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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.
Youngsu Kim,Jee Hyun Ma 한국영어어문교육학회 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.
The Effects of Purposeful Reading on Reading Comprehension and Task Motivation
Youngsu Kim,Jee Hyun Ma 한국영어어문교육학회 2014 영어어문교육 Vol.20 No.2
This study examined the effects of purposeful reading on reading comprehension and task motivation. Specifically, this study investigated whether purposeful reading could increase reading comprehension ability and students' task motivation through the comparison between purpose and no-purpose groups. Fifty eight 3rd-year middle school students participated in the study and were randomly assigned to one of either the purposeful (N=26) or the non-purposeful reading groups (N=32). The learners' reading comprehension was measured through three posttests, and their general motivation level toward English learning and task-specific motivation were also checked using questionnaires. The results demonstrated that purposeful reading played a positive role in reading comprehension especially when reading texts were more challenging for the learners. The results also revealed that the purpose group students showed a significantly higher level of task motivation than those in the no-purpose group even though the two groups displayed a similar level of general motivation toward English learning initially. The findings provided Korean EFL middle school students' characteristics and task motivation with regard to purposeful reading, and suggested pedagogical implications to pursue reading proficiency and task motivation enhancement.
A Study on Korean First Year High School Students` Compliment Responses Strategies
Youngsu Kim,Chul Joo Uhm 언어과학회 2014 언어과학연구 Vol.0 No.69
This research investigated how differently Korean first year high school students respond to compliments in Korean and in English depending on L2 proficiency, gender, and addressee`s social status. For this study, 54 students responded to a questionnaire consisting of six questions both in English and in Korean. Through this questionnaire survey, we investigated how differently the participants respond to compliments when they use English and Korean respectively. The results showed that a difference between Korean and English positive responses to compliments was minimal. However, the participants used more ‘accepting’ responses in English than in Korean, and high-level high school learners of English showed more ‘accepting’ responses than low-level high school learners of English. On the other hand, there was only a slight difference between male students and female students in compliment responses, but there was a considerably substantial difference between compliment responses to older people and to their friends, especially in terms of ‘accepting.’ Pedagogical implications related to these results have also been discussed.
The Effects of Purposeful Listening on Listening Proficiency and Task Motivation
( Youngsu Kim ),( Jee Hyun Ma ) 글로벌영어교육학회(구 호남영어교육학회) 2015 Studies in English education Vol.20 No.1
This study explored whether purposeful listening could have a positive impact on listening comprehension (L/C) ability and learners’ task motivation. Ninety-three high school students participated in this study and were assigned to either the purpose group or the no-purpose group. The participants’ L/C was measured through four L/C tests, and their trait motivation and task-specific motivation were also measured by using two types of questionnaires. In the first L/C test, the purpose group showed a bit numerically higher test scores but the result was not significant. However, in the following three L/C tests the purpose group displayed significantly higher test scores than the no-purpose group, showing the benefits of purposeful listening on improving learners’ listening proficiency. As for the learners’ motivation, the two groups initially indicated a similar level of general motivation toward English learning in the trait motivation survey. Yet, the purpose group displayed significantly higher levels of task motivation than the no-purpose groups in the task motivation surveys, suggesting that learners’ motivation is changeable depending on task conditions. These results showed the necessity of clear and purposeful task presentation in classroom settings to improve L2 learners’ listening proficiency and to enhance their task motivation.
( Youngsue Kim ),( Hyundong Jang ),( Seungjee Hong ),( Sounghun Kim ) 한국농업경제학회 2015 KOREAN JOURNAL OF AGRICULTURAL ECONOMICS(KJAT) Vol.56 No.3
Korean government has promoted agricultural companies to enlarge the size of management system in farm level, and thus korea has many large-size agricultural companies including 95 mandatory audited agricultural mandatory audited agricultural companies. The mandatory audited agricultural companies are located at the highest level of agricultural companies, and whether the management of mandatory audited agricultural companies are efficient or not is the one of the most important issues. The purpose of this paper is to analyze the management efficiency of mandatory audited agricultural companies, through the DEA(Data Envelopment Analysis) and WMW (Wilcoxon- Mann-Whitney) rank test. The results of analyses present that the external audit agriculture company need to increase the input with the improvement of technology. It’s also found that management number of years, education and training costs, the increase in advertising expenses offer a positive impact on the management efficiency of the external audit agriculture company. These findings in this paper may offer some policy implications for Korean government.