bluuebunny/crossref_metadata_2025 huggingface dataset:
Overview of Studies to Prevent Posttraumatic Epilepsy
Authors: Beghi Ettore
Published: December 2004

Summary:  Purpose: Prevention of posttraumatic epilepsy (PTE) is of primary importance to reduce the degree of functional morbidity following traumatic brain injury (TBI). However, the effects of antiepileptic drugs (AEDs) in patients with TBI must be assessed separately in terms of prevention and control of provoked seizures (which include immediate and early posttraumatic seizures) and prevention of subsequent unprovoked seizures (late posttraumatic seizures or PTE).

Methods: Potential mechanisms for prevention of epileptogenesis as well as reports and systematic reviews were evaluated to determine strategies and results of attempts to reduce or prevent the development of epilepsy following TBI.

Results: In observational studies, after a period ranging from 6 months to 13 years, the proportion of cases developing seizures was 0‐10% in patients receiving treatment compared to 2–50% in those who were left untreated. In randomized clinical trials, the difference between active treatment [phenytoin (PHT), phenobarbital, or carbamazepine (CBZ)] and placebo was less remarkable after a follow‐up ranging from 3 to 60 months and was virtually lacking for the prevention of PTE. In a Cochrane systematic review of 890 patients from 10 RCTs assessing PHT or CBZ, the pooled relative risk (RR) for prevention of early seizures was 0.33 (95% CI 0.21–0.52). By contrast, the RR for prevention of late seizures was 1.28 (95% CI 0.90–1.81). Mortality and neurological disability were similar in the two treatment groups. The use of PHT was followed by an increased (nonsignificant) risk of skin rashes. In addition, cognitive performance was significantly affected by PHT in severely injured patients at 1 month and treatment withdrawal was followed by improvement in cognitive function.

Conclusions: The failure to influence the risk of PTE in studies of patients with TBI are similar to findings of meta‐analysis of randomized clinical trials on seizure prevention in other conditions, such as febrile seizures, cerebral malaria, craniotomy, and excessive alcohol intake. For these reasons, the prophylactic use of AEDs should be short‐lasting and limited to the prevention of immediate and early seizures. Chronic treatment should be considered only after a diagnosis of PTE.
Fluctuation in Autonomic Tone is a Major Determinant of Sustained Atrial Arrhythmias in Patients with Focal Ectopy Originating from the Pulmonary Veins
Authors: ZIMMERMANN MARC , KALUSCHE DIETRICH
Published: December 2004

Autonomic Variations in Focal AF. Introduction: This study was designed to analyze dynamic changes in autonomic tone preceding the onset of sustained atrial arrhythmias in patients with focal atrial fibrillation (AF) to determine why patients with frequent discharge from the arrhythmogenic foci develop sustained AF.

Methods and Results: Holter tapes from 13 patients (10 men and 3 women; mean age 53 ± 5 years) with paroxysmal “lone” AF (mean 18 ± 13 episodes per week) and a proven focal origin (pulmonary veins in all cases) were analyzed. A total of 38 episodes of sustained AF (> 30 min) were recorded and submitted to frequency‐domain heart rate variability analysis. Six periods were studied using repeated measures analysis of variance: the 24–hour period, the hour preceding AF, and the 20 minutes before AF divided into four 5–minute periods. A significant increase in high‐frequency (HF, HF‐NU) components was observed during the 20 minutes preceding AF (P = 0.003 and 0.002, respectively), together with a progressive decrease in normalized low‐frequency (LF‐NU) components (P = 0.035). An increase in LF/HF ratio followed by a linear decrease starting 15 minutes before sustained AF also was observed, indicating fluctuations in autonomic tone, with a primary increase in adrenergic drive followed by a marked modulation toward vagal predominance immediately before AF onset.

Conclusion: In patients with focal ectopy originating from the pulmonary veins, sustained episodes of atrial arrhythmias are mainly dependent on variations of autonomic tone, with a significant shift toward vagal predominance before AF onset.
Breakthrough Waves During Ventricular Fibrillation Depend on the Degree of Rotational Anisotropy and the Boundary Conditions: A Simulation Study
Authors: ASHIHARA TAKASHI , NAMBA TSUNETOYO , IKEDA TAKANORI , ITO MAKOTO , KINOSHITA MASAHIKO , NAKAZAWA KAZUO
Published: December 2004

Breakthroughs in VF Depend on Rotational Anisotropy. Introduction: The left ventricle (LV) and right ventricle (RV) are characterized by specific fiber orientation known as “rotational anisotropy.” However, it remains unclear whether the LV and RV are different with regard to the effect of rotational anisotropy on the dynamics of scroll waves during ventricular fibrillation (VF). To resolve this issue, we used a computation‐based model to study scroll wave behavior.

Methods and Results: We composed an environment of simulated three‐dimensional ventricular wall slabs, with optional ratios of fiber rotation to wall thickness (0°, 6°, and 12°/mm thickness; LV 10 mm, RV 5 mm), using Luo‐Rudy phase I equations. When rotational anisotropy was not incorporated into the LV wall slab (θendo˜θepi= 0°), most scroll waves rotated around the filaments perpendicular to the tissue surface, with only a few accompanying breakthrough waves. In a twisted LV model (θendo˜θepi= 60° and 120°), the scroll waves were demonstrated as multiple wavelets scattered spatiotemporally, frequently accompanied by breakthrough waves that were promoted by rotational anisotropy. In a twisted RV model (θendo˜θepi= 30° and 60°), single scroll waves and/or figure‐of‐eight reentrant waves appeared, with comparatively few breakthrough waves, regardless of the degree of fiber twist.

Conclusion: The proportion of electrical effects of rotational anisotropy and tissue boundaries plays an important role in the genesis of breakthrough waves during VF, and the difference in wave propagating patterns and frequency spectrum of the ventricles may arise, in part, from the number of breakthrough waves promoted by rotational anisotropy.
Comparison of the Effects on Drug Concentrations, Electrophysiologic Parameters, and Termination of Atrial Fibrillation in Dogs when Procainamide and Ibutilide are Delivered into the Right Atrium versus Intravenously
Authors: VERECKEI ANDRAS , WARMAN EDUARDO , MEHRA RAHUL , ZIPES DOUGLAS P.
Published: December 2004

RA vs IV Antiarrhythmic Drug Delivery. Introduction: We tested the hypothesis that right intra‐atrial (IA) administration of antiarrhythmic drugs resulted in higher peak serum drug concentrations, greater electrophysiologic effects, and greater efficacy for termination of atrial fibrillation (AF) than intravenous (IV) drug delivery.

Methods and Results: Eight dogs were treated with 9.7 mg/kg procainamide infusion and eight dogs with 0.02 mg/kg ibutilide infusion, injected over 5 minutes. Each dog had both an electrophysiologic (EP) and an AF termination study during IA and IV drug administration at ≥2–day intervals (total four studies each). Right atrial pacing capture threshold, right atrial effective refractory period (ERP), right atrial and right ventricular monophasic action potential (MAP) durations at 70% and 90% of repolarization (MAPD70, MAPD90), AH, HV, and QT intervals, QRS width, intra‐arterial systolic and diastolic blood pressures, and cardiac output were measured at different time‐points. Blood samples were drawn from the coronary sinus and femoral vein for drug level determination. The right atrium was paced at 400–msec cycle length throughout the study. AF was induced by rapid right atrial pacing and maintained by methacholine infusion at 1.5 to 3 μg/kg/min. The sustained AF was allowed to persist for 10 minutes before starting the antiarrhythmic drug infusion. We found no significant difference between the procainamide concentrations in the coronary sinus and femoral vein during IA and IV drug delivery. The time course and extent of increase in right atrial ERP, MAPD70, MAPD90, and all the other measured EP parameters did not differ between the two routes of drug administration. No significant difference was found in termination of AF between IV (5/7 procainamide; 4/8 ibutilide) or IA (3/8 procainamide; 3/8 ibutilide) drug delivery or between drugs (8/15 procainamide; 7/16 ibutilide).

Conclusion: Our data do not support any beneficial effect of IA versus IV procainamide or ibutilide delivery.
Cooled Ablation
Authors: CALKINS HUGH
Published: December 2004

Research on cooled ablation has been evolving for the last 10 years. Findings and current applications are reviewed. A cooled ablation catheter is approved by the FDA for use in idiopathic ventricular tachycardia (VT) patients, based on data originally submitted by Cardiac Pathways, Inc. This technology has subsequently been used by the clinicians in atrial flutter cases, nonischemic VT, epicardial accessory pathways, and atrial fibrillation. The experience at Johns Hopkins suggests that cooled radiofrequency ablation has utility in a variety of situations and in some instances has come to be the ablation system of choice.
Optimizing RF Output for Cooled RF Ablation
Authors: STEVENSON WILLIAM G. , COOPER JOSHUA , SAPP JOHN
Published: December 2004

Cooled RF ablation catheters increase lesion size and facilitate ablation compared to standard RF ablation catheters. Cooling the ablation electrode increases the disparity between tissue temperature and electrode temperature, making use of temperature for guiding power application during ablation of less certain value. Appropriate energy titration is important, however, to produce large lesions, while avoiding overheating of tissue with steam formation leading to “pops.” In addition to power, the rate of irrigant flow can be controlled. Electrode–tissue contact and orientation and the cooling effect of blood flow around the electrode and within the tissue are not as easily adjusted and also influence tissue heating. In addition to electrode temperature, a decrease in impedance, bubble formation detected by intracardiac ultrasound, and evidence of tissue heating from an effect on recorded electrograms or the arrhythmia can be used to guide ablation energy. Guidelines for adjusting power delivery and avoiding “pops” and coagulum formation are suggested.
Some Exact Solutions of the Navier-Stokes and the Hydromagnetic Equations
Authors: Meecham William C.
Published: December 2004

Some exact, closed-form solutions of the Navier-Stokes equations for incompressible flow and of the hydromagnetic equations for high-conductivity, incompressible flow are presented. They can be considered to be generalizations of Taylor's solutions. The solutions are two dimensional and cellular containing a single-space Fourier component; the spatial behavior is chosen in such a way that the nonlinear inertial term and the pressure term cancel one another, leaving a linear system to be solved. The time behavior of the solutions is quite general. The solutions to the hydromagnetic equations are such that the velocity and the magnetic fields are parallel and decoupled. The velocity behaves as it does in the purely mechanical case while the magnetic field simply decays in time; there is no source term for it in the present treatment.
Similarity Spectra in Isotropic Turbulence
Authors: Reid W. H. , Harris D. L.
Published: December 2004

Similarity solutions are given for the energy spectrum and transfer function in the initial period of decay for a range of values of the Reynolds number using the transfer theory suggested by Kovásznay. Because of the simple form of the theory, the solution can be obtained in closed form for all values of the Reynolds number, and this exact solution is useful for analytical purposes. To obtain detailed results, however, it is more convenient to employ numberical methods. It is found, for example, that the skewness factor S of −∂u1/∂x1 varies only between 3.93 KK for Rλ = 0 and 2.86 KK for Rλ = ∞, where KK is the arbitrary constant that occurs in the theory. A comparison between the present results and those obtained by using Heisenberg's transfer formula is also made. Some results for the transfer function in the final period of decay are also given.
Shock-Tube Performance at Low Initial Pressure
Authors: Duff Russell E.
Published: December 2004

An electron beam densitometer has been used to investigate the behavior of a conventional 1⅛-in. i.d. shock tube operating at initial pressures of the order of 1 mm Hg. These experiments show that such a shock tube does not perform as predicted by simple theory. Most of the experiments were performed in argon with shock Mach numbers ranging between 1.2 and 7.0. The most striking observation was that for a given shock velocity, Ms = 1.6, the distance between the shock wave and contact surface as observed at the densitometer was proportional to initial pressure and independent of expansion chamber length over a tenfold range of tube length. At an initial pressure of 0.5 mm Hg the time interval between the arrival of the shock and the contact surface varied between 600 μsec at Ms = 1.2 and 20 μsec at Ms = 7.0. The diaphragm pressure ratio (Ar - Ar) required to produce a shock of velocity Ms = 1.6 varied from 200 at an initial pressure of 0.25 mm Hg to 20 at an initial pressure of 50 mm Hg. For a given diaphragm pressure ratio the shock velocity decreased with distance in a highly nonlinear manner. The density behind the shock wave was observed to increase significantly before the arrival of the contact surface under all conditions. This surprising shock-tube behavior is believed to be related to severe laminar boundary layer development behind the shock wave at low initial pressures.
On the Speed of Sound in Air
Authors: Gross R. A. , Eisen C. L.
Published: December 2004

In a high-temperature gas, the speed of sound depends upon the chemical composition, sound frequency, and chemical reaction rates. Two limiting sound speeds are normally distinguished: that of ``frozen'' or constant chemical composition, and the ``equilibrium'' sound speed. Equations to determine these two sound speeds are presented for a nitrogen-oxygen system and numerical data are presented for conditions behind a normal shock in air to a speed of Mach 20.
Seismic Scaling Law for Underground Explosions
Authors: Latter A. L. , Martinelli E. A. , Teller E.
Published: December 2004

Observations indicate that the amplitudes of distant seismic signals from underground nuclear explosions are approximately proportional to the total energy release. It is shown that these observations can be accounted for by a simple model which assumes that the nonlinear region close to the explosion is similar for all explosions and that the linear region transmits only low-frequency waves.
Free Surface Oscillations in a Rotating Liquid
Authors: Miles John W.
Published: December 2004

The disturbed motion of a liquid having a free surface in a vertical, rotating, circular cylinder and an equilibrium distribution of velocity corresponding to rigid body rotation is studied in linear approximation. It is shown that a vertical gradient of velocity necessarily generates vorticity, whence the disturbed motion cannot remain irrotational. (Earlier studies of this problem were based on shallow water theory, in which approximation the disturbed motion can remain irrotational.) The natural frequencies for the free surface oscillations are studied in some detail for a deep tank (say depth > diameter), and it is found that one effect of rotation is to split the pairs of frequencies (that would have been of equal magnitude and opposite sign) for the nonrotating liquid. In addition, new resonant frequencies are found that have no counterpart for a nonrotating liquid and for which the motion does not fall off exponentially with depth. The results are applied to forced, transverse oscillations of the tank, and explicit solutions are given for three special cases.
Integration Theory for One-Dimensional Viscous Flow
Authors: Rosen Gerald
Published: December 2004

The velocity of unsteady, one-dimensional real fluid flows is rigorously eliminated from the governing equations. A class of exact solutions for polytropic processes is then derived and discussed. The general solution for tangent-gas behavior is presented.
Instability in Hypersonic Flow about Blunt Bodies
Authors: Johnson Robert H.
Published: December 2004

Studies of the flow field associated with hypersonic helium flow over blunt bodies with surface cavities have shown a very violent instability to be connected with these cavities. The mechanism of this instability appears to involve the formation within the cavity of vortices which are subsequently ejected. Cavity shapes more conducive to vortex formation are associated with the least stable flow. Experiments using the hydraulic analogy for compressible gas flow have clarified the nature of these unstable flows. It is suggested that the violent action of such vortices may explain some of the deeper pits observed in many meteorites. The continuous ejection of vortices during atmospheric passage would ablate material from the cavities, whence the depth of any cavities initially present on a meteoric body would increase during passage through the earth's atmosphere.
Instability of Certain Electrohydrodynamic Systems
Authors: Stuetzer Otmar M.
Published: December 2004

The production of ion drag pressure under dynamic conditions, i.e., with the carrier medium in motion, is theoretically investigated. It is shown that for constant applied voltage the pressure increases with increasing velocity of the carrier fluid. This can lead to instability of the system which is theoretically discussed and experimentally demonstrated.
Electrostatic Field About an Ion Moving Slowly in a Plasma
Authors: Rand S.
Published: December 2004

A particle treatment is used to determine the potential distribution about an ion moving subsonicly through a plasma. A fore-aft asymmetry is obtained which has the effect of producing a drag on the ion. This asymmetry is the most important difference between the results of this treatment and those obtained for the subsonic case by the linearized treatment of the electrohydrodynamic equations.
Distribution of Density in a Planetary Exosphere
Authors: Öpik E. J. , Singer S. F.
Published: December 2004

A theory has been developed which gives the distribution of density with altitude for a planetary exosphere in the absence of local thermodynamic equilibrium. It gives values considerably lower than those conventionally calculated on the basis of the hydrostatic equation. Our results apply to the case where the field of force is gravitational; hence in the case of the earth, they give the density variation of only the neutral component of the exosphere.
Experimental Study of Alfvén-Wave Properties
Authors: Wilcox John M. , Boley Forrest I. , De Silva Alan W.
Published: December 2004

Alfvén hydromagnetic waves are propagated through a cylindrical plasma. The wave velocity, attenuation, impedance, and energy transfer are studied. The theoretical equations predict correctly the functional dependence of the velocity and attenuation, and from these quantities accurate measurements of plasma density and temperature can be obtained. A qualitative agreement between theory and experiment is obtained for the hydromagnetic coaxial waveguide impedance, and the energy transferred from an oscillating circuit to the hydromagnetic wave is measured to be 43 ± 10%.
Absorption of Plasma Waves
Authors: Stix Thomas H.
Published: December 2004

The propagation of waves through a plasma, wherein the density and/or magnetic field strength are slowly varying functions of position is discussed. If the local propagation constant, kx, is a slowly varying function of x, the adiabatic approximation will be valid. However, kx2 may pass through zero as a function of x. Using the WKB linear turning point connection formulas, examination shows that an incoming plasma wave is totally reflected in the region where kx2 ≈ 0. A similar analysis for the case where kx2 is a singular function of x shows that absorption of an incoming wave occurs in the vicinity of the singularity. Such singular behavior in kx2 can occur for propagation along the magnetic field when the wave frequency is equal to the local ion or electron cyclotron frequency. For propagation transverse to the magnetic field, an apparent singularity occurs at a frequency somewhat below the ion cyclotron frequency, and at the two hybrid frequencies of Auer, Hurwitz, and Miller. A detailed examination, including higher order effects in electron mass ÷ ion mass, finite electron and ion temperatures, and ion-ion and ion-electron collisions shows that the absorption will take place at the apparent singularity only if the physical damping processes are strong enough to swamp the reactive effects of the higher order corrections. Otherwise the higher order reactive effects introduce a new propagation mode into the dispersion equation with a root which, in the vicinity of the apparent singularity, is conjugate to the root of the original mode. Partial or total reflection now occurs at the apparent singularity instead of absorption. It is, however, conjectured that some of the original mode energy may be reflected into the new mode. As the new mode recedes from the region of the apparent singularity, its wavelength can become comparable to the particle Larmor radius. Energy in this mode may then be absorbed by phase-mixing processes which are of high order in the quantity (Larmor radius ÷ wavelength). Wave reflection from the apparent singularities will then heat ions in the case of the transverse ion cyclotron mode, and electrons in the case of the upper hybrid frequency.
Stability of an Idealized Atmosphere. II. Zeros of the Confluent Hypergeometric Function
Authors: Dyson Freeman J.
Published: December 2004

It is proved that the confluent hypergeometric function Wk,m(z) has no complex zeros when the index k is real while m is pure imaginary. Under these conditions, there is an infinite set of positive real zeros with a point of accumulation at zero. The zeros of Wk,m(z) are related to the stability of a model incompressible atmosphere, with density decreasing exponentially and horizontal wind velocity increasing linearly with height. The nonexistence of complex zeros indicates that this model atmosphere should be stable. The stability is rigorously proved in an accompanying paper by Case.
A Kinetic Theory of Liquid Displacement
Authors: De Witte A. J.
Published: December 2004

A theory is formulated for the displacement of a liquid from a porous system by another liquid, miscible with the first. In its most general form, the theory also may be applied to nonmiscible liquids. Differential equations are derived for the concentrations and fluxes of the two liquids as functions of time and distance in one-dimensional flow. The equations are hyperbolic, in contrast to the equations encountered in earlier theories of miscible liquid displacement which are parabolic. The differential equations are solved for given boundary conditions. Some numerical examples illustrate the solution in the simplest case of miscible displacement.
Relaxation Theory of Thermal Conduction in Liquids
Authors: Nettleton R. E.
Published: December 2004

A linear relaxation equation for the heat flux in a fluid, proposed by Vernotte as a generalization of Fourier's law, is shown for liquids to be consistent with the assumption that thermal energy is carried by elastic waves of very high frequency which may be envisaged as being propagated in a continuum. The elastic constants and the velocity of the waves are obtained from the infinite frequency limits of viscoelastic equations, derived in earlier papers to describe the relaxation of compressional and shearing strains, and from these, the relaxation time and thermal conductivity are calculated for several nonassociated liquids with the aid of a theory of Debye. It is shown that the Vernotte equation may be viewed formally, from the point of view of irreversible thermodynamics, as a force-flux equation linking two irreversible processes, and this interpretation makes it possible to calculate terms in the pressure and internal energy which are nonlinear in the temperature gradient.
Hydromagnetic Stability of a Streaming Cylindrical Incompressible Plasma
Authors: Zabusky N. J.
Published: December 2004

A dispersion relation is derived and analyzed for the case where the equilibrium velocity of an incompressible, nonresistive, cylindrical plasma has a spiral motion along magnetic field lines. The symmetric hydromagnetic equations are used to derive the plasma hydromagnetic pressure. The dispersion relation is found by matching plasma and outer-region hydromagnetic pressures across a sharp-moving interface. The zeros of the dispersion relation are obtained by a sequence of mappings between three complex planes. The presence of flow introduces overstable modes. For m = 0 the time-divergences are removed by flow. For m = 1 the divergences are enhanced by flow such that the growth rates and oscillation frequencies increase linearly with the flow velocity. The smaller is the wavelength of the disturbance in the z direction, the larger are the overstable eigenvalues.
Theory of the Stagnation-Point Langmuir Probe
Authors: Talbot Lawrence
Published: December 2004

A theory is developed for a Langmuir-type probe consisting of a collecting electrode placed at the stagnation point of a blunt body immersed in a supersonic partially ionized stream. It is shown that under certain conditions, the stagnation-point boundary layer equations and the probe sheath equations can be solved together to yield potential vs current relationships which permit the free stream ion and electron densities and temperatures to be measured by such a probe. It is shown also that the stagnation-point heat transfer will vary with probe potential, thus providing additional information useful in plasma jet diagnostics.
Variation Principles of Hydrodynamics
Authors: Eckart Carl
Published: December 2004

It is shown that the Lagrangian equations for the motion of both incompressible and compressible fluids can be derived from variation principles. As has been pointed out by C. C. Lin, an important feature of these principles is the boundary condition: The coordinates of each particle (and not merely the normal component of its velocity) must be specified. A systematic application of known results from the calculus of variations reveals new interrelations between such hydrodynamic results as Bernoulli's principle and the circulation theorem. Their derivation is both simplified and systematized. Clebsch's transformation is found to have an important relation to the problem of integrating the vorticity equation. The general solution of this problem for nonbarotropic flow is obtained. This reduces the second-order Lagrange equations to a set of first-order equations, in which the potential of the irrotational component replaces the pressure. The entropy gradients and a remarkable quantity, defined as the time-integral of the temperature of a particle of the fluid, also appear.
Ionization in Seeded Detonation Waves
Authors: Basu Satyaki
Published: December 2004

This paper reports an investigation of equimolal oxy-acetylene detonations at 1/10-atm initial pressure, which were seeded with potassium acetylide (C2HK) to obtain good electrical conductivity. Finely ground (10-μ mean diam) potassium acetylide was injected into the initial mixture and the density of the resulting aerosol was determined by a sedimentation technique. The electrical conductivity was determined by a magnetohydrodynamic interaction method developed by Lin. The measured conductivities were compared with the results of thermodynamic equilibrium calculations, which included the cooling effect due to the heat capacity of the additive. Predicted and measured conductivities have approximately the same dependence on the mole fraction of potassium which was varied from 0.1 to 10%. At the temperatures of interest (3500–4000°K), reported values of electron-gas (CO, H, and H2) and electron-potassium collision cross sections are about 10−15 cm2 and 40 × 10−15 cm2, respectively. With these values, the theoretical and measured electrical conductivities agreed within a factor of two, the agreement improving with increasing mole fraction of potassium. An electron-gas cross section of 2.5 × 10−15 cm2 gave good agreement between theory and experiment. The maximum measured conductivity was 2.7 mho/cm and occurred at about 3% potassium in the product gases. Ionization was essentially complete within about 40 μ sec behind the wave front.
Statistical Mechanics of Transport in Fluids
Authors: McLennan James A.
Published: December 2004

Transport processes in fluids are discussed in the framework of ensemble theory. A nonequilibrium ensemble is constructed by explicit consideration of the external forces which bring about the deviation from equilibrium. The resulting ensemble has the form of a product of factors, one characteristic of local equilibrium and the other containing a description of the irreversible processes. For states near equilibrium (to which the discussion is restricted) the ensemble depends linearly on the thermodynamic parameters which specify the deviation from equilibrium. Transport relations are obtained which are, in general, nonlocal in space and time; that is, the transport coefficients are frequency and wavelength dependent. An approximation procedure is used which amounts to an expansion in powers of the wave number, and in the lowest approximation one obtains the familiar local transport relations.
Flat Plate Drag in Magnetohydrodynamic Flow
Authors: Greenspan H. P.
Published: December 2004

In sub-Alfvén magnetohydrodynamic flow past a flat plate (the free stream fluid velocity is less than the Alfvén wave speed) the vorticity generated within the fluid is propagated upstream by Alfvén waves and produces a forward disturbance which in form is very similar to the viscous wake. The structure and strength of the wake and precursor are herein examined and compared for large Reynolds numbers and finite conductivity. As the conductivity increases, a larger proportion of the total vorticity is propagated upstream so that the precursor becomes more pronounced and the wake weakens. Explicit formulas for the skin friction and drag coefficient are determined for arbitrary values of the conductivity, and the results clearly exhibit the effects of the interaction of fluid flow and magnetic field.
Separation of Magnetic Driving and Ohmic Heating
Authors: Banister John R.
Published: December 2004

In this experiment, brief unidirectional current discharges were passed through nitrogen in the presence of a transverse uniform magnetic field. The gas between the electrodes was heated and given a directed velocity. Since flow is limited to the direction of this directed velocity, the usual shock-tube theory modified for this velocity may be used to describe shock development. This theoretical method, which provides separation of the roles of magnetic driving and Ohmic heating, was found to be precisely applicable until the material traverses more than half the electrode dimension during the discharge. The technique seems potentially useful for studying plasma conductivity and equation of state.
Growth of Vapor Bubbles in a Rapidly Heated Liquid
Authors: Zwick S. A.
Published: December 2004

The earlier theory of the growth of vapor bubbles in superheated liquids is extended to the situation in which the rate of temperature rise of the liquid is large. Numerical solutions are presented for the early stages of bubble growth for various rates of liquid temperature rise. The asymptotic behavior of a bubble is found explicitly for a temperature rise of the liquid which is linear in time. In this case the bubble radius grows initially as t½, as in asymptotic solutions found previously for small rates of temperature rise, but then deviates toward a late t32 variation.
Transport Properties for Gases Assuming Inverse Power Intermolecular Potentials
Authors: Kihara Taro , Taylor Marion H. , Hirschfelder Joseph O.
Published: December 2004

The integrals required for the calculation of transport properties for gases are carefully examined, assuming that the intermolecular potentials vary inversely as a power of the separation, Φ = −c/rn. When the potential corresponds to mutual attraction, the behavior at the origin, corresponding to the centers of the two molecules colliding, must be prescribed because some trajectories of the relative motion reach the origin. Calculations are made on the basis of three models: (a) A rigid core corresponding to the Sutherland potential in the limit that the rigid core approaches zero (for spherical models this is the most realistic model); (b) a transparent core model which corresponds to the limiting behavior of a well-shaped potential; and (c) a random-scattering core model which is an appropriate idealization for molecules without spherical symmetry. The behavior of the collision integrals is considered for the full range of potentials as n goes from one to infinity (or from the Coulomb to the rigid-sphere potential).
Transport Properties of Helium II in Fine Channels
Authors: Burnham J. , Reppy J. , Pearson G. , Spees A. H. , Reynolds C. A.
Published: December 2004

The thermal conductivity of liquid He II in the interstices of a column of packed jeweler's rouge (Fe2O3 powder) has been found to have a temperature dependence: k ∝ Tn, where n falls monotonically from a value of 13 at 1.5°K to possibly zero at the lambda point. The value of the thermal conductivity at the lambda point is 0.60 ± 0.03 w/cm°K. From the flow of helium, nitrogen, and water at room temperature it is estimated that a typical rouge column provides the equivalent of about 1.4 × 109 parallel channels having an average diameter of 0.18 ± 0.02μ. The viscosity of the normal component of He II, computed from the measured conductivity on the basis of the two-fluid model, follows a temperature dependence very similar to that observed for the bulk liquid and for 52-and 108-μ capillaries above 1.9°K. The magnitude of the values, however, is lower, but in agreement with that obtained in Leiden with 0.7-μ slits. Empirical values of a correcting slip coefficient are smaller in magnitude (0.007μ) and less temperature dependent (−0.018μ/°K) than theoretical values calculated at Oxford. It was not possible, though, to rule out a phonon mean free path effect of the order of magnitude calculated by Atkins. Points on the lambda line have been determined from the fountain effect for pressures below 0.4 atm. The slope of the line is approximately −70 atm/°K, in agreement with the slope determined at higher pressures by other means.
Electric Field Correlation and Plasma Dynamics
Authors: Taylor J. B.
Published: December 2004

The correlation function for the electric field in a fully ionized plasma is derived, and its application to the problem of finding the force on a charge moving slowly through a plasma is described. The correlation function is evaluated for a plasma with and without a magnetic field, and this function is then converted to the spectrum of the mean-square fluctuation in the random electric field. The application of the generalized fluctuation-dissipation theorem gives the mean force on a slowly moving test charge. The relation of this to other treatments is briefly discussed.
Superfast Pinch Experiment
Authors: Josephson Vernal
Published: December 2004

An assembly designed to accelerate deuterons to about 10 kev by means of a radially converging magnetic piston has been constructed and tested. The assembly operates with 300 kv on the energy storage condenser, the ringing frequency is 18 Mc, and present operation uses hydrogen gas at 50 μ. Both slow and fast pinches have been observed, the former being possibly thermal shock waves, and the latter possibly being associated with inward motion of the plasma sheath.
Kinetic Theory of Moderately Dense Gases: Rigid Sphere Limit
Authors: Snider R. F. , Curtiss C. F.
Published: December 2004

The rigid sphere limiting forms of the expressions for the first-order density corrections to the transport coefficients previously derived by the authors from the modified Boltzmann equation of Green and Bogoliubov are re-examined. It is shown that in this limit these expressions approach the classic results of Enskog.
Plasma Acceleration in a Radio-Frequency Field Gradient
Authors: Swartz G. A. , Reboul T. T. , Gordon G. D. , Lorber H. W.
Published: December 2004

Experiments have been performed at 140 Mc to determine the acceleration of a mercury plasma in an rf field gradient. With a maximum rf field amplitude of 170 v/cm, a tenuous plasma (of density less than a critical density) was accelerated from 5 × 105 to 25 × 105 cm/sec. A denser plasma (of density greater than the critical density) was decelerated in the same field. These experimental results are consistent with a theory based on energy considerations.
Three-Dimensional Standing Surface Waves of Finite Amplitude
Authors: Verma Ghasi R. , Keller Joseph B.
Published: December 2004

Three-dimensional gravity waves on the surface of an inviscid incompressible fluid of finite depth are considered. The waves are assumed to be periodic in time and in two perpendicular horizontal directions. The surface profile, potential function, pressure, and frequency of the motion are determined (to second order) as series in powers of the amplitude divided by the wavelength in one direction. As in the two-dimensional case previously considered by Tadjbakhsh and Keller, it is found that the frequency increases with amplitude for depths less than a critical value and decreases with increasing amplitude for greater depths. The critical depth depends upon the wavelengths in the two horizontal directions. The three-dimensional results do not reduce to the two-dimensional ones when one of the wavelengths becomes infinite. This is because the motion remains three dimensional.
Motion of Spherical Gas Bubbles in a Viscous Liquid at Large Reynolds Numbers
Authors: Chao B. T.
Published: December 2004

An analysis is made for the motion of a gas bubble rising steadily in a quiescent liquid of infinite extent. The disturbed layer of the fluid, due to viscosity, on either side of the interface is thin when the Reynolds number is sufficiently large and thus makes possible a considerable simplification of the governing equations of motion. Simultaneous solutions of the boundary-layer equations for the flow outside and inside of the bubble are obtained by considering that the tangential velocity components and the shear stresses on both sides of the interface are equal. From the calculated external stress field, the drag of a spherical bubble with negligible flow separation is evaluated. Good agreement is obtained with published data for spherical air bubbles in four different organic liquids. The experimental drag curve due to Haberman and Morton for air bubbles rising in filtered water deviates from that predicted from the present theory. The theoretical results are applicable to any fluid sphere moving steadily in a substantially immiscible, viscous liquid provided that the internal circulation is complete, the flow separation is negligible, and the Reynolds number is sufficiently large.
Landau Damping and the Attenuation of Whistlers
Authors: Scarf F. L.
Published: December 2004

Transverse electromagnetic oscillations in a gyrotropic plasma exhibit Landau damping when the wave is not monochromatic. The dependence of the damping on the equilibrium distribution and the boundary (or initial) values is investigated. The resulting dispersion relation is interpreted by examining the response of a single free electron to an incident wave. It is shown that the damping mechanism is associated with the Doppler shift caused by the thermal distribution, so that some particles are in cyclotron resonance for any laboratory frequency. The correlation of whistler data with this complex dispersion relation can be used to evaluate electron temperatures at several earth radii; a specific numerical example gives T ≈ 105 °K at R ≈ 4Re (geocentric).
Laminar Boundary Layer under a Wave
Authors: Grosch C. E.
Published: December 2004

The laminar boundary-layer flow resulting from a wave potential flow of form U = αc sin(kx — ωt), with α a parameter and c the wave velocity, is considered. It is shown, after suitable transformation, that there is an exact solution of the unsteady boundary-layer equations which is of the form of a power series in the phase kx — ωt. The coefficients φn are functions of a similarity variable, and are the solutions of an infinite set of linear third-order differential equations with nonlinear forcing terms. The forcing term in the equation for φn is a function of φ0, φ1, …, φn−1 and their derivatives. Solutions for φ0, φ1, and φ2 have been computed and are presented. The theory is applied to the laminar boundary layer under a progressive shallow-water wave, where α = a/h, and compared to a linearized theory. It is concluded that if α ≪ 1, or for any α in a sufficiently small region near kx — ωt = 0, the linearized theory is valid. Otherwise, the linear theory does not provide an adequate description of the flow.
Absorption of Radiation by the Ionosphere
Authors: Rand S.
Published: December 2004

The damping of transverse waves, propagating parallel to an external magnetic field, through a low-density plasma is studied. It is found that there is a limitation on the total amount of energy which may be absorbed in a unit volume of the gas. This saturation phenomenon is predicted on the basis of a particular nonlinear relativistic effect. The total amount of energy absorbed is found to be proportional to the two-thirds power of the incident radiation energy flux for a low flux, and proportional to the one-third power for a high flux.
Plasma Production by Neutral-Atom Injection: Equations and Numerical Solutions
Authors: Futch A. H. , Heckrotte W. , Damm C. C. , Killeen J. , Mish L. E.
Published: December 2004

Differential equations and their solutions for the formation of a high-energy plasma by the injection and trapping of energetic atoms in a magnetic-mirror geometry are discussed. The present approach differs from previous treatments in that the finite orbit size of the ions and the spatial dependence of the trapping process are included in the equations. By including the spatial dependence it was possible to evaluate the effect of charge exchange of trapped ions with neutral-beam atoms. Although not affecting the total number of trapped ions, this process results effectively in a change of the mean radial position of the ions. The effect on plasma growth rates of charge exchange of the trapped ions with beam atoms was found to be essentially negligible. The solutions for ion density vs time exhibit growth rates similar to those obtained when the plasma density is assumed to be spatially constant. Background gas variations during plasma buildup have also been investigated. Under the present set of conditions the effect of ``gas burnout'' and plasma pumping are small, even at high densities.
Application of the Monte Carlo Method to Heat Transfer in a Rarefied Gas
Authors: Haviland J. K. , Lavin M. L.
Published: December 2004

A Monte Carlo method was developed and applied to the heat transfer between two parallel walls in a rarefied gas, using the IBM 709 computer. Three solutions were obtained, all at a temperature ratio between the walls of 4:1. One was for hard-sphere molecules at a Knudsen number of 2.0, and two were for Maxwellian molecules at Knudsen numbers of 0.53 and 1.64. These results appear to be of sufficient accuracy to differentiate between some of the approximate analytical methods available at present. It is believed that solutions could be obtained to any degree of accuracy, given sufficient time on a high-speed computer.
Plasma Correction to Single-Particle Cyclotron Radiation
Authors: Chang David B.
Published: December 2004

The saddle-point evaluation used by Trubnikov and Kudryavtsev and Drummond and Rosenbluth to obtain the O (ωp2/ωωH) absorption coefficient for single particle cyclotron radiation from a mildly relativistic plasma, is extended to include terms of O(ωp4 / ω2ω2H) describing collective plasma effects—where ωp, ωH, and ω are the plasma frequency, electron cyclotron frequency, and observed frequency, respectively. The O(ωp4 / ω2ωH2) correction modifies the O(ωp2 / ωωH) calculation through the introduction of an additional steepest descent path; through the inclusion of additional terms in the expansion of the dispersion formula; by changing the location of the saddle points; and by altering the expressions evaluated at the saddle points. For a typical thermonuclear plasma, the fractional O(ωp4 / ω2ω2H) correction to the absorption coefficient for propagation perpendicular to the magnetic field is found to be approximately — ωp2/ωωH.
Interaction between a Plasma and the External Current and Flux
Authors: Jensen T. H. , Voorhies H. G.
Published: December 2004

The external current and flux in plasma devices are studied in order to obtain information on the plasma by the observation of these quantities. Two devices have been investigated, namely the long mirror and the cusp. The result of the investigations is that one can obtain approximately the following quantities: total kinetic energy of the plasma, energy exchange between plasma and field, and energy exchange between the plasma and the surroundings.
Similarity Solution for Cylindrical Magnetohydrodynamic Blast Waves
Authors: Greifinger Carl , Cole Julian D.
Published: December 2004

A similarity solution is obtained for the flow behind a very strong (in the hydrodynamic sense) cylindrical magnetohydrodynamic shock wave produced by the sudden release of energy along a line of infinite extent in a plasma. The plasma is assumed to be an ideal gas with infinite electrical conductivity, and to be permeated by the azimuthal magnetic field of a line current. It is shown that it is of critical importance to take into account the ambient magnetic pressure, no matter how small. It is found that, to preserve similarity, the external circuit is required to maintain a constant axial current; this result also appears in the related problem, treated by Greenspan, where the ambient plasma is nonconducting. This boundary condition is shown to have some interesting consequences, especially with regard to the energy content of the system. The dependence of the shock speed on the explosive energy is determined as a function of the ambient magnetic field both for the present case and for Greenspan's case, and interesting differences are noted. Other differences between the two cases are also discussed.
Inertia-Controlled Ambipolar Diffusion
Authors: Persson Karl-Birger
Published: December 2004

The general nonlinear ambipolar-flow equations are derived and discussed. The important non-linearities are caused by the inertia of the ions and by the heat-conduction mechanism. It is shown that all essential effects associated with these nonlinearities can be demonstrated in the plane-parallel case. The influence of the nonlinearity caused by the inertia is discussed in detail for the plane-parallel case and it is shown that this flow is analogous to the flow of a fluid with friction through a contracting nozzle. The limiting velocity—the isothermal or the adiabatic sound velocity—which is found in the exit of a nozzle is also found at the boundary in the case of inertia-controlled diffusion, provided this boundary acts like a perfect sink. Bohm's criterion—the ion drift velocity less than or equal to the sound velocity of the electron-ion gas in front of the boundary or the wall sheath—appears as an integral part of the inertia-controlled-diffusion theory. In the inertia-controlled-diffusion theory are incorporated, as integral parts, all the assumptions that necessarily must be added to the linear-diffusion theory in order to make it realistic. The isothermal and inertia-controlled diffusion leads always to wall-stabilized plasma configurations which directly correspond to the fundamental mode solution in the linear-diffusion theory.