Correction to "On the concepts used in return stroke models applied in engineering practice"

For original paper see V. Cooray, IEEE Trans. Electromagn. Compat., vol.44, p.101-108, (2003). This paper gives correction to several equations in the aforementioned paper.     

Guaranteed fault detection sequences for single transition faults in finite state machine models using concurrent fault simulation

This paper presents a new algorithm for the generation of test sequences for finite state machines. Test sequence generation is based on the transition fault model, and the generation of state-pair distinguishing sequences. We show that the use of state-pair distinguishing sequences generated from a fault-free finite state machine will remain a distinguishing sequence even in the presence of a single transition fault, thus guaranteeing complete single transition fault coverage. Analysis and experimental results show that the complexity of the test sequence generation algorithm is less than those of the previous algorithms. The utility of the transition fault model, and the generated test sequences is shown by their application to sequential logic circuits. These results show more than a factor of 10 improvement in the test generation time and some reduction in test length while maintaining 100% transition fault coverage.Now with Intel Corporation, FM5-161, 1900 Prairie City Road, Folsom, CA 95630.Now with Chrysalis Symbolic Design, 101 Billerica Ave., North Billerica, MA 01862.     

Calculating lightning-induced overvoltages in power lines. Acomparison of two coupling models

A comparison is made between two coupling models frequently used to estimate the lightning-induced overvoltages in power lines. The first model was introduced by Rusck (1957) and the second model by Agrawal, Price, and Gurbaxani (1980). In the nomenclature adopted in this paper, the first model is referred to as the “Rusck model” and the second as the “Wave Antenna Model.” The transmission line equations of the Rusck model can be written in such away that the forcing term in the equations is the horizontal electric field. The results show that the Rusck model is incomplete. It takes into account the portion of the horizontal electric field generated by the gradient of the scalar potential but neglects the contribution from the vector potential. This defect in the Rusck model makes it source-dependent. That is, the Rusck model can give accurate results only when the spatial location of the source that generates the electromagnetic field is such that the contribution of the vector potential to the horizontal field is either zero or can be neglected. Under such circumstances the Rusck model and the Wave Antenna Model are described by the same transmission line equations, and the results predicted by the two models are identical     

Scattering from a coated perfect electromagnetic conducting elliptic cylinder

An exact analytic solution is presented to the problem of scattering from a coated perfect electromagnetic conducting (PEMC) elliptic cylinder, when it is illuminated by a plane wave as well as a line source. The problem is formulated by expanding the various fields in terms of appropriate angular and radial Mathieu functions and a set of expansion coefficients. The expansion coefficients associated with the incident fields are known, but those associated with the scattered fields and the fields within the coating are unknown. Imposing boundary conditions at the surface of the PEMC elliptic cylinder and the surface of the coating, enables the determination of the unknown expansion coefficients. Results are presented in the form of normalized scattering widths for elliptic cylinders of various sizes, PEMC admittances, and different coatings, to show the effects of these on scattering.     

Scattering of electromagnetic waves by a system of two dielectricspheroids of arbitrary orientation

By means of modal series expansion of the incident, scattered, and transmitted electric and magnetic fields in terms of appropriate vector spheroidal eigenfunctions an exact solution is obtained to the problem of electromagnetic scattering by two dielectric spheroids of arbitrary orientation is obtained. The incident wave is considered to be a monochromatic uniform plane electromagnetic wave of arbitrary polarization and angle of incidence. To impose the boundary conditions at the surface of one spheroid, the electromagnetic field scattered by the other spheroids is expressed as an incoming field to the first one, in terms of the spheroidal coordinates attached to it, using rotational-translational addition theorems for vector spheroidal wave functions. The solution of the associated set of algebraic equations gives the unknown expansion coefficients. Numerical results are presented in the form of plots for the bistatic and backscattering cross sections of two lossless prolate spheroids having various axial ratios, center-to-center separations, and orientations     

Positive streamer discharges along liquid dielectric surfaces: effect of dielectric constant and surface properties

This paper presents investigations on positive streamer discharges propagating in air along the surface of two nonmixing dielectric liquids. By measuring the currents associated with the streamer discharge propagating along the surface of the two nonmixing liquids for varying ratio of their volume, we analyzed the effect of the dielectric constant (the capacitive effect) and the surface properties. Especially, we separated and quantified the magnitude of each contribution. Two different combinations were studied: silicone oil together with glycerol and transformer oil together with glycerol. For these material combinations, we found that the influence of the dielectric constant is about 3 times larger than the effect of the surface properties. Further, by using a simple model of the streamer discharge, we determined with a 3D field calculation program the capacitive behavior of the two nonmixing dielectric materials for varying ratio of their volume. We found that, in order to obtain the observed capacitive dependence, the streamer must propagate literally on the insulator surface.     

On the concepts used in return stroke models applied in engineering practice

In this paper, we investigate the similarities between two basic concepts used in engineering return stroke models. In one type, the current propagation (CP) models, the return stroke channel merely acts as a medium for the current propagation with the driving source being at the ground. In the other type, the current generation (CG) models, the current sources (corona current) are assumed to be distributed along the return stroke channel. Our analysis shows that popular CP models, such as transmission line (TL), the modified transmission-line exponential (MTLE) model , and the modified transmission-line linear (MTLL) can be converted to CG models leaving the temporal and spatial variation of the return stroke current the same. In this alternative representation, the equivalent corona currents of the TL, MTLE, and MTLL models are bipolar, indicating initial deposition and subsequent removal of positive charge from the channel. This knowledge is applied to construct a simple CG model which generates electromagnetic fields identical to those obtained with the TL model at short times, but free from the difficulties associated with the latter at longer times.     

The lightning radiation field spectra of cloud flashes in the interval from 20 kHz to 20 MHz

Electric radiation fields produced by lightning cloud flashes have been analyzed using Fourier methods to obtain amplitude spectra for frequencies in the range of 20 kHz to 20 MHz. Time to thunder measurements were used to extract the distances to the cloud flashes from the measurement site. The spectra were generated by analyzing the first 10 ms time window of cloud flashes with 10 ns sampling resolution, and they show f/sup -1/ frequency dependence up to 2 MHz followed by f/sup -2/ dependence and higher for frequencies above 2 MHz. The results agree very well with previous measurements carried out for individual pulses produced by various lightning processes. By utilizing digital filters, it has been shown that measurements taken with narrowband filters agree with the results produced under wideband measurements.     

Acidulated pegmatitic mica: A promising new multi-nutrient mineral fertilizer

Scrap grade pegmatitic phlogopite mica contains 5–7% K (8% K₂O), 10–14% Mg (23% MgO), 1–2% Ca (2.9% CaO), 0.03% Mn and 109 ppm Zn. On acidulation upto 65% of K and Mg and 15–100% Mn and Zn were recovered. Less than 13% of Ca was recovered in solution. Water soluble and Nh₄OAc extractable K and Mg of acidulated mica of pegmatitic origin increased a 10² to 10³ times compared to untreated mica. Acidulated mica remained non-hygroscopic even when mixed with acids at a 2:1 mica to acid ratio. X-ray diffraction analyses demonstrated that interlayer cations were easily leached from the mica structure leaving behind a kaolinitic residue, compared to the more stable tetrasilicate feldspars.The most significant achievement through these experiments was the yield increase obtained in the greenhouse experiment with rice by using the lowest application rate (200 kg ha^–1) so far reported for mica, - an exponential decrease from tonnes/ha previously reported. Acidulated phlogopite mica chips (200 kg ha^–1- 4 kg K, 8 kg Mg, trace elements Mn, Zn etc.) gave a yield increase of over 41% compared to a control with recommended muriate of potash and dolomite (17 kg K, 6 kg Mg). The response to acidulated feldspar (500 kg ha^–1- 1.5 kg K) and an acidulated feldspar-dolomite combined fertilizer (250 kg ha^–1- 0.6 kg K and 6 kg Mg) was not significant.The response to mica clearly shows a multinutrient deficiency in highly weathered tropical soils. The relatively high solubility of the acidulated mica, its range of nutrient element supply, its nonhygroscopic nature and its extremely simple manufacturing process makes mica, a cheap but effective fertilizer for the tropical regions where these nutrients are deficient, especially in highly metamorphosed crystalline terrains.