• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 74
  • 29
  • 20
  • 9
  • 4
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 164
  • 37
  • 33
  • 30
  • 25
  • 21
  • 16
  • 14
  • 13
  • 13
  • 13
  • 12
  • 12
  • 12
  • 11
  • 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.
21

Experimental study of single sided ventilation through a multi-configuration slotted louvre system

O'Sullivan, Paul D. January 2018 (has links)
Evidence based performance of novel ventilation systems in existing low energy buildings is invaluable as it provides data on the system operation in a real dynamic environment. This thesis presents the outcomes from research involving a number of experimental field studies of a single sided ventilation system installed in a single cell office space as part of a building retrofit pilot project in Cork, Ireland. The solution consists of a purpose provided, multi configuration opening, comprising a narrow slotted architectural louvre component split across a low level manual opening section and a high level automated opening section. A review of published research found that little experimental data exists on the performance of such systems and air flow rate correlations developed for plain openings are currently used by designers to make predictions about their performance. Three experimental campaigns were designed and carried out. First, in order to quantify performance of the system, long term and short term monitoring of the internal thermal and air flow environment at the experimental building was completed. Second, ventilation rate measurements in existing and retrofit spaces were completed using a tracer gas concentration decay technique. Thirdly, air flow through the single sided slot louvre opening was investigated. In addition, the annual cooling potential of the multi-configuration system was investigated computationally. Results show there was a significant difference between both thermal environments with the retrofit space consistently displaying lower air temperatures over the cooling season and throughout all Air Change Rate measurement periods. Lower levels of vertical thermal stratification and diurnal temperature variation were also observed. On average, across a wide range of boundary conditions, lower ventilation rates were observed for the slotted louvre system with a narrower spread of values when compared with the existing building. The dominant driving force was either buoyancy or wind depending on the opening configuration adopted in the slotted louvre system. The slot louvre was found to be wind dominant for lower opening heights when compared with a plain opening of the same dimensions. Existing single sided correlations were found to perform better when predicting airflow rates through a plain opening when compared with the slot louvre system and a new dimensionless exchange rate parameter is proposed for predicting wind driven airflow through the slot louvre. Simulations indicate that 80% of annual occupied hours required an enhanced ventilative cooling airflow rate to achieve internal thermal comfort. Using a combination of configurations the system was able to provide the required cooling airflow rate for 93% of the occupied hours.
22

Detecção e qualificação de lesões melanocíticas através de evidências locais e de contexto / Detection and qualification of melanocytic lesions using local and context evidences

Bernart, Eliezer Emanuel January 2016 (has links)
Neste trabalho, um novo método não-supervisionado para segmentação de lesões melanocíticas em imagens macroscópicas é proposto levando em consideração regiões suspeitas, e também uma nova abordagem para classificação de lesões que faz uso de evidências locais e de contexto para estimar um índice de probabilidade para malignidade em cada lesão. O método proposto realiza a segmentação das imagens em três tipos de regiões disjuntas: ‘pele saudável’, ‘região de incerteza’ e ‘lesão’. Regiões de incerteza são refinadas através da utilização de feições estocásticas também de forma não-supervisionada, resultando em uma máscara binária que discrimina a pele da lesão. As máscaras obtidas apresentam um erro XOR comparável aos métodos estado da arte. A imagem é segmentada utilizando um algoritmo de superpixels e as sub-regiões que intersectam a máscara obtida são categorizadas como evidências locais. Estas evidências são representadas por uma descrição especializada que explora as características como cor e textura. Estas sub-regiões são então associadas à evidências de contexto definidas pela borda da lesão de onde foram extraídas e classificadas de forma independente através de uma abordagem supervisionada. Com o resultado da classificação destas evidências é possível obter um indicador probabilístico para malignidade associado a cada lesão, e levando em consideração um valor de tolerância é possível identificar lesões malignas em potencial. Os resultados obtidos com o método proposto são promissores e apresentam maior acurácia do que os métodos existentes na literatura apesar do erro XOR da segmentação das lesões ser maior, o que tende a confirmar o potencial do método proposto para discriminar lesões melanocíticas benignas e malignas. / In this work, a novel unsupervised method for melanocytic macroscopic image segmentation is proposed considering suspicious regions, and also a novel approach for lesion classification using local and context evidence to estimate a probabilistic index of malignity or benignity in each lesion. The proposed method segment the macroscopic images in three types of disjoint regions: ‘healthy skin’, ‘suspicious region’ and ‘lesion’. Suspicious areas are refined using stochastic texture features also in an unsupervised approach, resulting in a binary mask discriminating skin and lesion. The resulting masks present an XOR error similar to other state-of-art methods. In the next step, the image is segmented using a superpixels algorithm and subregions that intersect the obtained mask categorized as local evidence. A specialized representation describes color and texture information present in the local evidence region. The border of the segmented skin lesion defines the context evidence and using a supervised approach, local and context evidence are combined and classified independently. With the evidence classification results is possible to obtain a probabilistic index of malignity and benignity associated to each lesion, and considering a tolerance value is possible to identify potential malignant lesions. The results achieved with the proposed method are promissing and present greater accuracy than other techniques in the literature, even with a greater XOR error in segmentation step, confirming the proposed method’s potential to discriminate benignant and malignant melanocytic lesions.
23

A Risk-based Evaluation of the Long-term Performance of Stormwater Infiltration Facilities

Sykes, Caitlin Elizabeth 15 February 2010 (has links)
Infiltration facilities are source control mechanisms that are implemented in urban developments with reduced natural permeable surfaces. Despite the development of design criteria for infiltration facilities, these systems continue to fail due to headloss development, overflow, or chemical breakthrough. The limited research on the long-term performance of these systems has emphasized the role of physical filtration mechanisms within porous media filters to address concerns surrounding system failure, namely filter clogging. A continuous macroscopic depth filtration model was developed to investigate the clogging potential of the underlying sand filter. This continuous model furthers the understanding of temporal and spatial changes in system performance for the development of more appropriate design criteria and more suitable maintenance regimes. The characterization of long-term system performance by defining three different failure modes and a probabilistic approach comprises a comprehensive methodology by considering several performance criteria rather than assuming that one criterion dictates the overall system performance.
24

A Risk-based Evaluation of the Long-term Performance of Stormwater Infiltration Facilities

Sykes, Caitlin Elizabeth 15 February 2010 (has links)
Infiltration facilities are source control mechanisms that are implemented in urban developments with reduced natural permeable surfaces. Despite the development of design criteria for infiltration facilities, these systems continue to fail due to headloss development, overflow, or chemical breakthrough. The limited research on the long-term performance of these systems has emphasized the role of physical filtration mechanisms within porous media filters to address concerns surrounding system failure, namely filter clogging. A continuous macroscopic depth filtration model was developed to investigate the clogging potential of the underlying sand filter. This continuous model furthers the understanding of temporal and spatial changes in system performance for the development of more appropriate design criteria and more suitable maintenance regimes. The characterization of long-term system performance by defining three different failure modes and a probabilistic approach comprises a comprehensive methodology by considering several performance criteria rather than assuming that one criterion dictates the overall system performance.
25

A non-continuum approach to obtain a macroscopic model for the flow of traffic

Tyagi, Vipin 17 September 2007 (has links)
Existing macroscopic models for the flow of traffic treat traffic as a continuum or employ techniques similar to those used in the kinetic theory of gases. Spurious two- way propagation of disturbances that are physically unacceptable are predicted by continuum models for the flow of traffic. The number of vehicles in a typical section of a freeway does not justify traffic being treated as a continuum. It is also important to recognize that the basic premises of kinetic theory are not appropriate for the flow of traffic. A model for the flow of traffic that does not treat traffic as a continuum or use notions from kinetic theory is developed in this dissertation and corroborated with traffic data collected from the sensors deployed on US 183 freeway in Austin, Texas, USA. The flow of traffic exhibits distinct characteristics under different conditions and reflects the congestion during peak hours and relatively free motion during off-peak hours. This requires one to use different governing equations to describe the diverse traffic characteristics, namely the different traffic flow regimes of response. Such an approach has been followed in this dissertation. An observer based on extended Kalman filtering technique has been utilized for the purpose of estimating the traffic state. Historical traffic data has been used for model calibration. The estimated model parameters have consistent values for different traffic conditions. These esti- mated model parameters are then subsequently used for estimation of the state of traffic in real-time. A short-term traffic state forecasting approach, based on the non-continuum traffic model, which incorporates weighted historical and real-time traffic information has been developed. A methodology for predicting trip travel time based on this approach has also been developed. Ten and fifteen minute predictions for traffic state and trip travel time seem to agree well with the traffic data collected on US 183.
26

Modeling Damage and Damage Evolution in Periodic Cellular Sandwich Panels

Ogundipe, Collins 21 March 2012 (has links)
Among the light bending structures currently available, truss core panels are one of the most efficient when properly designed. The proper selection of the truss core lattice allows the incorporation of additional functionality. To exploit the multi-functional advantages of truss core sandwich structures, it is crucial to understand how the materials survive in challenging environments. In this research, the strengths of truss core panels have been predicted. Numerical calculations and experiments were carried out to validate the predictions. The effects of damage and damage propagation on the overall strength of the panel were also addressed. The strength and failure surfaces of arrays of partially damaged truss core unit cells were calculated under shear and axial loading. The results highlight the modes and trends of damage propagation in truss core panel, and the estimated damaged strength. Experiments were also performed to validate the damaged strength.
27

The macroscopic fundamental diagram in urban network: analytical theory and simulation

Zhou, Yi 20 September 2013 (has links)
The Macroscopic Fundamental Diagram (MFD) is a diagram that presents a relationship between the average flow (production) and the average density in an urban network. Ever since the existence of low scatter MFD in urban road network was verified, significant efforts have been made to describe the MFD quantitatively. Due to the complexity of the traffic environment in urban networks, an accurate and explicit expression for the MFD is not yet developed and many recent research efforts for MFD rely on computer simulations. On a single corridor, an analytical approximation model for the MFD exists. However, this thesis expanded this theory in two directions. First, we specialize the method for models with equal road length on the corridor, which greatly reduces the complexity of the method. We introduce the adoption of seven straight cuts in approximation. Computer simulations are conducted and show a high compatibility with the approximated results. However the analytical approximation can only be applied with the assumption of constant circulating vehicles in the system without turnings and endogenous traffics. Secondly, we show that turnings and endogenous traffic can bring various impact on the shape of the MFD, the capacity, the critical density, the variance in density and cause a phenomenon of clustered traffic status along the MFD curve. Furthermore, the simulation using stochastic variables reveals that the variance in turning rates and endogenous traffic don’t have significant impact on the MFD. This discovery enables studies to focus on scenarios with deterministic parameters for those factors. While traditional objective of engineering for network is to maximize capacity and widen the range for the maximum capacity, our results indicate that traffic stability at the maximum performance is poor if the system does not stay constantly in equilibrium status. This thesis provides insights into the factors that affect the shape of the MFD by analytical approximation and simulation.
28

Modeling Damage and Damage Evolution in Periodic Cellular Sandwich Panels

Ogundipe, Collins 21 March 2012 (has links)
Among the light bending structures currently available, truss core panels are one of the most efficient when properly designed. The proper selection of the truss core lattice allows the incorporation of additional functionality. To exploit the multi-functional advantages of truss core sandwich structures, it is crucial to understand how the materials survive in challenging environments. In this research, the strengths of truss core panels have been predicted. Numerical calculations and experiments were carried out to validate the predictions. The effects of damage and damage propagation on the overall strength of the panel were also addressed. The strength and failure surfaces of arrays of partially damaged truss core unit cells were calculated under shear and axial loading. The results highlight the modes and trends of damage propagation in truss core panel, and the estimated damaged strength. Experiments were also performed to validate the damaged strength.
29

Evidência de incêndios em turfeira costeira do Rio Grande do Sul-Brasil e relação com flutuações climáticas no quaternário

Ribeiro, Veridiana January 2015 (has links)
A análise de carvão vegetal macroscópico na turfeira do distrito de Águas Claras, município de Viamão, Rio Grande do Sul, Brasil, foi efetuada com o objetivo de detectar a ocorrência efetiva de incêndios vegetacionais, tentando relacionar a origem desses eventos a processos naturais decorrentes de fatores climáticos ou a fatores antrópicos. As análises em estereomicroscópio e microscópio eletrônico de varredura centraram-se na obtenção de resultados relativos à dimensão, concentração e morfologia dos fragmentos de lenho, além da definição de padrões de homogeneização das paredes celulares. Incêndios vegetacionais foram detectados em fases distintas dos Sistemas Deposicionais Laguna-Barreira vigentes na Planície Costeira do Rio Grande do Sul. O primeiro pico de incêndio (25.400 anos AP) de idade Pleistoceno superior foi detectado em sedimentação lagunar (Sistema Laguna-Barreira III) e está relacionado com o clímax da glaciação Wisconsiana, que atingiu mais severamente o Hemisfério Norte e o sul do Hemisfério Sul, gerando na zona tropical da America do Sul, um clima muito frio e seco. O segundo pico de incêndio (4.016 a 4.232 anos AP) detectado na turfeira sobrejacente, originou-se ao final da Última Grande Transgressão Pós-glacial do Holoceno (Sistema Laguna- Barreira IV) e ocorreu durante vigência do Ótimo Climático Atlântico. Esse evento é coincidente com intervalos de início de ressecamento concomitantes, identificados anteriormente na própria turfeira de Águas Claras e em alagados de altitude no planalto Sul-rio-grandense, os quais poderiam estar relacionados a registros decorrentes do fenômeno El Nino/La Niña entre 4200–3800 anos AP, cuja ocorrência provocou oscilações climáticas rápidas no Hemisfério Sul, caracterizadas por resfriamento polar, aridez nas faixas tropicais e importantes modificações na circulação atmosférica. Os padrões morfológicos dos fragmentos de carvão vegetal macroscópico permitiram detectar que a vegetação dominante ao longo da deposição do perfil estudado era constituída por angiospermas mono e dicotiledôneas, sugerindo afinidade com vegetação eminentemente campestre, herbácea a arbustiva. O nicho ecológico em que essa associação se desenvolveu estava afastado da área de deposição lagunar durante a ocorrência do pico de incêndio pleistocênico, no entanto, o pico de incêndio holocênico ocorreu quando esse nicho se encontrava próximo à área de deposição da turfa. Evidências do impacto humano como causador do segundo pico de incêndio (4.016 a 4.232 anos A.P) não foram estabelecidas, dado que, os primeiros povoadores do litoral do Rio Grande do Sul, constituída por caçadores-coletores-pescadores, que instalou-se por volta de 4.000 anos AP, não tinham como protótipo cultural a utilização do fogo para cultivos e agricultura, tornando-se esta prática comum, somente a partir da colonização dos europeus. Apesar das incertezas quanto aos limites temporais dos resultados obtidos no nível de solo que capeia a turfa, os dados indicam a rara ocorrência de incêndios vegetacionais. Essa evidência pode estar racionada ao fato de que os processos recentes da interferência antrópica na turfeira de Águas Claras estão mais relacionados à drenagem do que a queimadas. Desta forma, pode-se concluir que a ocorrência de incêndios regionais na área da turfeira de Águas Claras tem sido regulada muito mais pelo clima do que pela ação antrópica, permitindo inferir que o fogo tem atuado como elemento fundamental na ecologia regional. / The macroscopic charcoal analysis in the peatlands in the District of Águas Claras, the Viamão municipality in Rio Grande do Sul, Brazil, was conducted in order to detect the actual occurrence of vegetation fires, trying to relate the origin of these events whether resulting from natural processes climatic factors or anthropic (human) factors. The analysis in stereomicroscope and scanning electron microscope focused on achieving results relating to the size, concentration and morphology wood fragments and the definition of homogenization of the cell walls standards. Vegetation fires were detected at different stages of Depositional Systems at the existing lagoon barrier in the coastal plain of Rio Grande do Sul. The first peak fire, (25.400 BP) was detected in a settling lagoon (high sea level, Lagoon/Barrier System III) and is related to the climax of Wisconsin Glaciation, which hit hardest the north hemisphere and south of the Southern Hemisphere, generating in the tropical zone of South America, a very cold and dry climate. The second peak of fire during (4016-4232 BP) detected in the peat lands overlying, was originated at the end of the Last Great Transgression Post-glacial Holocene (Lagoon/Barrier System IV) and occurred during the term of Great Climate Atlantic. This event coincides with the beginning of concomitant drying intervals, previously identified in the own peat lands of Águas Claras and altitude wetlands of the Planalto Sul-rio-grandense, which could be related to records resulting from the El Nino/La Niña between (4200-3800 BP), whose occurrence caused rapid climatic oscillations in the Southern Hemisphere, characterized by polar cooling, aridity in the tropical bands and important changes in atmospheric circulation. The morphological patterns of macroscopic charcoal fragments enabled detects the dominant vegetation along the deposition profile of the study consisted of mono and dicotyledonous angiosperms, suggesting affinity with vegetation eminently pleasant, herbaceous to shrubby. The ecological niche in which this association was evolved away from the lagoon deposition area during the occurrence of the peak Pleistocene fire, however, the peak holocenic fire occurred when this niche was near to the deposition area of peat. Evidence of human impact to the cause of the second peak fire during the period of (4016-4232 BP) have not been established, since the first coastal plains settlers of the Rio Grande do Sul, were initially occupied by groups of hunter, gatherers, fishermen (with no agricultural tradition) making this a common practice only from the colonization of Europe. Despite the uncertainty about the temporal limits of results obtained on the ground level of the peat, the data indicates the occurrence of vegetation fires at the topsoil level of the turf profile. This evidence may be rationed to the fact that the recent cases of human interference in Águas Claras peat land are more related to drainage than burned. Thus, it can be concluded that the occurrence of regional fires in the area is been regulated more by the weather than by human action, leading to the conclusion that the fire has been acting as a key element in the regional ecology.
30

Detecção e qualificação de lesões melanocíticas através de evidências locais e de contexto / Detection and qualification of melanocytic lesions using local and context evidences

Bernart, Eliezer Emanuel January 2016 (has links)
Neste trabalho, um novo método não-supervisionado para segmentação de lesões melanocíticas em imagens macroscópicas é proposto levando em consideração regiões suspeitas, e também uma nova abordagem para classificação de lesões que faz uso de evidências locais e de contexto para estimar um índice de probabilidade para malignidade em cada lesão. O método proposto realiza a segmentação das imagens em três tipos de regiões disjuntas: ‘pele saudável’, ‘região de incerteza’ e ‘lesão’. Regiões de incerteza são refinadas através da utilização de feições estocásticas também de forma não-supervisionada, resultando em uma máscara binária que discrimina a pele da lesão. As máscaras obtidas apresentam um erro XOR comparável aos métodos estado da arte. A imagem é segmentada utilizando um algoritmo de superpixels e as sub-regiões que intersectam a máscara obtida são categorizadas como evidências locais. Estas evidências são representadas por uma descrição especializada que explora as características como cor e textura. Estas sub-regiões são então associadas à evidências de contexto definidas pela borda da lesão de onde foram extraídas e classificadas de forma independente através de uma abordagem supervisionada. Com o resultado da classificação destas evidências é possível obter um indicador probabilístico para malignidade associado a cada lesão, e levando em consideração um valor de tolerância é possível identificar lesões malignas em potencial. Os resultados obtidos com o método proposto são promissores e apresentam maior acurácia do que os métodos existentes na literatura apesar do erro XOR da segmentação das lesões ser maior, o que tende a confirmar o potencial do método proposto para discriminar lesões melanocíticas benignas e malignas. / In this work, a novel unsupervised method for melanocytic macroscopic image segmentation is proposed considering suspicious regions, and also a novel approach for lesion classification using local and context evidence to estimate a probabilistic index of malignity or benignity in each lesion. The proposed method segment the macroscopic images in three types of disjoint regions: ‘healthy skin’, ‘suspicious region’ and ‘lesion’. Suspicious areas are refined using stochastic texture features also in an unsupervised approach, resulting in a binary mask discriminating skin and lesion. The resulting masks present an XOR error similar to other state-of-art methods. In the next step, the image is segmented using a superpixels algorithm and subregions that intersect the obtained mask categorized as local evidence. A specialized representation describes color and texture information present in the local evidence region. The border of the segmented skin lesion defines the context evidence and using a supervised approach, local and context evidence are combined and classified independently. With the evidence classification results is possible to obtain a probabilistic index of malignity and benignity associated to each lesion, and considering a tolerance value is possible to identify potential malignant lesions. The results achieved with the proposed method are promissing and present greater accuracy than other techniques in the literature, even with a greater XOR error in segmentation step, confirming the proposed method’s potential to discriminate benignant and malignant melanocytic lesions.

Page generated in 0.0621 seconds