It is commonly thought that blue phase II (BP II) is a simple-cubic structure. It is demonstrated that BP II in (+)-2-methylbutyl p-[(p-methoxybenzylidene)amino] cinnamate is fcc and it is argued that this is possibly true for all other BP II’s as well.

A new formula is derived for the information dimension ${\mathrm{D}}_1$ of the unscreened surface of a fractal pattern (its fractal dimension ${\mathrm{d}}_{\mathrm{f}}$). The formula yields ${\mathrm{D}}_1$=d-1, independent of ${\mathrm{d}}_{\mathrm{f}}$, when Brownian particles are used to probe the surface. The extension is made to the case of the probability distribution due to the growth rule of the η model. The approximate expression of the generalized dimension ${\mathrm{D}}_{\mathrm{q}}$ (q≥1) is then derived. All the results are found to be in very good agreement with our numerical results and the available data reported so far.

The room-temperature adsorption of oxygen on polycrystalline copper was studied with a novel combination of Auger-electron spectroscopy and time-of-flight analysis of direct surface recoils. By modeling the complex polycrystalline surface as an active ‘‘rough’’ and a nonactive ‘‘smooth’’ array, we obtain quantitative information regarding the kinetics of adsorption on each array. By a comparison with previous results from well-defined single crystals, the interrelation between arrays (and defects) affecting the overall kinetics of this complex surface was determined. The room-temperature adsorption of oxygen on polycrystalline copper displays significant interplane ‘‘spillover’’ effects, which enhances the apparent sticking coefficient of the ‘‘smooth’’ arrays.

We report the observation of an unusual series of spin-wave modes seen in continuous-wave NMR measurements on long cylindrical crystals of highly polarized solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. When a magnetic field and field gradient of appropriate magnitude are placed along the cylinder axis, the NMR spectrum breaks up into a series of discrete peaks whose spacing is geometric in mode number, with the spacing going to zero at an accumulation point. We show that this behavior is consistent with magnetostatic waves in the highly polarized medium.

Computer simulations of a Lennard-Jones fluid adsorbed at a structured solid substrate have been carried out with the Delft Molecular Dynamics Processor, using about 11 500 particles. Realistic density profiles have been obtained. By measurement of surface tensions and contact angles, a wetting as well as a drying phase transition have been identified. The wetting transition had not previously been seen in computer simulations of continuum fluids. Both transitions are of first order.

The continuum theory of self-avoiding D-dimensional manifolds with fixed connectivity, in d dimensions, is considered. The exponent γ is argued to exist only for integer D It is shown that its ε=4D-(2-D)d expansion is not universal at 0(ε), but depends on the shape of the manifold’s boundary. γ is calculated for a hyperellipsoid. New universal contact exponents are given for various points of a crumpled manifold.

Supersymmetric quantum mechanis is applied to the determination of a shallow potential which is phase equivalent to a deep potential, and whose bound spectrum is identical except for the ground state which is suppressed. With this method, the nonphysical bound states encountered in the spectrum of microscopically founded potentials can be eliminated. The resulting shallow potentials present for small r values an ${\mathrm{r}}^{\mathrm{-}2}$ singularity in accord with a generalized Levinson theorem.

We classify the equilibrium structures of sp-bonded tetramers with schemes based on valence electron orbital radii. Valence electron orbital radii plots show the transition from planar to nonplanar geometries, and account for trends in bond angles, thus confirming the success previously obtained by Andreoni, Galli, and Tosi for ${\mathrm{AB}}_2$ molecules.

Using translational spectroscopy, we have measured the released kinetic energies of the H fragments that are produced in the radiative decay of the g ${\mathrm{}}^3$${\mathrm{\Sigma }}_{\mathrm{g}}$(v=5,N=1) level to the repulsive b ${\mathrm{}}^3$${\mathrm{\Sigma }}_{\mathrm{u}}$ state. The energy distribution shows undulations directly related to the structure of the excited-state vibrational wave function. For the first time a distribution over the internuclear distance, which involves the excited-state wave function and the transition dipole moment, has been obtained by a transformation of the measured spectrum. We find differences with a calculated distribution for which we give a possible explanation.

We present femtosecond time-resolved transient reflectivity measurements on polydiacetylene performed at the peak of the exciton resonance. The magnitude of the nonlinear refractive index at 1.97 eV was found to be 3.0×${10}^{\mathrm{-}8}$ ${\mathrm{cm}}^2$/W. We discuss a model which accounts quantitatively for the large resonant and nonresonant optical nonlinearity observed in polydiacetylene in terms of phase-space filling by one-dimensional excitons.

We show that in a dynamic multiply scattering system, the intensity-intensity correlation function of universal optical fluctuations does not decay exponentially, but rather drops rapidly to half its initial value and then tails off very slowly to zero. We illustrate this dramatic behavior, and the approach to the ensemble average, with high-speed video images. We also present quantitative results for the correlation function, and provide a theory which is in excellent agreement with the data.

Measurements of the internal magnetic field structure of Texas Experimental Tokamak discharges are made by use of laser-induced fluorescence of an injected ${\mathrm{Li}}^0$ beam. From measurements near the magnetic axis, we obtain the axial safety factor, $q_0$ (or equivalently the rotational transform, ι=2π/q) for various discharge conditions. In particular, for low-$q_a$ sawtoothing discharges, we find time-averaged values of $q_0$ significantly less than 1 (∼0.7 to 0.8), in contrast with models used to describe the nonlinear internal relaxation process commonly known as sawteeth.

We demonstrate that the reconstruction of the Au(111) surface can be interpreted in terms of a new type of misfit dislocations, namely, double-sine-Gordon-type dislocations. First, we motivate the applicability of this class of solitons to the reconstruction problem. Second, we describe the procedure we have used to construct the model unit cell containing the double-sine-Gordon quasi one-dimensional dislocations. Finally, comparison with experimental He-scattering results is established by computation of the corresponding diffraction pattern using a hard corrugated wall and the eikonal approximation.

For Al adatom pairs on Al(100), first-principles calculations imply a small separation energy of 0.07 eV, resulting from Al-surface rebonding as adatom-adatom bonds break. Calculated barriers for Al-pair and single-Al diffusion are 0.66 and 0.80 eV. The pair barrier is lower because pairs reside farther above surfaces, where potential corrugation is weaker, and because an Al surmounting a barrier gains energy from its partner, whose bond to the surface strengthens.

We report an experiment demonstrating diffraction of cold neutrons by surface acoustic waves. We show that, in contrast to analogous experiments with light, the motion of the surface–acoustic-wave deformation of the surface requires significant modification of the diffraction equation applicable to stationary gratings. Diffracted beam intensities are in reasonable agreement with a simple theoretical treatment.

The effect of a finite bending rigidity κ’ on flexible, polymerized surfaces without self-avoidance is studied via the Monte Carlo method. Unlike linear polymers or liquid membranes, these surfaces undergo a remarkable finite-temperature crumpling transition, with a diverging specific heat. For small κ’/${\mathrm{k}}_{\mathrm{B}}$T, the surface is crumpled, and the radius of gyration ${\mathrm{R}}_{\mathrm{G}}$ grows as ln${\mathrm{L}}^{1/2}$, where L is the linear size of uncrumpled membrane. For large κ’/${\mathrm{k}}_{\mathrm{B}}$T, we find that the surface remains flat, i.e., ${\mathrm{R}}_{\mathrm{G}}$∼L. Our results strongly suggest a finite-temperature crumpling transition in polymerized self-avoiding membranes as well.

A model calculation of the dephasing rate of an adsorbate vibration due to electron-hole–pair scattering on a metal surface is presented. The standard Newns-Anderson model is used to describe the adsorbate-metal surface system in terms of a single electronic adsorbate level and a tight-binding metal band. The perturbation of the vibrational motion by the coupling between adsorbate and metal electrons is included to second order. The magnitude of the dephasing rate and its temperature dependence are obtained in terms of the model parameters and the adsorbate-orbital–projected electronic density of states. It is in reasonable agreement with recent experimental data for CO on Ni(111).

The rate at which crystalline-Si nucleates at the amorphous-Si/liquid-Si interface is estimated. On the basis of this estimate and physical arguments, we propose that under certain conditions a moving amorphous-Si/liquid-Si interface is unstable with respect to nucleation of crystalline Si. Such nucleation, followed by growth, is a possible mechanism for the well-known explosive crystallization of amorphous Si. Furthermore, a similar instability can explain the formation of amorphous Si from liquid Si.

On the basis of the premise that scaling is defined by a set of scaling transformations which form a simple product group, a scaling group is constructed for simple fractal scaling and the scaling of multifractal sets. The singularity strengths and densities are shown to be corollary to the scaling-group formalism. Fractal dimension and other exponents are shown to be generators of infinitesimal transformations. Applications are made to self-affine fractals and the scaling log-normal distribution.

We identify the mysterious high-T ‘‘twitch’’ transition in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ with the mean-field resonating-valence-bond transition of the Heisenberg model of Baskaran, Zou, and Anderson. The structure distortions are caused by Coulomb correlations of the pair wave function. In the pure compound the pseudo-Fermi surface of the spin soliton nests and antiferromagnetism occurs at 240 K. We discuss briefly superconductivity and the nature of excitations in the system.