Publications by authors named "Han Lim Choi"

6 Publications

  • Page 1 of 1

Optimal Cooperative Guidance Laws for Two UAVs Under Sensor Information Deficiency Constraints.

Sensors (Basel) 2020 Aug 25;20(17). Epub 2020 Aug 25.

Department of Electronic Engineering, Kyung Hee University, Yongin 17104, Korea.

This paper presents closed-form optimal cooperative guidance laws for two UAVs under information constraints that achieve the required relative approach angle. Two UAVs cooperate to optimize a common cost function under a coupled constraint on terminal velocity vectors and the information constraint which defines the sensor information availability. To handle the information constraint, a general two-player partially nested decentralized optimal control problem is considered in the continuous finite-horizon time domain. It is shown that under the state-separation principle the optimal solution of the decentralized control problem can be obtained by solving two centralized subproblems which cover the prediction problem for the information-deficient player and the prediction error minimization problem for the player with full information. Based on the solution of the decentralized optimal control problem, the explicit closed-form cooperative guidance laws that can be efficiently implemented on conventional guidance computers are derived. The performance of the proposed guidance laws is investigated on both centralized and decentralized cooperative scenarios with nonlinear engagement kinematics of networked two-UAV systems.
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http://dx.doi.org/10.3390/s20174790DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7506890PMC
August 2020

Deep Generative Models-Based Anomaly Detection for Spacecraft Control Systems.

Sensors (Basel) 2020 Apr 2;20(7). Epub 2020 Apr 2.

Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, Daejeon 341141, Korea.

A spacecraft attitude control system provides mechanical and electrical control to achieve the required functions under various mission scenarios. Although generally designed to be highly reliable, mission failure can occur if anomalies occur and the attitude control system fails to properly orient and stabilize the spacecraft. Because accessing spacecraft to directly repair such problems is usually infeasible, developing a continuous condition monitoring model is necessary to detect anomalies and respond accordingly. In this study, a method for detecting anomalies and characterizing failures for spacecraft attitude control systems is proposed. Herein, features are extracted from multidimensional time-series data of a simulation of the attitude control system. Then, the artificial neural network learning algorithms based on two types of generation models are applied. A Bayesian optimization algorithm with a Gaussian process is used to optimize the hyperparameters for the neural network to improve the performance. The performance is evaluated based on the reconstruction error through the algorithm using the newly generated data not used for learning as input data. Results show that the detection performance depends on the operating characteristics of each submode in the operation scenarios and type of generation model. The diagnostic results are monitored to detect anomalies in operation modes and scenarios.
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http://dx.doi.org/10.3390/s20071991DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7180941PMC
April 2020

Optimal Target Assignment with Seamless Handovers for Networked Radars.

Sensors (Basel) 2019 Oct 19;19(20). Epub 2019 Oct 19.

Department of Aerospace Engineering & KI for Robotics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea.

This paper proposes a binary linear programming formulation for multiple target assignment of a radar network and demonstrates its applicability to obtain optimal solutions using an off-the-shelf mixed-integer linear programming solver. The goal of radar resource scheduling in this paper is to assign the maximum number of targets by handing over targets between networked radar systems to overcome physical limitations such as the detection range and simultaneous tracking capability of each radar. To achieve this, time windows are generated considering the relation between each radar and target considering incoming target information. Numerical experiments using a local-scale simulation were performed to verify the functionality of the formulation and a sensitivity analysis was conducted to identify the trend of the results with respect to several parameters. Additional experiments performed for a large-scale (battlefield) scenario confirmed that the proposed formulation is valid and applicable for hundreds of targets and corresponding radar network systems composed of five distributed radars. The performance of the scheduling solutions using the proposed formulation was better than that of the general greedy algorithm as a heuristic approach in terms of objective value as well as the number of handovers.
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http://dx.doi.org/10.3390/s19204555DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6832481PMC
October 2019

Three-Dimensional Laparoscopic Anatomical Segment 8 Liver Resection with Glissonian Approach.

Ann Surg Oncol 2017 Jun 24;24(6):1606-1609. Epub 2017 Jan 24.

Department of Surgery, Chungbuk National University Hospital, Cheongju, Korea.

Background: Anatomical liver resection has been reported to have oncologic benefit over nonanatomical resection in surgery for hepatocellular carcinoma (HCC). Basic concept of anatomical resection is preventing tumor spread through the portal or venous flow. Few cases have been reported for laparoscopic anatomical segment 8 resection because of its technical difficulties. This video shows operative techniques for laparoscopic anatomical resection of segment 8, exposing middle and right hepatic vein and inferior vena cava using three-dimensional video.

Methods: A 61-year-old male was diagnosed to be a hepatitis B virus carrier 6 years ago. A 6.6-cm-sized HCC lesion was detected at segment 8 by computed tomography scan. We have used a high-definition, three-dimensional laparoscope with a deflectable tip (Olympus Medical Systems Corp., Japan), a trocar inserted in the right seventh intercostal space to obtain the optimal field of view on the superior-posterior portion of the liver. Using the Glissonian pedicle approach, we isolated and clamped the branch to the segment 8 to confirm the anatomical border of the segment 8. Segmentectomy was completed exposing the middle and right hepatic vein and inferior vena cava.

Results: Operation took 420 min. Estimated blood loss was 600 mL, and no red blood cell was transfused. Final pathology was an HCC with 0.3-cm safety margin. The patient discharged on the sixth day after operation with normal liver function test results. There was no operation-related complication from the operation day to the first outpatient visit day.

Conclusions: Laparoscopic anatomical resection of segment 8 is feasible.
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http://dx.doi.org/10.1245/s10434-017-5778-6DOI Listing
June 2017

Polyarteritis nodosa presented as a dilatation of the intrahepatic bile duct.

Ann Surg Treat Res 2014 Nov 24;87(5):273-5. Epub 2014 Oct 24.

Department of Surgery, Chungbuk National University College of Medicine and Medical Research Institute, Cheongju, Korea.

Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis of small- and medium-sized arteries in multiorgan systems. PAN may affect the gastrointestinal tract in 14%-65% of patients, but rarely involves the biliary tract and liver. We describe a patient without underlying disease who was diagnosed with PAN during resection of the gallbladder and liver.
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http://dx.doi.org/10.4174/astr.2014.87.5.273DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4217254PMC
November 2014

Bowel infarction due to intestinal mucormycosis in an immunocompetent patient.

J Korean Surg Soc 2012 Nov 29;83(5):325-9. Epub 2012 Oct 29.

Department of Surgery, Chungbuk National University College of Medicine and Medical Research Institute, Cheongju, Korea.

Mucormycosis is a fatal opportunistic fungal infection that typically occurs in immunocompromised patients. The classical manifestation of mucormycosis is a rhinocerebral infection, and although primary gastrointestinal infection is uncommon, it has an extremely high mortality rate in immunocompromised patients. Furthermore, cases of gastrointestinal mucormycosis in an immunocompetent host are rarely reported. Here, we describe our experience of a male patient, with no underlying disease, who succumbed to a bowel infarction caused by intestinal mucormycosis during mechanical ventilatory care for severe pneumonia and septic shock.
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http://dx.doi.org/10.4174/jkss.2012.83.5.325DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491236PMC
November 2012
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