• Nuclear Engineering and Technology
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• 제54권8호
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• pp.3117-3129
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• 2022

Deeply understanding the phase change of thin liquid sodium film inside wick pore is very important for further studying high-temperature sodium heat pipe's heat transfer. For the first time, the evaporation and condensation of thin liquid sodium film are investigated by the Lennard-Jones potential of molecular dynamics. Based on the startup and normal operation of the sodium heat pipe, three different cases are simulated. First, the equilibrium is achieved and the Mass Accommodation Coefficients of the three cases are 0.3886, 0.2119, 0.2615 respectively. Secondly, the non-equilibrium is built. The change of liquid film thickness, the number of gas atoms, the net evaporation flux (J_net), the heat transfer coefficient (h) at the liquid-gas interface are acquired. Results indicate that the magnitude of the J_net and the h increase with the basic equilibrium temperature. In 520-600 K (the startup of the heat pipe), the h has approached 5-6 W m^-2 K^-1 while liquid film thickness is in 11-13 nm. The fact shows that during the initial startup of the sodium heat pipe, the thermal resistance at the liquid-gas interface can't be negligible. This work is the complement and extension for macroscopic investigation of heat transfer inside sodium heat pipe. It can provide a reference for further numerical simulation and optimal design of the sodium heat pipe in the future.

• Journal of Photoscience
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• 제9권2호
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• pp.51-54
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• 2002

We propose a novel mechanism (Twist Sharing Mechanism) for the cis-trans photoisomerization of rhodopsin, based on the molecular dynamics (MD) simulation study. New things devised in our simulations are (1) the adoption of Mt. Fuji potentials in the excited state for twisting of the three bonds C9=C10, C11=C12 and C13=14 which are modeled using the detailed ab initio quantum chemical calculations and (2) to use the rhodopsin structure which was resolved recently by the X-ray crystallographic study. As a result, we found the followings: Due to the intramolecular steric hindrance between 20-methyl and 10-H in the retinal chromophore, the C12-C13 and C10-C11 bonds are considerably twisted counterclockwise in rhodopsin, allowing only counterclockwise rotation of the C11 =C12 in the excited state. The movement of 19-methyl in rhodopsin is blocked by the surrounding three amino acids, Thr 118, Met 207 and Tyr 268, prohibiting the rotation of C9=C10. As a result only all-trans form of the chromophore is obtainable as a photoproduct. At the 90$^{\circ}$ twisting of C11=C12 in the course of photoisomerization, twisting energies of the other bonds amount to about 20 kcal/mol. If the transition state for the thermal isomerization is assumed to be similar to this structure, the activation energy for the thermal isomerization around C11=C12'in rhodopsin is elevated by about 20 kcal/mol and the thermal isomerization rate is decelerated by 10$\^$-14/ times than that of the retinal chromophore in solution, protecting photosignal from the thermal noise.

• 한국축산식품학회지
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• 제37권5호
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• pp.682-689
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• 2017

The aim of this study was to investigate the digestibility of different Korean Hanwoo beef cuts using an in vitro digestion model, in vitro physicochemical upper gastrointestinal system (IPUGS). The four most commonly consumed cuts - tenderloin, sirloin, brisket and flank, and bottom round - were chosen for this study. Beef samples (75 g) were cooked and ingested into IPUGS, which was composed of mouth, esophagus, and stomach, thereby simulating the digestion conditions of humans. Digested samples were collected every 15 min for 4 h of simulation and their pH monitored. Samples were visualized under a scanning electron microscope (SEM) to examine changes in the smoothness of the surface after digestion. Analysis of the amino acid composition and molecular weight (MW) of peptides was performed using reverse-phase high performance liquid chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis, respectively. Following proteolysis by the gastric pepsin, beef proteins were digested into peptides. The amount of peptides with higher MW decreased over the course of digestion. SEM results revealed that the surface of the digested samples became visibly smoother. Total indispensable and dispensable amino acids were the highest for the bottom round cut prior to digestion simulation. However, the total amount of indispensable amino acids were maximum for the tenderloin cut after digestion. These results may provide guidelines for the elderly population to choose easily digestible meat cuts and products to improve their nutritional and health status.

• 한국세라믹학회지
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• 제53권4호
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• pp.417-428
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• 2016

In this review, an attempt is made to calculate one-dimensional (1-D) electron density profiles from experimentally determined (00l) XRD intensities and possible structural models as well in an effort to understand the collective intracrystalline structures of intercalant molecules of two-dimensional (2-D) nanohybrids with heterostructures. 2-D ceramics, including layered metal oxides and clays, have received much attention due to their potential applicability as catalysts, electrodes, stabilizing agents, and drug delivery systems. 2-D nanohybrids based on such layered ceramics with various heterostructures have been realized through intercalation reactions. In general, the physico-chemical properties of such 2-D nanohybrids are strongly correlated with their heterostructures, but it is not easy to solve the crystal structures due to their low crystallinity and high anisotropic nature. However, the powder X-ray diffraction (XRD) analysis method is thought to be the most powerful means of understanding the interlayer structures of intercalant molecules. If a proper number of well-developed (00l) XRD peaks are available for such 2-D nanohybrids, the 1-D electron density along the crystallographic c-axis can be calculated via a Fourier transform analysis to obtain structural information about the orientations and arrangements of guest species in the interlayer space.

• 공업화학
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• 제9권3호
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• pp.317-321
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• 1998

수열 방법으로 합성한 기체 분리용 제올라이트 흡착제의 분자체 및 이온교환 특성을 파악하기 위하여 KCl, $CaCl_2$, $YCl_3$ 그리고 $InCl_3$으로 제올라이트에 함유된 Na 이온을 치환시켰다. 치환시킨 X형 제올라이트를 $25^{\circ}C$에서 $CO_2$가스로 그리고 합성 제올라이트에 대하여 $O_2$, $N_2$가스로 부피법 장치를 통해 평형 흡착 특성을 각각 비교하였다. 측정결과를 Freundlich, Langmuir 그리고 Toth형 model 식을 이용하여 변수를 파악하였으며, 제올라이트의 $CO_2-PSA$ 흡착공정에 적용가능성을 측정하기 위하여 흡착파괴실험을 실시하고, 이를 PSA 공정 simulation에 적용하였다. 여기서 X형 제올라이트는 공정 배가스에서 $CO_2$회수에 적합한 흡착제로 사용할 수 있음을 확인하였다.

• 대한기계학회논문집B
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• 제38권7호
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• pp.595-600
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• 2014

충돌시 부서져 사라지는 승화성 나노 탄환입자로 표면 위에 붙어있는 고체 나노입자를 가격하는 과정에서 탄환입자로부터 목표입자로의 운동에너지 전달특성을 분자동역학 전산모사 방법을 이용하여 해석하였다. 탄환입자는 이산화탄소로 이루어져있으며 탄환의 크기, 온도 및 발사속도를 바꿔가며 전산모사를 수행하였다. 탄환입자로부터 목표입자에 전달되는 운동에너지 전달비율은 탄환 속도와 크기에 관계없이 일정하였지만 탄환의 온도에 따라 민감하게 변하였는데, 이는 온도에 따른 탄환입자의 결합력의 변화에서 기인하는 것이었다. 동일조건의 아르곤 탄환에 비하여 이산화탄소 탄환의 에너지 전달효율은 약 2 배 정도이며, 여기에서 이산화탄소 탄환의 높은 세정성능이 비롯됨을 최초로 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2057-2064
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• 2014

Thermochemical sulfate reduction (TSR) was conducted in autoclave on the system of crude oil and $MgSO_4$ at different temperatures. Gas chromatography pulsed flame photometric detector (GC-PFPD) was used to detected the composition of organic sulfur compounds in oil phase products. The results of the analysis indicate that with increased temperature, the contents of organic sulfur compounds with high molecular weight and thermal stability, such as benzothiophenes and dibenzothiophenes, gradually became dominated. In order to gain greater insight into the formation and distribution of organic sulphur compounds from TSR, positive ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used in detecting the detailed elemental composition and distribution of them. The mass spectra showed that the mass range of sulfur compounds was 200-550 Da. Four sulfur class species, $S_1$, $N_1S_1$, $O_1S_1$ and $O_2S_1$, were assigned in the positive-ion spectrum. Among the identified sulfur compounds, the $S_1$ class species was dominant. The most abundant $S_1$ class species increase associated with the DBE value and carbon number increasing which also indicates the evolution of organic sulfur compounds in TSR is from the labile series to the stable one. In pure blank pyrolysis experiments with crude oil cracking without TSR, different composition and distribution of organic sulfur compounds in oil phase products were seen from mass spectra in order to evaluate their pyrolysis behaviors without $MgSO_4$. FT-IR and XRD were used in analyzing the products of solid phases. Two distinct crystallographic phases MgO and $MgSO_4$ are found to coexist in the products which demonstrated the transformation of inorganic sulfur compounds into organosulfur compounds exist in TSR.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제14회 학술발표회 논문개요집
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• pp.20-20
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• 1998

I Ion beam technology has recently attracted much interest because it has exciting t technological p아:ential for surface analysis, ion beam mixing, surface cleaning and etching i in thin film growth and semiconductor fabrication processes, etc. Es야~cially, ion beam s sputtering has been widely used for sputter depth profiling with x-photoelectron S spectroscopy (XPS) , Auger electron s$\pi$~troscopy(AES), and secondary-ion mass S야i따oscopy(SIMS). However, The problem of surface compositional ch없1ge due to ion b bombardment remains to be understo여 없ld solved. So far sputtering processes have been s studied by s따face an외ysis tools such as XPS, AES, and SIMS which use the sputtering p process again. It would be improbable to measure the modified surface composition profiles a accurately due to ion beam bombardment with surface analysis techniques based on sputter d depth profiling. However, recently Medium energy ion scattering spectroscopy(MEIS) has b been applied to study the sputtering of solid surface at ion bombardment and has been p proved that it has been extremely valuable in probing the surface composition 뻐d s structure nondestructively and quantita디vely with less than 1.0 nm depth resolution. To u understand the sputtering processes of solid surface at ion bombardment, The Molecular D Dynamics(MD) and Monte Carlo(MC) simulation has been used and give an intimate i insight into the sputtering processes of solid surfaces. In this presentation, the sputtering processes of alloys and compound samples at ion b bombardment will be reviewed and the MEIS results for the Ar+ sputter induced altered l layer of the TazOs thin film 뻐dd없nage profiling of Ar+ ion sputt얹"ed Si(100) surface will b be discussed with the results of MD and MC simulation.tion.

• Journal of Photoscience
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• 제4권2호
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• pp.61-67
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• 1997

The model based on the idea that the p$_y$-orbital of the carbonyl oxygen is responsible to receiving hydrogen was devised for simulation of intramolecular hydrogen transfer. A Monte Carlo method was applied to free rotation of a molecular chain performed by changing the dihedral angles, and a "hit" was defined as the case when the migrating hydrogen comes within the region defined as the p$_y$-orbital and satisfies all the geometrical requirements for abstraction. A set of parameters was employed for defining the region and the requirements; $\tau$ was defined as the angle formed between O...H vector and its projection on the mean plane of the carbonyl group (- 43$\circ$ < $\tau$ < + 43$\circ$), $\Delta$ as the C=O...H angle (90 -15$\circ$ < $\Delta$ < 90 + 15$\circ$), $\theta$ as the O...H - C angle ( 180 - 80$\circ$< 0 < 180 + 80$\circ$), d as the distance from the center of the lobe of the p$_y$-orbital to hydrogen (0 < d < 1.04 ${\AA}$). The minimum value for the distance between carbonyl oxygen (O$_1$) and the migrating hydrogen (H$_i$) and for that between non-bonded atoms except the pair of O$_1$ and H$_i$ were assumed to be 0.52 ${\AA}$ and 1.54 ${\AA}$, respectively. The apphcation of this model to intramolecular $\beta$-, $\gamma$-, $\delta$-, $\epsilon$-, and $\zeta$-hydrogen abstraction in ketones and $\eta$- and $\theta$- proton transfer in oxoesters gave good results reflecting their photochemical behavior. The model was also used for prediction of photoreactivities of 2-(N,N-dibenzylamino)ethyl 2-, 3- and 4-benzoylbenzoate (1a - c). (1a - c).

• 분석과학
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• 제18권4호
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• pp.309-319
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• 2005

본 연구는 흡착제와 기체상 분자의 흡착특성을 연구하기 위하여 탄소질 흡착제의 세공크기 및 흡착 온도와 압력에 따른 기체상 분자들의 흡착용량을 Crand Canonical Monte Carlo(GCMC) 분자모사 방법으로 예측하였다. 사용된 흡착질에 대한 분자구조 및 분자 분광학적 성질에 대해서는 범밀도함수이론(DFT)을 이용하여 계산하였다. 온도에 따른 흡착효과는 온도가 증가할수록 흡착량은 감소하는 경향을 보였으며, 흡착질의 크기, 극성, 그리고 흡착질간의 상호작용 등에 따라서도 흡착효과는 일정한 상관관계를 나타내는 것으로 예측되었다. 본 연구에 사용된 모든 경우에 대하여 탄소질 흡착제에 흡착되는 순서는 $NH_3$ < $H_2S$ < $CH_3SH$ 순으로 예측되었으며, 이러한 이론적 예측은 실험에 의한 관찰 결과와 정성적으로 잘 일치하는 것으로 나타났다.