Dissertations / Theses on the topic 'Cost Optimality'

La conception de l'appareillage électrique relève dune méthodologie généralement fort complexe. Les problèmes posés par la conception de l'appareillage électrique sont analysés et montrent l'inefficacité des méthodes mathématiques. Une approche ensembliste floue est exposée et permet de modéliser l'aspect heuristique du problème ainsi que les aspects scientifiques et industriels de la conception. Un système expert d'aide à la conception des disjoncteurs à arc tournant a été réalisé. Les résultats obtenus sont commentés et montrent l'intérêt d'une telle approche

Un des challenges actuels de la planification est la résolution de problèmes pour lesquels on cherche à optimiser la qualité d'une solution telle que le coût d'un plan-solution. Dans cette thèse, nous développons une méthode originale pour la planification de coût optimal dans un cadre classique non temporel et avec des actions valuées.<br /><br />Pour cela, nous utilisons une structure de longueur fixée appelée graphe de planification. L'extraction d'une solution optimale, à partir de ce graphe, est codée comme un problème de satisfaction de contraintes pondérées (WCSP). La structure spécifique des WCSP obtenus permet aux solveurs actuels de trouver, pour une longueur donnée, une solution optimale dans un graphe de planification contenant plusieurs centaines de nœuds. <br /><br />Nous présentons ensuite plusieurs méthodes pour déterminer la longueur maximale des graphes de planification nécessaire pour garantir l'obtention d'une solution de coût optimal. Ces méthodes incluent plusieurs notions universelles comme par exemple la notion d'ensembles d'actions indispensables pour lesquels toutes les solutions contiennent au moins une action de l'ensemble. <br /><br />Les résultats expérimentaux effectués montrent que l'utilisation de ces méthodes permet une diminution de 60% en moyenne de la longueur requise pour garantir l'obtention d'une solution de coût optimal. La comparaison expérimentale avec d'autres planificateurs montre que l'utilisation du graphe de planification et des CSP pondérés pour la planification optimale est possible en pratique même si elle n'est pas compétitive, en terme de temps de calcul, avec les planificateurs optimaux récents.

Although ground stone artifacts comprise a substantial portion of the archaeological record, their use as an important source of information about the past has remained underdeveloped. This is especially true for milling tools (mortars, pestles, grinding slabs and handstones) used by hunter-gatherers. Three studies that apply novel techniques and approaches to prehistoric milling technology are presented here. Together they demonstrate that substantial opportunities exist for new avenues of inquiry in the study of these artifacts. The first combines a simple optimization model from behavioral ecology with experimental data to weigh manufacturing costs against gains in grinding efficiency for mobile hunter-gatherers. Results run counter to widespread assumptions that mobile hunter-gatherers should not spend time shaping grinding surfaces on milling tools. Next, gas chromatography-mass spectrometry (GC-MS) is used to analyze lipid preservation in modified rock features in dry caves at Gila Cliff Dwellings National Monument, New Mexico. A high concentration of lipids, derived from processing a seed resource, was recovered from a grinding surface in these caves. The lipid content in this surface is comparable to amounts recovered from select pottery sherds that have been used for radiocarbon dating. The third study uses synchronic and diachronic variability in morphology, use-wear, and symbolic content to analyze ground stone milling tools from mortuary contexts in the San Francisco Bay Area of California. Archaeological and ethnographic evidence supports the inferred association of certain mortars with feasting and ritual activities. Differences in the representation of some of these forms in male and female graves may reflect changes in the roles of women and men in community ritual and politics.

Un des challenges actuels de la planification est la résolution de problèmes pour lesquels on cherche à optimiser la qualité d'une solution telle que le coût d'un plan-solution. Dans cette thèse, nous développons une méthode originale pour la planification de coût optimal dans un cadre classique non temporel et avec des actions valuées. Pour cela, nous utilisons une structure de longueur fixée appelée graphe de planification. L'extraction d'une solution optimale, à partir de ce graphe, est codée comme un problème de satisfaction de contraintes pondérées (WCSP). La structure spécifique des WCSP obtenus permet aux solveurs actuels de trouver, pour une longueur donnée, une solution optimale dans un graphe de planification contenant plusieurs centaines de nœuds. Nous présentons ensuite plusieurs méthodes pour déterminer la longueur maximale des graphes de planification nécessaire pour garantir l'obtention d'une solution de coût optimal. Ces méthodes incluent plusieurs notions universelles comme par exemple la notion d'ensembles d'actions indispensables pour lesquels toutes les solutions contiennent au moins une action de l'ensemble. Les résultats expérimentaux effectués montrent que l'utilisation de ces méthodes permet une diminution de 60% en moyenne de la longueur requise pour garantir l'obtention d'une solution de coût optimal. La comparaison expérimentale avec d'autres planificateurs montre que l'utilisation du graphe de planification et des CSP pondérés pour la planification optimale est possible en pratique même si elle n'est pas compétitive, en terme de temps de calcul, avec les planificateurs optimaux récents<br>For planning to come of age, plans must be judged by a measure of quality, such as the total cost of actions. This thesis describes an optimal-cost planner in the classical planning framework except that each action has a cost. We code the extraction of an optimal plan, from a planning graph with a fixed number k of levels, as a weighted constraint satisfaction problem (WCSP). The specific structure of the resulting WCSP means that a state-of-the-art exhaustive solver was able to find an optimal plan in planning graphs containing several thousand nodes. We present several methods for determining a tight bound on the number of planning-graph levels required to ensure finding a globally optimal plan. These include universal notions such as indispensable sets S of actions: every valid plan contains at least one action in S. Different types of indispensable sets can be rapidly detected by solving relaxed planning problems related to the original problem. On extensive trials on benchmark problems, the bound on the number of planning-graph levels was reduced by an average of 60% allowing us to solve many instances to optimality. Thorough experimental investigations demonstrated that using the planning graph in optimal planning is a practical possibility, although not competitive, in terms of computation time, with a recent state-of-the-art optimal planner

Nos travaux concernent la mise en œuvre de méthodologies pour la résolution et l'optimisation de la production en tenant compte des impératifs économiques, jouant aujourd'hui un rôle déterminant dans la conduite de la production industrielle. Pour le problème du job-shop flexible dans lequel les interactions entre les critères sont supposées disponibles, cinq critères ont été retenus : le Makespan, la charge critique, la charge totale, la pénalité de retards/avance et le coût de la production. Dans ce sens, nous avons, d'abord, traité le problème de décision et d'évaluation d'une solution et introduit ensuite trois approches intégrées, basées sur les algorithmes génétiques, améliorant les approches évolutionnistes existant dans la littérature : la méthode statique basée sur l'intégrale de Choquet, la méthode approchée basée sur le concept Paréto-optimalité ainsi que la méthode basée sur le concept de ε-dominance Paréto-optimalité. Les approches adoptées consistent à générer une variété de solutions optimales diversifiées dans l'espace de recherche de solutions, et d'aider le décideur, quand il ne peut pas donner une préférence particulière à l'une des fonctions objectif. Les résultats proposés, obtenus globalement pour l'ensemble des critères, ont été comparés, avec succès, avec ceux obtenus par d'autres approches existantes sur plusieurs benchmarks de complexités distinctes.

Dans cette thèse, tout d’abord, nous faisons l’Analyse Mathématique du modèle exact du chauffage radiatif d’un corps semi-transparent $\Omega$ par une source radiative noire qui l’entoure. Il s’agit donc d’étudier le couplage d’un système d’Equations de Transfert Radiatif avec condition au bord de réflectivité indépendantes avec une équation de conduction de la chaleur non linéaire avec condition limite non linéaire de type Robin. Nous prouvons l’existence et l’unicité de la solution et nous démontrons des bornes uniformes sur la solution et les intensités radiatives dans chaque bande de longueurs d’ondes pour laquelle le corps est semi-transparent, en fonction de bornes sur les données, Deuxièmement, nous considérons le problème du contrôle optimal de la température absolue à l’intérieur du corps semi-transparent $\Omega$ en agissant sur la température absolue de la source radiative noire qui l’entoure. À cet égard, nous introduisons la fonctionnelle coût appropriée et l’ensemble des contrôles admissibles $T_{S}$, pour lesquels nous prouvons l’existence de contrôles optimaux. En introduisant l’espace des états et l’équation d’état, une condition nécessaire de premier ordre pour qu’un contrôle $T_{S}$ : t ! $T_{S}$ (t) soit optimal, est alors dérivée sous la forme d’une inéquation variationnelle en utilisant le théorème des fonctions implicites et le problème adjoint. Ensuite, nous considérons le problème de l’existence et de l’unicité d’une solution faible des équations de la thermoviscoélasticité dans une formulation mixte de type Hellinger- Reissner, la nouveauté par rapport au travail de M.E. Rognes et R. Winther (M3AS, 2010) étant ici l’apparition de la viscosité dans certains coefficients de l’équation constitutive, viscosité qui dépend dans ce contexte de la température absolue T(x, t) et donc en particulier du temps t. Enfin, nous considérons dans ce cadre le problème du contrôle optimal de la déformation du corps semi-transparent $\Omega$, en agissant sur la température absolue de la source radiative noire qui l’entoure. Nous prouvons l’existence d’un contrôle optimal et nous calculons la dérivée Fréchet de la fonctionnelle coût réduite<br>This thesis begins with a rigorous mathematical analysis of the radiative heating of a semi-transparent body made of glass, by a black radiative source surrounding it. This requires the study of the coupling between quasi-steady radiative transfer boundary value problems with nonhomogeneous reflectivity boundary conditions (one for each wavelength band in the semi-transparent electromagnetic spectrum of the glass) and a nonlinear heat conduction evolution equation with a nonlinear Robin boundary condition which takes into account those wavelengths for which the glass behaves like an opaque body. We prove existence and uniqueness of the solution, and give also uniform bounds on the solution i.e. on the absolute temperature distribution inside the body and on the radiative intensities. Now, we consider the temperature $T_{S}$ of the black radiative source S surrounding the semi-transparent body $\Omega$ as the control variable. We adjust the absolute temperature distribution (x, t) 7! T(x, t) inside the semi-transparent body near a desired temperature distribution Td(·, ·) during the time interval of radiative heating ]0, tf [ by acting on $T_{S}$. In this respect, we introduce the appropriate cost functional and the set of admissible controls $T_{S}$, for which we prove the existence of optimal controls. Introducing the State Space and the State Equation, a first order necessary condition for a control $T_{S}$ : t 7! $T_{S}$ (t) to be optimal is then derived in the form of a Variational Inequality by using the Implicit Function Theorem and the adjoint problem. We come now to the goal problem which is the deformation of the semi-transparent body $\Omega$ by heating it with a black radiative source surrounding it. We introduce a weak mixed formulation of this thermoviscoelasticity problem and study the existence and uniqueness of its solution, the novelty here with respect to the work of M.E. Rognes et R. Winther (M3AS, 2010) being the apparition of the viscosity in some of the coefficients of the constitutive equation, viscosity which depends on the absolute temperature T(x, t) and thus in particular on the time t. Finally, we state in this setting the related optimal control problem of the deformation of the semi-transparent body $\Omega$, by acting on the absolute temperature of the black radiative source surrounding it. We prove the existence of an optimal control and we compute the Fréchet derivative of the associated reduced cost functional

L'utilisation d'outils en tant qu'aide à la nutrition a évolué indépendamment dans plusieurs groupes taxonomiques. Parmi ces outils, certaines constructions animales sont destinées à piéger les proies (e.g. les toiles d'araignées). Le fonctionnement physique de ces pièges reste largement inconnu à ce jour. Les pièges de type « toile » sont particulièrement difficiles à analyser car leurs architectures et leurs propriétés mécaniques sont complexes. Le fourmilion utilise du sable sec pour creuser un piège afin de capturer des fourmis. La proie est amenée jusqu'au prédateur sans effort de sa part dans les conditions optimales. Ce piège offre une architecture simple en forme de cratère, modèle idéal pour la compréhension physique du fonctionnement d'un piège. Une architecture optimale théorique est définie comme un cratère parfaitement conique, mais avec une pente inférieure à ce qu'autorise la physique du sable, afin d'éviter des avalanches inutiles. Un système de balayage et de modélisation tridimensionnelle a permis une reconstitution fine de l'architecture des pièges. Grâce à cet appareillage, il a été montré que le piège construit par le fourmilion était proche de l'optimalité, mais qu'une dégradation architecturale suscitait un comportement d'attaque et un coût de prédation : des jets de sable, pour déstabiliser les fourmis s'échappant du piège, et des morsures. Un stimulus artificiel modélisant les pas d'une fourmi sur le sable à aboutit à l'élaboration d'un biotest. Il a prouvé que le fourmilion utilise l'information mécanique propagée dans le sable pour orienter morsures et jets de sable. L'exploitation des particularités physiques du milieu granulaire « sable » garantit ainsi l'efficacité de la prédation. Ces résultats sont discutés dans une perspective d'écologie évolutive.

Optimal strategies under worst-case scenarios have been studied in Bernard et al. [2013a]. Bernard et al. utilize copulas to construct cost-efficient strategies with a predefined dependence structure in the tail between the payoff and the market. In their study they show that such strategies with state-dependent copula constraints dominate traditional diversification strategies in terms of the provided protection in the states of market downturns. We derive similar strategies, however using correlation constraints instead of copula constraints in the tail. We found that for an investor seeking negative dependence with the market, it is cheaper to construct a strategy with conditional correlation constraint in the tail. However, the constructed strategies with conditional correlation constraints do not provide sufficient protection in bad states of the economy. Therefore, when analyzing a strategy, negative correlation with the market in the tail is not a sufficient indicator for the protection level in the event of a market crisis.

The average cost of operating a queueing network depends on several factors such as the complexity of the network and the service policy used. Approximate linear programming (ALP) is a method that can be used to compute an accurate lower bound on the optimal average cost as well as generate policies to be used in operating the network. These average cost solutions and policies are dependent on the type of basis function used in the ALP. In this paper, the ALP average cost solutions and policies are analyzed for twelve networks with four different types of basis functions (quadratic, linear, pure exponential, and mixed exponential). An approximate bound on the optimality gap between the ALP average cost solution and the optimal average cost solution is computed for each system, and the size of this bound is determined relative to the ALP average cost solution. Using the same set of networks, the performance of ALP generated policies are compared to the performance of the heuristic policies first-buffer-first-served (FBFS), last-buffer-first-served (LBFS), highest-queue-first-served (HQFS), and random-queue-first-served (RQFS). In general, ALP generated average cost solutions are considerably smaller than the simulated average cost under the corresponding policy, and therefore the approximate bounds on the optimality gaps are quite large. This bound increases with the complexity of the queueing network. Some ALP generated policies are not stabilizing policies for their corresponding networks, especially those produced using pure exponential and mixed exponential basis functions. For almost all systems, at least one of the heuristic policies results in mean average cost less than or nearly equal to the smallest mean average cost of all ALP generated policies in simulation runs. This means that generally there exists a heuristic policy which can perform as well as or better than any ALP generated policy. In conclusion, a useful bound on the optimality gap between the ALP average cost solution and the optimal average cost solution cannot be computed with this method. Further, heuristic policies, which are more computationally tractable than ALP generated policies, can generally match or exceed the performance of ALP generated policies, and thus computing such policies is often unnecessary for realizing cost benefits in queueing networks.<br>text

Dissertação de mestrado em Construção e Reabilitação Sustentáveis<br>Atualmente, no sector dos edifícios, verifica-se um consumo de 40 % da energia total na União Europeia (EU) e com a continuação do crescimento desse sector, prevê-se um aumento do consumo de energia, sendo por isso necessário implementar medidas para a redução do consumo da mesma, aumentando a eficiência na sua utilização e utilizando fontes renováveis para reduzir a dependência energética e emissões de gases com efeitos de estufa. Neste contexto, a Diretiva Europeia 2010/31/UE de 19 de Maio de 2010 relativa ao desempenho energético dos edifícios (EPBD recast) introduz medidas importantes para a redução da dependência energética da UE e das emissões de gases com efeito de estufa. Com a EPBD Recast, os Estados-Membros deverão garantir que os requisitos mínimos de desempenho energético são assegurados com níveis de rentabilidade ótimos, ou seja, com o custo mínimo considerando todo o seu ciclo de vida. Esta dissertação pretende determinar os níveis ótimos de rentabilidade dos requisitos mínimos de desempenho energético na reabilitação de um edifício unifamiliar de referência que é representativo da construção característica da época anterior ao ano de 1960, mediante o cálculo do custo de implementação de medidas de eficiência energética, bem como do custo de utilização do edifício durante o ciclo de vida económico estimado. É avaliada a variação dos níveis ótimos de rentabilidade na reabilitação de edifícios unifamiliares nessa época, localizados em várias regiões do país com diferentes condições climáticas. É caracterizado o parque edificado em Portugal e identificadas as medidas de melhoria para a reabilitação em duas vertentes diferentes: atuando na envolvente e atuando nos equipamentos de aquecimento, arrefecimento e aquecimento de águas sanitárias. São quantificados os custos globais associados a cada uma das variantes constituídas por combinações de medidas de melhoria ao nível da envolvente opaca e com a utilização de diferentes equipamentos de climatização e AQS, para conseguir que o desempenho energético do edifício ou da sua parte renovada seja melhorado, de forma a cumprir os requisitos mínimos de desempenho energético de edifícios e alcançar os níveis ótimos de rentabilidade. Finalmente conclui-se sobre quais as variantes mais vantajosas a nível de custo/beneficio a utilizar na reabilitação de edifícios de habitação com as mesmas características do edifício de referência, típicas da construção anterior ao ano 1960 em Portugal.<br>Currently, in the buildings sector, there is a 40% consumption of total energy in the EU and with the continued growth of this sector, there is an increase for energy consumption and it is therefore necessary to implement measures for the reduction of consumption, improving the efficiency in its use and using renewable sources to reduce energy dependency and emissions of greenhouse gases. In this way, European Directive 2010/31/EU of May 19, 2010 on the energy performance of buildings (EPBD recast) introduces important steps required to reduce EU energy dependency and emissions of greenhouse gases. With the EPBD Recast Member States shall ensure that minimum energy performance requirements are assured with good profitability levels, i.e. with minimum cost considering the entire life cycle. This thesis aims to determine the cost optimal levels of the minimum energy performance requirements in the renovation of a reference single-family building that represents the Portuguese construction before 1960, by calculating the cost of implementing energy efficiency measures, as well as the cost of using the building during the estimated economic life cycle. The variation of the cost optimal levels in the renovation of single-family buildings from the chosen period, located in various regions with different climatic conditions is evaluated. The residential building stock in Portugal is characterized and the improvement measures for renovation in are identified, including measures to improve the building envelope and also acting in the building systems for heating, cooling and domestic hot water (DHW). The overall costs associated with each of the combinations of measures to improve the energy performance of the bulding envelope and for the use of different AVAC and DHW systems is quantified, to get the energy performance of the building or the renovated part improved in order to meet minimum energy performance requirements for buildings in order to achieve cost optimal levels. Finally, it is identified the most advantageous combinations in terms of cost / benefit to use in the renovation of residential buildings with the same characteristics of the reference building, typical of pre-1960 construction in Portugal.

Tese de doutoramento em Engenharia Civil, ramo de Construções, apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra<br>O desenvolvimento sustentável implica o equilíbrio entre a exploração dos recursos naturais, de maneira a satisfazer atuais necessidades do ser humano, e a garantia de renovação destes recursos, preservando a capacidade de suprimento às gerações futuras. Todavia, é quase um consenso na comunidade científica de que as alterações climáticas vêm sendo causadas pela nossa sociedade e que a manutenção do cenário atual de uso de fontes esgotáveis de energia e de altos índices de emissões de gases com efeito estufa ocasionará um aumento das temperaturas globais. A eficiência energética e o uso de fontes de energia renováveis têm potencial para mudar este cenário e irão revelar-se uma parte muito significativa na resolução deste problema. Comparando-se os custos e benefícios, demonstra-se claramente as vantagens de uma ação rápida e forte que consiga integrar o crescimento económico com o equilíbrio ambiental e com a equidade social. Esta ação deve concentrar esforços nos setores mais intensivos no uso de energia. A indústria da construção e o uso de edifícios têm grande impacto no consumo de energia, constituindo-se importantes fontes de emissões de dióxido de carbono. Este trabalho de investigação evidencia o compromisso inequívoco da União Europeia (UE) com a sustentabilidade. Nele são apresentadas diretivas para a promoção do uso de fontes de energia renováveis e para a melhoria do desempenho energético dos edifícios, as quais demonstram uma ação coordenada de políticas e estratégias que têm impacto direto no setor da construção e no uso de edificações. Contudo, um dos aspetos essenciais que tem de ser considerado de forma mais contundente nestas estratégias é a baixa taxa de renovação do estoque. A participação dos edifícios novos é bastante reduzida, de 1 a 2% do parque edificado europeu. Logo, ainda que as grandes renovações consistam em intervenções complexas, devem ser privilegiados instrumentos para promover o cumprimento de critérios fundamentais de sustentabilidade nos edifícios existentes para que se possa alcançar os objetivos estabelecidos. Entre os proprietários de edifícios, predomina o sentimento de que as grandes renovações de edifícios são uma oportunidade para tomar medidas rentáveis de melhoria do desempenho energético. No entanto, a sua consciencialização em relação aos benefícios da reabilitação energética de edifícios está principalmente relacionada com a expectativa de retorno mensurável do investimento em cada medida de eficiência energética. Na ausência de dados e orientações, as decisões tendem a ser adiadas ou tomadas no plano subjetivo. Assim, o setor da reabilitação de edifícios continua a sofrer com investimentos insuficientes. As políticas para promoção da reabilitação energética têm falhado no incentivo ao investimento e no convencimento do setor privado e dos proprietários de edifícios em geral. Para além da escassez de recursos em todos os setores da economia, o capital que estaria disponível para investimento em reabilitação energética sofre a concorrência de outras opções com retorno mais tangível. Na falta de informações concretas, o investimento em reabilitação energética só ocorre por imposição regulamentar. O Regulamento Delegado (UE) n.º 244/2012 especifica regras para comparação da rentabilidade de medidas de eficiência energética e do uso de fontes de energias renováveis em edifícios novos e existentes. Subentende-se, portanto, uma preocupação da União Europeia em garantir que o investimento em medidas de eficiência energética seja rentável e que, ao mesmo tempo, os requisitos mínimos de desempenho energético dos edifícios não se afastem demasiadamente dos denominados níveis ótimos de rentabilidade. Ocorre que a metodologia apresentada neste regulamento é dirigida a autoridades nacionais e não a investidores, e os níveis ótimos de rentabilidade são somente calculados para desenvolver disposições regulamentares aplicáveis a nível nacional. O regulamento salvaguarda que os níveis ótimos de rentabilidade calculados não serão necessariamente os níveis ótimos para cada combinação edifício/investidor. O presente trabalho concentra-se no estudo da rentabilidade dos investimentos em reabilitação energética de edifícios. Pretende-se obter uma visão abrangente acerca desta temática e identificar oportunidades de melhoria na metodologia determinada pela Comissão Europeia, para que se aplique também a investidores. Para este efeito, identificam-se os parâmetros mais importantes nos cálculos e a interação entre eles, propõe-se um método de seleção e critérios de avaliação de rentabilidade de medidas, além de ferramentas de otimização que podem auxiliar o trabalho dos vários intervenientes. O método é aplicado ao caso de Portugal, sendo selecionados três casos de estudo contendo cenários para reabilitação energética de edifícios. Os casos de estudo contemplam o setor mais relevante de edifícios no contexto português (residencial), as épocas de construção com maior potencial de redução de consumo de energia e uma classe de edifícios com restrições arquitetónicas para implementação de medidas. Adicionalmente ao método proposto, é aplicada a metodologia de análise de ciclo de vida (ACV) e são realizados cálculos pelo método da simulação dinâmica. São utilizados ainda dois métodos multicritério para obter-se uma pequena amostra da perceção de moradores em relação ao valor e à utilidade da reabilitação energética de edifícios. Os resultados apresentados são confrontados com os atuais requisitos mínimos de desempenho energético, aos quais os proprietários de edifícios estão sujeitos. Como conclusão, são apresentadas recomendações para a promoção da reabilitação energética de edifícios.<br>Sustainable development means striking a balance between exploiting natural resources to meet the current needs of human beings and ensuring the renewal of these resources so as to safeguard the ability to supply future generations. However, it is almost a consensus in the scientific community that climate change has been caused by our society and that if the current scenario of using depletable energy sources and emitting high levels of greenhouse gases continues it will cause an increase in global temperature. Energy efficiency and the use of renewable energy sources have the potential to change this scenario and they will prove to be very significant in solving this problem. Comparing the costs and benefits clearly exposes the advantages of strong rapid action that can combine economic growth with environmental balance and social equity. This action should concentrate on the most intensive users of energy. The construction industry and the use of buildings have a major impact on energy consumption and have become important sources of carbon dioxide emissions. This research demonstrates the clear commitment of the European Union (EU) to sustainability. Directives that promote the use of renewable energy sources and improve the energy performance of buildings are presented to demonstrate the coordinated action of policies and strategies that have a direct impact on the construction sector and the use of buildings. However, one of the fundamental aspects that must be considered more forcefully in these strategies is the low rate of stock turnover. The share of new buildings is very small, 1-2% of the European building stock. Thus, although major renovations consist of complex interventions, they should be powerful tools to promote compliance with the core criteria of sustainability in existing buildings so that we can achieve the established objectives. A feeling prevails among building owners that the major renovation of a building offers an opportunity to take effective measures to enhance energy performance. However, their awareness of the benefits of energy retrofitting of buildings is mainly related to the measurable expected return on investment in each energy efficiency measure. In the absence of data and guidelines, decisions tend to be postponed or taken at a subjective level. Thus, the sector of building rehabilitation continues to suffer from insufficient investment. Policies to promote energy retrofit have failed to encourage investment and have not persuaded the private sector and building owners in general. In addition to the scarcity of resources in all sectors of the economy, the capital that could be available for investment in energy rehabilitation faces competition from other options with a more tangible return. In the absence of solid information, investment in energy rehabilitation only occurs by regulatory imposition. Delegated Regulation (EU) No. 244/2012 specifies rules for comparing the profitability of energy efficiency measures and the use of renewable energy sources in new and existing buildings. The European Union is therefore concerned to ensure that investment in energy efficiency measures should be profitable and, at the same time, that the minimum energy performance requirements for buildings does not differ too much from what are regarded as cost-optimal levels. In fact, the approach presented in this Regulation is addressed to national authorities rather than investors, and the optimum levels of profitability are only calculated to develop national regulation. The regulation underlines that the calculated cost-optimal levels does not necessarily secure the optimum levels of profitability for each building/investor combination. This work examines the profitability of investments in the energy retrofit of buildings. It sets out to obtain a comprehensive view of this issue and identify opportunities for improving the methodology imposed by the European Commission so that it also applies to investors. For this purpose, the most important parameters in the calculations and the interaction between them are identified and a method to select and evaluate the criteria of profitability measures is proposed. Optimization tools that can assist the work of the various stakeholders are also suggested. The method is applied to Portugal, with three case studies containing scenarios for the energy retrofit of buildings being selected. The case studies include residential buildings, which is the most important sector of buildings in the Portuguese context, construction ages with higher potential for energy consumption reduction and a class of buildings with architectural constraints for implementing measures. Life-cycle assessment (LCA) is applied in addition to the proposed method, and calculations are performed using dynamic simulation. Two multi-criteria decision-aid methods were also used to obtain a small sample of the preferences of residents regarding the value and benefits of the energy retrofit of buildings. The results are compared with the current minimum energy performance requirements with which building owners must comply. In conclusion, recommendations to promote the energy retrofit of buildings are put forward.

The rapid increase of content delivery over the Internet has lead to the proliferation of content distribution networks (CDNs). Management of CDNs requires algorithms for request routing, content placement, and eviction in such a way that user delays are small. Our objective in this work is to design feasible algorithms that solve this trio of problems. We abstract the system of front-end source nodes and back-end caches of the CDN in the likeness of the input and output nodes of a switch. In this model, queues of requests for different pieces of content build up at the source nodes, which route these requests to a cache that contains the content. For each request that is routed to a cache, a corresponding data file is transmitted back to the source across links of finite capacity. Caches are of finite size, and the content of the caches can be refreshed periodically. A requested but missing item is fetched to the cache from the media vault of the CDN. In case of a lack of adequate space at the cache, an existing, unrequested item may be evicted from the cache in order to accommodate a new item. Every such cache refresh or media vault access incurs a finite cost. Hence the refresh periodicity allowed to the system represents our system cost. In order to obtain small user delays, our algorithms must consider the lengths of the request queues that build up at the nodes. Stable policies ensure the finiteness of the request queues, while good polices also lead to short queue lengths. We first design a throughput-optimal algorithm that solves the routing-placement eviction problem using instantaneous system state information. The design yields insight into the impact of different cache refresh and eviction policies on queue length. We use this and construct throughput optimal algorithms that engender short queue lengths. We then propose a regime of algorithms which remedies the inherent problem of wastage of capacity. We also develop heuristic variants, and we study their performance. We illustrate the potential of our approach and validate all our claims and results through simulations on different CDN topologies.

Dissertação de Mestrado em Eficiência Acústica e Energética para uma Construção Sustentável apresentada à Faculdade de Ciências e Tecnologia<br>Sabe-se que uma parcela significativa (cerca de 40%) do consumo energético na União Europeia se deve aos edifícios e que este sector é responsável pela emissão de cerca de um terço do dióxido de carbono.O elevado ritmo de construção verificado nas décadas de 1970, 1980 e 1990, aliado à falta de regulamentação específica, o parque edificado português e em particular o do sector residencial, mesmo que de construção mais recente, encontra-se longe das condições atuais de referência, envelhecido ou mesmo bastante degradado.Muitos desses edifícios, apresentando uma deficiente qualidade térmica e energética, exigem intervenções de fundo que visam melhorar as suas características de habitabilidade.A reabilitação térmica e energética de edifícios, será porventura a via adequada à correção de situações de inadequação funcional, proporcionando uma melhoria da qualidade térmica e energética. Permite ainda reduzir o consumo de energia e dar resposta às necessidades de conforto térmico de uma forma sustentável, indo ao encontro das metas impostas pelas diretrizes Europeias relativas à redução do consumo energético até 2020. Deste modo, a melhoria do desempenho energético dos edifícios tornou-se num desafio tecnológico da construção e deve ser encarada como uma necessidade quer na construção de edifícios novos, quer na reabilitação de edifícios existentes. Esta dinâmica torna-se ainda mais importante no contexto de habitação social, dada a “pobreza energética” associada.Esta dissertação, utilizando um caso de estudo de habitação social em Coimbra, identifica e analisa um conjunto de medidas de melhoria e o seu impacto em termos energéticos, económi-cos (rentabilidade económica) e de “pegada de carbono”. Este estudo é efetuado em termos de impacto global, mas também desagregando os efeitos dessas medidas em função da tipologia da fração e da sua localização no edifício.<br>It is known that a substantial amount (about 40%) of the European Union energy consumption is due to buildings. The housing sector is responsible for about one third of the carbon dioxide emissions.The Portuguese building stock, particularly the residential stock, is far from being aligned with current specific guidelines, it is aged or quite degraded, due to the high rhythm of construc-tion in the 1970s, 1980s and 1990s and to the absence of specific regulations at that time.Many of these buildings show poor thermal and energy quality, requiring, consequently, deep interventions to improve habitability conditions.Thermal and energetic retrofitting of buildings is possibly the suitable way to correct the functional inadequacy, providing thermal and energy quality improvement. It also allows energy consumption reduction and provides the thermal comfort needed in a sustainable way, according the European 2020-goals regarding energy consumption.Therefore, improving the energy performance of buildings has become a technological chal-lenge and should be seen as a necessity, not only applied to new buildings’ construction but also to the retrofitting of existing buildings.This agenda becomes even more important in social housing context, given the "energy poverty" associated.Using a study case of social housing in Coimbra, this thesis identifies and analyses a set of improvement measures and its influence in energy savings, cost optimality results and “carbon footprint”. This study also evaluates the effects of these measures regarding the typology and location in the building.

Dissertação de mestrado integrado em Engenharia Civil<br>Atualmente, observa-se uma consciencialização da sociedade em geral, no que diz respeito ao desenvolvimento sustentável do planeta. Os edifícios europeus existentes são responsáveis pelo consumo de 40% da energia, constituindo um desafio importante no desenvolvimento sustentável das cidades. Como forma de mitigar este problema, a Diretiva para o Desempenho Energéticos dos Edifícios propôs o conceito de edifícios com necessidades quase nulas de energia (nZEB), que assenta em edifícios de elevado desempenho energético, integrando também fontes de energias renováveis, com critérios de rentabilidade económica. Os edifícios de habitação social são paradigmáticos que apresentam frequentemente patologias decorrentes de uma fraca qualidade construtiva e baixa eficiência energética. Existe assim a necessidade premente de intervir neste tipo de edifícios de forma a atingir o objetivo nZEB. Estes edifícios devem ser intervencionados ao nível da envolvente e sistemas técnicos e prever a produção de energia renovável no local, considerando não só as poupanças energéticas que proporcionam, mas também o custo global da solução em toda a vida útil do edifício. A investigação realizada analisou cenários de possíveis intervenções a serem implementadas num edifício de habitação social em Braga, utilizando a metodologia de custo-ótimo com o objetivo de atingir o nível nZEB. Inicialmente analisaram-se soluções para a envolvente do edifício através das medidas de melhoria isoladas. Numa segunda fase, as medidas foram combinadas em pacotes de reabilitação sem alteração dos sistemas técnicos. No final analisaram-se os pacotes de reabilitação combinados com sistemas técnicos e integração de fontes de energia renováveis. O estudo mostra que existe potencial para reduzir até 100% de energia primária não renovável (EPNR) com rentabilidade económica positiva. A solução de custo-ótimo levou a uma redução de 94% de EPNR e a uma diminuição de 54% dos custos globais, quando comparada com a reabilitação de referência. A solução de custo-ótimo é constituída por uma intervenção integrada que aglomera acréscimo de isolamento nas fachadas (através da aplicação de um painel modular pré-fabricado) e na cobertura, substituição dos vãos envidraçados por uma solução com vidro duplo e sistemas técnicos que incluem esquentador para aquecimento das águas sanitárias (AQS), ar condicionado para climatização ambiente e painéis fotovoltaicos. Os resultados deste estudo contribuem para a discussão relativamente ao modo de atingir as metas traçadas pela União Europeia (UE), o caminho a percorrer no sentido de alcançar os edifícios nZEB e até ZEB, e a oportunidade de ajudar a mitigar o problema da pobreza energética associado a este tipo de edifícios.<br>Nowadays, there is an increasing awareness of society regarding the sustainable development of the planet. The existing European buildings are responsible for 40% of the energy consumption, posing a major challenge in the sustainable development of cities. In order to mitigate this problem, the Energy Performance of Buildings Directive (EPBD) introduced the concept of nearly Zero Energy Buildings (nZEB), which is based on high energy performance buildings with the integration of renewable energy sources harvested on site within costeffectiveness criteria. Social housing buildings are paradigmatic of buildings that often present pathologies due to poor construction quality and low energy efficiency. There is this a pressing need to intervene in this type of buildings. In order to reach the nZEB level in this type of buildings, interventions should include improvements on the envelope and technical systems and production of renewable energy on site, considering not only the energy savings provided but also the global costs over the entire life cycle of the building. In this context, the research carried out analysed possible renovation scenarios to be implemented in a social housing building in Braga, using the cost-optimal methodology in order to reach the nZEB level. Initially, solutions just for the building envelope were analysed. In a second phase, these measures were combined into renovation packages with different technical systems. In the end, the renovation packages also included the integration of renewable energy sources. The study shows that there is a potential to cost-effectively reduce non-renewable primary energy (NRPE) up to 100%. The cost-optimal solution led to a 94% reduction in NRPE and to a 54% reduction in global costs when compared to the reference case renovation. The costoptimal solution consists of an integrated intervention considering the improvement of the façade (through the application of a prefabricated modular panel) and roof insulation, double glazing windows and a combination of systems that include domestic hot water preparation, a HVAC system and photovoltaic panels. The results of this study contribute to the discussion on how to achieve the goals set by the European Union (EU), the way forward to reach the nZEB and even ZEB buildings, and the opportunity to help mitigating the energy poverty problem associated to this type of buildings.

Cette thèse est composée de trois essais liés à la conception de mécanisme et aux enchères. Dans le premier essai j'étudie la conception de mécanismes bayésiens efficaces dans des environnements où les fonctions d'utilité des agents dépendent de l'alternative choisie même lorsque ceux-ci ne participent pas au mécanisme. En plus d'une règle d'attribution et d'une règle de paiement le planificateur peut proférer des menaces afin d'inciter les agents à participer au mécanisme et de maximiser son propre surplus; Le planificateur peut présumer du type d'un agent qui ne participe pas. Je prouve que la solution du problème de conception peut être trouvée par un choix max-min des types présumés et des menaces. J'applique ceci à la conception d'une enchère multiple efficace lorsque la possession du bien par un acheteur a des externalités négatives sur les autres acheteurs. Le deuxième essai considère la règle du juste retour employée par l'agence spatiale européenne (ESA). Elle assure à chaque état membre un retour proportionnel à sa contribution, sous forme de contrats attribués à des sociétés venant de cet état. La règle du juste retour est en conflit avec le principe de la libre concurrence puisque des contrats ne sont pas nécessairement attribués aux sociétés qui font les offres les plus basses. Ceci a soulevé des discussions sur l'utilisation de cette règle: les grands états ayant des programmes spatiaux nationaux forts, voient sa stricte utilisation comme un obstacle à la compétitivité et à la rentabilité. Apriori cette règle semble plus coûteuse à l'agence que les enchères traditionnelles. Nous prouvons au contraire qu'une implémentation appropriée de la règle du juste retour peut la rendre moins coûteuse que des enchères traditionnelles de libre concurrence. Nous considérons le cas de l'information complète où les niveaux de technologie des firmes sont de notoriété publique, et le cas de l'information incomplète où les sociétés observent en privée leurs coûts de production. Enfin, dans le troisième essai je dérive un mécanisme optimal d'appel d'offre dans un environnement où un acheteur d'articles hétérogènes fait face a de potentiels fournisseurs de différents groupes, et est contraint de choisir une liste de gagnants qui est compatible avec des quotas assignés aux différents groupes. La règle optimale d'attribution consiste à assigner des niveaux de priorité aux fournisseurs sur la base des coûts individuels qu'ils rapportent au décideur. La manière dont ces niveaux de priorité sont déterminés est subjective mais connue de tous avant le déroulement de l'appel d'offre. Les différents coûts rapportés induisent des scores pour chaque liste potentielle de gagnant. Les articles sont alors achetés à la liste ayant les meilleurs scores, s'il n'est pas plus grand que la valeur de l'acheteur. Je montre également qu'en général il n'est pas optimal d'acheter les articles par des enchères séparées.<br>This thesis is made of three essays related to mechanism design and auctions. In first essay I study Bayesian efficient mechanism design in environments where agents' utility functions depend on the chosen alternative even if they do not participate to the mechanism. In addition to an allocation rule and a payment rule the designer may choose appropriate threats in order to give agents the incentive to participate and maximize his own expected surplus; The planner may presume the type of an agent who does not participate. I show that the solution of the design problem can be found by a max - min choice of the presumed types and threats. I apply this to the design of an efficient multi-unit auction when a buyer in possession of the good causes negative externalities on other buyers.\\ The second essay considers the fair return rule used by the European Space Agency (ESA). It ensures each member state of ESA a return proportional to its contribution, in the form of contracts awarded to firms coming from that state. The fair return rule is in conflict with the principle of free competition since contracts are not necessarily awarded to firms with the lowest bids. This has raised debates on the use of this rule: it is well accepted by small states, but larger states with strong national space programs, see its strict use as an obstacle to competitiveness and cost effectiveness. It is easy to believe that this rule is more costly to the agency than traditional auctions. We show on the contrary that an adequate implementation of the fair return rule may cause it to be less expensive to the agency than the traditional auctions of free competition. We consider the case of complete information where firms' technology levels are common knowledge, and the case of incomplete information where firms observe privately their production costs. In both cases we show that adequate implementation of the fair return rule may help take advantage of asymmetries between countries in order to expect a lower cost than with traditional auctions.\\ Finally, in the third essay I derive an optimal procurement mechanism in an environment where a buyer of heterogeneous items faces potential suppliers from different groups, and is constrained to choose a winning list that is consistent with some exogenous quotas assigned to the different groups. The optimal allocation rule consists of assigning priority levels to suppliers on the basis of their cost reports. The way these priority levels are determined is subjective but known to all before the auction. The individual reports induce scores for each potential winning list. The items are then purchased from one of the lists with the best score, provided it is not greater than the buyer's valuation for the items. I also find that it is not optimal to purchase the items through separate auctions, unless the buyer's valuation is sufficiently high or low.