7,286 research outputs found
Dynamical nucleus-nucleus potential at short distances
The dynamical nucleus-nucleus potentials for fusion reactions 40Ca+40Ca,
48Ca+208Pb and 126Sn+130Te are studied with the improved quantum molecular
dynamics (ImQMD) model together with the extended Thomas-Fermi approximation
for the kinetic energies of nuclei. The obtained fusion barrier for 40Ca+40Ca
is in good agreement with the extracted fusion barrier from the measured fusion
excitation function, and the depth of the fusion pockets are close to the
results of time-dependent Hartree-Fock calculations. The energy dependence of
fusion barrier is also investigated. For heavy fusion system, the fusion pocket
becomes shallow and almost disappears for symmetric systems and the obtained
potential at short distances is higher than the adiabatic potential.Comment: 6 figures, accepted for publication in Phys. Rev.
SLIC: Self-Conditioned Adaptive Transform with Large-Scale Receptive Fields for Learned Image Compression
Learned image compression has achieved remarkable performance. Transform,
plays an important role in boosting the RD performance. Analysis transform
converts the input image to a compact latent representation. The more compact
the latent representation is, the fewer bits we need to compress it. When
designing better transform, some previous works adopt Swin-Transformer. The
success of the Swin-Transformer in image compression can be attributed to the
dynamic weights and large receptive field.However,the LayerNorm adopted in
transformers is not suitable for image compression.We find CNN-based modules
can also be dynamic and have large receptive-fields. The CNN-based modules can
also work with GDN/IGDN. To make the CNN-based modules dynamic, we generate the
weights of kernels conditioned on the input feature. We scale up the size of
each kernel for larger receptive fields. To reduce complexity, we make the
CNN-module channel-wise connected. We call this module Dynamic Depth-wise
convolution. We replace the self-attention module with the proposed Dynamic
Depth-wise convolution, replace the embedding layer with a depth-wise residual
bottleneck for non-linearity and replace the FFN layer with an inverted
residual bottleneck for more interactions in the spatial domain. The
interactions among channels of dynamic depth-wise convolution are limited. We
design the other block, which replaces the dynamic depth-wise convolution with
channel attention. We equip the proposed modules in the analysis and synthesis
transform and receive a more compact latent representation and propose the
learned image compression model SLIC, meaning Self-Conditioned Adaptive
Transform with Large-Scale Receptive Fields for Learned Image Compression
Learned Image Compression. Thanks to the proposed transform modules, our
proposed SLIC achieves 6.35% BD-rate reduction over VVC when measured in PSNR
on Kodak dataset.Comment: Submitted to TCSV
Long Fading Mid-Infrared Emission in Transient Coronal Line Emitters: Dust Echo of Tidal Disruption Flare
The sporadic accretion following the tidal disruption of a star by a
super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the
galactic nucleus. The gas and dust surrounding the black hole responses to such
a flare with an echo in emission lines and infrared emission. In this paper, we
report the detection of long fading mid-IR emission lasting up to 14 years
after the flare in four TDE candidates with transient coronal lines using the
WISE public data release. We estimate that the reprocessed mid-IR luminosities
are in the range between and erg~s
and dust temperature in the range of 570-800K when WISE first detected these
sources three to five years after the flare. Both luminosity and dust
temperature decreases with time. We interpret the mid-IR emission as the
infrared echo of the tidal disruption flare. We estimate the UV luminosity at
the peak flare to be 1 to 30 times erg s and for warm dust
masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results
suggest that the mid-infrared echo is a general signature of TDE in the
gas-rich environment
Mid-infrared variability of changing-look AGN
It is known that some active galactic nuclei (AGNs) transited from type 1 to
type 2 or vice versa. There are two explanations for the so-called changing
look AGNs: one is the dramatic change of the obscuration along the
line-of-sight, the other is the variation of accretion rate. In this paper, we
report the detection of large amplitude variations in the mid-infrared
luminosity during the transitions in 10 changing look AGNs using WISE and newly
released NEOWISE-R data. The mid-infrared light curves of 10 objects echoes the
variability in the optical band with a time lag expected for dust reprocessing.
The large variability amplitude is inconsistent with the scenario of varying
obscuration, rather supports the scheme of dramatic change in the accretion
rate.Comment: Published by ApjL, 7 pages, 3 figures, 2 table
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