摘要:

Atmospheric density values obtained from the motion of artificial earth satellites, at altitudes between 186 and 656 kilometers, are discussed. There is some doubt about the reliability of densities from satellites because of the effects of ionization and, in the case of nonspherical satellites, because of their orientation. Densities inferred from satellites are higher than for the ARDC model of the atmosphere. These densities are about ten times higher than densities inferred from rocket‐borne ionization gauges between 186 and 230 kilometers.The inference of atmospheric density from rocket‐borne ionization gauges is discussed critically, and densities so obtained are considered to be inferior in reliability to the satellite densities. The satellite densities suggest molecular scale temperatures higher than those of the ARDC model in one or more regions of altitude above 80 kilometers.

ISSN:0031-9171    

DOI:10.1063/1.1724338

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The dynamical properties of the solar wind blowing past the geomagnetic field are investigated by considering the effective viscosity and the resulting transition layer thickness. The collision of ions in the solar wind produces a negligible viscosity in the flow past the geomagnetic field, but such an inviscid flow is shown to be unstable. The resulting disordered interface between the field and the wind yields Fermi acceleration of ions and consequently a not insignificant effective viscosity. The Fermi acceleration results in suprathermal ions which may have an energy spectrum like that observed for primary auroral protons.The auroral zones and the agitated nature of the polar geomagnetic field are shown to follow from the depth of penetration of the solar wind into the geomagnetic field. The injection of gas into the geomagnetic field is studied. The effect at Earth of the distortion of the outer boundary of the geomagnetic field is computed; no matter how unevenly and anisotropically the outer field is distorted, the effect at Earth is a nearly uniform perturbation field which is closely parallel to the geomagnetic axis. Pushing in on the outer field increases the horizontal component at Earth, and pulling out decreases it; the total increase of the horizontal component is the algebraic sum of all the pushing and pulling. The simultaneous world‐wide onset and the main phase of a geomagnetic storm follow.The common tendency of large and/or violent bodies of plasma to produce suprathermal particles is noted and suggested to be a general dynamical property.

ISSN:0031-9171    

DOI:10.1063/1.1724339

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Studies of plasmas produced by sparks in vacuum are reported. The observations of principal interest concern the speed with which such plasmas leave the spark. The conclusions about plasma speeds are that they are approximately ten times greater than the thermal speeds associated with spark temperature, varying between 2 × 106and 2 × 107cm/sec, and in the range observed, the velocities are approximately independent of the spark parameters. It is suggested that the pinch effect may be the mechanism of plasma acceleration.

ISSN:0031-9171    

DOI:10.1063/1.1724340

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The velocity and attenuation of ordinary sound in liquid helium have been measured at a frequency of 1 Mc/sec in the neighborhood of the &lgr; point. By using measuring techniques of high resolution, it was possible to observe the behavior in this region in considerable detail. The velocity passes through a minimum approximately 2 × 10−4°K below the &lgr; point; the maximum attenuation occurs about 8 × 10−5°K belowT&lgr;. Both velocity and attenuation behave in a manner characteristic of a relaxation process, with the relaxation time a rapid function of temperature nearT&lgr;. The results belowT&lgr;can be described with good quantitative accuracy if this relaxation time is given by &tgr; = 8.8 × 10−12(T&lgr;−T)−1.Excess attenuation is also observed above the &lgr; point; this cannot be explained by the above relaxation process. The experimental uncertainties are so large in helium I that no reliable conclusions can be reached, but there is some indication that the quantity &agr;/&ohgr;2is not independent of frequency in this region.The behavior of the velocity is considered with regard to the Ehrenfest relations, and it is shown that the discontinuity in isothermal compressibility which those relations predict must be almost entirely due to a discontinuity in &ggr;. No contradiction of the Ehrenfest relations is implied, since present knowledge of &ggr; suggests that a discontinuity of the required magnitude may indeed occur.

ISSN:0031-9171    

DOI:10.1063/1.1724341

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Plesset and Zwick [M. S. Plesset and S. A. Zwick, J. Appl. Phys.23, 95–98 (1952);25, 493–500 (1954); J. Math. Phys.33, 308–330 (1955)] have calculated the rate of growth of vapor bubbles in slightly superheated steam under constant external pressure. Their calculation assumes that the temperature drop is localized in a thin ``boundary layer'' near the bubble wall; the predicted bubble radiusR(t) is asymptotically proportional tot1/2whenRis large enough for surface tension to be negligible. An analysis of this asymptotic phase is given, which avoids the above ``boundary layer'' assumption, and contains that part of the analysis of Plesset and Zwick dealing with this phase as a limiting case. The analysis is shown to be (approximately) applicable also to gas bubbles in supersaturated liquids.

ISSN:0031-9171    

DOI:10.1063/1.1724342

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Several authors studied experimentally the motion of a column of air in a long pipe, closed at one end and driven at the other by an oscillating piston. At resonance, they observed shock waves traveling in the tube. The paper presents a simple theoretical analysis of the motion, based on discontinuous linearized solutions and a secular equation. This equation guarantees that the motion remains periodic in spite of the cumulative effects of the nonlinear terms. For an inviscid gas, the amplitude at resonance is found to be finite and to be determined by nonlinear effects. This differs from previous results of Frederiksen. Friction can be taken into account and is included in the final results, which are presented in the form of a chart.

ISSN:0031-9171    

DOI:10.1063/1.1724343

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The spectrum of turbulence on Chandrasekhar's theory is derived.

ISSN:0031-9171    

DOI:10.1063/1.1724344

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The flow of a monatomic gas between two parallel plates kept at the same temperature and moving in opposite directions is studied. The relative velocity of the plates is much smaller than the speed of sound. The deviation from the equilibrium distribution, &fgr;(c,x), satisfies the linearized Boltzmann equation. The customary boundary conditions are adopted in which a fraction of the molecules is specularly reflected and the rest emitted with a Maxwellian distribution characteristic of the plate. The method consists of setting &fgr; = &fgr;+forcx> 0 and &fgr; = &fgr;−forcx< 0 so that positive and negative velocities are distinguished. We take &fgr;±=a0±(x)cz+a1±(x)czcx. The space functions are determined by taking half‐range velocity moments of the Boltzmann equation. Explicit results for the distribution function, flow velocity and stress are given for a general law of force. Numerical results are worked out for hard sphere molecules. The method treats both microscopic boundary conditions and conservation laws exactly. Precise results are obtained both for the low‐pressure region and for the high‐pressure coefficient of viscosity. The region of slip flow is analyzed. Maxwell's slip condition is remarkably close to the condition obtained here from the kinetic theory. In this region of pressures, the deviations from the velocity profile of the hydrodynamic slip flow theory are everywhere very small, and are completely negligible at distances greater than ⅛ of a mean free path from a plate.

ISSN:0031-9171    

DOI:10.1063/1.1724345

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

An electron beam densitometer is described for investigating the structure of a shock front in low‐density gases. The parameters measured by this technique are directly related to those parameters used in the accepted definition of shock front thickness. Hence the interpretation of the data is direct; no model of the shock front structure must be assumed and no theoretical treatment of nonequilibrium flow conditions is needed. An approximate method of data reduction is used for treating preliminary results. The measured value of the thickness of a Mach 4 shock in argon is about three mean free paths, measured in terms of the undisturbed gas. This technique provides a new tool for investigating relaxation phenomena behind shock waves.

ISSN:0031-9171    

DOI:10.1063/1.1724346

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The structure of a centered rarefaction wave in a relaxing ideal gas is studied theoretically, both analytically and numerically, with neglect of the Navier‐Stokes terms (viscosity, etc.) in the hydrodynamic equations. The role of the ``frozen'' sound speed is clarified, in that it is shown that there is a transition from ``frozen'' flow at short times to equilibrium flow at long times.

ISSN:0031-9171    

DOI:10.1063/1.1724347

出版商:AIP    

年代:1958

数据来源: AIP