Biomimetic Swimming Mini-Robots Using Electro-Magnetic Actuation (EMA) System

Hyunchul Choi,Semi Jeong,Cheong Lee,Youngho Ko,Seong Young Ko,Jong-Oh Park,Sukho Park 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10

For the actuation of mini-robots, electromagnetic based actuation (EMA) methods were proposed. EMA system has many advantages for the wireless actuation of mini-robots. This paper introduces our proposed biomimetic swimming mini-robots such as tadpole robot and jellyfish robot. The biomimetic swimming mini-robots could be driven by an external alternating magnet field using three pairs of Helmholtz coils. The swimming mini-robots consist of a buoyant robot body, permanent magnets, and fins. Especially, the tadpole mini-robot has a single fin which is directly linked to the permanent magnet and the jellyfish mini-robot has multiple fins which have a permanent magnet at the end of fin. The external alternating magnetic field from three pairs of Helmholtz coils could generate the propulsion and steering force of the tadpole mini-robot and the jellyfish mini-robot in 2- and 3-dimensional (-D) space. Firstly, we demonstrated the fabrications of the EMA coil system and the mini-robots. Secondly, we summarized the locomotive algorithms of the mini-robots using EMA. Thirdly, we setup the control system for the EMA driven mini-robots, which consists of EMA coils, dual cameras, controller, power amplifier, and conventional joystick. Through various experiments, we evaluated the locomotion algorithms the swimming mini-robots using EMA system. Finally, we demonstrated the performances of the swimming mini-robots in 2-D and 3-D space.

Simulation and Validation of Methanol Crossover in DMFCs

고요한(Ko, Johan),주현철(Ju, Hyunchul) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.06

In direct methanol fuel cells(DMFCs), it is well known that methanol crossover severely reduces the cell performance and the cell efficiency. There are a number of design and operating parameters that influence the methanol crossover. This indicates that a DMFC demands a high degree of optimization. For the successful design and operation of a DMFC system, a better understanding of methanol crossover phenomena is essential. The main objective of this study is to examine methanol-crossover phenomena in DMFCs. In this study, 1D DMFC model previously developed by Ko et al. is used. The simulation results were compared with methanol-crossover data that were measured by Eccarius et al. The numerical predictions agree well with the methanol crossover data and the model successfully captures key experimental trends.

액자구조와 상호텍스트성의 영화

고현철(Ko, Hyunchul) 한국영화학회 2014 영화연구 Vol.0 No.60

This paper aims to investigate the type 3 in the types of ‘narrationfocalization’ that is, ‘intradiegetic narrator-fixed internal focalization (‘intradiegetic narrator-fixed internal internal focalization)’ in Hong Sang-soo’ films. The results of the investigate are summarized as the following. First, the paper investigates that Tale of Cinema, Okhee’s Film, In Another Country are related with the type 3 in the types of ‘narration-focalization’ that is, ‘intradiegetic narrator-fixed internal internal focalization(‘intradiegetic narrator-fixed internal internal focalization)’. Second, it investigates that Tale of Cinema reveals a characteristic of postmodernism, that is, “a life imitates an art” and “no border between fiction and real”. Third, it investigates that Okhee’s Film reveals a characteristic of postmodernism, that is, “intertextuality” and “no border of the texts”. Fourth, the paper argues that In Another Country reveals a characteristic of postmodernism, that is, “parody” and “similitude”. Fifth, it is claimed that the difference of between the three films that is, Tale of Cinema, Okhee’s Film, In Another Country are suited to the difference of narrative-structure and time-structure.

High-Intensity Focused Ultrasound for the Treatment of Wrinkles and Skin Laxity in Seven Different Facial Areas

( Hyunchul Park ),( Eunjin Kim ),( Jeongeun Kim ),( Youngsuck Ro ),( Jooyeon Ko ) 대한피부과학회 2015 Annals of Dermatology Vol.27 No.6

Background: High-intensity focused ultrasound (HIFU) treatment has recently emerged in response to the increasing demand for noninvasive procedures for skin lifting and tightening. Objective: This study was aimed at evaluating the clinical efficacy of and patient satisfaction with HIFU treatment for wrinkles and laxity in seven different areas of the face in Asian skin. Methods: Twenty Korean patients with facial wrinkle and laxity were analyzed after a single session of HIFU treatment. Two independent, blinded clinicians evaluated the clinical improvement in seven areas of the face by comparison of standardized photographs obtained before, and at 3 and 6 months after treatment. Assessment of subjective satisfaction and adverse effects of treatment were done by using questionnaires. Results: The physicians` evaluation and patients` satisfaction with the clinical effects of HIFU in each area were similar regardless of the number of treatment shots. The jawline, cheek, and perioral areas were the sites where HIFU was most effective, in decreasing order. The adverse effects included erythema and swelling in six cases, and purpura and bruising in two cases. However, the adverse effects were mild and transient. Conclusion: HIFU could be a safe, effective, and noninvasive procedure that can be used to improve facial wrinkles and skin laxity in Asian skin. It is particularly effective for clinical improvement in the jawline, cheek, and perioral areas. (Ann Dermatol 27(6) 688∼693, 2015)

Laparoscopic Hepatic Resection Versus Laparoscopic Radiofrequency Ablation for Subcapsular Hepatocellular Carcinomas Smaller Than 3 cm: Analysis of Treatment Outcomes Using Propensity Score Matching

Ko Seong Eun,Lee Min Woo,Ahn Soohyun,Rhim Hyunchul,Kang Tae Wook,Song Kyoung Doo,Kim Jong Man,Choi Gyu Seong,Cha Dong Ik,Min Ji Hye,Sinn Dong Hyun,Choi Moon Seok,Lim Hyo Keun 대한영상의학회 2022 Korean Journal of Radiology Vol.23 No.6

Objective: To compare the therapeutic outcomes of laparoscopic hepatic resection (LHR) and laparoscopic radiofrequency ablation (LRFA) for single subcapsular hepatocellular carcinoma (HCC). Materials and Methods: We screened 244 consecutive patients who had received either LHR or LRFA between January 2014 and December 2016. The feasibility of LRFA in patients who underwent LHR was retrospectively assessed by two interventional radiologists. Finally, 60 LRFA-feasible patients who had received LHR and 29 patients who had received LRFA as the first treatment for a solitary subcapsular HCC between 1 cm and 3 cm were finally included. We compared the therapeutic outcomes, including local tumor progression (LTP), recurrence-free survival (RFS), and overall survival (OS) between the two groups before and after propensity score (PS) matching. Multivariable Cox proportional hazard regression was also used to evaluate the difference in OS and RFS between the two groups for all 89 patients. Results: PS matching yielded 23 patients in each group. The cumulative LTP and OS rates were not significantly different between the LHR and LRFA groups after PS matching (p = 0.900 and 0.003, respectively). The 5-year LTP rates were 4.6% and 4.4%, respectively, and OS rates were 100% and 90.7%, respectively. The RFS rate was higher in LHR group without statistical significance (p = 0.070), with 5-year rates of 78.3% and 45.3%, respectively. OS was not significantly different between the LHR (reference) and LRFA groups in multivariable analyses, with a hazard ratio (HR) of 1.33 (95% confidence interval, 0.12–1.54) (p = 0.818). RFS was higher in LHR (reference) than in LRFA without statistical significance in multivariable analysis, with an HR of 2.01 (0.87–4.66) (p = 0.102). Conclusion: There was no significant difference in therapeutic outcomes between LHR and LRFA for single subcapsular HCCs measuring 1–3 cm. The difference in RFS should be further evaluated in a larger study.

Wireless Biomimetic Swimming Mini-Robots Using Electro-Magnetic Actuation (EMA) System

Hyunchul Choi,Semi Jeong,Cheong Lee,Gwangjun Go,Kiduk Kwon,Seong Young Ko,Jong-Oh Park,Sukho Park 제어로봇시스템학회 2013 제어로봇시스템학회 국제학술대회 논문집 Vol.2013 No.10

For the actuation of mini-robots, various types of electromagnetic based actuation (EMA) methods were proposed. Compared with conventional actuation system using electric motor, EMA system has many advantages for the wireless actuation of mini-robots. This paper introduces our proposed biomimetic swimming mini-robots such as tadpole robot and jellyfish robot. The developed biomimetic swimming mini-robots could be driven by an external alternating magnet field using three pairs of Helmholtz coils. The swimming mini-robots consist of a buoyant swimming mini-robot body, permanent magnets, and fins. Especially, the tadpole swimming mini-robot has a single fin which is directly linked to the permanent magnet and the jellyfish swimming mini-robot has multiple fins which have a permanent magnet at the end of fins. The external alternating magnetic field from three pairs of Helmholtz coils could generate the propulsion and steering force of the tadpole mini-robot and the jellyfish mini-robot in 2- and 3-dimensional (D) space.

Comparison of numerical simulation results and experimental data during cold-start of polymer electrolyte fuel cells

Ko, Johan,Ju, Hyunchul Elsevier 2012 APPLIED ENERGY Vol.94 No.-

<P><B>Highlights</B></P><P>► We newly developed a multiphase, transient PEFC cold start model. ► Lower current density startup results in a longer cold start operation time. ► Higher startup temperature shows longer cold start operation. ► Cell shutdown time is extended with lower initial water content.</P> <P><B>Abstract</B></P><P>A multiphase transient model is developed to investigate key physical and transport phenomena during the startup of a polymer electrolyte fuel cell (PEFC) from subzero temperatures. The proposed PEFC cold start model rigorously considers ice/frost formation and evolution in the cathode electrode, and their complicated interactions with heat transport, mass transport, and electrochemical reactions. The proposed cold start model is extensively validated against experimental data measured under various key cold start conditions such as startup temperature, startup current density, and initial water content in the membrane. The model predictions are in good agreement with the experimental data, demonstrating the validity and accuracy of the cold start model. In addition, detailed simulation results, including multidimensional contours, clearly elucidate the cold start behavior of a PEFC under different cell designs and operating conditions. We suggest that the proposed cold start model could aid in the development of optimal cold start strategies.</P>

Stable Production of Transgenic Pepper Plants Mediated by Agrobacterium tumefaciens

Ko, Moon Kyung,Soh, Hyunchul,Kim, Kyung-Moon,Kim, Young Soon,Im, Kyunghoan American Society for Horticultural Science 2007 HortScience Vol.42 No.6

<P>The aim of this study was to establish a stable transformation method for hot pepper using the hygromycin phosphotransferase (<I>hpt</I>)/hygromycin selection strategy. Explants from aseptic pepper seedlings were inoculated with <I>Agrobacterium tumefaciens</I> carrying pCAMBIA1301. A number of calli were developed on the medium containing hygromycin to discriminate the induction of “false-positive buds,” and then shoots were successfully regenerated from the hygromycin-resistant calli. Southern and Northern hybridization analysis indicated that the <I>hpt</I> gene was integrated and expressed in the transgenic pepper plants (T0) and transmitted to the progeny (T1) without genetic modification. Most T1 progenies derived from self-pollination revealed a 3:1 segregation ratio for hygromycin resistance, indicating that one copy of the T-DNA was integrated into the respective transgenic lines. Both <I>uid</I>A and <I>hpt</I> genes were stably expressed in the T1 generation and coinherited in the progenies. Finally, homozygous progenies were identified in the T1 generation of the transgenic peppers, and the homozygous state was maintained in all progenies tested (T2). The results show the reliability and stability of the <I>hpt</I>/hygromycin selection protocol for pepper transformation.</P>

The Effect of Suicide Prevention Education on Attitudes Toward Suicide in Police Officers

Yujin Ko,HyunChul Youn,Soyoung Irene Lee,Jeewon Lee,Areum Lee,Shin-Gyeom Kim 대한신경정신의학회 2021 PSYCHIATRY INVESTIGATION Vol.18 No.11

Objective This study investigated the effect of suicide prevention education on attitudes toward suicide among police officers. Methods We used an anonymous questionnaire for 518 officers and surveyed the demographic profiles and examined attitudes toward suicide utilizing the Attitudes Towards Suicide Scale (ATTS) (1=totally agree, 5=totally disagree). Our study divided participants into two groups, based on whether or not they had received suicide prevention education, and examined the differences in attitudes toward suicide between the groups. Results Of the total population, 247 (47.7%) officers had received suicide prevention education. The education group thought suicide as a predictable matter, disagreeing significantly more with the ATTS factor ‘suicide is unpredictable’ (3.36 vs. 3.35; p=0.001) compared with the no education group. Also, the education group more perceived suicide as a cry for help and at the same time disagreed more with the notion ‘suicidal thoughts will never disappear’ (2.08 vs. 2.26; p=0.025, 3.2 vs. 3.05; p=0.035, respectively). Conclusion Officers with experience in suicide prevention education showed more positive attitude toward suicide and suicide prevention. These findings suggest a need to organize more opportunities of suicide prevention educations, such as making the training mandatory for police officers.

Three-Dimensional Swimming Tadpole Mini-Robot using Three-Axis Helmholtz Coils

Choi, Hyunchul,Jeong, Semi,Lee, Cheong,Park, Bang Ju,Ko, Seong Young,Park, Jong-Oh,Park, Sukho 제어로봇시스템학회 2014 Transaction on control, automation and systems eng Vol. No.

Electromagnetic-actuated robotic systems have been studied recently for special purposes. Because these systems use external magnetic fields to control their robots, the robots can have simple structures and move with much freedom. In particular, these electromagnetic actuation (EMA) systems are being widely adopted for the actuation of biomedical mini-robots and microrobots for minimally invasive surgery (MIS) and diagnosis. We previously reported, as a feasible biomedical robot, the biomimetic swimming tadpole mini-robot, which can only swim above water. Indeed, the two-dimensional (D) plane swimming tadpole mini-robot is limited in its use because of its motility in the 2D plane. Therefore, this paper proposes a 3D swimming tadpole mini-robot that can move freely in water. First, in the proposed 3D swimming tadpole mini-robot, the buoyancy force was regulated for subaqueous swimming, and the permanent magnet was rearranged for precise movement. Second, to attain a 3D swimming motion, the actuation mechanism of the robot was developed using an EMA system. Finally, various experiments verified that the proposed 3D swimming tadpole mini-robot can swim freely in a 3D water environment.