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Search Results: 1 - 10 of 6269 matches for " Vincent Achard "
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Double-tag events study with the L3 detector at sqrt(s)=189 GeV
Pablo Achard
Physics , 1999, DOI: 10.1016/S0920-5632(00)00133-X
Abstract: A preliminary study of double tag events using the L3 detector at center of mass energy sqrt{s}=189 GeV has been performed. The cross-section of gamma* gamma* collisions is measured at average =14.5 GeV2. The results are in agreement with predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data. The measurements lie below the LO and above the NLO BFKL calculations.
Inclusive pi0 and K0s in gamma-gamma at L3
Pablo Achard
Physics , 2000,
Abstract: The ee -> ee+pi0+X and ee -> ee+K0s+X reactions are studied at LEP using data collected with the L3 detector at sqrt{s}=189-202 GeV. Preliminary results for the differential cross section dsigma/dpt in the transverse momentum range 0.2 GeV < pt < 7.5 GeV at central values of pseudo-rapidity, |eta| < 0.5 or |eta| < 1.5, and the differential cross section dsigma/d|eta| for different values of pt are presented. For pt le 1 GeV, the pt -dependence of the data are well described by an exponential fit. For pt > 1 GeV the cross sections are compared to NLO QCD calculations and to LO Monte Carlo predictions.
A quadratic measure of dependence
Sophie Achard
Mathematics , 2006,
Abstract: Asymptotic properties of a dimension-robust dependence measure are investigated. It is related to those used in independence tests, but is derivable, thus suitable for independent component analysis. An adjustable kernel allows to accelerate the convergence of the estimator without affecting the bias.
Photonic nano-structures on (111) oriented diamond
Elke Neu,Patrick Appel,Marc Ganzhorn,Javier Miguel-Sanchez,Margarita Lesik,Vianney Mille,Vincent Jacques,Alexandre Tallaire,Jocelyn Achard,Patrick Maletinsky
Physics , 2014, DOI: 10.1063/1.4871580
Abstract: We demonstrate the fabrication of single-crystalline diamond nanopillars on a (111)-oriented chemical vapor deposited diamond substrate. This crystal orientation offers optimal coupling of nitrogen-vacancy (NV) center emission to the nanopillar mode and is thus advantageous over previous approaches. We characterize single native NV centers in these nanopillars and find one of the highest reported saturated fluorescence count rates in single crystalline diamond in excess of 10${}^6$ counts per second. We show that our nano-fabrication procedure conserves the preferential alignment as well as the spin coherence of the NVs in our structures. Our results will enable a new generation of highly sensitive probes for NV magnetometry and pave the way toward photonic crystals with optimal orientation of the NV center's emission dipole.
Efficiency and Cost of Economical Brain Functional Networks
Sophie Achard,Ed Bullmore
PLOS Computational Biology , 2007, DOI: 10.1371/journal.pcbi.0030017
Abstract: Brain anatomical networks are sparse, complex, and have economical small-world properties. We investigated the efficiency and cost of human brain functional networks measured using functional magnetic resonance imaging (fMRI) in a factorial design: two groups of healthy old (N = 11; mean age = 66.5 years) and healthy young (N = 15; mean age = 24.7 years) volunteers were each scanned twice in a no-task or “resting” state following placebo or a single dose of a dopamine receptor antagonist (sulpiride 400 mg). Functional connectivity between 90 cortical and subcortical regions was estimated by wavelet correlation analysis, in the frequency interval 0.06–0.11 Hz, and thresholded to construct undirected graphs. These brain functional networks were small-world and economical in the sense of providing high global and local efficiency of parallel information processing for low connection cost. Efficiency was reduced disproportionately to cost in older people, and the detrimental effects of age on efficiency were localised to frontal and temporal cortical and subcortical regions. Dopamine antagonism also impaired global and local efficiency of the network, but this effect was differentially localised and did not interact with the effect of age. Brain functional networks have economical small-world properties—supporting efficient parallel information transfer at relatively low cost—which are differently impaired by normal aging and pharmacological blockade of dopamine transmission.
Conscience et devoilement de la verité. Modus & Dictum dans Verité de Zola
Guy Achard-Bayle
Studi Linguistici e Filologici Online , 2006,
Abstract: In the first part of this paper, I analyze the arguments of last D. Cohn’s essay (The Distinction of Fiction, 1999, French translation 2001) on the logic of fiction and fictionality: the deal is to find formal and more precisely linguistic marks which allow to distinguish fictional vs historical narratives. In a second part, I study and I try to apply this model to Zola’s novel: Vérité (Truth). In this novel, which is the last in Zola’s works, and which reproduces the Dreyfus case, the problem the novelist must face is to conciliate the “documentary” -or the historical truth with his naturalist esthetics which favors indirect free speech -or what D. Cohn (op. cit.) calls the “mental quotations”.
Analyse de Texte et ordinateur. L'écriture réinventée ?
Guy Achard-Bayle
ALSIC : Apprentissage des Langues et Systèmes d'Information et de Communication , 1999,
Abstract: Cet article analyse un livre ou un document. This article reviews a book or document.
Complex Parameter Landscape for a Complex Neuron Model
Pablo Achard,Erik De Schutter
PLOS Computational Biology , 2006, DOI: 10.1371/journal.pcbi.0020094
Abstract: The electrical activity of a neuron is strongly dependent on the ionic channels present in its membrane. Modifying the maximal conductances from these channels can have a dramatic impact on neuron behavior. But the effect of such modifications can also be cancelled out by compensatory mechanisms among different channels. We used an evolution strategy with a fitness function based on phase-plane analysis to obtain 20 very different computational models of the cerebellar Purkinje cell. All these models produced very similar outputs to current injections, including tiny details of the complex firing pattern. These models were not completely isolated in the parameter space, but neither did they belong to a large continuum of good models that would exist if weak compensations between channels were sufficient. The parameter landscape of good models can best be described as a set of loosely connected hyperplanes. Our method is efficient in finding good models in this complex landscape. Unraveling the landscape is an important step towards the understanding of functional homeostasis of neurons.
Multivariate wavelet Whittle estimation in long-range dependence
Sophie Achard,Irène Gannaz
Statistics , 2014,
Abstract: Multivariate processes with long-range dependent properties are found in a large number of applications including finance, geophysics and neuroscience. For real data applications, the correlation between time series is crucial. Usual estimations of correlation can be highly biased due to phase-shifts caused by the differences in the properties of autocorrelation in the processes. To address this issue, we introduce a semiparametric estimation of multivariate long-range dependent processes. The parameters of interest in the model are the vector of the long-range dependence parameters and the long-run covariance matrix, also called functional connectivity in neuroscience. This matrix characterizes coupling between time series. The proposed multivariate wavelet-based Whittle estimation is shown to be consistent for the estimation of both the long-range dependence and the covariance matrix and to encompass both stationary and nonstationary processes. A simulation study and a real data example are presented to illustrate the finite sample behaviour.
The Intensity of IUGR-Induced Transcriptome Deregulations Is Inversely Correlated with the Onset of Organ Function in a Rat Model
Daniel Vaiman, Géraldine Gascoin-Lachambre, Farid Boubred, Fran?oise Mondon, Jean-Marc Feuerstein, Isabelle Ligi, Isabelle Grandvuillemin, Sandrine Barbaux, Eric Ghigo, Vincent Achard, Umberto Simeoni, Christophe Buffat
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0021222
Abstract: A low-protein diet applied during pregnancy in the rat results in intrauterine growth restricted (IUGR) fetuses. In humans, IUGR is associated with increased perinatal morbidity, higher incidence of neuro-developmental defects and increased risk of adult metabolic anomalies, such as diabetes and cardiovascular disease. Development and function of many organs are affected by environmental conditions such as those inducing fetal and early postnatal growth restriction. This phenomenon, termed “fetal programming” has been studied unconnectedly in some organs, but very few studies (if any) have investigated at the same time several organs, on a more comparative basis. However, it is quite probable that IUGR affects differentially most organ systems, with possible persistent changes in gene expression. In this study we address transcriptional alterations induced by IUGR in a multi-organ perspective, by systematic analysis of 20-days rat fetuses. We show that (1) expressional alterations are apparently stronger in organs functioning late in foetal or postnatal life than in organs that are functioning early (2) hierarchical classification of the deregulations put together kidney and placenta in one cluster, liver, lungs and heart in another; (3) the epigenetic machinery is set up especially in the placenta, while its alterations are rather mild in other organs; (4) the genes appear deregulated in chromosome clusters; (5) the altered expression cascades varies from organ to organ, with noticeably a very significant modification of the complement and coagulation cascades in the kidney; (6) we found a significant increase in TF binding site for HNF4 proteins specifically for liver genes that are down-regulated in IUGR, suggesting that this decrease is achieved through the action of HNF transcription factors, that are themselves transcriptionnally induced in the liver by IUGR (x 1.84 fold). Altogether, our study suggests that a combination of tissue-specific mechanisms contributes to bring about tissue-driven modifications of gene cascades. The question of these cascades being activated to adapt the organ to harsh environmental condition, or as an endpoint consequence is still raised.
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