908 resultados para Spatio-temporalité


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Archived soils could represent a valuable resource for the spatio-temporal inventory of soil carbon stability. However, archived soils are usually air-dried before storage and the impact of a drying pretreatment on physically and chemically-defined C fractions has not yet been fully assessed. Through the comparison of field-moist and corresponding air-dried (at 25oC for 2 weeks) forest soil samples, we examined the effect of air-drying on: a) the quantity and the quality of cold- (CWEC) and hot-water (HWEC) extractable C and b) the concentration of C in physically isolated fractions (free- and intra-aggregate light and organo-mineral). Soil samples were collected from the organic (O) and mineral (A and B) horizons of three different forest soils from southeastern England: (i) Cambisol under Pine (Pinus nigra); (ii) Cambisol under Beech (Fagus sylvatica) and (iii) Gleysol under oak (Quercus robur). CWEC concentrations for dry samples were up to 2 times greater than for corresponding field moist samples and had significantly (p < 0.001) higher phenolic content. However, the effect of drying pretreatment on HWEC, its phenolic content was not significant (p > 0.05) for most samples. Dried soils had significantly (p < 0.001) higher concentrations of free light-C while having lower concentrations of intra-aggregate-C when compared to moist samples (p < 0.001). However, fine silt and clay fractions were not significantly affected by the drying pretreatment (p=0.789). Therefore, based on the results obtained from gleysol and cambisol forest soils studied here, C contents in hot-water extractions and fine particle size physical fractions (< 25µm) seem to be robust measurements for evaluating C fractions in dried stored forest soils. Further soil types should be tested to evaluate the wider generality of these findings.

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The size and complexity of data sets generated within ecosystem-level programmes merits their capture, curation, storage and analysis, synthesis and visualisation using Big Data approaches. This review looks at previous attempts to organise and analyse such data through the International Biological Programme and draws on the mistakes made and the lessons learned for effective Big Data approaches to current Research Councils United Kingdom (RCUK) ecosystem-level programmes, using Biodiversity and Ecosystem Service Sustainability (BESS) and Environmental Virtual Observatory Pilot (EVOp) as exemplars. The challenges raised by such data are identified, explored and suggestions are made for the two major issues of extending analyses across different spatio-temporal scales and for the effective integration of quantitative and qualitative data.

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Synoptic wind events in the equatorial Pacific strongly influence the El Niño/Southern Oscillation (ENSO) evolution. This paper characterizes the spatio-temporal distribution of Easterly (EWEs) and Westerly Wind Events (WWEs) and quantifies their relationship with intraseasonal and interannual large-scale climate variability. We unambiguously demonstrate that the Madden–Julian Oscillation (MJO) and Convectively-coupled Rossby Waves (CRW) modulate both WWEs and EWEs occurrence probability. 86 % of WWEs occur within convective MJO and/or CRW phases and 83 % of EWEs occur within the suppressed phase of MJO and/or CRW. 41 % of WWEs and 26 % of EWEs are in particular associated with the combined occurrence of a CRW/MJO, far more than what would be expected from a random distribution (3 %). Wind events embedded within MJO phases also have a stronger impact on the ocean, due to a tendency to have a larger amplitude, zonal extent and longer duration. These findings are robust irrespective of the wind events and MJO/CRW detection methods. While WWEs and EWEs behave rather symmetrically with respect to MJO/CRW activity, the impact of ENSO on wind events is asymmetrical. The WWEs occurrence probability indeed increases when the warm pool is displaced eastward during El Niño events, an increase that can partly be related to interannual modulation of the MJO/CRW activity in the western Pacific. On the other hand, the EWEs modulation by ENSO is less robust, and strongly depends on the wind event detection method. The consequences of these results for ENSO predictability are discussed.

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We establish a methodology for calculating uncertainties in sea surface temperature estimates from coefficient based satellite retrievals. The uncertainty estimates are derived independently of in-situ data. This enables validation of both the retrieved SSTs and their uncertainty estimate using in-situ data records. The total uncertainty budget is comprised of a number of components, arising from uncorrelated (eg. noise), locally systematic (eg. atmospheric), large scale systematic and sampling effects (for gridded products). The importance of distinguishing these components arises in propagating uncertainty across spatio-temporal scales. We apply the method to SST data retrieved from the Advanced Along Track Scanning Radiometer (AATSR) and validate the results for two different SST retrieval algorithms, both at a per pixel level and for gridded data. We find good agreement between our estimated uncertainties and validation data. This approach to calculating uncertainties in SST retrievals has a wider application to data from other instruments and retrieval of other geophysical variables.

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The Castanhao reservoir was built in the state of Ceara, a dry region in Northeastern Brazil, to regulate the flow of the Jaguaribe River, for irrigation, and for power generation. It is an earth-filled dam, 60 m high, with a water capacity of 4.5 x 10(9) m(3). The seismicity in the area has been monitored since 1998, with a few interruptions, using one analog or one digital station and, during a few periods, a three-station network. The first earthquakes likely to be induced events were detected in 2003, when the water level was about 20 in high. In early 2004 a very heavy rainfall season quickly filled the reservoir. Shortly after, an increase in the seismic activity occurred and many micro-earthquakes were recorded. We suggest that this activity resulted from an increase in pore pressure due to undrained response. Therefore, we may classify this cluster of microearthquakes as ""initial seismicity."" We deployed a network with four analog stations in the area, following this activity, to determine the epicentral zone. At least three epicentral areas under the reservoir were detected. The spatio-temporal analysis of the available data revealed that the seismicity occurs in clusters and that these were activated at different periods. We identified four sets of faults (N-S-, E-W-, NW-SE-, and NE-SW-oriented), some of which moved in shallow crustal levels and as recently as the Quaternary (1.8 Ma). Under the present-day stress regime, the last two sets moved as strike-slip structures. We suggest a possible correlation between dormant faults and the observed induced seismicity. (c) 2008 Elsevier B.V. All rights reserved.

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Reactive oxygen species (ROS) appear to be involved in several neurodegenerative disorders. We tested the hypothesis that oxidative stress could have a role in the hippocampal neurodegeneration observed in temporal lobe epilepsy induced by pilocarpine. We first determined the spatio-temporal pattern of ROS generation, by means of detection with dihydroethidium oxidation, in the CA1 and CA3 areas and the dentate gyrus of the dorsal hippocampus during status epilepticus induced by pilocarpine. Fluoro-Jade B assays were also performed to detect degenerating neurons. ROS generation was increased in CA1, CA3 and the dentate gyrus after pilocarpine-induced seizures, which was accompanied by marked cell death. Treatment of rats with a NADPH oxidase inhibitor (apocynin) for 7 days prior to induction of status epilepticus was effective in decreasing both ROS production (by an average of 20%) and neurodegeneration (by an average of 61%). These results suggest an involvement of ROS generated by NADPH oxidase in neuronal death in the pilocarpine model of epilepsy. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

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Connexin (Cx) channels and hemichannels are involved in essential processes during nervous system development such as apoptosis, propagation of spontaneous activity and interkinetic nuclear movement. In the first part of this study, we extensively characterized Cx gene and protein expression during retinal histogenesis. We observed distinct spatio-temporal patterns among Studied Cx and an overriding, ubiquitous presence of Cx45 in progenitor cells. The role of Cx-mediated communication was assessed by using broad-spectrum (carbenoxotone, CBX) and Cx36/Cx50 channel-specific (quinine) blockers. In vivo application of CBX, but not quinine, caused remarkable reduction in retinal thickness, suggesting changes in cell proliferation/apoptosis ratio. Indeed, we observed a decreased number of mitotic cells in CBX-injected retinas, with no significant changes in the expression of PCNA, a marker for cells in proliferative state. Taken together, Our results pointed a pivotal role of Cx45 in the developing retina. Moreover, this study revealed that Cx-mediated Communication is essential in retinal histogenesis, particularly in the control of cell proliferation. (C) 2009 ISDN. Published by Elsevier Ltd. All rights reserved.

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The transition to turbulence (spatio-temporal chaos) in a wide class of spatially extended dynamical system is due to the loss of transversal stability of a chaotic attractor lying on a homogeneous manifold (in the Fourier phase space of the system) causing spatial mode excitation Since the latter manifests as intermittent spikes this has been called a bubbling transition We present numerical evidences that this transition occurs due to the so called blowout bifurcation whereby the attractor as a whole loses transversal stability and becomes a chaotic saddle We used a nonlinear three-wave interacting model with spatial diffusion as an example of this transition (C) 2010 Elsevier B V All rights reserved

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We investigated the transition to spatio-temporal chaos in spatially extended nonlinear dynamical systems possessing an invariant subspace with a low-dimensional attractor. When the latter is chaotic and the subspace is transversely stable we have a spatially homogeneous state only. The onset of spatio-temporal chaos, i.e. the excitation of spatially inhomogeneous modes, occur through the loss of transversal stability of some unstable periodic orbit embedded in the chaotic attractor lying in the invariant subspace. This is a bubbling transition, since there is a switching between spatially homogeneous and nonhomogeneous states with statistical properties of on-off intermittency. Hence the onset of spatio-temporal chaos depends critically both on the existence of a chaotic attractor in the invariant subspace and its being transversely stable or unstable. (C) 2008 Elsevier B.V. All rights reserved.

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We investigated the temporal dynamics and changes in connectivity in the mental rotation network through the application of spatio-temporal support vector machines (SVMs). The spatio-temporal SVM [Mourao-Miranda, J., Friston, K. J., et al. (2007). Dynamic discrimination analysis: A spatial-temporal SVM. Neuroimage, 36, 88-99] is a pattern recognition approach that is suitable for investigating dynamic changes in the brain network during a complex mental task. It does not require a model describing each component of the task and the precise shape of the BOLD impulse response. By defining a time window including a cognitive event, one can use spatio-temporal fMRI observations from two cognitive states to train the SVM. During the training, the SVM finds the discriminating pattern between the two states and produces a discriminating weight vector encompassing both voxels and time (i.e., spatio-temporal maps). We showed that by applying spatio-temporal SVM to an event-related mental rotation experiment, it is possible to discriminate between different degrees of angular disparity (0 degrees vs. 20 degrees, 0 degrees vs. 60 degrees, and 0 degrees vs. 100 degrees), and the discrimination accuracy is correlated with the difference in angular disparity between the conditions. For the comparison with highest accuracy (08 vs. 1008), we evaluated how the most discriminating areas (visual regions, parietal regions, supplementary, and premotor areas) change their behavior over time. The frontal premotor regions became highly discriminating earlier than the superior parietal cortex. There seems to be a parcellation of the parietal regions with an earlier discrimination of the inferior parietal lobe in the mental rotation in relation to the superior parietal. The SVM also identified a network of regions that had a decrease in BOLD responses during the 100 degrees condition in relation to the 0 degrees condition (posterior cingulate, frontal, and superior temporal gyrus). This network was also highly discriminating between the two conditions. In addition, we investigated changes in functional connectivity between the most discriminating areas identified by the spatio-temporal SVM. We observed an increase in functional connectivity between almost all areas activated during the 100 degrees condition (bilateral inferior and superior parietal lobe, bilateral premotor area, and SMA) but not between the areas that showed a decrease in BOLD response during the 100 degrees condition.

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Refraction, interference, and diffraction are distinguishing features of wavelike phenomena. Although they are usually associated only with a purely spatial wave-propagation pattern, analogs to interference and diffraction involving the spatio-temporal dynamics of waves in one dimension have been discussed. We complete the triplet of analogies by discussing how spatio-temporal analogs to refraction are exhibited by a quantum particle in one dimension that is scattering off a step barrier. Similarly, birefringence in spacetime occurs for a spin-1/2 particle in a magnetic field.

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This thesis contributes to the heuristic optimization of the p-median problem and Swedish population redistribution.   The p-median model is the most representative model in the location analysis. When facilities are located to a population geographically distributed in Q demand points, the p-median model systematically considers all the demand points such that each demand point will have an effect on the decision of the location. However, a series of questions arise. How do we measure the distances? Does the number of facilities to be located have a strong impact on the result? What scale of the network is suitable? How good is our solution? We have scrutinized a lot of issues like those. The reason why we are interested in those questions is that there are a lot of uncertainties in the solutions. We cannot guarantee our solution is good enough for making decisions. The technique of heuristic optimization is formulated in the thesis.   Swedish population redistribution is examined by a spatio-temporal covariance model. A descriptive analysis is not always enough to describe the moving effects from the neighbouring population. A correlation or a covariance analysis is more explicit to show the tendencies. Similarly, the optimization technique of the parameter estimation is required and is executed in the frame of statistical modeling. 

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No Sudoeste do Rio Grande do Sul ocorrem manchas de substrato arenoso sem cobertura vegetal, conhecidos regionalmente como areais. A tese reexamina o problema e suas causas, enfatizando o papel da vegetação natural e propondo estratégias para a revegetação e prevenção à arenização em sistemas pastoris. Evidências foram obtidas em levantamentos e experimento avaliando processos de degradação e regeneração da vegetação campestre do entorno de areais. Levantamento da vegetação, realizado em 41 parcelas de 4,5 x 9,0 m na borda de 11 areais indicou a existência de dois tipos de comunidades. Areais de Manoel Viana e aqueles usados pelo gado em São Francisco de Assis, com alto percentual de substrato exposto, são caracterizados principalmente por Elyonurus sp., Axonopus pressus e Butia paraguayensis. Areais de Alegrete e aqueles excluídos de pastejo em São Francisco de Assis, com menor percentual de substrato exposto, são caracterizados principalmente por Andropogon lateralis e Aristida laevis. Foi também avaliada a dinâmica da vegetação em gradientes de arenização, usando quadros (0,25 m2) contíguos em 16 transecções de 10 m localizadas em cinco areais. A dinâmica da vegetação foi associada ao uso das áreas pelo gado, pois houve aumento, após 14 meses, de substrato exposto em comunidades de areais sob pastoreio, enquanto que aquelas sem gado apresentaram uma dinâmica espacial-temporal de maior estabilidade da cobertura vegetal. Um experimento foi realizado para avaliar, durante 8 meses, o efeito de níveis controlados de soterramento por areia (0, 5, 10 e 20 cm) em comunidades do entorno de dois areais sob pastoreio. Comunidades caracterizadas por Elyonurus sp. e Axonopus pressus foram mais tolerantes ao soterramento. As evidências indicam que a exclusão do gado de areais pode ser uma alternativa eficaz para a revegetação de areais por espécies das comunidades naturais do entorno. Ademais, a arenização pode ser prevenida pelo uso adequado dos campos que mantenha a cobertura vegetal natural protegendo o solo dos processos erosivos hídrico e eólico.

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O objetivo deste trabalho foi avaliar cenários de níveis freáticos extremos, em bacia hidrográfica, por meio de métodos de análise espacial de dados geográficos. Avaliou-se a dinâmica espaço‑temporal dos recursos hídricos subterrâneos em área de afloramento do Sistema Aquífero Guarani. As alturas do lençol freático foram estimadas por meio do monitoramento de níveis em 23 piezômetros e da modelagem das séries temporais disponíveis de abril de 2004 a abril de 2011. Para a geração de cenários espaciais, foram utilizadas técnicas geoestatísticas que incorporaram informações auxiliares relativas a padrões geomorfológicos da bacia, por meio de modelo digital de terreno. Esse procedimento melhorou as estimativas, em razão da alta correlação entre altura do lençol e elevação, e agregou sentido físico às predições. Os cenários apresentaram diferenças quanto aos níveis considerados extremos - muito profundos ou muito superficiais - e podem subsidiar o planejamento, o uso eficiente da água e a gestão sustentável dos recursos hídricos na bacia.

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