59,546 research outputs found
Fluorine Abundances of Galactic Low-Metallicity Giants
With abundances and 2{\sigma} upper limits of fluorine (F) in seven
metal-poor field giants, nucleosynthesis of stellar F at low metallicity is
discussed. The measurements are derived from the HF(1-0) R9 line at 23358{\AA}
using nearinfrared K-band high-resolution spectra obtained with CRIRES at the
Very Large Telescope. The sample reaches lower metallicities than previous
studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13.
Effects of three-dimensional model atmospheres on the derived F and O
abundances are quantitatively estimated and shown to be insignificant for the
program stars. The observed F yield in the form of [F/O] is compared with two
sets of Galactic chemical evolution models, which quantitatively demonstrate
the contribution of Type II supernova (SN II) {\nu}-process and asymptotic
giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region,
models cannot well predict the observed distribution of [F/O], while the
observations are better fit by models considering an SN II {\nu}-process with a
neutrino energy of E_{\nu} = 3 x 10^53 erg. Our sample contains HD 110281, a
retrograde orbiting low-{\alpha} halo star, showing a similar F evolution as
globular clusters. This supports the theory that such halo stars are possibly
accreted from dwarf galaxy progenitors of globular clusters in the halo.Comment: 8 pages, 8 figures, 2 tables, published in The Astrophysical Journa
Sharp thresholds of blow-up and global existence for the coupled nonlinear Schrodinger system
In this paper, we establish two new types of invariant sets for the coupled
nonlinear Schrodinger system on , and derive two sharp thresholds
of blow-up and global existence for its solution. Some analogous results for
the nonlinear Schrodinger system posed on the hyperbolic space
and on the standard 2-sphere are also presented. Our arguments
and constructions are improvements of some previous works on this direction. At
the end, we give some heuristic analysis about the strong instability of the
solitary waves.Comment: 21 page
Entanglement created by spontaneously generated coherence
We propose a scheme able to generate on demand a steady-state entanglement
between two non-degenerate cavity modes. The scheme relies on the interaction
of the cavity modes with driven two or three-level atoms which act as a coupler
to build entanglement between the modes. We show that in the limit of a strong
driving, crucial for the generation of entanglement between the modes is to
imbalance populations of the dressed states of the driven atomic transition. In
the case of a three-level V-type atom, we find that a stationary entanglement
can be created on demand by tuning the Rabi frequency of the driving field to
the difference between the atomic transition frequencies. The resulting
degeneracy of the energy levels together with the spontaneously generated
coherence generates a steady-state entanglement between the cavity modes. It is
shown that the condition for the maximal entanglement coincides with the
collapse of the atomic system into a pure trapping state. We also show that the
creation of entanglement depends strongly on the mutual polarization of the
transition atomic dipole moments.Comment: Published versio
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