• Elastomers and Composites
• /
• v.35 no.1
• /
• pp.29-37
• /
• 2000

In this study as a basic research of the elastomer, we show the results of the behavior of the two different chain length polymers in the melt confined between two impenetrable planes. The cubic lattice simulations are conducted in the canonical ensemble with a method that is a combination of reptation and crackshaft bond flip motions. A total of 680 chains which are 544 short chains comprising 10 beads and 136 long chains comprising 160 beads were placed in 20 lattice layers. It was assumed that there is no energetic interactions between covalently connected beads. while all other neighbors will interact with a truncated 6-12 Lennard-Jones potential. From the analysis of the simulation results, it was shown that purely entropic effects caused the shorter chains to partition preferentially to the surface. We also showed that the center of mass density of the shorter chains shows maximum near the surface. This is the opposite phenomena when compared to that of the longer chains. However, the segments of the shorter and the longer chains did not display any significant changes in bond order.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.5
• /
• pp.437-443
• /
• 2014

Engine is one of the most important parts in a rocket for completing its mission successfully. In this paper, we provide a methodology for estimating reliability and development cost of a liquid rocket engine newly developed. To estimate reliability, a baseline engine is selected considering factors whose effects on reliability are unquantifiable. Then reliability of a baseline engine is adjusted to reflect the effect of factors that can be modeled quantitatively. Using the previous Transcost engine cost expressed in terms of mass and the number of hot firing tests, the engine development cost is reexpressed in reliability and thrust requirements. Finally, a numerical example is given to illustrate the application of the methodology to a turbopump rocket engine using staged combustion cycle with LOX/LH2 propellant.

• Journal of the Korean Geotechnical Society
• /
• v.31 no.11
• /
• pp.49-60
• /
• 2015

Open-water sediment disposal has many applications in costal construction. Dumping of sediment in open water can be divided into descending stage under water and sedimentation stage on the seabed, and retained rate is evaluated from analyzed results of these two successive stages. Descending particle cloud have two distinct thermal and swam phase, and trajectory equations for each phase are derived to describe settling velocity and radius of particle cloud. For sedimentation stage, a numerical simulator is used to calculate growth factors for particle fiction angle and current velocity. Retained rate is defined as a mass rate of remained sediment inside the circle which has a center at dumping point on the sea level and user-defined effective radius. Retained rate map for Singapore coast is presented with water depth of 20 m, current velocity of 0.0~1.5 m/s, and effective radius of 5 m. It will decrease sediment mass loss during disposal operation and minimize surrounding environmental pollution.

• Journal of the Korean earth science society
• /
• v.25 no.6
• /
• pp.495-501
• /
• 2004

Using numerous ground-based or space-based telescopes by many astronomers, AGN spectroscopic monitoring campaigns have been carried out over many years to study the variability of continua and emission lines. We investigate the SWP IUE spectra of a large aperture configuration for the Seyfert 1 galaxies NGC 4151 and NGC 5548. We estimate the BLR electron number densities and their variation from the line ratios of C III] 1909 to Si III] 1892. With the ratios of C IV 1550 to C III] 1909 which give us the information on the ionization parameter of BLR, we try to find the physical conditions of the BLR and activities of he super massive black hole surroundings. The BLR density variations scale as 4 and 8 for NGC 4151 and NGC 5548, respectively. Based on the BLR size and C III] line profiles, we found both black hole masses as about $10^7$ $M_{\odot}$.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.20 no.2
• /
• pp.111-118
• /
• 2010

연구목적: 본 연구는 일반인의 비직업적 노출에 대한 혈중 16종의 다환방향족탄화수소(PAHs) 의 농도르 분석하여 PAHs의 백그라운드 노출 농도를 평가하는 것이다. 내용 및 방법: 농촌지역에 거주(비직업적 노출로서 16종 다환방향족탄화수소가 특정한 환경오염을 받지 않은 지역에 거주)하는 156명의 연구 참여자의 혈중 16가지 다환방향족탄화수소 농도의 기하평균치를 간접흡연군, 구운 음식물섭취군과 각대조군을 비교 하였다. 혈중 16종의 다환방향족탄화수소의 농도는 질량분석기를 장착한 가스크로마토그라피법과 헤드스페이스 마이크로고체상 추출법에 의하여 분석하였다. 결과: 연구참여자 중, 간접흡연자들에서 4종의 다환방향족탄화수소 아세나프틸렌(p<0.01), 아세나프텐(p<0.1), 플로렌(p<0.01), 피렌(p=0.05)가 대조군 보다 유의하게 높았다. 또한 구운육류와 생선 섭취군에서는 벤조(a)피렌(p<0.1)이 대조군 보다 유의하게 높았다. 결론: 간접흡연과 구운음식물 섭취는 비직업적 노출에서 다환방향족탄화수소 노출원의 가능성이 높다고 추정된다. 혈중 다환방향족탄화수소는 한국일반인의 비직업적 노출 농도로 사용 가능하다고 생각된다.

• Journal of the Korean Society of Physical Medicine
• /
• v.9 no.1
• /
• pp.93-99
• /
• 2014

PURPOSE: The purpose of this study was to compare three dimensional displacement and peak velocity of the center of mass (COM) during obstacle crossing in young and older adults. METHODS: 10 young adults (6 males/4 females, $24.6{\pm}1.9$ years, age range: 22.0-26.9) and 10 older adults (1 male/9 females, $76.9{\pm}5.1$ years, age range: 65.2-81.2) participated in the study. Both groups crossed an obstacle, which is 10% of leg length, and COM was measured using motion analysis system. Independent t-test was used to find significant differences between two groups. RESULTS: The older adults showed significantly greater and faster COM displacement and peak velocity in mediolateral (M-L) direction as compared with young adults (p<.01 and p<.001 respectively). However, the young adults showed significantly greater and faster COM displacement and peak velocity in anteroposterior (A-P) direction as compared with older adults (p<.05 and p<.001 respectively). Furthermore, the young adults showed faster peak velocity of COM in vertical direction as compared with older adults (p<.001). However, no significant difference was found in the COM displacement in vertical direction between two groups. CONCLUSION: Greater and faster COM displacement and peak velocity in M-L direction in older adults were due to compensatory adjustment for appropriate contact on base of support of swing limb. Thus, the motion of the COM in M-L direction may be a crucial factor to identify risk of falls in older adults.

• Journal of Energy Engineering
• /
• v.2 no.3
• /
• pp.268-275
• /
• 1993

A series of parametric investigations are performed in order to resolve the flow characteristic of a Quebec city stoker incinerator. The parameters considered in this study are five internal configurations of the Quebec city stoker itself and its modified ones, primary air velocity, the injection velocity and angle of the secondary air, and the reduction of the stoker exit area. A control-volume based finite-difference method by Patankar together with the power-law scheme is employed for discretization. The resolution of the pressure-velocity coupling is made by the use of SIMPLEC algorithm. The standard, two equation, k-$\varepsilon$ model is incorporated for the closure of turbulence. The size of recirculation region, turbulent viscosity, the mass fraction of the secondary air and pressure drop are calculated in order to analyze the characteristics of flow field. The results are physically acceptable and discussed in detail. The flow field of the Quebec city stoker shows the strong recirculation zone together with the high turbulence intensity over the upper part of the incinerator.

• Journal of Astronomy and Space Sciences
• /
• v.18 no.3
• /
• pp.175-190
• /
• 2001

We investigated population of the elliptical galaxy NGC 4649 using the spectral synthesis technique based on the linear program in the spectral regions between $3160\AA$to $10800\AA$. We used the spectral data of stars obtained by Gunn & Striker (1983), and the integrated spectrum of NGC 4649 observed by Bertola et al. (1982). Among four models with different main sequence turn-off points, G8-K0V main sequence turn-off model is best fitted to the integrated spectrum of NGC 4649. We also found that super metal rich K giants are needed to describe the absorption lines in the long wavelength regions of integrated spectrum of NGC 4649. The mass to absolute light ratio obtained from the spectral synthesis is ~ 20 similar to those calculated dynamically.

• Communications of Mathematical Education
• /
• v.27 no.4
• /
• pp.487-498
• /
• 2013

Sang-Seol Lee(1870-1917) wrote a manuscript BaekSeungHoCho(百勝胡艸) in the late 19th century. BaekSeungHoCho was transcribed in classical Chinese from the 1879 Japanese book Physics(物理學) by Teizo Ihimori (1851-1916). Sang-Seol Lee, a famous independence activist, is also called Father of the Modern Mathematics Education of Korea, because of his early contribution to the modern mathematics education in the 19th century. In this paper, we introduce contents of his manuscript BaekSeungHoCho for the first time and discuss the significance of this book. Also, we show his contribution on the introduction to modern physics in the late 19th century Korea.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.3
• /
• pp.258-268
• /
• 2017

In this study, we aim to converge a technology for analyzing the hydraulic circuit of a loading arm with an- other one for analyzing multi-body dynamics by utilizing analysis software SimulationX. Further, this study intends to overcome the limitations of the existing technology for analyzing a hydraulic circuit with a variation at the rotation center of the moving mass and the difficulty of incorporating the behavior in a gravity field. First, the specifications of the hydraulic circuit components were reflected in an analysis model to secure reliability. Hydraulic circuit modeling was then performed using a single analysis model with a verified reliability. Subsequently, the multi-body system (MBS) model of the loading arm was formed. Finally, the analysis model of the hydraulic circuit and the MBS model were converged to check if the circuit analysis result was exactly reflected in the MBS model. The convergence analysis model has development cost-saving effect because it is capable of predicting the dynamic behavior of an object without the prototype.