Li2RuO3의 전이금속 이합체에 대한 연구

학위논문 (박사) -- 서울대학교 대학원 : 자연과학대학 물리·천문학부(물리학전공), 2020. 8. 박제근.Transition metal ions in the oxides, which have d orbitals as a valence orbital, has been considered that the only orbital overlap between ligands and the metal is essential to describe the behavior of electrons. Recent studies, however, show that a direct overlap can be formed between the d-orbitals by various factors: for instance, the periodicity of the transition metal, the shape of wave functions in the t2g manifold, and the local network of the metal-ligand polyhedral. In this case, the direct overlap becomes to be much essential to describe electronic behavior. Especially when those conditions are satisfied, the transition metal ions form a cluster, and the electronic wave function has to be described using molecular orbitals. In this thesis, I study on a dimer in Li2RuO3, which is a condensation of two transition metal ions. The 4d Ru oxide Li2RuO3 has a layered honeycomb structure composed by edge-sharing RuO6 octahedra. It exhibits a structural transition at T = 550 K, below which one-third of the Ru-Ru bonds in the honeycomb lattice becomes shorter than others by about 20%. This stable dimerization enhances the direct orbital overlap, so induces the spin-singlet, molecular orbital state. The main question of my thesis is how the dimerization influences the behavior of electrons in the Ru ion. The Ru-Ru dimers form a herringbone pattern; thus, it expected that this system would have anisotropic physical properties reflecting ones of the dimer. The single-crystal sample was required to verify this idea and successfully synthesized. With this crystal, the anisotropies in electrical and magnetic properties were measured. The DFT calculation shows that the opening of the electronic gap requires Coulomb interaction and the correlation between electrons affects the anisotropy of the resistivity. Based on this picture, a dimer model of correlation effect was constructed to simulate the magnetic anisotropy and the calculation with the exact diagonalization method verified its validity. Those results imply that electronic correlation plays a significant role in the dimer. X-ray Spectroscopic study is an excellent way to observe the correlated electrons directly. The experiment is carried out in the I16 beamline of Diamond Light Source. The X-ray absorption spectroscopy result shows that the energy gaps between the t2g and eg level absorption energies depend on the absorption edge; L2 or L3. Furthermore, resonant elastic x-ray scattering (REXS) result on (010) reflection also shows the absorption edge selective behaviors. The simulation with FDMNES, the code with a single electron approach, did not reproduce the experimental results. These results signify that not only the spin-orbit coupling of the 4d electrons is essential but also the direct overlap inducing the correlation exert a strong influence on the electronic structure of the dimer. Orbital radius, according to the periodicity of the transition metal, is one of the critical conditions for forming the cluster. Series of studies on Li2Ru1-xMnxO3 solid solution shows that the replacement with the ion with smaller orbital breaks the herringbone-patterned dimer phase at the Mn substitution rate of 20 %. Within this range, the entropy change during the structural phase transition decreases linearly with increasing the substitution rate, and the local structure around the Ru ion does not that change. Those results back up that the Mn ion does not participate in the dimer, and disrupts the inter-dimer interaction and breaks the herringbone pattern in the end. Also, the local structure measurement with the extended x-ray absorption fine structure (EXAFS) method exhibits the existence of the dimer above the transition temperature more significantly than the pair distribution function analysis with the total scattering.전이금속 산화물 내의 전이금속 이온들은 d-궤도 원자가 전자를 가지며, 해당 함수의 국소성으로 인하여 인접하는 리간드와의 궤도 겹침만이 이 전자의 거동을 기술하는데 중요한 영향을 미칠 것으로 생각되어왔다. 그러나 최근 연구는 해당 전이금속의 주기에 따른 궤도 반경의 변화, t2g 다양체의 특성, 리간드의 국지적 구조에 의하여 이 궤도 함수가 큰 직접 겹침이 가능하고 이러한 경우 이 궤도 겹침 또한 전자의 거동을 기술하는데 중요한 역할을 한다는 것을 보고하였다. 특히 이러한 조건들이 만족하는 경우 전이금속 이온들 몇몇씩 뭉치 (cluster)를 이루어 행동하며 이 때 뭉치 내 전자의 파동 함수는 분자 궤도 함수 (molecular orbital)로 기술된다. 본문에서는 이에 대한 연구의 일환으로 루테늄 산화물 Li2RuO3 내의 이합체 (dimer) 뭉치에 대하여 연구하였다. Li2RuO3는 리튬으로 분리되어있는 루테늄 벌집 모양 격자가 첩첩이 쌓여있는 구조를 갖는 물질이다. 이 육각격자 내의 루테늄 이온들은 두 개씩 짝지어 서로의 간격을 줄여 이합체를 이루며 550 K의 구조상전이를 통하여 청어뼈 (herringbone) 모양의 격자를 만든다. 이 청어뼈 유형의 격자는 비등방적인 기하를 갖고 있어, 격자 내의 방향에 따라 물성의 차이를 가질 것으로 예상되었고, 이를 통하여 루테늄 이합체 내의 전자들의 행태를 확인하고자 하였다. 이전의 연구에서 Li2RuO3의 여러가지 물성이 측정되어 왔으나, 이는 모두 다결정 시료를 이용한 것이었고 단결정 시료는 합성법이 보고되지 않았었다. 본 연구에서는 이방성을 측정하기 위하여 고품질의 단결정 시료를 합성하고 합성된 시료의 전기적, 자기적 비등방성을 측정하고 이를 밀도 범함수 이론 계산과 비교하였다. 그 결과, 이합체 내 두 루테늄 이온의 전자 간의 쿨롱 반발력 고려해야만 전기적 띠 틈의 존재를 모사할 수 있으며, 이에 의한 전자 간 상관 관계가 전기적 이방성에 영향을 미치는 것을 확인하였다. 이를 바탕으로 전자 간 상관 관계를 고려한 모델을 세워 완전 대각화 계산을 통하여 자기적 비등방성을 재현해낼 수 있었다. 이로부터, Li2RuO3 의 이합체의 전자 구조와 그 물성을 설명하기 위해서는 전자 간 상관 관계를 고려해야 함을 확인할 수 있었다. 이보다 좀 더 Li2RuO3의 전자구조와 스핀, 오비탈의 배열 형태에 대해 직접적인 관측을 통하여 이합체에 대한 이해를 증진하고자 X선을 이용한 일련의 연구를 진행하였다. 루테늄은 4주기 원소로서 약 2.9 keV에 해당하는 L-흡수 선단 (absorption edge)을 갖는데, 이 에너지는 전통적으로 연X선과 경X선으로 구분되는 두 영역의 중간에 위치하며 기술적 이유로 제어가 힘들다고 알려져 있다. 따라서 해당 영역대의 에너지를 활용한 실험을 지원하는 영국의 Diamond 방사광 가속기의 I16 빔라인에서 해당 연구를 수행하였다. Li2RuO3 시료에 대하여 루테늄 L2와 L3 두 흡수 선단에서 X선 흡수 분광학 (x-ray absorption spectroscopy)을 실시한 결과, Li2RuO3의 흡수 스펙트럼이 흡수 선단에 따라 다름을 확인하였다. 이를 바탕으로 (010) 봉우리에서 공명 탄성 X선 산란을 수행하였고, 두 흡수 선단에서 (010) 공명 봉우리의 거동이 다름을 확인하였다. 이는 공명 대상인 2p 속전자 (core-electron)의 각운동량에 따라 전이 규칙이 적용 됨을 시사하며, 이합체 내의 t2g 전자의 스핀-궤도 결합이 유효한 영향을 미침을 의미한다. 또한 두 흡수 선단에서의 공명 탄성 X선 산란 신호의 방위각 의존성을 확인한 결과 서로 다른 방위각 의존성을 갖는 두 신호가 간섭한 것을 확인하였다. 이러한 실험의 결과들을 단일 전자 근사 계산 코드인 FDMNES 계산과 비교한 결과 크게 맞지 않음을 확인하였으며, 이는 이합체화에 의한 오비탈의 직접 겹침과 이에 따른 전자간 상관이 물질의 전자/스핀/오비탈 구조에 영향을 미친 결과이다. Li2RuO3는 구조 상전이 (550 K)이상의 온도에서는 X선 산란 실험 결과로부터 벌집 모양 격자 내에 이합체가 존재하지 않는 것으로 간주되어왔다. 그러나 전산란 (total scattering)법을 이용한 짝분포 함수 분석 (pair distribution function analysis) 결과, 상전이 온도 이상에서도 이합체가 여전히 남아 있음이 확인되었다. 본문에서는 격자 내의 루테늄을 망간으로 치환한 고용체 (solid solution)를 합성하여 전이 금속 오비탈 간 직접 결합을 감소시켜 상전이가 변화하는 경향을 확인하고, 광역 엑스선 흡수 미세 구조법 (extended x-ray absorption fine structure, EXAFS) 방법을 이용하여 치환률과 계의 온도에 따른 국소 구조변화를 관찰하였다. 그 결과 치환률에 따른 구조와 저항, 자화율의 변화로부터 치환률이 20 %까지 Li2RuO3와 같은 이합체를 포함하는 청어뼈 격자를 갖는 것을 확인하였다. 또한 망간 치환에 따라 상전이 시의 엔트로피 변화가 선형적으로 감소하고 루테늄 이온 주변의 국소 구조가 거의 바뀌지 않는 것을 관측하였다. 이는 전이 금속의 주기에 따른 오비탈 반경의 차이에 의해 루테늄과 망간이 이합체를 형성하지 않고, 망간 치환은 이합체 청어 뼈 모양 격자를 와해시키는 역할을 함을 뒷받침한다. 또한 루테늄 주변 국소 구조가 상전이 전후로 바뀌지 않음을 확인하였는데, 이는 이합체가 상전이에 의해 사라지지 않음을 짝분포 함수 분석 결과보다 분명하게 보여준다.1. Introduction 1 1.1 Transition metal cluster in solid 1 1.1.1 Bonding in solids 1.1.2 Molecular orbital and Cluster formation 1.2 Li2RuO3: The layered honeycomb structural compound with dimerization 8 1.3 Outline of the thesis 14 2. Experimental Techniques 17 2.1 Sample synthesis 17 2.2 Resonant Elastic X-ray Scattering (REXS) 19 2.2.1 Electronic matter-radiation interaction Hamiltonian 2.2.2 Scattering cross-section (Elastic scattering) 3. Anisotropy and transition metal dimer in Li2RuO3 31 3.1 Structural distortion by the dimerization 31 3.1.1 Crystal Structure Analysis 3.1.2 The b/a ratio: a distortion parameter 3.2 Resistivity anisotropy and the dimerization 36 3.2.1 Resistivity anisotropy of Li2RuO3 3.2.2 DFT calculation 3.3 Van Vleck type magnetic Susceptibility and its anisotropy 40 3.3.1 Dimer array approximation and symmetry analysis 3.3.2 Exact diagonalization calculation 3.4 Discussion and Summary 46 4. Resonant Elastic X-ray Scattering on Li2RuO3 49 4.1 X-ray Absorption Spectroscopy on Li2RuO3 51 4.2 Searching superstructure reflection 52 4.3 Tensorial structure factor calculation for Li2RuO3 53 4.4 Characterization of the resonant reflection (010) 55 4.4.1 Polarization and temperature dependency 4.4.2 Azimuthal angle and absorption edge dependent behavior of (010)σπ 4.5 Discussion and Summary 60 5. An Mn doping study on the valence bond solid phase in Li2RuO3 65 5.1 Valence Bond Liquid phase in Li2RuO3 65 5.2 Structural variation of Li2RuO3 by Mn doping 67 5.3 Physical Properties of Li2Ru1-xMnxO3 69 5.3.1 Electrical properties 5.3.2 Magnetic properties 5.3.3 Thermal properties of the phase transition 5.4 Local Structure variation in Li2RuO3 by Mn doping 73 5.5 Discussion and Summary 74 6. Summary and Outlook 79 6.1 Summary 79 6.2 Outlook 80 Appendix. FDMNES Code for Li2RuO3 81 Publication lists 83 국문 초록 (Abstract in Korean) 85 감사의 글 (Acknowledgement) 88Docto

수직적 구조를 고려한 도시 수목의 증산량 산정 다층 모델

학위논문 (석사) -- 서울대학교 대학원 : 농업생명과학대학 생태조경·지역시스템공학부(생태조경학), 2020. 8. 이동근.As the urban heat island has been intensified, the cooling effect of urban trees is becoming important. Tree can reduce the radiant heat reaching the surface of the urban area by blocking or reflecting the radiant heat. In addition, the surface temperature of the tree is lower than that of the impervious surface such as asphalt and concrete, resulting in lower longwave radiation. Transpiration of tree also have cooling effect by releasing water into the atmosphere through the stomata of leaves, which reduces urban sensible heat by increasing latent heat. However, most previous studies which have conducted to calculate the transpiration rate have not focused on urban trees or oversimplified plant physiological process. I propose a multi-layer model for transpiration of urban tree accounting for plant physiological process considering the vertical structure of trees and buildings. It is expanded from urban canopy model to simulate photosynthetically active radiation and leaf surface temperature accurately. To evaluate how building and tree conditions affect transpiration, I simulate transpiration by scenarios varying conditions of building height, tree location and vertical leaf area variation of trees. Simulations are conducted on four LAD distribution of trees; (1) Constant Density (C.D), (2) High Density, few layers (H.D), (3) High Density in Middle layers (M.H.D), (4) High Density in lower layers (L.H.D). LAI and tree height is same in all cases. The scenarios include three types of surrounding building (12m, 24m, and 36m) and two types of tree location (South and North). One of the day that was a clear day, did not have rain back and forth, had high air temperature, low relative humidity is selected (1 August 2018) in Seoul (126.9658, 37.57142) to simulated, so that transpiration can occur highly. The result show transpirative-efficient LAD distribution differs depending on tree structure and surrounding building height. The north tree surrounded by low building is most efficient for transpiration. The difference in tree transpiration during a day is up to 24.1%(south), 13.2%(north) depending on the building height. In scenario where building height are high(3H) and low(1H), the variations in tree transpiration during a day is up to 8.3% (3H) and 7.4%(1H) according to LAD distribution. This model can be a useful tool for providing guideline on the plantation of thermo-efficient trees depending on the structure or environment of the city. And if radiant heat reduction effects are analyzed together in future studies, it will be able to get more accurate insight into the cooling effects of trees.도시 열섬 현상이 심해짐에 따라 도시 수목의 냉각 효과가 중요해지고 있다. 수목은 복사열을 차단하거나 반사시켜 도시 표면에 도달하는 복사열을 저감시킬 수 있고, 수목의 표면온도는 아스팔트나 콘크리트 등의 불투수 표면보다 낮아 방출하는 장파 복사열을 줄일 수 있다. 또한, 수목의 증산 작용은 뿌리를 통해 흡수한 물을 잎의 기공을 통해 대기로 방출함으로써 잠열을 증가시켜 현열을 감소시킨다. 그러나, 증산량을 계산하는 대부분의 연구들은 도시 수목에 집중하지 않거나, 수목의 생리학적인 과정을 지나치게 단순화한다. 나는 수목과 건물의 수직적 구조를 고려하여 도시 수목의 증산량 산정 다층 모델을 제안한다. 이것은 광합성 활성 방사선과 잎의 표면 온도를 정확하게 모의하기 위하여 도시 캐노피 모델에서 확장되었다. 건물과 수목 환경이 증산에 주는 영향을 평가하기 위하여 건물 높이, 수목의 위치, 그리고 수목의 수직적 잎 면적 분포에 따라 달라지는 시나리오들로 증산량을 시뮬레이션하였다. 시뮬레이션은 네 가지 잎 면적 밀도(LAD) 분포를 가진 수목을 실시하였다; (1) 일정한 밀도(C.D), (2) 높은 밀도와 적은 층 (H.D), (3) 중층부에서의 높은 밀도 (M.H.D), (4) 하층부에서 높은 밀도 (L.H.D). 잎 면적 지수(LAI)와 수목의 높이는 모든 경우에서 동일하였다. 시나리오는 세 가지 건물 높이(12m, 24m, 그리고 36m)와 두 가지 수목 위치(남쪽, 북쪽)을 포함하였다. 시뮬레이션을 위해 서울에서 전후 시간에 비가 오지 않았고 높은 기온, 낮은 습도를 가진 맑은 날(2018년 8월 1일)을 선정하여 증산 작용이 크게 일어나게 하였다. 시뮬레이션 결과는 수목 구조와 주변 건물 높이에 따라 증산-효율적인 LAD 분포가 다르다는 것을 보여준다. 낮은 건물로 둘러싸인 북쪽 수목은 증산에 가장 효율적이었다. 하루 동안 수목의 증산량의 차이는 건물 높이에 따라 최대 24.1%(남쪽), 13.2%(북쪽)까지 차이가 났다. 건물 높이가 높고(3H), 낮은(1H) 시나리오에서는 LAD 분포에 따라 하루 중 수목의 증산량의 편차가 최대 8.3%(3H), 7.4(1H)였다. 이 모델은 도시의 구조나 환경에 따라 열 효율이 높은 수목 식재에 관한 가이드라인을 제공하는 데 유용한 도구가 될 수 있을 것이다. 그리고 향후 연구에서 복사열 저감 효과와 함께 분석한다면 도시 수목의 냉각 효과에 대한 보다 정확한 통찰력을 얻을 수 있을 것으로 사료된다.Chapter 1. Introduction １ Chapter 2. Method ４ 2.1 Research flow ４ 2.2 Model description ５ 2.2.1 Input data ５ 2.2.2 Model processing ６ 2.3 Scenario simulation １５ 2.3.1. Tree location １５ 2.3.2. Building height １６ 2.3.3. LAD distribution １６ Chapter 3. Results and Discussion １９ 3.1. Parameter １９ 3.1.1. PAR & leaf surface temperature １９ 3.1.2. Resistances ２０ 3.2. Transpiration ２１ 3.2.1. Temporal variation ２１ 3.2.2. Scenarios simulation ２２ 3.3. Model limitations and future development ２５ Chapter 4. Conclusion ２７ Bibliography ２８ Appendix ４１Maste

원핵미생물 분류체계에 기반한 16S rRNA 유전자 및 유전체 데이터베이스의 개발

학위논문 (박사)-- 서울대학교 대학원 자연과학대학 생명과학부, 2017. 8. 천종식.In prokaryotic taxonomy, the 16S ribosomal RNA (rRNA) gene sequence-based approach has served as an alternative standard method to DNA-DNA hybridization (DDH), for which the 97% 16S rRNA gene sequence similarity was considered to be equivalent to the 70% DDH value for species demarcation. While the 16S rRNA-based method is unable to perfectly classify and identify bacterial and archaeal species using 16S rRNA gene, it is currently the most general tool to evaluate the taxonomic position of a prokaryotic strain at the same genus or species levels. Therefore, the 16S rRNA-based approach is still important in the classification of prokaryotes and the use of a database with taxonomically well-curated sequences such as EzTaxon-e is essential for accurate species identification. There has been a recent evolution of DNA sequencing technologies, called next-generation sequencing (NGS), which has been facilitating Culture-independent microbial community analysis using 16S ribosomal RNA gene as well as the use of genome sequencing data for more informative and precise classification and identification of Bacteria and Archaea. Because the current species definition is based on the comparison of genome sequences between type and other strains in a given species, building a genome database with accurate taxonomic information is a premium need to enhance our efforts in exploring prokaryotic diversity and discovering new species as well as for routine identifications. In this study, an integrated database, called EzBioCloud, was constructed to hold the taxonomic hierarchy of Bacteria and Archaea that are represented by quality-controlled 16S rRNA gene and genome sequences. The various bioinformatics pipelines, tools, and algorithms which were applied during the construction of the database were also developed to optimally utilize the database contents. For a more efficient 16S rRNA-based analysis, the pairwise sequence alignment algorithm was improved and a high-performance microbial community analysis pipeline was newly developed in order to better facilitate the analysis of massive NGS data and to produce better results than conventional methods. For whole genome based analyses, quality assessment methods for genome assembly and a genome annotation pipeline were developed and evaluated. The full-length 16S rRNA extraction method and efficient average nucleotide identity (ANI) calculation algorithm were utilized in the identification of public prokaryotic genomes. In order to construct the integrated genome database, whole genome assemblies in the NCBI Assembly Database were first screened to determine low-quality genomes and then subsequently subjected to a composite identification bioinformatics pipeline that employed gene-based searches followed by the calculation of average nucleotide identity. The resulting database consisted of 61,700 species/phylotypes including 13,132 with validly published names, and 62,362 whole genome assemblies that were taxonomically identified at the genus, species and subspecies level. Genomic properties, such as genome size and GC content, and the occurrence in human microbiome data were calculated for each genus or higher taxa. This comprehensive database of taxonomy, 16S rRNA gene, and genome sequences, with its accompaniment of bioinformatics tools, should accelerate genome-based classification and identification of Bacteria and Archaea. The database and related search tools are available at http://www.ezbiocloud.net/.CHAPTER 1 General introduction 1 1.1. Taxonomy of prokaryotes 2 1.1.1. Principle of prokaryotic taxonomy 2 1.1.2. Prokaryotic species concept 4 1.2. Next generation sequencing (NGS) 8 1.2.1. 454 Pyrosequencing 8 1.2.2. Illumina-Solexa sequencing 10 1.2.3. Pacific Bioscience SMRT sequencing 11 1.3. Use of 16S rRNA gene in microbiology 13 1.4. Prokaryotic genomics 17 1.5. Objectives of this study 21 CHAPTER 2 Development of bioinformatics pipelines and tools for EzBioCloud database 23 2.1. Introduction 24 2.1.1. 16S rRNA based prokaryote identification algorithm 25 2.1.2. Microbial community analysis 27 2.1.3. 16S rRNA sequence in genome with short-read sequencing data 31 2.1.4. Public genome data of prokaryotes 31 2.1.5. Quality of genome assembly 32 2.1.6. Average nucleotide identity 33 2.2. Materials and method 36 2.2.1. Improvement of 16S rRNA sequence based identification algorithm 36 2.2.2. Development of microbial taxonomic profiling (MTP) pipeline 38 2.2.3. Method for extracting full-length 16S rRNA genes from short-read sequencing data 42 2.2.4. Pipeline for prokaryotic whole genome analysis 44 2.2.5. Methods for the quality assessment of genome 48 2.2.6. Efficient calculation method for average nucleotide identity 52 2.3. Results 54 2.3.1. Advanced microbial taxonomic profiling (MTP) pipeline 54 2.3.2. Comparison of full length 16S rRNA extraction methods 62 2.3.3. Annotation of public genomes 66 2.3.4. Quality of bacterial genomes 68 2.3.5. Evaluation of algorithms for average nucleotide identity 75 2.4. Discussion 81 CHAPTER 3 Development of EzBioCloud: A taxonomically united database of 16S rRNA and whole genome assemblies 84 3.1. Introduction 85 3.2. Methods 87 3.2.1. Data collection 87 3.2.2. Identification of genome sequences 90 3.2.3. Calculation of genomics features for each taxon 93 3.2.4. Bacterial community analysis of human microbiome 93 3.2.5. Operating system and software development 95 3.3. Results 96 3.3.1. Comparison of databases 96 3.3.2. Hierarchical taxonomic backbone 99 3.3.3. Identification of genome projects 103 3.3.4. Genome-derived information 107 3.4. Discussion 108 CHAPTER 4 General conclusions 111 REFERENCES 115 국문초록 130Docto

풍력발전부품 제조업체에 특화된 국제운송경로 연구

Abstract Wind energy began to receive attention as a new alternative fuel since 20 years ago and is growing as a booming global business model. Power efficiency and reliability has greatly been improved during the past 15 years to perform the role as an alternative resource that replaces existing energy sources. Many suppliers and technological advancements are being introduced to provide quick installation of wind power generator around the world. Global wind power generation in the world has been continuously increasing for the past 10 years, accounting for over 30% of cumulative rate compared to total power generation. Global demand for wind power generation is gradually expanding due to restriction on carbon emission and environmental problems caused by increased greenhouse effect. Total wind power equipment capacity in 2008 was 120 GW (giga watt). The United States has largest market share in the world, followed by Germany, Spain and China that are progressively expanding their wind power equipment. Wind energy is receiving the spotlight with solar energy to replace fossil energy until 2020, as a means to reduce carbon dioxide emission and prevent further expansion of greenhouse effects. About 20 assembly parts are attached on the head of wind power equipment. Tower supporting this head is installed at a height of 80 ~ 150 meters from the ground. Size of tower components (container, flange, and frame) is being increased to a width of 2.3 ~ 5.5 meters. Size of such components can be further enlarged with future development of wind power generation technology and increase in energy use. The top two manufacturers of wind power equipment components in the world are located in Korea, as well as small and medium companies being established since 2009. Interest on transportation of products to major consumers such as Europe and the United States is demanding changes in existing perspective on distribution. The number one wind power equipment manufacturer in the world is company A (located in Jisa-dong, Gangseo-gu, Busan). This company is a free forging company that produces over 600,000 tons of wind power flange larger than 4.5 meters and exceeds annual sales of 300 billion won. From heating of original material until manufacture of finished products through forging and rough machining processes, materials must be transported 6.5 times on average. However, current traffic laws limit transportation by trucks up to a width of 2.3 meters unless a special permit on limited vehicles is obtained. Such limited vehicles can only be driven after midnight (00:00 ~ 06:00), which inevitably results in illegal drives. In fact, the company paid a fine of about 10 million won in 2010 on over-width vehicles. Considering the fact that there are 31 small and large corporations in Korea conducting similar businesses, size of total fines paid by these companies is probably beyond imagination. Furthermore during marine transportation for exports, FR container (flatrack container) is designated as an over-width cargo. There are serious problems in loading, as well as transportation to docks. The foremost task of wind power companies is to find an international transportation route for stable and economic transportation of large sized wind power components to wind power complexes in the United States, Germany, Spain, and China that are responsible for 65% of global wind power generation market. Since about 7 ~ 9% of sales is appropriated as distribution expense, potential value of this study is expected to be greater than 100 billion won. While existing studies were limited to specific transportation methods for large sized products, this study attempts to focus on an international transportation route for general application. The purpose is not only to create profit for specific companies but also to secure stable competitiveness of wind power generator component manufacturers in Korea, in the midst of growing wind power market around the world. Accordingly in this study, current transportation routes are classified into three types including access-priority route, economics-priority route, and convenience- priority route depending on distribution characteristics of wind power equipment in order to suggest transportation methods other than ships. Reflection of distribution characteristics of wind power equipment on wind power capacity to be expanded until 2030 will contribute to development of individual manufacturers and to create national benefit through transportation route applicable to other large sized products such as large plant industry and shipbuilding industry.Ⅰ. 서 론 1 1. 연구배경 및 목적 1 2. 연구 동향 3 3. 연구내용 및 방법 7 Ⅱ. 풍력발전부품의 물류적 특성 11 1. 풍력발전부품의 기능 11 2. 풍력발전부품의 물류적 특성 15 3. 국제 관련법의 특징 25 4. 풍력발전 부품의 운송제약 29 Ⅲ. 풍력발전부품의 국제운송경로 현황 및 문제점 32 1. 국제 운송경로 현황 32 2. 국제 운송경로상 문제점 49 Ⅳ. 풍력발전부품에 특화된 국제운송경로 제시 63 1. 미국지역 - SAVANNAH:접근성 우선 경로 64 2. 캐나다지역 -WINDSOR:경제성 우선 경로 69 3. 유럽지역 - GIJON:편의성 우선 경로 76 4. 국제운송경로에 대한 추가제안 80 Ⅴ. 결론 및 제언 84 1. 결론 84 2. 제언 87 《참고 문헌》 8

Magnetic nanoparticles control neural stem cell behavior in normal and ischemic brain

의과대학/박사Over the past few decades, the establishment of neural stem cells as a long-lasting source of neurons and glial cells had led to the development of novel therapeutic approaches for a variety of neurodegenerative disorders such as brain stroke. Neural stem cells graft promoted brain protection, regeneration and functional recovery. Nonetheless, the therapeutic benefits of neural stem cells had been limited due to their poor in vivo control of migration, engraftment and differentiation into target tissue. Recently, nanotechnologies are emerging platforms that could be useful in measuring, understanding and manipulating stem cells. Advanced nanoparticles, carbone nanotubes, and polyplexes have been widely used for stem cell labeling, tracking, differentiation and transplantation. Here we demonstrated magnetotactic human neural stem cells that can be directed to the desired target lesion via non-invasive, remote magnetic guidance. In the presence of an external magnetic field, the advanced magnetic nanoparticle allowed neural stem cells to possess strong attraction forces, which was sufficient for migration, and highly sensitive MRI contrast that enabled long-term tracking of neural stem cells. We found the enhanced migration and engraftment and promoted neuronal differentiation of non-invasively injected magnetotactic neural stem cells in animal stroke model which resulted in improved neurological function and pathology.ope

Analytical Tools and Databases for Metagenomics in the Next-Generation Sequencing Era

Metagenomics has become one of the indispensable tools in microbial ecology for the last few decades, and a new revolution in metagenomic studies is now about to begin, with the help of recent advances of sequencing techniques. The massive data production and substantial cost reduction in next-generation sequencing have led to the rapid growth of metagenomic research both quantitatively and qualitatively. It is evident that metagenomics will be a standard tool for studying the diversity and function of microbes in the near future, as fingerprinting methods did previously. As the speed of data accumulation is accelerating, bioinformatic tools and associated databases for handling those datasets have become more urgent and necessary. To facilitate the bioinformatics analysis of metagenomic data, we review some recent tools and databases that are used widely in this field and give insights into the current challenges and future of metagenomics from a bioinformatics perspective.

Real-Time Discrimination between Proliferation and Neuronal and Astroglial Differentiation of Human Neural Stem Cells

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural lineages, all of which are considered to be promising components for neural regeneration. However, for cell-replacement therapies, it is essential to monitor the process of in vitro NSC differentiation and identify differentiated cell phenotypes. We report a real-time and label-free method that uses a capacitance sensor array to monitor the differentiation of human fetal brain-derived NSCs (hNSCs) and to identify the fates of differentiated cells. When hNSCs were placed under proliferation or differentiation conditions in five media, proliferating and differentiating hNSCs exhibited different frequency and time dependences of capacitance, indicating that the proliferation and differentiation status of hNSCs may be discriminated in real-time using our capacitance sensor. In addition, comparison between real-time capacitance and time-lapse optical images revealed that neuronal and astroglial differentiation of hNSCs may be identified in real-time without cell labeling.ope

Human neural stem cells alleviate Alzheimer-like pathology in a mouse model

BACKGROUND: Alzheimer's disease (AD) is an inexorable neurodegenerative disease that commonly occurs in the elderly. The cognitive impairment caused by AD is associated with abnormal accumulation of amyloid-β (Aβ) and hyperphosphorylated tau, which are accompanied by inflammation. Neural stem cells (NSCs) are self-renewing, multipotential cells that differentiate into distinct neural cells. When transplanted into a diseased brain, NSCs repair and replace injured tissues after migration toward and engraftment within lesions. We investigated the therapeutic effects in an AD mouse model of human NSCs (hNSCs) that derived from an aborted human fetal telencephalon at 13 weeks of gestation. Cells were transplanted into the cerebral lateral ventricles of neuron-specific enolase promoter-controlled APPsw-expressing (NSE/APPsw) transgenic mice at 13 months of age. RESULTS: Implanted cells extensively migrated and engrafted, and some differentiated into neuronal and glial cells, although most hNSCs remained immature. The hNSC transplantation improved spatial memory in these mice, which also showed decreased tau phosphorylation and Aβ42 levels and attenuated microgliosis and astrogliosis. The hNSC transplantation reduced tau phosphorylation via Trk-dependent Akt/GSK3β signaling, down-regulated Aβ production through an Akt/GSK3β signaling-mediated decrease in BACE1, and decreased expression of inflammatory mediators through deactivation of microglia that was mediated by cell-to-cell contact, secretion of anti-inflammatory factors generated from hNSCs, or both. The hNSC transplantation also facilitated synaptic plasticity and anti-apoptotic function via trophic supplies. Furthermore, the safety and feasibility of hNSC transplantation are supported. CONCLUSIONS: These findings demonstrate the hNSC transplantation modulates diverse AD pathologies and rescue impaired memory via multiple mechanisms in an AD model. Thus, our data provide tangible preclinical evidence that human NSC transplantation could be a safe and versatile approach for treating AD patients.ope

Human fetal brain-derived neural stem/progenitor cells grafted into the adult epileptic brain restrain seizures in rat models of temporal lobe epilepsy

Cell transplantation has been suggested as an alternative therapy for temporal lobe epilepsy (TLE) because this can suppress spontaneous recurrent seizures in animal models. To evaluate the therapeutic potential of human neural stem/progenitor cells (huNSPCs) for treating TLE, we transplanted huNSPCs, derived from an aborted fetal telencephalon at 13 weeks of gestation and expanded in culture as neurospheres over a long time period, into the epileptic hippocampus of fully kindled and pilocarpine-treated adult rats exhibiting TLE. In vitro, huNSPCs not only produced all three central nervous system neural cell types, but also differentiated into ganglionic eminences-derived γ-aminobutyric acid (GABA)-ergic interneurons and released GABA in response to the depolarization induced by a high K+ medium. NSPC grafting reduced behavioral seizure duration, afterdischarge duration on electroencephalograms, and seizure stage in the kindling model, as well as the frequency and the duration of spontaneous recurrent motor seizures in pilocarpine-induced animals. However, NSPC grafting neither improved spatial learning or memory function in pilocarpine-treated animals. Following transplantation, grafted cells showed extensive migration around the injection site, robust engraftment, and long-term survival, along with differentiation into β-tubulin III+ neurons (~34%), APC-CC1+ oligodendrocytes (~28%), and GFAP+ astrocytes (~8%). Furthermore, among donor-derived cells, ~24% produced GABA. Additionally, to explain the effect of seizure suppression after NSPC grafting, we examined the anticonvulsant glial cell-derived neurotrophic factor (GDNF) levels in host hippocampal astrocytes and mossy fiber sprouting into the supragranular layer of the dentate gyrus in the epileptic brain. Grafted cells restored the expression of GDNF in host astrocytes but did not reverse the mossy fiber sprouting, eliminating the latter as potential mechanism. These results suggest that human fetal brain-derived NSPCs possess some therapeutic effect for TLE treatments although further studies to both increase the yield of NSPC grafts-derived functionally integrated GABAergic neurons and improve cognitive deficits are still needed.ope

Therapeutic Application of Neural Stem Cells for Neonatal Hypoxic-Ischemic Brain Injury

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural cell lineages, and migration toward damaged sites in the central nervous system (CNS). NSCs expanded in culture could be implanted into the brain where they integrate into host neural circuitry and stably express foreign genes. It hence appears that transplantation of NSCs has been proposed as a promising therapeutic strategy in neurological disorders. During hypoxic-ischemic (HI) brain injury, factors are transiently elaborated to which NSCs respond by migrating to degenerating regions and differentiating towards replacement of dying neural cells. In addition, NSCs serve as vehicles for gene delivery and appear capable of simultaneous neural cell replacement and gene therapy (e.g. with factors that might enhance neuronal differentiation, neurites outgrowth, proper connectivity, neuroprotection, and/or immunomodulatory substances). When combined with certain synthetic biomaterials, NSCs may be even more effective in 'engineering' the damaged CNS towards reconstitution. Human NSCs were isolated from the forebrain of an aborted fetus at 13 weeks of gestation and were grown as neurospheres in cultures. After the characterization of human NSCs in preclinical testing and the approval of the IRB, a clinical trial of the transplantation of human NSCs into patients with severe perinatal HI brain injury has been performed. The existing data from these clinical trials have shown to be safe, well tolerated, and of neurologically-some benefits. Therefore, long-term and large scale multicenter clinical study is required to determine its precise therapeutic effect and safety.ope