bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Theory of Drift-Wave Turbulence and Enhanced Diffusion
Authors: Dupree T. H.
Published: December 2004

The turbulent plasma state which develops from unstable, current-driven drift waves is analyzed. In the nonlinear theory, the wave growth predicted by the linear theory is ultimately suppressed by ion damping. Since the phase speeds of the unstable waves are much greater than the ion thermal velocity, the ions cannot absorb wave energy until they become trapped. The amplitude of the turbulent spectrum grows until trapping occurs, and a quasi-steady state is reached in which the directed electron energy is converted into ion thermal energy at a constant rate. In this state the perturbation of the density gradient due to the turbulence is equal to the mean gradient. Nonlinear limitation due to mode coupling does not suppress the unstable wave growth until much larger density perturbations have developed. Therefore, ion trapping is established as the controlling nonlinear mechanism. In the steady state, the ions diffuse across the magnetic field with a diffusion coefficient D⊥ ≈ (k⊥ −2γ)max, where γ is the growth rate predicted by the linear theory and k⊥ is a perpendicular wavenumber. Although the detailed treatment is for a specific instability, the general conclusions appear to apply to a variety of drift waves.
Magnetic-Compression Waves in Collisionless Plasma—Oblique Ambient Magnetic Field
Authors: Rossow Vernon J.
Published: December 2004

Numerical analysis is made of the structure of one-dimensional unsteady magnetic compression waves propagating into collisionless plasmas when the ambient magnetic field is oblique to the wave direction. Integration of the equations of motion is carried out by dividing the flow field into discrete elements or slabs of plasma and following their motion on a digital computer. Results from these calculations show that both the sub- and supercritical solutions change continuously from one limiting situation to the other. A similarity rule is found for correlating the subcritical cases so that the two-parameter family of solutions in mass ratio and field angle are reduced to a single set.
Electrical Conductivity of a Partially Ionized Gas
Authors: Johnson L. C.
Published: December 2004

Electron velocity distribution functions for a partially ionized gas in a weak, steady electric field are obtained by solving the Boltzmann-Fokker-Planck equation numerically. As in the case of a fully ionized gas, the electron-electron interactions in a partially ionized gas affect the velocity distribution function and, consequently, the electrical conductivity. Electrical conductivities are calculated for a variety of assumed electron-molecule collision frequencies. The results differ by only a few percent from those obtained using an approximation suggested by Frost. A simple procedure, requiring no numerical integrations, is given relating electron temperature to electrical conductivity for a partially ionized gas.
Heat Transfer from Circular Cylinders at Low Reynolds Numbers. I. Theory for Variable Property Flow
Authors: Kassoy D. R.
Published: December 2004

The low Reynolds number flow past a heated infinite cylinder is studied for cases involving significant variation of fluid properties, and when thermal and velocity slip is present at the wall. Initially, the inner and outer asymptotic expansions for the flow field variables are derived for an arbitrary thermal conductivity-temperature relationship. The corresponding Nusselt number, developed in terms of the expansion parameter ε = [ln (4/RePr) − γ̄ + β]−1 (where Re is the Reynolds number, Pr is the Prandtl number, γ̄ is the Euler's constant and β is the thermal slip parameter), is valid to order ε3. For the special case λ = Tω an explicit relationship Nu = Nu (Re, Pr, τ, ω, β) is given, where τ = (T′w − T′∞)/T′∞. It is shown that the continuum and slip Oseen-type analyses of Cole and Roshko, and Levey, respectively, are zeroth-order approximations for the Nusselt number in the limit τ → 0. The zeroth-order drag coefficient is also given in the form CDo = CDo(Re, τ, ω, f), where f is the velocity slip parameter.
Heat Transfer from Circular Cylinders at Low Reynolds Numbers. II. Experimental Results and Comparison with Theory
Authors: Aihara Y. , Kassoy D. R. , Libby Paul A.
Published: December 2004

The heat loss from wires in nitrogen, helium, and mixtures thereof has been measured at low Reynolds numbers and has been compared with the theory of Kassoy. The data in nitrogen agree well with previous data and with the theory for continuum flow and validate the experimental techniques. The helium data exhibit large slip effects at low Knudsen numbers due to the low thermal accommodation coefficient of helium; good agreement with the theory of Kassoy for slip effects is found. Some data exhibiting slip in helium-nitrogen mixtures are given. A mixture rule for the effective thermal accommodation coefficient in binary mixtures is suggested.
Adiabatic Excitation Transfer in Gases: Effects on Transport
Authors: Nyeland Carl , Mason E. A.
Published: December 2004

A calculation is made of the contribution to the transport coefficients from adiabatic excitation transfer in atomic gases. Atomic nitrogen is chosen as an example, and the necessary potential curves are determined partly from spectroscopic data and partly from Heitler-London calculations. Exchange greatly reduces the rate of diffusion of internal electronic energy, and the contribution of the 2D and 2P excited states of N to the thermal conductivity at 10 000°K is reduced by a factor of 3 (from 48% to 16% of the translational thermal conductivity). Reasons are given to suppose that such behavior is fairly general, and not restricted to nitrogen.
Measurement of Emission and Absorption of Radiation by an Argon Plasma
Authors: Evans D. L. , Tankin R. S.
Published: December 2004

Volumetric radiative loss measurements, correlated with temperature in the range of 10 000 to 26 000°K, have been made on an argon plasma. Pressures of 0.5, 1.0, and 2.0 atm have been used. The 1.0-atm measurements have been corrected for both absorption and ultraviolet emission and the results agree with those of Emmons in the common temperature range. The 6965 Ar I line has also been studied yielding lineshifts, halfwidths, absorption and emission coefficients. The line shift and halfwidth results are below theoretical predictions. Transition probabilities determined from both emission and absorption studies are found to be in reasonable agreement.
Test Waves in Weakly Turbulent Plasmas
Authors: Aamodt R. E.
Published: December 2004

The basic ideas of weak turbulence theory are discussed, and the nonlinear theory of collisionless plasma dynamics is formulated in terms of test-waves. The test-wave method is interpreted and compared to the usual mode coupling expansion technique. The smearing of the particle-wave resonances and the nonlinear coupling of unstable modes are discussed in detail.
Turbulent and Pressure Transport in a Curved Mixing Layer
Authors: Rapp A. F. , Margolis D. P.
Published: December 2004

The turbulent transport terms in an unstable curved mixing layer were measured so that the pressure transport terms were the terms in the energy balance obtained by difference. The turbulent and pressure transport terms are of the same order of magnitude.
Magnetic Moment Under Short-Wave Electrostatic Perturbations
Authors: Taylor J. B.
Published: December 2004

In the presence of an electrostatic wave the quantity μ0 = v⊥2/B is no longer an approximate invariant, contrary to the conclusion of earlier authors. The real invariant is calculated and an anomaly in minimum-B stability theory is thereby removed.
Direct Measurement of the Confinement Time of Cesium Plasma in a Q-Device
Authors: Von Goeler S. , Motley R. W.
Published: December 2004

The confinement time of a plasma in a Q machine has been measured by observing the decay of plasma density after the atomic beam producing the plasma has been shut off. At high density the main loss appears to be end plate recombination. At low densities anomalous losses occur.
Radiation-Driven Acoustic Waves in a Confined Gas
Authors: Long Hartwell R. , Vincenti Walter G.
Published: December 2004

Preliminary to a projected experimental program, the linearized theory of radiative gas dynamics is applied to the problem of the standing acoustic waves produced inside a closed cylindrical tube by a sinusoidal input of radiation at one end of the tube. The gas in the tube is taken to be perfect, optically grey, and in local thermodynamic equilibrium; the radiative transfer is treated on the basis of the differential approximation. The results of dimensionless, parametric calculations are analyzed in terms of the two types of simultaneous harmonic acoustic waves present in the theory: (1) the modified classical wave and (2) the radiation-induced wave. For temperatures and pressures attainable in the laboratory, the results show a marked resonance effect from tuning of the tube length with respect to the wavelength of the modified classical wave. The resonance condition exhibits equal levels of pressure and velocity response with marked spatial variation in both quantities. In certain situations the off-resonance condition is dominated by the radiation-induced wave. Here the pressure response is spatially uniform and several orders of magnitude larger than the nonuniform velocity response.
Free-Flight Theory of Gas Mixtures
Authors: Monchick L. , Mason E. A.
Published: December 2004

A free-flight theory is developed for transport processes in gases and gas mixtures. In the limit of infinitely many free flights, an integral equation is found similar to that given by the Chapman-Enskog second approximation, but the two theories are not equivalent because they obey somewhat different auxiliary conditions. This is interpreted to mean that the free-flight method describes a relaxation process and the Chapman-Enskog method a quasi-steady state. For Maxwellian molecules the free-flight theory is summed to all orders; this allows an estimate of the rate of convergence and demonstrates the close resemblance to the old persistence-of-velocity arguments. With no ad hoc assumptions, the free-flight theory yields a nonzero thermal diffusion effect in first order, which depends for its existence on the variation of the collision frequency with molecular speed. This furnishes the first rigorous elementary explanation of thermal diffusion.
Properties of the Fokker-Planck Equation
Authors: Liboff Richard L. , Fedele James B.
Published: December 2004

It is shown that the stochastically derived Fokker-Planck collision term, JF, satisfies the conservation equations regardless of the form of the interparticle force law. The form of JF for inverse power potential laws is obtained, and is compared with the form obtained from the expansion of the Boltzmann collision integral about grazing collisions. The two expressions are equal for the Coulomb case only. The expanded Boltzmann operator fails to satisfy the conservation laws for any other inverse power potential law. The relation between the ``diffusion'' coefficient b and the ``friction'' coefficient a, ▿·b = a, is found to hold only for the r−1 interparticle potential. An H-theorem is presented for the Fokker-Planck collision term.
Diffusion Approximation to Inertial Energy Transfer in Isotropic Turbulence
Authors: Leith C. E.
Published: December 2004

A diffusion approximation is described to the nonlocal inertial energy transfer between wavenumber components in the spectral representation of an isotropic turbulent flow. The approximation yields Kolmogorov's inertial-range spectrum and is shown to be the local limit of a class of approximations suggested by Kraichnan and Spiegel. A spectrum in the viscous dissipation range is computed with the diffusion approximation and compared to spectra obtained from approximations of Heisenberg and Kovasznay as well as a modification of Obukhov's approximation and a recent prediction of Kraichnan. It agrees closely with the last two. Similarity spectra and associated longitudinal correlation functions are computed for decaying turbulence at infinite Reynolds number. A comparison is made with corresponding results based on the Heisenberg approximation.
Magnetohydrodynamics in a Reacting Medium
Authors: Liboff Richard L. , Caroff Lawrence J.
Published: December 2004

The effect of ionization and recombination on the propagation of waves through a three-component, magnetoactive plasma is examined in the magnetohydrodynamic limit. Ionization and recombination are assumed to result from several types of reactions. A new set of nonlinear equations is derived to describe the dynamic behavior of the system. To first-order in the coupling frequencies, the magnetohydrodynamic waves are exponentially damped with a time constant which is isotropic for the Alfvén mode and slightly anisotropic for the fast and slow modes. The sound mode in the neutral fluid is damped with a time constant which is also isotropic. All modes are stable.
Electron Distribution Function in a Plasma with Excitation Collisions
Authors: Mjolsness R. C. , Petschek A. G.
Published: December 2004

The electron distribution function is obtained for a spatially uniform, steady-state plasma having electron-electron, electron-ion and excitation collisions. The Fokker-Planck terms are linearized and the field-particle distribution functions are approximated by highly singular functions which reproduce the first three moments of Maxwellian distributions. Approximate self-consistency of the procedure is shown. The simplification is such as to permit the second-order difference-differential equations describing the electron distribution function to be solved in simple analytic form. For energies larger than the excitation energy, the solution is a Maxwell distribution with an altered electron ``temperature'' which depletes the tail of the distribution. The solution is examined in various limiting cases, and its effect on reducing ionization rates in the plasma is discussed.
Quasi-Static Ion Cyclotron Waves
Authors: Swanson D. G.
Published: December 2004

Experiments by Kristiansen and Dougal have shown that ion cyclotron waves propagate in broad bands above the ion cyclotron frequency, and hence that finite Larmor radius effects are important even in moderate temperature plasmas. Investigation of the quasi-static dispersion relation leads to the observed features when the wavelength perpendicular to the field is allowed to be small compared to the Larmor radius. Results indicate that finite Larmor radius effects can dominate the dispersion relation, that the parallel wavelength is independent of density when they do, and that a maximum ion temperature from ion cyclotron resonance heating exists for quasi-static waves which depends only on the phase velocity parallel to the magnetic field.
Trajectories of Magnetic Field Lines in Toroidal Stellarators
Authors: Gibson A.
Published: December 2004

Computations are presented to show that in a toroidal ℓ=3 stellarator, in addition to the wellknown inward shift of the magnetic axis the following effects occur: the rotational transform on the last closed surface is substantially less than the winding transform; the closed and open surfaces are separated by a complex region; the shape of the surfaces in the central region is essentially as predicted by Aleksin. The maximum shear available in a feasible stellarator is estimated and compared to that required for stability. The effect of perturbations on the perfect toroidal system is computed.
Observations of a Resonance Probe Effect near the Ion Plasma Frequency
Authors: Toepfer Alan J.
Published: December 2004

The ion resonance effect, a phenomenon in which the rectified current to an ac-driven, positively biased Langmuir probe exhibits a peak near ion plasma frequency, is investigated experimentally. Results indicate that the resonance occurs above the ion plasma frequency.
Electrostatic Relaxation Waves in an Isotropic Lorentz Gas
Authors: Derfler Heinrich
Published: December 2004

A calculation of the dispersion of electrostatic waves in a Lorentzian electron gas takes Landau damping and the detailed balancing of elastic electron-atom collisions rigorously into account. As a special case, the further analysis is restricted to rigid elastic spherical molecules and a monoenergetic distribution of electron velocities. This eliminates Landau damping and Van Kampen modes in favor of new effects associated with the collision process. One thus exposes a discrete spectrum of pseudo-sound waves and a continuous spectrum of relaxation waves both due to the infinitely many harmonic patterns into which electrons can be scattered by elastic spheres.
Unsteady Magnetohydrodynamic Flow Past Thin Bodies with Inwardly Diffusing Magnetic Field
Authors: Fan Dah-Nien
Published: December 2004

A rational small-perturbation theory is proposed for treating an initial- and boundary-value problem in magnetohydrodynamic flow past thin symmetrical bodies with the thickness parameter ε as the perturbation parameter. An irrotational flow over the body is established initially in the total absence of electromagnetic interactions. The fluid is assumed to be incompressible, inviscid, and electrically conducting. Moreover, it is bounded by two infinite parallel planes outside which vacuum prevails. The external magnetic field is then imposed by turning on current sheets of constant intensity at the fluid-vacuum boundaries. The zeroth- and first-order solutions are obtained analytically for an arbitrary body shape. The establishment of Lary's steady flow past a thin body at super- or sub-Alfvénic conditions, the existence of small-perturbation solutions at exactly Alfvénic flows, and the appearance of an accumulation point of poles to characterize the transient behavior of a physical system are the interesting features which emerge in the course of the present work.
Similarity Solutions for the Compressible Laminar Boundary Layer with Heat and Mass Transfer
Authors: Ball K. O. W.
Published: December 2004

Similarity solutions are presented for the compressible boundary layer with reverse flow velocity profiles showing the quantitative effect of pressure gradient and heat and mass transfer on the wall shear stress and temperature gradient. Three suction parameters as well as wall temperatures ranging from absolute zero to twice the free-stream stagnation temperature are investigated for numerous adverse pressure gradients.
Thickness of a Shock Wave in Hydrogen
Authors: Gross Robert A.
Published: December 2004

Thickness of a shock wave in hydrogen is estimated over a wide range of shock velocity. Different speed regimes have their own characteristic shock thickness. Very strong shock thickness is proportional to the Coulomb mean free path in the post shock plasma.
Use of Self-Calibrating Catalytic Probes to Measure Free-Stream Atom Concentration
Authors: Reddy N. M.
Published: December 2004

A technique is presented to measure simultaneously the catalytic efficiency (φc) and the atom concentration (α∞) in a dissociated hypersonic free stream. The principle involved is to measure the differential heat transfer by using a combination of axisymmetric and two-dimensional differential catalytic probes, mounted side by side in an uniform free stream. Using these measured quantities in the appropriate stagnation point heat-transfer relations for a frozen flow, simple formulas for φc and α∞ are derived, which are independent of such quantities as viscosity, velocity, and density. This self-calibrating principle is shown to apply even in the viscous shock layer (merged layer) regime. The most suitable geometric proportions for the probes are given. The practical feasibility of this technique has been successfully demonstrated by measuring the gauge-catalytic efficiency of a silver surface and the free-stream oxygen atom concentrations in the University of Toronto Institute of Aerospace Studies 11 × 15-in. hypersonic shock tunnel test section. The free-stream atom concentration α∞ was measured at five reservoir conditions (14.2 atm ≤ P0 ≤ 40.7 atm, 4530°K ≤ T0 ≤ 4700°K, 0.54 ≥ α0 ≥ 0.32) and varied from 0.30 to 0.16. The measured values of α∞ compared favorably with those computed from coupled vibrational and dissociational nonequilibrium nozzle flow calculations.
Kinetic Theory of Two-Temperature Plasmas
Authors: Kruger C. H. , Mitchner M.
Published: December 2004

A closed formulation is presented for the electron energy equation together with the associated electron transport properties, applicable to a two-temperature partially ionized gas at intermediate and high degrees of ionization. Complete and simplified formulas to arbitrary levels of approximation in the Chapman-Enskog sense are given for the calculation of the electron thermal and electrical conductivities and thermal diffusion coefficients in the presence of a magnetic field. The effects of nonelastic collisions on electron transport property calculations are discussed and a criterion is presented for assessing when such collisions may be neglected.
Stability of a Magnetohydrodynamic Half-Jet. III. Inviscid Stability of a Compressible Magnetohydrodynamic Half-Jet
Authors: Lessen Martin , Deshpande Narayan V.
Published: December 2004

The inviscid stability of the laminar mixing of an infinitely conducting compressible fluid in the presence of an aligned magnetic field is investigated with respect to two-dimensional wavy disturbances. It is found that an increase in the Mach number increases the wave speed of a neutrally stable disturbance for all values of the magnetic field. With increasing Mach numbers the wavelength of a neutral disturbance increases for weak magnetic fields while it decreases for strong magnetic fields. The inviscid flow is unstable.
Large Amplitude Electrothermal Waves in a Nonequilibrium Plasma
Authors: Zukoski Edward E. , Gilpin Robert R.
Published: December 2004

Steady, one-dimensional current streamers have been observed in a nonequilibrium plasma subjected to crossed E and B fields. Their half-width and amplitude agree with a nonlinear model of electrothermal waves.
Doppler Measurements of the Kinetic Energies Produced in Radio-Frequency Plasmoids
Authors: Trimmier J. R. , Miller A.
Published: December 2004

Measurements of the Doppler widths of the emission lines from radio-frequency plasmoids show that the ions and atoms have much higher kinetic energies in a discharge which forms dark-ring radio-frequency plasmoids than in a discharge which does not form such plasmoids. The values of the translational kinetic energy are shown to depend on the peak rf excitation voltage and the system gas pressure. These experimental results seem to support the potential-well model of plasmoid formation at low pressure and at low rf excitation voltage.
Nonlinear Asymptotic Analysis of the Positive Column
Authors: Friedman Herbert W.
Published: December 2004

The positive column of a slightly ionized gas discharge confined by cold, insulating walls is described by a set of nonlinear fluid equations. The inertia, space charge, and collision terms are retained. A zeroth-order solution uniformly convergent to the exact solution in both plasma and sheath regions is derived using asymptotic boundary-layer analysis. The value of potential at the wall is calculated by means of a kinetic model. It is found that the density at the wall can be a significant fraction of the value at the center and that it vanishes only in the low electron temperature limit. The original Bohm criterion is recovered as a necessary condition for sheath stability and is interpreted to mean that the ambipolar sound speed (1) asymptotically separates the plasma from the sheath, and (2) is the maximum ambipolar diffusion velocity.
Effective Ohm's Law in a Partially Ionized Plasma with Electron Density Fluctuations
Authors: Louis Jean F.
Published: December 2004

Theories and experiments show that instabilities exist in plasma operating at Hall coefficient larger than one. An effective Ohm's law applicable to plasma with homogeneous electron density fluctuations appears to explain available experimental results.
Sound Dispersion in Dilute Monatomic Gases
Authors: Ranganathan S. , Nelkin Mark
Published: December 2004

The location of the frequency shifted peak in Brillouin scattering is analyzed within the Burnett approximation. The sound dispersion determined from this peak is negative whereas that from sound propagation is positive.
Dynamics of Hemispherical Phase Growth in Nonuniform Temperature Fields
Authors: Cheh H. Y. , Tobias Charles W.
Published: December 2004

Theoretical calculations on the dynamics of asymptotic bubble growth in initially nonuniform temperature fields resulting from the constant wall temperature and the constant heat flux experiments are presented.
Differential Formulations for Radiative Transfer in Nongray Gases
Authors: Liu J. T. C. , Clarke Joseph H.
Published: December 2004

Using approximate forms of the absorption coefficient, the frequency-integrated differential formulations for nongray gases are obtained for continuum and for line radiation.
Velocity of Moving Striations
Authors: Garscadden A. , Lee D. A.
Published: December 2004

The phase velocity of moving striations is calculated from the theory of Pekarek. It is shown that in the ambipolar diffusion regime this gives satisfactory agreement with recent measurements on the variation of striation velocity as the gas pressure is changed.
Development of Turbulence during the Build-Up of a Boundary Layer at a Concave Wall
Authors: Tillmann Walter
Published: December 2004

In an apparatus used earlier for experiments in the flow between concentric rotating cylinders, the boundary layer generated on the inner surface of the outer cylinder is investigated. The development of the laminar boundary layer can be calculated. Its instability against cellular disturbances (Görtler vortices) and the transition to turbulent motion are observed by flow visualization. The rapidly passing phenomena are recorded in slow-motion pictures. In regard to the wavelength of the vortices, it is discussed that the occurring vortices are those with maximum amplification. The distinct kinds of transition for different speeds of the initial flow are described.
Flow Disturbances Induced by Low-Drag Boundary-Layer Suction through Slots
Authors: Pfenninger W. , Bacon J. , Goldsmith J.
Published: December 2004

Suction flow fluctuations induced at higher slot flow Reynolds numbers Res ≡ v̄ s/v by oscillating slot wakes in the plenum chambers underneath the slots apparently caused premature transition on a 33° swept laminar suction wing at high wing chord Reynolds numbers. With viscous slot wakes at Res ≤ Rescrit such disturbances were absent with full laminar flow beyond 50 × 106 length Reynolds number. Rescrit increases from 100 for relatively deep plenum chambers to over 200 for shallow plenum chambers with two rows of suction holes located at opposite sides of the slot.
Stability of Couette Flow with Stabilizing Centrifugal Forces
Authors: Schultz-Grunow F.
Published: December 2004

The circular Couette flow is considered with the outer cylinder rotating and the inner at rest. The transcendental equation established earlier by Sexl is solved. In the limiting case of a very small gap the results for the stability parameter and the velocity of the perturbation waves is exact. The results, however, differ from earlier results obtained for plane walls. This case now appears to be singular.
Digital Experiment in Spiral Turbulence
Authors: Coles D. , Van Atta C. W.
Published: December 2004

Digital measurements in a stationary mixed laminar-turbulent flow show that the turbulent region is highly inhomogeneous and that the mean flow is highly three-dimensional.
Secondary Currents in Wall Turbulence
Authors: Hinze J. O.
Published: December 2004

Considering the region not too close to the wall, application of the usual boundary-layer approximations to the balance equation for the turbulence kinetic energy leads to the following rule: When in a localized region the production is much greater (smaller) than the dissipation, there must be a secondary current that transports turbulence-poor fluid into (outwards) this region and turbulence-rich fluid outwards (into) the region. Depending on conditions the secondary current is either towards or away from the wall. Experiments at Delft on turbulent flow through a conduit of rectangular cross section with one of the long side walls partly corrugated showed secondary currents in the transition region from rough to smooth wall as well as in the corner regions in agreement with the above rule.
New General Law for the Turbulent Dissipation Integral
Authors: Walz Alfred
Published: December 2004

The calculation of averaged turbulent boundary-layer quantities for given outer flow conditions is usually based upon the integral conditions for momentum and energy. To apply these equations some empirical relations, for instance for the dissipation integral, must be known. A new general representation of the dissipation integral is derived and successfully checked by characteristic examples.
Large Eddy Structure of the Turbulent Wake behind a Circular Cylinder
Authors: Payne F. R. , Lumley J. L.
Published: December 2004

Application of Lumley's definition of ``large eddy'' to Grant's measurements in a cylinder wake yields, for the dominant mode, a counter-rotating eddy pair having cores approximately normal to the wake plane, in a plane parallel to the cylinder, and planes of circulation roughly normal to the maximum positive strain rate.
Helical Circulations in the Planetary Boundary Layer
Authors: Angell J. K. , Pack D. H.
Published: December 2004

Constant volume balloon (tetroon) flights within the planetary boundary layer provide evidence for the existence of alternating, horizontal roll vortices with axes in the general direction of the mean flow. The dimensions of these vortices are a function of stability. A study of the energetics of the vortices suggests that the kinetic energy flux from mean sheared flow to vortex averages about 4 cm2 sec−3 whereas the kinetic energy flux from vortex to turbulent eddies averages about 21 cm2 sec−3. This implies that the vortices derive the bulk of their energy from buoyancy effects. The mean sheared flow appears not to provide any energy to the vortex which (with the assumption that the vortices are at an angle to the mean flow) is rotating in opposition to the shear of the mean flow.
Generation of Secondary Circulation in a Rotating, Stratified Fluid
Authors: Kao S.-K.
Published: December 2004

A general expression is developed for the generation of a secondary vorticity in a rotating, stratified fluid. The effects of the rotation, compressibility, and density stratification of the fluid on the generation of secondary circulation in various scales of motion are examined. Applications to the generation of the secondary circulation in the boundary layers of the atmosphere and ocean are made.
Turbulent Water-Vapor Transfer at Different Stability Conditions
Authors: Högström Ulf
Published: December 2004

An analysis is performed which is based mainly on 45 turbulent water-vapor flux measurements and simultaneous profile data. The Monin-Obukhov similarity theory is shown to be a convenient basis for the analysis except in the case of extremely stable stratification. Evidence is presented that the exchange coefficient for water vapor Kw, is equal to the exchange coefficient for heat KH, at all stabilities. For ``the free convection regime'' Priestley's constant h is determined to equal 1.25±0.1. The constant c2 of the Monin-Obukhov limiting linear expression for high stability is found to be 9.5. This gives an upper limit for the flux Richardson number of 0.10, in good agreement with recent findings. An attempt is also made to treat the case of stabilities beyond that of the ``critical Richardson number,'' based on Liljequist's measurements from the Antarctic.
Diffusion of Smoke from a High Stack
Authors: Hino Mikio , Homma Masao , Senshu Toshio
Published: December 2004

Experiments on smoke diffusion from high stacks of thermal electric power stations give the following results: The maximum time-average gas concentration at ground level is shown to decrease, within a range of sampling times from 1 to 5 h, inversely proportional to the ½ power of the sampling time as predicted from turbulence theory by Inoue, Ogura, and Hino. The diffusion formulas generally used give a higher estimation of ground-level concentration than the observed. The height of atmospheric surface boundary layer is greatest at neutral condition, becoming less with a deviation from neutral to stable or unstable stratification of atmosphere.
Upper Ocean Boundary-Layer Flow Determined by Dye Diffusion
Authors: Ichiye Takashi
Published: December 2004

Dye patches released in the upper layer of seas indicate that the rate of increase with time of the second moments of concentration follows the Kolmogoroff's hypothesis for the inertial subrange. The curvature of dye patches photographed from the air can be explained as the vertically differential advection by the Ekman type wind-driven currents in the upper boundary layer of the ocean. Striations of patches or plumes seem to be related to cellular motion generated by the short-crested surface waves. The power spectra of concentration fluctuations determined across a dye plume show shift of the peak towards lower wave numbers (measured lateral to the plume) and its flattering with time. These spectral features are compared with a model similar to Heisenberg's energy transfer model by use of Kolmogoroff's energy spectrum.
Turbulence in the Atmospheric Boundary Layer
Authors: Monin A. S.
Published: December 2004

The specific features of atmospheric boundary-layer turbulence are described. The small-scale properties of atmospheric turbulence depend very little on the peculiarities of its large-scale components and obey approximately the laws of locally isotropic turbulence. It is shown that turbulence is locally axisymmetric in respect to the vertical direction and depends upon the buoyancy parameter. Large-scale turbulence obeys a similarity theory based upon the ``external'' parameters such as the geostrophic wind velocity, potential temperature difference across the boundary layer, roughness height of the underlying surface, the Coriolis parameter and the buoyancy parameter. The dynamic equations for the first- and second-order statistical moments of turbulence are formulated and analyzed.
Handover in Scale of the Fluxes of Momentum, Heat, etc. in the Atmospheric Boundary Layer
Authors: Priestley C. H. B.
Published: December 2004

The handover of the vertical fluxes of momentum, heat, etc., from the small-scale turbulence close to the earth's surface into the larger-scale motions above is becoming an important question in the context of numerical treatment of atmospheric dynamics. In convective conditions, a decoupling of heat flow from the surface value is suggested at a height of some 5 to 10 times the Obukhov scale height, at times lower. Some changes in regime are already well documented below this level. Above it, the need for direct measurement of the eddy heat flux on the cumulus scale, and location of the roots of these circulations, is emphasized. For momentum flux the handover from microscale direct into the synoptic scale is considered primarily. At a level where the microscale flux has fallen from its surface value τ0 to τ, the vertical motion in unaccelerated flow is ρw = curl [(τ0 − τ)/f], where f is the Coriolis parameter. When this is viewed as a component of eddy motion on the global scale, the resultant eddy transport of momentum is found to be insignificant. But the asymmetry of acceleration patterns in the westerlies, particularly that broadly associated with the transient frontal systems, appears to yield significant momentum flux in the required direction. This defines the need for a clearer identification of the typical acceleration patterns and for numerical solutions of the appropriately modified boundary layer equations. The momentum flux attributable to thermal wind and the handover into mean meridional circulation are also discussed.
Variance of Local Concentration Fluctuations
Authors: Csanady G. T.
Published: December 2004

Some recent work on mean-square fluctuations in turbulent diffusion is extended to the case of a continuous line source in a uniform field. The balance equation for the mean-square fluctuation (which is obtained from the equation of continuity) is solved with the aid of ``K theory''-type hypotheses on the flux of concentration and on the flux of mean-square fluctuation. As in the case of the continuous point source, good agreement between theory and experiment is found. The results raise interesting questions regarding the dependence of the dissipation time scale on the structure of turbulence.
Contextual logic for quantum systems
Authors: Domenech Graciela , Freytes Hector
Published: December 2004

In this work we build a quantum logic that allows us to refer to physical magnitudes pertaining to different contexts from a fixed one without the contradictions with quantum mechanics expressed in no-go theorems. This logic arises from considering a sheaf over a topological space associated with the Boolean sublattices of the ortholattice of closed subspaces of the Hilbert space of the physical system. Different from standard quantum logics, the contextual logic maintains a distributive lattice structure and a good definition of implication as a residue of the conjunction.
Necessary and sufficient conditions for n-dimensional conformal Einstein spaces via dimensionally dependent identities
Authors: Edgar S. Brian
Published: December 2004

Listing has recently extended results of Kozameh, Newman, and Tod for four-dimensional space–times and presented a set of necessary and sufficient conditions for a metric to be locally conformally equivalent to an Einstein metric in all semi-Riemannian spaces of dimension n⩾4—subject to a nondegeneracy restriction on the Weyl tensor. By exploiting dimensionally dependent identities we demonstrate how to construct two alternative versions of these necessary and sufficient conditions which we believe will be useful in applications. The four-dimensional case is discussed in detail and examples are also given in five and six dimensions.
Two and three dimensional Hamiltonians with generalized and ordinary shape invariance symmetry
Authors: Panahi H. , Jafarizadeh M. A.
Published: December 2004

Two and three dimensional Hamiltonians with generalized and ordinary shape invariance symmetry have been obtained by Fourier transforming over some coordinates of the SU(3) Casimir operator defined on SU(3)∕SU(2) symmetric space. It is shown that the generalized shape invariance of the two dimensional Hamiltonian is equivalent to SU(3) symmetry while in the three dimensional one, the ordinary shape invariance is equivalent to contracted SU(3) and there is one to one correspondence between the representations of the generalized shape invariance symmetry of the two (three) dimensional Hamiltonian and SU(3) [contracted SU(3)] Verma bases.
The de Sitter relativistic top theory
Authors: Armenta J. , Nieto J. A.
Published: December 2004

We discuss the relativistic top theory from the point of view of the de Sitter (or anti–de Sitter) group. Our treatment rests on the Hanson–Regge spherical relativistic top Lagrangian formulation. We propose an alternative method for studying spinning objects via Kaluza–Klein theory. In particular, we derive the relativistic top equations of motion starting with the geodesic equation for a point particle in 4+N dimensions. We compare our approach with Fukuyama’s formulation of spinning objects, which is also based on Kaluza–Klein theory. We also report a generalization of our approach to a 4+N+D dimensional theory.
The difficulty of symplectic analysis with second class systems
Authors: Shirzad A. , Mojiri M.
Published: December 2004

Using the basic concepts of the chain by chain method we show that the symplectic analysis, which was claimed to be equivalent to the usual Dirac method, fails when second class constraints are present. We propose a modification in symplectic analysis that solves the problem.
Linear stability and energy growth of viscosity stratified flows
Authors: Malik Satish V. , Hooper Alison P.
Published: December 2004

The non-normality of the Orr–Sommerfeld equation leads to the possibility of disturbance growth even though all eigenvalues are stable. In single-fluid flow the disturbance growth converges to a limit once the number of modes exceeds a minimum number. In the case of a two-fluid flow, however, convergence is not found. The problem of nonconvergence is due to the presence of the interface and the corresponding interfacial mode. The interface is replaced with a miscible layer of variable viscosity. When the thickness of the miscible layer is approximately equal to the thickness of the critical layer, the flow resembles two-fluid flow and one of the modes starts behaving like the interfacial mode.
Rapid biogenesis and sensitization of secretory lysosomes in NK cells mediated by target-cell recognition
Authors: Liu Dongfang , Xu Liang , Yang Fan , Li Dongdong , Gong Feili , Xu Tao
Published: December 2004

Natural killer (NK) cells play important roles in defense against tumor, viral infection, and cell-mediated xenograft rejection through secretion of secretory lysosomes. In this study, we used high time-resolution membrane capacitance measurement and fluorescence-imaging techniques to study the biogenesis and exocytosis of secretory lysosomes in a human NK cell line. We demonstrated a high-affinity Ca2+-dependent exocytosis of secretory lysosomes, which is sensitized further after target-cell stimulation. Our data also suggest an unusual rapid and dramaticde novoformation of secretory lysosomes after target-cell recognition. The rapid biogenesis of secretory lysosomes was blocked by specific protein kinase C inhibitor but not by brefeldin A. We propose that target-cell recognition triggers rapid biogenesis and sensitization of secretory lysosomes in NK cells through activation of PKC.
Baxdeletion prevents neuronal loss but not neurological symptoms in a transgenic model of inherited prion disease
Authors: Chiesa Roberto , Piccardo Pedro , Dossena Sara , Nowoslawski Lisa , Roth Kevin A. , Ghetti Bernardino , Harris David A.
Published: December 2004

Transgenic Tg(PG14) mice express a mutant prion protein containing 14 octapeptide repeats, whose human homologue is associated with an inherited prion dementia. These mice develop a progressive neurological disorder characterized by ataxia and cerebellar atrophy, with massive apoptotic degeneration of granule neurons.Bax, a proapoptotic gene of theBcl-2family, plays a key role in regulating cell death in the nervous system. To analyze the role ofBaxin the Tg(PG14) phenotype, we crossed Tg(PG14) mice withBax-/-mice to obtain Tg(PG14)/Bax-/-offspring.Baxdeletion effectively rescued cerebellar granule neurons from apoptosis, implying that these cells die via aBax-dependent process. Surprisingly, however, the age at which symptoms began and the duration of the clinical phase of the illness were not altered in Tg(PG14)/Bax-/-mice. In addition,Baxdeletion failed to prevent shrinkage of the molecular layer of the cerebellum and loss of synaptophysin-positive synaptic endings. Our analysis indicates that synaptic loss makes a critical contribution to the Tg(PG14) phenotype. These results provide insights into the pathogenesis of prion diseases and have important implications for the treatment of these disorders.
The splicing of yeast mitochondrial group I and group II introns requires a DEAD-box protein with RNA chaperone function
Authors: Huang Hon-Ren , Rowe Claire E. , Mohr Sabine , Jiang Yue , Lambowitz Alan M. , Perlman Philip S.
Published: December 2004

Group I and II introns self-splice
in vitro
, but require proteins for efficient splicing
in vivo
, to stabilize the catalytically active RNA structure. Recent studies showed that the splicing of some
Neurospora crassa
mitochondrial group I introns additionally requires a DEAD-box protein, CYT-19, which acts as an RNA chaperone to resolve nonnative structures formed during RNA folding. Here we show that, in
Saccharomyces cerevisiae
mitochondria, a related DEAD-box protein, Mss116p, is required for the efficient splicing of all group I and II introns, some RNA end-processing reactions, and translation of a subset of mRNAs, and that all these defects can be partially or completely suppressed by the expression of CYT-19. Results for the aI2 group II intron indicate that Mss116p is needed after binding the intron-encoded maturase, likely for the disruption of stable but inactive RNA structures. Our results suggest that both group I and II introns are prone to kinetic traps in RNA folding
in vivo
and that the splicing of both types of introns may require DEAD-box proteins that function as RNA chaperones.
Studies of the properties of human origin recognition complex and its Walker A motif mutants
Authors: Giordano-Coltart Jennifer , Ying Carol Y. , Gautier Jean , Hurwitz Jerard
Published: December 2004

The eukaryotic six-subunit origin recognition complex (ORC) governs the initiation site of DNA replication and formation of the prereplication complex. In this report we describe the isolation of the wild-type
Homo sapiens
(Hs)ORC and variants containing a Walker A motif mutation in the Orc1, Orc4, or Orc5 subunit using the baculovirus-expression system. Coexpression of all six HsORC subunits yielded a stable complex containing HsOrc subunits 1–5 (HsORC1-5) with virtually no Orc6 protein (Orc6p). We examined the ATPase, DNA-binding, and replication activities of these complexes. Similar to other eukaryotic ORCs, wild-type HsORC1-5 possesses ATPase activity that is stimulated only 2-fold by single-stranded DNA. HsORC1-5 with a mutated Walker A motif in Orc1p contains no ATPase activity, whereas a similar mutation of either the Orc4 or Orc5 subunit did not affect this activity. The DNA-binding activity of HsORC1-5, using lamin B2 DNA as substrate, is stimulated by ATP 3- to 5-fold. Mutations in the Walker A motif of Orc1p, Orc4p, or Orc5p reduced the binding efficiency of HsORC1-5 modestly (2- to 5-fold).
Xenopus laevis
ORC-depleted extracts supplemented with HsORC1-5 supported prereplication complex formation and
X. laevis
sperm DNA replication, whereas the complex with a mutation in the Walker A motif of the Orc1, Orc4, or Orc5 subunit did not. These studies indicate that the ATP-binding motifs of Orc1, Orc4, and Orc5 are all essential for the replication activity associated with HsORC.
Counterexamples to the Neggers-Stanley conjecture
Authors: Brändén Petter
Published: December 2004

The Neggers-Stanley conjecture asserts that the polynomial counting the linear extensions of a labeled finite partially ordered set by the number of descents has real zeros only. We provide counterexamples to this conjecture.
Possible Roles for Mannitol and Mannitol Dehydrogenase in the Biotrophic Plant PathogenUromyces fabae
Authors: Voegele Ralf T. , Hahn Matthias , Lohaus Gertrud , Link Tobias , Heiser Ingrid , Mendgen Kurt
Published: December 2004

Levels of the C6-polyol mannitol were observed to rise dramatically in the biotrophic interaction of the rust fungus Uromyces fabae and its host plant Vicia faba. Mannitol was found in millimolar concentrations in extracts and apoplastic fluids of infected leaves and also in extracts of spores. We suggest that this polyol might have at least a dual function: first, as a carbohydrate storage compound, and second, as a scavenger of reactive oxygen species. Mannitol accumulation is accompanied by high expression of a mannitol dehydrogenase (MAD1) in haustoria. While MAD1 transcripts were detected in haustoria only, immunolocalization studies show that the gene product is also present in spores. Kinetic and thermodynamic analyses of the MAD1p catalyzed reactions indicate that the enzyme might be responsible for the production of mannitol in haustoria and for the utilization of mannitol in spores. Since V. faba is normally unable to synthesize or utilize polyols, the multipurpose usage of mannitol seems an ideal strategy for the fungal pathogen.