• International Journal of Precision Engineering and Manufacturing
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• v.5 no.1
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• pp.19-26
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• 2004

The growth of solid particles in TiC-XC-2vo1.% and TiC-XC-30vo1.% Ni alloys, (where X=Zr, W or Mo) was fitted to the equation of the form $d^3$-${do}^3$=Kt during the liquid phase sintering at 1,673K. Also, the grain growth behavior decreased markedly with the addition of ${MO}_2$C or WC and increased with the addition of zrC. The contiguity was greater in the alloys with a smaller growth rate constant and especially, decreased by increasing the Ni content in the TiC-${MO}_2$C-Ni alloy. In addition, the effect of the addition of carbide on the grain growth of 2 vo1.% Ni alloys was found to be similar to that of 30vo1.% Ni alloys. Consequently, the grain growth mechanism cannot be explained by the usual solution / reprecipitation process, but can be explained in terms of a new growth velocity equation, which includes the effects of contiguous carbide grain boundaries in restricting the overall grain growth, as well as the area of the solid / liquid interface in the alloy.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.251.2-251.2
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• 2013

Natural photosynthesis utilizes two proteins, photosystem I and photosystem II, to efficiently oxidize water and reduce NADP+ to NADPH. Artificial photosynthesis which mimics this process achieve water splitting through a two-step Z-schematic water splitting process using man-made synthetic materials for hydrogen fuel production. In this study, Z-scheme system was achieved from the hybrid materials which composed of hydrogen production part as photosystem I protein and water oxidizing part as semiconductor BiVO4. Utilizing photosystem I as the hydrogen evolving part overcomes the problems of existing hydrogen evolving p-type semiconductors such as water instability, expensive cost, few available choices and poor red light (>600 nm) absorbance. Some problems of photosystem II, oxygen evolving part of natural photosynthesis, such as demanding isolation process and D1 photo-damage can also be solved by utilizing BiVO4 as the oxygen evolving part. Preceding research has not suggested any protein-inorganic-hybrid Z-scheme composed of both materials from natural photosynthesis and artificial photosynthesis. In this study, to realize this Z-schematic electron transfer, diffusion step of electron carrier, which usually degrades natural photosynthesis efficiency, was eliminated. Instead, BiVO4 and Pt-photosystem I were all linked together by the mediator gold. Synthesized all-solid-state hybrid materials show enhanced hydrogen evolution ability directly from water when illuminated with visible light.

• Current Optics and Photonics
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• v.7 no.3
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• pp.254-262
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• 2023

Novel thermo-optically focus-switchable Fresnel zone plates based on phase-change metafilms are designed and analyzed at a visible wavelength (660 nm). By virtue of the large thermo-optic response of vanadium dioxide (VO₂) thin film, a phase-change material, four different plasmonic phase-change absorbers are numerically designed as actively tunable Gires-Tournois Al-VO₂ metafilms in two and three dimensions. The designed phase-change metafilm unit cells are used as the building blocks of actively focus-switchable Fresnel zone plates with strong focus switching contrast (40%, 83%) and high numerical apertures (1.52, 1.70). The Fresnel zone plates designed in two and three dimensions work as cylindrical and spherical lenses in reflection type, respectively. The coupling between the thermo-optic effect of VO₂ and localized plasmonic resonances in the Al nanostructures offer a large degree of freedom in design and high-contrast focus-switching performance based on largely tunable absorption resonances. The proposed method may have great potential in photothermal and electrothermal active optical devices for nonlinear optics, microscopy, 3D scanning, optical trapping, and holographic displays over a wide spectral range including the visible and infrared regimes.

• Journal of the Korean Chemical Society
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• v.39 no.8
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• pp.611-616
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• 1995

Oxovanadium(IV) complexes with salicylaldoxime, o-vanilline oxime, 2-hydroxy-4-methoxybenzaldoxime, 2-hydroxy-5-methoxybenzaldoxime and 2-hydroxy-5-nitrobenzaldoxime were synthesized. The complexes have been characterized by elemental analysis, electric conductivity measurement, infrared spectrometry, electronic spectrometry, mass spectrometry, and thermal analysis. The results of elemental analysis were well coincided with the theoretical values. The values of molar conductance of the complexes in DMF implicated that the complexes were non-electrolyte. The characteristic stretching frequency of V=O appeared strong band in the range of $980{\pm}20\;cm^{-1}.$ All the complexes showed two d-d transition in visible spectra and two charge transfer transitions in ultraviolet spectra. Results of mass spectrometry of $VO(sal)_2\;and\;VO(van)_2$ indicated two peaks corresponding to vanadium containing ion(I) of 1 : 2(metal to ligand) chelate and a fragment ion(II) of 1 : 1 chelate due to loss of ligand radical from ion(I). The thermal analysis showed the endothermic peak due to the thermal decomposition.

• Journal of Broadcast Engineering
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• v.16 no.2
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• pp.305-318
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• 2011

Since switched digital video (SDV) provides specific programs only to the subscribers who request the programs, SDV has attracted considerable interest of MSOs for bandwidth efficiency. In North America, MSOs service over 2.3 million households with the SDV for cable networks. In Korea, since demand of HD program, high-speed Internet, VoD, and VoIP is noticeably rising, the SDV is considered as the alternative for bandwidth saving and efficient managing. In this paper, the characteristics, operating structure, and bandwidth saving of the SDV are discussed and technical requirements for the SDV are also introduced. The channel switching performance and stability of the SDV are analyzed through the test-bed.

• Fire Science and Engineering
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• v.19 no.2 s.58
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• pp.1-7
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• 2005

An accurate knowledge of the minimum oxygen concentration(MOC) is important in developing appropriate prevention and control measures in industrial fire protection. In this study, by using the literature data and RSM(response surface methodology), the new equations for predicting the MOC are proposed. The A.A.P.E.(average absolute percent error) and the A.A.D.(average absolute deviation) of the reported and the calculated MOC for hydrocarbons were $3.48\%\;and\;0.37\;vol\%$, respectively and the correlation coefficient was 0.919. The A.A.P.E and the A.A.D of the reported and the calculated MOC for halogenated hydrocarbons and hydrocarbons were $5.06\%$ and $0.59vo1\%$, and the correlation coefficient was 0.938. The values calculated by the proposed equations were in good agreement with the literature data. Therefore, it is expected that this proposed equations will support the use of the research for other flammable substances.

• Journal of Communications and Networks
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• v.14 no.3
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• pp.286-295
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• 2012

To meet the increased demand of video-on-demand (VoD) services, peer-to-peer (P2P) mesh-based multiple video approaches have been recently proposed, where each peer is able to find a video segment interested without resort to the video server. However, they have not considered the constraint of the server's upload bandwidth and the fairness between upload and download amounts at each peer. In this paper, we propose a novel P2P VoD streaming system, named peer cache adaptation (PECAN) where each peer adjusts its cache capacity adaptively to meet the server's upload bandwidth constraint and achieve the fairness. For doing so, we first propose a new cache replacement algorithm that designs the number of caches for a segment to be proportional to its popularity. Second, we mathematically prove that if the cache capacity of a peer is proportional to its segment request rate, the fairness between upload and download amounts at each peer can be achieved. Third, we propose a method that determines each peer's cache capacity adaptively according to the constraint of the server's upload bandwidth. Against the proposed design objective, some selfish peers may not follow our protocol to increase their payoff. To detect such peers, we design a simple distributed reputation and monitoring system. Through simulations, we show that PECAN meets the server upload bandwidth constraint, and achieves the fairness well at each peer. We finally verify that the control overhead in PECAN caused by the search, reputation, and monitoring systems is very small, which is an important factor for real deployment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1398-1406
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• 2001

최근 초고속 통신망의 발전과 더불어 망을 통한 멀티미디어 서비스의 개발이 활발히 진행되고 있다. 특히 멀티미디어 서비스의 핵심 요소인 영상서비스에 관련된 많은 개발이 이루어졌다. 이러한 망에서의 영상서비스를 효과적으로 제공하기 위하여, 사용자로부터 요구되는 서비스 품질(QoS : Quality of Service)을 보장하고 관리하는 것이 서비스 제공의 핵심 사항이라 볼 수 있다. 최근 주문형 비디오(VoD : Video on Demand) 서비스와 같은 망을 통한 영상 전송이 실용화되고 있으며, 차세대 영상 압축 방식인 MPEG2 방식을 이용한 전송이 개발되고 있다. 이러한 망을 통한 MPEG2 서비스 시, 종단간의 QoS를 보장해 주기 위한 망 계층과 응용 계층간의 QoS 파라미터 측정과 이를 토대로 한 서비스 제공 및 관리가 필요하다. 본 논문에서는 MPEG2를 이용한 영상 전송 시 종단간의 QoS 측정을 위한 VoD 시스템 및 측정기 개발에 관해 논한다.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.487-489
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• 2004

최근 인터넷의 급속한 성장과 초고속 정보통신망의 구축으로 VoD(Video on Demand)와 같은 서비스가 증가하였다. 하지만, 기존의 VoD 서비스에서 제공되었던 기능들은 클라이언트의 자원을 고려하지 않고 있다. 각 클라이언트마다 통신회선에 따른 대역폭과 컴퓨터 사양에 따른 가용 버퍼의 크기가 다르다. 또한 하드웨어 기술의 발전으로 클라이언트의 처리속도에 있어서도 많은 발전을 하였다. 이러한 특성을 고려하여 클라이언트의 대역폭을 최대한 활용할 수 있도록 브로드케스팅 스케줄을 정하고. 클라이언트의 버퍼 등 컴퓨터의 자원을 충분히 고려하는 방법을 제안한다. 클라이언트의 대역폭을 고려하여 서버의 채널을 나누고, 각 채널을 다양한 크기의 세그먼트로 나누어서 전승한다. 전송 중의 패킷 손실을 고려하여 MPEG-4의 레이어 압축 방법을 사용하고, FEC(Forward Error Correction) 기법을 사용하여 에러 발생을 줄인다.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06b
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• pp.205-209
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• 2008

최근 지상파 서비스에도 양방향 데이터방송 TV 서비스 기능이 본격화되면서 t-learning(TV learning) 콘텐츠 개발도 활성화 되고 있다. 학습자가 데이터방송을 통해 콘텐츠를 학습할 때, 적절한 시기에 적절한 상호작용이 활성화되어야 한다. 현재 제공되는 데이터방송은 VoD(Video on Demand)의 패키지 기반이기 때문에, 프로그램이 처음 시작한 시간에 의지한 상대적인 시간으로 재생되는 방식이다. 그러나 학습자가 t-learning 콘텐츠를 시청하는 시점이 다양하기 때문에 VoD 방송으로는 적절한 시점에 적절한 데이터를 제공하기 어려운 동기화 문제가 발생하게 된다. 본 논문에서는 학습자가 t-learning 콘텐츠의 어느 시점에 접근하더라도 적절한 시점에 학습자와 콘텐츠 간의 상호작용이 가능한 동기화 메커니즘을 제시한다.