애기장대의 배축 길이 성장 과정에 있어서 HOS1을 통한 phytochrome B 기능 조절에 대한 분자적 메커니즘 연구

학위논문 (석사) -- 서울대학교 대학원 : 자연과학대학 화학부, 2021. 2. 박충모.During seedling development, response to light induces inhibition of hypocotyl elongation, cotyledon opening, and leaf greening, and those are called photomorphogenesis. For hypocotyl elongation, photoreceptors, especially one of the red/far-red light-sensing phytochromes, phytochrome B, is regarded as a crucial regulator of it. Although, it is not completely known how the phytochrome B regulates hypocotyl growth. Here, I showed that well known E3 ubiquitin ligase, HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1, prevents the transcriptional activation activity of PHYTOCHROME INTERACTING FACTOR 4 which induces hypocotyl cell growth. Also, photoactivated phyB is needed for activation of HOS1 in inhibiting PIF4 activity. Consequently, I found a new molecular mechanism for the phyB-dependent prohibition of hypocotyl growth in Arabidopsis.INTRODUCTION 1 MATERIALS AND METHODS 3 Plant materials and growth conditions. 3 Measurement of growth kinetics 3 Analysis of gene transcript levels 3 Yeast two hybrid assays. 4 BiFC assay. 4 ChIP assay. 4 Transcriptional activation activity assays. 5 Coimmunoprecipitation assay. 5 Cell fractionation assay. 6 RESULTS 8 HOS1 is associated with PIF4 function during hypocotyl elongation 8 HOS1 inhibits the transcriptional activation activity of PIF4 12 HOS1 is required for the phyB-mediated inhibition of PIF4 function 17 phyB activates HOS1 in inhibiting PIF4 activity 19 DISCUSSION 25 HOS1 is required for phyB-mediated inhibition of PIF4 activity 25 Requirement of additional factors for HOS1-mediated regulation of PIF4 26 How does phyB activates HOS1? 26 ACKNOWLEDGEMENT 28 REFERENCES 29 ABSTRACT IN KOREAN 34Maste

내열 스테인리스강에서 고온 산화 거동에 미치는 미세조직 및 집합조직의 영향 고찰

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2015. 8. 이경우.에너지 분야에서 효율을 높이기 위해 고민되는 여러 가지 시도 중 가장 쉽게 접근할 수 있는 방법으로는 시스템의 작동 온도를 높임으로써 연소 또는 변환 효율을 높이려는 시도를 들 수 있다. 전 세계적으로 가장 많은 발전량을 갖고 있는 화력발전에서는 수증기 온도를 700 °C 이상으로 올림으로써 발전 효율을 48%까지 끌어 올리는 차세대 화력발전소인 초초임계압 화력발전소의 개발이 이루어지고 있다. 화력발전소에 사용되는 보일러는 과열기/재열기, 절탄기 및 수냉벽으로 구성되어 있으며, 이들은 많은 파이프로 구성되어 있다. 파이프는 보일러에 사용되는 설비에 가장 핵심이 되는 부품으로 내부에 유체가 흐르고 외부에서 전달되는 열을 내부의 유체에 전달하는 주요한 역할을 하며, 이러한 파이프는 보일러가 대용량화 되어감에 따라, 점차 많은 양의 파이프가 배치된다. 기존 연구에 의하면 오스테나이트 스테인리스 강에 구리를 첨가하면 크리프 강도가 증가하고, 고온 내식성이 향상된다고 보고되고 있다. 이러한 오스테나이트 스테인리스 강은 우수한 고온 크리프 특성으로 차세대 화력발전소인 초초임계압 화력발전소의 과열기와 재열기안에 스팀 파이프로 고려되고 있다. 하지만, 지난 몇 년 동안 고온에서 내열강의 산화층 분석은 광범위하게 연구되었으며, 이는 극한 환경에서의 내열강 표면에 산화물의 박리로 인한 여러 가지 문제가 발생하였기 때문이다. 세계적인 에너지 문제 해결을 위한 청정 신재생 에너지원으로 다양한 종류의 연료전지 시스템 중 800 °C 부근에서 작동하는 고체연료 산화물 연료전지가 높은 효율과 탄력적인 연료 사용성으로 큰 관심을 받고 있다. 고체 산화물 연료전지 분리판용 재료는 가공성과 가격을 이유로 기존의 세라믹재료에서 금속재료로 빠르게 대체되고 있다. 페라이트계 스테인리스 강은 생성되는 산화물의 높은 전기전도도 뿐 아니라 소재 자체의 뛰어난 기계적 특성, 가공성, 경제성 및 다른 고체연료 산화물 연료전지 구성요소와 유사한 열팽창계수로 인해 분리판용 소재로 크게 각광받고 있다. 고체연료 산화물 연료전지의 작동온도는 650~800 °C 이며 이러한 온도에서 주요 관심사는 내산화성과 산화물의 형성으로 인한 전기전도도이다. 일반적으로 내산화성 개선을 위해서는 티타늄, 알루미늄등의 합금원소가 첨가되며 특히 망간은 페라이트 스테인리스 강에서 생성되는 산화물층의 전기전도도를 증가 시키기 위한 합금원소로 사용되고 있다. 이와 같은 고온 작동 조건에서 가장 문제가 되는 부분은 재료의 고온 안정성 문제로, 특히 고온 산화에 의한 재료의 열화를 극복하는 것이 가장 중요한 이슈 중 하나이다. 이러한 고온 산화 문제를 해결하기 위한 방법으로는 다양한 합금원소를 첨가함으로써 재료내의 확산을 제어하려는 접근이 주로 이루어지고 있는데, 최근 가격 절감 문제와 재료의 재활용 가능성 저하 문제로 인하여 합금 원소의 첨가를 줄이면서 기존 재료 이상의 물성을 얻고자 하는 시도가 조금씩 증가하고 있다. 본 논문에서는 기존의 소재와 같은 소재를 이용하면서도 재료의 결정립계 특성 또는 우선 결정방위를 제어함으로써 재료의 고온 내산화성을 개선할 수 있는 방안을 소개하고자 한다. 재료의 이방성이 적은 오스테나이트계 스테인리스 소재에서는 재료의 결정방위보다는 결정립계가 내산화성에 큰 영향을 미치는데, 에너지적으로 안정적인 Σ3 입계 등 특수 결정립계에서는 내산화성을 나타내지 못하지만, 15° 이상의 어긋남각을 갖는 고경각입계 주위에서는 뛰어난 내산화성을 나타내고 있으며, 결정립의 크기를 제어하는 것 만으로도 50배 이상의 산화속도 차이를 나타낼 수 있다. 따라서 결정립을 미세화 시킴으로써 내산화성을 증가 시킬 수 있으며, 결정립계를 따라 선택적 산화로 인하여 임계결정립 크기를 확인 하였다. 이에 반해 재료의 이방성이 큰 페라이트계 스테인리스 소재에서는 결정 방위가 더 큰 영향을 나타내는데, 모재의 결정학적 방위와 내산화성, 전기전도도의 관계를 이해하기 위해 {100}, {110}, {111}과 {112} 방위의 결정립에 형성된 산화물의 구조를 분석하였다. 충진도가 높은 {110} 결정면에서는 생성되는 산화물이 판상 형태를 갖는 고밀도의 산화물이 형성되는 것을 확인 할 수 있으며, 충진도가 낮은 {111} 결정면에서는 산화물의 형상이 입자 형태를 나타내고 밀도도 비교적 낮게 나타나는 것을 알 수 있었다. 따라서 모재의 {110} 결정면에서 내산화성과 전기전도도가 다른 결정면에 비해 우수하게 나타났으며, 이를 바탕으로 결정 방위 분포의 강도에 따른 내산화성과 전기전도도의 특성의 변화를 확인 하였다.Despite enormous research efforts into the renewable energy technologies, conventional thermal power plants are still by far the most important power generation source worldwidethermal power plants are expected to maintain this position for at least several decades. All power generation sources based on the fossil fuel burning inevitably produce CO2, one of the major causes of global warming. Considering the contribution to the total CO2 emission, improving fossil fuel-based energy conversion efficiency to 60% by increasing the reaction temperature is the most efficient way to reduce total CO2 emissions by up to 30%. Generally, the austenitic steels demonstrate excellent high temperature creep properties, making them a promising candidate for use in steam tubes for superheaters and reheaters of ultra-super-critical (USC) power plants. Previous studies have shown that adding Cu to austenitic stainless steels increases the creep rupture strength and enhances high temperature corrosion resistance. To examine the oxidation behavior of Cu added austenitic stainless steels in a water vapor atmosphere, we observed the oxidation behavior at 700 °C in air with 20 % water vapor. Samples were prepared by thermo-mechanical treatment to have similar ∑3 grain boundary fraction and different grain size, to eliminate the grain boundary characteristics effect. The early stages (< 12 h) of the oxidation behavior of Cu added austenitic stainless steels with various grain sizes was investigated using atom probe tomography (APT), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), electron probe microanalyzer (EPMA) and X-ray diffraction (XRD). A thin Cr-rich oxide layer is formed over the entire surface of a small grain (8 µm) sample, which is similar to that formed near grain boundaries of medium grain (17 µm) and large grain (27 µm) samples. Oxidation of all samples proceeds via the lattice and grain boundary diffusion of Cr, leading to the formation of a protective Cr-rich oxide first at the grain boundaries and then via lateral growth toward the grain interiors. APT and TEM studies on the initial stage of oxidation clearly reveal that within 4 μm of the grain boundaries, the oxide layer exhibits a duplex-layer structure consisting of a thin Fe-rich (Fe,Cr)3O4 oxide (~55 nm) above and a protective Cr2O3 oxide (~40 nm) below as a diffusion barrier. In contrast, further away from the grain boundaries, a non-protective Fe-rich (Fe,Cr)3O4 oxide (~160 nm) and a Cr-rich (Fe,Cr)3O4 oxide (~40 nm) are formed as the outer and inner layers, respectively. The oxidation kinetics was studied in terms of mass gain measurements. The critical grain size (< 8 µm) to prevent the formation of fast-growing, non-protective Fe-rich oxides is discussed based on the experimental findings. Through the calculation and experimental analysis, a critical grain size for the high oxidation resistance is suggested. During the later stages (< 500 h) of the oxidation of Cu added austenitic stainless steels with grain size smaller than 8 µm, uniform Cr2O3 layer was formed, which increased the overall oxidation resistance. Whereas in samples with grain size larger than 17 µm, Fe2O3 layer was formed on the Cr-rich oxide layer, which resulted in a relatively high oxidation rate. It can be inferred that the grain boundaries act as rapid diffusion paths for Cr and provide Cr enough to form Cr2O3 oxide at the area near to the grain boundary. Also, the oxide scales of high-alloyed steel are composed of complex phases that are difficult to differentiate. Here, we used electron backscatter diffraction (EBSD)-electron dispersive spectroscopy (EDS) simultaneous analysis technique to analyze the complex oxide layers formed on Cu added austenitic stainless steels. Multi-layered oxide scales composed of external Fe2O3, external Fe3O4, internal FeCr2O4, and internal Cr2O3 oxide were well distinguished. The addition of Cu to the austenitic stainless steel induced spinel structured oxide formation at the top surface of the external oxide. We have studied the phase transformation behavior of the austenite (γ) to ferrite (α) in Cu added austenite stainless steel after oxidation at 700 °C in air with 20% water vapor. Identification and observation of the phase transformation have been carried out on this steel by means of SEM, XRD, TEM and APT with Thermo-Calc program, respectively. The results of SEM, XRD and TEM reveal that α-BCC phase formed along the prior γ-FCC grain boundary after oxidation. According to the APT result, Fe and Ni are strongly concentrated and Cr is depleted in α-BCC phase. Oxidation behavior of ferritic stainless steels with 22 wt.% Cr was also investigated. The ferritic stainless steels have been preferred as a material for interconnects in solid oxide fuel cells (SOFC) because of their high electrical and thermal conductivity, good mechanical properties, good formability, cost effective and similar thermal expansion coefficient (TEC) to the other cell components. The SOFCs usually operate in the temperature in an intermediate range of 650~800 °C. The aim of this part is the study of the effect of crystallographic orientation on the high temperature oxidation behavior of ferritic stainless steels including Crofer 22 APU. Crofer 22 APU, specially developed for SOFC interconnect, was tested in an air atmosphere at 800 °C. To gain a better understanding of the relation between oxidation resistance and electrical conductivity, the oxide scales formed on surface was analyzed in terms of orientation, structure, composition and phase in the {100}, {110}, {111} and {112} substrate planes. Also, a nano-indenter with nanoscale electrical contact resistance (nano ECR) measurements has been used to study the changes in contact resistance during an oxidation. Oxide thickness and electrical contact resistance results showed that the surface orientation can have an effect on the oxidation resistance and electrical conductivity.Contents Abstract I Contents VI List of Tables XIII List of Figures XIV Chapter 1 Literature Review of High Temperature Oxidation 1 1.1 General mechanism of oxidation 1 1.1.1 Principles of oxidation 1 1.1.2 The initiation of oxidation 3 1.1.3 Transport mechanisms 5 1.1.4 Rate of oxidation 7 1.1.5 Oxidation of alloys 14 1.1.6 Alloy depletion 18 1.2 Oxidation in water vapor and steam 19 1.2.1 Water vapor and steam oxidation mechanisms 21 1.2.1.1 The dissociation mechanism 22 1.2.1.2 Oxidant-gas penetration mechanism 26 1.2.1.3 Formation and volatilization of Fe(OH)2 27 1.2.1.4 Formation and volatilization of CrO2(OH)2 29 1.2.1.5 Changes in the oxide defect structure via proton dissolution 30 1.2.2 Steam oxidation as a function of steel composition and alloy type 32 1.3 Stainless steel 33 1.3.1 Properties 33 1.3.2 Classification 34 1.3.2.1 Austenitic stainless steels 35 1.3.2.2 Ferritic stainless steels 37 Chapter 2 Characterization Techniques for Oxidation Analysis 39 2.1 Scanning electron microscope 39 2.2 Energy dispersive X-ray spectroscopy 42 2.3 Electron backscattered diffraction 44 2.3.1 Fundamentals of the electron backscattered diffraction 44 2.3.2 EBSD sample preparation (mechanical polishing) 50 2.4 X-ray diffraction 52 2.5 Focused ion beam 56 2.5.1 Fundamentals of the focused ion beam 56 2.5.2 FIB milling 59 2.5.3 FIB deposition 61 2.6 Transmission electron microscopy 63 2.6.1 Fundamentals of the transmission electron microscopy 63 2.6.2 Bright field/Dark field imaging 66 2.6.3 Selected area diffraction (SAD) 68 2.7 Atom Probe Tomography 71 2.7.1 Fundamentals of the atom probe tomography 71 2.7.2 APT sample preparation 79 Chapter 3 Effect of Grain Size on the Oxidation Resistance 82 3.1 Introduction 82 3.2 Experimental 85 3.2.1 Alloy processing 85 3.2.2 High temperature oxidation experiments 88 3.2.3 Initial (~30 min) oxidation stage analysis 90 3.2.3.1 Atom probe tomography and Transmission electron microscopy 90 3.2.4 Early (~12 h) and long term (~500 h) oxidation stage analysis 93 3.2.4.1 Scanning electron microscopy, electron backscattered diffraction and electron probe microanalysis 93 3.2.4.2 X-ray diffraction 94 3.3 Results 95 3.3.1 Initial oxidation (~30 min) stage 95 3.3.1.1 Initial stage of oxidation behavior of Cu added austenitic stainless steel 95 3.3.1.2 Oxide composition analysis using atom probe tomography 98 3.3.1.3 Oxide structure analysis using TEM 111 3.3.2 Early oxidation (~12 h) stage 114 3.3.2.1 Grain size & CSLBs analysis using EBSD 114 3.3.2.2 Mass gain analysis for the study of oxidation kinetics 116 3.3.2.3 Oxide Surface morphology analysis using SEM 121 3.3.2.4 Oxide phase analysis using EBSD 124 3.3.3 Long term oxidation (~500 h) stage 126 3.3.3.1 Phase analysis using X-ray diffraction 126 3.3.3.2 Surface and cross section of oxide composition analysis using EDS 130 3.4 Discussion 135 3.4.1 Initial oxidation (~30 min) stage 135 3.4.1.1 Oxidation of surface and grain boundary regions 135 3.4.1.2 Initial oxidation mechanism 140 3.4.2 Early (~12 h) & long term (~500 h) stage oxidation 144 3.4.2.1 Grain refinement effect 144 3.4.2.2 Critical grain size 147 3.5 Summary 152 Chapter 4 Effect of Alloy element on the structure of oxide layer 153 4.1 Introduction 153 4.2 Experimental 156 4.2.1 Sample information and preparation 156 4.2.2 EBSD-EDS simultaneous analysis 157 4.3 Results and Discussion 158 4.3.1 Oxide phase of Cu added austenitic stainless steels 158 4.3.2 Oxide composition analysis using EDS 161 4.3.3 Oxide phase and orientation analysis using EBSD-EDS simultaneous 163 4.3.4 The formation of Fe3O4 and Cu containing spinel oxide at the top surface 166 4.4 Summary 171 Chapter 5 Effect of Water Vapor on the Abnormal BCC Phase Transformations 172 5.1 Introduction 172 5.2 Experimental 175 5.2.1 Alloy synthesis 175 5.2.2 X-ray diffraction, Scanning electron microscopy and electron probe microanalysis 177 5.2.3 Transmission electron microscopy and Atom probe tomography 178 5.3 Results and Discussion 181 5.3.1 Phase identification of matrix and oxide using XRD 181 5.3.2 Cross-sectional morphology analysis using SEM 183 5.3.3 Structure analysis using TEM 185 5.3.4 Chemical composition analysis using APT 188 5.4 Summary 193 Chapter 6 Effect of Substrate Grain Orientation on the Oxidation Resistance and Electrical Conductivity 194 6.1 Introduction 194 6.2 Experimental 196 6.3 Results 200 6.3.1 Grain size and surface morphology of initial oxidation 200 6.3.2 Phase analysis using X-ray diffraction 203 6.3.3 Oxide thickness analysis for the study of oxidation kinetics 205 6.3.4 Oxide orientation analysis by using EBSD 208 6.3.5 Electrical contact resistance of oxide layer analysis by using ECR 210 6.4 Discussion 216 6.4.1 Orientation relationship between matrix and oxides 216 6.4.2 Contact resistance of oxides 218 6.5 Summary 221 Chapter 7 Conclusions 222 7.1 Cu added austenitic stainless steels (Super304H) 222 7.2 22 wt.% Cr ferritic stainless steels (Crofer 22 APU) 225 Bibliography 226 국문 초록 248 Curriculum Vitae 252 Education & Research Experience 252 Awards & Grants 253 Skills and Expertise 253 Journal Publications 254 Patents 256 Conference (International) 257Docto

A Study on the pattern matching method in the distrubuted knowledge representation by using a connectionist model

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