摘要:

The problem of normal wave propagation through an unbounded material which is mildly stratified or periodic is investigated. Rather than applying a standard approach, the problem is treated in the context of scattering theory. A first Born perturbative approximation is employed to calculate reflection and transmission amplitudes and transmission power flux losses due to reflections. A couple of sample calculations are performed.

ISSN:0021-8979    

DOI:10.1063/1.329870

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Density discontinuities have been observed behind the reflected shock produced by regular reflection of weak planar shock waves from rigid, smooth surfaces at various angles of incidence. These discontinuities occur behind the point where the incident and reflected shock waves meet and have been seen only for angles of incidence close to those at which transition from regular to Mach reflection takes place. The failure of two‐shock theory to predict the angle of transition from regular to Mach reflection for weak shocks may be explained by the experimental observation that near the transition, a simple two‐shock picture of the reflection process is not valid.

ISSN:0021-8979    

DOI:10.1063/1.329871

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The absolute emission intensities of lines originating from highly excited mercury levels in the positive column of a dc mercury discharge have been determined for various discharge conditions. For the same conditions, the densities in the 63P states have been determined with the hook method. From these experimental data the 63P− 63P collisional excitation cross sections for line emission can be derived for nine transitions. Generally, these cross sections are much smaller than those determined in previous experiments.

ISSN:0021-8979    

DOI:10.1063/1.329872

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The backscattered spectrum from short CO2laser pulses incident upon an overdense z‐pinch plasma has been measured. A clear red shift and an exponential growth in the reflectivity to a saturated value of approximately 4% has been observed. The results suggest the presence of strong damping on the scattering ion wave in the saturation region, consistent with predictions of an ion trapping model.

ISSN:0021-8979    

DOI:10.1063/1.330976

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A high‐density, laser‐initiated, gas‐embeddedZ‐pinch is modeled computationally in two dimensions. All aspects of an actual experiment are modeled: the computer model includes a laser optics package, a Marx‐bank/transmission line package, an electron avalanche prescription, and two‐dimensional magnetohydrodynamics. The experimental observations are reproduced to a very satisfactory degree. Predictions of performance in nonstandard operating modes are given.

ISSN:0021-8979    

DOI:10.1063/1.329873

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The 6‐TW, 0.4‐&OHgr; pulse generator at Maxwell Laboratories, Inc., was used to create hot, dense plasma pinches by imploding cylindrical arrays of fine aluminum wires. These plasmas have been diagnosed by observing their x‐ray emission at energies aboveh&ngr;∼1 keV. The results of various x‐ray measurements including x‐ray streak photography are presented.

ISSN:0021-8979    

DOI:10.1063/1.329874

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The electrical method is often used to study avalanches in gases. In this paper a substantial improvement of the time resolution of the measuring system is reported. To release the primary electrons within a very short time a transversely excited atmospheric pressure N2laser with a pulse width of 0.6 ns is used. Secondly the high‐frequency response of the entire circuit is analyzed. As one of the results of this analysis a subdivided cathode is used consisting of a central measuring electrode surrounded by a grounded electrode. The diameter of the circular measuring electrode determines a maximum gap distance for reliable measurements, which can be calculated from a theory of Shockley and Ramo. As an example of the high‐frequency response of our experimental setup avalanches in nitrogen are shown and analyzed. Avalanche measurements in air clearly show a dependence on the humidity, presumably caused by rapid detachment and conversion processes.

ISSN:0021-8979    

DOI:10.1063/1.331581

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In order to determine the resistivity of an electrostatically precipitated particulate layer of high resistivity material, a new technique is described using a conducting potential probe. The space‐charge potentials are first determined by the probe in a small parallel plate precipitator with wire‐to‐plate spacing of 75 mm at several distances from the collector plate, and a short extrapolation gives the potential at the dust surface. Using this potential and the associated measurements of collected layer thickness and current density, the operational resistivity &rgr;fof such a layer is determined while subject to the corona currents and high electric fields of normal electrostatic precipitator operation. The theory is given for the conducting potential probe in a unidirectional ionized field of a single wire to parallel plate unit. An example of the field dependence of the operational resistivity of a fly ash is given.

ISSN:0021-8979    

DOI:10.1063/1.331580

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A model is presented of the simultaneous spreading and cooling of the liquid drop in a hammer and anvil apparatus for rapid quenching of liquid metals. The viscosity of the melt is permitted to vary with temperature, and to avoid mathematical complications which would be associated with spatial variation of the viscosity, Newtonian cooling is assumed. From an expression for the force required to spread the specimen, coupled equations for the mechanical energy balance for the system and the heat transfer from the sample to the hearth and hammer were obtained, and solved numerically. The sample reaches its final thickness when the force required to deform it becomes greater than the force exerted on it by the decelerating hammer. The model was fit to measurements of sample thickness versus hammer speed, using the interface heat transfer coefficient,h, as an adjustable parameter. The values ofhso obtained vary somewhat with the melt alloy/substrate metal combination. From predicted cooling curves, the effects of hammer speed, sample size, and initial melt temperature on the cooling rate and the efficiency of glass formation can be assessed. Addition of sample superheat shifts the cooling curve relative to the expected position of the time‐temperature‐transformation curve for formation of crystalline material from the melt, and thus is an effective means of increasing the probability of glass formation in this type of apparatus.

ISSN:0021-8979    

DOI:10.1063/1.330639

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Images of grain boundaries obtained in the scanning electron microscope operated in the electron beam‐induced current mode are calculated. Images of boundaries in semicrystalline silicon solar cells are measured in the experiment and agree within 2% with theory. The calculated profiles depend strongly on the diffusion length of the semiconductor, providing a new method for determining the diffusion length of the material.

ISSN:0021-8979    

DOI:10.1063/1.330640

出版商:AIP    

年代:1982

数据来源: AIP