Phonon dispersion and density-of-states measurements are presented for VN, a cubic transition-metal compound with ten valence electrons. The acoustic phonons differ strongly from those observed in nine-valence-electron compounds. In particular, the prominent soft-mode region has moved from the interior to the boundary of the Brillouin zone. Using the theory of Varma and Weber, we find that these changes arise primarily from a rigid-band-like increase in the Fermi energy.

The emission of ${\mathrm{H}}^{+}$ sputtered from hydrogenated amorphous silicon has been studied for 3- to 30-keV noble-gas-ion bombardment. The results suggest that excited silicon atoms can be emitted as ${\left({\mathrm{Si}}_{2p}\mathrm{H}\right)}^{+}$ molecules. Auger deexcitation in vacuum results in ${\mathrm{}\left(\mathrm{SiH}\right)\mathrm{}}^{2+}$ which disintegrates into ${\mathrm{Si}}^{+}$ and ${\mathrm{H}}^{+}$ with a corresponding gain in kinetic energy due to Coulomb explosion. Direct emission of ${\mathrm{H}}^{+}$ is important only at ${\mathrm{H}}^{+}$ energies > 30 eV or at bombardment energies <3 keV.

The proton NMR spin-lattice relaxation time $T_1$ has been measured in the spin-½ one-dimensional antiferromagnet (1DAF) $\alpha$-bis (N-methylsalicylaldiminato)-copper (II) (CuNSal) at low temperatures and high fields. $T_1$ is dominated by electron spin fluctuations of the 1DAF, and we show that these fluctuations are described by Fermi-Dirac statistics for the one-magnon contribution to $T_1$ but that the two-magnon part is given by Bose-Einstein statistics.

We have observed deviations from Ohm's law in single crystals of methyltriphenylarsonium tetracyanoquinodimethane: $\mathrm{Me}{\varphi }_3\mathrm{As}{\left(\mathrm{TCNQ}\right)}_2$. We propose a model based upon tunneling of electrons through barriers in the conducting strands. Electrical conductivity and electron and nuclear magnetic resonance are used to accomplish a successful quantitative test of the model.

Electron-energy-loss spectra of stage-1 K-intercalated graphite single crystals were obtained with a scanning transmission electron microscope. The complex dielectric function with electric polarization perpendicular to the $c$ axis was derived by Kramers-Kronig analysis. The energy-loss peak at 2.5 eV is consistent with previous optical measurements, while the splitting of the one at 27 eV can be interpreted by folding the Brillouin zone of pristine graphite. Splittings and shifts of the interband transitions were observed and compared with calculations.

Thin-film structures composed of amorphous Se and polystyrene-hexylmethacrylate copolymer sandwiched between two semitransparent Al electrodes have been studied using transient photocurrent techniques. The dependence of the observed "transit time" on the applied voltage showed lengthening as the voltage was increased, contrary to the expected behavior in the time-of-flight experiments! This novel effect has been associated with a rate-limited charge-transfer mechanism across the Se-polymer interface.

$\frac{1}{f}$ noise has been predicted for simple physical systems that exhibit certain singularities in the fluctuation weighting function. We have produced a "quasi" singularity in the light-intensity pattern by focusing a laser beam with a cylindrical lens. The spectral density of the light scattered off polystyrene microspheres flowing through this region followed a $\frac{1}{f}$ dependence, as predicted. Other beam patterns gave the predicted noise spectra, including a $\frac{sin{\left(\pi f\tau \right)}^2}{{\left(\pi f\tau \right)}^2}$ spectral shape for flow past a slit.

A generalization of the Niemeijer-van Leeuwen renormalization-group transformation treating disordered cells of spins as vacancies is introduced and applied to the two-dimensional $q$-state Potts model. Finite-lattice approximations yield the changeover from continuous to first-order phase transitions predicted by Baxter but not observed in previous renormalization-group calculations. Exact results are conjectured for the tricritical exponents of dilute Potts models.

We present numerical estimates of the Hausdorff dimension $D$ of the largest cluster and its "backbone" in the percolation problem on a square lattice as a function of the concentration $p$. We fine that $D$ is an approximately linear function of $p$ in the region near $p=p_c (\simeq 0.59)$ with a dimension about equal to that of a self-avoiding walk when $p=0.455\mathrm{}$. The dimension of the backbone, or biconnected part, of the largest cluster equals that of the self-avoiding walk when $p\simeq p_c$. At $p=p_c$ the dimension of the largest cluster equals the anomalous dimension introduced by Stanley et al.

We prove the equivalence, near the critical point, of a $D$-dimensional spin system in a random external magnetic field with a ($D-2\mathrm{}$)-dimensional spin system in the absence of a magnetic field. This is due to the hidden supersymmetry of the associated stochastic differential equation. We identify a space with one anticommuting coordinate with a space having negative dimensions -2.

We suggest that the reactions $\mathrm{pp}\to W^{\pm }\gamma X$ and $p\overline{p}\to W^{\pm }\gamma X$ are good candidates for measuring the magnetic moment parameter $\kappa$ in ${\mu }_W=\left(\frac{e}{2M_W}\right)(1+\kappa )$. The angular distribution of the $W$ bosons in $p\overline{p}\to W^{\pm }\gamma X$ is particularly sensitive to this parameter. For the gauge-theory value of $\kappa =1\mathrm{}$, we have found a peculiar zero in $\frac{d\sigma (d\overline{u}\to W^{-}\gamma )}{d}cos\theta$ at $cos\theta =-\frac{1}{3}$, the location of this zero depending on the quark charge through $cos\theta =-(1+2\mathrm{}{Q}_d)$. A similar zero occurs in $\frac{d\sigma (u\overline{d}\to W^{+}\gamma )}{d}cos\theta$. We can offer no explanation for this behavior.

With use of a manifestly gauge-invariant formulation, a two-parameter Bäcklund transformation is constructed for the self-dual $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ Yang-Mills fields. Some of its properties and implications are discussed.

A symmetric deflection of a Na beam by resonant standing-wave radiation has been observed. The combination of absorption and stimulated emission of the two oppositely traveling waves ${\omega }_{+}$ and ${\omega }_{-}$ results in a net deflection of the beam. The observed magnitude of the beam deflection and its dependence on the radiation power agree with a calculation based on the random-walk picture that the two traveling waves ${\omega }_{+}$ and ${\omega }_{-}$ are utilized randomly in the stimulated-emission and absorption processes.

We report striking non-Franck-Condon vibrational intensity distributions associated with the shape resonance in the $5\sigma$ photoionization channel of CO. This example confirms the recent theoretical prediction that shape resonances will couple significantly with vibrational motion, leading to different resonance energies and profiles, and non-Franck-Condon intensities in alternative vibrational channels. Analogous effects are expected in connection with the widespread occurrence of shape resonances in both innershell and outershell molecular photoionization spectra.

Multiphoton dissociation of ethyl chloride was studied using a tunable 3.3-μm laser to excite CH stretches. Resonances in multiphoton dissociation yields match the position and shape of peaks in the fundamental, as narrow as 0.4 ${\mathrm{cm}}^{-1\mathrm{}}$, and first- and second-over-tone absorption spectra. Transitions through the discrete levels occur at or near resonance. Anharmonicity is compensated by the presence of five CH stretch modes.

We employ a numerical technique to optimize the shape of tokamak plasmas to achieve maximum stable volume-averaged $\beta$ with respect to ballooning modes. We have examined dee shapes with moderately peaked current profile, poloidal $\beta =1\mathrm{}$, and $\frac{R}{a}=2.76\mathrm{}$. The optimal shape is a strongly modified dee with a large indentation on the inside edge of the plasma. Maximum beta increases with elongation and exceeds 14% when $\frac{b}{a}=3\mathrm{}$.

Tritium is produced in deuterium discharges in the Princeton Large Torus by the reaction D($d$,$p$)T. These tritons undergo reactions D($t$,$n$)${}_{}{}^4{}_{}{}^{}\mathrm{He}$ creating 14-MeV neutrons which have been detected by two independent techniques at a level of 1% of the 2.5-MeV neutrons from the reaction D($d$,$n$)${}_{}{}^3{}_{}{}^{}\mathrm{He}$. The magnitude of the 14-MeV neutron emission is consistent with finite banana width, neoclassical predictions for the confinement of the energetic tritons.

The Raman spectra of 4-pyridine-carboxaldehyde-doped Al-${\mathrm{Al}}_2$${\mathrm{O}}_3$-Ag tunnel junctions evaporated onto Ca${\mathrm{F}}_2$ films and optical diffraction gratings show that the molecular Raman scattering is strongly enhanced under conditions which permit the direct excitation of the surface plasmon modes of Ag. This suggests that the surface plasmon is an intermediate state in surface-enhanced Raman scattering.

This paper presents a theory of the linear density response to an external time-dependent scalar potential for a Fermi system whose unperturbed density varies slowly. Simple local-density-functional response theory is valid except in a region of small $q$ and $\omega$ (wave number and frequency of the perturbation). For this region we have worked out a generalization, to the case of inhomogeneous systems of Landau Fermi-liquid theory.

A new and unusual yield enhancement [(20-30)% above Rutherford] has been observed in the energy spectra for ${\mathrm{He}}^{+}$ backscattering to 180° ± 0.25° in the energy range $0.2 \mathrm{MeV}<~E<~2.5 \mathrm{MeV}$ for a variety of amorphous and polycrystalline targets. The depth and angular dependence of the yield enhancement has been established for a variety of materials and experimental conditions. Several possible explanations are discussed.