1H Nuclear Magnetic Resonance study of Ferroelectric (NH4)3H(SO4)2

S. H. Choi,K. S. Han,S. K. Kwon,S. K. Nam,H. H. Choi,Moohee Lee,Ae Ran Lim 한국자기공명학회 2007 Journal of the Korean Magnetic Resonance Society Vol.11 No.2

1H nuclear magnetic resonance (NMR) experiments have been performed at 30 - 300 K and 7 T to investigate dynamics of hydrogen bond network in the single crystal (NH4)3H(SO4)2. The two proton sites, ammonium proton and hydrogen-bond proton, are identified from the 1H NMR MAS spectrum at 340 K. As temperature decreases, the 1H NMR spectrum shifts to the higher frequency side with a larger linewidth. The spectrum at 65 K shows a distinctive change in line shape toward the ferroelectric transition at 63 K. The measured values of T1 for ammonium and hydrogen-bond protons are similar in the whole range of temperature. T1 of 1H NMR shows a gradual decrease down to 120 K and starts to steeply increase below 100 K. Then T1 shows abrupt decrease below 70 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. This temperature dependence of spectrum and T1 clearly prove that the large change in the dynamics of hydrogen bond network is associated with the ferroelectric phase transition at 63 K.

1H NMR Measurements of the Phase Transition of (NH₄)₃H(SO₄)₂ Single Crystals

S. H. Choi,Moohee Lee,Ae Ran Lim,K. S. Han,S. K. Kwon,S. K. Nam 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2

$^1$H nuclear magnetic resonance (NMR) experiments have been performed in the temperature range of 30 -- 300 K at 7 T to investigate the phase-dependent nature of the dynamic network of hydrogen bonds in a ((NH₄)₃H(SO₄)₂ single crystal. The crystal has six phases, which are ferroelectric, antiferroelectric, incommensurate, antiferroelectric, ferroelastic, and superionic with the respective transition temperatures of 63, 133, 139, 256 and 413 K. The spin-lattice relaxation time, T₁, of ¹H NMR is similar for the ammonium protons and the hydrogen-bond protons over the entire range of experimental temperatures. The T₁, of ¹H NMR gradually decreases down to 120 K and starts to steeply increase below 100 K. Then, the T₁ shows an abrupt decrease below 68 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. The ¹H NMR spectrum shifts to the high-frequency side at temperatures below 63 K due to the ferroelectric phase transition. This behavior of the T₁ and the spectrum confirms a dramatic change in the dynamics of hydrogen bonds associated with the ferroelectric phase transition at 63 K. $^1$H nuclear magnetic resonance (NMR) experiments have been performed in the temperature range of 30 -- 300 K at 7 T to investigate the phase-dependent nature of the dynamic network of hydrogen bonds in a ((NH₄)₃H(SO₄)₂ single crystal. The crystal has six phases, which are ferroelectric, antiferroelectric, incommensurate, antiferroelectric, ferroelastic, and superionic with the respective transition temperatures of 63, 133, 139, 256 and 413 K. The spin-lattice relaxation time, T₁, of ¹H NMR is similar for the ammonium protons and the hydrogen-bond protons over the entire range of experimental temperatures. The T₁, of ¹H NMR gradually decreases down to 120 K and starts to steeply increase below 100 K. Then, the T₁ shows an abrupt decrease below 68 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. The ¹H NMR spectrum shifts to the high-frequency side at temperatures below 63 K due to the ferroelectric phase transition. This behavior of the T₁ and the spectrum confirms a dramatic change in the dynamics of hydrogen bonds associated with the ferroelectric phase transition at 63 K.

Solubility of oxcarbazepine in eight solvents within the temperature range T=(288.15-308.15)K

Nam, K.,Ha, E.S.,Kim, J.S.,Kuk, D.H.,Ha, D.H.,Kim, M.S.,Cho, C.W.,Hwang, S.J. Academic Press 2017 The Journal of chemical thermodynamics Vol.104 No.-

In this study, the solubility of oxcarbazepine in pure methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, acetonitrile, and tetrahydrofuran was analysed across the temperature range of 288.15-308.15K under atmospheric pressure by using a solid-liquid equilibrium method. The experimental values obtained data were correlated using the modified Apelblat model at each temperature. The mole fraction solubility of oxcarbazepine in all eight pure solvents increased gradually in a temperature-dependent manner. The highest mole fraction solubility of 3.08x10<SUP>-3</SUP> at 308.15K was observed for tetrahydrofuran, followed by acetone (1.82x10<SUP>-3</SUP> at 308.15K), acetonitrile (1.22x10<SUP>-3</SUP> at 308.15K), methanol (1.11x10<SUP>-3</SUP> at 308.15K), ethanol (6.17x10<SUP>-4</SUP> at 308.15K), 1-butanol (6.17x10<SUP>-4</SUP> at 308.15K), 1-propanol (6.16x10<SUP>-4</SUP> at 308.15K), and 2-propanol (4.13x10<SUP>-4</SUP> at 308.15K). The experimental solubility in all solvents correlated well with that calculated using the modified Apelblat equation across the temperature range of (288.15-308.15)K. Therefore, the experimental solubility and correlation equations established in this study could be useful during the crystallization/purification, pre-formulation, and formulation stages of oxcarbazepine production in laboratories and related industries.

S6K1 Phosphorylation of H2B Mediates EZH2 Trimethylation of H3: A Determinant of Early Adipogenesis

Yi, S.,Um, S.,Lee, J.,Yoo, J.,Bang, S.,Park, E.,Lee, M.,Nam, K.,Jeon, Y.,Park, J.,You, J.,Lee, S.J.,Bae, G.U.,Rhie, J.,Kozma, Sara C.,Thomas, G.,Han, J.W. Cell Press 2016 Molecular Cell Vol.62 No.3

S6K1 has been implicated in a number of key metabolic responses, which contribute to obesity. Critical among these is the control of a transcriptional program required for the commitment of mesenchymal stem cells to the adipocytic lineage. However, in contrast to its role in the cytosol, the functions and targets of nuclear S6K1 are unknown. Here, we show that adipogenic stimuli trigger nuclear translocation of S6K1, leading to H2BS36 phosphorylation and recruitment of EZH2 to H3, which mediates H3K27 trimethylation. This blocks Wnt gene expression, inducing the upregulation of PPARγ and Cebpa and driving increased adipogenesis. Consistent with this finding, white adipose tissue from S6K1-deficient mice exhibits no detectable H2BS36 phosphorylation or H3K27 trimethylation, whereas both responses are highly elevated in obese humans or in mice fed a high-fat diet. These findings define an S6K1-dependent mechanism in early adipogenesis, contributing to the promotion of obesity.

[ $^1H$ ] Nuclear Magnetic Resonance Study of Ferroelectric $(NH_4)_3H(SO_4)_2$

Choi, S.H.,Han, K.S.,Kwon, S.K.,Nam, S.K.,Choi, H.H.,Lee, Moo-Hee,Lim, Ae-Ran Korean Magnetic Resonance Society 2007 Journal of the Korean Magnetic Resonance Society Vol.11 No.2

[ $^1H$ ] nuclear magnetic resonance (NMR) experiments have been performed at 30 - 300 K and 7 T to investigate dynamics of hydrogen bond network in the single crystal $(NH_4)_3H(SO_4)_2$. The two proton sites, ammonium proton and hydrogen-bond proton, are identified from the $^1H$ NMR MAS spectrum at 340 K. As temperature decreases, the $^1H$ NMR spectrum shifts to the higher frequency side with a larger linewidth. The spectrum at 65 K shows a distinctive change in line shape toward the ferroelectric transition at 63 K. The measured values of $T_1$ for ammonium and hydrogen-bond protons are similar in the whole range of temperature. $T_1$ of $^1H$ NMR shows a gradual decrease down to 120 K and starts to steeply increase below 100 K. Then $T_1$ shows abrupt decrease below 70 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. This temperature dependence of spectrum and $T_1$ clearly prove that the large change in the dynamics of hydrogen bond network is associated with the ferroelectric phase transition at 63 K.

A DEFECT DISTRIBUTION STUDY OF Cz-GROWN 8" Si WAFER BY POSITRON ANNIHILATION

Nam, K.Y.,Joo, K.S.,Cho, Y.K.,Kim, Y.I.,Kim, C.S.,Yoo, K.G. 한국재료학회 1995 Fabrication and Characterization of Advanced Mater Vol.2 No.4

Due to the impurity gettering effect, the control of oxygen-related defects is still key technology for large size singel crystal growing. And to know the exact behavior of lattice defects is very important to solve many process problems which occurred during device fabrication. We have investigated the defect density distribution of oxygen-containing single crystal Si wafer(Xz-Si) by means of positron lifetimes and dopplar broadening method. From the experimentally obtained spectra, we obtained the mean-lifetimes of positrons and then compared with the S-parameters from doppler broadening measurement. We could confirm that the tendency of variation for the mean-lifetime with respect to positions on wafer is well agreement with that of S-parameters. Hence, we have found that the concentrations of oxygen-related defects at the range of edge are larger than those at the center ranges.

Thermoelectric Properties of Nanocrystalline Ca_3−<i>x</i>Cu_<i>x</i>Co₄O₉ (0 ≤ <i>x</i> ≤ 0.32) for Power Generation

Nam, S. W.,Lim, Y. S.,Choi, S.-M.,Seo, W.-S.,Park, K. American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.2

<P>We successfully synthesized nano-sized Ca(3-x)Cu(x)Co4O9 (0 < or = x < or = 0.32) powders by solution combustion process. Plate-like grains and porous structure were observed in the sintered Ca(3-x)Cu(x)Co4O9 ceramics. The sintered Ca(3-x)Cu(x)Co4O9 showed a monoclinic symmetry. The electrical conductivity of the Ca(3-x)Cu(x)Co4O9 increased with increasing temperature, indicative of a semiconducting behavior. The added Cu led to a significant increase in the electrical conductivity. The Seebeck coefficient of the Cu-added Ca(3-x)Cu(x)Co4O9 was much higher than that of the Cu-free Ca3Co4O9. The highest power factor (9.99 x 10(-4) Wm(-1)K-2) was obtained for Ca2.76Cu0.24Co4O9 at 800 degrees C.</P>

K-EMS 계통해석 어플리케이션을 위한 공통 데이터 모델 구축

윤상윤(S.-Y. Yun),조윤성(Y-S. Cho),이욱화(U.-H. Lee),손진만(J.-M. Sohn),남영우(Y.-W. Nam),이진(J. Lee),김홍래(H.-R. Kim),김병호(B.-H. Kim),김선구(S.-G. Kim),허성일(S.-I. Hur),이효상(H.-S. Lee),신만철(M.-C. Shin),민경일(K.-I. Min),최영진(Y.-J 대한전기학회 2008 대한전기학회 학술대회 논문집 Vol.2008 No.7(초록집)

TWB 보론강의 기계적 특성 및 성형성

남기우(K. W. Nam),황석환(S. H. Hwang),김대용(D. Y. Kim),이문용(M. Y. Lee),이상문(S. M. Lee) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.10

핫 스탬핑은 오스테나이트 변태 온도 이상에서 프레스 성형 후 급속히 냉각되는 고강도 부품을 제조하는 성형 방법이다. 매우 적은 양의 보론 성분을 가지고 있는 보론강은 핫 스탬핑에 사용되는 재료 중의 하나이다. 본 연구의 목적은 열처리 조건에 따르는 기계적 성질과 에릭슨 커핑 시험에 의하여 성형성을 조사하는 것이다. 다양한 온도에서 다이퀜칭은 대기 시간을 달리하여 실시하였다. 1173 K-0s에서 퀜칭 후 TWB는 1203 MPa의 인장 강도를 얻었다. 이것은 모재 인장강도(1,522 MPA)의 79 %이다. 금형 온도(298, 523, 673 K)에 따른 보론강 TWB의 성형성은 차이가 크지 않았다. 그러나 성형 속도가 증가함에 따라 성형성이 감소하는 것을 확인할 수 있었다. The hot-stamping technique is a forming method used for manufacturing high-strength parts, in which a part is cooled rapidly after press forming above the austenite transformation temperature. Boron steel, which contains a very small amount of boron, is one of the materials used for hot stamping. The purpose of this study is to investigate the mechanical properties of boron steel according to the heat-treatment conditions and the formability by using an Erichsen cupping test. Die quenching from various temperatures was conducted for different elapsed heat-treatment times. Laser-welded boron steel after quenching at 1173 K-0 s has a tensile strength of 1203 MPa. This is 79% of the tensile strength of the base metal (1522 MPa). The formability of boron steel was not significantly different from that at the mold temperature. However, it decreased with increasing forming speed. These properties provide practical information for the use of boron steels for hot stamping.

Cr-free 코팅액 개발을 위한 기초연구

남기우(K.W. Nam),문희준(H.J. Moon),박상현(S.H. Park),김은선(E.S. Kim),서현수(H.S. Seo),김종순(J.S. Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

Zinc coatings are widely used in practice for preventing the corrosion of steel. But the zinc coating can be involved by corrosion phenomena with the consequence that some steel surface is unprotected. The reduction of the corrosion rate of zinc is an important topic. In the past a very popular way to reduce the corrosion rate of zinc was the use of chemical conversion layers based on Cr??. However, there is the important problem that the use of chromium salts is now restricted because of environmental protection legislation. Therefore very important to develop new zinc surface treatments environmentally friendly to improve the corrosion resistance of zinc and the adhesion with the final organic protective layer. In this study, Urethane solution (only Urethane 20 % ; S-700) and organic/inorganic solution with Si (Si polysilicate 10 % + Urethane 6 % + hardner 4 % ; LRO317-1)are used. Based on the salt spray test of 72h, S-700 and LRO317-1 had a superior effect on EGI and HGI, respectively.