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Proportional Navigation-Based Collision Avoidance for UAVs
한수철,유창선,방효충 제어·로봇·시스템학회 2009 International Journal of Control, Automation, and Vol.7 No.4
A collision avoidance algorithm for unmanned aerial vehicles (UAVs) based on the conventional proportional navigation (PN) guidance law is investigated. The proportional navigation guidance law being applied to a wide range of missile guidance problems is tailored to the collision avoidance of UAVs. This can be accomplished by guiding the relative velocity vector of the aircraft to a vector con-necting the current aircraft position to the safety boundary of the target aircraft. Stability of the pro-posed algorithm is also studied using the circle criterion. The stability condition can be established by choosing the navigation coefficient within a certain bound. The guidance law is extended to 3-dimensional maneuver problems. Inherent simplicity and robustness of the PN guidance law provides satisfactory collision avoidance performance with different initial conditions.
k-중앙개체 군집방법을 이용한 한국 프로농구선수의 군집화
한수철,전수영,진서훈 한국자료분석학회 2008 Journal of the Korean Data Analysis Society Vol.10 No.6
주어진 데이터의 개체들을 비슷한 특징을 가지는 소그룹으로 나누어 그 그룹들의 특징이나 대표성을 찾는 분석 과정을 군집분석이라고 한다. 군집분석은 크게 분리 군집방법과 계층적 군집방법으로 구분할 수 있다. 본 연구에서는 계층적 군집방법을 이용하여 군집의 수를 정하고, 분리 군집방법 중 하나인 k-중앙개체 군집방법을 적용하여 한국 프로농구선수들의 군집화를 시도해 보았다. 프로농구선수들의 데이터는 몇몇 변수들에 있어 특이치가 존재하기 쉽다. 따라서 이런 경우에는 특이치에 영향을 크게 받는 k-평균 군집방법을 적용하는 것보다는 특이치에 덜 민감한 k-중앙개체 군집방법의 활용이 좋은 결과를 줄 수 있다. k-중앙개체 군집방법의 구현을 위해 PAM(partitioning around medoids) 알고리즘을 이용하였다. 군집분석결과 3개의 군집으로 선수들을 군집화하였고, 각 군집의 특징을 파악하였다. Cluster analysis is one of statistical methods for finding groups so that objects in the same group are similar each other and objects in the different group are dissimilar. There are two distinctive techniques in cluster analysis. One is hierarchical method the other is partitioning method. In this study, we built the clusters from the data of korean professional basketball players. The hierarchical method was used for finding the proper number of clusters and k-medoids clustering which is one of partitioning method was used for building clusters. The professional basketball players data generally has outliers in several variables. Therefore, instead of applying k-means clustering for this kind of data, k-medoids clustering which is not affected a lot by outliers can give a better result than that of k-means clustering. In order to implement k-medoids clustering PAM(partitioning around medoids) algorithm was used. The resulting clusters are obtained as three distinguished clusters and the characteristics of each cluster are summarized.
한수철,전수영,진서훈 한국자료분석학회 2009 Journal of the Korean Data Analysis Society Vol.11 No.2
Since Korea National Statistical Office has a main roll of statistical system in Korea, the central government has good quality of production in statistics. However, self- government dose not have capacity for producing various types of regional statistics. In accordance with the requirements for regional statistics, we have studied the problems of regional statistics. We have also analyzed the relevance of regional statistics with regional strategic industries. Only 49.6 workers, in average, are related to production of statistics in city or province. There are not enough regional statistics for regional strategic industries. In order to improve the level of the regional statistics human resource has to be reinforced for producing regional statistics. Also, statistics related workers have to improve their capability and Korea National Statistical Office should support the production of regional statistics. Government, university, and institute can work together for producing practically useful regional statistics. 우리나라의 통계제도는 통계청을 중심으로 집중화되어 있어 중앙정부의 통계생산체계와 질은 상당한 수준에 올라올 수 있었지만, 지방자치단체의 경우는 지역발전에 필요한 다양한 통계생산은 물론 기본적인 자료의 축적마저도 미비한 것이 현실이다. 본 연구에서는 지역통계의 통계작성활동 현황, 지방자치단체의 통계조직과 인력구성 등의 현황을 분석하고 지역통계의 문제점을 살펴보았다. 또한 지역별 전략산업과 관련한 통계생산을 분석하고 지역특성통계의 현황을 파악하였다. 2008년 9월 기준으로 광역시․도의 본청 내 통계를 담당하고 있는 직원 수는 총 794명으로 평균 49.6명으로 광역시․도의 규모를 고려할 때 매우 적은 수이며 지역전략산업과 연관된 통계의 생산수준이 미흡한 것으로 파악되었다. 효과적인 지역경제사회의 개발정책수립을 뒷받침하고 지역통계자료를 체계적으로 생산, 공급할 수 있도록 지역통계를 발전시키기 위해서는 통계담당인력을 확충하고 통계담당인력의 전문성을 제고하며 통계청의 지역통계개발에의 적극적인 지원이 필요하다. 또한 관․학․연간 협력을 통해 보다 실제적으로 필요한 통계를 생산해 내야 할 것이다.
Evaluation of Various Deformable Image Registrations for Point and Volume Variations
한수철,이순성,김미숙,지영훈,김금배,최상현,박승우,정해조,유형준,이철영 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.1
The accuracy of deformable image registration (DIR) has a significant dosimetric impact in radiation treatment planning. Many groups have studied the accuracy of DIR. In this study, we evaluated the accuracy of various DIR algorithms by using variations of the deformation point and volume. The reference image (Iref ) and volume (Vref ) were first generated by using virtual deformation QA software (ImSimQA, Oncology System Limited, UK). We deformed Iref with axial movement of the deformation point and Vref , depending on the type of deformation (relaxation and contraction) in ImSimQA software. The deformed image (Idef ) and volume (Vdef ) acquired by using the ImSimQA software were inversely deformed relative to Iref and Vref by using DIR algorithms. As a result, we acquired a deformed image (Iid) from Idef and volume (Vid) from Vref . Four intensity-based algorithms were tested by following the horn-schunk optical flow (HS), iterative optical flow (IOF), modified demons (MD) and fast demons (FD) with the Deformable Image Registration and Adaptive Radiotherapy Toolkit (DIRART) of MATLAB. The image similarity between Iref and Iid was calculated to evaluate the accuracy of DIR algorithms using by Normalized Mutual Information (NMI) and Normalized Cross Correlation (NCC) metrics, when the distance of point deformation was moved 4 mm, the value of NMI was above 1.81 and that of NCC was above 0.99 in all DIR algorithms. As the degree of deformation was increased, the degree of image similarity decreased. When the Vref was increased or decreased by about 12%, the difference between Vref and Vid was within ±5% regardless of the type of deformation, the deformation was classified into two types: deformation 1 increased the Vref (relaxation) and deformation 2 decreased the Vref (contraction). The value of the Dice Similarity Coefficient (DSC) was above 0.95 in deformation 1 except for the MD algorithm. In the case of deformation 2, the value of the DSC was above 0.95 in all DIR algorithms. The Idef and the Vdef were not completely restored to Iref and Vref , and the accuracy of the DIR algorithms were different, depending on the degree of deformation. Hence, the performance of DIR algorithms should be verified for the desired applications
한수철,김유신,표명호 대한화학회 2016 Bulletin of the Korean Chemical Society Vol.37 No.11
A reduced graphene oxide/disodium terephthalate (RGO/DST) composite was prepared via ultrasonic-assisted co-precipitation. The ultrasonication of an azeotropic H2O/acetonitrile solution at elevated temperature induced simultaneous precipitations of RGO and DST with solvent evaporation. RGO/DST, collected before complete evaporation, showed that the DST was in a well-dispersed state between the graphene layers of the RGO, giving the RGO/DST a more densely stacked microstructure. When applied as an anode for sodium ion batteries (SIBs), the RGO/DST revealed an enhancement in Na+-storage capability, relative to composites prepared via simple evaporation (E-RGO/DST) and mechanical mixing (M-RGO/DST). The RGO/DST delivered a reversible capacity of 422 mAh/g at a charge/discharge (C/D) rate of 50 mA/g, in contrast to 368 and 303 mAh/g for E-RGO/DST and M-RGO/DST, respectively. The superiority of the RGO/DST was maintained during repeated cycles. With an increase in the current densities, however, the reversible capability of the RGO/DST was decreased more substantially than that of the M-RGO/DST. Since Na+ diffusivity was greater in the RGO/DST than in the M-RGO/DST, this glitch in the high-rate performance of RGO/DST was considered because of a high level of charge-transfer impedance, in which a dense microstructure hampered the structural change of DST during reduction and oxidation.