摘要:

Plastic deformation of metal enhances the photoelectron emission producing so‐called exoelectrons In our experiments the metal surface is scanned by a small spot of ultraviolet light and the electron emission is recorded as a function of position of the light spot. Results for aluminum and steel demonstrate that fatigue deformation produces exoelectron emission after less than 1% of the fatigue life. The regions of emission are very localized; some are beyond the resolution of the apparatus (15 &mgr;m). The localized emission increases throughout the fatigue life, and failure finally occurs in the region of most intense emission. The regions of intense emission are attributed to the development and propagation of fatigue cracks.

ISSN:0021-8979    

DOI:10.1063/1.1662232

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The flow stress as a function of strain was measured in the temperature range from 77 to 400°K at strain rates between 10−1and 10−6sec−1for single crystals of molybdenum. The flow stress is characterized by a rate‐temperature parameter, defined through a general rate equation for low temperature thermally activated deformation processes in bcc structures. This parameter was utilized for testing the mechanical equation of state and in explaining the failure of such an equation in molybdenum. Whereas the rate of work hardening was found to be uniquely defined by strain and the parameter, the flow stress depended in addition on the thermal‐mechanical history of the material.

ISSN:0021-8979    

DOI:10.1063/1.1662233

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A set of computer programs has been developed for calculating the velocity of acoustic surface waves on a substrate with or without a film overlay where both the film and the substrate may be arbitrarily anisotropic and piezoelectric. Several examples of practical significance are presented. These include (i) propagation around the curved surface of a wrap‐around delay line, (ii) power flow angles for Rayleigh waves on LiNbO3and Bi12GeO20substrates, (iii) enhancement in the performance of an interdigital transducer due to the deposition of a film overlay (values of &Dgr;&ngr;/&ngr; as large as 5.45% have been calculated), (iv) &Dgr;&ngr;/&ngr; curves for piezoelectric films on nonpiezoelectric substrates.

ISSN:0021-8979    

DOI:10.1063/1.1662234

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The paper deals mainly with the voltage dependence of the dwell times of 130‐mm‐long tungsten wires with diameters of 0.05, 0.10, 0.15, and 0.20 mm. The results of the measurements reported show that tungsten wires have dwell times of only the short type, that the restrikes are always initiated at the exterior of the wires, and that during the dwell times tungsten wires have higher conductivity than copper or constantan wires. At low voltages the dwell times increase with increasing wire diameter. However, above 10 kV the dwell times within the range of experimental error are equal for all the diameters examined. A comparison with the results obtained from exploding copper wires with the same diameter shows that at low voltages the short dwell times of the copper wires are shorter than those of the tungsten wires and that at higher voltages the dwell times of the tungsten wires become much shorter than those of the copper wires, decreasing monotonically with increasing voltage. The special features of the exploding wires during the dwell times and the restrike phase are illustrated by films made by a rotating‐mirror streak camera, a camera with a Kerr‐cell shutter, and an image‐converter camera.

ISSN:0021-8979    

DOI:10.1063/1.1662235

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The low‐frequency response characteristics of an electron‐attracting cylindrical probe operating in the transition regime are presented. The analysis is applicable for probes of arbitrary ratios of radius to Debye length operating in plasmas where the collisional effects result from electron‐neutral interactions. Equations which relate the probe current fluctuations to fluctuations in the plasma properties are presented with the intent of providing an explicit formulation for data interpretation. Conditions are also defined which must be satisfied if the intensity of the electron density fluctuations are to be determined directly from probe current measurements. In addition, qualitative results are presented which describe the probe transient response when collisional effects result from electron‐ion interactions.

ISSN:0021-8979    

DOI:10.1063/1.1662236

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The effect of azimuthal variation of electron density on the surface‐wave propagation along the inner surface of an annular plasma column is described experimentally and analytically. Such inhomogeneity of electron density is induced by the earth's magnetic field, which is not parallel to the direction of electron drift along the column axis. In this case the azimuthal distribution of electric field intensity of the surface wave is distorted, and the dipole mode, which is normally degenerate, splits into two modes with different wave numbers. The field distortion becomes more intense as the inhomogeneity increases and the wavelength decreases. The theoretical analysis shows that the distortion results from the coupling between normal modes by the effect of the inhomogeneity. Experiments are carried out by using a mercury‐vapor‐discharge tube with hot cathode, and the results agree well with the calculations.

ISSN:0021-8979    

DOI:10.1063/1.1662237

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper represents an effort to derive a theoretical expression which will predict the influence of electrode configuration upon the electric breakdown voltage in electronegative gases. The initial portion of the paper is involved with a presentation and discussion of the generalized condition for breakdown in all gases for an unspecified electrode configuration or structure. The equation is then applied to the particular configuration consisting of two parallel wires of infinite length. An equation is derived, from which it is possible to calculate the breakdown voltage of any gas as a function of the radius of the wirer0. Knowledge of certain parameters, characteristic of a specific gas, is the only requirement necessary to accomplish this. The results of calculations are presented for the simple gas nitrogen, which does not have a tendency to produce negative ions by electron capture. These are compared with the results of similar calculations for the highly electronegative gas C3F8. The calculations show that the breakdown voltage of nitrogen is strongly dependent uponr0, which is in agreement with the experimental observations of previous investigators. C3F8, on the other hand, showed entirely different behavior. To be more specific, the value ofr0appeared to have little if any influence upon its breakdown voltage. Furthermore, it is shown that the electrode configuration, giving rise to distortion of the electric field, does not affect the final outcome of the calculations when the gas under consideration is highly electronegative. Experimental verification of this prediction has been achieved by measuring the breakdown voltage of C3F8in a uniform electric field, and comparing the results with those obtained with the point‐to‐plane configuration. For both cases, the results agree to within 10%, providing adequate verification of the conclusions derived from the theory.

ISSN:0021-8979    

DOI:10.1063/1.1662238

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The net axial focusing force for a non‐neutral cylindricalElayer in various Astron resistor configurations is calculated. There is strong focusing for cases in which there are resistors on the cantilever.

ISSN:0021-8979    

DOI:10.1063/1.1662239

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Variational bounds for plane strain bulk modulusk, transverse shear modulusm, longitudinal Young's modulusE1, and transverse Young's modulusE2are derived for transversely isotropic fiber‐reinforced composites with periodic structure. Our results are in satisfactory agreement with experimental data. We have also derived variational bounds for the shear modulusgof an orthotropic composite lamina. Our results are again in good agreement with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1662240

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Deviations from Hooke's law are caused by the third‐order elastic constants. These deviations have been measured for one orientation of cadmium and two orientations of zinc filamentary crystals (whiskers). Expressions for these deviations have been derived and used to calculate values of the linear combinations of third‐order moduli. The experimental values of the deviations for zinc are compared with values calculated from published third‐order constants.

ISSN:0021-8979    

DOI:10.1063/1.1662241

出版商:AIP    

年代:1973

数据来源: AIP