The p→${+}^{13}$C→ (polarized target) elastic-scattering spin observables ${\mathit{A}}_{000\mathit{n}}$ (target analyzing power) and ${\mathit{A}}_{00\mathit{n}\mathit{n}}$ (spin-correlation parameter) were determined at 497.5 MeV over the laboratory angular range 12°–30° with statistical uncertainties typically ±(0.02–0.06). Results of distorted-wave Born approximation calculations, based on either the relativistic or the nonrelativistic impulse approximation, are in reasonable agreement with these new data.

We have measured the fusion excitation function and γ-ray multiplicities ${\mathit{M}}_{\gamma }$ for the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{154}$Sm system. We have also measured ${\mathit{M}}_{\gamma }$ for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{166}$Er system that leads to the same compound nucleus, ${}_{}{}^{182}{}_{}{}^{}\mathrm{Os}$, as a calibration of the connection between ${\mathit{M}}_{\gamma }$ and the first moment of the spin distribution, 〈l〉. We find that the deduced 〈l〉 for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{154}$Sm agrees reasonably well with theoretical calculations, and in particular its energy dependence exhibits the barrier bump expected when a shape degree of freedom is strongly coupled to the relative motion.

A mass spectrometer consisting of two Penning traps has been set up for short-lived isotopes at the on-line mass separator ISOLDE at CERN. The ion beam is collected and cooled in the first trap. After delivery to the second trap, high-accuracy direct mass measurements are made by determining the cyclotron frequency of the stored ions. Measurements have been performed for ${}_{}{}^{118}{}_{}{}^{}–_{}^{137}{}_{}{}^{}$Cs. A resolving power of over ${10}^6$ and an accuracy of 1.4×${10}^{\mathrm{-}7}$ have been achieved, corresponding to about 20 keV.

We measured the 2E1 decay of the 1s2s ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$→1${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ transition in He-like germanium for 12- to 19-MeV/u ${\mathrm{Ge}}^{31+}$+${\mathrm{H}}_2$ collisions. The resonant population of the 2s2p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ state by transfer excitation was isolated due to its cascading to the 1s2s ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ state. The experimental cross sections compare well with calculations using dielectronic recombination rates. The method gives the unique possibility to populate selectively the ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ state in heavy He-like ions.

Using the adiabatic crossed-field method we have prepared for the first time doubly excited barium atoms with one valence electron in an oriented circular Rydberg state (n=21, l=m=20, denoted 21c) and the other electron in a ${6\mathrm{p}}_{\mathrm{j}}$ state. In a fraction of these atoms the inner electron decays radiatively to a ${5\mathrm{d}}_{\mathrm{j}\prime }$ metastable level. The obtained circular-metastable doubly excited atoms are very stable. For the (${5\mathrm{d}}_{3/2>\mathrm{}}$21c) state the autoionization lifetime τ is longer than 400 μs; for the (${5\mathrm{d}}_{5/2}$21c) state, τ=1±0.2 μs. the specific role of the 5d electron is demonstrated. © 1990 The American Physical Society

We have observed phase-diffusion noise 40% below the Schawlow-Townes limit in the relative phase of a two-mode HeNe Zeeman laser due to the correlated-emission-laser effect.

We develop the principle of ‘‘speckle-pattern tomography’’ in the multiple-scattering regime, i.e., the technique of using correlations between complex interference patterns to determine the position of a special scatterer for either electromagnetic or acoustical wave propagation through a diffusive scattering medium. We focus on two concrete examples which are relevant to experiments and possible applications: (i) detecting the position of a stationary special scatterer in a medium of moving scatterers; (ii) detecting the appearance and position of a new added scatterer.

We show that a qualitative theory of bifurcations can provide an understanding of the spontaneous symmetry breaking and the appearance of traveling waves leading to spatiotemporal complexity in the transverse patterns of the intensity of a ${\mathrm{CO}}_2$ laser.

A new regime of density-channel guiding of a relativistic electron beam in air has been found using a three-dimensional charged-particle simulation code, and confirmed in a double-pulse electron-beam experiment. The guiding results from the temperature dependence of the electron-neutral momentum-transfer frequency ${\nu }_{\mathit{m}}$. The mechanism does not require a deep channel to obtain a significant guiding force. For the 13-kA MEDEA II (and beams of similar parameters), guiding persists 10 ns into the beam pulse with the force per channel displacement as high as 4 G/cm.

The diffusion coefficient for particles in a field of randomly phased waves was calculated numerically. Spectra broad in wave number and broad in frequency exhibit identical behavior for the diffusion coefficient as a function of the overlap parameter ɛ. The diffusion coefficient exceeds the quasilinear value by a factor of about 2.5 at ɛ near 18. Differences greater than 25% between the two values exist far above the chaotic threshold (ɛ≊60). A mapping-based model with a small number of random phases qualitatively reproduces the results of the simulations.

In a binary mixture of oligomers of styrene and ε-caprolactone, we have studied a transition from metastability to instability by changing a quench depth systematically under an off-critical quench condition. The concentration distribution function turns out to be a good fingerprint for determining whether phase separation is nucleation-growth type or spinodal-decomposition type. We also demonstrate clear morphological and kinetice evidence of a diffuse metastable-unstable transition or crossover phenomena theoretically predicted for the system with a finite-range interaction.

The melting transition of ${\mathrm{N}}_2$ on graphite is examined using a Monte Carlo procedure with several different boundary conditions. On the basis of a simple interpretation of the experimental environment, we are able to explain and accurately reproduce the large change in melting temperature between partial and monolayer coverages.

After cooling below 80 K a considerable amount of diffuse scattering is observed in Li, in addition to 9R and fcc Bragg reflections. The diffuse scattering localized on the [101] line of the 9R reciprocal lattice is modulated along this line indicating a short-range order in the stacking sequence of the close-packed planes. The results show that, in addition to the long-range ordered fcc and 9R structures, Li forms at low temperatures a disordered polytype where short-range ordering tendencies of the hcp, fcc, and 9R types are simultaneously present. These observations may be explained in terms of competing cubic and hexagonal ordering tendencies in the stacking sequence of close-packed planes.

We present the results of an ab initio molecular-dynamics study of the Si(111) surface at low temperatures. Our findings for the equilibrium structure confirm the Pandey (2×1) chain model and are in very good agreement with both low-energy electron diffraction and medium-energy ion-scattering data, showing in particular a large buckling of the surface chains. We describe the dynamical path followed during the reconstruction from the ideal bulk-terminated surface, which is found to be unstable. The phonon spectrum, which is calculated ab initio for the first time, shows well-defined surface modes at frequencies close to the measured values.

Using a plane-wave expansion method, we have solved Maxwell’s equations for the propagation of electromagnetic waves in a periodic lattice of dielectric spheres (dielectric constant ${\mathrm{\epsilon }}_{\mathit{a}}$) in a uniform dielectric background (${\mathrm{\epsilon }}_{\mathit{b}}$). Contrary to experiment, we find that fcc dielectric structures do not have a ‘‘photonic band gap’’ that extends throughout the Brillouin zone. However, we have determined that dielectric spheres arranged in the diamond structure do possess a full photonic band gap. This gap exists for refractive-index contrasts as low as 2.

Measurements were made, at various emission angles, of energy spectra of electrons from Al induced by grazing-angle-incident ions of ${\mathrm{N}}^{6+}$, ${\mathrm{Ar}}^{12+}$, and ${\mathrm{Xe}}^{27+}$ with equal velocities corresponding to 0.98 MeV/amu. A new line which could not be explained by any of the hitherto identified mechanisms was observed at an energy obviously larger than that of an electron with a velocity equal to the projectile. The projectile and emission angle dependencies of the line are consistent with the dynamic image potential acceleration mechanism.

The energy distribution of the convoy electrons produced by fast highly charged ions is studied with classical-trajectory Monte Carlo calculation. We found that, in the case of small-angle incidence, the convoy peak is shifted to higher energy because of the anisotropy of the electron velocity distribution which is caused by the image potential of the incident ion.

The scanning force microscope is used to deposite charge carriers on insulating ${\mathrm{Si}}_3$${\mathrm{N}}_4$ films and to monitor their recombination. The charge decay shows up as a discontinuous staircase, demonstrating single-carrier resolution. The decay is found to be controlled by thermionic emission.

We have measured the correlation length of the ${\mathbf{q}}_1$ charge-density wave in ${\mathrm{NbSe}}_3$ using high-resolution x-ray scattering. For a heavily Ta-doped crystal having a residual resistivity ratio ${\mathit{r}}_{\mathit{R}}$ of 10, the T=77 K correlation lengths parallel and transverse to the quasi-one-dimensional ${\mathbf{b}}^{\mathrm{*}}$ direction are ${\mathit{l}}_{\mathit{b}}^{\mathrm{*}}$≊0.9 μm and ${\mathit{l}}_{\mathit{a}}^{\mathrm{*}}$≊0.1 μm, respectively. For an undoped crystal (${\mathit{r}}_{\mathit{R}}$≊300), we obtain lower bounds ${\mathit{l}}_{\mathit{b}}^{\mathrm{*}}$≊2.5 μm and ${\mathit{l}}_{\mathit{a}}^{\mathrm{*}}$≊1.9 μm, the latter value being comparable to the thickness of typical crystals. These results are in excellent agreement with a recent weak-impurity-pinning analysis of finite-size effects observed in transport properties.

We report the observation of major enhancements in the magneto-optical polar Kerr rotation in the Fe/Cu/Fe system. These enhancements are as much as a factor of 2 greater than those anticipated due to recently reported plasma-resonance effects. A close connection between these enhancements and antiferromagnetic coupling between the two Fe films is established by the observation of concurrent oscillations in the magnitude of these two effects as a function of Cu thickness.