摘要:

The numerical solution of potential problems using a method which reduces them to Fredholm integral equations of the first and second kinds is considered. The method is illustrated for potential problems of the Dirichlet type and solutions have been obtained for the case of a unit sphere. This method provides an alternative approach to the classical finite‐difference methods which have been widely used in the past. It overcomes some of the difficulties associated with the classical approach.

ISSN:0021-8979    

DOI:10.1063/1.327570

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

In passive microwave remote sensing of earth terrain, the application of the radiative transfer theory to the model of random medium has been used in the interpretation of various experimental data. For vegetation fields with cylindrical structures, we model the vegetation layer as a two‐layer random medium with a small correlation lengthl&rgr;in the horizontal direction, and a large correlation lengthlzin the vertical direction. The closed form solutions for the brightness temperatures are obtained aslzapproaches infinity. Using this model, the kernels in the scattering terms of the radiative transfer equations give rise to delta functions, indicating that forward scattering is dominant over all the other directions. For the case thatlzis only a few wavelengths long, we find the first‐order solution with an iterative method. The results are compared with that obtained using the Gaussian quadrature method to solve the radiative transfer equations numerically. We also apply this model to match experimental data collected from corn fields.

ISSN:0021-8979    

DOI:10.1063/1.327571

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Multistable systems, extended in one spatial dimension, can make transitions from one state of local stability to another local state of stability, in a spatially uniform way, or by motion of an interface. The literature on Sine‐Gordon and &fgr;4solitons, in nonlinear dipersive systems, emphasizes their role as phase boundaries of this sort. We emphasize that shock waves can also act as moving phase boundariesinmultistablesystems. Our analysis invokes ferroelectric transmission lines as the principal model, but also treats linear arrays of coupled bistable springs. The soliton causes a transition in a given local volume, passed by the disturbance, by directly controlling the multistable degree of freedom, whereas the shock wave controls the corresponding force.

ISSN:0021-8979    

DOI:10.1063/1.327572

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Piezoelectric ceramic strain transducers are shown to have a linear response to strain down to a strain level of 10−11(10 picostrain) at a frequency of 20 Hz. For measurement of vibrational resonances, their sensitivity to strain is 50 000 times greater than that obtainable from a comparably sized resistive strain gauge.

ISSN:0021-8979    

DOI:10.1063/1.327573

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

For some inertial confinement fusion experiments, a tracer impurity element is added to the deuterium‐tritium fuel gas as an aid in diagnosing the implosion conditions. We have developed a general, nondestructive technique for measuring the initial tracer density in an individual fusion target. We take advantage of the fact that beta emission from the tritium excites the tracer characteristic x‐ray lines. Using an energy dispersive x‐ray detector, we measure the intensity ratio of a tracer x‐ray line to the bremsstrahlung background. The ratio is proportional to the tracer density and the inner radius of the target and is independent of other parameters. We have measured argon tracer densities as low as 0.01 atm with an accuracy of ±15%.

ISSN:0021-8979    

DOI:10.1063/1.327574

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Two simple formulas are presented for the capacitance of a finite‐length, conducting right‐circular cylindrical tube which resides in a homogeneous medium of permittivity &egr;. The formulas may be used to determine capacitance for all ratios (radius/length). The range of (radius/length) over which each formula applies is established by comparisons with capacitance calculated from numerical solutions of an integral equation.

ISSN:0021-8979    

DOI:10.1063/1.327575

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This theoretical investigation addresses the propagation of a power pulse in a long magnetically insulated vacuum transmission line (MITL). Relativistic Brillouin flow, with an arbitrary choice of the potentialVmat the flow boundary, explains the relationships among anode voltage, anode current, and cathode current that have been observed experimentally. The results of this investigation suggest that minimum energy considerations may be used to establish the value ofVmand hence determine the operating point of the MITL. This operating point compares very favorably with experimental data and with results from numerical simulations.

ISSN:0021-8979    

DOI:10.1063/1.327576

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The influence of Lorentz and Doppler line‐broadening mechanisms on the small‐signal optical gain of lasers and, in particular, gasdynamic lasers, is discussed. A relationship between the critical parameter reflecting the line‐broadening mechanisms and some of the important parameters arising out of the gain optimization studies in CO2‐N2gasdynamic lasers is established. Using this relationship, methods by which the deleterious effect of the Doppler mechanisms on small‐signal gain can be suppressed are suggested.

ISSN:0021-8979    

DOI:10.1063/1.327577

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Two discharge geometries are commonly used for pumping high‐repetition‐rate transversely excited atmosphere (TEA) lasers. One uses solid electrodes with preionization provided by downstream spark pins. The other uses a solid electrode and a screen electrode with preionization provided by an auxiliary discharge behind the screen. In this study the performance of the two systems was compared. The repetition rate at which arcing occurs was found to increase linearly with flow velocity but decrease with increasing energy density. It was also dependent on system geometry and the spark pin preionized system performed better than the auxiliary discharge preionized system. Data are given for discharges in N2, CO2, He, and a CO2laser mixture.

ISSN:0021-8979    

DOI:10.1063/1.327558

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The laser oscillator and parametric oscillator are analyzed in the presence of an externally injected signal. Synchronization to the external signal is possible only if it is larger than a certain magnitude. In the weak synchronization limit, expressions for the oscillator frequency and linewidth as a function of detuning (&Dgr;i) are obtained. An exact expression for the stationary probability distribution is obtained for &Dgr;i=0. It is shown that laser noise due to reflected signal may result from the repetitions of the ’’locked’’ and ’’unlocked’’ state arising from temperature variation within the laser itself.

ISSN:0021-8979    

DOI:10.1063/1.327559

出版商:AIP    

年代:1980

数据来源: AIP