bluuebunny/crossref_metadata_2025 huggingface dataset:
Shared Rearing Environment in Migraine: Results From Twins Reared Apart and Twins Reared Together
Authors: Svensson Dan A. , Larsson Bo , Waldenlind Elisabet , Pedersen Nancy L.
Published: December 2004

Background.—Studies of twins who are separated from each other early in life and are reared in different environments offer the opportunity to resolve variation in liability to disease.

Objective.—To evaluate the importance of genetic and environmental influences in migraine; in particular, addressing the role of the shared rearing environment.

Methods.—A population‐based cohort of twins, including a subsample of 314 pairs reared apart and 364 matched control pairs reared together, was drawn from the Swedish Twin Registry. Data on lifetime migraine was collected via self‐administered questionnaires mailed to twins aged 42 to 81 years. Quantitative genetic models and regression models were used to analyze sources of twin similarity.

Results.—We found nonsignificant shared rearing environmental influences on migraine for men (17%) and no rearing effects at all for women. The heritability of migraine was estimated at 38% (95% confidence interval, 0 to 73) for men and 48% (95% confidence interval, 27 to 65) for women. Among monozygotic twins reared apart, those separated at 3 years of age or earlier were more similar for lifetime migraine than those separated later, and this was especially true for women.

Conclusion.—In agreement with previous twin data, family resistance in migraine is mainly due to genetic factors, whereas environmental influences make family members different, not similar.
Patent foramen ovale, a possible cause of symptomatic migraine: a study of 74 patients with acute ischemic stroke.
Authors: Sztajzel R , Genoud D , Roth S , Mermillod B , Le Floch‐Rohr J
Published: December 2004

Cerebrovasc Dis. 2002;13(2):102‐106

Recent studies reported an increased prevalence of patent foramen ovale (PFO) in patients with migraine with aura (MA  +). To investigate the possible relationship between MA  + and paradoxical embolism, we studied the prevalence of both conditions. Investigation of PFO was undertaken in 74 consecutive patients presenting with an acute stroke of undetermined origin. The patients were questioned about MA  + or migraine without aura (MA  −) according to the criteria of the International Headache Society. Follow‐up was performed to investigate the evolution of MA  + and MA  − according to different treatments of stroke. PFO was found in 44 of 74 patients, 16 of whom had MA  + (36%), compared to 4 (13%) MA  + patients without PFO (p  =  0.03). Of 25 patients in whom the PFO was considered to play a causal role in the stroke, 13 (52%) had MA  +, whereas only 3 (16%) of 19 patients in whom PFO was considered unrelated had MA  + (p  =  0.014). Thirty‐nine of the patients with MA  + and MA  − were studied over a mean follow‐up of 13 months. Seven of 15 patients with MA  + and PFO, treated either with surgical closure or anticoagulants, noticed complete disappearance of MA  + attacks. The prevalence of MA  + is high among stroke patients with PFO. In patients with a high presumption of paradoxical embolism, the proportion of MA  + is increased, and this suggests a possible role of this association in the occurrence of the cerebrovascular event. Forty‐seven percent of patients with PFO and MA  + reported complete suppression of their aura attacks after surgical closure or anticoagulant treatment. This finding suggests that at least in some patients, MA  + attacks may be due to paradoxical embolism.

Comment: Reach for the stethoscope/echocardiogram! This paper emphasizes the importance of physicians adopting a holistic approach to patients with migraine, not forgetting to check for clinical signs of a septal defect and, if in doubt, to refer for cardiological review to exclude a surgically treatable source of paradoxical emboli. DSM
What predicts evolution from episodic to chronic cluster headache?
Authors: Torelli P , Manzoni GC
Published: December 2004

Curr Pain Headache. Rep 2002 Feb;6(1):65‐70

Over the last few years, attention has increasingly been focused on the evolution of cluster headache over time. Predictive factors have been identified that are correlated with an increased risk of unfavorable evolution from the episodic form to the chronic form of cluster headache. Late onset, the presence of sporadic attacks, a high frequency of cluster periods, and short‐lived duration of remission periods when the headache is still in its episodic form all correlate with a possible worsening of the clinical picture over time. The reasons for evolution of episodic cluster headache to chronic are still unknown, but some factors, such as head trauma and other lifestyle factors—eg, cigarette smoking and alcohol intake—have been suggested as having a negative influence on the course of cluster headache over time.

Comment: Further longitudinal epidemiological research is needed to assess the impact of smoking cessation in these patients and to confirm or refute the hypotheses suggested in this paper. DSM

Lee Kudrow documented that smoking, like nitroglycerin, lowers oxygen tension, which in turn can precipitate cluster attacks. Another possibility is that smoking and nitroglycerine are nitric oxide (NO) delivery systems and that the NO both precipitates attacks and worsens long‐term cluster prognosis. SJT
Pristine New Zealand forest soil is a strong methane sink
Authors: Price Sally J. , Sherlock Robert R. , Kelliher Francis M. , McSeveny Tony M. , Tate Kevin R. , Condron Leo M.
Published: December 2004

Methanotrophic bacteria oxidize methane (CH4) in forest soils that cover ∼30% of Earth's land surface. The first measurements for a pristine Southern Hemisphere forest are reported here. Soil CH4 oxidation rate averaged 10.5±0.6 kg CH4 ha−1 yr−1, with the greatest rates in dry warm soil (up to 17 kg CH4 ha−1 yr−1). Methanotrophic activity was concentrated beneath the organic horizon at 50–100 mm depth. Water content was the principal regulator of (r2=0.88) from the most common value of field capacity to less than half of this when the soil was driest. Multiple linear regression analysis showed that soil temperature was not very influential. However, inverse co‐variability confounded the separation of soil water and temperature effects in situ. Fick's law explained the role of water content in regulating gas diffusion and substrate supply to the methanotrophs and the importance of pore size distribution and tortuosity. This analysis also showed that the chambers used in the study did not affect the oxidation rate measurements. The soil was always a net sink for atmospheric CH4 and no net CH4 (or nitrous oxide, N2O) emissions were measured over the 17‐month long study. For New Zealand, national‐scale extrapolation of our data suggested the potential to offset 13% of CH4 emissions from ca. 90 M ruminant animals. Our average was about 6.5 times higher than rates reported for most Northern Hemisphere forest soils. This very high was attributed to the lack of anthropogenic disturbance for at least 3000–5000 years and the low rate of atmospheric nitrogen deposition. Our truly baseline data could represent a valid preagricultural, preindustrial estimate of the soil sink for temperate latitudes.
Theory of the Electrostatic Probe in a Moderately Ionized Gas
Authors: Su C. H. , Sonin Ain A.
Published: December 2004

The collision-dominated theory of the spherical electrostatic probe is extended to moderate degrees of ionization by taking into account the effect of electron-ion collisions. It is shown that, in the limit R/λD → ∞, the solution of the moderately ionized case can be obtained from that of the weakly ionized case by a simple transformation.
Toroidal Containment of a Plasma
Authors: Grad Harold
Published: December 2004

The question of plasma containment in a torus is much more complicated than in an open-ended mirror system. Serious questions arise of the nonexistence of flux surfaces, of noncontained particle drifts, and of nonexistence of self-consistent equilibria at small gyroradius.
Nonlinear Plasma Waves I. Secular Behavior of Nonlinear Equations
Authors: Freidberg Jeffrey P.
Published: December 2004

A perturbation scheme is devised for investigating the periodic solutions of a nonlinear, second-order, ordinary differential equation with an additional small nonlinear term. It is assumed that when the additional term vanishes the solution to the remaining zeroth-order nonlinear equation is known. When this is the case, explicit expressions for the first-order solution and the first-order correction to the dispersion relation are given in terms of the known zeroth-order solution.
Transverse Electromagnetic Waves in Fully Ionized Vlasov Plasmas
Authors: Gibbons J. J. , Hartle R. E.
Published: December 2004

A general class of solutions is obtained for fully ionized plasmas which admit transverse electromagnetic waves with constant phase velocity. The solutions self-consistently satisfy Maxwell's equations and Vlasov's equations for both ions and electrons. It is shown, for plasmas admitting such waves, that the mean velocity in the direction of the propagating wave is equal to the wave speed when the plasma is in a stationary state and is different from the wave speed for nonstationary states. A specific set of ion and electron distribution functions is presented which admit monochromatic waves. The associated moments and compatibility relations are calculated.
Self-Consistent Description of a Warm Stationary Plasma in a Uniformly Sheared Magnetic Field
Authors: Sestero A.
Published: December 2004

An exact, self-consistent solution of the system of Vlasov's plus Maxwell's equations is derived, describing a warm stationary plasma in a uniformly sheared magnetic field. It is found that there is no upper limit for the rate of shear; that is, the distance over which the direction of the magnetic field rotates of an angle 2π can be as small as desired; in particular this distance can be smaller than the ion or even the electron Larmor radius. Within the assumed model, for any value of plasma density, magnetic field strength and rate of shear a priori assigned, there exists a one-parameter family of solutions, differing from each other essentially for the fraction of the total current that goes into ion or electron current, respectively. The two currents can also flow in opposite directions, thus subtracting from each other in producing the net total current; in this case, however, they cannot separately exceed certain limiting values, set by the requirement of integrability for the distribution functions.
Landau Damping and Growth of Electrostatic Modes with Effects of Spatial Variation
Authors: Book David L.
Published: December 2004

For a plasma with finite cross section of the sort which occurs typically in laboratory plasma waves experiments, in a constant magnetic field, the Landau damping (or growth) is obtained by a perturbation procedure in terms of the plasma velocity distribution function and potential and density profiles. The result is applied to the damping associated with the upper and lower branches of the dispersion curve for longitudinal electron plasma waves in the case of a Maxwellian velocity distribution in slab and cylindrical geometries. Application is also made to the growth rates resulting from a low-density electron beam with radially dependent energy superposed on a Maxwellian.
Potential Distribution in Collisionless Plasmas in a Weak Magnetic Field
Authors: Yamasaki H. , Paik S. F.
Published: December 2004

The perturbation of the potential distribution in collisionless plasmas by a weak magnetic field is calculated numerically by considering the effect of the field on the boundary condition at the insulating wall.
Pressure, Bernoulli Sum, and Momentum and Energy Relations in a Laminar Zone of Separation
Authors: Macagno Enzo O. , Hung Tin-Kan
Published: December 2004

The pressure field, the Bernoulli-sum variation, and the different terms of the impulse-momentum and work-energy relations have been determined computationally for a conduit expansion of 2:1 and a Reynolds number of 48 in the narrow part of the conduit. The procedure used was the integration of an explicit discretized form of the Navier-Stokes equations. The calculations were carried out with an IBM 7044 electronic computer. It was found that some terms of the differential and integrated forms of the basic equations were relatively small. The integrated form of the work-energy relation can be simplified to only three of its terms. The role of the eddy was found to be essentially that of shaping the main flow, the exchange of momentum and energy with the main flow being rather small.
Experimental Study of Normal Ionizing Shock Waves
Authors: Miller Bennett
Published: December 2004

A coaxial electromagnetic shock tube has been used to study normal ionizing shocks propagating through hydrogen. An experiment is described which produced plane switch-on ionizing shocks. Quantitative studies were conducted covering the sub-Alfvénic and trans-Alfvénic regimes. Data are presented that support the existence of switch-on fronts in both these regimes, thereby demonstrating the significant effect of the initial electric field on the shock jump conditions. The results are interpreted by appeal to Taussig's theory of normal ionizing shocks. To choose from among the several theoretically predicted ionizing waves propagating at a given speed, Taussig's theory is supplemented by a simple physical criterion modeled on the Chapman-Jouguet hypothesis of Gross and Kunkel. This criterion has strong intuitive support and results in a picture of ionizing shock propagation that is in general agreement with the experimental observations.
Simplified Expressions for the Transport Properties of Ionized Monatomic Gases
Authors: Devoto R. S.
Published: December 2004

Simplified theoretical expressions for the transport properties of ionized gas mixtures are derived within the framework of the Chapman—Enskog—Burnett method. The properties of equilibrium partially ionized argon are then computed with these expressions and compared with values obtained with the exact theory. Agreement is satisfactory.
Space-Charge Effects by Nonthermal Ions in a Magnetized Plasma
Authors: Lehnert B.
Published: December 2004

In combination with transverse density gradients the finite Larmor radius produces space-charge effects both in the interior and at the boundaries of a magnetized plasma. In a thermal plasma having moderately large density gradients, electric quasi-neutrality can be preserved by a smoothly varying electric potential of limited amplitude. It is not obvious that a plasma containing groups of nonthermal ions will behave in a similar way when there are steep density gradients. An example is given here where a strongly oscillating potential of sheath-like structure arises from nonthermal ions which are peaked at a singular velocity. Whenever nonthermal effects of this or a similar kind occur, they should introduce fundamental changes in the plasma behavior which cannot be described by elementary plasma theory. Possible applications are given by the motion of a plasma through a neutral gas, where groups of nonthermal ions arise from charge exchange and ionizing collisions. The electric fields generated by the nonthermal particles may affect the ionization process and become connected with the mechanisms of ionizing waves and with the observed voltage limitation in rotating plasmas and in certain types of plasma guns.
Large Amplitude Stabilization of Flute Growth
Authors: Byers J. A.
Published: December 2004

Numerical results show that finite amplitude oscillatory but stable flutes can result from exponentially growing flutes which are excited at small amplitudes. The case examined here is an unstable flute in the low-density regime where the flute smearing due to the ion precessional drifts is almost sufficient to produce linear regime stability. The mechanism of nonlinear stabilization can be explained by a plausible extension of the marginal stability condition obtained by linear analysis. That is, at finite amplitude, the basic growth mechanism is reduced by nonlinear effects so that the previously weaker competing process (the change of phase of the charge distribution due to the ion precessional drifts) becomes the stronger mechanism. Total disruption of the basic growth mechanism is not required. One application is that experimental observation of the onset of instability may occur well into the unstable regime predicted by linear analysis, and may thus affect the interpretation of experimental results.
Nonlinear Processes in a Magnetized Plasma
Authors: Cano R. , Etievant C. , Fidone I. , Olivain J. , Mattioli M. , Perulli M.
Published: December 2004

The nonlinear processes of interaction of three electrostatic waves are investigated in a cold magnetized plasma. The experimental results agree with the theoretical conditions for the existence of the generation of waves.
Parameters Governing the Generation of Free Vortices
Authors: Dergarabedian Paul , Fendell Francis
Published: December 2004

An asymptotic expansion of the Navier—Stokes equations is proposed which provides a new basis for previously stated free-vortex equations. Two main parameters emerge from the description of vortex generation. One is a conventional Ekman number, and the other indicates that unless the product of the area of the updraft and the average vertical gradient of the vertical velocity greatly exceeds the kinematic viscosity coefficient, no localized vortical flow develops. Although the model is largely axially invariant, the isobars described by the model are easily shown to have a funnel-cloud-like shape. Finally it is proposed that the analysis (although laminar) may suggest the counterforces basic to the generation of concentrated geophysical vortices: a vertical updraft induces a radial inflow, which may concentrate ambient angular momentum into a vortex unless turbulent viscous forces counteract the intensification.
Turbulence Transport Equations
Authors: Harlow Francis H. , Nakayama Paul I.
Published: December 2004

A generalized eddy viscosity function σ, is introduced in order that the Reynolds stress in an incompressible fluid be expressible as a linear combination of the Kronecker and rate-of-strain tensors. A transport equation for the eddy viscosity is derived from the general turbulence energy equation, thereby introducing two additional functions, the specific turbulence kinetic energy q, and a scale variable s. To determine the three variables, a transport equation for s is postulated, and a modified Prandtl—Wieghardt relation among the three variables is accepted. The theory is expressed in universal, invariant form, and validity is demonstrated by application to several problems.
Magnetohydrodynamic Gravity—Capillary Waves in a Liquid Film
Authors: Lu Pau-Chang , Sarma G. S. R.
Published: December 2004

The influence of a transverse magnetic field on the Kapitza capillary wave traveling down the surface of a falling, conducting liquid film is investigated. It is shown that, for small magnetic Reynolds numbers the range of admissible dimensionless celerity becomes narrower as the Hartmann number increases. When the Hartmann number reaches 4.63 there is but one single admissible wave celerity (1.43). With still stronger field strength, a traveling wave is no longer possible within the linear scheme employed.
Theory of Rarefaction Waves in Plasmas Bearing Large Currents
Authors: Paxton G. W.
Published: December 2004

A plasma bearing a large current is shown to permit three classes of expansions in the direction of the current path: (1) normal rarefaction, (2) discontinuous or shock rarefaction, (3) extension or waveless rarefaction. The general problems is analyzed and application is made to a hydrogen plasma.
Degeneration of Magnetohydrodynamic Modes in a Coaxial Channel with a Helical Field
Authors: Infeld E.
Published: December 2004

The effect of a rectilinear current on Alfvén waves in a bounded medium is investigated. An infinite spectrum of frequencies corresponds to each Alfvén frequency obtained without the current. Therefore the I = 0 case is considered as degenerate since eigenfrequencies tend to the Alfvén frequency in this limit. A radial component of the disturbed field will always be present, even though none need be present for the current-free case. This component is a discontinuous function of the current (discontinuous at zero). A formula connecting the radial and azimuthal components of the field is obtained. This formula carries through when the I →0 limit is taken. For the I = 0 case the azimuthal and radial fields are completely unconnected, hence the discontinuity. In particular the azimuthal component of the magnetic field will vanish on the boundaries for all finite currents and in the I → 0 limit, even though this is not true of the I = 0 case. The boundary conditions on the azimuthal component of the field are therefore seen to be discontinuous.
Noncorrelation of ``Anomalous'' Plasma Transport, Equilibrium Plasma Density, and Low-Frequency Potential Oscillations in a Q-Device
Authors: Decker John A. , Freyheit P. J. , McBee W. D. , Shepherd L. T.
Published: December 2004

The minimum-B magnetic field, provided by the superposition of a tranverse quadrupole-cusp field and a uniform axial field, suppressed certain of the low-frequency oscillations spontaneously present in the thermal cesium plasma of the TOPSY Q-device with the uniform axial field alone, in conjunction with a sharp increase in the center-line equilibrium plasma density of up to two orders of magnitude. However, measurements of the transverse plasma flux immediately prior to and immediately after oscillation suppression failed to detect any change in the radial plasma transport; the ``anomalous diffusion'' observed in the TOPSY plasma in a uniform magnetic field is still present in the absence of low-frequency potential oscillations. Rather than being a function of plasma-column oscillations, the observed cross-field plasma transport is quantitatively explained in terms of E/B drifts due to azimuthal ionizer-plate temperature gradients. The sharp density increase which accompanied oscillation suppression must thus be ascribed to changes in the ionizer sheath conditions leading to an increased ``source'' flux of plasma into the column from the ionizer, rather than to a decrease in the radial plasma ``loss'' flux. These results have serious implications for the study of transport processes in plasmas and, in particular, call into question the use of Q-devices for the experimental study of ``anomalous diffusion'' in complex magnetic field geometries.
Evolution of a Density Discontinuity as Governed by the Boltzmann Collision Integral
Authors: Kovitz A. A. , Springer R. W.
Published: December 2004

An initially discontinuous density distribution (the shock-tube configuration) is studied analytically as an initial value problem for the Boltzmann equation. The distribution function is expressed in an infinite series of orthogonal polynomials in velocity space. The early time behavior is dominated by a collisionless interaction; the weight function for the orthogonal polynomials is, therefore, taken as the distribution function corresponding to the collisionless evolution of the density discontinuity. Moment equations are developed for Maxwell molecules. Truncation of the series for the distribution function leads to a determinate system of six quasilinear partial differential equations for the first six moments. For sufficiently small initial number density ratio the system is totally hyperbolic with the characteristics determined from the known collisionless solution. Numerical solutions are obtained for initial number density ratios of 5, 10, and 100. Early time results show the departure from collisionless behavior; moreover, after a sufficient time, the shock, contact, and expansion regions become evident as in the classical case. The shock region evolves into a steady-state shock wave with structure similar to that obtained by steady-state theories. The contact and expansion regions also assume their expected asymptotic character.
Filling Rate of the Tail of the Velocity Distribution Function
Authors: De Boer P. C. T.
Published: December 2004

Using the Boltzmann equation, the initial filling rate of the high-energy tail of the distribution function is calculated for the case where the distribution function is zero above, and Maxwellian below a cutoff point. A general expression is obtained for the filling rate, as well as for the depletion rate of the distribution function below the cutoff point. The results are applied to hard sphere molecules, for which they can be evaluated analytically in terms of error functions. The resulting growth rate is compared with the corresponding one obtained using the Bhatnagar—Gross—Krook collision term. The latter rate correctly shows a number of aspects of the qualitative behavior, but is quite different numerically. The general result is also applied to Coulomb molecules, and the character of the resulting divergencies is exhibited. Relaxation of the distribution function in time is studied with the aid of a high-speed computer. It is concluded that under all conditions of physical interest, the characteristic filling time for the tail of the distribution function is of the order of the mean time between collisions.
Rotational Temperature Measurements in Electron-Beam Excited Nitrogen
Authors: Ashkenas Harry
Published: December 2004

Measurements of the rotational temperature of electron-beam excited nitrogen have been made along the axis of a free jet under various flow conditions. Temperatures calculated from the isentropic flow equations are compared with those derived from the rotational spectra. Discrepancies between the two temperature determinations led to an investigation of the rotational spectrum of nitrogen in thermodynamic equilibrium at 300 and at 78°K. Results of the ``static'' gas measurements are presented which indicate that existing models of the electron-beam excitation—de-excitation process may be incorrect.
Unified Shock Profile in a Plasma
Authors: Grad Harold , Hu Pung Nien
Published: December 2004

Previously [P.N.Hu, Phys. Fluids 9, 89 (1966)], a universal monotonic profile was found for a weak plasma shock propagating perpendicular to a magnetic field using an elaborate set of moment equations which included electron and ion viscosity, coupled electron and ion heat conduction, thermal diffusion, and resistivity, together with distinct Hall terms for the resistivity, stress, and heat flow. Inclusion of an additional term related to electron inertia now gives a one-parameter family of profiles which spans the entire range from collision dominated monotonic profiles to damped oscillatory profiles and the limiting collisionless case of purely oscillatory and solitary wave profiles.
Diffusion, Scattering, and Acceleration of Particles by Stochastic Electromagnetic Fields
Authors: Hall D. E. , Sturrock P. A.
Published: December 2004

The behavior of charged particles in an electromagnetic field composed of two parts is treated. The first is an unperturbed part, for which the solution of the Vlasov equation is assumed to be known; the second part is a perturbation which is assumed to be random and of small amplitude. Such a ``stochastic'' or ``turbulent'' electromagnetic field leads to diffusion, pitch-angle scattering, and acceleration. Equations governing these processes may be derived by test-particle calculations. The problem is first posed in a general way, and solved by a method similar to that used in quasi-linear theory. The connection of this method with the Fokker-Planck formulation is discussed. The case which is analyzed in detail is that of relativistic particles moving in a uniform magnetic field under the influence of a steady homogeneous spectrum of electromagnetic fluctuations. Results are given which are valid for any (weak) fluctuation spectrum and for finite test-particle gyroradii. The physical meaning of the results is discussed, and it is shown that in certain limits there is agreement with earlier, less general analyses.
Third Approximation to the Viscosity of Multicomponent Mixtures
Authors: Devoto R. S.
Published: December 2004

Expressions are given for the additional matrix elements necessary for the third approximation to the viscosity of multicomponent mixtures. The improved accuracy of this approximation is considered for several gas models.
Proposed Modification to Harris' Quasi-Linear Equations
Authors: Manheimer Wallace M.
Published: December 2004

Several modifications are made to the quasi-linear equations of Harris which distinguish between weakly and strongly damped modes and between the tail and body of the particle distribution function.
Instability of a Liquid Film Flowing down an Inclined Plane
Authors: Lin S. P.
Published: December 2004

The mechanism of the instability of a layer of liquid flowing down an inclined plane is studied. First, the instability of the flow with respect to Tollimen-Schlichting wave is investigated. The results obtained are then compared with the known results of the instability of the same flow with respect to surface wave formation. It is found that, for a given angle of inclination, there exists a critical wavelength of the surface wave. If the wavelengths of the free surface disturbances are shorter than this critical wavelength, the film can become unstable due to shear waves before it becomes unstable with respect to surface waves. On the other hand, if the wavelengths of the free surface disturbances are longer than this critical wavelength, then the film will always become unstable due to free surface disturbances.
Transport Properties of a Nonequilibrium Partially Ionized Gas
Authors: Chmieleski Robert M. , Ferziger Joel H.
Published: December 2004

A modified Chapman-Enskog approach for an ionized gas is presented. The method allows the electron and heavy particle temperatures to differ while requiring all species to have the same macroscopic velocity to zero order. Expressions are obtained for the transport properties of such a gas and a complete set of self-contained hydrodynamic equations is given. As an example, the transport properties of a fully ionized gas containing a single ion species are evaluated using the cutoff Coulomb potential. In the limit of equal electron and ion temperatures, the results are in agreement with previous results.
Electrostatic Sheath in a Weakly Ionized Gas
Authors: Bienkowski G. K.
Published: December 2004

The behavior of a thin electrostatic sheath adjacent to a body immersed in a flowing weakly ionized gas is analyzed on the basis of kinetic theory using a moment method. The study is confined to the regime of mean free path and Debye length small compared to body size but for arbitrary ratios between them. When the mean free path is the smallest parameter, the solution reduces to the continuum solution with a thin ``Knudsen layer'' at the body. In the opposite limit of smallest Debye length, a departure in the potential drop from that in the continuum regime occurs within the quasi-neutral solution. The point at which this solution terminates can be interpreted as a sonic point for the attracted particles. There is then a thin transitional layer, followed by a free-fall sheath. The case of negative potential is analyzed in detail, and the current-voltage characteristics are obtained in an explicit form.
Variational Study of the Runaway Instability in a Two-Component Plasma
Authors: Nicolis G. , Sels Ph.
Published: December 2004

The local potential variational method recently introduced by Prigogine and Glansdorff is applied to the study of the stability of a kinetic equation. The problem of runaway instability of a two-component plasma is especially considered and an expression for the critical field is derived. This expression explicitly takes account of the dissipative processes both in the steady state and in the perturbation from it. The relationship to the results by Dreicer et al. is briefly discussed.
Effect of Ion Collisions and Other Terms on the Resistive-g Instability in Plasmas
Authors: Stringer T. E.
Published: December 2004

The treatment is based on guiding center equations, which include collisional diffusion across the magnetic field lines. The eigenvalues of the resulting differential equation are found using phase integral methods. The localized resistive-g mode becomes stable at sufficiently low collision frequencies, the dominant stabilizing mechanism depending on the shear. For strong magnetic shear [shear length < radius of curvature of field lines × ¼(M/m)¼] ion collisional effects are found to first produce stability, whereas for weak magnetic shear the dominant effect comes from the electron acoustic term in Ohm's law. Analytic stability criteria are derived which show satisfactory agreement with a recent numerical solution of the same problem, but underline the danger of extrapolation based on the numerical solution.
Irregular Refraction of a Strong Shock Wave by a Wedge of Hot Gas
Authors: Skifstad J. G.
Published: December 2004

A theoretical model for the irregular refraction of a plane shock wave by a wedge of hot gas has been developed. The results of computations show the Mach number of the transmitted shock to be some 10 to 20% lower than that for normal refraction at the same incident Mach number.
A Simple Theory of Shock Structure
Authors: Hicks B. L. , Yen S. M.
Published: December 2004

A simple theory describing the shock structure may be constructed on the basis of the Navier-Stokes character of the wings of the shock. The calculated distribution of macroscopic properties agrees well with that of the Navier-Stokes shock up to M = 2.
Large Amplitude Whistler Waves in a Hot Collision-Free Plasma
Authors: Sonnerup B. U. Ö. , Su Shin-Yi
Published: December 2004

A dispersion relation is derived for large-amplitude circularly polarized plane waves propagating along a uniform magnetic field in a hot collision-free plasma.
Two-Dimensional Gravity Waves in a Stratified Ocean
Authors: Wu T. Yao-Tsu , Mei C. C.
Published: December 2004

The solution of the two-dimensional gravity waves in a plane stratified ocean previously calculated by the authors is rectified. By formulating a corresponding initial value problem, the steady-state solution becomes completely determinate without using the radiation condition.
Instabilities due to Temperature Gradients in Complex Magnetic Field Configurations
Authors: Coppi B. , Rosenbluth M. N. , Sagdeev R. Z.
Published: December 2004

An integral equation governing an instability due to ion temperature gradients is derived. In the presence of magnetic shear, localized non-convective normal modes of instability are shown to exist if the relative temperature gradient is larger than that of density, unless the shear is exceedingly strong, i.e., the field shears through a large angle in the distance in which the temperature drops. Quasi-modes which are less localized in the direction of the gradient can be constructed from these normal modes and a large thermal diffusion may be expected. Conversely the mass diffusion is shown to be rather slow so that it is reasonable to assume that an effective ``divertor'' should keep the actual heat loss quite small.
Experimental Investigation of Harmonic Ion Cyclotron Wave Propagation and Attenuation
Authors: Kristiansen Magne , Dougal Arwin A.
Published: December 2004

A new wave phenomenon was observed in the course of an experimental investigation of ion cyclotron resonance heating of hydrogen and deuterium plasmas in strong magnetic fields. It was found that the waves can propagate for frequencies larger than the ion cyclotron frequency fc, and attenuate at harmonics of fc with resulting increase in the transverse temperature-density product nβT⊥. The harmonic number at which the waves attenuate increases with increasing gas pressure. Attenuation at harmonics up to the 8th was observed. The plasma density is typically 6 × 1017 m−3, the transverse plasma temperature (Te⊥ + Ti⊥) ⪕ 50-eV equivalent, and the magnetic field 1–9 kG. A magnetic beach geometry is employed and the waves are excited by a Faraday shielded Stix coil from a 30 kW, 5.8 MHz driver. Harmonic cyclotron heating is related to large transverse wave numbers which are shown to exist in the experiment.
Relaxation Effects in an Initially Non-Maxwellian High-Temperature θ-Pinch
Authors: House L. L. , Swartztrauber P. N.
Published: December 2004

Numerical solutions of coupled Fokker-Planck equations for electron and deuteron velocity distribution functions are used to investigate the non-Maxwellian conditions existing in fast magnetic compression theta-pinch experiments. Initial distribution functions are chosen to stimulate the post shock-heating phase of operation and the subsequent relaxation is followed. Because of rapid changes in the deuteron distribution function, the neutron yield is found to increase significantly with time although the mean energy changes little. Distortions at high and low velocities occur in the electron distribution resulting from interaction with the ions. These distortions produce two effects: (1) At short wavelength the x-ray flux is lower than that from a Maxwellian with the same mean energy; and (2) the edge of recombination continua of impurities are flattened relative to the spectrum produced by a Maxwellian distribution. The influence of the distorted x-ray spectrum upon standard absorber foil techniques for temperature measurement is considered.
Plasma Electromagnetic Instabilities in a Magnetic Mirror Configuration
Authors: Scharer J. E.
Published: December 2004

An anisotropic Maxwellian velocity distribution with loss cones is used to investigate cyclotron wave instabilities occurring in a magnetic mirror configuration. The density of electrons in the loss cones is assumed to be negligible; this implies that the particle velocity distribution function is such that f0(v⊥, vz) = 0 for |vz| > v⊥(R − 1)½, where vz is the component of particle velocity along the magnetic field, v⊥ is the component of particle velocity transverse to the magnetic field, and R is the mirror ratio. Linearized Vlasov equations are solved to obtain the dispersion relation for transverse electromagnetic waves propagating along a uniform magnetic field. Numerical solutions of the growth and damping rates of the wave for a mirror ratio of 2.0 show that there is a long-wavelength instability for a Maxwellian electron distribution with loss cones. The applicability of the analysis to a finite-length mirror configuration is discussed.
Binary Correlations in a Stable Homogeneous Plasma
Authors: Barrett T. B. , Pytte A. , Wang C. Y.
Published: December 2004

It is shown that the general pair correlation function of Balescu and Taylor reduces directly to the correct expression in the case of equilibrium.
Some Aspects of Classical Diffusion
Authors: Bineau Michel
Published: December 2004

The rate of resistive diffusion is computed using an expansion near the magnetic axis of a hydromagnetic equilibrium under the hypothesis of a steady state. A different limiting case is mentioned for comparison.
Nonlinear Effects of Fluctuations in a Current-Carrying Plasma
Authors: Pearson Gary A.
Published: December 2004

A current-carrying electron-proton plasma is studied by calculating the velocity distribution of the particles with the Lenard-Balescu-Guernsey form of the Fokker-Planck equations rather than with the familiar Landau form. The Landau equations yield velocity distributions that become unstable to longitudinal ion waves when the temperature ratio Te/Ti is large and the electric field E0 that drives the current exceeds a critical magnitude Ecrit. The Landau equations are then not appropriate because they do not include the effect that the fluctuations associated with these ion waves have upon the velocity distributions. The Lenard-Balescu-Guernsey equations show that as E0 is increased toward Ecrit these fluctuations increase and affect the electron velocity distribution much as enhanced electron-electron collisions would do. In particular, this nonlinear process reduces the electrical conductivity by a noticeable amount (a few percent in the examples given). Although one might also expect the threshold electric field for instability to be increased significantly, this effect is found to be extremely weak, if it exists.
Screw Instability in a Linear Hall Accelerator
Authors: Garrison G. W. , Hassan H. A.
Published: December 2004

The stability of a weakly ionized plasma column against a screw type perturbation in the presence of an applied axial electric field and a predominantly radial magnetic field—a linear Hall current accelerator—is investigated. The analysis is based on the ion and electron conservation equations and takes into consideration the effects of ionization. It is shown that the observed instability cannot be explained when the axial component of the magnetic field is identically zero even when one takes into consideration steady-state solutions with both radial and axial dependence. On the other hand, when the axial component of the magnetic field is small, but not zero, the column is unstable in the absence of an axial density gradient to a right-handed helical perturbation (m = −1). The resulting instability, which is of the Kadomtsev and Nedospasov type, is analyzed using a normal mode analysis. The results are in qualitative agreement with experiment.
Kinetic Equation with Electromagnetic Interactions
Authors: Hogan J. T. , Lewis M. B.
Published: December 2004

A kinetic equation for a plasma with electromagnetic interactions is derived in the shielding approximation. The equation is the analog of the Landau equation and has the same structure as the Landau equation but with a velocity dependent interaction replacing the Coulomb interaction.
Limitation on Ion Cyclotron Heating in the Local Mirrors of the C Stellarator
Authors: Iiyoshi A. , Yamato H. , Yoshikawa S.
Published: December 2004

The experimental observation of the limiting phenomena of ion cyclotron resonance heating in the shallow magnetic beach is described and its explanation by the reflection of the wave is discussed. The temperature-anisotropic plasma dispersion relation is solved with the aid of an electronic computer. The unexpected singular point which causes the reflection of waves is found in the unstable region of the ion cyclotron wave. The calculated limiting value of the ion temperature due to the wave reflection is given by β⊥c ≈ 4(T∥/T⊥)2, in reasonable agreement with the experiment.
Self-Consistent Time-of-Flight Analysis of a Plasma Gun
Authors: Manka C. K. , Crawford J. R. , Zinke O. H.
Published: December 2004

The numbers, flow velocities, and temperatures of the positive ions emitted by helium and argon plasmas pulsed into an evacuated region by a plasma gun are determined by a time-of-flight analysis on freely expanding ions. Times of plasma release are also calculated. It is shown that the time-of-flight technique is applicable even with statistical variations in plasma characteristics observed under apparently identical conditions of plasma production. A slug-mode description of the average behavior of the gun is seen to agree with the time-of-flight analysis if ion recombination is assumed.
Shock Structure in a Gas of Rigid Noncentral Particles
Authors: Haight C. H. , Lundgren T. S.
Published: December 2004

A theory is presented capable of describing the structure of a strong shock in a diatomic gas. Strong shocks in a monatomic gas can be effectively treated using the bimodal distribution function of Mott-Smith. Relaxation effects are included in the present analysis by replacing the bimodal form with a weighted trimodal distribution function. The three weighting functions are determined to satisfy certain averages of the Boltzmann equation. Logical limitations occur when the trimodal distribution reduces to either a monatomic or a diatomic bimodal distribution. The molecular model under discussion is the rigid convex body of revolution. Specific cases include the loaded sphere and the spherocylinder. Solutions are obtained for slightly loaded spheres by applying a method of matched asymptotic expansions. A computer study is performed at infinite Mach number for a spherocylinder corresponding to a hypothetical ``real'' gas. Comparison with recent shock data suggests the possibility of solidly relating the geometry of a spherocylinder to a nitrogen molecule.
Solution of Nonlinear Flow Problems through Parametric Differentiation
Authors: Rubbert Paul E. , Landahl Marten T.
Published: December 2004

A method of obtaining solutions to nonlinear flow problems by integrating the rate of change of the solution with respect to a suitable parameter is described. The advantage of this method is that the nonlinearity of the problem is confined to a first order equation where it causes little difficulty. The Falkner-Skan boundary-layer problem and the problem of flow about a nonlifting airfoil at transonic speeds are used to illustrate the method.
Nearly Viscometric Flows
Authors: Pipkin A. C. , Owen D. R.
Published: December 2004

Constitutive equations describing small perturbations on viscometric flows are derived. The relations are similar in form to the linear integral stress-deformation relations of infinitesimal viscoelasticity theory. Restrictions imposed by material symmetry and by incompressibility are discussed. It is shown that certain relations between the stress-relaxation moduli and the basic viscometric functions must be satisfied for self-consistency of the theory.
Similarity and the Turbulent Energy Spectrum
Authors: Lumley J. L.
Published: December 2004

Spherically averaged spectral densities of quantities appearing in the turbulent energy equation are assumed to be locally similar: i.e., to depend on external parameters in a similar way when referred to local scales of flux and length. Dynamical equations are given for the influence of production (including anisotropy), viscosity, buoyancy, magnetic field, and elasticity. General solutions of these equations are obtained implicitly, and the leading term in a series expansion explicitly. This similarity is shown to be a generalization of the ideas of Kolmogorov, of the modified Onsager cascade used by Corrsin, and of the formulation of Kovasznay and Shur for the influence of viscosity and buoyancy. In the case of viscosity, the prediction of a spectral cutoff by the Kovasznay formulation is seen to be misleading, and due to the retention of only the leading term in the expansion.
Generation of a Quiescent, Variable-Parameter Arc Plasma
Authors: Woo J. C. , Rose D. J.
Published: December 2004

The production of a steady arc discharge with density 1012 ≤ ne = ni ≤ 1014 cm−3 that operates quiescently in a strong magnetic confining field is described.
Inverse Problem in Arc Physics
Authors: Anderson J. E.
Published: December 2004

From the energy and current equations for a constricted, water-cooled arc, equations are derived from which the thermal and electrical conductivity, and the volumetric radiated power of a gas can be computed as functions of temperature.
Generation of Vorticity by Waves in a Plasma
Authors: Ross James A. , Ingard Uno
Published: December 2004

The analysis of the generation of vorticity by waves in a neutral gas is extended to the case of a plasma. It is shown that waves can interact with a plasma in a uniform magnetic field to generate vorticity.