In experiments employing fast ion-guide-based on-line mass separation we have identified six new, rare nuclides of highly refractory elements produced in the fission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ by 20-MeV protons. The new isotopes ${}_{}{}^{105}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{107}{}_{}{}^{}\mathrm{Nb}$, ${}_{}{}^{109}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{110}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{113}{}_{}{}^{}\mathrm{Tc}$, and ${}_{}{}^{115}{}_{}{}^{}\mathrm{Ru}$ were identified through (β, ${\mathit{K}}_{\mathrm{\alpha }}$ x-ray) coincidences and β-delayed γ decay. The observed β half-lives range from 130 ms to approximately 1 s. All our recent β half-life data are compared with predictions of the deformed quasirandom-phase-approximation model. The main uncertainty is found to be the inaccuracy of the decay energy predictions.

Double-excitation Rydberg resonances of He below the N=2 threshold of ${\mathrm{He}}^{+}$ were studied with an energy resolution of ≃4 meV by photoionization using synchrotron radiation. All three Rydberg series of ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$ resonances accessible by photoabsorption, including the hitherto ‘‘missing’’ (2p,nd${)}^1$${\mathit{P}}^{\mathit{o}}$ series, were resolved. This settles a long-standing discrepancy between experiment and theoretical predictions and establishes a firm basis for testing the accuracy of atomic multiconfiguration calculations.

One-photon two-electron ionization of an atom by circularly polarized light yields triplet differential cross sections different for left and right circular polarization. Necessary kinematical conditions for a finite dichroism are worked out. A numerical calculation for helium which employs correlated wave functions shows the angular correlations of the escaping electron pair to be very different for left and right circular polarization such that the effect should be observable in a coincidence experiment.

Using velocity data obtained in the atmospheric surface layer, we examine Kolmogorov’s refined hypotheses. In particular, we focus on the properties of the stochastic variable V=Δu(r)/(r${\mathrm{\varepsilon }}_{\mathit{r}}$${)}^{1/3}$, where Δu(r) is the velocity increment over a distance r, and ${\mathrm{\varepsilon }}_{\mathit{r}}$ is the dissipation rate averaged over linear intervals of size r. We show that V has an approximately universal probability density function for r in the inertial range and discuss its properties; we also examine the properties of V for r outside the inertial range.

The clocklike emission of picosecond pulses of light with a peak power over 30 mW has been observed to originate from a bubble trapped at the velocity node of a resonant sound field in water. The spectrum of this bright sonoluminescence is broadband and our measurements show that if a spectral peak exists, it lies at photon energies above 6 eV.

Localization properties of third sound were studied experimentally in one-dimensional random lattices. Transmission spectra were measured and compared with those in periodic, Fibonacci, and Thue-Morse lattices. Not only the resonant transmission but also the phase-velocity renormalization of third sound was observed in the random lattices.

In connection with recent vibrationally excited sand-heaping observations we performed a series of experiments dealing with 2D compact triangular packings of monodisperse metallic beads under vibration. We report for the first time the observation of spontaneous heaping and associated convections for this system. We establish the mechanical conditions leading to this phenomenon and the domain of occurrence. We identify the microscopical mechanism to be a block-slip motion generated by the walls and we show that the heaping dynamics obeys a ln(t) law.

A new kind of instability is predicted for a system involving activator and inhibitor kinetics in a reactive flow. It is shown that a differential flow of activator and inhibitor, achievable, e.g., by selectively binding one component to a support, can destabilize the spatially homogeneous state of the system in a similar way as differential diffusivity does in the case of the Turing instability. The differential-flow-induced chemical instability is of the traveling-wave type. It is free from the restrictions of the Turning instability on the diffusion coefficients and can thus be expected to occur in a wide variety of physical, chemical, biological, and sociobiological systems.

The excitation of plasma waves by resonant absorption of an electromagnetic wave is studied experimentally near the top of a parabolic density profile. The experiment shows the development of a huge density cavity (2000${\lambda }_{\mathit{D}}$) inside which trapped plasma waves exhibit an oscillatory behavior, on a time scale smaller than the convection time.

We have performed a series of experiments on the Nova Laser Facility to examine the hydrodynamic behavior of directly driven planar foils with initial perturbations of varying wavelength. The foils were accelerated with a single, frequency doubled, smoothed and temporally shaped laser beam at 0.8×${10}^{14}$ W/${\mathrm{cm}}^2$. The experiments are in good agreement with numerical simulations using the computer codes LASNEX and ORCHID which show growth rates reduced to about 70% of classical for this nonlinear regime.

Density and temperature fluctuations have been measured in the plasma bulk side of the velocity-shear location of the TJ-I tokamak using a fast swept Langmuir probe technique. Evidence has been found that substantial temperature fluctuations have a phase difference of close to ψ with respect to the corresponding density fluctuations. This result suggests the possible role of radiation in determining edge fluctuation levels and calls into question the determination of the density and potential fluctuations from the Langmuir current probe and floating potential fluctuations.

We study D-dimensional polymerized membranes embedded in d dimensions using a self-consistent screening approximation. It is exact for large d to order 1/d, for any d to order ε=4-D, and for d=D. For flat physical membranes (D=2, d=3) it predicts a roughness exponent ζ=0.590. For phantom membranes at the crumpling transition the size exponent is ν=0.732. It yields identical lower critical dimension for the flat phase and crumpling transition ${\mathit{D}}_{\mathrm{lc}}$(d)=2d/(d+1) (${\mathit{D}}_{\mathrm{lc}}$= √2 for codimension 1). For physical membranes with random quenched curvature ζ=0.775 in the new T=0 flat phase in good agremeent with simulations.

We have studied the effect of quenched, bond randomness on the nature of the phase transition in the two-dimensional eight-state Potts model. Through extensive Monte Carlo simulations, we confirm that the phase transition changes from first order to second order. A finite-size-scaling analysis of several thermodynamic quantities strongly suggests that the critical exponents fall into the universality class of the two-dimensional Ising model.

The isotopic shift in the melting curve of He has been measured between 70 and 260 K. An exponential divergence from accurate path-integral Monte Carlo calculations is observed which leads to an opposite isotopic shift above 200 K. The same measurements have also been performed in isotopic ${\mathit{H}}_2$ at 296 K where a reasonable agreement with theory is obtained. Tentative explanations of this puzzling discrepancy in He are discussed: importance of many-body forces, breakdown of the Born-Oppenheimer approximation, and importance of statistics.

On the surface of a brine-surfactant (AOT) mixture, the long-chain alkanes (N>11) do not spread while the shorter ones (N<11) spread leaving a very thin oil film at the surface. The interactions between the oil-water and oil-air interfaces stabilizing the height of this film are a van der Waals attractive potential, a short-range repulsive potential due to the alkane-surfactant interactions, and a repulsive potential due to the fluctuations of the oil-brine interface constrained by the oil-air surface. This is related to the phase behavior of mixtures of brine, AOT, and n-alkanes.

We have determined the atomic structure of the Si(111)-(√7× √7)Co surface using scanning tunneling microscopy and ion scattering. The unit cell contains one surface substitutional cobalt atom centered under a six silicon adatom cluster. High-temperature annealing produces a low density lattice gas of these ringlike clusters, giving rise to an ‘‘impurity stabilized 1×1’’ structure. They occur for several other transition metals, suggesting a stable, universal, silicide related structure.

Time-resolved reflection high-energy electron diffraction is used to study the laser-induced superheating of Pb(111). For a heating laser pulse width of ∼180 ps, two regimes are observed depending upon the incident peak laser intensity. In the first regime, the time-resolved electron diffraction intensity indicates a transient superheating of the surface followed by cooling below the bulk melting temperature. In the second regime, which occurs at higher peak laser intensities, superheating is followed by melting. Superheating up to 120 K above the bulk melting temperature is observed.

We have performed first-principles pseudopotential calculations for H-terminated Si wires with thicknesses from 12 to 23 Å, calculating the band gaps and optical matrix elements. Comparison with effective-mass theory shows that the latter is valid for wires wider than 23 Å. We have used our data to analyze the luminescent properties of highly porous Si fabricated by electrochemical etching of Si wafers in HF-based solutions.

We present a solution of the Hubbard model at half filling in the limit of infinite dimensions which corresponds to the Mott-Hubbard insulating phase. We describe the metal-insulator transition between this regime and the Fermi-liquid regime. Our analysis is based on an analytic consideration and exact Monte Carlo simulations at low but finite temperatures.

We present a numerical solution of the infinite-dimensional Hubbard model at finite temperature in the paramagnetic phase. The problem reduces to a single-impurity Anderson model supplemented by a self-consistency condition. Using Monte Carlo methods and complete enumeration we determine the imaginary-time Green’s function, the density of doubly occupied sites, and the compressibility close to half filling. All three quantities present direct evidence for a Mott insulating phase above a critical value of U.