Martian meteorite Dhofar 019: A new shergottite     

L. A. Taylor  M. A. Nazarov  C. K. Shearer  H. Y. McSween  J. Cahill  C. R. Neal  M. A. Ivanova  L. D. Barsukova  R. C. Lentz  R. N. Clayton  T. K. Mayeda 《Meteoritics & planetary science》2002,37(8):1107-1128

Abstract— Dhofar 019 is a new martian meteorite found in the desert of Oman. In texture, mineralogy, and major and trace element chemistry, this meteorite is classified as a basaltic shergottite. Olivine megacrysts are set within a groundmass composed of finer grained olivine, pyroxene (pigeonite and augite), and maskelynite. Minor phases are chromite‐ulvöspinel, ilmenite, silica, K‐rich feldspar, merrillite, chlorapatite, and pyrrhotite. Secondary phases of terrestrial origin include calcite, gypsum, celestite, Fe hydroxides, and smectite. Dhofar 019 is most similar to the Elephant Moraine (EETA) 79001 lithology A and Dar al Gani (DaG) 476/489 shergottites. The main features that distinguish Dhofar 019 from other shergottites are lack of orthopyroxene; lower Ni contents of olivine; the heaviest oxygen‐isotopic bulk composition; and larger compositional ranges for olivine, maskelynite, and spinel, as well as a wide range for pyroxenes. The large compositional ranges of the minerals are indicative of relatively rapid crystallization. Modeling of olivine chemical zonations yield minimum cooling rates of 0.5‐0.8 °C/h. Spinel chemistry suggests that crystallization took place under one of the most reduced conditions for martian meteorites, at an fO₂ 3 log units below the quartz‐fayalite‐magnetite (QFM) buffer. The olivine megacrysts are heterogeneously distributed in the rock. Crystal size distribution analysis suggests that they constitute a population formed under steady‐state conditions of nucleation and growth, although a few grains may be cumulates. The parent melt is thought to have been derived from partial melting of a light rare earth element‐ and platinum group element‐depleted mantle source. Shergottites, EETA79001 lithology A, DaG 476/489, and Dhofar 019, although of different ages, comprise a particular type of martian rocks. Such rocks could have formed from chemically similar source(s) and parent melt(s), with their bulk compositions affected by olivine accumulation.  相似文献   

Applications of parallel processing to astrodynamics     

S. Coffey  L. Healy  H. Neal 《Celestial Mechanics and Dynamical Astronomy》1996,66(1):61-70

Parallel processing is being used to improve the catalog of earth orbiting satellites and for problems associated with the catalog. Initial efforts centered around using SIMD parallel processors to perform debris conjunction analysis and satellite dynamics studies. More recently, the availability of cheap supercomputing processors and parallel processing software such as PVM have enabled the reutilization of existing astrodynamics software in distributed parallel processing environments, Computations once taking many days with traditional mainframes are now being performed in only a few hours. Efforts underway for the US Naval Space Command include conjunction prediction, uncorrelated target processing and a new space object catalog based on orbit determination and prediction with special perturbations methods.GRC International, Colorado Springs, currently located at Naval Laboratory  相似文献   

High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table     

Colin Neal  Brian Reynolds  James W. Kirchner  Phil Rowland  Dave Norris  Darren Sleep  Alan Lawlor  Clive Woods  Sarah Thacker  Hayley Guyatt  Colin Vincent  Kathryn Lehto  Simon Grant  Jeremy Williams  Margaret Neal  Heather Wickham  Sarah Harman  Linda Armstrong 《水文研究》2013,27(17):2531-2539

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Location of the Rheic suture in the eastern Bohemian Massif: evidence from detrital zircon data     

Stanisław Mazur  Jacek Szczepański  Krzysztof Turniak  Neal J. McNaughton 《地学学报》2012,24(3):199-206

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In situ quantification of spatial and temporal variability of hyporheic exchange in static and mobile gravel‐bed rivers     

Donald O. Rosenberry  P. Zion Klos  Andrew Neal 《水文研究》2012,26(4):604-612

Seepage meters modified for use in flowing water were used to directly measure rates of exchange between surface and subsurface water in a gravel‐ and cobble bed river in western Pennsylvania, USA (Allegheny River, Q_mean = 190 m³/s) and a sand‐ and gravel‐bed river in Colorado, USA (South Platte River, Q_mean = 9·7 m³/s). Study reaches at the Allegheny River were located downstream from a dam. The bed was stable with moss, algae, and river grass present in many locations. Median seepage was + 0·28 m/d and seepage was highly variable among measurement locations. Upward and downward seepage greatly exceeded the median seepage rate, ranging from + 2·26 (upward) to ? 3·76 (downward) m/d. At the South Platte River site, substantial local‐scale bed topography as well as mobile bedforms resulted in spatial and temporal variability in seepage greatly in exceedence of the median groundwater discharge rate of 0·24 m/d. Both upward and downward seepage were recorded along every transect across the river with rates ranging from + 2·37 to ? 3·40 m/d. Despite a stable bed, which commonly facilitates clogging by fine‐grained or organic sediments, seepage rates at the Allegheny River were not reduced relative to those at the South Platte River. Seepage rate and direction depended primarily on measurement position relative to local‐ and meso‐scale bed topography at both rivers. Hydraulic gradients were small at nearly all seepage‐measurement locations and commonly were not a good indicator of seepage rate or direction. Therefore, measuring hydraulic gradient and hydraulic conductivity at in‐stream piezometers may be misleading if used to determine seepage flux across the sediment‐water interface. Such a method assumes that flow between the well screen and sediment‐water interface is vertical, which appears to be a poor assumption in coarse‐grained hyporheic settings. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

An automated routing methodology to enable direct rainfall in high resolution shallow water models     

Christopher C. Sampson  Paul D. Bates  Jeffrey C. Neal  Matthew S. Horritt 《水文研究》2013,27(3):467-476

Recent high profile flood events have highlighted the need for hydraulic models capable of simulating pluvial flooding in urban areas. This paper presents a constant velocity rainfall routing scheme that provides this ability within the LISFLOOD‐FP hydraulic modelling code. The scheme operates in place of the shallow water equations within cells where the water depth is below a user‐defined threshold, enabling rainfall‐derived water to be moved from elevated features such as buildings or curbstones without causing instabilities in the solution whilst also yielding a reduction in the overall computational cost of the simulation. Benchmarking against commercial modelling packages using a pluvial and point‐source test case demonstrates that the scheme does not impede the ability of LISFLOOD‐FP to match both predicted depths and velocities of full shallow water models. The stability of the scheme in conditions unsuitable for traditional two‐dimensional hydraulic models is then demonstrated using a pluvial test case over a complex urban digital elevation model containing buildings. Deterministic single‐parameter sensitivity analyses undertaken using this test case show limited sensitivity of predicted water depths to both the chosen routing speed within a physically plausible range and values of the depth threshold parameter below 10 mm. Local instabilities can occur in the solution if the depth threshold is >10 mm, but such values are not required even when simulating extreme rainfall rates. The scheme yields a reduction in model runtime of ~25% due to the reduced number of cells for which the hydrodynamic equations have to be solved. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A New Understanding of the Provinces of the Amazon Craton Based on Integration of Field Mapping and U-Pb and Sm-Nd Geochronology   总被引：1，自引：0，他引：1  

Joo Orestes Schneider Santos  Lo Afraneo Hartmann  Henri Eugene Gaudette  David Ian Groves  Neal Jesse Mcnaughton  Ian Robert Fletcher 《Gondwana Research》2000,3(4):453-488

New conventional and sensitive high-resolution ion microprobe zircon U-Pb dating has led to a new understanding of the subdivision and evolution of the Amazon Craton during Precambrian time, with major improvements and changes made to the previous Rb-Sr based model. The interpretation of U-Pb and Sm-Nd isotopic data identifies eight main Precambrian tectonic provinces in the Craton, with ages ranging from 3.1 to 0.99 Ga. Some of the provinces were generated by accretional, arc-related processes (Carajás, Transamazonic, Tapajós-Parima and Rondônia-Juruena) and others by recycling of continental crust (Central Amazon, Rio Negro and Sunsas). The exposed Archean crust is restricted to the east (Carajás and south Amapá in Brazil) and north (Imataca in Venezuela) of the craton, indicating that the Amazon Craton is largely a Proterozoic crust. The Carajás-Imataca (3.10–2.53 Ga) and Transamazonian (2.25–2.00 Ga) Provinces are composed predominantly of granite-greenstone terranes. The Tapajós-Parima (2.10–1.87 Ga) and Rondônia-Juruena (1.75–1.47 Ga) Provinces represent new crust added as orogenic belts, while the Rio Negro (1.86–1.52 Ga) and Sunsas (1.33–0.99 Ga) Provinces originated mainly by magmatic-tectonic recycling of the above two orogenic belts. The only zone with a prominent northeast trend is the poorly known K'Mudku Shear Belt, characterized by a 1.20 Ga shear zone which deforms the rocks of at least three different provinces (Rio Negro, Tapajós-Parima and Transamazonic). The Central Amazon Province comprises mostly Orosirian volcano-plutonic rocks (Uatumã Magmatism) and is a terrane in which the exposed crustal structure and deformation are pluton-related. The Sm-Nd T_DM model ages and _Nd suggest that the Central Amazon Province was generated by the partial melting of Archean continental crust (Carajás Province?), perhaps related to underplating that began at the end of the Tapajós-Parima Orogeny (1.88–1.86 Ga).  相似文献   

Magnetite biomineralization induced by Shewanella oneidensis     

Teresa Perez-Gonzalez  Andrew L. Neal  Alejandro Rodriguez-Navarro  Enrique Iañez-Pareja 《Geochimica et cosmochimica acta》2010,74(3):967-6858

Shewanella oneidensis is a dissimilatory iron reducing bacterium capable of inducing the extracellular precipitation of magnetite. This precipitation requires a combination of passive and active mechanisms. Precipitation occurs as a consequence of active production of Fe²⁺_(aq) when bacteria utilize ferrihydrite as a terminal electron acceptor, and the pH rise probably due to the bacterial metabolism of amino acids. As for passive mechanisms, the localized concentration of Fe²⁺_(aq) and Fe³⁺_(aq) at the net negatively charged cell wall, cell structures and/or cell debris induces a local rise of supersaturation of the system with respect to magnetite, triggering the precipitation of such a phase.These biologically induced magnetites are morphologically identical to those formed inorganically in free-drift experiments (closed system; 25 °C, 1 atm total pressure), both from aqueous solutions containing Fe(ClO₄)₂, FeCl₃, NaHCO₃, NaCO₃ and NaOH, and also from sterile culture medium added with FeCl₂. However, organic material becomes incorporated in substantial amounts into the crystal structure of S. oneidensis-induced magnetites, modifying such a structure compared to that of inorganic magnetites. This structural change and the presence of organic matter are detected by Raman and FT-IR spectroscopic analyses and may be used as a biomarker to recognize the biogenic origin of natural magnetites.  相似文献   

SDSS J131339.98+515128.3: a new gravitationally lensed quasar selected based on near-infrared excess     

Eran O. Ofek  Masamune Oguri  Neal Jackson  Naohisa Inada  Issha Kayo 《Monthly notices of the Royal Astronomical Society》2007,382(1):412-418

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Diatom response to recent climatic change in a high arctic lake (Char Lake, Cornwallis Island, Nunavut)     

Neal Michelutti  Marianne S. V. Douglas  John P. Smol   《Global and Planetary Change》2003,38(3-4):257-271

From 1968 to 1972, Char Lake (Resolute Bay, Cornwallis Island, Canadian High Arctic) was the site of a large-scale limnological study conducted under the auspices of the International Biological Programme. However, since that time, very little research has been done on the lake. We sampled Char Lake from 1992 to 2000 for a suite of physical, chemical, and biological variables. In general, there were no major differences between our water quality data and those collected 30 years earlier, showing that Char Lake is still oligotrophic, slightly alkaline, and dilute. However, a diatom-based paleolimnological analysis revealed that a subtle, yet distinct species assemblage shift has occurred beginning around 1987. The timing of this species shift does not correspond to the deposition of atmospherically transported persistent organic pollutants into the lake (beginning in the early 1950s) or to minor disturbances within its catchment (early 1970s). Instead, these subtle diatom changes are consistent with recent climatic changes during 1988–1997 (as documented by local meteorological measurements), and are likely related to reduced summer ice cover and a longer growing season.  相似文献