bluuebunny/crossref_metadata_2025 huggingface dataset:
Is sedimentation container-shape dependent?
Authors: Beenakker C. W. J. , Mazur P.
Published: July 2002

The question is addressed as to the dependence of sedimentation of a homogeneous suspension on the shape of the container. It is demonstrated, by comparing calculations for spherical and plane geometries, that shape-dependent contributions to the sedimentation velocity remain in the limit of infinitely distant container walls. Upon transformation from the laboratory reference frame to a local frame of reference that moves with the average volume velocity, this shape-dependence is found to disappear.
Flow of a separating mixture in a rotating cylinder
Authors: Ungarish M.
Published: July 2002

The rotating flow of a separating mixture of particles and fluid in a finite straight axisymmetric container is considered. The analysis employs the ‘‘mixture’’ (‘‘diffusion’’) model under the assumptions that the Ekman number E, the particle Taylor number β, and the relative density difference ε are small, and the volume fraction α possesses initially a slight ‘‘stratification’’ around A0. It is shown that the Ekman layers on the endplates may considerably affect the azimuthal motion of the inviscid core via a spin-up mechanism that has a relative importance reflected by λ=E1/2/εβH (H is the dimensionless height of the container). When λ≪1 a considerable retrograde motion, proportional to εA0/β, shows up in agreement with previous infinitely ‘‘long cylinder’’ (i.e., endcaps neglected) solutions; this motion is substantially reduced when λ∼1 and diminishes for λ≫1. On the other hand, the radial motion in the core is insignificantly influenced by the Ekman layers; therefore, the main separation process is properly represented by the long cylinder solutions for a wide range of H. In addition, it is shown that an initial radial stratification may induce a similar axial variation of α in the Ekman layers.
Vortex rings associated with strong double-diffusive fingering
Authors: Green Theodore , Schettle John W.
Published: July 2002

The strong, double-diffusive fingering associated with a warm suspension overlying colder, clear water is characterized by pronounced vortex rings, which evolve quickly from the bulbous tips of descending fingers.
The formation of a steady one-dimensional outflow
Authors: Schmalz R. F. , Eidmann K.
Published: July 2002

One-dimensional outflow of a gas into a vacuum in cylindrical and spherical geometry is considered. Using stationary boundary conditions, the filling of space with gas is simulated numerically and modeled analytically by combining steady-state and self-similar solutions. The impact on laser-generated pellet coronas is pointed out and the influence of the flow divergence on the ion velocity spectrum is discussed.
Mirror ratio scaling of axial confinement of a mirror-trapped collisional plasma
Authors: Lam K. L. , Leikind B. J. , Wong A. Y. , Dimonte G. , Kuthi A. , Olson L. , Zwi H.
Published: July 2002

The axial confinement time of a single cell mirror is found to be proportional to the mirror ratio over the range of 12–74 when the mean free path for Coulomb collisions is less than one-third of the length of the device. The reduction in total end-loss current is shown to correspond to the reduction of the cross-sectional area of the plasma at the mirror throat as the mirror ratio is increased. The end-loss current density is independent of the mirror ratio and is proportional to the product of the plasma density and the acoustic speed.
Theory of intense electromagnetic pulse propagation through the atmosphere
Authors: Yee Jick H. , Alvarez R. A. , Mayhall D. J. , Byrne D. P. , DeGroot J.
Published: July 2002

A set of fluid equations is derived to describe the interaction of a very strong electromagnetic pulse with a weakly ionized plasma. These equations are used to investigate the dynamic behavior of an intense electromagnetic pulse propagating through the atmosphere. Results show that the amount of energy transmitted through the medium depends very strongly on the initial energy of the pulse and such characteristics and its frequency, its shape, and its length. In addition, a pulse was propagated through an air filled waveguide to verify the acuracy of the theoretical model. The theory also predicts very accurately the pulse breakdown threshold.
An experiment on the plasma expansion into a wake
Authors: Raychaudhuri Santwana , Hill Jacqueline , Chang Hong Young , Tsikis Eugene K. , Lonngren Karl E.
Published: July 2002

Experiments on the expansion of a plasma into the wake region behind an object inserted in a flowing plasma are described. The dominant expansion mechanism that fills in the wake is determined to be a self-similar expansion. Accelerated ions with a velocity greater than the local ion-acoustic velocity are detected ahead of the self-similar expansion front. In a plasma with two species, two groups of accelerated ions are detected.
Helicity fluctuations in incompressible turbulent flows
Authors: Rogers Michael M. , Moin Parviz
Published: July 2002

Results from direct numerical simulations of several homogeneous flows and fully developed turbulent channel flow indicate that the probability distribution function (pdf) of relative helicity density exhibits at most a 20% deviation from a flat distribution. Isotropic flows exhibit a slight helical nature but the presence of mean strain in homogeneous turbulence suppresses helical behavior. All the homogeneous turbulent flows studied show no correlation between relative helicity density and the dissipation of turbulent kinetic energy. The channel flow simulations indicate that, except for low-dissipation regions near the outer edge of the buffer layer, there is no tendency for the flow to be helical. The strong peaks in the relative helicity density pdf and the association of these peaks with regions of low dissipation found in previous simulations by Pelz et al. [Phys. Rev. Lett. 54, 2505 (1985)] are not observed.
Cellular automaton formulation of passive scalar dynamics
Authors: Chen Hudong , Matthaeus William H.
Published: July 2002

Cellular automata modeling of the advection of a passive scalar in a two-dimensional flow is examined in the context of discrete lattice kinetic theory. It is shown that if the passive scalar is represented by tagging or ‘‘coloring’’ automation particles a passive advection–diffusion equation emerges without use of perturbation expansions. For the specific case of the hydrodynamic lattice gas model of Frisch, Hasslacher, and Pomeau [Phys. Rev. Lett. 56, 1505 (1986)] the diffusion coefficient is calculated by perturbation.
Diffusion of a plasma subject to neutral beam injection
Authors: Okuda H. , Hiroe S.
Published: July 2002

Two-dimensional numerical plasma simulations have been carried out in a uniform magnetic field to study the effects of neutral beam injection on plasma diffusion. Neutral beams injected across a magnetic field are assumed to be ionized by various ionization processes in a plasma. It is found that the suprathermal convective motion of a plasma generated by the injection of neutral beams is dissipated via anomalous viscosity, leading to enhanced cross-field diffusion. The diffusion coefficient depends weakly on the magnetic field and plasma density, similar to the diffusion caused by thermally excited convective cells. The magnitude of the diffusion increases with the injection energy and is much larger than the thermal diffusion because of the presence of suprathermal plasma convection. It is shown that a similar anomalous plasma diffusion may occur in a plasma subject to radio frequency (rf) wave heating where only a localized region of a plasma across the magnetic field is heated to a temperature much higher than the surrounding temperature. Theoretical investigations are described on the scaling of enhanced plasma diffusion.
Dynamics of explosive boiling of a droplet
Authors: Frost D. L.
Published: July 2002

The dynamical behavior of the unstable explosive boiling of single droplets (1–2 mm diam) of diethyl ether, pentane, and isopentane at the superheat limit has been exhibited in detail. A+high ambient pressures, boiling consists of normal stable growth of a smooth bubble. At intermediate pressures a transitional regime of stability occurs in which a drop initially vaporizes stably for several milliseconds while incipient instability waves develop on the evaporating interface, then increased heat flux from the host liquid initiates violent boiling near the edge of the remnant volatile liquid. Direct evidence has been obtained that during violently unstable boiling, fine liquid particles are torn from the liquid–vapor interface, generating a mass flux orders of magnitude greater than that characteristic of ordinary boiling. In this regime of transitional stability, one of a number of different possible kinds of disturbances could externally trigger a breakdown to violent instability. After the evaporative instability becomes nonlinear and saturates, the boiling appears quasisteady, with the evaporative front moving into the volatile liquid at a roughly constant velocity. Results obtained by modeling the evaporation wave as a Chapman–Jouguet deflagration show that the temperature at the unstably boiling interface is substantially above the saturated value.
Anomalous electron diffusion across a magnetic field in a beam–plasma system
Authors: Okuda H. , Ono M. , Armstrong R. J.
Published: July 2002

The diffusion of electrons across a magnetic field in the presence of a beam–plasma instability has been studied by means of two-dimensional numerical simulations. It is found that the beam electrons can diffuse much faster across the magnetic field than the thermal electrons. This can be explained by the fact that the electrons in the beam are in resonance with the waves excited by the beam–plasma instability so that they experience a nearly d.c. electric field, causing large cE×B/B2 excursions.
Heating efficiency of beat-wave excitation in a density gradient
Authors: Morales G. J. , Maggs J. E.
Published: July 2002

A simple model is presented that yields analytical expressions for the heating efficiency of beat-wave excitation in a plasma with a linear density profile. The effect of self-consistent Landau damping by tail electrons is included without recourse to WKB approximations.
Instability of strained counter-rotating vortices
Authors: Dagan A.
Published: July 2002

The stability of counter-rotating vortices subjected to a uniform plane straining flow has been examined in this study. The straining flow field flattens the vortices in a way that the resulting slender shape can be considered as a double shear layer. The linear analysis based on this assumption has indicated two regions of instability: decreasing slenderness ratio and increasing slenderness ratio with time, where the Orr–Sommerfeld equation has been found to describe the phenomenon when the slenderness ratio is time independent. Decreasing slenderness ratio with time, coupled with an extension of the line vortex, is a stabilizing mechanism, where the rate of change of the slenderness ratio plays an important role in this process. On the other hand, in the case of a contracting line vortex with decreasing slenderness ratio, instability will not reach full growth and the vortex will undergo irreversible elongation. Increasing slenderness ratio is found to be an unconditionally destabilizing mechanism. The nonlinear phenomenon, computed by the numerical solution, indicates that in the case of an extending line vortex and decreasing slenderness ratio, the vortices will collapse to form a pair of vortices with finite cores. In some other cases, the vortex pair will undergo irreversible elongation, where increased slenderness ratio is found numerically to be a destabilizing mechanism.
Turbulence transition and internal wave generation in density stratified jets
Authors: Sutherland B. R. , Peltier W. R.
Published: July 2002

The nonlinear evolution of an unstable symmetric jet in incompressible, density stratified fluid is simulated numerically. When N2 is constant and near zero, like-signed vortices pair by way of an instability of the mean flow to a subharmonic disturbance with wavelength twice that of the most unstable mode of linear theory. For small but finite and constant values of N2, however, the individual vortex cores are strained and vorticity is generated at small scales by the action of baroclinic torques. In this case, the mean flow of the fully evolved jet is stable to subharmonic disturbances. The linear stability of the two-dimensional nonlinear basic states to three-dimensional perturbations is examined in detail. From this stability analysis, it is inferred that jet flow with stratification characterized by constant N2 is a poor candidate for IGW generation. However, the existence of an efficient mechanism whereby IGW may be radiated to infinity from the jet core is demonstrated via simulations initialized with a density profile such that N2=J tanh2(z/R). This mechanism is expected to be an important contributor to the wave field observed in a variety of geophysical circumstances.
Direct numerical simulation and data analysis of a Mach 4.5 transitional boundary-layer flow
Authors: Dinavahi Surya P. G. , Pruett C. David , Zang Thomas A.
Published: July 2002

This paper describes the creation by temporal direct numerical simulation and the analysis based on the Reynolds stress transport equations of a high quality data set that represents the laminar–turbulent transition of a high-speed boundary-layer flow. Following Pruett and Zang [Theoret. Comput. Fluid Dyn. 3, 345 (1992)], and with the help of algorithmic refinements, the evolution of an axial, Mach 4.5 boundary-layer flow along the exterior of a hollow cylinder is simulated numerically. From a perturbed laminar initial state, the well-resolved simulation proceeds through laminar breakdown to the beginning of a turbulent flow regime. Favre-averaged Reynolds stress transport equations are derived in generalized curvilinear coordinates and are then specialized to the cylindrical geometry at hand. Reynolds stresses and various turbulence quantities, such as turbulent kinetic energy and turbulent Mach number, are calculated from the numerical data at various stages of the transition process. The kinetic energy ‘‘budgets’’ are also constructed from the transport equations. Various contributing terms for the evolution of kinetic energy, like the rates of production, dissipation, transport, and diffusion, are presented. The compressible dissipation rate is small in comparison with the solenoidal dissipation rate for all times. The pressure–dilatation term is of the same order of magnitude as the compressible dissipation rate. The authors hope that both the data set and the analysis presented will benefit those who attempt to model high-speed transitional flow.
The dynamics of ultrasonically levitated drops in an electric field
Authors: Trinh E. H. , Holt R. G. , Thiessen D. B.
Published: July 2002

Ultrasonic and electrostatic levitation techniques have allowed the experimental investigation of the nonlinear oscillatory dynamics of free droplets with diameter between 0.1 and 0.4 cm. The measurement of the resonance frequencies of the first three normal modes of large amplitude shape oscillations in an electric field of varying magnitude has been carried out with and without surface charges for weakly conducting liquids in air. These oscillations of nonspherical levitated drops have been driven by either modulating the ultrasonic field or by using a time-varying electric field, and the free decay from the oscillatory state has been recorded. A decrease in the resonance frequency of the driven fundamental quadrupole mode has been measured for increasing oblate deformation in the absence of an electric field. Similarly, a decrease in this frequency has also been found for increasing DC electric field magnitude. A soft nonlinearity exists in the amplitude dependence of the resonant mode frequencies for freely decaying as well as ultrasonically and electrically driven uncharged drops. This decrease in resonance frequency is accentuated by the presence of free surface charge on the drop. Subharmonic resonance excitation has been observed for drops in a time-varying electric field, and hysteresis exists for resonant modes driven to large amplitude. Mode coupling from lower-order resonances to higher-order modes has been found to be very weak, even for fairly large amplitude shape oscillations. Most of these results are in general agreement with predictions from recent analytical and numerical investigations.
Two-dimensional disturbance growth of linearly stable viscous shear flows
Authors: Hooper A. P. , Grimshaw R.
Published: July 2002

Instability of fluid flow has long been linked with the eigenvalues of the Orr-Sommerfeld equation. Recently, it has been shown that even though all eigenvalues may be stable, it is still possible to have disturbance growth. This is because the Orr-Sommerfeld operator is non-normal. We identify which eigenmodes are important in two-dimensional disturbance growth. We find a relationship between maximum growth and growth caused by the adjoint of the leading eigenmode for both plane Poiseuille flow and plane Couette flow. The work points to a connection between the occurrence of the first degeneracy of the Orr-Sommerfeld operator and the first appearance of disturbance growth.
Dispersion of passive tracers in closed basins: Beyond the diffusion coefficient
Authors: Artale V. , Boffetta G. , Celani A. , Cencini M. , Vulpiani A.
Published: July 2002

We investigate the spreading of passive tracers in closed basins. If the characteristic length scale of the Eulerian velocities is not very small compared with the size of the basin the usual diffusion coefficient does not give any relevant information about the mechanism of spreading. We introduce a finite size characteristic time τ(δ) which describes the diffusive process at scale δ. When δ is small compared with the typical length of the velocity field one has τ(δ)∼λ−1, where λ is the maximum Lyapunov exponent of the Lagrangian motion. At large δ the behavior of τ(δ) depends on the details of the system, in particular the presence of boundaries, and in this limit we have found a universal behavior for a large class of system under rather general hypothesis. The method of working at fixed scale δ makes more physical sense than the traditional way of looking at the relative diffusion at fixed delay times. This technique is displayed in a series of numerical experiments in simple flows.
Spreading and imbibition of viscous liquid on a porous base
Authors: Davis S. H. , Hocking L. M.
Published: July 2002

The competition between the viscous spreading of liquid on a substrate and the absorption by the substrate is studied using several models. The local behaviors near the contact lines, the time scales of droplet spreading and disappearance, and the dependencies on the physical factors that enter are discussed.
A quasilinear, Fokker–Planck description of fast wave minority heating permitting off-axis tangency interactions
Authors: Catto Peter J. , Myra J. R. , Russell D. A.
Published: July 2002

The off-axis quasilinear fast wave minority heating description of Catto and Myra [Phys. Fluids B 4, 187 (1992)] has been improved and implemented in a code which solves the combined quasilinear and collision operator equation for the minority distribution function. Geometrical complications of a minority resonance nearly tangent to a flux surface in the presence of trapped as well as passing particles are retained. The tangency interactions alter the moments and the fusion reaction rate parameter in a model which explores heating on a single flux surface. The strong tangency interactions enhance the more familiar interactions due to trapped particles turning in the vicinity of the minority resonance. An asymmetry in off-axis heating effects occurs because heating on the low field side of the magnetic axis heats more trapped particles than high field side heating. This asymmetry is responsible for the better performance of the low field side case relative to the high and on-axis cases and provides some control over the power absorbed by and the energy stored in the trapped particles.
Multifaceted asymmetric radiation from the edge of tokamak plasmas (MARFE): Pattern formation under nonlocal constraints
Authors: Meerson B. , Petviashvili N. , Tajima T.
Published: July 2002

A simplified two-dimensional nonlinear fluid model is developed to elucidate the basic mechanism of the formation of multifaceted asymmetric radiation from the edge of tokamak plasmas (MARFE). In the framework of a mixed Eulerian–Lagrangian description, the problem is reduced to a reaction-diffusion-type equation with nonlocality, which obeys the constraints of length constancy and mass conservation along the magnetic field. With sufficient radiative cooling, this model predicts formation of MARFE-like plasma condensations from a variety of initial conditions.
Nonlinear magnetohydrodynamic dynamo
Authors: Kleva Robert G. , Drake J. F.
Published: July 2002

The self-consistent nonlinear evolution and saturation of the dynamo, including the back reaction of the magnetic field on the flow through the Lorentz J×B force, is investigated via simulation of the fully compressible magnetohydrodynamic (MHD) equations. The saturated state is found to be highly turbulent. The energy in the saturated magnetic field is only a small fraction of the kinetic energy in the flow which drives the dynamo. However, as the collision frequency decreases and the Reynolds number R increases, the ratio of magnetic to kinetic energy in the saturated state increases gradually. The nonlinear viscosity generated by the turbulent fluctuations rises rapidly relative to the collisional viscosity as R increases, such that the total transport of momentum remains virtually unchanged as the collisional viscosity is reduced. The scale lengths of the magnetic and velocity fluctuations both decrease as R increases, so that the scale size of the magnetic field remains comparable to the scale size of the flow.
A new algebraic growth of nonlinear tearing mode
Authors: Li Ding
Published: July 2002

It is found that the quasilinear modification of magnetic field produces a nonlinear Lorentz force opposing the linear driving force and slowing down the vortex flow. A new algebraic growth appears due to this damping mechanism to oppose the linear growth of the tearing mode. This effect was eliminated in Rutherford’s model [Phys. Fluids 16, 1903 (1973)] under the flux average operation and the assumption ∂/∂t≪η/δ 2 (here η is the resistivity, δ is the resistive layer width). A unified analytical model is developed by using standard perturbation theory for the linear and nonlinear growth of the tearing mode. The inertia effect and quasilinear effects of both the current density and the magnetic field have been included. A nonlinear evolution equation is analytically derived for the tearing mode to describe the linear growth, Rutherford’s behavior, and the new behavior. The classical linear result is exactly recovered as the quasilinear effects are negligible. It is shown that a more slowly algebraic growth like Ψ1∝t can become dominant in the nonlinear phase instead of Rutherford behavior like Ψ1∝t2, provided the tearing mode in the linear phase is strongly unstable. Here Ψ1 is the magnetic flux perturbation.
Axial dynamics of the electron beam in the plasma beat-wave accelerator
Authors: Maroli C. , Petrillo V. , Giallombardo F.
Published: July 2002

Using the sheet model for the electron beam, a system of one-dimensional nonlinear equations has been constructed that describes the dynamics of the beam along with that of the three complex wave amplitudes in the plasma beat-wave accelerator scheme. This system can give directly the acceleration rate in terms of the basic parameters of the process.
Kinetic and transport theory near the tokamak edge
Authors: Hazeltine R. D. , Catto Peter J.
Published: July 2002

Conventional transport orderings employed in the core of a tokamak plasma allow large divergence-free flows in flux surfaces, but only weak radial flows. However, alternate orderings are required in the edge region where radial diffusion must balance the rapid loss due to free streaming to divertor plates or limiters. Kinetic equations commonly used to study the plasma core do not allow such a balance and are, therefore, inapplicable in the plasma edge. Similarly, core transport formulas cannot be extended to the edge region without major, qualitative alteration. Here the necessary changes are addressed. By deriving and solving a novel kinetic equation, distinctive collisional transport laws for the plasma edge are constructed. It is found that the new edge ordering retains the radial diffusion and parallel flow of particles, momentum, and heat to lowest order in the conservation equations. To higher order a surprising form for parallel transport in the scrape-off layer is found, in which the parallel flow of particles and heat are driven by a combination of the conventional gradients, viscosity, and new terms involving radial derivatives. The new terms are not relatively small, and could affect understanding of limiter and divertor operation.
Stability of vortex flows in magnetized plasmas. II. Boltzmann vortices
Authors: Chakrabarti Nikhil , Kaw Predhiman
Published: July 2002

The stability of elliptical vortex flow to the excitation of low-frequency electrostatic drift waves is investigated. It is demonstrated that finite ellipticity of flow drives the secondary instability of drift/drift-acoustic waves. When flow ellipticity is small, certain matching conditions between the rotation frequency and secondary wave frequency are needed for instability to occur. The case of large eccentricity is solved by asymptotic methods and gives a growth rate for the instability that depends logarithmically on eccentricity. Such secondary instability mechanisms can act as a sink of vortex energy (limiting the vortex condensation at the long-wavelength end) and thereby help in our understanding of nonlinear saturation of low-frequency instabilities.
Confinement analysis in low-confinement mode of hydrogen isotope experiments on the Tokamak Fusion Test Reactor
Authors: Barnes Cris W. , Scott S. D. , Bell M. G. , Bell R. , Budny R. V. , Bush C. E. , Fredrickson E. D. , Grek B. , Hill K. W. , Janos A. , Kamperschroer J. H. , LaMarche P. H. , Mansfield D. K. , Park H. K. , Phillips C. K. , Ramsey A. T. , Schivell J. , Stratton B. C. , Synakowski E. J. , Taylor G. , Wilson J. R. , Zarnstorff M. C.
Published: July 2002

The effect of isotope on confinement in high-recycling, L-mode plasmas is studied on the Tokamak Fusion Test Reactor (TFTR) [see D. M. Meade, J. Fusion Energy 7, 107 (1988)] by comparing hydrogen and deuterium plasmas with the same magnetic field and similar electron densities and heating power, with both Ohmic and deuterium-neutral-beam heating. Following a long operational period in deuterium, nominally hydrogen plasmas were created through hydrogen glow discharge and hydrogen gas puffing in Ohmic plasmas, which saturated the exposed limiter surface with hydrogen and raised the H/(H+D) ratio from 10±3% to 65±5%. Ohmic deuterium discharges obtained higher stored energy and lower loop voltage than hydrogen discharges with similar limiter conditions. Neutral-beam power scans were conducted in L-mode plasmas at minor radii of 50 and 80 cm, with plasma currents of 0.7 and 1.4 MA. To minimize transport differences from the beam deposition profile and beam heating, deuterium neutral beams were used to heat the plasmas of both isotopes. Total stored energy increased approximately 20% from nominally hydrogen plasmas to deuterium plasmas during auxiliary heating. Of this increase about half can be attributed to purely classical differences in the energy content of unthermalized beam ions. Kinetic measurements indicate a consistent but small increase in central electron temperature and total stored electron energy in deuterium relative to hydrogen plasmas, but no change in total ion stored energy. No significant differences in particle transport, momentum transport, and sawtooth behavior are observed. Overall, only a small improvement (∼10%) in global energy confinement time of the thermal plasma is seen between operation in hydrogen and deuterium.
Dielectric Čerenkov maser with a plasma column in a dielectric lined slow-wave waveguide
Authors: Jian-Qiang Wu
Published: July 2002

Dielectric Čerenkov maser with a plasma column in a dielectric lined slow-wave waveguide is studied in the absence of a longitudinal guided magnetic field by use of a fully self-consistent and relativistic field theory. Determinantal dispersion equations of the interaction of a thin annular relativistic electron beam (TAREB) with the wave are derived for the TAREB inside and surrounding the plasma column, respectively. These dispersion equations show that the beam–wave interaction results from the coupling of the transverse-magnetic (TM) mode in the dielectric lined slow-wave waveguide with the plasma column to the beam mode via the electron beam. Finally, the dispersion equations are directly solved numerically, and the cutoff frequency, the operation frequency, and the growth rate of the wave are obtained.
Structure of parallel-velocity-shear-driven mode in toroidal plasmas
Authors: Dong J. Q. , Xu W. B. , Zhang Y. Z. , Horton W.
Published: July 2002

It is shown that the Fourier-ballooning representation is appropriate for the study of short-wavelength drift-like perturbation in toroidal plasmas with a parallel velocity shear (PVS). The radial structure of the mode driven by a PVS is investigated in a torus. The Reynolds stress created by PVS turbulence, and proposed as one of the sources for a sheared poloidal plasma rotation, is analyzed. It is demonstrated that a finite ion temperature may strongly enhance the Reynolds stress creation ability from PVS-driven turbulence. The correlation of this observation with the requirement that ion heating power be higher than a threshold value for the formation of an internal transport barrier is discussed.
Oscillatory disintegration of a trans-Alfvénic shock: A magnetohydrodynamic simulation
Authors: Markovskii S. A. , Skorokhodov S. L.
Published: July 2002

Nonlinear evolution of a trans-Alfvénic shock wave (TASW), i.e., such at which the flow velocity passes through the Alfvén velocity, is computed in a magnetohydrodynamic approximation. The analytical theory suggests that an infinitesimal perturbation of a TASW results in its disintegration, and, thus, in finite variation of the flow, or in transformation into some other unsteady configuration. In the present paper, this result is confirmed by numerical simulations. It is shown that the disintegration time is close to its minimum value equal to the shock thickness divided by a velocity of separation of the emerging secondary structures. The secondary TASW that appears after the disintegration is again unstable with respect to disintegration. When the perturbation has a cyclic nature, the TASW undergoes oscillatory disintegration, during which it repeatedly transforms into another TASW. This process manifests itself as a train of shock and rarefaction waves, which consecutively emerge at one edge of the train and merge at the other edge.
Electrostatic fluctuations in the Current Sustained Torus IV at Nagoya University
Authors: Zhai K. , Kobayashi M. , Tashiro K. , Kojima H. , Takagi M. , Takamura S.
Published: July 2002

A detailed experimental investigation of plasma fluctuation and its modification due to radial electric field effects, both its shear and curvature, has been carried out on the Current Sustained Torus IV at Nagoya University [Takamura et al., J. Plasma Fusion Res. 74, 38 (1998)] through measurement with an array of Langmuir probes. The observed statistical dispersion relation indicates a drift-wave-type turbulence. An examination of the radial electric field shear and curvature effects on the fluctuations as well as comparisons to theoretical predictions are presented. The decorrelation of turbulence is found to be influenced by the radial electric field shear in our experiment. A modification of the poloidal correlation length and the two-poloidal-point coherency due to the radial electric field has also been identified. Nonlinear analysis of quadratic mode coupling indicates that the radial electric field can affect the fluctuation amplitudes by modifying the coupling between different spectral components of the fluctuations.
Analyzing spatially resolved line spectra emitted by Z pinches
Authors: Apruzese J. P. , Davis J. , Whitney K. G. , Yadlowsky E. J. , Carlson E. P. , Niemel J. , Barakat F. , Hazelton R. C. , Klepper C. C. , Moschella J. J. , Failor B. H. , Levine J. S. , Riordan J. C. , Song Y. , Whitton B. L.
Published: July 2002

The spatial profiles of key physical variables such as electron temperature and density are crucial in determining the overall radiating efficiency of a Z pinch as well as the emitted photon energy distribution. The present work uses spatially resolved x-ray lines emitted from shots taken on the 4 MA Double EAGLE generator [C. Deeney et al., Phys. Rev. A 44, 6762 (1991)] at Maxwell Physics International to infer such profiles. The loads were arrays of 15 wires consisting of 95% Al, 5% Si, producing nearly 50 kJ of K-shell radiation with relatively long pulsewidths of 41–43 ns. It is found that the spatial profile of the He-like intercombination to resonance line ratio is critically affected by self-absorption and re-emission (scattering) of resonance line photons emitted from the hot, dense interior of the pinch. This ratio cannot be correctly interpreted without taking the scattering into account. Also, at densities somewhat lower than those achieved by these pinches, this line ratio becomes more temperature than density dependent. The inferred temperature gradient is much less steep than that which had been diagnosed previously for a pinch emitting a much shorter x-ray pulsewidth of 13 ns.
Origin of the main deep electron trap in electron irradiated InP
Authors: Sibille Alain
Published: July 2002

The electrical activity and annealing behavior of the main electron trap in electron irradiated InP p+n junctions has been investigated. A very marked depth dependence of the annealing rate has been found. Moreover, this center apparently acts as if it were a deep donor, leading to an increase of carrier concentration on the n side. All these results are coherently interpreted with a model in terms of radiation defect D(P) (phosphorus interstitial or vacancy), residual shallow acceptor complexing, the final annealing resulting from a dissociation of the complex followed by a diffusion and either recapture or annihilation of D(P).
P
n
p GaAs/Ge/Ge phototransistor grown by molecular beam epitaxy: Implications for bipolar and hot-electron transistors
Authors: Chand N. , Klem J. , Morkoç H.
Published: July 2002

In order to exploit the potential of GaAs/Ge heterojunctions for high-speed heterojunction bipolar transistors and hot-electron transistors, a Pnp GaAs/Ge floating base phototransistor, sensitive to 1.1–1.55-μm wavelength range, was made. The gallium-doped Ge substrate was first exposed to the As2 flux in the growth chamber of a molecular beam epitaxy system to form a pn junction in Ge. This was followed by the growth of a p-type Be-doped GaAs layer which served as the emitter. The fabricated mesa devices showed an optical gain of 85 at 1.15 μm incident wavelength. The gain was found to be nearly independent of the incident light power indicating good quality of the GaAs/Ge heterointerface.
Photoluminescence in CdTe grown on GaAs substrates by molecular beam epitaxy
Authors: Leopold D. J. , Ballingall J. M. , Wroge M. L.
Published: July 2002

Single-crystal epitaxial layers of (100) and (111) oriented CdTe were grown on (100) oriented GaAs substrates by molecular beam epitaxy. Low-temperature (4.2 K) photoluminescence spectra exhibit free-exciton and bound-exciton peaks having linewidths on the order of 2 meV for both CdTe crystallographic orientations. However, defect-related photoluminescence is found to be stronger in (100) oriented CdTe.
Dynamical states and stability of linear arrays of Josephson junctions
Authors: Hadley P. , Beasley M. R.
Published: July 2002

We consider a one-dimensional array of dc-biased Josephson junctions shunted by a load of passive circuit elements. The load serves to couple the ac Josephson effect oscillations in the various junctions, giving rise to dynamical states of the system that do not appear for a single junction. Our results demonstrate two distinct phase-locked states of the array, hysteresis, and chaotic behavior depending on the load and the value of the bias current. Implications of these results for local oscillator applications of such arrays are also discussed.
Transverse instability of an electron beam in a beam-induced ion channel
Authors: Nguyen K. T. , Schneider R. F. , Smith J. R. , Uhm H. S.
Published: July 2002

Transverse oscillations of a relativistic electron beam propagating in a beam-induced ion channel have been theoretically investigated and experimentally observed. Good agreement between experimental observations and theoretical calculations strongly suggests that these oscillations may be caused by the ion hose (ion resonance) instability.
Measurement of ultrashort optical pulses with β-BaB2O4
Authors: Cheng K. L. , Bosenberg W. , Wise F. W. , Walmsley I. A. , Tang C. L.
Published: July 2002

We have evaluated barium metaborate ( β-BaB2O4) for its use in the measurement of ultrashort optical pulses. Using crystals grown in our laboratory, we have found that pulses as short as 50 fs can be measured accurately with a crystal 1.8 mm thick. The advantages of using barium metaborate rather than potassium dihydrogen phosphate (KDP) or ammonium dihydrogen phosphate (ADP) for autocorrelation measurements are discussed.
Enhanced visibility of hydrogen atoms by neutron crystallography on fully deuterated myoglobin
Authors: Shu Fong , Ramakrishnan Venki , Schoenborn Benno P.
Published: July 2002

Although hydrogens comprise half of the atoms in a protein molecule and are of great importance chemically and structurally, direct visualization of them by using crystallography is difficult. Neutron crystallography is capable of directly revealing the position of hydrogens, but its use on unlabeled samples faces certain technical difficulties: the large incoherent scattering of hydrogen results in background scattering that greatly reduces the signal to noise of the experiment. Moreover, whereas the scattering lengths of C, N, and O are positive, that of hydrogen is negative and about half the magnitude. This results in density for hydrogens being half as strong and close to the threshold of detection at 2.0-Å resolution. Also, because of its opposite sign, there is a partial cancellation of the hydrogen density with that from neighboring atoms, which can lead to ambiguities in interpretation at medium resolution. These difficulties can be overcome by the use of deuterated protein, and we present here a neutron structure of fully deuterated myoglobin. The structure reveals a wealth of chemical information about the molecule, including the geometry of hydrogen bonding, states of protonation of histidines, and the location and geometry of water molecules at the surface of the protein. The structure also should be of broader interest because it will serve as a benchmark for molecular dynamics and energy minimization calculations and for comparison with NMR studies.
Arsenite transport by mammalian aquaglyceroporins AQP7 and AQP9
Authors: Liu Zijuan , Shen Jian , Carbrey Jennifer M. , Mukhopadhyay Rita , Agre Peter , Rosen Barry P.
Published: July 2002

Much is known about the transport of arsenite and antimonite into microbes, but the identities of mammalian transport proteins are unknown. The
Saccharomyces cerevisiae FPS1
gene encodes a membrane protein homologous to the bacterial aquaglyceroporin GlpF and to mammalian aquaglyceroporins AQP7 and AQP9. Fps1p mediates glycerol uptake and glycerol efflux in response to hypoosmotic shock. Fps1p has been shown to facilitate uptake of the metalloids arsenite and antimonite, and the
Escherichia coli
homolog, GlpF, facilitates the uptake and sensitivity to metalloid salts. In this study, the ability of mammalian aquaglyceroporins AQP7 and AQP9 to substitute for the yeast Fps1p was examined. The
fps1Δ
strain of
S. cerevisiae
exhibits increased tolerance to arsenite and antimonite compared to a wild-type strain. Introduction of a plasmid containing AQP9 reverses the metalloid tolerance of the deletion strain. AQP7 was not expressed in yeast. The
fps1Δ
cells exhibit reduced transport of
73
As(III) or
125
Sb(III), but uptake is enhanced by expression of AQP9.
Xenopus laevis
oocytes microinjected with either AQP7 or AQP9 cRNA exhibited increased transport of
73
As(III). These results suggest that AQP9 and AQP7 may be a major routes of arsenite uptake into mammalian cells, an observation potentially of large importance for understanding the action of arsenite as a human toxin and carcinogen, as well as its efficacy as a chemotherapeutic agent for acute promyelocytic leukemia.
Suppressor of cytokine signaling-3 preferentially binds to the SHP-2-binding site on the shared cytokine receptor subunit gp130
Authors: Nicholson Sandra E. , De Souza David , Fabri Louis J. , Corbin Jason , Willson Tracy A. , Zhang Jian-Guo , Silva Anabel , Asimakis Maria , Farley Alison , Nash Andrew D. , Metcalf Donald , Hilton Douglas J. , Nicola Nicos A. , Baca Manuel
Published: July 2002

Suppressor of cytokine signaling-3 (SOCS-3) is one member of a family of intracellular inhibitors of signaling pathways initiated by cytokines that use, among others, the common receptor subunit gp130. The SH2 domain of SOCS-3 has been shown to be essential for this inhibitory activity, and we have used a quantitative binding analysis of SOCS-3 to synthetic phosphopeptides to map the potential sites of interaction of SOCS-3 with different components of the gp130 signaling pathway. The only high-affinity ligand found corresponded to the region of gp130 centered around phosphotyrosine-757 (pY757), previously shown to be a docking site for the tyrosine phosphatase SHP-2. By contrast, phosphopeptides corresponding to other regions within gp130, Janus kinase, or signal transducer and activator of transcription proteins bound to SOCS-3 with weak or undetectable affinity. The significance of pY757 in gp130 as a biologically relevant SOCS-3 docking site was investigated by using transfected 293T fibroblasts. Although SOCS-3 inhibited signaling in cells transfected with a chimeric receptor containing the wild-type gp130 intracellular domain, inhibition was considerably impaired for a receptor carrying a Y→F point mutation at residue 757. Taken together, these data suggest that the mechanism by which SOCS-3 inhibits the gp130 signaling pathway depends on recruitment to the phosphorylated gp130 receptor, and that some of the negative regulatory roles previously attributed to the phosphatase SHP-2 might in fact be caused by the action of SOCS-3.
Vitamin E succinate inhibits the function of androgen receptor and the expression of prostate-specific antigen in prostate cancer cells
Authors: Zhang Yu , Ni Jing , Messing Edward M. , Chang Eugene , Yang Chin-Rang , Yeh Shuyuan
Published: July 2002

Although epidemiological evidence indicates that a daily supplement of vitamin E may reduce the risk of prostate cancer, the detailed mechanism underlying this effect remains unclear. Here we demonstrate that α-tocopheryl succinate (VES) can suppress the expression of prostate-specific antigen (PSA), a marker for the progression of prostate cancer. VES can also suppress androgen receptor (AR) expression by means of transcriptional and posttranscriptional modulation, but not ligand binding, nuclear translocation, or AR dimerization. This VES-mediated inhibition of AR is selective because VES does not repress the expression of other nuclear receptors. Cell growth studies further show that VES inhibits the growth of prostate cancer LNCaP cells. In contrast, hydroxyflutamide (HF), an antiandrogen currently used to treat prostate cancer patients, only slightly inhibits LNCaP cell growth. Interestingly, simultaneous addition of HF and VES results in a more significant inhibition of LNCaP cell growth. Moreover, selenomethionine (SM), a prostate cancer treatment adjuvant, shows an inhibitory effect on LNCaP cell growth, yet has no effect on the AR/PSA pathway. Together, our data indicate that VES may suppress androgen/AR-mediated cell growth and PSA expression by inhibiting AR expression at both the transcription and translation levels. This previously undescribed mechanism may explain how VES inhibits the growth of prostate cancer cells and help us to establish new therapeutic concepts for the prevention and treatment of prostate cancer.
Genetic factors are major determinants of phenotypic variability in a mouse model of the DiGeorge/
del22q11
syndromes
Authors: Taddei Ilaria , Morishima Masae , Huynh Tuong , Lindsay Elizabeth A.
Published: July 2002

The
del22q11
syndrome is associated with a highly
variable phenotype despite the uniformity of the chromosomal deletion
that causes the disease in most patients.
Df1
/+ mice,
which model
del22q11
, present with reduced penetrance of
cardiovascular defects similar to those seen in deleted patients but
not with other
del22q11
-like findings. The reduced
penetrance of cardiovascular defects is caused by the ability of mutant
embryos to recover from a fourth pharyngeal arch artery growth
abnormality that is fully penetrant in early embryos. Here we show that
genetic background has a major effect on penetrance of cardiovascular
defects by affecting this embryonic recovery process. This effect could
not be explained by allelic variation at the haploid locus, and it is
likely to be caused by genetic modifiers elsewhere in the genome. We
also show that genetic factors control extension of the
Df1
/+ phenotype to include thymic and parathyroid
anomalies, establishing the
Df1
mouse as a model for the
genetic analysis of three major features of human
del22q11
syndrome. We found that in
Df1
/+ mice, as in human patients, expression of the
heart and thymic phenotypes are essentially independent from each
other, suggesting that they may be controlled by different genetic
modifiers. These data provide a framework for our understanding of
phenotypic variability in patients with
del22q11
syndrome and the tools for its genetic dissection.
Pb(II) distributions at biofilm–metal oxide interfaces
Authors: Templeton Alexis S. , Trainor Thomas P. , Traina Samuel J. , Spormann Alfred M. , Brown Gordon E.
Published: July 2002

The distribution of aqueous Pb(II) sorbed at the interface between
Burkholderia cepacia
biofilms and hematite (α-Fe
2
O
3
) or corundum (α-Al
2
O
3
) surfaces has been probed by using an application of the long-period x-ray standing wave technique. Attached bacteria and adsorbed organic matter may interfere with sorption processes on metal oxide surfaces by changing the characteristics of the electrical double layer at the solid–solution interface, blocking surface sites, or providing a variety of new sites for metal binding. In this work, Pb L
α
fluorescence yield profiles for samples equilibrated with 10
−7
to 10
−3.8
M Pb(II) were measured and modeled to determine quantitatively the partitioning of Pb(II) at the biofilm–metal oxide interface. Our data show that the reactive sites on the metal oxide surfaces were not passivated by the formation of a monolayer biofilm. Instead, high-energy surface sites on the metal oxides form the dominant sink for Pb(II) at submicromolar concentrations, following the trend α-Fe
2
O
3
(0001) > α-Al
2
O
3
(11̄02) > α-Al
2
O
3
(0001), despite the greater site density within the overlying biofilms. At [Pb] > 10
−6
M, significant Pb uptake by the biofilms was observed.