마이크로미터 이하 패턴 제작을 위한 디지털 포토리소그래피 기술

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 물리학과, 2021.8. 권여리.Digital photolithography based on digital micromirror device (DMD) is considered the next-generation low-cost lithographic technology. However, DMD-based digital photolithography has been implemented only for micrometer-scale pattern generation, whereas sophisticated photonic devices require feature sizes of submicron. In this thesis, we adopt a high-magnification imaging optical system for a custom-built digital photolithography system to generate submicron-scale patterns. We propose techniques to enhance the versatility of the digital photolithography, pattern tilting and grayscale exposure. We demonstrate that photonic crystal band-edge lasers of various lattice structures and periods can be quality-assessment testbeds. We also tried to enhance pattern uniformity. The experimentally determined pixel spread function predicted the exposure result well, which means that we can improve the pattern quality through preliminary correction.디지털 미세거울 장치에 기반한 디지털 포토리소그래피는 차세대 저비용 리소그래피 기술로 여겨진다. 그러나 디지털 미세거울 장치 기반 디지털 포토리소그래피는 주기가 1 마이크론 이상인 패턴 제작시에만 사용되었다. 광자결정레이저 등의 광소자 제작을 위해서는 패턴의 주기가 수백나노미터 수준이어야 하는데, 아직 디지털 포토리소그래피로 이러한 광소자를 제작한 사례는 없었다. 회절 한계를 계산해 보았을 때, 1 마이크론 이하 주기의 패턴 제작이 충분히 가능할 것으로 판단되어, 고배율 결상광학계를 활용하여 디지털 포토리소그래피 시스템을 구축하였다. 구축된 시스템을 사용하여 감광액이 코팅된 시편에 노광을 진행하였으며, 1 마이크론 이하 주기의 패턴 제작이 가능함을 보였다. 마이크로미터 이하 주기의 패턴을 제작할 때, 디지털 포토리소그래피의 패턴 설계 자유도를 향상시키기 위한 두 가지 방법인 패턴 기울임, 회색조 노광을 제안하였으며 실험적으로 시연하였다. 디지털 리소그래피 시스템의 검증에는 광자결정 띠 가장자리 레이저가 주로 사용되었는데, 레이저 발진 여부를 통해 노광 패턴의 품질을 파악할 수 있고 레이저 파장을 통해 노광 패턴의 주기를 파악할 수 있기 때문이다. 또한 픽셀 분산 함수를 도입하여 이미지의 회절 계산 및 패턴 품질 향상을 위한 밝기 보정을 제안하였다. 보정에 의해 패턴의 품질이 크게 향상되어, 전자빔 리소그래피로 제작한 것과 비교할 수 있는 수준이 되었다.Chapter1 Introduction 1 1.1. Photonic crystals 1 1.1.1. Introduction 1 1.1.2. Photonic crystal band-edge laser 4 1.1.3. Photonic crystal cavity laser 6 1.2. Conventional lithography techniques 8 1.3. Alternative lithography technique: digital photolithography 10 1.4. Outline of the manuscript 12 Chapter2 Submicron-scale digital photolithography 14 2.1. Introduction 14 2.1.1. Schematic of digital photolithography system 14 2.1.2. Proposed digital photolithography system 16 2.1.3. Pixel pitch at image plane 17 2.1.4. Resolving power of proposed digital photolithography system 19 2.2. Fabrication process of air-bridge photonic crystal 21 2.3. Square-lattice photonic crystal laser device 22 Chapter3 Fine-tuning the lattice constant: pattern tilting 26 3.1. Introduction 26 3.1.1. Wavelength division multiplexing application 26 3.1.2. Pattern tilting 28 3.1.3. All possible tilting configurations 30 3.2. Result and discussion 31 3.2.1. Tilting square-lattice 31 3.2.2. Tilting hexagonal-lattice 33 Chapter4 Fine structural tuning: grayscale exposure 36 4.1. Introduction 36 4.1.1. Implementation of gray pixel 36 4.2. Result and discussion 38 4.2.1. Grayscale exposed squre-lattice 38 4.2.2. Grayscale exposed hexagonal-lattice 41 Chapter5 Enhancing pattern uniformity 42 5.1. Introduction 42 5.1.1. Airy disk point spread function 42 5.1.2. Broadening factor and exposure dose profile 47 5.1.3. Experimental determination of broadening factor 49 5.2. Result and discussion 51 5.2.1. Diffraction simulation based on pixel spread function 51 5.2.2. Correction strategy 56 5.2.3. Analysis of correction result 58 Chapter6 Conclusion and perspective 61 References 63 Abstract in Korean 70박

Direct exfoliation of graphite using non-ionic polymer surfactant for fabrication of transparent and conductive graphene film

학위논문 (석사)-- 서울대학교 대학원 : 재료공학부, 2013. 2. 조원호.A high-yielding dispersion of graphene at high concentration in solvent is critical for practical applications. Herein, we demonstrate the formation of stable dispersion of pristine graphene in ethanol by exfoliating graphite flakes into individual graphene layers using a non-ionic polymer surfactant under bath-type sonication. Oligothiophene-terminated poly(ethylene glycol) was synthesized and used as a non-ionic and amphiphilic surfactant for exfoliating graphite into graphene. High-quality graphene film was fabricated from the exfoliated graphene solution by the vacuum filtration method. TEM and SEM reveal that the size of exfoliated graphene flake is larger than 1 m. When the graphene film was treated with nitric acid and thionyl chloride after washing with solvent, the film showed high performance with a sheet resistance of 0.3 kΩ sq−1 and a transparency of 74% at 550 nm.Chapter 1 Introduction 1 Chapter 2 Experimental 6 2.1 Materials 6 2.2 Synthesis 6 2.2.1 Synthesis of (2, 5-dibromo-thiophene-3-yl)-acetic acid (2Br-1TN) 6 2.2.2 Synthesis of 2Br-1TN-PEG 7 2.2.3 Synthesis of quinquethiophene-PEG (5TN-PEG) 7 2.3 Preparation of graphene solution 9 2.4 Fabrication of graphene film 9 2.5 Measurements 10 Chapter 3 Results and Discussion 12 3.1 Exfoiation and dispersion of graphene 12 3.2 Fabrication of graphene film 16 3.3 Chemical treatment of graphene film 23 3.4 Comparison of electro-optical property of our graphene film with other works reported in the literature 30 Chapter 4 Conclusions 37 Bibliography 38 Korean Abstract 43Maste

Fabrication of Transparent and Conductive Graphene Film from Graphite by Using Non-Ionic Polymer Surfactant

Graphene, a new material with 2-dimensional nanostructure consisting of a single layer of sp2 network of carbon atoms, has distinctive electronic properties such as room temperature quantum effects, arnbipolar electric field effects, and high carrier mobility. It is, however, difficult to fabricate graphene film from graphite via a solution process using organic solvent, though it is a cheap and convenient way compared to the CVD method. In this study, we report a new method to fabricate graphene film using a polymer surfactant to disperse homogeneously graphene sheets in ethanol. The surfactant consists of oligothiophene, which is strongly adsorbed onto the graphene surface, and polyethylene glycol, which interacts with ethanol. Hence, the surfactant is expected to effectively disperse graphene sheets in ethanol. Graphene film with a sheet resistance of 300 0/sq at 72% transmittance at 550 nrn was fabricated by vacuum filtration. When the film quality and thickness of graphene sheets are measured by Raman spectroscopy and transmission electron microscope, it reveals that our films have better quality as compared to graphene films reported previously.OAIID:oai:osos.snu.ac.kr:snu2012-01/104/0000001236/20SEQ:20PERF_CD:SNU2012-01EVAL_ITEM_CD:104USER_ID:0000001236ADJUST_YN:NEMP_ID:A004558DEPT_CD:445CITE_RATE:0FILENAME:2012추계학술대회_강민수.pdfDEPT_NM:재료공학부EMAIL:[email protected]:

Study of the inner space by human silhouette

20세기로 접어들면서 문화, 사회 전반이 급변함으로 예술 역시 격동적인 변화를 함께 겪어왔으며, 그러한 상황하에 여러 경향의 현대 회화는 시각적 대상과 비시각적인 대상의 진실을 추구하기 위하여 부단히 노력하며 그들의 가치체계를 형성하고 와해시킴을 반복하였다. 2차대전이후 인간의 실존과 반 전통적인것의 수용과 확산은 급속도로 유럽과 미국에 확산되었는데, 특히 1950년대 추상표현주와 앵포르멜 미술로부터 1960년대의 색면추상에까지 다양하게 전개되었다. 이러한 시대적 흐름은 형식에 대한 구속에서 벗어나, 삶의 경험속에 내재하는 내면세계의 추구와 작가 주관에 의한 주제 표현영역을 부각시키게 하였다. 이에, 작가개인의 예술관에 의한 인간성 탐구는 현대미술의 중요한 테마가 되었으며, 여러형태로 그들의 내적세계를 위해 지속적으로 탐구되고 있는 것이다. 본 논문의 주요 연구소재인 인간형상은 과거로부터 현재에 이르기까지 비례의 다양성과 동적인 변화, 내적 표현의 소재로서 지속적으로 예술가들에게 채택되었다. 생략과 변형을 용이하게 흡수하는 인체의 실루엣은 본인의 내면세계를 서술하는 좋은 매개체로서, 그 형태와 움직임, 그리고 거기에서 생성된 공간은 외적세계와 자아를 이어주는 매체가 된다. 칸딘스키는 "예술은 자기 고유의 형식으로써, 사물에서 심성에 이르는 말을 주고 받는 언어"라고 했다. 주관적 이미지의 창조라는 예술가의 태도는, 각자의 삶의 경험에서 비롯되는 다양한 예술 형식에 대한 추구와 그 조형성에 대한 모색이다. 따라서 본인은 주관적 시각에 의하여 일상 생활속의 대상에서 얻어지는 경험적 이미지를 인체의 실루엣을 소재로 하여 인식된 화면에 재구성하므로 평면속에서 느껴지는 공간을 내면세계의 서술적 공간으로 보고 작업을 전개하고자 한다. 화면구성의 방법은 여러가지 재료를 혼용하여 인체의 외곽선에서 오는 리듬감이나 율동성을 표현함으로써, 자칫 우울할 수 있는 주제에 즐거움의 요소를 부가 시키고자 하였다. 작업의 방법적 연구를 위해 전후 앵포르멜 미술의 선구가 된 포트리에(Jean Fautrier)와 타피에(Antonio Ta`pies)의 재료와 드로잉을 참고로 하고, 얇은 공간의 중첩과, 2차원의 화면에서 추구하는 3차원적 속성의 깊이있는 공간을 연구하고자 한다. 본 논문을 제작연구논문이므로, 본인작품을 분석, 진술하여, 연구내용과 작업을 동시에 고찰함으로써, '인간 형상을 통한 내적공간'에 대한 연구를 마친다.;During 20th century, abstract painting has undergone various experiments in pursuit of innovative forms of expression. Painters from each jeneration have been doing their best to have their artistic views and inner thought embodied in their individual works. This particular artistic genre, better known as "Post-modernism" as accomodates vary different forms and materials and is characterized by overiding belief in open minded artistic expression Modem painters, therefore, are required to be able to cope with many artistic views and are encouraged to cultivate their own thoughts about life and art. In this thesis, I am going to introduce my own understanding on life and art acquired through research into my psychological as well as my self perception on my graduation painting. I have attemped to transform and form by repeating and erasing to develope a motif for my psychological abject and inner images by using a human silhouette collage was introduced to express meaning inclusive human movements and Hautes-pates was used to beef up its image expression by mixing materials and expressions directly for a weakened silhouette. A combination of Collage and Hautes-Pates gave my painting sense of space and line-drawing was added to describe inner feelings. Throughout, concretness and abstractness, expression and implication, flatness and relief were being sought. In terms of artistics revealation, a multitude of prerequites should be cited but I selected only 2 modem painters ..., on the basis of the external semblance of artistic expression. I also feel handicapped in trying to draw a generalized conclusion from my work having only researched a few artists of a selective genre. That I would like ready to understand that I plated a significance in studying my work by context and method as I consider my graduation thesis a learning process. Franz Marc(German, 1880-1916) said a read artist escapes isolation only when he expresses his true self within the boundariest his environment (social and moral included). Conversely, finding one's true self cannot be realized by searching in the obscure past. Through this work, I came to realize the meaning of a true artist. In my opinion, a true artist knows no limits in expressing one's self and accumulating visual experiences for artistic objectivity. This graduation thesis will serve only as a transition in which I introduced the basis and embodiment of my self preception develped during my graduate work, It also serves as a reminder of how much I still have to learn to future my inner development.목차 = ⅲ 논문개요 = ⅴ Ⅰ. 서론 = 1 Ⅱ. 내용적 연구 = 3 A. 인간형상 표현의 변모 과정 = 3 B. 소재로서의 인체 = 9 Ⅲ. 방법적 연구 = 12 A. 다양한 재료의 혼용 = 13 B. 자동주의 드로잉 = 14 C. 평면과 깊이의 공존 = 16 Ⅳ. 본인 작품 분석 = 18 Ⅴ. 결론 = 37 참고작품 = 39 참고문헌 = 41 ABSTRACT = 4

원자계와 광학계에서의 거시 양자 상태 생성과 정량화

학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부,2015. 2. 정현석.We discuss a classification of quantum effects based on possibility of emergence in macroscopic scales. We regard a certain phenomena as a genuine macroscopic quantum effect, if it cannot be described by any classical physics nor an accumulation of microscopic quantum effects. A quantum state corresponding to such effect is called a macroscopic quantum state. One prominent aspect among various quantum effects is quantum entanglement. We investigate possibilities of generating macroscopic entanglement between an atom and a thermal state or even between multiple thermal states. We found entanglement is always risen for an arbitrarily large temperature of the thermal states. This indicates importance of coherent interactions rather than the necessity of initial purities. We also propose a generation scheme for hybrid entanglement, which is comprised of classical and quantum states, based on single–photon addition technique. The key idea is that adding a single photon into a coherent state makes another approximate coherent state with a larger amplitude. Since it does not require in–line nonlinear interactions, it is experimentally feasible compared to traditional schemes. Besides generating entanglement, we also attempt to quantify the macroscopic quantumness for arbitrary quantum states of spins. We construct a measure of macroscopic quantumness by counting oscillations of interference fringes in phase space. We apply the measure to typical and intuitive macroscopic quantum states and verify that the measure works properly. Remarkably, we show that quantum phase transition is a naturally occurring genuine macroscopic quantum effect in the spirit of Schr¨odingers cat.Abstract I. Introduction II. Macroscopic Quantum Effects 2.1 Accumulation of microscopic quantum effects 2.2 Genuine macroscopic quantum effects III. Generating Entanglement from High Temperature Thermal States 3.1 Quantum entanglement 3.2 Thermal states 3.3 Entanglement of thermal states 3.3.1 Entangling microscopic system and thermal state 3.3.2 Entangling two thermal states 3.4 Macroscopic quantumness of entangled thermal states 3.5 Remarks IV. Generating Hybrid Entanglement via Photon Addition Scheme 31 4.1 Concept of hybrid entanglement 4.2 Amplifying coherent state by photon addition 4.2.1 Photon addition scheme iii4.2.2 Coherent state amplification 4.3 Generating hybrid entanglement 4.4 Macroscopic quantumness of hybrid entanglement 4.5 Remarks V. Quantifying Macroscopic Quantumness of Spin States 5.1 Introduction 5.2 Review of macroscopic quantumness for optical states 5.3 Macroscopic quantumness of spin states 5.3.1 Wigner distribution of spin states 5.3.2 Measure of macroscopic quantumness of spin states 5.3.3 Comparison to existing measures 5.4 Applications 5.5 Quantum phase transition 5.5.1 Quantum phase transition of Ising model 5.5.2 Macroscopic quantumness of quantum phase transition 5.6 Remarks VI. Conclusion Bibliography 국문초록Docto

천초근(Indian madder color)의 F344 랫드에서 104 주 경구투여에 의한 발암성 연구

학위논문 (박사)-- 서울대학교 대학원 : 수의학과 수의병리학전공, 2013. 2. 김대용.천초근(Indian madder color, IMC), 즉 Rubia cordifolia Linne의 뿌리는 식용 색소와 섬유의 염색, 그리고 전통약재로 사용되었다. 그러나, 다른 천초근(Madder color, MC)의 추출물의 연구에서 랫드 간세포와 신장 세뇨관 상피세포에 대한 발암성이 보고되었다. IMC와 MC, 두 종은 유사하므로 IMC 발암성의 가능성이 제기되었으므로 이에 대한 평가가 필요하게 되었다. 그러므로 IMC의 발암성평가를 위해서, F344 rat를 이용한 104 주 발암성 연구를 수행하였다. 40, 200 및 1,000 mg/kg의 투여용량으로 104주 동안 일주일에 다섯 번씩 IMC추출물을 경구 투여하였다. 생존 분석에서 수컷 1,000 mg/kg 투여 그룹에서 비록 빈사동물의 수는 유의성있게 증가되었으나(P<0.05), 폐사와 빈사를 합친 개체 수의 변화는 유의성이 없었다. 투여 77 주 이전에 체중과 사료섭취량은 일부 변화가 관찰되었으나(P<0.05) 용량상관성을 보이지는 않았다. 부검 시 관찰된 대퇴골, 두개골의 뼈에서 주로 관찰된 분홍색으로의 변색은 암수1,000 mg/kg 투여 그룹에서 유의성(P<0.01)있게 증가되었다. 간세포의 난원세포증식은 수컷 40, 200, 그리고 1,000 mg/kg 투여 그룹에서 증가하였다. 그리고 신장 유두부위 광물화(mineralization)는 수컷 1,000 mg/ kg 투여 그룹에서 증가하였으나 수질부의 광물질화(mineralization)는 암컷 1,000 mg/kg 투여 그룹 (P<0.01)에서 감소하였다. 대조군에 비해 암수의 1,000 mg/kg 투여 그룹에서 종양성(neoplastic) 병변은 큰 차이를 보여주지 않았다. 그러므로 본 연구은 104 주 동안 IMC의 투여에 의한 발암성이 없는 것으로 나타났다. 이러한 결과에서 IMC의 NOAEL은 1,000 mg/kg 이었다.Indian madder color (IMC), one of Radix Rubiae in herbal medicine, has been used for food coloring, and dye of textiles. However, madder color, another kind of Radix Rubiae, has been reported to have carcinogenicity in the liver and kidney of laboratory animals. So a carcinogenicity evaluation of IMC was needed because they are close-related species. For the risk assessment of IMC, 104-week carcinogenicity study was carried out. F344 rats were treated with hydrothermal extract of IMC for five times per week during 104 weeks by oral gavage at dose levels of 40, 200 and 1,000 mg/kg. In survival analysis, the number of overall unscheduled dead rats was not significantly changed, though the number of moribund rats in male 1,000 mg/kg dose group was significantly increased (P<0.05). The body weight and food consumption were changed significantly until 77 weeks (P<0.05), but the changes did not show dose-dependency. Macroscopically, cases with pink discoloration of bone, mainly in femur and skull was significantly increased in male and female 1,000 mg/kg dose groups (P<0.01). Microscopically, hepatic oval cell hyperplasia was significantly increased in male 40, 200 and 1,000 mg/kg dose groups. And renal papillary mineralization and pigmentation was significantly increased in male 1,000 mg/kg dose group (P<0.01). And no significant difference in neoplastic lesions was in male and female 1,000 mg/kg dose groups compared to control. These results do not show that IMC had a toxic effect at 1,000 mg/kg dose. From these results, oral treatment of IMC for 104 weeks in F344 rats had no carcinogenicity and the no-observed-adverse-effect level of IMC was 1,000 mg/kg dose.Abstract i Table of Contents ii Literature Review 1 Carcinogenicity study 1 Carcinogenicity study of herbal medicine 3 Indian madder color (IMC) 4 Chemical constituents of IMC 4 Pharmacological effect of IMC 6 Carcinogenicity study of Rubiae Radix 8 Chapter 1. A 104-week carcinogenicity study of Indian madder color by gavage in F344 rats 9 Introduction 10 Materials and Methods 12 Chemicals 12 Experimental animals 12 Study design overview 13 Administration 14 Clinical signs 14 Body weight 14 Food consumption 14 Ophthalmic examination 15 Hematology 15 Serum biochemistry 15 Necropsy findings and organ weights 16 Histopathology 16 Statistical methods 17 Results 19 Chemicals 19 Survival analysis 19 Body weight 20 Clinical sign and ophthalmological results 20 Hematological and serum biochemistry results 21 Organ weights 21 Necropsy findings 21 Cause of death 21 Histopathological findings 22 Discussion 24 Chapter 2. Histopathological analysis in the IMC carcinogenicity study 27 Introduction 28 Methods 30 Histopathology 30 Statistical methods 31 Results 32 Scheduled dead rats 32 Unscheduled dead rats 33 Scheduled and unscheduled rats 37 Discussion 39 Conclusions 45 References 46 국문초록 120 Figures and Tables Figure 1. Flower, leaves, stalk and root of Rubia cordifolia Linne (left) and dried roots (right). 50 Figure 2-1. LuP metabolism in the rats. 51 Figure 2-2. AlP metabolism in the rats. 52 Figure 3. Kaplan-Meier survival curves (male). Survival curve of 1,000mg/kg dose group (G4), were dropped rapidly but the survival rate are insignificant by log-rank test. 53 Figure 4. Kaplan-Meier survival curves (female). There is no dose-dependent change in the graph and have no statistical significance by log-rank test. 54 Figure 5. Body weight graph of males and females. Body weight of treatment groups increase similarly with control group. 55 Figure 6. Average food consumption of males. Food consumption in male has significant changes in the graph, but they are fluctuating. 56 Figure 7. Average food consumption of females. Graph show the food consumption per day in females and is fluctuating but they have similar pattern. 57 Figure 8. Organ distribution of LGL leukemia/lymphoma in males. In male incidence of LGL leukemia/lymphoma is high over 60% and all of them can be recognizable by spleen suggesting primary site. 58 Figure 9. Organ distribution of LGL in females. In females, incidences of LGL leukemia/lymphoma are also high in the spleen and liver. 59 Figure 11. Spleen, LGL leukemia/lymphoma. Neoplastic round cells are abundant in red pulp with prominent congestion. 60 Figure 12. Liver, LGL leukemia/lymphoma. Neoplastic round cells are infiltrating into the sinusoid and the hepatic parenchyma. The cells tend to be pleomorphic and large, with round to irregular-shaped nuclei and cytoplasmic granules. 61 Figure 13. Testes, interstitial cell adenoma. Tumors are composed of neoplastic cells compressing adjacent tubules, abundant finely vacuolated/granular eosinophilic cytoplasm. 62 Figure 14. Adrenal gland, pheochromocytoma. Note the large mass of proliferating cells which has cytology variable range from small, dark, lymphocyte-like cells to plump pale basophilic cells. 63 Figure 15. Pituitary gland, the pars distalis adenoma. Note the well delineated mass of cells that compresses the surrounding parenchyma. The neoplastic cells are arranged in compact branching cords with marked hemangiectasis. 64 Figure 16. Thyroid gland, follicular adenoma. Neoplastic cells are monomorphic and arranged in the prominent tubular structures at the margin of the mass. 65 Table 1. Alizarin, lucidin and rubiadin concentration using the water-based or ethanol-based extract methods (Kim et al., 2007) 66 Table 2. Guidelines of carcinogenicity and chronic study by regulatory agencies 67 Table 3. Survival table 68 Table 4. Summary of hematological test 69 Table 5. Summary of clinical biochemistry test 71 Table 6. Significant changes of absolute and relative testis weights (scheduled sacrificed rats, Absolute (g) & relative (%) organ weights) 73 Table 7. Necropsy findings with significant changing when compare dose groups to control group 74 Table 8. Cause of death summary in all examined rats 76 Table 9-1. Group percent of neoplasm incidences (scheduled dead rats) 77 Table 9-2. Group percent of neoplasm incidences (unscheduled dead rats) 78 Table 9-3. Group percent of neoplasm incidences (unscheduled dead rats, week 81-105) 79 Table 10-1. Incidences of all lesions of unscheduled dead rats (week 51-80) 80 Table 10-2. Incidences of all lesions of unscheduled dead rats (week 81-105) 81 Table 11. Incidences of histopathological lesions in the liver of scheduled dead rats 82 Table 12. Incidences of histopathologic lesions in the kidney of scheduled dead rats 83 Table 13. Statistically significant neoplasm in unscheduled female groups with Fishers exact test 84 Table 14. LGL leukemia/lymphoma in the all examined rats with poly-3 test 85 Table 15. Nonneoplastic lesion incidence in selected organs (all examined rats) 86 Table 16. Summary table of increased lesions from the results of poly-3 test. 87 Table 17. Pathological findings with grade in the adrenal gland 88 Table 18. Pathological findings with grade in the kidney 89 Table 19. Pathological findings with grade in the preputial gland 90 Table 20. Pathological findings with grade in the lung 91 Table 21. Pathological findings with grade in the sternum (bone marrow) 92 Table 22. Pathological findings with grade in the spleen 93 Table 23. Pathological findings with grade in the liver 94 Table 24. Incidences of neoplastic and other proliferative lesions in all examined rats (in life time) 97 Table 25. Histopathology summary in the scheduled dead rats 104Docto

우리나라 歷代 國務總理의 政治的 位相에 관한 硏究

학위논문(석사)--서울大學校 行政大學院 :行政學科 行政學專攻,1995.Maste

앙상블학습, 생성모델링, 지속학습을 위한 지식 증류

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2024. 2. 한보형.Deep neural networks have achieved superior performance in various domains including computer vision, natural language processing, robotics, and many other applications. Despite their exceptional accomplishments, the applicability to resource-hungry systems is still limited due to their computational or physical costs in terms of model sizes, FLOPs, and power consumption. Besides the problem, when we train the models under the settings for a sequence of tasks in an online manner, they can not generalize well, especially on the previous tasks. In the dissertation, we address these two limitations of the deep neural networks via knowledge distillation. In case of ensemble learning, although it is effective and straightforward to achieve better generalization performance through the use of predictions based on multiple models, it significantly increases inference costs, which makes its application in portable devices more challenging. To tackle the issue, we compress multiple models into a single model via knowledge distillation, where we consider the ensemble models as a teacher. Based on the ensemble-based teacher, we propose an oracle knowledge distillation loss incorporated with neural architecture search techniques, which successfully addresses the model capacity issues and enables the target model to achieve competitive accuracy with the teacher. In the context of generative models, they also typically require high inference costs, which limit their application in low-power devices such as mobile phones. Existing knowledge distillation approaches for the compression of the generative models simply employ L1 or L2 norms to compute the pixel-wise difference between the representations of two networks, where these frameworks are widely adopted in image classification tasks. In addition to these methods, we propose a knowledge distillation approach that maximizes the mutual information between the student and the teacher. For the domain of generative modeling, different from the pixel-wise comparison methods, the proposed method is effective in considering spatial dependencies among pixels for natural images, which results in further improving the performance. In the field of the continual learning setting, we consider a class-incremental learning scenario, where the model incrementally learns new classes with limited accessibility to the data from the classes in the previous tasks. Due to the data imbalance problem, the model often achieves very poor generalization performance since the network can not generalize well on the previous tasks. To this end, we introduce an effective knowledge distillation approach involving feature map weighting to significantly mitigate the catastrophic forgetting problem, where the model trained for old tasks is considered as the teacher. The proposed method basically maintains important features to keep previously learned information while making less critical features flexible to learn new classes. Experimental results validate that the proposed knowledge distillation methods achieve outstanding performance in ensemble learning, generative modeling, and continual learning.심층신경망은 컴퓨터 비전, 자연어 처리 및 로봇 공학등 다양한 분야에서 뛰어난 성능을 달성하고 있다. 이러한 이례적인 업적에도 불구하고 모델 크기, 플롭스 및 전력 소비 관점에서 자원이 불충분한 시스템에서의 적용은 여전히 제한되고 있다. 그러한 문제 외에도, 일련의 작업들을 연속적으로 온라인 방식으로 모델을 학습시킬 때, 특히 이전 작업들에 대해 모델이 일반화를 잘하지 못하게 된다. 본 논문에서는 지식 증류를 통해 심층신경망의 이러한 두 가지 주요 문제점들을 해결하고자 한다. 앙상블 학습의 경우, 여러 모델의 예측을 사용하여 더 나은 일반화 성능을 달성하기 위한 간단하고 효과적인 방법이지만, 이로 인해 추론 비용이 증가하여 휴대용 기기에서의 적용이 더욱 어려워진다. 이를 해결하기 위해, 우리는 앙상블 모델들을 교사로 간주하는 방식의 지식 증류를 통해서 여러 모델들을 하나의 모델로 압축한다. 앙상블 기반 교사를 기반으로, 우리는 신경망 구조 탐색 기술과 통합하여 오라클 지식 증류 손실 함수를 제안하며, 해당 방법은 모델 용량 문제를 성공적으로 해결하여 학생 네트워크가 교사와 경쟁력 있는 성능을 달성할 수 있도록 해준다. 생성 모델링의 맥락에서, 생성 모델 또한 일반적으로 추론 비용이 굉장히 크기 때문에, 휴대폰과 같은 저전력 장치에서의 응용이 제한된다. 생성 모델 압축을 위한 기존의 지식 증류 접근법은 간단하게 두 네트워크 간의 픽셀 단위로 차이를 계산하기 위해 L1 또는 L2 노름을 사용하는데, 이러한 접근법들은 이미지 분류 작업에서도 널리 사용되고 있다. 이러한 방법들에 덧붙여서, 우리는 학생과 선생간의 상호 정보를 최대화하는 방향의 지식 증류방법으로 학생을 학습시킨다. 생성 모델링에서, 픽셀 단위 비교 방법과 달리 제안된 방법은 자연 이미지에서 픽셀 간 의존성을 고려하는데 효과적이며, 이는 성능을 더욱 향상시키는 결과를 가져온다. 연속 학습 분야에서, 우리는 클래스 증분 학습 시나리오를 고려한다. 이 시나리오에서는 모델은 이전 작업의 데이터에 제한된 접근성을 가지고 새로운 클래스를 점진적으로 학습한다. 이전 작업과 현재 작업간의 데이터 불균형 문제로 인해, 모델은 종종 파괴적 망각 문제를 겪게 된다. 여기서, 파괴적 망각 문제는 이전 작업들에 대해서는 일반화 성능이 낮고, 현재 작업에서만 일반화 성능이 좋은 경향을 띈다는 문제점을 의미한다. 이를 해결하기 위해, 우리는 이전 작업을 위해 학습된 모델을 선생으로 여기며 특징 맵 가중치를 포함하는 효과적인 지식 증류 접근법을 도입한다. 제안한 방법은 기본적으로 중요한 특징을 유지하여 이전에 학습된 정보를 보존하면서, 덜 중요한 특징을 유연하게 만들어 새로운 클래스 정보를 학습한다. 실험 결과를 통해, 제안된 지식 증류 방법들이 앙상블 학습, 생성 모델링, 지속적 학습에서 뛰어난 성능을 보였음을 확인하였다.1 Introduction 1 1.1 Motivation 1 1.2 Justification of Knowledge Distillation 2 1.3 Proposed Approaches 5 1.3.1 Knowledge Distillation for Ensemble Learning 5 1.3.2 Knowledge Distillation for Generative Modeling 6 1.3.3 Knowledge Distillation for Continual Learning 7 1.4 Summary of Contributions 8 1.5 Thesis Organization 9 2 Related Work 11 2.1 Knowledge Distillation 11 2.1.1 Ensemble Learning 11 2.1.2 Generative Modeling 12 2.1.3 Continual Learning 12 2.1.4 Multi-task Learning 13 2.1.5 Self-Supervised Learning 13 2.1.6 Federated Learning 14 2.1.7 Data-Free Learning 14 2.1.8 Learning with Noisy Labels 15 2.1.9 Computer Vision Applications 15 2.2 Model Compression 17 2.2.1 Matrix Decomposition 17 2.2.2 Quantization 17 2.2.3 Unstructured Pruning 18 2.2.4 Structured Pruning 18 3 Knowledge Distillation for Ensemble Learning 20 3.1 Overview 20 3.2 Related Work 23 3.3 Neural Architecture Search with Oracle Knowledge Distillation 24 3.3.1 Knowledge Distillation 25 3.3.2 Oracle Knowledge Distillation 26 3.3.3 Optimal Model Search for Knowledge Distillation 27 3.4 Experiments 30 3.4.1 Experimental Setup 30 3.4.2 Experimental Results 31 3.5 Summary 38 4 Knowledge Distillation for Generative Modeling 40 4.1 Overview 40 4.2 Related Work 42 4.2.1 Generative Adversarial Networks 42 4.2.2 GAN Compression 43 4.2.3 Cooperative Learning Methods 44 4.3 Variational GAN Compression with Energy-based Model 44 4.4 Training Procedures 46 4.4.1 Optimization of Energy-based Model 47 4.4.2 Optimization of Student Generator 49 4.4.3 Optimization of Teacher Generator 50 4.4.4 GAN Compression Baseline Algorithms 51 4.5 Experiments 54 4.5.1 Datasets and Models 54 4.5.2 Evaluation Metrics 55 4.5.3 Implementation Details 55 4.5.4 Results 60 4.5.5 Ablation Study about Mutual Information Maximization Techniques 62 4.5.6 Effect of λMI for Mutual Information 63 4.5.7 Training Cost 64 4.5.8 Qualitative Results 64 4.6 Summary 65 5 Knowledge Distillation for Continual Learning 75 5.1 Overview 75 5.2 Related Work 77 5.2.1 Architectural Methods 77 5.2.2 Rehearsal and Pseudo-Rehearsal Methods 78 5.2.3 Parameter Regularization Approaches 78 5.3 Adaptive Feature Consolidation 79 5.3.1 Problem Formulation 79 5.3.2 Practical Objective Function 81 5.3.3 More Robust Objective Function 82 5.3.4 Final Loss Function 84 5.3.5 Management of Exemplar Set 86 5.3.6 Discussion about Computational Cost 86 5.4 Experiments 86 5.4.1 Dataset 86 5.4.2 Implementation Details 87 5.4.3 Results on CIFAR100 87 5.4.4 Results on ImageNet 90 5.4.5 Analysis and Ablation Studies 90 5.5 Summary 95 6 Conclusion 98 6.1 Summary 98 6.2 Future Works 99 Abstract (In Korean) 127박

상완 근지구력 검사의 준거지향기준 설정에 관한 연구

학위논문(석사)--서울대학교 대학원 :체육교육과,1997.Maste