摘要:

The propagation characteristics for circularly symmetricTMmodes in a coaxial structure with two dielectrics offer many points of interest. For a given mode, the pertinent parameters are the ratio of the dielectric constants of the two media involved, the ratio of the two radii, and the operating frequency, expressed, say, in terms of the cut‐off frequency for theemptyguide. Among the results of special interest are the facts, previously pointed out by Frankel and by Bruck and Wicher, that the phase velocity for a given propagating mode may lie between the phase velocities corresponding to each of the two unbounded dielectrics and that, by proper choice of parameters, it is always possible to obtain a phase velocity of a preassigned value higher, of course, than the lower of the two velocities for the unbounded media. This suggests the possibility of using such structures in linear accelerators. The results of an extensive computational program are presented in the form of families of curves showing the dependence of the propagation constant and of the phase velocity on the parameters of interest. Some discussion of the power flow and field distribution is also given.

ISSN:0021-8979    

DOI:10.1063/1.1699911

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The two‐dimensional supersonic irrotational flow of a gas in a jet is studied by use of the Ka´rma´n‐Tsien pressure‐volume law. There are two limitations to such a study: (1) since the fluid flow is not continued from the subsonic range, arbitrary boundary conditions must be prescribed; (2) use of the Ka´rma´n‐Tsien pressure‐volume relation implies a restriction on the permissible range of pressure, density, and velocity. On the other hand, use of the Ka´rma´n‐Tsien law furnishes several advantages: (1) the velocity potential and stream function satisfy the wave equation in the hodograph plane and hence these functions can be easily determined; (2) the mappings between the physical and hodograph planes may be completely characterized and studied in detail. This gain in information should be valuable in the qualitative understanding of phenomena as well as in obtaining first approximations to quantitative solutions. In the case of jets, with free stream lines as boundaries, it is shown that two functionspossessing certain desired propertiescompletely determine the Ka´rma´n‐Tsien flow. Further, the phenomenon of the periodic recurrence of the free stream jet boundary is explainedby a folding property of the map of the flow in the hodograph plane.

ISSN:0021-8979    

DOI:10.1063/1.1699912

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A method is given for determining the residual stress in a sheet material by removing successive uniform layers of material from the surface of a test specimen and measuring the resulting curvature. From the condition of equilibrium of a free specimen, a stressvscurvature relation is derived which holds over the depth to which material has been removed. The method applies when the stress is constant in the plane of the specimen and varies through the thickness. An experimental technique is described which is believed to satisfy the essential requirement that the removal of surface layers should not affect the stress in the remaining material, and a practical example is given.

ISSN:0021-8979    

DOI:10.1063/1.1699913

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

An objective has been designed which is particularly suitable for the study of tissue sections. It consists of a large opening polepiece system operated at a focal length of 12 mm. It includes a diaphragm which can be centered (not during operation) and translated on the axis. Angular apertures of as low as 2×10−3radian with large areas of bright field can be achieved. A simple method of aligning the aperture is described.

ISSN:0021-8979    

DOI:10.1063/1.1699914

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The time dependence of current passed by commercial pentodes has been studied under pulsed conditions of operation. A decay of current is observed in the microsecond time range for those tubes operated for long periods under cut‐off conditions. This decay has been interpreted in terms of the resistance and capacitance of the interface layer known to exist from x‐ray diffraction studies. Techniques are developed and applied to the measurement of this interface resistance and capacitance as a function of temperature. Following the initial current decay, a partial recovery is observed when long pulses are used. This effect results from Joule heating of the interface layer.

ISSN:0021-8979    

DOI:10.1063/1.1699915

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Measurements have been made of the pressure ratio,R, due to thermal transpiration in hydrogen, helium, argon, and nitrogen between a warm temperature of 297°K and cold temperatures of 77.3 or 195°K. It is found thatRdepends onX, the product of the pressure and tube diameter according to the empirical relation,R=P1/P2=(AX2+BX+Rm)/(AX2+BX+1), whereAandBare constants which depend on the gas and on the warm and cold temperatures, andRm=(T1/T2)½. TheRagainstP2, and threforeX, curves for different gases are found to be related by a ``pressure shifting factor''f.The use of these results to correct measurements of adsorption equilibrium and vapor pressures at low pressures and low temperatures is discussed.Vapor pressures at 77.3°±0.5°K corrected for the thermomolecular pressure effect have been measured for krypton and xenon:Krypton1.754±0.002 mm;Xenon1.93 ±0.01×10−3 mm.

ISSN:0021-8979    

DOI:10.1063/1.1699916

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Experimental and theoretical directional patterns are compared for three polystyrene rod antennas of length variable from about 4 to 10 wavelengths, retaining relative shape in the length direction. The comparison shows that the apparent index of refraction,n, decreases with increasing length. Accordingly, the directional patterns are less sharp than might be expected from the estimated values ofnwhich are constant for a constant relative shape.

ISSN:0021-8979    

DOI:10.1063/1.1699917

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Asymptotic methods are used to find approximate solutions of the acoustic wave equation in a medium in which the velocity is a continuously variable function of one coordinate. It is shown that, when the velocity function has a minimum, undamped normal mode solutions exist and are closely analogous to the internally reflected waves in the case of a medium made up of discrete layers. By converting the sum of the high order normal modes into an equivalent integral, it is shown that superposition of these modes leads to geometrical ray theory modified by diffraction in a manner that may be computed from the incomplete fresnel and airy integrals.

ISSN:0021-8979    

DOI:10.1063/1.1699918

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

In dealing with numerical values for relative intensities derived from the Debye‐Scherrer technique, the alteration of diffracted intensities produced by absorption in the sample cannot be ignored. Claassen has shown how this effect can be allowed for in the case of homogeneous cylindrical samples. This paper deals with a sample consisting of a cylinder surrounded by another annular cylinder both when the core is inert (i.e., absorbing and producing only extraneous scattering) and when the annulus is inert. The method is applied to show how the diffraction pattern for a liquid enclosed in a glass container may be corrected for the diffuse diffraction of the container as well as for absorption in the liquid and in the glass.

ISSN:0021-8979    

DOI:10.1063/1.1699919

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Coefficients of static friction of six metals (Fe, Ni, Cu, Pb, Sn, and Zn) have been measured at temperatures ranging from liquid helium up to room conditions (and in two cases above this). Shear strengths and hardnesses of these metals were measured over the same range of temperatures. It was found that in spite of the generally large variation of both of these latter quantities with temperature, their ratio is in most cases dependent, to only a slight extent, on temperature, following rather closely the change of the static‐friction coefficient with temperature. This fact tends to substantiate the adhesion theory of friction proposed by F. P. Bowden.

ISSN:0021-8979    

DOI:10.1063/1.1699920

出版商:AIP    

年代:1951

数据来源: AIP