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Sim, JiSoo,Lee, SangGu,Kim, JunBeom,Shin, SangJoon,Park, SeungSoo,Ohm, WonSuk The Korean Society for Aeronautical and Space Scie 2017 International Journal of Aeronautical and Space Sc Vol.18 No.3
The pogo phenomenon refers to a type of multidiscipline-related instability found in space launch vehicles. It is caused by coupling between the fuselage structure and other structural propulsion components. To predict the pogo phenomenon, it is essential to undertake adequate structural modeling and to understand the characteristics of the feedlines and the propulsion system. To do this, a modal analysis is conducted using axisymmetric two-dimensional shell elements. The analysis is validated using examples of existing launch vehicles. Other applications and further plans for pogo analyses are suggested. In addition, research on the pogo phenomenon of Saturn V and the space shuttle is conducted in order to constitute a pogo stability analysis using the results of the present modal analysis.
JiSoo Sim,SangGu Lee,JunBeom Kim,SangJoon Shin,SeungSoo Park,WonSuk Ohm 한국항공우주학회 2017 International Journal of Aeronautical and Space Sc Vol.18 No.3
The pogo phenomenon refers to a type of multidiscipline-related instability found in space launch vehicles. It is caused by coupling between the fuselage structure and other structural propulsion components. To predict the pogo phenomenon, it is essential to undertake adequate structural modeling and to understand the characteristics of the feedlines and the propulsion system. To do this, a modal analysis is conducted using axisymmetric two-dimensional shell elements. The analysis is validated using examples of existing launch vehicles. Other applications and further plans for pogo analyses are suggested. In addition, research on the pogo phenomenon of Saturn V and the space shuttle is conducted in order to constitute a pogo stability analysis using the results of the present modal analysis.
초기 설계 단계 우주 발사체의 포고 현상 예측을 위한 시스템 구성과 안정성 해석
심지수(JiSoo Sim),이상구(SangGu Lee),신상준(SangJoon Shin),서용준(Yongjun Seo),안성준(Sungjun Ann),송희성(Huiseong Song),김유단(Youdan Kim) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
우주 발사체에서 발생하는 다양한 다분야 연계 문제 중 하나인 축방향 동적 불안정성 현상인 포고현상에 관한 연구를 수행하였다. 구조, 공급계, 추진 시스템의 연성에 의한 현상으로 구조 시스템과 추진 시스템이 닫힌계 시스템을 구성하여 전체 반응이 증폭하는 불안정성이 나타난다. 우주 발사체 개발에서 포고 현상에 대한 예측과 억제는 필수적이다. 따라서 포고 현상의 시스템 구성과 이를 해석하기 위한 방법에 대한 연구를 진행하였으며 이를 위하여 우주왕복선의 사례와 연구 방법을 참고하여 검증, 발전시키고자 하였다. This research is about pogo phenomenon which is one of the problems in the space launch vehicle caused by coupling within various disciplines. This phenomenon is a coupling of structure, feedlines, and propulsion system regarding the coincidence of the natural frequencies. Then, the system becomes closed-loop composed of the structural and propulsion system. In order to predict of the relevant pogo instability, an example of the space shuttle is analyzed.
Sim, Ji Hyun,Kim, Hang-Rae,Chang, Soog-Hee,Kim, In Je,Lipsky, Peter E.,Lee, Jisoo BioMed Central 2015 ARTHRITIS RESEARCH AND THERAPY Vol.17 No.-
<P><B>Introduction</B></P><P>Pre-naïve B cells represent an intermediate stage in human B-cell development with some functions of mature cells, but their involvement in immune responses is unknown. The aim of this study was to determine the functional role of normal pre-naïve B cells during immune responses and possible abnormalities in systemic lupus erythematosus (SLE) that might contribute to disease pathogenesis.</P><P><B>Methods</B></P><P>Pre-naïve, naïve, and memory B cells from healthy individuals and SLE patients were stimulated through CD40 and were analyzed for interleukin-10 (IL-10) production and co-stimulatory molecule expression and their regulation of T-cell activation. Autoreactivity of antibodies produced by pre-naïve B cells was tested by measuring immunoglobulin M (IgM) autoantibodies in culture supernatants after differentiation.</P><P><B>Results</B></P><P>CD40-stimulated pre-naïve B cells produce larger amounts of IL-10 but did not suppress CD4<SUP>+</SUP> T-cell cytokine production. Activated pre-naïve B cells demonstrated IL-10-mediated ineffective promotion of CD4<SUP>+</SUP> T-cell proliferation and induction of CD4<SUP>+</SUP>FoxP3<SUP>+</SUP> T cells and IL-10 independent impairment of co-stimulatory molecule expression and tumor necrosis factor-alpha (TNF-α) and IL-6 production. IgM antibodies produced by differentiated pre-naïve B cells were reactive to single-stranded deoxyribonucleic acid. SLE pre-naïve B cells were defective in producing IL-10, and co-stimulatory molecule expression was enhanced, resulting in promotion of robust CD4<SUP>+</SUP> T-cell proliferation.</P><P><B>Conclusions</B></P><P>There is an inherent and IL-10-mediated mechanism that limits the capacity of normal pre-naïve B cells from participating in cellular immune response, but these cells can differentiate into autoantibody-secreting plasma cells. In SLE, defects in IL-10 secretion permit pre-naïve B cells to promote CD4<SUP>+</SUP> T-cell activation and may thereby enhance the development of autoimmunity.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s13075-015-0687-1) contains supplementary material, which is available to authorized users.</P>
Dependence of Exciton Diffusion Length on Crystalline Order in Conjugated Polymers
Sim, Myungsun,Shin, Jisoo,Shim, Chiyeoung,Kim, Min,Jo, Sae Byeok,Kim, Joo-Hyun,Cho, Kilwon American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.2
<P>Exciton diffusion in organic semiconductors is crucial to the performance of organic solar cells. Here, we measured the exciton diffusion length in poly(3-hexylthiophene) (P3HT) as a function of the crystalline order using spectrally resolved photoluminescence quenching (SR-PLQ) techniques. The crystalline order in the P3HT films, characterized according to the mean crystal size and normalized crystallinity, was varied by changes in thermal treatment temperatures. The exciton diffusion length increased from 3 to 7 nm as the mean crystal size increased more than twice and the crystallinity increased by a factor of 6. A higher crystalline order improved the spectral overlap and reduced the distance between chromophores, enhancing Förster-mediated exciton diffusion. The higher crystalline order also lengthened the conjugated segments and reduced the energetic disorder, producing favorable condition for exciton hopping.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-2/jp409776s/production/images/medium/jp-2013-09776s_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp409776s'>ACS Electronic Supporting Info</A></P>