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61.
We clarify some misunderstandings currently found in the literature that arise from improper application of Newton's second law to variable mass problems. In the particular case of isotropic mass loss, for example, several authors introduce a force that actually does not exist.Facultad de Ciencias Astronómicas y Geofisicas de la Universidad Nacional de La PlataOn a Fellowship from the Comisión de Investigaciones Cientificas de la Provincia de Buenos Aires.Member of the Carrera del Investigador Cientifico del Consejo Nacional de Investigaciones Cientificas y Técnicas de la República Argentina. 相似文献
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Recently, several monitoring programmes have been undertaken to evaluate the impact of different anthropogenic activities, upon a range of coastal ecosystems located in the South-western Atlantic. In the present contribution, the applicability of the AZTI's Marine Biotic Index (AMBI) is tested, to establish the benthic health of the ecosystem using these data sets. As the AMBI was created previously for use in European estuarine and coastal environments, its general applicability to new geographical locations is discussed. In general, the results are in agreement with those obtained using traditional univariate and multivariate methods. Some inconsistent results are observed, when low abundances and/or number of taxa are recorded in the samples. Moreover, when the macrofauna samples are dominated by large nematodes, the classification of the benthic ecosystem health using AMBI is not consistent with previous results achieved applying other statistical techniques. Thus, parallel to the application of this index to a wider extend, the complementary use of different indices and/or methods is recommended to assess confidently the environmental quality of a coastal area. 相似文献
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A numerical solution of the dam failure problem as described by the one-dimensional shallow water equations is presented. The construction of the solution is based on the random choice method consisting in the superposition of locally theoretical solutions and sampling techniques. The search of the optimal sampling is performed through the application of the random choice method to the scalar wave equation. The dam failure problem is then solved and a comparison with the theoretical solution is presented. It is shown that the random choice method computes the bore with almost infinite resolution, represents exactly the constant state behind it and calculates the depression wave with great accuracy. 相似文献
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Angel Polvorinos del Río Leonardo García Sanjun Víctor Hurtado Prez M. Jesús Hernndez Arnedo 《Geoarchaeology》2005,20(3):263-284
Pottery from the Bronze Age of southwest Spain has traditionally been approached from a “typological” stand seeking the establishment of chronological sequences. This article examines ceramics from two different Bronze Age sites, a settlement (El Trastejón) and a necropolis (La Traviesa), from an archaeometric viewpoint. The methodology involved includes mineralogical characterization by XRD and optical microscopy, chemical analysis by XRF, and morphometric analysis through digital processing of thin sections. The analytical results are contextualized within the general framework of our current archaeological knowledge of both sites and their general background, and then a preliminary interpretation is proposed in terms of the prehistoric technology of pottery manufacture and functionality. © 2005 Wiley Periodicals, Inc. 相似文献
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Ramos-Gómez J Martins M Raimundo J Vale C Martín-Díaz ML DelValls TA 《Marine pollution bulletin》2011,62(7):1538-1549
Sediment toxicity assessments using caged organisms present advantages over using laboratory and native community studies. The use of caged Arenicola marina in sediment toxicity assessments was evaluated. Lugworms were exposed in situ to sediments from coastal and port areas in Spain for seven days, and the activities of the biotransformation enzymes ethoxyresorufin O-deethylase, dibenzylfluorescein dealkylase and glutathione S-transferase, the activities of the antioxidant enzymes glutathione reductase and glutathione peroxidase and lipid peroxidation were then analyzed as biomarkers. Biomarker results and sediment physicochemical data were integrated. Cádiz Bay (SW Spain) sediments presented metal contamination that was not linked to a biochemical response. In LPGC Port (SW Spain), Pb contamination exhibited a moderate toxic potential, while PAHs, and presumably pharmaceuticals, provoked biochemical responses that efficiently prevented lipid peroxidation. In Santander Bay (N Spain), exposure to PAHs and, presumably, pharmaceuticals induced biomarker responses, but lipid peroxidation occurred nevertheless. These results indicated that caged A. marina were effective for the assessment of sediment quality and that the selected biomarkers were sufficiently sensitive to identify chemical exposure and toxicity. 相似文献
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Overview of eutrophication indicators to assess environmental status within the European Marine Strategy Framework Directive 总被引:1,自引:0,他引:1