• 한국경영과학회지
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• 제34권4호
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• pp.91-112
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• 2009

The bullwhip effect means the phenomenon of increasing demand variation as moving UP to the upstream in the supply chain. Therefore, it is recognized that the bullwhip effect is problematic for effective supply chain operations. In this paper, we exactly quantifies the bullwhip effect for the case of stochastic lead time and seasonal demand in two-echelon supply chain where retailer employs a base-stock policy considering SARMA demand processes and stochastic lead time. We also investigate the behavior of the proposed measurement for the bullwhip effect with autoregressive and moving average coefficient, stochastic lead time, and seasonal factor.

• 산업융합연구
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• 제20권11호
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• pp.157-164
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• 2022

본 연구에서는 중학생의 학업소진이 자존감에 미치는 영향에서 학습시간의 매개효과를 파악하고자 하였다. 이를 위해 경상남도 소재의 중학생 1,045명을 대상으로 학업소진, 학습시간, 자존감에 대한 설문조사를 실시하였다. 설문응답을 통해 3가지로 분석하였다. 첫째, 학업소진, 학습시간, 자존감의 집단적 특성에 따른 차이를 분석한 결과 학업소진과 학습시간은 집단별차이가 나타나지 않았고, 자존감은 성별, 학년별 유의한 차이가 있었다. 둘째, 상관분석 결과 학업소진과 학습시간은 자존감과 부적 상관관계를 보이고, 학습시간과 자존감은 정적 상관관계를 보였다. 셋째, 회귀분석 결과 학업소진이 자존감에 미치는 영향에서 학습시간은 모두 부분매개하였다. 이는 학업소진이 중학생의 자존감에 직접적인 영향을 주고 있을 뿐 아니라, 학습시간을 통해 간접적인 영향을 주고 있다. 넷째, 성별로 구분하여 분석한 결과에서는 남학생의 경우 매개변인인 학습시간이 자존감에 통계적으로 유의한 영향을 미치지 못하였지만 여학생의 경우는 학습시간이 자존감에 유의미한 통계적 영향을 미치고 있어 여학생만 부분매개효과가 있는 것으로 확인되었다. 학년별로 구분하여 분석한 결과에서는 중학교 1,2학년은 학습시간이 자존감에 미치는 영향이 유의하였으나, 중학교 3학년의 경우 학업시간이 자존감에 미치는 영향력은 유의한 효과가 나타나지 않았다. 본 연구의 설문을 통해 급격한 성장기인 중학생 시기에는 남학생과 여학생의 성별에 따른 접근 뿐 아니라 학년별로도 학업소진이 학습시간과 자존감에 미치는 영향이 다르다는 것을 고려한 교육과 상담이 이루어져야 함을 제안하였다.

• 대한산업공학회지
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• 제42권6호
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• pp.377-385
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• 2016

The previous Adaptive Control of Thought-Rational (ACT-R) cognitive architecture model has a limitation in that it cannot accurately predict human visual search strategy, because time effect, one of important human cognitive features, is not considered. Thus, the present study proposes ACT-R cognitive modeling that contains the impact of time using a revised utility system in the ACT-R model. Then, the validation of the model is performed by comparing results of the model with eye-tracking experimental data and SEEV-T (SEEV-Time; SEEV model which considers time effect) model in "Where's Wally" game. The results demonstrate that the model data fit fairly well with the eye-tracking data ($R^2=0.91$) and SEEV-T model ($R^2=0.93$). Therefore, the modeling method which considers time effect using a revised utility system should be used in predicting the human visual search paradigm when the available time is limited.

• Earthquakes and Structures
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• 제19권4호
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• pp.287-301
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• 2020

Fragility as one of the most effective methods to evaluate seismic performance, which is greatly affected by damage index. Taking a multi span continuous rigid frame offshore bridge as an example. Based on fragility and reliability theory, considering coupling effect of time-varying durability damage of materials and time-varying attenuation effect of damage index to analyze seismic performance of offshore bridges. Results show that IDA curve considering time-varying damage index is obviously below that without considering; area enclosed by IDA of 1# pier and X-axis under No.1 earthquake considering this effect is 96% of that without considering. Area enclosed by damage index of 1# pier and X-axis under serious damage with considering time-varying damage index is 90% of that without considering in service period. Time-varying damage index has a greater impact on short pier when ground motion intensity is small, while it has a great impact on high pier when the intensity is large. The area enclosed by fragility of bridge system and X-axis under complete destruction considering time-varying damage index is 165% of that without considering when reach designed service life. Therefore, time-varying attenuation effect of damage index has a great impact on seismic performance of bridge in service period.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전력기술부문
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• pp.9-11
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• 2006

This paper suggests a revision method for historical fault data using Proportional Aging Reduction(PAR) to consider maintenance effect in time-varying failure rate. In order to product time-varying failure rate, the historical fault data are necessary. However, the maintenance record could be left out in historical data by spot operator's mistake. In this case, the failure rate is produced less than the average failure rate for increasing equipments' life-time by maintenance effect. Hence, it is necessary for new time-varying failure rate to extract maintenance effect from the existing fault data. In this paper, the revision method to reduce equipments' life-time, adversely using PAR among three techniques to consider maintenance effect.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.113-123
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• 1998

The present study is to investigate the effect of experimental parameters on the heat transfer characteristics of a spherical capsule storage system using paraffins. N-Tetradecane and mixture of n-Tetradecane 40% and n-Hexadecane 60% were used as paraffins. Water with inorganic material was also tested for the comparison. The experimental parameters were varied for the Reynolds number from 8 to 16 and for the inlet temperature from -7 to 2$^{\circ}C$. Measured local temperatures of spherical capsules in the storage tank were utilized to calculate charging and discharging times, dimensionless thermal storage amount, and the average heat transfer coefficients in the tank. Local charging and discharging times in the storage tank were significantly different. The effect of inlet temperature on charging time was larger than that on discharging time, but the effect of Reynolds number on charging time was smaller than that on discharging time. Charging time of paraffins was faster by 11~72% than that of water with inorganic material, but little difference of discharging time was found among them. The effect of Reynolds number on the dimensionless thermal storage was less during charging process and more during discharging process than the effect of inlet temperature. The effect of the inlet temperature and the Reynolds number on the average heat transfer coefficient of the storage tank was stronger during discharging process than during charging process. The average heat transfer coefficients of the spherical capsule system using paraffins were larger by 40% than those using water.

• 대한본초학회지
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• 제23권4호
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• pp.191-196
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• 2008

Objectives: This research was investigated to find out the effect of the anticoagulant Perillae folium extract. Methods: To examine an active effect of anticoagulation in Perillae folium extract, the study measured Prothrombin time(PT) and activated partial thromboplastin time(APTT) of human plasma in vitro and measured bleeding time and arterio-venous shunt model in rats in vivo. Results: Bleeding time of Perillae folium extract in vivo had a significant increase 1.6 times and thrombus weight of Perillae folium extract had a significant reduction of thrombus weight as 68%. Perillae folium extract had an effect of anticoagulation by operating on extrinsic pathway factor II, V, VII, X and intrinsic pathway factor VIII, IX, X, VI, VII in the coagulation system. Conclusions: Considering the above mentioned results, it is judged that a Perillae folium extract has a control effect of thrombus creation.

• Journal of the Korean Data and Information Science Society
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• 제20권5호
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• pp.787-796
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• 2009

이 논문에서는 반복측정치에 대한 분석모형 중, 혼합모형의 일종인 변량계수모형에 대하여 이론적으로 고찰한다. 특히 혼합모형의 설정, 모수 추정에 대하여 통계적으로 고찰하고 변량계수모형에 대한 가능한 모형을 열거하며, 그에 따르는 추정과 검정을 논의한다. 사례연구로 식이요법자료를 대상으로 가능한 변량계수모형을 적용하여 추정 및 검정을 실시한 결과, 고정인자인 사전값, 처리, 키 및 시간들의 인자는 체중감소에 대단히 유의함을 보여주었지만, 나이와 혈압은 유의하지 않았다. 처리효과에 있어서는 식이요법과 운동을 병행했을 때의 처리가 식이요법만 실시했을 때의 처리보다 체중이 더 감소했음을 알 수 있으며, 시간에 따른 체중감소의 효과는 삼차함수의 관계가 성립된다. 변량인자로는 개체효과는 유의하며 개체별 시간에 대한 교호작용의 효과는 차수가 높아질수록 급속도로 감소하여 3차 함수 관계가 적절한 모형으로 최종 선택되었다.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2002년도 추계 학술발표회 논문집
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• pp.197-201
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• 2002

The healthy worker effect is an important issue in occupational epidemiology. We proposed a new statistical method to test the relationship between exposure and time to death in the presence of the healthy worker effect. In this study, we considered the healthy worker hire effect to operate as a confounder and the healthy worker survival effect to operate as a confounder and an intermediate variable. The basic idea of the proposed method reflects the length bias-sampling caused by changing one's employment status. Simulation studies were also carried out to compare the proposed method with the Cox proportional hazards models. According to our simulation studies, both the proposed test and the test based on the Cox model having the change of the employment status as a time-dependent covariate seem to be satisfactory at an upper 5% significance level. The Cox models, however, are inadequate with the change, if any, of the employment status as time-independent covariate. The proposed test is superior in power to the test based on the Cox model including the time-dependent employment status.

• 한국환경보건학회지
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• 제6권1호
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• pp.10-21
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• 1979

In preventing the infection of Clonorchis sinensis, there is one way in which life cycle of Clonorchis sinensis is cut off by eradicating the first intermediate host viz Parafossarulus manchuoricus, with molluscicides or insecticides. This survey was carried out in order to evaluating the molluscicidal effect of several insecticides upon P. manchauricus. In this survey, diazinon, heptachlor, E.P.N., E.M., and malathion was applied as molluscidies. Those insecticides had been generaly used in farming area. The results are summarized as follows. 1) In molluscicidal effect, E.M. showed the higher molluscicidal effect than any other insecticides in all experiment parts, and the order of insecticides upon molluscicidal effect was that of E.M., E.P.N., heptachlor and malathion. 2) $LD_{50}$ values are varied according to the exposure time in insecticide solution, and the longer the exposure time is, the lower the values of $LD_{50}$ is. 3) To take the exposure time in low concentration of insecticide solution for the long time would obtain the more molluscicidal effect. 4) The mortality rate increases in proportion as the concentration of insecticides increases.