• Macromolecular Research
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• 제17권8호
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• pp.575-579
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• 2009

Copolymerization of L-lactide and s-caprolactone initiated by tin (II) octoate (Sn(Oct)$_2$) was carried out in supercritical chlorodifluoromethane (R22) with varying reaction conditions (time and temperature) and amounts of monomer and catalyst, under a pressure of 250 bar. The optimum conditions were a reaction time of 10 h and a temperature of 130 $^{\circ}C$, which is similar to the temperature used in bulk copolymerization system. The conversion increased from 56% to 76% by increasing the reaction time from 1 to 10 h. The molecular weight also increased to 75,900 g.mol$^{-1}$ over the same period, while the increased monomer concentration resulted in a high molecular weight of 86,400 g.mol$^{-1}$ and a monomer conversion of 84%. Raising the reaction temperature from 90 to 130 $^{\circ}C$ increased the monomer conversion as well as the poly-L-lactide-co-${\varepsilon}$-caprolactone (PLCL) molecular weight. The variation on the stannous octoate catalyst suggested that less catalyst would decrease the caprolactone content of the polymer.

• BMB Reports
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• 제52권10호
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• pp.607-612
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• 2019

During meiosis, programmed double-strand breaks (DSBs) are repaired via recombination pathways that are required for faithful chromosomal segregation and genetic diversity. In meiotic progression, the non-homologous end joining (NHEJ) pathway is suppressed and instead meiotic recombination initiated by nucleolytic resection of DSB ends is the major pathway employed. This requires diverse recombinase proteins and regulatory factors involved in the formation of crossovers (COs) and non-crossovers (NCOs). In mitosis, spontaneous DSBs occurring at the G1 phase are predominantly repaired via NHEJ, mediating the joining of DNA ends. The Ku complex binds to these DSB ends, inhibiting additional DSB resection and mediating end joining with Dnl4, Lif1, and Nej1, which join the Ku complex and DSB ends. Here, we report the role of the Ku complex in DSB repair using a physical analysis of recombination in Saccharomyces cerevisiae during meiosis. We found that the Ku complex is not essential for meiotic progression, DSB formation, joint molecule formation, or CO/NCO formation during normal meiosis. Surprisingly, in the absence of the Ku complex and functional Mre11-Rad50-Xrs2 (MRX) complex, a large portion of meiotic DSBs was repaired via the recombination pathway to form COs and NCOs. Our data suggested that Ku complex prevents meiotic recombination in the elimination of MRX activity.

• 한국지하수토양환경학회지:지하수토양환경
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• 제26권6호
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• pp.82-94
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• 2021

Facilities for low impact development (LID) or groundwater recharge have the high potential spreading groundwater nitrate contamination because of the rapid infiltration. This study was initiated to remove nitrate from the waters using agricultural byproducts as organic sources for denitrification during infiltration. As the first step of this purpose, we experimentally tested the denitrifying efficiency of 4 organic materials (pine tree woodchips, cherry leaves, rice straws, and rice hulls) and tried to identify the key factors controlling the efficiency. For this study, we precisely investigated the change of chemical reactions during the experiment by analyzing various geochemical parameters. The result shows that the denitrification efficiency is not simply linked to the availability of the easily decomposable contents in the organic matter. It is found that avoiding the severe pH decrease due to the CO₂ generation is the essence to derive the efficient denitrifying conditions when organic matters were used.

• 천문학회보
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• 제45권1호
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• pp.45.1-45.1
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• 2020

Light bridges (LBs) are relatively bright structures that divide sunspot umbrae into two or more parts. Chromospheric LBs are known to be associated with various activities including fan-shaped jet-like ejections and brightenings. Although magnetic reconnection is frequently suggested to be responsible for such activities, not many studies presented firm evidence to support the scenario. We carry out magnetic field measurements and imaging spectroscopy of a LB where fan-shaped jet-like ejections occur with co-spatial brightenings at their footpoints. We study their fine photospheric structures and magnetic field changes using TiO images, Near-InfraRed Imaging Spectropolarimeter data, and Hα data taken by the 1.6 m Goode Solar Telescope. As a result, we detect magnetic flux emergence in the LB that is of opposite polarity to that of the sunspot. The new flux cancels with the pre-existing flux at a rate of 5.6×1018 Mx hr-1. Both recurrent jet-like ejections and their footpoint brightenings are initiated at the vicinity of the magnetic cancellation, and show apparent horizontal extension along the LB at a projected speed of 4.3 km s-1 to form the fan-shaped appearance. Based on these observations, we suggest that the fan-shaped ejections may have resulted due to slipping reconnection between the new flux emerging in the LB and the ambient sunspot field.

• IMMUNE NETWORK
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• 제2권2호
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• pp.72-78
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• 2002

Background: The precise mechanism by which CTLA-4 regulates T cell immune responses is still not fully understood. Previously we proposed that CTLA-4 could downregulate T cell function by modulating a signaling cascade initiated from the T cell receptor complex. The evidence for this notion comes from our findings that CTLA-4 associated with the T cell receptor zeta (TCR zeta) chain, and hence regulated TCR zeta phosphorylation by co-associated SHP-2 tyrosine phosphatase (1). In this report, we investigated whether any other signaling molecules could be involved in the CTLA-4 signaling pathway. Methods: We have taken biochemical approaches, such as immunoprecipitation followed by autoradiography or immunoblotting, to identify the molecules associated with CTLA-4. To perform these assays, we used activated primary T cells and ectopically transfected 293 cells. Various truncation mutants of CTLA-4 were used to map the interaction site on CTLA-4. Results: We found that in addition to TCR zeta and SHP-2, a recently cloned small adaptor molecule, SAP (SLAM-associated protein), was also able to associate with CTLA-4. We identified the domain of SAP association in CTLA-4 being a motif involving GVYVKM. This motif has been previously found to bind SHP-2 through its phosphorylated tyrosine interaction with SH-2 domain of SHP-2. Indeed, co-expression of SAP and SHP-2 reduced their binding to CTLA-4 significantly, suggesting that SAP and SHP-2 compete for the common binding site, GVYVKM. Thus, by blocking SHP-2 recruitment SAP could function as a negative regulator of CTLA-4. Conclusion: Taken together, our data suggest the existence of complicate signaling cascade in regulating CTLA-4 function, and further provide evidence that SAP can act either as a positive or negative regulator depending on the nature of the associating receptors.

• IMMUNE NETWORK
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• 제13권4호
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• pp.157-162
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• 2013

Application of vaccine materials through oral mucosal route confers great economical advantage in animal farming industry due to much less vaccination cost compared with that of injection-based vaccination. In particular, oral administration of recombinant protein antigen against foot-and- mouth disease virus (FMDV) is an ideal strategy because it is safe from FMDV transmission during vaccine production and can induce antigen-specific immune response in mucosal compartments, where FMDV infection has been initiated, which is hardly achievable through parenteral immunization. Given that effective delivery of vaccine materials into immune inductive sites is prerequisite for effective oral mucosal vaccination, M cell-targeting strategy is crucial in successful vaccination since M cells are main gateway for luminal antigen influx into mucosal lymphoid tissue. Here, we applied previously identified M cell-targeting ligand Co1 to VP1 of FMDV in order to test the possible oral mucosal vaccination against FMDV infection. M cell-targeting ligand Co1-conjugated VP1 interacted efficiently with M cells of Peyer's patch. In addition, oral administration of ligand-conjugated VP1 enhanced the induction of VP1-specific IgG and IgA responses in systemic and mucosal compartments, respectively, in comparison with those from oral administration of VP1 alone. In addition, the enhanced VP1-specific immune response was found to be due to antigen-specific Th2-type cytokine production. Collectively, it is suggested that the M cell-targeting strategy could be applied to develop efficient oral mucosal vaccine against FMDV infection.

• 대한기계학회논문집A
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• 제36권6호
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• pp.707-712
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• 2012

본 연구에서는 Ti-6Al-4V 합금에 대한 초고주기 피로시험 연구를 통하여 사이클에 따른 파단면 관찰결과 2가지 타입으로 명확히 구분되는 것을 확인할 수 있었다. 첫번째로 106사이클 범위에서 확인할 수 있는 것은 표면부에서 피로크랙 사이트가 시작된 전형적인 피로 파단면이다. 두번째는 107~109사이클에서는 확연히 다른 피로파단 양상으로, 표면으로부터 $500{\mu}m$ 내부에서 피로크랙 사이트가 시작되어 크게 박리되어 나간 형상으로, 크랙 사이트 주변을 관찰한 결과 미세한 마이크로 크랙들이 입계파괴 양상으로 형성되어 있는 것을 확인 할 수 있었다. 이에 내부 크랙 사이트 피로거동에 대한 연구결과와 본 시험에서 사용된 초음파피로시험기술의 이론 및 적용사례를 소개하고 현재 활발히 진행중인 연구동향을 밝히고자 한다.

• 에너지공학
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• 제29권3호
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• pp.57-63
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• 2020

In this paper, we reported that the global trend of cement production and utilization as raw materials and as a fuel. As we know, cement is one of the significant materials required for the construction industry. The recent trend of rising urbanization, both the cement and construction industry played a vital role. The cement industry is a major sustainable infrastructure for the countries. Currently, China producing cement half of the world's cement production. During the year 2018, Korea producing cements nearly 57.5 million metric tons. Waste materials are used as circular resources and also having tremendous benefits for cement production. Another important use of these circular resources is fuel for the cement industry. There is a large potential benefit of the cement industry, but it's creating a severe environmental threat. The cement industry contributes to the major emissions of CO2. This leads the global warming. As per the Paris agreement, the Korean government initiated the recycling policy of waste materials and also the utilization of circular resources for the prevention of limited natural resources and also the global warming effect.

• 대한바이러스학회지
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• 제28권1호
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• pp.39-52
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• 1998

HIV-1 tat, a strong transactivator, is essential for the HIV-1 replication and AIDS progression. The Tat function is markedly inhibited by human anti-oncogene p53. This work was initiated to identify the p53-associated inhibitory mechanism on tat-mediated transactivation. Inhibitory function of p53 was confirmed by co-transfection of tat-expressing Jurkat cells with LTR-CAT plasmid, or H3T1 cells (LTR-CAT integrated HeLa cells) with different ratio of pSV-tat/pCDNA-p53 plasmids. Results from the direct protein-protein interaction between soluble p53 and tat, and yeast two-hybrid experiments showed that the co-suppression mechanism is unlikely to be due to the direct interaction. CAT activity was not affected by tat in Jurkat cells which were transfected with p53-promoter-CAT or p53-enhancer-CAT, suggesting that the tat-mediated p53 suppression is not directly associated with p53-promoter. Finally, we have tested protein kinase activity in p53-tranfected Jurkat cells, which might phosphorylate HIV-1 tat, resulting in inhibition of tat function. Some of our data lead us to assume that the p53-mediated tat inhibition is likely to be associated with p53-associated, signaling-mediated phosphorylation of tat, resulting in the dysfunction of tat. This study is now under investigation.

• 대한화학회지
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• 제36권5호
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• pp.644-651
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• 1992

기체상태의 오존(0.5torr)과 삼산화황간의 반응속도를 연구하였다. 69∼150${\circ}C$ 온도영역에서, 삼산화황은 6∼12 torr의 압력 범위에서 반응시켰다. 오존과 삼산화황의 반응속도는 $CO_2$가 단독으로 존재하고 있을 때의 오존의 반응속도보다 더욱 빨리 진행되었다. 오존과 삼산화황의 분자 반응에 대한 명백한 증거는 발견되지 않았고 빠른 반응속도는 $O_3\;＋\;HX\;{\rightarrow}\;OH\;＋\;O_2\;＋\;X$로 시작되는 연쇄반응을 일으키게 하는 $SO_3$ 반응물에 포함된 불순물(HX) 때문인 것 같고 또한 삼산화황은 더 큰 충돌직경을 가지고 있어 그것이 오존의 열적분해를 더욱 더 빠르게 하는 이유인 것으로 사료된다. 제안된 오존과 삼산화황의 실험속도식; $[-d(O_3)/dt]\;=\;k_a(SO_3)(O_3)\;＋\;k_b(O_3)^{3/2}$과 반응속도 상수 ; $k_a(M^{-1} s^{-1})\;=\;(1.55\;{\pm}\;0.67)\;{\times}\;105\;e-{(9.270 {\pm}0.43)kcal/RT}$을 얻었다..