Numerical results on liquid-glass transitions for Lennard-Jones systems are presented, based on a kinetic theory presented in two earlier papers. Detailed comparison is made with available computer simulation data and shows quite good agreement.

It is shown that the oscillation-center description of particle dynamics in a prescribed wave potential is a simple example of a subdynamics decomposition, at least in the absence of resonances. This equivalence then enables a new construction of the oscillation-center transformation and the ponderomotive Hamiltonian for a nonresonant particle in a sinusoidal wave. This is accomplished by evaluating the creation and destruction operators and solving the Mandel-Turner equation.

A systematic method for the decoupling of a relevant subspace of the Hilbert space from the rest of it is developed, on the basis of the dynamical properties of the observables one is interested in.

First, we demonstrate that careful simulations of fluids have enough accuracy that the resulting radial distribution function can be used to test inversion methods. Second, we introduce a method which allows extraction of the pair interaction starting from structural data for simple liquids even under triple-point condition. The method is an iterative predictor-corrector method in which the predictor is the modified hypernetted-chain equation and the corrector is simulation. We have verified the convergence of the method for the Lennard-Jones fluid and for a model potential for aluminum. We find that other methods of inversion give unreliable results. As a first application of our method we have inverted the experimental structural data of Na at 100 °C.

We consider a spin (1/2) placed in a small longitudinal constant field and strongly coupled to a transverse boson field. This system can model, for example, the motion of a small polaron between two sites of the molecular-crystal model of a lattice. The self-consistent and nonlinear character of this system causes a strong transverse counterreaction of the boson field polarized by the spin. For strong-enough coupling, this reaction overcomes the longitudinal field and leads by symmetry breaking to two equivalent spin directions modeling the small-polaron states. We show that self-trapping occurs through the relaxation of a slow variable—the density variable. This relaxation itself is rendered possible by the blurring of a fast variable—the phase variable—by the thermal fluctuations. The existence or not of self-trapped states is shown to depend on the Markovian or non-Markovian nature of the phase variable. The cases of white noise, Ornstein-Uhlenbeck noise, and narrow-band noise are considered. We point out that ergodicity breaking does not automatically result from the splitting of the phase space into well-defined components separated by high barriers.

Ultrasonic absorption has been measured in the smectic-A–isotropic phase transition region of p-(n-octoxy)benzylidene-p-(n-butyl)aniline(OOBBA) as a function of both temperature and frequency. An anomalous increase of the ultrasonic absorption has been observed at the transition temperature $T_c$. The critical ultrasonic absorption in the smectic-A phase has been interpreted by assuming, as for helium, that the critical fluctuations and the relaxation of the smectic order parameter both contribute to the attenuation. The excess absorption in the smectic-A phase has also been analyzed in the light of the Mazenko-Ramaswamy-Toner theory.

A density-functional theory for the Frank elastic constants described in an earlier paper is reformulated and simplified. The excess free energy of aligned nematic liquids subjected to curvature (i.e., ‘‘splay,’’ ‘‘twist,’’ and ‘‘bend’’) deformations is written in terms of the direct correlation functions of the isotropic liquids. This leads to expansion of the elastic constants in successively higher-order direct correlation functions. The truncation of this series at an early stage is found to introduce large error. The number of terms explicitly considered and the use of a [1,0] Padé approximant make our calculation reliable. The other expansion which our theory involves is one in powers (products) of order parameters. These order parameters are the coefficients of a spherical harmonic expansion of an orientational singlet distribution. The convergence of this series is also tested for a simple model of hard ellipsoids of revolution. Qualitative features exhibited by our calculation for both ordinary and discotic nematics are in agreement with the results of previous workers and experiments. While this paper focuses on the role of packing forces the theory can be generalized to include dispersion and other long-range interactions, noncylindrical geometry, and nonrigidity of molecules.

It is observed that the Frenkiel-Klebanoff-Huang turbulence data for the longitudinal correlation function at grid Reynolds numbers from 12 800 to 81 000 are subsumed by the simple empirical expression f=[1+(r/2L${\left)\right]}^{\mathrm{-}3}$, where r denotes the separation distance between two points in the turbulent fluid flow and L=L(t) is the integral scale. Hence, the longitudinal velocity correlation is rescaled by the self-similarity dilatation factor ${\lambda }^{\mathrm{-}3}$ under the separation-distance transformations r→λr+(λ-1)2L at fixed t.

We examine one-photon transitions in positronium (Ps) as possible tests of the discrete symmetries of C (charge-conjugation) and/or P (parity) and/or T (time-reversal) invariance. We discuss two general classes of experiment. The first class consists of direct searches for transitions forbidden by a given symmetry. The second class is composed of experiments that search for an asymmetry in the rate of an allowed transition upon reversal of an externally controllable vector quantity, such as an applied magnetic field B or rf photon spin ${\mathrm{S}}_{\gamma }$. For a given symmetry, we compare limits on symmetry-violating mixings, which can reasonably be expected from these Ps experiments, with limits placed by existing atomic experiments. We conclude from this analysis, that the most promising experiments in Ps are those that search for C violation with no P violation.

We show that Shastry’s exact solution of a nonlinear eigenvalue problem in one dimension can be recovered by a method which is familiar in the theory of nonlinear ordinary differential equations.

Via Nelson’s stochastic mechanics, a method for the solution of the hydrodynamical version of the logarithmic nonlinear Schrödinger equation (LNLSE), with a time-dependent forced-harmonic-oscillator potential, is presented. Based on a new interpretation of the interplay between dispersion and nonlinearity, a revealing general spreading-wave-packet solution is found. The complete stochastic process associated with the LNLSE is also derived and decomposed into underlying processes of independent nature (classical and quantum). Physical consequences and conditions which allow the existence of solitonlike (nonspreading) solutions are described: Among them, it is found that the zero-point energy is given by ${\epsilon }_0$=ħ${\Omega }_0$/2, where ${\Omega }_0$=λ/2+[(λ/2)+${\omega }_0^2$] ${}_{}{}^{1/2}{}_{}{}^{}$ with ${\omega }_0$ and λ being the harmonic frequency and the nonlinearity strength, respectively.

The gradient expansion of the molecular kinetic-energy functional is assessed through numerical results for fourteen diatomic and polyatomic molecules. The correlation of the dissociation energies ($D_e$) of molecules with the Weizsacker contribution to the kinetic energy ($T_W$) is established through a plot of $D_e$/$N^2$ against $T_W$ where N is the number of electrons. The conclusions support and extend the observations of Allan, et al. [J. Chem. Phys. 83, 4562 (1985)].

The jumping-ball system, corresponding to the modified Fermi-Ulam problem, is investigated experimentally. Using experimental data transferred to computer memory through the external interface, the correlation integral is estimated. In addition, the level of random noise is examined.

The predictions of a central-field molecular model, designed to represent a series such as ${\mathrm{CH}}_4$,${\mathrm{SiH}}_4$,...,${\mathrm{PbH}}_4$, are first derived, within a nonrelativistic framework, in the limit in which the nuclear charge $Z_2$e of the heavier atom is allowed to tend to infinity. It is shown that in this model, in which the four outer protons in ${\mathrm{PbH}}_4$, say, are smeared uniformly over the surface of a sphere of radius R equal to the Pb–H bond length, the equilibrium bond length $R_e$ can be calculated analytically in the limit as $Z_2$e tends to infinity. In the series of tetrahedral molecules ${\mathrm{CH}}_4$,${\mathrm{SiH}}_4$,...,${\mathrm{PbH}}_4$, $R_e$ tends in fact to a finite value equal to 2.68 Å. This prediction of a finite asymptotic bond length is then confronted with the experimental facts not only for the series ${\mathrm{CH}}_4$,${\mathrm{SiH}}_4$,...,${\mathrm{PbH}}_4$ but also for tetrahedral fluorides, chlorides, and bromides, and also for octahedral molecules. The empirical results are entirely consistent with the model prediction of a finite asymptotic limit of the bond length $R_e$ as $Z_2$→∞. A linear relationship is found between $Z_2$/$R_e$ and $Z_2$.

We report complementary measurements of the ${\mathrm{He}}^{+}$ signal from the laser-assisted collision ${\mathrm{He}}^{\mathrm{*}}$($2^1$S,$2^3$S)+He(1 ${}_{}{}^1{}_{}{}^{})+$ħω → ${\mathrm{He}}^{+}$${(1\mathrm{}}^2$S)+He${(1\mathrm{}}^1$S)+e ${}_{}{}^{\mathrm{-}}{}_{}{}^{}$. A new higher-performance laser has been used in order to improve signal-counting statistics and to determine the variation in the signal as a function of laser intensity. As expected, a linear variation is obtained over a wide range of intensities. This is an important characteristic of laser-assisted processes, which reinforces the proofs already reported in a previous work [P. Pradel et al., Phys. Rev. Lett. 54, 2600 (1985)].

Based on the theory for low-energy scattering in arbitrary dimension n≥2, derived previously [Phys. Rev. A 30, 1279 (1984)], an analytic expansion is obtained for the two-dimensional charged scattering length around its neutral counterpart, taking into account explicitly the finite extent of the charge.

A pulsed electron-nuclear coherence-transfer scheme is presented which allows the indirect observation of sublevel splittings by a Fourier-transform technique. The sensitivity of this method is larger than that of conventional techniques and exceeds the resolution of standard pulse techniques. The method is demonstrated for an electron-proton coupled system.

It is demonstrated that three different coherence phenomena, namely Rabi oscillations, the Bloch-Siegert shift, and spinor behavior, appear simultaneously in pulsed electron-nuclear double-resonance (ENDOR) experiments. New pulse sequences for the separation of these different effects are proposed.

By the example of single-photon ionization, it is shown that laser noise can induce major fluctuations of physical observables in strong-field laser-atom interactions.

A closed form two-photon core excitation transition moment for Rydberg states is derived using the isolated-core excitation model and two-channel multichannel quantum-defect theory to represent the intermediate-state wave functions.