Análise do comportamento in vitro de explantes foliares de pequizeiro (Caryocar brasiliense camb.) através de RAPD.

xEdição de resumos do 7º Congresso Brasileiro de Fisiologia Vegetal, Brasília, 1999

Dispersion and re-aggregation phenomena in carbon nanotube polymer composites

The preparation of polymer nanocomposites is usually carried out in twin-screw extruders or internal batch mixers. Previous studies have extensively shown that the resulting filler dispersion is strongly dependent on the characteristics of the melt mixing equipment. It is also known that the dispersion level of nanofillers strongly affects the final nanocomposite properties. The present work focuses on the study of the dispersion of carbon nanotubes (CNT) in polypropylene using a prototype mixer that develop high thermomechanical stress. The distribution and dispersion of the CNT was evaluated by optical and electron microscopy. The level of dispersion achieved was analysed, and the electrical resistivity of the composite, along the mixing cycles, was measured. The enhancement of the CNT dispersion along the mixing process correlated with a large decrease in electrical resistivity of the composite. A “percolation time”, defined as the time, or number of mixing cycles, required to achieve electrical conductivity, was measured, and correlated with mixing conditions. The composite formed was re-heated and reprocessed using the same mixing system. Re-agglomeration and loss of electrical conductivity was observed, and the final dispersion level varied with the mixing conditions imposed. Agglomerate size and electrical resistivity increased when reprocessing was performed at lower shear rate, as compared to the first processing cycle

Conical refraction in generalized biaxial media: A geometric algebra approach

It is well-know that conical refraction occurs for electric anisotropic biaxial crystals when the wave vector has the direction of the medium optic axes. In this paper, we show that conical refraction occurs in an analogous away for a more general type of biaxial media that have simultaneously electric and magnetic anisotropies. Furthermore, the new coordinate-free approach based on geometric algebra, developed by the authors in previous papers to address anisotropy, is shown to shed new light on this classic topic of optics that is conical refraction.info:eu-repo/semantics/acceptedVersio

Quantum tomography via equidistant states

We study the possibility of performing quantum state tomography via equidistant states. This class of states allows us to propose a non-symmetric informationally complete POVM based tomographic scheme. The scheme is defined for odd dimensions and involves an inversion which can be analytically carried out by Fourier transform

Asymmetric band diagrams in photonic crystals with a spontaneous nonreciprocal response

We study the propagation of electromagnetic waves in layered photonic crystals formed by materials with a spontaneous nonreciprocal response, such as Tellegen (axion) media or topological insulators. Surprisingly, it is proven that stratified Tellegen photonic crystals that break simultaneously the space inversion and time-reversal symmetries have always symmetric dispersion diagrams. Interestingly, we show that by combining chiral and nonreciprocal materials the photonic band diagrams can exhibit a spectral asymmetry such that omega(k) not equal omega(-k). Furthermore, it is demonstrated that in some conditions two juxtaposed Tellegen medium layers have an electromagnetic response analogous to that of a biased ferrite slab.info:eu-repo/semantics/publishedVersio

L0 and L1 Guidance and Path-Following Control for Airborne Wind Energy Systems

For an efficient and reliable operation of an Airborne Wind Energy System, it is widely accepted that the kite should follow a pre-defined optimized path. In this article, we address the problem of designing a trajectory controller so that such path is closely followed. The path-following controllers investigated are based on a well-known nonlinear guidance logic termed L1 and on a proposed modification of it, which we termed L0. We have developed and implemented both L0 and L1 controllers for an AWES. The two controllers have an easy implementation with an explicit expression for the control law based on the cross-track error, on the heading angle relative to the path, and on a single parameter L (L0 or L1, depending on each controller) that we are able to tune. The L0 controller has an even easier implementation since the explicit control law can be used without the need to switch controllers. Since the switching of controllers might jeopardize stability, the L0 controller has an important theoretical advantage in being able to guarantee stability on a larger domain of attraction.The simulation study shows that both nonlinear guidance logic controllers exhibit appropriate performance when the L parameter is adequately tuned, with the L0 controller showing a better performance when measured in terms of the average cross-track error. (c) 2022 by the authors. Licensee MDPI, Basel, Switzerland

Estudos sensoriais para determinação da vida de prateleira de barra de cereais com pipoca de sorgo.

O objetivo do trabalho foi determinar a vida de prateleira de barras de cereais elaboradas com pipoca de sorgo, a partir de avaliações sensoriais realizadas por uma equipe treinada, tendo como parâmetro a qualidade global do produto. Os produtos armazenados em duas condições de temperatura (30°C e sob condição acelerada, 40°C) foram avaliados em períodos pré-determinados durante 90 dias. Como alternativa, aplicou-se também um teste rápido de ordenação com consumidores comuns, com o objetivo de verificar se havia preferência pelo produto recém-elaborado em detrimento aos armazenados por 90 dias em condição acelerada. A vida de prateleira em condição acelerada foi estimada em 77 dias por meio dos dados obtidos da regressão linear dos valores da qualidade global, avaliada pelo painel sensorial e pelo tempo de estocagem. A vida de prateleira do produto a 30°C foi de 144 dias. Também foi possível concluir que não houve perda significativa da qualidade global do produto durante os 90 dias de armazenamento, segundo a percepção tanto de provadores treinados, quanto de consumidores comuns de barras de cereais

Potencialidades agricolas no municipio de Mundo Novo, BA.

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