摘要:

Application of voltage along thecaxis in rutile single crystals produces an increase in conductivity after a ``delay'' period. During this period, which may amount to several days at room temperature, the current decays as a result of trapping. The subsequent rise in current leads to thermal breakdown unless the current is limited externally. The destruction of the insulating properties reflects a change in the bulk, brought about by an injection of positive space charge from the anode. This charge, believed to be holes, is injected by field emission due to a steepening anode fall and allows the electron current to rise exponentially. The anode fall is approximately 10−3mm wide and sustains fields of 106V/cm. Trapping of electrons and holes produces two types of color centers, which are distinguishable by their color and migration in the applied field.

ISSN:0021-8979    

DOI:10.1063/1.1702997

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The derivation is outlined of a general relation connecting the macroscopic plastic strain rate with the configuration and velocity distribution of dislocations in a monocrystal with a single active glide system. This can be simplified for particular cases, the most simple being the case of parallel straight dislocation lines.A new form of the dynamical theory of plasticity is applied to detailed calculations and compared with previous work. The major modification is the use of the equationv=v* exp[−D/&tgr;] to express the quasi‐viscous behavior of dislocation velocities. Here,v=dislocation velocity,v*= terminal velocity,D=characteristic drag stress, and &tgr;=resolved shear stress. Also, a physical relation between dislocation density and plastic strain is derived.The nonlinear differential equation that results from combining the strain‐rate equation with an equation that describes the loading machine is integrated. Approximate analytic solutions, and numerical calculations, are given for the upper yield stress and the initial portion of the stress‐strain curve. The effects of initial dislocation density, characteristic drag stress, crosshead speed, machine stiffness, and dislocation multiplication rate on the upper yield stress are calculated. It is shown that the upper yield stress exceeds the cohesive stress at a critical crosshead speed. Delay times are also calculated for rapid load application followed by constancy of the load and compared with experiments for LiF. The effects of strain hardening are considered in a companion paper.

ISSN:0021-8979    

DOI:10.1063/1.1702998

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Mathematical descriptions of the stress‐strain‐time behavior of plastic crystals are developed using a statistical approach to dislocation dynamics. First, the ``easy‐glide'' portions of stress‐strain curves are described in terms of glide band propagation. Then, three models of strain hardening are developed and used in numerical calculations of stress‐strain curves. In one model, the mean density of mobile dislocations first increases and then decreases with increasing plastic strain. In another, strain introduces internal stress fluctuations which decrease the mean velocities of mobile dislocations. In the third (and preferred) model, strain increases the mean viscous drag acting on moving dislocations, thereby decreasing the mean velocity at a given stress. The numerically calculated curves show that the dynamical models provide realistic descriptions.

ISSN:0021-8979    

DOI:10.1063/1.1702999

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The method of analysis developed by the authors for the study of Faraday rotation in terms of the conduction‐current Hall field has been extended to include the effect of the Hall field due to dielectric current. The expression for the angle of rotation derived in this paper is different from that given by Barlow. The contribution of the dielectric‐current Hall field to rotation is found to be smaller than that obtained from Barlow's expressions.

ISSN:0021-8979    

DOI:10.1063/1.1703000

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An experimental investigation of the Faraday rotation at 3 cm in artificial dielectrics composed of paraffin wax and powdered indium antimonide is described. It is found that a rotation which can be ascribed to the dielectric properties of the medium does indeed occur. The experimental results are found to be in reasonable agreement with theoretical predictions made earlier.

ISSN:0021-8979    

DOI:10.1063/1.1703001

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Suppressed positive streamers are produced in a short (3 cm) positive‐point‐to‐plane gap in air by the discharge of the small anode capacitance. A study is made of the growth of current at the cathode plane, and the growth of luminosity at various positions in the gap with one or two photomultipliers and with a camera. The results are compared with some photographs obtained with an image converter. From a comparison of current and photomultiplier output it is shown that sharp peaks in the current are the result of the arrival of streamer tips at the cathode. The method has allowed measurement of streamer tip velocity at various positions in the gap. It has not proved possible to detect directly any return strokes produced when the streamers reach the cathode, but the subsequent growth of the discharge indicates that they are active in much the same way as previously shown for long (25 cm) gaps.

ISSN:0021-8979    

DOI:10.1063/1.1703002

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The dynamics of ``web'' growth have been investigated, with particular emphasis on the meniscus. The meniscus deflections have been expressed as a function of surface tension, and pulling force. An effort is being made to describe the parameters which influence surface tension, and its reflection on the process of web growth, and the properties of the material. The degree of supercooling, crucible design, and the control of thermal gradients have profound effects on the quality of the crystal and its physical dimensions.

ISSN:0021-8979    

DOI:10.1063/1.1703003

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

When a portion of a liquid dielectric was subjected to an electric dc field of high intensity, the level rose locally. The maximum rise attained by different liquids above the liquid level outside the field increased with their dielectric constant and polarizability.The following observations indicate that electrostriction rather than electrophoresis was the cause of the observed rise in liquid level. (a) Molten polymers, which have such high viscosities that electrophoretic motion of ions or charged particles is virtually suppressed, rose to the same heights as fluid liquids. (b) Neither inverting the direction of the field nor (c) adding 0.05% finely dispersed aluminum or 0.15% ultramarine powder to molten polyethylene affected the rise in the dc field qualitatively or quantitatively.Repulsion occurred in very high fields, producing a slight depression in the liquid level.

ISSN:0021-8979    

DOI:10.1063/1.1703004

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A directional dependence of the propagation of nonlinearly excited spin waves in anisotropic ferrites has been observed by measuring the radiation from the edge of a (110) YIG disk. The disk was excited by a parallel pump field normal to its plane and rotated through 360 deg. Measurements were made at dc field intervals of 10 Oe from 1800 to 2800 Oe (the experimental minimum of the butterfly curve). Radiation was observed at half the parallel pump frequency over a dc field range of 248 Oe (from 2294 to 2542 Oe). The direction for maximum radiation was along a [1¯10] axis in the plane of the disk, and a strong directional dependence was observed when the pump field was less than 4 dB above threshold. The ratio of maximum to minimum output as the disk was rotated was at least 10 dB. The directional dependence was found to be essentially independent of pump field strength up to 4 dB above threshold. Any further increase in pump field strength reduced the amount of radiation, and for pump field strengths higher than 8 dB above threshold no radiation was observed.

ISSN:0021-8979    

DOI:10.1063/1.1703005

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The internal quantum efficiency and spectral distribution of radiation from GaAs electroluminescent diodes is examined with a careful investigation of the optical absorption of both then‐type andp‐type layers of the diodes. A group of diodes so fabricated as to allow necessary corrections for internal absorption and reflection has internal quantum efficiencies greater than 50%. These diodes have more than 85% of all photons in the principal peak and the temperature variation of the emission is explainable on the basis of changes of the absorption with temperature. In addition, the shape of the emission can be interpreted in terms of radiation originating in a compensatedp‐type layer of relatively low carrier concentration.

ISSN:0021-8979    

DOI:10.1063/1.1703006

出版商:AIP    

年代:1965

数据来源: AIP