959 resultados para expansion stochastique


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Electricity is a strategic service in modern societies. Thus, it is extremely important for governments to be able to guarantee an affordable and reliable supply, which depends to a great extent on an adequate expansion of the generation and transmission capacities. Cross- border integration of electricity markets creates new challenges for the regulators, since the evolution of the market is now influenced by the characteristics and policies of neighbouring countries. There is still no agreement on why and how regions should integrate their electricity markets. The aim of this thesis is to improve the understanding of integrated electricity markets and how their behaviour depends on the prevailing characteristics of the national markets and the policies implemented in each country. We developed a simulation model to analyse under what circumstances integration is desirable. This model is used to study three cases of interconnection between two countries. Several policies regarding interconnection expansion and operation, combined with different generation capacity adequacy mechanisms, are evaluated. The thesis is composed of three papers. The first paper presents a detailed description of the model and an analysis of the case of Colombia and Ecuador. It shows that market coupling can bring important benefits, but the relative size of the countries can lead to import dependency issues in the smaller country. The second paper compares the case of Colombia and Ecuador with the case of Great Britain and France. These countries are significantly different in terms of electricity sources, hydro- storage capacity, complementarity and demand growth. We show that complementarity is essential in order to obtain benefits from integration, while higher demand growth and hydro- storage capacity can lead to counterintuitive outcomes, thus complicating policy design. In the third paper, an extended version of the model presented in the first paper is used to analyse the case of Finland and its interconnection with Russia. Different trading arrangements are considered. We conclude that unless interconnection capacity is expanded, the current trading arrangement, where a single trader owns the transmission rights and limits the flow during peak hours, is beneficial for Finland. In case of interconnection expansion, market coupling would be preferable. We also show that the costs of maintaining a strategic reserve in Finland are justified in order to limit import dependency, while still reaping the benefits of interconnection. In general, we conclude that electricity market integration can bring benefits if the right policies are implemented. However, a large interconnection capacity is only desirable if the countries exhibit significant complementarity and trust each other. The outcomes of policies aimed at guaranteeing security of supply at a national level can be quite counterintuitive due to the interactions between neighbouring countries and their effects on interconnection and generation investments. Thus, it is important for regulators to understand these interactions and coordinate their decisions in order to take advantage of the interconnection without putting security of supply at risk. But it must be taken into account that even when integration brings benefits to the region, some market participants lose and might try to hinder the integration process. -- Dans les sociétés modernes, l'électricité est un service stratégique. Il est donc extrêmement important pour les gouvernements de pouvoir garantir la sécurité d'approvisionnement à des prix abordables. Ceci dépend en grande mesure d'une expansion adéquate des capacités de génération et de transmission. L'intégration des marchés électriques pose des nouveaux défis pour les régulateurs, puisque l'évolution du marché est maintenant influencée par les caractéristiques et les politiques des pays voisins. Il n'est pas encore claire pourquoi ni comment les marches électriques devraient s'intégrer. L'objectif de cette thèse est d'améliorer la compréhension des marchés intégrés d'électricité et de leur comportement en fonction des caractéristiques et politiques de chaque pays. Un modèle de simulation est proposé pour étudier les conditions dans lesquelles l'intégration est désirable. Ce modèle est utilisé pour étudier trois cas d'interconnexion entre deux pays. Plusieurs politiques concernant l'expansion et l'opération de l'interconnexion, combinées avec différents mécanismes de rémunération de la capacité, sont évalués. Cette thèse est compose de trois articles. Le premier présente une description détaillée du modèle et une analyse du cas de la Colombie et de l'Equateur. Il montre que le couplage de marchés peut amener des bénéfices importants ; cependant, la différence de taille entre pays peut créer des soucis de dépendance aux importations pour le pays le plus petit. Le second papier compare le cas de la Colombie et l'Equateur avec le cas de la Grande Bretagne et de la France. Ces pays sont très différents en termes de ressources, taille des réservoirs d'accumulation pour l'hydro, complémentarité et croissance de la demande. Nos résultats montrent que la complémentarité joue un rôle essentiel dans l'obtention des bénéfices potentiels de l'intégration, alors qu'un taux élevé de croissance de la demande, ainsi qu'une grande capacité de stockage, mènent à des résultats contre-intuitifs, ce qui complique les décisions des régulateurs. Dans le troisième article, une extension du modèle présenté dans le premier article est utilisée pour analyser le cas de la Finlande et de la Russie. Différentes règles pour les échanges internationaux d'électricité sont considérées. Nos résultats indiquent qu'à un faible niveau d'interconnexion, la situation actuelle, où un marchand unique possède les droits de transmission et limite le flux pendant les heures de pointe, est bénéfique pour la Finlande. Cependant, en cas d'expansion de la capacité d'interconnexion, «market coupling» est préférable. préférable. Dans tous les cas, la Finlande a intérêt à garder une réserve stratégique, car même si cette politique entraine des coûts, elle lui permet de profiter des avantages de l'intégration tout en limitant ca dépendance envers les importations. En général, nous concluons que si les politiques adéquates sont implémentées, l'intégration des marchés électriques peut amener des bénéfices. Cependant, une grande capacité d'interconnexion n'est désirable que si les pays ont une complémentarité importante et il existe une confiance mutuelle. Les résultats des politiques qui cherchent à préserver la sécurité d'approvisionnement au niveau national peuvent être très contre-intuitifs, étant données les interactions entre les pays voisins et leurs effets sur les investissements en génération et en interconnexion. Il est donc très important pour les régulateurs de comprendre ces interactions et de coordonner décisions à fin de pouvoir profiter de l'interconnexion sans mettre en danger la sécurité d'approvisionnement. Mais il faut être conscients que même quand l'intégration amène de bénéfices pour la région, certains participants au marché sont perdants et pourraient essayer de bloquer le processus d'intégration.

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The elucidation of the mechanisms directing β-cell mass regeneration and maintenance is of interest, because the deficit of β-cell mass contributes to diabetes onset and progression. We previously found that the level of the microRNA (miRNA) miR-338-3p is decreased in pancreatic islets from rodent models displaying insulin resistance and compensatory β-cell mass expansion, including pregnant rats, diet-induced obese mice, and db/db mice. Transfection of rat islet cells with oligonucleotides that specifically block miR-338-3p activity increased the fraction of proliferating β-cells in vitro and promoted survival under proapoptotic conditions without affecting the capacity of β-cells to release insulin in response to glucose. Here, we evaluated the role of miR-338-3p in vivo by injecting mice with an adeno-associated viral vector permitting specific sequestration of this miRNA in β-cells. We found that the adeno-associated viral construct increased the fraction of proliferating β-cells confirming the data obtained in vitro. miR-338-3p is generated from an intron of the gene coding for apoptosis-associated tyrosine kinase (AATK). Similarly to miR-338-3p, we found that AATK is down-regulated in rat and human islets and INS832/13 β-cells in the presence of the cAMP-raising agents exendin-4, estradiol, and a G-protein-coupled Receptor 30 agonist. Moreover, AATK expression is reduced in islets of insulin resistant animal models and selective silencing of AATK in INS832/13 cells by RNA interference promoted β-cell proliferation. The results point to a coordinated reduction of miR-338-3p and AATK under insulin resistance conditions and provide evidence for a cooperative action of the miRNA and its hosting gene in compensatory β-cell mass expansion.

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Strategies for expanding hematopoietic stem cells (HSCs) include coculture with cells that recapitulate their natural microenvironment, such as bone marrow stromal stem/progenitor cells (BMSCs). Plastic-adherent BMSCs may be insufficient to preserve primitive HSCs. Here, we describe a method of isolating and culturing human BMSCs as nonadherent mesenchymal spheres. Human mesenspheres were derived from CD45- CD31- CD71- CD146+ CD105+ nestin+ cells but could also be simply grown from fetal and adult BM CD45--enriched cells. Human mesenspheres robustly differentiated into mesenchymal lineages. In culture conditions where they displayed a relatively undifferentiated phenotype, with decreased adherence to plastic and increased self-renewal, they promoted enhanced expansion of cord blood CD34+ cells through secreted soluble factors. Expanded HSCs were serially transplantable in immunodeficient mice and significantly increased long-term human hematopoietic engraftment. These results pave the way for culture techniques that preserve the self-renewal of human BMSCs and their ability to support functional HSCs.

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Previous studies have shown that regulated firms diversify for reasons that are different than for unregulated firms. We explore some of these differences by providing a theoretical model that starts by considering the firm-regulator relationship as an incomplete information issue, in which a regulated incumbent has knowledge that the regulator does not have, but the firm cannot convey hard information about this knowledge. The incumbent faces both market and nonmarket competition from a new entrant. In that context, we show that when the firm faces tough nonmarket competition domestically, going abroad can create a mechanism that makes information transmission to the regulator more credible. International expansion can thus be a way to solve domestic nonmarket issues in addition to being a catalyst for growth.

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The expansion of an isolated hot spherical nucleus with excitation energy and its caloric curve are studied in a thermodynamic model with the SkM∗ force as the nuclear effective two-body inter-action. The calculated results are shown to compare well with the recent experimental data from energetic nuclear collisions. The fluctuations in temperature and density are also studied. They are seen to build up very rapidly beyond an excitation energy of ∼9 MeV/u. Volume-conserving quadrupole deformation in addition to expansion indicates , however, nuclear disassembly above an excitation energy of ∼4 MeV/u.

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Different asymmetries between expansion and contraction (radial motions) have been reported in the literature. Often these patterns have been regarded as implying different channels for each type of radial direction (outward versus inwards) operating at a higher level of visual motion processing. In two experiments (detection and discrimination tasks) we report reaction time asymmetries between expansion and contraction. Power functions were fitted to the data. While an exponent of 0.5 accounted for the expansion data better, a value of unity yielded the best fit for the contraction data. Instead of interpreting these differences as corresponding to different higher order motion detectors, we regard these findings as reflecting the fact that expansion and contraction tap two distinct psychophysical input channels underlying the processing of fast and slow velocities respectively.

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Variante(s) de titre : Le Guide Sam pour l'expansion économique française dans le Levant

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Co-culture techniques associating both dermal fibroblasts and epidermal keratinocytes have shown to have better clinical outcome than keratinocyte culture alone for the treatment of severe burns. Since fat grafting has been shown to improve scar remodelling, new techniques such as cell-therapy-assisted surgical reconstruction with isolated and expanded autologous adipose-derived stem cells (ASCs) would be of benefit to increase graft acceptation. Therefore, integrating ASCs into standardized procedures for cultured skin grafting could be of benefit for the patient if cell quality and quantity could be maintained. The purpose of this study was to evaluate ASC processing from adult tissue with simple isolation (without enzymatic steps), expansion (low density of 325-3,000 cells/cm2) and storage conditions to assure methods to enhance the cellular resistance when transferred back to the patient. Co-culture with cell-banked skin progenitor cells (FE002-SK2) showed an increase of 40-50% ASCs yield at high passages alongside with a better preservation of morphology, proper adipogenic and osteogenic differentiation and efficient biocompatibility with 3D collagen scaffolds. ASCs can be considered as a valuable additional cell source to be delivered in biological bandages to the patient in a need of tissue reconstruction such as burn patients.

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We introduce the effect of cohabitation between generations to a previous model on the slowdown of the Neolithic transition in Europe. This effect consists on the fact that human beings do not leave their children alone when they migrate, but on the contrary they cohabit until their children reach adulthood. We also use archaeological data to estimate the variation of the Mesolithic population density with distance, and use this information to predict the slowdown of the Neolithic front speed. The new equation leads to a substantial correction, up to 37%, relative to previous results. The new model is able to provide a satisfactory explanation not only to the relative speed but also to the absolute speed of the Neolithic front obtained from archaeological data

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De afrikanska ekonomierna växer med nära fyra procent per år och detta är en god indikation på kontinentens växande betydelse. Under kalla kriget hade afrikanska regeringar haft ett begränsat utrymme för opportunistisk köpslående, och därmed även en marginal att positionera sig strategiskt. Alltför ofta uppmuntrade och beskyddade stormakterna diktatorer och små lokala eliter som främst ville berika sig själv. I och med att globaliseringen tog fart och USA allt mera kom att dominera globalt, började en ny era i fråga om förändringar. Trots dessa förändringar på den globala arenan, har Afrika som kontinent hamnat i bakgrunden och jämfört med andra utvecklingsländer har Afrika attraherat ett fåtal utländska investeringar. Fortfarande, speciellt i Norden, finns det lite kunskap om hur utländska företag expanderar sin affärsverksamhet på den afrikanska kontinenten. Det råder brist på empiriska undersökningar om vilken inverkan afrikanska institutionella förändringar och lokala affärsmiljöer har på internationaliseringen och på de utländska företagens affärsutvecklingsstrategier på den afrikanska kontinenten. Med denna avhandling vill jag lyfta fram ett exempel på ett land (Sydafrika), som har lyckat dra nytta av de förändringar som 1990-talet förde med sig. I denna avhandling har jag intervjuat olika personer i ledande positioner inom olika finländska företag i Finland och i Sydafrika. Avhandlingen skapar en referensram för att öka förståelse och fördjupa analys av hur en kombination av olika interna och externa resurser ökar företagens konkurrenskraft och på det sättet bidrar till en framgångsrik affärsutveckling i Afrika. De politiska och sociala aktörerna samt aktörerna inom affärslivet besitter resurser som ambitiösa företag kan dra nytta av i sin strävan att erövra de nya framgångsrika marknaderna i Afrika. Gradvis ökar finländska företag sina insatser på den afrikanska kontinenten i strävan att skapa mervärde för sina kunder. Den värdeskapande processen gör att parterna måste närma sig varandra utgående från sina egna strategiska målsättningar. Hittills har finländska företag varit intresserad att sälja till Afrika men inte intresserad att köpa därifrån. Förutom de praktiska råden till olika företag, föreslår avhandlingen hur den finska staten och den sydafrikanska staten kunde agera tillsammans för att främja ömsesidigt handelsutbyte.

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The thesis aims to clarify the mixed results of prior literature regarding the performance impacts of entrepreneurship and human capital through service innovation and international expansion. The thesis examines the factors affecting degree of internationalization (DOI) and performance in ICT SMEs. These factors are entrepreneurial orientation (EO), human capital and service innovation (SI). The data was collected via questionnaire from Finnish ICT SMEs. The results suggest that EO consist of three dimensions that have different impact in DOI and SI. Also DOI has inverted U-shaped relationship with international performance, whereas DOI-profitability relationship is linear. The results of the study suggest that SMEs should not blindly increase their DOI, and that strategic focus is important.