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Ricardo Lopes De Queiroz - One of the best experts on this subject based on the ideXlab platform.
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Sistemas de multiresolução para extração de redundancias e transmissão progressiva na codificação de imagens
[s.n.], 2018Co-Authors: Ricardo Lopes De QueirozAbstract:Orientador: João Baptista Tadanobu Yabu-UtiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia EletricaResumo: Este trabalho visa o desenvolvimento de técnicas que explorem múltiplas resoluções de uma imagem para sua codificação. Baseando-nos em técnicas de interpolação e codificação piramidal, foram estudados procedimentos para formação de pirâmides sem prefiltragem. Estas ferramentas serviram de base para a elaboração do DPCM em pirâmide que combina várias taxas de amostragem ao DPCM convencional, formando um sistema híbrido extra-interpolativo. Este novo sistema pode reduzir ainda mais a complexidade do DPCM, sendo mais flexível e eficiente. Além disto, métodos de codificação para transmissão progressiva foram abordados, motivando o desenvolvimento da Pirâmide Quincunx sem Prefiltragem e de um método bastante eficiente para tal, que utiliza a Lapped Orthogonal Transform em combinação com estratégias de transmissão seqüencial de coeficientes e planos-de-bitAbstract: This work is concerned about the development of techniques to explore multiple resolutions in image coding. Based on the knowledge of interpolation techniques, as well as Pyramid coding strategies, non-prefiltered Pyramids were studied. These tools were the base to develop the Pyramid DPCM. a scheme that combines multirat.e processing and regular DPCM, resulting in a hybrid extra-interpolative system. This new approach can raduce DPCM's complexity, and still be more efficient. Furthermore, new coding strategies for progressiva transmission were discussed through the development of the Non-prefiItered Quincunx Pyramid and by the efficient use of the Lapped Orthogonal Transform combined with sequential schemes for transmitting coefficients and bit-planesMestradoMestre em Engenharia Elétric
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Sistemas de multiresolução para extração de redundancias e transmissão progressiva na codificação de imagens
2014Co-Authors: Ricardo Lopes De QueirozAbstract:Resumo: Este trabalho visa o desenvolvimento de técnicas que explorem múltiplas resoluções de uma imagem para sua codificação. Baseando-nos em técnicas de interpolação e codificação piramidal, foram estudados procedimentos para formação de pirâmides sem prefiltragem. Estas ferramentas serviram de base para a elaboração do DPCM em pirâmide que combina várias taxas de amostragem ao DPCM convencional, formando um sistema híbrido extra-interpolativo. Este novo sistema pode reduzir ainda mais a complexidade do DPCM, sendo mais flexível e eficiente. Além disto, métodos de codificação para transmissão progressiva foram abordados, motivando o desenvolvimento da Pirâmide Quincunx sem Prefiltragem e de um método bastante eficiente para tal, que utiliza a Lapped Orthogonal Transform em combinação com estratégias de transmissão seqüencial de coeficientes e planos-de-bitAbstract: This work is concerned about the development of techniques to explore multiple resolutions in image coding. Based on the knowledge of interpolation techniques, as well as Pyramid coding strategies, non-prefiltered Pyramids were studied. These tools were the base to develop the Pyramid DPCM. a scheme that combines multirat.e processing and regular DPCM, resulting in a hybrid extra-interpolative system. This new approach can raduce DPCM's complexity, and still be more efficient. Furthermore, new coding strategies for progressiva transmission were discussed through the development of the Non-prefiItered Quincunx Pyramid and by the efficient use of the Lapped Orthogonal Transform combined with sequential schemes for transmitting coefficients and bit-plane
Thomas Mueller - One of the best experts on this subject based on the ideXlab platform.
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influence of random Pyramid surface texture on silver screen printed contact formation for monocrystalline silicon wafer solar cells
Solar Energy Materials and Solar Cells, 2015Co-Authors: Ankit Khanna, Prabir Kanti Basu, Aleksander Filipovic, Vinodh Shanmugam, Christian Schmiga, Armin G Aberle, Thomas MuellerAbstract:Abstract Most industrial monocrystalline silicon wafer (mono-Si) solar cells are metallised by screen printing. Silver (Ag) pastes are commonly used to form electrodes to phosphorus-doped n+ Si. However, there is still ambiguity about the influence of the random-Pyramid surface texture on Ag screen-printed contacts for mono-Si solar cells. We present an experimental study to investigate this influence using screen-printed p-type mono-Si cell groups fabricated with a controlled variation in the alkaline surface texturisation process. It is observed that cell groups fabricated on Czochralski (Cz) wafers with smaller Pyramids achieve higher average fill factor (FF) and lower average specific contact resistance than cell groups fabricated on Cz wafers with larger Pyramids. To explain these observations, the Pyramid texture height distributions are characterised statistically and the distribution statistics are correlated to electrical solar cell measurements and microstructure investigations of the Ag/n+ Si contact interface. Microstructure investigations reveal that most Ag crystallite growth is concentrated around the upper part of the Pyramids and hence Pyramid density is identified as an important parameter influencing contact formation. The influence of average Pyramid height and Pyramid height uniformity within a Pyramid texture height distribution is also clarified with regards to contact formation. It is further observed that direct Ag crystallite contacts to the bulk Ag metallisation are not a prerequisite for achieving high FF (>80%). Based on the study, guidelines are developed for tailoring random-Pyramid surface textures to optimise Ag screen-printed contact formation to n+ Si for mono-Si solar cells.
Lining He - One of the best experts on this subject based on the ideXlab platform.
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high efficiency si polymer hybrid solar cells based on synergistic surface texturing of si nanowires on Pyramids
Small, 2012Co-Authors: Hao Wang, Lining He, Changyun JiangAbstract:An efficient Si/PEDOT:PSS hybrid solar cell using synergistic surface texturing of Si nanowires (SiNWs) on Pyramids is demonstrated. A power conversion efficiency (PCE) of 9.9% is achieved from the cells using the SiNW/Pyramid binary structure, which is much higher than similar cells based on planar Si, Pyramid-textured Si, and SiNWs. The PCE is the highest reported to-date for hybrid cells based on Si nanostructures and PEDOT.
Gunnar Schubert - One of the best experts on this subject based on the ideXlab platform.
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influence of surface topography on the glass coverage in the contact formation of silver screen printed si solar cells
IEEE Journal of Photovoltaics, 2013Co-Authors: Enrique Cabrera, Sara Olibet, Dominik Rudolph, Radovan Kopecek, Daniel Reinke, Eckard Wefringhaus, Gunnar SchubertAbstract:For screen-printed Ag-paste metallization, the growth of Ag crystallites into Si is essential for the current conduction from the Si emitter to the silver finger. There are strong indications that for low contact resistances, some of these Ag crystallites need to be in direct contact with the silver finger without a separating glass layer in between. In this paper, we concentrate on the origin of Ag crystallites grown into Si in direct contact with the silver finger. On textured surfaces, we vary the Si Pyramid sizes, round the Pyramid tips to varying degrees, and fabricate flat smooth surfaces. We observe that the size of the Pyramids does not play an important role in the achievement of low specific contact resistivity unless the Pyramid heights become smaller than the thickness of the glass layer, but rounding of the Pyramid tips with standard heights increases specific contact resistivity significantly. From our microscopic investigations, we conclude that the largest influence on the topography-dependent contact resistance comes from the glass coverage governing the amount of Ag crystallites directly connected with the silver finger bulk. Furthermore, Ag crystallites in direct contact with the silver finger are also observed on c-Si without n+ emitter doping.
Devendra K Sadana - One of the best experts on this subject based on the ideXlab platform.
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surface texturing of single crystalline silicon solar cells using low density sio2 films as an anisotropic etch mask
Solar Energy Materials and Solar Cells, 2010Co-Authors: Jeehwan Kim, Daniel Inns, Keith E Fogel, Devendra K SadanaAbstract:Abstract Solar cells require surface texturing in order to reduce light reflectance, and to enhance light trapping. Anisotropic wet chemical etching is commonly used to form Pyramids on the (1 0 0) silicon wafer surface by etching back to the (1 1 1) planes. In this paper, we used a low density silicon dioxide layer to allow etching in localized regions as an etch mask, forming inverted Pyramid etch pits. Such an oxide can be deposited by plasma enhanced chemical vapor deposition using low deposition temperatures. The inverted Pyramids are ideal for reducing surface reflectance, and are used in the highest efficiency silicon solar cells. Depending on the etch time and oxide quality, a variety of surface texture morphologies can be achieved. Due to the oxide mask, very little silicon is removed. This is an economical ideal method for texturing thin film single-crystalline silicon solar cells, as it combines the benefits of low reflectance with minimal thickness removed, while no photolithography is employed.
