미생물전해전지에서 electrobiofuels 생산을 위한 탄화수소계 양이온 교환막 개발 및 성능 평가

A sulfonated poly(arylene ether sulfone) (SPAES)/polyimide nanofiber (PIN) composite proton exchange membrane was developed for use in microbial electrolysis cells (MECs), where diverse cations that compete with proton coexist in high concentrations. It was fabricated by impregnating SPAES as a proton-conducting polymer into PIN as a supporter for mechanical reinforcement. The membrane showed excellent mechanical and dimensional stability (tensile strength > 40 MPa) due to membrane reinforcement by nanofibers, despite having a high water uptake (35±3%) and ion exchange capacity (2.3±0.3 meq/g). This novel membrane was highly selective for protons while excluding other competing cations; thus, it significantly mitigated the proton accumulation problem in the anode when applied to actual MECs. In addition to 1.5-fold greater proton transport, the SPAES/PIN membrane exhibited 3–10-fold less undesirable crossover of other cations depending on the species and 2–2.5-fold less gas permeability compared to Nafion-211 membrane. The application of this membrane improved hydrogen production efficiency of MEC by 32.4% compared to Nafion-211 and better hydrogen purity (90.3% for SPAES/PIN vs. 61.8% for Nafion-211). Therefore, this novel membrane has good potential for MEC applications, especially when protons and other competing cations are present together, due to its superior proton selectivity.| Sulfonated poly(arylene ether sulfone) (SPAES)/polyimide nanofiber (PIN) 양이온 교환 복합막은 다양한 양이온들이 공존하는 미생물전해전지(Microbial electrolysis cells; MECs)에서 수소 이온을 효과적으로 전달하기 위해 개발되었다. 이 탄화수소계 양이온 교환 복합막은 물리적 강도를 보강하기 위한 지지체로 PIN을 사용하였고, PIN을 양이온 전도성 중합체인 SPAES에 함침 시켜 제조하였다. 이렇게 개발된 복합막은 높은 수분 흡수 능력(35 ± 3%) 및 이온 교환 능력(2.3 ± 0.3 meq/g)을 가짐에도 불구하고, PIN에 의해 우수한 치수 안정성(인장 강도> 40 MPa)을 나타냈다. 또한, 다른 경쟁 양이온들의 전달은 배제하면서 수소 이온을 선택적으로 전달하였는데 기존에 미생물전해전지에서 대표적으로 사용하던 불소계 양이온 교환막인 Nafion-211에 비해 수소 이온을 1.5배 빠르게 전달하였으며, 바람직하지 않은 다른 경쟁 양이온들의 전달과 기체 투과도는 각각 3-10배, 2-2.5배 더 적은 것으로 나타났다. 따라서, 미생물전해전지에 개발된 복합막을 적용하였을 때 anode에서 수소 이온이 축적되는 문제를 상당히 완화시켰고, Nafion-211을 적용했을 때보다 Cathode에서 수소 가스 생산 효율이 32.4% 향상되었으며, 발생한 수소 가스의 순도도 대폭 증가하였다(Nafion-211의 경우 61.8% vs SPAES / PIN의 경우 90.3%). 결론적으로 이 새로운 탄화수소계 양이온 교환 복합막은 우수한 수소 이온의 선택적 전도성과 높은 치수 안정성 그리고 낮은 기체 투과도로 인해 미생물전해전지 분야에서 높은 이용 가능성을 지니고 있는 것으로 판단된다.Chapter 1. Introduction 1 Chapter 2. Literature review 6 2.1 Microbial electrolysis cells (MECs) 6 2.1.1 Basic principles 7 2.1.2 Key influence factors 8 2.2 Hydrocarbon-based proton exchange membrane 11 Chapter 3. Materials and methods 13 3.1 Membrane preparation 13 3.2 Membrane property characterization 14 3.2.1 Morphology and mechanical property analysis 14 3.2.2 Water uptake, swelling ratio, and ion exchange capacity measurement 15 3.2.3 Ion conductivity: proton transport number measurement 16 3.3 Crossover measurement for the cation, substrate, and gas 17 3.4 Evaluation of actual membrane performance using a hydrogen-producing microbial electrolysis cell (MEC) 18 Chapter 4. Results and discussion 20 4.1 Water uptake, tensile strength, swelling ratio, and ion exchange capacity 20 4.2 Proton selectivity 23 4.2.1 Ion conductivity: proton transport number 24 4.2.2 Competitive cation crossover 25 4.2.3 High proton selectivity based on microphase separation 27 4.3 Gas and substrate crossover 30 4.4 Actual performance verification using MECs 32 Chapter 5. Conclusion 36 References 37 Academic achievement 52Maste

Cartesian 트리에 기반한 문자열 매칭 및 인덱싱

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 컴퓨터공학부, 2020. 8. 박근수.We introduce a new metric of match, called Cartesian tree matching, which means that two strings match if they have the same Cartesian trees. Based on Cartesian tree matching, we define single pattern matching for a text of length n and a pattern of length m, and multiple pattern matching for a text of length n and k patterns of total length m. We present an O(n+m) time algorithm for single pattern matching, and an O((n+m) log k) deterministic time or O(n+m) randomized time algorithm for multiple pattern matching. We also define an index data structure called Cartesian suffix tree, and present an O(n) randomized time algorithm to build the Cartesian suffix tree. Our efficient algorithms for Cartesian tree matching use a representation of the Cartesian tree, called the parent-distance representation.본 논문에서는 Cartesian 트리에 기반한 새로운 매칭 기준인 Cartesian 트리 매칭을 제안한다. 이는 두 문자열의 Cartesian 트리가 서로 같을 때, 두 문자열을 매칭된 것으로 정의하는 문제이다. Cartesian 트리 매칭의 기준 하에서, 본 연구에서는 길이 n인 텍스트와 길이 m인 패턴 사이의 단일패턴매칭 문제와 길이 n인 텍스트와 길이의 합이 m인 여러 개의 패턴 사이의 다중패턴매칭 문제를 정의하고, 단일패턴매칭 문제를 해결하는 O(n+m) 시간 알고리즘과 다중패턴매칭 문제를 해결하는 O((n+m) log k) 시간 결정론적 알고리즘 및 O(n+m) 시간 무작위 알고리즘을 제시한다. 또한, Cartesian 트리 매칭에 대한 인덱스 자료구조인 Cartesian 접미사트리를 정의하고, 이를 구축하는 O(n) 시간 무작위 알고리즘을 제시한다. 본 논문에서는 Cartesian tree를 표현하는 방식인 부모거리표현 (parent-distance representation)을 정의하고, 이를 이용하여 위 문제들을 해결하는 효율적인 알고리즘들을 제시한다.Chapter 1 Introduction 1 Chapter 2 Problem Definition 4 2.1 Basic notations 4 2.2 Cartesian tree matching 4 Chapter 3 Single Pattern Matching in O(n + m) Time 7 3.1 Parent-distance representation 7 3.2 Computing parent-distance representation 9 3.3 Failure function 11 3.4 Text search 13 3.5 Computing failure function 13 3.6 Correctness and time complexity 14 3.7 Cartesian tree signature 15 Chapter 4 Multiple Pattern Matching in O((n + m) log k) Time 17 4.1 Constructing the Aho-Corasick automaton 17 4.2 Multiple pattern matching 21 Chapter 5 Cartesian Suffix Tree in Randomized O(n) Time 22 5.1 Defining Cartesian suffix tree 22 5.2 Constructing Cartesian suffix tree 23 Chapter 6 Conclusion 26 Bibliography 27 요약 31Maste

전기화학적 활성 박테리아의 활성도 조절을 통한 미생물전해전지 내 지속가능한 수소 생산

A microbial electrolysis cell (MEC) is an environmentally sustainable energy production platform where electrochemically active bacteria (EAB) convert the organic substances in wastewater into hydrogen. MEC is driven by the two major processes: 1) degradation of organic matters into protons (H+), electrons (e-) and carbon dioxide (CO2) in the anode, and followed by 2) reduction of H+ and e- that produces hydrogen gas (H2) in the cathode. Therefore, the sufficient provision of H+ and e- is crucial for fluent H2 production via increasing both the electrobiochemical activity of the anode and the reduction efficiency of the cathode. In this study, the problems of core technology in MEC was identified and solved to increase the efficiency of bioelectrochemical hydrogen production. First, the inefficient use of space in carbon materials based anode, where EABs grow. Carbon-based materials are mainly used in oxidation electrodes due to their high electrical conductivity and porosity, but the hydrophobic nature of carbon-based anodes suppresses the release of the produced gas and water penetration, significantly reducing the possibility of microbial attachment. Therefore, we tried to utilize all areas smoothly through surface improvement. The next problem is the interspecies substrate competition of microorganisms. The anaerobic sludge used for microbial species contains a large amount of methane bacteria as well as EABs, and the electron generated by methane is a loss in terms of hydrogen production. In order to fully use this electrons for hydrogen production, methanogenesis were controlled to reduce methane production and increase hydrogen production. Finally, the reduction of hydrogen ion transfer efficiency due to biofilm formation on the surface of the proton exchange membrane (PEM). When MEC is operated for a long time, microorganisms formated bio-films on the surface of the PEM, a channel where protons are transferred, and these bio-films reduce the efficiency of proton transfer, reducing hydrogen production. Therefore, a synergistic anti-biofouling technology was developed and applied to increase durability of PEM. The development of such core technologies for MEC has enabled economic and efficient hydrogen production, which will contribute to the establishment of a diverse types of larger bioelectrochemical hydrogen production platform in the future.Chapter 1. General introduction 1 1.1 Background 2 1.1.1 Microbial fuel cells (MFCs) 3 1.1.2 Microbial electrolysis cells (MECs) 5 1.1.3 Microbial electrosynthesis (MES) 6 1.1.4 Microbial desalination cells (MDCs) 7 1.1.5 Problem statements 8 1.2 Research objectives 9 1.3 References 11 Chapter 2. Literature review 15 2.1 Microbial electrolysis cell: An overview of operation mechanism 16 2.2 Previous studies on factors governing the performance of MECs 17 2.3 Core technology in MEC 22 2.3.1 Anode materials 22 2.3.2 Cathode materials 24 2.3.3 Electrode modification for enhancing the performance of MECs 26 2.4 Previous studies for MEC scale-up 27 2.5 Scale-up Challenges of MECs 29 2.6 References 33 Chapter 3. Maximizing electrochemical microbial activity through an electrobiocompatible anode made by bi-functionalizing surface 56 3.1 Introduction 57 3.2 Experimental 61 3.2.1 Preparation of functionalized anode 61 3.2.2 Characterization of functionalized anodes 64 3.2.3 H2-producing MEC setup and operation 65 3.2.4 Electron transfer and produced gas evaluation 66 3.2.5 Microbial attachment and community analysis depending on depth of anode 67 3.3 Results and discussion 71 3.3.1 Confirmation of the functionalizing anode surface 71 3.3.2 Characterization of the anode 75 3.3.3 Performance of MEC equipped with functionalized anode 82 3.3.4 Microbial dynamics across the anode layers 87 3.4 Conclusion 92 3.5 References 92 Chapter 4. Intensive production of hydrogen and an on-demand strategy through methanogenesis control 100 4.1 Introduction 101 4.2 Experimental 106 4.2.1 Operational conditions of MEC 106 4.2.2 Methanogenesis stimulant and inhibitor 108 4.2.3 Produced gas measurement and analysis 109 4.2.4 Gas production kinetic model 110 4.2.5 Microbial community analysis 111 4.2.6 Quantitative PCR targeting mcrA genes 111 4.3 Results and discussion 112 4.3.1 Stimulation of methane production using CoM injection 112 4.3.2 Microbial community changes with CoM injection 118 4.3.3 Inhibition of methane production using 2-BES 121 4.3.4 Microbial community changes after 2-BES injection 125 4.3.5 Dual-methanogenic pathway 128 4.3.6 Overall energy conversion and efficiency depending on target electrobiofuels 131 4.4 Conclusion 134 4.5 References 136 Chapter 5. Biofouling mitigation on the surface of proton exchange membrane for maintenance of hydrogen production in MEC 145 5.1 Introduction 146 5.2 Experimental 149 5.2.1 Membrane preparation and modification 149 5.2.2 Membrane characterization (8 samples) 152 5.2.3 Evaluation of anti-biofouling effect using MEC after six-month operation (4 samples) 155 5.3 Results and discussion 157 5.3.1 Membrane characterization 157 5.3.2 Long-term performance verification for MEC use 168 5.4 Conclusion 172 5.5 References 173 Chapter 6. Overall conclusion & Further applications 181 Summary in Korean (국문요약) 185Docto

Factors for the intra-organizational diffusion of big data systems

학위논문(석사) - 한국과학기술원 : 정보경영프로그램, 2018.8,[iii, 34 p. :]본 논문에서는 빅데이터 시스템의 도입 후 조직 내 확산에 영향을 주는 요소를 빅데이터 시스템 공급업체의 입장에서 연구하고자 한다. 혁신 기술인 빅데이터 시스템의 조직내 확산 연구를 위해, 혁신의 궁극적인 채택 또는 거부 전에 어떤 형태로든 존재 하는 혁신에 대한 저항 이론을 바탕으로 확산에 영향을 주는 요인을 분석해 보았다. 특히 다양한 형태로 존재하는 저항을 유보, 거절, 만류로 나누고 각 유형에 영향을 주는 변수를 인지된 위험, 혁신 특성, 사용자 속성 및 조직 속성의 네 가지 독립변수군으로 나누어 분석하였다. 연구 결과 저항의 유형에 따라 각 변인의 영향도가 다름을 확인하였다. 저항의 강도가 세 질 수록 시도 가능성의 영향력이 커졌으며, 강도가 약할수록 기존 시스템에 대한 만족도가 저항에 대한 영향도가 컸다. 시간적 위험 및 기존 시스템에 대한 만족도는 모든 유형의 저항에 영향을 끼치는 것으로 나타났다. 저항의 정도에 따라, 확산을 위한 전략적 의미를 마케팅 또는 시스템 개발의 관점에서 제시하였다는 점에서 본 연구의 의의가 있다.한국과학기술원 :정보경영프로그램

Development of Immobilized Cell Separator and Its Application to Immobilized Continuous Process for the Production of Cyclosporin A

We have developed an efficient immobilized cell separator for continuous operation of immobilized fungal cell cultures, and applied this separator to actual fermentation process for the production of cyclosporin A (CyA), a powerful immunosuppressant. In the experiments employing highly viscous polymer (carboxymethyl cellulose) solution, the decantor showed good separating performances at high solution viscosites and fast dilution rates. Air duct and cylindrical separator installed inside the decantor turned out to play key roles for the efficient separation of the immobilized cells. By installing the decantor in an immobilized perfusion reactor system (IPRS), continuous immobilized culture was stably carried out even at high dilution rate for a long period, leading to high productivities of free cells and CyA. Almost no immobilized biomass existed in effuluent stream of the IPRS, demonstrating the effectiveness of the decan- tor system for a long-term continuous fermentation. It was noteworthy that we could obtain these results despite of the unfavorable fermentation conditions, i.e., reduced density of the biosupports caused by overgrowth of cells inside the bead particles and existence of high density of suspended fungal cells (10g/l) in the fermentation broth

Studies of Cyclosporin A Biosynthesis under the Conditions of Limited Dissolved Oxygen or Carbon Source in Fed-batch Culture

We investigated the effects of dissolved oxygen (D.O.) and fructose (C-source) on cell growth and biosynthesis of cyclosporin A (CyA) produced as a secondary metabolite by a wild-type filamentous fungus, Tolypocladium inflatum. This was performed by controlling the level of D.O. and the residual C-source, as required, through adjustment of medium flow rate, medium concentration and agitation rate in fed-batch cultures. CyA production was furned out to be maximal, when D.O. level was controlled around 10% saturated D.O. and concentration of the C-source was maintained sufficiently low (below 2 g/L) not to cause carbon catabolite repression. Under this culture condition, we obtained the highest values of CyA concentration (507.14 mg/L), Qp (2.11 mg CyA/L/hr), $Y_x/s$ (0.49 g DCW/g fructose), $Y_p/s$<(22.56 mg CyA/g fructose), and YTEX>$_p/x$</TEX> (48.31 mg CyA/g DCW), but relatively lower values of cell concentration (11.98 g DCW/L) and cell productivity (0.043 g DCW/L/hr), in comparison with other parallel fed-batch fermentation conditions. These results implied that, in the carbon-limited culture with 10% saturated D.O. level, the producer microorganism utilized the C-source more efficiently for secondary metabolism