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991.
Richard Metcalfe Mark B. Crawford Adrian H. Bath Anna K. Littleboy Paul J. Degnan Hugh G. Richards 《Applied Geochemistry》2007
A number of chemical and physical processes inside and outside a sedimentary basin (e.g. evaporite dissolution and topographic drive, respectively) affect groundwater flow near the basin’s margin. Contrasting formations at the margin, typically basinal sedimentary rocks and basement, are host to the interplay between these processes so that groundwater flows and compositions change within a relatively small volume. To interpret how groundwater flow and geochemistry have evolved, interactions between these processes must be understood. Such interactions were investigated near the margin of the East Irish Sea Basin in NW England, by sampling deep groundwaters (to 1500 m below sea level) from Ordovician volcanic basement rocks and Carboniferous to Triassic sedimentary cover rocks. Variable Br/Cl ratios and Cl concentrations in deep saline waters and brines indicate mixing patterns. Variations in 36Cl/Cl constrain the timing of mixing. Relatively low Br/Cl ratios (ca. 1 × 10−3 by mass) characterise brine from the western sedimentary cover and reflect halite dissolution further west. Saline water with relatively high Br/Cl ratios (ca. 2 × 10−3 by mass) of uncertain origin occupies the eastern basement. These two waters mix across the area. However, mixing alone cannot explain variable 36Cl/Cl ratios, which partly reflect differing in situ36Cl production rates in different rock formations. Most 36Cl/Cl ratios in groundwater sampled from the eastern metavolcanic basement (mean = 25 × 10−15) and western sedimentary cover (mean = 10 × 10−15) are at or close to equilibrium with in situ36Cl production. These variations in 36Cl/Cl across the site possibly took >1.5 Ma to be attained, implying that deep groundwater flow responded only slowly to the Quaternary glaciation of the site. Interplay between varied processes in basin marginal settings does not necessarily imply flow instability. 相似文献
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995.
Victoria K. Pearson Mark A. Sephton Anton T. Kearsley Philip A. Bland Ian A. Franchi Iain Gilmour 《Meteoritics & planetary science》2002,37(12):1829-1833
Abstract— As the solar system formed, it inherited and perpetuated a rich organic chemistry, the molecular products of which are preserved in ancient extraterrestrial objects such as carbonaceous chondrites. These organic‐rich meteorites provide a valuable and tangible record of the chemical steps taken towards the origin of life in the early solar system. Chondritic organic matter is present in the inorganic meteorite matrix which, in the CM and CI chondrites, contains evidence of alteration by liquid water on the parent asteroid. An unanswered and fundamental question is to what extent did the organic matter and inorganic products of aqueous alteration interact or display interdependence? We have used an organic labelling technique to reveal that the meteoritic organic matter is strongly associated with clay minerals. This association suggests that clay minerals may have had an important trapping and possibly catalytic role in chemical evolution in the early solar system prior to the origin of life on the early Earth. 相似文献
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Mark Clampin Marco Sirianni George F. Hartig Holland C. Ford Garth D. Illingworth Bill Burmester William Koldewynd Andre R. Martel Adam Riess Ronald J. Schrein Pamela C. Sullivan 《Experimental Astronomy》2002,14(2):107-115
The Advanced Camera for Surveys (ACS), installed in the Hubble Space telescope in March 2002, will significantly extend HST's
deep, survey imaging capabilities. ACS has met, or exceeded, all of its key performance specifications. In this paper we briefly
review the in-flight performance of the instrument's CCD detectors and preview early ACS science observations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
999.
Amateur astronomers have always represented an important observing group in cometary astronomy. Much of our knowledge of cometary
light curves has come from amateur data, initially in the form of total visual magnitude estimates and now increasingly in
the form of CCD observations. The increasingly widespread use by amateur astronomers of CCD cameras of excellent sensitivity
and good cosmetic quality has revolutionised astrometry, allowing far more intensive astrometric monitoring of comets to be
carried out down to magnitude 18 and fainter, with a corresponding enormous increase in the quality of calculated orbits.
Although amateur CCD photometry is extensively available in the Internet, its use has been less widespread. The reason is
the lack of standardisation in the way that this data is taken that leads to amateur CCD light curves having enormous dispersion.
All amateur CCD photometry is aperture photometry, but it is seen that neither does it represent well the equivalent of m1
(total visual magnitude), even with a large aperture, nor is it close to the definition of m2 (the nucleus magnitude). The problem is examined using data from the Spanish Comet Observers Group archives to show that
by careful standardisation of data acquisition amateur CCD data can produce high quality, well-sampled and physically meaningful
light curves. Examples are presented of the results for recent comets including 19P/Borrelly, 51P/Harrington, C/2001 TU80
(LINEAR-NEAT), C/2000 WM1 (LINEAR) & C/2001 A2 (LINEAR). 相似文献
1000.
Frank I. González Vasily V. Titov Harold O. Mofjeld Angie J. Venturato R. Scott Simmons Roger Hansen Rodney Combellick Richard K. Eisner Don F. Hoirup Brian S. Yanagi Sterling Yong Mark Darienzo George R. Priest George L. Crawford Timothy J. Walsh 《Natural Hazards》2005,35(1):89-110
The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers. 相似文献