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ATM 비연결형 서비스 제공을 위한 선협상 동적 대역폭 관리 알고리즘
차현철(Hyunchul Cha),한기준(Kijun Han) 한국정보과학회 1995 정보과학회논문지 : 시스템 및 이론 Vol.22 No.10
본 논문에서는 ATM 망에서 비연결형 서비스를 제공하기 위한 선협상 동적 대역폭 관리 방안을 제시하였다. 이 방안에서 각 CLS 노드는 이전 노드로 부터 전진된 대역폭 변경 정보와 자신의 버퍼 상황 정보를 종합하여 필요한 대역폭을 예측하여 미리 할당하게 된다. 시뮬레이션 결과에 의하면 제안한 알고리즘이 통일 환경 하에서 기존의 알고리즘에 비해 우수한 대역폭 절감 효과와 패킷 분실율 특성을 가짐을 알 수 있었다. In this paper, we propose a pre-negotiation dynamic bandwidth management algorithm to support connectionless service in ATM networks. In this scheme. a CLS(Connectionless Server) node predicts a necessary bandwidth based on its buffer status and information on the change in the allocated bandwidth from its previous node. Simulation results show the proposed algorithm offers a better bandwidth reduction effect and a lower packet loss rate than those of the existing algorithms under the same conditions.
Cha Dong Ik,Lee Min Woo,Song Kyoung Doo,Ko Seong Eun,Rhim Hyunchul 대한영상의학회 2022 Korean Journal of Radiology Vol.23 No.2
Objective: To compare the outcomes of radiofrequency ablation (RFA) using dual switching monopolar (DSM), switching bipolar (SB), and combined DSM + SB modes at two different interelectrode distances (25 and 20 mm) in an ex vivo study, which simulated ablation of a 2.5-cm virtual hepatic tumor. Materials and Methods: A total of 132 ablation zones were created (22 ablation zones for each protocol) using three separable clustered electrodes. The performances of the DSM, SB, and combined DSM + SB ablation modes were compared by evaluating the following parameters of the RFA zones at two interelectrode distances: shape (circularity), size (diameter and volume), peritumoral ablative margins, and percentages of the white zone at the midpoint of the two electrodes (ablative margin at midpoint, AMm) and in the electrode path (ablative margin at electrode path, AMe). Results: At both distances, circularity was the highest in the SB mode, followed by the DSM + SB mode, and was the lowest in the DSM mode. The circularity of the ablation zone showed a significant difference among the three energy groups (p < 0.001 and p = 0.002 for 25-mm and 20-mm, respectively). All size measurements, AMm, and AMe were the greatest in the DSM mode, followed by the DSM + SB mode, and the lowest were with the SB mode (all statistically significant). The white zone proportion in AMm and AMe were the greatest in the SB mode, followed by the DSM + SB mode and DSM in general. Conclusion: DSM and SB appear to be complementary in creating an ideal ablation zone. RFA with the SB mode can efficiently eradicate tumors and create a circular ablation zone, while DSM is required to create a sufficient ablative margin and a large ablation zone.
3-D Locomotive and Drilling Microrobot Using Novel Stationary EMA System
Hyunchul Choi,Kyoungrae Cha,Semi Jeong,Jong-oh Park,Sukho Park IEEE 2013 IEEE/ASME transactions on mechatronics Vol.18 No.3
<P>For 3-D locomotion and drilling of a microrobot, we proposed an electromagnetic actuation (EMA) system consisting of three pairs of stationary Helmholtz coils, a pair of stationary Maxwell coils, and a pair of rotating Maxwell coils in the previous research . However, this system could have limited medical applications because of the pair of rotational Maxwell coils. In this paper, we propose a new EMA system with three pairs of stationary Helmholtz coils, a pair of stationary Maxwell coils, and a new locomotive mechanism for the same 3-D locomotion and drilling of the microrobot as achieved by the previously proposed EMA system. For the performance evaluation of the proposed EMA system, we perform a 3-D locomotion and drilling test in a blood vessel phantom. In addition, the two EMA systems are compared to show that the newly proposed EMA system has 440% wider working space and 49% less power consumption than the previous EMA system.</P>
Lee, Jang-Sik,Kim, Hyunchul,Cha, Pil-Ryung,Kim, Jiyoung,Shin, Hyunjung American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4
<P>The size effects on the stabilization of ZrO2 polymorphs in nanoscale and the growth behavior of their crystallites in 1-D nanotubular structures were investigated. Polycrystalline nanotubular structures of ZrO2 with tetragonal nanocrystallites were fabricated using nanoporous polycarbonate (PC) templates and atomic layer deposition (ALD). The as-prepared ZrO2 nanotubes showed polycrystalline structures of stabilized tetragonal polymorphs at room temperature. The wall thickness of the ZrO2 nanotubes was well controlled by the number of ALD cycles. Faster growth of the tetragonal nanocrystallites was observed in the nanotubes with a 50 nm outer diameter, than those of 200 nm. The Gibbs-Thompson relation can be used to explain the observed nanosize effects on the growth of the tetragonal ZrO2 nanocrystallites.</P>
ISO 26262을 위한 저가 MCU기반 소프트웨어 플랫폼 설계
김진우(Jinwoo Kim),차현철(Hyunchul Cha),정승연(Seungyeon Jeong),김창선(Changsun Kim),황창국(Changkook Hwang) 한국자동차공학회 2015 한국자동차공학회 부문종합 학술대회 Vol.2015 No.5
The automotive E/E system is faced with various requirements increase and the short development time. Therefore, the latest software architecture needs to design a reusable platform and a standard platform. Besides, ISO26262 and IEC 61508 require Safety mechanism. So a legacy software platform has to develop the functional safety that is defined ISO26262 and IEC 61508. In order to combine a using software platform and safety mechanisms, it is defined and analyzed failure modes of developed software platform. But to apply the safety mechanism of highly diagnostic coverage, these are composed of special HW and redundancy mechanisms. The case leads to increase the unit cost. So it is important to select compatible safety mechanisms for measuring failure modes. This paper suggests safety mechanisms that apply to a low grade MCU and design guide-lines in a development process.
전자기 구동 시스템을 이용한 마이크로로봇의 3차원 이동 및 드릴링
이걸(Jie Li),최현철(Hyunchul Choi),차경래(Kyoungrae Cha),정세미(Semi Jeong),박종오(Jongoh Park),박석호(Sukho Park) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.12
이 논문에서는 전자기구동시스템을 기반으로 이동 및 드릴링 기능을 수행하는 의료용 마이크로로봇 시스템을 제작하고 평가하였다. 마이크로로봇은 너무 작아 내부에 배터리나 제어장치를 삽입 할수없다. 이 결점을 극복하기 위하여 외부에서 전자기 코일 시스템을 이용하여 전자기장의 힘으로 마이크로로봇을 구동 시킨다. 전자기 구동 코일 시스템은 x, y, z 각축에 사각형 타입의 헬름홀쯔 코일 3 쌍과 z축에 솔레노이드형 맥스웰 코일 1 쌍이 배치 되어 있고, 각 코일에 인가되는 전류값의 조절에 따라 구동에 필요한 자기장을 발생 시킨다. 다양한 실험을 통하여 우리는 제안된 시스템을 이용하여 마이크로로봇이 3 차원 공간에서 이동 가능하며 드릴링 기능을 수행할 수 있다는 것을 보였다. In this study, a novel electromagnetic microrobot system with locomotion and drilling functions in threedimensional space was developed. Because of size limitations, the microrobot does not have actuator, battery, and controller. Therefore, an electromagnetic actuation (EMA) system was used to drive the robot. The proposed EMA system consists of three rectangular Helmholtz coil pairs in x-, y- and z-axes and a Maxwell coil pair in the z-axis. The magnetic field generated in the EMA coil system could be controlled by the input current of the EMA coil. Finally, through various experiments, the locomotion and drilling performances of the proposed EMA microrobot system were verified.