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Throughput study for admission control in IEEE 802.11 DCF with ARF
Kunho Hong,Sukyoung Lee,Golmie, N. IEEE 2009 IEEE communications letters Vol.13 No.6
<P>We propose an analytical approach to determining the admission of new stations to a WLAN operating in IEEE 802.11 distributed coordination function (DCF) with auto rate fallback (ARF). The proposed approach is based on a cross layer analytical model of how the throughput of existing stations in the WLAN is affected by admitting the new station in non-saturated as well as saturated traffic conditions. The effectiveness of the proposed approach is verified by simulations.</P>
Kunho Bae,Chang Ki Yoon,Eun Kyoung Lee,Jae Hyup Lee,Hyeong Gon Yu 대한검안학회 2022 Annals of optometry and contact lens Vol.21 No.4
Purpose: To investigate the frequency of optic disc hyperfluorescence (ODH) and their association with macular and optic nerve head thickness in patients with active uveitis. Methods: This retrospective cross-sectional study included 37 eyes of 30 patients with active noninfectious uveitis who underwent spectral domain-optical coherence tomography (OCT) and fluorescein angiography. OCT parameters were compared between baseline and post-treatment according to the ODH. Results: ODH was observed clearly in 22 eyes (64.7%) and equivocally in five eyes (14.7%) at baseline. In subgroup analysis without clinically significant optic disc edema, central subfield thickness, peripapillary retinal nerve fiber layer thickness, disc rim area, and disc area were 262.2 μm, 110.9 μm, 1.49 mm2, and 2.02 mm2 at baseline and significantly decreased after treatment (249.5 μm, 102.1 μm, 1.34 mm2, and 1.95 mm2, respectively) in eyes with ODH (p = 0.044, p < 0.001, p = 0.001, p = 0.024, respectively). However, there was no significant changes in the eyes without ODH (all p > 0.05). Conclusions: There was a difference in the thickness reduction of the macula and optic nerve head according to the ODH. Baseline ODH should be regarded as a sign of ocular inflammation and carefully monitored.
Lee, Kunho,Kang, Juhyun,Lee, Jaeseok,Lee, Sanghun,Bae, Joongmyeon Pergamon Press 2018 International journal of hydrogen energy Vol.43 No.7
<P><B>Abstract</B></P> <P>The objective of this study is to evaluate metal-supported solid oxide fuel cells fabricated at low temperatures (∼1000 °C) in oxidizing environments using wet chemical coating processes and a catalyst impregnation method. Typically, applying general wet chemical coating processes and heat treatment at low temperature is desirable for fabricating metal-supported solid oxide fuel cells when considering manufacturing productivity and efficiency. However, in the case of conventional anodes, a well-organized structure for high performance is rarely formed by sintering at low temperatures when using general fabrication processes. For this reason, a catalyst-impregnated anode is designed and applied to overcome the above issue. First, to evaluate the electrochemical performance of the designed anode, the area-specific resistances of half-cells are investigated. Then, the newly designed anode is applied to a single cell, and microstructural analysis and electrochemical performance measurements are performed. These results confirm that the catalysts are well distributed, that the electrolyte is fully dense and that the electrochemical performances are reasonable. Additionally, the high durability is also verified through a long-term test over 1000 h. Finally, the metal-supported solid oxide fuel cell with a catalyst-impregnated anode fabricated at low temperature is completely validated through the evaluation of a large-size single cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ni-impregnated LST-GDC anode fabricated at low temperature was investigated. </LI> <LI> MS-SOFCs were fabricated in oxidizing environments at low sintering temperatures. </LI> <LI> MS-SOFCs were fabricated using conventional wet chemical coating processes. </LI> <LI> The fabricated MS-SOFCs showed reasonable performances, OCVs and durability. </LI> <LI> Large-size MS-SOFC cell was successfully fabricated and evaluated. </LI> </UL> </P>
Lee, Kunho,Kang, Juhyun,Jin, Sangbeom,Lee, Sanghun,Bae, Joongmyeon Elsevier 2017 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.42 No.9
<P><B>Abstract</B></P> <P>This paper presents a study on a solution coating process for depositing layers on porous surfaces, i.e., metal-supported SOFC electrolyte. PVP and nanoparticles are used to achieve the study objectives. PVP, which possesses a type of coiled long chain structure, can increase the solution viscosity and relieve stress. However, PVP can react with nitrate ions, consequently generating excessive ignition, which causes an inhomogeneous microstructure and forms many defects. The application of nanoparticles can control the stress and reduce cracks. Subsequently, to densify and repair the cracks, an additional solution coating process is applied. YSZ is selected as a candidate, and OCV and SEM measurements are conducted to confirm the YSZ density. The YSZ solution is multi-coated to the GDC layer, and a fully dense layer can be deposited on the coated GDC surface. The proposed coating process can fabricate a dense electrolyte under oxidation environments at a relatively low temperature using a wet-chemical process. Furthermore, in terms of spin coating and heat treatment, it can be continuously and automatically performed. Therefore, the multi-coating process developed in this research can be readily commercialized.</P> <P><B>Highlights</B></P> <P> <UL> <LI> To deposit dense layer on rigid porous surface, sol–gel coating was investigated. </LI> <LI> PVP, nanoparticles, and multi-coating process were applied. </LI> <LI> GDC modified by PVP and nanoparticles could be deposited on porous surface. </LI> <LI> YSZ solution was also investigated to improve density of GDC layer. </LI> <LI> The YSZ solution multi-coated GDC layer was fully dense. </LI> </UL> </P>
Cost-Based Vertical Handover Decision Algorithm for WWAN/WLAN Integrated Networks
Hong, KunHo,Lee, SuKyoung,Kim, LaeYoung,Song, PyungJung Hindawi Publishing Corporation 2009 Eurasip Journal on Wireless Communications and Net Vol.2009 No.-
<P>Next generation wireless communications are expected to rely on integrated networks consisting of multiple wireless technologies. Heterogeneous networks based on Wireless Local Area Networks (WLANs) and Wireless Wide Area Networks (WWANs) can combine their respective advantages on coverage and data rates, offering a high Quality of Service (QoS) to mobile users. In such environment, multi-interface terminals should seamlessly switch from one network to another in order to obtain improved performance or at least to maintain a continuous wireless connection. Therefore, network selection algorithm is important in providing better performance to the multi-interface terminals in the integrated networks. In this paper, we propose a cost-based vertical handover decision algorithm that triggers the Vertical Handover (VHO) based on a cost function for WWAN/WLAN integrated networks. For the cost function, we focus on developing an analytical model of the expected cost of WLAN for the mobile users that enter the double-coverage area while having a connection in the WWAN. Our simulation results show that the proposed scheme achieves better performance in terms of power consumption and throughput than typical approach where WLANs are always preferred whenever the WLAN access is available.</P>