Ground motion spatial variability effects on seismic response control of cable-stayed bridges     

Shehata E. Abdel Raheem  Toshiro Hayashikawa  Uwe Dorka 《地震工程与工程振动(英文版)》2011,10(1):37-49

The spatial variability of input ground motion at supporting foundations plays a key role in the structural response of cable-stayed bridges (CSBs); therefore, spatial variation effects should be included in the analysis and design of effective vibration control systems. The control of CSBs represents a challenging and unique problem, with many complexities in modeling, control design and implementation, since the control system should be designed not only to mitigate the dynamic component of the structural response but also to counteract the effects of the pseudo-static component of the response. The spatial variability effects on the feasibility and efficiency of seismic control systems for the vibration control of CSBs are investigated in this paper. The assumption of uniform earthquake motion along the entire bridge may result in quantitative and qualitative differences in seismic response as compared with those produced by uniform motion at all supports. A systematic comparison of passive and active system performance in reducing the structural responses is performed, focusing on the effect of the spatially varying earthquake ground motion on the seismic response of a benchmark CSB model with different control strategies, and demonstrates the importance of accounting for the spatial variability of excitations.  相似文献   

A Long-Term Study of Spawning Activity in a Florida Gulf Coast Population of Horseshoe Crabs (<Emphasis Type="BoldItalic">Limulus polyphemus</Emphasis>)     

H. Jane Brockmann  Sheri L. Johnson 《Estuaries and Coasts》2011,34(5):1049-1067

Populations of the American horseshoe crab (Limulus polyphemus) differ in broad areas of their biology. We observed a non-harvested, marked Florida Gulf coast population during their spring spawning (March–May) in 11 years across a 17-year period (1992–2009). Long-term changes occurred in the number of spawning pairs: the population was stable from 1992 to 2000 but increased markedly after 2000. Short-term variation in numbers of spawning pairs, unpaired females, unpaired males, and operational sex ratios was explained by changes over the season and during each week of spring tides and by differences in actual (not predicted) maximum high tide height. Wind direction strongly affected tidal inundation and the number of spawning horseshoe crabs. Tagging individuals revealed that females returned to the nesting beach less often than males and most females were re-sighted only within 1 week of spring tides. No animals were seen across more than 6 years. Implications for management are discussed.  相似文献   

On the potential for automated realtime detection of nonlinear internal waves from seafloor pressure measurements     

Uwe Stöber  James N. Moum 《Applied Ocean Research》2011,33(4):275-285

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Typhoon-induced precipitation impact on nutrient and suspended matter dynamics of a tropical estuary affected by human activities in Hainan,China     

Lucia S. Herbeck  Daniela Unger  Uwe Krumme  Su Mei Liu  Tim C. Jennerjahn 《Estuarine, Coastal and Shelf Science》2011

Typhoons regularly hit the coasts along the northern South China Sea during summer monsoon. However, little is known on the effects of typhoon-related heavy precipitation on estuarine dynamics and coastal ecosystems. We analyzed physico-chemical characteristics, and concentrations and composition of dissolved and suspended matter in the Wenchang/Wenjiao Estuary (WWE) on the tropical island of Hainan, China, prior to and after typhoon Kammuri in August 2008. Before the typhoon, the estuary displayed vertical and horizontal gradients. High nutrient inputs from agriculture and widespread aquaculture were to a large extent converted into biomass inside the estuarine lagoon resulting in low export of nutrients to coastal waters and a mainly autochthonous origin of total suspended matter (TSM). Heavy typhoon-associated precipitation increased river runoff, which moved the location of the estuarine salinity gradient seaward. It resulted in an export of dissolved and particulate matter to coastal waters one day after the typhoon. Dissolved nutrients increased by up to an order of magnitude and TSM increased approximately twofold compared to pre-typhoon values. Lower δ¹³C_org and δ¹⁵N and elevated C/N ratios of TSM together with lower chlorophyll a (chl a) concentrations indicated an increased contribution of terrestrial material originating from typhoon-induced soil erosion. Local uptake of excess nutrients inside the lagoon was inhibited because of reduced water transparency and the lack of phytoplankton, which had been washed out by the initial freshwater pulse. Two weeks after the typhoon, TSM concentration and composition had almost returned to pre-typhoon conditions. However, physico-chemical properties and nutrients were still different from pre-typhoon conditions indicating that the estuarine system had not fully recovered. Unusually high chl a concentrations in the coastal zone indicated a phytoplankton bloom resulting from the typhoon-induced nutrient export. The typhoon-induced flushing of the WWE resulted in hyposalinity, reduced water transparency, siltation, as well as temporary eutrophication of coastal waters. These are physiological stressors, which are known to impair the performance of adjacent seagrass meadows and coral reefs. The predicted increase in typhoon frequency and intensity will lead to a frequently recurring exposure of coastal ecosystems to these threats, particularly in the South China Sea region where aquaculture is widespread and tropical cyclone frequency is at a maximum.  相似文献   

Decadal fingerprints of freshwater discharge around Greenland in a multi-model ensemble   总被引：2，自引：2，他引：0  

Didier Swingedouw  Christian B. Rodehacke  Erik Behrens  Matthew Menary  Steffen M. Olsen  Yongqi Gao  Uwe Mikolajewicz  Juliette Mignot  Arne Biastoch 《Climate Dynamics》2013,41(3-4):695-720

The recent increase in the rate of the Greenland ice sheet melting has raised with urgency the question of the impact of such a melting on the climate. As former model projections, based on a coarse representation of the melting, show very different sensitivity to this melting, it seems necessary to consider a multi-model ensemble to tackle this question. Here we use five coupled climate models and one ocean-only model to evaluate the impact of 0.1 Sv (1 Sv = 10⁶ m³/s) of freshwater equally distributed around the coast of Greenland during the historical era 1965–2004. The ocean-only model helps to discriminate between oceanic and coupled responses. In this idealized framework, we find similar fingerprints in the fourth decade of hosing among the models, with a general weakening of the Atlantic Meridional Overturning Circulation (AMOC). Initially, the additional freshwater spreads along the main currents of the subpolar gyre. Part of the anomaly crosses the Atlantic eastward and enters into the Canary Current constituting a freshwater leakage tapping the subpolar gyre system. As a consequence, we show that the AMOC weakening is smaller if the leakage is larger. We argue that the magnitude of the freshwater leakage is related to the asymmetry between the subpolar-subtropical gyres in the control simulations, which may ultimately be a primary cause for the diversity of AMOC responses to the hosing in the multi-model ensemble. Another important fingerprint concerns a warming in the Nordic Seas in response to the re-emergence of Atlantic subsurface waters capped by the freshwater in the subpolar gyre. This subsurface heat anomaly reaches the Arctic where it emerges and induces a positive upper ocean salinity anomaly by introducing more Atlantic waters. We found similar climatic impacts in all the coupled ocean–atmosphere models with an atmospheric cooling of the North Atlantic except in the region around the Nordic Seas and a slight warming south of the equator in the Atlantic. This meridional gradient of temperature is associated with a southward shift of the tropical rains. The free surface models also show similar sea-level fingerprints notably with a comma-shape of high sea-level rise following the Canary Current.  相似文献   

Impact controversies: Impact recognition criteria and related issues     

Wolf Uwe Reimold  Ludovic Ferrière  Alex Deutsch  Christian Koeberl 《Meteoritics & planetary science》2014,49(5):723-731

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New mineralogical and chemical data on the Machinga (L6) chondrite,Malawi     

Christian Koeberl  Wolf Uwe Reimold  Hanna E. Horsch  Roland K. W. Merkle 《Meteoritics & planetary science》1990,25(1):23-26

Abstract— The Machinga, southern Malawi, Africa, L6 chondrite (observed fall, 22 January 1981) contains accessory phases of metal, troilite, chromite, and native Cu (which is associated with limonite and found in zones of aqueous alteration). Rare accessory phases are apatite and pentlandite, which are uncommon in L6 chondrites. Major mineral constituents (olivine, orthopyroxene, and plagioclase) indicate shock effects at a level of about 15–20 GPa shock pressure. The meteorite is thus classified to be of L6d type. Melt pockets of widely variable composition are abundant.  相似文献   

Geophysical signature of the Pretoria Saltpan impact structure and a possible satellite crater     

Dion Brandt  Wolf Uwe Reimold  Raymond J. Durrheim 《Meteoritics & planetary science》1994,29(3):379-384

Abstract— The genesis of the 1.13-km-diameter Pretoria Saltpan crater has long been the focus of a controversy. Its origin has been explained by either meteorite impact or “cryptoexplosive” volcanic activity, but it was recently confirmed, through detailed petrographic and chemical analysis of a breccia layer forming part of the crater fill, that the crater was formed by impact. As the limited previous geophysical work failed to support an impact origin, a more detailed gravity and magnetic study was conducted. A possible 400-m-diameter circular crater located 3 km to the southwest of the main crater was also investigated with geophysical methods, including resistivity, seismics and ground-probing radar. The gravity signature of the main crater is compatible with that of a simple impact crater and the magnetic signature (no magnetic anomaly could be detected) rules out the possibility of a central magnetic volcanic body below the crater-fill sediments. The results for the possible twin or satellite crater are inconclusive. As it is the only such feature in the entire region, it should not be overlooked. A drilling program may reveal interesting results.  相似文献   

Provenance analyses of the heavy-mineral beach sands of the Annaba coast,northeast Algeria,and their consequences for the evaluation of fossil placer deposit     

Asma Chemam  Soraya Hadjzobir  Menana Daif  Uwe Altenberger  Christina Günter 《Journal of Earth System Science》2018,127(8):118

The paper presents the first study of heavy-mineral sand beaches from the Mediterranean coast of Annaba/Algeria. The studied beaches run along the basement outcrops of the Edough massif, which are mainly composed by micaschists, tourmaline-rich quartzo-feldspathic veins, gneisses, skarns and marbles. Sand samples were taken from three localities (Ain Achir, Plage-Militaire and El Nasr). The heavy-mineral fraction comprises between 74 and 91 vol%. The garnets of the beaches are almandine rich and tourmalines vary with respect to their location from schorl to dravite. Tourmaline at Ain Achir and the Plage-Militaire is schorlits, while at El Nasr beach dravite is ubiquitous. The World Shale Average normalised REE of the sands and the basement outcrops reveal: (i) Ain Achir beach: REE pattern of sand and the coastal rocks from the studied beaches reflects a multiple sources; (ii) Plage-Militaire: the sand and the coastal outcrops show similar LREE and a strong enrichment in HREE, suggesting the presence HREE-rich phases found as inclusions in staurolite; (iii) El Nasr: two types of sand patterns are found: one with flat REE pattern similar to the proximal rocks and other one enriched in HREE suggesting a mixed source.  相似文献   

Local climate change induced by groundwater overexploitation in a high Andean arid watershed,Laguna Lagunillas basin,northern Chile   总被引：2，自引：0，他引：2  

Konstantin Scheihing  Uwe Tröger 《Hydrogeology Journal》2018,26(3):705-719

The Laguna Lagunillas basin in the arid Andes of northern Chile exhibits a shallow aquifer and is exposed to extreme air temperature variations from 20 to ?25 °C. Between 1991 and 2012, groundwater levels in the Pampa Lagunillas aquifer fell from near-surface to ~15 m below ground level (bgl) due to severe overexploitation. In the same period, local mean monthly minimum temperatures started a declining trend, dropping by 3–8 °C relative to a nearby reference station. Meanwhile, mean monthly maximum summer temperatures shifted abruptly upwards by 2.7 °C on average in around 1996. The observed air temperature downturns and upturns are in accordance with detected anomalies in land-surface temperature imagery. Two major factors may be causing the local climate change. One is related to a water-table decline below the evaporative energy potential extinction depth of ~2 m bgl, which causes an up-heating of the bare soil surface and, in turn, influences the lower atmosphere. At the same time, the removal of near-surface groundwater reduces the thermal conductivity of the upper sedimentary layer, which consequently diminishes the heat exchange between the aquifer (constant heat source of ~10 °C) and the lower atmosphere during nights, leading to a severe dropping of minimum air temperatures. The observed critical water-level drawdown was 2–3 m bgl. Future and existing water-production projects in arid high Andean basins with shallow groundwater should avoid a decline of near-surface groundwater below 2 m bgl and take groundwater-climate interactions into account when identifying and monitoring potential environmental impacts.  相似文献