5,251 research outputs found
Hydrogenated grain boundaries in graphene
We have investigated by means of first principles calculations the structural
and electronic properties of hydrogenated graphene structures with distinct
grain boundary defects. Our total energy results reveal that the adsorption of
a single H is more stable at grain boundary defect. The electronic structure of
the grains boundaries upon hydrogen adsorption have been examined. Further
total energy calculations indicate that the adsorption of two H on two neighbor
carbons, forming a basic unit of graphane, is more stable at the defect region.
Therefore, we expect that these extended defects would work as a nucleation
region for the formation of a narrow graphane strip embedded in graphene
region
Confining potential in a color dielectric medium with parallel domain walls
We study quark confinement in a system of two parallel domain walls
interpolating different color dielectric media. We use the phenomenological
approach in which the confinement of quarks appears considering the QCD vacuum
as a color dielectric medium. We explore this phenomenon in QCD_2, where the
confinement of the color flux between the domain walls manifests, in a scenario
where two 0-branes (representing external quark and antiquark) are connected by
a QCD string. We obtain solutions of the equations of motion via first-order
differential equations. We find a new color confining potential that increases
monotonically with the distance between the domain walls.Comment: RevTex4, 5 pages, 1 figure; version to appear in Int. J. Mod. Phys.
Lorentz-violating dimension-five operator contribution to the black body radiation
We investigate the thermodynamics of a photon gas in an effective field
theory model that describes Lorentz violations through dimension-five operators
and Horava-Lifshitz theory. We explore the electrodynamics of the model which
includes higher order derivatives in the Lagrangian that can modify the
dispersion relation for the propagation of the photons. We shall focus on the
deformed black body radiation spectrum and modified Stefan-Boltzmann law to
address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL
Non-additivity of decoherence rates in superconducting qubits
We show that the relaxation and decoherence rates 1/T_1 and 1/T_2 of a qubit
coupled to several noise sources are in general not additive, i.e., that the
total rates are not the sums of the rates due to each individual noise source.
To demonstrate this, we calculate the relaxation and pure dephasing rates 1/T_1
and 1/T_\phi of a superconducting (SC) flux qubit in the Born-Markov
approximation in the presence of several circuit impedances Z_i using network
graph theory and determine their deviation from additivity (the mixing term).
We find that there is no mixing term in 1/T_\phi and that the mixing terms in
1/T_1 and 1/T_2 can be positive or negative, leading to reduced or enhanced
relaxation and decoherence times T_1 and T_2. The mixing term due to the
circuit inductance L at the qubit transition frequency \omega_{01} is generally
of second order in \omega_{01}L/Z_i, but of third order if all impedances Z_i
are pure resistances. We calculate T_{1,2} for an example of a SC flux qubit
coupled to two impedances.Comment: 5 pages, 2 figure
From circular paths to elliptic orbits: A geometric approach to Kepler's motion
The hodograph, i.e. the path traced by a body in velocity space, was
introduced by Hamilton in 1846 as an alternative for studying certain dynamical
problems. The hodograph of the Kepler problem was then investigated and shown
to be a circle, it was next used to investigate some other properties of the
motion. We here propose a new method for tracing the hodograph and the
corresponding configuration space orbit in Kepler's problem starting from the
initial conditions given and trying to use no more than the methods of
synthetic geometry in a sort of Newtonian approach. All of our geometric
constructions require straight edge and compass only.Comment: 9 pages, 4 figure
Perdas econômicas decorrentes da Artrite-encefalite caprina na produção de gordura e sólidos totais de leite.
Resumo: Objetivou-se determinar as perdas econômicas decorrentes da Artrite-Encefalite Caprina, em parâmetros físico-químicos e de CCS do leite de cabras mestiças, criadas sob as condições ambientais do semiárido Cearense. A avaliação foi conduzida na Fazenda Experimental ? Santa Rita, pertencente à Embrapa Caprinos e Ovinos, em Sobral, CE. Foram utilizadas 40 cabras ½ Anglo-Nubiana x ½ Saanen. A produção leiteira foi verificada através de pesagens diárias durante 210 dias, e neste período, os parâmetros físico-químicos e de CCS foram mensurados a cada 28 dias. Foram calculadas as receitas com a venda de leite dos diferentes grupos, considerando-se a diferenciação de preço por qualidade. Observou-se que a CAE acarreta perdas econômicas significativas na receita da produção leiteira de cabras mestiças criadas nas condições ambientais do semiárido Cearense. Em virtude da pequena margem de lucro na produção de leite de cabra, estas perdas podem comprometer a rentabilidade da atividade. [Economic Losses Resulting from the Caprine Arthritis-Encephalitis in the Production of Fat and Milk Total Solids]. Abstract: The objective was to determine the economic losses in production of milk?s fat and total solids due to the CAE in goat crossbred dairy herd under semiarid environmental conditions of Ceara state. The evaluation was conducted at the Experimental Farm - Santa Rita, which belongs to Embrapa Goats and Sheep, in Sobral, CE. Used 40 ½ Anglo-Nubian x ½ Saanen goats. Milk production was measured by daily weighing during the period of 210 days. Was calculated the revenue from the sale of milk quality for the different groups, considering the price differentiation for quality. It was noted that the CAE causes significant economic losses in revenue from milk production of crossbred goats raised in semiarid environmental conditions of Ceara. As a very small profit margin in the production of goat milk, these losses can compromise the productivity of the activity for the raisers
The pasta phase within density dependent hadronic models
In the present paper we investigate the onset of the pasta phase with
different parametrisations of the density dependent hadronic model and compare
the results with one of the usual parametrisation of the non-linear Walecka
model. The influence of the scalar-isovector virtual delta meson is shown. At
zero temperature two different methods are used, one based on coexistent phases
and the other on the Thomas-Fermi approximation. At finite temperature only the
coexistence phases method is used. npe matter with fixed proton fractions and
in beta-equilibrium are studied. We compare our results with restrictions
imposed on the the values of the density and pressure at the inner edge of the
crust, obtained from observations of the Vela pulsar and recent isospin
diffusion data from heavy-ion reactions, and with predictions from spinodal
calculations.Comment: 15 pages, 11 figures and 7 table
Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics
The superposition principle is a very basic ingredient of quantum theory.
What may come as a surprise to many students, and even to many practitioners of
the quantum craft, is tha superposition has limitations imposed by certain
requirements of the theory. The discussion of such limitations arising from the
so-called superselection rules is the main purpose of this paper. Some of their
principal consequences are also discussed. The univalence, mass and particle
number superselection rules of non-relativistic quantum mechanics are also
derived using rather simple methods.Comment: 22 pages, no figure
A useful form of the recurrence relation between relativistic atomic matrix elements of radial powers
Recently obtained recurrence formulae for relativistic hydrogenic radial
matrix elements are cast in a simpler and perhaps more useful form. This is
achieved with the help of a new relation between the and the
terms ( is a Dirac matrix and are constants) in the
atomic matrix elements.Comment: 7 pages, no figure
Desempenho de bezerros em pastagem de capim-marandu recebendo suplementação com concentrados balanceados para diferentes níveis de produção.
Avaliou-se o fornecimento de concentrado para bezerros mantidos em pastagens de Brachiaria brizantha cv. Marandu durante a época seca do ano. Utilizaram-se 16 machos não-castrados da raça Canchim, com 7 meses de idade e 250 kg, distribuídos em delineamento inteiramente ao acaso em esquema fatorial 2 × 2, no qual os fatores foram suplementos balanceados para dois potenciais de fermentação microbiana ? 9,5 e 11,0 g de proteína bruta microbiana/MJ energia metabolizável fermentável e para ganhos de peso corporal (GPC) de 0,5 e 1,0 kg/dia. Os animais receberam suplementação individual diária por 168 dias, após 21 dias de adaptação. A ingestão diária de forragem foi estimada em 5,91 kg matéria seca/ animal. A suplementação para ganho de peso corporal de 0,5 kg/dia proporcionou ganhos de peso e conversão alimentar de 0,94 kg/dia e 2,08 kg suplemento/kg ganho, respectivamente, resultados inferiores aos obtidos para ganho de peso corporal de 1 kg/dia (1,09 kg/dia e 3,18 kg suplemento/kg ganho, respectivamente). Não houve efeito do potencial de fermentação sobre o ganho de peso corporal, a conversão alimentar e a área de olho-de-lombo, no entanto, a espessura final de gordura de cobertura foi maior com o potencial de fermentação mais elevado. A suplementação para ganho de peso corporal de 0,5 kg/dia mostrou melhor resultado econômico, mas não permitiu obter peso apropriado para abate. A suplementação com concentrado formulado para aumentar a eficiência de síntese de proteína microbiana no rúmen, porém reduziu a rentabilidade do sistema. Palavras-chave: avaliação econômica, Brachiaria brizantha cv. Marandu, Canchim, ganho de peso, potencial de fermentação microbian
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