9,457 research outputs found
Crystal engineering using functionalized adamantane
We performed a first principles investigation on the structural, electronic,
and optical properties of crystals made of chemically functionalized adamantane
molecules. Several molecular building blocks, formed by boron and nitrogen
substitutional functionalizations, were considered to build zincblende and
wurtzite crystals, and the resulting structures presented large bulk moduli and
cohesive energies, wide and direct bandgaps, and low dielectric constants
(low- materials). Those properties provide stability for such
structures up to room temperature, superior to those of typical molecular
crystals. This indicates a possible road map for crystal engineering using
functionalized diamondoids, with potential applications ranging from space
filling between conducting wires in nanodevices to nano-electro-mechanical
systems
Electronic properties and hyperfine fields of nickel-related complexes in diamond
We carried out a first principles investigation on the microscopic properties
of nickel-related defect centers in diamond. Several configurations, involving
substitutional and interstitial nickel impurities, have been considered either
in isolated configurations or forming complexes with other defects, such as
vacancies and boron and nitrogen dopants. The results, in terms of spin,
symmetry, and hyperfine fields, were compared with the available experimental
data on electrically active centers in synthetic diamond. Several microscopic
models, previously proposed to explain those data, have been confirmed by this
investigation, while some models could be discarded. We also provided new
insights on the microscopic structure of several of those centers.Comment: 21 pages, 8 figure
Experimental observation of fractional topological phases with photonic qudits
Geometrical and topological phases play a fundamental role in quantum theory.
Geometric phases have been proposed as a tool for implementing unitary gates
for quantum computation. A fractional topological phase has been recently
discovered for bipartite systems. The dimension of the Hilbert space determines
the topological phase of entangled qudits under local unitary operations. Here
we investigate fractional topological phases acquired by photonic entangled
qudits. Photon pairs prepared as spatial qudits are operated inside a Sagnac
interferometer and the two-photon interference pattern reveals the topological
phase as fringes shifts when local operations are performed. Dimensions and were tested, showing the expected theoretical values.Comment: 6 pages, 4 figure
Avaliação da composição química das espigas de três híbridos de milho (Zea mays L.) em quatro estádios de maturação.
O objetivo deste experimento foi avaliar a composição química das espigas dos três híbridos de milho BRS 1035, BRS 1031 e BRS 1001 em quatro idades de corte, a partir da determinação dos parâmetros: matéria seca (MS), proteína bruta (PB), fibra detergente neutro (FDN) e fibra detergente ácido (FDA). O delineamento utilizado foi inteiramente casualizado com fatorial3 (híbridos) x 4 (idades de corte), sendo as médias comparadas pelo teste SNK (P<0,05). Todos os híbridos demonstraram um aumento do teor de MS de 87 para 171 dias, com diferença (P<0,05) entre todos os cortes. Não houve diferença (P<0,05) nos valores de PB entre os cortes em todos os híbridos. Aos 94 dias o híbrido BRS 1001 (5,67%) demonstrou um valor de PB superior (P<0,05) ao BRS 1031 (4,66%) e ambos foram semelhantes (P<0,05) ao BRS 1035 (5,11%). Todos os híbridos apresentaram uma queda dos valores de FDN com o avanço da maturidade até 101 dias. A variação dos valores de FDA da espiga foi muito semelhante à variação do FDN já que a correlação dessas características foi 0,97 (P<0,001). Não houve diferença (P<0,05) nos valores de FDA entre os híbridos dentro dos cortes. Os híbridos avaliados neste experimento apresentaram as mesmas tendências de aumento da MS da' espiga com o avançar da maturidade fisiológica com provável acúmulo de amido na espiga, reduzindo os teores de carboidratos estruturais como FDN e FDA nessa fração da planta
Effectiveness of Surgery for Lumbar Spinal Stenosis : A Systematic Review and Meta-Analysis
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