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排序方式： 共有203条查询结果，搜索用时 15 毫秒
91.
Eva Leitholdt Christoph Zielhofer Stefanie Berg‐Hobohm Katharina Schnabl Britta Kopecky‐Hermanns Jens Bussmann Joachim W. Hrtling Klaus Reicherter Katrin Unger 《Geoarchaeology》2012,27(1):88-104
The Central European watershed passes through the southern Franconian Jura in Bavaria, Germany. This principal watershed divides the Rhine/Main catchment and the Danube catchment. In the early Middle Ages, when ships were an important means of transportation, Charlemagne decided to connect these catchments by the construction of a canal known as the Fossa Carolina. In this paper, we present for the first time 14C data from the Fossa Carolina fill and document a high‐resolution stratigraphic record of the Carolingian and post‐Carolingian trench infilling. Our results provide clear evidence for peat layers in different levels of the trench infill, suggesting a chain of ponds. However, the majority of these peat layers yield mid‐Medieval and younger ages. The period of major peat growth was during the Medieval climatic optimum. Therefore, our preliminary results do not prove the use of the trench during Carolingian times. However, first results from the reconstruction of the Carolingian trench bottom support the hypothesis that the Fossa was primarily planned as a navigable chain of ponds and not as a continuous canal. In the eastern part of the trench, a dam is located that was postulated in former studies to be part of a barrage for supplying the Carolingian canal with water. New 14C data indicate much younger ages and do not support the Carolingian barrage concept. 相似文献
92.
H. Lammer A. Hanslmeier J. Schneider I. K. Stateva M. Barthelemy A. Belu D. Bisikalo M. Bonavita V. Eybl V. Coudé du Foresto M. Fridlund R. Dvorak S. Eggl J. -M. Grießmeier M. Güdel E. Günther W. Hausleitner M. Holmström E. Kallio M. L. Khodachenko A. A. Konovalenko S. Krauss L. V. Ksanfomality Yu. N. Kulikov K. Kyslyakova M. Leitzinger R. Liseau E. Lohinger P. Odert E. Palle A. Reiners I. Ribas H. O. Rucker N. Sarda J. Seckbach V. I. Shematovich A. Sozzetti A. Tavrov M. Xiang-Grüß 《Solar System Research》2010,44(4):290-310
After the discovery of more than 400 planets beyond our Solar System, the characterization of exoplanets as well as their host stars can be considered as one of the fastest growing fields in space science during the past decade. The characterization of exoplanets can only be carried out in a well coordinated interdisciplinary way which connects planetary science, solar/stellar physics and astrophysics. We present a status report on the characterization of exoplanets and their host stars by reviewing the relevant space- and ground-based projects. One finds that the previous strategy changed from space mission concepts which were designed to search, find and characterize Earth-like rocky exoplanets to: A statistical study of planetary objects in order to get information about their abundance, an identification of potential target and finally its analysis. Spectral analysis of exoplanets is mandatory, particularly to identify bio-signatures on Earth-like planets. Direct characterization of exoplanets should be done by spectroscopy, both in the visible and in the infrared spectral range. The way leading to the direct detection and characterization of exoplanets is then paved by several questions, either concerning the pre-required science or the associated observational strategy. 相似文献
93.
We present results of an investigation of clustering evolution of field galaxies between a redshift of z ∼ 1 and the present epoch. The current analysis relies on a sample of ∼ 14000 galaxies in two fields of the COMBO 17 survey.
The redshift distribution extends to z ∼ 1. The amplitude of the three-dimensional correlation function can be estimated by means of the projected correlation function
w(r
p
). The validity of the deprojection was tested on the Las Campanas Redshift Survey (LCRS). In a flat cosmology with non-zero
cosmological constant for bright galaxies (M
B ≤-18) the clustering growth is proportional to (1+z)
-2. However, the measured clustering evolution clearly depends on Hubble type. While locally the clustering strength of early
type galaxies is equal to that of the bright galaxies, at high redshifts they are much stronger clustered, and thus the clustering
has to evolve much more slowly.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
94.
As the number of instruments applied in the area of energy and climate policy is rising, the issue of policy interaction needs to be explored further. This article analyses the interdependencies between the EU Emissions Trading Scheme (EU ETS) and the German feed-in tariffs (FITs) for renewable electricity in a quantitative manner using a bottom-up energy system model. Flexible modelling approaches are presented for both instruments, with which all impacts on the energy system can be evaluated endogenously. It is shown that national climate policy measures can have an effect on the supranational emissions trading system by increasing emission reduction in the German electricity sector by up to 79 MtCO2 in 2030. As a result, emission certificate prices decline by between 1.9 €/tCO2 and 6.1 €/tCO2 and the burden sharing between participating countries changes, but no additional emission reduction is achieved at the European level. This also implies, however, that the cost efficiency of such a cap-and-trade system is distorted, with additional costs of the FIT system of up to €320 billion compared with lower costs for ETS emission certificates of between €44 billion and €57 billion (cumulated over the period 2013–2020).Policy relevanceIn order to fulfil ambitious emission reduction targets a large variety of climate policy instruments are being implemented in Europe. While some, like the EU ETS, directly address CO2 emissions, others aim to promote specific low-carbon technologies. The quantitative analysis of the interactions between the EU ETS and the German FIT scheme for renewable sources in electricity generation presented in this article helps to understand the importance of such interaction effects. Even though justifications can be found for the implementation of both types of instrument, the impact of the widespread use of support mechanisms for renewable electricity in Europe needs to be taken into account when fixing the reduction targets for the EU ETS in order to ensure a credible long-term investment signal. 相似文献
95.
Mineralogy of the lunar crust: Results from Clementine 总被引：1，自引：0，他引：1
Abstract— The central peaks of 109 impact craters across the Moon are examined with Clementine ultraviolet-visible (UVVIS) camera multispectral data. The craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5–30 km beneath the surface to form the peaks, including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins. Representative five-color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters, including “key ratio” (which is related to mafic mineral abundance) and “spectral curvature” (linked to absorption band shape, which distinguishes between low- and high-Ca pyroxene and olivine). The spectral parameters are correlated to mineralogical abundances, related in turn to highland plutonic rock compositions. The derived rock compositions for the various central peaks are presented in a global map. From these results, it is evident that the lunar crust is compositionally diverse, both globally and at local 100 m scales found within individual sets of central peaks. Although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure, they also indicate a more anorthositic crust than generally assumed, with a bulk plagioclase content of ～81%, evolving from “pure” anorthosite near the surface towards more mafic, low-Ca pyroxene-rich compositions with depth (comparable to anorthositic norite). Evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types. However, the lower crust is more compositionally diverse than the highlands, with both a greater range of rock types and more diversity within individual sets of central peaks. 相似文献
96.
Hanna Hadler Andreas Vött Timo Willershäuser Dennis Wilken Ruth Blankenfeldt Claus von Carnap-Bornheim Kurt Emde Peter Fischer Ulf Ickerodt Stefanie Klooß Bente Majchczack Lea Obrocki Wolfgang Rabbel 《地球表面变化过程与地形》2021,46(15):3228-3251
In ad 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north-western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia. Initially, we deciphered long-term as well as event-related short-term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)-based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high-resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge-related land losses. 相似文献
97.
98.
Stefanie Seubert Sonia Fernández-Montes Andreas Philipp Elke Hertig Jucundus Jacobeit Gernot Vogt Andreas Paxian Heiko Paeth 《Theoretical and Applied Climatology》2014,117(1-2):257-275
The behaviour of precipitation and maximum temperature extremes in the Mediterranean area under climate change conditions is analysed in the present study. In this context, the ability of synoptic downscaling techniques in combination with extreme value statistics for dealing with extremes is investigated. Analyses are based upon a set of long-term station time series in the whole Mediterranean area. At first, a station-specific ensemble approach for model validation was developed which includes (1) the downscaling of daily precipitation and maximum temperature values from the large-scale atmospheric circulation via analogue method and (2) the fitting of extremes by generalized Pareto distribution (GPD). Model uncertainties are quantified as confidence intervals derived from the ensemble distributions of GPD-related return values and described by a new metric called “ratio of overlapping”. Model performance for extreme precipitation is highest in winter, whereas the best models for maximum temperature extremes are set up in autumn. Valid models are applied to a 30-year period at the end of the twenty-first century (2070–2099) by means of ECHAM5/MPI-OM general circulation model data for IPCC SRES B1 scenario. The most distinctive future changes are observed in autumn in terms of a strong reduction of precipitation extremes in Northwest Iberia and the Northern Central Mediterranean area as well as a simultaneous distinct increase of maximum temperature extremes in Southwestern Iberia and the Central and Southeastern Mediterranean regions. These signals are checked for changes in the underlying dynamical processes using extreme-related circulation classifications. The most important finding connected to future changes of precipitation extremes in the Northwestern Mediterranean area is a reduction of southerly displaced deep North Atlantic cyclones in 2070–2099 as associated with a strengthened North Atlantic Oscillation. Thus, the here estimated future changes of extreme precipitation are in line with the discourse about the influence of North Atlantic circulation variability on the changing climate in Europe. 相似文献
99.
Romed Ruggenthaler Gertraud Meißl Clemens Geitner Georg Leitinger Nikolaus Endstrasser Friedrich Schöberl 《水文科学杂志》2013,58(7):1263-1279
ABSTRACTThis study presents an adaptation of the double-ring infiltrometer (DRI) device, which allows several infiltration experiments to be conducted at the same location. Hence, it becomes possible to use the DRI method to investigate infiltration behaviour under different initial soil moisture conditions. The main feature is the splitting of the inner ring into two parts. While the lower part remains in the soil throughout the investigation period, the upper part is attached to the lower one just before the infiltration experiment. This method was applied to eight test sites in an Alpine catchment, covering different land-use/cover types. The results demonstrated the applicability of the adapted system and showed correlations between total water infiltration and initial soil moisture conditions on pastures, independent of the underlying soil type. In contrast, no correlation was found at forest sites or wetlands. Thus, the study emphasizes the importance of paying special attention to the impact of initial soil moisture conditions on the infiltration—and consequently the runoff behaviour—at managed areas. Given the differences in the total infiltrated water of between 30 and 1306 mm, consideration of the interplay between initial soil moisture conditions, land-use/cover type, and soil properties in rainfall–runoff models is a prerequisite to predict runoff production accurately.
EDITOR Z.W. Kundzewicz; ASSOCIATE EDITOR not assigned 相似文献
100.
Dynamic adjustment of training sets (‘moving-window’ reconstruction) by using transfer functions in paleolimnology—a new approach 总被引：1，自引：0，他引：1
Thomas Hübener Mirko Dreßler Anja Schwarz Kirsten Langner Sven Adler 《Journal of Paleolimnology》2008,40(1):79-95
This paper presents a new method (moving-windows) that optimizes diatom-based paleolimnological reconstructions of past environmental
conditions from supra-regional training sets. The moving-window method identifies the best number of nearest neighbours (window
size) from a merged supra-regional EDDI and local (MV) training set (n = 429) for each fossil diatom assemblage and the best type of transfer function (ML, WA-PLS) based on the error statistic
of each transfer function (highest cross-validated R
2, lowest cross-validated average bias, maximum bias and RMSEP). At first we evaluated the moving-window approach by comparing
measured TP-values with inferred TP-values using both the moving-window approach and the WA-PLS method. The relative errors
of the moving-window approach were not significantly different for 208 samples that had an error <15 μg/l TP using the WA-PLS
method. However, for the remaining 221 samples with errors >>15 μg/l TP using the WA-PLS method, the moving window approach
significantly reduced the relative error of the inferred TP levels. Secondly, the moving- window approach was used to reconstruct
epilimnetic total phosphorous (TP) for Lake Dudinghausen, Lake Rugensee, Lake Tiefer See and Lake Drewitzer See (Northern
Germany) using both the supra-regional EDDI training set and a local training set from Northern Germany (MV training set).
The moving-window inferred TP-levels of the four study lakes were compared with published reconstructed TP-values and with
inferred TP-values based on the local MV training set. Overall, the moving-window and the published TP-trends agree well with
each other. However, the moving-window reconstructions generally indicated lower TP-levels throughout the past ∼5,000 to 12,000 years,
including past maxima. Thus, the moving-window method seems to generate more realistic absolute TP levels due to the optimized
window size (highest number of modern analogues, best error statistics). The identification of more realistic absolute historic
TP-values is important for the validation of reference conditions for inland waters. This study also demonstrates that a robust
local training set may, similar to moving-window training sets, also lead to reliable reconstructions, if the geological settings
of the local training set lakes and the study lakes are similar. 相似文献