3,549 research outputs found
A generic theory for Majorana zero modes in 2D superconductors
It is well known that non-Abelian Majorana zero modes (MZM) harbor at vortex
cores in a topological superconductor, which can be
realized in a 2D spin-orbit coupled system with a single Fermi surface and by
proximity coupling to an -wave superconductor. Here we show that existence
of non-Abelian MZMs is unrelated to the bulk topology of a 2D superconductor,
and propose that such exotic modes can be resulted in much broader range of
superconductors, being topological or trivial. For a generic 2D system with
multiple Fermi surfaces and gapped out by superconducting pairings, we show
that at least a single MZM survives if there are only odd number of Fermi
surfaces of which the corresponding superconducting orders have vortices, and
such MZM is protected by an emergent Chern-Simons invariant, irrespective of
the bulk topology of the superconductor. This result may enrich new
experimental schemes for realizing non-Aelian MZMs. In particular, we propose a
minimal scheme to realize the MZMs in a 2D superconducting Dirac semimetal with
trivial bulk topology, which can be well achieved based on the recent cold atom
experiments.Comment: 5 pages, 3 figures, plus Supplementary Materia
C2FTrans: Coarse-to-Fine Transformers for Medical Image Segmentation
Convolutional neural networks (CNN), the most prevailing architecture for
deep-learning based medical image analysis, are still functionally limited by
their intrinsic inductive biases and inadequate receptive fields. Transformer,
born to address this issue, has drawn explosive attention in natural language
processing and computer vision due to its remarkable ability in capturing
long-range dependency. However, most recent transformer-based methods for
medical image segmentation directly apply vanilla transformers as an auxiliary
module in CNN-based methods, resulting in severe detail loss due to the rigid
patch partitioning scheme in transformers. To address this problem, we propose
C2FTrans, a novel multi-scale architecture that formulates medical image
segmentation as a coarse-to-fine procedure. C2FTrans mainly consists of a
cross-scale global transformer (CGT) which addresses local contextual
similarity in CNN and a boundary-aware local transformer (BLT) which overcomes
boundary uncertainty brought by rigid patch partitioning in transformers.
Specifically, CGT builds global dependency across three different small-scale
feature maps to obtain rich global semantic features with an acceptable
computational cost, while BLT captures mid-range dependency by adaptively
generating windows around boundaries under the guidance of entropy to reduce
computational complexity and minimize detail loss based on large-scale feature
maps. Extensive experimental results on three public datasets demonstrate the
superior performance of C2FTrans against state-of-the-art CNN-based and
transformer-based methods with fewer parameters and lower FLOPs. We believe the
design of C2FTrans would further inspire future work on developing efficient
and lightweight transformers for medical image segmentation. The source code of
this paper is publicly available at https://github.com/xianlin7/C2FTrans
Mid-infrared flare of TDE candidate PS16dtm: dust echo and implications for the spectral evolution
PS16dtm was classified as a candidate tidal disruption event (TDE) in a dwarf
Seyfert 1 galaxy with low-mass black hole () and has presented
various intriguing photometric and spectra characteristics. Using the archival
WISE and the newly released NEOWISE data, we found PS16dtm is experiencing a
mid-infrared (MIR) flare which started days before the first optical
detection. Interpreting the MIR flare as a dust echo requires close
pre-existing dust with a high covering factor, and suggests the optical flare
may have brightened slowly for some time before it became bright detectable
from the ground. More evidence is given at the later epochs. At the peak of the
optical light curve, the new inner radius of the dust torus has grown to much
larger size, a factor of 7 of the initial radius due to strong radiation field.
At days after the first optical detection, the dust temperature has
dropped well below the sublimation temperature. Other peculiar spectral
features shown by PS16dtm are the transient, prominent FeII emission lines and
outflows indicated by broad absorption lines detected during the optical flare.
Our model explains the enhanced FeII emission from iron newly released from the
evaporated dust. The observed broad absorption line outflow could be explained
by accelerated gas in the dust torus due to the radiation pressure.Comment: Accepted by ApJ, 5 figure
Connection Between Mid-Infrared Emission Properties and Narrow Line Region Outflows in Type 1 Active Galactic Nuclei
The location of warm dust producing the Mid-infrared (MIR) emission in Type 1
Active Galactic Nuclei (AGNs) is complex and not yet fully known. We explore
this problem by studying how the MIR covering factor (CF_{MIR}
=L_{MIR}/L_{bol}) correlates with the fundamental parameters of AGN accretion
process (such as L_{bol}, black hole mass MBH, and Eddington ratio L/LEdd) and
the properties of narrow emission lines (as represented by [O III] 5007), using
large data sets derived from the Sloan Digital Sky Spectroscopic Survey (SDSS)
and the Wide Infrared Sky Survey (WISE). Firstly we find that the luminosity of
the [O III] wing component (Lwing) correlates more tightly with the continuum
luminosity (L5100) than the luminosity of the line core component (Lcore) does,
which is in line with our previous conclusion that the wing component,
generally blueshifted, originates from the polar outflows in the inner
narrow-line region (NLR). We then find that the MIR CF shows the strongest
correlation with Lwing/L_{bol} rather than with Lcore/L_{bol} or the above
fundamental AGN parameters, and the correlation becomes stronger as the
infrared wavelength increases. We also confirm the anti-correlations of
CF_{MIR} with L_{bol} and MBH, and the lack of dependence of CF_{MIR} on the
Eddington ratio. These results suggest that a large fraction of the warm dust
producing MIR emission in AGNs is likely embedded in polar outflows in the NLR
instead of in the torus.Comment: 8 pages, 4 figures, 1 table, ApJ accepte
Analysis of an age-structured dengue model with multiple strains and cross immunity
Dengue fever is a typical mosquito-borne infectious disease, and four strains of it are currently found. Clinical medical research has shown that the infected person can provide life-long immunity against the strain after recovering from infection with one strain, but only provide partial and temporary immunity against other strains. On the basis of the complexity of transmission and the diversity of pathogens, in this paper, a multi-strain dengue transmission model with latency age and cross immunity age is proposed. We discuss the well-posedness of this model and give the terms of the basic reproduction number R0 = max{R1, R2} , where Ri is the basic reproduction number of strain i (i = 1, 2). Particularly, we obtain that the model always has a unique diseasefree equilibrium P0 which is locally stable for R0 1, the strain-i dominant equilibrium Pi is locally stable for Rj < R∗ i (i, j = 1, 2, i 6= j). Additionally, the threshold criteria on the uniformly persistence, the existence and global asymptotically stability of coexistence equilibrium are also obtained. Finally, these theoretical results and interesting conclusions are illustrated with some numerical simulations
Bicontrol of Pythium aphanidermatum and Damping-off Disease of Papaya Seedlings (Carica papaya cv. Tainung No.2) by Different Smoke-water
Two key trends of sustainable agriculture are reducing the amount of inputs such as pesticides, fungicides, or fertilizer and finding ways to reduce or reuse agricultural waste. Leafy plant waste can be burned to produced smoke-water extracts that have effective antimicrobial and germination properties. Damping-off disease caused by Pythium spp. leads to significant losses at the papaya seedling stage and is usually managed with fungicides. Five smoke-water extracts derived from burning different plant residues—namely, rice straw smoke-water (R-SW), wheat straw smoke-water (W-SW), pangola grass smoke-water (P-SW), cornstalk smoke-water (C-SW), and bamboo leave smoke-water (B-SW)—were prepared. These were mixed into the V8 media used for culture of Pythium aphanidermatum. In vitro treatment with 5% P-SW, C-SW, or B-SW reduced mycelial growth rate significantly, whereas 5% B-SW inhibited mycelial growth completely. All 1% smoke-water preparations reduced zoospore production significantly, but the inhibition rate of 3% R-SW, 3% W-SW, 1% P-SW, 1% C-SW, and 1% B-SW reached 100%. For in vivo experiments, P. aphanidermatum was inoculated in 1 kg of potting soil and mixed with B-SW in concentrations of 1% to 5%. The papaya seedlings treated with 2% to 5% B-SW maintained the growth parameter without damping-off symptoms
2,2′-[(1E)-3-Phenylprop-2-ene-1,1-diyl]bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-one)
In the title molecule, C25H30O4, the two cyclohexene rings adopt envelope conformations. The two hydroxy groups are involved in the formation of intramolecular O—H⋯O hydrogen bonds. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds link molecules related by translation along the axis a into chains
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