980 resultados para adaptation evolution


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Since the early years of the 21st century, and in particular since 2007, the U.S. has been awakening rapidly to the fact that climate change is underway and that even if stringent efforts are undertaken to mitigate greenhouse gas emissions, adaptation to the unavoidable impacts from the existing commitment to climate change is still needed and needs to be begun now. This report provides an historical overview of the public, political, and scientific concern with adaptation in the United States. It begins by briefly distinguishing ongoing, historical adaptation to environmental circumstances from deliberate adaptation to human‐induced climate change. It then describes the shift from the early concerns with climate change and adaptation to the more recent awakening to the need for a comprehensive approach to managing the risks from climate change. Ranging from the treatment of the topic in the news media to the drafting of bills in Congress, to state and local government activities with considerable engagement of NGOs, scientists and consultants, it is apparent that adaptation has finally, and explosively, emerged on the political agenda as a legitimate and needed subject for debate. At the same time, the current policy rush is not underlain by widespread public engagement and mobilization nor does it rest on a solid research foundation. Funding for vulnerability and adaptation research, establishing adequate decision support institutions, as well as the building of the necessary capacity in science, the consulting world, and in government agencies, lags far behind the need. (PDF contains 42 pages)

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Papillomaviruses (PVs) are widespread pathogens. However, the extent of PV infections in bats remains largely unknown. This work represents the first comprehensive study of PVs in Iberian bats. We identified four novel PVs in the mucosa of free-ranging Eptesicus serotinus (EserPV1, EserPV2, and EserPV3) and Rhinolophus ferrumequinum (RferPV1) individuals and analyzed their phylogenetic relationships within the viral family. We further assessed their prevalence in different populations of E. serotinus and its close relative E. isabellinus. Although it is frequent to read that PVs co-evolve with their host, that PVs are highly species-specific, and that PVs do not usually recombine, our results suggest otherwise. First, strict virus-host co-evolution is rejected by the existence of five, distantly related bat PV lineages and by the lack of congruence between bats and bat PVs phylogenies. Second, the ability of EserPV2 and EserPV3 to infect two different bat species (E. serotinus and E. isabellinus) argues against strict host specificity. Finally, the description of a second noncoding region in the RferPV1 genome reinforces the view of an increased susceptibility to recombination in the E2-L2 genomic region. These findings prompt the question of whether the prevailing paradigms regarding PVs evolution should be reconsidered.

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ENGLISH: The fishing power of the tuna purse-seine fleet of the eastern Pacific Ocean has increased since the early 1960's. Because the entire fleet seems to have adopted equipment and techniques to increase its efficiency in capturing tunas, traditional methods of adjusting catch rates to a reference vessel type of fixed efficiency to index tuna abundance from fishing success are inapplicable. Instead, a methodology for such adjustment based on a mathematical representation of purse seining activities is developed. Observed changes in efficiency in subprocesses of purse seining are then used to adjust catch rates when computing abundance histories for yellowfin and skipjack in large regions of the eastern Pacific Ocean. SPANISH: La eficacia de pesca de la flota de cerco atunera en el Océano Pacífico oriental ha aumentado desde el comienzo del decenio de 1960. Como toda la flota parece haber adoptado equipo y métodos para incrementar su eficaciaen capturar atunes, no se pueden aplicar los métodos tradicionales de ajustar los índices de captura a un tipo normalizado de barco (es decir de eficacia fija) para indicar la abundancia del atún según los resultados de pesca. En su lugar se ha desarrollado un método para realizar tal ajuste basado en una representación matemática de las actividades de las embarcaciones de cerco. Cuando se calcula la abundancia histórica del atún aleta amarilla y barrilete en grandes regiones del Océano Pacífico oriental, se usan entonces los cambios observados en la eficacia de los subprocesos cerqueros para ajustar los índices de captura. (PDF contains 120 pages.)

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Computer vision algorithms that use color information require color constant images to operate correctly. Color constancy of the images is usually achieved in two steps: first the illuminant is detected and then image is transformed with the chromatic adaptation transform ( CAT). Existing CAT methods use a single transformation matrix for all the colors of the input image. The method proposed in this paper requires multiple corresponding color pairs between source and target illuminants given by patches of the Macbeth color checker. It uses Delaunay triangulation to divide the color gamut of the input image into small triangles. Each color of the input image is associated with the triangle containing the color point and transformed with a full linear model associated with the triangle. Full linear model is used because diagonal models are known to be inaccurate if channel color matching functions do not have narrow peaks. Objective evaluation showed that the proposed method outperforms existing CAT methods by more than 21%; that is, it performs statistically significantly better than other existing methods.

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A simple derivation based on continuum mechanics is given, which shows the surface stress is critical for yield strength at ultra-small scales. Molecular dynamics (MD) simulations with modified embedded atom method (MEAM) are employed to investigate the mechanical behaviors of single-crystalline metal nanowires under tensile loading. The calculated yield strengths increasing with the decrease of the cross-sectional area of the nanowires are in accordance with the theoretical prediction. Reorientation induced by stacking faults is observed at the nanowire edge. In addition. the mechanism of yielding is discussed in details based on the snapshots of defects evolution. The nanowires in different crystallographic orientations behave differently in stretching deformation. This study on the plastic properties of metal nanowires will be helpful to further understanding of the mechanical properties of nanomaterials. (C) 2009 Elsevier B.V. All rights reserved.

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The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the 'penetration period', 'enhance period of strength', and 'macro-crack period'. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations occurred in two stages, the 'latent period' and the 'accelerated period'. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum. (C) 2008 Elsevier Ltd. All rights reserved.