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Marius-Victor Birsan Alexandru Dumitrescu Dana Magdalena Micu Sorin Cheval 《Natural Hazards》2014,74(3):1899-1910
The Carpathian Mountains region cover areas from seven countries of central and southeastern Europe, the mountain chain having major regional influences on the temperate climate, specific to latitudes between 43°N and 49°N. In order to identify changes in the annual temperature extremes, the Mann–Kendall nonparametric trend test has been applied to several thermal indices, recommended by the expert team on climate change detection and indices. The indices were computed from gridded daily datasets of minimum and maximum temperature at 0.1° resolution (~10 km), available online within the framework of the project CarpatClim (climate of the Carpathian region) for the period 1961–2010. The results show decreasing trends in cold-related indices, especially in the number of frost days, and increasing trends in warm-related ones. The trend patterns are consistent over the region, i.e., there are no mixed trends for a given index. Regional differences in climate extreme trends within the Carpathian region are related to altitude, rather than latitude. The number of summer days is increasing over the entire area, while the number of tropical nights presents upward trends mainly at lower elevations. The Warm Spell Duration Index presents upward trends over 60 % of the region. The (annual) East Atlantic pattern shows strong correlations with the warm-related indices. Our results are in agreement with previous temperature-related studies in the region. 相似文献
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R. Napiwotzki C.A. Karl T. Lisker U. Heber N. Christlieb D. Reimers G. Nelemans D. Homeier 《Astrophysics and Space Science》2004,291(3-4):321-328
We present the results of a radial velocity (RV) survey of 46 subdwarf B (sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new sdB binary systems, but only one (4%) He-sdO binary. Orbital parameters of nine sdB and sdO binaries, derived from follow-up spectroscopy, are presented. Our results are compared with evolutionary scenarios and previous observational investigations. 相似文献
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T. Lisker U. Heber R. Napiwotzki N. Christlieb D. Reimers D. Homeier 《Astrophysics and Space Science》2004,291(3-4):351-358
We report on the analysis of high-resolution optical spectra for 77 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey. Effective temperature, surface gravity, and photospheric helium abundance are determined simultaneously by spectral line profile fitting of hydrogen and helium lines, and are found to be in agreement with previous studies of sdB stars. Twenty four objects show spectral signs of a cool companion, being either companion absorption lines or a flux contribution at Hα. Five stars with relatively high luminosity show peculiar Hα profiles, possibly indicating stellar winds. Our results are compared to recent theoretical simulations by Han et al. [MNRAS, 341, 669] for the distribution in effective temperature and surface gravity, and are found to agree very well with these calculations. Finally, we present a binary system consisting of two helium-rich hot subdwarfs. 相似文献
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The influence of climate on gravitational processes within the Jiu river valley: G.I.S. applications
The dynamics of gravitational processes (e.g. landslides) is altered due to variation in climatic parameters. We have recorded an increasing number of such events which affect human settlements. The most important aspect that has to be emphasized is the way gravitational processes change and condition land utilization. Due to these circumstances, the analysis of these processes has great importance within the middle sector of the Jiu Valley. In order to correlate the occurrence of gravitational processes with climatic data, we have been collecting data within this valley sector during the last 15 years. The aim of this study is to describe the succession and dynamics of present processes, which should act as an alarm signal for local authorities to take adequate mitigating measures. We observe an increase in the mean annual temperature and the mean amplitude (by approximately 1?C), in addition to the frequency and severity of dry years (1992, 2000), and the frequency of rain showers. We correlate these data with knowledge of the lithology, morphometry, and piezometric levels in order to identify areas with a high potential for gravitational processes using a Geographical Information System (G.I.S.). This analysis allows us to draw a map rendering each layer separately — lithology, pedology, slope, vegetation etc. We present a map that emphasizes the areas with high potential for the development of gravitational processes in the region of the Jiu valley. 相似文献
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Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD tower in Bucharest, Romania 总被引：1，自引：0，他引：1
Matthieu Perrault Philippe Gueguen Alexandru Aldea Sorin Demetriu 《地震工程与工程振动(英文版)》2013,12(4):643-658
The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied： （1） adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson＇s criteria, （2） computation of the structure＇s response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements （IM）, and （3） construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd ） as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology. 相似文献
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This paper begins with a critical assessment of the concept of macroseismic intensity, on which traditional scales, such as MSK and EMS, are based. The main shortcoming identified is the model's failure to consider the spectral features of ground motion. This omission may lead to erroneous seismic zonation, as shown in the paper. As a result, the model is of little interest to engineers who must design and build safe structures while adopting economical solutions. The paper presents a way to radically improve this situation. The starting point for this approach was the experience of the destructive Vrancea earthquake of 1977.03.04, which made it clear that intensity appears to be different for structures having natural periods pertaining to different spectral domains. The solution proposed to the shortcomings of the traditional intensity concept is postulated on a system of analytical expressions, covering definitions of global intensities, of intensities related to oscillation frequency and of intensities related to a definite spectral band. The latter definition lies at the basis of a definition of discrete intensity spectra. Illustrative applications are presented, in relation to global intensities and to discrete intensity spectra. We then analyze an illustrative case in which the use of traditional macroseismic survey techniques led to erroneous seismic zonation. Finally, some conclusions and recommendations are presented. Based on the authors?? long-term experience, we strongly recommend close interaction between seismologists and engineers in working groups and joint projects targeted on radical improvement of the basic concepts of seismic intensity and of specific analysis procedures. 相似文献
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The synchronization between the orbital motion and axial rotation of the two component stars of a binary system is reviewed.
Some previous published papers are mentioned and the general conclusion is outlined: If we shall use a rotating coordinate
system synchronous with one of the two stellar axial rotations, it is not possible to obtain a Jacobi integral and the Roche
geometry cannot be further analyzed. In addition, a theoretical approach is summarized in order to use the axial rotations
of the two component stars, even if the constants of the stellar structure (k2)1, (k2)2must be taken into consideration. So it is found that if the stellar angular velocities are higher than the corresponding
Keplerian angular velocity (ωi≫ ωk, i=
), the problem of the rotational effect could be of practical consideration. Finally, a theoretical relationship between the
two constants (k2)1and (k2)2of the stellar structure is established. 相似文献
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Long-term landscape evolution of the northeastern margin of the Bohemian Massif: apatite fission-track data from the Erzgebirge (Germany) 总被引：3，自引：0，他引：3
To study the relative and absolute timing of post-Variscan cooling and denudation processes in the Erzgebirge of the Mid-European Variscides, eight samples for apatite fission-track (AFT) analysis were collected from a ~1,300 m drill-core. The fission-track data reveal two stages of accelerated cooling through the apatite partial annealing zone (APAZ; i.e., 110±10–60 °C) in the Late Jurassic-Late Cretaceous and in the late Cenozoic, respectively. Late Jurassic-Late Cretaceous cooling corresponding to denudation of 1.5–5.9 km has been related to wrench tectonics along the Elbe Zone during Triassic-Jurassic Pangea breakup. Late Cenozoic exhumation of 2.1–5.6 km, and the increase of the geothermal gradient from 17±5 °C km–1 (Oligocene/Miocene) to 25–27 °C km–1 (recent) is likely connected to the formation of the Eger Graben starting from the Oligocene, as a result of the late Alpine orogenic phases. 相似文献
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The East Antarctic Lambert Graben and the Indian Mahanadi Basin are considered to represent segments of an intra-Gondwanan rift structure that was active at least since the Paleozoic. Fission track analyses of apatites from a comprehensive data set across the shoulders of both grabens were used to compare their low temperature history, and to estimate the paleo-geothermal gradients before the onset of the last denudation/rifting stage (Late Jurassic). The paleo-geothermal gradients of both juxtaposed Gondwana margins similarly increase from the basement towards the respective rift shoulder from 15–20°Ckm−1 to 25–30°Ckm−1. This trend of increasing paleo-geothermal gradients, together with a denudation episode commencing in the Early Cretaceous and coeval igneous activity, indicates a common rifting stage accompanying the breakup of Gondwana in the India-Antarctica sector. 相似文献