Mesure de température par pyrométrie 2D à bande spectrale et pyrométrie spectrale de métaux chauffés par laser dans un environnement fortement oxydant

La calibration et la validation de deux techniques de mesure de température complémentaires basées toutes les deux sur la pyrométrie optique (pyrométrie 2D monobande et pyrométrie spectrale), utilisables dans le cadre de l'étude des métaux chauffés dans des conditions hautement oxydantes et plus généralement au cours des procédés laser sur des métaux dans la gamme de température 2000-4000 K ont été réalisées. Une bonne correspondance des résultats des deux méthodes est obtenue lorsque l'émissivité de l'objet est connue et varie peu, mais seule la pyrométrie spectrale est performante lors de grandes variations d'émissivité, fournissant à la fois une mesure de température et d'émissivité au cours du procédé. Les incertitudes ont été calculées et représentent respectivement 6 et 3% dans une gamme de 1800 à 4500 K pour la pyrométrie 2D et la pyrométrie spectrale

Experiments with document archive size detection

The size of a document archive is a very important parameter for resource selection in distributed information retrieval systems. In this paper, we present a method for automatically detecting the size (ie the number of documents) of a document archive, in case the archive itself does not provide such information. In addition, a method for detecting incremental change of the archive size is also presented, which can be useful for deciding if a resource description has become obsolete and needs to be regenerated. An experimental evaluation of these methods shows that they provide quite acurate information

Semiclassical Analysis of the Wigner 12j12j Symbol with One Small Angular Momentum

We derive an asymptotic formula for the Wigner $12j$ symbol, in the limit of one small and 11 large angular momenta. There are two kinds of asymptotic formulas for the $12j$ symbol with one small angular momentum. We present the first kind of formula in this paper. Our derivation relies on the techniques developed in the semiclassical analysis of the Wigner $9j$ symbol [L. Yu and R. G. Littlejohn, Phys. Rev. A 83, 052114 (2011)], where we used a gauge-invariant form of the multicomponent WKB wave-functions to derive asymptotic formulas for the $9j$ symbol with small and large angular momenta. When applying the same technique to the $12j$ symbol in this paper, we find that the spinor is diagonalized in the direction of an intermediate angular momentum. In addition, we find that the geometry of the derived asymptotic formula for the $12j$ symbol is expressed in terms of the vector diagram for a $9j$ symbol. This illustrates a general geometric connection between asymptotic limits of the various $3nj$ symbols. This work contributes the first known asymptotic formula for the $12j$ symbol to the quantum theory of angular momentum, and serves as a basis for finding asymptotic formulas for the Wigner $15j$ symbol with two small angular momenta.Comment: 15 pages, 14 figure

Semiclassical Analysis of the Wigner 9J9J-Symbol with Small and Large Angular Momenta

We derive a new asymptotic formula for the Wigner $9j$-symbol, in the limit of one small and eight large angular momenta, using a novel gauge-invariant factorization for the asymptotic solution of a set of coupled wave equations. Our factorization eliminates the geometric phases completely, using gauge-invariant non-canonical coordinates, parallel transports of spinors, and quantum rotation matrices. Our derivation generalizes to higher $3nj$-symbols. We display without proof some new asymptotic formulas for the $12j$-symbol and the $15j$-symbol in the appendices. This work contributes a new asymptotic formula of the Wigner $9j$-symbol to the quantum theory of angular momentum, and serves as an example of a new general method for deriving asymptotic formulas for $3nj$-symbols.Comment: 18 pages, 16 figures. To appear in Phys. Rev.

Asymptotics of Wigner 3nj-symbols with Small and Large Angular Momenta: an Elementary Method

Yu and Littlejohn recently studied in arXiv:1104.1499 some asymptotics of Wigner symbols with some small and large angular momenta. They found that in this regime the essential information is captured by the geometry of a tetrahedron, and gave new formulae for 9j, 12j and 15j-symbols. We present here an alternative derivation which leads to a simpler formula, based on the use of the Ponzano-Regge formula for the relevant tetrahedron. The approach is generalized to Wigner 3nj-symbols with some large and small angular momenta, where more than one tetrahedron is needed, leading to new asymptotics for Wigner 3nj-symbols. As an illustration, we present 15j-symbols with one, two and four small angular momenta, and give an alternative formula to Yu's recent 15j-symbol with three small spins.Comment: 17 page