A relativistic hadronic cascade is used to simulate collisions of Si on Au at 14.6 GeV/c per nucleon. When proper account is taken of resonances produced in elemental hadron-hadron collisions this cascade quantitatively describes most published E802 data from the BNL Alternating Gradient Synchrotn including the problematic proton transverse mass distributions. No medium effects seem required to explain the apparent enhancement of strangeness production nor any other features of the data.

Atoms subjected to an intense subpicosecond laser pulse (${10}^{13}$ W/${\mathrm{cm}}^2$, 100 fs) survive in excited states, as is shown by probing with a second laser. Electron spectroscopy with this 5-ns probe pulse enables identification of the resonant intermediate states as well as an unusually reliable energy calibration of the short-pulse electron spectrum. Only after incorporating population of intermediate levels is the mechanism for short-pulse multiphoton ionization consistent with the new data.

Double ionization of ${\mathrm{O}}_2$ induced by photons from a synchrotron radiation source has been studied in an electron-electron coincidence experiment. A new technique has been developed wherein only electrons with near zero energy are detected by use of the penetrating field method. In this way high sensitivity and energy resolution have been attained allowing ninteen vibrational levels of the ${\mathrm{O}}_2^{2+}$ ground state to be observed and molecular parameters of this state to be obtained.

We observe the kinetic energy of ionic fragments that result from the Coulomb explosion of molecular iodine ions produced by rapid multiphoton ionization. Because the ion energies produce a clear signature of the molecular ion state from which they originate, we are able to determine the intensity dependence of the molecular multiphoton ionization. Generalizations of atomiclike concepts are used to model the experimental results. Measurements of angular distributions indicate the importance of the molecular polarizability.

An intensity correlation experiment is proposed that would test the presence of true interference between independent gamma rays. Clear intensity correlations are predicted within a reasonable counting time, as the experiment is greatly benefitted by the pulsed time structure and high brilliance of the future dedicated synchrotron radiation sources. Applications of the novel method are suggested.

A family of scale-invariant, base-dependent, multiplier distributions is measured for the turbulence dissipation field in the atmospheric surface layer. The existence of these distributions implies the existence of the more traditional multifractal scaling functions, and we compute both positive and negative parts of the f(α) curve. The results support the conjecture of universality in the scaling properties of small-scale turbulence. A simple cascade model based on the measured multiplier distributions is shown to possess several advantages over previously considered models.

Measurements have been made of the probability density function (PDF) of velocity increments Δu(r) for a wide range of separation distances r. Stretched exponentials provide good working approximations to the tails of the PDF. The stretching exponent varies monotonically from 0.5 for r in the dissipation range to 2 for r in the integral scale range. Theoretical forms based on multifractal notions of turbulence agree well with the measured PDFs. When the largest scales in the velocity u are filtered out, the PDF of Δu(r) becomes symmetric and, for large r, close to exponential.

Homoclinic chaos is shown to occur in the electric current measured on an electrical discharge in argon. We report a clear sequence of four hesitations followed by a reverse period doubling. The experimental signals are used to construct return-time and time-of-flight maps that evidence a Shilnikov scenario in the system.

We present measurements of the effect of various levels of laser beam smoothing on both burnthrough time and the neutron yield in layered, deuterium-filled imploding microballoons. Burnthrough times are found to improve as smoothing is increased. This effect is believed to result from a reduction in the seeding of the Rayleigh-Taylor (RT) instability with increasing smoothing. The results are in agreement with simulations that model the development of the RT instability from initial perturbation spectra inconsistent with measured changes in uniformity. The neutron yields are also observed to increase in the presence of smoothing, but are much less sensitive to uniformity changes than the burnthrough rates.

Anamalously fast ion mixing is observed in a hybrid code simulation (particle ions and a massless electron fluid) of the Kelvin-Helmholtz instability in a collisionless plasma. While the traditional view predicts that the ion mixing occurs on a time scale longer than the roll-up time ${\mathit{T}}_{\mathit{V}}$ of the Kelvin-Helmholtz vortex by a factor of (velocity shear scale length)/(ion Larmor radius), the simulation results show that the mixing occurs within a time scale comparable to ${\mathit{T}}_{\mathit{V}}$. We show that this fast mixing is due to the scattering of ions by unsteady electromagnetic fields.

The dense packing of polymeric spheres in latex films has been investigated by means of small-angle neutron scattering. The films were prepared by evaporation of the water out of a dispersion consisting of monodisperse charged particles (diameter 130 nm). Analysis of the Bragg peaks found in the scattering reveals that the particles are arranged in a face-centered-cubic lattice structure with well defined crystalline domains. Furthermore, it is found that the system still owns a memory of its initial structure upon prolonged annealing at temperatures far above its glass temperature. An interesting suppression of some Bragg peaks due to the influence of the particle scattering form factor is observed.

We have used dynamical low-energy electron diffraction (LEED) to determine the adsorption site and the geometry of the surface region for the p(2×2) overlayer of potassium adsorbed on Ni(111). The structure consists of the potassium atoms adsorbed on top of the Ni atoms with vertical reconstructions of Ni atoms in the first and second substrate layers combined with a slight horizontal reconstruction of the first substrate layer. The potassium-nickel bond length is found to be 2.82±0.04 Å corresponding to a rather short effective potassium ‘‘radius’’ of about 1.57 Å.

Using the newly developed interfacial-force microscope, we present results for the first measurements of the mechanical relaxation of a Au supported, self-assembled monolayer film interacting with a microscopic tungsten tip. For a methyl-terminated n-alkanethiol film, we observe negligible adhesive film-tip interaction and complete passivation of tip-substrate bonding. The mechanical behavior of the film itself shows a time-dependent, elastic response.

A morphological and kinetic change is found in the late stage of surface pattern formation on a gel plate. It results from a dynamic ordering process originating from a strong constraint from the bottom surface. The scattering function changes its form from a single-peaked, broad function to a multipeaked one, reflecting the morphological change from a treelike pattern to a honeycomblike one. The characteristic size of the pattern initially grows as ${\mathit{t}}^{1/2}$, and then relaxes to its equilibrium value. This kinetic change coincides well with the morphological one.

Exploiting the high spatial resolution and sensitivity of chemical mapping, we measure the intermixing in a series of microscopic marker layers imbedded in GaAs to detect the passage of Ga vacancies injected at the surface before the steady state has been reached. We thus deduce each of the formation and migration enthalpies for the Ga vacancy under technologically relevant conditions. More generally, we show how multilayers may be used as microscopic laboratories to investigate the properties of intrinsic point defects in solids.

We show for the first time, using ab initio calculations, that the trend exhibited by the elastic constants in the transition metals can be simply understood. In particular, we show that the trend of the elastic constants of cubic transition metals is determined by the energy difference between the fcc and bcc structures of a given element, which in turn is determined by band filling. Our results suggest indirectly that the reason for the disagreement between calculated and ‘‘experimental’’ data for crystal energy differences does not lie in the calculated results.

New data on the thermal-conductivity temperature dependence k(T) of both natural abundance and isotopically enriched synthetic diamond gems are presented. The existing data on the thermal-conductivity temperature dependence k(T) of natural type-IIa diamond have been reanalyzed using a comprehensive Klemens-Callaway model. The high thermal conductivity of isotopically pure diamond is shown to be consistent with the model.

We have measured the superfluid fraction of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in pores of sintered silver. The superfluid fraction, which is suppressed by confinement, increases with pressure due to the decreasing coherence length. Coating the surfaces with a thin film of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ partially restores the suppressed superfluidity, but above 17 bars this effect diminishes as the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film solidifies. This solidification occurs over a range of about 9 bars and is hysteretic. With a slightly thicker ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film, solidification occurs at pressures greater than that required for bulk (25 bars).

New developments in spectroscopic ellipsometry (1.5≤hν≤4.3 eV) now provide quantitative information on thin films with a time resolution of 16 ms. We report submonolayer sensitivity to a surface smoothening effect associated with nuclei coalescence in the early stages of hydrogenated amorphous silicon (a-Si:H) preparation by plasma-enhanced chemical vapor deposition. An investigation of a-Si:H prepared on c-Si and Cr substrates under different conditions of substrate temperature and plasma power discloses a clear correlation between the magnitude of this effect and the ultimate bulk properties of the material.

Mass spectra of ${\mathrm{Al}}_{\mathit{N}}$ clusters produced by a laser vaporization source have been recorded via standard time-of-flight spectroscopic methods. Regular signal oscillations are observed in the size range N=200–900 when low-power near-threshold ionization is performed. This striking feature, which is a manifestation of the electronic shell structure of the aluminum clusters, is analyzed with the semiclassical theory of single-particle level density. The oscillation frequency is found to be well explained by the classical star orbit contribution.