Spectral Analysis of the MIXMAX Random Number Generators

International audienceWe study the lattice structure of random number generators of the MIXMAX family, a class of matrix linear congruential generators that produce a vector of random numbers at each step. These generators were initially proposed and justified as close approximations to certain ergodic dynamical systems having the Kolmogorov K-mixing property, which implies a chaotic (fast-mixing) behavior. But for a K-mixing system, the matrix must have irrational entries, whereas for the MIXMAX it has only integer entries. As a result, the MIXMAX has a lattice structure just like linear congruential and multiple recursive generators. Its matrix entries were also selected in a special way to allow a fast implementation and this has an impact on the lattice structure. We study this lattice structure for vectors of successive and non-successive output values in various dimensions. We show in particular that for coordinates at specific lags not too far apart, in three dimensions, all the nonzero points lie in only two hyperplanes. This is reminiscent of the behavior of lagged-Fibonacci and AWC/SWB generators. And even if we skip the output coordinates involved in this bad structure, other highly structured projections often remain, depending on the choice of parameters. We show that empirical statistical tests can easily detect this structure

RELATION BETWEEN HARDNESS OF (Ti, Al)N BASED MULTILAYERED COATINGS AND PERIODS OF THEIR STACKING

This study aims to model, by using a finite element method, the relationship between the hardness and the period Λ of metal/nitride multilayer coatings (Ti0.54Al0.46/Ti0.54Al0.46N)n in order to understand the increase of the hardness at the low periods [1] and then optimise the multilayer coating architecture to obtain the best mechanical properties. A 2D axisymmetric finite element model of the Berkovich nanoindentation test was developed. The coating was designed as a stacking of Ti0.54Al0.46 and Ti0.54Al0.46N nanolayers with, in the first hypothesis, equal thickness and perfect interface. The elastoplastic behaviours of the metal and nitride layers were identified by Berkovich nanoindentation experiments and inverse analysis on thick monolayer samples. The indentation curves (P-h) obtained by this model depend on the period Λ of the stacking. Simulated (P-h) curves were compared with experimental data on 2 μm thick films with different periods Λ ranging from 10 to 50 nm deposited by RF magnetron sputtering using reactive gas pulsing process (RGPP). The model forecasts are very consistent with the experience for the largest period but the model does not reproduce the hardness increase at the lowest periods. The Λ = 10 nm coating was analysed by electron energy loss spectroscopy (EELS) on a transmission electron microscope. Results show intermixing of the layers with the presence of nitrogen atoms in the metal layer over a few nanometers [1]. It was concluded that the metal/ceramic interface plays an important role at low periods. The addition in the model of a transition layer in the metal/nitride stacking, with an elastoplastic metal/ceramic medium behaviour, allows to reproduce the nanoindentation experimental curves. The thickness of this transition layer deduced from model updating method is in very good agreement with EELS observations

RELATION BETWEEN HARDNESS OF (Ti, Al)N BASED MULTILAYERED COATINGS AND PERIODS OF THEIR STACKING

This study aims to model, by using a finite element method, the relationship between the hardness and the period Λ of metal/nitride multilayer coatings (Ti0.54Al0.46/Ti0.54Al0.46N)n in order to understand the increase of the hardness at the low periods [1] and then optimise the multilayer coating architecture to obtain the best mechanical properties. A 2D axisymmetric finite element model of the Berkovich nanoindentation test was developed. The coating was designed as a stacking of Ti0.54Al0.46 and Ti0.54Al0.46N nanolayers with, in the first hypothesis, equal thickness and perfect interface. The elastoplastic behaviours of the metal and nitride layers were identified by Berkovich nanoindentation experiments and inverse analysis on thick monolayer samples. The indentation curves (P-h) obtained by this model depend on the period Λ of the stacking. Simulated (P-h) curves were compared with experimental data on 2 μm thick films with different periods Λ ranging from 10 to 50 nm deposited by RF magnetron sputtering using reactive gas pulsing process (RGPP). The model forecasts are very consistent with the experience for the largest period but the model does not reproduce the hardness increase at the lowest periods. The Λ = 10 nm coating was analysed by electron energy loss spectroscopy (EELS) on a transmission electron microscope. Results show intermixing of the layers with the presence of nitrogen atoms in the metal layer over a few nanometers [1]. It was concluded that the metal/ceramic interface plays an important role at low periods. The addition in the model of a transition layer in the metal/nitride stacking, with an elastoplastic metal/ceramic medium behaviour, allows to reproduce the nanoindentation experimental curves. The thickness of this transition layer deduced from model updating method is in very good agreement with EELS observations

Fertility islands, keys to the establishment of plant and microbial diversity in a highly alkaline hot desert

The distribution of plant communities in hot desert ecosystems is discontinuous and resembles the pattern of heterogeneous resource patches, known as “fertility islands”. Understanding the key factors that allow plants to establish in these conditions, as well as their associated microbial diversity, is crucial to the comprehension and preservation of these ecosystems. Saudi Arabia in the Arabian Peninsula, is one of the driest regions in the world, with a very low water regime and low soil nutrient contents. The establishment of ecosystems in these arid desert conditions is therefore subject to numerous constraints. Understanding the biotic and abiotic factors linked to the formation of fertility islands, from the perspective of soil composition and its associated microbiome, both in the soil and in the roots of associated plant community, is therefore a fundamental issue for the preservation of these ecosystems. In this study, we analyzed the soil composition between a fertility island and bare soil. The proportions of micro- and macro-elements important for plant nutrition, namely magnesium, phosphorus, potassium and iron were higher in the fertility island. We also observed that soil bacterial and fungal diversity increased in the fertility island. Key taxa such as Rhizobia and Glomeraceae which play important roles in ecosystem functioning were identified in both the fertility island soil and in the roots of the established plant community. These results confirm that plant establishment is linked to soil conditions, in line with the fertility island hypothesis, and that the microbial community in the fertility island differs both in diversity and in composition from that of the bare soil. Fertility islands soils and the roots of established plant community harbor a microbiome potentially crucial to ecosystem functioning, and are of major interest for conservation and agronomy programs

Maize Field Study Reveals Covaried Microbiota and Metabolic Changes in Roots over Plant Growth

Plant roots are colonized by microorganisms from the surrounding soil that belong to different kingdoms and form a multikingdom microbial community called the root microbiota. Despite their importance for plant growth, the relationship between soil management, the root microbiota, and plant performance remains unknown. Here, we characterize the maize root-associated bacterial, fungal, and oomycetal communities during the vegetative and reproductive growth stages of four maize inbred lines and the pht1;6 phosphate transporter mutant. These plants were grown in two long-term experimental fields under four contrasting soil managements, including phosphate-deficient and -sufficient conditions. We showed that the maize root-associated microbiota is influenced by soil management and changes during host growth stages. We identified stable bacterial and fungal root-associated taxa that persist throughout the host life cycle. These taxa were accompanied by dynamic members that covary with changes in root metabolites. We observed an inverse stable-to-dynamic ratio between root-associated bacterial and fungal communities. We also found a host footprint on the soil biota, characterized by a convergence between soil, rhizosphere, and root bacterial communities during reproductive maize growth. Our study reveals the spatiotemporal dynamics of the maize root-associated microbiota and suggests that the fungal assemblage is less responsive to changes in root metabolites than the bacterial community

Gestion de la qualité de la ressource en eau potable dans un système socio-écologique : développement d’un modèle multi-agents à partir d’analyse institutionnelle

Supplying citizens with quality drinking water is a public health issue, to which are added environmental and economic issues. Agriculture is one of the main threats to the quality of drinking water resources, particularly because of diffuse pollution in catchment areas. Programmes to protect water catchments from agricultural diffuse pollution rely mainly on the voluntary participation of farmers. The objective of this thesis is to study, with the help of an agent-based model, the impacts of governance on the evolution of agricultural practices, taking into account the interactions between the protection measures implemented, the behavioural dynamics of farmers and the characteristics of the ecological system. We first conducted a literature review of agent-based models of social-ecological systems representing governance to identify the contributions and perspectives of this field of research. We used this review to build an agent-based model to analyse the governance of water quality in a catchment area by describing farmers' behaviour using the theory of planned behaviour. A first model allowed us to analyse the effectiveness and efficiency of protection programmes composed of two measures, a financial compensation and a training measure. We tested the impact of behavioral characteristics of farmers and the interactions between farmers on the results of the programmes in terms of evolution of agricultural practices. In a second model, we focused on the effect of information on the water pollution level, in function of farmers' environmental preferences and the initial state of the ecological system. The simulations show the positive role of such information tools in water quality management. This thesis shows, on the basis of a multidisciplinary approach how the characteristics of protection measures, farmers and the ecological system interact in their effect on water quality governance.L’approvisionnement des citoyens en eau potable de qualité est un enjeu de santé publique, auquel s’ajoutent des enjeux environnementaux et économiques. L’agriculture est l’une des principales menaces pour la qualité de la ressource en eau potable, notamment à cause des pollutions diffuses dans les aires d’alimentation de captages. Les programmes de protection des captages vis-à-vis des pollutions diffuses d’origine agricole reposent principalement sur la participation volontaire des agriculteurs. L’objectif de cette thèse est d’étudier, à l’aide d’un modèle multi-agents, quels sont les impacts de la gouvernance sur l’évolution des pratiques agricoles, en prenant en compte les interactions entre les mesures de protection mises en œuvre, les dynamiques comportementales des agriculteurs et les facteurs liés au système écologique. Pour ce faire, nous avons dans un premier temps réalisé une revue de littérature des modèles multi-agents de systèmes socio-écologiques représentant la gouvernance. Nous nous sommes intéressés aux apports et perspectives de ce champ de recherche. Nous nous sommes appuyés sur cette revue afin de construire un modèle multi-agents pour analyser la gouvernance de la qualité de l’eau dans une aire l’alimentation de captage en décrivant les comportements des agriculteurs grâce à la théorie du comportement planifié. Un premier modèle nous a permis d’analyser l’efficacité et l’efficience de programmes de protection composés de deux mesures, une compensation financière et une mesure de formation. Nous avons ainsi pu tester l’impact des caractéristiques comportementales des agriculteurs et des interactions entre les agriculteurs sur les résultats des programmes en termes d’évolution des pratiques agricoles. Dans un second modèle, nous nous sommes intéressés plus particulièrement à l’effet de l’information sur le niveau de pollution de l’eau, en fonction des préférences environnementales des agriculteurs et de l’état initial du système écologique. Les simulations permettent de mettre en évidence le rôle positif des instruments d’information dans la gestion de la qualité de l’eau. Cette thèse met en évidence, sur la base d’une approche pluridisciplinaire, le rôle des caractéristiques des mesures de protection, des agriculteurs et du système écologique dans l’impact de la gouvernance de la qualité de l’eau sur les évolutions des pratiques agricoles

Governance of the drinking water quality in a social-ecological system : development of a agent-based model using institutional analysis

L’approvisionnement des citoyens en eau potable de qualité est un enjeu de santé publique, auquel s’ajoutent des enjeux environnementaux et économiques. L’agriculture est l’une des principales menaces pour la qualité de la ressource en eau potable, notamment à cause des pollutions diffuses dans les aires d’alimentation de captages. Les programmes de protection des captages vis-à-vis des pollutions diffuses d’origine agricole reposent principalement sur la participation volontaire des agriculteurs. L’objectif de cette thèse est d’étudier, à l’aide d’un modèle multi-agents, quels sont les impacts de la gouvernance sur l’évolution des pratiques agricoles, en prenant en compte les interactions entre les mesures de protection mises en œuvre, les dynamiques comportementales des agriculteurs et les facteurs liés au système écologique. Pour ce faire, nous avons dans un premier temps réalisé une revue de littérature des modèles multi-agents de systèmes socio-écologiques représentant la gouvernance. Nous nous sommes intéressés aux apports et perspectives de ce champ de recherche. Nous nous sommes appuyés sur cette revue afin de construire un modèle multi-agents pour analyser la gouvernance de la qualité de l’eau dans une aire l’alimentation de captage en décrivant les comportements des agriculteurs grâce à la théorie du comportement planifié. Un premier modèle nous a permis d’analyser l’efficacité et l’efficience de programmes de protection composés de deux mesures, une compensation financière et une mesure de formation. Nous avons ainsi pu tester l’impact des caractéristiques comportementales des agriculteurs et des interactions entre les agriculteurs sur les résultats des programmes en termes d’évolution des pratiques agricoles. Dans un second modèle, nous nous sommes intéressés plus particulièrement à l’effet de l’information sur le niveau de pollution de l’eau, en fonction des préférences environnementales des agriculteurs et de l’état initial du système écologique. Les simulations permettent de mettre en évidence le rôle positif des instruments d’information dans la gestion de la qualité de l’eau. Cette thèse met en évidence, sur la base d’une approche pluridisciplinaire, le rôle des caractéristiques des mesures de protection, des agriculteurs et du système écologique dans l’impact de la gouvernance de la qualité de l’eau sur les évolutions des pratiques agricoles.Supplying citizens with quality drinking water is a public health issue, to which are added environmental and economic issues. Agriculture is one of the main threats to the quality of drinking water resources, particularly because of diffuse pollution in catchment areas. Programmes to protect water catchments from agricultural diffuse pollution rely mainly on the voluntary participation of farmers. The objective of this thesis is to study, with the help of an agent-based model, the impacts of governance on the evolution of agricultural practices, taking into account the interactions between the protection measures implemented, the behavioural dynamics of farmers and the characteristics of the ecological system. We first conducted a literature review of agent-based models of social-ecological systems representing governance to identify the contributions and perspectives of this field of research. We used this review to build an agent-based model to analyse the governance of water quality in a catchment area by describing farmers' behaviour using the theory of planned behaviour. A first model allowed us to analyse the effectiveness and efficiency of protection programmes composed of two measures, a financial compensation and a training measure. We tested the impact of behavioral characteristics of farmers and the interactions between farmers on the results of the programmes in terms of evolution of agricultural practices. In a second model, we focused on the effect of information on the water pollution level, in function of farmers' environmental preferences and the initial state of the ecological system. The simulations show the positive role of such information tools in water quality management. This thesis shows, on the basis of a multidisciplinary approach how the characteristics of protection measures, farmers and the ecological system interact in their effect on water quality governance

Variabilité spatio-temporelle des HAP et des communautés microbiennes dans la rhizosphère d’un sol historiquement contaminé

Accès restreint aux membres de l'Université de Lorraine jusqu'au 2017-03-09Polycyclic Aromatic Hydrocarbons (PAH) are persistent organic pollutants in soil, whose degradation in aged-contaminated soil is limited by their low bioavailability. The ability of plants to promote pollutant dissipation through the action of rhizosphere microorganisms has been shown (rhizodegradation). However contrasted results were obtained suggesting spatio-temporal variability of processes. Different experiments, with different time and space scales, using microcosm and field trials were achieved to precise phenomena. Study of spatial variability of PAH and bacterial diversity were done in two-contrasted rhizospheres (ryegrass and alfalfa) at centimeter scale after 37 days of plant growth, on a wasteland aged contaminated soil Results showed spatial structuration of sugar content, pH, bacterial diversity and microbial density, depending on plant species, but no vertical gradient was observed for PAH concentration. Study of temporal variability of processes showed dissipation of bioavailable fraction of pollutant in just 6 days and in comparison with bare soil, a positive impact of plant was shown on PAH dissipation and on expression of PAH dioxygenase genes. A long-term study (over 6 years) in a field trial revealed that plant cover slowed down PAH dissipation and impacted bacterial and fungal diversity as edaphic parameters. All these results underlined the importance of PAH bioavailability for the dissipation process and of spatio-temporal dynamic of microbial community, in the rhizosphereLes Hydrocarbures Aromatiques polycycliques (HAP) sont des polluants organiques persistants, dont la faible disponibilité dans les sols historiquement contaminés limite leur biodégradation. La capacité des plantes à favoriser l’élimination de ces polluants par l’action des microorganismes associés à leur rhizosphère a été montrée (rhizodégradation). Toutefois les résultats sont variables, suggérant la variabilité spatio-temporelle des processus. Des études à différentes échelles de temps et d’espace, utilisant des microcosmes et des dispositifs in situ ont été menées pour préciser ces phénomènes. L’étude de la variabilité spatiale des HAP et de la diversité bactérienne a été menée au sein de deux rhizosphères contrastées (ray-grass et luzerne), à l’échelle centimétrique après 37 jours de culture sur un sol de friche industrielle. Les résultats ont montré une spatialisation de la teneur en sucre et du pH, de la diversité bactérienne et de l’abondance microbienne, spécifique de l’espèce végétale, mais sans structuration de la teneur en HAP. L’étude de la variabilité temporelle de ces processus a révélé la dissipation en 6 jours des polluants biodisponibles ainsi qu’un effet positif des plantes par rapport au sol nu sur la dissipation des HAP et sur l’expression des gènes de HAP-dioxygénase. Une étude à plus long terme (6 ans) et in situ a montré que le couvert végétal ralentit la dissipation des HAP et influencent fortement la diversité microbienne, tout comme certains paramètres édaphiques. L’ensemble de ces résultats montre l’importance de la biodisponibilité des HAP qui conditionne leur dissipation, et de la dynamique des communautés microbiennes dans la rhizosphèr

Identification des coefficients d'interaction entre les systèmes de glissement d'un cristal CFC par analyse inverse à partir d'empreintes de nanoindentation Berkovich

Improving the performances of critical industrial components (aeronautics, nuclear industry) requires an increasingly detailed description of the deformation mechanisms of metallic materials, using phenomenological laws. The increase in computational power now allows industrial scale components to be simulated using crystal scale plasticity model. Those are however governed by several crystal specific parameters, whose experimental identification has been only partially explored so far. This is particularly the case for the coefficient driving the interaction between slip systems. This thesis proposes a methodology to quantify these parameters using residual imprints from Berkovich nanoindentation tests.Repousser les performances de composants industriels critiques (aéronautique, nucléaire) nécessite l'utilisation de lois de comportement matériaux décrivant de plus en plus finement les mécanismes de déformation. L’augmentation de la puissance de calcul permet désormais de simuler des composants de taille industrielle par un modèle de plasticité cristalline. Cependant, ceux-ci sont pilotés par de nombreux paramètres caractéristiques du matériau considéré. Plus particulièrement les interactions entre les systèmes de glissement jouent un rôle important dans la plastification à l’échelle cristalline. Ce manuscrit propose une méthodologie pour quantifier ces paramètres en utilisant les empreintes résiduelles d’essais de nanoindentation

Spatio-temporal variability of PAH and microbial community in the rhizosphere of aged-contaminated soil

Les Hydrocarbures Aromatiques polycycliques (HAP) sont des polluants organiques persistants, dont la faible disponibilité dans les sols historiquement contaminés limite leur biodégradation. La capacité des plantes à favoriser l’élimination de ces polluants par l’action des microorganismes associés à leur rhizosphère a été montrée (rhizodégradation). Toutefois les résultats sont variables, suggérant la variabilité spatio-temporelle des processus. Des études à différentes échelles de temps et d’espace, utilisant des microcosmes et des dispositifs in situ ont été menées pour préciser ces phénomènes. L’étude de la variabilité spatiale des HAP et de la diversité bactérienne a été menée au sein de deux rhizosphères contrastées (ray-grass et luzerne), à l’échelle centimétrique après 37 jours de culture sur un sol de friche industrielle. Les résultats ont montré une spatialisation de la teneur en sucre et du pH, de la diversité bactérienne et de l’abondance microbienne, spécifique de l’espèce végétale, mais sans structuration de la teneur en HAP. L’étude de la variabilité temporelle de ces processus a révélé la dissipation en 6 jours des polluants biodisponibles ainsi qu’un effet positif des plantes par rapport au sol nu sur la dissipation des HAP et sur l’expression des gènes de HAP-dioxygénase. Une étude à plus long terme (6 ans) et in situ a montré que le couvert végétal ralentit la dissipation des HAP et influencent fortement la diversité microbienne, tout comme certains paramètres édaphiques. L’ensemble de ces résultats montre l’importance de la biodisponibilité des HAP qui conditionne leur dissipation, et de la dynamique des communautés microbiennes dans la rhizosphèrePolycyclic Aromatic Hydrocarbons (PAH) are persistent organic pollutants in soil, whose degradation in aged-contaminated soil is limited by their low bioavailability. The ability of plants to promote pollutant dissipation through the action of rhizosphere microorganisms has been shown (rhizodegradation). However contrasted results were obtained suggesting spatio-temporal variability of processes. Different experiments, with different time and space scales, using microcosm and field trials were achieved to precise phenomena. Study of spatial variability of PAH and bacterial diversity were done in two-contrasted rhizospheres (ryegrass and alfalfa) at centimeter scale after 37 days of plant growth, on a wasteland aged contaminated soil Results showed spatial structuration of sugar content, pH, bacterial diversity and microbial density, depending on plant species, but no vertical gradient was observed for PAH concentration. Study of temporal variability of processes showed dissipation of bioavailable fraction of pollutant in just 6 days and in comparison with bare soil, a positive impact of plant was shown on PAH dissipation and on expression of PAH dioxygenase genes. A long-term study (over 6 years) in a field trial revealed that plant cover slowed down PAH dissipation and impacted bacterial and fungal diversity as edaphic parameters. All these results underlined the importance of PAH bioavailability for the dissipation process and of spatio-temporal dynamic of microbial community, in the rhizospher