• Journal of Korea Entertainment Industry Association
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• v.13 no.2
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• pp.177-186
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• 2019

The purpose of this study was to investigate the influences of the smartphone overuse on health and academic impairment in adolescents. This study used data from Korea youth risk behavior web-based survey of 2017. This survey was conducted on 64,991 adolescents(middle and high school students), and 62,276 (95.8%) responded. The researchers used frequency analysis, independent t test, chi-square test and Pearson correlation analysis using SPSS 22. As a result, the usage rate of adolescents's smartphone was 54,603 out of 62,276, which was 87.7%. The purpose of smartphone usage was messenger(1st rank, 27.3%), SNS(2nd rank, 18.7%) and game(3rd rank, 13.3%). The average daily use time of the smartphone was 206.68±194.73 minutes. Girl students showed significantly more use time of smartphones than boy students(p<.001). Students with more than 206 minutes of smartphone use had worse health and academic performance than students with less than 206 minutes(p<.001). Time of smart phone usage and academic ability showed a weak correlation(p<.001, r=.245). The present findings showed that the higher the smartphone usage, the lower the health level and academic ability, and the author discussed these results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1453-1461
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• 1999

In this paper, we propose a new scheme that improve the performance of the conventional link access scheme in DSRC MAC and evaluate the performance of the proposed scheme. By using carrier sensing mechanism in random access channels, the proposed scheme can reduce the probability that the collisions among the link access traffics with different priorities may occur in random access channels, and provide differentiated link access delays according to the priorities. Furthermore, the proposed scheme can improve the performance of link access by using modified reservation mode. According to simulation results, it is shown that the proposed scheme is better than conventional method in view of the mean access delay and throughput in random access channels.

• Proceedings of the Korea Contents Association Conference
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• 2018.05a
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• pp.353-354
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• 2018

최근 스마트폰의 과다 사용과 관련한 문제를 해결하기 위하여 스마트폰 디톡스라는 새로운 개입방법이 소개되고 있다. 스마트폰 디톡스는 마치 단식을 통해 몸에 있는 독소와 노페물을 제거하듯이 스마트폰 사용을 잠시라도 중단하고 내면의 모습을 돌아봄으로써 스마트폰을 건강하게 활용하여 신체적 정신적 사회적 건강을 실천하자는 취지이다. 이러한 흐름에 발을 맞추어 본 연구에서는 대학생들의 과다한 스마트 폰 사용을 개선하고 전인적인 건강(well-being)을 실천하기 위하여 "스마트폰 디톡스 프로그램"을 개발하고 그 효과를 확인하였다. 서울의 S대학교 16명의 대학생이 전체 프로그램을 완료하였으며, 각 회기별 자기평가보고서와 사전-사후 설문조사(스마트폰 중독척도 정신건강척도 긍정심리자본척도 자기생활관리척도)를 완성하였다. SPSS 23을 이용하여, 사전검사와 사후검사에서 변수 간의 차이를 확인하기 위해 Wilcoxon 부호순위검정을 시행하고, 각 척도들 사이의 관계는 피어슨 상관분석을 이루어졌다. 그리고 자기평가보고서는 각 회기 참여에 대한 질적 자료로 분석되었다. 그 결과, 개입 프로그램을 통해 스마트 폰 중독 및 정신 건강 점수가 유의미하게 감소하였으며, 자기 관리 및 긍정심리자본의 평균 점수가 증가하였다. 더불어 프로그램이 진행되는 동안이라도 스마트폰 사용을 중단하고 건강한 신체, 긍정적인 정신, 역동적인 대인관계를 경험하면서 스마트폰을 지혜롭게 사용하고 주변을 여유롭게 돌아보는 변화가 생겼으며, 대학생들의 생활에서 스마트폰을 건강하게 사용할 수 있는 모습이 확인되었다.

• Journal of Animal Science and Technology
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• v.52 no.5
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• pp.349-356
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• 2010

This study was conducted to estimate heritabilities, repeatabilities and rank correlation coefficients among breeding values for litter size and sex ratio of Yorkshire and Landrace pigs using various single trait animal models. The analyses were carried out the data comprising 26,390 litters of Yorkshire and 26,173 litters of Landrace collected from the year 1998 to 2008 at a private swine breeding farm located in central part of Korea. Five different analytical models were used for genetic parameter estimation. Model 1 was most simple basic model fitted with year-month contemporary group fixed effect, random additive genetic effect and random residual effect. Model 2 was similar to the model 1 but permanent maternal environmental effect added as random effect, and model 3 was similar with the model 2 but linear and quadratic effects of sow age were added as fixed covariate effect. Model 4 was similar as model 2 except that the parity was added as fixed effect and model 5 was similar to model 3 or model 4 but covariate of sow age was nested within parity effect. The results obtained in this study are summarized as follows: The means and standard error of total number of pigs born per litter (TNB) and number of pigs born alive per litter (NBA) were $11.35{\pm}0.02$ and $10.04{\pm}0.02$ for Yorkshire, $10.97{\pm}0.02$ and $9.98{\pm}0.02$ for Landrace, respectively. The sex ratio (percentage of female per litter) was $45.75{\pm}0.11%$ and $45.75{\pm}0.11%$ for Yorkshire and Landrace, respectively. The heritability estimates of TNB (0.243) and NBA (0.192) from model 1 tended to be higher than those from any other models in both breeds. Differences in heritability and repeatability for TNB were not large among models 3, 4 and 5 and same tendency of negligible differences among estimates by models 3, 4 and 5 were observed for NBA, where heritability and repeatability ranged from 0.096 to 0.099 and from 0.188 to 0.193, respectively, in Yorkshire; and ranged from 0.092 to 0.098 and from 0.193 and 0.196, respectively, in Landrace. The heritability estimates for sex ratio were close to zero which was ranged from 0.002 to 0.003 for TNB and from 0.001 to 0.003 for NBA over the models applied. The rank correlation coefficients of breeding values by model 1 with those from other models (model 2, 3, 4 and 5), and breeding values by model 2 with those from other models (model 1, 3, 4 and 5) were highly positive but lower than the coefficients among breeding values by model 3, model 4 and model 5 which were high of 0.99, approximately, for TNB and NBA of both breeds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.435-445
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• 2018

This study analyzed factors that should be considered in the process of export diversification strategy formulation and priorities of strategies. We reviewed the extant literature and interviewed six experts. Cross-sectional analysis of a literature review and interview results were used to determine the influencing factors of export. The data for this study were collected from a survey of 68 export experts in Automotive Parts enterprises. Data were analyzed using AHP. As a result of the analysis, the order of importance appeared in the order of internal capacity, correlation buyer effect, entry barriers, technology response, and competition environment. The regions with a high overseas level were product differentiation, centralization, and low cost, whereas those with a low level were in the order of low cost, product differentiation, and concentration. It is meaningful to review the alternatives for adoption of the export diversification strategy and establish a strategy appropriate to the situation. It is necessary to establish a customized strategy considering the characteristics of the global region, and not only internal competence but also mutual relationship with local buyers are important.

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.156-166
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• 2005

Ethernet passive optical network is an economical and efficient access network that has received significant research attention in recent years. A MAC(Media Access Control) protocol of PON, the next generation access network, is based on TDMA(Time Division Multiple Access) basically. In this thesis, we addressed the problem of dynamic bandwidth allocation in QoS based Ethernet PONs. We augmented the bandwidth allocation to support QoS in a differentiated services framework. Our differentiated bandwidth guarantee allocation(DBGA) allocates effectively and fairly bandwidths among end users. Moreover, we showed that DBGA that perform weighted bandwidth allocation for high priority packets result in better performance in terms of average and maximum packet delay, as well as network throughput compared with existing dynamic bandwidth allocations. We used simulation experiments to study the performance and validate the effectiveness of the proposed bandwidth allocations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.132-141
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• 2000

In this paper, we proposed the MAC protocol of APON supporting multi-class traffic such as CBBUVBR, ABR, UBR, to guarantee the required QoS of each service. For this, we analyze the performance of variousrequest mechanisms and employee the different request mechanism for each traffic classes. Upstream anddownstream frame structures to minimize transmission overhead are proposed based on our request mechanism.The proposed MAC protocol applies the different priority to permit distribution process. CBBWBR traffic, withthe stringent requirements on CDV or delay, is allocated prior to any other class. ABR traffic, which hasnon-strict CDV or delay criteria, uses flexibly the available bandwidth but ensures a minimum cell rate (MCR).UBR traffic is allocated with lowest priority for the remaining capacity. The performance of proposed protocol isevaluated in terms of transfer delay and 1-point CDV with various offered load. The result of simulation showsthat the proposed protocol guarantees the required QoS of the corresponding category, while making use of theavailable resources in both an efficient and dynamical way.

• Journal of Advanced Navigation Technology
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• v.23 no.1
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• pp.1-7
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• 2019

Thisstudy presentsthe development of a fast-time airport surface simulator. The simulator usesthe output from a first-come first-served (FCFS) scheduler and has adopted one-dimensional dynamic model to simulate the movement of the aircraft on the surface. Higher collision risks situations in the airport surface traffic are analyzed to classify those situations into six cases. A conflict detection and resolution algorithm is implemented to maintain separation distance and to prevent deadlock. The simulator was tested with a scenario at the Incheon International Airport that contains 72 aircraft. Without the conflict detection and resolution, various conflict situations are identified. When the conflict detection and resolution algorithm is managing the traffic, it is confirmed that the conflicts are removed at the price of additional delays. In the conflict resolution algorithm, three prioritization strategies are implemented, and delayed aircraft count and average additional delays are compared. Prioritization based on remaining time or distance showed smaller total additional delay compared to choosing minimum delay priority for each situation.

• Environmental and Resource Economics Review
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• v.31 no.2
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• pp.141-163
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• 2022

This paper empirically analyzes the effect of renewable electricity generation on the System Marginal Price (SMP) in Korea. Using an ARX-GARCHX model with hourly data from 2016 to 2020, we evaluate SMP determinants and merit order effects. As a result, we find that solar and wind power, as well as gas price and total load, play a critical role in the SMP. In particular, solar power reduces the SMP level but raises volatility during peak and off-peak periods. This result implies that SMP may fall as renewable electricity generation increases, leading to a decrease in the profitability of existing power plants and investment in renewables. On the other hand, even if the subsidy of renewable energy increases the burden on the SMP, it can be offset by the merit order effect, which lowers the SMP.

• The Korean Journal of Financial Management
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• v.25 no.3
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• pp.33-78
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• 2008

This paper empirically examines whether firms engage in a dynamic adjustment process toward target capital structure and, whether there is a target capital structure or mean reverting using the partial adjustment model while allowing for costly adjustment. Also we investigate the empirical determinants of optimal target capital structure in long term equilibrium. As a result, our empirical model captures at least several important features of capital structure behavior for Korean listed firms. First, Korean firms pursue target capital structure and also there is mean reverting phenomenon. Second, Non-Chaebol and small firm in adjustment speed is faster than Chaebol and large firm. Third, even capital market restricts the adjustment speed interestingly. Fourth, Korean firms have target behavior according to a degree of observed gap. Fifth, Korean firms close about one-fourth of the gap between their actual and target debt ratios within one year and thence targeting behavior explains far more of the observed changes in capital structure than market timing or pecking order considerations. Sixth, capital market is significant in determining optimal capital structure.