bluuebunny/crossref_metadata_2025 huggingface dataset:
Spreading of a granular mass on a horizontal plane
Authors: Lajeunesse E. , Mangeney-Castelnau A. , Vilotte J. P.
Published: June 2004

The transient surface flow occurring when a cylindrical pile of dry granular material is suddenly allowed to spread on a horizontal plane is investigated experimentally as a function of the released mass M, the initial aspect ratio a of the granular cylinder pile, the properties of the underlying substrate (smooth or rough, rigid or erodible) and the bead size. Two different flow regimes leading to three different deposit morphologies are observed as a function of the initial aspect ratio a, whatever the substrate properties and the bead size. For a≲3, the granular mass spreads through an avalanche on its flanks producing either truncated cone or conical deposits. For a≳3, the upper part of the column descends conserving its shape while the foot of the pile propagates radially outward. The obtained deposit looks like a “Mexican hat” and the slope angle at the foot of the deposit is observed to saturate at a value of the order of 5°. For a given ground and bead size, the flow dynamics and the deposit morphology are found to be independent of M and to vary only with the initial aspect ratio a. Further investigation indicates that the deposit morphology depends only slightly on the substrate properties and the bead size, except when a becomes large. In particular the same dynamical regimes and deposit morphologies are recovered for the same range of a, independent of the substrate properties or the bead size. Moreover the rescaled deposit radius, the rescaled spreading velocity, and the fraction of energy dissipated during the flow do not depend on M, the substrate properties, or the bead size, but vary only with a. We believe this to be the signature of the fact that the flow develops near the free surface of the granular pile so that the dynamics is essentially controlled by grain/grain interactions.
Stability of time-modulated electroosmotic flow
Authors: Suresh V. , Homsy G. M.
Published: June 2004

We present a linear stability analysis of parallel electroosmotic flow in a slot geometry. A spatially uniform time harmonic electric field is applied to a dilute electrolyte solution contained between two infinite parallel plates. The base state ion concentrations and electric potential are determined using the Poisson–Boltzmann equation in the Debye–Hückel approximation. The base velocity field is found to be time harmonic and parallel. It is shown that the original system can be replaced by an equivalent one consisting of an electrically neutral fluid enclosed between oscillating parallel plates, whose speed and frequency of oscillation depend on the modulated electric field. Further, the system of linearized disturbance equations can be decoupled into two stability problems: The first, called the electrokinetic problem, describes the evolution of disturbance ion concentrations and electric potential and is independent of the disturbance velocity components. The second, called the Stokes layer problem describes an oscillatory Stokes layer forced by an electrical body force. The stability of each system is determined by Floquet analysis of a dynamical system obtained from a truncated Galerkin expansion of the perturbation quantities. Our calculations show the system to be linearly stable over a wide range of parameters, with damping rates that become quite small for certain combinations of Stokes and Reynolds numbers.
A dynamic Smagorinsky model with dynamic determination of the filter width ratio
Authors: Tejada-Martı́nez Andrés E. , Jansen Kenneth E.
Published: June 2004

Various low-pass, spatial test filters specific to dynamic model large-eddy simulation (LES) on finite element topologies are proposed and analyzed. A number of simulations of decaying isotropic turbulence are performed using the stabilized finite element method of Whiting and Jansen with the purpose of understanding the dependence of the dynamic model on the test filter of choice and the elusive filter width ratio. From these numerical experiments, a key assumption is extracted leading to the derivation of a new dynamic model in which the sole model parameter, the filter width ratio, is computed dynamically. Traditionally, the dynamic model parameter has taken the filter width ratio as a constant. The new dynamic model is tested on LES of decaying isotropic turbulence on hexahedral, tetrahedral, and wedge topologies.
A numerical study of breaking waves
Authors: Song Chiyoon , Sirviente Ana I.
Published: June 2004

This numerical study explores the physical processes involved in breaking waves. The two-dimensional, incompressible, unsteady Navier–Stokes equations are solved in sufficiently refined grids to capture viscous and capillary effects. The immiscible interface, characterized by a jump in density and viscosity, is embedded in the domain and a hybrid front tracking/capturing method is used to characterize the moving interface of this multiphase flow. A parametric study is conducted to assess the role of surface tension, Reynolds number, density, and viscosity on the breaking process, as well as their role in the vorticity redistribution and energy dissipation beneath the surface.
On physical mechanisms in chemical reaction-driven tip-streaming
Authors: Krechetnikov R. , Homsy G. M.
Published: June 2004

In this work we provide a basic physical modeling of the spatiotemporal pattern of emulsification produced by chemical reaction-driven tip-streaming and observed by Fernandez and Homsy [Phys. Fluids 16, 2548 (2004)]. Features of this phenomenon—nonlinear autooscillations, a conical drop shape, tip-streaming, and droplet trajectory splitting—are addressed in this paper. In particular, the experimentally found regimes of self-sustained periodic motion and the transitions between them are explained with the help of a nonlinear relaxation oscillator model. An exact self-similar solution for the steady tip-streaming mode supports the suggested mechanism of a Marangoni-driven phenomenon. Finally, the ionic nature of the surfactant produced at the interface offers a reasonable explanation for the formation of a spray cone, which is due to repulsive electrostatic interactions between droplets. These features distinguish this phenomenon from standard tip-streaming.
Analysis of convective instability and heat transfer characteristics of nanofluids
Authors: Kim Jake , Kang Yong Tae , Choi Chang Kyun
Published: June 2004

The convective instability driven by buoyancy and heat transfer characteristics of nanofluids are investigated analytically. This paper proposes a factor which describes the effect of nanoparticle addition on the convective instability and heat transfer characteristics of a base fluid. The Bruggeman model based on the mean field approach for expressing the thermal conductivity enhancement is chosen as a lower bound of the thermal conductivity relationship. The results show that as the density and heat capacity of nanoparticles increase and the thermal conductivity and the shape factor of nanoparticles decrease, the convective motion in a nanofluid sets in easily. The heat transfer coefficient of a nanofluid is enhanced by all parameters with respect to the volume fraction of nanoparticles.
Noise due to extreme bubble deformation near inception of tip vortex cavitation
Authors: Choi Jin-Keun , Chahine Georges L.
Published: June 2004

A study on the tip vortex cavitation inception based on extreme bubble deformation and jet noise is presented. First, two preliminary experiments involving bubble splitting between two plates in the absence of swirl are performed to provide a correlation between the numerically computed splitting/jet noise and the measured noise. The bubble behavior and pressure signal predicted by the axisymmetric method are compared with those recorded simultaneously by using a high-speed video camera and a hydrophone. Then, numerical studies on the bubble behavior in the tip vortex flow field are conducted. The tip vortex flow near a hydrofoil is provided by a viscous flow computation, and the bubble behavior is simulated by an axisymmetric boundary element method which accounts for the provided vortex flow field. The characteristics of the bubble behavior and jet noise over a range of cavitation numbers are investigated. The effect of initial bubble nucleus size and the Reynolds number effect of the tip vortex flow on the tip vortex cavitation inception, the bubble behavior including its splitting, and jet noise are also discussed.
Spot size effects on the stationary envelope of intense laser pulses in plasma
Authors: Abbasi H. , Pajouh H. Hakimi , Shukla P. K.
Published: June 2004

Nonlinear interactions between ultraintense laser pulses and plasmas reveals a great variety of important collective phenomena. Advances in laser technology have made possible compact terawatt lasers capable of generating subfemtosecond pulses at ultrahigh intensities. These ultrahigh intensities result in highly relativistic nonlinear electron dynamics. This paper addresses stationary stage of the interaction of an ultraintense short laser pulse with a plasma including finite spot size effects. The study is based on the approach that accounts for the transversal effects in an average manner. Following the standard method, a reduced wave equation for the slowly varying laser envelope is derived, including nonlinear effects associated with relativistic electron mass variation and relativistic ponderomotive force. Localized and periodic solutions of the envelope equation are presented and compared with the case when the transversal distribution is infinite. It is found that the finite transverse size of laser spot has significant effects on the propagation characteristics of the stationary profiles.
Observation of parametric decay spectrum in a cylindrical electron cyclotron resonance plasma system
Authors: Yadav Vipin K. , Bora D.
Published: June 2004

Nonlinear wave coupling phenomena in an electron cyclotron resonance (ECR) produced plasma are observed. Experiments are carried out in a small linear cylindrical system with hydrogen plasma. Microwave power in the system is delivered by a magnetron at 2.45 GHz in TE10 mode and is launched radially to have extraordinary (X) wave in plasma. The axial magnetic field configuration, required for ECR to occur in the system, is such that the first ECR surface (B=875 G) resides at the center of the system. Parametric decay spectrum of the launched electromagnetic wave is observed at the upper hybrid resonance (UHR) layer with the appearance of sidebands on the higher and lower side of the launched frequency. Experiments show that the appearance of parametric decay spectrum has a threshold on input microwave power. The decay spectrum is observed only at the UHR surface indicating strong spatial dependence. The parametric decay is also verified in argon and helium plasmas.
Simulation of saturated tearing modes in tokamaks
Authors: Nguyen Canh N. , Bateman Glenn , Kritz Arnold H.
Published: June 2004

A quasi-linear model, which includes the effect of the neoclassical bootstrap current, is developed for saturated tearing modes in order to compute magnetic island widths in axisymmetric toroidal plasmas with arbitrary aspect ratio and cross-sectional shape. The model is tested in a simple stand-alone code and is implemented in the BALDUR [C. E. Singer et al., Comput. Phys. Commun. 49, 275 (1982)] predictive modeling code. It is found that the widths of tearing mode islands increase with decreasing aspect ratio and with increasing elongation. Also, the island widths increase when the gradient of the current density increases at the edge of the islands and when the current density inside the islands is suppressed, such as the suppression caused by the near absence of the bootstrap current within the islands. In simulations of tokamak discharges, it is found that tearing mode island widths oscillate in time in response to periodic sawtooth crashes. The local enhancements in the transport produced by magnetic islands have a noticeable effect on global plasma confinement in simulations of low aspect ratio, high beta tokamaks, where saturated tearing mode islands can occur with widths that are greater than 15% of the plasma minor radius.
Ultimate regime in Rayleigh–Bénard convection: The role of plates
Authors: Chillà F. , Rastello M. , Chaumat S. , Castaing B.
Published: June 2004

The ultimate regime of convection, long ago predicted by Kraichnan [Phys. Fluids 5, 1374 (1962)], could be called elusive because some apparently equivalent experiments showed it while others did not, with no apparent reasons for this discrepancy. In this paper, we propose a model which accounts for the finite heat conductivity and heat capacity of real active boundaries. Bad thermal characteristics of the plates can explain differences between various experiments, in agreement with recent numerical simulations.
Design of the Ni-like Ag x-ray laser at 13.9 nm
Authors: Yan F. , Zhang J. , Lu X. , Zhong J. Y.
Published: June 2004

The Ni-like Ag x-ray laser at 13.9 nm (4d→4p, J=0→1) is numerically studied, using a one-dimensional hydrodynamic code coupled with an atomic physics code. The effects of the drive laser intensity, pulse duration, and delay time on the performance of the Ni-like Ag x-ray laser are investigated. A saturated x-ray laser output could possibly be generated for a short plasma length under the optimized drive pulse configuration. The analysis of the plasma conditions, including the evolution of gain in time and space, the electron temperature and the electron density, contribute to further understanding of the process of Ni-like x-ray lasers.
Interaction of a deep-water wave with a vertical cylinder at low Keulegan–Carpenter number: Transition from phase-locked modes of vortex formation
Authors: Ozgoren M. , Rockwell D.
Published: June 2004

Vortex formation from a cylinder in a deep-water wave is characterized using a technique of high-image-density particle image velocimetry for small values of wave amplitude, which corresponds to low magnitudes of the Keulegan–Carpenter (KC) number. Despite the fact that the deep-water wave involves particle trajectories in the form of circular orbits, whose axes are normal to the axis of the cylinder, it is possible to attain modes of vortex formation that are phase locked to the wave motion at lower values of KC. At a critical value of KC, however, the onset of non-phase-locked modes occurs. These modes, which are defined in terms of patterns of instantaneous vorticity, take three basic forms. Furthermore, when the cylinder undergoes self-excited vibrations at the critical value of KC, it is possible to identify the same basic modes as for the stationary cylinder.
Experiment on collisionless plasma interaction with applications to supernova remnant physics
Authors: Courtois C. , Grundy R. A. D. , Ash A. D. , Chambers D. M. , Woolsey N. C. , Dendy R. O. , McClements K. G.
Published: June 2004

Results from an experimental study of the collisionless interaction of two laser-produced plasmas in a magnetic field with applications to supernova remnant shock physics are presented. The dynamics of the two plasmas and their interaction are studied with and without magnetic field through spatially and temporally resolved measurements of the electron density. Experimental results show that counter-propagating collisionless plasmas interpenetrate when no magnetic field is present. In contrast, results obtained with the addition of a 7.5 T magnetic field perpendicular to plasma flow show density features in the interaction area that only occur when the field is present. The reason for this remains uncertain. It is suggested that this results from an increase in the effective collisionality as the magnetic field reduces the ion and electron gyroradius below the size of the experiment.
Loss rate of an electrically trapped non-neutral plasma
Authors: Chang Yongbin , Correa J. R. , Ordonez C. A.
Published: June 2004

A non-neutral plasma in a Malmberg–Penning trap can be allowed to escape confinement in a controllable way, because the depth of the applied electric potential well used to confine the plasma axially is adjustable. A theoretical approach is presented for predicting the collision-based axial plasma loss rate, just after the well depth in the trap is made shallower. The approach can also be used for predicting an upper limit for the loss rate of a near-thermal plasma from other types of traps, which may employ one-, two-, or three-dimensional electric potential wells. Example predictions are provided, and comparisons with existing theories are made.
Subignition fusion yields generated by fast heating of compressed deuterium–tritium and break-even scaling
Authors: Slutz S. A. , Vesey R. A. , Shoemaker I. , Mehlhorn T. A. , Cochrane K.
Published: June 2004

A simple model is presented to calculate the fusion yield from the fast heating of compressed deuterium–tritium (DT). The model is applicable when the fusion yield is small enough to neglect self-heating. Since 80% of the fusion yield escapes as 14 MeV neutrons, self-heating is small as long as the fusion yield is less than the deposited energy, i.e., the fusion gain, Q⩽1. We show the model is in good agreement with detailed numerical simulations when this condition is satisfied, as will be the case for fast ignition experiments in the near future. The model is used to calculate the fast heating fusion yields as a function of the important parameters such as the fuel density, deposited energy, and pulse length. The model is also used to obtain the minimum energy, Eq1, and the fuel diameter, d, necessary to obtain Q=1, which is given approximately by the scaling laws Eq1=15.3(ρ/100)−1.5 kJ, and d=16.5(ρ/100)−0.84 μm, where ρ is the DT density. These scaling laws should help the design of Q=1 experiments.
The penetration of plasma clouds across magnetic boundaries: The role of high frequency oscillations
Authors: Hurtig Tomas , Brenning Nils , Raadu Michael A.
Published: June 2004

Experiments are reported where a collision-free plasma cloud penetrates a magnetic barrier by self-polarization. Two closely related effects, both fundamental for the penetration mechanism, are studied quantitatively: anomalous fast magnetic field penetration (two orders of magnitude faster than classical), and anomalous fast electron transport (three orders of magnitude faster than classical and two orders of magnitude faster than Bohm diffusion). It is concluded that they are both mediated by highly nonlinear oscillations in the lower hybrid range, driven by a strong diamagnetic current loop which is set up in the plasma in the penetration process.
Compact toroids with Alfvénic flows
Authors: Wang Zhehui , Tang X. Z.
Published: June 2004

The Chandrasekhar equilibria form a class of stationary ideal magnetohydrodynamics equilibria stabilized by magnetic-field-aligned Alfvénic flows. Analytic solutions of the Chandrasekhar equilibria are explicitly constructed for both field-reversed configurations and spheromaks. Favorable confinement property of nested closed flux surfaces and the ideal magnetohydrodynamic stability of the compact toroids are of interest for both magnetic trapping of high energy electrons in astrophysics and confinement of high temperature plasmas in laboratory.
Modeling stimulated Brillouin scattering in the underdense corona of a direct drive inertial confinement fusion target
Authors: Myatt J. , Maximov A. V. , Seka W. , Craxton R. S. , Short R. W.
Published: June 2004

Motivated by recent long scale-length single- and multiple-beam experiments conducted on LLE’s OMEGA laser system [W. Seka et al., Phys. Rev. Lett. 89, 175002 (2002)], we have simulated backward stimulated Brillouin scattering (SBS) in inhomogeneous direct drive plasmas where a critical surface is present at all times. This was achieved by adapting pF3D, a parallel, three-dimensional laser–plasma interaction code developed at the Lawrence Livermore National Laboratory [R. L. Berger et al., Phys. Plasmas 5, 4337 (1998)]. The shortcomings of the paraxial approximation, inherent in pF3D, were identified and circumvented via a practical approach that has led to an improved understanding of the experiments. The results show a qualitative agreement between the simulated and experimental SBS backscattered power reflectivity, with the conclusion that the time dependence of the SBS reflectivity is governed by target hydrodynamics and a quantitative agreement in the blue-shift in the frequency of reflected light. The simulations have also shown a sensitivity of the backscattered reflectivity to the amplitude of the specularly reflected signal of an “opposing” beam.
Analytical solutions to the Grad–Shafranov equation
Authors: Atanasiu C. V. , Günter S. , Lackner K. , Miron I. G.
Published: June 2004

Two families of exact analytical solutions of the Grad–Shafranov equation are presented by specifying the highest polynomial dependence of the plasma current density on the flux function Ψ in such a way that the Grad–Shafranov equation becomes a linear inhomogeneous differential equation. Both the pressure profile and the poloidal current profile each have two free parameters. X-points can be represented by superposition of solutions. Examples of the exact equilibrium solution are given for both a D-shaped plasma and a toroidally diverted plasma.
AKS hierarchy and bi-Hamiltonian geometry of Gelfand–Zakharevich type
Authors: Guha Partha
Published: June 2004

A bi-Hamiltonian system is a system of differential equations which can be written in Hamiltonian form in two distinct ways. The applications of Gelfand–Zakharevich bi-Hamiltonian structure, which is an extension of a Poisson–Nijenhuis structure on phase space, has been extensively explored by Falqui, Magri, and Pedroni in the context of separation of variables. It is well known that the integrable Hamiltonian systems defined by the Adler–Kostant–Symes (AKS) scheme contains bi-Hamiltonian structure. In this paper we unveil the connection between Adler–Kostant–Symes formalism applied to loop algebra and the Gelfand–Zakharevich bi-Hamiltonian structure by superposition the results of Fordy and Kulish in the AKS scheme. We also study the commuting flows of the AKS hierachy and its connection to the Zakharov–Shabat hierarchy.
Characterization of Li7(p,n)7Be neutron yields from laser produced ion beams for fast neutron radiography
Authors: Lancaster K. L. , Karsch S. , Habara H. , Beg F. N. , Clark E. L. , Freeman R. , Key M. H. , King J. A. , Kodama R. , Krushelnick K. , Ledingham K. W. D. , McKenna P. , Murphy C. D. , Norreys P. A. , Stephens R. , Stöeckl C. , Toyama Y. , Wei M. S. , Zepf M.
Published: June 2004

Investigations of 7Li (p,n) 4Be reactions using Cu and CH primary and LiF secondary targets were performed using the VULCAN laser [C.N. Danson et al., J. Mod. Opt. 45, 1653 (1997)] with intensities up to 3×1019 W cm−2. The neutron yield was measured using CR-39 plastic track detector and the yield was up to 3×108 sr−1 for CH primary targets and up to 2×108 sr−1 for Cu primary targets. The angular distribution of neutrons was measured at various angles and revealed a relatively anisotropic neutron distribution over 180° that was greater than the error of measurement. It may be possible to exploit such reactions on high repetition, table-top lasers for neutron radiography.
Assessment of inflow boundary conditions for compressible turbulent boundary layers
Authors: Xu Sheng , Martin M. Pino
Published: June 2004

A description of different inflow methodologies for turbulent boundary layers, including validity and limitations, is presented. We show that the use of genuine periodic boundary conditions, in which no alteration of the governing equations is made, results in growing mean flow and decaying turbulence. Premises under which the usage is valid are presented and explained, and comparisons with the extended temporal approach [T. Maeder, N. A. Adams, and L. Kleiser, “Direct simulation of turbulent supersonic boundary layers by an extended temporal approach,” J. Fluid Mech. 429, 187 (2001)] are used to assess the validity. Extending the work by Lund et al. [J. Comput. Phys. 140, 233 (1998)], we propose an inflow generation method for spatial simulations of compressible turbulent boundary layers. The method generates inflow by reintroducing a rescaled downstream flow field to the inlet of a computational domain. The rescaling is based on Morkovin’s hypothesis [P. Bradshaw, “Compressible turbulent shear layers,” Annu. Rev. Fluid Mech. 9, 33 (1977)] and generalized temperature–velocity relationships. This method is different from other existing rescaling techniques [S. Stolz and N. A. Adams, “Large-eddy simulation of high-Reynolds-number supersonic boundary layers using the approximate deconvolution model and a rescaling and recycling technique,” Phys. Fluids 15, 2398 (2003); G. Urbin and D. Knight, “Large-eddy simulation of a supersonic boundary layer using an unstructured grid,” AIAA J. 39, 1288 (2001)], in that a more consistent rescaling is employed for the mean and fluctuating thermodynamic variables. The results are compared against the well established van Driest II theory and indicate that the method is efficient and accurate.
Double conditioning of reactive scalar transport equations in turbulent nonpremixed flames
Authors: Kronenburg A.
Published: June 2004

Double conditioning of reactive scalar transport equations on mixture fraction and sensible enthalpy is presented as a promising extension to conventional conditional moment closure (CMC) methods. Simple first order, singly conditioned CMC cannot accurately predict combustion phenomena such as partially premixed flames and flames with local extinction and reignition. CMC is applied to turbulent flames with significant temperature fluctuations that bring to light the deficiencies of the conventional CMC approach. Fluctuations of temperature and species around their conditional means cannot be neglected when these quantities are conditioned on mixture fraction only. Comparison with direct numerical simulation (DNS) results demonstrates, however, the great potential for doubly conditioned CMC. Doubly conditioned CMC gives excellent agreement with DNS at all times and it captures phenomena like local extinction and the onset of reignition accurately.
Foliation and mixing of the electron drift-kinetic distribution function in nonlinear two-dimensional magnetic reconnection
Authors: Liseikina T. V. , Pegoraro F. , Echkina E. Yu.
Published: June 2004

The nonlinear evolution of the two-dimensional collisionless magnetic field reconnection in a configuration with a null line and a strong perpendicular guide magnetic field is studied analytically and numerically by adopting a drift-kinetic description of the electron response. The foliation of the electron distribution function at fixed parallel canonical momentum allows us to establish a clear link between the fluid and the kinetic regimes of the collisionless reconnection instability in terms of the advection and mixing of Lagrangian invariants.
On quantum error-correction by classical feedback in discrete time
Authors: Gregoratti M. , Werner R. F.
Published: June 2004

We consider the problem of correcting the errors incurred from sending quantum information through a noisy quantum environment by using classical information obtained from a measurement on the environment. For discrete time Markovian evolutions, in the case of fixed measurement on the environment, we give criteria for quantum information to be perfectly corrigible and characterize the related feedback. Then we analyze the case when perfect correction is not possible and, in the qubit case, we find optimal feedback maximizing the channel fidelity.
Nonlinear plasma waves excitation by intense ion beams in background plasma
Authors: Kaganovich Igor D. , Startsev Edward A. , Davidson Ronald C.
Published: June 2004

Plasma neutralization of an intense ion pulse is of interest for many applications, including plasma lenses, heavy ion fusion, cosmic ray propagation, etc. An analytical electron fluid model has been developed to describe the plasma response to a propagating ion beam. The model predicts very good charge neutralization during quasi-steady-state propagation, provided the beam pulse duration τb is much longer than the electron plasma period 2π/ωp, where ωp=(4πe2np/m)1/2 is the electron plasma frequency, and np is the background plasma density. In the opposite limit, the beam pulse excites large-amplitude plasma waves. If the beam density is larger than the background plasma density, the plasma waves break. Theoretical predictions are compared with the results of calculations utilizing a particle-in-cell (PIC) code. The cold electron fluid results agree well with the PIC simulations for ion beam propagation through a background plasma. The reduced fluid description derived in this paper can provide an important benchmark for numerical codes and yield scaling relations for different beam and plasma parameters. The visualization of numerical simulation data shows complex collective phenomena during beam entry and exit from the plasma.
Plasma and electrical characteristics of inductive discharge in a magnetic field
Authors: Godyak V. A. , Alexandrovich B. M.
Published: June 2004

The electron energy distribution function and the azimuthal rf electric field (magnitude and phase) have been measured in a cylindrical inductively coupled plasma (ICP) immersed in a weak magnetic field and driven at 29 MHz. The measurements were performed under conditions of controlled rf power delivered to the plasma electrons taking into account power loss in the induction coil. It has been found that considerable modification of plasma parameters at electron cyclotron resonance (ECR) conditions occurs only at relatively small discharge power and plasma density, when electron–electron collisions are negligible. It is shown that enhancement in the plasma density with application of magnetic field found in earlier experiments is mainly due to a rise in the power transfer efficiency caused by reduction in the ICP sustaining rf electric field. The rf field reduction is due to strong cyclotron damping at ECR conditions and due to the onset of propagation and absorption of the wave for which the phase velocities were found to be close to the electron thermal velocity. This wave regime occurs at magnetic fields higher than that at ECR but much smaller than that in typical helicon plasma sources.
Langmuir probe interpretation for plasmas with secondary electrons from the wall
Authors: Sternovsky Z. , Robertson S.
Published: June 2004

A method is presented for analyzing the electron current to a cylindrical Langmuir probe in a low pressure, hot-filament discharge plasma containing secondary electrons from the wall in addition to colder bulk plasma electrons. Orbit-motion-limited probe theory is applied to each of the electron components, taking into consideration that the secondary electron current is in the saturation region for probe potentials more positive than the wall potential. The method resolves the probe current into ion, secondary electron, and bulk electron components and finds parameters for each. The fitted model curve follows the probe data with less than 5% relative error from below the floating potential to the saturation region. The analysis shows that the probe current of the bulk electrons alone is indistinguishable from zero for probe potentials more negative than the wall potential, indicating that there are indeed no bulk electrons with energies exceeding the ambipolar potential.
Studying Galactic Chemical Properties by using Cosmological Numerical Simulations
Authors: Tissera Patricia B. , Scannapieco Cecilia
Published: June 2004

We developed a chemical code within gadget2 which allows the description of the enrichment of the Universe as a function of redshift, taking into account detailed metal production by supernovae Ia and II, and metal-dependent cooling. This is the first numerical code that includes both chemical production and metal-dependent cooling in a cosmological context. By analysing the cosmic star formation rate, we found that the effects of considering a metal-dependent cooling are important, principally, for z ≤ 3. In simulations where primordial cooling functions are used, the comoving star formation rate could be up to 20%; lower than those obtained in runs with metal-dependent cooling functions. Within galaxy-like objects, the presence of chemical elements changes the star-formation rates and, consequently, the chemical production and patterns of stars. However, owing to non-linear evolution of the structure, the effects depend on the evolutionary history path of each galaxy-like object.
The Geneva–Copenhagen Survey of the Solar Neighbourhood
Authors: Nordström B. , Andersen J. , Holmberg J. , Jørgensen B. R. , Mayor M. , Pont F.
Published: June 2004

We report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new, accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2 proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary stars in the sample. Isochrone ages have been determined whenever reliable results are possible, with particular attention to realistic error estimates.

Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicity distribution of G-dwarfs and the age–metallicity and age–velocity relations of the solar neighbourhood. We confirm the lack of metal-poor G-dwarfs relative to classical model predictions (the 'G-dwarf problem'), the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of the kinematic signature of the thick disk ∼ 10 Gyr ago.
Interactions of Satellite Galaxies in Cosmological Dark Matter Halos
Authors: Knebe Alexander , Gill Stuart P. D. , Gibson Brad K.
Published: June 2004

We present a statistical analysis of the interactions between satellite galaxies in cosmological dark matter halos taken from fully self-consistent high-resolution simulations of galaxy clusters. We show that the number distribution of satellite encounters has a tail that extends to as many as three to four encounters per orbit. On average 30% of the substructure population had at least one encounter (per orbit) with another satellite galaxy. However, this result depends on the age of the dark matter host halo with a clear trend for more interactions in younger systems. We also report a correlation between the number of encounters and the distance of the satellites to the centre of the cluster — satellite galaxies closer to the centre experience more interactions. However, this can be simply explained by the radial distribution of the substructure population and merely reflects the fact that the density of satellites is higher in those regions.

In order to find substructure galaxies we applied (and present) a new technique based upon theN-body code MLAPM. This new halo finder MHF (MLAPM’s halo finder) acts with exactly the same accuracy as theN-body code itself and is therefore free of any bias and spurious mismatch between simulation data and halo finding precision related to numerical effects.
Can Dust Destabilise Galactic Disks?
Authors: Theis Christian , Orlova Natalya
Published: June 2004

We studied the dynamic influence of a dust component on the gaseous phase in central regions of galactic disks. We performed two-dimensional hydrodynamic simulations for flat, multicomponent disks embedded in a stellar and dark matter potential. The pressure-free dust component is coupled to the gas by a drag force depending on their velocity difference. The most unstable regions are those with either a low or near-to-minimum Toomre parameter or with rigid rotation, i.e. the central area. In those regions the dust-free disks become most unstable for a small range of high azimuthal modes (m ∼ 8), whereas in dusty disks all modes have similar amplitudes resulting in a patchy appearance. The structures in the dust have a larger contrast between arm and interarm regions than those of the gas. The dust peaks are frequently correlated with peaks of the gas distribution, but they do not necessarily coincide with them. This leads to a large scatter in the dust to gas ratios. The appearance of the dust is more cellular (i.e. sometimes connecting different spiral features), whereas the gas is organised in a multi-armed spiral structure. We found that an admixture of 2% dust (relative to the mass of the gas) destabilises gaseous disks substantially, whereas dust to gas ratios below 1% have no influence on the evolution of the gaseous disk. For a high dust to gas ratio of 10% the instabilities reach the saturation level after 30 Myr.
Cosmic Ray Production of 6Li by Virialisation Shocks in the Early Milky Way
Authors: Suzuki Takeru K. , Inoue Susumu
Published: June 2004

The energy dissipated by virialisation shocks during hierarchical structure formation of the Galaxy can exceed that injected by concomitant supernova (SN) explosions. Cosmic rays (CRs) accelerated by such shocks may therefore dominate over SNe in the production of 6Li through α + α fusion without co-producing Be and B. This process can give a more natural account of the observed 6Li abundance in metal-poor stars compared to standard SN CR scenarios. Future searches for correlations between the 6Li abundance and the kinematic properties of halo stars may constitute an important probe of how the Galaxy and its halo formed. Furthermore, 6Li may offer interesting clues to some fundamental but currently unresolved issues in cosmology and structure formation on sub-galactic scales.
Chemical Abundance Patterns of the Galaxy's Thick Disk Population
Authors: Brewer Mary-Margaret , Carney Bruce W.
Published: June 2004

We discuss our work on chemical abundance ratios of stars belonging to the thick-disk and thin-disk stellar populations. We discuss the selection of stars, and show that the two samples of stars have different [α/Fe] versus [Fe/H] behaviour.
Physical Processes in Star–Gas Systems
Authors: Spurzem R. , Berczik P. , Hensler G. , Theis Ch. , Amaro-Seoane P. , Freitag M. , Just A.
Published: June 2004

We first present a recently developed three-dimensional chemodynamic code for galaxy evolution from the Kiev–Kiel collaboration. It follows the evolution of all components of a galaxy, such as dark matter, stars, molecular clouds and diffuse interstellar matter. Dark matter and stars are treated as collisionless N-body systems. The interstellar matter is numerically described by a smoothed particle hydrodynamics approach for the diffuse (hot) gas and a sticky particle scheme for the (cool) molecular clouds. Physical processes, such as star formation, stellar death, or condensation and evaporation processes of clouds interacting with the ISM are described locally. An example application of the model to a star forming dwarf galaxy will be shown for comparison with other codes. Secondly, we will discuss new kinds of exotic chemodynamic processes, as they occur in dense gas–star systems in galactic nuclei, such as non-standard ‘drag’-force interactions, destructive and gas-producing stellar collisions. Their implementation in one-dimensional dynamic models of galactic nuclei is presented. Future prospects to generalise these to three dimensions are in progress and will be discussed.
Galaxy Genesis — Unravelling the Epoch of Dissipation in the Early Disk
Authors: Bland-Hawthorn Joss , Freeman Ken C.
Published: June 2004

How did the Galactic disk form and can the sequence of events ever be unravelled from the vast stellar inventory? This will require that some of the residual inhomogeneities from prehistory escaped the dissipative process at an early stage. Fossil hunting to date has concentrated mostly on the stellar halo, but a key source of information will be the thick disk. This is believed to be a ‘snap frozen’ relic which formed during or shortly after the last major epoch of dissipation, or it may have formed from infalling systems early in the life of the Galaxy. As part of the KAOS Galaxy Genesis project, we explore the early history of the halo and the thick disk by looking for discrete substructures, either due to infall or in situ star formation, through chemical tagging. This will require high signal-to-noise echelle spectroscopy of up to a million stars throughout the disk. Our program has a short-term and a long-term goal.

The short-term goal is to quantify the size and structure of the multi-dimensional chemical abundance space (C-space) for all major components of the Galaxy. We seek to establish how many axes in (C-space) are decoupled and have large intrinsic dispersions. A critical test of chemical tagging in the short term is that stellar streams in the halo, identified from detailed phase space information, are highly localised in (C-space), or are confined to chemical tracks. These trajectories presuppose that stars form in a closed box through progressive enrichments of the gas, leading to stars dispersed along a narrow track in a complex chemical space. The long-term goal is to identify unique chemical signatures in the thick disk, originating from different formation sites, for star clusters which have long since dispersed. This will require precise chemical abundances for heavy elements such that a star can be localised to a discrete point in (C-space). If the star clusters originally formed outside the Galaxy in a bound infalling system, the stellar abundances may fall along a chemical track, rather than a discrete point in (C-space).
The swift parrot Lathamus discolor (Psittacidae), social bees (Apidae), and native insects as pollinators of Eucalyptus globulus ssp. globulus (Myrtaceae)
Authors: Hingston A. B. , Potts B. M. , McQuillan P. B.
Published: June 2004

It has been argued that the production of sufficient nectar to attract bird pollinators would evolve if the fitness benefits accruing from pollination services by birds, compared with insects, outweighed the cost of increased allocation of photosynthate to nectar. This hypothesis implies that the pollination services provided by birds must be considerably better than those provided by insects with which the plant has evolved. Consistent with this, we found that the endangered native swift parrot Lathamus discolor (Shaw) was a very effective pollinator of the native tree Eucalyptus globulus Labill. in Tasmania, facilitating an average of 76% of the maximum possible seed set for open-pollinated flowers in just one visit to a flower, whereas single flower visits by native insects did not facilitate any seed production. Flowers visited once by either species of introduced social bees, the honeybee Apis mellifera L. or the bumblebee Bombus terrestris (L.), produced less than 7% of the maximum possible seed set for open-pollinated flowers. Hence, easily managed social bees appear to be poor substitutes for bird pollinators in commercial seed orchards of this tree. We propose three possible reasons why this largely bird-pollinated tree has not evolved characters that deter insects from removing nectar.
Seasonal impacts on leaf attributes of several tree species growing in three diverse ecosystems of south-eastern Australia
Authors: McPherson Skye , Eamus Derek , Murray Brad R.
Published: June 2004

Patterns of leaf attributes were examined for six woody species growing in a eucalypt woodland, a mangrove, or a heathland in coastal New South Wales, Australia, during winter and summer. It was found that the rate of assimilation per unit leaf dry mass (Amass) of the mangrove species was largest, woodland species exhibiting an intermediate rate and heathland species the smallest values of Amass. Mean habitat Amass did not change from winter to summer in the woodland or mangrove species but increased significantly in the heathland species. Average specific leaf area (SLA) was largest for the mangrove species and smallest for the heathland species, with woodland species showing intermediate values. SLA of all species within a habitat did not change from winter to summer. Mean foliar nitrogen (Nmass) of the mangrove species was highest, intermediate for woodland species and lowest for heathland species. Nmass was significantly related to Amass in both summer and winter and the individual slopes for this relationship in the summer and winter differed. In contrast, a common slope was fitted to the relationship between SLA and Amass for the two seasons. A common slope between seasons was also shown for the relationship between SLA and Nmass. There was no significant difference in slope elevation between summer and winter for the SLA v. Nmass relationship. Trends within relationships among leaf attributes were the same as those found for a wide range of plant species worldwide, but the absolute values were lower than those found elsewhere. Therefore, the 'global relationships' in terms of trends (positive or negative) that have been determined overseas apply in Australia but the elevation of the slope and the magnitude of the slope are reduced (Amass v. Nmass) or increased (Amass v. SLA and Nmass v. SLA) compared with global trends.
Floral development in Daviesia cordata (Leguminosae: Papilionoideae: Mirbelieae) and its systematic implications
Authors: Prenner G.
Published: June 2004

The floral development of Daviesia cordata Smith is studied by the use of scanning electron microscopy. This is the first study of a member of Mirbelieae. Although organ initiation in Papilionoideae is said to be almost uniformly unidirectional from the abaxial to the adaxial side, the presented floral development shows striking differences from this mode. Sepals, petals and the antepetalous stamens are initiated in simultaneous whorls, which is seen as a consequence of harmonisation of the plastochrons within the whorls. The antesepalous stamens are initiated unidirectional from the adaxial to the abaxial side, which is the reversed direction of the common mode of Papilionoideae. This is the first record of reversed unidirectionality in Papilionoideae, which can be linked with isolated findings in Caesalpinioideae and Mimosoideae. Concerning developmental aspects, the results seem to link the papilionoid flower closer to those of Caesalpinioideae and Mimosoideae. Further developmental studies are necessary to broaden the data matrix for a detailed phylogenetic analysis.
Pollination ecology of the Australian cycad Lepidozamia peroffskyana (Zamiaceae)
Authors: Hall John A. , Walter Gimme H. , Bergstrom Dana M. , Machin Peter
Published: June 2004

Experiments carried out to investigate the reproductive ecology of the Australian cycad Lepidozamia peroffskyana (Regal, Bull. Soc. Imp. Nat. Mosc. 1857, 1: 184) revealed that this species is pollinated exclusively by host-specific Tranes weevils (Pascoe 1875). The weevils carry out their life cycle within the tissues of the male cones but also visit the female cones in large numbers. Female cones from which insects (but not wind) was excluded had a pollination rate that was essentially zero. In contrast, female cones from which wind (but not insects) were excluded had a pollination rate comparable with naturally pollinated cones. Assessment of Tranes weevil pollen load indicated that they are effective pollen-carriers. No other potential insect pollinators were observed on cones of L. peroffskyana. Sampling of airborne loads of cycad pollen indicated that wind-dispersed grains were not consistently recorded beyond a 2-m radius surrounding pollen-shedding male cones. The airborne load of cycad pollen in the vicinity of pollination-receptive female cones was minimal, and the spatial distribution of the coning population indicated that receptive female cones did not usually occur close enough to pollen-shedding male cones for airborne transfer of pollen to explain observed natural rates of seed set. These multiple lines of evidence suggest that wind–once considered the only pollination vector for cycads and other gymnosperms–plays only a minimal role in the pollination of L. peroffskyana, if any at all. The global diversity of insects associated with cycads suggests that some lineages of pollinating beetles may have been associated with cycad cones since Mesozoic times.