10,470 research outputs found
Southern Chinese patients with systemic lupus erythematosus in Hong Kong have low vitamin D levels
BACKGROUND: Vitamin D insufficiency has been linked to pathogenesis of autoimmune diseases. This study aimed to measure serum 25(OH)D level in patients with systemic lupus erythematosus (SLE) in Hong Kong and to evaluate association between serum 25(OH)D level and disease activity. METHODS: Serum 25(OH)D level was measured by radioimmunoassay in SLE patients and healthy controls. Lupus disease activity was determined by SLE disease activity index (SLEDAI), serum anti-dsDNA antibody, C3 and C4 levels. RESULTS: Fifty-two SLE patients with mean ± standard deviation disease duration of 15.5±8.6 years were recruited. Five patients had active lupus disease. Five (9.6%) patients had serum 25(OH)D levels <30 nmol/L. Serum 25(OH)D level was significantly lower in SLE patients compared to age- and sex-matched controls (n=52) [45.5±12.3 vs 51.1±12.6 nmol/L, P=0.02]. Serum 25(OH)D levels were not found to be related to SLEDAI, elevated anti-dsDNA antibody, low C3 or C4 levels or medications. One vitamin D insufficient patient had low serum albumin-corrected calcium. Serum 25(OH)D levels were found to correlate negatively with estimated glomerular filtration rate (r= –0.30, P=0.03) but was not different between patients who had normal and impaired renal function (P=0.38). CONCLUSION: SLE patients in Hong Kong were found to have low serum 25(OH)D level despite its subtropical location.published_or_final_versionThe 15th Medical Research Conference (15th MRC), Department of Medicine, University of Hong Kong, Hong Kong, 16 January 2010. In Hong Kong Medical Journal, 2010, v. 16 n. 1, suppl. 1, p. 47, abstract no. 7
Optimal design of nonuniform FIR transmultiplexer using semi-infinite programming
This paper considers an optimum nonuniform FIR transmultiplexer design problem subject to specifications in the frequency domain. Our objective is to minimize the sum of the ripple energy for all the individual filters, subject to the specifications on amplitude and aliasing distortions, and to the passband and stopband specifications for the individual filters. This optimum nonuniform transmultiplexer design problem can be formulated as a quadratic semi-infinite programming problem. The dual parametrization algorithm is extended to this nonuniform transmultiplexer design problem. If the lengths of the filters are sufficiently long and the set of decimation integers is compatible, then a solution exists. Since the problem is formulated as a convex problem, if a solution exists, then the solution obtained is unique and the local solution is a global minimum
The Fundamental Plane of Gamma-ray Globular Clusters
We have investigated the properties of a group of -ray emitting
globular clusters (GCs) which have recently been uncovered in our Galaxy. By
correlating the observed -ray luminosities with various
cluster properties, we probe the origin of the high energy photons from these
GCs. We report is positively correlated with the encounter rate
and the metalicity which place an
intimate link between the gamma-ray emission and the millisecond pulsar
population. We also find a tendency that increase with the energy
densities of the soft photon at the cluster location. Furthermore, the
two-dimensional regression analysis suggests that , soft photon
densities, and / possibly span fundamental
planes which potentially provide better predictions for the -ray
properties of GCs.Comment: 17 pages, 4 figures, 3 tables, published in Ap
Vortices and the entrainment transition in the 2D Kuramoto model
We study synchronization in the two-dimensional lattice of coupled phase
oscillators with random intrinsic frequencies. When the coupling is larger
than a threshold , there is a macroscopic cluster of
frequency-synchronized oscillators. We explain why the macroscopic cluster
disappears at . We view the system in terms of vortices, since cluster
boundaries are delineated by the motion of these topological defects. In the
entrained phase (), vortices move in fixed paths around clusters, while
in the unentrained phase (), vortices sometimes wander off. These
deviant vortices are responsible for the disappearance of the macroscopic
cluster. The regularity of vortex motion is determined by whether clusters
behave as single effective oscillators. The unentrained phase is also
characterized by time-dependent cluster structure and the presence of chaos.
Thus, the entrainment transition is actually an order-chaos transition. We
present an analytical argument for the scaling for small
lattices, where is the threshold for phase-locking. By also deriving the
scaling , we thus show that for small , in
agreement with numerics. In addition, we show how to use the linearized model
to predict where vortices are generated.Comment: 11 pages, 8 figure
Gamma-ray emission from the globular clusters Liller 1, M80, NGC 6139, NGC 6541, NGC 6624, and NGC 6752
Globular clusters (GCs) are emerging as a new class of gamma-ray emitters,
thanks to the data obtained from the Fermi Gamma-ray Space Telescope. By now,
eight GCs are known to emit gamma-rays at energies >100~MeV. Based on the
stellar encounter rate of the GCs, we identify potential gamma-ray emitting GCs
out of all known GCs that have not been studied in details before. In this
paper, we report the discovery of a number of new gamma-ray GCs: Liller 1, NGC
6624, and NGC 6752, and evidence for gamma-ray emission from M80, NGC 6139, and
NGC 6541, in which gamma-rays were found within the GC tidal radius. With one
of the highest metallicity among all GCs in the Milky Way, the gamma-ray
luminosity of Liller 1 is found to be the highest of all known gamma-ray GCs.
In addition, we confirm a previous report of significant gamma-ray emitting
region next to NGC 6441. We briefly discuss the observed offset of gamma-rays
from some GC cores. The increasing number of known gamma-ray GCs at distances
out to ~10 kpc is important for us to understand the gamma-ray emitting
mechanism and provides an alternative probe to the underlying millisecond
pulsar populations of the GCs.Comment: 22 pages, 7 figures, 2 tables; ApJ, in pres
Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
Recent observations strongly suggest that the millisecond pulsar binary PSR
J1023+0038 has developed an accretion disk since 2013 June. We present a
multi-wavelength analysis of PSR J1023+0038, which reveals that 1) its
gamma-rays suddenly brightened within a few days in June/July 2013 and has
remained at a high gamma-ray state for several months; 2) both UV and X-ray
fluxes have increased by roughly an order of magnitude, and 3) the spectral
energy distribution has changed significantly after the gamma-ray sudden flux
change. Time variabilities associated with UV and X-rays are on the order of
100-500 seconds and 50-100 seconds, respectively. Our model suggests that a
newly formed accretion disk due to the sudden increase of the stellar wind
could explain the changes of all these observed features. The increase of UV is
emitted from the disk, and a new component in gamma-rays is produced by inverse
Compton scattering between the new UV component and pulsar wind. The increase
of X-rays results from the enhancement of injection pulsar wind energy into the
intra-binary shock due to the increase of the stellar wind. We also predict
that the radio pulses may be blocked by the evaporated winds from the disk and
the pulsar is still powered by rotation.Comment: 8 pages, 3 figures; accepted for publication in Ap
NuSTAR observations and broadband spectral energy distribution modeling of the millisecond pulsar binary PSR J1023+0038
We report the first hard X-ray (3-79 keV) observations of the millisecond
pulsar (MSP) binary PSR J1023+0038 using NuSTAR. This system has been shown
transiting between a low-mass X-ray binary (LMXB) state and a rotation-powered
MSP state. The NuSTAR observations were taken in both LMXB state and
rotation-powered state. The source is clearly seen in both states up to ~79
keV. During the LMXB state, the 3-79 keV flux is about a factor of 10 higher
that in the rotation-powered state. The hard X-rays show clear orbital
modulation during the X-ray faint rotation-powered state but the X-ray orbital
period is not detected in the X-ray bright LMXB state. In addition, the X-ray
spectrum changes from a flat power-law spectrum during the rotation-powered
state to a steeper power-law spectrum in the LMXB state. We suggest that the
hard X-rays are due to the intra-binary shock from the interaction between the
pulsar wind and the injected material from the low-mass companion star. During
the rotation-powered MSP state, the X-ray orbital modulation is due to Doppler
boosting of the shocked pulsar wind. At the LMXB state, the evaporating matter
of the accretion disk due to the gamma-ray irradiation from the pulsar stops
almost all the pulsar wind, resulting the disappearance of the X-ray orbital
modulation.Comment: 8 pages, 6 figures; accepted for publication in Ap
- …