• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.795-801
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• 2019

The aim of this study was to investigate the possibility of the skin-friction reduction by vortex control. A vortical system such as a horseshoe vortex, a hairpin vortex, and a wake region was induced around a hemisphere attached on a Perspex flat plate in the circulating water channel. Hairpin vortices were developed from the wake region and horseshoe vortices were formed by an adverse pressure gradient in front of the hemisphere. The horseshoe vortices located on the flank of the hemisphere induced a high momentum flow in the wake region by the direction of their vorticity. This process increased the frequency of the hairpin vortices as well as the frictional drag on the surface of the wake region. To reduce the skin-friction drag, suction control in front of the hemisphere was applied through a hole. Flow visualization was performed to optimize the free-stream velocity, size of the hemisphere, and size of the suction hole. Once the wall suction control mitigated the strength of the horseshoe vortex, the energy supplied to the wake region was reduced, causing the frequency of the hairpin vortex generation to decrease by 36.4 %. In addition, the change in the skin-friction drag, which was measured with a dynamometer connected to a plate in the wake region, also decreased by 2.3 %.

• Journal of Korea Water Resources Association
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• v.51 no.8
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• pp.655-664
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• 2018

The riverbed material survey is to investigate the particle size distribution, specific gravity, porosity, etc. as basic data necessary for river channel plan such as calculation of sediment transport and change of river bed. In principle, the survey spots are 1 km interval in the longitudinal direction of the river and 3 points or more in the 1 cross section. Therefore, depending on longitudinal length of the river to be investigated, the number of surveyed sites is very large, and the time and cost for the investigation are correspondingly required. This study is to compare the particle size analysis method with the volumetric method and the image analysis method in work efficiency and cost and to examine the applicability of the image analysis method. It was confirmed that the diameter of the equivalent circle converted by the image analysis method can be applied to the analysis of bed material particle size. In the gravel stream with a particle size of less than 10 cm and a large shape factor, the analytical result of the bed material by the image analysis method is accurate. However, when the shape factor decreases as the particle size increases, the error increases. In addition, analysis results of the work efficiency and cost of the volume method and the image analysis method showed a reduction of about 80%.

• Korean journal of communication and information
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• v.81
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• pp.75-121
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• 2017

Maeul Community Media is community media practice that media education combine with community activism based on the region. Maeul Community Media appeared with Seoul city's supporting policy in 2012 and is now enlarging on a national scale beyond Seoul. This study is aimed at understanding and investigating Maeul Community Media activists' practice process by using a grouned theory approach. In-depth interviews were carried out of study participants who worked on as activists based on visual and radio field since 2012. By open coding based on grounded theory, 16 categories and 59 subcategories were discovered. The outcome of axial coding showed the centeral phenomena that can be called 'sustainable desire for Maeul Community Media act'. On the condition of the instability of public support and the absence of a village channel, the strategic practices were discovered, which are diversification of participants recruitment and modes of participation, invention of space-media, seeking multilateral distribution methodologies and the collective action plans of networks to stabilize the management and to empower Maeul Community Media networks. As a result, Maeul Community Media and civil society were networked by discovering and agenda-setting pending issues. And we could find that the desire and expectation for the role as a village's public sphere were enlarging.

• International Commerce and Information Review
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• v.16 no.1
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• pp.163-183
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• 2014

This paper empirically investigated whether the strategic performance of dependence and commitment on output sector uncertainty based on the data from manufacturing firms in Korea. U.S. Also, the proposed model was proven by the structural equation model with the data gathered from 105 manufacturing firms in Korea, 103 in U.S. The success of the members of channel having limited resources and capabilities depends on how they cope with environment. Especially, it is insispensable for manufacturing firms and distributing firms to build up win win systems when environmental uncertainty is high in the output sector. The findings were as follows. Hypothesis 1 was accepted in all the nations. Hypothesis 2 was accepted in the United States yet not in Korea. Hypothesis 3, 4 was accepted in Korea yet not in the United States. Hypothesis 5 was accepted in every nation as well. In the future, the dependence, commitment and strategic performance of manufacturing and distribution firms should be investigated from a mutual perspective, and additional data should be obtained by selecting more subjects. As for environmental uncertainty, the uncertainty of distribution environments as well as output sector uncertainty should equally be investigated by making a comparative analysis.

• Journal of Digital Convergence
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• v.16 no.3
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• pp.145-156
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• 2018

Unlike the past, when distributors distributed games through retail stores, they are now selling digital content, which is based on online distribution channels. This study analyzes the effects of eWOM (electronic Word of Mouth) on sales volume of game sold on Steam, an online digital content distribution channel. Recently, data mining techniques based on Big Data have been studied. In this study, emotion index of eWOM is derived by emotional analysis which is a text mining technique that can analyze the emotion of each review among factors of eWOM. Emotional analysis utilizes Naive Bayes and SVM classifier and calculates the emotion index through the SVM classifier with high accuracy. Regression analysis is performed on the dependent variable, sales variation, using the emotion index, the number of reviews of each game, the size of eWOM, and the user score of each game, which is a rating of eWOM. Regression analysis revealed that the size of the independent variable eWOM and the emotion index of the eWOM were influential on the dependent variable, sales variation. This study suggests the factors of eWOM that affect the sales volume when Korean game companies enter overseas markets based on steam.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.12
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• pp.39-47
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• 2010

This paper proposes a fully-utilized block-based 2D DWT architecture, which consists of four 1D DWT filters with two-channel QMF PR Lattice structure. For 100% hardware utilization, we propose a new method which processes four input values at the same time. On the contrary to the image-based 2D DWT which requires large memories, we propose a block-based 2D DWT so that we only need 2MN-3N of storages, where M and N stand for filter lengths and width of the image respectively. Furthermore, the proposed architecture processes in horizontal and vertical directions simultaneously so that it computes the DWT for an $N{\times}N$ image within a period of $N^2(1-2^{-2J})/3$. Compared to existing approaches, the proposed architecture shows 100% of hardware utilization and high throughput rate. However, the proposed architecture may suffer from the long critical path delay due to the cascaded lattices in 1D DWT filters. This problem can be mitigated by applying the pipeline technique with maximum four level. The proposed architecture has been designed with VerilogHDL and synthesized using DongbuAnam $0.18{\mu}m$ standard cell.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1742-1754
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• 1999

In this paper, we propose a rate control scheme, using histogram based rate-distortion (R-D) estimation, which produces a consistent picture quality between consecutive frames. The histogram based R-D estimation used in our rate control scheme offers a closed-form mathematical model that enable us to predict the bits and the distortion generated from an encoded frame at a given quantization parameter (QP) and vice versa. The most attractive feature of the R-D estimation is low complexity of computing the R-D data because its major operation is just to obtain a histogram or weighted histogram of DCT coefficients from an input picture. Furthermore, it is accurate enough to be applied to the practical video coding. Therefore, the proposed rate control scheme using this R-D estimation model is appropriate for the applications requiring low delay and low complexity, and controls the output bit-rate ad quality accurately. Our rate control scheme ensures that the video buffer do not underflow and overflow by satisfying the buffer constraint and, additionally, prevents quality difference between consecutive frames from exceeding certain level by adopting the distortion constraint. In addition, a consistent considering the maximum tolerance BER of the voice service. Also in Rician fading channel of K=6 and K=10, considering CLP=$10^{-3}$ as a criterion, it is observed that the performance improment of about 3.5 dB and 1.5 dB is obtained, respectively, in terms of $E_b$/$N_o$ by employing the concatenated FEC code with pilot symbols.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.45-53
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• 2000

In wireless environment, due to the limited capacity of radio channels it is not easy to guarantee QoS provisioning to mobile users. Therefore, one of the key problems to support broadband multimedia multi-services in wireless ATM networks is to study an effective call admission control(CAC). The purpose of this paper is to propose a distributed CAC scheme that guarantees multi QoS and multi-class service. Control parameters of the proposed scheme are QoS threshold and channel overload probability. With these parameter control, we show that the scheme can guarantee the requested QoS to both new and handover calls. In the scheme, channels are allocated dynamically, and QoS measurements are made in a distributed manner. We show that by providing variable data rate to calls it can effectively prohibit the QoS degradation even if there are severe fluctuations of network traffic. We compare the proposed CAC scheme to the well-known schemes such as guard band call admission control scheme. Through numerical examples and simulations, the proposed scheme is shown to improve the performance by lowering the probability of handover call dropping

• International Commerce and Information Review
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• v.13 no.2
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• pp.121-148
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• 2011

Korean small and medium sized firms are dramatically expanding during the past two decades. Since small and medium sized firms begun to invest overseas to cope with the external and internal business environment. the influencing factors should defined for the successful foreign investment. This paper presents the research model explaining successful knowledge transfer between Korean small and medium sized firms and partners for foreign investment. This model examines investing companies' organizational characteristics, partners' learning capability and relational characteristics between two partners. Detail variables include the learning culture and codifiability of investing companies, and absorptive capability of partners, and communication and trust as a relational factors between investing companies and partners. The result of empirical analysis of sample companies shows that knowledge culture and codifiability of investing companies, and communication from the relational factors are important for knowledge transfer. These results provide some implications for the successful foreign investment of small and medium sized firms. Firstly the investing company should develop its own learning culture and internal procedure for the successful foreign investment. And frequent communication channel is necessary for knowledge transfer and the trustful relationship between investors and partner.

• Korean journal of communication and information
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• v.43
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• pp.359-384
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• 2008

Nowadays, newspaper industry faces a crisis in terms of two aspects: First, in this multi-channel era, it has competed with the online journalism appearing in many digital media. Second, with the decrease of numbers of readers and political participation, the roles of newspaper has to be changed accordingly. The concept of civic journalism emerged as a solution in this context. The purpose of the study is to explore the factors in how journalists perceive the civic journalism. The Q-methodology was adapted to identify the factors composing of the belief, values, attitudes, ideas, and opinions toward the civic journalism. Total of 24 Q-sample (statements) were sorted by 27 P-sample (journalists) who were selected by their gender, years of service, and the like. The Quanl program finally produced 3 factors that were interpreted and named as follows: Factor I, the Complimentary Journalism, the civic journalism would fulfill the functions that traditional journalism has neglected. Factor II, the Alternative Journalism inducing the citizen's participation in the public areas. Factor III, the Functional Journalism, emphasizing dysfunction of the civic journalism.