• Communications for Statistical Applications and Methods
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• 제31권2호
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• pp.203-212
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• 2024

The area under the ROC curve (AUC) is one of the most common criteria used to measure the overall performance of binary classifiers for a wide range of machine learning problems. In this article, we propose a L₁-penalized AUC-optimization classifier that directly maximizes the AUC for high-dimensional data. Toward this, we employ the AUC-consistent surrogate loss function and combine the L₁-norm penalty which enables us to estimate coefficients and select informative variables simultaneously. In addition, we develop an efficient optimization algorithm by adopting k-means clustering and proximal gradient descent which enjoys computational advantages to obtain solutions for the proposed method. Numerical simulation studies demonstrate that the proposed method shows promising performance in terms of prediction accuracy, variable selectivity, and computational costs.

• 대한한의학회지
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• 제20권4호
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• pp.39-49
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• 2000

This study was conducted to prove that there exists a relation between the spleen and learning and memory as Oriental medicine believesTo promote the function of the Spleen, Guibitang was administered to rats in this study. Rats were 250～300g Sprague-Dawley, and were divided into three groups. One was the normal group without any pretreatment. Another was the control group which was administered normal saline and the abdominal injection of L-NAME before learning and memory test. And the 3rd was the sample group, to which was administered Guibitang extract and (no 'the') abdominal injection of L-NAME before the learning and memory test. Each group was made up of 12 rats. Morris water maze and radial arm maze tasks were performed in the learning test and Morris water maze task in the memory test. For 2 days to evaluate the ability of learning in the Morris water maze, 16 trials were carried out and first latency(lapse time to find the escape platform for the first time) was measured. The next day, to evaluate the ability of memory, the escape platform was eliminated from the maze, and total path, target entry number, first latency and memory score were measured. 48hrs before the radial arm maze task was performed, bait was deprived from each group. After learning test, bait was permitted to each group. So 85% of the body weight was maintained for 6 days of the test. Each of the eight arms was baited; correct choice numer and error were counted; each trial was finished when the rat had entered each of the eight arms, or more than 10 minutes had elapsed. The results were as follows: In the learning test, the first latency of the sample group in the Morris water maze showed evident improvement of learning compared to control group at the 11th, 12th, 13th trial of 16 trials, and correct choice number in radial arm maze showed noticeable improvement compared to the control group at 3rd, 4th and 5th; In the memory test, the memory score of the sample group showed evident improvement compared to the control group. From the above results, the administration of Guibitang, which tonifies the function of the Spleen, could enhance the ability of learning and memory. So it was suggested that the Spleen has a relation with learning and memory.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2007년도 한국음성과학회 공동학술대회 발표논문집
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• pp.288-291
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• 2007

The aim of this study is to clarify degrees of difficulty of the Japanese L2 (second language) learners for learning Korean sounds and phonological rules. 31 subjects took a questionnaire survey and an identification test using words. In addition, each subject's pronunciation was evaluated by 3 Korean native speakers. As for Korean sounds, the results show that Japanese L2 learners have a tendency perceiving that listening is more difficult than pronouncing, although the listening test's scores were greater than the pronunciation test's scores for a majority of the items. As for Korean phonological rules, 1) there were some difficult items for applying the phonological rules, although Japanese L2 learners had knowledge of them, and 2) there were also some items that Korean native speakers evaluated Japanese L2 learners' pronunciations as the phonological rules were applied, even though learners pronounced them without any knowledge.

• 영어어문교육
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• 제9권2호
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• pp.133-149
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• 2003

As the world becomes a global village, national conferences become more frequent, and the language of choice to mediate the exchange of information is English. Accordingly, the purpose of this research is to find several methods to prepare L2 students for English communication at conferences. Various studies about discourse markers can be found in this study. Discourse markers are indicators of fluency in spoken language, and indicators of improvement from features of spoken English to more typical forms of formal writing. In this study the presentation styles of native speakers and Asian non-native speakers are compared, and the difference between efficient and non-efficient speakers at conferences are discussed. As a study of conference English teaching and learning method, this research targets suggestion and application of discourse markers for L2 speakers. As a result, the fact that discourse markers are very important in effective writing and conference English is found and accordingly we can see that developing the ability to use discourse markers in writing and speaking are essential for L2 speakers.

• 한국어교육
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• 제28권2호
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• pp.1-36
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• 2017

This study investigated the correlation between learners' psychological and social factors and their syntactic complexity of speaking. The study collected samples of Korean spoken production of 61 learners with English, Chinese, Japanese and other L1 backgrounds and applied mini-TOPIK, mini-AMTB, and SASIQ for 70 minutes. The study found that: (i) integrative motivation showed positive correlation with a number of simple complex clauses, but instrumental motivation correlated negatively with a number of adverbial clauses, indicating that high motivation hindered producing highly complex clauses although it triggered producing simple complex clauses, (ii) social contact with L2 native speakers showed positive correlation with general L2 development and a number of simple complex clauses, but revealed negative correlation with double or triple complex clauses, (iii) hours of L2 listening showed very strong positive correlation with producing triple complex clauses and general proficiency, but indicated negative correlation with a number of simple complex clauses. The study reported that high motivation toward Korean learning and active social activities with Korean native speakers helped produce simple complex clauses while hours of listening to Korean helped produce triple complex clauses.

• 디지털융복합연구
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• 제18권6호
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• pp.99-108
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• 2020

본 연구는 초급반 L2 쓰기 수업에서 번역기의 사용 현황을 조사하고, 그들이 응답한 번역기의 필요성, 신뢰도, 한계를 통해 그 타당성을 조명하고자 했다. 대학에서 초급 L2 수업을 수강한 117명의 학생이 설문조사에 참여했고, 그 가운데 11명은 추가적으로 실시된 심층면접에서 응답 내용을 설명했다. 수집된 자료에서 쓰기 수업에 활용된 번역기의 신뢰 정도, 효과, 사용 범위 등에 대한 다양한 관점들이 제시되었다. 응답자의 76.1%가 쓰기 활동에서 나름대로의 방법과 목적을 가지고 번역기를 사용하고 있었다. 그들은 번역기를 통해 부족한 영어 능력을 보완했고, 그 과정에서 수업참여의 동기와 자신감이 고취되었다고 설명했다. 반면에, 학생들은 부정확한 기계번역을 검토와 수정이라는 중요한 학습 과정을 생략한 채 그대로 옮겨 쓰게 된다면 학습 효과도 없을 뿐 아니라 표절행위가 될 수 있음을 지적했다. 그럼에도 불구하고 번역기는 이 시대에 새롭게 등장한 효율적인 학습 도구이며 효과적이고 완성도 있는 글쓰기를 위해 활용될 가치가 있는 것으로 나타났다.

• 영어어문교육
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• 제12권1호
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• pp.1-27
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• 2006

This study investigated how EFL readers critically read texts which are written in English. Although critical reading has been discussed in advanced EFL and ESL contexts there has not been much research on the critical reading of beginning EFL learners. Many educators are recommending that a critical perspective be adopted so that L2 learners can become empowered rather than indoctrinated. In this study, the researcher has examined the critical reading practices of five beginning level EFL readers in Korea and five first language readers of English in the United States as they read a news editorial article. The significant findings were discussed related to critical reading practice of L2 readers. The findings of the study can help the educators in English education in improving the curriculum, the teaching methodology and the learning theory for EFL reading for critical reading.

• 음성과학
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• 제12권1호
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• pp.75-87
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• 2005

In this study I investigate how native Korean listeners perceive English vowels /i/, /I/, and /$\epsilon$/. I extend Flege et al's (1997) study with synthesized /i/-/I/ and /I/-/$\epsilon$/ continua, and apply the results to Flege's (1995) Speech Learning Model (SLM). The statistical results show that native speakers of English rely more on spectral steps than on vowel duration when they identify the /i/-/I/ continuum, whereas native speakers of Korean rely more on vowel duration than on spectral steps when they identify the same continuum. In the case of the /I/-/$\epsilon$/ continuum, both groups rely on spectral steps when they identify the /$\epsilon$/, which supports the SLM; Koreans identified the /$\epsilon$/ categorically since Korean has the equivalent vowel. However, there was not statistical difference between Korean subjects with more English experience (KE) and those with less English experience in the identification of both continua. This contradicts the SLM, which posits that experienced L2 learners are better than inexperienced L2 learners in perception of L2 sounds. The exact nature of this should be further investigated in the SLM.

• Journal of Computing Science and Engineering
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• 제7권2호
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• pp.99-111
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• 2013

Approximating a divergence between two probability distributions from their samples is a fundamental challenge in statistics, information theory, and machine learning. A divergence approximator can be used for various purposes, such as two-sample homogeneity testing, change-point detection, and class-balance estimation. Furthermore, an approximator of a divergence between the joint distribution and the product of marginals can be used for independence testing, which has a wide range of applications, including feature selection and extraction, clustering, object matching, independent component analysis, and causal direction estimation. In this paper, we review recent advances in divergence approximation. Our emphasis is that directly approximating the divergence without estimating probability distributions is more sensible than a naive two-step approach of first estimating probability distributions and then approximating the divergence. Furthermore, despite the overwhelming popularity of the Kullback-Leibler divergence as a divergence measure, we argue that alternatives such as the Pearson divergence, the relative Pearson divergence, and the $L^2$-distance are more useful in practice because of their computationally efficient approximability, high numerical stability, and superior robustness against outliers.

• 한국과학교육학회지
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• 제21권3호
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• pp.516-528
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• 2001

학습행동에서의 뇌파 측정은 실시간으로 두뇌 기능 상태를 연구하는데 유용한 연구 방법이며, 대뇌의 부위 중 전전두엽은 새로움에 대한 지향반응과 사고 활동에 중요한 역할을 한다. 본 연구에서는 중학교 2학년 학생 20명에게 새로운 시청각 학습자료를 제시하고 4회의 반복학습이 이루어지는 과정에서 전전두부$(Fp_{1},\;Fp_{2})$의 뇌파를 측정하고 고속푸리에 변환(FFT)을 하여 정량적으로 분석하였다. 그 결과는 다음과 같다. 1) 새로운 내용의 첫번째 시청각 학습으로 기준상태에서보다 뇌신경의 속파 리듬인 $\beta_{2}$파(20-30Hz)와 $\beta_{1}$파(13-20Hz)의 활성은 증가하였으며, 서파 리듬인 $\theta$파(4-7Hz)와 $\alpha$ 파(8-13Hz)의 활성은 감소하였다. 2) $\beta_{2}$파와 $\beta_{1}$파의 활성은 1회의 반복학습 이후에 점차로 감소하였으며, $\beta_{2}$파가 $\beta_{1}$파보다 반복학습에 따른 활성도의 변화가 크게 이루어졌다. 3) 반복적인 시청각 학습이 이루어짐에 따라 $\alpha$ 파의 활성도는 기준상태에서보다 낮은 상태에서 완만하게 감소하였으며 $\theta$파의 활성은 2회의 반복학습 후에 감소하였다. 4) $\beta$와 $\theta$파의 활성이 함께 높은 2차 시청각 학습(1회 반복학습)에서 높은 학업 성취도의 향상을 보였다. 5) 처음 시청각 학습이 이루어질 때에는 전전두엽의 우뇌$(Fp_{2})$가 좌뇌$(Fp_{1})$보다 우세한 기능을 보였지만 반복적인 시청각 학습에서는 좌 우 뇌의 우세성이 구별되지 않았다. 따라서 교과학습과 관련된 인간의 정신행동에 있어서 뇌신경 반응의 습관화 현상이 나타나며, 학습 경험에 의해 두뇌 반구의 우세성이 변화할 수도 있음을 제시한다. 또한 시청각 학습에 있어서 두뇌 기능의 효율적 활용을 통한 학업 성취도 향상을 위해서는 l회의 반복 학습이 적합하다고 할 수 있다.