Evidence is reported for a nonrandom process by which laser-produced plasmas emit suprathermal electrons. Emission is dominated by a 1 to 2 psec monoenergetic burst, during which the electron energy decreases rapidly. The suprathermal tail on the energy distribution is due to the integrated temporal variation of the electron energy, not to statistical processes. The hot-electron temperature thus produced is practically independent of laser pulse energy.

Resonant absorption is investigated in expanding plasmas. The momentum deposition associated with the ejection of hot electrons toward low density via wave breaking readily exceeds that of the incident laser radiation and results in significant modification of the density profile at critical density. New scaling of hot-electron temperature with laser and plasma parameters is presented.

The propagation of the superthermal plasma from microdisk targets irradiated with single, nanosecond C${\mathrm{O}}_2$ laser pulses at intensities of ∼${10}^{14}$W ${\mathrm{cm}}^{-2\mathrm{}}$ is examined through the study of its effect on subsidiary passive targets. The observed propagation velocity is similar to the estimated superthermal ion acoustic speed and has an intensity dependence of $I^{0.14-0.21}$.

The implosion of spherical-shell targets driven ablatively by six 1.05-μm laser beams at an irradiance of ∼ ${10}^{13}$ W ${\mathrm{cm}}^{-2\mathrm{}}$ has been studied by streak time-resolved x-ray shadowgraphy. Measurements of acceleration determined the ablation pressure. Departures from one-dimensional simulations showed increasingly degraded implosions as the shell aspect ratio $\frac{\mathcal{r}}{\Delta \mathcal{r}}$ was increased from 10 to 110 for shells with surface perturbations of $\pm 0.05\Delta \mathcal{r}$.

The continuous nucleation of bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ from the liquid phase due to the presence of a MgO substrate is detected. For superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ there is no evidence of continuous nucleation of either the hcp or the bcc solid from the substrate. The experiment contrasts the influence of the square lattice of MgO with the triangular lattice of a basal-plane graphite substrate. The phenomenon of pore condensation for solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is discussed.

Photoelectrons and Auger electrons from Xe in adsorbed multilayers of Xe on Pd(001) as well as on spacer layers of Kr on Pd(001) exhibit well-resolved increases in kinetic energy with decreasing distance from the surface (2-28 Å), allowing a direct labeling of the layers. These relaxation shifts for core-hole excitations (0.9-2.1 eV) and for Auger excitations (3.3-6.6 eV) are well described by an image potential, where the position of the image plane agrees within 0.2 Å with local-density functional theory.

The nuclear specific heat of the hyperfine-enhanced Van Vleck paramagnet Pr${\mathrm{Ni}}_5$ has been measured from 0.2 to 100 mK in magnetic fields up to 6 T. The ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ nuclei order ferromagnetically at 0.40±0.02 mK. Other results reported are hyperfine enhancement factor $1+K=12.2\pm 0.5$, enhanced nuclear magnetic moment $\mu =(0.027\mathrm{}\pm 0.004){\mu }_{\mathrm{B}}$, internal field $B_0\mathrm{}(T=0\mathrm{})=66\mathrm{}\pm 10$ mT, and nuclear exchange parameter ${\Sigma }_j\frac{{J_{\mathrm{ij}}}^N}{k_{\mathrm{B}}}=0.20\mathrm{}\pm 0.04$ mK.

The spectacular decay mode $F^{+}\to p\overline{n}$ would be easily observed if the annihilation mechanism actually dominates the standard one (light-quark spectator) in the disintegrations of charmed particles. Its branching ratio would be about ${10}^{-2\mathrm{}}$. Otherwise, it should be very rare (≃ ${10}^{-6\mathrm{}}$) because of partial conservation of axial current.

The giant monopole resonance in the region of deformed nuclei has been investigated by inelastic scattering of 108.5 MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at very small scattering angles. Evidence is reported for coupling between the giant monopole and giant quadrupole vibrations, based both on energy shift and transition strength.

In ($\alpha$,${\alpha }^{\prime }$) measurements on spherical ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ and deformed ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$, the cross sections and energies of the two components of the isoscalar giant resonance are found to be consistent with a splitting of the giant monopole resonance in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ into two components of roughly equal strength. One component remains close to the giant-monopole-resonance energy of ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ while the second is coincident with the giant quadrupole resonance. This is shown to be consistent with simple schematic-model predictions.

It has been suggested that bags containing more than three interacting quarks may be formed in high-energy collisions; these states would appear as narrow resonances in the inelastic channels. We have measured the inclusive cross section $d+{}_{}{}^4{}_{}{}^{}\mathrm{He}\to p+X$ at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=6.25\mathrm{} \mathrm{to} 7.91$ GeV in steps of 50 to 100 MeV to search for an eighteen-quark bag resonance. No evidence for narrow resonances was found and upper limits on the production cross section are presented.

Parity nonconservation has been studied in ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, and ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$ for the Weinberg-Salam model. After careful treatment of nuclear structures aspects, values are predicted for the $\gamma$-ray asymmetry and circular polarizations in good agreement with experiment provided one employs meson-nucleon coupling constants somewhat weaker than the "best values" recently suggested by Desplanques, Donoghue, and Holstein.

The nucleon-nucleon parity-nonconserving potentials given by Desplangues, Donoghue, and Holstein (DDH) are used to calculate matrix elements between states of opposite parity in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$. The sensitivity of the parity-nonconserving matrix elements to various approximations in the microscopic shell-model wave functions is investigated. The final results using the DDH estimates for the weak mesonnucleon coupling constants based on the Weinberg-Salam theory are several times larger than experiment.

The first measurement is reported of the absolute cross section as a function of kinetic energy for a process involving a state-selected excited reactant, namely near-resonant ${\mathrm{H}}^{+}$-$\mathrm{Na}\mathrm{}\left(3p\right)\mathrm{}$ charge exchange. The ion-beam experiments show enhanced production of $L\alpha$ from ${\mathrm{H}}^{+}$-Na when the sodium is irradiated with laser light tuned to a $D$ line. The results presented here demonstrate unambiguously that of ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$, only ${\mathrm{H}}^{+}$ leads to enhancement; however, the effect occurs only for energies below 30 eV.

The shapes of continuum capture cusps arising from ejection of target electrons by 15-18 a.u. velocity ${\mathrm{Ar}}^{18+}$ nuclei traversing He, Ne, and Ar are investigated. Observed asymmetries are compared to the second-Born-term asymmetry conjecture by Shake-shaft and Spruch, and to the alternative, first-Born-term asymmetry counter-conjecture by Chan and Eichler. Present evidence favors the former conjecture.

A model is introduced of an ionospheric plasma cloud (deformable dielectric) with a piecewise-constant ion density and a diffusive-regularized boundary. The linear stability of a single-contour circular cloud is studied and a new evolution equation for modal amplitudes is obtained which has the property that the wave number of maximum amplitude decreases with time (downward cascade). Analytic expressions show that large clouds evolve more slowly and appear more dissipative.

Strandlike domains have been observed in Nb${\mathrm{Se}}_3$ at temperatures below 144 K by imaging in one of the satellite reflections produced by the phase transition. These appear to twinkle rapidly with many strands in the field of view lighting up and switching off in periods of a few seconds. In addition, fringes along these strands have been observed.

The modulation of incommensurate structures appears to have macroscopic consequences: On modulated single crystals satellite surfaces have been observed which can be interpreted by extending the classical morphological theory by including superspace group symmetry.

Data on spontaneous and stimulated emission, in the photon-energy range $E_g+5\mathrm{}\hslash {\omega }_{\mathrm{LO}}\gtrsim \hslash \omega \gtrsim E_g$, are presented on ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$-GaAs quantum-well heterostructures with ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ ($x\sim 0.4-0.5$) coupling barriers of size $L_B\sim 40-70$ Å and GaAs wells of size $L_z\sim 30-40$ Å. For $L_z$,$L_B\lesssim 50$ Å, Al-Ga disorder (clustering) in the alloy barriers is consistent with the observed spectral broadening and downward energy shift of the confined-particle transitions. A simple substitution of binary (AlAs) for ternary (AlGaAs) barriers eliminates alloy clustering and its effects, and makes unambiguous the identification of clustering in alloy barriers.

It is suggested that the considerable softening of the lattice of certain superconducting eutectic mixtures, and the accompanying increase in transition temperature are the result of large unrelieved strains that weaken the effective spring constant between neighboring atoms.