256 research outputs found
Vision-based localization methods under GPS-denied conditions
This paper reviews vision-based localization methods in GPS-denied
environments and classifies the mainstream methods into Relative Vision
Localization (RVL) and Absolute Vision Localization (AVL). For RVL, we discuss
the broad application of optical flow in feature extraction-based Visual
Odometry (VO) solutions and introduce advanced optical flow estimation methods.
For AVL, we review recent advances in Visual Simultaneous Localization and
Mapping (VSLAM) techniques, from optimization-based methods to Extended Kalman
Filter (EKF) based methods. We also introduce the application of offline map
registration and lane vision detection schemes to achieve Absolute Visual
Localization. This paper compares the performance and applications of
mainstream methods for visual localization and provides suggestions for future
studies.Comment: 32 pages, 15 figure
Stability of the Interface Between Two Immiscible Liquids During Injection Into a Tapered Hele-Shaw Cell
In the early twentieth century, petroleum and mining engineers noticed that water does not displace oil uniformly. This phenomenon, when water penetrates through oil, is now known as viscous fingering. This discovery and the following extensive research have contributed to enhancing oil recovery. In this paper, we describe a numerical study conducted on the stability of the interface between two immiscible liquids in converging and diverging Hele-Shaw cells with varying gradients. Hele-Shaw cells are narrow flow geometries that mimic the properties of a porous medium with fixed permeability. By using computational tools built on the OpenFOAM platform, the multiphase flow dynamics can be accurately resolved and observed at small scales. The flow is computed in several designed tapered cell, which emulate natural heterogeneity in an actual porous medium. By analyzing the finger length under the same time period in both parallel cells and tapered cells, we found that the diverging cell relatively decreases the growth compared with the converging cell. Our primary conclusion, confirming previous theoretical predictions, is that the gradient of the tapered geometry variation has an effect on the sign of interfacial growth rate, which means the interface could be destabilized or stabilized depending on the absolute value of the gradient
Adaptive Policy Learning to Additional Tasks
This paper develops a policy learning method for tuning a pre-trained policy
to adapt to additional tasks without altering the original task. A method named
Adaptive Policy Gradient (APG) is proposed in this paper, which combines
Bellman's principle of optimality with the policy gradient approach to improve
the convergence rate. This paper provides theoretical analysis which guarantees
the convergence rate and sample complexity of and
, respectively, where denotes the number of
iterations and denotes the accuracy of the resulting stationary
policy. Furthermore, several challenging numerical simulations, including
cartpole, lunar lander, and robot arm, are provided to show that APG obtains
similar performance compared to existing deterministic policy gradient methods
while utilizing much less data and converging at a faster rate
Broad-line region configuration of the supermassive binary black hole candidate PG1302-102 in the relativistic Doppler boosting scenario
PG1302-102 is thought to be a supermassive binary black hole (BBH) system
according to the periodical variations of its optical and UV photometry, which
may be interpreted as being due to the relativistic Doppler boosting of the
emission mainly from the disk around the secondary black hole (BH) modulated by
its orbital motion. In this paper, we investigate several broad emission lines
of PG1302-102 using archived UV spectra obtained by IUE, GALEX, and Hubble, to
reveal the broad-line region (BLR) emission properties of this BBH system under
the Doppler boosting scenario. We find that the broad lines Ly, NV,
CIV, and CIII] all show Gaussian profiles, and none of these lines exhibits
obvious periodical variation. Adopting a simple model for the BLR, we perform
Markov chain Monte Carlo fittings to these broad lines, and find that the BLR
must be viewed at an orientation angle of , close to face-on.
If the Doppler boosting interpretation is correct, then the BLR is misaligned
with the BBH orbital plane by an angle of , which suggests that
the Doppler boosted continuum variation has little effect on the broad-line
emission and thus does not lead to periodical line variation. We further
discuss the possible implications for such a BLR configuration with respect to
the BBH orbital plane.Comment: 9 pages, 6 figures, matches A&A version (only minor changes
Fair Division of Mixed Divisible and Indivisible Goods
We study the problem of fair division when the resources contain both
divisible and indivisible goods. Classic fairness notions such as envy-freeness
(EF) and envy-freeness up to one good (EF1) cannot be directly applied to the
mixed goods setting. In this work, we propose a new fairness notion
envy-freeness for mixed goods (EFM), which is a direct generalization of both
EF and EF1 to the mixed goods setting. We prove that an EFM allocation always
exists for any number of agents. We also propose efficient algorithms to
compute an EFM allocation for two agents and for agents with piecewise
linear valuations over the divisible goods. Finally, we relax the envy-free
requirement, instead asking for -envy-freeness for mixed goods
(-EFM), and present an algorithm that finds an -EFM
allocation in time polynomial in the number of agents, the number of
indivisible goods, and .Comment: Appears in the 34th AAAI Conference on Artificial Intelligence
(AAAI), 202
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