877 resultados para American Association for the Advancement of Science. Pacific Division. Meeting.
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Mode of access: Internet.
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Mode of access: Internet.
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Mode of access: Internet.
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Reports issued together.
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Mode of access: Internet.
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Description based on: 60th (1979).
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Puyasena et al. question our interpretation of climate-driven vegetation change on the Andean flank in western Amazonia during the middle Pleistocene and suggest that the use of Podocarpus spp. as a proxy of past climate change should be reassessed. We defend our assertion that vegetation change at the Erazo study site was predominantly driven by climate change due to concomitant changes recorded by multiple taxa in the fossil record.
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These guidelines have been prepared to assist in the planning, conduct and interpretation of studies for the assessment of the efficacy of acaricides (excluding vaccines and other bio-control agents) against single and multi-host ticks (Ixodidae) on ruminants. Information is provided on the selection of animals, dose determination, dose confirmation and field studies, record keeping and result interpretation. The use of pen facilities is advocated for dose determination and confirmation studies for defining therapeutic and persistent efficacy. A minimum of two studies per tick species for which claims are sought is recommended for each dose determination and dose confirmation investigation. If dose confirmation studies demonstrate greater than 95% efficacy the sponsor may proceed to field studies, where a minimum of two studies per geographical location is preferred to confirm the therapeutic and persistent efficacy under field conditions. If dose confirmation studies demonstrate less than 95% efficacy then longer-term field studies can be conducted over two tick seasons with a minimum of two studies per geographical location. These studies can incorporate other control methods such as tick vaccines, to demonstrate stable long-term tick management. Specific advice is also given on conducting studies with paralysis ticks. These guidelines are also intended to assist investigators on how to conduct specific experiments, to provide specific information for registration authorities involved in the decision-making process, to assist in the approval and registration of new acaricides, and to facilitate the worldwide adoption of standard procedures. (c) 2005 Elsevier B.V. All rights reserved.
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Transport between compartments of eukaryotic cells is mediated by coated vesicles. The archetypal protein coats COPI, COPII, and clathrin are conserved from yeast to human. Structural studies of COPII and clathrin coats assembled in vitro without membranes suggest that coat components assemble regular cages with the same set of interactions between components. Detailed three-dimensional structures of coated membrane vesicles have not been obtained. Here, we solved the structures of individual COPI-coated membrane vesicles by cryoelectron tomography and subtomogram averaging of in vitro reconstituted budding reactions. The coat protein complex, coatomer, was observed to adopt alternative conformations to change the number of other coatomers with which it interacts and to form vesicles with variable sizes and shapes. This represents a fundamentally different basis for vesicle coat assembly.
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Jarvis et al. (Research Articles, 12 December 2014, p. 1320) presented molecular clock analyses that suggested that most modern bird orders diverged just after the mass extinction event at the Cretaceous-Paleogene boundary (about 66 million years ago). We demonstrate that this conclusion results from the use of a single inappropriate maximum bound, which effectively precludes the Cretaceous diversification overwhelmingly supported by previous molecular studies.
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À l’origine, la nouvelle concernant l’occupation américaine d’Haïti en 1915 a suscité peu d’indignation aux États-Unis. En effet, on reproche à la république son instabilité politique et on juge aussi qu’une intervention américaine concourrait à l’édifice de l’autorité de la loi. À partir de 1915 et surtout en 1920, l’Association nationale pour l’avancement des gens de couleur (NAACP), fondée en 1909, critique cette ingérence et milite pour y voir un terme. W.E. B. Du Bois et James Weldon Johnson, deux figures publiques noires importantes travaillant au sein de l’organisation, dénoncent avec conviction l’occupation d’Haïti. Les historiens ont jusqu’ici jugé que la NAACP fut inspirée par des considérations de solidarité raciale en adhérant à la cause de la souveraineté haïtienne. Si la thèse présente ne réfute pas cette possibilité, elle cherche tout de même à démontrer que le cadre conceptuel de la solidarité raciale ne saurait illustrer toute la complexité de la campagne haïtienne érigée par la NAACP. Par conséquent, une attention dirigée davantage sur le contexte social et politique américain entre 1915 et 1922 révèle que pour la NAACP, la dénonciation de l’occupation américaine d’Haïti représentait d’une part une opportunité de discuter des problèmes sociaux touchant les Afro-Américains, et d’autre part, une occasion de renforcer sa position aux États-Unis.
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Climate models suggest that extreme precipitation events will become more common in an anthropogenically warmed climate. However, observational limitations have hindered a direct evaluation of model-projected changes in extreme precipitation. We used satellite observations and model simulations to examine the response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric moisture content. These observations reveal a distinct link between rainfall extremes and temperature, with heavy rain events increasing during warm periods and decreasing during cold periods. Furthermore, the observed amplification of rainfall extremes is found to be larger than that predicted by models, implying that projections of future changes in rainfall extremes in response to anthropogenic global warming may be underestimated.
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Our conclusions are unaffected by removal of the time series identified by Peacock and Garshelis as harvest data. The relationship between a population's growth rate and its size is generally concave in mammals, irrespective of their body sizes. However, our data set includes quality data for only five mammals larger than 20 kilograms, so strong conclusions cannot be made about these animals.
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The extinction of dinosaurs at the Cretaceous/Paleogene (K/Pg) boundary was the seminal event that opened the door for the subsequent diversification of terrestrial mammals. Our compilation of maximum body size at the ordinal level by sub-epoch shows a near-exponential increase after the K/Pg. On each continent, the maximum size of mammals leveled off after 40 million years ago and thereafter remained approximately constant. There was remarkable congruence in the rate, trajectory, and upper limit across continents, orders, and trophic guilds, despite differences in geological and climatic history, turnover of lineages, and ecological variation. Our analysis suggests that although the primary driver for the evolution of giant mammals was diversification to fill ecological niches, environmental temperature and land area may have ultimately constrained the maximum size achieved.