A simple model for understanding the qualitative features of a fragmentation process is proposed. At a particular point of a tuning parameter of this model, the fragment-size distribution has a scale-invariant power-law behavior. At relatively low values of this parameter, evaporation modes dominate and at high values of the parameter, multifragmentation takes place. The model is exactly soluble in all regimes of the tuning parameter. A unifying connection between evaporation and multifragmentation is found.

Energy spectra and angular distributions of evaporated protons from the reaction ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$${(}^{34}$S, 2p2n${)}^{82}$Sr at 130 MeV were measured in coincidence with discrete γ transitions. Large shifts and changes in the shape of the proton spectra were observed when high-spin states in different rotational bands are populated. They are interpreted as due to near-yrast stretched proton emission, which preferentially populates the yrast band by subbarrier protons.

Viscous fingers have been generated on square lattices of L×L sites using the diffusion-limited aggregation model plus a simple rule that we propose to take into account surface tension. The wi dths (λ) of the generated viscous fingers, as well as mass (m) of the dislodged fluid, depend properly on the capillary number (Ca): They fulfill the hydrodynamic scaling relations λ=${\mathrm{Ca}}^{\mathrm{-}1/2}$f(${\mathrm{Ca}}^{1/2}$L) and m=${\mathrm{Ca}}^{\mathrm{-}1}$g(${\mathrm{Ca}}^{1/2}$L). In addition, m∼${\mathrm{Ca}}^{\mathrm{-}\left[\right(\mathit{d}\mathrm{-}\mathit{D})/2\mathrm{}]}$${\mathit{L}}^{\mathit{D}}$ in the physically interesting regime a≪λ≪L (a is the lattice constant, d=2, and D∼1.6 in our simulations).

A renormalization-group fixed point is found, corresponding to chaotic mixing in the Rayleigh-Taylor instability problem. The outer envelope of the mixing region, adjacent to the heavy fluid, is dominated by a merger of unstable modes ( bubbles of light fluid) and dynamically changing length scales. A statistical model is introduced as an approximation to the full two-fluid Euler equation to describe the mixing envelope. Molecular-chaos and continuous-time approximations to this model define an approximate renormalization-group equation, which is shown to have a nontrivial fixed point.

The behavior of power spectra in a Rayleigh-Bénard convection experiment in a helium-gas cell is reported. The high-frequency part of the data for all Rayleigh numbers from 7×${10}^6$ to 4×${10}^{14}$ is fit by a single functional form, obtained by a natural generalization of a multifractal analysis. Low-frequency data cannot be fit in this form.

We report the first observation of current drive by injection of a spheromak plasma into a tokamak (Caltech ENCORE small reasearch tokamak) due to the process of helicity injection. After an abrupt 30% increase, the tokamak current decays by a factor of 3 due to plasma cooling caused by the merging of the relatively cold spheromak with the tokamak. The tokamak density profile peaks sharply due to the injected spheromak plasma (n${\mathrm{¯}}_3$ increases by a factor of 6) then becomes hollow, suggestive of an interchange instability.

Heat-capacity studies of the melting transition of the commensurate (√3 × √3 ) phase of CO on graphite yield, at appropriate coverages, critical exponents consistent with that expected for two-dimensional three-state-Potts tricritical and two-dimensional three-state-Potts critical-phase transitions.

We observe the spontaneous reemergence of long-range crystalline order in the electrochemical deposition of metal dendrites very far from equilibrium. This long-range order appears simultaneously with novel superlattice structures as revealed by high-resolution x-ray and electron diffraction. In order to explain these observations, we propose a simple picture, which we call the ‘‘keystone model,’’ for electrocrystallization in an aqueous environment.

Picosecond sum-frequency-generation measurements of the unreconstructed, ideally H-terminated Si(111) surface reveal that the lifetime of the Si-H stretching vibration is 0.8±0.1 ns.

X-ray reflectivity is used to study the temperature-dependent smectic layering of the cyanobiphenyl compounds (nCB) in the isotropic phase at alkylsilane-coated silicon surfaces. Layer-by-layer growth is observed for 11CB and 12CB. Comparison of the layering transition temperatures with measurements at the vapor interface is used to determine the relative anchoring strengths at the two interfaces.

The isotopic substitution method in neutron diffraction is applied to two chalcogenide glasses on the (${\mathrm{Ag}}_2$S${)}_{\mathit{x}}$(${\mathrm{As}}_2$${\mathrm{S}}_3$${)}_{1\mathrm{-}\mathit{x}}$ (0≤x≤1) tie line of the Ag-As-S system. It is shown that there is a reduction from ≃4 to ≃3 in the average number of S atoms covalently bonded to Ag as x is increased from 0.096 to 0.500, but that As remains threefold coordinated by S. The onset of ionic conductivity as x is increased and the occurrence of two homogeneous glass-forming regions is therefore associated with a change in the coordination environment of the metal atom.

We report observations of avalanchelike, topological rearrangements of cellular domain patterns in magnetic garnet films. Over significant intervals in applied magnetic field and cell density, the patterns self-organize into barely stable states. Small field increments trigger avalanches of cell destruction that span more than 2 orders of magnitude in size and lifetime.

We report the first systematic femtosecond pump-probe measurements of the electron-phonon coupling constant λ in thin films of Cu, Au, Cr, Ti, W, Nb, V, Pb, NbN, and ${\mathrm{V}}_3$Ga. The agreement between our measured λ values and those obtained by other techniques is excellent, thus confirming recent theoretical predictions of Allen. By depositing thin Cu overlayers when necessary, we can extend this technique to nearly any metallic thin film.

Exact calculated results of the photoemission spectrum of a two-layer {001} bcc-cobalt film are presented. Realistic band-structure results are used in the parametrization of the Hamiltonian in a periodic small-cluster approach. An intrasite electron-electron interaction fully allowed by atomic symmetry is introduced. Interesting new features induced by many-body effects are found in the calculated spectrum. Physical conclusions about the many-body states in ultrathin bcc-cobalt films are drawn. Surface-sensitive valence-band photoemission experiments are suggested to test our results.

Conducting gels of ultrahigh molecular weight polyethylene and the soluble conjugated polymer poly(3-octylthiophene), P3OT, were prepared by thermoreversible gelation from semidilute solutions in decalin, and subsequent doping with iodine. We report the results of frequency-dependent complex conductivity measurements (from 1 kHz to 1 GHz) on these gels. Although the volume fraction of P3OT in the gel range from less than 5×${10}^{\mathrm{-}4}$ to about 3×${10}^{\mathrm{-}2}$, we found evidence of connected conducting paths with no indication of a percolation threshold. The results are discussed in terms of adsorption of the P3OT onto the preformed polyethylene gel network which organizes the P3OT into connected paths at concentrations well below the nominal percolation threshold.

${\mathrm{U}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ amorphous ferromagnets were prepared that show a magnetoresistance anisotropy (AMR) reaching 26% at 10 K, in a 50 kOe field. This is a striking result, since the AMR of typical amorphous ferromagnets does not exceed 1%. Large excess resistivity caused by domain walls is found to scale with β${\mathcal{’}}^2$, where β’ is the tangent of the Hall angle.

Nuclear magnetic resonance on oriented nuclei was performed for the first time using as host matrix a hexagonal Co single crystal magnetized perpendicular to the c axis. The radioactive isotope ${}_{}{}^{191}{}_{}{}^{}\mathrm{Pt}$ was implanted using the mass-separator ISOLDE-3 at CERN. In comparison to the case of magnetization parallel to the c axis, a drastic enhancement of the resonance signal was observed. This observation opens new possibilities for precise measurements of nuclear moments of short-lived isotopes far from stability.

Forces on two parallel vortices in anisotropic materials are generally not directed along the line connecting the vortices. The interaction results not only in a repulsion but, in addition, in a torque. On a macroscopic scale, if the magnetic induction B or the anisotropy parameters ${\mathit{m}}_{\mathit{i}\mathit{k}}$ change within a crystal, the flux-line lattice is subject to forces associated with spatial variation of the torque originated by anisotropy. This force is additional to and different from the Lorentz force, and both forces are, in general, comparable in magnitude.

We explain the apparent sublinear intensity dependence of photoconductivity in barium titanate. In our model shallow acceptors act as a reservoir for charges optically excited from the donors. As this reservoir fills, the fraction of occupied donors changes appreciably, changing the lifetime of the free carriers. We identify two types of barium titanate crystals having quite different photorefractive characteristics, depending on their relative density of donors and acceptors, and we find that the depth of the shallow acceptor level is ∼0.4±0.1 eV in both types of crystals.

Long-wave excitations in Josephson arrays are investigated. The existence of excitations with square root or acoustic dispersion law, like plasmons in two-dimensional electron gas, is predicted. Observation of such excitations with frequency much lower than the frequency of the superconducting gap Δ/ħ is possible by use of a grating and the same far infrared or microwave techniques used for detection of the plasmons in semiconductor microstructures.