bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation transport in an ionizing current sheath
Authors: Bilbao L. , Kelly H. , Bruzzone H.
Published: July 2002

A model describing the structure of a plane and stationary ionizing current sheath taking into account radiation transport is presented. Five fluid magnetohydrodynamic equations together with radiative transfer equations for continuous radiation (free–free and free–bound) are solved numerically in terms of the pressure of the neutral gas and the value of the pushing magnetic field behind the current sheath, with the assumption that the system becomes opaque for line radiation. Solutions are given for values of the parameters typical of plasma focus device operation [in Methods of Experimental Physics, edited by R. H. Louberg and H. R. Grien (Academic, New York, 1971), Vol. 9B, p. 187]. At a fixed value of the magnetic field, drastic changes in the opacity and in the intensity of the emerging radiant flux are found when varying the neutral gas pressure. In particular, radiative losses can be very high, reaching about 30% of the available power in a frame of reference moving with the current sheath.
Three-dimensional linear instability of parallel shear flows
Authors: Magen Michael , Patera Anthony T.
Published: July 2002

The three-dimensional linear instability of parallel shear flows is investigated through simple geometrical constructions based on the classical Squire transformation. It is shown that if a profile is unstable for a finite Reynolds number and some value of (total) horizontal wavenumber, this profile is also unstable for all larger Reynolds numbers and the same wavenumber. In particular, the direction of the unstable mode tends toward the perpendicular as the Reynolds number increases, thus providing the viscous/shear balance required for resistive instability. The example of plane Poiseuille flow is discussed in detail, and the results compared with classical viscous and inviscid stability criteria.
Interaction between matter and radiation at very high temperatures. II. Electron–positron pairs
Authors: Herrera M. A.
Published: July 2002

The energy transfer between matter and radiation at very high temperatures is investigated. A previously presented formalism is applied to a mixture of electrons, positrons, and photons interacting through Compton scattering and pair creation and annihilation. The relaxation time toward thermal equilibrium and the bulk viscosity of the mixture are derived, and numerical results are presented for temperatures 3×108 K≤T≤1011 K. For temperatures T≳8×108 K pair creation and annihilation is found to be more efficient than Compton scattering in transferring energy between matter and radiation.
Overstability in magnetohydrodynamic convection revisited
Authors: Kumar Krishna , Bhattacharjee Jayanta K. , Banerjee Kalyan
Published: July 2002

The question of overstability in the magnetohydrodynamic convection is reexamined in view of the recent exact result stating that the principle of exchange of stabilities is valid only if Qp2≤π2, where Q is the Chandrasekhar number and p2 is the magnetic Prandtl number. It is shown by writing explicit solutions that in the limit Q≫1 and p2≪1, overstable oscillations are indeed possible, contradicting the Chandrasekhar–Gibson criterion [Hydrodynamic and Hydromagnetic Stability (Oxford, London, 1961), Chaps. 1 and 4; Proc. Cambridge Philos. Soc. 62, 287 (1966)]. Furthermore, the Chandrasekhar–Gibson criterion is shown to be a necessary condition for a codimension-2 bifurcation, but this is not a necessity for overstability.
Two-dimensional evolution of an ion-acoustic soliton
Authors: Chang Hong-Young , Lien Chuong , Hill Jacqueline , Raychaudhuri Santwana , Lonngren Karl E. , Gabl Edward F.
Published: July 2002

The two-dimensional evolution of an ion-acoustic soliton from a grid with regular or random perturbations in the direction transverse to the direction of the soliton propagation is experimentally examined. The soliton initially follows the contour of the exciting grid but evolves into a planar structure. These experimental results are compared with a model based on the higher dimensional Kadomtsev–Petviashvili equation. Both the theoretical and numerical predictions agree with the experiment.
Wave propagation on the von Karman trail
Authors: Lim Chjan C. , Sirovich Lawrence
Published: July 2002

The presence of wave propagation on vortex trails has been pointed out by Tritton [J. Fluid Mech. 6, 547 (1959)] who measured their speeds in the wake of a cylinder at moderate Reynolds numbers. It is shown here that the von Karman model of the vortex trail leads to such disturbance waves and, moreover, that they can be of growing amplitude. The theoretical values of the wave speeds are found to lie within the experimental error bounds.
Influence of the system response on the coherent structures in a confined shear layer
Authors: Veynante Denis , Candel Sebastien M. , Martin Jean-Pierre
Published: July 2002

The existence of coherent structures in mixing layers is now well-known but some aspects of their dynamics are not clarified. In particular, the influence of the eigenfrequency of the experimental apparatus on the layer development is generally not studied. The present experimental evidence indicates that the frequency response of an apparently unexcited plane mixing layer is, in fact, a characteristic of the setup.
Monte Carlo simulation of two-fluid flow through porous media at finite mobility ratio—the behavior of cumulative recovery
Authors: DeGregoria A. J.
Published: July 2002

Curves for cumulative recovery of driven fluid, as a function of pore volume injected of driving fluid, are computed using a previously developed Monte Carlo simulation of two-fluid flow through porous media at finite viscosity ratio. Both the linear channel and five-spot geometries are examined at various grid sizes. For a range of unfavorable viscosity ratios, the trend is toward greater recovery as grid size increases, in the opposite direction to the trend at infinite unfavorable viscosity ratio, which is toward zero recovery as grid size increases.
A numerical study on the transition to self-similar flow in collapsing cavities
Authors: Thomas L. P. , Pais V. , Gratton R. , Diez J.
Published: July 2002

In the collapse of a spherical cavity surrounded by a perfect gas initially at rest, the velocity Ṙ of the free gas boundary has an initial valve of −2c0/(γ−1) (c0 is the speed of sound in the undisturbed gas and γ is the adiabatic exponent). Hereafter Ṙ remains practically constant until R becomes a certain fraction ξ(γ) of the initial radius R0. Finally, for R<ξR0, Ṙ approaches the asymptotic behavior Ṙ∼R−τ(γ) predicted by self-similar solutions. The function ξ(γ), which has been obtained numerically, decreases as γ decreases and vanishes for a certain value of γ near 1.5. This fact, together with the analogous behavior of τ(γ), suggests that there exists a certain value γcr≊1.5 of the adiabatic exponent such that, for 1<γ<γcr the velocity Ṙ of the free boundary is strictly a constant during the entire collapse. This behavior seems to be closely related to the results obtained by Lazarus [Phys. Fluids 25, 1146 (1982)] who demonstrates that a degenerate stable, asymptotic solution, with Ṙ=const, exists for γ<3/2.
High-field launch electron-cyclotron heating experiments in a bumpy torus
Authors: Rasmussen D. A. , Batchelor D. B. , Swain D. W. , White T. L. , Kimrey H. D. , Bigelow T. S. , Cobble J. A. , Goldfinger R. C. , Hillis D. L. , Richards R. K. , Uckan T. , Wilgen J. B. , Hankins O. E.
Published: July 2002

The midplane microwave heating system in the ELMO Bumpy Torus (EBT) [in Proceedings of the Sixth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, 1976 (IAEA, Vienna, 1977), Vol. II, p. 145] was supplemented with power launched from the high-field side of the fundamental resonance by an antenna in the magnet coil throat. Up to 43 kW of polarized (extraordinary mode), 28 GHz power was successfully launched with one antenna. Measurements were made of changes in the core and hot-electron ring plasma parameters when throat-launch power was added. In sharp contrast to initial expectations, the bulk core-plasma parameters were degraded while the ring parameters, in the launch cavity, were improved. These results are consistent with a modified picture of electron-cyclotron heating (ECH) in EBT. A picture of localized microwave absorption and particle losses is supported by additional measurements.
Alfvén wave heating of low-beta, nonaxisymmetric, toroidal plasmas
Authors: Tataronis J. A. , Lewis H. R.
Published: July 2002

Solutions of the Alfvén wave continuum equation for a pressureless, magnetohydrodynamic plasma in nonaxisymmetric, toroidal geometry are presented. The analysis is based on the Hamiltonian form of the continuum equation along lines of force of the equilibrium magnetic field. Canonical transformation methods are invoked to determine approximate solutions of the continuum equation. The approximate solutions are used to identify the conditions that govern the Alfvén continuous spectrum in nonaxisymmetric toroidal geometry.
Steady-state temperature and energy balance for the relativistic ring electrons in bumpy tori
Authors: Hamasaki S. , Krall N. A. , Sperling J. L.
Published: July 2002

The effects of nonadiabaticity and electromagnetic fluctuations on the steady-state properties of the ELMO Bumpy Torus (EBT) [Nucl. Fusion 20, 403 (1980); Phys. Fluids 27, 1759 (1984)] hot electron annulus are calculated using a multifluid approach. These effects are added to those previously included to form a comprehensive picture of EBT ring properties, scaling, and spatial location.
Local effect of equilibrium current on tearing mode stability in the collisional regime. I
Authors: Cozzani Franco , Mahajan Swadesh
Published: July 2002

The local effect of the equilibrium current on the linear stability of low poloidal number tearing modes in the collisional regime is investigated analytically. The set of eigenmode equations describing the relevant mode dynamics inside the tearing layer, including the local effect of the equilibrium current, is solved variationally to derive the dispersion relations for the m≥2 and m=1 tearing modes. The local effect of the equilibrium current is found to increase the well-known FKR growth rate for the classical tearing mode, to enhance stabilization for the m≥2 drift-tearing mode, and to slightly increase the growth rate for the m=1 mode.
Comments on ‘‘Lightning return stroke. A numerical calculation of the optical radiation’’ [Phys. Fluids 2
9, 2736 (1986)]
Authors: Hill R. D.
Published: July 2002

It is noted that the energy computed by Paxton et al. [Phys. Fluids 29, 2736 (1986)] for the dissipation in unit length of a typical lightning channel is much less than a widely quoted experimental value, and also less than an earlier computed value. A further comment on the work of Paxton et al. that a large fraction of energy is ‘‘radiated away,’’ is also made.
Gallery of fluid motion
Authors: Reed Helen L.
Published: July 2002

This article displays winning photographs from the fourth Annual Fluid Mechanics Photo Contest held at the November 1986 meeting of the American Physical Society, Division of Fluid Dynamics, Columbus, Ohio.
Theory of trapped-particle-induced resistive fluid turbulence
Authors: Biglari H. , Diamond P. H.
Published: July 2002

A theory of anomalous electron heat transport, evolving from trapped-particle-induced resistive interchange modes, is proposed. The latter are a new branch of the resistive interchange-ballooning family of instabilities, destabilized when the pressure carried by the unfavorably drifting trapped particles is sufficiently large to overcome stabilizing contributions coming from favorable average curvature. Expressions for the turbulent heat diffusivity and anomalous electron thermal conductivity at saturation are derived for two regimes of trapped-particle energy: (i) a moderately energetic regime, which is ‘‘fluidlike’’ in the sense that the unstable mode grows faster than the time that it takes for particles in this energy range to precess once around the torus, and (ii) a highly energetic regime, where the trapped species has sufficiently high energy as to be able to interact resonantly with the mode. Unlike previous theories of anomalous transport, the estimates of diffusion and transport obtained here are self-consistent since the trapped particles do not ‘‘see’’ the magnetic flutter due to their rapid bounce motion. The theory is valid for moderate electron-temperature, high ion-temperature (auxiliary heated) plasmas and as such, is relevant for present- and future-generation experimental fusion devices.
Experimental studies of the dynamics of a linear high-beta stellarator
Authors: Hedin E. R. , Koepke M. E. , Ribe F. L.
Published: July 2002

In a linear l=1 stellarator [Phys. Fluids 30, 2885 (1987)] internal probes are used to measure the structure and temporal behavior of the plasma and magnetic field. At lower densities (and higher temperatures) diffuse-profile equilibria are produced that are perturbed by a k≊0 oscillation. At higher densities (and lower temperatures) sharp-boundary plasmas are produced that are unstable with an exponentially growing m=1, k≊0 mode. Finite Larmor radius (FLR) effects are adduced to explain the absence of the instability in the oscillatory regime.
Enhanced electron stochasticity from electrostatic waves in a sheared magnetic field
Authors: Robertson J. A. , Horton W. , Choi D. I.
Published: July 2002

Electron motion in a single electrostatic wave in a sheared magnetic field is shown to become stochastic in the presence of a second wave at an amplitude well below that obtained from the overlapping pendulum resonance approximation. The enhanced stochasticity occurs for low parallel velocity electrons for which the parallel trapping motion from eE∥/m interacts strongly with the E×B trapping motion due to the presence of magnetic shear. The single-wave particle motion is given by a two-parameter family of one-degree-of-freedom Hamiltonians which bifurcate from a pendulum phase space to a topology with three chains of elliptic and hyperbolic fixed points separated in radius about the mode-rational surface. In the presence of a perturbing wave with a different helicity, electrons in the small parallel velocity regime become stochastic at an amplitude scaling as the fourth root of the wave potential. The results obtained for stochastic motion apply directly to the problem of the diffusion of electrons in drift waves.
Electrode-adjacent boundary layer flow in magnetoplasmadynamic thrusters
Authors: Subramaniam V. V. , Lawless J. L.
Published: July 2002

The integral method developed in a companion paper [Phys. Fluids 31, xxx (1988)] is extended and applied in this work, to include electromagnetic body forces. A nonequilibrium ionizing argon boundary layer in an electric rocket thruster known as a magnetoplasmadynamic (MPD) thruster is studied. The steady boundary layer flow of a two-temperature plasma adjacent to the electrode in a self-field MPD thruster is analyzed for both frozen (zero ionization rate) flow and nonequilibrium (finite ionization rate) flow. The free-stream boundary conditions for this analysis are obtained from the results of an earlier quasi-one-dimensional nonequilibrium theory. The ionizing, two-temperature, compressible boundary layer equations with electromagnetic effects are solved using momentum and energy integral methods. This integral method without any electromagnetic effects has been described in the companion paper [Phys. Fluids 31, xxx (1988)]. This enables an approximate calculation of the wall shear and the heat transfer to the electrode. The most significant result of the two-temperature boundary layer theory presented herein is to show the strong dependence of the viscosity on the ionization slip (i.e., ionization fraction at the wall). This affects such relevant quantities as boundary layer thickness, wall shear, and wall heat flux, which in turn influence viscous drag and electrode erosion.
Effect of bulges on the stability of boundary layers
Authors: Nayfeh Ali H. , Ragab Saad A. , Al-Maaitah Ayman A.
Published: July 2002

The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear stability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Walker and Greening (British Aeronautical Research Council 5950, 1942). The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10.0, consistent with previous results for flat plates. The method accounts for both viscous and shear-layer instabilities. Separation is found to increase significantly the amplification factor.
Amplification of whistler waves propagating through inhomogeneous, anisotropic, mirror-confined hot-electron plasmas
Authors: Guest G. E. , Miller R. L.
Published: July 2002

A fully relativistic local dispersion relation for whistler waves has been solved at closely spaced points along the magnetic field lines of a 2:1 magnetic mirror in which a highly anisotropic, spatially inhomogeneous, hot-electron plasma is confined. The limiting plasma parameters for convective (spatial) growth have been determined numerically and used to identify plasma conditions leading to maximum amplification of input microwave signals introduced in the form of whistler waves. The maximum gain has been evaluated numerically for a range of values of the hot-electron plasma within which all major stability criteria are satisfied. Very high gains (∼40 dB) are indicated over the entire range of beta investigated.
Biological scattering particles for laser Doppler velocimetry
Authors: Jacobs Diane A. , Jacobs Charles W. , Andereck C. David
Published: July 2002

The use of formaldehyde-killed single-cell organisms as scattering particles for laser Doppler velocimetry studies in water and salt solutions is discussed. Advantages over traditional scattering particles include ready availability in large quantities, uniformity in size, monodispersity, and the ability to stay suspended in solution for several days. The tracers are colloidal sols for a wide range of densities of aqueous solutions. The microorganisms can be easily stained with a large variety of fluorescent and nonfluorescent dyes before they are used as tracer particles.
Equilibrium properties of the condensed states of a turbulent two-dimensional neutral vortex system
Authors: Viecelli J. A.
Published: July 2002

Monte Carlo extrapolation methods and approximate evaluations of the partition function are used to obtain the phase transition properties and spatial probability distribution exponents for the Hamiltonian system. A second condensation from dipole pairs to a liquid-like phase is found on cooling the system to a temperature approximately one-tenth the pair condensation temperature. In the condensed dipole pair temperature range the Metropolis algorithm yields dipole configurations similar to those observed in previous numerical integrations of the motion. In the region of the pair condensation transition the distribution of distances between plus and minus vortices follow Lévy probability laws over spatial scales extending from the vortex core diameter to the radius of the container enclosing the flow. The joint space-time probability density function for the travel times and lengths of the dipole translation paths between collisions is derived for thermodynamic equilibrium and yields Lévy flight like enhanced diffusion. Theoretical values for the diffusion exponent and its temperature dependence are obtained and found to be in agreement with diffusion rates measured during numerical integrations of the vortex motion.
On the determination of solenoidal or compressible velocity fields from measurements of passive or reactive scalars
Authors: Pearlstein Arne J. , Carpenter Bonnie N.
Published: July 2002

Several techniques have been proposed for determining two- or three-dimensional velocity fields from measurements of one passive scalar. It is shown that measurements of one scalar and knowledge of the equation governing its transport determine a velocity field, only up to an additive vector field locally perpendicular to the gradient of the scalar field but otherwise arbitrary. Three previously proposed procedures for selecting a unique velocity field from among the uncountable infinity consistent with the scalar transport data and equation are then discussed, and it is shown that a recent ‘‘iterative inversion’’ procedure for ‘‘solution’’ of a singular linear equation system (obtained using only measurements of one scalar and the equation governing its transport) cannot converge as claimed. A method for determining the correct n-dimensional (n=2 or 3) divergence-free velocity field from measurements of n−1 passive or reactive scalars is then developed. Finally, it is shown how the velocity field in an n-dimensional compressible flow can be determined from measurements of density and n−1 passive or reactive scalars.
Two-dimensional Gram–Charlier reconstruction of velocity correlations
Authors: Sullivan P. , Pollard A. , Delville J. , Bonnet J. P.
Published: July 2002

The two-point statistics obtained in a two-dimensional mixing layer and a three-dimensional wall jet are reconstructed from the summation of Hermite Polynomials. The use of Hermite Polynomials allows the rigorous and progressive decomposition of the statistical field into separate components, Gaussian and non-Gaussian. The influence of individual terms can then be investigated. Two different schemes are used: a one-dimensional temporal reconstruction of data from both experiments, which is capable of providing excellent agreement with the measurements, and a two-dimensional scheme with the mixing layer data, which captures spatial and temporal characteristics of the velocity cross-correlation. It is demonstrated that the technique can also recover information that may be lost or missing between two measuring points thereby providing a complementary method to linear stochastic estimation.
Baroclinic generation of vorticity by an axisymmetric vortex in a linearly stratified fluid; in the passive limit
Authors: Thoroddsen S. T. , Van Atta C. W.
Published: July 2002

We evaluate analytically the baroclinically generated vorticity that is produced by a stationary axisymmetric vortex that overturns a fluid having an initial linear mean density profile. The instantaneous net production of vorticity due to a point vortex is shown to be proportional to the buoyancy time Nt, where N is the Brunt–Väisälä frequency. These results are valid only for the nondiffusive, passive limit, where the baroclinically produced vorticity is negligible and does not alter the velocity field. Corresponding results for the Taylor vortex show maximum production of vorticity away from the center but zero net production. The Oseen vortex behaves more like the point vortex. These differences appear related to the total circulation of these vortices.
The Favre–Reynolds average distinction and a consistent gradient transport expression for the dissipation
Authors: Ristorcelli J. R. , Morrison J. H.
Published: July 2002

Two equation and higher order closures for compressible turbulence fail to capture the compressible wall layers’ log scaling. Accounting for the distinction between Favre and Reynolds averaged variables in the compressible moment equations indicate that turbulent transport expressions obtained using the ‘‘variable density approximation’’ are in error. The error is related to the enstrophy, a Reynolds averaged variable appearing in the equation for the Favre averaged k; recognizing this fact an expression for the transport of dissipation consistent with simple mixing length arguments is obtained. Within the (limited) context of a gradient transport hypothesis a rational form for the turbulent transport of the dissipation is found. Modestly better agreement with the well established compressible Van Driest log scaling is found in a k−ε calculation.
Thermoconvective instability of paramagnetic fluids in a uniform magnetic field
Authors: Huang Jie , Edwards Boyd F. , Gray Donald D.
Published: July 2002

The effect of a uniform oblique magnetic field on a laterally unbounded insulating paramagnetic fluid layer heated from below is studied using a linear stability analysis of the Navier–Stokes equations supplemented by Maxwell’s equations and the appropriate magnetic body force. Two-dimensional rolls in an arbitrary vertical plane are considered. Longitudinal rolls with axes parallel to the horizontal component of the field are the rolls most unstable to convection. The corresponding critical Rayleigh number and critical wavelength for the onset of such rolls are less than the well-known Rayleigh–Bénard values in the absence of magnetic fields. Vertical fields maximize these deviations, which vanish for horizontal fields. Horizontal fields increase the critical Rayleigh number and the critical wavelength for all rolls except longitudinal rolls. These effects should be observable in careful experiments at high fields.
Numerical study of thermoacoustic waves in an enclosure
Authors: Farouk Bakhtier , Oran Elaine S. , Fusegi Toru
Published: July 2002

The behavior of thermoacoustic waves in a nitrogen-filled two-dimensional cavity is numerically studied in order to investigate how these waves may be used as an effective heat removal mechanism. The compressible, unsteady Navier–Stokes equations were solved for a series of initial conditions by combining a flux-corrected transport algorithm for convection with models for temperature-dependent viscosity and thermal conduction. By considering a one-dimensional test problem and comparing the results to existing data, the accuracy of the present numerical method is verified. In the problems considered, the vertical walls of a cavity were heated or cooled to generate the thermoacoustic waves. Both impulsive and gradual changes of the wall temperatures were considered. When the vertical wall was heated impulsively and nonuniformly, the waves induced two-dimensional flows within the enclosure. The observed thermoacoustic waves oscillate and eventually decay due to viscous and heat dissipation.
Spectral and statistical properties of a two-field electron drift model
Authors: Pavlenko Vladimir P. , Uby Lars
Published: July 2002

The weakly nonlinear theory of two-dimensional electron drift modes is outlined and a double energy cascade is demonstrated, due to the presence of two rugged invariants. Statistical equilibrium spectra of the fully and weakly nonlinear systems are calculated using a discrete Fourier mode phase space and Hopf’s equation. A Monte Carlo simulation based on the weakly nonlinear theory gives a detailed energy spectrum with several similarity ranges, suggesting the existence of an approximate additional local (in k space) quadratic invariant. The inhomogeneity of the underlying system is reflected by spectral anisotropy. Some general problems of statistical fluid mechanics are discussed.
Exact solutions for helical magnetohydrodynamic equilibria. II. Nonstatic and nonbarotropic solutions
Authors: Villata Massimo , Ferrari Attilio
Published: July 2002

In the framework of the analytical study of magnetohydrodynamic (MHD) equilibria with flow and nonuniform density, a general family of well-behaved exact solutions of the generalized Grad–Shafranov equation and of the whole set of time-independent MHD equations completed by the nonbarotropic ideal gas equation of state is obtained, both in helical and axial symmetry. The helical equilibrium solutions are suggested to be relevant to describe the helical morphology of some astrophysical jets.
Measurement of plasma rotation velocities with electrode biasing in the Saskatchewan Torus-Modified (STOR-M) tokamak
Authors: Xiao C. , Jain K. K. , Zhang W. , Hirose A.
Published: July 2002

In the Saskatchewan Torus-Modified (STOR-M) tokamak [Phys. Fluids B 4, 3277 (1992)], application of a negative bias results in large negative radial electric field, Er, at the plasma edge, reduced plasma toroidal rotation velocity, and a large poloidal rotation in the electron diamagnetic drift direction. Conversely, a positive bias leads to a relatively small negative Er at the plasma edge, a positive Er in the scrape-off layer, increased toroidal rotation, and an increased poloidal rotation speed in the ion diamagnetic drift direction. Increases in edge plasma density and steepening of its radial profile have also been observed for both polarities.
Dissipative stationary plasmas: Kinetic modeling, Bennett’s pinch and generalizations
Authors: Kiessling Michael K.-H. , Lebowitz Joel L.
Published: July 2002

The structure of the self-consistent electromagnetic fields, E, B, and one-particle distribution functions, fs, of a stationary dissipative unbounded S-species plasma, which satisfy a system of Maxwell–Vlasov–Fokker–Planck–Boltzmann equations with velocity-independent (effective) dissipation coefficients and applied constant electric field ℰ, is studied. It is proven that when the plasma is invariant along the direction of ℰ, then (a) the fs are given by S drifting Maxwell–Boltzmann distributions, with densities satisfying self-consistent Poisson–Boltzmann equations of the type first considered by Bennett for S=2; (b) all smooth radial current profiles with normalized particle densities satisfy a generalized Bennett relation; (c) Bennett’s current profile is the only fully conformally invariant one; (d) there exist other radial solutions with profiles different from Bennett’s.
Analysis of electron cyclotron current drive using neoclassical Fokker–Planck code without bounce-average approximation
Authors: Takase H.
Published: July 2002

A new three-dimensional relativistic Fokker–Planck code (poloidal angle and two dimensions in momentum space) has been developed for the analysis of electron cyclotron current drive (ECCD) in tokamak plasmas. This numerical code takes into consideration trapped electron effects without using the bounce-average approximation. Simulations have been carried out using the code, and the results were compared with those of a bounce-averaged Fokker–Planck code. There are differences in the current drive efficiencies calculated by the two codes, and this difference is shown to be caused by a change in electron velocity parallel to the magnetic field due to the inhomogeneous magnetic field.
Gas-filled targets for large scale-length plasma interaction experiments on Nova
Authors: Powers L. V. , Berger R. L. , Kauffman R. L. , MacGowan B. J. , Amendt P. A. , Back C. A. , Bernat T. P. , Dixit S. N. , Eimerl D. I. , Estabrook K. G. , Harte J. A. , Kalantar D. H. , Klem D. E. , Lasinski B. F. , Montgomery D. S. , Moody J. D. , Munro D. H. , Shepard T. D. , Suter L. J. , Turner R. E. , Williams E. A. , Fernandez J. C. , Hsing W. W. , Wilde B. H. , Failor B. H.
Published: July 2002

Stimulated Brillouin backscatter from large scale-length gas-filled targets has been measured on the Nova laser. These targets were designed to approximate conditions in indirect drive ignition target designs in underdense plasma electron density (ne∼1021/cm3), temperature (Te≳3 keV), and gradient scale lengths (Ln∼2 mm, Lv≳6 mm) as well as calculated gain for stimulated Brillouin scattering (SBS). The targets used in these experiments were gas-filled balloons with polyimide walls (gasbags) and gas-filled hohlraums. Detailed characterization using x-ray imaging and x-ray and optical spectroscopy verifies that the calculated plasma conditions are achieved. Time-resolved SBS backscatter from these targets is <3% for conditions similar to ignition target designs.
Thermodynamic properties of anisotropic plasmas
Authors: Nambu Mitsuhiro
Published: July 2002

A novel aspect of the Onsager symmetries in magnetized plasmas is pointed out. If temperature anisotropy exists, the symmetry takes place only for electrostatic waves; for electromagnetic waves, the Onsager reciprocal relations are violated. The entropy production rate is obtained for the quasilinear relaxation. It is pointed out that the entropy production is not the Lyapunov function for the process. The quasi-H-theorem for the quasilinear stabilization is discussed by using Renyi’s entropy.
Theory of cyclotron resonance in a cylindrical non-neutral plasma
Authors: Gould Roy W.
Published: July 2002

Resonances near the cyclotron frequency of a cylindrical non-neutral plasma column with radial density and angular velocity profiles are studied. Cold plasma and warm plasma models are used to consider the various multipole modes (eimθ) for kz=0. For m=1 only a single resonance, a center of mass mode, is found. Its frequency is downshifted from the cyclotron frequency by an amount equal to the frequency of the low-frequency diocotron mode. For each m greater than 1 the cold plasma model gives a continuous absorption band with spatially localized absorption at each frequency, corresponding to a continuum of singular modes. In the warm plasma model, the continuuo go over to sets of discrete radially trapped azimuthally propagating Bernstein modes. For both cases, the plasma rotation Doppler-shifts the azimuthally propagating modes up in frequency. The angular velocity profile, together with plasma temperature, determine the spacing of the Bernstein modes within a band.
The elastic contribution to the linewidths
Authors: Bertuccelli D. , Di Rocco H. O.
Published: July 2002

The elastic contribution to the linewidths was calculated with the use of Quantum Defect Theory. The method is based on the connection at the ionization threshold between the quantum defects Δl, associated with the bound states, with the scattering phase shifts μl, associated with the short range potential due to the atomic core. Agreement with measurements of the line 5419 Å of Xe II at low electron temperatures is very good and reproduces the experimental trend w∝T−1, whereas the semiempirical calculations predict w∝T−1/2.
Second harmonic generation in collisionless plasma in parallel plate guide
Authors: Sinha S. K. , Sinha A. C.
Published: July 2002

An analysis of second harmonic power generation in collisionless, unmagnetized plasma bounded by parallel plates is presented, which predicts much higher yield under appropriate plate separation and input energy than the maximum reported yield for unbound plasma. One can therefore look for optimization of second harmonic power by choosing suitable parameters.
Measurement of the full polarimetric transition matrix of a magnetized plasma
Authors: Segre S. E.
Published: July 2002

It is shown that the full polarimetric transition matrix of a magnetized plasma can be determined with a good time resolution (down to 100 ns) and, furthermore, it is possible to make use mainly of phase measurements, which are less sensitive to noise than amplitude measurements. The simultaneous measurement of the nine elements of the absolute transition matrix (or of the eight elements of the normalized transition matrix) allows a significant enhancement of the information obtained for each probing beam.
Gain and bandwidth in stagger-tuned gyroklystrons
Authors: Nusinovich G. S. , Danly B. G. , Levush B.
Published: July 2002

An analytical theory describing the trade-off in the bandwidth and gain in multicavity, stagger-tuned gyroklystrons (GKLs) is developed. The assumption that the cavities are short and therefore the electron ballistic bunching proceeds in long drift sections (point-gap model) allows us to develop analytically both the small-signal and large-signal theories of stagger-tuned GKLs. The results for two-, three-, and four-cavity GKLs are presented which illustrate the bandwidth increase, the gain degradation, and the increase in gain-bandwidth product due to the stagger tuning.
Global consistency for thin flux tube treatments of toroidal geometry
Authors: Scott B.
Published: July 2002

In order to avoid a self-mapping problem due to a very long correlation length along a field line, present treatments of magnetized plasma turbulence in flux tube geometry often extend the computational domain to several times the field line connection length. This is shown to result in the admission of nonphysical parallel wavelengths, possibly corrupting the solution even if it is converged. Also shown is that if a flux tube domain is constructed by thinning the full spectrum of allowed wavelengths, the same boundary condition results as if the domain were the entire flux surface. The only consistent remedy is therefore to extend the domain in the perpendicular coordinate within the flux surface, possibly all the way back to the entire flux surface, remaining consistent with the global boundary conditions.
Surface deformation measurements following excimer laser irradiation of insulators
Authors: von Gutfeld R. J. , McDonald F. A. , Dreyfus R. W.
Published: July 2002

We have studied the surface deformation of polyimide and Pyrex glass samples resulting from local excitation with pulsed 193 nm excimer laser radiation. The objective is to understand the primary deformation modes characterizing the surface motion. A He-Ne probe beam was used to measure the deformation in conjunction with a fast rise time position sensitive detector. The data are compared to and found to be in agreement with a new detailed calculation. Three distinct temporal regimes are identified for the surface deformation: (1) local thermal expansion, (2) propagation of bulk and surface waves, and (3) simultaneous front and back surface motion (plate motion) for sufficiently thin samples.
Polarization and frequency control of a semiconductor laser with a new external cavity structure
Authors: Wakana S. , Shirasaki M. , Furukawa Y. , Inagaki T.
Published: July 2002

A technique using a new external cavity structure to cause degeneration at the frequencies of two orthogonally polarized modes and to control the polarization and the frequency in a semiconductor laser has been devised. The phase difference between the polarizations in the gain medium can be canceled in a round trip through quarter-wave plates set in the cavity. By rotating one of the quarter-wave plates, orthogonally polarized laser beams can theoretically be made to oscillate at slightly different frequencies. Experimentally, two orthogonally polarized oscillations with rather large frequency differences occurred. The difference between the two frequencies alternated according to the quarter-wave plate rotation. This phenomenon could be explained theoretically.
The
murMN
operon: A functional link between antibiotic resistance and antibiotic tolerance in
Streptococcus
pneumoniae
Authors: Filipe Sergio R. , Severina Elena , Tomasz Alexander
Published: July 2002

Inactivation of the recently identified
murMN
operon in penicillin-resistant strains of
Streptococcus pneumoniae
was shown already to cause two major effects: elimination of branched-structured muropeptides from the cell wall and complete loss of penicillin resistance. We now show that cells with inactivated
murMN
also have a third phenotype: an increased susceptibility to lysis when exposed to low concentrations of fosfomycin,
d
-cycloserine, vancomycin, and nisin, indicating a wide-spectrum hypersensitivity to inhibitors of both early and late stages of cell wall biosynthesis. Mutants of
murMN
also lysed faster than the parental strain when treated with the detergent deoxycholate. Several different alleles of
murM
cloned in plasmid pLS578 and introduced into a
murM
deletion mutant of the penicillin-resistant strain Pen6 were able to reconstitute each one of the three mutant phenotypes: the highly branched cell wall structure, original high level of penicillin resistance, and normal sensitivity to lysis. In a penicillin-susceptible strain the same experiments caused increased concentration of cell wall branched peptides and suppression of sensitivity to antibiotic induced lysis. The observations suggest that the
murMN
operon plays a key role in the regulation of a stress-response pathway that can be triggered by perturbation of cell wall biosynthesis in
S. pneumoniae
.
Coupling of histamine H
3
receptors to neuronal Na
+
/H
+
exchange: A novel protective mechanism in myocardial ischemia
Authors: Silver Randi B. , Mackins Christina J. , Smith Neil C. E. , Koritchneva Irina L. , Lefkowitz Kara , Lovenberg Timothy W. , Levi Roberto
Published: July 2002

In myocardial ischemia, adrenergic nerves release excessive amounts
of norepinephrine (NE), causing dysfunction and arrhythmias. With
anoxia and the concomitant ATP depletion, vesicular storage of NE is
impaired, resulting in accumulation of free NE in the axoplasm of
sympathetic nerves. Intraneuronal acidosis activates the
Na
+
/H
+
exchanger (NHE), leading to increased
Na
+
entry in the nerve terminals. These conditions favor
availability of the NE transporter to the axoplasmic side of the
membrane, causing massive carrier-mediated efflux of free NE. Neuronal
NHE activation is pivotal in this process; NHE inhibitors attenuate
carrier-mediated NE release. We previously reported that activation of
histamine H
3
receptors (H
3
R) on cardiac
sympathetic nerves also reduces carrier-mediated NE release and
alleviates arrhythmias. Thus, H
3
R activation may be
negatively coupled to NHE. We tested this hypothesis in individual
human SKNMC neuroblastoma cells stably transfected with H
3
R
cDNA, loaded with the intracellular pH (pH
i
) indicator
BCECF. These cells possess amiloride-sensitive NHE. NHE activity was
measured as the rate of Na
+
-dependent pH
i
recovery in response to an acute acid pulse (NH
4
Cl). We
found that the selective H
3
R-agonist imetit markedly
diminished NHE activity, and so did the amiloride derivative EIPA. The
selective H
3
R antagonist thioperamide abolished the
imetit-induced NHE attenuation. Thus, our results provide a link
between H
3
R and NHE, which may limit the excessive release
of NE during protracted myocardial ischemia. Our previous and present
findings uncover a novel mechanism of cardioprotection: NHE inhibition
in cardiac adrenergic neurons as a means to prevent ischemic
arrhythmias associated with carrier-mediated NE release.
Expression profiling of a human cell line model of prostatic cancer reveals a direct involvement of interferon signaling in prostate tumor progression
Authors: Shou Jianyong , Soriano Robert , Hayward Simon W. , Cunha Gerald R. , Williams P. Mickey , Gao Wei-Qiang
Published: July 2002

Cancer-associated fibroblasts induce malignant behavior in genetically initiated but nontumorigenic human prostatic epithelium. The genetic basis for such transformation is still unknown. By using Affymetrix GeneChip technology, we profiled genomewide gene expression of transformed [tumorigenic benign prostatic hyperplasia (BPH1)
CAFTD
] and parental (nontumorigenic BPH1) cells. We identified differentially expressed genes, which are associated with tumorigenesis or tumor progression. One striking finding is that a significant portion of the down-regulated genes belongs to interferon (IFN)-inducible molecules. We show that IFN inhibited the tumorigenic BPH1
CAFTD
cell proliferation and colony formation
in vitro
and inhibited tumor growth in xenografts
in vivo
. Expression of the IFN-inducible molecules correlates with the growth-inhibiting effects of IFN. In addition, these genes are reported to be mapped mainly to two chromosomal regions, 10q23–26 and 17q21, which are frequently deleted in human prostate cancers. Furthermore,
in silico
data-mining with the GeneLogic database revealed that expression of the IFN-inducible genes was down-regulated in approximately 30% of the 49 clinically characterized samples of prostatic adenocarcinomas. Collectively, we show that there seems to be a direct link between IFN-inducible molecules and prostatic tumor progression. These findings suggest IFN-inducible molecules as potential therapeutic targets for the treatment of prostate cancer.
Helicogenicity of solvents in the conformational equilibrium of oligo(m-phenylene ethynylene)s: Implications for foldamer research
Authors: Hill David J. , Moore Jeffrey S.
Published: July 2002

A (R)-binaphthol tethered bis-hexameric oligo(m-phenylene ethynylene) foldamer was examined in 30 solvents to correlate the unfolded–folded conformational equilibrium to bulk solvent properties and specific solvent–chain interactions. The oligomer is soluble in a variety of solvents of intermediate polarity, with the majority of these solvents being helicogenic. The amphiphilic nature of the chain allows the solvophobic backbone to be solubilized in a wide range of solvents through the polar triethylene glycol side chains. As demonstrated through UV and CD spectroscopic experiments, the helical conformation is increasingly stabilized with increasing solvent polarity in the absence of specific solvent–chain interactions. Surprisingly, very few solvents are capable of fully denaturing the helix, indicating the strength of the solvophobic driving forces in this cooperative system. The folding reaction for this amphiphilic oligomer can be described as a compromise in solubility properties, where chains collapse intramolecularly into helical conformations to minimize solvent–backbone contacts while maintaining favorable solvent–side chain interactions for solvation. In terms of mimicking the properties of biomacromolecules, foldamers using solvophobic driving forces must be tempered with functionalities that promote solubility of the folded state while at the same time allowing access to the unfolded state through the use of denaturants.
A glutamate residue at the C terminus regulates activity of inward rectifier K
+
channels: Implication for Andersen's syndrome
Authors: Chen Lei , Kawano Takeharu , Bajic Sibinka , Kaziro Yoshito , Itoh Hiroshi , Art Jonathan J. , Nakajima Yasuko , Nakajima Shigehiro
Published: July 2002

G protein-coupled inward rectifiers (GIRKs) are activated directly by G protein βγ subunits, whereas classical inward rectifiers (IRKs) are constitutively active. We found that a glutamate residue of GIRK2 (E315), located on a hydrophobic domain of the C terminus, is crucial for the channel activation. This glutamate (or aspartate) residue is conserved in all members of the Kir family. Substitution of alanine for the glutamate on GIRK1, GIRK2, and IRK2, expressed in HEK293 cells, greatly reduced the whole-cell currents. The whole-cell current of GIRK channels with a constitutively active gate, GIRK2(V188A), [Yi, B. A., Lin, Y. F., Jan, Y. N. & Jan, L. Y. (2001)
Neuron
29, 657–667] was also reduced by the same glutamate mutation. Mean open time and conductance of single channels in GIRK2 and IRK2 were not affected by the mutation, indicating that the reduced whole-cell current resulted from a lowered probability of channel activation. The mutated GIRK and IRK showed normal trafficking to the cell membrane. The mutated GIRK2 retained the ability to interact with G protein βγ subunits, and it showed almost the same inwardly rectifying property as the wild type. The mutated GIRK1 and GIRK2 retained ion selectivity to K
+
ions. This glutamate residue corresponds to one of the residues causing Andersen's syndrome [Plaster, N. M., Tawil, R., Tristani-Firouzi, M., Canun, S., Bendahhou, S., Tsunoda, A., Donaldson, M. R., Iannaccone, S. T., Brunt, E., Barohn, R.,
et al.
(2001)
Cell
105, 511–519]. Our interpretation is that this region of the glutamate residue is crucial in relaying the activating message from the ligand sensor region to the gate.