Decomposition of Triebel-Lizorkin and Besov spaces in the context of Laguerre expansions

A pair of dual frames with almost exponentially localized elements (needlets) are constructed on \RR_+^d based on Laguerre functions. It is shown that the Triebel-Lizorkin and Besov spaces induced by Laguerre expansions can be characterized in terms of respective sequence spaces that involve the needlet coefficients.Comment: 42 page

Subsampling needlet coefficients on the sphere

In a recent paper, we analyzed the properties of a new kind of spherical wavelets (called needlets) for statistical inference procedures on spherical random fields; the investigation was mainly motivated by applications to cosmological data. In the present work, we exploit the asymptotic uncorrelation of random needlet coefficients at fixed angular distances to construct subsampling statistics evaluated on Voronoi cells on the sphere. We illustrate how such statistics can be used for isotropy tests and for bootstrap estimation of nuisance parameters, even when a single realization of the spherical random field is observed. The asymptotic theory is developed in detail in the high resolution sense.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ164 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

A simple model for heterogeneous flows of yield stress fluids

Various experiments evidence spatial heterogeneities in sheared yield stress fluids. To account for heterogeneities in the velocity gradient direction, we use a simple model corresponding to a non-monotonous local constitutive curve and study a simple shear geometry. Different types of boundary conditions are considered. Under controlled macroscopic shear stress $\Sigma$, we find homogeneous flow in the bulk and a hysteretic macroscopic stress - shear rate curve. Under controlled macroscopic shear rate $\dot{\Gamma}$, shear banding is predicted within a range of values of $\dot{\Gamma}$. For small shear rates, stick slip can also be observed. These qualitative behaviours are robust when changing the boundary conditions.Comment: 13 pages, 13 figure

Asymptotics for spherical needlets

We investigate invariant random fields on the sphere using a new type of spherical wavelets, called needlets. These are compactly supported in frequency and enjoy excellent localization properties in real space, with quasi-exponentially decaying tails. We show that, for random fields on the sphere, the needlet coefficients are asymptotically uncorrelated for any fixed angular distance. This property is used to derive CLT and functional CLT convergence results for polynomial functionals of the needlet coefficients: here the asymptotic theory is considered in the high-frequency sense. Our proposals emerge from strong empirical motivations, especially in connection with the analysis of cosmological data sets.Comment: Published in at http://dx.doi.org/10.1214/08-AOS601 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Hydrogen maser development at Laval University

The physical construction of two hydrogen masers is described and results of measurements made on one of the masers are given. These include: cavity Q, thermal time constant, line Q, signal power output, magnetic shielding factor. Preliminary results indicate that the frequency stability will be mainly affected by the thermal of the cavity. The magnetic field and the barometric fluctuations should not affect the maser at the stability level above a few parts in 10 to the 15th power, which is the goal for averaging times of several hours

Audiências, consumidores e cidadãos: implicações das mudanças nas relações dos operadores de serviço público

Os media encontram-se perante um cenário muito diferente daquele que existia aquando da fundação da RTP, há 50 anos, o qual se caracterizava pela complexidade e pela turbulência do mercado. O primeiro aspecto resulta das dificuldades com as quais se debatem as empresas de comunicação, enquanto o segundo decorre da instabilidade e da falta de orientação clara nos mercados, factores que originam incerteza e riscos estratégicos. As pressões sobre os media são provocadas por cinco factores decisivos subjacentes ao desenvolvimento contemporâneo do sector: abundância de meios de comunicação; fragmentação e polarização das audiências; desenvolvimento de carteiras de produtos; erosão da força das empresas de media; e alterações de poder no processo comunicacional. O primeiro factor torna-se visível através do acréscimo dramático de tipos e unidades de media, bem como do crescimento da oferta, que excede largamente o aumento de procura em termos monetários e temporais. Dispararam a quantidade de páginas dos jornais e o número de horas diárias de emissão (tanto de rádio como de televisão) e de revistas e livros publicados. Nesta altura, as condições técnicas e económicas e as políticas públicas fomentam o aparecimento de novos fornecedores de conteúdos, aumentando, dramaticamente, a oferta de empresas

Picard: We must keep the focus on why plurality is important

Robert G. Picard is Director of Research at the Reuters Institute for the Study of Journalism, University of Oxford, a research fellow at Green Templeton College (Oxford), and a Fellow of the Royal Society of Arts. Here he argues that digital intermediaries should not be ignored in the debates over media pluralism, particularly when they perform editorial functions. This post is part of our series on the role of digital intermediaries in media plurality

How Europe talks about itself: Lessons from the Euro Crisis

Although the continuing Euro Crisis is currently being overshadowed by the refugee crisis in Europe, its economic and political effects continue to shake the foundation of Europe and dampen national economies

Book review: What Society needs from Media in the Age of digital communication, by Robert G. Picard

Media and communications are changing rapidly and their transformation is having a momentous impact on the abilities of individuals to communicate and how society communicates within itself. Such changes are important because media convey ideas, opinions, information, social values, experiences, and entertainment and those are influenced by social, economic, and political forces in society. The changing nature of communication is especially important because media and communication platforms are increasingly the primary location in which contemporary identity, culture, and values and norms are manifested and contested

Slow flows of yield stress fluids: complex spatio-temporal behaviour within a simple elasto-plastic model

A minimal athermal model for the flow of dense disordered materials is proposed, based on two generic ingredients: local plastic events occuring above a microscopic yield stress, and the non-local elastic release of the stress these events induce in the material. A complex spatio-temporal rheological behaviour results, with features in line with recent experimental observations. At low shear rates, macroscopic flow actually originates from collective correlated bursts of plastic events, taking place in dynamically generated fragile zones. The related correlation length diverges algebraically at small shear rates. In confined geometries bursts occur preferentially close to the walls yielding an intermittent form of flow localization.Comment: 4 pages, 4 figure