Browsing by Issue Date, starting with "2010-07"
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- Regressão não-linear utilizando a ferramenta Solver® do Microsoft Excel®Publication . Esteves, EduardoEm vários domínios do conhecimento científico são usados modelos matemáticos para descrever um conjunto de dados empíricos. Se no caso dos modelos lineares, a análise de regressão para obter os parâmetros dos modelos é "simples" e vulgarizada, é mais difícil ajustar aos dados funções (matematicamente) mais "complicadas", p.ex. modelos não-lineares. Neste artigo, pretende-se 1) apresentar os conceitos fundamentais da análise de regressão não-linear, 2) descrever, usando um exemplo, a utilização da ferramenta Solver® do Microsoft Excel® para analisar problemas cujo objectivo é "descrever" relações estatísticas (não-lineares) entre variáveis, e 3) compilar os "problemas" identificados com a utilização do Excel® (incluindo o Solver®) como ferramenta de análise estatística.
- The TV-APM interface: a web service for collaborative modelingPublication . Rodríguez, O. C.; Silva, A.; Zabel, F.; Jesus, S. M.Current development of Internet access, together with available zero-cost Open Source applications (like, for instance, PHP, Python, etc.) can be integrated in order to minimize the constrains induced by the geographical separation of international centers, which collaborate in a given project. The advantage of such approach lies in the sharing of common analysis methods, without particular constrains to specific directions of analysis. The discussion presented in this paper describes the Time Variable Acoustic Propagation Model (TV-APM) web interface, which was created as a collaborative service of acoustic modeling for the participants of the PHITOM and UAN projects. This paper describes the general architecture of the interface, its current shortcomings and advantages, and presents a set of modeling results for short range acoustic propagation, which accounts for source–array and sea surface motion.
- A permeance-based transformer model and its application to winding interturn arcing fault studiesPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper investigates the behavior of power transformers under the occurrence of permanent or intermittent winding insulation faults.
- Day-night differences in Cunene horse mackerel (Trachurus trecae) acoustic relative densities off AngolaPublication . Velho, Filomena Vaz; Barros, Pedro; Axelsen, Bjorn ErikThe assessment and the management of the Cunene horse mackerel in Angola rely heavily on abundance estimates from hydroacoustic surveys. Acoustic data collected from 1994 to 1999 were analysed to quantify diurnal variation in relative acoustic densities at 38 kHz. The nautical-area scattering coefficient (s(A), m(2) nautical mile(-2)) was characterized by clear day night differences: s(A) values recorded during the day were significantly higher (mean s(A): 135 m(2) nautical mile(-2)) than the corresponding night-time values (mean s(A) 83 m(2) nautical mile(-2)). This pattern is associated with differences in behaviour and horizontal and vertical distributions between day and night: by day, the fish school near the seabed, and by night, they move into the pelagic zone and disperse into widespread scattering layers. More than 40% of the total backscatter by day originated from the bottom 10 m, but at night this proportion decreased to <10%. The findings demonstrate considerable influences of behaviour and aggregation dynamics on acoustic measurements. Possible implications for the estimates of acoustic abundance are discussed in the light of the differences.
- Funcionalidade e incapacidade: aspectos conceptuais, estruturais e de aplicação da Classificação Internacional de Funcionalidade, Incapacidade e Saúde (CIF)Publication . Fontes, Ana Paula; Fernandes, Ana Alexandre; Botelho, Maria AmáliaO objectivo principal do presente artigo é apresentar a Classificação Internacional de Funcionalidade, Incapacidade e Saúde (CIF), que faz parte da “família” de classificações desenvolvidas pela Organização Mundial de Saúde. A CIF oferece uma linguagem unificada e normalizada, bem como um marco conceptual para descrever a saúde e os estados relacionados com a saúde, constituindo um valioso instrumento de utilidade prática em Saúde Pública. O modelo estabelece-se em duas grandes partes: a primeira que agrupa a Funcionalidade e a Incapacidade com duas componentes: a) Funções e Estruturas Corporais e b) Actividades e Participação. Uma segunda parte que engloba os Factores Contextuais, também com duas componentes: c) Factores Ambientais e d) Factores Pessoais. As componentes estão classificadas mediante categorias, organizadas numa estrutura hierárquica de 4 níveis. Neste trabalho analisamos o marco conceptual e a estrutura da CIF e descrevemos as linhas de acção relativamente à sua difusão e implementação.
- Interactions between Green Turtles (Chelonia mydas) and Foxes (Vulpes vulpes arabica, V. rueppellii sabaea, and V. cana) on Turtle Nesting Grounds in the Northwestern Indian Ocean: Impacts of the Fox Community on the Behavior of Nesting Sea Turtles at the Ras Al Hadd Turtle Reserve, OmanPublication . Mendonca, Vanda; Al Saady, Salim; Al Kiyumi, Ali; Erzini, KarimVanda Mariyam Mendonca, Salim Al Saady, Ali Al Kiyumi, and Karim Erzini (2010) Interactions between green turtles (Chelonia mydas) and foxes (Vulpes vulpes arabica, V. rueppellii sabaea, and V cana) on turtle nesting grounds in the northwestern Indian Ocean: impacts of the fox community on the behavior of nesting sea turtles at the Ras Al Hadd Turtle Reserve, Oman. Zoological Studies 49(4): 437-452. Green turtles Chelonia mydas nest year round at the Ras Al Hadd Nature Reserve, Oman, with a distinct lower-density nesting season from Oct. to May, and a higher-density nesting season from June to Sept. On these beaches, the main predators of turtle eggs and hatchlings are foxes Vulpes spp., wolves Canis lupus arabs, and wild cats Felis spp. and Caracal caracal schmitzi. During 1999-2001, both the nesting behavior of these turtles and the diets of foxes (the main predator on the beaches) were investigated, and we tested whether female turtles were able to avoid/reduce predation pressure on their eggs and hatchlings on the nesting grounds. Elsewhere in the region and globally, foxes are known to feed on rodents, lizards, birds, and insects, but at Ras Al Hadd, their diet is basically composed of sea turtle eggs and hatchlings (comprising about 95% in volume), with smaller contributions from other marine invertebrates (mostly ghost crabs Ocypode spp. and large gastropods), although they also sporadically ingested birds and lizards. The ability to adapt to a diet of sea turtle eggs and hatchlings, on these beaches, is certainly a factor behind the success of this carnivore community in the arid lands of the Arabian Peninsula. Field experiments indicated that nesting sea turtles recognized both natural predators and humans as threats to their offspring, and this was reflected in modifications to their nesting behavior. In relatively undisturbed areas (by both natural predators and humans), sea turtle nest density was significantly higher, and nests were placed further away from the surf's edge, in contrast to results from relatively disturbed areas, where turtle nests were closer to the surf's edge, thus reducing the distance hatchlings had to travel when they emerge and begin their journey to the sea. Nesting turtles interrupted their nesting cycle if they sensed the presence of people or foxes, returning to the sea without laying a clutch. However, if they had already initiated oviposition when they sensed the presence of people and/or predators, they continued, although they significantly increased efforts to camouflage their nests. Other reasons behind nest site abandonment included sand collapsing events (critical during preparation of the egg chamber) and intraspecific competition for nest sites. These behavioral patterns of sea turtles result from their evolutionary adaptation to nesting on beaches, which surely played a role in their survival, but also highlight the importance of minimizing human disturbance and activities on turtle nesting beaches. http://zoolstud.sinica.edu.tw/Journals/49.4/437.pdf
- Inferring modules from human protein interactome classesPublication . Marras, Elisabetta; Travaglione, Antonella; Chaurasia, Gautam; Futschik, Matthias; Capobianco, EnricoBackground: The integration of protein-protein interaction networks derived from high-throughput screening approaches and complementary sources is a key topic in systems biology. Although integration of protein interaction data is conventionally performed, the effects of this procedure on the result of network analyses has not been examined yet. In particular, in order to optimize the fusion of heterogeneous interaction datasets, it is crucial to consider not only their degree of coverage and accuracy, but also their mutual dependencies and additional salient features. Results: We examined this issue based on the analysis of modules detected by network clustering methods applied to both integrated and individual (disaggregated) data sources, which we call interactome classes. Due to class diversity, we deal with variable dependencies of data features arising from structural specificities and biases, but also from possible overlaps. Since highly connected regions of the human interactome may point to potential protein complexes, we have focused on the concept of modularity, and elucidated the detection power of module extraction algorithms by independent validations based on GO, MIPS and KEGG. From the combination of protein interactions with gene expressions, a confidence scoring scheme has been proposed before proceeding via GO with further classification in permanent and transient modules. Conclusions: Disaggregated interactomes are shown to be informative for inferring modularity, thus contributing to perform an effective integrative analysis. Validation of the extracted modules by multiple annotation allows for the assessment of confidence measures assigned to the modules in a protein pathway context. Notably, the proposed multilayer confidence scheme can be used for network calibration by enabling a transition from unweighted to weighted interactomes based on biological evidence.
- Combined adaptive time reversal and DFE technique for time-varying underwater communicationsPublication . Vilaipornsawai, U.; Silva, A.; Jesus, S. M.This work presents a combined geometry-adapted passive Time Reversal (pTR) and Decision Feedback Equalizer (DFE) technique for time-variant underwater communications. We consider sustainable high data rate communications between a moving source and/or a moving receiver array, i.e. there is the presence of geometry changes such as range and depth changes. Such geometry changes can be partially compensated by employing a proper frequency shift on the probe impulse response in the pTR processing. We then refer to the geometry-adapted pTR as Frequency Shift pTR (FSpTR). With dense and long receiver array, a pTR-based technique possesses pulse compression property and can eliminate Inter-Symbol Interference (ISI) problem in multipath static channels. However, with a practical-size array and time-varying channels, a residual ISI always exists. Hence, in this work, we apply an adaptive DFE to further mitigate the residual ISI from the FSpTR, and call the technique as FSpTR-DFE. Performance of the FSpTR-DFE is evaluated using both experimental and simulated data, where an information rate of 2000 bps and BPSK signaling are considered. The RADAR’07 experimental data and the simulated data of the south Elba site are considered. In both data sets, a fast moving source with speed of 1.5 m/s is considered. The results show that the FSpTR-DFE technique outperforms the FSpTR as well as the technique combining the conventional pTR with DFE.
- Classification of three-dimensional ocean features using three-dimensional empirical orthogonal functionsPublication . Martins, N.; Calado, L.; Paula, A. C. de; Jesus, S. M.Acoustic tomography is now a well known method for remote estimation of water column properties. The problem is ill-conditioned and computationally intensive, if each spatial point varies freely in the inversion. Empirical orhogonal functions (EOFs) efficiently regularize the inversion, leading to a few (2, 3) coefficients to be estimated, giving a coherent estimate of the field. At small scales, EOFs are typically depth-dependent basis functions. The extension of the concept to larger-scale anisotropic fields requires horizontal discretization into cells, with corresponding coefficients. This becomes unstable and computationally intensive, having been overcome by two-dimensional depth-range EOFs, in the past. The present work extends the empirical orthogonal function concept to three dimensions, assessing the performance of the inversion for an instantaneous sound speed field constructed from dynamical predictions for Cabo Frio, Brazil. The results show that the large-scale features of the field are correctly estimated, though with strong ambiguity, using an acoustic source tens of km from an acoustic hydrophone array. Work is under progress, to remove the ambiguity and estimate finer details of the three-dimensional field, via the addition of multiple acoustic arrays.
- Compensating for source depth change and observing surface waves using underwater communication signalsPublication . Ijaz, S.; Silva, A.; Jesus, S. M.Underwater communications impose great challenges due to the unpredictable changes in the environment. In order to accommodate for these changes, equalizers are used to track the Impulse Responses (IRs) and compensate the intersymbol interference (ISI). Source and array depth shifts are one of the major contributing factors to continuous amplitude and phase changes in IR. These changes magnify the problem of data processing in which correlation between successive received signals is involved, e.g. passive Time Reversal (pTR) where a probe signal is sent ahead of the data for post cross-correlation. In this paper, an environment based algorithm is used for pTR equalization, where an appropriate frequency shift of the estimated IR compensates for the geometric changes such as source and array depth shifts. We have applied this Frequency Shift pTR equalizer (FSpTR) on real data collected from Underwater Acoustic Barrier 2007 (UAB’07) sea trial having 1000 baud BPSK signaling at carrier frequency of 6.25 KHz with a sudden source depth change of 0.5 m at various known instants of time. The results illustrate that a considerable gain can be attained using the environment based equalizer in the presence of source and/or array depth changes. Moreover by close analysis of the FSpTR results we have detected surface wave motion through the frequency shifts caused by the array depth variations.