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排序方式: 共有675条查询结果,搜索用时 734 毫秒
51.
Aaron J. Beck Yoko Tsukamoto Antonio Tovar-Sanchez Miguel Huerta-Diaz Henry J. Bokuniewicz Sergio A. Sañudo-Wilhelmy 《Applied Geochemistry》2007
Seasonal (Spring and Summer 2002) concentrations of dissolved (<0.22 μm) trace metals (Ag, Al, Co, Cu, Mn, Ni, Pb), inorganic nutrients (NO3, PO4, Si), and DOC were determined in groundwater samples from 5 wells aligned along a 30 m shore-normal transect in West Neck Bay, Long Island, NY. Results show that significant, systematic changes in groundwater trace metal and nutrient composition occur along the flowpath from land to sea. While conservative mixing between West Neck Bay water and the groundwaters explains the behavior of Si and DOC, non-conservative inputs for Co and Ni were observed (concentration increases of 10- and 2-fold, respectively) and removal of PO4 and NO3 (decreases to about half) along the transport pathway. Groundwater-associated chemical fluxes from the aquifer to the embayment calculated for constituents not exhibiting conservative behavior can vary by orders of magnitude depending on sampling location and season (e.g. Co, 3.4 × 102– 8.2 × 103 μmol d−1). Using measured values from different wells as being representative of the true groundwater endmember chemical composition also results in calculation of very different fluxes (e.g., Cu, 6.3 × 103 μmol d−1 (inland, freshwater well) vs. 2.1 × 105 μmol d−1(seaward well, S = 17 ppt)). This study suggests that seasonal variability and chemical changes occurring within the subterranean estuary must be taken into account when determining the groundwater flux of dissolved trace metals and nutrients to the coastal ocean. 相似文献
52.
53.
Prog G. Rivalenti Dr. G. Garuti Dr. A. Rossi F. Slena Dr. S. Sinigoi 《Mineralogy and Petrology》1981,29(1):33-53
Summary Spinel occurs in the pyroxenitic, peridotitic and gabbroic layers of the Ivrea-Verbano layered igneous complex. Its composition varies between picotite and Mg-hercynite. Maximum Cr2O3 contents are found in the spinels of the dunitic cumulitic layers occurring at some height above the base of the complex. Chromium deposits are absent. The lack of chromite and of chromium deposits is attributed to the early fractionation of clinopyroxene (which depleted the residual liquid in chromium) instead of olivine, as a consequence of the relatively high pressure prevailing during crystallization (8 kb). The relationships betweenfO2-composition of spinel-composition of the silicate phases indicate thatfO2 exerted a major control on the internal stratigraphy of the single layers and on the pattern of fractionation. The variation offO2 are on their turn related to accidental variations of the pressure acting on the magma.It is finally suggested that chromium deposits are limited to low pressure layered intrusions, where the magma has been emplaced rapidly into a shallow magma chamber. No chromium concentration is to be expected in those complexes that crystallized into deep-seated magma chambers and that fractionated at relatively high pressure, not markedly different from that at which the magma was produced. One of the major controls on the presence of chromium deposits results, therefore, to be the geotectonic environment of intrusion.
With 7 Figures 相似文献
Chrom-Spinell im geschichteten vulkanischen Komplex von Ivrea-Verbano, Westalpen, Italien
Zusammenfassung Für die Spinelle der Pyroxenit-, Peridotit- und Gabbro-Lagen des Ivrea-Verbano-Intrusivkomplexes wurde eine Zusammensetzung im Bereich Picotit und Mg-Herzynit bestimmt. Die Dunit-Lagen im basalen Anteil des Komplexes führen Spinelie mit Cr2O3-Gehalten bis zu 30 Gew-%. Chromerz-Konzentrationen fehlen jedoch, was auf die fraktionierte Kristallisation von Klinopyroxen (und Entstehung Cr-Restschmelzen) an Stelle von Olivin, als Folge der bei relativ hohem Druck (8 kbar) erfolgten Intrusion, zurückzuführen ist. Die Beziehungen zwischen Sauerstoffpartialdruck und Spinell- und Silikat-Zusammensetzung zeigen den bedeutendenfO2-Einfluß auf den stratigraphischen Aufbau der einzelnen Gesteinslagen und auf die fraktionierenden Kristallisationsvorgänge. Die schwankendenfO2-Werter stehen in Zusammenhang mit den ebenfalls variierenden auf das Magma wirkenden Drücken.Es ist anzunehmen, daß Chromerzkonzentrationen nur in geschichteten Intrusivkomplexen vorkommen, die sich unter niederem Druck bzw. in einer oberflächennahen Magma-Kammer bildeten, und nicht in jenen, die tiefer intrudierten und bei hohem Druck kristallisierten. Von großer Bedeutung für die Bildung von Chromerzlagerstätten ist also das geotektonische Milieu der Intrusion.
With 7 Figures 相似文献
54.
F. De Luise D. Perna E. Dotto I.N. Belskaya G.B. Valsecchi A. Rossi P. Paolicchi 《Icarus》2007,191(2):628-635
In this paper we present the observational campaign carried out at ESO NTT and VLT in April and May 2006 to investigate the nature and the structure of the near-Earth object (144898) 2004 VD17. In spite of a great quantity of dynamical information, according to which it will have a close approach with the Earth in the next century, the physical properties of this asteroid are largely unknown. We performed visible and near-infrared photometry and spectroscopy, as well as polarimetric observations. Polarimetric and spectroscopic data allowed us to classify 2004 VD17 as an E-type asteroid. A good agreement was also found with the spectrum of the aubrite meteorite Mayo Belwa. On the basis of the polarimetric albedo (pv=0.45) and of photometric data, we estimated a diameter of about 320 m and a rotational period of about 2 h. The analysis of the results obtained by our complete survey have shown that (144898) 2004 VD17 is a peculiar NEO, since it is close to the breakup limits for fast rotator asteroids, as defined by Pravec and Harris [Pravec, P., Harris, A.W., 2000. Icarus 148, 12-20]. These results suggest that a more robust structure must be expected, as a fractured monolith or a rubble pile in a “strength regime” [Holsapple, K.A., 2002. Speed limits of rubble pile asteroids: Even fast rotators can be rubble piles. In: Workshop on Scientific Requirements for Mitigation of Hazardous Comets and Asteroids, Washington, September, 2002]. 相似文献
55.
56.
A new method for the quantification of different redox-species of molybdenum (V and VI) in seawater 总被引:1,自引:0,他引:1
A new method for the direct determination of reduced and oxidized Mo species (Mo (V) and Mo (VI)) in seawater was developed and used for the first time. The method includes the complexation of Mo (V) with tartrate, solid phase extraction of the Mo (V)–tartrate complex by a XAD 7HP resin, followed by elution with acidic acetone. In this study, the eluted Mo (V) was quantified by graphite furnace atomic absorption spectrometry. The detection limit of this protocol was on the order of 0.2 nM. The analytical precision was 10% of ~ 10 nM. This method was successfully applied to the determination of Mo (V) and Mo (VI) in surface and bottom waters at the head of Peconic River Estuary. Total Mo (Mo (V) + Mo (VI)) ranged from 100–120 nM in most bottom saline waters, and 2.5–15 nM for surface fresher waters. Concentrations of Mo (V) in these environments ranged from 0 nM to ~ 15 nM, accounting for 0%–15% of the total dissolved Mo pool. The time series experiments showed that the Mo speciation changed within 1 h after the water collection, and therefore it is strongly suggested that speciation analysis be carried out within the first 15 min. However, since these are the first Mo speciation data in concentration ranges typical of normal marine and coastal waters, additional research may be required to optimize the methodology and further explore Mo cycling mechanisms. 相似文献
57.
Valerio Iafolla David M. Lucchesi Sergio Nozzoli Francesco Santoli 《Celestial Mechanics and Dynamical Astronomy》2007,97(3):165-187
We have estimated a preliminary error budget for the Italian Spring Accelerometer (ISA) that will be allocated onboard the
Mercury Planetary Orbiter (MPO) of the European Space Agency (ESA) space mission to Mercury named BepiColombo. The role of
the accelerometer is to remove from the list of unknowns the non-gravitational accelerations that perturb the gravitational
trajectory followed by the MPO in the strong radiation environment that characterises the orbit of Mercury around the Sun.
Such a role is of fundamental importance in the context of the very ambitious goals of the Radio Science Experiments (RSE)
of the BepiColombo mission. We have subdivided the errors on the accelerometer measurements into two main families: (i) the
pseudo-sinusoidal errors and (ii) the random errors. The former are characterised by a periodic behaviour with the frequency
of the satellite mean anomaly and its higher order harmonic components, i.e., they are deterministic errors. The latter are
characterised by an unknown frequency distribution and we assumed for them a noise-like spectrum, i.e., they are stochastic
errors. Among the pseudo-sinusoidal errors, the main contribution is due to the effects of the gravity gradients and the inertial forces, while among the random-like errors the main disturbing effect is due to the MPO centre-of-mass displacements produced by the onboard High Gain Antenna (HGA) movements and by the fuel consumption and sloshing. Very subtle to be considered
are also the random errors produced by the MPO attitude corrections necessary to guarantee the nadir pointing of the spacecraft.
We have therefore formulated the ISA error budget and the requirements for the satellite in order to guarantee an orbit reconstruction
for the MPO spacecraft with an along-track accuracy of about 1 m over the orbital period of the satellite around Mercury in
such a way to satisfy the RSE requirements. 相似文献
58.
Paola De Rossi Fontanelli Luiz Fernando De Ros Marcus Vinicius Dorneles Remus 《Marine and Petroleum Geology》2009
The provenance of the Maastrichtian deep-water reservoir sandstones from the Jubarte oil field (Campos Basin, eastern Brazil), was studied using an integrated approach that included quantitative petrography, conventional heavy mineral analysis, garnet mineral chemistry and zircon geochronology. The reservoirs are predominantly coarse, poorly-sorted sandstones with feldspathic composition derived from uplifted basement terrains. The fourth- and fifth-order depositional sequences analyzed show no major variations in composition or in provenance through time. However, variations in apatite:tourmaline presents potential to be used as a parameter for sandstone correlation within the field. The composition of heavy minerals indicates derivation from high temperature and low-to-medium pressure aluminous metapelitic rocks, from granites and subordinate mafic rocks, derived from the Cabo Frio Tectonic Domain and the Oriental terrain of Ribeira orogen, characterizing a supply route from SW to NE. The low ZTR index, as well as the absence of low-grade stable heavy minerals and of metasedimentary rock fragments, suggest that by the end of Cretaceous all supracrustal, low-grade terrains had already been totally eroded, and that plutonic, infracrustal rocks were exposed, similarly to the present situation. 相似文献
59.
Second‐order transgressive–regressive (T–R) cycles, previously recognized using sedimentological criteria in Lower Jurassic hemipelagic deposits from northern Spain, are distinguishable based upon bulk‐rock organic geochemistry [total organic carbon (TOC) and hydrogen index (HI)] and the stable carbon isotope compositions from belemnite rostra. There is a coincidence between regressions and decreasing δ13Cbel, TOC and HI values, and between transgressions and increasing δ13Cbel, TOC and HI values. The δ18O and Mg/Ca records from the belemnite rostra are not always in phase with the T–R cycles. The δ18Obel record reveals, however, a prominent excursion towards higher values within the spinatum Zone that correlates, according to our results, with a regression and with negative shifts in Mg/Ca, δ13Cbel and TOC. On the other hand, an excursion in the δ18Obel towards lower values in the serpentinus Zone also correlates with a peak transgression and with positive shifts in Mg/Ca, δ13Cbel and TOC. These two excursions have been identified in other European regions as geochemical perturbations of the same characteristics. This suggests a link between second‐order relative sea‐level changes and variations in seawater geochemistry that may reflect local and regional palaeoceanographic perturbations in sea‐water temperature, salinity and water circulation during the Early Jurassic. Terra Nova, 18, 233–240, 2006 相似文献
60.
Enrico Costa Ronaldo Bellazzini Gianpiero Tagliaferri Giorgio Matt Andrea Argan Primo Attinà Luca Baldini Stefano Basso Alessandro Brez Oberto Citterio Sergio Di Cosimo Vincenzo Cotroneo Sergio Fabiani Marco Feroci Antonella Ferri Luca Latronico Francesco Lazzarotto Massimo Minuti Ennio Morelli Fabio Muleri Lucio Nicolini Giovanni Pareschi Giuseppe Di Persio Michele Pinchera Massimiliano Razzano Luigia Reboa Alda Rubini Antonio Maria Salonico Carmelo Sgro’ Paolo Soffitta Gloria Spandre Daniele Spiga Alessio Trois 《Experimental Astronomy》2010,28(2-3):137-183
Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 105 s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled. 相似文献