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DI, MATTEO LEONARDO. "CMS ECAL intercalibration with electrons from W and Z decays and Search for the Standard Model Higgs boson in the H > WW > lvqq channel with the CMS detector." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2013. http://hdl.handle.net/10281/41813.
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The usage of isolated electrons from W and Z leptonic decays for the intercalibration of the CMS ECAL single channel response is described. The statistics of 5 fb−1, collected at LHC in 2011 at sqrt(s)=7 TeV, allowed to reach a statistical precision of about 1% in the central part of the ECAL barrel and about 4% in the ECAL endcaps. The results obtained with this method are combined with others, and the impact on the Higgs to di-photon search is shown.
Subsequently, the thesis describes the search strategy for the Higgs boson in the H > WW > lvqq final state. The results are based on a data sample corresponding to an integrated luminosity of 17 fb−1 of proton-proton collisions accumulated during the 2011-2012 LHC run.
The standard model Higgs boson is excluded at 95% confidence level in the mass ranges [215 − 490] + [525 − 600] GeV.
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Simpson, Edward Thomas. "Electron holography of isolated and interacting magnetic nanocrystals." Thesis, University of Cambridge, 2009. https://www.repository.cam.ac.uk/handle/1810/252128.
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Fuller, G. W. "Electron microscopy and image analysis of isolated myosin filaments." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38322.
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Archer, Anthony D. "Spectroscopic studies of field-induced electron emission from isolated microstructures." Thesis, Aston University, 1992. http://publications.aston.ac.uk/8241/.
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A detailed investigation has been undertaken into the field induced electron emission (FIEE) mechanism that occurs at microscopically localised `sites' on uncoated and dielectric coated metallic electrodes. These processes have been investigated using two dedicated experimental systems that were developed for this study. The first is a novel combined photo/field emission microscope, which employs a UV source to stimulate photo-electrons from the sample surface in order to generate a topographical image. This system utilises an electrostatic lens column to provide identical optical properties under the different operating conditions required for purely topographical and combined photo/field imaging. The system has been demonstrated to have a resolution approaching 1m. Emission images have been obtained from carbon emission sites using this system to reveal that emission may occur from the edge triple junction or from the bulk of the carbon particle. An existing UHV electron spectrometer has been extensively rebuilt to incorporate a computer control and data acquisition system, improved sample handling and manipulation and a specimen heating stage. Details are given of a comprehensive study into the effects of sample heating on the emission process under conditions of both bulk and transient heating. Similar studies were also performed under conditions of both zero and high applied field. These show that the properties of emission sites are strongly temperature and field dependent thus indicating that the emission process is `non-metallic' in nature. The results have been shown to be consistent with an existing hot electron emission model.
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McKinley, A. J. "A study of matrix isolated ions by electron spin resonance spectroscopy." Thesis, University of Canterbury. Chemistry, 1985. http://hdl.handle.net/10092/9393.
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The objective of this project was to attempt to trap small molecular ions in an argon matrix and study the structure of these ions using electron spin resonance spectroscopy. To this end an apparatus designed for matrix isolation ESR was developed in a number of stages concurrently with matrix isolation experiments. Early experiments used conventional electron impact ion sources but these sources were found to be unsuitable for producing ions to trap in an argon matrix due to the energy of the ions. In these experiments problems arose due to contamination of the matrix by methyl radicals and hydrogen and nitrogen atoms which obscured the spectral range of interest that is around g = 2. Vacuum ultra-violet photolysis was used to produce ions and was found to be successful.
The molecular ion NH₃⁺ has been trapped in an argon matrix at 14K by photo-ionisation of an NH₃/Ar mixture during deposition. The NH₃⁺ cation has been found to be rigidly trapped in the argon matrix and exhibits a powder-type ESR spectrum. The derived magnetic parameters agree well with those obtained by other workers in different matrices. A strong reversible temperature dependence of the linewidth of the NH₃⁺ spectrum has been observed.
Argon resonance photolysis of methyl iodide and methyl bromide argon mixtures during deposition was found to produce free methyl radicals in addition to methyl radicals interacting weakly with a high spin nucleus or nuclei. These species have been tentatively assigned on chemical evidence as CH3̇ ⋯ and CH3̇ ⋯ Br- respectively. The complexity of the spectra resulted in complete solution not being possible.
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York, Jr John Benson. "An Isolated Micro-Converter for Next-Generation Photovoltaic Infrastructure." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19326.
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Photovoltaic (PV) systems are a rapidly growing segment in the renewable energy industry. Though they have humble origins and an uncertain future, the commercial viability of PV has significantly increased, especially in the past decade. In order to make PV useful, however, significant effort has to go into the power conditioning systems that take the low-voltage dc from the panel and create utility compatible ac output. Popular architectures for this process include the centralized inverter and the distributed micro-inverter, each with its own advantages and disadvantages. One attempt to retain the advantages of both architectures is to centralize the inverter function but construct PV panel-level micro-converters which optimize the panel output and condition the power for the inverter. The main focus of this work is to explore the technical challenges that face the evolution of the dc-dc micro-converter and to use them as a template for a vertically integrated design procedure. The individual chapters focus on different levels of the process: topology, modulation and control, transient mitigation, and steady-state optimization. Chapter 2 introduces a new dc-dc topology, the Integrated Boost Resonant (IBR) converter, born out of the natural design requirements for the micro-converter, such as high CEC efficiency, simple structure, and inherent Galvanic isolation. The circuit is a combination of a traditional PWM boost converter and a discontinuous conduction mode (DCM), series resonant circuit. The DCM operation of the high-frequency transformer possesses much lower circulating energy when compared to the traditional CCM behavior. When combined with zero-current-switching (ZCS) for the output diode, it results in a circuit with a high weighted efficiency of 96.8%. Chapter 3 improves upon that topology by adding an optimized modulation scheme to the control strategy. This improves the power stage efficiency at nominal input and enhances the available operating range. The new, hybrid-frequency method utilizes areas where the modulator operates in constant-on, constant-off, and fixed-frequency conditions depending on duty cycle, the resonant period length, and the desired input range. The method extends the operating range as wide as 12-48V and improves the CEC efficiency to 97.2% in the 250-W prototype. Chapter 4 considers the soft-start of the proposed system, which can have a very large capacitive load from the inverter. A new capacitor-transient limited (CTL) soft-start method senses the ac transient across the resonant capacitor, prematurely ending the lower switch on-time in order to prevent an excessive current spike. A prototype design is then applied to the IBR system, allowing safe system startup with a range of capacitive loads from 2μF to 500μF and a consistent peak current without the need for current sensing. Chapter 5 further investigates the impact of voltage ripple on the PV output power. A new method for analyzing the maximum power point tracking (MPPT) efficiency is proposed based on panel-derived models. From the panel model, an expression demonstrating the MPPT efficiency is derived, along with a ripple â "budgetâ " for the harmonic sources. These ripple sources are then analyzed and suggestions for controlling their contributions are proposed that enable circuit designers to make informed and cost-effective design decisions. Chapter 6 illustrates how results from a previous iteration can provide a basis for the next generation\'s design. A zero-voltage-switching (ZVS) version of the circuit in Chapter 2 is proposed, requiring only two additional MOSFETs and one inductor on the low-voltage side. The maximum switching frequency is then increased from 70kHz to 170kHz, allowing for a 46% reduction in converter volume (from 430cm3 to 230cm3) while retaining greater than 97% weighted efficiency.
Ph. D.
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Stetler, Fredrik. "Isolated magnetic field structures in the Saturn magnetosphere." Thesis, KTH, Rymd- och plasmafysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-214821.
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This report’s primary focus is to use the data gathered by the Cassini satellite and analyzeits magnetic field data around Saturn. By looking for isolated changes in magneticfield values locations of potential plasmoids can be determined and examined. Theseso called plasmoids are pockets of higher density plasma ,associated with an increaseor decrease of the magnetic field strength, inside the magnetosheath, which may be importantfor the interaction between the solar wind plasma and the magnetosphere. Thestudy has been made over 7 years, from the beginning of 2010 to the end of 2016. Duringthis period a number of magnetic field structures have been found and documentedin this report, along with analyzing some of their properties such as their width andmagnetic field strength.Denna rapports primära fokus är att använda data insamlad av Cassini satelliten ochanalysera dess magnetiska fältdata runt Saturnus. Genom att titta efter isolerade förändringari magnetiska fältvärdena går det att lokalisera och examinera potentiella plasmoider.Dessa så kallade plasmoider är fickor med högre densitet av plasma, associerademed en ökning eller minskning av magnetisk fältdata, inne i magnetoskiktet, vilket kanvara viktigt för interaktionen mellan solvindens plasma och magnetosfären. Studien hargjorts över 7 års tid, från början av 2010 till slutet av 2016. Under denna period harett antal magnetiska fältstrukturer hittats och dokumenterats i denna rapport, genom attanalysera några av deras egenskaper så som deras bredd och magnetisk fältstyrka.
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Jayanty, Vivi. "Miniaturized electron-impact-ionization pumps using double-gated isolated vertically aligned carbon nanotube arrays." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75659.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 67-71).
There is a need for microscale vacuum pumps that can be readily integrated with other MEMS and electronic components at the chip-scale level. Miniaturized ion pumps exhibit favorable scaling down because they are surface-limited and miniaturization increases the ratio between the active surface and the chamber volume, resulting in enhanced ionization and pump rates. Therefore, scaled-down ion pumps are a promising choice for a variety of applications including portable mass spectrometers and sub-mm wavelength vacuum amplifiers. Our micropump architecture consist of a field-emission electron source that is an array of double-gated isolated vertically aligned carbon nanotubes (VA-CNTs), an electronimpact- ionization region, and a non-evaporative ion-implantation getter. Single-gated VA-CNT FEAs were tested as field emitters in high vacuum (10-9 Torr). The current density of the tested device is ~0.5A/cm2 (total current of 0.4mA) and a field enhancement factor of 1.41 x106 V/cm was measured, which is comparable to the simulation results by COMSOL. Two ways to fabricate double-gated VA-CNT FEAs were reported: one has the focus gate in plane with the extractor gate and the other has the focus gate above the extractor gate. Due to problems on fabrication process of double-gated VA-CNTs (short circuit between emitters, extractor gate, and focus gate), we were not able to collect four-terminal measurement, electron-impact-ionization, and pump data. However, procedure on how to collect and analyze field emission data with two gates to find [beta]G and [beta]F was described. In addition, procedures on how to collect and analyze data on electron impact ionization pump were also presented.
by Vivi Jayanty.
S.M.
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Monzon, Eric V. "Seismic response of isolated bridge superstructure to incoherent ground motions." abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1438943.
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Murdoch, Fiona. "Evaluation of a manganese oxidising bacterium isolated from an upland water source." Thesis, University of the West of Scotland, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311781.
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Truxal, Laura T. "Characterization of novel compounds isolated from Karenia brevis cultures." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-3/rp/truxall/lauratruxal.pdf.
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ANDERSON, SUSAN RAE. "MATRIX ISOLATED INFRARED SPECTROSCOPIC STUDY OF THE OXIDATION REACTION INTERMEDIATES OF ELECTRON DONORS BY CHROMYL CHLORIDE." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1001953834.
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Soon, John Long. "Fault-Tolerant Design and Implementation for Non-Isolated Reconfigurable DC/DC Converters." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20266.
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This thesis mainly focuses on improving the conventional DC-DC converter topology by utilizing the redundancy concept (N+1) and fault-tolerant design to maintain an uninterrupted output operation even on primary switch failure. The proposed fault-tolerant converter (FTC) involves merging three configurations namely buck, boost and buck-boost to derive a new converter structure along with bidirectional capabilities. The proposed FTC is equipped with a single redundant switch and shared with one coupled inductor and one capacitor (1L-1C) to be capable of achieving the step-up and step-down operation. The major faults of the converter system are highly related to the power switching devices, which can be categorized as open circuit fault (OCF), and short circuit fault (SCF). The proposed fault diagnosis scheme is able to detect the OCF and SCF in less than half of the switching period by sampling the rising and failing edge of the pulsating signal to identify the switch fault behavior. Therefore, remedial action of the proposed FTC can be associated with the fault detection unit to anticipate the moment when the converter requires the activation of the redundant switches by providing a back-up operation. However, any reconfigurable decision is necessary to electrically isolate the faulty component in order to avoid the subsequent fault current within the circuit loop. The proposed method of isolation design adopts the joule-integral principle for selecting an appropriate rating between fuse and MOSFET pair. It provides the satisfactory result for protecting the proposed FTC. Finally, a converter reliability model is carried out based on Markov chain theory to formulate the mean time to failure (MTTF) profile for the proposed FTC. The reliability analysis shows that the proposed FTC can surpass the reliability performance of the conventional DC-DC converter through optimization of the circuit topology.
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Marais, Laurette Marlize. "Characterization of bacteria isolated from a platinum mine tailings dam / Laurette Marais." Thesis, North-West University, 2012. http://hdl.handle.net/10394/8721.
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Contamination from various sources has a huge impact on soil health and microbial community composition. Metal contamination of soil in mining scenarios is of concern and is not adequately addressed, particularly with respect to the microbial community. The mining industry is one of the largest contributors to heavy metal contamination of soil in South Africa, especially since the country is one of the major mining countries in the world. Platinum mining is of special importance, since the largest percentage of the world’s reserves of platinum group metals are found and mined in South Africa. Metals from mining activities become irreversibly immobilized in soil systems because they cannot be degraded and has a huge impact on soil systems. In this study, bacteria was isolated from soil samples collected from a platinum mine tailings dam outside Rustenburg. During the warm sampling season (March 2006) most isolates were found, especially in sites 3 and 4. During the colder and drier season (May 2006) there were less isolates. Most of the isolated cultures also displayed a wide temperature growth range, mostly between 24°C - 37°C. Paenibacillus lautus and Bacillus subtilus DN-10 had a growth range between 5°C - 40°C. Culturable metal tolerant bacteria were isolated, purified and identified using 16S rDNA sequences. Nine different species were found namely Paenibacillus lautus strain DS19, Paenibacillus lautus, Paenibacillus sp. C15, uncultured Paenibacillaceae, Bacillus subtilis strain DN-10, Bacillus sp. KDNB5, Bacillus cereus, Stenotrophomonas maltophilia and Alcaligenes sp. DJWH 146-2. The ability of these strains to tolerate metal concentrations were explored by determining their minimum inhibitory concentrations for a selection of metals e.g. aluminum, barium, cobalt, chromium, cadmium, copper, iron, lead, manganese, nickel and mercury. Most isolates were able to tolerate >5mM of the Al\Ni alloy and cobalt. Transmission electron microscopy was used to determine the location of metals inside bacterial cells and electron dispersive X-ray analysis was used to determine the levels of metals inside microbial cells. Bacillus subtilis DN-10 (LDK0306) showed a high MIC (>5mM) for most metals used, except Hg. This strain also had a high percentage (10.26%) of Pb detected in its cells by EDX. This was the highest percentage detected. Plasmids were extracted from the identified strains and can help gain a better understanding of metal tolerance mechanisms used by these isolates.Thesis(MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013
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York, David J. "A novel magnetorheological fluid-elastomer vibration isolator /." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1448335.
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Thesis (M.S.)--University of Nevada, Reno, 2007."August, 2007." Includes bibliographical references (leaves 83-86). Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2007]. 1 microfilm reel ; 35 mm.
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Roxlau, Elsa Tadele [Verfasser]. "Potential Effects of Electronic Cigarette Vapour on Isolated Lung Cells and in Mouse Lungs / Elsa Tadele Roxlau." Gießen : Universitätsbibliothek, 2020. http://d-nb.info/1223461718/34.
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Esmaeili, E., A. M. Rashidi, A. A. Khodadadi, Y. Mortazavi, and M. Rashidzadeh. "The Formation of the Intermetallic-Containing Pd2Sn Alloy: The Creation of the Isolated Adsorption Sites." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35214.
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In the current study, tin-promoted Pd / MWNTs synthesized via polyol process were developed. TEM images evidences resulted in the formation of highly-dispersed Pd-Sn nanoparticles. The formation of Pd2Sn structural phase was confirmed by XRD and TPR techniques, composed mainly of intermetallic spe-cies, supported by XPS results. In this research, we applied intermetallic-containing tin-promoted catalysts for the selective hydrogenation reaction of acetylene as the case study. The presence of a discontinuity in the Arrhenius plots could come from the kinetic factor as a result of change in acetylene coverage on Pd metallic ensembles. The intermetallic-containing assembled catalysts led to the good management of cata-lytic performance due to the creation of isolated adsorption sites on the catalyst surface, resulting in the higher ethylene selectivity.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35214
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Ayele, Mehari L. "Four-port miniaturized and highly isolated antenna for multiple-input multiple-output communication systems." Thesis, Wichita State University, 2012. http://hdl.handle.net/10057/6118.
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The objective of this paper is to present an efficient miniaturized antenna design and simulation of a highly isolated multi-port micro-strip antenna for multiple-input multiple-output communication (MIMO) systems. Three geometric configurations were proposed and compared to achieve an isolation of as low as –30 dB without affecting the antenna performance greatly. The antenna was designed to operate at a resonance frequency of 2.45 GHz (fc ). Ferrite material beneath each meander structure was used for miniaturization purposes as well as an FR4 substrate with a compact overall area of .75 lambda0 ×.5 lambda0 for a system board, where lambda0 is the free space wavelength. A ground plane with small etched slits was used for isolation purposes. A maximum gain of 4.6 dBi in the azimuthal plane was achieved. Index Terms: MIMO, meander antenna, four-port antenna, defected ground structureThesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science
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Rasmussen, Andrew J. "Structural Insights into the Regulation of Electron Transfer in Nitrogenase, and Modulating the Reactivity of the Isolated Iron Molybdenum Cofactor." DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/4897.
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Nitrogenase, EC: 1.18.6.1 is the enzyme that catalyzes the reduction of dinitrogen to ammonia; this is known as biological nitrogen fixation. Nitrogen fixation is so important to our daily lives, that we utilize approximately 2% of the annual energy produced worldwide to fix nitrogen industrially via the Haber-Bosch process. The industrial process requires a high input of energy in the form of heat (>450°C) and pressure (>200 atm>), while the enzymatic system is performed under ambient conditions. Research invested into understanding the mechanism of this biological catalyst could eventually lead to understanding how nature performs difficult chemical reductions, which could allow researchers to develop catalysts that mimic this enzyme to perform many important reactions, such as nitrogen fixation, much more efficiently than today.
Electron transfer in the nitrogenase is only partially understood, and is one of the key elements of understanding the mechanism of nitrogenase. Nitrogenase is composed of two proteins, the Fe protein delivers electrons to the MoFe protein, where N2 binds and is subsequently reduced. The conformational changes that take place upon Fe protein binding were investigated in order to better understand electron transfer within the enzyme. Further, studies were performed which probed the P-cluster, an iron sulfur cluster in the MoFe protein that acts as an intermediate in the electron transfer event, and successfully identified the biologically relevant redox state of the P-cluster, P+1. Other studies were performed which identified several variants of the MoFe protein which were able to accept electrons from a chemical reductant. These variants are the first examples of nitrogenase enzymes able to accept electrons from any source other than Fe protein and shown substrate reduction. These variants pinpoint where nitrogenase is likely to undergo conformational changes to allow electron transfer to the active site of the enzyme. Finally, studies were done on the isolated active site of the protein, the iron molybdenum cofactor to better understand how the active site of nitrogenase works The goal of this thesis is to better understand how electrons travel through nitrogenase, and how they are utilized at the active site, FeMo-cofactor, when they arrive.
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Enomoto, Bruno Yukio. "Conversores DC-DC Dual-Active-Bridge isolados bidirecionais." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-17072018-092952/.
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Este trabalho visa o estudo das regiões de operação de conversores CC/CC isolados bidirecionais do tipo DAB (Dual Active Bridge). É feito um estudo do comportamento do circuito com a variação dos valores das reatâncias de acoplamento, avaliando-se aspectos como eficiência, fator de potência, reativos, entre outros. A seguir é proposta uma estrutura de controle que permite a operação com tensões nos barramentos DC diferentes das nominais, minimizando as correntes absorvidas. Além disso, propõe-se uma estratégia de controle para regular a potência transferida. O trabalho inclui modelagem teórica, implementação em simulação computacional e medidas em protótipo experimental.This work investigates operation regions of Dual Active Bridge DC-DC isolated bidirectional converters, studying circuit behavior with the variation of the coupling reactance, evaluating parameters like efficiency, power factor, reactive flow etc. A control structure is proposed which allows operating with DC voltages different from nominal voltages, reducing the AC currents. Furthermore, a control strategy to regulate the power transferred is proposed. Methodology includes theoretical modeling, computer simulation and experimental prototype measurements.
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Maxwell, Erick N. "Ultra-wideband electronics, design methods, algorithms, and systems for dielectric spectroscopy of isolated B16 tumor cells in liquid medium." [Tampa, Fla] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002172.
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Rioux, Jean-Philippe. "Microbial activity of iron-reducing bacteria and sulfate-reducing bacteria isolated from mine tailings in the presence of various electron donors." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26757.
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Two abandoned mine tailings sites (Calumet near Ottawa, and Potter near Timmins, Ontario) have been shown to support active populations of iron- (IRB) and sulfate-reducing bacteria (SRB). The competition between IRB and SRB for similar electron donors was however never assessed. The present study looked into the potential competition between IRB and SRB isolated from those 2 sites since they represent different pH conditions and mineralogy. The Potter tailings are acidic to slightly acidic and contain large quantities of sulfides, whereas the Calumet tailings are alkaline and contain less pyrite and more carbonate minerals. Batch experiments were designed to test the competition between IRB and SRB for 3 electron donors (acetate, formate and lactate) and to determine the role of abiotic Fe(III) reduction. Results from abiotic systems indicated that Fe(II) was released overtime in the various systems due to the reduction of Fe(III)-rich minerals by the organic acids present in the medium and due to the chemical oxidation of pyrite by ferric iron. IRB could only grow in the Calumet systems containing inhibited SRB. In these systems, IRB growth was favored in the presence of acetate. In the systems containing active SRB, IRB growth was minimal in the presence of all electron donors, suggesting that they cannot compete with SRB under the conditions used in the systems. SRB present in all systems were capable of oxidizing all 3 electron donors, including acetate. Our results also showed that complete and incomplete lactate oxidizers were present in the Calumet and Potter systems.
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Banerjee, Sreetama [Verfasser], Dietrich R. T. [Akademischer Betreuer] Zahn, Dietrich R. T. [Gutachter] Zahn, and L. [Gutachter] Hueso. "HED-TIE: A wafer-scale approach for fabricating hybrid electronic devices with trench isolated electrodes and its application in sensing devices / Sreetama Banerjee ; Gutachter: Dietrich R. T. Zahn, L. Hueso ; Betreuer: Dietrich R. T. Zahn." Chemnitz : Technische Universität Chemnitz, 2019. http://d-nb.info/1215909853/34.
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Yadav, Anur. "Isolated Graphene Edge Nanoelectrodes: Fabrication, Selective Functionalization, and Electrochemical Sensing." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23114.
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Diese Arbeit präsentiert eine einfache eine einfache, auf Photolithographie basierende Methode zur Darstellung einer isolierten Graphenkante (oder GrEdge) einer Monolage als Nanoelektrode auf einem isolierenden Substrat vorgestellt. Trotz ihrer Millimeter-Länge verhält sich die nur einen Nanometer breite GrEdge-Elektrode wie ein Nanodraht mit einem hohen Seitenverhältnis von 1000000 zu 1. Des Weiteren wird der Einsatz von elektrochemischer Modifikation (ECM) demonstriert, um die GrEdge selektiv mit Metall-Nanopartikeln und organischen Schichten nicht-kovalente oder kovalente zu funktionalisieren, wodurch die Chemie der Kante verändert werden kann. Durch die Anbringung von Metall-Nanopartikeln kann zusätzlich oberflächenverstärkte Raman-Spektroskopie (SERS) genutzt werden, um die chemische Beschaffenheit sowohl der unberührten als auch der funktionalisierten GrEdge zu charakterisieren.
Die GrEdge weist sehr hohe Mass-entransportraten auf, was charakteristisch für Nanoelektroden ist. Dementsprechend wird die voltammetrische Antwort von der Kinetik des heterogenen Elektrontransfers (HET) diktiert. An der GrEdge-Elektrode werden hohe HET-Raten beobachtet: mindestens 14 cm/s für Außensphäre sonde Ferrocenmethanol (FcMeOH) mit einem quasi-Nernst'schen Verhalten und 0,06 cm/s oder höher für innere Sphäre sonde Ferricyanide ([Fe(CN)6]3-) mit einer kinetisch kontrollierten Reaktion. Nach der selektiven Modifikation der Kante mit Goldnanopartikeln erweist sich der HET als reversibel, mit einer massentransportbegrenztes Nernst‘sches Verhalten aufweisen für beide Redoxmoleküle. Darüber hinaus ermöglicht die schnelle HET-Kinetik die Detektion der reduzierten Form von Nicotinamid-Adenin-Dinukleotid (NADH) und Flavin-Adenin-Dinukleotid (FAD) mit niedrigen Ansatzpotentialen und hinunter bis zu niedrigen mikromolaren Konzentrationen. Entsprechend verbessert die vorliegende Arbeit das Verständnis der Kante von Graphen und deren Chemie.This thesis presents a simple photolithography-based method to realize the isolated monolayer graphene edge (or GrEdge) nanoelectrode on an insulating substrate. The millimeter-long and a nanometer-wide GrEdge is found to behave like a nanowire with a high aspect ratio of 1000000-to-1. Further, the use of electrochemical modification (ECM) is demonstrated to selectively functionalize the GrEdge with metal nanoparticles and organic moieties in a non-covalent/ covalent manner to tune the chemistry of the edge. The attachment of metal nanoparticles was used to exploit surface-enhanced Raman scattering (SERS) to characterize the chemistry of both the pristine and the functionalized GrEdge. The GrEdge electrodes were found to exhibit very high mass transport rates, characteristic of nanoelectrodes. Accordingly, the voltammetric response is found to be dictated by the kinetics of heterogeneous electron transfer (HET), attributed to the nanoscale geometry and a unique diffusional profile at such electrodes. At the GrEdge electrode, high HET rates are observed: at least 14 cm/s for outer-sphere probe, ferrocenemethanol (FcMeOH) with a quasi-Nernstian behavior; and 0.06 cm/s or higher for inner-sphere probe, ferricyanide ([Fe(CN)6]3-) with a kinetically controlled response. Upon selective modification of the edge with gold nanoparticles, the HET is found to be reversible, with a mass-transport-limited Nernstian response for both probes. Furthermore, the fast HET kinetics enables the sensing of the reduced form of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) with low onset potentials and down to low micromolar concentrations. Hence, this thesis improves the understanding of the edges of graphene and their chemistry. It also realizes isolated GrEdge as a new class of nanoelectrode which forms an important basis within the fields of fundamental electrochemistry and analytical sciences.
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Petersson, Magnus. "Microstrip Solutions for Innovative Microwave Feed Systems." Thesis, Linköping University, Department of Science and Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1034.
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This report is introduced with a presentation of fundamental electromagnetic theories, which have helped a lot in the achievement of methods for calculation and design of microstrip transmission lines and circulators. The used software for the work is also based on these theories.
General considerations when designing microstrip solutions, such as different types of transmission lines and circulators, are then presented. Especially the design steps for microstrip lines, which have been used in this project, are described. Discontinuities, like bends of microstrip lines, are treated and simulated. There are also sections about power handling capability of microstrip transmission lines and different substrate materials.
In the result part there are computed and simulated dimensions of the microstrip transmission lines used in the prototype system. Simulations of conceivable loads in the cavity illustrate quantitatively the reflection coefficient. Even practical measurements are made in a network analyzer and are presentedin this part.
Suitable materials and dimensions for the final microwave feed transmission line system for high powers are then presented. Since circulators are included in the system a basic introduction to the design of these in stripline and microstrip techniques is also made.
At last conclusions, examinations of the designed system and comparisons to the today’s systems are made.
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Griffith, Olga. "INSIGHT INTO THE ELECTRONIC PROPERTIES OF ORGANIC SEMICONDUCTORS: EXPERIMENTAL MEASURES FROM THE ISOLATED-MOLECULE LEVEL TO THE SOLID-STATE DEVICE LIMIT." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195928.
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Fundamental understanding of the electronic properties, and charge transfer mechanism of organic semiconductors and functionalized oligoacenes in particular, is of great importance for the design and fabrication of organic electronic devices. This work is devoted to the study of the electronic properties of organic semiconductors in the gas, solution, and solid phases, thus providing insights into the intra- and intermolecular electronic interactions of these materials from the isolated-molecule level to the solid-state device limit. The organic semiconductors investigated in this work are bis-triisopropylsilylethynyl-substituted (TIPS) anthracene, TIPS tetracene, TIPS pentacene, bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]-pentacene (TP-5), and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (EtTP-5). This research is conducted on the basis of experimental and computational studies. The experimental analysis is based on the combination of closely-related gas-phase and solid-phase photoelectron spectroscopy measurements, along with electrochemical measurements in solution. The electronic structure quantum-mechanical computations are performed at the density functional theory level, and are in good agreement with experimental results.This dissertation reports important findings on the electronic properties of organic semiconductors and how these properties change between phases. The role of polarization effects on the electronic properties of these materials was demonstrated to be significant and strongly dependant on the molecular structure and electronic interactions at the isolated- (or single-) molecule level as well as on the molecular packing and electronic interactions in the solid state at the device limit.
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Fridgen, Travis D. "FT-infrared spectroscopic and computational studies of the matrix-isolated products formed following gas-phase electron bombardment of rare-gas/organic molecule mixtures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0004/NQ38307.pdf.
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BOUET, VERONIQUE. "Interaction particules isolantes/electrode : mise en uvre de methodes electrochimiques. application aux revetements composites electrolytiques." Paris 6, 1994. http://www.theses.fr/1994PA066326.
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Cette etude concerne l'elaboration d'un nouveau type de materiaux composites constitues d'une matrice metallique contenant des inclusions liquides sous forme de microcapsules d'huile ou d'une solution aqueuse. Ils sont synthetises par electrodeposition a partir d'un bain electrolytique contenant les capsules en suspension. Le principal objet de ce travail est de developper une methode de detection du passage des capsules a proximite de la cathode, avant leur eventuelle incorporation. Une cellule a jet immerge a ete specialement concue pour controler parfaitement l'ecoulement parietal. Ses performances et le transport de matiere ont ete caracterises par des methodes electrochimiques. Les capsules circulant dans l'electrolyte sont detectees par le bruit electrochimique de resistance d'electrolyte et de courant qu'elles creent et qui resultent de la perturbation du champ primaire ou secondaire de potentiel de microelectrodes localisees en divers points de la paroi, face au jet d'electrolyte. En s'appuyant sur une modelisation theorique et une simulation experimentale, l'analyse de la forme des transitoires individuels, notamment leur amplitude et leur duree, permet de reconstituer la trajectoire des capsules. Enfin, a partir de la densite spectrale de puissance des fluctuations de resistance ou de courant, on a pu extraire des grandeurs moyennes permettant de decrire le comportement d'une suspension de particules et en particulier d'evaluer leur aptitude a se codeposer
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Gallardo, Angelo Miguel Asuncion. "Design and Construction of 1800W Modular Multiple Input Single Output Non-Isolated DC-DC Converters." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1739.
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This thesis report details the design and construction of non-isolated DC-DC converters to create a Multiple Input Single Output (MISO) converter for combining multiple renewable energy sources into one single output. This MISO uses the four-switch buck-boost topology to output a single 48V from multiple nominal 24V inputs. The MISO converter implements a modular approach to deliver 1800W output power. Each module in the MISO is rated at 600W and they share the output power equally. Hardware results show that the converter produces 1800W of output power from three sources with 96.4% efficiency. Each module also demonstrates equal sharing feature of the MISO converter.
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Rocha, Leandro Seixas. "Estrutura eletrônica de isolantes topológicos em duas e três dimensões." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-16102014-092038/.
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Nessa tese de doutorado apresentamos um estudo da estrutura eletronica de materiais isolantes topologicos. A teoria fundamental dos isolantes topologicos foi abordada atraves de invariantes topologicos Z2, assim como os seus metodos para o calculo desses invariantes topologicos e as consequencias da topologia de bandas nao-trivial. Assim como as propriedades atomisticas e energeticas, as propriedades eletronicas de alguns isolantes topologicos foram calculadas atraves de metodos de primeiros principios baseados na Teoria do Funcional da Densidade. Apresentamos nessa tese o estudo de quatro sistemas de interesse fisico: (1) Em isolantes topologicos do tipo Bi2Se3 e Bi2Te3 com falhas de empilhamentos, encontramos que o Bi2Te3 com falhas de empilhamentos apresentam estados metalicos na regiao do defeito; (2) Na interface Bi2Se3/GaAs com tratamento de Se na regiao do GaAs, encontramos que a interacao entre o cone de Dirac do Bi2Se3 com a banda de valencia do GaAs abre um gap de energia no ponto ; (3) Em nanoestradas de germaneno imersas em germanano com interfaces zigzag, encontramos que a partir de uma largura critica podemos observar o efeito Hall quantico de spin; e (4) nas ligas desordenadas hexagonais de SixGe1-x em duas dimensoes, o sistema desordenado compartilha a mesma topologia de bandas do siliceno e do germaneno, enquanto que a liga ordenada Si0.5Ge0.5 e um isolante trivial. As estruturas eletronicas desses sistemas foram investigadas no intuito de entender as consequencias fisicas da topologia de bandas nao-trivial nos estados de Bloch de bulk e de superficies/interfaces.In this doctoral thesis we present a study of the electronic structure of topological insulators materials. The fundamental theory of topological insulators was addressed through the Z2 topological invariants, as well as their methods to calculate these topological invariants and the consequences of non-trivial band topology. Just as atomistic and energetic properties, the electronic properties of some topological insulators were calculated using first-principles methods based upon Density Functional Theory. We present in this thesis the study of four systems of physical interest: (1) In topological insulators like Bi2Se3 and Bi2Te3 with stacking faults, we found that the Bi2Te3 with stacking faults presents metallic states in the region of the defect; (2) For Bi2Se3/GaAs interface with Se-treatment in the GaAs region, we found that the interaction between the Dirac cone of the Bi2Se3 and the valence band of the GaAs opens a bandgap at the -point; (3) In germanene nanoroads embedded on germanane with zigzag interfaces/edge, we found that from a critical width we can observe the quantum spin Hall effect; and (4) For SixGe1x two-dimensional hexagonal disordered alloy, the system shares the same non-trivial band topology of the silicene and germanene, while the ordered alloy Si0.5Ge0.5 is a trivial insulator. The electronic structures of these systems were investigated in order to understand the physical consequences of non-trivial band topology in the bulk and surfaces/interfaces Bloch states.
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Eleyele, Abidemi Oluremilekun. "Isolated Single-Stage Interleave Resonant PFC Rectifier with Active and Novel Passive Output Ripple Cancellation Circuit." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-423117.
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With the increasing demand for fast, cheaper, and efficient power converters come the need for a single-stage power factor correction (PFC) converter. Various single-stage PFC converter proposed in the literature has the drawback of high DC bus voltage at the input side and together with the shift to wide bandgap switches like GaN drives the converter cost higher. However, an interleaved topology with high-frequency isolation was proposed in this research work due to the drastic reduction in the DC bus voltage and extremely low input current ripple thereby making the need for an EMI filter circuit optional. Meanwhile, this research work focuses on adapting the proposed topology for a high voltage low current application (EV charger - 400V, 7KW) and low voltage high current application (telecom power supply - 58V, 58A) owing to cost benefits. However, all single-stage PFC are faced with the drawback of second-order (100Hz) output harmonic ripple. Therefore, the design and simulation presented a huge peak to peak ripple of about 50V/3A and 26V/26A for the EV charger and telecom power supply case, respectively. This created the need for the design of a ripple cancellation circuit as the research required a peak to peak ripple of 8V and 200mV for the EV - charger and telecom power supply, respectively. A novel output passive ripple cancellation technique was developed for the EV charger case due to the ease it offers in terms of control, circuit complexity and extremely low THDi when compared with the active cancellation approach. The ripple circuit reduced the 50V ripple to 431mV with the use of a total of 2.2mF capacitance at the output stage. Despite designing the passive technique, an active ripple cancellation circuit was designed using a buck converter circuit for the telecom power supply. The active approach was chosen because the passive has a slow response and incurs more loss at a high current level. Adding the active ripple cancellation circuit led to a quasi-single stage LLC PFC converter topology. A novel duty-ratio feedforward control was added to synchronize the PFC control of the input side with the buck topology ripple cancellation circuit. The addition of the ripple circuit with the feedforward control offered a peak to peak ripple of 6.7mV and a reduced resonant inductor current by half. After analysis, an extremely low THDi of 0.47%, PF of 99.99% and a peak efficiency of 97.1% was obtained for the EV charger case. The telecom power supply offered a THDi of 2.3%, PF of 99.96% with a peak efficiency of 95%.
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Thiele, Stefan. "Read-out and coherent manipulation of an isolated nuclear spin using a single-molecule magnet spin-transistor." Phd thesis, Université de Grenoble, 2014. http://tel.archives-ouvertes.fr/tel-00984973.
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La réalisation d'un ordinateur quantique fonctionnel est l'un des objectifs tech- nologiques les plus ambitieux pour les scientifiques d'aujourd'hui. Sa brique de base est composée d'un système quantique à deux niveaux, appelé bit quantique (ou qubit). Parmi les différents concepts existants, les dispositifs à base de spin sont très attractifs car ils bénéficient de la progression constante des techniques de nanofabrication et permettent la lecture électrique de l'état du qubit. Dans ce contexte, les dispositifs à base de spins nucléaires offrent un temps de cohérence supérieur à celui des dispositifs à base de spin electronique en raison de leur meilleure isolation à l'environnement. Mais ce couplage faible a un prix: la détection et la manipulation des spins nucléaires individuels restent des tâches difficiles. De très bonnes conditions expérimentales étaient donc essentielles pour la réussite de ce projet. Outre des systèmes de filtrage des radiofréquences à très basses températures et des amplificateurs à très faible bruit, j'ai développé de nouveaux supports d'échantillons et des bobines de champ magnétique trois axes compacts avec l'appui des services techniques de l'Institut Néel. Chaque partie a été optimisée afin d'améliorer la qualité de l'installation et évaluée de manière quantitative. Le dispositif lui-même, un qubit réalisé grâce à un transistor de spin nucléaire, est composé d'un aimant à molécule unique couplé à des électrodes source, drain et grille. Il nous a permis de réaliser la lecture électrique de l'état d'un spin nucléaire unique, par un processus de mesure non destructif de son état quantique. Par conséquent, en sondant les états quantique de spin plus rapidement que le temps de relaxation caractéristique de celui-ci, nous avons réalisé la mesure de la trajectoire quantique d'un qubit nucléaire isolé. Cette expérience a mis en lumière le temps de relaxation T1 du spin nucléaire ainsi que son mécanisme de relaxation dominant. La manipulation cohérente du spin nucléaire a été réalisée en utilisant des champs électriques externes au lieu d'un champ magnétique. Cette idée originale a plusieurs avantages. Outre une réduction considérable du chauffage par effet Joule, les champs électriques permettent de contrôler et de manipuler le spin unique de façon très rapide. Cependant, pour coupler le spin à un champ électrique, un processus intermédiaire est nécessaire. Un tel procédé est l'interaction hyperfine, qui, si elle est modifiée par un champ électrique, est également désigné sous le nom d'effet Stark hyperfin. En utilisant cet effet, nous avons mis en évidence la manipulation cohérente d'un spin nucléaire unique et déterminé le temps de cohérence T2 . En outre, l'exploitation de l'effet Stark hyperfin statique nous avons permis de régler le qubit de spin nucléaire à et hors résonance par l'intermédiaire de la tension de grille. Cela pourrait être utilisé pour établir le contrôle de l'intrication entre les différents qubits nucléaires. En résumé, nous avons démontré pour la première fois la possibilité de réaliser et de manipuler un bit quantique basé sur un aimant à molécule unique, étendant ainsi le potentiel de la spintronique moléculaire au delà du stockage de données classique. De plus, la grande polyvalence des molécules aimants est très prometteuse pour une variété d'applications futures qui, peut-être un jour, parviendront à la réalisation d'un ordinateur quantique moléculaire.
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Souza, Jean Carlo 1993. "Estudos de ressonância de spin eletrônico (RSE) em isolantes topológicos dopados com terras-rara." [s.n.], 2017. http://repositorio.unicamp.br/jspui/handle/REPOSIP/326704.
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Orientador: Pascoal José Giglio PagliusoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-09-02T11:57:27Z (GMT). No. of bitstreams: 1 Souza_JeanCarlo_M.pdf: 4438731 bytes, checksum: aaba7a375b2b45b638619e944111c41b (MD5) Previous issue date: 2017
Resumo: A ideia de topologia na Física da Matéria da Condensada, apesar de ter surgido com o efeito Hall quântico inteiro, só voltou a ser explorada recentemente na busca de novas fases da matéria depois do surgimento dos Isolantes Topológicos (ITs) 2D. Após a previsão teórica, e a descoberta experimental, foi proposto que esta nova fase poderia ser generalizada para sistemas 3D, em que o volume do material seria isolante com estados metálicos de superfície que possuiriam canais de spin polarizados. Apesar de diversos experimentos e o surgimento de outras fases topológicas da matéria subsequentes, ainda há dúvidas sobre a natureza dos ITs 3D. Os efeitos topológicos mais claros ainda não foram observados de forma inequívoca e reprodutível experimentalmente e ainda seria de extrema valia encontrar técnicas experimentais que possam complementar os mais discutidos experimentos de ARPES. Nesta dissertação foram estudadas duas famílias distintas de materiais propostas como possíveis ITs 3D: os binários Bi2Se3 e Sb2Te3 e o half-Heusler YPdBi. Utilizando a técnica de auto-fluxo e a fusão estequiométrica, os sistemas foram sintetizados dopados com os terras-rara Gd3+, Nd3+ e Er3+ para realizar estudos de ressonância de spin eletrônico (RSE) e do papel dos efeitos de campo cristalino (CEF) - no caso do half-Heusler. Para o ternário YPdBi foram feitos dois estudos. Na família dos half-Heuslers, a ordem topológica surge da relação entre o acoplamento spin-órbita e a hibridização, que está ligada com a mudança do parâmetro de rede, então os efeitos de CEF poderiam estar refletindo a transição entre a trivialidade e a não-trivialidade. A partir das medidas de susceptibilidade magnética em função da temperatura das amostras dopadas com Nd3+ e Er3+ combinadas com os estudos de RSE, foi possível extrair os parâmetros de campo cristalino (CFP) de quarta e sexta ordem. Comparando esses dados com resultados anteriores para o material, supostamente, não-trivial YPtBi, observou-se uma mudança sistemática no sinal dos CFP. Resultados prévios para as amostras de YPtBi dopadas com Nd3+ mostram uma evolução não usual para uma forma de linha difusiva com a potência de micro-onda. Neste trabalho também foi realizado um estudo da forma de linha em função da potência. Apenas a ressonância do Nd3+ para os monocristais de 10% de Nd em YPdBi mostrou uma forma de linha difusiva que evolui com a potência da micro-onda. No caso dos binários Bi2Se3 e Sb2Te3, o objetivo era otimizar a rampa de tratamento térmico para obter monocristais melhores que poderiam permitir a observação de um espectro totalmente resolvido do Gd3+. Após mudanças no crescimento dos monocristais, o espectro totalmente resolvido foi obtido para as amostras de Bi2Se3. No caso do Sb2Te3 apenas uma linha central com a estrutura fina colapsada foi observada. Acompanhando o deslocamento g e a evolução da largura de linha dH da RSE do Gd3+ com a temperatura, o comportamento negativo do deslocamento g para toda a faixa de temperatura indica que elétrons do tipo p são os grandes responsáveis pela formação da superfície de Fermi residual destes sistemas. Um aumento no coeficiente angular de dH em função da temperatura, a taxa Korringa b, foi observado em baixas temperaturas, logo diferentes concentrações de Gd3+ foram utilizadas para estudar este comportamento. Novamente observou-se um comportamento anômalo em baixas temperaturas, o que poderia estar relacionado com a evolução dos CFP com a temperatura. Todos esses resultados foram discutidos levando-se em conta a possibilidade de existência de topologia não-trivial na estrutura eletrônica desses materiais, com foco particular na relação da interação spin-órbita e os efeitos de campo cristalino com a manifestação da topologia não trivial nesses sistemas
Abstract: The idea of topological systems in Condensed Matter Physics, although already explored in the Quantum Hall Effect, has recently become a topic of intense scientific investigation. In particular, great efforts have been dedicated to the search for new quantum phases since the proposal of the Topological Insulators (TIs) in 2D. After the theoretical prediction and the experimental discovery of the TIs in the 2D case, the existence of the Quantum Hall Spin Effect in 3D, 3D TIs, was proposed, where an insulator bulk and metallic surface states with spin polarized channels could be experimentally realized. Although many experiments have been performed, and some groups claimed the direct observation of such new topological phases, there is still a lot of controversy about the nature of the 3D TIs and about the actual microscopic origin of the metallic states on the surface of the studied materials. Other signatures of the topological phases have not been unambiguously and repeatedly measured yet and there is an obvious lack of a supplementary lab technique to be compared to the most used technique to probe these states, which is ARPES. In this work we have studied two different classes of 3D TIs: the binaries Bi2Se3 and Sb2Te3 and the half-Heusler YPdBi. We have been able to grow single crystals of these materials pure and rare-earth doped with Gd3+, Nd3+ and Er3+ using the self-flux technique and the stoichiometric melting. The aim was to use these crystals to study Electron Spin Resonance (ESR) as a potential probe to investigate the existence of the metallic surface states and to explore the possible of the crystalline electrical field (CEF) effects on the formation of the non-trivial electronic structure of these materials. Regarding the YPdBi, our ESR and magnetization studies have revealed that, in the half-Heusler family, the topological order emerges from the interplay between spin-orbit coupling and the hybridization, which is connected with the changes on the lattice parameter. Thus, the CEF effects could reflect the transition from trivial to nontrivial topology. From the magnetic susceptibility data as a function of temperature from the Nd3+ and Er3+ doped samples combined with the ESR studies, it was possible to extract the fourth and sixth order crystal field parameters (CFP). Comparing our data with the previous results from YPtBi, which is a putative non-trivial material, a systematic change in the sign of the CFP was observed. Previous results with the YPtBi Nd-doped samples show an unusual evolution of the Nd3+ ESR line to a diusive-like line shape as a function of the microwave power. In this work we have performed a similar study of the Nd3+ ESR line shape as a function of the microwave power. Only for the single crystal of 10% Nd in YPdBi resonance shows a diffusive-like line shape that evolves with the microwave power. In the case of the binaries Bi2Se3 e Sb2Te3, the aim of this work was to optimize the heat treatment used in previous works of our group to obtain better single crystals that could allow the observation of the full resolved spectra from Gd3+. After many changes in the single crystal growth method, we were able to observe fully resolved Gd3+ ESR spectra in the Bi2Se3 samples. Regarding the Sb2Te3 single crystals, only a single Gd3+ Dysonian ESR line was observed. Following the Gd3+ ESR dg and dH as a function of temperature, the observed negative behavior of dg, in the whole temperature range studied, indicates that p-type electrons are the main source for the formation of the small the Fermi surface of these materials. An increase of the angular coefficient of dH as a function of temperature, the Korringa rate b, at low temperatures was observed and different concentrations of Gd3+ were required to investigate this anomaly. Again this anomalous behavior at low temperatures was observed for the all Gd-doped samples, which could be related to an evolution of CFP with temperature. We discuss our results taking into account the existence of non-trivial topological states in our samples and the role of spin-orbit and CEF effects might have in the formation of such states
Mestrado
Física
Mestre em Física
132653/2015-0
CNPQ
CAPES
FAPESP
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Sal, y. Rosas Celi Damian. "Étude et conception de convertisseurs réversibles multi sources isolés pour l’interfaçage au réseau de sources d'énergies renouvelables et de moyens de stockage." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAT024/document.
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Les accords internationaux pour la réduction des émissions polluantes dans l’environnement imposent l’insertion de plus en plus importante d’énergies renouvelables intermittentes dans le réseau électrique. De plus, l’intégration de dispositifs de stockage est envisagée dans les réseaux électriques du futur afin de résoudre le problème de l’intermittence et d’optimiser la consommation des utilisateurs. Cependant, du fait des caractéristiques différentes des signaux électriques mis en jeu (courant continu pour les sources renouvelables et les batteries, courant alternatif pour le réseau électrique), les structures actuelles reposent sur plusieurs convertisseurs connectés en cascade. Ceci engendre un coût pour le convertisseur en termes de volume et de pertes. De plus, les différents niveaux de tensions (tensions du pack batterie, des sources de production renouvelables et du réseau électrique) ainsi que des contraintes en termes de sécurité nécessitent souvent l’utilisation de transformateurs pour assurer l’isolation galvanique et l’adaptation des tensions.Cette thèse se focalise sur la conception d’une structure innovante à trois ports permettant les échanges de flux de puissances entre une source de production renouvelable, un pack de batteries et le réseau électrique (monophasé ou triphasé) avec un seul étage de conversion. La structure de type TAB (Triple Active Bridge) a été choisie à cet effet en raison de ses nombreux avantages comme l’isolation galvanique, la commutation douce (ZVS) de tous ses ponts actifs (permettant de travailler à haute fréquence de commutation) et la possibilité de contrôler aisément l’échange de puissance entre les différentes sources. L’analyse réalisée se compose d’une méthodologie pour le dimensionnement, d’une structure TAB DC/DC, d’une structure TAB DC/AC monophasée, d’une structure TAB DC/AC monophasée avec un filtre actif mis en série afin de filtrer la puissance fluctuante et, finalement, d’une structure TAB DC/AC triphaséeInternational agreements for the reduction of polluting emissions to the environment require the use of renewable energies in the electricity grid. In addition, the integration of storage devices is envisaged in the future electrical networks in order to solve the intermittence problems and to optimize the consumption of the users. However, due to the different characteristics of the electrical signals involved (DC current for renewable sources and batteries, AC current for the electrical network), the current structures consist on several cascaded converters. This results in a low energy density, higher costs and reduced efficiency for the system. In addition, the different voltage levels (battery voltages, renewable sources and power grid) and safety constraints often require the use of transformers to provide galvanic isolation and match the voltages.This thesis focuses on the design of an innovative three-port structure for the bidirectional power flows control between a renewable power source, a battery pack and the power grid (single phase or three-phase) with a single conversion stage. The TAB (Triple Active Bridge) structure has been chosen for this purpose, due to its many advantages such as galvanic isolation, soft switching (ZVS) in all of its active bridges (allowing to work at high switching frequency) and the possibility of an easy power flow control between the different sources. In this way, the analysis has established a methodology for the design of a TAB DC / DC structure, a single-phase TAB DC / AC structure, a single-phase TAB DC / AC structure with a series connected active filter in order to achieve a "single phase power decoupling" and finally, for the design of a three-phase TAB DC / AC structure
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Uehara, Vanessa Bernardo. "Efeito da radiação ionizante de feixe de elétrons em propriedades de biopolímeros comestíveis a base de proteína isolada de soja e fécula de mandioca." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-24072017-112750/.
Full textAbstract:
Nas últimas décadas, têm aumentado substancialmente a quantidade de pesquisas focando no desenvolvimento e caracterização de materiais biodegradáveis, particularmente, filmes comestíveis. O uso de polímeros de fontes renováveis, preparados a partir de produtos vegetais, vem ganhando importância nessa abordagem. O concentrado de proteína de soja e amido de mandioca podem ser considerados uma alternativa aos polímeros petroquímicos. O processamento pela radiação ionizante pode ser empregado para a modificação de polímeros e macromoléculas, resultando em novos materiais com grandes perspectivas de utilização industrial. A indústria de alimentos, uma das indústrias tradicionalmente mais inovadoras, exige o desenvolvimento constante de novos produtos. A capacidade de proteínas e polissacarídeos de formar filmes, amplamente conhecida, é um ponto de partida para o desenvolvimento de novos materiais que atendam os variados requerimentos dessa pungente indústria. Neste trabalho elaboraram-se filmes a base de fécula de mandioca e proteína isolada de soja em duas proporções diferentes e posteriormente irradiados e analisados quanto às suas propriedades mecânicas, cor, absorção de água, permeabilidade ao vapor de agua, análise térmica TGA e DSC entre outros. Os filmes tornaram-se aparentemente mais solúveis e menos resistentes a perfuração com o aumento da dose de radiação aplicada. Com relação às propriedades térmicas observou-se que os filmes com maior proporção de proteína são mais resistentes. Os filmes apresentaram-se menos permeáveis na dose de 40 kGy, e, com relação a absorção de água, esta foi reduzida em função da dose de radiação. Filmes com boa resistência ao vapor de água e com reduzida absorção podem ser considerados adequados para embalagens de alimentos. A radiação mostrou ser uma ferramenta conveniente na modificação de materiais poliméricos principalmente para elaboração de filmes solúveis onde esta é uma nova tendência para embalagens bioativas.In recent decades, there has been a substantial increase in the amount of research focusing on the development and characterization of biodegradable materials, particularly edible films. The use of polymers from renewable sources, prepared from plant products, has gained importance in this approach. Soy protein concentrate and cassava starch may be considered an alternative to petrochemical polymers. Processing by ionizing radiation can be used for the modification of polymers and macromolecules, resulting in new materials with great prospects of industrial use. The food industry, one of the traditionally most innovative industries, requires the constant development of new products. The widely known ability of film forming proteins and polysaccharides is a starting point for the development of new materials that meet the varying requirements of this pungent industry. In this work, films based on manioc starch and isolated soy protein were prepared in two different proportions and later irradiated and analyzed for their mechanical properties, color, water absorption, water vapor permeability, TGA and DSC thermal analysis between others. The films became apparently more soluble and less resistant to drilling with the increased radiation dose applied. Regarding the thermal properties, it was observed that the films with greater protein orientation are more resistant. Properties such as water vapor permeability and water absorption, the films were less permeable at the 40 kGy dose. With regard to water absorption, it was reduced as a function of the radiation dose. Films with good resistance to water vapor and with low absorption are considered efficient for food packaging. Radiation has proven to be a convenient tool in the modification of polymeric materials mainly for the production of soluble films where it is a new trend for bioactive packaging.
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Kalbitz, René. "Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5727/.
Full textAbstract:
Organic thin film transistors (TFT) are an attractive option for low cost electronic applications and may be used for active matrix displays and for RFID applications. To extend the range of applications there is a need to develop and optimise the performance of non-volatile memory devices that are compatible with the solution-processing fabrication procedures used in plastic electronics. A possible candidate is an organic TFT incorporating the ferroelectric co-polymer poly(vinylidenefluoride-trifluoroethylene)(P(VDF-TrFE)) as the gate insulator. Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) as the gate insu-lator. The capacitance spectra of MIS devices, were measured under different biases, showing the effect of charge accumulation and depletion on the Maxwell-Wagner peak. The position and height of this peak clearly indicates the lack of stable depletion behavior and the decrease of mobility when increasing the depletion zone width, i.e. upon moving into the P3HT bulk. The lack of stable depletion was further investigated with capacitance-voltage (C-V) measurements. When the structure was driven into depletion, C-V plots showed a positive flat-band voltage shift, arising from the change in polarization state of the ferroelectric insulator. When biased into accumulation, the polarization was reversed. It is shown that the two polarization states are stable i.e. no depolarization occurs below the coercive field. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flat-band voltage expected during the sweep to accumulation voltages. The measured output characteristics of the studied ferroelectric-field-effect transistors confirmed the results of the C-V plots. Furthermore, the results indicated a trapping of electrons at the positively charged surfaces of the ferroelectrically polarized P(VDF-TrFE) crystallites near the insulator/semiconductor in-terface during the first poling cycles. The study of the MIS structure by means of thermally stimulated current (TSC) revealed further evidence for the stability of the polarization under depletion voltages. It was shown, that the lack of stable depletion behavior is caused by the compensation of the orientational polarization by fixed electrons at the interface and not by the depolarization of the insulator, as proposed in several publications. The above results suggest a performance improvement of non-volatile memory devices by the optimization of the interface.Organische Transistoren sind besonders geeignet für die Herstellung verschiedener preisgünstiger, elektronischer Anwendungen, wie zum Beispiel Radio-Frequenz-Identifikations-Anhänger (RFID). Für die Erweiterung dieser Anwendung ist es notwendig die Funktion von organischen Speicherelementen weiter zu verbessern. Das ferroelektrische Polymer Poly(vinylidene-Fluoride-Trifluoroethylene) (P(VDF-TrFE)) eignet sich besonders gut als remanent polarisierbarer Isolator in Dünnschich-Speicherelementen. Um Schalt- und Polarisationsverhalten solcher Speicherelemente zu untersuchen, wurden P(VDF-TrFE)-Kondensatoren und Metall-Halbleiter-Isolator-Proben sowie ferroelektrische Feld-Effekt-Transistoren (Fe-FET) aus dem Halbleiter Poly(3-Hexylthiophene) (P3HT) und P(VDF-TrFE) hergestellt und dielektrisch untersucht. Die Charakterisierung der MIS-Strukturen mittels spannungsabhängiger Kapazitätsspektren machte deutlich, dass es nicht möglich ist, einen stabilen Verarmungzustand (Aus-Zustand) zu realisieren. Kapazität-Spannungs-Messungen (C-V) an MIS-Proben mit uni/bi-polaren Spannungszyklen zeigten eine stabile ferroelektrische Polarisation des P(VDF-TrFE)-Films. Eine Depolarisation des Isolators durch den Mangel an Minoritäts-Ladungsträgern konnte als Grund für die Instabilität des Verarmungs-Zustandes ausgeschlossen werden. Die C-V-Kurven wiesen vielmehr auf die Existenz fixierter, negativer Ladungsträger an der Grenzfläche hin. Zusammenfassend kann festgestellt werden: die Ursache der Ladungsträgerinstabilitäten in organischen ferroelektrischen Speicherelementen ist auf die Kompensation der ferroelektrischen Orientierungspolarisation durch "getrappte"(fixierte) negative Ladungsträger zurückzuführen. Dieses Ergebnis liefert nun eine Grundlage für die Optimierung der Isolator/Halbleiter-Grenzfläche mit dem Ziel, die Zahl der Fallenzustände zu minimieren. Auf diesem Wege könnte die Stabilität des Speicherzustandes in organischen Dünnschichtspeicherelementen deutlich verbessert werden.
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Souza, Aparecida Sonia de. "Efeitos da irradiação na composição e propriedades funcionais da soja." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256399.
Full textAbstract:
Orientador: Flavia Maria NettoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: O presente trabalho teve como objetivo estudar os efeitos da irradiação e do tempo de armazenamento na composição química de grãos de soja e funcionais de seus isolados protéicos. Os grãos de soja foram divididos em quatro lotes, sendo que dois foram irradiados em fonte de 60Cobalto, com doses de 2,0 ou 5,0 kGy, um lote foi irradiado em acelerador de elétrons com dose de 2,0 kGy e um lote foi utilizado como controle (não irradiado). Os lotes foram armazenados por um período de 12 meses. A cada quatro meses, uma porção de cada lote foi retirada para produção laboratorial de farinhas desengorduradas (FDSs) e isolados protéicos (IPSs). A composição centesimal nos grãos, FDSs e IPSs foi determinada. Nos grãos foram analisados a atividade de água, teor de isoflavonas e atividade antioxidante (IA) e nas FDSs, os teores de fitato e inibidores de tripsina (IT). O teor de acidez foi avaliado nos óleos obtidos do desengorduramento das farinhas. As características estruturais das proteínas dos IPSs obtidos foram avaliadas por análises de eletroforese em gel de poliacrilamida na presença de dodecil sulfato de sódio (SDS-PAGE) em condições não redutoras, das proteínas solúveis em diferentes sistemas, calorimetria diferencial de varredura (CDV), grupos sulfidrila livres (SH), fluorescência intrínseca (FI), cromatografia liqüida de alta eficiência de fase reversa (CLAE-FR) e cromatografia liqüida de alta eficiência de exclusão molecular (CLAE-EM). As propriedades funcionais avaliadas foram: solubilidade, gelificação, capacidade de retenção de água (CRA), capacidade emulsificante (CE), índice de atividade emulsificante (IAE) e estabilidade de emulsão (EE). O teor das isoflavonas totais e o índice de antioxidação, analisados nos grãos, não diferiu significativamente (p>0,05) e permaneceu estável ao longo do armazenamento, independente do tipo ou dose de radiação. No entanto, houve aumento das concentrações relativas dos b-glicosídeos e diminuição dos malonil glicosídeos ao longo do armazenamento. O teor de acidez aumentou em até 81,6% no óleo de grãos irradiados com dose de 5 kGy e armazenados por doze meses. As FDSs de grãos irradiados apresentaram os menores valores dos inibidores de tripsina e fitato. As análises de calorimetria diferencial de varredura, fluorescência intrínseca e cromatografia liqüida de alta eficiência de exclusão molecular indicaram não ter ocorrido alterações estruturais importantes nos isolados protéicos devido à irradiação ou ao armazenamento. Entretanto, os grupos sulfidrila livres aumentaram nos IPSs de grãos irradiados, mas sofreram pouca alteração ao longo dos 12 meses de armazenamento. Houve aumento da proporção relativa de frações hidrofóbicas observadas por CLAE-FR em todos os isolados após quatro meses de armazenamento dos grãos. Os IPSs de grãos irradiados apresentaram maior solubilidade protéica e capacidade emulsificante, enquanto que a estabilidade de emulsão e o índice de atividade emulsificante não diferiram significativamente (p>0,05). Os valores de dureza e capacidade de retenção de água dos géis dos IPSs não diferiram significativamente (p>0,05) em função do tratamento empregado. No entanto, os géis dos IPSs de grãos armazenados tiveram maiores valores de dureza. Os valores coesividade e elasticidade dos géis dos isolados, independente da dose e tipo de radiação, não diferiram significativamente (p>0,05). Nas condições estudadas, as radiações gama com doses de até 5 kGy e de feixe de elétrons com dose de 2 kGy podem ser utilizadas sem prejuízo as propriedades químicas de grãos e funcionais de seus isolados protéicos, durante o armazenamento
Abstract: The aim of this work was to study the effects of both irradiation and storage on the chemical composition of soybean grains and on the physicochemical and functional properties of their protein isolates. The soy grains were divided into four lots, two of them were irradiated with of 60Cobalt source in doses of 2.0 or 5.0 kGy, a third one was irradiated with an electron beam at 2.0 kGy and another was used as control (non-irradiated). All the lots were stored for a maximum of 12 months. Every four months, a portion of each lot was removed to produce deffated soy flour (DFS) and soy protein isolate (SPI). The proximal compositions of the grains, FDSs and SPIs were determined. In the grains, the water activity, total isoflavone content and antioxidant index (AI) were measured and in DFSs, the phytate content and trypsin inhibitor activity (TIA). The acidity content was measured in the oil obtained from the whole flours. The structural characteristics of SPIs were evaluated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDSPAGE) under non reducing conditions of the soluble proteins using different systems. Additionally, differential scanning calorimetry (DSC), free sulfhydryl groups (SH), intrinsic fluorescence (IF), reversed-phase high performance liquid chromatography (RP-HPLC) and of size exclusion high performance liquid chromatography (SE-HPLC) were also used to evaluate the effects. The analyses of the functional properties in SPIs were: solubility, gelation, water holding capacity (WHC), emulsifying capacity (EC), emulsifying activity index (EAI) and emulsifying stability (ES). The total isoflavone content and antioxidant index analyzed in the grains did not differ significantly (p>0.05) and remained stable throughout storage, as a function of the dose or type of irradiation. However, there was an increase in the b-glycosides and decrease in the mean percentage of malonyl glycosides. The acidity content increased in the percentage of 81.6% in the oil grains irradiated with 5 kGy and stored for 12 months. DFSs of irradiated grains exhibited smaller values of the trypsin inhibitor and phytate. The analyses of differential scanning calorimetry, intrinsic fluorescence and size exclusion high performance liquid chromatography showed that no important structural alterations occurred in the protein isolates due irradiation or storage. However, the free sulfhydryl groups increased in SPIs of irradiated grains, without further significant changes along the storage. There was an increase of the proportion of the hydrophobic fractions, showed by reversed-phase high performance liquid chromatography profile, for all the isolated after four months of storage of the grains. SPIs of irradiated grains presented high solubility, emulsifying capacity while emulsifying stability and emulsifying activity index did not differ significantly (p>0.05). The values of hardness and water holding capacity of the SPIs gels did not differ significantly (p>0.05) for all treatment. However, SPIs gels of stored grains had high values of hardness. The values cohesiveness and elasticity of the SPIs gels did not differ significantly (p>0.05), independent of the dose and type of irradiation. Under the studied conditions, gamma irradiation at doses of 5 kGy and of electron beam of 2 kGy can be used without damage to the grain composition or storage property or to the physicochemical properties of the protein isolates
Doutorado
Nutrição Experimental e Aplicada à Tecnologia de Alimentos
Doutor em Alimentos e Nutrição
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Marçal, Nei. "Estudo da estrutura eletrônica e das propriedades ópticas de copolímeros formados por vinilenos e anéis de tiofeno." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277368.
Full textAbstract:
Orientador: Bernardo LaksTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Antes da década de 70, todos os materiais poliméricos eram considerados como isolantes e suas aplicações tecnológicas levavam em conta esta característica. De lá para cá, uma nova classe desses materiais, os polímeros conjugados, determinaram uma nova forma de aplicação de sistemas poliméricos baseados em suas propriedades elétricas e de ótica não-linear. Um maior estímulo surgiu a partir do experimento de Mac Diarmid, Heeger e Shirakawa [1] que, expondo o Poliacetileno a agentes oxidantes, demonstraram ser possível obter um sistema no estado metálico. Atualmente encontramos filmes de Poliacetileno com condutividade elétrica da ordem do cobre (105 S/cm). O Poliacetileno, quando no regime metálico, i.e., sob alta dopagem, apresenta algumas características de metal comum: alta condutividade elétrica (cresce 13 ordens de grandeza), susceptibilidade de Pauli finita e absorção no infravermelho. Já outras propriedades como a presença de modos vibracionais localizados no infravermelho e o não comportamento da condutividade com o inverso da temperatura evidenciam ser este um material não usual. Estes polímeros conjugados que apresentam uma extensiva delocalização de elétrons são considerados semicondutores orgânicos com gap de energia relativamente pequeno, da ordem de 1,5 a 2,0 eV. O comportamento semicondutor e as propriedades decorrentes entre os elétrons e a luz têm originado a construção de vários dispositivos semicondutores e optoeletrônicos [2, 7, 3]. Problemas técnicos como estabilidade ao ambiente, processabilidade e solubilidade destes materiais provocaram a produção de uma nova classe de materiais poliméricos que foi obtida por polimerização eletroquímica [57, 58, 59] cuja estrutura molecular trata-se de sistemas que introduzem grupos vinilas (V) entre anéis de tiofeno (T). Experimentos de voltametria cíclica, espectroscopia de absorção ótica e ressonância eletrônica de spin indicam que esses sistemas possuem potencial de ionização e gap de energia menores que o apresentado pelo Politiofeno. Estudos com oligômeros de tiofeno (T) com vinilenos (V) sugerem a possibilidade de escolha desse material como alternativa ao politiofeno. O objetivo deste trabalho foi investigar teoricamente a influência do grupo vinila (V) sobre as propriedades eletrônicas nestes polímeros, reproduzir os resultados experimentais e determinar qual proporção de vinilenos (V) e tiofenos (T) que provoque o menor gap de energia de forma que quando sobre dopagem possibilite uma transição isolante metal. Desta maneira, primeiramente, determinamos as geometrias dos sistemas de interesse utilizando métodos semi-empíricos. Posteriormente investigamos a estrutura eletrônica dos polímeros de tiofeno (T) com vinilenos (V), sendo que estes polímeros foram estudados para o caso neutro e na presença de defeitos conformacionais do tipo pólaron e bipólaron. Finalizamos o estudo investigando as absorções ópticas UV-vis dos sistemas de interesse através de cálculos semi-empíricos utilizando o código ZINDO/S.
Abstract: Before the 1970s, all polymeric materials were considered insulators; therefore their technological applications would take this trait into account. Since then, a new development on these materials, the conjugated polymers, determined new applications for polymeric systems based in their electrical and nonlinear optical properties. Greater interest arose from the experiment by Mac Diarmid, Heeger and Shirakawa [1] who, by using polyacetylene and oxidizing agents, showed that it is possible to obtain a system in the metallic state. Nowadays it is possible to find polyacetylene films with electrical conductivity of the order of copper (10-5 S/cm). Polyacetylene, when in its metallic behavior, i.e., under high dopage, presents some characteristics of real metal: high electrical conductivity (increased by 13 orders of magnitude), finite Pauli susceptibility and infrared absorption. On the other hand, other properties such as the presence of vibrational modes localized on infrared and the odd behavior of conductivity versus the inverse of temperature make clear that this is a unusual material. These conjugated polymers, presenting an extensive delocalization of electrons, are considered organic semiconductors with relatively low energy gap, of the order of 1.5 to 2.0 eV. The semiconductive behavior and the resulting properties of the interaction between electrons and light have been the drive for the manufacturing of several semiconductor and optoelectronic devices [2, 7, 3]. Technical problems, such as environmental stability, processability and solubility of these materials, gave rise to the production of a new kind of polymeric materials that were obtained by electrochemical polymerization [57, 58, 59], in which the molecular structure is a system that introduces vinylene groups (V) between tiophene rings (T). Experiments involving cyclic voltametry, optical absorption spectrometry and spin electronic ressonance indicate that these systems have ionization potential and energy gap smaller than those presented by Polythiophene. Studies with thiopene oligomers (T) with vinylene (V) suggest this material can be chosen as an alternative to Polytiophene. The goal of this work is to theoretically investigate the in uence of the vinyle group (V) on the electronic properties on these polymers, reproduce experimental results and determine what is the vinylene (V) to thiophene (T) rate that causes the smallest energy gap, such that doping will produce a insulator-metal transition. Therefore, we first determine the target systems' geometry using semi-empirical methods. Then we investigate the electronic structure of the tiophene (T) and vinylene (V) polymers both for neutral systems and in the presence of conformational defects of polaron and bipolaron types. We nalized the study by investigating the UV-vis optical absorption of the target systems through semi-empirical calculations using ZINDO/S code.
Doutorado
Estrutura Eletronica de Atomos e Moleculas ; Teoria
Doutor em Ciências
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Grün, Mathias. "Les nanocristaux de silicium comme source de lumière : analyse optique et réalisation de microcavités." Thesis, Nancy 1, 2010. http://www.theses.fr/2010NAN10108/document.
Full textAbstract:
Ce travail de thèse concerne la réalisation et l'analyse des propriétés optiques de nanocristaux de silicium. Ces objets de taille nanométrique possèdent des propriétés optiques remarquables, en particulier de photoluminescence. Les propriétés de confinement quantique qui les caractérisent permettent d'obtenir un signal de luminescence intense dans le domaine du visible. Des composants optoélectroniques et photoniques ont été envisagés à base de nanocristaux de silicium. Les raisons physiques du fort signal de luminescence en revanche sont encore mal comprises. Les nanocristaux de silicium sont élaborés par évaporation. L'élaboration et le recuit thermique de multicouches SiO/SiO2 permet d'obtenir des nanocristaux de silicium de diamètre moyen bien contrôlé. Ceux-ci sont issus de la démixtion de la couche de SiO selon la réaction SiOx --> Si + SiO2. Le contrôle du diamètre des nanocristaux de silicium permet de maîtriser la région spectrale de luminescence dans la région du visible.La première partie de ce travail de thèse vise à isoler un ou quelques nanocristaux de silicium. L'objectif est de remonter à la largeur homogène de ces nano-objets. Dans un premier temps, une étude centrée sur le matériau SiOx est réalisée afin de réduire la densité surfacique de nanocristaux de silicium. Dans un deuxième temps, des moyens de lithographie ultime sont mis en oeuvre afin de réaliser des masques percés de trous de diamètres de l'ordre de la centaine de nanomètre. Des expériences de spectroscopie optique sont réalisées sur ces systèmes.La deuxième partie de ce travail vise à contrôler l'émission spontanée de lumière issue des nanocristaux de silicium. Ceci se fait en couplant les modes électroniques aux modes optiques confinés d'une microcavité optique. Le manuscrit détaille les moyens développés afin d'obtenir une microcavité optique dont les modes optiques puissent se coupler efficacement aux nanocristaux de silicium. Les propriétés optiques de ces systèmes sont finalement analyséesThis work concerns the implementation and analysis of optical properties of silicon nanocrystals. These nanoscaled objects have remarkable optical properties, especially in photoluminescence. The properties of quantum confinement that characterize them allow obtaining an intense luminescence signal in the visible range. Optoelectronic and photonic devices have been proposed based on silicon nanocrystals. The physical reasons of the strong luminescence signal, however, are still poorly understood. The silicon nanocrystals are prepared by evaporation. The preparation and thermal annealing of multilayers SiO/SiO2 leads to silicon nanocrystals with a well controlled average diameter. They are created during the demixing of the SiO layer by the reaction SiO ? Si + SiO2. The control the diameter of the silicon nanocrystals influences directly the spectral region of luminescence in the visible region.The aim of first part of this work is to isolate one or a few silicon nanocrystals. The intent is to trace the homogeneous width of these nano-objects. Initially, a study focusing on the SiOx material is conducted to reduce the surface density of silicon nanocrystals. In a second step, lithography is implemented to make masks with holes with diameters of about one hundred nanometers. Optical spectroscopy experiments were performed on these systems.The second part of this work aims controlling the spontaneous emission of light from silicon nanocrystals. This is done by coupling the electronic transmission to optical modes confined in an optical microcavity. The manuscript describes the methods developed to obtain an optical microcavity whose optical modes can be coupled effectively to the silicon nanocrystals. The optical properties of these systems are finally analyzed
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Zimmermann, Stephan. "Elektronenspinresonanz an niederdimensionalen und frustrierten magnetischen Systemen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-215546.
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In der eingereichten Dissertation wird eine Reihe von niederdimensionalen und frustrierten magnetischen Systemen mit Hilfe der Elektronenspinresonanz (ESR) untersucht, um deren magnetische Eigenschaften und Wechselwirkungen zu charakterisieren.
Sowohl niederdimensionale als auch frustrierte Systeme können exotische magnetische Phänomene zeigen, da es in beiden Fällen trotz starker magnetischer Korrelationen zu einer Unterdrückung von konventioneller langreichweitiger magnetischer Ordnung kommen kann. Auf der anderen Seite sind zweidimensionale Systeme wie Graphen und die damit verwandten topologischen Isolatoren interessant für Anwendungen in der Spintronik oder in Quantencomputern. Über das Einbringen von magnetischer Ordnung soll dabei die Kontrolle über den Spin von Elektronen erlangt werden.
Es werden quasieindimensionale Spinketten in Cu(py)2Br2 untersucht, die ein gutes Modellsysteme für den Vergleich mit exakten theoretischen Berechnungen darstellen. Durch eingehende ESR-Messungen ist es gelungen, ein Modell für die Ausrichtung der Anisotropieachse zu entwickeln, die senkrecht zur Kettenachse steht. Zusätzlich zum g-Tensor konnten durch Magnetisierungsmessungen das Austauschintegral und dessen Anisotropie bestimmt werden. Die Austauschwechselwirkung kann über die Substitution von Br- mit Cl-Ionen in Cu(py)2(Cl1-xBrx)2 gezielt variiert werden.
Des Weiteren wird eine kombinierte Studie aus STM- und ESR-Untersuchungen an monolagigem Graphen mit induzierten Fehlstellen vorgestellt. Es wurden Defekte durch den Beschuss mit Ar-Ionen in Graphen kontrolliert hergestellt, deren lokale elektronische Eigenschaften sich mit STM- und STS-Messungen charakte-risieren lassen. Mit ESR-Messungen konnte gezeigt werden, dass die an den einzelnen Fehlstellen lokalisierten magnetischen Momente eine dominant antiferromagnetische Austauschwechselwirkung besitzen.
Die Charakterisierung der magnetischen Wechselwirkungen zwischen lokalisierten Momenten stand auch für den mit Mn dotierten topologischen Isolator Bi2Te3 im Vordergrund, welcher einen ferromagnetischen Phasenübergang bei tiefen Temperaturen zeigt. Anhand des mit ESR beobachteten Korringa-Verhaltens wurde bewiesen, dass die lokalisierten Mn-Spins an leitende Bänder gekoppelt sind und die ferromagnetische Ordnung folglich per RKKY-Wechselwirkung vermittelt wird. Es wurden kurzreichweitige magnetische Korrelationen in einem ausgedehnten Temperaturbereich oberhalb der Ordnungstemperatur beobachtet, die Hinweise auf einen zweidimensionalen Charakter zeigen.
Ausgedehnte Temperaturbereiche mit kurzreichweitigen Korrelationen werden ebenfalls in den untersuchten magnetisch frustrierten Materialien beobachtet. In einer kombinierten Studie aus HF-ESR, NMR und µSR wird die Spindynamik in CoAl2O4 charakterisiert, in dem moderate Unordnung zu einem Verschwimmen der Phasengrenze zwischen Neél-Ordnung und einer Spinflüssigkeit mit spiralförmigen Korrelationen führt. Außerdem werden zwei Vertreter aus der Klasse der Swedenborgite behandelt, in denen die Spinstruktur in YBaCo4O7 durch Substitution modifiziert wird. Ziel ist die Entkopplung der enthaltenen Kagome-Schichten, welche ein zweidimensionales frustriertes System darstellen. In den vorgestellten HF-ESR- und NMR-Messungen beobachtet man ein Spinglasverhalten für YBaCo3AlO7, das aus der Unordnung bei der Besetzung der Gitterplätze resultiert. In YBaCo3FeO7 ist die Unordnung geringer und mit ESR-Untersuchungen konnte gezeigt werden, dass es zu einer effektiven Entkopplung der Fe-Spins zwischen den Kagome-Schichten kommt.
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Esmail, Adam Ashiq. "Charge dynamics in superconducting double dots." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270018.
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The work presented in this thesis investigates transitions between quantum states in superconducting double dots (SDDs), a nanoscale device consisting of two aluminium superconducting islands coupled together by a Josephson junction, with each dot connected to a normal state lead. The energy landscape consists of a two level manifold of even charge parity Cooper pair states, and continuous bands corresponding to charge states with single quasiparticles in one or both islands. These devices are fabricated using shadow mask evaporation, and are measured at sub Kelvin temperatures using a dilution refrigerator. We use radio frequency reflectometry to measure quantum capacitance, which is dependent on the quantum state of the device. We measure the quantum capacitance as a function of gate voltage, and observe capacitance maxima corresponding to the Josephson coupling between even parity states. We also perform charge sensing and detect odd parity states. These measurements support the theoretical model of the energy landscape of the SDD. By measuring the quantum capacitance in the time domain, we observe random switching of capacitance between two levels. We determine this to be the stochastic breaking and recombination of single Cooper pairs. By carrying out spectroscopy of the bath responsible for the pair breaking we attribute it to black-body radiation in the cryogenic environment. We also drive the breaking process with a continuous microwave signal, and find that the rate is linearly proportional to incident power. This suggests that a single photon process is responsible, and demonstrates the potential of the SDD as a single photon microwave detector. We investigate this mechanism further, and design an experiment in which the breaking rate is enhanced when the SDD is in the antisymmetric state rather than the symmetric state. We also measure the quantum capacitance of a charge isolated double dot. We observe 2e periodicity, indicating the tunnelling of Cooper pairs and the lack of occupation of quasiparticle states. This work is relevant to the range of experiments investigating the effect of non-equilibrium quasiparticles on the operation of superconducting qubits and other superconducting devices.
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Yengui, Mayssa. "Manipulation de molécules organiques sur couches ultra-minces semi-isolantes et plots métalliques pour la fabrication de circuits moléculaires." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112289/document.
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L’objectif globale de cette thèse est l’étude de la croissance de plots de siliciure de cobalt (CoSi2) individuels combinés à une surface semi-isolante de silicium hydrogénée (Si(100):H) afin de créer un environnement propice à l’interconnexion de molécules fonctionnalisées, prémisse des circuits moléculaires. Cette étude, liée au contexte de l’électronique moléculaire ascendante, est réalisée à l’aide d’un microscope à effet tunnel (STM) à basse température (9 K) sous ultra-vide. Ce travail de thèse débute par l’étude de l’adsorption d’atomes de Co, à basse température (12 K) sur la surface de Si(100)-2x1. Nos investigations nous ont permis d’observer, pour la première fois, des sites d’adsorption à la surface et des sites interstitiels métastables en surface et subsurface. Grâce aux excitations électroniques induites par les électrons tunnels, certains sites d’adsorption ont pu être manipulés sur la surface de Si(100). Cette étude préliminaire est suivie par la croissance de plots de siliciure de cobalt individuels sur le Si(100) dont les propriétés électroniques ont été étudiées à basse température (9 K). Ceci nous a permis d’identifier deux géométries de plot de CoSi2 de tailles nanométriques dont le caractère métallique est démontré et ayant de faibles barrières de Schottky à l’interface métal/semi-conducteur. Dans un second temps, nous avons examiné les propriétés de molécules de Co-TPP individuelles et de leurs interactions avec les surfaces de Si(100) et de Si(100) hydrogénées. Les topographies STM révèlent différentes conformations d’adsorption ayant des propriétés physico-chimiques particulières telles qu’une fonction bistable intramoléculaire, ainsi que des propriétés électroniques surprenantes permettant de sonder la physisorption totale ou partielle de l’adsorbat. Un troisième volet de cette thèse adresse la possibilité d’exploiter les propriétés intrinsèques de la surface de Si(100):H afin de créer des ponts moléculaires grâce au couplage successif de liaisons pendantes créées sur la surface du Si(100):H. Les mesures de spectroscopie tunnel effectuées sur ces structures exhibent des états inoccupés caractéristiques du couplage orbitalaire entre les liaisons pendantes dont l’énergie est fonction de l’orientation de la ligne déshydrogénée sur la surface. Finalement, après avoir vérifié que le processus d’hydrogénation ne perturbe pas le caractère métallique des plots de CoSi2, nous avons pu exploiter nos connaissances acquises lors des chapitres précédents. Ceci nous a permis d’étudier, pour la première fois, le contact entre molécules de Co-TPP et plots métalliques. Grâce aux techniques de manipulation latérale, les molécules de Co-TPP ont pu être déplacées et contactées aux plots métalliques. La spectroscopie tunnel effectuée sur différentes molécules montre, d’une part, qu’en fonction de leur orientation par rapport à l’îlot de CoSi2, la structure électronique de chaque molécule est modifiée de manière spécifique. D’autre part, nous avons observé que la position de la mesure des spectres tunnels influe sur le gap de la molécule associé, révélant probablement une signature du transport électronique entre la molécule et le plot métallique. L’ensemble de ces résultats ouvre de nouvelles perspectives extrêmement riches et prometteuses pour la réalisation de circuits moléculaires planaires comme prototype d’études fondamentalesFor the fabrication of molecular circuitsThe overall objective of this thesis is to study the growth of individual cobalt silicide (CoSi2) dots combined with a semi-insulating hydrogenated silicon surface (Si(100):H) to create a controlled and suitable environment for the interconnection of functionalized molecules, the premises to molecular circuits. This study, related to the context of the bottom-up molecular electronics, is performed using a scanning tunneling microscope (STM) at low temperature (9 K) under ultrahigh vacuum. This thesis begins with the study of the adsorption of Co atoms on the surface of Si (100)-2x1 kept at low temperature (12 K). Our investigations have led us to observe, for the first time, adsorption sites that are either stable or metastable interstitial sites on the surface and/or subsurface. With electronically induced excitations, some of the Co adsorption sites have been modified or manipulated on the Si(100) surface. This preliminary study is followed by the growth of individual cobalt silicide dots on the Si(100) while their properties are investigated at low temperature (9 K). This allowed us to identify two different types of silicide dots of nanometric sizes whose metallic character is demonstrated while low Schottky barriers at the metal/semiconductor interface are identified. In a second step, we examined the properties of individual Co-TPP molecules and their interactions with the Si(100) and hydrogenated Si(100) surfaces. The STM topographies reveal various conformations with specific properties such as an intra-molecular bistable function, as well as surprising electronic properties that allow probing the physisorbed parts of the adsorbate. A third part of this thesis addresses the possibility of exploiting the intrinsic properties of the Si(100):H surface to create molecular bridges through successive coupling of dangling bonds created at the surface of Si(100):H. Tunnel spectroscopy measurements carried out on these structures exhibit unoccupied states orbitals, signature of the coupling between dangling bonds, whose energy depends on the orientation of the dangling bond lines across the hydrogenated surface. Finally, after checking that the hydrogenation process of the Si(100) surface does not disturb the metallic character of the CoSi2 dots, we used our knowledge gained in previous chapters. This allowed us to study, for the first time, the contact between molecules of Co-TPP and metal dots. With lateral manipulation techniques, the Co-TPP molecules have been displaced and contacted to metallic pads. The tunneling spectroscopy performed on different molecules shows, firstly, that depending on their orientation relative to the CoSi2 dot, the electronic structure of each molecule is modified in a specific manner. On the other hand, we observed that the conductance spectrum influences the gap of the associated molecule, indicating a signature of electron transport between the molecule and the metal pad. Taken together, these results open new extremely rich and promising perspectives for the realization of planar molecular circuit as a prototype for fundamental studies
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Jenderka, Marcus. "Pulsed Laser Deposition of Iridate and YBiO3 Thin Films." Doctoral thesis, Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-219334.
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Die vorliegende Arbeit befasst sich mit dem Dünnfilmwachstum der ternären Oxide Na2IrO3, Li2IrO3, Y2Ir2O7 und YBiO3. All diesen oxidischen Materialien ist gemein, dass sie Verwirklichungen sogenannter Topologischer Isolatoren oder Spin-Flüssigkeiten sein könnten. Diese neuartigen Materiezustände versprechen eine zukünftige Anwendung in der Quantencomputation, in magnetischen Speichern und in elektrischen Geräten mit geringer Leistungsaufnahme. Die Herstellung der hier gezeigten Dünnfilme ist daher ein erster Schritt zur Umsetzung dieser Anwendungen in der Zukunft. Alle Dünnfilme werden mittels gepulster Laserplasmaabscheidung auf verschiedenen einkristallinen Substraten hergestellt. Die strukturellen, optischen und elektrischen Eigenschaften der Filme werden mittels etablierter experimenteller Verfahren wie Röntgenbeugung, spektroskopischer Ellipsometrie und elektrischenWiderstandsmessungen untersucht. Die strukturellen Eigenschaften von erstmalig in der Masterarbeit des Authors verwirklichten Na2IrO3-Dünnfilmen können durch Abscheidung einer ZnO-Zwischenschicht deutlich verbessert werden. Einkristalline Li2IrO3-Dünnfilme mit einer definierten Kristallausrichtung werden erstmalig hergestellt. Die Messung der dielektrischen Funktion gibt Einblick in elektronische Anregungen, die gut vergleichbar mit Li2IrO3-Einkristallen und verwandten Iridaten sind. Des Weiteren wird aus den Daten eine optische Energielücke von ungefähr 300 meV bestimmt. In Y2Ir2O7-Dünnfilmen wird eine mögliche (111)-Vorzugsorientierung in Wachstumsrichtung gefunden. Im Vergleich mit der chemischen Lösungsabscheidung zeigen die hier mittels gepulster Laserplasmaabscheidung hergestellten YBiO3-Dünnfilme eine definierte, biaxiale Kristallausrichtung in der Wachstumsebene bei einer deutlich höheren Schichtdicke. Über die gemessene dielektrische Funktion können eine direkte und indirekte Bandlücke bestimmt werden. Deren Größe gibt eine notwendige experimentelle Rückmeldung an theoretische Berechnungen der elektronischen Bandstruktur von YBiO3, welche zur Vorhersage der oben erwähnten, neuartigen Materiezuständen verwendet werden. Nach einer Einleitung und Motivation dieser Arbeit gibt das zweite Kapitel einen Überblick über den gegenwärtigen Forschungsstand der hier untersuchten Materialien. Die folgenden zwei Kapitel beschreiben die Probenherstellung und die verwendeten experimentellen Untersuchungsmethoden. Anschließend werden für jedes Material einzeln die experimentellen Ergebnisse dieser Arbeit diskutiert. Die Arbeit schließt mit einer Zusammenfassung und einem AusblickThe present thesis reports on the thin film growth of ternary oxides Na2IrO3, Li2IrO3, Y2Ir2O7 and YBiO3. All of these oxides are candidate materials for the so-called topological insulator and spin liquid, respectively. These states of matter promise future application in quantum computation, and in magnetic memory and low-power electronic devices. The realization of the thin films presented here, thus represents a first step towards these future device applications. All thin films are prepared by means of pulsed laser deposition on various single-crystalline substrates. Their structural, optical and electronic properties are investigated with established experimental methods such as X-ray diffraction, spectroscopic ellipsometry and resistivity measurements. The structural properties of Na2IrO3 thin films, that were previously realized in the author’s M. Sc. thesis for the first time, are improved significantly by deposition of an intermediate ZnO layer. Single-crystalline Li2IrO3 thin films are grown for the first time and exhibit a defined crystal orientation. Measurement of the dielectric function gives insight into electronic excitations that compare well with single crystal samples and related iridates. From the data, an optical energy gap of about 300 meV is obtained. For Y2Ir2O7 thin films, a possible (111) out-of-plane preferential crystal orientation is obtained. Compared to chemical solution deposition, the pulsed laser-deposited YBiO3 thin films presented here exhibit a biaxial in-plane crystal orientation up to a significantly larger film thickness. From the measured dielectric function, a direct and indirect band gap energy is determined. Their magnitude provides necessary experimental feedback for theoretical calculations of the electronic structure of YBiO3, which are used in the prediction of the novel states of matter mentioned above. After the introduction and motivation of this thesis, the second chapter reviews the current state of the science of the studied thin film materials. The following two chapters introduce the sample preparation and the employed experimental methods, respectively. Subsequently, the experimental results of this thesis are discussed for each material individually. The thesis concludes with a summary and an outlook
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Andrade, Eric de Castro e. "Cálculos numéricos de sistemas eletrônicos desordenados correlacionados." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277676.
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Orientador: Eduardo MirandaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-16T08:19:56Z (GMT). No. of bitstreams: 1 Andrade_EricdeCastroe_D.pdf: 5537554 bytes, checksum: 1391d5fcc710b5e471f0814a4a6d484f (MD5) Previous issue date: 2010
Resumo: Sistemas eletrônicos fortemente correlacionados desordenados possuem dois mecanismos básicos para a localização eletrônica e a subsequente destruição do estado metálico: o de Mott (causado pela interação elétron-elétron) e o de Anderson (causado pela desordem). Nesta tese, estudamos como estes mecanismos competem dentro da fase metálica e também como afetam o comportamento crítico do sistema, empregando uma generalização para o caso desordenado do cenário de Brinkman-Rice para a transição de Mott. Investigamos os efeitos de desordem fraca e moderada sobre a transição metal-isolante de Mott a T = 0 em duas dimensões. Para desordem sucientemente baixa, a transição mantém sua característica do tipo Mott, na qual temos os pesos de quasipartícula Zi indo a zero na transição e uma forte blindagem da desordem na região crítica. Em contraste com o comportamento encontrado para d = 8 , no nosso caso as flutuações espaciais dos pesos de quasipartícula são fortemente amplificadas próximo à transição de Mott de tal forma que eles adquirem uma distribuição do tipo lei de potência P (Z) ~ Z a-1 ,com a --> 0 na transição. Tal comportamento altera completamente as características desta transição com relação ao caso limpo, e é um indício robusto da emergência de uma fase de Griffiths eletrônica precedendo a transição metal-isolante de Mott, com uma fenomenologia surpreendentemente similar àquela do "ponto fixo de desordem infinita" encontrada em magnetos quânticos. Uma consequência imediata dessas novas características introduzidas pela desordem é que estados eletrônicos próximos à superfície de Fermi tornam-se mais homogêneos na região crítica, ao passo que estados com maiores energias têm o comportamento oposto: eles apresentam uma grande inomogeneidade precisamente nas vizinhanças da transição de Mott. Sugerimos que uma desordem efetiva dependente da interação é uma característica comum a todos os sistemas de Mott desordenados. Estudamos também como os efeitos bem conhecidos das oscilações de longo alcance de Friedel são afetados por fortes correlações eletrônicas. Primeiramente, mostramos que sua amplitude e alcance são consideravelmente suprimidos em líquidos de Fermi fortemente renormalizados. Posteriormente, investigamos o papel dos espalhamentos elásticos e inelásticos na presença dessas oscilações. Em geral, nossos resultados analíticos mostram que um papel proeminente das oscilações de Friedel é relegado a sistemas fracamente interagentes. Abordamos, por m, os efeitos das interações sobre o isolante de Anderson em uma dimensão. Construímos a função de escala ß (g) e mostramos que a escala de "crossover" g *, que marca a transição entre o regime ôhmico e o localizado da condutância, é renormalizada pelas interações. Como consequência, embora não haja a emergência de estados verdadeiramente estendidos, o regime ôhmico de g estende-se agora por uma região consideravelmente maior do espaço de parâmetros.
Abstract: Disordered strongly correlated electronic systems have two basic routes towards localization underlying the destruction of the metallic state: the Mott route (driven by electron-electron interaction) and the Anderson route (driven by disorder). In this thesis, we study how these two mechanisms compete in the metallic phase, and also how they change the critical behavior of the system, within a generalization to the disordered case of the Brinkman-Rice scenario for the Mott transition. We investigate the effects of weak to moderate disorder on the Mott metal-insulator transition at T = 0 in two dimensions. For sufficiently weak disorder, the transition retains the Mott character, as signaled by the vanishing of the local quasiparticle weights Zi and strong disorder screening at criticality. In contrast to the behavior in d = 8, here the local spatial fluctuations of quasiparticle parameters are strongly enhanced in the critical regime, with a distribution function P(Z) ~ Z a-1 and a --> 0 at the transition. This behavior indicates the robust emergence of an electronic Griffiths phase preceding the MIT, in a fashion surprisingly reminiscent of the " Infinite Randomness Fixed Point" scenario for disordered quantum magnets. As an immediate consequence of these new features introduced by disorder, we have that the electronic states close to the Fermi energy become more spatially homogeneous in the critical region, whereas the higher energy states show the opposite behavior: they display enhanced spatial inhomogeneity precisely in the close vicinity to the Mott transition. We suggest that such energy-resolved disorder screening is a generic property of disordered Mott systems. We also study how well-known effects of the long-ranged Friedel oscillations are affected by strong electronic correlations. We first show that their range and amplitude are signifficantly suppressed in strongly renormalized Fermi liquids. We then investigate the interplay of elastic and inelastic scattering in the presence of these oscillations. In the singular case of two-dimensional systems, we show how the anomalous ballistic scattering rate is conned to a very restricted temperature range even for moderate correlations. In general, our analytical results indicate that a prominent role of Friedel oscillations is relegated to weakly interacting systems. Finally, we discuss the effects of correlations on the Anderson insulator in one dimension. We construct the scaling function ß(g) and we show that the crossover scaling g*, which marks the transition between the ohmic and the localized regimes of the conductance, is renormalized by the interactions. As a consequence, we show that, although truly extend states do not emerge, the ohmic regime covers now a considerably larger region in the parameter space.
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Fil, Nicolas. "Caractérisation et modélisation des propriétés d’émission électronique sous champ magnétique pour des systèmes RF hautes puissances sujets à l’effet multipactor." Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0025/document.
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La fusion nucléaire contrôlée par confinement magnétique avec les réacteurs de type Tokamaks et les applications spatiales ont en commun d’utiliser des composants Haute-Fréquence (HF) sous vide à forte puissance. Ces composants peuvent être sujets à l’effet multipactor qui augmente la densité électronique dans le vide au sein des systèmes, ce qui est susceptible d’induire une dégradation des performances des équipements et de détériorer les composants du système. Ces recherches consistent à améliorer la compréhension et la prédiction de ces phénomènes. Dans un premier temps nous avons réalisé une étude de sensibilité de l’effet multipactor au rendement d’émission électronique totale (noté TEEY). Cette étude a permis de montrer que l’effet multipactor est sensible à des variations d’énergies autour de la première énergie critique et dans la gamme d’énergies entre la première énergie critique et l’énergie du maximum. De plus, les composants HF utilisés dans les réacteurs Tokamak et dans le domaine du spatial peuvent être soumis à un champ magnétique continu. Nous avons donc développé un nouveau dispositif expérimental afin d’étudier ce phénomène. Le fonctionnement du dispositif et la méthode de mesure ont été analysées et optimisées à l’aide de modélisations numériques avec le logiciel PIC SPIS. Une fois que l’utilisation du dispositif a été optimisée et que le protocole de mesures a été validé, nous avons étudié l’influence d’un champ magnétique uniforme et continu sur le TEEY du cuivre. Nous avons démontré que le rendement d’émission électronique totale du cuivre est influencé par la présence d’un champ magnétique et par conséquent également l’effet multipactorSpace communication payload as well as magnetic confinement fusion devices, among other applications, are affected by multipactor effect. This undesirable phenomenon can appear inside high frequency (HF) components under vacuum and lead to increase the electron density in the vacuum within the system. Multipactor effect can thus disturb the wave signal and trigger local temperature increases or breakdowns. This PhD research aims to improve our understanding and the prediction of the multipactor effect. The multipactor phenomenon is a resonant process which can appear above a certain RF power threshold. To determine this power threshold, experimental tests or/and simulations are commonly used. We have made a study to evaluate the multipactor power threshold sensitivity to the TEEY. Two particular critical parameters have been found: first cross-over energy and the energies between the first cross-over and the maximum energies. In some situations, the HF components are submitted to DC magnetic fields which might affect the electron emission properties and hence the multipactor power threshold. Current multipactor simulation codes don’t take into account the effect of the magnetic field on the TEEY. A new experimental setup specially designed to investigate this effect was developed during this work. Our new experimental setup and the associated TEEY measurement technique were analysed and optimized thanks to measurements and SPIS simulations. We used the setup to study the influence of magnetic field perpendicular to the sample surface on the TEEY of copper. We have demonstrated that the magnetic field affects the copper TEEY, and hence multipactor power threshold
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Bui, Thi Thanh Huyen. "Terminaisons verticales de jonction remplies avec des couches diélectriques isolantes pour des application haute tension utilisant des composants grand-gap de forte puissance." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI061/document.
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Le développement de l’énergie renouvelable loin des zones urbaines demande le transport d'une grande quantité d’énergie sur de longues distances. Le transport d’électricité en courant continu haute tension (HVDC) présente beaucoup d’avantages par rapport à celui en courant alternatif. Dans ce contexte il est nécessaire de développer des convertisseurs de puissance constitués par des composants électroniques très haute tension, 10 à 30 kV. Si les composants en silicium ne peuvent pas atteindre ces objectifs, le carbure de silicium (SiC) se positionne comme un matériau semiconducteur alternatif prometteur. Pour supporter des tensions élevées, une région de "drift", relativement large et peu dopée constitue le cœur du composant de puissance. En pratique l’obtention d’une tension de blocage effective dépend de plusieurs facteurs et surtout de la conception d'une terminaison de jonction adaptée. Cette thèse présente une méthode pour améliorer la tenue en tension des composants en SiC basée sur l’utilisation des terminaisons de jonctions : Deep Trench Termination. Cette méthode utilise une tranchée gravée profonde en périphérie du composant, remplie avec un matériau diélectrique pour supporter l'étalement des lignes équipotentielles. La conception de la diode avec cette terminaison a été faite par simulation TCAD, avec deux niveaux de tension 3 et 20 kV. Les travaux ont pris en compte les caractéristiques du matériau, les charges à l’interface de la tranchée et les limites technologiques pour la fabrication. Ce travail a abouti sur la fabrication de démonstrateurs et leur caractérisation pour valider notre conception. Lors de la réalisation de ces structures, la gravure plasma du SiC a été optimisée dans un bâti ICP de manière à obtenir une vitesse de gravure élevée et en conservant une qualité électronique de l'état des surfaces gravées. Cette qualité est confirmée par les résultats de caractérisation obtenus avec des tenues en tension proches de celle idéaleThe development of renewable energy away from urban areas requires the transmission of a large amount of energy over long distances. High Voltage Direct Current (HVDC) power transmission has many advantages over AC power transmission. In this context, it is necessary to develop power converters based on high voltage power electronic components, 10 to 30 kV. If silicon components cannot achieve these objectives, silicon carbide (SiC) is positioned as a promising alternative semiconductor material. To support high voltages, a drift region, relatively wide and lightly doped is the heart of the power component. In practice obtaining an effective blocking voltage depends on several factors and especially the design of a suitable junction termination. This thesis presents a method to improve the voltage withstand of SiC components based on the use of junction terminations: Deep Trench Termination. This method uses a trench deep etching around the periphery of the component, filled with a dielectric material to support the spreading of the equipotential lines. The design of the diode with this termination was done by TCAD simulation, with two voltage levels 3 and 20 kV. The work took into account the characteristics of the material, the interface charge of the trench and the technological limits for the fabrication. This work resulted in the fabrication of demonstrators and their characterization to validate the design. During the production of these structures, plasma etching of SiC has been optimized in an ICP reactor so as to obtain a high etching rate and maintaining an electronic quality of the state of etched surfaces. This quality is confirmed by the results of characterization obtained with blocking voltage close to the ideal one
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VIELZA, DE LA CRUZ Yoandris. "Evolução da superfície de Fermi do La2-xSrxCuO4: estados locais de Wannier/Hartree-Fock." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/18562.
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Este trabalho é uma extensão de uma modelagem tight−binding de estados de Wannier com interação coulombiana de screening para a descrição de elétrons correlacionados nas camadas de CuO2 do La2CuO4. Na condição de banda semicheia e temperatura T = 0 K, esta modelagem é capaz de predizer um estado fundamental antiferromagnético isolante e um estado excitado paramagnético com pseudo-gap, cuja natureza ainda é debatido na literatura. Esses estados são obtidos no contexto de uma solução auto-consistente tipo Hartree-Fock na modelagem de uma banda efetiva de estados de Wannier, sob condições de quebra de simetria de translações espaciais e efeito de emaranhamento (entanglement) na estrutura espinorial dos estados eletrônicos. No regime dopado com buracos, esses estados ficam degenerados num ponto crítico de concentração de buracos igual a xc = 0.2, resultando em uma transição de fase quântica de segunda ordem para um estado paramagnético. A modelagem dá assim explicação à existência detectada experimentalmente desta transição de fase. Em nosso trabalho generalizamos o termo cinético da modelagem acima mencionada através da inclusão de hopping entre segundos vizinhos, de acordo com observações experimentais. De fato, a inclusão deste novo termo cinético resulta em melhor concordância da previsão da modelagem e as observações experimentais da evolução da superfície de Fermi com dopagem de buracos. Em particular, enquanto na modelagem restrita a primeiros vizinhos não podemos conciliar a transição de fase quântica observada a xc = 0.2 com as características experimentais da evolução da superfície de Fermi, isto torna-se possível com a inclusão do hopping de segundos vizinhos com amplitude sugerida pelos resultados experimentais.
This work is an extension of a tight - binding model of states of Wannier with screened Coulomb interaction to the description of correlated electrons in the layers of CuO2 of the La2CuO4. In condition of half-filled band and temperature T = 0 K, this model is able to predict a antiferromagnetic insulating ground state and a paramagnetic excited state with pseudo-gap, which nature is still debated in the literature. These states are obtained in the context of a self-consistent solution type Hartree-Fock in the model of an effective band of the Wannier states under breaking conditions of symmetry of space translations and entanglement effect in the spinor structure of the electronic states. In scheme doped with holes, these states are degenerate at critical point of hole concentration equal to xc = 0.2, resulting in a quantum phase transition of second order to paramagnetic state. The model thus gives explanation to the existence of this experimentally detected phase transition. In our work we generalize the kinetic term of above mentioned model by inclusion of hopping between seconds neighboring, according to experimental observations. In fact, the inclusion of this new kinetic term results in better agreement of the forecast of the model and experimental observations of the evolution of the Fermi surface with holes doping. In particular, while the model is restricted to the first neighbors can not reconcile quantum phase transition observed at xc = 0.2 with the experimental characteristics of the evolution of the Fermi surface, this becomes possible with the inclusion of hopping between second neighboring with ampliude suggested by experimental results.
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Delille, Gauthier Marc Aimé. "Contribution du Stockage à la Gestion Avancée des Systèmes Électriques : approches Organisationnelles et Technico-économiques dans les Réseaux de Distribution." Phd thesis, Ecole Centrale de Lille, 2010. http://tel.archives-ouvertes.fr/tel-00586088.
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Des solutions innovantes doivent être développées pour envisager l'avenir des systèmes électriques face à un nombre grandissant de contraintes. En particulier, le stockage d'énergie est pressenti comme un soutien indispensable à l'essor massif dans les réseaux de distribution de sources de production exploitant les énergies renouvelables. Les présents travaux visent à apporter des éléments de réflexion sur cette option technique qui arrive à maturité et suscite l'intérêt. Dans un premier temps, des méthodes d'étude sont proposées pour cerner le potentiel et les opportunités du stockage distribué. Une grille de caractérisation des technologies est introduite et sa mise en œuvre souligne des performances intéressantes à des coûts qui, cependant, demeurent élevés. Pour rendre leur utilisation réaliste, la valeur de ces dispositifs pour les systèmes électriques est donc critique. Nous l'analysons en deux étapes : une classification de leurs services pour les différents acteurs en présence est définie avant d'aborder la mutualisation de fonctions, requise pour favoriser l'atteinte d'une rentabilité, via une approche originale. Cette démarche aboutit à l'identification de configurations porteuses qui méritent des études plus poussées. Pour ce faire, un modèle général de comportement des unités de stockage est développé dans un second temps. Interfacé à un logiciel de simulation dynamique des réseaux, il permet d'évaluer l'utilisation de telles installations pour diverses offres de services. Ces outils sont appliqués et validés expérimentalement sur la caractérisation d'une réserve impulsionnelle fournie par le stockage pour réduire les délestages dans les systèmes insulaires
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Rahim, Abdur. "Efeito Hall de spin em nanoestruturas semicondutoras: rumo à novos dispositivos de spintrônica." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-12072015-080251/.
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Este trabalho apresenta as propriedades de transporte eletrônico de isolantes topológicos bidimensionais (TI) baseados em poços quânticos de HgTe/CdTe. Estas heteroestruturas, no regime de bandas invertido, contem um novo estado conhecido como isolante de spin Hall quântico (QSHI). Este estado apresenta um comportamento de isolante no corpo (bulk), mas exibe estados condutores sem lacunas nas bordas (edges), as quais podem ser verificadas em medidas de transporte. Medidas de resistência de quatro terminais foram observadas perto do valor quantizado em amostras mesoscópicas. No entanto, para amostras com mais de um m, a resistência pode ser muito maiores que h/2e2 devido à presença de defasagem de spin, não homogeneidade ou desordem na amostra. Esta tese aborda o problema da resistência não quantizado observada em amostras macroscópicas de dimensões maiores a algum mícron. Nós relatamos observação e investigação sistemática de transporte local e não local em poços quânticos de HgTe (8.0-8.3 nm) com estrutura de banda invertida correspondente à fase de isolante de spin Hall quântico. O dispositivo MCT1 consiste de três segmentos consecutivos de largura 4 m e de comprimentos diferentes (2 m, 8 m, 32 m), e sete sondas de tensão. O dispositivo MCT2 foi fabricado com um comprimento litográfico de 6 m e largura 5 m. Ambos dispositivos estão equipados com uma porta superior (top gate), que permite ajustar a densidade de portadores do dispositivo. A aplicação de uma tensão de porta muda a densidade de portadores, transformando a condutividade do poço quântico de tipo n para tipo p através de uma fase intermediária chamada de ponto a neutralidade de carga (CNP). Picos acentuados não universais (R >> h/2e2) em ambas as resistividades, local e não local, foram observados próximos ao CNP os quais diminuem rapidamente a medida que se afasta do CNP. Tal comportamento próximo ao CNP pode ser explicado usando o modelo de transporte de bordas (edge) e corpo (bulk), que inclui tanto os estados de borda como o corpo para a contribuição à corrente. O desvio dos valores da resistência de quarto terminais do valor quantizado (R >> h/2e2) em amostras macroscópicas com dimensões acima de algum mícron é um dos principais problemas no campo dos isolantes topológicos. Recentemente foi proposto um modelo por Vayrynen et al., onde tem sido considerado a influência de poças de carga, resultantes de distribuições de carga não homogêneas em isolantes topológicos 2d, na condutância de estados de borda helicoidal. Os estados de borda são acoplados por tunelamento a essas poças metálicas ou pontos quânticos. A permanência dos elétrons em pontos quânticos pode levar a um retroespalhamento inelástico significativo dentro da borda e modifica o transporte balístico. Portanto transporte balístico coerente é esperado somente na região entre poças, e o total de resistência de quatro terminais excede o valor quantizado. Introduzindo as interações elétron-elétron em sistemas de uma dimensão resulta em um liquido de Luttinger (LL). Os estados de borda helicoidais em isolantes topológicos 2d, podem ser tratados como um líquido de Luttinger ideal, uma vez que, naturalmente, aparecem em poços quânticos de HgTe. Entre as várias assinaturas específicas do comportamento do LL, como a dependência da temperatura, é importante se concentrar nas propriedades de não equilíbrio do LL. Em contraste com os líquidos de Fermi convencionais, nenhum estado excitado decairá ao estado de equilíbrio, caracterizado pela temperatura, na ausência de desordem. Medidas de elétron-aquecimento podem ser usadas para entender a física que governa os processos de relaxamento em LL. Nós temos realizado medidas de transporte não linear no CNP em isolantes topológicos 2d de HgTe. Este método, juntamente com a dependência da resistência com a temperatura, pode ser utilizado para determinar o mecanismo de relaxação da energia dos estados de borda helicoidais em QSHI. Nosso experimento falhou em confirmar as assinaturas especificas do comportamento do líquido de Luttinger. No entanto, o efeito de aquecimento de elétron pode ser descrito pelo mecanismo convencional de relaxamento de energia, esperado para espalhamento elétron-fônon.This thesis present electronic transport properties of two-dimensional topological insulators (TI) based on HgTe/CdTe quantum wells. These heterostructures, in the band inverted regime, hosts a novel state known as the quantum spin Hall insulator. This state is identified as insulator in the bulk, but exhibits gapless conducting states at their edges which can be verified in transport experiments. Four-terminal resistance close to the quantized value has been observed in mesoscopic samples. However, for samples longer than 1 m, the resistance might be much higher than h/2e2 due to the presence of spin dephasing, inhomogeneity or disorder in the sample. This thesis address the problem of non-quantized resistance observed in macroscopic samples of dimensions longer than few microns. We report on the observation and a systematic investigation of local and nonlocal transport in HgTe quantum wells (8.0-8.3 nm) with inverted band structure corresponding to the quantum spin Hall insulating (QSHI) phase. The device MCT1 consists of three 4 m wide consecutive segments of different length (2 m, 8 m, 32 m), and seven voltage probes. The device MCT2 was fabricated with a lithographic length 6 m and width 5 m. Both devices are equipped with a top gate which allows tuning the carrier density of the device. Applying gate bias changes the carrier density transforming the quantum well conductivity from n-type to p-type via an intermediate phase, called the charge neutrality point (CNP). Non-universal (R >> h/2e2) peaks in both local and nonlocal resistivity were observed near the CNP which decreases rapidly going away from CNP. Such a behavior near CNP can be explained using the edge plus bulk transport model, which includes both the edge states and bulk contribution to the total current. Deviation of the four-terminal resistance from quantization (R >> h/2e2) in macroscopic samples, with dimensions above a few microns, is one of the major issue in the field of topological insulators. Recently a model was proposed by Vayrynen et al., where influence of charge puddles, resulting from inhomogeneous charge distribution in 2d topological insulators, on its helical edge conductance has been considered. The edge states are tunnel coupled to these metallic puddles or quantum dots. Electron´s dwelling in the quantum dot may lead to significant inelastic backscattering within the edge and modifies the ballistic transport. Therefore ballistic coherent transport is expected only in the region between the puddles, and the total four-terminal resistance exceeds the quantized value. Introducing electron-electron interactions in one-dimensional systems results in a Luttinger liquid (LL). The helical edge states in 2d topological insulator, can be treated as ideal Luttinger liquid, since it naturally appears in HgTe quantum wells. Among the various specific signatures of the LL behavior, such as temperature dependence, it is important to focus on non-equilibrium properties of LL. In contrast to conventional Fermi liquids, none of the excited state will decay to equilibrium state, characterized by temperature, in the absence of disorder. Electron-heating measurements can be used to understand the physics governing relaxation processes in LL. We have performed non-linear transport measurements at the CNP in HgTe based 2d topological insulators. This method together with temperature dependence of resistance can be used to determine the energy relaxation mechanism of the helical edge modes in QSHI. Our experiments fail to confirm the specific signatures of Luttinger liquid behavior. However, electron heating effect can be described by conventional energy relaxation mechanism, expected for electron-phonon interactions.
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Yu, Defen. "Study of electric discharge and space charge formation phenomena in the air gaps of an ice-covered insulator using an icicle/ice-covered plate electrode system = Étude des processus des décharges électriques et formation de charges d'espace dans les intervalles d'air d'un isolateur recouvert de glace à l'aide d'une configuration d'électrodes glaçon/plaque recouverte de glace /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2007. http://theses.uqac.ca.
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Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2007.La p. de t. porte en outre: Thèse présentée à l'Université du Québec à Chicoutimi comme exigence partielle du doctorat en ingénierie. CaQQUQ Bibliogr.: f. 222-239. Document électronique également accessible en format PDF. CaQQUQ