摘要:

When the anode potential of a nonoscillating magnetron is lower than the cut‐off potential, the discrete electron‐to‐electron interaction has an effect on the space‐charge distribution which would be negligible if only resulting in fluctuations about a known steady state. However the states proposed by Brillouin, Slater, and others are not steady states in this sense. The electron interaction must, therefore, be expected to produce a steady drift away from such initial states. This paper discusses qualitatively the final steady state to be expected and its dependence on the ratio of anode voltage to cut‐off voltage. Because of the involved nature of the electron distribution function no attempt is made to calculate the space‐charge distribution explicitly.

ISSN:0021-8979    

DOI:10.1063/1.1702363

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

This paper describes both a traveling‐wave method and a standing‐wave method for determining complex dielectric constants of liquids from measurements made at 10‐cm wavelength with a traveling probe immersed in a dielectric‐filled slotted line. An interferometric null technique was developed for improving the accuracy of the measurements, especially in highly absorptive media. In the traveling‐wave method, absolute measurements of both wavelength and absorption index can be made simultaneously; from these two quantities the complex dielectric constant is readily computed. In the standing‐wave method, the absorption index is determined graphically from the power‐standing‐wave ratio while the wavelength is obtained by a modified null technique. For low loss media, a simplified standing‐wave method is practical whereby the absorption index is obtained from measurements of the breadths of successive minima of the standing wave. Corrections for the finite resistance of the short circuit used in the standing‐wave method and for conductor losses along the slotted line are fully treated.

ISSN:0021-8979    

DOI:10.1063/1.1702364

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The paper deals with the propagation of unattenuated elastic waves in a cylindrical bore through an elastic material of infinite extent filled with a fluid. The phase and group velocity dispersion curves are plotted for axial symmetric waves in the coupled fluid‐solid system.

ISSN:0021-8979    

DOI:10.1063/1.1702365

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The effect of Co60&ggr;‐irradiation on the direct current conductivity &sgr; of polyethylene has been determined up to an intensityIof 4000 roentgens per hour at room temperature. The equation&sgr;/&sgr;00=1+(I/I0)34describes the data where &sgr;00is the conductivity without radiation and is the order of 10−18(ohm cm)−1andI0is 20 roentgen/hr. Measurements at liquid nitrogen temperatures give a factor of 20 decrease in the normal conductivity and a factor of 25 decrease in the radiation induced conductivity below their respective room temperature values.The temperature data serves to suggest an ionic mechanism for electrical conduction in polyethylene as opposed to an electronic mechanism. In fact, the ion contributing most to the conduction in the polyethylene may well be the proton.

ISSN:0021-8979    

DOI:10.1063/1.1702336

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A new theory of metal transfer and wear is suggested in this paper. The essence of the theory is as follows: Metal transfer and wear take place at points of actual contact. The interfaces of the high spots that actually make contact are roughened as the result of plastic deformation when they carry normal load. The mechanical interlocking effect of these roughened interfaces is the primary cause of metal transfer and wear. Due to the mechanical interlocking effect of the roughened interface, and the strain‐hardening that accompanies plastic deformation, the application of a tangential force will break one of the pair of the contacting high spots a certain distance away from the interface rather than at the original interface. A secondary cause of metal transfer is the adhesion or the diffusion process which takes place during the temperature flash that occurs during breakage. If the adhesive force is very weak and the diffusion process is not rapid enough to cause the sheared‐off peak of the high spot to become a blob of transferred metal, the small piece of metal sheared from the high spot can leave as a loose wear particle. This proposed theory explains the welding of the sheared‐off peak to its opponent high spot as the consequence of friction, whereas, in the ``welding'' theory of friction, welding is considered as the cause of friction. Most metallic surfaces in ordinary atmosphere are always covered by a surface film. The effect of surface contamination on metal transfer, wear, and the shear component of friction is discussed. Difficulties encountered in applying the ``welding'' theory to explain the friction of and metal transfer between contaminated surfaces where metallic adhesion is absent, are obvious. Experimental support of this new theory is given here. It includes as direct evidence (1) the roughening of the interface as the result of the plastic deformation, (2) the perfect matching at the roughened interface, which gives a strong mechanical interlocking effect, and (3) a definite region of severely strain‐hardened metal near the interface.

ISSN:0021-8979    

DOI:10.1063/1.1702337

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

In current theories of the concentration dependence the solute molecules are treated as point centers of disturbance. The finite size that produces a shielding of two interacting particles in the presence of intervening ones reduces the interaction calculated in the point approximation and thus reduces the discrepancy between experiment and theory. An approximate treatment for a spherical solute based on the cage model, and hence more adequate at high concentrations, is presented. It operates with a spherical enclosure around a central particle. The position of this shell reflects the relative extent to which particles beyond nearest neighbors can hydrodynamically interact with the central molecule. Thus, a parameterfappears in the theory which increases slowly with concentration and approaches a limit corresponding to the coincidence of the shell with the wall of the nearest neighbor cage at high concentrations. In the framework of the present theory,fmust be regarded as a semiempirical quantity. The hydrodynamic problem can be handled rigorously. The relative viscosity calculated is in satisfactory agreement over a range of concentrations with empirical expressions successfully applied to pertinent systems. The initial value offderived from the observed coefficient of the quadratic term is also reasonable.

ISSN:0021-8979    

DOI:10.1063/1.1702338

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Using empirical relations established in the study of electron diffraction patterns of uniform thin films of aluminum, the contrast between the most intense ring and the background is calculated for other morphologies as a function of the accelerating voltage on the camera.In all cases the contrast increases with voltage. The gain is marked if the specimen is nowhere very thick. For specimens that have very thick regions the contrast increases approximately as the square root of the voltage in the range 50 to 150 kv. The situation in reflection‐diffraction in general lies between these extremes. Increasing the voltage has a more limited effect on increasing the range of specimen thicknesses that can be examined than had been previously supposed.

ISSN:0021-8979    

DOI:10.1063/1.1702339

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Experimental methods are given for determining the complex admittance and electron density of gas discharges by the use of microwave techniques. Applications are discussed where the discharge is contained in either high or lowQresonant cavities.

ISSN:0021-8979    

DOI:10.1063/1.1702340

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Self‐diffusion in pure polycrystalline silver has been measured using Ag110as a tracer. The results of the high temperature experiments, where volume diffusion is predominant, are in excellent agreement with those of other investigators. A least‐squares calculation using all available data on volume diffusion of silver gives as a value for the diffusion coefficientD=0.724e−45, 500/RT. The occurence at low temperatures of grain boundary diffusion, in which the activity decreases exponentially with the first power of the penetration depth, as reported by Hoffman and Turnbull, is confirmed.

ISSN:0021-8979    

DOI:10.1063/1.1702341

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Experimental investigations show that Langmuir probe measurements can give quite erroneous results, due to work function changes of the probe, insulating layers on the probe surface, or different work functions at different places of the probe. The deposition of evaporated cathode compounds, the adsorption of oxygen released from oxide cathodes, and the sputtering and evaporation from the probe may change the work function of a pure tungsten probe in time scales of seconds. In oxide cathode tubes especially, it is necessary to measure immediately after the probe has been thoroughly cleaned. AnX ‐ Yplotter, which recorded the whole probe characteristic in seconds, was found to be most suitable. No deviation from the Maxwellian velocity distribution of the plasma electrons could be found over a range of nearly four orders of magnitude in probe current, even in oxide cathode tubes under conditions where such deviations have been found by other authors.

ISSN:0021-8979    

DOI:10.1063/1.1702342

出版商:AIP    

年代:1952

数据来源: AIP