Generalized Toeplitz operators and cyclic vectors

We give in this paper some asymptotic Von Neumann inequalities for power bounded operators in the class C subrho intersection C sub 1. and some spacial von Neumann inequalities associated with non zero elements of the point spectrum, when it is non void, of generalized Toeplitz operators. Introducing perturbed kernel, we consider classes C sub R which extend the classical classes C subrho. We give results about absolute continuity with respect to the Haar measure for operators in class C sub R intersection C sub 1. This allows us to give new results on cyclic vectors for such operators and provides invariant subspaces for their powers. Relationships between cyclic vectors for T and T* involving generalized Toeplitz operators are given and the commutativity of left brace T right brace', the commutant of T is discussed

Preliminary Acoustic Study of 3D Localization of Buried Polyethylene Pipe

International audienceAcoustic waves are commonly used to locate buried polyethylene pipes. In this preliminary study we are particularly interested in pipes depth. To obtain depth information we are moving towards a multi-sensor solution. Several estimators are implemented and tested on real data. A depth estimator according to the relative delays between sensors is proposed. We compare two relative delays estimators : the method using the cross-correlation and the one using the coherence function. We will verify on real measurements that the second method is much more efficient than the first one. Before discussing the results we will present another approach which consists in adapting the MUSIC (MUltiple SIgnals Classification) algorithm to our problem

Information sharing and the stability of cooperation in research joint ventures*

The model studies information sharing and the stability of cooperation in cost reducing Research Joint Ventures (RJVs). In a three-stage game-theoretic framework, firms decide on participation in a RJV, information sharing along with R&D expenditures, and output. An important feature of the model is that voluntary information sharing between cooperating firms increases information leakage from the RJV to outsiders. It is found that RJVs representing a larger portion of firms in the industry are more likely to share information. It is also found that when sharing information is costless, firms generally don't choose intermediate levels of information sharing: they share all the information or none at all. The size of the RJV is found to depend on three effects: a coordination effect, an information sharing effect, and a competition effect. Depending on the relative magnitudes of these effects, the size of the RJV may increase or decrease with spillovers. In response to an increase in leakages, RJV members reduce their R&D spending. In addition, they either increase the RJV size while maintaining information sharing unchanged (when leakages are low), or they reduce both information sharing and RJV size (when leakages are high).Endogenous R&D Spillovers, Information Sharing, R&D Cooperation, Research Joint Ventures,