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Search Results: 1 - 10 of 257 matches for " Beau Cronin "
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Sensory Adaptation and Short Term Plasticity as Bayesian Correction for a Changing Brain
Ian H. Stevenson,Beau Cronin,Mriganka Sur,Konrad P. Kording
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012436
Abstract: Neurons in the sensory system exhibit changes in excitability that unfold over many time scales. These fluctuations produce noise and could potentially lead to perceptual errors. However, to prevent such errors, postsynaptic neurons and synapses can adapt and counteract changes in the excitability of presynaptic neurons. Here we ask how neurons could optimally adapt to minimize the influence of changing presynaptic neural properties on their outputs. The resulting model, based on Bayesian inference, explains a range of physiological results from experiments which have measured the overall properties and detailed time-course of sensory tuning curve adaptation in the early visual cortex. We show how several experimentally measured short term plasticity phenomena can be understood as near-optimal solutions to this adaptation problem. This framework provides a link between high level computational problems, the properties of cortical neurons, and synaptic physiology.
Dynamics of orientation tuning in cat V1 neurons depend on location within layers and orientation maps
James Schummers,Beau Cronin,Klaus Wimmer,Marcel Stimberg,Robert Martin,Klaus Obermayer,Konrad Koerding,Mriganka Sur
Frontiers in Neuroscience , 2007, DOI: 10.3389/neuro.
Abstract: Analysis of the timecourse of the orientation tuning of responses in primary visual cortex (V1) can provide insight into the circuitry underlying tuning. Several studies have examined the temporal evolution of orientation selectivity in V1 neurons, but there is no consensus regarding the stability of orientation tuning properties over the timecourse of the response. We have used reverse-correlation analysis of the responses to dynamic grating stimuli to re-examine this issue in cat V1 neurons. We find that the preferred orientation and tuning curve shape are stable in the majority of neurons; however, more than forty percent of cells show a significant change in either preferred orientation or tuning width between early and late portions of the response. To examine the influence of the local cortical circuit connectivity, we analyzed the timecourse of responses as a function of receptive field type, laminar position, and orientation map position. Simple cells are more selective, and reach peak selectivity earlier, than complex cells. There are pronounced laminar differences in the timing of responses: middle layer cells respond faster, deep layer cells have prolonged response decay, and superficial cells are intermediate in timing. The average timing of neurons near and far from pinwheel centers is similar, but there is more variability in the timecourse of responses near pinwheel centers. This result was reproduced in an established network model of V1 operating in a regime of balanced excitatory and inhibitory recurrent connections, confirming previous results. Thus, response dynamics of cortical neurons reflect circuitry based on both vertical and horizontal location within cortical networks.
The second critical density and anisotropic generalised condensation
M. Beau
Condensed Matter Physics , 2010,
Abstract: In this letter we discuss the relevance of the 3D Perfect Bose gas (PBG) condensation in extremely elongated vessels for the study of anisotropic condensate coherence and the "quasi-condensate". To this end we analyze the case of exponentially anisotropic (van den Berg) boxes, when there are two critical densities ρc<ρm for a generalised Bose-Einstein Condensation (BEC). Here ρc is the standard critical density for the PBG. We consider three examples of anisotropic geometry: slabs, squared beams and "cigars" to demonstrate that the "quasi-condensate" which exists in domain ρc<ρ<ρm is in fact the van den Berg-Lewis-Pulé generalised condensation (vdBLP-GC) of the type III with no macroscopic occupation of any mode. We show that for the slab geometry the second critical density ρm is a threshold between quasi-two-dimensional (quasi-2D) condensate and the three dimensional (3D) regime when there is a coexistence of the "quasi-condensate" with the standard one-mode BEC. On the other hand, in the case of squared beams and "cigars" geometries, critical density ρm separates quasi-1D and 3D regimes. We calculate the value of the difference between ρc, ρm (and between corresponding critical temperatures Tm, Tc) to show that the observed space anisotropy of the condensate coherence can be described by a critical exponent γ(T) related to the anisotropic ODLRO. We compare our calculations with physical results for extremely elongated traps that manifest "quasi-condensate".
Probing High Parton Densities at Low-$x$ in d+Au Collisions at PHENIX Using the New Forward and Backward Muon Piston Calorimeters
Beau Meredith
Physics , 2009, DOI: 10.1016/j.nuclphysa.2009.10.109
Abstract: The new forward Muon Piston Calorimeters allow PHENIX to explore low-$x$ parton distributions in d+Au collisions with hopes of observing gluon saturation. We present a two-particle azimuthal $\Delta \phi$ correlation measurement made between a mid-rapidity particle ($|\eta_1| < 0.35$) and a forward $\pi^0$ ($3.1 < \eta_2 < 3.9$) wherein we compare correlation widths in d+Au to p+p and compute $I_{dA}$.
Scaling approach to existence of long cycles in Casimir boxes
Mathieu Beau
Physics , 2008, DOI: 10.1088/1751-8113/42/23/235204
Abstract: We analyse the concept of generalized Bose-Einstein condensation (g-BEC), known since 1982 for the perfect Bose gas (PBG) in the Casimir (or anisotropic) boxes. Our aim is to establish a relation between this phenomenon and two concepts: the concept of long cycles and the Off-Diagonal-Long-Range-Order (ODLRO), which are usually considered as some adequate way to describe the standard BEC on the ground state for the cubic boxes. First we show that these three criterions are equivalent in this latter case. Then, basing on a scaling approach, we revise formu- lation of these concepts to prove that the classification of the g-BEC into three types I,II,III, implies a hierarchy of long cycles (depending on their size scale) as well as a hierarchy of ODLRO which depends on the coherence length of the condensate.
Comment on higher derivative Lagrangians in relativistic theory
Mathieu Beau
Physics , 2013,
Abstract: We discuss the consequences of higher derivative Lagrangians of the form $\alpha_1 A_{\mu}(x)\dot{x}^\mu$, $\alpha_2 G_{\mu}(x)\ddot{x}^\mu$, $\alpha_3 B_{\mu}(x)\dddot{x}^\mu$, $\alpha_4 K_{\mu}(x)\ddddot{x}^\mu$, $\cdots$, $U_{(n)\mu}(x)x^{(n)\mu}$ in relativistic theory. After establishing the equations of the motion of particles in these fields, we introduce the concept of the generalized induction principle assuming the coupling between the higher fields $U_{(n),\mu}(x),\ n\geq1$ with the higher currents $j^{(n)\mu}=\rho(x)x^{(n)\mu}$, where $\rho(x)$ is the spatial density of mass or of electric charge. In addition, we discuss the analogy of the field $G_\mu(x)$ with the gravitational field and its inclusion in the general relativity framework in the last section. This letter is an invitation to reflect on a generalisation of the concept of inertia and we also discuss this problem in the last section.
Feynman Path Integral approach to electron diffraction for one and two slits, analytical results
Mathieu Beau
Physics , 2011, DOI: 10.1088/0143-0807/33/5/1023
Abstract: In this article we present an analytic solution of the famous problem of diffraction and interference of electrons through one and two slits (for simplicity, only the one-dimensional case is considered). In addition to exact formulas, we exhibit various approximations of the electron distribution which facilitate the interpretation of the results. Our derivation is based on the Feynman path integral formula and this work could therefore also serve as an interesting pedagogical introduction to Feynman's formulation of quantum mechanics for university students dealing with the foundations of quantum mechanics.
Théorie des champs des contraintes et déformations en relativité générale et expansion cosmologique: Theory of stress and strain fields in general relativity and cosmological expansion
Mathieu Beau
Physics , 2012,
Abstract: In this article we propose to add stress-energy tensor to the Einstein equations, assuming that the matter-energy and the metric space-time is nothing but a continuous medium with some elastic properties. We first give a general expression of the stress tensor which is linearly related to the strain tensor. Then, we give the particular expression of the stress tensor for a spatially homnogeneous and isotropic cosmological medium. After that we derive the modified Friedmann equations. In first approximation, we end up with the usual term $\Lambda g_{\mu\nu}$ , where the cosmological constant $\Lambda=K\varepsilon$ is related with the bulk modulus K and the relative variation of volume (dilatation). Then we derive corrections to the standard model in second approximation, which depend on these two new parameters.
Peirce's and Cohen's for Measures of Rater Reliability
Beau Abar,Eric Loken
Journal of Probability and Statistics , 2010, DOI: 10.1155/2010/480364
Abstract: This study examined a historical mixture model approach to the evaluation of ratings made in “gold standard” and two-rater contingency tables. Peirce's and the derived average were discussed in relation to a widely used index of reliability in the behavioral sciences, Cohen's . Sample size, population base rate of occurrence, the true “science of the method”, and guessing rates were manipulated across simulations. In “gold standard” situations, Peirce's tended to recover the true reliability of ratings as well as better than . In two-rater situations, ave tended to recover the true reliability as well as better than in most situations. The empirical utility and potential theoretical benefits of mixture model methods in estimating reliability are discussed, as are the associations between the statistics and other modern mixture model approaches. 1. Introduction In 1884, Peirce proposed an index of association, , for a 2 2 contingency table. Peirce’s index went beyond simple percent agreement, as a set of predictions can show substantial agreement with observed reality in situations when the predicted event rarely occurs. For example, by consistently predicting that a tornado will not occur [1, 2], a meteorologist could almost always be correct. Peirce derived a way to quantify what he called the “science of the method” [1] with his coefficient that predates even Pearson’s correlation coefficient of association [2]. To understand Peirce’s coefficient, suppose that a 2 2 contingency table with predictions and outcomes is constructed as follows: Peirce then defined i as In this derivation, agreement between the prediction and the outcome is considered a combination of events due to the science of the method employed to arrive at the prediction and chance agreement. In Peirce’s mixture, the science of the method refers to the predictions of a hypothetical “infallible observer,” who correctly makes predictions (i.e., according to science). The chance component is produced by a hypothetical completely “ignorant observer” [1] whose random predictions are sometimes correct and sometimes incorrect. Although Peirce’s has rarely been mentioned in the behavioral sciences [2, 3], it was “rediscovered and renamed” in the meteorological literature three times in the 20th century as the Hanssen-Kuipers discriminant, the Kuipers performance index, and the true skill statistic [4]. It currently serves as a popular measure of the precision and utility of a weather forecasting system [5]. The model was also proposed by Martín Andrés and Luna del Castillo [6] in the context
Georges Palante, un précurseur oublié de la Sociologie de l’individu .
Stéphane Beau
EspacesTemps.net , 2006,
Abstract: Depuis plusieurs années l’individu revient à la mode dans le domaine de la réflexion sociologique. Parmi les sociologues fran ais qui travaillent à redonner un sens à l’individualisme, nous notons les noms de Philippe Corcuff, Fran ois de Singly, Fran ois Dubet, Bernard Lahire … L’originalité de ce retour de l’individu réside pour l’essentiel dans le souhait affiché de dépasser l’opposition classique entre le holisme et l’individualisme méthodologique. Toutefois, une des principales faiblesses des défenseurs de l’actuelle sociologie de l’individu est d’oublier que la question individualiste n’est pas une question nouvelle dans le domaine de la sociologie, et qu’elle a déjà été posée dans le passé. Georges Palante (1862-1925) a été un des premiers à s’intéresser à la question individualiste. Dès les prémisses de la sociologie, il pose la question de la place de l’individu dans la société. Pour lui, la question individualiste est avant tout une question politique : l’émancipation collective n’a de sens que si elle passe par l’émancipation de chacun. Intimement persuadé qu’il existe entre l’individu et la société une antinomie irréductible, Palante nous invite à être vigilants sur plusieurs points. Tout d’abord sur le fait que l’opposition entre l’individu et la société (ou entre le holisme et l’individualisme méthodologique) est fondamentalement insoluble : c’est le principe même de lutte qui donne son sens à l’idée d’individu comme à celle de société. Ensuite, sur les risques de dérives utilitaristes de la sociologie officielle plus soucieuse de justifier la réalité que de l’expliquer. Enfin, sur la question de l’opposition entre l’individu et la masse , l’individu et le troupeau , zone d’ombre dans laquelle la réflexion sociologique n’est pas très à l’aise. Autant de questions sur lesquelles devront se pencher les chercheurs contemporains qui s’intéressent à la question individualiste . For several years, the notion of individual has become more important in the field of sociological thinking. Philippe Corcuff, Fran ois de Singly, Fran ois Dubet and Bernard Lahire are some of the French sociologists who have endeavoured to give more sense to the notion of individual. The growing importance of the place of the individual lies most of all in an unconcealed wish to go beyond the classic opposition between holism and methodological individualism. However, there is a weakness to the work of the defenders of the current theory about the individual. One of their weaknesses is that they have forgotten that the issue about individualism is not some
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