Determination of first-order degradation rate constants from monitoring networks   总被引：1，自引：0，他引：1  

Beyer C  Chen C  Gronewold J  Kolditz O  Bauer S 《Ground water》2007,45(6):774-785

In this article, different strategies for estimating first-order degradation rate constants from measured field data are compared by application to multiple, synthetic, contaminant plumes. The plumes were generated by numerical simulation of contaminant transport and degradation in virtual heterogeneous aquifers. These sites were then individually and independently investigated on the computer by installation of extensive networks of observation wells. From the data measured at the wells, that is, contaminant concentrations, hydraulic conductivities, and heads, first-order degradation rates were estimated by three 1D centerline methods, which use only measurements located on the plume axis, and a two-dimensional method, which uses all concentration measurements available downgradient from the contaminant source. Results for both strategies show that the true rate constant used for the numerical simulation of the plumes in general tends to be overestimated. Overestimation is stronger for narrow plumes from small source zones, with an average overestimation factor of about 5 and single values ranging from 0.5 to 20, decreasing for wider plumes, with an average overestimation factor of about 2 and similar spread. Reasons for this overestimation are identified in the velocity calculation, the dispersivity parameterization, and off-centerline measurements. For narrow plumes, the one- and the two-dimensional strategies show approximately the same amount of overestimation. For wider plumes, however, incorporation of all measurements in the two-dimensional approach reduces the estimation error. No significant relation between the number of observation wells in the monitoring network and the quality of the estimated rate constant is found for the two-dimensional approach.  相似文献   

Dissolved iron(III) speciation in the high latitude North Atlantic Ocean     

Khairul N. Mohamed  Sebastian Steigenberger  Maria C. Nielsdottir  Martha Gledhill  Eric P. Achterberg 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(11):1049-1059

On voyages in the Iceland Basin in 2007 and 2009, we observed low (ca. 0.1 nM) total dissolved iron concentrations [dFe] in surface waters (<150 m), which increased with depth to ca. 0.2–0.9 nM. The surface water [dFe] was low due to low atmospheric Fe inputs combined with biological uptake, with Fe regeneration from microbial degradation of settling biogenic particles supplying dFe at depth. The organic ligand concentrations [L_T] in the surface waters ranged between 0.4 and 0.5 nM, with conditional stability constants (log K′_FeL) between 22.6 and 22.7. Furthermore, [L_T] was in excess of [dFe] throughout the water column, and dFe was therefore largely complexed by organic ligands (>99%). The ratio of [L_T]/[dFe] was used to analyse trends in Fe speciation. Enhanced and variable [L_T]/[dFe] ratios ranging between 1.6 and 5.8 were observed in surface waters; the ratio decreased with depth to a more constant [L_T]/[dFe] ratio in deep waters. In the Iceland Basin and Rockall Trough, enhanced [L_T]/[dFe] ratios in surface waters resulted from decreases in [dFe], likely reflecting the conditions of Fe limitation of the phytoplankton community in the surface waters of the Iceland Basin and the high productivity in the Rockall Trough.Below the surface mixed layer, the observed increase in [dFe] resulted in a decrease of the [L_T]/[dFe] ratios (1.2–2.6) with depth. This indicated that the Fe binding ligand sites became occupied and even almost saturated at enhanced [dFe] in the deeper waters. Furthermore, our results showed a quasi-steady state in deep waters between dissolved organic Fe ligands and dFe, reflecting a balance between Fe removal by scavenging and Fe supply by remineralisation of biogenic particles with stabilisation through ligands.  相似文献   

The 2dF–SDSS LRG and QSO (2SLAQ) Survey: the z < 2.1 quasar luminosity function from 5645 quasars to g= 21.85     

Gordon T. Richards  Scott M. Croom  Scott F. Anderson  Joss Bland-Hawthorn  Brian J. Boyle  Roberto De Propris  Michael J. Drinkwater  Xiaohui Fan  James E. Gunn  &#;eljko Ivezi&#;  Sebastian Jester  Jon Loveday  Avery Meiksin  Lance Miller  Adam Myers  Robert C. Nichol  Phil J. Outram  Kevin A. Pimbblet  Isaac G. Roseboom  Nic Ross  Donald P. Schneider  Tom Shanks  Robert G. Sharp  Chris Stoughton  Michael A. Strauss  Alexander S. Szalay  Daniel E. Vanden Berk  Donald G. York 《Monthly notices of the Royal Astronomical Society》2005,360(3):839-852

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On the Relationship Between the Jets from X-Ray Binaries and Agn     

Sebastian Heinz  Andrea Merloni  Tiziana Di Matteo  Rashid Sunyaev 《Astrophysics and Space Science》2005,300(1-3):15-21

The scale invariance model (Heinz, S. and Sunyaev, R.A.: 2003, MNRAS 343, L59) can be used to derive robust scaling relations between the radio luminosity from accreting black holes and the black hole mass and accretion rate. These relations agree well with the recently found “fundamental plane” of black hole activity (Merloni, A., Heinz, S. and Di Matteo, T.: 2003, MNRAS 345, 1057). This relation provides a new, powerful tool for the comparison of jets from black holes of different masses and accretion rates. The regression coefficients of this relation contain information about the nature of the X-ray emission mechanism driving the correlation. We argue that X-ray synchrotron emission from the base of the jets is unlikely to be the dominant contribution to the X-ray spectrum in most of the sources.  相似文献   

Hydrological heterogeneity of an alpine stream–lake network in Switzerland     

Christopher T. Robinson  Sebastian Matthaei 《水文研究》2007,21(23):3146-3154

Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ～60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ～4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm^?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l^?1) than in the south basin (seasonal average: 2 µg l^?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l^?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l^?1) than in the south basin (seasonal average: 12 µg l^?1). Total inorganic carbon was low (usually <0·8 mg l^?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l^?1) than in the south basin (average: 0·2 mg l^?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The hydrodynamics of dead radio galaxies     

Christopher S. Reynolds †  Sebastian Heinz  Mitchell C. Begelman 《Monthly notices of the Royal Astronomical Society》2002,332(2):271-282

We present a numerical investigation of dead, or relic, radio galaxies and the environmental impact that radio galaxy activity has on the host galaxy or galaxy cluster. We perform axisymmetric hydrodynamical calculations of light, supersonic, back-to-back jets propagating in a β -model galaxy/cluster atmosphere. We then shut down the jet activity and let the resulting structure evolve passively. The dead source undergoes an initial phase of pressure driven expansion until it achieves pressure equilibrium with its surroundings. Thereafter, buoyancy forces drive the evolution and lead to the formation of two oppositely directed plumes that float high into the galaxy/cluster atmosphere. These plumes entrain a significant amount of low entropy material from the galaxy/cluster core and lift it high into the atmosphere. An important result is that a large fraction (at least half) of the energy injected by the jet activity is thermalized in the interstellar medium (ISM)/intracluster medium (ICM) core. The whole ISM/ICM atmosphere inflates in order to regain hydrostatic equilibrium. This inflation is mediated by an approximately spherical disturbance which propagates into the atmosphere at the sound speed. The fact that such a large fraction of the injected energy is thermalized suggests that radio galaxies may have an important role in the overall energy budget of rich ISM/ICM atmospheres. In particular, they may act as a strong and highly time-dependent source of negative feedback for galaxy/cluster cooling flows.  相似文献   

Sedimentary evolution of Lake Van (Eastern Turkey) reconstructed from high-resolution seismic investigations   总被引：1，自引：0，他引：1  

Deniz Cukur  Sebastian Krastel  Filiz Demirel-Schlüter  Emin Demirbağ  Caner Imren  Frank Niessen  Mustafa Toker 《International Journal of Earth Sciences》2013,102(2):571-585

This paper presents results of a multi-channel seismic reflection survey at Lake Van and provides constraints on the sedimentary evolution of the lake. The geophysical data of the lake confirm the existence of three physiographic provinces: a shelf, a slope, and a deep, relatively flat basin. The most prominent features identified on the shelf and slope are clinoforms, submerged channels, as well as closely spaced lake floor depressions, reflecting a highly variable lake-level history. The morphological depressions are interpreted as resulting from subaquatic erosion by channelized, sediment-laden currents into horizontally bedded fan sediments. Submerged channels on the eastern shelf are interpreted as meandering-slope channels, probably as a consequence of a lake-level fall that exposed the shelf area. Clinoforms on the Eastern fan may represent relict deltas formed during stationary or slightly rising lake-level intervals. Merging subsurface imaging interpretation with morphological studies of exposed sediments reveals lake-level fluctuations of several hundreds of meters during the past ca. ~550 ka. The lake has three prominent basins (Tatvan, Deveboynu, and the Northern basin) separated by basement ridges (e.g., the Northern ridge). The seismic units in the Tatvan and Northern basins are dominated by alternations of well-stratified and chaotic reflections, while the Deveboynu basin subsurface consists mainly of chaotic units. The chaotic seismic facies are interpreted as mass-flow deposits, probably triggered by earthquakes and/or rapid lake-level fluctuations. The moderate-to-high-amplitude, well-stratified facies seen in the deeper parts of the basins are interpreted as lacustrine deposits intercalated with tephra layers. The occurrence of a clinoform in the deepest part of the lake suggests a major flooding stage of Lake Van more than ~400 ka ago. Seismic profiles from the deepest part of the lake basin show remarkably uniform and continuous stratigraphic units without any major erosional feature following the flooding event, indicating that the lake was never completely dry afterward and therefore significantly older than previously suggested.  相似文献   

Meteorological observations 2006 and ground temperature variations over 12-year at the Sermilik Station,Ammassalik Island,Southeast Greenland     

Sebastian H. Mernild  Bent Hasholt  Bjarne H. Jakobsen  Birger U. Hansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):153-161

Geografisk Tidsskrift, Danish Journal of Geography 108(1):153–161, 2008

Meteorological stations have been in operation since 1993 at the Sermilik Research Station (65°40′N, 38°10′W), Ammassalik Island, Southeast Greenland. This note presents meteorological observations for the calendar year 2006 from the two meteorological stations: Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). The year 2006 record is not complete due to a temporal break down of Station Coast (from end-of June through beginning of August). Special focus is given to ground temperature measurements at the meteorological Station Nunatak (1994–2006) 0.1 and 0.3 m below the surface. Data are presented to illustrate the intra- and inter-annual temperature variability and possible trends in the upper part of the soil.  相似文献   

Seismic stratigraphical record of Lake Levinson‐Lessing,Taymyr Peninsula: evidence for ice‐sheet dynamics and lake‐level fluctuations since the Early Weichselian     

Elodie Lebas  Sebastian Krastel  Bernd Wagner  Raphael Gromig  Grigory Fedorov  Marlene Baumer  Natalia Kostromina  Haflidi Haflidason 《Boreas: An International Journal of Quaternary Research》2019,48(2):470-487

A multi‐channel, high‐resolution seismic reflection survey using a Micro‐GI airgun was carried out in the framework of the Russian‐German project PLOT (Paleolimnological Transect) on Lake Levinson‐Lessing, Taymyr Peninsula, in 2016. In total, ~70 km of seismic reflection profiles revealed in unprecedented detail the glacial and postglacial sedimentary infill of the lake basin. Five main seismic units have been recognized and interpreted as glacial (Unit V), subglacial and proglacial (Unit IV), marine (Unit III), fluvial‐lacustrine (Unit II) and lacustrine (Unit I) sediments. Of particular significance are imbricated, south‐orientated structures present in the southernmost part of the lake basin within Unit V and a large topographic ridge recognized in front of those structures. We interpret these structures as push moraines and an end moraine, respectively, left by the glacier after its retreat. The depositional pattern of the units above the moraines documents past lake‐level fluctuations. We interpret Unit IV, Unit III and Unit I as highstand deposits, and Unit II as lowstand deposits. Gas‐charged sediments dominate the northern part of the lake basin, whilst they occur only sporadically and in limited spatial extent in the central and southern parts of the lake. In the latter areas, the seismic and echo‐sounder data suggest recent tectonic activity. Our study contributes to the reconstruction of environmental conditions in the Taymyr Peninsula directly following the Early Weichselian deglaciation and shows that deep tectonic lake basins affected by several glaciations can preserve important palaeoenvironmental records, which contributes significantly to our understanding of palaeoenvironmental changes in the Taymyr Peninsula and the central Russian Arctic.  相似文献   

A Taylor basis for kinematic nonlinear real-time simulations. Part II: The Taylor basis     

Sebastian Andersen  Peter Noe Poulsen 《地震工程与结构动力学》2019,48(8):929-948

Real-time simulations are used to a significant extent in many engineering fields. However, if nonlinearities are included, the real-time requirement significantly limits the size and complexity of numerical models. The present work constitutes the second of two papers where a general basis method to simulate kinematic nonlinear structures more efficiently is introduced. The advantage of the basis formulation is that it enables the number of basis vectors to be increased without increasing the number of unknown basis co-ordinates. This allows for larger numerical kinematically nonlinear models to run in real time. The basis is organized from a Taylor series that includes the system mode shapes and their complete first-order modal derivatives derived in Part I. The Taylor series predicts fixed linear relations between the modal co-ordinates of the system mode shapes and the modal derivatives, respectively. Thus, the full solution is known solely by determining the modal co-ordinates of the mode shapes, which significantly minimizes the computational costs. Furthermore, it is illustrated that the stability of the Taylor basis formulation is dependent on the mode shape frequencies only, allowing the applied time steps to be significantly larger than in standard nonlinear basis analysis. An example illustrates a case where the computational time can be decreased by one order of magnitude using a Taylor basis formulation compared with a standard basis formulation including identical basis vectors.  相似文献