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排序方式: 共有219条查询结果,搜索用时 15 毫秒
1.
2.
The prevalence of dermal neoplasia among neotenic tiger salamanders (Ambystoma tigrinum) collected from the Reese Air Force Base sewage lagoon far exceeded that among salamanders from nearby uncontaminated lagoons. Perylene was the predominant pglycyclic aromatic hydrocarbon contaminant in this lagoon. Perylene was shown to be a substrate for monooxygenases in skin and liver homogenates and formed DNA-binding metabolites. Perylene exposure appeared to augment subsequent perylene metabolism by dermal enzymes but it was not a strong inducer of hepatic monooxygenases. Aroclor 1254 induced benzo(a)pyrene and perylene metabolism by both skin and liver enzymes. However, perylene apparently was not activated by salamander enzymes, as suggested by its lack of in vitro mutagenicity and failure to induce tumors. 相似文献
3.
Rodrigo Wiff Andrés Flores Angel M. Segura Mauricio A. Barrientos Vilma Ojeda 《新西兰海洋与淡水研究杂志》2020,54(2):218-232
ABSTRACT Genypterus blacodes, in terms of its fishing history and local economic importance, is an emblematic species harvested in Chilean Patagonia (41°00’–57°00’S). Most of the current fisheries and biological knowledge of this species come from the open ocean, whereas information about the species in fjords and inner channels is fragmentary. In 2018, two research surveys targeting G. blacodes were conducted in the fjords and inner channels of Chilean Patagonia. A total of 253 pairs of sagittal otoliths were sampled at three different localities, and their contours were modelled using wavelet analysis as a tool for stock discrimination. Contours were compared using canonical analysis, and classification was performed using linear discriminant and Random Forest analyses. The results indicated that the wavelet method is efficient in modelling otolith contours, and the discriminant analyses showed differences among fishing grounds across the latitudinal gradient, thus confirming the hypothesis that G. blacodes conform to at least two separate stock units in Chilean Patagonia. Fishing grounds that were closer in space showed higher levels of misclassification. The discussion focuses on how environmental variables and the geography of fjords shape stock differences and how this information can be used for the sustainable management of G. blacodes. 相似文献
4.
Arantxa Luzón Angel González Arsenio Muñoz Belén Sánchez-Valverde 《Journal of Paleolimnology》2002,28(4):441-456
The lacustrine facies from two sections (Candasnos and Fraga) ofthe Oligocene-Miocene Torrente de Cinca lithostratigraphic Unit in thecentral part of the Ebro Basin (Spain) have been analysed to determine theinfluence of orbital parameters in lacustrine sedimentation. The unit ispredominantly composed of limestones and marls, and represents a shallowlacustrine freshwater system. The sedimentological features of the faciesstudied demonstrate that the lower part of the Candasnos section representsoffshore lacustrine subenvironments whereas the upper part, and the whole ofthe Fraga section, characterise marginal lacustrine areas. Series of stratalthickness variations of limestone, marl, and limestone/marl couplets fromboth sections have been analysed using spectral analysis. This shows thatinformation corresponding to periodic cycles only appears in the offshorefacies, that is to say, in the lower part of Candasnos section, and disappearsin the marginal facies where non-periodic cycles exist. Furthermore, thespectral analysis of the offshore facies highlights the existence of a peak inthe power spectrum with a period of around 7 (6.8 to 7.8) that can berecognised in the field as shallowing-upward lacustrine sequences.Magnetostratigraphic data from the Candasnos section allow us to establish atime span of 2,808 years for the limestone/marl couplet from the lower partof this section, and between 19,000 and 22,000 years for the periodic cycleidentified, thus representing the climatic precession cycle. Shallowingsequences from marginal areas do not correspond with any periodiccycle. 相似文献
5.
The structure of coesite has been determined at ten pressures up to a maximum of 8.68 GPa by single-crystal X-ray diffraction.
The dominant mechanism of compression is the reduction of four of the five independent Si–O–Si angles within the structure.
There is no evidence of the fifth linkage, Si1–O1–Si1, deviating from 180°. Some Si–O bond distances also decrease by up to
1.6% over the pressure range studied. The pattern of Si–O–Si angle reduction amounts to a rotation of the Si2 tetrahedron
around the [001] direction. This rotation induces significant internal deformation of the Si1 tetrahedron. Comparison of the
experimental data with rigid-unit distance least-squares simulations of coesite suggests that this pattern of compression,
the anomalous positive values of both s23 and K′′ in the equation of state of coesite, its high elastic anisotropy and the unusual straight Si1–O1–Si1 linkage within
the structure are all consequences of the connectivity of the tetrahedral framework.
Received: 11 July 2002 / Accepted: 14 January 2003
Acknowledgements The help of Christian Baerlocher of ETH Zurich in providing both the DLS-76 software and advice in its use is gratefully
acknowledged, as are discussions with Paul Ribbe of Virginia Tech and the comments of two anonymous reviewers. The data analysis
was supported by the National Science Foundation under grant EAR-0105864 to N.L. Ross and R.J. Angel. 相似文献
6.
Borja A Barbone E Basset A Borgersen G Brkljacic M Elliott M Garmendia JM Marques JC Mazik K Muxika I Magalhães Neto J Norling K Rodríguez JG Rosati I Rygg B Teixeira H Trayanova A 《Marine pollution bulletin》2011,62(3):499-513
In recent times many benthic indices have been proposed to assess the ecological quality of marine waters worldwide. In this study we compared single metrics and multi-metric methods to assess coastal and transitional benthic status along human pressure gradients in five distinct environments across Europe: Varna bay and lake (Bulgaria), Lesina lagoon (Italy), Mondego estuary (Portugal), Basque coast (Spain) and Oslofjord (Norway). Hence, 13 single metrics (abundance, number of taxa, and several diversity and sensitivity indices) and eight of the most common indices used within the European Water Framework Directive (WFD) for benthic assessment were selected: index of size spectra (ISS), Benthic assessment tool (BAT), Norwegian quality index (NQI), Multivariate AMBI (M-AMBI), Benthic quality index (BQI), (Benthic ecosystem quality index (BEQI), Benthic index based on taxonomic sufficiency (BITS), and infaunal quality index (IQI). Within each system, sampling sites were ordered in an increasing pressure gradient according to a preliminary classification based on professional judgement. The different indices are largely consistent in their response to pressure gradient, except in some particular cases (i.e. BITS, in all cases, or ISS when a low number of individuals is present). Inconsistencies between indicator responses were most pronounced in transitional waters (i.e. IQI, BEQI), highlighting the difficulties of the generic application of indicators to all marine, estuarine and lagoonal environments. However, some of the single (i.e. ecological groups approach, diversity, richness) and multi-metric methods (i.e. BAT, M-AMBI, NQI) were able to detect such gradients both in transitional and coastal environments, being these multi-metric methods more consistent in the detection than single indices. This study highlights the importance of survey design and good reference conditions for some indicators. The agreement observed between different methodologies and their ability to detect quality trends across distinct environments constitutes a promising result for the implementation of the WFD’s monitoring plans. Moreover, these results have management implications, regarding the dangers of misclassification, uncertainty in the assessment, use of conflicting indices, and testing and validation of indices. 相似文献
7.
This paper investigates the impact of climate change on destination choice decisions in a context of domestic coastal tourism in Spain. Destinations are characterized in terms of travel cost and coastal ‘attractors’, such as temperature and beach-related attributes. By means of a discrete choice model based on the random utility theory, these variables are used to explain the observed pattern of interprovincial domestic trips, showing trade-offs between temperature and attractiveness in the probability of a particular destination being chosen. The model is used to investigate the impact of two climate change scenarios on the allocation of domestic tourism within Spain. The findings show that while Spain’s northern colder provinces would benefit from rising temperatures, provinces in the south would experience a decrease in the frequency of trips. 相似文献
8.
Angel Paniagua 《The Professional geographer》2016,68(3):511-518
To date, only limited research has focused on the individual in rural geography compared to the importance given to the rural community. With the sociocultural turn and moral positions in rural geography, however, the individual is acquiring more relevance but encapsulated in analytical traditions of locality community and of marginal situations and people. This article synthesizes the most significant works about the individual, especially within rural geography, and its key dimensions are identified: citizenship (political and normative dimension), emotional aspects (the extraordinary moments in peoples' lives), everyday life (the relationship between the individual and the rural place), and difference and otherness (between and within others). To develop an individual rural geography, these four dimensions, which reflect different aspects of the rural individual, must be used in a complementary manner. The relevance of each dimension suggests different types of individualities in rural areas. Ultimately, this article proposes a “new humanism” in contrast with antihumanistic poststructural approaches. 相似文献
9.
Diagnosis of trace metal contamination in sediments: the example of Ensenada and El Sauzal, two harbors in Baja California, Mexico 总被引:1,自引:0,他引:1
Huerta-Diaz MA Delgadillo-Hinojosa F Hernández-Ayón M Segovia-Zavala JA García-Esquivel Z López-Zárate H Siqueiros-Valencia A Galindo-Bect S 《Marine environmental research》2008,66(3):345-358
Total metal concentrations in sediments from within Ensenada and El Sauzal Harbors are generally higher than at the mouths. Grain-size analyses suggested that this enrichment could be due to the presence of fine-grained sediments in the inner part of the harbors rather than to anthropogenic perturbations. The (Me/Al)(sample) ratios for Pb, Co, Ni and Fe were significantly higher for Ensenada Harbor relative to El Sauzal Harbor, whereas the ratios for Cd, Mn, Zn and Cu were statistically equivalent for both harbors. Calculated enrichment factors [EF(Me)=(Me/Al)(sample)/(Me/Al)(shale)] indicated that the metals showing slight enrichment were those associated with anthropogenic contamination (Pb, Zn), or probably related to primary productivity in the water column (Cd, Co). The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake. 相似文献
10.
Mohamed Ali Kalefa El-Ghali Sadoon Morad Howri Mansurbeg Miguel Angel Caja George Ajdanlijsky Neil Ogle Ihsan Al-Aasm Manhal Sirat 《Marine and Petroleum Geology》2009
Sequence stratigraphy of fluvial deposits is a controversial topic because changes in relative sea level will eventually have indirect impact on the spatial and temporal distribution of depositional facies. Changes in the relative sea level may influence the accommodation space in fluvial plains, and hence have impact on types of fluvial system, frequency of avulsion, and style of vertical and lateral accretion. This study aims to investigate whether depositional facies and changes in the fluvial system of the Lower Triassic Petrohan Terrigenous Group sandstones (NW Bulgaria) in response to changes in the relative sea level have an impact on the spatial and temporal distribution of diagenetic alterations. 相似文献