951 resultados para Multiple-Time Scale Problem


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Baseado no conjunto de dados diários de precipitação e temperatura do ar de oito estações meteorológicas sobre o Pará, pertencentes ao INMET, disponíveis no período 1961-2007, foram calculados índices de extremos climáticos através da metodologia estatística do software RClimdex. Utilizando-se ainda um conjunto de dados mensais de precipitação de 134 estações pluviométricas da Amazônia oriental, provenientes da ANA e INMET, foram analisadas as tendências anual e sazonal num período de 25 a 37 anos (1970-2009), através da aplicação da estatística não-paramétrica (teste de Mann-Kendall e método de Sen). E por fim, utilizaram-se dados de desmatamento do PRODES/INPE no período 2000-2007, para analisar a possível influência do desmatamento nas tendências de precipitação anual e sazonal do Pará. Considerando os índices de extremos climáticos referentes aos dados diários de precipitação, constatou-se que a variabilidade interanual dos índices possui relações com os episódios ENOS e as fases do Dipolo do Atlântico. Para os extremos climáticos de temperatura evidenciaram-se reduções sistemáticas dos dias frios (TX10p) e aumentos sistemáticos da mínima da máxima temperatura (TXN), da percentagem de noites quentes (TX90p) e da temperatura máxima da máxima (TXX). Os resultados das tendências da precipitação anual usando os testes não-paramétricos evidenciaram que do total de 134 estações, em torno de 51% apresentam tendências positivas e 41% tendências negativas sobre a Amazônia oriental. Contudo, essas tendências anuais “mascararam” de certa forma as tendências sazonais, cujos resultados mostraram-se mais diversificados, explicando melhor os aspectos da variabilidade climática regional. Para o trimestre MAM, observaram-se 99 estações (74%) com tendências positivas, indicando que a quantidade de precipitação durante o período chuvoso principal vem aumentando sistematicamente durante a última década. Em DJF, notaram-se 45 estações (34%) com tendências positivas e 78 estações (58%) com tendências negativas. Por outro lado, nos trimestres que englobam o período seco ou menos chuvoso verificaram-se tendências sazonais predominantemente negativas, com 84 estações (62%) em JJA e 89 estações (66%) em SON. Portanto, a evidência observacional de que a precipitação do período seco encontra-se em diminuição gradativa nas últimas décadas corrobora com a hipótese de que o desmatamento associa-se com a redução da precipitação em escala regional, porém sugere-se que isso ocorra em escala de tempo sazonal.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Pós-graduação em Engenharia Elétrica - FEIS

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Experimental etch/leach of Carboniferous Limestone gravels on a laboratory time-scale has demonstrated that 234U 238U activity ratios (AR's) greater than the radiochemical equilibrium value may be generated on short time-scales. The molar U/Ca and Mg/Ca ratios show that both U and Mg are leached preferentially relative to Ca whereas the molar U/Mg ratio is only slightly greater than that of the rock matrix. The generation of enhanced AR's is attributed to a two-stage process in which the limestone surface is dissolved by zero-order etch and silicate minerals so released are subjected to first-order chemical leach of U and Mg. The implications of these results for the production of enhanced AR's in Carboniferous Limestone groundwater are discussed. It is suggested that chemical leaching or exchange of U between groundwater and its particulate load or at the aquifer fluid-solid interface is an important mechanism controlling AR changes as groundwater migrates beyond a redox boundary. AR's for dissolved U in groundwater are more probably related to chemical equilibria than to groundwater age. © 1993.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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On the basis of the full analytical solution of the overall unitary dynamics, the time evolution of entanglement is studied in a simple bipartite model system evolving unitarily from a pure initial state. The system consists of two particles in one spatial dimension bound by harmonic forces and having its free center of mass initially localized in space in a minimum uncertainty wavepacket. The existence of such initial states in which the bound particles are not entangled is discussed. Galilean invariance of the system ensures that the dynamics of entanglement between the two particles is independent of the wavepacket mean momentum. In fact, as shown, it is driven by the dispersive center of mass free dynamics, and evolves in a time scale that depends on the interparticle interaction in an essential way.

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The estimation of reference evapotranspiration (ETo), used in water balance, allows to determine soil water content, assisting on irrigation management. The present study aimed to compare simple ETo estimating methods with the Penman-Monteith (FAO), in the folowing time scales: daily, 5, 10, 15 and 30 days and monthly in the counties of Frederico Westphalen and Palmeira das Missoes, in the Rio Grande do Sul state, Brazil. The methods tested had their efficiency improved by increasing the time scale of analysis, keeping the same performance for both locations. The highest and lowest ETo values occurred in December and June, respectively. Most methods underestimated ETo. For any of the time scales Makking and Radiaton FAO24 methods can replace the Penman-Monteith for estimating ETo.

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Aims. We study galaxy pair samples selected from the Sloan Digital Sky Survey (SDSS-DR7) and we perform an analysis of minor and major mergers with the aim of investigating the dependence of galaxy properties on interactions. Methods. We build a galaxy pair catalog requiring r(p) < 25 kpc h(-1) and Delta V < 350 km s(-1) within redshift z < 0.1. By visual inspection of SDSS images we remove false identifications and we classify the interactions into three categories: pairs undergoing merging, M; pairs with evident tidal features, T; and non disturbed, N. We also divide the pair sample into minor and major interactions according to the luminosity ratio of the galaxy members. We study star formation activity through colors, the 4000 angstrom break, and star formation rates. Results. We find that similar to 10% of the pairs are classified as M. These systems show an excess of young stellar populations as inferred from the D-n(4000) spectral index, colors, and star formation rates of the member galaxies, an effect which we argue is directly related to the ongoing merging process. We find similar to 30% of the pairs exhibiting tidal features (T pairs) with member galaxies showing evidence of old stellar populations. This can be associated either to the disruptive effect of some tidal interactions, or to the longer time-scale of morphological disturbance with respect to the bursts of the tidal induced star formation. Regardless of the color distribution, we find a prominent blue peak in the strongest mergers, while pairs with tidal signs under a minor merger show a strong red peak. Therefore, our results show that galaxy interactions are important in driving the evolution of galaxy bimodality. By adding stellar masses and star formation rates of the two members of the pairs, we explore the global efficiency of star formation of the pairs as a whole. We find that, at a given total stellar mass, major mergers are significantly more efficient (a factor approximate to 2) in forming new stars, with respect to both minor mergers or a control sample of non-interacting galaxies. We conclude that the characteristics of the interactions and the ratio of luminosity galaxy pair members involved in a merger are important parameters in setting galaxy properties.

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The overall aim of the present thesis was to develop and characterise an age assessment method based on incremental lines in dental cementum using contemporary bovine teeth and teeth from archaeological faunal assemblages. The investigations also included two other age assessment methods: tooth wear pattern and macroscopic dental measurements. The first permanent mandibular molar and lower jaws from 70 contemporary cattle of known age and 170 archaeological molar sets from ten different Swedish archaeological sites were used. The following conclusions were drawn: • The number of incremental lines in the dental cementum varied between different parts of the tooth root as well as within one and the same individual. The results from contemporary cattle of known age showed a strong relationship between age and incremental lines in the cementum of the distal part of the mesial root (R2=65.5%) and the known ages of the animals. • With the “best” model variation in age could be explained to 65.5% (R2) by the number of incremental lines. Thus, the remaining age variation (approximately 35%) could not be explained by these lines. Other factors than must thus be responsible. However, with the exception of calves born the present material did not reveal any such significant relationship. • The results from cattle of known age indicate that the method of assessing age on the basis of cemental incremental lines is more reliable than other methods such as tooth wear or tooth measurements. However, by combining counting incremental lines and one variable assessing tooth dimension (tooth height) a slightly stronger relationship could be obtained (R2=74.5%). The results from age assessment of the medieval and post-Reformation cattle emphasize the importance of supplementing any age estimation of archaeological assemblages based on dental indicators with characteristics for the particular assessment model. Furthermore, conclusions based on age assessment with such models can not be drawn with any more detailed time scale than about 2 years leaving at best only 25% (R2) of factors influencing the dental indicator(s) utilized in the model unexplained. The accuracy of the age assessment required by the particular historical context in which the archaeological remains are found should thus decide what level of accuracy should be chosen.

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Temporal and spatial variations of the larval fish community off the island of Gran Canaria (Canary Islands) were studied in weekly surveys from October 2005 to June 2006. A total of 156 taxa, belonging to 51 families and 15 orders, were identified. Myctophidae was by far the most abundant family (30%), followed by Sparidae (11%), Clupeidae (9%) and Gonostomatidae (7%). As expected for an oceanic island, neritic and oceanic taxa contributed in similar proportions. Leeward and windward retention areas were found for total egg and neritic larval abundance. However, seasonality showed a stronger influence on the annual larval assemblage than sampling site, as the latter was not significant on a long time scale. Results suggest that there are two seasonal larval assemblages corresponding to the two main characteristic periods of the water column in these waters: mixing (winter) and stratification (summer). In addition, a significant relationship was recorded between lunar illumination and small mesozooplankton biomass, suggesting that this relationship may be extended to certain neritic families. The most abundant neritic larvae (Sparidae) showed this lunar pattern, which partially supports a recent hypothesis about the effect of lunar illumination on larval fish survival and development in subtropical waters.