Local and global diffusion in the Arnold web of a priori unstable systems     

Nataša Todorović  Elena Lega  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2008,102(1-3):13-27

Using the numerical techniques developed by Froeschlé et al. (Science 289 (5487): 2108–2110, 2000) and by Lega et al. (Physica D 182: 179–187, 2003) we have studied diffusion and stochastic properties of an a priori unstable 4D symplectic map. We have found two different kinds of diffusion that coexist for values of the perturbation below the critical value for the Chirikov overlapping of resonances. A fast diffusion along some resonant lines that exist already in the unperturbed case and a slow diffusion occurring in regions of the phase space far from such resonances. The latter one, although the system does not satisfy the Nekhoroshev hypothesis, decreases faster than a power law and possibly exponentially. We compare the diffusion coefficient to the indicators of stochasticity like the Lyapunov exponent and filling factor showing their behavior for chaotic orbits in regions of the Arnold web where the secondary resonances appear, or where they overlap.  相似文献   

Evidence of multiple evaporite recycling processes in a salt‐tectonic context,Sivas Basin,Turkey          下载免费PDF全文

Alexandre Pichat  Guilhem Hoareau  Jean‐Paul Callot  Etienne Legeay  Kaan Sevki Kavak  Sidonie Révillon  Corinne Parat  Jean‐Claude Ringenbach 《地学学报》2018,30(1):40-49

The isotopic composition of evaporites can shed light on their environment of precipitation and their subsequent recycling processes. In this study, we performed Sr, O and S isotopic analyses on evaporitic sulphates in the halokinetic Sivas Basin. The main objectives were to decipher the age and origin of the evaporites responsible for the salt tectonics, and to test whether diapir dissolution acts as the source of younger evaporitic layers in continental mini‐basins. The Sr isotopes demonstrate that the first evaporites precipitated from seawater during the Middle–Late Eocene. The similar isotopic values measured in the halokinetic domain confirm that the Eocene evaporites triggered the salt tectonics and were continuously recycled in Oligo‐Miocene mini‐basins as lacustrine to sabkha evaporites. Modern halite precipitates suggest that the dissolution and recycling of diapiric halite is ongoing. This study demonstrates the efficiency of isotopic analyses in constraining evaporite recycling processes in continental halokinetic domains.  相似文献   

Difference in petrophysical properties between foliated and dilatant fault rocks in deeply buried clastics: The case of the Grès d'Annot Formation,SW French Alps     

Thibault Cavailhes  Pierre Labaume  Jean‐Pierre Sizun  Roger Soliva  Claude Gout  Jean‐Luc Potdevin  Martine Buatier  Aurélien Gay  Alain Chauvet  Delphine Charpentier  Anna Travé 《地学学报》2014,26(4):298-306

This study describes normal fault zones formed in foreland arkosic turbidites (the Grès d'Annot Formation, SW French Alps) under deep diagenesis conditions (~200 °C) and highlights the occurrence of two markedly different fault‐rock types: (1) the foliated fault rocks of the Moutière‐Restefond area; and (2) the dilatant fault rocks of the Estrop area. The deformation of (1) is dominated by intra‐ and transgranular fracturing, pressure solution of quartz and feldspar grains and syn‐kinematic phyllosilicate precipitation resulting from feldspar alteration. The combination of these mechanisms results in a strongly anisotropic strain with intense shortening normal to the foliation (pressure solution) and extension parallel to the foliation (quartz‐ and calcite‐sealed extension veins). This deformation implies local mass transfer that may be achieved without (or with limited) volume change. The deformation of (2) is expressed as dilatant quartz‐sealed veins and breccia textures in which the main mechanisms are transgranular fracturing and quartz precipitation. Type (2) implies fault volume increase, isotropy of deformation and mass transfer at distances larger than in type (1). This study discusses the origins of (1) and (2) and shows that the permeability of (1) is anisotropic, with higher values than the host rocks parallel to the Y main deformation axis (i.e. perpendicular to the slip vector), whereas the permeability of (2) is isotropic and equivalent to that of the host rocks.  相似文献   

Combating Desertification and Improving Local Livelihoods through the GGWI in the Sahel Region: The Example of Senegal     

Salif Diop  Aliou Guisse  Claude Sene  Birane Cisse  Ndeye Rokhaya Diop  Sokhna Di  Ka  Amady Gnagna Cisse  Saly Sambou  Ousmane Ndiaye  Adand  Belarmain Fandohan  FU Chao  WANG Guoqin  WANG Yongdong 《资源与生态学报(英文版)》2018,9(3):257-265

The Great Green Wall Initiative (GGWI) has an overall objective of fighting desert encroachment through proven practices of sustainable management of land, and the reinforcement and protection of natural resources and systems of production and transformation, while also ensuring socio-economic development of local communities through multi-purpose activity platforms. The activities described in the present study are designed to accomplish several goals: (1) generate wealth, (2) strengthen access to basic social services, (3) manage the transition to a green economy as a means of creating suitable conditions for the emergence of rural production centers, (4) integrate sustainable development in order to eradicate poverty and food insecurity, and (5) strengthen adaptation and resilience capacities of local populations. The present study was undertaken on the basis of a wide variety of available publications and documentation, including articles and scientific papers, thesis, meeting summaries and reports, concerning the implementation of the Great Green Wall Initiative/GGWI in Senegal.  相似文献   

Silica diagenesis in Eocene shallow-water platform carbonates, southern Pyrenees   总被引：1，自引：0，他引：1  

Jordi Giménez-Montsant  Francesc Calvet  & Maurice E. Tucker 《Sedimentology》1999,46(6):969-984

Spectacularly developed lower Eocene chert in the Corones platform carbonates of the Spanish Pyrenees is concentrated within a restricted, brackish-water, laminated ostracod-rich facies, which also contains abundant sponge spicules. The chert occurs as nodular, bedded and mottled varieties, and four petrographic types of quartz are developed: microquartz; length-fast (LF) chalcedony; megaquartz; and microspheres. δ¹⁸O values of chert range from 29·6‰ to 30·9‰ (SMOW), which correspond to a broad isotope rank common for biogenic and diagenetic replacement cherts. Calcian dolomite crystals with high Fe and Na are disseminated within the microquartz and LF-chalcedony, but are absent from the megaquartz and host carbonate. The chert is closely associated with desiccation cracks and with interstratal dewatering structures. Load casts are silicified, and laminae rich in sponge spicules are convoluted. Early cracks related to dewatering are filled by microquartz and quartz cements. Ostracod shells within chert are locally fractured; those in the host carbonate are commonly flattened. Late fractures are filled by LF-chalcedony and megaquartz. There is much evidence for the dissolution of sponge spicules and their calcitization in the carbonate host rock. Silica for the Corones cherts was derived from sponges during early diagenesis and shallow burial. Early mechanical compaction and sediment dewatering played a major role in sponge spicule dissolution, migration of silica-rich fluids and the consequent precipitation of chert. Quartz cements continued to be precipitated into the burial environment.  相似文献   

Isochron‐burial dating of glaciofluvial deposits: First results from the Swiss Alps          下载免费PDF全文

Naki Akçar  Susan Ivy‐Ochs  Vasily Alfimov  Fritz Schlunegger  Anne Claude  Regina Reber  Marcus Christl  Christof Vockenhuber  Andreas Dehnert  Meinert Rahn  Christian Schlüchter 《地球表面变化过程与地形》2017,42(14):2414-2425

In this study, we use isochron‐burial dating to date the Swiss Deckenschotter, the oldest Quaternary deposits of the northern Alpine Foreland. Concentrations of cosmogenic ¹⁰Be and ²⁶Al in individual clasts from a single stratigraphic horizon can be used to calculate an isochron‐burial age based on an assumed initial ratio and the measured ²⁶Al/¹⁰Be ratio. We suggest that, owing to deep and repeated glacial erosion, the initial isochron ratio of glacial landscapes at the time of burial varies between 6.75 and 8.4. Analysis of 22 clasts of different lithology, shape, and size from one 0.5 m thick gravel bed at Siglistorf (Canton Aargau) indicates low nuclide concentrations: <20 000 ¹⁰Be atoms/g and <150 000 ²⁶Al atoms/g. Using an ²⁶Al/¹⁰Be ratio of 7.6 (arithmetical mean of 6.75 and 8.4), we calculate a mean isochron‐burial age of 1.5 ± 0.2 Ma. This age points to an average bedrock incision rate between 0.13 and 0.17 mm/a. Age data from the Irchel, Stadlerberg, and Siglistorf sites show that the Higher Swiss Deckenschotter was deposited between 2.5 and 1.3 Ma. Our results indicate that isochron‐burial dating can be successfully applied to glaciofluvial sediments despite very low cosmogenic nuclide concentrations. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Chronology of Quaternary terrace deposits at the locality Hohle Gasse (Pratteln,NW Switzerland)     

Anne Claude  Naki Akçar  Susan Ivy-Ochs  Fritz Schlunegger  Philippe Rentzel  Christine Pümpin  Dmitry Tikhomirov  Peter W. Kubik  Christof Vockenhuber  Andreas Dehnert  Meinert Rahn  Christian Schlüchter 《Swiss Journal of Geoscience》2017,110(3):793-809

The Quaternary stratigraphy of the Alpine Foreland consists of distinct terrace levels, which have been assigned to four morphostratigraphic units: Höhere (Higher) Deckenschotter, Tiefere (Lower) Deckenschotter, Hochterrasse (High Terrace) and Niederterrasse (Lower Terrace). Here, we focus on the terrace gravels at Hohle Gasse, SSE of Pratteln near Basel, which are mapped as Tiefere Deckenschotter. Petrographic and morphometric data established from clasts allowed to infer the transport mechanisms and sources of the gravels. Sedimentological analyses indicate that the gravels were transported by a braided river and deposited in a distal glaciofluvial setting. In addition, it can be shown that the majority of the clasts display multiple reworking and only a minority maintained a distinct glaciofluvial shape. Cosmogenic multi-isotope dating using ¹⁰Be and ³⁶Cl allowed direct dating of the sediments at the study site. A depth-profile age of \(2 70_{ - 1 90}^{ + 8 30}\) ka for ¹⁰Be was achieved for the deposits at Hohle Gasse. Unfortunately, no age could be modelled from the ³⁶Cl concentrations as the blank correction was too high. Furthermore, this age proves that the studied terrace level should be assigned to the morphostratigraphic unit Hochterrasse.  相似文献   

Multiscale modelling in soil and rock mechanics     

Jolanta Lewandowska  Claude Boutin  Moulay Said El Youssoufi 《Acta Geophysica》2014,62(5):991-992

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Retrieval of the boundary layer height from active and passive remote sensors. Comparison with a NWP model     

Livio Belegante  Doina Nicolae  Anca Nemuc  Camelia Talianu  Claude Derognat 《Acta Geophysica》2014,62(2):276-289

In this study, we used boundary layer heights derived from lidar in Romania to validate the Weather Research Forecast (WRF) model improved by ARIA Technologies SA in the framework of ROMAIR LIFE project. Lidar retrievals were also compared to the retrievals from meteorological data, both modeled (Global Data Assimilation System; GDAS) and measured (microwave radiometry). Both the gradient and the wavelet covariance methods were used to compute the boundary layer height (BLH) from the range corrected lidar signal, and their equivalence was shown. The analysis was performed on 102 datasets, spread over all seasons and 3 years (2009–2011). A good agreement was found for the remote sensors (lidar and microwave radiometer) which are co-located and measure simultaneously. The correlation of the measured boundary layer height and the modelled one was 0.66 for the entire dataset, and 0.73 when considering daytime data, i.e., for a well defined boundary layer. A systematic underestimation of the boundary layer height by the WRF during non-convective periods (nocturne, stable atmosphere) was found.  相似文献   

Modelling colloid association with plutonium: The effect of pH and redox potential     

Claude Degueldre  Magdalena Bolek 《Applied Geochemistry》2009,24(2):310-318

An analytical expression that evaluates the effect of pH and the redox potential (E) on Pu-colloid association was studied on a model basis. It includes surface complexation with one type of surface site and its formulation leads to a distribution coefficient (K_d) as a function of the pH (hydrolysis) and E (redox sensitive species). The formulation also considers the values of the stability and hydrolysis constants for all species present in solution and associated at the surface. Correlations between hydrolysis and surface complexation constants reported in the literature have been applied systematically to evaluate sorption of all species for each colloid system. The presence of ligands in solution was also taken into account. The model was applied to study the association of Pu onto colloids coated with AlOH, FeOH or SiOH groups in the presence and in the absence of carbonates in solution. The tests performed with the model suggest that the oxidation of Pu(III) to Pu(IV) has the potential to increase sorption, as demonstrated by the increased K_d values. Under natural conditions Pu may be present at oxidation states of (III)--(VI), and the effect of redox potential is significant because of the differences in the sorption of each oxidation state. When carbonates are present in the solution, the calculated values of distribution coefficient were lower than those calculated in the absence of carbonates, particularly in the case of Pu(VI). The K_d values obtained with the developed model are compared with experimental values reported for the sorption of Pu onto colloids. This model can equally be applied to study the sorption of other redox sensitive elements.  相似文献