Interpreting an action from what we perceive and what we expect

International audienceIn update logic as studied by Baltag, Moss, Solecki and van Benthem, little attention is paid to the interpretation of an action by an agent, which is just assumed to depend on the situation. This is actually a complex issue that nevertheless complies to some logical dynamics. In this paper, we tackle this topic. We also deal with actions that change propositional facts of the situation. In parallel, we propose a formalism to accurately represent an agent's epistemic state based on hyperreal numbers. In that respect, we use infinitesimals to express what would surprise the agents (and by how much) by contradicting their beliefs. We also use a subjective probability to model the notion of belief. It turns out that our probabilistic update mechanism satisfies the AGM postulates of belief revision

Dynamics of Macrophage Trogocytosis of Rituximab-Coated B Cells

Macrophages can remove antigen from the surface of antibody-coated cells by a process termed trogocytosis. Using live cell microscopy and flow cytometry, we investigated the dynamics of trogocytosis by RAW264.7 macrophages of Ramos B cells opsonized with the anti-CD20 monoclonal antibody rituximab. Spontaneous and reversible formation of uropods was observed on Ramos cells, and these showed a strong enrichment in rituximab binding. RAW-Ramos conjugate interfaces were highly enriched in rituximab, and transfer of rituximab to the RAW cells in submicron-sized puncta occurred shortly after cell contact. Membrane from the target cells was concomitantly transferred along with rituximab to a variable extent. We established a flow cytometry-based approach to follow the kinetics of transfer and internalization of rituximab. Disruption of actin polymerization nearly eliminated transfer, while blocking phosphatidylinositol 3-kinase activity only resulted in a delay in its acquisition. Inhibition of Src family kinase activity both slowed acquisition and reduced the extent of trogocytosis. The effects of inhibiting these kinases are likely due to their role in efficient formation of cell-cell conjugates. Selective pre-treatment of Ramos cells with phenylarsine oxide blocked uropod formation, reduced enrichment of rituximab at cell-cell interfaces, and reduced the efficiency of trogocytic transfer of rituximab. Our findings highlight that dynamic changes in target cell shape and surface distribution of antigen may significantly influence the progression and extent of trogocytosis. Understanding the mechanistic determinants of macrophage trogocytosis will be important for optimal design of antibody therapies

Logics of knowledge and action: critical analysis and challenges

International audienceWe overview the most prominent logics of knowledge and action that were proposed and studied in the multiagent systems literature. We classify them according to these two dimensions, knowledge and action, and moreover introduce a distinction between individual knowledge and group knowledge, and between a nonstrategic an a strategic interpretation of action operators. For each of the logics in our classification we highlight problematic properties. They indicate weaknesses in the design of these logics and call into question their suitability to represent knowledge and reason about it. This leads to a list of research challenges

Plasmodium falciparum Adhesion on Human Brain Microvascular Endothelial Cells Involves Transmigration-Like Cup Formation and Induces Opening of Intercellular Junctions

Cerebral malaria, a major cause of death during malaria infection, is characterised by the sequestration of infected red blood cells (IRBC) in brain microvessels. Most of the molecules implicated in the adhesion of IRBC on endothelial cells (EC) are already described; however, the structure of the IRBC/EC junction and the impact of this adhesion on the EC are poorly understood. We analysed this interaction using human brain microvascular EC monolayers co-cultured with IRBC. Our study demonstrates the transfer of material from the IRBC to the brain EC plasma membrane in a trogocytosis-like process, followed by a TNF-enhanced IRBC engulfing process. Upon IRBC/EC binding, parasite antigens are transferred to early endosomes in the EC, in a cytoskeleton-dependent process. This is associated with the opening of the intercellular junctions. The transfer of IRBC antigens can thus transform EC into a target for the immune response and contribute to the profound EC alterations, including peri-vascular oedema, associated with cerebral malaria

Biodiversity of fungal community associated to lichens active against Candida biofilms

International audienceLichens are symbiotic organisms and their thalli constitute an ecological niche for associated microbial communities (fungi and bacteria) classified as epi- and endobionts, possibly able to form biofilm-like structures [1]. Interactions exist within this complex ecosystem and appear to be at the origin of the production of defense metabolites [2] which contribute to the resistance of lichens to fungi. These compounds also display interesting biological activities such as antimicrobials [3] or inhibitors of bacterial biofilms [4]. A screening of fifty lichen extracts was previously performed against sessile Candida albicans yeasts by evaluating their anti-adherent activity and highlighted the interest of 7 lichen extracts. In order to explore the possible link between fungal inhibition of these extracts and biotic existing balances within the lichen, the study of fungal community associated to thalli of active lichens was performed. Endolichenic and epilichenic fungi were isolated on MEA and PDA culture media after sterilisation step or not of the thalli respectively [5] and the characterisation of the total fungal community by high-throughput sequencing (MiSeq) from crushed thalli was carried out. Sequencing of the ITS rDNA and/or 18S and comparison with sequence databases were performed from cultures. The results, especially with thalli of the 2 most active lichens (Evernia prunastri and Ramalina fastigiata) showed a wide fungal diversity. The endolichenic versus epilichenic communities are well differentiated with a predominance of Sordariomycetes for endolichenic fungi and Dothideomycetes for epilichenic fungi. Eurotiomycetes, Leotiomycetes and Pezizomycetes are also present. Epi and endobionts belong to classes that are distinct from that of mycobiont (Lecanoromycetes) [5]. Only the species Sordaria fimicola was found to be both epi and endolichenic fungus. The analyse of results obtained by high-throughput sequencing after ITS1 amplification is in progress

Sabotage modal logic: Some model and proof theoretic aspects

We investigate some model and proof theoretic aspects of sabotage modal logic. The first contribution is to prove a characterization theorem for sabotage modal logic as the fragment of first-order logic which is invariant with respect to a suitably defined notion of bisimulation (called sabotage bisimulation). The second contribution is to provide a sound and complete tableau method for sabotage modal logic. We also chart a number of open research questions concerning sabotage modal logic, aiming at integrating it within the current landscape of logics of model update

Computational Properties of Delay-Coupled Systems

Tesis Doctoral presentada por Miguel Angel Escalona Morán para optar al título de Doctor, en el Programa de Física del Departamento de Física de la Universitat de les Illes Balears, realizada en el IFISC bajo la dirección de Claudio Mirasso, catedrático de universidad y Miguel Cornelles Soriano, contratado postdoctoral CAIB.In this research work we study the computational properties of delay-coupled systems. In particular, we use a machine learning technique known as reservoir computing. In machine learning, a computer learns to solve different tasks using examples and without knowing explicitly their solution. For the study of the computational properties, a numerical toolbox, written in Python, was developed. This toolbox allows a fast implementation of the different scenarios described in this thesis. Using a reservoir computer, we studied several computational properties, focusing on its kernel quality, its ability to separate different input samples and the intrinsic memory capacity. This intrinsic memory is related to the delayed- feedback of the reservoir. We used a delay-coupled system as reservoir to study its computational ability in three different kinds of tasks: system’s modeling, time-series prediction and classification tasks. The system’s modeling task was performed using the Nonlinear Autoregressive Moving Average (of ten steps), NARMA10. The NARMA10 model creates autoregressive time series from a set of normally distributed random sequences. The reservoir computer learns how to emulate the system using only the sequence of random numbers and the autoregressive time series, but without knowing the equations of the NARMA10. The results of our approach are equivalent to those published by other authors and show the computational power of our method. For the time-series prediction tasks, we used three kinds of time series: a model that gives the variations in temperature of the sea surface that provoke El Niño phenomenon, the Lorenz system and the dynamics of a chaotic laser. Different scenarios were explored depending on the nature of the time series. For the prediction of the variation in temperature of the sea surface, we perform estimations of one, three and six months in advance. The error was measured as the Normalized Root Mean Square Error (NRMSE). For the different prediction horizons, we obtained errors of 2%, 8% and 24%, respectively. The classification tasks were carried out for a Spoken Digit Recognition (SDR) task and a real-world biomedical task. The SDR was used to illustrate different scenarios of a machine learning problem. The biomedical task consists on the automatic classification of heartbeats with cardiac arrhythmias. We use the MIT-BIH Arrhythmia database, a widely used database in cardiology. For comparison purposes, we followed the guidelines of the Association for the Advancement of Medical Instrumentation for the evaluation of arrhythmia-detector algorithms. We used a biostatistical learning process named logistic regression that allowed to compute the probability that a heartbeat belongs to a particular class.This is in contrast to the commonly used linear regression. The results obtained in this work show the versatility and efficiency of our implemented reservoir computer. Our results are equivalent and show improvement over other reported results on this problem under similar conditions and using the same database. To enhance the computational ability of our delay-coupled system, we included a multivariate scheme that allows the consideration of different variables of a system. We evaluated the influence of this multivariate scenario using a time- series prediction and the classification of heartbeat tasks. The results show improvement in the performance of the reservoir computer in comparison with the same tasks in the univariate case.Peer reviewe

Dynamic epistemic logics: promises, problems, shortcomings, and perspectives

International audienceDynamic epistemic logics provide an account of the evolution of agents’ belief and knowledge when they learn the occurrence of an event. These logics started to become popular about 20 years ago and by now there exists a huge number of publications about them. The present paper briefly summarises the existing body of literature, discusses some problems and shortcomings, and proposes some avenues for future research