We present numerical results on a model in which quantization of chaos (instead of suppression of the diffusion) leads to a diffusive or even faster excitation with infinite conductance in the corresponding solid-state model. We suggest a possible mechanism for this effect.

The homogeneous cosmology of Bianchi type IX (mixmaster cosmology) is quantized in a supersymmetric form, allowing the Dirac-type square root of its Wheeler-DeWitt equation to be taken. A supersymmetric solution is given exactly in closed form.

One-particle-irreducible amputated graphs differ qualitatively at finite temperature when calculated in the imaginary-time and real-time formalisms. Here we show within the real-time formalism for the three-point function that when external propagators are attached certain amputated functions can be inferred which have a close relation to those of the imaginary-time formalism.

A technique for estimating the large-order QCD perturbative contributions to the total ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ total cross section is presented which is based upon the renormalization group and momentum analyticity. Our estimate for the coefficient of (${\mathrm{\alpha }}_{\mathit{s}}$/π${)}^3$ has recently been confirmed by two exact calculations. We find that the effective expansion parameter is, in fact, not ${\mathrm{\alpha }}_{\mathit{s}}$/π but rather 4${\mathrm{\pi }}^2$${\mathit{eb}}_1$(${\mathrm{\alpha }}_{\mathit{s}}$/π), where ${\mathit{b}}_1$ is the first coefficient in the expansion of the β function.

We study the effects of quark degrees of freedom on the nucleon-nucleon observables. The model we consider is built from the Paris potential for large and intermediate distances, supplemented by the quark cluster model for the core. The fit to the existing pp data set is not good. These results suggest that the good description of the NN interaction at short distances by quark models sometimes claimed in the literature could be questioned.

We have analyzed the pion-induced double-charge-exchange data for the direct population of the ground state of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ by the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$${)}^{11}$Li reaction. We find that the measured cross section determines the rms radius of the last two neutrons in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ to be 5.$1_{\mathrm{-}0.9}^{+0.6\mathrm{}}$ fm, which corresponds to a total neutron rms radius for the nucleus of 3.${28}_{\mathrm{-}0.33}^{0.24}$ fm. We show that for large assumed neutron-halo radii the cross section decreases as the radius of the halo to the inverse sixth power and that a radius of 12 fm leads to a cross section which is 3 orders of magnitude smaller than that measured.

We derive a two-photon bound-state solution to the problem of quantum propagation of light in Kerr-effect nonlinear media which classically would exhibit self-focusing and self-trapping. We propose an experiment to see this two-photon bound state.

A relativistic basis set composed of products of Slater- and Landau-type functions is introduced and applied to the accurate calculation of the ground-state energy of an electron in a static Coulomb field and a magnetic field of arbitrary strength. The relativistic corrections for strong magnetic fields differ from previous relativistic adiabatic approximations. It is found that the sign of the relativistic correction changes from negative to positive; for hydrogen this occurs near B=${10}^{11}$ G. The accuracy of the nonrelativistic-limit results matches or exceeds that of previous nonrelativistic calculations.

Differential cross sections have been measured for the electron-impact excitation of a multiply charged ion. In a crossed-beam experiment the resonant 3s-3p transition of sodiumlike ${\mathrm{Ar}}^{7+}$ is studied at an electron energy of 100 eV in an angular range between 13° and 29°. The experimental cross sections are found to be in good agreement with theoretical predictions obtained in Coulomb-Born distorted-wave approximation.

We report the observation of substantial amplification due to multiwave (more than four) mixing in a Josephson-parametric amplifier. Amplification was achieved with subharmonic pumping at 2/3, 2/5, and 2/7 of the signal frequency near 19 GHz. The processes reponsible for the amplification were, correspondingly, five-, seven-, and nine-wave mixing. For the case of five-wave mixing we have observed amplification in excess of 35 dB and noise referred to input of a few degrees kelvin before the amplifier undergoes a pitchfork instability. The noise rise at the pitchfork bifurcation was also studied and compared with theory.

We examine the dynamics of atomic ionization in superintense fields directly in the Kramers-Henneberger frame. We show that atomic stabilization is intimately dependent not only on intensity and frequency, but also on pulse turn-on characteristics which determine the distribution of Kramers-Henneberger states in the superposition which is excited.

Tang, Toennies, and Yiu have shown that unsymmetrized Rayleigh-Schrödinger perturbation theory can be used to calculate the leading terms in the ground-state exchange energy of ${\mathrm{H}}_2^{+}$ using the method of Holstein and Herring. We clarify this seemingly puzzling result by showing that their approximation to the polarization wave function is exactly he leading term of the Herring-Holstein function. We also show that a generalization of their method yields the leading asymptotic exchange energy terms for excited states, thereby suggesting the existence of a general underlying property and the applicability of the method to many-electron systems.

${\mathrm{C}}_{60}$Buckminsterfullerene exhibits a large ultrafast third-order nonlinear optical response. Degenerate four-wave-mixing measurements in ${\mathrm{C}}_{60}$-benzene solutions were performed using 50-psec pulses at 1.064 μm. The magnitude of the nonlinear susceptibility per ${\mathrm{C}}_{60}$ molecule is ‖γ‖=1.5×${10}^{\mathrm{-}42}$ ${\mathrm{m}}^5$ ${\mathrm{V}}^{\mathrm{-}2}$ and of the same size as that observed in polydiacetylene. In contrast to conjugated polymers, however, a dominant positive real part of the nonlinearity is found, 3 times larger than the imaginary component. The nonlinear response can be described within the model of a free electron in a spherical box, confirming the complete delocalization of electrons on the ${\mathrm{C}}_{60}$ molecule.

We address the problem of identifying the dynamical variables representing the phase of a quantum field by analyzing what is measured in two simple homodyne experiments. This leads us to identify operators C${\mathrm{^}}_{\mathit{M}}$,S${\mathrm{^}}_{\mathit{M}}$ corresponding to the measured cosine and sine of the phase difference. The predictions of the theory are tested in an experiment in which the input fields are derived from a highly stable He:Ne laser. Photon-counting measurements extending from mean photon numbers 30 down to ${10}^{\mathrm{-}2}$ show good agreement between theory and experiment. The implications for identifying the ‘‘correct’’ phase operator are briefly discussed.

The evolution of fluid interfaces in parallel flow in Hele-Shaw cells is studied theoretically and experimentally in the limit of large capillary number. It is shown that such interfaces support wave motion, the amplitude of which for long waves is governed by a set of Korteweg–de Vries and Airy equations. Experiments conducted in a long Hele-Shaw cell validate the theory in the symmetric case.

The electron-density fluctuation spectra induced by stimulated Compton scattering (SCS) are directly observed for the first time. A ${\mathrm{CO}}_2$ laser is focused into plasmas with densities ${\mathit{n}}_{\mathit{e}}$ spanning (0.4–6)×${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$. The fluctuations corresponding to backscatter are probed using Thomson scattering. At low ${\mathit{n}}_{\mathit{e}}$, the scattered spectrum peaks at a frequency shift Δω=${\mathit{kv}}_{\mathit{e}}$ and appears to be in a linear convectively saturated regime. At the highest ${\mathit{n}}_{\mathit{e}}$, a nonlinear saturation of the SCS instability is observed possibly due to a self-induced perturbation of the electron distribution function.

Electrostatic fluctuations have been measured in a large reversed-field pinch, and are large (n${\mathrm{̃}}_{\mathit{e}}$/n∼20%–40%, T${\mathrm{̃}}_{\mathit{e}}$/T∼10%–25%). Frequency and wave-number spectra are broad (Δn∼70–150, Δm∼3–6), and differ from measured magnetic fluctuation spectra. The transport inferred from correlation measurements indicates that electrostatic fluctuations can account for significant particle losses, but contribute <15% to energy loss.

Analysis of the Frank free energy for nematics confined to cylindrical regions indicates that the director pattern is dependent on the surface elastic constant ${\mathit{K}}_{24}$ if there is weak normal anchoring and escape along the cylinder axis. Using deuterium nuclear-magnetic-resonance techniques on samples of submicrometer-size cavities in Nuclepore membranes, we report the first measurement of ${\mathit{K}}_{24}$.

The idea of the shadow wave function, which incorporates quantum delocalization of particles in the description of quantum liquids and solids, is applied to excited states of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. With a simple Feynman shadow wave function we compute the phonon-roton excitation spectrum by a Monte Carlo method at three different densities. The variation of the excitation energy with density is consistent with the behavior of the experimental data. The energy near the roton minimum is in excellent agreement with experiment at all densities.

Experimental results have been obtained on the segregation coefficients of boron, phosphorus, and arsenic in the Si-(${\mathrm{Ge}}_{\mathit{x}}$${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$) heterostructure. It is found that boron tends to segregate into the ${\mathrm{Ge}}_{\mathit{x}}$${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ layer, while phosphorus and arsenic tend to segregate away from it. The results are discussed within the framework of Hu’s recent theory. The important factor is the ‘‘ideal work function’’ difference between two regions of the heterostructure; this difference can be estimated from the band-gap change and the band offsets. The effect of pseudomorphic strain energy is found to be appreciable for boron. Within experimental error, the diffusivities have not been appreciably affected.