摘要:

Both dislocation climb and glide are known to occur in solid‐state physics, but only climb has been observed in dislocation defects (pinches) in convection cells. A search of movies of convection has uncovered observations of dislocation glide in the cross rolls in bimodal convection. The climb also exists with the dislocation moving in a direction opposite of the climb previously observed in convection rolls, i.e., toward long wavelength.

ISSN:0031-9171    

DOI:10.1063/1.864540

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A shock wave propagating from liquid metal into water via a corrugated interface produces quasiperiodic perturbations in the compressed water, as determined by shadowgraphy. Theoretical analysis indicates that the shadows are caused by density gradients which occur from the coherent interaction among reverberating pressure waves.

ISSN:0031-9171    

DOI:10.1063/1.864541

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The electron‐cyclotron maser instability is studied in a plasma with a loss‐cone distribution for parameters relevant to tandem mirror devices. Both linear theory and particle simulations are employed. The effects of finitek⊥are found to be very significant, and in general, the largest growth rate occurs for radiation emission perpendicular to the magnetic field. The instability persists at much lower densities (&ohgr;pe/&OHgr;e<0.1) than indicated by previous analyses, which were limited to the case of parallel emission.

ISSN:0031-9171    

DOI:10.1063/1.864542

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Exact solutions of the time‐dependent Euler equations are presented which correspond to uniform columnar vortices with elliptical cross sections undergoing rotation and deformation in a uniform three‐dimensional straining flow. In this work, the recent solutions of Kida [J. Phys. Soc. Jpn.50, 3517 (1981)] are generalized to include the effect of a strain component along the axis of the vortex which results in its stretching. The time‐dependent solutions should play a very useful role in modeling time‐dependent vortex interactions in more complicated flows such as the mixing layer.

ISSN:0031-9171    

DOI:10.1063/1.864543

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The effect of radius ratio on the stability of Couette flow to axisymmetric and nonaxisymmetric disturbances and the stability of Taylor vortex flow to nonaxisymmetric disturbances is considered. It is assumed that the outer cylinder is at rest. As the ratio &eegr; of the radius of the inner cylinder to the radius of the outer cylinder is decreased, it is found that (i) the number of unstable normal modes for Couette flow at a fixed Taylor number decreases rapidly, and (ii) there is a critical value of &eegr; equal to about 0.65, below which there is no instability of the Taylor vortex flow for the range of Taylor numbers considered here. Recent experimental observations are summarized.

ISSN:0031-9171    

DOI:10.1063/1.864544

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A complete set of independent real parameters and its dynamic equation are worked out to describe the vorticity dynamics of two‐dimensional turbulence. The corresponding Liouville equation is solved by a perturbation method upon the basis of a Langevin–Fokker–Plank Model. The dynamic damping coefficient &eegr; of the LFP model is treated as an optimum control parameter to minimize the error of the perturbation solution. Thereby two integral equations, the enstrophy equation and the &eegr; equation, are obtained for two unknown functions: the spectrum and the &eegr;. The equilibrium spectrum for the inviscid case is obtained as a stationary solution of the enstrophy equation. The nonlocalness of the enstrophy transfer makes the enstrophy equation divergent for a simple power‐law spectrum. In order to avoid the divergence problem, a localization factorgis introduced to characterize the actual spectrum. Finally, the localized forms of the two integral equations are numerically solved, leading to the inertial‐range spectrum,E(k)=1.82(ln g−1.23)−2/3&khgr;2/3k−3forg≥10, &khgr; is the dissipation rate of the enstrophy.

ISSN:0031-9171    

DOI:10.1063/1.864545

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A conventional schlieren system has been used to study second‐sound shock waves produced in a shock tube with optical windows. Initially planar shocks are observed to remain so, even after several reflections from the end walls. No interaction of the shocks with the side wall boundary layers is seen, attesting to the thinness of these layers. Second‐sound shocks are reflected from the liquid–vapor interface, producing transmitted gasdynamic shocks and reflected second‐sound shocks. Several strong shocks are fired with short separation times, generating observable fluctuations in the fluid.

ISSN:0031-9171    

DOI:10.1063/1.864546

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Quasi‐one‐dimensional inviscid flows of helium‐argon mixtures are computed from a two‐fluid flow model in a convergent divergent nozzle. Results show not only velocity and temperature slip but also critical mass flow rates larger than those predicted by isentropic one‐dimensional flow.

ISSN:0031-9171    

DOI:10.1063/1.864547

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The nonlinear frequency shift of coherent ion‐acoustic waves in the presence of background ion‐acoustic turbulence is reexamined in the framework of weak turbulence theory. In contrast to previous findings, the frequency shift always remains positive irrespective of the propagation direction of the coherent waves.

ISSN:0031-9171    

DOI:10.1063/1.864548

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The equation describing the excitation of a Bernstein wave near the upper‐hybrid frequency by the coupling of two electromagnetic waves in an inhomogeneous plasma is derived. The basic assumptions are (i) the three waves propagate perpendicularly to the external magnetic field, and (ii) the Bernstein wave is electrostatic. The excited electric field may be expressed in terms of Airy functions. The power flowing in the upper‐hybrid mode is calculated as a function of the coupling length, the inhomogeneity length, and the angle between the incident waves. Numerical results are given for the case of ionosphere.

ISSN:0031-9171    

DOI:10.1063/1.864524

出版商:AIP    

年代:1984

数据来源: AIP