127,553 research outputs found
The asymmetric structure of the Galactic halo
Using the stellar photometry catalogue based on the latest data release (DR4)
of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using
star counts is carried out for selected areas of the sky. The sample areas are
selected along a circle at a Galactic latitude of +60, and 10 strips of
high Galactic latitude along different longitudes. Direct statistics of the
data show that the surface densities of from to
are systematically higher than those of from
to , defining a region of overdensity (in the direction of Virgo)
and another one of underdensity (in the direction of Ursa Major) with respect
to an axisymmetric model. It is shown by comparing the results from star counts
in the colour that the density deviations are due to an asymmetry of
the stellar density in the halo. Theoretical models for the surface density
profile are built and star counts are performed using a triaxial halo of which
the parameters are constrained by observational data. Two possible reasons for
the asymmetric structure are discussed.Comment: 17 pages, 7 figures, 5 tables, MNRAS accepte
Comparison of different measures for quantum discord under non-Markovian noise
Two geometric measures for quantum discord were recently proposed by Modi et
al. [Phys. Rev. Lett. 104, 080501 (2010)] and Dakic et al. [Phys. Rev. Lett.
105, 190502 (2010)]. We study the similarities and differences for total
quantum correlations of Bell-diagonal states using these two geometry-based
quantum discord and the original quantum discord. We show that, under
non-Markovian dephasing channels, quantum discord and one of the geometric
measures stay constant for a finite amount of time, but not the other geometric
measure. However, all the three measures share a common sudden change point.
Our study on critical point of sudden transition might be useful for keeping
long time total quantum correlations under decoherence.Comment: 10 pages, 3 figures submitted for publicatio
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Enhanced forward stimulated Brillouin scattering in silicon photonic slot waveguide Bragg grating
We study the forward stimulated Brillouin scattering process in a suspended silicon slot waveguide Bragg grating. Full-vectorial formalism is applied to analyze the interplay of electrostriction and radiation pressure. We show that radiation pressure is the dominant factor in the proposed waveguide. The Brillouin gain strongly depends on the structural parameters and the maximum value in the order of 106 W−1 m−1 is obtained in the slow light regime, which is more than two orders larger than that of the stand-alone strip and slot waveguides
Simulation of Near-Tip Crack Behaviour and Its Correlation to Fatigue Crack Growth with a Modified Strip-Yield Model
A modified strip-yield model has been developed to simulate the plasticity-induced crack closure under the constant amplitude (CA) and a single overload loading conditions. The paper focuses on the simulation of the near tip crack profiles and stress distributions during the fatigue process. Detailed information on near-tip stress and displacement fields at the maximum load (Pmax), the minimum load (Pmin), and the crack opening load (Pop) of a fatigue load cycle have been presented. The correlation of the crack closure to the near-tip material fatigue damage has been investigated and used to rationalize the crack growth behaviour under the CA and a single overload loading conditions.Peer reviewedSubmitted Versio
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