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Kim, Changho,Ko, Youngsu,Kim, Taemin,Yoo, Chan-Sei,Choi, BeomJin,Han, Seung Ho,Jang, YongHo,Kim, Youngho,Kim, Namsu Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.22 No.2
Increasing interest in prognostics and health management has heightened the need for wireless sensor networks (WSN) with efficient power sources. Piezoelectric energy harvesters using Pb(Zr,Ti)O3 (PZT) are one of the candidate power sources for WSNs as they efficiently convert mechanical vibration energy into electrical energy. These types of devices are resonated at a specific frequency, which has a significant impact on the amount of energy harvested, by external vibration. Hence, precise prediction of mechanical deformation including modal analysis of piezoelectric devices is crucial for estimating the energy generated under specific conditions. In this study, an experimental vibrational system capable of controlling a wide range of frequencies and accelerations was designed to generate mechanical vibration for piezoelectric energy harvesters. In conjunction with MATLAB, the system automatically finds the resonance frequency of harvesters. A small accelerometer and non-contact laser displacement sensor are employed to investigate the mechanical deformation of harvesters. Mechanical deformation under various frequencies and accelerations were investigated and analyzed based on data from two types of sensors. The results verify that the proposed system can be employed to carry out vibration experiments for piezoelectric harvesters and measurement of their mechanical deformation.
Changho Kim,Youngsu Ko,Taemin Kim,유찬세,BeomJin Choi,한승호,YongHo Jang,Youngho Kim,Namsu Kim 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.2
Increasing interest in prognostics and health management has heightened the need for wireless sensor networks (WSN) with efficient power sources. Piezoelectric energy harvesters using Pb(Zr,Ti)O3 (PZT) are one of the candidate power sources for WSNs as they efficiently convert mechanical vibration energy into electrical energy. These types of devices are resonated at a specific frequency, which has a significant impact on the amount of energy harvested, by external vibration. Hence, precise prediction of mechanical deformation including modal analysis of piezoelectric devices is crucial for estimating the energy generated under specific conditions. In this study, an experimental vibrational system capable of controlling a wide range of frequencies and accelerations was designed to generate mechanical vibration for piezoelectric energy harvesters. In conjunction with MATLAB, the system automatically finds the resonance frequency of harvesters. A small accelerometer and non-contact laser displacement sensor are employed to investigate the mechanical deformation of harvesters. Mechanical deformation under various frequencies and accelerations were investigated and analyzed based on data from two types of sensors. The results verify that the proposed system can be employed to carry out vibration experiments for piezoelectric harvesters and measurement of their mechanical deformation.
Usefulness of Goal Attainment Scaling in Intensive Stroke Rehabilitation During the Subacute Stage
Youngsu Jung,Jaehoon Sim,Joonhyun Park,Jongmoon Kim,MinYoung Kim 대한재활의학회 2020 Annals of Rehabilitation Medicine Vol.44 No.3
Objective To investigate the usefulness of goal attainment scaling (GAS) in intensive stroke rehabilitation during the subacute stage. Methods Medical records of subacute post-stroke patients who had undergone intensive rehabilitation under hospitalization, before and after the application of GAS, were collected. GAS was conducted at the initial evaluation of each patient. Specific goals were suggested by physical and occupational therapists and were determined by the responsible physiatrist. A 5-point scale was used for the GAS score after 4 weeks of rehabilitation according to the preset criteria of each goal. To evaluate the influence of GAS in rehabilitation practice, functional improvements were compared between two patient groups before (n=121) and after (n=141) GAS. To assess progress in GAS practice, the standard GAS score was calculated, and the changes were observed over a 3-year period. The standard GAS score converged to 50 points when the goal was achieved. The therapists who used GAS also completed a survey regarding its usefulness. Results There were no statistical differences in the motor and cognitive outcomes of the patient groups before and after applying GAS scoring. Successive yearly changes in the standard GAS scores showed progressive convergence to 50 points, signaling that the patient’s goal-setting abilities improved. According to the survey, most therapists felt that GAS enhanced the quality of therapies (84.6%). Conclusion GAS improved goal-setting for the rehabilitation of subacute post-stroke patients and might have a positive effect on rehabilitation.
A Study on the Effects of a TETE Class on English Learners’ Motivation and Anxiety
( Youngsu Kim ),( Young Ah Cho ) 대한언어학회 2018 언어학 Vol.26 No.2
The Linguistic Association of Korea Journal, 26(2), 107-131. This study investigates the effects of a TETE (Teaching English through English) class on English learners’ motivation and anxiety based on gender and English proficiency. 207 first-year high school students participated in this study and were assigned to low-, mid-, and high-level groups according to their proficiency. In the study, a background questionnaire, an English motivation questionnaire, an English anxiety questionnaire, and National United Achievement Tests were employed. The results showed that there were no significant differences between the females and the males in the four motivation components, except for the self-determination component, while significant differences were found in all motivation components among the three levels. The findings also revealed that there were significant gender differences in speaking and other types of anxiety, and they were displayed among the levels. Based on these findings, ways for English teachers to lead their TETE classes effectively and their roles in the classes are suggested. Pedagogical implications are also discussed in detail.
Kim, Youngsu,Ma, Jee Hyun The English Teachers Association in Korea 2011 영어어문교육 Vol.17 No.3
This study examined the effects of collocation-based instruction on L2 vocabulary acquisition and learners' interests in it. Fifty one students were randomly assigned to the experimental group (collocation-based instruction group) and to the control group. The participants' English vocabulary capacity was checked through pre and post tests, and two surveys were used to probe the learners' vocabulary learning behaviors and their interests in English vocabulary learning respectively. To better understand the participants' opinions and feelings on the collocation-based learning, follow-up interviews were also carried out. The results showed that second language (L2) learners' vocabulary capacity was significantly improved through collocation-based instruction. However, the participants' degree of interest in vocabulary learning did not reach our expectation partly because of external factors such as the Test for the College Scholastic Ability Test (CSAT) and lack of familiarity of collocations. Such results indicate that the high school students' rooted perception of putting importance on test-based language learning could not be easily changed since it is closely related to their immediate needs. Based on the results, this study suggested how to implement collocations into L2 classrooms effectively.
( Youngsu Kim ),( Jee Hyun Ma ) 글로벌영어교육학회(구 호남영어교육학회) 2016 Studies in English education Vol.21 No.1
This study aims to explore whether purposeful reading instruction influences Korean high school L2 learners’ reading comprehension, task motivation, and perceived difficulty in EFL settings employing both qualitative and quantitative approaches. Ninety-one high school students participated and were assigned to either the purpose group (N=48) or the non-purpose group (N=43). The purpose group was given purpose-specific reading explicitly by the instructor, but not the non-purpose group. The participants were engaged in reading tasks along with reading comprehension tests and questionnaires on task motivation and their perceived difficulty. This study was conducted once a week over a period of four months, thirteen times in total. All the participants completed thirteen reading tasks including pre-, immediate, and delayed reading comprehension tests and questionnaire surveys. After completing the tasks, the participants answered exit surveys asking their opinions and feelings on the tasks. The results show that purposeful reading instruction has a positive impact on L2 learners’ reading comprehension, task motivation, and perceived difficulty, revealing the benefits of purposeful reading instruction to L2 learners in EFL classroom settings.
Kim, YoungSu,Kim, GwangSeok,Lee, SangYul American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.10
<P>In this study, CrZrN films were synthesized by unbalanced magnetron sputtering (UBM) under various N2 partial pressures and their characteristics such as crystalline structure, surface morphology, microstructure and mechanical properties as a function of the N2 partial pressures were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, wear tests, and corrosion tests. Results revealed that, with increasing the N2 partial pressure from 0.05 to 0.21 Pa, the nitrogen content of the films increased from approximately 40.9 to 53.7 at%, the deposition rate decreased from approximately 100 to 59 nm/min and the surface roughness (Rms value) was increased from approximately 0.57 to 1.79 nm. The Cr37.3-Zr9.0-N53.7 film has the highest hardness, elastic modulus, and plastic deformation resistance of 36 GPa, 380 GPa, and 0.41, respectively. The Cr37.3-Zr9.0-N53.7 film also has the lowest friction coefficient and wear rate of 0.19 and 3.01 (10(-6)m3/Nm) at room temperature. In addition, the potentiodynamic test results showed the corrosion resistance of the CrZrN films became increased significantly and their corrosion current density (i(corr)), corrosion potentials (Ecorr) and corrosion rate decreased with increasing N2 partial pressure.</P>