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Boczar, J., A. Dorobczynski, and J. Miakotoi. "Modèle de transfert et de diffusion de masse dans un écoulement, en présence de gradients de vitesse et de gradients du coefficient de diffusion turbulente." Revue des sciences de l'eau 5, no. 3 (April 12, 2005): 353–79. http://dx.doi.org/10.7202/705136ar.
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Le travail présente un modèle mathématique conceptuel de transfert et de diffusion de masse destiné à l'étude des migrations d'effluents en rivière. Ce modèle prend en compte l'existence d'écoulements cisaillés ainsi que la présence de gradients de diffusion turbulente. Il permet de calculer les champs de concentrations et les valeurs moyennes de concentration à travers toute section transversale de l'écoulement. La localisation et la taille relative du rejet sont respectées. L'influence des rives sur les processus de dispersion est prise en considération.Pour quantifier l'influence des berges, une relation est établie entre les concentrations calculées en écoulement de largeur infinie et les concentrations en écoulement d'extension limitée. La méthode utilisée est fondée sur l'emploi d'un champ de vitesse et d'un champ de coefficient de diffusion, symétriques par rapport à des lignes riveraines séparant le courant nul d'un courant fictif situé de part et d'autre de ces limites.Les résultats des tests du modèle mathématique, réalisés à l'aide du programme moniteur « Gradient 2 », sont présentés. Dans le cas d'écoulements cisaillés, on a constaté que la valeur moyenne de concentration d'effluent calculée au travers de sections transversales à l'écoulement n'était pas une quantité invariante tout au long de l'écoulement. Un gradient de vitesse négatif induit une augmentation de cette moyenne à mesure que l'on s'éloigne du rejet alors qu'un gradient positif produit l'effet inverse. Un gradient du coefficient de diffusion turbulente détermine un changement du profil de concentration à l'intérieur d'une section transversale donnée, sans en changer cependant la valeur moyenne. Un gradient négatif augmente la valeur maximale de la distribution des concentrations. Un gradient positif fait diminuer la valeur maximale en aplatissant l'allure du profil.Le modèle mathématique a ensuite été vérifié à l'aide d'un modèle physique. Un modèle réduit respectant les similitudes d'écoulement a été bâti. Les gradients de vitesse du fluide et les gradients du coefficient de diffusion étaient provoqués par l'introduction de tirants d'eau non uniformes dans chaque section transversale. Les mesures réalisées ont permis d'estimer les coefficients de diffusion turbulente.
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Gallinari, F., S. Elmaleh, and R. Ben Aïm. "Influence de la dissipation énergetique sur l'efficacité de la flottation à air dissous : analogie avec la floculation." Revue des sciences de l'eau 9, no. 4 (April 12, 2005): 485–98. http://dx.doi.org/10.7202/705263ar.
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Les flottateurs à air dissous sont classiquement dimensionnés à partir de deux paramètres: le rapport mA/mS des masses d'air et de solides en présence et le temps de contact entre phases. Une série d'essais effectués sur cinq différentes unités continues ou discontinues montre que ces seules variables opératoires ne suffisent pas à déterminer l'efficacité. De plus, l'extrapolation des données obtenues sur un floculateur discontinu conduirait à des besoins en air dissous considérables pouvant limiter le développement industriel. La dissipation d'énergie, habituellement négligée, peut être quantifiée par le gradient de vitesse tel qu'il a été introduit en théorie de la floculation. De plus, une analogie entre la capture bulles-particules et le processus de floculation des particules primaires sur les flocs déjà formés permet d'étendre les équations de vitesse de la floculation et d'obtenir un modèle cinétique où interviennent seulement le gradient de vitesse et la concentration de particules; ce modèle remplace avantageusement l'approche classique qui considère la flottation comme un processus du premier ordre par rapport aux particules. L'efficacité d'une cellule discontinue ou d'un floculateur piston est alors fonction du seul nombre de Camp. Les résultats montrent l'existence d'un intervalle optimal pour le gradient de vitesse, 3000 à 4000 s-¹, et pour le nombre de Camp 105 à 106. Le modèle devra être amélioré par introduction de la tension critique de mouillage des particules.
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Golse, N., F. Joly, Q. Nicolas, P. Combari, A. Sa Cunha, D. Cherqui, R. Adam, E. Vibert, and I. Vignon Clementel. "Utilisation d’un modèle mathématique dans la prédiction du gradient porto-cave post-résection hépatique." Journal de Chirurgie Viscérale 157, no. 3 (September 2020): S180. http://dx.doi.org/10.1016/j.jchirv.2020.07.113.
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Abouo, N’guessan Verdier, Alhassane Fofana, Yevi Delphine N’guessan, and Nogbou Emmanuel Assidjo. "Modélisation mathématique du séchage dans un four (air chaud) de tranches de mangue (Mangiféra indica L.)." International Journal of Biological and Chemical Sciences 14, no. 7 (December 4, 2020): 2476–90. http://dx.doi.org/10.4314/ijbcs.v14i7.9.
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Ce travail vise à étudier le séchage de la mangue à différentes épaisseurs et températures en vue de valorisation. Les expériences ont été menées à partir d’une matrice factorielle par la méthode gravimétrique statique. Les valeurs expérimentales ont été ajustées à huit modèles empiriques par la méthode du gradient afin d’estimer les paramètres et coefficients des modèles. Les critères statistiques que sont le R², l’erreur quadratique moyenne (EQM) et le χ² ont servi à justifier le choix du modèle de séchage. Le séchage a duré 16-18 ; 23-27 et 29-33 minutes respectivement aux températures 60, 50 et 40°C pour les épaisseurs 1,5 et 1 cm. Le modèle logarithmique est retenu et présente les valeurs du R² (0,9984 ; 0,9984 ; 0,9981 ; 0,9987 ; 0,9988 ; 0,9985) les plus élevées et les plus faibles valeurs de χ² (2,43 e-07 ; 1,58 e-07 ; 1,25 e-06 ; 2,02 e-07 ; 4,56 e-06 et 1,37 e-06) et EQM (2,42 e-04 ; 1,95 e-07 ; 5,47 e-04 ; 2,20 e-04 ; 0,0010 et 5,69 e-04). Le coefficient de diffusion varie de 8,615 e-09 à 9,155 e-09 m² / s et dépend fortement de la température de séchage. L’énergie d’activation est estimée entre 22,430 – 25,358 KJ / mol.Mots clés : Séchage, mangue, modèle, coefficient de diffusion, énergie d’activation.
English Title: Mathematical modeling of the drying in an oven (hot air) of slices of mango (Mangifera indica L.)This work aims to study the drying of mango at different thicknesses and temperatures a view to valorization. The experiments were carried out from a factor matrix by the static gravimetric method. The experimental values were fitted to eight empirical models by the gradient method in order to estimate the parameters and coefficients of the models. The statistical criteria of R², mean square error (MSE) and χ² were used to justify the choice of the drying model. Drying lasted 16-18; 23-27 and 29-33 minutes respectively at temperatures 60, 50 and 40 °C for thicknesses 1.5 and 1 cm. The logarithmic model is retained and presents the highest values of R² (0.9984; 0.9984; 0.9981; 0.9987; 0.9988; 0.9985) and the lowest values of χ² (2.43 e-07; 1.58 e-07; 1.25 e-06; 2.02 e-07; 4.56 e-06 and 1.37 e-06) and MSE (2.42 e-04; 1.95 e-07; 5.47 e-04; 2.20 e-04; 0.0010 and 5.69 e-04). The diffusion coefficient varies from 8.615 e-09 to 9.155 e-09 m² / s and strongly depends on the drying temperature. The activation energy is estimated to be 22.430 - 25.358 KJ / mol.Keywords : Drying, mango, models, diffusion coefficient, activation energy.
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Soto Molina, Victor Hugo, and Hugo Delgado Granados. "Estimación de la temperatura del aire en la alta montaña mexicana mediante un modelo de elevación del terreno: caso del volcán Nevado de Toluca (México) / Estimation of the air temperature in the Mexican high mountain environment by means of a model of elevation of the terrain, case of the Nevado de Toluca volcano (Mexico)." Ería 2, no. 2 (July 19, 2020): 167–82. http://dx.doi.org/10.17811/er.2.2020.167-182.
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La carencia de estaciones climatológicas por encima de 3.500 metros sobre el nivel del mar (msnm) en México condiciona que los estudios sobre ecosistemas de alta montaña sean realizados con datos de estaciones cercanas, pero sin considerar la diferencia altitudinal de la temperatura debida al relieve y al gradiente vertical. Por tal razón, se realiza un modelo mensual y anual de la distribución espacial de la temperatura del aire en superficie para el volcán Nevado de Toluca (4.680 msnm) y zonas adyacentes, mediante el uso de un Modelo Digital de Elevaciones y el Gradiente Vertical de la Temperatura Troposférica. Este último se ha obtenido a partir de los valores medios de los elementos meteorológicos de cada una de las estaciones situadas alrededor del edificio volcánico y a diferente altitud entre sí. La precisión del modelo ha sido comprobada mediante las observaciones registradas en una estación climatológica instalada al noroeste de la cima del estratovolcán a 4.283 msnm. En el mapa ráster resultante con resolución espacial de 15 metros por pixel se aprecia que los valores estimados son estadísticamente semejantes a aquellos observados in situ. Los resultados en el modelo muestran un aceptable grado de exactitud, y éste puede implementarse fácilmente en cualquier zona a cualquier escala temporal, donde la falta de estaciones climatológicas limite o impida el análisis de la relación de la temperatura con los ecosistemas de alta montaña.L'absence de stations climatologiques au Mexique à plus de 3 500 mètres d'altitude conditionne la réalisation d'études sur les écosystèmes de haute montagne à partir de données provenant de stations à proximité, sans tenir compte de la différence d'altitude en température due au relief et le gradient vertical de celui-ci. Cela a conduit à l'élaboration de ce travail où une modélisation mensuelle et annuelle de la distribution spatiale de la température de l'air au niveau de la surface pour le volcan Nevado de Toluca (4 680 mètres d'altitude) et les zones adjacentes a été réalisée à l'aide d'un modèle altimétrique numérique et du gradient vertical de la température troposphérique; ces derniers ont été obtenus à partir des normales climatiques de chacune des stations situées autour du bâtiment volcanique et à différentes altitudes. La précision du modèle a été vérifiée par des observations enregistrées dans une station météorologique installée au nord-ouest du sommet de la montagne à 4 283 mètres d'altitude. Dans la carte raster résultante avec une résolution spatiale de 15 mètres par pixel, il a été constaté que les valeurs estimées sont statistiquement similaires à celles observées in situ. Les résultats du modèle montrent un degré de précision acceptable, ce qui peut être facilement mis en œuvre dans n'importe quelle zone et à n'importe quelle échelle de temps, lorsque le manque de stations climatologiques limite ou empêche l'analyse de la relation entre la température et les écosystèmes de haute montagne.The lack of climatological stations above 3,500 meters above sea level (m asl) in Mexico, conditions that the studies on high mountain ecosystems are made with data from nearby stations, but without considering the altitudinal difference of the temperature due to the relief and the vertical gradient of it. This led to the elaboration of this work where a monthly and annual modeling of the spatial distribution of air temperature at the surface level for the Nevado de Toluca volcano (4,680 m asl) and adjacent areas was carried out using a Digital Elevation Model and the Vertical Gradient of the Tropospheric Temperature. The latter having been obtained based on the climatic normals of each of the stations located around the volcanic mountain and at different altitudes. The accuracy of the model has been verified by observations recorded in a weather station installed northwest of the mountain top at 4,283 meters above sea level. In the resulting raster map with spatial resolution of 15 meters per pixel, it was found that the estimated values are statistically similar to those observed in situ. The results in the model show an acceptable degree of accuracy, and this can be easily implemented in any area at any time scale, where the lack of climatological stations limits the analysis of the relationship of air temperature with high mountain ecosystems.
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Albayda, Alaa, Olivier Bartier, Xavier Hernot, and Gérard Mauvoisin. "Identification de la déformation représentative et de la loi d’écrouissage des matériaux avec l’indentation sphérique en se basant sur un modèle de gradient de dureté." Matériaux & Techniques 110, no. 2 (2022): 205. http://dx.doi.org/10.1051/mattech/2022025.
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L’application du concept de la déformation représentative est souvent utilisée pour déterminer la courbe d’écrouissage d’un matériau à partir d’un essai d’indentation. Une nouvelle méthodologie de détermination de la déformation représentative en indentation sphérique est présentée dans cet article. Cette méthodologie est basée sur celle définie par Hernot et al. (2013) (X. Hernot, C. Moussa, O. Bartier, Study of the concept of representative strain and constraint factor introduced by Vickers indentation, Mech. Mater. 68, 1–14 (2014), https://doi.org/10.1016/j.mechmat.2013.07.004 [29]) pour le cas de l’indentation Vickers et consiste à calculer les gradients de la grandeur mesurée en fonction des paramètres mécaniques de la loi de comportement du matériau testé. Pour montrer la validité de la méthode de détermination de la déformation représentative proposée, le calcul des gradients de la grandeur est effectué à partir du modèle analytique proposé par Lee et al. (2005) (H. Lee, J. Haeng Lee, G.M. Pharr, A numerical approach to spherical indentation techniques for material property evaluation, J. Mech. Phys. Solids 53(9), 2037–2069 (2005), https://doi.org/10.1016/j.jmps.2005.04.007 [31]). Parmi les différents modèles proposés dans la littérature, ce modèle a l’avantage d’être complet et propose des équations analytiques reliant la hauteur de contact réel, la profondeur de pénétration et l’effort appliqué par l’indenteur sphérique. Les résultats obtenus par cette méthodologie montrent que la déformation représentative n’évolue pas linéairement en fonction du rayon de contact adimensionnel a/R contrairement à ce que prédit le modèle de Tabor (1951) D. Tabor, The Hardness of Metals, Oxford University Press, Oxford, New York, 2000. [7]). Les valeurs de déformation représentatives déterminées par notre méthode se situent entre celles proposées par Tabor (1951), Ahn et Kwon (2001) (J.-H. Ahn, D. Kwon, Derivation of plastic stress–strain relationship from ball indentations: Examination of strain definition and pileup effect, J. Mater. Res. 16(11), 3170–3178 (2001), https://doi.org/10.1557/JMR.2001.0437 [8]) et Jeon et al. (2005) (E. Jeon, M. Baik, S. Kim, et al., Determining representative stress and representative strain in deriving indentation flow curves based on finite element analysis, Key Eng. Mater. 297-300, 2152–2157 (2005), https://doi.org/10.4028/www.scientific.net/KEM.297-300.2152 [9]). Les résultats montrent aussi que la déformation représentative proposée par Chaudhri (1996) (M.M. Chaudhri, Subsurface plastic strain distribution around spherical indentations in metals, Philos. Mag. A 74(5), 1213–1224 (1996), https://doi.org/10.1080/01418619608239721 [27]) est largement surestimée et que celle calculée par Lee et al. (2005) est trop élevée pour des rayons de contact adimensionnels (a/R) supérieurs à 0,3. Les valeurs de déformations et contraintes représentatives obtenues par la méthode proposée permettent de conclure qu’il n’existe pas de facteur de confinement universel constant indépendant du rapport adimensionnel a/R et du matériau indenté. Pour terminer, dans le cas d’une application expérimentale de la méthode proposée, ces valeurs de déformation et contrainte représentatives permettent d’obtenir une courbe d’écrouissage très proche de celle obtenue classiquement par un essai de traction.
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N’guessan, Yevi Delphine, N’guessan Verdier Abouo, Essoh Eric Akpa, Yacouba Kamara, and Nogbou Emmanuel Assidjo. "Modélisation mathématiques du séchage artificiel (sous air chaud) de la pomme de cajou (<i>Anacardium occidentale</i> L.)." International Journal of Biological and Chemical Sciences 17, no. 4 (September 19, 2023): 1606–18. http://dx.doi.org/10.4314/ijbcs.v17i4.25.
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Le séchage est une technique utilisée pour la conservation des produits agricole. Ce travail de recherche visait à étudier le séchage des pommes de cajou préalablement trempées dans des solutions (mélasse et saccharose) osmotiques afin d’optimaliser le processus. Les expériences ont été menées à partir d’une matrice composite et le séchage s’est réalisé en suivant la méthode gravimétrique statique. Les valeurs expérimentales ont été ajustées à huit modèles empiriques à l’aide de la méthode du gradient (développée puis implémentée dans le logiciel MatlabR2016a) afin d’estimer les paramètres et coefficients. Les critères statistiques que sont le coefficient de corrélation r, l’erreur quadratique moyenne (EQM) et le χ2 ont servi à justifier le choix du modèle d’ajustement idéal. Le séchage a duré en moyenne 34 heures pour l’ensemble des échantillons trempés dans les solutions (mélasse, saccharose). Le modèle de l’approche diffusion est retenu et présente les valeurs du r (0,9822 ; 0,9986; 0,9966) les plus élevées et les plus faibles valeurs de χ2 (0,0013 ; 0,0035 et 0,0072) et EQM (0,0019 ; 0,0005 et 0,0003). Le coefficient de diffusion varie de 9,876 E-09 à 7,416 E-08 m²/s et dépend fortement de la température de séchage. L’énergie d’activation est estimée entre 18,548 – 21,430 KJ/ mol.
Drying is a technique used to preserve agricultural products. The aim of this research was to study the drying of cashew apples previously soaked in osmotic solutions (molasses and sucrose) in order to optimize the process. The experiments were conducted using a composite matrix and the drying was carried out following the static gravimetric method. The experimental values were fitted to eight empirical models using the gradient method (developed and then implemented in MatlabR2016a software) to estimate the parameters and coefficients. The statistical criteria of correlation coefficient r, root mean square error (RMSE), and χ2 were used to justify the selection of the ideal fitting model. Drying time averaged was 34 hours for all samples soaked in the solutions (molasses, sucrose). The diffusion approach model is selected and has the highest values of r (0.9822; 0.9986; 0.9966) and the lowest values of χ2 (0.0013; 0.0035 and 0.0072) and MSE (0.0019; 0.0005 and 0.0003). The diffusion coefficient varies from 9.876 E-09 to 7.416 E-08 m²/s and is strongly dependent on the drying temperature. The activation energy is estimated between 18.548 - 21.430 KJ / mol.
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Edwards, T. L., X. Fettweis, O. Gagliardini, F. Gillet-Chaulet, H. Goelzer, J. M. Gregory, M. Hoffman, et al. "Probabilistic parameterisation of the surface mass balance–elevation feedback in regional climate model simulations of the Greenland ice sheet." Cryosphere 8, no. 1 (January 30, 2014): 181–94. http://dx.doi.org/10.5194/tc-8-181-2014.
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Abstract. We present a new parameterisation that relates surface mass balance (SMB: the sum of surface accumulation and surface ablation) to changes in surface elevation of the Greenland ice sheet (GrIS) for the MAR (Modèle Atmosphérique Régional: Fettweis, 2007) regional climate model. The motivation is to dynamically adjust SMB as the GrIS evolves, allowing us to force ice sheet models with SMB simulated by MAR while incorporating the SMB–elevation feedback, without the substantial technical challenges of coupling ice sheet and climate models. This also allows us to assess the effect of elevation feedback uncertainty on the GrIS contribution to sea level, using multiple global climate and ice sheet models, without the need for additional, expensive MAR simulations. We estimate this relationship separately below and above the equilibrium line altitude (ELA, separating negative and positive SMB) and for regions north and south of 77° N, from a set of MAR simulations in which we alter the ice sheet surface elevation. These give four "SMB lapse rates", gradients that relate SMB changes to elevation changes. We assess uncertainties within a Bayesian framework, estimating probability distributions for each gradient from which we present best estimates and credibility intervals (CI) that bound 95% of the probability. Below the ELA our gradient estimates are mostly positive, because SMB usually increases with elevation: 0.56 (95% CI: −0.22 to 1.33) kg m−3 a−1 for the north, and 1.91 (1.03 to 2.61) kg m−3 a−1 for the south. Above the ELA, the gradients are much smaller in magnitude: 0.09 (−0.03 to 0.23) kg m−3 a−1 in the north, and 0.07 (−0.07 to 0.59) kg m−3 a−1 in the south, because SMB can either increase or decrease in response to increased elevation. Our statistically founded approach allows us to make probabilistic assessments for the effect of elevation feedback uncertainty on sea level projections (Edwards et al., 2014).
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El Khatib, Hamed, and René Javelas. "Modèle correctif de la mesure de la température d'un gaz par couple thermoélectrique. Application à une zone à fort gradient thermique." Revue Générale de Thermique 35, no. 417 (October 1996): 571–79. http://dx.doi.org/10.1016/s0035-3159(96)80020-1.
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Dias, Vivian Cristina, and Bianca Carvalho Vieira. "Parâmetros morfométricos e corridas de detritos: índice de suscetibilidade e magnitude de bacias hidrográficas na Serra do Mar." GEOUSP Espaço e Tempo (Online) 26, no. 2 (September 22, 2022): 23–49. http://dx.doi.org/10.11606/issn.2179-0892.geousp.2022.191937.
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Les coulées de débris sont parmi les mouvements de masse les plus destructeurs en raison du potentiel de transport. Cette recherche visait à évaluer la relation entre les caractéristiques morphométriques des bassins versant et l'occurrence de coulées de débris et la classification avec d'un indice de susceptibilité et de magnitude. Pour cartographier la morphométrie des bassins, le Modèle Numérique d'élévation (MNE) Alos PALSAR (résolution de 12,5 mètres) a été utilisé; une description statistique et une classification des bassins ont été faites avec d'un indice de susceptibilité et de magnitude. Les résultats ont indiqué l'influence du gradient altimétrique, du rapport de relief, de l'indice de rugosité, de l'amplitude altimétrique et l'indice Melton dans les bassins affectés par le récent coulées de débris. La classification des bassins basée sur l'indice de sensibilité et de magnitude s'est avérée cohérente avec l'occurrence de coulées de débris et peut être utilisée dans d'autres zones sensibles.
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KABRÉ, Blaise, Mamounata BELEM/OUÉDRAOGO, Benjamin LANKOANDÉ, and Amadé OUÉDRAOGO. "Variabilité démographique de Saba senegalensis (A. DC.) Pichon suivant le gradient climatique au Burkina Faso." BOIS & FORETS DES TROPIQUES 345 (October 27, 2020): 75–85. http://dx.doi.org/10.19182/bft2020.345.a31930.
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Saba senegalensis (A. DC.) Pichon est une liane ligneuse de la famille des Apocynaceae. Elle est aussi appelée liane goïne. Les produits forestiers non ligneux obtenus à partir de cette espèce ont une grande importance socio-économique au Burkina Faso. Cependant, les caractéristiques démographiques de l’espèce sont peu connues bien que nécessaires pour mettre en place des programmes de gestion durable. La présente étude a pour objectif d’évaluer les caractéristiques démographiques de S. senegalensis suivant le gradient climatique au Burkina Faso. Un échantillonnage aléatoire orienté a conduit à installer des placeaux de 1 000 m2 pour l’inventaire des populations. Les mesures dendrométriques ont concerné le diamètre de la tige au collet et à 1,30 m du sol pour les individus adultes et les diamètres à 20 cm du sol et au collet, respectivement pour les jeunes plants et les plantules. L’indice de Green, la densité, le diamètre moyen des tiges et la surface terrière ont été calculés et comparés entre les zones climatiques. Les résultats ont montré une distribution agrégative de S. senegalensis révélée par l’indice de Green. La densité, le diamètre moyen et la surface terrière ont varié significativement (p < 0,05) entre les zones climatiques. Les fortes densités des sujets adultes de S. senegalensis se trouvent dans les zone sahélienne et soudanienne. Le modèle linéaire généralisé montre que la température et les précipitations ont une influence sur l’établissement de la régénération de S. senegalensis. La structure démographique a révélé une abondance de juvéniles qui représentent un important potentiel de renouvellement des populations. S. senegalensis montre une certaine résilience de ses populations ; mais, du fait de la péjoration climatique et de la pression anthropique, la conservation de l’espèce dans son habitat naturel reste aléatoire.
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Iboum Kissaaka, Joseph Bertrand, François Mvondo Owono, Paul Gustave Fowe Kwetche, Jeannette Ngo Elogan Ntem, Serge Edouard Angoua Biouele, and Marie Joseph Ntamak-Nida. "Subsidence et évolution thermique des bassins de la marge atlantique camerounaise : premiers résultats à partir des puits en mer du sous-bassin de Kribi-Campo (Marge passive Ouest Africaine, Golfe de Guinée)." Canadian Journal of Earth Sciences 58, no. 7 (July 2021): 573–92. http://dx.doi.org/10.1139/cjes-2020-0146.
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L’histoire de la subsidence et de l’évolution thermique du sous-bassin de Kribi-Campo situé dans le Golfe de Guinée a été contrainte à l’aide de 10 puits en mer en utilisant la technique de délestage après décompaction. Quatre principales phases de subsidence ont été discriminées : la première, du Barrémien à l’Aptien (130–112 Ma); la deuxième, de l’Albien au Sénonien (112–65 Ma); la troisième, s'étendant du Paléocène au Miocène (65–5 Ma); et la quatrième du Pliocène au Pléistocène (5–2 Ma). Les cartes de quantité et de vitesse de subsidence et de sédimentation montrent une grande zone subsidente dans la partie ouest du bassin autour de Kribi. Le facteur d’extension β pour le modèle d’extension uniforme correspond à des valeurs allant de 1,04 à 1,06. Graphiquement, les courbes de subsidence tectonique apparaissent encadrées par les courbes correspondant à β = 1,03 et β = 1,09. Les pentes des courbes linéaires de la subsidence tectonique par rapport à la racine carrée du temps, t, ont permis d’avoir des paléotempératures des sédiments ainsi que des gradients géothermiques en parfait accord avec les valeurs observées dans les puits. Par exemple, un gradient de température de 35,316 °C·km−1 a été calculé avec les températures maximales tandis que celui obtenu à partir des puits est de 35,554 °C·km−1. La comparaison des valeurs calculées de la réflectance de la vitrinite Ro avec les valeurs mesurées montre une bonne correspondance. Ces valeurs de la vitrinite indiquent que les roches-mères d’âge Crétacé et Tertiaire inférieur ont probablement atteint la maturité thermique.
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Grelier, Benjamin, Gilles Drogue, Michel Pirotton, Pierre Archambeau, and Emilie Gernez. "Peut-on estimer l’effet du changement climatique sur l’écoulement à l’exutoire d’un bassin sans modèle pluie-débit ? un test de la méthode de transfert climat-écoulement par régression dans le bassin transnational de la meuse." Climatologie 14 (2017): 48–81. http://dx.doi.org/10.4267/climatologie.1232.
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L’étude de l’impact futur du changement climatique sur l’écoulement à l’exutoire d’un bassin repose généralement sur l’utilisation d’un modèle pluie-débit. Cet article explore les potentiels et les limites d’une stratégie alternative, fondée sur une méthode de transfert climat-écoulement par régression multiple. Cette méthode s’appuie sur un séquençage d’une régression des moindres carrés partiels (PLS) et d’une régression linéaire multiple (RLM) destinée à estimer des indices d’écoulement via les meilleurs prédicteurs climatiques identifiés par régression PLS. Les modèles de régression RLM paramétrés sur des critères quantitatifs, et par jugement expert des conditions hydro-climatiques actuelles, sont ensuite forcés par des sorties de modèles de climat pour produire des projections hydrologiques à différents horizons. L’application de la méthode de transfert climat-écoulement par régression multiple à deux cours d’eau du bassin de la Meuse décrits à partir d’indices d’écoulement de basses, de moyennes et de hautes eaux, montre que : i) cette méthode fonctionne convenablement pour certains indices d’écoulement seulement; ii) une connaissance minimale de la variabilité climatique à l’échelle régionale (apportée dans notre cas, par la pression atmosphérique et le gradient régional de pression en surface et à 500 hPa) suffit à décrire de façon acceptable le forçage climatique sur ces indices; iii) le jugement expert est indispensable pour identifier les prédicteurs climatiques hydrologiquement pertinents; iv) la force du lien entre climat et écoulement est propre à chaque bassin versant; v) les changements d’écoulement prédits par la méthode de transfert climat-écoulement sous scénarios climatiques CMIP5 (Coupled Model Intercomparison Project Phase 5) pour les prochaines décennies sont en accord avec ceux prédits par la modélisation pluie-débit. Au stade de nos investigations, trois limites majeures de la méthode de transfert climat-écoulement par régression multiple ont été identifiées : 1) elle exige de longues chroniques hydro-climatiques; 2) elle a tendance à sous-estimer la variabilité interannuelle de l’écoulement à l’exutoire des bassins testés; 3) elle n’est pas en capacité de garantir avec certitude l’évolution des indices d’écoulement dans des conditions climatiques très différentes de celles de la période d’observation.
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Lang, C., X. Fettweis, and M. Erpicum. "Future climate and surface mass balance of Svalbard glaciers in an RCP8.5 climate scenario: a study with the regional climate model MAR forced by MIROC5." Cryosphere 9, no. 3 (May 7, 2015): 945–56. http://dx.doi.org/10.5194/tc-9-945-2015.
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Abstract. We have performed a future projection of the climate and surface mass balance (SMB) of Svalbard with the MAR (Modèle Atmosphérique Régional) regional climate model forced by MIROC5 (Model for Interdisciplinary Research on Climate), following the RCP8.5 scenario at a spatial resolution of 10 km. MAR predicts a similar evolution of increasing surface melt everywhere in Svalbard followed by a sudden acceleration of melt around 2050, with a larger melt increase in the south compared to the north of the archipelago. This melt acceleration around 2050 is mainly driven by the albedo–melt feedback associated with the expansion of the ablation/bare ice zone. This effect is dampened in part as the solar radiation itself is projected to decrease due to a cloudiness increase. The near-surface temperature is projected to increase more in winter than in summer as the temperature is already close to 0 °C in summer. The model also projects a stronger winter west-to-east temperature gradient, related to the large decrease of sea ice cover around Svalbard. By 2085, SMB is projected to become negative over all of Svalbard's glaciated regions, leading to the rapid degradation of the firn layer.
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Chatonnet, Pascal, and Jean-Noël Boidron. "Incidence du traitement thermique du bois de chêne sur sa composition chimique. 1ere partie : définition des paramètres thermiques de la chauffe des fûts en tonnellerie." OENO One 23, no. 2 (June 30, 1989): 77. http://dx.doi.org/10.20870/oeno-one.1989.23.2.1725.
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<p style="text-align: justify;">La chauffe des fûts est une opération fondamentale de la fabrication d'une barrique. En effet, poursuivi au-delà des simples nécessités du cintrage, le brûlage (ou bousinage) entraîne l'apparition de nouveaux composés par thermolyse et hydrothermolyse du bois. Ces derniers sont susceptibles d'influencer ultérieurement les propriétés organoleptiques des vins élevés en barriques.</p><p style="text-align: justify;">La chauffe des bois est encore réalisée totalement empiriquement, les écarts entre tonneliers peuvent être importants. De plus, il n'existe pas de classification objective des niveaux de brûlage. L'optimalisation de cette opération passe préalablement par la connaissance de ses caractéristiques thermiques. A cette fin, on a mesuré les températures du bois au cours des processus de cintrage et de brûlage, en fonction de différents modes de chauffe et rythmes d'humidification.</p><p style="text-align: justify;">Les données recueillies permettront d'établir un modèle thermique de la chauffe traditionnelle en tonnellerie qui aidera à mieux comprendre les mécanismes de thermodégradation du bois de chêne. Une prochaine étude précisera l'évolution de la nature et de la quantité des produits de thermolyse en fonction du niveau de brûlage et du gradient thermique du bois. La modélisation de ces réactions devrait permettre l'optimisation de la régularisation de la chauffe du bois en tonnellerie.</p>
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Pellerin-Massicotte, Jocelyne, Bruno Vincent, and Émilien Pelletier. "Évaluation écotoxicologique de la baie des Anglais à Baie-Comeau (Québec)." Water Quality Research Journal 28, no. 4 (November 1, 1993): 665–86. http://dx.doi.org/10.2166/wqrj.1993.035.
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Résumé La baie des Anglais à Baie-Comeau (Québec) est un site industriel reconnu comme étant contaminé aux hydrocarbures et aux biphényls polychlorés (BPC). Une expérience de transfert à moyen terme de deux bivalves marins, Mya arenaria et Mytilus edulis L., a été réalisée entre un site de référence en aval de la baie des Anglais (Franquelin) et des sites contaminés près de Baie-Comeau suivant un gradient de contamination déterminé selon des données physico-chimiques antérieures. Les analyses chimiques de contaminants ont montré qu’il n’y a pas eu d’enrichissement en hydrocarbures, au mercure et en BPC pour toute la durée du protocole mais, parmi les sondes bioanalytiques choisies pour évaluer l’état de santé de cet écosystème, celles qui se sont avérées les plus sensibles chez Mya arenaria furent le glycogène et les lipides dans les gonades, et pour les deux bivalves, la fragilité de la membrane lysosomale de la glande digestive qui est un excellent indicateur de stress toxique. Les présents résultats sont compatibles avec un modèle qui consisterait à établir une évaluation ecotoxicologique d’un écosystème que l’on soupçonne perturbé par la pollution par (i) l’analyse de la bioaccumulation des substances toxiques que l’on croit présentes dans l’écosystème (hydrocarbures, BPC et métaux lourds) et (ii) l’évaluation des effets physiologiques et biochimiques des polluants à l’aide de sondes bioanalytiques appropriées.
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Chen, Xinquan, Junqi Gao, Biqing Qi, Dong Li, Yiang Luo, Fangyuan Li, and Pengfei Li. "Fast and Slow Gradient Approximation for Binary Neural Network Optimization." Proceedings of the AAAI Conference on Artificial Intelligence 39, no. 25 (April 11, 2025): 26913–21. https://doi.org/10.1609/aaai.v39i25.34896.
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Binary Neural Networks (BNNs) have garnered significant attention due to their immense potential for deployment on edge devices. However, the non-differentiability of the quantization function poses a challenge for the optimization of BNNs, as its derivative cannot be backpropagated. To address this issue, hypernetwork based methods, which utilize neural networks to learn the gradients of non-differentiable quantization functions, have emerged as a promising approach due to their adaptive learning capabilities to reduce estimation errors. However, existing hypernetwork based methods typically rely solely on current gradient information, neglecting the influence of historical gradients. This oversight can lead to accumulated gradient errors when calculating gradient momentum during optimization. To incorporate historical gradient information, we design a Historical Gradient Storage (HGS) module, which models the historical gradient sequence to generate the first-order momentum required for optimization. To further enhance gradient generation in hypernetworks, we propose a Fast and Slow Gradient Generation (FSG) method. Additionally, to produce more precise gradients, we introduce Layer Recognition Embeddings (LRE) into the hypernetwork, facilitating the generation of layer-specific fine gradients. Extensive comparative experiments on the CIFAR-10 and CIFAR-100 datasets demonstrate that our method achieves faster convergence and lower loss values, outperforming existing baselines.
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Luo, Sangyu, Haoran Bai, Ruizhe Huang, Zhaoliang Qu, Bowen Lv, and Daining Fang. "An in situ micro-indentation apparatus for investigating mechanical parameters of thermal barrier coatings under temperature gradient." Review of Scientific Instruments 93, no. 4 (April 1, 2022): 045102. http://dx.doi.org/10.1063/5.0083087.
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Premature failure of thermal barrier coatings (TBCs) under a temperature gradient is an overriding concern in many applications, and their mechanical parameters are essential to failure analysis. In this study, an in situ micro-indentation apparatus, including a heating module, cooling module, and micro-indentation module, was developed to study the mechanical parameters of TBCs with a temperature gradient. The upper surface of the TBC was heated by radiation to simulate high-temperature service conditions, and the bottom surface was gas-cooled. Different temperature gradients are obtained by changing the velocity of the cooling gas. The temperatures through the thickness of the TBCs were analyzed by numerical simulations and experiments. During exposure to the temperature gradient, micro-indentation tests of the TBC samples were conducted to obtain their mechanical parameters. In situ micro-indentation tests at different cooling gas flow rates (0, 20, and 40 l/min) were performed on the TBCs. The elastic modulus and stress evolution of the TBCs were extracted by analyzing the load–displacement curves at different gas velocities. The elastic modulus remains almost constant with increasing velocity while the stress difference increases.
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Bašták Ďurán, Ivan, and Pascal Marquet. "Les travaux sur la turbulence : les origines, Toucans, Cost-ES0905 et influence de l'entropie." La Météorologie, no. 112 (2021): 079. http://dx.doi.org/10.37053/lameteorologie-2021-0023.
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Le schéma de turbulence Toucans est utilisé dans la configuration opérationnelle Alaro du modèle Aladin depuis début 2015. Son développement a été initié, guidé et en grande partie conçu par Jean-François Geleyn. Ce développement a commencé avec le prédécesseur du schéma Toucans, le schéma « pseudo-pronostique » en énergie cinétique turbulente, lui-même basé sur l'ancien schéma de turbulence de Louis, mais étendu dans Toucans à un schéma pronostique. Le schéma Toucans a pour objectif de traiter de manière cohérente les fonctions qui dépendent de la stabilité verticale de l'atmosphère, de l'influence de l'humidité et des échelles de longueur de la turbulence (de mélange et de dissipation). De plus, de nouvelles caractéristiques ont été ajoutées : une représentation améliorée pour les stratifications très stables (absence de nombre de Richardson critique), une meilleure représentation de l'anisotropie, un paramétrage unifié de la turbulence et des nuages par l'ajout d'une deuxième énergie turbulente pronostique et la paramétrisation des moments du troisième ordre. The Toucans turbulence scheme is a turbulence scheme that is used in the operational Alaro configuration of the Aladin model since early 2015. Its development was initiated, guided and to a large extend authored by Jean-François Geleyn. The development started with the predecessor of the Toucans scheme, the "pseudo-prognostic" turbulent kinetic energy scheme which itself was built on the "Louis" turbulence scheme, but extended to a prognostic scheme. The Toucans scheme aims for a consistent treatment of stability dependency functions, influence of moisture, and turbulence length scales. Additionally, new features were added to the turbulence scheme: improved representation of turbulence in very stable stratification (absence of critical gradient Richardson number), better representation of anisotropy, unified parameterization of turbulence and clouds via addition of second prognostic turbulence energy, and parameterization of third order moments.
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Yang, Yunji, Yonggi Hong, and Jaehyun Park. "Efficient Gradient Updating Strategies with Adaptive Power Allocation for Federated Learning over Wireless Backhaul." Sensors 21, no. 20 (October 13, 2021): 6791. http://dx.doi.org/10.3390/s21206791.
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In this paper, efficient gradient updating strategies are developed for the federated learning when distributed clients are connected to the server via a wireless backhaul link. Specifically, a common convolutional neural network (CNN) module is shared for all the distributed clients and it is trained through the federated learning over wireless backhaul connected to the main server. However, during the training phase, local gradients need to be transferred from multiple clients to the server over wireless backhaul link and can be distorted due to wireless channel fading. To overcome it, an efficient gradient updating method is proposed, in which the gradients are combined such that the effective SNR is maximized at the server. In addition, when the backhaul links for all clients have small channel gain simultaneously, the server may have severely distorted gradient vectors. Accordingly, we also propose a binary gradient updating strategy based on thresholding in which the round associated with all channels having small channel gains is excluded from federated learning. Because each client has limited transmission power, it is effective to allocate more power on the channel slots carrying specific important information, rather than allocating power equally to all channel resources (equivalently, slots). Accordingly, we also propose an adaptive power allocation method, in which each client allocates its transmit power proportionally to the magnitude of the gradient information. This is because, when training a deep learning model, the gradient elements with large values imply the large change of weight to decrease the loss function.
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Tritsch, Isabelle, Valéry Gond, Johan Oszwald, Damien Davy, and Pierre Grenand. "Dynamiques territoriales des Amérindiens wayãpi et teko du moyen Oyapock, Camopi, Guyane française." BOIS & FORETS DES TROPIQUES 311, no. 311 (March 1, 2012): 49. http://dx.doi.org/10.19182/bft2012.311.a20510.
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Les populations amérindiennes expérimentent depuis plusieurs décennies des changements socio-économiques et territoriaux importants, dans un contexte d'augmentation démographique forte. L'article aborde l'adaptation des systèmes d'occupation du territoire et d'exploitation des ressources naturelles des Amérindiens de Guyane française face aux contraintes exercées sur leur territoire et leur mode de vie. Quelle est la résilience des systèmes amérindiens d'utilisation du territoire et de ses ressources naturelles ? La concentration de l'habitat amérindien autour du bourg de Camopi, liée à l'implantation des infrastructures de type centre de santé et école, et à la promotion de l'habitat sédentaire, contribue à générer une pénurie des ressources naturelles et un mal-être social. Le système s'adapte par un éclatement de l'habitat en villages périphériques et par une extension des terroirs agricoles le long des cours d'eau, afin de retrouver de l'espace. Ces villages reproduisent un modèle d'organisation spatiale semblable à l'organisation traditionnelle des villages wayãpi et teko. L'habitat reste cependant sédentaire, les familles souhaitant voir leur village se faire équiper des services minimaux : eau potable et électrification. La limite spatiale à l'éclatement de l'habitat demeure les déplacements journaliers vers l'école, et par conséquent la desserte par le transport scolaire (pirogue). Ainsi, les services et infrastructures conditionnent l'occupation du territoire. Des abattis complémentaires sont maintenus à plus grande distance du bourg et l'habitat devient bilocal : un habitat principal desservi par les services et infrastructures et un habitat secondaire, éloigné et itinérant, conditionné par la qualité des terres agricoles, les ressources cynégétiques, l'histoire du lieu et les réseaux familiaux. Le maintien de ces habitations éloignées est possible grâce à l'investissement des revenus issus des aides sociales dans le transport. Il est ainsi montré que les systèmes amérindiens d'occupation du territoire et d'exploitation des ressources naturelles ont un potentiel adaptatif fort : ils s'appuient sur la recomposition de mobilités circulaires, organisées selon un gradient d'intensité d'utilisation des ressources, qui garantit la durabilité du système.
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Fan, Yu, and Xue Feng Wu. "Three Mirrors Aberrations Optical Transform Function with the Thermal Elastic Deformation." Applied Mechanics and Materials 143-144 (December 2011): 181–84. http://dx.doi.org/10.4028/www.scientific.net/amm.143-144.181.
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The field angle of TMA (three mirrors aberration) optical system is larger than coaxial optical system and more susceptible to the structure deformation. Thermal optical analysis is proposed for evaluating the optical MTF (module transform function). Temperature loads, such as X axial, Y axial and Z axial temperature gradients, are put on the optical system. The thermal elasticity deformations of reflector mirror surfaces made by frame deformation are computed. The deformations of reflector mirror surfaces are expressed in Zernike polynomial. With the optical design software optical MTF is computed. The results show that the X axial temperature gradient causes the MTF of optical system reduced furthest, the Y axial temperature gradient causes the minor MTF change, and the Z axial temperature gradient causes the least change of MTF. The research jobs could give some guidance and reference for the thermal design for TMA optical system.
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Mao, Axiu, Endai Huang, Haiming Gan, and Kai Liu. "FedAAR: A Novel Federated Learning Framework for Animal Activity Recognition with Wearable Sensors." Animals 12, no. 16 (August 21, 2022): 2142. http://dx.doi.org/10.3390/ani12162142.
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Deep learning dominates automated animal activity recognition (AAR) tasks due to high performance on large-scale datasets. However, constructing centralised data across diverse farms raises data privacy issues. Federated learning (FL) provides a distributed learning solution to train a shared model by coordinating multiple farms (clients) without sharing their private data, whereas directly applying FL to AAR tasks often faces two challenges: client-drift during local training and local gradient conflicts during global aggregation. In this study, we develop a novel FL framework called FedAAR to achieve AAR with wearable sensors. Specifically, we devise a prototype-guided local update module to alleviate the client-drift issue, which introduces a global prototype as shared knowledge to force clients to learn consistent features. To reduce gradient conflicts between clients, we design a gradient-refinement-based aggregation module to eliminate conflicting components between local gradients during global aggregation, thereby improving agreement between clients. Experiments are conducted on a public dataset to verify FedAAR’s effectiveness, which consists of 87,621 two-second accelerometer and gyroscope data. The results demonstrate that FedAAR outperforms the state-of-the-art, on precision (75.23%), recall (75.17%), F1-score (74.70%), and accuracy (88.88%), respectively. The ablation experiments show FedAAR’s robustness against various factors (i.e., data sizes, communication frequency, and client numbers).
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Zhao, Chunna, Junjie Ye, Zelong Zhu, and Yaqun Huang. "FLRNN-FGA: Fractional-Order Lipschitz Recurrent Neural Network with Frequency-Domain Gated Attention Mechanism for Time Series Forecasting." Fractal and Fractional 8, no. 7 (July 22, 2024): 433. http://dx.doi.org/10.3390/fractalfract8070433.
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Time series forecasting has played an important role in different industries, including economics, energy, weather, and healthcare. RNN-based methods have shown promising potential due to their strong ability to model the interaction of time and variables. However, they are prone to gradient issues like gradient explosion and vanishing gradients. And the prediction accuracy is not high. To address the above issues, this paper proposes a Fractional-order Lipschitz Recurrent Neural Network with a Frequency-domain Gated Attention mechanism (FLRNN-FGA). There are three major components: the Fractional-order Lipschitz Recurrent Neural Network (FLRNN), frequency module, and gated attention mechanism. In the FLRNN, fractional-order integration is employed to describe the dynamic systems accurately. It can capture long-term dependencies and improve prediction accuracy. Lipschitz weight matrices are applied to alleviate the gradient issues. In the frequency module, temporal data are transformed into the frequency domain by Fourier transform. Frequency domain processing can reduce the computational complexity of the model. In the gated attention mechanism, the gated structure can regulate attention information transmission to reduce the number of model parameters. Extensive experimental results on five real-world benchmark datasets demonstrate the effectiveness of FLRNN-FGA compared with the state-of-the-art methods.
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Chen, L., F. Rottensteiner, and C. Heipke. "INVARIANT DESCRIPTOR LEARNING USING A SIAMESE CONVOLUTIONAL NEURAL NETWORK." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences III-3 (June 2, 2016): 11–18. http://dx.doi.org/10.5194/isprsannals-iii-3-11-2016.
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In this paper we describe learning of a descriptor based on the Siamese Convolutional Neural Network (CNN) architecture and evaluate our results on a standard patch comparison dataset. The descriptor learning architecture is composed of an input module, a Siamese CNN descriptor module and a cost computation module that is based on the L2 Norm. The cost function we use pulls the descriptors of matching patches close to each other in feature space while pushing the descriptors for non-matching pairs away from each other. Compared to related work, we optimize the training parameters by combining a moving average strategy for gradients and Nesterov's Accelerated Gradient. Experiments show that our learned descriptor reaches a good performance and achieves state-of-art results in terms of the false positive rate at a 95 % recall rate on standard benchmark datasets.
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Chen, L., F. Rottensteiner, and C. Heipke. "INVARIANT DESCRIPTOR LEARNING USING A SIAMESE CONVOLUTIONAL NEURAL NETWORK." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences III-3 (June 2, 2016): 11–18. http://dx.doi.org/10.5194/isprs-annals-iii-3-11-2016.
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In this paper we describe learning of a descriptor based on the Siamese Convolutional Neural Network (CNN) architecture and evaluate our results on a standard patch comparison dataset. The descriptor learning architecture is composed of an input module, a Siamese CNN descriptor module and a cost computation module that is based on the L2 Norm. The cost function we use pulls the descriptors of matching patches close to each other in feature space while pushing the descriptors for non-matching pairs away from each other. Compared to related work, we optimize the training parameters by combining a moving average strategy for gradients and Nesterov's Accelerated Gradient. Experiments show that our learned descriptor reaches a good performance and achieves state-of-art results in terms of the false positive rate at a 95 % recall rate on standard benchmark datasets.
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Mir, Mustahsan, and M. Hasan Imam. "A gradient-based method for module placement." Computers & Electrical Engineering 16, no. 2 (January 1990): 109–13. http://dx.doi.org/10.1016/0045-7906(90)90028-e.
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Dubey, Prahit, Gautam Pulugundla, and A. K. Srouji. "Direct Comparison of Immersion and Cold-Plate Based Cooling for Automotive Li-Ion Battery Modules." Energies 14, no. 5 (February 25, 2021): 1259. http://dx.doi.org/10.3390/en14051259.
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The current paper evaluates the thermal performance of immersion cooling for an Electric Vehicle (EV) battery module comprised of NCA-chemistry based cylindrical 21700 format Lithium-ion cells. Efficacy of immersion cooling in improving maximum cell temperature, cell’s temperature gradient, cell-to-cell temperature differential, and pressure drop in the module are investigated by direct comparison with a cold-plate-cooled battery module. Parametric analyses are performed at different module discharge C-rates and coolant flow rates to understand the sensitivity of each cooling strategy to important system performance parameters. The entire numerical analysis is performed using a validated 3D time-accurate Computational Fluid Dynamics (CFD) methodology in STAR-CCM+. Results demonstrate that immersion cooling due its higher thermal conductance leads to a lower maximum cell temperature and lower temperature gradients within the cells at high discharge rates. However, a higher rate of heat rejection and poor thermal properties of the dielectric liquid results in a much higher temperature non-uniformity across the module. At lower discharge rates, the two cooling methods show similar thermal performance. Additionally, owing to the lower viscosity and density of the considered dielectric liquid, an immersion-cooled battery module performs significantly better than the cold-plate-cooled module in terms of both coolant pressure drop.
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Chen, Yuwei, Yadong Wu, and Weihan Zhang. "Parameter Estimation Model for Stellar Spectral Data based on RDN." International Journal of Computer Science and Information Technology 1, no. 1 (December 30, 2023): 171–81. http://dx.doi.org/10.62051/ijcsit.v1n1.22.
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The temperature, gravity and other key parameters of stars change during their evolution, and finding the relationship between these parameters and the life cycle of stars has always been the research focus in astrophysics. How to estimate the parameters of massive spectral data more accurately is of great significance for studying the properties of stars. However, the current conventional parameter estimation methods have problems such as exploding gradient, vanishing gradient and mismatch of newly added stellar parameters in the face of explosive growth of astronomical data, resulting in low parameter estimation accuracy. The Residual Dense neural network (RDN) model proposed in this paper is mainly improved based on two more advanced neural networks, ResNet and DenseNet. The core of RDN is a new Residual Dense Block (RDB), which includes two modules: residual and dense. The purpose of the residual module is to learn the residual between input and output and add the identity map to it, which aims to solve the problem of vanishing gradient and exploding gradient in deep network training. The dense module is where each layer is directly connected to all the layers before it, allowing better utilization of gradients and feature reuse. Its main purpose is feature extraction. The proposed model was trained on the preprocessed LAMOST DR7 dataset, making uncertainty predictions for 17 stellar parameters in LAMOST DR7 spectra with a signal-to-noise ratio (SNR) equal to or greater than 10. The results show that the proposed model has high estimation accuracy and solves the problems existing in previous methods. Compared with ResNet, DenseNet and StarNet, the key indicators such as the mean absolute error of RDN are optimized.
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Tang, Xuebin, Ke Zhang, Xiaolei Zhou, Lingbin Zeng, and Shan Huang. "Enhancing Binary Convolutional Neural Networks for Hyperspectral Image Classification." Remote Sensing 16, no. 23 (November 24, 2024): 4398. http://dx.doi.org/10.3390/rs16234398.
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Hyperspectral remote sensing technology is swiftly evolving, prioritizing affordability, enhanced portability, seamless integration, sophisticated intelligence, and immediate processing capabilities. The leading model for classifying hyperspectral images, which relies on convolutional neural networks (CNNs), has proven to be highly effective when run on advanced computing platforms. Nonetheless, the high degree of parameterization inherent in CNN models necessitates considerable computational and storage resources, posing challenges to their deployment in processors with limited capacity like drones and satellites. This paper focuses on advancing lightweight models for hyperspectral image classification and introduces EBCNN, a novel binary convolutional neural network. EBCNN is designed to effectively regulate backpropagation gradients and minimize gradient discrepancies to optimize BNN performance. EBCNN incorporates an adaptive gradient scaling module that utilizes a multi-scale pyramid squeeze attention (PSA) mechanism during the training phase, which can adjust training gradients flexibly and efficiently. Additionally, to address suboptimal training issues, EBCNN employs a dynamic curriculum learning strategy underpinned by a confidence-aware loss function, Superloss, enabling progressive binarization and enhancing its classification effectiveness. Extensive experimental evaluations conducted on five esteemed public datasets confirm the effectiveness of EBCNN. These analyses highlight a significant enhancement in the classification accuracy of hyperspectral images, achieved without incurring additional memory or computational overheads during the inference process.
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Hu, Chun Zhi, Fan Ming Zeng, and Jin Sheng Xiao. "Modeling and Simulation of Ceramic/Metal Gradient Thermal Barrier Coating." Key Engineering Materials 368-372 (February 2008): 1337–40. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.1337.
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Using the development tool C++ Builder and adopting object oriented programming method, the ceramic/metal gradient thermal barrier coating design software (CCDS) is developed according to software engineering criterion. The CCDS, which has user-friendly interface, is composed of three functional modules: preprocess module, analysis module and post process module. In addition, this software is attached with an optimal design module and an expert module. The calculation and design of the ceramic/metal gradient thermal barrier coating can be carried out by the CCDS, and the numerical results show good agreement with the analytical results.
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Li, Kun-Fang, Jie Feng, Yu-Dong Li, Lin Wen, Yong-Jia Kan, and Qi Guo. "A Method for Restoring γ-Radiation Scene Images Based on Spatial Axial Gradient Discrimination." Electronics 12, no. 17 (September 4, 2023): 3734. http://dx.doi.org/10.3390/electronics12173734.
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Clear and reliable visual information is the premise and basis of work for nuclear robots. However, the ubiquitous γ rays in the nuclear environment will produce radiation effects on CMOS cameras and bring in complex visual noise. In this paper, combining the mechanism and characteristics of γ radiation noise, a method for restoring γ-radiation scene images based on spatial axial gradient discrimination is proposed. Firstly, interframe difference is used to determine the position of radiated noise on the image. Secondly, the gray gradients of different axes at noise pixels are calculated, and two axes with lager gray gradients are selected. Then, the adaptive medians are selected on the two axes, respectively and are weighted according to the gradient as the new value of the noise pixel. Finally, the Wallis sharpening filter is applied to enhance the detailed information and deblur the image. Plenty of experiments have been carried out on images collected in real γ radiation scenes, and image quality has been significantly improved, with Peak Signal to Noise ratio (PSNR) reaching 30.587 dB and Structural Similarity Index Mean (SSIM) reaching 0.82. It is obvious that this method has advanced performance in improving the quality of γ-radiation images. It can provide method guidance and technical support for the software module design of the anti-nuclear radiation camera.
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Pham, Kim, and Jean-Jacques Marigo. "Approche variationnelle de l'endommagement : II. Les modèles à gradient." Comptes Rendus Mécanique 338, no. 4 (April 2010): 199–206. http://dx.doi.org/10.1016/j.crme.2010.03.012.
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Rafiq, T., C. Wilson, L. Luo, J. Weiland, E. Schuster, A. Y. Pankin, W. Guttenfelder, and S. Kaye. "Electron temperature gradient driven transport model for tokamak plasmas." Physics of Plasmas 29, no. 9 (September 2022): 092503. http://dx.doi.org/10.1063/5.0104672.
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A new model for electron temperature gradient (ETG) modes is developed as a component of the multi-mode anomalous transport module [Rafiq et al., Phys Plasmas 20, 032506 (2013)] to predict a time-dependent electron temperature profile in conventional and low aspect ratio tokamaks. This model is based on two-fluid equations that govern the dynamics of low-frequency short- and long-wavelength electromagnetic toroidal ETG driven drift modes. A low collisionality NSTX discharge is used to scan the plasma parameter dependence on the ETG real frequency, growth rate, and electron thermal diffusivity. Electron thermal transport is discovered in the deep core region where modes are more electromagnetic in nature. Several previously reported gyrokinetic trends are reproduced, including the dependencies of density gradients, magnetic shear, β and gradient of β [Formula: see text], collisionality, safety factor, and toroidicity, where β is the ratio of the plasma pressure to the magnetic pressure. The electron heat diffusivity associated with the ETG mode is discovered to be on a scale consistent with the experimental diffusivity determined by power balance analysis.
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Pelletier, Mariane. "Propriétés asymptotiques des estimateurs du gradient et du gradient moyennisé pour les modèles autorégressifs stables." Comptes Rendus de l'Académie des Sciences - Series I - Mathematics 325, no. 2 (July 1997): 207–10. http://dx.doi.org/10.1016/s0764-4442(97)84601-0.
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Gao, Yi, Mengjiao Qin, Sensen Wu, Feng Zhang, and Zhenhong Du. "GSA-SiamNet: A Siamese Network with Gradient-Based Spatial Attention for Pan-Sharpening of Multi-Spectral Images." Remote Sensing 16, no. 4 (February 7, 2024): 616. http://dx.doi.org/10.3390/rs16040616.
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Pan-sharpening is a fusion process that combines a low-spatial resolution, multi-spectral image that has rich spectral characteristics with a high-spatial resolution panchromatic (PAN) image that lacks spectral characteristics. Most previous learning-based approaches rely on the scale-shift assumption, which may not be applicable in the full-resolution domain. To solve this issue, we regard pan-sharpening as a multi-task problem and propose a Siamese network with Gradient-based Spatial Attention (GSA-SiamNet). GSA-SiamNet consists of four modules: a two-stream feature extraction module, a feature fusion module, a gradient-based spatial attention (GSA) module, and a progressive up-sampling module. In the GSA module, we use Laplacian and Sobel operators to extract gradient information from PAN images. Spatial attention factors, learned from the gradient prior, are multiplied during the feature fusion, up-sampling, and reconstruction stages. These factors help to keep high-frequency information on the feature map as well as suppress redundant information. We also design a multi-resolution loss function that guides the training process under the constraints of both reduced- and full-resolution domains. The experimental results on WorldView-3 satellite images obtained in Moscow and San Juan demonstrate that our proposed GSA-SiamNet is superior to traditional and other deep learning-based methods.
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Sanapala, Lavanya, and Lakshmeeswari Gondi. "Mitigating Gradient-Based Data Poisoning Attacks on Machine Learning Models: A Statistical Detection Method." Indian Journal Of Science And Technology 17, no. 21 (May 25, 2024): 2218–31. http://dx.doi.org/10.17485/ijst/v17i21.1035.
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Objectives: This research paper aims to develop a novel method for identifying gradient-based data poisoning attacks on industrial applications like autonomous vehicles and intelligent healthcare systems relying on machine learning and deep learning techniques. These algorithms performs well only if they are trained on good quality dataset. However, the ML models are prone to data poisoning attacks, targeting the training dataset, manipulate its input samples such that the machine learning algorithm gets confused and produces wrong predictions. The current detection techniques are effective to detect known attacks and lack generalized detection to unknown attacks. To address this issue, this paper aims to integrate security elements within the machine learning framework, guaranteeing effective identification and mitigation of known and unknown threats and achieve generalized detection. Methods: ML Filter, a unique attack detection approach integrates ML-Filter Detection Algorithm and the Statistical Perturbation Bounds Identification Algorithm to determine the given dataset is poisoned or not. DBSCAN algorithm is used to divide the dataset into several smaller subsets and perform algorithmic analysis for detection. The performance of the proposed method is evaluated in terms of True positive rate and significance test accuracy. Findings: The probability distribution differences between original and poisoned datasets vary with change in perturbation size rather than the datasets and ML models use for application. This finding lead to determine the perturbation bounds using statistical pairwise distance metrics and corresponding significance tests computed on the results. ML Filter demonstrates a high detection rate of 99.63% for known attacks and achieves a generalized detection accuracy of 98% for unknown attacks. Novelty: A secured ML architecture and a unique statistical detection approach ML-Filter, effectively detect data poisoning attacks, demonstrating significant advancements in detecting both known and unknown threats in industrial applications utilizing machine learning and deep learning algorithms. Keywords: Privacy and security, Adversarial machine learning, Secured ML Architecture, ML-Filter, Statistical Perturbation Bounds Identification Algorithm
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Song, Cheng, Zhichao Wang, Weiping Peng, and Nannan Yang. "Secure and Efficient Federated Learning Schemes for Healthcare Systems." Electronics 13, no. 13 (July 4, 2024): 2620. http://dx.doi.org/10.3390/electronics13132620.
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The swift advancement in communication technology alongside the rise of the Medical Internet of Things (IoT) has spurred the extensive adoption of diverse sensor-driven healthcare and monitoring systems. While the rapid development of healthcare systems is underway, concerns about the privacy leakage of medical data have also attracted attention. Federated learning plays a certain protective role in data, but studies have shown that gradient transmission under federated learning environments still leads to privacy leakage. Therefore, we proposed secure and efficient federated learning schemes for smart healthcare systems. In this scheme, we used Paillier encryption technology to encrypt the shared training models on the client side, ensuring the security and privacy of the training models. Meanwhile, we designed a zero-knowledge identity authentication module to verify the authenticity of clients participating in the training process. Second, we designed a gradient filtering compression algorithm to eliminate locally updated gradients that were irrelevant to the convergence trend and used computationally negligible compression operators to quantize updates, thereby improving communication efficiency while ensuring model accuracy. The experimental results demonstrated that the proposed scheme not only had high model accuracy but also had significant advantages in communication overhead compared with existing schemes.
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Huixia Jin, Weiming Zuo, and Xiaojun Deng. "Design and Realization of Gradient Module in Digital MRI Spectrometer." INTERNATIONAL JOURNAL ON Advances in Information Sciences and Service Sciences 4, no. 14 (August 15, 2012): 53–61. http://dx.doi.org/10.4156/aiss.vol4.issue14.7.
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Chernyi, A. V., and A. I. Yakimchik. "Recovery of potential using module values of its gradient. 1." Geofizicheskiy Zhurnal 21, no. 3 (April 1, 1999): 55–72. http://dx.doi.org/10.24028/gzh.0203-3100.v21i3.1999.214577.
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Chernyi, A. V., and A. I. Yakimchik. "Recovery of potential using module values of its gradient. 2." Geofizicheskiy Zhurnal 22, no. 6 (December 1, 2000): 166–83. http://dx.doi.org/10.24028/gzh.0203-3100.v22i6.2000.214576.
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Sampson, Joseph, Stephen S. T. Yau, and Yung Yu. "Classification of Gradient Space as sℓ(2, ℂ) Module I." American Journal of Mathematics 114, no. 5 (October 1992): 1147. http://dx.doi.org/10.2307/2374893.
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Hu, Haotian, Fanyi Wang, Zhiwang Zhang, Yaonong Wang, Laifeng Hu, and Yanhao Zhang. "GAM: Gradient Attention Module of Optimization for Point Clouds Analysis." Proceedings of the AAAI Conference on Artificial Intelligence 37, no. 1 (June 26, 2023): 835–43. http://dx.doi.org/10.1609/aaai.v37i1.25162.
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In the point cloud analysis task, the existing local feature aggregation descriptors (LFAD) do not fully utilize the neighborhood information of center points. Previous methods only use the distance information to constrain the local aggregation process, which is easy to be affected by abnormal points and cannot adequately fit the original geometry of the point cloud. This paper argues that fine-grained geometric information (FGGI) plays an important role in the aggregation of local features. Based on this, we propose a gradient-based local attention module to address the above problem, which is called Gradient Attention Module (GAM). GAM simplifies the process of extracting the gradient information in the neighborhood to explicit representation using the Zenith Angle matrix and Azimuth Angle matrix, which makes the module 35X faster. The comprehensive experiments on the ScanObjectNN dataset, ShapeNet dataset, S3DIS dataset, Modelnet40 dataset, and KITTI dataset demonstrate the effectiveness, efficientness, and generalization of our newly proposed GAM for 3D point cloud analysis. Especially in S3DIS, GAM achieves the highest index in the current point-based model with mIoU/OA/mAcc of 74.4%/90.6%/83.2%.
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Maduabuchi, Chika, Kevwe Ejenakevwe, Agwu Ndukwe, and Chigbo Mgbemene. "High Performance Solar Thermoelectric Generator Using Asymmetrical Variable Leg Geometries." E3S Web of Conferences 239 (2021): 00005. http://dx.doi.org/10.1051/e3sconf/202123900005.
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This paper presents a computational study of the combined effects of variable geometry and asymmetry in the legs of thermocouples of thermoelectric modules used in solar thermoelectric generators (STEGs). Six different models were considered for the thermocouples in each module, namely: rectangular-rectangular legs, rectangular-trapezoidal legs, rectangular-X legs, trapezoidal-trapezoidal legs, trapezoidal-X legs, and X-X legs. Simulations of the six different modules under the same heat flux was carried out in ANSYS 2020 R2 software. Temperature and voltage distributions were obtained for each model and the results indicate significant variations due to the utilization of varying leg geometries. Results show that the X-X leg module generated the highest temperature gradient and electric voltage. In comparison, a temperature gradient and electric voltage of 297 K and 16 V, respectively were achieved with the X-X leg module as against 182 K and 8.4 V, respectively, achieved in a conventional rectangular leg module. This suggests a 63.2% and 90.5% increase in the temperature gradient and electric voltage of the conventional TE module. Therefore, this study demonstrates that X geometry gives the best performance for thermoelectric modules and STEGs.
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Wang, Lei, Jun Lu, and Xian Qing Ling. "A Hybrid Filtering Method Based on Triangle-Module Fusion." Advanced Materials Research 268-270 (July 2011): 1239–44. http://dx.doi.org/10.4028/www.scientific.net/amr.268-270.1239.
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Edge is the basic feature of the image, and is easily damaged in the image processing. This paper proposed an edge-preserving method for image filtering. The scheme can improve the capability of protecting the edge information. The proposed method firstly defined two information measures that were based on fuzzy entropy and image gradient. Then the two information measures were fused by triangle-module operator to determine the image edges. At last, we used the modified filter to eliminate noise and retain the determined edge points. The experiment results, compared with AMAWM, can achieve better effects on PSNR and AG (Average Gradient), which illustrates that more edge information may be preserved after the filtering operation.
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Cao, Liu, Luo Zhang, Rui-Fan Meng, and Qin-Dan Zhang. "Analyzing effects of temperature gradient and scan rate on metal additive manufacturing microstructure by using phase field-finite element method." Modelling and Simulation in Materials Science and Engineering 30, no. 3 (February 16, 2022): 034003. http://dx.doi.org/10.1088/1361-651x/ac4f3a.
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Abstract Predicting the evolutionary behavior of microstructures with the help of numerical simulation techniques has become an essential tool for studying the solidification process of metal additive manufacturing. As a mesoscopic model based on the diffusion interface theory, phase field method (PFM) can be used to predict the evolution of solidification microstructure. The open-source PFM framework PRISMS-PF can not only efficiently solve systems of equations with billions of degrees of freedom, but also provide a simple adaptive mesh control module. In this paper, based on the open-source PFM framework PRISMS-PF, a phase field-finite element method (PFM-FEM) simulation flow for the solidification process of A356 aluminum alloy additive manufacturing in the two-dimensional case was established. The effects of temperature gradient, scan rate and initial solid-phase morphology on solute concentration, dendrite spacing and dendrite morphology were analyzed and compared with experimental results for verification. Analyzing the results for different temperature gradients and scan rates cases, it was found that the increase of temperature gradient or scan rate made the primary dendrite arm space decrease; as the ratio of temperature gradient to scan rate decreased, the solidification morphology gradually changed from flat crystal to cellular crystal, columnar crystal, and even dendritic structure. Analyzing the results for different initial solid-phase morphology cases, it was found that the influence of initial solid-phase morphology on dendrite growth increased as the ratio of temperature gradient to scan rate decreased. The above influence rules were mainly related to the composition overcooling zone under different conditions. This paper is expected to provide a theoretical support for the effective regulation of solidification microstructure in metal additive manufacturing.
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Geldhauser, Carina, Andreas Daniel Matt, and Christian Stussak. "I AM A.I. Gradient Descent – an Open-Source Digital Game for Inquiry-Based CLIL Learning." Proceedings of the AAAI Conference on Artificial Intelligence 36, no. 11 (June 28, 2022): 12751–57. http://dx.doi.org/10.1609/aaai.v36i11.21553.
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We present an interactive online workshop for K-12 students, which aims in familiarizing students with core concepts of AI. The workshop consists of a variety of resources, inspired by inquiry-based learning techniques, of which we present in detail one module, centered around a browser-based game called Gradient Descent. This module introduces the mathematical concepts behind a gradient descent-based optimization algorithm through the computer game of a treasure hunt at an unknown sea surface landscape. Finally, we report on student feedback for the module in a series of content and language integrated learning in German (CLiLiG) workshops for students aged 14-17 in 30 countries.
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Zhu, Xiangyuan, Kehua Guo, Hui Fang, Rui Ding, Zheng Wu, and Gerald Schaefer. "Gradient-Based Graph Attention for Scene Text Image Super-resolution." Proceedings of the AAAI Conference on Artificial Intelligence 37, no. 3 (June 26, 2023): 3861–69. http://dx.doi.org/10.1609/aaai.v37i3.25499.
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Scene text image super-resolution (STISR) in the wild has been shown to be beneficial to support improved vision-based text recognition from low-resolution imagery. An intuitive way to enhance STISR performance is to explore the well-structured and repetitive layout characteristics of text and exploit these as prior knowledge to guide model convergence. In this paper, we propose a novel gradient-based graph attention method to embed patch-wise text layout contexts into image feature representations for high-resolution text image reconstruction in an implicit and elegant manner. We introduce a non-local group-wise attention module to extract text features which are then enhanced by a cascaded channel attention module and a novel gradient-based graph attention module in order to obtain more effective representations by exploring correlations of regional and local patch-wise text layout properties. Extensive experiments on the benchmark TextZoom dataset convincingly demonstrate that our method supports excellent text recognition and outperforms the current state-of-the-art in STISR. The source code is available at https://github.com/xyzhu1/TSAN.
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Pajitnov, Andrei. "Incidence coefficients in the Novikov Complex for Morse forms: rationality and exponential growth properties." Proceedings of the International Geometry Center 13, no. 4 (March 10, 2021): 125–77. http://dx.doi.org/10.15673/tmgc.v13i4.1747.
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Let f : M → S 1 be a Morse map, v a transverse f -gradient. Theconstruction of the Novikov complex associates to these data a free chain complexC ∗ (f, v) over the ring Z[t]][t −1 ], generated by the critical points of f and computingthe completed homology module of the corresponding infinite cyclic covering of M .Novikov’s Exponential Growth Conjecture says that the boundary operators in thiscomplex are power series of non-zero convergence raduis.In [12] the author announced the proof of the Novikov conjecture for the case ofC 0 -generic gradients together with several generalizations. The proofs of the firstpart of this work were published in [13]. The present article contains the proofs ofthe second part.There is a refined version of the Novikov complex, defined over a suitable com-pletion of the group ring of the fundamental group. We prove that for a C 0 -genericf -gradient the corresponding incidence coefficients belong to the image in the Novikovring of a (non commutative) localization of the fundamental group ring.The Novikov construction generalizes also to the case of Morse 1-forms. In thiscase the corresponding incidence coefiicients belong to a certain completion of thering of integral Laurent polynomials of several variables. We prove that for a givenMorse form ω and a C 0 -generic ω-gradient these incidence coefficients are rationalfunctions.The incidence coefficients in the Novikov complex are obtained by counting thealgebraic number of the trajectories of the gradient, joining the zeros of the Morseform. There is V.I.Arnold’s version of the exponential growth conjecture, whichconcerns the total number of trajectories. We confirm this stronger form of theconjecture for any given Morse form and a C 0 -dense set of its gradients.We give an example of explicit computation of the Novikov complex.
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Li, Wenjie, David Stokes, Bed Poudel, Udara Saparamadu, Amin Nozariasbmarz, Han Byul Kang, and Shashank Priya. "High-Efficiency Skutterudite Modules at a Low Temperature Gradient." Energies 12, no. 22 (November 11, 2019): 4292. http://dx.doi.org/10.3390/en12224292.
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Thermoelectric skutterudite materials have been widely investigated for their potential application in mid-temperature waste heat recovery that has not been efficiently utilized A large amount of research has focused on developing materials with a high thermoelectric figure of merit (zT). However, the translation of material properties to device performance has limited success. Here, we demonstrate single-filling n-type Yb0.25Fe0.25Co3.75Sb12 and multi-filling La0.7Ti0.1Ga0.1Fe2.7Co1.3Sb12 skutterudites with a maximum zT of ~1.3 at 740 K and ~0.97 at 760 K. The peak zT of skutterudites usually occurs above 800 K, but, as shown here, the shift in peak zT to lower temperatures is beneficial for enhancing conversion efficiency at a lower hot-side temperature. In this work, we have demonstrated that the Fe-substitution significantly reduces the thermal conductivity of n-type skutterudite, closer to p-type skutterudite thermal conductivity, resulting in a module that is more compatible to operate at elevated temperatures. A uni-couple skutterudite module was fabricated using a molybdenum electrode and Ga–Sn liquid metal as the thermal interface material. A conversion efficiency of 7.27% at a low temperature gradient of 366 K was achieved, which is among the highest efficiencies reported in the literature at this temperature gradient. These results highlight that peak zT shift and optimized module design can improve conversion efficiency of thermoelectric modules at a low temperature gradient.