• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.11
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• pp.5323-5343
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• 2018

Mobile applications and social networks tend to enhance the need for high-quality content access. To address the rapid growing demand for data services in mobile networks, it is necessary to develop efficient content caching and distribution techniques, aiming at significantly reduction of redundant content transmission and thus improve content delivery efficiency. In this article, we develop optimal cooperative content cache and distribution policy, where a geographical cluster model is designed for content retrieval across the collaborative small cell base stations (SBSs) and replacement of cache framework. Furthermore, we divide the SBS storage space into two equal parts: the first is local, the other is global content cache. We propose an algorithm to minimize the content caching delay, transmission cost and backhaul bottleneck at the edge of networks. Simulation results indicates that the proposed neighbor SBSs cooperative caching scheme brings a substantial improvement regarding content availability and cache storage capacity at the edge of networks in comparison with the current conventional cache placement approaches.

• Journal of Biosystems Engineering
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• v.14 no.2
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• pp.115-122
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• 1989

The objective of this study was to develop a portable auger for handling rough rice in bulk. For this purpose, a system analysis was taken for the systems of harvesting, drying, storage and transportation of rough rice and an optimal handling capacity of portable auger was determined. Then a portable auger of which capacity is 9.2 $m^3/h$ (Indica type rough rice, 19.5%, w.b.) was designed and manufactured by design requirements and tested. Test results showed that the performance of portable auger developed satisfied most design requirements.

• Journal of the military operations research society of Korea
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• v.30 no.2
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• pp.133-140
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• 2004

In this paper, with the limited range of ammunition supply point(ASP) at ammunition battalion in specific corps and light automobile battalion(LAB) directly supports its vehicle for ammunition supply, we propose optimal model to minimize transportation time and logistics cost using integer programming(IP) for efficient ammunition resupply allocation during a given operation period of front combat unit. And then, we consider ammunition treatment and supply capacity of ammunition supply point(ASP), constraint elements of transportation ability considering time and cost, ammunition storage capacity of combat unit, combat situation and unit mission to propose this model. Finally, through numerical example, we examine the applicable feasibility of proposed model.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.585-597
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• 2008

The aim of this study was to find an analytic solution to the problem of determining the optimal capacity (lot-size) of a batch-storage network to meet demand for a finished product in a system undergoing random failures of operating time and/or batch material. The superstructure of the plant considered here consists of a network of serially and/or parallel interlinked batch processes and storage units. The production processes transform a set of feedstock materials into another set of products with constant conversion factors. The final product demand flow is susceptible to short-term random variations in the cycle time and batch size as well as long-term variations in the average trend. Some of the production processes have random variations in product quantity. The spoiled materials are treated through regeneration or waste disposal processes. All other processes have random variations only in the cycle time. The objective function of the optimization is minimizing the total cost, which is composed of setup and inventory holding costs as well as the capital costs of constructing processes and storage units. A novel production and inventory analysis, the PSW (Periodic Square Wave) model, provides a judicious graphical method to find the upper and lower bounds of random flows. The advantage of this model is that it provides a set of simple analytic solutions while also maintaining a realistic description of the random material flows between processes and storage units; as a consequence of these analytic solutions, the computation burden is significantly reduced.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.981-987
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• 2017

In this paper, we estimate the economic benefits of Energy Storage Systems (ESSs) for peak load shaving in an urban railway substation using the annual cost. The annual investment cost of ESSs is estimated using Net Present Value (NPV) and compared with the cost reduction of electricity by the ESS. The optimal capacities of the battery and Power Converting System (PCS) are determined for peak load shaving. The optimal capacity of the ESS and the peak load shaving is determined to maximize the profit by the ESS. The proposed method was applied to real load data in an urban railway substation, and the results show that electric power costs can be reduced. Other aspects of the ESS, such as the lifetime and unit price of the battery, are also investigated economically.

• Journal of the East Asian Society of Dietary Life
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• v.14 no.5
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• pp.443-448
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• 2004

In order to investigate the optimal factors for frozen dough production, the freezing and thawing condition such as temperature and time, storage period and the effect of ingredient addition were determined. A pre-fermentation of dough at 30℃ for 120 minutes was appeared to be the best for the production of frozen dough. The dough was frozen at -18℃ and then stored for 7 days. The quality of frozen dough was found to be optimal when thawed at 30℃ for 80 minutes. As ingredient of frozen dough, an addition of 3% of yeast and 4% of butter was good as well as the addition of skim milk and sugar in terms of fermentation capacity after thawing.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.5
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• pp.61-69
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• 2017

The study on interference channel is very important information theoretically and many studies have been done on it. However, even in the simplest case, even in the case of two user interfering channels, the channel capacity is not yet known except in special cases. Recently, research on the multiplexing gain that shows the tendency of the transmission rate in the high signal to noise ratio (SNR) band has been actively carried out, instead of accurately grasping the channel capacity. Obtaining optimal multiplexing gain can reveal trends in channel capacity at high signal-to-noise ratio bands. In an interfering channel with two users, the best multiplexing gain can be obtained by eliminating the interference. However, recent research shows that when the number of users is more than three, the optimal multiplexing gain can not be obtained only by zero forcing and a new technique called interference sorting is needed. There are two types of interference sorting techniques. Beamforming A method of effectively separating signals and interference by properly selecting matrices and constructing structured codes using rational numbers and irrational numbers. The interference alignment technique can achieve optimal multiplexing gain in various environments such as interference channel, X channel, compound broadcast channel, and multi hop network for multi source multi destination. In recent years, it has also been applied to distributed storage. Lee et al., "Lattice Code Interference Alignment in Cooperative Multipoint Transmission (COMP) for Interference Channels of Three Users", Journal of the Institute of Electronics Engineers, vol.49-TC,no.6,2012. In this paper, the DoF of delayed channel information is obtained.

• Journal of Electrical Engineering and Technology
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• v.13 no.6
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• pp.2168-2177
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• 2018

The unavoidable forecast error of wind power is one of the biggest obstacles for wind farms to participate in day-ahead electricity market. To mitigate the deviation from forecast, installation of energy storage system (ESS) is considered. An accurate model of wind power forecast error is fundamental for ESS sizing. However, previous study shows that the error distribution has variable kurtosis and fat tails, and insufficient measurement data of wind farms would add to the difficulty of modeling. This paper presents a comprehensive way that makes the use of mixed skewness model (MSM) and copula theory to give a better approximation for the distribution of forecast error, and it remains valid even if the dataset is not so well documented. The model is then used to optimize the ESS power and capacity aiming to pay the minimal extra cost. Results show the effectiveness of the new model for finding the optimal size of ESS and increasing the economic benefit.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.5
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• pp.683-694
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• 2024

Flood control capacity enhancement measures in watersheds can be broadly categorized into structural and non-structural approaches. In this study, we propose the improvement of the flood control capacity in the Seomjin River basin through non-structural measures by optimizing the operation of the Seomjin River Dam, specifically by introducing a flexible flood season restricted water level (FSRWL). The flexible operation of FSRWL involves setting lower restricted water levels at the beginning of the flood season to increase flood control capacity and gradually raising them as the season progresses to manage flood control more effectively. As a structural measure, we examined the installation of riverside storage areas, a representative technique of nature-based solutions (NbS). Using the 2020 flood event as a case study, we analyzed the flood level reduction effects of implementing structural and non-structural measures both separately and simultaneously to identify the most effective and economical approach. The results indicate that the optimal flood prevention strategy for the main stream of the Seomjin River during the 2020 flood event involves operating the Seomjin River Dam FSRWL at EL. 190 m during the mid-flood season as a non-structural measure and installing a riverside storage area downstream of Godalgyo Bridge in Daepyeong-ri, Gokseong-gun as a structural measure.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.555-560
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• 2016

Recently, many countries have placed great attention on energy security and climate changes. Governments are promoting the construction of renewable energy projects with regulatory support in Korea. Despite an increasing penetration of renewable resources, however, the photovoltaic and wind power are underutilized due to the endemic problems such as difficulties of output control and intermittent output. The Energy Storage System (ESS) is proposed as a good solution for solving the problems and has been studied in both the private business and the government. However, because of inefficient aspects, the research has been carried out for improving high costs and a small capacity. In addition, the ESS is currently installed for using only one purpose which is frequency regulation or transmission congestion relief such that has an economic limitation. Therefore, methods which are becoming economically justifiable to increase the penetration of the ESS is required. Thus, this paper presents in terms of operation efficiency to improve economic feasibility of the ESS currently used. mainly, there are two aspects for the operation efficiency. Firstly, it is intended to improve the utilization rate through a process that can utilize the ESS for various purposes. It is necessary to be able to use for other purposes by classifying and clustering for increasing the efficiency of availability. The clustering method is proposed to conduct the grouping the ESS. Especially, it is proposed to utilize ESS for frequency regulation service which is the one of ancillary services in the power system. Through case studies, it is confirmed to secure the necessary resources by clustering small size ESS.