摘要:

An analytical solution is presented for the atomic displacements in the steady motion of a dislocation in a modified Frenkel‐Kontorova model of the form treated previously by Atkinson and Cabrera. It is found that at a critical dislocation velocity, here termed the breakdown velocity, &ngr;B, the regular dislocation motion postulateda prioribreaks down, so that the analytical solution is not valid for dislocation velocities &ngr; ≥ &ngr;B. Furthermore, &ngr;Bis less than the corresponding macroscopic sound velocity for this model. The results of computer‐simulation studies of the behavior of the model at stress levels greater than those which cause dislocation breakdown are also presented.

ISSN:0021-8979    

DOI:10.1063/1.1663291

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The equations for the xerographic discharge of the potential are solved analytically by means of a flow line technique. The solution is for single‐carrier discharge corresponding to charge generation using strongly absorbed light. Exact analytical solutions are given for two cases in which both the photoinjection efficiency and the mobility are field dependent, including the Poole‐Frenkel effect. The surface potentialV(t) andd V(t)/d tare calculated for specific cases, and the effect of variations in mobility, thickness, and injection rate are discussed. Under certain conditions the discharge can remain emission limited for all times. It is shown that a discontinuity in the conduction current exists at the transit time of the lead carriers, corresponding to the cusp in the constant‐potential case when the current is space‐charge limited.

ISSN:0021-8979    

DOI:10.1063/1.1663292

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A schlieren technique is used to give a direct accurate measurement of Rayleigh phase velocity on various materials. Plane solid interfaces underwater are insonified by finite acoustic beams. Sound incident at the Rayleigh angle produces a null strip in the radiated field which uniquely identifies the Rayleigh angle. This null strip is caused by the mutual cancellation of equal amplitude specular and Rayleigh radiations which are 180° out of phase. Rayleigh phase velocity is then calculated from the measured Rayleigh angle by a simple equation. The measured Rayleigh velocities are used to give estimates of shear velocity, and these estimates are compared with direct shear velocity measurements. The attenuation of the Rayleigh wave in the low‐MHz region is due to radiation into the water and is found to be directly proportional to frequency and inversely proportional to material density as predicted by theory.

ISSN:0021-8979    

DOI:10.1063/1.1663293

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A 600‐MW CO2laser oscillator has been used to induce breakdown in hydrogen with filling pressures in the range 10–20 Torr. The breakdown region is observed to undergo a transition from an optically thin symmetric expansion at laser fluxes in excess of ∼ 108W/cm2to an optically thick undirectional expansion at laser intensities below this.

ISSN:0021-8979    

DOI:10.1063/1.1663294

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The electrical conductivity of FeyMn1−yO1+xsingle crystals in equilibrium with various partial pressures of oxygen was measured in the temperature range 900–1150°C. When the conductivity data were plotted as functions ofxory, sigmoidally shaped curves were obtained. This composition dependence is consistent with a region of solid‐solid immiscibility within the (Fe,Mn)O phase field. The visible and near‐infrared absorption spectra of (Fe,Mn)O crystals exhibited crystal‐field peaks characteristic of both the Mn2+and Fe2+cations. The position of Fe2+peaks was found to shift with MnO content although the peaks corresponding to the Mn2+ion did not shift. It was concluded that the manganese ions are located on undistorted lattice sites which may be grouped into phase‐separated regions. Thus, both the electrical and optical results reflect a miscibility gap in the pseudobinary phase field.

ISSN:0021-8979    

DOI:10.1063/1.1663295

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

This work reports on observations of a diffuse discharge in a turbulent air flow. The discharge power was monitored as a function of velocity and turbulence spectrum in a fixed electrode configuration. The flow direction was also reversed to check on the effect of convection. The flow increased the sparking voltage, and turbulence made the current distribution considerably more homogeneous; the discharge power increased from about 1 W with no flow to about 250 W with 60‐m/sec grid‐generated turbulent flow. This turbulence was most intense in the range between 1 and 10 kHz.

ISSN:0021-8979    

DOI:10.1063/1.1663296

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The vector potential has been obtained for a coil coaxial with an arbitrary number of cylindrical conductors. The derivation is quite general and employs an iterative process that has been adapted to computer programs. After the vector potential has been obtained, it is used to calculate the mutual and self‐impedance of multiple and single coils, the effect of defects in the conductors on the mutual and self‐impedances, and the induction heating density in the conductors.

ISSN:0021-8979    

DOI:10.1063/1.1663297

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Techniques of thermoelectric and photothermoelectric analysis have been applied to investigate the electrical transport properties of both solution‐sprayed and evaporated polycrystalline CdS films. Dark electron densities are independent of temperature between 200 and 330°K because of shallow donors; dark electron mobilities are thermally activated with energies between 0.09 and 0.23 eV. Photoconductivity of solution‐sprayed films is caused primarily by an increase in electron mobility. Other effects investigated are the adsorption and desorption of oxygen, the diffusion of Cu acceptors, and field‐assisted drift of Cu impurities in the film at a slightly elevated temperature (100°C). The structure and characteristics of intergrain boundaries dominate the transport processes in these polycrystalline films.

ISSN:0021-8979    

DOI:10.1063/1.1663298

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The ion chemistry of the ions derived from wire spring relays has been found to be dominated by the presence of diethylphthalate (DEP), C12H14O4, derived from the cellulose acetate around the relay coil. Under our experimental conditions, using 0.5‐A resistive break arcs in air and in pure gases at a pressure of about 1 Torr, the positive ion current extracted from the arc was found to consist almost exclusively of this compound and its derivatives; with both air and contact metal ions present as minority species if at all. This indicates that the characteristics of DEP are such that charge‐exchange and clustering mechanisms operate to selectively transfer the charge to the organic material. Minute amounts (< 10−5Torr) of DEP will accomplish this transformation in less than 1 msec. DEP has been found to activate relay contacts when present in air in part per million quantities. There are indications that the reactions of diethylphthalate are not unique and that other organic materials will similarly affect the ion species derived from the relay arc.

ISSN:0021-8979    

DOI:10.1063/1.1663299

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Examination of the electrode damage due to various types of low‐current (< 5 A) atmospheric pressure arcs has led to the conclusion that a similar contact erosion mechanism exists for each. These arcs have included high‐voltage‐gas‐breakdown arcs, resistive‐make arcs, and both resistive‐and inductive‐break arcs. Material transfer is considered to result from the ejection of molten metal out of the electrode craters by the recoil force, which follows the abrupt cessation of ion bombardment. In the so‐called ``cathode arcs'', i.e., arcs burning predominantly in cathode material, metal droplets have been observed on the anode. In ``anode'' arcs, i.e., arcs burning predominantly in anode material, droplets have been observed on the cathode, an observation that is consistent with the above model using electron instead of ion bombardment.

ISSN:0021-8979    

DOI:10.1063/1.1663300

出版商:AIP    

年代:1974

数据来源: AIP