[1] Return stroke current pulses can propagate at speeds approaching the speed of light c. Such a fast-moving pulse is expected to radiate differently than conventional dipole emitters. In this study, we revisit the theoretical analysis for the high-speed effect on the radiation beam pattern. Instead of starting with specific return stroke models, as has been done before by other investigators, we start the analysis with a general moving current pulse. Through a simple differential transformation between the retarded time and stationary time/space, the so-called F factor (1 À v cos q/c) À1 can be readily obtained. This factor is found to be fundamental and is explicitly associated with the radiation beam pattern but is not limited only to the lossless transmission line (TL) return stroke model. It is demonstrated that different beam pattern factors could be derived from this fundamental factor under different return stroke model assumptions.

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Age and growth data extracted from scales are often used when managing fish populations. However, accurate interpretation of scale annuli in certain species, such as muskellunge Esox masquinongy, has been suspect. The accuracy of age determination was tested with three experienced esocid scale readers who interpreted positive photo images made from acetate slide impressions projected on a microfiche reader. Images were made from scales of 25 known-age muskellunge (3-10 years old) from five Wisconsin lakes. Each scale image was interpreted twice; once with fish length, sex, and date of capture given and once without any information. Of 149 scale interpretations. 32% were assessed with the correct age. 54% underaged. and 14% overaged. The average interpretation deviated from the known age by 1.0 years. Accuracy did not improve when additional fish information was available. General confidence in the interpreter's age assessments was low and possibly related to quality of the photo images. Interpreters were accustomed to using acetate images with several impressions rather than a single photo image. As a follow-up, we selected 12 acetate slides used to make the photo images and allowed each interpreter to determine age from the slides. The percentage correctly aged with the subsample improved from 24% to 47% with the acetate slide impressions. Increasing the magnification of acetate slides from 23 x to 35 x magnification did not affect accuracy. Image quality and multiple impressions can improve accuracy of age determination; however, accuracy was still less than 50%. The low accuracy when interpreting scale annuli of muskellunge 3-10 years of age suggests that managers need to use caution when evaluating data taken from muskellunge scales.

Aims. The principal aim of this project is to determine the structural parameters of the rapidly pulsating subdwarf B star PG 0911+456 from asteroseismology. Our work forms part of an ongoing programme to constrain the internal characteristics of hot B subdwarfs with the long-term goal of differentiating between the various formation scenarios proposed for these objects. So far, a detailed asteroseismic interpretation has been carried out for 6 such pulsators, with apparent success. First comparisons with evolutionary theory look promising, however it is clear that more targets are needed for meaningful statistics to be derived. Methods. The observational pulsation periods of PG 0911+456 were extracted from rapid time-series photometry using standard Fourier analysis techniques. Supplemented by spectroscopic estimates of the star's mean atmospheric parameters, they were used as a basis for the "forward modelling" approach in asteroseismology. The latter culminates in the identification of one or more "optimal" models that can accurately reproduce the observed period spectrum. This naturally leads to an identification of the oscillations detected in terms of degree and radial order k, and infers the structural parameters of the target. Results. The high S/N low-and medium resolution spectroscopy obtained led to a refinement of the atmospheric parameters for PG 0911+456, the derived values being T eff = 31 940 ± 220 K, log g = 5.767 ± 0.029, and log He/H = −2.548 ± 0.058. From the photometry it was possible to extract 7 independent pulsation periods in the 150−200 s range with amplitudes between 0.05 and 0.8% of the star's mean brightness. There was no indication of fine frequency splitting over the ∼68-day time baseline, suggesting a very slow rotation rate. An asteroseismic search of parameter space identified several models that matched the observed properties of PG 0911+456 well, one of which was isolated as the "optimal" model on the basis of spectroscopic and mode identification considerations. All the observed pulsations are identified with low-order acoustic modes with degree indices = 0, 1, 2 and 4, and match the computed periods with a dispersion of only ∼0.26%, typical of the asteroseismological studies carried out to date for this type of star. The inferred structural parameters of PG 0911+456 are T eff = 31 940 ± 220 K (from spectroscopy), log g = 5.777 ± 0.002, M * /M = 0.39 ± 0.01, log M env /M * = −4.69 ± 0.07, R/R = 0.133 ± 0.001 and L/L = 16.4 ± 0.8. We also derive the absolute magnitude M V = 4.82 ± 0.04 and a distance d = 930.3 ± 27.4 pc.