bluuebunny/crossref_metadata_2025 huggingface dataset:
Re‐creating Semi‐natural Communities: Vacuum Harvesting and Hand Collection of Seed on Calcareous Grassland
Authors: Stevenson Mark J. , Ward Lena K. , Pywell Richard F.
Published: December 2004

Agricultural set‐aside and compensation land provide restoration ecologists with opportunities to re‐create semi‐natural habitats. Restoration sites often have high soil fertility and inadequate seed banks of desirable species. Sowing additional seed is a proven method for establishing chalk grassland vegetation. If seed of local provenance is required, it may be collected by hand or by using specialized machines. Ultimately, the mix collected must provide seed suitable for recreating vegetation similar to that of the donor site. We examine the ability of a vacuum machine to meet this requirement by comparison with hand collection, and we discuss possible effects on invertebrates. Microscope analysis and glasshouse and field trials were used to compare the abundance of seed of different species in harvested mixes with the vegetation composition of the donor site. Seed heads of individual species were examined to determine the number of viable seeds per head and attack rates by phytophagous insects. The mix contained seed of over half the species recorded on the donor site. The seed of taller, more common species was overrepresented in the mix, at the expense of some smaller, mat‐forming plants. After one season, however, the vegetation of the field trial plots was of the same type as that of the donor site, although the proportions of the constituent species differed slightly and certain species were absent. Mechanical collection is more efficient than hand collection. Endophagous invertebrates are unlikely to be affected by the machine. Seed collection requires a combination of methods, precise timing, and careful planning to provide a full range of species and to minimize impacts on plant and invertebrate populations.
Constructed Crevasses and Land Gain in the Mississippi River Delta
Authors: Boyer Mark E. , Harris James O. , Turner R. Eugene
Published: December 2004

Extensive land loss, which is mostly wetland loss, has taken place during this century in the Mississippi River delta and other river deltas. Our purpose was to evaluate the effectiveness of constructing “artificial” crevasses, or cuts in the natural levee, made by the U.S. Fish and Wildlife Service in the Delta National Wildlife Refuge (DNWR) to slow or reverse this type of land loss. Land growth of the crevasses was determined from aerial photographs and was related to crevasse‐site characteristics. The newly constructed crevasses create emergent wetlands after 2 years of subaqueous growth at about 4.7 ha/year and an average cost of $21,377 per crevasse. The present total cost per hectare declines with age as new land builds, and it will equal $48 per hectare if all the open water in the receiving ponds fills in. At these rates, the net land loss rates in the DNWR measured from 1958 to 1978 would be compensated for by the building of 63 crevasses, 24 of which are already in place.
Neurophatic Pain Treatment: The Challenge
Authors: Andrés Jose De , Garcia‐Ribas Guillermo
Published: December 2004

Abstract:Neuropathic pain covers a heterogeneous group of pain conditions characterized by a primary lesion or dysfunction of the sensory nervous system. Its pathophysiology is not yet clear, but neuronal hyperexcitability in those neurons that have lost their normal patterned input seems to be a common denominator for neuropathic pain. A mechanism‐based approach is being developed, but still the clinical workup is being based on the anatomical location and the determination of an underlying cause. In addition, clinicians are presented with a challenge because neuropathic pain does not respond well to traditional pain therapies and there are greater individual variations in pain responsiveness. A number of drug classes have been evaluated in the treatment of neuropathic pain syndromes; these are mainly drugs developed for other nervous system diseases, although their precise action and whether their action is central or peripheral remains unknown for the majority of them. First‐line agents used in the treatment of neuropathic pain conditions are tricyclic antidepressants and anticonvulsants, especially carbamazepine and gabapentin. Novel therapies are currently being developed for neuropathic pain that are based in experimental models and theoretical frameworks on the pathosphysiological events that initiate this type of pain.
Neuropathic Pain: Mechanisms and Treatment Options
Authors: Teng James , Mekhail Nagy
Published: December 2004

Abstract: Neuropathic pain results from damage to the nervous system. The diseases responsible for neuropathic pain are diverse but they may have in common pathophysiological mechanisms. This review will focus on these mechanisms both in the peripheral as well as within the central nervous system. In addition, there will be discussion on the various treatment choices including both pharamcological and interventional options.
Correction of Defective Early Tyrosinase Processing by Bafilomycin A1 and Monensin in Pink‐Eyed Dilution Melanocytes
Authors: Chen Kun , Minwalla Ljiljana , Ni Li , Orlow Seth J.
Published: December 2004

Mutations in the human P gene result in oculocutaneous albinism type 2, the most common form of albinism. Mouse melan‐p1 melanocytes, cultured from mice null at the homologous pink‐eyed dilution (p) locus, exhibit defective melanin production. A variety of compounds including tyrosine, NH4Cl, bafilomycin A1, concanamycin, monensin, and nigericin are capable of restoring melanin synthesis in these cells. In the current study, we investigated the subcellular effects of bafilomycin A1 and monensin treatment of melan‐p1 cells. Both agents play two roles in the processing of tyrosinase (Tyr) in melan‐p1 cells. First, combined glycosidase digestion and immunoblotting analysis showed that these agents reduce levels of Tyr retained in the endoplasmic reticulum (ER) and facilitate the release of Tyr from the ER to the Golgi. Secondly, treatment with these compounds resulted in the stabilization of Tyr. Surprisingly, induction of melanin synthesis corresponds more closely with diminution of ER‐retained Tyr, rather than the absolute amount of Tyr. Our results suggest that bafilomycin A1 and monensin induce melanin synthesis in melan‐p1 cells mainly by facilitating Tyr processing from the ER to the Golgi by increasing the pH in either the ER or the ER–Golgi intermediate compartment.
During Human Melanoma Progression AP‐1 Binding Pairs are Altered with Loss of c‐Jun In Vitro
Authors: Yang Sun , McNulty Susan , Meyskens Frank L.
Published: December 2004

We demonstrated previously that c‐Jun, JunB and c‐Fos RNA were dysregulated in metastatic melanoma cells compared with normal human melanocytes. The purpose of this study was to evaluate the distribution in composition of AP‐1 dimers in human melanoma pathogenesis. We investigated AP‐1 dimer pairing in radial growth phase‐like (RGP) (w3211) and vertical growth phase‐like (VGP) (w1205) human melanoma cells and metastatic cell lines (cloned from patients, c83‐2c, c81‐46A, A375, respectively) compared with melanocytes using electrophoretic mobility shift assay (EMSA), Western blot and transfection analyses. There are progressive variations in AP‐1 composition in different melanoma cell lines compared with normal melanocytes, in which c‐Jun, JunD and FosB were involved in AP‐1 complexes. In w3211, c‐Jun, JunD and Fra‐1 were involved in AP‐1 binding, while in w1205, overall AP‐1 binding activity was decreased significantly and supershift binding was detected only with JunD antibodies. In metastatic c81‐46A and A375 cells, only JunD was involved in AP‐1 binding activity, but in a third (c83‐2c) c‐Jun, JunD and Fra‐1 were present. Western blot evaluation detected c‐Jun in melanocytes and w3211, but this component was decreased significantly or was not detectable in w1205, c81‐46A and A375 cells. In contrast, JunD protein was elevated in c81‐46A and c83‐2c cells compared with melanocytes and RGP and VGP cell lines. Normal melanocytes and c83‐2c cells (which have c‐Jun involved in AP‐1 binding), transfected with c‐Jun antisense and treated with cisplatin, showed higher viability compared with untransfected cells, while in c81‐46A cells (in which only JunD is detectable) no change in cell viability was observed following treatment with cisplatin and c‐jun antisense transfection. A dominant‐negative c‐Jun mutant (TAM67) significantly increased the soft agar colony formation of w3211 and c83‐2c cells. These results suggest that components of AP‐1, especially c‐Jun, may offer a new target for the prevention or treatment of human melanoma progression.
Motion of Thin Bodies in a Highly Rarefied Plasma
Authors: Yoshihara Hideo
Published: December 2004

Magnetic effects are considered negligible, and the velocity of the body is in a range between the electron and positive ion thermal speeds. The self-consistent field approach is used in which the electron distribution is assumed to be Maxwellian, while the positive ion distribution function is given by the ``collision-free'' Boltzmann equation. It is assumed that the ion reflection at the body surface is specular, and the body is sufficiently thin so that the ion distribution function is a small perturbation of a Maxwellian distribution. The solution for the simple case of a dielectric body with a given surface charge, as well as some general properties to be expected for a conducting body are given.
Coefficient of Dynamic Friction for Slow Ions
Authors: Rand S.
Published: December 2004

The coefficient of dynamic friction for a subsonic ion is determined, in a phenomenological manner, by requiring that the drag force acting on a test particle in a plasma be identical with the drag force on a field particle. The drag coefficient is determined in both a fully ionized gas and in a specialized partially ionized gas. The effects of collisions between ions and neutral particles on the drag force is considered. It is found that, with some rather special conditions, the stopping power on a charged particle traversing a plasma may be reduced when the density of neutral particles is increased.
Diffusion and Recombination of a Highly Ionized Cold Plasma in a Magnetic Field
Authors: D'Angelo N. , Rynn N.
Published: December 2004

Measurements of the diffusion coefficients of cold, highly ionized cesium and potassium plasmas across a magnetic field are described. The field was varied between 3000 and 9000 gauss, the ion density between 1010 cm−3 and 1012 cm−3. No current was passed through the plasma. The results support the view that diffusion proceeds according to the predictions of the classical theory (D⊥ ∼ 1/B2). No agreement is possible with Bohm's diffusion theory. Also, some support is given to the theory of recombination through electron-electron-ion collisions and radiative cascading between excited states.
Structure of Detonations in Dilute Sprays
Authors: Williams F. A.
Published: December 2004

Solutions to the differential equations governing the structure of a steady-state detonation in a spray are obtained both numerically and by means of analytical approximations for the case in which the droplets in the spray burn heterogeneously. It is shown that, for reasonable droplet burning rates, the detonation structure corresponds almost precisely to the spray analog of the von Neumann hypothesis of a shock wave followed by a deflagration zone. The size of the burning region is demonstrated to be large enough to cast doubt upon the stability of a spray detonation not supported to a significant extent by purely gaseous reactions.
Shear Coefficients for a Viscoelastic Substance in the Sonic Region
Authors: Miles D. O.
Published: December 2004

A pure sinusoidal shear is applied to a sample of diphenyl hexachloride at several temperatures in the frequency range 20 to 103 cps. The shear rigidity and shear viscosity are obtained as functions of frequency at each temperature. Comparison of viscosity at low frequencies and rigidity at high frequencies with measurements by others is within experimental errors. The experimental data deviate slightly from single relaxation theory for the Debye-Frenkel model of liquids. Comparison of the distribution with that observed for compressional processes reveals a difference in shape, also predicted by the Debye-Frenkel model. The temperature dependence of the high-frequency shear rigidity is obtained and the expected plateau is observed below the glass transition.
Virial Coefficients of Hydrogen-Hydrocarbon Mixtures
Authors: Connolly J. F.
Published: December 2004

Virial coefficients have been obtained for mixtures of hydrogen with benzene, n-octane, and 2,2,4-trimethylpentane. The measurements were made by two methods and cover the temperature range 50° to 300°C. The mixed 2nd virial coefficients predicted by the Kihara intermolecular potential-energy function are in better agreement with experiment than those predicted by that of Lennard-Jones.
Rotating Plasma Experiments. I. Hydromagnetic Properties
Authors: Baker D. A. , Hammel J. E. , Ribe F. L.
Published: December 2004

Experiments on Ixion III, the Los Alamos rotating plasma device, using electrostatic and magnetic probe techniques are discussed. Analysis of the data indicates the presence of a two-liter annular volume of rotating plasma whose mean mass density is ∼ 1 × 10−8 g/cm3 and whose rotation decays with the supply voltage in ∼ 300 μsec. The plasma energy content of ∼ 130 joules appears to be nearly equipartitioned between ordered rotational drift motion and random thermal motion. Under typical operating conditions the data show the existence of drift velocities of ∼ 8 × 106 cm/sec (∼ 65 ev for deuterium) and temperatures of the order of 30 ev. The operation of Ixion as a hydromagnetic capacitor in an oscillatory circuit is described.
Statistical Distribution of the Magnetic Microfield in a Plasma
Authors: Kalman G.
Published: December 2004

The static magnetic field due to randomly distributed charged particles in phase space is investigaged. A Holtsmark-like distribution is derived, centered around 2.0091 B0, the latter being the magnetic field caused by a particle moving with the average velocity at an average interparticle distance.
Turbulent Flow in a Circular Pipe with Porous Wall
Authors: Yuan S. W. , Brogren E. W.
Published: December 2004

A theoretical investigation of an isothermal turbulent flow in a porous wall pipe with fluid injection or suction at the wall has been made. An exact solution of the Reynolds equations, reduced to ordinary nonlinear differential equations with appropriate boundary conditions, is obtained. The axial velocity distribution is expressed as functions of velocity through the porous wall, the axial pressure gradient and the mixing length proportionality constant K. Experimental data are used in conjunction with the solution to calculate the values of K over a range of injection-to-main-stream velocity ratio. Good agreement is obtained between the present velocity profiles and such data.
Parametric Study of the Conical Shock Tube
Authors: Josephson Vernal , Hales Richard W.
Published: December 2004

A parametric study has been made on the performance of a conical discharge shock generator. From these studies it has been possible to formulate general ground rules to be followed in designing a shock tube of this type capable of producing a single high-velocity shock at gas pressures varying from 25–2000 μ. Typically, shocks of Ms ≈ 150 have been produced in D2 at 100 μ pressure.
Experiments with Pulsed Magnetic Cusps
Authors: Watteau Jean-Paul H.
Published: December 2004

Experiments with a simple pulsed magnetic field in cusped geometry are described. The plasma is generated inside the containment region rather than injected from an external source. It was found that creation of the plasma by a linear pinch discharge is most successful. Only qualitative studies have been carried out so far, using time-resolved visual observation of the plasma. Well-defined plasma bodies located in the central region between the coils were photographed. In order to make them clearly visible, a few percent of argon was added to the hydrogen.
Stability of Nonrotationally Symmetric Disturbances for Viscous Flow between Rotating Cylinders
Authors: DiPrima R. C.
Published: December 2004

The stability of a viscous fluid between two concentric rotating cylinders to nonrotationally symmetric disturbances is investigated. It is assumed that the cylinders are rotating in the same direction and that the spacing between the cylinders is small. It is found that the critical Reynolds number increases slightly as the ``number of waves'' in the azimuthal direction in the assumed form of the disturbance increases.
Persistence of Stability in Lagrangian Systems
Authors: Low F. E.
Published: December 2004

It is shown for a large class of Lagrangian systems that a steady state configuration of the system which is linearly stable remains so under a small variation of the steady state, to all orders of perturbation theory in the variation. The principle is applied to two special systems: an incompressible ideal fluid, and a gas of charged particles interacting through their average fields.
Determination of Hydromagnetic Equilibria
Authors: Greene John M. , Johnson John L.
Published: December 2004

Techniques for calculating hydromagnetic equilibria in toroidal systems which differ little from a uniform field are developed. The zeroth-order magnetic surfaces in these systems differ appreciably from concentric circular toroids. Care is taken to match onto reasonable external fields at the plasma boundary. Expressions for various equilibrium properties including the rotational transform, the net current on each surface, and the magnetic lines of force are obtained. As an illustration of the theory it is shown that the application of a particular field perpendicular to the plane of the torus reduces the distortion associated with the introduction of pressure into the system.
Mach Reflection of Detonation Waves in Condensed High Explosives
Authors: Dunne B. B.
Published: December 2004

By preshocking a condensed high explosive before the passage of a detonation front, it is possible to increase the peak pressure in the front to a level at which reflection phenomena can be readily observed by means of the Dautriche effect. Also, by the use of a tracer detonation wave, which intersects the shock configuration, it is possible to observe the oncoming detonation shock, the reflected shock, the Mach stem, and their intersection in a triple point. This method has been used to obtain strong evidence for the existence of Mach reflection of detonation waves in a preshocked explosive (RDX). The transition from regular to Mach reflection for an estimated 50-kbar precompression shock occurs discontinuously at a critical angle of 44.5° ±2° and quite rapidly, often in less than 3 × 10−8 sec.
Determination of Isentropic Pressure-Density Curves for Argon from a Rapid Dynamic Process
Authors: Ho L. T. , Vanderslice J. T. , Fallon R. J. , Seigel A. E. , Slawsky Z. I.
Published: December 2004

Isentropic pressure-density curves for argon have been obtained from measurements on the rapid expansion of the gas behind a piston. Results are given for cases when the argon was initially at room temperature and at pressures of from 400 to 900 atm. The agreement with equilibrium data is good.
Magnetohydrodynamic Results for Highly Dissociated and Ionized Air Plasma
Authors: Nagamatsu H. T. , Sheer R. E.
Published: December 2004

An investigation of air plasma moving through a constant (2300 gauss) transverse magnetic field was conducted in a shock tube. As the plasma traveled through the field, an electromotive force was produced in the plasma. Two diametrically opposite, ½-in. diameter, copper electrodes were used to measure this potential. The shock Mach number varied from 10 to 32 with corresponding equilibrium plasma temperatures from 3600° to 11 000°K. At Mach 30 the observed potential across the electrodes, with a 1-meg external load, was 236 v, which agreed with the theoretical value, but at lower Mach numbers the observed potentials were much lower than theory. By varying the external load for a shock Mach number of 30, the current from the plasma varied from nearly zero to 115 amp. This high current was extracted from the copper electrodes at nearly room temperature. The observed potential decreased linearly with increasing current indicating a nearly constant plasma resistance. For this resistance the electrical conductivity was calculated and was much less than the theoretical prediction. The maximum power extracted from the plasma was 7.8 kw with an external load of 1.85 ohms.
Electromagnetic Acceleration of a Plasma Slug
Authors: Mostov Philip M. , Neuringer Joseph L. , Rigney Donald S.
Published: December 2004

The slug model of a plasma accelerator is formulated and analyzed. The coupled nonlinear system equations involving seven parameters are transformed into a three-parameter set. The formulation includes as special cases Artsimovich's treatment, which neglects all system resistances, and Schock's treatment, which assumes negligible resistance of the accelerator electrodes. Small coupling, as well as small and large time asymptotic, solutions, which include the effect of variable rail resistance, are derived and compared with exact analog computations. In cases of practical concern, the small time solutions are valid well past the first maximum of the current discharge, bridging the gap left by Schock's approximate solution whose applicability is restricted to cases where the acceleration takes place over a number of cycles. Finally, it is shown how to optimize the efficiency of an accelerator through suitable adjustment of the system parameters.
On a Variational Principle for a Classical Plasma
Authors: Gartenhaus S.
Published: December 2004

A time-dependent version of the Hartree-Fock method is set up for a classical system, by making use of the formal similarity between Liouville's equation for such a system and the Schrödinger equation. The use of a product trial function in the resultant variational principle produces, for a plasma, the collisionless Boltzmann equation. A second application is made to a system for which short-range correlations are small but not negligible. It is found that regardless of the range of the interparticle forces and the magnitude of the density, equilibrium is described only by a Maxwellian velocity distribution.
Experiments on Ion Cyclotron Waves
Authors: Hooke W. M. , Tenney F. H. , Brennan M. H. , Hill H. M. , Stix T. H.
Published: December 2004

Experiments have been performed on the generation of ion cyclotron waves and their propagation into a magnetic beach. The experiments were carried out on the B-66 machine, which is currently a magnetic mirror device. Studies of the production of neutrons have provided evidence for the absorption of the energy of these waves via ion cyclotron damping.

Microwave phase-shift measurements have now been made, and the addition of electron density completes the list of parameters required for direct comparison of experimental and theoretical dispersion relations. The experimental data yield a smooth monotonic relation between density and frequency which is qualitatively similar to that predicted by theory. There are, however, unexplained quantitative differences.

Wave propagation into the magnetic beach region was observed with a single turn rf magnetic probe. The variation of the amplitude of these waves in the magnetic beach is in qualitative agreement with the theory of ion cyclotron wave propagation and cyclotron damping.
Hydromagnetic and Plasma Scaling Laws
Authors: Beiser A. , Raab B.
Published: December 2004

The Buckingham II theorem is applied to derive two sets of dimensionless parameters; one set for the quantities in the equations of Maxwell and Navier-Stokes, and the other containing the quantities involved in the Boltzmann equation. Ten independent dimensionless parameters are thus derived, which represent a complete set of scaling laws for phenomena describable by the these equations and which contain among them the ordinary fluid-dynamic scaling parameters: the Mach and Reynolds numbers.
Physical Principles of Magnetohydrodynamic Power Generation
Authors: Rosa Richard J.
Published: December 2004

Some phenomena apt to be of importance in a magnetohydrodynamic power generator are discussed. Particular attention is given to the effects of seeding on gas conductivity and to the Hall effect as it appears in nonuniform gases of finite extent. An experimental 10-kw magnetohydrodynamic generator is described. An arc wind tunnel or ``plasma jet'' is used as a convenient laboratory ``furnace'' to heat the working fluid. The generator's performance, including some observed Hall effects, is presented and discussed.
Electrons as a Shock Driver Gas
Authors: Fowler R. G. , Paxton G. W. , Hughes H. G.
Published: December 2004

The electric shock tube, below a transition pressure characteristic of the tube diameter and the gas under study, exhibits two clearly distinguishable luminous fronts having the apparent attributes of shocks. The first front is initiated too quickly to be ascribed to a temperature increase of the gas molecules, and seems therefore to depend directly on the electrons and their fields in some way. It is hypothesized that electron pressure is the primary source of this motion. This hypothesis is consonant with the extensive evidence at hand.
Dielectric Properties of a Weakly Turbulent Plasma
Authors: Ichikawa Yoshi H.
Published: December 2004

Generalization of the Herring-Yoshikawa theory has been developed to take into account the dynamical effect of turbulent fluctuation on the dielectric properties of the weakly turbulent plasma. According to the hydrodynamic description of electron plasma, the turbulent fluctuation gives rise to appreciable modification of the dielectric properties in the low frequency region and at the frequency of twice of the electron plasma frequency. An expression of the static dielectric constant shows that the characteristic correlation distance of the weakly turbulent plasma becomes longer than the Debye distance of corresponding homogeneous plasma in thermal equilibrium state. Contrary to the hydrodynamic scheme, the integral equation has been derived for the induced fluctuation in the kinetic description of the plasma. This integral equation suggests that the turbulent fluctuation may modify the dielectric properties of the turbulent plasma also at the electron plasma frequency.
Stagnation of Energetic Plasma
Authors: Stuart G. W.
Published: December 2004

A finite stream of cool plasma comprised of high A ions incident on a rigid plate, with the stream velocity u0 between 107-108 cm/sec is considered. The plate drives a strong ion shock upstream. The ion shock is about a mean free path thick. Overlapping and downstream from the ion shock is a thicker region in which electrons are collisionally heated, multiply by collisional ionization processes, and undergo radiative transition; within the thicker region the directed velocity u continues to decay. The entire structure (stagnation region) is treated in a steady-state shock frame. Except when the stream is very large, most of the energy escapes upstream to infinity as radiation, and the behavior is markedly different from that of the usual shock analysis where radiant flux vanish at infinity, e.g., in the former case material compressions are vastly greater. The atomic populations within the stagnation region are not those of local thermodynamic equilibrium; the more appropriate coronal description predicts a much softened radiation spectrum for u0 = 108 cm/sec, but only slight softening for u0 = 107 cm/sec.
Free-Streaming Plasma Experiments
Authors: Eastlund B. J. , Chu C. K.
Published: December 2004

Experiments are described with plasma pulses free-streaming from a source plate into a vacuum along a magnetic field. An analytic solution is derived for the pulse shape as a function of position and time in terms of the initial pulse shape at the launching plate. The experimental results agree extremely well with this free-flow theory, in which the initial pulse is assumed to have a Maxwellian velocity distribution. These experiments allow quantitative observations of free-flow phenomena under carefully controlled laboratory conditions.
Effect of Weak Collisions on Ion Waves
Authors: Kulsrud R. M. , Shen C. S.
Published: December 2004

The linearized Fokker-Planck equation is solved by an iteration method which assumes the collision term is one order higher than the other terms. It is solved (1) for the case of ion wave instabilities, where the unperturbed situation consists of a constant electric field, electrons with the Spitzer-Härm distribution, and ions with a Maxwellian distribution of much lower temperature. The effect of collisions on the critical current for instability is determined, and it is found that the electron-ion collisions predominate and lower the critical current. An attempt is made to justify the use of the Fokker-Planck equation when the distribution functions are nearly unstable. The linearized Fokker-Planck equation is also solved for (2) the case of ion waves in a cesium plasma. Here the electrons are taken as an isothermal fluid. The propagation and time damping constants are obtained as a function of collision rate. Also, the first root of the dispersion relation is applied to the space damping of ion waves in order to make a comparison with the experiment of Motley and Wong.
Boundary Condition Effects in a Magnetic Mirror Compression Experiment
Authors: Coensgen F. H. , Cummins W. F. , Nexsen W. E. , Sherman A. E.
Published: December 2004

The transition from unstable operation to quasi-stable plasma containment in a plasma-injected magnetic compression experiment has been found to be dependent upon the density and lifetime of plasma external to the confinement chamber. Transverse motion of the confined plasma is limited and the magnetic compression proceeds nearly adiabatically, provided the density of the external plasma is greater than ∼0.1% of the confined plasma. If the electrical connection to external conducting surfaces is lost after the magnetic compression is well under way (later than 50 μsec after beginning of compression for a magnetic field rise time of 120 μsec), the trapped plasma suddenly moves to the wall between the magnetic mirrors giving dramatic evidence of instability. In any case, during the magnetic compression the shifting external plasma-wall contact results in intermittent particle and/or energy losses from the hot plasma. Later than 100 μsec, the untrapped portion of the injected plasma which has been cooled, neutralized, and contaminated through its interaction with vacuum chamber walls diffuses into the containment chamber. Thus, at all times, there are loss processes in competition with the magnetic compression.
Microinstability Limitations of the DCX-1 Energetic Plasma
Authors: Dunlap J. L. , Haste G. R. , Nielsen C. E. , Postma H. , Reber L. H.
Published: December 2004

A steady state plasma with an energetic (≈ 300 keV) proton component is formed by dissociation of part of a 600-keV H2+ beam that makes a single pass in the midplane of a 2: 1 magnetic mirror field with a central field value of 10 kG. Both gas dissociation and Lorentz dissociation have been employed. The pontentially accessible density (density expected in the absence of instabilities) with Lorentz dissociation is the larger by more than an order of magnitude. The plasma is stable against flute instabilities, but microinstabilities (ion-electron or negative mass instabilities) are evidenced by radio frequency signals at ω ≳ ωci. The lowest density threshold for observation of these signals is 4 × 105 fast protons cm−3. With Lorentz dissociation the microinstabilities eventually eject protons, as observed by detection of these direct losses correlated with microinstability signals and by failure of charge-exchange accountability. The losses are first observed at densities of 5−10 × 107 cm−3; they amount to as much as 0.9 of the proton input current to the plasma; and, along with instability-driven scattering to larger plasma volume, they limit the proton density to 1−2 × 108 cm−3, as much as a factor of 15 below the density expected in the absence of such effects.
Velocity Overshoot within the Boundary Layer in Laminar Pulsating Flow
Authors: O'Brien V. , Logan F. E.
Published: December 2004

Parallel pulsating flow theories predict off-center velocities greater than centerline velocity. Measurements of the velocity overshoot in plane flows allow quantitative comparison with theory.
Central Potentials for Nonpolar Polyatomic Molecules
Authors: Konowalow Daniel D.
Published: December 2004

The effects of molecular acentricity on the intermolecular pair potential have been investigated for the n-alkane homologs (ethane through n-octane) and for benzene. Morse potentials were determined by fitting simultaneously the experimental viscosities and second virial coefficients. Although these potentials afford neither a compatible nor a consistent description of these two properties (according to the criteria of Konowalow and Carrá), the experimental data are reproduced with errors of only a few per cent. The ``most-likely'' Morse potentials determined here change shape fairly smoothly as the length of the n-alkane chain increases. Empirical rules are suggested to describe these changes.
Statistical Mechanics of the Moment Stress Tensor
Authors: Keller Evelyn F. , Keller Joseph B.
Published: December 2004

The stress tensor Tij determines the force per unit area exerted by the matter on one side of a surface upon that on the other side. The moment per unit area is usually assumed to be that corresponding to this force, but there is an additional part. It is expressible in terms of the moment stress tensor Mijk, introduced by Voigt and elaborated by Cosserat and Cosserat. Expressions for Mijk and Tij are obtained in terms of intermolecular forces and the two-particle distribution function. Both expressions are valid in an inhomogeneous medium. From them expressions are obtained for the new elastic constants associated with Mijk, as well as for the usual elastic constants. In a homogeneous medium it is found that Mijk vanishes. If the interparticle potential is spherically symmetric and the medium is homogeneous, Tij reduces to a scalar. However, for a fluid in equilibrium in an external potential, Mijk does not vanish and Tij is not a scalar.
Cylindrical Poiseuille Flow of a Rarefied Gas
Authors: Cercignani Carlo , Sernagiotto Franco
Published: December 2004

The Poiseuille flow of a rarefied gas in a cylindrical tube is analyzed numerically for an inverse Knudsen number ranging from 0–10. The Bhatnagar, Gross, and Krook model is used and the transport integro-differential equation is reduced to a purely integral one, which is solved numerically. The plot of the volume flow rate versus the pressure is shown to have the expected minimum; it also fits rather well with empirical correlation curves.
Transition and Strouhal Number for the Incompressible Wake of Various Bodies
Authors: Goldburg A. , Florsheim B. H.
Published: December 2004

Incompressible wakes behind three-dimensional bluff bodies have been studied in order to gain information about the effects of body geometry. The results of Magarvey and Bishop achieved by dropping liquid droplets through another liquid were duplicated using solid spheres, and observations were made of the wakes of bodies of various shapes, particularly cones. It was found that wake transition, defined as the first occurrence of finite unsteadiness, could be approximately correlated for a range of spheres and cones by a Reynolds number based on the total wake momentum thickness, θ2 = CDA/2π, Reθt ≈ 95. The cases of the teardrop and the disc deviate from this correlation, and explanations are discussed. It was also found that for regular vortex shedding the data for spheres and cones could be correlated with the Rayleigh-Strouhal formula based on θ; Sθ=0.305 [1−(95/Reθ)].Constraining the body to travel along a wire, thus reducing body-fluid interactions, produced an aperiodicity in the shedding phenomenon but left the value of the Strouhal number effectively unchanged.
Boundary Layer of an Equilibrium Plasma Atmosphere
Authors: Abraham B. W.
Published: December 2004

An isothermal atmosphere of a fully ionized equilibrium plasma in a gravitational field maintains charge neutrality except near the surface. The atmosphere, held to a spherically symmetric planet or star by a gravitational field, has a charged layer near the surface of approximate width of a Debye length. The charge excess near the boundary is the order of ε2n where n is the total density of ions or electrons and ε is the ratio of the Debye length to the scale height which is quite small for most atmospheres. The solution is performed by methods used in boundary-layer problems and gives as an example the correction to an equilibrium configuration arising from the presence of boundaries.
Magnetic Field Geometry and the Adiabatic Invariants of Particle Motion
Authors: Siambis John G. , Northrop Theodore G.
Published: December 2004

The first correction term to the lowest-order magnetic moment of a charged particle is written in terms of the curl of the magnetic field and the eight coefficients specifying the torsions, shears, and curvatures of the field lines. Certain of the coefficients are absent; thus in a vacuum field the lowest-order magnetic moment will not be affected by them. The influence of field geometry on the first correction to the second invariant is also investigated. A surface on which the lowest-order term of the invariant is constant is composed of field lines, as is well known. In portions of a surface, where the field lines have large components of curvature tangent to the surface, the first-order correction term is large, and the guiding center deviates from the surface more than where the radii of field line curvature are normal to the surface. This fact explains some phenomena observed in recent numerical integrations of guiding-center trajectories in Ioffe-type mirror geometries.
Contribution of Electron-Electron Collisions to the Emission of Bremsstrahlung by a Plasma
Authors: Birmingham Thomas J. , Dawson John M. , Kulsrud Russell M.
Published: December 2004

A new model for treating plasma radiation processes in plasmas is extended to the problem of bremsstrahlung emission from electron-electron collisions. The spectra of longitudinal and transverse waves, including dielectric effects, are derived to lowest nonvanishing (quadrupole) order. A resonance in the spectrum of transverse waves near ω = 2ωp, the first harmonic of the electron plasma frequency, is noted. The high-frequency form of the transverse spectrum is approximately evaluated and found to be relativistically small by comparison with the dominant electron-ion bremsstrahlung. Finite wavelength corrections to the radiation generated by electron-ion collisions are also discussed.
Dipolar Radiative Modes of a Plasma Cylinder
Authors: Bullock D. L. , Oltman George
Published: December 2004

Radiative modes associated with a thin, infinitely long circular plasma cylinder and having dipolar azimuthal field variations are investigated. The plasma is treated as a lossless dielectric with ε = ε0(1 − ωp2/ω2). No thermal effects are considered, and, contrary to the strong background magnetic field case investigated by Dawson and Oberman, no background magnetic field is introduced. The procedure requires the investigation of the dispersion equation resulting from the matching of tangential electromagnetic field components across a plasma-free space boundary, with emphasis on satisfying the radiation boundary conditions. Modes having axial phase velocities in the range c < vp < ∞ are shown to exist and are analyzed. A comparison with the analog of such modes for cylinders of finite length, which have been experimentally verified, is made, indicating the utility of the infinite structure analysis in explaining the experimental results for radiative modes on finite structures.
Density Gradient Effects on Alfvén Wave Propagation in a Cylindrical Plasma
Authors: McPherson D. A. , Pridmore-Brown D. C.
Published: December 2004

The propagation of nonaxisymmetric Alfvén waves in a linear discharge tube filled with a nonuniform plasma under a 30-kG axial field has been investigated theoretically and experimentally in the frequency range 1–5 Mc/sec. Typical plasma densities were 3–4 × 1015 ions/cm3 near the center of the tube and fell to low values at the wall. It was found that the density gradient introduces a frequency dependent coupling between the torsional and compressional waves of the uniform plasma. As a result, an axial component of the magnetic field perturbation, which is normally associated only with the compressional wave, is now carried by the torsional wave as well, and was in fact detected at frequencies well below the lowest waveguide cutoff of the compressional wave. At still lower frequencies, this component disappeared, and the remaining transverse field components were found to propagate at a radially varying speed which agreed well with the local Alfvén speed deduced from the measured ion density profile. A theoretical analysis is presented, and its predictions are compared with experimental measurements of signal amplitudes, wave speeds, attenuation rates, and density profiles.
Shear-Flow Transients from a Suddenly Changed Blowing Current
Authors: Inger George R.
Published: December 2004

A solution is given for the transient response of a Couette shear flow to a step-function change in blowing velocity across a channel, assuming constant property incompressible motion. An arbitrary steady-state blowing current prior to the step change is allowed. The solutions for the unsteady velocity profile and shear stress are obtained in analytical form by operational methods. The results show clear evidence of boundary-layer ``blowoff'' from the lower stationary wall when blowing rates are sufficiently high.
Ohm's Law in Multicomponent Nonisothermal Plasmas with Temperature and Pressure Gradients
Authors: Demetriades S. T. , Argyropoulos G. S.
Published: December 2004

A closed set of transport equations with collision terms evaluated by the 13-moment approximation is used, under well-defined assumptions, to derive a generalized Ohm's law in multicomponent nonisothermal plasmas as a function of the electric and magnetic fields and the temperature and pressure gradients. The nine coefficients defining this dependence are obtained in two successive approximations and are expressed in terms of component properties for any number N of components in the plasma, each component having its own temperature. The matrixes and determinants involved in these expressions are of order N. Results obtained for N = 4 and 5 allow the investigation of new effects that cannot be studied with the available 3-fluid expressions. It is shown that the only temperature gradient that needs to be considered in Ohm's law is that of the electrons and that all plasma properties, except those that describe or include interactions between heavy components, must be determined at the electron temperature. It is concluded that interactions between heavy particles cannot always be neglected in favor of electron-heavy particle interactions and that the results of this study may be used for a more general evaluation of all the coefficients of Ohm's law in multicomponent nonisothermal plasmas. The results are valid for any degree of ionization greater than approximately 10−7 and are presented in a form useful for many applications.
Plasma Expansion in a Magnetic Field
Authors: O'Neil Thomas , Fowler T. K.
Published: December 2004

The expansion of a hot plasma in a magnetic field is treated. A background atmosphere may be present, but in examples emphasized the atmospheric pressure is low enough so that its influence is less than that of the magnetic field. The calculation begins after an initial collisional phase, during which free expansion transforms most of the energy into outward radial motion. It is demonstrated by means of a modified virial theorem that this initial outward momentum then dominates the dynamics until expansion is first halted by the field. Though allowed by the theorem, complications such as shock formation, plasma instability, and sweeping up an atmospheric mass comparable to that of the plasma have limited effect. We derive from the virial theorem a lower bound on the plasma radius as a function of time which compares well with simple models neglecting these complications.
Excitation of Electrostatic Ion Cyclotron Oscillations
Authors: Levine A. M. , Kuckes A. F.
Published: December 2004

It has been observed that an electron current drawn to an electrode immersed in a magnetized plasma can excite oscillation near the ion cyclotron frequency. A theory is derived which predicts such oscillation due to a destabilizing influence of the sheath voltage drop at the electrode on the plasma column. Experimental evidence is presented which shows that the present theory is more compatible with observations than an earlier explanation in terms of resonantly drifting electrons.
Excitation of Waves in a Compressible Partially Ionized Plasma by Sources of Different Kinds
Authors: Samaddar S. N.
Published: December 2004

A three-fluid isotropic homogeneous compressible plasma is described by a set of linearized hydrodynamic and Maxwell's equations containing acoustic (or mechanical) and electromagnetic sources. It is shown, in general, that under suitable assumptions, these equations can be decomposed into transverse electromagnetic waves and longitudinal plasma-acoustic waves. Though the total fields can be decomposed in this manner, the total energy (or the Poynting vector) cannot be expressed as the sum of the energy associated with electromagnetic fields and plasma-acoustic fields alone. That is, there is an energy transfer between these two decomposed waves due to collisions among the plasma elements.
Intrusion of Plasma into a Model Magnetosphere
Authors: Bostick W. H. , Byfield H. , Jermakian A.
Published: December 2004

Photographic evidence is supplied to support previous probe measurements which indicate that, in the plasma flow over a magnetic dipole, the plasma front breaks up into columnar vortices which line up with the magnetic field.
Further Results on Stability of a Swirling Fluid with Variable Density in the Presence of a Circular Magnetic Field
Authors: Pao Hsien Ping
Published: December 2004

A new branch of solution which corresponds to negative critical Taylor number is found for the stability of a swirling fluid with variable density in a circular magnetic field. Some clarification is made in the previously published results.
``Turbulence'' of a Low-β Plasma
Authors: D'Angelo N. , Enriques L.
Published: December 2004

The fluctuation spectra of Cs and K plasmas have been measured in the Q-3 device. They appear to be in agreement with a recent prediction by Chen.
Linearized Boundary Value Problem for a Gas and Sound Propagation
Authors: Buckner John K. , Ferziger Joel H.
Published: December 2004

A complete set of eigenfunctions of the linearized modeled kinetic theory Boltzmann equation appropriate to the boundary value problem is constructed. These functions are then used to solve a boundary value problem which contains the essential features of sound propagation experiments. The calculated pressure field correctly gives the hydrodynamic solution as its high-density limit and modified free flow behavior as its low-density limit. Even for very simple models the results are in remarkably good agreement with experiments.
Extension of the Fokker-Planck Equation
Authors: Price John C.
Published: December 2004

A simple collision term valid to order 1/ln Λ is derived for small-amplitude waves in a uniform plasma. This result extends the validity of Fokker-Planck type equations from the domain 0 ≤ ω ≪ ωp, 0 ≤ k ≪ kd to the domain 0 ≤ ω ≪ Λωp, 0 ≤ k ⪝ kd.