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Structural Diversification of Macrolactones by Substrate-Flexible Cytochrome P450 Monooxygenases
Lee, Sang ,Kil,Basnet, Devi ,B.,Hong, Jay ,Sung ,Joong,Jung, Won ,Seok,Choi, Cha ,Yong,Lee, Hei ,Chan,Sohng, Jae ,Kyung,Ryu, Keun ,Garp,Kim, Dae WILEY-VCH 2005 Advanced Synthesis & Catalysis Vol.347 No.10
<P>The substrate flexibilities of several cytochrome P450 monooxygenases involved in macrolide biosynthesis were investigated to test their potential for the generation of novel macrolides. PikC hydroxylase in the pikromycin producer Streptomyces venezuelae accepted oleandomycin as an alternative substrate and introduced a hydroxy group at the C-4 position, which is different from the intrinsic C-12 hydroxylation position in the natural substrate. This is the first report of C-4 hydroxylation activity of cytochrome P450 monooxygenase involved in the biosynthesis of 14-membered macrolides. EryF hydroxylase from the erythromycin biosynthetic pathway of Saccharopolyspora erythraea and OleP oxidase from the oleandomycin biosynthetic pathway of Streptomyces antibioticus also showed a certain degree of plasticity towards alternative substrates. In particular, EryF and OleP were found to oxidize a 12-membered macrolactone as an alternative substrate. These results demonstrate the potential usefulness of these enzymes to diversify macrolactones by post-PKS oxidations.</P>
Cancer Incidence among Pesticide Applicators Exposed to Alachlor in the Agricultural Health Study
Lee, Won Jin,Hoppin, Jane A.,Blair, Aaron,Lubin, Jay H.,Dosemeci, Mustafa,Sandler, Dale P.,Alavanja, Michael C. R. Oxford University Press 2004 American Journal of Epidemiology Vol.159 No.4
<P> The authors evaluated the incidence of cancer among pesticide applicators with exposure to alachlor in the Agricultural Health Study, a prospective cohort study of licensed pesticide applicators in Iowa and North Carolina. A total of 49,980 pesticide applicators are included in this analysis; 26,510 applicators (53%) reported use of alachlor on the enrollment questionnaire. Detailed pesticide exposure and other information were obtained from a self-administered questionnaire completed at the time of enrollment (1993–1997). Poisson regression analysis was used to evaluate the exposure-response relations between alachlor and cancer incidence controlled for the effects of potential confounding factors. A total of 1,466 incident malignant neoplasms were diagnosed during the study period, 1993–2000. Among alachlor-exposed applicators, the authors found a significant increasing trend for incidence of all lymphohematopoietic cancers associated with lifetime exposure-days (<I>p</I> for trend = 0.02) and intensity-weighted exposure-days (<I>p</I> for trend = 0.03) to alachlor. The risks of leukemia (rate ratio = 2.83, 95% confidence interval: 0.74, 10.9) and multiple myeloma (rate ratio = 5.66, 95% confidence interval: 0.70, 45.7) were increased among applicators in the highest alachlor exposure category. Our findings suggest a possible association between alachlor application and incidence of lymphohematopoietic cancers among applicators in the Agricultural Health Study.</P>
Analytical study of failure damage to 270,000-kL LNG storage tank under blast loading
Lee, Sang Won,Choi, Seung Jai,Kim, Jang-Ho Jay Techno-Press 2016 Computers and Concrete, An International Journal Vol.17 No.2
The outer tank of a liquefied natural gas (LNG) storage tank is a longitudinally and meridianally pre-stressed concrete (PSC) wall structure. Because of the current trend of constructing larger LNG storage tanks, the pre-stressing forces required to increase wall strength must be significantly increased. Because of the increase in tank sizes and pre-stressing forces, an extreme loading scenario such as a bomb blast or an airplane crash needs to be investigated. Therefore, in this study, the blast resistance performance of LNG storage tanks was analyzed by conducting a blast simulation to investigate the safety of larger LNG storage tanks. Test data validation for a blast simulation of reinforced concrete panels was performed using a specific FEM code, LS-DYNA, prior to a full-scale blast simulation of the outer tank of a 270,000-kL LNG storage tank. Another objective of this study was to evaluate the safety and serviceability of an LNG storage tank with respect to varying amounts of explosive charge. The results of this study can be used as basic data for the design and safety evaluation of PSC LNG storage tanks.
Lee, Hojae,Kim, Jang-Ho Jay,Moon, Jae-Heum,Kim, Won-Woo,Seo, Eun-A Elsevier 2019 Construction & building materials Vol.226 No.-
<P><B>Abstract</B></P> <P>Recently, researches on additive manufacturing (AM) method have been actively carried out as the latest technique for building concrete structures in the construction field. It is known that the additive manufacturing method, also called 3D printing technique, is a method of constructing a structure by printing layers, and the adhesion strength in the interlayer between the layers plays a dominant role in the performance of the structure. In this study, we focused on the formation of interlayer of concrete structure built using additive manufacturing method. In this study, the position of the interlayer was analyzed using the computed tomography (CT) method and the correlation between porosity and tensile bond strength in the analyzed interlayer was tried. As a result of the CT analysis of 13 specimens extracted from the printed specimens, it was confirmed that the porosity was formed high in the interlayer. The porosity of the interlayer was at least 2.15% and 6.66% higher than the average porosity. After analyzing the porosity by CT, the tensile bond strength of the specimens was measured to confirm the tensile bond strength and location of the fracture surface. Tensile bond strengths were 2.58–3.77 MPa with an average of 2.80 MPa using 10 specimens. It was confirmed that all of the fracture surfaces occurred along the interlayer. It was confirmed that there was no correlation between the tensile bond strength and porosity of the test specimens used in this study. Six of the ten specimens failed in the other interlayer, but four specimens failed in the interlayer with the highest porosity. As a result of analysis of the fracture surfaces of six specimens without fracture at the highest porosity, the porosity at the fracture surface was 5.73–9.18%, which was higher by 0.6–3.3% than the average porosity. However, defects occurred during layer output were confirmed from the failure of six specimens. Through this study, we confirmed that the interlayer is the weakest when tensile stress is applied in the perpendicular direction of printing, and that it is necessary to review the defects when applying the printing method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pore distribution in the interlayer analyzed using X-ray Computed Tomography. </LI> <LI> Relationship between pore fraction and position of tensile bond fracture determined. </LI> <LI> Tensile bond strength of 6.27% of compressive strength obtained. </LI> <LI> Weakest layer occurred when tensile stress is perpendicular to printing direction. </LI> </UL> </P>