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.

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

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.

Computational modeling and design for the development of environment-friendly power systems: 1.5 MW coal-natural gas co-firing boiler, 250 kg/day hydrogen production system, and 5 kW-class solid oxide fuel cell power system

Iman rahimipetroudi University of Science and Technology (UST) 2022 국내박사

Climate change around the world has a profound impact on the global environment and the activities of life and has become a major global problem. Fossil fuels, in particular coal, is the most widely used fuel, especially in the field of power generation, and considered to be the main contributor to climate change and air pollution due to its high-intensity carbon levels. On the other hand, because worldwide fossil-fuel resources are significantly diminishing, however, energy consumption around the world is intensifying. Researchers agree that hydrogen and fuel cell technologies are contributing significantly to the transition to a low-carbon society, given their performance and flexibility in comparison with fossil fuel combustion technologies. Therefore, due to growing concern over the environmental impacts of coal-fired power facilities in continuous operation, an effective transition to more efficient units is required. Thus having good knowledge of the designs and configurations of the burners in boilers will be helpful to realize further improvements in the combustion characteristics and to comply with NOx emission standards. Besides, with the increase in the number of hydrogen vehicles worldwide, localized hydrogen refueling stations (HRS) are required, and empirical and technological improvements are therefore essential to overcome technological challenges related to durability, reliability, convenience, and supply network efficiency. In addition, before full-scale commercialization of SOFC power system, system-level design and operation glitches must be resolved. Accordingly, the main objective of this dissertation are computational modeling and design for the development of environment-friendly power systems in response to energy demands and low emissions for a sustainable future. This study composed of five chapters. In chapter one, background and an overview of power systems conditions that impact the global environment are given. The second chapter of the dissertation is focused on developing and designing an effective state-of-the-art dual-fuel pulverized coal (PC)-natural gas (NG) burner for use in dual-fuel fired power plant boiler utilities. The novelty of these study results, relate to burner modifications that are cost-effective, do not require large and complex additional structures, and incorporate a variety of technologies including fuel-air staging, flow swirling, preheating, and co-firing to increase performance and minimize emissions. The work reported in this chapter includes experimental and numerical modeling to study the effect of different operating conditions, excess air ratio, fuel staging, and NG blending. An optimal experimental design using a response surface methodology was also adopted to examine the significance of the operating parameters. Analysis of variance indicates that the regression equation can correctly represent the responses (p-value < 0.0001). It is also indicated that the excess air ratio and percentage of preheated PC have significant effects on NOx emissions (p < 0.005). The optimal conditions were determined to include an excess air ratio of 1.2 and 50 % PC injection into the preheating stream. Meeting these conditions, the predicted average NOx emission was 430±3.1 ppm and the average measured NOx emission 436±11.2 ppm, with 6% O2. Moreover, further reduction of NOx emission by up to 50% highlights the beneficial approach of NG co-firing. This design allows intensifying of recirculation and a mixture of fuels and oxidizers appropriate for improving the combustion characteristics significantly. The third chapter provides a comprehensive study of the effect of a developed co-firing burner and its front-wall, opposed-wall, and tangential firing arrangements on the performance improvement and emissions reduction of coal-natural gas combustion in a boiler. Understanding the combustion characteristics inside a boiler is essential to increase the efficiency and reduce environmental-related concerns. The novelty of this work is associated with a detailed analysis of the effectiveness of a developed co-firing coal-natural gas burner and the arrangements of the burners in the boiler for efficient combustion. Comparisons were made between the three main types of firing; front-wall, the opposite-wall, and the tangential firing types. The characteristics of the flow, the coal particle motion, the temperature distribution, the concentrations of species, and NOx emission levels are examined. The results showed that each burner in the front-wall-fired type creates independent long flame zones. In an opposite-wall fired type, the flames of burners impinge upon the center of the furnace to create turbulence. Results show that front-wall and opposite-wall firing configurations exhibit hot peak zones and temperature imbalances near the furnace sidewall. This emphasizes the need for heavily swirling vanes in the main burner to shorten the flame length and mix the fuel and oxidant well for efficient combustion. The state-of-the-art tangentially fired configuration produced a fireball, ensuring thorough mixing in the furnace and allowing for the complete combustion and uniform distribution of the temperature such that NOx reduction occurs preferentially. Additionally, these results confirm the advantage of combusting coal with natural gas in the main burner, as doing so reduces NOx emissions up to 19%. The technological options identified offer potential for interested manufacturers, researchers, and others in related industries to improve the performance and reduce the emissions of industrial dual-fuel-fired combustion utilities. The fourth chapter focuses on developing and undertaking a comprehensive CFD analysis of an effective state-of-the-art 250 kg/day hydrogen generation unit for an on-site hydrogen refueling station (HRS), an essential part of the infrastructure required for fuel cell vehicles and various aspects of hydrogen mobility. This design consists of twelve reforming tubes and one newly designed metal fiber burner to ensure superior emission standards and performance. Experimental and computational modeling steps are conducted to investigate the effects of various operating conditions, the excess air ratio (EAR) at the burner, the gas hourly space velocity (GHSV), the process gas inlet temperature, and the operating pressure on the hydrogen production rate and thermal efficiency. The results indicate that the performance of the steam methane reforming reactor increased significantly by improving the combustion characteristics and preventing local peak temperatures along the reforming tube. It is shown that EAR should be chosen appropriately to maximize the hydrogen production rate and lifetime operation of the reformer tube. It is found that high inlet process gas temperatures and low operating pressure are beneficial, but these parameters have to be chosen carefully to ensure proper efficiency. Also, a high GHSV shortens the residence time and provides unfavorable heat transfer in the bed, leading to decreased conversion efficiency. Thus, a moderate GHSV should be used. It is shown that heat transfer is an essential factor for obtaining increased hydrogen production. This study addresses the pressing need for the HRS to adopt such a compact system, whose processes can ensure greater hydrogen production rates as well as better durability, reliability, and convenience. The fifth chapter deals with designing, analyzing, and optimizing for the development of a 5 kW-class solid oxide fuel cell (SOFC) power system using anode-off gas recycling. This system is evaluated through modeling and simulation of stacks, including the balance-of-plant equipment using Aspen Plus. A portion of the anode off-gases from the fuel cell stack is recycled in the proposed system to achieve higher efficiency. The remainder is reacted with the depleted oxidant in the afterburner. The thermal energy from the combustor is utilized in the steam generator, reformer, and heat exchangers to balance the heat requirements of the SOFC system. The model performs heat and mass balances and considers ohmic, activation, and concentration losses for the voltage calculation. In addition, sensitivity analyses of major operating parameters, such as anode off-gas recycling ratio (AOGRRatio), fuel utilization factor (Ufuel,i), operating temperature (Top), current density (j), and steam to carbon ratio (S/C) on the system performance, are investigated. It is found that anode off-gas recycling provides an alternative approach to eliminate the need for an external water supply during operation of the SOFC system and increase the electrical efficiency while still maintaining the fuel utilization rate of the stack at a permissible level. Key words: Computational modeling, Design, Environment-friendly, Power generation system, Coal-natural gas co-firing boiler, Hydrogen production system, Solid oxide fuel cell system, Emission reduction, Performance improvement

Efficiency Enhancement in Ultrathin Cu(In,Ga)Se2 Solar Cells Prepared on Transparent Conducting Oxide Back Contacts

MuhammadSaifUllah University of Science and Technology (Campus: Kore 2018 국내박사

Analog and Digital Designs for On-Chip Learning in Neuromorphic Systems : 온칩 학습용 뉴로모픽 시스템을 위한 아날로그/디지털 디자인

Vladimir Kornijcuk University of Science and Technology 2018 국내박사

현대 디지털 컴퓨터는 인간의 두뇌에 비해 훨씬 더 빠르고 정확하게 논리 및 산술 연산을 수행할 수 있다. 그러나 주변의 환경을 실시간으로 인식하고 학습하는 능력에서 디지털 컴퓨터를 비롯한 인공 시스템은 아직 포유동물의 두뇌 수준엔 미치지 못한다. 지난 수십 년 동안 하드웨어 인공 시스템으로 포유동물 신경망의 기능을 실현하기 위한 연구가 이루어져 왔으며, 이는 ‘뉴로몰픽 (neuromorphic) 공학’ 이란 이름으로 알려져 있다. 본 논문은 확장가능성과 전력 효율성을 갖추면서 온칩(on-chip) 학습이 가능한 뉴로몰픽 시스템용 회로와 시스템을 제시함으로써 뉴로몰픽 공학에 기여하였다. 첫 번째로, leaky integrate and fire(LIF)에 기반한 새로운 형식의 인공 스파이킹(spiking) 뉴런을 제시하였다. 제시된 디자인은 통상적으로 축전기 기반 integrator를 활용하는 것과 달리 플로팅 게이트(floating gate, FG) integrator를 활용하고 있다. FG에 저장된 전하의 방전시간은 터널의 넓이보다는 높이, 두께에 대한 의존성이 더 크며, 이는 뉴런의 집적도 향상 가능성이 높음을 시사한다. 회로 동작은 BSIM 4.6.0 상보성 금속 산화막 반도체(CMOS) 모델을 활용한 시뮬레이션을 통해 진행되었다. 다음으로, spike timing dependent plasticity(STDP) 모델을 구현한 시냅스 회로를 제안하였다. FG-LIF 뉴런과 마찬가지로, 이 회로 역시 FG leaky integrator를 기반으로 구성되었다. randomly spiking neuron을 적용한 비지도 학습과 지도학습을 시키는 회로 시뮬레이션 결과, 두 경우 모두 시냅스간의 경쟁이 나타남을 확인하였다. 또한 몬테-카를로 시뮬레이션을 통해 CMOS의 오차가 존재할 경우에 대한 평가도 진행하였다. 세 번째로, 온칩 학습을 위해 random access memory, content addressable memory, partitioned RAM, pointer(PTR)의 네 종류의 순람표(look-up table, LUT) 기반 스파이크 라우팅 시스템을 제안하였다. 각각의 시스템에 대하여 라우팅의 지연이 발생하지 않는 최대의 네트워크 크기를 측정하기 위한 이론적인 근거를 제시하였고 스파이크 라우팅 속도, 가능한 신경 네트워크의 크기, 회로의 과부하 등에 관련된 장, 단점을 분석하였다. 마지막으로, a Xilinx Virtex-7 field programmable gate array (FPGA)를 활용한 완전 디지털화 뉴로몰픽 시스템의 프로토타입을 제시하였다. 이 프로토타입은 1024개의 LIF 뉴런들과 199,680개의 STDP 시냅스들로 구성되어있다. 비지도학습을 통해 시각적인 자극(막대)의 방향을 정확히 인식하도록 학습시킬 수 있었고, 이를 통해 이 시스템에서 온칩 학습이 가능함을 확인하였다. Achieving human-level cognitive performance using artificial systems has long been a motivating challenge that inspires researchers across different research fields. To date, one of the most widely used platforms to this end is general-purpose hardware, which partially owes to its rapid development and availability. The astonishing computational precision and speed make this platform very powerful in simulating behavioral models of biological neurons, synapses, and spiking neural networks (SNNs). Simulating large-scale SNNs in real time, however, is a daunting challenge due to the complexity, which makes their behavior description immensely complex at large scales. An alternative approach, neuromorphic system engineering, attempts to overcome this issue by using very large-scale integrated circuits to synthesize SNNs on a silicon wafer, instead of simulating their behaviors. This dissertation makes a contribution to this approach by proposing a range of circuits and systems for realizing scalable and power-efficient neuromorphic systems capable of on-chip learning. First of all, a new type of artificial spiking neuron based on leaky integrate-and-fire (LIF) behavior is proposed. A distinctive feature of the proposed design is the use of a floating gate (FG) integrator rather than a capacitor-based one. The relaxation time of the charge on the FG relies mainly on the tunnel barrier profile, e.g., barrier height and thickness (rather than the area). This opens up the possibility of large-scale integration of neurons. The circuit was designed by using 65 nm complementary metal oxide semiconductor (CMOS) technology and its feasible operation was examined by performing circuit simulation using the BSIM 4.6.0 CMOS model. The circuit simulation results offered biologically plausible spiking activity (<100 Hz) with a capacitor of merely 6 fF, which is hosted in an FG metal-oxide-semiconductor field-effect transistor. The FG-LIF neuron also has the advantage of low operation power (<30 pW/spike). Additionally, the proposed circuit was subject to possible types of noise, e.g., thermal noise and burst noise. In particular, thermal noise is likely prominent with regard to the use of such low capacitance. The simulation results indicated remarkable distributional features of interspike intervals that are fitted by Gamma distribution functions, similar to biological neurons in the neocortex. Second, a scalable synaptic circuit realizing spike timing dependent plasticity (STDP) model is presented. Like the FG-LIF neuron, this circuit is based on FG leaky integrators and is designed by using 65 nm CMOS technology. The circuit simulations feature (i) weight-dependent STDP that spontaneously limits the synaptic weight growth, (ii) competitive synaptic adaptation within both unsupervised and supervised frameworks with randomly spiking neurons. The estimated power consumption is merely 34 pW, perhaps meeting one of the most crucial principles (power-efficiency) of neuromorphic engineering. Additionally, the robustness of the proposed circuit in light of CMOS process variability effects (line edge roughness and random dopant fluctuations) was evaluated by performing Monte Carlo simulations. Despite notable parameter variability, the STDP behavior of the circuit could be validated as a whole, other than few exceptions. Third, four look-up table (LUT)-based spike routing schemes aimed for on-chip learning are presented. These are the random access memory, content addressable memory, partitioned RAM, and pointer (PTR)-based routing schemes. First of all, theoretical means are provided for evaluating the maximum network size for each scheme without routing congestion—experimentally justified using field-programmable gate array (FPGA) implementations. Given that they vary in spike routing rate, allowable neural network size, and circuit overhead, the pros and cons of each scheme are analyzed with regard to them. The results indicate that the PTR-based scheme supports a neuromorphic core consisting of 50,000 neurons (simultaneously firing at 50 Hz) and 10 million synapses at 1 GHz clock speed with minimum circuit overhead. The PTR-based scheme was further applied to multiple cores in a large-scale neuromorphic cluster, revealing that the cluster can theoretically hold 3.63 million neurons and 3.63 billion synapses at 200 MHz global clock speed when all cores operate at 1 GHz local clock speed. Finally, a fully-digital neuromorphic system prototype implemented in a Xilinx Virtex-7 FPGA is presented. The prototype comprised arrays of 1,024 LIF neurons and 199,680 STDP synapses and employed partitioned RAM routing scheme. The on-chip learning in the system was verified by performing a real-time orientation selectivity development experiment, during which it successfully “learned” to recognize the orientation of a visual stimulus (a bar) in the absence of teaching supervisor (unsupervised learning).

(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.

AZ61 마그네슘 합금 마찰교반용접부의 기계적 특성 평가 연구

선승주 University of Science and Technology 2017 국내석사

Environmental regulations related to exhaust gas are being strengthened globally, and the transportation industry is trying to overcome these problems by conducting high efficiency and light weight research. The optimum design or structural design of the vehicle exterior reduces air resistance and weight of the car body to achieve high efficiency and light weight. However, the optimum design of the exterior and the structural design have reached the limit, and research on the replacement of the body material is necessary. In fact, in the railway industry, the material of the vehicle has been replaced by steel, stainless steel, and aluminum alloy in order of weight. As a result, it showed the results of acceleration and energy saving. Magnesium alloys are under the lead of some advanced countries because of their low specific gravity, high strength to weight ratio, castability, electron shielding ability and excellent cutting ability. Particularly, the specific gravity of the magnesium(1.74) is 2/3 of aluminum, 1/3 of titanium and 1/5 of steel. Therefore, it is very attractive for lightweight research. In addition, when applied to a car body, since the manufacturing process is similar to that of aluminum alloy, reinvestment of equipment is not required, which is economical advantage. Therefore, it is expected that it will not only reduce the energy consumption through light weight, but also have a ripple effect on the entire industry. Welding technology is essential to apply metal materials to vehicles. Friction stir welding can overcome the disadvantages of conventional fusion welding and is regarded as economical and eco-friendly technology. Currently, it is applied to railway car body construction, propellant tank, and ship hull assembly, but it is still recognized as a new technology domestically. For this reason, the research on the application of friction stir welding of magnesium alloy is less than other metals domestically. Therefore, fundamental research on friction stir welding behavior of magnesium alloy, which is attracting attention as a next generation new material, should be conducted. The purpose of this study is to formulate an approach to derive optimized welding conditions for AZ61 magnesium alloys. Application of non-systematic welding conditions to conduct friction stir welding requires a established approach to the friction stir welding process because that is wasted time and cost. This study presents the friction stir welding parameters suitable for the AZ61 magnesium alloy by using the heat input relationship and then investigated the fracture behavior of the FS Weled zone for the application of the structure. Tensile and hardness tests were conducted to evaluate the mechanical properties of the welds, and optical microscope(OM) and scanning electron microscope(SEM) were used for defect and texture observation in welds. In order to understand the fracture behavior and mechanism of the weld, fracture surface and cross sections of welds were analyzed using scanning electron microscope and Electron Backscatter Diffraction(EBSD). As a result, when friction stir welding was performed within the heat input range of 3 ≤ Q <4, the welds without defects was obtained and the best mechanical properties were recorded. And the UTS, yield strength, and elongation of the welded region showed values of about 100.8%, 84.5%, and 60.6%, respectively, of those of the base metal. In addition, fracture surface and fracture location analysis show that the fracture of the welded part by the tensile behavior has two characteristics. First, the fracture occurred along the interface between the thermo-mechanical affected zone(TMAZ) and stir zone(SZ) from the bottom of the welds. Second, the cup-cone fracture shape, which is a typical characteristic of ductile fracture, is observed. The fracture locations of all specimens occurred in the AS region. Through the EBSD analysis, it was revealed that the cause of this behavior was due to the orientation variation of the magnesium alloy crystal. 세계적으로 배기가스와 관련된 환경규제가 강화되고 있으며, 수송기기 산업에서는 높은 에너지 효율과 경량화 연구를 통해 해당 문제점을 극복하려 노력하고 있다. 이에 차량 외관의 최적 설계 또는 구조적 설계를 통해서 공기 저항과 차체 무게를 감소시켜 고효율과 경량화를 실현하였다. 하지만 외관 최적 설계와 구조적 설계는 한계에 이르렀고, 차체를 구성하는 소재의 대체에 대한 연구가 시급하다. 실제로 철도 산업에서는 차량의 소재를 스틸, 스테인레스 스틸, 알루미늄 합금 순으로 대체하여 경량화에 성공하였고, 이는 차량의 고속화와 에너지 절감의 성과로 나타났다. 이에 더 가벼운 소재로 대체하여 더욱더 경량화를 기대하고 있다. 마그네슘 합금은 낮은 비중, 무게 대비 높은 강도, 주조성, 전자파 차폐성, 우수한 절삭성 등의 장점으로 구조물 산업 전반에 적용하기 위한 연구가 일부 선진국들의 주도하에 진행되고 있다. 마그네슘의 비중(1.74)은 알루미늄의 2/3, 티타늄의 1/3, 철강의 1/5 수준으로 차체 경량화에 매우 매력적이다. 또한 산업 전반에 있어 제작공정이 알루미늄 합금과 유사하기 때문에 설비의 재투자가 불필요한 경제적 이점이 있다. 따라서 경량화를 통한 에너지 절감 효과뿐만 아니라 산업 전반에 파급효과를 불러올 것으로 예상한다. 금속 소재를 차량에 적용하기 위해서는 용접 기술이 필수적이다. 마찰교반용접의 경우 기존에 용융용접의 단점을 극복할 수 있으며, 경제적이고 친환경 기술로 평가받고 있다. 해외에서는 철도차량 차체 제작과 항공 분야에서는 추진제 탱크 그리고 선박의 선체부재 조립 등에 적용되고 있는 상황이지만 여전히 국내에서는 익숙하지 않아 신기술로 인식되고 있다. 이 때문에 국내에서 마그네슘 합금의 마찰교반용접 적용에 대한 연구는 타 금속에 대한 연구보다 미흡한 상황이다. 따라서 차세대 신소재로 주목받고 있는 마그네슘 합금의 마찰교반용접 거동에 대한 기초적 연구가 절실하다. 본 연구는 AZ61 마그네슘 합금 소재에 마찰교반용접을 적용하여 가장 적합한 마찰교반용접조건을 도출하는 접근 방식에 목적이 있다. 임의의 용접조건을 선정하여 수행하는 것은 시간적, 경제적으로 소비가 크기 때문에 정립된 접근 방식의 체계화가 필요하다. 본 연구는 입열량 관계식을 이용하여 AZ61 마그네슘 합금에 적합한 마찰교반용접 변수 최적화를 제시하였고, 추후 구조물 적용에 대비한 마찰교반용접부의 파괴 거동에 대한 연구를 수행하였다. 용접부의 기계적 물성 평가를 위하여 인장 및 경도 시험을 진행하였고, 용접부 내의 결함 및 조직 관찰을 위하여 광학현미경과 주사전자현미경을 이용하였다. 또한 용접부의 파괴 거동 및 매커니즘을 이해하기 위해 주사전자현미경과 전자후방산란회절 장치를 이용하여 파괴 단면과 용접부 횡단면을 분석하였다. 그 결과 입열량 조건 3≤Q〈4 범위 내에서 마찰교반용접을 수행할 경우 결함이 없는 용접부를 얻었으며 가장 우수한 기계적 물성이 기록되었다. 기계적 물성은 최대인장강도, 항복강도 그리고 연신율이 모재대비 각각 약 100.8%, 84.5% 그리고 60.6% 수준으로 나타났다. 또한 파괴 단면 관찰과 파괴 위치 분석 결과 인장거동에 의한 용접부 파괴는 두 가지 특징을 보였다. 첫 번째, 용접 툴 핀 하부에서부터 열-기계적 영향부와 교반부 사이 경계면을 따라 파괴되었고, 두 번째, 컵-원뿔 파괴와 유사한 파괴 거동이 나타났으며, 내부 균열 발생 및 진전으로 인해 파괴된 것으로 판단된다. 용접부의 파단 위치는 모두 AS영역에서 발생하였는데, 이러한 거동의 원인은 EBSD 분석결과 마그네슘 합금 결정의 방위 변화에 의한 것으로 확인되었다.

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