Recombination Models

We review the current status of recombination and coalescence models that have been successfully applied to describe hadronization in heavy ion collisions at RHIC energies. Basic concepts as well as actual implementations of the idea are discussed. We try to evaluate where we stand in our understanding at the moment and what remains to be done in the future.Comment: Plenary Talk at Quark Matter 2004, submitted to J. Phys. G, 8 pages, 3 figure

Pade-Improvement of QCD Running Coupling Constants, Running Masses, Higgs Decay Rates, and Scalar Channel Sum Rules

We discuss Pad\'e-improvement of known four-loop order results based upon an asymptotic three-parameter error formula for Pad\'e-approximants. We derive an explicit formula estimating the next-order coefficient $R_4$ from the previous coefficients in a series $1+R_1 x + R_2x^2 + R_3x^3$. We show that such an estimate is within 0.18% of the known five-loop order term in the O(1) $\beta$-function, and within 10% of the known five-loop term in the O(1) anomalous mass-dimension function $\gamma_m(g)$. We apply the same formula to generate a [2$|$2] Pad\'e-summation of the QCD $\beta$-function and anomalous mass dimension in order to demonstrate both the relative insensitivity of the evolution of $\alpha_s(\mu)$ and the running quark masses to higher order corrections, as well as a somewhat increased compatibility of the present empirical range for $\alpha_s(m_\tau)$ with the range anticipated via evolution from the present empirical range for $\alpha_s(M_z)$. For $3 \leq n_f \leq 6$ we demonstrate that positive zeros of any [2$|$2] Pad\'e-summation estimate of the all-orders $\beta$-function which incorporates known two-, three-, and four-loop contributions necessarily correspond to ultraviolet fixed points, regardless of the unknown five-loop term. Pad\'e-improvement of higher-order perturbative expressions is presented for the decay rates of the Higgs into two gluons and into a $b \bar{b}$ pair, and is used to show the relative insensitivity of these rates to higher order effects. However, Pad\'e-improvement of the purely-perturbative component of scalar/pseudoscalar current correlation functions is indicative of large theoretical uncertainties in QCD sum rules for these channels, particularly if the continuum-threshold parameter $s_0$ is near 1 GeV$^2$.Comment: latex, 22 pages, 8 figures, references correcte

MODÉLISATION DE L'INTELLIGIBILITÉ ET SONORISATION DU STADE OLYMPIQUE DE MONTRÉAL

In addition to mechanical background noise, whose influence has been demonstrated by measurements of the RASTI Index, and which is a function of the location in the stands, the initial reverberation time EDT was measured at different points in the stadium, taking into account the relative positions of the source and receiver. Parallel research, carried out in a large room with homogeneous initial reverberation time, showed that the decreasing of temporal rate of decay of acoustical pressure could be measured in the very first decibels (EDT-5 dB permitting a better correlation with the RASTI index than EDT-10 or -15) ; the RASTI index could then be modelled from the in-situ measurements of the EDT, for a future source of known directivity and location.Afin de disposer d'une procédure de modélisation convenable de l'intelligibilité pour le nouveau système de sonorisation du Stade Olympique de Montréal, une recherche complémentaire a été entreprise, pour mette en évidence l'influence du temps de réverbération initial EDT et de la directivité de la source, sur l'indice RASTI mesuré. En tenant compte de la situation acoustique complexe de cette vaste enceinte, on est arrivé à bâtir un modèle informatique susceptible de reproduire convenablement l'intelligibilité existante ou projetée

L'utilisation des mesures intensimétriques en acoustique des salles

The intensity measurement technics in architectural acoustics have been developed since the early 1980's. Its utilization has mainly been directed towards the solution of noise transmission or sound isolation problems to analyse the radiation of partition with or without opening and, in some more specialized absorption measurements. As far as the acoustics related to concert halls, the impulse response analysis continues to be the predominant measurement method, since the intensity measurement technics are not very compatible with the time analysis. However, different experiments of data gathering, recorded either in a tightly controlled directional mode or in a omnidirectional mode using a robot or a tridimensional probe, have been reported in concert halls and auditoriums. This paper reviews some of these experiments and presents more recent measurements made in concert halls, showing different technics of reflection analysis as well as a propagation summary at different points of location