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排序方式: 共有131条查询结果,搜索用时 15 毫秒
111.
Kim K. N. Lim J. H. Lim W. S. Yeom G. Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2010,38(2):133-136
112.
Yeom HS Koo J Park HS Wang Y Liang Y Yu ZX Shin S 《Journal of the American Chemical Society》2012,134(1):208-211
A gold-catalyzed intermolecular reaction of propiolic acids with alkenes led to a [4 + 2] annulation or enyne cross metathesis. The [4 + 2] annulation proceeds with net cis-addition with respect to alkenes and provides an expedient route to α,β-unsaturated δ-lactones, for which preliminary asymmetric reactions were also demonstrated. For 1,2-disubstituted alkenes, unprecedented enyne cross metathesis occurred to give 1,3-dienes in a completely stereospecific fashion. DFT calculations and experiments indicated that the cyclobutene derivatives are not viable intermediates and that the steric interactions during concerted σ-bond rearrangements are responsible for the observed unique stereospecificity. 相似文献
113.
114.
115.
Inside Cover: Coordination Assembly of Discoid Nanoparticles (Angew. Chem. Int. Ed. 31/2015) 下载免费PDF全文
116.
Ali Kilic Eunkyoung Shim Bong Yeol Yeom Behnam Pourdeyhimi 《Journal of Electrostatics》2013,71(1):41-47
Barium titanate (BaTiO3) containing polypropylene (PP) composite filaments were melt spun to modify polymer electrostatic charging characteristics. Sample filaments were charged with a corona instrument and their surface potentials were measured. Initial surface potential as well as potential stability was monitored through an accelerated decay procedure. It was found that both BaTiO3 concentration and charging temperature influence the charging characteristics of the fibers. When BaTiO3/PP composite filaments were charged at 130 °C, significant enhancements were observed when compared to samples charged at room temperature. The distribution of BaTiO3 particles within the filaments and changes in the crystal structure were also examined. 相似文献
117.
Chang-Eun Yeom 《Tetrahedron》2007,63(4):904-909
A convenient and versatile method was developed for aza-Michael addition using a substoichiometric amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Various nitrogen nucleophiles were efficiently introduced to α,β-unsaturated carbonyl compounds employing 0.5 equiv of DBU. Furthermore, other heteroatomic nucleophiles could also be introduced successfully under the same reaction conditions. 相似文献
118.
Suk Keu Yeom Jae Ho Byun Hye Jin Kim Seong Ho ParkNamkug Kim Yong Moon ShinPyo Nyun Kim 《Magnetic resonance imaging》2013
Objective
To evaluate the image findings of focal fat deposition (FFD) in the liver on gadobenate dimeglumine (Gd-BOPTA)- and gadoxetic acid (Gd-EOB-DTPA)-enhanced MRI, particularly during the hepatobiliary phase (HBP), and the relationship between relative enhancement (RE) and fat signal fraction (FSF) of FFD.Subjects and Methods
Twenty-one patients with 27 FFDs (mean diameter, 21.9 mm), which showed low signal intensity on opposed-phase compared with in-phase MRI, were retrospectively evaluated. RE of the liver (REliver) and FFD (REFFD) and liver-to-lesion contrast-to-noise ratio (CNR) of FFD were measured on dynamic phases and HBP images with fat-saturated in-phase gradient-echo sequence. The FSF of each FFD was measured on in- and opposed-phase dual gradient-echo images. We qualitatively analyzed imaging findings of FFDs, including signal intensity, shape, margin, and homogeneity on HBP images, and enhancement pattern during dynamic phases. The correlations between REFFD and FSF and between CNR and FSF on HBP images were evaluated using Pearson’s correlation tests and a simple linear regression model.Results
There were no significant differences between REFFD and REliver in dynamic phases and HBP, regardless of contrast agents (p ≥ 0.075). On HBP images, CNR (p = 0.008) but not REFFD (p = 0.122) was significantly correlated with FSF of FFDs (mean FSF, 19%). On HBP images, 21 of the 27 (77.8%) FFDs were hypointense, and 17 (63%) were homogeneous. Of the 21 hypointense FFDs, 12 (57.1%) had an ovoid shape and 11 (52.4%) were well margined. Although the 27 FFDs showed various enhancement patterns, 17 (63%) showed no enhancement.Conclusion
Most FFDs appeared as hypointense lesions on Gd-BOPTA- and Gd-EOB-DTPA-enhanced MRI during HBP, with various enhancement patterns during dynamic contrast-enhanced phases. REFFD on HBP images was not significantly correlated with FSF of low grade FFDs. 相似文献119.
Libin Fu Vahid G. Ta’eed Eric C. Mägi Ian C. M. Littler Mark D. Pelusi Michael R. E. Lamont Alexander Fuerbach Hong C. Nguyen Dong-Il Yeom Benjamin J. Eggleton 《Optical and Quantum Electronics》2007,39(12-13):1115-1131
Chalcogenide glasses offer many attractive properties for all-optical signal processing including large Kerr nonlinearity (up to 500 × silica glass), an intrinsic ultrafast response time and low to moderate two-photon absorption (TPA). These properties together with the convenience of a fibre format allow us to achieve all-optical signal processing at low peak power and in a very compact form. In this paper, several nonlinear processing functions will be demonstrated including: femto-second pedestal free, pulse compression; all-optic wavelength conversion; and all-optical regenerator. In addition, we show enhanced nonlinearity for more efficient signal processing by tapering the As2Se3 fibre. These applications show chalcogenide glass fibres are very promising candidate materials for nonlinear all-optic signal processing. 相似文献
120.
A controversial issue of the driving force for the phase transition of the one-dimensional (1D) metallic In wires on Si(111) is studied by low-temperature scanning tunneling microscopy and spectroscopy. The energy gap opening and the longitudinal charge ordering through charge transfer at the Fermi level are unambiguously observed. The vacancy defects induce a local charge ordering decoupled from a lattice distortion above T(c), and pin the phase of charge order below T(c). All these results below and above T(c) including the detailed features such as local fluctuations strongly support the 1D charge-density-wave mechanism for the phase transition. 相似文献