摘要:

Helium permeation, diffusion, and solubility have been measured for lithium, sodium, potassium, rubidium, and cesium borate glasses. The compositional dependence of each of these properties is related to the compositional dependence of the molar volume. Initial additions of alkali oxides (with the possible exception of lithium) to vitreous B2O3serve to compact the glass network and reduce helium mobility and solubility. However, at higher alkali oxide concentrations, the network is expanded and helium diffusion actually increases with increasing alkali oxide concentration. These results are contrary to any previously reported for glasses, as inert gas mobility has always been reported to decrease with increasing alkali oxide content. However, the molar volume considerations used here can be applied to previous studies with equal success.

ISSN:0021-8979    

DOI:10.1063/1.1662865

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The plane of the wedge disclination loop is assumed to be parallel to the basal plane in hexagonal‐close‐packed crystals. The rotation axis of the loop lies in the basal plane. Closed‐form solutions have been obtained for the stress field and elastic energy of the disclination loop. Unlike the case of a twist disclination loop, there is a dilatational field associated with a wedge disclination. The strain energies of wedge disclinations are computed for some common hexagonal crystals. It is noted that for the same loop dimension and angle of rotation, the strain energy of a wedge disclination loop is generally larger than that of a twist disclination loop. This is mainly due to the fact that, for these materials, the Young's moduli along theCaxes are higher than those in the basal planes.

ISSN:0021-8979    

DOI:10.1063/1.1662866

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The lattice dynamics, second‐ and third‐order elastic constants, and the temperature variation of the lattice thermal expansion of erbium are worked out on the basis of Keating's method. The ten third‐order elastic constants are calculated using four third‐order anharmonic parameters. The model used here reproduces the measured pressure derivatives of the second‐order elastic constants of erbium well. The low‐ and high‐temperature limits&ggr;¯Land&ggr;¯Hof the lattice thermal expansion are evaluated and the calculated&ggr;¯His compared with that obtained from the thermal expansion and specific heat data. The dispersion relations in erbium are found to be similar to those in holmium.

ISSN:0021-8979    

DOI:10.1063/1.1662867

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A self‐consistent solution for finding the complex dielectric constant of a multiphase mixture with confocal ellipsoidal shell inclusions is presented. Implicit in the solution are the first‐order effects of neighboring inclusions, and hence, the high inclusion density limit is approached correctly. The solution contains the special cases of spherical shells, ellipsoids, spheres, disks, and needles. Reasonable agreement of the theory with some experimental data for wet wood is found. The presence of ellipsoidal shells in a mixture gives rise to a much greater separation between the upper and lower bounds of a mixture dielectric constant as compared to the limits obtained for solid ellipsoidal or spherical inclusions.

ISSN:0021-8979    

DOI:10.1063/1.1662868

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The perfection of dislocation‐free silicon crystals has been followed as a function of heat treatment at 1000°C by x‐ray anomalous transmission. For floating‐zone silicon crystals carefully grown to exclude oxygen and carbon, the intensity of the x‐ray anomalous transmission does not change following heating for several hundreds of hours at 1000°C. This contrasts with previous measurements on floating‐zone silicon where the intensity decreased drastically following the same heat treatment. Suitable experiments have ruled out carbon or vacancies as being responsible for the effects observed in the floating‐zone crystals. A Czochralski crystal with 7.5 × 1017cm−3of oxygen shows a rapid decrease in perfection when heated at 1000°C. The x‐ray anomalous transmission is more sensitive to the heat treatment effects in the early stages of precipitation than the usual infrared 9‐&mgr;m absorption measurements. The defects contributing to the decreased x‐ray anomalous transmission have been detected by x‐ray section topographs. Although the precipitate has not been directly identified, these and previous experiments allow the conclusion that oxygen clustering is responsible for the heat treatment effects observed. The results are discussed in the light of recent theory on the effect of clustering on x‐ray anomalous transmission.

ISSN:0021-8979    

DOI:10.1063/1.1662869

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The pressure in the scattered wave resulting from irradiation of an infinitely long, circularly cylindrical, thin isotropic viscoelastic shell by a plane monochromatic sound wave is calculated. The shell is assumed to be freely suspended in an ideal fluid and to enclose a second ideal fluid. The motion of the shell is described by means of Lagrange's equations, altered so as to account for viscoelasticity. The result for the scattered wave has the form of that for the elastic case except that an expression involving elastic constants is replaced by an impedance function involving viscoelastic parameters. Some properties of this impedance function are drawn from electrical circuit theory and used in discussing the usefulness of the viscoelastic parameters relative to modifying the scattered wave.

ISSN:0021-8979    

DOI:10.1063/1.1662870

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

By use of an ultracentrifuge, the force of adhesion between small gold spheres (2–8 &mgr; in diameter) and the following types of substrates has been measured: (111) cleavage planes of silicon single crystals with or without a chemisorbed oxygen monolayer and, alternatively, cleavage planes covered with oxide layers 40 and 130 Å thick. Further, instead of the silicon, gold substrates prepared in three different ways were used. The experiments were carried out at room temperature under ultrahigh vacuum (uhv) conditions. The experimentally determined forces are compared with the results of the theory of van der Waals interaction between extended solid bodies.

ISSN:0021-8979    

DOI:10.1063/1.1662871

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The thermal expansion of 15 alkali halides has been investigated from 70 to 570 K. The single‐crystal specimens of LiF, LiCl, LiBr, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbI, CsCl, CsBr, and CsI are examined using a high‐precision differential dilatometer in conjunction with an electronic micrometer. The results are compared with those available in the literature and are found to be in reasonable agreement. The Gru¨neisen parameter &ggr; has been calculated using the present thermal expansion data. For a given cation group, the value of &ggr; is very close, but increase in the cation size decreases &ggr; slightly. The indications are that in the temperature range under investigation &ggr; increases very slowly with temperature.

ISSN:0021-8979    

DOI:10.1063/1.1662872

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Assuming that small crystallites can perform noninteracting random walks on a substrate, one may calculate the expected rate of collisions between them and the rate of decrease of their numbers. Comparison with experimental results for gold on potassium chloride at temperatures less than 150°C (for which coalescence is not observed despite large root mean square displacements) indicates either that those crystallites do not diffuse as entities or that coalescences are inhibited. It is suggested that inhibition be due to elastic interactions, electrostatic interactions, or impurity effects.

ISSN:0021-8979    

DOI:10.1063/1.1662873

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The diffraction of optical guided waves in thin films through an acousto‐optic effect is treated. The diffraction of the bounded optical waves in thin films is a rather complicated phenomenon as compared with that of the free waves in bulk media. An expression for the diffraction efficiency has been derived using coupled‐wave equations. Acousto‐optical figure of merit and the mode coupling factor applicable to the diffraction in thin films are defined. The TE0and TM0waves in an As2S3film deposited onto a LiNbO3substrate were diffracted by Rayleigh waves with 93 and 72% efficiency at electrical input powers of 150 and 50 mW, respectively. The present experiment revealed that approximately 5% of the total acoustic power penetrated into the film and took part in the diffraction.

ISSN:0021-8979    

DOI:10.1063/1.1662874

出版商:AIP    

年代:1973

数据来源: AIP