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41.
Kyeong‐Yong Park Jinyong Lee Seong Jun Park Jung‐Nyoung Heo Hwan Jung Lim 《Advanced Synthesis \u0026amp; Catalysis》2015,357(18):3917-3926
A series of 1,2‐ and 1,4‐dihydroquinolines has been successfully prepared. The Pd‐catalyzed intramolecular N‐arylation of Z‐enamines, formally prepared by the Horner–Wadsworth–Emmons olefination, proceeded efficiently to furnish the cyclized products. Depending on the cyclization conditions, substituted 1,4‐dihydroquinolines and further isomerized 1,2‐dihydroquinolines were independently obtained in high yields with an excellent control of isomerization of the double bond.
42.
Role of Nd3+ ions on the nucleation and growth of PbS quantum dots (QDs) in silicate glasses 下载免费PDF全文
Won Ji Park Min Gyu Kim Ju Eun Kim Jing Wang Ho Jeong Lee Chan Gyung Park Jong Heo 《Journal of the American Ceramic Society》2017,100(7):2879-2884
The influence of Nd2O3 addition on the precipitation kinetics of lead chalcogenide (PbS) quantum dots (QDs) in silicate glasses was investigated. Energy dispersive X‐ray spectroscopy (EDS) indicated that the Nd3+ ions are preferentially located inside the PbS QDs rather than in the glass matrix. Changes in diameter (D) of PbS QDs exhibited smaller time dependencies (i.e., D≈t0.270‐0.286) than that predicted by the classical Lifshitz–Slyozov–Wagner (LSW) theory. This is due to the limited concentrations of Pb2+ and S2? ions and the large diffusion distance inside the glass matrix. In addition, extended X‐ray absorption fine structure (EXAFS) results indicated that the formation of PbS QDs was retarded due to the presence of Nd2O3 in the glasses, as the large NdOx polyhedra interrupt the diffusion of Pb2+ and S2? ions. We believe that these Nd3+ ions are primarily located in PbS QDs in the form of Nd–O clusters, and that the PbS QDs are built on top of these clusters. 相似文献
43.
ABSTRACT: The photoelectrochemical (PEC) responses of electron-irradiated 66-phenyl-C61-butyric acid methyl ester (PCBM)/TiO2 electrodes were evaluated in a PEC cell. By coating PCBM on TiO2 nanoparticle film, the light absorption of PCBM/TiO2 electrode has expanded to the visible light region and improved the PEC responses compared to bare TiO2 electrode. The PEC responses were further improved by irradiating an electron beam on PCBM/TiO2 electrodes. Compared to non-irradiated PCBM/TiO2 electrodes, electron irradiation increased the photocurrent density and the open-circuit potential of PEC cells by approximately 90% and approximately 36%, respectively at an optimum electron irradiation condition. The PEC responses are carefully evaluated correlating with the optical and electronic properties of electron-irradiated PCBM/TiO2 electrodes. 相似文献
44.
ABSTRACT: A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy * cm2 min1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution. 相似文献
45.
The effects of the stress intensity factor and dissolved hydrogen on the crack growth rate in primary water reactor environments was investigated with alloy 600 with continuous carbide films at grain boundaries. A primary water stress corrosion cracking of intergranular fracture mode was observed. The intergranular crack growth rate decreased with a decreasing stress intensity factor, and the dissolved hydrogen content influenced the crack growth rate. Such results are consistent with those reported previously. 相似文献
46.
Joon-Young Heo Jin-Han Gwon Jong-Kwan Park Kee-Ahn Lee 《Metals and Materials International》2018,24(3):586-596
Hypereutectic Al–Si alloy is an aluminum alloy containing at least 12.6 wt.% Si. It is necessary to evenly control the primary Si particle size and distribution in hypereutectic Al–Si alloy. In order to achieve this, there have been attempts to manufacture hypereutectic Al–Si alloy through a liquid phase sintering. This study investigated the microstructures and high temperature mechanical properties of hypereutectic Al–14Si–Cu–Mg alloy manufactured by liquid phase sintering process and changes in them after T6 heat treatment. Microstructural observation identified large amounts of small primary Si particles evenly distributed in the matrix, and small amounts of various precipitation phases were found in grain interiors and grain boundaries. After T6 heat treatment, the primary Si particle size and shape did not change significantly, but the size and distribution of CuAl2 (θ) and AlCuMgSi (Q) changed. Hardness tests measured 97.36 HV after sintering and 142.5 HV after heat treatment. Compression tests were performed from room temperature to 300 °C. The results represented that yield strength was greater after heat treatment (RT?~?300 °C: 351?~?93 MPa) than after sintering (RT?~?300 °C: 210?~?89 MPa). Fracture surface analysis identified cracks developing mostly along the interface between the primary Si particles and the matrix with some differences among temperature conditions. In addition, brittle fracture mode was found after T6 heat treatment. 相似文献
47.
Joon-Young Heo Min-Seok Baek Kwang-Jun Euh Kee-Ahn Lee 《Metals and Materials International》2018,24(5):992-1001
This study investigated the microstructure, tensile and fatigue properties of Al–5 wt.%Mg alloy manufactured by twin roll strip casting. Strips cast as a fabricated (F) specimen and a specimen heat treated (O) at 400 °C/5 h were produced and compared. In the F specimen, microstructural observation discovered clustered precipitates in the center area, while in the O specimen precipitates were relatively more evenly distributed. Al, Al6(Mn, Fe), Mg2Al3 and Mg2Si phases were observed. However, most of the Mg2Al3 phase in the heat-treated O specimen was dissolved. A room temperature tensile test measured yield strength of 177.7 MPa, ultimate tensile strength of 286.1 MPa and elongation of 11.1% in the F specimen and 167.7 MPa (YS), 301.5 MPa (UTS) and 24.6% (EL) in the O specimen. A high cycle fatigue test measured a fatigue limit of 145 MPa in the F specimen and 165 MPa in the O specimen, and the O specimen achieved greater fatigue properties in all fatigue stress conditions. The tensile and fatigue fracture surfaces of the above-mentioned specimens were observed, and this study attempted to investigate the tensile and fatigue deformation behavior of strip cast Al–5 wt.%Mg based on the findings. 相似文献
48.
Shuhei Yamada Seijung Park Suhee Song Mihee Heo Youngeup Jin Heesoo Lee Kohji Yoshinaga Hongsuk Suh 《Polymer》2010,51(26):6174-6181
We report the synthesis and characterization of new series of the fluorene based polymers with carbazole and oxadiazole pendants for the generation of the white emission out of the EL device. In the fluorene backbone, hole transporting units such as carbazole or phenothiazine were incorporated to improve the EL brightness and efficiency. The PFCzOxd-co-PCzs and PFCzOxd-co-PPTZs in EL spectra showed maximum peaks at around 430 nm and additional large peaks at around 530 and 500 nm, respectively. In case of PFCzOxd-alt-PCz and PFCzCzPCz-co-PFOxdOxdPCz, the EL spectra of the polymers showed two distinct peaks comprising the maximum at 427 nm, which corresponds to the EL spectra of the conjugated backbone, and additional broad peaks at around 540 and 530 nm, respectively. The CIE coordinates of the devices from PFCzOxd-alt-PCz and PFCzCzPCz-co-PFOxdOxdPCz were (0.28, 0.33) and (0.25, 0.32), respectively, approaching the value of the standard white of National Television System Committee (NTSC) (0.33, 0.33). 相似文献
49.
50.
Mixed-effects linear regression models have become more widely used for analysis of repeatedly measured outcomes in clinical trials over the past decade. There are formulae and tables for estimating sample sizes required to detect the main effects of treatment and the treatment by time interactions for those models. A formula is proposed to estimate the sample size required to detect an interaction between two binary variables in a factorial design with repeated measures of a continuous outcome. The formula is based, in part, on the fact that the variance of an interaction is fourfold that of the main effect. A simulation study examines the statistical power associated with the resulting sample sizes in a mixed-effects linear regression model with a random intercept. The simulation varies the magnitude (Δ) of the standardized main effects and interactions, the intraclass correlation coefficient (ρ), and the number (k) of repeated measures within-subject. The results of the simulation study verify that the sample size required to detect a 2×2 interaction in a mixed-effects linear regression model is fourfold that to detect a main effect of the same magnitude. 相似文献