183 research outputs found
Communicability Angles Reveal Critical Edges for Network Consensus Dynamics
We consider the question of determining how the topological structure
influences a consensus dynamical process taking place on a network. By
considering a large dataset of real-world networks we first determine that the
removal of edges according to their communicability angle -an angle between
position vectors of the nodes in an Euclidean communicability space- increases
the average time of consensus by a factor of 5.68 in real-world networks. The
edge betweenness centrality also identifies -in a smaller proportion- those
critical edges for the consensus dynamics, i.e., its removal increases the time
of consensus by a factor of 3.70. We justify theoretically these findings on
the basis of the role played by the algebraic connectivity and the
isoperimetric number of networks on the dynamical process studied, and their
connections with the properties mentioned before. Finally, we study the role
played by global topological parameters of networks on the consensus dynamics.
We determine that the network density and the average distance-sum -an
analogous of the node degree for shortest-path distances, account for more than
80% of the variance of the average time of consensus in the real-world networks
studied.Comment: 15 pages, 2 figure
Oscillations in the G-type Giants
The precise radial-velocity measurements of 4 G-type giants, 11Com,
Hya, Tau, and Her were carried out. The short-term variations
with amplitudes, 1-7m/s and periods, 3-10 hours were detected. A period
analysis shows that the individual power distribution is in a Gaussian shape
and their peak frequencies () are in a good agreement with the
prediction by the scaling law. With using a pre-whitening procedure,
significant frequency peaks more than 3 are extracted for these
giants. From these peaks, we determined the large frequency separation by
constructing highest peak distribution of collapsed power spectrum, which is
also in good agreement with what the scaling law for the large separation
predicts. Echelle diagrams of oscillation frequency were created based on the
extracted large separations, which is very useful to clarify the properties of
oscillation modes. In these echelle diagrams, odd-even mode sequences are
clearly seen. Therefore, it is certain that in these G-type giants, non-radial
modes are detected in addition to radial mode. As a consequence, these
properties of oscillation modes are shown to follow what Dzymbowski et
al.(2001) and Dupret et al.(2009) theoretically predicted. Damping times for
these giants were estimated with the same method as that developed by Stello et
al.(2004). The relation of Q value (ratio of damping time to period) to the
period was discussed by adding the data of the other stars ranging from dwarfs
to giants.Comment: 28 pages, 16 figures, accepted for publication in PASJ 62, No.4, 201
Beryllium Abundances of Solar-Analog Stars
An extensive beryllium abundance analysis was conducted for 118 solar analogs
(along with 87 FGK standard stars) by applying the spectrum synthesis technique
to the near-UV region comprising the Be II line at 3131.066 A, in an attempt to
investigate whether Be suffers any depletion such as the case of Li showing a
large diversity. We found that, while most of these Sun-like stars are
superficially similar in terms of their A(Be) (Be abundances) around the solar
value within ~ +/- 0.2dex, 4 out of 118 samples turned out strikingly
Be-deficient (by more than ~2 dex) and these 4 stars belong to the group of
lowest v_e sin i (projected rotation velocity). Moreover, even for the other
majority showing an apparent similarity in Be, we can recognize a tendency that
A(Be) gradually increases with an increase in v_e sin i. These observational
facts suggest that any solar analog star (including the Sun) generally suffers
some kind of Be depletion during their lives, where the rotational velocity (or
the angular momentum) plays an important role in the sense that depletion tends
to be enhanced by slower rotation. Hence, our findings require that the
occasionally stated view "G-type dwarfs with T_eff ~< 6000 K are essentially
homogeneous in Be with their original composition retained" should be revised.
Also, our analysis indicates that the difference of ~0.2 dex in A(Be) between
the solar photosphere and the meteorite really exists, implying that "UV
missing opacity" is irrelevant at least for this Be II line.Comment: 18 pages, 12 figures, 3 tables and 3 electronic tables (included as
ancillary files), accepted for publication in Publ. Astron. Soc. Japan (2011,
Vol. 63, No. 4
Detection of Lead in the Carbon-Rich, Very Metal-Poor Star LP625-44: A Strong Constraint on s-Process Nucleosynthesis at Low Metallicity
We report the detection of the Pb I 4057.8A line in the very metal-poor
([Fe/H]=-2.7), carbon-rich star, LP625-44. We determine the abundance of Pb
([Pb/Fe] = 2.65) and 15 other neutron-capture elements. The abundance pattern
between Ba and Pb agrees well with a scaled solar system s-process component,
while the lighter elements (Sr-Zr) are less abundant than Ba. The enhancement
of s-process elements is interpreted as a result of mass transfer in a binary
system from a previous AGB companion, an interpretation strongly supported by
radial velocity variations of this system.
The detection of Pb makes it possible, for the first time, to compare model
predictions of s-process nucleosynthesis in AGB stars with observations of
elements between Sr and Pb. The Pb abundance is significantly lower than the
prediction of recent models (e.g., Gallino et al. 1998), which succeeded in
explaining the metallicity dependence of the abundance ratios of light
s-elements (Sr-Zr) to heavy ones (Ba-Dy) found in previously observed
s-process-enhanced stars. This suggests that one should either (a) reconsider
the underlying assumptions concerning the 13C-rich s-processing site
(13C-pocket) in the present models, or (b) investigate alternative sites of
s-process nucleosynthesis in very metal-poor AGB stars.Comment: 10 pages, 3 figures, Astrophysical Journal Letters, in pres
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