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排序方式: 共有422条查询结果,搜索用时 187 毫秒
191.
192.
Temporal variability of sedimentation rates and mobile fauna inside and outside a gorgonian garden 下载免费PDF全文
Paramuricea clavata (Cnidaria, Octocorallia) is an important ecosystem engineer of coralligenous assemblages increasingly threatened by anthropogenic activities and climate changes. As climate warming is predicted to continue in the coming years it is important to hypothesize future scenarios. Here we tested the influence of gorgonian colonies on sedimentation rates and vagile fauna trends, comparing sediments collected by traps inside and outside a gorgonian garden, in a coralligenous community of the Western Ligurian Sea, at 32 m depth, over a period of 1 year. The results indicated that sea fans created a sort of homeostatic effect on the surrounding habitat. We found evidence that where gorgonian colonies were present, the monthly fluctuations of sediments rate were lower than outside a garden. Gorgonian colonies also influenced the distribution of the associated vagile fauna; these organisms were generally more abundant inside than outside the garden. The data collected in this work appear to confirm the role of P. clavata as an ecosystem engineer, affecting biomass and variability of the surrounding habitat at both spatial and temporal scales. 相似文献
193.
Broadband (0.05 to 20 s) prediction of displacement response spectra based on worldwide digital records 总被引:6,自引:0,他引:6
A new set of empirical equations for prediction of displacement response spectral ordinates from 20 Hz to T = 20 s is illustrated. The coefficients of the equations were obtained by regressing a dataset based on 1,155 tri-axial digital
and 9 analog accelerometer records from 60 earthquakes worldwide. Long period disturbances in the accelerograms were evaluated
and removed using a very recent method, aimed at preserving the long-period spectral content of the records. Analysis of variance
has disclosed only little evidence for regional dependence of ground motions, while a carefully conducted evaluation of site
effects resulted in clearly differentiated spectral amplification bands associated to the main ground types B, C, and D of
Eurocode 8. Spectral ordinates for vibration periods >5 s were found to scale with magnitude quite consistently with theoretical
scaling from Brune’s model. On the other hand, comparison of results with those yielded by recent prediction models in Europe
and the United States (NGA), indicated that the latter may not be uniformly reliable at long periods. The proposed empirical
equations are easily implemented in computer programs for seismic hazard assessment, being characterized by a simple functional
form and a restricted number of predictor variables.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
194.
Waldo Sven Lavado Casimiro David Labat Josyane Ronchail Jhan Carlo Espinoza Jean Loup Guyot 《水文研究》2013,27(20):2944-2957
The hydroclimatology of the Peruvian Amazon–Andes basin (PAB) which surface corresponding to 7% of the Amazon basin is still poorly documented. We propose here an extended and original analysis of the temporal evolution of monthly rainfall, mean temperature (Tmean), maximum temperature (Tmax) and minimum temperature (Tmin) time series over two PABs (Huallaga and Ucayali) over the last 40 years. This analysis is based on a new and more complete database that includes 77 weather stations over the 1965–2007 period, and we focus our attention on both annual and seasonal meteorological time series. A positive significant trend in mean temperature of 0.09 °C per decade is detected over the region with similar values in the Andes and rainforest when considering average data. However, a high percentage of stations with significant Tmean positive trends are located over the Andes region. Finally, changes in the mean values occurred earlier in Tmax (during the 1970s) than in Tmin (during the 1980s). In the PAB, there is neither trend nor mean change in rainfall during the 1965–2007 period. However, annual, summer and autumn rainfall in the southern Andes presents an important interannual variability that is associated with the sea surface temperature in the tropical Atlantic Ocean while there are limited relationships between rainfall and El Niño‐Southern Oscillation (ENSO) events. On the contrary, the interannual temperature variability is mainly related to ENSO events. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
195.
Barbara Delmonte Carlo Baroni Per S. Andersson Hans Schoberg Margareta Hansson Sarah Aciego Jean‐Robert Petit Samuel Albani Claudia Mazzola Valter Maggi Massimo Frezzotti 《第四纪科学杂志》2010,25(8):1327-1337
A new ice core (TALDICE) drilled at Talos Dome (East Antarctica, Ross Sea sector) preserves a ca. 250 ka long record of palaeoclimate and atmospheric history. We investigate dust variability and provenance at the site during glacial periods and the Holocene through the Sr–Nd isotopic composition of ice core dust and potential source areas (PSA). We provide new isotopic data on dust sources from Victoria Land such as regoliths, glacial drifts, aeolian sands and beach deposits. Some of these sources are located at high altitude and are known to have been ice free throughout the Pleistocene. The major features of the TALDICE dust record are very similar to those from central East Antarctica. During glacial times, South America was the dominant dust supplier for Talos Dome as well as for the entire East Antarctic plateau. Conversely, during the Holocene the principal input of mineral dust at Talos Dome probably derives from proximal sources which are the ice‐free areas of northern Victoria Land, located at similar altitude with respect to the drilling site. Atmospheric mobilisation of dust from these neighbouring areas and transport inland to Talos Dome can be ultimately associated with advection of maritime air masses from the Pacific/Ross Sea region. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
196.
Fatma Trabelsi Abdallah Ben Mammou Jamila Tarhouni Carlo Piga Gaetano Ranieri 《水文研究》2013,27(14):2004-2020
The time domain electromagnetic method (TDEM) is applied to monitor, to delineate and to map the saltwater intrusion zones in the Mediterranean Plio‐Quaternary aquifer. Forty‐two TDEM soundings were carried out in the coastal plain of Nabeul–Hammamet region (NE Tunisia). TDEM resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater–seawater transition zone. The geoelectric sections showing the vertical configuration of seawater intrusion, with the brackish‐salty‐saturated zones, have a resistivity ranging from ~0.1 to 5 Ω?m and are detected at a depth lower than 1.5 m. The salinized zones are located at Nabeul (Sidi Moussa, Sidi El Mahrsi, Al Gasba and Mrazgua) and at Hammamet (Touristic zone of Hammamet north and south, Baraket Essahel) and reached a distance of 4 km from the coastline, indicating a severe state for the aquifer in these zones. These TDEM results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells. Moreover, in the northeastern part, the presence of a saltwater front located far from the coast and along the NW–SE major surface fault can be explained by two hypothesis: (i) this fault seems to provide a conduit for seawater to move readily towards the water wells and (ii) the clay and gypsum infiltration of marine Messinian deposits through the fault plane leads to low resistivities. Finally, it comes out from this study that TDEM survey has successfully depicted salinized zones of this coastal aquifer. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
197.
Giovanni Zanchetta Carlo Giraudi Roberto Sulpizio Michel Magny Russell N. Drysdale Laura Sadori 《Quaternary Research》2012,78(2):236-247
A study of six tephra layers discovered in different deposits between 1600 and 2700 m a.s.l. in the Apennine chain in central Italy allowed precise stratigraphic constraints on environmental and climatic changes between ca. 4.5 and 3.8 cal ka BP. Chemical analyses allowed the correlation of these tephra layers with the eruptions of Agnano Mt Spina (AMST) from Phlegrean Field and Avellino (AVT) from Somma–Vesuvius. Major environmental changes in the high mountains of the Central Apennines occurred just after the deposition of the AMST and predate the deposition of the AVT. At this time, renewed growth of the Calderone Glacier occurred, marking the onset of the Apennine “Neoglacial”. The presence of the AMST and AVT enabled us to make a precise, physical correlation with other archives in central Italy. Synchronization of records between sites showed that the period intervening the deposition of the AMST and AVT layers coincided with environmental changes that were not always exactly in phase. This highlights the fact that stratigraphic correlations using only radiocarbon chronologies (the most common method used for dating archives during the Holocene) could produce erroneous correlation of events, giving rise to oversimplified paleoclimatic reconstructions. 相似文献
198.
Carlo Graziani 《New Astronomy》2011,16(2):57-64
Beginning with the 2002 discovery of the “Amati Relation” of GRB spectra, there has been much interest in the possibility that this and other correlations of GRB phenomenology might be used to make GRBs into standard candles. One recurring apparent difficulty with this program has been that some of the primary observational quantities to be fit as “data” – to wit, the isotropic-equivalent prompt energy Eiso and the collimation-corrected “total” prompt energy Eγ – depend for their construction on the very cosmological models that they are supposed to help constrain. This is the so-called “circularity problem” of standard candle GRBs. This paper is intended to point out that the circularity problem is not in fact a problem at all, except to the extent that it amounts to a self-inflicted wound. It arises essentially because of an unfortunate choice of data variables – “source-frame” variables such as Eiso, which are unnecessarily encumbered by cosmological considerations. If, instead, the empirical correlations of GRB phenomenology which are formulated in source-variables are mapped to the primitive observational variables (such as fluence) and compared to the observations in that space, then all taint of circularity disappears. I also indicate here a set of procedures for encoding high-dimensional empirical correlations (such as between Eiso, , and ) in a “Gaussian Tube” smeared model that includes both the correlation and its intrinsic scatter, and how that source-variable model may easily be mapped to the space of primitive observables, to be convolved with the measurement errors and fashioned into a likelihood. I discuss the projections of such Gaussian tubes into sub-spaces, which may be used to incorporate data from GRB events that may lack some element of the data (for example, GRBs without ascertained jet-break times). In this way, a large set of inhomogeneously observed GRBs may be assimilated into a single analysis, so long as each possesses at least two correlated data attributes. 相似文献
199.
Groundwater Modeling of Fractured Aquifers in Mines: The Case Study of Gavorrano (Tuscany,Italy) 总被引:3,自引:1,他引:2
Carlo Alberto Garzonio Leonardo Piccinini Alessandro Gargini 《Rock Mechanics and Rock Engineering》2014,47(3):905-921
In this paper, we describe the hydrogeological problems related to the closure of the mine at Gavorrano (Tuscany, Italy). The geological and geo-structural settings of the Gavorrano area affect the groundwater flow systems and their chemical composition; hence, the settings also affect the chance and modalities to rehabilitate and re-utilize these water resources. This paper reports the results of studies, analyses of existing data and the consequent implementation of preliminary numerical models with particular reference to the effects of controlled water recovery and the complex measures required for stopping dewatering. The study incorporates recent data and the available historical records in an analysis of the hydrodynamic impact of water recovery and an assessment of the consequences of water recovery for water resources restoration. The applied numerical simulations have been demonstrated to be a promising and effective tool for planning and managing the future applications of groundwater recovery in the Gavorrano mining area. Using these applications, it will be possible to implement mitigation measures and types of re-use that consider thermal, chemical and discharge features. 相似文献
200.
Ghislain Dubois Benjamin Sovacool Carlo Aall Maria Nilsson Carine Barbier Alina Herrmann Sébastien Bruyère Camilla Andersson Bore Skold Franck Nadaud Florian Dorner Karen Richardsen Moberg Jean Paul Ceron Helen Fischer Dorothee Amelung Marta Baltruszewicz Jeremy Fischer Françoise Benevise Valérie R. Louis Rainer Sauerborn 《Chemie der Erde / Geochemistry》2010
Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy. 相似文献