Wavelet analysis of the multivariate fractional Brownian motion

The work developed in the paper concerns the multivariate fractional Brownian motion (mfBm) viewed through the lens of the wavelet transform. After recalling some basic properties on the mfBm, we calculate the correlation structure of its wavelet transform. We particularly study the asymptotic behavior of the correlation, showing that if the analyzing wavelet has a sufficient number of null first order moments, the decomposition eliminates any possible long-range (inter)dependence. The cross-spectral density is also considered in a second part. Its existence is proved and its evaluation is performed using a von Bahr-Essen like representation of the function \sign(t) |t|^\alpha. The behavior of the cross-spectral density of the wavelet field at the zero frequency is also developed and confirms the results provided by the asymptotic analysis of the correlation

Robust correlation for aggregated data with spatial characteristics

The objective of this paper is to study the robustness of computation of correlations under spatial constraints. The motivation of our paper is the specific case of functional magnetic resonance (fMRI) brain imaging data, where voxels are aggregated to compute correlations. In this paper we show that the way the spatial components are aggregating to com- pute correlation may have a strong influence on the resulting estimations. We then propose various estimators which take into account this spatial structure

Graphe de connectivité cérébrale et longue dépendance

National audienceIn this communication, a decomposable graph based partial correlation matrix estimator is proposed for the analysis of time series exhibiting long memory properties. The estimator is derived from the set of wavelet coefficients computed at a given scale; the obtained coefficient are asymptotically uncorrelated, thus avoiding to introduce bias in the estimation. Decomposability of the graph leads to derive an explicit formulation of the maximum likelihood estimation of the partial correlation matrix; however, some spurious links must be introduced in order to insure graph decomposability. Surrogate data that mimik fMRI records are used to illustrate the pertinence and accuracy of the proposed approach. The simulations show that even for small size samples, the proposed methods outperforms the classical approaches. Furthermore, the added links do not affect the quality of the estimation. An appealing feature of decomposabilty resides in the possibility to account for conditional dependences through a clique based approach

Simulation numérique de l'interaction de systèmes énergétiques du bâtiment à l'aide d'une plateforme de simulation basée sur le solveur SPARK

Pour contrer l'augmentation de la demande mondiale en énergie, l'efficacité énergétique dans les bâtiments est un levier majeur. On parle donc de plus en plus de bâtiments basse énergie et de maisons passives. Nous verrons à quoi correspondent ces notions. L'idée est ici de travailler à partir d'une plateforme de simulation (SimSpark) basée sur le solveur Spark pour décrire le comportement thermo-aéraulique dans les bâtiments. A partir de cette plateforme, on peut facilement intégrer tout type de système. En exploitant la modularité de l'environnement, il est possible d'évaluer le gain apporté par différents types d'enveloppes ou par l'ajout de différents systèmes. On peut également connaître les interactions qui peuvent avoir lieu pour en déduire quelles sont les associations les plus efficaces. Nous présenterons ici une évaluation de l'effet de la mise en place d'une ventilation double flux sur les besoins de chauffage ainsi que l'effet de l'ajout de casquettes au dessus des fenêtres sur le comportement thermique du bâtiment

Phytosphingosine-phosphate is a signal for AtMPK6 activation and Arabidopsis response to chilling

Long-chain bases (LCBs) are pleiotropic sphingolipidic signals in eukaryotes. We investigated the source and function of phytosphingosine-1-phosphate (PHS-P), a phospho-LCB rapidly and transiently formed in Arabidopsis thaliana on chilling.PHS-P was analysed by thin-layer chromatography following in vivo metabolic radiolabelling. Pharmacological and genetic approaches were used to identify the sphingosine kinase isoforms involved in cold-responsive PHS-P synthesis. Gene expression, mitogen-activated protein kinase activation and growth phenotypes of three LCB kinase mutants (lcbk1, sphk1 and lcbk2) were studied following cold exposure. Chilling provoked the rapid and transient formation of PHS-P in Arabidopsis cultured cells and plantlets. Cold-evoked PHS-P synthesis was reduced by LCB kinase inhibitors and abolished in the LCB kinase lcbk2 mutant, but not in lcbk1 and sphk1 mutants. lcbk2 presented a constitutive AtMPK6 activation at 22°C. AtMPK6 activation was also triggered by PHS-P treatment independently of PHS/PHS-P balance. lcbk2 mutants grew comparably with wild-type plants at 22 and 4°C, but exhibited a higher root growth at 12°C, correlated with an altered expression of the cold-responsive DELLA gene RGL3. Together, our data indicate a function for LCBK2 in planta. Furthermore, they connect PHS-P formation with plant response to cold, expanding the field of LCB signalling in plants

Adipose tissue transcriptomic signature highlights the pathological relevance of extracellular matrix in human obesity

Analysis of the transcriptomic signature of white adipose tissue in obese human subjects revealed increased interstitial fibrosis and an infiltration of inflammatory cells into the tissue