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A case study of Seoul
No full text학위논문(박사) -- 서울대학교 대학원 : 환경대학원 환경계획학과, 2024. 2. Steven Jige Quan.The link between urban contextual form and building energy use has been attracting attention. Most studies measure urban form using a set of parameters which are then used to explain building energy use variation. Typically, the results obtained are explained using different mechanisms and the balance between them. However, such approaches are unable to measure the mechanisms contribution and their relative importance. Further, it cannot be determined if these mechanisms support or counter each other's effect. This study uses mediation models with the building solar insolation (SI), context temperature (CT), and occupant behavior (OB) as mediators of urban contextual forms influence on building energy use. Two types of models are used. First, the OLS-mediation model, provides a higher degree of interpretability, with coefficients and significance of each feature and mediator. Second, the SEM-ANN model has lower interpretability than the OLS-mediation model but has 11.94% higher explanatory power and 11.76% lower error. Summer electricity, winter electricity, and winter gas use intensity are analyzed individually. The results show that all the mediators can be significant for different contextual variables, seasons, and types of energy use. For summer electricity, 29.52%, 26.12%, and 18.06% of the effect was mediated by SI, CT, and OB, respectively. For winter electricity, 42.51%, 37.28%, and 5.18% of the effect was mediated by SI, CT, and OB, respectively. Finally for winter gas, 17.52%, 52.51%, and 8.10% of the effect was mediated by SI, CT, and OB, respectively. These mediators often counteract the effect of contextual variables, reducing the total effect of contextual form. The results also show that the effect of mediators can vary by season and type of use. Finally, the results also significant nonlinearity in the relationship between urban form and building energy use. Thus urban form energy efficiency interventions need to consider the target period, relative environmental impact of energy type, and nonlinearity of relationships.1. Introduction 8
1.1 Background and problem statement 8
1.2 Research gap and research questions 9
1.3 Theoretical background of the research process 9
1.4 Research outline 11
2. Literature review 13
2.1 Influence of urban contextual form on building energy consumption 13
2.1.1 Mechanisms of influence 14
2.2 Relationship between urban form, UHI, and EUI 14
2.3 Relationships between urban form, daylight, and EUI 18
2.4 Relationships between urban form, human behavior, and EUI 20
2.5 Consideration for pathways linking urban form to building energy use 22
3. Conceptual framework and methodology 25
3.1 Conceptual framework 25
3.2 Methodology 26
3.2.1 Study scope 26
3.2.2 Data collection and processing 28
3.2.3 Contextual spatial unit specification 41
3.3 Model specifications 44
3.3.1 Mediation model 1 45
3.3.2 Mediation model 2 & 3 47
3.4 Analysis structure 51
4. Results 53
4.1 Mediated effect of urban form 53
4.1.1 Model performance 53
4.1.2 OLS mediation models 53
4.1.3 SEM-ANN mediation model 57
5. Discussion 59
5.1 Role of different mediators 59
5.1.1 Electricity model 59
5.1.2 Gas model 60
5.1.3 Interpreting direct effect 61
5.2 Nature of relationship and feature importance 62
5.2.1 Nonlinearity in relationship 64
5.2.2 Feature importance 66
5.3 Temporal sensitivity of mediators 67
5.4 Spatial sensitivity of mediators 69
5.5 Alternative model specifications 76
5.6 Combining spatial, statistical, and machine learning methods 78
5.7 Comparison of results with existing literature 79
6. Implications and conclusion 82
6.1 Implications for urban planning 82
6.1.1 Contextual form and building energy use. 82
6.1.2 Mediators and building energy use. 83
6.1.3 Strategies based on differences in contextual features 88
6.2 Limitations 90
6.3 Conclusion 91
References 94
Appendix A 104
Acknowledgment 106
Publications 107박
페로브스카이트 산화물 : 높은 밴드갭을 가지는 반도체 SrSnO3, 고유전상수와 낮은 누설전류를 가지는 유전체 SrHfO3
No full text학위논문(박사) -- 서울대학교 대학원 : 자연과학대학 물리·천문학부(물리학전공), 2024. 2. 차국린.Perovskite oxides have attracted extensive attention in oxide electronics due to their remarkable array of properties, including high-k, superconductivity, ferroelectricity, and high-density 2-dimensional electron gas (2DEG) behaviors. The versatility of their structures, commonly found in oxides such as silicates, offers an extensive template for research. A particularly noteworthy advantage is the ability to stack perovskite oxides with various properties into heterostructures. Among the perovskite oxides, BaSnO3 (BSO) exhibits outstanding properties compared to other oxides. As a wide bandgap semiconductor, BSO has a high electron mobility as high as 320 cm2 V-1 s-1 even in degenerate doping region. Its high oxygen stability and low diffusion coefficient ensure the material integrity during fabrication process and allow the devices to maintain electrical properties, even under high-temperature in high-vacuum conditions.
This dissertation delves into the expansive potential of perovskite oxides, focusing on the ultra-wide bandgap semiconductor SrSnO3 (SSO) and high-k, low leakage dielectric SrHfO3 (SHO). The substitution of Ba2+ in BSO with Sr2+ leads to the formation of SrSnO3 (SSO), an ultrawide bandgap semiconductor. SSO shares the high mobility characteristics of BSO and features an ultrawide bandgap, which makes it a promising candidate for high-power device application. This work successfully achieves the high conductivity (σ ~ 3100 S cm-1) and high transmittance in deep-UV region (T ~ 78% at a wavelength of 300 nm) through systematic study of electrical and optical properties. A 120-nm-thick La-doped SSO film has the highest figure of merit (φTC = 2.65×10-3 Ω-1) among the well-known candidates for deep-UV transparent conducting oxides reported to date.
In addition, this dissertation explores the properties of the high-k dielectric SHO, grown on BSO, notable for SHOs ultra-low leakage current density. By finetuning the growth conditions and optimizing structural properties, we achieved a remarkably low leakage current density in SHO. The optimized dielectric properties include a high dielectric constant (k = 32), a leakage current density lower than 10-8 A cm-2 at 2 MV cm-1, and large breakdown field exceeding 4 MV cm-1. The significantly low leakage current density in SHO is attributed to its large bandgap (Eg ~ 6.1 eV), a substantial conduction band offset relative to BSO (CB offset ~ 3.3 eV), and a low density of defect states within the bandgap. Furthermore, the large conduction band offset, similar to that between SiO2 and Si (3.2 eV), also enables the epitaxial growth of SHO on Si substrates. These distinctive properties position SHO as an ideal gate oxide for low-power consumption devices, suitable for integration into both silicon-based and perovskite oxide semiconductor technologies.
Moreover, this study highlights the unique ability of the perovskite oxides to form epitaxial heterostructures with both dielectric and metallic layers. As a pioneering step, we have for the first time successfully demonstrated the fabrication of all perovskite epitaxial double gate field effect transistors (DG-FETs). These innovative DG-FETs integrate three distinct types of perovskite oxides: BaSnO3(BSO) as a high-mobility semiconductor, degenerately La-doped BaSnO3 (BLSO) as a metallic layer, and SrHfO3 (SHO) as a low-leakage high-k dielectric. DG-FETs are supposed to improve the performance and scalability of transistors by enhancing the gate controllability and effectively reducing short channel effect compared to traditional MOSFETs. In line with such expectations, our integration of an additional top gate to bottom-gate FETs (BG-FETs), thus forming a DG-FET, has led to enhancements in subthreshold swing, current drivability, and field-effect mobility compared. Advancing further, we have developed double-level DG-FETs (DL DGFETs) by adding another double gate FET on top of a DG-FET, demonstrating the remarkable stackability of the device structure and its performance. This was also validated by the confirmation of a 12-layer epitaxial growth through scanning transmission electron microscopy (STEM). This work does not only reveal the advantages of the BSO-SHO system but also paves a way for integration with other perovskite oxides and/or Si for more advanced electronic applications.페로브스카이트 산화물은 그들의 뛰어난 특성들로 인해 산화물 전자기술 분야에서 광범위한 관심을 받고 있다. 이러한 특성에는 높은 유전상수, 초전도성, 강유전성 및 고밀도 2차원 전자 가스(2DEG) 현상 등이 포함된다. 페로브스카이트 구조는 지구 맨틀에서 가장 많이 발견되는 규산염과 같은 산화물에서 발견되며, 이러한 구조의 다양성은 연구를 위한 풍부한 템플릿을 제공한다. 특히 주목할 만한 장점은 다양한 특성을 가진 페로브스카이트 산화물들을 적층하여 이종구조를 만들 수 있는 능력이다. 페로브스카이트 산화물 중에서 BaSnO3(BSO)는 다른 산화물들에 비해 뛰어난 특성을 보여준다. 넓은 밴드갭을 가지는 반도체인 BSO는 높은 도핑 영역에서도 320 cm2 V-1s-1의 높은 전자 이동성을 가지고 있다. 또한, 높은 산소 안정성과 낮은 확산 계수는 제작 과정 중 재료의 무결성을 보장하고, 고온 고진공 조건에서도 장치의 전기적 특성을 유지하게 한다.
이 학위 논문에서는 페로브스카이트 산화물의 광범위한 잠재력에 주목하며, 특히 초광대역 밴드갭 반도체인 SrSnO3(SSO)와 높은 유전상수, 낮은 누설 전류를 가지는 유전체인 SrHfO3(SHO)에 초점을 맞춘다. Ba2+를 Sr2+으로 대체함으로써 SrSnO3(SSO), 초광대역 밴드갭 반도체가 형성됩니다. SSO는 BSO의 높은 이동성 특성을 공유하며, 초광대역 밴드갭을 가지고 있어 고전력 장치 응용에 유망한 후보가 될 수 있다. 이 연구는 체계적인 전기 및 광학적 특성 연구를 통해 깊은 자외선 영역에서 높은 전도성(σ ~ 3100 S cm-1)과 높은 투과율(T ~ 78% at a wavelength of 300 nm)을 성공적으로 달성했다. 120 nm 두께의 란타늄이 도핑된 SSO 필름은 현재까지 보고된 깊은 자외선 투명 전도 산화물 후보 중 최고의 성능 지수(φTC = 2.65×10-3 Ω-1)를 가진다.
또한, 이 논문은 BSO 위에 성장된 높은 유전상수를 가지는 SHO의 특성을 탐구하며, 특히 SHO의 초저누설 전류 밀도에 주목한다. 성장 조건을 미세 조정하고 구조적 특성을 최적화함으로써 SHO에서 현저히 낮은 누설 전류 밀도를 달성했다. 최적화된 유전 특성에는 높은 유전 상수(k = 32), 2 MV cm-1 에서 10-8 A cm-2 이하의 낮은 누설 전류 밀도, 그리고 4 MV cm-1 를 초과하는 큰 파괴 전계가 포함된다. SHO의 놀랍도록 낮은 누설 전류 밀도는 큰 밴드갭(Eg ~ 6.1 eV), BSO와의 큰 전도대 오프셋(CB offset ~ 3.3 eV), 밴드갭 내 낮은 결함 상태 밀도로 인한 것이다. 또한 SHO와 BSO 사이의 높은 전도대 오프셋은 SiO2와 Si 사이의 오프셋(3.2 eV)과 비슷하며, 이미 SHO를 Si 기판 위에 에피택셜하게 성장시킬 수 있음이 알려져 있다. 이러한 독특한 특성은 SHO를 실리콘 기반 및 페로브스카이트 산화물 반도체 기술에 적합한 저전력 소비장치의 이상적인 게이트 산화물로 위치시킨다.
더 나아가 이 연구는 페로브스카이트 산화물이 다른 금속 또는 절연층과의 다층 이종 구조를 형성할 수 있는 독특한 능력을 강조한다. 이를 증명하기 위한 첫 번째 단계로, 우리는 BSO를 고이동성 반도체로, 과량으로 란타늄이 도핑된 BaSnO3 (BLSO)를 금속층으로, 그리고 SHO를 저누설 및 고유전율 유전체로 사용하여 모든 층이 에피텍셜하게 성장한 페로브스카이트 이중 게이트 트랜지스터 (DG-FET)를 성공적으로 구현하였다. DG-FET는 게이트 제어 능력을 향상시키고 기존 MOSFET에 비해 단채널 효과를 효과적으로 줄여 트랜지스터의 성능과 확장성을 향상시킨다. 우리는 바닥 게이트 FET(BG-FET)에 추가 상단 게이트를 통합하여 DG-FET를 형성함으로써, 서브스레숄드 스윙, 전류 구동 능력 및 필드 이펙트 이동성에 대한 향상을 이루었다. 한 단계 더 나아가, 우리는 DG-FET 위에 추가적인 이중 게이트를 증착함으로써 doublelevel DG-FET (DL DG-FET)를 제작하였으며, 장치 구조의 뛰어난 적 층성과 성능을 시연하였다. 또한, 주사 투과 전자 현미경(STEM)을 통해 디바이스의 모든 층이 에피텍셜하게 성장했음을 확인하였다. 이 성과는 BSO-SHO 시스템의 적층 가능성을 강조할 뿐만 아니라 보다 복잡한 장치 구조에 대한 잠재력을 시사한다. 이 연구는 페로브스카이트 기반 장치 분야에 튼튼한 기반을 마련하고 다른 페로브스카이트 산화물 또는 실리콘과의 통합을 통해 보다 진보된 전자 응용 분야로의 길을 열어줄 것이다.Abstract i
List of Contents iv
List of Figures and Tables vi
1. Introduction 1
1.1. Perovskite oxides 1
1.2. Ultra-wide bandgap semiconductors 1
1.3. High-k and low leakage dielectric 4
References 7
2. Deep-UV transparent conducting oxide La-doped SrSnO3 with high figure of merit 11
2.1. Introduction 11
2.2. Electrical properties of La-doped SrSnO3 thin films 16
2.2.1. Dependence of La-doping concentration 16
2.2.2. Dependence of the film thickness 18
2.3. Structural properties of 4% La-doped SrSnO3 thin films 20
2.4. Optical properties of 4% La-doped SrSnO3 thin films 31
2.5. Conclusion 33
References 35
3. Low leakage in high-k perovskite gate oxide SrHfO3 42
3.1. Introduction 42
3.2. Dielectric properties of SrHfO3 capacitors 46
3.3. Field-effect transistors using gate oxide SrHfO3 52
3.4. Structural properties of SrHfO3 55
3.5. Conclusion 65
References 67
4. Epitaxially stacked 12-layer perovskite oxides heterostructure as a double-level double-gate field-effect transistor 72
4.1. Introduction 72
4.2. Fabrication process 76
4.3. Electrical properties 78
4.4. Structural properties 88
4.5. Conclusion 90
References 92
5. Future works 97
5.1. Annealing effects on electrical properties of SLSO films 97
5.2. Conclusion 101
List of publications and presentations 103
Abstract in Korean 105박
Changes in the flavor formation and sensory attributes of Maillard reaction products by different oxidation degrees of beef tallow via cold plasma
No full textIt remains unclear how the oxidation degree of animal fat affects the flavor formation and sensory attributes of Maillard reaction products (MRPs). To oxidize beef tallow differentially under mild conditions, an atmospheric pressure cold plasma (APCP) was applied due to its easy, economical, and controllable manipulation and effectiveness. As the duration of APCP increased after 10 min, the oxidation degree of beef tallow increased significantly (p < 0.05). The beef tallow was incorporated into the cysteine-xylose model system and heated at 120 °C for 90 min. Volatiles from lipid oxidation products increased, whereas sulfur-containing compounds decreased significantly when the model included APCP-treated beef tallow (p < 0.05). MRPs with 10-min APCP-treated beef tallow showed reduced off-odor (p < 0.05). Thus, moderate APCP treatment to beef tallow may be beneficial for sensory attributes of MRPs. It suggests the potential of APCP to improve the flavor of heat-sensitive foods by controlling lipid oxidation.N
A sequential transit network design algorithm with optimal learning under correlated beliefs
No full textMobility service route design requires demand information to operate in a service region. Transit planners and operators can access various data sources including household travel survey data and mobile device location logs. However, when implementing a mobility system with emerging technologies, estimating demand becomes harder because of limited data resulting in uncertainty. This study proposes an artificial intelligence-driven algorithm that combines sequential transit network design with optimal learning to address the operation under limited data. An operator gradually expands its route system to avoid risks from inconsistency between designed routes and actual travel demand. At the same time, observed information is archived to update the knowledge that the operator currently uses. Three learning policies are compared within the algorithm: multi-armed bandit, knowledge gradient, and knowledge gradient with correlated beliefs. For validation, a new route system is designed on an artificial network based on public use microdata areas in New York City. Prior knowledge is reproduced from the regional household travel survey data. The results suggest that exploration considering correlations can achieve better performance compared to greedy choices and other independent belief-based techniques in general. In future work, the problem may incorporate more complexities such as demand elasticity to travel time, no limitations to the number of transfers, and costs for expansion.Y
Efficient Deep-Blue Light-Emitting Diodes Through Decoupling of Colloidal Perovskite Quantum Dots
No full textMetal halide perovskite light-emitting diodes (PeLEDs) have exceptional color purity but designs that emit deep-blue color with high efficiency have not been fully achieved and become more difficult in the thin film of confined perovskite colloidal quantum dots (PeQDs) due to particle interaction. Here it is demonstrated that electronic coupling and energy transfer in PeQDs induce redshift in the emission by PeQD film, and consequently hinder deep-blue emission. To achieve deep-blue emission by avoiding electronic coupling and energy transfer, a QD-in-organic solid solution is introduced to physically separate the QDs in the film. This physical separation of QDs reduces the interaction between them yielding a blueshift of approximate to 7 nm in the emission spectrum. Moreover, using a hole-transporting organic molecule with a deep-lying highest occupied molecular orbital (approximate to 6.0 eV) as the organic matrix, the formation of exciplex emission is suppressed. As a result, an unprecedently high maximum external quantum efficiency of 6.2% at 462 nm from QD-in-organic solid solution film in PeLEDs is achieved, which satisfies the deep-blue color coordinates of CIEy < 0.06. This work suggests an important material strategy to deepen blue emission without reducing the particle size to <approximate to 4 nm.Y
Structural Isomerism in Bimetallic Ag20Cu12 Nanoclusters
No full textStructural isomers of atomically precise metal nanoclusters are highly sought after for investigating structure-property relationships in nanostructured materials. However, they are extremely rare, particularly those of alloys, primarily due to the challenges in their synthesis and structural characterization. Herein, for the first time, a pair of bimetallic isomeric AgCu nanoclusters has been controllably synthesized and structurally characterized. These two isomers share an identical molecular formula, Ag20Cu12(C equivalent to CR)(24) (denoted as Ag20Cu12-1 and Ag20Cu12-2; HC equivalent to CR is 3,5-bis(trifluoromethyl)phenylacetylene). Single-crystal X-ray diffraction data analysis revealed that Ag20Cu12-1 possesses an Ag17Cu4 core composed of two interpenetrating hollow Ag11Cu2 structures. This core is stabilized by four different types of surface motifs: eight -C equivalent to CR, one Cu(C equivalent to CR)(2), one Ag3Cu3(C equivalent to CR)(6), and two Cu-2(C equivalent to CR)(4) units. Ag20Cu12-2 features a bitetrahedron Ag-14 core, which is stabilized by three Ag2Cu4(C equivalent to CR)(8) units. Interestingly, Ag20Cu12-2 undergoes spontaneous transformation to Ag20Cu12-1 in the solution-state. Density functional theory calculations explain the electronic and optical properties and confirm the higher relative stability of Ag20Cu12-1 compared to Ag20Cu12-2. The controlled synthesis and structural isomerism of alloy nanoclusters presented in this work will stimulate and broaden research on nanoscale isomerism.N
Expanding the diversity of lithium electrolytes
No full textImproving battery performance requires the careful design of electrolytes. Now, high-performing lithium battery electrolytes can be produced from non-solvating solvents by using a molecular-docking solvation strategy that takes advantage of intermolecular interactions between solvents to precisely control the solvation dynamics of lithium ions.N
Rates and Risk Factors of Progression in Patients With Nontuberculous Mycobacterial Pulmonary Disease: Secondary Analysis of a Prospective Cohort Study
No full textBackground: The clinical course of nontuberculous mycobacterial pulmonary disease (NTM-PD) is varied, and a watchful waiting management strategy is appropriate for a subset of patients. Understanding disease progression and risk factors for progression is essential for deciding on an appropriate follow-up strategy. Research Question: What is the rate of NTM-PD progression, and what are the predictors of progression? Study Design and Methods: Patients with NTM-PD who were enrolled in a prospective observational cohort study between July 1, 2011, and December 31, 2022, were included in this analysis. Clinical, bacterial, laboratory, and radiographic data were collected at enrollment and then regularly during follow-up. NTM-PD progression was defined as either the initiation of treatment or the clinician's intention to treat. The rate of progression was calculated and the predictors for progression were analyzed. Results: Of the 477 patients enrolled, NTM-PD progressed in 192 patients over a median follow-up of 5.4 years. The incidence of NTM-PD progression was 11.0 cases per 100 person-years (95% CI, 9.5-12.7 cases per 100 person-years). The proportion of patients experiencing disease progression was 21.4% at 1 year, 33.8% at 3 years, and 43.3% at 5 years. The final multivariable analysis model identified female sex (adjusted hazard ratio [aHR], 1.69; 95% CI, 1.19-2.39), elevated erythrocyte sedimentation rate (aHR, 1.79; 95% CI, 1.31-2.43), FEV1 % predicted (aHR, 0.89; 95% CI, 0.82-0.96), and the presence of a cavity (aHR, 2.78; 95% CI, 2.03-3.80) as predictors of progression. Interpretation: About one-half of patients with NTM-PD experienced progression during an observation period of > 5 years. Patients with risk factors for progression should be observed closely. Trial Registry: ClinicalTrials.gov; No.: NCT01616745; URL: www.clinicaltrials.govN
A Career in Catalysis: Mark E. Davis
No full textMark E. Davis led an independent research program from 1981 to 2023, beginning at the Virginia Polytechnic Institute and State University (VPI) and then transitioning to the California Institute of Technology (Caltech). His research program was marked by exceptional creativity, breadth, and depth. With classical training in reaction engineering, Davis developed expertise in experimental heterogeneous catalysis and led work in this discipline for more than 40 years. His name is synonymous with zeolites, and today, he is one of the most widely recognized experts in zeolite synthesis, characterization, and catalysis in the world. Early work at the VPI focused on zeolites and catalysis with supported metal coordination complexes. His creativity was evident at the earliest stages of his career, with the development of supported aqueous phase catalysts and the world's first crystalline, extra-large pore molecular sieve, both reported in the late 1980s. A move to Caltech saw a significant expansion of his zeolite synthesis program and the rapid acceleration of a multidecade collaboration with Dr. Stacey I. Zones of Chevron. At Caltech, his work expanded to include studies of molecular recognition and catalysis with organic/inorganic hybrid materials, and he developed a large, parallel program in drug delivery. His work on catalysis heavily emphasized zeolite catalysis, including major thrusts on the conversion of sugars in the liquid phase and methanol in the gas phase. Numerous new zeolites and molecular sieves were discovered throughout the four decades of the Davis laboratory, highlighted by a successful, multidecade quest to prepare a chiral zeolite with enantioselective catalytic properties. Davis is one of the most decorated researchers of the last four decades. He is one of only 21 living people currently elected to all of the US National Academies (Engineering, Science, Medicine) and elected as a Fellow of the National Academy of Inventors. He was the first engineer to win the NSF's Alan T. Waterman Award and is one of only two researchers (to date) to win the International Zeolite Association's Donald Breck Award twice (1989, 2019). Awards from the ACS (Ipatieff, Murphree, and Somorjai Awards), AIChE (Colburn, Professional Progress Awards), and North American Catalysis Society (Emmett Award) are among his accolades.Y
Aligning Large Language Models via Fine-grained Supervision
No full textPre-trained large-scale language models (LLMs) excel at producing coherent articles, yet their outputs may be untruthful, toxic, or fail to align with user expectations. Current approaches focus on using reinforcement learning with human feedback (RLHF) to improve model alignment, which works by transforming coarse human preferences of LLM outputs into a feedback signal that guides the model learning process. However, because this approach operates on sequence-level feedback, it lacks the precision to identify the exact parts of the output affecting user preferences. To address this gap, we propose a method to enhance LLM alignment through fine-grained token-level supervision. Specifically, we ask annotators to minimally edit less preferred responses within the standard reward modeling dataset to make them more favorable, ensuring changes are made only where necessary while retaining most of the original content. The refined dataset is used to train a token-level reward model, which is then used for training our fine-grained Proximal Policy Optimization (PPO) model. Our experiment results demonstrate that this approach can achieve up to an absolute improvement of 5.1% in LLM performance, in terms of win rate against the reference model, compared with the traditional PPO model.N