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Lee, Younghun,Lee, Sungho,Zhao, Xing Guan,Lee, Dongoh,Kim, Taemin,Jung, Hoeryong,Kim, Namsu Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.22 No.2
In the last decade, there has been an exponential increase of scientific interest in smart additive manufacturing (AM) technology. Among the different AM techniques, one of the most commonly applied processes is digital light processing (DLP). DLP uses a digital projector screen to flash an ultraviolet light which cures photopolymer resins. The resin is cured to form a solid to produce parts with precise high dimensional accuracy. During the curing process, there are several process parameters that need to be optimized. Among these, the exposure time affects the quality of the 3D printed specimen such as mechanical strength and dimensional accuracy. This study examines optimal exposure times and their impact on printed part. It was found that there is optimal exposure time for printed part to have appropriate mechanical strength and accurate dimensions. The gel fraction and TGA test results confirmed that the improvement of mechanical properties with the increasing UV exposure time was due to the increase of crosslinked network formation with UV exposure time in acrylic resins. In addition, gel fraction and thermogravimetric analysis were employed to microscopically investigate how this process parameter impacts mechanical performance.
Younghun Lee,Sungho Lee,Xing Guan Zhao,Dongoh Lee,Taemin Kim,정회룡,Namsu Kim 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.2
In the last decade, there has been an exponential increase of scientific interest in smart additive manufacturing (AM) technology. Among the different AM techniques, one of the most commonly applied processes is digital light processing (DLP). DLP uses a digital projector screen to flash an ultraviolet light which cures photopolymer resins. The resin is cured to form a solid to produce parts with precise high dimensional accuracy. During the curing process, there are several process parameters that need to be optimized. Among these, the exposure time affects the quality of the 3D printed specimen such as mechanical strength and dimensional accuracy. This study examines optimal exposure times and their impact on printed part. It was found that there is optimal exposure time for printed part to have appropriate mechanical strength and accurate dimensions. The gel fraction and TGA test results confirmed that the improvement of mechanical properties with the increasing UV exposure time was due to the increase of crosslinked network formation with UV exposure time in acrylic resins. In addition, gel fraction and thermogravimetric analysis were employed to microscopically investigate how this process parameter impacts mechanical performance.
Fabrication and ink-jet patterning of copper nanoparticles with improved dispersion stability.
Lee, Kun-Jae,Kim, Namwoo,Hong, Sung-Jei,Lee, Kyu Bok,Lee, Dong-Jun,Oh, Je Hoon,Byun, Younghun,Choa, Yong-Ho American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.5
<P>Copper (Cu) nanoparticles as the metal nanoparticles in the conductive ink were synthesized using electrochemical reaction. This method is characterized as the synthesis process without any metal salts and the post-treatment of washing and drying. It means that it does not need to consider about oxidized and agglomerated metal nanoparticles during the extra treatments. The Cu nanoparticles were synthesized in the various conditions of electrolyte to investigate the mechanism of the synthesis reaction of Cu nanoparticles. And also, the synthesized Cu nanoparticles were controlled the dispersion stability with the addition of dispersion agent such as PVP and Dextran. Finally, it was achieved the ink-jet printed Cu patterns using the synthesized Cu nanoparticles, and examined the morphology of the patterns.</P>
Influence of Crown Size of Day-neutral Strawberry on Its Growth, Flowering, and Yield
( Younghun Lee ),( Young-rog Yeoung ) 강원대학교 농업생명과학연구원 2021 강원 농업생명환경연구 Vol.33 No.3
The use of cold storage transplants is becoming popular in summer strawberry production, replacing freshly dug bare-root transplants, in which the crown size indicates vigor. Three cultivars of day-neutral strawberry, Albion, Seascape, and San Andreas, were grown at the Daegwallyeong Research Center, Korea, inside a glasshouse during the summer growing season. Since the crown size of the strawberry transplant is associated with transplant vigor, this experiment was carried out to evaluate plant growth, development, and fruit yield of strawberry plants from cold storage bare-root transplants with different crown diameters. Three classes of crown diameters (small, medium, and large) were compared in a 3 × 3 factorial and completely randomized experimental design with four replications. Transplants were planted on April 17, 2013, and ripe fruits were harvested from June 11 to August 21, 2013. Fresh fruit yield was determined throughout the experiment, and plant growth and development were determined at the end of the experiment. The number of leaves, shoot dry weight, number of crowns, and fruit yield were significantly different among the three cultivars. Seascape showed the best vegetative and generative growth performance compared to the other cultivars. There was no correlation between the crown diameter, plant growth, or fruit yield of the cultivars; however, a larger crown diameter induced significantly earlier flower initiation. This result suggests that crown size is not an important indicator of the growth and yield of day-neutral strawberries from cold storage transplants.