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1. Fault-Tolerant Mapping and Localization for Quadrotor UAVs

   Gilson, Max; Gauthier, Jason; Garcia, Kaylee; Kienzle, Cory; Muse, Jonathan A; Zhang, Xiaodong (January 2021, AIAA Scitech 2021 Forum)

   null (Ed.)

   This paper presents a fault-tolerant control method for a quadrotor UAV using solely on-board sensors. A simultaneous localization and mapping (SLAM) system is developed utilizing a laser rangefinder and an open source SLAM algorithm called GMapping. This system allows for mapping of the surrounding environment as well as localizing the position of the quadrotor, enabling real-time position control. However, the SLAM system using the laser rangefinder may fail in certain degenerate environment like featureless tunnels or straight hallways. In order to compensate for possible faults in the SLAM measurements, a fault detection and fault-tolerant control method is developed. An observer is designed to estimate the translational velocity of the quadrotor using SLAM position measurements. The fault detection residual is defined as the deviation between this SLAM-based velocity estimate and another velocity estimate generated by an optical flow algorithm utilizing measurements provided by a downward facing camera. Real-time experimental results have shown the effectiveness of the fault-tolerant control algorithm. 

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2. Real-Time Trajectory Generation for Soft Robot Manipulators Using Differential Flatness

   Dickson, A; Pacheco_Garcia, JC; Jing, R; Anderson, ML; Sabelhaus, AP (April 2025, IEEE International Conference on Soft Robotics)

   Soft robots have the potential to interact with sensitive environments and perform complex tasks effectively. However, motion plans and trajectories for soft manipulators are challenging to calculate due to their deformable nature and nonlinear dynamics. This article introduces a fast realtime trajectory generation approach for soft robot manipulators, which creates dynamically-feasible motions for arbitrary kinematically-feasible paths of the robot’s end effector. Our insight is that piecewise constant curvature (PCC) dynamics models of soft robots can be differentially flat, therefore control inputs can be calculated algebraically rather than through a nonlinear differential equation. We prove this flatness under certain conditions, with the curvatures of the robot as the flat outputs. Our two-step trajectory generation approach uses an inverse kinematics procedure to calculate a motion plan of robot curvatures per end-effector position, then, our flatness diffeomorphism generates corresponding control inputs that respect velocity. We validate our approach through simulations of our representative soft robot manipulator along three different trajectories, demonstrating a margin of 23x faster than realtime at a frequency of 100 Hz. This approach could allow fast verifiable replanning of soft robots’ motions in safety-critical physical environments, crucial for deployment in the real world. 

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3. Pursuit-Evasion Problems Involving Two Pursuers and One Evader

   https://doi.org/10.2514/6.2018-2107  

   Makkapati, Venkata Ramana; Sun, Wei; Tsiotras, Panagiotis (January 2018, AIAA Guidance, Navigation, and Control Conference)

   Time-optimal evading strategies for pursuit-evasion problems involving two pursuers and one evader are analyzed. It is assumed that both pursuers are identical and possess higher speed capabilities when compared to the evader. The problems are categorized into two scenarios, which are based on the evader's information provided to the pursuers. In the rst scenario, the pursuers have information of the evader's position and velocity at each instant of time and follow a constant bearing strategy. In the second scenario, the pursuers have only positional information of the evader and follow a pure pursuit strategy. 

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4. Observer-based event-triggered boundary control of the one-phase Stefan problem

   https://doi.org/10.1080/00207179.2024.2313677  

   Rathnayake, Bhathiya; Diagne, Mamadou (December 2024, International Journal of Control)

   This paper presents an observer-based event-triggered boundary control strategy for the one-phase Stefan problem, utilising the position and velocity measurements of the moving interface. The design of the observer and controller is founded on the infinite-dimensional backstepping approach. To implement the continuous-time observer-based controller in an event-triggered framework, we propose a dynamic event triggering condition. This condition specifies the instances when the control input must be updated. Between events, the control input is maintained constant in a Zero-Order-Hold manner. We demonstrate that the dwell-time between successive triggering moments is uniformly bounded from below, thereby precluding Zeno behaviour. The proposed event-triggered boundary control strategy ensures the wellposedness of the closed-loop system and the satisfaction of certain model validity conditions. Additionally, the global exponential convergence of the closed-loop system to the setpoint is established using Lyapunov approach. A simulation example is provided to validate the theoretical findings. 

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5. Quasar outflow deceleration or acceleration: predictions and a search

   https://doi.org/10.1093/mnras/stae330  

   Hall, P. B.; Weiss, E.; Brandt, W. N.; Mulholland, C. J. (February 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Quasar winds can shock and sweep up ambient interstellar medium (ISM) gas, contributing to galactic quenching. We combine and extend past models of energy-conserving shock bubbles around quasars, investigate model implications from an observational standpoint, and test model predictions using new high-resolution spectroscopic observations of the broad absorption-line quasar SDSS J030000.56+004828.0 (J0300). Even with constant energy input from the wind, a bubble’s expansion decelerates over time as more ISM gas is swept up. Our new observations enable a direct search for this deceleration. We obtain the tightest reported 3σ limit on the average rest-frame deceleration (or acceleration) of a quasar outflow: |a| < 0.1 km s−1 yr−1 (<3 × 10−4 cm s−2) in the relatively low-velocity Ca ii outflow of J0300 over 9.65 rest-frame years. We can satisfy these limits with certain parameter choices in our model, but the large velocity range of the Ca ii absorption in J0300 rules out the hypothesis that such gas shares the velocity of the swept-up ISM gas in a self-similar shock bubble. We investigate the possibility of ram-pressure acceleration of preexisting ISM clouds and conclude that the velocity range seen in Ca ii in J0300 is potentially consistent with such an explanation. The Ca ii-absorbing gas clouds in J0300 have been inferred to have high densities by Choi et al., in which case they can only have been accelerated to their current speeds if they were originally at least an order of magnitude less dense than they are today. 

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