104 research outputs found
GRB 120729A: External Shock Origin for Both the Prompt Gamma-Ray Emission and Afterglow
Gamma-ray burst (GRB) 120729A was detected by Swift/BAT and Fermi/GBM, and then rapidly observed by Swift/XRT, Swift/UVOT, and ground-based telescopes. It had a single long and smooth \gamma-ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II), shallow decay (Phase III), and post-jet break (Phase IV). The spectral energy distribution (SED) evolves from prompt \gamma-ray emission to the afterglow with photon index from Γγ=1.36 to Γ≈1.75. There is no obvious evolution of the SED during the afterglow. ...(Please see article full tet for complete abstract.
Polysaccharide from Fuzi (FPS) Prevents Hypercholesterolemia in Rats
<p>Abstract</p> <p>Background and aim</p> <p>Polysaccharide from fuzi (FPS), a Chinese herbal medicine extract, has been demonstrated to exert lipid lowering affects. In this study we examined potential mechanisms underlying this affect, specifically alterations in expression of the LDL-receptor (LDL-R), 3-hydroxy-3-methyl glutaryl (HMG)-CoA reductase and cytochrome P450 7α-1 (CYP7α-1), using a rat model of hypercholesterolemia.</p> <p>Methods and results</p> <p>Male rats were fed either a normal or high cholesterol (HC) diet for two-weeks. Half of the rats on the HC diet were orally gavaged with FPS (224 mg/kg, 448 mg/kg or 896 mg/kg diet) daily. Serum lipid levels were quantified at end of the study period as were liver levels of LDL-R protein and mRNA expression of CYP7α-1 and HMG-CoA. Serum cholesterol and LDL-C concentrations were significantly elevated from control in HC rats, but not in those treated with FPS (P < 0.05). LDL-R expression was significantly decreased in the HC group compared to control (P < 0.05), but significantly increased in the FPS group (P < 0.05). HMG-CoA mRNA levels were significantly increased in the HC group compared both other groups (P < 0.05), while CYP7α-1 expression was significantly higher in the FPS group compared to both other groups (P < 0.05).</p> <p>Conclusion</p> <p>These findings suggest that the cholesterol lowering effect of FPS in hypercholesteremic rats is caused at least in part by increased hepatic LDL-R and CYP7α-1 expression and decreased HMG-CoA expression. Further study is needed to determine precisely where and how FPS exerts these effects. FPS offers potential as a therapeutic agent for the treatment of hypercholesterolemia.</p
Context-TAP: Tracking Any Point Demands Spatial Context Features
We tackle the problem of Tracking Any Point (TAP) in videos, which
specifically aims at estimating persistent long-term trajectories of query
points in videos. Previous methods attempted to estimate these trajectories
independently to incorporate longer image sequences, therefore, ignoring the
potential benefits of incorporating spatial context features. We argue that
independent video point tracking also demands spatial context features. To this
end, we propose a novel framework Context-TAP, which effectively improves point
trajectory accuracy by aggregating spatial context features in videos.
Context-TAP contains two main modules: 1) a SOurse Feature Enhancement (SOFE)
module, and 2) a TArget Feature Aggregation (TAFA) module. Context-TAP
significantly improves PIPs all-sided, reducing 11.4% Average Trajectory Error
of Occluded Points (ATE-Occ) on CroHD and increasing 11.8% Average Percentage
of Correct Keypoint (A-PCK) on TAP-Vid-Kinectics. Demos are available at this
.Comment: Project Page: this
$\href{https://wkbian.github.io/Projects/Context-TAP/}{webpage}
NeuralMarker: A Framework for Learning General Marker Correspondence
We tackle the problem of estimating correspondences from a general marker,
such as a movie poster, to an image that captures such a marker.
Conventionally, this problem is addressed by fitting a homography model based
on sparse feature matching. However, they are only able to handle plane-like
markers and the sparse features do not sufficiently utilize appearance
information. In this paper, we propose a novel framework NeuralMarker, training
a neural network estimating dense marker correspondences under various
challenging conditions, such as marker deformation, harsh lighting, etc.
Besides, we also propose a novel marker correspondence evaluation method
circumstancing annotations on real marker-image pairs and create a new
benchmark. We show that NeuralMarker significantly outperforms previous methods
and enables new interesting applications, including Augmented Reality (AR) and
video editing.Comment: Accepted by ToG (SIGGRAPH Asia 2022). Project Page:
https://drinkingcoder.github.io/publication/neuralmarker
Orbital Origin of Intrinsic Planar Hall Effect
Recent experiments reported an antisymmetric planar Hall effect, where the
Hall current is odd in the in-plane magnetic field and scales linearly with
both electric and magnetic fields applied. Existing theories rely exclusively
on a spin origin, which requires spin-orbit coupling to take effect. Here, we
develop a general theory for the intrinsic planar Hall effect (IPHE),
highlighting a previously unknown orbital mechanism and connecting it to a band
geometric quantity -- the anomalous orbital polarizability (AOP). Importantly,
the orbital mechanism does not request spin-orbit coupling, so sizable IPHE can
occur and is dominated by orbital contribution in systems with weak spin-orbit
coupling. Combined with first-principles calculations, we demonstrate our
theory with quantitative evaluation for bulk materials ,
, and . We further show that AOP and its
associated orbital IPHE can be greatly enhanced at topological band crossings,
offering a new way to probe topological materials
Evidence of a Two-Component Jet in the Afterglow of GRB 070419A
A two-component jet model is proposed to explain the unusual afterglow of GRB
070419A. Regarding the optical light curve, a wide "jet" with an opening angle
of > 30-40 degrees is assumed to produce the late shallow decay, while the
three early power-law segments must be caused by a narrow jet with an opening
angle of about 2-4 degrees. Additional energy injections to both components are
required. Late X-ray emission may come from either the wide jet or the narrow
one. If the latter is correct, the jets may run into an ISM environment and the
temporal index of the late energy injection q may be about 0.65.Comment: 3 pages, PDF only, accepted for publication in Science in China
Series
Berry connection polarizability tensor and third-order Hall effect
One big achievement in modern condensed matter physics is the recognition of
the importance of various band geometric quantities in physical effects. As
prominent examples, Berry curvature and Berry curvature dipole are connected to
the linear and the second-order Hall effects, respectively. Here, we show that
the Berry connection polarizability (BCP) tensor, as another intrinsic band
geometric quantity, plays a key role in the third-order Hall effect. Based on
the extended semiclassical formalism, we develop a theory for the third-order
charge transport and derive explicit formulas for the third-order conductivity.
Our theory is applied to the two-dimensional (2D) Dirac model to investigate
the essential features of BCP and the third-order Hall response. We further
demonstrate the combination of our theory with the first-principles
calculations to study a concrete material system, the monolayer FeSe. Our work
establishes a foundation for the study of third-order transport effects, and
reveals the third-order Hall effect as a tool for characterizing a large class
of materials and for probing the BCP in band structure.Comment: 7 pages, 4 figure
Time-Reversal-Even Nonlinear Current Induced Spin Polarization
We propose a time-reversal-even spin generation in second order of electric
fields, which dominates the current induced spin polarization in a wide class
of centrosymmetric nonmagnetic materials, and leads to a novel nonlinear
spin-orbit torque in magnets. We reveal a quantum origin of this effect from
the momentum space dipole of the anomalous spin polarizability.
First-principles calculations predict sizable spin generations in several
nonmagnetic hcp metals, in monolayer TiTe, and in ferromagnetic monolayer
MnSe, which can be detected in experiment. Our work opens up the broad
vista of nonlinear spintronics in both nonmagnetic and magnetic systems.Comment: 4 pages, 2 figure
Optical and Ultraviolet Observations of the Very Young Type IIP SN 2014cx in NGC 337
Extensive photometric and spectroscopic observations are presented for SN
2014cx, a type IIP supernova (SN) exploding in the nearby galaxy NGC 337. The
observations are performed in optical and ultraviolet bands, covering from -20
to +400 days from the peak light. The stringent detection limit from
prediscovery images suggests that this supernova was actually detected within
about 1 day after explosion. Evolution of the very early-time light curve of SN
2014cx is similar to that predicted from a shock breakout and post-shock
cooling decline before reaching the optical peak. Our photometric observations
show that SN 2014cx has a plateau duration of ~ 100 days, an absolute V-band
magnitude of ~ -16.5 mag at t~50 days, and a nickel mass of 0.056+-0.008 Msun.
The spectral evolution of SN 2014cx resembles that of normal SNe IIP like SN
1999em and SN 2004et, except that it has a slightly higher expansion velocity
(~ 4200 km/s at 50 days). From the cooling curve of photospheric temperature,
we derive that the progenitor has a pre-explosion radius of ~ 640 Rsun,
consistent with those obtained from SNEC modeling (~ 620 Rsun) and
hydrodynamical modeling of the observables (~ 570 Rsun). Moreover, the
hydrodynamical simulations yield a total explosion energy of ~ 0.4*10e51 erg,
and an ejected mass of ~ 8 Msun. These results indicate that the immediate
progenitor of SN 2014cx is likely a red supergiant star with a mass of ~ 10
Msun.Comment: 47 pages, 12 figures and 7 tables. Accepted by Ap
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