Signal and idler waves produced by a nondegenerate parametric amplifier feature strong positive correlation between their photon numbers, or in-phase amplitudes. They feature equally strong negative correlation between their phases, or quadrature-phase amplitudes. These photon twins can produce arbitrarily squeezed states via state reduction by appropriate measurements of an idler wave. When the quadrature amplitude of an idler wave is measured, the signal wave is collapsed to a quadrature-amplitude squeezed state. When the two-quadrature amplitudes of an idler wave are measured simultaneously, the signal wave becomes a coherent state.

We have studied in the femtosecond regime the transient dynamics of dichroism (anisotropic absorption), birefringence, and frequency shift induced by an intense femtosecond pump beam in the dye malachite green in solution. Vibrational quantum beats were observed superimposed on the saturated absorption and dispersion signals and quantitatively explained in terms of impulsive-stimulated Raman scattering close to an electronic resonance. The selectivity for observation of the vibrations in the two electronic states is described for the different experimental schemes. We discuss the access to vibrational and electronic dynamics in both ground and excited electronic states and compare the possibilities to those of previous techniques.

The effects of squeezing the reservoir coupled to the atoms of a laser are compared with the effects of squeezing the electromagnetic vacuum modes entering the laser cavity. The analysis includes the semiclassical theory, a calculation of the phase diffusion rate and the laser linewidth in the rotating-wave van der Pol model of the laser, and squeezing spectra calculated from a linearized theory without adiabatic elimination of the atoms. It is demonstrated that good squeezing is achievable in the laser output if an appropriate classical field driving the atoms is added.

We introduce in lattice-gas hydrodynamics an interface between two fluids. The interface deforms locally under the impact of fluid particles. We define and measure a surface tension from Laplace’s law applied to a circular bubble. Surface tension can be varied by changing the stiffness of the interface. A Boltzmann-type calculation gives an expression of surface tension in agreement with the numerical results.

Numerical simulation of coupled amplitude equations is used to investigate the effect of the wave propagation on the one-dimensional spatial structure of nonlinear wave states in finite geometries. The work is motivated by experiments on oscillatory convection in binary fluid convection. Predictions of confined states, temporally modulated confined states, and other dynamic states are discussed and compared with experiment.

Spatially periodic fluid ‘‘vortical’’ velocity fields are utilized to model the role of microscale convection upon the sedimentation and dispersion of isolated spherical particles. In particular, generalized Taylor dispersion theory is employed to calculate the mean Stokes sedimentation velocity vector and dispersivity dyadic for a finite-size spherical Brownian particle settling in a laminar, spatially periodic fluid velocity field with zero mean flow (but nonzero ‘‘circulation’’). Surprisingly, such local cellular vortexlike motions are shown to have no effect whatsoever upon the long-time mean sedimentation velocity of the sphere, which is identical to its steady-state Stokes-law value occurring in a quiescent fluid. This conclusion is, inter alia, independent of the sphere size a relative to the spatial period l of the cellular flow (provided that a/l≪1), as well as of the ratio of the particle settling velocity to the magnitude of the cellular fluid velocity or circulation. On the other hand, local convection does affect particle dispersion relative to the mean particle velocity in these systems, consistent with recent calculations for a particular cellular velocity field (Mofatt [Rep. Prog. Phys. 46, 621 (1983)], Sagues and Horsthemke [Phys. Rev. A 34, 4136 (1986)], Rosenbluth et al. [Phys. Fluids 30, 2636 (1987)]). We obtain a general expression for the dispersion coefficient for sedimenting, finite-size spheres in the limit of low Peclét number; this general result is consistent with the specific formula derived by the latter authors for the particular cellular ‘‘Taylor’’ flow analyzed by them, applicable to the case of a nonsedimenting, point-size tracer particle.

An effective pair interionic potential for liquid lead has been found using the molecular-dynamics (MD) simulation method. The assumed form of the potential includes long-range soft repulsion as well as steep repulsive and oscillating ‘‘Friedel’’ components. An extensive simulation using 16 384 particles has been carried out in order to fit the assumed parametrized form of the pair potential to the static structure factor of liquid lead measured by neutron scattering close to the melting point. The fit covers the first three peaks in S(Q), as well as the small-Q region, including the long-wavelength limit. The use of a relatively large number of particles avoids the systematic errors typical of smaller-scale simulations and allows us to obtain a quantitatively reliable relationship between the pair potential and S(Q). The calculated diffusion coefficient is in good agreement with the experimental value. Simulation of liquid lead at 1170 K and at the corresponding density using the same pair potential also gave good agreement with the experimental data on S(Q) and the self-diffusion at that temperature. This fact indicates that the interionic interaction in lead may be independent of temperature and density within the liquid domain. The potential for liquid lead derived earlier from the fourth moment of S(Q,ω) was also tested in an MD simulation and proved to be inadequate. A revised version of this potential obtained after removing constraints has a shape similar to that reported in this paper. The self-diffusion coefficient was found to be highly sensitive to the potential’s shape.

In hot, dense, and partially ionized plasmas, both the electronic shielding and the ion-ion correlation modify the emission and absorption coefficients of the bremsstrahlung. Based on the Thomas-Fermi model and the hypernetted-chain equation, it has been shown that the emission and absorption coefficients are significantly reduced by these effects.

We show how the modified Enskog theory for single-component fluids may be extended to the case of mixtures. The extended theory uses the Enskog kinetic theory for hard-sphere mixtures and equilibrium virial coefficient data to provide predictions of the transport coefficients of real mixtures. We show that the extended theory provides reasonable predictions of the ratio η/${\eta }_0$ in the case of He-Ar and Ne-Ar mixtures, where η is the shear viscosity and ${\eta }_0$ is the shear viscosity in the low-density limit.

In this paper we discuss a variety of physical aspects of the nonlinear regime of the plasma wake-field accelerator: general nonlinear properties, thermal effects, particle trapping, and maximum acceleration. The unifying motivation for this investigation is to discover the limit on the size of the plasma waves, as the interesting characteristics of the nonlinear scheme depend strongly on amplitude. Implications for laboratory and cosmic-ray acceleration are discussed.

Beat-wave heating in an inhomogeneous laser-produced plasma is investigated by considering the beat between two standing light waves. We find that the energy absorbed in this process depends not only on intensities of the incident waves, but also on their coupling coefficient at the beat-wave resonant point. The dependence of this coefficient on the frequency ratio of light waves and scale length of the plasma are calculated.

The effect of annealed randomness caused by impurities diffusing in a polymer solution (i.e., a cloudy solvent) is analyzed exactly within the framework of the continuum Edwards model, in dimension d. It is shown that an infinite series of local P-body interactions of all orders P≥2 is generated in the cloudy solvent, whose coefficients are calculated as functions of the impurity density. The impurities can be repulsive or attractive for the chains. The present state of polymer theory (perturbation expansion, regularization, and renormalization) allows a detailed study of the effect of these interactions to all orders, as a function of dimension d, 2<d≤4. For an impurity density below a special threshold ${\rho }_c$, the polymer solution is not cloudy and is as it would be in a pure solvent. At ${\rho }_c$ the polymer chains undergo a transition toward a standard tricritical FTHETA state, and beyond that density to a dense state with phase separation. For 3<d≤4 the transition is Gaussian. The universal tricritical behavior at the transition in 2<d≤3 is given. The limiting dimension d=2 is singular and subtle and is the cornerstone of a new type of behavior for 0≤d<2.

We study a random-bias model defined by a random walk with stochastic transition probabilities modeled by a dichotomic Markov noise. Conditions under which the model can be described by a Markovian chain with internal states are given. The effective Green’s function of the problem is calculated using the resolvent-matrix method. The moments of this distribution and the non-Markovian master equation which it satisfies are analyzed. Nondiffusive behavior is found during a transient regime. The model of random bias is extended to a situation with static disorder modeled by a waiting-time density with a long-time tail. It is found that the random bias leads to a change of the coefficient in the anomalous diffusion law.

We study the roughness of aggregates that are formed by ballistic deposition with nonzero flux density of incoming particles. The flux density is controlled by a parameter 0≤p≤1. The scaling behavior of the interfacial width ξ does not depend on p and is the same as ξ found in a variety of other, related models. For short times ξ∝$t^{1/3}$ for a one-dimensional substrate and ξ∝$t^{0.22}$ for two-dimensional ones. The latter is not consistent with various theoretical predictions. Rough numerical estimates for the long-time exponent are also presented. In addition, we derive a relation between the width of the geometrical boundary of the aggregate and the width of the active region of growth. This relation, true for models in which the active zone is asymptotically correlated to the surface of the aggregate, is verified by our simulations.

The symmetry dynamics and the fluctuation dynamics for local expansion rates are investigated in the vicinity of two kinds of intermittency transition points. This is done with the aid of the characteristic function ${\lambda }_q$ and the fluctuation spectrum σ(α) describing the global characteristics of time series. In both cases they obey the scaling laws ${\lambda }_q$=${\epsilon }^{\mu }$L(q/${\epsilon }^{\nu }$) and σ(α)=${\epsilon }^{\mu +\nu }$S(α/${\epsilon }^{\mu }$), where ε is the deviation from the transition point, and L and S are the scaling functions, μ and ν being constants.

Due to roundoff, digital computer simulations of orbits on chaotic attractors will always eventually become periodic. The expected period, probability distribution of periods, and expected number of periodic orbits are investigated for the case of fractal chaotic attractors. The expected period scales with roundoff ε as ${\epsilon }^{\mathrm{-}d/2\mathrm{}}$, where d is the correlation dimension of the chaotic attractor.

The potential of Fokker-Planck equations lacking detailed balance is calculated by systematically applying a power-series-expansion approach. With respect to the expansion approach, five kinds of points in variable space, i.e., hyperbolic stable and unstable points, saddles, bifurcation singular points, regular points, and singular points of higher orders, are distinguished.

We report the results of light scattering on liquid-crystal materials near the nematic–smectic-A phase transition. Measurements were made both in the nematic and smectic-A phases. The critical exponents for the twist elastic coefficient ($K_2$) and the layer dilation elastic coefficient (B¯) were measured and appear to scale, within experimental uncertainty, as predicted by the de Gennes model. The exponents for these relatively wider nematic range materials are somewhat larger than those found in most previous light scattering studies, indicating somewhat better agreement with the theoretically predicted values for the isotropic 3D XY model, though still considerably smaller.

We study by exact enumerations a lattice model of polymers with fused loops (which also describes polymeric networks with even functional units). As the relative concentration of fused crossings of the chain (or that of the tetrafunctional units in the network) is increased, the conformations change their shapes from swollen (with self-avoiding-walk scaling properties) to compact. Earlier renormalization-group studies predicted the tricritical point associated with this transition to be in a new universality class, distinct from the Θ point. In particular, non-Gaussian behavior with ${\nu }_t$<(1/2 and ${\gamma }_t$<1 in three dimensions (3D) was predicted. We have enumerated all conformations according to their length l and number of crossings (or tetrafunctional units) I with their end-to-end distance r, on triangular (up to l=15, I=7), square (l=21, I=7), and cubic (l=15, I=5) lattices. The locations of their respective transitions are determined from the divergence of the specific-heat plots. Tricritical couplings and exponents are extracted by a D log Padé analysis. The tricritical scaling exponents we find are ${\nu }_t$≃0.52(2), ${\gamma }_t$≃1.25(20) in 2D, and ${\nu }_t$≃0.465(10), ${\gamma }_t$≃0.60(5) in 3D, in fair agreement with the renormalization-group predictions.

A system of hard spherocylinders near an impenetrable wall is studied in the low-density Onsager approximation. Using a simple local approximation for the one-particle distribution function, we show that the preferred orientation of the nematic director is parallel to the wall. The density and order-parameter profiles are calculated. The nematic main order parameter Q is enhanced near the wall even though the density is reduced. The wall-induced biaxiality P is small in the interfacial region. We find that wetting by the nematic phase should occur at the nematic-isotropic coexistence.