125 research outputs found
Adsorption of molecular oxygen on doped graphene: atomic, electronic and magnetic properties
Adsorption of molecular oxygen on B-, N-, Al-, Si-, P-, Cr- and Mn-doped
graphene is theoretically studied using density functional theory in order to
clarify if O2 can change the possibility of using doped graphene for gas
sensors, electronic and spintronic devices. O2 is physisorbed on B-, and Ndoped
graphene with small adsorption energy and long distance from the graphene
plane, indicating the oxidation will not happen; chemisorption is observed on
Al-, Si-, P-, Cr- and Mn-doped graphene. The local curvature caused by the
large bond length of X-C (X represents the dopants) relative to CC bond plays a
very important role in this chemisorption. The chemisorption of O2 induces
dramatic changes of electronic structures and localized spin polarization of
doped graphene, and in particular, chemisorption of O2 on Cr-doped graphene is
antiferromagnetic. The analysis of electronic density of states shows the
contribution of the hybridization between O and dopants is mainly from the p or
d orbitals. Furthermore, spin density shows that the magnetization locates
mainly around the doped atoms, which may be responsible for the Kondo effect.
These special properties supply a good choice to control the electronic
properties and spin polarization in the field of graphene engineering.Comment: 7 pages, 10 figure
A Case based Online Trajectory Planning Method of Autonomous Unmanned Combat Aerial Vehicles with Weapon Release Constraints
As a challenging and highly complex problem, the trajectory planning for unmanned combat aerial vehicle (UCAV) focuses on optimising flight trajectory under such constraints as kinematics and complicated battlefield environment. An online case-based trajectory planning strategy is proposed in this study to achieve rapid control variables solution of UCAV flight trajectory for the of delivery airborne guided bombs. Firstly, with an analysis of the ballistic model of airborne guided bombs, the trajectory planning model of UCAVs is established with launch acceptable region (LAR) as a terminal constraint. Secondly, a case-based planning strategy is presented, which involves four cases depending on the situation of UCAVs at the current moment. Finally, the feasibility and efficiency of the proposed planning strategy is validated by numerical simulations, and the results show that the presented strategy is suitable for UCAV performing airborne guided delivery missions in dynamic environments
Bregman Graph Neural Network
Numerous recent research on graph neural networks (GNNs) has focused on
formulating GNN architectures as an optimization problem with the smoothness
assumption. However, in node classification tasks, the smoothing effect induced
by GNNs tends to assimilate representations and over-homogenize labels of
connected nodes, leading to adverse effects such as over-smoothing and
misclassification. In this paper, we propose a novel bilevel optimization
framework for GNNs inspired by the notion of Bregman distance. We demonstrate
that the GNN layer proposed accordingly can effectively mitigate the
over-smoothing issue by introducing a mechanism reminiscent of the "skip
connection". We validate our theoretical results through comprehensive
empirical studies in which Bregman-enhanced GNNs outperform their original
counterparts in both homophilic and heterophilic graphs. Furthermore, our
experiments also show that Bregman GNNs can produce more robust learning
accuracy even when the number of layers is high, suggesting the effectiveness
of the proposed method in alleviating the over-smoothing issue
Quantum Langevin molecular dynamics determination of the solar-interior equation of state
The equation of state (EOS) of the solar interior is accurately and smoothly
determined from \textit{ab initio} simulations named quantum Langevin molecular
dynamics (QLMD) in the pressure range of Mbar at
the temperature range of eV. The central pressure is
calculated, and compared with other models. The effect of heavy elements such
as carbon and oxygen on the EOS is also discussed.Comment: to publish in AP
Thermal conductivity of MgO in giant planetary interior conditions predicted by deep potential
Thermal conductivity of MgO plays a fundamental role in
understanding the thermal evolution and mantle convection in the interior of
terrestrial planets. However, previous theoretical calculations deviate from
each other and the of high-pressure B2 phase remains undetermined.
Here, by combining molecular dynamics and deep potential trained with
first-principles data, we systematically investigate the of MgO from
ambient state to the core-mantle boundary (CMB) of super-Earth with
. We point out the significance of 4-phonon scatterings and modify
the conventional thermal conductivity model of MgO by considering the
density-dependent proportion of 3-phonon and 4-phonon scatterings. The
profiles of MgO in Earth and super-Earth are further estimated. For
super-Earth, we predict a significant reduction of at the B1-B2 phase
transition area near the CMB. This work provides new insights into thermal
transport under extreme conditions and an improved thermal model for
terrestrial planets.Comment: 4 figure
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