We discuss the macroscopic behavior of an isotropic liquid containing aggregates with a handedness. We present a reversible dynamic cross-coupling between vorticity gradients and the induced orientational order parameter and suggest a simple experiment to observe the predicted effect. The equations presented are expected to be applicable not only, for example, for solutions of tubules with a handedness, but also in the isotropic phase above a cholesteric-isotropic liquid-crystal phase transition.

We consider the steady-state rheology of aggregating colloidal suspensions, where cluster size is limited by the imposed shear. Brittle versus work-hardening behavior of the clusters is distinguished. For brittle clusters at large shear rates we predict a scaling law for their size and corresponding viscosity increment, Δη∼γ̇ ${}_{}{}^{\mathrm{-}\left(3\mathrm{}\mathrm{-}\mathit{D}\right)/3\mathrm{}}{}_{}{}^{}$, where D is their fractal dimension. At low shear rates the system will gel due to cluster interpenetration and we discuss a crossover from brittle to work-hardening behavior at large length scales, and the corresponding yield stress. Above this yield stress we find a power-law creep regime with viscosity η∼${\mathrm{\sigma }}^{\mathrm{-}2/3}$. The predictions are compared with experimental results.

A self-consistent variational theory for obtaining the size of a polyelectrolyte chain, R, for arbitrary values of the experimentally controllable parameters characterizing a dilute polyelectrolyte solution is derived using the Edwards model for the chain. In appropriate limits the theory reproduces the scaling behavior in a good solvent, a Θ solvent, and a poor solvent. In particular, we show that, if the solvent is sufficiently poor, the size of the polyelectrolyte chain changes abruptly from a swollen state (R∼${\mathit{bN}}^{3/5}$, N is the number of monomers, b is the monomer size) to a globule state (R∼${\mathit{bN}}^{1/3}$) or from a rodlike configuration (R∼Na) to a globule depending on the limiting values of the salt concentration.

We study the multifractal properties of the set of growth probabilities {${\mathit{p}}_{\mathit{i}}$} for three-dimensional (3D) off-lattice diffusion-limited aggregation (DLA) in two distinct ways: (i) from the histogram of the ${\mathit{p}}_{\mathit{i}}$ and (ii) by Legendre transform of the moments of the distribution of ${\mathit{p}}_{\mathit{i}}$. We calculate the {${\mathit{p}}_{\mathit{i}}$} for 50 off-lattice clusters with cluster masses up to 15 000. We discover that for 3D DLA, in contrast to 2D DLA, there appears to be no phase transition in the multifractal spectrum. We interpret this difference in terms of the topological differences between two and three dimensions.

An approach to study correlated percolation in lattice models of microemulsions is presented. Mean-field-like equations for the percolation locus for each of the molecular species are obtained, whose only input are the structure functions of the microemulsion model. Using a spin-1 Hamiltonian considered by Gompper and Schick [Phys. Rev. B 41, 9148 (1990)] as a model for microemulsions, we find that the water-percolation threshold increases as the surfactant becomes more lipophilic. This is in qualitative agreement with the behavior found in real microemulsions as salt is added to the system.

The detailed x-ray-energy response of silicon-surface-barrier (SSB) semiconductor detectors is investigated using synchrotron radiation from a 2.5-GeV positron storage ring. These data are found to be contrary to existing theoretical predictions for the response based on (i) the silicon-depletion-layer thickness (the commonly held belief described in textbooks), and (ii) the silicon-wafer thickness (a recent proposal). This finding affects not only previously published conclusions on analyzed plasma-electron temperatures using these existing SSB theories, but also the resultant discussions on plasma behavior reported from various plasma devices. Also, this information is of importance for ongoing and future analyses of SSB data so as to avoid making further misinterpretations from the analyzed results. A possible physical interpretation for these unexpected SSB response data is discussed using thermal charge-diffusion effects in the SSB substrate. These discussions provide the physics bases to solve this unexpected problem for the actual SSB response; that is, where the actual SSB-sensitive layer is, and what the physical mechanism for this SSB response is.

We show that multiple dipole scattering of zero-point radiation gives rise to the nonadditive contributions to the van der Waals dispersion interaction, and use the Ewald-Oseen extinction theorem to justify the Lifshitz theory of macroscopic (Casimir) effects of intermolecular van der Waals forces in the limit of continuous media. We derive the interaction energy between an atom and a dielectric medium of identical atoms and obtain, using standard ‘‘cavity-QED’’ methods, results identical to those of the source theory of Schwinger, DeRaad, and Milton [Ann. Phys. (N.Y.) 115, 1 (1978)]. Following Schwinger, DeRaad, and Milton, we apply the results to estimate the latent heat of liquid helium. We argue that the macroscopic theory does not unambiguously justify the conclusion that the dispersion interaction makes a significant contribution to the latent heat and surface tension. Simpler and well-established microscopic models, without the divergences incurred in the macroscopic theory, are invoked to support this conclusion.

A model of dielectric microspheres, sharing a single dipole-moment oscillation frequency but with variable volume, exhibits an analog of the Casimir effect: a ‘‘differentiating pressure’’ that segregates microspheres of similar size so that localized regions of space develop relatively high matter concentration.

We present computational results of quantum-mechanical sequential measurements of a single dynamical variable (position) in a barrier penetration system. Our model is based on a well-rounded two-minima potential with a particle initially located on one side of the barrier. First we allow the particle wave function to propagate without further disturbance and calculate its barrier penetration time, then we perform measurements of the particle’s position and contrast the barrier penetration time T with the results for the undisturbed system. The time-dependent Schrödinger equation for the problem was solved using fast-Fourier-transform techniques. The barrier penetration time was found to depend on (1) the type of measurement made, (2) the strength of the interaction of the system with the meter, (3) the rate at which the measurements were performed, and (4) the precision of the meter (which in our model is related to the width of the meter’s wave function). We find no evidence in support of the Zeno effect. However, by using a caricature of quantum mechanics we can obtain results similar to the Zeno effect.

A formalism that allows the formulation of quantum mechanics in terms of non-negative smoothed Wigner functions, in a simple and straightforward way, is developed. It contains the formulation of quantum mechanics in terms of Husimi distributions as a special case.

It is shown that application of the time-dependent variational principle to trial wave functions of a particular form results in a description of the quantum system as a classical system consisting of two mutually interacting parts: the ordinary classical analog of the quantum system and a (generally finite) number of additional degrees of freedom. This holds out the prospect of simulating quantum dynamics by coupling the corresponding classical system to additional degrees of freedom, and it is pointed out that such calculations have, in effect, already been performed. Since the trial wave functions that qualify for this treatment may be arbitrarily accurate, there is no limitation to the accuracy of the resulting classical description. In a particular case, the canonical coordinates and momenta for all degrees of freedom of the overall classical system are identified and investigated. In general, certain parameters appearing in the trial wave functions treated in this work may become redundant at certain times, leading to singularities in the Hamiltonian equations of motion. It is shown, however, that in certain such cases, a classical formalism for the quantum dynamics remains valid if the Hamiltonian function is suitably modified. Calculations applying the present Hamiltonian formalism are carried out that demonstrate that it has better convergence properties than an alternative, nonvariational, Hamiltonian technique suggested by previous work. These numerical studies also suggest that the observed spreading of wave packets and development of complicated structure in wave functions may be interpreted classically in terms of energy transfer among the various degrees of freedom in the overall classical system.

Extending the results obtained in previous papers, an asymptotic analysis is applied to the problem of the penetration of a square potential barrier; it is shown that also in the classically forbidden case a velocity can be attributed to the particle, analogous to the usual group velocity and determining the traversal time.

We present a multichannel extension of our method of determining quantum defects which uses a smooth K matrix which is free of poles throughout the energy spectrum. This method uses alternative boundary conditions for the wave function which remove the poles in the usual negative-energy Green’s function and yields a K matrix from which a smooth quantum-defect curve can be determined. Application of the bound-state boundary condition to this curve locates the bound states for an entire Rydberg series. The boundary conditions are applied in the closed channels via reduction of the K matrix prior to calculation of the quantum-defect curve, and a projection operator is used to enforce orthogonality between the basis functions and the target states. Results are presented for a multichannel calculation of the quantum defects of He i.

Tables of radiative transition rates (A) are provided for allowed singlet and triplet transitions between Sr states below n≃11. These are obtained from a combination of R-matrix, multichannel-quantum-defect-theory (MQDT), and modified Coulomb-approximation calculations, plus branching-ratio measurements. Measurements of some spin-changing branchings and of the 4 ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_{2–}$5 ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ quadrupole transition rate are also reported. Lifetime and A-value measurements from the literature are included in the tables and compared to the calculations. These and the present measurements provide the most comprehensive test to date of calculated transition probabilities for divalent atoms. The MQDT calculation achieves 0–20 % agreement with experiment in the great majority of cases tested.

We have calculated separation-energy spectra following the removal of the xenon 5s valence electron either by a photon [(γ,e) reaction] or by a fast electron [(e,2e) reaction]. Relative line intensities in the (e,2e) spectrum are equal to the corresponding spectroscopic factors being determined as the single-hole Green’s-function pole strength. The Green’s function accounts for virtual two-hole–one-electron excitations of 5${\mathit{p}}^4$nl(l=d,s) type. Spin-orbit interaction is taken into account by constructing 5${\mathit{p}}^4$nl ${\mathrm{J}}^{\mathrm{\pi }}$=1/$2^{+}$ eigenvectors from different 5${\mathit{p}}^4$(${\mathit{L}}_1$${\mathit{S}}_1$)nl LS Hartree-Fock states of which only the 5${\mathit{p}}^4$${(}^1$D)nd ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$ states are allowed to interact directly with the one-hole 5${\mathit{s}}^1$5${\mathit{p}}^6$ ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$ state. Relative line intensities in the (γ,e) spectrum are influenced by the atomic ground-state correlations, which change most significantly the intensity of the main line and the continuous spectrum. Results of the calculation are discussed in connection with the difference between the experimental (γ,e) and (e,2e) spectra.

Electrons ejected in collisions with neutral hydrogen and helium projectiles (200 keV/u) into the forward direction are measured in coincidence with the charge-state-analyzed outgoing projectile (${\mathrm{H}}^0$, ${\mathrm{H}}^{+}$; ${\mathrm{He}}^0$, ${\mathrm{He}}^{+}$, ${\mathrm{He}}^{2+}$). All electron spectra, including those recorded in coincidence with ${\mathrm{H}}^0$ and ${\mathrm{He}}^0$ atoms, where the long-range Coulomb field is screened, show a cusplike structure. The data are compared with available theories for electron capture to the continuum.

The total (elastic plus inelastic) cross sections for positron scattering from all the rare gases are reported at intermediate and high energies (20–1000 eV), where experimental data are available for comparison except for the case of radon gas. A complex-optical-potential [${\mathit{V}}_{\mathrm{opt}}$(r)] approach is employed in which the real part (static plus polarization terms) is calculated from Hartree-Fock or Dirac-Hartree-Fock target wave functions. The imaginary part of the optical potential, i.e., the absorption potential [${\mathit{V}}_{\mathrm{abs}}^{+}$(r)], is derived for each gas semiempirically from the corresponding electron absorption potential [${\mathit{V}}_{\mathrm{abs}}^{\mathrm{-}}$(r)] in the form of ${\mathit{V}}_{\mathrm{abs}}^{+}$(r)=f(k,r)${\mathit{V}}_{\mathrm{abs}}^{\mathrm{-}}$(r), where f(k,r) depends on the incident energy (${\mathit{k}}^2$) and radial distance (r). The ${\mathit{V}}_{\mathrm{abs}}^{\mathrm{-}}$ is taken from the work of Truhlar and co-workers. The ${\mathit{V}}_{\mathrm{opt}}$(r) is treated exactly in a partial-wave analysis under the variable-phase method. With the present form of ${\mathit{V}}_{\mathrm{opt}}$(r), we are able to reproduce experimental ${\mathrm{\sigma }}_{\mathit{t}}$ values at all energies considered here. An additional feature of the present results is that the inelastic cross sections compare very well with the measured inelastic (sum of positronium formation, excitation, and ionization cross sections) values for rare gases, where such experimental data are available. The ${\mathrm{\sigma }}_{\mathit{t}}$ for the positron-Rn system are predicted.

We also discuss the correlation between scattering cross section and the atomic properties. We found that at intermediate and high energies, the positron-gas total cross section can be represented by an analytic formula ${\mathrm{\sigma }}_{\mathit{t}}$(${10}^{\mathrm{-}16}$ ${\mathrm{cm}}^2$)=21.16 √${\mathrm{\alpha }}_0$(${\mathit{a}}_0^3$)/E(eV) , where ${\mathrm{\alpha }}_0$ is the target polarizability and E is the impact energy. This simple form of the ${\mathrm{\sigma }}_{\mathit{t}}$ in terms of target polarizability works very well for highly polarizable targets such as the alkali-metal atoms and several hydrocarbon molecules. In particular, by using the above analytic formula for ${\mathrm{\sigma }}_{\mathit{t}}$, we have shown that our results for Na, K, Rb, ${\mathrm{C}}_2$${\mathrm{H}}_4$, ${\mathrm{C}}_2$${\mathrm{H}}_6$, and ${\mathrm{C}}_3$${\mathrm{H}}_6$ targets compare very well with the experimental data.

We have presented a theoretical description of J-mixing (the transfer of excitation between fine structure) cross sections of a Rydberg Cs atom induced by thermal collisions with noble-gas atoms. The theory is based on the application of impulse approximation theory and a kind of model-potential wave function. The results agree well with available recent experimental values for He, Ne, and Ar atoms. But for the heavier noble-gas atoms Kr and Xe, the theoretical cross sections are larger than the experimental ones.

Absolute doubly differential cross sections have been measured as a function of electron energy and angle of observation for electron emission in collisions of 3.5-MeV/u ${\mathrm{Fe}}^{17+}$ and ${\mathrm{Fe}}^{22+}$ ions with He and Ar gas targets under single-collision conditions. The measured electron emission cross sections are compared to theoretical and scaled cross sections based on the Born approximation. The results using intermediate-mass ions are discussed with reference to previously reported cross sections from collisions with highly charged lighter- and heavier-ion species at MeV/u projectile energies. The continuum–distorted-wave–eikonal-initial-state approximation shows good agreement with experiments except in the ‘‘binary-encounter peak’’ where the interaction between projectile electrons and target electrons could play an important role.

Inert-gas-induced collisional transfer between the first four excited states of Sr has been measured by determining excited-state densities following pulsed laser excitation of the 5 ${}_{}{}^1{}_{}{}^{}$P state. We observe 5 ${}_{}{}^1{}_{}{}^{}$P collisional transfer exclusively to the 4 ${}_{}{}^3{}_{}{}^{}$D state, with (∼800 K) rate coefficients ranging from 0.24 to 2.0×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ for the various gases. We also measure 4 ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ transfer primarily to the 4 ${}_{}{}^3{}_{}{}^{}$D state, with rate coefficients of 0.65 to 6.8×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$. The 4 ${}_{}{}^3{}_{}{}^{}$D state radiative lifetime is observed to be 2.9±0.2 μs, collisional mixing between the 4 ${}_{}{}^3{}_{}{}^{}$${\mathit{D}}_{\mathit{j}}$ fine-structure levels is essentially gas kinetic (k∼5×${10}^{\mathrm{-}10}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$), and k<${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ for 4 ${}_{}{}^3{}_{}{}^{}$D→5 ${}_{}{}^3{}_{}{}^{}$P collisional transfer.