摘要:

A chemical transport process for the growth of zinc sulfide single crystals is described. The reaction employed isZnCl2(g)+H2S(g)=2HCl(g)+ZnS(s).The rate of transport of ZnS is discussed, and details of the thermodynamics of the system and the conditions for the growth of single crystals with a pure cubic structure are given. Crystals having this structure and as high a chemical purity have been difficult to obtain heretofore. The chemical analysis and some of the luminescent properties of these crystals are described briefly.

ISSN:0021-8979    

DOI:10.1063/1.1728830

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A general theoretical expression is derived for an electron trajectory in an oscillating electric field. This result is extended to an electron stream, and the current and velocity are found exactly, in the absence of space charge, for any plane within the region of the oscillating field. The limits on the validity of the analysis are established, and application is made to the parallel‐plane diode or klystron gridded gap. Within the restriction that the normalized gap voltage be less than the normalized gap lenth, exact results for current and velocity are obtained.

ISSN:0021-8979    

DOI:10.1063/1.1728831

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Single crystals of commercially pure (2S) aluminum were stressed in push‐pull and the development of surface fatigue cracks observed continuously with a specially mounted 300× optical microscope. Time‐lapse photographic sequences were used to measure the propagation rate and to determine the relation between surface slip markings and crack propagation mechanisms. Cross‐sectional views of the internal disposition of the crack were obtained by sectioning in a microtome. Back reflection x‐ray photographs were used to gather evidence concerning the deformation substructure near the fatigue crack. The data thus assembled allow the mechanism of fatigue crack propagation to be described in terms of surface slip bands, the stress concentration at the edges of these bands, and subgrain formation which occurs in the vicinity of the crack tip. The linear relationship between the logarithm of the instantaneous crack length and the number of stress cycles was confirmed and the proportionality between the crack length and the plastic zone immediately ahead of the tip was demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.1728832

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The thermodielectric converter, a device employing a ferroelectric material as the active element in converting thermal to electrical energy, is analyzed. The efficiency and power‐handling capacity are calculated for operation of a ferroelectric material in the induced‐ferroelectric region on the basis of an idealization of the polarization (P‐E) characteristics. The idealization includes the induced‐ferroelectric transition but excludes hysteresis and other nonlinear effects. For a barium titanate‐like material, the following values are obtained: A maximum theoretical efficiency of about 0.5% in an ideal temperature cycle of Carnot efficiency 7.1%; and a power‐handling capacity of roughly 32 w/lb per temperature cycle per sec.

ISSN:0021-8979    

DOI:10.1063/1.1728833

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The boundary value problem for a superconductor has been solved for specific axially symmetric geometries. The interior field of a right circular shell is found to be quite uniform. Also it is found that the ends of the shell can be shaped to overcome a singularity at the end. This permits a near critical and uniform field to be obtained over a very large volume of the central region. Experimentally it was found that a simple geometric shape electrolytically coated with lead would trap a field of 630 gauss with homogeneity in agreement with calculation.

ISSN:0021-8979    

DOI:10.1063/1.1728834

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A cooling system referred to here as the Ettingshausen cooler, based on the Ettingshausen and Nernst‐Ettingshausen effects is studied. It is shown that under dynamic conditions, these two effects are coupled and provide a mechanism for producing a cooling effect. Thermodynamic analysis is carried out and the coefficient of performance is determined. The analysis produced a dimensionless thermomagnetic figure of merit, which sets the requirements on the material's properties. For effective cooling, materials with high thermomagnetic numbers are required. A brief review of the relevent transport processes is made, which shows that intrinsic semiconductors, within certain temperature ranges, are most suitable for the Ettingshausen cooler.

ISSN:0021-8979    

DOI:10.1063/1.1728835

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Measurements of internal friction and Young's modulus as a function of temperature and 13.7‐Mev deuteron bombardment flux are reported for polycrystalline tungsten. A dislocation‐relaxation peak in the internal friction as a function of temperature is observed. The peak height is found to be reduced by irradiation. The background internal friction decreases and the modulus increases with bombarding flux. The experimental results for modulus change with bombardment is shown to fit a simple dislocation pinning model reasonably well. The effect of immobile radiation induced vacancies on Young's modulus in tungsten is observed to be −0.44% per atomic percent of vacancies compared with Dienes' prediction of −1.0%.

ISSN:0021-8979    

DOI:10.1063/1.1728836

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Ice growing dendritically from supercooled water along some foreign surfaces changes its orientation as it grows, in response to asymmetrical temperature gradients. A qualitative, preliminary description and discussion of this phenomenon is presented. The only stable growth is with thecaxis [0001] perpendicular to the surface. Other orientations in general curve toward this. Increased initial supercooling sharpens the curvature, and dissolved NaCl inhibits it. The curvature is discussed in terms of edge dislocations introduced during growth. The density of dislocations responsible for the curvature reaches 108lines/cm2. Orientations of ice grown in containers is a consequence of curved growth. Direct formation of polycrystalline ice from supercooled water is reported. The method used in observing curved ice growth also allows observation of the formation of striations and related phenomena.

ISSN:0021-8979    

DOI:10.1063/1.1728837

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A beat frequency bridge for large signal field effect measurements based on an ac modulation method is described. Some field effect measurements with this bridge on low resistivity germanium and gallium arsenide are reported.

ISSN:0021-8979    

DOI:10.1063/1.1728838

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The Hall mobility in semiconductors and insulators can be greatly affected by inhomogeneous impurity distributions. This is due to the formation of large space‐charge regions surrounding local inhomogeneities. The scattering cross section of Coulombic centers can be increased by over an order of magnitude when inhomogeneously distributed. The mobility resulting from scattering from inhomogeneities varies roughly asT−½and decreases with decreasing carrier concentration. Assuming that inhomogeneities can occur frequently, various anomalous Hall mobility effects can be explained, such as mobility ``killers'' in GaAs, InAs, and InP; giant scattering cross sections in GaAs, InP, CdS, and CdSe; abnormally low mobilities in compensated InAs; and low mobilities in ZnO containing precipitates.

ISSN:0021-8979    

DOI:10.1063/1.1728839

出版商:AIP    

年代:1962

数据来源: AIP