Agent-Based Facilitation of Water Allocation: Case Study in the Drome River Valley

International audienceThe purpose of the 1992 French Water Act is to encourage negotiation and dialogue among local stakeholderswithin a framework which is very similar to a patrimonial approach. Potential use of models in such post-normalapproaches is analyzed. Two kinds of models are compared: one is agent-based, the other follows a more classicalapproach. They are compared according to their contributions as negotiation support tools. This comparisonis based on a specific collective decision process dealing with water allocation at the sub-basin scale, in whichauthors are involved. Both are used to support collective decision processes through simulation of resource usedynamics. Agent-Based Models entail the broadening of spatial information of actors in the process, revealinginter-connected topics not taken into consideration earlier. This makes it possible to remain relevant, despite thesometimes rapidly evolving stakes. The central point of this paper is the implementation, within a practical application,of theories advocating the use of ABM as a collective decision support system. This application promotesa better understanding of the kind of support ABM provides and the way it does so. This is broughtabout more by re-framing the discussion and modifying the representation of the system on the part of thestakeholders than by providing specific agreements

Evidencing the role of plants vs soils in the understanding of 137Cs phyto availability using a coupled experimental and modelling approach

International audience137Cs is a radionuclide with a half-life of 30 years that is commonly found in soils after nuclear fallout due to nuclear incidents or atmospheric nuclear weapon testing. Due to their properties of accumulation and retention, soils are key compartments for the transfer of contaminants such as 137Cs in the trophic chain. Ingestion of contaminated agricultural products being one of the main component of human exposure, it is essential to be able to predict the fate of 137Cs throughout the soil-plant continuum.The contaminant mobility into the soil, its transfer to the plant and its final distribution between all components are generally described by simple models (equilibrium-based, linear distributions). These models are operational but are not able to account for the variability of soils and plants encountered.Bioavailability is function of both soil physico-chemical characteristics, that impact the environmental availability, and plant physiology which determines the uptake rate and accumulation. The aim of this work is to highlight the preponderant factors controlling the 137Cs bioavailability in the soil-solution-plant continuum by using a model that account for both soil and plant characteristics. The proposed mechanistic model is based on thermodynamic reactions describing the interactions of Cs with the different soil reactive components, coupled with a physiological model of root absorption.Series of experiments were conducted to produce a contrasted data set of 137Cs soil to plant transfer. For those experiments, 2 different plants with contrasted Cs uptake capacities (Millet, Mustard) and 3 different soils with varying texture and mineralogy have been studied. Three weeks exposure studies were conducted with the RHIZOtest® which is a normative device to assess the bioavailability of contaminants in soil. They were completed with batch experiments aiming at characterizing the environmental availability of Cs in soils. A large range of 137Cs soil to plant transfer rates was measured for the different soil/pant combinations. For example a contrasted bioavailability of 137Cs was observed, with the same plant accumulating 10% to 40% of total Cs’s stock depending on the soils. We also observed that during the time of the experiment the plant had absorbed most of the estimated environmental available Cs.Modelling those experiments allowed us to highlight the main soil and plant properties that have a great impact on the contaminant mobility. For example, plant physiological factors were the main driver of bioavailability in condition where environmental availability was not limited (e.g. sandy soils), whereas their roles were reduced in soils with high 137Cs sorption capacity. Such a model may help to reduce uncertainties in the prediction of 137Cs transfer to plants in environmental risk assessment, with a great potential to cover a large range of soils and plants

Enabling silicon-on-silicon photonics with pedestalled Mie resonators

High-refractive-index Mie resonators are regarded as promising building blocks for low-loss all-dielectric nanophotonic applications. To avoid the otherwise excessive damping and loss of symmetry such devices typically need to be implemented over a low-index substrate, which hampers their integration in many practical applications. In this paper we propose a new photonic structure consisting of silicon-on-silicon spheroidal-like resonators, each one supported by a slim silicon pedestal that makes the micro-cavities stand optically separated from the substrate while providing both mechanical stability and electrical contact with the substrate. These structures are produced in high-quality monocrystalline Si and their size and arrangement can be precisely controlled through standard lithography. We demonstrate that such structures present an optical performance similar to the one achieved with low-index substrates, opening new avenues for developing novel hybrid photonic/electronic devices.Postprint (author's final draft

Deriving a germinal center lymphocyte migration model from two-photon data

Recently, two-photon imaging has allowed intravital tracking of lymphocyte migration and cellular interactions during germinal center (GC) reactions. The implications of two-photon measurements obtained by several investigators are currently the subject of controversy. With the help of two mathematical approaches, we reanalyze these data. It is shown that the measured lymphocyte migration frequency between the dark and the light zone is quantitatively explained by persistent random walk of lymphocytes. The cell motility data imply a fast intermixture of cells within the whole GC in approximately 3 h, and this does not allow for maintenance of dark and light zones. The model predicts that chemotaxis is active in GCs to maintain GC zoning and demonstrates that chemotaxis is consistent with two-photon lymphocyte motility data. However, the model also predicts that the chemokine sensitivity is quickly down-regulated. On the basis of these findings, we formulate a novel GC lymphocyte migration model and propose its verification by new two-photon experiments that combine the measurement of B cell migration with that of specific chemokine receptor expression levels. In addition, we discuss some statistical limitations for the interpretation of two-photon cell motility measurements in general

Deriving a germinal center lymphocyte migration model from two-photon data

Recently, two-photon imaging has allowed intravital tracking of lymphocyte migration and cellular interactions during germinal center (GC) reactions. The implications of two-photon measurements obtained by several investigators are currently the subject of controversy. With the help of two mathematical approaches, we reanalyze these data. It is shown that the measured lymphocyte migration frequency between the dark and the light zone is quantitatively explained by persistent random walk of lymphocytes. The cell motility data imply a fast intermixture of cells within the whole GC in approximately 3 h, and this does not allow for maintenance of dark and light zones. The model predicts that chemotaxis is active in GCs to maintain GC zoning and demonstrates that chemotaxis is consistent with two-photon lymphocyte motility data. However, the model also predicts that the chemokine sensitivity is quickly down-regulated. On the basis of these findings, we formulate a novel GC lymphocyte migration model and propose its verification by new two-photon experiments that combine the measurement of B cell migration with that of specific chemokine receptor expression levels. In addition, we discuss some statistical limitations for the interpretation of two-photon cell motility measurements in general

Role of CCR8 and Other Chemokine Pathways in the Migration of Monocyte-derived Dendritic Cells to Lymph Nodes

Studying the influence of chemokine receptors (CCRs) on monocyte fate may reveal information about which subpopulations of monocytes convert to dendritic cells (DCs) and the migration pathways that they use. First, we examined whether prominent CCRs on different monocyte subsets, CCR2 or CX3CR1, mediated migration events upstream of the accumulation of monocyte-derived DCs in lymph nodes (LNs). Monocytes were labeled and traced by uptake of latex microspheres in skin. Unexpectedly, neither CCR2 nor CX3CR1 were required. However, absence of CCR2 led to an increased labeling of the minor Gr-1int monocyte population, and the number of latex+ DCs that emigrated to LNs was correspondingly increased. Characterization of Gr-1int monocytes revealed that they selectively expressed CCR7 and CCR8 mRNA in blood. CCR7 and CCR8 pathways were used by monocyte-derived DCs during mobilization from skin to LNs. The role of CCR8 in emigration from tissues also applied to human monocyte-derived cells in a model of transendothelial trafficking. Collectively, the data suggest that Gr-1int monocytes may be most disposed to become a lymphatic-migrating DCs. When these monocyte-derived DCs exit skin to emigrate to LNs, they use not only CCR7 but also CCR8, which was not previously recognized to participate in migration to LNs