abstract: Silicon photovoltaics (PV) is approaching its theoretical efficiency limit as a single-junction technology. To break this limit and further lower the PV-generated levelized cost of electricity, it is necessary to engineer a silicon-based “tandem” technology in which a solar cell of another material is stacked on top of silicon to make more efficient use of the full solar spectrum. This dissertation understands and develops four aspects of silicon-based tandem PV technology. First, a new “spectral efficiency” concept is proposed to understand how tandem cells should be designed and to identify the best tandem partners for silicon cells. Using spectral efficiency, a top-cell-design guide is constructed for silicon-based tandems that sets efficiency targets for top cells with various bandgaps to achieve targeted tandem efficiencies. Second, silicon heterojunction solar cells are tuned to the near-infrared spectrum to enable world-record perovskite/silicon tandems both in two- and four-terminal configurations. In particular, for the 23.6%-efficient two-terminal tandem, a single-side textured silicon bottom cell is fabricated with a low-refractive-index silicon nanoparticle layer as a rear reflector. This design boosts the current density to 18.5 mA/cm2; this value exceeds that of any other silicon bottom cell and matches that of the top cell. Third, “PVMirrors” are proposed as a novel tandem architecture to integrate silicon cells with various top cells. A strength of the design is that the PVMirror collects diffuse light as a concentrating technology. With this concept, a gallium-arsenide/silicon PVMirror tandem is demonstrated with an outdoor efficiency of 29.6%, with respect to the global irradiance. Finally, a simple and versatile analytical model is constructed to evaluate the cost competitiveness of an arbitrary tandem against its sub-cell alternatives. It indicates that tandems will become increasingly attractive in the market, as the ratio of sub-cell module cost to area-related balance-of-system cost—the key metric that will determine the market success or failure of tandems—is decreasing. As an evolution of silicon technology, silicon-based tandems are the future of PV. They will allow more people to have access to clean energy at ultra-low cost. This thesis defines both the technological and economic landscape of silicon-based tandems, and makes important contributions to this tandem future. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018

Made available in DSpace on 2014-06-12T18:03:38Z (GMT). No. of bitstreams: 2 arquivo3714_1.pdf: 874379 bytes, checksum: 1a27595bb5f2f12e52d96545dd1b301b (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A definição das taxas de mutação dos locos de microssatélites ou Short Tandem Repeats (STRs) usados em análises forenses são úteis para a correta interpretação dos resultados dos perfis genéticos e para a definição dos critérios de exclusão em testes de paternidade. Mutações da linhagem germinativa de 14 locos de STRs foram estudadas através das análises de 54.105 transferências alélicas genitorcriança a partir de 2.575 casos de testes de paternidade realizados durante 2000- 2007 na população de Pernambuco, Nordeste do Brasil. O parentesco, em cada um desses casos, foi altamente validado (probabilidade > 99.99%). Foram identificadas 43 mutações em 12 locos. As taxas de mutação específicas para cada loco variaram entre 2 x 10-4 e 2 x 10-3, e a taxa de mutação total foi estimada em 8 x 10-4. Eventos de mutação na linhagem germinativa masculina foram mais freqüentes do que na feminina. A maioria das mutações (95%) pode ser explicada pela perda ou ganho de uma unidade repetitiva e não houve evidência para seleção entre mutações de adição ou deleção. Nossos dados foram comparados aos dados referentes a populações americanas e européias e demonstraram que as taxas de mutação dos locos de STRs não diferem entre as diferentes populações

The ever-worsening environmental crisis has stimulated development of less wasteful “green” technologies. To this end, tandem catalysis enables multiple catalytic cycles to be performed within a single reaction vessel, thereby eliminating intermediate processing steps and reducing solvent waste. Assisted tandem catalysis employs suitable chemical triggers to transform the initial catalyst into new species, thereby providing a mechanism for “switching on” secondary catalytic activity. This thesis demonstrates the importance of highly productive secondary catalysts through a comparative hydrogenation study involving prominent hydrogenation catalysts of tandem ring-opening metathesis polymerization (ROMP)-hydrogenation, of which hydridocarbonyl species were proved superior. This thesis illuminates optimal routes to hydridocarbonyls under conditions relevant to our ROMP-hydrogenation protocol, using Grubbs benzylidenes as isolable proxies for ROMP-propagating alkylidene species. Analogous studies of ruthenium methylidenes and ethoxylidenes illuminate optimal routes to hydridocarbonyls following ring-closing metathesis (RCM) and metathesis quenching, respectively. The formation of unexpected side products using aggressive chemical triggers is also discussed, and emphasizes the need for cautious design of the post-metathesis trigger phase.

La compréhension de la dynamique des réarrangements génomiques est une problématique importante en phylogénie.La phylogénie est l'étude de l'évolution des espèces. Un but majeur est d'établir les relations d'évolution au sein d'un groupe d'espèces, pour déterminer la topologie de l'arbre d'évolution formé par ce groupe et des ancêtres communs à certains sous-ensembles.Pour ce faire, il est naturellement très utile de disposer d'un moyen d'évaluer les distances évolutionnaires relatives entre des espèces, ou encore d'être capable d'inférer à un groupe d'espèces le génome d'un ancêtre commun à celles-ci.Ce travail de thèse, dans la lignée d'autres travaux, consiste à élaborer de tels moyens, ici dans des cas particuliers où les génomes possèdent des gènes en multiples copies, ce qui complique les choses.Plusieurs hypothèse explicatives de la présence de duplications ont été considérées, des formules de distance ainsi que des algorithmes de calcul de scénarios ont été élaborés, accompagnés de preuves de complexité. / Understanding the dynamics of genome rearrangements is a major issue of phylogenetics. Phylogenetics is the study of species evolution. A major goal of the field is to establish evolutionary relationships within groups of species, in order to infer the topology of an evolutionary tree formed by this group and common ancestors to some of these species. In this context, having means to evaluate relative evolutionary distances between species, or to infer common ancestor genomes to a group of species would be of great help.This work, in the vein of other studies from the past, aims at designing such means, here in the particular case where genomes present multiple occurrencies of genes, which makes things more complex. Several hypotheses accounting for the presence of duplications were considered. Distances formulae as well as scenario computing algorithms were established, along with their complexity proofs.

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With the rapid increase in energy demand and the rise of CO2 levels due to traditional energy production from fossil fuels, it is critical to the transition to a sustainable and renewable energy sources. Recently, photovoltaic technology has been raised as a promising alternative to fossil fuel energy production. Solar cells, predominately crystalline silicon technology, are currently 3.6% of electricity production. To maintain this progress, coupling the perovskite and silicon in tandem devices has enormous potential to increase the efficiency of solar energy production, where perovskite solar cells emerged as a promising technology. Textured silicon solar cells are a well-established technology; keeping the advantage of this technology, it is crucial to employ the perovskite to be a compatible top cell for silicon-based tandems. Here, we optimize the silicon bottom cell by understanding the influence of temperature, time, and etchant concentration on the optical properties and performance of the device. Then, we investigate the impact of the textured silicon on the optoelectronic properties of perovskite. Using hyperspectral imaging, we demonstrate that different texturing substrates influence the PL of perovskite, which is associated with the thickness of the perovskite. Lastly, we explored the delamination of the devices due to the weak adhesion between C60/SnO2 after the deposition of IZO and MgF2, which was found to be caused by the deposition conditions. The high temperature and power density caused a weak adhesion between C60/SnO2. Overall, these findings will help to alter the design of Perovskite/Silicon tandem devices to accelerate the commercialization of tandem technology.

One-dimensional vertical nanostructures, nanowire arrays, are investigated for applications in photovoltaics. Specifically, III-V core-shell p-i-n nanowire arrays are grown by molecular beam epitaxy on silicon substrates, using the self-assisted vapour-liquid-solid growth method. GaAs1-xPx nanowires are grown with an optimized composition to maximize the potential efficiency of a GaAsP nanowire-on-silicon tandem solar cell under AM1.5G illumination. Photovoltaic devices are fabricated and assessed by optical and electrical characterization techniques, to identify areas for refinement of device design and processing. Combining the unique properties of nanowire arrays, the quality and tunability of III-V materials, and the economics and infrastructure of silicon-based device fabrication, this work examines a novel approach to affordable renewable energy. Methods of substrate removal via etching are investigated for optical characterization of nanowire arrays, and an improved technique for electrical characterization of ITO contacts is explored. The first nanowire-on-silicon tandem device utilizing a radial p-n junction nanowire structure is reported, achieving an open circuit voltage of 1.2 V, a short circuit current density of 7.6 mA/cm2, a fill factor of 40%, and an efficiency of 3.5%. Finally, projects for future improvements to the work described herein are suggested. / Thesis / Master of Applied Science (MASc)

Axial ventilation fans are used to improve the air quality, remove contaminants, and to control the temperature and humidity in occupied areas. Ventilation fans are one of the most harmful sources of noise due to their close proximity to occupied areas and widespread use. The prolonged exposure to hazardous noise levels can lead to noise-induced hearing loss. Consequently, there is a critical need to reduce noise levels from ventilation fans. Since fan noise scales with the 4-6th power of the fan tip speed, minimizing the fan tip speed and optimizing the duct geometry are effective methods to reduce fan noise. However, there is a tradeoff between reducing fan speed, noise and aerodynamic efficiency. To this end, a new innovative comprehensive optimum design methodology considering both aerodynamic efficiency and noise was formulated and implemented using a multi-objective genetic algorithm. The methodology incorporates a control vortex design approach that results in a spanwise chord and twist distribution of the blades that maximize the volumetric flow rate contribution of the outer radii, i.e. the axial flow velocity increases from the fan hub to the tip. The resulting blade geometry generates a given volumetric flow rate at the minimum fan tip speed. The fan design is complemented by the design of the optimum inlet duct geometry to maximize volumetric flow rate and minimize BL thickness for low noise generation. Good agreement with experimental results validates the design process. The present study also incorporates multi-element airfoils to further increase the aerodynamic characteristics of the fan blades and enable lower fan speeds and noise. Good agreement between experiments and predictions indicate that traditional blade element momentum methods can be implemented in conjunction with multi-element airfoil aerodynamic characteristics with good accuracy. A direct comparison of fans designed with single and multi-element airfoils has shown that fans designed with multi-element airfoils aerodynamically outperform single element fans. / Doctor of Philosophy / Axial ventilation fans are widely used to improve the air quality, remove contaminants, and to control the temperature and humidity in occupied areas. However, high noise levels from ventilations fans are a harmful source of noise that can lead to irreversible noise-induced hearing loss. Therefore, this work addresses a critical need for quiet and efficient ventilation fans. To this end, a new innovative comprehensive optimum design methodology considering both aerodynamic efficiency and noise was formulated, implemented, and tested. The methodology optimizes the fan geometry to maximize the volumetric flow rate and minimize noise. The fan design is complemented by the design of the optimum inlet duct geometry to increase the volumetric flow rate and minimize BL thickness for low noise generation. Good agreement with experimental results validates the design process. The present study also incorporates multi-element airfoils to further increase the aerodynamic characteristics of the fan blades. A direct comparison of fans designed with single and multi-element airfoils has shown that fans designed with multi-element airfoils aerodynamically outperform single element airfoil fans.

Au cours des dernières décennies, les avancées techniques dans la biologie moléculaire telles que les projets de séquençage de génome ont eu pour conséquence un accroissement du volume des banques de données biologiques. Parmi ces données, des séquences présentent des motifs similaires entre eux, répétés de façon juxtaposée, appelés répétitions en tandem. L'objectif de cette thèse est de comprendre l'existence de ces répétitions dans les séquences protéiques via une analyse à grande échelle. / Over the last decades, technical advances in molecular biology such as the genome sequencing projects led to a huge increase of data in the biological databanks. Among them, there are particular motifs which are adjacently repeated and similar between them, called tandem repeats. The purpose of this thesis is to understand the existence of these repeats in protein sequences through a large-scale analysis.

Devido as frequentes dúvidas dos usuários das câmaras de ionização do tipo lápis calibradas no Laboratório de Calibração de Instrumentos do IPEN (LCI IPEN), em como aplicar corretamente os fatores indicados em seus certificados de calibração, foi elaborado um guia orientativo para dosimetria em tomografia computadorizada. O guia orientativo inclui o conhecimento prévio da Camada Semirredutora (CSR), já que é necessário conhecer a energia efetiva do feixe para aplicação do fator de correção para qualidade (kq). A avaliação da CSR em tomógrafos torna-se uma difícil tarefa devido à geometria do sistema e por essa razão foi realizado um levantamento das metodologias existentes para a determinação da CSR em feixes clínicos de Tomografia Computadorizada (TC), levando em consideração fatores técnicos, práticos e econômicos. Neste trabalho, optou-se em testar um Sistema Tandem composto por capas absorvedoras confeccionado na oficina do IPEN, baseado em estudos preliminares devido ao baixo custo e boa reposta. O Sistema Tandem é composto por 5 capas absorvedoras cilíndricas de 1 mm, 3 mm, 5 mm, 7 mm, e 10 mm de alumínio e por 3 capas absorvedoras cilíndricas de 15 mm, 25 mm e 35 mm de acrílico (PMMA) acopladas à câmara de ionização do tipo lápis comercial amplamente utilizada em testes de controle de qualidade na dosimetria em feixes clínicos de Tomografia Computadorizada. Através das curvas Tandem, foi possível avaliar os valores de CSR e, através da curva de calibração da câmara de ionização do tipo lápis, encontrar o Kq adequado ao feixe. O Guia elaborado traz informações de como construir a curva de calibração em função da CSR, para encontrar o Kq, bem como informações para construção da curva Tandem, para encontrar valores próximos de CSR. / Due to frequent questions from users of ionization chambers pencil type calibrated in the Instrument Calibration Laboratory of the Institute of Energy and Nuclear Research (LCI - IPEN), on how to properly apply the factors indicated in their calibration certificates, a guide was prepared guidance for dosimetry in computed tomography. The guide includes guidance prior knowledge of half value layer (HVL), as it is necessary to know the effective beam energy for application quality for correction factor (kq). The evaluation of HVL in TC scanners becomes a difficult task due to system geometry and therefore a survey was conducted of existing methodologies for the determination of HVL in clinical beams Computed Tomography, taking into account technical, practical and economic factors. In this work it was decided to test a Tandem System consists of absorbing covers made in the workshop of IPEN, based on preliminary studies due to low cost and good response. The Tandem system consists of five cylindrical absorbing layers of 1mm, 3mm, 5mm, 7mm and 10mm aluminum and 3 cylindrical absorbing covers 15mm, 25mm and acrylic 35mm (PMMA) coupled to the ionization chamber of commercial pencil type widely used in quality control tests in dosimetry in clinical beams Computed tomography. Through Tandem curves it was possible to assess HVL values and from the standard curve pencil-type ionization chamber, Kq find the appropriate beam. The elaborate Guide provides information on how to build the calibration curve on the basis of CSR, to find the Kq and information for construction Tandem curve, to find values close to CSR.