42,383 research outputs found
Probing the structure of the outflow in the tidal disruption flare Sw J1644+57 with long-term radio emission
The recently discovered high-energy transient Sw J1644+57 is thought to arise
from the tidal disruption of a passing star by a dormant massive black hole.
The long-term, bright radio emission of Sw J1644+57 is believed to result from
the synchrotron emission of the blast wave produced by an outflow expanding
into the surrounding medium. Using the detailed multi-epoch radio spectral
data, we are able to determine the total number of radiating electrons in the
outflow at different times, and further the evolution of the cross section of
the outflow with time. We find that the outflow gradually transits from a
conical jet to a cylindrical one at later times. The transition may be due to
collimation of the outflow by the pressure of the shocked jet cocoon that forms
while the outflow is propagating in the ambient medium. Since cylindrical jets
usually exist in AGNs and extragalactic jets, this may provide independent
evidence that Sw J1644+57 signals the onset of an AGN.Comment: 7 pages, 4 figures, accepted by Ap
Strain-Fluctuation-Induced Near-Quantization of Valley Hall Conductivity in Graphene Systems
We develop a theory of the valley Hall effect in high-quality graphene
samples, in which strain fluctuation-induced random gauge potentials have been
suggested as the dominant source of disorder. We find a near-quantized value of
valley Hall conductivity in the band transport regime, which originates from an
enhanced side jump of a Dirac electron when it scatters off the gauge
potential. By assuming a small residue charge density our theory reproduces
qualitatively the temperature- and gap-dependence of the observed valley Hall
effect at the charge neutral point. Our study suggests that the valley Hall
effect in graphene systems represents a new paradigm for the anomalous Hall
physics where gauge disorder plays an important role
New Realization of the Conversion Calculation for Reactor Antineutrino Fluxes
Validation of the effective conversion method in the reactor antineutrino
flux calculation is examined using the \textit{ab initio} calculation of the
electron and antineutrino spectra from the state-of-the-art nuclear database.
It turns out that neglecting the shape variation of beta decay branches between
the allowed and forbidden transitions would induce significant bias in the
total inverse-beta-decay yields and energy spectral distributions. We propose a
new realization of the conversion method with both the allowed and forbidden
virtual branches, and apply it to both the \textit{simulated} data from the
nuclear database and \textit{real} data from the fission measurements at ILL by
virtue of statistical properties of the allowed and forbidden decays in the
database. Two kinds of dominant uncertainty sources are identified and it turns
out that the new realization of the conversion calculation can largely reduce
the rate and spectral bias and thus present a reliable prediction of the
antineutrino fluxes if accurate beta decay information is available in the high
endpoint energy range.Comment: 23 pages, 9 figures, 2 tables, with new results on uncertainty study,
and ILL beta spectrum conversion, to appear in PR
Predictions for the Abundance of High-redshift Galaxies in a Fuzzy Dark Matter Universe
During the last decades, rapid progress has been made in measurements of the
rest-frame ultraviolet (UV) luminosity function (LF) for high-redshift galaxies
(). The faint-end of the galaxy LF at these redshifts provides
powerful constraints on different dark matter models that suppress small-scale
structure formation. In this work we perform full hydrodynamical cosmological
simulations of galaxy formation using an alternative DM model composed of
extremely light bosonic particles ( eV), also known as fuzzy
dark matter (FDM), and examine the predictions for the galaxy stellar mass
function and luminosity function at for a range of FDM masses. We
find that for FDM models with bosonic mass eV, the number
density of galaxies with stellar mass is
suppressed by at z = 9, at z = 5, and the UV LFs within
magnitude range of -16 < < -14 is suppressed by at , at comparing to the CDM counterpart simulation.
Comparing our predictions with current measurements of the faint-end LFs (), we find that FDM models with are ruled out at confidence level. We expect that
future LF measurements by James Webb Space Telescope (JWST), which will extend
down to for , with a survey volume that is
comparable to the Hubble Ultra Deep Field (HUDF) would have the capability to
constrain FDM models to eV
Holographic Photon Production with Magnetic Field in Anisotropic Plasmas
We investigate the thermal photon production from constant magnetic field in
a strongly coupled and anisotropic plasma via the gauge/gravity duality. The
dual geometry with pressure anisotropy is generated from the axion-dilaton
gravity action introduced by Mateos and Trancancelli and the magnetic field is
coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find
that the photon spectra with different quark mass are enhanced at large
frequency when the photons are emitted parallel to the anisotropic direction
with larger pressure or perpendicular to the magnetic field. However, in the
opposite conditions for the emitted directions, the spectra approximately
saturate isotropic results in the absence of magnetic field. On the other hand,
a resonance emerges at moderate frequency for the photon spectrum with heavy
quarks when the photons move perpendicular to the magnetic field. The resonance
is more robust when the photons are polarized along the magnetic field. On the
contrary, in the presence of pressure anisotropy, the resonance will be
suppressed. There exist competing effects of magnetic field and pressure
anisotropy on meson melting in the strongly coupled super Yang-Mills plasma,
while we argue that the suppression led by anisotropy may not be applied to the
quark gluon plasma.Comment: 22 pages, 16 figures, references added, journal versio
Towards Adversarial Training with Moderate Performance Improvement for Neural Network Classification
It has been demonstrated that deep neural networks are prone to noisy
examples particular adversarial samples during inference process. The gap
between robust deep learning systems in real world applications and vulnerable
neural networks is still large. Current adversarial training strategies improve
the robustness against adversarial samples. However, these methods lead to
accuracy reduction when the input examples are clean thus hinders the
practicability. In this paper, we investigate an approach that protects the
neural network classification from the adversarial samples and improves its
accuracy when the input examples are clean. We demonstrate the versatility and
effectiveness of our proposed approach on a variety of different networks and
datasets.Comment: Accepted for publication in Uncertainty in Deep Learning Workshop at
Uncertainty in Artificial Intelligence (UAI) 201
Sharp-interface limits of a phase-field model with a generalized Navier slip boundary condition for moving contact lines
The sharp-interface limits of a phase-field model with a generalized Navier
slip boundary condition for moving contact line problem are studied by
asymptotic analysis and numerical simulations. The effects of the {mobility}
number as well as a phenomenological relaxation parameter in the boundary
condition are considered. In asymptotic analysis, we focus on the case that the
{mobility} number is the same order of the Cahn number and derive the
sharp-interface limits for several setups of the boundary relaxation parameter.
It is shown that the sharp interface limit of the phase field model is the
standard two-phase incompressible Navier-Stokes equations coupled with several
different slip boundary conditions. Numerical results are consistent with the
analysis results and also illustrate the different convergence rates of the
sharp-interface limits for different scalings of the two parameters
Cosmic Microwave Background Dipole Asymmetry could be explained by Axion Monodromy Cosmic Strings
Observations by the Wilkinson Microwave Anisotropy Probe and the Planck
mission suggest a hemispherical power amplitude asymmetry in the cosmic
microwave background, with a correlation length on the order of the size of the
observable Universe. We find that this anomaly can be naturally explained by an
axion-like particle (ALP) cosmic string formed near our visible Universe. The
field variation associated to this cosmic string creates particle density
fluctuations after inflation, which consequently decay into radiation before
the Big Bang Nucleosynthesis (BBN) era and resulted in the observed power
asymmetry. We find in this scenario that the hemispherical power amplitude
asymmetry is strongly scale dependent: .
Admittedly, typical inflation models predict a relic number density of
topological defects of order one per observable Universe and so in our model
the cosmic string must be tuned to have an impact factor of order .
Interestingly, the constraints based on purely cosmological considerations also
give rise to a Peccei-Quinn scale of order larger then the Hubble
scale of inflation . Assuming GeV, we then have an ALP
with GeV, which coincides with the presumed scale of grand
unification. As we require ALP decays occur before the BBN era, which implies a
relatively heavy mass or strong self-coupling, and considering that the
associated potential should break the shift symmetry softly in order to protect
the system from radiative corrections, we also conclude that the required ALP
potential should be monodromic in nature.Comment: 16 pages, 2 figures, references and comments added, published versio
Bayesian Estimation Based Load Modeling Report
This report presents the detailed steps of establishing the composite load
model in the power system. The derivations of estimation the ZIP model and IM
model parameters are proposed in this report. This is a supplementary material
for the paper submitted to PES GM 2019
Spin responses and effective Hamiltonian for the two dimensional electron gas at oxide interface {LaAlO}/{SrTiO}
Strong Rashba spin-orbit coupling (SOC) of the two-dimensional electron gas
(2DEG) at the oxide interface underlies a
variety of exotic physics, but its nature is still under debate. We derive an
effective Hamiltonian for the 2DEG at the oxide interface
and find a different anisotropic Rashba SOC for
the and orbitals. This anisotropic Rashba SOC leads to
anisotropic static spin susceptibilities and also distinctive behavior of the
spin Hall conductivity. These unique spin responses may be used to determine
the nature of the Rashba SOC experimentally and shed light on the orbital
origin of the 2DEG.Comment: 10 pages, 2 figures, final published versio
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