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11.
P. Nomikou S. Carey K. L. C. Bell D. Papanikolaou K. Bejelou K. Cantner D. Sakellariou I. Perros 《Natural Hazards》2014,72(3):1375-1390
Kolumbo submarine volcano, located NE of Santorini caldera in the Aegean Sea, has only had one recorded eruption during historic times (1650 AD). Tsunamis from this event severely impacted the east coast of Santorini with extensive flooding and loss of buildings. Recent seismic studies in the area indicate a highly active region beneath Kolumbo suggesting the potential for future eruptive activity. Multibeam mapping and remotely operated vehicle explorations of Kolumbo have led to new insights into the eruptive processes of the 1650 AD eruption and improved assessments of the mechanisms by which tsunamis were generated and how they may be produced in future events. Principal mechanisms for tsunami generation at Kolumbo include shallow submarine explosions, entrance of pyroclastic flows into the sea, collapse of rapidly accumulated pyroclastic material, and intense eruption-related seismicity that may trigger submarine slope collapse. Compared with Santorini, the magnitude of explosive eruptions from Kolumbo is likely to be much smaller but the proximity of the volcano to the eastern coast of Santorini presents significant risks even for lower magnitude events. 相似文献
12.
Evaggelos Ntotsios Costas Papadimitriou Panagiotis Panetsos Grigorios Karaiskos Kyriakos Perros Philip C. Perdikaris 《Bulletin of Earthquake Engineering》2009,7(2):469-483
A bridge health monitoring system is presented based on vibration measurements collected from a network of acceleration sensors.
Sophisticated structural identification methods, combining information from the sensor network with the theoretical information
built into a finite element model for simulating bridge behavior, are incorporated into the system in order to monitor structural
condition, track structural changes and identify the location, type and extent of damage. This work starts with a brief overview
of the modal and model identification algorithms and software incorporated into the monitoring system and then presents details
on a Bayesian inference framework for the identification of the location and the severity of damage using measured modal characteristics.
The methodology for damage detection combines the information contained in a set of measurement modal data with the information
provided by a family of competitive, parameterized, finite element model classes simulating plausible damage scenarios in
the structure. The effectiveness of the damage detection algorithm is demonstrated and validated using simulated modal data
from an instrumented R/C bridge of the Egnatia Odos motorway, as well as using experimental vibration data from a laboratory
small-scaled bridge section. 相似文献
13.
L. Menut R. Vautard C. Flamant C. Abonnel M. Beekmann P. Chazette P. H. Flamant D. Gombert D. Guédalia D. Kley M. P. Lefebvre B. Lossec D. Martin G. Mégie P. Perros M. Sicard G. Toupance 《Annales Geophysicae》2000,18(11):1467-1481
The Étude et Simulation de la QUalité de lair en Ile de France (ESQUIF) project is the first integrated project dedicated to the study of the processes leading to air pollution events over the Paris area. The project was carried out over two years (summer 1998 to winter 2000) to document all types of meteorological conditions favourable to air quality degradation, and in particular to photo oxydant formation. The goals of ESQUIF are (1) to improve our understanding of the relevant chemical and dynamical processes and, in turn, improve their parametrizations in numerical models, and (2) to improve and validate existing models dedicated to pollution analysis, scenarios and/or forecasting, by establishing a comprehensive and thorough database. We present the rationale of the ESQUIF project and we describe the experimental set-up. We also report on the first experiments which took place during the summer of 1998 involving surface networks, and remote sensing instruments as well as several aircraft. Focusing on three days of August 1998, the relative contributions of long-range transported and locally-produced ozone to the elevated ozone concentrations observed during this period are discussed and chemistry-transport model preliminary results on this period are compared to measurements. 相似文献
14.
B. Cros P. Durand H. Cachier Ph. Drobinski E. Frjafon C. Kottmeier P. E. Perros V. -H. Peuch J. -L. Ponche D. Robin F. Saïd G. Toupance H. Wortham 《Atmospheric Research》2004,69(3-4):241-279
In this paper, the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphérique et de Transport d'Emissions” (ESCOMPTE) program is presented. The ESCOMPTE program is used to produce a relevant set of data for testing and evaluating regional pollution models. It includes high-resolution (in space and time) atmospheric emission inventories and field experiments, and covers an area of 120×120 km, centered over the Marseilles-Berre area in the southeast of France during Summer 2001. This region presents a high occurrence of photochemical pollution events, which result from numerous industrial and urban sources of primary pollutants. From the dynamical characteristics of the area, sea-breeze circulation and channeling effects due to terrain features highly influence the location of the pollutant plumes. ESCOMPTE will provide a highly documented framework for dynamics and chemistry studies.Campaign strategies and experimental set up are described. During the planning phase, existing modeling results helped defining the experimental design. The campaign involved surface measurement networks, remote sensing, ship-borne, balloon-borne, and airplane measurements. Mean standard meteorological parameters and turbulent fluxes, ozone, ozone precursors, photochemically active trace gases, and aerosols were measured. Five intensive observation periods (IOPs) were documented using a wide spectrum of instruments, involving aircraft (7) (one of them equipped with a Doppler lidar, the others for in situ meteorological and chemical measurements), constant volume balloons (33), ozone lidars (5), wind profilers (15 sodars and radars), Doppler scanning lidar (1), radiosonde systems (at 4 locations), instrumented ships (2). In addition to the air quality networks from environmental agencies, 15 supplementary ground stations equipped for chemistry and/or meteorology and/or surface flux measurements, were operational. All instruments were calibrated and compared during a Quality Control/Quality Assurance (QC/QA) week, at the very beginning of the campaign.Fifteen days were intensively documented during five IOPs, referenced as 1, 2a, 2b, 3, and 4. High pollution levels were encountered during sea-breeze conditions observed during IOPs 2b and 3, whereas IOPs 2a and 4 corresponded to moderate wind, and channeled plume regimes. In addition, hourly emissions inventories for all IOPs were established to complete data sets and to finalize the ESCOMPTE database (EDB).Two other projects were associated to ESCOMPTE: urban boundary layer (UBL) and tropospheric water vapor content by GPS tomography (GPS/H2O). They took advantage of the scientific environment provided by ESCOMPTE. 相似文献
15.
Benedikt Soja Richard S. Gross Claudio Abbondanza Toshio M. Chin Michael B. Heflin Jay W. Parker Xiaoping Wu Tobias Nilsson Susanne Glaser Kyriakos Balidakis Robert Heinkelmann Harald Schuh 《Journal of Geodesy》2018,92(9):1063-1077
The Global Geodetic Observing System requirement for the long-term stability of the International Terrestrial Reference Frame is 0.1 mm/year, motivated by rigorous sea level studies. Furthermore, high-quality station velocities are of great importance for the prediction of future station coordinates, which are fundamental for several geodetic applications. In this study, we investigate the performance of predictions from very long baseline interferometry (VLBI) terrestrial reference frames (TRFs) based on Kalman filtering. The predictions are computed by extrapolating the deterministic part of the coordinate model. As observational data, we used over 4000 VLBI sessions between 1980 and the middle of 2016. In order to study the predictions, we computed VLBI TRF solutions only from the data until the end of 2013. The period of 2014 until 2016.5 was used to validate the predictions of the TRF solutions against the measured VLBI station coordinates. To assess the quality, we computed average WRMS values from the coordinate differences as well as from estimated Helmert transformation parameters, in particular, the scale. We found that the results significantly depend on the level of process noise used in the filter. While larger values of process noise allow the TRF station coordinates to more closely follow the input data (decrease in WRMS of about 45%), the TRF predictions exhibit larger deviations from the VLBI station coordinates after 2014 (WRMS increase of about 15%). On the other hand, lower levels of process noise improve the predictions, making them more similar to those of solutions without process noise. Furthermore, our investigations show that additionally estimating annual signals in the coordinates does not significantly impact the results. Finally, we computed TRF solutions mimicking a potential real-time TRF and found significant improvements over the other investigated solutions, all of which rely on extrapolating the coordinate model for their predictions, with WRMS reductions of almost 50%. 相似文献
16.
I. Fenneteaux P. Colin A. Etienne H. Boudries A. L. Dutot P. E. Perros G. Toupance 《Journal of Atmospheric Chemistry》1999,32(2):233-280
The atmospheric concentrations of O3, NMHCs, PAN and NOx were measured at the TOR station in Porspoder (Brittany, France) from 1992 to 1995. The results from April 1992 to December 1994 are reported here. In order to study the behaviour of trace gases in the air masses coming from the Atlantic Ocean, the origin of these air masses was characterised by the analysis of the five-day back-trajectories reaching 950 mbar at Porspoder. Three kinds of oceanic air masses are considered, depending on their origin: North Atlantic northern and southern latitudes and North American continent. It appears that the oceanic high-latitude troposphere was strongly influenced by continental emissions, which in turn impacted the median latitude troposphere during polar outflow events. A greater accumulation of anthropogenic compounds in the Arctic sector was calculated and may be at the origin of the high oxidant levels measured in spring in this same sector. The influence of north American emissions on the European coast was also studied and seems to reach a maximum in spring. Long-range transport of long- lived species was observed throughout the year, but evidence for winter transport of more reactive species, such as ethene, is also shown. Meteorological parameters and local photochemistry appear to play an important role in the distribution of the pollutants over the North Atlantic Ocean throughout the year. Further investigations are needed to give more complete information about the origin, formation and destruction of the secondary pollutants. 相似文献
17.
Jun Zhang Kyriakos Mouratidis Zhu Manli 《International journal of geographical information science》2013,27(10):1091-1111
Despite the existence of obstacles in many database applications, traditional spatial query processing assumes that points in space are directly reachable and utilizes the Euclidean distance metric. In this paper, we study spatial queries in the presence of obstacles, where the obstructed distance between two points is defined as the length of the shortest path that connects them without crossing any obstacles. We propose efficient algorithms for the most important query types, namely, range search, nearest neighbours, e‐distance joins, closest pairs and distance semi‐joins, assuming that both data objects and obstacles are indexed by R‐trees. The effectiveness of the proposed solutions is verified through extensive experiments. 相似文献
18.
Tobias Nilsson Benedikt Soja Kyriakos Balidakis Maria Karbon Robert Heinkelmann Zhiguo Deng Harald Schuh 《Journal of Geodesy》2017,91(7):857-866
The very long baseline interferometry (VLBI) Intensive sessions are typically 1-h and single-baseline VLBI sessions, specifically designed to yield low-latency estimates of UT1-UTC. In this work, we investigate what accuracy is obtained from these sessions and how it can be improved. In particular, we study the modeling of the troposphere in the data analysis. The impact of including external information on the zenith wet delays (ZWD) and tropospheric gradients from GPS or numerical weather prediction models is studied. Additionally, we test estimating tropospheric gradients in the data analysis, which is normally not done. To evaluate the results, we compared the UT1-UTC values from the Intensives to those from simultaneous 24-h VLBI session. Furthermore, we calculated length of day (LOD) estimates using the UT1-UTC values from consecutive Intensives and compared these to the LOD estimated by GPS. We find that there is not much benefit in using external ZWD; however, including external information on the gradients improves the agreement with the reference data. If gradients are estimated in the data analysis, and appropriate constraints are applied, the WRMS difference w.r.t. UT1-UTC from 24-h sessions is reduced by 5% and the WRMS difference w.r.t. the LOD from GPS by up to 12%. The best agreement between Intensives and the reference time series is obtained when using both external gradients from GPS and additionally estimating gradients in the data analysis. 相似文献
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20.
Maria Izquierdo Nikolaos Koukouzas Sofia Touliou Kyriakos D. Panopoulos Xavier Querol Grigorios Itskos 《Applied Geochemistry》2011,26(9-10):1599-1606
The mobility of inorganic pollutants is of key concern for a range of industrial and engineering applications of fly ash produced during the combustion of lignite in power generation. This paper investigates the role that the geochemical features of lignite, the ash composition and the partitioning of elements during combustion play in determining leaching properties of lignite fired by-products. The work is based on surveys on three lignite-fired power plants in Greece. Calcium-rich ashes show a high abatement potential for SO2 and other gaseous pollutants. For most elements, the concentrations in the parent lignite and the ashes follow the same trend. Relative enrichments in Cd, Co, Cr, Cu, Mo, Ni, Pb, U, V, W, Zn fingerprint the regional and local geological settings of the lignite basins. The total and leachable concentrations of highly volatile elements are strongly influenced by the interaction with ubiquitous free lime. A broad array of elements is highly insoluble in alkaline ash, while a few oxyanionic-forming elements display substantial mobility. Their mode of occurrence in the parent lignite plays a primary role in the leaching of combustion ashes. The outcomes of this study may assist in addressing the impact of co-firing high ash or high Ca alternative fuels on the leaching properties of combustion by-products. 相似文献