摘要:

Weakly nonlinear analysis is used to calculate the possible two‐ and three‐dimensional convection patterns in a rectangular parallelepiped of saturated porous media when the horizontal dimensions are integral multiples of the vertical dimension. A two‐term expansion for the Nusselt number is found for values of the Rayleigh number close to the critical values. It is shown that the two‐dimensional roll configurations transfer heat more effectively than does the three‐dimensional pattern of motion when the Rayleigh number is just above the critical value.

ISSN:0031-9171    

DOI:10.1063/1.862066

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Depending on the concentration, the capillary tube diameter influences two parameters: the apparent viscosity and the critical shear rate for which the transition from steady to unsteady flow regimes occurs. A possible length parameter, characteristic of a given polymer concentration, is defined on the basis of these two parameters.

ISSN:0031-9171    

DOI:10.1063/1.862078

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The irreversible thermodynamics of viscous solids with microstructures is developed in a new approach. In this general theory, the ’’particle’’ in the continuous medium is a composite ’’molecule.’’ The field equations describing the motions of the mass points making up the molecule are written down in terms of an internal energy potentialUand a dissipation functionD. The irreversible mechanical force acting on the mass point is related toD. The conservation laws of momentum, energy, and angular momentum are derived from the spatial invariance properties ofUandD, and are thus automatically satisfied. The balance of entropy is a built‐in process. The cases of anisotropic liquids and liquid crystals can be developed in a similar fashion.

ISSN:0031-9171    

DOI:10.1063/1.862086

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

General properties of linearized internal waves are developed in preparation for a treatment of nonlinear waves. Two sets of results are obtained. The first pertain to propagation in an arbitrary stability stratified medium. The second set refer to the case when the Boussinesq approximation is made. Special attention is paid to the completeness of the normal modes and their use in solving initial value problems. Some novel sum rules are obtained. The principal tools of the investigations are two variational principles.

ISSN:0031-9171    

DOI:10.1063/1.862065

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An incompressible and inviscid model for the Rayleigh–Taylor stability of an ablating fluid in the absence of convection is presented and solved analytically for boundary conditions appropriate to laser produced plasmas. The wavenumberskperpendicular to the density gradient of scale lengthLare found to be relatively insensitive to ablative stabilization for the most unstable radial eigenmodes,k2L2≳1.

ISSN:0031-9171    

DOI:10.1063/1.862067

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Calculations have been made of the rate at which confined magnetic flux compressed by an imploding cylindrical liquid metal liner diffuses into the latter because of finite electrical resistivity. The diffused magnetic field profile and associated magnetic energy and Joule heating are also calculated. In the limit of high magnetic Reynolds numberRm, the skin depth, total diffused flux, and associated energy scale likeRm−1/2. It is shown that cylindrical liner motion mitigates the diffusion calculated in slab models, owing to the reduction in the surface area through which the flux must diffuse. The influence of the form of the liner motion on the results is displayed.

ISSN:0031-9171    

DOI:10.1063/1.862068

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The problem of an electromagnetic wave packet, incident on a relativistically moving plane ionization or recombination front in a stationary gas, is considered. The frequency of the reflected wave packet is found to obey the usual double Doppler shift relation. However, the reflection coefficients and the physics can differ significantly from the case of reflection from moving material objects. In the unmagnetized case, the ratio of the energy in the reflected wave packet to that in the incident wave packet is found to be &egr;r*/&egr;i*=&ohgr;i*/&ohgr;r* for an oncoming overdense ionization front, for which &ohgr;i*<&ohgr;r* (where &ohgr;i* and &ohgr;r* are the incident and reflected wave frequencies in the laboratory frame). For an oncoming ionization front in the presence of an applied magnetic field normal to the front, &egr;r*/&egr;i* can considerably exceed &ohgr;i*/&ohgr;r*. For a retreating recombination front (&ohgr;i*≳&ohgr;r*), in the overdense unmagnetized case, &egr;r*/&egr;i*=&ohgr;r*/&ohgr;i*. These results have important implications for the production of sub‐millimeter wavelength pulses by upshifted reflection from a relativistically moving ionization front.

ISSN:0031-9171    

DOI:10.1063/1.862069

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The dispersion relation for nonpotential ion harmonic waves propagating at any angle to the magnetic field in plasmas with arbitrary &bgr; is derived for &ohgr;/kz≫Vi, where &ohgr;/kzis the parallel phase velocity andViis the ion thermal speed. It is shown that these slow waves can propagate in plasmas when the electron plasma pressure to magnetic pressure ratio &bgr;e, is much less than 1 and only in the wavenumber rangek≳ (&Pgr;e/c)(&ohgr;/&OHgr;ecos&Vthgr;)1/2, where &Pgr;eis the plasma frequency, &OHgr;eis the electron gyrofrequency,cis the velocity of light, and &Vthgr; is the propagation angle. Finally, a comparison between the properties of these slow waves and those of the fast electromagnetic ones, is given.

ISSN:0031-9171    

DOI:10.1063/1.862079

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The influence of finite ion Larmor radius effects on the ion resonance instability in a nonneutral plasma column aligned parallel to a uniform axial magnetic fieldB0eˆzis investigated. The analysis is carried out within the framework of a hybrid Vlasov‐fluid model in which the ions are described by the Vlasov equation and the electrons are described as a macroscopic, cold fluid. Electrostatic stability properties are calculated for the case in which the equilibrium electron and ion density profiles are rectangular and the ion distribution function is specified byf0i=const×&dgr; (H⊥−&ohgr;iP&Vthgr;−T⁁i)G(vz). The resulting eigenvalue equation for the perturbed electrostatic potential &fgr;⁁l(r) is solved exactly to give a closed algebraic dispersion relation for the complex eigenfrequency &ohgr;. This dispersion relation is solved numerically, and it is shown that the growth rate of the ion resonance instability exhibits a sensitive dependence on plasma parameters. For example, finite ion Larmor radius effects can have a strong stabilizing influence for azimuthal mode numbersl⩾2, particularly when the equilibrium self‐electric field is sufficiently weak. For the fundamental mode (l=1), however, stability properties are identical to those calculated from a macroscopic two‐fluid model, and the growth rate is unaffected by the value of the ion Larmor radius.

ISSN:0031-9171    

DOI:10.1063/1.862080

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Electromagnetic instabilities which propagate parallel to an external magnetic field in an infinite, homogeneous Vlasov plasma are considered. Linear theory is used to construct second‐order expressions for the time rates of change of momentum, as well as perpendicular, parallel, and total energies of each plasma species. The results are expressed in a concise form appropriate for many instabilities of this type. The ion cyclotron (T⊥i≳T∥i) and firehose (T∥i≳T⊥i) instabilities are considered as examples.

ISSN:0031-9171    

DOI:10.1063/1.862081

出版商:AIP    

年代:1978

数据来源: AIP