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Collision-Free Adaptive Control for UAV Formation with Input Saturation and Communication Delays
Jianhui Lu,Fan Luo,Zhong Zheng,Mingxin Hou,Lin Wang 한국항공우주학회 2022 International Journal of Aeronautical and Space Sc Vol.23 No.3
This paper addresses the collision-free adaptive formation control problem for multiple unmanned aerial vehicles subject to input saturation and communication delays. First, a novel collision-free adaptive saturated control scheme is proposed using potential function and anti-windup compensator approaches. It shows that the velocity consensus and collision avoidance are realized when the directed communication topology is strongly connected. Second, the collision-free adaptive saturated control algorithm is proposed considering communication delays and collision avoidance, and it enables the asymptotic stability of the closed-loop system when the time-varying communication delays are decreasing to zero eventually. Finally, numerical simulations demonstrate that the proposed control approaches are effective, while the objectives of collision avoidance and velocity consensus are fulfilled.
Paween Wongkornchaovalit,Min Feng,Hongjian He,Jianhui Zhong 대한자기공명의과학회 2022 Investigative Magnetic Resonance Imaging Vol.26 No.4
Diffusion MRI (dMRI) has been widely utilized to probe the random motion of water molecules in tissues. In a dMRI acquisition protocol, diffusion weighting or b-value is one of the most important parameters to consider. In recent years, high and ultrahigh b-values have become popular partly due to advances in hardware. In this mini-review, we will discuss impacts of high/ultrahigh b-values in three different areas: brain microstructure, tractography, and clinical applications. We will emphasize advantages of high b-value in probing diffusion within highly restricted regions or fine structures with enhanced diffusion contrast. A short summary is included at the end of each section to illustrate both advantages and disadvantages of using a high/ultrahigh b-value for each purpose.
Diffusion Encoding Methods in MRI: Perspectives and Challenges
Alan Finkelstein,Xiaozhi Cao,Congyu Liao,Giovanni Schifitto,Jianhui Zhong 대한자기공명의과학회 2022 Investigative Magnetic Resonance Imaging Vol.26 No.4
Diffusion MRI (dMRI) is an important imaging modality that is used extensively to diagnose and monitor diseases. dMRI measures random motion of water molecules and helps elucidate microstructural properties of tissues. Optimal diffusion encoding paradigms have been developed to reduce acquisition time, minimize artifacts, and acquire high fidelity data needed for advanced modeling of tissue properties. To further probe microstructural properties, joint diffusion-relaxometry and diffusion weighted MR fingerprinting have garnered interest. A thorough knowledge of different diffusion encoding methods is essential to accurately encode diffusion in MR experiments. Here, we review fundamental physics of diffusion encoding methods, their associated challenges, and how to address them. Advanced diffusion acquisition methods are also discussed.