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Publications FYMA
Recherchez une publication dans la base de données FYMA en
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22 publications trouvées pour ' 2002'
UCL-IPT-05-15
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Auteurs:
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Radelet-de Grave Patricia (éd.)
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Titre:
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Symétries
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Références:
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Contributions au séminaire de Han-sur-Lesse, septembre 2002, Réminisciences 7, Turnhout, Brepols, 2005, 524 p.
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Résumé:
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UCL-IPT-05-14 : ( pdf)
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Auteurs:
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Radelet-de Grave Patricia
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Titre:
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Symétrie et peinture
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Références:
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Symétries, Contributions au séminaire de Han-sur-Lesse, septembre 2002, Réminisciences 7, P. Radelet-de Grave (éd.), Turnhout, Brepols, 2005, pp.385-424
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Résumé:
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UCL-IPT-03-02 : ( pdf)
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Auteurs:
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Jean Pestieau
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Titre:
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A remarkable relation in the gauge sector of electroweak dynamics
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Références:
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X Mexican School on Particles and Fields, Playa del Carmen, Mexico (2002)
hep-ph/0301139
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Résumé:
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A precise empirical relation between the electromagnetic coupling $\alpha(m_Z)$ and $\sin^2 (\theta^ell_{eff})$ --where $\theta^ell_{eff}$ is the effective electroweak mixing angle extracted from Z leptonic decays-- is made manifest: $\alpha(m_Z)$ =
$\sin^3 (\theta^ell_{eff})* \cos(\theta^\ell_{eff}}/(4\pi}$.
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UCL-IPT-02-17 : ( pdf)
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Auteurs:
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Bricmont, Jean
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Titre:
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Ergodicity and mixing for stochastic differential equations
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Références:
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Proceedings of the International Congress of Mathematicians, Beijing, August 20-28, vol. 1, (2002) pp. 567-585
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Résumé:
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Recently, a number of authors have investigated the conditions under which a stochastic perturbation acting on an infinite dimensional dynamical system, e.g. a partial differential equation
written as an infinite set of differential equations coupling the different
modes, makes the system ergodic and mixing. In particular, one is interested in finding minimal and physically natural conditions on the nature of the stochastic perturbation.
I shall review recent results on this question; in particular, I shall discuss the Navier-Stokes equation on a two dimensional torus with a random force which is white noise in time, and excites only a finite number of modes. The number of excited modes depends on the viscosity $nu$, and grows like $nu^{-3}$ when $nu$ goes to zero. As I shall explain, this Markov process has a unique invariant measure and is exponentially mixing in time.
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UCL-IPT-02-14 : ( ps.gz)
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Auteurs:
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Jean Pestieau, C. Smith
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Titre:
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A New Basis for QED Bound State Computations
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Références:
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hep-ph/0111380, Int. J. Mod. Phys. A17, 4113-4132
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Résumé:
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A simple method to compute QED bound state properties is presented, in which binding energy effects are treated non-perturbatively. It is shown that to take the effects of all ladder Coulomb photon exchanges into account, one can simply perform the derivative of standard QED amplitudes with respect to the external momentum. For example, the derivative of the light-by-light scattering amplitude gives an amplitude for orthopositronium decay to three photons where any number of Coulomb photon exchanges between the e^+ e^- is included.
Various applications are presented. From them, it is shown that binding energy must be treated non-perturbatively in order to preserve the analyticity of positronium decay amplitudes.
Interesting perspectives for quarkonium physics are briefly sketched.
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UCL-IPT-02-13 : ( ps.gz)
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Auteurs:
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Jean Pestieau, C. Smith
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Titre:
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Soft Photon Spectrum in Orthopositronium and Vector Quarkonium Decays
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Références:
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hep-ph/0111264, Phys. Lett. B524, 395-399
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Résumé:
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QED gauge invariance, when combined with analyticity, leads to constraints on the low energy end of the emitted photon spectra. This is known as Low's theorem. It is shown that the Ore-Powell result, as well as further developments for the orthopositronium differential decay rate, are in contradiction with Low's theorem, i.e. that their predicted soft photon spectra are incorrect.
A solution to this problem is presented. The implications for the orthopositronium lifetime puzzle, the charmonium \rho-\pi puzzle, the prompt photon spectrum in inclusive quarkonium decays and the extraction of \alpha_S from quarkonium annihilation rates are briefly ommented.
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UCL-IPT-02-12 : ( pdf)
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Auteurs:
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Escribano R., Gallegos A., Lucio M. J.L., Moreno G., Pestieau Jean
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Titre:
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On the mass, width and coupling constants of the f_0(980)
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Références:
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UAB-FT-524
April 2002
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Résumé:
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Using the pole approachwedetermine the mass and width of the
$f_0$(980), in particular we analyze the possibility that two nearbypoles
are associated to it. We restrict our analysis to a neighborhood of
the resonance, using $\pi\pi$ data for the phase shift and inelasticity, and
the invariant mass spectrum of the $J/\psi \to \phi\pi\pi, \phi K\bar K$ decays. The formalism weuse is based on unitarity and a generalized version of the Breit Wigner parameterization. We find that a single pole describes the $f_0$(980) leading to $m_{f_0}$ = 999$\pm$2 MeV ($m_{f_0}$ = 987$\pm$3 MeV) and $\Gamma_{f_0}$=39$\pm$8 MeV ($\Gamma_{f_0}=42$\pm$9 MeV) depending upon the $\pi\pi$
phase shift data used. As a byproduct values for the $g_{f_0\pi\pi}$ and $g_{f_0 K \bar K}$ coupling constants are obtained.
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UCL-IPT-02-08 : ( pdf)
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Auteurs:
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Kanfon A.D., Fufza A., Lambert D.
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Titre:
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Some examples of exponentially harmonic maps
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Références:
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Journal of Phys. A : Math. Gen 137977 (2002)
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Résumé:
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The aim of this paper is to study some examples of exponentially harmonic maps. We study such maps firstly on flat euclidean and Minkowski spaces and secondly on Friedmann-Lemaître universes. We also consider some new models of exponentially harmonic maps which are coupled with gravity which happen to be based on a generalization of the lagrangian for bosonic strings coupled with dilatonic field.
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UCL-IPT-02-07
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Auteurs:
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Radelet-de Grave Patricia
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Titre:
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Arthur Vierendeel (1852-1940), pour une architecture du fer
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Références:
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Towards a history of construction, Ed. A. Becchi, M. Corradi, F. Foce, O. Pedemonte (2002) pp. 417-135
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Résumé:
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UCL-IPT-02-05
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Auteurs:
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Radelet-de Grave, Patricia
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Titre:
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Les mathématiques au secours d'une solution magnétique de la longitude
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Références:
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it{Le calcul des longitudes, un enjeu pour les mathématiques, l'astronomie, la mesure du temps et la navigation}, pp. 203-233; Presses Universitaires de Rennes, Brest, 2002
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Résumé:
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UCL-IPT-02-04
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Auteurs:
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Jean-Pierre Antoine, L. Demanet, J-F. Hochedez, L. Jacques, R. Terrier, E. Verwichte
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Titre:
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Application of the 2-D wavelet transform to astrophysical images
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Références:
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Physicalia Magazine 24 (2002) pp. 93-116
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Résumé:
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UCL-IPT-02-03
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Auteurs:
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J-F. Hochedez, L. Jacques , A. Zhukov, F. Clette, Jean-Pierre Antoine
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Titre:
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Small features in the EIT-SOHO images
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Références:
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Proc. SOHO-11 Conference 'From Solar Min to Max: Half a Solar Cycle with SOHO' (March 2002, Davos, CH), pp. 295-298; ESA SP-508, (2002)
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Résumé:
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UCL-IPT-02-02 : ( pdf)
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Auteurs:
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Ruelle Philippe
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Titre:
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A c=-2 boundary changing operator for the Abelian sandpile model
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Références:
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Physics Letters B 539 (2002) 172-177
hep-th/0203105
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Résumé:
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We consider the unoriented two-dimensional Abelian sandpile model on the half-plane with open and closed boundary conditions. We show
that the operator effecting the change from closed to open, or from open to closed, is a boundary primary field of weight $-1/8$, belonging to a
$c=-2$ logarithmic conformal field theory.
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UCL-IPT-02-01 : ( pdf)
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Auteurs:
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Ruelle Philippe and Verhoeven O.
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Titre:
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Non periodic Ishibashi states: the su(2) and su(3) affine theories
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Références:
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Nuclear Physics B 633 (2002) 345-364
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Résumé:
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We consider the su(2) and su(3) affine theories on a cylinder, from the point of view of their discrete internal symmetries. To this end, we adapt the usual treatment of boundary conditions leading to the Cardy equation to take the symmetry group into account. In this context, the role of the Ishibashi states from all (non periodic) bulk sectors is emphasized. This formalism is then applied to the su(2) and su(3) models, for which we determine the action of the symmetry group on the boundary conditions, and we compute the twisted partition functions. Most if not all data relevant to the symmetry properties of a specific model are hidden in the graphs associated with its partition function, and their subgraphs. A synoptic table is provided that summarizes the many connections between the graphs and the symmetry data that are to be expected in general.
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UCL-IPT-01-20
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Auteurs:
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Pestieau Jean, Smith C. and Trine S.
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Titre:
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Positronium decay: Gauge invariance and analyticity
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Références:
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International Journal of Modern Physics A17 (2002) 1355-
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Résumé:
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UCL-IPT-01-16
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Auteurs:
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Füfza A., Gérard Jean-Marc, Lambert D.
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Titre:
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The Lemaître-Schwarzschild problem revisited
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Références:
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General Relativity and Gravitation 34 (2002) 1411-1422
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Résumé:
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UCL-IPT-01-14
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Auteurs:
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Gérard Jean-Marc and Wiaux Y.
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Titre:
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Gravitational dipole radiations from binary systems
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Références:
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Physical Review D 66 (2002)
gr-qc/0109062
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Résumé:
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We investigate the possibility of generating sizeable dipole radiations in relativistic theories of gravity. Optimal parameters to observe their effects through the orbital period decay of binary star systems are discussed. Constraints on gravitational couplings beyond general relativity are derived.
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UCL-IPT-01-12
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Auteurs:
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Ngakeu F., Majid S., Lambert D.
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Titre:
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Noncommutative Riemannian geometry of the alternating group A_4
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Références:
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Journal of Geometry and Physics 42 (2002) 259-282
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Résumé:
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We study the noncommutative Riemannian geometry of the alternating group $A_4 = Z_2 \times Z_2) \rtimes Z_3$ using the recent formulation for finite groups. We find a unique `Levi-Civita' connection for the invariant metric, and find that it has Ricci-flat but nonzero Riemann curvature. We show that it is the unique Ricci-flat connection on A_4 with the standard framing (we solve the vacuum Einstein's equation). We also propose a natural Dirac operator for the associated spin connection and solve the Dirac equation. Some of our results hold for any finite group equipped with a cyclic conjugacy class of 4 elements. In this case the exterior algebra $\Omega (A_4)$ has dimensions 1 : 4 : 8 : 11 : 12 :12 : 11 : 8 : 4 : 1 with top-form 9-dimensional. We also find the noncommutative cohomology $H^1 (A_4) = C$.
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UCL-IPT-01-03 : ( pdf)
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Auteurs:
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Bricmont Jean, Kupiainen A., Lefevere R.
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Titre:
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Exponential Mixing of the 2D Stochastic Navier-Stokes Dynamics
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Références:
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Communications in Mathematical Physics 230 (2002) pp. 87-132
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Résumé:
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We consider the Navier-Stokes equation on a two dimensional torus with a random force which is white noise in time, and excites only
a finite number of modes. The number of excited modes depends on the viscosity nu, and grows like nu^{-3} when nu goes to zero. We prove that this Markov process
has a unique invariant measure and is exponentially mixing in time.
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UCL-IPT-00-19
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Auteurs:
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Jean-Pierre Antoine, F. Bagarello
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Titre:
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Localization properties and wavelet-like orthonormal bases for the lowest Landau level
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Références:
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Advances in Gabor Analysis pp. 221-257; H.G. Feichtinger and T. Strohmer, Birkhaüser, Boston-Basel-Berlin, 2002
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Résumé:
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UCL-IPT-00-15 : ( pdf)
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Auteurs:
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Jean-Pierre Antoine, L. Demanet, L. Jacques and P. Vandergheynst
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Titre:
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Wavelets on the sphere : Implementation and approximations
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Références:
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Applied and Computational Harmonic Analysis 13 (2002) pp. 177-200
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Résumé:
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We continue the analysis of the continuous wavelet transform on the
2-sphere, introduced in a previous paper. After a brief review of the
transform, we present a calculation method for data given on a regular
spherical grid $\mathcal{G}$. This technique, which uses the FFT, is based on the invariance of $\mathcal{G}$ under discrete rotations around the $z$ axis preserving the $\varphi$ sampling. Next, a numerical criterion is
given for controlling the scale interval where the spherical wavelet transform makes sense, and examples are given, both academic and realistic.
In a second part, we establish conditions under which the reconstruction formula holds in strong $L^2$ sense. This opens the door to techniques for approximating functions on the sphere, by use of an approximate identity, obtained by a suitable dilation of the mother wavelet.
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UCL-IPT-99-11
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Auteurs:
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Gobbers J-F., Vandergheynst P.
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Titre:
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Directional wavelet frames : design and algorithms
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Références:
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IEEE Transactions on Signal Processing 11 (2002) pp. 363-372
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Résumé:
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