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排序方式: 共有1467条查询结果,搜索用时 15 毫秒
21.
De-Long Zhang Ping-Rang Hua Edwin Yue-Bun Pun Guei-Gu Siu 《Journal of the American Ceramic Society》2007,90(9):2893-2899
Vapor transport equilibration (VTE) treatments were performed on a Y-cut bulk Er (1.6 mol%)-doped congruent LiNbO3 crystal and an X-cut pure congruent crystal, on one surface of which a 40 nm-thick film of erbium metal was coated before the VTE treatment. Scanning electron microscope, powder or single-crystal X-ray diffraction (XRD), polarized infrared absorption/emission of Er3+ as well as micro-Raman spectroscopy were used to study the two VTE crystals. The results are discussed in comparison with a corresponding as-grown bulk Er-doped crystal, calcined ErNbO4 powder, and a locally Er-doped congruent LiNbO3 crystal prepared by using the standard Er-diffusion technique. The experimental results show that the VTE treatment induces the formation of micrometer-sized ErNbO4 precipitates with the crystallographic morphology of a flat polyhedron not only on the surfaces of both crystals but also in the bulk of the homogeneously Er-doped one. The optical absorption and emission studies show that the formation of the precipitates results in substantial spectral changes in both the 0.98 and 1.5 μm regions. The micro-Raman studies allow to resolve four additional Raman peaks around 800 cm−1 in the E(TO) spectra of the two VTE crystals. These additional Raman peaks are associated with the characteristic vibrations with respect to the NbO4 3− group. Characteristic XRD, optical absorption, and emission and Raman peaks for identifying the ErNbO4 phase are proposed. Finally, the formation mechanism and light-scattering effect of the precipitates are discussed. 相似文献
22.
Effect of natural antioxidants in virgin olive oil on oxidative stability of refined,bleached, and deodorized olive oil 总被引:1,自引:0,他引:1
M. Teresa Satue Shu-Wen Huang Edwin N. Frankel 《Journal of the American Oil Chemists' Society》1995,72(10):1131-1137
The factors influencing the oxidative stability of different commercial olive oils were evaluated. Comparisons were made of
(i) the oxidative stability of commercial olive oils with that of a refined, bleached, and deodorized (RBD) olive oil, and
(ii) the antioxidant activity of a mixture of phenolic compounds extracted from virgin olive oil with that of pure compounds
andα-tocopherol added to RBD olive oil. The progress of oxidation at 60°C was followed by measuring both the formation (peroxide
value, PV) and the decomposition (hexanal and volatiles) of hydroperoxides. The trends in antioxidant activity were different
according to whether PV or hexanal were measured. Although the virgin olive oils contained higher levels of phenolic compounds
than did the refined and RBD oils, their oxidative stability was significantly decreased by their high initial PV. Phenolic
compounds extracted from virgin olive oils increased the oxidative stability of RBD olive oil. On the basis of PV, the phenol
extract had the best antioxidant activity at 50 ppm, as gallic acid equivalents, but on the basis of hexanal formation, better
antioxidant activity was observed at 100 and 200 ppm.α-Tocopherol behaved as a prooxidant at high concentrations (>250 ppm) on the basis of PV, but was more effective than the
other antioxidants in inhibiting hexanal formation in RBD olive oil.o-Diphenols (caffeic acid) and, to a lesser extent, substitutedo-diphenols (ferulic and vanillic acids), showed better antioxidant activity than monophenols (p- ando-coumaric), based on both PV and hexanal formation. This study emphasizes the need to measure at least two oxidation parameters
to better evaluate antioxidants and the oxidative stability of olive oils. The antioxidant effectiveness of phenolic compounds
in virgin olive oils can be significantly diminished in oils if their initial PV are too high. 相似文献
23.
Cholesterol 5α,6α-epoxide (α-epoxide) and cholesterol 5β,6β-epoxide (β-epoxide) were individually suspended in simulated gastric
juice (pH 1.2) at 37 C, and their reaction was followed by gradient high performance liquid chromatography (HPLC) with flame
ionization (FID) detection. Both epoxides reacted rapidly in the aqueous acid medium. The α-epoxide formed 6β-chlorocholestane-3β,5α-diol
(α-chlorohydrin) and 5α-cholestane-3β,5,6β-triol (triol), while the β-epoxide formed 5α-chlorocholestane-3β,6β-diol (β-chlorohydrin)
and triol. The isomeric chlorohydrins reacted further to form the triol. In mildly alkaline aqueous medium, each chlorohydrin
reverted to the epoxide from which it was formed. The data suggest that both epoxides, which have been reported to have adverse
health effects in animals, would be largely hydrolyzed in the stomach and to the triol, which also has been reported to have
biological activity. The data furher suggest that residual chlorohydrins surviving stomach residence can be expected to revert
to epoxide in the more alkaline intestinal environment. 相似文献
24.
25.
W.Wade Adams Robert M. Briber Edward S. Sherman Roger S. Porter Edwin L. Thomas 《Polymer》1985,26(1):17-26
The microstructure of a series of solid state extruded polyethylene fibres was examined by wide- and small-angle X-ray scattering. By measuring absolute intensities using a two dimensional position sensitive detector, accurate values of the small-angle invariant for anisotropic samples were obtained. This measurement coupled with wide-angle X-ray scattering and d.s.c. permitted determination of the density of the noncrystalline component. The use of a two phase model for solid state extruded polyethylene is justified if consideration is given to the effective densities of the crystalline and noncrystalline phases, which change with deformation. The effective density of the crystalline phase decreases by 1% (0.999–0.990 g cm?3) from the unextruded billet compared to a 36 draw ratio extrudate, while the noncrystalline phase density increases by 6% (0.84–0.89 g cm?3). These changes lead to an overall decrease in the mean squared electron density fluctuation of 63%. The average axial crystallite length measured by wide-angle X-ray scattering increases with extrusion draw ratio while the SAXS long period decreases and weakens considerably. These observations and the electron microscopy results from the previous paper, (Polymer, 1982, 23, 1069), are fully consistent with the key features of the Peterlin model of fibre microstructure. 相似文献
26.
Front cover: MALDI mass spectrometry imaging: A cutting‐edge tool for fundamental and clinical histopathology 下载免费PDF全文
27.
28.
Reactive power compensation is an important issue in the control of electric power system. Reactive power from the source increases the transmission losses and reduces the power transmission capability of the transmission lines. Moreover, reactive power should not be transmitted through the transmission line to a longer distance. Hence Flexible AC Transmission Systems (FACTS) devices such as static compensator (STATCOM) unified power flow controller (UPFC) and static volt–ampere compensator (SVC) are used to alleviate these problems. In this paper, a voltage source converter (VSC) based STATCOM is developed with PI and Artificial Neural Network Controller (ANNC). The conventional PI controller has more tuning difficulties while the system parameter changes, whereas a trained neural network requires less computation time. The ANNC has the ability to generalize and can interpolate in between the training data. The ANNC designed was tested on a 75 V, ±3KVAR STATCOM in real time environment via state-of-the-art of digital signal processor advanced control engineering (dSPACE) DS1104 board and it was found that it was producing better results than the PI controller. 相似文献
29.
The Electrochemical Response of Single Crystalline Copper Nanowires to Atmospheric Air and Aqueous Solution 下载免费PDF全文
Bowei Zhang Bensong Chen Junsheng Wu Shiji Hao Guang Yang Xun Cao Lin Jing Minmin Zhu Siu Hon Tsang Edwin Hang Tong Teo Yizhong Huang 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(10)
In this paper, single crystalline copper nanowires (CuNWs) have been electrochemically grown through anodic aluminum oxide template. The environmental stability of the as‐obtained CuNWs in both 40% relative humidity (RH) atmosphere and 0.1 m NaOH aqueous solution has been subsequently studied. In 40% RH atmosphere, a uniform compact Cu2O layer is formed as a function of exposure time following the logarithmic law and epitaxially covers the CuNW surfaces. It is also found that the oxide layers on CuNWs are sequentially grown when subjected to the cyclic voltammetry measurement in 0.1 m NaOH solution. An epitaxially homogeneous Cu2O layer is initially formed over the surface of the CuNW substrates by solid‐state reaction (SSR). Subsequently, the conversion of Cu2O into epitaxial CuO based on the SSR takes place with the increase of applied potential. This CuO layer is partially dissolved in the solution forming Cu(OH)2, which then redeposited on the CuNW surfaces (i.e., dissolution‐redeposition (DR) process) giving rise to a mixed polycrystalline CuO/Cu(OH)2 layer. The further increase of applied potential allows the complete oxidation of Cu2O into CuO to form a dual‐layer structure (i.e., CuO inner layer and Cu(OH)2 outer layer) with random orientations through an enhanced DR process. 相似文献
30.
Edwin Geo Varuvel Nadia Mrad Fethi Aloui Mohand Tazerout 《Clean Technologies and Environmental Policy》2017,19(4):1099-1108
In the present work, biofuel derived from industrial fish processing industry waste is used in diesel engines to study its suitability . Biofuel from industry fish waste is produced through catalytic cracking, and its quality has been improved through distillation. A single cylinder 4.5 kW at 1500 rpm was used to find the suitability of biofuel and undistilled biofuel in diesel engine. Experimental results show that the brake thermal efficiency of biofuel and undistilled biofuel is similar. Brake thermal efficiency for diesel, undistilled biofuel and biofuel is 29.98, 32.12 and 32.4%, respectively, at 80% load. Carbon monoxide, unburnt hydrocarbons, particulate matter and oxides of nitrogen emissions increase with undistilled biofuel compared to biofuel. There is a small reduction in carbon dioxide emission with undistilled biofuel compared to biofuel. Even though the cylinder pressure is high with undistilled biofuel, the intensity of premixed combustion is lower than distilled biofuel. The ignition delay and combustion duration increase with undistilled biofuel. Finally, it is concluded that the fuel derived from fish processing industry waste can be used as a fuel for diesel engine after distillation. 相似文献