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941.
Shear modulus and damping ratio of grouted sand 总被引:2,自引:0,他引:2
Estelle Delfosse-Ribay Irini Djeran-Maigre Richard Cabrillac Daniel Gouvenot 《Soil Dynamics and Earthquake Engineering》2004,24(6):461-471
An experimental comparative study of three different grouted sands in terms of their effects on the values of two dynamic properties is presented. The dynamic properties studied are the shear modulus and the damping ratio which are determined with resonant column tests and cyclic triaxial tests. The behaviour of a pure Fontainebleau sand is compared with the behaviour of a Fontainebleau sand grouted with a silicate grout, a micro-fine cement grout and a mineral grout. The effects of the grouting treatment, the type of grout, the confining pressure, and the strains, on the shear modulus and the damping ratio are studied. The test results have shown that grouting improves the stiffness of the sand especially for small strains. Whatever the type of material, confining stress improves the shear modulus whereas it has a negligible effect on the damping ratio. When strain increases, the shear modulus decreases and the damping ratio increases. 相似文献
942.
Classical multivariate analyses are based on matrix algebra and enable the analysis of a table containing measurements of a set of variables for a set of sites. Incomplete mapped data consist of measurements of a set of variables recorded for the same geographical region but for different zonal systems and with only a partial sampling of this zone. This kind of data cannot be analysed with usual multivariate methods because there is no common system of sites for all variables. We propose a new approach using GIS technology and NIPALS, an iterative multivariate method, to analyse the spatial patterns of this kind of data. Moreover, an extension of our method is that it can be used for areal interpolation purposes. We illustrate the method in analysing data concerning the distribution of roe deer weights over several years in a reserve. 相似文献
943.
Glacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m?2 in wide, low‐gradient valley segments to as high as 51 700 W m?2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
944.
Daniel J. Frost 《Earth and Planetary Science Letters》2003,216(3):313-328
To calculate accurately the pressure interval and mineral proportions (i.e. yields) across the olivine to wadsleyite and wadsleyite to ringwoodite transformations requires a detailed knowledge of the non-ideality of Fe-Mg mixing in these (Mg,Fe)2SiO4 solid solutions. In order to constrain the activity-composition relations that describe non-ideal mixing, Fe-Mg partitioning experiments have been conducted between magnesiowüstite and (Mg,Fe)2SiO4 olivine, wadsleyite and ringwoodite as a function of pressure at 1400°C. Using known activity-composition relations for magnesiowüstite the corresponding relations for the three polymorphs were determined from the partitioning data. In all experiments the presence of metallic iron ensured redox conditions compatible with the Earth’s transition zone. The non-ideality of the (Mg,Fe)2SiO4 solid solutions was found to decrease in the order WwadsleyiteFeMg>WringwooditeFeMg>WolivineFeMg. These partitioning data were used, along with published phase equilibria measurements for the Mg2SiO4 and Fe2SiO4 end-member transformations, to produce an internally consistent thermodynamic model for the Mg2SiO4-Fe2SiO4 system at 1400°C. Using this model the pressure interval of the olivine to wadsleyite transformation is calculated to be significantly smaller than previous determinations. By combining these results with Fe-Mg partitioning data for garnet, the widths of transition zone phase transformations in a peridotite composition were calculated. The olivine to wadsleyite transformation at 1400°C in dry peridotite was found to occur over a pressure interval equivalent to approximately 6 km depth and the mineral yields were found to vary almost linearly with depth across the transformation. This transformation is likely to be even sharper at higher temperatures or could be significantly broader in wet mantle or in regions with a significant vertical component of mantle flow. The entire range of estimated widths for the 410 km discontinuity (4-35 km) could, therefore, be explained by the olivine to wadsleyite transformation in a peridotite composition over a range of quite plausible mantle temperatures and H2O contents. The wadsleyite to ringwoodite transformation in peridotite mantle was calculated to take place over an interval of 20 km at 1400°C. This transformation yield was also found to be near linear. 相似文献
945.
Variability of atmospheric 14C content often complicates radiocarbon-based chronologies; however, specific features such as periods of constant 14C age or steep changes in radiocarbon ages can be useful stratigraphic markers. The Younger Dryas event in the Northern Hemisphere is one of those periods, showing conspicuous 14C wiggles. Although the origin of those variations is not fully understood, we can make practical use of them and determine: (i) whether the Younger Dryas was global in extent; if so, (ii) were the initial cooling and the final warming synchronous worldwide; and (iii) what are the implications of these similarities/differences? Here we report high-resolution AMS 14C chronologies from the mid-latitudes of South America that pinpoint a cool episode between 11,400 and 10,20014C yr B.P. The onset of the final cool episode of the Late Glacial in the southern mid-latitudes, i.e., the Huelmo/Mascardi Cold Reversal, preceded the onset of the Younger Dryas cold event by ∼550 calendar years. Both events ended during a radiocarbon-age plateau at ∼10,20014C yr B.P. Thus, the Huelmo/Mascardi Cold Reversal encompasses the Younger Dryas, as well as a couple of short-term cool/warm oscillations that immediately preceded its onset in the North Atlantic region. 相似文献
946.
Christian Coulon M'hamed Megartsi Serge Fourcade Ren C. Maury Herv Bellon Amina Louni-Hacini Joseph Cotten Alain Coutelle Daniel Hermitte 《Lithos》2002,62(3-4):87-110
During the Neogene, a magmatic change from calc-alkaline to alkaline types occurred in all the regions surrounding the western Mediterranean. This change has been studied in Oranie (western Algeria). In this area, potassic to shoshonitic calc-alkaline andesites (with La/Nb ratios in the range 4–6) were mainly erupted between 12 and 9 Ma. They were followed (between 10 and 7 Ma) by basalts displaying geochemical features which are transitional between calc-alkaline and alkaline lavas (La/Nb=1–1.7). After a ca. 3-Ma quiescence period, volcanic activity resumed, with the eruption of OIB-type alkaline basalts (La/Nb=0.5–0.6), from 4 to 0.8 Ma. A combined geochemical approach, using incompatible elements and Sr, Nd and O isotopes, allows us to conclude that the transitional basalts derived from the melting of a heterogeneous mantle source, at the boundary between lithosphere and asthenosphere. We propose that melting of a previously subduction-modified lithospheric mantle occurred between 12 and 10 Ma, in response to the upwelling of hot asthenosphere flowing up into an opening gap above a detached sinking slab. As a result, calc-alkaline magmas were formed. From 10 to 7 Ma, the transitional basalts were generated through melting of the boundary mantle zone between the lithosphere and the upwelling asthenosphere. During that stage, the contribution of the lithospheric source was still predominant. Then, as sinking of the oceanic slab progressed, the increasing uprise of the asthenosphere led to the formation and emplacement (from 4 to 0.8 Ma) of typical within-plate alkaline basalts derived from a plume-modified asthenospheric mantle. 相似文献
947.
Gold-copper mineralization in alkaline rocks 总被引:4,自引:0,他引:4
Daniel Müller 《Mineralium Deposita》2002,37(1):1-3
948.
Chemical characterization of high molecular weight dissolved organic matter in fresh and marine waters 总被引:1,自引:0,他引:1
Daniel J. Repeta Tracy M. QuanLihini I. Aluwihare AmyMarie Accardi 《Geochimica et cosmochimica acta》2002,66(6):955-962
The high molecular weight fraction of dissolved organic matter in a suite of lakes, rivers, seawater, and marine sediment interstitial water samples was collected by ultrafiltration and characterized by molecular level and spectroscopic techniques. Proton nuclear magnetic resonance spectra of all samples show a high degree of similarity, with major contributions from carbohydrates, bound acetate, and lipids. Molecular level analyses of neutral sugars show seven monosaccharides, rhamnose, fucose, arabinose, xylose, mannose, glucose, and galactose, to be abundant, and to occur in comparable relative amounts in each sample. Previous studies have emphasized the distinctive composition of dissolved humic substances in fresh and marine waters, and have attributed these differences to sources and transformations of organic matter unique to each environment. In contrast we find a large fraction of freshwater high molecular weight dissolved organic matter (HMWDOM; > 1kD) to be indistinguishable from marine HMWDOM in bulk and molecular-level chemical properties. Aquatic HMWDOM is similar in chemical composition to biologically derived acylated heteropolysaccharides isolated from marine algal cultures, suggesting a biological source for some fraction of persistent HMWDOM. High molecular weight DOC contributes 51 ± 26% of the total DOC, and monosaccharides 18 ± 8% of the total HMWDOC in our freshwater samples. These contributions are on average higher and more variable, but not significantly different than for surface seawater (30% and 16% respectively). Biogeochemical processes that produce, accumulate, and recycle DOM may therefore share important similarities and be broadly comparable across a range of environmental settings. 相似文献
949.
New biostratigraphical data based on foraminifers, algae and pseudo-algae indicate that the limestone pebbles of the channelized polygenic conglomerates of the Migoumess formation contain Late Visean (V3bγ–V3c) assemblages. That confirms the Westphalian age attributed to this formation by Hollard [Zdt. Geol. Ges. 129 (1978) 495–512]. The Tournaisian age assigned to it by palynology [C. R. Acad. Sci. Paris, série II 310 (1990) 1573–1576] cannot be retained. The Tirhela formation, Late Visean and Serpukhovian (E1) in age, is coeval with the Akerchi formation [Berkhli, thèse d'État, 1999; Berkhli et al., J. Afr. Earth Sci. (accepté)]. The Idmarrach formation, mapped as a thrust sheet [C. R. Acad. Sci. Paris, série II 310 (1990) 1573–1576], is dated as Serpukhovian (E1) and its thrusting is consequently post-Serpukhovian. Palaeogeographic and geodynamic consequences are listed. To cite this article: M. Berkhli, D. Vachard, C. R. Geoscience 334 (2002) 67–72 相似文献
950.
Jean-François Royer Daniel Cariolle Fabrice Chauvin Michel Déqué Hervé Douville Rong-Ming Hu Serge Planton Annie Rascol Jean-Louis Ricard David Salas Y Melia Florence Sevault Pascal Simon Samuel Somot Sophie Tyteca Laurent Terray Sophie Valcke 《Comptes Rendus Geoscience》2002,334(3):147-154
Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154. 相似文献