• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.295-298
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• 2006

Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate. It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation. Edge flame oscillations in low strain rate flames are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.257-264
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• 1989

For the extension of the flash method the heat diffusion equation with heat loss and with an arbitrary heat pulse is mathematically analyzed. In the analysis the heat loss includes the axial and radial directions on the front, rear and peripheral surfaces. The heat pulse is irradiated from the source to the front surface of the sample and the heat receiving area on the front surface is controlled by the apertures of an optical system. From this analysis the thermal diffusivity of the samples can be determined more precisely than before by the data reduction method using various percent time. The data can be obtained by the extended radial flash technique adjusted correctly the heating area on the central part of the front surface with a proper aperture or the conventional axial flash technique heated uniformly all parts of the front surface.

• Korean Journal of Materials Research
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• v.6 no.12
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• pp.1221-1232
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• 1996

용접부 인성을 향상시키기 위해 Ti 산화물을 첨가한 Ti 산화물강에 대하여 용접시 최고가 열온도와 냉각속도의 변화가 용접열영향부의 미세조직에 미치는 영향을 조사하였다. 용접열영향부의 인성향상에 기여하는 acicular ferrite는 140$0^{\circ}C$ 이상의 최고가열온도와 $\Delta$t800-500가 40초보다 빠른 냉각속도에서 활발해 생성되었다. 오스테나이트 결정립내에서 개재물로부터 핵생성된 일차 acicular ferite의 생성량은 전체 aicular ferrite의 약 20% 정도로 적었으며 대부분의 acicular ferrite는 일차 acicular ferrite로부터 생성된 이차 acicular ferrite인 것으로 나타났다. 이차 acicular ferrite는 plate사이에 Fe3C층이 존재하는 것으로 보아 확산기구에 의해 생성되는 것으로 생각된다. 개재물은 TiO, TiO2, TiN, MnS, AI2O3 MnO(galaxite)등으로 구성된 복합상이었으며 개재물이 일차 acicular ferrite의 핵생성 site로 작용하기 위해서는 약 1$\mu\textrm{m}$이상의 크기가 효과적인 것으로 나타났다. Ti 산화물과 TiN는 직접적인 acicular ferrite의 핵생성 site로 작용하기보다는 MnS, galaxite 등의 석출 site로 작용하여 개재물의 크기를 증가시킴으로써 acicular ferrite의 생성을 촉진시키는 것으로 생각된다.

• Journal of the Korean Institute of Gas
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• v.2 no.2
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• pp.61-69
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• 1998

The risk assessments for gas leak in underground pipeline are conducted about the explosion accident of AHYUN-DONG underground service-base on December, 1994(Gaussian gas, LNG) and the accident of TAEGU subway on April 1995(Heavy gas LPG). We have calculated the total mass of gas release and have respected the efficient of explosions with report of the spot. The dispersion zones of LNG were calculated as large as fifteen times to those of LPG by ALOHA. The effects of thermal radiation from LNG explosion were assumed less than that from LPG by PHAST.

• Journal of Information Management
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• v.37 no.1
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• pp.1-16
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• 2006

Due to the dramatic development of the Internet, the ICT market has changed from a voice based services to data based services. Substitution and complementary dynamism has emerged from communication technology services such as the Internet, mobile phone, and telephone. This paper analyses diffusion patterns of communication technologies such as the Internet, cellular phones, and telephones in different country groups. We estimate modified logistic growth model using time series data for the years 1975-2002. As a result, it is possible to categorize country groups according to the patterns of diffusions. This research creates essential information to forecast demand for new services based on incumbent services as well as provide information on strategies for entering the network industry.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1297-1303
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• 2012

In this paper, the standard procedures for measuring the moisture sorption properties of thin polymeric materials such as polyethylene terephthalate (PET) by using the thermo-gravimetric method to characterize the moisture diffusion in the polymer are presented, and the sorption properties are quantified. The moisture diffusivity and solubility are characterized to investigate the effect of temperature and humidity on the moisture sorption properties according to the Arrhenius equation. The validation of the obtained sorption properties using thermogravimetry is discussed with the measured permeability based on Fickian diffusion. The nonlinear behavior of the concentration dependent moisture diffusion is investigated experimentally, and the nonlinearity is characterized numerically for the case of having an interface with an inorganic material such as a metal. The Fickian/Non-Fickian model based on the obtained moisture sorption properties is compared and discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1629-1637
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• 2003

In this paper, we analyzed the performance of a hybird DS/SFH(Direct­Sequency­Slow Frequency­Hopping) Spread Spectrum system with BFSK modulation over Nakagami­m fading channel with multitone jamming. The performance of the system was improved when a frequency bowing rate increased. In case that process gain of hybrid DS/SFH Spread Spectrum system to be fixed, the hybrid DS/SFH Spread Spectrum takes the low bit error probability than a DS Spread Spectrum system. Also, when the fading index m increases, the fading effect decrease, when the JSR(jamming to signal power ratio) increases ,the performance of a hybrid DS/SFH Spread Spectrum system improved than DS Spread Spectrum system. The result, we have been proved that performance of a hybrid DS/SFH Spread Spectrum was superior to DS Spend Spectrum system over Nakagami­m fading with tome jamming.

• Fire Science and Engineering
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• v.19 no.1 s.57
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• pp.80-86
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• 2005

In this study effects of the natural wind and the forced smoke ejection by operating the exhaust fan are studied numerically to examine the flow characteristics of the smoke and heat generated from a fire on the platform of an underground subway station. Three different situations, including 1) the case with no natural wind and no exhaust fan operation, 2) the case with natural wind but no exhaust fan operation and 3) the case with no natural wind but exhaust fan operation, are considered for the numerical analyses. The numerical results show that the natural wind causes a rapid spread of the fire along the tunnel resulting in rapid spread of the smoke and heat over the platform which affects the escape. The operation of the exhaust fan also results in the rapid spread of smoke and heat over the platform, but the time required for reaching the safe escaping height of the smoke layer with the exhaust fan operation is much longer than that without the exhaust fan operation. The numerical results also show that the required capacity of the exhaust fan becomes larger when the effect of the natural wind is included.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1995.10a
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• pp.146-151
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• 1995

원자력, 화력발전소 및 임해공업시설로부터 방출되는 냉각용 온수는 하천 또는 연안일대의 수계환경에 전반적인 수중온도의 상승과 가동 중단시 갑작스러운 수온 저하 등의 열균형 파괴를 가져온다. 따라서 여러가지 형태의 주위수에 영향을 받는 온배수의 이동 및 확산에 대한 정성, 정량적 예측을 위한 수치모델의 개발은 환경관리 및 생태계 보전 측면에서 매우 중요하다. (중략)

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2016.10a
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• pp.222-222
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• 2016