3,577 research outputs found
Parameter constraints from shadows of Kerr-Newman-dS black holes with cloud strings and quintessence
The motion of photons around the Kerr-Newman-dS black hole surrounded by
quintessence and a cloud of strings is investigated. The existence of the
Carter constant leads to that of unstable circular photon orbits on a
two-dimensional plane not limited to the equatorial plane and unstable
spherical photon orbits in the three-dimensional space. These circular or
spherical photon orbits can determine two impact parameters, which are used to
calculate black hole shadows. For the case of a spherically symmetric
nonrotating black hole, the black hole shadow is circular and its size is
independent of an observation angle and a plane on which a circular photon
orbit exists. The shadow sizes are significantly influenced by the parameters
involving the cloud of strings, quintessence parameter, magnitude of
quintessential state parameter, and cosmological constant. When the black hole
is spinning and axially symmetric, the black hole shadow is dependent on the
observation angle. The effects of the parameters excluding the spin parameter
on the sizes of black hole shadows in the rotating case are similar to those in
the nonrotating case. Based on the Event Horizon Telescope observations of
M87*, the constraint of the curvature radius is used to constrain these
parameters. For slowly rotating black holes, the allowed regions of the
parameters including the cosmological constant are given.Comment: 21 pages, 7 figure
The advection-dominated accretion flow+thin accretion disk model for two low-luminosity active galactic nuclei: M81 and NGC4579
It was found that the advection-dominated accretion flow (ADAF)+thin disk
model calculations can reproduce the observed spectral energy distributions
(SED) of the two low luminosity AGN, provided they are accreting at ~0.01-0.03
Eddington rates and the thin disks are truncated to ADAFs at ~100 R_s
(Schwarzschild radii) for M81 and NGC4579 (Quataert et al., 1999). However, the
black hole masses adopted in their work are about one order of magnitude lower
than recent measurements on these two sources. Adopting the well estimated
black hole masses, our ADAF+thin disk model calculations can reproduce the
observed SEDs of these two LLAGN, if the black hole is accreting at 2.5e-4
Eddington rates with the thin disk truncated at 120 R_s for M81 (3.3e-3 and
R_tr = 80R_s are required for NGC4579). The observed widths of the thermal
X-ray iron lines at 6.8 keV are consistent with the Doppler broadening by the
Keplerian motion of the gases in the transition zones at ~100R_s. The observed
thermal X-ray lines provide a useful diagnosis on the physical properties of
the transition zones. We calculate the thermal X-ray line emission from the
transition zone between the ADAF and the thin disk with standard software
package Astrophysical Plasma Emission Code (APEC), and the physical
implications on the models of the transition zones are discussed.Comment: 10 pages, 2 figures, accepted by ChJA
Recent progress in migraine and cognitive disorder
Migraine is a chronic neurovascular disease characterized by recurrent unilateral headache, which induces incapacity. At present, there are many methods to evaluate cognitive function, and the cognitive function scale is commonly used. Recently, event-related potentials, resting state functional magnetic resonance imaging and other new technologies have been widely used to assess the cognitive function of migraine patients because of their high temporal resolution and high spatial resolution. In this paper, we can overview that the research progress of the relationship between migraine and methods of evaluate cognitive function
EUCLIA - Exploring the UV/optical continuum lag in active galactic nuclei. I. a model without light echoing
The tight inter-band correlation and the lag-wavelength relation among
UV/optical continua of active galactic nuclei have been firmly established.
They are usually understood within the widespread reprocessing scenario,
however, the implied inter-band lags are generally too small. Furthermore, it
is challenged by new evidences, such as the X-ray reprocessing yields too much
high frequency UV/optical variations as well as it fails to reproduce the
observed timescale-dependent color variations among {\it Swift} lightcurves of
NGC 5548. In a different manner, we demonstrate that an upgraded inhomogeneous
accretion disk model, whose local {\it independent} temperature fluctuations
are subject to a speculated {\it common} large-scale temperature fluctuation,
can intrinsically generate the tight inter-band correlation and lag across
UV/optical, and be in nice agreement with several observational properties of
NGC 5548, including the timescale-dependent color variation. The emergent lag
is a result of the {\it differential regression capability} of local
temperature fluctuations when responding to the large-scale fluctuation. An
average speed of propagations as large as of the speed of light
may be required by this common fluctuation. Several potential physical
mechanisms for such propagations are discussed. Our interesting
phenomenological scenario may shed new light on comprehending the UV/optical
continuum variations of active galactic nuclei.Comment: 18 pages, 8 figures. ApJ accepted. Further comments are very welcome
Demystifying Dependency Bugs in Deep Learning Stack
Deep learning (DL) applications, built upon a heterogeneous and complex DL
stack (e.g., Nvidia GPU, Linux, CUDA driver, Python runtime, and TensorFlow),
are subject to software and hardware dependencies across the DL stack. One
challenge in dependency management across the entire engineering lifecycle is
posed by the asynchronous and radical evolution and the complex version
constraints among dependencies. Developers may introduce dependency bugs (DBs)
in selecting, using and maintaining dependencies. However, the characteristics
of DBs in DL stack is still under-investigated, hindering practical solutions
to dependency management in DL stack. To bridge this gap, this paper presents
the first comprehensive study to characterize symptoms, root causes and fix
patterns of DBs across the whole DL stack with 446 DBs collected from
StackOverflow posts and GitHub issues. For each DB, we first investigate the
symptom as well as the lifecycle stage and dependency where the symptom is
exposed. Then, we analyze the root cause as well as the lifecycle stage and
dependency where the root cause is introduced. Finally, we explore the fix
pattern and the knowledge sources that are used to fix it. Our findings from
this study shed light on practical implications on dependency management
An intrinsic link between long-term UV/optical variations and X-ray loudness in quasars
Observations have shown that UV/optical variation amplitude of quasars depend
on several physi- cal parameters including luminosity, Eddington ratio, and
likely also black hole mass. Identifying new factors which correlate with the
variation is essential to probe the underlying physical processes. Combining
~ten years long quasar light curves from SDSS stripe 82 and X-ray data from
Stripe 82X, we build a sample of X-ray detected quasars to investigate the
relation between UV/optical variation amplitude () and X-ray
loudness. We find that quasars with more intense X-ray radiation (com- pared to
bolometric luminosity) are more variable in UV/optical. Such correlation
remains highly significant after excluding the effect of other parameters
including luminosity, black hole mass, Ed- dington ratio, redshift, rest-frame
wavelength (i.e., through partial correlation analyses). We further find the
intrinsic link between X-ray loudness and UV/optical variation is gradually
more prominent on longer timescales (up to 10 years in the observed frame), but
tends to disappear at timescales < 100 days. This suggests a slow and long-term
underlying physical process. The X-ray reprocessing paradigm, in which
UV/optical variation is produced by a variable central X-ray emission
illuminating the accretion disk, is thus disfavored. The discovery points to an
interesting scheme that both the X-ray corona heating and UV/optical variation
is quasars are closely associated with magnetic disc turbulence, and the
innermost disc turbulence (where corona heating occurs) correlates with the
slow turbulence at larger radii (where UV/optical emission is produced).Comment: 9 pages, 4 figures, 1 table, accepted by Ap
Constraining the equation of state with heavy quarks in the quasi-particle model of QCD matter
In a quasi-particle model of QCD matter at finite temperature with thermal
masses for quarks and gluons from hard thermal loops, the equation of state
(EOS) can be described by an effective temperature dependence of the strong
coupling . Assuming the same effective coupling between the exchanged
gluon and thermal partons, the EOS can also be related to parton energy loss.}
Based on the quasi-particle linear Boltzmann transport (QLBT) model coupled to
a (3+1)-dimensional viscous hydrodynamic model of the quark-gluon plasma (QGP)
evolution and a hybrid fragmentation-coalescence model for heavy quark
hadronization, we perform a Bayesian analysis of the experimental data on
meson suppression and anisotropy at RHIC and the LHC. We
achieve a simultaneous constraint on the QGP EOS and the heavy quark transport
coefficient, both consistent with the lattice QCD results.Comment: 8 pages, 5 figure
- …