Structure and nuclear density distribution in the cheralite—CaTh(PO4)2: studies of its behaviour under high pressure (36?GPa)     

Philippe E. Raison  Stephen Heathman  Gilles Wallez  Carmen E. Zvoriste  Denis Bykov  Ga?l Ménard  Emmanuelle Suard  Karin Popa  Nicolas Dacheux  Rudy J. M. Konings  Roberto Caciuffo 《Physics and Chemistry of Minerals》2012,39(8):685-692

The crystal structure of the cheralite—CaTh(PO₄)₂—has been revisited by neutron diffraction and its behaviour under high pressure investigated by X-ray diffraction up to 36?GPa. The neutron diffraction data at ambient pressure gave a more accurate determination of the Ca/Th cation position than previous XRD data, taking advantage that the neutron scattering lengths of calcium and thorium are of same order of magnitude. The nuclear density distribution was also determined using the maximum entropy method (MEM) confirming that the two cations are not located at the same position in the unit cell but are slightly displaced from one another along a specific direction in order to minimize the electrostatic repulsion with the surrounding phosphorus atoms. At high pressure, the compound did not show any phase transition or amorphization. From the evolution of the unit-cell volume as a function of the pressure, the zero-pressure bulk modulus B₀ and its pressure derivative B₀ ^′ have been determined by fitting the experimental compressibility curve to the Birch–Murnaghan equation of state. The results are B₀?=?140(2) GPa and B ₀ ^′ ?=?4.4(4) GPa.  相似文献   

The role of international environmental instruments in enhancing transboundary marine protected areas: An approach in East Africa     

José Guerreiro  Aldo Chircop  David Dzidzornu  Catarina Grilo  Raquel Ribeiro  Rudy van der Elst  Ana Viras 《Marine Policy》2011

The increasing degradation of marine ecosystems has led to multiple calls for greater protection through the establishment of marine protected areas (MPAs). If created at the ecosystem or ecoregion level, MPAs will likely straddle maritime boundaries and therefore necessitate international cooperation. International environmental law and international law of the sea may facilitate cooperation between States in creating transboundary MPAs. The extent to which this body of law is actually or potentially useful for the establishment of transboundary MPAs is examined in the context of the East African Marine Ecoregion, focusing on Mozambique, South Africa, and Tanzania. A general survey and assessment of the applicable global, regional, and bilateral instruments in relation to the three States is conducted. Although some global instruments are relevant in the East African context, regional and bilateral instruments are more conducive to the establishment of transboundary MPAs. The article concludes that although a trilateral agreement between Mozambique, South Africa, and Tanzania would be an ideal vehicle for the establishment of a transboundary network of MPAs addressing both national and ecoregional conservation interests, a separate solution at each border will be the first step towards this goal.  相似文献   

Geogene Versus Anthropogene Origin of Trace Metals in Sediments in Cua Luc Estuary and Ha Long Bay, Vietnam     

Huu Hieu Ho  Rudy Swennen  Valérie Cappuyns  Elvira Vassilieva  Gerda Neyens  Mustafa Rajabali  Tan Van Tran 《Estuaries and Coasts》2013,36(1):203-219

In the present study, the geochemistry of 49 surficial-bed and 101 core sediment samples is investigated to clarify the origin of trace metals in the Cua Luc Estuary and Ha Long Bay, which is a famous World Natural Heritage Site in Vietnam. Moreover, the potential mobility of trace metals is also assessed and their relationship with reference elements (Al, Fe, and Ca) and organic matter is established in order to make recommendations for sediment management and monitor future pollution. Generally, trace metals display higher concentrations in Ha Long Bay compared to the Cua Luc Estuary. However, this is controlled by the distribution of the fine (clay?+?silt) fraction, and hence the concentrations of Al, Fe, Ca, and organic matter (OM). The comparison of concentrations of trace metals (normalized towards Al) between the surficial sediments and the subsurface core sediments based on ¹³⁷Cs datings indicates that almost all surficial-sediment data fall inside or deviate slightly from the 95 % prediction interval of a background regression line. In addition, as determined by a Community Bureau of Reference three-step extraction, trace metals mainly dominate in the residual fraction (assumed to relate to crystal lattice of primary and secondary minerals), and this fraction does not change much in recent sediment layers. Therefore, trace metals are supposed to be derived from natural bio/geochemical processes and are characterized by a low potential mobility. Consequently, the established linear regression relationships of trace metal vs. Al or multiple regression relationships of trace metal vs. multi-elements (Al, Fe, Ca, and OM) are useful for the prediction of background levels of trace metals in sediments in future pollution monitoring and assessment programs.  相似文献   

Elevation adjustments of paired natural levees during flooding of the Saskatchewan River     

Norman D. Smith  Marta Pérez‐Arlucea  Douglas A. Edmonds  Rudy L. Slingerland 《地球表面变化过程与地形》2009,34(8):1060-1068

Natural levees control the exchange of water between an alluvial channel and its floodplain, but little is known about the spatial distribution and evolution of levee heights. The summer 2005 flood of the Saskatchewan River (Cumberland Marshes, east‐central Saskatchewan) inundated large areas of floodplain for up to seven weeks, forming prominent new deposits on natural levees along main‐stem channels. Measurements of flood‐deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre‐flood levee in 80% of the sites, though no clear relationship exists between deposit thickness and magnitude of height difference. Only 16% of the pairs displayed thicker deposits on the higher levee, half of which occurred at sites where relatively clear floodbasin waters re‐entered turbid channels during general flooding. Difference in crest elevation (ΔE) between paired levees is approximately log‐normally distributed, both before and after the flood, though with different mean values. Supplemental observations from tank experiments indicate that during near‐bankfull flows, temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension. During floods, preferential deposition in lows tends to even out crest heights. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Fractal analysis of the Oyo River, cave systems, and topography of the Gunungsewu karst area, central Java, Indonesia   总被引：1，自引：0，他引：1  

Sari B. Kusumayudha  M. T. Zen  Sudarto Notosiswoyo  Rudy Sayoga Gautama 《Hydrogeology Journal》2000,8(3):271-278

Gunungsewu, the southernmost subzone of the Southern Mountains, central Java, is a classic karst terrain, bounded by the Oyo River on the north and the Indian Ocean on the south. In this study, the Oyo River, the main drainage in the area, is divided into 14 segments, and the fractal dimension of each segment is determined by the box-counting method. The 14 segments show various values of fractal dimensions, which are controlled by lithology and geologic structures of the area that is being dissected by the river. Easily eroded lithologies have larger fractal dimensions, and the value changes abruptly when the river crosses faults. Fractal dimensions of six underground rivers in the Bribin, Sodong, Semuluh, Jomblang, Soga, and Sumurup caves, and the surface topography above the caves were also determined. The caves have fractal dimensions that range from 1.043 ±0.01 to 1.08±0.01; the surface topography has fractal dimensions that range from 1.49±0.01 to 1.732±0.01. The fractal dimension of an underground river is proportional to the fractal dimension of the surface topography over the passage. Larger fractal dimensions of underground rivers are associated with smaller flow rates of the rivers. Received, June 1998Revised, March 1999, August 1999, February 2000Accepted, February 2000  相似文献   

Water extractable material from the B horizon of a contiguous aspen and birch forest in interior Alaska     

Rudy Candler 《Organic Geochemistry》1985,8(1):127

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Chandra and XMM–Newton observations of the low-luminosity X-ray pulsators SAX J1324.4−6200 and SAX J1452.8−5949     

R. Kaur  Rudy Wijnands  Alessandro Patruno  Vincenzo Testa  GianLuca Israel  Nathalie Degenaar  Biswajit Paul  Brijesh Kumar 《Monthly notices of the Royal Astronomical Society》2009,394(3):1597-1604

We present results from our Chandra and XMM–Newton observations of two low-luminosity X-ray pulsators  SAX J1324.4−6200  and  SAX J1452.8−5949  which have spin periods of 172 and 437 s, respectively. The XMM–Newton spectra for both sources can be fitted well with a simple power-law model of photon index,  Γ∼ 1.0  . A blackbody model can equally well fit the spectra with a temperature,   kT ∼  2 keV, for both sources. During our XMM–Newton observations,  SAX J1324.4−6200  is detected with coherent X-ray pulsations at a period of 172.86 ± 0.02 s while no pulsations with a pulse fraction greater than 18 per cent (at 95 per cent confidence level) in 0.2–12 keV energy band are detected in  SAX J1452.8−5949  . The spin period of  SAX J1324.4−6200  is found to be increasing on a time-scale of     which would suggest that the accretor is a neutron star and not a white dwarf. Using subarcsec spatial resolution of the Chandra telescope, possible counterparts are seen for both sources in the near-infrared images obtained with the son of infrared spectrometer and array camera (SOFI) instrument on the New Technology Telescope. The X-ray and near-infrared properties of  SAX J1324.4−6200  suggest it to be a persistent high-mass accreting X-ray pulsar at a distance  ≤8 kpc  . We identify the near-infrared counterpart of  SAX J1452.8−5949  to be a late-type main-sequence star at a distance ≤10 kpc, thus ruling out  SAX J1452.8−5949  to be a high-mass X-ray binary. However, with the present X-ray and near-infrared observations, we cannot make any further conclusive conclusion about the nature of  SAX J1452.8−5949  .  相似文献   

Zinc speciation in mining and smelter contaminated overbank sediments by EXAFS spectroscopy     

An Van Damme  Erik Smolders  Géraldine Sarret  Rudy Swennen 《Geochimica et cosmochimica acta》2010,74(13):3707-7820

Overbank sediments contaminated with metalliferous minerals are a source of toxic metals that pose risks to living organisms. The overbank sediments from the Geul river in Belgium contain 4000-69,000 mg/kg Zn as a result of mining and smelting activities, principally during the 19th century. Three main Zn species were identified by powder Zn K-edge EXAFS spectroscopy: smithsonite (ZnCO₃), tetrahedrally coordinated sorbed Zn (sorbed ^IVZn) and Zn-containing trioctahedral phyllosilicate. Smithsonite is a primary mineral, which accounts for approximately 20-60% of the Zn in sediments affected by mining and smelting of oxidized Zn ores (mostly carbonates and silicates). This species is almost absent in sediments affected by mining and smelting of both sulphidic (ZnS, PbS) and oxidized ores, presumably because of acidic dissolution associated with the oxidation of sulphides, as suggested by the lower pH of this second type of sediment (pH(CaCl₂) <7.0 vs. pH(CaCl₂) >7.0 for the first type). Thus, sulphide minerals in sediment deposits can act as a secondary source of dissolved metals by a chemical process analogous to acid mine drainage. The sorbed ^IVZn component ranges up to approximately 30%, with the highest proportion occurring at pH(CaCl₂) <7.0 as a result of the readsorption of dissolved Zn²⁺ on sediments constituents. Kerolite-like Zn-rich phyllosilicate is the major secondary species in all samples, and in some the only detected species, thus providing the first evidence for pervasive sequestration of Zn into this newly formed precipitate at the field scale.  相似文献   

Pollen analysis of some mid-Pleistocene interglacial lagoonal sediments from southern Delaware     

Rudy J. Nickmann  James M. Demarest 《Quaternary Research》1982,17(1):93-104

Results of pollen analysis on lagoonal sediments from southern Delaware, dated at 500,000–1,000,000 yr B.P. by amino acid racemization, are presented. Three pollen zones are identified in sediments that were deposited during the final stage of an interglacial cycle. A closed forest of mixed conifer-deciduous trees dominated by Tsuga, Pinus, Fagus, Liquidambar, and Quercus is recorded in the basal zone (Zone I). The inferred climate at this time was temperate and moist. A probable lowering of sea level during the deposition of Zone II exposed large areas in the surrounding estuaries and tidal flats which were colonized by marsh and bog plant taxa. Zone III is characterized by Pinus, Quercus, and Picea pollen. A scrub oak-pine association may have been favored on the coarse sandy soils of the Delmarva Peninsula at this time because of a drop in the local water table. The inferred climate during this interval was colder and probably drier than in Zone I.  相似文献   

Cooling of Accretion-Heated Neutron Stars     

Rudy Wijnands  Nathalie Degenaar  Dany Page 《Journal of Astrophysics and Astronomy》2017,38(3):49

We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.  相似文献