Journal of Next-Generation Research 5.0
Not a member yet
7559 research outputs found
Sort by
M-theta Method on Mode I and II Failure of Two Cameroonian Hardwoods in Bending
No full textInternational audienceThis work deals with the numerical simulation on bending test to characterize two Cameroonian hardwoods under mode I and II loading for different crack lengths. The finite element analysis for fracture in orthotropic medium is developed. The algorithm of fracture is introduced in a finite element software Cast3M. According to the Mtheta method, the calculation of the stress intensity factors and the energy release rate for pure mode I and II fracture are deduced using a SENB (Single Edge Notch Bending) specimen. The path independence of Mθ-method on the specimen is confirmed
Empirical investigation of friction weakening of terrestrial and Martian landslides using discrete element models
No full textInternational audienceUnderstanding what controls the travelling distance of large landslides has been the topic of considerable debate. By combining observation and experimental data with depth-averaged continuum modelling of landslides and generated seismic waves, it was empirically observed that lower effective friction had to be taken into account in the models to reproduce the dynamics and runout distance of larger volume landslides. Moreover , such simulation and observation results are compatible with a friction weakening with velocity as observed in earthquake mechanics. We investigate here as to whether similar empirical reduced friction should be put into discrete element models (DEM) to reproduce observed runout of large landslides on Earth and on Mars. First we show that, in the investigated parameter range and for a given volume, the runout distance simulated by 3D DEM is not much affected by the number (i.e. size) of grains once this number attains ~ 8000. We then calibrate the model on laboratory experiments and simulate other experiments of granular flows on inclined planes, making it possible for the first time to reproduce the observed effect of initial volume and aspect ratio on runout distances. In particular, the normalised runout distance starts to depend on the volume involved only above a critical slope angle > 16-19°, as observed experimentally. Finally, based on field data (volume, topography, deposit), we simulate a series of landslides on simplified inclined topography. The empirical friction coefficient, calibrated to reproduce the observed runout for each landslide, is shown to decrease with increasing landslide volume (or velocity), going down to values as low as 0.1-0.2. No distin-guishable difference is observed between the behaviour of terrestrial and Martian landslides
Present-day uplift of the European Alps: Evaluating mechanisms and models of their relative contributions
No full textInternational audienceRecent measurements of surface vertical displacements of the European Alps show a correlation between vertical velocities and topographic features, with widespread uplift at rates of up to ~2–2.5 mm/a in the North-Western and Central Alps, and ~1 mm/a across a continuous region from the Eastern to the South-Western Alps. Such a rock uplift rate pattern is at odds with the horizontal velocity field, characterized by shortening and crustal thickening in the Eastern Alps and very limited deformation in the Central and Western Alps. Proposed mechanisms of rock uplift rate include isostatic response to the last deglaciation, long-term erosion, detachment of the Western Alpine slab, as well as lithospheric and surface deflection due to mantle convection. Here, we assess previous work and present new estimates of the contributions from these mechanisms. Given the large range of model estimates, the isostatic adjustment to deglaciation and erosion are sufficient to explain the full observed rate of uplift in the Eastern Alps, which, if correct, would preclude a contribution from horizontal shortening and crustal thickening. Alternatively, uplift is a partitioned response to a range of mechanisms. In the Central and Western Alps, the lithospheric adjustment to deglaciation and erosion likely accounts for roughly half of the rock uplift rate, which points to a noticeable contribution by mantle-related processes such as detachment of the European slab and/or asthenospheric upwelling. While it is difficult to independently constrain the patterns and magnitude of mantle contributions to ongoing Alpine vertical displacements at present, future data should provide additional insights. Regardless, interacting tectonic and surface mass redistribution processes, rather than an individual forcing, best explain ongoing Alpine elevation changes
Geochemical study of carbonate concretions from the aqueduct of Nîmes (southern France): a climatic record for the first centuries AD?
No full textInternational audienceThe first centuries AD in the Mediterranean region have generally been associated with a warm, stable climate. High-resolution sedimentary archives sensitive to local environmental change are needed to switch from this general frame to the regional scale. Similarly to cave speleothems, laminated carbonate deposits can grow in the channels of aqueducts which transported water from karstic springs during the Roman period. The deposits of the aqueduct of Nîmes (SE France) are exceptional since they may represent several centuries of paleoenvironmental record with a seasonal resolution. δ18O, δ13C and trace elements were measured in three samples from this aqueduct. The comparison of the geochemical signals with the fine texture of the deposits evidenced the seasonal nature of the lamination observed. This allowed us to document the evolution of environment as recorded through the deposit for the period 50–275 AD. The concretions of the aqueduct of Nîmes document rather stable climatic conditions for the first three centuries AD, as well as a local vegetation change possibly linked to an increased in land use
Unraveling the hydrological budget of isolated and seasonally contrasted subtropical lakes
No full textInternational audienceComplete understanding of the hydrological functioning of large-scale intertropical watersheds such as the Lake Chad basin is becoming a high priority in the context of climate change in the near future and increasing demographic pressure. This requires integrated studies of all surface water and groundwater bodies and of their quite-complex intercon-nections. We present here a simple method for estimating the annual mean water balance of sub-Sahelian lakes subject to high seasonal contrast and located in isolated regions with no road access during the rainy season, a situation which precludes continuous monitoring of in situ hydrological data. Our study focuses for the first time on two lakes, Iro and Fitri, located in the eastern basin of Lake Chad. We also test the approach on Lake Ihotry in Madagascar, used as a benchmark site that has previously been extensively studied by our group. We combine the δ 18 O and δ 2 H data that we measured during the dry season with altimetry data from the SARAL satellite mission in order to model the seasonal variation of lake volume and isotopic composition. The annual water budget is then estimated from mass balance equations using the Craig-Gordon model for evaporation. We first show that the closed-system behavior of Lake Ihotry (i.e., precipitation equal to evaporation) is well simulated by the model. For lakes Iro and Fitri, we calculate evaporation to influx ratios (E/I) of 0.6 ± 0.3 and 0.4 ± 0.2, respectively. In the case of the en-dorheic Lake Fitri, the estimated output flux corresponds to the infiltration of surface water toward the surface aquifer that regulates the chemistry of the lake. These results constitute a first-order assessment of the water budget of these lakes, in regions where direct hydrological and meteorological observations are very scarce or altogether lacking. Finally, we discuss the implications of our data on the hydro-climatic budget at the scale of the catchment basins. We observe that the local evaporation lines (LELs) obtained on both lake and aquifer systems are slightly offset from the average rainfall isotopic composition monitored by IAEA at N'Djamena (Chad), and we show that this difference may reflect the impact of vegetation transpiration on the basin water budget. Based on the discussion of the mass balance budget we conclude that, while being broadly consistent with the idea that transpiration is on the same order of magnitude as evaporation in those basins, we cannot derive a more precise estimate of the partition between these two fluxes, owing to the large uncertainties of the different end-members in the budget equations
AdCofInov: Innovating coupling technologies for Adding Coffee waste value
No full textFiche bilan résumé du projet AdCofInov financé par Agropolis Fondation sous la référence ID 1403-026 dans la cadre du programme «Investissements d’avenir» (Labex Agro:ANR-10-LABX-0001-01
Expression of adiponectin receptors in the brain of adult zebrafish and mouse: Links with neurogenic niches and brain repair
No full textInternational audienceAdiponectin and its receptors (adipor) have been initially characterized for their role in lipid and glucose metabolism. More recently, adiponectin signaling was shown to display anti‐inflammatory effects and to participate in brain homeostasis and neuroprotection. In this study, we investigated adipor gene expression and its regulation under inflammatory conditions in two complementary models: mouse and zebrafish. We demonstrate that adipor1a, adipor1b, and adipor2 are widely distributed throughout the brain of adult fish, in neurons and also in radial glia, behaving as neural stem cells. We also show that telencephalic injury results in a decrease in adipor gene expression, inhibited by an anti‐inflammatory treatment (Dexamethasone). Interestingly, adiponectin injection after brain injury led to a consistent decrease (a) in the recruitment of microglial cells at the lesioned site and (b) in the proliferation of neural progenitors, arguing for a neuroprotective role of adiponectin. In a comparative approach, we investigate Adipor1 and Adipor2 gene distribution in the brain of mice and demonstrated their expression in regions shared with fish including neurogenic regions. We also document Adipor gene expression in mice after middle cerebral artery occlusion and lipopolysaccharide injection. In contrast to zebrafish, these inflammatory stimuli do no impact cerebral adiponectin receptor gene expression in mouse. This work provides new insights regarding adipor expression in the brain of fish, and demonstrates evolutionary conserved distribution of adipor with mouse. This is the first report of adipor expression in adult neural stem cells of fish, suggesting a potential role of adiponectin signaling during vertebrate neurogenesis. It also suggests a potential contribution of inflammation in the regulation of adipor in fish
Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO<sub>2</sub> conditions
No full textInternational audienceRising atmospheric CO2 is acidifying the world's oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ )3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 degrees C under night and daylight (200 µmol photons m-2s-1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 +/- 0.7 at ΩArag ~ 2 and 5.6 +/- 0.4mmol CaCO3 m-2 day-1 at ΩArag ~ 3-3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification
