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유춘상,황우준,김경식,최성용,김종욱,Yoo, Chun-sang,Hwang, Woo-jun,Kim, Kyung-sik,Choi, Sung-yong,Kim, Jong-uk The Korean AcupunctureMoxibustion Medicine Society 2004 대한침구의학회지 Vol.21 No.2
홍채학은 대체의학의 한 분야로서 홍채 침착의 불규칙성을 주시함으로써 의학적 상태를 진단한다. 홍채학적 분류에 의한 체질은 가족력을 보이고 있으며 이는 홍채체질의 유전성을 의미한다. 강력한 면역조절자이며 전 염증성 사이토카인인 종양괴사인자(tumor necrosis factor-a, TNF-${\alpha}$)는 많은 병리적 과정에서 중요한 역할을 한다. 따라서 본 연구자는 고혈압환자에서 홍채체질과 TNF-${\alpha}$ 유전자 다형성과의 관련성을 조사하였다. 87명의 고혈압 환자와 79명의 정상인을 홍채체질에 따라 분류하였으며 이들의 TNF-${\alpha}$ 유전자형을 분석하였다. 결과적으로 정상인에 비하여 TNF-${\alpha}$ GA 이형접합체의 빈도가 고혈압 환자군에서 감소하였다. 이 같은 결과는 TNF-${\alpha}$ 다형성이 고혈압에 대한 저항성과 관련 있음을 의미한다. 또한 고혈압환자에서 콜레스테롤 침착체질과 심신 결합조직 허약 체질은 42.5%로서 정상인 16.5%에 비하여 현저하게 증가하였다 (P<0.001). GG TNF-${\alpha}$ 유전자형을 갖고 있는 군에서 심신 결합조직 허약체질과 콜레스테롤 침착체질의 빈도는 정상인보다 환자에서 유의하게 높았다(P<0.001). 본 연구에서 저자는 홍채체질과 고혈압사이의 관련성을 발견함과 동시에 TNF-${\alpha}$ 유전자 다형성과 고혈압, 그리고 홍채 체질과의 관련성을 최초로 입증하였다.
DNS of ignition of a lean n-heptane/air mixture under HCCI conditions
유춘상(Chun Sang Yoo),Jackquiline H. Chen 한국연소학회 2010 KOSCOSYMPOSIUM논문집 Vol.- No.41
The effect of thermal stratification on the ignition of a lean homogeneous n-heptane/air mixture at constant volume and high pressure is investigated by direct numerical simulations (DNS) with a new 58-species reduced kinetic mechanism. 2-D DNS are performed in a fixed volume with a two-dimensional isotropic velocity spectrum and temperature fluctuations superimposed on the initial scalar fields. The influence of variations in the initial temperature field, imposed by changing the mean and variance of temperature on multi-stage ignition of a lean n-heptane/air mixture is studied. In general, the mean heat release rate increases more slowly with increasing thermal stratification regardless of the mean initial temperature. Ignition delay decreases with increasing thermal stratification for high mean initial temperature relative to the negative temperature coefficient (NTC) regime. It is, however, retarded with increasing thermal fluctuations for relatively low mean initial temperature resulting from a longer overall ignition delay of the mixture. Displacement speed and Damkohler number analyses reveal that the high degree of thermal stratification induces deflagration rather than spontaneous ignition at the reaction fronts, and hence, the mean heat release rate is smoother subsequent to thermal runaway occurring at the highest temperature regions in the domain. These results suggest that the critical degree of thermal stratification for smooth operation of homogeneous charge compression-ignition (HCCI) engines depends on both the mean and fluctuations in initial temperature which should be considered in controlling ignition timing and preventing an overly rapid increase in pressure in HCCI combustion.
유춘상(Chun Sang Yoo) 한국연소학회 2011 KOSCOSYMPOSIUM논문집 Vol.- No.43
The effect of thermal stratification, spark-ignition, and turbulence on the ignition of a lean homogeneous iso-octane/air mixture at constant volume and high pressure is investigated by direct numerical simulations (DNS) with a new 99-species reduced kinetic mechanism developed for very lean mixtures from the detailed mechanism (Mehl et al., 4th European Combustion Meeting, Vienna, Austria, 2009). Two-dimensional DNS are performed in a fixed volume with two-dimensional isotropic velocity spectrums, temperature fluctuations, and ignition source superimposed on the initial scalar fields. The influence of variations in the initial temperature field imposed by changing the variance of temperature, the ignition-timing by changing the time at which ignition source is superimposed, and the turbulence intensity and length scale on ignition of a lean iso-octane/air mixture is elucidated. The mean heat release rate increases more slowly and ignition delay decreases with increasing thermal stratification under homogeneous charge compression-ignition (HCCI) condition since the present mean temperature lies far outside of the negative temperature coefficient (NTC) regime. The spark-ignition induces relatively short ignition delay under spark-assisted compression ignition (SACI) condition while slightly spreading out the mean heat release rate. For SACI combustion, high turbulence intensity decreases the ignition delay more by increasing turbulent flame area. Displacement speed and Damkohler number analyses reveal that the high degree of thermal stratification induces deflagration at the reaction fronts, and hence, the mean heat release rate is smoother subsequent to thermal runaway occurring at the highest temperature regions in the domain. For SACI combustion, the heat release occurs solely by deflagration prior to the occurrence of the maximum heat release and subsequently by the mixed mode of deflagration and spontaneous ignition. These results suggest that the thermal stratification is more effective for smooth operation of HCCI engines and the spark-ignition can precisely control the ignition timing for SACI combustion.
복사열손실이 있는 비예혼합 튜브형 화염에 관한 수치 해석적 연구
박현수(Hyun Su Bak),유춘상(Chun Sang Yoo) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.12
The characteristics of opposed nonpremixed tubular flames with radiation heat loss are investigated using linear stability analysis and 2-D numerical simulations. Two extinction limits, as the Damköhler number is small or large, are confirmed using finite difference method with a simple continuation method. It is verified that the results of linear stability analysis predict the number of flame cells and the critical Da starting cellular instability or amplification of temperature near both extinction limits with good resolution.
Minh Bau Luong,Chun Sang Yoo(유춘상) 한국연소학회 2013 KOSCOSYMPOSIUM논문집 Vol.2013 No.12
Two-dimensional direct numerical simulations of ignition of a biodiesel/air mixture with temperature (Τ) and equivalence ratio (Φ) stratifications are investigated using a 73-speices reduced chemistry. This study aims at three case studies (1) baseline cases With either only thermal stratification or only fuel concentration stratification: and the two highly feasible scenarios of the Τ-Φ distribution (2) uncorrelated Τ-Φ correlations; and (3) negatively correlated Τ-Φ correlations. The uncorrelated Τ-Φ distribution leads to a smooth combustion due to a mixed mode of combustion of deflagration and spontaneous ignition. The negatively-correlated Τ-Φ distribution results in a severe occurrence of heat release rate throught the whole domain because of spontaneous ignition.