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Atomistic Simulation of Sintering Mechanism for Copper Nano-Powders
Seong, Yujin,Hwang, Sungwon,Kim, See Jo,Kim, Sungho,Kim, Seong-Gon,Kim, Hak Jun,Park, Seong Jin The Korean Powder Metallurgy Institute 2015 한국분말재료학회지 (KPMI) Vol.22 No.4
The sintering mechanisms of nanoscale copper powders have been investigated. A molecular dynamics (MD) simulation with the embedded-atom method (EAM) was employed for these simulations. The dimensional changes for initial-stage sintering such as characteristic lengths, neck growth, and neck angle were calculated to understand the densification behavior of copper nano-powders. Factors affecting sintering such as the temperature, powder size, and crystalline misalignment between adjacent powders have also been studied. These results could provide information of setting the processing cycles and material designs applicable to nano-powders. In addition, it is expected that MD simulation will be a foundation for the multi-scale modeling in sintering process.
Yujin Seong,Youngkyu Kim,Im Doo Jung,Sungho Kim,See Jo Kim,Seong-gon Kim,Hak Jun Kim,Seong Jin Park 대한금속ㆍ재료학회 2017 대한금속·재료학회지 Vol.55 No.11
The material characterization of single crystalline Cu columns was numerically carried out at the submicroscopic level. A molecular dynamics (MD) simulation was employed using the embedded-atom method (EAM) interatomic potential between a pair of Cu atoms to describe the interactions among Cu atoms. First, the relationship between mechanical properties and factors affecting their behavior were numerically investigated using a crystal structure including several defects. The factors were specimen size, strain rate, and temperature. As the specimen size increased the normalized yield stress decreased, which was similar to results obtained at other length-scale. The yield stress tended to lead to exponential strain rate-hardening and a linear temperature-softening. Next, material characterization was conducted based on these results. These computational results can lead to the development of an in silico platform to characterize material properties and MD simulation can lay the groundwork for multi-scale modeling and simulation. (Received June 16, 2017; Accepted June 29, 2017)
The role of platelet to lymphocyte ratio and neutrophil to lymphocyte ratio in ulcerative colitis
( Yujin Jeong ),( Seong Ran Jeon ),( Hyun Gun Kim ),( Jung Rock Moon ),( Tae Hee Lee ),( Jae Young Jang ),( Jun-hyung Cho ),( Jun Seok Park ),( Heesu Park ),( Ki-hun Lee ),( Jin-oh Kim ),( Joon Seong 대한장연구학회 2021 Intestinal Research Vol.19 No.1
Background/Aims: Neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) can serve as biomarkers for diagnosing and assessing disease activity in ulcerative colitis (UC). We investigated their clinical significance in UC. Methods: We analyzed 48 patients with UC who underwent measurement of fecal calprotectin (FC) and endoscopy and 96 age- and sex-matched healthy controls. NLR and PLR were compared between the patients and healthy controls. The endoscopic activity was divided into 2 groups: group 1 (mild to moderate inflammation) and group 2 (severe inflammation) according to the Mayo endoscopic subscore in UC. Results: To diagnose UC, the optimal cutoff of NLR and PLR was 2.26 (sensitivity 54.2%; specificity 90.6%; positive likelihood ratio 5.778, 95% confidence interval [CI] 2.944-11.339; area under the curve [AUC] 0.774, 95% CI, 0.690-0.859) and 179.8 (sensitivity 35.4%; specificity 90.6%; positive likelihood ratio 3.778, 95% CI 1.821-7.838; AUC 0.654, 95% CI 0.556-0.753), respectively. The optimal cutoff to differentiate group 1 and group 2 was 3.44, 175.9, and 453 μg/g for NLR, PLR, and FC, respectively (sensitivity, 63.6% vs. 90.9% vs. 81.8%; specificity, 81.1% vs. 78.4% vs. 73.0%; positive likelihood ratio, 3.364 vs. 4.205 vs. 3.027; AUC, 0.714 vs. 0.897 vs. 0.813). PLR had the highest AUC and positive likelihood ratio. Conclusions: NLR and PLR help differentiate patients with UC from healthy controls. NLR, PLR, and FC indicate endoscopic activity and may reflect intestinal mucosal conditions. (Intest Res 2021;19:62-70)
Yujin Seong,Dami Yim,Min Ji Jang,Jeong Min Park,Seong Jin Park,Hyoung Seop Kim 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.2
A physics-based constitutive model of porous materials is proposed to enhance the accuracy of numerical analysis in die/isostatic compaction. The correlation between the yield function and equivalent work equation was derived, and the numericalintegration method was modifed with the correlation. It is found that the apparent work of porous materials is lower than theproduct of relative density and equivalent work of solid materials at the beginning of compaction, implying the kinematicmotion of powders and the resultant particle rearrangement. For verifcation of the proposed model, fnite element analyseswere performed for the die/isostatic compaction of three metal powders: Ti, SUS316L, and Al6061 powders. Compared withtwo conventional constitutive models, the proposed model improves the accuracy of the densifcation behaviors in all thestage during die/isostatic compaction. Furthermore, this study is a groundwork to link the densifcation behavior of porousmaterials at bulk scale to the particulate behavior of powders at microscale.
눈물주머니코안연결술을 시행한 눈물소관폐쇄에서 수술 중과 수술 후 사용한 마이토마이신 C 효과
최유진(YuJin Choi),김성재(Seong Jae Kim),유지명(Ji Myong Yoo),서성욱(Seong Wook Seo) 대한안과학회 2018 대한안과학회지 Vol.59 No.10
목적: 눈물소관폐쇄 환자에서 눈물주머니코안연결술 중 마이토마이신 C (mitomycin C) 사용 및 수술 후 마이토마이신 C 점안액의 효과를 알아보았다. 대상과 방법: 2012년 6월부터 2016년 6월까지 본원에서 눈물소관폐쇄로 진단되어 눈물주머니코안연결술을 시행한 46명 46안을 대상으로 후향적으로 분석하였다. 눈물점을 확장시킨 후 lacrimal trephine으로 눈물소관폐쇄 부위를 개통하였고, 수술 중 0.02% 마이토마이신 C로 노출된 눈물주머니에 3분간 도포 후 생리식염수 20 mL로 세척하고 실리콘 튜브를 삽입, 수술 후 1일째 항생제 점안, 2일째부터 0.02% 마이토마이신 C와 0.5% 스테로이드 점안액을 1개월간 점안하였다. 수술 전후 전안부 빛간섭단층촬영기를 사용하여 눈물띠 높이를 측정하였고 눈물흘림 정도를 Munk’s score에 따라 기능적 호전을 평가, 관류검사로 해부학적 호전을 평가하였다. 결과: 눈물띠 높이는 비측 571.64 ± 260.51 μm에서 267.16 ± 59.25 μm (p=0.043), 중앙 580.16 ± 186.24 μm에서 271.14 ± 45.10 μm (p=0.018), 가측 480.52 ± 260.23 μm에서 220.16 ± 63.79 μm (p=0.029)로 감소하였다. 기능적 성공률은 93.5% (43/46)였으며 해부학적 성공률은 95.7% (44/46)였다. 결론: 눈물소관폐쇄 시 수술 중 마이토마이신 C의 사용과 수술 이후 마이토마이신 C 점안액 및 스테로이드 점안액을 사용하는 것은 효과적인 치료 방법으로 수술 성공률을 높인다. Purpose: This study investigated the efficacy of intraoperative and postoperative mitomycin C eye drops in patients with canalicular obstructions. Methods: In total, 46 eyes of 46 patients diagnosed with canalicular obstruction at our hospital between June 2012 and June 2016 were analyzed. Canalicular trephination was done and, after applying 0.02% mitomycin C for 3 minutes on the exposed lacrimal sac during endoscopic dacryocystorhinostomy, the area was washed with 20 mL of saline solution, and a silicon tube was inserted. On postoperative day 1, an antibiotic eye drop was applied; beginning on postoperative day 2, 0.02% mitomycin C eye drops were applied, and 0.5% steroid eye drops were applied. Pre- and postoperative anterior segment optical coherence tomography was used to measure the nasal, central, and lateral tear meniscus heights. The extent of functional improvement was assessed by measuring the degree of tear according to Munk’s score, and anatomical improvement was assessed using a syringing test. Results: The nasal tear meniscus height decreased from 571.64 ± 260.51 μm to 267.16 ± 59.25 μm (p = 0.043); central tear meniscus height from 580.16 ± 186.24 μm to 271.14 ± 45.10 μm (p = 0.018); and lateral tear meniscus height from 480.52 ± 260.23 μm to 220.16 ± 63.79 μm (p = 0.029). The functional success rate was 93.5% (43/46), and the anatomical success rate was 95.7% (44/46). Conclusions: Intraoperative and postoperative mitomycin C and steroid eye drops may be an effective treatment for canalicular obstruction patients and should help increase surgical success rates.
전단응력비 개념에 기초한 강화노반의 영구변형 모델 수립
임유진(Yujin Lim),이성혁(Seong-Hyeok Lee),김대성(Dae-Seong Kim),박미연(Mi-Yun Park) 한국철도학회 2011 한국철도학회 학술발표대회논문집 Vol.2011 No.10
The reinforced-roadbed materials composed of crushed stones are used for preventing vertical deformation and reducing impact load caused by highspeed train. Repeated load application can induce deformation in the reinforced-roadbed layer so that it causes irregularity of track. Thus it is important to understand characteristics of permanent deformation in the reinforced-subbase materials. The characteristics of permanent deformation can be simulated by prediction model that can be obtained by performing repetitive triaxial test. The prediction model of permanent deformation is a key-role in construction of design method of track. The prediction model of permanent deformation is represented in usual as the hyperbolic function with increase of number of load repetition. The prediction model is sensitive to many factors including stress level etc. so that it is important to define parameters of the model as clearly as possible. Various data obtained from repetitive triaxial test and resonant column test using the reinforced-roadbed of crushed stone are utilized to develop a new prediction model based on concept of shear-stress ratio and elastic modulus. The new prediction model of permanent deformation can be adapted for developing design method of track in the future.
Genome Architecture and Transcriptome Analysis of Marine Cyanobacteria Synechocystis sp. PCC 7338
Yujin JEONG,Seong-Joo HONG,Sang-Hyeok CHO,Seonghoon YOON,Hookeun LEE,Hyung-Kyoon CHOI,Dong-Myung KIM,Choul-Gyun LEE,Suhyung CHO,Byung-Kwan CHO 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.4
Cyanobacteria producing various bio-products are considered promising microbial cell factories. The marine cyanobacterium Synechocystis sp. PCC 7338 has the advantage of growing in seawater, rather than requiring arable land or freshwater. However, how this marine cyanobacterium grows under the high salt stress condition remains unknown. Here, we determined the 3.70 Mbp complete genome of Synechocystis sp. PCC 7338. Differential RNA-seq and Term-seq data provided genome-wide information on genetic regulatory elements. Comparison with freshwater Synechocystis sp. strains revealed that Synechocystis sp. PCC 7338 genome encodes additional genes, which facilitate the adaptation to high salt and high osmotic pressure. A cyclic electron transport through photosystem I actively used by Synechocystis sp. PCC 7338 satisfied the demand for ATP under high salt environment. Our comprehensive analyses provide valuable information to discover the various genomic functions and regulations available for engineering Synechocystis sp. PCC 7338.