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Intensifying Humid-Heat Extremes in Asia
No full textThis dissertation investigates the intensification of humid-heat extremes across monsoon Asia, emphasizing the roles of monsoon dynamics and external forcings such as greenhouse gases (GHGs) and aerosols. The first part demonstrates that humid-heat extremes (ExTw) are rising rapidly in the monsoon-influenced parts of Asia due to increasing specific humidity (Q). Diagnostics based on RH and Q indicate that moisture availability, modulated by SST warming, urbanization, irrigation, and circulation changes including the westward expansion of the WPSH, is not just a modifier but a central driver f heat stress. The second part focuses on the Indo-Gangetic Plain (IGP) and finds that long-term RH increases are driven mainly by rising Q, aerosol-induced surface cooling, and stabilized T, while GHG-driven warming tends to suppress RH by enhancing saturation vapor pressure. CESM2-LE, CESM1-LE, and CMIP6 simulations confirm these opposing thermodynamic responses. Future projections show RH increase under high aerosol loadings (e.g., early SSP3-7.0), followed by reversals as aerosol decline and GHG warming accelerates. This scenario contrast is clearly seen across SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, emphasizing that future RH trajectories over the IGP are shaped by a delicate balance between competing forcings, and that their evolution remains highly uncertain, contingent on the pace of aerosol decline and the strength of GHG-driven warming. The third part examines structural intensification of the East Asian summer monsoon (EASM) lifecycle, characterized by stronger active phases and prolonged breaks. Observation shows this intensification is ties to WPSH expansion, which multiple studies suggest, via a thermodynamic response to greenhouse warming. This altered lifecycle increases the likelihood of sequential extremes, such as flood-to-heatwave transitions, and is better captured by models that realistically simulate the EASM rainband and its migration. Together these findings highlight that rising humid- heat risks result from the coupled effect of atmospheric moistening, seasonal reorganization of monsoon system, and externally forced thermodynamic shifts. While RH trends are governed by a balance between moisture accumulation and temperature-driven saturation, changes in the EASM lifecycle, particularly the intensification of monsoon break, further compound the risks of sequential extremes. Effective climate risk assessments must account for both humidity and temperature, along with structural changes in the monsoon, especially under shifting emission pathways. Mitigation strategies should jointly address GHG and aerosol emissions, and heat risk frameworks must incorporate humidity to more accurately represent compound heat stress.DoctorAbstract i
LIST OF FIGURES v
LIST OF TABLES vii
Ⅰ. Introduction 1
1.1. Research background and motivation 1
1.2. Objective and Overview 5
1.3. Literature review 6
1.3.1. Humidity and the Divergence of Heat Extremes in Asia 6
1.3.2. External Forcings and Humidity Dynamics in Asian Monsoon Region 8
1.3.3. Seasonality Change in the East Asian Summer Monsoon 10
Ⅱ. Rising Humid-Heat Extremes and Their Underlying Mechanisms in Monsoon Asia 12
2.1. Introduction 12
2.2. Data and Methodology 15
2.2.1 Reanalysis Datasets 15
2.2.2 Definition of Heat Extremes 16
2.2.3 Defining Regions and Periods for Comparative Analysis of Extreme Heat Trends 17
2.3. Results 18
2.3.1 Divergent Trends in Extreme Heat Events Across the Monsoon-Arid Gradient 18
2.3.2 Climatic Drivers of Diverging Heatwaves 26
2.4. Discussion 32
Ⅲ. Quantifying External Drivers of Rising Relative Humidity in the Indo-Gangetic Plain 34
3.1. Introduction 34
3.2. Data and Methodology 38
3.2.1 Reanalysis Datasets 38
3.2.2 Model Datasets 40
3.2.3 Humidity Metrics: Derivation and Decomposition by T and Q 43
3.2.4 Single-to-Noise Ratio (SNR) Analysis 44
3.3. Results 45
3.3.1 Long-Term Trends in RH over the IGP 45
3.3.2 Attribution of RH Trends to External Forcings: GHGs and Aerosols 53
3.3.3 Future Evolution of RH over the IGP: Insights from CESM2-LE Projections 64
3.4. Discussion 66
IV. EASM Lifecycle Change and the Rising Risk of Compound Extremes in East Asia 69
4.1. Introduction 69
4.2. Data and Methodology 71
4.2.1 Observational and reanalysis data 71
4.2.2. CMIP6 Model Data 73
4.2.3. Definition of Monsoon Lifecycle Phases 75
4.2.4. Diagnostics of Dry Spell Characteristics and Moisture Convergence 77
4.2.5. Model Group Classification 78
4.3. Results 79
4.3.1 Analysis from Observational and reanalysis data 79
4.3.2. Model evaluation and Group Classification Based on EASM Lifecycle Representation 88
4.4. Discussion 97
Ⅴ. Summary and Conclusion 99
Ⅵ. Reference 102
Curriculum Vitae 10
Transcriptomic Responses of Testis to Aging and Ethanol in Mice
No full textPART I: Transcriptomic Responses of Testis to Aging in Mice
Male reproductive aging, or andropause, is associated with gradual age-related changes in testicular properties, sperm production, and erectile function. The testis, which is the primary male reproductive organ, produces sperm and androgens. To understand the transcriptional changes underlying male reproductive aging, I performed transcriptome analysis of aging testes in mice. A total of 31,386 mRNAs and 9387 long non-coding RNAs (lncRNAs) were identified in the mouse testes of diverse age groups (3, 6, 12, and 18 months old) by total RNA sequencing. Of them, 1571 mRNAs and 715 lncRNAs exhibited changes in their levels during testicular aging. Most of these aging-related transcripts exhibited slight and continuous expression changes during aging, whereas some (9.6%) showed larger expression changes. The aging-related transcripts could be classified into diverse expression patterns, in which the transcripts changed mainly at 3-6 months or at 12-18 months. My subsequent in silico analysis provided insight into the potential features of testicular aging-related mRNAs and lncRNAs. I identified testis-specific aging-related transcripts (121 mRNAs and 25 lncRNAs) by comparison with a known testis-specific transcript profile, and then predicted the potential reproduction-related functions of the mRNAs. By selecting transcripts that are altered only between 3 and 18 months, I identified 46 mRNAs and 34 lncRNAs that are stringently related to the terminal stage of male reproductive aging. Some of these mRNAs were related to hormonal regulation. Finally, my in silico analysis of the 34 aging-related lncRNAs revealed that they co-localized with 19 testis-expressed protein-coding genes, 13 of which are considered to show testis-specific or -predominant expression. These nearby genes could be potential targets of cis-regulation by the aging-related lncRNAs. Collectively, my results identify a number of testicular aging-related mRNAs and lncRNAs in mice and provide a basis for the future investigation of these transcripts in the context of aging-associated testicular dysfunction.
PART II: Transcriptomic Responses of Testis to Ethanol in Mice
Alcohol consumption is widely known to have detrimental effects on various organs and tissues. The effects of ethanol on male reproduction have been studied at the physiological and cellular levels, but no systematic study has examined the effects of ethanol on male reproduction-related gene expression. I employed a model of chronic ethanol administration using the Lieber-DeCarli diet. Ethanol-fed mice showed normal testicular and epididymal integrity, and sperm morphology, but decreased sperm count. Total RNA sequencing analysis of testes from ethanol-fed mice showed that a small fraction (∼ 2%) of testicular genes were differentially expressed in ethanol-fed mice and that, of these genes, 28% were cell-type specific in the testis. Various in silico analyses were performed, and gene set enrichment analysis revealed that sperm tail structure-related genes, including forkhead box J1 (Foxj1), were down-regulated in testes of ethanol-fed mice. Consistent with this result, ethanol- fed mice exhibited decreased sperm motility. This study provides the first comprehensive transcriptomic profiling of ethanol-induced changes in the mouse testis, and suggests gene expression profile changes as a potential mechanism underlying ethanol-mediated reproductive dysfunction, such as impaired sperm motility.|Part I. 생쥐에서의 노화에 따른 정소 전사체 반응
남성 생식 노화 (Andropause)는 정소의 구조 및 기능 변화, 정자 생성 감소, 발기 기능 저하 등과 관련된 점진적인 생리적 변화로 정의된다. 본 연구에서는 생쥐 고환의 연령별 전사체 분석을 통해 생식 노화에 수반되는 전사적 변화를 규명하고자 하였다. RNA 시퀀싱을 통해 3, 6, 12, 18 개월령 생쥐 정소에서 31,386 개의 mRNA 와 9387 개의 긴 비암호화 RNA (lncRNA)를 동정하였으며, 이 중 1571 개의 mRNA 와 715 개의 lncRNA 가 연령에 따라 유의한 발현 변화를 보였다. 대부분의 노화 관련 전사체는 작고 점진적인 발현 변화 양상을 보였으나, 약 9.6%는 뚜렷한 변화 폭을 나타냈다. 발현 패턴 분석을 통해 이들 전사체는 3–6 개월 또는 12–18 개월 구간에서 주요한 변화를 보이는 군으로 분류되었다. 이어진 in silico 분석을 통해 정소 특이적 전사체와의 비교를 통해 노화 관련 정소 특이 전사체(121 개 mRNA, 25 개 lncRNA)를 규명하였고, 일부는 생식 기능 조절과 관련된 기능을 가질 것으로 예측되었다. 특히, 3 개월과 18 개월 사이에서만 변화하는 전사체를 기준으로 노화와 연관된 mRNA(46 개)와 lncRNA(34 개)를 선별하였으며, 일부는 호르몬 조절에 관여하는 것으로 나타났다. 또한, 노화 관련 lncRNA 중 34 개는 정소 특이적으로 발현되는 단백질 코딩 유전자(19 개)에 가까이 위치 (co-localize)하며, 이들 중 13 개는 cis-조절의 잠재적 표적일 수 있음을 제시하였다. 본 연구는 정소 노화와 관련된 전사체 네트워크를 포괄적으로 제시하며, 남성 생식 기능 저하의 분자적 기전을 이해하는 데 기초 자료를 제공한다.
Part II. 생쥐에서의 에탄올 급여에 따른 정소 전사체 반응
알코올 섭취는 다양한 장기와 조직에 해로운 영향을 미치는 것으로 널리 알려져 있다. 에탄올이 남성 생식에 미치는 영향은 생리학적 및 세포 수준에서 여러 차례 연구되었지만, 생식 관련 유전자 발현에 미치는 영향을 체계적으로 분석한 연구는 없었다. 본 연구에서는 Lieber-DeCarli 식이법을 이용한 만성 에탄올 급여 모델을 사용하였다. 에탄올을 투여받은 마우스는 정소과 부정소의 구조적 이상은 없었으며, 정자 형태 역시 정상이었으나 정자 수는 감소하였다. 에탄올 급여 마우스의 정소에 대해 수행한 RNA 시퀀싱 분석 결과, 정소 유전자 중 약 2% 정도만이 차등 발현되었으며, 이 중 28%는 정소 내의 세포 특이 발현 유전자였다. 다양한 in silico 분석을 수행한 결과, 유전자 집합 풍부도 분석 (GSEA)에서 Foxj1 을 포함한 일부 정자 꼬리 구조 관련 유전자의 발현이 감소됨이 확인되었다. 이러한 결과에 부합하게, 에탄올 급여 마우스는 정자 운동성 감소를 보였다. 본 연구는 에탄올 급여에 따른 정소 전사체 변화를 포괄적으로 규명한 최초의 연구로서, 에탄올로 인한 생식 장애, 특히 정자 운동성 저하의 잠재적 기전으로서 유전자 발현 변화의 가능성을 제시한다.DoctorABSTRACT ⅰ
CONTENTS iii
LIST OF FIGURES v
LIST OF TABLES vii
PART I. Transcriptomic Responses of Testis to Aging in Mice
1. INTRODUCTION 2
2. MATERIALS AND METHODS 4
2. 1. Animals and RNA preparation 4
2. 2. Total RNA sequencing 4
2. 3. Tissue expression estimation 4
2. 4. Investigating the potential features of aging-related transcripts 5
3. RESULTS 6
3. 1. Identification of mRNAs and lncRNAs in mouse testes during aging 6
3. 2. Global expression and transcriptomic features of mRNAs and lncRNAs expressed in mouse testes
during aging 6
3. 3. Aging-related expression patterns of mRNAs and lncRNAs 7
3. 4. Testis-specific expression of aging-related mRNAs and lncRNAs 8
3. 5. Potential features of aging related transcripts showing changes between 3M and 18M 9
3. 6. Potential cis-regulatory targets of aging-related lncRNAs 9
4. DISCUSSION 64
PART II. Transcriptomic Responses of Testis to Ethanol in Mice
1. INTRODUCTION 68
2. MATERIALS AND METHODS 70
2. 1. Animals 70
2. 2. Ethanol administration 70
2. 3. Total RNA sequencing 70
2. 4. Histological analysis of testis and liver 71
2. 5. Sperm motility analysis with OpenCASA 71
2. 6. Quantitative real-time RT-PCR 71
3. RESULTS 72
3. 1. Effect of ethanol administration on male reproductive tissues 72
3. 2. Transcriptomic analysis of testes from ethanol-fed mice 72
3. 3. Gene set enrichment analysis (GSEA) of testes from ethanol-fed mice 73
3. 4. Motility of sperm from ethanol-fed mice 74
4. DISCUSSION 116
REFERENCES 119
ABSTRACT IN KOREAN 123
ACKNOWLEDGEMENT 125
CURRICULUM VITAE 12
Development of tRNA Scaffold for Facilitated Recombinant RNA Purification
No full textThis study explored novel methods for RNA purification using recombinant RNA engineering. Existing RNA purification methods often involve denaturing processes that are time-consuming and compromise RNA stability and folding. In this study, two innovative approaches were developed for RNA purification. First, mRNA capping was applied to recombinant RNA to function as an affinity tag for RNA. Second, split and circularly permuted tRNA scaffolds were designed to carry a target RNA stably. The integration of these two strategies enables the development of a new non-denaturing RNA purification method. The Vaccinia virus capping enzyme and recombinant RNA were successfully co-expressed in Escherichia coli. Binding assays with the cap-binding protein eIF4E did not confirm the capping. Next, recombinant tRNA scaffolds were designed using the E. coli tRNA operons (LeuP-LeuV and AlaW-AlaX) fused to the FMN riboswitch as a target RNA. While the expressions of the tRNALeu P-V scaffold-FMN riboswitch fusions were confirmed, evaluating factors such as identifying the exact target band on a gel and high expression levels was challenging. In contrast, the tRNAAla W-X scaffold-FMN riboswitch fusions exhibited higher expression levels. Notably, the FMN riboswitch-tRNAAlaW-X construct showed more promise. Although further optimization is necessary, this study suggests new pathways for RNA purification technologies.MasterAbstract ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ i
Contents ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ ii
List of Tables ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ ⅳ
List of Figures ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ ⅴ
I. INTRODUCTION ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 1
1. 1. Ribonucleic acid ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 1
1. 2. Existing Methods for RNA Purification ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 1
1. 3. Capping of Recombinant RNA ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 2
1. 4. Split and Circularly Permuted tRNA Scaffold Development ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 3
1. 5. Research Directions ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 5
II. Materials and Methods ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 7
2. 1. tRNASer Cloning and In vivo Transcription ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 7
2. 2. tRNASer Extraction and Purification ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 7
2. 3. Cloning of the Vaccinia Virus Capping Enzyme ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 8
2. 4. Co-expression and Purification of D1∙D12 and tRNASer ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 8
2. 5. Expression and Purification of eIF4E ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 8
2. 6. Binding Assay of Co-expressed tRNASer and eIF4E ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 9
2. 6. 1. Size Exclusion Chromatography ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 9
2. 6. 2. Affinity Chromatography․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 9
2. 7. Cloning and In vivo Transcription of tRNA-RNA Fusion Constructs ․․․․․․․․․․․․․․․․․ 10
2. 8. Extraction of tRNA-RNA Fusion ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 10
2. 9. Isolation of tRNA-RNA Fusion with Size Exclusion Chromatography․․․․․․․․․․․․․․․․ 10
2. 10. Purification of tRNA-RNA Fusion with Anion Exchange Chromatography ․․․․․․․․ 11
2. 11. Binding assay with Co-lysis of Co-expressed tRNA Scaffold-FMN Riboswitch
Fusion and eIF4E Protein ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 11
Ⅲ. Results ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 12
3. 1. Co-expression of Vaccinia Virus Capping Enzyme and tRNA in E. coli ․․․․․․․․․․․․․․․ 12
3. 2. Binding Assays of Co-expressed tRNA and Cap-binding Protein ․․․․․․․․․․․․․․․․․․․․․․․ 12
3. 3. Construct Design of Circularly Permuted Split tRNA Scaffold ․․․․․․․․․․․․․․․․․․․․․․․․․․ 13
3. 4. Expression and Purification of the tRNALeu P-V Scaffold-FMN Riboswitch Fusion ․․․․ 13
3. 5. Binding Assay with Co-lysis of Capping Enzyme Co-expressed
tRNALeu P-V Scaffold-FMN Riboswitch Fusion and eIF4E Protein ․․․․․․․․․․․․․․․․․․․․․․․ 14
3. 6. Expression of the tRNAAla W-X Scaffold-FMN Riboswitch Fusion ․․․․․․․․․․․․․․․․․․․․․․․ 14
Ⅳ. Discussion ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 16
References ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 33
Summary ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 36
Acknowledgments ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 3
Development of Transition Metal Catalysts bearing N-Heterocyclic Carbene for Bond-Forming Reactions
No full textN-Heterocyclic carbenes (NHCs) have been widely utilized in organic synthesis since the first isolation of a representative free carbene by Arduengo in 1991.Their strong σ-donating ability and tunable steric hinderance have established NHCs as essential ligands in transition-metal catalysis. In 2005, Glorius and Lassaletta introduced Imidazo[1,5-a]pyridin-3-ylidene (ImPy) as a bicyclic, backbone-modified variant of NHCs. ImPy uniquely enables substituents to be positioned in close proximity to the metal coordination sphere, while simultaneously allowing the introduction of a substituent on the N-wingtip side. This orthogonality inherent to ImPy has facilitated the development of novel catalysts, which have been applied to a variety of reactions. In Part 1, the thesis aims to review the development and applications of previously reported ImPy ligands. The key feature of ImPy is its orthogonality, which allows for flexible combinations of its C5 and N2 positions with a wide variety of substituents. Examples of substituents introduced at each position will be categorized. The ImPy derivatives have been used to introduce new catalytic concepts and enhance reactivity in transition-metal- catalyzed transformations. Part 2 focuses on the development of bifunctional ImPy palladium complexes, where ImPy is modified with an ether linkage at the N2-wingtip. These complexes are then applied in the activation of the deprotonation step in Pd-catalyzed amination reactions. Various NHCs have been developed as catalysts for Pd-catalyzed amination, typically following the common strategy. This common strategy involves the strong σ-donating ability of NHC ligands accelerating oxidative addition, while steric effects control the reductive elimination step. We propose that specifically targeting the deprotonation step could introduce novel improvements in catalytic performance while maintaining the advantages of existing strategies. By comparing the reactivity of bifunctional ImPy-Pd complexes, we sought to validate this hypothesis. The molecular structure of ImPy-Pd complexes was confirmed through single-crystal X-ray diffraction studies. Based on these crystal structures, we further supported our findings with PhD/CH 20172015 buried volume analysis and computational calculations. In Part 3, an in-situ generated phosphine-chelated ImPy nickel complex is employed in the catalytic conversion of ethylene and CO2 into acrylates. This reaction presents an innovative method of transforming CO2, a major greenhouse gas, into acrylates, which are traditionally produced from petrochemical sources. However, significant challenges remain in achieving this transformation efficiently. We aim to address these challenges by employing a rigid, highly planar catalyst, which has demonstrated the highest reported turnover number (TON) for this reaction while maintaining high yields. This chapter will detail the development of this catalytic system and the optimization process that led to its exceptional reactivity.DoctorABSTRACT·i
TABLE OF CONTENTS·iii
LIST OF FIGURESvii
LIST OF SCHEMESix
LIST OF TABLES x
CHAPTER 1. Overview of Imidazo[1,5-a]pyridin-3-ylidene 1
1.1 Introduction to ImPy Ligands· 2
1.2 C5-Position Substituents 4
1.2.1 C5-Alkyl and Aryl Substituents 4
1.2.2 C5-Nitrogen-Containing Groups· 7
1.2.3 C5-Oxygen-Containing Groups· 10
1.2.4 C5-Miscellaneous-Containing Groups 13
1.2.5 C5-Chirality-Containing Groups 16
1.3 N2-Position Substituents 19
1.3.1 N2-Position Steric Adjustments· 19
1.3.2 N2-Bifunctionality 21
1.3.3. N2-Chirality 22
1.4 References 23
CHAPTER 2. Bifunctional Palladium Imidazo[1,5-a]pyridin-3-ylidene Catalysts for
Buchwald-Hartwig Amination 25
2.1 Introduction· 26
2.2 Results and Discussion 29
2.2.1 Synthesis of ImPy-Pd-PEPPSI Complexes 29
2.2.2 Catalytic activity of ImPy-Pd-PEPPSI Complexes 30
2.2.3 Synthesis of Bifunctional ImPy-Pd-PEPPSI Complexes 33
2.2.4 Catalytic Activity of Bifunctional ImPy-Pd-PEPPSI Complexes 35
2.2.5 Characterization of ImPy-Pd-PEPPSI Complexes 38
2.3 Conclusion 39
2.4 Experimental Section 40
2.4.1 General Information 40
2.4.2 General Procedure for Synthesis of ImPy Ligands and Catalysts· 41
2.4.3 General Procedures for Pd-Catalyzed Amination Reaction 62
2.5 References 64
APPENDIX 1: NMR Spectra of Compounds Relevant to Chapter 2· 66
CHAPTER 3. In Situ Generated Diphenylphosphine-Chelated Imidazo[1,5-a]pyridin-3-
ylidene Nickel(0) Catalysts for Highly Efficient Acrylate Synthesis from Ethylene and
CO 285
3.1 Introduction· 86
3.2 Results and Discussion 89
3.2.1 Synthesis and Structural Analysis of PPh2-ImPy Nickel Complexes 89
3.2.2 Proposed Catalytic Mechanism for Ethylene-CO2 Conversion 90
3.2.3 Structural Comparison of Nickelalactone Complexes 93
3.2.4 Acrylate Synthesis with Ethylene and CO2· 95
3.2.5 Control Experiments· 98
3.2.6 Isolation of Sodium Acrylate Product 100
3.2.7 Potential Role of Sodium Acetate 101
3.3 Conclusion· 103
3.4 Experimental Section· 104
3.4.1 General Information 104
3.4.2 Synthesis of PPh2-ImPy ligand precursors and nickel complexes· 105
3.4.3 General procedures for acrylate synthesis from ethylene and CO 2111
3.4.4 Previously reported results and additional optimizations· 112
3.4.5 Structure refinement data 116
3.4.6 Computational Details 120
3.5 References· 135
APPENDIX 2: NMR Spectra of Compounds Relevant to Chapter 313
High-Performance Nickel-Bismuth Oxide Electrocatalysts Applicable to Both the HER and OER in Alkaline Water Electrolysis
No full textAs an electrocatalyst for water electrolysis, nickel oxide (NiO) has received significant attention due to its cost-effectiveness and high reactivity among non-noble-metal-based catalytic materials. However, NiO still exhibits poor alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics compared to conventional noble metal-based catalysts. This is because NiO has a strong interaction with protons for the HER and too low free energy of the OH* state, resulting in slower rate-determining step (RDS) kinetics for the OER. To address these issues, adding a dopant is suggested as an efficient method to modify the electron structure of the NiO electrocatalyst favorably for each reaction kinetics. In this context, we demonstrate that Bismuth (Bi), due to its higher electronegativity than that of Nickel (Ni), induces a positive charge on Ni sites. This enhances the catalytic activity by reducing the number of excessive cation interactions with the NiO electrocatalyst. Moreover, as the Bi ratio increases, the Ni reaction sites in NiO become more positively charged, and these changes in the electronic structure directly impact the free energy of the reaction mechanism. Particularly, it is confirmed that for the HER, Bi additives increase the proton-adsorbed free energy toward a near-zero value and, additionally, decrease the free energy difference of the second step considered as the RDS in the OER, as calculated by density functional theory. The positive effects of Bi in both the HER and the OER are demonstrated in practical electrochemical evaluations of half/single cells. Notably, the Bi-containing catalysts Bi05:NiO and Bi02:NiO exhibit remarkable alkaline HER and OER kinetics, showing performance improvements of 97.0% and 21.9%, respectively. © 2025 The Authors. Published by American Chemical Society.TRUEsciescopu
Divergent trends of Tmax-based and Tw-based heat extremes across Asia's climatic divide
No full textThis study investigates the contrasting trends in extreme Tmax events and extreme wet-bulb temperature (Tw) events across the monsoon and arid regions of Asia using the ERA5 reanalysis dataset. Our analysis reveals a substantial shift in the monsoon region, where extreme Tw events have risen by 1.95 days, outpacing the increase in extreme Tmax events. In the arid region, extreme Tmax events have increased more significantly, exceeding extreme Tw by an average of 2.05 days in recent years, reflecting the limited moisture availability in this area. Spatiotemporal analyses also reveal the widespread prevalence of humid-heat extremes in monsoon Asia and the intensification of primarily dry heat extremes in arid regions. These divergent trajectories highlight the pivotal role of climatological differences, with the change in monsoonal circulations amplifying humid extremes, while the inherent aridity constrains humidity increases. Our findings emphasize the need for regional adaptation strategies and mitigation efforts to address the escalating impacts on human society and ecosystems across Asia's climatic divide.TRUEsciescopu
Speech Enhancement based on cascaded two flows
No full textSpeech enhancement (SE) based on diffusion probabilistic models has exhibited impressive performance, while requiring a relatively high number of function evaluations (NFE). Recently, SE based on flow matching has been proposed, which showed competitive performance with a small NFE. Early approaches adopted the noisy speech as the only conditioning variable. There have been other approaches which utilize speech enhanced with a predictive model as another conditioning variable and to sample an initial value, but they require a separate predictive model on top of the generative SE model. In this work, we propose to employ an identical model based on flow matching for both SE and generating enhanced speech used as an initial starting point and a conditioning variable. Experimental results showed that the proposed method required the same or fewer NFEs even with two cascaded generative methods while achieving equivalent or better performances to the previous baselines. © 2025 International Speech Communication Association. All rights reserved
Biophysical investigation of the molecular interaction between minichromosome maintenance protein 6 and Bloom syndrome helicase
No full textThe minichromosome maintenance protein (MCM) complex and Bloom syndrome helicase (BLM) are crucial components in DNA replication and cell division. MCM, a hexameric helicase that unwinds double-stranded DNA, serves as an important diagnostic and prognostic biomarker for cancer cells and a target for anticancer drug development. BLM, associated with G-quadruplex structures, is another key helicase in maintaining genomic stability. In this study, we investigate the interaction between MCM6 and BLM at the atomic level, as their expression levels are highly correlated in various cancer types, with elevated levels indicating poor prognosis. To elucidate the molecular basis of MCM6/BLM interaction, we employed fluorescence polarization anisotropy analysis, NMR chemical shifts perturbation analysis (CSP), and paramagnetic relaxation enhancement (PRE) experiments. MCM6 binding domain (MBD) C and D exhibit similar binding affinities to MCM6 winged-helix domain (WHD). However, significant CSPs with MBD-D and PRE experiments suggested that MBD-D is closer to MCM6 WHD than MBD-C. Despite both proteins containing numerous negatively charged residues, hydrophobic interactions govern the association between MCM6 WHD and BLM MBD-D. This biophysical characterization of the MCM6/BLM interaction provides new insights into their functional relationship and challenges existing models. Our findings reveal that MCM6 binds BLM at a different site than its other known partner chromatin licensing and DNA replication factor. Understanding these protein-protein interactions at the molecular level may contribute to the development of novel anticancer therapies targeting the MCM6/BLM interaction.TRUEsciescopu
Assessment of surface water quality impacted by upstream artisanal mining in Prek Te area, Cambodia
No full textMining activities can significantly impact water quality by introducing various contaminants into water sources. The purpose of this study is to assess heavy metal concentrations and other elemental contaminants in water from the Prek Te area across two seasons and evaluate the potential health risks associated with drinking contaminated water. Surface water samples were collected twice in 2023: from March 5 – 11 (dry season) to October 20 – 26 (rainy season). A total of 21 surface water samples were collected from different locations along the Prek Te area. On-site measurements included pH, electrical conductivity, dissolved oxygen, and total dissolved solids, while laboratory analyses determined arsenic (As), chromium, nickel (Ni), copper, zinc, cadmium, and lead concentrations using inductively coupled plasma mass spectrometry. The results indicated that most parameters were within the World Health Organization guidelines and Cambodia Drinking Water Quality Standards, except for As and Ni. During the rainy season, the highest As concentration was 58.1 µg/L, followed by 22.0 µg/L and 10.8 µg/L. Health risk assessments revealed that the hazard index and hazard quotient for children exceeded 1, indicating potential non-carcinogenic health risks. In addition, children exhibited the highest lifetime cancer risk for As (>1.8 × 10−1), followed by women (>1.2 × 10−1) and men (>1 × 10−1). These findings suggest that children are more vulnerable to health risks associated with drinking contaminated water compared to adults. To ensure safe drinking water for communities along the Prek Te area, an urgent monitoring program and appropriate water treatment measures—particularly to remove As contamination—are recommended. © 2025 Elsevier B.V., All rights reserved.TRUEscopu
Fabrication and Characterization of GaAs Photoconductive Semiconductor Switches
No full textPhotoconductive Semiconductor Switches (PCSSs) are being researched as promising optoelectronic devices capable of playing critical roles in high-power electronics. PCSSs have unique advantages over traditional high-power switches, such as spark gaps, insulated gate bipolar transistors (IGBTs), and thyristors, including ultra-fast switching speed, stable operation, and very low jitter characteristics. These features make PCSSs attractive in high- power applications requiring rapid response, especially in solid-state microwave generation technologies, which are key for ultra-wideband (UWB) signal and high-power microwave (HPM) signal generation devices. Various semiconductor materials can be used for PCSS, each with distinct material properties suitable for specific applications. Gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), and diamond are candidate materials being explored for PCSS applications. In this study, we fabricated and analyzed the characteristics of semi-insulating GaAs- based PCSSs. The output characteristics of the fabricated PCSSs were measured using both front-side and back-side illumination, with back-side illumination demonstrating higher operating voltages and peak output voltages. Simulation results indicated that back-side illumination contributes to an even distribution of the electric field within the semiconductor, reducing the susceptibility to surface flashover at the edges of the electrodes caused by high electric fields. Additionally, back-side illumination was found to lower the contact resistance between the semiconductor and metal, improving overall output performance by generating electron-hole pairs within the semiconductor. Jitter, a key factor affecting device reliability and synchronization, was measured using TDSJIT3 equipment, yielding a value of 7–17 ps under a bias voltage of up to 1.5 kV. The operating limit voltage of the PCSS is primarily determined by the breakdown voltage of the semiconductor material; however, practically, the surface flashover occurring at electric fields above 10 kV/cm restricts both the operating voltage and the device lifetime. Although theoretical explanations for surface flashover are not yet fully established, we analyzed this phenomenon based on existing literature to enhance surface withstand characteristics. Surface passivation using silicon resin (Eb>165 kV/cm), SiNx, and SiO₂ was attempted, with silicon resin in particular proving effective. Compared to the previous back-side illumination where flashover occurred at 1.8 kV, devices with silicon resin passivation exhibited flashover at 3.8 kV, significantly enhancing the operating and flashover voltages of the PCSS. To enhance PCSS output, an interdigitated structure was investigated, which increases electrode perimeter. In this study, we applied a comb electrode structure and analyzed its characteristics. By varying the comb electrode length from 0 to 750 μm, we found that as the comb electrode length increased, the peak voltage increased by up to 3.53 times under a 1 kV bias voltage. Additionally, the operating voltage improved from 1.5 kV to over 3 kV, and the device's on-resistance decreased by up to a factor of 10, leading to enhanced output voltage, operating voltage, and breakdown voltage. To further investigate the effect of the comb structure, we conducted experiments using a cylindrical lens to restrict light to specific regions. We observed that the device output improved even in regions where light did not directly reach the electrodes, validating the mechanism by which the comb electrode structure affects the device’s resistance and enhances output performance. Moreover, when comparing back-side illumination with a PCSS with a 500 μm comb electrode, higher output and operating voltages were achieved compared to a structure without comb electrodes. Finally, vertical GaAs PCSSs were fabricated to enable stable operation under high voltages and analyzed its characteristics. In the vertical structure, the distance between the device edge and electrodes was varied to measure output efficiency and the operating limit voltage. The results indicated that as the distance between the electrode and device edge increased, the output decreased, showing a proportional relationship with the light absorption between electrodes. Additionally, the flashover voltage increased with the distance between the electrode and edge, enhancing operating stability. Furthermore, we observed that the pulse width of the output pulse decreased as the bias voltage increased in the vertical PCSS, suggesting the potential for pulse-width modulation. This study demonstrates the potential for enhancing the performance and stability of GaAs-based PCSSs by applying various structures and illumination methods. These findings will contribute to advancements in photoconductive semiconductor switch research for high- power applications. © 2025 Yong Pyo Kim ALL RIGHTS RESERVED|광전도 반도체 스위치(Photoconductive Semiconductor Switch, PCSS)는 고전력 전자기기에서 중요한 역할을 할 수 있는 유망한 광전소자로 연구되고 있다. PCSS 는 스파크 갭, 절연 게이트 양극성 트랜지스터(Insulated Gate Bipolar Transistor, IGBT), 사이리스터와 같은 기존의 고전력 스위치와 비교하여 초고속 스위칭 속도, 안정적인 동작, 매우 낮은 지터 특성 등 여러 가지 고유한 장점을 갖추고 있다. 이러한 특성으로 PCSS 는 고속 동작이 필요한 고전력 응용 분야에서 큰 관심을 받고 있다. 특히, PCSS 를 이용한 고체 기반 마이크로파 발생 기술은 초광대역(UWB) 신호 및 고전력 마이크로파(HPM) 신호 발생 장치에서 중요한 기술로 주목받고 있다. PCSS 는 다양한 반도체 재료를 사용할 수 있으며, 각 재료는 고유한 물질적 특성으로 인해 특정 응용 분야에 적합하다. 갈륨비소(GaAs), 탄화규소(SiC), 질화갈륨(GaN), 다이아몬드 등의 반도체 재료가 PCSS 에 사용될 수 있는 후보 물질로 연구되고 있다. 본 연구에서는 반절연 GaAs 기반의 PCSS 를 제작하고 특성을 분석하였다. 제작된 PCSS 의 출력 특성은 전면 및 후면 조사 방식을 통해 측정되었으며, 후면 조사 방식이 더 높은 동작 전압과 피크 출력 전압을 나타냈다. 시뮬레이션 결과, 후면 조사가 반도체 내부 전계를 고르게 분포시키는 데 기여하여, 전극 가장자리에서 발생할 수 있는 고전계에 의한 surface flashover(표면 절연 파괴)에 강점을 가지는 것으로 분석되었다. 또한, 후면 조사를 통해 반도체 내부에서 생성된 전자-홀 쌍이 반도체-금속 간의 접촉 저항을 낮추어 전체적인 출력 성능을 향상시키는 것으로 나타났다. 소자의 신뢰성에 영향을 미치고 동기화에 중요한 요소인 지터는 TDSJIT3 장비를 통해 측정하였으며, 1.5 kV 바이어스 전압까지 측정했을 때 7~17 ps 수준으로 관찰되었다. PCSS 의 동작 한계 전압은 반도체 재료의 breakdown 전압에 의해 결정되지만, 실질적으로는 10 kV/cm 이상의 동작 전계에서 발생하는 surface flashover 가 동작 전압과 수명을 제한하는 요인으로 작용한다. Surface flashover 에 대한 이론적 설명은 아직 정립되지 않았으나, 기존 문헌들을 토대로 분석하여 표면의 내압 특성을 개선하고자 silicon resin(Eb>165 kV/cm), SiNx, SiO₂ 등을 이용한 표면 패시베이션을 시도하였다. 특히, silicon resin 을 적용한 소자는 기존 후면 조사 방식에서 flashover 가 1.8 kV에서 발생하던 것에 비해 3.8 kV에서 flashover가 발생하는 것으로 나타나, 표면 패시베이션이 소자의 동작 전압과 flashover 전압을 크게 향상시킬 수 있음을 확인하였다. PCSS 의 출력 향상을 위해 전극 페리미터를 증가시키는 interdigitated 구조가 연구된 바 있으며, 본 연구에서는 이를 응용하여 빗 모양 전극 구조를 도입하고 특성을 분석하였다. 빗 전극의 길이를 0~750 μm 까지 변화시켜가며 분석한 결과, 빗 전극의 길이가 길어질수록 피크 전압이 1 kV 바이어스 전압에서 최대 3.53 배 증가하였으며, 동작 전압이 기존 1.5 kV 에서 3 kV 이상으로 개선되었다. 또한, 소자의 온 저항이 최대 10 배 이상 감소하여 출력 전압과 동작 전압, 방전 전압 모두가 개선되었다. 빗 모양 구조의 효과를 보다 구체적으로 분석하기 위해 cylindrical lens 를 사용하여 제한된 영역에 빛을 조사하는 실험을 진행하였고, 빛이 전극에 직접 닿지 않는 영역에서도 소자의 출력이 향상되는 것을 확인하였다. 이를 통해 빗 모양 전극 구조가 소자의 저항에 영향을 미쳐 출력 성능을 높이는 메커니즘을 검증할 수 있었다. 또한, 500 μm 길이의 빗 전극을 가진 PCSS 를 사용하여 후면 조사 효과를 비교 분석하였으며, 빗 전극이 없는 구조보다 더 높은 출력과 동작 전압을 나타냈다. 마지막으로, PCSS 가 고전압에서 안정적으로 작동할 수 있도록 수직형 GaAs PCSS 를 제작하여 특성을 분석하였다. 수직형 구조에서는 소자 가장자리에서 전극까지의 거리를 변화시키며 출력 효율 및 동작 한계 전압을 측정하였다. 그 결과, 소자의 출력은 전극과 소자 가장자리 간 거리가 길어질수록 감소하였고, 전극 간의 빛 흡수도와 비례하는 특성을 보였다. 또한, 전극과 가장자리 간 거리가 길어질수록 flashover 전압이 증가하여 동작 안정성이 향상되는 것으로 나타났다. 추가적으로, 수직형 PCSS 에서 바이어스 전압이 증가함에 따라 출력 펄스의 폭이 감소하는 현상을 관찰하였으며, 이를 통해 펄스 폭의 모듈레이션이 가능함을 확인하였다. 본 연구는 GaAs 기반 PCSS 의 제작 공정과 특성 분석을 통해 다양한 구조와 조사 방식을 적용함으로써 소자의 성능과 안정성을 개선할 수 있는 가능성을 확인하였으며, 고전력 응용에 있어 광전도 반도체 스위치의 연구에 기여할 수 있을 것으로 기대된다. ©2025 김 용 표 ALL RIGHTS RESERVEDDoctorList of Contents
Abstract vi
국 문 요 약 ix
List of Contents xii
List of Figures xiv
List of Tables xix
Introduction 1
Photoconductive semiconductor switch (PCSS) 1
Switch operation mode 3
Industrial application of PCSS 9
Direction of Research 13
References 16
Frontside illumination and Backside illumination of GaAs
Photoconductive Semiconductor Switch 20
Experimental setup for GaAs photoconductive semiconductor switch 20
Output characteristics of front illumination and back illumination GaAs
photoconductive semiconductor switch 24
Jitter characteristics of front illuminated GaAs PCSS 31
Conclusion 35
References 37
Surface Passivation of GaAs Photoconductive Semiconductor Switch 39
Surface flashover of PCSS 39
Effects of surface passivation of GaAs PCSS 43
Conclusion 47
References 48
Output Characteristics of GaAs Photoconductive Semiconductor Switch
with Comb electrodes 50
Design and fabrication of comb electrodes on S.I GaAs 50
Output characteristics of GaAs PCSS with comb electrodes 53
PCSSs with and without a comb under front and back side illumination 59
Conclusion 63
References 64
Vertical structure GaAs PCSS 67
Design of vertical structure GaAs PCSS 67
Output characteristics of vertical structure GaAs PCSSs 69
References 72
Summary & Future work 73
Acknowledgement 76
Curriculum Vitae 7