Fast Temporal And Spatial Changes In Auroras

Thesis (Ph.D.) University of Alaska Fairbanks, 196

Gravitational synchrotron radiation from cosmic strings

This work studies the gravitational synchrotron radiation emitted from arbitrary cusps of cosmic strings. The results are expressed in terms of four parameters describing the motion of such a cusp. The power spectrum is derived for cusps moving at unit velocity. By using a phenomenological approach the authors also derive the power emitted when the radiation reaction on the cusps is taken into account. In both cases, the synchrotron nature of the radiation produces a power spectrum emitted in a narrow forward cone. If cosmic strings do exist, the radiation emitted by their cusps would seem to be a potential candidate for gravitational-wave detectors

Comparing migratory connectivity across species : the importance of considering the pattern of sampling and the processes that lead to connectivity

Measuring the degree of migratory connectivity – how much and where different populations of species mix as they migrate over their annual cycle – is important because it informs the understanding of the evolution of migration, how populations will be affected by both habitat and climate change, and which areas to prioritize for conservation. But existing measures of connectivity may be difficult to compare because they measure different things and are confounded by sampling bias. Here we use tagging data from all available published landbird tracks up to July 2019 (224 populations, 86 species and 1524 individuals tracked in the three main global flyways) to identify robust measures to compare migratory connectivity across species. We consider two widely used descriptive measures: (1) degree of breeding population overlap on the non-breeding grounds and (2) Mantel correlation, which tests the degree of spatial autocorrelation between the breeding and non-breeding individuals; as well as one causative measure of the main process that leads to connectivity patterns: migratory spread of individuals from the same breeding population across the non-breeding area. We investigated the sensitivity of these three measures to the distance between breeding locations of sampled populations (breeding distance) and their sample size. We also considered the confounding effects of migration distance because longer migrations decreased overlap and increased Mantel correlations and migratory spread. We found that the degree of overlap between breeding populations on the non-breeding grounds decreased with increasing breeding distance and increased with increasing sample size. Mantel correlation coefficients also increased significantly with increasing breeding distance; sample size did not affect accuracy, but precision was greatly improved above a sample size of about 15 individuals. Migratory spread, however, was independent of breeding distance; sample size had only small effects on accuracy and precision, with no significant effects when more than four individuals per population were included. Furthermore, migratory spread was highly positively correlated with the maximum non-breeding range. Overlap and Mantel correlations were highly confounded by the spatial pattern and amount of sampling, whereas migratory spread was relatively unconfounded, even by migratory distance. Although any descriptive migratory connectivity measure can help set priorities by determining current areas for conservation on the non-breeding grounds, migratory spread, which leads to these patterns, needs fewer data, is comparable, and gives information on evolutionary flexibility and so ability to deal with changing habitat and climate.Publisher PDFPeer reviewe

Geste technique, fait social total. Le technique est-il dans le social ou face à lui ?

Le titre de cet ensemble d’essais préconise trois thèmes. L’argument de cet article est que l’ordre dans lequel sont abordés ces thèmes est pertinent. De plus l’auteur énonce que la difficulté majeure découle de ce qu’à un certain niveau d’analyse, la technologie culturelle existe en tant que domaine séparé de la réalité sociale et ainsi appelle un champ autonome d’étude (ce qui implique une méthodologie spécifique), et qu’à un autre niveau d’analyse les techniques font structurellement partie intégrante de la société. Ainsi, les processus techniques et les structures sociales interagissent de deux manières. Pour prendre tout cela en compte, l’auteur propose non seulement d’agrandir la chaîne opératoire afin d’y inclure les canaux économiques de distribution et les interactions symboliques, mais aussi il suggère un cadre élaboré pour inclure les niveaux d’analyse et d’abstraction dans lequel pourraient prendre place les faits et les théories, l’action inconsciente et la signification inconsciente.Technological act, a total social fact. Technics are in society, or confronting society ?.The title of this group of essays presupposes three themes. It is argued here that the order in which these are taken up is meaningful. In addition the author states that the essential difficulty is that on one level cultural technology sets out techniques as a separate domain of social reality and therefore calls for a autonomous field of study (which implies a distinctive methodology), and on another level technology is structurally an integral part of society. Thus technological processes and social structures interact in two ways. To take all this into account, the author proposes not only to enlarge the operative model of a work chain to include economic channels of distribution as well as symbolic interactions, but also suggests a framework consisting of levels of analysis and abstraction within which can be set fact and theory, conscious action and unconscious meaning

La réalité et/de la nature

À propos de : Alan Sokal & Jean Bricmont, Impostures intellectuelles. Paris, Éditions Odile Jacob, 1997, 276 p

Techniques et culture : les bases d’un programme de travail

En 1976 le CNRS créa un laboratoire pour étudier des phénomènes relevant du domaine de la technologie culturelle. L’équipe « Techniques et culture » qui vit le jour esquissa alors dans un premier bulletin un programme qui devait guider ses recherches dans les années à venir. La présente rédaction résume les grandes lignes de ce premier texte. Le regroupement des techniques en deux grandes divisions – celles qui « créent » des rapports sociaux, celles qui « reflètent » le fonctionnement et l’architecture des relations intra et intergroupes – est expliqué et justifié. Après un court rappel de l’épistémologie et de la méthodologie de l’enquête dans ce domaine, qui soulèvent entre autres les problèmes de l’innovation et de l’évolution, sont abordés quelques exemples de techniques « créatrices » tirées de l’époque médiévale : la charrue, l’étrier, le ferrage des animaux, l’assolement triennal, sous l’angle de leur influence sur les structures sociales. Puis l’habitation en tant qu’inscription de la société sur le sol permet de dégager des nouvelles avenues de recherche anthropologique. Enfin une dernière analyse compare le passage en Irlande de l’horticulture à la bêche à l’agriculture attelée, puis des animaux aux tracteurs d’où il ressort que parfois des facteurs sociaux revêtent autant d’importance que des critères purement techniques dans l’acceptation ou le refus de nouveautés.In 1976 the CNRS (Centre national de la recherche scientifique) founded a laboratory for studying differents aspects of cultural technology. The work group « Techniques and culture » wich thus came into being laid down in its first research bulletin the general framework wich would be the cadre of its researches in the years to come. This article sums up the principal axes of that first text. The reasoning that explains and justifies, the grouping of techniques into two large divisions – those that « create » social relations, and those that mirror the architecture and the functioning of intra- and inter-relations within social groups – is analysed. After a short reminder of the epistemology and metholology obtaining in this domain wich among other things brings up the problems of innovation and evolution, a few examples from medieval Europe: the plough, the stirrup, iron shoes for animals, triennal crop rotatation, are examined from the point of view of their influence on social structure. The study of housing and urbanism (house grouping) as an imprinting of society on a geographical territory opens up news avenues of anthropological research. A final analysis compares the passage in, Ireland from horticulture with a spade to agriculture with harnessed animals, then from animals to tractors, from which it appears that social criteria are at least as important as purely technical ones as to the acceptance or denial of new vectors of change