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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:
28 publications trouvées pour ' 1999'
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-00-03 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Two-dimensional directional wavelets as a symmetry scanner
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Références:
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Contemporary Problems in Mathematical Physics (Proc. First
Int.Workshop, Cotonou, Bénin, Nov.1999), 2000, pp.47-60, J.Govaerts, M.N.Hounkonnou, W.A.Lester, Jr. (eds.)
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Résumé:
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The analysis of oriented features in images requires 2-D
directional wavelets, for instance, in standard tasks such as edge
detection or directional filtering. In addition, we present here a
new application, namely, a technique for determining all the
(statistical) symmetries of a given pattern with respect to
rotations and dilations. Examples are Penrose tilings,
mathematical quasicrystals or various quasiperiodic planar point
sets or patterns.
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UCL-IPT-00-02 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Coherent states, wavelets and beyond
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Références:
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Contemporary Problems in Mathematical Physics (Proc. First
Int.Workshop, Cotonou, Bénin, Nov.1999), 2000, pp.3-46, J.Govaerts, M.N.Hounkonnou, W.A.Lester, Jr. (eds.)
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Résumé:
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The first lecture describes classical coherent states (CS),
starting from the (canonical) harmonic oscillator CS, and
proceeding to the theory of Gilmore and Perelomov, who derive
CS from suitable (square integrable) group representations.
The second lecture is devoted to a highly successful example,
namely wavelets, which are simply the CS of the affine group
of the line (dilations and translations) or the similitude
group of the plane, for the 2-D case. In the third lecture,
we conclude with a far-reaching generalization of the
classical theory, namely CS associated with a group
representation which is square integrable only over a
homogeneous manifold of the group. This case, while
technically more involved, covers a whole family of groups
inaccessible to the standard Gilmore--Perelomov approach, and
among them, in particular, the relativity groups.
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UCL-IPT-
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Auteurs:
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Radelet Patricia
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Titre:
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Relativité galiléenne et lois de conservation
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Références:
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Revue des Questions scientifiques, tome 170, nr 3 (1999) pp. 209-261
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Résumé:
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UCL-IPT-
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Auteurs:
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Radelet Patricia
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Titre:
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Article : Maxwell
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Références:
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Dictionnaire du patrimoine littéraire européen, vol. 11, De Boeck Université (1999) pp. 152-161
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Résumé:
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UCL-IPT-99-16 : ( ps.gz)
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Auteurs:
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Jean Bricmont, A. Kupiainen and J. Taskinen
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Titre:
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Stability of Cahn-Hilliard fronts
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Références:
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Communications on Pure and Applied Mathematics 52 (1999) 839-871
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Résumé:
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We prove stability of the kink solution of the Cahn-Hilliard equation $\partial_t u = \partial_x^2 \bigl( - \partial_x^2 u - u /2 + u^3 / 2 \bigr),$ $x \in {\BbbR}$. The proof is based on an inductive Renormalization Group
method and we obtain detailed asymptotics of the solution as
$t\to\infty$.
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UCL-IPT-99-13 : ( pdf)
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Auteurs:
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Radelet Patricia
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Titre:
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Sur les lignes courbes qui sont propres à former les voûtes en dôme de Pierre Bouguer : jeu mathématique et enjeu pratique
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Références:
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Sciences et Techniques en Perspective, IIe série, 3 (1999) 397-421
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Résumé:
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UCL-IPT-99-10 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, L. Jacques, P. Vandergheynst
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Titre:
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Penrose tilings, quasicrystals, and wavelets
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Références:
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Wavelet Applications in Signal and Image Processing VII, pp. 28-39; Proc. SPIE, vol. 3813, 1999
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Résumé:
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The analysis of oriented features in images requires 2-D directional wavelets, for instance in standard tasks such as edge detection or directional filtering. In addition we present here a new application, namely a technique for determining all the (statistical) symmetries of a given pattern with respect to rotations and dilations. Examples are Penrose tilings, mathematical quasicrystals or various quasiperiodic planar point sets or patterns.
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UCL-IPT-99-06 : ( 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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Phases and Amplitudes in Inclusive $\Psi$ and $\Psi'$ Decays
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Références:
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Phys. Lett. B 462 (1999) pp. 324-328
hep-ph/9906357
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Résumé:
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In inclusive decays of the $\Psi$ (3097), electromagnetic and gluonic annihilation amplitudes add incoherently, namely they are 90$^\circ$ out of phase. We argue that this incoherence must persist in each exclusive decay channel. For inclusive $\Psi'$ (3686) decays, we suggest the absence of a significant direct annihilation amplitude into three gluons and propose a new amplitude via QCD anomalies and the $h_c$ (3526) off shell. Phenomenological implications for exclusive decay channels are pointed out.
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UCL-IPT-99-04 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, L. Jacques, R. Twarock
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Titre:
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Wavelet analysis of a quasiperiodic tiling with fivefold symmetry
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Références:
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Physics Letters A261 (1999) pp. 265-274
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Résumé:
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We determine all (statistical) rotation-dilation symmetries of a planar quasiperiodic tiling with fivefold symmetry, with a two-dimensional continuous wavelet transform, using a modified Cauchy wavelet and the scale-angle measure. The tiling is constructed via an affine extension of the Coxeter group $H_2$ and its statistical symmetries were unknown.
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UCL-IPT-99-02 : ( ps.gz)
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Auteurs:
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Philippe Ruelle
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Titre:
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Symmetric Boundary Conditions in Boundary Critical Phenomena
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Références:
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J. Phys. A: Math. Gen. 32 (1999) 8831-8850
hep-th/9904100
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Résumé:
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Conformally invariant boundary conditions for minimal models on a
cylinder are classified by pairs of Lie algebras $(A,G)$ of ADE
type. For each model, we consider the action of its (discrete)
symmetry group on the boundary conditions. We find that the
invariant ones correspond to the nodes in the product graph $A
imes G$ that are fixed by some automorphism. We proceed to
determine the charges of the fields in the various Hilbert spaces,
but, in a general minimal model, many consistent solutions occur.
In the unitary models $(A,A)$, we show that there is a unique
solution with the property that the ground state in each sector of
boundary conditions is invariant under the symmetry group. In
contrast, a solution with this property does not exist in the
unitary models of the series $(A,D)$ and $(A,E_6)$. A tempting
interpretation of this fact is that a certain (large) number of
invariant boundary conditions have unphysical (negative) classical
boundary Boltzmann weights. We give a tentative characterization
of the problematic boundary conditions.
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UCL-IPT-99- : ( pdf)
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Auteurs:
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Bricmont, Jean
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Titre:
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What is the meaning of the wave function ?
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Références:
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In: Fundamental interactions: from symmetries to black holes,
pp. 53-67, J.-M. Frère, M. Henneaux, A. Sevrin, Ph. Spindel (Eds.), Conference held on the occasion of the ``Eméritat'
of François Englert, Université Libre de Bruxelles, Brussels, 1999.
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Résumé:
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I will review the constraints that the no hidden variable theorems put on the interpretations of quantum mechanics and on the locality of the universe. I will also briefly explain how Bohm's theory gives a clear and objective meaning to the wave function and, at the same time, explains in the simplest possible way the most paradoxical aspects of quantum mechanics.
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UCL-IPT-98-22 : ( ps.gz)
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Auteurs:
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G. Lopez Castro, J.H Munoz, Jean Pestieau
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Titre:
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Mixing of two-level unstable systems
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Références:
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Eur.Phys.J. C9 (1999) pp.409-411
hep-ph/9805201
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Résumé:
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Unstable particles can be consistently described in the framework of quantum field theory. Starting from the full S-matrix amplitudes of $B^+ \to (2\pi, 3\pi)l^+ \nu$ decays as examples in the energy region where the $\rho-\omega$ resonances are dominating, we propose a prescription for the mixing of two quasi `physical' unstable states that differs from the one obtained from the diagonalization of the $M-i\Gamma/2$ non-hermitian hamiltonian. We discuss some important consequences for CP violation in the $K_L - K_S$ system.
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UCL-IPT-98-19 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, I. Mahara
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Titre:
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Galilean wavelets: Coherent states of the affine Galilei group
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Références:
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Journal of Mathematical Physics 40 (1999) pp. 5956-5971
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Résumé:
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We derive Galilean wavelets, by which we mean coherent states of the affine Galilei group, that is, the Galilei group extended by independent space and time dilations. The construction follows a general method based on square integrable group representations, possibly modulo a subgroup, i.e., on a homogeneous space of the underlying group. We also examine the restriction to the Schrödinger subgroup, which contains only dilations that leave invariant the Schrödinger and the heat equations.
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UCL-IPT-98-16 : ( ps.gz)
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Auteurs:
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R. Lefevere
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Titre:
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Weakly Gibbsian Measures and Quasilocality: a long range pair-interaction counterexample
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Références:
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J. Stat. Phys. 95 (1999) 785-789
preprint mp_arc 98-701
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Résumé:
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We exhibit an example of a measure on a discrete and finite spin system whose conditional probabilities are given in terms of an almost everywhere absolutely summable potential but are discontinuous almost everywhere.
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UCL-IPT-98-15 : ( ps.gz)
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Auteurs:
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R. Lefevere
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Titre:
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Variational Principle for Some Renormalized Measures
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Références:
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J. Stat. Phys. 96 (1999) 109-134
preprint mp_arc 98-613
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Résumé:
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We show that some measures suffering from the so-called
Renormalization Group pathologies satisfy a variational principle
and that the corrresponding limit of the pressure, with boundary
conditions in a set of measure 1, is proportional to the pressure
of the Ising model.
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UCL-IPT-98-14 : ( ps.gz)
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Auteurs:
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Jean Bricmont, K. Gawedzki, A. Kupiainen
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Titre:
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KAM Theorem and Quantum Field Theory
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Références:
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Communications in Mathematical Physics 201 (1999) 699-727
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Résumé:
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We give a new proof of the KAM theorem for analytic Hamiltonians. The proof is inspired by a quantum field theory formulation of the problem and is based on a renormalization group argument treating the small denominators inductively scale by scale. The crucial cancellations of resonances are shown to follow from the Ward identities expressing the translation invariance of the corresponding field theory.
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UCL-IPT-98-13 : ( ps.gz)
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Auteurs:
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D. Altschüler, Philippe Ruelle, E. Thiran
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Titre:
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On parity functions in conformal field theories
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Références:
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J. Phys. A: Math. Gen. 32 (1999) 3555-3570
hep-th/9808158
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Résumé:
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We examine general aspects of parity functions arising in rational conformal field theories, as a result of Galois theoretic properties of modular transformations. We focus more specifically on parity functions associated with affine Lie algebras, for which we give two efficient formulas. We investigate the consequences of these for the modular invariance problem.
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UCL-IPT-98-08 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, P. Vandergheynst
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Titre:
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Wavelets on the 2-sphere and related manifolds
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Références:
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Proc. Workshop on geometrical methods in physics (Bialowiecza, July 1997) - Reports on Mathematical Physics 43 (1999) pp. 13-24
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Résumé:
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We present a group theoretical derivation of the continuous wavelet transform (CWT) on the 2-sphere, based on the construction of coherent states associated to square integrable group representations. The parameter space X is the product of SO(3) X R^+_*, embedded into the Lorentz group SO(3,1) via the Iwasawa decomposition, and X = SO(3,1)/C. The space L^2(S^2) carries a unitary irreducible representation of SO(3,1) which is square integrable over X, and thus yields the wavelets on S^2 and the associated CWT.
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UCL-IPT-97-20 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Partial inner product spaces of analytic functions
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Références:
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Generalized Functions, Operator Theory and Dynamical Systems, Research Notes in Mathematics 399 (1999) pp. 26-47; I. Antoniou and G. Lumer (eds.) Chapman & Hall/CRC, Boca Raton, FL
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Résumé:
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UCL-IPT-97-18 : ( 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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Isospin Amplitudes and CP violation in $(B\to K \pi)$ Decays
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Références:
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Eur. Phys. J. C 7 (1999) pp. 1-3
hep-ph/9711469
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Résumé:
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We present a simple isospin invariant parametrization for $(B \to K\pi)$ decay amplitudes which consistently includes CP violation and (quasi-elastic) hadronic final states interactions. We find that the observed $(B \to K\pi)$ decays do not lead to a significant bound on the angle $\gamma$ of the unitarity triangle. On the other hand, we claim that a sizeable CP violation asymmetry in $(B^{\pm} \to K\pi^{\pm})$ rates is by no means excluded.
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UCL-IPT-97-17 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, P. Vandergheynst
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Titre:
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Wavelets on the 2-sphere: a group theoretical approach.
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Références:
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Applied and Computational Harmonic Analysis 7 (1999) pp. 262-291
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Résumé:
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We present a purely group-theoretical derivation of the continuous wavelet transform (CWT) on the 2-sphere $S^2$, based on the construction of general coherent states associated to square integrable group representations. The parameter space $X$ of our CWT, is the product of $SO_o(3,1)$ via the Iwasawa decomposition, so that $X \simeq SO_o(3,1)/N$, where $N \simeq \BC$. We select an appropriate unitary representation of $SO_o(3,1)$ acting in the space $L^2(S^2,d\mu)$ of finite energy signals on $S^2$. This representation is square integrable over $X$, thus it yields immediately the wavelets on $S^2$ and the associated CWT. We find a necessary condition for the admissibility of a wavelet, in the form of a zero mean condition. Finally, the Euclidean limit of this CWT on $S^2$ is obtained by redoing the construction on a sphere of radius $R$ and performing a group contraction for $R \to \infty$. Then the parameter space goes into the similitude group of $R^2$ and one recovers exactly the CWT on the plane, including the usual zero mean necessary condition for admissibility.
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UCL-IPT-97-16 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, F. Bagarello, C. Trapani
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Titre:
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Topological partial *-algebras: Basic properties and examples
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Références:
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Reviews in Mathematical Physics 11 (1999) pp. 267-302
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Résumé:
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Let $A$ be a partial *-algebra endowed with a topology $\tau$ that makes it into a locally convex topological vector space $A[ \tau]$. Then $A$ is called a topological partial *-algebra if it satisfies a number of conditions, which all amount to require that the topology $\tau$ fits with the multiplier structure of $A$. Besides the obvious cases of topological quasi *-algebras and CQ*-algebras, we examine several classes of potential topological partial *-algebras, either function spaces (lattices of $L^p$ spaces on $[0,1]$ or on $BR$, amalgam spaces), or partial *-algebras of operators (operators on a partial inner product space, $O$*-algebras).
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UCL-IPT-97-01 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, R. Murenzi, P. Vandergheynst
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Titre:
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Directional wavelets revisited: Cauchy wavelets and symmetry detection in patterns
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Références:
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Applied and Computational Harmonic Analysis 6 (1999) pp. 314-345
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Résumé:
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We introduce a new class of 2-D directional wavelets, called the Cauchy wavelets, strictly supported in a (narrow) convex cone in spatial frequency space. They have excellent angular selectivity, as shown by a standard calibration test and they have minimal uncertainty. As an application, we present a new technique for determining the symmetries of a given pattern with respect to rotations and dilation.
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UCL-IPT-96-15 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Wavelets in molecular and condensed-matter physics
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Références:
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Workshop on Spline Functions and the Theory of Wavelets (Montréal 1996) AMS, Providence, CRM Proceedings and Lecture Notes, vol. 18 (1999) pp. 245-259, S. Dubuc, G. Deslauriers (eds.)
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Résumé:
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UCL-IPT-95-29
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Auteurs:
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Patricia Radelet
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Titre:
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La composition des moments en mécanique, ou la querelle des
couples
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Références:
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Editeur: Colloque: Les enfants du siècle, sciences et
savants à l'époque romantique, Nantes octobre 1994
Sciences et Techniques en Perspective (1999) (to appear)
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Résumé:
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Cet article confronte les points de vues de Poinsot et de Poisson
à propos de la notion de couple. Le dernier, qui ne considère que
les composantes des forces n'en voit pas l'utilité. Le premier,
par contre, se montre fier d'introduire un nouvel objet
mathématique pour représenter ce couple. Il s'agit, dans notre
langage actuel, du vecteur axial (le moment). Poinsot l'introduit
parce qu'il concentre les propriétés du couple et surtout parce
qu'il a la propriété d'obéir à la même loi de composition que la
force elle-même, que le vecteur glissant dans notre langage.
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UCL-IPT-95-20 : ( ps.gz)
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Auteurs:
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G. Lopez Castro, J.L. Lucio M., Jean Pestieau
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Titre:
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Tests of flavor symmetry in $J/\psi$ decays
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Références:
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AIP Conf. Proceed., Proc. of CAM-94 (1st Physics Meeting of the Canadian, American and Mexican Physics Societies, Cancun, Mexico, Sept. 26-30, 1994), American Institute of Physics (1995), vol.342 (1999) pp. 441-448
hep-ph/9902300
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Résumé:
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We use $SU(3)$ flavor symmetry to analyze the $PP', VP$ and baryon-antibaryon decays of $J/\psi$. Both, the $SU(3)$-invariant and -violating contributions are considered. Particular attention is paid to the interference of the electromagnetic and strong amplitudes.
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UCL-IPT-94-20 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, A. Inoue, C. Trapani
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Titre:
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O*-dynamical systems and *-derivations of unbounded operator algebras
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Références:
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Mathematische Nachrichten vol 204 (1999) pp. 5-28
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Résumé:
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A spatial theory is developed for *-derivations of an algebra of unbounded operators, in terms of the concept of O*-dynamical systems. Three notions of spatiality emerge, depending on the nature of the corresponding generator. Special emphasis is put on O*-dynamical systems generated by one-paramater groups of *-automorphisms and their *-derivations.
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