We present the first full band-structure calculations for periodic, elastic composites. For transverse polarization of the vibrations we obtain a ‘‘phononic’’ band gap which extends throughout the Brillouin zone. A complete acoustic gap or a low density of states should have important consequences for the suppression of zero-point motion and for the localization of phonons, and may lead to improvements in transducers and in the creation of a vibrationless environment.

We report experiments on convection patterns in a cylindrical cell with a large aspect ratio. The fluid had a Prandtl number σ≊1. We observed a chaotic pattern consisting of many rotating spirals and other defects in the parameter range where theory predicts that steady straight rolls should be stable. The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell. This suggests that the chaotic behavior is intrinsic to large aspect ratio geometries.

A numerical solution of a generalized Swift-Hohenberg equation in two dimensions reveals the existence of a spatiotemporal chaotic state comprised of a large number of rotating spirals. This state is observed for a reduced Rayleigh number ε=0.25. The power spectrum of the state is isotropic, and the spatial correlation function decays exponentially, with an estimated decay length ξ≊2.5${\lambda }_{\mathit{c}}$, where ${\lambda }_{\mathit{c}}$ is the critical wavelength near the onset of convection. Our study suggests that this spiral defect state occurs for low Prandtl numbers and large aspect ratios.

Chaotic spatiotemporal patterns can have highly ordered time averages. This fact is demonstrated for Faraday waves by averaging shadowgraph images. The averages exhibit box quantization effects, and their spatial form is similar to that predicted for patterns near onset, despite the large fluctuations. Patches of the disordered instantaneous patterns retain significant phase coherence with the ordered averages.

The incremental electron heat diffusivity ${\mathrm{\chi }}^{\mathrm{inc}}$ is determined in Rijnhuizen Tokamak Project plasmas by measurements of simultaneous heat pulses due to (1) the sawtooth instability and (2) modulated electron cyclotron heating. No systematic difference is observed between the two measured ${\mathrm{\chi }}^{\mathrm{inc}}$ values, which are both significantly larger (${\mathrm{\chi }}^{\mathrm{inc}}$/${\mathrm{\chi }}_{\mathit{e}}^{\mathrm{PB}}$=2-4) than the diffusivity obtained from power balance analysis, ${\mathrm{\chi }}_{\mathit{e}}^{\mathrm{PB}}$.

Results from a fully nonlinear three-dimensional toroidal electrostatic gyrokinetic simulation of the ion temperature gradient instability are presented. The model has adiabatic electrons and the complete gyrophase-averaged ion dynamics, including trapped particles. Results include the confirmation of the radially elongated ballooning mode structure predicted by linear theory, and the nonlinear saturation of these toroidal modes. The ensuing turbulent spectrum retains remnants of the linear mode structure, and has very similar features as recent experimental fluctuation measurements.

The effects of thermal trapped particles on the internal kink mode are studied using drift kinetic theory. For equal electron and ion temperatures, the trapped particles increase the marginal poloidal beta at q=1 substantially. For unequal temperatures, drift resonance with the hotter species is destabilizing and can lead to instability below the ideal magnetohydrodynamics threshold. An electrostatic potential is weakly stabilizing for the internal kink. At high beta, fluctuations of trapped particle modes couple to the internal kink mode and can lead to large displacements of the central region.

We have measured the absolute structure factor of liquid water over the wave-number range 0.05<k<0.30 A${\mathrm{̊}}^{\mathrm{-}1}$ and temperature range -34<T<25 °C with small-angle x-ray scattering. The correlation lengths of density fluctuations are small and change very little with temperature, suggesting that supercooled water may not be approaching a proposed spinodal point. The increasing density fluctuations with supercooling in water appear to be due to an increasing fraction of water molecules participating in clusters, not an increasing range of correlations.

A recently proposed direct method has been applied to the analysis of experimental backscattering photoelectron diffraction data for the three adsorption systems Cu{110}-CO, Cu{111}-${\mathrm{OCH}}_3$, and Cu{111}-${\mathrm{C}}_2$${\mathrm{H}}_2$. The local adsorption sites are determined through the identification of the nearest-neighbor substrate atom directions which can be determined with an accuracy of ±5°.

A new type of finite-amplitude traveling or standing wave with an exact sinusoidal form and a short commensurate wavelength is predicted to exist in lattices with cubic and/or quartic anharmonic potential between any arbitrary number of nearest and non-nearest neighbors. Fast traveling nonlinear sinusoidal waves (NSW) can generate sinusoidal lattice solitons. Superposition of two NSW or sinusoidal solitons propagating in opposite directions can result in the formation of an extended or a localized standing-wave eigenmode. New exact solutions for localized standing-wave structures are found within a rigorous discrete-lattice approach.

Low-frequency Raman spectra of strong and fragile glass forming liquids were measured in a wide temperature range. From an analysis of the spectra and literature data it is found that the main difference in the dynamic structure factor is the ratio of vibrational to relaxational contributions: The stronger the glass former the higher this ratio. It is shown that this difference survives even at very low temperatures and determines the low-temperature anomalies of glasses. A possible way how the observed difference influences the fragility of a liquid is discussed.

A self-consistent mode coupling model for supercooled fluids is derived from fluctuating nonlinear hydrodynamics (extended to short wavelengths) with attention to detailed balance constraints. The sharp glass transition predicted by mode coupling models based only on pressure nonlinearities does not occur here. Instead, the long time asymptotic behavior of the density autocorrelation function is determined by additional nonlinearities imposed by the detailed balance constraints.

New Monte Carlo methods are presented for efficient simulation of nonequilibrium processes in spin systems. The elementary moves are flips of connected sets of spins (clusters), subject to constraints. Use of a constraint on the cluster size gives rapid short-wavelength equilibration and accelerated diffusive long-wavelength kinetics; additional constraints can enforce local conservation laws.

We study the morphology and dynamics of an interface driven through a disordered two-dimensional medium by an applied force. At large length scales the interface is self-affine with roughness exponent α=1/2. The structure at small scales may be self-similar or self-affine, depending on the degree of disorder. Simulations of wetting invasion produce self-affine interfaces with α=0.8 and a power law distribution of local interface velocities. Numerical results are in excellent agreement with expreiment. A technique that distinguishes between true self-affine scaling and a crossover is presented, and applied to the invasion model and a model for magnetic domain growth.

CO adsorbed on Ni(100) displays a reversible change in the occupation of bridge and top sites with temperature. The equilibrium is controlled by the contribution of the hindered translation modes to the free energy.

The motion of naturally occurring vacancies on Si(001)-(2×1) has been investigated in real time with scanning tunneling microscopy, using a novel method in which repeated line scans are displayed in the form of a time-versus-position pseudoimage. Individual jumps of the vacancies are resolved. Vacancy diffusion is one dimensional along the dimer row. An activation energy of 1.7±0.4 eV has been measured for the diffusion of the single dimer vacancy.

The present tunneling microscopy study reveals that the growth of silver on Pt(111) at substrate temperatures above 620 K results in the formation of a two-dimensional alloy consisting of Ag clusters dissolved in the Pt layer [${\mathit{FTHETA}}_{\mathrm{Ag}}$<0.5 monolayer (ML)] and Pt clusters in the Ag matrix layer (0.5 ML<${\mathit{FTHETA}}_{\mathrm{Ag}}$<1 ML), respectively. The embedded clusters have a narrow size distribution centered around 10 Å. The dissolution of silver into the Pt surface layer and vice versa proceeds from the step edges and is confined to the topmost layer. The second silver layer does not dissolve into the interface, but grows layerwise on top.

Heat-capacity studies have been carried out on submonolayers of (CO${)}_{1\mathrm{-}\mathit{x}}$(${\mathrm{N}}_2$${)}_{\mathit{x}}$ mixtures physisorbed on graphite. We find that pure CO undergoes an end-to-end ordering transition at ${\mathit{T}}_{\mathit{c}}$=5.18 K, which is shown to belong to the two-dimensional Ising universality class. In diluting CO with ${\mathrm{N}}_2$ the heat-capacity peaks become progressively rounded until the phase transition is completely suppressed at a ${\mathrm{N}}_2$ concentration of only x=0.07. The analysis of the data shows that this behavior is in quantitative agreement with predictions of the random-field theory applied to adsorbed films.

Desorption of molecularly adsorbed ${\mathrm{O}}_2$ from Pt(111) by 620 nm femtosecond laser pulses shows a nonlinear fluence dependence of the yield and a subpicosecond response time. The measurements were carried out by means of a two-pulse correlation scheme using a pulse counting quadrupole mass spectrometer. These results can be understood with a model involving multiple reexcitations of the adsorbate by photogenerated carriers.

Organic multilayered thin films of copper phthalocyanine (CuPc) and naphthalene-1,4,5,8-tetracarboxylic-1,8:4,5-dianhydride were fabricated by an organic molecular beam deposition technique. The analyses by an x-ray photoelectron spectroscopy and a transmission electron microscopy directly revealed an alternating layer-by-layer structure, with a few nanometers thickness for each layer. The optical absorption spectra at the Q band for CuPc layers indicates an extraordinary electronic state in an organic superlattice structure.