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排序方式: 共有114条查询结果,搜索用时 15 毫秒
91.
Fish accumulate several trace elements in muscle, gills and liver, however studies also indicate that metals can be excreted through bile. Since metal contamination leads to modifications in bile composition, biliary excretion offers an alternative way to evaluate the presence of trace-elements. Bile is easier to obtain than other organs and presents a simpler matrix, making it easier for chemical pre-treatment. To verify if bile can be useful as a biomonitoring tool for metal contamination, liver and bile trace element concentrations were determined and correlated. The Artificial Neural Networks statistical technique was used to verify if liver trace-element quantification could be substituted by bile analysis. Results show that significant correlations were obtained between trace elements in bile and liver and the ANN validated the hypothesis that certain trace-elements in bile could be utilized instead of liver trace-elements. Further studies in this field are of interest to further validate this biomarker.  相似文献   
92.
93.
Abstract. During the austral summer 1993 – 94, microalgal density and biomass were investigated in the sea ice, in the underlying water column, in the melt water and during the formation of the sea ice. Of the 96 taxa identified, 59 were diatoms and 32 were dinoflagellates. Among the remaining five species, Pseudopleurochloris antarctica  was very abundant both in the sea ice and in the ice-free waters. Cell densities and biomass of microalgae were higher in the bottom of the sea ice and during the formation of the ice than in the seawater, and diatoms were the dominant group at higher microalgal biomass. Among these, Entomoneis kufferathii , Chaetoceros dichaeta and Fragilariopsis species were the most common taxa.  相似文献   
94.
This article analyzes the life trajectories of twelve early-career geographers in relation to their life–work experiences in an increasingly neoliberal academia and its constant demands of hypermobility. Using (auto)ethnographic research methods, it delves into the manifestations and effects of the pervasive myth of the detached, always ready-to-move scholar. We analyze the role of mobility in imaginaries and practices of academia and its close relationship with privilege and precarity. Our findings show how academic work is inescapably located despite the systematic erasure of the bodies, places, and networks that scholars are part of. By taking into account the centrality of place making in academic experience, our conclusions point to more comprehensive ways in which academic mobility can be understood, reflected on as part of geographers’ professional training, and transformed.  相似文献   
95.
Natural Hazards - The increase in the frequency of natural disasters in recent years and its consequent social, economic and environmental impacts make it possible to prioritize areas of risk as an...  相似文献   
96.
The amphiboles from Kakanui and Arenal are two natural minerals that have been used worldwide as microanalytical reference materials, but their compositions and crystal structures are still poorly constrained. In this paper, we report new data on H2O and trace element mass fractions and single-crystal structural refinement of these two amphiboles. H2O mass fractions of the Kakanui and Arenal amphiboles determined via Karl-Fischer titration are 0.92 ± 0.18 (2s) and 1.56 ± 0.22% m/m (2s), respectively; these values estimated based on crystal-structure refinement are 0.86 and 1.46% m/m, respectively. Trace element mass fractions measured via LA-ICP-MS in two laboratories are in good agreement, and spots from five fragments for both Kakanui and Arenal amphiboles are generally consistent within reproducibility precision (2s). Our measurements indicate a better homogeneity for the amphiboles from Kakanui than that from Arenal. According to the latest scheme for amphibole classification and nomenclature (Hawthorne et al. 2012), the sample from Arenal is a (partially dehydrogenated) pargasite, and that from Kakanui is a kaersutite. The significant amount of oxo-component and that CTi4+ content is strongly ordered at the M(1) site for both amphiboles indicate crystallisation under high fO2 conditions.  相似文献   
97.
Studies of shock metamorphism of feldspar typically rely on qualitative petrographic observations, which, while providing invaluable information, can be difficult to interpret. Shocked feldspars, therefore, are now being studied in greater detail by various groups using a variety of modern techniques. We apply in situ micro‐X‐ray diffraction (μXRD) to shocked lunar and terrestrial plagioclase feldspar to contribute to the development of a quantitative scale of shock deformation for the feldspar group. Andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada, and anorthite from Earth's Moon, returned during the Apollo program, were examined using optical petrography and assigned to subgroups of the optical shock level classification system of Stöffler (1971). Two‐dimensional μXRD patterns from the same samples revealed increased peak broadening in the chi dimension (χ), due to strain‐related mosaicity, with increased optical signs of deformation. Measurement of the full width at half maximum along χ (FWHMχ) of these peaks provides a quantitative way to measure strain‐related mosaicity in plagioclase feldspar as a proxy for shock level.  相似文献   
98.
To investigate the behavior of Li during low-grade metamorphism and fluid flux in an accretionary prism we measured the Li concentrations ([Li]) and isotopic compositions (δ7Li) of sub-greenschist and greenschist-facies Otago Schist composites, as well as cross-cutting quartz veins, which are interpreted to have precipitated from slab-derived fluids. The average [Li] of sub-greenschist facies composites (41 ± 13 μg/g, 2σ) is statistically distinct (97% confidence level, student t test) to that of greenschist facies composites (34 ± 9 μg/g, 2σ), which have experienced mass addition of silica in the form of quartz veins having [Li] between 0.4–2.3 μg/g. A linear regression of the correlation between [Li] and calculated mass additions suggests that the depletion of [Li] in greenschist facies composites is due to both dilution from the addition of the quartz veins, as well as metamorphic dehydration. The [Li] of both groups of composites correlates with their CIA (Chemical Index of Alteration) values (50–58), which are low, consistent with the inferred graywacke protolith of the Otago Schist. The δ7Li of sub-greenschist and greenschist facies composites are remarkably constant, with an average δ7Li of 0.2 ± 1.7 (2σ) and ?0.5 ± 1.9 (2σ), respectively, and comparable to that of the average upper continental crust. Thus, metamorphism has had no discernable effect on δ7Li in these samples. The Li isotopic signature of the schists is similar to that seen in pelitic sedimentary rocks and likely reflects the δ7Li of the protoliths. The surprisingly light δ7Li of the quartz veins (?2.8 to ?1.4) likely records kinetic fractionation associated with Li ingress into the veins from surrounding wallrock.An isotopic equilibrium fluid flow model indicates that: 1) if the [Li] of slab-derived fluids is less than a few μg/g, the δ7Li of the overlying lithologies (i.e., the schists) is not significantly influenced by the fluid flux, regardless of the δ7Li of the fluids, 2) the slab-derived fluids will have heavy δ7Li of > + 10 after reacting with the prism sediments during their ascent, and 3) the [Li] of the slab-derived fluids is likely in the range of 0 < [Li]  41(μg/g). Thus, isotopically heavy slab-derived fluids that traverse sediments in accretionary prisms may leave little trace in the rocks and their surface compositional characteristics will reflect the net result of their interaction with the sediments of the prism.  相似文献   
99.
Roberta Hawkins 《Geoforum》2012,43(4):750-759
Much of the current work in the field of ‘gender and environment’ has been developed around case studies of environmental roles, rights and responsibilities at the community or household scale in the South. This paper asserts that the theoretical insights developed through these case studies can be of great use when examining issues of gender and environment in the North, particularly when it comes to issues of ethical consumption. In this paper I examine the promotional discourses of two cause-related marketing (CRM) campaigns (where consumption of a CRM product triggers a donation to a development cause) using two such insights: (i) the mutual constitution of gendered subjectivities and environments and (ii) a gender and environment approach to questioning neoliberalization. This approach highlights the ways in which – through consumption – gender is constituted transnationally at the same time that it is constituted in relation to environments. This approach also emphasizes a series of questions about the neoliberal aspects of CRM campaigns that are usually hidden behind discourses of motherhood and responsibility. Overall, I argue that bringing gender and environment and ethical consumption research together allows us to advance both areas of study in critical and insightful ways.  相似文献   
100.
Olivine, clinopyroxene and orthopyroxene in variably metasomatised peridotite xenoliths from three lithospheric mantle sections beneath the East African Rift in Tanzania (Lashaine, Olmani, Labait) show systematic differences in their average Li concentrations (2.4 ppm, 2.0 ppm and 1.5 ppm, respectively) and intermineral isotopic fractionations, with olivine being heaviest (δ7Li = + 2.3 to + 13.9‰, average + 5.0‰), followed by orthopyroxene (? 4.1 to + 6.5‰, average + 0.8‰) and clinopyroxene (? 6.7 to + 4.1‰, average ? 1.6‰). These features are ascribed to the effects of kinetic Li isotope fractionation combined with different Li diffusivities in mantle minerals.Two main mechanisms likely generate diffusion-driven kinetic Li isotope fractionation in mantle xenoliths (1) Li diffusion from grain boundary melt into minerals during recent metasomatism or entrainment in the host magma and (2) subsolidus intermineral Li-redistribution. The latter can produce both isotopically light (Li-addition) and heavy (Li-loss) minerals and may occur in response to changes in pressure and/or temperature.Modelling shows that non-mantle-like δ7Li in clinopyroxene (< + 2‰), combined with apparent equilibrium olivine-clinopyroxene elemental partitioning in most peridotite xenoliths from all three Tanzanian localities probably reflects incipient Li addition during interaction with the host magma. Low δ7Li (< ? 3‰), combined with high Li concentrations (> 3 ppm) in some clinopyroxene may require very recent (minutes) Li ingress from a Li-rich melt (100s of ppm) having mantle-like δ7Li. This might happen during late fragmentation of some mantle xenoliths caused by a volatile- (and Li-) rich component exsolved from the host basalt. In contrast, high Li concentrations (> 2 ppm) and δ7Li (> 4‰) in olivine from many Labait and Olmani samples are attributed to an older, pre-entrainment enrichment event during which isotopic equilibrium was attained and whose signature was not corrupted during xenolith entrainment. Low Li concentrations and mantle-like isotopic composition of olivine from most Lashaine xenoliths indicate limited metasomatic Li addition.Thus, Li concentrations and isotope compositions of mantle peridotites worldwide may reflect two processes, with olivine mainly preserving a signature of depletion in refractory samples (low Li contents and δ7Li) or of older (precursory) melt addition in metasomatised samples (high Li contents and δ7Li), while non mantle-like, low δ7Li in almost all clinopyroxene can be due to Li ingress during transport in the host magma and/or slow cooling, if the samples were erupted in lavas. In Tanzania, the peridotites experienced rift-related heating prior to entrainment and were quenched upon eruption, so Li ingress is the most likely process responsible for the isotopically light clinopyroxene here.  相似文献   
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