Adaptive beamforming for large arrays in satellite communications systems with dispersed coverage

Conventional multibeam satellite communications systems ensure coverage of wide areas through multiple fixed beams where all users inside a beam share the same bandwidth. We consider a new and more flexible system where each user is assigned his own beam, and the users can be very geographically dispersed. This is achieved through the use of a large direct radiating array (DRA) coupled with adaptive beamforming so as to reject interferences and to provide a maximal gain to the user of interest. New fast-converging adaptive beamforming algorithms are presented, which allow to obtain good signal to interference and noise ratio (SINR) with a number of snapshots much lower than the number of antennas in the array. These beamformers are evaluated on reference scenarios

On convergence of the auxiliary-vector beamformer with rank-deficient covariance matrices

The auxiliary-vector beamformer is an algorithm that generates iteratively a sequence of beamformers which, under the assumption of a positive definite covariance matrix R, converges to the minimum variance distortionless response beamformer, without resorting to any matrix inversion. In the case where R is rank-deficient, e.g., when R is substituted for the sample covariance matrix and the number of snapshots is less than the number of array elements, the behavior of the AV beamformer is not known theoretically. In this letter, we derive a new convergence result and show that the AV beamformer weights converge when R is rank-deficient, and that the limit belongs to the class of reduced-rank beamformers

Robust approaches to remote calibration of a transmitting array

We consider the problem of estimating the gains and phases of the RF channels of a M-element transmitting array, based on a calibration procedure where M orthogonal signals are sent through M orthogonal beams and received on a single antenna. The received data vector obeys a linear model of the type y ¼ AFg þ n where A is an unknown complex scalar accounting for propagation loss and g is the vector of unknown complex gains. In order to improve the performance of the least-squares (LS) estimator at low signal to noise ratio (SNR), we propose to exploit knowledge of the nominal value of g, viz g. Towards this end, two approaches are presented. First, a Bayesian approach is advocated where A and g are considered as random variables, with a non-informative prior distribution for A and a Gaussian prior distribution for g. The posterior distributions of the unknown random variables are derived and a Gibbs sampling strategy is presented that enables one to generate samples distributed according to these posterior distributions, leading to the minimum mean-square error (MMSE) estimator. A second approach consists in solving a constrained least-squares problem in which h ¼ Ag is constrained to be close to a scaled version of g. This second approach yields a closed-form solution, which amounts to a linear combination of g and the LS estimator. Numerical simulations show that the two new estimators significantly outperform the conventional LS estimator, especially at low SNR

Kiri A. de Vignolles`ile

http://tartu.ester.ee/record=b1863794~S1*es

The Limerick bubbly flow rig: design, performance, hold-up and mixing pattern

peer-reviewedAs Euler-Euler CFD simulations of bubbly flows suffer from uncertainties due to the many underpinning models, there is an obvious need of accurate experimental data for validation. With this in mind, a new bubbly flow test rig was built to be operated with and without liquid co-flow, with bubble size as uniform as possible in the range 4–7 mm, and with a very even horizontal bubble distribution. We designed the gas sparging system such that we can also produce an essentially bi-modal bubble size distribution. The column consists of two square sections to allow for studying the mixing of two originally separated bubbly flows with either the same or a different bubble size. The bubbles are produced from 2 × 196 needles, bubble sizes are determined with high-speed imaging and with a simple acoustical method, overall volume fractions in the column by means of air chamber pressure measurements. Overall volume fractions are presented as a function of gas and liquid flow rates, with slip velocity mostly increasing with increasing void fraction. First results are obtained on (a) producing bi-model bubble size distributions and the pertinent volume fractions in the column, and (b) flow patterns in the case of unequal aeration

Orthodontie sur parodonte réduit

Le patient adulte est de plus en plus demandeur de traitement orthodontique. Or le vieillissement induit des modifications physiologiques et pathologiques du parodonte, modifiant donc les conditions dans lesquelles la thérapeutique est envisagée. Ces traitements sont conduits pour des motifs esthétiques et fonctionnels sur des parodontes souvent réduits, c'est-à-dire non-inflammatoires avec des poches peu profondes. Les indications sont souvent la prothèse et le maintien ou l'obtention d'une situation parodontale pérenne. On cherche à rendre équilibrée, une nouvelle situation physiologique modifiée avec l'âge. La réalisation du traitement orthodontique dans ces conditions doit être adaptée : les principes biomécaniques doivent intégrer les forces légères et continues. Les dispositifs mis en place, utilisant des techniques récentes, sont adaptés selon la situation parodontale du patient, en privilégiant plus particulièrement les techniques fixes. Les résultats parodontaux obtenus sont favorables au niveau d'attache, tant que les conditions d'hygiène et biomécaniques sont suivies, évitant les conséquences délétères parodontales et dentaires.NANTES-BU Médecine pharmacie (441092101) / SudocPARIS-BIUM (751062103) / SudocLILLE2-UFR Odontologie (593502202) / SudocNANTES-Bib.Odontologie (441092219) / SudocSudocFranceF

La complémentarité stratégique entre grande entreprise et PME en matière d'innovation

Le rôle respectif joué d’une part par les grandes entreprises et, d’autre part, par les PME en matière d’innovation technologique fait l’objet de nombreuses controverses dans la littérature en sciences de gestion. Prolixe sur ce sujet, cette littérature s’est moins intéressée, jusqu’à une date récente, aux interrelations existantes entre firmes de toutes tailles dans le processus d’innovation. Les observations récentes concernant ces interrelations en particulier dans les nouvelles technologies permettent d’avancer qu’il existe en matière d’innovation technologique une complémentarité stratégique entre grandes firmes et PME. Dans une première partie, cet article met en évidence cette complémentarité stratégique entre grandes et petites entreprises dans les industries fondées sur la science (IFS). La troisième partie de cet article est consacrée aux implications de ces analyses en matière de « création » et de « diffusion » de l’innovation dans les IFSIn management literature the respective importance of big firms on the one hand and small and medium firms on the other is a highly controversial subject. While management literature has long proved verbose in this area, little attention has been paid, until recently, to the existing relations between firms of all sizes during the innovation process.Recent studies concerning such relations, particularly in respect of new technologies, lead us to the following conclusion: in the technological process there does indeed exist a strategic complementarity between big and small firms. The first part of this article concentrates on this complementarity. The second part analyses the characteristics and the dynamics of the strategic commplementarity between big and small firms in science-based industries. The third part of the article is devoted to the implications of this analysis concerning technological strategies and the production and distribution of innovations in science-based industries.El papel respectivo desarrollado por las grandes empresas y por otra parte por las PyME en materia de inovacion technologica es objecto de numerosas controversias en la literatura de ciencias de gestión.Esta literatura se interesa menos desde hace poco tiempo po las inter- relaciones que existen entre las empresas de cualquier dimension en el proceso de inovacion. Las recientes observaciones relativas a estas inter- relaciones, en particular en las nuevas tecnologias, permiten decir que en la inovacion existe una complementaridad estratégica entre las grandes y pequeñas empresas.En una primera parte, este articulo pone de relieve esta complementaridad. Una segunda parte define las características entre las grandes y pequeñas empresas en las industrias fundadas sobre la ciencia. La tercera parte de este articulo se interesa a las implicaciones de estos analisis que se aplican a la « creation » y la « difusión » de la inovacion en las industrias fundadas sobre la ciencia

Science-technologie et stratégies industrielles dans les pays en voie de développement : rôle des FMN et autres acteurs

Larue de Tournemine Régis. Science-technologie et stratégies industrielles dans les pays en voie de développement : rôle des FMN et autres acteurs. In: Tiers-Monde, tome 29, n°113, 1988. Multinationales et développement, sous la direction de Wladimir Andreff et Jean Masini. pp. 121-136