• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 74
  • 26
  • 16
  • 12
  • 10
  • 7
  • 4
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 171
  • 171
  • 42
  • 33
  • 29
  • 22
  • 20
  • 20
  • 20
  • 20
  • 19
  • 17
  • 16
  • 15
  • 15
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Translationsaktivatoren der mitochondrialen Cytochrom b-Synthese in Saccaromyces cerevisiae: Membranassoziation, Mutagenese und Protein-Wechselwirkungen von Cbs1p

Krause-Buchholz, Udo 10 September 2000 (has links) (PDF)
Die vorliegende Arbeit beschäftigt sich mit Cbs1p und Cbs2p, zwei spezifische Translationsaktivatoren der COB-mRNA. Im Mittelpunkt standen sowohl die weitere molekularbiologische und biochemische Charakterisierung von Cbs1p als auch ein Screening von Interaktionskandidaten, die mit Cbs1p und/oder Cbs2p physikalisch wechselwirken könnten. Cbs1p liegt als peripheres Membranprotein fest mit der inneren Mitochondrienmembran matrixseitig assoziiert vor. Dabei spielen möglicherweise hydrophobe und/oder Protein-Protein-Wechselwirkungen mit integralen Membranproteinen eine essentielle Rolle bei der Membranverankerung von Cbs1p. Durch die Identifizierug von atmungsdefekten Cbs1p-Mutanten, deren Mutationen in Bereichen mit Homologie zu RNA-bindenden Proteinen liegt, verstärken sich die Hinweise zur Beteiligung von Cbs1p an der direkten physikalischen Wechselwirkung mit dem 5´-leader der COB-mRNA. Darüber hinaus konnte gezeigt werden,, dass die abspaltbare Präsequenz nicht notwendig für einen mitochondrialen Import ist. Die Ergebnisse präzisieren und erweitern das vorliegende Modell der Wirkungsweise der Translationsaktivatoren Cbs1p und Cbs2p (Michaelis, 1991). Aufgrund der Membranverankerung von Cbs1p wird auch die gebundene COB-mRNA in räumlicher Nähe zur Membran gebracht. Darüber hinaus definiert Cbs1p damit möglicherweise auch den Ort der Insertion des nascierenden Apocytochrom b in die Membran. Cbs2p vermittelt die Bindung zur kleinen Untereinheit der mitochondrialen Ribosomen und könnte seinerseits ebenfalls in Interaktionen mit Untereinheiten des bc1-Komplexes involviert sein.
72

Modélisation, observabilité et commande de convertisseurs multicellulaires parallèles dans un environnement dédié / Modeling, observability and control of multi-cell chopper in dedicated environment

Amghar, Bilal 01 July 2013 (has links)
Les convertisseurs de puissance multicellulaires trouvent une place privilégiée dans le contrôle des systèmes de très forte puissance. Dans ce travail de thèse une nouvelle classe de convertisseurs de puissance est étudiée les Convertisseurs Multicellulaires Parallèles (CMP). La topologie de ces convertisseurs repose sur une association de n cellules de commutationinterconnectées par l'intermédiaire d'inductances indépendantes, appelées aussiinductances de liaison. Le CMP permet d'atteindre un courant de sortie égal à n fois le courant d'entrée du convertisseur, l'inconvénient majeur de ce type de convertisseur est le déséquilibrage des courants de branches . Dans le but de réduire et d'économiser le nombre de capteurs, nous avons proposé dans la première partie de la thèse une analyse d'observabilité spécifique à une classe de système dynamique hybride appelée Z(TN)-Observability et synthétisé un observateur hybride en utilisant l'algorithme super twisting. La deuxièmepartie du travail a été consacrée à la synthèse d'une loi de commande pour la régulation des courants de branches. En effet, le régulateur proposé est un régulateur hybride en basant sur la modélisation par réseaux de pétri de l'algorithme de contrôle. Enfin, Les deux parties théoriques sont suivies par une réalisation pratique d'un CMP à trois cellules de commutation pour valider les deux approches proposées. Les résultats expérimentaux nous ont montré les performances de l'observateur et le régulateur de courant et de tension de sortie. / This study deals with observability problems and control of the parallel multicell chopper. In the area of strong currents with high switching frequencies, new structures based on the combination of components have been developed. This type of chopper is a DC/DC static power converter which has an output current equals to n (n is the number of cells) times the source current. After recalling the dynamical equations of the converter, its hybrid dynamical behaviour and properties are highlighted. This particular hybrid system induces new and difficult observability problems, such problem can be tackled by a new observability concept [the Z(TN)-observability]. However, for a large number of switching cells in parallel, the complexity of the system makes it impossible to predict the transient behaviour of the converter and therefore all predimensioning. The main disadvantage of this type of converter is the imbalance branches of current with increasing number of cells. Therefore modelling and control with Petri net is proposed to solve the problems of imbalanced of currents and the voltage output regulation with variation of the load. The authors approaches are attested by several numerical simulations and experimental results considering noisy measurements and load variations.
73

Design of a PV-Diesel Hybrid System with Unreliable Grid Connection in Lebanon

Alayan, Sophia January 2016 (has links)
This thesis is a study on integration of photovoltaic generators into an existing diesel-unreliable grid connected system at the Lebanese village of Khiam. The main goal of implementing PV-diesel hybrid system is to reduce diesel consumption and the import of fossil fuel used in electricity power supply. Before designing the system, it is necessary to create a load profile for 120 households and pre-design the size of the PV generator, the capacity of storage system and inverter type/size selection. The load profile data is based on the average of monthly energy consumption gathered from Khiam village households. Detailed simulations and financial analysis are performed with HOMER to compare different systems and their viability. The simulations include four different designs starting from the existing system, diesel generator with unreliable grid, followed by PV generator and unreliable grid, PV and diesel generator and ended with the complete hybrid system. Once the Hybrid system is determined a detailed design is done to optimize the lowest cost PV-diesel hybrid system. The final simulated PV-diesel hybrid system is suggested with a PV capacity of 270 kWp, existing diesel capacity with 200 kVA, an inverter output of 115 kW and battery bank nominal capacity is 1872 kWh. The system renewable fraction is 53% and the project life cycle is 25 years. The PV-diesel hybrid system is projected to produce electricity at a cost of 0.12 USD/kWh. This cost is significantly lower than the 0.26 USD/kWh paid to the diesel operator, as well as lower than 0.13 USD/kWh paid to the utility grid. In addition, and according to the given information from the owner, an estimated diesel consumption of 104000 ltr/year, the simulation result shows diesel consumption at 40000 ltr/year. The reduced carbon dioxide production by 65%, from 776 to 272 tons per year, provides further justification for the PV installation in a commercial PV-diesel hybrid system.
74

Dynamic bipedal locomotion based on hybrid zero dynamics control. / Locomoção bípede dinâmica baseada na dinâmica zero híbrida.

Oliveira, Arthur Castello Branco de 11 March 2019 (has links)
This work presents an alternative method for 3D bipedal gait design using independent controllers for the plane of motion frontal and sagittal. The use of virtual constraints to design a stable gait for the frontal system is fully developed and studied in this work and the resulting gait simulated. The results, although not definitive, are promising. / Esta tese apresenta um método alternativo de síntese de marcha bípede 3D usando controladores independentes projetados para os planos de movimento frontal e sagital. O uso de restrições virtuais no projeto de uma marcha estável para o plano frontal é completamente desenvolvido e estudado neste trabalho. A marcha resultante é simulada e os resultados, apesar de ainda não definitivos, são promissores.
75

Desempenho tÃcnico-financeiro de sistema hÃbrido eÃlico-solar aplicado ao bombeamento de Ãgua / Technical and financial performance of wind-solar hybrid system applied to water pumping

Marcelo Ferreira de Arruda 05 August 2015 (has links)
A presente dissertaÃÃo apresenta como objetivo principal a instalaÃÃo e avaliaÃÃo de desempenho tÃcnico-financeiro de um sistema hÃbrido eÃlico-fotovoltaico aplicado ao bombeamento de Ãgua. Adicionalmente, à proposta uma metodologia de dimensionamento de sistema hÃbrido de geraÃÃo baseado em fontes renovÃveis em funÃÃo do menor custo e do potencial disponÃvel. O sistema de geraÃÃo hÃbrido foi instalado na jusante do aÃude do Campus do Pici da Universidade Federal do Cearà (UFC), em Fortaleza/CE, Brasil. O sistema hÃbrido à composta por 01 aerogerador de 1 kW, 04 mÃdulos fotovoltaicos de 87 Wp, sistema de banco de baterias com 05 unidades de 150 Ah. O sistema de bombeamento à composto por um conjunto moto-bomba de 0,5 cv. A anÃlise tÃcnica foi efetuada mediante anÃlise dos dados (elÃtricos e nÃo elÃtricos) coletados atravÃs de sensores instalados a um sistema supervisÃrio. Os resultados indicam que a variaÃÃo do recurso eÃlico para o local à mais elevada, quando comparado ao recurso solar, e que a disponibilidade do potencial de ambos os recursos sÃo praticamente concomitantes ao longo do perÃodo diurno, caracterÃstica esta tambÃm observada no perÃodo analisado. O sistema de geraÃÃo com banco de baterias, operando tanto na configuraÃÃo hÃbrida ou individual, assegurou o fornecimento de eletricidade para o sistema de bombeamento no perÃodo de funcionamento da carga. A partir dos indicadores de eficiÃncia, verificou-se que as unidades de conversÃo apresentaram divergÃncia entre a geraÃÃo de eletricidade estimada e a mensurada, tendo a unidade eÃlica a qual apresentou maior divergÃncia. O custo da energia elÃtrica do sistema hÃbrido instalado (eÃlico-solar) com banco de baterias à de 0,86 R$/kWh. O dimensionamento do sistema de geraÃÃo indicou que a configuraÃÃo hÃbrida para o local nÃo se ajusta em virtude do elevado potencial solar disponÃvel e da baixa disponibilidade do recurso eÃlico no 1 trimestre do ano. O dimensionamento indicou que a configuraÃÃo hÃbrida foi a de menor custo (1,52 R$/kWh) quando dimensionada em funÃÃo dos recursos do mÃs de Outubro. Indicando assim que quando mais de uma fonte renovÃvel se destaca a configuraÃÃo hÃbrida pode ser sim uma alternativa viÃvel. / This work has as main objective the installation and technical - financial evaluation of a hybrid wind - photovoltaic system applied to water pumping . In addition, a sizing methodology is proposed based on renewable sources considering low cost and available potential. The hybrid system was installed in front of the Pici Campus reservoir of the Federal Univers ity of Cearà (UFC) in Fortaleza /CE, Brazil. The hybrid system consists of 01 wind turbine of 1 kW, 04 photovoltaic modules of 87 Wp, a battery bank with 05 units of 150 Ah. The pumping system con sists of a motor - pump 0, 5 cv . Technical analysis was performed by analyzing the data (electric and non - electric) collected by sensors to a supervisory system. The results indicate that the wind resource variation for the site is higher, when compared to the solar resource, and the availability of the potential of both resources are concomitant during the daytime period, a characteristic also observed in the anal yzed period. T he generation system with battery bank, operating in either the hybrid configuration or individual, assured the supply of electricity to the pumping system during operating time . From the indicators of efficiency, it was found that the conver sion units showed divergence between estimated and measured electricity generation, and wind unit which presented greater divergence. The electricity cost of the hybrid system (wind - solar) installed with battery bank is 0.86 R$/kWh. The sizing of the generating system indicated that the hybrid configuration at the site does not fit due to the high solar potential available and the low availability of wind resources in the 1 st trimester of the year . The sizing generation system indicated that th e hybrid configuration has the lowest cost (1.52 R$/kWh) when sizing with the resources of October month . Indicating thus , that when more than one renewable source stands out , the hybrid configuration can be viable alternative
76

Stochastic Modeling and Analysis of Energy Commodity Spot Price Processes

Otunuga, Olusegun Michael 27 June 2014 (has links)
Supply and demand in the World oil market are balanced through responses to price movement with considerable complexity in the evolution of underlying supply-demand expectation process. In order to be able to understand the price balancing process, it is important to know the economic forces and the behavior of energy commodity spot price processes. The relationship between the different energy sources and its utility together with uncertainty also play a role in many important energy issues. The qualitative and quantitative behavior of energy commodities in which the trend in price of one commodity coincides with the trend in price of other commodities, have always raised the questions regarding their interactions. Moreover, if there is any interaction, then one would like to know the extent of influence on each other. In this work, we undertake the study to shed a light on the above highlighted processes and issues. The presented study systematically deals with the development of stochastic dynamic models and mathematical, statistical and computational analysis of energy commodity spot price and interaction processes. Below we list the main components of the research carried out in this dissertation. (1) Employing basic economic principles, interconnected deterministic and stochastic models of linear log-spot and expected log-spot price processes coupled with non-linear volatility process are initiated. (2) Closed form solutions of the models are analyzed. (3) Introducing a change of probability measure, a risk-neutral interconnected stochastic model is derived. (4) Furthermore, under the risk-neutral measure, expectation of the square of volatility is reduced to a continuous-time deterministic delay differential equation. (5) The by-product of this exhibits the hereditary effects on the mean-square volatility process. (6) Using a numerical scheme, a time-series model is developed and utilized to estimate the state and parameters of the dynamic model. In fact, the developed time-series model includes the extended GARCH model as special case. (7) Using the Henry Hub natural gas data set, the usefulness of the linear interconnected stochastic models is outlined. (8) Using natural and basic economic ideas, interconnected deterministic and stochastic models in (1) are extended to non-linear log-spot price, expected log-spot price and volatility processes. (9) The presented extended models are validated. (10) Closed form solution and risk-neutral models of (8) are outlined. (11) To exhibit the usefulness of the non-linear interconnected stochastic model, to increase the efficiency and to reduce the magnitude of error, it was essential to develop a modified version of extended Kalman filtering approach. The modified approach exhibits the reduction of magnitude of error. Furthermore, Henry Hub natural gas data set is used to show the advantages of the non-linear interconnected stochastic model. (12) Parameter and state estimation problems of continuous time non-linear stochastic dynamic process is motivated to initiate an alternative innovative approach. This led to introduce the concept of statistic processes, namely, local sample mean and sample variance. (13) Then it led to the development of an interconnected discrete-time dynamic system of local statistic processes and (14) its mathematical model. (15) This paved the way for developing an innovative approach referred as Local Lagged adapted Generalized Method of Moments (LLGMM). This approach exhibits the balance between model specification and model prescription of continuous time dynamic processes. (16) In addition, it motivated to initiate conceptual computational state and parameter estimation and simulation schemes that generates a mean square sub-optimal procedure. (17) The usefulness of this approach is illustrated by applying this technique to four energy commodity data sets, the U. S. Treasury Bill Yield Interest Rate and the U.S. Eurocurrency Exchange Rate data sets for state and parameter estimation problems. (18) Moreover, the forecasting and confidence-interval problems are also investigated. (19) The non-linear interconnected stochastic model (8) was further extended to multivariate interconnected energy commodities and sources with and without external random intervention processes. (20) Moreover, it was essential to extend the interconnected discrete-time dynamic system of local sample mean and variance processes to multivariate discrete-time dynamic system. (21) Extending the LLGMM approach in (15) to a multivariate interconnected stochastic dynamic model under intervention process, the parameters in the multivariate interconnected stochastic model are estimated. These estimated parameters help in analyzing the short term and long term relationship between the energy commodities. These developed results are applied to the Henry Hub natural gas, crude oil and coal data sets.
77

Combining Acoustic Echo Cancellation and Suppression / Att kombinera akustisk ekoutsläckning och ekodämpning

Wallin, Fredrik January 2003 (has links)
<p>The acoustic echo problem arises whenever there is acoustic coupling between a loudspeaker and a microphone, such as in a teleconference system. This problem is traditionally solved by using an acoustic echo canceler (AEC), which models the echo path with adaptive filters. Long adaptive filters are necessary for satisfactory echo cancellation, which makes AEC highly computationally complex. Recently, a low-complexity echo suppression scheme was presented, the perceptual acoustic echo suppressor (PAES). Spectral modification is used to suppress the echoes, and the complexity is reduced by incorporating perceptual theories. However, under ideal conditions AEC performs better than PAES. </p><p>This thesis considers a hybrid system, which combines AEC and PAES. AEC is used to cancel low-frequency echo components, while PAES suppresses high-frequency echo components. The hybrid system is simulated and assessed, both through subjective listening tests and objective evaluations. The hybrid scheme is shown to have virtually the same perceived quality as a full-band AEC, while having a significantly lower complexity and a higher degree of robustness.</p>
78

Hydraulic Regenerative System for a Light Vehicle

Guinart Trayter, Xavier, Orpella Aceret, Jordi January 2010 (has links)
<p>The thesis is based in a constructed light vehicle that must be improved by adding a hydraulic energy recovery system. This vehicle named as TrecoLiTH, participated in the Formula Electric and Hybrid competition (Formula EHI) 2009 in Italy -Rome- and won several awards.</p><p>This system consists in two hydraulic motors hub mounted which are used to store fluid at high pressure in an accumulator when braking. Through a valve the pressure will flow from the high pressure accumulator to the low pressure one, and consequently the vehicle will get extra acceleration.</p><p>This thesis consists in finishing the assembly and testing it, as the main idea was already thought and some of the necessary parts were acquired before. Firstly, a quick overview of the bike is done and the current state of it at the end of the thesis is discussed. After that, the mechanism used to actuate the system is developed and explained, with which some CAD software was used to design and make some FEA. Straight afterwards the work focused on the tests and its development. A quick discussion about what tests should be done, the preparations and also the way that some measurements were done is commented. In order to do these measurements a data acquisition device and some software to deal with it was used.</p><p>Thereupon, calculations to know if the system auto-compensates the weight added, causing more rolling resistance, and the oil frictions are done. In this part the performance and reliability of the system is discussed, as well as the feelings of the driver. Finally, improvements and possible modifications are listed with the aim of upgrade the vehicle, the system and the way of work.</p>
79

Hybrid intelligent machine systems : design, modeling and control

Ouyang, Puren 02 September 2005
To further improve performances of machine systems, mechatronics offers some opportunities. Traditionally, mechatronics deals with how to integrate mechanics and electronics without a systematic approach. This thesis generalizes the concept of mechatronics into a new concept called hybrid intelligent machine system. A hybrid intelligent machine system is a system where two or more elements combine to play at least one of the roles such as sensor, actuator, or control mechanism, and contribute to the system behaviour. The common feature with the hybrid intelligent machine system is thus the presence of two or more entities responsible for the system behaviour with each having its different strength complementary to the others. The hybrid intelligent machine system is further viewed from the systems structure, behaviour, function, and principle, which has led to the distinction of (1) the hybrid actuation system, (2) the hybrid motion system (mechanism), and (3) the hybrid control system. <p>This thesis describes a comprehensive study on three hybrid intelligent machine systems. In the case of the hybrid actuation system, the study has developed a control method for the true hybrid actuation configuration in which the constant velocity motor is not mimicked by the servomotor which is treated in literature. In the case of the hybrid motion system, the study has resulted in a novel mechanism structure based on the compliant mechanism which allows the micro- and macro-motions to be integrated within a common framework. It should be noted that the existing designs in literature all take a serial structure for micro- and macro-motions. In the case of hybrid control system, a novel family of control laws is developed, which is primarily based on the iterative learning of the previous driving torque (as a feedforward part) and various feedback control laws. This new family of control laws is rooted in the computer-torque-control (CTC) law with an off-line learned torque in replacement of an analytically formulated torque in the forward part of the CTC law. This thesis also presents the verification of these novel developments by both simulation and experiments. Simulation studies are presented for the hybrid actuation system and the hybrid motion system while experimental studies are carried out for the hybrid control system.
80

Hydraulic Regenerative System for a Light Vehicle

Guinart Trayter, Xavier, Orpella Aceret, Jordi January 2010 (has links)
The thesis is based in a constructed light vehicle that must be improved by adding a hydraulic energy recovery system. This vehicle named as TrecoLiTH, participated in the Formula Electric and Hybrid competition (Formula EHI) 2009 in Italy -Rome- and won several awards. This system consists in two hydraulic motors hub mounted which are used to store fluid at high pressure in an accumulator when braking. Through a valve the pressure will flow from the high pressure accumulator to the low pressure one, and consequently the vehicle will get extra acceleration. This thesis consists in finishing the assembly and testing it, as the main idea was already thought and some of the necessary parts were acquired before. Firstly, a quick overview of the bike is done and the current state of it at the end of the thesis is discussed. After that, the mechanism used to actuate the system is developed and explained, with which some CAD software was used to design and make some FEA. Straight afterwards the work focused on the tests and its development. A quick discussion about what tests should be done, the preparations and also the way that some measurements were done is commented. In order to do these measurements a data acquisition device and some software to deal with it was used. Thereupon, calculations to know if the system auto-compensates the weight added, causing more rolling resistance, and the oil frictions are done. In this part the performance and reliability of the system is discussed, as well as the feelings of the driver. Finally, improvements and possible modifications are listed with the aim of upgrade the vehicle, the system and the way of work.

Page generated in 0.0348 seconds