排序方式： 共有62条查询结果，搜索用时 15 毫秒
41.
Abessa DM Carr RS Rachid BR Sousa EC Hortelani MA Sarkis JE 《Marine pollution bulletin》2005,50(8):875-885
The submarine sewage outfall of Santos (SSOS) is situated in the Santos Bay (São Paulo, Brazil) and is potentially a significant source of contaminants to the adjacent marine ecosystem. The present study aimed to assess the influence of SSOS on the sediment toxicity and contamination at Santos Bay. At the disposal site, sediments tended to be finer, organically richer and exhibited higher levels of surfactants and metals, sometimes exceeding the “Threshold Effect Level” values. The SSOS influence was more evident toward the East, where the sediments exhibited higher levels of TOC, total S and metals during the summer 2000 sampling campaign. Sediment toxicity to amphipods was consistently detected in four of the five stations studied. Amphipod survival tended to correlate negatively to Hg, total N and % mud. This work provides evidence that the SSOS discharge affects the quality of sediments from Santos Bay, and that control procedures are warranted. 相似文献
42.
The convective atmospheric vortex models of Kuo (1966) and Kendall (1978) are extended to allow the formulation of similarity equations for the unsteady vortex arising from an ambient flow with unstable stratification and rotation. In particular, a new analytical solution is found which allows flow at large radius that is more physically realistic than in any earlier solutions. Additional unsteady solutions are obtained numerically but at large radius these are subject to the limitations of earlier solutions. 相似文献
43.
Valentino Di Donato Paola Esposito Elda Russo-Ermolli Arianna Scarano Rachid Cheddadi 《Quaternary International》2008,190(1):146
Planktonic foraminifera and pollen data from core GNS84-C106 (Gulf of Salerno, Tyrrhenian Sea) were analysed through the Modern Analogue Technique, Constrained Cluster Analysis and relative variation biplots. A long period of mild climate, centred around 25 ka BP, is evident in both marine and continental reconstructions. The cooling phase from 17 to 14.7 ka BP, correlated to the H1 Heinrich event, is indicated by a sea surface temperature (SST) decrease, which roughly coincides with the cold-arid phase identified by annual and January temperatures. A rapid increase in atmospheric temperatures and precipitation, culminating at 13.8 ka BP, marks the BA cronozone. The corresponding increase in summer and winter SSTs, of 11 and 6.5 °C, respectively, occurred over 600 years. The beginning of the YD, centred around 12.5 ka BP, is marked by a decrease in summer and winter SSTs of, respectively, 4.5 and 3.5 °C in one century. The atmospheric evidence of the YD is primarily reflected in low January temperatures, reaching −6 °C, the lowest values ever experienced in the analysed time interval. The Late Glacial–Holocene transition is clearly recorded in both the continental and marine realms. From 11.5 to 9 ka BP, atmospheric temperatures record a period of substantial stability followed by a drop at 8.9 ka BP, which chronologically fall within the first RCC event (9–8 ka BP) of Mayewski et al. [2004. Holocene climate variability. Quaternary Research 62, 243–255], in correspondence with a phase of relatively high seasonality, indicated by foraminifera. 相似文献
44.
Ismail Benessalah Ahmed Arab Pascal Villard Khayra Merabet Rachid Bouferra 《Geotechnical and Geological Engineering》2016,34(6):1775-1790
During the last earthquake that occurred in Chlef (El Asnam 1980, Algeria), a significant decrease in the shear strength has caused major damages to several civil and hydraulic structures (earth dams, embankments, bridges, slopes and buildings), especially for the saturated sandy soil of the areas near Chlef valley. This paper presents a laboratory study of drained compression triaxial tests conducted on sandy soil reinforced with horizontal layers of geotextile, in order to study the influence of geotextile layer characteristics both on shear stress–strain and on volumetric change–strain. Tests were carried out on medium and dense sand. The experimental programme includes some drained compression tests performed on reinforced sand samples, for different values of the geotextile layers number (N g), of confining pressure (\( \sigma_{\text{c}}^{\prime } \)) and relative density (D r). The test results have shown that the contribution of the geotextile at low values of the axial strain (ε 1) is negligible, for higher values of (ε 1); geotextile induces a quasi-linear increase in the deviator stress (q) and leads to an increase in the volume contractiveness within the reinforced samples. A negligible influence of geotextile layers number (N g) on the stress–strain behaviour and the volumetric change has been shown, when normalized with N g. The results indicate that the contribution of geotextile to the stress–strain mobilization increases with increasing confining pressure, while its contribution to the volume contraction decreases with the increase in the confining pressure. 相似文献
45.
Mohammed Chemmam Mostefa Belkhatir Rachid Bouferra 《Marine Georesources & Geotechnology》2016,34(4):384-394
This article presents a laboratory study of static behavior of silty-sand soils. The objective of this laboratory investigation is to study the effect of initial confining pressures and fines content on the undrained shear strength (known as liquefaction resistance) response, pore pressure, and hydraulic conductivity of sand–silt mixtures. The triaxial tests were conducted on reconstituted saturated silty-sand samples at initial relative density Dr = 15% with fines content ranging from 0 to 50%. All the samples were subjected to a range of initial confining pressures (50, 100, and 200 kPa). The obtained results indicate that the presence of low plastic fines in sand–silt mixture leads to a more compressible soil fabric, and consequently to a significant loss in the soil resistance to liquefaction. The evaluation of the data indicates that the undrained shear strength can be correlated to fines content (Fc), inter-granular void ratio (eg), and excess of pore pressure (Δu). The undrained shear strength decreases with the decrease of saturated hydraulic conductivity and the increase of fines content for all confining pressures under consideration. There is a relatively high degree of correlation between the peak shear strength (qpeak) and the logarithm of the saturated hydraulic conductivity (ksat) for all confining pressures. 相似文献
46.
Landslides - Submarine landslides are a ubiquitous geohazard in the marine environment and occur at multiple scales. Increasing efforts have been made during the last decade to catalogue and... 相似文献
47.
48.
Comparison of climatic threshold of geographical distribution between dominant plants and surface pollen in China 总被引：12，自引：0，他引：12
Zhuo Zheng KangYou Huang QingHai Xu HouYuan Lu Rachid Cheddadi YunLi Luo Celia Beaudouin ChuanXiu Luo YanWei Zheng ChunHai Li JinHui Wei ChunBin Du 《中国科学D辑(英文版)》2008,51(8):1107-1120
The geographical distribution of dominant plant species in China was georeferenced and climatic variables were interpolated into all grids.Accordingly,the percentage distributions of principal pollen taxa based on 1860 surface pollen sites in China were selected and the related climate values were interpolated with the same method. The geographical and climatic comparison between the two data-sets indicated that the climate threshold of most pollen taxa from surface pollen is coherent with plant distributions. The climatic envelopes of dominant plant are mostly accordant with those of pollen taxa at certain levels. However, some distinct offsets of the climate ranges exist between the two datasets for most pollen taxa identified at family level, such as Ericaceae,Asteraceae, Poaceae and Chenopodiaceae. The present study provides for the first time rich information on temperature and precipitation in relation to pollen and plant distribution based on the datasets on a continental scale useful for global ecological modeling and Quaternary palaeoclimate reconstruction. 相似文献
49.
The Importance of the Precipitation and the Susceptibility of the Slopes for the Triggering of Landslides Along the Roads 总被引：3，自引：1，他引：2
Clemente Irigaray Francisco Lamas Rachid El Hamdouni Tomás Fernández José Chacón 《Natural Hazards》2000,21(1):65-81
In order to characterise the influence of the heavyrains on the observed landslides during the 1996–1997hydrological cycle, rainfall records for the last 100years are analysed from 104 stations in easternAndalusia. Regarding the amounts of rain recordedbetween October 1996 and March 1997 in the 104stations studied, 31 presented new all-time records;15 presented values that were 80–100% of thepre-1995 record; 49 stations, 80–50%; and 9stations, < 50%. A map has been devised of thesusceptibility of the materials through which thesouth-eastern Andalusian road network crosses,together with an inventory of the damage caused byinstability phenomena on banks and cuttings of theroad network during the winter of 1996–1997. Therelationships between the rainfall during the studyperiod, the damage caused to the road network and thesusceptibility of the materials affected are analysed.The results indicate that there is a clearcorrespondence between the rainfall recorded and thesusceptibility of the materials with the inventorieddamage. It is concluded that the widespread seriousdamage caused in early 1997 to the roads andsurrounding areas in the Alpujarra region and thecoast of the Province of Granada was mainly caused bythe extraordinarily heavy rains. However, considerablyless damage was observed where the susceptibility ofthe terrain is low, thus highlighting the extremeusefulness of terrain-susceptibility maps for riskprevention and territorial planning. 相似文献
50.
为了揭示闽江下游闽侯盆地第四纪沉积环境演变与人类活动历史,对闽江下游闽侯盆地庄边山遗址附近的FZ5钻孔进行了孢粉、硅藻分析。结果表明：闽侯盆地全新世海侵初始发生时间约为9 000 cal. a B.P.,至7 500 cal. a B.P.达到最大海侵范围,晚全新世海退的发生时间在闽侯盆地大约为1 900 cal. a B.P.。孢粉分析证实了当地早中全新世温暖的亚热带气候以及浓密的常绿阔叶林植被。在7 500―1 900 cal. a B.P.之间无论植被覆盖还是气候环境均比较稳定,高海平面时期的适宜气候以及海湾环境也有利于当地以渔猎经济方式为主的新石器文化（昙石山文化）的兴起和发展。自1 900 cal. a B.P.以后,孢粉组合突变为以先锋植物芒萁属（Dicranopteris）、禾本科（Poaceae）、松属（Pinus）等类型为主,揭示了当地植被受到人类农业刀耕火种的影响而发生显著变化。高含量的禾本科花粉（含一定数量的水稻）仅在剖面上部明显增加这一事实,证实了闽侯和福州一带水稻种植的大面积发展始于距今1 900 a前后。 相似文献