19,540 research outputs found
A New Photometric Model of the Galactic Bar using Red Clump Giants
We present a study of the luminosity density distribution of the Galactic bar
using number counts of red clump giants (RCGs) from the OGLE-III survey. The
data were recently published by Nataf et al. (2013) for 9019 fields towards the
bulge and have RC stars over a viewing area of . The data include the number counts, mean distance modulus
(), dispersion in and full error matrix, from which we fit the data
with several tri-axial parametric models. We use the Markov Chain Monte Carlo
(MCMC) method to explore the parameter space and find that the best-fit model
is the model, with the distance to the GC is 8.13 kpc, the ratio of
semi-major and semi-minor bar axis scale lengths in the Galactic plane
, and vertical bar scale length , is (close to being prolate). The scale length of the stellar
density profile along the bar's major axis is 0.67 kpc and has an angle
of , slightly larger than the value obtained from a similar study
based on OGLE-II data. The number of estimated RC stars within the field of
view is , which is systematically lower than the observed
value. We subtract the smooth parametric model from the observed counts and
find that the residuals are consistent with the presence of an X-shaped
structure in the Galactic centre, the excess to the estimated mass content is
. We estimate the total mass of the bar is . Our results can be used as a key ingredient to construct new density
models of the Milky Way and will have implications on the predictions of the
optical depth to gravitational microlensing and the patterns of hydrodynamical
gas flow in the Milky Way.Comment: 15 pages, 6 figures, 4 tables. MNRAS accepte
Delay-dependent robust stability of stochastic delay systems with Markovian switching
In recent years, stability of hybrid stochastic delay systems, one of the important issues in the study of stochastic systems, has received considerable attention. However, the existing results do not deal with the structure of the diffusion but estimate its upper bound, which induces conservatism. This paper studies delay-dependent robust stability of hybrid stochastic delay systems. A delay-dependent criterion for robust exponential stability of hybrid stochastic delay systems is presented in terms of linear matrix inequalities (LMIs), which exploits the structure of the diffusion. Numerical examples are given to verify the effectiveness and less conservativeness of the proposed method
Neutron spin polarization in strong magnetic fields
The effects of strong magnetic fields on the inner crust of neutron stars are
investigated after taking into account the anomalous magnetic moments of
nucleons. Energy spectra and wave functions for protons and neutrons in a
uniform magnetic field are provided. The particle spin polarizations and the
yields of protons and neutrons are calculated in a free Fermi gas model.
Obvious spin polarization occurs when G for protons and
G for neutrons, respectively. It is shown that the neutron spin
polarization depends solely on the magnetic field strength.Comment: Replaced by the revised version; 10 pages, including 3 eps figure
Bose-Einstein condensation in linear sigma model at Hartree and large N approximation
The BEC of charged pions is investigated in the framework of O(4) linear
sigma model. By using Cornwall-Jackiw-Tomboulis formalism, we have derived the
gap equations for the effective masses of the mesons at finite temperature and
finite isospin density. The BEC is discussed in chiral limit and non-chiral
limit at Hartree approximation and also at large N approximation.Comment: 11 pages, 9 figure
Quadratic Quantum Measurements
We develop a theory of quadratic quantum measurements by a mesoscopic
detector. It is shown that quadratic measurements should have non-trivial
quantum information properties, providing, for instance, a simple way of
entangling two non-interacting qubits. We also calculate output spectrum of a
quantum detector with both linear and quadratic response continuously
monitoring coherent oscillations in two qubits.Comment: 5 pages, 2 figure
Effects of solute concentrations on kinetic pathways in Ni-Al-Cr alloys
The kinetic pathways resulting from the formation of coherent L12-ordered
y'-precipitates in the g-matrix (f.c.c.) of Ni-7.5 Al-8.5 Cr at.% and Ni-5.2
Al-14.2 Cr at.% alloys, aged at 873 K, are investigated by atom-probe
tomography (APT) over a range of aging times from 1/6 to 1024 hours; these
alloys have approximately the same volume fraction of the y'-precipitate phase.
Quantification of the phase decomposition within the framework of classical
nucleation theory reveals that the y-matrix solid-solution solute
supersaturations of both alloys provide the chemical driving force, which acts
as the primary determinant of the nucleation behavior. In the coarsening
regime, the temporal evolution of the y'-precipitate average radii and the
y-matrix supersaturations follow the predictions of classical coarsening
models, while the temporal evolution of the y'-precipitate number densities of
both alloys do not. APT results are compared to equilibrium calculations of the
pertinent solvus lines determined by employing both Thermo-Calc and
Grand-Canonical Monte Carlo simulation.Comment: Submitted to Acta Materialia, June, 200
Emergence of intrinsic superconductivity below 1.178 K in the topologically non-trivial semimetal state of CaSn3
Topological materials which are also superconducting are of great current
interest, since they may exhibit a non-trivial topologically-mediated
superconducting phase. Although there have been many reports of pressure-tuned
or chemical-doping-induced superconductivity in a variety of topological
materials, there have been few examples of intrinsic, ambient pressure
superconductivity in a topological system having a stoichiometric composition.
Here, we report that the pure intermetallic CaSn3 not only exhibits topological
fermion properties but also has a superconducting phase at 1.178 K under
ambient pressure. The topological fermion properties, including the nearly zero
quasi-particle mass and the non-trivial Berry phase accumulated in cyclotron
motions, were revealed from the de Haas-van Alphen (dHvA) quantum oscillation
studies of this material. Although CaSn3 was previously reported to be
superconducting at 4.2K, our studies show that the superconductivity at 4.2K is
extrinsic and caused by Sn on the degraded surface, whereas its intrinsic bulk
superconducting transition occurs at 1.178 K. These findings make CaSn3 a
promising candidate for exploring new exotic states arising from the interplay
between non-trivial band topology and superconductivity, e.g. topological
superconductivityComment: 20 pages,4 figure
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