Dissertationen zum Thema „Electromagnetism - electricity“
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Borges, A. Tarisco. „Mental models of electromagnetism“. Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342567.
Der volle Inhalt der QuelleNascimento, Fernando José Barros. „Sequência de práticas com recursos multimídia para o ensino de eletromagnetismo no EJA e PROEJA“. Volta Redonda, 2017. https://app.uff.br/riuff/handle/1/4700.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Universidade Federal Fluminense. Instituto de Ciências Exatas. Programa de Pós-Graduação em Ensino de Física. Volta Redonda, RJ
O ensino de Física utilizando-se apenas a lousa, algumas exemplificações abstratas e matematizações como fundamento se revela inócuo para a modalidade de Ensino de Jovens e Adultos como o EJA e PROEJA, especialmente a eletricidade básica, o Magnetismo e Eletromagnetismo, em que, muito embora sejam interessantes na produção de conhecimento que vise ao entendimento sobre a geração de energia elétrica, tema importante em nossa sociedade atual, pouca ou nenhuma oportunidade é dada ao professor e ao aluno, no sentido de poderem desenvolver esses três temas de forma interligada, concisa e pragmática. Assim, motivar o aluno com o saber fazer, com resultados mais objetivos, ajudando-os na manipulação das práticas com a orientação do professor e o uso de vídeos livremente disponíveis ou editados dos aplicativos mais usuais para o ensino de Física, contribui para aprendizagem mais significativa, permitindo o pleno desenvolvimento das capacidades do alunado. As matérias aqui propostas de forma geral não são ensinados pelos professores na modalidade de ensino referida, até mesmo para os discentes cuja idade e série seguem os padrões considerados regulares ou próprios, o que torna as atividades aqui elaboradas de extrema importância para o ensino de Física no século XXI.
Teaching Physics using only the board, some abstract exemplification and too much mathematics the foundation reveals innocuous to the form of Youth and Adult Education as the EJA and PROEJA, especially the basic electricity, magnetism and electromagnetism, which even though they are interesting in the production of knowledge aimed at the understanding of the generation of electricity, a major issue in our society today, little or no opportunity is given to the teacher and student, in order to be able to develop these three themes interconnected, concise and pragmatic way. So Motivating students with the know-how, more objective results, helping them handling practices with the teacher's guidance and the use freely available videos or of even edited videos of the most common applications for teaching physics, contributes to more meaningful learning allowing the full development of the student body's capabilities. The materials proposed here generally are not taught by teachers in that type of education, even for students whose age series follow the standards considered regular or own, which makes the activities here developed extremely important for teaching physics at XXI century.
Lombardi, Giulia. „Unified nonlinear electrical interfaces for hybrid piezoelectric-electromagnetic small-scale harvesting systems“. Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI101.
Der volle Inhalt der QuelleIn this research work, electronic nonlinear interfaces for hybrid energy harvesting systems combining piezoelectric and electromagnetic transducers are presented. Such systems have received great attention due to their ability to detect mechanical vibrations and convert them into electrical energy sufficient to power low-power sensors. In order to supply these microelectronic devices the generated sinusoidal signal needs to be rectified into a constant DC voltage. In other words, once the energy is converted, a proper and smart extraction of such energy needs to be implemented with a dedicated unit. The proposed nonlinear hybrid interfaces developed in this work, aimed at incorporating as much as electroactive parts as possible in the circuit, not only increase the final output power of the involved transducers but also provide a solution for obtaining a common optimal load value, despite dealing with elements singularly presenting different working principles and values of optimal load, without the use of additional load adaptation stages. A first solution is derived from the previously developed SSHI (Synchronized Switch Harvesting on Inductor) and based on the Synchronized Switching technique. This method aims at replacing the passive inductor in the SSHI interface with an active electromagnetic system, leading to an all-active microgenerators interface and increasing the final output power. A second solution is derived from a combination of the SECE (Synchronous Electric Charge Extraction) and SMFE (Synchronous Magnetic Flux Extraction) techniques. Its main principle consists of transferring the energy from the piezoelectric to the electromagnetic transducer and then extracting the boosted energy from the electromagnetic system. The strategy of including as much as electroactive parts within the same electrical interface open many different possibilities of interfacing more than one electroactive system, constituting hybrid energy harvesters, without including extra circuit stages, thus maintaining a relative simplicity without high power losses
Henning, Andrew John. „Electromagnetic wave chaos in photonic crystals“. Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/11155/.
Der volle Inhalt der QuelleYoung, Jeffrey Lee. „Electromagnetic response of thin wires over an homogeneous earth“. Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184906.
Der volle Inhalt der QuelleMarcum, Frank. „Analysis of a test technique for hardness surveillance“. Ohio : Ohio University, 1988. http://www.ohiolink.edu/etd/view.cgi?ohiou1182866116.
Der volle Inhalt der QuelleSimmons, Daniel. „Hybrid methods for modelling advanced electromagnetic systems using unstructured meshes“. Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33230/.
Der volle Inhalt der QuelleCobos, Sanchez Clemente. „Forward and inverse analysis of electromagnetic fields for MRI using computational techniques“. Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/10629/.
Der volle Inhalt der QuelleKnaak, Allison. „3D synthetic aperture for controlled-source electromagnetics“. Thesis, Colorado School of Mines, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3682006.
Der volle Inhalt der QuelleLocating hydrocarbon reservoirs has become more challenging with smaller, deeper or shallower targets in complicated environments. Controlled-source electromagnetics (CSEM), is a geophysical electromagnetic method used to detect and derisk hydrocarbon reservoirs in marine settings, but it is limited by the size of the target, low-spatial resolution, and depth of the reservoir. To reduce the impact of complicated settings and improve the detecting capabilities of CSEM, I apply synthetic aperture to CSEM responses, which virtually increases the length and width of the CSEM source by combining the responses from multiple individual sources. Applying a weight to each source steers or focuses the synthetic aperture source array in the inline and crossline directions. To evaluate the benefits of a 2D source distribution, I test steered synthetic aperture on 3D diffusive fields and view the changes with a new visualization technique. Then I apply 2D steered synthetic aperture to 3D noisy synthetic CSEM fields, which increases the detectability of the reservoir significantly. With more general weighting, I develop an optimization method to find the optimal weights for synthetic aperture arrays that adapts to the information in the CSEM data. The application of optimally weighted synthetic aperture to noisy, simulated electromagnetic fields reduces the presence of noise, increases detectability, and better defines the lateral extent of the target. I then modify the optimization method to include a term that minimizes the variance of random, independent noise. With the application of the modified optimization method, the weighted synthetic aperture responses amplifies the anomaly from the reservoir, lowers the noise floor, and reduces noise streaks in noisy CSEM responses from sources offset kilometers from the receivers. Even with changes to the location of the reservoir and perturbations to the physical properties, synthetic aperture is still able to highlight targets correctly, which allows use of the method in locations where the subsurface models are built from only estimates. In addition to the technical work in this thesis, I explore the interface between science, government, and society by examining the controversy over hydraulic fracturing and by suggesting a process to aid the debate and possibly other future controversies.
Barnum, Benjamin Heath. „Electromagnetic and optical characteristics of lightning measured in the earth's ionosphere /“. Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/6843.
Der volle Inhalt der QuelleAssi, Fadi Ismail 1963. „Electromagnetic wave scattering by a sphere on a layered substrate“. Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277882.
Der volle Inhalt der QuelleLee, Robert 1962. „Electromagnetic coupling by a wire penetrating a circular aperture in an infinite planar conducting screen“. Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276731.
Der volle Inhalt der QuelleWright, Diana Beth 1963. „Electromagnetic coupling by a wire through a cavity-backed circular aperture in an infinite screen“. Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276823.
Der volle Inhalt der QuelleJuan, Garcia Pablo. „Evaluación no destructiva de estructuras de obra civil mediante métodos electromagnéticos“. Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/110467.
Der volle Inhalt der QuelleNon-destructive testing and evaluation methods in the field of civil engineering provide an alternative to traditional control methods. The availability of techniques to obtain relevant information about the physical characteristics of a structure (or its evolution) without modifying the sample results in both financial savings and greater reliability from the construction point of view. This thesis develops a method for measuring concrete structures using planar sensors, which can characterise the electromagnetic properties of the material by placing the sensor in contact with only one side of the structure or sample, which allows to measure in many real situations as dams or tunnels, in which only one side of the material can be accessed. The operating principle of the sensors developed is based on the transmission of a broadband electromagnetic wave along a planar transmission line. The measurement of the propagation time as well as the attenuation of the wave, determines the permittivity, permeability and conductivity of the material, which acts as the dielectric of the system. Thus, these variables are indicators of the structural characteristics of concrete: in this thesis they are applied to monitor the humidity level in a sample of concrete, as well as the dosage of fibres in steel fibre reinforced concrete (SFRC). From an electromagnetic point of view, both the presence of water and the addition of steel fibres are modelled similarly, since both phenomena involve an increase in the conductivity and effective permittivity, which is justified by the different theoretical models of composite materials that have been studied. Similarly, the electromagnetic properties of the measurement of the electromagnetic wave propagation can be obtained by means of the theoretical models of planar lines, both in the time or frequency domain. The development of the method involves establishing the appropriate geometry of the sensors used on each application, which entails the study of broadband baluns. Later on, once the measurement configuration and the instrumentation used are established, as well as the processing of the measured signals, a calibration method (TYS) suitable for planar sensors has been developed, for which other methods showed some difficulties. Finally, the application of the proposed method is reported. Firstly, the setting of a mortar slab was monitored for 28 days, showing the decrease of water in the sample, and secondly the dosage of steel fibres in concrete specimens was measured, showing promising results in order to the apply this technique in field measurements.
Iqbal, Muhammad Zahir. „Structural and electrical characterization of doped graphene and carbon nanotube networks“. Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/277570.
Der volle Inhalt der QuelleEl grafè, considerat com una xarxa bidimensional d’àtoms de carboni units per enllaços híbrids sp2, és un tema de recerca molt prolífer en els últims anys, com a model de sòlid bidimensional, i molt particularment degut a les seves propietats electròniques, que poden tenir aplicacions interessants en dispositius electrònics, spintrònics o quàntics. La primera part de la Tesi descriu la modificació de les propietats estructurals i elèctriques del grafè utilitzant diferents mètodes per a dopar-lo: radiació ultraviolada d’alta energia (DUV) en atmosfera ambient, DUV en diferents gasos tals com oxigen o nitrogen, o irradiant amb un feix d’electrons (e-beam). Hem fabricat transistors d’efecte de camp (FET) amb grafè (exfoliat a partir del grafit, o bé obtingut per deposició química en fase vapor, CVD) utilitzant fotolitografia i e-beam litografia, i els hem caracteritzat mitjançant AFM, espectroscòpia Raman i mesures de transport elèctric, per a les que hem utilitzat la tècnica d’amplificació de baix soroll, el lock-in. Hem investigat com l’exposició a la llum ultraviolada en atmosfera ambient, modula les propietats elèctriques del grafè, de manera que la posició del punt de Dirac es desplaça cap a tensions de porta positives, cosa que implica dopatge de tipus-p, sense que hi hagi degradació de la mobilitat. El dopatge és estable al menys durant mesos. Amb el mateix mètode, quan només la meitat del dispositiu és exposat a la radiació ultraviolada mentre l’altre meitat és recobert per una màscara metàl·lica, hem obtingut una unió p-n. L’efecte de dopatge és més important i controlable, quan és fet en atmosfera d’oxigen. L’efecte més interessant que hem observat és la reversibilitat, quan el grafè dopat retorna al seu estat primitiu, en ser irradiat amb llum ultraviolada en atmosfera de nitrogen. També hem investigat el dopatge amb llum ultraviolada del grafè exfoliat mecànicament, de una, dues o tres capes, observant que es produeix sense una degradació significativa de la mobilitat dels portadors de càrrega. Posteriorment hem estudiat la deformació estructural del grafè quan és irradiat amb un feix d’electrons. Hem observat canvis estructurals en diferents etapes: el grafè evoluciona gradualment, a partir de la forma cristal·lina, cap a una fase d’estructura nanocristal·lina i finalment, després d’una certa dosi de irradiació, presenta una estructura amorfa. L’efecte d’ irradiar el grafè amb electrons actua com a dopant tipus-n, però en aquest cas la mobilitat decreix en incrementar la dosi, això implica que hi ha formació d’estats localitzats. La segona part de la Tesi tracta de capes primes de nanotubs de carboni, com a elèctrodes flexibles i transparents per a dispositius electrònics, en particular per aplicacions d’alta freqüència. Els resultats obtinguts mostren que, a baixes freqüències, la impedància augmenta en disminuir la densitat de nanotubs, tal com cal esperar. Tan la part real com la part imaginària de la impedància (mesurada fins a 20 GHz) decreixen abruptament en augmentar la freqüència més enllà de la freqüència de tall. La freqüència de tall no depèn únicament de la densitat de nanotubs en la capa, sinó també de la geometria de la mostra. El diagrama de Nyquist es pot interpretar amb un circuit equivalent consistent simplement en una resistència i un condensador en paral·lel. Els resultats experimentals s’ajusten bé a les simulacions fetes per espectroscòpia d’impedàncies (EIS). Els resultats posen en evidència que el comportament elèctric queda majoritàriament determinat per la resistència de contacte entre els nanotubs, que formen la xarxa amb una distribució totalment desordenada. Hem vist que capes primes de nanotubs de carboni conductores i flexibles, que poden ser també transparents, poden ser competitives en diferents aplicacions, com ara pantalles, cel·les solars fotovoltaiques o sensors selectius
Rigla, Pérez Juan Pablo. „Design and characterization of magnetic systems in race-track microtrons“. Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/128671.
Der volle Inhalt der QuelleTaminiau, Tim Hugo. „Optical antennas for single emitters“. Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/132097.
Der volle Inhalt der QuelleLa interacción entre luz y materia es fundamental tanto en ciencia básica como en tecnología aplicada. En el corazón de esta interacción están la emisión y absorción de fotones en transiciones electrónicas de, por ejemplo, átomos, moléculas o semiconductores. Tales emisores cuánticos son más pequeños que la longitud de onda de la radiación con la que interaccionan. La interacción es entonces lenta y omnidireccional, lo que limita los procesos de absorción y emisión. En radio frecuencias este mismo problema fue resuelto tiempo atrás. Los circuitos eléctricos radián poco por ser más pequeños que las ondas de radio. La comunicación inalámbrica es posible sólo si los circuitos están conectados a antenas con dimensiones del orden de la longitud de onda. Las antenas son diseñadas para convertir efectivamente señales eléctricas en radiación y viceversa. Este principio se extender a la óptica. La idea central de esta tesis es que la interacción entre la luz y un emisor cuántico incrementa cuando éste es acoplando, en el campo cercano, a los modos plasmónicos resonantes de una nano-partícula metálica. La partícula actúa entonces como una antena óptica. Es posible entonces aumentar las tasas de excitación y emisión, y controlar la dependencia angular, espectral y en polarización. El capítulo 1 de ésta tesis explica estos conceptos e introduce las antenas ópticas para emisores individuales. Para implementar experimentalmente una antena óptica es necesario acoplar en campo cercano un emisor individual a una antena resonante. Como las antenas ópticas monopolares fueron fabricadas sobre sondas de barrido, podemos ubicarlas con precisión cerca a una molécula fluorescente. Es así como escaneando un emisor cuántico singular cerca a la antena es posible mapear los cambios en la excitación y la emisión. El capítulo 2 presenta los resultados relativos a la parte de la interacción correspondiente a la excitación. El campo excitado en la antena está altamente confinado (25 nm); el emisor solo interactúa con los modos de la antena dentro de esta pequeña región. Las resonancias, probadas directamente en el campo cercano, muestran que en efecto la antena es el análogo óptico a una antena monopolar. Los experimentos en el capítulo 3 muestran como la antena controla la emisión. Cuando el emisor se ubica en la posición correcta y la antena está en resonancia, la emisión del sistema acoplado es determinada por el modo de la antena, independientemente de la dirección del emisor. El capítulo 4 explora esta característica. Teórica y experimentalmente, hemos demostrado la alta direccionalidad de la radiación de un emisor individual cuando es acoplado a una antena Yagi-Uda de múltiples elementos. Por reciprocidad, esta direccionalidad incrementa tanto el campo de excitación como la eficiencia de acoplamiento. En una forma intuitiva las antenas ópticas se pueden entender como cavidades para los plasmones-polaritones de superficie. Tratando las antenas como cavidades, el capítulo 5 presenta una descripción de la interacción entre los emisores dipolares y la radiación mediada por los modos de las nano-antenas. Los resultados muestran como las propiedades de estos modos evolucionan desde las antenas macroscópicas perfectamente conductoras hasta las nano-antenas plasmónicas. Los resultados también explican las diferencias entre las antenas ópticas y las convencionales. Los resultados presentados en esta tesis prueban que las antenas ópticas son una nueva alternativa para acoplar luz a emisores cuánticos individuales. Las propiedades de absorción y emisión del emisor pueden ser controladas diseñando adecuadamente las antenas. Las antenas ópticas permiten amplificar y controlar la interacción entre radiación y materia en la escala nanométrica, convirtiéndolas en herramientas importantes en campos muy diversos. Por ejemplo, en microscopia óptica de campo cercano, en información cuántica, en óptica no lineal, en espectroscopia y en dispositivos fotovoltaicos
Kleban, Elena. „Investigating electromagnetic properties of brain tissue using 7 T MRI“. Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/51795/.
Der volle Inhalt der QuelleAllgood, Michael David Baginski Michael E. „Finite element analysis of the mesosphere's electromagnetic response to large scale lightning associated with sprites and other transient luminous events“. Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SPRING/Electrical_and_Computer_Engineering/Thesis/Allgood_Michael_37.pdf.
Der volle Inhalt der QuelleOrlando, Andrea. „Numerical modeling and analysis of complex electromagnetic structures, including those containing ferrites“. Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Orlando_09007dcc80705498.pdf.
Der volle Inhalt der QuelleVita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 17, 2009) Includes bibliographical references (p. 83-84).
Turkyilmaz, Serol. „Design And Prototyping Of An Electromagnetic Mems Energy Harvester For Low Frequency Vibrations“. Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613637/index.pdf.
Der volle Inhalt der QuelleW, respectively. In an improved prototype, the metal springs are replaced with rubber ones, providing higher energy conversion efficiency and flexibility to tune the resonance frequency of both diaphragms to desired values. This prototype provides 104 µ
W maximum power and 37.7 mV maximum voltage in response to vibration levels of 30 Hz. The proposed structure is also suitable to be realized by using microfabrication techniques. Hence, the structure to be microfabricated is studied and optimized for this purpose. When scaled to microelectromechanical dimensions, the expected maximum power and voltage from the 10 x 8.5 x 2.5 mm3 generator is 119 nW and 15.2 mV, respectively. A microfabrication process has also been designed for the proposed generator structure. According to this process, the structure consists of a stack of two pieces, each carrying different diaphragms. The diaphragms are made of parylene, and the coil and the magnetic piece are electroplated copper and nickel, respectively. As a result of this study, a new topology is proposed for harvesting energy at low frequency vibrations by the frequency up-conversion technique, and an efficiency improvement is expected with more than three orders of magnitude (119 nanoWatts output for the same size) compared to the study realized in our laboratory in converting low frequency (70-150 Hz) environmental vibrations to electrical energy.
Mallorquí, Jordi J. (Jordi Joan). „Métodos numéricos para aplicaciones biomédicas: problemas directo e inverso electromagnéticos“. Doctoral thesis, Universitat Politècnica de Catalunya, 1995. http://hdl.handle.net/10803/6934.
Der volle Inhalt der QuelleSe incluye una extensa recopilación de resultados, tanto simulados como obtenidos a partir de medidas reales, que permiten conocer el comportamiento de los distintos algoritmos en función de los parámetros de diseño de un tomógrafo.
Tyler, Robert H. „Electromagnetic fields generated by ocean currents and the potential for using geomagnetic data in ocean and climate studies“. Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39884.
Der volle Inhalt der QuelleFirst, general relativity theory is used to formally establish the proper set of electromagnetic equations to be used for observers in a rotating (accelerating) frame of reference observing a medium (the ocean, in this case) with relative velocity. Extra terms due to rotation are derived and described and a generalized Schiff's charge density is shown to be potentially significant for the application to ocean circulation.
We extend the theory of electromagnetic fields generated by ocean currents. Many analytical solutions are found for idealized ocean features including sheared flow, jets, and a Stommel gyre. Results indicate that the ocean-induced magnetic fields will typically have magnitudes of 10's-100's of nT within the ocean. Outside of the ocean, the magnitudes are smaller (typically 1-10 nT) but decay on scales set by the horizontal scale of the ocean feature.
We investigate the time-scales associated with the adjustment of electromagnetic fields generated by low-frequency ocean currents. We find that the time scales can be quite long, prohibiting a quasistatic assumption in the treatment of the electromagnetic fields generated by the important tidal, inertial, and diurnal-frequency ocean currents.
Three-dimensional explicit time-dependent and steady-state finite-difference numerical models are constructed to study the electromagnetic fields generated by more realistic ocean current and conductivity features.
The ocean currents generate electromagnetic forces on the fluid at the surface of the earth's core. If these forces lead to significant core motion, the effect of the oceans on the generation and variability of the earth's magnetic field may be nontrivial. We estimate the form and magnitude of these forces and make comparisons with observations. Despite many uncertainties, we find evidence to suggest the ocean forcing mechanism may be significant and conclude that this process should be further investigated in the context of a larger study.
This work indicates that it is likely that the geomagnetic record has captured oceanic signals. From a preliminary data analyses we find that aside from the oceanic tidal signals, the magnetic record shows other signals of possible oceanic origin including an apparent correlation between magnetic records from the equatorial Pacific and the Southern Oscillation Index. We discuss the prerequisites that are necessary to extract information about ocean circulation variability from the geomagnetic record.
Berg, Matthew James. „A microphysical model of scattering, absorption, and extinction in electromagnetic theory“. Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1040.
Der volle Inhalt der QuelleDing, Zhiguang. „Electromagnetic Shielding Properties of Iron Oxide Impregnated Kenaf Bast Fiberboard“. Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699998/.
Der volle Inhalt der QuelleDias, Bruno José da Cruz Teixeira. „Application of conducting polymers in nanobiotechnology“. Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/131948.
Der volle Inhalt der QuelleThis Thesis reports different nanobiotechnological applications of electrochemically and electrically conducting polymers. The central, and also common, focus of all the studies and experiments described in Chapters 4 to 6 is the interaction between synthetic conducting polymers and bioentities (DNA, proteins, polysaccharides, small peptides, drugs and cells). One of the major challenges of this Thesis consisted on the characterization of the interactions between conducting polymers and DNA. The studies described in Chapter 4 evidenced that specific hydrogen bonding interactions, in addition to conventional electrostatic interactions, are formed between conducting polymers bearing polar groups and plasmid DNA. In order to get more information about such interactions, studies were essentially focused on poly(3,4-ethylenedioxythiophene), a conducting polymer with excellent technological properties. On the basis of both the structural changes undergone by the DNA upon the formation of specific interactions with the conducting polymer and the preferences of the latter towards well-defined nucleotide sequences and bases, a mechanism has been proposed to explain the interaction between the two macromolecules. This mechanism, which is supported by theoretical calculations, is consistent with all the experimental data reported in this Thesis. Chapter 5 is devoted to examine the interaction between morphine molecules and conducting polymers. Within this general context, this block of results is essentially focused on the optimization of the conditions necessary for the detection of this drug using poly(Nmethylpyrrole) and poly(3,4- ehylenedioxythiophene). Studies have been performed considering the effect of: the polymer morphology (i.e. both flat films and films containing hollow microstructures with doughnut-like morphologies have been examined), the time of incubation with morphine, and the pH of the environment. In all cases detection was carried out using electrochemical techniques, which include electrochemical impedance spectroscopy and cyclic voltammetry. Results reflect that, under controlled conditions, the investigated conducting polymers exhibit a high ability to capture morphine molecules, retaining them for a long period of time. In addition, the fabrication of a portable drug detector device based on conducting polymers has been proposed. Finally, Chapter 6 is devoted to the preparation and characterization of new hybrid conducting biocomposites for nanobiotechnological and biomedical purposes. More specifically, this block of the work presents the electropolymerization of poly(3,4-ethylenedioxythiophene) with different biomolecules (i.e. an enzyme, poly- and oligosaccharides, and a small peptide) and the interaction of these new hybrid materials with cells. It was found that, in general, the prepared biocomposites retain the electrical and electrochemical properties of the individual conducting polymer and, in addition, show a prominent cellular activity. Lysozyme-containing biocomposites, which form compact and stable films, exhibit a high bactericidal activity against Gram (+) bacteria, which is promoted by a controlled release of the enzyme. The remarkable cellular activity of dextrins-containing materials suggests that they are potential candidates for the fabrication of cellular scaffolds. Finally, the incorporation of a low concentration of CREKA peptide into the polymer matrix resulted in a very positive effect on the electrochemical properties of the conducting polymer, which were considerably enhanced.
Planas, Badenas Ramon. „Stabilized finite element formulations for solving incompressible magnetohydrodynamics“. Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/134740.
Der volle Inhalt der QuelleNapolitano, Mario. „Interaction-based nonlinear quantum metrology with a cold atomic ensemble“. Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/144558.
Der volle Inhalt der QuelleEn aquest manuscrit presentem una recerca experimental i teòrica sobre mesures limitades pel soroll quàntic fetes mitjançant interferometria no lineal, o des de un altra perspectiva, mitjançant interacció. En el treball experimental es va fer servir una interfície quàntica de polarització entre polsos de llum en propagació i àtoms freds de rubidi-87 atrapats en una trampa òptica de dipol. Primer, farem un repàs de la teoria de la metrologia quàntica i de la teoria de la estimació, descriurem la proposició teòrica sobre metrologia quàntica no lineal tal i com la va desenvolupar el grup de Carlton M. Caves al Universitat de Nou Mèxic. A continuació descriurem la nostra proposta, feta al 2010, de com implantar la idea del grup de Caves fent servir interaccions òptiques no lineals en un conjunt d’àtoms freds amb la finalitat d’efectuar una mesura no lineal de spin. Per avaluar aquesta proposta vam desenvolupar dues aproximacions teòriques fent ús de dos mètodes diferents. En primer lloc vam estendre la tècnica de variables quàntiques col lectives cap als processos òptics no lineals, aquesta tècnica sovint és utilitzada per descriure interfícies quàntiques i conjunts de spin atòmics. Això dóna com a resultat un Hamiltonià efectiu que conté termes no lineals de la forma descrita pel grup de Caves, i demostra una equivalència qualitativa entre el nostre esquema i el seu. El segon mètode fa ús de les equacions de Maxwell-Bloch per descriure la propagació no lineal dels polsos a través del conjunt de spins atòmics, tenint en compte deshomogeneïtats i efectes de relaxació. D’aquesta manera podem fer prediccions quantitatives sobre senyals de rotació de polarització òptica en les condicions d’un experiment real. Seguirem amb la descripció de com vam implementar al laboratori la nostra proposta teòrica mitjançant una interfície quàntica de polarització entre llum i àtoms. Descriurem el ja existent sistema de confinament i sondeig dels àtoms, concentrant-nos en les característiques que permeten fer mesures al limit del soroll quàntic i del soroll de projecció. Aleshores detallarem com vam adaptar el sistema per l’ús amb polsos més curts i intensos, tal i com requereix la mesura no lineal, i al mateix temps com vam calibrar el sistema de detecció de llum en aquestes diferents condicions. El calibratge de la rotació no lineal de polarització en funció de la freqüència del làser de sonda, ens permet obtenir un senyal de rotació casi purament no lineal. Finalment, presentarem els resultats experimentals que mostren senyals de rotació no lineal limitats pel soroll quàntic al llarg de tres ordres de magnitud en el número N de fotons. Tals resultats son consistents amb els nostres models teòrics i confirmen una important predicció del treball del grup de Caves, és a dir que la interacció de dos fotons dóna una llei d’escala de N-3/2 per a la sensibilitat de la mesura. Per concloure, una concisa discussió relaciona aquesta observació experimental amb discussions teòriques sobre el “limit d’Heisenberg” de la metrologia quàntica, i amb d’altres possibles aplicacions de tècniques de mesura no lineal
Ebertsohn, Nolan Wade. „Cable trays and EMC : modelling and measurement“. Thesis, Stellenbosch : Stellenbosch University, 2005. http://hdl.handle.net/10019.1/50293.
Der volle Inhalt der QuelleENGLISH ABSTRACT: Common mode currents are a major source of interference in electrical and electronic systems. A universal solution to counteract common mode interference is to introduce an electromagnetic shield with known characteristics. Cable trays are often used to shield cables from unwanted electromagnetic interference (EM!) and its shielding characteristics are defined in terms of its transfer impedance. This thesis pursues the modelling and measurement of the transfer impedance and mutual inductance of non-magnetic cable trays. Theoretical analysis is firstly employed by means of Maxwell's equations after which method of moments (MoM) simulations are performed in order to determine the transfer impedance and mutual inductance within the interior region of a cable tray. The results obtained through simulation are then validated with measurements conducted with an automatic network analyser (ANA). The computational and measured data are in good agreement and the developed model can be used to predict the transfer impedance in the cross-section of non-magnetic cable trays.
AFRIKAANSE OPSOMMING: Gemenernodus strome is 'n bron van interferensie in elektriese en elektroniese stelsels. 'n Universele oplossing om hierdie gemenernodus interferensie teen werk is om 'n elektromagnetiese skerm met bekende eienskappe te implementeer. Geleier leikanale word dikwels gebruik om kabels teen elektromagnetiese interferensie te beskerm en die afskermings eienskappe word in terme van die kanaal se oordragsimpedansie gedefinieer. Hierdie tesis ondersoek die modelering en meting van die wedersydse induktansie en oordragsimpedansie van nie-magnetiese geleier leikanale. 'n Teoretiese analise word eers uitgevoer deur middel van Maxwell se vergelykings waarna metode van momente (MvM) simulasies uitgevoer word om die oordragsimpedansie en wedersydse induktansie in die interne gebied van 'n leikanaal te bepaal. Die resultate verkry deur simulasie word dan bevestig deur meting wat uitgevoer word met behulp van 'n automatiese netwerk analiseerder (ANA). Die numeriese en gemete data stem goed ooreen en die ontwikkelde model kan deurgaans gebruik word om die oordragsimpedansie in die deursnit area van nie-magnetiese geleier leikanale te voorspel.
Kably, Khalil. „Microdecharges entre hydrometeores : initialisation de l'eclair et rayonnement electromagnetique submicroseconde associe“. Toulouse 3, 1988. http://www.theses.fr/1988TOU30142.
Der volle Inhalt der QuelleBayerl, Albin. „Variability and reliability at the nanoscale of gate dielectrics of MOS devices and graphene based structures“. Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/126515.
Der volle Inhalt der QuelleIn the first chapter of this thesis, the MOSFET transistor and an overview of the implications of ongoing device shrinking will be given. Possible alternatives to allow the scaling down such as the introduction of high-k dielectrics and the potential of graphene for nanoelectronic applications are also explained. The second chapter will be devoted to describe in more detail the AFM (Atomic Force Microscope), which has been used to investigate the electrical properties of different materials at the nanoscale. In the third chapter, different fabrication conditions of HfO2 layers based devices, such as the annealing temperature (and polycrystallization), the thickness and the precursor with which it was grown will be investigated at the nanoscale. The influence of an electrical stress at the device level is also studied. In chapter 4, the impact of different electrical stresses on the nanoscale electrical properties of ultra-thin SiON based MOSFETs is investigated. Using a CAFM, the gate oxide has been analyzed after a BTI (Bias Temperature Instability) and CHC (Channel Hot Carriers) stress. Since with the CAFM tip very small areas can be studied, the degradation induced at different regions of the gate oxide along the channel was analyzed. Chapter 5 describes the invention of a completely new approach to significantly improve the intrinsic mechanical and electrical properties of commercially available CAFM tips by coating them with graphene. Finally, in chapter 6, the usability of graphene for nanoelectronic applications will be investigated at the nanoscale. One aspect that will be analyzed is the presence of corrugations, wrinkles and grain boundaries, which are shown to increase the device-to-device variability. The impact of the substrate on which graphene is transferred to will be also studied. Since graphene has been recently started to be used as top electrode in memory devices, in the second part of this chapter, the variability and reliability of Graphene-Insulating-Semiconductor (GIS) structures based on HfO2 will be preliminarily investigated.
Kong, Kang-Chuen. „Real time simulations of EMTP results“. Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07292009-090324/.
Der volle Inhalt der QuelleZago, Fernando. „O impacto do aumento da urbanização nos niveis das tensões induzidas por descargas atmosfericas nas proximidades de linhas de transmissão“. [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260911.
Der volle Inhalt der QuelleTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: Alguns dos principais danos causados por descargas atmosféricas são de origem indireta, ou seja, originam-se dos campos eletromagnéticos provenientes deste tipo de fenômeno natural resultando em problemas de compatibilidade eletromagnética ou em desafios para os projetistas de sistemas de proteção de surtos e de blindagens contra este tipo de interferência. Este trabalho trata de um destes efeitos indiretos, tensões induzidas em linhas aéreas por descargas atmosféricas próximas, utilizando-se das mais recentes pesquisas na área de campos eletromagnéticos provenientes deste tipo de fenômeno natural. Através de uma rigorosa formulação matemática do canal da descarga atmosférica, assim como, dos campos eletromagnéticos provenientes dele, no caso de conexão direta com o solo ou com um objeto elevado (torre ou prédio aterrados), e da consideração de diferentes expressões para o cálculo do raio de atração dos objetos elevados, foi possível realizar um estudo comparativo dos efeitos da urbanização nas proximidades de uma linha aérea com relação ao aumento ou diminuição dos níveis de tensões e correntes induzidas quando da ocorrência de descargas atmosféricas próximas. Estes efeitos foram analisados através de simulações computacionais considerando variações em diversos parâmetros associados à urbanização, tais como: quantidade de objetos elevados, altura média dos objetos elevados, modelo de raio de atração e densidade de ocupação ou de urbanização. A partir da pesquisa realizada durante este trabalho e do programa computacional desenvolvido, são propostas metodologias para se avaliar as modificações nos padrões de ocorrência dos níveis de tensões induzidas de origem atmosférica em linhas aéreas localizadas em diferentes cenários de ocupação urbana ou nas proximidades de objetos elevados como, por exemplo, torres de telecomunicações.
Abstract: Some of the worst damage caused by lightning is indirect, that is, it is caused by electromagnetic fields radiated from this kind of natural phenomenon resulting in electromagnetic compatibility problems or in challenges for designers of surge protection systems and shields against these interferences. This work considers one of these indirect effects, induced voltages on overhead lines by nearby atmospheric lightning discharges, using some of the most recent research in the area of electromagnetic fields generated by these natural phenomena. Starting from a rigorous mathematical formulation for a lightning channel, as well as for the electromagnetic fields generated by them, for the case of lightning striking the soil directly or an elevated grounded object, it was possible to carry out a comparative study of the urbanization effects close to an overhead line with respect to the increase or decrease of the induced voltages and currents when nearby lightning discharges occur. These effects were analyzed using computational simulations considering variations in some parameters associated with urbanization, such as: number of elevated objects, elevated objects average height, different models for the calculation of attractive radius and occupation or urbanization density. Taking into account the research and the computational program developed in this work, methodologies to evaluate the modifications on the occurrence patterns of lightning induced voltages on overhead lines localized at different urban occupation landscapes or at the vicinity of elevated objects like telecommunication towers, were proposed.
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica
Llatser, Martí Ignacio. „On the scalability limits of communication networks to the nanoscale“. Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/144561.
Der volle Inhalt der QuelleKoldan, Jelena. „Numerical solution of 3-D electromagnetic problems in exploration geophysics and its implementation on massively parallel computers“. Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/130833.
Der volle Inhalt der QuelleMartí, Diaz Zeus. „Disseny i caracterització d'un ondulador helicoïdal per a la producció de llum de sincrotró, i millores en el seu procés de construcció“. Doctoral thesis, Universitat Autònoma de Barcelona, 2006. http://hdl.handle.net/10803/3384.
Der volle Inhalt der QuelleEls estudis que es presenten s'han dut a terme en associació al LLS ("Laboratori de Llum de Sincrotró": consorci format per a la Universitat Autònoma de Barcelona, la Generalitat i l'Estat).
En el capítol 1 es presenten els onduladors dins del marc dels sincrotrons, així com de forma resumida les propietats principals dels primers. Es tracta doncs d'una introducció teòrica.
El contingut dels capítols 2 i 4 va ser recollit i desenvolupat durant la meva estada al sincrotró Elettra de Trieste, Itàlia.
El capítol 2 conté una descripció intensiva i exhaustiva de les tècniques i mètodes de caracterització i implementació dels onduladors. Es tracta d'una descripció del mètode experimental.
El capítol 3 conté una sèrie d'estudis de diferents mètodes per al disseny d'un ondulador. Aquests mètodes han estat desenvolupats per l'autor per tal d'implementar un dels 4 onduladors que s'instal·larà en el futur sincrotró ALBA a Cerdanyola, Espanya.
En el capítol 4 descriu el muntatge d'un ondulador de polarització helicoïdal. En aquest apartat ressaltarem els problemes originats per les inhomogeneïtats dels blocs magnètics.
En el capítol 5 es planteja un nou mètode d'ordenació de blocs per al muntatge d'onduladors basat en el desenvolupament multipolar. Amb aquest mètode es pretén solucionar les mancances d'altres mètodes existents com els utilitzats en el capítol 3, en particular les mancances relacionades amb les inhomogeneïtats dels blocs.
En el capítol 6 es presenten les conclusions resumides de tots aquests estudis.
Este estudio se presenta como resultado de la mayor parte de la búsqueda que he llevado a cabo en los cuatro años de mi doctorado (2002-2006), el cual ha estado financiado por el AGAUR (acrónimo de Agencia de gestión de ayudas universitarias y de búsqueda).
Los estudios que se presentan se han llevado a cabo en asociación al LLS ("Laboratorio de Luz de Sincrotón": consorcio formado por la Universidad Autónoma de Barcelona, la Generalidad y el Estado).
En el capítulo 1 se presentan los onduladores dentro del marco de los sincrotones, así como de forma resumida las propiedades principales de los primeros. Se trata pues de una introducción teórica.
El contenido de los capítulos 2 y 4 fue recogido y desarrollado durante mi estancia al sincrotón Elettra de Trieste, Italia.
El capítulo 2 contiene una descripción intensiva y exhaustiva de las técnicas y métodos de caracterización e implementación de los onduladores. Se trata de una descripción del método experimental.
El capítulo 3 contiene una serie de estudios de diferentes métodos para el diseño de uno ondulador. Estos métodos han estado desarrollados por el autor para implementar uno de los 4 onduladores que se instalará en el futuro sincrotón ALBA a Cerdanyola, España.
En el capítulo 4 describe el montaje de uno ondulador de polarización helicoidal. En este apartado resaltaremos los problemas originados por las inhomogenidades de los bloques magnéticos.
En el capítulo 5 se plantea un nuevo método de ordenación de bloques para el montaje de onduladores basado en el desarrollo multipolar. Con este método se pretende solucionar las deficiencias de otros métodos existentes como los utilizados en el capítulo 3, en particular las deficiencias relacionadas con las inhomogenidades de los bloques.
En el capítulo 6 se presentan las conclusiones resumidas de todos estos estudios.
This study appears as resulting from most of the search which I have carried out in the four years of my doctorate (2002-2006), which has been financed by the AGAUR (acronym of Agència de gestió d'ajuts universitaris i de recerca).
The studies that we present have been carried out in association to the LLS ("Laboratori de Llum de Sincrotró": partnership formed by the Autonomous University of Barcelona, the Catalan local Government and the state Goverment).
In chapter 1 we present the undulators within the frame of synchrotrons, as well as the summarized study of their main properties.
The content of chapters 2 and 4 was gathered and developed during my stay synchrotron Elettra de Trieste, Italy.
Chapter 2 contains an intensive and exhaustive description of the techniques and methods of characterization and implementation of the undulators.
Chapter 3 contains a series of studies of different methods for the design for one undulator. These methods have been developed by the author to implement two of the 4 undulators that will used in the future in synchrotron ALBA in Cerdanyola, Spain.
In chapter 4 it describes the assembly of one undulator of helical polarization. In this section we will emphasize the problems originated by the inhomogeneities of the magnetic blocks.
In chapter 5 a new method of arrangement of blocks for the assembly of undulators considers based on the multipolar development. With this method we try to solve the lacks of other existing methods like the used ones in chapter 3, in particular the lacks related to the inhomogeneities of the blocks. In chapter 6 we summarize the conclusions of all these studies.
Rouco, Gómez Víctor. „Controlling Vortex Pinning and Dynamics of Nanostructured YBCO Thin Films Grown by Chemical Solution Deposition“. Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/133329.
Der volle Inhalt der QuelleSince the discovery of High-Temperature Superconductors (HTS) a huge effort has been devoted in order to optimize the electric power properties of these materials. As a difference from conventional Low-Temperature Superconductors (LTS), some HTS are able to achieve the superconducting state at the boiling point of nitrogen (77K), making these materials much more attractive for technological applications due to their reduced operating costs. One of the main applications of HTS is the electrical transport. Due to the zero electrical resistance of these materials when they are below the critical temperature, Tc, they can transmit up to 10 times more power than conventional cables or can carry equivalent power at much lower voltages. On the other hand, HTS materials have been deeply studied in the field of electronics. In particular, HTS nanowires can be functionally scaled to smaller sizes due to their extremely short intrinsic lengths. Furthermore, their characteristic fast relaxation rates offer higher counting rates in photodetection experiments when compared to LTS. However, one of the most important issues to take into account in the study of HTS, is the presence of quantified magnetic flux lines, referred as vortex, into their phase diagram. The main difference from LTS concerning the vortex behavior arises from the high thermal excitations. Consequently a great variety of different pinning centers are needed in order to avoid (or control) the vortex dynamics and therefore, the resulting electrical dissipation. Controlling vortex pinning and dynamics is the aim of this thesis where the main results are presented in chapters 3, 4 and 5. Previously, in chapter 1 we present the main superconducting properties, and in particular, the regarding to vortex behavior in YBa2Cu3O7-x (YBCO -HTS with the widest operating range-) samples grown following the Chemical Solution Deposition (CSD) technique. In chapter 2 we show the experimental techniques used in our analysis and the measurement procedure. In chapter 3, a huge analysis of vortex pinning is presented. An unprecedented phenomenon for vortex pinning is demonstrated which allows improving the critical current density and its anisotropy in the presence of non-superconducting secondary phases into the YBCO matrix. Furthermore, an analysis of the vortex dynamics with YBCO-CSD natural defects is performed. In chapters 4 and 5 we have focused in controlling vortex dynamics in YBCO thin films. In chapter 4 a preferential sense for the vortex movement is demonstrated when asymmetric nanostructures are patterned in the YBCO layer. Consequently, a controlled AC-DC rectification is obtained. In chapter 5, the studies are centered in the interaction between superconducting and ferromagnetic materials. It is demonstrated that by inserting ferromagnetic nanorods into the YBCO matrix, a huge control of the critical current density is possible as a function of the magnetic state of the nanorod. General conclusions of the thesis are presented and summarized in the last chapter. Finally, the analytical procedure used in a theoretical simulation presented in chapter 5 is exposed in the appendix.
Massana, Gracia Valentí. „Optimització del procés de construcció d'un ondulador d'imants permanents per a una font de llum sincrotró“. Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/120236.
Der volle Inhalt der QuelleThis thesis is a research work on the inhomogeneities of permanent magnets that are used to construct insertion devices in synchrotron light sources, especially undulators. The work has two objectives. First, try to model the effect of these inhomogeneities in the magnetic fields generated by magnets. Mainly we studied their magnetic characteristics from direct measurements of the blocks, and we have focused the study of inhomogeneities in the minority components of the magnetization vector, as these are one of the biggest limitations in the performance of the insertion devices. Secondly, based on the measurements of these magnetic characteristics, work has focused on how you can minimize the effects of inhomogeneities in the insertion devices. This is typically done through a specific arrangement of the blocks to compensate errors caused by the inhomogeneities. In this part, numerical methods have been applied multivariate optimization functions. In the first part of the thesis is described all experimental equipment that has been used to make the measurements magnetic and mechanical of blocks and where explains how to have been characterized all the benches of the insertion devices laboratory at Alba synchrotron, determining the error associated with each of them. The individual magnetic blocks, which are the ones that form the whole structure of the undulator have been measured with Helmholtz coils to get the magnetization vector. With these results, and using an algorithm that minimizes the main component of the field, magnets are grouped into groups (modules) of 1 (singlets) and three blocks (triplets). These modules have been measured with benches based on the principle of Faraday's induction to determine the signature, that is, the transversal dependence of the integral field. Again, using an algorithm that minimizes the total field integral of the device, the order of the modules within the overall magnetic structure has been determined. The second part describes the theoretical foundations that create mathematical models for magnets and allow implementing programs to fit parameterized models of morphological inhomogeneities, and optimize the magnet sorting and the final optimization of the insertion devices. The aim of this second part was the preparation of an algorithm that allows building segments of undulators with low error using magnets with a certain degree of inhomogeneity. Finally, we focused on in-situ monitoring of assembly in order to verify that the predictions made based on this model are very consistent with the experimental measurements.
Abad, Muñoz Libertad. „Efectos Estructurales y de Interfase en Capas Finas de La(2/3)Ca(1/3)MnO(3)“. Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3403.
Der volle Inhalt der QuelleNuestro trabajo ha puesto de manifiesto que la técnica de pulverización catódica de RF es adecuada para el crecimiento de capas epitaxiales de LCMO de alta calidad sobre sustratos monocristalinos diversos (STO, LaAlO3 (LAO)). Las heteroestructuras LCMO/STO y LCMO/LAO han sido objeto de un detallado análisis poniendo de manifiesto que el desacoplo de parámetros de red juega un papel muy importante tanto sobre el tipo de crecimiento de las heteroestructuras como sobre las propiedades físicas. El sistema LCMO/STO (δ=1.2%) crece tensionado en el plano y permite crecer capas de hasta unos 100 nm sin que haya relajación parcial de la tensión estructural. En cambio, el sistema LCMO/LAO (δ=-1.8%) crece comprimido en el plano y muestra señales de relajación parcial de la tensión estructural incluso para espesores en torno a los 10 nm.
El análisis de las propiedades magnéticas y de transporte muestran que ambos sistemas LCMO/STO y LCMO/LAO adolecen de una notable disminución tanto de su temperatura de transición magnética, TC, como de su magnetización de saturación, MS, al disminuir el espesor de las capas, siendo éste más acusado en el caso del LCMO/STO. Tratamientos térmicos al aire a alta temperatura permiten una mejora sustancial de las propiedades magnéticas y de transporte en ambos sistemas. La mejora es mucho más rápida en el sistema LCMO/LAO. Así mismo, el aumento del espesor de las capas también promueve una mejora de las propiedades, que se aproximan a las del material en forma masiva conforme el grosor aumenta. Esta evolución se ha relacionado con la aparición de una capa no magnética en la superficie de las capas de LCMO que se pone de manifiesto, predominantemente para las capas de LCMO/LAO ultra delgadas. Por otro lado, hemos visto como esta capa inerte puede ser reducida hasta un orden de magnitud mediante tratamientos térmicos de las muestras a alta temperatura.
Nuestro trabajo ha puesto de manifiesto que la tensión estructural juega un papel fundamental y que las mejoras de TC y MS con los tratamientos térmicos están fundamentalmente ligadas a una relajación parcial de la tensión estructural. Otras posibilidades, tales como la incorporación de oxigeno o la variación de la microestructura de las muestras han sido descartadas en base a medidas de efecto Hall y análisis de microscopía electrónica de alta resolución.
Para el estudio de las propiedades de transporte en las interfases hemos desarrollado un procedimiento experimental basado en la utilización de un microscopio de fuerzas atómicas trabajando en modo corriente permitiendo la caracterización de barreras aislantes e interfases entre un metal noble y un óxido complejo. Este método permite la caracterización de barreras y superficies soslayando los problemas derivados del desconocimiento preciso del contacto entre la punta de AFM y la superficie de la capa. Se realizaron medidas mediante la definición de nanocontactos de diferente geometría y tamaño realizados por distintas técnicas de nanofabricación. Mediante el estudio de las curvas I(V) en nanocontactos de LCMO/metal noble (Au, Pt) constatamos la existencia de una barrera superficial aislante (túnel) para capas finas vírgenes de LCMO/LAO. Mediante el ajuste de las curvas I(V) utilizando el modelo de Simmons hemos derivado valores para la capa aislante que concuerdan muy bien con otros datos reportados, además esta capa aislante puede ser reducida drásticamente mediante tratamientos térmicos en atmósfera ambiente.
In this Thesis we have analyzed different preliminary aspects related to the use of complex oxides, such as manganes perovskites, for implementation of functional devices with potential application on magnetoelectronics. To be precise, we have faced in deep the different aspects related with the fabrication of magnetic tunnel junctions based on the La2/3Ca1/3MnO3 (LCMO)/SrTiO3 (STO) system.
Our work makes evident the suitability of RF sputtering technique for growing high quality epitaxial layers of LCMO onto several single-crystalline substrates (STO, LaAlO3 (LAO)). The heterostructures LCMO/STO and LCMO/LAO have been object of a detailed analysis showing up that structural misfit plays a significant role both on the heterostructures growth process and on the physical properties. The system LCMO/STO (δ=1.2%) is under in-plane tensile strain but, thin films up to 100 nm thick can be grown without any partial relieve of the structural strain. In contrast, the system LCMO/LAO (δ=-1.8%) grows under in-plane compressive strain and shows clear traces of partial relaxation of structural strain even for thicknesses around 10nm.
The analysis of the magnetic and transport properties indicates that both systems have an outstanding depression on both the temperature transition, TC, and the saturation magnetization, MS, when decreasing the thin film thickness, being this phenomenon more pronounced in the case of LCMO/STO. High temperature annealing processes in air promote a remarkable improvement of the magnetic and transport properties in both systems. This improvement is faster and more evident in the LCMO/LAO system.
In addition, we have verified that the increment of the film thicknesses also promotes an improvement of the physical properties, approaching that of bulk samples. This evolution has been correlated with the existence of a non magnetic layer at the topmost layers of the LCMO thin films, whose effect becomes more relevant as the film thickness decreases and being dominant for ultra-thin films in the LCMO/LAO system. It has been observed that this dead layer can be reduced up to one order of magnitude by high temperature annealing processes.
Our work has demonstrated that structural strain plays a fundamental role on the magnetic and transport properties of these systems and the improvements of TC and MS with annealing processes is strongly linked to a partial relaxation of the structural strain. Other possibilities, such as oxygen uptake or modifications of the microstructure of the samples have been ruled out in base of Hall Effect measurements and high resolution transmission electron microscopy analysis.
To study transport properties at the interfaces we have developed an experimental procedure based on the use of an atomic forces microscope (AFM) working in current sensing mode, permiting the electrical characterization of insulating barriers and the interfaces between the precious metal and the complex oxide. This method allows characterizing transport properties of barriers and interfaces avoiding the problems related to the uncertainty of the exact nature of the contact between the AFM tip an the analyzed surface. Measurements were realized by defining nanocontacts, with different geometries and sizes, using different nanofabrication techinques.
Fondevilla, Sala Núria. „Desenvolupament de microgeneradors inercials electromagnètics en tecnologia de microsistemes per a la recuperació d’energia mecànica residual de l’ambient“. Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/124219.
Der volle Inhalt der QuelleThis thesis describes the design and optimization of a ressonant electromagnetic inertial microgenerator for energy scavenging applications, compatible with Si technology and a relatively high electromechanical coupling with simple designs. It consists of a fixed micromachined coil and a movable magnet (inertial mass) mounted on a resonant structure. This device is well suited for harvesting of mechanical energy from vibrations induced by operating machines which are characterized by a well defined frequency and low displacement amplitudes. Adjusting the resonant frequency of the system to that of the targeted vibrations allows amplification of these low amplitude displacements. ANSYS simulations are carried out to investigate the influence of the coil parameters (density of tracks and tracks cross section) and resonator geometry (resonant frequency and parasitic damping) on the device performance. The experimental mechanical and electrical characterization of a first prototype fabricated with a modular manufacturing process (not optimized) has allowed the validation of the model developed for the inertial electromagnetic microgenerators, which is then used as a roadmap for a number of optimizations for the final device design. Generator prototypes have been fabricated with resonant membranes with different dimensions, using in all cases the same design of electromagnetic transducer. This has allowed investigating the influence of the membrane geometry on the parasitic damping which is a key parameter for the generator performance. In relation to the first prototypes a significant increase in the generated power has been achieved by the implementation of electrochemical processes for the fabrication of coils with thicker metal tracks. The results obtained have shown the ability of these devices to generate power and output voltages in the range of state of the art. The characterization of the fabricated prototypes has allowed to observe the presence of non-linear effects that lead to the appearance of hysteretic vibrational phenomenon and strongly affect the output of the microgenerator. These effects are likely related to the mechanical characteristics of the polymeric membrane, and determine an additional dependence of vibration frequency on the excitation amplitude. Rewriting and solving the equations of movement including a nonlinear term in restoring force leads to a simple model that successfully reproduces the hysteresis of the resonator.
Gertrudes, João Bosco. „Influência da condutividade e permissividade do solo em função da frequência no cálculo da impedância longitudinal e admitância transversal de linhas aéreas de transmissão“. [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260993.
Der volle Inhalt der QuelleTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Esta tese tem como objetivo o desenvolvimento de modelos mais precisos para o cálculo de parâmetros elétricos de linhas aéreas de transmissão para estudos de transitórios na faixa de frequência 0 a 2 MHz. Esta faixa de frequência cobre a maioria das perturbações eletromagnéticas nos sistemas elétricos: energização, faltas simétricas e assimétricas, rejeições de carga, descargas atmosféricas, perturbações harmônicas, etc. Na faixa de frequência citada, em consequência da dependência dos parâmetros do solo com a frequência, a condutividade elétrica do solo (sg) tem a mesma ordem de grandeza que o produto entre a frequência angular do sinal incidente no solo (w) e a permissividade elétrica do solo (eg). Portanto, as suposições de baixa frequência tradicionalmente adotadas - sg constante e weg desprezível (sg >> weg) - podem levar a modelos que não representam de forma adequada a resposta da linha no caso de transitórios rápidos (com espectro de frequência acima de 1 kHz). O objetivo central desta tese é verificar a influência da dependência dos parâmetros do solo no cálculo da impedância longitudinal e admitância transversal por unidade de comprimento em comparação com os modelos tradicionais de cálculo. As análises são feitas inicialmente para o caso de um único condutor acima do solo e posteriormente através de um estudo para uma linha de transmissão trifásica, 440 kV, em operação no sistema elétrico brasileiro. As impedâncias longitudinais e as admitâncias transversais de retorno pelo solo são avaliadas através de métodos tradicionais de cálculo e através de integração numérica das formulações de Carson modificadas para inclusão do modelo de solo que considera a depêndencia de sg e weg em função da frequência
Abstract: This thesis aims to propose more accurate models for calculating the electrical parameters of overhead power transmission lines. The influence of earth's conductivity and permittivity frequency dependence is evaluated when calculating transversal and longitudinal transmission lines' parameters in the frequency range 0 to 2 MHz. This frequency range covers the majority of the electromagnetic transients in electrical systems (switching transients, faults' transients, load rejections, harmonic disturbances, etc). Between 1 kHz to 2 MHz, the product of the signal angular frequency (w) by the dielectric constant (eg) of the soil may have the same order of magnitude as the conductivity (sg), due to the variation of these parameters with frequency. Therefore, the assumptions of low frequency traditionally used - the soil conductivity (sg) considered as constant and weg that can be negligible (sg >> weg) - can lead to incorrect models that do not adequately represent the transmission line's response, in cases of fast transients phenomena (with frequency spectrum above 1 kHz). The importance of properly considering the frequency dependent soil model is presented for the one-conductor case and for a single three-phase transmission line (440 kV, considered ideally transposed). The aim is to compare the transmission line parameters calculated considering the conductivity and weg frequency dependence ground model in relation to the common ground representation, with constant conductivity and weg that may be neglected. It is also compared the results obtained from the complex plane method with those obtained from the Carson's modified expressions for longitudinal parameters and between Carson's modified potential-coefficient correction factors and from the most common approximated methods for transversal admittance parameters
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica
Gàzquez, Alabart Jaume. „TEM investigation of growth mechanisms and microstructure of model YBCO coated conductor architectures deposited by metalorganic decomposition“. Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3401.
Der volle Inhalt der Quellecharacterization of the CSD thin films presented in this work. The results, chapters 3, 4 , 5 and 6, are presented in two parts: Part I reports many aspects governing the growth mechanisms of CSD films, in particular the identification of those factors controlling the evolution of microstructures, which remain poorly established in comparison with vacuum deposited films. We give first an account of the evolution from a partially oriented granular microstructure to a dense epitaxial one in CeO2 films deposited from chemical solutions (chapter 3), and second the microstructural evolution of YBCO from trifluoroacetate precursors, which follow a complex compositional trajectory (chapter 4). In part II the microstructure of TFA-YBCO thin films with high critical current densities is analysed. We depict intrinsic structural defects occurring within YBCO films, focusing in extended defects which can lead to strong flux-pinning and high critical current density (chapter 5). The microstructure of TFA-YBCO films with artificial defects has been also studied (chapter 6). The inclusion of BaZrO3 results in strong increase of the critical current density, demonstrating that chemical solution growth is a very flexible methodology to nanostructure YBCO films and coated conductors.
Finally, we present the general conclusions of this study.
Saureu, Artesona Sergi. „From mononuclear to dinuclear: magnetic properties of transition metal complexes“. Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/386451.
Der volle Inhalt der QuelleEn las últimas décadas, el mundo de la tecnologia y el desarrollo de nuevos aparatos electrónicos se han convertido en vitales para nuestra sociedad. Considerando la creciente demanda para la interpretación de resultados experimentales, la mejora de los métodos teóricos y el crecimiento de los recursos computacionales nos han permitido un mejor entendimiento de los comportamientos magnéticos en los sistemas con metales de transición. El objetivo de esta tesis es contribuir a este campo de investigación con el estudio de materiales magnéticos usando herramientas computacionales (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), y en algunos casos, combinando con resultados experimentales. La primera parte (Capítulo 3 y 4) incluye el estudio de los estados electrónicos de los complejos de spin-crossover de Fe(II) y Fe(III) combinando la teoria funcional de la densidad (DFT y TD-DFT) con métodos multiconfiguracionales (CASSCF, CASPT2). Además, usando la misma combinación, hemos descrito el fenómeno LIESST en complejos de Fe(III). La segunda parte (Cap. 5 y 6) expone el estudio de las propiedades magnéticas asociadas al acoplamiento magnético utilizando metodos variacionales (DDCI, DDCI-2), en un complejo de Fe(IV) y un complejo bimetálico [MnCr]-oxalato, y como los cambios estructurales afectan a ese acoplamiento. Por otra parte, hemos hecho un riguroso analisis de la estructura electrónica del complejo de Fe(IV) para aportar la información para la descripción mas adecuada del sistema.
Over the last decades the world of technology and the development of new devices have become vital for our society. Considering the growing demand for interpretation of experimental observations, the improvement of theoretical methods and the increasing of the computational resources has allowed us to deepen the understanding of magnetic beahvior of metal transitions architectures. The aim of this thesis is to contribute to this research field with the study of magnetic materials by using computational tools (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), and in some cases combining it with experimental results. The first part (Chapters 3 and 4) includes the study of the electronic states of Fe(II) and Fe(III) spin-crossover complexes combining the density functional theory (DFT and TD-DFT) with multiconfigurational methodologies (CASSCF, CASPT2). In addition, we have described the LIESST phenomenon in Fe(III) using the same combination. The second part (Chapters 5 and 6) exposes the study of the magnetic properties related to the magnetic coupling using variational methods (DDCI, DDCI-2) of a Fe(IV) complex and bimetallic [MnCr] oxalate-based complexes and how changes can influence to the coupling. Moreover, a rigorous analysis of the electronic structure of the Fe(IV) system has been performed to provide more information about the most adequate description of the system in terms of intuitive chemical concepts.
Heideier, Raphael Bertrand. „Metodologia para avaliar o emprego de técnicas de seleção e conversão da radiação solar sobre a produção de energia elétrica de células fotovoltaicas“. Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-05122017-151838/.
Der volle Inhalt der QuelleThis thesis proposes a methodology to evaluate the use of solar radiation selection and conversion techniques to increase the production of electric energy of photovoltaic solar cells. A review of the photovoltaic mechanisms for the production of electrical energy and the obstacles to increase its efficiency, especially the impacts of temperature and the absorption of the solar spectrum was done. A methodology was developed to define an optimal optical filter to be used in a region in the presence or not of solar spectrum conversion, through computational simulations, which defines the range of the solar radiation that must be absorbed by the cell in order to have the best balance between absorption and heating. A mathematical model was created and implemented computationally to calculate the energy production of a photovoltaic module in a given region with or without the application of solar radiation conversion and selection techniques. A case study with data from the city of Petrolina, PE, Brazil, concluded that the expected gain for the use of an optical filter that reflects wavelengths above 1000 nm is about 1% of the power generated. Empirical tests allowed validating the proposed methodology comparing the actual data with the theoretical data obtained by the simulations of the mathematical model. After calibration of the mathematical model, it was verified that the instantaneous power results calculated with the mathematical model vary about 5% for both the filter module and the unfiltered module. To avoid the constructive constraint of the optical filter and to verify other possible gains are proposed experiments with solar radiation conversion compounds associated with optical filters to select the solar radiation. With this, it is expected to significantly increase the electricity production of crystalline silicon photovoltaic cells.
Sort, Viñas Jordi. „Magnetic hardening induced by ferromagnetic-antiferromagnetic coupling“. Doctoral thesis, Universitat Autònoma de Barcelona, 2002. http://hdl.handle.net/10803/3340.
Der volle Inhalt der QuelleFerromagnetic (FM) - antiferromagnetic (AFM) exchange interactions induced after field cooling FM-AFM composites through the Néel temperature of the AFM are known to increase the coercivity, HC, of the FM component. We have studied the effect of milling different FM (Co or SmCo5) with AFM powders (with TN, either above room temperature, e.g. NiO, or below room temperature, e.g. CoO). Several combinations (i.e. Co + NiO, SmCo5 + NiO and SmCo5 + CoO) have been studied, with special focus on FM + NiO composites. The different structural and magnetic behaviors of Co and SmCo5 during ball milling or heat treatments make it necessary to properly adapt the processing route for each case. Thus, in Co + AFM composites the effects of FM-AFM exchange interactions are mainly induced after field cooling the as-milled powders from above TN. Contrarily, in SmCo5 + AFM powders, heating results in deterioration of the hard magnetic properties. However, comparison of the magnetic properties of SmCo5 milled with NiO or with CoO indicates that for SmCo5 + NiO some exchange interactions can be actually induced during the milling. FM-AFM exchange interactions result in a shift of the hysteresis loop and in enhancements of HC and the squareness ratio, MR/MS. These effects are observed at room temperature, provided that TN is above room temperature (i.e. for NiO). In addition, an enhancement of the energy product, (BH)Max, can also be accomplished, to a certain extent, after optimization of the FM:AFM ratio and milling conditions. On the one hand, an increase of the AFM content brings about an increase of FM-AFM exchange interactions (i.e. an increase of HC and MR/MS). Nevertheless, on the other hand, since the AFM has a zero net magnetization, the overall saturation magnetization, MS, of the FM-AFM composites decreases proportionally to the amount of AFM. As a consequence of these competing effects, it has been found that the compositions resulting in maximum coercivities are not the optimum ones to enhance (BH)Max. Therefore, both the milling time and the FM-AFM ratio need to be optimized depending on the desired properties for the final materials.
Sancristóbal, Alonso Belén de. „Neuronal oscillations: from single-unit activity to emergent dynamics and back“. Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/129072.
Der volle Inhalt der QuelleThe main objective of this thesis is to better understand information processing in neuronal networks in the presence of subthreshold oscillations. Most neurons propagate their electrical activity via chemical synapses, which are only activated when the electric current that passes through them surpasses a certain threshold. Therefore, fast and intense discharges produced at the neuronal soma (the action potentials or spikes) are considered the basic unit of neuronal information. The neuronal code is understood, then, as a binary language that expresses any message (sensory stimulus, memories, etc.) in a train of action potentials. Circuits of thousands of interconnected neurons give rise to certain rhythms, revealed in collective activity measures such as electroencephalograms (EEG) and local field potentials (LFP). Synchronization of action potentials of each cell, triggered by stochastic fluctuations of the synaptic currents, cause this periodicity at the network level.To understand whether these rhythms are involved in the neuronal code we studied three situations. First, in Chapter 2, we showed how an open chain of neurons with an intrinsically oscillatory membrane potential filters a periodic signal coming from one of its ends. The response of each neuron (to spike or not) depends on its phase, so that each cell receives a message filtered by the preceding one. Each presynaptic action potential causes a phase change in the postsynaptic neuron, which depends on its position in the phase space. Those incoming periods that are able to synchronize the subthreshold oscillations, keep the phase of arrival of action potentials fixed along the chain. The original message reaches intact the last neuron provided that this phase allows the discharge of the transmembrane voltage.I the second case, we studied a neuronal network with connections to both long range and close neighbors, in which the subthreshold oscillations emerge from the collective activity apparent in the synaptic currents. The inhibitory neurons provide a rhythm to the excitability of the network. When inhibition is low, the likelihood of a global discharge of the neuronal population is high. In Chapter 3 we show how this rhythm causes a gap in the discharge frequency of neurons: either they pulse single spikes or they fire bursts of high intensity. The LFP phase determines the state of the neuronal network, coding the activity of the population: its minima indicate the simultaneous discharge of many neurons, while its maxima indicate the coexistence of bursts due to local decreases of inhibition at global states of excitation. In Chapter 4 we consider coupling between two neural networks in order to study the interaction between different rhythms. The oscillations indicate recurrence in the synchronization of collective activity, so that during these time windows a population optimizes its impact on a target network. When the rhythm of the emitter and receiver population differ significantly, the communication efficiency decreases as the phases of maximum response of each LFP signal do not maintain a constant difference between them.Finally, in Chapter 5 we studied how oscillations typical of the collective sleep state give rise to stochastic coherence. For an optimal noise intensity, modulated by the excitability of the network, the LFP reaches a maximal regularity leading to a refractory period of the neuronal population.In summary, this Thesis shows scenarios of interaction between action potentials, characteristics of the dynamics of individual neurons, and the subthreshold oscillations, outcome of the coupling between the cells and ubiquitous in the dynamics of neuronal populations . The results obtained provide functionality to these emerging rhythms, triggers of synchronization and modulator agents of the neuronal discharges and regulators of the communication between neuronal networks.
Llobet, Megías Anna. „Contribution à l'étude du magnéto-transport et aux phénomènes de ségrégation de phase dans les manganites“. Doctoral thesis, Universitat Autònoma de Barcelona, 2000. http://hdl.handle.net/10803/3332.
Der volle Inhalt der QuelleSvozilík, Jiŕí. „Photonic entanglement : new sources and new applications“. Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284225.
Der volle Inhalt der QuelleLas correlaciones cuánticas, normalmente conocidas como entanglement, son uno de los temas más estudiados y discutidos de la Mecánica Cuántica, desde la introducción del concepto en la década de 1930. Incluso hoy en día, una gran cantidad de esfuerzos, tanto teóricos como experimentales, se dedican en este tema, que cubre muchas áreas distintas de la física, tales como medición cuántica (quantum metrology), computación cuántica (quantum computing), comunicaciones cuánticas (quantum communications), física de estado sólido, química e incluso biología. Las tareas fundamentales de investigación que uno debe considerar en relación con entrelazamiento son: -Cómo crear estados cuánticos entangled. -Cómo mantener el entanglement durante la propagación, en contra de las fuentes que pueden crear de-coherencia. -Cómo emplear los beneficios que el entanglement ofrece. Esta tesis, dividida en cuatro capítulos, se centra en la primera y últimas tareas consideradas. En el capítulo 1, se da una breve introducción y una visión general de lo que es el entrelazamiento (entanglement), empezando por el famoso artículo de Einstein, Podolosky y Rosen, y continuando con la formulación de John Bell de las llamados desigualdades de Bell. Definimos aquí conceptos generales acerca de los estados cuánticos enrelazados e introducimos algunas medidas de entrelazamiento importantes, que se utilizan posteriormente a lo largo de toda la tesis. En este capítulo, algunas fuentes de partículas entrelazadas (fotones) se mencionan brevemente. La importancia se pone en fuentes basadas en el proceso no lineal de generación paramétrica espontánea (SPDC, Spontaneous Parametric Down Conversion). La última parte de este capítulo está dedicado a mencionar algunas aplicaciones que se benefician de la utilización de estados entrelazados. El capítulo 2 se dedica al estudio sistemático de la generación de pares de fotones entrelazados, o no, en guías semiconductores de tipo Bragg. En primer lugar, se presenta una fuente de pares de fotones espectralmente no correlacionados, lo que se puede conseguir utilizando la geometría adecuada y la adecuada dispersión del material, a través del diseño estructural de las guías de onda. En segundo lugar, las guías de onda de Bragg se diseñan de manera que dan como resultado la generación de pares de fotones entrelazados en el grado de libertad de polarización con un ancho de banda grande. Finalmente, se presentan resultados experimentales de pares de fotones generados en este tipo de estructuras. En el capítulo 3, se explora la viabilidad de la generación de pares de fotones entrelazados en el grado espacial de libertad, es decir, en el momento angular orbital (OAM). En primer lugar, se investiga cómo crear un espacio de Hilbert altamente multidimensional utilizando modos OAM Para ello se ahce uso de materiales no lineales con chirped-qausi-phase-matching. Aquí mostramos cómo un aumento del chirp puede aumentar efectivamente el número de Schmidt en varios órdenes de magnitud. En segundo lugar, se investiga como fibras de vidrio con un núcleo en forma de anillo son capaces de generar y propagar los modos con OAM más simples. El Capítulo 4 se dedica a la localización Anderson y a los llamados paseos aleatorios cuánticos (Quantum random walks). En primer lugar se presenta una propuesta experimetnal para la realización de un paseo aleatorio discreto cuántico utilizando un interferómetro MAch-Zehnder con un modulador espacial de luz, que nos permite introducir diferentes tipos de ruido con diferentes tipos de estadística. En segundo lugar, se muestra cómo la localización transveral Anderson de luz parcialmente coherente se puede estudiar haciendo uso de pares de fotones entrelazado
Madinehei, Milad. „Improvement of corrosion and mechanical properties of amorphous steels by microalloying and nanocrystallization“. Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/319456.
Der volle Inhalt der QuelleAmorphous steels containing optimal quantities of chromium are very attractive for practical applications due to their corrosion behavior. These alloys have extraordinary corrosion resistant properties even in hostile environments. All the amorphous steels compositions studied so far for their corrosion resistance have a relatively large amount of Cr and one consequence is the reduction of the glass forming ability (GFA). Also mechanical properties of metallic glasses are highly sensitive to composition change. A detailed study on the effect of low amount of Cr on the glass forming ability, corrosion resistance and mechanical behavior has been done in order to determine the optimal amount of Cr needed to obtain good corrosion and mechanical properties while maintaining a high GFA. The composition showed drastically different effects on the different properties of the alloy depending on the amount of Cr. The results show that Fe–Cr–Mo–C–B alloys with remarkable GFA, high thermal stability, high hardness, as well as superior corrosion and wear resistance can be obtained with Cr additions near 5 at.%. Higher Cr-content (Cr˃6 at.%) alloys are better candidates only for applications where plasticity is not an issue and the material is exposed to aggressive environments. Although alloys with relatively low Cr contents exhibited the best plasticity among all the studied alloys, their high tendency to corrode limits their applications to inert environments. The chemical properties of metallic glasses are closely related to their unique amorphous structure so thermally induced structural transformations (structure relaxation and crystallization) and their effect on the corrosion resistance were investigated. Electrochemical measurements of the heat treated samples unveiled a strong dependence of corrosion resistance on structural transformation. Although structural relaxation improved the corrosion resistance by forming a more ideal glass, the best corrosion resistance was obtained for the sample showing a structure consisting of nanocrystalline Cr-rich phase embedded in an amorphous matrix. Precipitation of a second crystalline phase (Mo-rich) had a detrimental effect on corrosion resistance but the alloys exhibited good anticorrosion properties until the Mo-rich grains exceed the critical limit of 50 nm, where the Cr-rich passive film was not able to cover them completely
Pérez, Tomàs Amador. „Novel materials and processes for gate dielectrics on Silicon carbide“. Doctoral thesis, Universitat Autònoma de Barcelona, 2005. http://hdl.handle.net/10803/3381.
Der volle Inhalt der QuelleHowever, very near the definitive emergence, the SiC technology needs to address two fundamental limitations: The price of the wafers and the poor SiC/SiO2 interface. The high density of imperfections encountered at the SiC/oxide interface represents a major obstacle in the development of functional SiC devices. The main efforts of this thesis have been directed to the detection and reduction of interface traps in the oxide/SiC interface. To achieve this demanding objective, two different ways have been contemplated: (1) Investigations have been carried out to improve the thermal oxidation or even to improve the formation of the interface with alternative techniques as nitridation or deposited oxides. (2) The classical insulator made up with SiO2 has been replaced by other innovative dielectrics.
Innovative gate fabrication processes have been proposed in this thesis using deposited SiO2 gate oxides from PECVD with silane and TEOS as precursors. SiO2-TEOS deposited oxides are an alternative to thermal oxidation. 4H-SiC MOSFET with mobilities up to 38-45 cm2/Vs [(0001) face] and 216 cm2/Vs [(11-20) face] have been fabricated.
We have demonstrated that the thermal oxidation of Ta2Si is a simple way to achieve a high-k dielectric on SiC (and on Si). We have fabricated one of the first well behaved high-k MOSFET on SiC with a mobility peak up to 45 cm2/Vs
In the last section, a field-effect mobility model including Coulomb scattering at interface traps has been proposed fitting the experimental channel mobility of SiC MOSFETs and the device behavior depending on the density of interface traps, the substrate doping level and the temperature.