159 research outputs found
Diffusion metamaterials for plasma transport
Plasma technology has found widespread applications in numerous domains, yet
the techniques to manipulate plasma transport predominantly rely on magnetic
control. In this review, we present a streamlined diffusion-migration method to
characterize plasma transport. Based on this framework, the viability of the
transformation theory for plasma transport is demonstrated. Highlighted within
are three model devices designed to cloak, concentrate, and rotate plasmas
without significantly altering the density profile of background plasmas.
Additionally, insights regarding potential implications for novel physics are
discussed. This review aims to contribute to advancements in plasma technology,
especially in sectors like medicine and chemistry.Comment: For more details, see Chapter 15 of the forthcoming Springer
monograph entitled "Diffusionics: Diffusion Process Controlled by Diffusion
Metamaterials.
Bi-level Actor-Critic for Multi-agent Coordination
Coordination is one of the essential problems in multi-agent systems.
Typically multi-agent reinforcement learning (MARL) methods treat agents
equally and the goal is to solve the Markov game to an arbitrary Nash
equilibrium (NE) when multiple equilibra exist, thus lacking a solution for NE
selection. In this paper, we treat agents \emph{unequally} and consider
Stackelberg equilibrium as a potentially better convergence point than Nash
equilibrium in terms of Pareto superiority, especially in cooperative
environments. Under Markov games, we formally define the bi-level reinforcement
learning problem in finding Stackelberg equilibrium. We propose a novel
bi-level actor-critic learning method that allows agents to have different
knowledge base (thus intelligent), while their actions still can be executed
simultaneously and distributedly. The convergence proof is given, while the
resulting learning algorithm is tested against the state of the arts. We found
that the proposed bi-level actor-critic algorithm successfully converged to the
Stackelberg equilibria in matrix games and find an asymmetric solution in a
highway merge environment
Probing the dipole portal to heavy neutral leptons via meson decays at the high-luminosity LHC
We consider the dipole portal to sterile neutrinos, also called heavy neutral
leptons (HNLs). The dipole interaction with the photon leads to HNL production
in meson decays, as well as triggers the HNL decay into an active neutrino and
a photon. HNLs with masses of order of 0.01-1 GeV are naturally long-lived if
the dipole coupling is sufficiently small. We perform Monte-Carlo simulations
and derive the sensitivities of the proposed FASER2 and FACET long-lived
particle experiments to HNLs produced via the dipole operator in meson decays
at the high-luminosity LHC. Our findings show that these future detectors will
be complementary to each other, as well as to existing experiments, and will be
able to probe new parts of the parameter space, especially in the case of the
dipole operator coupled to the tau neutrino.Comment: 16 pages+refs, 5 figures, 2 table
ProgressLabeller: Visual Data Stream Annotation for Training Object-Centric 3D Perception
Visual perception tasks often require vast amounts of labelled data,
including 3D poses and image space segmentation masks. The process of creating
such training data sets can prove difficult or time-intensive to scale up to
efficacy for general use. Consider the task of pose estimation for rigid
objects. Deep neural network based approaches have shown good performance when
trained on large, public datasets. However, adapting these networks for other
novel objects, or fine-tuning existing models for different environments,
requires significant time investment to generate newly labelled instances.
Towards this end, we propose ProgressLabeller as a method for more efficiently
generating large amounts of 6D pose training data from color images sequences
for custom scenes in a scalable manner. ProgressLabeller is intended to also
support transparent or translucent objects, for which the previous methods
based on depth dense reconstruction will fail. We demonstrate the effectiveness
of ProgressLabeller by rapidly create a dataset of over 1M samples with which
we fine-tune a state-of-the-art pose estimation network in order to markedly
improve the downstream robotic grasp success rates. ProgressLabeller is
open-source at https://github.com/huijieZH/ProgressLabeller.Comment: IROS 2022 accepted paper; project page:
https://progress.eecs.umich.edu/projects/progress-labeller
TransNet: Transparent Object Manipulation Through Category-Level Pose Estimation
Transparent objects present multiple distinct challenges to visual perception
systems. First, their lack of distinguishing visual features makes transparent
objects harder to detect and localize than opaque objects. Even humans find
certain transparent surfaces with little specular reflection or refraction,
like glass doors, difficult to perceive. A second challenge is that depth
sensors typically used for opaque object perception cannot obtain accurate
depth measurements on transparent surfaces due to their unique reflective
properties. Stemming from these challenges, we observe that transparent object
instances within the same category, such as cups, look more similar to each
other than to ordinary opaque objects of that same category. Given this
observation, the present paper explores the possibility of category-level
transparent object pose estimation rather than instance-level pose estimation.
We propose \textit{\textbf{TransNet}}, a two-stage pipeline that estimates
category-level transparent object pose using localized depth completion and
surface normal estimation. TransNet is evaluated in terms of pose estimation
accuracy on a large-scale transparent object dataset and compared to a
state-of-the-art category-level pose estimation approach. Results from this
comparison demonstrate that TransNet achieves improved pose estimation accuracy
on transparent objects. Moreover, we use TransNet to build an autonomous
transparent object manipulation system for robotic pick-and-place and pouring
tasks
Phenomena of electrostatic perturbations before strong earthquakes (2005–2010) observed on DEMETER
International audienceDuring the DEMETER operating period in 2004– 2010, many strong earthquakes took place in the world. 69 strong earthquakes with a magnitude above 7.0 during January 2005 to February 2010 were collected and analysed. The orbits, recorded in local nighttime by satellite, were chosen by a distance of 2000 km to the epicentres during the 9 days around these earthquakes, with 7 days before and 1 day after. The anomaly is defined when the disturbances in the electric field PSD increased to at least 1 order of magnitude relative to the normal median level about 10 −2 µV 2 /m 2 /Hz at 19.5–250 Hz frequency band, and the starting point of perturbations not exceeding 10 • relative to the epicentral latitude. Among the 69 earthquakes, it is shown that electrostatic perturbations were detected at ULF-ultra low frequency and ELF-extremely low frequency band before the 32 earthquakes, nearly 46 %. Furthermore, we extended the searching scale of these perturbations to the globe, and it can be found that before some earthquakes, the electrostatic anomalies were distributed in a much larger area a few days before, and then they concentrated to the closest orbit when the earthquake would happen one day or a few hours later, which reflects the spatial developing feature during the seismic preparation process. The results in this paper contribute to a better description of the electromagnetic (EM) disturbances at an altitude of 660– 710 km in the ionosphere that can help towards a further understanding of the lithosphere-atmosphere-ionosphere (LAI) coupling mechanism
Learning to Select Cuts for Efficient Mixed-Integer Programming
Cutting plane methods play a significant role in modern solvers for tackling
mixed-integer programming (MIP) problems. Proper selection of cuts would remove
infeasible solutions in the early stage, thus largely reducing the
computational burden without hurting the solution accuracy. However, the major
cut selection approaches heavily rely on heuristics, which strongly depend on
the specific problem at hand and thus limit their generalization capability. In
this paper, we propose a data-driven and generalizable cut selection approach,
named Cut Ranking, in the settings of multiple instance learning. To measure
the quality of the candidate cuts, a scoring function, which takes the
instance-specific cut features as inputs, is trained and applied in cut ranking
and selection. In order to evaluate our method, we conduct extensive
experiments on both synthetic datasets and real-world datasets. Compared with
commonly used heuristics for cut selection, the learning-based policy has shown
to be more effective, and is capable of generalizing over multiple problems
with different properties. Cut Ranking has been deployed in an industrial
solver for large-scale MIPs. In the online A/B testing of the product planning
problems with more than variables and constraints daily, Cut Ranking has
achieved the average speedup ratio of 12.42% over the production solver without
any accuracy loss of solution.Comment: Paper accepted at Pattern Recognition journa
Biological Monitoring of Cadmium Exposed Workers in a Nickel-Cadmium Battery Factory in China
Abstract: Biological Monitoring of Cadmium Exposed Workers in a Nickel-Cadmium Battery Factory in China: Guicheng ZHANG, et al. School of Public Health, Curtin University of Technology-A cross-sectional study of renal damage in workers from a Chinese Ni-Cd battery factory is reported in this paper. The present exposure of surveyed workers to Cd may be likened to that of factories in developed countries prior to the 1950s. The results show urinary cadmium did not increase significantly with the years of exposure in aged workers exposed to cadmium. In these occupationally exposed workers urinary cadmium levels of 3 to 60 µg/g creatinine relate to between 15% and 20% of the workers having B 2 -MG proteinura, and blood cadmium levels less than 5 µg/l relate to more than 10% of the workers having B 2 -MG proteinura. The results suggest that a urinary cadmium concentration of 5 µg/g cr or a blood cadmium concentration of 5 µg/ l would not be a safe level. (J Occup Health 2002; 44: 15-21
Controlling mass and energy diffusion with metamaterials
Diffusion driven by temperature or concentration gradients is a fundamental
mechanism of energy and mass transport, which inherently differs from wave
propagation in both physical foundations and application prospects. Compared
with conventional schemes, metamaterials provide an unprecedented potential for
governing diffusion processes, based on emerging theories like the
transformation and the scattering cancellation theory, which enormously
expanded the original concepts and suggest innovative metamaterial-based
devices. We hereby use the term ``diffusionics'' to generalize these remarkable
achievements in various energy (e.g., heat) and mass (e.g., particles and
plasmas) diffusion systems. For clarity, we categorize the numerous studies
appeared during the last decade by diffusion field (i.e., heat, particles, and
plasmas) and discuss them from three different perspectives: the theoretical
perspective, to detail how the transformation principle is applied to each
diffusion field; the application perspective, to introduce various intriguing
metamaterial-based devices, such as cloaks and radiative coolers; and the
physics perspective, to connect with concepts of recent concern, such as
non-Hermitian topology, nonreciprocal transport, and spatiotemporal modulation.
We also discuss the possibility of controlling diffusion processes beyond
metamaterials. Finally, we point out several future directions for diffusion
metamaterial research, including the integration with artificial intelligence
and topology concepts.Comment: This review article has been accepted for publication in Rev. Mod.
Phy
Preparation and electrochemical properties of pomegranate-shaped Fe₂O₃/C anodes for li-ion batteries
Due to the severe volume expansion and poor cycle stability, transition metal oxide anode is still not meeting the commercial utilization. We herein demonstrate the synthetic method of core-shell pomegranate-shaped Fe2O3/C nano-composite via one-step hydrothermal process for the first time. The electrochemical performances were measured as anode material for Li-ion batteries. It exhibits excellent cycling performance, which sustains 705 mAh g-1 reversible capacities after 100 cycles at 100 mA g-1. The anodes also showed good rate stability with discharge capacities of 480 mAh g-1 when cycling at a rate of 2000 mA g-1. The excellent Li storage properties can be attributed to the unique core-shell pomegranate structure, which can not only ensure good electrical conductivity for active Fe2O3, but also accommodate huge volume change during cycles as well as facilitate the fast diffusion of Li ion
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