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Search Results: 1 - 10 of 4997 matches for " Yonghwan Choi "
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Preliminary Simulation of Beam Extraction for the 28 GHz ECR Ion Source
Bum-Sik Park,Yonghwan Kim,Seokjin Choi
Physics , 2015,
Abstract: The 28 GHz ECR(Electron Cyclotron Resonance) ion source is under development to supply various beams from proton to uranium at RISP(Rare Isotope Science Project). The superconducting magnet system for a 28 GHz ECR ion source consists of four solenoid coils and a saddle type sextupole. To meet the design requirement of ECR ion source, a numerical simulation was accomplished by using the KOBRA3-INP to optimize the extraction system which is the three dimensional ion optics code. The influence of the three dimensional magnetic field and the space charge effect was considered to extract the highly charged ion beam. In this paper, the design results of the extraction system were reported in detail.
Power Efficiency Calculation of Acoustic Energy Transmission by a Stepped-Plate Radiator  [PDF]
Yonghwan Hwang, Wonkyu Moon
Energy and Power Engineering (EPE) , 2017, DOI: 10.4236/epe.2017.94016
Abstract: One performance measure of in-air ultrasonic radiators, such as wireless power transmission, is the power efficiency of the transducers. The efficiency of most in-air acoustic radiators is low, even at ultrasonic frequencies; however, a large radiating plate with steps introduced by Gallego-Juarez et al., can provide efficient radiation. Their in-air acoustic radiator consists of a Langevin transducer for wave excitation, a mechanical amplifier, and a stepped plate with a large radiating area. This study describes a design processing technique for a stepped-plate radiator developed for optimum energy transmission at the target point in air. The total efficiency required to transfer the acoustic energy was divided into three categories, and the design parameters of each category were calculated to maximize the efficiency. This design technique allows optimum acoustic radiation efficiency and maximum acoustic energy transmission depending on various acoustic energy transfer conditions.
OASIS: Online Application for the Survival Analysis of Lifespan Assays Performed in Aging Research
Jae-Seong Yang, Hyun-Jun Nam, Mihwa Seo, Seong Kyu Han, Yonghwan Choi, Hong Gil Nam, Seung-Jae Lee, Sanguk Kim
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0023525
Abstract: Background Aging is a fundamental biological process. Characterization of genetic and environmental factors that influence lifespan is a crucial step toward understanding the mechanisms of aging at the organism level. To capture the different effects of genetic and environmental factors on lifespan, appropriate statistical analyses are needed. Methodology/Principal Findings We developed an online application for survival analysis (OASIS) that helps conduct various novel statistical tasks involved in analyzing survival data in a user-friendly manner. OASIS provides standard survival analysis results including Kaplan-Meier estimates and mean/median survival time by taking censored survival data. OASIS also provides various statistical tests including comparison of mean survival time, overall survival curve, and survival rate at specific time point. To visualize survival data, OASIS generates survival and log cumulative hazard plots that enable researchers to easily interpret their experimental results. Furthermore, we provide statistical methods that can analyze variances among survival datasets. In addition, users can analyze proportional effects of risk factors on survival. Conclusions/Significance OASIS provides a platform that is essential to facilitate efficient statistical analyses of survival data in the field of aging research. Web application and a detailed description of algorithms are accessible from http://sbi.postech.ac.kr/oasis.
Biologically Inspired Robotic Arm Control Using an Artificial Neural Oscillator
Woosung Yang,Jaesung Kwon,Nak Young Chong,Yonghwan Oh
Mathematical Problems in Engineering , 2010, DOI: 10.1155/2010/107538
Abstract: We address a neural-oscillator-based control scheme to achieve biologically inspired motion generation. In general, it is known that humans or animals exhibit novel adaptive behaviors regardless of their kinematic configurations against unexpected disturbances or environment changes. This is caused by the entrainment property of the neural oscillator which plays a key role to adapt their nervous system to the natural frequency of the interacted environments. Thus we focus on a self-adapting robot arm control to attain natural adaptive motions as a controller employing neural oscillators. To demonstrate the excellence of entrainment, we implement the proposed control scheme to a single pendulum coupled with the neural oscillator in simulation and experiment. Then this work shows the performance of the robot arm coupled to neural oscillators through various tasks that the arm traces a trajectory. With these, the real-time closed-loop system allowing sensory feedback of the neural oscillator for the entrainment property is proposed. In particular, we verify an impressive capability of biologically inspired self-adaptation behaviors that enables the robot arm to make adaptive motions corresponding to an unexpected environmental variety.
Validation of a Control Algorithm for Human-like Reaching Motion using 7-DOF Arm and 19-DOF Hand-Arm Systems
Tapomayukh Bhattacharjee,Yonghwan Oh,Sang-Rok Oh
Computer Science , 2013,
Abstract: This technical report gives an overview of our work on control algorithms dealing with redundant robot systems for achieving human-like motion characteristics. Previously, we developed a novel control law to exhibit human-motion characteristics in redundant robot arm systems as well as arm-trunk systems for reaching tasks [1], [2]. This newly developed method nullifies the need for the computation of pseudo-inverse of Jacobian while the formulation and optimization of any artificial performance index is not necessary. The time-varying properties of the muscle stiffness and damping as well as the low-pass filter characteristics of human muscles have been modeled by the proposed control law to generate human-motion characteristics for reaching motion like quasi-straight line trajectory of the end-effector and symmetric bell shaped velocity profile. This report focuses on the experiments performed using a 7-DOF redundant robot-arm system which proved the effectiveness of this algorithm in imitating human-like motion characteristics. In addition, we extended this algorithm to a 19-DOF Hand-Arm System for a reach-to-grasp task. Simulations using the 19-DOF Hand-Arm System show the effectiveness of the proposed scheme for effective human-like hand-arm coordination in reach-to-grasp tasks for pinch and envelope grasps on objects of different shapes such as a box, a cylinder, and a sphere.
Non-linear Task-Space Disturbance Observer for Position Regulation of Redundant Robot Arms against Perturbations in 3D Environments
Tapomayukh Bhattacharjee,Yonghwan Oh,Sang-Rok Oh
Computer Science , 2013,
Abstract: Many day-to-day activities require the dexterous manipulation of a redundant humanoid arm in complex 3D environments. However, position regulation of such robot arm systems becomes very difficult in presence of non-linear uncertainties in the system. Also, perturbations exist due to various unwanted interactions with obstacles for clumsy environments in which obstacle avoidance is not possible, and this makes position regulation even more difficult. This report proposes a non-linear task-space disturbance observer by virtue of which position regulation of such robotic systems can be achieved in spite of such perturbations and uncertainties. Simulations are conducted using a 7-DOF redundant robot arm system to show the effectiveness of the proposed method. These results are then compared with the case of a conventional mass-damper based task-space disturbance observer to show the enhancement in performance using the developed concept. This proposed method is then applied to a controller which exhibits human-like motion characteristics for reaching a target. Arbitrary perturbations in the form of interactions with obstacles are introduced in its path. Results show that the robot end-effector successfully continues to move in its path of a human-like quasi-straight trajectory even if the joint trajectories deviated by a considerable amount due to the perturbations. These results are also compared with that of the unperturbed motion of the robot which further prove the significance of the developed scheme.
The development of a culturally relevant preventive intervention  [PDF]
Heeseung Choi
Open Journal of Nursing (OJN) , 2012, DOI: 10.4236/ojn.2012.22019
Abstract: Researchers often publish the numerical findings of their intervention studies while overlooking the experiential findings that could help promote more appropriate and effective interventions in the future. The present paper describes the process by which we developed a culturally relevant preventive intervention for Korean American adolescents aged 11 to 14 years and their parents. We discuss the main findings of a series of pilot studies and demonstrated how lessons learned from each study guided the development process and informed the research that followed. Program development is an iterative process that incorporates feedback from study participants. Cultural relevance is ensured when participants’ voices are reflected in the program development, implementation, and evaluation process. The final outcome of the development process was the preventive intervention improving parent-child relationships, increasing parental knowledge, enhancing parental self-efficacy, and decreasing parental stress among Korean American parents, and ultimately promoting Korean American adolescents’ mental health. The specific aims of this two-group, repeated-measures, controlled randomized study were to test the feasibility of the PRIDE (Promoting Intergenerational Dialogue about Emotional Problems) intervention and to compare its efficacy with an attention control (AC) group regarding parental knowledge, parental and filial self-efficacy, parent-child (P-C) communication, P-C conflicts, and P-C satisfaction.
How a Proactive Interventionist Can Make Strikes More Effective: Evidence from the Korean Banking Sector  [PDF]
ChungIL Choi
American Journal of Industrial and Business Management (AJIBM) , 2013, DOI: 10.4236/ajibm.2013.34051

This paper argues, through a case study of two industry-wide strikes in the Korean banking sector, that a proactive interventionist strike is more effective than a reactive pragmatist one in a union’s response to restructuring. Evidence from the two strikes shows that unions were able to achieve more successful outcomes from the strike in which they engaged proactively by an interventionist mode. In this case the unions identified opportunities, took the initiative and devised effective strategies that pre-empted the other parties before they had fully prepared their restructuring planning. Such a strategic capacity was gained from active organizational learning in unions derived from their previous strike failure.

The Impact of Atmospheric Phenomena on South Korean Students’ Engagement at School through the Mediating Effect of the Students’ Health  [PDF]
Shelley Choi
Atmospheric and Climate Sciences (ACS) , 2018, DOI: 10.4236/acs.2018.83020
Abstract: This study examined how South Korea’s regular significant atmospheric phenomena, the yellow dust and the monsoon, affected students’ health and academic engagement at school. Five hundred middle and high school students were surveyed to figure out the atmospheric impacts on the students’ lives. The results of this study found that the severity of yellow dust and monsoon conditions experienced by the students negatively influenced their academic engagement. However, the variable of students’ concerns about their health was shown to have a mediating effect between the intensity of yellow dust and the level of academic engagement. These results indicated the need to alleviate the yellow dust and monsoon atmospheric phenomena and their effects at both the school and national levels in order to improve the academic engagement of students in South Korea.
“Smart” Surveillance of Dusty Behavior: Illuminating the Relationship between Particulate Matter and the Atmosphere  [PDF]
Shelley Choi
Computational Water, Energy, and Environmental Engineering (CWEEE) , 2018, DOI: 10.4236/cweee.2018.73008
Abstract: Although large amounts of research have been completed to find the relationship between particulate matter and climate change, they have still proven to be inadequate. Efforts to lay the foundations for understanding atmospheric chemical reactions have been repeatedly foiled by both the size and complexity of the task, which require more than the effort of a handful of researchers. Since the development of advanced physical models for dust behavior is projected to take years, what if laypeople could dramatically expedite this process by using their mobile devices as measurement tools? With relatively little effort by many individuals, previously unknown information about the earth’s atmosphere may at last become accessible thanks to recent advances in artificial intelligence. However, there are potential obstacles. Even if all technical problems are resolved, viable plans for battling particulate matter pollution will likely need to be accompanied by environmental policies. While technological breakthroughs give reason to hope for a brighter future, the resolution of global issues requires both grassroots changes and global efforts.
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