Navegando por Palavras-chave "Spectral analysis"
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- ItemSomente MetadadadosThe Impact of Haze on Performance Ratio and Short-Circuit Current of PV Systems in Singapore(Ieee-inst Electrical Electronics Engineers Inc, 2014-11-01) Liu, Haohui; Nobre, Andre Maia; Yang, Dazhi; Ye, Jia Ying; Martins, Fernando Ramos [UNIFESP]; Ruether, Ricardo; Reindl, Thomas; Aberle, Armin Gerhard; Peters, Ian Marius; Natl Univ Singapore; Universidade Federal de Santa Catarina (UFSC); Universidade Federal de São Paulo (UNIFESP)The spectral content of sunlight directly affects the power output of solar photovoltaic (PV) devices. the extent of the effect of seasonal and weather-related spectral variations on the power output will depend largely on the semiconductor bandgap. in this study, haze, which is a common weather condition in many parts of the world, is found to affect the power output of PV systems. An analysis of a recent haze event in Singapore in mid-June 2013 reveals that haze has an impact on the performance ratios and short-circuit currents of PV systems. the performance ratio of amorphous silicon thin-film PV systems dropped during the haze event, while that of crystalline silicon wafer-based systems exhibited a slight increase. A detailed analysis showed that the main cause of the observed performance ratio variations was changes in the generated short-circuit currents, which were due to a red shift of the solar spectrum arriving in the module plane during the haze period. Therefore, PV systems with different semiconductor bandgaps were affected differently.
- ItemAcesso aberto (Open Access)Linear and nonlinear analysis of heart rate variability in healthy subjects and after acute myocardial infarction in patients(Associação Brasileira de Divulgação Científica, 2012-05-01) Kunz, Vandeni Clarice; Borges, Érica Nicolau; Coelho, Regina Célia [UNIFESP]; Gubolino, Luiz Antonio; Martins, Luiz Eduardo Barreto; Silva, Ester da; Universidade Federal de São Carlos Departamento de Fisioterapia Núcleo de Pesquisa em Exercício Físico; Universidade Metodista de Piracicaba Faculdade de Ciências da Saúde; Universidade Federal de São Paulo (UNIFESP); Unidade Coronariana do Hospital dos Fornecedores de Cana de Piracicaba; Universidade Estadual de Campinas (UNICAMP)The objectives of this study were to evaluate and compare the use of linear and nonlinear methods for analysis of heart rate variability (HRV) in healthy subjects and in patients after acute myocardial infarction (AMI). Heart rate (HR) was recorded for 15 min in the supine position in 10 patients with AMI taking β-blockers (aged 57 ± 9 years) and in 11 healthy subjects (aged 53 ± 4 years). HRV was analyzed in the time domain (RMSSD and RMSM), the frequency domain using low- and high-frequency bands in normalized units (nu; LFnu and HFnu) and the LF/HF ratio and approximate entropy (ApEn) were determined. There was a correlation (P < 0.05) of RMSSD, RMSM, LFnu, HFnu, and the LF/HF ratio index with the ApEn of the AMI group on the 2nd (r = 0.87, 0.65, 0.72, 0.72, and 0.64) and 7th day (r = 0.88, 0.70, 0.69, 0.69, and 0.87) and of the healthy group (r = 0.63, 0.71, 0.63, 0.63, and 0.74), respectively. The median HRV indexes of the AMI group on the 2nd and 7th day differed from the healthy group (P < 0.05): RMSSD = 10.37, 19.95, 24.81; RMSM = 23.47, 31.96, 43.79; LFnu = 0.79, 0.79, 0.62; HFnu = 0.20, 0.20, 0.37; LF/HF ratio = 3.87, 3.94, 1.65; ApEn = 1.01, 1.24, 1.31, respectively. There was agreement between the methods, suggesting that these have the same power to evaluate autonomic modulation of HR in both AMI patients and healthy subjects. AMI contributed to a reduction in cardiac signal irregularity, higher sympathetic modulation and lower vagal modulation.
- ItemAcesso aberto (Open Access)Measuring network's entropy in ADHD: A new approach to investigate neuropsychiatric disorders(Elsevier B.V., 2013-08-15) Sato, João Ricardo; Takahashi, Daniel Yasumasa; Hoexter, Marcelo Queiroz [UNIFESP]; Massirer, Katlin Brauer; Fujita, André; Fed Univ ABC; Princeton Univ; Universidade Federal de São Paulo (UNIFESP); Universidade Estadual de Campinas (UNICAMP); Universidade de São Paulo (USP)The application of graph analysis methods to the topological organization of brain connectivity has been a useful tool in the characterization of brain related disorders. However, the availability of tools, which enable researchers to investigate functional brain networks, is still a major challenge. Most of the studies evaluating brain images are based on centrality and segregation measurements of complex networks. in this study, we applied the concept of graph spectral entropy (GSE) to quantify the complexity in the organization of brain networks. in addition, to enhance interpretability, we also combined graph spectral clustering to investigate the topological organization of sub-network's modules. We illustrate the usefulness of the proposed approach by comparing brain networks between attention deficit hyperactivity disorder (ADHD) patients and the brain networks of typical developing (TD) controls. the main findings highlighted that GSE involving sub-networks comprising the areas mostly bilateral pre and post central cortex, superior temporal gyrus, and inferior frontal gyri were statistically different (p-value = 0.002) between ADHD patients and TO controls. in the same conditions, the other conventional graph descriptors (betweenness centrality, clustering coefficient, and shortest path length) commonly used to identify connectivity abnormalities did not show statistical significant difference. We conclude that analysis of topological organization of brain sub-networks based on GSE can identify networks between brain regions previously unobserved to be in association with ADHD. (C) 2013 Elsevier Inc. All rights reserved.
- ItemAcesso aberto (Open Access)Monitoramento das transições de regime em um leito de jorro empregando a análise wavelet(Universidade Federal de São Paulo, 2022-02-01) Silva, Talita Cerqueira [UNIFESP]; Maranhão, Vinicius Trindade [UNIFESP]; Silva, Carlos Alexandre Moreira da [UNIFESP]; http://lattes.cnpq.br/7740144753810520O leito de jorro surgiu como uma adaptação do leito fluidizado, mas diferente deste, a velocidade do ar gera um movimento ordenado e cíclico, que se assemelha ao de uma fonte de jardim. Tal operação unitária apresenta grande interesse por proporcionar uma intensa transferência de massa e calor, tornando-a altamente versátil, sendo muito empregada na indústria farmacêutica, de alimentos, química e agrícola. Infelizmente o leito de jorro apresenta dificuldades em sua operação em larga escala, devido aos problemas associados a determinação e controle de seus regimes fluidodinâmicos. Em função disso, este trabalho visou compreender e identificar os regimes fluidodinâmicos do leito de jorro, com base nos experimentos preliminares realizados por Butzge (2012) e utilizando-se processamento de sinais via a análise Wavelet. Existem diversas técnicas de processamento de sinais. A análise espectral transforma os sinais do domínio do tempo para o da frequência e a análise wavelet decompõe o sinal original em diversos sub-sinais, possibilitando assim o acesso a informações que não são facilmente observadas no sinal original por análise espectral. Foram realizadas análises sob os dados de flutuação de pressão em leito seco, com partículas de vidro que possuem diâmetros entre as faixas de 1,4 a 1,68mm e 2,4 a 2,6mm. Além disso, foram utilizadas no leito massas de 300 , 600 , 900 e 1200 g. A combinação entre os diâmetros das diferentes massas de leito geraram oito ensaios de flutuação de pressão que foram tratados inicialmente utilizando-se a análise espectral e posteriormente a análise wavelet. Os ensaios foram realizados aplicando-se uma variação de voltagem aos inversores que assim aumentavam a intensidade de vazão do gás, gerando diferentes sinais de pressão que foram utilizados neste trabalho. Notou-se alguns padrões de regime por análise espectral, sendo esta muito acertiva para a identificação dos leitos fixos e rompimento do jorro. No caso do regime de início do jorro, pequeno jorro, jorrinho e movimento circular, a melhor forma de identificação dos regimes foi a observação concomitante das duas análises. As instabilidades no jorro foi o único comportamento observado de forma nítida apenas na análise wavelet.
- ItemAcesso aberto (Open Access)Revealing the role of the autonomic nervous system in the development and maintenance of Goldblatt hypertension in rats(Elsevier B.V., 2014-07-01) Oliveira-Sales, Elizabeth Barbosa de [UNIFESP]; Toward, Marie Ann; Campos, Ruy Ribeiro [UNIFESP]; Julian Francis Richmond; Univ Bristol; Universidade Federal de São Paulo (UNIFESP)Despite extensive use of the renovascular/Goldblatt model of hypertension-2K-1C, and the use of renal denervation to treat drug resistant hypertensive patients, autonomic mechanisms that underpin the maintenance of this hypertension are important yet remain unclear. Our aim was to analyse cardiovascular autonomic function by power spectral density analysis of both arterial pressure and pulse interval measured continuously by radio telemetry for 6 weeks after renal artery clipping. Mean arterial pressure increased from 106 +/- 5 to 185 +/- 2 mm Hg during 5 weeks post clipping when it stabilized. A tachycardia developed during the 4th week, which plateaued between weeks 5 and 6. the gain of the cardiac vagal baroreflex decreased immediately after clipping and continued to do so until the 5th week when it plateaued (from -2.4 +/- 0.09 to -0.8 +/- 0.04 bpm/mm Hg; P < 0.05). A similar time course of changes in the high frequency power spectral density of the pulse interval was observed (decrease from 13.4 +/- 0.6 to 8.3 +/- 0.01 ms(2); P < 0.05). There was an increase in both the very low frequency and low frequency components of systolic blood pressure that occurred 3 and 4 weeks after clipping, respectively. Thus, we show for the first time the temporal profile of autonomic mechanisms underpinning the initiation, development and maintenance of renovascular hypertension including: an immediate depression of cardiac baroreflex gain followed by a delayed cardiac sympathetic predominance; elevated sympathetic vasomotor drive occurring after the initiation of the hypertension but coinciding during its mid-development and maintenance. (C) 2014 the Authors. Published by Elsevier B.V.