748 research outputs found
Design, construction and commissioning of a packed bed reactor system for methane to methanol conversion
The direct conversion of methane to methanol can have great economic implications and have been under extensive research for the past century. It is speculated that platinum-based catalysts may achieve this due to its ability to adsorb molecular oxygen as reactive surface oxygen species that may react with methane to form methanol. The selective conversion to methanol over such a catalyst might be possible through site blocking action with in presence of steam and/or high oxygen partial pressures as well as the presence of a promoter. Thus, a packed bed reactor system capable of safely operating under high pressures (< 50 bar) is designed and constructed to investigate the performance of platinum-based catalysts in the direct oxidative conversion of methane to methanol whilst co-feeding steam. The design procedure is carried out from flowsheet development to the detailed design of individual units of the reactor system. The constructed reactor system is built around a quartz lined microreactor 200 mm long and 2.4 mm in diameter to minimize risks associated with the flammability of methane and oxygen mixtures. A method for complete product analysis of all carbon containing reaction products using gas chromatography with flame ionization detector in conjunction with an oxidizer-methanizer microreactor is developed which is capable of quantifying minor carbon containing reaction products formed at low conversions with yields greater than 10 μmol/mol. Flow, pressure and temperature controls are also developed for the reactor system to ensure steady state operation
Accelerated K-Serial Stable Coalition for Dynamic Capture and Resource Defense
Coalition is an important mean of multi-robot systems to collaborate on
common tasks. An effective and adaptive coalition strategy is essential for the
online performance in dynamic and unknown environments. In this work, the
problem of territory defense by large-scale heterogeneous robotic teams is
considered. The tasks include exploration, capture of dynamic targets, and
perimeter defense over valuable resources. Since each robot can choose among
many tasks, it remains a challenging problem to coordinate jointly these robots
such that the overall utility is maximized. This work proposes a generic
coalition strategy called K-serial stable coalition algorithm (KS-COAL).
Different from centralized approaches, it is distributed and complete, meaning
that only local communication is required and a K-serial Stable solution is
ensured. Furthermore, to accelerate adaptation to dynamic targets and resource
distribution that are only perceived online, a heterogeneous graph attention
network (HGAN)-based heuristic is learned to select more appropriate parameters
and promising initial solutions during local optimization. Compared with manual
heuristics or end-to-end predictors, it is shown to both improve online
adaptability and retain the quality guarantee. The proposed methods are
validated rigorously via large-scale simulations with 170 robots and hardware
experiments of 13 robots, against several strong baselines including GreedyNE
and FastMaxSum.Comment: 8 pages, 10 figures, 1 tabl
MASTERKEY: Practical Backdoor Attack Against Speaker Verification Systems
Speaker Verification (SV) is widely deployed in mobile systems to
authenticate legitimate users by using their voice traits. In this work, we
propose a backdoor attack MASTERKEY, to compromise the SV models. Different
from previous attacks, we focus on a real-world practical setting where the
attacker possesses no knowledge of the intended victim. To design MASTERKEY, we
investigate the limitation of existing poisoning attacks against unseen
targets. Then, we optimize a universal backdoor that is capable of attacking
arbitrary targets. Next, we embed the speaker's characteristics and semantics
information into the backdoor, making it imperceptible. Finally, we estimate
the channel distortion and integrate it into the backdoor. We validate our
attack on 6 popular SV models. Specifically, we poison a total of 53 models and
use our trigger to attack 16,430 enrolled speakers, composed of 310 target
speakers enrolled in 53 poisoned models. Our attack achieves 100% attack
success rate with a 15% poison rate. By decreasing the poison rate to 3%, the
attack success rate remains around 50%. We validate our attack in 3 real-world
scenarios and successfully demonstrate the attack through both over-the-air and
over-the-telephony-line scenarios.Comment: Accepted by Mobicom 202
Large Magnetoresistance over an Extended Temperature Regime in Monophosphides of Tantalum and Niobium
We report extremely large magnetoresistance (MR) in an extended temperature
regime from 1.5 K to 300 K in non-magnetic binary compounds TaP and NbP. TaP
exhibits linear MR around at 2 K in a magnetic field of 9
Tesla, which further follows its linearity up to in a magnetic
field of 56 Tesla at 1.5 K. At room temperature the MR for TaP and NbP follows
a power law of the exponent about with the values larger than in
a magnetic field of 9 Tesla. Such large MR in a wide temperature regime is not
likely only due to a resonance of the electron-hole balance, but indicates a
complicated mechanism underneath.Comment: 13 pages, 4 figures; submitted in May 20, 2015; accepted for
publicatio
Deep Partial Updating
Emerging edge intelligence applications require the server to continuously
retrain and update deep neural networks deployed on remote edge nodes in order
to leverage newly collected data samples. Unfortunately, it may be impossible
in practice to continuously send fully updated weights to these edge nodes due
to the highly constrained communication resource. In this paper, we propose the
weight-wise deep partial updating paradigm, which smartly selects only a subset
of weights to update at each server-to-edge communication round, while
achieving a similar performance compared to full updating. Our method is
established through analytically upper-bounding the loss difference between
partial updating and full updating, and only updates the weights which make the
largest contributions to the upper bound. Extensive experimental results
demonstrate the efficacy of our partial updating methodology which achieves a
high inference accuracy while updating a rather small number of weights
Robust and accurate depth estimation by fusing LiDAR and Stereo
Depth estimation is one of the key technologies in some fields such as
autonomous driving and robot navigation. However, the traditional method of
using a single sensor is inevitably limited by the performance of the sensor.
Therefore, a precision and robust method for fusing the LiDAR and stereo
cameras is proposed. This method fully combines the advantages of the LiDAR and
stereo camera, which can retain the advantages of the high precision of the
LiDAR and the high resolution of images respectively. Compared with the
traditional stereo matching method, the texture of the object and lighting
conditions have less influence on the algorithm. Firstly, the depth of the
LiDAR data is converted to the disparity of the stereo camera. Because the
density of the LiDAR data is relatively sparse on the y-axis, the converted
disparity map is up-sampled using the interpolation method. Secondly, in order
to make full use of the precise disparity map, the disparity map and stereo
matching are fused to propagate the accurate disparity. Finally, the disparity
map is converted to the depth map. Moreover, the converted disparity map can
also increase the speed of the algorithm. We evaluate the proposed pipeline on
the KITTI benchmark. The experiment demonstrates that our algorithm has higher
accuracy than several classic methods
Different phase leads to different transport behavior in PbCu(PO)O compounds
The recent claimed room-temperature superconductivity in Cu-doped lead
apatite at ambient pressure are under highly debate. To identify its physical
origin, we studied the crystal structures, energy band structures, lattice
dynamics and magnetic properties of the parent Pb(PO)O compound,
in which two different phases of the LK-99 compound are analyzed in detail. Our
results show that the Pb(PO)O compound is an indirect band gap
semiconductor, where Cu doping at the 4 site of Pb leads to a semiconducting
to half-metallic transition. Two half-filled flat bands spanning the Fermi
energy levels are present in the 4-phase of LK-99, which are mainly formed
by hybridization of the and orbitals of Cu with the 2
orbitals of O. In addition, 6-phase of LK-99 always has spin polarity at the
bottom of the conduction band and at the top of the valence band, making the
material a bipolar magnetic semiconductor. Our results are basically consistent
with the recent experimental transport properties of LK-99 posted on
arXiv:2308.05778.Comment: 6 pages and 4 figure
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