The phenomenon of Anderson localization in the quantum kicked rotator is analyzed by means of concepts which were originally introduced in condensed matter physics. A diagrammatic language similar to the impurity diagram technique employed in the theory of disordered conductors is developed. The method is applied to a calculation of the quantum return probability and leads to results which coincide (apart from numerical factors) with recent numerical findings.

We demonstrate for the first time that in a homogeneous nonamplifying physical system described by the nonlinear Schrödinger equation, the combined effects of two different perturbations (delayed nonlinear response and higher-order dispersion) can lead to adiabatic compression of fundamental solitons. This is unexpected since each of these perturbations operating independently destroys soliton propagation. Experimentally this is demonstrated by showing that 95 fsec fundamental solitons are redshifted from 1.57 to 1.62 μm and adiabatically compressed to 55 fsec in 65 m of a single-mode silica fiber with modified dispersion.

The nonlinear polarization close to the band gap of GaAs is studied by spectrally and temporally resolved four-wave mixing. Excitonic and free carrier contributions both excited within the bandwidth of the 100 fs pulses are distinguished for the first time. The excitonic part dominates at carrier densities below ${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$. At higher density, nonthermalized free carriers give rise to an additional component resonant to the pulse that shows a photon-echo-like time behavior. Monte Carlo simulations including the coherent polarization and the scattering dynamics of the carriers account for the data.

A system of electromagnetic and ion acoustic wave equations coupled via the ponderomotive force are solved numerically in a two-dimensional planar geometry. The competition between forward, side, and backward Brillouin scattering of the finite size laser beam is studied for the first time without the standard paraxial optics approximation. Simulations reveal a strong dependence of the scattered light characteristics on the geometry of the interaction region, the shape of the pump beam, and the ion acoustic wave damping. The main effects include side and forward scattering enhancement and a stimulation of collimated backward scattered radiation.

Molecular dynamics simulations of porous silica in the density range 2.2–0.1 g/${\mathrm{cm}}^3$ are carried out on a 41 472 particle system using a multiple instruction multiple data computer. The internal surface area, pore surface-to-volume ratio, pore size distribution, fractal dimension, correlation length, and mean particle size are determined as a function of the density. Structural transition between a condensed amorphous phase and a low-density porous phase is characterized by these quantities. Various dissimilar porous structures with different fractal dimensions are obtained by controlling the preparation schedule and temperature.

Nonclassical universal critical behavior is revealed in several one dimensionally modulated incommensurate (IC) crystals by means of quadrupolar perturbed NMR. In the IC phase the temperature dependence of the NMR line shape leads to the same critical order parameter exponent β for all systems. Above the phase transition a nonclassical exponent was found for the critical contributon to the spin-lattice relaxation. All results agree with the theoretical predictions of the 3d XY model.

The dynamics of bistable stochastic systems driven by oscillating fields is analyzed by numerically solving the Fokker-Planck equation. The long time response is oscillatory in time and out of phase with respect to the field. The phase shift as a function of the noise D has a peak for weak fields and low frequencies if intrawell fluctuations are considered, in agreement with linear response theory. The amplitude has a peak, but for a different value of D, even if intrawell fluctuations are neglected. We also analyze the behavior for strong fields so that linear response theory becomes questionable.

Two-dimensional, partially flexible polymers interacting with each other through the Onsager-like excluded-volume interaction are shown to exhibit a second-order, isotropic-nematic transition at a sufficiently high density. The instability of the free energy under the influence of a nematic state is investigated and the critical density at which the isotropic-nematic phase transition takes place is determined analytically. It is shown that both second- and fourth-rank order parameters must be included in order to deduce a Landau expansion of the free energy.

This paper reports the results of the first measurements of the thermal conductivity of the α, β, and γ phases of solid oxygen over the temperature range of 1–52 K. A simple qualitative analysis was performed to explain the observed anomalies in thermal conductivity, which manifested themselves by a jump at the α-β transition, the anomalously weak temperature dependence in the β phase and an increase of the conductivity with temperature in the γ phase.

We present an algebraic structure that provides an interesting and novel link between supersymmetry and quantum integrability. This structure underlies two classes of models that are exactly solvable in one dimension and belong to the 1/${\mathit{r}}^2$ family of interactions. The algebra consists of the commutation between a ‘‘super-Hamiltonian’’ and two other operators, in an enlarged Hilbert space. These reduce to quantal Ordered Lax equations when projected onto the original subspace, and to a statement about the ‘‘Harmonic Lattice Potential’’ structure of the Lax operator, leading to a highly automatic proof of the integrability of these models and to an interesting hierarchy of new models.

With CPT-invariant initial conditions that commute with CPT-invariant final conditions, the respective probabilities (when defined) of a set of histories and its CPT reverse are equal, giving a CPT-symmetric universe. This leads me to question whether the asymmetry of the Gell-Mann–Hartle decoherence functional for ordinary quantum mechanics should be interpreted as an asymmetry of time.

Pseudo Goldstone bosons couple with photons through a P and T violating interaction of the form L=${\mathit{g}}_{\mathrm{\alpha }\gamma \gamma }$αFF̃. Strong magnetic fields in rotating compact stars induce a nonzero E⋅B outside the stellar surface which acts as a source for the pseudoscalar field. Pulsar signals propagating through this pseudoscalar ‘‘hair’’ suffer a differential time lag between the left and the right circularly polarized modes because of the P and T violating pseudoscalar-boson–photon interaction. Determination of this time lag up to a microsecond accuracy can lead to a measurement of (or rule out) pseudo-Goldstone-boson–photon coupling up to ${\mathit{g}}_{\mathit{a}\gamma \gamma }$≤2.0×${10}^{\mathrm{-}11}$ ${\mathrm{GeV}}^{\mathrm{-}1}$.

The W production cross section times the branching ratio for W→lν, l=e,μ decays has been measured as a function of the associated jet multiplicity. The data have been recorded at the Collider Detector at Fermilab during the 1988–89 run. A recent leading order QCD calculation agrees well with the data up to a jet multiplicity of 4.

A new technique, based on relative measurements of the longitudinal polarization (P) of positrons emitted in two opoosite directions with respect to the nuclear polarization (R=${\mathit{P}}^{\mathrm{-}}$/${\mathit{P}}^{+}$), is used to provide constraints on extensions of the standard model (${\mathit{R}}_0$). The first result, i.e., R/${\mathit{R}}_0$=0.926±0.041, was obtained with ${}_{}{}^{107}{}_{}{}^{}\mathrm{In}$. Interpreted in the framework of left-right symmetric models and assuming no mixing, it provides a 90% C.L. lower limit of 225 GeV/${\mathit{c}}^2$ for the mass of a possible right-handed charged W gauge boson, reducing the mass range allowed by other semileptonic experiments.

A method to calculate the mean squared matrix element of the weak interaction between compound states is developed. The result is expressed in terms of matrix elements of the nucleon-nucleon strong and weak interactions times the Fermi distribution functions at finite temperature. Numerical calculations for ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ are in agreement with recent measurements of parity nonconservation effects in neutron capture. In fact, our calculations prove that the factor of dynamical enhancement (ratio of compound-nucleus effect to single-particle one) really exceeds 100, thus making it unnecessary to assume a value of the weak constant bigger than standard one (g≃${10}^8$ε∼1–4).

High energy γ rays from the decay of the giant dipole resonance built on highly excited states in ${}_{}{}^{164}{}_{}{}^{}\mathrm{Yb}$ at ${\mathit{E}}_{\mathrm{ex}}$=49 MeV formed in two different reactions have been measured. While standard statistical model calculations can describe the γ-ray spectrum from the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{148}{}_{}{}^{}\mathrm{Sm}$ reaction they fail to reproduce the γ-ray spectra from the more symmetric reaction ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$. Simple model calculations which include particle evaporation and γ-ray decay during the formation process suggest that the observed differences may be related to a long fusion time in the more symmetric reaction.

Theoretical and experimental presentations are given of a drastic suppression, during the interval of the excitation pulse, of forward-directed optically pumped stimulated emission from a two-photon resonantly excited state to a lower state which is also coupled to the ground state. The effect is caused by a self-induced interference from the difference-frequency mixing field that is generated during the time that the excitation fields are present. Several other implications of this effect are given and some puzzling observations in other studies are noted and clarified.

The response of weakly disordered metallic grains to Aharonov-Bohm flux suggests a rescaling in which statistical correlators become universal. We derive an exact expression for a correlator of level ‘‘velocities,’’ and provide numerical evidence which suggests that the universality extends to a wider class of systems and generalizes to arbitrary perturbations providing a new characterization of quantum chaos. These results are applied to Fermi velocities of complex lattices.

We present measurements of local temperature fluctuations from a convection cell of aspect ratio 1, using gas at room temperature, for Rayleigh numbers (Ra) ranging from 5×${10}^5$ to 1×${10}^{11}$. The thermal boundary layer thickness is measured; its scaling is close to ${\mathrm{Ra}}^{\mathrm{-}2/7}$ for Ra≥2×${10}^7$. A second length scale is measured through the cutoff frequency of the power spectrum, which we relate to the velocity of the large scale circulation. The Rayleigh number dependence of this length changes at Ra=2×${10}^9$.

A transition from low to high radial confinement mode is triggered by biasing a limiter in the HIEI tandem mirror. Positive dc biasing gives rise to reduction of fluctuation level in density and potential in the periphery, drop of neutral line emission, and bifurcation in limiter current. After the transition, the plasma exhibits density rise in the bulk and steepening of the density gradient. Significant radial rotational shear is observed when the edge turbulence is suppressed by the biasing. The total feature shows similar characteristics of L- to H-mode transition observed in tokamak devices.