bluuebunny/crossref_metadata_2025 huggingface dataset:
Symmetry-adapted distributed approximating functionals: Theory and application to the ro-vibrational states of H3+
Authors: Iyengar Srinivasan S. , Parker Gregory A. , Kouri Donald J. , Hoffman David K.
Published: July 2002

Symmetry-adapted Distributed Approximating Functionals (SADAFs) are derived and used to obtain a coordinate representation for the A¯diabatically Adjusting P¯rincipal Axis H¯yperspherical (APH) coordinates kinetic energy operator. The resulting expressions are tested by computing (J=0) ro-vibrational states for the well-studied H3+ molecular ion system, by iterative diagonalization of the Hamiltonian matrix using the Arnoldi procedure. The SADAF representation and APH coordinate system are found to be computationally robust and accurate.
Path integral centroid variables and the formulation of their exact real time dynamics
Authors: Jang Seogjoo , Voth Gregory A.
Published: July 2002

A formalism is presented in this paper which, for the first time, establishes the theoretical basis for the quantum time evolution of path integral centroid variables and also provides clear motivation for using these variables to study condensed phase quantum dynamics. The equilibrium centroid distribution is first shown to be a well-defined distribution function which is specific to the canonical density operator. A quantum mechanical quasi-density operator (QDO) is associated with each value of the distribution so that, upon application of the standard quantum mechanical formalism, the QDO can be used to provide a rigorous definition of both static and dynamical centroid variables. Various properties of the dynamical centroid variables are derived, including the perspective that the centroid constraint on the imaginary time paths introduces a nonstationarity in the equilibrium ensemble which, in turn, can be shown to yield information on the correlations of spontaneous fluctuations. The analytic solution for the harmonic oscillator and a numerical solution for a double well system are provided which illustrate the various aspects of the theory. The theory contained herein provides the basis for a derivation of Centroid Molecular Dynamics, as well as the systematic improvements of that theory.
Photoacoustic measurements of the vibrational relaxation of the selectively excited ozone (ν3) molecule in pure ozone and its binary mixtures with O2, N2, and noble gases
Authors: Zeninari V. , Tikhomirov B. A. , Ponomarev Yu. N. , Courtois D.
Published: July 2002

The vibrational-translational relaxation time of the ν3 state of ozone was deduced from the phase shift of the photoacoustic detector signal relative to the amplitude-modulated radiation of the CO2 laser used for excitation of O3. A special photoacoustic cell with a third electrode is used to eliminate an instrumentation phase shift caused by inertia of the microphone membrane. A three-level kinetic model of O3 is presented and used to fit the experimental and calculated phase shifts to determine the vibrational relaxation rate coefficients for pure O3 and binary mixtures of O3 with O2, N2, and noble gases He, Ne, Ar, Kr, and Xe. These results are presented and compared with experimental data obtained for O3, O3–O2, and O3–N2 by fluorescence and double resonance techniques. Experimental data for ν3 state relaxation in binary mixtures with all noble atoms have been obtained for the first time. These new results are compared with the simplest model of interaction. Thus we obtain a very good agreement for the decrease of constants with the increase of the colliding partner mass.
Polarization dependence of photochromism in an N-salicylideneaniline single crystal
Authors: Shen M. Y. , Zhao L. Z. , Goto T. , Mordzinski A.
Published: July 2002

We have grown clean N-salicylideneaniline (SA) single crystals large enough for optical measurements. The photochromism of a SA single crystal is investigated at different optical polarizations. Based on theoretical calculations, the structure configurations of the SA molecules in the colored keto form are analyzed. When an ultraviolet (UV) light is irradiated on the sample at 200 K, about 40% of the keto form molecules are found to be in the cis configuration and about 60% of them in the trans configuration. The activation energies of the single crystal are obtained in different optical polarizations, and the energy-level schemes of the photochromic reactions are established. Investigation of a single crystal can provide us with new information on the photochromism of SA, because SA molecules are regularly arranged and the environment of each molecule is the same.
Multiconfiguration linear response approach to the calculation of parity violating potentials in polyatomic molecules
Authors: Berger Robert , Quack Martin
Published: July 2002

We present a multiconfiguration linear response approach to electroweak quantum chemistry including effects from the parity violating weak nuclear force. Compared to our previous configuration interaction singles-restricted Hartree–Fock (CIS-RHF) approach [A. Bakasov, T. K. Ha, and M. Quack, J. Chem. Phys. 109, 7263 (1998)], the parity violating potential Epv is introduced by the linear response function and by solving the linear response equations in a direct iterative manner. Calculations are carried out within the multiconfiguration linear response approximation (MCLR) and its special cases, the configuration interaction approach (CI) and the random phase approximation (RPA). The systematic approach presented here, provides a systematic check and improvement upon various approximations used in the calculation of Epv. Extensive results are obtained for hydrogen peroxide at the CISDT (CI singles, doubles and triples) and CISDTQ (CI singles, doubles, triples, and quadruples) as well as at the complete active space self-consistent-field–linear response (CASSCF–LR) level. We compare to carlier results at the CIS-RHF level and confirm the order of magnitude increase in Epv reported earlier as compared to the widely used single determinant excitation-restricted Hartree–Fock (SDE-RHF) method. The new approach overcomes previous limitations for calculating Epv with biradicaloid structures such as twisted ethylene, for which numerical results are presented. This allows us to calculate Epv for a similar unsaturated system such as allene derivatives, which may be of experimental interest.
Infrared spectroscopy of CH stretching vibrations of jet-cooled alkylbenzene cations by using the “messenger” technique
Authors: Fujii Asuka , Fujimaki Eiji , Ebata Takayuki , Mikami Naohiko
Published: July 2002

The CH stretching vibrations of the benzene–Ar, toluene–Ar, and ethylbenzene–Ar clusters prepared in jet expansion were observed in both the neutral and cationic ground states by using infrared–ultraviolet double resonance and infrared photodissociation spectroscopy, respectively. Vibrational frequencies for the in-plane modes of the clusters have been found to be practically the same as those of the corresponding bare molecules. The aromatic CH stretching vibrations showed high frequency shifts upon ionization, and their infrared absorption intensities remarkably decreased. The alkyl CH stretching vibrations were also significantly changed in both frequency and intensity upon ionization. Density functional calculations well reproduced the observed infrared spectra of the neutral and cationic states, and enhancement of hyperconjugation in the cationic state was pointed out.
Direct kinetic measurements on reactions of atomic carbon, C(3P), with O2 and NO at temperatures down to 15 K
Authors: Chastaing Delphine , Le Picard Sébastien D. , Sims Ian R.
Published: July 2002

A CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus has been used to measure rate coefficients for the reactions of C (3P) with O2 and NO at temperatures from 295 K down to 15 K. C (3P) atoms were, for the first time in a kinetic study, monitored directly by vacuum ultraviolet laser-induced fluorescence. The rate coefficients for both reactions increase as the temperature is lowered, matching the expressions k(C+O2)=(4.9±0.8)×10−11 (T/298 K)−(0.32±0.08) cm3 molecule−1 s−1 and k(C+NO)=(1.5±0.4)×10−10 (T/298 K)−(0.16±0.14) cm3 molecule−1 s−1.
Effect of quantum modes in biological electron transfer reactions: A useful approximation for the harmonic model with frequency change and Duchinsky rotation
Authors: Lee EunJoo , Medvedev Emile S. , Stuchebrukhov Alexei A.
Published: July 2002

Although general theory of quantum effects in nonadiabatic electron transfer (ET) reactions based on spin-boson Hamiltonian is well known, its application to problems of biological interest is hampered by the amount of computational work needed to map the details of the real system onto the parameters of the model. In this paper we propose a new formulation of theory of quantum effects which remedies many defects of the usual approach. In the harmonic approximation an exact expression for the rate of electron transfer has long been known that includes effects of frequency change and Duchinsky rotation (mixing) of vibrational modes of donor and acceptor complexes. This expression, however, is not suitable for practical applications due to its complexity. We have developed an exceptionally accurate approximation that is capable of capturing all details of real redox systems typical for biological problems, yet simple enough to be practical. The approximation is based on the well-known Jortner expression for the quantum rate. We describe a method for calculation of the parameters of the Jortner model, average quantum frequency and average excitation number, which are usually treated as adjustable parameters, and in our case are calculated by ab initio quantum chemistry methods. The model is tested against the exact result. We also have tested another useful approximation, which is as good as the first one, however, in a limited region around maximum of ET rate. In this approximation the rate constant has the same form as the semiclassical Marcus expression, except that instead of one reorganization energy λ, it contains two λ’s. We show how these parameters can be calculated for realistic systems. Examples of such calculations are presented for a novel electron transfer between tryptophan and tyrosine, which was discovered recently in photolyase, a DNA repair enzyme, and some other biological systems.
Mo/ller–Plesset convergence issues in computational quantum chemistry
Authors: Stillinger Frank H.
Published: July 2002

The Hartree–Fock self-consistent-field approximation has provided an invaluable conceptual framework and a standard computational procedure for atomic and molecular quantum theory. Its shortcomings are significant however, and require remediation. Mo/ller–Plesset perturbation theory offers a popular correction strategy: it formally expands eigenfunctions and eigenvalues as power series in a coupling parameter λ that switches the Hamiltonian continuously between the Hartree–Fock form (λ=0) and the electron-correlating “physical” Hamiltonian (λ=1). Recent high-order Mo/ller–Plesset numerical expansions indicate that the series can either converge or diverge at λ=1 depending on the chemical system under study. The present paper suggests at least for atoms that series convergence is controlled by the position of a singularity on the negative real λ axis that arises from a collective all-electron dissociation phenomenon. Nonlinear variational calculations for the two-electron-atom ground state illustrate this proposition, and show that series convergence depends strongly on oxidation state (least favorable for anions, better for neutrals, better yet for cations).
A helium atom scattering study of the structure and phonon dynamics of the ice surface
Authors: Glebov A. , Graham A. P. , Menzel A. , Toennies J. P. , Senet P.
Published: July 2002

The structure and phonons of an ordered ice surface, prepared in situ under ultra high vacuum conditions, have been studied by high resolution helium atom scattering. The angular distributions are dominated by sharp hexagonal (1×1) diffraction peaks characteristic of a full bilayer terminated ice Ih crystal. Additional, very broad and weak, p(2.1×2.1) peaks may indicate the presence of small domains of antiphase oriented molecules. An eikonal analysis of the 1×1 peaks is compatible with either a proton disordered or a proton ordered surface with corrugations of 0.76 Å and 0.63 Å, respectively. Inelastic time-of-flight spectra reveal not only a dispersionless phonon branch reported previously at 5.9 meV, but also the first evidence for the surface Rayleigh phonons, which are reproduced well by a Born–von Kármán simulation of a full bilayer terminated ice surface using the unmodified force constants derived from neutron scattering bulk phonon measurements. Since the lattice dynamics simulations do not reproduce the dispersionless branch, it is attributed to the vibrations of single water molecules on the ice surface.
Effective action on the hyperbolic plane in a constant external field
Authors: Comtet A. , Houston P. J.
Published: July 2002

Massive scalar and spin 1/2 fields are considered on a two-dimensional space-time with constant background curvature and in the presence of an external constant field. For each case, the Euler–Heisenberg effective action and the pair creation rate and their dependence on both the curvature and external field is determined exactly.
Generalized Bergman kernels and geometric quantization
Authors: Tuynman G. M.
Published: July 2002

In geometric quantization it is well known that, if f is an observable and F a polarization on a symplectic manifold (M,ω), then the condition ‘‘Xf leaves F invariant’’ (where Xf denotes the Hamiltonian vector field associated to f ) is sufficient to guarantee that one does not have to compute the BKS kernel explicitly in order to know the corresponding quantum operator. It is shown in this paper that this condition on f can be weakened to ‘‘Xf leaves F+F° invariant’’and the corresponding quantum operator is then given implicitly by formula (4.8); in particular when F is a (positive) Kähler polarization, all observables can be quantized ‘‘directly’’ and moreover, an ‘‘explicit’’ formula for the corresponding quantum operator is derived (Theorem 5.8). Applying this to the phase space R2n one obtains a quantization prescription which ressembles the normal ordering of operators in quantum field theory. When we translate this prescription to the usual position representation of quantum mechanics, the result is (a.o) that the operator associated to a classical potential is multiplication by a function which is essentially the convolution of the potential function with a Gaussian function of width ℏ, instead of multiplication by the potential itself.
Higher-dimensional Vaidya metric with an electromagnetic field
Authors: Chatterjee S. , Bhui B. , Banerjee A.
Published: July 2002

An exterior solution is obtained for a charged radiating sphere in higher dimensions. The solution reduces to an earlier one obtained by Krori and Barua [J. Phys. A 7, 2125 (1974)] when the space-time dimension is four, and to one obtained by Iyer and Vishveshwara [J. Phys. 32, 749 (1989)] when the electromagnetic field is switched off.
Two-point quasifractional approximant in physics. Truncation error
Authors: Martín Pablo , Baker George A.
Published: July 2002

The quasifractional approximation method is developed in a systematic manner. This method uses simultaneously the power series, and at a second point, the asymptotic expansion. The usual form of the approximants is two or more rational fractions, in terms of a suitable variable, combined with auxiliary nonfractional functions. Coincidence in the singularities in the region of interest is pursued. Equal denominators in the rational fractions is required so that the solution of only linear algebraic equations is needed to determine the parameters of the approximant. An upper bound is obtained for the truncation error for a certain class of functions, which contains most of the functions for which this method has been applied so far. It is shown that quasifractional approximants can be derived as a mixed German and Latin polynomial problem in the context of Hermite–Padé approximation theory.
Semidirect product of CCR and CAR algebras and asymptotic states in quantum electrodynamics
Authors: Herdegen Andrzej
Published: July 2002

A C*-algebra containing the CCR and CAR algebras as its subalgebras and naturally described as the semidirect product of these algebras is discussed. A particular example of this structure is considered as a model for the algebra of asymptotic fields in quantum electrodynamics in which Gauss’ law is respected. The appearance in this algebra of a phase variable related to electromagnetic potential leads to the universal charge quantization. Translationally covariant representations of this algebra with energy-momentum spectrum in the future lightcone are investigated. It is shown that vacuum representations are necessarily nonregular with respect to total electromagnetic field. However, a class of translationally covariant, irreducible representations is constructed explicitly, which remain as close as possible to the vacuum, but are regular at the same time. The spectrum of energy-momentum fills the whole future lightcone, but there are no vectors with energy-momentum lying on a mass hyperboloid or in the origin.
Geometric algebra and the causal approach to multiparticle quantum mechanics
Authors: Somaroo Shyamal , Lasenby Anthony , Doran Chris
Published: July 2002

It is argued that geometric algebra, in the form of the multiparticle spacetime algebra, is well suited to the study of multiparticle quantum theory, with advantages over conventional techniques both in ease of calculation and in providing an intuitive geometric understanding of the results. This is illustrated by comparing the geometric algebra approach for a system of two spin-1/2 particles with the nonrelativistic approach of Holland [Phys. Rep. 169, 294 (1988)].
Asymptotics of Clebsch–Gordan coefficients
Authors: Reinsch Matthias W. , Morehead James J.
Published: July 2002

Asymptotic expressions for Clebsch–Gordan coefficients are derived from an exact integral representation. Both the classically allowed and forbidden regions are analyzed. Higher-order approximations are calculated. These give, for example, six digit accuracy when the quantum numbers are in the hundreds.
A class of quadratic matrix algebras arising from the quantized enveloping algebra Uq(A2n−1)
Authors: Jakobsen Hans Plesner , Zhang Hechun
Published: July 2002

A natural family of quantized matrix algebras is introduced. It includes the two best studied such. Located inside Uq(A2n−1), it consists of quadratic algebras with the same Hilbert series as polynomials in n2 variables. We discuss their general properties and investigate some members of the family in great detail with respect to associated varieties, degrees, centers, and symplectic leaves. Finally, the space of rank r matrices becomes a Poisson submanifold, and there is an associated tensor category of rank ⩽r matrices.
Steady streaming induced by a cylinder performing transverse and torsional oscillations
Authors: Panagopoulos A. A. , Psillakis Z. M. , Karahalios G. T.
Published: July 2002

The induced flow of an incompressible, unbounded fluid is considered when a circular cylinder performs small transverse and torsional oscillations. An analytic solution, valid into the inner layer provides the necessary conditions for the matching with the numerical solution at the outer layer. The results are compared with those of the single transverse oscillation. It is shown that the torsional oscillation significantly affects the depth of the boundary layer and the position of the jet axis, especially when its amplitude becomes larger.
Standing waves in deep water: Their stability and extreme form
Authors: Mercer G. N. , Roberts A. J.
Published: July 2002

A stable and accurate numerical method to calculate the motion of an interface between two fluids is used to calculate two-dimensional standing water waves. The general method calculates arbitrary time-dependent motion of an interface, possibly including interfacial tension and different density ratios between the fluids. Extremely steep standing waves are determined, significantly steeper than has been previously reported. The peak crest acceleration is used as the determining parameter rather than the wave steepness as the wave steepness is found to have a maximum short of the most extreme wave. Profiles with crest accelerations up to 98% of gravity are calculated (a sequence of raster images of this profile as it evolves in time over one period may be obtained upon application to the authors: e-mail gmercer@spam.ua.oz.au or aroberts@spam.ua.oz.au), and the shape of these extreme standing wave profiles are discussed. The stability of the standing waves is examined and growth rates of the unstable modes are calculated. It is found that all but very steep standing waves are generally stable to harmonic perturbations. However, standing waves are typically unstable to subharmonic perturbations via a sideband-type instability.
Hydrodynamic stability of a fluid layer flowing down a rotating inclined plane
Authors: Dávalos-Orozco L. A. , Ruiz-Chavarría G.
Published: July 2002

The linear stability of a fluid layer flowing down a rotating inclined plane is investigated. The analysis leads to a system of two coupled ordinary differential equations that generalizes the well-known Orr–Sommerfeld equation. These coupled equations are solved by means of two approximations: the small wave-number approximation and the small Reynolds number approximation. For the small wave-number approximation, it is shown that the Coriolis force not only may decrease the growth rate of the instability, but it may stabilize the flow for all angles of propagation of the perturbation. For the small Reynolds and Taylor numbers and small angle of inclination, it is shown that an increase in Taylor number may destabilize the fluid layer.
Kinetic effects of Alfvén wave nonlinearity. I. Ponderomotive density fluctuations
Authors: Spangler Steven R.
Published: July 2002

The Vlasov theory is used to study kinetic corrections to fluid descriptions of Alfvén wave nonlinearity. The method is to obtain an expression for the second-order perturbed distribution function produced by a nonlinear Alfvén wave. From this distribution function a kinetically correct expression is obtained for δn, the plasma density perturbation associated with an envelope-modulated Alfvén wave. This kinetic theory result differs substantially from the fluid expression when the plasma β≳1, and the electron and ion temperatures are approximately equal. This result is of interest because density fluctuations are an observationally accessible indicator of wave nonlinearity in solar system Alfvén waves. It also will assist in the determination of properties of Alfvén waves in the interstellar medium. Finally, this analysis also yields a kinetically correct expression for u, the magnetic field-aligned component of the plasma fluid velocity. For parallel-propagating wave packets, this field-aligned flow is a major or even predominant contributor to the wave nonlinearity. Therefore these results provide a starting point for a general discussion of kinetic effects on Alfvén wave nonlinearity.
Nonlinear features of stimulated Brillouin and Raman scattering
Authors: Estabrook Kent , Kruer W. L. , Haines M. G.
Published: July 2002

Kinetic simulations illustrate some important nonlinear features of Raman and Brillouin backscattering. Steepening of the Brillouin-generated ion wave is observed and compared to theory. Examples of the rich competition between the Raman and Brillouin instabilities are discussed.
Observation of trapped particle modes in a tandem mirror
Authors: Gerver M. J. , Golovato S. N. , Irby J. H. , Kesner J. , Casey J. A. , Guss W. C. , Horne S. F. , Lane B. G. , Machuzak J. S. , Post R. S. , Sevillano E. , Zielinski J.
Published: July 2002

An instability with azimuthal mode number m≥3 localized to an axisymmetric end cell of the Tara tandem mirror [Nucl. Fusion 22, 549 (1982)] has been observed, most prominently during strong ion cyclotron resonance heating in the end cell. The instability, which causes enhanced radial losses, becomes either more stable or flutelike when the connection (passing fraction) between the central cell and end cell is increased, depending on whether sufficient stabilization is provided in the central cell. The beta is sufficiently low to rule out the possibility of magnetohydrodynamic ballooning modes. Based on the plasma parameters, the instability appears to be a collisionless curvature-driven trapped particle mode that has been predicted to be unstable in linked minimum- and maximum-B mirror devices.
Chaos in driven Alfvén systems
Authors: Hada T. , Kennel C. F. , Buti B. , Mjo/lhus E.
Published: July 2002

The chaos in a one-dimensional system, which would be nonlinear stationary Alfvén waves in the absence of an external driver, is characterized. The evolution equations are numerically integrated for the transverse wave magnetic field amplitude and phase using the derivative nonlinear Schrödinger equation (DNLS), including resistive wave damping and a long-wavelength monochromatic, circularly polarized driver. A Poincaré map analysis shows that, for the nondissipative (Hamiltonian) case, the solutions near the phase space (soliton) separatrices of this system become chaotic as the driver amplitude increases, and ‘‘strong’’ chaos appears when the driver amplitude is large. The dissipative system exhibits a wealth of dynamical behavior, including quasiperiodic orbits, period-doubling bifurcations leading to chaos, sudden transitions to chaos, and several types of strange attractors.
Simulation of the collapse and dissipation of Langmuir wave packets
Authors: Newman D. L. , Winglee R. M. , Robinson P. A. , Glanz J. , Goldman M. V.
Published: July 2002

The collapse of isolated Langmuir wave packets is studied numerically in two dimensions using both particle-in-cell (PIC) simulations and by integrating the Zakharov partial differential equations (PDE’s). The initial state consists of a localized Langmuir wave packet in an ion background that either is uniform or has a profile representative of the density wells in which wave packets form during strong plasma turbulence. Collapse thresholds are determined numerically and compared to analytical estimates. A model in which Langmuir damping is significantly stronger than Landau damping is constructed which, when included in the PDE simulations, yields good agreement with the collapse dynamics observed in PIC simulations for wave packets with initial wave energy densities small compared to the thermal level. For more intense initial Langmuir fields, collapse is arrested in PIC simulations at lower field strengths than in PDE simulations. Neither nonlinear saturation of the density perturbation nor fluid electron nonlinearities can account for the difference between simulation methods in this regime. However, at these wave levels inhomogeneous electron heating and coherent jets of transit-time accelerated electrons in phase space are observed, resulting in further enhancement of wave damping and the consequent reduction of fields in the PIC simulations.
The theory and simulation of relativistic electron beam transport in the ion-focused regime
Authors: Swanekamp Stephen B. , Holloway James Paul , Kammash Terry , Gilgenbach Ronald M.
Published: July 2002

Several recent experiments involving relativistic electron beam (REB) transport in plasma channels show two density regimes for efficient transport; a low-density regime known as the ion-focused regime (IFR) and a high-pressure regime. The results obtained in this paper use three separate models to explain the dependency of REB transport efficiency on the plasma density in the IFR. Conditions for efficient beam transport are determined by examining equilibrium solutions of the Vlasov–Maxwell equations under conditions relevant to IFR transport. The dynamic force balance required for efficient IFR transport is studied using the particle-in-cell (PIC) method. These simulations provide new insight into the transient beam front physics as well as the dynamic approach to IFR equilibrium. Nonlinear solutions to the beam envelope are constructed to explain oscillations in the beam envelope observed in the PIC simulations but not contained in the Vlasov equilibrium analysis. A test particle analysis is also developed as a method to visualize equilibrium solutions of the Vlasov equation. This not only provides further insight into the transport mechanism but also illustrates the connections between the three theories used to describe IFR transport. Separately these models provide valuable information about transverse beam confinement; together they provide a clear physical understanding of REB transport in the IFR.
Direct measurement of tube wall effect on the Stokes force
Authors: Ambari A. , Gauthier-Manuel B. , Guyon E.
Published: July 2002

Using an original apparatus, an accurate measurement of the correction factor of the Stokes force is given for a sphere moving along the axis of a cylindrical tube.
Numerical simulation of electromagnetic turbulence in tokamaks
Authors: Waltz R. E.
Published: July 2002

Nonlinear two- and three-fluid equations are written for the time evolution of the perturbed electrostatic potential, densities, vector potential, and parallel ion motion of collisional and trapped electron plasmas in tokamak geometry. The nonlinear terms arise from the Ẽ×B0 convection (d̃/dt=∂/∂t+ṽE ⋅ ∇⊥) and magnetic flutter [∇̃∥=∇∥+(B⊥/B0) ⋅ ∇⊥]. Simplified two-dimensional (k⊥) mode coupling simulations with a fixed average parallel wavenumber (k∥=1/Rq) and curvature drift [ωg=(Ln/R)ω* ] characteristic of outward ballooning are performed. Homogeneous stationary turbulent states of the dissipative drift and interchange modes from 0≤β<βcrit for both the collisional and trapped electron plasmas are obtained. Transport coefficients associated with E×B and magnetic motions are calculated. The problem of simulating plasmas with high viscous Reynolds number is treated with an absorbing mantle at the largest wavenumbers. The results are summarized by comparison to simple mixing length rules: ñ/n0∼1/k⊥Ln, B̃/B0 ∼(β/2) ⋅ q ⋅ ñ/n0, DE∼γ/k2⊥.
Difficulties with three-dimensional weak solutions for inviscid incompressible flow
Authors: Saffman P. G. , Meiron D. I.
Published: July 2002

The representation of an inviscid three-dimensional incompressible flow by vortex singularities is considered and shown to lead to dynamical inconsistencies.
Interchange, rotational, and ballooning stability of long-thin axisymmetric systems with finite-orbit effects
Authors: Cohen Bruce I. , Freis Robert P. , Newcomb William A.
Published: July 2002

The stability of axisymmetric tandem mirror plasmas with respect to interchange, rotational, and ballooning modes is investigated in the paraxial approximation. The stabilizing effects of finite orbits, rigid energetic fast-drifting electrons, nearby conducting walls, and line-tying by a cold plasma halo are incorporated. Numerical calculations are performed to construct equilibria with finite plasma pressure and to determine linear stability by integrating a two-dimensional, initial-value equation. These numerical calculations support and extend analytical results. Analytical and numerical stability criteria are obtained.
Theory of hot particle stability
Authors: Berk H. L. , Wong H. V. , Tsang K. T.
Published: July 2002

The investigation of stabilization of hot particle drift reversed systems to low frequency modes has been extended to arbitrary hot beta βH, for systems that have unfavorable field-line curvature. Steep profile equilibria are considered where the thickness of the pressure drop Δ, is less than plasma radius rp. The analysis describes layer modes which have mΔ/rp <1, where m is the mode number, and radial structure larger than Δ. Stabilization is classified as either being ‘‘robust,’’ where all excitations are positive energy, or ‘‘fragile,’’ where stability criteria exist to magnetohydrodynamic (MHD)-like and drift-compressional instabilities, but positive and negative energy waves are present (with the possibility that negative energy waves are destabilized by dissipative mechanisms). It is shown that in making a continuous transition from the fragile stability regime to the robust stability regime one must go through an unstable region. To bridge the unstable band in a physical manner one must either produce robust stability conditions very rapidly, or use transient stability techniques such as ponderomotive forces or transient minimum-B coils. The positive energy stabilization terms of the layer mode from wall stabilization terms and finite Larmor radius terms are explicitly exhibited.

It is shown the robust stability can even be achieved with only wall stabilization for all possible m values of the layer modes if βH > (2)/(3) . When robust stability conditions are fulfilled, the hot particles will have their bounce frequency less than their grad-B drift frequency. This allows for a low bounce frequency expansion to describe the axial dependence of the magnetic compressional response. Such as expansion provides for another negative energy source in the theory, with the system then being susceptible to the drift compressional instability if dβH/dr >dβw/dr, where βw is the beta of the background plasma. If robust stabilization conditions are not fulfilled, the regions of fragile stability are extremely small if the MHD-like modes, the diamagnetic compressional and drift-compressional modes are to be simultaneously avoided.
Pulse interactions in an unstable dissipative-dispersive nonlinear system
Authors: Kawahara Takuji , Toh Sadayoshi
Published: July 2002

An attempt is made to understand several features of the wave evolutions in an unstable dissipative-dispersive nonlinear system in terms of the interactions of localized solitonlike pulses. It is found that the wave evolutions can be qualitatively well described by weak interactions of pulses, each of which is the steady solution to the original evolution equation. The oscillatory structure of a tail of the pulse for weakly dispersive cases is responsible for the existence of bound states of pulses, which explains the numerical result that the interpulse distances in the initial value problem take certain fixed values or values in the definite regions. In cases of monotone tails for strongly dispersive cases, the effects of pulse interactions become repulsive, which explains the result that the pulses asymptotically tend to be arranged periodically, adjusting to the periodic boundary conditions in the numerical simulation.
On the structure of a two-dimensional wake behind a pair of flat plates
Authors: Higuchi Hiroshi , Lewalle Jacques , Crane Paul
Published: July 2002

Unsteady and asymmetric vortex shedding was investigated experimentally in the wake of two flat plates placed side by side normal to the flow. The experiment was conducted in water at Re=1500 based on an individual plate width. The spacing between the plates was varied from one plate width to two plate widths. For a small spacing between the plates, the deflection of the jet passing through the gap resulted in a larger wake with mostly symmetric vortex shedding on one side and a smaller wake with asymmetric shedding on the other. The intermediate wake for the small plate spacing resembled that of a single bluff body, whereas a more intermittent structure was observed at the wider spacing. The velocity time traces were obtained by laser Doppler velocimetry (LDV) at several locations in the wake. The Fourier spectra of the velocity data at certain positions indicated the presence of more than one dominating frequency. Wavelet analysis mapped the intermittent near-periodic structures, and quantified their mean energy spectrum in relation to the ensemble mean. These results are interpreted by comparison with flow visualization data.
Lagrangian chaos, Eulerian chaos, and mixing enhancement in converging–diverging channel flows
Authors: Amon Cristina H. , Guzmán Amador M. , Morel Benoit
Published: July 2002

A study of Lagrangian chaos, Eulerian chaos, and mixing enhancement in converging–diverging channel flows, using spectral element direct numerical simulations, is presented. The time-dependent, incompressible Navier–Stokes and continuity equations are solved for laminar, transitional, and chaotic flow regimes for 100≤Re≤850. Classical fluid dynamics representations and dynamical system techniques characterize Eulerian flows, whereas Lagrangian trajectories and finite-time Lagrangian Lyapunov exponents identify Lagrangian chaotic flow regimes and quantify mixing enhancement. Classical representations demonstrate that the flow evolution to an aperiodic chaotic regime occurs through a sequence of instabilities, leading to three successive supercritical Hopf bifurcations. Poincaré sections and Eulerian Lyapunov exponent evaluations verify the first Hopf bifurcation at 125<Re<150 and the onset of Eulerian chaos at Re≊550. Lagrangian trajectories and finite-time Lagrangian Lyapunov exponents reveal the onset of Lagrangian chaos, its relation with the appearance of the first Hopf bifurcation, the interplay between Lagrangian and Eulerian chaos, and the coexistence of Lagrangian chaotic flows with Eulerian nonchaotic velocity fields. Last, Lagrangian and Eulerian Lyapunov exponents are used to demonstrate that the onset of Eulerian chaos coincides with the spreading of a strong Lagrangian chaotic regime from the vortex region to the whole fluid domain.
Statistics of turbulence in a generalized random-force-driven Burgers equation
Authors: Zikanov Oleg , Thess Andre , Grauer Rainer
Published: July 2002

The statistics of solutions to a family of one-dimensional random-force-driven advection-diffusion equations is studied using high resolution numerical simulations. The equation differs from the usual Burgers equation by the non-local form of the nonlinear interaction term mimicking the non-locality of the Navier–Stokes equation. It is shown that under an appropriate choice of random forcing the statistical properties of the solution (energy spectrum and scaling exponents of structure functions) coincide with those of Kolmogorov turbulence. Also, a generalization is proposed which allows intermittency effects to be modeled.
Inertial effects on contact line instability in the coating of a dry inclined plate
Authors: López P. G. , Miksis M. J. , Bankoff S. G.
Published: July 2002

It has been observed that when a thin liquid film coats an initially dry inclined plane, a spanwise instability occurs at the leading edge. Here we develop a model for the evolution of this coating film which includes inertia, gravity, surface tension and the contact angle at the leading edge of the film. A Kármán–Pohlhausen method is used to include inertia. We determine steady state profiles of the film and investigate their stability. The predictions of the model are compared to some recent experiments and we find good agreement. This theory gives improvement over a lubrication theory in experiments where Reynolds numbers are significantly larger than one.
Vortex rings from cylinders with inclined exits
Authors: Webster D. R. , Longmire E. K.
Published: July 2002

A typical experimental vortex generator was perturbed by inclining the exit orifice. Instantaneous velocity fields were measured with particle image velocimetry at a Reynolds number, Γ0/ν, of 2800, which falls in the laminar regime for the axisymmetric case. Despite the nearly uniform velocity of the axisymmetric piston, the velocity exiting the cylinder is spatially and temporally non-uniform. Specifically, the exit velocity and the entrainment are larger on the short cylinder side. This fluid motion leads to an initial vortex roll-up with maximum and minimum circulation at the shortest and longest cylinder locations, respectively. A highly complex vortex structure forms, consisting of a primary vortex ring with varying circulation and branched vortex tubes that initially extend from the primary ring upstream toward the cylinder. The variation of the circulation in the primary ring and the strength of the branched vortex tubes increase with incline angle. The branched vortex tubes induce a strong cross-stream sweep of fluid toward the long cylinder side. The branched tubes convect across the cylinder exit with the sweep, break free of the cylinder, and pass through the primary ring. Beyond this time, the vortex structure consists of two closed-loop branches connected on the short cylinder side. As the flow progresses, the center of momentum moves toward the short cylinder side. As the cylinder incline angle is increased, the migration away from the centerline increases, and the flow becomes increasingly disorganized. The propagation speed and penetration distance are reduced because of the loss of coherent circulation. Qualitatively similar velocity fields and flow visualization photographs are presented for a larger (nominally turbulent) Reynolds number of 23000.
Shielding of a slowly moving test charge in dusty plasmas
Authors: Shukla P. K.
Published: July 2002

The far-field potential of a slowly moving test charge in dusty plasmas is calculated accounting for the dust grain charge fluctuations. It is found that the latter cause a damping, which in turn gives rise to a dipole-like far-field potential. The presence of the dipole-like potential is attributed to the dust grain charge perturbations caused by the oscillating electron and ion currents induced by the motion of a test charge.
Squeezed state of high-current electron beam
Authors: Ignatov A. M. , Tarakanov V. P.
Published: July 2002

The results of the computer simulation of an electron beam propagating serially through two coaxial tubes with different radii are presented. It is shown that the virtual cathode in this system may be located in one of two positions depending on the injection current, variation of which yields fast movements of the potential barrier. Under certain conditions, a part of the beam may be in its squeezed state, forming, therefore, a cloud of a dense warm plasma. The qualitative analytical theory based on the consideration of the energy and momentum balance is also discussed.
Single-mode and multimode Rayleigh–Taylor experiments on Nova
Authors: Remington B. A. , Weber S. V. , Marinak M. M. , Haan S. W. , Kilkenny J. D. , Wallace R. J. , Dimonte G.
Published: July 2002

Rayleigh–Taylor (RT) experiments have been conducted with planar CH(Br) foils accelerated by x-ray ablation from a shaped, low adiabat drive. The surface perturbations investigated consisted of single-mode, two-mode, and eight-mode sinusoids. The perturbation evolution begins during the shock transit phase, when perturbations show gradual growth due to Richtmyer–Meshkov-like dynamics. After shock breakout, the compressed foils accelerate and perturbation growth continues due to the Rayleigh–Taylor instability. Detailed comparisons with simulations indicate that in the linear Rayleigh–Taylor regime, the single-mode perturbations grow exponentially in time. In the nonlinear regime, the growth slows and the perturbation shape changes from sinusoidal to ‘‘bubble and spike’’ with the appearance of higher Fourier harmonics. In the multimode perturbations, the individual modes grow independently in the linear regime, but become coupled in the nonlinear regime. In addition to the higher harmonics of the individual modes, coupling leads to the appearance of ki±kj ‘‘beat’’ modes. This results in a redistribution of the perturbation into a broader Fourier spectrum causing a change of shape: bubbles become broader and flatter and spikes narrower, in agreement with simulations and multimode theory.
Description of turbulent transport in tokamaks by invariants
Authors: Yankov V. V. , Nycander J.
Published: July 2002

In general, turbulent transport drives a plasma toward a state of turbulent equipartition, in which Lagrangian invariants are uniformly distributed. Different invariants decay with different rates, and in tokamaks the frozen-in law of particles in the poloidal magnetic field survives longer than the corresponding law for the toroidal field, assuming that the trapped particles dominate the turbulent transport. Therefore, the plasma profiles depend on the safety factor q(r), and the condition for convection of trapped particles is that the shear dq/dr is positive. There are two ways to suppress this convection and thereby enhance confinement. The first one is to reverse the magnetic shear. The energy of typical trapped particles then increases outward instead of inward, which suppresses instabilities. The second method is to eliminate the trapped ions by poloidal rotation, and thereby create a transport barrier.
Liquid metallic hydrogen and the structure of brown dwarfs and giant planets
Authors: Hubbard W. B. , Guillot T. , Lunine J. I. , Burrows A. , Saumon D. , Marley M. S. , Freedman R. S.
Published: July 2002

Electron-degenerate, pressure-ionized hydrogen (usually referred to as metallic hydrogen) is the principal constituent of brown dwarfs, the long-sought objects which lie in the mass range between the lowest-mass stars (about eighty times the mass of Jupiter) and the giant planets. The thermodynamics and transport properties of metallic hydrogen are important for understanding the properties of these objects, which, unlike stars, continually and slowly cool from initial nondegenerate (gaseous) states. Within the last year, a brown dwarf (Gliese 229 B) has been detected and its spectrum observed and analyzed, and several examples of extrasolar giant planets have been discovered. The brown dwarf appears to have a mass of about 40 to 50 Jupiter masses and is now too cool to be fusing hydrogen or deuterium, although we predict that it will have consumed all of its primordial deuterium. This paper reviews the current understanding of the interrelationship between its interior properties and its observed spectrum, and also discusses the current status of research on the structure of giant planets, both in our solar system and elsewhere.
Evidence of plasma fluctuations and their effect on the growth of stimulated Brillouin and stimulated Raman scattering in laser plasmas
Authors: Montgomery D. S. , Afeyan B. B. , Cobble J. A. , Fernández J. C. , Wilke M. D. , Glenzer S. H. , Kirkwood R. K. , MacGowan B. J. , Moody J. D. , Lindman E. L. , Munro D. H. , Wilde B. H. , Rose H. A. , Dubois D. F. , Bezzerides B. , Vu H. X.
Published: July 2002

The reflectivity levels of stimulated Brillouin scattering (SBS) in recent large scale length laser plasma experiments is much lower than expected for conditions where the convective gain exponent is expected to be large [J. C. Fernández et al., Phys. Plasmas 4, 1849 (1997)]. Long-wavelength velocity fluctuations caused during the plasma formation process, or by parametric instabilities themselves, have been proposed as a mechanism to detune SBS in these experiments and reduce its gain [W. L. Kruer et al., Phys. Plasmas 3, 382 (1996); H. A. Rose, Phys. Plasmas 4, 437 (1997)]. Evidence of large-velocity fluctuation levels is found in the time-resolved SBS spectra from these experiments, and correlates with observed changes in the reflectivity of both SBS and stimulated Raman scattering (SRS). Evidence of fluctuations that increase with increasing plasma density is presented, and their effect on the growth of parametric instabilities is discussed.