• Bulletin of the Korean Chemical Society
• /
• 제13권1호
• /
• pp.17-20
• /
• 1992

Photoionization processes of TMPD in $H_2O$ and $D_2O$ were studied, by measuring steady-state absorption, emission, fluorescence excitation spectra, and fluorescence lifetimes on picosecond time scale. The steady-state absorption spectra showed that there exists a cation-ion pair (Wurster's Blue) in $H_2O$ and in $D_2O$ in the electronic ground state. Temperature and excitation wavelength dependence were also studied and the results show that the photoionization reaction in water is an activated process and the fluorescence lifetime is independent of the vibrational excess energy in the uv excitation range of 283-310 nm.

• 대한전자공학회논문지
• /
• 제23권6호
• /
• pp.801-806
• /
• 1986

The effect of SiH2Cl2 -HCl gas on the growth rate of epitaxial layer is studied. The temperature, pressure and gas mixing ratio of SiH2Cl2 and HCl are varied to study the growth rate dependence and selective Si epitaxy. The P-n junction diode is fabricated on the epitaxial layer and electrical characteristics are examined. Also, using selective Si epitaxy, a possibility of thin dielectric isolation process, that gives an independent isolation width on the mask dimension, is examined.

• 동력기계공학회지
• /
• 제20권3호
• /
• pp.17-21
• /
• 2016

The corrosion behavior of aluminum alloys in the $H_2SO_4$ solution was investigated based on potentiodynamic techniques. Electrochemical properties, such as corrosion potential($E_c$), passive potential($E_p$), corrosion current density($I_c$), corrosion rate(mpy), of Al-Mg-Si, Al-Cu-Si and Al-Si alloys were characterized at room temperature. Passive aluminum oxide film, which including $Al_2(SO_4)_3$ and $3Al_2O_34SO_38H_2O$, were uniformly formed on the surface via the reaction of Al with $SO{_3}^{2-}$ or $SO{_4}^{2-}$ ions in the $H_2SO_4$ solution and the dependence of the corrosion behavior on the alloying element was discussed. The selective leaching of alloy element increased with increasing Cu content in the aluminum alloys.

• Bulletin of the Korean Chemical Society
• /
• 제23권3호
• /
• pp.395-399
• /
• 2002

The voltammetric behavior of spontaneously adsorbing Mo layers on Pt(111) and Pt(100) electrodes has been studied to estimate the number of electrons involved in the electrochemical processes of spontaneously adsorbed Mo and the number of the bloc ked Pt sites for hydrogen adsorption. On Pt(111) and Pt(100) surfaces, the spontaneously adsorbed Mo layers showed redox peaks at 0.10 V and 0.15 V, respectively, and continuous current-potential waves in the conventional hydrogen region. Since the potential range of the Mo redox processes on both surfaces overlapped partially with the potential range of hydrogen adsorption, the variation in the ratio of the total charge of Mo and H ($Q_H$ +$Q_{MO}$) to the hydrogen charge of clean Pt electrode ($Q_H^0$) was analyzed. From the analysis, six electrons were estimated to be involved in the electrochemical processes of the spontaneously adsorbed Mo, and four Pt sites for hydrogen adsorption were calculated to be blocked by one adsorbed Mo atom. Based on these figures and the pH dependence of the Mo redox processes, we have proposed an electrochemical equation for the spontaneously adsorbed Mo. This electrochemical equation led us to conclude that the saturation coverage of the spontaneously adsorbed Mo is 0.25. The coverage of Mo less than 0.25, however, could not be determined voltammetrically due to the convolution of the charges of Mo and H.

• 기술경영경제학회:학술대회논문집
• /
• 기술경영경제학회 2003년도 제22회 동계학술발표회 논문집
• /
• pp.63-77
• /
• 2003

In this paper, we investigate the co-movements of the real GDP cycle and the telecommunications service expenditure cycle over 1980 through 2000 in Korea. We used several appropriate statistical tools to characterize and to compare the co-movements between the two aforementioned variables. The statistics presented in this paper are common, easy to Interpret and capture important visual, descriptive information and the dynamics of data that would be lost if one focused only on the unconditional correlation coefficients of de-trended data. This paper examines four possible characteristics for the co-movements of real GDP and telecommunications service expenditure in Korea. The first is that in low frequency, the cyclical movements in telecommunications service expenditure are very similar to the cyclical movements in real GDP, The second is that in the high frequency, the estimated stationary cyclical telecommunications service expenditure is not closely related to the estimated stationary cyclical real GDP. Third, according to co-spectra analysis, the strong relationships between the variables are found in the mid-term frequency and as such this empirical finding has important implications for telecommunications policy and telecommunications service implementation strategies. Finally, in the short-term period, our empirical results support telecommunications network theories such as path dependence properties, lock-in, positive feedback externality, and network externality.

• BMB Reports
• /
• 제32권4호
• /
• pp.326-330
• /
• 1999

An aspartase purified from Hafnia alvei was inactivated by diethylpyrocarbonate (DEP) in a pseudo-first-order inactivation. The first-order plot was biphasic. The inactivation process was not saturable and the second order rate constant was $1.3\;M^{-1}s^{-1}$. The inactivated aspartase was reactivated with NH₂OH. The difference absorption spectrum of DEP-inactivated vs native enzyme preparations revealed a marked peak around 242 nm. The pH dependence of the inactivation rate suggests that an amino acid residue having a pK value of 7.2 was involved in the inactivation. L-aspartate, fumarate (substrates), and chloride ion (inhibitor) protected the enzyme against inactivation, indicating that histidine residues for the enzyme activity are located at the active site of this aspartase. Inspection of the presence and absence of $Cl^-$ ion demonstrated that the number of essential histidine residues is less than two. Thus, one or two histidines are in or near the aspartate binding site and participate in an essential step of the catalytic reaction.

• BMB Reports
• /
• 제30권2호
• /
• pp.113-118
• /
• 1997

Aspartase from Hafnia alvei was inactivated by N-ethylmaleimide (NEM) and 5,5' -Dithiobis-(2-znitrobenzoic acid) (DTNB) following pseudo-first order kinetics. Their apparent reaction orders were 0.83 and 0.50 for NEM and DTNB modifications, respectively, indicating that inactivation was due to a sulfhydryl group in the active site of aspartase and participation of the sulfhydryl group in an essential step in the catalytic reaction. When aspartase was modified by DTNB, the enzyme activity was restored by dithiothreitol treatment, indicating that cysteine residuetsl islarel possibly at or near the active site. The pH-dependence of the inactivation rate by NEM suggested that an amino acid residue having pK value of 8.3 was involved in the inactivation. When aspartase was incubated with NEM and L-aspartate together, L-aspartate markedly protected the enzyme from inactivation by NEM, but the other reagents used did not.

• 생명과학회지
• /
• 제12권1호
• /
• pp.32-42
• /
• 2002

합성된 hexanoylthiocholine을 기질로 하여 butyrylcholinesterase와의 반응을 연구하였다. 기질의 농도 변화에 따른 초기반응속도 관찰을 통해 아실기의 탄소수가 증가함에 따라 반응성은 감소하나 $K_{m}$ 값은 0.140(mM)으로 더 강한 ES 복합체를 형성함을 알 수 있었다. Hexanoylthio-choline의 촉매화된 acetylcholinesterase 가수분해에 대한 pH-V/K profile에서 p $K_{a}$ 값 4.974$\pm$0.02을 얻었다. 이는 최근 문헌의 보고와 상통하는 것으로 p $K_{a}$ =6.2~6.4를 갖는 잔류물의 기본형에 활성이 의존하는 것으로부터 하나의 잔류물 또는 p $K_{a}$ =4.7~5.0을 갖는 잔류물들의 촉매작용으로 계통적인 자리밀림을 보여준다. 이는 촉매화된 BChE의 활성영역 esteratic site 주변에 긴 사슬 아실기의 가수분해에 관여하는 새로운 활성영역이 존재함을 밝히는 증거이다. 분자 조형은 기질의 아실기의 탄소수에 따라 acetylcholinesterase에 의해 표현되어지는 반응과정의 변화의 합리성을 제공한다. 본 연구에서는 한국과학기술원 도핑컨트롤센터와 연계하여 acetylcholinesterase와 기질인 acylthiocholine과의 입체적으로 둘러싸인 acyl-binding site를 분자 조형하고자 노력 중에 있다.

• 대한화학회지
• /
• 제46권3호
• /
• pp.187-193
• /
• 2002

온도 (10, 15, 20, $25^{\circ}C$)와 압력(1, 200, 500, 1000 bar)변화에 따라 p-치환염화벤조일류 ($p-CH_3$, p-H, $p-NO_2$ )와 6-클로로퀴놀린(6-chloroquinoline)의 반응을 아세토니트릴 용매내에서 전기전도도법에 의하여 속도상수 ($k_2$)를 구하였다. 이로부터 여러활성화파라미터-활성화에너지(Ea, ${\Delta}V^{\neq}$, ${\Delta}H^{\neq}$,${\Delta}S^{\neq}$, ${\Delta}G^{\neq}$) 를 구하였으며 또한 기질의 치환기 효과에 따른 Hammentt 반응상수 p를 구하였다. 속도상수는 온도와 압력 증가에 따라 증가하였으며 친핵체인 6-chloroquinoline과 기질에 전자 받게 치환기 ($p-NO_2$)가 치환된 경우 더욱 증가하였다. 이 때 활성화부피(${\Delta}V^{\neq}$), 활성화엔트로피(${\Delta}S^{\neq}$)는 모두 음의 값으로 나타났으며 모든 압력 조건에 따라서 p는 양의 값을 나타내었다. 이러한 속도론적인 연구 결과 전반적인 반응은 $S_N2$반응메카니즘을 따르며, 압력이 증가함에 따라 결합형성이 진전되어지는 반응 메카니즘으로 진행 됨을 알 수 있었다.

• 한국식품영양과학회지
• /
• 제31권5호
• /
• pp.775-781
• /
• 2002

hTATl에 의해 수송되는 방향족 아미노산들의 수송특성을 밝히기 위해 hTATl의 cRNA를 미세주입한 Xenopus laevis oocyte에서 hTATl에 의 해 유도되는 방향족 아미노산의 up-take를 여러 조건 하에서 관찰하였긴. hTATl은 L-[$^{14}$ C]tryp-tophan의 uptake를 유도하였으며, 그 uptake는 $Na^{+}$-과 Cl$^{-}$-비 의존적이었다. hTATl은 L-($^{14}$ C)tryptophan의 uptake를 시간의 존적으로 유도함을 알 수 있었다. hTATl에 의한 L-($^{14}$ C) tryptophan의 uptake는 방향족 아미노산인 phenylalanine, tyrosine 및 tryptophan에 의해서 억제되었으며 , hTATl에 의한 아미노산들의 uptake 실험에서 L-($^{14}$ C)phenylalanine, L-($^{14}$ C)tyrosine 및 L-($^{14}$ C)tryptophan의 수송을 확인하였다 hTATl에 의 한 L-($^{14}$ C)tryptophan의 uptake는 포화되었으며, Km치는 452.2$\pm$27.8 UM, V$_{max}$ 값은 2.1 $\pm$0.3 pmol/oocyte/min 이었다. L-($^{14}$ C)tyrosine 및 L-[$^{14}$ C]phenylalanine의 Km치는 각각 636.3$\pm$59.4 UM과 740.5$\pm$96.7 HM이었다. 실험용액의 pH 5.5에서 8.5까지의 변화는 hTATl에 의한 L-[$^{14}$ C]tfpto- phan의 uptake에 별다른 영향을 미치지 못하였다. hTATl의 CRNA를 미 세주입한 oocyte에서 배양시간 의존적 인 L-($^{14}$ C) tryptophan의 efflux를 볼 수 있었으며, 이 efflux는 oocyte 외 용액의 tryptophan존재 유무에는 영향을 받지 않았다. 따라서 본 연구의 결과로 hTATl이 상피세포로부터 혈류로의 방향족 아미노산의 수송에 중요한 역할을 할 것으로 사료된다.