bluuebunny/crossref_metadata_2025 huggingface dataset:
Precision Measurement of Parabolic Profile for Laminar Flow of Air between Parallel Plates
Authors: Breslin John A. , Emrich Raymond J.
Published: December 2004

Photography of tiny oil drop tracers carried by air flowing in a rectangular pipe has been used to measure the fluid velocity at various distances from the wall. Measuring accuracy of better than±0.5% over most of the profile yields agreement with the predicted parabolic profile. The measurements are carried out in an all-glass section of pipe of cross section 9.5 × 102 mm; the pipe flow Reynolds number is 15, and the duration of the measurement is 0.2 sec.
A Theory of the Low-Pressure Positive Column in a Transverse Magnetic Field
Authors: Aničin B.A.
Published: December 2004

When a positive column is submitted to a transverse magnetic field the Lorentz force compresses the electron gas towards one side of the vessel containing the plasma. This phenomenon is analysed in planar geometry at low gas pressure. The ion mean free path is assumed to be at least several times the discharge width. The behavior of the ionic gas is treated using a fluid type version of free fall theory. Plasma density and potential profiles are obtained for various magnetic field strengths. The potential difference between the two insulating discharge walls, or the Hall voltage, is derived and found to be a nonlinear function of the magnetic field. The solution of the free-fall problem permits to formulate the five equations of balance of a magnetized plasma slab. These are used to determine the electron temperature and the longitudinal electric field of the positive column.
Angular Spectrum of Ion Cyclotron Harmonics
Authors: Furutani Y. , Kalman G.
Published: December 2004

The combined effect of the anisotropic and frequency-dependent character of the polarizability of a magnetoplasma which gives rise to a very peculiar and energy-dependent angular distribution of the radiation emitted by a test ion, is considered.
Nonlinear Plasma Waves. III. Nonlinear Temperature Effects in the Electron—Ion Two-Stream Instability
Authors: Freidberg Jeffrey P.
Published: December 2004

The nonlinear interaction of two warm interpenetrating electron and ion streams is treated by investigating the traveling wave solutions to the two fluid macroscopic plasma equations. These equations are reduced to the form of a nonlinear differential equation with an additional small nonlinear term. Application of the perturbation procedure, described previous by [J.P. Freidberg, Phys. Fluids 10, 171 (1967)], leads to (1) conditions on the maximum amplitudes for which traveling wave solutions exist and (2) a nonlinear amplitude dependent dispersion relation. An examination of this dispersion relation indicates that below a certain critical temperature there is a range of wavenumbers where the two stream instability may level off before the amplitude reaches the maximum amplitude for existence of traveling wave solutions. This range of wavenumbers decreases with increasing temperture and therefore is largest when the temperature is zero.
Internal Gravitational Instability in a Stratified Anisotropic Plasma
Authors: Yu C. P. , Sanborn J. V.
Published: December 2004

The instability induced by external gravitational forces in an infinite, stratified, anisotropic plasma with a magnetic field has been studied using the Chew, Goldberger, and Low approximation. A plasma whose equilibrium properties vary with height in a horizontal variable magnetic field and a vertical gravitational field is considered. Three stability criteria are derived from the energy principle, two of which lead to the ``firehose'' and ``mirror'' instabilities found in a uniform anisotropic plasma while the third criterion is for the convective instability arising from gravity. In contrast to the isotropic case, it is found that the convective criterion depends explicitly upon the magnetic field. An increase of the magnetic field by a constant quantity shows that the plasma is more stable. The growth rates of the unstable displacements in the least stable regions are calculated using a normal mode analysis.
Couple Stresses in Fluids
Authors: Ariman Teoman , Cakmak Ahmet S.
Published: December 2004

Applications of couple stress and micropolar theories to the problems of Couette and Poiseuille flows between two parallel plates are discussed and the results are compared.
Variational Formulation for Nonisothermal Viscous Liquids
Authors: Butler H. W. , Rackley Robert L.
Published: December 2004

A variational formulation is presented for the slow motion of viscous, heat-conducting liquids whose viscosity and conductivity are realistic functions of temperature. The formulation reduces to previous results as special cases.
On the Ionized Laminar Boundary Layer Equations
Authors: Tabaczynski R. J. , Goldstein M. E.
Published: December 2004

The results of previous work on the multi-component laminar boundary layer problem are extended to include two temperature ionized gases and calculations are performed for the equilibrium thermal conductivity of partially ionized argon.
Plasma Oscillations in an External Electric Field
Authors: Gorman D.
Published: December 2004

A diffusely reflecting wall bounding an electron plasma modifies the law of penetration of longitudinal waves excited by an external field from that found by Landau for the case of specular reflection.
Flow of Micropolar Fluids between Two Concentric Cylinders
Authors: Ariman T. , Cakmak A. S. , Hill L. R.
Published: December 2004

The flow of micropolar fluids between two concentric cylinders, is analyzed first for the use of Couette flow with ∂p/∂θ, then for the case of Poiseuille flow. The results are presented graphically and compared with the classical ones, and the differences are discussed.
Dynamical Properties of Truncated Wiener-Hermite Expansions
Authors: Orszag Steven A. , Bissonnette L. R.
Published: December 2004

The use of truncated Wiener-Hermite functional expansions as a basis for the theory of turbulence is critically examined. An account is given of the application of such expansions to Burgers' model equation. The nature of Wiener-Hermite expansions is such that certain important consistency requirements, such as realizability, follow immediately. In order to gain insight into other aspects of the predicted turbulence dynamics, a simpler model problem in which there are only three interacting modes is first studied. It is shown that Wiener-Hermite closures do not faithfully represent the dynamics for this latter model. Then, the analysis is extended to Burgers' equation. It is shown that Wiener-Hermite closures do not preserve fundamental properties of the exact dynamics in equilibrium. Inviscid equipartition solutions do not survive in the closures. In addition, it is shown that these closures do not treat the effects of large scales on small scales properly. Numerical calculations be extended to the corresponding theory of Navier-Stokes turbulence. We conclude that truncated Wiener-Hermite expansions are unsuitable for the theory of high Reynolds-number turbulence.
Effect of a High-Frequency Spatially Uniform External Electric Field on a Plasma
Authors: Prasad R.
Published: December 2004

Dispersion relation for transverse waves in a fully ionized plasma in the presence of a spatially uniform field E0 cos vt has been obtained and the possibility of instabilities has been discussed. It has been shown that the analysis also gives the Dawson-Oberman formula for the force of an ion on the electrons for the uncoupled longitudinal field.
Stimulated Brillouin Effect in Magnetoplasmas
Authors: Pomeau Y.
Published: December 2004

The manner in which a pumping wave of high amplitude can produce parametric instabilities in a plasma is investigated. A very simple derivation of the nonlinear polarizabilities is given for the case when the pumping wave is homogeneous. From this nonlinear polarizability, a derivation of the accurate nonlinear dispersion relation is given. One finds unstable waves by solving this nonlinear dispersion relation. The critical level of the pumping wave is very much reduced if the proper modes allow carrying out the stimulated Brillouin effect. A pumping wave with a cyclotron resonance gives a particularly low critical level.
Rayleigh Problem in a Radiating Compressible Gas. II. Plate Mach Number Large
Authors: Solan Alexander , Cohen Ira M.
Published: December 2004

The Rayleigh problem for a compressible radiating gray gas is analyzed by asymptotic methods and solved numerically for one limiting case. The problem is formulated for large ratio of the photon to molecular mean free path N, large Mach number M, and general values of the Boltzmann number Bo. Using Kruskal's ``principle of maximal complication,'' a detailed formal asymptotic analysis is carried out for various combinations of N, M, and Bo. Attention is focused on those limiting cases in which the asymptotic scaling of main interest yields an optically thin hot boundary layer with emission but no absorption, which may be solved independently of the corresponding outer flow. One representative case of such boundary-layer flow is solved numerically.
Approximations to the Structure of a Laminar Detonation Wave by the Method of Matched Asymptotic Expansions
Authors: Bowen J. Ray
Published: December 2004

The method of matched asymptotic expansions is used to develop higher-order approximations to the Zeldovich-von Neumann-Döring theory for the structure of a laminar detonation which is supported by an irreversible unimolecular chemical reaction. The Arrhenius rate expression is replaced by the Hirschfelder strong ignition temperature approximation so that analytical solutions are obtainable for the shock and the reaction zone. The perturbation parameter δ is the ratio of the molecular collision time to the chemical reaction time (evaluated at the hot boundary). The solutions are correct to O(δ) for the shock zone and to O(δ2) for the reaction zone. The strong ignition temperature approximation is shown to overestimate the effects of chemical reaction in the shock zone and to give erroneous estimates of the effects in the reaction zone. More realistic rate expressions may be treated by the method of matched asymptotic expansions at the expense of additional numerical computations, if a more accurate description of the laminar detonation structure is desired. However, the results for the strong ignition temperature approximation may be useful as the basis of a stability analysis.
Plane Couette Flow of Rarefied Gases
Authors: Weinstein Herbert G. , Schowalter W. R.
Published: December 2004

The thirteen-moment approximation to the molecular velocity distribution function has been used to develop a system of moment equations and boundary conditions for plane Couette flow. Following linearization, an iteration scheme is proposed for study of nonlinear aspects of the problem. Results of this analysis show explicitly the effects of Mach number, Knudsen number, and accommodation coefficient on velocity, stresses, and heat fluxes. Two types of systems are discussed. In one (open system), pressure between the plates is maintained at a constant predetermined value; in the other (closed system), the average of gas density between the plates is maintained at a constant predetermined value. Results are compared with earlier treatments of plane Couette flow.
Transport Coefficients of Partially Ionized Argon
Authors: Devoto R. S.
Published: December 2004

The complete Chapman-Enskog-Burnett expressions for the transport coefficients of multicomponent gas mixtures are applied to the computation of the properties of partially ionized argon. Studies of the rate of convergence of the approximations to the coefficients show that the third approximation to the thermal conductivity and the second to the viscosity are adequate at all degrees of ionization. The ordinary ambipolar diffusion coefficient is given to excellent accuracy by twice the binary ion-atom diffusion coefficient but, at low ionization, apparently not even the fourth approximation to the electrical conductivity has converged to the true value. The computed electrical and thermal conductivities are compared with experimental measurements.
Linearized Superposition Theory of a Classical One-Component Plasma
Authors: Levitt Leo C. , Richardson John M. , Cohen E. Richard
Published: December 2004

The equilibrium theory of a one-component nondegenerate charged gas, in a uniform continuum of a neutralizing charge, is studied on the basis of a linear-closure procedure for the BBGKY hierarchy which, in the present instance, corresponds to the use of the linearized Kirkwood superposition approximation, and leads to a second-order linear differential equation for the radial distribution function. Its solution is studied, numerically and analytically, for a wide range of the plasma parameter γ = e2/kTΛD, where ΛD is the Debye length. Results for γ ≪ 1 are compared with corrections to the Debye-Hückel theory derived by Abe and others. Solutions for γ ≫ 1, which approach an ordered state of the system as γ increases, are compared with two simple ``model'' calculations of the equilibrium theory of a body-centered cubic lattice of charges in a uniform background of compensating charge. The thermodynamic properties of these ``Coulomb lattice'' models are in qualitative agreement with those of the plasma as computed via our closure approximation for γ ≫ 1. The possibility is therefore suggested that, even for large γ, the linear closure approximation has a larger degree of validity than might be expected a priori.
Velocity Space Instabilities in a Toroidal Geometry
Authors: Berk H. L. , Galeev A. A.
Published: December 2004

A self-consistent equilibrium is derived for a simple toroidal model from knowledge of the particle orbits. This equilibrium is investigated for velocity space instabilities analogous to the loss cone of mirror machines. An ion instability generated by particles in ``trapped'' or nearly ``trapped'' orbits is found when the rotational transform is relatively weak, but is stabilized with larger rotational transform. Instability is also found at the plasma edge due to a loss of particles in a preferred region of velocity space. A qualitative discussion of the quasi-linear development of these instabilities is presented.
Effect of Pressure on Negative V″ Stellarators
Authors: Johnson John L.
Published: December 2004

Stability with respect to hydromagnetic interchanges can be achieved in closed configurations if V″(ψ) < 0 with V″(ψ) the volume inside a magnetic surface of flux ψ. A low-pressure expansion is used to examine the effects of plasma currents in a negative V″ configuration which utilizes an l = 2 shaping field and an l = 1, l = 3 corrugating field and in which toroidal curvature is neglected. Numerical calculations indicate that the effect on stability of these currents is small. Since the basic features of all the proposed negative V″ configurations are similar, this strengthens the belief that vacuum field considerations provide an adequate approximation.
Wall Temperature and Speed Ratio Effects on Free Molecule Flat Plate Flows
Authors: Ortloff Charles R.
Published: December 2004

The dependence upon plate temperature and free-stream speed ratio of the number density distribution about a diffusely reflecting flat plate under free-molecule flow conditions is determined.
Stabilization of Helical Modes by Magnetic Wells
Authors: Fowler T. K.
Published: December 2004

Helical modes are found to be stabilized by magnetic wells of finite but small depth, and thus provide a practical test of the general principle of stabilization by deep wells.
Expansion and Contraction of Jets of Newtonian Liquids in Air: Effect of Tube Length
Authors: Gavis J. , Modan M.
Published: December 2004

An experimental study of the effect of tube length-to-diameter ratio, L/d0, on the expansion and contraction of jets of Newtonian liquids into air is described. For Reynolds numbers based on tube diameter, Red, above 16 the jets contracted. Jet diameter correlated with the degree of development of the velocity profile in the tube, a function of L/d0, and was unaffected by viscous dissipation. At Red = 16 the jet diameter was equal to the tube diameter and was independent of L/d0. When Red < 16 the jets expanded. Jet diameter was affected by viscous dissipation. Most of the data in this range could be correlated as a function of the Reynolds number based upon tube length, ReL, and of the ratio of the Brinkman number to the product of the Prandtl number and ReL. How the stresses acting in the jet and in the tube are influenced by profile development and by viscous dissipation and affect jet diameter is discussed.
Shock-Induced Flow Interactions with Transverse Magnetic Fields
Authors: Johnson Milton R.
Published: December 2004

The one-dimensional phenomena which occur when shock-induced flows in ideal gases interact with transverse magnetic fields of finite extent are analyzed from both the steady-state and transient viewpoints. The steady-state analysis assumes steady flow exists within the interaction zone. It is shown that there are four types of interactions. These involve the presence or absence of standing or upstream-propagating reflected shock waves, and rarefaction waves on the downstream side of the interaction zone. The types of interactions are functions of the initial Mach number of the shock-induced flow, the interaction parameter, the magnetic Reynolds number, and the amount of electrical energy withdrawn from the flow. The method of characteristics is used to analyze transient phenomena. The transient problem is described by a five-characteristic network, which is reduced to four characteristic directions when the flow velocity is small compared to the electromagnetic signal velocity. The transient analysis can be used to determine the position where the reflected shock wave forms and the length of time required for the flow within the interaction zone to approach steady-state conditions.
Stability of a Self-Gravitating Plasma Cylinder Including Hall Effect
Authors: Hosking R. J.
Published: December 2004

A self-gravitating, infinite cylinder of conducting, homogeneous, incompressible fluid in an axial magnetic field is considered with Hall effect included. In the case of axisymmetric modes, an asymptotic analysis for small, nonzero Hall current indicates a destabilizing effect of O(ε), where ε is the perturbation parameter. It appears that the increased instability is due to the electron-ion diffusion current, which contributes a radial Lorentz force that is absent in the single-fluid theory. This radial Lorentz force increases the tendency for the cylinder to break up into lengths defined by the perturbation wavenumber.
Small Rotational Transforms
Authors: Lindner J. , Lortz D.
Published: December 2004

If a solenoidal field B can be separated into a fundamental component B0 with closed field lines and a perturbation B1 of the order ε, it is possible to integrate the differential equations for the field lines up to the second order in ε. It turns out that the rotational transform is of the order ε if the flux of the field B1 through a surface limited by any closed field line of B0 does not vanish. When the transform is of the order ε2 one can derive an explicit expression for the magnetic surfaces.
Intensification of Magnetic Field in Plasmas
Authors: Jaggi R. K.
Published: December 2004

An infinite plasma containing a uniform magnetic field is considered. Self-consistent solutions were found to two examples concerning the intensification of magnetic field by using magnetohydrodynamic equations with finite conductivity. In the first example, half of the infinite plasma moves perpendicular to the magnetic field and a finite amount of magnetic field is produced in the direction of motion of the plasma. When the velocity of the semi-infinite plasma is assumed to be independent of time, the magnetic field produced is proportional to t½ and it is possible to produce any amount of magnetic field. However, the later situation is not realistic. In the second example, it is assumed that at t = 0 an external force along x axis acts in the region − a ≤ z ≤ a and produces a component of the magnetic field along its direction of motion. The application of this example to the sun shows that large convective cells rising in the presence of the magnetic field of the sun can give rise to a strong magnetic field (∼ 104 G) in the direction of the convective motion.
Numerical Calculation of the Relaxation of an Electron Gas
Authors: Gu Alston Lee-Van
Published: December 2004

It is found that for disturbance at about 0.5 of the thermal speed approximately one self-collision time is enough for the distribution function to approach Maxwellian, and the time required increases rapidly as the disturbance moves to high velocity.
Observation of Ion Heating Using a Modulated Electron Beam in a Magnetic Mirror Field
Authors: Haas G. M. , Dandl R. A.
Published: December 2004

The interaction of a modulated electron beam of modest current with a plasma formed in a hydrogen gas produces protons with energies up to several hundred electron volts. The energetic proton flux from the plasma is dependent on the beam current and modulation frequency.
Compressible Magnetogasdynamic Free Jet
Authors: Smith David C. , Cambel Ali Bulent
Published: December 2004

The problem of an electrically conducting, compressible, viscous free jet in the presence of transverse magnetic and electric fields is solved analytically by a perturbation technique. The velocity and temperature profiles are expanded about the nonmagnetic jet solutions, the expansion parameter being the magnetic interaction parameter. The first-order perturbation solution is obtained in closed form for both the velocity and temperature profiles when a transverse magnetic field interacts with the free jet. Finally, the velocity profiles are obtained in closed form for an electric field transverse to both the jet axis and the magnetic field.
Laminar Boundary-Layer Heat Transfer from a Partially Ionized Monatomic Gas
Authors: Back L. H.
Published: December 2004

Laminar boundary-layer heat transfer from a partially ionized monatomic gas to a highly cooled wall with no applied external electric or magnetic fields is analyzed by the similarity solution approach. The gas is assumed to be electrically neutral with ambipolar diffusion by ion-electron pairs. In addition, equal electron and atom-ion temperatures are assumed, and sheath effects are not considered. From existing perfect gas similarity solutions, the number of parameters that need to be investigated is reduced to those directly related to ionization effects. Solutions for the limiting cases of a large diffusion rate compared to the net production rate of ions and for local equilibrium are obtained for a range of Prandtl and Lewis numbers. An approximate prediction method that includes variable property considerations is then suggested to account for variable free-stream velocity and ionization effects in a flow over a highly cooled wall.
Supersonic Gas-Particle Flow with Chemical Reactions
Authors: Migdal David , Agosta Vito D.
Published: December 2004

The characteristic equations for a two-dimensional, steady, supersonic gas flow with source terms and chemical reactions are developed. A continuum mixture of gas and particles with negligible volume is used to define the particle source terms. Mass sources which give rise to chemical reaction with the surrounding gas are considered. The mass, momentum and heat sources are defined to be compatible with experimental data for a single particle.
Nonlinear Extraordinary Waves in a Cold Plasma
Authors: Boyd T. J. M.
Published: December 2004

The methods of Bogoliubov, Krylov, and Mitropolskii which have been generalized and applied recently to various types of plasma waves are used to calculate the frequency shift associated with the nonlinear extraordinary wave in a cold plasma.
Development of Short-Period Temperature Fluctuations in Thermal Convection
Authors: Willis G. E. , Deardorff J. W.
Published: December 2004

For thermal convection between horizontal plates a certain Rayleigh number greater than the critical value must be attained before well-defined, unsteady temperature fluctuations occur. Their appearance is found to be a strong function of Prandtl number, and has apparently been explained for large Prandtl number by a theory of Howard. These fluctuations at a given point midway between plates are intermittent in appearance over a considerable range in Rayleigh number. The Rayleigh number at which the intermittency essentially ceases and irregular fluctuations are nearly always present is determined and also found to be strongly dependent upon Prandtl number. There is no apparent association between the development of these short-period fluctuations and the heat-flux transitions of Malkus.
Thirteen-Moment Theory of the Thermal Force on a Spherical Particle
Authors: Dwyer Harry A.
Published: December 2004

A linearized version of Grad's thirteen-moment equations have been solved with generalized velocity slip and temperature jump boundary conditions, and a theory of the thermal force acting on a spherical particle obtained for the entire range of Knudsen numbers. The theory is in good general agreement with all experimental data and gives the correct dependence on the thermal conductivity of the particle. In the range of large Knudsen numbers the solution is functionally the same as Waldman's and also gives the correct infinite mean free path limit. As a by-product of the theory, thermal accommodation coefficients can be predicted with fair to good accuracy. For particles of high thermal conductivity and high thermal accommodation coefficient, the theory also predicts the possibility of a reversal of the thermal force near the continuum limit.
Magneto-Fluid-Mechanic Channel Flow. I. Experiment
Authors: Brouillette E. C. , Lykoudis P. S.
Published: December 2004

An experiment is described in which fully developed turbulent channel flow of mercury was investigated in the presence of a uniform transverse magnetic field. The channel test section was constructed from an electrical insulator and was rectangular in cross section. The flow was studied in the range of Reynolds numbers: 58 000–180 000, based on channel equivalent diameter. Hartmann number was varied between zero and values sufficiently high to change the flow from turbulent to laminar at the corresponding Reynolds number. Skin friction coefficients were deduced from static pressure measurements along the length of the channel. Velocity profiles were obtained from traversing probe total head measurements.
Comparison of Oblique, Normal and Transverse Ionizing Shock Waves
Authors: Taussig Robert T.
Published: December 2004

The jump equations for an oblique ionizing shock wave are examined in detail. A qualitative description of the shock structure helps to eliminate one of the four possible solutions and to limit the electric currents which the remaining shock solutions can carry. The criterion of evolutionarity is applied to ionizing shock waves to obtain necessary conditions for the existence of unique solutions. A shock structure restriction is proven which allows one to define a unique solution for every shock speed. Using these results, the Chapman-Jouguet mode of electromagnetic shock tube operation is justified in the weak-ionizing shock-wave limit. Oblique, normal and transverse ionizing shocks in hydrogen, including the effects of ionization and dissociation, are compared. The temperature, thermalization efficiency, heating time, conversion ratio of magnetic to thermal energies and the specific impulse obtained by such shocks are used as measures of comparison. The transverse type of shock is shown to be the most effective one for producing a hot plasma sample. Results of several recent experiments are compared to the theoretical predictions, and the accuracy of the shock model and conclusions drawn from it are criticized briefly.
Traveling-Wave Bulk Electroconvection Induced across a Temperature Gradient
Authors: Melcher James R. , Firebaugh Millard S.
Published: December 2004

If a temperature gradient is imposed on a slightly conducting liquid, a gradient in natural electrical conductivity generally results. It is shown that if the liquid is then subjected to a wave of electric field traveling perpendicular to the temperature and conductivity gradients, charges are induced in the liquid bulk. These charges relax to form a traveling wave which interacts with the imposed field to pump the liquid. The sign of the conductivity gradient determines whether the liquid is pumped in the same direction or a direction opposite to that of the traveling wave. Equations are given for the velocity profile in plane flow, showing the effect of fluid properties as well as of the frequency, wavelength, and potential of the traveling wave. Experiments support the significance of the theory. Observations of a type of bulk Rayleigh-Taylor instability are discussed.
Numerical Solutions of Hypersonic Sharp-Leading-Edge Flows
Authors: Butler Thomas Daniel
Published: December 2004

A numerical study is made of hypersonic flow past the leading edge of a flat plate. The full time-dependent Navier-Stokes equations are solved using the particle-in-cell and fluid-in-cell computing methods. The effects of several plate boundary conditions are investigated for two free-stream Mach numbers. These conditions include velocity slip and temperature jump at the plate surface. Solutions reveal the existence of an appreciable boundary layer pressure gradient near the leading edge. Comparisons are made with both experiment and analytical theory for a cooled plate in Mach 25 flow. These comparisons show good agreement between the calculations and experiment in the magnitude of the surface pressures.
Bremsstrahlung of Slow Electrons in Neutral Gases and Free-Free Absorption of Microwaves
Authors: Akcasu A. Z. , Wald L. H.
Published: December 2004

Bremsstrahlung of nonrelativistic electrons in a neutral gas is investigated including the polarization and exchange effects. The intensity and spectrum of the bremsstrahlung and of the induced dipole radiation are obtained for a Maxwellian distribution of electron energy in terms of the elastic scattering cross section of the atom for electrons and its polarizability. The interference of the induced dipole radiation with the bremsstrahlung is also considered. It is found that the exchange effects and the induced dipole radiation are negligible as far as the total radiated power is concerned. The latter, however, may be important at the short-wave end of the spectrum. Finally, the absorption coefficient is obtained from the bremsstrahlung cross section. The results are evaluated explicitly for a Maxwellian distribution.
Viscous Effects on the Axisymmetric Instability of a Current Carrying Annular Jet
Authors: Gokhale M. H.
Published: December 2004

Viscous effects on the instability of an experimental liquid model of hard-core pinch are considered. For typical experimental values viscosity reduces the growth rates of axisymmetric perturbations by less than one-tenth of their values in the absence of viscosity.
Simplified Variational and Physical Analysis of Heat Transfer in Laminar and Turbulent Flow
Authors: Biot M. A.
Published: December 2004

The fundamental physical features of convective heat transfer for laminar and turbulent flow in ducts and boundary layers are brought out and analyzed quantitatively. A simplified variational method is used which is shown to be remarkably accurate by applying it to special cases where exact solutions are known. Results are expressed in nondimensional form by means of two universal trailing functions which embody the essential features of heat transfer for laminar and turbulent flow and are approximated by very simple piece-wise analytic expressions. The results are applicable to nonparallel streamlines as encountered in duct entry and most boundary layers. This is achieved by introducing a new transformation which provides a suitable extension of the ``conduction analogy'' to these cases. Drastic simplifications are derived in the analysis of convective heat transfer. In particular it is shown how the trailing function is used in evaluating the heat transfer in heat exchangers and in the much more complex problem of transient heat conduction in a structure adjacent to a moving fluid. In the latter case it is pointed out how the use of the trailing function avoids serious errors in thermal stress analysis.
Growth and Decay of Discontinuities in Fluids with Internal State Variables
Authors: Coleman Bernard D. , Gurtin Morton E.
Published: December 2004

In the nonlinear theory of one-dimensional motions of fluids exhibiting mechanical dissipation through the relaxation of internal state variables, one can derive exact expressions for the growth and attenuation of acceleration waves and higher-order waves. The methods and concepts used are simpler than those required for analogous problems in the general theory of materials with fading memory. Detailed calculations are reported of the time dependence of the amplitude of waves propagating into homogeneous regions at equilibrium.
Use of Two-Dimensional Slab Models in Hydromagnetic Stability Theory
Authors: Johnson John L.
Published: December 2004

The use of two-dimensional models with a varying gravitational field to simulate the effect of curvature of the magnetic field lines is justified by a study of localized instabilities in general toroidal configurations. This clarifies the limitations of such models.
Plasma State in a Coaxial Accelerator
Authors: Lie T. N. , Ali A. W. , McLean E. A. , Kolb A. C.
Published: December 2004

Spectroscopic measurements of electron temperature and density are reported for plasmas produced in a coaxial accelerator filled with helium to a static pressure of 0.5–1.0 Torr. Luminous front velocities of ∼6 cm/μsec were attained. Since the validity of these measurements depended on the assumption of local thermal equilibrium, the collisional and the radiative processes which determine the population densities of HeIII, and the various bound states of HeII and HeI, are examined. It is concluded that the local thermal equilibrium assumption is in fact a satisfactory approximation for the conditions of this experiment, i.e., the actual temperature deviates by no more than 10–15% from the local thermal equilibrium value. Electron temperatures and densities were found to be ∼4.0 eV and ∼1017 cm−3, respectively, in the region outside the end of the accelerator but before the plasma focus. Density distributions were found to vary greatly in the radial direction and to have strong dependence on polarity effects. For the case of a positive inner electrode, a large fraction of the gas was found to ``snowplow'' at the plasma front.
Effect of Rotation on the Growth of Alfvén Wave
Authors: Nariboli G. A.
Published: December 2004

The presence of rotation leads to a nonvanishing rate of growth of the discontinuity across an Alfvén wave front. The differential equations describing the growth are integrated completely when the state ahead is steady, but otherwise arbitrary.
Stochastic Magnetic Pumping
Authors: Hall D. E. , Sturrock P. A.
Published: December 2004

The results of a simple model for betatron-type collisionless statistical heating of particles by random fields are presented, and the relation of this study to other work of this type is discussed.
Gravitational Instability of a Rotating Anisotropic Plasma
Authors: Bhatia P. K.
Published: December 2004

Gravitational instability in an anisotropic plasma has been studied to include the effect of rotation. It is shown that the stability criterion is dependent upon rotation as well as magnetic field.
Temporary Trapping of Charged Particles in a Static Magnetic Bottle
Authors: Hubert Pierre , Touche Jacques
Published: December 2004

A temporary trapping device which combines the resonant perturbation method (Sinelnikov method) and the method of injection through a saddle point in the Störmer potential configuration is discussed theoretically and experimental results are presented. A temporary trapping duration corresponding to 450 transits on the average for the whole beam has been obtained in agreement with a theoretical prediction which assumes a uniform density in all the phase space available inside the bottle.
Constants of the Motion and Microscopic Stability of Plasmas
Authors: Völk Heinrich J.
Published: December 2004

The possibility of sidestepping the direct solution of the Vlasov equation in order to obtain information about the stability of a plasma by employing certain constants of the motion is discussed. For plane equilibria a large set of conservation laws is derived in the electrostatic approximation, including those for the total energy and momentum of the system. For some special equilibria the positive—definiteness of the energy yields a (well-known) sufficient stability criterion. The aim of the paper is to investigate how far such criteria can be extended to more general cases with the help of the more general class of constants. In the one-dimensional homogeneous case without magnetic field one thus can establish an ``energy-principle'' for the Vlasov equation. An earlier attempt by Oberman and Dawson using energy and momentum conservation only is discussed in this context. However, the generalization even to the corresponding three-dimensional case turns to be impossible. It is concluded that, except for the plasma equilibria mentioned, even the most general constants of the motion known up to now do not lead to stability criteria of the Liapounov type.
Injection of a Drag-Reducing Fluid into Turbulent Pipe Flow of a Newtonian Fluid
Authors: Wells C. Sinclair , Spangler Jack G.
Published: December 2004

Recent experiments with additives which reduce turbulent skin friction in turbulent shear flow of liquids have suggested that the significant changes in the shear flow occur in the flow very near the wall, in the region of the viscous sublayer. A series of experiments, in which dilute solutions of drag-reducing fluids were injected into turbulent pipe flow of a Newtonian fluid, were performed in order to determine whether the presence of the additive only in the wall region could produce significant local shear stress reduction. It was found that the local pressure gradient could be reduced by an amount comparable to the flow of a uniform concentration when the fluid was injected in the wall region. Conversely, when the fluid was injected into the turbulent core no reduction in local pressure gradient occurred until the fluid diffused into the wall region. The effects of the injection flow process and the injection apparatus were evaluated and found to be small compared to the results of injection of the drag-reducing fluid.
Effect on Shock Trajectory of the Opening Time of Diaphragms in a Shock Tube
Authors: Simpson C. J. S. M. , Chandler T. R. D. , Bridgman K. B.
Published: December 2004

Diaphragm opening times and shock trajectories have been measured in a shock tube. The distance over which the shock accelerates is proportional to the product of the shock speed and the diaphragm opening time.
Experimental Study of Collision-Free Shock Waves and Anomalous Electron Heating
Authors: Goldenbaum George C.
Published: December 2004

Cylindrically converging magnetic compression waves have been observed propagating into a low density hydrogen plasma (ne = 3 × 1014, kTe = 1.4 eV) in a fast theta pinch discharge with the compressing field and initial field both parallel and antiparallel. For parallel fields, the waves are nonstationary in this experiment and cylindrical convergence effects cannot be ruled out. The thickness of the transition is greater than 1 cm which is less than the ion gyroradius and the ion mean free path for ions travelling with the wave front across the initial magnetic field. The electron heating rate (≃10 eV/nsec) and the transition thickness are both greater than one would expect for resistive heating with the Spitzer-Härm resistivity. In the case where the compressing field and the initial field are antiparallel, a wave flow develops which appears to be an almost plane and nearly stationary collision-free shock. For an initial field of −450 G the Alfvén Mach number is estimated between 4 and 9. The magnetic transition has a slowly rising front part (>1 cm) followed by a faster rising part (l ≃ 3 mm).
Method of Analysis of Ion Swarm Experiments
Authors: Barnes William S.
Published: December 2004

Means are presented for analyzing the data and estimating the values of parameters of interest in certain kinds of ion swarm experiments by use of maximum likelihood estimators. Means are also presented for estimating the fluctuations in the estimates of the parameters and several other statistics which are produced by the statistical fluctuations of the ion populations themselves. Methods are discussed for using these estimates to judge the appropriateness of the model hypothesized for both the ion transport process and the functioning of the experimental equipment. The use of the maximum likelihood methods in connection with several different initial ion distributions and several possible experimental geometries, is explored. The application of these methods to data from actual experiments involving the ions N+ and N2+ in nitrogen is discussed.
Plasma Wave Reflection in Slowly Varying Media
Authors: Berk H. L. , Horton C. W. , Rosenbluth M. N. , Sudan R. N.
Published: December 2004

Two mathematical formalisms are presented to describe wave reflection in a slowly varying spatially inhomogeneous thermal plasma described by the Vlasov equation. It is found that the transmitted wave, which is the Wentzel-Kramer-Brillouin solution, and the reflected wave, can be expressed in terms of the local dielectric properties of the medium. In a numerical example, it is shown that the intrinsic thermal properties of the plasma can supply reflection mechanisms that compete with the reflection coefficient predicted when the plasma is described by fluid equations.
Stabilization of a Stellarator Plasma by Finite-Larmor-Radius and Ion-Ion-Collision Effects
Authors: Ellis R. A. , Bol K. , Stix T. H.
Published: December 2004

The magnetic field, Bc, for onset of nonreproducible fluctuations in stellarator afterglows varies with ion mass as mi0.44. For ion viscous stabilization of drift waves Bc ∼ mi⅜; for finite ion Larmor radius or ion cyclotron frequency stabilization, Bc ∼ mi½.
Transition in Incompressible Near-Wakes
Authors: Roshko Anatol
Published: December 2004

An experimental study of the near-wakes of a family of flat-based cylinders of varying chord-thickness ratio, L/d, shows that the phenomena of vortex shedding and transition are similar to those for a cylinder of circular section. The Reynolds number for appearance of turbulence in the wake is correlated with L/d.
Flow around the Separation Point and in the Near-Wake of a Circular Cylinder
Authors: Maekawa T. , Mizuno S.
Published: December 2004

The velocity fluctuations in the boundary layer around the separation point and in the near-wake of a cylinder were measured at Re = 3.7 × 104 ∼2.8 × 105. All the phenomena found seem to be interpreted by (1) the oscillation fore and aft of the separation point, (2) the transverse oscillation of the separated shear layer, (3) the temporary immersion in the ``tongue'' of potential flow and (4) the oscillation in the plane of the axis of wake vortex.
Suppression of Vortex Shedding and Turbulence behind Oscillating Cylinders
Authors: Berger E.
Published: December 2004

The laminar Kármán vortex flow in the wake of a cylinder can be suppressed in a certain Reynolds number range, if the cylinder is stimulated to small oscillations in a direction normal to the mean flow either externally by high-frequency fluctuations, or internally by negative feedback of a hot-wire signal picked up in the wake. If suppression is obtained, the transverse mean velocity profiles become deeper in comparison with those of vortex shedding, however the drag is of the same order in both cases. On the other hand the laminar vortex flow can be stabilized and extended to both lower and higher Reynolds numbers, by exciting the cylinder with frequencies, which synchronize the wake fluctuations.
Determination of the Effect of Roughness Change on the Wind Profile
Authors: Blackadar A. K. , Panofsky H. A. , Glass P. E. , Boogaard J. F.
Published: December 2004

Wind profiles have been measured over the marshes of southern New Jersey, where the natural vegetation has been uniformly cut over a large area. Observations have been made with the wind at right angles to the roughness discontinuity, both in near-neutral and in unstable air. Preliminary results from the analysis of near-neutral cases are the following: (1) Over the cut grass the friction velocity is essentially a linear function of height. (2) The statement kz/u* (∂V/∂z) = 1 seems to hold in the transition zone. (3) The error in the function φ = kz/u* (∂V/∂z) made when assuming u* constant is about 5% at one-tenth the height of the interface between the air influenced by rough and smooth terrain, and is nearly a linear function of height.
Suspensoid Stratification in the Atmosphere
Authors: Fletcher Robert D.
Published: December 2004

It is shown that, at levels (e.g., temperature-inversion bases) where atmospheric turbulence diminishes with height, suspensoid clouds should settle more slowly than elsewhere. The theory provides a relationship between wind speed and the rate of dust deposition on the ground. It is confirmed by observations of aerosol concentrations beneath the tropopause and lower-level inversions. It helps explain mesopause dust accumulations which appear necessary for noctilucent-cloud formation. It shows that droplets should accumulate near cloud tops and thus adds to the explanation of rain formation.
Stability Effects on Turbulent Mixing in Tidal Currents
Authors: Bowden K. F.
Published: December 2004

Vertical mixing in many estuaries and coastal waters depends mainly on the turbulence due to tidal currents. At the same time, the influx of relatively low salinity water gives rise to vertical gradients of density which inhibit the mixing. Values of the vertical eddy diffusivity Kz, effective over a complete tidal period, have been derived from observations in certain areas and are related to the stability conditions. The values of Kz decrease rather more rapidly with increasing Richardson number than would be expected from the results reported for analogous types of flow.
Breakdown of Eddies and Probability Distributions for Small-Scale Turbulence
Authors: Gurvich A. S. , Yaglom A. M.
Published: December 2004

A rigorous mathematical description is given for the physical concept of the cascade process of sequential breakdown of turbulent eddies. It is assumed that the probability distribution for the ratio of typical values of turbulent fluctuations averaged over a small volume v to those averaged over a surrounding larger volume V is invariant under the group of space similarity transformations, provided that the length scales of both volumes are much smaller than the external scale of turbulence and much larger than the Kolmogoroff scale. This assumption is in general agreement with the conclusions of Kolmogoroff and Obukhov and with the existing measurements of the power spectrum for the square of the velocity derivative. Some measurements of probability distributions for smallscale turbulent fluctuations are also discussed.
Relation between Eulerian and Lagrangian Statistics
Authors: Philip J. R.
Published: December 2004

R (x, r, t) is the Eulerian correlation function in the space with zero mean motion. R(t), the Lagrangian correlation function, may be found from the correlation function R'(x, r, t) based on the sub-ensemble of ``Eulerian trials'' for which the fluid particle at (x, r, t) is the same as that at (0, 0, 0). The hypothesis that R may be substituted for R' yields a connection between R(t) and R(x, r, t). The Lagrangian time scale is found to be about one-third the Eulerian time scale. The apparent Eulerian time scale depends on the intensity of turbulence. Data on the ratio of Lagrangian to apparent Eulerian time scales agree farily well with the analysis.