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고영대 ( Ko Young Dae ),오용희 ( Oh Yonghui ) 한국품질경영학회 2018 품질경영학회지 Vol.46 No.4
Purpose: Generally, since the population density is lower in suburban areas, the distance to school is inevitably long. Therefore, schools in suburban areas often operate school buses to improve student welfare. However, since school buses are usually used only during going to and from school, the utilization rates are relatively low. Therefore, this study aims to establish integrated operation plan of public school bus covering all schools. Methods: It is necessary to decide which school buses will serve the specific demand node which want to go to certain school in order to design an integrated operation plan for school buses. Therefore, a mathematical model is developed for minimizing the total number of vehicles and the distance of transportation by reflecting the characteristics of school buses and students as constraints. To solve the proposed mathematical model, CPLEX, a commercial solver, is applied. Results: To validate and to confirm the proposed process, numerical example is designed with the comparison between before and after integrated operations of school buses in terms of total operation cost. The result shows that the integrated operation can lead the reduction of the number of school buses as well as the decreasing of the fuel cost. Conclusion: This study provides the quantitative method to perform the integrated operation of school buses in suburban areas. The optimal operation strategy is required because there are more complex decision-making elements considering the integrated operation. It is expected to apply this research result at real situation to expand this services based on an optimal operation.
고영대 ( Young-dae Ko ),오용희 ( Yong-hui Oh ) 한국경영공학회 2015 한국경영공학회지 Vol.20 No.4
The customer behaviors for the fashion commodities are diverse according to the perception about them such as price sensitivity or personal preference. If the customers feel that some commodities have sufficient values comparing their list sales prices, then the customers tend to purchase them without waiting of discount or outlet sales periods. Otherwise, the customers will postpone their purchasing decisions until discount or outlet sales periods to confirm the discount or outlet sales prices whether they have sufficient values or not. Therefore, this study tries to evaluate the sales policies at fashion industry whether outlet channel is used or not while objective is to maximize total profit. The demand functions in case of list, discount and outlet sales are proposed considering demand leakage about both price differences and sales periods. In addition, the mathematical models are developed by reflecting the sales policy with proposed demand functions. To validate the developed model, numerical examples and sensitivity tests are performed and presented.
고영대(Young Dae Ko),오용희(Yonghui Oh) 한국경영과학회 2012 經營 科學 Vol.29 No.3
For the past several decades, personnel scheduling and rostering problem has been one of the most popular research topics in optimization area. Among the numerous applications, airline (aviation) industry has been given most attention due to the economic scale and impact. Most of the literatures about the staff scheduling problem in airline industry are dealing with the air crew, pilots and flight attendances, and the rest of the literatures are about the ground staff, by whom cleaning, maintenance, fueling of aircraft and handling luggage are done from landing to taking off. None of the literatures found by the authors are dealing with the airline ground crew. In this paper roster of airline ground crew, who is responsible for issuing boarding pass, checking baggage, etc, is introduced, formulated and solved using CPLEX. Some expressions of the mathematical formulations, which are not suitable input format of the CPLEX, were transformed. Numerical examples are presented for the validation of proposed scheduling system.
쇼핑몰 방문고객 수 및 방문점포 정보 기반 최적 점포위치 할당 문제
고영대 ( Young Dae Ko ),오용희 ( Yonghui Oh ) 한국경영공학회 2016 한국경영공학회지 Vol.21 No.2
There are several kinds of stores such as a clothing store, a shoe store, a jewelry store, a book store, a restaurant and so on. Those stores should be allocated at limited region of each floor of the shopping mall. It is required to make an efficient layout plan for all stores at proper location with both width and area according to the purpose or concept of that shopping mall because the number of customers who visits at certain store can be different with the store layout. There are two kinds of customers who visit there both with buying purpose and by chance. It is assumed that the number of customers who wants to visit at each store initially with buying purpose is known as constant. In addition, the customers have a chance to visit certain store which is located at their walking paths by getting an influence from attractive promotion, display of items, suggestion of clerk and so on. Therefore, the number of customers who visits at each store by chance can be regarded as a function of both the total number of customers passing by that store and the attractiveness of it. Based on these situations, a mathematical model is developed to derive an optimal store layout with the objective of maximizing the total revenue of all stores. To validate the proposed mathematical model, numerical example is designed and performed. As a result, an optimal solution about store layout at shopping mall can be generated with several insights.
홍현선,고영대,강이승,김건홍,정항철,Hong, Hyun-Seon,Ko, Young-Dae,Kang, Lee-Seung,Kim, Geon-Hong,Jung, Hang-Chul 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.3
Spherical nanosized cobalt powder with an average size of 150-400 nm was successfully prepared at room temperature from cobalt sulfate heptahydrate ($CoSO_4{\cdot}7H_2O$). Wet chemical reduction method was adopted to synthesize nano cobalt powder and hypophosphorous acid ($H_3PO_2$) was used as reduction agent. Both the HCP and the FCC Co phase were developed while $CoSO_4{\cdot}7H_2O$ concentration ranged from 0.7 M to 1.1 M. Secondary phase such as $Co(OH)_2$ and $CO_3O_4$ were also observed. Peaks for the crystalline Co phase having HCP and FCC structure crystallized as increasing the concentration of $H_3PO_2$, indicating that the amount of reduction agent was enough to reduce $Co(OH)_2$. Consequently, a homogeneous Co phase could be developed without second phase when the $H_3PO_2/CoSO_4{\cdot}7H_2O$ ratio exceeded 7.
DBR 다공성 실리콘/고분자 Composite 재료-이중적 광학특성
박철영,장승현,김지훈,박재현,고영대,김성진,고영춘,손홍래,Park, Cheol-Young,Jang, Seung-Hyun,Kim, Ji-Hoon,Park, Jae-Hyun,Koh, Young-Dae,Kim, Sung-Jin,Ko, Young-Chun,Sohn, Hong-Lae 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.3
DBR (distributed Bragg reflectors) PSi (porous silicon) composite films displaying dual optical properties, both optical reflectivity and photoluminescence had been developed. DBR PSi samples were prepared by electrochemical etch of heavily doped $p^{++}-type$ silicon wafers (boron doped, polished on the <100> face, resistivity of $0.8-1.2m{\Omega}-cm$, Siltronix, Inc.). Free-standing DBR PSi films were treated with PMMA (polymethyl methacrylate) to produce flexible, stable composite materials in which the PSi matrix is covered with PMMA containing photoluminescent polysiloles. Optical characteristics of DBR PSi/polysilole-impregnated PMMA composite materials exhibit both their photonic reflectivity at 565 nm and photoluminescence at 510 nm, simultaneously. A possible application of this materials will be discussed. 광 발광성 (photoluminescence, PL)과 광 반사성(reflectivity)의 두 가지 광학적 성질을 동시에 가지고 있는 새로운 다층 DBR(distributed Bragg reflector) 다공성 실리콘 composite 필름을 개발하였다. 발광 효율이 높은 실리콘 고분자 폴리실올을 PMMA(polymethylmethacrylate)에 첨가하여 다층 DBR 다공성 실리콘 표면에 코팅을 한 composite 필름을 제조하였다. 이 composite 필름은 510 nm에서의 발광스펙트럼과 565 nm에서의 반사스펙트럼을 동시에 나타낸다. 이러한 composite 필름은 광학적 정보가 저장되어있고 물리적인 힘을 가하여도 그 광학적 정보를 잃지 않는 장점을 갖는다. 또한 다층 DBR 다공성 실리콘 필름은 쉽게 부서지는 단점 때문에 다루기가 어려운 반면 composite 필름은 고분자로 고형화 되어있으므로 기계적인 안정도를 증가시킬 수 있었다.