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Anisotropic Magnetization and Charge Density Wave in a Na0.78CoO2 Single Crystal
이종수,J. B. Peng,S. M. Lee,C. T. Lin 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2
Single crystals of γ-Na0.78CoO2 were grown using the floating zone method. The static magnetic susceptibility M/H(T) of Na0.78CoO2 showed significant anisotropic behavior for different crystal orientations of H ∥ (ab) and H ∥ (c). While (M/H)ab(T) for a magnetic field H= 1 T in an ab-plane followed the Curie-Weiss law at high temperatures (T ≥ 100 K), (M/H)c(T) for H ∥ c-axis deviated from Curie-Weiss behavior, which may be understood by using phonon localization from strong electron-phonon coupling. The impurity spin-1/2 effect, dressed by spin fluctuation, was significant at low temperatures (T ≤ 30 K) for both field orientations of H ∥ (ab) and H ∥ (c). The electrical resistivity ρ(T) of Na0.78CoO2 showed a clear metallic character down to 16 K, with a weak increase in the resistivity ρ(T) at low temperatures T ≤ 16 K). The gap-like behavior of ρ(T) was insensitive to applied magnetic fields up to 7 T, which indicates a non-degenerate charge gap. The electrical conductivity σ(T) followed the density wave behavior with a small energy gap (0.64 meV) at low temperatures. We discussed the electrical resistivity ρ(T)$ and the anisotropic M/H(T) behavior of Na0.78CoO2 in terms of the charge density wave and a strong electron-phonon interaction. Single crystals of γ-Na0.78CoO2 were grown using the floating zone method. The static magnetic susceptibility M/H(T) of Na0.78CoO2 showed significant anisotropic behavior for different crystal orientations of H ∥ (ab) and H ∥ (c). While (M/H)ab(T) for a magnetic field H= 1 T in an ab-plane followed the Curie-Weiss law at high temperatures (T ≥ 100 K), (M/H)c(T) for H ∥ c-axis deviated from Curie-Weiss behavior, which may be understood by using phonon localization from strong electron-phonon coupling. The impurity spin-1/2 effect, dressed by spin fluctuation, was significant at low temperatures (T ≤ 30 K) for both field orientations of H ∥ (ab) and H ∥ (c). The electrical resistivity ρ(T) of Na0.78CoO2 showed a clear metallic character down to 16 K, with a weak increase in the resistivity ρ(T) at low temperatures T ≤ 16 K). The gap-like behavior of ρ(T) was insensitive to applied magnetic fields up to 7 T, which indicates a non-degenerate charge gap. The electrical conductivity σ(T) followed the density wave behavior with a small energy gap (0.64 meV) at low temperatures. We discussed the electrical resistivity ρ(T)$ and the anisotropic M/H(T) behavior of Na0.78CoO2 in terms of the charge density wave and a strong electron-phonon interaction.
Ti-13Nb-13Zr 합금의 저 변형량에서 초미세 결정립 형성 및 기계적 적합성 향상
박찬희(C. H. Park),염종택(J. T. Yeom),전영수(Y. S. Chun),이종수(C. S. Lee) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
Microstructural evolution of alpha and beta phases during dynamic globularization of near-beta Ti-13Nb-13Zr alloy was investigated to determine the optimum processing conditions. The submicrocrystalline alloy sheet with ~80% of high-angle grain boundaries was produced utilizing dynamic globularization at temperature of 600℃, equivalent strain rate of 10<SUP>-1</SUP> s<SUP>-1</SUP> and strain of 1.4. The refined structure with the grain size of ~0.4 ㎛ showed 25-60% enhanced mechanical compatibility as compared to those of the conventional mill-annealed or solution treated and aged microstructures.
{10-12} 쌍정 특성이 AZ31 마그네슘 합금 압연재의 변형거동에 미치는 영향
박성혁(S. H. Park),홍성구(S. G. Hong),이종수(C. S. Lee) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
The active twin variants during {10-12} twinning of magnesium alloys were dependent on the activation mode (i.e., compression perpendicular to the c-axis or tension parallel to the c-axis) and their section mechanism was governed by the Schmid law. The activation of specific twin variants depending on the activation mode induced a significant difference in twinning characteristics, such as twin morphology, volume fraction of twins with strain, and twin texture, and consequently gave rise to a totally different effect on the deformation. The differences in the deformation characteristics (flow stress and strain hardening) between both activation modes were explained in relation with activation stresses for twinning and slips, activities of twinning and slips in the deformation, Hall-Petch effect by twinning-induced grain size change, and twinning-induced change in activities of slips.
연직상향(鉛直上向) 사각충돌수분류(四角衝突水噴流)의 포화비등 열전달에 관한 연구
이종수,엄기찬,서정윤,Lee, J.S.,Ohm, K.C.,Seo, J.Y. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.5
The purpose of this investigation was to characterize nucleate boiling and burn-out heat flux for rectangular free jet with saturated water impinging perpendicularly and upward against a flat uniform heat flux surface. Heat flux measured for Reynolds number based on rectangular nozzle width and for aspect ratio. The result of nucleate boiling heat transfer was presented nondimensional experimental equation including Nusselt, Boiling, Subcooling, Reynolds and Weber number. The effect of aspect ratio of heated surface in the burn-out heat flux had not appeared distinctly. But for the same aspect ratio, burn-out heat flux increased linearly with increment of nozzle exit velocity.
사각(四角) 충돌수분류(衝突水噴流)의 열전달증진(熱傳達增進)에 관(關)한 연구(硏究)
박성연,이종수,엄기호,서정민,Park, S.Y.,Lee, J.S.,Ohm, K.C.,Seo, J.Y. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.1
The purpose of this study is an augmentation of heat transfer in the case of upward rectangular impinging water jet system. The variables of this study are nozzle-to-heated surface distance, jet velocity and supplementary water height. Optimum heights of supplementary water which augment the heat transfer rate are S/B=2 for H/B=30 and S/B=I for H/B=40, 50. On the Y-direction of nozzle, there exhibits the secondary peak of heat transfer coefficient when supplementary water is not used, however using the supplementary water, it does not exhibits. In the case of using supplementary water, heat transfer coefficient increases not only in stagnation region but also in wall jet region.
엄기찬(K.C.Ohm),이종수(J.S.Lee),서정윤(J.Y.Seo) 한국태양에너지학회 1994 한국태양에너지학회 논문집 Vol.14 No.1
본 연구에서는 내부곡선이 정현곡선형으로 된 노즐(출구형 : 6㎜)로부터 상향으로 반원통의 내면 및 외면(직경 : 각각 40㎜, 50㎜, 60㎜, 70㎜의 4종류)에 충돌시켜 그 열전달 특성을 구명하고, 동시에 보조수를 사용하여 열전달 촉진현상을 실험적으로 구명하였다. 그 결과 다음과 같은 결론을 얻었다.<br/> 반원통의 내외면 공히 국소열전달계수는 정체점으로부터 벽면을 따라 단순 감소하는데, 요면의 경우는 보조수를 사용하지 않는 경우에는 정체점으로부터 벽면을 따라 노즐직경의 10배 이후의 영역에서 거의 균일한 분포를 갖는다. 최대 열전달계수는 보조수층 높이가 노즐직경의 1배의 조건에서 나타나며, 凸面에 비하여 凹面의 경우에 열전달계수가 크다. 평균열전달계수는 전열면직경/노즐직경의 비가 작을수록 크게 나타나고 있다. Experiments are performed to study heat transfer processes over a convex and concave surface. A single water jet issuing from nozzle and a water jet accompanied by supplementary water impinge normally on the convex side or the concave side of a heated semi-cylindrical surface. The local heat transfer Nusselt number along the surface is measured. In the experiment, the Reynolds number ranges from 24000 to 54000, and the supplementary water height to nozzle diameter ratio S/D is from 0 to 3.<br/> The local heat transfer and the average heat transfer are maximum value in the condition of S/D=1 and them of concave surface are larger than those of convex surface. The average heat transfer increases with decreasing d/D. Correlations of both the stagnation point and the average Nusselt number over the curved surface, which account for the surface curvature effect, are presented.
상이한 초미세립 구조를 갖는 OFHC Cu의 연성에 영향을 미치는 요소인자
박이주(L. J. Park),감형원(H. W. Kim),이종수(C. S. Lee),황시우(S. W. Hwang),박경태(K.-T.Park) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
Tensile ductility of OFHC Cu with the different ultrafine grained (UFO) structures, which were fabricated by the different routes of equal channel angular pressing (ECAP), was associated in detail with the microstructural characteristics developed by ECAP. OFHC Cu having the lamellar and equiaxed UFO structures was prepared by ECAP of routes A and Bc respectively up to 8 and 16 passes. Their microstructures were closely examined by transmission electron microscopy and orientation image mapping. Tensile tests at room temperature were conduced on the ECAPed samples under the quasi- static condition of 10?³ s?¹ and 1 s?¹. Uniform elongation of the lamellar UFO samples decreased with increasing the ECAP passage while both uniform and total elongations of the equiaxed UFO samples increased. In the case of route A producing the lamellar UFO structure, the fractions of high angle grain boundaries and grains less than 0.5 ㎛ increased significantly but an analysis revealed that the dislocation free length decreased with increasing the ECAP passage. For route Be resulting in the equiaxed UFO structure, the fraction of high angle grain boundaries increased but the grain size distribution and the dislocation free length remained nearly unchanged with increasing the ECAP passage. From the present experiments and analyses, it was found that tensile ductility of lamellar UFO OFHC Cu is primarily controlled by the dislocation free length and that of the equiaxed one is mainly dependent on the fraction of high angle grain boundaries.