• Journal of Electrochemical Science and Technology
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• v.8 no.3
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• pp.183-196
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• 2017

The research efforts directed at advancing water electrolysis technology continue to intensify together with the increasing interest in hydrogen as an alternative source of energy to fossil fuels. Among the various water electrolysis systems reported to date, systems employing a solid polymer electrolyte membrane are known to display both improved safety and efficiency as a result of enhanced separation of products: hydrogen and oxygen. Conducting water electrolysis in an alkaline medium lowers the system cost by allowing non-platinum group metals to be used as catalysts for the complex multi-electron transfer reactions involved in water electrolysis, namely the hydrogen and oxygen evolution reactions (HER and OER, respectively). We briefly review the anion exchange membranes (AEMs) and electrocatalysts developed and applied thus far in alkaline AEM water electrolysis (AEMWE) devices. Testing the developed components in AEMWE cells is a key step in maximizing the device performance since cell performance depends strongly on the structure of the electrodes containing the HER and OER catalysts and the polymer membrane under specific cell operating conditions. In this review, we discuss the properties of reported AEMs that have been used to fabricate membrane-electrode assemblies for AEMWE cells, including membranes based on polysulfone, poly(2,6-dimethyl-p-phylene) oxide, polybenzimidazole, and inorganic composite materials. The activities and stabilities of tertiary metal oxides, metal carbon composites, and ultra-low Pt-loading electrodes toward OER and HER in AEMWE cells are also described.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.12C
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• pp.1238-1244
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• 2002

In this paper, H.235-based security mechanism for H.323 multimedia applications was implemented. H.235 covers authentication using HMAC, Diffie-Hellman key exchange, session key management for voice channel, and encryption functions such as DES, 3DES, RC2. Extra encryption algorithms such as SEED, and AES were also included for possible use in the future. And, we also analyzed the quality of service (QoS), the requirement of implementation, and interoperability to the result in this study. The results could be applied to secure simple IP phone terminals, gateways, or gatekeepers.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.1
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• pp.3-11
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• 2009

Forward secrecy in an e-mail system means that the compromising of the long-term secret keys of the mail users and mail servers does not affect the confidentiality of the previous e-mail messages. Previous forward-secure e-mail protocols used the certified public keys of the users and thus needed PKI(Public Key Infrastructure). In this paper, we propose a password-based authenticated e-mail protocol providing forward secrecy. The proposed protocol does not require certified public keys and is sufficiently efficient to be executed on resource-restricted mobile devices.

• Journal of Mechanical Science and Technology
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• v.19 no.4
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• pp.1018-1026
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• 2005

The proton exchange membrane (PEM) fuel cell system consisting of stack and balance of plant (BOP) was modeled in a MATLAB/Simulink environment. High-pressure operating (compressor type) and low-pressure operating (air blower type) fuel cell systems were con­sidered. The effects of two main operating parameters (humidity and the pressure of the supplied gas) on the power distribution characteristics of BOP and the net system efficiency of the two systems mentioned above were compared and discussed. The simulation determines an optimum condition regarding parameters such as the cathode air pressure and the relative humidity for maximum net system efficiency for the operating fuel cell systems. This study contributes to get a basic insight into the fuel cell stack and BOP component sizing. Further research using muli­object variable optimization packages and the approach developed by this study can effectively contribute to an operating strategy for the practical use of fuel cell systems for vehicles.

• Journal of Electrical Engineering and Technology
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• v.6 no.5
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• pp.605-612
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• 2011

As the power grids are integrated into one big umbrella called a "smart grid," communication protocol plays a key role in successful operations. The successful deployment of smart grid interoperability is a major hurdle that must be overcome. The micro grid, a small power system that distributes energy resource, is operated in diverse regions. Different vendors use different communication protocols in the operation of the micro grid. Recently, the IEC 61850 has been legislated to solve the interoperability problems in power utility automation. The present paper presents a micro grid system based on the IEC 61850 protocol. It consists of a micro grid monitoring system, a protocol converter that transforms serial data to IEC 61850 data, and distributed energy resource controllers for diverse DER nodes. A developed communication gateway can be deployed for DER controllers with serial links to exchange data with IEC 61850-based devices. The gateway can be extended to IEC 61850-based distribution automation systems, substation automation systems, or SCADA.

• Journal of KIISE:Computing Practices and Letters
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• v.8 no.5
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• pp.530-539
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• 2002

Recently, there have been a lot of researches to develop an archive system for news videos that usually has a fixed structure. However, since the meta-data representation and storing schemes for news video are different from each other in the previously proposed archive systems, it was very hard to exchange these meta-data. This paper proposes a scheme for news video based on MPEG-7 MDS that is an international standard to represent the contents of multimedia, and a summarization mechanism reflecting the characteristics of shots in the news videos. The proposed scheme for news video uses the MPEG-7 MDS schemes such as VideoSegment and TextAnnotation to keep the original structure of news video, and the proposed summarization mechanism uses a slide-show style presentation of key frames with associated audio to reduce the data size of the summary video.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.89-94
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• 2011

The EGR system is one of important components in diesel engine. The regulation on NOx emission has been tightened up. Therefore, it is a significant issue to develop and commercialize the high efficient EGR cooler system that reduces NOx emission in DI diesel engine. Key performance factor of the EGR cooler system is how to properly design both wavy cooling fins and gas tubes. This paper proposes a high efficient EGR cooler that has been upgraded with both the optimized wavy cooling fins and the improved shape of structure. The evaluation of the heat exchange efficiency, outlet temperature, and gas pressure drop of the EGR cooler is performed with the prototype of the proposed EGR cooler. The result shows a good solution and will be implemented to the model of a clean diesel engine being developed for both domestic and overseas market.

• The KIPS Transactions:PartC
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• v.9C no.3
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• pp.367-374
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• 2002

IPsec offers not odd Internet security service such as Internet secure communication and authentication but also the safe key exchange and anti-replay attack mechanism. Recently IPsec is implemented on the various operating systems. But there is no existing tool that checks the servers, which provide IPsec services, work properly and provide their network security services well. In this paper, we design and implement the rule based security evaluation system for IPsec engine. This system operated on Windows and UNX platform. We developed the system using Java and C language.

• Journal of Navigation and Port Research
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• v.28 no.8
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• pp.673-678
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• 2004

The ENC standard, S-57 Specification was established to exchange hydrographic data between it's users such as HOs ECDIS users, etc. The digital navigation chart which is produced according to the S-57 Specification is called an ENC(Electronic Navigational Chart) and the SENC(System ENC) is a by-product of ENC suitable for computer graphics system Even though the efficient structure of SENC is a key element of measuring ECDIS performance, the amount of papers about these topics are small compared with other research fields. In this paper, the author designed an efficient spatial data structure of SENC, called Mesh This paper also includes the implementation result of the 'Mesh' which displays SENC on computer screen.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.9
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• pp.2590-2608
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• 2023

The high-altitude and mobility characteristics of unmanned aerial vehicles (UAVs) have made them a key element of new radio systems, particularly because they can exceed the limits of terrestrial networks. However, at high altitudes, UAVs can be significantly affected by intercell interference at a high line-of-sight probability. To mitigate this drawback, we propose an algorithm that selects the optimal beam to reduce interference and maximize transmission efficiency. The proposed algorithm comprises two steps: constructing a user-location-based fingerprint database according to the user types presented herein and cooperative beam selection. Simulations were conducted using cellular cooperative downlink systems for analyzing the performance of the proposed method, and the signal-to-interference-plus-noise cumulative distribution function and spectral efficiency cumulative distribution function were used as performance analysis indicators. Simulation results showed that the proposed algorithm could reduce the effect of interference and increase the performance of the desired signal. Moreover, the algorithm could efficiently reduce overheads and system cost by reducing the amount of resources required for information exchange.