Academic literature on the topic 'Capactive'

Pour lutter efficacement contre le réchauffement climatique, il est nécessaire d'augmenter la production d'énergies propres et renouvelables. L'énergie solaire, l'énergie éolienne, l’hydroélectrique et l'énergie marémotrice sont des technologies matures. L'augmentation de la production d'énergie renouvelable nécessite l'utilisation de sources d'énergie peu ou pas exploitées, comme l’énergie bleue. Cette forme d’énergie correspond à l’énergie générée lors du mélange d'eau douce et d'eau salée. Cependant, les procédés actuels d’extraction d'énergie à partir de gradients de sel restent inefficaces, principalement parce que les membranes sélectives commerciales sont peu performantes comme le cas de l’électrodialyse inverse ou l’Osmose à pression retardée qui ne sont toujours pas économiquement rentable. Les espoirs de membranes non sélectives dotées de canaux nanofluidiques chargés qui ont été conçus pour réduire la résistance interne de la cellule semblent être vains. Une nouvelle solution est proposée qui consiste à augmenter le potentiel de circuit ouvert de la membrane en y attachant des électrodes capacitives avec des groupements fonctionnels chargés négativement qui permet l’adsorption des ions, essentiellement les ions positifs. Une telle configuration nous permet de doubler le potentiel du circuit ouvert de la cellule sans trop modifier la résistance ohmique globale et donc de multiplier par 4 la puissance brute potentiellement récupérable.Après une étude approfondie réalisée dans le but de caractériser le procédé et une optimisation de la consommation énergique due aux pertes de charge, nous présentons un dispositif de quelques centimètres carrés avec une seule membrane récoltant une densité de puissance nette de 2 Watts par mètre carré de membrane (densité de puissance potentielle nette estimée à 5.4 W.m-2, ce qui rend le système économiquement viable<br>To effectively combat global warming, it is necessary to increase the production of clean, renewable energy. Solar, wind power, hydroelectric dams and tidal power plants are mature technologies. Increasing the production of this energy requires the use of energy sources that are little or not exploited like the blue energy which is the a less-known source with enormous potential that can be generated directly from the mixing of fresh and salt water. However, current processes for energy harvesting from salt gradients remain inefficient mainly because commercial selective membranes have poor performance as in the reverse electrodialysis or in the pressure retarded osmosis and still not economically viable. Hopes for nonselective membranes with charged nanofluidic channels which have been designed to reduce the internal resistance of the cell seem to be in vain. Here we present a novel solution that involves increasing the open circuit potential of the membrane by attaching tailored capacitive layers with negatively charged functional groups on the surface that adsorb ions, mainly the positive ones. Such a configuration allows us to double the potential of the open circuit of the cell without modifying too much the global ohmic resistance and thus to multiply by 4 the potentially recoverable power.After a thorough study carried out in order to characterize the process and an optimization of the energy consumption caused by the hydraulic pressure drop, we display a device of a few squared centimeters with only one membrane harvesting a net power density of 2 Watts per square meter of the membrane (estimated net potential power density 5.4 W.m−2 ) which makes the system economically viable

Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management; and, Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1998.<br>Includes bibliographical references (leaf 76).<br>by Brian C. Hintzman.<br>M.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.<br>Includes bibliographical references (leaves 67-68).<br>This thesis defines the capacity of single-hop communication links in wireless ad hoc networks as the transferable data rate over that link determined by the Shannon limit and by the fixed modulation scheme and bit error rate. The resulting capacity formulas are derived under the assumption of r-3.8 path loss and uniform, but random, distribution of users. Rank of the link R is defined and included in the capacity formulas. After defining link capacity, the improvement of capacity is studied when different network components are implemented. These include successive interference cancellation (SIC), and multiple antenna arrays at the transmitting and the receiving end of the link. These strategies are then compared in terms of the dB improvement of capacity that they provide. Network parameter NP is defined in order to characterize spatial reuse in the network, and optimal network parameter is determined for maximizing link capacity in the process of dividing the network single frequency channel into equally sized subchannels.<br>by Filip S. Antic.<br>M.Eng.

A execução de obras apoiadas em solos moles constitui um desafio para a engenharia geotécnica. Pela baixa capacidade de suporte do solo mole, tais obras estão sujeitas a sofrer colapso, geralmente por ruptura do solo de base; e recalques excessivos, que ocorrem ao longo do tempo por efeito do adensamento do solo mole. Em virtude destes problemas, quaisquer soluções que promovam o aumento da capacidade de carga do solo mole representam uma enorme contribuição ao tema. Este trabalho apresenta resultados de uma série de provas de carga realizadas em laboratório sobre uma camada de areia apoiada em solo mole. A camada de areia foi ensaiada em três condições: sem reforço, reforçada apenas por geocélulas e pela associação de geocélulas e geogrelha. Foram utilizadas geocélulas de geotêxtil com ligações costuradas e geocélulas de polietileno com ligações soldadas nas alturas de 5, 10 e 15 cm. Os resultados apontam uma melhora significativa quando do confinamento com geocélulas, tanto em termos de recalque quanto de capacidade de suporte. A utilização de geocélulas conjugadas a um reforço basal com geogrelha permitiu uma melhora do desempenho ainda mais significativa<br>Works resting on soft soils represent a large task to geotechnical engineers. Due to the soft soil low bearing capacity, such works might present a rotational failure or present large settlements that occurwith time due to consolidation. For these problems any technical contribution that would allow an increase fo the bearing capacity of the soft soils would represent an enormous help to geotechnical engineering. This work presents results of laboratory loading plate tests carried out on a sandy layer resting on the topo of a soft soil deposit. The sandy layer was tested in there different conditions: unreinforced, reiforced with geocells and with geocells and geogrids. Geocells made out of strips of non woven geotextile with sewed joints and made from welded joint poliethylene strips were used. The results of plate tests showed a significant improvement not only in terms of bearing capacity but also in terms of settlement reduction when geocells alonge were used. The use of geocells associated with geogrids allowed further improvements in the bearing capacity and settlement reductions

Die vorliegende Arbeit befasst sich mit einem detaillierten Vergleich von Mehrpunkt-Schaltungstopologien mit zentralem Gleichspannungszwischenkreis für den Einsatz in Mittelspannungsanwendungen. Im Rahmen dieser Untersuchungen wird die 3-Level Neutral Point Clamped Spannungswechselrichter Schaltungstopologie (3L-NPC VSC) sowohl mit Multilevel Flying Capacitor (FLC) als auch mit Multilevel Stacked Multicell (SMC) Schaltungstopologien verglichen, wobei unter Verwendung von aktuell verfügbaren IGBT-Modulen Stromrichterausgangsspannungen von 2.3 kV, 4.16 kV und 6.6 kV betrachtet werden. Neben der grundlegenden Funktionsweise wird die Auslegung der aktiven Leistungshalbleiter und der passiven Energiespeicher (Zwischenkreiskondensatoren, Flying Capacitors) für die untersuchten Stromrichtertopologien dargestellt. Unter Berücksichtigung verschiedener Modulationsverfahren und Schaltfrequenzen werden Kennwerte für den Oberschwingungsgehalt in der Ausgangsspannung und dem Ausgangsstrom vergleichend evaluiert. Die installierte Schalterleistungen, die Halbleiterausnutzungsfaktoren, die Stromrichterverlustleistungen sowie die Verlustleistungsverteilungen werden für die betrachteten Stromrichtertopologien detailliert gegenübergestellt und bewertet<br>The thesis deals with a detailed comparison of voltage source converter topologies with a central dc-link energy storage device for medium voltage applications. The Three-Level Neutral Point Clamped Voltage Source Converter (3L-NPC VSC) is compared with multilevel Flying Capacitor (FLC) and Stacked Multicell (SMC) Voltage Source Converters (VSC) for output voltages of 2.3 kV, 4.16 kV and 6.6 kV by using state-of-the-art 6.5 kV, 3.3 kV, 4.5 kV and 1.7kV IGBTs. The fundamental functionality of the investigated converter topologies as well as the design of the power semiconductors and of the energy storage devices (Flying Capacitors and Dc-Link capacitors) is described. The installed switch power, converter losses, the semiconductor loss distribution, modulation strategies and the harmonic spectra are compared in detail

This thesis describes a finite element analysis (FEA) model of an indirect heating thermal actuator. The heat transfer mechanisms are investigated and the conductive heat transfer is found to be the dominant heat transfer mode. A model simplification method is discussed and used in the analysis to reduce the degrees of freedom and avoid meshing failures. The device is fabricated with the MetalMUMPs process. Measurements of the displacement as a function of the driving voltage are made to verify the FEA model. The results show that the simulation result of the FEA model produced a reasonable agreement with the experimental data. The difference between the FEA result and test result is investigated. A novel thermal actuator with integrated capacitive position sensor is also investigated. This new thermal actuator with an integrated capacitive sensor uses the indirect heating thermal actuator discussed in the first part of the thesis to achieve a new integration method. The displacement of the actuator provided by the sensor enables a feedback control capability. The analytical model, FEA and test results for the capacitive sensor are presented to validate the design concept. The test results show a reasonable agreement with the analytical analysis and the FEA. Finally, a manual displacement tuning application and a PI feedback control application with the designed thermal actuator with integrated capacitive sensor are documented.<br>Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-07-03 16:17:02.633

碩士<br>國立成功大學<br>電機工程學系<br>85<br>In this thesis, we present a general method to calculate the error performance of cellular mobile systems which employ frequency-hopped spread spectrum (FH/SS) signaling and error-correction coding. The developement utilizes the concept of circularly symmetric signals and expresses the problem in terms of Bessel integral. The method provides an efficient evaluation of error probability with respect to unequal power levels, delays, cochannel interference, interchannel interference, noise, and data streams of interfering users. By using this analysis, we can investigate the multiple-access capability of the FH/SS systems in the presence of multiple tone interference and channel noise. As a result, the system capacities of different FH/SS system are derived and shown in this thesis.