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Search Results: 1 - 10 of 21929 matches for " Jean-Sebastien Gagnon "
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Dark goo: Bulk viscosity as an alternative to dark energy
Jean-Sebastien Gagnon,Julien Lesgourgues
Physics , 2011, DOI: 10.1088/1475-7516/2011/09/026
Abstract: We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an "effective" pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a dark energy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a dark energy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local equilibrium today for viscous effects to be important.
Clues on chemical mechanisms from renormalizability: The example of a noisy cubic autocatalytic model
Jean-Sebastien Gagnon,Juan Perez-Mercader
Physics , 2015,
Abstract: We study the effect of noise on the renormalizability of a specific reaction-diffusion system of equations describing a cubic autocatalytic chemical reaction. The noise we are using is gaussian with power-law correlations in space, characterized by an amplitude $A$ and a noise exponent $y$. We show that changing the noise exponent is equivalent to the substitution $d_{s} \rightarrow d_{\rm eff} = d_{s} - y$ and thus modifies the divergence structure of loop integrals ($d_{s}$ is the dimension of space). The model is renormalizable at one-loop for $d_{\rm eff} < 6$ and nonrenormalizable for $d_{\rm eff} \geq 6$. The effects of noise-generated higher order interactions are discussed. In particular, we show how noise induces new interaction terms that can be interpreted as a manifestation of some (internal) "chemical mechanism". We also show how ideas of effective field theory can be applied to construct a more fundamental chemical model for this system.
Small-scale properties of a stochastic cubic-autocatalytic reaction-diffusion model
Jean-Sebastien Gagnon,David Hochberg,Juan Perez-Mercader
Physics , 2015, DOI: 10.1103/PhysRevE.92.042114
Abstract: We investigate the small-scale properties of a stochastic cubic-autocatalytic reaction-diffusion (CARD) model using renormalization techniques. We renormalize noise-induced ultraviolet divergences and obtain beta functions for the decay rate and coupling at one-loop. Assuming colored (power law) noise, our results show that the behavior of both decay rate and coupling with scale depends crucially on the noise exponent. Interpreting the CARD model as a proxy for a (very simple) living system, our results suggest that power law correlations in environmental fluctuations can both decrease or increase the growth of structures at smaller scales.
Luc Boltanski, On Critique: A Sociology of Emancipation.
Jean-Sebastien Guy
The Canadian Journal of Sociology , 2011,
Abstract: Book Review
Exact Multifractality for Disordered N-Flavour Dirac Fermions in Two Dimensions
Jean-Sebastien Caux
Physics , 1998, DOI: 10.1103/PhysRevLett.81.4196
Abstract: We present a nonperturbative calculation of all multifractal scaling exponents at strong disorder for critical wavefunctions of Dirac fermions interacting with a non-Abelian random vector potential in two dimensions. The results, valid for an arbitrary number of fermionic flavours, are obtained by deriving from Conformal Field Theory an effective Gaussian model for the wavefunction amplitudes and mapping to the thermodynamics of a single particle in a random potential. Our spectrum confirms that the wavefunctions remain delocalized in the presence of strong disorder.
GENIUS: Generating Usable User Interfaces
Jean-Sebastien Sottet,Alain Vagner
Computer Science , 2013,
Abstract: In this report we describe the implementation and approach developed during the GENIUS Project. The GENIUS project is about the generation of usable user interfaces. It tries to cope with issues related to automatic generation where, usually end-user complain about the poor quality (in term of usability) of generated UI. To solve this issue GENIUS relies on Model-Driven Engineering principles and several MDE tools. Notably, it consists in a set of metamodels specific to the interaction, a set of model transformation embedding usability criteria and an environment for model execution/ interpretation.
Spatial and Temporal Heterogeneities of Aedes albopictus Density in La Reunion Island: Rise and Weakness of Entomological Indices
Sebastien Boyer, Coralie Foray, Jean-Sebastien Dehecq
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0091170
Abstract: Following the 2006 Chikungunya disease in La Reunion, questions were raised concerning the monitoring survey of Aedes albopictus populations and the entomological indexes used to evaluate population abundance. The objectives of the present study were to determine reliable productivity indexes using a quantitative method to improve entomological surveys and mosquito control measures on Aedes albopictus. Between 2007 and 2011, 4 intervention districts, 24 cities, 990 areas and over 850,000 houses were used to fulfil those objectives. Four indexes including the classical Stegomyia index (House Index, Container Index, Breteau Index) plus an Infested Receptacle Index were studied in order to determine whether temporal (year, month, week) and/or spatial (districts, cities, areas) heterogeneities existed. Temporal variations have been observed with an increase of Ae. albopictus population density over the years, and a seasonality effect with a highest population during the hot and wet season. Spatial clustering was observed at several scales with an important autocorrelation at the area scale. Moreover, the combination among these results and the breeding site productivity obtained during these 5 years allowed us to propose recommendations to monitor Aedes albopictus by eliminating not the most finding sites but the most productive ones. As the other strategies failed in La Reunion, this new approach should should work better.
Exact mesoscopic correlation functions of the pairing model
Alexandre Faribault,Pasquale Calabrese,Jean-Sebastien Caux
Physics , 2007, DOI: 10.1103/PhysRevB.77.064503
Abstract: We study the static correlation functions of the Richardson pairing model (also known as the reduced or discrete-state BCS model) in the canonical ensemble. Making use of the Algebraic Bethe Ansatz formalism, we obtain exact expressions which are easily evaluated numerically for any value of the pairing strength up to large numbers of particles. We provide explicit results at half-filling and extensively discuss their finite-size scaling behavior.
Decay of superfluid currents in the interacting one-dimensional Bose gas
Alexander Yu. Cherny,Jean-Sebastien Caux,Joachim Brand
Physics , 2009, DOI: 10.1103/PhysRevA.80.043604
Abstract: We examine the superfluid properties of a 1D Bose gas in a ring trap based on the model of Lieb and Liniger. While the 1D Bose gas has nonclassical rotational inertia and exhibits quantization of velocities, the metastability of currents depends sensitively on the strength of interactions in the gas: the stronger the interactions, the faster the current decays. It is shown that the Landau critical velocity is zero in the thermodynamic limit due to the first supercurrent state, which has zero energy and finite probability of excitation. We calculate the energy dissipation rate of ring currents in the presence of weak defects, which should be observable on experimental time scales.
Biaxial spin-nematic phase of two dimensional disordered rotor models and spin-one bosons in optical lattices
Jean-Sebastien Bernier,K. Sengupta,Yong Baek Kim
Physics , 2005, DOI: 10.1103/PhysRevB.74.155124
Abstract: We show that the ground state of disordered rotor models with quadrupolar interactions can exhibit biaxial nematic ordering in the disorder-averaged sense. We present a mean-field analysis of the model and demonstrate that the biaxial phase is stable against small quantum fluctuations. We point out the possibility of experimental realization of such rotor models using ultracold spin-one Bose atoms in a spin-dependent and disordered optical lattice in the limit of a large number of atoms per site and also suggest an imaging experiment to detect the biaxial nematicity in such systems.
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