CCET - DFTE - Artigos publicados em periódicos

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Acoustic phonon transmission spectra in piezoelectric AlN/GaN Fibonacci phononic crystals
(Springer Verlag, 2007-09-22) Sesion Júnior, P.D.; Albuquerque, E.L.; Feitosa, Carlos Chesman de Araújo; Freire, V.N.
We study the acoustic-phonon transmission spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from the III-V nitride materials AlN and GaN. The phonon dynamics is described by a coupled elastic and electromagnetic equations within the static field approximation model, stressing the importance of the piezoelectric polarization field in a strained condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing a neat analytical expressions for the phonon transmission coefficients. Numerical results, for the normal incidence case, show a strike self-similar pattern for both hexagonal (class 6 mm) and cubic symmetries crystalizations of the nitrides
Activity and rotation of Kepler-17
(The American Astronomical Society, 2017) Valio, Adriana; Estrela, Raissa; Netto, Yuri; Bravo, J. P.; Medeiros, José Renan de
Magnetic activity on stars manifests itself in the form of dark spots on the stellar surface, which cause modulations of a few percent in the light curve of the star as it rotates. When a planet eclipses its host star, it might cross in front of one of these spots, creating a "bump" in the transit light curve. By modeling these spot signatures, it is possible to determine the physical properties of the spots such as size, temperature, and location. In turn, monitoring of the spots' longitude provides estimates of the stellar rotation and differential rotation. This technique was applied to the star Kepler-17, a solar–type star orbited by a hot Jupiter. The model yields the following spot characteristics: average radius of 49 ± 10 Mm, temperatures of 5100 ± 300 K, and surface area coverage of 6 ± 4%...
Addition of magnetic markers for non-destructive evaluation of polymer composites
(UFSCar - Dep. de Engenharia de Materiais, 2011-10) Fulco, Ana Paula Pereira; Melo, José Daniel Diniz; Paskocimas, Carlos Alberto; Medeiros, Suzana Nóbrega de; Machado, Fernando Luis de Araujo; Rodrigues, Alexandre Ricalde
Polymer composite pipes are an appealing option as a substitute for conventional steel pipes, particularly due to their inherent corrosion resistance. However, the composite pipes currently used do not allow non-destructive evaluation (NDE) using instrumented devices which operate with magnetic sensors. The present work aims at the development of polymer composites with the addition magnetic markers to allow the application non-destructive evaluation techniques which use magnetic sensors. Glass-polyester composite flat, circular plates were fabricated with the addition of ferrite particles (barium ferrite and strontium ferrite) and four types of notches were introduced on the plates' surfaces. The influence of these notches on the measured magnetic properties of each material was measured. X-ray diffraction (XRD), X-ray fluorescence (XRF) and Brunauer, Emmett, and Teller (BET) nitrogen adsorption were used for the characterization of the ferrite particles. Particle dispersion in the polymer matrix was analyzed by scanning electron microscopy (SEM). According to the results, a particular variation in magnetic field was detected over the region surrounding each type of notch. The results suggest that the proposed technique has great potential for damage detection in polymer composites using magnetic sensors and thus constitute a valuable contribution which may ultimately lead to the development of non-destructive evaluation techniques for assessing the structural integrity polymer composite pipes
Age and mass of solar twins constrained by lithium abundance
(Astronomy & Astrophysics, 2009) Nascimento Jr, J. D. do; Castro, M.; Meléndez, J.; Bazot, M.; Théado, S.; Mello, G. F. Porto de; Medeiros, José Renan de
Aims. We analyze the non-standard mixing history of the solar twins HIP 55 459, HIP 79 672, HIP 56 948, HIP 73 815, and HIP 100 963, to determine as precisely as possible their mass and age. Methods. We computed a grid of evolutionary models with non-standard mixing at several metallicities with the Toulouse-Geneva code for a range of stellar masses assuming an error bar of ±50 K in Teff. We choose the evolutionary model that reproduces accurately the observed low lithium abundances observed in the solar twins. Results. Our best-fit model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. HIP 56 948 is the most likely solar-twin candidate at the present time and our analysis infers a mass of 0.994 ± 0.004 M and an age of 4.71 ± 1.39 Gyr. Conclusions. Non-standard mixing is required to explain the low Li abundances observed in solar twins. Li depletion due to additional mixing in solar twins is strongly mass dependent. An accurate lithium abundance measurement and non-standard models provide more precise information about the age and mass more robustly than determined by classical methods alone.
An overview of the rotational bechavior of metal-poor stars
(Sociedade Astronômica Americana, 2009) Cortes, C.; Silva, J. R. P.; Recio-Blanco, A.; Catelan, M.; Nascimento Junior, Jose Dias do; Medeiros, José Renan de
This paper describes the behavior of the rotational velocity in metal-poor stars ([Fe/H] ≤ –0.5 dex) in different evolutionary stages, based on vsin i values from the literature. Our sample is comprised of stars in the field and some Galactic globular clusters, including stars on the main sequence, the red giant branch (RGB), and the horizontal branch (HB). The metal-poor stars are, mainly, slow rotators, and their vsin i distribution along the HR diagram is quite homogeneous. Nevertheless, a few moderate to high values of vsin i are found in stars located on the main sequence and the HB. We show that the overall distribution of vsin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating main sequence stars in our sample present rotation rates similar to their metal-rich counterparts, suggesting that some of them may actually be fairly young, in spite of their low metallicity, or else that at least some of them would be better classified as blue straggler stars. We do not find significant evidence of evolution in vsin i values as a function of position on the RGB; in particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue HB stars has been suggested to be due to angular momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms most likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and vsin i values. We present an extensive tabulation of all quantities discussed in this paper, including rotation velocities, temperatures, gravities, and metallicities [Fe/H], as well as broadband magnitudes and colors.
Análise da transmissão de Leishmaniose visceral no Nordeste brasileiro, no período 2001-2015
(Anuário do Instituto de Geociências, 2019) Lima, Patrícia Viana de; Mendes, David; Spyrides, Maria Helena Constantino; Andrade, Lara de Melo Barbosa; Barreto, Naurinete de Jesus da Costa; Pedra, George Ulguim
A Leishmaniose Visceral (LV) representa um grave problema de saúde pública, considerada pela Organização Mundial de Saúde (OMS, 2016) como uma das doenças tropicais negligenciadas pelo poder público. A LV tem como fatores de exposição a sua expansão geográfica, as condições sociodemográficas da população e as condições climáticas. Diante desse cenário, o objetivo deste estudo é identificar possíveis fatores climáticos e sociodemográficos que influenciam na transmissão da LV no Nordeste brasileiro (NEB). Os dados climáticos foram coletados a partir de informações disponibilizadas pelo Climate Prediction Center / National Oceanic and Atmospheric Administration (CPC/NOAA), de janeiro de 2001 a dezembro de 2015. As informações sociodemográficas foram obtidas dos censos 2000 e 2010, enquanto as estimativas populacionais foram disponibilizadas pelo Instituto Brasileiro de Geografia e Estatística (IBGE). As notificações dos casos registrados de LV foram disponibilizadas pelo Departamento de Informática do SUS (DATASUS). Para análise espacial dos dados, aplicou-se o Índice de Moran , para as médias trianuais 2001-2003 e 2013-2015. Detectou-se correlação espacial significativa tanto no triênio de 2001-2003 quanto no 2013-2015 ). Além disso, utilizou-se o teste estatístico de Mantel-Haenszel para análise da relação entre o tipo de transmissão e as variáveis (Estimativa populacional, grau de urbanização, Índice de Desenvolvimento Humano Municipal - IDHM, saneamento inadequado, temperatura mínima, temperatura média, temperatura máxima, precipitação acumulada, umidade relativa do ar e altitude). Através do teste Mantel-Haenszel detectou-se associação significativa para os dois períodos estudados entre as variáveis: população residente estimada, grau de urbanização, IDHM e saneamento inadequado versus o tipo de transmissão de LV. O teste Mantel-Haenzsel mostrou associação significativa para tipo de transmissão e as variáveis climáticas, Temperatura Média, Temperatura Mínima, Temperatura Máxima, Precipitação Acumulada e Umidade Relativa do ar, principalmente no período 2013-2015. Além disso, foi usado o teste estatístico de Mantel-Haenszel para análise da relação entre o tipo de transmissão de LV e algumas variáveis (estimativa populacional, grau de urbanização, Índice de Desenvolvimento Humano Municipal - IDHM, saneamento inadequado, temperatura mínima, temperatura média, temperatura máxima, precipitação acumulada, umidade relativa do ar, altitude). Através deste teste foi verificada associação significativa, para os dois períodos estudados, entre as variáveis: população residente estimada, grau de urbanização, IDHM e saneamento inadequado versus o tipo de transmissão de LV. O teste Mantel-Haenszel também mostrou associação significativa para tipo de transmissão e as variáveis climáticas tais como temperatura (média, mínima e máxima), precipitação acumulada e umidade relativa do ar, principalmente no período 2013-2015
Analysis of fractal groups of the type d-(m, r)-Cantor within the framework of Kaniadakis statistics
(Elsevier, 2014-05-02) Anselmo, Dory Hélio Aires de Lima; Souza, N. T. C. M.; Mello, V. D.; Silva Junior, Raimundo
We have used Kaniadakis statistics in the analysis of fractal structures of the type d-(m,r)-Cantor. The κ-entropy associated with these structures shows linearity with respect to the dimension L of the system and power-law type behavior with respect to the block size s used in the scanning of a determined sequence. The fractal dimension d f is related to the entropic parameter κ through an inverse-type law
Angular dependence of asymmetric magnetoimpedance in exchange biased NiFe/IrMn multilayers
(AIP Publishing LLC, 2014-03-11) Silva, Ricardo Barreto da Silva; Corrêa, Marcio Assolin; Silva, Edimilson Felix da; Mori, Thiago José de Almeida; Della Pace, Rafael Domingues; Pinto, Roberta Dutra de Oliveira; Viegas, Alexandre Da Cas; Bohn, Felipe; Sommer, Rubem Luis
We investigate the angular dependence of asymmetric magnetoimpedance of NiFe/IrMn multilayers and explore the possibility of tuning the linear region of the magnetoimpedance curves by modifying the angle between the applied external magnetic field and exchange bias field, and probe current frequency. We quantify the sensitivity by calculating the ratio jDZj=jDHj at low magnetic fields as a function of the frequency for samples cut with different orientations and show that considerable values in the linear region around zero field can be reached. The results extend the possibilities for application of exchange biased magnetoimpedance multilayers as probe element for the development and improvement of auto-biased linear magnetic field sensors
Angular dependence of hysteresis shift in oblique deposited ferromagnetic/ antiferromagnetic coupled bilayers
(AIP Publishing LLC, 2014-07-17) Oliveira, Alexandre Barbosa de; Rodrigues-Suarez, R. L.; Michea, S.; Vega, H.; Azevedo, A.; Rezende, S. M.; Aliagla, Carolina; Denardin, J.
The angular dependence of the hysteresis shift has been investigated in ferromagnetic/antiferromagnetic (NiFe/IrMn) bilayers grown by oblique deposition under the influence of a static magnetic field applied perpendicular to the uniaxial anisotropy direction induced during the growth process. It was found that at low oblique deposition angles, the unidirectional anisotropy field is much greater than the uniaxial anisotropy field and the corresponding anisotropies directions are noncollinear. In these conditions, the angular dependence of the hysteresis loop shift exhibits the well know cosine like shape but demanding a phase shift. Contrary to this, at high oblique deposition angle (70), the uniaxial anisotropy plays the fundamental role and the anisotropies directions are collinear. In this case, the exchange bias displays a jump phenomenon. The numerical calculations are consistent with the experimental data obtained from magneto-optical Kerr effect and ferromagnetic resonance.
Anisotropy field and transverse susceptibility in nanocrystalline hexaferrites
(Physica B: Condensed Matter, 2006-10-01) Araújo, José Humberto de; Soares, J. M.; Machado, F. L. A.; Cabral, F. A. O.; Rodrigues, H. A. B.; Ginani, Marconi Floripe
Nanocrystalline strontium and barium hexaferrites were produced by an ionic coordination reaction method. The average particle size obtained using the Rietveld X-ray refinement technique and by scanning electron microscopy was quite uniform and close to 50 nm. Transverse susceptibility measurements yielded both the coercive and the anisotropy magnetic fields. The results were analysed using a theoretical model proposed by Aharoni et al. [Bull. Res. Counc. Isr. A 6 (1957) 215]. This overall procedure seems to be quite useful in determining the distribution of the anisotropy magnetic fields in granular materials
Anisotropy field and transverse susceptibility in nanocrystalline hexaferrites
(Elsevier, 2006-10-01) Araujo, Jose Humberto; Soares, J. M.; Machado, F. L. A.; Cabral, F. A. O.; Rodrigues, H. A. B.; Ginani, Marconi Floripe
Nanocrystalline strontium and barium hexaferrites were produced by an ionic coordination reaction method. The average particle size obtained using the Rietveld X-ray refinement technique and by scanning electron microscopy was quite uniform and close to 50 nm. Transverse susceptibility measurements yielded both the coercive and the anisotropy magnetic fields. The results were analysed using a theoretical model proposed by Aharoni et al. [Bull. Res. Counc. Isr. A 6 (1957) 215]. This overall procedure seems to be quite useful in determining the distribution of the anisotropy magnetic fields in granular materials.
Annealing effects on the microwave linewidth broadening of FeCuNbSiB ferromagnetic films
(AIP Publishing LLC, 2015-03-26) Alves, Marcos José Pereira; Gonzalez-Chavez, Diego Ernesto; Bohn, Felipe; Sommer, Rubem Luis
We systematically investigate the annealing effects on the microwave linewidth broadening of FeCuNbSiB ferromagnetic films with thickness of 100 nm. We correlate the non-uniform residual stress obtained from grazing incidence x-ray diffraction measurements with the ferromagnetic resonance (FMR) linewidth due to effective field inhomogeneities measured from broadband ferromagnetic resonance absorption measurements. We also estimate the annealing temperature effect on the Gilbert and two-magnon scattering contributions to the total ferromagnetic resonance FMR linewidth. We show that the effective field inhomogeneities constitute the main contribution to the microwave linewidth, while this contribution is related to the non-uniform residual stress in the films which is reduced by thermal annealing
Anomalous magnetoresistance in Fibonacci multilayers
(American Physical Society, 2012-06-15) Bezerra, Claudionor Gomes; Machado, Leonardo Dantas; Corrêa, Marcio Assolin; Feitosa, Carlos Chesman de Araújo; Pearson, J.E.; Hoffman, A.
We theoretically investigated magnetoresistance curves in quasiperiodic magnetic multilayers for two different growth directions, namely, [110] and [100]. We considered identical ferromagnetic layers separated by nonmagnetic layers with two different thicknesses chosen based on the Fibonacci sequence. Using parameters for Fe/Cr multilayers, four terms were included in our description of the magnetic energy: Zeeman, cubic anisotropy, bilinear coupling, and biquadratic coupling. The minimum energy was determined by the gradient method and the equilibrium magnetization directions found were used to calculate magnetoresistance curves. By choosing spacers with a thickness such that biquadratic coupling is stronger than bilinear coupling, unusual behaviors for the magnetoresistance were observed: (i) for the [110] case, there is a different behavior for structures based on even and odd Fibonacci generations, and, more interesting, (ii) for the [100] case, we found magnetic field ranges for which the magnetoresistance increases with magnetic field
Application of Fibonacci oscillators in the Debye model
(JOURNAL OF PHYSICS. CONFERENCE SERIES, 2014-12-08) Marinho, André A. A.; Brito, F. A.; Feitosa, Carlos Chesman de Araújo
In this paper we study the thermodynamics of a crystalline solid by applying q-deformed algebra of Fibonacci oscillators through the generalized Fibonacci sequence of two real and independent deformation parameters q1 and q2. We find a (q1, q2)-deformed Hamiltonian and consequently the q- deformed thermodynamic quantities. The results led us to interpret the deformation parameters acting as disturbance or impurities factors modifying the characteristics of a crystal structure. More specifically, we found the possibility of adjusting the Fibonacci oscillators to describe the change of thermal conductivity of a given element as one inserts impurites
Asymmetric magnetoimpedance effect in ferromagnetic multilayered biphase films
(Elsevier, 2015-05-27) Silva, Edimilson Felix da; Silva, Ricardo Barreto da; Gomes, Matheus Gamino; Andrade, Antonio Marcos Helgueira de; Vázquez, M.; Corrêa, Marcio Assolin; Bohn, Felipe
We investigate the magnetoimpedance effect in ferromagnetic multilayered biphase films. We verify that the films present asymmetric magnetoimpedance behavior and, by playing with the number of the repetitions of the base structure of the multilayer and the probe current frequency, we explore the possibility of tailoring the linear region around zero magnetic field in order to achieve higher sensitivity values. The highest sensitivity is observed for the thicker film, reaching 15 mΩ/Oe at ∼0.52 GHz. Thus, the results open the possibilities for application of ferromagnetic multilayered biphase films with asymmetric magnetoimpedance effect in sensors devices
Atomic hopping in AlCuFe quasicrystal
(Elsevier, 1996-03) Araujo, Jose Humberto; Gomes, A. A.; Cunha, J. B. M. da
High temperature 57Fe MOsshaner effect measurements in annealed icosahedral A1CuFe alloy are reported. The anomalous decrease in Debye-Waller factor is qualitatively interpretated. It is suggested using consistent parameters that the isomer shift decreases linearly with temperature in agreement with a second-order Doppler shift in the Debye approximation.
Avaliação da Potencialidade de Argilas do Rio Grande do Norte – Brasil
(Associação Brasileira de Cerâmica – ABCERAM, 2006) Dutra, Ricardo Peixoto Suassuna; Varela, Márcio Luiz; Nascimento, Rubens Maribondo do; Gomes, Uílame Umbelino; Paskocimas, Carlos Alberto; Melo, Pedro Terceiro de
Foram estudadas argilas de diferentes regiões do estado do Rio Grande do Norte, Brasil, visando uma caracterização completa e indicar potencialidades industriais. A composição mineralógica das argilas foi identificada por difração de raios X. A composição química foi determinada por fluorescência de raios X. Foi determinada por difração de laser a distribuição do tamanho de partículas das argilas. Os limites de Atterberg foram utilizados para classificar as amostras quanto à plasticidade. Os efeitos térmicos presentes nas amostras foram estudados por análise térmica diferencial. A predominância do mineral argiloso ilita, de composição química homogênea, com duas distribuições de tamanho de partículas e com plasticidades muito diferentes, foram os resultados predominantes. O exame das variáveis de processamento e das características intrínsecas de cada material indica o uso destas argilas para fabricação de blocos e telhas, bem como para fabricação de pavimentos e revestimentos, podendo ser uma nova área industrial no Estado
Avaliação de modelos do CMIP5 que melhor expressam a atuação dos vórtices ciclônicos em altos níveis (VCANS) no Nordeste Brasileiro (NEB)
(Revista Brasileira de Geografia Física, 2014) Pinheiro, José Ueliton; Neves, Josemir Araújo; Chaves, Rosane Rodrigues; Mendes, David; Barreto, Naurinete de Jesus da Costa
A pesquisa estudou a saída de modelos de mudanças climáticas que melhor expressam a atuação dos Vórtices Ciclônicos em Altos Níveis (VCANs) no Nordeste Brasileiro (NEB). Os VCANs foram quantificados pela sua ocorrência diária durante 5 anos (1995-1999), no período de outubro a março. O objeto de estudo foram 13 modelos do CMIP5/IPCC/AR5 (Coupled Model Intercomparison Project Phase 5/Intergovernmental Panel on Climate Change/Fifth Assessment Report), comparados com os resultados do NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research), por meio de métodos estatísticos para escolha do modelo que melhor indica a presença dos VCANs no NEB. A primeira análise comparativa foi feita através das correlações de Pearson, Kendall e Spearman, Raiz quadrada do erro quadrático médio, Raiz quadrada do erro quadrático médio normalizada e os índices de Eficiência e desempenho, Nash-Sutcliffe (NSE), Kling-Gupta (KGE) e o Índice de Concordância de Willmott (d). Em seguida foram selecionados os modelos de melhor desempenho e com significância estatística para uma análise posterior de acertos e erros através dos índices: Índice de Proporção Correta (PC), Índice de Sucesso Crítico (ISC), Probabilidade de Detecção (POD), Taxa de alarme Falso (TAF) e Taxa de Tendência (VIÉS). Para os testes estatísticos aplicados na primeira avaliação realizada o modelo MIROC4h foi o que apresentou os melhores índices seguido pelo MIROC-ESM e inmCM4, respectivamente. Além destes, ainda apresentaram correlação estatística significante o MPI-ESM-LR,o MRI-CGCM3 e o CSIRO-MK3-6-0. A segunda análise também apresentou o MIROC4h com os melhores valores de PC, ISC e POD, excetuando-se o VIÉS que apresentou o segundo melhor resultado e o TAF com o pior resultado em relação aos outros 5 modelos. Dessa forma o MIROC4h apresentou-se como o mais indicado entre os modelos do CMIP5 para estudos de cenários presentes e futuros de VCANs no NEB
Avaliação preliminar da sensibilidade dos modelos do CMIP5 a precipitação sazonal do Brasil tropical
(Revista Brasileira de Geografia Física, 2013-09) Barreto, Naurinete de Jesus da Costa; Mendes, David; Lucio, Paulo Sergio
As perfomances das simulação do clima presente sobre o Brasil Tropical (BrT) são avaliadas com base em 8 modelos de simulação climática globais, pertencentes ao conjunto de experimentos “phase five of the Coupled Model Inter-comparison Project” (CMIP5). Em comparação com as observações, os modelos são capazes de capturar as características dominantes da precipitação pluvial durante o período de 1979 a 2005, incluindo o padrão espacial e variações sazonais, entretanto avaliações por trimestre regionalizadas mostraram discrepâncias entre os modelos e o observado. Em termos de correlação o trimestre de Março a Maio (MAM) foi mais bem representado pelos modelos, e o trimestre o de Dezembro a Fevereiro (DJF) obteve pior desempenho. O RMSE médio foi mais elevado durante o período chuvoso (verão e outono austral), e valores menos intenso durante o período de estiagem. Os resultados dos modelos do CMIP5 mostram que ainda existe dificuldade em simular o padrão climático de algumas regiões e períodos sazonais
Bandgap oscillation in quasiperiodic (BN)xCy nanotubes
(Elsevier, 2016-12) Freitas, Aliliane Almeida de; Bezerra, Claudionor Gomes; Azevedo, Sérgio; Machado, Leonardo Dantas; Pedreira, Danilo Oliveira
In the present contribution, we apply first-principles calculations to study the effects of quasiperiodic disorder on the physical properties of BN and C nanotubes. We take BN nanotubes (BNNTs) and C nanotubes (CNTs) as building blocks and construct quasiperiodic BNxCy nanotubes according to the Fibonacci sequence. We studied armchair and zigzag nanotubes of varying diameters. Our results demonstrate that the energy gap oscillates as a function of the n-generation index of the Fibonacci sequence. Moreover, we show that the choice of the BNNTs and CNTs may lead to a quasiperiodic BNxCy nanotube presenting an adjustable energy gap. We obtained a variety of quasiperiodic nanotubes with energy gaps ranging from 0.29 eV to 1.06 eV, which may be of interest for specific technological applications. Finally, it is also demonstrated that the specific heat of the quasiperiodic zigzag and armchair nanotubes presents an oscillatory behavior in the low temperature regime, and that this behavior depends on the curvature of the nanotube

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