• Journal of the Korean earth science society
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• v.28 no.1
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• pp.87-104
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• 2007

As part of the SPVS (Short-Period Variability Survey) which is a wide-field $(90'{\times}60')$ photometric monitering program at Bohyunsan Optical Astronomy (BOAO), we performed V band time-series CCD photometric observations ofthe young open cluster NGC 129 for 11 nights between October 12, 2004 and November 3, 2005 using the 155mm refractor equipped with $3K{\times}2K$ CCD camera. From the observation we obtained 2400 V band CCD frames and color-magnitude diagram of the cluster. To transform instrumental magnitude to standard magnitude, we applied ensemble normalization technique to all observed time-series data. After the photometric reduction process, we examined variations of 9537 stars. As a result, sixty six of the new variable stars were discovered. To determine the periods of the sevariables, we used DFT(Discrete Fourier Transform) and phase-matching technique. According to light curve shape, period, amplitude and the position on a C-M diagram, we classified these variables as 9 SPB type, 9 ${\delta}$ Scuti type, 29 eclipsing, 17 long term variables. However, two of them were not classified. From this study, we learned that small telescopes could be a very useful tool to observe variable stars in the open cluster in survey program.

• 한국노년학
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• v.38 no.1
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• pp.243-259
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• 2018

The purpose of this study is to investigate the moderating effect of home-based welfare facilities for older adults on the associations between the activities of daily living (ADL) / instrumental activities of daily living (IADL) and the depressive symptoms among Koreans in later life. Multilevel analysis was conducted with Korean Longitudinal Study of Aging 5th data and the public report about welfare facilities from Ministry of Health and Welfare in Korea. Samples were 4,139 older adults over 65 years old. The dependent variable was depressive symptoms, and individual level independent variables were ADL and IADL. The ratio of home-based welfare facilities out of 10,000 older adults in each city and province was the moderator. As a result, the effects of ADL on depressive symptoms vary according to the proportion of elderly welfare facilities out of the old population in the community. In specific, the older adults who live in the place where the elderly welfare facility rate was higher were less affected by ADL. Also, the more IADL people had, the more depressive symptoms they had. However, the interaction effect between IADL and the proportion of home-based welfare facilities was not significant. It suggests that delivering welfare services helping ADL through the home-based welfare facilities may be useful for decreasing depressive symptoms. Moreover, considering the proportion of facilities and older population will be helpful to make the welfare facilities efficiently work.

• Environmental and Resource Economics Review
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• v.23 no.3
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• pp.409-434
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• 2014

This paper estimates household demand for electricity using a micro-level household expenditure data set. A two-stage estimation method where the endogenous block price estimates are obtained from a discrete block choice model is used. This method successfully identifies a downward sloping conditional demand function with the data, while both the usual two-stage method with instrumental variable estimation and the Hewitt-Hanemann discrete-continuous model fail to do that. The paper simulates the impacts of two hypothetical pricing reforms that reduce the number of blocks and make the price gap smaller. It is shown that the reform may increase the overall consumer benefit, but is regressive.

• The Korean Journal of Financial Management
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• v.10 no.2
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• pp.303-317
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• 1993

Banz(1981)와 Reinganum(1981)에 의한 실증연구에 의한 소기업과 대기업간의 수익률차이는 자본자산가격결정모형(CAPM)에 의하여 설명될 수가 없는 결과 즉, 과거의 체계적 위험과 기업규모를 기준으로 보면 도구변수(instrumental variable)인 기업규모는 추정된 CAPM의 베타에 대하여 통제한 연후에도 포트플리오간의 평균수익률에 대하여 통계적으로 유의적인 설명력을 가진다는 것이다 이것은 주식의 위험조정후수익률(risk-adjusted return)이 기업규모와 부(負)의 관계에 있다는 것으로서, CAPM으로서는 설명되지 않는 이상(異常)수익률 현상이다. Banz와 Reinganum 이후 미국학계에서 그동안 수많은 연구들이 규모효과에 대한 설명을 시도하였으나 아직도 완전한 설명은 존재하지 않고 있다. 본 연구는 우리나라 주식시장에서의 규모효과 존재여부에 관한 기존의 몇몇 연구들이 갖고 있는 방법론상의 문제점들을 제거함으로써 규모효과의 존재여부를 새로이 검증하였다. 특히, 동일가중지수수익률(equal-weighted index return)은 효율적 포트폴리오수익률이 나 종합주가지수수익률은 비효율적 포트폴리오수익률이라는 황선웅 이일균(1991)의 연구 결과를 고려하여, 시장수익률 대용치로서 종합주가지수수익률을 사용할 경우 규모효과의 검증결과가 어떠한 영향을 받는지도 아울러 분석하였다. 1980-90년의 기간을 대상으로 하여 실증분석한 결과, 먼저 동일가중지수수익률을 시장수익률로 사용할 경우 체계적위험 추정치와 기업규모간에는 부(負)의 관계가 존재하고 있음이 관측되고 있으며, 기업규모포트폴리오의 초과수익률 추정치도 대형주는 물론 소형주의 경우에도 통계적으로 유의하게 영(零)과 다르지 않다. 그 결과 최소한 1980-90년의 경우 우리나라 주식시장에는 규모효과가 존재하였다는 실증적 증거가 발견되지 않는다. 그러나 종합주가 지수수익률을 시장수익률로 사용하면 소형주에 대한 체계적위험이 대형주의 경우보다 오히려 작게 나타나고 있으며, 그에 따라 통제적으로 유의한 규모효과가 존재하는 것처럼 나타나고 있어 종합주가지수수익률은 시장수익률 대용치로 적절하지 않음을 제안하고 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.147-152
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• 1995

실험에 의한 모우드 해석 방법들은 1980년대부터 활발히 연구되어 많은 새로운 방법들이 개발되어 발표되었다. 그러나 개발된 대부분의 방법들은 측정된 데이타를 일괄처리하는 밸치(또는 off-line) 방법들이다. 최근에는 시간에 따라서 변하는 구조물의 동특성을 규명하는 분야에 모우드 해석 방법이 응용되어 사용되고 있다. 이러한 응용분야에서는 모우드 변수들의 변화되는 값을 새로운 데이타가 샘플링 될 때마다 그 값들을 수정하면서 추정할 수 있는 회귀적인(recursive 또는 on-line) 방법을 사용하여야 한다. Davies와 Hammond[1]는 회귀적 선형 자승법(Recursive Least Squares : RLS)을 이용하여 모우드 변수를 구하고 이를 벧치방법인 Instrumental Variable 방법과 Fourier 방법의 결과와 비교하였다. 그러나, 그 결과에서 보여준것처럼 RLS 방법은 잡음 대 시호비가 낮을 때에만 모우드 변수 값들을 정확하게 추정할 수 있었다. Sundararajan과 Montgomrey[2]는 회귀적 선형 최소자승 격자필터(lattice filter)를 이용하여 구조물의 차수(order)와 고유진동형, 그리고 진폭을 결정한 후 이를 토대로 회귀적 gradient형태의 방정식 오차 규명 방법(equation-error identification algorithm)에 의하여 모우드 변수들을 추정하였다. 이 방법은 2차원 격자구조물의 모우드 변수 추정에 사용되었으며, 또한 적응모우드제어에도 성공적으로 이용되었다. 그러나, 이 방법도 잡음 대 신호비가 낮은 환경에서만 사용할 수 있다는 단점이 있다. 위에서 언급한 방법들은 모두 RLS 방법을 기초로 하여 개발되었으나, RLS 방법은 전형적인 결정적(deterministic)방법으로서 잡음이 섞인 데이타를 처리하기에는 부적절한 방법임이 널리 알려진 사실이다[3]. 최근에 Ben Mrad와 Fassois[4]는 신호에 잡음이 존재하여도 이를 잘 처리할 수 있는 확률적(stochastic) 방법을 개발하여 기존의 결정적 방법들과 그 결과를 비교하였다. 그러나, 개발된 방법은 응답 신호에 백색잡음(white noise)이 섞이는 특수한 경우에만 사용할 수 있게 만들어져서 이 방법의 실질적인 적용에는 어려움이 있다. 본 연구에서는 기존의 방법들의 단점을 극복할 수 있는 새로운 회귀적 모우드 변수 규명 방법을 개발하였다. 이는 Fassois와 Lee가 ARMAX모델의 계수를 효율적으로 추정하기 위하여 개발한 뱉치방법인 Suboptimum Maximum Likelihood 방법[5]를 기초로 하여 개발하였다. 개발된 방법의 장점은 응답 신호에 유색잡음이 존재하여도 모우드 변수들을 항상 정확하게 구할 수 있으며, 또한 알고리즘의 안정성이 보장된 것이다.

• Journal of Korean Public Health Nursing
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• v.17 no.1
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• pp.35-46
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• 2003

The purpose of this study was to examine the self-rated health and to find various factors affecting it for elderly women in a rural community, to provide data necessary to establish health promotion programs for elderly. The subjects of the study included a total of 245 women with above 70 years of age reside in one rural community. VAS (Visual Analogue Scale) for self-rated health, Lawton's physical & instrumental activity of daily living scales, social network were evaluated. The results of the study were as follows: 1. The self-rated health of the elderly women were measured on a 100 point(VAS) scale and the score was 53.6, indicating that women rated their health as moderate. 2. Factors such as income(p=0.008), family size(p=0.031), the level of ADL(p=0.039), urinary symptom(p=0.039), nocturia(p=0.001), visual difficulty(p=0.023), the number of chronic diseases(p=0.015), presence of arthritis or neuralgia(p=0.015), social network(p=0.002), housework assistant(p=0.008), emotional support(p=0.031) were significantly related to self-rated health. 3. Through the stepwise multiple regression, social network, family size, visual difficulty, and housework assistant were identified as significant predictors of self-rated health(p<0.05), explaining $21.0\%$ of the variance of the dependent variable. Better understanding of the determinants of healthy aging hopefully will lead to effective interventions to improve the quality of life of the elderly.

• Journal of Labour Economics
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• v.34 no.2
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• pp.79-107
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• 2011

This study investigates the status of English scores in the Korean labor market. We provide an empirical explanation of how English scores affect labor performances in Korea. Specifically, we focus on the effects of TOEIC scores on college graduates' job opportunity and wage premium. Our empirical tests for TOEIC scores are implemented in three dimensions: (1) Screening effects (2) Signaling effects (3) Wage effects. The results are as follows. First, we find the positive correlation between TOEIC scores and job opportunities, which implies that TOEIC scores play an important role in employee selection process. Second, our tests give the same results when it comes to job seeker's use of TOEIC scores as signaling instrument. That is, high TOEIC scores have positive signaling effects in the labor market. However, there also exists disadvantage effect of low TOEIC scores, in that job applicants with TOEIC scores below certain level are even more disadvantageous than those with no TOEIC scores. Finally, wage premium of TOEIC scores are found, even when other variables (e.g. GPA) are controlled or we use the instrumental variable estimate.

• KDI Journal of Economic Policy
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• v.34 no.2
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• pp.139-171
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• 2012

This paper examines the effect of private tutoring expenditures on academic performance of middle school students in South Korea, using data from "Analysis of the Level of School Education and Its Actual condition: Middle School". In the face of endogeneity of private tutoring expenditures, the paper employs an instrumental variable (IV) method and a nonparametric bounding method. Using both methods we show that the true effect of private tutoring on middle school students remains at most modest in Korea. The IV results suggest that a 10 percent increase in tutoring expenditure for Korean, English and math raises a student's test score of the subject at the largest by 1.24, 1.28, and 0.75 percent, respectively. The bounding results also fail to show evidence that an increase in tutoring expenditure leads to economically and statistically significant improvements in test score.

• Journal of Korean Academy of Nursing
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• v.43 no.1
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• pp.1-10
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• 2013

Purpose: The purpose of this study was to develop a prediction model for the characteristics of older adults with depression using the decision tree method. Methods: A large dataset from the 2008 Korean Elderly Survey was used and data of 14,970 elderly people were analyzed. Target variable was depression and 53 input variables were general characteristics, family & social relationship, economic status, health status, health behavior, functional status, leisure & social activity, quality of life, and living environment. Data were analyzed by decision tree analysis, a data mining technique using SPSS Window 19.0 and Clementine 12.0 programs. Results: The decision trees were classified into five different rules to define the characteristics of older adults with depression. Classification & Regression Tree (C&RT) showed the best prediction with an accuracy of 80.81% among data mining models. Factors in the rules were life satisfaction, nutritional status, daily activity difficulty due to pain, functional limitation for basic or instrumental daily activities, number of chronic diseases and daily activity difficulty due to disease. Conclusion: The different rules classified by the decision tree model in this study should contribute as baseline data for discovering informative knowledge and developing interventions tailored to these individual characteristics.

• Journal of the Korean Society of Child Welfare
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• no.59
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• pp.1-23
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• 2017

Using a subsample of 3,409 unmarried smothers and their children from the Fragile Families and Child Wellbeing study, the present study examined the cross-lagged effects of unmarried fathers' involvement on their children's behavior problems. Father involvement was used as a latent variable to measure the frequency of fathers' visits to the child, fathers' instrumental support, and their supportive parenting. Both variables of father involvement and child behavior problems were repeatedly measured at child ages 3, 5, and 9 to estimate their trends over time. The results indicated that fathers' more active engagement in parenting at child ages 3 to 5 reduced behavior problems in children at ages 5 to 9. Further discussions include programs and services to support unmarried fathers through education and training opportunities for effective parenting, relationship skills, and conflict resolutions as well as policy strategies to encourage their continuous involvement in the lives of their children.