• Transactions of the Korean Society of Mechanical Engineers B
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• 제26권6호
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• pp.883-892
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• 2002

A numerical study has been carried out to investigate the flow and heat transfer from an aluminum foam heat sink in a confined channel. A uniform heat flux is given at the bottom of the aluminum foam heat sink, which is horizontally placed on the heated surface. The channel walls are assumed to be adiabatic. Cold air is supplied from the top opening of the channel and exhausted to the channel outlet. Comprehensive numerical solutions are acquired to the governing Wavier-Stokes and energy equations, using the Brinkman-Forchheimer extended Darcy model and the local thermal non-equilibrium model f3r the region of porous media. Details of flow and thermal fields are examined over wide ranges of the principal parameters; i.e., the Reynolds number Re, the height of heat sink h/H, porosity $\varepsilon$and pore diameter ratio $R_{H}$.

• International journal of advanced smart convergence
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• 제5권4호
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• pp.21-25
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• 2016

Recent development in multi-channel surround is emerging in various formats to provide better stereoscopic and sound effects to consumers in recent broadcasting. The ability sound localize the sound sources in space is most considerable design factor on multi-channel surround system for human earing perception model. However, this paper propose the change of the sound localization according to the spacing of the speakers, which is not covered in the existing research focus on sound system design. Presently the sound system uses the position and number of the speakers to localize the sound. In the multi-channel surround environment, the proposed design uses the sound localization is caused by the directional characteristics of the speaker, the distance between the speakers and the distance between the listener and the speaker according to the directivity is required. The proposed design is simulated using virtual measurement with MATLAB simulation environment and performances are measured.

• Journal of Information Technology Applications and Management
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• 제31권3호
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• pp.1-18
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• 2024

This study analyzed the impact of YouTube creator characteristics and channel access factors on the intention to continue watching content, noting that the development of the digital media environment has diversified media audiences' content preferences and access routes. Specifically, we analyzed the effects of YouTube creator trustworthiness, attractiveness, familiarity, and social influence, as well as the effects of recommendation services on perceived usefulness, perceived ease, and perceived enjoyment. The study found that creator credibility and recommendation service had a positive impact on the perceived usefulness of content, while intimacy and charm were important factors in increasing the easy of use and playfulness of content. These perceived usefulness, ease, and playfulness also had a strong positive impact on users' intention to continue watching the channel. This suggests that trust and intimate relationships with creators and appropriate content recommendations play an important role in increasing user satisfaction and channel persistence. The significance of this study's analysis of creator and channel access factors based on the extended technology acceptance model is that it shows the potential for extending and applying the existing technology acceptance model to the digital content environment.

• Journal of Communications and Networks
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• 제15권1호
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• pp.77-86
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• 2013

Cognitive radio (CR) has emerged as one of effective methods to enhance the utilization of existing radio spectrum. Main principle of CR is that secondary users (SUs) are allowed to use the spectrum unused by primary users (PUs) without interfering PU's transmissions. In this paper, PUs operate on a slot-by-slot basis and SUs try to exploit the slots unused by PUs. We propose OSA protocols in the single channel and we propose an opportunistic spectrum access (OSA) protocols in the multi-channel cognitive radio networks with one control channel and several licensed channels where a slot is divided into contention phase and transmission phase. A slot is divided into reporting phase, contention phase and transmission phase. The reporting phase plays a role of finding idle channels unused by PUs and the contention phase plays a role of selecting a SU who will send packets in the data transmission phase. One SU is selected by carrier sense multiple access / collision avoidance (CSMA/CA) with request to send / clear to send (RTS/CTS) mechanism on control channel and the SU is allowed to occupy all remaining part of all idle channels during the current slot. For mathematical analysis, first we deal with the single-channel case and we model the proposed OSA media access control (MAC) protocol by three-dimensional discrete time Markov chain (DTMC) whose one-step transition probability matrix has a special structure so as to apply the censored Markov chain method to obtain the steady state distribution.We obtain the throughput and the distribution of access delay. Next we deal with the multi-channel case and obtain the throughput and the distribution of access delay by using results of single-channel case. In numerical results, our mathematical analysis is verified by simulations and we give numerical results on throughput and access delay of the proposed MAC protocol. Finally, we find the maximum allowable number of SUs satisfying the requirements on throughput and access delay.

• Horticultural Science & Technology
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• 제29권3호
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• pp.201-210
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• 2011

This experiment was conducted to investigate physical and chemical characteristics by volume fractions of root media using peatmoss, perlite, and vermiculite, along with effects on the growth of pot chrysanthemums (Dendranthema ${\times}$ grandiflorum 'Vemini') in a C-channel mat irrigation system. To evaluate the physico-chemical properties of 20 root media, the bulk density, particle density, total pore space, pore space, ash content, organic matter, pH, and electrical conductivity were measured and data were analyzed using principal component analysis (PCA). PCA scores revealed that physico-chemical properties changed by the blending of peatmoss, perlite, and vermiculite. The 20 root media were divided into three main groups by hierarchical cluster analysis. At the end of the experiment, the pH and EC of the root media were measured from media divided into four layers. The pH of root media without plants showed a strong linear relationship and the pH of root media with plants increased exponentially. The change of EC in the root medium was indicated as a hyperbolic curve. Plant growth characteristics according to growth in the 20 root media were analyzed by PCA. It was found that the mixing ratios of the root media affected plant growth characteristics. Therefore, mixing ratio is an important factor for pot-plant production in a subirrigation system.

• ETRI Journal
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• 제37권3호
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• pp.439-449
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• 2015

Human body communication (HBC) is being recognized as a new communication technology for mobile and wearable devices in a body area network (BAN). This paper presents co-channel interference experienced by HBC supporting the physical layer in the IEEE 802.15.6 BAN standard. To analyze the co-channel interference, a co-channel interference model is introduced, and space-domain and time-domain parameters representing an interference environment are generated using the co-channel interference model. A new signal-to-interference ratio (SIR) parameter depending on the peak amplitudes of the data signals causing co-channel interference is defined; co-channel interference can be easily analyzed and modelled using the newly defined SIR. The BER degradation model derived using the co-channel interference model and SIR in this paper can be effectively used to estimate the performance.

• Journal of Digital Convergence
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• 제10권8호
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• pp.119-133
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• 2012

Recent rise of social media channel is changing social and economic paradigm and is being used as an effective communication in marketing. The following research analyzes the most employed social marketing tools such as portal advertisement, blogs, and SNS channels to effectively execute social media marketing from performance indicator and ICSI perspective, analyzes each channel's characteristics and results based on Korea distribution companies' case studies and suggests a framework to effectively use each channel. Portal site advertisements are the most effective channel to draw customers with new information and are thus linked to profit by corporations with excessive budget and workforce. Blogs target a specific range of customers providing quality information and knowledge thus improving a corporation's and its product's trustworthiness, spread the word by allowing customers to scrap the information, form social groups and synthesize ideas, events, new contents and social involvement with loyal customers. SNS channels allow customers to get involved in real time information and events, grow through network by the power of customers, react immediately to customers' needs, and execute real-time market and customer reports. Though national corporations currently rely heavily on portal site advertisements, insightful marketing professionals are showing financial results with blog and SNS. In the future, based on a precise understanding of each channel's benefits and expected results, and with a focus on flexibility, timeliness and integrated use of each channel, a portfolio of dynamic marketing as a maximizing strategy could be synthesized.

• Journal of Broadcast Engineering
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• 제19권4호
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• pp.510-520
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• 2014

By adopting the MAC(Media Access Control) protocol which enables to pack multiple MPDUs(MAC-level Protocol Data Units) into a single PPDU(Physical Layer Protocol Data Unit), IEEE 802.11n WLAN supports high throughput. Up to now, there have been a lot of existing channel information-based A-MPDU schemes dynamically determining the number of MSDUs according to the wireless channel condition information which is sent from the receiver to sender. However, the channel information-based scheme has a serious drawback having a high system overhead due to the frequent channel feedback information. To reduce the system overhead, the proposed BA-base dynamic A-MPDU scheme simply chooses the number of MSDUs to be retransmitted by not the frequent channel feedback information but the BA signal representing whether MPSUs belonging to the A-MPDU are received or not. Through NS-2(Network Simulator-2), we found that the proposed scheme had higher throughput and lower packet error rate than the existing fixed A-MPDU scheme.

• Information Systems Review
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• 제25권3호
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• pp.121-138
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• 2023

The advancement in mobile technology brought disruptive innovation in media industry. The introduction of mobile devices broke spatial and temporal restrictions in media consumption. This study investigates the impact of mobile channel adoption on video viewing behavior, using real-world dataset obtained from a particular on-demand service provider in South Korea. We find that the adoption of a mobile channel significantly increases the total viewing time of video-on-demand via TV and the number of contents viewed. Our results suggest that the mobile channels act as a complement channel to conventional TV channels. We provide theoretical and practical insights on consumer usage in the emerging over-the-top market.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제38A권9호
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• pp.739-743
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• 2013

In this paper, a two-dimensional (2-D) channel code for magnetic patterned media is proposed. Patterned media records an information bit on a magnetized dot. Since the space between adjacent tracks is narrow in order to increase the storage density, inter-track interference (ITI) and inter-symbol interference (ISI) can be problems. The amplitude of a bit signal can be corrupted by the 2-D ISI. The signal of the bit surrounded by the same value can be especially destructive, i.e. when its value is the same as the values of the eight surrounding bits. The proposed modulation coding scheme improves the decoding performance of patterned media by preventing this worst case and provides a better code rate than conventional channel codes.