Astronomical Image Denoising Using Dictionary Learning

Astronomical images suffer a constant presence of multiple defects that are consequences of the intrinsic properties of the acquisition equipments, and atmospheric conditions. One of the most frequent defects in astronomical imaging is the presence of additive noise which makes a denoising step mandatory before processing data. During the last decade, a particular modeling scheme, based on sparse representations, has drawn the attention of an ever growing community of researchers. Sparse representations offer a promising framework to many image and signal processing tasks, especially denoising and restoration applications. At first, the harmonics, wavelets, and similar bases and overcomplete representations have been considered as candidate domains to seek the sparsest representation. A new generation of algorithms, based on data-driven dictionaries, evolved rapidly and compete now with the off-the-shelf fixed dictionaries. While designing a dictionary beforehand leans on a guess of the most appropriate representative elementary forms and functions, the dictionary learning framework offers to construct the dictionary upon the data themselves, which provides us with a more flexible setup to sparse modeling and allows to build more sophisticated dictionaries. In this paper, we introduce the Centered Dictionary Learning (CDL) method and we study its performances for astronomical image denoising. We show how CDL outperforms wavelet or classic dictionary learning denoising techniques on astronomical images, and we give a comparison of the effect of these different algorithms on the photometry of the denoised images

Effect of Hypoxia on Dental Pulp Mesenchymal Stem Cells in a Purpose of Tissue Engineering

International audienceDuring life, teeth are exposed to severe injuries (decay, traumatisms…), which can result in dental pulp necrosis. Creating a “pulp tissue equivalent” constitutes a promising therapeutic approach to replace the current invasive treatments. Dental pulp of deciduous teeth contains mesenchymal stem cells (SHEDs: Stem cells from Human Exfoliated Deciduous teeth), shown to have a high proliferation and differentiation potential. Our approach aims to assess the effect of severe hypoxia on these cells, mimicking the clinical conditions of the matrix implantation in the pulp space. 3D collagen matrices seeded with SHEDs (1.5 million of cells/ml) were cultivated under severe hypoxia (1% O2) during 3 days. Then, to mimic the kinetics of revascularization, the matrices were replaced in normoxic conditions (21% O2). Induced mRNA and protein modifications were studied by qPCR, ELISA, Western Blot and immunocytochemistry, at several time points. A transcriptomic analysis (DNA affymetrix chips “gene” type) of the samples was then performed at the time point with the highest VEGF mRNA expression. The capacity of SHEDs exposed to hypoxia to induce angiogenenis was then tested in a tubulogenesis model. Finally, SHEDs pretreated by hypoxia were induced toward osteogenic differentiation in 3D plastic compressed collagen matrix. Our data show that hypoxic conditions induce: 1) an increase of the transcription factor HIF‐1 alpha observed in the cell nucleus, 2) a x4 increase of VEGF mRNA expression at 24 h (qPCR), confirmed by ELISA analysis, 3) the up‐regulation of numerous genes activated by HIF‐1 alpha and involved in angiogenesis, apoptosis and glycolysis regulation. Furthermore, SHEDs pretreated by hypoxia enhanced capillary formation by endothelial cells. In parallel, osteogenic differentiation assay showed that pretreatment by hypoxia did not impair matrix mineralization by SHEDs, which was slightly enhanced.These cells are good candidate for tissue engineering approaches, in particular for treating damaged dental tissues

The interaction of heparan sulfate proteoglycans with endothelial transglutaminase-2 limits VEGF165-induced angiogenesis

International audienceSprouting angiogenesis is stimulated by vascular endothelial growth factor (VEGF165) that is localized in the extracellular matrix (ECM) and binds to heparan sulfate (HS)-bearing proteins known as heparan sulfate proteoglycans (HSPGs). VEGF165 presentation by HSPGs enhances VEGF receptor-2 (VEGFR2) signaling. We investigated the effect of TG2, which binds to HSPGs, on the interaction between VEGF165 and HS and angiogenesis. Mice with tg2 deficiency showed transiently enhanced retina vessel formation and increased vascularization of VEGF165-containing Matrigel implants. In addition, endothelial cells in which TG2 was knocked down exhibited enhanced VEGF165-induced sprouting and migration, which was associated with increased phosphorylation of VEGFR2 at Tyr(951) and its targets Src and Akt. TG2 knockdown did not affect the phosphorylation of VEGFR2 at Tyr(1175) or cell proliferation in response to VEGF165 and sprouting or signaling in response to VEGF121. Decreased phosphorylation of VEGFR2 at Tyr(951) was due to ECM-localized TG2, which reduced the binding of VEGF165 to endothelial ECM in a manner that required its ability to bind to HS but not its catalytic activity. Surface plasmon resonance assays demonstrated that TG2 impeded the interaction between VEGF165 and HS. These results show that TG2 controls the formation of VEGF165-HSPG complexes and suggest that this regulation could be pharmacologically targeted to modulate developmental and therapeutic angiogenesi

Territorial competition and globalisation: Scylla and Charbydis of European cities

Policy-makers in Europe have been concerned with developing and sustaining the competitiveness of their cities. This concern comes from the view that the determing parameter of urban regions is globalisation. By engaging in a process of territorial competition, the economic and social welfare of cities' constituent territories can be maintained. What this paper argues is that there is a danger that territorial competition is as much an abstraction as globalisation and its application to policy-making will bring about distortions in economic development. By examining the specification of globalisation and territorial competition and the relevant literature, a debate may be initiated in which the consequences for the economic environment of European cities are addressed. The discussion is given some context by drawing on the cursory examples, one global and one local, of London and Lille

La dynamique spatiale de l'économie contemporaine

397 p., fig., ref. bib. : dissem.Ce livre essaie d'éclairer les fondements géographiques du capitalisme industriel moderne. Les auteurs présentent différentes approches des mutations du système productif et leurs effets sur l'organisation territoriale. En empruntant des chemins variés, les chapitres de cet ouvrage sont construits autour des thèmes majeurs du développement économique spatial : l'industrialisation, l'organisation de la production et les activités de services, le rôle des PME, etc. Certains d'entre eux ont une orientation principalement théorique, la plupart combinent les arguments théoriques et empiriques. Livre de recherche, mais aussi guide précieux pour étudiants en sciences sociales géographie, sociologie, urbanisme) et économiques, et pour responsables politiques et économiques