An investigation of isolated bursts of solar radio noise

The literature on isolated bursts and possible mechanisms of origin has been critically reviewed, and observations point to a mechanism involving omission of electromagnetc radiation from plasma oscillations in the solar corona excited by outward travelling disturbances. Solar noise observations on 125 Mc./s. recorded at Rhodes University during the period November 26 1957 - February 6 1958 have been analysed by the author for isolated bursts, and these observations show the same general features reported by previous investigators. In interpretation of these records particular attention has been devoted to two aspects of isolated bursts; namely the preponderance on single frequency records of double-humped bursts, and the shape of isolated burst profiles. The authors suggests that a probable explanation of double-humped bursts observed on any frequency f is that the first hump represents omission at or near the level of zero refractive index for f radiation, and that the second hump corresponds to harmonic omission at the f/2 level. Source velocities may be calculated from the time delay between the peaks and an average value of 2 x 10⁴ km./sec. was obtained from an analysis of 21 double-humped bursts. This value is in very good agreement with that deduced by Wild (1950b) from the rate of frequency drift of peak intensity of isolated bursts. Simple isolated bursts had decay profiles which are approximatley exponential in shape, and this is usually interpreted in terms of the natural decay of plasma oscillations in the medium of origin. The author has verified that the exponential function is a good fit to the observed decay profiles, but shows that a relation of the form I - ¹/n (superscript) ⋉ t (where I is intensity and t is time) fits just as well. An alternative model is suggested which would lead to an exponential-like decay profile which is not determined by the natural decay of plasma oscillations. The work concludes with some suggestions for further research

Allendorf 1993), inbreeding (Flick and Webster 1964; NRC 1995), relaxed natural selection pressures

Abstract.-Hatcheries play a key role in augmenting populations for conservation, harvest, or both, although rapid domestication and adaptation to hatchery conditions may lead to fish that are maladapted to natural environments. Three processes may lead to domestication: (1) negative selection against fish adapted to wild environments, (2) positive selection for fish that thrive in artificial conditions, or (3) relaxation of selection pressures. In this study, early life history traits and survival were contrasted among wild-and hatchery-origin lake trout Salvelinus namaycush reared in a common hatchery environment to address the hypotheses of processes leading to domestication. Examination of egg size, egg survival, fry deformity, and early growth rate found no evidence of negative selection against wild-origin lake trout or positive selection for hatchery-origin lake trout when reared in a hatchery environment. Wild-origin lake trout outperformed hatchery-origin fish in all life history traits examined, suggesting that relaxation of natural selective pressures may be occurring in the hatchery environment. Furthermore, the hatchery-origin strains failed to show maternal effects on egg size and exhibited limited variability in egg size and hatching time, as well as no significant differences in early growth rate, suggesting potential homogenization of life history traits as a result of the hatchery environment. Hatcheries have long been used to both provide fishing opportunities and to supplement declining wild population numbers. Despite their value and widespread use, however, numerous studies examining performance differences between hatchery and wild salmonids in seminatural to natural environments (termed ''natural'' environments hereafter) have found hatchery fish to be maladapted to natural environments. This has been attributed to genetic drift (Allendorf an

Evaluation of the responsiveness of the crustacean zooplankton community size spectrum to environmental change and an exotic invader in a sample of Canadian Shield lakes

We evaluated the crustacean zooplankton size spectrum as an indicator of lake characteristics and ecosystem change. First, we used time series from seven Canadian Shield lakes to identify the factors associated with among-lake and among-year variability in the spectrum slope (relative abundance of small and large zooplankton) and centered height (total abundance). Second, we used time series from an invaded and three control lakes to assess change in mean and variability in slope and height due to a Bythotrephes invasion. We found that the slope and height reflected among-lake predictors related to morphometry. The slope was responsive to long-term declining lake phosphorus levels, whereas the height reflected both increases in dissolved organic carbon and decreases in ice duration. We detected a significant increase (i.e., flattening) in mean slope and substantial (up to 120%) increases in the CV of height after Bythotrephes invaded Harp Lake. Thus, the zooplankton size spectrum was responsive to long-term environmental change, and a strong top-down perturbation can be detected through regular and frequent monitoring programs.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Appendix B. Additional information related to the population model.

Additional information related to the population model

Appendix A. Additional information related to the pond experiment.

Additional information related to the pond experiment