bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproductive and Metabolic Disorders in Women with Epilepsy
Authors: Morrell Martha J.
Published: December 2004

Summary:  Epilepsy is a common neurologic disorder affecting women during the reproductive years. Seizures and some antiepileptic drugs (AEDs) can compromise reproductive health, and some AEDs can adversely affect carbohydrate and bone metabolism. Women with epilepsy have lower birth rates and more frequent anovulatory menstrual cycles. This appears to be related to seizure‐ and AED‐associated reproductive endocrine disturbances. Carbamazepine (CBZ), phenytoin (PHT), and phenobarbital (PB) induce hepatic cytochrome P450 enzymes and lower endogenous estrogens, adrenal and ovarian androgens, and contraceptive steroids. Valproate (VPA) inhibits steroid hormone metabolism, elevates androgens, and predisposes to phenotypic signs of hyperandrogenism‐hirsutism, obesity, acne, and frequent anovulatory cycles. VPA is associated with weight gain, probably by altering insulin metabolism. CBZ, PHT, and VPA, but not lamotrigine (LTG), are associated with lower levels of calcium. PHT, but not VPA or LTG, appears to accelerate bone turnover. AED effects on bone mineral metabolism may explain the elevated risk of fracture described in women with epilepsy. Prospective pregnancy registries are beginning to provide information about AED‐associated teratogenesis. The North American Antiepileptic Drug Pregnancy Registry reports a 12% rate of major malformations after first trimester exposure to PB and an 8.6% rate after first trimester exposure to VPA. A prospective LTG‐specific registry reports a 1.8% chance of major malformations after the first trimester. The registries will continue to release information as data become significant. In the meantime, practitioners can be alert to signs and symptoms of reproductive or metabolic health disturbances and participate in pregnancy registry efforts.
Review of New Antiepileptic Drugs as Initial Therapy
Authors: Gil‐Nagel Antonio
Published: December 2004

Summary:  The new onset of epilepsy usually leads to initiation of treatment with antiepileptic drugs (AEDs). Selection of the appropriate drug in this clinical situation is usually based on several factors, including efficacy for the suspected epilepsy type, tolerability, acute and long‐term idiosyncratic side effects, pharmacokinetic interactions, possibility of rapid titration, formulation, and expense. Over the last several years, the choices for treatment in newly diagnosed epilepsy have increased because a number of new AEDs have been approved for use in monotherapy. This article reviews randomized, controlled studies that have evaluated the use of new AEDs in monotherapy.
Interleukin‐6 Levels are Inversely Correlated with Heart Rate Variability in Patients with Decompensated Heart Failure
Authors: ARONSON DORON , MITTLEMAN MURRAY A. , BURGER ANDREW J.
Published: December 2004

Interleukin‐6 and Heart Rate Variability.
Introduction: Increased local and systemic elaboration of cytokines have an important role in the pathogenesis of congestive heart failure (CHF) through diverse mechanisms. Because cytokines are known to act at the neuronal level in both the peripheral and central nervous system, we sought to determine whether increased cytokine levels are associated with the autonomic dysfunction that characterizes CHF.

Methods and Results: We studied 64 patients admitted for decompensated CHF (mean age 59 ± 12 years). Autonomic function was assessed using time– and frequency‐domain heart rate variability (HRV) measures, obtained from 24‐hour Holter recordings. In addition, norepinephrine, tumor necrosis factor‐α (TNF‐α), and interleukin‐6 (IL‐6) were measured in all patients. TNF‐α levels did not correlate with any of the HRV measures. IL‐6 inversely correlated with the time‐domain parameters of standard deviation of RR intervals (SDNN) (r =−0.36, P = 0.004) and standard deviation of all 5–minute mean RR intervals (SDANN) (r =−0.39, P = 0.001), and with the frequency‐domain parameters of total power (TP) (r =−0.37, P = 0.003) and ultralow‐frequency (ULF) power (r =−0.43, P = 0.001). No correlation was found between IL‐6 and indices of parasympathetic modulation. Using multiple linear regression models, adjusting for clinical variables and drug therapies, the strong inverse relationship between IL‐6 and SDNN (P = 0.006), SDANN (P = 0.001), TP (P = 0.04), and ULF power (P = 0.0007) persisted.

Conclusion: Reduction of long‐term HRV indices is associated with increased levels of IL‐6 in patients with decompensated heart failure. The ability of long‐term HRV parameters to better reflect activation of diverse hormonal systems may explain their greater prognostic power for risk stratification in patients with CHF.
Nonthoracotomy Implantable Cardioverter Defibrillator Placement in Children: Use of Subcutaneous Array Leads and Abdominally Placed Implantable Cardioverter Defibrillators in Children
Authors: GRADAUS RAINER , HAMMEL DIETER , KOTTHOFF STEFAN , BÖCKER DIRK
Published: December 2004

Nonthoracotomy ICD in Children. Introduction: The need to access the right ventricle might preclude transvenous placement of a defibrillation lead at implantable cardioverter defibrillator (ICD) placement, especially in small children or children with complex congenital heart defects. We investigated a subcutaneous array lead in addition to an abdominally placed “active can” ICD device in two children to avoid a thoracotomy.

Methods and Results: The first child (age 12 years, 138 cm, 41 kg) had transposition of the great arteries with a subsequent surgical intra‐atrial correction by the Mustard technique. The second child (age 14 years, 161 cm, 54 kg) had a single atrium and a single ventricle, d‐transposition of the aorta, and atresia of the main pulmonary artery with a surgical anastomosis between the aorta and the right pulmonary artery by the Cooley technique. The defibrillation threshold was 18 J and < 20 J at initial implantation and at generator replacement in the first patient and 20 J in the second patient. During follow‐up of 6 years and 1 month, respectively, no ICD‐related complications occurred.

Conclusion: In children in whom endocardial, right ventricular placement of a defibrillation lead is precluded, defibrillation is possible and safe between an abdominally placed “active can” ICD device and a subcutaneous array lead. This approach may avoid a thoracotomy in children with no possibility for transvenous ICD placement.
Radiofrequency Catheter Ablation of Postinfarction Ventricular Tachycardia from the Proximal Coronary Sinus
Authors: KAUTZNER JOSEF , BYTEŠNÍK JAN , ČIHÁK ROBERT , VANČURA VLASTIMIL
Published: December 2004

VT Ablation from the Coronary Sinus. Optimum strategy for radiofrequency (RF) catheter ablation of ventricular tachycardia (VT) after inferior wall myocardial infarction (MI) that originates from the posteroseptal process of the left ventricle is not known. We describe a case report of a 57–year‐old man who developed recurrent post‐MI VT with ECG morphology consistent with this type of VT (i.e., left bundle branch block pattern with predominant R waves from V2 to V6 and left‐axis deviation). Endocardial mapping and entrainment during VT demonstrated a critical isthmus of the reentrant circuit in the proximal coronary sinus. RF application terminated VT and rendered it noninducible.
Cryoablation:
Authors: SKANES ALLAN C. , KLEIN GEORGE , KRAHN ANDREW , YEE RAYMOND
Published: December 2004

The use of cryoablation in the electrophysiology lab provides some distinct advantages not seen with conventional radiofrequency ablation. Ice mapping allows a functional assessment of a putative ablation site prior to the formation of a permanent lesion. This provides a distinct advantage adjacent to the AV node for para‐hisian pathways and difficult cases of AVNRT. Cryoablation also produces minimal endothelial disruption and thrombus formation and causes no collagen shrinkage. This is likely advantageous when ablation is required within venous structures. There is also mounting experimental evidence that cryoablation is safe adjacent to the arterial system, especially within the middle cardiac vein or distal coronary sinus. As the technology evolves and further iterations of the catheter proceed, the role for this new but well‐established technology is likely to grow.
Optical Refractivity of High-Temperature Gases. I. Effects Resulting from Dissociation of Diatomic Gases
Authors: Alpher Ralph A. , White Donald R.
Published: December 2004

Shock-tube and discharge techniques make it possible to generate in the laboratory significant volumes of dissociated and/or ionized gases. This paper describes some studies of the optical index of refraction μ of dissociated diatomic gases. The physical interpretation of specific refractivity K = (μ − 1)/ρ is discussed and related to polarizability, and various methods of computing such quantities are reviewed briefly. Shock-tube experiments are described in which optical interferometry has been utilized to measure the polarizability of atomic oxygen and nitrogen with the result ᾱ(O I)=0.77±0.06 A3 and ᾱ(N I)=1.13±0.06 A3. The use of optical interferometry for determination of gas density has been justified for experiments involving air at temperatures to at least 5000°K.
Liquid Behavior of Exploding Wires
Authors: Chace William G.
Published: December 2004

Experiments were performed to secure evidence of the mechanism during the early stages of a wire explosion. High-speed (0.3 μsec) photographs were taken, using a second exploding wire to back-light the first. The results showed no surface irregularities (unduloids) as frequently postulated for the liquid phase of exploding wires. Instead, the evidence points to a condition of extreme super-heating of the liquid, followed by sudden explosive vaporization (``transplosion''). Stria in the ensuing vapor cloud were found to develop after the explosion is complete.
Collision Frequency of Electrons in the Terrestrial Atmosphere
Authors: Nicolet Marcel
Published: December 2004

An analysis of the collision frequency of electrons in the terrestrial atmosphere has been made using recent experimental and observational data. Application to collisions of electrons with neutral particles and positive ions shows that the electronic collision frequency is due to neutral particles below the peak of the F1 layer and results from positive ions in the F2 layer.
Lifetimes of Trapped Radiation Belt Particles Determined by Coulomb Scattering
Authors: Wentworth R. C. , MacDonald W. M. , Singer S. F.
Published: December 2004

Once introduced into captive orbits, protons and electrons should be strictly trapped in the earth's dipole magnetic field. However, various mechanisms exist which limit their lifetimes, such as collisions with atoms and ions in the earth's outer atmosphere, charge exchange, and scattering by hydromagnetic waves. This paper considers only the effect of the scattering of these particles by the ionized hydrogen and electron components of the outer atmosphere. However, the effect of scattering from neutral atoms can be qualitatively taken into account by using the radius of the atom in place of the Debye shielding length in the scattering formulas. The Fokker-Planck equation has been used to derive an expression for the change in the distribution function due to small-angle, single-particle Coulomb collisions. Upper lifetime limits, as determined by this mechanism, of both protons and electrons are derived as functions of their initial energies.
Nonlinear Alfvén Waves in a Cold Ionized Gas
Authors: Montgomery David
Published: December 2004

Nonlinear constant-profile Alfvén waves are studied in an ionized gas in which thermal motions are negligible. The system of differential equations possesses numerous integrals, and can be solved up to a single quadrature. Many properties of the waves can be inferred without performing any numerical integrations. The waves necessarily involve nonzero magnetic field components in both directions perpendicular to the direction of propagation, and plane polarized waves are impossible except in the special case of equal mass particles. Circularly polarized modes are also a special case, and, unlike the more general solutions, involve neither longitudinal electric fields nor compression of the gas.
Moving Magnetic Field behind a Strong Deuterium Shock
Authors: Scott F. R. , Wenzel R. F.
Published: December 2004

By introducing a spiral in the return conductor of a conical discharge tube with a hollow electrode, a magnetic multipole has been observed propagating down a cylinder extending out from the hollow electrode. This magnetic field appears to have an extremely complicated internal structure when observed with small magnetic probes; when observed by an external loop, the net axial leakage flux shows a structure consistent with the characteristics of a shock produced deuterium plasma.
Some Interior Problems of Hydromagnetics
Authors: Cole J. D. , Huth J. H.
Published: December 2004

The static boundary problems of line currents and dipoles immersed in a perfectly conducting static fluid are considered first. The perturbing effect of moving fluid on the magnetostatic boundary about an isolated line current is then investigated. In this case, the initial circular boundary is distorted into an ellipse with major axis transverse to the direction of flow.
Transport Properties of High-Temperature Multicomponent Gas Mixtures
Authors: Mason Edward A. , Vanderslice Joseph T. , Yos Jerrold M.
Published: December 2004

An investigation is made of some modifications in the kinetic theory of gaseous transport properties which are necessary to take account of effects encountered at high temperatures. In particular, complications arise because of the existence of a multiplicity of different interaction energy curves governing collisions, and because of the possibility of resonant excitation and charge exchange during collisions. It is shown that the results of classical kinetic theory can be kept in the same form, but the cross sections or collision integrals have to be computed differently. It is pointed out that the present modifications are valid to all orders of Chapman-Enskog approximation. It is also shown that excitation exchange is important in determining the transport properties of mixtures at high temperatures, and the method of calculation of the excitation exchange probability is extended to cases for which multiple interaction curves are involved.
Heat Flow Between Parallel Plates
Authors: Gross E. P. , Ziering S.
Published: December 2004

A study is made of the flow of heat between parallel plates of slightly different temperatures. The problem is described by the linearized Boltzmann equation which is subject to microscopic boundary conditions. We approximate the distribution function by half-range polynomials in velocity space and determine the space-dependent coefficients by forming half-range moment equations. An approximation involving four pairs of space functions suffices to give an accurate treatment of the heat flow and of the density and temperature profiles for the entire range of conditions from free molecule to hydrodynamic. Detailed numerical results for the temperature slip and molecular boundary structure are obtained for hard-sphere molecules. The accuracy of cruder half-range approximations and other methods of fixing the coefficients is established.
Diffusion Coefficients in Flames and Detonations With Constant Enthalpy
Authors: Hirschfelder Joseph O.
Published: December 2004

It is found that the entropy per gram of mixture remains constant in a flame or a one-dimensional chemically reacting gaseous flow system if all the binary diffusion coefficients are equal to each other and Dij=λ/(C̄pmn), where C̄p is the specific heat at constant pressure per gram of the mixture, m is the average molecular weight of the mixture, and n is the number of moles per gram. This value for each of the binary diffusion coefficients corresponds to setting each of the Lewis numbers equal to unity. For detonations, or systems having large kinetic energy, the enthalpy (per gram) including kinetic energy remains constant if, in addition to the diffusion coefficients having this special value, the Prandtl number is equal to ¾. It is clear that the assumption of constant enthalpy should not be applied to hydrogen-bromine or hydrogen-oxygen flames where some coefficients of diffusion are very large and others very small. The constant enthalpy assumption is applied to unimolecular decomposition flames supported by the reaction A → sB′. It is found that, to a rough approximation, the flame velocity varies as the 1/12th power of s.
Steady State Solutions of the Radiofrequency Discharge with Flow
Authors: Romig Mary F.
Published: December 2004

The electron density distribution and diffusion length have been investigated for a steady-state, diffusion-controlled radiofrequency discharge acting over a finite portion of an infinite cylinder in which there is a uniform axial gas flow. This model simulates to some extent the flow in a plasma wind tunnel. A qualitative relationship is obtained for the influence of active cylinder length and gas velocity parameter on the diffusion length. The effect of these parameters on the electric field necessary to sustain the discharge is also discussed. It is shown that the peak of the electron density distribution shifts downstream with increasing gas velocity, but never leaves the region of production. A numerical example is calculated for the case of helium, indicating that while there is moderate effect on breakdown parameters, the ambipolar case may be changed considerably by the presence of flow.
A Theory of Decaying Homogeneous Turbulence
Authors: Deissler Robert G.
Published: December 2004

By considering correlations between fluctuating quantities at four points in a turbulent fluid, an equation containing quadruple and quintuple correlations is obtained. The equation is made determinate by neglecting the higher-order (quintuple) correlations. The combining of this equation with the two-and three-point correlation equations, and assuming a particular set of initial conditions, result in a solution which appears to represent the turbulence for times between the initial and final periods. The results reproduce most of the trends observed experimentally.
Wake of a Satellite Traversing the Ionosphere
Authors: Rand S.
Published: December 2004

The particle treatment is applied to a study of the structure of the wake behind a charged body moving supersonically through a low-density plasma. For the case of a body whose dimensions are considerably smaller than a Debye length, a solution is obtained which is very similar in structure to the solution obtained by using the linearized fluid dynamics equation. For the case of a disk whose radial dimensions are much larger than a Debye length, two conical regions are found in the wake. At the surface of each of these cones, over thicknesses of the order of a Debye length, the ion and electron densities are increased over their ambient values. Formulae for the electrohydrodynamic drag on a wire, and on a large disk are obtained.
Stability of Large Amplitude Waves in the One-Dimensional Plasma
Authors: Montgomery David
Published: December 2004

The problem of the stability of the nonlinear plasma oscillations of Bernstein, Greene, and Kruskal is discussed. The eigenvalue equation for the perturbed distribution function possesses an expansion in powers of a parameter proportional to the maximum value of the equilibrium electrostatic potential. The stability of any given distribution can be inferred from consideration of the zeroth order alone.
Boltzmann Equation for an Electron Guide Field Accelerator. II. Stability Analysis for an Electron Beam
Authors: Ehrman Joachim B.
Published: December 2004

The short time behavior of the quasi-stationary solution of an earlier paper is investigated by linearizing the Boltzmann equation in the perturbations. By the use of a suitable boundary condition on the distribution function in phase space, four one-dimensional coupled inhomogeneous Fredholm equations of the second kind are obtained for Fourier components of the Laplace transforms with respect to time of the perturbation charge-current density components. The asymptotic time behavior of the perturbations is determined by that root of the Fredholm determinant (considered as a function of s, the Laplace transform variable) whose real part is algebraically greatest, provided that this real part is nonnegative. If the real part is negative, then the asymptotic time behavior is sometimes determined by this root of the determinant and sometimes by branch points of the kernel on the imaginary axis. If the determinant has no roots for Re s > 0 and no multiple roots for Re s = 0, the quasi-stationary solution is stable. For the azimuthally symmetric Fourier components, the equation for ρvθ is not coupled to the others and is studied in more detail. In the approximate betatron regime, the Landau damping rate for this mode is estimated without use of the Fredholm determinant. In the extreme betatron regime, the undamped vibration frequencies are obtained.
Frequency Spectrum of Finite Amplitude Ultrasonic Waves in Liquids
Authors: Keck Winfield , Beyer Robert T.
Published: December 2004

The theory of harmonic growth for finite-amplitude sound waves in a nondissipative fluid is discussed. The perturbation analysis of such waves in a dissipative fluid has been extended to higher orders of calculation, so that the location of the maximum of the second harmonic can be ascertained with some accuracy. The results agree well with experimental data. The effective absorption coefficient for finite-amplitude waves also has been calculated to terms of higher order.
Taylor Instability of an Inverted Atmosphere
Authors: Case K. M.
Published: December 2004

The stability of an idealized inverted atmosphere is investigated. It is shown that an initial perturbation grows in a manner similar to that found by Taylor for the instability of accelerated fluid surfaces.
Radio Emission from Plasma Shocks
Authors: Parker E. N. , Tidman D. A.
Published: December 2004

From recent calculations of the efficiency of rf emission from longitudinal plasma oscillations, and from simple considerations of charge separation in collisionless plasma shocks, it is shown that one can predict a quantitative value for the energy of a type II solar radio burst in agreement with observation. Application of the same methods to the solar corona suggests that the radio spectrum of the quiet sun may be nonthermal below 20 Mc, and that the solar wind may generate at earth as much as a megawatt of power at 1 Mc.
On Rayleigh's Problem in Magnetohydrodynamics
Authors: Rossow Vernon J.
Published: December 2004

A comparison is made of three flow fields that may be described as Rayleigh's problem in magnetohydrodynamics and that differ only in the state of motion of the magnetic field. Deviation of approximate expressions for the velocity from the more exact relations are also presented when the ratio of the viscous and magnetic Reynolds numbers is unity.
Oscillations of a Nonuniform Plasma
Authors: Weibel Erich S.
Published: December 2004

The oscillations of a plasma which is confined by an rf field are investigated. The confining potential is approximated as ψ(x) = ½mω02x2. Longitudinal plasma oscillations in the x direction are determined from the self-consistent Boltzmann transport equation without the collision term (Vlasov equation). This equation is linearized about equilibrium velocity distribution f0 = exp [−(ψ + ½mv2)/κT]. By expanding the electric field in Hermite polynomials, it is possible to reduce exactly the resulting integro-differential equation to an infinite system of linear equations for the expansion coefficients. The resonant frequencies are the roots of the determinant of the system. The frequency spectrum so obtained is quite unlike those obtained for Sturm-Liouville problems. This spectrum contains the integral multiples of ω0 as limit points. As e2n/mω02 → 0, the resonant frequencies coalesce into these limit points, each of these frequencies μω0 (μ = integer) being infinitely degenerate. Since all frequencies are real, the oscillations are not damped. The resonant frequencies are determined approximately as functions of e2n/mω02 as the roots of principal sub-determinants of finite order N. This procedure converges rapidly with increasing N.
Hydromagnetic Waveguide with Finite Conductivity and Arbitrary Cross Section
Authors: Shmoys J. , Mishkin E.
Published: December 2004

Low pressure magnetohydrodynamic waveguides of arbitrary cross section, having a dc axial magnetic field, exhibit both TE and TM modes. The longitudinal electric field vanishes when the conductivity of the plasma is infinite, converting the TM modes into principal ones. The propagation constants for both modes are derived from the solutions of the eigenvalue problems. Linearized magnetohydrodynamic equations are used.
Electron Diffusion ahead of Shock Waves in Argon
Authors: Weymann H. D.
Published: December 2004

Experiments with electrostatic and magnetic probes were performed to investigate the electron diffusion ahead of shock waves of Ms = 8 to 12 in argon. Negative electrostatic signals of several volts were obtained with pronounced fronts propagating with velocities up to several times the shock velocity. The current produced by the diffusing electrons was determined from a measurement of the azimuthal magnetic field and found to be of the order of 10−5 amp for Ms = 12. By assuming that the electron flow velocity is approximately equal to the velocity of the electrostatic front, the measured current corresponds to an electron density of ne ≈ 107 cm−3 at about 1 m ahead of the shock front.
Damping of the Satellite Wake in the Ionosphere
Authors: Rand S.
Published: December 2004

Landau damping of the ion plasma oscillations which constitute the wake of a line charge moving supersonically through a low-density plasma is studied. Maxwellian distribution functions in the ambient plasma for both electrons and ions have been assumed. It is found that the damping is critical to the question of whether the electrohydrodynamic wake produced by a satellite in the ionosphere is observable, unless the electron temperature is at least an order of magnitude greater than the ion temperature.
Density Compression Ratio across Relativistic-Strong-Shock Waves
Authors: Guess Arnold W.
Published: December 2004

The relativistic Rankine-Hugoniot shock wave conditions of Taub are extended to include radiation pressure and energy density. Specialization to the situation of a nonrelativistic ambient gas gives strong shocks, and solutions are obtained separately for the cases of a pure material gas and a pure radiation gas behind the shock. The material gas is considered to have a constant adiabatic exponent γ ≤ 2, or to be itself relativistic, and the value γ=43 gives the radiation gas results. The rest density compression increases above its nonrelativistic strong shock limit (γ + 1)/(γ − 1), by a term proportional to β2 in the lowest order, where β is the ratio of shock velocity to light velocity. As β → 1 (extreme relativistic strong shock) the rest density compression goes as 1/(1 − β2)½, but there is no setting-in of degeneracy in the shocked gas. In shock coordinates, the flow velocity ratio across the shock (front to back) decreases monotonically from its nonrelativistic limit and approaches the value 1/(γ − 1) as β → 1. An expression is also obtained for the velocity of relativistic sound wave propagation in a mixture of a thermally perfect material gas and a radiation gas.
Diffusion through a Finite Plasma in a Uniform Magnetic Field
Authors: Tonks Lewi
Published: December 2004

The anisotropic diffusion of ions and electrons in a nonmultiplying partially ionized plasma lying in a strong uniform magnetic field has been analyzed to zero and first order in the parameter Ω−1, where Ω2 is the ratio of the reduction of transverse electron mobility to the reduction of transverse ion mobility due to the magnetic field. This obviates the need for an earlier erroneous assumption. Potential distribution and electron and ion current flows have been formulated for two-dimensional flow, using a lowest-harmonic charged-particle distribution in a rectangular space and various wall-current conditions. The encroachment of sheaths inward from the walls has not been considered on the basis that, in principle, the charged-particle concentration could always be assumed to be large enough to keep this complication small.
Shock Wave and Solitary Wave Structure in a Plasma
Authors: Greenberg O. W. , Trève Y. M.
Published: December 2004

Plane steady shock waves and solitary waves in a hydrogen plasma without external magnetic fields are studied using a simple kinetic theory model to describe the plasma. This model uses a Mott-Smith distribution for the protons and a local Maxwellian distribution for the electrons. Charge separations occur inside the shock front because of the proton-electron mass difference. The proton and electron densities, and the electric field, have an oscillatory fine structure with characteristic length ∼10 MλD, where M is the Mach number and λD the Debye length, going through the shock. In these oscillations, the densities overshoot their final Rankine-Hugoniot condition values. The distance in which the oscillations decay to 1/e, which we take as the shock width, is ∼4λ, where λ is the mean free path in the unshocked gas, in the range of Mach numbers considered. There are no continuous solutions for this model above Mach 2.19. The peak electric fields inside the shock are large; in a plasma of λ/λD = 2 × 104, the electric field reaches 2.2 × 106 v/cm in a Mach 2.1 shock. The large-amplitude solitary waves, which are the basic ingredient of the fine structure of the shock, are studied separately, and a heuristic picture is presented of the growth of these solitary waves, which is due to the coupling between the bulk flow of the plasma and the internal electric fields generated by charge separation. The rate of decay of these solitary waves is estimated.
Nonlinear Behavior of the Electrical Conductivity of a Slightly Ionized Gas
Authors: Epstein Melvin
Published: December 2004

Attention is directed to the nonlinear relationship between the current density and field strength of an applied oscillating electromagnetic field. It is pointed out that the general solution of this problem obtained by Margenau is too complex for use in further analyses except for the limiting case of vanishing field strength. A further approximation is introduced which yields a relatively simple expression for the current-field strength relationship, valid for large frequencies and moderate field strengths. It is found that significant nonlinear effects may occur even at small field strengths if the gas density is sufficiently low. The effect of the nonlinearity is to increase that part of the current in phase with the applied field.
Kinematics of Ohmic Heated Plasmas in the B-1 Stellarator
Authors: Bernstein W. , Kranz A. Z. , Tenney F.
Published: December 2004

A kinematic description of the B-1 stellarator plasma during various stages of Ohmic heating discharges is presented. It is shown that for specific ranges of plasma current, for a given confining field, the plasma assumes a shape which has an azimuthal distribution of the form exp im θ. It is further shown that the plasma column rotates at high velocity while the distortion is present. The possible relationship between these current ranges and the predictions of hydromagnetic instability theory is considered.
On Flow Duration in Low-Pressure Shock Tubes
Authors: Roshko Anatol
Published: December 2004

The severe decrease of flow duration in shock tubes operating at low pressures, previously reported by Duff, is confirmed by experiment and by an analysis of the effects of the laminar-boundary layer behind the shock wave. The latter leads to a shock tube similarity length parameter X, which depends on the tube pressure, diameter and shock Mach number, and to a flow duration parameter T. The theoretical relation T = T(X) is determined and compared with experimental results. From the theoretical result Tmax = 1, the maximum possible flow duration τm in a shock tube is determined; it increases linearly with the initial pressure and the square of the tube diameter and decreases strongly with shock Mach number.
Theory of Gas Bubble Dynamics in Oscillating Pressure Fields
Authors: Plesset Milton S. , Hsieh Din-Yu
Published: December 2004

The behavior of a permanent gas bubble in a liquid with an oscillating pressure field is analyzed with a linearized theory. If the assumption is made that conditions within the bubble are uniform, the thermodynamic relations found are as expected; i.e., at low frequencies the bubble behaves isothermally and at high frequencies the behavior becomes adiabatic. However, a more detailed analysis, which allows the bubble interior to vary not only in time but also in space, leads to an average isothermal behavior for the bubble even in the high-frequency limit.
Kirkendall Effect in Gaseous Diffusion
Authors: McCarty K. P. , Mason E. A.
Published: December 2004

An experiment is described which is the analog in gases of the well-known Kirkendall effect in solids. The experiment can also be thought of as a measurement of the pressure differences arising in a diffusing gas mixture. Seven gas mixtures were measured at 30°C and over a maximum pressure range of about 0.2 to 1.7 atm as follows: H2–D2, CO2–C3H8, He–Ar, He–CO2, H2–CO2, D2–CO2, and H2–(H2 + CO2 mixture). The results are discussed in terms of the usual phenomenological theory of the Kirkendall effect and the rigorous kinetic theory of gases. The phenomenological theory is shown to be incorrect, but the kinetic theory is capable of accounting for all the effects observed, usually quantitatively. The results can be used to determine gaseous diffusion coefficients from the observed marker motion, and the diffusion coefficients obtained are in reasonable agreement with those obtained by other methods.
Stabilization of Pinch Discharges
Authors: Colgate Stirling A. , Furth Harold P.
Published: December 2004

The hydromagnetic stability properties of ``hard-core'' pinches are shown to be more favorable than those of conventional ``stabilized pinches.'' Linear ``hard-core'' pinch experiments with a wide range of configurations show a basic consistency with hydromagnetic theory, but all configurations studied so far become unstable at sufficiently high current densities and low particle densities, even if possessed of theoretical hydromagnetic stability. Pinches with nulls in Bθ tend to be much less stable than those with nulls in Bz. ``Inverse stabilized pinches'' yield perfectly reproducible magnetic probe traces at power levels several times those at which ``stabilized pinches'' are unstable. A technique for the study of plasma density distributions is given, based on the propagation of radial compressional waves. The theory of the steady-state pinch is enlarged to include convective effects and is documented by experiment. The role of electrodes is considered, and an anode-cathode asymmetry in instability behavior is demonstrated for the linear ``stabilized pinch.'' The prospects of stable, high-temperature operation with the toroidal hard-core pinch, or ``levitron,'' are discussed.
Deviations from Kinetic Equilibrium in a Stellarator Plasma
Authors: Hirschberg J. G. , Palladino R. W.
Published: December 2004

The increase in Doppler temperature with charge number, found in stellarators, has been remeasured with improved precision for observation parallel to the lines of force. No dependence on position was found, and the results are ascribed tentatively to positive-ion waves parallel to the magnetic field.
Progressive Deformation of a Curved Vortex Filament by its Own Induction
Authors: Hama Francis R.
Published: December 2004

Progressive three-dimensional deformation of an initially parabolic, plane curved vortex due to its own induction is numerically obtained in this paper by the use of the localized-induction concept instead of through the full Biot—Savart law. It is shown that, after the region near the vertex rises up from the plane of the initial orientation, a helical deformation takes place on the legs of the parabola. The helix, which rotates in the direction opposite to the circulatory rotation around the vortex filament, is found to travel away toward the far ends of the parabola as the vertex keeps rising up, while increasing the amplitude and extent of the helical deformation. Similar computations also carried out with a hyperbolic initial shape resulted in essentially the same conclusions as the parabola but with much better numerical stability, as well as with an exponential initial configuration, which grew into somewhat more complicated patterns, yet maintained the essential feature of the helical deformation.
Wave Properties of a Plasma with a Doubly Humped Velocity Distribution
Authors: Ichimaru Setsuo
Published: December 2004

Properties of growing waves are investigated in a uniform plasma with a doubly humped velocity distribution by studying the character of the boundary curves between growing waves and damped waves. The specific family of distribution functions mainly investigated is one which is composed of a Maxwellian main part plus a small gentle bump (also Maxwellian) on its tail. When a parameter describing the shape of the distribution (the relative strength of the small bump, the separation between the two peaks, etc.) is changed from the region of stability, there is a certain wavenumber kc at which the onset of plasma-wave instabilities is expected. Studies are made of the conditions for which kc vanishes, since kc = 0 is associated with a special kind of excitations. A proof is given that the growing wave is not on the same branch of the solution to the dispersion relation as the usual plasma wave.
Some Aspects of Shock Structure According to the Bimodal Model
Authors: Muckenfuss Charles
Published: December 2004

Calculations are made of the shock thickness for several realistic intermolecular force laws, viz., those derived from the Lennard-Jones 6–12, the modified Buckingham exp−6, and the exponential repulsive potentials. Argon and helium are explicitly considered for these calculations; agreement with recent experimental results is good. The central feature of the results for such force laws, as well as for point centers of force, is the interminable broadening of the shock zone with increasing Mach number. It is demonstrated that the shock zone is bounded by an appropriately defined mean free path localized anywhere in the gas, although the definition of a mean free path is not necessary for the calculation of shock thickness. The relationship and properties of the density, velocity, and temperature profiles are investigated. It is found that the center of the temperature profile is upstream of the center of the velocity profile which, in turn, is upstream of the center of the density profile. These results are obtained without explicit evaluation of the extent of the shock zones. Calculations have been made of the number of collisions suffered by a typical molecule in traversing the density and velocity shock zones. These collision numbers approach a finite, nonzero limit as the Mach number increases without limit.
Radiation-Resisted Shock Waves
Authors: Clarke John F.
Published: December 2004

Using a gray-gas quasi-equilibrium theory to describe the radiation effects, the basic integro-differential equation for the one-dimensional flow of a radiating gas is reduced to a nonlinear differential equation by approximating to the radiation absorption functions. The integral curves show that compression waves with velocity profiles having continuous first and second derivatives can exist in the absence of other dissipative mechanisms (radiation-resisted shocks) and approximate analytical solutions for these profiles are constructed.
Stability of a Heterogeneous Shear Layer in a Magnetic Field
Authors: Menkes J.
Published: December 2004

The stability of a horizontal, heterogeneous shear layer subject to a vertical magnetic field of constant magnitude has been investigated. The stabilizing effect of the magnetic field is clearly demonstrated. The behavior of a medium with an exponential density distribution is considered in detail.
Transverse Magnetohydrodynamic Flow Past a Semi-Infinite Plate
Authors: Radlow James , Ericson William B.
Published: December 2004

A viscous, incompressible, conducting fluid flows past a semi-infinite flat plate; the free-stream velocity of the fluid is taken parallel to the plate, and there is an applied magnetic field perpendicular to the plate. Physical arguments are given for a certain linearization of the basic steady-state equations, and the linearized equations are solved by an approximation method based on the Wiener-Hopf technique. An error estimate for the approximation is derived. The induced magnetic field, measured at the plate, is found to differ from the applied magnetic field by a multiplicative factor, whose value depends on the physical properties of the fluid and is constant for any given fluid. If the conducting fluid is a liquid metal (mercury or liquid sodium), edge effects can reasonably be neglected in calculating skin friction at the plate. An experimental study of the physical conclusions should be relatively manageable.
Structure of Collision-Free Magnetohydrodynamic Waves
Authors: Wilson Theodore A.
Published: December 2004

Properties of the two-fluid plasma equations which lead to a partial theoretical model for the collisionless shock wave are investigated. First, a nonlinear symmetric-pulse solution to the two-fluid equations for a cold collisionless plasma is described. The propagation speed of the pulse is between the Alfvén speed and the fast-wave speed, and the pulse thickness is of the order of (mic2/4πe2N)½, except for geometries in which the wave normal makes an angle of the order of (me/mi)½ or less with the upstream magnetic field. An effective conductivity is then introduced in the equations of motion of the plasma and a shock thickness is estimated. The calculated dependence of shock thickness on Mach number is shown to agree with the available experimental data. Finally, the growth of a sinusoidal pinch instability of a current-carrying plasma is shown to have the average effect of a finite conductivity as was postulated.
Poiseuille Plasma Experiment
Authors: Emmons H. W. , Land R. I.
Published: December 2004

The flow of gas and electric current simultaneously through a tube provides an experimental arrangement for the study of the flow of high-temperature gases capable of precision measurements and a precise mathematical theory. The precision experimental technique and some initial experimental results together with a simplified theory are presented in this paper. Mean electrical conductivities and kinematic viscosities are given for a number of gases. The arc performance is shown to be predictable with fair precision by a very simple discontinuous model of the plasma properties which is capable of wide exploitation in magnetohydrodynamics.
High-Frequency Conductivity of a Fully Ionized Plasma
Authors: Oberman Carl , Ron Amiram , Dawson John
Published: December 2004

A complete classical derivation of the frequency-dependent conductivity is presented which properly takes into account collective dynamics. This treatment rests on the joint solution of the first two members of the BBGKY hierarchy, in the plasma limit, when both are able to change on the same time scale. For arbitrary frequencies this leads to an integral equation for the one-particle distribution function which can be solved by conventional variational and/or numerical procedures. For frequencies high compared to the collision frequency, an explicit statement of the conductivity is possible. This high-frequency limit is further examined in the limit of small electron to ion mass ratio and these limiting results are compared with those of other authors.
Interaction between Cold Plasmas and Guided Electromagnetic Waves. II
Authors: Mower Lyman , Buchsbaum S. J.
Published: December 2004

The interaction between cylindrically symmetric anisotropic plasma column and bounded electro-magnetic waves is analyzed theoretically. The properties of a cylindrical cavity coaxial with a cold plasma column and a coaxial with a static magnetic field are determined. The shift in the resonant frequency of the cavity-plasma system is calculated in the high-electron-density limit and compared with the numerical solution presented earlier.
Momentum Transfer between Gas Molecules and Metallic Surfaces in Free Molecule Flow
Authors: Stickney Robert E.
Published: December 2004

Measurements of the normal momentum transfer between gases and metallic surfaces were obtained under conditions of free molecule flow with a torsion balance and molecular beam apparatus. Helium, hydrogen, neon, nitrogen, carbon dioxide, and argon were investigated on tungsten, platinum-blackened-tungsten, platinum, and aluminum surfaces which were contaminated to an undetermined degree with oxides and adsorbed gases. A thermal beam of gas molecules was directed against the test surface at normal incidence, and momentum transfer measurements were obtained with the surface at various temperatures over the range 25° to 550° C.

The experimental results indicate that the efficiency of the momentum transfer process increases with the molecular weight of the test gas and the roughness of the test surface, but is relatively independent of the substrate material under the present conditions. The momentum transfer rates for helium and hydrogen are significantly less than those measured for the heavier gases at the same surface temperature. The accommodation of the test gases to the surface temperature appears to be incomplete except, possibly, for argon and carbon dioxide. The results cannot be explained successfully by means of the classical model which assumes that the re-emitted gas consists of two components, one experiencing specular reflection and the other complete accommodation at the surface. A modified model and a corresponding momentum accommodation coefficient are introduced and employed in the discussion of the experimental data.
Comparison of Kinetic Theory Analyses of Linearized Couette Flow
Authors: Willis D. Roger
Published: December 2004

Linearized Couette flow is considered for Knudsen numbers ranging from zero to unity using Krook's kinetic model. The velocity and stress are calculated from the numerical solution of an integral equation for the velocity. By comparison with independent calculations the relative error of these results is estimated as less than 0.2%. For the particular case of slip flow, the constant in the boundary condition is evaluated from a numerical quadrature. The accuracy of several analytic methods is compared with particular emphasis on the method of Gross, Jackson, and Ziering and that of Lees.

Using previous results obtained for Knudsen numbers greater than unity it is confirmed that some form of iteration, based on an integral equation formulation, is needed to give accurate results in the nearly free molecular regime. Further, such an iteration significantly increases the accuracy of the results over the entire transition regime down to Knudsen numbers as low as one third.