The case for absolute ligand discrimination : modeling information processing and decision by immune T cells

Some cells have to take decision based on the quality of surroundings ligands, almost irrespective of their quantity, a problem we name "absolute discrimination". An example of absolute discrimination is recognition of not-self by immune T Cells. We show how the problem of absolute discrimination can be solved by a process called "adaptive sorting". We review several implementations of adaptive sorting, as well as its generic properties such as antagonism. We show how kinetic proofreading with negative feedback implements an approximate version of adaptive sorting in the immune context. Finally, we revisit the decision problem at the cell population level, showing how phenotypic variability and feedbacks between population and single cells are crucial for proper decision

Spreading Properties and Complex Dynamics for Monostable Reaction–Diffusion Equations

International audienceThis paper is concerned with the study of the large-time behaviour of the solutions u of a class of one-dimensional reaction-diffusion equations with monostable reaction terms f , including in particular the classical Fisher-KPP nonlinearities. The nonnegative initial data u 0 (x) are chiefly assumed to be exponentially bounded as x tends to +∞ and separated away from the unstable steady state 0 as x tends to −∞. On the one hand, we give some conditions on u 0 which guarantee that, for some λ > 0, the quantity c λ = λ+f (0)/λ is the asymptotic spreading speed, in the sense that lim t→+∞ u(t, ct) = 1 (the stable steady state) if c c λ. These conditions are fulfilled in particular when u 0 (x) e λx is asymptotically periodic as x → +∞. On the other hand, we also construct examples where the spreading speed is not uniquely determined. Namely, we show the existence of classes of initial conditions u 0 for which the ω−limit set of u(t, ct + x) as t tends to +∞ is equal to the whole interval [0, 1] for all x ∈ R and for all speeds c belonging to a given interval (γ 1 , γ 2) with large enough γ 1 < γ 2 ≤ +∞

Comparison of three combustion models for simulating anode baking furnaces

Carbon anode blocks used in the Hall-Héroult process for primary aluminum production have to be baked up to 1100 °C in dedicated furnaces. These furnaces are equipped with burner ramps to heat the air circulating in the flues at 1200 °C, so that the anodes reach the required temperature. It is therefore mandatory to include the heat provided by the burners in a numerical model of an anode baking furnace. In this work, we modeled the heat input at the burners in three ways: the Eddy-Dissipation model, the Mixture Fraction/PDF approach and a simplified approach consisting in injecting an equivalent calorific value at the burners' inlets. Results obtained with the first two models are very similar in terms of anode baking prediction but slightly different in terms of flame temperature prediction. Results obtained with the simplified approach show that the model can replace combustion model to predict anode baking, but calibration of boundary conditions is necessary in order to match more elaborate combustion models. The importance of other elements of the model in the flue channel of the furnace has been verified: radiation (cannot be ignored, large influence on the spatial temperature distribution), heat transfer due to species diffusion (negligible influence on the baking, but slight effect on flame shape and temperature), and buoyancy (no significant effect on the results in the furnace firing sections)

What is Expected from a Reviewer?

Most scientists are asked to review many papers every year. Many times, even experienced scientists are not totally aware of what is and what isn’t a good review. His own analysis follows what he has received from others. Is there a guide to produce good and valuable paper reviews? This summary points out what is, and what is not expected by journal editors from a peer review. DOI:&nbsp;http://dx.doi.org/10.17807/orbital.v13i5.165

A viscosity solution method for the spreading speed formula in slowly varying media

International audienceIn this paper, we consider reaction-diffusion-advection equations in slowly periodi-cally oscillating media. We prove the existence of and we give explicit expressions of the asymptotic spreading speeds of invasion of the unstable state 0 in any direction, when the period of the invaded medium becomes infinitely large. The limiting sprea-ding speeds involve families of 1-periodic Hamilton-Jacobi equations. In the case of one-dimensional reaction-diffusion equations, we analyze the relative effects of small perturbations of the diffusion and the reaction coefficients, and we compare the spreading speeds in slowly oscillating media to the homogenized spreading speeds in rapidly oscillating media

Thickness control in structural optimization via a level set method

International audienceIn the context of structural optimization via a level-set method we propose a framework to handle geometric constraints related to a notion of local thickness. The local thickness is calculated using the signed distance function to the shape. We formulate global constraints using integral functionals and compute their shape derivatives. We discuss diff erent strategies and possible approximations to handle the geometric constraints. We implement our approach in two and three space dimensions for a model of linearized elasticity. As can be expected, the resulting optimized shapes are strongly dependent on the initial guesses and on the speci fic treatment of the constraints since, in particular, some topological changes may be prevented by those constraints

Molding direction constraints in structural optimization via a level-set method

International audienceIn the framework of structural optimization via a level-set method, we develop an approach to handle the directional molding constraint for cast parts. A novel molding condition is formulated and a penalization method is used to enforce the constraint. A first advantage of our new approach is that it does not require to start from a feasible initialization, but it guarantees the convergence to a castable shape. A second advantage is that our approach can incorporate thickness constraints too. We do not adress the optimization of the casting system, which is considered a priori defined. We show several 3d examples of compliance minimization in linearized elasticity under molding and minimal or maximal thickness constraints. We also compare our results with formulations already existing in the literature

Analyse scalimétrique de la croissance marine du saumon atlantique (Salmo salar L.) de la rivière Matane au Québec pour les périodes d'échantillonnage 1965-1980 et 1997-2015

RÉSUMÉ: Les stocks de saumon atlantique (Salmo salar L.) se sont effondrés au début des années 1990 en réponse à une combinaison de facteurs incluant la surpêche. Jusqu’à maintenant, peu de stocks ont présenté des signes de rétablissement malgré la fermeture de la majorité des pêches commerciales et la mise en place de mesures de gestion visant à réduire les captures accidentelles par d’autres pêches. Des études suggèrent que les faibles niveaux actuels d’abondance des stocks de saumon atlantique seraient le résultat d’une hausse de la mortalité naturelle en mer causée par une diminution de la croissance. À cet égard, l’objectif de la présente étude est de vérifier, pour la première fois pour les saumons d’une rivière du Québec, si la croissance marine de ces saumons a diminué au cours des dernières années. Pour répondre à cet objectif, des indices de croissance ont été calculés à partir de mesures scalimétriques incluant le nombre de circuli et la distance intercirculi. Les écailles à analyser ont été tirées de la collection historique de la rivière Matane. Cette collection, qui débute en 1965, est l’une des plus importantes au Québec. Les résultats indiquent que les indices de croissance présentent des différences annuelles significatives qui sont accompagnées d’une tendance à la hausse entre 1963 et 1979, et d’une tendance à la baisse du milieu des années 1990 jusqu’au début des années 2010. Ces tendances sont très similaires au patron dominant de l’indice de l’oscillation nord-atlantique (IONA) ce qui suggère que la baisse de croissance mesurée chez les saumons de la rivière Matane serait associée à une hausse de la température de l’eau. Les résultats démontrent également que la croissance réalisée entre juillet et octobre de chaque année passée en mer supporte l’hypothèse de l’atteinte d’une longueur automnale minimale permettant de répondre adéquatement aux demandes métaboliques de l’hiver. Aucune relation n’est mesurée entre la croissance et les retours en rivière. Cette absence de relation suggère la présence d’autres facteurs de mortalité affectant les saumons de la rivière Matane. Ces résultats mettent en valeur le rôle de l’environnement dans la croissance marine du saumon atlantique. Ils représentent également une première étape vers une meilleure compréhension des mécanismes affectant le recrutement de cette espèce pour une rivière du Québec. -- Mot(s) clé(s) en français : Saumon atlantique, mortalité naturelle, croissance, circuli, distance intercirculi, indice de l’oscillation nord-atlantique, recrutement. -- ABSTRACT: The Atlantic salmon (Salmo salar L.) stocks collapsed in the early 1990s owing to a combination of factors including overfishing. Until now, few stocks have shown signs of recovery despite the closure of the majority of the commercial fisheries and the implementation of management measures to reduce the by-catches by other fisheries. Studies suggest that the current low levels of abundance of the Atlantic salmon stocks would be the result of an increase in the natural mortality at sea caused by a reduction in growth. In this regard, the objective of this study is to verify, for the first time for the salmons of a Quebec river, if the marine growth of these salmons has decreased in recent years. To meet this objective, growth indices were calculated from scalimetric measurements including the number of circuli and the inter-circuli distance. The scales to be analyzed were taken from the historical collection of the Matane River. This collection that dates back to 1965 is one of the most important in Quebec. The results indicate that the growth indices show significant annual differences that are accompanied by an upward trend between 1963 and 1979, and a downward trend from the mid-1990s to the early 2010s. These trends are very similar to the dominant pattern of the North Atlantic Oscillation Index (NAOI) suggesting that the reduction in growth of the Matane River salmons is associated with an increase in water temperature. The results also show that the growth achieved between July and October of each year spent at sea supports the hypothesis of reaching a minimum autumn length to adequately meet the metabolic demands of winter. No relationship is measured between growth and the river returns. This lack of relationship suggests the presence of other mortality factors affecting the salmons of the Matane River. These results highlight the role of the environment in the marine growth of the Atlantic salmon. They also represent a first step towards a better understanding of the mechanisms affecting the recruitment of this species for a Quebec river. -- Mot(s) clé(s) en anglais : Atlantic salmon, natural mortality, growth, circuli, inter-circuli distance, North Atlantic Oscillation Index, recruitment

Sensitivity of carbon anode baking model outputs to kinetic parameters describing pitch pyrolysis

Carbon anode blocks, used in aluminum electrolysis cells, are usually baked in furnaces for several days, during which they release volatiles due to pitch pyrolysis. Therefore, numerical modeling of anode baking furnaces has to include some representation of pitch pyrolysis via a set of kinetic parameters. These kinetic parameters can vary with raw materials and baking parameters and are tedious to determine experimentally. In this work, we studied how the main outputs of an anode baking model are affected by the variance of the kinetic parameters. Results show that certain model outputs are not considerably influenced by changes in the kinetic parameters (e.g., spatial variation of anode porosity, maximum heating value from volatiles), while others are significantly affected (e.g., time evolution of anode porosity, time of maximum heating value of volatiles, internal pressure of anode), in particular by activation energy variability