145,477 research outputs found
Could 2S 0114+650 be a magnetar?
We investigate the spin evolution of the binary X-ray pulsar 2S 0114+650,
which possesses the slowest known spin period of hours. We argue
that, to interpret such long spin period, the magnetic field strength of this
pulsar must be initially \gsim 10^{14} G, that is, it was born as a magnetar.
Since the pulsar currently has a normal magnetic field G, our
results present support for magnetic field decay predicted by the magnetar
model.Comment: 7 pages, 1 figure, accepted for publication in ApJ
Conflict-free connection numbers of line graphs
A path in an edge-colored graph is called \emph{conflict-free} if it contains
at least one color used on exactly one of its edges. An edge-colored graph
is \emph{conflict-free connected} if for any two distinct vertices of ,
there is a conflict-free path connecting them. For a connected graph , the
\emph{conflict-free connection number} of , denoted by , is defined
as the minimum number of colors that are required to make conflict-free
connected. In this paper, we investigate the conflict-free connection numbers
of connected claw-free graphs, especially line graphs. We first show that for
an arbitrary connected graph , there exists a positive integer such that
. Secondly, we get the exact value of the conflict-free
connection number of a connected claw-free graph, especially a connected line
graph. Thirdly, we prove that for an arbitrary connected graph and an
arbitrary positive integer , we always have , with only the exception that is isomorphic to a star of order
at least~ and . Finally, we obtain the exact values of ,
and use them as an efficient tool to get the smallest nonnegative integer
such that .Comment: 11 page
Analytical models for quark stars
We find two new classes of exact solutions to the Einstein-Maxwell system of
equations. The matter content satisfies a linear equation of state consistent
with quark matter; a particular form of one of the gravitational potentials is
specified to generate solutions. The exact solutions can be written in terms of
elementary functions, and these can be related to quark matter in the presence
of an electromagnetic field. The first class of solutions generalises the Mak
and Harko model. The second class of solutions does not admit any singularities
in the matter and gravitational potentials at the centre.Comment: 10 pages, To appear in Int. J. Mod. Phys.
Quantum heat engine with continuum working medium
We introduce a new quantum heat engine, in which the working medium is a
quantum system with a discrete level and a continuum. Net work done by this
engine is calculated and discussed. The results show that this quantum heat
engine behaves like the two-level quantum heat engine in both the
high-temperature and the low-temperature limits, but it operates differently in
temperatures between them. The efficiency of this quantum heat engine is also
presented and discussed.Comment: 5 pages, 3 figure
Tensor correlation, pairing interaction and deformation in Ne isotopes and Ne hypernuclei
We study tensor and pairing effects on the quadruple deformation of neon
isotopes based on a deformed Skyrme-Hartree-Fock model with BCS approximation
for the pairing channel. We extend the Skyrme-Hartree-Fock formalism for the
description of single- and double-lambda hypernuclei adopting two different
hyperon-nucleon interactions. It is found that the interplay of pairing and
tensor interactions is crucial to derive the deformations in several neon
isotopes. Especially, the shapes of Ne are studied in details in
comparisons with experimentally observed shapes. Furthermore the deformations
of the hypernuclei are compared with the corresponding neon isotopic cores in
the presence of tensor force. We find the same shapes with somewhat smaller
deformations for single -hypernuclei compared with their core
deformations. It is also pointed out that the latest version of hyperon
interaction, the ESC08b model, having a deeper potential makes
smaller deformations for hypernuclei than those of another NSC97f model.Comment: 13 pages, 5 figures, Physical Review C 2013 in pres
Relations Among Universal Equations For Gromov-Witten Invariants
In this paper, we study relations among known universal equations for
Gromov-Witten invariants at genus 1 and 2.Comment: LaTex file, 13 page
Are There Any Redshift >8 Gamma-Ray Bursts in the BATSE Catalog?
Several luminosity indicators have been found for Gamma-Ray Bursts (GRBs)
wherein measurable light curve and spectral properties are well-correlated with
the peak luminosity. Several papers have each applied one different luminosity
relation to find redshifts for BATSE GRBs and claim to identify specific bursts
with z>8. The existence of such high redshift events is not surprising, as
BATSE has enough sensitivity to see them and GRBs are expected out to the
redshift of the first star formation. To improve results we used five
luminosity relations with updated calibrations to determine redshifts with
error bars. Combining these relations, we calculated the redshifts of 36 BATSE
GRBs with claimed z>8. Our results include 13 bursts with our derived best
redshift z_best>8, which looks promising at first. But the calculated redshift
uncertainties are significantly large in these selected cases. With only one
exception, all of our bursts have z_1siglow<9. The one exception (BATSE trigger
2035) is likely a short duration burst at z>~4. Our best case for a very high
redshift event is BATSE trigger 3142 with z_best>20 and z_1siglow=8.9, however
we can only say z>4.1 at the two-sigma confidence level. In all, we cannot
point toward any one BATSE burst as confidently having z>8. One implication is
to greatly weaken prior claims that GRBs have a steeply rising rate-density out
to high redshifts.Comment: ApJ in press, 18 page
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