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71.
Remediating Ground Water with Zero-Valent Metals: Chemical Considerations in Barrier Design 总被引:2,自引:0,他引:2
Paul G. Tratnyek Timothy L. Johnson Michelle M. Scherer Gerald R. Eykholt 《Ground Water Monitoring & Remediation》1997,17(4):108-114
To gain perspective and insight into the performance of permeable reactive barriers containing granular iron metal, it is useful to compare the degradation kinetics of individual chlorinated solvents over a range of operating conditions. Pseudo first-order disappearance rate constants normalized to iron surface area concentration (kSA ) recently have been reported for this purpose. This paper presents the results of further exploratory data analysis showing the extent to which variation in kSA is due to initial halocarbon concentration, iron type, and other factors. To aid in preliminary design calculations, representative values of kSA and a reactive transport model have been used to calculate the minimum barrier width needed for different ground water flow velocities and degrees of halocarbon conversion. Complete dechlorination of all degradation intermediates requires a wider treatment zone, but the effect is not simply additive because degradation occurs by sequential and parallel reaction pathways. 相似文献
72.
A new solution for the planetary perturbations of the Moon is being built in the frame of ELP 2000, using Bretagnon's planetary theories, and achieved at the first order. It contains the two actions commonly distinguished: direct and indirect. The internal precision of computation is 2×10–6 arcsec. First-order planetary perturbations, in the direct case (Venus & Mars), have been compared to Standaert's solution. The major discrepancy reaches 70 cm in the longitude of Venus. Perturbations of the second order with respect to planetary masses, have been undertaken and illustrations are given. Finally, new values for the perigee and node motions are proposed.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980. 相似文献
73.
Maria Eugenia Varela Michelle Bonnin- Mosbah Jean Paul Gallien 《Geochimica et cosmochimica acta》2003,67(6):1255-1265
Measured were the abundance and distribution of nitrogen in glasses of glass inclusions in olivines of CV3, CO3, CR, C4, CH3, and LL chondritic meteorites by means of the 14N(d, p)15N nuclear reaction. Similar to what was observed with carbon, nitrogen is present in low concentrations (<20 ppm) in the structure of olivines but can by stored in variable amounts in glasses of glass inclusions. These primitive glasses, characterized by a Si-Al-Ca-rich composition, have highly variable nitrogen contents (30 to 1500 ppm) and highly inhomogeneous nitrogen distribution. Nitrogen contents are independent of the chemical composition of the glasses. The heterogeneous distribution is a common feature of all studied inclusions, as is evidenced by the variable contents of nitrogen in glass inclusions occurring in the same olivine grain. Nitrogen heterogeneity is suggestive of trapping of solid nitrogen carrier phases during formation of the constituents of chondrules. However, part of the originally trapped nitrogen appears to have been lost, possibly, by ulterior oxidation and subsequent transformation into volatile species. 相似文献
74.
Craig E. Divine Tracy Roth Michelle Crimi Abrahm C. DiMarco Matt Spurlin Jeff Gillow Gastón Leone 《Ground Water Monitoring & Remediation》2018,38(1):56-65
A new in‐situ remediation concept termed a Horizontal Reactive Media Treatment Well (HRX Well®) is presented that utilizes horizontal wells filled with reactive media to passively treat contaminated groundwater in‐situ. The approach involves the use of large‐diameter directionally drilled horizontal wells filled with granular reactive media generally installed parallel to the direction of groundwater flow. The design leverages natural “flow‐focusing” behavior induced by the high in‐well hydraulic conductivity of the reactive media relative to the aquifer hydraulic conductivity to passively capture and treat proportionally large volumes of groundwater within the well. Clean groundwater then exits the horizontal well along its downgradient sections. Many different types of solid granular reactive media are already available (e.g., zero valent iron, activated carbon, ion exchange resins, zeolite, apatite, chitin); therefore, this concept could be used to address a wide range of contaminants. Three‐dimensional flow and transport simulations were completed to assess the general hydraulic performance, capture zones, residence times, effects of aquifer heterogeneity, and treatment effectiveness of the concept. The results demonstrate that capture and treatment widths of up to tens of feet can be achieved for many aquifer settings, and that reductions in downgradient concentrations and contaminant mass flux are nearly immediate. For a representative example, the predicted treatment zone width for the HRX Well is approximately 27 to 44 feet, and contaminant concentrations immediately downgradient of the HRX Well decreased an order of magnitude within 10 days. A series of laboratory‐scale physical tests (i.e., tank tests) were completed that further demonstrate the concept and confirm model prediction performance. For example, the breakthrough time, peak concentration and total mass recovery of methylene blue (reactive tracer) was about 2, 35, and 20 times (respectively) less than chloride (conservative tracer) at the outlet of the tank‐scale HRX Well. 相似文献
75.
Predominant period and equivalent viscous damping ratio identification for a full‐scale building shake table test 下载免费PDF全文
Michelle C. Chen Rodrigo Astroza José I. Restrepo Joel P. Conte Tara Hutchinson Yehuda Bock 《地震工程与结构动力学》2017,46(14):2459-2477
The predominant period and corresponding equivalent viscous damping ratio, also known in various loading codes as effective period and effective damping coefficient, are two important parameters employed in the seismic design of base‐isolated and conventional building structures. Accurate determination of these two parameters can reduce the uncertainty in the computation of lateral displacement demands and interstory drifts for a given seismic design spectrum. This paper estimates these two parameters from data sets recorded from a full‐scale five‐story reinforced concrete building subjected to seismic base excitations of various intensities in base‐isolated and fixed‐base configurations on the outdoor shake table at the University of California, San Diego. The scope of this paper includes all test motions in which the yielding of the reinforcement has not occurred and the response can still be considered ‘elastic’. The data sets are used with three system identification methods to determine the predominant period of response for each of the test configurations. One of the methods also determines the equivalent viscous damping ratio corresponding to the predominant period. It was found that the predominant period of the fixed‐base building lengthened from 0.52 to 1.30 s. This corresponded to a significant reduction in effective system stiffness to about 16% of the original stiffness. The paper then establishes a correlation between predominant period and peak ground velocity. Finally, the predominant periods and equivalent viscous damping ratios recommended by the ASCE 7‐10 loading standard are compared with those determined from the test building. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
76.
John D. Monnier Stefan Kraus Michael J. Ireland Fabien Baron Amelia Bayo Jean-Philippe Berger Michelle Creech-Eakman Ruobing Dong Gaspard Duchêne Catherine Espaillat Chris Haniff Sebastian Hönig Andrea Isella Attila Juhasz Lucas Labadie Sylvestre Lacour Stephanie Leifer Antoine Merand Ernest Michael Stefano Minardi Christoph Mordasini David Mozurkewich Johan Olofsson Claudia Paladini Romain Petrov Jörg-Uwe Pott Stephen Ridgway Stephen Rinehart Keivan Stassun Jean Surdej Theo ten Brummelaar Neal Turner Peter Tuthill Kerry Vahala Gerard van Belle Gautam Vasisht Ed Wishnow John Young Zhaohuan Zhu 《Experimental Astronomy》2018,46(3):517-529
The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H2O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality. 相似文献
77.
Suhas S. Shetye Hema Naik Siby Kurian Damodar Shenoy Nandakumar Kuniyil Michelle Fernandes Afreen Hussain 《Marine Ecology》2020,41(5):e12614
The increasing atmospheric CO2 concentration in the last few decades has resulted in a decrease in oceanic pH. In this study, we assessed the natural variability of pH in coastal waters off Goa, eastern Arabian Sea. pHT showed large variability (7.6–8.1) with low pH conditions during south-west monsoon (SWM), and the variability is found to be associated with upwelling rather than freshwater runoff. Considering that marine biota inhabiting dynamic coastal waters off Goa are exposed to such wide range of natural fluctuations of pH, an acidification experiment was carried out. We studied the impact of low pH on the local population of sea urchin Stomopneustes variolaris (Lamarck, 1816). Sea urchins were exposed for 210 days to three treatments of pHT: 7.96, 7.76 and 7.46. Our results showed that S. variolaris at pHT 7.96 and 7.76 were not affected, whereas the ones at pHT 7.46 showed adverse effects after 120 days and 50% mortality by 210 days. However, even after exposure to low pH for 210 days, 50% organisms survived. Under low pH conditions (pHT 7.46), the elemental composition of sea urchin spines exhibited deposition of excess Sr2+ as compared to Mg2+ ions. We conclude that although the sea urchins would be affected in future high CO2 waters, at present they are not at risk even during the south-west monsoon when low pH waters reside on the shelf. 相似文献
78.
Polycyclic aromatic pollutants produced by a range of industrial processes and the combustion of fossil fuels. They eventually enter the marine environment, and are bioaccumulated in the tissues of sessile, filter-feeding bivalves, causing a variety of sublethal effects. Few studies, however, have examined immune inhibition in molluscs by these xenobiotics. Here, the immunotoxic effects of PAHs were investigated in marine mussels (Mytilus edulis) by means of in vivo exposure experiments. Animals were exposed to a PAH cocktail of anthracene, fluoranthene and phenanthrene for 2 or 4 weeks. The haemolymph was then extracted, and phagocytosis and lysosomal neutral red retention assays performed to examine the effects of PAHs on particle uptake by haemocytes and lysosome integrity, respectively. PAHs were found to inhibit phagocytosis and damage lysosomes. It is hypothesized that PAHs exert their toxicity directly on the lysosomes. A possible consequence of such lysosomal damage will be immune impairment in mussels leading to reduced resistance to infectious diseases. 相似文献
79.
John H. Trefry Robert P. Trocine Michelle L. McElvaine Robert D. Rember Lucas T. Hawkins 《Environmental Geology》2007,53(2):375-385
Concentrations of total Hg in sediments near six drilling sites in the Gulf of Mexico were elevated well above average background
values of 40–80 ng/g. The excess Hg was associated with barite from discharged drilling mud. In contrast with total Hg, concentrations
of methylmercury (MeHg) in these sediments did not vary significantly at nearfield (<100 m) versus farfield (>3 km) distances
from the drilling sites. Observed variability in concentrations of MeHg were related to local differences in redox state in
the top 10 cm of sediment. Low to non-detectable concentrations of MeHg were found in nearfield sediments that were anoxic,
highly reducing and contained abundant H2S. At most drilling sites, nearfield samples with high concentrations of total Hg (>200 ng/g) had similar or lower amounts
of MeHg than found at background (farfield) stations. Higher values of MeHg were found in a few nearfield sediments at one
site where concentrations of TOC were higher and where sediments were anoxic and moderately reducing. Overall, results from
this study support the conclusion that elevated concentrations of MeHg in sediments around drilling sites are not a common
phenomenon in the Gulf of Mexico. 相似文献
80.
A portable rainfall simulator for field assessment of splash and slopewash in remote locations 总被引:1,自引:0,他引:1
This paper describes the design, operation and performance of a field‐portable ‘drip‐type’ simulator and erosion measurement system. The system was constructed specifically for soil erosion research in the humid tropics and has been used extensively in Malaysian Borneo. The simulator is capable of producing replicable storms of up to 200 mm h?1 intensity and 20–30 minutes duration with a drop‐size distribution close to that of natural storms of such intensity (D50 of simulated rainfall is 4·15 mm at 200 mm h?1 and 3·65 mm at 160 mm h?1, D50 measured during natural rainfall = 3·25 mm). The simulator is portable and simply constructed and operates without a motor or electronics, thus making it particularly useful in remote, mountainous areas. The erosion measurement system allows assessment of: (1) rainsplash detachment and net downslope transport from the erosion plot; (2) slopewash (erosion transported by overland flow); and (3) infiltration capacity and overland flow. The performance of the simulator–erosion system compared with previous systems is assessed with reference to experiments carried out in primary and regenerating tropical rainforest at Danum Valley (Malaysian Borneo). The system was found to compare favourably with previous field simulators, producing a total storm kinetic energy of 727 J m?2 (over a 20‐minute storm event) and a kinetic energy rate of 0·61 J m?2 s?1, approximately half that experienced on the ground during a natural rainfall event of similar intensity, despite the shorter distance to the ground. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献