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51.
Anastasios Tselepides Konstantia-N. Papadopoulou Dimitris Podaras Wanda Plaiti Drosos Koutsoubas 《Progress in Oceanography》2000,46(2-4)
Macrobenthic faunal composition, abundance, biomass and diversity together with a suite of sedimentary environmental parameters were investigated on a seasonal basis in order to determine factors regulating faunal distribution over the oligotrophic continental margin of the island of Crete (South Aegean Sea, North Eastern Mediterranean). Macrofaunal species composition was similar to that of the western Mediterranean and the neighboring Atlantic having several common dominant species. Mean benthic biomass, abundance and diversity decreased with depth, with a major transition zone occurring at 540 m, beyond which values declined sharply. At comparable depths biomass and abundance values were considerably lower to those found in the Atlantic, high-lighting the extreme oligotrophy of the area. The continental margin of Crete was characterised by a high diversity upper continental shelf environment (dominated by surface deposit feeding polychaetes) and a very low diversity slope and deep-basin environment (dominated by carnivorous and filter feeding polychaetes). Classification and ordination analyses revealed the existence of four principle clusters divided by a faunal boundary between 200 and 540 m, as well as beyond 940 m depth. Significant correlations between macrofauna and sediment parameters led to the conclusion that besides depth, food availability (as manifested by the concentration of chloroplastic pigments) is the principle regulating factor in the system. Such being the case, the prevailing hydrographic features that structure the pelagic food web and are directly responsible for the propagation of organic matter to the benthos also affect its community structure. 相似文献
52.
Ahmer Ali Raffaele De Risi Anastasios Sextos Katsuichiro Goda Zhiwang Chang 《地震工程与结构动力学》2020,49(1):24-50
The increasing number of wind turbines in active tectonic regions has attracted scientific interest to evaluate the seismic vulnerability of offshore wind turbines (OWTs). This study aims at assessing the deformation and collapse susceptibility of 2MW and 5MW OWTs subjected to shallow-crustal pulse-like ground motions, which has not been particularly addressed to date. A cloud-based fragility assessment is performed to quantify the seismic response for a given intensity measure and to assess the failure probabilities for pulse-like and non-pulse-like ground motions. The first-mode spectral acceleration Sa(T1) is found to be an efficient response predictor for OWTs, exhibiting prominent higher-mode behavior, at the serviceability and ultimate conditions. Regardless of earthquake type, it is shown that records with strong vertical components may induce nonlinearity in the supporting tower, leading to potential failure by buckling in three different patterns: (i) at tower base near platform level, (ii) close to tower top, and (iii) between the upper half of the main tower and its top. Type and extent of the damage are related to the coupled excitation of vertical and lateral higher modes, for which tower top acceleration response spectra Sa,i(Top) is an effective identifier. It is also observed that tower's slenderness ratio (l/d), the diameter-to-thickness ratio (d/t), and the rotor-nacelle-assembly mass (mRNA) are precursors for evaluating the damage mode and vulnerability of OWTs under both pulse-like and non-pulse-like ground motion records. 相似文献
53.
The paper aims to evaluate the way Eurocode 8 treats the consideration of asynchronous earthquake ground motion during the
seismic design of bridges, and to discuss alternative solutions for cases wherein existing provisions do not lead to satisfactory
results. The evaluation of EC8-2 new provisions and simplified methods is performed through comparison with a more refined
approach whereas an effort is made to quantitatively assess the relative importance of various design and analysis assumptions
that have to be made when spatial variability of ground motion is taken into consideration, based on the study of the dynamic
response of 27 different bridges. It is concluded that, despite the complexity of the problem, there are specific cases where
EC8 provisions can be safely and easily applied in practice, while in other cases ignoring the effect of asynchronous excitation
or performing simplified calculations can significantly underestimate the actual seismic demand. 相似文献
54.
George Papaioannou George Varlas Anastasios Papadopoulos Athanasios Loukas Petros Katsafados Elias Dimitriou 《水文研究》2021,35(4):e14151
A common source of uncertainty in flood inundation forecasting is the hydrograph used. Given the role of sea-air-hydro-land chain processes on the water cycle, flood hydrographs in coastal areas can be indirectly affected by sea state. This study investigates sea-state effects on precipitation, discharge, and flood inundation forecasting implementing atmospheric, ocean wave, hydrological, and hydraulic-hydrodynamic coupled models. The Chemical Hydrological Atmospheric Ocean wave System (CHAOS) was used for coupled hydro-meteorological-wave simulations ‘accounting’ or ‘not accounting’ the impact of sea state on precipitation and, subsequently, on flood hydrograph. CHAOS includes the WRF-Hydro hydrological model and the WRF-ARW meteorological model two-way coupled with the WAM wave model through the OASIS3-MCT coupler. Subsequently, the 2D HEC-RAS hydraulic-hydrodynamic model was forced by the flood hydrographs and map the inundated areas. A flash flood event occurred on 15 November 2017 in Mandra, Attica, Greece, causing 24 fatalities, and damages was selected as case study. The calibration of models was performed exploiting historical flood records and previous studies. Human interventions such as hydraulic works and the urban areas were included in the hydraulic modelling geometry domain. The representation of the resistance caused by buildings was based on Unmanned Aerial System (UAS) data while the local elevation rise method was used in the urban-flood simulation. The flood extent results were assessed using the Critical Success Index (CSI), and CSI penalize. Integrating sea-state affected the forecast of precipitation and discharge peaks, causing up to +24% and from −8% to +36% differences, respectively, improving inundation forecast by 4.5% and flooding additional approximately 70 building blocks. The precipitation forcing time step was also highlighted as significant factor in such a small-scale flash flood. The integrated multidisciplinary methodological approach could be adopted in operational forecasting for civil protection applications facilitating the protection of socio-economic activities and human lives during similar future events. 相似文献
55.
Polymenakou PN Tselepides A Stephanou EG Bertilsson S 《Marine pollution bulletin》2006,52(11):1396-1405
Sediment samples collected from polluted (Augusta Bay) and pristine regions of the Eastern Mediterranean Sea (South Ionian Sea, Thracian Sea) were analyzed for black carbon, aliphatic hydrocarbons and phospholipid ester-linked fatty acids (PLFA). The aim of the study was to investigate the anthropogenic and biogenic inputs into the Eastern Mediterranean Sea and to evaluate the effects of refractory organic matter (e.g. black carbon) and the level of hydrocarbon contamination on benthic microbial community composition. Black carbon, generally considered to be chemically and biologically inert, comprised a significant but highly variable fraction of the sedimentary carbon pool in the analyzed sediments with a ratio to total organic carbon ranging from 0.02 to 0.66. Principal component analysis of the chemical characteristics of the sediments (organic carbon content, black carbon, bioavailable organic carbon, chlorophyll a, phaeopigments, aliphatic hydrocarbons) revealed clustering of samples along a gradient from the most productive and contaminated region of Augusta Bay to the carbon-poor and pristine sediments of the Thracian Sea. PLFA analysis revealed that gram-negative bacteria and microeukaryotes were most abundant in Augusta Bay and in the most impacted station of the Thracian Sea. The high levels of branched and odd-chain fatty acids recorded for these stations is probably linked to the elevated amounts of hydrocarbons at these stations; e.g. microbial communities may have developed the ability to degrade either naturally occurring aliphatic hydrocarbons or hydrocarbons derived from oil contamination. 相似文献
56.
Community structure and dynamics in climate networks 总被引:1,自引:1,他引:0
Anastasios A. Tsonis Geli Wang Kyle L. Swanson Francisco A. Rodrigues Luciano da Fontura Costa 《Climate Dynamics》2011,37(5-6):933-940
We consider climate networks constructed from observed and model simulated fields of three climate variables and investigate their community structure. We find that for all fields the number of effective communities is rather small (four to five). We are able to trace the origin of these communities to certain dynamical properties of climate. Our results suggest that the complete complexity of the climate system condenses beyond the ??weather?? time scales into a small number of low-dimensional interacting components and provide clues as to the nature of the climate subsystems underlying these components. 相似文献
57.
Anastasios G. Sextos Evangelos I. KatsanosGeorge D. Manolis 《Soil Dynamics and Earthquake Engineering》2011
This study investigates the applicability and limitations of the Eurocode 8 earthquake ground motion selection framework for the assessment of both elastic and inelastic structural response of multi-storey, irregular R/C buildings subjected to bi-directional loading. In order to minimize modelling uncertainties inherent in the quantification of structural damage and the consideration of the supporting soil–foundation system for complex structural systems, an existing building damaged by the 2003 Lefkada earthquake was adopted as case study. This selection has an advantage in that ground excitation, soil profile and damage observations are all available, thus permitting calibration of the finite element model with the observed response, especially in terms of use of appropriate plasticity models and damage indices, plus the assessment of soil–structure interaction effects. After establishing a reliable finite element model of the structure under study, extensive parametric analyses for different EC8 compliant sets of records were conducted, permitting quantification of the discrepancy of the structural response due to record-to-record and set-to-set variability (i.e., intra-set and inter-set scatter, respectively). The results confirm that many of the observations found in the literature regarding the effect of ground motion selection on the predicted seismic performance of SDOF systems are also valid for bi-directionally excited, multi-storey, irregular buildings. Finally, the results also highlight specific limitations of the EC8 provisions that may lead to erroneous results in many practical cases. 相似文献
58.
59.
David L. Jauncey Lucyna Kedziora-Chudczer James E.J. Lovell Jean-Pierre Macquart George D. Nicolson Rick A. Perley John E. Reynolds Anastasios K. Tzioumis Mark H. Wieringa Hayley E. Bignall 《Astrophysics and Space Science》2001,278(1-2):87-92
Intra-day variability (IDV) of active galactic nuclei (AGN) has been detected from gamma-ray energies to radio wavelengths.
At high energies, such variability appears to be intrinsic to the sources themselves. However, at radio wavelengths, brightness
temperatures as high as1018 to 1021 K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evidence showing that, at radio
wavelengths where the highest brightness temperatures are encountered, interstellar scintillation (ISS) is the principal mechanism
causing IDV. While ISS reduces the implied brightness temperatures, they still remain uncomfortably high.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
60.
Influence of frequency‐dependent soil–structure interaction on the fragility of R/C bridges
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Bridge performance under earthquake loading can be significantly influenced by the interaction between the structure and the supporting soil. Even though the frequency dependence of the interaction mentioned in this study has long been documented, the simplifying assumption that the dynamic stiffness is dominated by the mean or predominant excitation frequency is still commonly made, primarily as a result of the associated numerical difficulties when the analysis has to be performed in the time domain. This study makes use of the advanced lumped parameter models recently developed 1 in order to quantify the impact of the assumption on the predicted fragility of bridges mentioned in this study. This is achieved by comparing the predicted vulnerability for the case of a reference, well studied, actual bridge using both conventional, frequency‐independent, Kelvin–Voigt models and the aforementioned lumped parameter formulation. Analysis results demonstrate that the more refined consideration of frequency dependence of soil–structure interaction at the piers and the abutments of a bridge not only leads to different probabilities of failure for given intensity measures but also leads to different hierarchy and distribution of damage within the structure for the same set of earthquake ground motions even if the overall probability of exceeding a given damage state is the same. The paper concludes with the comparative assessment of the effect for different soil conditions, foundation configurations, and ground motion characteristics mentioned in this study along with the relevant analysis and design recommendations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献