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[en] Now the investigation of possibilities of amplification of high frequency waves (Langmuir, electromagnetic etc.) attracts the attention of many physicists. The nonlinear interaction of resonant and nonresonant waves in turbulent plasma, first considered by Tsytovich et al., is of considerable interest. The resonant waves, as a rule, are considered to be low frequency oscillations. If there is a sufficiently high extra-thermal level of the energy of the resonant oscillations, a nonlinear amplification of the high frequency nonresonant waves will take place. Such a type of interaction is called an up-conversion of the plasma oscillations energy or plasma-maser effect. Examples of this nonlinear interaction have been observed more than once both in laboratory experiments and in astrophysics. In the latter case, the random magnetic fields, presented in many space plasmas, can play the role of low frequency resonant oscillations. The purpose of the present paper is to point out that very high frequency electromagnetic waves can be amplified in a plasma with random magnetic fields in the presence of weak regular magnetic field. (author) 4 refs
Journal
Europhysics Conference Abstracts; ISSN 0378-2271; 
; CODEN ECABDW; v. 16C(Part II); p. II-1321-II-1324
; CODEN ECABDW; v. 16C(Part II); p. II-1321-II-1324
[en] The stability against long-wavelength small parallel perturbations of a class of exact standing wave solutions of the equations that describe an unmagnetized relativistic overdense cold electron plasma is considered. A dispersion relation valid for long-wavelength perturbations is obtained. This dispersion relations is discussed for the whole range of the two parameters revealing, in particular, the existence of a region in parameter space where the nonlinear waves are stable. (author)
Journal
[en] Developmental effects of extremely low frequency (ELF) electric and magnetic fields are briefly reviewed in this paper. The results of animal studies on ELF electric fields are rather consistent, and do not suggest adverse effects on development. The results of studies on ELF magnetic fields suggest effects on bird embryo development, but not consistently in all studies. Results from experiments with other non-mammalian species have also suggested effects on developmental stability. In mammals, pre-natal exposure to ELF magnetic fields does not result in strong adverse effects on development. The only finding that shows some consistency is increase of minor skeleton alterations. Epidemiological studies do not establish an association between human adverse pregnancy outcomes and maternal exposure to ELF fields, although a few studies have reported increased risks associated with some characteristics of magnetic field exposure. Taken as a whole, the results do not show strong adverse effects on development. However, additional studies on the suggested subtle effects on developmental stability might increase our understanding of the sensitivity of organisms to weak ELF fields. (author)
Journal
[en] Two methods were developed by which daily net short-wave radiation (K∗) can be evaluated from Bellani pyranometer readings. The first method involves a simple regression equation. The second method uses a physical approach taking into account the effect of the Bellani's geometry on its response to direct and diffuse radiation throughout the day. Both methods, when tested on experimental data, tended to underestimate the measured K∗, the regression approach exhibiting a higher variance of the error
[fr]
Deux méthodes sont développées pour estimer le rayonnement net de courte longueur d'onde (K∗) a partir de lectures d'un pyranometre Bellani. La premiere méthode consiste en une simple équation de régression. La seconde méthode, basée sur des relations physiques, tient compte de l'effet de la géométrie du Bellani sur sa réaction au rayonnement direct et diffus tout au long de la journée. Les deux méthodes, testées sur des valeurs expérimentales, tendent a sous-estimer K∗, l'équation de régression ayant la plus grande variance de l'erreurJournal
Agricultural Meteorology; ISSN 0002-1571; ; v. 30(3); p. 175-184
; v. 30(3); p. 175-184
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