Hydrogrammes de ruissellement superficiel et transport des sédiments en milieu agricole

Nous présentons ici une méthode simple qui permet de mesurer simultanément l'eau et les sédiments en transit à la surface du sol en milieu agricole. Des hydrogrammes de ruissellement superficiel sont comparés pour évaluer la variabilité saisonnière et spatiale du ruissellement et de l'érosion lors de trois précipitations naturelles (1,16, 1,76, 1,78 mm h-1). Les mesures ponctuelles sur le terrain sont utilisées pour caler une équation de transport des sédiments compatible avec les modèles hydrologiques distribués. Le débit solide (Qs) est exprimé par:Qs = k Qm lpoù Q est le débit liquide et l l'intensité des précipitations. Les hydrogrammes montrent que les débits varient dans l'espace selon la distance entre deux points d'échantillonnage et, dans le temps selon l'état de la surface. Pendant la saison, la concentration moyenne des sédiments dans l'eau et le taux de transport demeurent constants. Le transport par le ruissellement sur la parcelle est faible et semble limité par la capacité du processus à maintenir les sédiments en mouvement. Ce comportement affecte le paramètre m associé au débit liquide dans l'équation de transport, qui est en dessous des valeurs théoriques proposées dans la littérature. Le transport de sédiments est également fonction de l, qui par le biais de l'impact des gouttes de pluie sur la surface détache et facilite le transport des particules.Data are needed to validate a storm by storm model of sheetwash erosion, to assess spatial and temporal variations of runoff and erosion and to calibrate a sediment transport equation on agricultural fields. This remains a major problem in the development of distributed hydrological models. This paper presents a simple method to measure simultaneously water and sediment discharges on hillslopes. Hillslope hydrographs and sediment transport rates are used to investigate spatial and seasonal variations in runoff and erosion. Measurements are also used to calibrate a sheetwash sediment transport equation compatible with distributed hydrological models. Sediment discharge (Qs) is expressed by :Qs = k Qm lpwhere Q is water discharge, S is hillslope gradient and l rainfall intensity. Parameters k, m, n and p are constants for a given context.The experimental site is located in the Eastern Townships (Québec, Canada). It is a corn field (1 000 m2) where sheetwash erosion is active. Simultaneous measurements of water and sediment discharges are collected using hydraulically efficient samplers specially designed to minimize direct rainsplash input and to prevent sediment accumulation within the receptacle. Data were collected during three natural rainfalls with low average intensities monitored in June (l -1,76 mm h-1), September (l = 1,78 mm h-1) and October (l = 1,16 mm h-1) 1987. Because rainfall intensity varies within a precipitation, each rainfall event was subdivided into distinct measurement periods of short duration (5 to 60 min) with intensities ranging from 0,12 to 8,9 mm h-1. For each precipitation two samplers were operated simultaneously over the field. One of the sampler occupied a fixed spatial location, which allows comparison between event according to variations in vegetation cover and soil compaction. The second sampler is located at a different location for each event in order to sample different spatial contexts. Overall 80 samples with a measurable amount of water and sediments were obtained.Firstly, our results show that peaks in sediment transport rates are in most cases associated with peaks of water discharges, which occur simultaneously or just after the maxima in rainfall intensities. For the first and second rainfall events similar hydrological and erosional responses of the field were observed at the two spatial locations. For there events, the distance between the two samplers on the field M short (respectively 7 and 4 meters). For a given event, the two hydrographs have the same shape, although the downslope hydrograph is target and there is a lag (5 min) between peak discharges. These characteristics suggest a kinematic response of runoff on the field. For the third precipitation, the two samplers are located 13 meters apart. There is an important diminution of runoff and erosion downslope. The inversion of the size (volume of water) of the hydrographs is attributed to the divergence of runoff caused by the microtopography and the presence of obstacles on the surface.Over the season there is a difference in the hydrological response of the field. In September, the vegetation cover is dense and the mean infiltration and interception rates are high. Mean water and sediment discharges are low in comparison with those measured in June and October where the vegetation is sparse or absent (no interception). In October, the compaction of the soil surface is high and the infiltration capacity is low. Despite the tact that the mean rainfall intensity is slightly lower for this event, the highest amount of water and sediment discharges are observed. Average sediment concentration in water is constant for the three precipitation events. This suggests that the amount of loose sediments on the surface ready to be transported is always sufficient. The comparison of hill slope hydrographs on the field and at different times showed that water and sediment vary : i) in space according to slope length between sampling locations, and ; ii) over the season according to vegetation cover and soil surface properties.Secondly, parameters of the sediment transport equation are estimated for the three events. The results show that water discharge and rainfall intensity are positively related with sediment discharge, but also that the effect of hillslope gradient is negligible. This is explained by the fact that only four low gradient values are used in this study and that a wide range of discharges are measured on each gradient. The overall measurements yields the empirical equationQs = 0,02 Q0,97 l0,6There is a good agreement between water discharge, rainfall intensity and sediment transport (R2 = 0,91). Over the season, variation in mean discharges are not followed by fluctuations in the rate of sediment discharge which remained constant for the three events. Sediment transport appears to be low and under the limit of transport for rainwash erosion. As a result, the rate of increase in sediment transport (m = 0,97) is under the lower limit of the theoretical range of values (from 1,4 to 2,4) proposed in literature. Sediment discharge is also influenced by the contribution of rainsplash to particle detachment and transport. This process is evaluated by the incorporation of rainfall intensity into the sediment transport equation. The value obtained from the empirical estimation of p (0,6) is not significantly different from the theoretical value (p = 0,5) proposed in the literature. The contribution of rainfall intensity to the prediction of sediment transport is low but significant.In conclusion, results of this experiment show that spatially and temporally distributed data can be used to increase our knowledge on runoff and erosion at the scale of an agricultural field. The rote of low rainfall intensities on runoff and erosion is also important despite the presence of vegetation. These events contribute to the transfer of particles downslope and they increase the amount of loose sediments ready to be transported on the surface. Notwithstanding the fact that the net erosion on the field is negligible, sediment transport is active and predictable using a simple sediment transport equation

Plateforme web pour les finances communales

L’objectif principal de ce travail de Bachelor était de créer un prototype de plateforme web donnant la possibilité d’afficher différentes visualisations des comptes de la ville. Celles-ci leur permettraient de prendre des décisions, si nécessaire. Avant la réalisation, il fallait d’abord comprendre la thématique, analyser les données et choisir les outils et les langages de programmation. En se basant sur le framework PHP (Hypertext Preprocessor) « Laravel », il serait possible de développer sans problème de nouvelles fonctionnalités. Avec « D3.js » la manipulation des éléments DOM (Document Object Model) est facile à gérer. Il existait déjà certains mock-ups, plusieurs proofs of concepts réalisés avec Excel et des fragments de code JavaScript non documenté

Variations de la forme des versants le long d’un cours d’eau miniature

Le long du cours d'eau principal d'un bassin-versant miniature, la forme des versants est en partie contrôlée par l'exposition et la distance de l'embouchure. Les versants exposés au SE sont plus raides, plus courts et comportent moins de segments rectilignes que ceux exposés au NW. Par contre, l'angle des versants n'augmente ni ne diminue de la tête du cours d'eau vers l'embouchure. Les versants convexes à l'amont deviennent brusquement concaves à l'aval. Ce changement morphométrique s'effectue à l'endroit où le cours d'eau cesse de s'inciser activement.Along the main channel of a miniature drainage network, slope form is partly explained by aspect and distance from the outlet. Slopes exposed to the SE are steeper, shorter and less complex than those exposed to the NW. Slope angle, however, is unrelated with distance to the outlet while the percentage of convexity of the slopes decreases downstream. This change in slope convexity is very abrupt and it takes place where active stream downcutting ceases

A New Tensile Test for Aluminum Alloys in the Mushy State: Experimental Method and Numerical Modeling

A fairly simple experimental setup has been designed for testing the resistance of the mushy zone of alloys during solidification under tensile conditions. It has been used to study the effect of coalescence among the solid grains at a late stage of solidification. The experimental approach involves both tensile-strength measurements and scanning electron microscope (SEM) observations of fracture surfaces. Complementary information can be obtained by numerical modeling of this solidification process. The latter takes into account heat flow in the sample, rheology of the mushy alloy, liquid feeding, and porosity formation. All of the available information indicates that the transition from a granular mushy alloy to a coalesced solid-skeleton behavior starts for a solid fraction of approximately 92pc

Two-Phase Modeling of Hot Tearing in Aluminum Alloys: Applications of a Semicoupled Method

Hot tearing formation in both a classical tensile test and during direct chill (DC) casting of aluminum alloys has been modeled using a semicoupled, two-phase approach. Following a thermal calculation, the deformation of the mushy solid is computed using a compressive rheological model that neglects the pressure of the intergranular liquid. The nonzero expansion/compression of the solid and the solidification shrinkage are then introduced as source terms for the calculation of the pressure drop and pore formation in the liquid phase. A comparison between the simulation results and experimental data permits a detailed understanding of the specific conditions under which hot tears form under given conditions. It is shown that the failure modes can be quite different for these two experiments and that, as a consequence, the appropriate hot tearing criterion may differ. It is foreseen that a fully predictive theoretical tool could be obtained by coupling such a model with a granular approach. These two techniques do, indeed, permit coverage of the range of the length scales and the physical phenomena involved in hot tearin

The role of cardiac troponin T quantity and function in cardiac development and dilated cardiomyopathy

Background: Hypertrophic (HCM) and dilated (DCM) cardiomyopathies results from sarcomeric protein mutations, including cardiac troponin T (cTnT, TNNT2). We determined whether TNNT2 mutations cause cardiomyopathies by altering cTnT function or quantity; whether the severity of DCM is related to the ratio of mutant to wildtype cTnT; whether Ca2+ desensitization occurs in DCM; and whether absence of cTnT impairs early embryonic cardiogenesis. Methods and Findings: We ablated Tnnt2 to produce heterozygous Tnnt2+/ mice, and crossbreeding produced homozygous null Tnnt2-/-embryos. We also generated transgenic mice overexpressing wildtype (TGWT) or DCM mutant (TGK210Δ) Tnnt2. Crossbreeding produced mice lacking one allele of Tnnt2, but carrying wildtype (Tnnt2+/-/TGWT) or mutant (Tnnt2+/-/TGK210Δ) transgenes. Tnnt2+/-mice relative to wildtype had significantly reduced transcript (0.82 ± 0.06 [SD] vs. 1.00 ± 0.12 arbitrary units; p = 0.025), but not protein (1.01 ± 0.20 vs. 1.00 ± 0.13 arbitrary units; p = 0.44). Tnnt2+/-mice had normal hearts (histology, mass, left ventricular end diastolic diameter [LVEDD], fractional shortening [FS]). Moreover, whereas Tnnt2+/-/ TGK210Δ mice had severe DCM, TGK210Δ mice had only mild DCM (FS 18 ± 4 vs. 29 ± 7%; p < 0.01). The difference in severity of DCM may be attributable to a greater ratio of mutant to wildtype Tnnt2 transcript in Tnnt2+/-/TGK210Δ relative to TGK210Δ mice (2.42±0.08, p = 0.03). Tnnt2+/-/TGK210Δ muscle showed Ca2+ desensitization (pCa50 = 5.34 ± 0.08 vs. 5.58 ± 0.03 at sarcomere length 1.9 μm. p<0.01), but no difference in maximum force generation. Day 9.5 Tnnt2-/-embryos had normally looped hearts, but thin ventricular walls, large pericardial effusions, noncontractile hearts, and severely disorganized sarcomeres. Conclusions: Absence of one Tnnt2 allele leads to a mild deficit in transcript but not protein, leading to a normal cardiac phenotype. DCM results from abnormal function of a mutant protein, which is associated with myocyte Ca2+ desensitization. The severity of DCM depends on the ratio of mutant to wildtype Tnnt2 transcript. cTnT is essential for sarcomere formation, but normal embryonic heart looping occurs without contractile activity. © 2008 Ahmad et al

Material differentiation in forensic radiology with single-source dual-energy computed tomography

The goal of this study was to investigate the use of dual-energy computed tomography (CT) in differentiating frequently encountered foreign material on CT images using a standard single-source CT scanner. We scanned 20 different, forensically relevant materials at two X-Ray energy levels (80 and 130kVp) on CT. CT values were measured in each object at both energy levels. Intraclass correlation coefficient (ICC) was used to determine intra-reader reliability. Analysis of variance (ANOVA) was performed to assess significance levels between X-Ray attenuation at 80 and 130kVp. T test was used to investigate significance levels between mean HU values of individual object pairings at single energy levels of 80 and 130kVp, respectively. ANOVA revealed that the difference in attenuation between beam energies of 80kVp compared to 130kVp was statistically significant (p<0.005) for all materials except brass and lead. ICC was excellent at 80kVp (0.999, p<0.001) and at 130kVp (0.998, p<0.001). T test showed that using single energy levels of 80 and 130kVp respectively 181/190 objects pairs could be differentiated from one another based on HU measurements. Using the combined information from both energy levels, 189/190 object pairs could be differentiated. Scanning with different energy levels is a simple way to apply dual-energy technique on a regular single-energy CT and improves the ability to differentiate foreign bodies with CT, based on their attenuation value

Comportement différé des marnes du tunnel d’Arbus (France) soumises à des essais de fluage et de gonflement

Le travail présenté se concentre sur le comportement différé des marnes consécutif à la modification de l’état de contrainte et à l’action de l’eau. L’historique des chargements et la présence d’eau peuvent induire des changements importants dans le comportement des géomatériaux. Au cours du temps, leurs effets peuvent se superposer et créer des dégâts considérables dans les différents domaines miniers et du génie civil, notamment en construction souterraine. Sept essais ont été réalisés avec des oedomètres sur des marnes du tunnel d’Arbus (France). Les échantillons sont d’abord soumis à un chargement sous un seul palier (fluage mono palier) ou à un chargement par paliers successifs (fluage multi paliers), ensuite ils sont hydratés puis déchargés selon plusieurs paliers. Le comportement dû au fluage est simulé par le modèle de Lemaitre et le gonflement est modélisé par une loi hyperbolique. Le modèle global considérant la partition des déformations pendant le fluage et le gonflement reproduit fidèlement la déformation expérimentale mesurée.Mots clés: Marnes - Fluage - Viscoplasticité - Modèle J. Lemaitre - GonflementDiffered behavior from marl of Arbus tunnel (France) subjected to creep and swelling testsThe paper focuses on the delayed behavior of marls induced by a change in stress state and by the effect of water. Loading history and presence of water can induce important changes in the behavior of geomaterials. During time, their effects may enhanced-up and generate great damage in different applications in mining and civil engineering, in particular in underground construction.Seven experiments were conducted in oedometric cells on marl from the Arbus tunnel (France). The samples were subjected to a single loading step (one-stage creep test) or to successive loading steps (multi-stage creep test), after they are hydrated and discharged according to a several stages.The creep behavior was simulated by Lemaitre model and swelling was modeled by a hyperbolic law. A global model that partitions the deformation during the creep and swelling allows to faithfully giving the measured experimental deformation.Keywords: Marls - Creep - Viscoplasticity - J. Lemaitre model - Swellin

Two-phase modelling of hot tearing in aluminium alloys using a semi-coupled method

Hot tearing is one of the most severe defects observed in castings, e.g. in billets or sheet ingots of aluminum alloys produced by DC casting. It is due to both tensile strains and a lack of interdendritic feeding in the mushy zone. In order to predict this phenomenon at the scale of an entire casting, the two-phase averaged conservation equations for mass and momentum must be solved in the mushy (i.e. mixed solid and liquid) region of the material. In recent contributions, M'Hamdi et al [1] proposed a strongly coupled resolution scheme for this set of equations. The solution of the problem was obtained using a rheological model established by Ludwig et al [2] and that captures the partially cohesive nature of the mushy alloy. In the present contribution, the problem is addressed using a slightly different approach. The same rheological model (i.e. saturated porous media treatment) is used, but the influence of the liquid pressure is neglected at this stage. This assumption allows for a weakly coupled resolution scheme in which the mechanical problem is first solved alone using ABAQUS™ and user subroutines. Then the pressure in the liquid phase is calculated separately accounting for the viscoplastic deformation of the porous solid skeleton and solidification shrinkage. This is done with a code previously developed for porosity calculations, and that uses a refined mesh in the mushy zone [3]. This semi-coupled method was implemented and its numerical convergence studied from the point of view of both time step and mesh size. Guidelines for selecting these numerical parameters as well as the conditions under which the semi-coupled method may be applied are provided. The model was then applied to three cases, i.e. two tensile tests conducted on mushy alloys [4, 5] and the casting of an entire billet [6]. Experimental data was indeed available concerning these problems prior to the present work. This information was used for the validation of the thermal and mechanical models that were setup to describe these different cases. The results of the semi-coupled approach were also used to describe in more details these different castings. First of all, the numerical study of the mushy zone tearing test [5] proved helpful for distinguishing different fracture modes. The role of the high strain rate applied to the mushy alloy in this case was also outlined. Another tensile test, referred to as the rig test [4], was successfully modeled in the present framework. The numerical results could be used to quantify the redistribution of strain in the mushy sample. As a consequence, intrinsic properties of the material, such as its ductility, could be extracted from the results. This study also gave further insight about the conditions under which tearing occurs in the samples. Finally, the semi-coupled method was used to study the DC casting process. In this case, a real process performed under realistic conditions for the production of an industrial scale billet was modeled. As it is more complex and difficult to characterize experimentally, the conditions for hot tearing formation are less accessible. However, the isotherm velocity, the strain, the strain rate and the liquid pressure could be described reasonably accurately. It was thus possible to correlate experimental observations of the hot tear with various calculated indicators of hot tearing susceptibility. Even with this information, it remains difficult to formulate new hot tearing criteria because all the indicators follow a similar trend during the casting and their respective contributions can thus not be distinguished. The present work showed that the level of accuracy and detail that can be reached using two-phase models with appropriate materials properties and boundary conditions is satisfactory. It is indeed possible to model the relevant phenomena (heat flow, solid deformation and liquid feeding) at the scale of an entire casting. The variation of the different simulated fields can be described down to a scale of the order of a few millimeters. In that sense, this approach is one important aspect required to build a multiscale model for the problem of hot tearing. It is expected that coupling such a method with granular models (which cover length scales from a few microns to a few centimeters [7]) will allow for a more complete description of the phenomena at hand. In the future, the development of such a multiscale numerical tool may prove to be the most efficient way towards quantitative predictions of hot tearing formation in real solidification processes