In the angular correlation of the (${\pi }^{\mathrm{-}}$,pp) reaction, two rather sharp peaks were observed for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and C. These peaks were considered to be associated with two-step processes; one is pp-pp scattering after the (${\pi }^{\mathrm{-}}$,pn) reaction, and the other is the ${\pi }^{\mathrm{-}}$p-${\pi }^0$n reaction followed by the (${\pi }^0$,pp) reaction. The intranuclear cascade model reproduced very well the two peaks. These results show that two-step processes are important in pion-absorption reactions for light nuclei.

The ground-state charge densities of ${}_{}{}^{204}{}_{}{}^{}$,206,207,208Pb have been accurately determined by elastic electron scattering. Mean-field calculations fail to describe the individual charge densities in the central region of the nucleus. However, they properly account for polarization mechanisms in the nuclear interior, as they accurately describe the corresponding charge-density differences. We show that these data are sensitive to the value of the nuclear compressibility κ and that they are compatible with the value κ=230 MeV.

Emission in the visible has been observed from dense, cold helium gas in contact with solid hydrogen when irradiated by a 15-MeV proton beam. All four stable isotopic combinations have been studied, and the spectrum of one of them, ${}_{}{}^4{}_{}{}^{}\mathrm{HeD}$, appears highly perturbed. Spectral identification of rotational features and a plausible explanation of the perturbation have been provided by rovibrational energy-level calculations.

The resonance fluorescence of a single atomic ion stored in a radio-frequency trap was investigated. The photon correlation in the fluorescent light shows antibunching, and the probability distribution of the photon number is sub-Poissonian, both of these being properties of a nonclassical radiation field.

We report a coincidence experiment between energy-selected Auger electrons and the ions produced in the molecular fragmentation following core photoionization of ${\mathrm{N}}_2$. In this type of measurement it is possible to correlate the ion fragmentation products, their kinetic energy, and their electronic configuration with the hole configuration in the doubly charged molecule following the Auger decay of the initial core hole. These data produce new insight into the potential energy curves of the doubly charged molecular ions.

The competition between the bunching force of the ponderomotive potential and the repulsive force of the self electrostatic potential in a tapered free electron laser limits the beam density, deceleration rate due to tapering, and the local electric field spatial exponentiation rate. The limit on the spatial exponentiation rate is below that predicted by linear theory at the transition from the Compton to Raman regimes. Furthermore, this limit is independent of the form of the particle energy distribution function.

The formation of laser-driven shocks in fused silica was observed from shock trajectory measurements. The result reveals an anomalously slow buildup of the strong shock which suggests a sig- nificant volume change at pressures ≳ 1 Mbar. Nonsteady propagation of the strong shock was also observed for a transient period immediately following its formation.

The general form of the field correlations within a fluctuating homogeneous medium is determined in terms of the corresponding source correlations. Under very general conditions, the degree of spectral coherence has a universal form, independent of the source, if the fluctuations are isotropic. It they are anisotropic, the degree of coherence at separations that are large compared with the wavelength directly yields the generalized dynamical structure factor of the medium.

An experiment is performed in which a topological line defect (S=-(1/2)) is forced to move with constant speed c under the action of an applied voltage V. We argue that the line speed is determined by a competition between the viscous damping and the free energy that the system gains by displacing the line, so that c=βV, with β=1/2γb(${\mathrm{\epsilon }}_{\mathrm{a}}$K/π${)}^{1/2}$ and b a number ∼1 determined only by viscous effects close to the core of the defect.

A ‘‘pseudosphere’’ approximation is introduced to describe quantitatively the localization of acoustic and optic waves. The localization length ξ is obtained in terms of experimentally accessible parameters (scatterer density and size, speed of sound or light, frequency). For d=3 it is predicted that acoustic Anderson localization will not be observed unless the scatterers are more efficitent than hard spheres. A phase diagram for the optic problem is obtained; it suggests the sudden onset of localization at moderate values of the scatterer density.

A density-functional theory is developed to calculate the elastic moduli of crystals and quasicrystals. It is found that the nonaffine character of deformations below the unit-cell scale causes the Poisson ratio of a hard-sphere solid to be negative. An elastic instability is found for the icosahedral quasicrystals which lowers their symmetry to $D_3$ or $D_5$. The distortions of the diffraction pattern are in qualitative agreement with experiments.

Impurity-dopant effects on grain-boundary cohesion have been studied in a first-principles local spin-density atomic-cluster model of octahedral hole sites in nickel. Rigorous calculations of the total energy and gradient forces on the host atoms show that boron (an enhancer of cohesion) increases the maximum sustainable restoring force in the cluster, and sulfur (an embrittler) decreases the value of this force, consistent with observed segregation behaviors of these atoms.

High-power pulsed-laser–induced reactive quenching at liquid-solid interface is used for the first time to synthesize a metastable form of iron oxide. The oxide phase is characterized by using the techniques of conversion-electron Mössbauer spectroscopy, Rutherford backscattering spectrometry, x-ray diffraction, and x-ray photoelectron spectroscopy.

The vibrational properties of the reconstructed (√2 × √2 )R45°W(100) surface are calculated from a force-constant model with parameters determined from recent total-energy calculations. We find that the reconstruction causes a strong dipole-active surface resonance at ≊4 THz to be folded back onto the surface-zone center. A weaker dipole-active surface resonance near the top of the bulk spectrum and resonances polarized parallel to the surface also are found at the zone center. These results provide an interpretation of recent electron-energy-loss spectroscopy data. Their connection to recent He-atom scattering data also is discussed.

A general, analytically tractable, nonperturbative theory of the equilibrium structure of dense polymer melts is proposed on the basis of modern integral-equation theories of molecular liquids. Calculations are presented for polymer rings obeying Gaussian statistics and interacting via hard-core repulsions. The correlation hole, compressibility, and static structure factor are found to be sensitive functions of liquid density and degree of polymerization.

Time-of-flight laser resonance ionization is used to measure state-selective translational energies of neutral NO, CO, and metastable CO (${\mathrm{a}}^3$Π) desorbed from Pt(111) upon electron impact. A novel and dominant NO channel has a threshold of ∼6 eV and a peak translational energy of 0.05 eV. Lifetime calculations reveal a long-lived simple excitation (5${\mathrm{\sigma }}^{\mathrm{-}1}$). Dynamical calculations reproduce translational and rotational energy distributions and suggest that the excitation frees the hindered rotation of NO.

We present measurements of ultrasonic damping and velocity, carried out in the smectic-C phase of terephthal-bis-p-${\mathrm{p}}^1$-butylaniline (TBBA), showing that conventional hydrodynamics does not apply in the smectic-C phase of liquid crystals. The angular variation of the abnormal part of the damping is quite different from that obtained in the smectic-A phase of the same compound, and can be explained by the fact that the B/C ratio of the elastic constants, which is greater than 1 in the smectic-A phase, becomes less than 1 in the smectic-C phase.

We have calculated acoustic-phonon scattering and the resulting intrachain diffusion constant ${\mathrm{D}}_{\mathrm{?}}$ for neutral solitons in trans-polyacetylene. The result, with no arbitrary parameters, agrees with ${\mathrm{D}}_{\mathrm{?}}$ determined by magnetic resonance experiments from ∼150 to 300 K. The more rapid decrease with decreasing temperature seen below 150 K can be obtained with the introduction of a barrier-to-soliton motion of 0.01 eV. Such barriers may result from remanent cis linkages in the Shirakawa trans-polyacetylene used for the experiments.

Electric-field–dependent conductivity measurements in the organic two-chain conductor TTF-TCNQ are reported in the pressure (P) range 4≤P≤24 kbar. Deviations from Ohm’s law, with a threshold field ${\mathrm{E}}_{\mathrm{T}}$, are found at all P at temperatures below the upper Peierls transition. At low P, we find that the ${\mathrm{E}}_{\mathrm{T}}$ temperature dependence approaches that found for ${\mathrm{NbSe}}_3$. As TTF-TCNQ is driven through third-order commensurability at ∼19 kbar, we observe a peak in ${\mathrm{E}}_{\mathrm{T}}$ and a dip in the excess current at constant field. The results are discussed in terms of charge-density wave and/or discommensuration transport.

We show, within a Kondo-boson 1/N expansion, that the infinite-U lattice Anderson model is unstable to d-wave superconductivity in the limit in which the model describes heavy-fermion behavior. The pairing mechanism is Kondo-boson exchange between heavy quasiparticles found in mean-field theory. The model is extended to include the Coulomb pseudopotential.