摘要:

It is the purpose of this report to describe an instrument for the determination of densities in rarefied gas streams which utilizes the attenuation of an electron beam. The electron beam in passage through a rarefied gas becomes scattered in a number of elastic and inelastic processes, and decays to a fraction of its initial intensity in the distance of a few electron mean free paths. Where the optical aperture of the detector is suitably small, the familiar linear absorption law applies. The mass absorption coefficient in this case is higher and more favorable for work at the lowest test section densities than in other absorption techniques investigated to the present. The instrument was used in an investigation of air flows about a sphere and a wedge, and in the undisturbed stream. The flow was maintained constant for all portions of the test at Mach 1.95, Re/in. ∼200, test section static pressure ∼80 &mgr; Hg. Plots of the original and the reduced data show adequate internal consistency and a qualitative conformity with expected configurations.

ISSN:0021-8979    

DOI:10.1063/1.1735151

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The rate of generation of Barkhausen pulses in barium titanate when the polarization direction is slowly reversed is profoundly influenced by the form of the voltage cycling given to the crystal. It is concluded that the rate of nucleation of new domains is determined by the field near the electrodes which, in turn, is the resultant of the applied field and a relaxing space charge field. This result follows directly if the Barkhausen pulses represent individual nucleations though this assumption is not crucial since the generation rate of the pulses parallels the total current at all stages of the polarization reversal. It is concluded also that the majority of the Barkhausen pulses occur independently of each other and of their surroundings.

ISSN:0021-8979    

DOI:10.1063/1.1735152

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Germanium surfaces were bombarded with argon ions and then heat‐treated under high vacuum. Room‐temperature values of surface recombination velocity, surface conductivity, dark field effect, and field effect under illumination were measured after successive heat treatments. In addition, the temperature dependence of these quantities was determined. It was confirmed that after annealing of the bombardment damage, a large number of acceptor type surface states approximately clamped the surface potential. Two types of recombination centers were identified: type 1, located near the middle of the gap and type 2, located near the valence band. The various heat treatments produced changes in the density of the type 1 centers but did not appear to effect the density of the type 2 centers.

ISSN:0021-8979    

DOI:10.1063/1.1735153

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

This paper describes a method for the simulation of space charge in an electrolytic tank by the introduction of currents into the electrolyte by means of sources projecting through the tank floor. The theory and design criteria for this space‐charge simulation system are presented. This method of simulation is used as a means for introducing detailed space‐charge effects into the determination of electron trajectories in axially symmetric, high‐perveance electron guns. The trajectories determined by use of this system are compared with beam characteristics measured experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1735154

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The driving force leading to densification during sintering in the presence of a liquid phase and the material transport phenomena have been analyzed and relationships for the densification rate during the rearrangement process, the solution‐precipitation process, and the final coalescence process have been determined. These relationships allow an experimental determination of the mechanism of sintering in the presence of a liquid phase on the basis of the time, particle size and temperature dependence of the densification rate. In addition, they allow direct calculations of densification rates to be made for certain simple systems for which property data are available.

ISSN:0021-8979    

DOI:10.1063/1.1735155

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Experimental measurements of the densification rate and microstructure changes taking place during sintering of the iron‐copper system, which is typical of those systems showing spheroidal grain development, indicate that in this system the rate of densification during liquid phase sintering is controlled by diffusion through a liquid film between particles. Dependence of the sintering rate on time, particle size and temperature are in agreement with theoretical predictions. A theoretical estimation of the sintering rate is in good agreement with experimental measurements.

ISSN:0021-8979    

DOI:10.1063/1.1735156

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Diffused diodes, fabricated from plastically deformed germanium, were examined for high‐speed switching response. The degradation of minority carrier lifetime caused by dislocations generated during plastic deformation greatly reduced the minority carrier storage effect and permitted fabrication of diodes with turnoff times of the order of 10−9sec.

ISSN:0021-8979    

DOI:10.1063/1.1735157

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The temperature coefficients of resistance (TCR) of films of sputtered Au, Ir, Mo, Ni, Pd, Pt, Rh, Ta, and W, of evaporated Al, Cr, Ti, and Zr, and of the alloy films Pt&sngbnd;Au, Pt&sngbnd;Ir, and Pt&sngbnd;Ni have been measuredin vacuoover the temperature range 25° to 600°C; the film thickness range was 75 to 2000 A. The TCR values of films of the substantially pure metals were in the range ⅓ to ⅔ those of the respective bulk metals whether deposited on glass, Vycor, or Stupalith substrates. The departure of the conditions of growth of the film from those usual for the bulk metal, i.e., rapid cooling effects and impurities present, contributed imperfections which reduced the TCR of the film. The TCR values of alloy films were low, 0.0004 per °C for Au&sngbnd;Pt, and resistivities were 3 to 4 times that of either constituent. The TCR values of sputtered films of Mo, W, and Ta and of evaporated Cr, Zr, and Ti were generally less than 0.0001 per °C. Electron diffraction examination of films of these latter metals revealed oxide inclusions in the films. The presence of the oxide of the metal reduced the TCR and increased the R/sq of the film as compared to those of the pure metal. Only films of gold, platinum, and iridium were corrosion resistant in air near 600°C. Overcoats of evaporated SiO provided partial protection for the others. Powers up to 15 watts were dissipated by refractory metal films only132by ½ in. and about 750 A thick. These high values contrasted with less than ¼ w for a gold film of similar dimensions.

ISSN:0021-8979    

DOI:10.1063/1.1735158

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The density of both solid and liquid silicon has been measured in the vicinity of its melting point. From the average of several determinations, the increase in density upon melting is 9±1%.

ISSN:0021-8979    

DOI:10.1063/1.1735159

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The maximum switching velocity (&Dgr;P/&Dgr;t)max·1/Psin BaTiO3single crystals, obtained by the ultrasonic method, is discussed not only as the function of the applied pulse field, but also of the pulse width. Maximum switching current response (dP/dt) measured by the single pulse method and expressed as the exponential function of the field by Merz, is also considered as the limiting case of our expression as the applied pulse width becomes infinitely wide.

ISSN:0021-8979    

DOI:10.1063/1.1735160

出版商:AIP    

年代:1959

数据来源: AIP