14,000 research outputs found
Tensor modules over Witt superalgebras
In this paper, we study the tensor module over the Witt
superalgebra (resp. ), where is a simple module over
the Weyl superalgebra (resp. ) and is simple weight
module over the general linear Lie superalgebra . We obtain
the necessary and sufficient conditions for to be simple, and
determine all simple subquotient of when it is not simple. All the
work leads to completion of some classification problems on the weight
representation theory of and .Comment: The paper has been accepted for publication in SCIENCE CHINA
Mathematic
Self-Supervised Deep Visual Odometry with Online Adaptation
Self-supervised VO methods have shown great success in jointly estimating
camera pose and depth from videos. However, like most data-driven methods,
existing VO networks suffer from a notable decrease in performance when
confronted with scenes different from the training data, which makes them
unsuitable for practical applications. In this paper, we propose an online
meta-learning algorithm to enable VO networks to continuously adapt to new
environments in a self-supervised manner. The proposed method utilizes
convolutional long short-term memory (convLSTM) to aggregate rich
spatial-temporal information in the past. The network is able to memorize and
learn from its past experience for better estimation and fast adaptation to the
current frame. When running VO in the open world, in order to deal with the
changing environment, we propose an online feature alignment method by aligning
feature distributions at different time. Our VO network is able to seamlessly
adapt to different environments. Extensive experiments on unseen outdoor
scenes, virtual to real world and outdoor to indoor environments demonstrate
that our method consistently outperforms state-of-the-art self-supervised VO
baselines considerably.Comment: Accepted by CVPR 2020 ora
Turbo-FLASH based arterial spin labeled perfusion MRI at 7 T.
Motivations of arterial spin labeling (ASL) at ultrahigh magnetic fields include prolonged blood T1 and greater signal-to-noise ratio (SNR). However, increased B0 and B1 inhomogeneities and increased specific absorption ratio (SAR) challenge practical ASL implementations. In this study, Turbo-FLASH (Fast Low Angle Shot) based pulsed and pseudo-continuous ASL sequences were performed at 7T, by taking advantage of the relatively low SAR and short TE of Turbo-FLASH that minimizes susceptibility artifacts. Consistent with theoretical predictions, the experimental data showed that Turbo-FLASH based ASL yielded approximately 4 times SNR gain at 7T compared to 3T. High quality perfusion images were obtained with an in-plane spatial resolution of 0.85×1.7 mm(2). A further functional MRI study of motor cortex activation precisely located the primary motor cortex to the precentral gyrus, with the same high spatial resolution. Finally, functional connectivity between left and right motor cortices as well as supplemental motor area were demonstrated using resting state perfusion images. Turbo-FLASH based ASL is a promising approach for perfusion imaging at 7T, which could provide novel approaches to high spatiotemporal resolution fMRI and to investigate the functional connectivity of brain networks at ultrahigh field
On the minimum jet power of TEV BL Lac objects in the p- model
We study the requirement on the jet power in the conventional p-
models (photopion production and Bethe-Heitler pair production) for TeV BL Lac
objects. We select a sample of TeV BL Lac objects whose SEDs are difficult to
be explained by the one-zone leptonic model. Based on the relation between the
p- interaction efficiency and the opacity of absorption,
we find that the detection of TeV emission poses upper limits on the p-
interaction efficiencies in these sources and hence minimum jet powers can be
derived accordingly. We find that the obtained minimum jet powers exceed the
Eddington luminosity of the supermassive black holes. Implications for the
accretion mode of the supermassive black hole in these BL Lac objects and the
origin of their TeV emissions are discussed.Comment: 11 pages, 4 figures, 2 tables, accepted for publication in Ap
Anomalous pressure behavior of tangential modes in single-wall carbon nanotubes
Using the molecular dynamics simulations and the force constant model we have
studied the Raman-active tangential modes (TMs) of a (10, 0) single-wall carbon
nanotube (SWNT) under hydrostatic pressure. With increasing pressure, the
atomic motions in the three TMs present obvious diversities. The pressure
derivative of E1g, A1g, and E2g mode frequency shows an increased value (), a
constant value (), and a negative value () above 5.3 GPa, respectively. The
intrinsic characteristics of TMs consumedly help to understand the essence of
the experimental T band of CNT. The anomalous pressure behavior of the TMs
frequencies may be originated from the tube symmetry alteration from D10h to
D2h then to C2h.Comment: 15 pages, 3 pages, submitted to Phys. Rev.
Quantum Spin Liquid with Even Ising Gauge Field Structure on Kagome Lattice
Employing large-scale quantum Monte Carlo simulations, we study the extended
model on the kagome lattice. A quantum spin liquid phase
with effective even Ising gauge field structure emerges from the delicate
balance among three symmetry-breaking phases including stripe solid, staggered
solid and ferromagnet. This spin liquid is stabilized by an
extended interaction related to the Rokhsar-Kivelson potential in the quantum
dimer model limit. The phase transitions from the staggered solid to a spin
liquid or ferromagnet are found to be first order and so is the transition
between the stripe solid and ferromagnet. However, the transition between a
spin liquid and ferromagnet is found to be continuous and belongs to the 3D
universality class associated with the condensation of spinons. The
transition between a spin liquid and stripe solid appears to be continuous and
associated with the condensation of visons.Comment: 7 pages, 8 figure
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