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131.
Juske Horita António M. dos Santos Christopher A. Tulk Bryan C. Chakoumakos Veniamin B. Polyakov 《Physics and Chemistry of Minerals》2010,37(10):741-749
A neutron powder diffraction study of hydrogenated and deuterated brucite was conducted at ambient temperature and at pressures
up to 9 GPa, using a Paris–Edinburgh high-pressure cell at the WAND instrument of the ORNL High Flux Isotope Reactor. The
two materials were synthesized by the same method and companion measurements of neutron diffraction were conducted under the
same conditions. Our refinement results show that the lattice-parameters of the a axis, parallel to the sheets of Mg–O octahedra, decrease only slightly with pressure with no effect of H–D substitution.
However, the c axis of Mg(OD)2 is shorter and may exhibit greater compressibility with pressure than that of Mg(OH)2. Consequently, the unit-cell volume of deuterated brucite is slightly, but systematically smaller than that of hydrogenated
brucite. When fitted to a third-order Birch–Murnaghan equation in terms of the normalized unit-cell volume, values of the
bulk modulus for hydrogenated and deuterated brucite (K
0 = 39.0 ± 2.8 and 40.4 ± 1.3 GPa, respectively) are, however, indistinguishable from each other within the experimental errors.
The measured effect of H–D substitution on the unit-cell volume also demonstrates that brucite (and other hydrous minerals)
preferentially incorporate deuterium over hydrogen under pressure, suggesting that the distribution of hydrogen isotopes in
deep-earth conditions may differ significantly from that in near-surface environments. 相似文献
132.
133.
Augusto César Coelho Dias da Silva Jaqueline Comin de Castilhos Erik Allan Pinheiro dos Santos Luciana Sonnewend Brondízio Leandro Bugoni 《Ocean & Coastal Management》2010,53(9):570-576
The neritic waters of the state of Sergipe in Northeastern Brazil is adjacent to the main nesting area of the olive ridley sea turtles (Lepidochelys olivacea) in the Western Atlantic Ocean and an important area for shrimp trawl fishery. To address the problem of incidental mortality of sea turtles captured during trawling and reduce the risk of overexploitation of shrimp stocks, Projeto TAMAR/ICMBio, a Brazilian sea turtle conservation program, has adopted two main strategies: (1) the implementation of a marine monitoring program and (2) active participation in local forums. This paper describes the conflicts among stakeholders, the arrangements and established mechanisms of negotiation aimed to protect sea turtles and shrimp grounds, and strategies to reduce conflicts between user groups. The analysis of this co-management process highlights the importance of stakeholder participation in resource management decision-making through a cooperative process, the role assumed by non-governmental organizations as mediators, and the factors that influence this system. The key factors and actions learnt from the current study include clear identification of the conflicts, identification of stakeholders – both local and external, and local leaders, encouragement of actors and leaders to participate, support and strengthening of local groups, legitimization of the discussion forums through involvement with government, formalization of decisions taken through legislation, and monitoring of the management efficacy. 相似文献
134.
135.
Lieu R Bonamente M Mittaz JP Durret F Dos Santos S Kaastra JS 《The Astrophysical journal》1999,527(2):L77-L80
The EUV excess emission from the clusters A2199 and A1795 remains an unexplained astrophysical phenomenon. There has been many unsuccessful attempts to "trivialize" the findings. In this Letter, we present direct evidence proving that the most recent of such attempts, which attributes the detected signals to a background nonuniformity effect, is likewise excluded. We address the issue by a reobservation of A2199 that features a new filter orientation, usage of a more sensitive part of the detector, and, most crucially, the inclusion of a background pointing at approximately 2 degrees offset-the first in situ measurement of its kind. We first demonstrate quantitatively two facts: (1) the offset pointing provides an accurate background template for the cluster observation, while (2) data from other blank fields do not. We then performed a point-to-point subtraction of the in situ background from the cluster field, with an appropriate propagation of errors. The resulting cluster radial profile is consistent with that obtained by our original method of subtracting a flat asymptotic background. The emission now extends to a radius of 20&arcmin;; it confirms the rising prominence of EUV excess beyond approximately 5&arcmin; as previously reported. 相似文献
136.
Ayan Santos Fleischmann Vinícius Alencar Siqueira Sly Wongchuig-Correa Walter Collischonn Rodrigo Cauduro Dias De Paiva 《水文科学杂志》2020,65(8):1358-1373
ABSTRACT This study provides a spatio-temporal analysis of the great floods that occurred in South America in 1983 using hydrometeorological data and outputs from a continental-scale hydrological-hydrodynamic model. In the extreme year 1983, there were three main flooding periods (February, June and July) in many South American river basins, such as the Araguaia, Tocantins, São Francisco, Uruguay, La Plata and its tributaries, resulting in high discharge of the Paraguay River for many months. Depth–area–duration curves show that 3-day precipitation events in northern regions of South America were among the largest 15 events in the period 1980–2015 but only for specific locations, whereas in southern areas, the most extreme events in the same period were for larger durations (≥7-day precipitation). Modelled total export of water volume to the oceans indicates that rivers draining to the South Atlantic reached an anomaly of 3.7 during 1983, followed by 1998 (1.9) and 1992 (1.1), all of them corresponding to El Niño years. 相似文献
137.
J. M. Santos Oliveira 《Journal of Geochemical Exploration》1982,17(2):81-92
Selected results of a geochemical survey using stream-sediment sampling for ore minerals are presented. The study was undertaken in the Mogadouro (Cravezes) region, northeastern Portugal in order to investigate prospecting parameters for scheelite (tungsten) mineralization within calc-silicate rocks (skarnoids).Statistical and mathematical treatment of the data obtained during prospecting aided the interpretation, particularly, factor analysis. Five factors explaining about 85% of the variability in the data, were extracted; some were characteristic lithological and mineralization factors which are still imprinted in the secondary environment. Two apparently non-correlated types of mineralization are demonstrated: a scheelite (tungsten)-tin mineralization, and a copper-lead-zinc mineralization.Anomalous patterns delineating the scheelite ore deposit are revealed by the spatial distribution of various chemical elements. This highlights the importance of some pathfinder elements which can be used for tungsten prospecting in this type of geological environment. Copper, Pb, Zn, Ni, Co, V, and Cr are suitable pathfinders for W and Sn in the Mogadouro region. 相似文献
138.
Almeida-Filho R. Rosenqvist A. Shimabukuro Y.E. dos Santos J.R. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(4):409-412
Japanese Earth Resources Satellite 1 (JERS-1) synthetic aperture radar (SAR) data were evaluated to map areas of deforestation in a Brazilian Amazo/spl circ/nia test-site. The results were compared with information derived from a Landsat TM multitemporal series. Unambiguous detection of deforested areas was observed only when the entire deforestation process (slash, burning, and terrain clearing) had already occurred. This result recommends further investigations on the effectiveness of horizontal polarization SAR data to map deforestation in a consistent basis. The cross-polarized (horizontal-vertical) channel designed to be in the ALOS/PALSAR system is expected to improve the distinction between forested and recently deforested areas. 相似文献
139.
Geochemical signatures and mechanisms of trace elements dispersion in the area of the Vale das Gatas mine (Northern Portugal) 总被引:2,自引:1,他引:2
P. Freire vila J.M. Santos Oliveira E. Ferreira da Silva E. Cardoso Fonseca 《Journal of Geochemical Exploration》2005,85(1):17-29
A geochemical survey involving the collection and analysis of 170 stream sediment samples was carried out in Vale das Gatas area in order to delineate geochemical signatures and to detect pollution hazards due to mining.Factor analysis applied to the data showed that the most important variables accounting for the first factor are Ag, Pb, Bi, As, W, Cd, Zn and Cu. These variables represent the most significant metalliferous elements of the original paragenesis, which still maintain a close relationship in the secondary geological environment. The spatial distribution of the factor scores referred to factor 1 indicates that positive scores occur predominantly in the Vale das Gatas and Sabrosa streams and in the main Pinhão river. The results also show that the Vale das Gatas mine is the most important contamination source in the Vale das Gatas district.In order to study the dispersion, transfer and uptake mechanisms of trace elements from the Vale das Gatas mine, additional sample media were collected, i.e., stream sediments, tailings, coatings, waters (surficial and mine waters) and specific biological species. Four sample stations were selected, namely two in connection with abandoned adits of the Vale das Gatas mine, one located in the Vale das Gatas stream and one located in the Pinhão River. The results show that chemical reactions of leaching and precipitation took place controlling the heavy metals in areas near the Vale das Gatas mine.At the same time, positive anomalous patterns are visible along the Pinhão river for about 20 km. The mineralogical composition of the stream sediments suggests that processes of mechanical dispersion also interfere in the secondary distribution of the metalliferous elements in that media. 相似文献
140.
Rezende CE Lacerda LD Ovalle AR Souza CM Gobo AA Santos DO 《Marine pollution bulletin》2002,44(7):680-684
The concentrations of Al, Fe, Mn, Zn, Cu, Pb, Ni, Cr, Ba, V, Sn and As in offshore bottom sediments from the Bacia de Campos oil field, SE Brazil, were measured at the beginning and at 7 months after completion of the drilling operation. Concentrations of Al, Fe, Ba, Cr, Ni and Zn were significantly higher closer to the drilling site compared to stations far from the site. Average concentrations of Al, Cu, and in particular of Ni, were significantly higher at the end of the drilling operation than at the beginning. Comparison between drilling area sediments with control sediments of the continental platform, however, showed no significant difference in trace metal concentrations. Under the operation conditions of this drilling event, the results show that while changes in some trace metal concentrations do occur during drilling operations, they are not significantly large to be distinguished from natural variability of the local background concentrations. 相似文献