bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectra of Ar–CO2 from ab initio potential energy surfaces
Authors: Misquitta Alston J. , Bukowski Robert , Szalewicz Krzysztof
Published: July 2002

Potential energy surface for the interaction of Ar with CO2 has been calculated using different levels of symmetry-adapted perturbation theory (SAPT) and the supermolecular many-body perturbation theory (MBPT) and coupled-cluster methods. These potentials have been used to compute the rovibrational spectra of Ar–CO2 and the interaction virial coefficients. The best reproduction of experimental data was achieved by the SAPT potential at the level of theory similar to the second-order of MBPT. The accuracy of this potential is in fact very close to that of the recent semiempirical surface of Hutson et al. [J. Chem. Phys. 106, 9130 (1996)] which was fitted to this set of data. Somewhat surprisingly, the more advanced methods considered here performed not as well.
Reaction field treatment of charge penetration
Authors: Chipman Daniel M.
Published: July 2002

Treatment of the important electrostatic effects of solvation by means of reaction field theory is becoming common in electronic structure calculations on molecules. Most extant reaction field methods neglect or crudely approximate the often important influence of volume polarization arising from solute charge that quantum mechanically penetrates outside the cavity that nominally encloses it. This work proposes and examines a new formulation that provides an accurate simulation of volume polarization effects while being much simpler to implement and use than an exact treatment. Detailed comparisons with other related methods are also given.
Modeling proton mobility in acidic zeolite clusters: II. Room temperature tunneling effects from semiclassical rate theory
Authors: Fermann Justin T. , Auerbach Scott
Published: July 2002

We have developed a novel semiclassical transition state theory (SC-TST) for truncated parabolic barriers, based on the formulation of Hernandez and Miller [Chem. Phys. Lett. 214, 129 (1993)]. Our SC-TST rate coefficient has the form kSC-TST=kTST⋅Γ, where Γ depends on the zero point corrected barrier, ΔE0, and the barrier curvature, |ωF‡|. Our rate expression is stable to arbitrarily low temperatures, as opposed to purely harmonic SC-TST, because we identify the maximum possible semiclassical action in the reaction coordinate. For low temperatures, we derive an analytical approximation for Γ that is proportional to eβ ΔE0. We develop a theory for the tunneling crossover temperature, Tx, yielding kBTx≅ℏ|ωF‡|ΔE0/(2π ΔE0−ℏ|ωF‡|ln 2), which generalizes the harmonic theory for systems with large but finite barriers. We have calculated rate coefficients and crossover temperatures for the O(1)→O(4) jump in H–Y and D–Y zeolites, yielding Tx=368 K and 264 K, respectively. These results suggest that tunneling dominates proton transfer in H–Y up to and slightly above room temperature, and that true proton transfer barriers are being underestimated by neglecting tunneling in the interpretation of experimental mobility data.
Global qualitative study of Bianchi universes in the presence of a cosmological constant
Authors: Weber Edmond
Published: July 2002

A particular class of nonempty spatially homogeneous orthogonal cosmologies of the Bianchi classification is considered in the presence of a nonzero cosmological constant Λ, i.e., cosmologies that can be transformed into a three-dimensional autonomous dynamical system: these are the axisymmetric type II, the pseudoaxisymmetric type VI0, and the (nαα=0) types V, VIh (including III=VI−1). A qualitative method to investigate such dynamical systems as a whole is presented. The qualitative study yields for every type a set of solutions of nonzero measure and another one of zero measure becoming isotropic in an infinite cosmological time when Λ>0.
Invariants of Lagrangians and their classifications
Authors: Dȩbecki Jacek , Gancarzewicz Jacek , de León Manuel , Mikulski Wl/odzimierz
Published: July 2002

A complete classification of natural transformations of finite order of Lagrangians into energies over n-dimensional manifolds, where n≥2, is given herein. The classification of natural transformations of finite order of vector fields and Lagrangians into energies and constants of the motion is also obtained for n≥3. By using these results, a classification of Lagrangians into Poincaré–Cartan one-forms and Legendre transformations is obtained.
Space of test functions for higher-order field theories
Authors: Bollini C. G. , Oxman L. E. , Rocca M.
Published: July 2002

The fundamental space ζ is defined as the set of entire analytic functions [test functions φ(z)], which are rapidly decreasing on the real axis. The variable z corresponds to the complex energy plane. The conjugate or dual space ζ′ is the set of continuous linear functionals (distributions) on ζ. Among those distributions are the propagators, determined by the poles implied by the equations of motion and the contour of integration implied by the boundary conditions. All propagators can be represented as linear combinations of elementary (one pole) functionals. The algebra of convolution products is also determined. The Fourier transformed space ζ̃ contains test functions φ̃(x). These functions are extra-rapidly decreasing, so that the exponentially increasing solutions of higher-order equations are distributions on ζ̃.
The untruncated Marinari–Parisi superstring
Authors: Ferretti G.
Published: July 2002

It is shown that the bosonic angular degrees of freedom in the one dimensional Marinari–Parisi superstring can be integrated out exactly in the Hamiltonian formulation. The resulting quantum mechanical Hamiltonian is that of a supersymmetric Calogero system plus a four fermions interaction. This extra interaction vanishes for all physical states with fermion number 0 or 1 where supersymmetry is manifest.
Scattering matrix in external field problems
Authors: Langmann Edwin , Mickelsson Jouko
Published: July 2002

We discuss several aspects of second quantized scattering operators Ŝ for fermions in external time-dependent fields. We derive our results on a general, abstract level having in mind as a main application potentials of the Yang-Mills type and in various dimensions. We present a new and powerful method for proving the existence of Ŝ which is also applicable to other situations like external gravitational fields. We also give two complementary derivations of the change of phase of the scattering matrix under generalized gauge transformations which can be used whenever our method of proving the existence of Ŝ applies. The first is based on a causality argument, i.e., Ŝ (including phase) is determined from a time evolution, and the second exploits the geometry of certain infinite-dimensional group extensions associated with the second quantization of one-particle operators. As a special case we obtain a Hamiltonian derivation of the axial fermion-Yang-Mills anomaly and the Schwinger terms related to it via the descent equations, which is on the same footing and traces them back to a common root.
Coulomb-oscillator duality in spaces of constant curvature
Authors: Kalnins E. G. , Miller W. , Pogosyan G. S.
Published: July 2002

In this paper we construct generalizations to spheres of the well-known Levi-Civita, Kustaanheimo–Steifel, and Hurwitz regularizing transformations in Euclidean spaces of dimensions two, three, and five. The corresponding classical and quantum mechanical analogs of the Kepler–Coulomb problem on these spheres are discussed.
The quantum N-body problem
Authors: Hunziker W. , Sigal I. M.
Published: July 2002

This selective review is written as an introduction to the mathematical theory of the Schrödinger equation for N particles. Characteristic for these systems are the cluster properties of the potential in configuration space, which are expressed in a simple geometric language. The methods developed over the last 40 years to deal with this primary aspect are described by giving full proofs of a number of basic and by now classical results. The central theme is the interplay between the spectral theory of N-body Hamiltonians and the space–time and phase-space analysis of bound states and scattering states.
Null surfaces formulation in three dimensions
Authors: Forni Diego M. , Iriondo Mirta , Kozameh Carlos N.
Published: July 2002

The null surface formulation of general relativity is developed for 2+1 dimensional gravity. The geometrical meaning of the metricity condition is analyzed and two approaches to the derivation of the field equations are presented. One method makes explicit use of the conformal factor while the other only uses conformal information. The resulting set of equations contains the same geometrical meaning as the four-dimensional formulation without the technical complexities of the higher dimensional analog. A canonical family of null surfaces in this formulation, the light cone cuts of null infinity, are constructed on asymptotically flat space–times and some of their kinematical aspects are discussed. A particular example, which nevertheless contains most of the generic features, is explicitly constructed and analyzed, revealing the behavior predicted in the full theory.
Temperature Dependence of Physical–Chemical Properties of Selected Chemicals of Environmental Interest. I. Mononuclear and Polynuclear Aromatic Hydrocarbons
Authors: Shiu Wan-Ying , Ma Kuo-Ching
Published: July 2002

Physical–chemical property data, which control air–water partitioning, namely vapor pressure, aqueous solubility and Henry’s law constant over the environmentally relevant temperature range of 5–50 °C, are compiled and reviewed for the mononuclear aromatic and polynuclear aromatic hydrocarbons. Corresponding enthalpies of phase transition are also reported. As result of a critical review, selected values are given at 25 °C, and where possible equations expressing the temperature dependence are given. Twenty-one aromatic hydrocarbons are studied, with approximately 300 references.
Double-peaked character of the temperature dependence of resistance of perovskite manganites for a broadened ferromagnetic transition
Authors: Tovstolytkin A. I. , Pogorilyi A. N. , Kovtun S. M.
Published: July 2002

The behavior of a system consisting of a mixture of paramagnetic semiconducting and ferromagnetic metallic phases is examined in the framework of the percolation model. As the temperature decreases below the Curie point, the paramagnetic phase fraction is assumed to decreases according to an exponential law. The evolution of the temperature variation of the resulting resistance is considered as a function of the magnetic transition broadening. An explanation is offered for the low-temperature resistance anomaly observed experimentally in a number of perovskite manganites.
On the mechanism of the reduction of nonlinearity in the incompressible Navier–Stokes equation
Authors: Shtilman Leonid , Polifke Wolfgang
Published: July 2002

The mechanism of the reduction of nonlinearity recently observed in simulations of decaying isotropic turbulence by Kraichnan and Panda [Phys. Fluids 31, 2395 (1988)] is investigated. It is shown that although the alignment of velocity and vorticity in physical space is not the sole source of the effect, it can enhance the effect significantly. Another source of the reduction seems to be a tendency of the Lamb vector v×ω in Fourier space to align with the wave vector k. The ordering of the energy transfer is suggested to be a dynamically generic effect driving the reduction.
Collapsing solutions to the 3-D Euler equations
Authors: Pumir Alain , Siggia Eric
Published: July 2002

A three-dimensional adaptive mesh code is used to search for singularities in the incompressible Euler equations. For the initial conditions examined, the maximum vorticity eventually grows only exponentially. The small scales are quasi-two-dimensional and the vorticity has a pronounced tendency to develop sharp jumps in magnitude. The vorticity is very nearly parallel to the eigenvector of the rate-of-strain matrix whose eigenvalue is the smallest in magnitude. This eigenvalue is positive and much smaller than the others.
The universal constant for the Lagrangian structure function
Authors: Rodean Howard C.
Published: July 2002

The Langevin equation has been used for many years to model the dispersion of passive scalars in turbulent flow. It is a stochastic differential equation for the incremental change of Lagrangian particle velocity as a function of the sum of a deterministic term and a stochastic term. The stochastic term is the product of a coefficient and an incremental Wiener process. The coefficient can be written as (C0ε)1/2, where C0 is a universal constant associated with the Lagrangian structure function and ε is the mean rate of turbulent kinetic energy dissipation. There is considerable uncertainty about the value of C0. The values obtained by different investigators are reviewed. A value of C0=5.7 is calculated for the constant-stress region in the neutral boundary layer.
Experimental and computational studies of the fluid mechanics in an opposed jet mixing head
Authors: Wood Philip , Hrymak Andrew , Yeo Ronald , Johnson David , Tyagi Ashok
Published: July 2002

The flow field created by two impinging liquid jets in a cylindrical chamber is investigated using particle tracing, laser Doppler anemometry, and three-dimensional numerical simulation. The jet Reynolds number (based on the mean jet velocity and diameter) range is from 50–300. Results show that there is a threshold value of the Reynolds number beyond which the flow exhibits oscillations. Computer simulations agree well with the experimental visualizations, for both the overall observed flow pattern and a quantitative measure of the oscillations.
Asymmetric instability of a liquid jet
Authors: Yang H. Q.
Published: July 2002

The existing aerodynamic theory is not capable of predicting the phenomenon of nonaxisymmetric breakup of a liquid jet, which has long been observed in experiments. A dispersion equation that accounts for the growth of asymmetric waves is derived in this paper. It is demonstrated that there exists a critical Weber number, below which the nonaxisymmetric disturbance becomes unstable. The Weber number here is defined as the ratio of surface tension force to the inertial force. The present theory indicates the possible growth of sinuous wave and the subsequent formation of curling flat sheet from an axisymmetric jet. According to the present analysis for a high-speed jet, the drops break away from the jet surface, instead of rings as predicted by the theory based on the axisymmetric assumption.
Quantification of the inelastic interaction of unequal vortices in two-dimensional vortex dynamics
Authors: Dritschel D. G. , Waugh D. W.
Published: July 2002

The interaction of two isolated vortices having uniform vorticity is examined in detailed contour dynamics calculations, and quantified using a diagnostic that measures the coherence of the final state. The two vortices have identical vorticity, leaving two basic parameters that determine the evolution: the radius ratio and separation distance. It is found that the term ‘‘vortex merger’’ inadequately describes the general interaction that takes place. Five regimes are found: (1) elastic interaction, (2) partial straining-out, (3) complete straining-out, (4) partial merger, and (5) complete merger. Regime 5 is what used to be called ‘‘merger,’’ but occurs in less than one-quarter of the parameter space. Contrary to popular belief, inelastic vortex interactions (IVI’s) do not always lead to vortex growth. In fact, in over half of the parameter space, smaller vortices are produced. These results bring into question commonly accepted ideas about nearly inviscid two-dimensional turbulence.
Effect of surfactants on the motion of drops through circular tubes
Authors: Borhan Ali , Mao Ching-Feng
Published: July 2002

The effect of surfactants on the motion and deformation of liquid drops in Poiseuille flow through circular tubes at low Reynolds numbers is examined. Assuming no bulk transport of surfactant, the boundary integral method is used in conjunction with a convective–diffusion equation to determine the distribution of surfactant on the deformed surface of the drop. The velocity and shape of the drop as well as the extra pressure loss due to the presence of the drop are calculated. Increasing the surface Péclet number is found to produce large variations in surfactant concentration across the surface of the drop. The resulting interfacial tension gradients lead to tangential (Marangoni) stresses that oppose surface convection and retard the motion of the drop as a whole. For large Péclet numbers, Marangoni stresses immobilize the surface of the drop, leading to a significant increase in the extra pressure loss required to move the drop through the tube. The accumulation of surfactant near the trailing end of the drop partially lowers the interfacial tension on that side, thereby requiring larger deformations to satisfy the normal stress balance. At the same time, the increase in interfacial area associated with drop deformation causes an overall dilution of the surfactant, which, in turn, counteracts the effect of convective transport of surfactant at large Péclet numbers. The effects of these coupled responses are studied over a wide range of the dimensionless parameters.
Chaotic motion of a solid through ideal fluid
Authors: Aref Hassan , Jones Scott W.
Published: July 2002

Numerical evidence is presented that the motion of a solid body through incompressible, inviscid fluid, moving irrotationally and otherwise at rest, is chaotic.
Energy and enstrophy transfer in numerical simulations of two-dimensional turbulence
Authors: Maltrud Mathew E. , Vallis Geoffrey K.
Published: July 2002

Numerical simulations of statistically steady two-dimensional (2-D) turbulence are analyzed to determine the relative importance of the types of wave-vector triad interactions that transfer energy and enstrophy in the both the energy and enstrophy inertial ranges. In the enstrophy inertial range, it is found (in agreement with previous studies [J. Fluid Mech. 72, 305 (1975); Phys. Fluids A 2, 1529 (1990)]) that the important triads (i.e., those associated with the highest transfer rates) are typically very elongated. On the average, nearly all of the enstrophy transfer within these triads is directed from the intermediate to the largest wave-number mode (i.e., downscale transfer). Energy, too, is transferred downscale in this manner, but is also transferred upscale due to the interaction of the intermediate with the smallest wave-number mode of the triad, resulting in no net flux of energy in the enstrophy inertial range. Analysis of the geometry of the important triads indicates they are not of similar shapes at all scales, and that the enstrophy transferring triads generally consist of one wave vector near the scale of the energetic peak, no matter how large the other wave vectors are. In the energy inertial range, elongated triads are also important. As in the enstrophy inertial range, there is downscale transfer of energy and enstrophy due to the interaction of the intermediate with the largest wave-number mode. There is also upscale transfer of both energy and enstrophy due to a very nonlocal interaction involving the smallest wave-number modes. The result is a net upscale flux of energy and no net flux of enstrophy in the energy inertial range. Comparison of the transfer functions from the simulations with those calculated by an eddy-damped quasinormal closure show agreement in the gross functional forms, but display certain quantitative differences in integrated quantities such as total transfer into and flux past a given wave number.
Quasilinear ballooning mode saturation
Authors: Riedel K. S.
Published: July 2002

At small amplitudes, resistive ballooning modes form a quasilinear sheet current, which opposes the magnetic flux reconnection. In the ensuing Rutherford regime [Phys. Fluids 16, 1903 (1973)] the sheet current at each resonance surface decays. To remain in a quasistatic equilibrium, magnetic islands form and thereby flatten the pressure at each resonance surface. For local instabilities, a spectrum of modes are excited, each flattening the pressure gradient at its resonance surface. The resulting averaged quasilinear pressure profile has a Cantor setlike structure. Using the equivalence of harmonics, the calculation of the saturated amplitudes is reformulated as a nonlinear eigenvalue problem of an integral differential equation with the quasimode formalism.
The physics of positively biased conductors surrounded by dielectrics in contact with a plasma
Authors: Hastings Daniel E. , Chang Patrick
Published: July 2002

The physics of a positively biased conductor surrounded by dielectrics in contact with plasma is investigated. It is shown that because of the presence of secondary emission from the surrounding dielectrics the voltage of the surfaces near the conductor has three solutions. Of the three possible solutions, the high- and low-voltage solutions are stable while the intermediate voltage solution is unstable. For the stable solutions, the low-voltage solution always has very low secondary emission while the high-voltage solution has high secondary emission. The secondary current emitted from the neighboring dielectrics is collected by the conductor. When the voltage on the dielectric undergoes a transition from one bistable solution to another this will be seen as a concomitant increase in the current collected to the conductor. This theory is applied to explain the ‘‘snapover’’ effect. The snapover effect is observed on high-voltage solar arrays that involve the use of highly biased surfaces in contact with the space environment. It has been observed that when such surfaces are postively biased the current undergoes an anomalous increase at a critical voltage.
The lower-hybrid drift instability in a slab geometry
Authors: Fruchtman Amnon
Published: July 2002

The lower-hybrid drift instability is studied within a model problem with some of the features that characterize the anode plasma in the magnetic insulated diode experiment at the Weizmann Institute (Phys. Rev. A, in press). The spatial dependence of the amplitude of the linear electrostatic perturbations is calculated. First the equilibrium is determined by selecting distribution functions that depend on the constants of motion in a collisionless plasma and by imposing quasineutrality. In the particular equilibrium studied, the electric field, temperature, and drift velocities are uniform and the density decreases exponentially. The Vlasov–Poisson equations are then linearized assuming magnetized electrons and unmagnetized ions. The governing equation is a second-order ordinary differential equation for the perturbed electrostatic potential. A dispersion relation is derived and analytical solutions are written for the eigenfunctions. The growth rate of each mode is determined by the plasma parameters at its respective turning point. Since the only plasma parameter that is not uniform is the density, the growth rates of the different eigenmodes are similar when the roots of the local dispersion relation depend only weakly on the density. Since the distance between successive turning points is usually very small, it is concluded that for the chosen equilibrium the perturbations will grow uniformly across the plasma.
The bispectrum and three-wave coupling between fast magnetosonic waves and interchange modes
Authors: Intrator T. , Meassick S. , Browning J. , Majeski R. , Hershkowitz N.
Published: July 2002

The bispectrum is used to demonstrate that wave–wave coupling occurs when ponderomotive forces due to wave fields in the ion cyclotron range of frequencies are used to stabilize a magnetized plasma column against magnetohydrodynamic (MHD) interchange instabilities. The three waves that interact resonantly are an applied wave, a MHD wave, and the nonlinearly coupled sideband wave. The net ponderomotive forces contain partially canceling and augmenting contributions from each induced sideband field.
Dimensional analysis and laser-produced plasmas
Authors: Pakula Ricardo A.
Published: July 2002

A schematic overview of the heating and hydrodynamical behavior of laser-produced plasmas is provided by using an extensive set of self-similar models. The range of validity of the self-similar models is derived in conjunction with the definition of natural boundaries among them. It is proved that over these boundaries, a continuous transition for the scaling laws of all plasma variables takes place. This important result allows for the division of the parameter space of laser-produced plasmas (for example, in terms of the plasma temperature and time) into different regions where the associated self-similar regime can be understood as an intermediate-asymptotic description followed by the plasma evolution. The scaling laws derived initially by dimensional analysis have direct physical interpretation, allowing for the identification of the primary physical processes underlying the plasma behavior and affording a better understanding of the plasma evolution. Nonequilibrium states and thermal emission are allowed for in the hydrodynamic processes. This technique is applied together with simple thermodynamical models for the evaluation of an Au target irradiated by an Nd laser.
On transverse instability of large-amplitude Langmuir solitons
Authors: Hadžievski Lj. R. , Škorić M. M.
Published: July 2002

The transverse instability of a large-amplitude Langmuir soliton in a weakly magnetized plasma is examined in the framework of the generalized nonlinear Schrödinger type of equation with a nonadiabatic ion response. Making use of a numerical ‘‘shooting’’ method, the instability eigenfunctions and eigenvalues (growth rates) are calculated and depend on the magnetic field, soliton strength, and perturbation wave number. Results in small-amplitude and curl-free Zakharov equation limits are discussed.
The effect of gradient magnetic fields on the properties of the scrape-off layer in a cylindrical plasma
Authors: Ohira T. , Grossman A. , Miya K.
Published: July 2002

A boundary plasma fluid model that takes into account nonuniform magnetic fields is presented. The model is based on the approach described by LaBombard et al. [Bull. Am. Phys. Soc. 33, 2103 (1988)] but has been enhanced to consider nonuniform magnetic fields and applied to the scrape-off layer (SOL) of a cylindrical plasma. The two-dimensional code based on this model has been developed and used for studying the effect of the large changes in magnetic fields and B×■B drift on the properties of the SOL plasma, which include potential, density, electric field, and plasma particle flux. The code is validated by comparison with experimental results in PISCES using constant magnetic fields. From the numerical simulations, it is observed that particle fluxes in cylindrical SOL plasma are influenced by combined local radial and azimuthal (poloidal) gradients in applied axial magnetic fields. These local steep gradient magnetic fields in the SOL plasma can thus be an effective means to actively control plasma and impurity transport.
Three-dimensional particle simulation of heavy-ion fusion beams*
Authors: Friedman Alex , Grote David P. , Haber Irving
Published: July 2002

The beams in a heavy-ion-beam-driven inertial fusion (HIF) accelerator are collisionless, nonneutral plasmas, confined by applied magnetic and electric fields. These space-charge-dominated beams must be focused onto small (few mm) spots at the fusion target, and so preservation of a small emittance is crucial. The nonlinear beam self-fields can lead to emittance growth, and so a self-consistent field description is needed. To this end, a multidimensional particle simulation code, warp [Friedman et al., Part. Accel. 37-38, 131 (1992)], has been developed and is being used to study the transport of HIF beams. The code’s three-dimensional (3-D) package combines features of an accelerator code and a particle-in-cell plasma simulation. Novel techniques allow it to follow beams through many accelerator elements over long distances and around bends. This paper first outlines the algorithms employed in warp. A number of applications and corresponding results are then presented. These applications include studies of: beam drift-compression in a misaligned lattice of quadrupole focusing magnets; beam equilibria, and the approach to equilibrium; and the MBE-4 experiment [AIP Conference Proceedings 152 (AIP, New York, 1986), p. 145] recently concluded at Lawrence Berkeley Laboratory (LBL). Finally, 3-D simulations of bent-beam dynamics relevant to the planned Induction Linac Systems Experiments (ILSE) [Fessenden, Nucl. Instrum. Methods Plasma Res. A 278, 13 (1989)] at LBL are described. Axially cold beams are observed to exhibit little or no root-mean-square emittance growth at midpulse in transiting a (sharp) bend. Axially hot beams, in contrast, do exhibit some emittance growth.
Two-fluid magnetohydrodynamic description of the internal kink mode in tokamaks
Authors: Zakharov L. , Rogers B.
Published: July 2002

The two-fluid linear magnetohydrodynamic (MHD) theory of the internal kink mode is studied in finite β regimes relevant to recent high-temperature tokamak experiments. It is found that the scale length of the plasma motion decouples due to the Hall term from the scale length of the current layer and becomes the ‘‘ion-sound Larmor radius’’ ρs=cs/Ωci, where cs=√(Te+γiTi)/mi is the ion-sound speed (γi=5/3 for adiabatic ions), and Ωci is the ion-cyclotron frequency. The predictions of two-fluid MHD for the m=1 reconnection mode are shown to be in good quantitative agreement with analogous results of kinetic studies. An important nonlinear consequence of this relatively large scale length for the plasma motion is that the reconnection time in Kadomtsev’s model becomes τ = τ*Aa1/1/ρs∝ a1/1R√n/[(1 − q0)√Te+(5/3)Ti], which seems able to account for the fast sawtooth crash.
Reply to ‘‘Comments on ‘Ion acoustic parametric decay instability in laser-produced plasma with varying ionic charge’ [Phys. Fluids B 3, 1983 (1991)]’’
Authors: Mizuno K. , Drake R. P. , Young P. E. , Bahr R. , Seka W. , Estabrook K. G.
Published: July 2002

The authors of the comment have correctly identified an area in which our paper is neither sufficiently clear nor fully correct. Unfortunately, we do not agree with their equations or their physical arguments.
Electromagnetic instability and emission from counterpropagating Langmuir waves
Authors: Glanz James , Goldman Martin V. , Newman David L. , McKinstrie C. J.
Published: July 2002

This paper analyzes fundamental electromagnetic (em) emission, near the plasma frequency, from a pair of counterpropagating Langmuir pump waves in an externally driven plasma. The emission is a result of parametric instabilities of both Stokes (frequency-downshifted) and anti-Stokes (frequency-upshifted) em waves. A new, sixth-order dispersion relation is derived for the linearly unstable em waves. Previous treatments of this problem neglected the existence of two independent density ‘‘gratings’’ produced by the beating together of high-frequency waves. These gratings, which can be resonant ion-acoustic waves, are of comparable importance, and must be considered together in order to give the correct growth rates. The present results may have relevance to fundamental emission from laser-driven targets and to other systems, such as the radio-wave-modified ionosphere.
Tandem-mirror trapped-particle modes at arbitrary collisionality
Authors: Cohen R. H. , Nevins W. M. , Berk H. L.
Published: July 2002

Tandem-mirror trapped-particle modes are studied in a model system consisting of two connected square wells representing the solenoid and the end cells. Collisions are described by a Lorentz operator. A dispersion relation that is valid for arbitrary ν/ω (ω=wave frequency, ν=collision frequency) is derived. Four limits are investigated. When ε≡νRam/ω ≪1+pi/pe, where Ram is the mirror ratio separating electrons trapped in the anchor from those passing to the solenoid and pe and pi are the fractions of passing electrons and ions, collisions destabilize a trapped-particle mode that is stable in the collisionless limit; the growth rate is proportional to ε1/2 for ε≪1 and ε/ln ε for 1+pi/pe ≫ε≫1. When ε ≫1+pi/pe, the trapped-particle mode becomes a weakly growing drift wave with growth rate proportional to ε−1 ln ε for ν/ω≪1 and ν−1 for ν/ω≫1; additionally identified are two flute modes, one of which is unstable for some parameters, and a strongly damped high-frequency mode.
Observations of stimulated Raman scattering using simultaneous Thomson scattering, fast electron spectroscopy, and infrared diagnostics
Authors: McIntosh G. , Meyer J. , Yazhou Zhang
Published: July 2002

Stimulated Raman scattering (SRS) in a CO2 laser(λ0=10.6 μm) produced plasma has been studied experimentally. The enhanced electron plasma wave (epw) fluctuations observed with ruby laser Thomson scattering have been compared with the scattered infrared (IR) spectra and the high-energy (near 100 keV) electrons. No scattered IR light in the range 1.5λ0 <λ<2λ0 was observed although the epw fluctuations suggested there should be IR light in this range. A signal was detected at 2λ0 which is due to the two plasmon decay instability. The number and energy spectra of the fast electrons are well correlated with the Thomson scattered wave vector spectra.
The theory of Langmuir probes in strong electrostatic potential structures
Authors: Borovsky Joseph E.
Published: July 2002

The inside of a time-stationary strong electrostatic potential structure is characterized by the absence of thermal plasma and by the presence of electron and ion beams, the beam energies being related to the local plasma potential. The operation of collecting and emitting Langmuir probes and double probes within such potential structures is analyzed. It is demonstrated that a floating double probe will not measure the electric field of a strong potential structure without substantial reinterpretation of the potential between the probes. A prescription for the reinterpretation is given. Some probe–surface effects are considered, as are the effects of strong magnetic fields.
Intrinsic diffraction pattern inside the resonance cone
Authors: de Feraudy H.
Published: July 2002

The oscillatory pattern of the electrostatic potential radiated in a hot magnetoplasma at frequencies ω<min (ωp, ωc) is examined in terms of the intrinsic diffraction phenomenon: ωp and ωc are, respectively, the electron plasma and cyclotron frequencies. It is shown that the potential maxima are located on equally spaced cones parallel to the resonance cone. The spacing of these cones, measured along the ambient magnetic field, is simply related to k∥I, the parallel component of the largest unattenuated wave vector. The consistency of these features with experimental observations is shown. A method of measurement of the electron temperature is derived.
Structural similarity and lifetimes of turbulence structures in fully developed pipe flow
Authors: Bullock K. J. , Cooper R. E. , Kronauer R. E. , Lai J. C. S.
Published: July 2002

Cross correlation measurements of the longitudinal velocity fluctuations in fully developed pipe flow have been performed with a reference hot-wire probe at a distance y+1 =100 from the wall for five different y+2 locations (namely, 50, 100, 200, 400, and 600) of a second probe with zero longitudinal separation but nonzero transverse separations. The pipe flow Reynolds number is 69 000 based on the pipe radius and the centerline velocity. The covariant (Co) and quadrature (Quad) correlations, which have been determined for each of the seven frequencies ω+ used to constrain the longitudinal wavenumber k+x, have been Fourier transformed with the transverse wavenumber k+z, y+1, y+2, and ω+ as the independent variables. The data presented in this form enable similarity to be examined in terms of waves of different sizes and inclinations. By using a similarity variable k+y+, where k+=[k+2x k+2z]1/2, the relative phases determined from the Co and Quad correlations and the wave intensity function for various wave angles have been shown to collapse. These results support the similarity hypothesis that the phase and intensity of the turbulance components is scaled by wave size k+ and distance from the wall y+. The dimension over which a turbulence structure retains its coherence has been deduced from the correlation data for various wave angles. Two estimates for the lifetime of turbulence structures have been derived, one from the phase-shifting effects of shear contained in the relative phase data, and the other from spectral sheet thickness data. Their significance and implications have been discussed.
Self-similar potential in the near wake
Authors: Diebold D. , Hershkowitz N. , Intrator T. , Bailey A.
Published: July 2002

The plasma potential is measured near the edge of an electrically floating obstacle placed in a steady-state, supersonic, unmagnetized, neutral plasma flow. Equipotential contours show the sheath of the upstream side of the obstacle wrapping around the edge of the obstacle and fanning out into the near wake. Both fluid theory and the data find the near-wake plasma potential to be self-similar when ionization, charge exchange, and magnetic field can be neglected. The theory also finds that fluid velocity is self-similar, the near wake is nonneutral, and plasma density is not self-similar. Strong electric fields are found near the obstacle and equipotential contours are found to conform to all boundaries.
The evolution of the drift instability from onset to saturation
Authors: Marshall E. Marden , Ellis R. F.
Published: July 2002

Collisional drift waves are repetitively destabilized in a weakly ionized argon plasma. The time evolution of the radial density profile and relative wave power from initial destabilization to the time of saturation is presented. The real and imaginary frequencies are found to change during this time. The reduction of the density gradient is also documented.
Note on the bubbles that form at the surface of the highest capillary–gravity waves
Authors: Hogan S. J.
Published: July 2002

Graphical evidence is provided that the bubbles that form at the surface of the highest capillary–gravity waves are virtually unaffected by gravity, in agreement with recent work by Longuet-Higgins (submitted to J. Fluid Mech). The bubble of the highest pure capillary wave is examined in detail.
Velocity spectra in the irrotational flow outside a turbulent shear layer
Authors: Wood D. H. , Westphal R. V.
Published: July 2002

The relationship between the spectra of the three normal stresses near a turbulent shear layer is derived from the constraint of irrotationality. This relationship, together with the scaling of the spectra that follows from Phillips’s theory [Proc. Cambridge Philos. Soc. 51, 220 (1955)], suggests that time scales measured outside the turbulence do not relate simply to those within the shear layer.
Deformation of a free surface as a result of vortical flows
Authors: Tryggvason Grétar
Published: July 2002

The deformation of a free surface caused by the roll up of a vortex sheet below the surface is studied. The large amplitude motion depends on both the strength and depth of the vortex sheet. A distinction is made between three different scenarios of the free-surface motion: a breaking wave, entrainment of air, and the generation of relatively short surface waves.
Nonlinear vortex trail dynamics
Authors: Lim Chjan C. , Sirovich Lawrence
Published: July 2002

The nonlinear evolution of periodic disturbances on vortex trails is considered. In addition to following small initial perturbations, large amplitude initial disturbances of the vortex trails are also studied. It is shown that the equations support a rich variety of essentially nonlinear solutions including unbounded and quasisteady ones. These solutions are found to correspond to various modes of vortex clustering in the physical plane. At the close of the paper, comparisons of these results with recent numerical and experimental findings on the wakes behind stationary cylinders, and also transversely oscillating bluff objects, are made.
Linear mode conversion of an electrostatic wave at the upper-hybrid frequency
Authors: Randriamboarison O. , Braun F. , Leclert G.
Published: July 2002

An analysis of the mode conversion of an electrostatic Bernstein wave in a plasma near the upper-hybrid resonance is developed. The conversion coefficients for the reflected extraordinary and electrostatic waves and for the transmitted electromagnetic wave are derived and calculated for various values of the inhomogeneity length and wave frequency.
Simulations of electrically polarized gravitational condensations in a grain plasma
Authors: Gisler G. R. , Wollman E. R.
Published: July 2002

The two long-range forces in nature, gravitation and electromagnetism, are generally not jointly important in determining the dynamics of physical systems. There is, however, a case in which equilibrium large-scale electrostatic and gravitational forces can be similar in magnitude. In a two-component plasma, in which the massive species is a charged grain with charge-to-mass ratio of order (G)1/2, self-gravitation and thermalization result in strong electrical polarization since the oppositely charged low-mass component has a scale height much greater than that of the grains. Preliminary results of a computer simulation of this behavior are presented here. Properties of steady-state gravitational condensations in grain plasmas have been studied with a one-dimensional particle-in-cell code, and an investigation of the ratio of electrostatic to gravitational energy for various values of the grain charge-to-mass ratio has been performed. As expected, this ratio is maximized when the grain charge-to-mass ratio is approximately (G)1/2.
Space-time correlations of wall pressure fluctuations in shock-induced separated turbulent flows
Authors: Bonnet J. P.
Published: July 2002

An experimental study of the structure of wall pressure fluctuations is performed in shock-induced separated supersonic turbulent flows. Two test conditions are studied for external Mach numbers of 2.25 at low Reynolds number and Mach 3.3 at high Reynolds number. Piezoelectric pressure transducers, isolated from the main facility to minimize vibration effects, are used to sense the pressure fluctuations. Pressure fluctuations are given for several locations and analyzed in the frequency domain. The results exhibit the usual behavior. Space-time correlations are measured and subsequently analyzed using coherence analysis. The results are discussed in terms of structural modifications induced by the shock. Typical results are given for several positions in the incoming boundary layer, at the mean shock location, and in the recirculation region. Some new features concerning the behavior of characteristic scales at the shock traverse are identified, and the results are compared and scaled for both test conditions.
Some special wave solutions in an adiabatic gas in solid-body rotation
Authors: Dodgson N.
Published: July 2002

Waves occurring in a compressible inviscid fluid rotating as a solid body within a circular cylinder are reexamined for the particular case where the disturbance frequency in the rotating system is equal to twice that of the rotating fluid. It is shown that for this frequency there exists a stable wave provided a certain relationship is satisfied between the harmonic m, the axial wavenumber b, and the peripheral Mach number M of the flow. For γ=1.4, where γ is the ratio of the specific heats of the gas, there are solutions for only the first five harmonics and for γ=1 there are solutions for all harmonics. These results are at variance with the conclusions of Gans [J. Fluid Mech. 62, 657 (1974)] and Kerrebrock [AIAA J. 15, 794 (1977)], who suggested that there are no waves for this configuration.
Nonlinear focusing and the Kelvin–Helmholtz instability in ferrofluid/nonmagnetic fluid systems
Authors: Malik S. K. , Singh M.
Published: July 2002

The nonlinear focusing or collapse is considered for the superposed magnetic fluids in motion at uniform speeds. The magnetic field is applied along the direction of streaming. It is shown that the evolution of the amplitude is governed by a two-dimensional Schrödinger equation with cubic nonlinearity. This equation gives rise to a self-focusing singularity when the velocity difference is in the subcritical regime. It is shown that such a self-focusing effect is direction dependent, and predominant at shorter wavelengths.
On the stability of the swirling jet shear layer
Authors: Martin J. E. , Meiburg E.
Published: July 2002

The linear stability analysis of a simple model of a swirling jet illuminates the competition and interaction of centrifugal and Kelvin–Helmholtz instabilities. By employing potential theory, analytical expressions are derived for the growth rate and propagation velocity of both axisymmetric and helical waves. The results show that centrifugally stable flows become destabilized by sufficiently short Kelvin–Helmholtz waves. The asymptotic limits demonstrate that for long axisymmetric waves the centrifugal instability dominates, while long helical waves approach the situation of a Kelvin–Helmholtz instability in the azimuthal direction, modulated by a stable or unstable centrifugal stratification. Both short axisymmetric and short helical waves converge to the limit of a plane Kelvin–Helmholtz instability feeding on the azimuthal vorticity.
Flows induced in a cylinder with both end walls rotating
Authors: Valentine Daniel T. , Jahnke Craig C.
Published: July 2002

The flow field inside a cylindrical container induced by the rotation of the top and bottom end walls with a fixed sidewall is described. For this problem, this paper shows that stagnation points occur along the axis of rotation between the midplane of symmetry and the rotating end walls for appropriate values of the characteristic parameters, viz., the Reynolds number and the aspect ratio of the container. Aspect ratios of 0.5, 0.8, 1.0, and 1.5 were examined over a range of Reynolds numbers from 100 to 2000. As the Reynolds number increased beyond a critical value a recirculation zone surrounding a columnar vortex core in the meridional-plane flow pattern is predicted to occur near the midplane. This toroidal vortex is different from the type B vortex breakdown phenomenon that occurs in cylindrical containers with only one end wall rotating.
Investigation of the use of Prandtl/Navier–Stokes equation procedures for two-dimensional incompressible flows
Authors: Anderson Christopher R. , Reider Marc B.
Published: July 2002

The technique of combining solutions of the Prandtl equations with solutions of the Navier–Stokes equations to compute incompressible flow around two-dimensional bodies is investigated herein. Computational evidence is presented which shows that if the ‘‘obvious’’ coupling is used to combine the solutions, then the resulting solution is not accurate. An alternate coupling procedure is described which greatly improves the accuracy of the solutions obtained with the combined equation approach. An alternate coupling that can be used to create a more accurate vortex sheet/vortex blob method is then shown.