967 resultados para Arc-flash hazard
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The safe and responsible development of engineered nanomaterials (ENM), nanotechnology-based materials and products, together with the definition of regulatory measures and implementation of "nano"-legislation in Europe require a widely supported scientific basis and sufficient high quality data upon which to base decisions. At the very core of such a scientific basis is a general agreement on key issues related to risk assessment of ENMs which encompass the key parameters to characterise ENMs, appropriate methods of analysis and best approach to express the effect of ENMs in widely accepted dose response toxicity tests. The following major conclusions were drawn: Due to high batch variability of ENMs characteristics of commercially available and to a lesser degree laboratory made ENMs it is not possible to make general statements regarding the toxicity resulting from exposure to ENMs. 1) Concomitant with using the OECD priority list of ENMs, other criteria for selection of ENMs like relevance for mechanistic (scientific) studies or risk assessment-based studies, widespread availability (and thus high expected volumes of use) or consumer concern (route of consumer exposure depending on application) could be helpful. The OECD priority list is focussing on validity of OECD tests. Therefore source material will be first in scope for testing. However for risk assessment it is much more relevant to have toxicity data from material as present in products/matrices to which men and environment are be exposed. 2) For most, if not all characteristics of ENMs, standardized methods analytical methods, though not necessarily validated, are available. Generally these methods are only able to determine one single characteristic and some of them can be rather expensive. Practically, it is currently not feasible to fully characterise ENMs. Many techniques that are available to measure the same nanomaterial characteristic produce contrasting results (e.g. reported sizes of ENMs). It was recommended that at least two complementary techniques should be employed to determine a metric of ENMs. The first great challenge is to prioritise metrics which are relevant in the assessment of biological dose response relations and to develop analytical methods for characterising ENMs in biological matrices. It was generally agreed that one metric is not sufficient to describe fully ENMs. 3) Characterisation of ENMs in biological matrices starts with sample preparation. It was concluded that there currently is no standard approach/protocol for sample preparation to control agglomeration/aggregation and (re)dispersion. It was recommended harmonization should be initiated and that exchange of protocols should take place. The precise methods used to disperse ENMs should be specifically, yet succinctly described within the experimental section of a publication. 4) ENMs need to be characterised in the matrix as it is presented to the test system (in vitro/ in vivo). 5) Alternative approaches (e.g. biological or in silico systems) for the characterisation of ENMS are simply not possible with the current knowledge. Contributors: Iseult Lynch, Hans Marvin, Kenneth Dawson, Markus Berges, Diane Braguer, Hugh J. Byrne, Alan Casey, Gordon Chambers, Martin Clift, Giuliano Elia1, Teresa F. Fernandes, Lise Fjellsbø, Peter Hatto, Lucienne Juillerat, Christoph Klein, Wolfgang Kreyling, Carmen Nickel1, and Vicki Stone.
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A high-resolution U-Pb zircon geochronological study of plutonic units along the south Peruvian margin between 17 degrees and 18 degrees S allows the integration of the geochemical, geodynamic and tectonic evolution of this part of the Andean margin. This study focuses on the composite Jurassic-early Cretaceous Ilo Batholith that was emplaced along the southern Peruvian coast during two episodes of intrusive magmatism; a first period between 173 and 152 Ma (with a peak in magmatic activity between roughly 168 and 162 Ma) and a second period between 110 and 106 Ma. Emplacement of the Jurassic part of the composite Ilo Batholith shortly post-dated the accumulation of the volcanosedimentary succession it intruded (Chocolate formation), which allows to estimate a subsidence rate for this unit of similar to 3.5 km/Ma. The emplacement of the main peak of Jurassic plutonism of the Ilo Batholith was also closely coeval with widespread and repeated slumping (during deposition of the Cachios Formation) in the back-arc region, suggesting a common causal link between these phenomena, which is discussed in the context of an observed 100 km trenchward arc migration at similar to 175 Ma, and the relation with extensional tectonics that prevailed along the Central Andean margin during Pangaea break-up. (C) 2012 Elsevier B.V. All rights reserved.
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Référence bibliographique : Weigert, 483
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Référence bibliographique : Weigert, 235
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Référence bibliographique : Weigert, 237
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Référence bibliographique : Weigert, 30
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Référence bibliographique : Weigert, 31
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Except for the first 2 years since July 29, 1968, Arenal volcano has continuously erupted compositionally monotonous and phenocryst-rich (similar to35%) basaltic andesites composed of plagioclase (plag), orthopyroxene (opx), clinopyroxene (cpx), spinel olivine. Detailed textural and compositional analyses of phenocrysts, mineral inclusions, and microlites reveal comparable complexities in any given sample and identify mineral components that require a minimum of four crystallization environments. We suggest three distinct crystallization environments crystallized low Mg# (<78) silicate phases from andesitic magma but at different physical conditions, such as variable pressure of crystallization and water conditions. The dominant environment, i.e., the one which accounts for the majority of minerals and overprinted all other assemblages near rims of phenocrysts, cocrystallized clinopyroxene (Mg# similar to71-78), orthopyroxene (Mg# similar to71-78), titanomagnetite and plagioclase (An(60) to An(85)). The second environment cocrystallized clinopyroxene (Mg# 71-78), olivine (<Fo(78)), titanomagnetite, and very high An (similar to90) plagioclase, while the third cocrystallized clinopyroxene (Mg# 71-78) with high (>7) Al/Ti and high (>4 wt.%) Al2O3, titanomagnetite with considerable Al2O3 (10-18 wt.%) and possibly olivine but appears to lack plagioclase. A fourth crystallization environment is characterized by clinopyroxene (e.g., Mg#=similar to78-85; Cr2O3=0.15-0.7 wt.%), Al-, Cr-rich spinel olivine (similar toFo(80)), and in some circumstances high-An (>80) plagioclase. This assemblage seems to record mafic inputs into the Arenal system and crystallization at high to low pressures. Single crystals cannot be completely classified as xenocrysts, antecrysts (cognate crystals), or phenocrysts, because they often contain different parts each representing a different crystallization environment and thus belong to different categories. Bulk compositions are mostly too mafic to have crystallized the bulk of ferromagnesian minerals and thus likely do not represent liquid compositions. On the other hand, they are the cumulative products of multiple mixing events assembling melts and minerals from a variety of sources. The driving force for this multistage mixing evolution to generate erupting basaltic andesites is thought to be the ascent of mafic magma from lower crustal levels to subvolcanic depths which at the same time may also go through compositional modification by fractionation and assimilation of country rocks. Thus, mafic magmas become basaltic andesite through mixing, fractionation and assimilation by the time they arrive at subvolcanic depths. We infer new increments of basaltic andesite are supplied nearly continuously to the subvolcanic reservoir concurrently to the current eruption and that these new increments are blended into the residing, subvolcanic magma. Thus, the compositional monotony is mostly the product of repetitious production of very similar basaltic andesite. Furthermore, we propose that this quasi-constant supply of small increments of magma is the fundamental cause for small-scale, decade-long continuous volcanic activity; that is, the current eruption of Arenal is flux-controlled by inputs of mantle magmas. (C) 2004 Elsevier B.V. All rights reserved.
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Référence bibliographique : Weigert, 614
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Référence bibliographique : Weigert, 491
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Référence bibliographique : Weigert, 493
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Référence bibliographique : Weigert, 492
