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261.
Ryan R. Jensen Sandra S. Brake Stephen F. Wolf Matthew F. Bekker Perry James Hardin Mark W. Jackson 《Environmental Earth Sciences》2010,60(7):1391-1405
The Green Valley Mine in Indiana was abandoned in 1963 after 15 years of coal mining. Reclamation began in 1994 and ended
in 1999 with the dense planting of twelve different tree species. By 2006, only green ash (Fraxinus pennsylvanica Marsh.) and black locust (Robinia pseudoacacia L.) had survived in any significant numbers. Given the acid mine drainage found at the site, we sought to determine whether
element toxicity originating from mine waste was responsible for the extirpation of the trees. Leaf samples taken from 125
mine trees and 29 control trees were acquired and assayed for 41 element concentrations using inductively coupled plasma mass
spectrometry (ICPMS). Except for sodium, there was no compelling evidence to indicate that toxic elemental levels were responsible
for the widespread tree deaths. In addition to sodium toxicity, we suspect that micronutrient deficiency was a primary factor
explaining the extirpation of trees at the mine. 相似文献
262.
Nikhil Padmanabhan Tamás Budavári David J. Schlegel Terry Bridges Jonathan Brinkmann Russell Cannon rew J. Connolly Scott M. Croom István Csabai Michael Drinkwater Daniel J. Eisenstein Paul C. Hewett Jon Loveday Robert C. Nichol Kevin A. Pimbblet Roberto De Propris Donald P. Schneider Ryan Scranton Uro Seljak Tom Shanks István Szapudi Alexander S. Szalay David Wake 《Monthly notices of the Royal Astronomical Society》2005,359(1):237-250
263.
Ryan A. ZEIGLER Randy L. KOROTEV Bradley L. JOLLIFF Larry A. HASKIN 《Meteoritics & planetary science》2005,40(7):1073-1101
Abstract— We report on the bulk composition and petrography of four new basaltic meteorites found in Antarctica—LAP (LaPaz Icefield) 02205, LAP 02224, LAP 02226, and LAP 02436—and compare the LAP meteorites to other lunar mare basalts. The LAP meteorites are coarse‐grained (up to 1.5 mm), subophitic low‐Ti basalts composed predominantly of pyroxene and plagioclase, with minor amounts of olivine, ilmenite, and a groundmass dominated by fayalite and cristobalite. All of our observations and results support the hypothesis that the LAP stones are mutually paired with each other. In detail, the geochemistry of LAP is unlike those of any previously studied lunar basalt except lunar meteorite NWA (Northwest Africa) 032. The similarities between LAP and NWA 032 are so strong that the two meteorites are almost certainly source crater paired and could be two different samples of a single basalt flow. Petrogenetic modeling suggests that the parent melt of LAP (and NWA 032) is generally similar to Apollo 15 low‐Ti, yellow picritic glass beads, and that the source region for LAP comes from a similar region of the lunar mantle as previously analyzed lunar basalts. 相似文献
264.
C. Zurita J. Casares T. Shahbaz R. M. Wagner C. B. Foltz P. Rodríguez-Gil R. I. Hynes P. A. Charles E. Ryan G. Schwarz S. G. Starrfield 《Monthly notices of the Royal Astronomical Society》2002,333(4):791-799
We present the results of our monitoring of the halo black hole soft X-ray transient (SXT) XTE J1118+480 during its decline to quiescence. The system has decayed 0.5 mag from 2000 December to its present near-quiescent level at R ≃18.65 (2001 June). The ellipsoidal light curve is distorted by an additional modulation that we interpret as a superhump of P sh =0.17049(1) d i.e. 0.3 per cent longer than the orbital period. This implies a disc precession period P prec ∼52 d . After correcting the average phase-folded light curve for veiling, the amplitude difference between the minima suggests that the binary inclination angle lies in the range i =71–82° . However, we urge caution in the interpretation of these values because of residual systematic contamination of the ellipsoidal light curve by the complex form of the superhump modulation. The orbital-mean H α profiles exhibit clear velocity variations with ∼500 km s−1 amplitude. We interpret this as the first spectroscopic evidence of an eccentric precessing disc. 相似文献
265.
266.
Ryan E. Morse Jian Shen Jose L. Blanco-Garcia William S. Hunley Scott Fentress Mike Wiggins Margaret R. Mulholland 《Estuaries and Coasts》2011,34(5):1006-1025
Massive blooms of the harmful alga Cochlodinium polykrikoides Margalef occurred in the lower Chesapeake Bay and its tributaries during the summers of 2007 and 2008. The Lafayette and
Elizabeth Rivers appeared to act as initiation grounds for these blooms during both years. However, in 2008 there were also
localized sites of initiation and growth of populations within the mesohaline portion of the James River. Bloom initiation
appeared to be correlated with intense, highly localized rainfall events during neap tides. Subsequent spring tides increased
tidal flushing and transport of C. polykrikoides from the Lafayette and Elizabeth Rivers into the lower James River where it was transported upriver by local estuarine circulation.
Blooms dissipated in response to increased wind-driven mixing associated with frontal systems moving through the region. A
combination of physical factors including, seasonal rainfall patterns, increased stratification, nutrient loading, spring-neap
tidal modulation, and complex estuarine mixing and circulation allowed C. polykrikoides to spread and form massive blooms over large portions of the tidal James River and the lower Chesapeake Bay. 相似文献
267.
Kevin Righter Ryan S. Jakubek Marc D. Fries John Schutt Kellye Pando Roger Harrington 《Meteoritics & planetary science》2023,58(1):25-40
Carbonaceous chondrites of the Vigarano group (CV) are primitive (nearly un-metamorphosed) meteorites that provide a wealth of information about the early solar system, including constraints on chondrule formation, origin of calcium-aluminum inclusions, stability of organic compounds, and redox conditions. The US Antarctic meteorite collection contains 119 CV samples from 15 dense collection areas (DCAs) from the TransAntarctic Mountains; these samples have been assigned a preliminary classification as CVs, but not to the subgroups oxidized A, oxidized B, and reduced. Furthermore, variation in petrologic grade can be determined non-destructively using Raman spectroscopy. To update the classification of both subgroups and petrologic types in the collection, we have acquired magnetic susceptibility, metal and sulfide compositions, and Raman spectra. Overall, there are 55 oxidized A samples, 18 oxidized B samples, and 46 reduced samples. Several of the CVs are quite primitive (Lewis Cliffs Ice Tongue and MacAlpine Hills) but are also very small. Multiple pairing groups have been identified in the Miller Range (MIL), Queen Alexandra Range, and Larkman Nunatak DCAs, including all of the subgroups. In MIL 090981, there is evidence for multiple lithologies. We make suggested updates for all the samples, knowing that this information will help to better guide researchers interested in studying the CV chondrites in the US Antarctic meteorite collection. 相似文献
268.
Widespread observations of ecohydrological separation are interpreted by suggesting that water flowing through highly conductive soil pores resists mixing with matrix storage over periods of days to months (i.e., two ‘water worlds’ exist). These interpretations imply that heterogeneous flow can produce ecohydrological separation in soils, yet little mechanistic evidence exists to explain this phenomenon. We quantified the separation between mobile water moving through preferential flow paths versus less mobile water remaining in the soil matrix after free-drainage to identify the amount of preferential flow necessary to maintain a two water world's scenario. Soil columns of varying macropore structure were subjected to simulated rainfall of increasing rainfall intensity (26 mm h−1, 60 mm h−1, and 110 mm h−1) whose stable isotope signatures oscillated around known baseline values. Prior to rainfall, soil matrix water δ2H nearly matched the known value used to initially wet the pore space whereas soil δ18O deviated from this value by up to 3.4‰, suggesting that soils may strongly fractionate 18O. All treatments had up to 100% mixing between rain and matrix water under the lowest (26 mm h−1) and medium (60 mm h−1) rainfall intensities. The highest rainfall intensity (110 mm h−1), however, reduced mixing of rain and matrix water for all treatments and produced significantly different preferential flow estimates between columns with intact soil structure compared to columns with reduced soil structure. Further, artificially limiting exchange between preferential flow paths and matrix water reduced bypass flow under the most intense rainfall. We show that (1) precipitation offset metrics such as lc-excess and d-excess may yield questionable interpretations when used to identify ecohydrological separation, (2) distinct domain separation may require extreme rainfall intensities and (3) domain exchange is an important component of macropore flow. 相似文献
269.
In this study, the multi‐intensity seismic response of code‐designed conventional and base‐isolated steel frame buildings is evaluated using nonlinear response history analysis. The results of hazard and structural response analysis for three‐story braced‐frame buildings are presented in this paper. Three‐dimensional models for both buildings are created and seismic response is assessed for three scenario earthquakes. The response history analysis results indicate that the design objectives are met and the performance of the isolated building is superior to the conventional building in the design event. For the Maximum Considered Earthquake, isolation leads to reductions in story drifts and floor accelerations relative to the conventional building. However, the extremely high displacement demands of the isolation system could not be accommodated under normal circumstances, and creative approaches should be developed to control displacements in the MCE. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
270.