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排序方式: 共有97条查询结果,搜索用时 15 毫秒
61.
Sandra Hacon Elaine R.R. Rochedo Reinaldo R.R. Campos Luis Drude Lacerda 《Journal of Geochemical Exploration》1997,58(2-3)
This work addresses the mercury exposure scenarios through fish consumption in the urban area of Alta Floresta, by comparing the different patterns of mercury exposure from fish ingestion for different population groups. This study was based on field surveys that could provide background information, such as the characteristics of Hg sources, characteristics of local and regional environment, Hg concentrations in different media, and the characterization of the local urban population. The urban area of Alta Floresta is one of the most important gold-trading centers in Amazonia, where approximately 1 ton of gold has been commercialized monthly. The general adult urban population is exposed to low-level mercury concentration via fish consumption with an average daily intake of 0.2 μg/kg (b.w.) and an estimated hazard quotient of 0.7. However, the fishermen families present an average daily intake of 2.2 μg/kg (b.w.) and a hazard quotient of 8.6. The children of fishermen families between 5 and 14 years old are the main risk group for Hg exposure via fish ingestion. Based on the uncertainty analysis, the Hg fish concentrations and the fish ingestion rate were found to be the main parameters affecting the variability of the model outputs. 相似文献
62.
63.
Coudé spectra taken in the red region of 49 bright B and Be stars were examined for the behaviour of Hα and the He I λλ 5876
and 6678 line profiles. 51 per cent of the stars were found to show Hα emission to some degree and 22 per cent showed helium
emission. Evidence is presented for the existence of drastic changes in the line profile and the radial velocity in some of
the stars on a time scale of fractions of a day.
Visiting Astronomer, Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory, operated by the Association
of Universities for Research in Astronomy, under contract with the National Science Foundation. 相似文献
64.
Joseph A. Stewart Steven J. Christopher John R. Kucklick Louise Bordier Thomas B. Chalk Arnaud Dapoigny Eric Douville Gavin L. Foster William R. Gray Rosanna Greenop Marcus Gutjahr Freya Hemsing Michael J. Henehan Philip Holdship Yu‐Te Hsieh Ana Kolevica Yen‐Po Lin Elaine M. Mawbey James W. B. Rae Laura F. Robinson Rachael Shuttleworth Chen‐Feng You Shuang Zhang Russell D. Day 《Geostandards and Geoanalytical Research》2021,45(1):77-96
The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca < 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes. 相似文献
65.
James Rose Jenni Turner Elaine Turton James B. Riding Adrian Palmer John K. Wright Jonathan R. Lee Nicholas S. J. Q. Bullimore 《第四纪科学杂志》2021,36(4):547-569
This paper provides a record and analysis of a site in east-midland England, at which organic and soil material are found between two Middle Pleistocene tills. This is the first discovery of its kind in the area, and demonstrates unequivocally that the region was glaciated on two separate occasions, something that has long been inferred and articulated, but not actually demonstrated. The landforms, sediments and soils are studied with respect to their geomorphological, lithological, pedological, palaeobotanical and structural properties. The organic and soil material along with soil structures indicate, sequentially, a periglacial climate, a long period of warm temperate weathering and a cool temperate climate. Evaluation of this evidence in terms of existing published work identifies a number of problems with existing models and suggests that the most likely model for the glacial history of this part of midland England is an early Middle Pleistocene glaciation which is represented only by trace erratics, a Marine Isotope Stage (MIS) 12 age glaciation which moved across the area from the NW and deposited a chalk-free till, and an MIS 8 age glaciation that transported and deposited an upper chalky till from the NE. © 2021 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd. 相似文献
66.
Migration‐as‐development repackaged? The globalizing imperative of the Singaporean state's diaspora strategies 下载免费PDF全文
Diaspora strategizing is becoming an important field of public policy in countries that seek to advance development through migration. Diaspora strategies present a way of complicating interpretations of development, as countries that represent different levels of development seek to mobilize diaspora networks nonetheless. While Singapore's diaspora strategies prioritize diaspora knowledge networks, it bears the stamp of the country's colonial history, postcolonial priorities and developmental state apparatus. We suggest that these factors result in a distinctive diaspora strategy characterized by a centralized and technocratic approach more similar to diaspora strategies found in emerging economies. Earlier research on diaspora strategies has been concerned with assessing successes or failures, but a more critical scholarship that questions the logics and outcomes of diaspora strategizing is emerging. We bring the Singaporean case into dialogue with four such critiques: first, the intellectual foundations of diaspora‐centred development; second, the hyperextension of state infrastructure for emigration and stakeholder alignment; third, the selective mobilization of the idea of diaspora; and fourth, the evidence base upon which diaspora‐centred development is predicated. Our goal is to further critical interrogation into the logics, efficacy and sustainability of diaspora strategizing. We situate our analyses in the international literature on diaspora knowledge mobilization. 相似文献
67.
Elaine M. FitzGerald Christopher J. Bean & Ronan Reilly 《Geophysical Prospecting》1999,47(6):1031-1044
Borehole-wall imaging is currently the most reliable means of mapping discontinuities within boreholes. As these imaging techniques are expensive and thus not always included in a logging run, a method of predicting fracture frequency directly from traditional logging tool responses would be very useful and cost effective. Artificial neural networks (ANNs) show great potential in this area. ANNs are computational systems that attempt to mimic natural biological neural networks. They have the ability to recognize patterns and develop their own generalizations about a given data set. Neural networks are trained on data sets for which the solution is known and tested on data not previously seen in order to validate the network result. We show that artificial neural networks, due to their pattern recognition capabilities, are able to assess the signal strength of fracture-related heterogeneity in a borehole log and thus fracture frequency within a borehole. A combination of wireline logs (neutron porosity, bulk density, P-sonic, S-sonic, deep resistivity and shallow resistivity) were used as input parameters to the ANN. Fracture frequency calculated from borehole televiewer data was used as the single output parameter. The ANN was trained using a back-propagation algorithm with a momentum learning function. In addition to fracture frequency within a single borehole, an ANN trained on a subset of boreholes in an area could be used for prediction over the entire set of boreholes, thus allowing the lateral correlation of fracture zones. 相似文献
68.
Deon E. Barnes Peter J. Wright Sandra M. Graham Elaine A. Jones-Watson 《Geostandards and Geoanalytical Research》2000,24(2):183-195
The determination of cyanide in various forms is important for industrial processes as well as for environmental investigations and monitoring associated with these processes. The accurate determination of cyanide is difficult for various reasons. Depending on the pH of the solution, cyanide is present both in molecular form (HCN) and ionic form (CN). Furthermore, cyanide is a good complexing reagent and reacts with almost all cations resulting in complexes with widely varying properties, such as stabilities, solubilities and rates of reaction. Cyanide also breaks down in sunlight and air, so that sampling and sample treatment become very important aspects to consider in the methodologies. During the last fifty years the determination of cyanide has been approached from various angles and a myriad of methods has been developed for its determination. This study represents a survey of methods commonly used in industrial laboratories for the analysis of cyanide-containing solutions. An overview of the nomenclature often used for the various forms of cyanides is discussed and the values resulting from a particular analysis will be interpreted. Most common interferences in samples originating from gold processing plants will be discussed. 相似文献
69.
Pterosaur pelves feature prominently in discussions of pterosaur terrestrial locomotion (e.g. Wellnhofer 1988; Bennett 1990), but have otherwise received scant attention. 相似文献
70.
Rodolpho Vilhena de Moraes Regina Elaine Santos Cabette Maria Cecília Zanardi Teresinha J. Stuchi Jorge Kennety Formiga 《Celestial Mechanics and Dynamical Astronomy》2009,104(4):337-353
The stability of the rotational motion of artificial satellites is analyzed considering perturbations due to the gravity gradient
torque, using a canonical formulation, and Andoyer’s variables to describe the rotational motion. The stability criteria employed
requires the reduction of the Hamiltonian to a normal form around the stable equilibrium points. These points are determined
through a numerical study of the Hamilton’s equations of motion and linear study of their stability. Subsequently a canonical
linear transformation is used to diagonalize the matrix associated to the linear part of the system resulting in a normalized
quadratic Hamiltonian. A semi-analytic process of normalization based on Lie–Hori algorithm is applied to obtain the Hamiltonian
normalized up to the fourth order. Lyapunov stability of the equilibrium point is performed using Kovalev and Savchenko’s
theorem. This semi-analytical approach was applied considering some data sets of hypothetical satellites, and only a few cases
of stable motion were observed. This work can directly be useful for the satellite maintenance under the attitude stability
requirements scenario. 相似文献