摘要:

A generalT‐matrix is formulated to study the scalar scattering response of an impenetrable, biperiodic surface in the presence of az‐directed medium inhomogeneity, and reductions thereof are discussed. A numerical scheme for constructing potential reflection coefficients used for generating an appropriate Green’s function has also been described. Numerical results presented demonstrate that the effect of the inhomogeneity cannot be ignored without inducing severe errors.

ISSN:0021-8979    

DOI:10.1063/1.335787

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A self‐consistent thermodynamics is developed for nonrelaxation hysteretic processes. This theory, nonequilibrium thermostatics, is based upon macroscopic empirical descriptions of hysteretic behavior and the laws of thermodynamics. It is shown that the empirical behavior of hysteretic systems does not satisfy the conditions required for application of either equilibrium or relaxation nonequilibrium thermodynamics. Therefore, modified thermodynamic assumptions are proposed which are consistent with empirical hysteretic behavior. The principal new assumptions are (1) that processes (energy dissipation permitted) consists of a differential sequence of nonequilibrium states; (2) that three new ‘‘state variables’’ describe all of the ‘‘history dependence of a state;’’ (3) that at least some ‘‘reversible’’ processes exist; (4) that the time‐independent ‘‘modified Gibbs relation’’ can be used to describe the Second Law constraints. With these assumptions, it is shown that the thermodynamic relationships derived from the First Law are identical to those for standard equilibrium thermodynamics, but Second Law implications are significantly different, e.g., a new ‘‘dissipation’’ state function is derived; it is proven that hysteretic behavior is a positive indication of a dissipative process and that dissipation always causes hysteresis. It is concluded that nonequilibrium thermostatics provides a self‐consistent theory which extends the useful domain of thermodynamics to include nonrelaxation, hysteretic (dissipative)processes. A comparison of detailed predictions and experimental measurements of heat capacities, adiabatic paths, etc., for a hysteretic system is provided in a separate paper.

ISSN:0021-8979    

DOI:10.1063/1.335788

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Electrons produced by two‐photon ionization of CS2, SO2, and (CH3)3N in N2and CH4buffer gases at 193 nm were investigated using a parallel‐plate drift‐tube apparatus. At a low charge density, the transient voltage induced by electron motion between the electrodes is proportional to the gas pressure and the square of laser power. The two‐photon‐ionization coefficients measured from the number of electrons produced are 3.3×10−27, 8.3×10−30, and 1.7×10−27cm4/W for CS2, SO2, and (CH3)3N, respectively. The coefficient for (CH3)3N agrees with the earlier value measured by ion current. At a high charge density, the number of electrons observed deviates from the square dependence of laser power. The numbers of ions and electrons are greatly reduced by charge recombination whose reaction rate is enhanced in the presence of space charge.

ISSN:0021-8979    

DOI:10.1063/1.335789

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We develop a theory describing the propagation of a pulse of electromagnetic energy through a gas in which breakdown is occurring (by means of the pulse‐induced electron cascade). The theory is based on solutions to a model wave equation for the pulse electric field, which incorporates the electron cascade in an approximate fashion, and which is derived from the appropriate Maxwell equations coupling the pulse fields to the cascading electron current. Nonlinear effects are ignored, but solutions to the model wave equation appear useful in identifying major trends in the pulse propagation, such as the pulse attenuation and its dependence on the input pulse nominal frequency, spectral breadth, width, rise time, and overall shape. Our results are of relatively simple analytical form, they semiquantitatively confirm available data, and they imply that the pulse energy transport through the electron cascade can be enhanced by choice of certain combinations of the input pulse parameters.

ISSN:0021-8979    

DOI:10.1063/1.335790

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A quantum model of the single particle free‐electron laser in a uniform magnetic field is given. Here the classical electron current due to electrons in helical orbits (caused by a uniform magnetic field) interacts with a quantized radiation in the interaction volume of finite extent. The description of this free‐electron laser is through theSmatrix which incorporates the quantum recoil completely and yields directly the full ‘‘quantum mechanical’’ gain. Taking the relativistic electron factor &ggr; to be approximately equal to 2.4 and the magnitude of the magnetic field in the range of 0.6–1.6 T, this free‐electron laser should be capable of generating radiation in the far infrared‐microwave spectral region. From the analysis of the asymptotic (classical limit) gain (a gain due to the ‘‘infinite’’ number of photons in the interaction volumeV), we conclude that it is generally easier to generate radiation in the forward, rather than backward, direction. We also discuss the dependence of the gain on the electron velocity in thezdirection, the strength of the uniform magnetic field, and the fact that our (asymptotic) gain scales asL3, which is similar to the gain of the usual (wiggler) free‐electron laser.

ISSN:0021-8979    

DOI:10.1063/1.335791

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The Shifrin perturbation theory is applied to the scattering of light from finite cylinders and spheroids, and a procedure is described for averaging over the possible orientations of the symmetry axes of these various target shapes. The possible axis orientations of very long cylinders is limited by the conical shape of the scattering patterns, and the manner of taking this into account in the averaging process is detailed. It is found that the scattering intensities for the scattering of light from randomly oriented long cylinders, with aspect ratios (length/diameter) less than about 200, show differences compared with infinite cylinders of the same radius and dielectric constant (m=1.5). This is especially true for high and low scattering angles and when the plane of linear polarization is changed by the scattering. Moreover, the scattering intensities for the scattering of light from randomly oriented short cylinders and spheroids, with aspect ratios ranging from 0.1 to 10 and the same volume, show significant differences when the plane of polarization is changed by the scattering.

ISSN:0021-8979    

DOI:10.1063/1.335792

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A theoretical consideration is given of the transverse multimode generation in a laser which is equipped with a lossy layer below an active layer for mode control, e.g., the buried twin‐ridge substrate laser, the channeled substrate planar laser, and the V‐shape inner stripe laser. The multimode generation occurs as a result of the reduction of the first‐order mode threshold to the fundamental mode threshold. It is shown that even a small asymmetry of the lossy layer causes large reduction of the first‐order mode threshold.

ISSN:0021-8979    

DOI:10.1063/1.335793

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A systematic theoretical study of approximations to the Kirchhoff diffraction integral is presented, stressing the improved behavior at large angles. This work was motivated by consideration of diffraction in dual tilted dispersive interdigital transducers for surface acoustic wave generation, but the salient features are applicable to diffraction problems in general. Previous treatments of surface acoustic wave (SAW) propagation were limited to nearly forward directions perpendicular to transducer fingers, where the simple Fresnel diffraction theory was adopted. Improvement of the theory for nonforward angles is obtained in which both the Fraunhofer and Fresnel diffractions are correctly included. The conventional diffraction treatment used in optics (as in the textbook by Born and Wolf) is found inaccurate and a new form is presented.

ISSN:0021-8979    

DOI:10.1063/1.335794

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The development of the general flux formulation for heat conduction based on the modified Fourier’s law is presented. This new formulation produces a hyperbolic vector equation in heat flux which is more convenient to use for analysis in situations involving specified flux conditions than the standard temperature formulation. The recovery of the temperature distribution is obtained through integration of the energy conservation law with respect to time. The Green’s function approach is utilized to develop a general solution for hyperbolic heat conduction in a finite medium. The utility of the flux formulation and the unusual nature of heat conduction based on the hyperbolic formulation are demonstrated by developing analytical expressions for the heat flux and temperature distributions in a finite slab exposed to a pulsed surface heat flux.

ISSN:0021-8979    

DOI:10.1063/1.335795

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A simple model is employed to explain the anomalous surface‐flashover characteristics observed when insulators in vacuum are stressed with bipolar voltage waveforms. Under unipolar stress, the flashover field is found to vary as the inverse square root of the prebreakdown time delay over the first few tens of nanoseconds, thereafter becoming less dependent on delay. The short‐delay behavior, according to our model, results from the accumulation of ionic charge adjacent to the insulator‐vacuum interface. At longer delays ions are swept away nearly as rapidly as they are created. Flashover data from conventional insulator assemblies subjected to unipolar stress is consistent with ions being swept away. With the application of a roughly 10 MHz, bipolar voltage waveform a different behavior is observed. The holdoff is unexpectedly low and an anomalous inverse‐square‐root dependence on delay persists over hundreds of nanoseconds. Analysis of ion motion indicates that some fraction of the ions follow small‐amplitude oscillatory trajectories and continue to accumulate for relatively long periods of time. An insulator has been modified to enhance ion removal by decreasing the thickness of polystyrene segments fourfold to 4.7 mm. A 50% improvement in performance is found, although the holdoff remains below standards applicable to unipolar stress.

ISSN:0021-8979    

DOI:10.1063/1.335796

出版商:AIP    

年代:1985

数据来源: AIP