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Search Results: 1 - 10 of 16357 matches for " Alex Sander Barros Queiroz "
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Optical Bistability in an Acousto-Optic Tunable Filter (AOTF) Operating with Short Optical Pulses  [PDF]
Karlo David Alves Sabóia, Alex Sander Barros Queiroz, Francisco Tiago Lima, Cícero Saraiva Sobrinho, Jose Wally Mendon?a Menezes, Antonio Sergio Bezerra Sombra
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2012, DOI: 10.4236/jemaa.2012.43015
Abstract: In this paper we report for the first time the presence of bistability in an acoustic-optic tunable filter (AOTF) operating with ultrashort (2 ps) optical light pulses. The results for the study of bistability has shown the dependence of the hysteresis curve with the product of the coupling constant (κ) by the length of the device (ξL) and the conversion power-coupling constant factor (G). The range of bistability varies significantly with both G and with κξL parameters. The variation of κξL directly increases the size of the range of bistability hysteresis while the increase in G causes the bistability to occur at low powers. The phenomenon of optical bistability (OB) is the object of increasing interest due to its possibilities for important device applications. A bistable device is a device with a capability to generate two different outputs for a given input and the physical requirements for this are an intensity-dependence refractive index and an optical feedback mechanism.
Analysis of the Performance of Optical Code-Division Multiple-Access System (OCDMA), Operating with Gold Codes under Nonlinear Effects  [PDF]
Glendo de Freitas Guimar?es, Agliberto Melo Bastos, Alisson da Concei??o Ferreira, Alex Sander Barros Queiroz, José Wally Mendon?a Menezes, José Rubens Rodrigues de Sousa, Antonio Sergio Bezerra Sombra
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.52008

A numerical simulation study of the performance of encoding and decoding of short optical pulse in OCDMA (Optical Code Division Multiple Access) systems under non-linear optical effects is presented. The performance of encoding and decoding short pulses is obtained through use of device FBG (fiber Bragg grating) where the codes are inserted through discrete jumps in the optical phase (±π). The multiuser interference is also the object of the present study, where a figure of merit (interference figure) is used to quantify the interference in multiuser auto and cross correlation. We evaluate the dependence of the multiuser interference for the coupling constant of FBG. Finally, the interference inserted in the autocorrelation due to nonlinear effects generated in the nonlinear switching of the coded pulse in a dual core nonlinear directional coupler is examined, where temporal broadening of pulses decoded is observed.

O jogo das identidades na forma o de professores/as: tens es e dilemas de estudantes negros/as
Alex Sander da Silva
Poiésis , 2010,
Abstract: In this short paper I present some issues and questions related to the racial problem in thecontext of teacher education and articulate an understanding of the implications of black studentsidentities within universities. In the process of teacher formation, the affirmative identity means theability to perceive the tensions and dilemmas of identity construction. It also means looking for newelements to understand the construction of a new political culture of confrontation of racialinequalities in Brazil.
Justi a como reconhecimento do outro: dimens es éticas e pedagógicas das políticas de a o afirmativa
Alex Sander da Silva
Roteiro , 2011,
Abstract: Justice as recognition of others: ethical and pedagogicaldimensions of affirmative action policiesAbstractThis brief essay aims to examine the ethical dimensions of affirmative action (for the black population), which has reference to justice as recognition of the other, its central value. It is intended here to present a limited way, some notes andquestions that relate to the theming of affirmative action on the issue of racial inequality in Brazil. This is an initial draft, and as the issue of race progresses, consolidates the need for ethical debate on the recognition of racism and all forms ofracial inequality. In general, affirmative action must be understood as any effort to promote equality of groups that suffer or are vulnerable to discrimination. However,not considering the issue of racial justice as meaning automatically, this is about the necessity of recognizing the other as a fundamental ethical dimension.Accordingly, we refer the thought of Emmanuel Levinas’s alterity, in which we encounter the centrality of the ethical sense and the proper notice of otherness in the pursuit of justice.
Ana Emília de Melo Queiroz,Alex Sandro Gomes
Revista Brasileira de Informática na Educa??o , 2009,
Abstract: O uso de softwares educativos constitui objeto de estudo durante a sua inser o nas práticas escolares, pressupondo uma avalia o criteriosa da sua forma de utiliza o, bem como durante o seu desenvolvimento, pois o propósito do seu uso o diferencia de outros softwares n o educativos. Por esse motivo, faz-se necessário agregar mecanismos capazes de influenciar na aprendizagem dos conceitos para os quais foram desenvolvidos. O objetivo deste trabalho foi o de averiguar se o estilo de intera o, oferecido pela interface, foi capaz de promover reflex o sobre os conceitos por ela veiculados, bem como verificar indícios do desenvolvimento de autonomia, por parte dos usuários, durante a resolu o de problemas. Para tanto, adotamos uma metodologia qualitativa composta por observa o participante, grava es e entrevistas. Como resultado, apresentamos uma análise dos protocolos verbais coletados durante a execu o da tarefa proposta, sob a influência do estilo de intera o.
Neuron-Specific Regulation of Associative Learning and Memory by MAGI-1 in C. elegans
Attila Stetak,Frederic H?rndli,Andres V. Maricq,Sander van den Heuvel,Alex Hajnal
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0006019
Abstract: Identifying the molecular mechanisms and neural circuits that control learning and memory are major challenges in neuroscience. Mammalian MAGI/S-SCAM is a multi-PDZ domain synaptic scaffolding protein that interacts with a number of postsynaptic signaling proteins and is thereby thought to regulate synaptic plasticity [1], [2], [3].
A methodology to assess robust stability and robust performance of automatic flight control systems
Silva, Alex Sander Ferreira da;Paiva, Henrique Mohallem;Kienitz, Karl Heinz;
Sba: Controle & Automa??o Sociedade Brasileira de Automatica , 2011, DOI: 10.1590/S0103-17592011000500001
Abstract: this article presents a methodology to assess the robust stability and the robust performance of automatic flight control systems (afcs). the mathematical tool used in the proposed methodology is the structured singular value, μ. for comparison purposes, the paper uses a method largely employed in the aircraft industry to measure the quoted afcs attributes. the issues existing in this methodology are discussed and it is shown that the proposed method presents one elegant path to deal with the mentioned drawbacks. a step by step procedure is provided, incorporating the advantages offered by the approach currently used in the industry and eliminating its weaknesses.
Computing the Greedy Spanner in Linear Space
Sander P. A. Alewijnse,Quirijn W. Bouts,Alex P. ten Brink,Kevin Buchin
Computer Science , 2013,
Abstract: The greedy spanner is a high-quality spanner: its total weight, edge count and maximal degree are asymptotically optimal and in practice significantly better than for any other spanner with reasonable construction time. Unfortunately, all known algorithms that compute the greedy spanner of n points use Omega(n^2) space, which is impractical on large instances. To the best of our knowledge, the largest instance for which the greedy spanner was computed so far has about 13,000 vertices. We present a O(n)-space algorithm that computes the same spanner for points in R^d running in O(n^2 log^2 n) time for any fixed stretch factor and dimension. We discuss and evaluate a number of optimizations to its running time, which allowed us to compute the greedy spanner on a graph with a million vertices. To our knowledge, this is also the first algorithm for the greedy spanner with a near-quadratic running time guarantee that has actually been implemented.
Distribution-Sensitive Construction of the Greedy Spanner
Sander P. A. Alewijnse,Quirijn W. Bouts,Alex P. ten Brink,Kevin Buchin
Computer Science , 2014,
Abstract: The greedy spanner is the highest quality geometric spanner (in e.g. edge count and weight, both in theory and practice) known to be computable in polynomial time. Unfortunately, all known algorithms for computing it take Omega(n^2) time, limiting its applicability on large data sets. We observe that for many point sets, the greedy spanner has many `short' edges that can be determined locally and usually quickly, and few or no `long' edges that can usually be determined quickly using local information and the well-separated pair decomposition. We give experimental results showing large to massive performance increases over the state-of-the-art on nearly all tests and real-life data sets. On the theoretical side we prove a near-linear expected time bound on uniform point sets and a near-quadratic worst-case bound. Our bound for point sets drawn uniformly and independently at random in a square follows from a local characterization of t-spanners we give on such point sets: we give a geometric property that holds with high probability on such point sets. This property implies that if an edge set on these points has t-paths between pairs of points `close' to each other, then it has t-paths between all pairs of points. This characterization gives a O(n log^2 n log^2 log n) expected time bound on our greedy spanner algorithm, making it the first subquadratic time algorithm for this problem on any interesting class of points. We also use this characterization to give a O((n + |E|) log^2 n log log n) expected time algorithm on uniformly distributed points that determines if E is a t-spanner, making it the first subquadratic time algorithm for this problem that does not make assumptions on E.
Sobrevivência de pupas de Lucilia eximia (Wiedemann) (Diptera, Calliphoridae) após submers?o em laboratório
Souza, Alex Sandro Barros de;Keppler, Ruth Leila Ferreira;
Revista Brasileira de Entomologia , 2009, DOI: 10.1590/S0085-56262009000300028
Abstract: between may and june of 2008, the survival of the pupae of lucilia eximia (diptera, calliphoridae) was observed after submersion in laboratory. for this experiment 480 pupae of same age were used, these were divided in eight groups: the group control was not submerged and the other groups were submerged from one to seven days. the increase of the submersion period reduces the survival, with one day of submersion the survival is of 80%, with two days 40%, of 30% with three days, in the fourth day it falls to 23,34% and in the fifth day it is 10%. after this period the mortality rises to 100%. this pattern can be explained by the curve "u-shaped" that happens in the consumption of o2 during the pupal period, where the consumption is larger at the beginning and at the end of the pupal period. the time of submersion also affects the development time, increasing the pupal period. these data are potentially useful in estimating duration of submergence of a corpse in forensic entomology investigations.
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