Avaliação da composição de híbridos amarelos de mandioca em duas idades.

O cultivo da mandioca é de grande relevância socioeconômica para o Brasil e para o mundo. A mandioca apresenta facilidade de cultivo, resistência a doenças e a variações climáticas, propiciando a oportunidade de se preparar vários alimentos, sendo o teor de compostos cianogênicos contido nas raízes um dos fatores que definem a finalidade de uso da mandioca, com as variedades classificadas em 'mansas' e 'bravas'

Development of an Interpretive Simulation Tool for the Proton Radiography Technique

Proton radiography is a useful diagnostic of high energy density (HED) plasmas under active theoretical and experimental development. In this paper we describe a new simulation tool that interacts realistic laser-driven point-like proton sources with three dimensional electromagnetic fields of arbitrary strength and structure and synthesizes the associated high resolution proton radiograph. The present tool's numerical approach captures all relevant physics effects, including effects related to the formation of caustics. Electromagnetic fields can be imported from PIC or hydrodynamic codes in a streamlined fashion, and a library of electromagnetic field `primitives' is also provided. This latter capability allows users to add a primitive, modify the field strength, rotate a primitive, and so on, while quickly generating a high resolution radiograph at each step. In this way, our tool enables the user to deconstruct features in a radiograph and interpret them in connection to specific underlying electromagnetic field elements. We show an example application of the tool in connection to experimental observations of the Weibel instability in counterstreaming plasmas, using $\sim 10^8$ particles generated from a realistic laser-driven point-like proton source, imaging fields which cover volumes of $\sim10$ mm$^3$. Insights derived from this application show that the tool can support understanding of HED plasmas.Comment: Figures and tables related to the Appendix are included in the published journal articl

Escala de perceção dos alunos sobre o feedback dos professores: construção e validação

O presente estudo procura testar as propriedades psicométricas de um questionário que avalia (a) perceção do aluno sobre o feedback do professor; a identificação escolar do aluno; as trajetórias escolares (factos e expectativas) e; a perceção do aluno sobre o seu envolvimento escolar. O questionário foi aplicado a 1089 alunos dos 6º, 7º, 9º e 10º anos de escolaridade (M=13.4, DP=1.7), sendo que 52% são do sexo feminino. A amostra é composta por alunos essencialmente de nacionalidade portuguesa (95.9%). A partir dos resultados da análise factorial e seguindo o racional teórico, chegou-se a uma estrutura composta por oito dimensões principais. O QFITE apresenta bons índices de consistência interna, com sete das oito principais dimensões a obterem valores entre .77 e .89. Assim, as análises psicométricas realizadas revelam valores satisfatórios, concluindo-se que o QFITE é um instrumento útil e adequado para avaliar a identificação escolar dos alunos, o envolvimento comportamental escolar, e as perceções dos alunos sobre o feedback do professor

Scale of student perceptions regarding their Behavioral Engagement in school: construction and validation

Este estudo descreve a construção e validação de uma escala que avalia a perceção dos alunos sobre o seu envolvimento comportamental escolar. Os questionários foram aplicados a 1089 alunos do 6 º, 7 º, 9 º e 10º anos de escolaridade (idade mediana = 13) em Portugal Continental, a partir dos quais foram extraídas duas subamostras aleatórias. Uma subamostra foi submetida a análise fatorial exploratória e a segunda, a uma análise fatorial confirmatória. Emergiram duas dimensões: envolvimento no trabalho acadêmico e participação na aula. A primeira escala revelou uma consistência interna aceitável, revelando-se útil e adequada para avaliar as percepções dos alunos sobre o seu envolvimento comportamental escolar. A segunda dimensão necessita de maior desenvolvimento em futuras investigações.info:eu-repo/semantics/publishedVersio

Neutrino Oscillations at Supernova Core Bounce Generate the Strongest Gravitational-Wave Bursts

During the core bounce of a supernova collapse resonant active-to-active ($\nu_a \to \nu_a$), as well as active-to-sterile ($\nu_a \to \nu_s$) neutrino ($\nu$) oscillations can take place. Besides, over this phase weak magnetism increases antineutrino ($\bar{\nu}$) mean free paths, and thus its luminosity. Because the oscillation feeds mass-energy into the target $\nu$ species, the large mass-squared difference between species ($\nu_a \to \nu_s$) implies a huge amount of power to be given off as gravitational waves ($L_{\textrm{GWs}} \sim 10^{49}erg s$^{-1}$), due to anisotropic but coherent$\nu$flow over the oscillation length. This anisotropy in the$\nu$-flux is driven by both the {\it universal spin-rotation} and the spin-magnetic coupling. The new spacetime strain estimated this way is still several orders of magnitude larger than those from$\nu$ diffusion (convection and cooling) or quadrupole moments of the neutron star matter. This new feature turns these bursts the more promising supernova gravitational-wave signal that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Comment: 10 pages, 1 figure, Proceedings of International Workshop on Astronomy and Relativistic Astrophysics, Olinda (Brazil), October 12-16 (2003), to be published in Int. J. Mod. Phys.

Persistence of magnetic field driven by relativistic electrons in a plasma

The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma length confirm the experimental measurements. These results open new paths for the exploration and modelling of ultra high energy particle driven magnetic field generation in the laboratory

Enabling Lorentz boosted frame particle-in-cell simulations of laser wakefield acceleration in quasi-3D geometry

When modeling laser wakefield acceleration (LWFA) using the particle-in-cell (PIC) algorithm in a Lorentz boosted frame, the plasma is drifting relativistically at beta(b)c towards the laser, which can lead to a computational speedup of similar to gamma(2)(b)=(1-beta(2)(b))-1. Meanwhile, when LWFA is modeled in the quasi-3D geometry in which the electromagnetic fields and current are decomposed into a limited number of azimuthal harmonics, speedups are achieved by modeling three dimensional (3D) problems with the computational loads on the order of two dimensional r-z simulations. Here, we describe a method to combine the speedups from the Lorentz boosted frame and quasi-3D algorithms. The key to the combination is the use of a hybrid Yee-FFT solver in the quasi-3D geometry that significantly mitigates the Numerical Cerenkov Instability (NCI) which inevitably arises in a Lorentz boosted frame due to the unphysical coupling of Langmuir modes and EM modes of the relativistically drifting plasma in these simulations. In addition, based on the space-time distribution of the LWFA data in the lab and boosted frame, we propose to use a moving window to follow the drifting plasma, instead of following the laser driver as is done in the LWFA lab frame simulations, in order to further reduce the computational loads. We describe the details of how the NCI is mitigated for the quasi-3D geometry, the setups for simulations which combine the Lorentz boosted frame, quasi-3D geometry, and the use of a moving window, and compare the results from these simulations against their corresponding lab frame cases. Good agreement is obtained among these sample simulations, particularly when there is no self-trapping, which demonstrates it is possible to combine the Lorentz boosted frame and the quasi-3D algorithms when modeling LWFA. We also discuss the preliminary speedups achieved in these sample simulations.info:eu-repo/semantics/submittedVersio