• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.175-181
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• 2019

In the case of a conventional single stage decompression regulator used for large depressurization in the hydrogen fuel cell system of a fuel cell electric vehicle (FCEV), problems can arise, such as pulsation, slow response, hydrogen brittleness, leakage, high weight, and high cost due to high decompression. Most of these problems can be overcome easily using two decompression mechanisms (two-stage structures). In addition, a wide outlet-pressure control range can be secured if an electronic solenoid is applied to the second decompression. Accordingly, it is necessary to improve the precision of the outlet pressure of a two-stage pressure-reducing regulator and develop techniques, such as leakage prevention, durability, light weight, and price reduction. Therefore, to improve the outlet pressure accuracy and prevent leakage, the structural part before and after decompression to improve the air tightness were divided and the analysis was carried out assuming that the valve part was closed (open ratio: 0%) after each initial internal pressure application.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.227-230
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• 2009

Currently the country's foreign energy dependence reaches approximately 97% and the total energy consumption percentage of buildings(commercial and domestic parts) reaches approximately 24%. Building energy saving by enhanced insulation will be very important issue. Therefore, the solution is required to reduce energy loss and increasing displeasure caused by excessive influx of solar energy through windows, to solve the problems like decoloration on indoor furniture an clothes by harmful ultraviolet rays, air conditioning and increased cost. This research used for commercialization and ills semination by basic information through a evaluation on insulation performance of the window of high efficiency energy equipment which can improve the insulation performance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2670-2675
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• 2010

Wall of hanok is related to exterior, inner environment, and the period and cost of construction. This study analyzes traditional wall execution method and suggests improved one. The characters of the improved execution method are use of ready made goods, application of dry and prefabricated method and improvement of airtightness and insulation capacity etc. The result of this study needs production of pilot productions and tests of capacity. But this new method will be useful to save the period and cost of hanok construction.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.517-519
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• 2002

침입탐지 시스템은 정밀성자 적응성, 그리고 확장성을 필요로 한다. 이와 같은 조건을 포함하면서 복잡한 Network 환경에서 중요하고 기밀성이 유지되어야 할 리소스를 보호하기 위해, 우리는 더욱 구조적이며 지능적인 IDS(Intrusion Detection Systems) 개발의 필요성이 요구되고 있다. 본 연구는 데이터 마이닝(Data mining)을 통해 입 패턴, 즉 침입 규칙(Rules)을 생성한다. 데이터 마이닝 기법 중 분류(Classification)에 초점을 맞추어 분석과 실험을 하였으며, 사용된 데이터는 KDD데이터이다. 이 데이터를 중심으로 침입 규칙을 생성하였다. 규칙생성에는 유전자알고리즘(Genetic Algorithm : GAs)을 적용하였다. 즉, 오용탐지(Misuse Detection) 기법을 실험하였으며, 생성된 규칙은 침입데이터를 대표하는 규칙으로 비정상 사용자와 정상 사용자를 분류하게 된다. 규칙은 "Time Based Traffic Model", "Host Based Traffic Model", "Content Model" 이 세 가지 모듈에서 각각 상이한 침입 규칙을 생성하게 된다. 본 시스템에서 도출된 침입 규칙은 430M Test data set에서 테스트한 결과 평균 약94.3%의 성능 평가 결과를 얻어 만족할 만한 성과를 보였다.의 성능 평가 결과를 얻어 만족할 만한 성과를 보였다.

• Journal of Energy Engineering
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• v.27 no.4
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• pp.1-12
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• 2018

The code and standards related to fuel cells were analyzed to derive the SOFC(Solid Oxide Fuel Cell) stack safety performance evaluation items and evaluation methode. Safety performance evluation of the SOFC stack was tested by quoting derived test items. The stack used in the test is an anode-supported type 2 Cell stack (Active surface area : 220cm) manufactured by MICO Inc, and SOFC stack safety performance evaluation system used for the test is self-manufactured. We conducted a leakage test, current voltage characteristic test, rated output test, and power response characteristics test. In the safety performance evaluation test, the stack showed no gas leakage, the maximum output and rated output was recorded to 65.6 W(1.41 V, 46.5 A, $422mA/cm^2$), 62.3 W(1.57 V, 40 A, $363mA/cm^2$). In the power response characteristics test verified that the output is kept stable within two seconds. At the maximum load (40 A) and the minimum load (8 A), the output was recorded 62 W and 16W in $750^{\circ}C$. This study will contribute to the universalization and to provide much safe environment of operating the solid oxide fuel cell system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.31-38
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• 2005

Ipsec is a security protocol suite that provides encryption and authentication services for IP messages at the network layer of the internet. Internet Key Exchange (IKE) is a protocol that is used to negotiate and provide authenticated keying materials in a protected manner for Security Associations (SAs). In this paper, we propose a dynamic key lifetime change algorithm for performance enhancement of virtual private networks using IPSec. The proposed algorithm changes the key lifetime according to the number of secure tunnels. The proposed algorithm is implemented with Linux 2.4.18 and FreeS/WAN 1.99. The system employing our proposed algorithm performs better than the original version in terms of network performance and security.

• KIPS Transactions on Computer and Communication Systems
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• v.5 no.3
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• pp.71-78
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• 2016

Recently, The interest about underwater acoustic communication is increase such as marine resources, disaster prevention, weather prediction, and so on. Because the underwater acoustic communication uses a water as media, the underwater acoustic communication has a lot of restrictions. Although the underwater acoustic communication is hard, it is important to consider the security. In this paper, we estimate the performance of cryptographic algorithms(AES, ARIA, and LEA) on a various devices, available in underwater acoustic communication, and analysis the results. This result will be provide effective data confidentiality for underwater communication.

• Fire Science and Engineering
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• v.23 no.6
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• pp.91-97
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• 2009

The mass flow rates and performance of natural smoke ventilators in high-rise buildings with 40, 80, 120 stories were evaluated using CONTAMW tool. The results showed that only limited part of smoke ventilators can have positive exhaust flow in high-rise buildings due to stack effect and wind velocities. In the higher story buildings larger stack effect can overcome outside strong wind effect to give more ventilation performance. The air tightness of the building have strong effect on the exhaust performance of the ventilators to give lower performance with loose air tightness of the exterior walls.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.297-306
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• 2011

In this paper, we performed thermodynamic energy balance analysis of the underground lined rock cavern for compressed air energy storage (CAES) using the results of multi-phase heat flow analysis to simulate complex groundwater-compressed air flow around the cavern as well as heat transfer to concrete linings and surrounding rock mass. Our energy balance analysis demonstrated that the energy loss for a daily compression and decompression cycle predominantly depends on the energy loss by heat conduction to the concrete linings and surrounding rock mass for a sufficiently air-tight system with low permeability of the concrete linings. Overall energy efficiency of the underground lined rock caverns for CAES was sensitive to air injection temperature, and the energy loss by heat conduction can be minimized by keeping the air injection temperature closer to the ambient temperature of the surroundings. In such a case, almost all the heat loss during compression phase was gained back in a subsequent decompression phase. Meanwhile, the influence of heat conductivity of the concrete linings to energy efficiency was negligible.

• KIEAE Journal
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• v.17 no.4
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• pp.59-65
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• 2017

Purpose: Thermal performance and air tightness of window are improved for the building energy efficiency. As the deteriorated houses are increased, the improve measures with low cost and easy installation are developed in the energy performance of window. Attached glazing and windbreak can be easily applied to the window with low cost. In this paper, the effect of the attached glazing and windbreak on the thermal performance and air tightness of window is analyzed as the measure to improve performance of window. Method: Thermal transmittance of glazing is evaluated through WINDOW simulation according to thickness of attached glazing and air cavity. Based on the simulation results, thermal transmittance, air tightness and condensation resistance performance of four cases are tested according to Korea standards. One type of PVC sliding double window is chosen as the specimen. For the analysis on low performance of window, the outside of window is excluded in the PVC sliding double window. Result: This study shows that thermal performance of glazing can be increased by the application of attached glazing. Furthermore, lower thermal performance of glazing can obtain the higher effect of attached glazing. The application of attached glazing and windbreak can effect on increasing thermal performance and air tightness of window.