摘要:

The aim of this paper is to investigate the elastic fields of a twist disclination loop and a wedge disclination line in hexagonal crystals. The plane of the twist disclination loop and the wedge disclination line are assumed to be parallel and normal to the basal planes, respectively. Closed‐form solutions have been obtained for disclination stress fields and elastic energies. It is noted that the elastic field of twist loops in thin hexagonal crystals and nonhomogeneous systems can be found by the method of images. Energy values for several common hexagonal crystals are calculated.

ISSN:0021-8979    

DOI:10.1063/1.1661940

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The thermal conductivity of Lucalox, a high‐purity form of aluminum oxide, has been measured over the temperature range 870–1400°C. The technique employed is a novel one using a lithium‐filled heat pipe in series with a gas gap variable heat conductance unit as a heat source. The procedure enables one to measure heat flux through the sample directly. The measurements indicate that the thermal conductivity of high‐purity aluminum oxide has a minimum value of about 0.05 W/cm°C at 950°C and increases with higher temperatures to values in the range of 0.3 W/cm°C at 1400°C.

ISSN:0021-8979    

DOI:10.1063/1.1661941

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Ultraviolet radiation is one of the principal forms of energy which is dissipated from an electrical discharge in water. For a stored capacitor energy of 1500 J, up to 28% or 420 J has been converted to uv radiation with a peak radiant power of 200 MW. Of the energy transferred to the plasma, 36% was converted to radiation. The efficiency of radiation was maximum for a length of the discharge channel of approximately 3.8 cm. Scaling rules are given.

ISSN:0021-8979    

DOI:10.1063/1.1661943

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The growth of an electrical discharge channel in water has been simulated by a finite‐difference solution of the partial differential equations of motion along with the descriptive equations of the medium. The computation is based upon a set of parameters which describe experimentally controllable conditions. Close agreement is obtained between simulations and experiments by adjusting arbitrary parameters included in the description of the medium. However, the simulation is relatively insensitive to these parameters.

ISSN:0021-8979    

DOI:10.1063/1.1661944

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A crossed field or rotating plasma gun is investigated to determine detailed processes taking place during the ionization and acceleration phases. Measurements suggest that the gun breaks down via a spoke which subsequently rotates at the limiting velocity. Internal shorting occurs subsequent to break down and limits the usefulness of the source. Methods of reducing the effects of this shorting are presented as are some measurements of the properties of the plasma after it leaves the gun region. These suggest that about 1019particles can be accelerated to energies of several hundred eV.

ISSN:0021-8979    

DOI:10.1063/1.1661945

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A study has been conducted, for several electron‐density distributions, of the reflection of electromagnetic waves from stratified overdense plasmas in which the rate of collision frequency to incident frequency is large and the transmission negligible. With positive power profiles where the density changes slowly near the turning point, the reflection coefficient is small, whereas for inverse power profiles where the density gradient is large near the turning point, the reflection is large. In the case of a symmetric type of profile where the maximum density is finite, the results are dependent upon profile type. In an inverse profile type, the reflection is fairly sensitive to maximum density, decreasing with it. With a Gaussian distribution, reflection increases slowly with maximum density, whereas for a sech2model, the reflection is, for the most part, independent of this parameter.

ISSN:0021-8979    

DOI:10.1063/1.1661946

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Data taken from the literature on a variety of photoelectric effects are analyzed considering that the maximum photoresponse occurs at the wavelength at which the absorptance of the volume element responsible for the photoeffect is a maximum. The spectral response of certain photosensitive systems is shown to parallel the absorption of a thin volume element next to the rear surface. The thickness of surface recombination layers for cadmium sulfide is estimated from calculations involving the transmittance of the sample at the wavelength at which the maximum photoresponse occurs and the thickness of the sample.

ISSN:0021-8979    

DOI:10.1063/1.1661947

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Microwave and photometric techniques are used to study the temporal and spatial behavior of a transient microwave‐generated air plasma sheath in a coaxial transmission line. In particular, breakdown times, stabilization times, and thickness of the ionized sheath are investigated at different pressures and generating signal amplitudes.

ISSN:0021-8979    

DOI:10.1063/1.1661843

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The present work demonstrates the disintegration of thin electrically exploding tungsten wires in a vacuum. The drawn tungsten wires split into tiny fibers in a time close to that at which the wire reaches its melting point. Similar results were obtained for wires exploded at low pressures and at atmospheric pressure. The results show, within the limits of the experimental accuracy, that, when the wire reaches its melting point, dips are observed on the current derivative and the voltage oscillograms and x rays are produced. The results support the suggestion that the production of hard x rays from drawn thin exploding tungsten wires is due to the splitting of the wire, which has a fiberlike crystalline structure. Moreover the oscillograms of the first current pulse show that for thin wires the electrical conduction up to melting point is due only to the solid wire material and that the influence of the ambient pressure on the crest value of the first current pulse for wires exploded at the same condenser‐bank voltage is almost negligible.

ISSN:0021-8979    

DOI:10.1063/1.1661844

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Ultrashort laser pulses emitted by a neodymium glass laser system were focused on the surface of solid targets situated in a high‐vacuum environment. The laser pulse duration as measured by the two‐photon fluorescence technique was less than 10−11sec. Pulse energies up to 3 J were obtained corresponding to a maximum energy release of 3×104J cm−2in the focal area. The plasmas produced from targets of solid deuterium, carbon, and thin foils of Mylar were investigated by x‐ray measurements, time‐of‐flight measurements using charge collecting probes, and, in the case of deuterium, by neutron counting measurements. Only 10% of the incident light energy was found to be reflected from the targets. Electron temperatures of 500 and 200 eV were measured for deuterium and carbon plasmas, respectively. The experimental results are found to be consistent with the predictions of the model of a thermal wave penetrating into the solid.

ISSN:0021-8979    

DOI:10.1063/1.1661845

出版商:AIP    

年代:1973

数据来源: AIP