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341.
Fluvial systems can be preserved in inverted relief on both Earth and Mars. Few studies have evaluated the applicability of various paleohydrological models to inverted fluvial systems. The first phase of this investigation focused on an extensive (spanning 12 km) inverted paleochannel system that consists of four sandstone-capped, carbonate-cemented, sinuous ridges within the Early Cretaceous Cedar Mountain Formation located southwest of Green River, Utah. Morphologic and sedimentologic observations of the exhumed paleochannels were used to evaluate multiple numerical models for reconstructing paleofluvial hydrological parameters. Another objective of the study was to determine whether aerial or orbital observations yield model results that are consistent with those constrained by field data. The models yield an envelope of plausible dominant discharge values (100–500 m3/s), reflecting the limitations of the approach, and no single model can be used to reliably estimate paleodischarge. On Mars, landforms with attributes consistent with inverted channels have been identified. In spite of differences in the formation history between these martian landforms and the terrestrial analog described here, including potential differences in cement composition and the erosional agent that was responsible for relief inversion, these numerical models can be applied (with modification) to the martian landforms and yield an envelope of plausible values for dominant discharge. 相似文献
342.
A two-dimensional probabilistic acute human-health risk assessment of insecticide exposure after adult mosquito management 总被引:1,自引:1,他引:0
Jerome J. Schleier III Paula A. Macedo Ryan S. Davis Leslie M. Shama Robert K. D. Peterson 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(5):555-563
Ultra-low-volume (ULV) aerosol applications of insecticides are used to manage high densities of adult mosquitoes. We used
two-dimensional probabilistic risk assessment methodologies to evaluate three pyrethroid insecticides (phenothrin, resmethrin,
and permethrin), pyrethrins, and two organophosphate insecticides (malathion and naled), applied by truck-mounted ULV sprayer.
Piperonyl butoxide, a synergist commonly used in pyrethroid and pyrethrins formulations, was also assessed. The objective
of our study was to evaluate probabilistically if a deterministic human-health risk assessment of mosquito insecticides was
sufficiently conservative to protect human-health. Toddlers and infants were the highest risk groups while adult males were
the lowest risk group assessed in this study. Total acute exposure ranged from 0.00003 to 0.0003 mg/kg day−1 for the chemicals and subgroups assessed examining inhalation, dermal, oral, and hand-to-mouth exposure. We used the risk
quotient (RQ) method for our risk assessment, which is calculated by dividing the total potential exposure for each subgroup
and chemical by its ingestion toxic endpoint value (RfD). Mean RQs ranged from 0.000004 to 0.034 for all subgroups and chemicals,
with none exceeding the RQ level of concern. Naled had the highest RQs of any chemical assessed while PBO had the lowest.
Sensitivity analysis demonstrated that the exposure from inhalation and deposition contributed the largest variance to the
model output. Results support the findings of previous studies that the risks from adult mosquito management are most likely
negligible, and that the human-health deterministic risk assessment is most likely sufficiently conservative. 相似文献
343.
344.
Wisconsin's Central Sand Plain east of the Wisconsin River is composed of eolian sand forming high-relief dunes surrounded by sand sheets and scattered low-relief dunes. To establish a maximum age for dune formation, three samples for optical dating were taken from glacial Lake Wisconsin lacustrine sediment that underlies eolian sand. These age estimates range from 19.3 to 13.6ka. Age estimates taken from within or at the base of the dunes range from 14.0 to 10.6ka. Samples taken from < 2m of the ground surface were slightly younger, indicating dunes were stabilized between 11.8 and 5.5ka. The younger ages near the surface of some dunes were most likely the result of pedoturbation or localized problems with applying the optical dating method. The majority of the optical age estimates from dunes (18 of 21) indicated that most of the dunes were active between 14 and 10ka and that most dune activity ended by 10ka. These ages suggest that localized activity on dune crests may have occurred in the Holocene but would have been limited to < 1m of sand accumulation. The timing of dune activity and the lack of any significant Holocene reactivation suggest that dune activation in this setting cannot be attributed solely to changes in aridity. Instead, we attribute dune formation to changes in sediment availability from either sand inputs from the Wisconsin River or the melting of permafrost. 相似文献
345.
W.J. Jenkins D.J. McGillicuddy Jr. D.E. Lott III 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1389
We present and discuss the distribution of 3He and its relationship to nutrients in two eddies (cyclone C1 and anticyclone A4) with a view towards examining eddy-related mechanisms whereby nutrients are transported from the upper 200–300 m into the euphotic zone of the Sargasso Sea. The different behavior of these tracers in the euphotic zone results in changes in their distributions and relationships that may provide important clues as to the nature of physical and biological processes involved.The cyclonic eddy (C1) is characterized by substantial 3He excesses within the euphotic zone. The distribution of this excess 3He is strongly suggestive of both past and recent ongoing deep-water injection into the euphotic zone. Crude mass balance calculations suggest that an average of approximately 1.4±0.7 mol m−2 of nitrate has been introduced into the euphotic zone of eddy C1, consistent with the integrated apparent oxygen utilization anomaly in the aphotic zone below. The 3He–NO3 relationship within the eddy deviates substantially from the linear thermocline trend, suggestive of incomplete drawdown of nutrients and/or substantial mixing between euphotic and aphotic zone waters.Anticyclone (A4) displays a simpler 3He–NO3 relationship, but is relatively impoverished in euphotic zone excess 3He. We suggest that because of the relatively strong upwelling and lateral divergence of water the residence time of upwelled 3He is relatively short within the euphotic zone of this eddy. An estimate of the recently upwelled nutrient inventory, based on the excess 3He observed in A4's lower euphotic zone, is stoichiometrically consistent with the oxygen maximum observed in the euphotic zone. 相似文献
346.
Jianzhen Yu David R. Cocker III Robert J. Griffin Richard C. Flagan John H. Seinfeld 《Journal of Atmospheric Chemistry》1999,34(2):207-258
Atmospheric oxidation of monoterpenes contributes to formation of tropospheric ozone and secondary organic aerosol, but their products are poorly characterized. In this work, we report a series of outdoor smog chamber experiments to investigate both gaseous and particulate products in the ozone oxidation of four monoterpenes: -pinene, -pinene, 3-carene, and sabinene. More than ten oxygenated products are detected and identified in each monoterpene/O3 reaction by coupling derivatization techniques and GC/MS detection. A denuder/filter pack sampling system is used to separate and simultaneously collect gas and aerosol samples. The identified products, consisting of compounds containing carbonyl, hydroxyl, and carboxyl functional groups, are estimated to account for about 34–50%, 57%, 29–67%, and 24% of the reacted carbon mass for -pinene, sabinene, -pinene, and 3-carene, respectively. The identified individual products account for >83%, 100%, >90%, and 61% of the aerosol mass produced in the ozone reaction of -pinene, sabinene, -pinene, and 3-carene. The uncertainty in the yield data is estimated to be ±50%. Many of the products partition between gas and aerosol phases, and their gas-aerosol partitioning coefficients are determined and reported here. Reaction schemes are suggested to account for the products observed. 相似文献
347.
This issue of Hydrological Processes is dedicated to Dr. Edward P. Glenn, a frequent contributor to the journal, who suddenly passed away in late 2017. The articles within this volume are by a number of his former co-authors and others who have been greatly influenced by his professional work on hydrological processes. 相似文献
348.
Iraklis S. Konstantopoulos Nate Bastian Linda J. Smith Gelys Trancho Mark S. Westmoquette Jay S. Gallagher III 《Astrophysics and Space Science》2009,324(2-4):343-346
The post-starburst region B in M82 and its massive star cluster component have been the focus of multiple studies, with reports that there is a large population of coeval clusters of age ~1 Gyr, which were created with a Gaussian initial mass distribution. This is in disagreement with other studies of young star clusters, which invariably find a featureless power-law mass distribution. Here, we present Gemini-North optical spectra of seven star clusters in M82-B and show that their ages are all between 10 and 300 Myr (a factor of 3–100 younger than previous photometric results) and that their extinctions range between near zero and 4 mag (A V ). Using new HST ACS-HRC U-band observations we age date an additional ~30 clusters whose ages/extinctions agree well with those determined from spectroscopy. Completeness tests show that the reported ‘turn-over’ in the luminosity/mass distributions is most likely an artefact, due to the resolved nature of the clusters. We also show that the radial velocities of the clusters are inconsistent with them belonging to a bound region. 相似文献
349.
The rate of granule ripple movement on Earth and Mars 总被引:1,自引:0,他引:1
The rate of movement for 3- and 10-cm-high granule ripples was documented in September of 2006 at Great Sand Dunes National Park and Preserve during a particularly strong wind event. Impact creep induced by saltating sand caused ∼24 granules min−1 to cross each cm of crest length during wind that averaged ∼9 m s−1 (at a height well above 1 m), which is substantially larger than the threshold for saltation of sand. Extension of this documented granule movement rate to Mars suggests that a 25-cm-high granule ripple should require from hundreds to thousands of Earth-years to move 1 cm under present atmospheric conditions. 相似文献
350.
Ying Wang Alex L. Sessions Robert J. Nielsen William A. Goddard III 《Geochimica et cosmochimica acta》2009,73(23):7076-7086
Equilibrium 2H/1H fractionation factors (αeq) for various H positions in alkanes, alkenes, ketones, carboxylic acids, esters, alcohols, and ethers were calculated between 0 and 100 °C using vibrational frequencies from ab initio QM calculations (B3LYP/6-311G**). Results were then corrected using a temperature-dependent linear calibration curve based on experimental data for Hα in ketones (Wang et al., 2009). The total uncertainty in reported αeq values is estimated at 10–20‰. The effects of functional groups were found to increase the value of αeq for H next to electron-donating groups, e.g. OR, OH or O(CO)R, and to decrease the value of αeq for H next to electron-withdrawing groups, e.g. (CO)R or (CO)OR. Smaller but significant functional group effects are also observed for Hβ and sometimes Hγ. By summing over individual H positions, we estimate the equilibrium fractionation relative to water to be −90‰ to −70‰ for n-alkanes and around −100‰ for pristane and phytane. The temperature dependence of these fractionations is very weak between 0 and 100 °C. Our estimates of αeq agree well with field data for thermally mature hydrocarbons (δ2H values between −80‰ and −110‰ relative to water). Therefore the observed δ2H increase of individual hydrocarbons and the disappearance of the biosynthetic δ2H offset between n-alkyl and linear isoprenoid lipids during maturation of organic matter can be confidently attributed to H exchange towards an equilibrium state. Our results also indicate that many n-alkyl lipids are biosynthesized with δ2H values that are close to equilibrium with water. In these cases, constant down-core δ2H values for n-alkyl lipids cannot be reliably used to infer a lack of isotopic exchange. 相似文献