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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

A numerical investigation of hot spotting origin of ventilated disc brakes

Tang, Jinghan, Bryant, David, Qi, Hong Sheng January 2015 (has links)
no / Hot spots are high thermal gradients on the disc surface during brake events which can cause the undesired phenomena of thermal judder and drone. The origin of hot spotting has been presented by various theories such as Thermo elastic instability (TEI) and progressive waviness distortions (PWD). However, majority of the numerical models based on these theories mainly concentrated on solid disc rather than ventilated disc which is the most commonly used nowadays. According to the experimental work done by the authors, disc geometry factors such as vents and pins also have correlations with hot spot distribution; these phenomena are difficult to be predicted analytically. Thus a convenient 2D asymmetric finite element simulation has been performed in order to obtain the correlations observed in experiments. Further parameter studies investigated factors such as uneven initial temperature, vents, pins and pad length. The results have been correlated with the experimental data and demonstrate the contribution of geometric factors in the generation of hot spots and hot judder.
42

Caractérisation des hot spots de réactivité biogéochimique dans les eaux souterraines / Characterization of biogeochemical reactivity hot spots in groundwater

Bochet, Olivier 08 December 2017 (has links)
Les processus microbiens ont une importance déterminante dans la dynamique des processus réactifs dans les eaux souterraines. La compréhension de la variabilité spatiale et temporelle de ces phénomènes, et le développement de méthodes expérimentales de terrain, ouvrent de nouveaux champs de recherches et d'applications allant de la remédiation des aquifères contaminés à la compréhension des grands cycles biogéochimiques naturels. Dans le premier volet de cette thèse nous présentons des observations de terrain permettant de comprendre le rôle des fractures sur la formation d'un ''hotspot'' d'activité microbienne en profondeur. Du fait de leur forte réactivité, ces ''hotspots'' peuvent dominer la dynamique biogéochimique des milieux souterrains, malgré leur faible extension spatiale. Nous avons ainsi analyser les conditions de formation d'un tapis microbien par des bactéries ferro-oxydantes à 60 mètres de profondeur sur l'observatoire de Ploemeur (réseau H+) alors que ces phénomènes ont été observé jusqu'à présent en surface. Les résultats de cette étude montrent que des circulations hétérogènes, liées à la structure des milieux fracturés, créent des zones mélanges entre des eaux riches en fer et des eaux oxygénées, à l'origine de ce hotspot microbien. Le deuxième volet de ce travail de thèse a été consacré au développement d'une méthode innovante pour la mesure en continu de l'activité microbienne dans les eaux souterraines. La méthode est basée sur l'utilisation de la Fluoréscéine DiAcétate (FDA) dont le produit de réaction peut être mesuré en continu par un fluorimètre de terrain. Après avoir testé et validé les protocoles sur des solutions enzymatiques et des eaux naturelles en laboratoire, nous avons mis en œuvre cette technique sur le terrain au cours d'expériences de traçages réactifs. Un modèle cinétique nous a permis d'approcher les résultats obtenus en laboratoire, et de comparer nos résultats de terrain aux calibrations effectuées in vitro. Cette méthode ouvre ainsi de nouvelles perspectives pour la caractérisation des processus biogéochimiques sur le terrain. / Microbial processes play a key role in controlling biogeochemical reactivity in groundwater. The understanding of the spatial and temporal variability of these phenomena and the development of novel experimental field methods, has opened new fields of research and applications, ranging from groundwater remediation to understanding of global biochemical cycles. In the first part of this thesis, we present field observations providing new insights on the role of fractures in the formation of a hotspot of microbial activity. Because of their large reactivity, these hotspots can dominate the biogeochemical dynamics of subsurface systems, despite their small spatial extent. We have thus analyzed the conditions for the formation of a microbial mat composed of iron-oxidizing bacteria at 60 meters depth in the Ploemeur fractured rock observatory (H+ network) while these phenomena are usually observed at the surface. These results show that heterogeneous flowpaths, linked to the structure of fractured media, create mixing zones between iron rich water and oxygen rich water, at the origin of the microbial hotspot. The second part of this work was devoted to the development of a novel method for a continuous measurement of microbial activity in groundwater. The method is based on the use of Fluorescein DiAcetate (FDA) whose product of reaction can be measured continuously by a field fluorimeter. After testing and validating protocols in the lab on enzymatic solutions and natural water, we have implemented this technic in the field in reactive tracer test experiments. A kinetic model allowed us to interpret the lab results, and to compare them to the field kinetics. This method thus opens new perspectives for the characterization of biogeochemical processes in the field.
43

Nanoestruturas metálicas e de silício para intensificação de campo próximo. / Metal and silicon nanostructures to near-field intensification.

Raimundo, Daniel Scodeler 08 October 2009 (has links)
Durante os últimos cinco anos, a nanotecnologia tem atingido avanços significativos em diversas áreas da ciência e tecnologia. Um dos assuntos que está sendo intensamente estudado pela comunidade científica é a intensificação de campo próximo (hot spot) que pode ser aplicada em dispositivos sensores com capacidade de detecção de apenas uma molécula e em nano-antenas ópticas aplicadas na fabricação de dispositivos plasmônicos. Neste sentido, as principais contribuições da presente tese são processos de fabricação de nanoestruturas metálicas e de silício e o estudo da intensificação de campo próximo denominada de pontos quentes (hot spots) nestas estruturas. As nanoestruturas metálicas de Au (ouro) foram obtidas a partir do processo de auto-organização de esferas de poliestireno. As esferas de poliestireno serviram como camada sacrificial (molde) para a obtenção de nanoestruturas metálicas organizadas. Sobre as estruturas de Au organizadas foram depositadas moléculas de cristal violeta para serem utilizadas como moléculas de prova (sondas) no monitoramento da existência dos pontos quentes com o auxílio do espalhamento Raman das moléculas. As nanoestruturas de Au possibilitaram uma intensificação do espalhamento Raman devido à intensificação do campo próximo na superfície metálica periódica de Au. As nanoestruturas e microestruturas de silício foram obtidas a partir da tecnologia de silício poroso. As propriedades do silício poroso foram moduladas através da implantação de íons de hidrogênio (H +) que possibilitou a formação de silício microporoso com forte emissão fotoluminescente (PL) e intensificação do espalhamento Raman superficial devido ao fenômeno de Raman ressonante. Sobre as estruturas macroporosas de silício foram adsorvidas moléculas de azul de metileno para serem utilizadas como moléculas de prova para monitoramento da intensificação do campo próximo e do efeito SERS no silício. A obtenção da intensificação de campo próximo em silício é uma contribuição completamente inédita, pois este fenômeno devia-se, até o momento, somente a materiais metálicos (nanoestruturas metálicas), mostrando sua existência também no silício. / During the last five years, nanotechnology has achieved significant progress in several areas of science and technology. One of the issues that are being intensively studied by the scientific community is the intensification of near-field (hot spot) that can be applied to devices with sensors capable of detecting a single molecule and nano-optical antennas used in the fabrication of plasmonic devices. In this sense, the main contributions of this thesis are processes for manufacture of metal and silicon nanostructures and the study of near-field intensification called hot spots in these structures. The metal nanostructures of Au (gold) were obtained from the process of self-assembling of polystyrene beads. The polystyrene beads were used as sacrificial layer (mold) for obtaining organized metallic nanostructures. On the structures of organized Au were deposited molecules of violet crystal to be used as proof of molecules (probes) to monitor the existence of hot spots with the help of Raman scattering of molecules. The Au nanostructures allowed an intensification of the Raman scattering due to the intensification of the near-field in the periodic Au surface. The microstructures and nanostructures of silicon were obtained using the porous silicon technology. The properties of porous silicon were modulated by the implantation of hydrogen ions (H +) that allowed the formation of microporous silicon which showed high photoluminescence emission (PL) and Raman scattering intensification of the surface due to the phenomenon of resonant Raman. Methylene blue molecules were adsorbed on the macroporous silicon structures to be used as probe molecule for the monitoring of near-field intensification and the SERS effect in silicon. The obtaining of near-field intensification in silicon is an entirely unprecedented contribution, because this phenomenon had been observed, so far, only on the metallic materials (metal nanostructures), showing its existence in the silicon too.
44

Identificação de pontos quentes em transformadores de potência por meio de técnicas não invasivas. / Identification of hot spots in power transformers using non-invasive techniques.

Melo, André de Souza 31 August 2017 (has links)
Esta pesquisa apresenta uma metodologia, baseada em duas técnicas não invasivas para identificação e diagnóstico de pontos quentes em transformadores de potência durante plena operação ou em fase de projeto. A primeira técnica é baseada na medição de radiação infravermelha, emitida pelo equipamento em funcionamento e registrada por meio de análise termográfica. A segunda técnica é possível a partir do conhecimento prévio das características construtivas do transformador, fazendo uso do Método dos Elementos Finitos (MEF). A segunda técnica pode ser validada a partir das medições realizadas utilizando a primeira técnica. A formação de gases no interior dos transformadores de potência, devido à elevação da temperatura do óleo isolante em função dos pontos quentes, é discutida em detalhes com base nas normas técnicas estabelecidas pelo IEEE e IEC. As técnicas e procedimentos abordados ao longo dessa pesquisa foram obtidos a partir de um transformador com potência nominal de 120 MVA e relação de tensão 13,8/230 kV, projetado para integrar uma fazenda eólica ao Sistema Interligado Nacional (SIN). / This research presents a methodology based on two noninvasive techniques for identification and diagnostic of hot spots in power transformers during operation or project development. The first is based on measurements of infrared radiation from the equipment during operation and recording by thermography. The second technique is possible from the previous knowing of the constructive characteristics of the power transformer, by using the Finite Element Method (FEM). The second technique can be validated from measurements obtained using the first technique. The gas formation into the power transformers, because of the high temperatures in the insulating oil due to the hot spots, is discussed in details based on normative recommendations well established by the IEEE and IEC. All techniques and procedures to be approached in this research were obtained using a 120-MVA power transformer with voltage relationship of 13.8/230 kV that was projected to interconnect a wind farm to the Interconnected Brazilian System (Sistema Interligado Nacional - SIN).
45

Identificação de pontos quentes em transformadores de potência por meio de técnicas não invasivas. / Identification of hot spots in power transformers using non-invasive techniques.

André de Souza Melo 31 August 2017 (has links)
Esta pesquisa apresenta uma metodologia, baseada em duas técnicas não invasivas para identificação e diagnóstico de pontos quentes em transformadores de potência durante plena operação ou em fase de projeto. A primeira técnica é baseada na medição de radiação infravermelha, emitida pelo equipamento em funcionamento e registrada por meio de análise termográfica. A segunda técnica é possível a partir do conhecimento prévio das características construtivas do transformador, fazendo uso do Método dos Elementos Finitos (MEF). A segunda técnica pode ser validada a partir das medições realizadas utilizando a primeira técnica. A formação de gases no interior dos transformadores de potência, devido à elevação da temperatura do óleo isolante em função dos pontos quentes, é discutida em detalhes com base nas normas técnicas estabelecidas pelo IEEE e IEC. As técnicas e procedimentos abordados ao longo dessa pesquisa foram obtidos a partir de um transformador com potência nominal de 120 MVA e relação de tensão 13,8/230 kV, projetado para integrar uma fazenda eólica ao Sistema Interligado Nacional (SIN). / This research presents a methodology based on two noninvasive techniques for identification and diagnostic of hot spots in power transformers during operation or project development. The first is based on measurements of infrared radiation from the equipment during operation and recording by thermography. The second technique is possible from the previous knowing of the constructive characteristics of the power transformer, by using the Finite Element Method (FEM). The second technique can be validated from measurements obtained using the first technique. The gas formation into the power transformers, because of the high temperatures in the insulating oil due to the hot spots, is discussed in details based on normative recommendations well established by the IEEE and IEC. All techniques and procedures to be approached in this research were obtained using a 120-MVA power transformer with voltage relationship of 13.8/230 kV that was projected to interconnect a wind farm to the Interconnected Brazilian System (Sistema Interligado Nacional - SIN).
46

Spatial Resolution, Costs, and Equity in Air Toxics Regulation

Turaga, Rama Mohana Rao 09 July 2007 (has links)
Concern about environmental injustice has been driving the recent effort to characterize risks from exposures to air toxics at very fine spatial resolutions. However, few studies seek to understand the potential policy implications of regulating risks at increasingly finer spatial resolutions and the impact of resulting policies on distribution of risks. To address this gap, the broad question for this research is how could the choice of spatial resolution for regulation of risks from toxic air pollutants affect emission controls and the consequences thereof? This research develops a formal model of a hypothetical decision maker choosing emission controls within a risk-based regulatory framework. The model suggests that optimal controls on air toxics emissions vary depending on the spatial resolution chosen to regulate risks; net social costs are non-decreasing as one regulates at finer and finer spatial resolutions. An empirical application of the model using air toxic emission data for Escambia and Santa Rosa Counties in Florida demonstrates the sensitivity of optimal emissions to spatial resolution chosen for regulation. The research then investigates the equity implications of regulating at different spatial resolutions with regard to the spatial distribution of cancer risks. The empirical results indicate that regulation at finer spatial resolutions could involve a tradeoff between costs and equitable distribution of risks. For example, at a threshold cancer risk of 100 in a million, regulating at census block level resolution could be twice as costly as regulating at census tract resolution while reducing the maximum individual risk by almost half. Further, regulation at finer spatial resolutions might not address environmental injustice by itself unless such concerns are more explicitly incorporated into emission control decisions. Finally, this research shows that spatial resolution at which air toxics risks are regulated could matter in predictable ways even after taking into account the uncertainties that the decision maker faces.
47

Nanoestruturas metálicas e de silício para intensificação de campo próximo. / Metal and silicon nanostructures to near-field intensification.

Daniel Scodeler Raimundo 08 October 2009 (has links)
Durante os últimos cinco anos, a nanotecnologia tem atingido avanços significativos em diversas áreas da ciência e tecnologia. Um dos assuntos que está sendo intensamente estudado pela comunidade científica é a intensificação de campo próximo (hot spot) que pode ser aplicada em dispositivos sensores com capacidade de detecção de apenas uma molécula e em nano-antenas ópticas aplicadas na fabricação de dispositivos plasmônicos. Neste sentido, as principais contribuições da presente tese são processos de fabricação de nanoestruturas metálicas e de silício e o estudo da intensificação de campo próximo denominada de pontos quentes (hot spots) nestas estruturas. As nanoestruturas metálicas de Au (ouro) foram obtidas a partir do processo de auto-organização de esferas de poliestireno. As esferas de poliestireno serviram como camada sacrificial (molde) para a obtenção de nanoestruturas metálicas organizadas. Sobre as estruturas de Au organizadas foram depositadas moléculas de cristal violeta para serem utilizadas como moléculas de prova (sondas) no monitoramento da existência dos pontos quentes com o auxílio do espalhamento Raman das moléculas. As nanoestruturas de Au possibilitaram uma intensificação do espalhamento Raman devido à intensificação do campo próximo na superfície metálica periódica de Au. As nanoestruturas e microestruturas de silício foram obtidas a partir da tecnologia de silício poroso. As propriedades do silício poroso foram moduladas através da implantação de íons de hidrogênio (H +) que possibilitou a formação de silício microporoso com forte emissão fotoluminescente (PL) e intensificação do espalhamento Raman superficial devido ao fenômeno de Raman ressonante. Sobre as estruturas macroporosas de silício foram adsorvidas moléculas de azul de metileno para serem utilizadas como moléculas de prova para monitoramento da intensificação do campo próximo e do efeito SERS no silício. A obtenção da intensificação de campo próximo em silício é uma contribuição completamente inédita, pois este fenômeno devia-se, até o momento, somente a materiais metálicos (nanoestruturas metálicas), mostrando sua existência também no silício. / During the last five years, nanotechnology has achieved significant progress in several areas of science and technology. One of the issues that are being intensively studied by the scientific community is the intensification of near-field (hot spot) that can be applied to devices with sensors capable of detecting a single molecule and nano-optical antennas used in the fabrication of plasmonic devices. In this sense, the main contributions of this thesis are processes for manufacture of metal and silicon nanostructures and the study of near-field intensification called hot spots in these structures. The metal nanostructures of Au (gold) were obtained from the process of self-assembling of polystyrene beads. The polystyrene beads were used as sacrificial layer (mold) for obtaining organized metallic nanostructures. On the structures of organized Au were deposited molecules of violet crystal to be used as proof of molecules (probes) to monitor the existence of hot spots with the help of Raman scattering of molecules. The Au nanostructures allowed an intensification of the Raman scattering due to the intensification of the near-field in the periodic Au surface. The microstructures and nanostructures of silicon were obtained using the porous silicon technology. The properties of porous silicon were modulated by the implantation of hydrogen ions (H +) that allowed the formation of microporous silicon which showed high photoluminescence emission (PL) and Raman scattering intensification of the surface due to the phenomenon of resonant Raman. Methylene blue molecules were adsorbed on the macroporous silicon structures to be used as probe molecule for the monitoring of near-field intensification and the SERS effect in silicon. The obtaining of near-field intensification in silicon is an entirely unprecedented contribution, because this phenomenon had been observed, so far, only on the metallic materials (metal nanostructures), showing its existence in the silicon too.
48

Sinergismo entre eventos clim?ticos extremos, desmatamento e aumento da suscetibilidade a inc?ndios florestais no Estado do Acre / Synergism between extreme weather events, deforestation and increased susceptibility and risk of forest fires in Acre state

Tostes, Juliana de Oliveira 29 February 2016 (has links)
Submitted by Sandra Pereira (srpereira@ufrrj.br) on 2016-10-25T11:21:37Z No. of bitstreams: 1 2016 - Juliana de Oliveira Tostes.pdf: 4618564 bytes, checksum: 951350c8676b3f82092fedfc3a9e0f79 (MD5) / Made available in DSpace on 2016-10-25T11:21:37Z (GMT). No. of bitstreams: 1 2016 - Juliana de Oliveira Tostes.pdf: 4618564 bytes, checksum: 951350c8676b3f82092fedfc3a9e0f79 (MD5) Previous issue date: 2016-02-29 / This research analyzes the temporal and spatial variables that can affect the distribution and frequency of hot spots in the state of Acre. Given the scarcity of regular spatial information and long time series for the study area, it was initially carried out a validation between air temperature and precipitation data in Global Grid Precipitation Climatology Centre (GPCC), University of Delaware (UDEL) and Global Historical Climatology Network (GHCN) with data from five Weather Stations Mainstream (EMC) to Acre and region, through an analysis of precision and accuracy of the data. Regarding precipitation, it was found that both the GPCC UDEL represented as the average variability significantly throughout the series. In relation to the air temperature standards, although the accuracy of GHCN and UDEL was low, it was satisfactory accuracy according to statistical methods. Assuming that the extreme weather events increase susceptibility to forest fires, then it was carried out an analysis of the influence of climate variability modes in generating categorized scenarios dry or wet years, based on the Standardized Precipitation Index (SPI) and Harmonic and Spectral (AHE). It was found that the AHE is not able to identify the intensity of the events, but was satisfactory in the signal cycles identifying the anomaly, i.e., whether the abnormality SPI was positive or negative. It was found that the Atlantic signal had greater influence on the precipitation of the Pacific. For the regions that correspond to Groups 1, 2 and 3 there was an inverse pattern for precipitation in relation to ENSO compared to the North and East Amazon. Thus, it identified negative precipitation anomalies during La Ni?a and El Ni?o events during positive events for the dry and rainy seasons. For the area corresponding to the effect Group 4 was otherwise. The natural climate variability patterns identified in this study may contribute to the establishment of strategies for prevention and adaptation to extreme events. Finally, in Chapter 3 was carried out an analysis of the spatial and temporal patterns of the fire in Acre, through a discussion of various climatic, environmental and anthropogenic variables that contribute to its occurrence. Thus, through the Random Forest algorithm were generated susceptibility maps that estimated the probability of fires and burned in the state. . It was found that although drought triggers an increase in the number of hot spots, its spatial pattern is more related to human factors such as the proximity areas already cleared. / A presente pesquisa analisa as vari?veis temporais e espaciais que podem afetar a distribui??o e frequ?ncia dos focos de calor no estado do Acre. Diante da escassez de dados regularmente espacializados e com longa s?rie temporal para a ?rea de estudo, inicialmente foi realizada uma valida??o entre os dados de temperatura do ar e precipita??o em grade do Global Precipitation Climatology Centre (GPCC), Universidade de Delaware (UDEL) e Global Historical Climatology Network (GHCN) com dados de cinco Esta??es Meteorol?gicas Convencionais (EMC) para o Acre e regi?o, atrav?s de uma an?lise da precis?o e exatid?o dos dados. Em rela??o ? precipita??o, verificou-se que tanto o GPCC quanto da UDEL representaram significativamente as variabilidades m?dias ao longo da s?rie. Em rela??o aos padr?es da temperatura do ar, embora a precis?o do GHCN e da UDEL tenha sido baixa, a exatid?o foi satisfat?ria segundo os m?todos estat?sticos. Partindo do pressuposto que os eventos clim?ticos extremos aumentam a suscetibilidade a inc?ndios florestais, em seguida foi realizada uma an?lise da influ?ncia dos modos de variabilidade clim?tica na gera??o de cen?rios categorizados de anos secos ou ?midos, baseado no ?ndice de Precipita??o Padronizado (SPI) e na An?lise Harm?nica e Espectral (AHE). Verificou-se que a AHE n?o foi capaz de identificar a intensidade dos eventos, mas mostrou-se satisfat?ria na identifica??o dos ciclos de sinal da anomalia, ou seja, se anomalia do SPI foi positiva ou negativa. Verificou-se que o sinal do Atl?ntico teve maior influ?ncia sobre a precipita??o do que o Pac?fico. Para as regi?es que correspondem os Grupos 1, 2 e 3 observou-se um padr?o inverso para a precipita??o em rela??o ao ENOS, quando comparado com a Amaz?nia Norte e Oriental. Assim, foram identificadas anomalias negativas de precipita??o durante eventos de La Ni?a e positivas durante eventos de El Ni?o para as esta??es seca e chuvosa. Para a regi?o que corresponde ao Grupo 4 o efeito foi contr?rio. Os padr?es de variabilidade natural do clima identificados nesse trabalho podem contribuir para o estabelecimento de estrat?gias de preven??o e adapta??o aos eventos extremos. Finalmente, no Cap?tulo 3 foi realizada uma an?lise sobre o padr?o espacial e temporal do fogo no Acre, atrav?s de uma discuss?o sobre diversas vari?veis clim?ticas, ambientais e antr?picas que contribuem para a sua ocorr?ncia. Assim, por meio do algoritmo Random Forest foram gerados mapas de suscetibilidade que estimaram a probabilidade de ocorr?ncia de inc?ndios e queimadas no estado. Verificou-se que, embora a estiagem propicie um aumento do n?mero de focos de calor, o seu padr?o espacial est? mais relacionado a fatores antr?picos, tais como a proximidade de ?reas j? desmatadas.
49

Cortical spatiotemporal plasticity in visual category learning

Xu, Yang 01 August 2013 (has links)
Central to human intelligence, visual categorization is a skill that is both remarkably fast and accurate. Although there have been numerous studies in primates regarding how information flows in inferiortemporal (ITC) and prefrontal (PFC) cortices during online discrimination of visual categories, there has been little comparable research on the human cortex. To bridge this gap, this thesis explores how visual categories emerge in prefrontal cortex and the ventral stream, which is the human homologue of ITC. In particular, cortical spatiotemporal plasticity in visual category learning was investigated using behavioral experiments, magnetoencephalographic (MEG) imaging, and statistical machine learning methods. From a theoretical perspective, scientists from work on non-human primates have posited that PFC plays a primary role in the encoding of visual categories. Much of the extant research in the cognitive neuroscience literature, however, emphasizes the role of the ventral stream. Despite their apparent incompatibility, no study has evaluated these theories in the human cortex by examining the roles of the ventral stream and PFC in online discrimination and acquisition of visual categories. To address this question, I conducted two learning experiments using visually-similar categories as stimuli and recorded cortical response using MEG—a neuroimaging technique that offers a millisecond temporal resolution. Across both experiments, categorical information was found to be available during the period of cortical activity. Moreover, late in the learning process, this information is supplied increasingly in the ventral stream but less so in prefrontal cortex. These findings extend previous theories by suggesting that the ventral stream is crucial to long-term encoding of visual categories when categorical perception is proficient, but that PFC jointly encodes visual categories early on during learning. From a methodological perspective, MEG is limited as a technique because it can lead to false discoveries in a large number of spatiotemporal regions of interest (ROIs) and, typically, can only coarsely reconstruct the spatial locations of cortical responses. To address the first problem, I developed an excursion algorithm that identified ROIs contiguous in time and space. I then used a permutation test to measure the global statistical significance of the ROIs. To address the second problem, I developed a method that incorporates domainspecific and experimental knowledge in the modeling process. Utilizing faces as a model category, I used a predefined “face” network to constrain the estimation of cortical activities by applying differential shrinkages to regions within and outside this network. I proposed and implemented a trial-partitioning approach which uses trials in the midst of learning for model estimation. Importantly, this renders localizing trials more precise in both the initial and final phases of learning. In summary, this thesis makes two significant contributions. First, it methodologically improves the way we can characterize the spatiotemporal properties of the human cortex using MEG. Second, it provides a combined theory of visual category learning by incorporating the large time scales that encompass the course of the learning.
50

Dinâmica populacional de Euterpe edulis Martius em Floresta Ombrófila Densa no sul da Bahia

Mafei, Rodolpho Antunes 02 March 2011 (has links)
Made available in DSpace on 2016-06-02T19:32:01Z (GMT). No. of bitstreams: 1 4244.pdf: 1071959 bytes, checksum: 6ba82849d82a8316bf2d47e4273770cb (MD5) Previous issue date: 2011-03-02 / Euterpe edulis is a very important palm tree from the Brazilian Atlantic Forest due to its ecological and economic role. However, due to the indiscriminate overexploitation its populations has been reducing greatly. This study aimed to characterize the conservation status of a E. edulis population in a fragment of Atlantic Forest at Southern Bahia. We monitored this population along 5 running years in a 0.8 hectare. Environmental variables were also collected to test which factors could affect plant development and projection matrices analysis were performed to estimate the population growth rate and sensibility. The results showed that population s density is lower if compared with others studies. We verified a decrease in the seedling s recruitment over years, which were attributed to fragmentation side-effects, such as microclimate changes and / or reproductive isolation or inbreeding depression. We also observed that the low rate of transition from stages 1 to 2, represents a bottleneck for the population growth. These results emphasize the urgency of more long-term studies on the population ecology and genetic of E. edulis and also management strategies to promote the sustainability of such natural populations. / Euterpe edulis é uma das espécies de maior importância ecológica e econômica na Mata Atlântica brasileira. Apesar de a espécie possuir características que favorecem o manejo sustentável, a exploração predatória gerou um cenário de populações naturais severamente reduzidas. Este estudo procurou caracterizar o atual estado de conservação de uma população no sul da Bahia. Para tanto foi definido um bloco amostral 0,8 hectare, onde foi monitorada uma população de E. edulis, dividida em seis estágios de desenvolvimento. Foram geradas matrizes de projeção para verificar a tendência atual de conservação da população e variáveis ambientais foram analisadas para inferir sobre como tais fatores podem afetar o desenvolvimento da espécie. Os resultados mostraram que a densidade da população encontrada nesse estudo é menor que a relatada em outros estudos já realizados com a espécie. Verificou-se também a diminuição abrupta no recrutamento de plântulas a cada ano, o que foi atribuído a algum efeito colateral da fragmentação florestal, tal como alterações microclimáticas, e/ou efeitos do isolamento reprodutivo, como a depressão endogâmica. A lenta transição do estágio jovens 1 para jovens 2 se mostrou como principal gargalo ao crescimento populacional, o que sugere a necessidade de estudos sobre a redução na fecundidade. Ambientes com maior homogeneidade de dossel propiciaram maior crescimentos em jovens 2. Propõe-se que a produção e manutenção de mudas em viveiros até a idade de um ano, seguida de plantio em áreas próximas às bordas de clareiras, possa diminuir a mortalidade dos estágios iniciais e garantir maior êxito na perpetuação das populações de Euterpe edulis no sul da Bahia.

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