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991.
Andreas Iordanidis Jan Schwarzbauer Andreas Georgakopoulos Barend van Lagen 《Geochemistry International》2012,50(2):159-178
Several lignite samples were collected from boreholes of the Amynteo opencast lignite mine, northern Greece. Organic geochemical
characteristics were investigated with the help of various analytical techniques, comprising Gas Chromatography (GC) and Gas-chromatography-Mass
Spectrometry (GC-MS), Fourier Transform Infrared Spectroscopy (FTIR), solid-state Nuclear Magnetic Resonance (NMR) and Electron
Paramagnetic Resonance (EPR) spectroscopy, petrographical measurements as well as determination of bulk parameters. In the
low rank (Rr = 0.21%) Amynteo lignites, huminite is the most abundant maceral group, inertinite has relatively low percentages
and liptinite concentrations are rather high. Carbon Preference Index (CPI) reveals the predominance of odd-numbered, long-chained
aliphatic hydro-carbons, which is related to a higher terrestrial plant input. The Pr/Ph ratio suggests that reducing conditions
were persistent during peatification. Gymnosperm biomarkers such as isoprimarane, abietane, phyllocladane and sandaracopimarane,
as well as angiosperm indicators (lupane) and hopanoid compounds with bacterial origin were identified. Analyses of the aromatic
fractions revealed the presence of naphthalene, alkyl benzenes and phenols, pyrene, cadalene, cadinane, fluoranthene and dibenzofurane.
Based on the FTIR analysis, aliphatic and oxygen containing structures were prevailed over the aromatic moieties. The intensity
of the mineral bands was preferentially increased in the FTIR spectra of insoluble material. According to NMR analysis, the
aliphatic carbons (0–50 ppm) have higher proportions comparing to aromatic carbons (100–160 ppm). The aromaticity fraction
is low (fa = 0.32), as expected for these low rank coals. The presence of free organic radicals and Fe3+ and Mn2+ paramagnetic ions was revealed by EPR. In summary, the combined application of complementary analytical techniques allowed
a deep inside into the geochemical characteristics of Amynteo lignites. 相似文献
992.
In this study, rapid topographic changes and increased erosion rates caused by massive slope failures in a glacierized and permafrost‐affected high‐mountain face were investigated with respect to the current climatic change. The study was conducted at one of the highest periglacial rock faces in the European Alps, the east face of Monte Rosa, Italy. Pronounced changes in ice cover and repeated rock and ice avalanche events have been documented in this rock wall since around 1990. The performed multi‐temporal comparison of high‐resolution digital terrain models (DTMs) complemented by detailed analyses of repeat photography represents a unique assessment of topographic changes and slope failures over half a century and reveals a total volume loss in bedrock and steep glaciers in the central part of the face of around 25 × 106 m3 between 1988 and 2007. The high rock and ice avalanche activity translates into an increase in erosion rates of about one order of magnitude during recent decades. The study indicates that changes in atmospheric temperatures and connected changes in ice cover can induce slope destabilization in high‐mountain faces. Analyses of temperature data show that the start of the intense mass movement activity coincided with increased mean annual temperatures in the region around 1990. However, once triggered, mass movement activity seems to be able to proceed in a self‐reinforcing cycle, whereby single mass movement events might be strongly influenced by short‐term extreme temperature events. The investigations suggest a strong stability coupling between steep glaciers and underlying bedrock, as most bedrock instabilities are located in areas where surface ice has disappeared recently and the failure zones are frequently spatially correlated and often develop from lower altitudes progressively upwards. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
993.
Abstract Solar radiation, direct and diffuse, is affected by surface characteristics, such as slope, aspect, altitude and shading. The paper examines the effects of topography on radiation, at multiple spatiotemporal scales, using suitable geometric methods for the direct and diffuse components. Two indices are introduced for comparing the direct radiation received by areas at the same and different latitudes. To investigate the profile of direct radiation across the whole of Greece, these are evaluated from an hourly to annual basis, via GIS techniques. Moreover, different approaches are examined for estimating the actual global radiation at operational spatial scales (sub-basin and terrain), according to the available meteorological data. The study indicates that the errors of typical hydrometeorological modelling formulas, which ignore the topographic effects and the seasonal allocation of direct and diffuse radiation, depend on the spatial scale and are non-uniformly distributed in time. In all cases, the estimations are improved by applying the proposed adjustment approaches. In particular, the adjustment of the measured global radiation ensures up to 10% increase of efficiency, while the modified Angström formula achieves slight (i.e. 2–4%) increase of efficiency and notable reduction of bias. Editor Z.W. Kundzewicz Citation Mamassis, N., Efstratiadis, A. and Apostolidou, I.-G., 2012. Topography-adjusted solar radiation indices and their importance in hydrology. Hydrological Sciences Journal, 57 (4), 756–775. 相似文献
994.
ABSTRACTFlood quantile estimation based on partial duration series (peak over threshold, POT) represents a noteworthy alternative to the classical annual maximum approach since it enlarges the available information spectrum. Here the POT approach is discussed with reference to its benefits in increasing the robustness of flood quantile estimations. The classical POT approach is based on a Poisson distribution for the annual number of exceedences, although this can be questionable in some cases. Therefore, the Poisson distribution is compared with two other distributions (binomial and Gumbel-Schelling). The results show that only rarely is there a difference from the Poisson distribution. In the second part we investigate the robustness of flood quantiles derived from different approaches in the sense of their temporal stability against the occurrence of extreme events. Besides the classical approach using annual maxima series (AMS) with the generalized extreme value distribution and different parameter estimation methods, two different applications of POT are tested. Both are based on monthly maxima above a threshold, but one also uses trimmed L-moments (TL-moments). It is shown how quantile estimations based on this “robust” POT approach (rPOT) become more robust than AMS-based methods, even in the case of occasional extraordinary extreme events.
Editor M.C. Acreman Associate editor A. Viglione 相似文献
995.
996.
Robert Andritschke Andreas Zoglauer Gottfried Kanbach Peter F. Bloser Florian Schopper 《Experimental Astronomy》2005,20(1-3):395-403
MEGA, short for Medium Energy Gamma-ray Astronomy, is the development of a new technology telescope in the energy band 0.4--50\ MeV. The wide energy range of MEGA, which spans nuclear γ-ray lines and energetic continuum spectra, the large field of view, and the capacity for polarimetry enables unique investigations into cosmic nucleosynthesis, particle accelerators around compact objects, and explosive high-energy events. We describe the development and tests of a prototype detector. Results from laboratory tests using radioactive sources and from a beam test calibration are presented and an outlook of a potential space mission is sketched. 相似文献
997.
998.
Wilbert Weijer Wilhelmus P. M. De Ruijter Andreas Sterl Sybren S. Drijfhout 《Global and Planetary Change》2002,34(3-4)
The heat and salt input from the Indian to Atlantic Oceans by Agulhas Leakage is found to influence the Atlantic overturning circulation in a low-resolution Ocean General Circulation Model (OGCM). The model used is the Hamburg Large-Scale Geostrophic (LSG) model, which is forced by mixed boundary conditions. Agulhas Leakage is parameterized by sources of heat and salt in the upper South Atlantic Ocean, which extend well into the intermediate layers.It is shown that the model's overturning circulation is sensitive to the applied sources of heat and salt. The response of the overturning strength to changes in the source amplitudes is mainly linear, interrupted once by a stepwise change. The South Atlantic buoyancy sources influence the Atlantic overturning strength by modifying the basin-scale meridional density and pressure gradients. The non-linear, stepwise response is caused by abrupt changes in the convective activity in the northern North Atlantic.Two additional experiments illustrate the adjustment of the overturning circulation upon sudden introduction of heat and salt sources in the South Atlantic. The North Atlantic overturning circulation responds within a few years after the sources are switched on. This is the time it takes for barotropic and baroclinic Kelvin waves to reach the northern North Atlantic in this model. The advection of the anomalies takes three decades to reach the northern North Atlantic.The model results give support to the hypothesis that the re-opening of the Agulhas Gap at the end of the last ice-age, as indicated by palaeoclimatological data, may have stimulated the coincident strengthening of the Atlantic overturning circulation. 相似文献
999.
1000.
We compare results from numerical simulations with observations of edge-on galaxies interacting/merging with a small companion
(Schwarzkopf and Dettmar,2000), hereafter S&D00). Observations show a clear influence of the merging and interacting process
on disk scale parameters h (radial scalelength), z
0 (vertical scalelength) and their ratio (h/z
0), leading to a heating and thickening of the stellar disk. Our numerical simulations show the same behaviour but differ significantly
in the magnitude of the change of the disk scale parameters.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献