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Jun‑hyun Jo,Min‑seok Park,Kyung‑woo Yi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.11
Hypo peritectic steels exhibit a high possibility of longitudinal crack during continuous casting. Therefore, many researchershave studied the mechanisms of crack generation in hypo peritectic steel. Stress in solidified shell, or volume contractionwith small liquid fractions were suggested as the mechanisms of crack generation. A new model was developed for predictingpossibility of crack generation by calculating strain rates in solid, volume contraction rate during solidification, and theprobability of liquid unfilling in continuous cooling processes. The results show that massive transformation from the δphase to the γ phase, and peritectic transformation during solidification can be the main crack generation mechanisms. Furthermore,a linear relationship exists between the amount of undercooling for peritectic transformation (dTp) and the carboncontent of the boundary for dividing the two crack generation mechanisms. Additionally, the longitudinal crack ratios ofthe field results are analyzed through strain rates in solid and liquid unfilling possibilities. Relative positions in the range ofhypo peritectic steel and effective carbon contents are suggested to analyze the crack ratio of steels with alloying elements. This analysis shows that the results obtained from the new models for crack generation possibility are usable, and dTpcangenerate the behavioral differences in crack generation according to the conditions.
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Phase Transformation Modeling for Hypo Peritectic Steel in Continuous Cooling
Jun‑hyun Jo,Kyung‑woo Yi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7
Phase change of steel during cooling affects the slab qualities in continuous casting. Especially, crack susceptibility of hypoperitectic steel is high because large volume shrinkage occurs by peritectic phase transformation during solidification andcooling. In continuous cooling, phase change is different from the behaviors under the equilibrium condition, such as undercoolingand extend of peritectic reaction, etc. Therefore, we develop a new phase change model considering thermodynamics,empirical equations, and carbon diffusion in each phase to predict phase change behavior during continuous cooling. Inthis model, phase change of hypo peritectic steel comprises 5 stages until all phases become the γ phase. The velocities ofthe δ/γ interface and phase fractions during cooling are calculated according to cooling rate, undercooling of the γ phase,and carbon contents. The results show that if solidification ends by the δ phase during dTp,the γ phase is formed by massivetransformation. On the contrary, if peritectic reaction starts with liquid, the γ phase is formed and grows by diffusionaltransformation. In latter case, massive transformation of remaining δ phase can occur with high undercooling or very fastcooling rates. This analysis shows that there are several different paths depending on carbon contents of hypo peritectic steels.
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Hyun Chul Kim,Chi Hoon Lee,Sung Pyu Hur,Byeong Hoon Kim,Jun Young Park,Young Don Lee 한국발생생물학회 2015 발생과 생식 Vol.19 No.1
This study investigated possible involvement of photoperiodic regulation in reproductive endocrine system of female olive flounder. To investigate the influence on brain-pituitary axis in endocrine system by regulating photoperiod, compared expression level of Kisspeptin and sbGnRH mRNA in brain and FSH-β, LH-β and GH mRNA in pituitary before and after spawning. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from Aug. 2013 to Jun. 2014. Continuous long photoperiod treatment from Aug. (post-spawning phase) was inhibited gonadal development of female olive flounder. In natural photoperiod group, the Kiss2 expression level a significant declined in Mar. (spawning period). And also, FSH-β, LH-β and GH mRNA expression levels were increasing at this period. However, in long photoperiod group, hypothalamic Kiss2, FSH-β, LH-β and GH mRNA expression levels did not show any significant fluctuation. These results suggest that expression of hypothalamic Kiss2, GtH and GH in the pituitary would change in response to photoperiod and their possible involvement of photoperiodic regulation in reproductive endocrine system of the BPG axis.
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Jun‑Woo Song,Jin‑Ju Park,Gyoung‑Ja Lee,Min‑Ku Lee,Kyu‑Hyun Park,Soon‑Jik Hong,Jung Gu Lee 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.3
The weldability window in magnetic pulse welding (MPW) is proposed for the end-closure joining of HT-9 steel tubularworkpieces. Based on both theoretical and experimental investigations, the impact velocity of the flyer tube at the momentof collision had a dominant effect on the bonding characteristics of the resultant joints and the optimal impact velocity wasestimated to be in the range of 265–290 m/s in this alloy system. Under the optimal process conditions, no leak was detectedduring helium leak testing. Moreover, the integrity of the joint interface was preserved until the tube section ruptured duringinternal pressure burst testing. For HT-9 steel, the ductile δ-ferrite phase produced by the localized interfacial melting duringMPW acted as an effective obstacle to crack propagation, thereby enhancing the fracture resistance of the joint interface. Allof the results demonstrated the high integrity and durability of the HT-9 steel tube assembly fabricated by the MPW process.
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Kim, Hyun Chul,Lee, Chi Hoon,Hur, Sung Pyu,Kim, Byeong Hoon,Park, Jun Young,Lee, Young Don The Korean Society of Developmental Biology 2015 발생과 생식 Vol.19 No.1
This study investigated possible involvement of photoperiodic regulation in reproductive endocrine system of female olive flounder. To investigate the influence on brain-pituitary axis in endocrine system by regulating photoperiod, compared expression level of Kisspeptin and sbGnRH mRNA in brain and FSH-${\beta}$, LH-${\beta}$ and GH mRNA in pituitary before and after spawning. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from Aug. 2013 to Jun. 2014. Continuous long photoperiod treatment from Aug. (post-spawning phase) was inhibited gonadal development of female olive flounder. In natural photoperiod group, the Kiss2 expression level a significant declined in Mar. (spawning period). And also, FSH-${\beta}$, LH-${\beta}$ and GH mRNA expression levels were increasing at this period. However, in long photoperiod group, hypothalamic Kiss2, FSH-${\beta}$, LH-${\beta}$ and GH mRNA expression levels did not show any significant fluctuation. These results suggest that expression of hypothalamic Kiss2, GtH and GH in the pituitary would change in response to photoperiod and their possible involvement of photoperiodic regulation in reproductive endocrine system of the BPG axis.
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Park Sang‐Hyun,Ha Young‐Ho,Kim Dong Eon,Kim Chang‐Jun,Choi Moon Bo 한국곤충학회 2021 Entomological Research Vol.51 No.3
Argentine ants (Linepithema humile) are one of the world’s most invasive species and were first reported in South Korea, near Busan Port in 2019. The distribution of their initial spread was investigated here from April to July 2020. In the invasion area, numerous nests and individuals were identified, indicating that they had settled and successfully invaded the habitat. To track the invasion of the Argentine ants we conducted haplotype analysis using COI, COII, and Cytb sequences of their mitochondrial DNA. The invasive ants had the same mitochondrial haplotype (H3) as Argentine ants from America (Chile, Ecuador, Bermuda) and East Asia (Japan). When comparing the import trade volumes at Busan port with the Argentine ant haplotypes from other countries, it was determined that the invasive ants may have originated from the United States or Japan. Numerous ecological and economic impacts due to their invasion and spread in other countries has previously been reported. Therefore, prompt control measures for the Argentine ants found at Busan port, at this relatively early stage of settlement, is required.
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혼합유화제 비율에 따른 인계난연제 캡슐의 제조 및 특성 연구
백경현,이준영,홍상현,김중현 한국공업화학회 2004 응용화학 Vol.8 No.1
The microcapsules containing triphenyl phosphate (TPP) flame retardant have been prepared by using the epoxy resin (Novolac Type) with good physical properties and network structure. The reactants including TPP, epoxy resin and mixed surfactants were emulsified to oil in water (O/W) by the phase inversion technology and then conducted on the crosslinking of epoxy resin by In-situ polymerization. The capsule size and size distribution of TPP microcapsules was controlled by mixed surfactant ratio. The thermal property of TPP capsules were measured by the TGA. The morphology and capsule size were also investigated by the SEM respectively. TPP capsules with 1 : 1 of mixed surfactant (F127 : SDBS) ratio were more spherical and uniform than it with others. The TPP capsule size was 12~17㎛ and TGA results shows that TPP capsule efficiency was about 73%.
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기초운동기술 프로그램 참여가 유아의 자기효능감과 사회적 능력에 미치는 효과
전선혜(Jun, Sun-Hye),백효현(Baeck, Hyo-Hyun) 한국체육과학회 2015 한국체육과학회지 Vol.24 No.5
The purpose of this study was to examine the effects of participation in basic motor skill programs on children’s self-efficacy and social competence. Jun’s physical education program for children was conducted in 46 children in experimental group, and a childhood education institute’s own program was conducted in 48 children in control group. Also, to compare scores of self-efficacy and social competence of each group before and after the programs, the independent sample t-test and analysis of covariance (ANCOVA) were performed, and the following results were obtained. First, the basic motor skill program for children had effects on self-efficacy and its sub-domains including physical, cognitive, social and emotional domains. Second, the basic motor skill program for children showed effectiveness in improving children’s social competence and its sub-factors including social activity, stability, cooperativeness, autonomy, adaptability, and leadership. The children in experimental group, particularly, generally exhibited higher degree of improvement in self-efficacy and social competence than those in control group. Hence, it was found that the basic motor skill program could facilitate children’s self-efficacy and social competence more effectively than the child education institute’s own physical education program did. These results implied that it is necessary to improve conditions of education for dissemination of systemic children’s physical activity programs and invigoration and change the way of dealing with these programs.
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