245 research outputs found
The progenitors of type Ia supernovae in the semidetached binaries with red giant donors
Context. The companions of the exploding carbon-oxygen white dwarfs (CO WDs)
for producing type Ia supernovae (SNe Ia) are still not conclusively confirmed.
A red-giant (RG) star has been suggested to be the mass donor of the exploding
WD, named as the symbiotic channel. However, previous studies on the this
channel gave a relatively low rate of SNe Ia. Aims. We aim to systematically
investigate the parameter space, Galactic rates and delay time distributions of
SNe Ia from the symbiotic channel by employing a revised mass-transfer
prescription. Methods. We adopted an integrated mass-transfer prescription to
calculate the mass-transfer process from a RG star onto the WD. In this
prescription, the mass-transfer rate varies with the local material states.
Results. We evolved a large number of WD+RG systems, and found that the
parameter space of WD+RG systems for producing SNe Ia is significantly
enlarged. This channel could produce SNe Ia with intermediate and old ages,
contributing to at most 5% of all SNe Ia in the Galaxy. Our model increases the
SN Ia rate from this channel by a factor of 5. We suggest that the symbiotic
systems RS Oph and T CrB are strong candidates for the progenitors of SNe Ia.Comment: 8 pages, 6 figure
Improved Gaussian mixture probability hypothesis density for tracking closely spaced targets
Probability hypothesis density (PHD) filter is a suboptimal Bayesian multi-target filter based on random finite set. The Gaussian mixture PHD filter is an analytic solution to the PHD filter for linear Gaussian multi-target models. However, when targets move near each other, the GM-PHD filter cannot correctly estimate the number of targets and their states. To solve the problem, a novel reweighting scheme for closely spaced targets is proposed under the framework of the GM-PHD filter, which can be able to correctly redistribute the weights of closely spaced targets, and effectively improve the multiple target state estimation precision. Simulation results demonstrate that the proposed algorithm can accurately estimate the number of targets and their states, and effectively improve the performance of multi-target tracking algorithm
Automatic Image Annotation Based on Particle Swarm Optimization and Support Vector Clustering
With the progress of network technology, there are more and more digital images of the internet. But most images are not semantically marked, which makes it difficult to retrieve and use. In this paper, a new algorithm is proposed to automatically annotate images based on particle swarm optimization (PSO) and support vector clustering (SVC). The algorithm includes two stages: firstly, PSO algorithm is used to optimize SVC; secondly, the trained SVC algorithm is used to annotate the image automatically. In the experiment, three datasets are used to evaluate the algorithm, and the results show the effectiveness of the algorithm
New insights into the helium star formation channel of AM CVn systems with explanations of Gaia14aae and ZTFJ1637+49
We model helium-rich stars with solar metallicity ()
progenitors that evolve to form AM Canum Venaticorum systems through a
helium-star formation channel, with the aim to explain the observed properties
of Gaia14aae and ZTFJ1637+49. We show that semi-degenerate, H-exhausted (), He-rich () donors can be formed after a common
envelope evolution (CEE) phase if either additional sources of energy are used
to eject the common envelope, or a different formalism of CEE is implemented.
We follow the evolution of such binary systems after the CEE phase using the
Cambridge stellar evolution code, when they consist of a He-star and a white
dwarf accretor, and report that the mass, radius, and mass-transfer rate of the
donor, the orbital period of the system, and the lack of hydrogen in the
spectrum of Gaia14aae and ZTFJ1637+49 match well with our modelled trajectories
wherein, after the CEE phase Roche lobe overflow is governed not only by the
angular momentum loss (AML) owing to gravitational wave radiation
() but also an additional AML owing to
dynamos in the donor. This additional AML is modelled with our double-dynamo
(DD) model of magnetic braking in the donor star. We explain that this
additional AML is just a consequence of extending the DD model from canonical
cataclysmic variable donors to evolved donors. We show that none of our
modelled trajectories match with Gaia14aae or ZTFJ1637+49 if the systems are
modelled only with .Comment: 11 pages, 11 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Probability hypothesis density filter with adaptive parameter estimation for tracking multiple maneuvering targets
AbstractThe probability hypothesis density (PHD) filter has been recognized as a promising technique for tracking an unknown number of targets. The performance of the PHD filter, however, is sensitive to the available knowledge on model parameters such as the measurement noise variance and those associated with the changes in the maneuvering target trajectories. If these parameters are unknown in advance, the tracking performance may degrade greatly. To address this aspect, this paper proposes to incorporate the adaptive parameter estimation (APE) method in the PHD filter so that the model parameters, which may be static and/or time-varying, can be estimated jointly with target states. The resulting APE-PHD algorithm is implemented using the particle filter (PF), which leads to the PF-APE-PHD filter. Simulations show that the newly proposed algorithm can correctly identify the unknown measurement noise variances, and it is capable of tracking multiple maneuvering targets with abrupt changing parameters in a more robust manner, compared to the multi-model approaches
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