Success Factors of Agribusiness Information Systems Outsourcing in the Public Sector

학위논문(박사) --서울대학교 대학원 :농경제사회학부,2007.Docto

High-temperature Tribological Properties of CoCrW and CoCrMo Alloys

As global demand for environmental protection rises, efforts are underway across various fields to reduce pollutant emissions. One area of focus is to enhance engine efficiency by minimizing friction and wear in marine engines that utilize eco-friendly fuels. Friction and wear significantly affect energy efficiency and durability, high lighting the need for a systematic understanding of the tribological characteristics of marine engine components and materials. This study investigates the friction and wear properties of CoCr-based alloys in high-temperature envi ronments. Experiments are conducted using a pin-on-disk tribo-tester at temperatures ranging from 250°C to 450°C. The results indicate that the friction and wear characteristics of CoCrWand CoCrMo, when tested against NiCr, gen erally increase with temperature. Notably, although the friction coefficients of CoCrW and CoCrMo are relatively sim ilar, CoCrMo exhibits significantly better wear resistance. Abrasive and adhesive wear are identified as the primary wear mechanisms, with the degree of tribo-film formation playing a critical role in wear progression. These findings offer valuable insights into the tribological properties of CoCr-based alloys and are expected to provide foundational data for the design of efficient and durable components in high-temperature environments

Study of the Friction and Wear Characteristics of Piston Ring/Cylinder Liner Systems in Marine Engines

As global awareness of environmental protection increases and regulations on ship engine emissions tighten, the demand for eco-friendly marine engine technology is growing. The degradation of the tribological properties of key components can lead to decreased engine efficiency, increased fuel consumption, and higher maintenance costs due to failures. Therefore, improving the tribological properties of key engine components such as the piston ring and cylinder liner system is crucial for developing eco-friendly marine engines. This study experimentally investigates the friction and wear properties of the piston ring and cylinder liner system in marine engines. Tests are conducted under various experimental conditions using a tribo-tester designed for this system. Notably, the Stribeck curve is obtained that shows the variations in the friction coefficient with respect to the Hersey number. The wear characteristics of the cylinder liner are quantitatively assessed, and major wear mechanisms are then proposed based on experimental observations. The findings contribute to a fundamental under standing of the friction and wear characteristics of the piston ring and cylinder liner in marine engines, thus aiding in the tribological design of eco-friendly marine engines

DOT1L regulates DNMT1 expression via p53 in cellular senescence

학위논문(석사)--아주대학교 일반대학원 :의생명과학과,2022. 2세포 노화(cellular senescence)는 노화 과정 중에서 세포의 표현형이 변하고, 세포주기가 정지하는 상태를 말한다. 세포 노화는 다양한 원인들에 의해 일어나고, 다양한 노화 관련 질병유발에 관여한다. 선행연구에서 DNA methyltransferase 1(DNMT1)가 초기 세포 노화에서 중요조절자 역할을 한다는 것이 밝혀졌기 때문에 이를 토대로 DNMT1을 조절하는 상위조절자를 찾기 위해 후성 유전학적 변화 조절자를 중심으로 연구를 진행하였다. RNA sequencing데이터를 이용하여 산화스트레스에 의한 노화(oxidative stress induced senescence, OSIS)모델에서 활성이 감소한 히스톤 메틸기 전달효소의 발현 패턴을 분석하였다. 그 중 H3K79의 메틸기 전달효소로 알려진 disruptor of telomeric silencing 1-like (DOT1L)은 DNMT1과 양의 상관관계(positive correlation)을 나타냈다. qPCR 및 western blot 분석을 통해 확인한 결과 DOT1L이 감소할 때, DNMT1이 감소하여 노화가 유도되었으나, DNMT1이 감소할 때, DOT1L은 감소하지 않지만 노화가 유도되는 것이 확인되었다. 이를 통해 DOT1L이 DNMT1의 발현을 조절하여 노화를 유도하는 것을 확인하였다. DNMT1은 세포 노화과정에서 중요한 조절인자로 알려져 있지만, 그 DNMT1을 조절하는 매커니즘은 잘 알려져 있지 않다. DOT1L이 DNMT1을 조절하는 매커니즘으로 p53을 선정하여 실험을 진행하였다. p53은 DNMT1을 조절한다고 보고되어 있고, 라이신 메틸화에 의해 활성이 조절된다고 알려져 있다. 따라서 DOT1L이 p53의 활성을 조절하여 DNMT1의 활성을 조절하는지 알아보기 위해 실험을 진행하였다. DOT1L을 knockdown하면 p53이 증가하고 DNMT1이 감소하는 패턴을 보였지만, DOT1L과 p53을 동시에 knockdown하면 DNMT1이 감소하지 않는 것을 확인하였다. 이를 통해 DOT1L은 p53을 통해 DNMT1을 조절하는 것을 알 수 있었다. 본 연구를 통해 DNMT1을 조절하는 상위 조절자를 찾고 그 기전을 밝혀 냄으로써 노화의 발현을 조절하는 새로운 방법을 제시할 수 있을 것으로 기대된다.제 1장 서론 1 제 2장 실험재료 및 방법 11 제 1절 세포주 배양 및 복제 노화 유도 11 제 2절 Western blot analysis 11 제 3절 RNA 분리 및 cDNA 합성 12 제 4절 Quantitative Real-time Polymerase Chain Reaction 12 제 5절 Senescence Associated Beta Galactosidase assay 13 제 6절 Small Interfering RNA(siRNA) Transfection 13 제 7절 Plasmid 재조합 13 제 8절 통계적 분석 14 제 3장 결과 16 제 1절 OSIS model에서 DNMT1과 DOT1L의 시계열 분석 16 제 2절 OSIS model에서 DNMT1과 DOT1L의 발현 18 제 3절 DOT1L 활성 억제 시 DNMT1 발현 감소에 의한 세포노화 22 제 4절 DNMT1 상위 조절자로 작용하는 DOT1L 24 제 5절 DOT1L/p53 axis에 의한 DNMT1 발현 조절 26 제 6절 p53 결합부위 돌연변이 DNMT1 프로모터 제작 30 제 4장 고찰 및 결론 32 참고문헌 34Maste

Simulation of the Initial Wear and Lubrication Performance of Marine Engine Components

Recently, the demand for improving energy efficiency has rapidly increased because of the growing concerns over environmental issues. In this work, the tribo-test and simulation for the initial wear and lubrication performance were performed for the piston pin in the small end system of the connecting rod of a marine engine, to obtain useful data for improving the efficiency of marine engine systems. In addition, a diamond-like carbon (DLC) coating was applied to the piston pin to explore feasibility of eliminating the bush used in the system. The initial wear and lubrication characteristics between the uncoated piston pin and bush were compared with that between the DLC-coated piston pin and connecting rod in the tribo-test. The simulation for the wear and lubrication performance according to the wear progression was conducted based on the data obtained from the test. The wear characteristics were quantitatively assessed by the wear depth and wear volume, and the lubrication performance was characterized with the change of pressure and minimum oil film thickness with respect to the crank angle. It was found that the DLC-coated piston pin may provide better initial wear characteristics and lubrication performance. The results of this work may provide fundamental information for marine engines with improved efficiency

Assessment of Tribological Characteristics of CoCrW and CoCrMo Alloys

Cobalt–chromium (CoCr)-based alloys have been used for wear applications because of their excellent mechanical properties and wear resistance. With growing concern over environmental problems, CoCr alloys are expected to be used for various tribological applications in degraded lubrication states. To expand the applicability of the materials, data should be accumulated across a broad spectrum of experimental parameters. In this work, the friction and wear characteristics of cobalt–chromium–tungsten (CoCrW) and cobalt–chromium–molybdenum (CoCrMo) alloys are investigated experimentally. The tests are conducted using a pin-on-reciprocating-plate tribo-tester in dry lubrication. CoCrW and CoCrMo are used as pin and plate materials to investigate the effect of the counter material. The results show that the friction coefficients between CoCrW and CoCrMo generally range from 0.4 to 0.5. The friction coefficient between the CoCrW pin and plate is found to be slightly small. However, the total wear between the CoCrW pin and plate is found to be the largest. In contrast, the total wear between the CoCrW pin and plate is relatively small. Furthermore, CoCrW may cause a faster wear progression of CoCrMo, especially for the case in which CoCrMo is used as the pin material. The results of this work provide a better understanding of the tribological properties of CoCrW and CoCrMo alloys. In addition, this work provides a practical guideline for the use of CoCrW and CoCrMo from the tribological design viewpoint

Study on of Friction and Degradation Characteristics of TPV Glass Run Channel

Recently, the demand for electric vehicles is intensively increasing in accordance with environmental issues in automotive industries. Given that noise level from the electric vehicles is significantly lower than that from conventional vehicles with internal combustion engine, noise management has become more critical. Conventionally, glass run channel (GRC) is used to block the noise and contaminants from outside of vehicle. In this work, the friction and degradation characteristics of GRC with thermoplastic vulcanizate substrate were assessed. The tests were performed using the reciprocating tribo-tester developed to replicate the contact sliding between GRC and window glass. Also, the test conditions were determined in consideration of operating condition of GRC. As a result, the plastic deformation of the lips due to creep and wear of the slip coating deposited on the lip surface were found to be major degradation mechanisms. Furthermore, it was shown that the friction and degradation increased significantly due to the misalignment between GRC and window glass, associated with the significant increase in the reaction force. The results of this work provide fundamental understanding of the degradation characteristics of GRC, and therefore are expected to be useful for the design of GRC with improved performance