11,022 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
Geometric phase in open systems: beyond the Markov approximation and weak coupling limit
Beyond the quantum Markov approximation and the weak coupling limit, we
present a general theory to calculate the geometric phase for open systems with
and without conserved energy. As an example, the geometric phase for a
two-level system coupling both dephasingly and dissipatively to its environment
is calculated. Comparison with the results from quantum trajectory analysis is
presented and discussed
Berry phase in a composite system
The Berry phase in a composite system with only one subsystem being driven
has been studied in this Letter. We choose two spin- systems with
spin-spin couplings as the composite system, one of the subsystems is driven by
a time-dependent magnetic field. We show how the Berry phases depend on the
coupling between the two subsystems, and what is the relation between these
Berry phases of the whole system and those of the subsystems.Comment: 4 pages, 6 figure
A smoothing SQP method for nonlinear programs with stability constraints arising from power systems
This paper investigates a new class of optimization problems arising from power systems, known as nonlinear programs with stability constraints (NPSC), which is an extension of ordinary nonlinear programs. Since the stability constraint is described generally by eigenvalues or norm of Jacobian matrices of systems, this results in the semismooth property of NPSC problems. The optimal conditions of both NPSC and its smoothing problem are studied. A smoothing SQP algorithm is proposed for solving such optimization problem. The global convergence of algorithm is established. A numerical example from optimal power flow (OPF) is done. The computational results show efficiency of the new model and algorithm. © The Author(s) 2010.published_or_final_versionSpringer Open Choice, 21 Feb 201
Assistive control system using continuous myoelectric signal in robot-aided arm training for patients after stroke
Author name used in this publication: Kai-yu Tong2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
A smoothing projected Newton-type algorithm for semi-infinite programming
2008-2009 > Academic research: refereed > Publication in refereed journa
EXPERIMENTAL STRESS CONCENTRATION FACTOR IN CONCRETE-FILLED STEEL TUBULAR T-JOINTS
© 2018 Elsevier Ltd An experimental investigation of stress concentration factor (SCF) in Steel circular hollow section brace welded to concrete-filled circular hollow section chord (CHS-to-CFCHS) T-joints has been performed under axial tension, axial compression, in-plane bending and out-of-plane bending. The distribution of SCF around the welded brace-to-chord intersection on both the brace and chord has been investigated using three CHS-to-CFCHS T-joint specimens. The experimental SCF results have been compared with the predicted SCF in empty T-joints. The relationship between the maximum SCF in relation to parameter β, with fixed other geometrical parameters, has been investigated for the basic load conditions. The experimental maximum SCF under axial tension has been compared with the predicted maximum SCF from parametric equations for CHS-to-CFCHS T-joints previously developed by the authors. The results show that the concrete has a significant effect in reducing the SCF, mostly under axial tension and the parametric equations for predicting SCFs in empty T-joints are not suitable for CHS-to-CFCHS T-joints. The effect of parameter β on the maximum SCF in CHS-to-CFCHS T-joints is significant under axial tension and out-of-plane bending moment
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