Inference for Partially Observed Multitype Branching Processes and Ecological Applications

Multitype branching processes with immigration in one type are used to model the dynamics of stage-structured plant populations. Parametric inference is first carried out when count data of all types are observed. Statistical identifiability is proved together with derivation of consistent and asymptotically Gaussian estimators for all the parameters ruling the population dynamics model. However, for many ecological data, some stages (i.e. types) cannot be observed in practice. We study which mechanisms can still be estimated given the model and the data available in this context. Parametric inference is investigated in the case of Poisson distributions. We prove that identifiability holds for only a subset of the parameter set depend- ing on the number of generations observed, together with consistent and asymptotic properties of estimators. Finally, simulations are performed to study the behaviour of the estimators when the model is no longer Poisson. Quite good results are obtained for a large class of models with distributions having mean and variance within the same order of magnitude, leading to some stability results with respect to the Poisson assumption.Comment: 31 pages, 1 figur

Neurophysiological Mechanisms Involved in Auditory Perceptual Organization

In our complex acoustic environment, we are confronted with a mixture of sounds produced by several simultaneous sources. However, we rarely perceive these sounds as incomprehensible noise. Our brain uses perceptual organization processes to independently follow the emission of each sound source over time. If the acoustic properties exploited in these processes are well-established, the neurophysiological mechanisms involved in auditory scene analysis remain unclear and have recently raised more interest. Here, we review the studies investigating these mechanisms using electrophysiological recordings from the cochlear nucleus to the auditory cortex, in animals and humans. Their findings reveal that basic mechanisms such as frequency selectivity, forward suppression and multi-second habituation shape the automatic brain responses to sounds in a way that can account for several important characteristics of perceptual organization of both simultaneous and successive sounds. One challenging question remains unresolved: how are the resulting activity patterns integrated to yield the corresponding conscious percepts

Réseaux sociaux, discussions instantanées, jeux en ligne; quel temps reste-t-il pour les devoirs ?

Les outils de communication modernes occupent une place prépondérante au sein de notre société. Nos élèves sont aussi touchés par ce phénomène et ils engagent un temps considérable dans ces outils. Quels sont ces outils de communication ? Qui les utilisent ? Combien de temps passent-ils sur ces outils ? Qu’y font-ils ? Afin de répondre à ces questions, j’ai commencé par m’informer sur le sujet. Puis ayant acquis un certain bagage, j’ai mené une recherche pratique au sein de deux classes. J’ai distribué des questionnaires à ces élèves puis je les ai privés de tout outil durant une semaine. Après cela, j’ai redistribué un questionnaire afin de comparer leur attitude face aux outils de communication avant, et après avoir été privés de ces outils. Cette recherche a été très intéressante. Elle m’a permis de trouver les réponses à mes interrogations

Effect of atmosphere change paths on the induced chemical expansion

International audienceThis study presents the relevant aspects of the approach developed at Institut PRISME to model strain in the mixed ionic and electronic conductors (MIEC) membrane for reforming of methane into synthesis gas (H2/CO). This macroscopic approach is based on the assumption of strain partition and on the choice of oxygen activity as a state variable. It leads to a thermo-chemo-mechanical model taking into account oxygen diffusion as well as elastic, thermal and chemical expansion phenomena. A chemical expansion model is proposed. The kinetics of a macroscopic bulk diffusion model has been fitted by simulation to chemical dilatometry tests. The transient and the steady-state stress distribution in a membrane reactor for partial oxidation of methane (POM) have been simulated in various conditions

The spectrin family of proteins: a unique coiled-coil fold for various molecular surface properties

International audienceThe spectrin superfamily is composed of proteins involved in cytolinker functions. Their main structural feature is a large central subdomain with numerous repeats folded in triple helical coiled-coils. Their similarity of sequence was considered to be low without detailed quantification of the intra- and intermolecular levels. Among the superfamily, we considered as essential to propose an overview of the surface properties of all the repeats of the five proteins of the spectrin family, namely α- and β-spectrins, α-actinin, dystrophin and utrophin. Therefore, the aim of this work was to obtain a quantitative comparison of all the repeats at both the primary sequence and the three-dimensional levels. For that purpose, we applied homology modelling methods to obtain structural models for successive and overlapping tandem repeats of the human erythrocyte α- and β-spectrins and utrophin, as previously undertaken for dystrophin, and we used the known structure of α-actinin. The matrix calculation of the pairwise similarities of all the repeat sequences and the electrostatic and hydrophobic surface properties throughout the protein family support the view that spectrins and α-actinin on one hand and utrophin and dystrophin on the other hand share some structural similarities, but a detailed molecular characterisation highlights substantial differences. The repeats within the family are far from identical, which is consistent with their multiple interactions with different cellular partners, including proteins and membrane lipids

Les « vivants haillons » d’Ernest Pignon-Ernest

Comme le jour se lève sur la ville, sur Naples ou Paris, Lyon, Martigues ou Santiago du Chili, des habitants nouveaux se tiennent dans les rues, ou plutôt se tiennent aux rues, aux parois transparentes des cabines téléphoniques, aux murs des maisons effondrées ou aux façades encore droites, le long des cheminées d’usines ou à même les marches du métro Charonne. A la faveur de la nuit tombée et dans le vacillement de ses silhouettes, Ernest Pignon-Ernest a collé partout ses images. Il a rythmé le grand support de la ville de ses trompe-l’œil fantomatiques. Il a, traversant en sens inverse le fleuve des morts, fait revenir des ombres, des chairs et des visages décolorés. Il a répété dans la ville des séries d’hommes et de femmes, des figures martyrisées, des Rimbaud en habit de départ, des expulsés, des Pasolini apposés sur des véroniques, des souvenirs de peinture, des icônes, des traces. Par cette présence menacée, ces vivants haillons nous disent l’acceptation d’un temps et la fragilité de l’être au monde

Non-Verbal Auditory Cognition in Patients with Temporal Epilepsy Before and After Anterior Temporal Lobectomy

For patients with pharmaco-resistant temporal epilepsy, unilateral anterior temporal lobectomy (ATL) – i.e. the surgical resection of the hippocampus, the amygdala, the temporal pole and the most anterior part of the temporal gyri – is an efficient treatment. There is growing evidence that anterior regions of the temporal lobe are involved in the integration and short-term memorization of object-related sound properties. However, non-verbal auditory processing in patients with temporal lobe epilepsy (TLE) has raised little attention. To assess non-verbal auditory cognition in patients with temporal epilepsy both before and after unilateral ATL, we developed a set of non-verbal auditory tests, including environmental sounds. We could evaluate auditory semantic identification, acoustic and object-related short-term memory, and sound extraction from a sound mixture. The performances of 26 TLE patients before and/or after ATL were compared to those of 18 healthy subjects. Patients before and after ATL were found to present with similar deficits in pitch retention, and in identification and short-term memorisation of environmental sounds, whereas not being impaired in basic acoustic processing compared to healthy subjects. It is most likely that the deficits observed before and after ATL are related to epileptic neuropathological processes. Therefore, in patients with drug-resistant TLE, ATL seems to significantly improve seizure control without producing additional auditory deficits

MAS Simulation of a “Bush Taxi” Transportation Service : Summary of a project carried out during the MAPS training course

International audienceThe human and social sciences have always sought to improve their tools and resources in order to spread their knowledge. The most recent of these tools, Multi-Agent Systems (MAS), also known as Agent-Based Models (ABM), is a remarkable means of formalization and visualization of spatial processes. Multi-Agent Systems have already proved to be extremely useful modeling tools in various disciplines such as epidemiology, biology, and ecology, but also economics and geography (Amblard F. 2006). Today's research and methods aiming to deal with spatial problems are more and more treated within the paradigm and theories of complex systems. Indeed, one of the advantages of multi-agent systems, in the domain of human and social sciences, is their ability to accurately represent the underlying systems in the simplest way possible, while at the same time successfully integrating complexity in each of the scales considered (Daudé E. 2003). The main problem, when using this approach, is to design, in accordance with Occam's Razor, simple operating rules and strategies for the agents, which are carefully chosen to respond to a clearly identified problem. Given the components and parameters of the system, this tool allows us to observe and understand the comprehensive self-organized behavior, including the effects of structuring, transition, emergence, etc. (M. Vidal J. 2007). Today's society is increasingly mobile and people's daily mobility is determined by processes linked to their behavior, the infrastructure, and their environment (roads, etc.), but also by the services available to them (busses, taxis, etc.) (Marilleau N. et al. 2005). Therefore, their movements are strongly influenced by the environment which surrounds them. Working on a variety of themes which are all relevant to the same problem, mobility, our group has brought together several young researchers for whom the MAPS training course fulfills the need for training in the domain of the science of complexity, in the realms of both methodological skills and practical multi-agent modeling.Les sciences humaines et sociales ont toujours cherché à améliorer leurs outils afin de diffuser leurs connaissances. Le dernier d'entre eux, les Systèmes Multi-Agents (S.M.A.) est un vecteur remarquable de la formalisation et de la visualisation des processus spatiaux. Les SMA ont déjà fait leurs preuves en tant qu'outil puissant de modélisation, dans différentes disciplines comme l'épidémiologie, la biologie, l'écologie, mais aussi l'économie et la géographie (Amblard F. 2006). La multiplication des recherches et des méthodes visant à répondre à des problématiques spatiales s'inscrivent, aujourd'hui, dans le paradigme et les théories des systèmes complexes. En effet, l'un des atouts des systèmes multi-agents, dans les domaines relevant des sciences humaines et sociales, réside dans leur pertinence à représenter les systèmes sous-jacents le plus simplement possible, tout en intégrant au mieux la complexité aux différentes échelles considérées (Daudé E. 2003). Tout l'enjeu de cette approche est de concevoir, selon le principe de parcimonie, des règles de fonctionnement et des stratégies simples des agents, mais précisément choisies pour répondre à une problématique clairement identifiée. Connaissant les composantes et les paramètres du système, l'outil permet alors d'observer et de comprendre un comportement global auto-organisé, avec des effets de structuration, de transition, d'émergence, etc. (M. Vidal J. 2007). Vivant dans une société chaque jour plus mobile, les personnes se déplacent quotidiennement selon des dynamiques dictées par leurs comportements, par les infrastructures, leur milieu (routes, etc.), mais aussi par les services qui leurs sont proposés (bus, taxis, etc.) (Marilleau N. et al. 2005). Les déplacements sont ainsi fortement conditionnés par l'environnement qui nous entoure. Travaillant sur des thématiques différentes, mais relevant toutes d'une problématique commune : celle de la mobilité, notre groupe réunit de jeunes chercheurs, pour lesquel la formation MAPS est une réponse à nos besoins d'aprentissage dans le domaine des sciences de la complexité, tant sur le plan des compétences méthodologiques que sur le plan pratique de modélisation multi-agents

Ion Channels as Promising Therapeutic Targets for Melanoma

n.