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排序方式: 共有1243条查询结果,搜索用时 15 毫秒
31.
Antioxidant activities of aqueous extracts of selected plants 总被引:1,自引:0,他引:1
The antioxidant properties of 25 edible tropical plants, expressed as Trolox equivalent antioxidant capacity (TEAC), were studied using DPPH (1,1-diphenyl-2-picrylhydrazyl free radical) scavenging and reducing ferric ion antioxidant potential (FRAP) assays. Their cupric ion chelating activities (CCA) and total polyphenol contents (TPC) were also determined. A strong correlation between TEAC values obtained for the DPPH assay (TEACDPPH) and those for the FRAP assay (TEACFRAP) implied that compounds in the extracts were capable of scavenging the DPPH free radical and reducing ferric ions. A satisfactory correlation of TPC with TEACDPPH and TEACFRAP suggested that polyphenols in the extracts were partly responsible for the antioxidant activities while its correlation with CCA was poor, indicating that polyphenols might not be the main cupric ion chelators. Principal component analysis (PCA) indicated that TEACDPPH, TEACFRAP and TPC contributed to the total variation in the antioxidant activities of the plants. 相似文献
32.
Low loss ferroelectric materials have been extensively investigated for the high frequency device applications. Especially, weak frequency dispersion materials with high dielectric permittivity and low loss tangent have enormous potential for electronic components including filters, and embedded capacitors. Ag(Ta0.5Nb0.5)O3 thick films have been prepared by low temperature sintering aid Li2CO3 (0, 1, 3 and 5 wt%). Ag(Ta0.5Nb0.5)O3 thick films were characterized by X-ray diffraction analysis and scanning electron microscopy. The dielectric and ferroelectric properties were also investigated. We observed very weak frequency dispersion of dielectric permittivity at the microwave frequency range. 相似文献
33.
ZnBO-doped (Ba, Sr)TiO3 ceramics were investigated for low-temperature co-fired ceramics (LTCCs) applications. Until now, B2O3 and Li2CO3 dopants have been commonly employed as the low-temperature sintering aids. In this paper, we suggest ZnBO as an alternative dopant to the B2O3 and Li2CO3. To reduce the sintering temperature of (Ba, Sr)TiO3, we have added 1–5 wt.% of ZnBO to (Ba, Sr)TiO3. ZnBO-doped (Ba, Sr)TiO3 ceramics were respectively sintered from 750 to 1350 °C by 50 °C to confirm the sintering temperature with different dopant contents. By adding 5 wt.% of ZnBO to the (Ba, Sr)TiO3 ceramics, the sintering temperature of (Ba, Sr)TiO3 ceramics can be reduced to 1100 °C. From the XRD analysis, ZnBO-doped (Ba, Sr)TiO3 has no pyro phase. By adding ZnBO dopants to (Ba, Sr)TiO3 ceramics, both of relative dielectric permittivity and loss tangent were decreased. From the frequency dispersion of dielectric properties, the relative dielectric permittivity and loss tangent of 5 wt.% ZnBO-doped (Ba, Sr)TiO3 were 1180 and 3.3 × 10−3, while those of BST were 1585 and 4.8 × 10−3, respectively. 相似文献
34.
A series of novel hexene‐1–propylene random copolymers with isotactic sequence of propylene was synthesized with a MgCl2‐supported Cr(acac)3 catalyst. The molecular weight distribution of copolymers and homopolymers was considerably narrower than that of typical polyolefins produced by heterogeneous Ziegler–Natta catalysts. The crystallizability of the copolymers having a propylene‐unit content of more than 50 mol % drastically decreased with decreasing propylene‐unit content, and the copolymers with a propylene content of less than 50 mol % were completely amorphous. In the present novel type of random copolymers with crystallizable and noncrystallizable units, a single glass transition was observed between pure polypropylene and polyhexene‐1, and a major component was found to govern the final morphology and the mechanical characteristics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2949–2954, 2004 相似文献
35.
Do-Hyoung Kim Da-Hee Kwak Sang-Beom Han Hyun-Suk Park Jin-Young Park Ji-Eun Won Kyeng-Bae Ma Seok-Hyeon Yun Suk-Hui Kwon Moon Hyun Koh Kyung-Won Park 《International Journal of Hydrogen Energy》2018,43(3):1479-1488
Doped carbon nanostructures as non-precious metal (NPM) catalysts for oxygen reduction reaction (ORR) in acid medium are mainly synthesized using 5, 10, 15, 20-tetrakis (4-methoxyphenyl)-porphyrin-Fe (III) chloride (Fe-TMPP) as doping and carbon sources. In this study, the doped carbon nanostructures used as cathode NPM catalysts for ORR are prepared using a mixture of iron phthalocyanine (FePc) and arginine as doping and carbon sources. The morphology and composition of the as-prepared samples are characterized using field-emission scanning electron microscopy, field-emission transmission electron microscopy, and energy dispersive X-ray (EDX) spectroscopy. The crystal and pore structures are analyzed using X-ray diffraction method, Raman spectroscopy, and nitrogen adsorption/desorption method. The sample prepared using a precursor mixture with a proper ratio of FePc and arginine exhibits significantly superior ORR performance, i.e. high specific activity, enhanced half-wave potential, and improved stability in an acid medium, as even compared to a commercial Pt/C. The improved ORR properties is mainly attributed to high portion of pyridinic N state with a relatively high specific surface area, which can result from the FePc precursor surrounded by the fused arginine. 相似文献
36.
Sangho Koh Seika Imamura Naoto Fujino Masahiro Mizuno Nobuaki Sato Satoshi Makishima Peter Biely Yoshihiko Amano 《Journal of Applied Glycoscience》2019,66(4):131
The carbohydrate esterase family 1 (CE1) in CAZy contains acetylxylan esterases (AXEs) and feruloyl esterases (FAEs). Here we cloned a gene coding for an AXE belonging to CE1 from Irpex lacteus (IlAXE1). IlAXE1 was heterologously expressed in Pichia pastoris, and the recombinant enzyme was purified and characterized. IlAXE1 hydrolyzed p-nitrophenyl acetate, α-naphthyl acetate and 4-methylumbelliferyl acetate, however, it did not show any activity on ethyl ferulate and methyl p-coumarate. We also examined the activity on partially acetylated and feruloylated xylan extracted from corncob by hydrothermal reaction. Similarly, ferulic and p-coumaric acids were not liberated, and acetic acid was only detected in the reaction mixture. The results indicated that IlAXE1 is an acetylxylan esterase actually reacted to acetyl xylan. However, since IlAXE1 was unable to completely release acetic acid esterifying xylopyranosyl residues, it is assumed that acetyl groups exhibiting resistance to deacetylation by IlAXE1 are present in corn cob xylan. 相似文献
37.
38.
Jayven Chee Chuan Yeo Joseph Kinyanjui Muiruri Justin Junqiang Koh Warintorn Thitsartarn Xikui Zhang Junhua Kong Ting Ting Lin Zibiao Li Chaobin He 《Advanced functional materials》2020,30(30)
The future of green electronics possessing great strength and toughness proves to be a promising area of research in this technologically advanced society. This work develops the first fully bendable and malleable toughened polylactic acid (PLA) green composite by incorporating a multifunctional polyhydroxybutyrate rubber copolymer filler that acts as an effective nucleating agent to accelerate PLA crystallization and performs as a dynamic plasticizer to generate massive polymer chain movement. The resultant biocomposite exhibits a 24‐fold and 15‐fold increment in both elongation and toughness, respectively, while retaining its elastic modulus at >3 GPa. Mechanism studies show the toughening effect is due to an amalgamation of massive shear yielding, crazing, and nanocavitation in the highly dense PLA matrix. Uniquely distinguished from the typical flexible polymer that stretches and recovers, this biocomposite is the first report of PLA that can be “bend, twist, turn, and fold” at room temperature and exhibit excellent mechanical robustness even after a 180° bend, attributes to the highly interconnected polymer network of innumerable nanocavitation complemented with an extensively unified fibrillar bridge. This unique trait certainly opens up a new horizon to future sustainable green electronics development. 相似文献
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