64,813 research outputs found
The optical/UV excess of isolated neutron stars in the RCS model
The X-ray dim isolated neutron stars (XDINSs) are peculiar pulsar-like
objects, characterized by their very well Planck-like spectrum. In studying
their spectral energy distributions, the optical/UV excess is a long standing
problem. Recently, Kaplan et al. (2011) have measured the optical/UV excess for
all seven sources, which is understandable in the resonant cyclotron scattering
(RCS) model previously addressed. The RCS model calculations show that the RCS
process can account for the observed optical/UV excess for most sources . The
flat spectrum of RX J2143.0+0654 may due to contribution from bremsstrahlung
emission of the electron system in addition to the RCS process.Comment: 6 pages, 2 figures, 1 table, accepted for publication in Research in
Astronomy and Astrophysic
AXPs and SGRs in the outer gap model: confronting Fermi observations
Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are
magnetar candidates, i.e., neutron stars powered by strong magnetic field. If
they are indeed magnetars, they will emit high-energy gamma-rays which are
detectable by Fermi-LAT according to the outer gap model. However, no
significant detection is reported in recent Fermi-LAT observations of all known
AXPs and SGRs. Considering the discrepancy between theory and observations, we
calculate the theoretical spectra for all AXPs and SGRs with sufficient
observational parameters. Our results show that most AXPs and SGRs are
high-energy gamma-ray emitters if they are really magnetars. The four AXPs 1E
1547.0-5408, XTE J1810-197, 1E 1048.1-5937, and 4U 0142+61 should have been
detected by Fermi-LAT. Then there is conflict between out gap model in the case
of magnetars and Fermi observations. Possible explanations in the magnetar
model are discussed. On the other hand, if AXPs and SGRs are fallback disk
systems, i.e., accretion-powered for the persistent emissions, most of them are
not high-energy gamma-ray emitters. Future deep Fermi-LAT observations of AXPs
and SGRs will help us make clear whether they are magnetars or fallback disk
systems.Comment: 15 pages, 3 figures, 1 table, accepted for publication in The
Astrophysical Journa
Inversely Unstable Solutions of Two-Dimensional Systems on Genus-p Surfaces and the Topology of Knotted Attractors
In this paper, we will show that a periodic nonlinear, time-varying
dissipative system that is defined on a genus-p surface contains one or more
invariant sets which act as attractors. Moreover, we shall generalize a result
in [Martins, 2004] and give conditions under which these invariant sets are not
homeomorphic to a circle individually, which implies the existence of chaotic
behaviour. This is achieved by studying the appearance of inversely unstable
solutions within each invariant set.Comment: 19 pages with 20 figures, AMS La-TeX, to be published in
International Journal of Bifurcation and Chao
Quark Orbital Angular Momentum in the Baryon
Analytical and numerical results, for the orbital and spin content carried by
different quark flavors in the baryons, are given in the chiral quark model
with symmetry breaking. The reduction of the quark spin, due to the spin
dilution in the chiral splitting processes, is transferred into the orbital
motion of quarks and antiquarks. The orbital angular momentum for each quark
flavor in the proton as a function of the partition factor and the
chiral splitting probability is shown. The cancellation between the spin
and orbital contributions in the spin sum rule and in the baryon magnetic
moments is discussed.Comment: 26 pages, 3 figures, revised version with minor eq. no and ref. no.
corrections. Discussion on the spin and a new ref. are adde
Self-management of context-aware overlay ambient networks
Ambient Networks (ANs) are dynamically changing and heterogeneous as they consist of potentially large numbers of independent, heterogeneous mobile nodes, with spontaneous topologies that can logically interact with each other to share a common control space, known as the Ambient Control Space. ANs are also flexible i.e. they can compose and decompose dynamically and automatically, for supporting the deployment of cross-domain (new) services. Thus, the AN architecture must be sophisticatedly designed to support such high level of dynamicity, heterogeneity and flexibility. We advocate the use of service specific overlay networks in ANs, that are created on-demand according to specific service requirements, to deliver, and to automatically adapt services to the dynamically changing user and network context. This paper presents a self-management approach to create, configure, adapt, contextualise, and finally teardown service specific overlay networks
Unitary transformation for the system of a particle in a linear potential
A unitary operator which relates the system of a particle in a linear
potential with time-dependent parameters to that of a free particle, has been
given. This operator, closely related to the one which is responsible for the
existence of coherent states for a harmonic oscillator, is used to find a
general wave packet described by an Airy function. The kernel (propagator) and
a complete set of Hermite-Gaussian type wave functions are also given.Comment: Europhysics Letters (in press
Physical decomposition of the gauge and gravitational fields
Physical decomposition of the non-Abelian gauge field has recently solved the
two-decade-lasting problem of a meaningful gluon spin. Here we extend this
approach to gravity and attack the century-lasting problem of a meaningful
gravitational energy. The metric is unambiguously separated into a pure
geometric term which contributes null curvature tensor, and a physical term
which represents the true gravitational effect and always vanishes in a flat
space-time. By this decomposition the conventional pseudo-tensors of the
gravitational stress-energy are easily rescued to produce definite physical
result. Our decomposition applies to any symmetric tensor, and has interesting
relation to the transverse-traceless (TT) decomposition discussed by Arnowitt,
Deser and Misner, and by York.Comment: 11 pages, no figure; significant revision, with discussion on
relations of various metric decomposition
Stereociliary Myosin-1c Receptors Are Sensitive to Calcium Chelation and Absent from Cadherin 23 Mutant Mice
The identities of some of the constituents of the hair-cell transduction apparatus have been elucidated only recently. The molecular motor myosin-1c (Myo1c) functions in adaptation of the hair-cell response to sustained mechanical stimuli and is therefore an integral part of the transduction complex. Recent data indicate that Myo1c interacts in vitro with two other molecules proposed to be important for transduction: cadherin 23 (Cdh23), a candidate for the stereociliary tip link, and phosphatidylinositol 4,5-bisphosphate (PIP2), which is abundant in the membranes of hair-cell stereocilia. It is not known, however, whether these interactions occur in hair cells. Using an in situ binding assay on saccular hair cells, we demonstrated previously that Myo1c interacts with molecules at stereociliary tips, the site of transduction, through sequences contained within its calmodulin (CaM)-binding neck domain, which can bind up to four CaM molecules. In the current study, we identify the second CaM-binding IQ domain as a region of Myo1c that mediates CaM-sensitive binding to stereociliary tips and to PIP2 immobilized on a solid support. Binding of Myo1c to stereociliary tips of cochlear and vestibular hair cells is disrupted by treatments that break tip links. In addition, Myo1c does not bind to stereocilia from mice whose hair cells lack Cdh23 protein despite the presence of PIP2 in the stereociliary membranes. Collectively, our data suggest that Myo1c and Cdh23 interact at the tips of hair-cell stereocilia and that this interaction is modulated by CaM
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