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221.
Manuela A. Fehr Mark Rehkämper Alex N. Halliday Uwe Wiechert Detlef Günther Jennifer L. Eigenbrode Douglas Rumble III 《Geochimica et cosmochimica acta》2005,69(21):5099-5112
New precise Te isotope data acquired by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) are presented for selected extraterrestrial and terrestrial materials. Bulk samples of carbonaceous, ordinary and enstatite chondrites as well as the metal and sulfide phases of iron meteorites were analyzed to search for nucleosynthetic isotope anomalies and to find evidence of formerly live 126Sn, which decays to 126Te with a half-life of 234,500 yr. None of the meteorites show evidence of mass dependent Te isotope fractionations larger than 2‰ for δ126/128Te. Following internal normalization of the data to 125Te/128Te, the Te isotope ratios of all analyzed meteorites were found to be identical to a terrestrial standard, within uncertainties. This provides evidence that the regions of the solar disk that were sampled during accretion of the meteorite parent bodies were well mixed and homogeneous on a large scale, with respect to Te isotopes. The data acquired for bulk carbonaceous chondrites indicate that the initial 126Sn/118Sn ratio of the solar system was <4 × 10−5, but this is dependent on the assumption that no redistribution of Sn and Te occurred since the start of the solar system. Five Archean sedimentary sulfides that display both mass dependent and mass-independent isotope effects for S yield internally normalized Te isotope data, which indicate that mass-independent Te isotope effects are absent. The mass dependent fractionations in these samples are constrained to be less than ∼1‰ for δ126/128Te. 相似文献
222.
Jennifer Linton Alexandra Navrotsky Yingwei Fei 《Physics and Chemistry of Minerals》1998,25(8):591-596
The enthalpies of formation from ilmenite, FeTiO3, and perovskite, CaTiO3, of two intermediate ordered perovskite phases, CaFeTi2O6 and CaFe3Ti4O12, have been measured at 801°C using oxide melt solution calorimetry. These data, in combination with experiments at high pressure
and temperature, indicate that below 1518±50°C CaFe3Ti4O12 is stable at lower pressures (∼7 GPa at 1200°C) than CaFeTi2O6 (∼13 GPa at 1200°C). This relationship should be reversed, and CaFeTi2O6 should become stable at lower pressures than CaFe3Ti4O12, at temperatures above 1518±50°C. These intermediate phases are of petrological interest because they form as a reaction
between two minerals, ilmenite and perovskite, which are commonly associated in kimberlites, and because their pressure-temperature
range of formation overlaps that of origin of kimberlites.
Received: 10 November 1997 / Revised; accepted: 15 January 1998 相似文献
223.
224.
Thomas J. Jackson Terry L. Wade José L. Sericano James M. Brooks Jennifer M. Wong Bernardo Garcia-Romero Thomas J. McDonald 《Estuaries and Coasts》1998,21(4):718-730
The temporal distributions for six classes of trace organic contaminants (chlordanes, DDTs, dieldrin, PAHs, PCBs, and butyltins) in oysters from six Galveston Bay sites from National Oceanic and Atmospheric Administration’s National Status and Trends (NS&T) Mussel Watch Program are compared with other NS&T sites from the Gulf of Mexico as well as all NS&T sites of the United States (East Coast, West Coast, and Gulf of Mexico). Decreases in the median for the Gulf-wide concentration of chlordanes, dieldrin, and butyltins occurred during 1986–1994. The Gulfwide median concentrations of DDTs, PAHs, and PCBs exhibited a strong cyclic distribution with time. For Galveston Bay oysters, “high” concentration is defined as the concentration greater than the median plus one standard deviation for all Gulf of Mexico sites. The percentage of sites having high concentrations during 1986–1994 for Galveston Bay oysters are 49% for dieldrin, 45% for butyltins, 40% for chlordanes, 38% for PCBs, 30% for PAHs, and 21% for DDTs. For PCBs, 43% of Galveston Bay oyster samples analyzed over the first 9 yr have concentrations high enough for potential biological effects to be observed in oysters. The percentages in other agents were chlordanes (22%), butyltins (22%), dieldrin (5%), and PAHs (4%). National Academy of Science-proposed regulatory limits for oysters were exceeded in only 2% of Galveston Bay samples for DDTs and 1% for PCBs. All other contaminants were below proposed NAS limits. 相似文献
225.
226.
The determination of trace element release from geologic materials, such as oil shale and coal overburden, is important for
proper solid waste management planning. The objective of this study was to determine a correlation between trace element residency
and concentration to trace element release using the following methods: (1) sequential selective dissolution for determining
trace element residencies, (2) toxicity characteristic leaching procedure (TCLP), and (3) humidity cell weathering study simulating
maximum trace element release. Two eastern oil shales were used, a New albany shale that contains 4.6 percent pyrite, and
a Chattanooga shale that contains 1.5 percent pyrite. Each shale was analyzed for elemental concentrations by soluble, adsorbed,
organic, carbonate, and sulfide phases. All leachates were analyzed to determine total trace element concentrations.
The results of the selective dissolution studies show that each trace element has a unique distribution between the various
phases. Thus, it is possible to predict trace element release based on trace element residency. The TCLP results show that
this method is suitable for assessing soluble trace element release but does not realistically assess potential hazards. The
results of the humidity cell studies do demonstrate a more reasonable method for predicting trace element release and potential
water quality hazards. The humidity cell methods, however, require months to obtain the required data with a large number
of analytical measurements. When the selective dissolution data are compared to the trace element concentrations in the TCLP
and humidity cell leachates, it is shown that leachate concentrations are predicted by the selective dissolution data. Therefore,
selective dissolution may represent a rapid method to assess trace element release associated with acid mine drainage. 相似文献
227.
Uniaxial compressive stress-strain curves have been measured on a suite of 26 commercial grades of tungsten carbide cermets and three maraging steels of interest for use in high-pressure apparatus. Tests were conducted on cylindrical specimens with a length to diameter ratio of two. Load was applied to the specimens by tungsten carbide anvils padded by extrudable lead disks. Interference fit binding rings of maraging steel were pressed on to the ends of the specimens to inhibit premature corner fractures. Bonded resistance strain gages were used to measure both axial and tangential strains. Deformation was exremely uniform in the central, gauged portion of the specimens. Tests were conducted at a constant engineering strain rate of 1×10–5s–1. The composition of the specimens was principally WC/Co with minor amounts of other carbides in some cases. The Co weight fraction ranged from 2 to 15%. Observed compressive strengths ranged from about 4 to just above 8 GPa. Axial strain amplitude at failure varied from 1.5% to 9%. Representative stress-strain curves and a ranking of the grades in terms of yield strength and strain at failure are presented. A power law strain hardening relation and the Ramberg-Osgood stress-strain equation were fit to the data. Fits were very good for both functions to axial strain amplitudes of about 2%. The failure of these established functions is accompanied by an abrupt change in the trend of volumetric strain consistent with the onset of substantial microcrack volume. 相似文献
228.
Eugene E. Epstein Bryan H. Andrew Frank H. Briggs Bruce M. Jakosky Frank D. Palluconi 《Icarus》1983,56(3):465-475
Measurements at 3.5 mm of the disk-average brightness temperature of Mars during the 1978 opposition can be represented by (The errors cited are from the internal scatter; the estimated absolute calibration uncertainty is 3%.) This longitudinal variation must be taken into account if Mars is to be used as a calibration source at millimeter wavelengths. The total range of the 3.5-mm variation is three to four times larger than both the 2.8-cm and 20-μm variations. This unexpected result can possibly be explained by subsurface scattering from rocks ?1.5-cm radius. 相似文献
229.
Ari Matmon Onn Crouvi Yehouda Enzel Paul Bierman Jennifer Larsen Naomi Porat Rivka Amit Marc Caffee 《地球表面变化过程与地形》2003,28(5):493-506
Activities of 26Al and 10Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert‐bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26Al/10Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP . If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My?1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
230.