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Briard A.,University Pierre and Marie Curie | Gomez T.,USTL
Journal of Turbulence | Year: 2017

Decaying homogeneous isotropic turbulence with an imposed mean scalar gradient is investigated numerically, thanks to a specific eddy-damped quasi-normal Markovian closure developed recently for passive scalar mixing in homogeneous anisotropic turbulence (BGC). The present modelling is compared successfully with recent direct numerical simulations and other models, for both very large and small Prandtl numbers. First, scalings for the cospectrum and scalar variance spectrum in the inertial range are recovered analytically and numerically. Then, at large Reynolds numbers, the decay and growth laws for the scalar variance and mixed velocity–scalar correlations, respectively, derived in BGC, are shown numerically to remain valid when the Prandtl number strongly departs from unity. Afterwards, the normalised correlation ρwθ is found to decrease in magnitude at a fixed Reynolds number when Pr either increases or decreases, in agreement with earlier predictions. Finally, the small scales return to isotropy of the scalar second-order moments is found to depend not only on the Reynolds number, but also on the Prandtl number. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Briard A.,University of Paris Descartes | Gomez T.,USTL
Journal of Fluid Mechanics | Year: 2017

The dynamics of helicity in homogeneous skew-isotropic freely decaying turbulence is investigated, at very high Reynolds numbers, thanks to a classical eddy-damped quasi-normal Markovian (EDQNM) closure. In agreement with previous direct numerical simulations, a inertial range is obtained for both the kinetic energy and helical spectra. In the early stage of the decay, when kinetic energy, initially only present at large scales cascades towards small scales, it is found that helicity slightly slows down the nonlinear transfers. Then, when the turbulence is fully developed, theoretical decay exponents are derived and assessed numerically for helicity. Furthermore, it is found that the presence of helicity does not modify the decay rate of the kinetic energy with respect to purely isotropic turbulence, except in Batchelor turbulence where the kinetic energy decays slightly more rapidly. In this case, non-local expansions are used to show analytically that the permanence of the large eddies hypothesis is verified for the helical spectrum, unlike the kinetic energy one. Moreover, the law for the two-point helical structure function is assessed numerically at very large Reynolds numbers. Afterwards, the evolution equation of the helicity dissipation rate is investigated analytically, which provides significant simplifications and leads notably to the definition of a helical derivative skewness and of a helical Taylor scale, which is numerically very close to the classical Taylor longitudinal scale at large Reynolds numbers. Finally, when both a mean scalar gradient and helicity are combined, the quadrature spectrum, linked to the antisymmetric part of the scalar flux, appears and scales like and then like in the inertial range. © 2017 Cambridge University PressÂ.

Vert R.,French Atomic Energy Commission | Chicot D.,USTL | Decoopman X.,Lille Laboratory of Mechanics | Gruescu I.C.,University of Lille Nord de France | And 3 more authors.
Thin Solid Films | Year: 2011

In order to characterize the adhesion of nanostructured plasma-sprayed Y2O3-ZrO2 coatings presenting some geometrical specificities, it is here suggested to apply the Vickers Indentation Cracking (VIC) technique, which is capable of initiating a crack at the interface by performing the indentation test close to the interface within the substrate. This method renders it possible to overcome the difficulties concerning the characterization of the adhesion of nanostructured Y2O 3-ZrO2 (YSZ) coatings. It was suggested to calculate an adhesive stress parameter by employing two physical parameters, i.e., the critical load to initiate the crack and the indentation distance measured between the interface and the indent center. In addition, for the case of brittle coatings, the crack was found to deviate from the interface toward the coating. Under such conditions and on the basis of the critical point (given by the two parameters: load and indentation distance), a stress parameter representative of the cohesive properties of the coating was defined according to the crack deviation conditions. © 2011 Elsevier B.V. All rights reseved.

Marcon L.,Interdisciplinary Research Institute | Kherrouche Z.,French National Center for Scientific Research | Lyskawa J.,USTL | Fournier D.,USTL | And 3 more authors.
Chemical Communications | Year: 2011

The paper reports on covalent linking of a modified amphiphilic polymer, the alkynyl-terminated Zonyl, to azide-terminated nanodiamonds by click chemistry. An analysis of the hybrid particle stability is presented based on size and zeta potential measurements. The antifouling character of the grafted nanodiamonds was investigated using bovine serum albumin as a model protein. The protein adsorption was quantified using a Bradford assay and found to be reduced by 30% in the presence of the Zonyl layer. © 2011 The Royal Society of Chemistry.

Lequette Y.,French National Institute for Agricultural Research | Garenaux E.,USTL | Garenaux E.,French National Center for Scientific Research | Tauveron G.,French National Institute for Agricultural Research | And 7 more authors.
Applied and Environmental Microbiology | Year: 2011

Bacillus cereus spores are surrounded by a loose-fitting layer called the exosporium, whose distal part is mainly formed from glycoproteins. The role played by the exosporium glycoproteins of B. cereus ATCC 14579 (BclA and ExsH) was investigated by considering hydrophobicity and charge, as well as the properties of spore adhesion to stainless steel. The absence of BclA increased both the isoelectric point (IEP) and hydrophobicity of whole spores while simultaneously reducing the interaction between spores and stainless steel. However, neither the hydrophobicity nor the charge associated with BclA could explain the differences in the adhesion properties. Conversely, ExsH, another exosporium glycoprotein, did not play a significant role in spore surface properties. The monosaccharide analysis of B. cereus ATCC 14579 showed different glycosylation patterns on ExsH and BclA. Moreover, two specific glycosyl residues, namely, 2-O-methyl-rhamnose (2-Me-Rha) and 2,4-O-methyl-rhamnose (2,4-Me-Rha), were attached to BclA, in addition to the glycosyl residues already reported in B. anthracis. © 2011, American Society for Microbiology.

Verbeke S.,French Institute of Health and Medical Research | Verbeke S.,University of Lille Nord de France | Meignan S.,French Institute of Health and Medical Research | Meignan S.,University of Lille Nord de France | And 11 more authors.
Cellular Signalling | Year: 2010

The p75 neurotrophin receptor (p75NTR) plays a critical role in various neuronal and non-neuronal cell types by regulating cell survival, differentiation and proliferation. To evaluate the influence of p75NTR in breast cancer development, we have established and characterized breast cancer cells which stably overexpress p75NTR. We showed that p75NTR overexpression per se promoted cell survival to apoptogens with a concomitant slowdown of cell growth. The pro-survival effect is associated with an increased expression of the inhibitor of apoptosis protein-1 (c-IAP1), a decrease of TRAIL-induced cleavage of PARP, procaspase 9 and procaspase 3, and a decrease of cytochrome C release from the mitochondria. The anti-proliferative effect is due to a cell accumulation in G0/G1, associated with a decrease of Rb phosphorylation and an increase of p21waf1. Interestingly, inhibition of p21waf1 with siRNA not only restores proliferation but also abolishes the pro-survival effect of p75NTR, indicating the key role of p21waf1 in the biological functions of p75NTR. Finally, using a SCID mice xenograft model, we showed that p75NTR overexpression favors tumor growth and strongly increases tumor resistance to anti-tumoral treatment.Together, our findings suggest that p75NTR overexpression in breast tumor cells could favor tumor survival and contribute to tumor resistance to drugs. This provides a rationale to consider p75NTR as a potential target for the future design of innovative therapeutic strategies. © 2010 Elsevier Inc.

Romon R.,French Institute of Health and Medical Research | Romon R.,University of Lille Nord de France | Adriaenssens E.,USTL | Adriaenssens E.,French National Center for Scientific Research | And 9 more authors.
Molecular Cancer | Year: 2010

Background: Although several anti-angiogenic therapies have been approved in the treatment of cancer, the survival benefits of such therapies are relatively modest. Discovering new molecules and/or better understating signaling pathways of angiogenesis is therefore essential for therapeutic improvements. The objective of the present study was to determine the involvement of nerve growth factor (NGF) in breast cancer angiogenesis and the underlying molecular mechanisms.Results: We showed that both recombinant NGF and NGF produced by breast cancer cells stimulated angiogenesis in Matrigel plugs in immunodeficient mice. NGF strongly increased invasion, cord formation and the monolayer permeability of endothelial cells. Moreover, NGF-stimulated invasion was under the control of its tyrosine kinase receptor (TrkA) and downstream signaling pathways such as PI3K and ERK, leading to the activation of matrix metalloprotease 2 and nitric oxide synthase. Interestingly, NGF increased the secretion of VEGF in both endothelial and breast cancer cells. Inhibition of VEGF, with a neutralizing antibody, reduced about half of NGF-induced endothelial cell invasion and angiogenesis in vivo.Conclusions: Our findings provided direct evidence that NGF could be an important stimulator for breast cancer angiogenesis. Thus, NGF, as well as the activated signaling pathways, should be regarded as potential new targets for anti-angiogenic therapy against breast cancer. © 2010 Romon et al; licensee BioMed Central Ltd.

Bonne C.,Lille University of Science and Technology | Pahwa A.,Ecole Nationale Supérieure de Chimie de Lille | Picard C.,USTL | Visseaux M.,CNRS Laboratory of Catalysis and Solid State Chemistry
Inorganica Chimica Acta | Year: 2016

Ring Opening Polymerization of rac-lactide and ε-caprolactone as well as their copolymerization was achieved by means of bismuth tris-silylamide in solution and at temperatures below 75. °C. The best performances in terms of control of the polymerization were obtained in presence of an alcohol as chain transfer agent. A PLA-based copolymer containing up to 23% ε-caprolactone can be prepared. When activated with a borane molecule, bismuth tris-silylamide produces polymers having narrower polymer distributions. © 2016 Elsevier B.V.

Briard A.,CNRS Jean Le Rond d'Alembert Institute | Gomez T.,USTL | Mons V.,CNRS Jean Le Rond d'Alembert Institute | Sagaut P.,Aix - Marseille University
Journal of Turbulence | Year: 2016

ABSTRACT: Homogeneous anisotropic turbulence has been widely studied in the past decades, both numerically and experimentally. Shear flows have received a particular attention because of the numerous physical phenomena they exhibit. In the present paper, both the decay and growth of anisotropy in homogeneous shear flows at high Reynolds numbers are revisited thanks to a recent eddy-damped quasi-normal Markovian closure adapted to homogeneous anisotropic turbulence. The emphasis is put on several aspects: an asymptotic model for the slow part of the pressure–strain tensor is derived for the return to isotropy process when mean velocity gradients are released. Then, a general decay law for purely anisotropic quantities in Batchelor turbulence is proposed. At last, a discussion is proposed to explain the scattering of global quantities obtained in DNS and experiments in sustained shear flows: the emphasis is put on the exponential growth rate of the kinetic energy and on the shear parameter. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Lamonier J.-F.,USTL | Nguyen T.B.,USTL | Franco M.,USTL | Siffert S.,University of the Littoral Opal Coast | And 5 more authors.
Catalysis Today | Year: 2011

The effect of two calcining temperatures (400 °C, 600 °C) on the texture, structure and thermal stability of a meso-macroporous ZrO 2-TiO2 of equal molar amount (ZrTix; x = 4, 6) synthesized from hydrothermal conditions using a surfactant and metal alkoxide precursors was studied. Pd (0.5 wt.%) was dispersed on these innovative supports (Pd/ZrTix; x = 4, 6) by a classic wet impregnation and calcined at 400 °C. The resulting catalysts were characterized by Elemental analysis (EA), X-Ray Diffraction (XRD), N2 adsorption-desorption, H 2-Temperature Programmed Reduction (H2-TPR), Pd dispersion and tested as pre-reduced in the total oxidation of chlorobenzene. It was found that the calcination temperature did not provoke a significant effect on the physicochemical properties of the resulting binary oxide except the acidity which significantly decreased. The support was stable against phase transformation upon calcination as no crystalline phase could be detected indicating a homogeneous mixing of the Zr and Ti components. The Specific Surface Areas (SSAs) were superior to 400 m2/g even after calcination at 600 °C. The Pd dispersion was around 40% and the palladium was totally reduced before catalytic testing. Lowering the temperature of calcination of the support enhanced the performances of the catalyst. Indeed PhCl conversion increased as the calcination temperature decreased and correlates with the Pd dispersion and SSA of the catalyst. A significant amount of polychlorinated benzenes PhClx (x = 2-6) was detected in the course of the reaction which practically disappeared at 100% PhCl conversion. This amount was reduced by a factor 2 as the temperature of calcination decreased. Compared to the performances of Pd/Tix and Pd/Zrx for the same reaction, all things being kept equal, calcined ZrO2-TiO2 supports show higher surface areas and higher thermal stability than their ZrO 2 and TiO2 counterparts. In terms of activity for PhCl total oxidation based on T50 values the ZrO2-TiO 2 supports showed an intermediate behaviour while a beneficial effect was observed regarding the by-products production which is the lowest herein for the Pd/TiZr4 catalyst. © 2011 Elsevier B.V. All rights reserved.

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