摘要:

It is shown by an example that in the balance equation for the kinetic energy of a velocity component in a Newtonian viscous fluid, the term usually interpreted as viscous dissipation rate can have negative regions, although the second law of thermodynamics requires that total kinetic energy dissipation rate be positive at each point in space‐time. After exploration of an alternate form, it is concluded that the conventional form is correct, and that the thermodynamic requirement is simply not relevant for kinetic energies of individual velocity components.

ISSN:0031-9171    

DOI:10.1063/1.863801

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Velocity discontinuity surfaces can be inserted at will in a Gerstner edge wave on an inclined boundary in a rotating fluid.

ISSN:0031-9171    

DOI:10.1063/1.863802

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The mean temperature distribution is analyzed in the turbulent wake of a circular cylinder when there is a linear temperature gradient flow upstream of the cylinder. Using the same variable eddy diffusivity derived from published temperature measurements in the wakes of heated cylinders, it is shown that the mean temperature distribution has a self‐similar form which agrees with experimental results of Alexopoulos and Keffer. But, the location and magnitude of the maximum temperatureperturbationsare in error by 25% and 50%, respectively. The reasons for the limitations of the eddy diffusivity model in wake flows are discussed. The variance of temperature fluctuations (&thgr;′¯)2¯in a linear temperature gradient mixed by homogeneous grid turbulence are then analyzed on the basis of Durbin's theory. It is shown that the measurements of (&thgr;′¯)2¯are more plausibly fitted by the curve (&thgr;′¯)2¯∝x1/2than by Sullivan’s analysis of the same data.

ISSN:0031-9171    

DOI:10.1063/1.863803

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The injection of a relativistic electron beam (0.8 MeV, 6 kA, 150 nsec) into hydrogen gas of 190 Pa pressure results in a plasma with densityne≃1020m−3and temperaturekTe≲kTi≃3.5 eV. The results of the measurements show good agreement with computations based on a model combining gas ionization and turbulent plasma heating. It is found that a quasistationary state exists in which the energy lost by the beam (about 6% of the total kinetic energy of the beam) is partly used to further ionize and dissociate the gas and for the other part is lost as line radiation.

ISSN:0031-9171    

DOI:10.1063/1.863804

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The initial nonlinear evolution of two unstable waves in a cold beam‐plasma system can be described by a single wave with a slow modulated amplitude and phase. The modulational calculation is tested quantitatively on the analogous wave‐particle interaction in a traveling wave tube. The model is found to be valid for one autocorrelation time following the onset of nonlinearities. Stochastic behavior follows the breakdown of the modulational approximation, i.e., after one autocorrelation time, in agreement with reasonance overlap theory.

ISSN:0031-9171    

DOI:10.1063/1.863805

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A set of double‐adiabatic fluid equations with additional collisional relaxation between the ion temperatures parallel and perpendicular to a magnetic field are shown to reduce to a set involving a single temperature and a parallel viscosity. This result is applied to a recently published paper [R. V. Bravenec, A. J. Lichtenberg, M. A. Leiberman, and H. L. Berk, Phys. Fluids 24, 1320 (1981)] on viscous flow in a multiple‐mirror configuration.

ISSN:0031-9171    

DOI:10.1063/1.863806

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The nonlinear evolution of the one‐dimensional Buneman instability after saturation due to electron trapping is studied both by analysis and by computer simulation. A nonlinear dispersion relation proposed previously is shown to describe the nonlinear evolution even after the electron trapping sets in. After electron trapping is completed, amplitude oscillation at a frequency close to &ohgr;pi(ion plasma frequency) appears due to the exchange of energy between the ions and the electric field. The maximum energy acquired by the ions reaches more than 10% of the initial electron drift energy.

ISSN:0031-9171    

DOI:10.1063/1.863807

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Charge, mass, and electron density fluctuation spectra of strongly correlated, fully ionized two‐component plasmas within the framework of the Mori–Zwanzig memory function formalism are analyzed. All dynamical correlation functions are expressed in terms of the memory functions of the ion and electron velocity autocorrelation functions by a generalized effective field approximation which preserves the exact initial values (i.e., static correlations). The theory reduces correctly to the mean field (or collisionless Vlasov) results in the weak coupling limit, and yields charge density fluctuation spectra in good agreement with available computer simulation data, as well as reasonable estimates of the transport coefficients. The collisional damping and frequency shift of the plasma oscillation mode are sizeable, even in the long wavelength limit. The theory also predicts the propagation of well‐defined sound waves in dense plasmas in thermal equilibrium.

ISSN:0031-9171    

DOI:10.1063/1.863808

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Near the resonance (&ohgr;o≊&ohgr;p) a high‐amplitude plasma wave decays into a purely growing electromagnetic perturbation and two Langmuir wave sidebands. The growth rate of the instability &ggr;≃&ohgr;pk20v20/ 8k2v2efor a Langmuir pump wave of finite wavenumberk0≳kve/cand the threshold due to the finite extent,x0, of the pump isv20/v2e≳4k2v2e(k2x0+&bgr;)/ &ohgr;2p&bgr;x0;v0andveare the oscillatory and thermal velocities of electrons and &bgr; is thexcomponent of propagation vector k of the perturbation. This instability may be a possible source of spontaneous generation of random magnetic field in laser‐produced plasmas.

ISSN:0031-9171    

DOI:10.1063/1.863784

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A stationary negative potential with a solitary‐wave structure can exist in a nonequilibrium plasma withTe≫Ti. The peak value of the potential can exceed the electron temperature,Te/e. The existence of such a structure is responsible for the formation of a double layer in the presence of current.

ISSN:0031-9171    

DOI:10.1063/1.863785

出版商:AIP    

年代:1982

数据来源: AIP