54,454 research outputs found
NeIII/OII as an oxygen abundance indicator in the HII regions and HII galaxies
To calibrate the relationship between Ne3O2 (Ne3O2 =
log(\neiii/\oii)) and oxygen abundances, we present a
sample of 3000 \hii galaxies from the Sloan Digital Sky Survey (SDSS)
data release four. They are associated with a sample from the literature
intended to enlarge the oxygen abundance region. We calculated the electron
temperatures () of 210 galaxies in the SDSS sample with the direct method,
and of the other 2960 galaxies in SDSS sample calculated with an
empirical method. Then, we use a linear least-square fitting to calibrate the
Ne3O2 oxygen abundance indicator. It is found that the Ne3O2 estimator follows
a linear relation with \zoh\ that holds for the whole abundance range covered
by the sample, from approximately 7.0 to 9.0. The best linear relationship
between the Ne3O2 and the oxygen abundance is calibrated. The dispersion
between oxygen abundance and Ne3O2 index in the metal rich galaxies may come
partly from the moderate depletion of oxygen onto grains. The method
has the virtue of being single-valued and not affected by internal reddening.
As a result, the method can be a good metallicity indicator in the \hii
regions and \hii galaxies, especially in high-redshift galaxies.Comment: 7 pages, 6 figures. A&A accepte
Entangled Superfluids
We study the condensate dynamics of the so-called entangled Bose-Einstein
condensation (EBEC), which is the ground state of a mixture of two species of
pseudospin- atoms with interspecies spin-exchange scattering in
certain parameter regimes. EBEC leads to four inter-dependent superfluid
components, each corresponding to the orbital wave function associated with a
spin component of a species. The four superflows have various
counter-relations, and altogether lead to a conserved total supercurrent and a
conserved total spin supercurrent. In the homogenous case, we also obtain the
elementary excitations due to variations of the single-particle orbital wave
functions, by exactly solving the generalized time-dependent Bogoliubov
equations. There are three gapless Bogoliubov modes and one Klein-Gordon-like
gapped mode. The origin of these excitations are also discussed from the
perspective of spontaneous breaking of the symmetries possessed by the system.Comment: 10 pages. Published in PR
Fuzzy Chance-constrained Programming Based Security Information Optimization for Low Probability of Identification Enhancement in Radar Network Systems
In this paper, the problem of low probability of identification (LPID) improvement for radar network systems is investigated. Firstly, the security information is derived to evaluate the LPID performance for radar network. Then, without any prior knowledge of hostile intercept receiver, a novel fuzzy chance-constrained programming (FCCP) based security information optimization scheme is presented to achieve enhanced LPID performance in radar network systems, which focuses on minimizing the achievable mutual information (MI) at interceptor, while the attainable MI outage probability at radar network is enforced to be greater than a specified confidence level. Regarding to the complexity and uncertainty of electromagnetic environment in the modern battlefield, the trapezoidal fuzzy number is used to describe the threshold of achievable MI at radar network based on the credibility theory. Finally, the FCCP model is transformed to a crisp equivalent form with the property of trapezoidal fuzzy number. Numerical simulation results demonstrating the performance of the proposed strategy are provided
Video Compressive Sensing for Dynamic MRI
We present a video compressive sensing framework, termed kt-CSLDS, to
accelerate the image acquisition process of dynamic magnetic resonance imaging
(MRI). We are inspired by a state-of-the-art model for video compressive
sensing that utilizes a linear dynamical system (LDS) to model the motion
manifold. Given compressive measurements, the state sequence of an LDS can be
first estimated using system identification techniques. We then reconstruct the
observation matrix using a joint structured sparsity assumption. In particular,
we minimize an objective function with a mixture of wavelet sparsity and joint
sparsity within the observation matrix. We derive an efficient convex
optimization algorithm through alternating direction method of multipliers
(ADMM), and provide a theoretical guarantee for global convergence. We
demonstrate the performance of our approach for video compressive sensing, in
terms of reconstruction accuracy. We also investigate the impact of various
sampling strategies. We apply this framework to accelerate the acquisition
process of dynamic MRI and show it achieves the best reconstruction accuracy
with the least computational time compared with existing algorithms in the
literature.Comment: 30 pages, 9 figure
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