Toward Socially Agreeable Aggregate Functions for Group Recommender Systems

옥창수(Changsoo Ok),이석천(Seokcheon Lee),정병호(Byungho Jeong) 한국경영과학회 2007 韓國經營科學會誌 Vol.32 No.4

In ubiquitous computing, shared environments are required to adapt to people intelligently. Based on information about user preferences, the shared environments should be adjusted so that all users in a group are satisfied as possible. Although many group recommender systems have been proposed to obtain this purpose, they only consider average and misery. However, a broad range of philosophical approaches suggest that high inequality reduces social agreeability, and consequently causes users’ dissatisfactions. In this paper, we propose social welfare functions, which consider inequalities in users’ preferences, as alternative aggregation functions to achieve a social agreeability. Using an example in a previous work[7], we demonstrate the effectiveness of proposed welfare functions as socially agreeable aggregate functions in group recommender systems.

A stochastic simulation-based holistic evaluation approach with DEA for vendor selection

Park, SeJoon,Ok, Changsoo,Ha, Chunghun Elsevier 2018 COMPUTERS & OPERATIONS RESEARCH - Vol.100 No.-

<P><B>Abstract</B></P> <P>This paper aims to propose a new vendor evaluation framework by incorporating stochastic discrete event simulation and data envelopment analysis (DEA) approaches. The proposed approach enables the assessment of decision-making units (DMUs) in a holistic manner by adopting a simulation scheme and defining DMUs not as individual vendors, but as entire supply chains. Extensive experimental results show that the efficiency of a supply chain is not critically proportional to the efficiencies of individual suppliers. Moreover, procurement performance depends on the harmonic performance of the entire supply chain that includes vendors, procurement structure, ordering and safety stock policy of buyer, and demand variability rather than each supplier's performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose a new vendor evaluation method by incorporating simulation and DEA. </LI> <LI> The proposed method adopts a stochastic simulation scheme to consider uncertainties. </LI> <LI> The approach evaluates vendors, procurement structure, ordering and safety stock policy of buyer, and demand variability simultaneously. </LI> <LI> Experimental results show that procurement performance depends on the harmonization of supply chain rather than individual suppliers. </LI> </UL> </P>

RTP-Based Residential Energy Consumption Scheduling Model with an Energy Storage System as an Independent Provider

Kim Sehwan,Ok Changsoo,Seok Hyesung 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.4

Various real-time pricing (RTP)-based residential consumption scheduling models have been developed to deal with the blackout problem and supply electricity more stably. However, most RTP-based models cause a rebound peak problem. Hence, we propose an innovative RTP-based model with an energy storage system (ESS) as an independent power provider, which is a more reliable and practical solution (called RTP with ESS in this study) than previous models. The price competition between the ESS power provider and wholesale market reduces the power consumption cost of the consumer and peak load of the supply. We compared three models: (1) Non-scheduling, (2) RTP-based Scheduling, and (3) RTP with ESS Scheduling models. Test results reveal that the RTP with ESS Scheduling model reduced consumer power usage costs by 35.24% and 25.86% more than the two models above, respectively. In addition, the RTP with ESS Scheduling model reduced the peak-to-average power ratio of power consumption by 35.10% and 8.71% more than those of the non-scheduling and the existing RTP models, respectively. The consumer standard deviation of power consumption cost was 25.70% and 49.25% lower than those of the non-scheduling and existing RTP models, respectively, and had a fair distribution of power usage costs

Network Structure-Aware Ant-Based Routing in Large-Scale Wireless Sensor Networks

Kim, Kyungdoh,Ha, Chunghun,Ok, Changsoo Taylor & Francis 2015 INTERNATIONAL JOURNAL OF DISTRIBUTED SENSOR NETWOR Vol.2015 No.-

<P>Routing algorithms for large-scale sensor networks should be capable of finding energy efficient paths to prolong the lifetime of the networks in a decentralized manner. With this respect, Ant System has several proper characteristics for routing algorithm in large-scale wireless sensor networks. First, its distributed mechanism enables routing algorithm to find a solution with only local information and be robust for uncertainties in wireless sensor networks. Second, the framework of the Ant System is proper to solve dynamic problems such as routing problem. Transition probability in Ant System can be used to estimate how good a given routing path is. Capturing these features, this work proposes two Ant Systems based routing algorithms, which are AS-RWSNs (Ant System for Routing in Wireless Sensor Networks) and SAAS-RWSN (Structure-Aware AS-RWSN). The AS-RWSN applies the original Ant System to routing algorithm for wireless sensor network and SAAS-RSN upgrades AS-RWSN with considering properties of network structure such as degree of node. In SAAS-RSN, sensors with high node degree have high data traffic since they have more routing paths. Consequently, SAAS-RSN achieves an energy balance over sensor network through this routing scheme. We demonstrate the effectiveness of the proposed algorithms by comparing three existing routing algorithms.</P>

Magnetic Facet domains and Spin Torques

Kyoung-Woong Moon,Changsoo Kim,Jungbum Yoon,Jun Woo Choi,Dong-Ok Kim,Kyung Mee Song,Dongseuk Kim,Byong Sun Chun,Chanyong Hwang 한국자기학회 2018 한국자기학회 학술연구발표회 논문개요집 Vol.2018 No.11

Evaluation of forecasting methods in aggregate production planning: A Cumulative Absolute Forecast Error (CAFE)

Ha, Chunghun,Seok, Hyesung,Ok, Changsoo Elsevier 2018 COMPUTERS & INDUSTRIAL ENGINEERING Vol.118 No.-

<P><B>Abstract</B></P> <P>The purpose of forecasting error measures is to estimate forecasting methods and choose the best one. Most typical forecasting error measures are designed based on the gap between forecasts and actual demands and, consequently, a forecasting method yielding forecasts in accordance with real demands is considered as good. However, in some applications such as aggregate production planning, these measures are not suitable because they are not capable for considering any effects caused by forecasting error such as increasing cost or decreasing profit. To tackle this issue, we propose a new measure, CAFE (Cumulative Absolute Forecast Error), to evaluate forecasting methods in terms of total cost. Basically, the CAFE is designed to consider not only forecasting errors but also costs occured by errors in aggregate production planning which is set up based on forecasts. The CAFE is a product sum of cumulative forecasting error and weight factors for backorder and inventory costs. We have demonstrated the effectiveness of the proposed measure by conducting intensive experiments with demand data sets from M3-competition.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new measure for forecasting error is designed to consider the cost which the error causes. </LI> <LI> The proposed measure enables to calculate the real effect of forecasting error. </LI> <LI> Extensive experiments with datasets from M3 competition. </LI> </UL> </P>

신부전환자의 신장이식 전후 골밀도변화 분석

박형후(Hyong-Hu Park),옥치상(Chi-Sang Ok),박영인(Young-In Park),이진수(Jin-Soo Lee),김창수(Changsoo Kim) 한국콘텐츠학회 2012 한국콘텐츠학회논문지 Vol.12 No.9

골밀도 감소에 의해서 발생되는 골감소증, 골다공증 등은 폐경 후 여성에게 유병률이 높은 질환이며, 골다공증 골절에 따른 사회적 의료비 상승으로 의학적 관심이 급증하고 있다. 신부전환자는 체내에 비타민D 합성 능력이 저하되어 칼슘 흡수가 감소하여 뼈의 섬유화가 발생되고, 골밀도가 감소하는 현상이 나타난다. 따라서 신부전환자는 신장 기능 장애로 그치지 않고, 골다공증과 같은 골밀도 감소에 따른 합병증에 노출되어 있다. 본 연구에서는 치료 중에 있는 신부전환자들의 골밀도 변화를 관찰하였고, 신장이식 전후에서 발견되는 골밀도 변화를 분석하였다. 조사대상은 부산 B종합병원 신장내과 내원환자 중 신부전환자 214명을 신장이식의 유무에 따라 골밀도의 변화를 세대별, 성별로 나누어 분석했다. 분석결과 신장이식 환자군에서는 골밀도가 유지되거나 개선되었지만, 비신장이식 환자군에서는 골밀도가 꾸준히 나빠지는 결과를 보였다. 신부전환자는 신장이식을 받는 것이 최선의 치료책으로 사료되며, 신장이식을 통해서 골밀도의 개선이 가능함을 확인하였다. 이는 추가적으로 예상되는 합병증을 예방하기 위한 자료로도 활용할 수 있다. Disease, such as osteopenia, osteoporosis, etc caused by reduced bone density are common to women after menopause and as the social medical cost increases due to osteoporosis fractures the medical interest in bone density reduction has increased. The bone density reduction is observed even for renal failure patients, due to their decreased ability to synthesize vitamin D which leads to bone fibrosis because of deficiency in calcium absorption. Thus renal failure patients not only suffer from kidney dysfunction, but also are exposed to complications, such as osteoporosis, due to reduced bone density. This research observed the change in bone density of patients receiving renal failure treatment and analyzed the change in bone density before and after kidney transplantations. Subjects were 214 renal failure patients at the department of nephrology Busan B General Hospital. The change in bone density was studied for subjects with and without kidney transplantation according to their age and sex. The research showed improvement or maintenance of bone density for subjects that received kidney transplantation, but showed a tendency of consistent decrease in bone density for subjects without kidney transplantation. Kidney transplantation can be considered as the best cure for renal failure patients, and this researched confirmed that bone density can be improved through kidney transplantation. Thus, this study can also be used as data for preventing complications due to renal failures.

Unstructured Data Quantification Scheme Based on Text Mining for User Feedback Extraction

Jung-Heum Jo,Yong-Taek Chung,Seong-Wook Choi,Changsoo Ok 한국산업경영시스템학회 2018 한국산업경영시스템학회지 Vol.41 No.4

People write reviews of numerous products or services on the Internet, in their blogs or community bulletin boards. These unstructured data contain important emotions and opinions about the author's product or service, which can provide important information for future product design or marketing. However, this text-based information cannot be evaluated quantitatively, and thus they are difficult to apply to mathematical models or optimization problems for product design and improvement. Therefore, this study proposes a method to quantitatively extract user’s opinion or preference about a specific product or service by utilizing a lot of text-based information existing on the Internet or online. The extracted unstructured text information is decomposed into basic unit words, and positive rate is evaluated by using existing emotional dictionaries and additional lists proposed in this study. This can be a way to effectively utilize unstructured text data, which is being generated and stored in vast quantities, in product or service design. Finally, to verify the effectiveness of the proposed method, a case study was conducted using movie review data retrieved from a portal website. By comparing the positive rates calculated by the proposed framework with user ratings for movies, a guideline on text mining based evaluation of unstructured data is provided.

계층적분석기법을 이용한 APS 개선방안 도출

하정훈(Chunghun Ha),이영관(Young Kwan Lee),옥창수(Changsoo Ok) 한국산업경영시스템학회 2011 한국산업경영시스템학회지 Vol.34 No.3

The advanced planning and scheduling(APS) is an well known enterprise information system that provides optimal production schedules and supports to complete production on time by solving the complex scheduling problems including capacity and due dates. In this paper, we focused on the improvement of the APS that is already established on a real company. The existing APS had several drawbacks, thus utilization and satisfaction were very low. We performed the focused group interviews and the process analysis and could find that the end users and developers have various objectives and the frequently used functions are different. We applied the analytical hierarchy process(AHP) to converge opinions of them on quantitative data. The results show that it is necessary to enhance visibility, to improve user interfaces and response speed, and to reconcile the real business process and the APS’s process.