Distribuição Espacial da Susceptibilidade à Erosão Hídrica nas Bacias das Ribeiras de Picos e Seca (Santiago, Cabo Verde)

Os processos de erosão hídrica em Cabo Verde são os mais marcantes da dinâmica actual das vertentes, pois são os mais comuns e que afectam áreas extensasdurante a curta estação húmida de três meses. A ocorrência de episódios chuvosos concentrados no tempo e com uma evidente irregularidade espacial permitem umaacentuada erosividade das precipitações, marcada por uma forte irregularidade regional. A forte variabilidade das formas de relevo, a diversidade da natureza das unidadesgeológicas e a multiplicidade de ocupação do solo favorecem condições deerodibilidade muito contrastadas no espaço. O objectivo deste trabalho é estabelecer um modelo desusceptibilidade à erosão hídricaem função de factores geomorfológicos (declive, perfil e traçado das vertentes eerodibilidade das unidades litológicas e dos materiais de cobertura), climáticos(intensidade pluviométrica) e de ocupação do solo para as bacias das ribeiras dos Picose Seca. Os resultados foram obtidos com recurso ao ambiente de Sistemas deInformação Geográfica (SIG). Este trabalho surge na sequência de outros já realizadospelos autores, onde se apresentaram as condições de erodibilidade e erosividade paraáreas mais restritas da Ilha de Santiago. O modelo de susceptibilidade à erosão hídrica resultou do cruzamento dos mapas dedeclives, de perfil e do traçado das vertentes, obtidos a partir do modelo digital deterreno (DTM), do mapa geológico, da distribuição espacial da intensidadepluviométrica e da densidade de ocupação do solo, tendo em conta que são estas asprincipais condicionantes de erosão hídrica, referidas pelos autores que estudaram estaregião. Cada um destes mapas foi reclassificado com base numa análise qualitativa dograu de erodibilidade, sendo atribuído um número de ordem a cada classe, em função da sua susceptibilidade à erosão hídrica, conforme foi localmente reconhecido. Verifica-se que as áreas de maior susceptibilidade à erosão hídrica são as do sectorsudeste da bacia da Ribeira Seca e as vertentes dos principais vales da bacia da Ribeira dos Picos, onde se encontram as unidades geológicas mais friáveis, os declives mais acentuados e onde predominam sectores das vertentes de traçado côncavo, a que seassocia pontualmente a mais elevada intensidade pluviométrica.

Competing engines of growth: Innovation and standardization

We study a dynamic general equilibrium model where innovation takes theform of the introduction of new goods whose production requires skilled workers.Innovation is followed by a costly process of standardization, whereby these newgoods are adapted to be produced using unskilled labor. Our framework highlightsa number of novel results. First, standardization is both an engine of growth anda potential barrier to it. As a result, growth is an inverse U-shaped function ofthe standardization rate (and of competition). Second, we characterize the growthand welfare maximizing speed of standardization. We show how optimal protection of intellectual property rights affecting the cost of standardization vary withthe skill-endowment, the elasticity of substitution between goods and other parameters. Third, we show that, depending on how competition between innovatingand standardizing firms is modelled and on parameter values, a new type of multiplicity of equilibria may arise. Finally, we study the implications of our model forthe skill-premium and we illustrate novel reasons for linking North-South trade tointellectual property rights protection.

On payoff heterogeneity in games with strategic complementarities

Payoff heterogeneity weakens positive feedback in binary choice models intwo ways. First, heterogeneity drives individuals to corners where theyare unaffected by strategic complementarities. Second, aggregate behaviouris smoother than individual behaviour when individuals are heterogeneous.However, this smoothing does not necessarily eliminate positive feedbackor guarantee a unique equilibrium. In games with an unbounded, continuouschoice space, heterogeneity may either weaken or strengthen positive feedback,depending on a simple convexity/concavity condition. We conclude that positivefeedback phenomena derived in representative agent models will often be robustto heterogeneity.

A dilution cost approach to financial intermediation and securities markets

This paper proposes a model of financial markets and corporate finance,with asymmetric information and no taxes, where equity issues, Bankdebt and Bond financing may all co-exist in equilibrium. The paperemphasizes the relationship Banking aspect of financial intermediation:firms turn to banks as a source of investment mainly because banks aregood at helping them through times of financial distress. The debtrestructuring service that banks may offer, however, is costly. Therefore,the firms which do not expect to be financially distressed prefer toobtain a cheaper market source of funding through bond or equity issues.This explains why bank lending and bond financing may co-exist inequilibrium. The reason why firms or banks also issue equity in our modelis simply to avoid bankruptcy. Banks have the additional motive that theyneed to satisfy minimum capital adequacy requeriments. Several types ofequilibria are possible, one of which has all the main characteristics ofa "credit crunch". This multiplicity implies that the channels of monetarypolicy may depend on the type of equilibrium that prevails, leadingsometimes to support a "credit view" and other times the classical "moneyview".

Circulation of private notes during a currency shortage

This paper provides a search theoretical model that captures two phenomena that have characterized several episodes of monetary history: currency shortages and the circulation of privately issued notes. As usual in these models, the media of exchange are determined as part of the equilibrium. We characterize all the different equilibria and specify the conditions under which there is a currency shortage and/or privately issued notes are used as means of payment. There is multiplicity of equilibria for the entire parameter space, but there always exist an equilibrium in which notes circulate, either alone or together with coins. Hence, credit is a self-fulfilling phenomenon that depends on the beliefs of agents about the acceptability and future repayment of notes. The degree of circulation of coins depends on two crucial parameters, the intrinsic utility of holding coins and the extent with which it is possible to find exchange opportunities in the market.

Alfabetização de crianças caboverdianas em língua portuguesa como língua não materna : o ensino da leitura

abstract: Cape Verde is a country of bilingual characteristics, where coexist two languages: the mother tongue – the Creole of Cape Verde (CCV) or the Capeverdian Language (LCV) and the Non Maternal language – the Portuguese that is the official language and, therefore, the language used in the process of education and learning. This situation generates conflicts so much to linguistic level as to cultural level. The two languages presents some lexical resemblances, what drives, many times, to misconceptions and linguistics errors that complicate children in the learning, in particular, of reading that constitute the base for the learning of others knowledge. The learning of reading, in the Non Maternal language, requires a development of the oral language in Portuguese Language, which stimulates the reasoning of the child through playful exercises and cognitivists and construtivists approaches. In this way, the competences of phonological processing in the acquisition of the competences of reading are important for the discrimination of written text and favor the learning and the development of reading. The child, through the discovery, begins to elaborate concepts in the way to obtain a relation with the written language, by functional form. Adopting a methodology of case study and through questionnaires, direct observation and collect of documentary information, this dissertation presents and analyzes connected aspects to the literacy of capeverdian children in the beginning of the schooling and to the learning of reading as basic support for the learning of Non Maternal language. The subsidies collected by the study, presented in this dissertation will contribute for the education progress of reading and, also, for implement successfully the learning of reading of the students, developing to practical of reading and the expectations in uncover the multiplicity of the dimensions of experience in that domain and contribute for a relative comprehension of written and reading modes.

Alfabetização de crianças caboverdianas em língua portuguesa como língua não materna : o ensino da leitura

abstract: Cape Verde is a country of bilingual characteristics, where coexist two languages: the mother tongue – the Creole of Cape Verde (CCV) or the Capeverdian Language (LCV) and the Non Maternal language – the Portuguese that is the official language and, therefore, the language used in the process of education and learning. This situation generates conflicts so much to linguistic level as to cultural level. The two languages presents some lexical resemblances, what drives, many times, to misconceptions and linguistics errors that complicate children in the learning, in particular, of reading that constitute the base for the learning of others knowledge. The learning of reading, in the Non Maternal language, requires a development of the oral language in Portuguese Language, which stimulates the reasoning of the child through playful exercises and cognitivists and construtivists approaches. In this way, the competences of phonological processing in the acquisition of the competences of reading are important for the discrimination of written text and favor the learning and the development of reading. The child, through the discovery, begins to elaborate concepts in the way to obtain a relation with the written language, by functional form. Adopting a methodology of case study and through questionnaires, direct observation and collect of documentary information, this dissertation presents and analyzes connected aspects to the literacy of capeverdian children in the beginning of the schooling and to the learning of reading as basic support for the learning of Non Maternal language. The subsidies collected by the study, presented in this dissertation will contribute for the education progress of reading and, also, for implement successfully the learning of reading of the students, developing to practical of reading and the expectations in uncover the multiplicity of the dimensions of experience in that domain and contribute for a relative comprehension of written and reading modes.

Aplicação dos Sistemas de Informação Geográfica em Estudos de Caracterização Biofísica da Ilha de Santo Antão em Cabo Verde

Com características morfológicas e edafo-climáticas extremamente diversificadas, a ilha de Santo Antão em Cabo Verde apresenta uma reconhecida vulnerabilidade ambiental a par de uma elevada carência de estudos científicos que incidam sobre essa realidade e sirvam de base à uma compreensão integrada dos fenómenos. A cartografia digital e as tecnologias de informação geográfica vêm proporcionando um avanço tecnológico na colecção, armazenamento e processamento de dados espaciais. Várias ferramentas actualmente disponíveis permitem modelar uma multiplicidade de factores, localizar e quantificar os fenómenos bem como e definir os níveis de contribuição de diferentes factores no resultado final. No presente estudo, desenvolvido no âmbito do curso de pós-graduação e mestrado em sistemas de Informação geográfica realizado pela Universidade de Trás-os-Montes e Alto Douro, pretende-se contribuir para a minimização do deficit de informação relativa às características biofísicas da citada ilha, recorrendo-se à aplicação de tecnologias de informação geográfica e detecção remota, associadas à análise estatística multivariada. Nesse âmbito, foram produzidas e analisadas cartas temáticas e desenvolvido um modelo de análise integrada de dados. Com efeito, a multiplicidade de variáveis espaciais produzidas, de entre elas 29 variáveis com variação contínua passíveis de influenciar as características biofísicas da região e, possíveis ocorrências de efeitos mútuos antagónicos ou sinergéticos, condicionam uma relativa complexidade à interpretação a partir dos dados originais. Visando contornar este problema, recorre-se a uma rede de amostragem sistemática, totalizando 921 pontos ou repetições, para extrair os dados correspondentes às 29 variáveis nos pontos de amostragem e, subsequente desenvolvimento de técnicas de análise estatística multivariada, nomeadamente a análise em componentes principais. A aplicação destas técnicas permitiu simplificar e interpretar as variáreis originais, normalizando-as e resumindo a informação contida na diversidade de variáveis originais, correlacionadas entre si, num conjunto de variáveis ortogonais (não correlacionadas), e com níveis de importância decrescente, as componentes principais. Fixou-se como meta a concentração de 75% da variância dos dados originais explicadas pelas primeiras 3 componentes principais e, desenvolveu-se um processo interactivo em diferentes etapas, eliminando sucessivamente as variáveis menos representativas. Na última etapa do processo as 3 primeiras CP resultaram em 74,54% da variância dos dados originais explicadas mas, que vieram a demonstrar na fase posterior, serem insuficientes para retratar a realidade. Optou-se pela inclusão da 4ª CP (CP4), com a qual 84% da referida variância era explicada e, representando oito variáveis biofísicas: a altitude, a densidade hidrográfica, a densidade de fracturação geológica, a precipitação, o índice de vegetação, a temperatura, os recursos hídricos e a distância à rede hidrográfica. A subsequente interpolação da 1ª componente principal (CP1) e, das principais variáveis associadas as componentes CP2, CP3 e CP4 como variáveis auxiliares, recorrendo a técnicas geoestatística em ambiente ArcGIS permitiu a obtenção de uma carta representando 84% da variação das características biofísicas no território. A análise em clusters validada pelo teste “t de Student” permitiu reclassificar o território em 6 unidades biofísicas homogéneas. Conclui-se que, as tecnologias de informação geográfica actualmente disponíveis a par de facilitar análises interactivas e flexíveis, possibilitando que se faça variar temas e critérios, integrar novas informações e introduzir melhorias em modelos construídos com bases em informações disponíveis num determinado contexto, associadas a técnicas de análise estatística multivariada, possibilitam, com base em critérios científicos, desenvolver a análise integrada de múltiplas variáveis biofísicas cuja correlação entre si, torna complexa a compreensão integrada dos fenómenos.

On p-beauty contest integer games

In this paper we provide a full characterization of the pure-strategyNash Equilibria for the p-Beauty Contest Game when we restrict player schoices to integer numbers. Opposed to the case of real number choices,equilibrium uniqueness may be lost depending on the value of p and thenumber of players: in particular, as p approaches 1 any symmetric profileconstitutes a Nash Equilibrium. We also show that any experimental p-BeautyContest Game can be associated to a game with the integer restriction andthus multiplicity of equilibria becomes an issue. Finally, we show thatin these games the iterated deletion of weakly dominated strategies maynot lead to a single outcome while the iterated best-reply process alwaysdoes (though the outcome obtained depends on the initial conditions).

Phylogenetic analyses of C4 photosynthesis evolution in grasses: genetics of convergence and convergence of genes

Summary : During the evolutionary diversification of organisms, similar ecological constraints led to the recurrent appearances of the same traits (phenotypes) in distant lineages, a phenomenon called convergence. In most cases, the genetic origins of the convergent traits remain unknown, but recent studies traced the convergent phenotypes to recurrent alterations of the same gene or, in a few cases, to identical genetic changes. However, these cases remain anecdotal and there is a need for a study system that evolved several times independently and whose genetic determinism is well resolved and straightforward, such as C4 photosynthesis. This adaptation to warm environments, possibly driven by past atmospheric CO2 decreases, consists in a CO2-concentrating pump, created by numerous morphological and biochemical novelties. All genes encoding C4 enzymes already existed in C3 ancestors, and are supposed to have been recruited through gene duplication followed by neo-functionalization, to acquire the cell specific expression pattern and altered kinetic properties that characterize Ca-specific enzymes. These predictions have so far been tested only in species-poor and ecologically marginal C4 dicots. The monocots, and especially the grass family (Poaceae), the most important C4 family in terms of species number, ecological dominance and economical importance, have been largely under-considered as suitable study systems. This thesis aimed at understanding the evolution of the C4 trait in grasses at a molecular level and to use the genetics of C4 photosynthesis to infer the evolutionary history of the C4 phenotype and its driving selective pressures. A molecular phylogeny of grasses and affiliated monocots identified 17 to 18 independent acquisitions of the C4 pathway in the grass family. A relaxed molecular clock was used to date these events and the first C4 evolution was estimated in the Chloridoideae subfamily, between 32-25 million years ago, at a period when atmospheric CO2 abruptly declined. Likelihood models showed that after the COZ decline the probability of evolving the C4 pathway strongly increased, confirming low CO2 as a likely driver of C4 photosynthesis evolution. In order to depict the genetic changes linked to the numerous C4 origins, genes encoding phopshoenolpyruvate carboxylase (PEPC), the key-enzyme responsible for the initial fixation of atmospheric CO2 in the C4 pathway, were isolated from a large sample of C3 and C4 grasses. Phylogenetic analyses were used to reconstruct the evolutionary history of the PEPC multigene family and showed that the evolution of C4-specific PEPC had been driven by positive selection on 21 codons simultaneously in up to eight C4 lineages. These selective pressures led to numerous convergent genetic changes in many different C4 clades, highlighting the repeatability of some evolutionary processes, even at the molecular level. PEPC C4-adaptive changes were traced and used to show multiple appearances of the C, pathway in clades where species tree inferences were unable to differentiate multiple C4 appearances and a single appearance followed by C4 to C3 reversion. Further investigations of genes involved in some of the C4 subtypes only (genes encoding decarboxylating enzymes NADP-malic enzyme and phosphoenolpyruvate carboxykinase) showed that these C4-enzymes also evolved through strong positive selection and underwent parallel genetic changes during the different Ca origins. The adaptive changes on these subtype-specific C4 genes were used to retrace the history of the C4-subtypes phenotypes, which revealed that the evolution of C4-PEPC and C4-decarboxylating enzymes was in several cases disconnected, emphasizing the multiplicity of the C4 trait and the gradual acquisition of the features that create the CO2-pump. Finally, phylogenetic analyses of a gene encoding the Rubisco (the enzyme responsible for the fixation of CO2 into organic compounds in all photosynthetic organisms) showed that C4 evolution switched the selective pressures on this gene. Five codons were recurrently mutated to adapt the enzyme kinetics to the high CO2 concentrations of C4 photosynthetic cells. This knowledge could be used to introgress C4-like Rubisco in C3 crops, which could lead to an increased yield under predicted future high CO2 atmosphere. Globally, the phylogenetic framework adopted during this thesis demonstrated the widespread occurrence of genetic convergence on C4-related enzymes. The genetic traces of C4 photosynthesis evolution allowed reconstructing events that happened during the last 30 million years and proved the usefulness of studying genes directly responsible for phenotype variations when inferring evolutionary history of a given trait. Résumé Durant la diversification évolutive des organismes, des pressions écologiques similaires ont amené à l'apparition récurrente de certains traits (phénotypes) dans des lignées distantes, un phénomène appelé évolution convergente. Dans la plupart des cas, l'origine génétique des traits convergents reste inconnue mais des études récentes ont montré qu'ils étaient dus dans certains cas à des changements répétés du même gène ou, dans de rares cas, à des changements génétiques identiques. Malgré tout, ces cas restent anecdotiques et il y a un réel besoin d'un système d'étude qui ait évolué indépendamment de nombreuses fois et dont le déterminisme génétique soit clairement identifié. La photosynthèse dite en Ça répond à ces critères. Cette adaptation aux environnements chauds, dont l'évolution a pu être encouragé par des baisses passées de la concentration atmosphérique en CO2, est constituée de nombreuses nouveautés morphologiques et biochimiques qui créent une pompe à CO2. La totalité des gènes codant les enzymes Ç4 étaient déjà présents dans les ancêtres C3. Leur recrutement pour la photosynthèse Ç4 est supposé s'être fait par le biais de duplications géniques suivies par une néo-fonctionnalisation pour leur conférer l'expression cellule-spécifique et les propriétés cinétiques qui caractérisent les enzymes C4. Ces prédictions n'ont jusqu'à présent été testées que dans des familles C4 contenant peu d'espèces et ayant un rôle écologique marginal. Les graminées (Poaceae), qui sont la famille C4 la plus importante, tant en termes de nombre d'espèces que de dominance écologique et d'importance économique, ont toujours été considérés comme un système d'étude peu adapté et ont fait le sujet de peu d'investigations évolutives. Le but de cette thèse était de comprendre l'évolution de la photosynthèse en C4 chez les graminées au niveau génétique et d'utiliser les gènes pour inférer l'évolution du phénotype C4 ainsi que les pressions de sélection responsables de son évolution. Une phylogénie moléculaire de la famille des graminées et des monocotylédones apparentés a identifié 17 à 18 acquisitions indépendantes de la photosynthèse chez les graminées. Grâce à une méthode d'horloge moléculaire relâchée, ces évènements ont été datés et la première apparition C4 a été estimée dans la sous-famille des Chloridoideae, il y a 32 à 25 millions d'années, à une période où les concentrations atmosphériques de CO2 ont décliné abruptement. Des modèles de maximum de vraisemblance ont montré qu'à la suite du déclin de CO2, la probabilité d'évoluer la photosynthèse C4 a fortement augmenté, confirmant ainsi qu'une faible concentration de CO2 est une cause potentielle de l'évolution de la photosynthèse C4. Afin d'identifier les mécanismes génétiques responsables des évolutions répétées de la photosynthèse C4, un segment des gènes codant pour la phosphoénolpyruvate carboxylase (PEPC), l'enzyme responsable de la fixation initiale du CO2 atmosphérique chez les plantes C4, ont été séquencés dans une centaine de graminées C3 et C4. Des analyses phylogénétiques ont permis de reconstituer l'histoire évolutive de la famille multigénique des PEPC et ont montré que l'évolution de PEPC spécifiques à la photosynthèse Ça a été causée par de la sélection positive agissant sur 21 codons, et ce simultanément dans huit lignées C4 différentes. Cette sélection positive a conduit à un grand nombre de changements génétiques convergents dans de nombreux clades différents, ce qui illustre la répétabilité de certains phénomènes évolutifs, et ce même au niveau génétique. Les changements sur la PEPC liés au C4 ont été utilisés pour confirmer des évolutions indépendantes du phénotype C4 dans des clades où l'arbre des espèces était incapable de différencier des apparitions indépendantes d'une seule apparition suivie par une réversion de C4 en C3. En considérant des gènes codant des protéines impliquées uniquement dans certains sous-types C4 (deux décarboxylases, l'enzyme malique à NADP et la phosphoénolpyruvate carboxykinase), des études ultérieures ont montré que ces enzymes C4 avaient elles-aussi évolué sous forte sélection positive et subi des changements génétiques parallèles lors des différentes origines de la photosynthèse C4. Les changements adaptatifs sur ces gènes liés seulement à certains sous-types C4 ont été utilisés pour retracer l'histoire des phénotypes de sous-types C4, ce qui a révélé que les caractères formant le trait C4 ont, dans certains cas, évolué de manière déconnectée. Ceci souligne la multiplicité du trait C4 et l'acquisition graduelle de composants participant à la pompe à CO2 qu'est la photosynthèse C4. Finalement, des analyses phylogénétiques des gènes codant pour la Rubisco (l'enzyme responsable de la fixation du CO2 en carbones organiques dans tous les organismes photosynthétiques) ont montré que l'évolution de la photosynthèse Ça a changé les pressions de sélection sur ce gène. Cinq codons ont été mutés de façon répétée afin d'adapter les propriétés cinétiques de la Rubisco aux fortes concentrations de CO2 présentes dans les cellules photosynthétiques des plantes C4. Globalement, l'approche phylogénétique adoptée durant cette thèse de doctorat a permis de démontré des phénomène fréquents de convergence génétique sur les enzymes liées à la photosynthèse C4. Les traces génétiques de l'évolution de la photosynthèse C4 ont permis de reconstituer des évènements qui se sont produits durant les derniers 30 millions d'années et ont prouvé l'utilité d'étudier des gènes directement responsables des variations phénotypiques pour inférer l'histoire évolutive d'un trait donné.

A simple model of multiple equilibria based on risk

This paper shows how risk may aggravate fluctuations in economies with imperfect insurance and multiple assets. A two period job matching model is studied, in which risk averse agents act both as workers and as entrepreneurs. They choose between two types of investment: one type is riskless, while the other is a risky activity that creates jobs.Equilibrium is unique under full insurance. If investment is fully insured but unemployment risk is uninsured, then precautionary saving behavior dampens output fluctuations. However, if both investment and employment are uninsured, then an increase in unemployment gives agents an incentive to shift investment away from the risky asset, further increasing unemployment. This positive feedback may lead to multiple Pareto ranked equilibria. An overlapping generations version of the model may exhibit poverty traps or persistent multiplicity. Greater insurance is doubly beneficial in this context since it can both prevent multiplicity and promote risky investment.

Hypothesis on immigration and welfare

The number of hypothesis trying to explain which are the reasons behind the decision to migrate to work into a developed country are diverse and at the same time, difficult to test due to the multiplicity of factors which affect it. This papers attempts to move forward trying to disentangle which are the socio-economic factors that explain the differences in the figures of immigrants in the OECD countries. We show empirical evidence about the determinants of the migratory flows to 17 OECD countries from 65 countries in the 1980-2000 period. Our results reveal the importance to differentiate the inflows composition by at least income in the origin countries. Thus, regarding inflows from non-high-income countries, the results suggest that there is a pull effect from monetary and not real income, and then, the welfare magnets hypothesis should be rejected. This group reacts more to the migratory policy than the inflows coming from high-income countries, although those policies designed to slow down the inflows have not been able, in the aggregate, to reduce them.

Acute neurorehabilitation: does a neurosensory and coordinated interdisciplinary programme reduce tracheostomy weaning time and weaning failure?

BACKGROUND/PURPOSE: A new coordinated interdisciplinary unit was created in the acute section of the department of clinical neurosciences, the Acute NeuroRehabilitation (NRA) unit. The objective was to evaluate the impact of the unit and its neurosensory programme on the management of tracheostomy patients in terms of reduction in the average time taken for weaning, weaning success rate and therapeutic efficiency. METHODS: This 49-month retrospective study compares 2 groups of tracheostomy patients before (n = 34) and after (n = 46) NRA intervention. The outcome measures evaluate the benefits of the NRA unit intervention (time to decannulation, weaning and complication rates) and the benefits of the coordination (time to registration in a rehabilitation centre and rate of non-compliance with standards of care). RESULTS: Weaning failure rate was reduced from 27.3% to 9.1%, no complications or recannulations were observed in the post-intervention group after weaning and time to decannulation following admission to our unit decreased from 19.13 to 12.75 days. The rate of non-compliance with patient standards of care was significantly reduced from 45% to 30% (Mann-Whitney p = 0.003). DISCUSSION/CONCLUSIONS: This interdisciplinary weaning programme helped to reduce weaning time and weaning failure, without increased complications, in the sample studied. Coordination improved the efficiency of the interdisciplinary team in the multiplicity and complexity of the different treatments.

Improved statistical evaluation of group differences in connectomes by screening-filtering strategy with application to study maturation of brain connections between childhood and adolescence.

Detecting local differences between groups of connectomes is a great challenge in neuroimaging, because the large number of tests that have to be performed and the impact on multiplicity correction. Any available information should be exploited to increase the power of detecting true between-group effects. We present an adaptive strategy that exploits the data structure and the prior information concerning positive dependence between nodes and connections, without relying on strong assumptions. As a first step, we decompose the brain network, i.e., the connectome, into subnetworks and we apply a screening at the subnetwork level. The subnetworks are defined either according to prior knowledge or by applying a data driven algorithm. Given the results of the screening step, a filtering is performed to seek real differences at the node/connection level. The proposed strategy could be used to strongly control either the family-wise error rate or the false discovery rate. We show by means of different simulations the benefit of the proposed strategy, and we present a real application of comparing connectomes of preschool children and adolescents.

A cell therapy approach for erythropoietin delivery using encapsulated human primary fibroblasts

Summary Cell therapy has emerged as a strategy for the treatment of various human diseases. Cells can be transplanted considering their morphological and functional properties to restore a tissue damage, as represented by blood transfusion, bone marrow or pancreatic islet cells transplantation. With the advent of the gene therapy, cells also were used as biological supports for the production of therapeutic molecules that can act either locally or at distance. This strategy represents the basis of ex vivo gene therapy characterized by the removal of cells from an organism, their genetic modification and their implantation into the same or another individual in a physiologically suitable location. The tissue or biological function damage dictates the type of cells chosen for implantation and the required function of the implanted cells. The general aim of this work was to develop an ex vivo gene therapy approach for the secretion of erythropoietin (Epo) in patients suffering from Epo-responsive anemia, thus extending to humans, studies previously performed with mouse cells transplanted in mice and rats. Considering the potential clinical application, allogeneic primary human cells were chosen for practical and safety reasons. In contrast to autologous cells, the use of allogeneic cells allows to characterize a cell lineage that can be further transplanted in many individuals. Furthermore allogeneic cells avoid the potential risk of zoonosis encountered with xenogeneic cells. Accordingly, the immune reaction against this allogeneic source was prevented by cell macro- encapsulation that prevents cell-to-cell contact with the host immune system and allows to easy retrieve the implanted device. The first step consisted in testing the survival of various human primary cells that were encapsulated and implanted for one month in the subcutaneous tissue of immunocompetent and naturally or therapeutically immunodepressed mice, assuming that xenogeneic applications constitute a stringent and representative screening before human transplantation. A fibroblast lineage from the foreskin of a young donor, DARC 3.1 cells, showed the highest mean survival score. We have then performed studies to optimize the manufacturing procedures of the encapsulation device for successful engraftment. The development of calcifications on the polyvinyl alcohol (PVA) matrix serving as a scaffold for enclosed cells into the hollow fiber devices was reported after one month in vivo. Various parameters, including matrix rinsing solutions, batches of PVA and cell lineages were assessed for their respective role in the development of the phenomenon. We observed that the calcifications could be totally prevented by using ultra-pure sterile water instead of phosphate buffer saline solution in the rinsing procedure of the PVA matrix. Moreover, a higher lactate dehydrogenase activity of the cells was found to decrease calcium depositions due to more acidic microenvironment, inhibiting the calcium precipitation. After the selection of the appropriate cell lineage and the optimization of encapsulation conditions, a retroviral-based approach was applied to DARC 3.1 fibroblasts for the transduction of the human Epo cDNA. Various modifications of the retroviral vector and the infection conditions were performed to obtain clinically relevant levels of human Epo. The insertion of a post-transcriptional regulatory element from the woodchuck hepatitis virus as well as of a Kozak consensus sequence led to a 7.5-fold increase in transgene expression. Human Epo production was further optimized by increasing the multiplicity of infection and by selecting high producer cells allowing to reach 200 IU hEpo/10E6 cells /day. These modified cells were encapsulated and implanted in vivo in the same conditions as previously described. All the mouse strains showed a sustained increase in their hematocrit and a high proportion of viable cells were observed after retrieval of the capsules. Finally, in the perspective of human application, a syngeneic model using encapsulated murine myoblasts transplanted in mice was realized to investigate the roles of both the host immune response and the cells metabolic requirements. Various loading densities and anti-inflammatory as well as immunosuppressive drugs were studied. The results showed that an immune process is responsible of cell death in capsules loaded at high cell density. A supporting matrix of PVA was shown to limit the cell density and to avoid early metabolic cell death, preventing therefore the immune reaction. This study has led to the development of encapsulated cells of human origin producing clinically relevant amounts of human EPO. This work resulted also to the optimization of cell encapsulation technical parameters allowing to begin a clinical application in end-stage renal failure patients. Résumé La thérapie cellulaire s'est imposée comme une stratégie de traitement potentiel pour diverses maladies. Si l'on considère leur morphologie et leur fonction, les cellules peuvent être transplantées dans le but de remplacer une perte tissulaire comme c'est le cas pour les transfusions sanguines ou les greffes de moelle osseuse ou de cellules pancréatiques. Avec le développement de la thérapie génique, les cellules sont également devenues des supports biologiques pour la production de molécules thérapeutiques. Cette stratégie représente le fondement de la thérapie génique ex vivo, caractérisée par le prélèvement de cellules d'un organisme, leur modification génétique et leur implantation dans le même individu ou dans un autre organisme. Le choix du type de cellule et la fonction qu'elle doit remplir pour un traitement spécifique dépend du tissu ou de la fonction biologique atteintes. Le but général de ce travail est de développer .une approche par thérapie génique ex vivo de sécrétion d'érythropoïétine (Epo) chez des patients souffrant d'anémie, prolongeant ainsi des travaux réalisés avec des cellules murines implantées chez des souris et des rats. Dans cette perpective, notre choix s'est porté sur des cellules humaines primaires allogéniques. En effet, contrairement aux cellules autologues, une caractérisation unique de cellules allogéniques peut déboucher sur de nombreuses applications. Par ailleurs, l'emploi de cellules allogéniques permet d'éviter les riques de zoonose que l'on peut rencontrer avec des cellules xénogéniques. Afin de protéger les cellules allogéniques soumises à une réaction immunitaire, leur confinement dans des macro-capsules cylindriques avant leur implantation permet d'éviter leur contact avec les cellules immunitaires de l'hôte, et de les retrouver sans difficulté en cas d'intolérance ou d'effet secondaire. Dans un premier temps, nous avons évalué la survie de différentes lignées cellulaires humaines primaires, une fois encapsulées et implantées dans le tissu sous-cutané de souris, soit immunocompétentes, soit immunodéprimées naturellement ou par l'intermédiaire d'un immunosuppresseur. Ce modèle in vivo correspond à des conditions xénogéniques et représente par conséquent un environnement de loin plus hostile pour les cellules qu'une transplantation allogénique. Une lignée fibroblastique issue du prépuce d'un jeune enfant, nommée DARC 3 .1, a montré une remarquable résistance avec un score de survie moyen le plus élevé parmi les lignées testées. Par la suite, nous nous sommes intéressés aux paramètres intervenant dans la réalisation du système d'implantation afin d'optimaliser les conditions pour une meilleure adaptation des cellules à ce nouvel environnement. En effet, en raison de l'apparition, après un mois in vivo, de calcifications au niveau de la matrice de polyvinyl alcohol (PVA) servant de support aux cellules encapsulées, différents paramètres ont été étudiés, tels que les procédures de fabrication, les lots de PVA ou encore les lignées cellulaires encapsulées, afin de mettre en évidence leur rôle respectif dans la survenue de ce processus. Nous avons montré que l'apparition des calcifications peut être totalement prévenue par l'utilisation d'eau pure au lieu de tampon phosphaté lors du rinçage des matrices de PVA. De plus, nous avons observe qu'un taux de lactate déshydrogénase cellulaire élevé était corrélé avec une diminution des dépôts de calcium au sein de la matrice en raison d'un micro-environnement plus acide inhibant la précipitation du calcium. Après sélection de la lignée cellulaire appropriée et de l'optimisation des conditions d'encapsulation, une modification génétique des fibroblastes DARC 3.1 a été réalisée par une approche rétrovirale, permettant l'insertion de l'ADN du gène de l'Epo dans le génome cellulaire. Diverses modifications, tant au niveau génétique qu'au niveau des conditions d'infection, ont été entreprises afin d'obtenir des taux de sécrétion d'Epo cliniquement appropriés. L'insertion dans la séquence d'ADN d'un élément de régulation post¬transcriptionnelle dérivé du virus de l'hépatite du rongeur (« woodchuck ») ainsi que d'une séquence consensus appelée « Kozak » ont abouti à une augmentation de sécrétion d'Epo 7.5 fois plus importante. De même, l'optimisation de la multiplicité d'infection et la sélection plus drastique des cellules hautement productrices ont permis finalement d'obtenir une sécrétion correspondant à 200 IU d'Epo/10E6 cells/jour. Ces cellules génétiquement modifiées ont été encapsulées et implantées in vivo dans les mêmes conditions que celles décrites plus haut. Toutes les souris transplantées ont montré une augmentation significative de leur hématocrite et une proportion importante de cellules présentait une survie conservée au moment de l'explantation des capsules. Finalement, dans la perspective d'une application humaine, un modèle syngénique a été proposé, basé sur l'implantation de myoblastes murins encapsulés dans des souris, afin d'investiguer les rôles respectifs de la réponse immunitaire du receveur et des besoins métaboliques cellulaires sur leur survie à long terme. Les cellules ont été encapsulées à différentes densités et les animaux transplantés se sont vus administrer des injections de molécules anti-inflammatoires ou immunosuppressives. Les résultats ont démontré qu'une réaction immunologique péri-capsulaire était à la base du rejet cellulaire dans le cas de capsules à haute densité cellulaire. Une matrice de PVA peut limiter cette densité et éviter une mort cellulaire précoce due à une insuffisance métabolique et par conséquent prévenir la réaction immunitaire. Ce travail a permis le développement de cellules encapsulées d'origine humaine sécrétant des taux d'Epo humaine adaptés à des traitements cliniques. De pair avec l'optimalisation des paramètres d'encapsulation, ces résultats ont abouti à l'initiation d'une application clinique destinée à des patients en insuffisance rénale terminale.