Symmetry-breaking phase transition in a dynamical decision model

We consider a simple decision model in which a set of agents randomly choose one of two competing shops selling the same perishable products (typically food). The satisfaction of agents with respect to a given store is related to the freshness of the previously bought products. Agents select with a higher probability the store they are most satisfied with. Studying the model from a statistical physics perspective, both through numerical simulations and mean-field analytical methods, we find a rich behaviour with continuous and discontinuous phase transitions between a symmetric phase where both stores maintain the same level of activity, and a phase with broken symmetry where one of the two shops attracts more customers than the other.Comment: 13 pages, 6 figures, submitted to JSTA

La protection sanitaire niçoise au XIXe siècle : Magistrat de santé et Protomédicat

8 pagesArticle scientifique, histoire de la médecine.De manière générale, les dispositions qui assurent l'hygiène publique dans un Etat moderne remontent fort loin dans le temps. Abordant le thème du choléra, certains écrits traduisent bien le sentiment de désespoir qu'ont véhiculé la maladie et le besoin urgent et nécessaire d'y remédier. Ce fléau peut-être considéré comme un révélateur car il dresse un état des lieux de la médecine et de son époque. Avant l'arrivé au XIXe siècle du choléra-morbus dans les Alpes-Maritimes, la question de politique sanitaire préoccupait déjà la Maison de Savoie. Ce sentiment de responsabilité en la matière était accompagné de mesures concrètes et prévalait dans la législation. Dans le but d'illustrer ce qu'a pu être la protection sanitaire de cette époque, nous pouvons nous intéresser à deux institutions ayant joué un rôle prédominant dans ce domaine : le Magistrat de santé puis le Protomédicat

Overestimates of maternity and population growth rates in multi-annual breeders

There has been limited attention to estimating maternity rate because it appears to be relatively simple. However, when used for multi-annual breeder species, such as the largest carnivores, the most common estimators introduce an upward bias by excluding unproductive females. Using a simulated dataset based on published data, we compare the accuracy of maternity estimates derived from standard methods against estimates derived from an alternative method. We show that standard methods overestimate maternity rates in the presence of unsuccessful pregnancies. Importantly, population growth rates derived from a matrix model parameterized with the biased estimates may indicate increasing populations although the populations are stable or even declining. We recommend the abandonment of the biased standard methods and to instead use the unbiased alternative method for population projections and assessments of population viabilit

Selfish and Altruistic Bacterial Populations Maximize Fitness Under Stress by Local Segregation

Landscapes in ecology have a profound influence on the adaption and evolution of competing populations for resources. We are interested in how altruistic populations survive in the presence of selfish individuals in a non-stirred, closed and complex nutrient landscape. Well-stirred (landscape-free) but closed environments have a depressing future when selfish individuals arise in a population, a fate known as the tragedy of the Commons. Over-exploitation of a well-stirred communal habitat by selfish individuals which do not follow rules of communal self-regulation ends up in the elimination (extinction) of both the original altruistic inhabitants and the selfish population. In the context of bacterial population, the Commons tragedy that occurs is the consumption of limited resources by the individuals, resulting in metabolic stressing of the bacteria and growth advantages to be gained by defection from a ``social contract" of altruistic cooperation. There is no avoidance of this tragedy and the collapse of an original altruistic wild-type population by an emergent selfish population in a well-stirred but closed environment is inevitable. However, there is a fundamental difference between resource exploitation in a well-stirred homogenous commons and in a heterogenous landscape of nutrients which is not stirred. We show here using a non-stirred nanofabricated habitat landscape that altruists and selfish bacteria can in fact coexist, that they can maintain phenotype diversity and avoid the tragedy of the Commons. This emergent spatial segregation of competing populations under stress greatly changes, we believe, our perception of the true sophistication of bacterial response to stress and competition, and has broad implications for the adaptive strategies of higher organisms under stress in complex environments

Frugal day-ahead forecasting of multiple local electricity loads by aggregating adaptive models

We focus on day-ahead electricity load forecasting of substations of the distribution network in France; therefore, our problem lies between the instability of a single consumption and the stability of a countrywide total demand. Moreover, we are interested in forecasting the loads of over one thousand substations; consequently, we are in the context of forecasting multiple time series. To that end, we rely on an adaptive methodology that provided excellent results at a national scale; the idea is to combine generalized additive models with state-space representations. However, the extension of this methodology to the prediction of over a thousand time series raises a computational issue. We solve it by developing a frugal variant, reducing the number of parameters estimated; we estimate the forecasting models only for a few time series and achieve transfer learning by relying on aggregation of experts. It yields a reduction of computational needs and their associated emissions. We build several variants, corresponding to different levels of parameter transfer, and we look for the best trade-off between accuracy and frugality. The selected method achieves competitive results compared to state-of-the-art individual models. Finally, we highlight the interpretability of the models, which is important for operational applications

La pratique médicale dans les Alpes-Maritimes au XIXe siècle où l'idée d'une médecine à plusieurs visages.

Article scientifique, Histoire de la Médecine.La pratique médicale qui « nourrissait largement son homme » semble avoir suscité l'ambition des enfants cultivés de Nice ou du Comté. Embrasser la profession médicale n'était pas pour autant un gage de prospérité. L'art médical durant cette période s'exerce dans un cadre non lisse et non clairement établi. L'arrivée du XXe siècle voit véritablement naître la notion d'attractivité de la « saison d'hiver ». Les « Grands » qu'ils soient étrangers ou français ont réussi à attirer à Nice une clientèle aisée et avide de soins. L'arrivée de cette nombreuse clientèle, on le comprend, sera suivie par celle des praticiens

Controlling the Cyanobacterial Clock by Synthetically Rewiring Metabolism

SummaryCircadian clocks are oscillatory systems that allow organisms to anticipate rhythmic changes in the environment. Several studies have shown that circadian clocks are connected to metabolism, but it is not generally clear whether metabolic signaling is one voice among many that influence the clock or whether metabolic cycling is the major clock synchronizer. To address this question in cyanobacteria, we used a synthetic biology approach to make normally autotrophic cells capable of growth on exogenous sugar. This allowed us to manipulate metabolism independently from light and dark. We found that feeding sugar to cultures blocked the clock-resetting effect of a dark pulse. Furthermore, in the absence of light, the clock efficiently synchronizes to metabolic cycles driven by rhythmic feeding. We conclude that metabolic activity, independent of its source, is the primary clock driver in cyanobacteria