• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1481-1500
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• 2016

Device-to-Device (D2D) communication underlaying macro-small cell networks, as one of the promising technologies in the era of 5G, is able to improve spectral efficiency and increase system capacity. In this paper, we model the cross- and co-tier D2D communications in two-tier macro-small cell networks. To avoid the complicated interference for cross-tier D2D, we propose a mode selection scheme with a dedicated resource sharing strategy. For co-tier D2D, we formulate a joint optimization problem of power control and resource reuse with the aim of maximizing the overall outage capacity. To solve this non-convex optimization problem, we devise a heuristic algorithm to obtain a suboptimal solution and reduce the computational complexity. System-level simulations demonstrate the effectiveness of the proposed method, which can provide enhanced system performance and guarantee the quality-of-service (QoS) of all devices in two-tier macro-small cell networks. In addition, our study reveals the high potential of introducing cross- and co-tier D2D in small cell networks: i) cross-tier D2D obtains better performance at low and medium small cell densities than co-tier D2D, and ii) co-tier D2D achieves a steady performance improvement with the increase of small cell density.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3D
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• pp.375-381
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• 2011

This study presents an analysis of $CO_2$ emission reduction effect on bus information system (BIS) which is operated to improve various services of bus transit such as rapid and on-time service. Although the Intergovernmental Panel on Climate Change (IPCC) released three methodological types of models for analyzing the amount of greenhouse gas reduction, this study used the Tier 3 method that is the most concrete one. A case study was performed to a 8.3 km section of Daejun-Chungjoo BIS system, and dataset required to the Tier 3 method was obtained from ITS-based surveillance systems. The study result showed that the reduction effect of $CO_2$ on BIS operation was yearly $39.45tCO_2/km$. Therefore, such effect can be potentially useful to a measurement of effectiveness (MOE) of BIS projects hereafter.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.05b
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• pp.171-174
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• 2003

다자간 채팅은 인터넷 기반에서 진보적인 발전을 한 분야이고, 네트워크 게임과 같은 어플리케이션 제작에 있어 필수적인 기술이다. 본 논문에서는 자바 기술을 이용하여 one-tier, two-tier 구조가 가진 불편한 유지보수, 데이터 은닉의 문제점을 해결하기 위하여 multi-tier architecture로 아바타를 사용하여 다자간 채팅시스템을 구현하였다. 또한 채팅에서 흥미를 유발하기 위한 캐릭터 전송기술, 다양한 문자를 보내기 위한 문자 포맷 기술을 구현하였다.

• The Transactions of the Korea Information Processing Society
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• v.5 no.9
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• pp.2248-2255
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• 1998

The property of connectivity between DBMS and application system developed in java is very important under the distributed object environments with heterogeneous systems. In these days, mostly used JDBC 3-tier model, which supports the connectivity, has two problems: the one is the restricted connectivity needed for the Java applet as application programs and the other is the additional efforts to design and implemtnt in linking any application program with the middleware from being deficit of standard protocol. In order to solve these problems, we have worked on Enlarging the properties of JDBC 3 tier model by applying CORBA distributed object environments. Thus, the enlarged 3-tier model has an ORB-JDBC sub protocol for the client sub-protocol and a middleware whose property is supported by CORBA.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.11
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• pp.231-239
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• 2020

The aim of this paper is to review the role of board size as part of the corporate governance system. This paper discusses one aspect of corporate governance, namely, boards, in the Indonesian context. Using the literature review method, this paper explores factors that need to be considered to determine the optimal number of boards, especially in Indonesia. We explore some determinants of board size, such as complexity and leverage, ownership structure, and financial ratio support. The results reveal that an understanding of the differences found in the two-tier board model helps us understand that the different functions of the board of commissioners and the board of directors require different test treatments from countries that adhere to one-tier systems. A review of the relationship between board size and company performance is expected to provide the corporate governance literature with insights into optimizing the sizes of boards that can improve company performance, both in terms of boards of commissioners and boards of directors. This paper proposes the simultaneous testing of board size's relationship with company performance. The results of this study are expected to make a more real contribution about the effect of board size on company performance.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.24 no.2
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• pp.208-218
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• 2014

Objectives: The major objective of this study was to develop and validate a tier 1 exposure model utilizing worker exposure monitoring data and characteristics of worker activities routinely performed at construction sites, in order to estimate worker exposures without sampling. Methods: The Registration, Evaluation, Authorization and Restriction of Chemicals(REACH) system of the European Union(EU) allows the usage of exposure models for anticipating chemical exposure of manufacturing workers and consumers. Several exposure models have been developed such as Advanced REACH Tools(ART). The ART model is based on structured subjective assessment model. Using the same framework, a tier 1 exposure model has been developed. Worker activities at construction sites have been analyzed and modifying factors have been assigned for each activity. Korean Occupational Safety and Health Agency(KOSHA) accrued work exposure monitoring data for the last 10 years, which were retrieved and converted into exposure scores. A separate set of sampling data were collected to validate the developed exposure model. These algorithm have been realized on Excel spreadsheet for convenience and easy access. Results: The correlation coefficient of the developed model between exposure scores and monitoring data was 0.36, which is smaller than those of EU models(0.6~0.7). One of the main reasons explaining the discrepancy is poor description on worker activities in KOSHA database. Conclusions: The developed tier 1 exposure model can help industrial hygienists judge whether or not air sampling is required or not.

• International Journal of CAD/CAM
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• v.7 no.1
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• pp.81-89
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• 2007

As the modular production is an important issue in globalized manufacturing industries, sub modules or parts of the final product are provided by many suppliers. Some part suppliers design their own products for themselves. In some cases, part supplier may provide the same type product to multiple 1-tier companies. Because all suppliers and 1-tier companies can not use the same CAD system in general case, the engineering change in the CAD model of one company could not propagate to related CAD models of other companies directly. Although they use the same CAD system, it is hard to share their CAD model with each other because of company security policy. In this paper, the neutral reference model, which consists of the neutral skeleton model and the external reference model, is proposed to apply a global top-down modeling approach to collaborating companies.

• Journal of Information Technology Applications and Management
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• v.10 no.4
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• pp.149-157
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• 2003

In this paper, we propose a ceil model based on the wraparound method to simulate the hierarchical CDMA cellular system in an effective and efficient manner. The model uses the minimal number of cells by considering only one tier but compensates the interference by other cells in the higher tiers sufficiently. Various numerical tests demonstrate that the proposed model can be used to simulate the complex and large-sized hierarchical cellular system effectively. Especially, the interference compensation can reduce the required simulation time to 1/100 for 10 tiers cellular system.

• Journal of the Korea Convergence Society
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• v.10 no.1
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• pp.25-33
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• 2019

The security of the data dealt by the smart city system is important because they have many privacy and public information. Therefore, it is necessary to study security in the smart city system. In this paper, we define the security factors for the smart city system composed of three tiers and describe the technologies for each. In addition, the design and implementation of the security layer in the Smart City middleware for the security management of the urban component in the Smart City Infrastructure and middleware, which is one of the most important issues in the Smart City system, is introduced.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.39 no.3
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• pp.30-38
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• 2016

Shuttle-Based Storage/Retrieval System (SBS/RS) is relatively new to industry. The system is in the category of Automated Storage/Retrieval System (AS/RS), but it is different in that the SBS/RS uses shuttles as Storage/Retrieval (SR) machine instead using a stacker crane. The shuttles are assigned to each tier on multi-tier system and operated for pick-up or drop-off order. Since the system can handle multiple orders simultaneously, it can provide much higher throughput than that of general AS/RS with single stocker crane. Thus, this new system is well fit to recent tendency of increasing small quantity batch production and orders. One of the drawback of this system is that it needs a lot of investment to set up. The efficient operation of the system would be one of the critical matters to increase economic efficiency of capital investment. In this study, we focused on the dwell point policy for shuttles to find efficient way of operating the system. There are four basic policies for the dwell point and we had simulation-based experiment for two different scenarios based on the speed of the shuttle and inter-arrival time of the loads coming to the system combined with four different policies. As it was mentioned above, this SBS/RS relatively new to the field and there is no such experiment shown on previous research and the study of dwell point policy for this SBS/RS could provide the direct comparison of each policy with different hardware specification; the capability of the system. The policy that achieves most efficient operation among the given environment is proposed and the usability of the system is discussed.