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- 검색키워드
- 저자 : Changhee Lee (검색결과 535 건)
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Correlation Between Constituent Phase and Weld Metal Properties in Ni-Reduced Duplex Stainless Steel
Youngchai Lee,Jae Hee Lee,Joonoh Moon,Tae‑Ho Lee,Changhee Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8
The intrinsic properties of austenite and ferrite on the mechanical properties and corrosion resistance of the duplex stainlesssteel weld metals was studied by substituting Ni with Mn, N, and Mn + N. The properties of the weldments fabricated throughgas tungsten arc welding (GTAW) were evaluated using tensile test, Vickers hardness, and potentiodynamic polarizationtests. The mechanical properties and corrosion resistance of the constituent phases were measured using nanoindentationand electron probe microanalysis, respectively. The austenite and ferrite phase fractions of the weld metal were maintainedat approximately 50:50, and no harmful phases degraded the properties. Excessive Mn decreased the corrosion resistance; alarge difference in corrosion resistance between austenite and ferrite also decreased the overall corrosion resistance. In thefiller metal in which Ni was replaced with only Mn or N, the austenite became harder than ferrite, as a result cracks initiatedinside the austenite. The tensile test showed that austenite, which became a relatively hard phase compared to ferrite accordingto the chemical composition, increased the yield strength and decreased the elongation of the weld metal.
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Changhee Lee,Inseok Park,Jungbin Kim,Hyunjin Cho,Keunho Yang,Yujin Lee,Kyeongmee Park,Jiyoung Kim,신영주,Geumhee Gwak 한국유방암학회 2021 Journal of Breast Disease Vol.9 No.1
Purpose: To investigate the characteristics of HER2-positive breast cancer according to HER2 low (2+) or high (3+) classification using immunohistochemistry (IHC). Methods: Data were collected from 205 HER2-positive breast cancer patients in the final assay, regardless of IHC or in situ hybridization (ISH). We thus classified patients into two groups: HER2 2+/low and HER2 3+/high based on the IHC assay. We subsequently compared the clinical and pathological characteristics between groups. Results: The median patient age was 49 years in the HER2 2+/low group and 53 years in the HER2 3+/high group. We observed a significantly lower Allred score for estrogen receptor (ER) and progesterone receptor (PR) (0-6) (p<0.001), less lymphatic invasion (LI), (p=0.010), neural invasion (p=0.041), higher Ki-67 (p=0.001), and lower Bcl-2 (p<0.001) in the HER2 3+/high group than in the HER2 2+/low group. Lymph node recurrence was more frequently observed in the HER2 2+/low group than in HER2 3+/high group (p=0.005). Disease-free survival (DFS) was better in the HER2 3+/high group than in the HER2 2+/low group (p=0.028), but there were no significant differences in overall survival between the groups (p=0.233). Conclusion: The HER2 3+/high group was associated with lower ER and PR expression, less LI, higher Ki-67, and lower Bcl-2 than that in HER2 2+/low group in HER2-positive breast cancer. Furthermore, compared to the HER2 2+/low group, the HER2 3+/high group had an improved DFS.
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Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC+NiCr
Lee, Changmin,Park, Hyungkwon,Yoo, Jaehong,Lee, Changhee,Woo, WanChuck,Park, Sunhong Elsevier 2015 APPLIED SURFACE SCIENCE - Vol.345 No.-
<P><B>Abstract</B></P> <P>Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC+NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55wt% stellite#6 and 45wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures combined with the crack initiation sites such as the fractured WC particles, pores and solidification cracks. WC particles directly caused clad cracks by particle fracture under the tensile stress. The pores and solidification cracks also affected as initiation sites and provided an easy crack path ways for large brittle fractures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Major problem, clad cracking in laser cladding process, was researched. </LI> <LI> Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. </LI> <LI> Relationship between the residual stress and crack initiation was showed clearly. </LI> <LI> Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. </LI> <LI> Initiation sites of generating clad cracks were specifically studied in MMC coatings. </LI> </UL> </P>
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Lee, Changhee,Kim, Youngnam,Jeon, Ji Hyun Elsevier 2016 VIRUS RESEARCH Vol.222 No.-
<P><B>Abstract</B></P> <P>The mitogen-activated protein kinase (MAPK) pathways, which are central building blocks in the intracellular signaling network, are often manipulated by viruses of diverse families to favor their replication. Among the MAPK family, the extracellular signal-regulated kinase (ERK) pathway is known to be modulated during the infection with porcine epidemic diarrhea virus (PEDV); however, involvement of stress-activated protein kinases (SAPKs) comprising p38 MAPK and c-Jun NH<SUB>2</SUB>-terminal kinase (JNK) remains to be determined. Therefore, in the present study, we investigated whether activation of p38 MAPK and JNK cascades is required for PEDV replication. Our results showed that PEDV activates p38 MAPK and JNK1/2 up to 24h post-infection, whereas, thereafter their phosphorylation levels recede to baseline levels or even fall below them. Notably, UV-irradiated inactivated PEDV, which can enter cells but cannot replicate inside them, failed to induce phosphorylation of p38 MAPK and JNK1/2 suggesting that viral biosynthesis is essential for activation of these kinases. Treatment of cells with selective p38 or JNK inhibitors markedly impaired PEDV replication in a dose-dependent manner and these antiviral effects were found to be maximal during the early times of the infection. Furthermore, direct pharmacological inhibition of p38 MAPK or JNK1/2 activation resulted in a significant reduction of viral RNA synthesis, viral protein expression, and progeny release. However, independent treatments with either SAPK inhibitor did not inhibit PEDV-induced apoptotic cell death mediated by activation of mitochondrial apoptosis-inducing factor (AIF) suggesting that SAPKs are irrelevant to the apoptosis pathway during PEDV infection. In summary, our data demonstrated critical roles of the p38 and JNK1/2 signaling pathways in facilitating successful viral infection during the post-entry steps of the PEDV life cycle.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PEDV infection activated p38 MAPK and JNK1/2 <I>in vitro</I>. </LI> <LI> UV-inactivated virus failed to induce p38 MAPK and JNK1/2 activation. </LI> <LI> Pharmacological inhibition of p38 MAPK or JNK activation impaired PEDV replication. </LI> <LI> SAPK cascades do not affect the apoptosis pathway during PEDV infection. </LI> <LI> PEDV exploits the p38 MAPK and JNK signaling pathways for optimal replication. </LI> </UL> </P>
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Lee, Hyunho,Tyagi, Priyanka,Rhee, Seunghyun,Park, Myeongjin,Song, Jiyun,Kim, Jaehoon,Lee, Changhee IEEE 2017 IEEE journal of photovoltaics Vol.7 No.6
<P>We present the analysis of photovoltaic properties in perovskite solar cells to explore the impact of excitonic features, disorder, recombination, and space charge effects using temperature and photo-intensity dependence. Photo-intensity dependence reveals an enhancement of classical Einstein relation due to the presence of traps and formation of space charge effects resulting in reduced conductivity. Exciton versus free charge density upon photo-excitation is analyzed from temperature dependence of photocurrent. Temperature dependence of V-OC is excellently explained by considering a combined energetic disorder in a solar cell, and a moderately high value of variance similar to 125 meV is obtained.</P>
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Lee, Changhee,Rathi, Servin,Khan, Muhammad Atif,Lim, Dongsuk,Kim, Yunseob,Yun, Sun Jin,Youn, Doo-Hyeb,Watanabe, Kenji,Taniguchi, Takashi,Kim, Gil-Ho IOP 2018 Nanotechnology Vol.29 No.33
<P>Molybdenum disulfide (MoS<SUB>2</SUB>) based field effect transistors (FETs) are of considerable interest in electronic and opto-electronic applications but often have large hysteresis and threshold voltage instabilities. In this study, by using advanced transfer techniques, hexagonal boron nitride (hBN) encapsulated FETs based on a single, homogeneous and atomic-thin MoS<SUB>2</SUB> flake are fabricated on hBN and SiO<SUB>2</SUB> substrates. This allows for a better and a precise comparison between the charge traps at the semiconductor-dielectric interfaces at MoS<SUB>2</SUB>−SiO<SUB>2</SUB> and hBN interfaces. The impact of ambient environment and entities on hysteresis is minimized by encapsulating the active MoS<SUB>2</SUB> layer with a single hBN on both the devices. The device to device variations induced by different MoS<SUB>2</SUB> layer is also eliminated by employing a single MoS<SUB>2</SUB> layer for fabricating both devices. After eliminating these additional factors which induce variation in the device characteristics, it is found from the measurements that the trapped charge density is reduced to 1.9?×?10<SUP>11</SUP> cm<SUP>−2</SUP> on hBN substrate as compared to 1.1?×?10<SUP>12</SUP> cm<SUP>−2</SUP> on SiO<SUB>2</SUB> substrate. Further, reduced hysteresis and stable threshold voltage are observed on hBN substrate and their dependence on gate sweep rate, sweep range, and gate stress is also studied. This precise comparison between encapsulated devices on SiO<SUB>2</SUB> and hBN substrates further demonstrate the requirement of hBN substrate and encapsulation for improved and stable performance of MoS<SUB>2</SUB> FETs.</P>
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Lee, Changhee,Jeong, Soon-Ki Elsevier 2018 ELECTROCHIMICA ACTA Vol.265 No.-
<P><B>Abstract</B></P> <P>We report on the effects of the changed hydration number of calcium ions due to the variation in the electrolyte concentration in a Prussian blue analogue electrode, CuHCF, and aqueous electrolyte system on its performance, for calcium-ion batteries (CIBs). As determined by Raman spectroscopy, the coordination number of the calcium ions, that is, the number of nitrate anions surrounding it in the aqueous electrolyte gradually increased upon increasing the electrolyte concentration from 1.0 to 8.4 mol dm<SUP>−3</SUP>. In other words, the hydration number of calcium ions gradually decreased. Additionally, the activation energy, <I>E</I> <SUB> <I>a</I> </SUB>, for the interfacial charge transfer during the process of calcium ion insertion into the CuHCF electrode was estimated from the temperature dependence of the charge transfer resistance in these aqueous electrolytes <I>via</I> electrochemical impedance spectroscopy. The <I>E</I> <SUB> <I>a</I> </SUB> value gradually decreased with increasing electrolyte concentration. These results are directly related to the electrochemical performance such as the discharge/charge capacities, rate capability, and cyclability in this system for CIBs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Prussian blue electrode/aqueous electrolyte system for calcium-ion battery is studied. </LI> <LI> Ca(NO<SUB>3</SUB>)<SUB>2</SUB> dissolved in water at various concentrations is used as the electrolyte. </LI> <LI> The radius of the hydrated Ca ion decreased with increasing Ca(NO<SUB>3</SUB>)<SUB>2</SUB> concentration. </LI> <LI> Superior electrochemical performance is achieved at high electrolyte concentration. </LI> </UL> </P>
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