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Return Intervals Analysis of the Korean Stock Market
양재석,Woong Jeon,문희태,오갑진,정우성 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3
We analyze the return intervals in Korean stock prices. While scaling and memory effects prevail in mature markets, such as the US and Japanese markets, the Korean market does not exhibit the scaling effect, but rather the memory effect. Multiscaling behavior appears as well. Interestingly,the return interval distribution of the Korean market shows neither a stretched exponential nor an exponential distribution. We propose that the features we have found can be a distinct feature of the Korean market.
양재석,박재형,오범환,박세근,이승걸 한국광학회 2016 Current Optics and Photonics Vol.20 No.5
In this paper, we propose a novel differential equation method for designing a total internal reflection(TIR) LED lens with double freeform surfaces. A complete set of simultaneous differential equations forthe method is derived from the condition for minimizing the Fresnel loss, illumination models, Snell’sLaw of ray propagation, and a new constraint on the incident angle of a ray on the light-exiting surfaceof the lens. The last constraint is essential to complete the set of simultaneous differential equations. Byadopting the TIR structure and applying the condition for minimizing the Fresnel loss, it is expected thatthe proposed TIR LED lens can have a high luminous flux efficiency, even though its beam-spread angleis narrow. To validate the proposed method, three TIR LED lenses with beam-spread angles of less than22.6° have been designed, and their performances evaluated by ray tracing. Their luminous flux efficienciescould be obviously increased by at least 35% and 5%, compared to conventional LED lenses with a singlefreeform surface and with double freeform surfaces, respectively.
렌즈 최적설계에 있어 Merit Function 구성이 최적화 성능에 미치는 영향
양재석,박혜민,김대찬,오범환,박세근,이일항,이승걸 한국조명·전기설비학회 2012 한국조명·전기설비학회 학술대회논문집 Vol.2012 No.10
In the optimal design of an illumination LED lens with complex type, the influence of merit function on the lens performance was numerically analyzed, and the best merit function for satisfying an illuminance requirement was estimated. The lens was assumed to have freeform surfaces. Simulated annealing method was applied for the optimization, and merit function was composed of an ray arrival rate, a luminous flux efficiency, and an illuminance uniformity. From the analysis it was found that the composition ratio of the illuminance uniformity was the most sensitive to the performance of the optimized lens.
Perceptions of preservice teachers on AI chatbots in English education
양재석 한국인터넷방송통신학회 2022 International Journal of Internet, Broadcasting an Vol.14 No.1
With recent scientific advances and growing interest in AI technologies, AI-based chatbots have been viewed as a practical learning aid for English language development. The purpose of this study is to examine preservice teachers' perceptions on the potential benefits of employing AI chatbots in English instruction and its pedagogical aspects. 28 preservice teachers majoring in English education were asked to use Kuki chatbots for a week with a guidance of a researcher and then report on their perceptions of AI chatbots in terms of perceived usefulness after use, applicability, and educational benefits and drawbacks. Emerging codes and themes were identified and evaluated using Thematic Analysis(TA) based on qualitative data from surveys and interviews. The findings show that six emerging themes were identified, encompassing perspectives on teacher, learner, communication, linguistic, affective, and assessment. The overall findings of this study revealed that AI-based chatbots can play a significant role as learning tools for stimulating interactive communication in a target language. Most preservice primary teachers acknowledge that AI chatbots can be useful as teaching and learning aids for both teachers and students. Furthermore, when applying various learner data to chatbot technology, such as learner assessment and diagnosis, a guided approach is necessary to perform a conversation appropriate for the learner's level and characteristics. Finally, as chatbots have a variety of benefits in terms of affective aspects, they may improve EFL learners' confidence in speaking English and learning motivation.
ESL Students’ Vocabulary Learning Strategies in L2 Verbal Skills
양재석 현대영미어문학회 2015 현대영미어문학 Vol.33 No.4
This study investigated vocabulary learning strategies in L2 listening and speaking, drawing on the 432 tertiary level ESL participants. It yielded factors underlying vocabulary learning strategies related to L2 verbal skills. Based on the results of factor analysis, the relationship between the identified factors and vocabulary proficiency level was also examined. The results revealed statistically distinct underlying constructs in strategies for both skill areas. In addition, memory & L1-oriented resource strategies and compensation strategies were employed more frequently in listening by learners with low and mid-level proficiency than by those with high-level. Moreover, in speaking, high proficiency learners used both direct translation & make-up strategies and memory strategies less frequently than did the other two groups. The findings imply that ESL learners ought to be provided with focused training on vocabulary learning strategies tied to listening and speaking, depending on their vocabulary proficiency.