79 research outputs found
The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124
The relative high fluxes of the Galactic ultra-luminous X-ray pulsar Swift
J0243 allow a detailed study of its spin-down regime in quiescence state, for a
first time. After the 2017 giant outburst, its spin frequencies show a linear
decreasing trend with some variations due to minor outbursts. The linear
spin-down rate is Hz/s during the period of lowest
luminosity, from which one can infer a dipole field G.
The relation during the spin-down regime is complex, and the
is close to 0 when the luminosity reaches both the high end
() and the lowest value (). The luminosity of
zero-torque is different for the giant outburst and other minor outbursts. It
is likely due to different accretion flows for different types of outburst, as
evidenced by the differences of the spectra and pulse profiles at a similar
luminosity for different types of outburst (giant or not). The pulse profile
changes from double peaks in the spin-up state to a single broad peak in the
low spin-down regime, indicating the emission beam/region is larger in the low
spin-down regime. These results show that accretion is still ongoing in the low
spin-down regime for which the neutron star is supposed to be in a propeller
state.Comment: 7 pages, 7 figs, to appear in ApJ, comments welcom
Pulsar Glitches: A Review
of all known pulsars have been observed to exhibit sudden spin-up
events, known as glitches. For more than fifty years, these phenomena have
played an important role in helping to understand pulsar (astro)physics. Based
on the review of pulsar glitches search method, the progress made in
observations in recent years is summarized, including the achievements obtained
by Chinese telescopes. Glitching pulsars demonstrate great diversity of
behaviours, which can be broadly classified into four categories: normal
glitches, slow glitches, glitches with delayed spin-ups, and anti-glitches. The
main models of glitches that have been proposed are reviewed and their
implications for neutron star structure are critically examined regarding our
current understanding. Furthermore, the correlations between glitches and
emission changes, which suggest that magnetospheric state-change is linked to
the pulsar-intrinsic processes, are also described and discussed in some
detail.Comment: Accepted for publication in Universe. 50 pages, 11 figures,
contribution to special issue "Frontiers in Pulsars Astrophysics
1Cademy @ Causal News Corpus 2022: Leveraging Self-Training in Causality Classification of Socio-Political Event Data
This paper details our participation in the Challenges and Applications of
Automated Extraction of Socio-political Events from Text (CASE) workshop @
EMNLP 2022, where we take part in Subtask 1 of Shared Task 3. We approach the
given task of event causality detection by proposing a self-training pipeline
that follows a teacher-student classifier method. More specifically, we
initially train a teacher model on the true, original task data, and use that
teacher model to self-label data to be used in the training of a separate
student model for the final task prediction. We test how restricting the number
of positive or negative self-labeled examples in the self-training process
affects classification performance. Our final results show that using
self-training produces a comprehensive performance improvement across all
models and self-labeled training sets tested within the task of event causality
sequence classification. On top of that, we find that self-training performance
did not diminish even when restricting either positive/negative examples used
in training. Our code is be publicly available at
https://github.com/Gzhang-umich/1CademyTeamOfCASE.Comment: Paper from CASE workshop at EMNLP 202
Measurement of the vertical atmospheric density profile from the X-ray Earth occultation of the Crab Nebula with Insight-HXMT
In this paper, the X-ray Earth occultation (XEO) of the Crab Nebula is
investigated by using the Hard X-ray Modulation Telescope (Insight-HXMT). The
pointing observation data on the 30th September, 2018 recorded by the Low
Energy X-ray telescope (LE) of Insight-HXMT are selected and analyzed. The
extinction lightcurves and spectra during the X-ray Earth occultation process
are extracted. A forward model for the XEO lightcurve is established and the
theoretical observational signal for lightcurve is predicted. The atmospheric
density model is built with a scale factor to the commonly used MSIS density
profile within a certain altitude range. A Bayesian data analysis method is
developed for the XEO lightcurve modeling and the atmospheric density
retrieval. The posterior probability distribution of the model parameters is
derived through the Markov Chain Monte Carlo (MCMC) algorithm with the
NRLMSISE-00 model and the NRLMSIS 2.0 model as basis functions and the best-fit
density profiles are retrieved respectively. It is found that in the altitude
range of 105--200 km, the retrieved density profile is 88.8% of the density of
NRLMSISE-00 and 109.7% of the density of NRLMSIS 2.0 by fitting the lightcurve
in the energy range of 1.0--2.5 keV based on XEOS method. In the altitude range
of 95--125 km, the retrieved density profile is 81.0% of the density of
NRLMSISE-00 and 92.3% of the density of NRLMSIS 2.0 by fitting the lightcurve
in the energy range of 2.5--6.0 keV based on XEOS method. In the altitude range
of 85--110 km, the retrieved density profile is 87.7% of the density of
NRLMSISE-00 and 101.4% of the density of NRLMSIS 2.0 by fitting the lightcurve
in the energy range of 6.0--10.0 keV based on XEOS method. This study
demonstrates that the XEOS from the X-ray astronomical satellite Insight-HXMT
can provide an approach for the study of the upper atmosphere.Comment: 31 pages, 15 figures, 5 tables, accepted for publication in
Atmospheric Measurement Technique
Cancer-targeted and intracellular delivery of Bcl-2-converting peptide with functional macroporous silica nanoparticles for biosafe treatment
Abstract(#br)Therapeutic peptide, NuBCP-9 (N9) as a Bcl-2 functional converter, has been demonstrated to have the remarkable anticancer efficiency in Bcl-2-abundant cancer. However, it faced technical challenges in clinical use, such as the low bioavailability, the easily-destroyed bio-stability, and the insusceptibility to cellular interior. With the potential of mesoporous silica nanoparticles (MSNs) as the promising delivery vehicle of therapeutic macromolecules, we developed a kind of MSNs with the surface coating of folic acid (FA) for cancer cell targeting and with the macropore loading of N9 peptide for cancer therapy. Our results showed that the functional MSNs had the relatively greater biosafety than the naked MSNs in zebrafish models, leading to less than 30% embryo of death at 200 μg/ml, which could further specifically target the folate receptor (FR)-overexpressed cervical cancer HeLa cells instead of FR-negative normal embryonic kidney HEK 293T cells in a FA-competitive manner. N9 peptide with the delivery of functional MSNs could be internalized by HeLa cells, and co-localized with mitochondria in a Bcl-2-dependent manner. Moreover, N9 peptide delivered by FA-modified MSNs displayed the excellent anticancer efficiency with great selectivity, inducing approximately 52% HeLa cells into apoptosis. In summary, our results illustrated the potential of functional MSNs with large pore size as an efficient nanocarrier for the intracellular delivery of peptide drugs with targeting proteins to realize cancer therapy
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