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61.
The transport of chemically reactive solutes (e.g. surfactants, CO2 or dissolved minerals) is of fundamental importance to a wide range of applications in oil and gas reservoirs such as enhanced
oil recovery and mineral scale formation. In this work, we investigate exponential time integrators, in conjunction with an
upwind weighted finite volume discretisation in space, for the efficient and accurate simulation of advection–dispersion processes
including non-linear chemical reactions in highly heterogeneous 3D oil reservoirs. We model sub-grid fluctuations in transport
velocities and uncertainty in the reaction term by writing the advection–dispersion–reaction equation as a stochastic partial
differential equation with multiplicative noise. The exponential integrators are based on the variation of constants solution
and solve the linear system exactly. While this is at the expense of computing the exponential of the stiff matrix representing
the finite volume discretisation, the use of real Léja point or the Krylov subspace technique to approximate the exponential
makes these methods competitive compared to standard finite difference-based time integrators. For the deterministic system,
we investigate two exponential time integrators, the second-order accurate exponential Euler midpoint (EEM) scheme and exponential
time differencing of order one (ETD1). All our numerical examples demonstrate that our methods can compete in terms of efficiency
and accuracy compared with standard first-order semi-implicit time integrators when solving (stochastic) partial differential
equations that model mixing and chemical reactions in 3D heterogeneous porous media. Our results suggest that exponential
time integrators such as the ETD1 and EEM schemes could be applied to typical 3D reservoir models comprising tens to hundreds
of thousands unknowns. 相似文献
62.
Claudio L. Rosenberg Sebastian Garcia 《International Journal of Earth Sciences》2012,101(5):1457-1464
63.
Xiangfang Zeng Zhongwen Zhan Yong Zheng Mengcheng National Geophysical Observatory School of Earth Space Sciences University of Science Technology of China China Seismological Laboratory California Institute of Technology Pasadena CA USA CAS Key Laboratory of Dynamical Geodesy 《地震学报(英文版)》2011,(2):143-150
Estimated Green’s function (EGF) between stations has been extracted from ambient seismic noise, direct surface wave and coda waves. It is also confirmed by laboratory experiments on ultrasonics and theoretical derivations assuming diffusive wave field, equi-partition of modes or random sources on an enclosed surface. This method provides a new approach to study the crust and mantle structure at regional scale, continental scale and global scale. Following the achievements with seismometer records, the reco... 相似文献
64.
Sebastian Sobek Roland Zurbrügg Ilia Ostrovsky 《Aquatic Sciences - Research Across Boundaries》2011,73(3):355-364
Even though lake sediments constitute a significant long-term carbon sink, studies on the regulation of carbon burial in lakes
sediments have, to date, been surprisingly few. We investigated to what degree the organic carbon (OC) being deposited onto
the bottom of Lake Kinneret (Israel) is buried in the sediment at four different sites with varying degrees of oxygenation
and varying supply of allochthonous particles from the River Jordan. For estimation of the OC burial efficiency (OC BE), i.e.,
the ratio between buried and deposited OC, we calculated OC burial from dated sediment cores, and calculated OC deposition
using three different approaches. Calculation of OC deposition from sediment trap-derived mass deposition rates multiplied
with the OC content of surface sediment yielded OC BE values that were at odds with published values for sediments dominated
by autochthonous OC sources. Calculation via sediment trap data on organic matter flux collected within the Lake Kinneret
monitoring program, as well as calculation of OC deposition as the sum of OC burial plus OC mineralization, returned fairly
congruent estimates of OC BE (range 10–41%), but only if the sediment trap data were corrected for the proportion of resuspended
particles in the traps. Differences in OC BE between sites were small, indicating that OC source (common to all sites) was
a more important regulator of OC BE in Lake Kinneret than oxygen exposure or mineral particles characteristics. 相似文献
65.
In the night from 8/9 April 2009, shortly after midnight on Maundy Thursday before Easter, several people in Gross Flottbek,
Hamburg, felt unusual strong ground shocks so that some of them left their houses in fear of earthquake shaking. Police and
fire brigade received phone calls of worried residents. A few days later, Internet pages were published where people reported
their observations. On 21 April 2009 at about 8 p.m. local time, a second ground-shaking event was felt. Damage to buildings
or infrastructure did not occur to our knowledge. The Institute of Geophysics, University of Hamburg, installed from 22 April
to 17 May 2009 three temporal seismic stations in the epicentral area. Seismological data from two nearby stations at the
Deutsches Elektronen-Synchrotron at 1 km and the Geophysical Institute at 7 km distance were collected and integrated to the
temporal network. The events occurred above the roof of the shallow Othmarschen Langenfelde salt diapir, in an area known
for active sinkhole formation and previous historic ground-shaking events. The analysis of the seismological data shows that
three shallow micro-earthquakes occurred from 8 to 21 April at a depth of about 100 m, the largest one with a moment magnitude
of about M
W 0.6. Depth location of such shallow events is difficult with standard methods and is here constrained by waveform modeling
of surface waves. Earthquakes occurring in soft sediments within the uppermost 100 m are a rare phenomena and cannot be explained
by standard models. Rupture process in soft sediments differs from those on faults in more competent rock. We discuss the
rupture and source mechanism of the events in the context of previous historic shocks and existing sinkhole and deformation
data. Although the event was weak, the rupture duration of 0.3 s was unusual long. Three possible models for the generation
of repeated ground-shaking events in Gross Flottbek are developed and discussed, implying quit different hazards for subsidence,
ground motion, and sinkhole formation. Our favored model postulates that roof failure occurs in an existing soil cavity beneath
the epicenter at a depth of about 100 m. Other models bearing a smaller geo-hazard cannot be disproved with the data available,
but future geophysical experiments may be planned to resolve this question. 相似文献
66.
G��nther J. Redhammer Anatoliy Senyshyn Martin Meven Georg Roth Sebastian Prinz Astrid Pachler Gerold Tippelt Clemens Pietzonka Werner Treutmann Markus Hoelzel Bj?rn Pedersen Georg Amthauer 《Physics and Chemistry of Minerals》2011,38(2):139-157
The compound NaFeGe2O6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe2O6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5?K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5?K and room temperature, while the GeO4 tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33?K, which marks the onset of low-dimensional magnetic ordering. Below 12?K NaFeGe2O6 transforms to an incommensurately modulated magnetic spin state, with k?=?[0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe2O6 with NaFeSi2O6 is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2??/c?? symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane. 相似文献
67.
68.
Mario Schirmer Frido Reinstorf Sebastian Leschik Andreas Musolff Ronald Krieg Gerhard Strauch John W. Molson Marion Martienssen Kristin Schirmer 《Environmental Earth Sciences》2011,64(3):607-617
Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany. 相似文献
69.
70.
Bartosz Czernecki Marek Półrolniczak Leszek Kolendowicz Michał Marosz Sebastian Kendzierski Natalia Pilguj 《Journal of Atmospheric Chemistry》2017,74(1):115-139
This study investigates atmospheric conditions’ influence on the mean and extreme characteristics of PM10 concentrations in Poznań during the period 2006–2013. A correlation analysis was carried out to identify the most important meteorological variables influencing the seasonal dynamics of PM10 concentrations. The highest absolute correlation values were obtained for planetary boundary layer height (r = ?0.57), thermal (daily minimum air temperature: r = ?0.51), anemological (average daily wind speed: r = ?0.37), and pluvial (precipitation occurrence: r = ?0.36) conditions, however the highest correlations were observed for temporal autocorrelations (1 day lag: r = 0.70). As regulated by law, extreme events were identified on the basis of daily threshold value i.e. 50 μg m?3. On average, annually there are approximately 71.3 days anywhere in the city when the threshold value is exceeded, 46.6 % of those occur in winter. Additionally, 83.7 % of these cases have been found to be continuous episodes of a few days, with the longest one persisting for 22 days. The analysis of the macro-scale circulation patterns led to the identification of an easy-to-perceive seasonal relations between atmospheric fields that favour the occurrence of high PM10 concentration, as well as synoptic situations contributing to the rapid air quality improvement. The highest PM10 concentrations are a clear reaction to a decrease in air temperature by over 3 °C, with simultaneous lowering of PBL height, mean wind speed (by around 1 m s?1) and changing dominant wind directions from western to eastern sectors. In most cases, such a situation is related to the expansion of a high pressure system over eastern Europe and weakening of the Icelandic Low. Usually, air quality conditions improve along with an intensification of westerlies associated with the occurrence of low pressure systems over western and central Europe. Opposite relations are distinguishable in summer, when air quality deterioration is related to the inflow of tropical air masses originating over the Sahara desert. 相似文献