Intensity Correlation between Observations at Differrent Wavelengths for Mkn 501 in 1997

The CAT imaging telescope on the site of the former solar plant Th'emis in southern France observed gamma-rays from the BL Lac object Mkn501 above 250 GeV for more than 60 usable hours on-source from March to October 1997. This source was in a state of high activity during all this period. By studying the correlation between the photons of different energies detected by the CAT imaging telescope and by the ASM/RXTE experiment (1.3-12.0 keV) on board the Rossi X-Ray Timing Explorer, we may constrain the mechanisms which could lead to the emission of these photons.Comment: Proceedings of the 19th Texas Symposium. 8 pages, 7 figure

Reconstruction of directed neuronal networks in a microfluidic device with asymmetric microchannels

International audienceMicrofluidic devices for controlling neuronal connectivity in vitro are extremely useful tools for deciphering pathological and physiological processes occurring in neuronal networks. These devices allow the connection between different neuronal populations located into separate culture chambers through axon-selective microchannels. In order to implement specific features of brain connectivity such as directionality, it is necessary to control axonal growth orientation in these devices. Among the various strategies proposed to achieve this goal, one of the most promising and easily reproducible is the use of asymmetric microchannels. We present here a general protocol and several guidelines for the design, production and testing of a new paradigm of asymmetric microchannels geometries based on a “return to sender” strategy. In this method, axons are either allowed to travel between the emitting and receiving chambers within straight microchannels (forward direction), or are rerouted toward their initial location through curved microchannels (reverse direction). We introduce variations of these “arches” microchannels and evaluate their respective axonal filtering capacities. Importantly, one of these variants presents an almost complete filtration of axonal growth in the non-permissive direction while allowing robust axonal invasion in the other one, with a selectivity ratio as high as 99.7%

Combining Microfluidics, Optogenetics and Calcium Imaging to Study Neuronal Communication In Vitro

International audienceIn this paper we report the combination of microfluidics, optogenetics and calcium imaging as a cheap and convenient platform to study synaptic communication between neuronal populations in vitro. We first show that Calcium Orange indicator is compatible in vitro with a commonly used Channelrhodopsine-2 (ChR2) variant, as standard calcium imaging conditions did not alter significantly the activity of transduced cultures of rodent primary neurons. A fast, robust and scalable process for micro-chip fabrication was developed in parallel to build micro-compartmented cultures. Coupling optical fibers to each micro-compartment allowed for the independent control of ChR2 activation in the different populations without crosstalk. By analyzing the post-stimuli activity across the different populations, we finally show how this platform can be used to evaluate quantitatively the effective connectivity between connected neuronal populations

Electrochemical Boron-Doped Diamond Film Microcells Micromachined with Femtosecond Laser: Application to the Determination of Water Framework Directive Metals

Planar electrochemical microcells were micromachined in a microcrystalline boron-doped diamond (BDD) thin layer using a femtosecond laser (Photo 1). The electrochemical performances of the new laser-machined BDD microcell were assessed by differential pulse anodic stripping voltammetry (DPASV) determinations, at nM level, of the four heavy metal ions of the European Water Framework Directive (WFD): Cd(II), Ni(II), Pb(II), Hg(II). The results are compared with those of previously published BDD electrodes [1]. The calculated detection limits are 0.4 nM, 6.8 nM and 5.5 nm 2.3 nM, and the linearities go up to 35nM, 97nM, 48nM and 5nM for respectively Cd(II), Ni(II) Pb(II) and Hg(II). The detection limits meet with the environmental quality standard of the WFD for three of the four metals. It was shown that the four heavy metals could be detected simultaneously, in the concentration ratio usually measured in sewage or runoff waters

Excursion Ardèche (13-15 mai 1977)

International audienceLes massifs hercyniens ont été longuement érodés pendant le Permien. Des sédiments gréseux et dolomitiques du Trias se sont ensuite déposés sur une plate-forme uniformisée et peu profonde. Toutefois la monotonie de l'ensemble n'excluait pas l'influence de reliefs sous-marins d'origine hercynienne. Les termes liasiques montrent à la fois une épaisseur réduite et des variations de faciès dues à une plate-forme sous-marine instable. Les influences obéissent d'une part à la direction cévenole (NE-SW) et d'autre part à une direction qui lui est orthogonale. A partir du Callovien les conditions deviennent homogènes dans l'ensemble de la région et paraissent le rester jusque dans le Jurassique terminal

Conception et émergence de processeurs neuronaux

Being able to harness the processing power of biological neurons will openthe door to ground breaking applications in many scientific fields. Glucosepoweredneural implants could repair or enhance cerebral functions in thefield of medicine, in vitro cognitive assays could foster drug screening in thepharmaceutical industry, and biological processors could lead to new kinds ofartificial intelligence.Any neuronal culture assigned with a computable function (actual or intended)can go under the name of a neuronal device. This thesis representsa multi-frontal effort towardsmaking this concept a more tangible thing, withoutholding to firmly onto preconceptions of what might and might not berelevant for computation. Our strategy is based on the exploitation of culturedneuronal networks’ properties that are both resilient and experimentally easilyaccessible rather than on the urge to reproduce the machinery of the brain.This seemingly naive engineering approach is disputable in the same waychance and necessity are in general disputable in biology. In spite of their mindbogglingcapabilities, one can argue that brains are the product of historicalcontingency and are therefore not necessarily optimal for the functions theysupport in vivo. This would be evenmore so the case for alternative functionsonly relevant to disembodied cultures.Whereas it might then be defendable to distance ourselves from naturalbrains, there are several benefits to the use of living components in the firstplace. Living cells have evolved to be energetically very efficient, they can repairthemselves and adapt to environmental changes. On a more fundamentallevel, in vitro discoveries, originating from the making and characterizationof neuronal devices, might be transposable to processes at play in vivo butdifficult to access ; such undertaking is therefore also relevant to the field ofneurosciences in general. Finally and most importantly, this work could help todefine the kind of computations that can be performed by neuronal assembliesand bring new elements to the field of artificial intelligence, which is bound tobe determinant in our future.La possibilité d'exploiter la puissance de calcul des neurones biologiques ouvrira la porte à des applications pionnières dans plusieurs champs scientifiques. Des implants neuronaux alimentés par le glucose pourraient réparer ou renforcer des fonctions cérébrales dans le domaine médical; des essais cognitifs in vitro pourraient permettre le criblage de remèdes dans l'industrie pharmaceutique. Enfin des processeurs biologiques pourraient conduire à de nouveaux types d'intelligence artificielle.On peut appeler dispositif neuronal toute culture de neurones affectée d'une fonction calculatoire. Cette thèse constitue un effort dans différentes directions pour rendre ce concept plus tangible, sans s'en tenir fermement à des idées préconçues sur ce qui pourrait être pertinent ou pas pour le calcul. Notre stratégie est basée sur l'exploitation des propriétés des réseaux de neurones en culture qui soient à la fois résilientes et facilement accessibles expérimentalement plutôt que sur la reproduction de la machinerie du cerveau.cette approche d'ingénieur en apparence naïve est discutable de la même façon que hasard et nécessité sont discutables en biologie de manière générale. En dépit de leurs faramineuses capacités, on peut défendre l'idée que le cerveau est le produit de contingences historiques et donc non nécessairement optimal pour les fonctions qu'il assure in vivo. Cela pourrait être encore plus le cas pour des fonctions alternatives seulement pertinentes dans le cas de cultures désincarnées.Alors qu'on pourrait défendre l'idée de se distancier du cerveau naturel, il y a de nombreux avantages à utiliser directement des éléments vivants. Les cellules vivantes ont évolué pour être énergétiquement très efficaces, elles peuvent se réparer elles mêmes et s'adapter aux changements d'environnement. A un niveau plus fondamental, les découvertes in vitro issues de la fabrication et de la caractérisation de dispositifs neuronaux pourraient être transposables à des processus en jeu in vivo mais difficiles à atteindre.Une telle entreprise fait donc sens dans le champ des neurosciences en général. Finalement, et de manière plus importante, ce travail pourrait contribuer à définir le genre de calcul qui pourrait être effectué par des assemblées de neurones et apporter des éléments nouveaux au domaine de l'intelligence artificielle, ce qui est voué à être déterminant dans l'avenir

Nature et subjectivité (l'énigme de l'homme chez Freud et Merleau-Ponty)

CLERMONT FD-BCIU Lettr./Sci.Hum. (631132101) / SudocLYON3-Bibliothèques (693872102) / SudocSudocFranceF

Monnaie fiduciaire, monnaie électronique et crypto-monnaies : La monnaie à l’heure du digital

International audienceDepuis 10 ans, de nouvelles formes de monnaies ont vu le jour : les cryptomonnaies, dont la plus connue est le bitcoin. Elles ne sont cependant ni la première forme de monnaie alternative, ni la première forme de monnaie digitale. Mais elles présentent des caractéristiques qui leur sont propres. Explication et comparaison par rapport aux autres formes de monnaies, fiduciaire ou électronique

Valeur d'usage d'une monnaie: Les cryptomonnaies peuvent-elles se substituer aux monnaies traditionnelles ?

International audienc

Memory decay and loss of criticality in quorum percolation

International audienceIn this paper, we present the effects of memory decay on a bootstrap percolation model applied to randomdirected graphs (quorum percolation). The addition of decay was motivated by its natural occurrence in physicalsystems previously described by percolation theory, such as cultured neuronal networks, where decay originatesfrom ionic leakage through the membrane of neurons and/or synaptic depression. Surprisingly, this featurealone appears to change the critical behavior of the percolation transition, where discontinuities are replacedby steep but finite slopes. Using different numerical approaches, we show evidence for this qualitative changeeven for very small decay values. In experiments where the steepest slopes can not be resolved and still appearas discontinuities, decay produces nonetheless a quantitative difference on the location of the apparent criticalpoint. We discuss how this shift impacts network connectivity previously estimated without considering decay.In addition to this particular example, we believe that other percolation models are worth reinvestigating, takinginto account similar sorts of memory decay