Études des interactions détergents/lipides dans les systèmes membranaires

Les liposomes sont des structures sphériques formés par l'auto-assemblage de molécules amphiphiles sous forme d'une bicouche. Cette bicouche sépare le volume intérieur du liposome du milieu extérieur, de la même manière que les membranes cellulaires. Les liposomes sont donc des modèles de membranes cellulaires et sont formulés pour étudier les processus biologiques qui font intervenir la membrane (transport de molécules à travers la membrane, effets des charges en surface, interactions entre la matrice lipidique et d'autres molécules, etc.). Parce qu'ils peuvent encapsuler une solution aqueuse en leur volume intérieur, ils sont aussi utilisés aujourd'hui comme nanovecteurs de principes actifs. Nous avons formulé des liposomes non-phospholipidiques riches en stérol que nous avons appelés stérosomes. Ces stérosomes sont composés d'environ 30 % d'amphiphiles monoalkylés et d'environ 70 % de stérols (cholestérol, Chol, et/ou sulfate de cholestérol, Schol). Quand certaines conditions sont respectées, ces mélanges sont capables de former une phase liquide ordonnée (Lo) pour donner, par extrusion, des vésicules unilamellaires. Certaines de ces nouvelles formulations ont été fonctionnalisées de manière à libérer leur contenu en réponse à un stimulus externe. En incorporant des acides gras dérivés de l’acide palmitique possédant différents pKa, nous avons pu contrôler le pH auquel la libération débute. Un modèle mathématique a été proposé afin de cerner les paramètres régissant leur comportement de libération. En incorporant un amphiphile sensible à la lumière (un dérivé de l’azobenzène), les liposomes formés semblent répondre à une radiation lumineuse. Pour ce système, il serait probablement nécessaire de tracer le diagramme de phase du mélange afin de contrôler la photo-libération de l’agent encapsulé. Nous avons aussi formulé des liposomes contenant un amphiphile cationique (le chlorure de cétylpyridinium). En tant que nanovecteurs, ces stérosomes montrent un potentiel intéressant pour la libération passive ou contrôlée de principes actifs. Pour ces systèmes, nous avons développé un modèle pour déterminer l’orientation des différentes molécules dans la bicouche. La formation de ces nouveaux systèmes a aussi apporté de nouvelles connaissances dans le domaine des interactions détergents-lipides. Aux nombreux effets du cholestérol (Chol) sur les systèmes biologiques, il faut ajouter maintenant que les stérols sont aussi capables de forcer les amphiphiles monoalkylés à former des bicouches. Cette nouvelle propriété peut avoir des répercussions sur notre compréhension du fonctionnement des systèmes biologiques. Enfin, les amphiphiles monoalkylés peuvent interagir avec la membrane et avoir des répercussions importantes sur son fonctionnement. Par exemple, l'effet antibactérien de détergents est supposé être dû à leur insertion dans la membrane. Cette insertion est régie par l'affinité existant entre le détergent et cette dernière. Dans ce cadre, nous avons voulu développer une nouvelle méthode permettant d'étudier ces affinités. Nous avons choisi la spectroscopie Raman exaltée de surface (SERS) pour sa sensibilité. Les hypothèses permettant de déterminer cette constante d’affinité se basent sur l’incapacité du détergent à exalter le signal SERS lorsque le détergent est inséré dans la membrane. Les résultats ont été comparés à ceux obtenus par titration calorimétrique isotherme (ITC). Les résultats ont montré des différences. Ces différences ont été discutées.

Modélisation de répartition d’espèces aviaires et de feux en forêt boréale du Québec dans un contexte de changement climatique

Les changements climatiques prennent une importance grandissante dans l’étude des phénomènes spatiaux à grande échelle. Plusieurs experts affirment que les changements climatiques seront un des principaux moteurs de changement écologique dans les prochaines décennies et que leurs conséquences seront inévitables. Ces changements se manifesteront sur le milieu physique par la fonte des calottes glaciaires, le dégel du pergélisol, l’instabilité des versants montagneux en zone de pergélisol, l’augmentation de l’intensité, de la sévérité et de la fréquence des événements climatiques extrêmes tels les feux de forêt. Les changements climatiques se manifesteront aussi sur le milieu biologique, tel la modification de la durée de la saison végétative, l’augmentation des espèces exotiques invasives et les changements dans la distribution en espèces vivantes. Deux aspects sont couverts par cette étude : 1) les changements dans la répartition spatiale de 39 espèces d’oiseaux et 2) les modifications dans les patrons spatiaux des feux, en forêt boréale québécoise, tous deux dans l’horizon climatique de 2100. Une approche de modélisation statistique démontre que la répartition spatiale des oiseaux de la forêt boréale est fortement liée à des variables bioclimatiques (R2adj = 0.53). Ces résultats permettent d’effectuer des modélisations bioclimatiques pour le gros-bec errant et la mésange à tête noire quivoient une augmentation de la limite nordique de distribution de l’espèce suivant l’intensité du réchauffement climatique. Finalement, une modélisation spatialement explicite par automate cellulaire permet de démontrer comment les changements climatiques induiront une augmentation dans la fréquence de feux de forêt et dans la superficie brûlée en forêt boréale du Québec.

Programmable Self-Assembly: Constructing Global Shape using Biologically-inspire

In this thesis I present a language for instructing a sheet of identically-programmed, flexible, autonomous agents (``cells'') to assemble themselves into a predetermined global shape, using local interactions. The global shape is described as a folding construction on a continuous sheet, using a set of axioms from paper-folding (origami). I provide a means of automatically deriving the cell program, executed by all cells, from the global shape description. With this language, a wide variety of global shapes and patterns can be synthesized, using only local interactions between identically-programmed cells. Examples include flat layered shapes, all plane Euclidean constructions, and a variety of tessellation patterns. In contrast to approaches based on cellular automata or evolution, the cell program is directly derived from the global shape description and is composed from a small number of biologically-inspired primitives: gradients, neighborhood query, polarity inversion, cell-to-cell contact and flexible folding. The cell programs are robust, without relying on regular cell placement, global coordinates, or synchronous operation and can tolerate a small amount of random cell death. I show that an average cell neighborhood of 15 is sufficient to reliably self-assemble complex shapes and geometric patterns on randomly distributed cells. The language provides many insights into the relationship between local and global descriptions of behavior, such as the advantage of constructive languages, mechanisms for achieving global robustness, and mechanisms for achieving scale-independent shapes from a single cell program. The language suggests a mechanism by which many related shapes can be created by the same cell program, in the manner of D'Arcy Thompson's famous coordinate transformations. The thesis illuminates how complex morphology and pattern can emerge from local interactions, and how one can engineer robust self-assembly.

Multipotent stem cells from umbilical cord: Cord is richer than blood!

The identification of mesenchymal stem cell ( MSC) sources that are easily obtainable is of utmost importance. Several studies have shown that MSCs could be isolated from umbilical cord (UC) units. However, the presence of MSCs in umbilical cord blood (UCB) is controversial. A possible explanation for the low efficiency of MSCs from UCB is the use of different culture conditions by independent studies. Here, we compared the efficiency in obtaining MSCs from unrelated paired UCB and UC samples harvested from the same donors. Samples were processed simultaneously, under the same culture conditions. Although MSCs from blood were obtained from only 1 of the 10 samples, we were able to isolate large amounts of multi-potent MSCs from all UC samples, which were able to originate different cell lineages. Since the routine procedure in UC banks has been to store the blood and discard other tissues, such as the cord and/or placenta, we believe our results are of immediate clinical value. Furthermore, the possibility of originating different cell lines from the UC of neonates born with genetic defects may provide new cellular research models for understanding human malformations and genetic disorders, as well as the possibility of testing the effects of different therapeutic drugs.

FAST, PARALLEL AND SECURE CRYPTOGRAPHY ALGORITHM USING LORENZ`S ATTRACTOR

A novel cryptography method based on the Lorenz`s attractor chaotic system is presented. The proposed algorithm is secure and fast, making it practical for general use. We introduce the chaotic operation mode, which provides an interaction among the password, message and a chaotic system. It ensures that the algorithm yields a secure codification, even if the nature of the chaotic system is known. The algorithm has been implemented in two versions: one sequential and slow and the other, parallel and fast. Our algorithm assures the integrity of the ciphertext (we know if it has been altered, which is not assured by traditional algorithms) and consequently its authenticity. Numerical experiments are presented, discussed and show the behavior of the method in terms of security and performance. The fast version of the algorithm has a performance comparable to AES, a popular cryptography program used commercially nowadays, but it is more secure, which makes it immediately suitable for general purpose cryptography applications. An internet page has been set up, which enables the readers to test the algorithm and also to try to break into the cipher.

Multi-scale rheological model for discontinuous phenomena in materials under deformation conditions

A study of possibilities given by the developed Cellular Automata–Finite Element (CAFE) multi-scale model for prediction of the initiation and propagation of micro-shear bands and shear bands in metallic materials subjected to plastic deformation is described in the paper. Particular emphasis in defining the criterion for initiation of micro-shear and shear bands, as well as in defining the transition rules for the cellular automata, is put on accounting for the physical aspects of those phenomena occurring in two different scales in the material. The proposed approach led to the creation of the real multi-scale model of strain localization. This model predicts material behavior in various thermo-mechanical processes. Selected examples of applications of the developed model to simulations of metal forming processes, which involve strain localization, are presented in the paper. An approach based on the Smoothed Particle Hydrodynamic, which allows to overcome difficulties with remeshing in the traditional CAFE method, is presented in the paper as well. In this approach remeshing becomes possible and mesh distortion, which limits application of the CAFE method to simple deformation processes, is eliminated.

Comparison of the strain distribution obtained from multi scale and conventional approaches to modelling extrusion

An investigation of the application of a multi scale CAFE model to prediction of the strain localization phenomena in industrial processes, such as extrusion, is presented in this work. Extrusion involves the formation of a strong strain localization zone, which influences the final product microstructure and may lead to a coarse grain layer close to the surface. Modelling of the shape of this zone and prediction of the strain magnitude will allow computer aided design of the extrusion process and optimisation of the technological parameters with respect to the microstructure and properties of the products. Thus, the particular objective of this work is comparison of the FE and CAFE predictions of strain localization in the shear zone area in extrusion. Advantages and disadvantages of the developed CAFE model are also discussed on the basis of the simulation results.

Numerical simulation of the static recrystalization at micro shear bands

The main aim of this work is application of the developed cellular automata (CA) model to investigate influence of the micro shear bands that are present in the heavily deformed material on the static recrystallization. This initial work is the results of recent experimental analyses indicating that the micro shear bands are preferred sites for nucleation of the recrystallization. The procedure of creation of the initial microstructure with features such as grains and micro shear bands as well as basis of the developed CA code for the static recrystallization are also presented in the paper. Finally, the simulation results obtained from different recrystallization temperatures for the microstructures with and without micro shear bands are compared with each other and differences are discussed.

Application of the strain localization CAFE model to investigate extrusion with various die shapes

Multi scale CAFE model for the prediction of initiation and propagation of the micro shear bands and shear bands in metallic materials subjected to plastic deformation is presented. The CAFE approach is the combination of the Cellular Automata (CA) and the Finite Element (FE) methods. The application of the developed CAFE model to analyze material flow during extrusion is the objective of the present work. The proposed CAFE approach is applied in this work to simulation of the extrusion with flat face and convex dies and to investigate differences in the material flow. The initial FE meshes with the set of the CA point are generated for the numerical tests and the results of the metal flow predicted by the CAFE method are presented in the paper.

Development of the multi-scale analysis model to simulate strain localization occurring during material processing

Abstract A detailed description of possibilities given by the developed Cellular Automata—Finite Element (CAFE) multi scale model for prediction of the initiation and propagation of micro shear bands and shear bands in metallic materials subjected to plastic deformation is presented in the work. Particular emphasis in defining the criterion for initiation of micro shear and shear bands, as well as in defining the transition rules for the cellular automata, is put on accounting for the physical aspects of these phenomena occurring in two different scales in the material. The proposed approach led to the creation of the real multi scale model of strain localization phenomena. This model predicts material behavior in various thermo-mechanical processes. Selected examples of applications of the developed model to simulations of metal forming processes, which involve strain localization, are presented in the work. An approach based on the Smoothed Particle Hydrodynamic, which allows to overcome difficulties with remeshing in the traditional CAFE method, is a subject of this work as well. In the developed model remeshing becomes possible and difficulties limiting application of the CAFE method to simple deformation processes are solved. Obtained results of numerical simulaA detailed description of possibilities given by the developed Cellular Automata—Finite Element (CAFE) multi scale model for prediction of the initiation and propagation of micro shear bands and shear bands in metallic materials subjected to plastic deformation is presented in the work. Particular emphasis in defining the criterion for initiation of micro shear and shear bands, as well as in defining the transition rules for the cellular automata, is put on accounting for the physical aspects of these phenomena occurring in two different scales in the material. The proposed approach led to the creation of the real multi scale model of strain localization phenomena. This model predicts material behavior in various thermo-mechanical processes. Selected examples of applications of the developed model to simulations of metal forming processes, which involve strain localization, are presented in the work. An approach based on the Smoothed Particle Hydrodynamic, which allows to overcome difficulties with remeshing in the traditional CAFE method, is a subject of this work as well. In the developed model remeshing becomes possible and difficulties limiting application of the CAFE method to simple deformation processes are solved. Obtained results of numerical simulations are compared with the experimental results of cold rolling process to show good predicative capabilities of the developed model.tions are compared with the experimental results of cold rolling process to show good predicative capabilities of the developed model.

Avaliação do crescimento de ocupação da bacia do rio Pitimbu com subsídios para estudos de possíveis impactos sobre os recursos hidricos

The Pitimbu River Watershed (PRW), belonging to Potiguar capital metropolitan area, State of Rio Grande do Norte, contributes, among other purposes, to human using and animal watering. This watershed is extremely important because, besides filling up with freshwater approximately 30% of the south part of Natal (South, East and West Zones), contributes to the river shore ecosystem equilibrium. Face to the current conjuncture, this study aims to evaluate the urban development dynamics in the PRW, applying Cellular Automata as a modeling instrument, and to simulate future urban scenarios, between 2014 and 2033, using the simulation program SLEUTH. In the calibration phase, urban spots for 1 984, 1992, 2004 and 2013 years were used, with resolution from 100 meters. After the simulation, it was found a predominance of organic growth, expanding the BHRP from existing urban centers. The spontaneous growth occurred through the fullest extent of the watershed, however the probability of effective growth should not exceed 21%. It was observed that, there was a 68% increase for the period between 2014 and 2033, corresponding to an expansion area of 1,778 ha. For 2033, the source of Pitimbu River area and the Jiqui Lake surroundings will increase more than 78%. Finally, it was seen an exogenous urban growth tendency in the watershed (outside-in). As a result of this growth, hydraulics resources will become scarcer

Controlling dispersal dynamics of Aedes aegypti

The dengue virus is transmitted in regions previously infested with the mosquito Aedes aegypti. To assess the spreading and establishment of the dengue disease vector, a mathematical model is developed that takes into account the diffusion and advection phenomena. A discrete model based on the cellular automata approach, which is a good framework to deal with small populations, is also developed to be compared with the continuous modeling.

ASSESSING THE SUITABILITY of STERILE INSECT TECHNIQUE APPLIED TO AEDES AEGYPTI

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Neighborhood Interactions and Larval Dispersal Behavior in Blowflies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)