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排序方式: 共有175条查询结果,搜索用时 31 毫秒
111.
Thermal tracer testing in a sedimentary aquifer: field experiment (Lauswiesen,Germany) and numerical simulation 总被引:1,自引:0,他引:1
Valentin Wagner Tao Li Peter Bayer Carsten Leven Peter Dietrich Philipp Blum 《Hydrogeology Journal》2014,22(1):175-187
An active and short-duration thermal tracer test (TTT) was conducted in a shallow sedimentary aquifer at the Lauswiesen test site, near Tübingen, Germany. By injecting 16 m3 of warm water at 22°C, a thermal anomaly was created, which propagated along the local groundwater flow direction. This was comprehensively monitored in five observation wells at a few meters distance. The purpose of this well-controlled experiment was to determine the practicability of such a TTT and its suitability to examine hydraulic characteristics of heterogeneous aquifers. The results showed that the thermal peak arrival times in the observation wells were consistent with previous observations from alternative field testing such as direct-push injection logging (DPIL). Combined analysis of depth-dependent temperatures and peak arrival times, and comparison with a numerical heat transport model, offers valuable insights into the natural flow field and spatial distribution of hydraulic conductivities. The study was able to identify vertical flow focusing and bypassing, which are attributed to preferential flow paths common in such sedimentary sand and gravel aquifers. These findings are fundamental for further development of experimental designs of active and short-duration TTTs and provide a basis for a more quantitative analysis of advective and conductive transport processes. 相似文献
112.
Uta Sauer Claudia Schütze Carsten Leven Stefan Schlömer Peter Dietrich 《Acta Geotechnica》2014,9(1):127-133
This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for naturally occurring CO2 deposits (analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects. 相似文献
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115.
Brett J. Gladman Donald R. Davis Robert Jedicke J.J. Kavelaars Hans Scholl Ben Warrington Pasquale Tricarico 《Icarus》2009,202(1):104-118
For absolute magnitudes greater than the current completeness limit of H-magnitude ∼15 the main asteroid belt's size distribution is imperfectly known. We have acquired good-quality orbital and absolute H-magnitude determinations for a sample of small main-belt asteroids in order to study the orbital and size distribution beyond H=15, down to sub-kilometer sizes (H>18). Based on six observing nights over a 11-night baseline we have detected, measured photometry for, and linked observations of 1087 asteroids which have one-week time baselines or more. The linkages allow the computation of full heliocentric orbits (as opposed to statistical distances determined by some past surveys). Judged by known asteroids in the field the typical uncertainty in the (a/e/i) orbital elements is less than 0.03 AU/0.03/0.5°. The distances to the objects are sufficiently well known that photometric uncertainties (of 0.3 magnitudes or better) dominate the error budget of their derived H-magnitudes. The detected asteroids range from HR=12-22 and provide a set of objects down to sizes below 1 km in diameter. We find an on-sky surface density of 210 asteroids per square degree in the ecliptic with opposition magnitudes brighter than mR=23, with the cumulative number of asteroids increasing by a factor of 100.27/mag from mR=18 down to the mR?23.5 limit of our survey. In terms of absolute H magnitudes, we find that beyond H=15 the belt exhibits a constant power-law slope with the number increasing proportional to 100.30H from H?15 to 18, after which incompleteness begins in the survey. Examining only the subset of detections inside 2.5 AU, we find weak evidence for a mildly shallower slope for H=15-19.5. We provide the information necessary such that anyone wishing to model the main asteroid belt can compare a detailed model to our detected sample. 相似文献
116.
We applied a Monte Carlo method-simulated annealing algorithm-to carry out the design of multilayer achromatic waveplate. We present solutions for three-, six-and ten-layer achromatic waveplates. The optimized retardance settings are found to be 89°51'39"±0°33'37" and 89°54'46"±0°22'4" for the six-and ten-layer waveplates, respectively, for a wavelength range from 1000nm to 1800nm. The polarimetric properties of multilayer waveplates are investigated based on several numerical experiments. In contrast to previously proposed three-layer achromatic waveplate, the fast axes of the new six-and ten-layer achromatic waveplate remain at fixed angles, independent of the wavelength. Two applications of multilayer achromatic waveplate are discussed, the general-purpose phase shifter and the birefringent filter in the Infrared Imaging Magnetograph (IRIM) system of the Big Bear Solar Observatory (BBSO). We also checked an experimental method to measure the retardance of waveplates. 相似文献
117.
Kathrin?FassmerEmail author Iwona?Klonowska Katarzyna?Walczak Barbro?Andersson Nikolaus?Froitzheim Jaros?aw?Majka Raúl?O.?C.?Fonseca Carsten?Münker Marian?Janák Martin?Whitehouse 《Contributions to Mineralogy and Petrology》2017,172(11-12):103
The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430–400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between ~ 505 and ~ 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet–phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25–27 kbar/680–760 °C for the garnet–phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25–26 kbar/650–700 °C). Metamorphic rims of zircons from the garnet–phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu–Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm–Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction–exhumation cycle. 相似文献
118.
J. Elis Hoffmann Carsten Münker Ali Polat Klaus Mezger Minik T. Rosing 《Geochimica et cosmochimica acta》2010,74(24):7236-6628
Growing evidence from the accessible geological record reveals that crust-mantle differentiation on Earth started as early as 4.4 Ga. In order to assess the extent of early Archean mantle depletion, we obtained 176Lu-176Hf, 147Sm-143Nd, and high field strength element (HFSE) concentration data for the least altered, well characterized boninite-like metabasalts and associated metasedimentary rocks from the Isua supracrustal belt (southern West Greenland). The metasediments exhibit initial εHf(3720) values from −0.7 to +1.5 and initial εNd(3720) values from +1.6 to +2.1. Initial εHf(3720) values of the least altered boninite-like metabasalts span a range from +3.5 to +12.9 and initial εNd(3720) values from −0.3 to +3.2. These initial Hf-isotope ratios display coherent trends with SiO2, Al2O3/TiO2 and other relatively immobile elements, indicating contamination via assimilation of enriched components, most likely sediments derived from the earliest crust in the region. This model is also consistent with previously reported initial γOs(3720) values for some of the samples. In addition to the positive εHf(3720) values, the least disturbed samples exhibit positive εNd(3720) values and a co-variation of εHf(3720) and εΝd(3720) values. Based on these observations, it is argued, that the most depleted samples with initial εHf(3720) values of up to +12.9 and high 176Lu/177Hf of ∼0.05 to ∼0.09 tap a highly depleted mantle source with a long term depletion history in the garnet stability field. High precision high field strength element (HFSE) data obtained for the Isua samples confirm the contamination trend. Even the most primitive samples display negative Nb-Ta anomalies and elevated Nb/Ta, indicating a subduction zone setting and overprint of the depleted mantle sources by felsic melts generated by partial melting of eclogite. Collectively, the data for boninite-like metabasalts support the presence of strongly depleted mantle reservoirs as previously inferred from Hf isotope data for Hadean zircons and combined 142Nd-143Nd isotope data for early Archean rocks. 相似文献
119.
Peter Sprung Stephan Schuth Carsten Münker Leonore Hoke 《Contributions to Mineralogy and Petrology》2007,153(6):669-687
The geologic evolution of the New Zealand microcontinent was characterised by intermittent Cretaceous to Quaternary episodes
of intraplate volcanism. To evaluate the corresponding mantle evolution beneath New Zealand with a specific focus on the tectonic
evolution, we performed a combined major and trace element and Hf, Nd, Pb, Sr isotope investigation on a suite of representative
intraplate volcanic rocks from both main islands and the Chatham Islands. Isotopically, the data set covers a range between
“HIMU-like” end member compositions (206Pb/204Pb: 20.57, 207Pb/204Pb: 15.77, 87Sr/86Sr: 0.7030, εHf: + 3.8, εNd: + 4.2), compositions tending towards MORB (206Pb/204Pb: 19.01, 207Pb/204Pb: 15.62, 87Sr/86Sr: 0.7028, εHf: + 9.9, εNd: + 7.0) and compositions reflecting the influence of subducted sediments (206Pb/204Pb: 18.99, 207Pb/204Pb: 15.67, 87Sr/86Sr: 0.7037, εHf: + 4.4, εNd: + 3.9). Whereas volcanism on the Chatham Islands constitutes the HIMU end member of our data
set, intraplate volcanic rocks from the North Island are dominated by MORB-like compositions with relatively radiogenic 206Pb/204Pb signatures. Volcanic rocks from the South Island form a trend between the three end members. Assuming a polybaric melting
column model, the primary melt compositions reflect variations in the degree of melting, coupled to variable average melting
depths. As the three isotope and trace element end members occur throughout the volcanic episodes, the “HIMU-like” and the
sediment influenced signatures most likely originate from a heterogeneous subcontinental lithospheric mantle, whereas an asthenospheric
origin is inferred for the MORB-like component. For the South Island, affinities to HIMU wane with decreasing average melting
depths whereas MORB and sediment-like signatures become more distinct. We therefore propose a polybaric melting model involving
upper asthenospheric mantle and a lithospheric mantle source that has been modified by subduction components and veins of
fossil “HIMU-like” asthenospheric melts. The proportion of asthenospheric versus lithospheric source components is controlled
by variations in lithospheric thickness and heat flow, reflecting the different tectonic settings and rates of extension.
Generally, low degree melts preferentially tap enriched vein material with HIMU signatures. The widespread occurrence of old
Gondwana-derived lithospheric mantle beneath intraplate volcanic fields in East Gondwana is suggested by overall similarities
between New Zealand intraplate volcanic rocks and volcanic rocks in East Australia and Antarctica. The petrogenetic model
proposed here may therefore serve as a general model for the petrogenesis of Cretaceous to Recent intraplate volcanic rocks
in former East Gondwana.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
120.
A study has been made, using the National Centers for Environmental Prediction and National Center for Atmospheric Research
re-analysis 500 hPa geopotential height data, to determine how intraseasonal variability influences, or can generate, coherent
patterns of interannual variability in the extratropical summer and winter Southern Hemisphere atmospheric circulation. In
addition, by separating this intraseasonal component of interannual variability, we also consider how slowly varying external
forcings and slowly varying (interannual and longer) internal dynamics might influence the interannual variability of the
Southern Hemisphere circulation. This slow component of interannual variation is more likely to be potentially predictable.
How sea surface temperatures are related to the slow components is also considered. The four dominant intraseasonal modes
of interannual variability have horizontal structures similar to those seen in both well-known intraseasonal dynamical modes
and statistical modes of intraseasonal variability. In particular, they reflect intraseasonal variability in the high latitudes
associated with the Southern Annular Mode, and wavenumber 4 (summer) and wavenumber 3 (winter) patterns associated with south
Pacific regions of persistent anomalies and blocking, and possibly variability related to the Madden-Julian Oscillation (MJO).
The four dominant slow components of interannual variability, in both seasons, are related to high latitude variability associated
with the Southern Annular Mode, El Nino Southern Oscillation (ENSO) variability, and South Pacific Wave variability associated
with Indian Ocean SSTs. In both seasons, there are strong linear trends in the first slow mode of high latitude variability
and these are shown to be related to similar trends in the Indian Ocean. Once these are taken into account there is no significant
sea surface temperature forcing of these high latitude modes. The second and third ENSO related slow modes, in each season,
have high correlations with tropical sea surface temperature variability in the Pacific and Indian Oceans, both contemporaneously
and at one season lag. The fourth slow mode has a characteristic South Pacific wave structure of either a wavenumber 4 (summer)
or wavenumber 3 (winter) pattern, with strongest loadings in the South Pacific sector, and an association simultaneously with
a dipole SST temperature gradient in the subtropical Indian Ocean. 相似文献