No description available.

O Método das Densidades de Força (MDF), proposto primeiramente por Linkwitz (1971) e depois por Scheck (1974), é uma alternativa conveniente para encontrar configurações de redes de cabos e membranas, uma vez que fornece geometrias viáveis com uma única análise linear de equilíbrio. O Método das Densidades de Força Natural (MDFN) é uma extensão do MDF para busca de formas de estruturas de membranas, que preserva a linearidade do método original e supera suas dificuldades em lidar com malhas irregulares. Foi primeiramente sugerido por Pauletti em 2006, baseado no elemento triangular de membrana introduzido por Argyris em 1974. O Método tem sido aplicado com sucesso em vários projetos. O MDFN original requer o uso de malhas compostas exclusivamente por elementos triangulares. Esta dissertação apresenta uma extensão do método para elementos quadrangulares, considerando um elemento composto por quatro subelementos triangulares. Mesmo que a ideia básica seja muito simples, algumas dificuldades surgem do fato de que nesta abordagem, o elemento de quatro nós pode não conter todos os nós em um mesmo plano, especialmente no caso de superfícies anticlásticas, sendo que não existe um campo de tensões bem definido para o interior do elemento. O trabalho compara alguns resultados obtidos com malhas exclusivamente triangulares, como requerido pelo método original, com os resultados obtidos com o elemento quadrangular proposto, discutindo a forma de combinar as tensões dos subelementos triangulares para originar as tensões atuantes no elemento quadrangular. Os modelos obtidos no MDFN são inseridos no programa Ansys, e os resultados são comparados para analisar a viabilidade da solução proposta e dos resultados obtidos por meio desta. / The Force Density Method (FDM), first proposed by Linkwitz(1971) and after by Scheck(1974), is a convenient alternative for finding configurations of cable nets and membranes, since it provides viable geometries in a single linear equilibrium analysis. The Natural Force Density Method (NFDM) is an extension of the FDM to the shape finding of membrane structures, which preserves the linearity of the original method and overcomes the difficulties of the original method to deal with irregular meshes. It was first suggested by Pauletti in 2006, based on a triangular membrane element introduced by Argyris in 1974. The method has been successfully applied to several design cases. The original NFDM required the use of meshes composed exclusively of triangular elements. This text presents an extension of the method to quadrangular elements, considering an equivalent assemblage of flat triangular elements. Even if the basic idea is very simple, some difficulties arise from the fact that in this approach, the quadrangular element can have a non-flat configuration, especially in the anticlastic shape, and there is not a know stress field into the interior of the element. The text compares several results obtained with fully triangulated meshes, as required by the original NFDM, to those obtained with the proposed quadrangular element, discussing the different strategies that have been explored to map stresses from the internal triangular mesh to the four nodes of the element. The models obtained in the NFDM are inserted in software Ansys and the results compared to approve the solution and the results obtained.

O Método das Densidades de Força (MDF), proposto primeiramente por Linkwitz (1971) e depois por Scheck (1974), é uma alternativa conveniente para encontrar configurações de redes de cabos e membranas, uma vez que fornece geometrias viáveis com uma única análise linear de equilíbrio. O Método das Densidades de Força Natural (MDFN) é uma extensão do MDF para busca de formas de estruturas de membranas, que preserva a linearidade do método original e supera suas dificuldades em lidar com malhas irregulares. Foi primeiramente sugerido por Pauletti em 2006, baseado no elemento triangular de membrana introduzido por Argyris em 1974. O Método tem sido aplicado com sucesso em vários projetos. O MDFN original requer o uso de malhas compostas exclusivamente por elementos triangulares. Esta dissertação apresenta uma extensão do método para elementos quadrangulares, considerando um elemento composto por quatro subelementos triangulares. Mesmo que a ideia básica seja muito simples, algumas dificuldades surgem do fato de que nesta abordagem, o elemento de quatro nós pode não conter todos os nós em um mesmo plano, especialmente no caso de superfícies anticlásticas, sendo que não existe um campo de tensões bem definido para o interior do elemento. O trabalho compara alguns resultados obtidos com malhas exclusivamente triangulares, como requerido pelo método original, com os resultados obtidos com o elemento quadrangular proposto, discutindo a forma de combinar as tensões dos subelementos triangulares para originar as tensões atuantes no elemento quadrangular. Os modelos obtidos no MDFN são inseridos no programa Ansys, e os resultados são comparados para analisar a viabilidade da solução proposta e dos resultados obtidos por meio desta. / The Force Density Method (FDM), first proposed by Linkwitz(1971) and after by Scheck(1974), is a convenient alternative for finding configurations of cable nets and membranes, since it provides viable geometries in a single linear equilibrium analysis. The Natural Force Density Method (NFDM) is an extension of the FDM to the shape finding of membrane structures, which preserves the linearity of the original method and overcomes the difficulties of the original method to deal with irregular meshes. It was first suggested by Pauletti in 2006, based on a triangular membrane element introduced by Argyris in 1974. The method has been successfully applied to several design cases. The original NFDM required the use of meshes composed exclusively of triangular elements. This text presents an extension of the method to quadrangular elements, considering an equivalent assemblage of flat triangular elements. Even if the basic idea is very simple, some difficulties arise from the fact that in this approach, the quadrangular element can have a non-flat configuration, especially in the anticlastic shape, and there is not a know stress field into the interior of the element. The text compares several results obtained with fully triangulated meshes, as required by the original NFDM, to those obtained with the proposed quadrangular element, discussing the different strategies that have been explored to map stresses from the internal triangular mesh to the four nodes of the element. The models obtained in the NFDM are inserted in software Ansys and the results compared to approve the solution and the results obtained.

In vivo, les phopholipides interagissent avec des structures moléculaires rugueuses, telles des clusters ou fibrilles de protéines. Ce thème n’est pourtant que trop peu abordé dans la littérature scientifique, alors qu’il semblerait que la topologie de la surface sur laquelle repose ces molécules ou mêmes protéines influencent leurs propriétés. Notre projet s’est donc concentré sur les effets qu’un support accidenté pouvait soulever sur les bicouches lipidiques supportées (BLS).Dans un premier temps, nous avons étudié la mobilité de phopholipides déposés sur des supports plus ou moins rugueux par la méthode de recouvrement après photobleaching patterné (FRAPP pour Fluorescence Recovery After Patterned Photobleaching en anglais). Ces derniers ont été créés afin d’obtenir une large gamme de rugosité et caractérisés par Microscopie à Force Atomique.Nous sommes ensuite intéressés à la conformation d’une membrane sur ces substrats à l’aide de la technique non invasive de réflectivité de neutrons.Enfin, nous avons commencé à nous pencher sur les propriétés tribologiques des lipides lubrifiants nos surfaces rugueuses / In vivo lipid membranes interact with rough supramolecular structures such as protein clusters and fibrils However, this issue is not very developped in the state of art, while surface topology which interact with these molecules affects their properties. In this project, effects of rough surface on supported lipid bilayer (BLS) are investigated.First, lipid mobility are studied with the FRAPP method (Fluorescence Recovery After Photobleaching). BLS are deposited on rough supports which are characterized by AFM (Atomic Force Microscopy).Then, BLS structure on our rough surfaces are investigated by Neutron Reflectivity.Finally, first results on tribological properties of our systems are introduced

In this study, effects of nanoparticles, including 7 nm TiO2, 200 nm TiO2, and hydrophilic and hydrophobic SiO2 with mean diameter in the range of 15–20 nm and their concentration on the membrane properties and vacuum membrane distillation (VMD) performance were evaluated. The effect of membrane thickness and support materials were also investigated. The membranes were characterised extensively in terms of morphology (SEM), water contact angle, water liquid entrance pressure (LEPw), surface roughness, and pore size. While the best nanocomposite membranes with 200 nm TiO2 Nanoparticles(NPs) were obtained at 2% particle concentration, the optimal particle concentration was 5% when 7 nm TiO2 was integrated. Using nanocomposite membrane containing 2 wt% TiO2 – 200 nm nanoparticles, VMD flux of 2.1 kg/m2h and LEPw of 34 PSI was obtained with 99% salt rejection. Furthermore, it was observed that decreasing the membrane thickness would increase the portion of finger-like layer in membrane and reduce the spongy-like layer when hydrophilic nanoparticles were used. Using continuous flow VMD, a flux of 3.1 kg/m2h was obtained with neat PVDF membranes, which was 600% higher than the flux obtained by the static flow VMD with the same membrane at the same temperature and vacuum pressure. The fluxes of both static and flow-cell VMD increased with temperature. Furthermore, it was evident that the continuous flow VMD at 2 LPM yielded 300% or higher flux than static VMD at any given temperature, indicating strong effects of turbulence provided in the flow-cell VMD.

Secretory phospholipase A2 (sPLA2) is an important part of apoptosis and disposal of damaged and dying cells. However, healthy cells are not susceptible to attack by sPLA2. Recent studies have focused on membrane properties necessary to induce susceptibility in both artificial and biological membranes. Hydrolysis of phospholipids by sPLA2 requires at least two preliminary steps: first, adsorption of the enzyme to the cellular membrane, and second, movement of a phospholipid into the active site of the enzyme. We determined the effects of susceptibility on each of the two steps and determined the contributions changing the equilibrium constants have on susceptibility. The equilibrium constant for step one increased by a factor of 2 during susceptibility, while the equilibrium constant for step two increased by a factor of 4. The rise in the second equilibrium constant caused the majority of the change in hydrolysis rate seen during susceptibility; the influence of the first equilibrium constant is minimal. We confirmed these results with adsorption studies (assessment of the first step). We additionally found that sPLA2 has a high affinity for the cellular membrane and that only a small percentage (3-5%) of the membrane is covered when all adsorption sites are filled by the enzyme. We proposed a mathematical model describing the mechanism of action of sPLA2, and we were able to experimentally justify the assumptions made in the model.

No description available.

La littérature des dernières décennies regorge de références concernant les bienfaits des acides gras oméga 3, tels que l’EPA (C20:5 n-3) et le DHA (C22:6 n-3) qui jouent un rôle essentiel dans la prévention de nombreuses pathologies comme les maladies neurodégénératives (type Alzheimer). Les sources majeures d’EPA et DHA sont celles d’origine marine. C’est dans ce contexte que cette étude a choisi de s’intéresser aux phospholipides provenant de têtes de saumon. L’objectif était de les extraire, de purifier la phosphatidylcholine (PC) issue du mélange de lipides et d’en déterminer ses propriétés d’auto-assemblage en bicouches. Une approche expérimentale par la caractérisation physico-chimique de ce PC a été complétée par une étude théorique du même composé en utilisant les techniques de simulation par dynamique moléculaire qui a permis une caractérisation à l’échelle moléculaire des bicouches lipidiques. La caractérisation a permis d’aboutir au profil détaillé de la composition du mélange PC saumon, d’élaborer le diagramme de phase PC –eau, de déterminer les propriétés d’empaquetage d’hydratation de ce lipide. Les paramètres choisis pour l’étude en dynamique moléculaire ont permis de reproduire de manière fidèle les résultats expérimentaux, validant ainsi le modèle et les conditions de simulations déterminés au préalable. La caractérisation des propriétés structurales de la PC de saumon sous forme de multicouches a permis d’approfondir la compréhension des mécanismes d’interactions à l’échelle moléculaire existant entre les lipides insaturés eux-mêmes. / The literature of recent decades is replete with references regarding the benefits of omega 3 fatty acids such as EPA (C20:5 n-3) and DHA (C22:6 n-3) which play an essential role in preventing many diseases such as neurodegenerative diseases (Alzheimer's type). The major sources of EPA and DHA are those of marine origin. It is within this context that this study chose to deal with phospholipids from salmon heads. The objective was to extract, purify phosphatidylcholine (PC) derived from the mixture of lipids and determine its properties of self-assembly into bilayers. An experimental approach by the physicochemical characterization of this PC was supplemented by a theoretical study of the same compound using the techniques of molecular dynamics simulation that allowed a molecular-scale characterization of lipid bilayers. The characterization resulted in detailed profile of the mixture composition of salmon PC, to draw up the phase diagram of PC-water, to determine the packing and hydration properties of this lipid. The parameters chosen for the study of molecular dynamics have faithfully reproduced the experimental results, thus validating the model and simulation conditions determined in advance. The characterization of structural properties of the PC as a multilayer salmon has deepened the understanding of interaction mechanisms at the molecular level between unsaturated lipids themselves.

Des pathologies telles que la myopathie et certains types de cancer, peuvent être causées par une mauvaise formation de l’enveloppe nucléaire (EN), processus se produisant lors de chaque division cellulaire mais aussi lors de la formation du pronoyau mâle. Un modèle in vitro, dérivé de gamètes d’oursins, a été utilisé afin d’étudier les différentes étapes de formation de l’EN et a permis de révéler plusieurs informations essentielles. Un des points critiques est que des membranes fortement enrichies en phosphoinositides polyphosphorylés (PPIs) sont essentielles à la formation de l’EN, notamment lors des étapes de fusion membranaire. Ces membranes proviennent du cytoplasme de l’ovocyte fécondé (MV1) et des noyaux de spermatozoïdes (NERs). Nous avons construit des modèles membranaires mimant les compositions lipidiques de ces membranes, puis étudié leur structure, leur dynamique ainsi que leur morphologie par spectroscopie de RMN des solides et microscopie électronique. Nous avons montré que les PPIs induisent une courbure membranaire positive, conduisant à la formation de petites vésicules ou de micelles allongées. Plus important encore, dans le modèle « MV1», les membranes sont très fluides. Le modèle « NERs » est constitué de membranes globalement ordonnées, semblables aux phases dites « liquides ordonnées » avec une modulation apportée par la PPIs. Nous avons également construit un modèle membranaire minant la composition lipidique des vésicules MV2, membranes non-enrichies en PPIs mais représentant 90 % des vésicules participant à la formation de l’EN. Ce modèle membranaire présente une dynamique intermédiaire à celle observée pour les modèles MV1 et NERs. Ces propriétés nouvelles ont permis de proposer un mécanisme décrivant le rôle des PPIs lors de la fusion membranaire conduisant à la formation de l’enveloppe nucléaire. / Diseases, such as myopathies and some types of cancer, can be caused by abnormal nuclear envelope (NE) assembly, a process that takes place at each cell division and during male pronuclear formation. A cell-free assay from sea urchin gametes, that mimics the in vivo male pronucleus formation, has been used to dissect the various stages of NE assembly. This in vitro assay has revealed several novel features. One of the critical aspects is that membranes highly enriched in polyphosphorylated phosphoinositides (PPIs), are essential for NE formation, especially during the stage of membrane fusion. Theses membranes are extracted from the cytoplasm of the fertilised oocyte (MV1) and sperm nuclei (NERs). We made model membranes with similar lipid composition to MV1 and NERs and studied their structure, dynamics and morphologies by solid-state NMR spectroscopy and electron microscopy. We show that PPIs have a positive membrane curvature, inducing small vesicles and elongated micelles. More importantly, we illustrate that “MV1-like” membranes are very fluid. “NERs-like” membranes are globally ordered and belong to the family of liquid ordered phases. We also evidenced that PPIs can counterbalance in part the ordering effect of cholesterol. Moreover we made model membranes with similar lipid composition to MV2, non-enriched in PPIs membranes which constitute 90% of the vesicles forming the NE. This model membrane shows an in-between dynamics compared to MV1 and NERs. We therefore propose a mechanism describing the role of PPIs during membrane fusion leading to nuclear membrane assembly.

Vanderghem Caroline. (2009). La membrane du globule gras du lait : études physico-chimiques et sa valorisation technofonctionnelle dans les babeurres (Thèse de doctorat en Anglais). Gembloux, Belgique, Faculté Universitaire des Sciences Agronomiques de Gembloux. 198p., 14 tabl., 59 fig. Résumé La membrane du globule gras du lait (MGGL) est une structure complexe qui enveloppe, protège et délivre des composants bioactifs et des nutriments dune façon efficace au nouveau-né. Sa structure est unique par rapport à dautres systèmes biologiques de transport de lipides. Lobjectif général de ce travail a été de contribuer à augmenter les connaissances et la compréhension de cet émulsifiant naturel. La première partie de cette thèse concerne létude de la structure de la MGGL. Limportance des protéines membranaires concernant la stabilité et leur disposition dans la MGGL ont été étudiés. Les protéines de la MGGL sont présentes en petite quantité dans le lait et une technique de pré-fractionnement simpose afin de les isoler par rapport aux autres protéines du lait (caséines et protéines du lactosérum). Une technique dextraction qui a été développée dans notre laboratoire a été testée afin disoler la MGGL de la crème laitière. Une analyse détaillée a révélé que cette procédure est très bien adaptée pour lélimination dun maximum de protéines du lait écrémé. Une approche protéomique a été établie et a permis lidentification de protéines majeures de la MFGM ainsi que dautres protéines mineures (GTP-binding proteins, annexins, actin) afin de compléter le protéome. Par la suite, différentes protéases ont été testées en vue dobtenir différents degrés et/ou sélectivité dhydrolyse des protéines de la MGGL. La distribution asymétrique des protéines de la MGGL a été étudiée par une approche basée sur lattaque protéolytique du globule gras natif. Sur base de nos résultats et des données bibliographiques récentes, un nouveau modèle de la structure de la MGGL est proposé. La deuxième partie de cette thèse est consacrée à évaluer les propriétés technofonctionnelles de la MGGL dans les babeurres. Les propriétés interfaciales, moussantes et émulsifiantes du babeurre sont comparées à dautres ingrédients laitiers comme le lait écrémé et le concentré protéique de lactosérum. Nos résultats montrent le bon pouvoir émulsifiant du babeurre en comparaison des autres ingrédients laitiers. Dans les émulsions recombinées, la stabilité envers le crémage a été améliorée et les membranes ont présenté une meilleure résistance face à la coalescence. Les résultats sur la tension interfaciale et les propriétés rhéologiques interfaciales ont été mis en relation avec certaines propriétés des mousses et des émulsions. Vanderghem Caroline. (2009). The milk fat globule membrane: physico-chemical studies and its techno-functional valorisation in buttermilk (Thèse de doctorat). Gembloux, Belgium, Gembloux Agricultural University, 198p., 14 tabl., 59 fig. Summary The milk fat globule membrane (MFGM) is a complex structure that surrounds, protects and delivers bioactive compounds and nutrients in an efficient manner to the neonate. Its structure is unique in relation with any other biological lipid transport system. The overall aim of this work was to contribute to increase the knowledge and comprehension of this natural emulsifier. The first part of this thesis concerned the study of the structure of the MFGM. Membrane proteins were targeted and their importance regarding stability and disposition in the MFGM was studied. MFGM proteins are present at low concentrations in milk and a pre-fractionation of the sample is required in order of MFGM proteins to be visible among other milk proteins (caseins and whey proteins). A mild procedure developed in our laboratory was tested in order to isolate MFGM from cream. Detailed analysis revealed that this procedure is very well suited for the elimination of a maximum of skim milk proteins. A proteomic approach was established and allowed the identification of the most important MFGM proteins and additional minor MFGM proteins for additional completion of the proteome (GTP-binding proteins, annexins, actin). Subsequently, different proteases were screened in an attempt to obtain different degrees and/or selective proteolysis of MFGM proteins. Asymmetric arrangement of MFGM proteins was studied with an approach based on the proteolytic attack on the native fat globule. Based on our results and recent bibliographic data, an updated model of the MFGM structure was proposed. The second part of this thesis was devoted to assess the techno-functional properties of the MFGM in buttermilks. Interfacial, foaming and emulsifying properties of buttermilk were assessed and compared to classic milk ingredients such as skim milk and whey protein concentrate. Our results highlighted that buttermilk possesses good emulsifying power compared to other milk ingredients. In buttermilk recombined emulsions stability towards creaming was improved and the recombined membrane presented a great resistance to coalescence. Results of the interfacial pressure and the interfacial rheological properties were related to some foams and emulsions properties.