48,714 research outputs found
The heavy-element abundances of AGB stars and the angular momentum conservation model of wind accretion for barium stars
Adpoting new s-process nucleosynthesis scenario and branch s-process path, we
calculate the heavy-element abundances and C/O ratio of solar metallicity
3M_sun TP-AGB stars. The evolutionary sequence from M to S to C stars of AGB
stars is explained naturally by the calculated results. Then combining the
angular momentum conservation model of wind accretion with the heavy-element
abundances on the surface of TP-AGB stars, we calculate the heavy-element
overabundances of barium stars via successive pulsed accreting and mixing. Our
results support that the barium stars with longer orbital period, P>1600 days,
form through wind accretion scenario.Comment: 14 pages, LaTex, 17 PS figures included, accepted for publication in
A &
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
Non-leptonic two-body weak decays of
We study the non-leptonic two-body weak decays of with () representing as the baryon (meson) states. Based
on the flavor symmetry, we can describe most of the data reexamined by
the BESIII Collaboration with higher precisions. However, our result of is larger than the
current experimental limit of (90\% C.L.) by BESIII. In
addition, we find that , , and , which are accessible
to the BESIII experiments.Comment: 12 pages, 1 figure, revised version accepted by PL
Orbital elements of barium stars formed through a wind accretion scenario
Taking the total angular momentum conservation in place of the tangential
momentum conservation, and considering the square and higher power terms of
orbital eccentricity e, the changes of orbital elements of binaries are
calculated for wind accretion scenario. These new equations are used to
quantitatively explain the observed (e,logP) properties of normal G, K giants
and barium stars. Our results reflect the evolution from G, K giant binaries to
barium binaries, moreover, the barium stars with longer orbital periods P>1600
days may be formed by accreting part of the ejecta from the intrinsic AGB stars
through wind accretion scenario.Comment: 7 pages, LaTex, 4 PS figures and 1 table included, accepted for
publication in A &
Spin-dependent transport in a quasiballistic quantum wire
We describe the transport properties of a 5 m long one-dimensional (1D)
quantum wire. Reduction of conductance plateaux due to the introduction of
weakly disorder scattering are observed. In an in-plane magnetic field, we
observe spin-splitting of the reduced conductance steps. Our experimental
results provide evidence that deviation from conductance quantisation is very
small for electrons with spin parallel and is about 1/3 for electrons with spin
anti-parallel. Moreover, in a high in-plane magnetic field, a spin-polarised 1D
channel shows a plateau-like structure close to which
strengthens with {\em increasing} temperatures. It is suggested that these
results arise from the combination of disorder and the electron-electron
interactions in the 1D electron gas.Comment: 4 pages, 5 figures, latex to be published in Phys. Rev. B (15/3/2000
Surface States of the Topological Insulator Bi_{1-x}Sb_x
We study the electronic surface states of the semiconducting alloy BiSb.
Using a phenomenological tight binding model we show that the Fermi surface of
the 111 surface states encloses an odd number of time reversal invariant
momenta (TRIM) in the surface Brillouin zone confirming that the alloy is a
strong topological insulator. We then develop general arguments which show that
spatial symmetries lead to additional topological structure, and further
constrain the surface band structure. Inversion symmetric crystals have 8 Z_2
"parity invariants", which include the 4 Z_2 invariants due to time reversal.
The extra invariants determine the "surface fermion parity", which specifies
which surface TRIM are enclosed by an odd number of electron or hole pockets.
We provide a simple proof of this result, which provides a direct link between
the surface states and the bulk parity eigenvalues. We then make specific
predictions for the surface state structure for several faces of BiSb. We next
show that mirror invariant band structures are characterized by an integer
"mirror Chern number", n_M. The sign of n_M in the topological insulator phase
of BiSb is related to a previously unexplored Z_2 parameter in the L point k.p
theory of pure Bi, which we refer to as the "mirror chirality", \eta. The value
of \eta predicted by the tight binding model for Bi disagrees with the value
predicted by a more fundamental pseudopotential calculation. This explains a
subtle disagreement between our tight binding surface state calculation and
previous first principles calculations on Bi. This suggests that the tight
binding parameters in the Liu Allen model of Bi need to be reconsidered.
Implications for existing and future ARPES experiments and spin polarized ARPES
experiments will be discussed.Comment: 15 pages, 7 figure
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