Rodrigo A. Miranda

Lagrangian coherent structures at the onset of hyperchaos in the two-dimensional Navier-Stokes equations

We study a transition to hyperchaos in the two-dimensional incompressible Navier-Stokes equations with periodic boundary conditions and an external forcing term. Bifurcation diagrams are constructed by varying the Reynolds number, and a transition to hyperchaos (HC) is identified. Before the onset of HC, there is coexistence of two chaotic attractors and a hyperchaotic saddle. After the transition to HC, the two chaotic attractors merge with the hyperchaotic saddle, generating random switching between chaos and hyperchaos, which is responsible for intermittent bursts in the time series of energy and enstrophy. The chaotic mixing properties of the flow are characterized by detecting Lagrangian coherent structures. After the transition to HC, the flow displays complex Lagrangian patterns and an increase in the level of Lagrangian chaoticity during the bursty periods that can be predicted statistically by the hyperchaotic saddle prior to HC transition.

On–off intermittency and amplitude-phase synchronization in Keplerian shear flows

We study the development of coherent structures in local simulations of the magnetorotational instability in accretion discs in regimes of on-off intermittency. In a previous paper [Chian et al., Phys. Rev. Lett. 104, 254102 (2010)], we have shown that the laminar and bursty states due to the on-off spatiotemporal intermittency in a one-dimensional model of nonlinear waves correspond, respectively, to nonattracting coherent structures with higher and lower degrees of amplitude-phase synchronization. In this paper we extend these results to a three-dimensional model of magnetized Keplerian shear flows. Keeping the kinetic Reynolds number and the magnetic Prandtl number fixed, we investigate two different intermittent regimes by varying the plasma beta parameter. The first regime is characterized by turbulent patterns interrupted by the recurrent emergence of a large-scale coherent structure known as two-channel flow, where the state of the system can be described by a single Fourier mode. The second regime is dominated by the turbulence with sporadic emergence of coherent structures with shapes that are reminiscent of a perturbed channel flow. By computing the Fourier power and phase spectral entropies in three-dimensions, we show that the large-scale coherent structures are characterized by a high degree of amplitude-phase synchronization.

Reconstruction of chaotic saddles by classification of unstable periodic orbits: Kuramoto-Sivashinsky equation.

The unstable periodic orbits (UPOs) embedded in a chaotic attractor after an attractor merging crisis (MC) are classified into three subsets, and employed to reconstruct chaotic saddles in the Kuramoto-Sivashinsky equation. It is shown that in the post-MC regime, the two chaotic saddles evolved from the two coexisting chaotic attractors before crisis can be reconstructed from the UPOs embedded in the pre-MC chaotic attractors. The reconstruction also involves the detection of the mediating UPO responsible for the crisis, and the UPOs created after crisis that fill the gap regions of the chaotic saddles. We show that the gap UPOs originate from saddle-node, period-doubling, and pitchfork bifurcations inside the periodic windows in the post-MC chaotic region of the bifurcation diagram. The chaotic attractor in the post-MC regime is found to be the closure of gap UPOs.

Chaotic saddles in nonlinear modulational interactions in a plasma

A nonlinear model of modulational processes in the subsonic regime involving a linearly unstable wave and two linearly damped waves with different damping rates in a plasma is studied numerically. We compute the maximum Lyapunov exponent as a function of the damping rates in a two-parameter space, and identify shrimp-shaped self-similar structures in the parameter space. By varying the damping rate of the low-frequency wave, we construct bifurcation diagrams and focus on a saddle-node bifurcation and an interior crisis associated with a periodic window. We detect chaotic saddles and their stable and unstable manifolds, and demonstrate how the connection between two chaotic saddles via coupling unstable periodic orbits can result in a crisis-induced intermittency. The relevance of this work for the understanding of modulational processes observed in plasmas and fluids is discussed.A nonlinear model of modulational processes in the subsonic regime involving a linearly unstable wave and two linearly damped waves with different damping rates in a plasma is studied numerically. We compute the maximum Lyapunov exponent as a function of the damping rates in a two-parameter space, and identify shrimp-shaped self-similar structures in the parameter space. By varying the damping rate of the low-frequency wave, we construct bifurcation diagrams and focus on a saddle-node bifurcation and an interior crisis associated with a periodic window. We detect chaotic saddles and their stable and unstable manifolds, and demonstrate how the connection between two chaotic saddles via coupling unstable periodic orbits can result in a crisis-induced intermittency. The relevance of this work for the understanding of modulational processes observed in plasmas and fluids is discussed.

Permanent magnet Hall Thrusters development and applications on future brazilian space missions

The Plasma Physics Laboratory (PPLUnB) has been developing a Permanent Magnet Hall Thruster (PHALL) for the Space Research Program for Universities (UNIESPACO), part of the Brazilian Space Activities Program (PNAE) since 2004. The PHALL project consists on a plasma source design, construction and characterization of the Hall type that will function as a plasma propulsion engine and characterized by several plasma diagnostics sensors. PHALL is based on a plasma source in which a Hall current is generated inside a cylindrical annular channel with an axial electric field produced by a ring anode and a radial magnetic field produced by permanent magnets. In this work it is shown a brief description of the plasma propulsion engine, its diagnostics instrumentation and possible applications of PHALL on orbit transfer maneuvering for future Brazilian geostationary satellite space missions.

Multi-spectral optical imaging of the spatiotemporal dynamics of ionospheric intermittent turbulence.

Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmosphere, causing rapid fluctuations in the power of radio signals used in telecommunication and GPS navigation, thus playing a crucial role in space weather impacts. Complex structuring and self-organization of equatorial plasma depletions involving bifurcation, connection, disconnection and reconnection are the signatures of nonlinear evolution of interchange instability and secondary instabilities, responsible for the generation of coherent structures and turbulence in the ionosphere. The aims of this paper are three-fold: (1) to report the first optical imaging of reconnection of equatorial plasma depletions in the South Atlantic Magnetic Anomaly, (2) to investigate the optical imaging of equatorial ionospheric intermittent turbulence, and (3) to compare nonlinear characteristics of optical imaging of equatorial plasma depletions for two different altitudes at same times. We show that the degree of spatiotemporal complexity of ionospheric intermittent turbulence can be quantified by nonlinear studies of optical images, confirming the duality of amplitude-phase synchronization in multiscale interactions. By decomposing the analyses into North-South and East-West directions we show that the degree of non-Gaussianity, intermittency and multifractality is stronger in the North-South direction, confirming the anisotropic nature of the interchange instability. In particular, by using simultaneous observation of multi-spectral all-sky emissions from two different heights we show that the degree of non-Gaussianity and intermittency in the bottomside F-region ionosphere is stronger than the peak F-region ionosphere. Our results are confirmed by two sets of observations on the nights of 28 September 2002 and 9 November 2002.

Formative evaluation in Psychology: instrument for instructional material analysis

Resumo: Livros de texto para o ensino superior muito raramente sao objeto de avaliacao formativa. Este estudo teve como objetivo desenvolver e validar para o contexto brasileiro um instrumento para a captacao de dados de avaliacao formativa, visto que no Brasil ainda sao escassas as tentativas de aplicacao de avaliacoes dessa natureza. Contou-se com a participacao de duas turmas de estudantes da graduacao do curso de Psicologia e duas do curso de Administracao de uma universidade publica federal. Apos ser submetido a uma analise fatorial exploratoria, o instrumento apresentou indicadores psicometricos que apontaram evidencias de validade de construto, sendo util para a avaliacao de materiais instrucionais. Espera-se que este estudo possa contribuir para o fortalecimento do processo de avaliacao formativa de materiais didaticos no contexto brasileiro.Palavras-chave: Qualidade da educacao. Ensino em Psicologia. Materiais didaticos.Abstract: Text books for undergraduation are seldom the focus of formative evaluation. The goal of this study was to develop and validate for the Brazilian context an instrument for data collection in formative evaluation. Brazil has scarce attempts of this nature. Participants of the study were psychology and management undergraduate students in a federal public university. Data collected with these participants were submitted to an exploratory factor analysis and the results have pointed out evidences of construct validity. The instrument may be useful for the evaluation of instructional materials. This study may contribute for the strengthening of the process of formative evaluation of teaching materials. Keywords: Educational quality. Psychology teaching. Teaching materials.Resumen: Libros de texto para la ensenanza superior muy raramente son objeto de evaluacion formativa. Este estudio tuvo como objetivo desarrollar y validar para el contexto brasileno un instrumento para la captacion de datos de evaluacion formativa, visto que en Brasil aun son escasos los intentos de aplicacion de evaluaciones de esa naturaleza. Se conto con la participacion de dos grupos de estudiantes de la graduacion del curso de Psicologia y dos del curso de Administracion de una universidad publica federal. Despues de ser sometido a un analisis factorial exploratorio, el instrumento presento indicadores psicometricos que senalaron evidencias de validez de constructo, siendo util para la evaluacion de materiales de instruccion. Se espera que este estudio pueda contribuir con el fortalecimiento del proceso de evaluacion formativa de materiales didacticos en el contexto brasileno.Palabras clave: Calidad de la educacion. Ensenanza en Psicologia. Materiales didacticos.Text books for undergraduation are seldom the focus of formative evaluation. The goal of this study was to develop and validate for the Brazilian context an instrument for data collection in formative evaluation. Brazil has scarce attempts of this nature. Participants of the study were psychology and management undergraduate students in a federal public university. Data collected with these participants were submitted to an exploratory factor analysis and the results have pointed out evidences of construct validity. The instrument may be useful for the evaluation of instructional materials. This study may contribute for the strengthening of the process of formative evaluation of teaching materials.

Evaluación formativa en Psicología: instrumento para análisis de material instrucional

Resumo: Livros de texto para o ensino superior muito raramente sao objeto de avaliacao formativa. Este estudo teve como objetivo desenvolver e validar para o contexto brasileiro um instrumento para a captacao de dados de avaliacao formativa, visto que no Brasil ainda sao escassas as tentativas de aplicacao de avaliacoes dessa natureza. Contou-se com a participacao de duas turmas de estudantes da graduacao do curso de Psicologia e duas do curso de Administracao de uma universidade publica federal. Apos ser submetido a uma analise fatorial exploratoria, o instrumento apresentou indicadores psicometricos que apontaram evidencias de validade de construto, sendo util para a avaliacao de materiais instrucionais. Espera-se que este estudo possa contribuir para o fortalecimento do processo de avaliacao formativa de materiais didaticos no contexto brasileiro.Palavras-chave: Qualidade da educacao. Ensino em Psicologia. Materiais didaticos.Abstract: Text books for undergraduation are seldom the focus of formative evaluation. The goal of this study was to develop and validate for the Brazilian context an instrument for data collection in formative evaluation. Brazil has scarce attempts of this nature. Participants of the study were psychology and management undergraduate students in a federal public university. Data collected with these participants were submitted to an exploratory factor analysis and the results have pointed out evidences of construct validity. The instrument may be useful for the evaluation of instructional materials. This study may contribute for the strengthening of the process of formative evaluation of teaching materials. Keywords: Educational quality. Psychology teaching. Teaching materials.Resumen: Libros de texto para la ensenanza superior muy raramente son objeto de evaluacion formativa. Este estudio tuvo como objetivo desarrollar y validar para el contexto brasileno un instrumento para la captacion de datos de evaluacion formativa, visto que en Brasil aun son escasos los intentos de aplicacion de evaluaciones de esa naturaleza. Se conto con la participacion de dos grupos de estudiantes de la graduacion del curso de Psicologia y dos del curso de Administracion de una universidad publica federal. Despues de ser sometido a un analisis factorial exploratorio, el instrumento presento indicadores psicometricos que senalaron evidencias de validez de constructo, siendo util para la evaluacion de materiales de instruccion. Se espera que este estudio pueda contribuir con el fortalecimiento del proceso de evaluacion formativa de materiales didacticos en el contexto brasileno.Palabras clave: Calidad de la educacion. Ensenanza en Psicologia. Materiales didacticos.Text books for undergraduation are seldom the focus of formative evaluation. The goal of this study was to develop and validate for the Brazilian context an instrument for data collection in formative evaluation. Brazil has scarce attempts of this nature. Participants of the study were psychology and management undergraduate students in a federal public university. Data collected with these participants were submitted to an exploratory factor analysis and the results have pointed out evidences of construct validity. The instrument may be useful for the evaluation of instructional materials. This study may contribute for the strengthening of the process of formative evaluation of teaching materials.

Avaliação Formativa em Psicologia: Instrumento para Análise de Material Instrucional

Resumo: Livros de texto para o ensino superior muito raramente sao objeto de avaliacao formativa. Este estudo teve como objetivo desenvolver e validar para o contexto brasileiro um instrumento para a captacao de dados de avaliacao formativa, visto que no Brasil ainda sao escassas as tentativas de aplicacao de avaliacoes dessa natureza. Contou-se com a participacao de duas turmas de estudantes da graduacao do curso de Psicologia e duas do curso de Administracao de uma universidade publica federal. Apos ser submetido a uma analise fatorial exploratoria, o instrumento apresentou indicadores psicometricos que apontaram evidencias de validade de construto, sendo util para a avaliacao de materiais instrucionais. Espera-se que este estudo possa contribuir para o fortalecimento do processo de avaliacao formativa de materiais didaticos no contexto brasileiro.Palavras-chave: Qualidade da educacao. Ensino em Psicologia. Materiais didaticos.Abstract: Text books for undergraduation are seldom the focus of formative evaluation. The goal of this study was to develop and validate for the Brazilian context an instrument for data collection in formative evaluation. Brazil has scarce attempts of this nature. Participants of the study were psychology and management undergraduate students in a federal public university. Data collected with these participants were submitted to an exploratory factor analysis and the results have pointed out evidences of construct validity. The instrument may be useful for the evaluation of instructional materials. This study may contribute for the strengthening of the process of formative evaluation of teaching materials. Keywords: Educational quality. Psychology teaching. Teaching materials.Resumen: Libros de texto para la ensenanza superior muy raramente son objeto de evaluacion formativa. Este estudio tuvo como objetivo desarrollar y validar para el contexto brasileno un instrumento para la captacion de datos de evaluacion formativa, visto que en Brasil aun son escasos los intentos de aplicacion de evaluaciones de esa naturaleza. Se conto con la participacion de dos grupos de estudiantes de la graduacion del curso de Psicologia y dos del curso de Administracion de una universidad publica federal. Despues de ser sometido a un analisis factorial exploratorio, el instrumento presento indicadores psicometricos que senalaron evidencias de validez de constructo, siendo util para la evaluacion de materiales de instruccion. Se espera que este estudio pueda contribuir con el fortalecimiento del proceso de evaluacion formativa de materiales didacticos en el contexto brasileno.Palabras clave: Calidad de la educacion. Ensenanza en Psicologia. Materiales didacticos.Text books for undergraduation are seldom the focus of formative evaluation. The goal of this study was to develop and validate for the Brazilian context an instrument for data collection in formative evaluation. Brazil has scarce attempts of this nature. Participants of the study were psychology and management undergraduate students in a federal public university. Data collected with these participants were submitted to an exploratory factor analysis and the results have pointed out evidences of construct validity. The instrument may be useful for the evaluation of instructional materials. This study may contribute for the strengthening of the process of formative evaluation of teaching materials.