摘要:

The scattering functionS(Q,&ohgr;) for droplets of superfluid helium near absolute zero is calculated. Assuming that the surface tension &tgr;=&tgr;0+&tgr;˜ (t) is fluctuating with correlation strength &agr;, a wave diffusion decay mechanism for a nondissipative system is found. For eachlth multipole of droplet shape oscillation,S(Q,&ohgr;) contains two Lorentzian peaks at frequency shifts ± (Cl&tgr;0)1/2, with a width &agr;Cl/2&tgr;0, whereClis the Rayleigh form factor. Applying Bose statistics, it is found that the magnitude of &tgr;˜ is not greatly different from that of &tgr;0. Estimates of the scattering intensity show that with present day techniques measurements are possible.

ISSN:0031-9171    

DOI:10.1063/1.862390

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Approximate solutions of nonlinear boundary‐value problems arising in inviscid stratified shear fluid flows over relatively small obstacles are considered. The presence of a critical layer in the flow field leads to a failure of the linear theory, necessitating the derivation of a nonlinear critical layer equation. The solution of this second‐order differential equation for the horizontal velocity is found to be discontinuous along the streamline which passes through the upstream critical point. In the analysis, three constants of motion along a streamline are used to study flows involving slip and split streamlines emanating from this point. The matching of the critical layer (inner) and the linearized outer solutions is discussed and some examples of steady flows over an obstacle and waves propagating with constant speed are given.

ISSN:0031-9171    

DOI:10.1063/1.862391

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In order to investigate the significance of cyclic interaction in the evolution of fluctuating convective flow in a rectangular cell of porous material, the behavior of confined and unconfined flows are compared. In the latter case the constant pressure boundary condition at the top surface does not force the fluid to recirculate around the cell. However, regular oscillatory flow similar to that which occurs in an enclosed cell is still observed. This indicates that the oscillatory flow arises from the instability of the thermal boundary layer on the heated bottom surface. In both cases the frequency of the oscillatory flow is proportional to the Rayleigh number to the power of 3/2.

ISSN:0031-9171    

DOI:10.1063/1.862392

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Propagation of nonlinear waves in a vibrationally relaxing gas is considered. The nonlinear behavior of wave fronts, the characteristic front and the shock front, are investigated in detail. The flows are thought of as being produced in a semi‐infinite cylindrical pipe terminated by a piston, when the piston begins to move with a small velocity compared with the frozen speed of sound. The gas is initially at rest, but some nonuniformities are introduced into the initial state of the gas along the axis of the cylinder.

ISSN:0031-9171    

DOI:10.1063/1.862393

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A simple relationship between the Benjamin–Feir instability associated with uniform solutions of the nonlinear Schro¨dinger equation and the long time evolution of the unstable solution is reported. The number of modes which actively participate in the energy sharing process associated with the instability is governed by the number of harmonics of the initial disturbance which lie within the unstable region as predicted by the Benjamin–Feir analysis. Generalization of this observation implies that equations which possess high wavenumber cutoffs in the instability characteristics should not thermalize in the conventional sense when undergoing such an instability, since active modes are confined to a finite range of wavenumbers.

ISSN:0031-9171    

DOI:10.1063/1.862394

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Current‐voltage characteristics of drifting spherical Langmuir probes have been studied experimentally in collisionless plasmas. In order to single out the effect of probe speed on the ion current collection, the experiment was carried out by a rotating arm facility. With this device the probe speed as well as the properties of the undisturbed plasma were accurately determined. As predicted by the theories of Kanal, Godard, and Laframboise, the ion current at small speed ratios was found to be either increased or decreased as the probe speed increased depending on the ratio of probe radius to Debye lengthR/&lgr;D. As for the absolute magnitude of ion current change by the probe speed, however, discrepancies were found between these theories and the present experiment. The difference is considered to originate from asymmetry in the potential distribution, which is not included in these theories.

ISSN:0031-9171    

DOI:10.1063/1.862395

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The role of kinetic velocity distributions on the interaction between resonant laser beams and atoms or ions is shown to affect, and under some conditions dominate, the intensity, line shape, and spatial distribution of diagnostic fluorescence in hot plasmas and gases.

ISSN:0031-9171    

DOI:10.1063/1.862396

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The parallel currents in a toroidally‐confined plasma is shown to consist of the current in response to the parallel electric field, the Pfirsch–Schlu¨ter current which is required by charge neutrality, and the bootstrap current which flows to maintain a balance between the viscous and friction forces along the magnetic field. The steady state momentum equation is used to obtain an Ohm’s law relating the neoclassical current to the cross‐field fluxes of particles and heat in a multiple ion species plasma. It is found that the presence of impurities does not alter the magnitude of the bootstrap current. Thus, the neoclassical beta limit established by the bootstrap current is insensitive to the impurity content of the plasma. The magnitudes of the bootstrap current and conjugate Ware fluxes are calculated in the transition from the long mean‐free‐path to collisional regime.

ISSN:0031-9171    

DOI:10.1063/1.862397

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The Bennett equilibrium is shown to be a particular case of a class of Vlasov equilibria characterized by a constant axial macroscopic velocity for the ions and the electrons, and by a constant ratio of the densities. It is established that any collisionless plasma column in radial equilibrium, carrying a very high current, may be considered as the superposition, on the thermal background of ions, of two counterstreaming electron beams, the more intense of which carries most energetic electrons in the vicinity of the axis. This property could be interpreted as a partial ’’magnetic neutralization,’’ and thus explain the absence of any current limitation.

ISSN:0031-9171    

DOI:10.1063/1.862371

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It is shown that the interaction of collisionless drift waves propagating in different directions can effectively exchange energy via interaction of a quasi‐mode. The process is nonlinear electron Landau damping, and may explain the near isotropic distribution of drift waves in tokamak experiments.

ISSN:0031-9171    

DOI:10.1063/1.862398

出版商:AIP    

年代:1978

数据来源: AIP