Ion dynamics and acceleration in relativistic shocks

Ab-initio numerical study of collisionless shocks in electron-ion unmagnetized plasmas is performed with fully relativistic particle in cell simulations. The main properties of the shock are shown, focusing on the implications for particle acceleration. Results from previous works with a distinct numerical framework are recovered, including the shock structure and the overall acceleration features. Particle tracking is then used to analyze in detail the particle dynamics and the acceleration process. We observe an energy growth in time that can be reproduced by a Fermi-like mechanism with a reduced number of scatterings, in which the time between collisions increases as the particle gains energy, and the average acceleration efficiency is not ideal. The in depth analysis of the underlying physics is relevant to understand the generation of high energy cosmic rays, the impact on the astrophysical shock dynamics, and the consequent emission of radiation.Comment: 5 pages, 3 figure

Electron - positron cascades in multiple-laser optical traps

We present an analytical and numerical study of multiple-laser QED cascades induced with linearly polarised laser pulses. We analyse different polarisation orientations and propose a configuration that maximises the cascade multiplicity and favours the laser absorption. We generalise the analytical estimate for the cascade growth rate previously calculated in the field of two colliding linearly polarised laser pulses and account for multiple laser interaction. The estimate is verified by a comprehensive numerical study of four-laser QED cascades across a range of different laser intensities with QED PIC module of OSIRIS. We show that by using four linearly polarised 30 fs laser pulses, one can convert more than 50 % of the total energy to gamma-rays already at laser intensity $I\simeq10^{24}\ \mathrm{W/cm^2}$. In this configuration, the laser conversion efficiency is higher compared with the case with two colliding lasers

Electromagnetic field generation in the downstream of electrostatic shocks due to electron trapping

A new magnetic field generation mechanism in electrostatic shocks is found, which can produce fields with magnetic energy density as high as 0.01 of the kinetic energy density of the flows on time scales $\tilde \, 10^4 \, {\omega}_{pe}^{-1}$. Electron trapping during the shock formation process creates a strong temperature anisotropy in the distribution function, giving rise to the pure Weibel instability. The generated magnetic field is well-confined to the downstream region of the electrostatic shock. The shock formation process is not modified and the features of the shock front responsible for ion acceleration, which are currently probed in laser-plasma laboratory experiments, are maintained. However, such a strong magnetic field determines the particle trajectories downstream and has the potential to modify the signatures of the collisionless shock

The impact of kinetic effects on the properties of relativistic electron-positron shocks

We assess the impact of non-thermally shock-accelerated particles on the magnetohydrodynamic (MHD) jump conditions of relativistic shocks. The adiabatic constant is calculated directly from first principle particle-in-cell simulation data, enabling a semi-kinetic approach to improve the standard fluid model and allowing for an identification of the key parameters that define the shock structure. We find that the evolving upstream parameters have a stronger impact than the corrections due to non-thermal particles. We find that the decrease of the upstream bulk speed yields deviations from the standard MHD model up to 10%. Furthermore, we obtain a quantitative definition of the shock transition region from our analysis. For Weibel-mediated shocks the inclusion of a magnetic field in the MHD conservation equations is addressed for the first time

ICT in higher education in Portugal. Call computer assisted language learning

Este artículo pretende explorar el Aprendizaje de Lenguas Asistido por Ordenador (CALL, Computer-Assisted Language Learning) en Portugal. Para ello, se centrará en el nivel de educación superior. La escasa explotación del CALL en Portugal ha sido ampliamente estudiado en varios informes, por ejemplo, el informe encargado por la UE titulado The Impact of Information and Communications Technologies on the Teaching of Foreign Languages and on the Role of Teachers of Foreign Languages (2002: 5): "The use and employment of ICT in FLT and FLL is far from satisfactory, as ICT resources are traditionally reserved for '(computer) science' subjects, and rarely assigned to art subjects. A general lack of appropriate training of language teachers in meaningful uses of ICT tends to strengthen this trend". Este artículo abordará dichas necesidades centrándose en los resultados de proyectos europeos como POOLS. Analizaremos cuestiones relativas a los materiales en línea que pueden utilizarse para desarrollar contenidos de clases de lengua, hacienda uso de las ventajas del e-Learning.G.I. HUM 767 (ayudas a Grupos de Investigación de la Junta de Andalucía) / Editorial Comares (colección interlingua

DC magnetic field generation in unmagnetized shear flows

The generation of DC magnetic fields in unmagnetized plasmas with velocity shear is predicted for non relativistic and relativistic scenarios either due to thermal effects or due to the onset of the Kelvin-Helmholtz instability (KHI). A kinetic model describes the growth and the saturation of the DC field. The predictions of the theory are confirmed by multidimensional particle-in-cell simulations, demonstrating the formation of long lived magnetic fields ($t \sim 100s \omega_{pi}^{-1}$) along the full longitudinal extent of the shear layer, with transverse width on the electron length scale ($\sqrt{\gamma_0}c/\omega_{pe}$), reaching magnitudes $eB_{\mathrm{DC}}/m_ec\omega_{pe}\sim \beta_0\sqrt{\gamma_0}$

O profissional bibliotecário frente as tecnologias da informação

TCC (graduação em Biblioteconomia) - Universidade Federal de Santa Catarina, FlorianópolisOs bibliotecários fazem parte de uma categoria das mais influenciadas com os avanços tecnológicos, principalmente, pelas chamadas Tecnologias da Informação (TI) que se apresentam com novas ferramentas de trabalho, que contribuem com uma nova rotina. Nessa perspectiva, a pesquisa tem como objetivo principal apresentar as principais contribuições das tecnologias da informação nas práticas bibliotecárias, por meio dos seguintes objetivos específicos: compreender o fenômeno da tecnologia; analisar o processo de inclusão das tecnologias da informação nas práticas bibliotecárias e apresentar as contribuições possíveis do bibliotecário frente às TIs. Para alcançar estes objetivos, a análise do tema, tem na pesquisa bibliográfica, sua principal metodologia para coleta de dados. São analisados textos em concordância com os objetivos definidos, em diversos suportes que contribuíram para que se chegassem possíveis conclusões. Com esta base teórica, observou-se que com a introdução das ferramentas tecnológicas na Biblioteconomia ocorreram profundas mudanças nas práticas e na mentalidade dos bibliotecários que tentam responder ao desafio de desenvolverem novos produtos e serviços que atendam as necessidades dos usuários. Esta resposta pode ser encontrada na formação contínua, na interação e integração com áreas tecnológicas, que podem levar o bibliotecário a aquisição de novas competências e a novos postos de trabalho, além dos já tradicionais. Sendo assim, com uma postura mais dinâmica, resta ao bibliotecário, manter-se atento e buscar sempre aprender para acompanhar a evolução da tecnologi

Cosmology with intensity mapping techniques using atomic and molecular lines

We present a systematic study of the intensity mapping technique using updated models for the different emission lines from galaxies and identify which ones are more promising for cosmological studies of the post reionization epoch. We consider the emission of ${\rm Ly\alpha}$, ${\rm H\alpha}$, H$\beta$, optical and infrared oxygen lines, nitrogen lines, CII and the CO rotational lines. We then identify that ${\rm Ly\alpha}$, ${\rm H\alpha}$, OII, CII and the lowest rotational CO lines are the best candidates to be used as IM probes. These lines form a complementary set of probes of the galaxies emission spectra. We then use reasonable experimental setups from current, planned or proposed experiments to access the detectability of the power spectrum of each emission line. Intensity mapping of ${\rm Ly\alpha}$ emission from $z=2$ to 3 will be possible in the near future with HETDEX, while far-infrared lines require new dedicated experiments. We also show that the proposed SPHEREx satellite can use OII and ${\rm H\alpha}$ IM to study the large-scale distribution of matter in intermediate redshifts of 1 to 4. We found that submilimeter experiments with bolometers can have similar performances at intermediate redshifts using CII and CO(3-2).Comment: 18 pages, 21 figures, 5 tables, published in MNRAS, typos correcte