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191.
Sara M. Klemm Eric A. Seagren Jennifer G. Becker Alex S. Mayer 《Ground Water Monitoring & Remediation》2021,41(4):33-48
Porous aquifer materials are often characterized by layered heterogeneities that influence groundwater flow and present complexities in contaminant transport modeling. Such flow variations also have the potential to impact the dissolution flux from dense nonaqueous phase liquid (DNAPL) pools. This study examined how these heterogeneous flow conditions affected the dissolution of a tetrachloroethene (PCE) pool in a two-dimensional intermediate-scale flow cell containing coarse sand. A steady-state mass-balance approach was used to calculate the PCE dissolution rate at three different flow rates. As expected, aqueous PCE concentrations increased along the length of the PCE pool and higher flow rates decreased the aqueous PCE concentration in the effluent. Nonreactive tracer studies at two flow rates confirmed the presence of a vertical flow gradient, with the most rapid velocity located at the bottom of the tank. These results suggest that flow focusing occurred near the DNAPL pool. Effluent PCE concentrations and pool dissolution flux rates were compared to model predictions assuming local equilibrium (LE) conditions at the DNAPL pool/aqueous phase interface and a uniform distribution of flow. The LE model did not describe the data well, even over a wide range of PCE solubility and macroscopic transverse dispersivity values. Model predictions assuming nonequilibrium mass-transfer-limited conditions and accounting for vertical flow gradients, however, resulted in a better fit to the data. These results have important implications for evaluating DNAPL pool dissolution in the field where subsurface heterogeneities are likely to be present. 相似文献
192.
Michael Solontoi Željko Ivezić Mario Jurić Andrew C. Becker Lynne Jones Andrew A. West Steve Kent Robert H. Lupton Mark Claire Gillian R. Knapp Tom Quinn James E. Gunn Donald P. Schneider 《Icarus》2012,218(1):571-584
We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10 million SDSS photometric objects. Five-band (u, g, r, i, z) photometry is used to determine the comets’ colors, sizes, surface brightness profiles, and rates of dust production in terms of the Afρ formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(<H) ∝ 10(0.49±0.05)H for H < 18, with evidence of a much shallower fit N(<H) ∝ 10(0.19±0.03)H for the faint (14.5 < H < 18) comets. The resolved comets show an extremely narrow distribution of colors (0.57 ± 0.05 in g ? r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets. 相似文献
193.
AbstractThis study was carried out in the framework of the Surface Water and Ocean Topography (SWOT) programme of the French National Centre of Space Studies (CNES). Based on discharge measurements and Gravity Recovery and Climate Experiment (GRACE) determination of total water storage (TWS), we have investigated the hydrological variability of the main French drainage basins (Seine, Loire, Garonne and Rhône) using a wavelet approach (continuous wavelet analyses and wavelet coherence analyses). The results of this analysis have shown a coherence ranging between 82% and 90% for TWS and discharge, thus demonstrating the potential use of TWS for characterization of the hydrological variability of French rivers. Strong coherence between the four basin discharges (between 73% and 92%) and between their associated TWS data (from 82% to 98%) suggested a common external influence on hydrological variability. To determine this influence, we investigated the relationship between hydrological variability and the North Atlantic Oscillation (NAO), considered as an index of prevailing climate in Europe. Basin discharges show strong coherence with NAO, ranging between 64% and 72% over the period 1959–2010. The coherence between NAO and TWS was 62% to 67% for 2003–2009. This is similar to the coherence between NAO and basin discharges detected for the same period. According to these results, strong influence of the NAO was clearly observed on the TWS and discharges of the major French river basins.
Editor Z.W. Kundzewicz 相似文献
194.
T. Dahm D. Becker M. Bischoff S. Cesca B. Dost R. Fritschen S. Hainzl C. D. Klose D. K��hn S. Lasocki Th. Meier M. Ohrnberger E. Rivalta U. Wegler Stephan Husen 《Journal of Seismology》2013,17(1):197-202
Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology. 相似文献
195.
Ana Lorena Esteban‐García Raquel Lebrero Manuel Alejandro de los Santos Raúl Muñoz Juan Ignacio Tejero 《洁净——土壤、空气、水》2013,41(5):469-472
A study was performed in two submerged, pilot‐scale biofilm bioreactors operated under different conditions to determine the relationship between the operating parameters and H2S emission. H2S was always detected in the exhaust air at concentrations varying from 1 to 353 ppmv. The specific aeration rate was the most influencing parameter, with As < 30 kg COD (dissolved oxygen concentrations <4 mg L?1) increasing noticeably the H2S production. The periodical removal of the accumulated sludge reduced H2S emissions by ~14%. 相似文献
196.
Ignacio?Torresi Roberto?Perez?XavierEmail author Diego?F.?A.?Bortholoto Lena?V.?S.?Monteiro 《Mineralium Deposita》2012,47(3):299-323
The Alvo 118 iron oxide–copper–gold (IOCG) deposit (170 Mt at 1.0 wt.% Cu, 0.3 g/t Au) lies in the southern sector of the
Itacaúnas Shear Belt, Carajás Mineral Province, along a WNW–ESE-striking, 60-km-long shear zone, close to the contact of the
~2.76-Ga metavolcano-sedimentary Itacaiúnas Supergroup and the basement (~3.0 Ga Xingu Complex). The Alvo 118 deposit is hosted
by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following
hydrothermal alteration sequence towards the ore zones: (1) poorly developed sodic alteration (albite and scapolite); (2)
potassic alteration (biotite or K-feldspar) accompanied by magnetite formation and silicification; (3) widespread, pervasive
chlorite alteration spatially associated with quartz–carbonate–sulphide infill ore breccia and vein stockworks; and (4) local
post-ore quartz–sericite alteration. The ore assemblage is dominated by chalcopyrite (~60%), bornite (~10%), hematite (~20%),
magnetite (10%) and subordinate chalcocite, native gold, Au–Ag tellurides, galena, cassiterite, F-rich apatite, xenotime,
monazite, britholite-(Y) and a gadolinite-group mineral. Fluid inclusion studies in quartz point to a fluid regime composed
of two distinct fluid types that may have probably coexisted within the timeframe of the Cu–Au mineralizing episode: a hot
(>200°C) saline (32.8‰ to 40.6 wt.% NaCl eq.) solution, represented by salt-bearing aqueous inclusions, and a lower temperature
(<200°C), low to intermediate salinity (<15 wt.% NaCl eq.) aqueous fluid defined by two-phase (LH2O + VH2O) fluid inclusions. This trend is very similar to those defined for other IOCG systems of the Carajás Mineral Province. δ
18OH2O values in equilibrium with calcite (−1.0‰ to 7.5‰ at 277°C to 344°C) overlap the lower range for primary magmatic waters,
but the more 18O-depleted values also point to the involvement of externally derived fluids, possibly of meteoric origin. Furthermore, sulphide
δ
34S values (5.1‰ to 6.3‰), together with available boron isotope and Cl/Br–Na/Cl data provide evidence for a significant component
of residual evaporative fluids (e.g., bittern fluids generated by seawater evaporation) in this scenario that, together with
magma-derived brines, would be the main sources of the highly saline fluids involved in the formation Alvo 118 IOCG deposit.
The restricted high temperature sodic alteration, the pervasive overprinting of the potassic alteration minerals by chlorite
proximal to the ore zones, ore breccias with open-space filling textures in brittle structures, microthermometric and stable
isotope data indicate, collectively, that the Alvo 118 IOCG system developed at structurally high levels and may be considered
the shallower representative of the IOCG systems of the CMP. 相似文献
197.
We present detailed pollen and charcoal records from Lago Pichilafquén (~ 41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600 yr. Here, temperate rainforests have dominated the landscape since 2600 cal yr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430 cal yr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690 cal yr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140 cal yr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340 cal yr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600 yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes. 相似文献
198.
This paper presents a non‐linear, kinematic model for triple friction pendulum isolation bearings. The model, which incorporates coupled plasticity and circular restraining surfaces for all sliding surfaces, is capable of capturing bi‐directional behavior and is able to explicitly track the movement of each internal component. The model is general so that no conditions regarding bearing properties, which effect the sequence of sliding stages, are required for the validity of the model. Controlled‐displacement and seismic‐input experiments were conducted using the shake table at the University of California, Berkeley to assess the fidelity of the proposed model under bi‐directional motion. Comparison of the experimental data with the corresponding results of the kinematic model shows good agreement. Additionally, experiments showed that the performance of TFP bearings is reliable over many motions, and the behavior is repeatable even when initial slider offsets are present. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
199.
A. C. Becker E. Agol N. M. Silvestri J. J. Bochanski C. Laws A. A. West G. Basri V. Belokurov D. M. Bramich J. M. Carpenter P. Challis K. R. Covey R. M. Cutri N. W. Evans M. Fellhauer A. Garg G. Gilmore P. Hewett P. Plavchan D. P. Schneider C. L. Slesnick S. Vidrih L. M. Walkowicz D. B. Zucker 《Monthly notices of the Royal Astronomical Society》2008,386(1):416-424
We report on Two-Micron All-Sky Survey (2MASS) J01542930+0053266, a faint eclipsing system composed of two M dwarfs. The variability of this system was originally discovered during a pilot study of the 2MASS Calibration Point Source Working Data base. Additional photometry from the Sloan Digital Sky Survey yields an eight-passband light curve from which we derive an orbital period of 2.639 0157 ± 0.000 0016 d. Spectroscopic followup confirms our photometric classification of the system, which is likely composed of M0 and M1 dwarfs. Radial velocity measurements allow us to derive the masses (M1 = 0.66 ± 0.03 M⊙ ; M2 = 0.62 ± 0.03 M⊙ ) and radii (R1 = 0.64 ± 0.08 R⊙ ; R2 = 0.61 ± 0.09 R⊙ ) of the components, which are consistent with empirical mass–radius relationships for low-mass stars in binary systems. We perform Monte Carlo simulations of the light curves which allow us to uncover complicated degeneracies between the system parameters. Both stars show evidence of Hα emission, something not common in early-type M dwarfs. This suggests that binarity may influence the magnetic activity properties of low-mass stars; activity in the binary may persist long after the dynamos in their isolated counterparts have decayed, yielding a new potential foreground of flaring activity for next generation variability surveys. 相似文献
200.
ABSTRACT. Pressured by structural adjustment loan conditions, Côte d'Ivoire reduced state support for rice production and processing during the 1990s. In this article we examine how various actors in the rice commodity chain adapted to the macroeconomic reforms. Following a brief history of the rice sector, we present the results of fieldwork based on interviews conducted in 2002 of farmers, millers, traders, and workers in the state extension service and nongovernmental organizations. We found that, in the absence of state supports for farmers, private millers became the focal point of regional producer‐processor rice networks. The four networks identified became the sole source of domestic commercial rice when the state removed subsidies for fertilizer and modern seeds, privatized extension, and liberalized prices and imports. To increase their role in the national rice supply, the rice networks may need support through microlending and a focus on niche markets. 相似文献