Controllability of Non-thermal Effect in Low Current Arc Plasma and Its Applications in Fuel Conversion : 저전류 아크 플라즈마에서의 저온 플라즈마 효과 제어 가능성 및 이를 이용한 연료 전환 공정

DINH DUY KHOE University of Science and Technology (UST) 2019 국내박사

Scientific and Technological Knowledge Production Trends and Collaboration Patterns Based on an Ecosystem Perspective: Case of Educational Robotics

RICHA KUMARI University of Science and Technology 2020 국내박사

The new and emerging technologies such as artificial intelligence, machine learning, and robotics have changed the current industrial structure and recreated the new industries that are majorly based on the value chain of the global network environment. In a recent setting, the emergence of technological development and innovation is much dependent on a collaborative structure that can facilitate the recombination of existing knowledge and technologies to generate innovation. To enhance the collaborative structure and technological recombination, it is important to establish an environment that is less bounded and blurry and supports an open ecosystem environment. The innovation and knowledge ecosystem is characterized by a community of actors that assist evolving characters of knowledge structure and performance to co-produce innovation. The changing dynamics of interactions in an ecosystem provide a better understanding of the development and competitive strategy of emerging technology leading to value creation. Hence, this study utilizes the perspective of an ecosystem to analyze the development trends of scientific and technological knowledge and knowledge flow structure of a specific emerging technology. For this, the study uses the case of educational robotics technology and developed a framework to examine the comprehensive knowledge structure, evolutionary trends, and collaborative patterns in this technological area. In the first part of the study, the ecosystem framework is evaluated and the theory of the knowledge ecosystem is updated in the context of this study. The theoretical study evaluates the knowledge production pattern and type of knowledge produced within the structure. In the second part, the importance of educational robots has been highlighted to understand its role and future potentials. A special focus is given to highlight the role of educational robots in the current scenario of the COVID-19 pandemic. Moreover, the paper analyzed the scientific knowledge structure by applying the bibliometric and scientometric based evaluation methods to examine the productivity and performance of major countries and players in educational robotics domain. Also, the different principles of social network analysis like hubs, authorities, and broker analysis are used to identify the key countries and institutions working in the educational robotics area. The co-citation analysis at the country and institutional level is done to quantify and evaluate the connections among these players. Finally, an interaction among the players has been visualized by using a network map. The findings of the analysis showed that educational robotics research is more prominent in developed countries like the US, UK, Japan, and East Asian, and countries of other developing regions still lack scientific research in this area. USA, UK, Belgium, and the Netherlands are the most significant hubs and authorities acting as an important point in knowledge transfer. Netherland, Japan, and the USA play an important role as gatekeeper functionalities by acting as important bridge agents in knowledge transfer activities. Similarly, the most important institutions found were also mostly from advanced nations like Australia, the US, Sweden, and Canada. The competitive analysis is helpful to evaluate the country’s position and performance and the result can support R&D investment and policy-related decisions. In the next part of the study, the paper identified the important concepts and representative research areas from the scientific knowledge data by using keyword co-occurrence analysis. Further, representative research areas are selected by using centrality based measures that were used to find important and influential keywords. Also, topic modeling based on latent Dirichlet allocation (LDA) algorithms is applied to technological knowledge (patents) data to identify the latent knowledge structure and valuable topics. The model offers emerging technology areas and trends and contribute to the understanding of the emergence and development of technology over time and in forecasting the technology for the near future. At the final step of the analysis, the views and expectations of users on educational robotics technology have been analyzed by using the hype curve, and sentiment analysis. The analysis is conducted on twitter data to provide a better understanding of the response and sentiments of users. Social media, as a source of knowledge exchange, has an impact on the innovation ecosystem and support open innovation models. Understanding the polarity and sentiments by using social media helpful in analyzing the market expectation on technology. This result of the analysis can be useful to understand the educational technology adoption process in the market and can assist in other market-related decisions. 인공지능, 기계학습 및 로봇공학과 같은 신흥기술은 현재의 산업 구조를 변화시켰으며, 글로벌 네트워크 환경의 가치사슬을 기반으로 하는 신산업을 재창조하였다. 이러한 최근 환경에서 기술 개발과 혁신의 등장은 기술혁신을 창출하기 위해 기존 지식과 기술의 재조합을 촉진할 수 있는 협력구조에 크게 의존하고 있다. 협력구조 및 기술의 재조합을 강화하기 위해서는 경계가 보다 명확하고 개방된 생태계 환경을 구축하는 것이 중요하다. 혁신과 지식 생태계는 진화하는 지식 구조와 성과를 통해 혁신을 공동 창출하는 행위자들의 커뮤니티로 특징지어진다. 생태계 내에서 변화하는 상호작용의 역학관계는 가치창출로 이어지는 신흥 기술의 개발 및 경쟁 전략에 대해 보다 깊은 이해를 제공한다. 따라서 동 연구는 생태계 관점을 활용하여 특정 신기술의 과학기술 지식 및 지식 흐름 구조의 개발 동향을 분석하고자 한다. 이를 위해 동 연구에서는 교육용 로봇의 사례를 이용하며, 해당 기술분야의 포괄적인 지식 구조, 발전 추세 및 협력 패턴을 검토하기 위한 프레임 워크를 개발하였다. 제1장에서는 생태계 프레임워크를 평가하고, 동 연구의 맥락에서 지식 생태계 이론을 업데이트하였다. 이론적 연구에서는 지식 생산 패턴과, 그 체계 내에서 생성된 지식의 유형을 평가한다. 제2장에서는 교육용 로봇의 역할과 미래 잠재력에 대한 언급을 통해 교육용 로봇의 중요성을 강조하였고, 현재 COVID-19 시나리오 하에서 교육용 로봇의 역할에 특별히 중점을 두었다. 또한 교육용 로봇 분야에서 중심적인 역할을 수행하는 국가 및 기관의 성과를 조사하기 위해 계량서지 및 사이언토매트릭 기반의 평가 방법을 적용하여 과학적 지식 구조를 분석하였다. 또한 교육용 로봇 분야에서 협력하고 있는 주요 국가 및 기관을 식별하기 위해 허브, 권위 및 브로커 지수 등 다양한 소셜 네트워크 분석 원리를 활용하였다. 국가 및 기관 수준에서의 공동 열거 분석은 이러한 참여자 간의 연관성을 수량화 및 평가하기 위해 수행되었다. 마지막으로 네트워크 지도를 활용하여 참여자 간의 상호작용을 시각화 하였다. 분석 결과에 따르면 미국, 영국, 일본 및 동아시아와 같은 선진국에서 교육용 로봇 연구가 더욱 두드러지고 있으며, 다른 개발도상국에서는 여전히 동 분야에 대한 과학적 연구가 부족한 것으로 나타났다. 미국, 영국, 벨기에 및 네덜란드는 지식 이전의 중요한 요충지로서 작용하는 가장 중요한 허브 역할을 하고 있다. 네덜란드, 일본 및 미국은 지식 이전 활동에서 중요한 교량 역할을 수행하고 있다. 마찬가지로, 핵심 기관들은 호주, 미국, 스웨덴 및 캐나다와 같은 선진국에서 나타났다. 경쟁분석은 국가의 연구단계 및 성과를 평가하는 데 도움이 되며, 그 결과는 R&D 투자 및 정책 관련 의사 결정에 활용될 수 있다. 제3장에서는 키워드 동시 발생 분석을 통해 과학 지식 데이터에서 중요한 개념과 대표 연구 영역을 파악하였다. 또한 중요하고 영향력 있는 키워드를 찾는 데 사용된 중심성 지표를 사용하여 대표 연구 영역을 선별하였다. 또한 잠재 디리클레 할당(LDA) 알고리즘을 기반으로 하는 토픽 모델링은 기술 지식(특허) 데이터에 적용되어 잠재적 지식 구조 및 중요 주제를 식별하였다. 동 모델은 신흥 기술 분야 및 트렌드를 제공하고, 기술의 출현 및 발전을 이해하는 데 도움을 주며, 가까운 미래의 기술 예측에 기여한다. 또한 정책 결정자와 기업의 향후 의사 결정에 도움이 될 수 있다. 분석의 마지막 단계인 제4장에서는 하이프 사이클과 감정분석을 활용하여 교육용 로봇 기술에 대한 사용자 견해 및 요구를 분석하였다. 트위터 데이터에 대한 분석은 사용자 반응 및 정서를 보다 잘 이해할 수 있도록 제공되었다. 지식 교환의 원천인 소셜 미디어는 혁신 생태계에 영향을 미치며 개방형 혁신 모델을 지원한다. 소셜 미디어를 활용하여 극성 및 정서를 이해하는 것은 기술에 대한 시장의 기대치를 분석하는 데 도움이 된다. 동 분석 결과는 시장의 교육 기술 채택 과정을 이해하고 다른 시장 관련 의사 결정에 도움이 될 수 있다.

AmoebaNet : an efficient and scalable SDN-enabled network service for extreme-scale distributed science

Shah, Syed Asif Raza University of Science and Technology 2019 국내박사

The extreme-scale distributed science workflows play an essential function for scientific discoveries. Today’s large scientific experimental facilities are generating tremendous amount of data. In recent years, the significant growth of scientific data analysis has been observed across scientific centers. The scientific experimental facilities are producing unprecedented amount of data and scientific community encounters new challenges to data intensive computing. The performance of extreme-scale distributed science is highly depends on high-performance, adaptive, and robust network service infrastructures. To support data transfer for extreme-scale distributed science, there is the need of high performance, scalable, end-to-end, and programmable networks that enable scientific applications to use network efficiently. The existing network paradigm that support extreme-scale distributed science workflows consists of three major components: terabit networks that provide high network bandwidths, Data Transfer Nodes (DTNs) and Science DMZ architecture that bypasses the performance hotspots in typical campus networks, and on-demand secure circuits/paths reservation systems, such as ESNet OSCARS and Internet2 AL2S, which provides automated, guaranteed bandwidth service in WAN. This network paradigm has proven to be very successful. However, to reach its full potentials, we claim that existing network paradigm for extreme-scale distributed science must address three major problems: last mile problem; scalability problem; and the agility, automation and programmability problem. The recently emerged concept in network world is called Software-Defined Networking (SDN). This latest technology introduced the new methods of configuration and management of networking. In SDN, the underlying network devices are simply considered as packets forwarding elements and control logic of network is managed centrally by using a software program that dictates the entire network behavior. To address above mentioned problems, this thesis proposed a solution called AmoebaNet. AmoebaNet applies SDN technology to provide “QoS-guaranteed” network services in campus or local area networks. AmoebaNet complements existing network paradigm for extreme-scale distributed science: it allows application to program networks at run-time for optimum performance; and, in conjunction with WAN circuits/paths reservation system such as ESNet OSCARS and Internet2 AL2S; in result, it solves the problems of last mile, scalability, and the agility, automation and programmability. In this thesis, we also presented Congestion Aware Multipath Optimal Routing (CAMOR) solution which can be an additional service for AmoebaNet.

Development of human ear-mimetic construct based on three dimensional cell printing technology

이정섭 Pohang University of Science and Technology 2016 국내박사

Tissue engineering is an interdisciplinary field integrating biotechnology, materials engineering and mechanical engineering that focuses on restoring and regenerating various tissues and organs, such as the bladder, airways, and myocardium. In particular, cell printing is a promising technology for effectively regenerating tissues and organs whereby a construct is fabricated based on a layer-by-layer process using appropriate cells at a high cell density, effective hydrogels, and growth factors. Such cell-printing technology allows three dimensional (3D) living tissues and organs to have anatomical cell arrangements and geometrical shapes similar to native tissues and organs by directly printing cells. Despite the outstanding potential of cell-printing technology, most studies remain in the early stages of regenerating tissues, with relatively simple shapes and functions. Furthermore, there is a limitation with regard to regenerating composite tissues of similar shape and size to human tissues and organs because the technology needed to fabricate complex-shaped constructs of large volumetric size has not yet been developed. In this research, a 3D human ear-mimetic cell-printing technology was developed and applied to ear regeneration. Here, the 3D human ear-mimetic cell-printing technology was validated through fabricating a human ear-mimetic cell-printed construct and evaluating the cartilage and adipose tissue formation. Human tissues and organs are composite tissues, comprising two or more types of cells and tissues. With respect to fabricating the cell-printed construct, a multi-head tissue/organ building system (MtoBS) with six independent dispensing heads was developed to enable the dispensing of widely varying biomaterials with high- and low-viscosity properties. Additionally, in fabricating the human ear-mimetic cell-printed construct, the prolonged 3D printing time can cause low cell viability and inadequate performance of the construct because the cells can be exposed to a harsh environment over a long printing time. With this in mind, the MtoBS was improved, with a clean-air workstation, a humidifier, and a Peltier system, providing a more suitable printing environment for a large-volume construct to maintain high cell viability. With the advanced MtoBS, it was confirmed that better control of the printing temperature enabled the enhanced printability of hydrogels and higher cell viability for the construct, despite a prolonged printing time. The human ear has a complex shape and an anatomically complex composition of tissues. A bottom-up fabrication method has the limitation of not being able to stack constructs with overhanging, curved, or hollowed shapes, given the cell-printing technology. To fabricate a cell-printed construct with a complex shape, a sacrificial layer process and computer-aided design and manufacturing (CAD/CAM) technologies were developed. In the sacrificial layer process, the main part was printed with poly-caprolactone (PCL) and the cell-laden hydrogel, and polyethylene glycol (PEG) was then deposited as a sacrificial layer to support the main structure. PEG can be removed readily in aqueous solutions, and the procedure for removing PEG does not affect cell viability. CAD/CAM software was developed to enable a cell-printed construct to be fabricated with two polymers and two cell-laden hydrogels by independent control of the dispensing heads. Fabrication conditions were established for creating a construct for ear regeneration. Appropriate line widths and pore sizes were determined for fabricating the construct with an ear-like shape and similar mechanical properties to those of the human ear through the evaluation of mechanical strength. Once the fabrication conditions were established, the sacrificial layer process, and cell-printing technologies allowed an ear-shaped cellular construct to be manufactured. According to these results, the advanced MtoBS enabled a cell-printed construct with complex shapes to be fabricated while maintaining high cell viability using the sacrificial layer process and CAD/CAM technology. For the effective regeneration of composite tissue in the ear, porcine auricular cartilage and human adipose tissue-derived decellularized extracellular (ear-cdECM and adECM) hydrogels were developed for printing cells and inducing target tissue formation. Human adipose-derived stem cells (ASC) were encapsulated with 2% ear-cdECM and 3% adECM hydrogels, and the cell-laden hydrogels were used to fabricate the cell-printed construct, which regenerated cartilage and adipose tissue in both in vitro and in vivo tests. Compared with control groups, which consisted of cell-printed constructs with 4% alginate hydrogel and transforming growth factor-beta (TGF‒β) for cartilage tissue formation, and with 3% collagen hydrogel and basic fibroblast growth factor (bFGF) for adipose tissue formation, it was confirmed that the two kinds of dECM hydrogels induced cartilage and adipose tissue formation at the same level of tissue regeneration as with specific growth factors. Based on the powerful dECM effect, the cell-printed construct in the shape of an ear was fabricated successfully with ASC-laden ear cdECM and adECM hydrogels, and was implanted subcutaneously in a nude mouse model for in vivo testing. For 4 and 8 weeks, the human ear-mimetic cell-printed constructs maintained their initial shapes, and cartilage and adipose tissue were formed in the parts with ear-cdECM and adECM hydrogels. These results demonstrated that dECM hydrogel can induce target tissue formation without specific growth factors and allow the cell-printed construct to form composite tissues. Thus, this validated the 3D cell-printing technology developed for fabricating human ear-mimetic cell printed constructs and regenerating composite tissues.

Fabrication and Electrochemical Investigation of Composite Cathodes for Solid Oxide Fuel Cells

SAEED UR REHMAN University of Science and Technology 2018 국내박사

Solid oxide fuel cell (SOFC) technology has made significant progress in the past 50 years for a wide range of power generation applications. The SOFC technology is attractive due to its efficiency for the direct conversion of the chemical energy stored in fuels such as hydrogen and hydrocarbons into electricity. The SOFC features an all solid-state construction and high-temperature operation. The combination of these characteristics provides a number of advantages for SOFCs, including flexibility in cell and stack designs, manufacturing processes, fuel type and generator sizes. However, for successful commercialization, it is essential to greatly improve the performance and durability of the SOFC technology. In this regard, SOFC cathodes need special attention because of their lower activity for oxygen reduction reaction (ORR) and gradual degradation over time. The composition and microstructure of cathode materials have a large impact on the performance of SOFCs. The purpose of this dissertation is fabrication and characterization of composite SOFC cathodes by using the existing SOFC materials to extend the triple-phase boundaries through microstructure optimization. Chapter 1 and 2 provide an introduction and current status of the SOFC technology. Basic principles, thermodynamics, and state of the art materials for SOFCs are discussed. The designs of SOFC (tubular and planar) and their characteristics, benefits, and shortcomings are explained. New methods and strategies are discussed to improve the SOFC designs for better performance. Chapter 3 discusses the effect of Gd0.1Ce0.9O2-δ (GDC) addition on the phase stability, sintering behavior, thermal expansion, and porosity of La0.65Sr0.3MnO3-δ/(Y2O3)0.08(ZrO2)0.92 (LSM/YSZ) composite. The sintering temperature and the porosity of the LSM/YSZ composite were observed to increase with an increase in the amount of GDC. An LSM/YSZ/GDC tri-composite with optimized properties was selected to fabricate the tubular cathode-supported DCFCs (LSM/YSZ/GDC|YSZ|NiO/YSZ) through extrusion, slurry coating, and co-firing. A special chamber was designed for the in situ steam gasification of carbonaceous fuels and operation of the tubular SOFC. Electrochemical characterization was done by measuring the polarization curves and electrochemical impedance spectroscopy, using the syngas produced by in situ steam gasification of carbon black. Chapter 4 discusses the effect of GDC addition method on the properties of LSM-YSZ composite cathode support for SOFCs. Equal amounts of GDC were added to LSM/YSZ powder either by physical mixing or by a sol-gel process, to produce a highly porous cathode support for SOFCs. The effect of the GDC mixing method was analyzed in view of sinterability, thermal expansion coefficient, microstructure, porosity, and electrical conductivity of the LSM/YSZ composite. GDC infiltrated LSM/YSZ (G-LY) composite showed a highly porous microstructure when compared with mechanically mixed LSM/YSZ (LY) and LSM/YSZ/GDC (LYG) composites. The cathode support composites were used to fabricate the button SOFCs by a slurry coating of YSZ electrolyte and a nickel/YSZ anode functional layer, followed by co-firing at 1250 °C. The G-LY composite cathode-supported SOFC showed maximum power densities of 215, 316, and 396 mW cm-2 at 750, 800, and 850 °C, respectively, using dry hydrogen as fuel. Results showed that the GDC deposition by a sol-gel process on LSM/YSZ powder before sintering is a promising technique for producing porous cathode support for the SOFCs. Planar design of SOFCs is very attracted as an alternative to tubular design due to its higher power density, short current path, and lower operating temperature. Chapter 5 explains a new fabrication method of nanofibrous composite cathodes for planar SOFCs. The proposed method involves chemically assisted electrodeposition (CAED) of mixed metal hydroxide onto a carbon nanotube (CNT) template, followed by a low-temperature heat-treatment process. The CNT template is first fabricated on porous zirconia-based ion-conducting scaffolds (ICS) by catalytic chemical vapor deposition (CCVD) of C2H4. Perovskite-type LCO is then fabricated on the CNT template by CAED process of mixed La-Co hydroxide combined with thermal conversion of hydroxide to perovskite oxide. The method proposed here allows for the fabrication of LCO perovskites with a unique nanofibrous structure at reduced temperatures (~900 °C) while avoiding the formation of pyrochlore phases (e.g., La2Zr2O7), which are typically observed during conventional high-temperature sintering processes of LaCoO3 with zirconia-based electrolytes. The new method also provides the precise control needed to achieve desired oxide loadings without the need for repeated deposition-annealing processes. The anode-supported SOFCs with nanofibrous LCO cathodes on zirconia and ceria scaffolds show high and stable electrochemical performance of 0.95 and 1.27 W cm-2, respectively, at 800 °C. In addition to the absence of insulating pyrochlore phases, the unique nanostructure of the LCO cathode is believed to play a beneficial role in improving the electrochemical properties by providing a large number of active reaction sites and by facilitating mass transport through the porous nanofibrous structure Solid oxide fuel cell (SOFC) technology has made significant progress in the past 50 years for a wide range of power generation applications. The SOFC technology is attractive due to its efficiency for the direct conversion of the chemical energy stored in fuels such as hydrogen and hydrocarbons into electricity. The SOFC features an all solid-state construction and high-temperature operation. The combination of these characteristics provides a number of advantages for SOFCs, including flexibility in cell and stack designs, manufacturing processes, fuel type and generator sizes. However, for successful commercialization, it is essential to greatly improve the performance and durability of the SOFC technology. In this regard, SOFC cathodes need special attention because of their lower activity for oxygen reduction reaction (ORR) and gradual degradation over time. The composition and microstructure of cathode materials have a large impact on the performance of SOFCs. The purpose of this dissertation is fabrication and characterization of composite SOFC cathodes by using the existing SOFC materials to extend the triple-phase boundaries through microstructure optimization. Chapter 1 and 2 provide an introduction and current status of the SOFC technology. Basic principles, thermodynamics, and state of the art materials for SOFCs are discussed. The designs of SOFC (tubular and planar) and their characteristics, benefits, and shortcomings are explained. New methods and strategies are discussed to improve the SOFC designs for better performance. Chapter 3 discusses the effect of Gd0.1Ce0.9O2-δ (GDC) addition on the phase stability, sintering behavior, thermal expansion, and porosity of La0.65Sr0.3MnO3-δ/(Y2O3)0.08(ZrO2)0.92 (LSM/YSZ) composite. The sintering temperature and the porosity of the LSM/YSZ composite were observed to increase with an increase in the amount of GDC. An LSM/YSZ/GDC tri-composite with optimized properties was selected to fabricate the tubular cathode-supported DCFCs (LSM/YSZ/GDC|YSZ|NiO/YSZ) through extrusion, slurry coating, and co-firing. A special chamber was designed for the in situ steam gasification of carbonaceous fuels and operation of the tubular SOFC. Electrochemical characterization was done by measuring the polarization curves and electrochemical impedance spectroscopy, using the syngas produced by in situ steam gasification of carbon black. Chapter 4 discusses the effect of GDC addition method on the properties of LSM-YSZ composite cathode support for SOFCs. Equal amounts of GDC were added to LSM/YSZ powder either by physical mixing or by a sol-gel process, to produce a highly porous cathode support for SOFCs. The effect of the GDC mixing method was analyzed in view of sinterability, thermal expansion coefficient, microstructure, porosity, and electrical conductivity of the LSM/YSZ composite. GDC infiltrated LSM/YSZ (G-LY) composite showed a highly porous microstructure when compared with mechanically mixed LSM/YSZ (LY) and LSM/YSZ/GDC (LYG) composites. The cathode support composites were used to fabricate the button SOFCs by a slurry coating of YSZ electrolyte and a nickel/YSZ anode functional layer, followed by co-firing at 1250 °C. The G-LY composite cathode-supported SOFC showed maximum power densities of 215, 316, and 396 mW cm-2 at 750, 800, and 850 °C, respectively, using dry hydrogen as fuel. Results showed that the GDC deposition by a sol-gel process on LSM/YSZ powder before sintering is a promising technique for producing porous cathode support for the SOFCs. Planar design of SOFCs is very attracted as an alternative to tubular design due to its higher power density, short current path, and lower operating temperature. Chapter 5 explains a new fabrication method of nanofibrous composite cathodes for planar SOFCs. The proposed method involves chemically assisted electrodeposition (CAED) of mixed metal hydroxide onto a carbon nanotube (CNT) template, followed by a low-temperature heat-treatment process. The CNT template is first fabricated on porous zirconia-based ion-conducting scaffolds (ICS) by catalytic chemical vapor deposition (CCVD) of C2H4. Perovskite-type LCO is then fabricated on the CNT template by CAED process of mixed La-Co hydroxide combined with thermal conversion of hydroxide to perovskite oxide. The method proposed here allows for the fabrication of LCO perovskites with a unique nanofibrous structure at reduced temperatures (~900 °C) while avoiding the formation of pyrochlore phases (e.g., La2Zr2O7), which are typically observed during conventional high-temperature sintering processes of LaCoO3 with zirconia-based electrolytes. The new method also provides the precise control needed to achieve desired oxide loadings without the need for repeated deposition-annealing processes. The anode-supported SOFCs with nanofibrous LCO cathodes on zirconia and ceria scaffolds show high and stable electrochemical performance of 0.95 and 1.27 W cm-2, respectively, at 800 °C. In addition to the absence of insulating pyrochlore phases, the unique nanostructure of the LCO cathode is believed to play a beneficial role in improving the electrochemical properties by providing a large number of active reaction sites and by facilitating mass transport through the porous nanofibrous structure

(A) study on the high performance electromagnetic energy harvesting technology for vehicle suspension

Duong Minh Trung University of Science and Technology 2019 국내박사

Owing to the shortage of fossil fuel and a significant increase in the number of electric vehicles, it is mandatory to find alternative energy supplies to extend the mileage or operating time. Recovery of the wasted energy has been tremendously investigated for different sources, such as regenerative braking energy, thermal energy, and vibration energy from the suspension system. According to recent reports, harvestable power from the suspension system in a typical passenger car is between 100 and 400 W. This leads to a fuel efficiency improvement in the hybrid and electric vehicles by 7-10%. The major drawback of this technology lies in the difficulty of enhancing output power for a given space. The objective of this dissertation is the development of a high performance electromagnetic shock absorber applied to the vehicle energy harvesting technology. Operating conditions are based on the assumption that when a passenger car is moving on a road class C at a speed of 96 km/h, vibration speed, vibration frequency, and peak-to-peak stroke length on the shock absorber are 0.25 m/s, 10 Hz and 11.25 mm, respectively. Design targets for maximum and average output power are 250 and 100 W, maximum and average power density are 0.250 and 0.100 W/cm3, respectively. In this dissertation, direct-drive using a linear tubular generator is selected due to its simple structure, elimination of the transmission mechanisms, fast responses, etc. Different from most of the conventional devices, the novel machine combines both mechanical damper and electrical generator. Because of this specific configuration, the electromagnetic force has to be minimized to ensure safety and driving comfort. Based on the actual size of a commercial shock absorber in an SUV-Korando car, available space, and dimensions of the proposed machine are decided. To achieve the design targets, various topologiess including coreless model, cored model, inner and outer permanent magnet model, slot-pole combination, and number of phases are investigated. On top of that, to significantly increase the power density, a hybrid-permanent magnet structure is innovated. To simultaneously maximize output power and minimize electromagnetic force, multi-objective optimization based response surface method is implemented. Magnetic design and analytical prediction of performance are performed using an extensive finite-element analysis. Prototypes of the coreless and cored model are fabricated to evaluate the performance and verify the validity of the analysis. Experimental results are well-matched with analysis and all the design targets are successfully achieved.

Processability and stability studies of polymer solar cells

Rasool, Shafket University of Science and Technology 2020 국내박사

There is more sunlight reaching Earth in one hour than all the combined renewable (except solar) and non-renewable resources. To solve the increasing world’s energy demand when urbanization is coupled with industrialization, harnessing solar energy is one of the key to solve the prevailing energy issues. Greener raw material based polymer solar cells (PSCs) are regarded as next generation of thin-film solar cell technology due to its versatile and distinct applications such as low-cost, light-weight, mechanical flexibility and robust solution processability. With PCEs on the rise, the morphological tunings in bulk of the bulk heterojunction (BHJ) PSCs still have a big room to get optimized morphologies so that PCEs can be further improved. Other than morphological play in these PSCs, the major limiting factor still lies in their PCE’s transfer to the mass scale industrial roll-t-roll (R2R) production techniques. Therefore, the processability of the photoactive layers on the nano-morphological scale and on the R2R large scale is a huge challenge to overcome. Not only that, the device PSC’s stability when tested under light and heat/humidity is a major hurdle for the mass adoption of this class of solar cell technology. Keeping in view about the morphological optimizations at small area and the translation of small area PCEs to large area scale, this thesis has been focused on the processability and then the stability of these PSCs. First of all, the processability of the PSCs is addressed. Recently, the role of morphology in PSCs has been studied extensively and it has been found out that the photoactive layer’s blend morphology play vital role in polymer:PC71BM based BHJ PSCs. For this purpose, the relationship between the chemical structures of the photoactive materials and morphological understandings has been studied and its effect on the charge carriers as well the performances of the PC71BM based PSCs has been presented. The data helped us to develop the structure-morphology relationship for achieving highly efficient halogen free solvent processed PSCs. After morphological optimizations in small area, the compatibility of the photoactive materials used in small area PSCs has been investigated, especially using highly efficient PCBM based photoactive systems for the fabrication of large area modules. For instance, most commonly employed organic photovoltaic (OPV) materials, including PCE-10, PffBT4T-C9C13, PffBT4T-T3, PNTz4T etc have shown PCEs over 10% with PC71BM acceptor on small area via spin coating. These materials show very low PCEs due to probably unoptimized morphology arising from the material’s intrinsic constraint (such as processing conditions including processing temperatures) which limits the universal applicability of these materials for large area module fabrication. When considering the application of PSCs on small and large area simultaneously, then having produced high PCEs on small area with novel polymer design is not the only important parameter for selecting the material of choice. Keeping in view of the material’s compatibility on small area and large area module size, a series of polymers have been tested on large area OPV modules and their processing conditions have been optimized leading to produce module PCEs over 8% (area ≥ 50 cm2), based on fullerene acceptor from halogen-free solvent system. Final part of the thesis is devoted to the stability studies in PSCs. The roles of buffer layers have been thoroughly investigated with special emphasis on the cathode buffer layer (CBL). Firstly, modified CBL (PEIE modified ZnO) is employed in PSCs and the reason for enhancement in LS stability is investigated. In the second part, a stable CBL is employed in a photoactive layer consisting of ester modified electron donor polymers and PC71BM as electron acceptors. The aggregation of the fullerenes have been retarded via morphological interlocking and the reason behind the degradations in unoptimized morphology containing system or the enhanced stability in the morphologically interlocked polymer:PC71BM system has been investigated in detail and the underlying degradation mechanisms have been put forward. The morphological tuning of the photoactive systems, the optimizations of the small area and then the large area PCEs from the same photoactive system, and finally the study of the degradations and circumventing the reasons for degradation to fabricate highly stable PSC provides the basis for the development and the actual deployment of this solar cell technology for mass adoption.

Toward precise and accurate modeling of matter clustering in redshift space

오민지 University of Science and Technology 2018 국내박사

This dissertation presents the results on two-dimensional Redshift space distortion (hereafter RSD) analyses of the large-scale structure of the universe using spectroscopic data and on improvement of modeling of the RSD effect. RSD is an effect caused by galaxies’ peculiar velocity on their clustering feature in observation along the line of sight and is thus intimately connected to the growth rate of the structure in the universe, from which we can test the origin of cosmic acceleration and Einstein’s theory of gravity at cosmic scales in the end. However, there are several challenges in modeling precise and accurate RSD effect, such as non-linearities and the existance of an exotic component, e.g. massive neutrino. As part of endeavors for modeling more precise and accurate galaxy clustering in redshift space, this dissertation includes a series of works for this issue.

A Study on the Wastewater Treatment System by Advanced Phytoreactors

Oktavia Ratnasari University of Science and Technology 2012 국내석사

The increase of human activities in industrial or agricultural sectors to supply global consumptions causes deterioration in environment. In aquatic environment, water eutrophication is known as notorious for primary environment destruction. In atmospheric environment, anthropogenic global warming is continuously becoming one of the most important problems, despite many efforts have been done. It has been recognized that global warming is caused by CO2 emission mainly from fossil fuels. Various methods in capturing and sequestering CO2 have been intensively researched throughout the world. Phytoremediation is one of promising new technologies in addition to conventional treatment systems. This technology works by utilizing plants to remove contaminants in various media such as water, air, and soil. Through phytoremediation process, it may stimulate biological processes or physico-chemical characteristics of plants to aid the process. It also has been applied for treating numerous contaminants including heavy metals, pesticides, petroleum hydrocarbons, chlorinated solvents, explosives, radioactive substances and landfill leachates. These technologies have been broadly used in various fields because of its advantages in economic aspect, sustainability and operation as well as providing aesthetical value. In water environment, aquatic plants play a major contribution for sustaining nitrogen cycle and returning N2 gas back to the atmosphere through bacteria-mediated reactions of nitrification and denitrification. Several studies have demonstrated the effectiveness of these plants to remove nutrients, especially nitrogen and phosphorus, from polluted water. In the aspect of air pollution, studies have proven that phytoremediation has an important function in removing excessive amount of CO2 in the atmosphere by photosynthesis process of plants in terrestrial and aquatic ecosystems. Photosynthesis can produce plant biomass which can be utilized to produce renewable material for bioenergy. Since 1990s, light-emitting diodes (LEDs) have been developed as advanced light sources for indoor plant cultivation, replacing traditional fluorescent and incandescent lamps. LEDs have a very superior life span compared to conventional lamps and excellent features including energy efficiency, specific wavelength, easily modified light intensity and quality, small size, low thermal output, and high photoconversion efficiency. LEDs have been widely developed in indoor cultivation of various plant species, plant tissue culture, space agriculture, algaculture and plant disease reduction. In the aspect of light spectra, blue LED (400-470 nm) and red LED (630-665 nm) match with the absorption spectra of chlorophylls and carotenoids. As for phytochrome for plant growth, their peak absorbance of 660 nm and 730 nm can also be matched with red LED (630-665 nm) and far-red LED (730 nm). Since the discovery of LED technology, research related to plant growth and photosynthesis has been increased. This study was conducted to investigate nutrient removals from wastewater using effective aquatic plants in various systems incorporated into advanced phytoremediation of wastewater. Three types of phytoreactors were studied for their performances in removing nitrogen, phosphorus and organic contaminants. Nutrient removals were determined by kinetics, removal rates, and removal efficiencies. In the experiments using advanced plant growth acceleration technology, the growth rates of studied plants were also measured and compared to plant’s growth rates under controlled condition. The effects of light wavelengths in ABPs, ASBPs and ASCPs were also analyzed. In addition, the effect of CO2 enrichment in ASCPs was also considered. Lastly, prediction of nutrient removal using kinetic models was presented. Surface area occupied by plants and plant’s weights were employed to evaluate the performance of plants (P.stratiotes, E.crassipes and A.gramineus) to remove TN, TP and COD by batch reactors under normal and accelerated conditions. The removal of TN, TP and COD by plants differed between the treatment of light sources (p < 0.05). Using first order kinetic equation, based on unit area, TN removal rates by batch reactors ranged from 1,760 mg N to 3,720 mg N m-2 d-1, while based on unit weight, removals ranged from 862 mg N to 1,990 mg N kg-1 d-1. Area-based TP removals were between 141 mg P and 508 mg P m-2 d-1, and weight-based removals varied from 101 mg P to 283 mg P kg-1 d-1. For COD, area-based removals ranged from 528 to 1,330 mg COD m-2 d-1, and weight-based resulted in the range of 281 and 703 mg COD kg-1 d-1. Water lettuce (Pistia stratiotes) was selected for experiments with advanced plant growth acceleration (PGA) technology. In advanced sequential batch phytoreactor (ASBP), statistical analysis by ANOVA declared that the difference of area-based and weight-based nutrient removal rates by FL and PGA treatments was significant (p < 0.05 for TN, TP and COD removals. TN and COD removals were best achieved by phytoreactors treated using red light (=630+660 nm), while highest TP removal was reached using blue light (=400+440 nm). Further, in experiments using advanced sequential continuous phytoreactor (ASCP), in which different concentrations of CO2 were employed, p < 0.01 validated that kinetic coefficients for TN and TP removals was significantly different between normal and advanced phytoreactors. COD removal showed a p value of 0.08, suggesting that the application of LED didn’t improve the removal of COD in the system. Plants cultivated under advanced reactors showed superior results of growth rates compared to controls. In batch experiment under red light (=660 nm), P.stratiotes showed growth rate of 1.86 times higher than those grown under FL lamps, while for E.crassipes and A.gramineus, their growth rates were 2.14 times and 2.29 times compared to those grown under FL lamps. In ex

The Dry Coal Separation Characteristics Using Autogenous Medium

DAVAASUREN JAMBAL University of Science and Technology 2018 국내박사

초록 Autogenous medium 이용한 건식 석탄 분리 특성 석탄과 그 속에 혼재되어 있는 맥석들 간에는 비중 및 표면특성 등이 서로 다른데, 이러한 특성들은 석탄과 맥석들을 분리하는 주요한 수단으로 사용되고 있다. 습식처리 방법을 기반으로 하는 분리기술(습식선탄)은 분리도(율) 면에서는 우수하나, 많은 량의 물과 여러 단계의 처리공정들(예, 탈수/건조 및 폐수처리 등)이 병행되어야 하기 때문에 선탄시설 비용과 운영비용이 크다는 것이 가장 큰 단점이다. 이러한 단점들을 극복하고자 최근 들어 물을 사용하지 않고 분리하는 건식 선탄기술에 대한 관심이 미국, 중국등 석탄보유국들을 중심으로 세계적으로 높아 지고 있는 상태이다. 기존의 건식선탄 장치로는 공압식 지그(Air Jig), 공압식 테이블(Air shaking table), 유동층 고밀도 매질 선별기 (Dense medium fluidized bed separator), optical and x-ray sorter 등이 대표적이며, 이들은 석탄과 그 속에 함유되어 있는 맥석들 간의 특성에 따라 선별적으로 사용되고 있다. 이러한 기술 중에서 석탄과 맥석들간의 비중도 차이를 기반으로 하는 비중층 분리막 생성을 이용한 기술이 보편적으로 널리 사용되고 있다. 그러나 이와 같은 기존의 건식 선탄 장치들은 6 ~ 80mm 크기의 ROM 원탄을 처리하는 데는 효과적이지만, 대부분의 경우 6mm보다 작은 입자에서는 분리성능이 크게 감소하기 때문에 주로 6mm 이상의 크기에서만 적용하여야 하는 한계가 있다. DOE, Coaltech 등 선탄관련 평가 보고서 등에 따르면 입자크기가 약 6 mm 미만인 ROM 석탄은 일반적으로 건식 분리에 효과적이지 않다고 보고하고 있다. 이를 극복하기 위하여 많은 비용이 소요되는 고밀도의 층간 매개물질(분리막 생성물질)을 사용하기도 한다 보고 된 Ep 값은 6mm 이하의 미립자에 대한 분리 효율이 좋지 않음을 보여 주고 있다. 따라서 현재 개발중인 건식 선탄기술들은 미립자 크기에서의 분리효율 향상이 주요 쟁점으로 대두되고 있다. 일반적으로 한국지질자원연구원(KIGAM)은 최근 KAT process라는 효율적인 건식 선탄기술을 개발하였다. (김병곤, 전호석, Davaasuren Jambal). 이 기술의 주요특징은 원탄자체에서 Autogenous medium 생성 및 이로 인한 석탄과 맥석들 간의 자가 분리 기술이다. 이 기술을 기반으로, 본 연구에서는 석탄입자와 맥석들 간에 비중차이에 의한 계층화 유도 및 분리 메커니즘을 개발하고자, 인위적으로 외부에서 충간분리 생성 및 유지를 위한 매체(medium)를 투입하지 않고, 선탄 대상인 ROM 원탄으로부터 이들이 자연발생적으로 생성(Autogenous medium)되도록 하였다. 또한 이를 기계적으로 구현하기 위한 KAT table 구동 메커니즘을 개발하였다. 본 연구에서 제시한 Autogenous medium 생성 메커니즘을 이용하면 기존기술의 분리한계 입자인 6mm 이하의 미립자에서도 분리특성이 우수한 효과틑 얻을 수 있었다. Autogenous medium에 의하여 분린된 분리 층은 비중이 높은 입자(맥석)는 맨 아래 층으로, 상대적으로 비중이 낮은 가벼운 입자(석탄)들은 분리층 상부로 이동시킬수 있었고, 이러한 현상들이 지속적으로 일어날 수 있었다. 즉, Autogenous medium 생성 메커니즘과 이를 구현하기 의한 KAT table의 구조적 특징에 따른 구동 메커니즘 개발이 본 연구의 특징이다. Autogenious medium 생성율은 KAT table의 구조적 특징인 Coal stream측에 설치한 Block wall의 높이와 Coal stream과 맥석 stream과의 수직방향으로 작용하는 table의 운동거리에 비례하였다. 또한 석탄과 맥석들 간의 자율 계층화(Self-stratification)는 Autogenious medium 생성율과 shaking table의 진폭의 크기와 공기 압력 영향을 받으며, 특히 6mm이하의 미립자 영역는 진폭의 영향이 더욱 크게 나타났으며, 분리효율에도 많은 영향을 미친다. 유연탄의 경우, 평균 분리 비중은 D50에서 약 1.9-2.0 g/cm³ 이었고, 확률오차 Ep는 0.08-0.15의 범위 이었으며, 5-10mm 크기의 회분함량은 원탄 44%에서 선탄후 8.4%로 감소하였으며, 이때 회분 제거율은 89.5%였다. 1-5 mm 크기에서의 회분 함량은 원탄 33.7%에서 선탄후 9.4%로 감소하였다. 이 때의 평균 분리 비중은 D50에서 약 1.85-2.0 g/cm³ 이었고, 확률오차 Ep는 0.1-0.15의 정도였다. 석탄과 맥석들간의 비중차이가 작은 무연탄의 경우, 평균 분리 비중은 D50에서 약 2.3-2.45 g/cm³ 이었고, 확률오차 Ep는 0.18-0.2의 범위 이었으며, 5-10mm 크기의 회분함량은 원탄 50.46%에서 선탄후 25%로 감소하였으며, 이때 회분 제거율은 72.3%였다. 1-5 mm 크기에서의 회분 함량은 원탄 61.9%에서 선탄후 28.2%로 감소하였다. 이 때의 평균 분리 비중은 D50에서 약 2.5 g/cm³ 이었고, 확률오차 Ep는 0.2의 정도였다. 키워드 : 건식 선탄, Autogenous medium, Density Stratification   ABSTRACT The Dry Coal Separation Characteristics Using Autogenous Medium Coal and gangue minerals have different densities and surface characteristics, which are used as the primary means of separating coal and gangue. Water based separation methods (wet coal cleaning) are very efficient among other methods those using differences in densities or surface characteristics for the separation. The efficiency of wet processing is undeniable, with nearly ideal density based separations achievable. But these wet technologies require huge amounts of process water and several steps of treatments (e.g., dewatering, drying, waste water treatment) which increase its operating cost and it pointed as disadvantage of wet methods. One potentially attractive method is the dry coal cleaning technology. Dry methods offer significant advantages over wet methods, including reduced surface moisture, enhanced heating value, elimination of processing water and waste, and interest in non-water-based dry coal cleaning technology has been increasing worldwide, mainly in coal-rich countries such as the United States and China. There are several kinds of dry separation devices such as pneumatic jig, pneumatic table, dry dense medium (fluidized bed) separator, optical and x-ray sorter, and tribo-electrostatic separator etc., have been developed based on the differences in the particular properties specific density and surface characteristics of coal and its associated minerals. Among these technologies the density based separators which use density stratification of light and dense particles are most widespread. The modern air-based density separator achieves effective density-based separation for particle sizes greater than 6 mm and in most cases, the separation performance is significantly reduced for particles smaller than 6 mm. According to the coal preparation related evaluation reports, ROM coal with a size of less than 10 mm is generally not effective for dry separation. The reported Ep values show that the separation efficiency for fine size particles is poor. Therefore, in the dry coal technology field, the separation of fine particle size coal is becoming a major issue. Pneumatic separators generally utilize an upward air-flow along with vibration to create a stratification of high and low density particles. Coal particles are not able to penetrate through the bed and thus remain on top whereas high-density, high-ash content particles move through the bed. Therefore, in order to obtain sufficient separation, layering between coal particles and gangue particles must be generated and maintained constantly. Korea Institute of Geoscience and Mineral Resources (KIGAM) has recently developed an efficient dry coal technology called the KAT process. (Kim Byoung-Gon, Jeon Ho-Seok, Davaasuren Jambal). The main feature of this technology is that autogenous medium is generated in the raw coal itself and the self-separation behavior between coal and gangue is used. The main proposed attempt in this work was a possible use of self-formed autogenous medium of feed coal for the separation of coal and gangue by increasing the separation bed height to induce density based stratification process. The possible vertical stratification of particles in the bed relative to the bed height was predicted by stratification coefficient (C_s) and it was developed using the bed height, the average diameter of particles and the density differences of two fractions. To achieve sufficient stratification in the separation bed it was required to increase the bed height on the air table using the block wall. The block wall was designed to intentionally halt the cross-sectional flow at the lower end to generate an accumulation of feed to use as an autogenous medium for the separation. The generation of autogenous medium was proportional to the height of the block wall installed on the coal stream side, which is a structural feature of the KAT table, and the moving distance of the table acting in the vertical direction of the coal stream and the gangue stream. In addition, the self-stratification between coal and gangue is influenced by the generation of autogenous medium and the amplitude of the shaking table and air pressure. Particularly, the particle size of 6mm or less is more affected by the amplitude and has a large effect on the separation efficiency. Conducted tests showed that the increased bed height and an autogenous separation bed had a significant effect on the separation efficiency. The average separation density was around 1.9-2.0 g/cm3 at D50 and the probable error Ep was ranged from 0.08 to 0.15 for bituminous coals and for high ash difficult to clean coals (anthracite), the Ep value was around 0.15-0.2. After dry separation, 5-10 mm size bituminous coal feed ash 46-48% was decreased to 7.1-13.6% in a product with 83-89.8% ash rejection rate. The clean coal yield was ranged between 51-58%. High-density fractions discharged to reject stream with 83-90% ash content. It indicates that the air table effectively removed the dense fraction with relative density >2.0 g/cm3. For bituminous coal 1-5 mm size fraction, the feed ash 34-41% was decreased to 9.4-10.7% in product and the product yield was 60-70%, and the separation density was around 1.85-2.0 g/cm³ and the Ep value was ranged from 0.1 to 0.15. It was observed that the increased bed height and the higher feed rates jointly responsible for forming sufficient amount of autogenous separation bed and thus promotes the stratification process. The formation of the stable autogenous separation bed is strongly related to characteristics of original feed material. Keywords: Dry coal preparation, Autogenous medium, Density stratification,