In this letter, we report an enhanced MFDFA algorithm to compute the singu-larity spectra of the ... more In this letter, we report an enhanced MFDFA algorithm to compute the singu-larity spectra of the so-called E-F valley transition region, which is considered the most complex ionospheric layer because its plasma instability mechanisms are still not well understood. The results found for ∆α confirm the multifractal behaviour which is expected to be related to instabilities in the ionosphere as a whole, allowing, in an integrated scenario, to discuss new thermodynamic and plasma structural properties of the atmospheric layers that make up the Earth's ionosphere. Keywords: ionospheric plasma instabilities, multifractal analysis, equatorial valley region irregularities, inhomogeneous turbulence. With advances in the scientific computing, some nonlinear methods based 1 on fractal formalism and multiplicative cascade processes have found increased 2 application in ionospheric studies to understand the scaling structures and com-3 plexity, in recent times, and also, undergoing continuous improvements and wide 4 usability (Fornari et al., 2016; Neelakshi et al., 2019; Joshi et al., 2020). 5 In the ionospheric studies, the valley region, located in between the top 6 of the E region and the base of the F region with reduction in the electron 7 density, is still a less explored area of research compared to the F region as it 8 can be explored using powerful incoherent and coherent scatter radar and in 9 situ experiments. 10 Our earlier studies have demonstrated the potential of the DFA and MFDFA 11 on ionospheric data. The DFA studies (Fornari et al., 2016; Neelakshi et al., 12 2019) reveal the long-range correlation and non-homogeneous nature of the 13 ionospheric irregularities. We have reported the wide variation in the spec-14 tral indices and their large deviation from the homogeneous turbulence spectral 15 index. Also, we have shown that this wide variation in spectral indices is nei-16 * Neelakshi J.
Handbook of Research on Opinion Mining and Text Analytics on Literary Works and Social Media
In recent decades, the internet access growth has generated a substantial increase in the informa... more In recent decades, the internet access growth has generated a substantial increase in the information circulation in social media. Within the information variety circulating on the internet, extreme social events such as armed conflicts have become areas of great public interest because of their direct influence on society. The study of such data from social media is useful in understanding an event's evolution, in particular how threats over time can generate an endogenous evolution resulting in an extreme event. This chapter uses the technique of sentiment analysis to identify the threat degree of news about armed conflicts distributed in social media. This analysis generates an endogenous threat time series that is used to predict the future threat variation of the analyzed extreme social events. In the prediction of the endogenous time series, the authors apply the deep learning technique in a structure that uses the long short-term memory (LSTM) neural network.
A CUDA Algorithm for Two-Dimensional Detrended Fluctuation Analysis
16th International Conference on Information Technology-New Generations (ITNG 2019), 2019
This work presents a parallel implementation of the Two-Dimensional Detrended Fluctuation Analysi... more This work presents a parallel implementation of the Two-Dimensional Detrended Fluctuation Analysis (2D-DFA) algorithms using GPGPU-CUDA through the PyCUDA Wrapper. Both the monofractal and multifractal versions of 2D-DFA present poor performance in their sequential implementations because of high computational complexity, rendering ineffective the use for real-time applications and those classified as Big Data. However, these algorithms present the requirements needed to be parallelized using GPUs. Mainly because the same computation is performed in different sub-matrices of the data. Therefore, the concepts of data parallelism and independence, necessary for computation in GPUs were attending. The parallelization strategy was process simultaneously several sub-matrices, and not parallelizes the internal procedure in each sub-matrix. Matrices with different dimensions and Hurst exponents were generated for the validation of the method implemented. The results showed that both algori...
Pronóstico del índice planetario Kp usando modelos autoregresivos
Resumen El indice geomagnetico Kp se deriva del indice K a partir de las mediciones de trece esta... more Resumen El indice geomagnetico Kp se deriva del indice K a partir de las mediciones de trece estaciones localizadas alrededor de la Tierra entre las latitudes geomagneticas 48◦ y 63◦. Este indice se procesa cada tres horas, es cuasi-logaritmico y estima la actividad geomagnetica. Los valores de Kp estan dentro de un rango de 0 a 9 y conforman un conjunto de 28 valores discretos, se utiliza como uno de los parametros de entrada en muchos modelos ionosfericos y magnetosfericos. El objetivo de este trabajo es utilizar datos historicos del indice Kp para desarrollar una metodologia que permita hacer un pronostico del mismo en un intervalo de tiempo, como minimo, de tres horas. Se prueban cinco diferentes modelos de pronostico de los indices geomagneticos Kp y ap. Se utilizan como datos de entrada a los modelos, una serie temporal de valores del indice Kp desde 1932 hasta el 15/12/2012 a las 21:00 horas UT. La finalidad del modelo es pronosticar los tres valores posteriores al ultimo valor medido del indice Kp (las proximas 9 horas). El modelo AR resulta ser el de menor costo computacional y ofrece buenos resultados. El modelo ARIMA es eficiente para la prediccion del indice Kp en condiciones de perturbacion geomagnetica. Este trabajo ofrece una forma rapida y eficiente de hacer una prediccion del indice Kp, sin necesidad de usar datos de satelites que muchas veces demoran en ser publicados. Aunque se informa que los resultados del pronostico son mejores cuando se utilizan datos de satelites. Segun datos publicados, la correlacion lineal entre los valores pronosticados y los valores reales esta entorno de un 77 %, valor que es mejor que el 68.5% obtenido en este trabajo. Sin embargo, teniendo en cuenta que se trabajo solamente sobre la serie temporal estocastica del Kp, este valor de correlacion puede considerarse satisfactorio.
Journal of Computational Interdisciplinary Sciences, 2012
The study of the magnetic fields present in the solar corona is attracting increasing interest du... more The study of the magnetic fields present in the solar corona is attracting increasing interest due to strong evidence of its relation to the phenomena observed in that region of the solar atmosphere. From the last two decades we have available images of the solar corona with increasingly better resolution, so that the comparison of these images with the physical models developed to study the dynamics of coronal magnetic fields is a task of extreme importance in solar astrophysics. We present in this work a new approach for the use of Hough Transform (HT) in order to extract features from the solar coronal images obtained in the Extreme UltraViolet (EUV). Our methodology is based on the fragmentation of the image and using of Hough Transform to get results from each fragment, and then identifying the fragments of the same magnetic field line using an interconnection algorithm. Finally we developedthe evaluation of our methodology, where we proceed to compare the pixel coordinates of extracted magnetic field lines with those generated synthetically by the physical model. The features extraction algorithm is still under evaluation, but the early results have proved satisfactory.
An East-West, one-dimensional radio interferometer array consisting of five parabolic dish antenn... more An East-West, one-dimensional radio interferometer array consisting of five parabolic dish antennas has been set up at Cachoeira Paulista (longitude 45°0 20 W, latitude 22°41 19 S) for observations of the Sun and some of the strong sidereal sources by the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil. This is Phase-I of the proposed Brazilian Decimetric Array and can be operated at any frequency in the range 1.2-1.7 GHz. The instrument has been in operation since November 2004 onwards at 1.6 GHz. The an
Oscar Manley passed away in the Fall of 2001. He was a remarkable scientist, with great physical ... more Oscar Manley passed away in the Fall of 2001. He was a remarkable scientist, with great physical intuition and mathematical acumen. His influence on his coauthors and other collaborators will be permanent. This article is the direct result of his repeated request to work with the more physical concept of finite time averages.
Spectral and polarization parameters of geomagnetic pulsations are computed from geomagnetic data... more Spectral and polarization parameters of geomagnetic pulsations are computed from geomagnetic data recorded at ground station, using multitaper and singular value decomposition (SVD) analysis. These techniques were adapted to provide appropriate polarization parameters of pulsations. The spectra are comparable to those obtained from classical methods, but the dynamic spectra of degree of polarization present more localized spectral information, allowing easier identification of polarized pulsation events mixed to noise, which are associated by coherent sources of MHD waves. The time-frequency polarization parameters of polarized pulsations show different signatures to regular and irregular pulsation events, and the multiwavelet polarization method is used to compare with multitaper. The regular pulsation events showed to be more continuous on time with a narrow spectral frequency band, while the irregular events showed to be more localized on time with a wide spectral frequency band. The dynamic analysis of multitaper method is indicated to characterize regular pulsations and the time-frequency analysis of multiwavelet method efficiently detects irregular pulsations. The continuous multiwavelet analysis of ellipticity and azimuth is useful in progressively monitoring the propagations of MHD waves in the magnetosphere, mainly in the irregular pulsations as observed on the magnetic storm of March 24, 1991.
Asymmetry Spectrum Analysis of ADCP Data and Characterization of Tidal Currents Non-Stationary Dynamics
... Authors: Rosa, R.; Viana, M.; Barbosa, E.; Vijaykumar, N.; Menezes, V.; Zanandrea, A.; Bolzan... more ... Authors: Rosa, R.; Viana, M.; Barbosa, E.; Vijaykumar, N.; Menezes, V.; Zanandrea, A.; Bolzan, M ... shelf is characterized by the presence of a rich suite of quartz sand bedforms having ... in the shallow shelf through bottom interactions Recent analysis of the tidal band obtained from ...
Proceeding Series of the Brazilian Society of Computational and Applied Mathematics, 2020
Resumo. Supernovas são cataclismos cósmicos. Estas explosões representam o ciclo final de evoluçã... more Resumo. Supernovas são cataclismos cósmicos. Estas explosões representam o ciclo final de evolução das estrelas. A classificação do fenômenoé complexa e está condicionadaà perícia de um astrônomo que identifica as peculiaridades do espectroóptico e das linhas espectrais. Desta forma, este trabalho apresenta SUZAN (Sistema fUZzy Avaliador de superNovas) um método de classificação de supernovas utilizando o paradigma da Lógica Fuzzy, simulando o especialista humano no momento da análise espectral e da classificação espectral. SUZAN avalia um grande número de espectros obtendo seu melhor desempenho para supernovas Ia em sua fase de luminosidade máxima.
O desenvolvimento de aplicações que lidam com processamento de sinais deve considerar a qualidade... more O desenvolvimento de aplicações que lidam com processamento de sinais deve considerar a qualidade dos dados. Técnicas de aprendizado de máquina e técnicas estatísticas requerem ajustes e normalizações no conjunto de dados antes da análise de um dado fenômeno. Quando um conjunto de dados não é tratado para reduzir inconsistências e ruídos fornecidos por instrumentos ou por condições naturais, a análise acrescenta uma tendência, ou seja, os resultados não podem ser reproduzidos porque o conjunto de dados recebe inconsistências condicionadas pelo ruído. Neste sentido, o trabalho a seguir apresenta um sistema para processamento de sinais e ajuste de dados, utilizando como estudo de caso a aplicação em dados espectrais de supernovas, para configurar uma normalização automática e uniforme em grandes conjuntos de dados. Este trabalho propõe uma estratégia de dupla filtragem utilizando o filtro Savitzky-Golay para otimização da redução de ruído. Este sistema produz um sinal filtrado capaz d...
Turbulent-like behaviour is an important and recent ingredient in the investigation of large scal... more Turbulent-like behaviour is an important and recent ingredient in the investigation of large scale structure formation in the observable universe. Recently, an established statistical method was used to demonstrate the importance of considering chaotic advection (or Lagrange turbulence) in combination with gravitational instabilities in the ΛCDM simulations performed from the Virgo Consortium (VC). However, the Hubble volumes simulated from GADGET-VC algoritm have some limitations for direct lagrangian data analysis due to the large amount of data and no real time computation for particle kinetic velocity along the dark matter structure evolution. We use our COsmic LAgrangian TUrbulence Simulator (COLATUS), based on GPU/CUDA technology, to perform gravitational Cosmological N-body simulations and tracking the particles paths. In this work we discuss the chaotic advection behavior of tracers galaxies based on the angular velocity fluctuation analysis of single particles during its trajectory to the gravitational collapse of super clusters at low redshifts.
Physica A: Statistical Mechanics and its Applications, 2004
In this paper we perform gradient pattern analysis (GPA) of convection diffusion given by the sol... more In this paper we perform gradient pattern analysis (GPA) of convection diffusion given by the solution of 2D Burgers' equation. GPA leads to characterize initial condition coherence and spatio-temporal pattern equilibrium through the local/global averaging by using two different matrix computational operators: the Asymmetric Amplitude Fragmentation (AAF) and the Complex Entropic Form (CEF). The transport phenomenon is discussed in terms of its dependence to the initial condition distribution. The initial condition variability is given by a set composed by Gaussian and non-Gaussian distributions. The results have shown that the GPA is able to characterize different spatio-temporal nonlinear diffusion regimes.
Technological applications in opto-electronic devices have increased the interest in characterizi... more Technological applications in opto-electronic devices have increased the interest in characterizing porous silicon structure patterns. Due to its physical properties, solutions from KPZ 2D are adopted to simulate the structure of porous material interface whose spatial characteristics are equivalent to those found in porous silicon samples. The analysis of the simulated and real Scanning Force Microscopy (SFM) surfaces was done using the Gradient Pattern Analysis (GPA). We found that the KPZ 2D model presented asymmetry levels compatible with the irregular surfaces observed by means of SFM images of p-Si.
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