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L’homogénéisation est une technique de passage Micro-Macro en tenant compte de l’influence des paramètres morphologiques, mécaniques et statistiques de la microstructure représentative d’un matériau hétérogène. La modélisation numérique a contribué fortement au développement de cette technique en vue de déterminer les propriétés physico-mécaniques des matériaux hétérogènes bi et multiphasiques. L’objectif principal de ce travail est la prédiction du comportement macroscopique élastique et thermique de matériaux hétérogènes. Les comportements mécaniques et thermiques ont été déterminés numériquement puis comparés aux résultats expérimentaux et analytiques. La variation du volume élémentaire représentatif (VER) en fonction de la fraction volumique et du contraste a été analysée. Cette étude a mis en évidence l’intérêt d’une détermination rigoureuse de la taille optimale du VER. En effet, celle-ci doit prendre en compte plusieurs paramètres tels que la fraction volumique, le contraste, le type de la propriété et la morphologie de l’hétérogénéité. Un nouveau concept de morphologie équivalente a été proposé. Ce concept introduit le principe d’équivalence des caractéristiques élastiques et thermiques des matériaux hétérogènes d’une microstructure de morphologie complexe avec celles d’une microstructure contenant des particules sphériques. Ce travail a conduit à l’élaboration d’une démarche globale de design microstructural en intégrant la morphologie réelle des phases des microstructures hétérogènes intégrant à la fois la visualisation des images, l’étude morphologique et la modélisation géométrique et numérique. / The homogenization is a technique of Micro-Macro passage taking into account the influence of morphological, mechanical and statistical parameters of the representative microstructure of an heterogeneous material. Numerical modeling has contributed significantly to the development of this technique to determine the physical and mechanical properties of bi-and multi-phase heterogenous materials. The main objective of this work is the prediction of the macroscopic elastic and thermal behaviors of heterogeneous materials. The mechanical and thermal behaviors was determined numerically and compared with experimental and analytical results. The variation of the representative volume element (RVE) versus volume fraction and the contrast was analyzed. This study showed the importance of a rigorous determination of the optimal RVE size. Indeed, it must take into account several parameters such as : volume fraction, contrast, type of property and the morphology of the heterogeneity. A new concept of the equivalent morphology was proposed. This concept introduces the equivalence of the elastic and thermal characteristics of a microstructure of heterogeneous materials with complex morphology and those of a microstructure containing spherical particles. This work led us to developement of a comprehensive approach to microstructural design by integrating the real morphology of heterogeneous microstructure phases incorporating at the same time the image visualization, the morphological study and the geometric and numerical modeling.

A colheita mecanizada florestal é uma atividade custosa com diversos fatores a serem gerenciados e controlados para que se torne uma atividade viável e competitiva. Para a aplicação em povoamentos florestais de baixo volume por hectare, a escolha do sistema de colheita ideal é fator determinante para o sucesso operacional e financeiro do processo. O presente estudo avaliou dois sistemas de colheita: um convencional - composto por: \"Harvester\" e \"Forwarder\" - e outro alternativo - composto por: \"Feller-buncher\", \"Skidder\", \"Flail\", \"Power-Clamp\" e \"Garra-Traçadora\". Os sistemas de colheita foram aplicados em florestas de baixo volume unitário, sendo a UP-A com 0,14 m³.árv.-1 com 48,07 hectares e a UP-B com 0,11 m³.árv.-1 com 80,88ha. Foi realizado estudo de tempo contínuo para o apontamento dos indicadores de desempenho de disponibilidade mecânica, eficiência operacional e índice de utilização, bem como coleta do número de árvores produzidas por cada máquina de cada um dos sistemas em ciclos de 30min. de forma aleatória. Os custos horários foram divididos em: custos fixos - compostos por: custo de depreciação, juros, seguros e estrutura - e custos variáveis - representados pelos valores correspondentes a: combustível, lubrificantes, mão de obra e manutenção. O custo de produção (R$.m-3 de cada máquina e somatório de cada sistema) foi obtido por meio da soma dos custos fixos e variáveis de cada máquina e divisão entre sua produção horária apontada pelos técnicos florestais ao longo do estudo. Na análise estatística, aplicou-se o teste de BOX-COX para avaliar a homogeneidade da variância da produção horária (m³.h-1) com a variância homogeneizada pela transformação logarítmica, fez-se a análise de variância (ANOVA) da variável m³.h-1 de cada um dos sistemas para cada uma das unidades de produção e, sequencialmente, realizou-se o teste de comparação de médias dos sistemas de colheita e unidades de produção, comparados pelo teste de Tukey a 5%. Os custos fixos do sistema convencional totalizaram 221,59 R$.h-1, sendo estes 52,77% dos custos totais deste sistema, já o sistema alternativo apresentou um custo total fixo de 668,55 R$.h-1, representando 45,75% dos custos totais horários. Os custos variáveis do sistema convencional totalizaram 198,29 R$.h-1, compondo 47,23% dos custos totais, e para o sistema alternativo, os custos variáveis totalizaram 792,68 R$.h-1, representando 54,25% dos custos totais. O custo de produção do sistema convencional na UP-A foi de 19,38 R$.m-³ e na UP-B foi de 23,85 R$.m-³. Já para o sistema alternativo, obteve-se na UP-A um custo de 14,62 R$.m-³ e para UP-B um valor de 19,99 R$.m-³. Em conclusão, verificou-se que, para ambas as situações de floresta estudadas, o sistema alternativo de colheita foi mais competitivo em relação ao sistema convencional. / The forest mechanized harvesting operation is a costly activity with many factors to be managed and controlled in order to become a viable and competitive activity. Thus when applied to forest stands with low volume per hectare, choosing the ideal harvesting system is a determining factor for the operational and financial success. The present study analyzed two harvesting systems, one named traditional, which is composed of \"Harvester\" and \"Forwarder\" and a second named alternate consisting of \"Feller-buncher\", \"Skidder\", \"Flail\", \"Power-Clamp\" and \"Grapple-Saw\". Both systems were applied to harvest forests of low unit volume, and the UP-A with 0.14 m³.tree-1 with 48.07 hectares and UP-B with 0.11 m³.tree-1 with 80.88 hectares. The study was conducted with continuous time for the appointment of the performance indicators of mechanical availability, operational efficiency and utilization rates, also was collected the number of trees produced by each machine in each system in cycles of 30 minutes at random. Hourly costs were divided into fixed costs, consisting of depreciation cost, interest, insurance and variable cost structure was represented by the cost of fuel, lubricants, labor and maintenance. The production cost of R$.m-3 of each machine and the sum of each system was obtained by the sum of the fixed and variable costs of each machine and divided by their hourly production indicated by forest technicians throughout the study. Statistical analysis was applied to the BOX-COX test to evaluate the homogeneity of the variance of output per hour (m³.hour-1), with the variance homogenized by logarithmic transformation was made the variance analysis (ANOVA) of the variable m³.hour-1 of each harvest system for each forest production units and sequentially held the mean test comparison of harvest systems and forest production units, compared by Tukey test at 5%. The fixed costs of the traditional system totaled R$ 221.59 per hour effective worked these being 52.77% of the total costs of the system, since the alternative system presented a total fixed cost of R$ 668.55 per effective worked hour, representing 45.75% of the total costs. The variable costs of the traditional system totaled R$ 198.29 per effective worked hour, composing 47.23% of total costs, and for the alternative system, variable costs totaled R$ 792.68 per worked hour effectively representing 54.25% of total costs. The production cost of the traditional system in UP-A was R$ 19.38 per m³ and UP-B of R$ 23.85 per m³, for the alternative system has obtained in the UP-A a cost of R$ 14.62 per m³ and for the UP-B R$ 19.99 per m³. It is concluded that for both situations of forests studied, the alternative harvest system was more competitive compared to the traditional system in terms of R$.m-3.

A Tomografia de Impedância Elétrica (TIE) é um método de imagem que permite estudarmos alterações regionais de ventilação pulmonar com alta resolução temporal. Estudamos a influência da posição corporal e do esforço expiratório no esvaziamento regional pulmonar comparando dados de espirometria com os da TIE adquiridos simultaneamente. MÉTODOS: Oito voluntários monitorados continuamente com TIE, realizaram manobras de capacidade vital lenta (CVL) com washout de nitrogênio (WN2) e capacidade vital forçada (CVF) nas posições sentado, decúbito lateral direito (DLD) e esquerdo (DLE). Em todas as posições, comparamos a variação global de impedância (Z) com os volumes da espirometria. Analisamos também as variações regionais de volume do pulmão direito e esquerdo, em cada posição, e a cada 10% da expiração total através da TIE; estes dados foram comparados com análise do WN2. RESULTADOS: Na espirometria e na TIE, houve uma redução no volume total expirado na CVF e na CVL dos decúbitos laterais quando comparados à posição sentada (P = 0,001). Na análise da CVL através da TIE, observamos um fluxo maior no pulmão dependente (de 2 a 10 vezes maior), em ambos os decúbitos laterais, com inversão deste padrão aproximadamente na metade da capacidade vital. Já na CVF o Z foi semelhante entre os pulmões ao longo da expiração, independente do decúbito, semelhante à situação isogravitacional (i.e., sentado) (p<0,001). O traçado de WN2 mostrou uma inclinação precoce (fase IIIb) ocorrendo apenas nos decúbitos laterais, além da fase IV ao final. A ascensão lenta da fase IIIb esteve sempre associada a uma significativa mudança no padrão de esvaziamento observado à TIE, onde o esvaziamento preferencial do pulmão dependente dava lugar a um esvaziamento preferencial do pulmão não-dependente. CONCLUSÃO: Em indivíduos sadios e nas situações de baixo esforço expiratório (CVL), a gravidade exerce forte influência na distribuição e variação dos volumes pulmonares ao longo da expiração, sugerindo um significante gradiente vertical de pressões pleurais. O esforço expiratório máximo atenua esta influência da gravidade, sugerindo que outros fatores passam a determinar o fluxo expiratório. / Electrical Impedance Tomography, (EIT) is an imaging method that allows studying changes in regional pulmonary ventilation with high temporal resolution. We studied the influence of body position and expiratory effort on regional lung emptying comparing data from spirometry with the EIT acquired simultaneously. METHOD: Eight volunteers monitored continuously with EIT, performed slow vital capacity (SVC) with single-breath nitrogen washout (SBNW) and forced vital capacity (FVC) maneuvers in sitting position, right (RLD) and left lateral decubitus (LLD). In all three positions we compared the impedance change (Z) with spirometry absolute volumes and analyzed the regional volume variation of right and left lungs in each position and every 10% step of total expiration with EIT; this data was compared with SBNW analysis. RESULTS: In spirometry and EIT, there was a reduction in the total volume expired in FVC and SVC in lateral recumbency when compared to the sitting position (P = 0,001). In the analysis of the SVC with EIT we noticed a greater flow in the dependent lungs (from 2 to 10 times higher) on both lateral decubitus, with reversal of this pattern in approximately half of the expired vital capacity. On FVC the Z was similar between the lungs during the entire expiration, regardless of decubitus, and similar to the situation isogravitacional (ie, sitting) (p<0,001). The SBNW curves showed an early inclination (phase IIIb) occurring only in the lateral decubitus, besides the final rise of phase IV. The slow rise of phase IIIb was always associated with a significant change in the emptying pattern observed with the EIT, when the preferential emptying of the dependent lung gave place to preferential emptying in the non-dependent lung. CONCLUSION: In healthy subjects and in situations of low effort (SVC), gravity exerts strong influence on the distribution and variation of lung volume during the expiration, suggesting a significant vertical gradient of pleural pressure. The maximum expiratory effort mitigates this gravitational influence, suggesting that other factors may determine the expiratory flow

Denna rapport är ett examensarbete på C-nivå som görs i sammarbete med teknikkonsulten Ramböll. Det vanligaste sättet att ventilera en byggnad idag är med så kallad CAV-ventilation (Constant Air Volume). Denna metod bygger på att ett luftflöde bestäms för rummet och upprätthålls med konstant flöde. En annan metod är så kallad VAV (Variable Air Volume) som bygger på att flödet varierar efter behovet. Anledningen till varför man väljer VAV istället för CAV är att med CAV finns det ofta en stor risk att man överventilerar ett rum eller byggnad, just på grund av att flödet är konstant. Problemet med VAV är att det är en högre investeringskostnad än för CAV så metoden lämpar sig bara där energibesparingen är så stor så den täcker mellanskillnaden i pris. Denna utredning visar i vilka typer av rum som det kan löna sig att installera VAV istället för det traditionella CAV-systemet. För att undersöka detta sker simuleringar av fiktiva modeller i programmet IDA Indoor Climate &amp; Energy (IDA). IDA är ett simuleringsverktyg som används till att simulera den termiska komforten i byggnader samt byggnadens energianvändning. De olika rumstyperna som simuleras är: klassrummet, kontoret och mötesrummet. De olika fallen är utformade så att de liknar så som de ser ut i verkligheten både till geometri och nyttjandegrad. Om något av fallen visade sig vara en bra kandidat för att förse med VAV fortsätter utredningen med att fastställa hur stort bör flödet vara för att energibesparingen ska bli så stor så att det täcker investeringskostnaden. Den ekonomiska kalkyleringen sker både med en livscykelkostnadsanalys och med en enklare återbetalningstidskalkyl. Resultatet för simuleringarna visade att den enda rumstypen i denna utredning som var lönsam var mötesrummet. Klassrummet och kontoret visade sig båda ge en förlust. Detta var eftersom nyttjandegraden för dessa rum var så pass hög så att ventilationen med VAV var igång nästan lika mycket som för CAV. För mötesrummet var nyttjandegraden betydligt lägre vilket innebar att energibesparingen blev så pass hög att den täckte den höga investeringskostnaden. För mötesrummet gjordes sedan en flödesanalys som visade att rummets luftflöde bör vara dimensionerat för mellan omkring 20 – 30 personer för att vara en lönsam investering.

The essays empirically show the impact of investors speculation and disagreements on the returns and trading volume of securities. The results also shed light on the central issues of price formation and investors’ trading motives in security markets. The first essay investigates whether the trading activities of retail investors affect option prices through volatility speculation. This essay empirically shows that higher retail trading proportions are related to lower delta-hedged option returns. The phenomenon is more pronounced before earnings announcements and among stocks with more time-varying and positively skewed volatility. The results suggest that retail investors speculate and pay a lottery premium on the expected future volatility, resulting in more expensive options in terms of higher implied volatilities. This systematic deviation of option-implied volatility from realized volatility suggests retail investor clientele as a behavioral-based driving force of volatility risk premium. The second essay investigates the motive of option trading. It is shown that option trading is mostly driven by differences of opinion, a finding different from the current literature that attempts to attribute option trading to information asymmetry. First, option trading around earnings announcements is speculative in nature and mostly dominated by small, retail investors. Second, around earnings announcements, option turnovers do not predict stock returns, once prior stock returns are controlled for. Third, regression results reveal that option trading is also significantly explained by differences of opinion at ordinary times. While informed trading is present in stocks, it is not detected in options. The third essay provides strong evidence of reduction in informational efficiency when there are short-sale constraints and disagreements. Post earnings announcement returns are found to be significantly lower for stocks with more dispersed opinions and stocks that are exogenously short-sale prohibited by the Hong Kong Stock Exchange, supporting Miller’s (1977) overvaluation hypothesis. The results also suggest short-sale constraint as an explanation to negative post earnings announcement drift.

The essays empirically show the impact of investors speculation and disagreements on the returns and trading volume of securities. The results also shed light on the central issues of price formation and investors’ trading motives in security markets. The first essay investigates whether the trading activities of retail investors affect option prices through volatility speculation. This essay empirically shows that higher retail trading proportions are related to lower delta-hedged option returns. The phenomenon is more pronounced before earnings announcements and among stocks with more time-varying and positively skewed volatility. The results suggest that retail investors speculate and pay a lottery premium on the expected future volatility, resulting in more expensive options in terms of higher implied volatilities. This systematic deviation of option-implied volatility from realized volatility suggests retail investor clientele as a behavioral-based driving force of volatility risk premium. The second essay investigates the motive of option trading. It is shown that option trading is mostly driven by differences of opinion, a finding different from the current literature that attempts to attribute option trading to information asymmetry. First, option trading around earnings announcements is speculative in nature and mostly dominated by small, retail investors. Second, around earnings announcements, option turnovers do not predict stock returns, once prior stock returns are controlled for. Third, regression results reveal that option trading is also significantly explained by differences of opinion at ordinary times. While informed trading is present in stocks, it is not detected in options. The third essay provides strong evidence of reduction in informational efficiency when there are short-sale constraints and disagreements. Post earnings announcement returns are found to be significantly lower for stocks with more dispersed opinions and stocks that are exogenously short-sale prohibited by the Hong Kong Stock Exchange, supporting Miller’s (1977) overvaluation hypothesis. The results also suggest short-sale constraint as an explanation to negative post earnings announcement drift.

The goal of this method is to implement the volume and mass conserving characteristic method. This method is appropriate to the equation with advections and diffusions. Characteristic mixed FEM with piecewise constant approximation is applied to the advection part, and the diffusion part is handled by FDM.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 153-170). Also available in print.

The regenerator is the key component in magnetic cycles for refrigeration and heat pumping. It works as temporal thermal energy storage and separates two thermal reservoirs. Regenerators are typically made up of porous structures which may create complex flow pathways for the heat transfer fluid through the regenerator. The periodically reversing flow allows the thermal energy exchange with the packing material in the regenerators. The performance of such thermal devices depends greatly on the geometry of the porous structure, material properties as well as operating conditions. This thesis is a study about the thermo-hydraulic properties of passive regenerators under oscillating flow conditions. The first part of the thesis presents a passive regenerator testing apparatus used to measure temperature distribution and pressure drop for various types of regenerators. Three kinds of loose spheres packed regenerator beds are characterized, and the regenerator effectiveness is evaluated. In the second part of the thesis, a numerical model is developed for the predictions of pressure drop and temperature field, and the theoretical findings are applied to experimentally obtained data to interpret regenerator performance. The dead volume is investigated quantitatively and considered to affect the regenerator performance adversely. / Graduate