Development on hybrid-capacitor with high energy density

Ha, Seong-Ji Graduate School of UNIST 2019 국내석사

In this thesis, I observe the methods to overcome the low energy density in the supercapacitor system which is the crucial issue in energy storage industries. I challenge simple and easy approaches to achieve better capacitor properties than before by fabricating the three-dimensional structure of current collector and colloid structure of active material. First, rational design of the current collector with large surface area and high electrical conductivity is the very important factor in the hybrid-capacitor system for high performance. Nickel particles-coated three-dimensional graphene foam current collector (Ni-GF) was fabricated by two simple steps from cost-effective commercial cotton and nickel chloride, based on the growth of graphene on the surface of nickel particles. The welded nickel particles on graphene sheets and three-dimensional graphene networks enhance the electrical conductivity and various pores in graphitic carbon domains gives the high surface area, generated by the thermal decomposition of organic precursors during a carbonization or pyrolysis process. This strategy provides the high performance in the supercapacitor system as the current collector. The high surface area of Ni-GF supports a lot of reaction sites of active materials and high electrical conductivity helps the good rate capability and long-term cycle life. The prepared Ni(OH)2/Ni-GF//MnO2/Ni-GF capacitor exhibited an excellent energy density of 175 Wh kg-1 at a power density of 722 W kg-1 for a two-electrode system. Also, I improve the weakness of supercapacitors such as low energy density by utilizing cobalt and nickel ion colloidal electrodes on a carbonized cotton. Ni2+ and Co2+-coated carbonized cotton (NC/CC) were prepared by simple and rapid fabrication process. The metal colloidal electrode on three-dimensional carbon foam provides many active sites, which leads to a lot of redox reactions in whole colloids of CNFs. CNFs were optimized by adjusting the contents of Co2+ and Ni2+ on carbon foams, and it showed high capacitance and stable cycle stability. The optimized NC/CC//Mn/CC capacitor leads to overcome a limitation of supercapacitor and to achieve the enhancement of capacitor properties. The outstanding performance of NC/CC//Mn/CC is attributed to the increased active sites of metal colloidal electrodes as well as to the good stability for carbon foams. These excellent electrochemical results have the great potential for energy storage devices with high values of energy density and power density.

An Analysis of the Sources and Influences in the Creation of "Korean Folk Song Suite" by Ji-Soo Hwang

황지수 Univ. of Minnesota 2004 해외박사

새로운 음악을 창조하는 데 있어서 한국과 서양적인 요소의 융합은 많은 한국 작곡가들에게 중요한 요소이다. 황지수 작곡의 "Korean Folk Song Suite"에서 한국 민요가 전통음악의 형태 속에 가지는 구조와 지방마다 다른 성격을 보이며 나타나는 여러 특징들이 서양 음악의 틀에서 어떻게 발현되는지 분석되어있다. 한국 민요의 잠재력이 한국 음악의 정수를 보여주며 이 곡에 미친 영향은 지대하다. 생생한 아이디어와 음악의 고유성은 뚜렷이 구분되는 특징을 통해 새로운 음악의 창조에 갚이 관여하고 있다. "Korean Folk Song Suite"은 헝가리 작곡가인 벨라 바르톡의 "헝가리 농부의 민요에 의한 즉흥곡 Op. 20"의 형식에 영향을 받기도 했다. 새로운 화성과 즉흥적인 음악이 흐름이 그것이다. 그리고 또다른 영향은 황병기의 많은 작곡과 연주라 하겠다. 한국 고유의 음악과 악기로 새로운 지경을 실험적으로 개척하여 새로운 음악을 만들어낸 것이다. "Korean Folk Song Suite" 곡의 분석을 하게 된 기회를 통해 새로운 음악을 창조하는 과정에서 어떻게 서로 다른 음악이 통합되어 나타나는지 배경과 자료들을 밝힌다. 제 1장에서는 역사적 발전과 지리적 구분이 음악에 어떤 영향을 미치며 다른 성격을 보이는지 밝히고, 한국 음악의 여러 특징을 기술하고 있다. 제 2장에서는 각 민요의 역사적 배경의 중요성과 함께 가사 및 음악적 분석을 통해 이 곡에서 어떻게 표현되고 있는지 각 곡의 분석하고 있다.

A Highly Utilizable Web Service Planner with Extended Capabilities : 확장된 기능을 가진 고기능 웹 서비스 플랜너

KIM, JI-HYEON GRADUATE SCHOOL OF CHUNGNAM NATIONAL UNIVERSITY 2005 국내박사

웹 서비스란 네트워크 상에서 컴퓨터간의 상호 운용이 가능한 소프트웨어 시스템이다. 이는 컴퓨터가 인지할 수 있는 형식 (예를 들어 DAML-S, WSDL) 으로 기술되고 이 서비스를 필요로 하는 쪽에서는 SOAP등과 같은 표준 프로토콜을 사용해 미리 기술된 방법에 따라 서비스를 활용하게 된다. 웹 서비스 플랜닝은 사용자의 서비스 요구를 만족시킬 수 있도록 필요한 웹 서비스들을 찾아 조합하는 것이다. 사용자의 서비스 요청을 만족시킬 만한 웹 서비스가 없을 때 웹 서비스 플랜너는 자동으로 가용한 서비스들을 조합해 사용자의 요구를 만족시키도록 플랜닝한다. 사용자의 서비스 요구는 서비스 형태로 표현되며 이는 웹 서비스들과 비교, 매칭을 하게 된다. 웹 서비스 플랜닝의 중요한 관건은 어떻게 하면 사람의 간섭을 최소화시켜 필요한 서비스들을 조합하느냐 하는데 있다. 실제 많은 웹 서비스 플랜너들은 자동으로 플랜 닝을 하고 있다. 그러나 현재까지 알려진 방법들은 몇 가지 문제점들을 갖고 있다. 즉 1) 기존의 서비스 플랜너들은 컨셉트간의 충돌을 고려하고 있지 않다. 만약 두 매칭 서비스간의 컨셉트 충돌이 발생한 경우 충돌된 컨셉트를 갖고 있는 웹 서비스는 플랜닝 패스를 만들 때 선택되어서는 안 된다. 기존의 플랜너들은 이 경우 단지 충돌된 컨셉트간에 내포관계가 없는 것으로만 단정한다. 2) 기존의 플랜너들은 위음성(false-negative) 조건을 고려하지 않는다. 위음성 조건이란 플랜어가 찾은 서비스 집합은 답의 일부만을 찾아낼 수도 있다는 것을 말한다. 주어진 사용자의 요구를 만족시키는 플랜닝 패스는 일반적으로 여러 개가 존재한다. 기존의 서비스 플랜너들은 일단 하나의 서비스 패스가 성공적으로 작성되면 이 찾아진 서비스 패스를 보완해줄 수 있는 다른 서비스 패스를 더 이상 찾지 않는다. 그러나 실제로는 다른 서비스 패스가 존재해서 이미 찾아진 서비스 패스를 보완해줄 수 있는 기회가 있다는 것이다. 3) 기존의 서비스 플랜너들은 백트랙킹 플랜닝을 하지 않는다. 현재까지의 플랜너들은 다소 단순한 출력-입력 파이프라인을 통한 직진 플랜너들이다. 위에 언급된 이러한 문제점들을 해결하기 위하여 이 논문에서는 확장된 플랜닝 메커니즘을 제안하였다. 제안된 플랜너는 다음의 두 액션을 통해 자동화된 서비스 플랜닝을 하게 된다. 첫째, 만약 요청 서비스가 발견된 서비스의 입력 요구사항을 만족 시키지 못할 경우 이 요구 사항을 만족하기 위한 서비스 플랜닝을 한다. 둘째로 만약 찾은 서비스가 요청 서비스의 출력 요구를 부분적으로밖에 만족시킬 수 없는 경우 이 요청 서비스를 만족시키기 위한 서비스 플랜닝을 수행한다. 제안된 플랜닝 메커니즘은 플랜닝 성공 율을 높이기 위해 백트랙킹 플랜닝을 하다. 이 플랜닝 메커니즘은 플랜닝 패스를 만들 때 잘못된 서비스를 선택하는 오류를 피하기 위해 컨셉트 충돌을 검사한다. 또한 제안된 플랜닝은 위음성 조건 발생시 보완 서비스 플랜닝을 수행한다. A Web service is a software system designed to support interoperable machine-tomachine interaction over a network. It has an interface described in a machineprocessable format (e.g., DAML-S, WSDL) and other systems interact with the Web service in a manner prescribed by its description using standard protocols like SOAP. Web service planning is to find an executable sequence of Web services that achieves a given user’s service request. When there is no available service that satisfy the user’s request, the Web Service planner tries to find out a way that can satisfy the request through service planning with available services automatically. User’s requst is expressed as a service that can be compared and matched to Web services. One of the essential problems of Web service planning is how to compose the services together with minimal human effort. There are many Web service planners that do the service planning automatically. Although the service planning is done automatically the current plannings methods still have several problems, i.e., 1) the planners don’t consider the concept conflict. When there is a concept conflict between two matching services, the conflicted provider’s service should not be selected in planning path generation. The known planners just consider the concept conflict as there being no subsumption relationship between the two conflict concepts. 2) the current planning methods don’t consider the false-negative conditions. The false-negative condition means that the found service set may return just a part of answers. There may exist several provider’s service paths that can satisfy the current request. When planning finished with success for the requester’s service request, the known planners no longer consider the complement planning paths that can complement the pre-found service paths. One thing we can notice is that, in some cases, even the planned path can satisfy the request, another planning path can complement the pre-found service sets that can supply the service results that the pre-found service sets can’t supply. 3) the web service planners don’t consider the backtracking planning. To the present, there are relatively simple straight forward planners that do the planning through outputinput pipelining. These methods can limit the planning success rate. To solve the problems mentioned above, we suggested an extended planning mechanism. The service composition method suggested in this dissertation does automatic Web service planning with the following two actions. Firstly, if the request service is not entitled to receive a found service, the planner tries to find the complement services for the request service so that the request service is entitled to get the found service. Secondly, if the request service is partially satisfied by a found service, then the planner tries to find the complement service that can complete the request. The proposed extended planning mechanism entails backtracking to increase the service availability and planning success rate. The planning mechanism also considers the concept conflict to avoid selecting the wrong service in planning path generation. The proposed planner also does complement planning for false-negative condition.

Physical and chemical modification of ordered mesoporous carbon materials for CF4 adsorption

Park, Hyeonji Sungkyunkwan University 2023 국내석사

Due to the increase in global energy demand, greenhouse gas concentrations are increasing every year. Among the PFCs, which are widely used in the semiconductor industries and possess extremely high global warming potentials, carbon tetrafluoride (CF4) contributes significantly to the greenhouse effect despite its low atmospheric concentration. In order to prevent CF4 emission, adsorption is considered a potential option because of its relatively low cost and convenience to operate without producing byproducts. Various candidates with large surface area and highly porous structure have been studied for CF4 adsorption, and carbon-based adsorbents are especially promising due to the merits of physical and chemical stability and facile synthesis. In this research, physical and chemical modification of ordered mesoporous carbon (OMC) materials were conducted. The micropore developed OMC with phosphoric acid catalyst and boron oxide doped OMC for addition of Lewis acid sites were synthesized to enhance the CF4 adsorption performance. In order to evaluate the adsorption capacities of the materials, CF4 dynamic adsorption, isotherms, breakthrough experiments were performed. 전 세계 에너지 수요의 증가로 인해 온실가스 농도는 매년 증가하고 있다. 소량으로도 문제를 일으키는 온실가스 중 CF4는 반도체 제조 공정에서 사용되며 안정적인 사면체 구조로 인해 대기 수명이 5만년으로 매우 길다. CF4 배출을 방지하기 위한 방법들 중 흡착은 상대적으로 비용이 저렴하고 부산물을 생성하지 않고 운영이 편리하여 효과적이다. CF4 흡착을 위해 넓은 표면적과 높은 다공성 구조를 가진 다양한 물질들이 연구되어 왔으며, 특히 탄소계 흡착제는 물리적, 화학적 안정성과 합성이 용이하다는 장점 때문에 유망하다. 본 연구에서는 메조기공성 탄소(OMC) 물질의 물리적 및 화학적 변형을 수행하였고, 인산 촉매를 사용한 미세기공이 발달된 OMC와 boron oxide가 도핑된 OMC를 합성하여 기존의 일반적인 OMC에 비해 CF4 흡착 성능을 향상시켰다. 물질의 흡착능을 평가하기 위해 CF4 동적 흡착, 등온선, 파과 실험을 수행하였다.

Comparison of Li-Ion storage behaviors between graphite and ordered mesoporous carbon electrodes

Kim, Minji Sungkyunkwan university 2019 국내석사

Since the first introduction of lithium ion battery, it has been widely used for various kinds of electronic devices. As the expansion of applying lithium ion batteries to the electric vehicles (EV) or energy storage systems (ESS), demands for improved ability increase, too. So researches for developing high-capacity anode materials are actively in progress. Various candidates are appeared for alternative of graphite but ordered mesoporous carbon (OMC) is excluded because of its seriously low initial coulombic efficiency. However there are some advantages of ordered mesoporous carbon when it is used as electrode material in lithium ion battery. For example, short ion transfer distance derived from nanostructure can develop the electrochemical performances and pore structures can play as a physical buffer that accommodates the strain. If the drawbacks can be overcome, OMC would be a good electrode material. Herein, we controlled the OMC framework and compared each electrochemical performance. Then we investigate the relationship between physical properties and electrochemical performances. As the surface area and micropore volume increase, reversible capacity increases and initial efficiency decrease. Graphitic character has similar tendency with initial efficiency but it shows no relationship with capacity. And the retention is almost similar regardless of physical properties. Lastly OMC can be used with graphite as additive that this co-using can increase both capacity and initial efficiency of OMC. With further research, ordered mesoporous carbon could show developed electrochemical performances. 리튬이온전지는 여러 휴대용 전자기기를 비롯한 전기 차, 에너지 저장 장치 등 다양한 분야에서 활용되며 그 쓰임이 계속해서 늘어나고 있다. 현재 상용화된 리튬이온전지는 양극소재로 리튬 코발트 산화물, 리튬 망간 산화물 혹은 리튬 코발트-망간 이종산화물을 사용하고 음극소재로는 흑연을 사용하고 있다. 하지만 흑연은 이론용량이 372 mAhg-1정도로 작기 때문에 이를 대체할 수 있는 새로운 음극소재에 관한 연구가 활발하게 진행되고 있다. 각광받는 소재들은 실리콘, 주석 등이고 이 외에도 이론용량이 높은 여러 금속산화물에 대한 연구가 활발하게 진행되고 있다. 반면 탄소소재, 특히 다공성 탄소 물질의 경우 리튬이온배터리의 음극소재로 적용이 어려운데 이는 큰 비표면적에서 비롯된 많은 SEI층의 생성으로 인해 초기용량이 매우 낮기 때문이다. 때문에 나노 구조, 다공성 구조가 주는 여러 가지 이점들이 있음에도 불구하고 다공성 탄소는 리튬이온전지의 전극소재로 적용하는 연구가 크게 진행되지 못하고 있다. 본 연구에서는 다공성 탄소를 리튬이온전지의 음극소재로 적용할 수 있을지 그 가능성을 찾기 위해 여러 가지 물리화학적 특성을 조절하고자 하였다. 다공성 탄소를 전극소재로 사용하기 위해 해결해야 하는 가장 큰 문제는 낮은 초기효율을 높이는 것이다. 이는 큰 비표면적에서 비롯된 것이기 때문에 현재의 흑연보다는 높은 가역용량을 유지하면서 초기효율을 높일 수 있는 비표면적을 찾고자 하였다. 이 외에도 가역용량을 높이거나 수명이 저하되는 현상을 막아주는 등 전기화학적 성능이 더 좋아지도록 하는 물리화학적 성질의 조건을 찾고자 한다. 본 연구진은 먼저 규칙적인 메조기공을 갖는 탄소소재를 합성한 뒤 흑연과의 비교를 통해 다공성 탄소가 가지는 전극소재로서의 장단점을 확인하였다. 이후 합성과정에서 전구체와 산 촉매를 변화시켜서 물리화학적 성질이 조절된 탄소소재를 만들어 물리화학적 성질변화에 따라 전기화학성능이 어떻게 변화되는지를 살펴보고 그 상관관계를 찾아내었다. 이러한 물리화학적 성질과 전기화학성능간의 상관관계들은 탄소소재를 리튬이온전지의 전극물질로 활용하기 위한 추후 연구에 활용될 수 있을 것으로 기대된다.

中國加强軍事力量 對韓半島安全的影響

박지영 韓國外國語大學校 國際地域大學院 2005 국내석사

Since the cold war, the security strategy of China has become more region-centered and economy -priented. The security and domestic economy environments of China changed its judgement on the external risk and the goals of diplomatic policy. Modernization of the Chinese poeple's army, domestic problems, economic development, its interests in the regional economy have become important elements shich have an efect on its security strategy. Though the Chinse view toward the Korean Peninsular's situation shows a fluctuation agitating according to period and momentum, it cannot be seperated from the neighboring countries including the U.S, Japan and Russia, which share great interests from the security-strategical point of view, considering its history and geopolitics. In particular, the change of security envirenment of Northeast Asia centering around the Korean Peninsular under the new international order which began to change from late 1980s gave a great variable factor to the Chinese policy to the Korean Peninsular. In order words, China has given a top priority to 4 modernization schemes emphasizing the revitailzation of the national economy consistnet with the pragmatic line, and this self-renewal from the hegemonistic ideology acts a no less than variable factor to its view of the Korean Peninsular. Though the stability of the Korean Peninsular is relatively less given priority ti that of the countures near the South China, it will remains an important region to China. The strategical goal of china toward the Korean Peninsular is to make the Peninsular stabl0 an peaceful without nuclear weapons. China doesn't want disorder and unrest in the Korean Peninsular , for which may lead to a military strife between the South and North Koreans. China ir worrying if it will be involved in the strife which results in the destruction of its economic result as well as its cooperations with the western countires it has established until now. For this reason, it is most consistent with the national interests of China to promote friend relations, go ahead with unification of the local economies, and maintain the regional stability in the Northeast Asia and the Korean Peninsular. Above all, China is striving to creating a peaceful surrounding environment for its economic development, while containing the increasing influence of the U.S. and Japan in the Northeast Asia through a policy of power balance. China will demand its interests more directly to the neighbring countries when it carries forward a successful economic develpment and achieve the army;s modernization to the significant level. Appearance of the modernized army of China might build up tension in the Northeast Asia including the Korean Peninsular by furthering Russia's reinforcement of its military powers in the Far East and Japan's rearmament. In addition, the augmentation of the military powers of China might act as a factor to change its friendly countries' policies toward the Korean Peninsualr including the U.S. and Japan, if it increase its assistance ti the North Korea at ordinaty or non-ordinaty times and strenghthens its position and its right to speak about the problem of the Korean Peninsular. In the current of the post-cold war, the East Asia which puts spurs to arms build up has an aptitude for a new cold war owing to all kinds of the regional problems. The competitive relations with the neighboring countries which are seeking after the actual economic profit will assume much more fluid and elastic aspect. In these complex security environments, in which China is pursuing for great ecinimic growth and augmentation f military powers, Japan is trying to strenthen its political status and resultant increase in war potencial, the U.S. are utilizing the relationship between China and Japan in order to contain China, and Russia is making its efforts to reinforce its weak but signficant influence on the region, Korea should reestablishits relationship with each country from a longitudinal point of view and augment its subtantial national power lest it commit its historical blunder in the past. 냉전 이후 중국의 안보전략은 좀더 지역 중심적이고 경제 지향적이다. 냉전 후 안보 환경과 국내 경제 환경은 외부적 위험에 대한 중국의 판단과 외교 정책의 목표를 바꾸어 놓았다. 인민해방군의 현대화, 국내 문제, 경제 발전, 지역경제에 관한 이해관계 등은 중국의 안보 전략에 영향을 미치는 중요한 요소가 되었다. 중국의 대 한반도 정세관은 시기별, 계기별로 변화하는 부침현상을 보이고 있으나, 역사적, 지정학적 차원에서 본다면 안보전략상 큰 이해를 갖고 있는 미, 일, 러 등 주변국과의 관계를 분리시키고서는 생각할 수 없는 한계를 지니고 있다. 특히 1980년대 말부터 변화하기 시작한 새로운 국제질서 하에서 한반도를 중심으로 한 동북아 안보환경 변화는 중국의 대 한반도 정책에 큰 변화요인을 제공하였다. 즉 중국의 대 한반도 정세관은 실용주의 노선에 따라 국가경제 건설에 중점을 둔 4개 현대화 계획에 국가목표의 최우선 순위를 두게 되었고, 이러한 패권주의 이데올로기로부터의 탈피는 대 한반도 시각에도 적지 않은 변화 요인으로 작용하였던 것이다. 한반도의 안정은 남중국해 주변국과의 안보순위에 비하면 상대적으로 우선수위가 낮지만 여전히 중국의 중요한 안보 관심 지역이다. 중국의 한반도에 대한 전략 목표는 안정적이고 평화로우며 핵무기가 없는 한반도를 만드는 것이다. 중국은 한반도에서 혼란과 불안을 원치 않는다. 왜냐하면 이러한 혼란과 불안이 남북한간의 군사분쟁으로 이어지고 분쟁에 개입하게 될 경우 지금껏 이루어 놓은 경제적 성과와 서방국과의 관계협력들이 깨어질 것을 우려하고 있기 때문이다. 이러한 이유로 우호관계를 촉진하고 지역경제의 통합을 추진하며 동북아와 한반도의 지역적 안정을 우지하는 것이 중국의 국익과 가장 잘 일치한다. 중국은 경제 발전을 위해 무엇보다 먼저 평화로운 주변환경 조성을 위해 노력하고 있으며, 세려균형 정책을 통해 동북아에 있어 미국과 일본의 영향력 증대를 견제하고 있다. 그러나 경제성장이 성공적으로 추진되고, 이와 함께 군의 현대화가 상당한 수준까지 달성될 경우 중국은 보다 직접적으로 주변국에 대해 자신의 이해를 요구하게 될 것이다. 현대화된 중국군의 등장은 소련의 극동 군사력의 증강과 일본의 재무장을 촉진시켜 한반도를 비롯한 동북아의 긴장을 고조시킬 수 있다. 뿐만 아니라 중국의 군사력 강화는 평시 및 유사시 대북한 지원역량을 증대시키는 결과와 한반도 문제에 대한 중국의 입장과 발언권을 강화시켜 미, 일 등 우방국의 대한반도 정책을 변질케 하는 요인으로 작용할 가능성도 배제할 수 없다. 탈 냉전의 세계적 조류속에서도 동아시아는 아직도 군비 증강에 박차를 가하는 등 각종 지역문제로 인하여 신 냉전이 도래할 소지를 안고 있는 곳이다. 경제적 실리로 대변되는 주변국들과의 경쟁관계들은 더욱 더 유동적이고 탄력적인 모습을 띄게 될것이다. 중국의 경제대국화와 군사력 증강, 일본의 정치적 위상 강화노력과 이에 따른 전력증강, 중국견제를 위해 중,일 관계를 이용하여 일본을 활용하려는 미국, 미약하지만 지역 내 영향력 재강화를 위해 노력하는 러시아 등 이러한 복잡한 동북아 안보환경속에서 한국은 각국과의 관계를 장기적인 안목에서 재설정하고 실질적인 국력을 증강시키는 것이 과거의 역사적 과오를 범하지 않는 길일 것이다.

Ti-doped mesoporous Si/SiOx anode materials for high-performance lithium-ion batteries

Lee, Jihye Sungkyunkwan university 2021 국내석사

리튬 이온 전지는 다른 충전식 전지에 비해 가볍고 높은 에너지 밀도로 인해 다양한 영역에서 선택되는 에너지 저장 시스템이다. 그리드 수준의 기술의 발전에 의해 더욱 높은 에너지 밀도의 전지가 요구되고 있다. 기존 널리 쓰이고 있는 음극재인 흑연은 적당한 용량과 안정적인 사이클 성능을 가지고 있지만 계속 늘어나는 에너지 요구를 충족시키기에는 한계가 있다. 따라서, 높은 이론 용량을 가진 실리콘과 안정적인 사이클 성능을 가진 SiOx (0 < x < 2) 음극 물질들이 흑연의 대채제로 각광받고 있다. 두 물질의 각각의 단점은 충방전시의 극심한 부피 변화와 다소 낮은 용량이라는 것인데, 이에 여러 전략들이 제안되었다. 특히, 서로를 보완하며 시너지 효과를 갖는 Si/SiOx물질이 새로운 전도유망한 전극 물질로 등장하였다. 논문의 목적은 메조 포어와 소량의 Ti를 도입하여 Si/SiOx (0 < x < 2) 전극의 성능을 더욱 향상시키는 것이다. Si의 활성 물질과 SiOx의 구조적 안정성을 기반으로 메조 포어는 Si에 대한 또 다른 물리적 완충제일뿐만 아니라 Li에 대한 짧은 확산 경로를 제공한다. 메조 포러스 Si/SiOx 내에 Ti 도핑은 열처리 중에 SiOx 매트릭스를 Si로 환원시켜 전극의 용량 활용을 극대화 시킬 수 있다. 또한, Ti 도핑은 메조 포러스 Si / SiOx의 낮은 전기 전도도를 향상시킬 수 있다. Ti도핑된 메조포러스 Si/SiOx은 triethoxysilane의 솔-겔 반응과 계면활성제 P123을 사용하여 합성된 m-HSQ에 미리 제조해둔 Ti를 함유한 용액을 함침한 후 5% 수소/95% 아르곤 가스 조건하에 열처리하여 수월하게 합성되었다. 합성된 Ti 도핑된 메조포러스 Si/SiOx은 XRD와 XPS 데이터를 통해 매우 규칙적인 기공 구조를 가졌으며, Ti가 도입되기 전보다 Si 결정질의 양이 증가한 것이 확인되었다. 또한, 이 음극 물질을 리튬 이온 전지에 적용하였을 때, 메조포러스 Si/SiOx 의 전기화학적 성능보다 두 배 높은 용량과 10 % 가량 증가한 초기 효율 등의 우수한 전기화학적 성능을 보였다. 이번 연구에서 우리는 소량의 Ti 도핑한 메조포러스 Si/SiOx 전극의 잠재 가능성을 볼 수 있었다. Silicon and silicon suboxides (SiOx, 0 < x < 2) are promising anode materials for lithium-ion batteries, yet volume changes of anode materials upon lithiation/delithiation and relatively low capacity, respectively, remain challenges with practical applications in lithium-ion batteries. Therefore, the combined anode material of Si and SiOx has emerged as effective anode materials for lithium-ion batteries. Here we propose a new anode material, Ti-doped mesoporous Si/SiOx, for lithium-ion batteries. Based on the synergetic combination of Si and SiOx materials, mesopores and a small amount of Ti doping are introduced to enhance the electrochemical performance of Si/SiOx. Mesopores provide buffer matrixes to alleviate the volume changes upon cycles and shorten the Li diffusion pathway. Interestingly, the introduction of Ti doping can induce reduced Si from SiOx, thereby providing more capacity to mesoporous Si/SiOx.

Alternative family ties in Thomas Hardy's fictional Wessex

홍지현 Graduate School, Yonsei University 2015 국내석사

토마스 하디의 소설 속에는 가부장적 핵가족을 벗어난, 대안가족이 전반적으로 나타난다. 전통적인 가족이란 혈연으로 맺어진 직계가족으로 부모와 아이들의 관계가 자연적으로 이루어지며, 가장 효과적이고 안정적인 가족 형태를 의미한다. 그러나 하디는 이러한 전통적인 가족 개념의 한계를 설파하였다. 그는 가족의 항상성을 만들어 나가기 위해 서로 서로를 향한 강한 의지를 보여주면서 순조롭게 살아가는 비전통적 가정을 묘사하고 있다. 『하디의 푸른 눈동자』, 『캐스터브리지의 시장』, 『미천한 사람 주드』등의 작품에서 아이들은 생물학적 부모로부터 느끼지 못하는 사랑, 애정, 정서적 동질감 등을 양부모로부터 충족시킨다. 『귀향』에서는 미혼모가 안정적인 가족을 유지하기 위해 자신의 생물학적 아이와 입양아 모두를 동시에 적극적으로 부양한다. 하디는 그의 작품들에서 아이들은 양부모의 지원으로 혜택을 받으며, 양부모는 절망의 시기에 의붓아이들로부터 위로를 얻는다는 것을 묘사하고 있다. 하디의 작품세계에서 부모와 아이들 사이의 상호 친밀한 관계의 확립은 바로 고립으로부터의 탈출이 되는 것이다.이러한 긍정적인 의붓부모-자녀 관계 또는 부모-자녀 관계는 웨섹스에 만연되어있는 비전통적인 가족 단위를 파괴하려는 외부의 힘과 갈등관계를 갖는다. 웨섹스는 시작 국면에서 전통적인 농촌 83 사회가 그대로 보존되어 있는 장소로 묘사되지만, 종말 국면에서는 절망적이고 적대적인 미래를 갖춘 시골로 끝을 맺고 있다. 이와 같은 반전 중에서도 변화하지 않고 그대로 남아있는 하나의 요소는 미묘하지만 반복적으로 나타나는 열정적인 가족의 사랑이다. 본 논문은 하디의 소설에서 부모-자녀 관계에 초점을 맞추어, 자연적 또는 유전적 관계를 넘어서는 친밀한 상호 대인 관계로 성립하는 대안가족의 존재가그의 작품 속에서 어떻게 나타났는지를 고찰하는데 그 목적이 있다. Alternative families appear predominantly in Thomas Hardy’s novels, deviating from the patriarchal nuclear family. The traditional family assumes immediate family sealed by blood ties “naturally” links parent and children and thereby establishes the most effective and stable family form. Hardy, however, exposes the limitations in this traditional sense of family. He chronicles positively functioning non-conventional families’ strong commitment towards one another to create a family homeostasis. In A Pair of Blue Eyes (1873), The Mayor of Casterbridge (1886), and Jude the Obscure (1895), the biological parent’s failure to provide love, affection, and emotional bond to children is fulfilled by a stepparent. In The Return of the Native (1878), the single mother equally supports both her biological and adopted children for the stability of the family. Offering parental affection not only benefits the children, but also comforts and motivates a constructive change in the parents’ or stepparents’ lives in times of despair. Such positive stepparent-child or parent-child relationships, however, wrangle with external forces in Wessex that threaten to rupture the nontraditional family unit. Wessex starts as a place where traditional rural community stays intact and ends with a picture of a bleak and alienating future of the countryside. Yet the one element that remains intact is the subtle yet identifiable echo of passionate familial love even in its last, distorted form in Hardy’s last novel, Jude the Obscure. Focusing on the stepparent-child and parent-child relationship in Hardy’s novels, this thesis aims to show that Hardy uses alternative families to privilege close, mutual interpersonal relationships built beyond “natural” or biological tie which strengthen familial endurance in the heart of dim future of the Wessex.

Accuracy of models for fixed dental prostheses fabricated by digital workflow

심지영 Korea University 2018 국내박사

As CAD (Computer Aided Design)/CAM (Computer-Aided Manufacturing) and intraoral scanner are used in dentistry, the production of dental prosthesis and models is rapidly converted into the complete process of digital production [1-2]. The dental prosthesis digital manufacturing consists of the process of obtaining digital image by scanning oral information of patients, the process of designing prosthesis with CAD software with digital impressions, and the process of manufacturing design into appropriate materials [3,4]. Therefore, three-dimensional dental digital models are essential to create prosthesis by using CAD/CAM. There are indirect method and direct method to obtain three-dimensional dental digital models [5]. The indirect method obtains oral impressions by using dental impression materials, and obtain virtual 3D model by scanning stone cast with lab scanner. However, elastomeric impression material and dental stone are cured through chemical reaction. Thus, errors occur due to the volume change like material contraction and expansion. Since it should scan stone model with lab scanner, it is disadvantageous in that errors recur [6-8]. The direct method directly obtains digital impressions by using intraoral scanner. As oral scanners recently developed faster, demand for oral scanners is rising. Since impression taking by using intraoral scanner does not use impression materials, discomforts caused by these materials can be alleviated. As it can be identified immediately through monitors, impression can be obtained rapidly and conveniently as those parts can be scanned again [9]. As prosthetic appliances can be produced by transmitting digital impression to CAD/CAM equipment, work efficiency is high [10-12]. In addition, physical model can be made based on digital impression data obtained from intraoral scanners by using milling machine or 3D printer. Since some restorations can be made by using CAD/CAM system after obtaining digital impressions with intraoral scanner, physical models are unnecessary. However, physical models are still needed to determine the relationship between adjacent and opposing teeth in case of manual veneering restorations. Subtractive processing technique is frequently used in digital dentistry as CAM method. This technology wastes too much materials and representation is poor if it forms complicated forms such as undercut and void like teeth. To improve this poor part, additive manufacturing was introduced and more practical studies are underway to apply it into a variety of dental fields. Additive manufacturing is a technology which produces desired objects by layering materials one by one [13]. This is useful in making complicated objects. Since it can produce various forms at the same time, it can save time and minimize labors [14]. Due to these advantages, 3D printer is increasingly adopted in surgical guide and producing final prosthetic appliance and dental models. Precise impression making and production of models are crucial factors. Therefore, evaluating the accuracy of digital impression and 3D printed model obtained by using intraoral scanner is essential for manufacturing prosthetic appliances using CAD/CAM. Recently various studies on the evaluation of the accuracy of digital impression and 3D printed model made by using digital workflow are reported [5, 10, 15-19]. Nonetheless, most studies assessed the accuracy of complete arch or a single abutment. Complete arch without preparations shows the accuracy of model for correction, while it does not present the accuracy of preparation for making prosthetic appliance. A study that evaluates the accuracy of preparation is limited to reflect more complicated clinical situations. Thus, research that assesses the accuracy of models for manufacturing dental prosthesis made by digital method is needed, to fulfill this necessity, this study was designed. First, the purpose of this study is to compare and evaluate the accuracy of virtual 3D model for manufacturing fixed dental prostheses created by digital and conventional workflow. Study methods are presented as follows. Reference model that consist of abutments such as single crown, 3 unit, and inlay for making three types of restorations was scanned by using a high-resolution industrial optical reference scanner. The reason why three types of abutments were included is that the accuracy of models would be distinct according to the size and forms of abutments. After making impressions from the reference model according to the conventional outflow, lab scanner was used to scan the model, and finally virtual 3D model was completed. Virtual 3D model was drawn by scanning the reference model with intraoral scanner in accordance with digital workflow. All scan data was converted to STL files. By using 3D analysis software, this study evaluated the accuracy of complete arch and the trueness of abutment. Independent T-test and two-way analysis of variance were carried out to assess the accuracy of both models and the trueness of three types of abutments and then post-test was conducted. The first paper demonstrated that complete arch showed better outcomes in the trueness and precision of the previous conventional work. However, no significant difference was observed regarding the trueness. Two-way ANOVA showed significant difference on the trueness between model group and types of abutments. Virtual 3D model groups manufactured by digital workflow exhibited better trueness values in three types of abutments. The aim of the second study is to measure the accuracy of virtual models of complete arch by digital workflow and 3D printed models as well as the trueness of abutments. It also aims to compare them with the previous stone model and evaluate them. Study methods are as follows. A reference model that includes abutments (single crown, 3 unit, and inlay) was developed to manufacture three types of abutments. It obtained impressions according to the conventional workflow and developed a stone model. Using intraoral scanner, it obtained digital impressions and developed physical model by using 3D printer. After scanning reference model, stone model, and 3D printed model with industrial optical scanner, they were converted into STL files. By using 3D analysis software, the accuracy of complete arch was measured. Moreover, the trueness of abutments was assessed. One-way or two-way ANOVA was performed to evaluate the accuracy of complete arch and the trueness of abutments of three model groups. There were significant differences in three groups in terms of precision as the second study suggested. However, the trueness of stone model and digital model (virtual 3D model) showed no significant difference. However, the 3D printed model showed the poorest accuracy. Two- way ANOVA demonstrated that there was a significant difference in the trueness between model groups and types of abutments. To summarize results from both studies, virtual 3D model (Lab scanner) group produced by conventional workflow showed higher accuracy than the group by digital workflow. However, there was no statistically significant difference in the trueness. The virtual model group made by the digital workflow revealed higher trueness in all three types of abutments. Thus, the digital workflow can adequately replace the conventional workflow method in case of producing virtual 3D model for dental restorations. However, 3D printed model showed the poorest accuracy of complete arch and the trueness of abutments. Therefore, the 3D printed model is assumed to replace the previous stone model until additional technological advance is performed.

Quenching effects of selected non-polar phenolic antioxidants on singlet oxygen and their suppressive activities on the photosensitized oxidation of vegetable oils

김지인 Graduate School, Yonsei University 2009 국내박사

It is interesting that molecular oxygen and lipid matrices share a paradoxical phenomenon as they are essential but not may be detrimental to the survival and health of the human species. Foods containing lipids in an oxygen and light-rich environment are prone to be faced upon the potential risk of oxidative processes. The molecular oxygen is an essential ingredient to support life on earth from biological point of view. Roles of the oxygen in foods involve direct or indirect interactions with light. Understanding of the interactions of lipids with oxygen and/or light is important to evaluate functions of conventional antioxidants and to develop novel antioxidants with a broad antioxidative protection. The purpose of this study was to examine the quenching effects of selected non-polar phenolic antioxidants (nPhOH) on singlet oxygen in the organic solvents and linoleic acid of homogeneous system and their suppressive activities on the photosensitized oxidation in the vegetable oils of heterogeneous system. In part I, singlet oxygen quenching effects of selected nPhOH, i.e., tert-butylated hydroxyanisole (BHA), tert-butylated hydroxytoulene (BHT), tert-butylated hydroquinone (TBHQ), and α-tocopherol, on a methylene blue (MB)-sensitized photooxidation of linoleic acid have been studied. The singlet oxygen quenching mechanism was studied using both electron spin resonance (ESR) spectroscopy in a 2,2,6,6-tetramethylpiperidone (TMPD)-MB system and spectroscopic analysis of rubrene oxidation induced by a chemical source (sodium molybdate + hydrogen peroxide) of the singlet oxygen. Total singlet oxygen quenching rate constants (kox-Q + kq) were determined using a steady state kinetic equation. Among the synthetic antioxidants in this study TBHQ showed the highest protective activity on the MB-sensitized photooxidation of linoleic acid, followed by BHA and BHT. TBHQ (1.0 x 10-3 M) exhibited 86.5% and 71.4% inhibition of peroxide and conjugated diene formations, respectively, in linoleic acid photooxidation after 60 min fluorescent illumination. The protective activity of TBHQ on the photosensitized oxidation of linoleic acid system was almost comparable to that of α-tocopherol (88.8% to peroxides and 73.9% to conjugated dienes). The data obtained from 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (TAN) formation in ESR and rubrene oxidation studies clearly showed the strong singlet oxygen quenching ability of TBHQ as 81.6% and 74.8%, respectively. These data were as compared with those of α-tocopherol (77.7% to TAN formation and 82.0% to rubrene oxidation). The (kox-Q + kq) of BHA, BHT, and TBHQ were 3.37 x 107, 4.26 x 106 and 1.67 x 108 M-1sec-1, respectively. The (kox-Q + kq) of TBHQ was within the same order of magnitude of that of α-tocopherol (3.54 x 108 M-1sec-1), an efficient singlet oxygen quencher. There was a high correlation (r2 = 0.991) between logarithmic value of (kox-Q + kq) and reported the ionization potentials for BHA, BHT, and TBHQ, showing their charge-transfer mechanism for singlet oxygen quenching. This is the first report on the kinetic study on the (kox-Q + kq) of TBHQ in methanol as compared with other commonly used commercial synthetic antioxidants and α -tocopherol. In Part II, the stoichiomtric correlation between free radical scavenging activities and singlet oxygen quenching activities of nPhOH was investigated. To compare with the singlet oxygen quenching activities determined in Part I, antiradical activities of nPhOH have been estimated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH?) bleaching assay. The DPPH? bleaching assay showed linear dose-responses in the range of 0 to 0.27 [nPhOH]/[DPPH?] molar ratio. Different parameters such as radical scavenging capacity (RSC, %), 50% inhibition concentration (IC50), remaining [DPPH?], 50% efficient concentration (EC50), time taken to scavenging 50% of the initial [DPPH?] (T50%30uM/min), and antiradical efficiency (AE) were measured within the 0 to 0.27 of [nPhOH]/[DPPH?] molar ratio. Reaction stoichiometries such as antiradical power (ARP), stoichiometric value (SV), and n value were calculated for mechanistic speculation on structure-activity relationship. The DPPH? bleaching assay showed that RSC at [nPhOH = 8 μM] was in the order of TBHQ (79.4%) > α-tocopherol (71.3%) > BHA (56.9%) > BHT (41.7%). The nPhOH showed the same decreasing orders with the RSC data in the IC50, EC50, T50%30uM/min and SV, while they showed the same increasing orders in the AE, ARP, and n value. It was interesting to speculate that the strongest antiradical effectiveness of TBHQ was resulted from its specific structure-activity relationship. Particularly, the n value calculated based on EC50 confirmed the implication of more than one step in the reaction of nPhOH with the DPPH?. In the n value, TBHQ also exhibited the highest level (n = 2.96), followed by α-tocopherol (n = 2.63), BHA (n = 2.25), and BHT (n = 1.53). The n values of nPhOH, except the α-tocopherol which is structurally different, showed significantly higher correlations with their logarithmic value of (kox-Q + kq) given in Part I of the present study. This result indicates a close relationship between the antioxidative activities of nPhOH for both singlet oxygen quenching and free radical scavenging, suggesting their synergistic actions via charge-transfer and/or hydrogen-donation. In Part III, the inhibitory effects of the selected nPhOH on the photosensitized oxidation of commercial vegetable oils (soybean oil, corn oil, and canola oil) under fluorescent light at room condition were investigated. The inhibitory effects of nPhOH to the formation of primary oxidation products, secondary oxidation products, and sensory impact compounds in the system have been evaluated by monitoring peroxide value (POV), total volatile compounds in headspace (TVC), and C3-aldehydes by solid phase microextraction (SPME)/GC-MS analysis. POV (an indicator of primary oxidation) at day 0, 1, 2, 3, 4, and 5 were 2.8, 11.7, 19.26, 28.4, 33.3, and 45.9 meqO2/kg oil for the soybean oil; 0.6, 5.8, 9.8, 18.4, 20.5, and 24.4 meqO2/kg oil for the canola oil; and 1.3, 5.5, 10.8, 16.9, 19.8, and 21.8 meqO2/kg oil for the corn oil, respectively. TVC (an indicator of secondary oxidation) at day 0, 3, and 5 were 112.5 x 104, 374.2 x 104, and 601.3 x 104 mVsec for the soybean oil; 6.9x104, 179.0 x 104, 287.5 x 104 mVsec for the canola oil; and 6.9 x 104, 179.0 x 104, and 287.5 x 104 mVsec for the corn oil, respectively. C3-aldehydes (an indicators of sensory impact) at day 0, 3, and 5 were 14.7 x 104, 68.0 x 104, and 61.5 x 104 mVsec for the soybean oil; ~ 0.0 x 104, 30.5 x 104, and 51.2 x 104 mVsec for the canola oil; and 12.0 x 104, 26.3 x 104, 58.9 x 104 mVsec for the corn oil, respectively. These oxidation markers showed that the photosensitized oxidation of vegetable oils increased significantly as the fluorescent light exposure time increased (P < 0.05). A possible mechanism of light-induced oxidation was speculated as singlet oxygen-mediated photosensitized oxidation via excitation of chlorophyll species under fluorescent light in the presence of ordinary oxygen. The regression analysis of data obtained from the photosensitized oxidation of the vegetable oils revealed a high correlation (r2 = 0.995 for soybean oil, 0.978 for canola oil, and 0.914 for corn oil, respectively) between POV and TVC, suggesting that TVC can also be used as a reliable indicator to measure the antioxidant activities. At 200 ppm, TBHQ showed the highest decrease (22.7%) in the POV, followed by BHT (11.2%), BHA (5.1%), and α-tocopherol (-5.9%). As expected but it was interesting that α-tocopherol promoted the formation of hydroperoxides in the photosensitized oxidation of vegetable oils. TBHQ exhibited the highest decrease (57.7%) in the TVC, followed by α-tocopherol (30.5%), BHT (24.7%), and BHA (13.2%). TBHQ also showed the highest decrease (80.5%) in the development of C3-aldehydes, followed by α-tocopherol (34.0%), BHT (24.8%), and BHA (14.5%). Contrary to the inhibitory effect on the basis of POV, the addition of nPhOH significantly inhibited the development of TVC and C3-aldehydes in the vegetable oils (P < 0.05). The data showed that the TBHQ treatment contributed to retard the photosensitized oxidation of vegetable oils in the order of sensory impact (80.5%) > secondary oxidation (57.7%) > primary oxidation (22.7%). The high antioxidant activity of TBHQ in homogeneous system such as the organic solvents and linoleic acid and in heterogeneous system such as the vegetable oils can be explained as the combined effects of free radical species scavenging by hydrogen donation, singlet oxygen quenching by partial charge-transfer, and a deactivation of triplet excited chlorophyll species. In aspect oriented multifunctional antioxidative activity of TBHQ, which have been observed in Part I, II, and III of the present study, it is expected that TBHQ under regulation could be economically and broadly applied to medical, food, cosmetic, and polymer industries to effectively prevent the singlet oxygen-mediated photosensitized oxidation and/or triplet oxygen-mediated free radical autooxidation of various biological compounds such as unsaturated lipids, oil-soluble vitamins and other oil-soluble components including cholesterol, limonene, conjugated terpernes, and photodegradation of industrial materials like polymers.