The discovery of 1982 DB,the most accessible asteroid known     

Eleanor F. Helin  Neal D. Hulkower  David F. Bender 《Icarus》1984,57(1):42-47

A small Apollo object was found while photographing the split comet DuToit 2-Hartley on February 27/28, 1982. Designated 1982 DB, this Earth-crossing asteroid passed the Earth at a distance of 4.08 million km about 1 month prior to its discovery. Asteroid 1982 DB has been determined to be the most accessible near-Earth minor planet known. It provides many excellent opportunities for rendezvous and sample return missions, and a rare dual rendezvous mission with 1980 AA as the second target. For a mission to be realized, opportunities to observe 1982 DB during future apparitions must be taken.  相似文献   

Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil   总被引：1，自引：0，他引：1  

Edson F. Mello  Roberto P. Xavier  Neal J. McNaughton  Steffen G. Hagemann  Ian Fletcher  Larry Snee 《Mineralium Deposita》2006,40(8):849-866

U–Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152±6 Ma in monazite crystals and 2,155±9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130±7 Ma and 2,128±8 Ma in zircon crystals derived from the Teofilândia tonalite. The emplacement age of the syntectonic Ambrósio dome as indicated by a 2,080±2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar–Ar plateau age of 2,080±5 Ma obtained in hornblendes from an amphibolite and with a U–Pb SHRIMP age of 2,076±10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambrósio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937±16, 3,111±13 and 3,162±13 Ma. Ar–Ar plateau ages of 2,050±4 Ma and 2,054±2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar–Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen.Electronic supplementary material Supplementary material is available for this article at  相似文献   

Mobilization and transport of organic compounds from reservoir rock and caprock in geological carbon sequestration sites     

Lirong Zhong  Kirk Cantrell  Alex Mitroshkov  Jesse Shewell 《Environmental Earth Sciences》2014,71(9):4261-4272

Supercritical CO₂ (scCO₂) is a good solvent for organic compounds such as benzene, toluene, ethyl-benzene, and xylene (BTEX), phenols, and polycyclic aromatic hydrocarbons (PAHs). Monitoring results from geological carbon sequestration (GCS) field tests have shown that organic compounds are mobilized following CO₂ injection. Such results have raised concerns regarding the potential for groundwater contamination by toxic organic compounds mobilized during GCS. Knowledge of the mobilization mechanism of organic compounds and their transport and fate in the subsurface is essential for assessing risks associated with GCS. Extraction tests using scCO₂ and methylene chloride (CH₂Cl₂) were conducted to study the mobilization of volatile organic compounds (VOCs, including BTEX), the PAH naphthalene, and n-alkanes by scCO₂ from representative reservoir rock and caprock obtained from depleted oil reservoirs and coal from an enhanced coal-bed methane recovery site. Results showed that the extent of mobilization for the organic compounds was a function of the source rock. In fate and transport sand column experiments, moisture content was found to have an important influence on the transport of the organic compounds. In dry sand columns the majority of the compounds were retained in the column except benzene and toluene. In wet sand columns the mobility of the BTEX was much higher than that of naphthalene. Based upon the results determined for the reservoir rock, caprock, and coal samples studied here, the risk to aquifers from contamination by organic compounds appears to be relatively low; however, further work is necessary to fully evaluate the risks.  相似文献   

Estimating <Emphasis Type="Italic">probable maximum loss</Emphasis> from a Cascadia tsunami     

Dale Dominey-Howes  Paula Dunbar  Jesse Varner  Maria Papathoma-Köhle 《Natural Hazards》2010,53(1):43-61

The Cascadia margin is capable of generating large magnitude seismic-tsunami. We use a 1:500 year tsunami hazard flood layer produced during a probabilistic tsunami hazard assessment as the input to a pilot study of the vulnerability of residential and commercial buildings in Seaside, OR, USA. We map building exposure, apply the Papathoma Tsunami Vulnerability Assessment Model to calculate building vulnerability and estimate probable maximum loss (PML) associated with a 1:500 year tsunami flood. Almost US$0.5 billion worth of buildings would be inundated, 95% of single story residential and 23% of commercial buildings would be destroyed with PML’s exceeding US$0.5 billion worth of buildings would be inundated, 95% of single story residential and 23% of commercial buildings would be destroyed with PML’s exceeding US116 million. These figures only represent a tiny fraction of the total values of exposed assets and loss that would be associated with a Cascadia tsunami impacting the NW Pacific coast. Not withstanding the various issues associated with our approach, this study represents the first time that PML’s have ever been calculated for a Cascadia type tsunami, and these results have serious implications for tsunami disaster risk management in the region. This method has the potential to be rolled out across the United States and elsewhere for estimating building vulnerability and loss to tsunami.  相似文献   

Development and skill assessment of a real-time hydrologic-hydrodynamic-wave modeling system for Lake Champlain flood forecasting     

Titze  Daniel  Beletsky  Dmitry  Feyen  Jesse  Saunders  William  Mason  Lacey  Kessler  James  Chu  Philip  Lee  Deborah 《Ocean Dynamics》2023,73(5):231-248

Ocean Dynamics - In response to record-breaking flooding on Lake Champlain in 2011, the International Joint Commission launched a 5-year study to explore solutions to flooding in the binational...  相似文献   

Can Hydraulic Conductivity of Fluvial Sediments be Informed by Spectral Reflectance?     

Yao Li  Liu  Can  Ou  Gengxin  Wang  Zhaowei  Korus  Jesse  Jiang  Ran 《Water Resources》2020,47(5):846-854

Water Resources - This study explores the statistical relationship between spectral reflectance and hydraulic conductivity (K) of fluvial sediments in two Nebraska rivers. The spectral reflectance...  相似文献   

Source of Pb in orogenic lode-gold mineralisation: Pb isotope constraints from deep crustal rocks from the southwestern Archaean Yilgarn Craton, Australia     

Y. Qiu  N. J. McNaughton 《Mineralium Deposita》1999,34(4):366-381

Southern Cross was one of the earliest gold mining centres in Western Australia. Over 142 tonnes of gold have been produced from the district, and, on a gold per hectare basis, the Southern Cross greenstone belt in the southwestern Yilgarn Craton is the most productive of Western Australia's Archaean greenstone belts. The SW Yilgarn Craton is characterised by high-grade (amphibolite- to granulite-facies) metamorphism, extensive granitoid magmatism and older greenstone volcanism ages, compared to the well-known greenschist-facies metamorphism and younger (2.7 Ga) eruption ages which dominate in the Eastern Goldfields Province. The Pb-isotope compositions of deep-seated granitoids in the SW Archaean Yilgarn Craton, which were emplaced coeval with a craton-wide major orogenic lode-gold mineralization event at about 2.64–2.63 Ga, have been determined for 96 whole-rock and 24 K-feldspar samples. The Pb isotope data of the granitoids are consistent with a crustal origin for their genesis, probably by reworking (partial melting) of older continental crust. The Pb isotope composition of greenstones, which are the main host rocks for gold mineralisation, and pyrites from the komatiite-hosted syngenetic Ni deposits in the amphibolite-facies Forrestania greenstone belt, have also been determined, with initial Pb-isotope ratios higher than that for the Eastern Goldfields Province. The Pb isotopic character of the orogenic lode-gold deposits in the region is intermediate between coeval granitoid and greenstone Pb, indicating that the ore fluids contained metals from both reservoirs. The Pb in the ore fluid of the most deeply formed deposit, Griffin's Find, overlaps the isotopic composition of coeval granitoids, indicating the deep-seated granitoid magmatism was the primary source for Pb in the ore fluids. Received: 8 October 1998 / Accepted 22 December 1998  相似文献   

Modern-day deltas     

H. Jesse Walker 《地球表面变化过程与地形》1998,23(6):579-580

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Silent ships do not always encounter more fish: comparison of acoustic backscatter recorded by a noise-reduced and a conventional research vessel     

De Robertis  Alex; Hjellvik  Vidar; Williamson  Neal J.; Wilson  Christopher D. 《ICES Journal of Marine Science》2008,65(4):623-635

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Use of archaeology to date liquefaction features and seismic events in the New Madrid seismic zone,Central United States     

Martitia P. Tuttle  Robert H. Lafferty  Margaret J. Guccione  Eugene S. Schweig  Neal Lopinot  Robert F. Cande  Kathleen Dyer-Williams  Marion Haynes 《Geoarchaeology》1996,11(6):451-480

Prehistoric earthquake-induced liquefaction features occur in association with Native American occupation horizons in the New Madrid seismic zone. Age control of these liquefaction features, including sand-blow deposits, sand-blow craters, and sand dikes, can be accomplished by extensive sampling and flotation processing of datable materials as well as archaeobotanical analysis of associated archaeological horizons and pits. This approach increases both the amount of carbon for radiocarbon dating and the precision dating of artifact assemblages. Using this approach, we dated liquefaction features at four sites northwest of Blytheville, Arkansas, and found that at least one significant earthquake occurred in the New Madrid seismic zone between A.D. 1180 and 1400, probably about A.D. 1300 ± 100 yr. In addition, we found three buried sand blows that formed between 3340 B.C. and A.D. 780. In this region where very large to great earthquakes appear to be closely timed, archaeology is helping to develop a paleoearthquake chronology for the New Madrid seismic zone. © 1996 John Wiley & Sons, Inc.  相似文献