11,388 research outputs found
Porto Oscillation Code (POSC)
The Porto Oscillation Code (POSC) has been developed in 1995 and improved
over the years, with the main goal of calculating linear adiabatic oscillations
for models of solar-type stars. It has also been used to estimate the
frequencies and eigenfunctions of stars from the pre-main sequence up to the
sub-giant phase, having a mass between 0.8 and 4 solar masses.
The code solves the linearised perturbation equations of adiabatic pulsations
for an equilibrium model using a second order numerical integration method. The
possibility of using Richardson extrapolation is implemented. Several options
for the surface boundary condition can be used. In this work we briefly review
the key ingredients of the calculations, namely the equations, the numerical
scheme and the output.Comment: Accepted for publication in Astrophysics and Space Science
Construction of a non-standard quantum field theory through a generalized Heisenberg algebra
We construct a Heisenberg-like algebra for the one dimensional quantum free
Klein-Gordon equation defined on the interval of the real line of length .
Using the realization of the ladder operators of this type Heisenberg algebra
in terms of physical operators we build a 3+1 dimensional free quantum field
theory based on this algebra. We introduce fields written in terms of the
ladder operators of this type Heisenberg algebra and a free quantum Hamiltonian
in terms of these fields. The mass spectrum of the physical excitations of this
quantum field theory are given by , where denotes the level of the particle with mass in an infinite
square-well potential of width .Comment: Latex, 16 page
Comportamento do fósforo em solos argiluviados da Região do Alentejo: sorção de fosfato
O Encontro decorreu na Universidade do Algarve.O poster apresenta os resultaos de um estudo sobre o comportamento do fósforo em solos argiluviados da Região do Alentejo
Phosphate desorption in luvisols and solonetz from a Mediterranean region
Poster apresentado no 6th International Phosphorus Workshop, que decorreu em Sevilha de 27 de Setembro a 1 de Outubro de 2010.Transfer of P from soil to water is controlled by the P retention
capacity in the solid phase, namely by the equilibrium between
adsorbed and precipitated forms. Desorption of P and/or phosphate
dissolution govern the amount of P released into drainage
water, runoff or freshwater. Soil P evaluated by Olsen
method showed a strong correlation with the capacity of soil to
desorb P and, within certain limits, to the transfer of P to
water. This transfer of P relates to losses that occur either in
surface horizons, or in subsurface horizons (to drainage water,
to runoff or by soil erosion to freshwater)
Narrowband Photon Pair Source for Quantum Networks
We demonstrate a compact photon pair source based on a periodically poled
lithium niobate nonlinear crystal in a cavity. The cavity parameters are chosen
such that the emitted photon pair modes can be matched in the region of telecom
ultra dense wavelength division multiplexing (U-DWDM) channel spacings. This
approach provides efficient, low-loss, mode selection that is compatible with
standard telecommunication networks. Photons with a coherence time of 8.6 ns
(116 MHz) are produced and their purity is demonstrated. A source brightness of
134 pairs(s.mW.MHz) is reported. The high level of purity and
compatibility with standard telecom networks is of great importance for complex
quantum communication networks
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