1,721,687 research outputs found
Techniques to Study Automethylation of Histone Methyltransferases and its Functional Impact
No full textThe catalytic activity of histone methyltransferases is not restricted to histones but also includes noncanonical substrates. Increasing evidence shows that histone methyltransferases methylate themselves, and automethylation has emerged as a self-regulatory mechanism. Here, we introduce experimental procedures to identify automethylation sites of histone methyltransferases and to investigate the function of automethylation in a reconstituted biochemical system and in cellular contexts.N
Photoreflectance studies of Si-doped GaAs
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 1994.2, [ 58 p. ]한국과학기술원 : 물리학과
Study on the optical properties of gallium nitride
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 1999.2, [ iv, 133 p. ]본 연구에서는 비교적 양질의 에피층을 이용해 GaN의 광학적 특성을 photoluminescence (PL)와 photoreflectance (PR), Raman, photoluminescence excitation (PLE)등의 방법을 이용해 분석함으로써 GaN에 대한 전반적인 이해를 돕고자 한다. 시료는 hydride vapor phase epitaxy (HVPE), MBE, 그리고 MOCVD 방법으로 길러진 양질의 에피층을 이용하여 기판의 종류와 성장 조건에 따른 광특성을 분석하고, 이를 이용해 양질의 에피층을 만들 수 있는 조건을 제시하였다. 또한 에피층의 PL 스펙트럼이 가지는 특성을 분석함으로써 불순물의 에너지 준위를 확인하고, 농도에 따른 변화를 (예를 들면, 전자들간의 many body interaction, Burstein-Moss shift, band tailing 등) 정량화 하였다. 한편, Photoreflectance 실험에서는 운반자의 농도 변화에 따른 전기장 변조뿐만 아니라, mobility가 작은 운반자들의 행동을 분석함으로써 PR에 대한 이해를 넓히고자 한다.
이와 더불어서 아직 까지도 많은 논란이 되고있는 Mg을 도핑한 GaN의 발광 특성 및 yellow emission band의 근원을 밝히려는 연구도 수행하였다. MOCVD 방법으로 키워진 Mg을 도핑한 시료의 PL 스펙트럼을 분석하여 2.8∼2.9 eV 영역에 나타나는 blue emission band가 conduction band와 Mg과 관련된 deep level 사이에서 일어나는 전이라는 것을 알 수 있었다. HVPE 방법으로 키워진 unintentionally Mg-doped n형 GaN를 이용해서 Mg과 관련이 있다고 믿어지는 red와 blue emission band, 그리고 거의 모든 시료에서 나타나는 yellow emission band의 PLE 스펙트럼을 10 K에서 상온까지 온도를 변화시키면서 측정하였다. 한편, annealing 실험을 통해서 red와 blue emission band들이 Mg으로 유도된 deep level 불순물과 관련이 있다는 결론을 얻을 수 있었다. 온도 변화에 따른 PLE 스펙트럼에서는 red와 yellow emission에 공통의 excited state가 관계되어 있음을 알 수 있었고, 그 공통의 excited state가 deep donor 임을 확인할 수 있었다. 이상과 같은 결과들을 많은 phonon들이 관련된 deep level 사이의 전이를 잘 설명하는 configuration coordinate (CC) 모델에 적용하여 CC diagram으로 표현하였다. CC 모델은 PL 스펙트럼에 나타난 모든 emission band를 성공적으로 설명하였고, 온도 변화에 따른 PLE 스펙트럼의 line shape analysis를 통해서 구한 thermal barrier의 존재도 훌륭하게 설명하였다. 또한 CC diagram에서 yellow emission band는 deep donor와 shallow acceptor 사이의 전이라는 결론을 얻었고, deep donor와 shallow acceptor의 CC curvature가 같다는 가정 하에서 구한 deep donor의 binding 에너지는, deep level transient spectroscopy 실험을 수행하여 얻은 다른 연구결과들과 유사한 것을 알 수 있었다. 이러한 결과는 GaN에 intrinsic deep donor가 존재한다는 것을 의미하는데 그 근원에 대해서 논의하였다.한국과학기술원 : 물리학과
Chromatin remodelers fine-tune h3k36me-directed deacetylation of neighbor nucleosomes by Rpd3S
No full textChromatin remodelers have been implicated in the regulation of histone-modifying complexes. However, the underlying mechanism remains poorly understood. The Rpd3S histone deacetylase complex is recruited by elongating RNA polymerase II to remove histone acetylation at coding regions in a manner that is dependent on methylation of lysine 36 on histone 3 (H3K36me), and Rpd3S prefers dinucleosomes. Here, we show that the binding of Rpd3S to dinucleosomes and its catalytic activity are sensitive to the length of nucleosomal linker in a nonlinear fashion. Intriguingly, we found that H3K36me on one nucleosome stimulates Rpd3S to deacetylate the neighboring nucleosomes when those two nucleosomes are within an optimal distance. Finally, we demonstrate that chromatin remodelers enhance Rpd3S activity by altering nucleosomal spacing, suggesting that chromatin remodelers prime chromatin configuration to fine-tune subsequent histone modification reactions. This mechanism is important for accurate temporal control of chromatin dynamics during the transcription elongation cycle. © 2013 Elsevier Inc.Y
취성 층상소재의 접촉손상 거동
No full text학위논문(박사) - 한국과학기술원 : 재료공학과, 2003.2, [ xii, 123 p. ]The mechanics of contact-induced damage in brittle layers on soft support substrates are of interest for their relevance to lifetime-limiting failures of technological laminate systems in concentrated loading. This is particularly true of biomechanical applications-dental crowns and hip prosthesis-which must withstand intense biting or body weight forces under exacting cyclic contact loading and in vivo environmental conditions. Such prostheses may consist of several different material types-ceramic, metal, polymer, and composite-in layered configurations. Other, more engineering-oriented layer applications include cutting tools, thermal barrier coatings, electronic multi-layer devices, car windscreens and eyeglasses. The recent advances in the understanding and analysis of damage initiation and evolution in brittle layer structures will be presented. The results of experiments model bilayer that enable in-situ viewing during loading with simple concentrated loads (spherical indenters) and yet simulate the essential features of damage in a wide range of engineering layer structures are described. The experiments reveal a competition between damage modes-cone cracks or quasiplasticity at the top (near-contact) brittle-layer surfaces and laterally extending radial cracks at the lower surfaces due to the brittle coating layer thickness.
Brittle coating structures may be subjected to complex concentrated loading, including tangential component. Results of Hertzian contact tests investigating the effects of superposed tangential loads on the critical conditions for radial cracking at the undersurfaces of brittle coatings on compliant substrates are reported. Bilayer specimen is prepared from glass coating bonded to polycarbonate substrate and blunt indenter is load with tangential motion as well normal motion. In order to change the friction coefficient the loading geometry is changed to the inclined fixture. Changes in near-surface stress fields from tangential for...한국과학기술원 : 재료공학과
PRC2 is high maintenance
No full textAs the process that silences gene expression ensues during development, the stage is set for the activity of Polycomb-repressive complex 2 (PRC2) to maintain these repressed gene profiles. PRC2 catalyzes a specific histone posttranslational modification (hPTM) that fosters chromatin compaction. PRC2 also facilitates the inheritance of this hPTM through its self-contained "write and read" activities, key to preserving cellular identity during cell division. As these changes in gene expression occur without changes in DNA sequence and are inherited, the process is epigenetic in scope. Mutants of mammalian PRC2 or of its histone substrate contribute to the cancer process and other diseases, and research into these aberrant pathways is yielding viable candidates for therapeutic targeting. The effectiveness of PRC2 hinges on its being recruited to the proper chromatin sites; however, resolving the determinants to this process in the mammalian case was not straightforward and thus piqued the interest of many in the field. Here, we chronicle the latest advances toward exposing mammalian PRC2 and its high maintenance
Technology Sourcing Strategies and Cooperative Patterns in Vertical Cooperative R&D Projects
No full textSince 1982, the government of Korea has actively promoted vertical cooperative R&D programs between government-sponsored research institutes (GRIs) and private firms. A number of firms participated in the programs because cooperative R&D could lower the risk and could contribute to rapid commercialization of many technologies. This paper examines the effectiveness of vertical cooperative R&D projects by the modes of cooperation between GRIs and industrial firms and analyzes the performance of participating firms technology sourcing strategies for commercial utilization of cooperative R&D results at the project level. The data have been obtained from 128 cases of vertical cooperative R&D Program from 1982 to 1989 under the Government-Industry Cooperative R&D Program sponsored by the Ministry of Science and Technology(MOST) in Korea. The cooperative R&D projects are classified into 4 groups by two criteria, i,e., the level of participation of firms and the breadth of cooperation. The findings suggest that firms should actively participate in cooperative R&D projects. In addition, in order to enhance commercial success, cooperation between GRIs and industrial firms should not be limited to R&D projects in Korea usually lack internal technological capabilities that are needed to commercialize the results of cooperative R&D. Three different technology sourcing strategies - exclusive cooperative R&D strategy, in-house development augmented cooperative R&D strategy, and licensing-in supplemented cooperative R&d strategy - are empirically derived through cluster analysis of the relative usage rates cooperative R&D and of other supplementary technology acquisition methods. The findings suggest that the firms participating in vertical cooperative R&D projects should try to utilize other supplementary technology acquisition methods in order to achieve commercial utilization of the vertical cooperative R&D results
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
