摘要:

High‐velocity disturbances are observed to propagate along the walls of a high‐explosive operated shock tube in advance of the plane shock. Experiments are presented which determine the dependence of the geometry, energy, and velocity of the disturbance on such variables as the gas contained in the shock tube, the shock strength, and the roughness and composition of the supporting boundary. A model is constructed to explain the flow within the disturbance. Arguments are presented which show the disturbance to result from radiation originating in the luminous plane shock.

ISSN:0021-8979    

DOI:10.1063/1.1721633

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The activation of electrical contacts by decomposition products from organic vapors depends upon an adequate surface layer of adsorbed molecules. In earlier work minimum vapor pressures were given for activation by a number of organic compounds. From new experiments reported here the time available for adsorption between successive arcs is equally important, so that the minimum vapor pressure for activation to occur is inversely proportional to the time available for adsorption, or directly proportional to the rate of operation. The effective contact area and the energy are important also and, although quantitative data have not been obtained, it is reasonable to guess that these variables are connected by a relation not far fromp/n=KE/A, wherenis the minimum rate for activation to occur for the pressurepon the effective contact areaAwith the available energyE. Quantitative experiments have been made only upon the activation of palladium contacts by vapor of the organic compound known as fluorene, and only the proportionality betweenpandnhas been established.

ISSN:0021-8979    

DOI:10.1063/1.1721634

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A technique is given by which nonlinear differential equations may be solved approximately, using variational principles for which certain restrictions are made. Ordinary first‐ and second‐order equations are discussed in detail. The method is extended to encompass partial differential equations and applied to the Boltzmann transport equation.

ISSN:0021-8979    

DOI:10.1063/1.1721635

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Measurements of the apparent densities of copper and silver films formed by evaporation are described. The interpretation of the results and the manifestations of low apparant densities in physical experiments are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721636

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

With intended application to the theory of current noise in semiconductors, the spectrum is calculated of a random signal which may be in one of two states (YES‐NO: random telegraph signal), where the mean lives &sgr; and &tgr; of the two states may be different. The form of the spectrum is the same as for the case with equal lives, the single parameter &tgr; for that (classical) case now being replaced by 2[(1/&sgr;)+(1/&tgr;)]−1; i.e., the rates of transition are additive.

ISSN:0021-8979    

DOI:10.1063/1.1721637

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Effects of fast neutron irradiation in a nuclear reactor on order‐disorder in a series of nickel‐manganese alloys ranging from 16.5 to 31.9 atomic percent manganese have been studied by resistivity and magnetic induction measurements. Attainment of an ``irradiated state'' differing from either cold work or thermal disordering is suggested by comparison of exposure results on initially cold work disordered and initially thermally disordered Ni3Mn. In a region from 16.5 to approximately 22 percent manganese, thermally disordered alloys are markedly affected by irradiation. These effects also appear to be superposed on the disordering produced by irradiation of initially ordered alloys.From theoretical exponential dependence on period of irradiation, fast neutron disordering of Ni3Mn is determined by relating the Bragg and Williams order parameter quadratically with resistivity and linearly with magnetic induction. This leads to an estimate of 5000 for the ratio of the number of atomic replacements to primary collisions with neutrons of energy in excess of 0.5 Mev.

ISSN:0021-8979    

DOI:10.1063/1.1721638

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The linear dynamic Young's modulus of a vulcanized Buna‐N gum rubber is measured at frequencies of 0.05, 0.10, and 1.00 cps, in the temperature range −22°C to 30°C, by a method in which a small differential sinusoidal elongation is superimposed on a 5 percent static elongation. The width of the dispersion range on the temperature scale (the range in which the logarithm of the modulus increases steeply with decreasing temperature) is only about 10°C, as contrasted with widths as great as 25°C found in previous measurements on a similar compound at frequencies of several kilocycles. The modulus‐temperature plot shifts upward by only about 4°C per decade of frequency increase in the present range, as contrasted with about 10°C per decade in the previous measurements at higher frequencies. It is concluded that this elastomer cannot be described properly by means of the ``method of reduced variables,'' in which the dynamic properties are ascribed to mechanisms having identical temperature dependence, and that the low‐temperature behavior is governed by mechanisms distinct from those effective in the audio‐frequency range at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.1721639

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Theoretical relations between statistical scatter diagrams of two random variables and their joint probability density functions are used to derive a simple method of estimating correlation coefficients. The cases considered are those of variables with Gaussian and Rayleigh distributions. Theoretical curves and experimental scatter diagrams are given for each case. Some factors which may influence the accuracy of the proposed method are discussed, and it is concluded that the errors in estimating correlation coefficient will be of the order ±0.1.

ISSN:0021-8979    

DOI:10.1063/1.1721640

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Analysis has been made of pre‐onset streamers in room air at 760 mm with fast oscilloscope using both photomultiplier and electrical registration. The shape of the photon pulse observed by W. N. English is confirmed, and is interpreted. Current and luminosity roughly parallel each other in the streamer. Tip velocities ranged from 6×107cm/sec to 2×107cm/sec being highest near the point. The luminosity is constant over the path except at the very beginning and at the end of the path suggesting that ionization is also constant. The net number of positive ions left behind per cm length of streamer in consequence of the electron flow into the point is constant, and has been measured to be about 8×109ions per cm in general agreement with earlier work. Lateral deflection of the ends of streamer tracks by space charge left behind from previous streamers was directly observed.

ISSN:0021-8979    

DOI:10.1063/1.1721641

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Radioactive tracer techniques have been utilized to measure the rate of diffusion of gold into polycrystal‐line copper over the temperature range from 1000° to 375°C. These experiments have yielded the valuesQ=44 900±1300 cal/mole andD0=0.10±0.06 cm2/sec for the volume diffusion process in the temperature range from 1000°C to 750°C. Diffusion measurements at 550°C and 375°C indicated that the measured rates at these temperatures had been enhanced by grain‐boundary diffusion. Considerable attention was directed toward the variation of the diffusion coefficient with (1) the purity of the copper, (2) the grain size of the copper, (3) the thickness of the plating, and (4) the time of anneal. Variations of these parameters showed no significant effect on the diffusion coefficient, with the exception of the time of anneal. The measured diffusion rate at 1000°C was observed to decrease with increasing time of anneal.

ISSN:0021-8979    

DOI:10.1063/1.1721642

出版商:AIP    

年代:1954

数据来源: AIP