摘要:

By consideration of the equations of motion and the electromagnetic theory of a moving medium, the reversible work done on a fluid, per unit mass, in a small change of state is shown to be −pd(1/&rgr;) +E·d(D/&rgr;) +H·d(B/&rgr;), wherepis the pressure due to thejoint actionof the mechanical and electromagnetic changes; &rgr; is the density;EandBare, respectively, the electric field strength and magnetic induction;DandHare, respectively, the electric and magnetic excitation. Only the nonrelativistic version of Minkowski's theory has been used in this derivation. This formula provides the basis for a complete study of the thermodynamics of fluid medium under the action of both electromagnetic and mechanical changes.As an application, basic formulas which may be used to calculate the electrocaloric effect, the magnetocaloric effect, and electro‐ and magnetostriction effects are deduced. In particular, the additional pressure and pondermotive force due to these effects are obtained in a simple manner which, from the thermodynamic point of view, is better than Kortweg and Helmholtz' derivation given in the classical electromagnetic theory. As a second application, the energy equation of magnetohydromechanics is derived. The derivation is more general than previous derivations in that it does not presuppose the form of the electromagnetic constitutive equations (e.g.,D= &egr;E, B= &mgr;H) which the medium satisfies.

ISSN:0031-9171    

DOI:10.1063/1.1705937

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The structure of an extremely strong magnetohydrodynamic shock is discussed in the limit of no particle collisions. It is tentatively concluded that the shock transition takes place through the mechanism of a strong electric field produced by charge separation. The pressure in the shocked plasma is due primarily to a very high electron temperature. The entropy increase occurs by Landau damping of the coherent electron oscillation. The ions, on the other hand, undergo an irreversible temperature change of only 3.

ISSN:0031-9171    

DOI:10.1063/1.1705938

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

In this paper the authors have discussed the confinement of plasma by a one‐dimensional stationary electromagnetic wave. Their analysis is similar to that carried out by former workers for aTM0.1mode but they have examined the assumptions limiting the applicability of present theories in detail. One of the conditions for the applicability of the present theory is that the frequency of the electromagnetic wave should be of the same order or greater than the plasma frequency at the nodes where particle density is maximum. This condition makes the present theories nonapplicable in cases of thermonuclear interest.

ISSN:0031-9171    

DOI:10.1063/1.1705939

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Once introduced into captive orbits, protons and electrons should be strictly trapped in the earth's dipole magnetic field. However, various mechanisms exist which limit their lifetimes, such as collisions with atoms and ions in the earth's outer atmosphere, charge exchange, and scattering by hydromagnetic waves. This paper considers only the effect of the scattering of these particles by the ionized hydrogen and electron components of the outer atmosphere. However, the effect of scattering from neutral atoms can be qualitatively taken into account by using the radius of the atom in place of the Debye shielding length in the scattering formulas. The Fokker‐Planck equation has been used to derive an expression for the change in the distribution function due to small‐angle, single‐particle Coulomb collisions. Upper lifetime limits, as determined by this mechanism, of both protons and electrons are derived as functions of their initial energies.

ISSN:0031-9171    

DOI:10.1063/1.1705940

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The equation of motion for steady, incompressible, axially symmetric flow in a pipe with uniform wall suction or injection is expressed in terms of a ``dimensionless stream function,''F(&zgr;, &eegr;) = &psgr;(x, r)/&psgr;(x, a), where &psgr; is the usual stream function,xandrare cylindrical polar coordinates,ais the radius of the pipe, &zgr; = 1 − [2Rx/(aN)], &eegr; = (r/a)2.RandNare Reynolds numbers which specify the flows through the pipe wall and through the inlet, respectively. This equation, which includes as a special case the equation previously obtained by Yuan and Finkelstein for similar (affine) velocity profiles, is greatly simplified by passing to the limit which is approached asNincreases. Nonsimilar, &zgr;‐dependent solutions are approximated by a generalization of the method applied by Morduchow to the &zgr;‐independent equation of Yuan and Finkelstein. The results show the manner in which the condition of similarity of the velocity profiles is approached for a prescribed (e.g., parabolic) inlet profile. They also indicate the development of reverse flow at the wall of the pipe in the range ofRvalues for which no similar solutions exist.

ISSN:0031-9171    

DOI:10.1063/1.1705941

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The velocity of unsteady, one‐dimensional real fluid flows is rigorously eliminated from the governing equations. A class of exact solutions for polytropic processes is then derived and discussed. The general solution for tangent‐gas behavior is presented.

ISSN:0031-9171    

DOI:10.1063/1.1705942

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A differential equation is derived for the pressure along the axis of a longitudinally slotted tube through which there is supersonic gas flow, for the general case in which both the tube cross section and the slot width vary with axial position. An approximate method of solution for the special case, in which the tube cross section and slot width are constant, is then found in closed form and confirmed experimentally to within a constant factor. This factor is attributed to the formation of a boundary layer along the slot walls.

ISSN:0031-9171    

DOI:10.1063/1.1705943

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Studies of the flow field associated with hypersonic helium flow over blunt bodies with surface cavities have shown a very violent instability to be connected with these cavities. The mechanism of this instability appears to involve the formation within the cavity of vortices which are subsequently ejected. Cavity shapes more conducive to vortex formation are associated with the least stable flow. Experiments using the hydraulic analogy for compressible gas flow have clarified the nature of these unstable flows. It is suggested that the violent action of such vortices may explain some of the deeper pits observed in many meteorites. The continuous ejection of vortices during atmospheric passage would ablate material from the cavities, whence the depth of any cavities initially present on a meteoric body would increase during passage through the earth's atmosphere.

ISSN:0031-9171    

DOI:10.1063/1.1705944

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Experiments were performed in air on the mutual reflection of a pair of weak shock waves of strength &xgr; = 0.915. The strengths of the shock waves were measured interferometrically. The regular reflection data agreed with the weak shock regular reflection solution for the flow. Regular reflection terminated at the extreme angle &agr;e, and Mach reflection was found for larger angles. Four sets of experiments were performed in air with pairs of mutually reflecting shock waves of unequal strengths. The strengths of these shock waves were also measured interferometrically. The regular data agreed with the weak shock regular reflection solution for the flow. Mach reflection was found to occur for angles larger than the extreme angle. The experiments failed to resolve any of the difficulties concerned with Mach reflection.

ISSN:0031-9171    

DOI:10.1063/1.1705945

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Some experimental results are presented of colliding shock waves and the associated spherical flows generated by the blasts from two high‐pressure gas spheres. Glass spheres, 2 in. in diam, with their centers located 9 in. apart, containing air or helium up to 500 psi were used to produce the explosions. Instantaneous spark shadowgrams, multi‐spark schlieren photographs, and wave‐speed schlieren records of the radius‐time plane indicate that this method can be used successfully to study such interactions.

ISSN:0031-9171    

DOI:10.1063/1.1705946

出版商:AIP    

年代:1959

数据来源: AIP