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941.
Biological invasions represent a relevant ecological and economic problem of our globalized world. While a few species have been classified as invasive due to their ecological and economic impacts on the invaded ecosystems (e.g., zebra mussel), others show contrasting invasive potential, depending on the invaded ecosystem and/or the traits of the exotic species. This paper reviews the worldwide distribution, ecological impacts and the reasons that explain the invasive success of the aquatic mud snail Potamopyrgus antipodarum Gray (Hydrobiidae, Mollusca), which is native to New Zealand. This review shows that most studies on P. antipodarum distribution have been conducted in Europe, North America and Australia, and few studies in Asia. The distribution of this snail is still unknown in other parts of the world (e.g., Africa, South and Central America). The range of invaded aquatic ecosystems varies from fresh to salt water and from lentic to lotic ecosystems. The ecological impact of this species is due to the fast population growth rate and to the extremely high densities that it can reach, leading to altered C and N cycles in invaded ecosystems. However, at low densities mud snails have been shown to enhance secondary production. Additionally, P. antipodarum has been found to overcome the negative effects of predators and parasites (e.g., it survives the pass through the digestive tracts of fish). This review contributes to assess the magnitude and ecological risk of P. antipodarum invasion throughout the world. 相似文献
942.
Alexandre A. Costa António Arêde Aníbal Costa Jo?o Guedes Bruno Silva 《Bulletin of Earthquake Engineering》2012,10(1):135-159
Stone masonry is one of the oldest building techniques used worldwide and it is known to exhibit poor behaviour under seismic
excitations. In this context, this work aims at assessing the in-plane behaviour of an existing double-leaf stone masonry
pier by experimental testing. Additionally, a detailed 3D finite element numerical analysis based on micro-modelling of the
original pier is presented (fully describing the geometry and division of each individual elements, namely infill, blocks
and joints) aiming at simulating the experimental test results. This numerical strategy can be seen as an alternative way
of analysing this type of constructions, particularly useful for laboratory studies, and suitable for the calibration of simplified
numerical models. As part of a wider research activity, this work is further complemented with the presentation of an effective
retrofit/strengthening technique (reinforced connected plaster) to achieve a significant improvement of its in-plane cyclic
response which is experimentally verified in the results presented herein. 相似文献
943.
Romeu Silva Vicente Hugo Rodrigues Humberto Varum Aníbal Costa Jos António Raimundo Mendes da Silva 《地震工程与工程振动(英文版)》2012,11(1):23-34
This paper discusses the issue of performance requirements and construction criteria for masonry enclosure and infill walls.Vertical building enclosures in European countries are very often constituted by non-load-bearing masonry walls, using horizontally perforated clay bricks.These walls are generally supported and confined by a reinforced concrete frame structure of columns and beams/slabs.Since these walls are commonly considered to be nonstructural elements and their influence on the structural response is ignored,their consideration in the design of structures as well as their connection to the adjacent structural elements is frequently negligent or insufficiently detailed.As a consequence,nonstructural elements,as for wall enclosures,are relatively sensitive to drift and acceleration demands when buildings are subjected to seismic actions. Many international standards and technical documents stress the need for design acceptability criteria for nonstructural elements,however they do not specifically indicate how to prevent collapse and severe cracking,and how to enhance the overall stability in the case of moderate to high seismic loading.Furthermore,a review of appropriate measures to improve enclosure wall performance and both in-plane and out-of-plane integrity under seismic actions is addressed. 相似文献
944.
Judith Hebelen Rodriguez Eduardo Daniel Wannaz María Luisa Pignata Andreas Fangmeier Jürgen Franzaring 《洁净——土壤、空气、水》2012,40(12):1315-1319
In order to study the pollution gradient in the vicinity of a large aluminium production facility in Patagonia (Argentina), a passive biomonitoring was performed employing foliage from three tree species. Primary scope was to identify pollution gradients and to select suitable tree species which can be used as biomonitor plants in the study area. Therefore, leaves of Eucalyptus rostrata, Populus hybridus and different needle ages of Pinus radiata were collected at different distances from the industry and the fluoride concentration was analysed in washed and unwashed samples in order to determine the amount of external fluoride. Washing reduced the F‐concentrations by 24, 39 and 51% on average in E. rostrata, P. hybridus and P. radiata, respectively, indicating that species‐specific characteristics determine the accumulation and wash‐off of dust‐associated fluorine. F‐concentrations varied from 6 to 3652 ppm F in unwashed samples indicating a steep pollution gradient in the study area. The influence of F‐emissions was discernible in all samples up to a distance of 3500 m from the smelter. E. rostrata accumulated more fluorine than the other species at equal distance from the emission source. The present study confirms that aluminium smelting results in high F deposition in the study area. Establishing a biomonitor network around large emitters is suitable and feasible to evaluate the efficiency of air control measures. 相似文献
945.
José Tavares Araruna Júnior Paula Elias Benedetti Patrício José Moreira Pires Ricardo Froitzheim Rinelli de Almeida 《洁净——土壤、空气、水》2012,40(9):906-910
In order to aid in the efforts of the 2016 Olympic Games, the organizers of 2011 Rock in Rio decided to build a permanent venue next to the Olympic Park. The area is problematic from the geotechnical point of view since it presents soils with low shear strength, low permeability, and high plasticity, so major soil improvement works were carried out. Bored soil–cement columns were placed to increase soil shear strength and reduce compressibility. A meter thick fill composed of gneiss residual soil was placed and trenches were digged to drain rainwater. However, earlier studies conducted on Jacarepaguá Lagoon have detected the presence of heavy metals in these sediments. In this study, an environmental survey on the Jacarepaguá Lagoon sediments took place in order to choose a place where its sediments could be dredged to be later used in the drainage facilities. The results indicated areas where the threshold level 1 (low probability of adverse effects) issued by the general procedures for sediments quality assessments for dredging purposes, Resolution no 344 of the Brazilian Federal Government, was surpassed. Levels above the limits established for cadmium (Cd), lead (Pb), copper (Cu), nickel (Ni), and zinc (Zn) were detected. Based on this consideration the State Environmental Agency issued a permit allowing the organizers of 2011 Rock in Rio to dredge an area close to City of Rock in order to obtain coarse sediments for the drainage facilities. In addition, it was found that those sediments were ideal for this application since their hydraulic conductivity is on the order of 10?2 cm/s. 相似文献
946.
947.
948.
Coherent structure dynamics and sediment particle motion around a cylindrical pier in developing scour holes 总被引:1,自引:1,他引:0
Oscar Link Christian González María Maldonado Cristián Escauriaza 《Acta Geophysica》2012,60(6):1689-1719
Recent investigations on the dynamics of the turbulent horseshoe vortex system (THV) around cylindrical piers have shown that the rich coherent dynamics of the vortical structures is dominated by low-frequency bimodal fluctuations of the velocity field. In spite of these advances, many questions remain regarding the changes of the flow and sediment transport dynamics as scour progresses. In this investigation we carry out laboratory experiments to register the development of the scour hole around a cylindrical pier in a fine-sand bed (d 50 = 0.36 mm). We use the bathymetry measured in the experiment to simulate the flow field employing the detached-eddy simulation approach (DES), which has shown to resolve most of the turbulent stresses around surface-mounted obstacles. From these simulations we compare the dynamics of the THV to the flat-bed case, and analyze the effects on particle transport and sediment flux using the Lagrangian particle model of Escauriaza and Sotiropoulos (2011b) to study the impact of the changes of the flow on the sediment dynamics. 相似文献
949.
Evaluation of a set of individual geological and petrophysical parameters is necessary in many geoscientific studies or those
with constructional purposes. However, correlation and mutual evaluation of these parameters are very complicated. Our methodology,
which is part of the expert evaluation, is based on compilation of four significant effects: local subsurface geology, groundwater
table (and accumulation of surface water), deformation of the surface due to mining (subsidence), and landslides. Different
values of specified significances were assigned to all four selected effects. The class of foundation conditions was selected
according to the summary of values of specified significances for a given point. This value describes how the selected parameters
influence vibration effect on the surface and resistance of buildings to this seismic loading. The pilot map of foundation
conditions, which was elaborated as part of the evaluation of Stonava area in 2008, is presented. 相似文献
950.
Ramón A. López‐Pérez Luis E. Calderón‐Aguilera Héctor Reyes‐Bonilla José D. Carriquiry Pedro Medina‐Rosas Amilcar L. Cupul‐Magaña María D. Herrero‐Pérezrul Héctor A. Hernández‐Ramírez Miguel Á. Ahumada‐Sempoal Betsabe M. Luna‐Salguero 《Marine Ecology》2012,33(4):407-416
Corals in the Eastern Pacific extend south from the Gulf of California to Ecuador and oceanic Chile, and west from Colombia to Clipperton Atoll. Nevertheless, large stretches of the Mexican Pacific remain fundamentally unstudied. Therefore, to assess the current conditions of coral communities, a coastal fringe ~300 km long (17°40′ N, 101°39′ W to 16°46′ N, 99°49′ W) was surveyed within the Southern Mexican Pacific, between 2005 and 2009. Fifteen stony coral species were identified at 13 coral communities and six Pocillopora‐dominated fringing reefs, with Pocillopora verrucosa and Pocillopora damicornis the primary contributing taxa. Reef development was identified in embayments or behind rocks or islands that offered shelter from northern and northwestern winds. Observations of Pocillopora effusus, Pocillopora inflata, Porites lobata, Pavona clavus, and Pavona varians expanded the species known geographic ranges by several degrees of latitude, suggesting reef building fauna comprised a mixture of widespread and relatively rare Eastern Pacific corals. Results indicated greater live coral cover in the Ixtapa‐Zihuatanejo area (15–73%) than in the Acapulco localities, which had high algal dominance; the reefs in the latter region exhibited high erosion. Regional differences are likely the result of long‐standing anthropogenic pressures around Acapulco since 1950, when it became an important tourist destination. This paper is the first detailed report of ecologically stressed corals and coral reefs from the state of Guerrero on the Mexican Southern Pacific coast. 相似文献