Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy

Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni substrate. The morphology of h-BN was found to evolve from dendritic, star-shaped islands to larger, smooth triangular ones with increasing growth temperature

Análise de sistemas de produção animal - bases conceituais.

De maneira geral a utilização do enfoque sistêmico é um assunto muito falado, pouco entendido e muito pouco utilizado. Entretanto, pressões, especialmente, do mercado, exigindo maior eficiência nas diferentes atividades da agropecuária, tem contribuído para a maior utilização do método e a maior procura por informação técnica sobre o assunto nas diferentes áreas do conhecimento. Todavia existe necessidade de intensificar a difusão dos conceitos e das ferramentas que são utilizadas para implantar o enfoque de sistemas nas atividades técnicas, com objetivo de caracterizar os sistemas de produção e de verificar qual a forma de torná-los mais eficientes.bitstream/CPAP/55968/1/DOC79.pdfFormato Eletrônic

Genetic analysis of growth traits in polled Nellore cattle raised on pasture in tropical region using bayesian approaches.

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Efeito da endogamia sobre pesos aos 120 e 210 dias de idade de bovinos da raça Nelore mocho criado no bioma cerrado.

Objetivou-se com este trabalho estudar os efeitos da endogamia sobre pesos calculados aos 120 e 210 dias de idade, em bovinos da raça Nelore pertencentes ao rebanho da Embrapa Cerrados. Os dados foram coletados no período de 1990 a 2010. O coeficiente de endogamia foi calculado por meio do aplicativo MTDFREML. A matriz de parentesco incluiu 23.513 animais, cuja estimativa média e máxima dos animais endogâmicos foi 2,17% e 14,10%, respectivamente. Os resultados indicaram que a endogamia direta provocou redução dos pesos calculados aos 120 e 210 dias de idade, possivelmente, devido à redução na variância genética aditiva. A endogamia é um processo prejudicial para as características de interesse econômico, quando utilizada indiscriminadamente e deve ser utilizada com parcimônia e bastante cuidado ao se promover acasalamentos entre animais consanguíneos

AdS4 flux vacua in type II superstrings and their domain-wall solutions

We investigate the emergence of supersymmetric negative-vacuum-energy ground states in four dimensions. First, we rely on the analysis of the effective superpotential, which depends on the background fluxes of the internal manifold, or equivalently has its origin in the underlying gauged supergravity. Four-dimensional, supersymmetric anti-de Sitter vacua with all moduli stabilized appear when appropriate Ramond and Neveu--Schwarz fluxes are introduced in IIA. Geometric fluxes are not necessary. Then the whole setup is analyzed from the perspective of the sources, namely D/NS-branes or Kaluza--Klein monopoles. Orientifold planes are also required for tadpole cancellation. The solutions found in four dimensions correspond to domain walls interpolating between AdS4 and flat spacetime. The various consistency conditions (equations of motion, Bianchi identities and tadpole cancellation conditions) are always satisfied, albeit with source terms. We also speculate on the possibility of assigning (formal) entropies to AdS4 flux vacua via the corresponding dual brane systems.Comment: Acknowledgment replace

Supergravity description of spacetime instantons

We present and discuss BPS instanton solutions that appear in type II string theory compactifications on Calabi-Yau threefolds. From an effective action point of view these arise as finite action solutions of the Euclidean equations of motion in four-dimensional N=2 supergravity coupled to tensor multiplets. As a solution generating technique we make use of the c-map, which produces instanton solutions from either Euclidean black holes or from Taub-NUT like geometries.Comment: 35 pages, some clarifications adde

LATTES: a novel detector concept for a gamma-ray experiment in the Southern hemisphere

The Large Array Telescope for Tracking Energetic Sources (LATTES), is a novel concept for an array of hybrid EAS array detectors, composed of a Resistive Plate Counter array coupled to a Water Cherenkov Detector, planned to cover gamma rays from less than 100 GeV up to 100 TeVs. This experiment, to be installed at high altitude in South America, could cover the existing gap in sensitivity between satellite and ground arrays. The low energy threshold, large duty cycle and wide field of view of LATTES makes it a powerful tool to detect transient phenomena and perform long term observations of variable sources. Moreover, given its characteristics, it would be fully complementary to the planned Cherenkov Telescope Array (CTA) as it would be able to issue alerts. In this talk, a description of its main features and capabilities, as well as results on its expected performance, and sensitivity, will be presented.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC2017), Busan, South Korea. Presented by R. Concei\c{c}\~{a}o. 8 pages; v2: correct affiliation + journal referenc

Higher Derivative Corrections to Eleven Dimensional Supergravity via Local Supersymmetry

In this paper we derive higher derivative corrections to the eleven dimensional supergravity by applying the Noether method with respect to the N=1 local supersymmetry. An ansatz for the higher derivative effective action, which includes quartic terms of the Riemann tensor, is parametrized by 132 parameters. Then we show that by the requirement of the local supersymmetry, the higher derivative effective action is essentially described by two parameters. The bosonic parts of these two superinvariants completely match with the known results obtained by the perturbative calculations in the type IIA superstring theory. Since the calculations are long and systematic, we build the computer programming to check the cancellation of the variations under the local supersymmetry. This is an extended version of our previous paper hep-th/0508204.Comment: 67 pages, no figure, references added, typos correcte