Using the transmission method we have measured the circular polarization, $P_{\gamma }$, of $\gamma$ rays from excited projectilelike fragments in the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at 100 MeV. The polarizations are large with values up to $\left|P_{\gamma }\right|\cong 100$%. Over the whole $Q$ range, the sign and magnitude of $P_{\gamma }$ can be interpreted in terms of matching conditions familiar from direct-reaction analysis, contrasting the statistical character of the associated heavy-fragment excitation.

Four-wave optical parametric amplification enhanced by the ac Stark effect has been observed, with the use of a dye laser tuned near the $D_2$ line of sodium. This process leads to the generation of sidebands displaced from the laser frequency by the generalized Rabi frequency. Under certain experimental conditions, the emitted radiation is in the form of a cone surrounding the transmitted laser beam. A theoretical model that describes these effects is presented.

This Letter reports accurate values for the oscillator strength of potassium, and possible resolution of some outstanding discrepancies concerning the oscillator strengths and photoionization cross sections of this atom. Our results establish a value of (5.2 ± 0.5) × ${10}^{-21\mathrm{}}$ ${\mathrm{cm}}^2$ for the photoionization cross section at the series limit.

Laser-plasma interaction experiments have been performed with both 1.05- and 0.53-μm-wavelength light incident on spherical glass targets. Comparisons of hard x-ray spectra and fast-ion energy imply a substantial reduction of hot-electron levels at the shorter wavelength. Increased absorbed energy fractions at the shorter wavelength are in agreement with the expected scaling of inverse bremsstrahlung absorption.

Thin plastic foils of various thicknesses (0.13-5.0 μm) were irradiated by iodine-laser pulses with an incident intensity of 4×${10}^{15}$ W ${\mathrm{cm}}^{-2\mathrm{}}$. Time-of-flight charge collectors and a Thomson parabola mass spectrometer were used to measure the asymptotic ion velocity distribution at the back and the front (laser) sides of the target. Analysis of these data yielded the ratios of the hot-electron densities and of the hot-electron temperatures at both sides of the foil target. The results disagree with calculations based on classical electron penetration into the foil.

Homodyne detection of scattered C${\mathrm{O}}_2$-laser light demonstrates a close relation between microturbulence level and energy confinement in the Wendelstein VII A stellarator during both Ohmic and neutral-beam heating experiments. With the onset of neutral injection an abrupt order of magnitude decrease in ${\left(\frac{\delta n}{n}\right)}^2$ accompanied by a broadening of the fluctuation spectra is observed, indicating an almost immediate improvement of containment time.

A new method for detection of zone-boundary phonons is presented. Phonons generated by nonradiative transitions in thallium halide crystals are detected by phonon difference absorption with use of time-resolved far-infrared laser spectroscopy. Our experiments, performed at crystal temperatures between 3 and 20 K, give experimental evidence of strongly-temperature-dependent anharmonic lifetimes of transverse-acoustic zone-boundary phonons.

We report measurements of the specific heat of the one-dimensional ionic conductor hollandite for temperatures between 0.07 and 3 K. An anomalous contribution is observed which exhibits a pronounced peak unlike most disordered systems. The peak height strongly depends on the concentration of the diffusing ions. A theoretical interpretation is given.

We present a theory of the cholesteric blue phase, assuming a first-order cholesteric-isotropic transition. We show, on the basis of the Oseen-Frank elasticity equations, that the planar helix structure, generally associated with the cholesteric phase, becomes unstable at temperatures near the transition point. It transforms into a phase characterized by a network of disclination lines.

Aluminum thin films containing helium microbubbles produced by ${\mathrm{He}}^{+}$-ion implantation have been investigated by ultraviolet absorption and electron-energy-loss spectroscopies in the range 1-30 eV. The shape and position of the $1{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-n{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ helium line series and several Al plasmon bands are discussed in terms of the physical state of helium in the bubbles. Results imply helium densities 3 to 6 times that of liquid He at 2°K and 1 bar pressure.

Thermalization of photoinduced carriers in $a$-Si and $a$-Si: H was studied with use of subpicosecond-pump and probe techniques with parallel and perpendicular polarizations. The underlying process was identified as hot-carrier absorption whose cross section increases with the carrier excess energy. The energy dissipation rate in $a$-Si is ≃0.5 eV/ps ($\simeq \hslash {{\nu }^2}_{\mathrm{phonon}}$) and is less than 0.1 eV/ps in $a$-Si: H; Fröhlich interaction with polar phonons can explain this smaller rate. A photoinduced dichroism associated with polarization memory was observed.

First-principles surface charge densities are calculated and used to form He-surface interaction potentials which can account for atom-beam diffraction intensities from GaAs(110) and Ni(110)-H 2×1 surfaces.

Electroreflectance measurements have been performed on the GaAs-${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ superlattice, and the observed structure has been related to interband transitions at different points of the Brillouin zone. For increasing $x$ the energies of these transitions shift progressively to higher values with respect to those of bulk GaAs, indicating the effect of the superlattice potential on the band structure beyond the zone center. In contrast, similar shifts observed in ${\mathrm{In}}_{1-x}{\mathrm{Ga}}_x\mathrm{As}-\mathrm{Ga}{\mathrm{Sb}}_{1-y}{\mathrm{As}}_y$ only occur for $x$,$y>\mathrm{}0.2\mathrm{}$, an anomaly arising from its unusual periodic potential.

The anisotropy in the static susceptibility of ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$-P${\mathrm{F}}_6$ has been investigated above and below the metal-insulator transition for a range of fields between 4 and 25 kOe. The results are consistent with the occurrence of an Overhauser antiferromagnetic transition to a spin-density-wave state with an easiest axis perpendicular to the stacks. Below the transition, evidence for a spin-flop transition is seen. Above the transition, evidence for a crossover, possibly from $n=3\mathrm{}$ to $n=1\mathrm{}$ spin behavior, is seen.

We examine the response of an ultrasmall, low-critical-current Josephson junction to an external magnetic field. We find that the dc supercurrent exhibits an anomalous field dependence which reflects large-amplitude phase fluctuations. These fluctuations, which arise from zero-point charge oscillations, cannot be described within the context of conventional linear theories.

The chemisorption of ${\mathrm{H}}_2$ on Ti(0001) is treated with use of an ab initio configuration-interaction theory for the surface region. Dissociation of ${\mathrm{H}}_2$ occurs above the surface but more stable threefold coordination sites lie closer to the surface at ∼ 1.3 Å. Adsorption in adjacent threefold sites is less stable than in separated sites sharing only one surface atom. Bonding is predominantly with the $4s$ electrons of the metal leading to hydridic hydrogens and a polarized lattice electronic distribution.

${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ $\gamma$-ray resonance-absorption spectra in crystals of the iron-storage protein, ferritin, display above 265°K, in addition to a normal quadrupole doublet, wide Lorentzian wings extending to velocities of ± 2 cm/sec. The results are interpreted in terms of the dynamics of the iron-containing core of the protein, undergoing bounded diffusive motion within a "cage," characterized by a jump probability per unit time of about 0.5×${10}^8$ ${\sec }^{-1\mathrm{}}$ and a mean-square displacement of about 4.8×${10}^{-2\mathrm{}}$ ${\mathrm{\AA }}^2$ at 298°K.

Recent, precise analyses of $p-p$ and $n-p$ scattering data up to 800 MeV by Arndt et al. have provided the strongest evidence to date for the existence of dibaryon states in the $I=1\mathrm{}$, ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}F_3^{}{}_{}{}^{}$ nucleon-nucleon channels. Model fits to their new phases reveal poles located near the "$N\Delta$" threshold ($2.15-0.05i$ GeV). Because of their strong coupling to this channel, these dibaryon resonances are highly inelastic.

In a sample of 10 000 ${\Upsilon }^{\prime }$ decays observed with our nonmagnetic detector at the Cornell Electron Storage Ring, we find 23 events consistent with the decay ${\Upsilon }^{\prime }\to \Upsilon {\pi }^{+}{\pi }^{-}\to e^{+}{e}^{-}{\pi }^{+}{\pi }^{-}$. We derive a branching fraction of 0.20±0.07 for ${\Upsilon }^{\prime }\to \Upsilon {\pi }^{+}{\pi }^{-}$ and estimates of the partial width for this decay. The invariant-mass spectrum of the pion pairs shows a strong preference for large di-pion mass.

Rotational bands in both the irrotational and the rigid limits are constructed in the context of the microscopic CM(3) and $\mathrm{O}\mathrm{}(N-1\mathrm{})\mathrm{}$ algebraic models. The symplectic algebra Sp(3, $R$) determines the physical $\mathrm{O}\mathrm{}(N-1\mathrm{})\mathrm{}$ representation. A potential energy in the collective vortex coordinates of a particularly simple form is required in order to obtain the rigid limit.