7,874 research outputs found
Broadband lightcurve characteristics of GRBs 980425 and 060218 and comparison with long-lag, wide-pulse GRBs
It has been recently argued that low-luminosity gamma-ray bursts (LL-GRBs)
are likely a unique GRB population. Here, we present systematic analysis of the
lightcurve characteristics from X-ray to gamma-ray energy bands for the two
prototypical LL-GRBs 980425 and 060218. It is found that both the pulse width
() and the ratio of the rising width to the decaying width () of theses
two bursts are energy-dependent over a broad energy band. There exists a
significant trend that the pulses tend to be narrower and more symmetry with
respect to the higher energy bands for the two events. Both the X-rays and the
gamma-rays follow the same and relations. These facts may
indicate that the X-ray emission tracks the gamma-ray emission and both are
likely to be originated from the same physical mechanism. Their light curves
show significant spectral lags. We calculate the three types of lags with the
pulse peaking time (), the pulse centroid time (), and the
cross-correlation function (CCF). The derived and are a
power-law function of energy. The lag calculated by CCF is strongly correlated
with that derived from . But the lag derived from is less
correlated with that derived from and CCF. The energy dependence of
the lags is shallower at higher energy bands. These characteristics are well
consistent with that observed in typical long-lag, wide-pulse GRBs, suggesting
that GRBs 980425 and 060218 may share the similar radiation physics with them.Comment: 26 pages, 10 figures, 3 tables, accepted for publication in Ap
Bridgeness: A Local Index on Edge Significance in Maintaining Global Connectivity
Edges in a network can be divided into two kinds according to their different
roles: some enhance the locality like the ones inside a cluster while others
contribute to the global connectivity like the ones connecting two clusters. A
recent study by Onnela et al uncovered the weak ties effects in mobile
communication. In this article, we provide complementary results on document
networks, that is, the edges connecting less similar nodes in content are more
significant in maintaining the global connectivity. We propose an index named
bridgeness to quantify the edge significance in maintaining connectivity, which
only depends on local information of network topology. We compare the
bridgeness with content similarity and some other structural indices according
to an edge percolation process. Experimental results on document networks show
that the bridgeness outperforms content similarity in characterizing the edge
significance. Furthermore, extensive numerical results on disparate networks
indicate that the bridgeness is also better than some well-known indices on
edge significance, including the Jaccard coefficient, degree product and
betweenness centrality.Comment: 10 pages, 4 figures, 1 tabl
Fractal property of generalized M-set with rational number exponent
Dynamic systems described by fc(z) = z2 + c is called Mandelbrot set (M-set), which is important for fractal and chaos theories due to its simple expression and complex structure. fc(z) = zk + c is called generalized M set (k–M set). This paper proposes a new theory to compute the higher and lower bounds of generalized M set while exponent k is rational, and proves relevant properties, such as that generalized M set could cover whole complex number plane when k 1), and that k–M set can be divided into |p–q| isomorphic parts
Hadronic B Decays to Charmed Baryons
We study exclusive B decays to final states containing a charmed baryon
within the pole model framework. Since the strong coupling for is larger than that for , the two-body charmful decay
has a rate larger than
as the former proceeds via the pole while the latter via the
pole. By the same token, the three-body decay receives less baryon-pole contribution than
. However, because the important charmed-meson
pole diagrams contribute constructively to the former and destructively to the
latter, has a rate slightly larger than
. It is found that one quarter of the rate comes from the resonant contributions. We discuss
the decays and
and stress that they are not color suppressed even though they can only proceed
via an internal W emission.Comment: 25 pages, 6 figure
Source, transport and impacts of a heavy dust event in the Yangtze River Delta, China, in 2011
Dust invasion is an important type of particle pollution in China. During 1
to 6 May in 2011, a dust event was observed in the Yangtze River Delta
region (YRD). The highest PM<sub>10</sub> (particles up to 10 μ in diameter) concentration reached over 1000 μg m<sup>−3</sup>
and the visibility was below 3 km. In this study, the Community
Multi-scale Air Quality modeling system (CMAQ5.0) coupled with an in-line
windblown dust model was used to simulate the formation, spatial and
temporal characteristics of this dust event, and analyze its impacts. The
threshold friction velocity for loose, fine-grained soil with low surface
roughness in the dust model was revised based on Chinese data to improve the
model performance. This dust storm broke out in Xinjiang and Mongolia during
28 to 30 April and arrived in the YRD region on 1 May. The transported dust
particles contributed to the mean surface layer concentrations of PM<sub>10</sub>
in the YRD region 78.9% during 1 to 6 May with their impact weakening
from north to south due to the removal of dust particles along the path. The
dry deposition, wet deposition and total deposition of PM<sub>10</sub> in the YRD
reached 184.7 kt, 172.6 kt and 357.32 kt, respectively. The dust particles also
had significant impacts on optical/radiative characteristics by absorption
and scattering. In Shanghai, the largest perturbations of aerosol optical depth (AOD) and irradiance
were about 0.8 DU and −130 W m<sup>−2</sup>, which could obviously influence the
radiation balance in this region. The decrease of actinic fluxes
impacts future photochemistry. In Shanghai, the negative effects on the
NO<sub>2</sub> and O<sub>3</sub> photolysis could be −35% when dust particles
arrived. The concentrations of O<sub>3</sub> and OH were reduced by 1.5% and
3.1% in the whole of China, and by 9.4% and 12.1% in the YRD region,
respectively. Such changes in O<sub>3</sub> and OH levels can affect the
future formation of secondary aerosols in the atmosphere by directly determining the
oxidation rate of their precursors. The work of this manuscript is
meaningful for understanding the dust emissions in China as well as for the
application of CMAQ in Asia. It is also helpful for understanding the formation
mechanism and impacts of dust pollution in the YRD
Isolation and characterization of a salt-tolerant denitrifying bacterium Alishewanella sp. F2 from seawall muddy water
A salt-tolerant denitrifying bacterium strain F2 was isolated from seawall muddy water in Dalian City, Liaoning Province, China. Strain F2 was identified by morphological observations, physiological and biochemical characteristics and 16 S rDNA identification. The salt tolerance of strain F2 was verified and the factors affecting the removal ability of strain F2 to nitrous nitrogen (NO2–N) and nitrate nitrogen (NO3–N) in saline conditions were investigated. Strain F2 was identified as Alishewanella sp., named Alishewanella sp. F2. Strain F2 can tolerate NaCl concentrations up to 70 g/L, and its most efficient denitrification capacity was observed at NaCl concentrations of 0−30 g/L. In the medium with NaCl concentrations of 0−30 g/L, strain F2 exhibited high removal efficiencies of NO2–N and NO3–N, with the removal percentages for both NO2–N and NO3–N of approximately 99%. In saline conditions with 30 g/L NaCl, the optimum culture pH, NaNO2 initial concentrations and inoculation sizes of strain F2 were 8−10, 0.4−0.8 g/L and 5−7%, respectively. Strain F2 was highly effective in removing NO2–N and NO3–N in saline conditions, and it has a good application potential in saline wastewater treatment
Entanglement control in one-dimensional random XY spin chain
The entanglement in one-dimensional random XY spin systems where the
impurities of exchange couplings and the external magnetic fields are
considered as random variables is investigated by solving the different
spin-spin correlation functions and the average magnetization per spin. The
entanglement dynamics near particular locations of the system is also studied
when the exchange couplings (or the external magnetic fields) satisfy three
different distributions(the Gaussian distribution, double-Gaussian
distribution, and bimodal distribution). We find that the entanglement can be
controlled by varying the strength of external magnetic field and the different
distributions of impurities. Moreover, the entanglement of some
nearest-neighboring qubits can be increased for certain parameter values of the
three different distributions.Comment: 13 pages, 4 figure
- …