Spectral analysis of stationary random bivariate signals

A novel approach towards the spectral analysis of stationary random bivariate signals is proposed. Using the Quaternion Fourier Transform, we introduce a quaternion-valued spectral representation of random bivariate signals seen as complex-valued sequences. This makes possible the definition of a scalar quaternion-valued spectral density for bivariate signals. This spectral density can be meaningfully interpreted in terms of frequency-dependent polarization attributes. A natural decomposition of any random bivariate signal in terms of unpolarized and polarized components is introduced. Nonparametric spectral density estimation is investigated, and we introduce the polarization periodogram of a random bivariate signal. Numerical experiments support our theoretical analysis, illustrating the relevance of the approach on synthetic data.Comment: 11 pages, 3 figure

Density estimation on the rotation group using diffusive wavelets

This paper considers the problem of estimating probability density functions on the rotation group $SO(3)$. Two distinct approaches are proposed, one based on characteristic functions and the other on wavelets using the heat kernel. Expressions are derived for their Mean Integrated Squared Errors. The performance of the estimators is studied numerically and compared with the performance of an existing technique using the De La Vall\'ee Poussin kernel estimator. The heat-kernel wavelet approach appears to offer the best convergence, with faster convergence to the optimal bound and guaranteed positivity of the estimated probability density function

Expansion-maximization-compression algorithm with spherical harmonics for single particle imaging with X-ray lasers

In 3D single particle imaging with X-ray free-electron lasers, particle orientation is not recorded during measurement but is instead recovered as a necessary step in the reconstruction of a 3D image from the diffraction data. Here we use harmonic analysis on the sphere to cleanly separate the angu- lar and radial degrees of freedom of this problem, providing new opportunities to efficiently use data and computational resources. We develop the Expansion-Maximization-Compression algorithm into a shell-by-shell approach and implement an angular bandwidth limit that can be gradually raised during the reconstruction. We study the minimum number of patterns and minimum rotation sampling required for a desired angular and radial resolution. These extensions provide new av- enues to improve computational efficiency and speed of convergence, which are critically important considering the very large datasets expected from experiment

Centre d’anthropologie des mondes contemporains

Nicolas Flamant Anthropologie et entreprise Depuis deux ans, ce séminaire effectue un état des lieux des recherches en anthropologie sur l’entreprise et vise à restituer la diversité de leurs objets et de leurs approches. Toutefois, afin d’éviter un éparpillement des présentations, le choix a été de fait de se limiter pour l’instant aux travaux menés en France, ce qui n’empêche pas, d’ores et déjà, des allers-retours avec des terrains plus « exotiques » qui seront abordés l’an prochain. La pr..

Le patronat en Inde

Drawing a sociological profile of the Indian entrepreneur is an ambitious and tricky task. India is a world of diversities, and the same is true in its corporate world. Some great Indian businessmen developed worldwide activities, while others confined themselves to the local market. They may be deeply attached to the traditions of their religious or caste community, whereas others are very westernized and have been so for generations. They may be heirs to an hundred-year old family business, or self-made men whose affairs flourished within a few years. They may have studied in prestigious business schools, or given up their studies rather early. In order to have an overview of these various universes, and also to provide a practical guide of key names and concepts, this book focuses on three different levels: the socio-cultural world (family, community and value-concepts in India), the politics of business (history and strategy of five Indian industrial empires) and the employer in his enterprise (international leather shoemakers in the southern state of Tamil Nadu).Inde ; patronat ; sociologie

Turbulent forcing of gravity waves during the morning transition of the Atmospheric Boundary Layer: analogy with water-tank experiments

In a series of atmospheric observations during the morning transition of the Atmospheric Boundary Layer (ABL), internal gravity waves were observed to propagate in the atmospheric Residual Layer. This requires an energy source for the waves and a stably stratified Residual Layer, which is usually though to be neutral. To understand these observations in a simplified and controlled environment, a series of laboratory experiments was carried out to examine the properties of internal gravity waves generated by a turbulent region and transmitted through a salt-stratified system similar to the atmospheric stratification during the transition. The turbulence was generated by an oscillating grid and analyzed using PIV technique to obtain the characteristic velocity U_t and lengthscale L_t of the energy containing eddies. The waves in the stratified layers were visualized using shadowgraph technique

Histoire de l’action et des rationalités pratiques au XXe siècle

Yves Cohen, directeur d’études Le séminaire s’est occupé cette année de quelques nouveaux aspects de ce que peut une histoire de l’action par rapport aux autres disciplines d’étude de l’action (sociologie, psychologie, anthropologie, philosophie, etc.). Pour ne prendre qu’un nombre restreint d’exemples, on peut constater historiquement le basculement de certaines évidences, ainsi lorsque nous passons de celle selon laquelle l’action collective est une action de lutte ou de révolte à celle sel..

Histoire de l’action et des rationalités pratiques au XXe siècle (industrie, politique et sciences humaines)

Yves Cohen, directeur d’études Histoire de l’action et des rationalités pratiques au XXe siècle Les accents de cette année ont porté sur trois questions qui se sont entrelacées. De quels actes une histoire de l’action est-elle susceptible de s’occuper ? Comment régler au mieux le rapport entre les catégories des acteurs et celles des chercheurs ? Que pouvons-nous dire aujourd’hui d’une histoire de l’autorité au XXe siècle et quel est l’apport du concept de gouvernementalité inventé par Foucau..

Histoire de l’action et des rationalités pratiques au XXe siècle

Yves Cohen, directeur d’études Le séminaire s’est occupé cette année de quelques nouveaux aspects de ce que peut une histoire de l’action par rapport aux autres disciplines d’étude de l’action (sociologie, psychologie, anthropologie, philosophie, etc.). Pour ne prendre qu’un nombre restreint d’exemples, on peut constater historiquement le basculement de certaines évidences, ainsi lorsque nous passons de celle selon laquelle l’action collective est une action de lutte ou de révolte à celle sel..