3{}_{}{}^{}P_j^{}{}_{}{}^{}$ product-state emission than a ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ state aligned parallel. These results are discussed in terms of physical models of the curve-crossing interaction.

The total energies of hydrogen interacting with small clusters of lithium atoms have been calculated self-consistently by means of the unrestricted Hartree-Fock scheme. The total energy is found to be lowered when hydrogen moves away from the most symmetric site in the cluster. This observation is independent of the cluster geometry as long as its size remains small. These results, which are analogous to Jahn-Teller distortion, have important consequences on cluster calculations designed to mimic the bulk solid.

A model of acoustic turbulence is investigated for its bifurcation structure by the calculation of spectral as well as ordinary bifurcation diagrams and (subharmonic) attractor maps. A superstructure resulting from nonlinear resonances is found with period-doubling Feigenbaum direct cascades and Grossmann inverse cascades as fine structure. Connected with the superstructure is a new family of periodic chaos with a different type of chaos belonging to each basic subharmonic period of oscillation.

A new fluid instability has been discovered which arises from the coupling of the drifttearing mode at the diamagnetic frequency with a mode with a velocity just below the curvature drift velocity. This mode, which can also be destabilized by cross-field transport, is unstable over a wide range of conditions and mode numbers for reversed-field pinches or spheromaks.

We report the observation of two types of multiple spin echoes in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ below 100 mK. It is shown that these are generated by (i) Fermi-liquid interaction effects at the transition to the collisionless regime at low $T$, and (ii) the dipolar demagnetizing field in the regime of slow spin diffusion at higher temperatures. A perturbative solution of the appropriately generalized Bloch equations accounts for the qualitative features observed in experiment.

The vibrational excitations in vitreous silica above 150 GHz were investigated at 50, 100, and 290 K by inelastic scattering of cold neutrons. A detailed study of the frequency and wave-vector dependence shows that even at the lowest frequencies only a small part of the scattering is due to acoustic phonons. The type of motion of the dominating additional low-frequency modes is identified as a coupled rotation of Si${\mathrm{O}}_4$ tetrahedra. Possible connections to the low-temperature glass anomalies are discussed.

The activation energy for thermally generating conduction electrons in fluids such as Hg, Cs, and Rb decreases with increasing fluid density and eventually vanishes resulting in a transition to semimetallic behavior. A dominant contribution to this evolution is held to be the cohesion within thermally generated positive molecular ions.

We relate the metal-nonmetal transition in expanded liquid mercury to the dielectric transition in dense mercury vapor. Condensation of Frenkel excitons into an excitonic-insulator phase is shown to occur at the dielectric transition. The excitons unbind at the associated (Mott) metal-nonmetal transition. The permanent dipole moments of the condensed excitons are estimated to order as a ferroelectric phase; the critical exponents of the liquid-gas transition therefore become classical.

Monte Carlo simulations are used to study the charge-density-wave to spin-density-wave transition in the one-dimensional Hubbard model with on-site ($U$) and nearest-neighbor ($V$) repulsion. The transition is found to be continuous for small $U$ and first order for large $U$, with the crossover occurring around $U\sim 3$. The transition line deviates somewhat from the theoretical prediction $U=2V$ towards the charge-density-wave phase for intermediate coupling. A qualitative explanation for the results is given by use of strong-coupling arguments.

Synchrotron-radiation photoemission, angle-resolved Auger, and LEED studies show Ce cluster formation on Si(111). These nonmetallic clusters grow for coverages of 0.1 to 0.6 monolayer, interact weakly with the substrate, and induce 200-meV band-bending changes. At ∼ 0.6 monolayer, they stimulate surface disruption, producing a metallic interfacial silicide. The association of $d$- or $f$-band metal clusters with surface reaction substantially extends the cluster-induced-reaction model proposed for Al-GaAs.

A new simple method is presented for calculating properties of nonuniform real metals, i.e., surfaces, vacancies, small clusters, etc. The bulk metal is represented by a jelliumlike homogeneous electron gas with an effective exchange-correlation energy that includes electron-ion correlations. As an example, the method is applied to calculate surface energies. One-dimensional calculations, with no further corrections for the lattice, give results in reasonable agreement with experiment.

Photoemission and bremsstrahlung-isochromat-spectroscopy data on a cleaved NiO single crystal are presented and compared to band- and cluster-theory predictions. In contrast to band-theory predictions the band gap is found to be large but not determined solely by the even larger $d-d$ Coulomb interactions so that NiO is not a Mott-Hubbard insulator in the simplest sense. A large $d-d$ interaction need not prevent NiS from being a metal.

Photoemission measurements on cleaved NiO(100) identify both the O $2p$ $\pi$ valence orbitals and the previously undetected O $2p$ $\sigma$ orbitals. An upper limit of 0.8±0.1 eV is set on the width of the Ni $3d$ $t_{2g}\downarrow$ emission. A large maximum in the empty density of states is detected in the secondary-electron spectrum, explaining previously debated photoabsorption data. We conclude from the available data that NiO is not a conventional band-gap insulator, as has been suggested recently, but is in fact a Mott insulator.