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Al-6%Cu-0.4%Zr(Supral 100)합금의 온도와 변형 속도에 따른 초소성 특성 연구
최원호,박율민,김현철,신평우 國立 昌原大學校 産業技術硏究所 2000 産技硏論文集 Vol.14 No.-
Superplastic materials have a characteristics to undergo large uniform strain prior to failure. Superplasticity usually indicates that elongation to failure in the uni-axial tension is above 200%. There are several superplastic materials to be elongated up to 1000%. The microstructures were evaluated with temperature changes just before superplastic deformation in static recrystallization experiments, and it was found that amount of recrystallization was small below 425℃ and grain coarsening occured above 475℃ as ZrAl₃precipitation lost in inhibiting ability grain coarsening. Therefore optimum superplastic forming temperature proved 450℃. Optimum strain rate sensibility at superplastic tensile test was ?? reasonable.
Laser-Induced Solid-Phase Doped Graphene
Choi, Insung,Jeong, Hu Young,Jung, Dae Yool,Byun, Myunghwan,Choi, Choon-Gi,Hong, Byung Hee,Choi, Sung-Yool,Lee, Keon Jae American Chemical Society 2014 ACS NANO Vol.8 No.8
<P>There have been numerous efforts to improve the performance of graphene-based electronic devices by chemical doping. Most studies have focused on gas-phase doping with chemical vapor deposition. However, that requires a complicated transfer process that causes undesired doping and defects by residual polymers. Here, we report a solid-phase synthesis of doped graphene by means of silicon carbide (SiC) substrate including a dopant source driven by pulsed laser irradiation. This method provides <I>in situ</I> direct growth of doped graphene on an insulating SiC substrate without a transfer step. A numerical simulation on the temperature history of the SiC surface during laser irradiation reveals that the surface temperature of SiC can be accurately controlled to grow nitrogen-doped graphene from the thermal decomposition of nitrogen-doped SiC. Laser-induced solid-phase doped graphene is highly promising for the realization of graphene-based nanoelectronics with desired functionalities.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-8/nn5032214/production/images/medium/nn-2014-032214_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5032214'>ACS Electronic Supporting Info</A></P>
The Heterogeneous Effects of Shadow Education on SAT Scores
Yool Choi 서울대학교 사회발전연구소 2018 Journal of Asian Sociology Vol.47 No.3
As many prior studies have pointed out, private shadow education, which includes commercial coaching and one-on-one tutoring, has important implications for educational opportunity and the process of social stratification. In this study, I analyze the heterogeneous effects of private shadow education on SAT scores by individual likelihood of participation using the Educational Longitudinal Study 2002. The key finding of this study is that the effects of shadow education are substantively different across propensity strata and that its effects increase as the propensity to participate in shadow education increases. That is, those who are more likely to use shadow education, who are socioeconomically advantaged and possess higher educational capital, benefit more from shadow education than those who are less likely to use it. Moreover, use of public resources neither alleviates the effects of shadow education nor changes the pattern of the heterogeneous effects of shadow education based on likelihood of use.
Flexible NO2 gas sensor using multilayer graphene films by chemical vapor deposition
HongKyw Choi,Hu Young Jeong,Dae-Sik Lee,Choon-Gi Choi,Sung-Yool Choi 한국탄소학회 2013 Carbon Letters Vol.14 No.3
We report a highly sensitive NO2 gas sensor based on multi-layer graphene (MLG) films synthesized by a chemical vapor deposition method on a microheater-embedded flexible substrate. The MLG could detect low-concentration NO2 even at sub-ppm (<200 ppb) levels. It also exhibited a high resistance change of ~6% when it was exposed to 1 ppm NO2 gas at room temperature for 1 min. The exceptionally high sensitivity could be attributed to the large number of NO2 molecule adsorption sites on the MLG due to its a large surface area and various defect-sites, and to the high mobility of carriers transferred between the MLG films and the adsorbed gas molecules. Although desorption of the NO2 molecules was slow, it could be enhanced by an additional annealing process using an embedded Au microheater. The outstanding mechanical flexibility of the graphene film ensures the stable sensing response of the device under extreme bending stress. Our large-scale and easily reproducible MLG films can provide a proof-of-concept for future flexible NO2 gas sensor devices.