Modélisation du procédé de cuisson de composites infusés par chauffage infra rouge

L'utilisation des matériaux composites dans les secteurs aéronautique et aérospatial a évolué au cours des dernières années. Ces matériaux à hautes performances présentent des propriétés mécaniques et physiques élevés. Une nouvelle méthode de mise en œuvre de ces matériaux qui pourrait amener un gain en temps et d'énergie est la polymérisation du composite à l'aide d'un four infrarouge. Cette technique de chauffage infrarouge peut s'appliquer en particulier au processus d'infusion de résine LRI (Liquid Resin Infusion) où la résine est infusée à pression atmosphérique dans un demi moule qui contient le renfort fibreux et ayant une surface de recouvrement semi-transparente aux rayons infrarouges. L'injection se fait à l'aide d'une pompe à vide et le composite est placé face aux émetteurs infrarouges. Ces émetteurs sont de type halogène et sont fournis par la société TOSHIBA LIGHTING. Le chauffage commence après injection totale de la résine et sa stabilisation dans le moule. Par conséquent, le composite est soumis à un flux radiatif incident, lequel est absorbé par le premier pli de carbone présent à sa surface. Ceci est due au fait que les fibres de carbone présentent une absorptivité assez élevée qu'on peut donc considérer le composite opaque vis-à-vis de l'infrarouge. Un modèle de calcul par éléments finis basé sur la méthode des radiosités a été développé afin de prédire le flux radiatif absorbé par le composite. Ce modèle a été validé par une solution référence basée sur les algorithmes de lancer de rayons. Ce flux radiatif absorbé est imposé comme condition aux limites dans le logiciel commercial COMSOLMULTIPHYSICS. Celui ci résout par la méthode des éléments finis l'équation de chaleur couplée avec la cinétique de réticulation de la résine afin de modéliser la polymérisation par infrarouge. La température et le degré de réticulation au sein du composite sont ainsi calculées. Un algorithme d'optimisation a été couplé avec le modèle radiatif afin d'obtenir une distribution de température optimale dans le composite. Ces données issues de l'optimisation en été utilisée dans le protocole expérimental. Ce montage expérimental permettant le chauffage infrarouge du composite instrumenté a été réalisé au laboratoire afin de valider les résultats numériques de l'étape de chauffage à l'aide de thermocouple et de la thermographie infrarouge pour le cas d'une plaque composite et le cas d'une pièce 3D.Epoxy resins have several applications in the aerospace and automobile industry. Because of their good adhesive properties, superior mechanical, chemical and thermal properties, and resistance to fatigue and microcracking, they produce high performance composites. In the technology presented here, the composite is cured in an IR oven which includes halogen lamps. The liquid resin infusion (LRI) process is used to manufacture the composite, whereby liquid resin is infused through a fiber reinforcement previously laid up in a one-sided mold. These epoxy resins release an exothermic heat flux during the curing process, which can possibly cause an excessive temperature in the thickness. Consequently, for the production of high performance composites, it is necessary to know the thermal behavior of the composite during curing. In our work, we studied IR interactions with the composite, which is placed in an IR oven. Using an IR spectrometer Bruker Vertex 70 (1-27 µm), we measured radiative properties and determined the fraction of IR rays absorbed by the composite. Since it is necessary to optimize the manufacturing time and costs and to determine the performance of these composites, the purpose of this study is to model the IR curing of a composite part (carbon fiber reinforced epoxy matrix) in the infrared oven. The work consists in two parts. In the first part, a FE thermal model based on radiosity method was developed, for the prediction of the infrared incident heat flux on the top surface of the composite during the curing process. This model was validated using a reference solution based on ray tracing algorithms developed in Matlab(r) (In-lab software called Rayheat based on ray tracing algorithms is used to compute the radiative heat flux that impacts the composite). Through the FE thermal model, an optimization study on the percentage power of each infrared heater is performed in order to optimize the incident IR heat flux uniformity on the composite. This optimization is performed using the Matlab(r) optimization algorithms based on Sequential Quadratic Programming method. In a second part, the optimized parameters set is used in a three-dimensional numerical model which is developed in the finite element software, where the heat balance equation is coupled with the cure kinetic model of the resin. This numerical model allows calculation of the temperature distribution in the composite during curing, which is a key parameter that affects its mechanical properties. In this model, we can predict also the evolution of the degree of cure as function of time

Analysis of anchor-size effects on pinned scroll waves and measurement of filament rigidity.

Inert, spherical heterogeneities can pin three-dimensional scroll waves in the excitable Belousov-Zhabotinsky reaction. Three pinning sites cause initially circular rotation backbones to approach equilateral triangles. The resulting stationary shapes show convex deviations that increase with decreasing anchor radii. This dependence is interpreted as a transition between filament termination at large surfaces and true, local pinning of a continuous curve. The shapes of the filament segments are described by a hyperbolic cosine function which is predicted by kinematic theory that considers filament tension and rigidity. The latter value is measured as (1.0±0.7)×10-6 cm4/s.National Science Foundatio

Passive administration of monoclonal antibodies to Anthrolysin O prolong survival in mice lethally infected with Bacillus anthracis

<p>Abstract</p> <p>Background</p> <p><it>Bacillus anthracis </it>has two major virulence factors: a tripartite toxin that produces lethal and edema toxins and a polyglutamic acid capsule. A recent report suggested that a toxin belonging to the cholesterol dependant cytolysin (CDC) family, anthrolysin O (ALO) was a new virulence factor for <it>B. anthracis </it>but subsequent studies have questioned its relevance in pathogenesis. In this study, we examined the immunogenicity of recombinant anthrolysin O (rALO) in mice.</p> <p>Results</p> <p>BALB/c mice immunized with rALO and boosted after two weeks, produce sera with strong Ab responses with a predominance of IgG1 and IgG2a. Five hybridomas to rALO were recovered representing the IgM, IgG1, and IgG2b isotypes. Passive administration of 3 of the five monoclonal antibodies (mAbs) to rALO prior to infection with lethal intravenous (i.v.) <it>B. anthracis </it>Sterne strain infection in mice was associated with enhanced average survival and a greater likelihood of surviving infection. A combination of two mAbs to ALO was more effective than either mAb separately. One mAb (64F8) slowed the toxicity of rALO for J774.16 macrophage-like cells.</p> <p>Conclusion</p> <p>Our results suggest that ALO contributes to the virulence of <it>B. anthracis </it>Sterne strain in this infection model and that Ab response to ALO may contribute to protection in certain circumstances.</p

Biomimetic mineral self-organization from silica-rich spring waters

Purely inorganic reactions of silica, metal carbonates, and metal hydroxides can produce self-organized complex structures that mimic the texture of biominerals, the morphology of primitive organisms, and that catalyze prebiotic reactions. To date, these fascinating structures have only been synthesized using model solutions. We report that mineral self-assembly can be also obtained from natural alkaline silica-rich water deriving from serpentinization. Specifically, we demonstrate three main types ofmineral self-assembly: (i) nanocrystalline biomorphs of barium carbonate and silica, (ii) mesocrystals and crystal aggregates of calcium carbonate with complex biomimetic textures, and (iii) osmosis-driven metal silicate hydrate membranes that form compartmentalized, hollow structures. Our results suggest that silica-induced mineral self-assembly could have been a common phenomenon in alkaline environments of early Earth and Earth-like planets.We acknowledge funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/European Research Council grant agreement no. 340863 (Prometheus). This work was also supported by the NSF under grant no. 1609495We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

Age-related difference in cardiac adaptation to chronic hypertension in rats, with and without nifedipine treatement

Three myosin isozymes, V1 (αα MHC = Myosin Heavy Chain gene), V2 (αβ MHC) and V3 (ββ MHC) that are identified in the cardiac ventricles of most mammals have been shown to shift to a V3 predominance pattern during cardiac growth and in response to left ventricular pressure overload, and to V1 predominance following anti hypertensive treatment. This study examined whether long-term hypertension impairs the ability of the adult heart to restructure myosin isozyme proportions. Using pyrophosphate gel electrophoresis, we studied proportions of cardiac myosin isozymes (V1 and V3) in young (16 weeks) and adult (36 weeks) spontaneously hypertensive rats (SHR), and following 12 weeks of nifedipine (N) treatment in age-matched SHR rats (SHR-N). The values of V1 and V3 myosin isozymes were derived by adding half of the value of V2 to each isozyme proportion. The V3 proportion in the young SHR control (SHR-C) group (49%) was 34% higher (p < 0.05) than in the young Wistar Kyoto control (WKY-C) group (37%). However, the proportion was similarly high, though not statistically significant, in both the adult SHRC (73%) and WKY-C (71%) groups. The proportion in the young SHR-N group (29%) was 41% lower (p < 0.05) than in the young SHR-C group (49%), and the proportion in the adult SHR-N group (47%) was 34% lower (p < 0.05) than in the adult SHR-C group (73%). The ratio of left ventricular weight to body weight (LVW/BW), which determines left ventricular hypertrophy (LVH), was higher in both young and adult SHR-C (26%, p < 0.05, and 42%, p < 0.05, respectively) than in WKY-C groups. The mean LVW/BW was 27% (p lt; 0.05) greater in adult than in young SHR-C rats. The LVW/BW in both age groups of treated SHR-N was similar to that in age matched WKY-C rats. Conclusion: Our study showed that a rise in the V3 level occurs in young hypertensive rats, but no rise occurs in the V3 level in adult hypertensive rats. High blood pressure seems to contribute to the high V3 level in young hypertensive rats, but in adult hypertensive rats, high blood pressure does not accentuate the V3 rise already acquired due to the aging process. Nifedipine treatment in both young and adult hypertensive rats prevented the V3 rise due to hypertension and to the aging process. This effect of nifedipine seems to be through its antihypertensive action.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45335/1/11010_2004_Article_199277.pd

Simulation du chauffage infrarouge des composites

National audienceRESUME: L'utilisation des matériaux composites dans les secteurs aéronautique et aérospatial a évolué au cours des dernières années. Ces matériaux à hautes performances présentent des propriétés mécaniques et physiques qui leur permettent de concurrencer les métaux. Une nouvelle méthode de mise en oeuvre de ces matériaux qui pourrait amener un gain en temps et d'énergie est la polymérisation du composite à l'aide d'un four infrarouge. Cette technique de chauffage infrarouge peut s'appliquer en particulier au processus d'infusion de résine LRI (Liquid Resin Infusion) où la résine est injectée à pression atmosphérique dans un demi moule qui contient le renfort fibreux et ayant une surface de recouvrement semi-transparente aux rayons infrarouges. L'injection se fait à l'aide d'une pompe à vide et le composite est placé face aux émetteurs infrarouges. Ces émetteurs sont de type halogène et sont fournis par la société TOSHIBA LIGHTING. Le chauffage commence après injection totale de la résine et sa stabilisation dans le moule. Le composite est modélisé par une plaque composée de plusieurs plis de carbone imprégnés d'une résine époxy (RTM6). La plaque est soumise à un flux radiatif incident, lequel est absorbé par le premier pli de carbone présent à la surface du composite. Ceci est due au fait que les fibres de carbone présentent une absorptivité assez élevée qu'on peut donc considérer le composite opaque vis-à-vis de l'infrarouge. L'ICA Albi a développé un logiciel (RAY-HEAT) qui calcule le terme source radiatif en 3D induit par le four infrarouge. Ce logiciel a été utilisé dans cette étude essentiellement pour calculer les rayons qui impactent la surface du composite ainsi que pour le calcul du flux radiatif. Le flux radiatif calculé à l'aide du logiciel RAYHEAT est imposé comme condition aux limites dans le logiciel commercial COMSOLMULTIPHYSICS. Celui ci résout par la méthode des éléments finis l'équation de chaleur couplée avec la cinétique de réticulation de la résine afin de modéliser la polymérisation par infrarouge. La température et le degré de réticulation au sein du composite sont ainsi calculées. Un montage expérimental permettant le chauffage infrarouge du composite instrumenté a été réalisé au laboratoire afin de valider les résultats numériques de l'étape de chauffage

Antibody Responses in HIV-Infected Patients With Advanced Immunosuppression and Asymptomatic Cryptococcal Antigenemia.

BACKGROUND: There are no host biomarkers of risk for HIV-associated cryptococcal meningitis (CM) except CD4+ T-cell deficiency. At present, serum cryptococcal antigen (CrAg) screening of those with CD4 <100 cells/µL is used to identify persons at risk for HIV-associated CM. We determined if plasma antibody profiles could discriminate CrAg+ from CrAg- patients. METHODS: We performed serological analyses of 237 HIV-infected asymptomatic Zimbabwean patients with CD4 <100 cells/µL; 125 CrAg- and CrAg+ but cerebrospinal fluid CrAg- by CrAg lateral flow assay. We measured plasma immunoglobulin M (IgM), immunoglobulin G (IgG) 1, and IgG2 concentrations by Luminex, and titers of Cryptococcus neoformans (Cn) glucuronoxylomannan (GXM) polysaccharide and naturally occurring Laminarin (natural Lam, a β-(1-3)-glucan linked polysaccharide)-binding IgM and IgG by enzyme-linked immunosorbent assay. RESULTS: GXM-IgG, -IgM, and -IgG2 levels were significantly higher in CrAg+ patients, whereas natural Lam-IgM and Lam-IgG were higher in CrAg- patients before and after adjustment for age, sex, and CD4 T-cell count, despite overlap of values. To address this variability and better discriminate the groups, we used Akaike Information Criteria to select variables that independently predicted CrAg+ status and included them in a receiver operating characteristic curve to predict CrAg status. By inclusion of CD4, GXM-IgG, GXM-IgM, and Lam-IgG, -IgG2, and -IgM, this model had an 80.4% probability (95% confidence interval, 0.75-0.86) of predicting CrAg+ status. CONCLUSIONS: Statistical models that include multiple serological variables may improve the identification of patients at risk for CM and inform new directions in research on the complex role that antibodies may play in resistance and susceptibility to CM

Fungal Melanins Differ in Planar Stacking Distances

Melanins are notoriously difficult to study because they are amorphous, insoluble and often associated with other biological materials. Consequently, there is a dearth of structural techniques to study this enigmatic pigment. Current models of melanin structure envision the stacking of planar structures. X ray diffraction has historically been used to deduce stacking parameters. In this study we used X ray diffraction to analyze melanins derived from Cryptococcus neoformans, Aspergillus niger, Wangiella dermatitides and Coprinus comatus. Analysis of melanin in melanized C. neoformans encapsulated cells was precluded by the fortuitous finding that the capsular polysaccharide had a diffraction spectrum that was similar to that of isolated melanin. The capsular polysaccharide spectrum was dominated by a broad non-Bragg feature consistent with origin from a repeating structural motif that may arise from inter-molecular interactions and/or possibly gel organization. Hence, we isolated melanin from each fungal species and compared diffraction parameters. The results show that the inferred stacking distances of fungal melanins differ from that reported for synthetic melanin and neuromelanin, occupying intermediate position between these other melanins. These results suggest that all melanins have a fundamental diffracting unit composed of planar graphitic assemblies that can differ in stacking distance. The stacking peak appears to be a distinguishing universal feature of melanins that may be of use in characterizing these enigmatic pigments