Dielectric mismatch and shallow donor impurities in GaN/HfO2 quantum wells

In this work we investigate electron-impurity binding energy in GaN/HfO$_2$ quantum wells. The calculation considers simultaneously all energy contributions caused by the dielectric mismatch: (i) image self-energy (i.e., interaction between electron and its image charge), (ii) the direct Coulomb interaction between the electron-impurity and (iii) the interactions among electron and impurity image charges. The theoretical model account for the solution of the time-dependent Schr\"odinger equation and the results shows how the magnitude of the electron-impurity binding energy depends on the position of impurity in the well-barrier system. The role of the large dielectric constant in the barrier region is exposed with the comparison of the results for GaN/HfO$_2$ with those of a more typical GaN/AlN system, for two different confinement regimes: narrow and wide quantum wells.Comment: 6 Pages, 7 figure

Caracterização dos sedimentos da Lagoa da Apúlia (PNLN), Esposende, NW de Portugal

A Lagoa da Apúlia é um espaço natural enquadrado no Parque Natural Litoral do Norte (PNLN). Tem existido interesse, por parte do PNLN, em reabilitar este ambiente classificado como zona de proteção parcial do tipo 1 e com o seu Habitat classificado como prioritário pela Diretiva Habitats. O objetivo do estudo é compreender os processos que controlam o enchimento da lagoa e, para tal, aproveitou-se uma intervenção levada a cabo pelo PNLN, para amostrar o material proveniente até 4 metros profundidade. Foram recolhidas 10 amostras provenientes de 3 perfis. As amostras foram sujeitas ao seguinte tratamento laboratorial: secagem em estufa a temperatura inferior a 40 °C; quartilhamento; análise dimensional obtida por crivação no RoTap durante 15 minutos, segundo uma escala dimensional com intervalos iguais a √2, e por Sedigraph, para as partículas inferiores a 62 μm. Para os cálculos granulométricos e dos parâmetros estatísticos foi usado o programa SEDMAC/SEDPC (Henriques, 2003). Cada fração retida nos crivos foi observada à lupa binocular, tendo sido registada qualitativamente a composição, a sua abundância relativa, a forma e o desgaste dos grãos. O enchimento da Lagoa da Apúlia, até 4 metros de profundidade, é genericamente constituído por sedimentos areno-lodosos, variando de areão, 15 % nas camadas mais profundas, a areia, 30 % nas intermédias, contendo uma fração fina abundante, até cerca de 60 % de limo e argila nas camadas do topo. Os grãos são, na sua maioria, de quartzo, biotite e moscovite, de modo geral, com forma esférica a subdiscoide e apresentando-se angulosos a subangulosos. No estudo à lupa existiu uma especial atenção para a pesquisa de organismos (ou seus restos) de origem marinha e terrestre, que se verificou serem inexistentes, no caso dos de origem marinha, aparecendo apenas restos de origem vegetal. Os resultados indicam que os sedimentos até à profundidade amostrada, são de origem próxima, cujo transporte ocorreu com variações de energia, atingindo condições para a deposição gravítica da fração fina de lodo. Conclui-se que a Lagoa da Apúlia tem sido dominada por assoreamento, por ação de transporte fluvial. A condição lacustre com interesse a ser preservada em termos de Habitat, embora historicamente instalada, está ameaçada, sendo a colmatação da lagoa a tendência dominante atualmente. Os estudos realizados na região por Granja, et al. (2010), indicam que a área esteve sujeita a três fases distintas, sendo a primeira correspondente a um ambiente do tipo estuarino ou fluvial, a segunda a um ambiente de lagoa e a terceira a um ambiente eólico, terminando com a pedogénese deste. Neste contexto, a Lagoa da Apúlia pode ser usada como testemunho da evolução ambiental da zona litoral norte.info:eu-repo/semantics/publishedVersio

Chaos and Synchronized Chaos in an Earthquake Model

We show that chaos is present in the symmetric two-block Burridge-Knopoff model for earthquakes. This is in contrast with previous numerical studies, but in agreement with experimental results. In this system, we have found a rich dynamical behavior with an unusual route to chaos. In the three-block system, we see the appearance of synchronized chaos, showing that this concept can have potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures

Spin configurations in hard-soft coupled bilayer systems: from rigid magnet to exchange spring transitions

We investigate equilibrium properties of an exchange-spring magnetic system constituted of a soft layer (e.g. Fe) of a given thickness on top of a hard magnetic layer (e.g. FePt). The magnetization profile M(z) as a function of the atomic position ranging from the bottom of the hard layer to the top of the soft layer is obtained in two cases with regard to the hard layer: i) in the case of a rigid interface (the FePt layer is a single layer), the profile is obtained analytically as the exact solution of a sine-Gordon equation with Cauchy's boundary conditions. Additional numerical simulations also confirm this result. Asymptotic expressions of M(z) show a linear behavior near the bottom and the top of the soft layer. In addition, a critical value of the number of atomic planes in the soft layer, that is necessary for the onset of spin deviations, is obtained in terms of the anisotropy and exchange coupling between the adjacent plane in the soft layer. ii) in the case of a relaxed interface (the FePt layer is a multilayer), the magnetization profile is obtained numerically for various Fe and FePt films thicknesses and applied field.Comment: 10 pages, 9 figures, PRB submitted (12-07-2010

Negative Energy Densities in Extended Sources Generating Closed Timelike Curves in General Relativity with and without Torsion

Near a spinning point particle in (2+1)-dimensional gravity (or near an infinitely thin, straight, spinning string in 3+1 dimensions) there is a region of space-time with closed timelike curves. Exact solutions for extended sources with apparently physically acceptable energy-momentum tensors, have produced the same exterior space-time structure. Here it is pointed out that in the case with torsion, closed timelike curves appear only for spin densities so high that the spin energy density is higher than the net effective energy density. In models without torsion, the presence of closed time-like curves is related to a heat flow of unphysical magnitude. This corroborates earlier arguments against the possibility of closed timelike curves in space-time geometries generated by physical sources.Comment: (to be published in Phys. Rev. D), 5 pages, REVTEX 3.0, NORDITA 93/62 A (Sept. 10/Revised Nov. 1, 1993

Subsidies for ecosystem-based management in an offshore oil and gas exploration area, Santos Basin, Brazil

This special issue examines the latestdiscoveries from the interdisciplinary project,“Regional Characterization of the Santos Basin –(PCR-BS),” designed by the Brazilian oil companyPetrobras as part of its environmental programinitiatives. Future environmental managementpractices are threatened by lack of comprehensiveoceanographic knowledge in offshore oil & gasregions. This concern inspired this special issue.The 13 articles here present data primarilygathered during the 2019 campaigns. The studycollected physical, chemical, sedimentological,and biological data from both benthic and pelagicenvironments in the basin. The findings areclassified into four categories: methodologicalaspects, hydrographic conditions, and pelagicand benthic ecosystems. The scientific researchpresented in this special issue represents an initialeffort towards reconciling sustainable oil and gasexploration and production with the preservationof regional biodiversity and environmental health

Injúria ao milho Bt Cry1Ab causada por populações de Spodoptera frugiperda previamente expostas à toxina.

Resumo

Blockchain-based raw material shipping with PoC in Hyperledger Composer

In today’s world, a lot of various kinds of raw materials are shipped from one place to another as per the requirement of industries. This shipping process involved many multiple levels with multiple personalities or authorities. The intermediates may be influenced by some illegal external factors and there may be some theft or modification in the raw material which is in the shipping process. This generates a significant loss if the material is of high cost. Presently, the advancements in information technology precede a method to restrict this loss and it is blockchain. Blockchain technology is an essential feature in enabling a comprehensive view of events back to origination. The shipping chain of raw materials that provides integrity and tamper resistance for raw materials in the shipping process is proposed in the manuscript. we have also provided proof of concept (PoC) in Hyperledger Composer with performance evaluation.info:eu-repo/semantics/publishedVersio