摘要:

Diamond explosively synthesized from metal/graphite mixtures in shock configurations resulting in high temperatures, moderately high pressures, and relatively long holding times at pressure were investigated by electron microscopy and electron diffraction. Particles up to 5‐&mgr; diameter consist of a matrix of 10–40 Å, variously oriented crystallites which contain clusters of randomly oriented 100–1600‐Å crystallites. Particles larger than 4–5 &mgr; are densely fused aggregates of such composite units.

ISSN:0021-8979    

DOI:10.1063/1.1660052

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

It is shown that the development of low‐index crystallographic facets in pits produced in the surface of polycrystalline iron is controlled primarily by the relative dissolution rates of different crystallographic orientations. The successive shapes of dissolving iron whiskers are used to predict the observed etch‐pit shapes using a topographical theory of crystal dissolution.

ISSN:0021-8979    

DOI:10.1063/1.1660053

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The arrangement of oxygen atoms in hexagonal rings in crystals of ice and muscovite gives two possible alternatives of epitaxial connection between these two structures. Which one of these two alternatives is favored depends entirely on the location of potassium atoms in the cleavage plane of the muscovite structure. Since potassium atoms are displaced from the normal environment by the slip taking place along partial Burgers vectors, epitaxial growth of ice crystals on muscovite can be used for the determination of the slip directions and hence for the study of partial dislocations in muscovite crystals.

ISSN:0021-8979    

DOI:10.1063/1.1660054

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Acoustic velocity, acoustic absorption coefficient, and acousto‐optical figure of merit for longitudinal acoustic modes of this crystal have been measured at room temperature. Among some interesting combinations of acoustic and optical modes, the longitudinal wave propagated parallel to the principal axisXof the index ellipsoid which lies in the (010) plane with the light polarized parallel to theYaxis (two‐fold axis,b) has been found to be particularly useful for acousto‐optical device applications because of its high figures of meritM(=n6p2/ &rgr;v3) = 127×10−18sec3/g andM′(=n7p2/ &rgr;v) = 242×10−7cm2sec/g and relatively low acoustic loss, 4.2 dB/cm at 300 MHz.

ISSN:0021-8979    

DOI:10.1063/1.1660055

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

This paper deals with the photoelectret effect in a natural plant product, Boswellia Glabra. It is found that this material in the pure form makes one of the best photoelectrets and gives a much more stable charge than other photoelectret substances. The sample is polarized for 5 min by the simultaneous application of field and illumination, then it is reilluminated and the depolarization current reveals the nature of the polarization. This paper also deals with the effect on photoelectret formation of continued application of the polarizing field for five more minutes, keeping the sample in the dark. It is found that this process gives much better stability of charge and longer life to the electret.

ISSN:0021-8979    

DOI:10.1063/1.1660056

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Thermal currents have been obtained from corona‐charged Mylar films exposed to a humid atmosphere for variable times. A theory that we have recently developed to account for the current ``spectrum'' of these ``near surface'' charged specimens is put into a form that facilitates routine analysis of the peaks. Exposure of Mylar to 100% RH at 50°C has a drastic effect on the four traps previously reported. After 5 days, they have completely disappeared, and only 0.6% of the total initial charge remains. Ninety percent of this latter charge is held in a trap at a depth of 2.6 eV, and the remainder at 1.3 eV. Assuming that the traps empty under monomolecular conditions, trap densities are of the order of 1014/cm3, and mobility‐lifetime products, 10−8cm2/V; to be compared with 1016/cm3and 10−10cm2/V for the dry samples. The thermal current spectra show, in explicit detail, how humidity affects charge storage in Mylar.

ISSN:0021-8979    

DOI:10.1063/1.1660057

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The18O(p, &ggr;)19F nuclear reaction has been employed for measuring self‐diffusion coefficients, in sintered U16O2at temperatures between 925° and 1425°C. This method allows the determination of concentrations in a well‐defined diffusion layer due to the resonant nature of the reaction.

ISSN:0021-8979    

DOI:10.1063/1.1660058

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements have been made of the velocity distribution of the flow of cesium gas from an orifice in the near‐free molecule regime. The apparatus design is based on the time‐of‐flight method using a single disk chopper and a surface ionization gauge. Measured velocity distributions are compared with the corresponding Maxwellian distribution adjusted to have the same peak amplitude. Although the two distributions agree closely at high Knudsen numbers (i.e., Kn>10), the comparison at smaller Knudsen numbers indicates that the measured distribution is deficient in low‐speed molecules. This deficiency increases with decreasing Knudsen number and with decreasing angular position from the centerline of the orifice. The experimental results are compared with the predictions of existing analyses of near‐free molecule flow through an orifice.

ISSN:0021-8979    

DOI:10.1063/1.1660059

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An approximate expression is derived for the firstnterms of exact series expansions for the electromagnetic fields inside a metallic spherical shell due to an impinging plane monochromatic wave. The formulas derived are valid if the ratio (n+1) (n+2) / 2Ri|k2| ≪1, wherek2is the propagation constant in the metallic screen andRiis the radius of the inner sphere. Contrary to some existing approximate formulas, the present ones describe the fields also at the resonance frequencies corresponding to the firstnterms. They fail to represent the fields near or at the resonance frequencies corresponding to the (n+1) th term and higher ones.

ISSN:0021-8979    

DOI:10.1063/1.1660060

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Electromagnetic responses of hollow cylinders under ac excitations are discussed with a particular reference to the end effect and the skin effect. When hollow cylinders are used for damping ripples, a specific shape factor, length‐to‐diameter ratio of 0.88, was found to be most effective. The electromagnetic characteristics revealed in the present analysis are shown to manifest themselves also in the superconducting states.

ISSN:0021-8979    

DOI:10.1063/1.1660061

出版商:AIP    

年代:1971

数据来源: AIP