High pressure behaviour of lead feldspar (PbAl2Si2O8)     

M. Tribaudino  P. Benna  E. Bruno  M. Hanfland 《Physics and Chemistry of Minerals》1999,26(5):367-374

An in situ high pressure powder diffraction study, using high-brilliance synchrotron radiation, on lead feldspar (PbAl₂Si₂O₈) was performed. Two samples, with Q _od=0.68 and 0.76, were loaded in a diamond anvil cell and were compressed up to 11 GPa. Up to P=7.1 GPa the only phase present is lead feldspar. In the range 7.1–9.4 GPa sudden changes in the position of the reflections suggest the transformation of lead feldspar to a new phase (probably feldspar-like). The absence of split that would be compatible with triclinic symmetry rules out the monoclinic-triclinic transition, that was reported for the structurally similar strontium feldspar. At P>9.4 GPa some new extra reflections not indexable in the feldspar cell are present as well. During decompression the lead feldspar was the only phase present at P<6 GPa. Peak enlargement was observed with pressure, probably preliminary to amorphization. However almost complete amorphization was observed only after fortuitous shock compression at ∼18 GPa; the crystallinity was recovered at room pressure after decompression. The bulk modulus for lead feldspar was K=71.0(9) and 67.6(1.2) GPa for the two samples, in the range reported for feldspars. The cell parameters show a compression pattern which is similar to that observed in anorthite, with Δa/a ₀>Δc/c ₀>Δb/b ₀; comparison with the high temperature behaviour shows that for lead feldspar the strain tensor with pressure is more isotropic and the deformation along a is less prominent. A turnover in the behaviour of the β angle with pressure suggests a change in the compression behaviour at P∼2 GPa. Rietveld refinement of the Pb coordinates was performed in a series of spectra with pressure ranging from 0.6 to 6.5 GPa. The combined analysis of cell parameters and Pb coordinates with pressure showed that the compression of the structure is mainly achieved by an approach of Pb atoms along a *. Received: 21 July 1998 / Revised, accepted: 13 October 1998  相似文献   

Benthic geochemistry of manganese in the Bay of Biscay,and sediment mass accumulation rate     

Aurélia Mouret  Pierre Anschutz  Pascal Lecroart  Gwénaëlle Chaillou  Christelle Hyacinthe  Jonathan Deborde  Frans J. Jorissen  Bruno Deflandre  Sabine Schmidt  Jean-Marie Jouanneau 《Geo-Marine Letters》2009,29(3):133-149

Manganese is a major redox reactive element of benthic metabolism. We have built a database of existing knowledge on the benthic geochemistry of Mn in the Bay of Biscay, in order to comprehensively assess the behaviour of Mn in a variety of environments during early diagenesis. The database contains vertical profiles of particulate and dissolved Mn species of 59 cores collected during 17 cruises between 1997 and 2006 at nine stations positioned between 140 and 4,800 m water depths. At all studied stations, Mn species follow the conventional distribution, where Mn(III,IV) species are enriched in the oxic layer, and dissolved Mn is present in the anoxic sediments. A minor part of Mn-oxides originates from sedimenting particles. The major part is of diagenetic origin, and derives from the oxidation of upward-diffusing dissolved Mn(II). Mn-oxide inventories are higher at the deeper stations than at the shallower ones. This difference cannot be attributed to different sources of sedimenting particles, but it must depend on sedimentation rate and diagenetic processes. At depth, dissolved Mn(II) concentrations are constant. This probably reflects equilibrium with an authigenic Mn(II) phase, which is the ultimate phase into which Mn is fossilized. The Mn content of deeper anoxic sediments is similarly low in all the cores studied, associated with corresponding trends of Mn content in sedimenting particles of the Bay of Biscay. Bioturbation, rather than redox oscillations, can convey Mn(III,IV) species downwards into the anoxic sediments where they are reduced, associated with a peak of dissolved Mn. Because dissolved Mn(II) is re-oxidized when it diffuses towards the oxic layer, the inventory of the diagenetic Mn(III,IV) phase remains at steady state, especially at stations where the oxic layer is thick. It then becomes possible to calculate the residence time of diagenetic Mn(III,IV) particles within the oxic layer, using the upward-directed flux of pore water Mn(II). By applying this residence time to the accumulation of sediments within the oxic layer, we obtain the sediment mass accumulation rate. The values calculated for the sediments of the Bay of Biscay fit well with accumulation rates obtained from radionuclides or sediment traps. The method has also been validated with data collected in other marine sedimentary environments. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Can the gold coast beaches withstand extreme events?     

Bruno?CastelleEmail author  Yann?Le?Corre  Rodger?Tomlinson 《Geo-Marine Letters》2008,28(1):23-30

The Gold Coast sandy beaches of Queensland (Australia) are exposed to energetic wave conditions. Storms, particularly tropical cyclones, have a high potential of destruction. The Gold Coast has not experienced excessive erosive events over the past 30 years. However, some climate indicators suggest that cyclone frequency is likely to increase in response to global climate change within the near future. Over a 2-month period in early 2006, beach surveys were undertaken with a theodolite total station at four different sites. Offshore wave conditions were provided by SWAN regional wave modelling. During this study, the Gold Coast was exposed to three major storms, the first one being the second most energetic over the past 30 years. Results show a substantial variability of the beach response to these events along the Gold Coast, and that engineering structures do not have marked effects. Easterly swells have the greatest impact on the Gold Coast sub-aerial beach morphology. When low wave-energy conditions prevail, the southern Gold Coast beaches recover more quickly than the northern ones, as they are sheltered from high SE waves and draw advantage from the artificial sand bypassing system. Nevertheless, the data show that the Gold Coast beaches are exceedingly fragile. For instance, the early March decadal event considerably weakened the beaches, which resulted in surprisingly high erosion rates all along the Gold Coast during the two following annual wave events. This study suggests that the Gold Coast beaches would not be able to withstand the impact of an increased frequency of extreme events similar in scale to those of 1967.  相似文献   

黄金岸线海滩能否抵挡极端事件的冲击     

Bruno Castelle  Yann Le Corre  刘锐 《海洋地质前沿》2008,24(9):21-24

砂质海滩是最变化莫测和脆弱的海岸带类型之一。众所周知,海滩在高能环境中会被侵蚀,但海滩上不同位置点对于极端事件的抵御能力则大不相同。而且,侵蚀速率通常受控于海滩状况、机械结构和前期补给。  相似文献   

Seismic reliability‐based ductility demand evaluation for inelastic base‐isolated structures with friction pendulum devices          下载免费PDF全文

Paolo Castaldo  Bruno Palazzo  Tatiana Ferrentino 《地震工程与结构动力学》2017,46(8):1245-1266

The aim of this work is to propose seismic reliability‐based relationships between the strength reduction factors and the displacement ductility demand of nonlinear structural systems equipped with friction pendulum isolators (FPS) depending on the structural properties. The isolated structures are described by employing an equivalent 2dof model characterized by a perfectly elastoplastic rule to account for the inelastic response of the superstructure, whereas, the FPS behavior is described by a velocity‐dependent model. An extensive parametric study is carried out encompassing a wide range of elastic and inelastic building properties, different seismic intensity levels and considering the friction coefficient as a random variable. Defined a set of natural seismic records and scaled to the seismic intensity corresponding to life safety limit state for L'Aquila site (Italy) according to NTC08, the inelastic characteristics of the superstructures are designed as the ratio between the average elastic responses and increasing strength reduction factors. Incremental dynamic analyses (IDAs) are developed to evaluate the seismic fragility curves of both the inelastic superstructure and the isolation level assuming different values of the corresponding limit states. Integrating the fragility curves with the seismic hazard curves related to L'Aquila site (Italy), the reliability curves of the equivalent inelastic base‐isolated structural systems, with a design life of 50 years, are derived proposing seismic reliability‐based regression expressions between the displacement ductility demand and the strength reduction factors for the superstructure as well as seismic reliability‐based design (SRBD) abacuses useful to define the FPS properties. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Conceptual design and full‐scale experimentation of cladding panel connection systems of precast buildings          下载免费PDF全文

Giandomenico Toniolo  Bruno Dal Lago 《地震工程与结构动力学》2017,46(14):2565-2586

Despite the long series of European research projects that has led to the setting of fully reliable seismic design criteria for precast structures, recent earthquakes have shown that a weak point still exists in the proportioning of the connection systems of cladding wall panels. Following this finding, this paper outlines an organic setting of the design problem of precast concrete structures including cladding–structure interaction and describes three possible solutions, namely, the isostatic, integrated, and dissipative systems. The related fastening arrangements, with the use of existing and innovative connection devices, are also described. This paper comments on the results of the pseudo‐dynamic and cyclic tests performed at ELSA Laboratory of the European Joint Research Centre of Ispra (Italy) on a full‐scale prototype of precast structure. The conception and the experimental performance of the structure with nine different configurations of either vertical or horizontal wall panel claddings are presented. The analysis of the results highlights the effectiveness of the different solutions in a comparative way. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Beach recovery from extreme storm activity during the 2013–14 winter along the Atlantic coast of Europe     

Guillaume Dodet  Bruno Castelle  Gerd Masselink  Timothy Scott  Mark Davidson  France Floc'h  Derek Jackson  Serge Suanez 《地球表面变化过程与地形》2019,44(1):393-401

The storm sequence of the 2013–14 winter left many beaches along the Atlantic coast of Europe in their most eroded state for decades. Understanding how beaches recover from such extreme events is essential for coastal managers, especially in light of potential regional increases in storminess due to climate change. Here we analyse a unique dataset of decadal beach morphological changes along the west coast of Europe to investigate the post-2013–14 winter recovery. We show that the recovery signature is site specific and multi-annual, with one studied beach fully recovered after 2 years, and the others only partially recovered after 4 years. During the recovery phase, winter waves primarily control the timescales of beach recovery, as energetic winter conditions stall the recovery process whereas moderate winter conditions accelerate it. This inter-annual variability is well correlated with climate indices. On exposed beaches, an equilibrium model showed significant skill in reproducing the post-storm recovery and thus can be used to investigate the recovery process in more detail. © 2018 John Wiley & Sons, Ltd.  相似文献   

Decentralized water supply by reservoir network reduces power demand for water distribution in a semi-arid basin     

Antônia Tatiana Pinheiro do Nascimento  Natália Holanda Maia Cavalcanti  Bruno Parente Leitão de Castro 《水文科学杂志》2019,64(1):80-91

In the Brazilian semi-arid region, thousands of small dams have been built over time to enhance water availability, accumulating water and hydraulic energy at high altitudes. Simulations were performed in this study to assess how the arrangement of reservoirs impacts on the power demand for water distribution in the Banabuiú River Basin (19?800 km²), Brazil. The power required to pump water from 1405 reservoirs to all districts with diffuse demands is 6.5 GWh/year, whereas in the scenario with only the 12 larger strategic reservoirs, the power demand reached 45.3 GWh/year. Alone, the largest reservoir in the basin can supply water to all districts. Nonetheless, in that scenario, the power demand would reach 195 GWh/year, which is 30 times the power required in the real reservoir arrangement. Thus, decentralization by small reservoirs not only promotes more democratic access to water, but also increases energy efficiency by storing it at higher altitudes and closer to the diffuse demands.  相似文献   

粤北晚泥盆世天子岭组遗迹组构及其环境解释   总被引：1，自引：0，他引：1  

齐永安  胡斌  Bruno Mistiaen 《煤田地质与勘探》2005,33(2):11-14

遗迹组构是由生物成因改造的沉积岩组构,它是物理过程和生物过程相互作用的产物。本文在广东韶关晚泥盆世天子岭组碳酸盐岩沉积中建立了4个遗迹组构,即反映局限台地或封闭海湾环境的Planolies montanus遗迹组构,反映台地潮下低能环境的Thalassinoides—Planolites遗迹组构,反映潮上-潮间环境的．Skolithos遗迹组构和受固底底质控制的Thalassinoides遗迹组构。对遗迹化石和生物扰动构造进行阶层分析,从中识别出受固底底质控制的遗迹化石Thalassinoides.sp,这类遗迹化石常常代表层序地层学中的重要界面。  相似文献   

Chemical defenses against generalist fish predators and fouling organisms in two invasive ahermatypic corals in the genus Tubastraea     

Bruno G. Lages  Beatriz G. Fleury  Angelo C. Pinto  Joel C. Creed 《Marine Ecology》2010,31(3):473-482

The introduction of exotic marine species has caused considerable economic and ecological damage around the world. Some of these species possess adaptations such as secondary metabolites which facilitate their successful invasion into new areas. In this study we tested two hypotheses: (i) crude extracts produced by two invasive hard corals Tubastraea coccinea and Tubastraea tagusensis, introduced to the southwest Atlantic, inhibit predation by generalist fish; (ii) substances found in the crude extracts of both species reduce or enhance the settlement of other organisms. In an in situ palatability bioassay the extract of T. tagusensis reduced predation by generalist fish. The extracts of both species of coral showed species‐specific effects on fouling organisms in in situ gel plate bioassays. Control and extract plates had similar total cover, although plates with extracts had significantly fewer Cladophora sp., and Lithophyllum sp. was only detected on control gels. In contrast, a hydrozoan was only found on plates with extracts and overall community ordination demonstrated clear differences in the fouling communities between treatments. These results demonstrate that both coral species have chemical substances which can bring about a negative interaction with potential fish predators and competitors such as algal and invertebrate foulers and the advantage gained could explain their success in invading new regions to the detriment of local fauna and flora.  相似文献