On Galois-Division Multiple Access Systems: Figures of Merit and Performance Evaluation

A new approach to multiple access based on finite field transforms is investigated. These schemes, termed Galois-Division Multiple Access (GDMA), offer compact bandwidth requirements. A new digital transform, the Finite Field Hartley Transform (FFHT) requires to deal with fields of characteristic p, p \neq 2. A binary-to-p-ary (p \neq 2) mapping based on the opportunistic secondary channel is introduced. This allows the use of GDMA in conjunction with available digital systems. The performance of GDMA is also evaluated.Comment: 6 pages, 4 figures. In: XIX Simposio Brasileiro de Telecomunicacoes, 2001, Fortaleza, CE, Brazi

Inter- and intra-layer excitons in MoS2_2/WS2_2 and MoSe2_2/WSe2_2 heterobilayers

Accurately described excitonic properties of transition metal dichalcogenide heterobilayers (HBLs) are crucial to comprehend the optical response and the charge carrier dynamics of them. Excitons in multilayer systems posses inter or intralayer character whose spectral positions depend on their binding energy and the band alignment of the constituent single-layers. In this study, we report the electronic structure and the absorption spectra of MoS$_2$/WS$_2$ and MoSe$_2$/WSe$_2$ HBLs from first-principles calculations. We explore the spectral positions, binding energies and the origins of inter and intralayer excitons and compare our results with experimental observations. The absorption spectra of the systems are obtained by solving the Bethe-Salpeter equation on top of a G$_0$W$_0$ calculation which corrects the independent particle eigenvalues obtained from density functional theory calculations. Our calculations reveal that the lowest energy exciton in both HBLs possesses interlayer character which is decisive regarding their possible device applications. Due to the spatially separated nature of the charge carriers, the binding energy of inter-layer excitons might be expected to be considerably smaller than that of intra-layer ones. However, according to our calculations the binding energy of lowest energy interlayer excitons is only $\sim$ 20\% lower due to the weaker screening of the Coulomb interaction between layers of the HBLs. Therefore, it can be deduced that the spectral positions of the interlayer excitons with respect to intralayer ones are mostly determined by the band offset of the constituent single-layers. By comparing oscillator strengths and thermal occupation factors, we show that in luminescence at low temperature, the interlayer exciton peak becomes dominant, while in absorption it is almost invisible.Comment: 17 pages, 4 figure

Fatty acids profile and thermal properties of macauba palm pulp oil from Cerrados and Pantanal biomes, Brazil.

Pôster

Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films

We present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetization reversal processes, of well characterized half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3 (STO) substrates with three different surface orientations, i.e. (001), (110) and (1-18). The latter shows step edges oriented parallel to the [110] (in-plane) crystallographic direction. Room temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied magnetic field directions in the whole angular range. In general, the magnetic properties of the LSMO films can be interpreted with just the uniaxial term with the anisotropy axis given by the film morphology, whereas the strength of this anisotropy depends on both structure and film thickness. In particular, LSMO films grown on nominally flat (110)-oriented STO substrates presents a well defined uniaxial anisotropy originated from the existence of elongated in-plane [001]-oriented structures, whereas LSMO films grown on nominally flat (001)-oriented STO substrates show a weak uniaxial magnetic anisotropy with the easy axis direction aligned parallel to residual substrate step edges. Elongated structures are also found for LSMO films grown on vicinal STO(001) substrates. These films present a well-defined uniaxial magnetic anisotropy with the easy axis lying along the step edges and its strength increases with the LSMO thickness. It is remarkable that this step-induced uniaxial anisotropy has been found for LSMO films up to 120 nm thickness. Our results are promising for engineering novel half-metallic magnetic devices that exploit tailored magnetic anisotropy.Comment: 10 pages, 10 figures, 1 tabl

Transport and mixing simulation along the continental shelf edge using a Lagrangian approach

Este trabajo presenta la comprobación de un modelo bioquímico a partir de dos modelos hidrodinámicos diferentes: un modelo 1D (Coelho, 1996) y un modelo 3D (Santos, 1995), correspondientes a dos fases de trabajo sucesivas. En la primera fase el modelo hidrodinámico 1D fue usado para calibrar el modelo biogeoquímico; los resultados de esta fase permitieron el análisis de la evolución de los perfiles temporales verticales. Se usaron tanto la aproximación euleriana como la lagrangiana para el transporte de las propiedades bioquímicas. En la segunda fase 3D se aplicó el modelo hidrodinámico, lo que permitió obtener una visión a escala regional de los procesos involucrados. El transporte de las propiedades bioquímicas fue realizado a partir de la aproximación lagrangiana, habiéndose destacado el origen del agua procedente de afloramientos (upwelling). Los datos obtenidos en Goban Spur/La Chapelle durante el Ocean Margin Exchange Project (Anon., 1996) fueron usados para definir las condiciones iniciales y de contorno para los modelos bioquímicos e hidrodinámicos. Nuestra principal conclusión es que el modelo 3D de seguimiento de la dinámica de partículas, junto con el modelo hidrodinámico 3D (con un modelo de turbulencia cerrado apropiado) y con un modelo bioquímico, puede ser una excelente herramienta para cuantificar intercambios entre la plataforma continental y el océano abierto.This paper presents the coupling of a biochemical model with two different hydrodynamic models, a 1-D model (Coelho, 1996) and a 3-D model (Santos, 1995), corresponding to two successive work phases. In the first phase the 1-D hydrodynamic model was used to calibrate the biochemical model; the results of this phase made it possible to analyse temporal vertical profiles evolution. Both an Eulerian and a Lagrangian approach were used to transport biochemical properties. In the second phase, the 3-D hydrodynamic model was applied; this gave a regionalscale view of the processes involved. Biochemical properties transport was made with a Lagrangian approach, highlighting the origin of upwelled water. Goban Spur/La Chapelle field data collected during the Ocean Margin Exchange project (Anon., 1996) were used as initial and boundary conditions in hydrodynamic and biochemical models. Our main conclusion is that a 3-D particle-tracking model, coupled with a 3-D hydrodynamic model (with a proper turbulence closure model) and with a biochemical model, can be an excellent tool to quantify exchanges between the continental shelf and deep ocean.Instituto Español de Oceanografí

Potencial de dano de Heliothis virescens (Fabricius, 1977) (Lepidoptera: Noctuidae) em diferentes estádios reprodutivos da soja [Glycine max (L.) Merril] em casa de vegetação.

Heliothis virescens (Lepidoptera: Noctuidae) é uma praga conhecida pelos cotonicultores, e em safras recentes tem causado danos à cultura da soja em algumas regiões, alimentando-se de folhas e de estruturas reprodutivas. Assim esse trabalho teve como objetivo avaliar os danos de H. virescens em diferentes estádios reprodutivos da soja. O ensaio foi conduzido na Embrapa Arroz e Feijão localizada no município de Santo Antônio de Goiás - GO, em nível de casa-devegetação, utilizando um delineamento inteiramente casualizado, com 5 tratamentos e 6 repetições, com cada vaso contendo 3 plantas, sendo que cada vaso correspondeu a uma repetição. Os tratamentos foram: T1 - Testemunha sem infestação; T2 - Infestação em R1 (Início de florescimento); T3 - Infestação em R3 (Início da formação da vagem); T4 - Infestação em R5 (Início do enchimento de grãos) e T5 - Infestação em R6 (Enchimento de grãos pleno). As plantas foram infestadas com lagartas de terceiro ínstar. As variáveis avaliadas aos 2, 4 e 6 dias após a infestação foram: número de estruturas reprodutivas danificadas e produção final. Os maiores danos são observados nas fenologias R3 e R5 e os menores danos em R6. Não houve diferença na produção entre os tratamentos testados. H. virescens danificou um total de 64,6 estruturas de soja, podendo uma lagarta danificar cerca de 21,5 vagens. As fenologias R3 e R5 foram as mais propícias aos danos nas vagens