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排序方式: 共有852条查询结果,搜索用时 15 毫秒
161.
Journal of Atmospheric Chemistry - In this study, the aerosol removal coefficients based on 7Be, 210Pb and 210Po radionuclides in the urban air, in Lodz, Poland, were investigated over 3 years,... 相似文献
162.
Boundary-Layer Meteorology - The Obukhov length, although often adopted as a characteristic scale of the atmospheric boundary layer, has been introduced purely based on a dimensional argument... 相似文献
163.
The environmental conditions of the Szczecin Bay, which existed prior to Szczecin Lagoon, have been reconstructed on the basis of the stable carbon and oxygen isotope (18O and 13C) analysis and radiocarbon dates obtained for subfossil shells of Cerastoderma (Cardium) glaucum. The shells in the collected core were well preserved in their life positions, representing a geochemical record of past temperature variation over the middle Holocene. Three major periods with different thermal conditions have been distinguished in the interval ~ 6000–4300 cal yr BP, when the important Littorina regional transgression took place. During the first period, 6000–5250 cal yr BP, water temperature decreased by 1.4°C, and then remained constant over the second period (5250–4750 cal yr BP). In contrast, during the third period (4750–4300 cal yr BP) both δ-values were highly variable and the mean summer temperature (March–November) increased by about 3.5°C. During first two periods, δ18O and δ13C were significantly correlated, indicating stability of the environmental conditions. 相似文献
164.
Juan Carlos Carracedo Francisco Pérez Torrado Alejandro Rodríguez González Vicente Soler José Luis Fernández Turiel Valentin R. Troll Sebastian Wiesmaier 《Geology Today》2012,28(2):53-58
Forty years after the Teneguía Volcano (La Palma, 1971), a submarine eruption took place off the town of La Restinga, south of El Hierro, the smallest and youngest island of the Canarian Archipelago. Precursors allowed an early detection of the event and its approximate location, suggesting it was submarine. Uncertainties derived from insufficient scientific information available to the authorities during the eruption, leading to disproportionate civil protection measures, which had an impact on the island's economy—based primarily on tourism—while residents experienced extra fear and distress. 相似文献
165.
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
166.
Claudio L. Rosenberg Sebastian Garcia 《International Journal of Earth Sciences》2012,101(5):1457-1464
167.
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
168.
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
169.
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
170.
Ryszard Kryza Jolanta Muszer Joanna Haydukiewicz Czesław August Marta Jurasik Nickolay Rodionov 《International Journal of Earth Sciences》2011,100(6):1227-1235
A Lower Carboniferous platform sedimentary sequence (the Paprotnia Beds) in the Bardo Unit of the central Sudetes (NE part
of the Bohemian Massif, SW Poland) is biostratigraphically well dated, based on rich macro- and micro-fossil evidence, as
Late Viséan (late Asbian, crenistria, Go III α zone). The beds contain several bentonite layers, one of which was dated using the U–Pb SHRIMP method on volcanic
zircons and yielded an age of 334 ± 3 Ma. This date fits well to the recently established chronostratigraphic limits of the
Viséan, and is consistent with the newest isotopic age constraints of 336.5–332 Ma for the Asbian boundaries. 相似文献