• Journal of Communications and Networks
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• v.17 no.2
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• pp.172-183
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• 2015

To provide an efficient link maintenance approach, we propose a cross layer medium access control (LM-MAC) protocol for multichannel cognitive radio ad hoc networks. Link establishment and reliable transmission are two key problems for a perfect link maintenance mechanism. Since the cognitive user (CU) pairs have to reestablish their links each frame, in the proposed MAC protocol, three different access modes are designed to guarantee transmission efficiency in continuous frames. To enhance the transmission reliability, each CU will create a father spectrum list (FSL) after joining in the network. FSL is divided into three groups of sub-channels with different functions to compensate the packet loss caused by the primary users' appearance and the deep fading. Meanwhile, since the transmitter and the receiver will share the same FSL, periodical cooperative sensing is adopted to further optimize the former problem. Finally, compared with the existing opportunistic multichannel (OMC)-MAC protocol, the proposed LM-MAC protocol achieves better system performance in terms of saturation throughput, continuity and access delay.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.8
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• pp.1420-1426
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• 2008

This paper derives medium access delay of each AC(Access Category) in a stationary station using inter-departure time of IEEE 802.11e WLAN(Wireless LAN). Inter-departure time of IEEE 802.11e WLAN is obtained using saturation throughput of IEEE 802.11e WLAN which was the topic of our prior work. By using a simple queueing model, we evaluate mean queue length and mean delay for each AC on stationary condition. We calculate performance of each AC using this simple model and validate results using simulation.

• Mycobiology
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• v.50 no.1
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• pp.55-65
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• 2022

Lichen is a symbiotic mutualism of mycobiont and photobiont that harbors diverse organisms including endolichenic fungi (ELF). Despite the taxonomic and ecological significance of ELF, no comparative investigation of an ELF community involving isolation of a pure culture and high-throughput sequencing has been conducted. Thus, we analyzed the ELF community in Parmotrema tinctorum by culture and metabarcoding. Alpha diversity of the ELF community was notably greater in metabarcoding than in culture-based analysis. Taxonomic proportions of the ELF community estimated by metabarcoding and by culture analyses showed remarkable differences: Sordariomycetes was the most dominant fungal class in culture-based analysis, while Dothideomycetes was the most abundant in metabarcoding analysis. Thirty-seven operational taxonomic units (OTUs) were commonly observed by culture-and metabarcoding-based analyses but relative abundances differed: most of common OTUs were underrepresented in metabarcoding. The ELF community differed in lichen segments and thalli in metabarcoding analysis. Dissimilarity of ELF community intra lichen thallus increased with thallus segment distance; inter-thallus ELF community dissimilarity was significantly greater than intra-thallus ELF community dissimilarity. Finally, we tested how many fungal sequence reads would be needed to ELF diversity with relationship assays between numbers of lichen segments and saturation patterns of OTU richness and sample coverage. At least 6000 sequence reads per lichen thallus were sufficient for prediction of overall ELF community diversity and 50,000 reads per thallus were enough to observe rare taxa of ELF.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.9
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• pp.681-688
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• 2013

Several problems caused by inevitable increment of airplane have been issued. The most effective solution to solve the issues is considered as establishing appropriate Air Traffic Management (ATM) that reduces aircraft's delay at an airport and intensify the airport's capacity. The purpose of this paper is to produce the optimum aircraft schedules that maximize the aircraft throughput by smooth air traffic flow near terminal area of an airport In this paper, mathematical formulations of the scheduling problem are firstly specified. Based on the mathematical modelling, an Optimization-Based Flight Scheduler that provides the optimum flight schedules for arriving aircraft is developed by introducing the Mixed Integer Linear Programming(MILP) and the Genetic Algorithms(GA). With this scheduler, we calculated the optimum schedules to compare to real schedule data from an Incheon Airport. As a result, it is validated that aircraft throughput produced by the optimum schedule is much better than that of the schedule from the Incheon airport. The optimization-based flight scheduler is expected to deal with problems due to the aircraft saturation in near future.

• The KIPS Transactions:PartC
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• v.16C no.1
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• pp.133-142
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• 2009

This paper proposes an analytical performance model of IEEE 802.15.4 in the presence of hidden nodes. Conventional 802.15.4 mathematical models assume ideal situations where every node can detect the transmission signal of every other nodes different from the realistic environments. Since nodes can be randomly located in real environments so that some nodes' presence is hidden from other ones, this assumption leads to wrong performance evaluation of 802.15.4. For solving this problem, we develop an extended performance model which combines the traditional 802.15.4 performance model with one for accounting the presence of hidden nodes. The extended model predicts the rapid performance degradation of 802.15.4 due to the small number of hidden nodes. The performance, for example, degrades by 62% at maximum when 5% of the total nodes are hidden. These predictions are confirmed to be equal to those of ns-2 simulations by less than 6% difference.

• BMB Reports
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• v.30 no.5
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• pp.303-307
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• 1997

Grb2, which is composed of a Src homology 2 (SH2) domain and two Src homology 3 (SH3) domains, is known to serve as an adaptor protein in signaling for Ras activation. Thus, a blocker of the Grb2 interactions with other proteins can be a potential candidate for an anticancer drug. In this study, we have developed a high throughput screening method for SH3 domain binding ligands and blockers. Firstly, we made and purified the glutathione S-transferase (GST)-fusion proteins with the Grb2 SH2 and SH3 domains, and the entire Grb2. This method measures the binding of a biotin-labeled oligopeptide, derived from a Grb2/SH3 binding motif in the hSos, to the GST-fusion proteins, which are precoated as glutathione S-transferase fusion protein on a solid phase. When $1\;{\mu}g$ of each fusion protein was used to coat the wells, both N- and C- terminal SH3 the domains as well as the whole of Grb2 were able to interact with the biotin-conjugated ligand peptide, while the SH2 domain and GST alone showed no binding affinity. Although N- and C- terminal SH3 domains showed an increase of binding to the ligand peptide in proportion to the amount of peptide, the GST fusion protein with Grb2 demonstrated much higher binding affinity. GST-Grb2 coating on the solid phase showed a saturation curve; 66 and 84% of the maximal binding was observed at 100 and 300 ng/$100\;{\mu}l$, respectively. This binding assay system was peptide sequence-specific, showing a dose-dependent inhibition with the unlabeled peptide of SH3 binding motif. Several other peptides, such as SH2 domain binding motifs and PTB domain binding motif, were ineffective to inhibit the binding to the biotin-conjugated ligand peptide. These results suggest that our method may be useful to screen for new anticancer drug candidates which can block the signaling pathways mediated by SH3 domain binding.