Radar signal delay in the Dvali-Gabadadze-Porrati gravity in the vicinity of the Sun     

Ioannis Haranas  Omiros Ragos  Ioannis Gkigkitzis 《Astrophysics and Space Science》2012,342(1):281-285

In this paper we examine the recently introduced Dvali-Gabadadze-Porrati (DGP) gravity model. We use a space-time metric in which the local gravitation source dominates the metric over the contributions from the cosmological flow. Anticipating ideal possible solar system effects, we derive expressions for the signal time delays in the vicinity of the Sun. and for various ranges of the angle θ of the signal approach, The time contribution due to DGP correction to the metric is found to be proportional to b ^3/2/c ² r ₀. For r ₀ equal to 5 Mpc and θ in the range [−π/3,π/3], Δt is equal to 0.0001233 ps. This delay is extremely small to be measured by today’s technology but it could be probably measurable by future experiments.  相似文献   

Multi‐objective risk‐informed design of floor isolation systems          下载免费PDF全文

Ioannis Gidaris  Alexandros A. Taflanidis  Diego Lopez‐Garcia  George P. Mavroeidis 《地震工程与结构动力学》2016,45(8):1293-1313

The design of floor isolation systems (FISs) for the protection of acceleration sensitive contents is examined considering multiple objectives, all quantified in terms of the probabilistic system performance. The competing objectives considered correspond to (i) maximization of the level of protection offered to the sensitive content (acceleration reduction) and (ii) minimization of the demand for the isolator displacement capacity and, more importantly, for the appropriate clearance to avoid collisions with surrounding objects (floor displacement reduction). Both of these objectives are probabilistically characterized utilizing a versatile, simulation‐based framework for quantifying seismic risk, addressing all important uncertainties related to the seismic hazard and the structural model. FIS performance is assessed through time‐history analysis, allowing for all important sources of nonlinearity to be directly addressed in the design framework. The seismic hazard is described through a stochastic ground motion model. For efficiently performing the multi‐objective optimization, an augmented surrogate modeling methodology is established, considering development of a single metamodel with respect to both the uncertain model parameters and the design variables for the FIS system. This surrogate model is then utilized to simultaneously support the probabilistic risk assessment and the design optimization to provide the Pareto front of dominant designs. Each of these designs establishes a different compromise between the considered risk‐related objectives offering a variety of potential options to the designer. Within the illustrative example, the efficiency of the established framework is exploited to compare three different FIS implementations, whereas the impact of structural uncertainties on the optimal design is also evaluated. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A Study of Fog Characteristics Using a Coupled WRF–COBEL Model Over Thessaloniki Airport, Greece     

Stavroula Stolaki  Ioannis Pytharoulis  Theodore Karacostas 《Pure and Applied Geophysics》2012,169(5-6):961-981

An attempt is made to couple the one dimensional COBEL-ISBA (Code de Brouillard à l’échelle Locale-Interactions Soil Biosphere Atmosphere) model with the WRF (Weather Research and Forecasting)–ARW (Advanced Research WRF) numerical weather prediction model to study a fog event that formed on 20 January 2008 over Thessaloniki Airport, Greece. It is the first time that the coupling of COBEL and WRF models is achieved and applied to a fog event over an airport. At first, the performance of the integrated WRF–COBEL system is investigated, by validating it against the available surface observations. The temperature and humidity vertical profiles were used for initializing the model. The performance of WRF–COBEL is considered successful, since it realistically simulated the fog onset and dissipation better than the WRF alone. The COBEL’s sensitivity to initial conditions such as temperature and specific humidity perturbations was also tested. It is found that a small increase of temperature (~1°C) counteracts fog development and results in less fog density. On the other hand, a small decrease of temperature results in much denser fog formation. It is concluded that the integrated model approach for aviation applications can be useful to study fog impact on local traffic and aviation.  相似文献   

Climate change effects on the marine characteristics of the Aegean and Ionian Seas     

Christos Makris  Panagiota Galiatsatou  Konstantia Tolika  Christina Anagnostopoulou  Katerina Kombiadou  Panayotis Prinos  Kondylia Velikou  Zacharias Kapelonis  Elina Tragou  Yannis Androulidakis  Gerasimos Athanassoulis  Christos Vagenas  Ioannis Tegoulias  Vassilis Baltikas  Yannis Krestenitis  Theodoros Gerostathis  Kostantinos Belibassakis  Eugen Rusu 《Ocean Dynamics》2016,66(12):1603-1635

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Relaxation base seismic isolator          下载免费PDF全文

Duc Chuan Vu  Ioannis Politopoulos  Sette Diop 《地震工程与结构动力学》2016,45(12):2027-2037

This paper deals with the use, for seismic applications, of a Maxwell element in parallel with a low damping isolator. The study of the properties of the frequency response function shows that this isolator is capable to reduce the base displacement of isolated structures with no considerable amplification of the non‐isolated modes. This is, also, confirmed by the floor response spectra under earthquake excitations. Hence, the previously mentioned isolator does not present the drawbacks met when base displacement is reduced by increasing damping. Moreover, it seems that its performance is comparable with that of more elaborated and expensive techniques combining passive and semi‐active devices. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Behavior of rigid blocks with geometrical defects under seismic motion: an experimental and numerical study          下载免费PDF全文

Charlie Mathey  Cyril Feau  Ioannis Politopoulos  David Clair  Laurent Baillet  Michel Fogli 《地震工程与结构动力学》2016,45(15):2455-2474

The present work investigates the influence of small geometrical defects on the behavior of slender rigid blocks. A comprehensive experimental campaign was carried out on one of the shake tables of CEA/Saclay in France. The tested model was a massive steel block with standard manufacturing quality. Release, free oscillations tests as well as shake table tests revealed a non‐negligible out‐of‐plane motion even in the case of apparently plane initial conditions or excitations. This motion exhibits a highly reproducible part for a short duration that was used to calibrate a numerical geometrically asymmetrical model. The stability of this model when subjected to 2000 artificial seismic horizontal bidirectional signals was compared with the stability of a symmetrical one. This study showed that the geometrical imperfections slightly increase the rocking and overturning probabilities for earthquake signals in a narrow range of peak ground acceleration. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Experimental investigation of the seismic response of classical temple columns     

Vasileios A. Drosos  Ioannis Anastasopoulos 《Bulletin of Earthquake Engineering》2015,13(1):299-310

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Regeneration of the Acrylic Weak Base Anion Exchange Resin by Means of Sodiumcarbonate     

Z. Matjka  J. Erlebach  K. Savvides  H. Ioannis  J. Eli&#x;ek 《洁净——土壤、空气、水》1980,8(2):187-190

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A Strong Motion Database in Greece     

Kalogeras  Ioannis S. 《Natural Hazards》2002,26(3):265-277

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Fault scarps and deformation rates in Lazio–Abruzzo, Central Italy: Comparison between geological fault slip-rate and GPS data     

Ioannis D. Papanikolaou  Gerald P. Roberts  Alessandro M. Michetti 《Tectonophysics》2005,408(1-4):147

We compare new and literature data concerning the integrated deformation rate since 18 ka for the central Apennines with deformation rate data derived from a 6-year GPS campaign. We constructed topographic profiles across the majority of the active faults in the area. We derived deformation rate data from displaced post-glacial sediments and slopes associated with the last major glacial retreat that occurred in the region about 18 kyr ago. Paleoseismic investigations in this region clearly show that offset of these features is the cumulative effect of repeated surface faulting earthquakes with magnitudes in the range 5.5 ≤ Ms ≤ 7.0. A cumulative throw-rate diagram, incorporating both our values and the values extracted from the literature (i.e., previously published trenching studies, scarp profiles and offset terraces), is presented providing a regional picture of the spatial deformation rate distribution in the central Apennines, during the latest Pleistocene and Holocene. By converting cumulative throw-rates into heave rates, we calculate maximum extension rates of ca. 2 mm/year at the location of the same transect where 6 ± 2 mm/year has been measured with GPS over 6 years. This discrepancy between geodetic and geological fault slip-rate data implies that we have to be cautious whenever we use GPS data for seismic hazard assessment purposes or when attempting to reconstruct the tectonic processes in an area, because geodetic data may be unrepresentative of the longer-term deformation rates. On the other hand, this discrepancy may provide insights into the mechanics of the seismic cycle. We discuss various scenarios that may explain the mis-match between long-term and short-term measurements.  相似文献