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Publications FYMA
Recherchez une publication dans la base de données FYMA en
entrant des mots clés (auteurs, année, titre, ...) dans la case suivante:
27 publications trouvées pour ' 2001'
UCL-IPT-01-19
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Auteurs:
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L. Vanhamme, A. Coron, Jean-Pierre Antoine, P. Van Hecke, S. Van Huffel
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Titre:
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A unifying interprezation of filtering approaches to water peak suppression in MRS
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Références:
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Proc. 9th Conf. Intern. Soc. of Magnetic Resonance in Medicine pp. 209; Glasgow, Scotland (2001)
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Résumé:
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UCL-IPT-01-18 : ( pdf)
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Auteurs:
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Radelet-de Grave, Patricia
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Titre:
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Le mouvement des projectiles d'après Galilée
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Références:
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Histoire et épistémologie dans l'éducation mathématique. IIIe Université d'été Européenne. Proceeding II (2001) pp.119-146
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Résumé:
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UCL-IPT-01-17
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Auteurs:
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Radelet-de Grave, Patricia (Ed.)
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Titre:
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Histoire et épistémologie dans l'éducation mathématique 'De la maternelle à l'université'
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Références:
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IIIe Université d'été européenne Proc. I + II
Louvain-la-Neuve 2001
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Résumé:
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UCL-IPT-01-13 : ( ps.gz)
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Auteurs:
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Bricmont Jean
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Titre:
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Bayes, Boltzmann and Bohm: Probabilities in physics
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Références:
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Chances in Physics - Foundations and Perspectives. Lecture Notes in Physics 574, pp. 3-21. Bricmont J., Dûrr D., Galavotti M.C., Ghirardi G., Petruccione F., Zanghi N. (Eds.), Springer-Verlag, Berlin et al., 2001
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Résumé:
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In this introductory essay I shall make some
remarks on the role of probabilities in physics, and
discuss some concrete examples illustrating Boltzmann's explanation
of approach to equilibrium.
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UCL-IPT-01-11
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Auteurs:
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Bricmont Jean, Dürr D., Galavotti M.C., Ghirardi G., ... (eds.)
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Titre:
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Chances in Physics - Foundations and Perspectives
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Références:
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Lecture Notes in Physics 574 (2001) pp. xii + 292
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Résumé:
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UCL-IPT-01-10
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Auteurs:
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R Terrier, L. Demanet, I.A. Grenier, Jean-Pierre Antoine
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Titre:
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Wavelet analysis of EGRET data
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Références:
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Proc. of ICRC 2001 (Int. Cosmic Ray Conf.) pp. 1-4 (2001)
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Résumé:
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UCL-IPT-01-09 : ( pdf)
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Auteurs:
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S. Mahieu and Philippe Ruelle
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Titre:
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Scaling fields in the two-dimensional abelian sandpile model
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Références:
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Physical Review E, volume 64, 066130-(1-19)
hep-th/0107150
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Résumé:
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We consider the isotropic two-dimensional abelian sandpile model from a perspective based on two-dimensional (conformal) field theory. We compute lattice correlation functions for various cluster variables (at and off criticality), from which we infer
the field-theoretic description in the scaling limit. We find a perfect agreement with the predictions of a c=-2 conformal field theory and its massive perturbation, thereby providing direct evidence for conformal invariance and more
generally for a description in terms of a local field theory. The question of the height 2 variable is also addressed, with however no definite conclusion yet.
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UCL-IPT-01-08 : ( ps.gz)
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Auteurs:
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A.J. Buras and Jean-Marc Gérard
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Titre:
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What is the $(\varepsilon'/\varepsilon)_\exp$ Telling Us ?
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Références:
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hep-ph/0106104
Physics Letters 517B (2001) pp. 129-134.
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Résumé:
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Nature might be kinder than previously thought as far as $\varepsilon'/\varepsilon$ is concerned. We show that the recently obtained experimental value for $\varepsilon'/\varepsilon$ does not require sizeable 1/N and isospin-breaking corrections. We propose to display the theoretical results for $\varepsilon'/\varepsilon$ in a $(P^{1/2},P^{3/2})$ plane in which the experimental result is represented by a $(\varepsilon'/\varepsilon)_\exp$-path. This sould allow to exhibit transparently the role of 1/N and isospin-breaking corrections in different calculations of $\varepsilon'/\varepsilon$. From now on theorists are allowed to walk only along this $(\varepsilon'/\varepsilon)_\exp$-path.
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UCL-IPT-01-07
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Auteurs:
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Jean-Pierre Antoine, A. Coron
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Titre:
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Time-frequency and time-scale approach to magnetic resonance spectroscopy
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Références:
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J. of Computational Methods in Science and Engineering, 1 (2001) 327-352
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Résumé:
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We review various applications of time-frequency and time-scale representations of signals in Magnetic Resonance Spectroscopy (MRS). First we give a brief survey of the mathematical tools, essentially the wavelet transform and the Gabor transform, both continuous and discrete. Then we turn to the applications and review the literature on signal correction and rephasing, solvent peak suppression, denoising, metabolite quantitation, etc. We conclude with some indications on available software.
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UCL-IPT-01-06 : ( ps.gz)
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Auteurs:
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Bricmont Jean, Kupiainen A., Schenkel A.
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Titre:
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Renormalization group and the Melnikov problem for PDE's
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Références:
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Communications in Mathematical Physics 221 (2001) pp. 101-140
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Résumé:
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We give a new proof of persistence of quasi-periodic, low dimensional
elliptic tori in infinite dimensional systems. The proof is based on a
renormalization group iteration that was developed recently in [BGK] to
address the standard KAM problem, namely, persistence of invariant
tori of maximal dimension in finite dimensional, near integrable systems.
Our result covers situations in which the so called normal frequencies
are multiple. In particular, it provides a new proof of the existence of
small-amplitude, quasi-periodic solutions of nonlinear wave equations
with periodic boundary conditions.
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UCL-IPT-00-23
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Auteurs:
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Radelet-de Grave, Patricia
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Titre:
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D'une édition à l'autre, l'influence de l'analyse sur la statique graphique de Culmann
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Références:
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Actes du Colloque Culmann ``Entre mécanique et Architecture II' pp. (to appear), Birkhaüser, Basel (2001)
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Résumé:
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UCL-IPT-00-22
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Auteurs:
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Radelet-de Grave, Patricia
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Titre:
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Nord géographique et nord magnétique
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Références:
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Histoire de la Mesure. Ordre des Géomètres-Experts (2001) 20-29
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Résumé:
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Pierre Le Pélerin, Christophe Colomb, Mercator, Simon Stevin, Edmund Halley, Daniel Bernoulli... A travers les siècles, les navigateurs, les géographes, les scientifiques ont contribué à la recherche et à la mesure du champ et de la déclinaison magnétiques.
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UCL-IPT-00-21 : ( ps.gz)
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Auteurs:
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G. Lopez Castro, Jean Pestieau, C. Smith, S. Trine
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Titre:
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Analytical behavior of positronium decay amplitudes
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Références:
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hep-ph/0006018 (2001) (in preparation)
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Résumé:
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Positronium annihilation amplitudes that are computed by assuming a factorization approximation with on-shell intermediate leptons do not exhibit good analytical behaviour. Using dispersion techniques, we find new contributions that interfere with the known results to restore analytical properties. Those new amplitudes which cannot be obtained using standard factorized amplitude formalism, contribute at ${\cal O}(\alpha^2)$. Therefore they have to be evaluated before any theoretical conclusion can be drawn upon the orthopositronium lifetime puzzle.
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UCL-IPT-00-18 : ( ps.gz)
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Auteurs:
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G. Lopez Castro, Jean Pestieau, C. Smith
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Titre:
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Binding energy corrections in positronium decays
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Références:
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hep-ph/0004209
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Résumé:
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Positronium annihilation amplitudes that are computed by assuming a factorization approximation with on-shell intermediate leptons, so not exhibit good analytical behavior. We propose an {\em ansatz} which allows to include binding energy corrections and obtain the correct analytical and gauge invariance behavior of these QED amplitudes. As a consequence of these non-perturbative corrections, the parapositronium and orthopositronium decay rates receive corrections of order $\alpha^4$ and $\alpha^2$, respectively. These new corrections for orthopositronium are relevant in view of a precise comparison between recent theoretical and experimental developments. Implications are point out for analogous decays of quarkonia.
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UCL-IPT-00-17 : ( ps.gz)
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Auteurs:
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Jean-Marc Gérard, Jacques Weyers
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Titre:
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Trace anomalies and the $\Delta I = {1\over 2}$ rule
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Références:
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Physics Letters B 503 (2001) 99-103
hep-ph/0011391 (revised January 31, 2001)
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Résumé:
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Trace Anomaly Dominance in weak $K$-decays successfully reproduces
the $\Delta I = {1\over 2}$ selection rule results, as observed in $K_S \to \pi\pi, K_L \to \pi\pi\pi, K_S \to \gamma\gamma$ and $K_L \to \pi^0 \gamma\gamma$.
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UCL-IPT-00-16 : ( ps.gz)
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Auteurs:
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M. Feuillat, J.L. Lucio M., Jean Pestieau
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Titre:
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Masses and widths of the $\rho^{\pm 0}$ (770)
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Références:
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Physics Letters B501 (2001) pp. 37-43
hep-ph/0010145
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Résumé:
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Isospin violation in the $\rho$(770) mass and width is considered within the $S$ matrix approach using combined fits to the $e^+e^- \to \pi^+\pi^-$ and $\tau^- \to \nu_\tau \pi^-\pi^0$ data performed by the ALEPH collaboration. We show that the pole position following from the parameters obtained from the ALEPH fits are not sensitive to the details of the parametrization. In this context, we have found that the pole mass difference and the pole width difference between the charged and neutral $\rho$ are consistent with zero. We show that a one loop calculation including vector, axial vector and pseudo-scalar mesons can satisfactorily describe the observed isospin breaking. We also give an estimate for the mass difference between the neutral and charged states of the $a_1$ (1260).
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UCL-IPT-00-10 : ( ps.gz)
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Auteurs:
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A. Coron, L. Vanhamme, Jean-Pierre Antoine, P. Van Hecke, S. Van Huffel
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Titre:
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The filtering approach to solvent peak suppression in MRS: a critical review
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Références:
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Journal of Magnetic Resonance 152 (2001) 26-40
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Résumé:
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Suppressing the solvent peak is important in many applications of biomedical NMR spectroscopy in order to quantify the metabolites with a great accuracy. Among the postprocessing methods proposed in the literature, many are dealing with the concept of filtering. However, several proposals lack a theoretical perspective and some
have not been explicitly applied to quantification problems. The present article is intended to bridge this gap: 5 methods are analysed from a theoretical perspective. Then, the different
methods are applied to the same set of data and then the latter
are quantified using the model fitting method AMARES. With our
set, the scheme proposed by T.~Sundin etal ({em J. Magn. Reson.}, 139(2):189--204, 1999) proved to be the most reliable method.
Keywords: Peak suppression, Quantitation, Filter, Time-frequency analysis
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UCL-IPT-00-09 : ( pdf)
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Auteurs:
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Jean Bricmont, A. Kupiainen and R. Lefevere
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Titre:
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Renormalizing the renormalization group pathologies
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Références:
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Physics Reports 348 (2001) pp. 5-31
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Résumé:
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We review the status of the ``pathologies' of the Renormalization Group (RG) encountered when one tries to define rigorously the RG transformation as a map between Hamiltonians. We explain their origin and clarify their status by relating them to the Griffiths' singularities appearing in disordered systems; moreover, we suggest that the best way to avoid those pathologies is to use the contour representation rather than the spin representation for lattice spin models at low temperatures. Finally, we outline how to implement the RG in the contour representation.
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UCL-IPT-00-08 : ( ps.gz)
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Auteurs:
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G. Lopez Castro, Jean Pestieau, Ch. Smith and S. Trine
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Titre:
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Parapositronium decay and dispersion relations
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Références:
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hep-ph/0006016 (2001) (in preparation)
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Résumé:
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Positronium decay rates are computed at the one-loop level, using convolution-type factorized amplitudes. The dynamics of this factorization is probed with dispersion relations, showing that unallowed approximations are usually made, and some ${\cal O}(\alpha^2)$ corrections missed. Further, we discuss the relevance of the Schrödinger wavefunction as the basis for perturbative calculations. Finally, we apply our formalism to the parapositronium two-photon decay.
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UCL-IPT-00-07
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Auteurs:
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Mélice J.L., Coron A., Berger A.
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Titre:
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Amplitude and frequency modulation of the Earth's obliquity for the last million years
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Références:
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Journal of Climate 14 pp. 1043-1054 (2001)
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Résumé:
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UCL-IPT-00-06 : ( ps.gz)
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Auteurs:
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S. Liénart, Philippe Ruelle and O. Verhoeven
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Titre:
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On Discrete Symmetries in $su(2)$ and $su(3)$ Affine Theories and
Related Graphs
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Références:
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Nuclear Physics B592 (2001) pp. 479-511
hep-th/0007095
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Résumé:
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We classify the possible finite symmetries of conformal field
theories with an affine Lie algebra $widehat{su}(2)$ and
$widehat{su}(3)$, and discuss the results from the perspective of
the graphs associated with the modular invariants. The highlights
of the analysis are first, that the symmetries we found in either
case are matched by the graph data in a perfect way in the case of
$su(2)$, but in a looser way for $su(3)$, and second, that some of
the graphs lead naturally to projective
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UCL-IPT-00-05 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, J-P Gazeau, J.R. Klauder, P. Monceau and K. Penson
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Titre:
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Temporally stable coherent states for infinite well and Pöschl-Teller potentials
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Références:
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Journal of Mathematical Physics 42 (2001) pp. 2349-2387
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Résumé:
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This paper is a direct illustration of a construction of coherent states which has been recently proposed by two of us (JPG and JK). We have chosen the example ot a particle trapped in an infinite square-well and also in Pöschl-Teller potentials of the trigonometric type. In the construction of the corresponding coherent states, we take advantage of the simplicity of the solutions, which ultimately stems from the fact they share a common $SU(1,1)$ symmetry {\it à la} Barut--Girardello. Many
properties of these states are then studied, both from mathematical and
from physical points of view.
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UCL-IPT-00-04 : ( pdf)
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Auteurs:
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Jean Bricmont, A. Kupiainen and R. Lefevere
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Titre:
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Ergodicity of the 2D Navier-Stokes equations with random forcing
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Références:
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Communications in Mathematical Physics 224 (2001) pp. 65-81
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Résumé:
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We consider the Navier-Stokes equation on a two dimensional torus
with a random force, acting at discrete times and analytic in
space, for arbitrarily small viscosity coefficient. We prove the
existence and uniqueness of the invariant measure for this system
as well as exponential mixing in time.
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UCL-IPT-99-12
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Auteurs:
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Jean-Pierre Antoine, C. Chauvin, A. Coron
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Titre:
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Wavelets and related time-frequency techniques in Magnetic Resonance Spectroscopy
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Références:
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NMR in Biomedicine 14 pp. 265-270 (2001)
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Résumé:
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We survey the various applications in MRS of the wavelet transform and related time-frequency methods. For the sake of completeness, we first quickly review the mathematical tools needed.
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UCL-IPT-99-08
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Auteurs:
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Jean-Marc Gérard, S. Pireaux
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Titre:
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The observable light deflection angle
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Références:
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Internal report (2001) (unpublished)
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Résumé:
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UCL-IPT-99-05 : ( ps.gz)
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Auteurs:
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E. Van Vyve, P. Vandergheynst, A. Goldberg, Jean-Pierre Antoine and I. Doghri
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Titre:
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Modelling and simulation of an impact test using wavelets, analytical and finite element models
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Références:
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International J. of Solids and Structure 38 (2001) 5481-5508
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Résumé:
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We discuss the results of several tests of instrumented falling weight impact in two cases, that of a rebound and that of a rupture in the sample. First we analyze the force signal by the continuous wavelet transform. This time-frequency method is able to locate precisely the moment of the rupture, if any, and also to detect the frequencies that are excited at the impact. In a second part, we perform a theoretical analysis of the event, both by an analytical method and by finite element modelling. These theoretical results confirm the experimental ones obtained in the first part.
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UCL-IPT-96-24 : ( pdf)
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Auteurs:
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Radelet-de Grave, Patricia
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Titre:
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Mathématique, architecture et mécanique à l'école de François d'Aguillon et de Grégoire de Saint-Vincent
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Références:
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Actes du Colloque Viola, Turin 1996, sous presse
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Résumé:
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Le but de cet article ne sera pas de suivre un thème scientifique précis mais au contraire, comme l'œuvre de Viola nous y invite, d'établir des liens et des recoupements entre différents types de travaux historiques. Il s'agit principalement de recoupements entre travaux d'historiens de l'art , d'historiens de la compagnie de Jésus et d'historiens des sciences.
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