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Scheduling policies in flexible Bernoulli lines with dedicated finite buffers
Park, Kyungsu,Li, Jingshan,Feng, Shaw C. Elsevier 2018 Journal of manufacturing systems Vol.48 No.1
<P><B>Abstract</B></P> <P>This paper is devoted to studying scheduling policies in flexible serial lines with two Bernoulli machines and dedicated finite buffers. Priority, cyclic and work-in-process (WIP)-based scheduling policies are investigated. For small scale systems, exact solutions are derived using Markov chain models. For larger ones, a flexible line is decomposed into multiple interacting dedicated serial lines, and iteration procedures are introduced to approximate system production rate. Through extensive numerical experiments, it is shown that the approximation methods result in acceptable accuracy in throughput estimation. In addition, system-theoretic properties such as asymptotic behavior, reversibility, and monotonicity, as well as impact of buffer capacities are discussed, and comparisons of the scheduling policies are carried out.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An analytical model of scheduling policies in a flexible Bernoulli two-machine line is presented. </LI> <LI> Markov chain and decomposition methods are introduced to evaluate system production rate. </LI> <LI> Three scheduling policies are considered: priority, cyclic, and WIP-based policies. </LI> <LI> Conservation of flow, monotonicity and asymptotic properties are analyzed. </LI> </UL> </P>
Exit Recursion Models of Clustered Photolithography Tools for Fab Level Simulation
Park, Jung Yeon,Park, Kyungsu,Morrison, James R. Institute of Electrical and Electronics Engineers 2017 IEEE transactions on semiconductor manufacturing Vol.30 No.1
<P>In semiconductor wafer fabricators (fabs), clustered photolithography tools (CPTs) are often the bottleneck. With a focus on fab-level simulation, we propose a new class of equipment models for CPTs called exit recursion models (ERMs). These models are inspired by concepts from flow line theory. We describe the intuition behind ERMs and provide the parameterization and simulation equations. These ERMs are data-driven empirical models and we develop three types based on different data perspectives: 1) tool log; 2) wafer log; and 3) lot log. To assess the quality of the proposed models, we conduct three classes of simulation experiments. A detailed CPT model, an affine model, and an empirical flow line model are used as the baselines. We consider mean cycle time, lot residency time, throughput time, and computation time as our primary performance metrics. The results suggest that ERMs are more accurate and robust than the affine models for all metrics and sometimes rival the performance of the empirical flow line models considered. ERMs require about 1.9 times as much computation as an affine model and about 250 times less computation than an empirical flow line model. ERMs may be helpful to increase the accuracy of fab-level simulation results without significant additional computation.</P>
박경수(Kyungsu Park),김우성(Woo-sung Kim) 한국경영과학회 2017 韓國經營科學會誌 Vol.42 No.4
Due to rapid market changes, customized demands, and the upcoming era of smart factories, flexible manufacturing systems are becoming more prevalent. Multiple types of customized products are being produced in the same production line, in which each machine should be flexible enough to serve those types. This paper studies a two-machine production line with Bernoulli reliability machines for multiple types of products. Each product type has dedicated buffers. Given that scheduling and control polices play a critical role in ensuring efficient production, three prevalent control policies are considered: priority-, cyclic-, and work-in-process (WIP)-based policies. The solutions are derived based on the Markov chain models. In addition, system properties, such as non-conservation of flow, monotonicity, and asymptotic behavior, are addressed theoretically and numerically.
유도상 아스팔트 노반의 최적두께 및 설계수명 산정 연구
박경수(KyungSu Park),이성혁(Seong Hyeok Lee),이진욱(Jin Wook Lee),류태진(Tae Jin Lyu),원상수(Sang Soo Won) 한국철도학회 2013 한국철도학회 학술발표대회논문집 Vol.2013 No.5
유도상 아스팔트 노반은 빗물의 침투방지 효과로 인한 노반부의 강도저하와 연약화방지 효과, 열차하중의 분산으로 인한 노반 두께 감소 효과, 노반 분니 방지 및 동상방지에 의한 유지보수비 절감 효과를 얻을 수 있다. 이와 같은 장점들로 인하여 강화노반과 자갈도상 사이에 아스팔트 층을 부설하는 유도상 아스팔트 노반은 이탈리아, 일본 등에서 설계기준에 명시되어 널리 적용되고 있다. 따라서 국내에서도 유도상 아스팔트 노반 도입이 필요하다. 본격적인 도입에 앞서 다양한 실내외 실험 및 해석적 연구가 필요하므로 본 연구에서는 궤도해석 프로그램인 GEOTRACK과 KENTRACK 프로그램을 이용하여 고속철도 강화노반 설계 조건에 부합하는 아스팔트 노반과 강화노반의 최적두께를 산정하고 최적두께에서의 응력상태 및 설계수명을 비교 분석하였다. Ballasted asphalt roadbed can be beneficial in reducing maintenance cost from various effects such as (i) prevention of both strength reduction and weakening in roadbed system due to the effect of preventing rainwater penetration; (ii) decreasing the thickness of roadbed by dispersing a train load; (iii) prevention of roadbed mud-pumping and frostbite. Due to these beneficial effects, the ballasted asphalt roadbed, which is layered between reinforced and ballasted roadbeds, has been widely applied in design standards of Italy and Japan. In light of this trend, the domestic railway industry is also considering the introduction of the ballasted asphalt roadbed system in practice. Prior to the introduction of this asphalt system, various laboratory and field experiments as well as analytical studies are required. In this study, the optimum thickness of asphalt and reinforced roadbeds, corresponding to the design standards for reinforced roadbed of high-speed railway, was estimated. The stress state in the optimum thickness and its design life were also compared and analyzed.
박경수(Kyungsu Park),엄지은(Ji Eun Eom),박정수(Jeongsu Park),이동훈(Dong Hoon Lee) 한국정보보호학회 2015 정보보호학회논문지 Vol.25 No.1
중복 제거 기술(Deduplication)은 동일한 데이터에 대하여 중복 저장을 방지하는 기법으로 클라이언트(Client)와 클라우드 서버(Cloud Server) 간에 데이터를 저장하고 관리하는데 있어 효율성을 제공한다. 하지만 공개된 환경의 클라우드 서버에 데이터를 저장하고 관리하기 때문에, 클라이언트가 저장한 데이터에 대한 프라이버시 문제가 발생할 뿐만 아니라 데이터의 손실이 발생할 수도 있다. 최근 이러한 문제점들을 해결하기 위해 안전한 중복 제거 기술이 제안되었지만, 여전히 각각의 공격의 안전성에 대한 문제가 발생할 뿐만 아니라 비효율적이다. 본 논문에서는 2013년 Bellare 등이 제안한 기법의 키 서버(Key Server)와 질의-응답 메커니즘(Challenge-Response)을 이용하여 안전하고 효율적인 클라이언트 사이드 중복 제거 기술을 제안한다. 제안 기법은 클라이언트 사이드 중복 제거 기술에서 발생하는 다양한 공격에 대해 안전성을 제공하며, 크기가 큰 데이터를 업로드 하는 환경에서 높은 효율성을 제공한다. Deduplication, which is a technique of eliminating redundant data by storing only a single copy of each data, provides clients and a cloud server with efficiency for managing stored data. Since the data is saved in untrusted public cloud server, however, both invasion of data privacy and data loss can be occurred. Over recent years, although many studies have been proposed secure deduplication schemes, there still remains both the security problems causing serious damages and inefficiency. In this paper, we propose secure and efficient client-side deduplication with Key-server based on Bellare et. al’s scheme and challenge-response method. Furthermore, we point out potential risks of client-side deduplication and show that our scheme is secure against various attacks and provides high efficiency for uploading big size of data.