Turbulence in the solar wind: spectra from Voyager 2 data at 5 AU

Fluctuations in the flow velocity and magnetic fields are ubiquitous in the Solar System. These fluctuations are turbulent, in the sense that they are disordered and span a broad range of scales in both space and time. The study of solar wind turbulence is motivated by a number of factors all keys to the understanding of the Solar Wind origin and thermodynamics. The solar wind spectral properties are far from uniformity and evolve with the increasing distance from the sun. Most of the available spectra of solar wind turbulence were computed at 1 astronomical unit, while accurate spectra on wide frequency ranges at larger distances are still few. In this paper we consider solar wind spectra derived from the data recorded by the Voyager 2 mission during 1979 at about 5 AU from the sun. Voyager 2 data are an incomplete time series with a voids/signal ratio that typically increases as the spacecraft moves away from the sun (45% missing data in 1979), making the analysis challenging. In order to estimate the uncertainty of the spectral slopes, different methods are tested on synthetic turbulence signals with the same gap distribution as V2 data. Spectra of all variables show a power law scaling with exponents between -2.1 and -1.1, depending on frequency subranges. Probability density functions (PDFs) and correlations indicate that the flow has a significant intermittency.Comment: 14 pages, 7 figures. Discussion improved since the previous versio

Cross and magnetic helicity in the outer heliosphere from Voyager 2 observations

Plasma velocity and magnetic field measurements from the Voyager 2 mission are used to study solar wind turbulence in the slow solar wind at two different heliocentric distances, 5 and 29 astronomical units, sufficiently far apart to provide information on the radial evolution of this turbulence. The magnetic helicity and the cross-helicity, which express the correlation between the plasma velocity and the magnetic field, are used to characterize the turbulence. Wave number spectra are computed by means of the Taylor hypothesis applied to time resolved single point Voyager 2 measurements. The overall picture we get is complex and difficult to interpret. A substantial decrease of the cross-helicity at smaller scales (over 1-3 hours of observation) with increasing heliocentric distance is observed. At 5 AU the only peak in the probability density of the normalized residual energy is negative, near -0.5. At 29 AU the probability density becomes doubly peaked, with a negative peak at -0.5 and a smaller peak at a positive values of about 0.7. A decrease of the cross-helicity for increasing heliocentric distance is observed, together with a reduction of the unbalance toward the magnetic energy of the energy of the fluctuations. For the smaller scales, we found that at 29 AU the normalized polarization is small and positive on average (about 0.1), it is instead zero at 5 AU. For the larger scales, the polarization is low and positive at 5 AU (average around 0.1) while it is negative (around - 0.15) at 29 AU.Comment: 14 pages 5 figures. Accepted for publication on European Journal of Mechanics B/Fluids (5/8/2015

Novas mídias e produção de conteúdos digitais educativos.

Este trabalho, de caráter conceitual, aborda o potencial da televisão digital como uma nova ferramenta que pode estar integrada ao processo educativo, contribuindo para estimular a reflexão e o aprendizado coletivo.Publicado originalmente no Grupo de Pesquisa Comunicação e Educação do XXXIV Congresso Brasileiro de Ciências da Comunicação, realizado em Recife, PE, set. 2011

Energy and water vapor transport in a turbulent stratified environment

We present direct numerical simulations about the transport of kinetic energy and unsaturated water vapor across a thin layer which separates two decaying turbulent flows with different energy. This interface lies in a shearless stratified environment modeled by means of Boussinesq’s approximation. Water vapor is treated as a passive scalar (Kumar et al. 2014). Initial conditions have Fr2 between 0.64 and 64 (stable case) and between -3.2 and -19 (unstable case) and Re_lambda = 250. Dry air is in the lower half of the domain and has a higher turbulent energy, seven times higher than the energy of moist air in the upper half. In the early stage of evolution, as long as Fr^2 > 1, stratification plays a minor role and the flows follows closely neutral stratification mixing. As the buoyancy terms grows, Fr2 ~ O(1), the mixing process deeply changes. A stable stratification generates a separation layer which blocks the entrainment of dry air into the moist one, characterized by a relative increment of the turbulent dissipation rate compared to the local turbulent energy. On the contrary, an unstable stratification sligthy enhances the entrainment. Growth-decay of energy and mixing layer thichness are discussed and compared with laboratory and numerical experiments

Voyager 2 solar plasma and magnetic field spectral analysis for intermediate data sparsity

The Voyager probes are the furthest, still active, spacecraft ever launched from Earth. During their 38-year trip, they have collected data regarding solar wind properties (such as the plasma velocity and magnetic field intensity). Unfortunately, a complete time evolution of the measured physical quantities is not available. The time series contains many gaps which increase in frequency and duration at larger distances. The aim of this work is to perform a spectral and statistical analysis of the solar wind plasma velocity and magnetic field using Voyager 2 data measured in 1979, when the gaps/signal ratio is of order of unity. This analysis is achieved using four different data reconstruction techniques: averages on linearly interpolated subsets, correlation of linearly interpolated data, compressed sensing spectral estimation, and maximum likelihood data reconstruction. With five frequency decades, the spectra we obtained have the largest frequency range ever computed at 5 astronomical units from the Sun; spectral exponents have been determined for all the components of the velocity and magnetic field fluctuations. Void analysis is also useful in recovering other spectral properties such as integral scales (see for instance Table 4) and, if the confidence level of the measurements is sufficiently high, the decay variation in the small scale range due, for instance, to dissipative effects.Comment: 11 pages, 7 figure

O direito autoral na sociedade da informação.

Com o avanço das tecnologias de informação e comunicação (TIC), configura-se um novo cenário que favorece o compartilhamento e a construção coletiva de conhecimento, especialmente em espaços virtuais. Na sociedade da informação, o paradigma é a participação, a colaboração e a troca de conhecimento. Por isso, a questão dos direitos autorais precisa ser melhor refletida e debatida, para que o conhecimento possa circular e promover inclusão social. Algumas iniciativas têm surgido, principalmente por parte da comunidade de desenvolvedores de software de código aberto e de setores voltados ao entretenimento - como música, jogos e filmes, que adotam o modelo colaborativo de produção e buscam tornar disponível a sua produção ao maior número de pessoas possível, aproveitando os recursos tecnológicos para reduzir os custos de trabalhos produzidos em rede. Entretanto, os aspectos econômicos que envolvem o tema têm representado entraves a essa disseminação. Neste artigo, vamos apresentar dados que mostram porque o assunto é tão polêmico e merece maior atenção das políticas públicas, no sentido de democratizar o acesso ao conhecimento e favorecer o processo de educação

Uso de SMS na educação de jovens e adultos.

O artigo relata o desenvolvimento de uma proposta de uso da ferramenta de SMS em práticas pedagógicas na educação de jovens e adultos (EJA), em uma escola municipal de ensino fundamental, em Campinas, SP. O estudo baseou-se nos princípios do "Design Thinking", uma metodologia de desenvolvimento de projetos centrados nas necessidades dos usuários. Inicialmente, realizou-se um diagnóstico de utilização do telefone celular junto aos estudantes de EJA, com vistas à identificação do seu perfil, dos seus hábitos e de suas necessidades de interação social no ambiente escolar. Com base no conhecimento dos hábitos e das necessidades desses alunos, procurou-se investigar "o que poderia ser feito para melhorar a integração do aluno de EJA na comunidade escolar". Como resultado de pesquisa obteve-se uma proposta de uso de SMS na educação de jovens e adultos (EJA), em apoio a atividades pedagógicas, com o intuito de contribuir para promover uma maior aproximação e integração entre o aluno,o professor e a escola

O comportamento do aluno em um curso a distância dentro do ambiente Moodle: contrapontos entre a ótica inicial e seu uso atual.

O objetivo deste trabalho é analisar as dificuldades apresentadas pelos alunos de cursos em EaD. Para tanto, utilizou-se dados extraídos de um questionário de inscrição para um curso on-line, em que era solicitado aos alunos que listassem seus maiores problemas com os cursos que já haviam feito. Puderam ser identificadas seis categorias de problemas com: AVA, tutor, técnicos, de organização, de colaboração e de conteúdo