• Journal of Broadcast Engineering
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• v.2 no.2
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• pp.182-193
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• 1997

In this paper, we propose technical and structural solutions for various problems in two-way digital communication services in CATV networks by actual field tests. The two-way digital communication services include VOD, video conferencing, distance learning, interactive game and internet service. We investigate the quality of T -1 level 0.544 Mbps) upstream digital signal while varying the number of subscribers in three different cells in accordance with ITU-T G.821. Based on this investigation, several ways to cope with the problems identified are suggested.

• Current Optics and Photonics
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• v.1 no.4
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• pp.315-324
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• 2017

In recent years, multicast services such as high-definition television (HDTV), video conferencing, interactive distance learning, and distributed games have increased exponentially, and wavelength-division multiplexing (WDM) networks are considered to be a promising technology due to their support for multicast applications. Multicast survivability in WDM networks has been the focus of extensive attention since a single-link failure in an optical network may result in a massive loss of data. But the improvement of network survivability increases energy consumption due to more resource allocation for protection. In this paper, an energy-efficient multicast algorithm (EEMA) is proposed to reduce energy consumption in WDM networks. Two cost functions are defined based on the link state to determine both working and protection paths for a multicast request in WDM networks. To increase the number of sleeping links, the link cost function of the working path aims to integrate new working path into the links with more working paths. Sleeping links indicate the links in sleep mode, which do not have any working path. To increase bandwidth utilization by sharing spare capacity, the cost function of the protection path is defined to use sleeping fibers for establishing new protection paths. Finally, the performance of the proposed algorithm is evaluated in terms of energy consumption, and also the blocking probability is evaluated under various traffic environments through OPNET. Simulation results show that our algorithm reduces energy consumption while maintaining the quality of service.

• Communications of Mathematical Education
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• v.38 no.2
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• pp.93-120
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• 2024

On-line education in mathematics education changed in various aspects before and after COVID-19. This study conducted a systematic literature review of 98 academic papers on on-line education published from 2017 to 2023 in the field of mathematics education before and after COVID19. In particular, this study conducted content analysis to organize on the definitions of various similar terms related to online education. In addition, this study explored research trends on year, research subject, research method, on-line education type, and research topic by the pre-COVID-19, COVID-19, and post-COVID-19 era. Also, a comparative analysis was conducted on literatures on the effects of online education. As a result, first, it was confirmed that there is a need to organize the definitions of terms similar to online education. Also, the implications of identifying the differences and hierarchies between each term can be found. Second, it was confirmed that teachers' expertise for on-line mathematics education was emphasized based on the result of the rapid increase in the number of on-line education studies on teachers since COVID-19. Third, it was confirmed that the number of studies on blended and flipped learning was high in pre-COVID-19, but decreased in the COVID-19 era. Instead, in the COVID-19 era, studies on real-time interactive classes were rapidly active, and even in the post-COVID-19 era, studies on real-time interactive classes still occupied a large proportion. Finally, it was confirmed that the effectiveness of on-line education varies depending on the research background and model. Accordingly, the need to be cautious in interpreting the results of each study on the effectiveness of on-line education was confirmed. Based on these findings, this study presented implications for future research on on-line education in mathematics education.

• Journal of Distribution Research
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• v.15 no.4
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• pp.61-85
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• 2010

Introduction: Diffusion is process by which an innovation is communicated through certain channel overtime among the members of a social system(Rogers 1983). Bass(1969) suggested the Bass model describing diffusion process. The Bass model assumes potential adopters of innovation are influenced by mass-media and word-of-mouth from communication with previous adopters. Various expansions of the Bass model have been conducted. Some of them proposed a third factor affecting diffusion. Others proposed multinational diffusion model and it stressed interactive effect on diffusion among several countries. We add a spatial factor in the Bass model as a third communication factor. Because of situation where we can not control the interaction between markets, we need to consider that diffusion within certain market can be influenced by diffusion in contiguous market. The process that certain type of retail extends is a result that particular market can be described by the retail life cycle. Diffusion of retail has pattern following three phases of spatial diffusion: adoption of innovation happens in near the diffusion center first, spreads to the vicinity of the diffusing center and then adoption of innovation is completed in peripheral areas in saturation stage. So we expect spatial effect to be important to describe diffusion of domestic discount store. We define a spatial diffusion model using multinational diffusion model and apply it to the diffusion of discount store. Modeling: In this paper, we define a spatial diffusion model and apply it to the diffusion of discount store. To define a spatial diffusion model, we expand learning model(Kumar and Krishnan 2002) and separate diffusion process in diffusion center(market A) from diffusion process in the vicinity of the diffusing center(market B). The proposed spatial diffusion model is shown in equation (1a) and (1b). Equation (1a) is the diffusion process in diffusion center and equation (1b) is one in the vicinity of the diffusing center. $$\array{{S_{i,t}=(p_i+q_i{\frac{Y_{i,t-1}}{m_i}})(m_i-Y_{i,t-1})\;i{\in}\{1,{\cdots},I\}\;(1a)}\\{S_{j,t}=(p_j+q_j{\frac{Y_{j,t-1}}{m_i}}+{\sum\limits_{i=1}^I}{\gamma}_{ij}{\frac{Y_{i,t-1}}{m_i}})(m_j-Y_{j,t-1})\;i{\in}\{1,{\cdots},I\},\;j{\in}\{I+1,{\cdots},I+J\}\;(1b)}}$$ We rise two research questions. (1) The proposed spatial diffusion model is more effective than the Bass model to describe the diffusion of discount stores. (2) The more similar retail environment of diffusing center with that of the vicinity of the contiguous market is, the larger spatial effect of diffusing center on diffusion of the vicinity of the contiguous market is. To examine above two questions, we adopt the Bass model to estimate diffusion of discount store first. Next spatial diffusion model where spatial factor is added to the Bass model is used to estimate it. Finally by comparing Bass model with spatial diffusion model, we try to find out which model describes diffusion of discount store better. In addition, we investigate the relationship between similarity of retail environment(conceptual distance) and spatial factor impact with correlation analysis. Result and Implication: We suggest spatial diffusion model to describe diffusion of discount stores. To examine the proposed spatial diffusion model, 347 domestic discount stores are used and we divide nation into 5 districts, Seoul-Gyeongin(SG), Busan-Gyeongnam(BG), Daegu-Gyeongbuk(DG), Gwan- gju-Jeonla(GJ), Daejeon-Chungcheong(DC), and the result is shown