Validity of the 6-minute walk test and step test for evaluation of cardiorespiratory fitness in the patients with type Ⅱ diabetes mellitus

학위논문(석사) --서울대학교 대학원 :체육교육과,2007.Maste

ICP-CVD와 ELA를 이용하여 180도 온도에서 제작된 多結晶 실리콘 薄膜 트랜지스터에 關한 硏究

Thesis (doctoral)--서울대학교 대학원 :전기·컴퓨터공학부,2004.Docto

페인트 스프레이용 후드의 효율 향상에 관한 연구

학위논문(석사)--서울대학교 보건대학원 :환경보건학과 산업보건전공,2000.Maste

위치 특이적으로 고안된 실리콘 나노리본 기반의 장치를 이용한 다기능성 전자 피부

학위논문 (석사)-- 서울대학교 대학원 : 협동과정 바이오엔지니어링전공, 2015. 8. 김대형.Advances in prosthetic technology facilitate amputees restoring movements to the missing body parts. An accurate restoring motor function of missing parts requires feedback of sensory signals from the prosthesis as actual human skin. However, despite the advances, providing sensory function to prosthesis and connecting the sensory function to the nerve system are still challenging. To provide prosthesis with sensing abilities, researches on electronic skin with various sensors and materials were conducted. But with limited performances such as stretchability, detection range, and spatio-temporal resolution, it was difficult to mimic actual human skin. Here, a stretchable, electronic skin with various sensing capabilities: strain, pressure, and humidity is demonstrated. Using site-specifically designed monocrystalline silicon nanoribbon, high sensitivity and enhanced range of sensing ability under the skin deformation are achieved. For connecting the signals from electronic skin to the nervous system, transmission of sensed signals to the nervous system is performed, from the peripheral nerve to the brain, using stretchable multi-electrode arrays decorated with neuro-protective nanoparticles. Combined with sensory and actuating functions, this system provides an effective solution for emerging classes of prostheses.1. Introduction········································································································· 1 2. Site-specifically designed silicon nanoribbon based sensors····························· 3 2.1 Heterogeneous nature of skin-deformation depends on location··················3 2.2 Material characterization of single crystalline silicon for strain sensor ·······8 2.3 SiNR strain gauges with different curvatures············································· 10 2.4 SiNR pressure sensors with serpentine design··········································· 15 3. Metal based humidity sensor and heater with stretchable designs ··················· 19 3.1 Characterization of humidity sensor ·························································· 19 3.2 Characterization of stretchable heater ······················································· 24 4. Sensing capability of electronic skin in simulated daily life ···························· 27 5. Connecting electronic skin and nervous system ·············································· 33 5.1 Low impedance multi-electrode array with neuro-protective nanoparticles····· 34 5.2 Stretchable multi-electrode array contacting peripheral nerves ················ 37 5.3 In vivo experiment of interfacing electronic skin with nervous system ·····39 6. Experimental Section························································································ 41 7. Conclusion········································································································· 47 8. References········································································································· 48Maste

금속 환경에서의 UWB 방식 RTLS 시스템 구축을 위한 Reader의 최적 배치 방법 연구

MasterRecently, various location-based services have been realized through the advanced wireless communication system. In particular, RTLS (Real Time Location System) with UWB-based active RFID (Radio Frequency Identification) is remarkable due to its high accuracy. When the UWB-based RTLS system is deployed on the ground, most system engineers select location of readers with their intuition and know-how in the trial-and-error manner. However, such manner becomes inefficient or impossible as the complexity as well as the size of the system increases. Thus, a system engineering methodology is required for deploying UWB-based RTLS system, which has been studied in this thesis.As the first step, this study is focused on the metal environment. However, it is realistic considering that the UWB-based RTLS system is typically applied to the industrial environment surrounded by the metal, such as steel making industry. The read rate of the UWB-based RTLS system is modeled by experiments, and optimization problem for determining the minimum number of the readers and their locations is formulated and solved by solution algorithm. The developed method is verified by simulations and real experiments, followed by discrepancy analysis between the two results

Characterizationof a complex manifold by is isotropy subgroup

Maste

전이금속 화합물에서의 결맞음 포논 진동 현상에 대한 비평형 분광학 연구

학위논문 (박사)-- 서울대학교 대학원 : 자연과학대학 물리·천문학부(물리학전공), 2019. 2. 노태원.본 학위 논문에서는 초고속 분광학 실험을 이용하여 Ca2RuO4, Sr2RuO4, BaFe2As2 물질 등과 같은 전이금속 화합물에서의 결맞음 포논 진동 현상을 연구하였다. 기존 반도체 물질 군에서의 연구를 통해 결맞음 포논 진동의 발생 원리에 대한 탐구는 이루어져 왔으나, 물질의 상태 변화에 따른 포논 진동의 변이 현상은 구체적으로 다루어진 바 없었다. 특히, 철(Fe)이나 루테늄(Ru)과 같은 전이금속을 포함한 화합물의 경우, 강한 전자를 비롯하여 스핀/오비탈 자유도와 격자 구조 사이의 상호 작용에 따라 다양한 바닥 상태를 가지게 되는데, 이러한 강상 관계 물질 군에서의 결맞음 포논 진동 현상 연구는 그 시도가 많지 않았다. 이에 따라, 앞서 언급된 전이금속 화합물들에서 실시간 포논 진동 현상을 관찰한 결과, 온도에 따라 진동의 주파수, 세기, 그리고 위상이 크게 변화함을 발견하였고, 이러한 변화가 스핀/오비탈 정렬 현상에 따른 강상 관계 물질 내 격자 구조 변화와 밀접한 관련이 있음을 알아낼 수 있었다. 모트 절연체로 잘 알려진 Ca2RuO4에서는 저온 상태에서 스핀 정렬 현상과 오비탈 정렬 현상이 113 K과 260 K의 각기 다른 온도에서 일어난다. 해당 물질에서 온도에 따라 적외선 들뜸-탐침 분광학 실험을 수행하여 실시간 반사율 변화를 측정한 결과, Ag 대칭의 포논들이 실시간 결맞음 진동의 형태로 나타남을 확인하였다. 이 중 가장 낮은 주파수의 포논 진동의 경우, 오비탈 정렬과 스핀 정렬 온도를 지나며 큰 변화가 나타남을 발견하였다. 우선 오비탈 정렬 온도 근처에서 진동 세기가 급격히 감소하고, 온도를 지나며 진동의 위상이 180도가량 급격히 변화함을 확인하였고, 스핀 정렬 온도 아래에서는 급작스럽게 진동 세기가 증가하며 위상이 90도 변하는 것을 관찰할 수 있었다. 특히, 90도 위상 변화는 최초로 발견된 결과이며, 제일 원리 계산과 기존 구조 분석 연구를 자세히 살펴본 결과, 스핀과 오비탈 정렬 현상과 함께 포논 진동과 밀접하게 연관된 격자 구조 뒤틀림 현상이 일어남을 추가로 확인할 수 있었다. 이러한 연구 결과는 결맞음 포논 진동 현상에서의 위상 정보가, 스핀 또는 오비탈과 같은 다른 자유들과 강하게 상호 작용하고 있는 환경에서의 격자 구조를 탐구할 수 있는 중요한 지표로 작용할 수 있음을 제시하고 있다. 철 기반 초전도 물질은 구리 계 초전도체와 더불어 초전도 현상을 연구키 위한 새로운 발판으로 새롭게 대두되었다. 특히 철 계 초전도 물질 내 스핀/오비탈 정렬 상태, 격자 구조 뒤틀림 현상 및 초전도 상태의 상호 작용에 대한 연구가 활발히 이루어지고 있다. 본 연구에서는 BaFe2As2에서 적외선 들뜸-탐침 분광학 실험을 이용해 온도에 따른 실시간 반사율 변화를 측정하였고, 특히 탐침 빛의 선형 편광 방향을 달리하며 변화 양상을 관찰하였다. 그 결과, 모든 온도에서 A1g 대칭의 포논 진동 현상을 관찰하는 데 성공하였고, 해당 진동의 온도 변화가 네마틱 (nematic) 정렬 현상과 관련 있음을 발견하였다. 구체적으로, 탐침 편광 방향이 각각 사방정계(orthorhombic) 단위 격자에서의 a/b 기준 방향 축으로 설정되었을 때, 10 K 가량의 극저온에서 A1g 포논 진동 현상의 위상이 탐침 빛의 편광 방향에 따라 180도 뒤집힌 상태로 관찰되었다. 이러한 탐침 편광 방향에 따른 격자 진동의 위상 차이는 스핀 정렬이 없는 140 K의 고온 조건에서 역시 나타났으며, 물질 내 네마틱 상태에 대한 또 다른 증거로써 제시할 수 있었다. 해당 연구를 통해 탐침 빛의 편광 조건에 따른 결맞음 포논 진동 관찰이 강상관계 물질 내 오비탈 또는 스핀 자유도의 정렬 형태에 대한 새로운 정보를 제공할 수 있음을 제시할 수 있었다.This thesis comprises researches of coherent phonon oscillations in transition metal compounds Ca2RuO4, Sr2RuO4 and BaFe2As2 studied by time-resolved optical reflectivity experiments. Specifically, we investigate how various orderings of spin and orbital degrees of freedom change properties of coherent phonon oscillations in a Mott insulator Ca2RuO4 and a parent compound of pnictide superconductors BaFe2As2. Far from the conventional notion of oscillation-phase as a static property simply determined by generation mechanisms, we observe dramatic variations in oscillation-phase of coherent phonons with strong correlations. Ca2RuO4, a prototype 4d Mott insulator, is one of the rare examples in which all of the quantum degrees of freedom play active roles in distinctive phase transitions. A metal-insulator transition (MIT) occurs at TMIT = 357 K, accompanied by a structural phase transition that involves strong distortions of octahedral flattening and tilting, which suggests a strong charge-lattice coupling. Upon cooling, the octahedral distortions continue to develop and ultimately saturate when the spins become antiferromagnetically ordered at TN = 113 K. In addition, a resonant X-ray scattering technique captured the antiferromagnetic orbital ordering even in the paramagnetic state below TOO = 260 K. Using optical pump-probe technique, we investigate coherent phonon oscillations in Ca2RuO4 across the spin and orbital ordering temperatures. In particular, coherent oscillations of an Ag symmetric phonon show dramatic changes not only in oscillation-amplitude, but also oscillation-phase, even with 180 and 90-degree variations across TOO and TN, respectively. Density functional theory (DFT) calculations and a careful inspection on the crystal structures of Ca2RuO4 suggest that unexpected phase variations can originate from structural deformation across the spin and orbital orders. This results indicate that time-resolved observation on coherent phonons can be extremely sensitive to structural transitions correlated with quantum degrees of freedom. BaFe2As2 is a parent compound of pnictide superconductors, such as holedoped (Ba,K)Fe2As2 and electron-doped Ba(Fe,Co)2As2/BaFe2(As,P)2. Recently, of particular interests in the phase diagram of pnictide superconductors has been a nematic state below Tnem, which represents by a broken C4 symmetry upon unbroken spin-rotational symmetry. The nematic transition precedes the antiferromagnetic spin ordering transition at TN and the tetragonal-to-orthorhombic structural transition at TS, namely Tnem > TN, TS. We investigate coherent phonon oscillations of BaFe2As2 by using near-infrared femtosecond optical pulses. Time-resolved reflectivity data show A1g symmetric phonon oscillations of arsenate vibrations along c-axis. We observe an anisotropic behavior in initial phase values of the A1g phonon oscillations, robustly depending on probe polarizations along orthorhombic structural axes. Notably, the anisotropy in the oscillation-phase presents even in the paramagnetic phase, which can originate from a nematic response of d-orbitals to the A1g lattice vibrations of BaFe2As2. Our study on coherent phonons suggests that investigation on oscillation-phase can offer a unique evidence of phase transition of a nematic ordering strongly coupling to lattice instability.1 Introduction 1 1.1 Introduction to coherent phonon oscillations 2 1.2 Generation mechanisms of coherent phonon oscillations 4 1.2.1 Impulsive stimulated Raman scattering (ISRS) 5 1.2.2 Displacive excitations of coherent phonons (DECP) 7 1.2.3 Transiently stimultaed Raman scattering (TSRS) 11 1.3 Outline of Thesis 15 2 Experimental Methods 19 2.1 Introduction to pump-probe spectroscopy 20 2.2 Optical pump - optical probe technique 21 2.3 Determination of the absolute time zero 23 3 Results and Discussion I: Ca2RuO4 and Sr2RuO4 25 3.1 Phase transitions in Ca2-xSrxRuO4 26 3.2 Abnormal phase flip in the coherent phonon oscillations 28 3.2.1 Results: phase-flip across TOO 29 3.2.2 Discussion 1: phase-flip by lattice deformation 34 3.2.3 Discussion 2: octahedral deformation across TOO 36 3.3 Spin-phonon coupling unveiled by coherent phonon oscillations 42 3.3.1 Results: DECP-ISRS transition across TN 42 3.3.2 Discussion 1: spin-phonon coupling 46 3.3.3 Discussion 2: spin-order-induced lattice deformation 49 3.3.4 Discussion 3: phonon enhancement by spin order 52 3.4 Coherent phonon oscillations of Sr2RuO4 57 3.4.1 Results and discussion: invariant phase above TC 57 3.5 Conclusion 59 4 Results and Discussion II: BaFe2As2 60 4.1 Phase diagram of Fe-based superconductor 61 4.2 A1g coherent phonon oscillations of BaFe2As2 62 4.3 Anisotropic responses of coherent phonon oscillations in BaFe2As2 67 4.3.1 Result 1: optical anisotropy in A1g phonon oscillations 67 4.3.2 Result 2: nematic responses of coherent phonon oscillations 73 4.3.3 Discussion 1: anisotropy in aR/ax 75 4.3.4 Discussion 2: orbital order fluctuation in nematic state 77 4.4 Conclusion 81 5 Summary and Concluding Remarks 82 6 References 84 7 Appendix 93 7.1 Details of studies on Ca2RuO4 93 7.1.1 Pump fluence dependence of coherent phonon oscillations 93 7.1.2 Fitting parameters of coherent phonon oscillations 95 7.1.3 Temperature dependence of absorption 98 7.1.4 Details on DFT calculations 99 7.2 Previous reports on oscillation-phase 100 7.3 Optical pump - THz probe spectroscopy 101 7.4 Art in Science 104 8 Publication List 106 8.1 Publications for this thesis 106 8.2 Other publications 107 9 Korean abstract 109Docto

An Experimental Study on Combustion Instability and NOX Emission Characteristics of H2/CO/CH4 Syngas in a Gas Turbine Combustor

학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2014. 2. 윤영빈.The effects of the H2/CO/CH4 syngas compositions and the N2/CO2/steam dilution ratios are investigated in a partially-premixed gas turbine model combustor, which can prevent flashback problem even in high hydrogen content to understand the combustion characteristics of new fuel for IGCC and SNG plants. The temperatures of flame and combustor, NOx/CO emissions, combustion instability, flame stability, and flame structures are examined. Cause and effects of each combustion characteristics were determined from the relationship between them. For example, in order to identify the detailed flame structure during combustion instability, OH*-chemiluminescence images were taken at the rate of 12500 frame/sec using the high-speed intensified ICCD camera and/or planar OH* distribution in flame was obtained using phase-locked OH*-PLIF setup. First, the fuel composition effects of H2/CO/CH4 syngas (0~100%, span: 12.5% by LHV) on trends of each combustion performance were investigated by using ternary diagram. A lot of NOx is emitted at high H2 composition due to high flame temperature and high CO composition due to long residence time. This feature could be also explained by flame structure and combustor temperature. H2/CH4 syngas flame generated high combustion instability at the frequency of 750 Hz, 1000 Hz and 1500 Hz correspond to 3L, 4L and 6L mode which varies according to the fuel composition. This self-excited high multi-mode combustion instability characteristics have been studied by investigating combustion properties, flame structure, Rayleigh indices, proper orthogonal decomposition and characteristic time scales from the images of high-speed chemiluminescence and OH*-PLIF. The flames have different shapes and generate different combustion instability frequency at near 4L or 3L mode with their harmonics. The combustion oscillation frequency which is non-linear for fuel composition was appeared to be linearly proportional to Tad and SL. Phase-synchronized OH*-PLIF images suggested clues of an important combustion instability driving mechanism including the periodic alternation of flame attachment/detachment and coupling of vortex with everlasting heat release at the outer recirculation zone due to high reactivity of high hydrogen fuels. These images also used for the precise calculation of 2-D flame length by obtaining centroid of heat release intensity when performing time-lag analysis. The Rayleigh index results notified the dependence of the location and intensity of combustion instability driving/damping on the fuel composition and instability mode. For higher H2 containing flame (4th mode), driving and damping is occurred in narrow region but with high heat release density and the frequency of Rayleigh index was doubled. Otherwise in case of 3rd mode Rayleigh index shape was similar with pressure fluctuation due to the characteristics of multi-mode combustion instability with high superposition of higher harmonics. Analysis of proper orthogonal decomposition from high-speed OH* images showed the distinct coherent structures and large roll-up of flame are responsible for generating flame oscillations for each mode. High cross-correlation was found between proper orthogonal modes of 4th mode indicating convection of these coherent structures. When conducting time-lag analysis for syngas in a partially-premixed gas turbine model combustor, the significance of skewness time induced by wave distortion and importance of careful inspection on Lflame using 2-D OH*-PLIF is verified by showing the improvement in prediction accuracy. Next, the effect of the fuel-side dilution of N2, CO2 and steam on the combustion characteristic of syngas has been studied. This fuel-side dilution reduced flame temperature, combustor temperature and consequently NOx but significantly increased CO emission due to incomplete combustion at low flame temperature. From the NOx results of each diluent, it can be obtained that the dilution of syngas with nonflammable gas decreases NOx emissions, and the amount of NOx reduction per unit power is logarithmically related to only the diluents heat capacity which is the product of mass flow rate of the diluent and constant pressure heat capacity. This relationship between NOx reduction and diluent heat capacity is verified by inducing analytic solutions with some appropriate assumptions. Finally, based on the combustion results of H2/CO/CH4 syngas with N2/CO2/steam dilution, the combustion tests were performed for the commercial fuels: coal-derived syngas and SNG. The results of coal gas of which H2/CO ratio is 1/2 showed that N2 dilution is appeared to be negative in view of flame stability and CO emission but can be operable with enough stability margins and to be very positive in view of NOx emission. Combustion test of C0, C1, C3 and C5 SNGs of which H2 content is 0%, 1%, 3% and 5% but Weber index is constant was performed. Combustion characteristics of temperature and NOx/CO emission were almost identical for all SNGs but combustion instabilities of C0 and C1 were slightly differed from that C3 and C5 in frequency as well as amplitude. This feature also closely visualized by examining the high-speed unsteady flame behaviors. Even though the impact on combustion instability is not so significant for SNG which contains over 1% H2, this 1% where the change of combustion starts can be provided as the quality standard in SNG considering the existence of various types of natural gas firing gas turbines.ABSTRACT i KEYWORDS iii CONTENTS iv LIST OF FIGURES vii LIST OF TABLES xii NOMENCLATURE xiii CHAPTER 1 INTRODUCTION 1 CHAPTER 2 EXPERIMENTAL APPARATUS AND TECHNIQUES 9 2.1 The gas turbine combustion test facility and test conditions 9 2.2 Model gas turbine combustor 12 2.3 Measurements and optical setup 14 CHAPTER 3 COMBUSTION CHARACTERISTICS OF H2/CO/CH4 SYNGAS 18 3.1 Determination of test conditions 18 3.2 Test results of temperature, combustion instability, NOx and CO emissions and flame structure 20 3.2.1 Temperature characteristics 20 3.2.2 NOx and CO emission characteristics 21 3.2.3 Combustion instability characteristics 24 3.2.4 Flame structures 25 3.3 Analysis of combustion instability 27 3.3.1 Frequency and mode analysis 27 3.3.2 OH*-PLIF 33 3.3.3 Rayleigh indices 34 3.3.4 Proper orthogonal decomposition analysis 38 3.3.5 Time-lag analysis in multi-mode combustion instability 39 3.3.6 Summary and conclusion of the CI analysis for H2/CO/CH4 syngas 42 CHAPTER 4 EFFECT OF N2/CO2/STEAM DILUTION ON THE SYNGAS COMBUSTION 43 4.1 Effect of N2 dilution on the combustion Characteristics of H2/CO/CH4 syngas 43 4.2 Effect of N2/CO2/steam dilution on the combustion characteristics H2/CO syngas 48 4.2.1 NOx emission characteristics 49 4.2.2 CO emission characteristics 53 4.2.3 Combustion oscillation characteristics 53 4.2.4 Temperature characteristics 56 4.2.5 Summary and conclusion of N2/CO2/steam dilution study 59 CHAPTER 5 APPLICATION ON THE COMMERCIAL GASES: COAL GAS AND SYNTHETIC NATURAL GAS 60 5.1 Coal-derived syngas combustion 60 5.1.1 Flame stability map 63 5.1.2 Temperature characteristics 67 5.1.3 NOx and CO emission characteristics 68 5.1.4 Combustion oscillation characteristics 73 5.1.5 Flame structures 75 5.1.6 Summary and conclusions of coal gas combustion study 77 5.2 Synthetic natural gas combustion 78 5.2.1 Temperature characteristics 80 5.2.2 CO and NOx emission characteristics 81 5.2.3 Combustion oscillation characteristics 83 5.2.4 Flame structures and heat release oscillation 84 5.2.5 Summary and conclusions of SNG combustion study 89 CHAPTER 6 CONCLUSION 91 APPENDICES 94 Appendix A. Calculation of adiabatic flame temperature 94 Appendix B. Calculation of ignition delay time 97 Appendix C. Calculation of larminar flame speed 99 Appendix D. Analysis of proper orthogonal decomposition 100 Appendix E. Carbonyl trapper 105 REFERENCES 107 ABSTRACT IN KOREAN 115 KEYWORDS IN KOREAN 118 ACKNOWLEDGEMENT IN KOREA 119Docto

Poly-Si TFT의 ONOFF 전류비 향상을 위한 새로운 레이저 어닐링 방법과 소자 구조에 관한 연구

학위논문(석사)--서울대학교 대학원 :전기공학부,2000.Maste