ISSN:0021-8979    

DOI:10.1063/1.1658385

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experimental results on harmonic generation and parametric mixing of surface acoustic waves are reported. Harmonics of signals at 615 MHz and 1.69 GHz propagating on YZ LiNbO3substrates were observed: the experiments on parametric mixing used two surface acoustic waves atf1=490 MHz andf2=1.09 GHz. Optical probing technique was used to observe directly the spatial variations of the harmonics, the sum, and difference frequency signals. It will be shown that the nonlinear interactions can be phenomenologically described by coupled amplitude equations. The nonlinear coupling constants are determined by comparing the experimental results with the calculations.

ISSN:0021-8979    

DOI:10.1063/1.1658386

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The suggestion that mechanical oscillations in the solid wire are in part responsible for the production of striations observed in a class of wire explosions is investigated using the dispersion relation for elastic waves in isotropic solid cylinders. It is proposed that these oscillations arise due to the transient nature of the electrical energy deposition and that axial waves originate at points of discontinuities such as impurities and grain boundaries. Numerical solutions are obtained using the first shear‐ and dilatationalmode cutoff frequencies, and the wave numbers of these and standing waves are presented as a function of Poisson's ratio. Experimental data on the average distance between striations and new data are found to lie within the range predicted by the theoretical analysis.

ISSN:0021-8979    

DOI:10.1063/1.1658387

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The x‐rayKandLIIIemission bands and absorption spectra from TiO, TiN, and TiC are superimposed and compared with the calculated density‐of‐states histograms. For TiO the agreement is remarkably good. It is a little less good for TiC and still less for TiN, the disagreements probably being due in part to the presence of more ionicity in the bonding than was considered in the calculations. Results of the comparisons point up the importance of the transition probabilities in contributing to the x‐ray spectra and can help indicate needed refinements in the calculated electronic structure.

ISSN:0021-8979    

DOI:10.1063/1.1658388

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The lattice parameter of AlAs has been very accurately measured as a function of temperature between 15° and 840°C, and the coefficient of thermal expansion has been determined. The lattice parameter at 0°C is 5.6605±0.0005 Å and the coefficient of thermal expansion is (5.20±0.05) ×10−6/°C. A comparison is made to GaAs which indicates that there is a perfect lattice match at about 900°C and 0.14% lattice mismatch at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.1658389

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The absorption coefficient of LiIO3has been measured at 300°, 80°, and 7°K for the ordinary and extra‐ordinary ray. The corresponding indices of refraction at 300°, 80°, and 17°K were also determined. Upon cooling from 300° to 7°K, the absorption coefficients decrease drastically in the 10–150‐cm−1spectral region. At 7°K the absorption coefficient is less than 1 cm−1for frequencies up to 80 and 90 cm−1forE∥candE ⊥ c,respectively. This characteristic is important for far‐infrared generation by mixing of two laser frequencies.

ISSN:0021-8979    

DOI:10.1063/1.1658390

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Three equal orthogonal double forces without moment aligned along the cubic axes are used as a model for a point defect in a cubic medium. The method of Fourier transforms is used to obtain the solution for the displacement and stress fields. The solution is presented in a polynomial form. The elastic interaction between a point defect and an edge dislocation is computed for copper by making the displacement of the edge dislocation against the stress field of the defect. The interaction with the physically significant [112¯] edge dislocation on the (111) plane in copper is presented. The computer program was verified by the agreement of its results with those for the hypothetical [001] edge dislocation on the (010) plane, for which the stresses can be calculated in closed form. Near the slip plane, the calculated anisotropic interaction was almost twice that of a corresponding isotropic one. The elastic interaction between two point defects in copper is calculated, indicating regions of attraction of like defects along the cube axes and repulsion along the cube diagonals. Eshelby's perturbation analysis for materials with slight anisotropy predicts qualitatively similar effects, but the repulsion is much greater than that predicted by his approximate analysis.

ISSN:0021-8979    

DOI:10.1063/1.1658391

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The piezoelectric strain coefficientd11has been determined in alpha quartz using a Fabry‐Perot dilatometer to measure the strain. The results obtained with eight specimens of Brazilian quartz give an average value of (6.81±0.03) ×10−8cm/statvolt or (2.27±0.01) ×10−12m/V. This value is compared with those reported in the literature which range from 5.5 to 7.1×10−8esu.

ISSN:0021-8979    

DOI:10.1063/1.1658392

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

During measurement of preferred crystallographic orientation with the Schulz x‐ray diffraction technique, several factors can cause defocusing. Earlier investigations showed that tilt of the specimen in &PHgr;, the angle between the normal to the sample surface and the normal to the diffracting plane, is the most severe limitation for the Schulz reflection technique. The present study shows that this defocusing effect is strongly dependent on the size of the Bragg diffraction angle &thgr;: The greater the Bragg angle, the smaller the decrease in intensity for a given tilt angle of &PHgr;. On the other hand, the absorption coefficient &mgr; of the sample has no influence on the decrease in intensity with increasing tilt in &PHgr;, and its effect is negligibly small for most metals. Correction factors for the loss of intensity can be derived and have a general analytic form, but different coefficients are required for each goniometer setting.

ISSN:0021-8979    

DOI:10.1063/1.1658393

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A direct measure of the effect of porosity on powder diffraction intensities can be obtained by measuring the ratio of the x‐ray scattering from a porous, amorphous material vs its nonporous counterpart. The amorphous specimen eliminates the effects of extinction and preferred orientation inherent in diffraction from crystalline samples. Measurements on glass powders of controlled particle size vs solid specimens were used to obtain porosity corrections for scattering angles 10°<&thgr;<80° and for particle sizes in the range &mgr;t=1.0 to &mgr;t=3.2. With particles of the largest values of &mgr;tthe error can be as great as 30% for &thgr;≈30°. For a given specimen the correction approaches zero as &thgr;→90° and also gets smaller as &thgr;→0°. For specimens of about 50% relative density the maximum correction is approximately (10×&mgr;t)%. Extrapolating to particles with attenuation factors of only 10% (&mgr;t=0.1) corrections as large as 1% in a powder integrated intensity measurement may be necessary.

ISSN:0021-8979    

DOI:10.1063/1.1658394

出版商:AIP    

年代:1970

数据来源: AIP