4,307 research outputs found
Sequential clustering of star formation in IC 1396
We present in this paper a comprehensive study of the H II region IC 1396 and
its star formation activity, in which multi-wavelength data ranging from the
optical to the near- and far-infrared were employed. The surface density
distribution of all the 2MASS sources with certain detection toward IC 1396
indicates the existence of a compact cluster spatially consistent with the
position of the exciting source of the H II region, HD 206267. The spatial
distribution of the infrared excessive emission sources selected based on
archived 2MASS data reveals the existence of four sub-clusters in this region.
One is in association with the open cluster Trumpler 37. The other three are
found to be spatially coincident with the bright rims of the H II region. All
the excessive emission sources in the near infrared are cross-identified with
the AKARI IRC data, an analysis of the spectral energy distributions (SEDs) of
the resultant sample leads to the identification of 8 CLASS I, 15 CLASS II and
15 CLASS III sources in IC 1396. Optical identification of the sample sources
with R magnitudes brighter than 17 mag corroborates the results from the SED
analysis. Based on the spatial distribution of the infrared young stellar
objects at different evolutionary stages, the surrounding sub-clusters located
in the bright rims are believed to be younger than the central one. This is
consistent with a scenario of sequential star formation in this region. Imaging
data of a dark patch in IC 1396 by Herschel SPIRE, on the other hand, indicate
the presence of two far-infrared cores in LDN 1111, which are likely new
generation protostellar objects in formation. So we infer that the star
formation process in this H II region was not continuous but episodic
Universality of competitive networks for weighted networks
In this paper, we propose a new model that allows us to investigate this
competitive aspect of real networks in quantitative terms. Through theoretical
analysis and numerical simulations, we find that the competitive network have
the universality for a weighted network. The relation between parameters in the
weighted network and the competitiveness in the competitive network is
obtained. So we can use the expression of the degree distribution of the
competitive model to calculate that and the strength of the weighted network
directly. The analytical solution reveals that the degree distribution of the
weighted network is correlated with the increment and initial value of edge
weights, which is verified by numerical simulations. Moreover, the evolving
pattern of a clustering coefficient along with network parameters such as the
size of a network, an updating coefficient, an initial weight and the
competitiveness are obtained by further simulations. Specially, it is necessary
to point out that the initial weight plays equally significant role as updating
coefficient in influencing the topological characteristics of the network.Comment: 18 pages, 6 figures. arXiv admin note: text overlap with
arXiv:cond-mat/0406238 by other author
Probing the linear polarization of photons in ultraperipheral heavy ion collisions
We propose to measure the linear polarization of the external electromagnetic
fields of a relativistic heavy ion through azimuthal asymmetries in dilepton
production in ultraperipheral collisions. The asymmetries estimated with the
equivalent photon approximation are shown to be sizable.Comment: The version accepted by the journal, 7 pages, 4 figure
Drama of HII regions: Clustered and Triggered Star Formation
In order to understand the star formation process under the influence of HII
regions, we have carried out extensive investigations to well selected
star-forming regions which all have been profoundly affected by existing
massive O type stars. On the basis of multi-wavelength data from mid-infrared
to millimeter collected using , , and ground based radio
telescopes, the physical status of interstellar medium and star formation in
these regions have been revealed. In a relatively large infrared dust bubble,
active star formation is undergoing and the shell is still expanding. Signs of
compressed gas and triggered star formation have been tentatively detected in a
relatively small bubble. The dense cores in the Rosette Molecular Complex
detected at 1.1 mm using SMA have been speculated to have a likely triggered
origin according to their spatial distribution. Although some observational
results have been obtained, more efforts are necessary to reach trustworthy
conclusions.Comment: Appear in IAUS 31
Studies of the hybrid star structure within 2+1 flavors NJL model
In this paper we use the equation of state (EOS) of 2+1 flavors
Nambu-Jona-Lasinio (NJL) model to study the structure of compact stars. To
avoid the ultraviolet divergence, we employ the proper-time regularization
(PTR) with an ultraviolet cutoff. For comparison, we fix three sets of
parameters, where the constraints of chemical equilibrium and electric charge
neutrality conditions are taken into consideration. With a certain
interpolation method in the crossover region, we construct three corresponding
hybrid EOSs but find that the maximum masses of hybrid stars in the three
different cases don't differ too much. It should be pointed out that, the
results we get are in accordance with the recent astro-observation PSR
J0348+0432, PSR J1614-2230, PSR J1946+3417
Investigation of Star Formation toward the Sharpless 155 H II region
We present a comprehensive study of star formation toward the H II region
S155. Star-formation activities therein were investigated based on
multi-wavelength data from optical to the far-infrared. The surface density
distribution of selected 2MASS sources toward S155 indicates the existence of a
compact cluster, which is spatially consistent with the position of the
exciting source of the H II region, HD 217086. A sample of more than 200
excessive emission sources in the infrared were selected based on their 2MASS
color indices. The spatial distribution of the sample sources reveals the
existence of three young sub-clusters in this region, among which, sub-cluster
A is spatially coincident with the bright rim of the H II region. In addition,
photometric data from the WISE survey were used to identify and classify young
stellar objects (YSOs). To further explore the evolutionary stages of the
candidate YSOs, we fit the spectral energy distribution (SEDs) of 44 sources,
which led to the identification of 14 Class I, 27 Class II, and 3 Class III
YSOs. The spatial distribution of the classified YSOs at different evolutionary
stages presents a spatio-temporal gradient, which is consistent with a scenario
of sequential star formation. On the other hand, Herschel PACS observations
toward the interface between S155 and the ambient molecular cloud disclose an
arc-shaped dust layer, the origin of which could be attributed to the UV
dissipation from the early type stars e.g. HD 217061 in S155. Four dusty cores
were revealed by the Herschel data, which hints for new generations of star
formation.Comment: arXiv admin note: text overlap with arXiv:1212.153
Experimental nonlocal steering of Bohmian trajectories
Interpretations of quantum mechanics (QM), or proposals for underlying
theories, that attempt to present a definite realist picture, such as Bohmian
mechanics, require strong non-local effects. Naively, these effects would
violate causality and contradict special relativity. However if the theory
agrees with QM the violation cannot be observed directly. Here, we demonstrate
experimentally such an effect: we steer the velocity and trajectory of a
Bohmian particle using a remote measurement. We use a pair of photons and
entangle the spatial transverse position of one with the polarization of the
other. The first photon is sent to a double-slit-like apparatus, where its
trajectory is measured using the technique of Weak Measurements. The other
photon is projected to a linear polarization state. The choice of polarization
state, and the result, steer the first photon in the most intuitive sense of
the word. The effect is indeed shown to be dramatic, while being easy to
visualize. We discuss its strength and what are the conditions for it to occur.Comment: 10 pages, 3 figure
Impact parameter dependence of the azimuthal asymmetry in lepton pair production in heavy ion collisions
We investigate the impact parameter dependence of the azimuthal
asymmetry for electromagnetic lepton pair production in heavy ion collisions.
The asymmetry induced by linearly polarized coherent photons exhibits strong
impact parameter dependence.Comment: 6 pages, 4 figure
Cross-correlations between soft and hard light curves depending on luminosity in the transient neutron star XTE J1701-462
Using all the observations from Rossi X-ray Timing Explorer for accreting
neutron star XTE J1701-462, we carry out a systematic study on the
cross-correlation between its soft and hard light curves. The anti-correlations
appear at the hard vertex and on the upper normal branch (NB) in the Cyg-like
interval, occur on the horizontal branch (HB) and/or upper NB in the first and
second Sco-like intervals, and display at the upper flaring branch (FB) in the
third Sco-like interval. We suggest that the anti-correlation might evolve with
luminosity, because with decreasing of luminosity, the source evolved from a
Cyg-like Z source, via a Sco-like Z source, to an atoll source. In the Cyg-like
interval, the positive correlations are mostly distributed on the HB, which is
not consistent with that of the Cyg-like Z source GX 5-1 and Cyg X-2 whose HBs
host ambiguous correlations and anti-correlations. From our spectral analyses,
it is found that the ratio of the hard emission to the soft emission basically
keeps unvaried from the HB to the hard vertex, which might result in the
positive correlation. Additionally, we compare the spectra in the third
Sco-like interval with those of atoll source 4U 1735-44 and find that their
spectral evolution along the tracks in the color-color diagrams are similar,
indicating that in this interval, XTE J1701-462 approaches an atoll source.
Both hard time lags and soft time lags are detected and the possible origins of
them are discussed
Demonstration of MultiSetting One-Way Einstein-Podolsky-Rosen Steering in Two-Qubit Systems
Einstein-Podolsky-Rosen (EPR) steering describes the ability of one party to
remotely affect another's state through local measurements. One of the most
distinguishable properties of EPR steering is its asymmetric aspect. Steering
can work in one direction but fail in the opposite direction. This type of
one-way steering, which is different from the symmetry concepts of entanglement
and Bell nonlocality, has garnered much interest. However, an experimental
demonstration of genuine EPR steering in the simplest scenario, i.e., one that
employs two-qubit systems, is still lacking. In this work, we experimentally
demonstrate one-way EPR steering with multimeasurement settings for a class of
two-qubit states, which are still one-way steerable even with infinite
settings. The steerability is quantified by the steering radius, which
represents a necessary and sufficient steering criterion. The demonstrated
one-way steering in the simplest bipartite quantum system is of fundamental
interest and may provide potential applications in one-way quantum information
tasks.Comment: 5 pages, 4 figure
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