Estimating Travel Time in Bank Filtration Systems from a Numerical Model Based on DTS Measurements          下载免费PDF全文

Bas F. des Tombe  Mark Bakker  Frans Schaars  Kees‐Jan van der Made 《Ground water》2018,56(2):288-299

An approach is presented to determine the seasonal variations in travel time in a bank filtration system using a passive heat tracer test. The temperature in the aquifer varies seasonally because of temperature variations of the infiltrating surface water and at the soil surface. Temperature was measured with distributed temperature sensing along fiber optic cables that were inserted vertically into the aquifer with direct push equipment. The approach was applied to a bank filtration system consisting of a sequence of alternating, elongated recharge basins and rows of recovery wells. A SEAWAT model was developed to simulate coupled flow and heat transport. The model of a two‐dimensional vertical cross section is able to simulate the temperature of the water at the well and the measured vertical temperature profiles reasonably well. MODPATH was used to compute flowpaths and the travel time distribution. At the study site, temporal variation of the pumping discharge was the dominant factor influencing the travel time distribution. For an equivalent system with a constant pumping rate, variations in the travel time distribution are caused by variations in the temperature‐dependent viscosity. As a result, travel times increase in the winter, when a larger fraction of the water travels through the warmer, lower part of the aquifer, and decrease in the summer, when the upper part of the aquifer is warmer.  相似文献   

Seasonal variability of living benthic foraminifera from the outer continental shelf of the Bay of Biscay   总被引：1，自引：0，他引：1  

Grald Duchemin  Frans J. Jorissen  Franois Le Loc'h  Franoise Andrieux-Loyer  Christian Hily  Grard Thouzeau 《Journal of Sea Research》2008,59(4):297-319

Living benthic foraminiferal faunas of six stations from the continental shelf of the Bay of Biscay have been investigated during three successive seasons (spring, summer and autumn 2002). For the three investigated stations, bottom water oxygen concentration, oxygen penetration into the sediment and sediment organic carbon contents are all relatively similar. Therefore, we think that the density and the composition of the foraminiferal faunas is mainly controlled by the quantity and quality of organic input resulting from a succession of phytoplankton bloom events, occurring from late February to early September. The earliest blooms are positioned at the shelf break, late spring and early summer blooms occur off Brittany, whereas in late summer and early autumn, only coastal blooms appear, often in the vicinity of river outlets. In spring, the benthic foraminiferal faunas of central (B, C and D) and outer (E) continental shelf stations are characterised by strong dominance in the first area and strong presence in the second area of Nonionella iridea. In fact, station E does not serve as a major depocenter for the remains of phytoplankton blooms. If station E is not considered, the densities of this taxon show a clear gradient from the shelf-break, where the species dominates the assemblages, to the coast, where it attains very low densities. We explain this gradient as a response to the presence, in early spring, of an important phytoplankton bloom, mainly composed of coccolithophorids, over the shelf break. This observation is supported by the maximum particles flux values at stations close to the shelf break (18.5 g m^− 2 h^− 1) and lower values in a station closer to the coast (6.8 g m^− 2 h^− 1). In summer, the faunal density is maximum at station A, relatively close to more varied phytoplancton blooms that occur off Brittany until early June. We suggest that the dominant species, Nonion fabum, Cassidulina carinata and Bolivina ex. gr. dilatata respond to phytodetritus input from these blooms. In autumn, the rich faunas of inner shelf station G are dominated by N. fabum, B. ex. gr. dilatata, Hyalinea balthica and Nonionella turgida. These taxa seem to be correlated with the presence of coastal blooms phenomena, in front of river outlets. They may be favoured by an organic input with a significant contribution of terrestrial, rather low quality organic matter.  相似文献   

Condensation processes in astrophysical environments: The composition and structure of cometary grains     

Joseph A. NUTH  Frans J. M. RIETMEIJER  Hugh G. M. HILL 《Meteoritics & planetary science》2002,37(11):1579-1590

Abstract— We review the results of our recent experimental studies of astrophysical dust analogs. We discuss the condensation of amorphous silicates from mixed metal vapors, including evidence that such condensates form with metastable eutectic compositions. We consider the spectral evolution of amorphous magnesium silicate condensates as a function of time and temperature. Magnesium silicate smokes anneal readily at temperatures of about 1000–1100 K. In contrast we find that iron silicates require much higher temperatures (?1300 K) to bring about similar changes on the same timescale (days to months). We first apply these results to infrared space observatory observations of crystalline magnesium silicate grains around high‐mass‐outflow asymptotic giant branch stars in order to demonstrate their general utility in a rather simple environment. Finally, we apply these experimental results to infrared observations of comets and protostars in order to derive some interesting conclusions regarding large‐scale nebular dynamics, the natural production of organic molecules in protostellar nebulae, and the use of crystalline magnesium silicates as a relative indicator of a comet's formation age.  相似文献   

Visualization of trace-element zoning in fluorapatite using BSE and CL imaging,and EPMA and μPIXE/μPIGE mapping     

Katarzyna Gros  Ewa Słaby  Hans-Jürgen Förster  Przemysław P. Michalak  Frans Munnik  Jens Götze  Dieter Rhede 《Mineralogy and Petrology》2016,110(6):809-821

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Benthic geochemistry of manganese in the Bay of Biscay,and sediment mass accumulation rate     

Aurélia Mouret  Pierre Anschutz  Pascal Lecroart  Gwénaëlle Chaillou  Christelle Hyacinthe  Jonathan Deborde  Frans J. Jorissen  Bruno Deflandre  Sabine Schmidt  Jean-Marie Jouanneau 《Geo-Marine Letters》2009,29(3):133-149

Manganese is a major redox reactive element of benthic metabolism. We have built a database of existing knowledge on the benthic geochemistry of Mn in the Bay of Biscay, in order to comprehensively assess the behaviour of Mn in a variety of environments during early diagenesis. The database contains vertical profiles of particulate and dissolved Mn species of 59 cores collected during 17 cruises between 1997 and 2006 at nine stations positioned between 140 and 4,800 m water depths. At all studied stations, Mn species follow the conventional distribution, where Mn(III,IV) species are enriched in the oxic layer, and dissolved Mn is present in the anoxic sediments. A minor part of Mn-oxides originates from sedimenting particles. The major part is of diagenetic origin, and derives from the oxidation of upward-diffusing dissolved Mn(II). Mn-oxide inventories are higher at the deeper stations than at the shallower ones. This difference cannot be attributed to different sources of sedimenting particles, but it must depend on sedimentation rate and diagenetic processes. At depth, dissolved Mn(II) concentrations are constant. This probably reflects equilibrium with an authigenic Mn(II) phase, which is the ultimate phase into which Mn is fossilized. The Mn content of deeper anoxic sediments is similarly low in all the cores studied, associated with corresponding trends of Mn content in sedimenting particles of the Bay of Biscay. Bioturbation, rather than redox oscillations, can convey Mn(III,IV) species downwards into the anoxic sediments where they are reduced, associated with a peak of dissolved Mn. Because dissolved Mn(II) is re-oxidized when it diffuses towards the oxic layer, the inventory of the diagenetic Mn(III,IV) phase remains at steady state, especially at stations where the oxic layer is thick. It then becomes possible to calculate the residence time of diagenetic Mn(III,IV) particles within the oxic layer, using the upward-directed flux of pore water Mn(II). By applying this residence time to the accumulation of sediments within the oxic layer, we obtain the sediment mass accumulation rate. The values calculated for the sediments of the Bay of Biscay fit well with accumulation rates obtained from radionuclides or sediment traps. The method has also been validated with data collected in other marine sedimentary environments. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Pastas: Open Source Software for the Analysis of Groundwater Time Series     

Raoul A. Collenteur  Mark Bakker  Ruben Caljé  Stijn A. Klop  Frans Schaars 《Ground water》2019,57(6):877-885

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Solving Groundwater Flow Problems with Time Series Analysis: You May Not Even Need Another Model     

Mark Bakker  Frans Schaars 《Ground water》2019,57(6):826-833

Time series analysis is a data-driven approach to analyze time series of heads measured in an observation well. Time series models are commonly much simpler and give much better fits than regular groundwater models. Time series analysis with response functions gives insight into why heads vary, while such insight is difficult to gain with black box models out of the artificial intelligence world. An important application is to quantify the contributions to the head variation of different stresses on the aquifer, such as rainfall and evaporation, pumping, and surface water levels. Time series analysis may be applied to answer many groundwater questions without the need for a regular groundwater model, such as what is the drawdown caused by a pumping station? Or, how long will it take before groundwater levels recover after a period of drought? Even when a regular groundwater model is needed to solve a groundwater problem, time series analysis can be of great value. It can be used to clean up the data, identify the major stresses on the aquifer, determine the most important processes that affect flow in the aquifer, and give an indication of the fit that can be expected. In addition, it can be used to determine calibration targets for steady-state models, and it can provide several alternative calibration methods for transient models. In summary, the overarching message of this paper is that it would be wise to do time series analysis for any application that uses measured groundwater heads.  相似文献   

GEMS,hydrated chondritic IDPs,CI‐matrix material: Sources of water in 81P/comet Wild 2     

Frans J. M. Rietmeijer 《Meteoritics & planetary science》2019,54(2):259-266

So far there is no conclusive evidence for water in the nucleus of 81P/comet Wild 2. Recently magnetite in collected Wild 2 samples was cited as proxy evidence for parent body aqueous alteration in this comet (Hicks et al. 2017 ). A potentional source for water of hydration would be layer silicates but unfortunately there is no record, neither texturally nor chemically, for hydrated layer silicates that survived hypervelocity impact in the Wild 2 samples. This paper reports large vesicles in the matrix of allocation C2044,2,41,2,5 from a volatile‐rich type B/C Stardust track. These vesicles were probably caused by boiling water that were generated when hydrated Wild 2 silicates impacted the near‐surface silica aerogel layer. Potential water sources were partially and fully hydrated GEMS (glass with embedded metal and sulfides) and CI carbonaceous chondrite materials among the earliest dusts that experienced hydration and icy‐body formation and long‐range transport and mixing with materials from across the solar system.  相似文献   

The age and palæoenvironmental significance of the Kalahari Sands in western Zimbabwe: a thermoluminescence reconnaissance study     

Kennedy Munyikwa  Peter Van Den Haute  Dimitri Vandenberghe  Frans De Corte 《Journal of African Earth Sciences》2000,30(4):199

Thermoluminescence (TL) dating, has been applied to 10 samples from the æolian Kalahari Sands of western Zimbabwe using the total bleach (additive dose) and regeneration techniques on coarse-grain quartz separates. The results suggest that the main phases of sand accumulation occurred between 10 and 96 ka. This Upper Pleistocene age is consistent with current opinions and argues against an important period of Holocene æolian activity. The oldest sands were found in the Victoria Falls area where they overlie a ferricrete horizon. Based on our age determinations, we were able to constrain the age of this horizon to between 96±8 and 160±23 ka, which approximately coincides with the Last Integlaciation in the high latitudes. The youngest ages were obtained for sands from the southeastern part of the Hwange dune field but our limited sampling permits assigning only a minimum age of ca 20 ka to the ferricrete horizon observed in this area. Thus, we cannot ascertain if this ferricrete horizon is isochronous with the one at Victoria Falls or if it developed during a younger humid phase.Dune building activity most probably occurred in recurrent cycles of aridity interspersed with periods during which æolian activity was limited or non-existent. Unfortunately, besides the ferricrete horizons, no other stratigraphical evidence of climatic fluctuation has been observed in the study area. However, it is possible that palæosols have been entirely eroded before the subsequent deposition of new sediment, resulting in an incomplete stratigraphical record. The possibilities and limitations of luminescence dating for elucidating phases of climatic fluctuation in such situations are discussed briefly. In addition, we noticed serious discrepancies between the results yielded by the different techniques that were used for determining the dose rate. Hence, further work is needed to validate the accuracy of our dose rate measurements that may cause our TL ages to be about 30% too young.  相似文献   

Interrelationships among meteoric metals,meteors, interplanetary dust,micrometeorites, and meteorites     

Frans J. M. RIETMEIJER 《Meteoritics & planetary science》2000,35(5):1025-1041

Abstract— Meteor science, aeronomy, and meteoritics are different disciplines with natural interfaces. This paper is an effort to integrate the chemistry and mineralogy of collected interplanetary dust particles (IDPs), micrometeorites, and meteorites with meteoric data and with atmospheric metal abundances. Evaporation, ablation, and melting of decelerating materials in the Earth's atmosphere are the sources of the observed metal abundances in the upper atmosphere. Many variables ultimately produce the materials and phenomena we can analyze, such as different accretion and parent‐body histories of incoming extraterrestrial materials, different interactions of meteors with the Earth's middle atmosphere, meteor data reduction, and complex chemical interactions of the metals and ions with the ambient atmosphere. The IDP‐like and unequilibrated ordinary chondrite matrix materials are reasonable sources for observed meteoric and atmospheric metals. The hypothesis of hierarchical dust accretion predicts that low, correlated refractory element abundances in cometary meteors may be real. It implies that the CI or cosmic standard is not useful to appreciate the chemistry of incoming petrologically heterogeneous cometary matter. The quasi steady‐state metal abundances in the lower thermosphere and upper mesosphere are derived predominantly from materials with cometary orbital characteristics and velocities such as comets proper and near‐Earth asteroids. The exact influence of atmospheric chemistry on these abundances still needs further evaluation. Metal abundances in the lower mesosphere and upper stratosphere region are mostly from materials from the asteroidal belt and the Kuiper belt.  相似文献