5 research outputs found
Air Traffic Controller Workload Level Prediction using Conformalized Dynamical Graph Learning
Air traffic control (ATC) is a safety-critical service system that demands
constant attention from ground air traffic controllers (ATCos) to maintain
daily aviation operations. The workload of the ATCos can have negative effects
on operational safety and airspace usage. To avoid overloading and ensure an
acceptable workload level for the ATCos, it is important to predict the ATCos'
workload accurately for mitigation actions. In this paper, we first perform a
review of research on ATCo workload, mostly from the air traffic perspective.
Then, we briefly introduce the setup of the human-in-the-loop (HITL)
simulations with retired ATCos, where the air traffic data and workload labels
are obtained. The simulations are conducted under three Phoenix approach
scenarios while the human ATCos are requested to self-evaluate their workload
ratings (i.e., low-1 to high-7). Preliminary data analysis is conducted. Next,
we propose a graph-based deep-learning framework with conformal prediction to
identify the ATCo workload levels. The number of aircraft under the
controller's control varies both spatially and temporally, resulting in
dynamically evolving graphs. The experiment results suggest that (a) besides
the traffic density feature, the traffic conflict feature contributes to the
workload prediction capabilities (i.e., minimum horizontal/vertical separation
distance); (b) directly learning from the spatiotemporal graph layout of
airspace with graph neural network can achieve higher prediction accuracy,
compare to hand-crafted traffic complexity features; (c) conformal prediction
is a valuable tool to further boost model prediction accuracy, resulting a
range of predicted workload labels. The code used is available at
\href{https://github.com/ymlasu/para-atm-collection/blob/master/air-traffic-prediction/ATC-Workload-Prediction/}{}
Reinforcement Learning With Reward Machines in Stochastic Games
We investigate multi-agent reinforcement learning for stochastic games with
complex tasks, where the reward functions are non-Markovian. We utilize reward
machines to incorporate high-level knowledge of complex tasks. We develop an
algorithm called Q-learning with reward machines for stochastic games (QRM-SG),
to learn the best-response strategy at Nash equilibrium for each agent. In
QRM-SG, we define the Q-function at a Nash equilibrium in augmented state
space. The augmented state space integrates the state of the stochastic game
and the state of reward machines. Each agent learns the Q-functions of all
agents in the system. We prove that Q-functions learned in QRM-SG converge to
the Q-functions at a Nash equilibrium if the stage game at each time step
during learning has a global optimum point or a saddle point, and the agents
update Q-functions based on the best-response strategy at this point. We use
the Lemke-Howson method to derive the best-response strategy given current
Q-functions. The three case studies show that QRM-SG can learn the
best-response strategies effectively. QRM-SG learns the best-response
strategies after around 7500 episodes in Case Study I, 1000 episodes in Case
Study II, and 1500 episodes in Case Study III, while baseline methods such as
Nash Q-learning and MADDPG fail to converge to the Nash equilibrium in all
three case studies
Strontium-Doped Low-Temperature-Processed CsPbI<sub>2</sub>Br Perovskite Solar Cells
Cesium
(Cs) metal halide perovskites for photovoltaics have gained
research interest due to their better thermal stability compared to
their organic–inorganic counterparts. However, demonstration
of highly efficient Cs-based perovskite solar cells requires high
annealing temperature, which limits their use in multijunction devices.
In this work, low-temperature-processed cesium lead (Pb) halide perovskite
solar cells are demonstrated. We have also successfully incorporated
the less toxic strontium (Sr) at a low concentration that partially
substitutes Pb in CsPb<sub>1–<i>x</i></sub>Sr<sub><i>x</i></sub>I<sub>2</sub>Br. The crystallinity, morphology,
absorption, photoluminescence, and elemental composition of this low-temperature-processed
CsPb<sub>1–<i>x</i></sub>Sr<sub><i>x</i></sub>I<sub>2</sub>Br are studied. It is found that the surface of
the perovskite film is enriched with Sr, providing a passivating effect.
At the optimal concentration (<i>x</i> = 0.02), a mesoscopic
perovskite solar cell using CsPb<sub>0.98</sub>Sr<sub>0.02</sub>I<sub>2</sub>Br achieves a stabilized efficiency at 10.8%. This work shows
the potential of inorganic perovskite, stimulating further development
of this material