摘要:

Earlier work on a simple inverse transport problem is extended. An infinite set of sum rules are obtained which relate sums of products of the Legendre coefficients of the scattering function to Fourier coefficients of the logarithm of the spectral function. Further, simple formulas are obtained for sensitivity coefficients which describe how the Legendre coefficients are altered by small changes in experimentally measured moments.

ISSN:0031-9171    

DOI:10.1063/1.861262

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Low Reynolds number flow is considered in a pure fluid near the thermodynamic critical point and in a binary mixture near the critical mixing ’’point.’’ It is shown that, due to the breakdown of the assumption of imcompressibility, a sphere rotating with steady angular velocity &OHgr; in a stream U experiences an extra force proportional to &OHgr;×U, but no extra torque.

ISSN:0031-9171    

DOI:10.1063/1.861263

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The linear stability of the plane Couette flow of a dilute particle‐fluid mixture with lift forces included is studied. An instability is found for Stokes number greater than about 1.23×10−4. An initial particle velocity component at an angle of about 135° from the direction of the fluid flow will grow as it propagates with the fluid for Stokes numbers greater than the critical value.

ISSN:0031-9171    

DOI:10.1063/1.861264

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The stability of plane Couette flow is studied by applying a finite two‐dimensional disturbance to the basic laminar motion and following the timewise evolution of the quasi‐steady flow and the disturbance. This is accomplished by combining a Meksyn–Stuart type method with a quasi‐steady technique. Results show that plane Couette flow tends to slowly converge to a stable state for the Reynolds numbers and disturbance intensities studied. This is in disagreement with past investigations which were able to obtain nonlinear neutral stability curves.

ISSN:0031-9171    

DOI:10.1063/1.861265

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The spatial stability of two‐dimensional incompressible boundary‐layer flows is analyzed using the method of multiple scales. The analysis takes into account the streamwise variations of the mean flow, the disturbance amplitude, and the wavenumber. The theory is applied to the Blasius and the Falkner–Skan flows. For the Blasius flow, the nonparallel analytical results are in good agreement with the experimental data. The results show that the nonparallel effects increase as the pressure gradient decreases.

ISSN:0031-9171    

DOI:10.1063/1.861266

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Three‐dimensional steady boundary layer equations are considered as a model case of a more general class of problems called ’’multitime initial‐value problem’’ for a parabolic system. Ideas developed in recent years for solving three‐dimensional steady boundary layers are generalized for application to other similar problems, such as unsteady two‐dimensional boundary layers. An unsteady counterpart of the wedge‐shaped zones of influence and dependence is defined and then used to rationalize the calculation of reversed flow in two‐dimensional unsteady case. Schemes used previously for the latter flow are re‐examined in light of this dependence rule, and it is found that these schemes could satisfy such a rule.

ISSN:0031-9171    

DOI:10.1063/1.861267

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The evolution and interaction of nonlinear wavepackets on deep water is studied both theoretically and experimentally. The nonlinear Schro¨dinger equation, first derived in this context by Hasimoto and Ono, is shown to be a special case of Whitham’s theory. The exact solution to this equation predicts the existence of stable envelope solitons, which is indeed verified by laboratory experiments. A comparison between laboratory data and a numerical solution of the nonlinear Schro¨dinger equation is also given.

ISSN:0031-9171    

DOI:10.1063/1.861268

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A theoretical study is presented of the hydromagnetic waves which are generated in a rotating fluid when its boundaries are started into transverse oscillation. Particular attention is focused on the very low‐frequency waves that occur when the rotation speed greatly exceeds the Alfve´n speed, in view of their probable importance in connection with the dynamics of the Earth’s liquid core. Estimates of their magnetic field amplitude are obtained for the case when the viscosity of the fluid is very small, and it is found that the amplitude increases with the conductivity &sgr;sof the boundaries unless this exceeds a certain threshold value, in which case the amplitude is virtually independent of &sgr;s. When the motion of the boundaries is transient and of very high frequency, the magnetic field amplitude of the fluid oscillations at the forcing frequency may greatly exceed that of the accompanying low‐speed hydromagnetic waves. The transient response is nevertheless of very limited spatial extent, and application of these results to the dynamics of the Earth’s deep interior then indicates that high‐frequency magnetic fluctuations in the core (which are shielded from observation at the Earth’s surface by the skin effect in the mantle) cannot have sufficient amplitude to significantly enhance electromagnetic core‐mantle coupling.

ISSN:0031-9171    

DOI:10.1063/1.861269

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Electron density, electron temperature, and concentration of excited sodium atoms are measured in the weakly ionized regime behind a shock wave in impure argon in a shock tube using microwave techniques and spectrally resolved radiometry. Evidence is presented to show that an apparent increase in the rate of ionization is due to electron detachment of negative chlorine ions produced from sodium chloride vapor contained as an impurity. To be consistent with this chemical model, rate coefficients are found for 5500<T<8600 °K to be as follows: for NaCl+Ar+5.8 eV→Na++Cl−+Ar,k4=0.082exp(−67 315/T)/T2cm3sec−1; for Cl−+Ar+3.61 eV→Cl+e+Ar,k5=6×10−12exp(−41 900/T) cm3sec−1; and for the branching ratio between the reaction NaCl+Ar+5.8 eV→Na++Cl−+Ar(k4) and reaction NaCl+Ar+4.27 eV→Na+Cl+Ar(k3),k4/k3=1.6×104exp(−17 760/T). Electron temperature is lower than heavy particle temperature by roughly 1000 °K. The electron‐argon impact ionization rate coefficient is a weak function of electron temperature in contradiction to expectation.

ISSN:0031-9171    

DOI:10.1063/1.861270

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

In a laser‐heated magnetically confined column of plasma separated from material walls by a vacuum field, laser energy absorption near the center leads to a ’’light pipe’’ effect essential to the concept of heating long columns to fusion temperatures. Outward diffusion of particles at the vacuum‐plasma boundary tends to move the position of maximum density inward, and hence to narrow the light pipe, while over‐all expansion of the heated column against the field tends to widen it. A model is formulated to describe these effects and is treated analytically and numerically. The results indicate that for conditions of interest, the light pipe will persist long enough to permit heating of reactor‐scale columns.

ISSN:0031-9171    

DOI:10.1063/1.861271

出版商:AIP    

年代:1975

数据来源: AIP