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541.
First-principles molecular dynamics simulations of complex material systems such as geophysically relevant oxide and silicate
liquids produce massive amounts of time-varying three-dimensional data for the atomic configurations. Given the high accuracy
of these data, it is desirable to extract as much information hidden in the data as possible. In this paper, we elaborate
on our recently proposed scheme to support interactive visualization at space–time multiresolution of the atomistic simulation
data. Instead of just focusing on direct rendering of the given data, additional data (containing more quantitative and qualitative
information) that usually have to be extracted by some other means are extracted and rendered on the fly. This allows us to
gain better insight into the global as well as local spatio-temporal behavior of the data in the context of bonding, radial
distribution, atomic coordination, clustering, structural stability and distortion, and diffusion. We illustrate such visualization
for the simulation data on the liquid phases of MgO and MgSiO3—the two most abundant components of Earth’s mantle. Our analysis shows that the structure and dynamics of both liquids change
substantially with compression, with no discernible effects of temperature in most cases. 相似文献
542.
Manuel Helbig Julia Boike Moritz Langer Peter Schreiber Benjamin R. K. Runkle Lars Kutzbach 《Hydrogeology Journal》2013,21(1):133-147
The summer water balance of a typical Siberian polygonal tundra catchment is investigated in order to identify the spatial and temporal dynamics of its main hydrological processes. The results show that, besides precipitation and evapotranspiration, lateral flow considerably influences the site-specific hydrological conditions. The prominent microtopography of the polygonal tundra strongly controls lateral flow and storage behaviour of the investigated catchment. Intact rims of low-centred polygons build hydrological barriers, which release storage water later in summer than polygons with degraded rims and troughs above degraded ice wedges. The barrier function of rims is strongly controlled by soil thaw, which opens new subsurface flow paths and increases subsurface hydrological connectivity. Therefore, soil thaw dynamics determine the magnitude and timing of subsurface outflow and the redistribution of storage within the catchment. Hydraulic conductivities in the elevated polygonal rims sharply decrease with the transition from organic to mineral layers. This interface causes a rapid shallow subsurface drainage of rainwater towards the depressed polygon centres and troughs. The re-release of storage water from the centres through deeper and less conductive layers helps maintain a high water table in the surface drainage network of troughs throughout the summer. 相似文献
543.
The multiple scales of landscape topography produce a wide distribution of groundwater circulation cells that control the
hydro-geological environments surrounding geological repositories for nuclear waste. The largest circulation cells tend to
discharge water into major river reaches, large freshwater systems or the nearby Baltic Sea. We investigated numerically the
release of radionuclides from repositories placed in bedrock with depths between 100 to 2000 meters in a Swedish coastal area
and found that leakage from the deeper positions emerges primarily in the major aquatic systems. In effect, radionuclides
from the deeper repositories are more rapidly transported towards the Sea by the stream system compared to leakage from more
shallow repositories. The release from the shallower repositories is significantly retained in the initial stage of the transport
in the (superficial) landscape because the discharge occurs in or near low-order streams with high retention characteristics.
This retention and residence time for radioactivity in the landscape control radiological doses to biota and can, thus, be
expected to constitute an essential part of an associated risk evaluation. 相似文献
544.
This paper reports on the Middlesboro impact structure (36°37′03″ N; 83°43′39″ W), a complex impact structure located in the Appalachian foreland fold-and-thrust belt of southeast Kentucky, USA. The structure forms a basin approximately 5.5 km in diameter exposing intensely deformed Pennsylvanian sediments. Based on field data, microstructural observation, and geophysical analyses we qualitatively assess degree and distribution of fragmentation of target rocks within the impact structure. Shock deformation features, especially feather features, are reported for the impact structure. Shallow seismic refraction data were acquired along a radial profile from outside the impact structure to the center of the structure. Seismic (P-wave) velocity trends indicate that fracture intensity increases toward the center, reducing the overall seismic velocity. However, intense rock sealing in some parts of the central uplift increases the strength of rock samples and locally increases seismic velocities. We present a modified geologic map of the Middlesboro impact structure based on high-resolution lineament analysis, field work, and reevaluation of existing structural data from geologic maps. The modified map suggests that crater circularity at Middlesboro is skewed by the reactivation of pre-existing zones of structural anisotropy in the target. We propose that due to an oblique impact from northerly direction the sub-horizontal Pine Mountain thrust plane beneath the impact structure became reactivated with a top-to-the south shear component. The impact-induced formation/reactivation of the Doublings Fault Zone as a thrust ramp appears to have deflected the otherwise straight strike of the Cumberland Mountains southward. The Rocky Face fault approaches the crater rim fault, and we propose that this sinistral strike-slip fault was formed, or at least reactivated, by the impact and accommodated the oblique impact's horizontal momentum. 相似文献
545.
The dissimilarity of temperature and humidity transfer in the marine surface layer (MSL) is investigated through the relative transport efficiency and correlation coefficient of these two scalars. We examine their variability and relationship with mean values, as well as spectral characteristics. It is shown that the dissimilarity between these two scalars in the MSL is a function of stability, the boundary-layer depth, and flow steadiness. In general the temperature and humidity are less correlated in shallow marine boundary layers compared to deep marine boundary layers, due to the stronger impact of the boundary-layer scale in breaking the “same source, same sink” assumption for scalar similarity. This is supported by the combination of our spectral analysis of scalar fluxes and corresponding measured and modelled boundary-layer depth. This assumption is also broken in near-neutral conditions, when there is an efficient latent heat transfer but negligible sensible heat transfer. Our data suggest that parametrization of humidity fluxes via similarity theory could still be reliable when the correlation coefficient $>$ 0.5, and in near-neutral conditions the humidity flux can be estimated without use of the sensible heat flux. 相似文献
546.
Stephen K. Donovan David A. T. Harper Zhan Renbin Lars Stemmerik Liu Jianbo Svend Stouge 《Geological Journal》2012,47(6):653-660
A collection of numerous crinoid pluricolumnals from the uppermost Darriwilian (Middle Ordovician) of Tibet were derived from one biological species of crinoid. The specimens were collected from well‐lithified, bioclastic shelf limestones of the upper part of the Lower Chiatsun Group, Pygodus serra Biozone; coeval rocks of similar lithology outcrop at the summit of Everest. A new crinoid morphospecies, Segmentocolumnus (col.) hanshessi, is tentatively considered a ‘stem‐group cladid’, perhaps a dendrocrinid. The proxistele is broad and pentagonal in section with a broad, pentagonal axial canal; the mesistele of similar gross morphology is more slender with a regularly heteromorphic column and a similarly wide axial canal; the dististele is a terminal dendritic radice with a pentastellate axial canal. In the mesistele, the meric sutures correspond to the centres of the sides of the column, but in the dististele they occur in the angles. This range of morphologies would have led to their inclusion in at least two morphogenera if they had not been closely associated; as they belong to a single biological species, they have been ‘lumped’ together herein. This is a rare contribution to our knowledge of the early crinoids from a region outside Europe and North America. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
547.
Groundwater deterioration in Nankou—a suburban area of Beijing: data assessment and remediation scenarios 总被引:4,自引:4,他引:0
Feng Sun Haibing Shao Wenqing Wang Norihiro Watanabe Lars Bilke Zhongshan Yang Zhenfang Huang Olaf Kolditz 《Environmental Earth Sciences》2012,67(6):1573-1586
Since the 1980s, high-nitrate concentration in one of the groundwater sampling wells at the Nankou site, northwest of the Beijing Plain, has become a major concern for the local water authority. In a previous study (Sun et?al. in Environ Earth Sci 64(5):1323?C1333, 2011), a hydrogeological structural model was developed based on the borehole logs of this area and the steady, as well as transient groundwater-flow models, were calibrated using the measured hydraulic heads. In this paper, the potential pollution sources in this area are investigated. The chemical analysis of the groundwater is also presented. The results demonstrate that the most likely pollution source is the untreated wastewater discharge from a nearby fertilizer factory. Furthermore, a mass transport model is developed to reproduce the nitrate transport process in the aquifer at the Nankou site under different pollution sources, i.e., a fertilizer factory, river with wastewater and an agriculture field. The combined effects of the river and agriculture fields present a better understanding of the nitrate transport in the local aquifer. In addition, a pumping scenario is designed to clean up the current nitrate concentration. The pumping rate and the well location are first estimated with 2-D analytical solutions of the type curves method. Then a 3-D numerical model is used to calculate the nitrate-concentration changes after the pumping activities start. In the downstream direction of the regional groundwater flow, three pumping wells are set up for the clean-up strategy. The calculated pumping rate in each well is about 1,500 m3/day. After 1?year, the nitrate concentration in the observation well recedes to 68?mg/l from the initial value of 72.9?mg/l, and it will be lower than the limitation value (20?mg/l) after 5,400 days of groundwater extraction. The data assessment and clean-up scenarios reported in this paper are fundamental for the contaminated aquifer management in the future. 相似文献
548.
Torbjörn Sundberg Scott A. Boardsen James A. Slavin Lars G. Blomberg Judy A. Cumnock Sean C. Solomon Brian J. Anderson Haje Korth 《Planetary and Space Science》2011,59(15):2051-2057
A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin–Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath. 相似文献
549.
Amy M. GAFFNEY Lars E. BORG Yemane ASMEROM Charles K. SHEARER Paul V. BURGER 《Meteoritics & planetary science》2011,46(1):35-52
Abstract– To better determine the effects of impact‐related processes on radiometric chronometers in meteorites, we undertook an isotopic study of experimentally shocked and heated samples of lunar basalt 10017. Shock experiments at 55 GPa were completed on one subsample, and a second subsample was heated in an evacuated quartz tube at 1000 °C for 170 h. A third subsample was maintained as a control. Samarium‐neodymium, Rb‐Sr, 238U‐206Pb, and 206Pb‐207Pb isotopic analyses were completed on mineral fractions (leached and unleached), leached whole rocks, and complementary acid leachates. Disturbance in the shocked and heated samples was evaluated through comparison of their isochron diagrams with those of the control sample. The Sm‐Nd isotope system was the least disturbed, the Rb‐Sr isotope system was more disturbed, and the 238U‐206Pb and 206Pb‐207Pb isotope systems were the most disturbed by shock and annealing. Samples that experienced extended heating demonstrated greater isotopic disturbances than shocked samples. In some cases, the true crystallization age was preserved, and in others, age information was degraded or destroyed. In no case did the experiments generate isochrons that maintained linearity while being rotated or completely reset. Although our results show that neither experimental shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in some Martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible than its unshocked counterpart to subsequent disturbance during extended impact‐related heating or aqueous alteration. The combination of these processes may result in the disparate chronometric information preserved in some meteorites. 相似文献