• 한국수자원학회논문집
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• 제40권10호
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• pp.755-768
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• 2007

본 연구는 자갈하천에서 실측한 자료를 사용하여 유량 변화에 따른 조도계수의 변화를 분석하고, 기존 조도계수 경험식의 적용성을 검토하는 것이 목적이다. 실측자료를 이용한 조도계수의 산정을 위하여 미 지질조사국의 NCALC 모형을 이용하여 대상구간의 조도계수를 산정하였고, 산정된 결과를 4가지 경험적인 방법에 의해 산정된 조도계수와 비교하였다. 분석결과 기존의 경험적 방법들은 홍수기에 국한하여 근사적인 해를 제공할 수 있으나 판단의 주관성, 방법에 따른 결과의 차이 등으로 인하여 산정결과의 불확실도가 높을 것으로 판단되었다. 평저수기의 조도계수는 기존 경험적 방법으로 산정이 어려울 것으로 나타났으며, 특히 Manning 공식을 이용하여 조도계수를 산정하는 경우, 상한치와 하한치의 범위가 크므로 사용 시 주의가 필요함을 알 수 있었다. 그리고 평저수기에도 조도계수와 하상입도가 상관성이 있는 것으로 확인되었으나 홍수기의 상관성과 다르게 나타남을 확인하였다.

• 아동학회지
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• 제37권4호
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• pp.17-29
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• 2016

Objective: The purpose of this study was to examine the bidirectional relation between mobile phone dependency (MPD) and self-regulated learning (SRL) of early Korean adolescents in $4^{th}$, $6^{th}$ and $8^{th}$ grade, while taking into account gender differences. Methods: The study made use of panel data from the Korean Children and Youth Panel Study (KCYPS), and three waves of data collected from 2,264 adolescents were analyzed by means of autoregressive cross-lagged modeling. Results: The results can be summarized as follows. Firstly, MPD and SRL were consistently stable for adolescents in $4^{th}$, $6^{th}$ to $8^{th}$ grades. Secondly, a bidirectional relations between MPD and SRL were confirmed. In other words, there was a significant influence of a high level of MPD on a subsequent low level of SRL, and the high level of SRL also had a significant effect on the lower level of MPD across time. According to multi-group analysis, no gender differences were found in the relations between two constructs during the studied period. Conclusion: Findings highlighted not only the necessary media usage education but also parenting intervention strategies may help early adolescents to be prevented from negative effects of media usage and to enhance self-regulated learning ability. Based on the results, more implications were also discussed.

• 한국수학사학회지
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• 제29권6호
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• pp.325-333
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• 2016

Chinese Mathematics during the period of Jin (1115-1234) and Yuan (1271-1368) is an integral part of the high achievements of traditional mathematics during the Song (962-1279) and Yuan dynasties, which is another peak in the history of Chinese mathematics, following the footsteps of the high accomplishments during the Warring States period (475-221 BCE), the Western Han (206 BCE-24 ADE), Three Kingdoms (220-280 AD), Jin dynasty (265-420 AD), and Southern and Northern Dynasties (420-589 AD). During the Jin-Yuan period, Quanzhen Taoism was a dominating branch in Taoism. It offered certain political protection and religious comforts to many during troubled times; it also provided a relatively stable environment for intellectual development. Li Ye (1192-1279), Zhu Shijie (fl. late 13th C to early 14th C) and Zhao Youqin (fl. late 13th C to early 14th C), the major actors and contributors to the Jin-Yuan Mathematics achievements, were either heavily influenced by the philosophy of Quanzhen Taoism, or being its followers. In certain Taoist Classics, Li Ye read the records of the relations of a circle and nine right triangles which has been known as Dongyuan jiurong 洞渊九容 of Quanzhen Taoism. These relations made significant contributions in the study of the circles inscribed in a right triangle, the reasoning of which directly led to the birth of the Method of Celestial Elements (Tianyuan shu 天元术), which further developed into the Method of Two Elements (Eryuan shu ⼆元术), the Method of Three Elements (Sanyuan shu 三元术) and the Method of Four Elements (Siyuan shu 四元术).

• Journal of Communications and Networks
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• 제15권5호
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• pp.504-513
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• 2013

Communication in delay tolerant networks (DTNs) relies on message transport by mobile nodes, and a correct understanding of the node mobility characteristics is therefore crucial to the design of an efficient DTN routing protocol. However, previous work has mainly focused on uncovering all behaviors of node movement, which is not conducive to accurately detecting the specific movement characteristics of a different node. In this paper, we seek to address this problem based on a consideration of social relationships. We first consider social ties from both static and dynamic perspectives. For a static perspective, in addition to certain accidental events, social relations are considered for a long time granularity and tend to be stable over time. For a dynamic perspective, social relations are analyzed in a relatively short time granularity and are likely to change over time. Based on these perspectives, we adopted different efficient approaches to dividing node pairs into two classes, i.e., familiar and unfamiliar pairs. A threshold approach is used for static social ties whereas a density-based aggregation method is used for dynamic social relationships. Extensive experimental results show that both familiar and unfamiliar node pairs have the same inter-contact time distribution, which closely follows a power-law decay up to a certain point, beyond which it begins to exponentially decay. The results also demonstrate that the inter-contact time distribution of familiar pairs decays faster than that of unfamiliar pairs, whether from a static or dynamic perspective. In addition, we also analyze the reason for the difference between the inter-contact time distributions of both unfamiliar and familiar pairs.

• 구강회복응용과학지
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• 제25권4호
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• pp.431-436
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• 2009

심한 치조골 흡수를 동반한 III급 악골 관계 환자의 총의치 제작의 경우 안정적이고 지속적인 교합을 제공하는 치료계획을 세워야 한다. 불리한 치관 대 치근 비와 임상적 동요도가 관찰되는 하악 잔존치를 고정하여 사용함으로써 환자의 불편감을 줄이고 시간적, 경제적으로 효율적인 치료를 제공할 수 있다. 본 증례에서는 상악 편악 무치악 환자의 기능적인 하악 운동과 조화로운 총의치 균형 교합을 이루기 위해 T-Scan System을 이용하였다.

• 국제지역연구
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• 제14권2호
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• pp.297-323
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• 2010

냉전기간 중국과 아프리카의 경제관계의 특징은 중국의 '순수한 이념적, 정치적 목적(purely ideological and political purpose)'으로 인하여 아프리카와의 상당한 무역규모에도 불구하고 경제관념이 전혀 대두되지 않았다. 냉전이라는 거대한 시대적 흐름으로 인해 '원조' 또는 '지원' 이라는 개념으로 대체되어 왔던 것이다. 그러나 탈냉전 이후 중국과 아프리카의 관계는 정치적, 이념적 목적이 퇴색하였거나 완전히 배제되는 특징을 보이고 있다. 1990년대 들어 철저한 경제관념, 즉 실용주의(pragmatism)에 입각한 중국에게 있어 아프리카는 안정된 에너지 공급원으로서의 역할뿐만 아니라 물품 수출 및 직접 투자가 가능한 '신흥시장'으로 부각되기에 이르렀기 때문이다. 본 연구는 중국과 아프리카의 냉전과 이후의 경제관계 비교를 통해 드러나는 명확한 차이점을 분석함으로써 중국의 변화된 대(對) 아프리카 경제정책을 이해하고자 한다. 이를 통해 현재 아프리카라는 신흥시장에서 투자와 수출입을 포함하는 통상 관계 전반에 걸쳐 영향력 확대를 위해 심혈을 기울이고 있는 한국에 시사점을 제공하는데 그 목적이 있다.

• 한국가족관계학회지
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• 제21권2호
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• pp.77-96
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• 2016

Objectives: The aims of this study are to examine the associations between marital satisfaction and life satisfaction among Korean retirees in later life and to test whether the degrees of associations increased over time. Method: Nationally representative Korean Longitudinal Study of Ageing data from wave 1 (in 2006) to wave 4 (in 2012) was utilized and retirees in later life (65-89 years old, N=402) were analyzed. Latent growth modeling (LGM) and model constraint were applied using Mplus 7.3. Age, sex, household income, subjective health, depressive symptoms and elapsed time after retirement were included as control variables. Results: Linear unconditional LGM fitted the data well and showed gradual decrease in life satisfaction. Conditional LGM revealed significant associations between marital satisfaction and life satisfaction from time 1 to time 4. According to model constraint test, the size of associations between marital satisfaction and life satisfaction did not change with time. Conclusions: To sum up these results, the associations between marital satisfaction and life satisfaction were significant and relatively stable over time among retirees in later life. This study suggests one's spouse is a fundamental component of social convoy among Korean retirees in later life. Therefore, intervention programs targeted toward enhancing marital relationships among retirees' couples will help them to live a better life.

• 아태비즈니스연구
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• 제13권3호
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• pp.183-208
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• 2022

Purpose - The main purpose of this study is to widely investigate the impact of recent pandemic crises on the synchronization of the world capital markets through 25 stock indices from major developed countries. Design/methodology/approach - This study collects 25 stock indices from major developed countries and the time period is between January 5, 2001 and February 24, 2022. The data sets used in the study include finance.yahoo.com and Investing.com.. The Granger causality analysis, unit-root test, VAR analysis, and forecasting error variance decomposition were hired in order to analyze the data. Findings - First, there are significant inter-relations among 25 countries around recent major pandemic crises(such as SARS, A(H1N1), MERS, and COVID19), which is consistent result with previous literature. Second, COVID19 shows much stronger impact on the world-wide synchronization than other pandemics. Third, the return volatility of each stock market varies, unit root tests show that daily stock index data are unstable while daily stock index returns are stable, and VAR(Vector Auto Regression) analyses presents significant inter-relations among 25 capital markets. Fourth, from the impulse response function analyses, we find that each market affects the other markets for short term periods, about 2~4 days, and no long term effect was not found. Fifth, Granger causality tests show one-side or two-sides synchronization between capital markets and we estimate, through forecasting error variance decomposition method, that the explanatory portions of each capital market on other markets vary from 10 to 80%. Research implications or Originality - The above results all together show that pandemic crises have strong effects on the synchronization of world capital markets and imply that these synchronizations should be carefully considered both in the investment decisions by individual investors and in the financial and economic policies by governments.

• 한국식생활문화학회지
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• 제24권6호
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• pp.728-738
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• 2009

The purpose of this study was to evaluate job stress factors of school food service nutritionists according to the number of years they have worked. The subjects of this survey included 125 nutritionists (69 from full-time employees and 56 from part-time nutritionists) from elementary school, middle school, and high school in the Gangwon area. The results showed that stress related to duty was the top job stress factor, followed by environment-related stress, personal stress, organization-related stress and stress caused by human relations. In terms of the degree of stress, part-time nutritionists have more stress compared to full-time nutritionists. This was especially true for nutritionists that had been employed for one year. In this case, the degree of stress was much higher than long time employed nutritionists. In terms of how to deal with job stress, school nutritionists eliminated stress directly (with direct countermeasures). In order to deal with stress, workers expected stable employment such as pay (wages), promotions, etc. In particular, part-time school nutritionists had stronger expectations. When correlation between job stress factors were examined, environment-related, duty-related, organization-related, human relations-related and personal stress were all shown to be mutually related.

• 한국정밀공학회지
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• 제30권5호
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• pp.493-498
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• 2013

The present study treats the optimization process for a non-linear grinding system with dual time delay, mainly from the energetic viewpoint. To this end, the stability of the grinding system is investigated first with regard to the grinding wheel rotation speed. The concept of grinding energy density is newly proposed as the primary figure of merit and this quantity is evaluated at various stable and limit cycle conditions. The computational results show that simple monotonic trend in energy density is observed under stable conditions, whilst rather complicated behaviors can appear when the conditions are associated with limit cycle oscillations. Finally, the relations between the vibration amplitude and the energy density and their implications on the engineering decision/compromise are discussed.