지속 가능한 수자원 관리를 위한 지표수-지하수 연계이용 최적화

서승범,김영오,Seo, Seung-Beom,Kim, Yeong-O 한국수자원학회 2018 물과 미래(한국수자원학회지) Vol.51 No.12

Asymptotically Optimal Solution for TSF-Constrained Staffing Problem

서승범 대한경영학회 2019 大韓經營學會誌 Vol.32 No.9

Finding the right balance between the customer service and personnel expenditure has been an important task both in practice and academia and in academia this problem was usually approached using a total cost problem. However, it is difficult to directly apply this formulation in practice and hence recent works in queueing systems have investigated this problem with staffing minimization with constraints on quality-of-service constraints. Our work contributes on this stream of works by studying TSF measure, which shows the percentage of customers who waited beyond the prespecified threshold. TSF measures the proportion of customers whose waiting time exceed a certain threshold. It is one the most prevalent kind of quality of service measure, along with ASA, which measures the average of waiting time. TSF measure is intuitive to understand and hence widely been used but has not received sufficient attention in academia. Part of the reason comes from the unnatural property of TSF measure. Once a customer waits more than the threshold, the incentive to serve that customer starkly diminishes since decreasing the eventual waiting time of him does not enhance the performance of the system. Hence a policy that is far from FIFO turns out to be more efficient. Especially we are interested in context where service level differentiation among various classes of customers. Hence, we work on V-model where multiple classes of customer and homogeneous pool of servers exist. Our task is to come up with the minimum possible number of servers while maintaining TSF measure on the pre-defined level. The decision variables are two-kind: number of servers and prioritization policy. The prioritization policy defines which class of customer to server first when a server becomes available. The nature of TSF measure, which tends to give lower priority to the customers who had already waited beyond the threshold, makes the problem more difficult to solve and hence it was usually treated in literature more added conditions or constraints added. We devise an optimal solution of TSF constrained problem without adding more structures. Since the problem is difficult to solve in exact analysis, we apply the heavy traffic technique to solve the problem. First, we show that our suggested staffing level is the lower bound for all the feasible solutions. Second, it is proved that the proposed prioritization policy combined with our staffing level actually is feasible and hence asymptotically optimal.

이차원 소재 및 응용 소자 기술 동향

서승범,장병철,최성율,Seo, Seung-Beom,Jang, Byeong-Cheol,Choe, Seong-Yul 한국정보디스플레이학회 2016 인포메이션 디스플레이 Vol.17 No.3

Minimization of Concave Holding Costs in Queueing System

서승범 연세대학교 경영연구소 2020 연세경영연구 Vol.57 No.2

Since the advent of basic  rule, minimization of holding costs has been one of the most fundamental problems in queueing theory. The first results on holding cost minimization was under the linear cost assumption and the more general case of convex costs has been solved with help of queueing approximation method named heavy traffic. Even with many sophisticated solutions on general settings, there is scarce literature that goes beyond convex or linear cost structure. Especially, a holding cost minimization problem with concave cost structure has not been discuessed yet. As far as we know, our work is the first to study concave cost structure in queueing theory. We study how the customers from multiple classes should be prioritizized. We figure out that so-called bang-bang policy is always included in the set of optimal prioritization policies when the costs are concave and that all the optimal solutions to strict concave costs are bang-bang. With this property, we construct a simple and general solution for the concoave cost minimization problem. We also provide a condition that produces a solution that assigns the whole workload to a single class.

수익공유계약, 환매계약, 단순선형가격계약에 관한 대면 행동 실험 연구

서승범 대한경영학회 2023 大韓經營學會誌 Vol.36 No.11

수익공유계약과 환매계약은 공급사슬에서 단순선형가격계약을 사용했을 때 나타나는 이중한계비용화 현상을해결하기 위해 고안된 계약 형태이다. 이중한계비용화 현상이란 공급 사슬 내 기업들이 하나의 기업으로 통합되어있을 때보다 개별 기업으로 분리되어 있을 때 수익이 더 낮은 현상을 나타낸다. 이론적으로 수익공유계약과 환매계약은단순선형가격계약보다 더 높은 성과를 가져오는 것으로 밝혀졌지만, 행동적인 연구방법론을 사용한 선행 연구에따르면 실제 사람이 의사결정을 할 때에는 이론과는 다른 행태를 보인다는 것 역시 보여졌다. 실제로 수익공유계약과 환매계약이 사용되는 경우가 많지 않은데 그 이유로 공급사슬 내 실제 기업 의사 결정자의선택이 이론에서 예측하는 것과는 다른 것을 들 수 있다. 공급사슬 계약과 관련해서 그동안 다양한 행동적 실험들이이루어졌고, 여러 가지 실험 환경에서 피실험자들은 어떤 의사 결정을 내리는지에 대해 관찰하였다. 특히 대부분의실험에서는 계약 상대방이 누구인지 모르거나 상대방이 사람이 아닌 컴퓨터인 상태에서 계약 의사 결정을 보았다. 이는 현실에서 이루어지는 공급사슬 계약 관련한 다양한 측면 중 일부에 집중하기 위해 의도적으로 조성된 것이나현실에서는 계약 상대방이 누구인지 알 수 있다는 사실을 불가피하게 반영하지 못했다. 본 연구에서는 특히 대면 상황에서 도매상과 소매상 역할을 하는 피실험자가 세 가지 계약에 대해 어떤 의사결정을 내리는지에 대해 실험적으로 탐구하였다. 실험에서 수요가 불확실한 상태에서 도매상은 계약의 계수를 정하고, 이를 본 소매상이 재고량을 정했다. 그 결과, 단순선형가격계약의 경우 이중한계비용화 현상이 이론적인 예측보다적게 나타나고, 수익공유계약에서는 도매가격이 최적 수준보다 작게, 환매계약에서는 더 크게 지정되는 것을 관찰했다. 전체이익 면에서는 환매계약이 수익공유계약보다 더 크고 소매상은 환매계약을 더 선호하는 것으로 나타났다. Revenue sharing contracts and buyback contracts are designed to address the double-marginalization problem that may occur when simple linear price contracts are used in supply chains. Double-marginalization refers to the phenomenon where companies in a supply chain are less profitable when separated into individual entities than when integrated into a single company. In the supply chain literature, various means were proposed to overcome double-marginalization. Among these, revenue-sharing contracts and buyback contracts are widely studied. In the revenue-sharing contract, the supplier earns additional revenue from the sales of the retailer besides the initial wholesale revenue. In the buyback contract, the retailer can resell its leftover inventories to the supplier. While these two contracts appear superficially different, mathematically they are equivalent. For a given parameter set of the revenue-sharing contract, an equivalent parameter set for the buyback contract can be constructed to provide the same amount of cash flow in every situation. It has alson been theoretically shown that the performance of revenue-sharing contracts and buyback contracts are higher than that of simple linear price contracts. However, prior behavioral research has also indicated that real people make different decisions than the theory predicts. In practice, revenue sharing contracts and buyback contracts are not as frequently used and the reason can be traced back to the fact that the decision-making in practice might be different from the one predicted by theory. There have been many behavioral experiments with various settings on supply chain contracts. In particular, subjects had to make decisions without knowing who the other party of the contract is or the other party was a computer. Those settings were deliberately composed to focus on specific aspects of real-world supply chain, but they did not reflect the fact that two decision makers of the contract may know each other. In this study, we experimentally explore how subjects taking the roles as wholesalers and retailers make decisions about the three contracts, especially in face-to-face situations. The experiment was conducted on undergraduate students. Two subjects made one group and each of them took the role of the supplier and the retailer. The groups were allowed to make face-to-face communication. The demand was assumed to follow the discrete uniform distribution from 1 to 20 and the consumer price of the product was given as 12. The production cost was given as 3. No salvage value was assumed. The same group went through the experiment for the simple linear contract, the revenue-sharing contract and the buyback contract. Overall, there were two separate experiments and in each of them, the sequence of the contracts that the subjects are exposed to was altered to figure out the possibility of the learning effect. In the first experiment, the subjects encountered the simple linear contract - the revenue-sharing contract – the buyback contract and the subjects in the second one encountered the simple linear constract – the buyback contract - the revenue-sharing contract. For each of the contracts, 10 stages of contracting game were executed and hence overall the subjects went through 30 stages. Following the tradition of supply chain contract literature, we assume that the supplier first determines the parameters of the contract and next, the retailer determines the inventory to purchase in each of the stages. The uncertain demand is realized after all the players determined their parameters and the resulting profit for each of the player is calculated. In the next stage, the supplier and the retailer adjusted their parameters and encountered the new demand. All the subjects went through the basic education of the newsvendor model before the experiments. Nine hypotheses regarding the performances of the contracts are constructed. We observed that double-marginaliza...

히어로, 안티히어로, 빌런의 캐릭터 유형에 따른 유제품 유통기한 소비자 평가

서승범,김지호 한국소비자·광고심리학회 2023 한국심리학회지 소비자·광고 Vol.24 No.2

This study attempted to confirm evaluation of consumers according to the character type, And it was verified whether these effects changed according to the sell by date and the involvement. Hero characters can alleviate perceived risk by providing as sense of security and protection, but villain and anti-hero were expected to have different effects. Accordingly, an online survey of 387 people was conducted, and results are as follows. First, consumers perceived the highest level of performance risk in heroes, which showed a significant difference from villain. However, antiheroes showed no difference from both types. Second, the difference in character types for purchase intention was found to be signnificant, and it was high in the order of villain, anti-hero, and hero. Based on this, the sell by date date, involvement, and the effect of the character type of the package were discussed. 본 연구는 캐릭터 유형에 따른 소비자의 평가를 확인하고자 하였다. 그리고 유통기한 잔여일과 소비자의 관여 수준에 따라, 이러한 효과가 달라지는지를 검증하였다. 히어로 캐릭터들은 안정감과 보호감을 제공함에 따라, 지각된 위험을 완화할 수 있지만, 빌런과 불완전한 히어로인 안티히어로 캐릭터들은 서로 다른 효과를 낼 수 있을 것으로 기대되었다. 이에 총 387명을 대상으로 한 온라인 설문조사를 시행하였으며, 조사 결과는 다음과 같다. 먼저, 소비자들은 히어로에서 가장 높은 수준의 수행적 위험을 지각하였으며, 이는 빌런과 유의한 차이를 보였다. 그러나 안티히어로는 두 유형 모두와 차이를 보이지 않았다. 둘째, 구매 의도에 대한 캐릭터 유형의 차이가 유의한 것으로 나타났으며, 빌런, 안티히어로, 히어로 순으로 높은 구매의도를 보였다. 이를 바탕으로 유통기한 잔여일, 관여 수준, 패키지의 캐릭터 유형이 가지는 효과에 대해 논의하였다.

가뭄 대응을 위한 헤징룰 및 저수지 운영 최적화 연구 사례

서승범,김기주,김영오,Seo, Seung-Beom,Kim, Gi-Ju,Kim, Yeong-O 한국수자원학회 2022 물과 미래(한국수자원학회지) Vol.55 No.1

전완부 후골간 동맥 유리피판술을 이용한 안면부 조직 결손 재건 치험례

서승범,이상원,안태황,정성균,김창현,Seo, Seung Bum,Lee, Sang Won,An, Tae Whang,Jung, Sung Gyun,Kim, Chang Hyun 대한미세수술학회 2000 Archives of reconstructive microsurgery Vol.9 No.2

With esthetic concern in the reconstruction of skin and soft tissue defects of face, the use of local flap has been the method of choice. However, when there is extensive tissue loss in the face, local flaps do not provide satisfactory results. The amazing development of microsurgical technique has decreased the percentage of free flap failure, thus making free flap use in reconstruction of facial soft tissue defects. Many free flaps has been applied for reconstruction of face defects. Especially, the radial forearm flap has numerous advantages with which facial reconstruction is made possible. But, its disadvantages are ; the sacrifice of one major artery supplying the hand and donor site complications. In order to circumvent these disadvantages, we employed posterior interosseous artery(PIA) forearm free flap for the reconstruction of the face defects. The posterior interosseous forearm island flap was first described by Zancolli and Angrigiani(1985). Currently, the PIA island flap and free flap have been used for hand reconstructions. The disadvantages of the PIA flap are ; the small caliber of the pedicle, different locations of the perforating branches, and the proximity of the motor branch of the radial nerve. But, its advantages lies in preserving the major artery of the hand, minimal donor site morbidity, and fairly well matched skin texture and color, and that the flap volume is sufficient, not too bulky with convenient handling. By using this flap, we performed 1 case of tumor resection and 1 case of traumatic defect. From our experiences we conclude that it is one of many useful methods in the reconstruction of the skin and soft tissue defects of the face. We also have discussed advantages and some limitations of various free flaps for reconstruction of the face.

IGS 內 Random Effect Regression을 활용한 정부 R&D 재정과 정책금융 연계효과 분석

서승범,조용래,김원준 대한산업공학회 2024 대한산업공학회 춘계학술대회논문집 Vol.2024 No.5

수자원의 합리적 배분 방안 마련 기초연구 : 합리적 물 수급 분석 방안 연구

서승범 한국환경정책평가연구원 2019 한국환경정책평가연구원 기초연구보고서 Vol.2019 No.-

■ 연구의 주요 내용 ○ 국가 수자원계획의 물 수급 전망 현황을 파악하고 미흡한 점과 개선방향을 제시 ○ 국내 수자원계획의 물 수급 전망기법의 현황 분석 ○ 물 수급 전망기법 개선 연구 사례분석 ○ 물 수급 전망기법 개선 방향에 대한 시사점 도출 ■ 정책 제안 ○ 목표 이수안전도 도입을 위한 정책 연구가 필요 ○ 광범위한 물 수급 자료의 DB화 추진 필요 ○ 기후변화에 대응하기 위한 중장기적 수자원계획 수립 필요