Spatial and Temporal Patterns in <Emphasis Type="Italic">Thalassia testudinum</Emphasis> Leaf Tissue Nutrients at the Chandeleur Islands,Louisiana, USA     

Kelly M. Darnell  Tim J. B. Carruthers  Patrick Biber  Ioannis Y. Georgiou  Thomas C. Michot  Ronald G. Boustany 《Estuaries and Coasts》2017,40(5):1288-1300

Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows.  相似文献   

Nonstationary stochastic response of structural systems equipped with nonlinear viscous dampers under seismic excitation   总被引：1，自引：0，他引：1       下载免费PDF全文

Enrico Tubaldi  Ioannis A. Kougioumtzoglou 《地震工程与结构动力学》2015,44(1):121-138

Nonlinear viscous dampers are supplemental devices widely used for enhancing the performance of structural systems exposed to seismic hazard. A rigorous evaluation of the effect of these damping devices on the seismic performance of a structural system should be based on a probabilistic approach and take into account the evolutionary characteristics of the earthquake input and of the corresponding system response. In this paper, an approximate analytical technique is proposed for studying the nonstationary stochastic response characteristics of hysteretic single degree of freedom systems equipped with viscous dampers subjected to a fully nonstationary random process representing the seismic input. In this regard, a stochastic averaging/linearization technique is utilized to cast the original nonlinear stochastic differential equation of motion into a simple first‐order nonlinear ordinary differential equation for the nonstationary system response variance. In comparison with standard linearization schemes, the herein proposed technique has the significant advantage that it allows to handle realistic seismic excitations with time‐varying frequency content. Further, it allows deriving a formula for determining the nonlinear system response evolutionary power spectrum. By this way, ‘moving resonance’ effects, related to both the evolutionary seismic excitation and the nonlinear system behavior, can be observed and quantified. Several applications involving various system and input properties are included. Furthermore, various response parameters of interest for the seismic performance assessment are considered as well. Comparisons with pertinent Monte Carlo simulations demonstrate the reliability of the proposed technique. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Evaluation of a multimode pushover procedure for asymmetric in plan buildings under biaxial seismic excitation     

Grigorios Manoukas  Ioannis Avramidis 《Bulletin of Earthquake Engineering》2014,12(6):2607-2632

In this paper a recently developed multimode pushover procedure for the approximate estimation of structural performance of asymmetric in plan buildings under biaxial seismic excitation is evaluated. Its main idea is that the seismic response of an asymmetric multi-degree-of-freedom system with \(N\) degrees of freedom under biaxial excitation can be related to the responses of \(N\) ‘modal’ equivalent single-degree-of-freedom (E-SDOF) systems under uniaxial excitation. The steps of the proposed methodology are quite similar to those of the well-known modal pushover analysis. However, the establishment of the (E-SDOF) systems is based on a new concept, in order to take into account multidirectional seismic effects. The proposed methodology does not require independent analysis in the two orthogonal directions and therefore the application of simplified superposition rules for the combination of seismic component effects is avoided. After a brief outline of the theoretical background and the application process, an extensive evaluation study is presented, which shows that, in general, the proposed methodology provides a reasonable estimation for the vast majority of the calculated response parameters.  相似文献   

Petrographic and geochemical characterization of Archaic‐Hellenistic tableware production at Solunto,Sicily     

Giuseppe Montana  Ioannis Iliopoulos  Valeria Tardo  Caterina Greco 《Geoarchaeology》2009,24(1):86-110

A selected assortment of Archaic‐Hellenistic tableware samples from Solunto, a Phoenician‐Punic site located 20 km east of Palermo (Sicily), has been subjected to thin‐section petrography and chemical analysis (XRF). In this settlement several ceramic kilns remained operative over a long time period (7th to 3rd century B.C.). The main goal of this analytical study is to distinguish the ceramics manufactured locally from regional and off‐island imports. Analytical results were matched to similar data concerning local natural clay sources and to coeval tableware productions from other sites in the same area. The ceramic pastes used by the ancient craftsmen of Solunto in the case of this class of pottery could be differentiated clearly by their petrochemical characteristics. We conclude that ceramics were locally produced far beyond satisfying just internal consumption needs, indicating interaction of Solunto with neighboring Greek colonies, indigenous people, and Phoenician‐Punic colonies of Sicily. © 2009 Wiley Periodicals, Inc.  相似文献   

Coastal vulnerability assessment based on video wave run-up observations at a mesotidal,steep-sloped beach     

Michalis Ioannis Vousdoukas  Dagmara Wziatek  Luis Pedro Almeida 《Ocean Dynamics》2012,62(1):123-137

Coastal imagery obtained from a coastal video monitoring station installed at Faro Beach, S. Portugal, was combined with topographic data from 40 surveys to generate a total of 456 timestack images. The timestack images were processed in an open-access, freely available graphical user interface (GUI) software, developed to extract and process time series of the cross-shore position of the swash extrema. The generated dataset of 2% wave run-up exceedence values R ₂ was used to form empirical formulas, using as input typical hydrodynamic and coastal morphological parameters, generating a best-fit case RMS error of 0.39 m. The R ₂ prediction capacity was improved when the shore-normal wind speed component and/or the tidal elevation η _tide were included in the parameterizations, further reducing the RMS errors to 0.364 m. Introducing the tidal level appeared to allow a more accurate representation of the increased wave energy dissipation during low tides, while the negative trend between R ₂ and the shore-normal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravity-to-incident frequency energy contributions to the total swash spectra was in general lower than the ones reported in the literature E _infra/E _inci > 0.8, since low-frequency contributions at the steep, reflective Faro Beach become more significant mainly during storm conditions. An additional parameterization for the total run-up elevation was derived considering only 222 measurements for which η _total,2 exceeded 2 m above MSL and the best-fit case resulted in RMS error of 0.41 m. The equation was applied to predict overwash along Faro Beach for four extreme storm scenarios and the predicted overwash beach sections, corresponded to a percentage of the total length ranging from 36% to 75%.  相似文献   

Nonlinear analysis of earthquake fault rupture interaction with historic masonry buildings     

Marianna Loli  Ioannis Anastasopoulos  George Gazetas 《Bulletin of Earthquake Engineering》2015,13(1):83-95

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Restrain of a seismically isolated bridge by external stoppers     

Stergios A. Mitoulis  Ioannis A. Tegos 《Bulletin of Earthquake Engineering》2010,8(4):973-993

The current design of seismically isolated bridges usually combines the use of bearings and stoppers, as a second line of defence. The stoppers allow the development of the in-service movements of the bridge deck, without transmitting significant loads to the piers and their foundations, while during earthquake they transmit the entire seismic action. Despite the fact that stoppers, which restrain the transverse seismic movements of the deck, are used frequently in seismically isolated bridges, the use of longitudinal stoppers is relatively rare, mainly due to the large in-service constraint movements of bridges. The present paper proposes a new type of external longitudinal stoppers, which are installed in stiff sub-structures-boundaries, aiming at limiting the bridge seismic movements. The parametric investigation, which was conducted in order to identify the seismic efficiency of the external stoppers, showed that the interaction of the bridge with the stiff boundaries can lead to significant reductions in the seismic movements of the bridge. Serviceability is appropriately arranged in the paper by expansion joints and approach slabs.  相似文献   

Analysis of cut-and-cover tunnels against large tectonic deformation   总被引：2，自引：0，他引：2  

Ioannis Anastasopoulos  George Gazetas 《Bulletin of Earthquake Engineering》2010,8(2):283-307

Tunnels are believed to be rather “insensitive” to earthquakes. Although a number of case histories seem to favor such an argument, failures and collapses of underground structures in the earthquakes of Kobe (1995), Düzce–Bolu (1999), and Taiwan (1999) have shown that there are exceptions to this “rule”. Among them: the case of tunnels crossed by fault rupture. This paper presents the analysis and design of two highway cut-and-cover tunnels in Greece against large tectonic dislocation from a normal fault. The analysis, conducted with finite elements, places particular emphasis on realistically modeling the tunnel-soil interface. Soil behavior is modeled thorough an elastoplastic constitutive model with isotropic strain softening, which has been extensively validated through successful predictions of centrifuge model tests. A primary conclusion emerging from the paper is that the design of cut-and-cover structures against large tectonic deformation is quite feasible. It is shown that the rupture path is strongly affected by the presence of the tunnel, leading to development of beneficial stress-relieving phenomena such as diversion, bifurcation, and diffusion. The tunnel may be subjected either to hogging deformation when the rupture emerges close to its hanging-wall edge, or to sagging deformation when the rupture is near its footwall edge. Paradoxically, the maximum stressing is not always attained with the maximum imposed dislocation. Therefore, the design should be performed on the basis of design envelopes of the internal forces, with respect to the location of the fault rupture and the magnitude of dislocation. Although this study was prompted by the needs of a specific project, the method of analysis, the design concepts, and many of the conclusions are sufficiently general to merit wider application.  相似文献   

Modern sands derived from the Vertiskos Unit of the Serbomacedonian Massif (N. Greece): a preliminary study on the weathering of the Unit     

Ioannis K. Georgiadis  Antonios Koroneos  Ananias Tsirambides  Michael Stamatakis 《Central European Journal of Geosciences》2012,4(3):465-477

Modern sand samples were collected from the Vertiskos Unit of the Serbomacedonian Massif, northern Greece, and were examined for their texture and mineralogical composition. They were collected from active channels and torrents. The textural study demonstrated that these modern sands are moderately to very-poorly sorted, often polymodal in grain size distribution, texturally and mineralogically immature to submature, and consist of coarse-grained gravelly sands to slightly-gravelly muddy sands. The dominant composition is quartzofeldspathic. All samples contain detrital minerals of metamorphic origin, mainly amphibole and garnet, in addition to minor amounts of pyroxene and detrital calcite. These sediments were deposited rapidly and close to their source, the metamorphic basement of the Vertiskos Unit. The mineral constituents of the samples indicate that the Vertiskos Unit is undergoing rapid physical weathering due to the temperate and seasonal climate. The results of this study suggest that these modern sands constitute one sedimentary petrologic province comprised of primarily of amphibole-garnet.  相似文献   

An overview of seismic testing needs in Europe: towards a new advanced experimental facility     

Francesco Marazzi  Ioannis Politopoulos  Alberto Pavese 《Bulletin of Earthquake Engineering》2011,9(2):623-640

This paper presents a synthesis of the activities carried out in the framework of the European project EFAST (design study of a European Facility for Advanced Seismic Testing) to determine the general characteristics of a new European world-class facility for earthquake testing of structures. To this end the demands for the necessary testing to support the modern seismic engineering research have been investigated and compared to the actual capabilities of European laboratories. The outcome is the determination of performance objectives and requirements in the gross. On the basis of the needs assessment carried out during the first phase of the project and taking into account the technological advances in both experimental techniques and equipment (hardware and software) for seismic testing, a modern facility for experimental seismic research should be composed, mainly, of a high performance shaking tables array and a large reaction structure where both traditional (pseudo-static/dynamic) and innovative testing techniques (e.g. real time hybrid testing) can be applied and combined. A tentative layout of the facility is also proposed and issues related to the best utilization of such a laboratory are discussed.  相似文献