Dynamic active earth pressure on cantilever retaining walls     

Anna Scotto di Santolo  Aldo Evangelista 《Computers and Geotechnics》2011

In normal practice, the active earth pressure on cantilever retaining wall is evaluated with different procedures relating to an ideal vertical plane passing through the heel of the wall. If the wall presents a long heel, failure planes do not interfere with the vertical stem, so that the limit Rankine conditions can develop freely in the backfill. The inclination of lateral actions along the ideal plane is assumed to be constant and depends on the geometry of the ground level and on the friction angle φ. The Authors recently proposed a new method to evaluate the active earth pressure coefficient due to seismic loading with a pseudo-static stress plasticity solution. The present paper describes the application of this method to a retaining wall supporting a φ soil backfill with an irregular surface. For two different configurations of wall-soil system, the behaviour is also studied by continuum FDM dynamic analyses, utilising four Italian accelerometric time-histories scaled at the same peak ground acceleration. The comparison between different procedures is also analysed.  相似文献   

Determination of chemical weathering rates from U series nuclides in soils and weathering profiles: Principles,applications and limitations     

François Chabaux  Lin Ma  Peter Stille  Eric Pelt  Mathieu Granet  Damien Lemarchand  Raphael di Chiara Roupert  Susan L. Brantley 《Applied Geochemistry》2011

The development of U-series nuclides for investigating weathering processes has been significantly stimulated by the analytical improvement made over the last decades in measuring the ²³⁸U series with intermediate half-lives (i.e., ²³⁴U–²³⁰Th–²²⁶Ra). It is proposed in this paper to present principles and methods that are now being developed to determine weathering rates from the study of U-series nuclides in soils and weathering profiles. Mathematical approaches, developed to calculate such rates, are based on some implicit assumptions that are also presented and must be kept in mind if one wants to correctly interpret the obtained ages.  相似文献   

Numerical Simulations of the Microscale Heterogeneities of Turbulence Observed on a Complex Site     

Hanane Zaïdi  Eric Dupont  Maya Milliez  Luc Musson-Genon  Bertrand Carissimo 《Boundary-Layer Meteorology》2013,147(2):237-259

We simulate the microscale heterogeneities of turbulent variables observed at a complex site for different wind directions. The atmospheric computational fluid dynamics (CFD) results are compared with an ensemble of 36 months of data collected at the experimental site SIRTA “Site Instrumental de Recherche par Télédétection Atmosphérique”, located near Paris (France) in a semi-urban environment. The experimental data show that the normalized turbulent kinetic energy (TKE) k/U ² (where k is TKE and U is the wind speed) at 10-m height, for two different locations, is highly dependent on wind direction and strongly influenced by trees. These measurements show a strong increase of the normalized TKE downstream of the forest canopies with a large variability within the 36-month period in part due to the variation of the tree foliage. The numerical simulations are carried out using the CFD code Code_Saturne with the standard k?ε closure, in neutral stratification. The buildings are taken into account explicitly in the mesh and the forested areas are modelled with two approaches: the classical roughness wall law and a drag porosity. A comparison has been performed between the calculated values and the median of measured values of the normalized TKE and the normalized friction velocity, for each wind sector of 10°. A very good agreement is obtained with the drag porosity model, whereas the classical roughness law leads to a strong underestimation downstream of the forested areas. However, this large improvement of the results using the drag porosity model can only be obtained with a refinement of the grid, especially in forested areas, and an accurate land-use map.  相似文献   

Zarafasaura oceanis, a new elasmosaurid (Reptilia: Sauropterygia) from the Maastrichtian Phosphates of Morocco and the palaeobiogeography of latest Cretaceous plesiosaurs     

Peggy Vincent  Nathalie Bardet  Xabier Pereda Suberbiola  Badi Bouya  Mbarek Amaghzaz  Saïd Meslouh 《Gondwana Research》2011,19(4):1062-1073

Though the Maastrichtian Phosphates of Morocco have yielded very rich marine vertebrate assemblages, plesiosaurs remain very scarce in these strata. The only hitherto recognized taxon was Plesiosaurus mauritanicus Arambourg, 1952, regarded here as a nomem dubium. Here we describe a new genus and species of elasmosaurid plesiosaur, Zarafasaura oceanis, which represents the first valid elasmosaurid plesiosaur described from the latest Cretaceous of Africa, and the second one from this continent. A phylogenetic analysis of plesiosauroids indicates that Zarafasaura oceanis has close affinities with elasmosaurids from the Late Cretaceous of North America and Japan. Among its distinctive suite of characters, the general shape and organisation of its squamosal and palate are unique among elasmosaurids. This new taxon completes our understanding of Late Cretaceous plesiosaur palaeobiodiversity and palaeobiogeography, and shows that Maastrichtian plesiosaurs were characterized by a quite high degree of endemism. They were also highly diversified and distributed worldwide, which supports the hypothesis of a catastrophic extinction of plesiosaurs at the K/T boundary.  相似文献   

Kinematically quiet haloes around z∼ 2.5 radio galaxies. Keck spectroscopy     

M. Villar-Martín  J. Vernet  S. di Serego Alighieri  R. Fosbury  A. Humphrey  L. Pentericci 《Monthly notices of the Royal Astronomical Society》2003,346(1):273-294

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Fractal dimension estimations of drainage network in the Carpathian–Pannonian system   总被引：1，自引：1，他引：0  

Endre Dombrdi  Gbor Timr  Gbor Bada  Sierd Cloetingh  Frank Horvth 《Global and Planetary Change》2007,58(1-4):197

The development of drainage network in the intra-Carpathian realm is influenced by a complex Quaternary tectonic evolution manifested with differential vertical motions. The present-day configuration of the left-hand side tributary system of the Tisza river was studied by means of fractal analysis. Fractal dimensions describing the complexity of the network were obtained by different methods. These include the early estimations based on stream ordering hierarchy and the application of the box-counting and sandbox algorithms representing fixed-size algorithms considered as efficient tools in fractal set analysis. Besides calculations made for the entire drainage system, the region was subdivided into three distinct areas characterised by different Quaternary uplift history. These are the Apuseni Mts., the Transylvanian basin and a part of the Eastern Carpathians, investigated separately. The concept of multifractality was also taken into consideration and dimensions of both higher and lower orders were determined along with the corresponding singularity spectra. Non-space-filling and multifractal behaviour of the network structure was validated. However, small but tendentious variations of the support dimensions (D₀) were observed in the three sub-regions. The Transylvanian basin is characterised by the lowest estimated dimensions, while higher values represent the Apuseni Mts., and the western slopes of the Eastern Carpathians. In addition, fractal dimension values showed consistency within each sub-region. Correlation of these measures with average uplift rates was performed. As a major outcome, differential uplift, affecting the morphology of catchments, appears to influence the obtained fractal dimensions, whereas surface lithology conceivably plays only a secondary role.  相似文献   

AN APPROACH TO OBTAINING AN OPTIMAL DESIGN IN THE NON-LINEAR LEAST SQUARES DETERMINATION OF BINDING PARAMETERS IN A COMPLEX BIOCHEMICAL SYSTEM     

GUIDO CRISPONI  VALERIA NURCHI  M.LUISA GANADU 《地理学报(英文版)》1990,(2)

The design of an experiment for the determination of binding parameters in the association between aligand and a macromolecule with two groups of non-interacting binding sites is proposed.In theGauss-Newton non-linear least squares treatment the standard deviation of each parameter is given asthe product of two terms:one depending on the experimental error and the other,the diagonal elementof the dispersion matrix,depending only on the independent variables of the system.In order to reachan optimal experimental design,these diagonal elements of the information matrix have to be minimized.In our approach this is achieved by searching those values of the independent variable which maximizethe determinant of the information matrix.Furthermore,the limits of validity of the model are deducedfrom an analysis of the diagonal elements of the information matrix obtained under optimal conditions.  相似文献   

Changes in gas composition during simulated maturation of sulfur rich type II-S source rock and related petroleum asphaltenes     

Eric Lehne  Volker Dieckmann  Rolando di Primio  Andreas Fuhrmann  Brian Horsfield 《Organic Geochemistry》2009,40(5):604-616

Asphaltenes extracted from crude oils are proposed to possess structural features of the related source rock kerogen. For the present study micro-scale sealed vessel pyrolysis (MSSV) and combustion isotope ratio mass spectrometry (GC–C–IRMS) were used to compare gas generation from a whole rock (type II-S kerogen) from southern Italy with that from related sulfur rich asphaltenes isolated from a low maturity heavy crude oil. The purpose of was to determine whether experimental pyrolysis of oil asphaltenes can be used to predict the timing and the chemical and isotopic composition of hydrocarbon gases generated from genetically related kerogen in the source rock during burial maturation. The results show that parameters such as (gas to oil ratio) GOR and oil and gas formation timing are very similar for these two sample types, whereas gas composition, product aromaticity and sulfur content are remarkably different. Slight differences in GOR are mainly due to differences in gas formation characteristics at very high levels of thermal alteration. Secondary gas formation from the whole rock covers a much broader temperature range under geological conditions than that from the asphaltene products. However, it is remarkable that both the onset and the maximum temperature are nearly identical under geological conditions. The observed differences in gas generation characteristics are supported by discrepancies in the carbon isotopic characteristics of the gas range compounds and indicate different precursors and/or mechanisms for gas generated from whole rock and asphaltenes.  相似文献   

Scintillometer-Based Turbulent Fluxes of Sensible and Latent Heat Over a Heterogeneous Land Surface – A Contribution to Litfass-2003     

W. M. L. Meijninger  F. Beyrich  A. Lüdi  W. Kohsiek  H. A. R. De. Bruin 《Boundary-Layer Meteorology》2006,121(1):89-110

The performance of a combined large aperture scintillometer (LAS) and a millimetre wave scintillometer (MWS) for estimating surface fluxes of sensible and latent heat over natural landscape is investigated, using data gathered during LITFASS-2003. For this purpose the LAS–MWS system was installed in a moderate heterogeneous landscape over a path length of 4.7 km with an effective beam height of 43 m. The derived surface fluxes have been compared with aggregated eddy-covariance (EC) measurements. The fluxes of sensible and latent heat from the LAS–MWS combination, as well as sensible heat fluxes of the single LAS, agreed fairly well with the EC-based fluxes, considering the uncertainties of the similarity stability functions and observed energy imbalance.  相似文献   

Geophysical Constraints on the Location and Nature of the North Saharan Flexure in Southern Tunisia     

Hakim Gabtni  Chokri Jallouli  Kevin Mickus  Hédi Zouari  Mohamed Moncef Turki 《Pure and Applied Geophysics》2005,162(11):2051-2069

Gravity data, integrated with seismic refraction/reflection data, well data and geological investigations, were used to determine the location of the paleogeographic boundary between the Precambrian Saharan domain and the younger Tunisian Atlas domain. This boundary (North Saharan Flexure or NSF) has not been as clearly defined as it has been to the west in Algeria and Morocco. The gravity data analysis, which included the construction of complete Bouguer and residual gravity anomaly maps, revealed that the Atlasic domain is characterized by relative negative gravity anomalies and numerous linear gravity trends implying a thick and deformed sediment cover. The Saharan domain is characterized by relatively positive gravity anomalies with few gravity trends implying a thin and relatively undeformed sediment cover. An edge-enhancement analysis of the residual gravity anomalies revealed that the NSF is characterized by a series of discontinuous east- and northwest-trending linear anomalies south of 34°N that are not related to the well-known faults within the Gafsa and Accident de Medenine regions. Based on the continuity of the amplitudes of seismic reflection data and the trends of the residual gravity anomalies, the NSF is not an abrupt discontinuity but a series of step faults dipping toward the Atlasic domain. To obtain a more quantitative representation of the southern edge of Tunisian Atlas, a regional gravity model constrained by two wells and seismic reflection/refraction data was constructed along a north-south trending profile which confirms the presence of thicker sediments north of the NSF. Our analysis shows that the NSF has controlled the depositional environment of the sedimentary rocks within the region since at least Triassic time and has acted as a barrier to Atlasic deformation south of the NSF. The NSF is considered an important tectonic feature that has controlled the paleogeographic evolution of the southern margin of the Tethys Ocean, and it continues to be active today based on seismicity hazard studies.  相似文献