A molecular-dynamics calculation on a hydrated protein, crambin, demonstrates that (i) neighboring dihedral angles are correlated to local transitions in the protein backbone, and that (ii) the amplitude of collective excitations, representing correlated global motions in the protein, samples multicentered distributions. The time dependence of the multicentered dihedral and collective excitations show rapid transitions from the center of one distribution to another, followed for some time by damped, low-amplitude motions around one center. The global nonlinear collective excitations are responsible for most of the atomic fluctuations of the molecule. An analysis appropriate to multimodal conformations is reported.

The scalar version of the Aharonov-Bohm effect predicts a phase shift for de Broglie waves due to the action of a scalar potential in an otherwise field-free (i.e., force-free) region of space. Unlike the more familiar effect due to the magnetic vector potential, the scalar effect has hitherto remained unverified due, presumably, to technical difficulties in electron interferometry. Rather than using electrons acted on by electrostatic potentials, we have performed an analogous interferometry experiment with thermal neutorns subject to pulsed magnetic fields. The expected phase shifts have been observed to a high degree of accuracy.

Analytic reflectionless potentials ${\mathrm{\omega }}^2$(τ) are constructed for the one-dimensional equation ${\mathrm{\epsilon }}^2$${\mathit{d}}^2$q/d${\mathrm{\tau }}^2$+${\mathrm{\omega }}^2$(τ)q=0. Unlike generic potentials which reflect waves with amplitudes of order exp(-1/ε) as ε→0, these potentials have reflection coefficients which are identically 0. It is shown that in the reflectionless case the adiabatic perturbation or iteration does not converge absolutely or terminate at some order. Since exact integrability is less restrictive than having a reflectionless potential, the case studied also shows that integrability does not imply convergence of the approximation methods used.

Generic, deterministic, nonconservative models displaying self-organized criticality are shown to exhibit 1/f noise. The exponent of the power spectrum depends on the level of conservation.

We have demonstrated for the first time that single photons in glass travel at the group velocity, and have observed a novel, nonlocal dispersion-cancellation effect. We used a two-photon interferometer in which a conjugate pair of photons produced in parametric fluorescence travel separate paths and are detected in coincidence after being recombined at a beam splitter. A piece of glass was placed in the path of one of the photons, and a variable delay was adjusted to precisely compensate for it. The single-photon propagation time was thus measured to within approximately 4 fsec.

With the aim of determining the scale of inhomogeneities produced by the transition of quarks to hadrons in the early Universe, we study the hydrodynamic stability of slow combustion (deflagration). For a front velocity v, the phase boundary is unstable on a time scale τ∼(1/${\mathit{v}}^3$) fm; surface tension stabilizes bubbles below a critical size. For supercoolings implied by the bubble separations of interest for inhomogeneous nucleosynthesis (∼1 m), τ is much less than the duration of the phase transition. Bubble disruption could restore homogeneous nucleosynthesis.

We report the first experiments in which 5-MeV alpha particles are detected via evaporation from a bath of superfluid helium. The α excites phonons and rotons in the liquid helium, and these excitations are sufficiently energetic to evaporate helium atoms when they reach the free surface of the liquid. The approximate overall efficiency of this process has been determined, and we compare this with expectations. We have also been able to detect evaporation induced by a flux of γ’s from a ${}_{}{}^{137}{}_{}{}^{}\mathrm{Cs}$ source.

We have measured ρ, the ratio of the real to the imaginary part of the p¯p forward elastic-scattering amplitude, at √s =1.8 TeV. Our result, ρ=0.140±0.069, is compared with extrapolations from lower-energy data based on dispersion relations, and with the UA4 value at √s =546 GeV.

Preequilibrium parton scattering is shown to make an important contribution to the charm production in relativistic heavy ion collisions. In contrast to the gluon shadowing effect in the initial parton scattering, the enhancement of the final total open charm in the central region due to preequilibrium production could be used as a measure of the thermalization time of the dense partonic system.

By means of a phase-conjugation experiment by nondegenerate six-wave mixing, we demonstrate a transient ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ grating induced by a nonzero ${\mathit{E}}^3$ time average in a solution of noncentrosymmetric dye molecules. The origin of the induced phase-matched second-harmonic generation is found in an orientational hole-burning effect. Its lifetime, limited by molecule rotation, is 210±10 psec and the ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ magnitude reaches 2.5×${10}^{\mathrm{-}3}$ pm/V for 1 GW ${\mathrm{cm}}^{\mathrm{-}2}$ pumps at 1064 nm.

Modulation of the gas feed to a tokamak induces a density modulation and also a temperature modulation. Although the density change is fractionally small and the response is linear, the perturbed particle flux can exceed the equilibrium flux. The particle flux Γ thus cannot be a simple homogeneous function of ∇n. The ratio of thermal to particle flux is quite different for the equilibrium and perturbations, precluding a simple linkage of particle and thermal transport. The modulation of the amplitude of density turbulence does not correlate with any of the modulated fluxes.

We report observations of the transverse acceleration of ions in localized regions of intense lower hybrid waves at altitudes near 1000 km in the auroral ionoshpere. The acceleration regions are thin filaments with dimensions across geomagnetic field lines of about 50–100 m corresponding to 5–10 thermal ion gyroradii or one hot ion gyroradius. Within the acceleration region lower hybrid waves reach peak-to-peak amplitudes of 100–300 mV/m and ions are accelerated transversely with characteristic energies of the order of 10 eV. These observations are consistent with theories of lower hybrid wave collapse.

Symmetric binary mixtures of partially deuterated polymers were prepared at the critical composition. The segment-segment interaction energy parameter ${\mathrm{\chi }}_{\mathrm{eff}}$ was varied by adjusting the difference in deuterium content Δ${\mathit{X}}_{\mathrm{D}}$ between species. ${\mathrm{\chi }}_{\mathrm{eff}}$ was measured as a function of temperature, Δ${\mathrm{\chi }}_{\mathrm{D}}$, and molecular weight by small-angle neutron scattering. The critical point for demixing was determined to scale as ${\mathrm{\chi }}_{\mathrm{e}\mathrm{f}\mathrm{f},}$c∼${\mathit{N}}^{\mathrm{-}\mathrm{\delta }}$ with δ=1.01±0.05, where N is the degree of polymerization. This result confirms the mean-field prediction of Flory and Huggins.

We report femtosecond pump-probe difference absorption experiments on polydiacetylene-para-toluene sulfonate. Theoretical analysis using a three-mode Brownian oscillator model for the nuclear dynamics reveals spectral diffusion in this conjugated polymer; this effect cannot be accounted for using the optical Bloch equations. Sequential (pump first) time ordering is dominant for resonant excitation, whereas experiments utilizing an off-resonant pump are dominated by nonsequential time orderings of the pump and the probe; the latter represent coherent (Raman-type) processes.

A combiation of video polarization microscopy and extensive digital line pattern analysis has been invoked to examine in quantitative detail the transformation of a lamellar into a ‘‘labyrinthine’’ magnetic-stripe domain pattern. The evolution of disorder is found to be mediated by a sequence of transverse, ‘‘smectic’’ instabilities culminating in the generation of disclination dipoles. Their subsequent continuous ‘‘unbinding’’ facilitates the formation of a globally isotropic nonequilibrium pattern adopting the topology of a binary tree and displaying a well-defined morphology with a motif in the form of oblong, polygonal clusters of linear-stripe segments.

Brillouin light scattering measurements of surface acousta modes propagating in an ion-milled holographic grating on a Si(001) wafer have revealed clear evidence of hybridization between the Rayleigh wave and the longitudinal resonance which leads to an unexpected gap. Other new acoustic features include the folding of the Rayleigh wave about the first two zone boundaries associated with the grating, band gaps which increase with zone number, and different propagation velocities parallel and perpendicular to the grating.

We have explored the stable phases of solid hydrogen by calculating band-theoretical energies in the local density approximation, for the system of oriented molecules at Mbar pressures and at zero temperature. It is shown that the hexagonal-close-packed lattice persists up to ∼300 GPa with a structure of space group Pca$2_1$, which has wide band gaps. The subsequent phase is still molecular with a rutile structure with c/a∼0.9 which must be conducting. The molecular phase terminates at ∼600 GPa, where the atomic phase with a planar structure appears.

The single-length-scale postulate for fractons and the scaling hypothesis for the dynamic structure factor are confirmed for scalar elasticity on bond-percolation clusters. The strain exponent σ is determined in two and three dimensions. Because of granularity and finite-size effects, these results cannot be obtained from site-percolation models for which the short-range structure fails to scale. Dipole-induced-dipole scattering is particularly sensitive to granularity.

The critical dynamics near the consolute point of a relatively low molecular weight asymmetric critical binary polymer mixture is studied with dynamic light scattering. In contrast to a single exponential decay showing a critical slowing down, as has been reported for another low molecular weight polymer blend, we observe both a ‘‘fast’’ and a ‘‘slow’’ relaxation rate. The critical slowing down of the concentration fluctuations is seen to be contained in these two modes.

In four different compounds of the alkyl(oxy)cyanobiphenyl series, the elastic modulus B is found not to vanish at the nematic–smectic-A (Sm-A) phase transition, contrary to most theoretical expectations. The phase transition is marginal, as the Sm-A phase is a one-dimensional solid in three-dimensional space, and it seems that B cannot decrease below a limiting value (about ${10}^7$ dyn ${\mathrm{cm}}^{\mathrm{-}2}$ here) where the fluctuations of the layers due to the Landau-Peierls instability, which scale as ${\mathit{B}}^{\mathrm{-}0.25}$, would destroy the Sm-A ordering.