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111.
A new MODFLOW package (Nonlinear Flow Process; NLFP) simulating nonlinear flow following the Forchheimer equation was developed and implemented in MODLFOW‐2005. The method is based on an iterative modification of the conductance calculated and used by MODFLOW to obtain an effective Forchheimer conductance. The package is compatible with the different layer types, boundary conditions, and solvers as well as the wetting capability of MODFLOW. The correct implementation is demonstrated using four different benchmark scenarios for which analytical solutions are available. A scenario considering transient flow in a more realistic setting and a larger model domain with a higher number of cells demonstrates that NLFP performs well under more complex conditions, although it converges moderately slower than the standard MODFLOW depending on the nonlinearity of flow. Thus, this new tool opens a field of opportunities to groundwater flow simulation with MODFLOW, especially for core sample simulation or vuggy karstified aquifers as well as for nonlinear flow in the vicinity of pumping wells. 相似文献
112.
The influence of leaf litter diversity and soil fauna on initial soil erosion in subtropical forests 总被引:4,自引:0,他引:4
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Steffen Seitz Philipp Goebes Pascale Zumstein Thorsten Assmann Peter Kühn Pascal A. Niklaus Andreas Schuldt Thomas Scholten 《地球表面变化过程与地形》2015,40(11):1439-1447
Although the protective role of leaf litter cover against soil erosion is known for a long time, little research has been conducted on the processes involved. Moreover, the impact of soil meso‐ and macrofauna within the litter layer on erosion control is not clear. To investigate how leaf litter cover and diversity as well as meso‐ and macrofauna influence sediment discharge in subtropical forest ecosystems, a field experiment has been carried out in Southeast China. A full‐factorial random design with 96 micro‐scale runoff plots and 7 domestic leaf species was established and erosion was triggered by a rainfall simulator. Our results demonstrate that leaf litter cover protects soil from erosion (?82 % sediment discharge on leaf covered plots) by rainfall and this protection is removed as litter decomposes. The protective effect is influenced by the presence or absence of soil meso‐ and macrofauna. Fauna presence increases soil erosion rates significantly by 58 %, while leaf species diversity shows a non‐significant negative trend. We assume that the faunal effect arises from arthropods slackening and processing the soil surface as well as fragmenting and decomposing the protecting leaf litter covers. Even though the diversity level did not show a significant influence, single leaf species in monocultures show rather different impacts on sediment discharge and thus, erosion control. In our experiment, runoff plots with leaf litter from Machilus thunbergii showed the highest sediment discharge (68.0 g m?2) whereas plots with Cyclobalanopsis glauca showed the smallest rates (7.9 g m?2). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
113.
Comparison of Phytoscreening and Direct‐Push‐Based Site Investigation at a Rural Megasite Contaminated with Chlorinated Ethenes
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Arno Rein Olaf Holm Stefan Trapp Steffen Popp‐Hofmann Martin Bittens Carsten Leven Peter Dietrich 《Ground Water Monitoring & Remediation》2015,35(4):45-56
The reliable characterization of subsurface contamination of spatially extended contaminated sites is a challenging task, especially with an unknown history of land use. Conventional technologies often fail due to temporal and financial constraints and thus hinder the redevelopment of abandoned areas in particular. Here we compare two site screening techniques that can be applied quickly at relatively low cost, namely Direct Push (DP)‐based groundwater sampling and tree core sampling. The effectiveness of both methods is compared for a rural megasite contaminated with chlorinated hydrocarbons. Unexpected pollution hot spots could be identified using both of these methods, while tree coring even enabled the delineation of the contaminant plume flowing into an adjacent wetland inaccessible for DP units. Both methods showed a good agreement in revealing the spatial pattern of the contamination. The correlation between groundwater concentrations and equivalent concentrations in wood was linear and highly significant for trichloroethene. Correlation was less obvious for its metabolite cis‐dichloroethene, but still significant. As outcome of our study we recommend tree coring and for initial screening in combination with a DP sampling to retrieve quantitative data on groundwater pollutants in order to assess the contamination situation of a non‐ or only partly investigated site. The subsequent placement of monitoring wells for long‐term monitoring of contamination levels is recommended. A combination of methods would achieve more relevant information at comparable or possibly even lower efforts in comparison to a conventional site investigation. 相似文献
114.
A multi-technique approach for characterizing the SVN49 signal anomaly, part 2: chip shape analysis 总被引:2,自引:1,他引:1
Steffen Thoelert Michael Meurer Stefan Erker Oliver Montenbruck André Hauschild Pat Fenton 《GPS Solutions》2012,16(1):29-39
Due to a satellite internal reflection at the L5 test payload, the SVN49 (PRN1) GPS satellite exhibits a static multipath
on the L1 and L2 signals, which results in elevation-dependent tracking errors for terrestrial receivers. Using a 30-m high-gain
antenna, code and carrier phase measurements as well as raw in-phase and quadrature radio frequency samples have been collected
during a series of zenith passes in mid-April 2010 to characterize the SVN49 multipath and its impact on common users. Following
an analysis of the receiver tracking data and the IQ constellation provided in Part 1 of this study, the present Part 2 provides
an in-depth investigation into chip shapes for the L1 and L2 signals. A single reflection model is found to be compatible
with the observed chip shape distortions and key parameters for an elevation dependent multipath model are derived. A good
agreement is found between multipath parameters derived independently from raw IQ-samples and measurements of a so-called
Vision Correlator. The chip shapes and their observed variation with elevation can be used to predict the multipath response
of different correlator types within a tracking receiver. The multipath model itself is suitable for implementation in a signal
simulator and thus enables laboratory testing of actual receiver hardware. 相似文献
115.
A multi-technique approach for characterizing the SVN49 signal anomaly, part 1: receiver tracking and IQ constellation 总被引:3,自引:1,他引:2
André Hauschild Oliver Montenbruck Steffen Thoelert Stefan Erker Michael Meurer Javad Ashjaee 《GPS Solutions》2012,16(1):19-28
A characterization of the signal anomaly of SVN49 is presented. A mathematical model is developed to relate the observed multipath
to the internal signal reflection. The analyses provided are based on measurements, which have been collected during a dedicated
tracking campaign with a 30-m dish antenna. Data on the L1 and L2 frequency have been collected with four different receivers.
In addition, IQ samples have been recorded directly with a spectrum analyzer. The multipath combination of the receiver measurements
on L1 and L2 is analyzed to demonstrate the effect of the signal reflections on different correlator spacing. The capability
to suppress the signal reflection with receiver multipath mitigation methods is demonstrated. Finally, preliminary estimates
of the attenuation, delay, and phase shift over elevation are obtained from an IQ sample analysis. 相似文献
116.
William Perrie Zhenxia Long Hayley Hung Amanda Cole Alexandra Steffen Ashu Dastoor Dorothy Durnford Jianmin Ma Jan W. Bottenheim Stoyka Netcheva Ralf Staebler James R. Drummond N. T. O’Neill 《Climatic change》2012,115(1):35-58
This paper summarizes the main elements of four IPY projects that examine the Arctic Atmosphere. All four projects focus on present conditions with a view to anticipating possible climate change. All four investigate the Arctic atmosphere, ocean, ice, and land interfacial surfaces. One project uses computer models to simulate the dynamics of the Arctic atmosphere, storms, and their interactions with the ocean and ice interface. Another project uses statistical methods to infer transports of pollutants as simulated in large-scale global atmospheric and oceanic models verifying results with available observations. A third project focuses on measurements of pollutants at the ice-ocean?Catmosphere interface, with reference to model estimates. The fourth project is concerned with multiple, high accuracy measurements at Eureka in the Canadian Archipelago. While these projects are distinctly different, led by different teams and interdisciplinary collaborators, with different technical approaches and methodologies, and differing objectives, they all strive to understand the processes of the Arctic atmosphere and climate, and to lay the basis for projections of future changes. Key findings include: ? Decreased sea ice leads to more intense storms, higher winds, reduced surface albedo, increased surface air temperature, and enhanced vertical mixing in the upper ocean. ? Arctic warming may affect toxic chemicals by remobilizing persistent organic pollutants and augmenting mercury deposition/retention in the environment. ? Changes in sea ice can dramatically change processes in and at the ice surface related to ozone, mercury and bromine oxide and related chemical/physical properties. ? Structure and properties of the Arctic atmospheric??troposphere to stratosphere??and tracking of transport of pollution and smoke plumes from mid-latitudes to the poles. 相似文献
117.
Hauke Marquardt Steffen Ganschow Frank R. Schilling 《Physics and Chemistry of Minerals》2009,36(2):107-118
Knowledge of heat transport properties as a function of mineral- and rock-composition and temperature is of major relevance
to understand and model heat transfer in the Earth’s interior. A systematic study on 13 natural and 4 synthetic garnets was
carried out in an attempt to obtain a better systematic understanding of the processes that affect the heat transport in minerals,
especially the effect of chemical substitution in solid solution series. It is found that substitution significantly lowers
the thermal diffusivity from end-member values for both synthetic and natural garnets with a minimum of thermal diffusivity
at an intermediate composition. The thermal diffusivity as a function of the degree of substitution can be described by the
approach of Padture and Klemens (J Am Ceram Soc 80 (4):1018–1020, 1997). With increasing temperature the thermal diffusivity decreases due to phonon-phonon-scattering effects. A quantitative analysis
of the high-temperature behaviour was carried out by using the model of Roufosse and Klemens (J Geophys Res 79 (5):703–705,
1974), which takes a lower limit of thermal diffusivity at elevated temperatures into account. The model allows for an extrapolation
of the deduced room temperature thermal diffusivities to higher temperatures. Furthermore, the model was modified to determine
the high temperature limit of the thermal diffusivity for all investigated natural garnets D
min to be 0.64 ± 0.03 mm2/s. 相似文献
118.
Steffen Kiel 《地学学报》2009,21(4):279-284
The anaerobic oxidation of methane (AOM) in marine sediments, most obviously at cold seeps, is a major sink for this important greenhouse gas and is associated with the precipitation of carbonates. The geological record of seep carbonates provides insights into the long-term dynamics of this process. Since the Late Jurassic, rates of seep-carbonate precipitation have been high during times of low sea levels and cold deep-water temperatures, and vice versa. One possibility is that sea-level fall decreases the thickness of the methane hydrate stability zone in the sediment so that gas hydrates decompose in deeper sediments, thereby increasing seepage and carbonate precipitation. Alternatively, low deep-water temperature facilitates gas hydrate formation on continental slopes and may thereby increase methane availability for AOM-performing consortia and associated carbonate precipitation. These correlations and their potential causes may be of interest for the modelling of global carbon budgets and of past and future climates. 相似文献
119.
Matthias Braun Jefferson Cardia Sim“非汉字符号”es N.Blindow Steffen Vogt U.F.Bremer M.Pfender H.Saurer F.E.Aquino F.A.Ferron 《地球空间信息科学学报》2001,4(2):47-51
1 IntroductionAtpresent,KingGeorgeIsland (KGI)isoneofthemostfrequentedsitesinAntarctica .Intotal,9permanentresearchstationsareinoperationandseveralresearchcabinshavebeenconstructed .DuetotheeasyaccessviatheChileanairstripthenum beroftheisland’sinhabitantsr… 相似文献
120.
Richard M. Vielreicher Noreen M. Vielreicher Steffen G. Hagemann Greg Jones 《Mineralium Deposita》2002,38(5):538-554
The Jian Cha Ling gold deposit is sited in folded and faulted Palaeoproterozoic rocks of the uplifted Mian-Lue-Yang block, adjacent to the Mianlue suture zone within the West Qinling mineral province, along the northern margin of the South China craton. Early Mesozoic gold mineralization at Jian Cha Ling, which has a pre-mined resource of about 536,000 oz Au, is controlled by the so-called F 1 45 fault. The fault is a generally steeply N-dipping, WNW-trending deformation zone that is the result of dislocation along bedding planes, early foliation and axial planar surfaces of regional folds. The fault zone marks the contact between serpentinized, lower greenschist-facies dunites, harzburgites and minor gabbroic units in the footwall, and a metasedimentary sequence in the hanging wall that is dominated by metadolomite, metalimestone and phyllitic schists. Brittle–ductile deformation, partitioning of strain along pre-existing zones of weakness, and the formation of intrashear zone lozenges contributed to the development of a complex fault zone geometry. Variations in both dip and strike of discrete dislocation surfaces related to oblique, sinistral–reverse movement along the F 1 45 fault zone focussed auriferous hydrothermal fluids along three dominant structural orientations. Gold was preferentially deposited along shallowly NNE-dipping and shallowly to moderately NNW-dipping fault segments, and is also associated with shallowly WSW-dipping, dolomite-dominated vein sets. Disseminated, economic gold grades (>4 g/t Au) are restricted to the footwall ultramafic rocks to within about 5 to 10 m of the contact with the hanging wall. Gold is related to laminated, realgar- and orpiment- bearing sheeted veins and hydrothermal breccias, as well as slickolites and fault gouge. Gold-bearing vein sets are located within the relatively undeformed, ultramafic intrashear zone lozenges. Gold-related alteration is dominated by extremely fine-grained, arsenic-bearing sulphide minerals and dolomite, with additional white mica and clay minerals. The structural setting of the deposit, combined with published data on the geological evolution of the West Qinling mineral province, suggest that the Jian Cha Ling gold deposit developed in an uplifted basement block during the final phases of northward subduction and suturing of the South China craton with the South Qinling orogen along the Mianlue Suture Zone, during the changeover from a compressional to transpressional tectonic regime in Late Triassic to Middle Jurassic times. 相似文献