13,288 research outputs found
LDSO: Direct Sparse Odometry with Loop Closure
In this paper we present an extension of Direct Sparse Odometry (DSO) to a
monocular visual SLAM system with loop closure detection and pose-graph
optimization (LDSO). As a direct technique, DSO can utilize any image pixel
with sufficient intensity gradient, which makes it robust even in featureless
areas. LDSO retains this robustness, while at the same time ensuring
repeatability of some of these points by favoring corner features in the
tracking frontend. This repeatability allows to reliably detect loop closure
candidates with a conventional feature-based bag-of-words (BoW) approach. Loop
closure candidates are verified geometrically and Sim(3) relative pose
constraints are estimated by jointly minimizing 2D and 3D geometric error
terms. These constraints are fused with a co-visibility graph of relative poses
extracted from DSO's sliding window optimization. Our evaluation on publicly
available datasets demonstrates that the modified point selection strategy
retains the tracking accuracy and robustness, and the integrated pose-graph
optimization significantly reduces the accumulated rotation-, translation- and
scale-drift, resulting in an overall performance comparable to state-of-the-art
feature-based systems, even without global bundle adjustment
Electronic structures and magnetic orders of Fe-vacancies ordered ternary iron selenides TlFeSe and AFeSe (A=K, Rb, or Cs)
By the first-principles electronic structure calculations, we find that the
ground state of the Fe-vacancies ordered TlFeSe is a
quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy
gap of 94 meV, in agreement with experimental measurements. This
antiferromagnetic order is driven by the Se-bridged antiferromagnetic
superexchange interactions between Fe moments. Similarly, we find that crystals
AFeSe (A=K, Rb, or Cs) are also antiferromagnetic semiconductors
but with a zero-gap semiconducting state or semimetallic state nearly
degenerated with the ground states. Thus rich physical properties and phase
diagrams are expected.Comment: Add results about AFeSe (A=K, Rb, or Cs);4 pages and 7
figure
Jet-cloud/star interaction as an interpretation of neutrino outburst from the blazar TXS 0506+056
Recently, a high-energy neutrino event IceCube-170922A in the spatial and
temporal coincidence with the flaring gamma-ray blazar TXS 0506+056 was
reported. A neutrino outburst between September 2014 and March 2015 was
discovered in the same direction by a further investigation of years of
IceCube data, while the blazar is in a quiescent state during the outburst with
a gamma-ray flux only about one-fifth of the neutrino flux. In this letter, we
propose the neutrino outburst originates from the interaction between a
relativistic jet and a dense gas cloud which may be formed via the tidally
disrupted envelope of a red giant being blown by the impact of the jet.
Gamma-ray photons and electron/positron pairs that are produced correspondingly
will induce electromagnetic cascades. Comptonization of the cascade emission
inside the cloud forms an X-ray photon field with Wien distribution. GeV flux
is suppressed due to the absorption by the Comptonized photon field and, as a
result, a hard spectrum above 10 GeV is formed. The gamma-ray spectrum
predicted in our model is consistent with the Fermi-LAT data of TXS 0506+056.Comment: 6 pages, 3 figure
A theoretic model for sonogenetic antiarrhythmia
Sonogenetics can be used as a new alternative for treating arrhythmia due to
its advantages of noninvasive, high safety and strong penetration. In the
treatment of arrhythmias by sonogenetics, cardiac myocytes are deformed by
ultrasonic radiation force. We quantitatively calculated the shape variation of
cardiomyocytes under ultrasonic radiation force, and the deformation of
cardiomyocytes caused the change of membrane tension. Membrane tension consists
of two parts, plasma membrane tension and cortical tension between the cell
membrane and cytoskeleton. Since plasma membrane tension was mainly considered
in existing experiments, we proposed a quantitative model of the relationship
between ultrasonic radiation force and plasma membrane tension. The Boltzmann
relationship between plasma membrane tension and ion channel opening
probability is presented based on the experimental results of ion channel
activation by stretching. Finally, a quantitative model was obtained for
ultrasonic radiation force to regulate the opening probability of ion channel
activated by stretching. Based on this quantitative model, we proposed the
regulation mechanism of ultrasonic radiation force under hypercompression and
hyperstretching, and verified that this mechanism can eliminate arrhythmias by
sonogenetics.Comment: 13pages,5 figure
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