The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Vassilios Zervas - One of the best experts on this subject based on the ideXlab platform.
-
Spatial Variation of seismic ground motions: An overview
Applied Mechanics Reviews, 2002Co-Authors: Aspasia Zerva, Vassilios ZervasAbstract:This study addresses the topic of the Spatial Variation of seismic ground motions as evaluated from data recorded at dense instrument arrays. It concentrates on the stochastic description of the Spatial Variation, and focuses on Spatial coherency. The estimation of coherency from recorded data and its interpretation are presented. Some empirical and semi-empirical coherency models are described, and their validity and limitations in terms of physical causes discussed. An alternative approach that views the Spatial Variation of seismic motions as deviations in amplitudes and phases of the recorded data around a coherent approximation of the seismic motions is described. Simulation techniques for the generation of artificial Spatially variable seismic ground motions are also presented and compared. The effect of coherency on the seismic response of extended structures is highlighted. This review article includes 133 references. @DOI: 10.1115/1.1458013#
Maria Q. Feng - One of the best experts on this subject based on the ideXlab platform.
-
Fragility analysis of bridges under ground motion with Spatial Variation
International Journal of Non-Linear Mechanics, 2003Co-Authors: Sang-hoon Kim, Maria Q. FengAbstract:Seismic ground motion can vary significantly over distances comparable to the length of a majority of highway bridges on multiple supports. This paper presents results of fragility analysis of highway bridges under ground motion with Spatial Variation. Ground motion time histories are artificially generated with different amplitudes, phases, as well as frequency contents at different support locations. Monte Carlo simulation is performed to study dynamic responses of an example multi-span bridge under these ground motions. The effect of Spatial Variation on the seismic response is systematically examined and the resulting fragility curves are compared with those under identical support ground motion. This study shows that ductility demands for the bridge columns can be underestimated if the bridge is analyzed using identical support ground motions rather than differential support ground motions. Fragility curves are developed as functions of different measures of ground motion intensity including peak ground acceleration, peak ground velocity, spectral acceleration, spectral velocity and spectral intensity. This study represents a first attempt to develop fragility curves under Spatially varying ground motion and provides information useful for improvement of the current seismic design codes so as to account for the effects of Spatial Variation in the seismic design of long-span bridges.
Aspasia Zerva - One of the best experts on this subject based on the ideXlab platform.
-
Spatial Variation of seismic ground motions: An overview
Applied Mechanics Reviews, 2002Co-Authors: Aspasia Zerva, Vassilios ZervasAbstract:This study addresses the topic of the Spatial Variation of seismic ground motions as evaluated from data recorded at dense instrument arrays. It concentrates on the stochastic description of the Spatial Variation, and focuses on Spatial coherency. The estimation of coherency from recorded data and its interpretation are presented. Some empirical and semi-empirical coherency models are described, and their validity and limitations in terms of physical causes discussed. An alternative approach that views the Spatial Variation of seismic motions as deviations in amplitudes and phases of the recorded data around a coherent approximation of the seismic motions is described. Simulation techniques for the generation of artificial Spatially variable seismic ground motions are also presented and compared. The effect of coherency on the seismic response of extended structures is highlighted. This review article includes 133 references. @DOI: 10.1115/1.1458013#
Barbara Tschirren - One of the best experts on this subject based on the ideXlab platform.
-
Small‐scale Spatial Variation in infection risk shapes the evolution of a Borrelia resistance gene in wild rodents
Molecular ecology, 2018Co-Authors: Luca Cornetti, Daniela Hilfiker, Mélissa Lemoine, Barbara TschirrenAbstract:Spatial Variation in pathogen-mediated selection is predicted to influence the evolutionary trajectory of host populations and lead to Spatial Variation in their immunogenetic composition. However, to date few studies have been able to directly link small-scale Spatial Variation in infection risk to host immune gene evolution in natural, nonhuman populations. Here, we use a natural rodent-Borrelia system to test for associations between landscape-level Spatial Variation in Borrelia infection risk along replicated elevational gradients in the Swiss Alps and Toll-like receptor 2 (TLR2) evolution, a candidate gene for Borrelia resistance, across bank vole (Myodes glareolus) populations. We found that Borrelia infection risk (i.e., the product of Borrelia prevalence in questing ticks and the average tick load of voles at a sampling site) was Spatially variable and significantly negatively associated with elevation. Across sampling sites, Borrelia prevalence in bank voles was significantly positively associated with Borrelia infection risk along the elevational clines. We observed a significant association between naturally occurring TLR2 polymorphisms in hosts and their Borrelia infection status. The TLR2 variant associated with a reduced likelihood of Borrelia infection was most common in rodent populations at lower elevations that face a high Borrelia infection risk, and its frequency changed in accordance with the change in Borrelia infection risk along the elevational clines. These results suggest that small-scale Spatial Variation in parasite-mediated selection affects the immunogenetic composition of natural host populations, providing a striking example that the microbial environment shapes the evolution of the host's immune system in the wild.
T. Nakamura - One of the best experts on this subject based on the ideXlab platform.
-
Reef structure regulates small-scale Spatial Variation in coral bleaching
Marine Ecology Progress Series, 2008Co-Authors: H.s. Lenihan, M. Adjeroud, M.j. Kotchen, J.l. Hench, T. NakamuraAbstract:Coral bleaching is often characterized by high Spatial Variation across reef systems. Using a field survey and manipulative experiment, we tested whether the physical structure of coral reefs modifies environmental conditions that, in turn, influence Spatial Variation in bleaching in 3 scleractinian corals, Pocillopora verrucosa, Acropora elseyi, and Porites rus. Corals inhabit mainly the hard-bottom seafloor, or dead or partially dead coral heads (‘bommies'). Bommies (0.10 to 3.0 m tall) position corals at different water depths and expose them to differences in light, temperature, hydrodynamics, and sedimentation, factors that can influence patterns of bleaching. We conducted our study in association with a 14 d warming event that caused bleaching in lagoons of Moorea, French Polynesia. Bleaching in naturally occurring colonies of Pocillopora spp. and Acopora spp. was greater on the seafloor (0 m tall) than on short (0.35 to 0.40 m tall) and tall bommies (1.0 to 1.2 m tall). Bleaching in P. verrucosa and A. elseyi transplanted to reef structures in the experiment generally decreased with increasing reef height (seafloor > short bommies > tall bommies). P. rus did not bleach under any conditions observed. Regression analyses revealed that reef structure controlled current speed and sedimentation at the microhabitat scale (from centimeters to meters), and that these factors regulated bleaching and mortality in P. verrucosa and A. elseyi. Our results imply that the physical structure of shallow water reef habitat influences the performance of coral colonies by modifying environmental stress, and that accounting for this structure is important in managing coral reef systems.
