• 한국자동차공학회논문집
• /
• 제21권1호
• /
• pp.43-50
• /
• 2013

The stringent emission regulation and future shortage of fossil fuel motivate the research of alternative powertrain. In this study, a system of proton exchange membrane fuel cell has been modeled to analyze the performance of the fuel cell system for automotive application. The model is composed of the fuel cell stack, air compressor, humidifier, and intercooler, and hydrogen supply which are implemented by using the Matlab/Simulink(R). Fuel cell stack model is empirical model but the water transport model is included so that the system performance can be predicted over various humidity conditions. On the other hand, the model of air compressor is composed of motor, static air compressor, and some manifolds so that the motor dynamics and manifold dynamics can be investigated. Since the model is concentrated on the strategic operation of compressor to reduce the power consumption, other balance of components (BOP) are modeled to be static components. Since the air compressor model is empirical model which is based on curve fitting of experiments, the stack model is validated with the commercial software and the experiments. The dynamics of air compressor is investigated over unit change of system load. The results shows that the power consumption of air compressor is about 12% to 25% of stack gross power and dynamic response should be reduced to optimize the system operation.

• 한국산업정보학회:학술대회논문집
• /
• 한국산업정보학회 2001년도 춘계학술대회논문집:21세기 신지식정보의 창출
• /
• pp.224-231
• /
• 2001

2.45 GHz 마이크로웨이브를 사용하는 전자회전공명 플라즈마를 이용하여 화학적 기상증착(electron cyclotron resonance plasma enhanced chemical vapor deposition; ECR-PECVD) 방법으로 ECR 마이크로웨이브 power, CH$_4$/H$_2$가스 혼합비와 유량, 증착시간, 그리고 기판 bias 전압 등을 변화시켜 가면서 수소가 함유된 비정질 탄소(a-C:H) 박막을 증착하였고, 증착시킨 박막의 특성을 AES(Auger electron spectroscopy), ERDA(elastic recoil detection analysis), FTIR(Fourier transform infrared) 및 Raman 측정 등으로 조사하였다. 증착시킨 a-C:H 박막은 탄소 및 수소원소들로만 구성되어 있음을 AES 측정으로 확인하였다. 그리고 FTIR 측정으로부터 a-C:H 박막은 대부분 sp$^3$결합을 하고 있고 일부는 sp$^2$결합을 하고 있음을 확인하였으며, CH$_4$/H$_2$가스 혼합비와 유량의 변화가 a-C:H 박막의 탄소와 수소의 결합구조에 큰 영향을 미치지 않았으며, 다만 증착시간이 증가할수록 탄소와 수소 원자들의 결합구조가 $CH_3$구조에서 CH$_2$나 CH 구조로 변하고 있음을 알았다. 또한 Raman 스펙트럼의 Gaussian curve fitting을 통하여 sp$^3$/sp$^2$의 결합수에 비례하는 D 및 G peak의 면적 강도비(I$_{D}$/l$_{G}$)는 기판 bias 전압을 증가시킬수록 증가하였으며, 경도도 역시 증가하였다.하였다.

• 통합자연과학논문집
• /
• 제3권4호
• /
• pp.231-236
• /
• 2010

Partial charge is an important and fundamental concept which can explain many aspects of chemistry. Since a molecule can be regarded as neclei surrounded by electron cloud, there is no way to define a partial charge accurately. Nevertheless, there have been many attempts to define these seemingly impossible parameters, since they would facilitate the understanding of molecular properties such as molecular dipole moment, solvation, hydrogen bonding, molecular spectroscopy, chemical reaction, etc. Common methods are based on the charge equalization, orbital occupancy, charge density, and electric multipole moments, and electrostatic potential fitting. Methods based on the charge equalization using electronegativity are very fast, and therefore they have been used to study many compounds. Methods to subdivide orbital occupancy using basis set conversion, relies on the notion that molecular orbitals are composed of atomic orbitals. The main idea is to reduce overlap integral between two nuclei using converted orthogonal basis sets. Using some quantum mechanical observables like electrostatic potential or charge multipole moments. Using potential grids obtained from wavefunction, partial charges can be fitted. these charges are most useful to describe intermolecular electrostatic interactions. Methods to using dipole moment and its derivatives, seems to be sensitive the level of theory, Dividing electron density using density gradient being the most rigorous theoretically among various schemes, bears best potential to describe the charge the most adequately in the future.

• 융복합기술연구소 논문집
• /
• 제7권2호
• /
• pp.13-16
• /
• 2017

The design of sealing mechanisms of a manual pressure valve was analyzed with FE analysis for a hydrogen fuels charge and discharge system of FCEV. The damage prediction of the O-ring with respect to the material models of rubbers was calculated by the gap analysis of the backup ring and O-ring according to the internal pressure. Two kinds of the rubber material characteristic models were adopted to the O-ring. One was the linear elastic and the other was hyperelastic of Ogden $3^{rd}$ order model. The experimental data of urethane of Shore hardness 90 was utilized to the curve fitting of hyperelastic properties. It was found that the contact pattern of the backup ring was different in two models and the sealing mechanism was better in the case of the hyperelastic characteristic model.

• 천문학회보
• /
• 제44권1호
• /
• pp.75.1-75.1
• /
• 2019

The universe has been ionized in the post-reionization by several photon contributors. The dominant source to produce the hydrogen ionizing photons is not revealed so far. Faint quasars have been expected to generate UV photon budgets required to maintain ionization state of universe. Observational limits, however, hinder to discover them despite their higher number density than bright one. Consequently, the influence of faint quasars on post-reionization are not considered sufficiently. Therefore, a survey to find faint quasars at z ~ 5 is crucial to determine the main ionizing source in the post-reionization era. Deep images from the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) allow us to search for quasar swith low luminosities in the ELAIS-N1 field. J band information are obtained by the Infrared Medium-deep Survey (IMS) and the UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep ExtragalacticSurvey (DXS). Faint quasar candidates were selected from several multi-band color cut criteria based on simulated quasars on color-color diagram. To choose the reliable candidates with possible Lyman break, we have performed medium-bands observations. Whether a candidate is a quasar or a dwarf star contamination was decided by results from chi-square minimization of quasar/dwarf model fitting. Spectroscopic follow-up observations confirm three quasars at z ~ 5. 100% spectral confirmation success rate implies that the medium-band observations effectively select faint quasars with strong Lyman alpha emission.

• Nuclear Engineering and Technology
• /
• 제53권1호
• /
• pp.304-313
• /
• 2021

Nickel base Alloy X-750, which is used as fastener parts in light-water reactor (LWR), has experienced many failures by environmentally assisted cracking (EAC). In order to improve the reliability of passive components for nuclear power plants (NPP's), it is necessary to study the failure mechanism and to predict crack growth behavior by developing a probabilistic failure model. In this study, The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model (FCGR) was developed by fitting into Paris' Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode. These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were successfully updated to reduce the uncertainty in the model by using the Bayesian inference method. It is demonstrated that probabilistic failure models for passive components can be developed by updating a laboratory model with field-inspection data, when crack growth rates (CGRs) are low and multiple inspections can be made prior to the component failure.

• 천문학회보
• /
• 제44권2호
• /
• pp.75.4-75.4
• /
• 2019

We present a quantitative analysis of the relationship between the gas dynamics and star formation history of DDO 210 which is an irregular dwarf galaxy in the local Universe. We perform profile analysis of an high-resolution neutral hydrogen (HI) data cube of the galaxy taken with the large Very Large Array (VLA) survey, LITTLE THINGS using newly developed algorithm based on a Bayesian Markov Chain Monte Carlo (MCMC) technique. The complex HI structure and kinematics of the galaxy are decomposed into multiple kinematic components in a quantitative way like 1) bulk motions which are most likely to follow the underlying circular rotation of the disk, 2) non-circular motions deviating from the bulk motions, and 3) kinematically cold and warm components with narrower and wider velocity dispersion. The decomposed kinematic components are then spatially correlated with the distribution of stellar populations obtained from the color-magnitude diagram (CMD) fitting method. The cold and warm gas components show negative and positive correlations between their velocity dispersions and the surface star formation rates of the populations with ages of < 40 Myr and 100~400 Myr, respectively. The cold gas is most likely to be associated with the young stellar populations. Then the stellar feedback of the young populations could influence the warm gas. The age difference between the populations which show the correlations indicates the time delay of the stellar feedback.

• 대한화학회지
• /
• 제28권4호
• /
• pp.210-216
• /
• 1984

MeOH-MeCN 혼합용매의 Taft용매 파라미터인 ${\pi}^{\ast}$(용매의 polarity-polarizability), ${\alpha}$(용매의 수소결합 주게 산도) 그리고 ${\beta}$(용매의 수소결합 받게 염기도)를 여러 지시약을 사용하여 분광용매화 비교법으로 구하였다. 또한 Swain의 용매 파라미터인 A(음이온을 용매화 시키는 척도)와 B(양이온을 용매화 시키는 척도)를 반응속도 자료를 이용하여 최소 자승법으로 구하였다. 용매 상수 ${\beta}$는 용매의 염기도에 의존하며 혼합용매의 MeOH 함량이 증가할 수록 $(MeOH)_n$의 기여에 의해 증가하는 것을 알 수 있었다. ${\pi}^*$는 용매의 쌍극자 모멘트에 의존하며 혼합용매의 MeCN 함량이 증가할 수록 ${\pi}^{\ast}$값도 커지며 ${\alpha}$는 MeOH의 수소결합주게 효과에 의해 혼합용매의 MeOH함량이 증가할 수록 크게 증가하는 것을 나타냈다. 앞서 보고된 반응들에 용매 파라미터를 적용하여 반응상수를 구하였으며 Taft의 반응상수 a, s와 Swain의 반응상수 a, b사이에는 용매 척도의 차이 때문에 서로 연관성이 없었다. 그러나 그들의 비인 a/s와 a/b는 서로 좋은 직선관계를 보여 주었으며 이들 반응상수 비를 이용하여 반응 메카니즘이나 치환기 변화 및 이탈기 변화에 미치는 용매효과를 논의 하였다.

• 공업화학
• /
• 제31권4호
• /
• pp.443-451
• /
• 2020

본 연구에서는, 축분 고형연료의 연료적 가치를 판단하기 위해 물리화학적 특성과 열분해 동역학 분석을 수행하였다. 원소분석과 공업분석결과는 축분 고형연료는 휘발성 물질(64.94%), 탄소(44.35%) 및 수소(5.54%)의 함량이 높았다. 축분 고형연료의 저위발열량(3,880 kcal/kg) 또한 가축분뇨 고형 연료 기준(3,000 kcal/kg)보다 높았다. 열중량분석결과 축분연료는 3개의 분해온도구간을 가졌다. 첫 번째 온도구간(130~330 ℃)은 추출물의 기화, 헤미셀룰로우스 및 셀룰로우스의 분해로 구성되었다. 두 번째(330~480 ℃)와 세 번째(550~800 ℃) 온도 구간들은 리그닌의 분해와 carbonaceous materials 분해에 의한 것이었다. Friedman, FWO, KAS 같은 model free 분석방법에 의해 구해진 축분 고형연료의 열분해에 대한 활성화 에너지 값은 전환율 0.1에서 0.9 범위에서 173.98에서 525.79 kJ/mol로 나타났다. 특히, 전환율이 0.6보다 높은 구간에서 활성화에너지가 크게 증가하였다. Curve fitting 방법을 사용한 동역한 분석은 축분 고형연료가 5단계의 분해 단계로 구분될 수 있는 다단계 반응에 의해 분해됨을 제안하였다.

• Korean Chemical Engineering Research
• /
• 제44권5호
• /
• pp.444-452
• /
• 2006

298.15 K 및 1 atm에서 2성분계 {1,2-dichloropropane+2-(2-methoxyethoxy)ethanol} 및 {1,2-dichloropropane+2-(2-ethoxyethoxy)ethanol}에 대한 과잉몰부피와 과잉몰엔탈피를 측정하였다. 과잉몰부피를 측정하기 위한 밀도는 vibrating glass-tube 방식의 densimeter를 이용하였고, 과잉몰엔탈피는 flow mixing 형의 isothermal microcalorimeter를 이용하였다. 측정한 과잉몰부피 및 과잉몰엔탈피는 조성과 상관지어 모두 S자형을 나타내었다. 초기 2-(2-alkoxyethoxy)ethanol 의 강한 자체 회합현상으로 음의 편차를 나타내며, 할로겐화탄화수소 분자의 증가에 따라 2-(2-alkoxyethoxy)ethanol 분자간의 수소결합을 끊기 위한 에너지가 상대적 더 많이 필요함을 보여주고 있다. 실험으로부터 얻어진 $V^E_m$ 및 $H^E_m$ data는 Nelder-Mead의 simplex pattern search method를 이용하여 Redlich-Kister 다항식에 접합(fitting)하였고, Wilson, NRTL 및 UNIQUAC model을 이용하여 $V^E_m$ data와 조성과의 상관관계를 조사하였다.