Treating some solid state problems with the Dirac equation

The ambiguity involved in the definition of effective-mass Hamiltonians for nonrelativistic models is resolved using the Dirac equation. The multistep approximation is extended for relativistic cases allowing the treatment of arbitrary potential and effective-mass profiles without ordering problems. On the other hand, if the Schrodinger equation is supposed to be used, our relativistic approach demonstrate that both results are coincidents if the BenDaniel and Duke prescription for the kinetic-energy operator is implemented. Applications for semiconductor heterostructures are discussed.Comment: 06 pages, 5 figure

Quantum key distribution with higher-order alphabets using spatially-encoded qudits

We propose and demonstrate a quantum key distribution scheme in higher-order $d$-dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio

Uniformidade de aplicação de água em um sistema de irrigação por gotejamento com duas fitas por fileira de planta.

O objetivo da pesquisa foi avaliar a uniformidade de emissão de água em um sistema de irrigação localizada com duas linhas laterais por fileira de planta. Os procedimentos experimentais foram conduzidos na propriedade hidroagrícola Fazenda Vale do Sol no município de Jequié-Bahia, no período de Março a Junho de 2011. A área experimental de 0,18ha era irrigada por sistema de irrigação localizada por gotejamento composto de duas linhas laterais por fileira de planta com gotejadores autocompensantes, de vazão 1,6 L.h-1 e pressão de 196 kPa. Foi aplicada a metodologia de Keller e Kermelli (1975) considerando três situações: as vazões da linha lateral a direita da fileira de planta, as vazões da linha lateral a esquerda da fileira de planta e a média das vazões entre estas posições. Os coeficientes de uniformidade em sua maioria, apresentaram valores classificados como excelentes sendo o valor médio entre todos de 90,15%; 93,10% e 94,13% para as situações a direita, esquerda e entre a média destas posições respectivamente

Influência de água e nitrogênio nas características físicas do cacau forasteiro no seminário baiano.

O objetivo deste trabalho foi analisar as características físicas dos frutos de cacau comum, (Forasteiro), submetido a lâminas de irrigação e doses de nitrogênio aplicadas via água de irrigação. O experimento foi realizado em campo na propriedade Vale do Sol em Jequié, Ba. Os fatores lâminas de água e doses de nitrogênio cada um com 4 níveis foram fatorialmente combinados resultando em 16 tratamentos, foi considerado o delineamento de blocos ao acaso para as analises estatísticas onde se utilizou 64 plantas, distribuídas em 2 blocos. Foram realizadas coletas sucessivas nas plantas a partir do primeiro semestre de 2012. Os níveis de nitrogênio utilizados influenciaram positivamente nas variáveis comprimento, diâmetro, peso dos frutos, número de grãos, peso dos grãos e no número de frutos por planta. A combinação ótima física de lâmina de água e dose de nitrogênio foi de 1982,8 mm e 331,5 kg ha-1 respectivamente, encontrando uma estimativa de 4,8 frutos.planta-1

Magnetic phases evolution in the LaMn1-xFexO3+y system

We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to x=1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn-Teller distortion, thus favoring a ferromagnetic (FM) superexchange (SE) interaction between Mn^{3+}-O-Mn^{3+}. For x=0.0 the oxygen excess (y ~ 0.09) produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn^{4+} ions and 82% of the usual Mn^{3+} ions, with possible double exchange interaction between them. The Fe doping in this system is known to produce only stable Fe^{3+} ions. We find an evolution from a fairly strong FM phase with a Curie temperature T_{C} ~ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with T_{N} = 790 K, for x=1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease (increase) of the FM (AFM) phase, accompanied by a systematic transition broadening for 0.2 < x < 0.7. A model based on the expected exchange interaction among the various magnetic-ion types, accounts very well for the saturation-magnetization dependence on Fe doping.Comment: 27 pages, 9 figure

Tracking e-learning through published papers: a systematic review

Electronic learning (e-learning) is a broader approach to learning that brings new opportunities for learning and teaching in many fields of education far from the traditional classroom environment. Over the past decades, research in the field indicates a proliferation of e-learning contents and discrepancies that affect interoperability patterns in education for students and teachers; however, little has been done to assess the usability of e-learning systems. From a different perspective, this study aims to provide information on the numerous findings relating to the cumulative results of e-learning in education. This systematic review uses a full protocol with the aim of standardizing and specifying all the procedures adopted to collect and code 99 academic articles from 2010 to 2018 with keywords: education and e-learning. The text analysis as conducted using the qualitative software Leximancer to extract meaning from the large number of articles retrieved. The results highlight four dominant themes, namely education systems and learning issues that in turn promote student behaviours and the use of online learning tools. This research contributes towards providing research propositions that can be used in a cogent theoretical framework and, based on the analysis, we also propose a new definition of e-learning.info:eu-repo/semantics/acceptedVersio

Stability in microcanonical many-body spin glasses

We generalize the de Almeida-Thouless line for the many-body Ising spin glass to the microcanonical ensemble and show that it coincides with the canonical one. This enables us to draw a complete microcanonical phase diagram of this model