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排序方式: 共有93条查询结果,搜索用时 16 毫秒
1.
E. J. Pavlina A. M. Meier P. Monteleone J. D. Weigner 《Journal of Materials Science》2007,42(2):705-713
Existing multi-layer devices using lead-based piezoelectric ceramics utilize an internal electrode that does not bond the
ceramic layers. Improvements in device performance and processing could be gained if the electrode also acted as a bond between
the ceramic layers. In the current work, the feasibility of brazing lead zirconate titanate (PZT) in ambient conditions utilizing
silver-based alloys containing low melting temperature metal oxides was investigated. Wettability, joint fracture strength,
and microstructural analyses were conducted for various PZT/silver–metal oxide systems. The metal oxide additions included
copper (II) oxide, vanadium pentoxide, lead (II) oxide, and eutectic lead oxide-titanium (IV) oxide. The silver–copper oxide
(Ag–CuO) system demonstrated the most potential; exhibiting an apparent contact angle of approximately 64° and an average
braze joint fracture strength that was approximately 62% of the monolithic PZT strength. In addition, no significant reaction
product formation was observed at the silver/PZT interface. However, a preliminary investigation of multi-layer devices electroded
with Ag–CuO alloys indicated a decrease in the resistivity of the brazed PZT by several orders of magnitude. 相似文献
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Zhidong Xu Kevin Harvey Thomas Pavlina Guy Dutot Gary Zaloga Rafat Siddiqui 《Lipids》2010,45(2):199-208
The existing protocols for analyzing fatty acid methyl esters (FAMEs) using a one-step acetyl chloride (AC) catalyzed transesterification and extraction procedure cannot accurately determine the medium- and long-chain fatty acids simultaneously in clinical (enteral, parenteral) formulations. For example: (1) addition of AC at room temperature generates an exothermic reaction that often results in loss of sample and possible injury to the analyst; (2) certain polyunsaturated fatty acids (PUFAs) are less stable at elevated temperatures during the transesterification and contribute to the over-estimation of the C16:0 and C18:1 fatty acids; and (3) the flame-ionization detector (FID) response varies depending on the carbon chain length of the fatty acids, that consequently impacts the underestimation of medium-chain fatty acid (C6–C10) recoveries. To overcome these deficiencies and accurately determine FAMEs, we have developed an improved one-step transesterification method that employs the addition of AC in tubes kept on a dry ice bath, the transesterification at room temperature, and the data analysis using relative response factors. Using this modified protocol, we determined the fatty acid composition of lipid emulsions (Omegaven® and Lipidem®) on a Shimadzu GC2010 gas chromatography (GC) system using a capillary GC column (Zebron ZB-WAX plus, 30 m, 0.25 mm ID, 0.25 μm). Our data suggest that the improved method can be easily used to accurately determine fatty acids (C6–C24) in functional foods and lipid emulsions. 相似文献
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Kousi P Remoundaki E Hatzikioseyian A Battaglia-Brunet F Joulian C Kousteni V Tsezos M 《Journal of hazardous materials》2011,189(3):677-684
A batch upflow fixed-bed sulphate-reducing bioreactor has been set up and monitored for the treatment of synthetic solutions containing divalent iron (100mg/L and 200mg/L), zinc (100mg/L and 200mg/L), copper (100mg/L and 200mg/L), nickel (100mg/L and 200mg/L) and sulphate (1700 mg/L and 2130 mg/L) at initial pH 3-3.5, using ethanol as the sole electron donor. The reactor has been operated at the theoretical stoichiometric ethanol/sulphate ratio. Complete oxidation of ethanol has been achieved through complete oxidation of the intermediately, microbially produced acetate. This is mainly attributed to the presence of Desulfobacter postgatei species which dominated the sulphate-reducing community in the reactor. The reduction of sulphate was limited to about 85%. Quantitative precipitation of the soluble metal ions has been achieved. XRD and SEM-EDS analyses performed on samples of the produced sludge showed poorly crystalline phases of marcasite, covellite and wurtzite as well as several mixed metal sulphides. 相似文献
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Zitka O Krystofova O Sobrova P Adam V Zehnalek J Beklova M Kizek R 《Journal of hazardous materials》2011,192(2):794-800
The synthesis of phytochelatins is catalyzed by γ-Glu-Cys dipeptidyl transpeptidase called phytochelatin synthase (PCS). Aim of this study was to suggest a new tool for determination of phytochelatin synthase activity in the tobacco BY-2 cells treated with different concentrations of the Cd(II). After the optimization steps, an experiment on BY-2 cells exposed to different concentrations of Cd(NO3)2 for 3 days was performed. At the end of the experiment, cells were harvested and homogenized. Reduced glutathione and cadmium (II) ions were added to the cell suspension supernatant. These mixtures were incubated at 35 °C for 30 min and analysed using high performance liquid chromatography coupled with electrochemical detector (HPLC-ED). The results revealed that PCS activity rises markedly with increasing concentration of cadmium (II) ions. The lowest concentration of the toxic metal ions caused almost three fold increase in PCS activity as compared to control samples. The activity of PCS (270 fkat) in treated cells was more than seven times higher in comparison to control ones. Km for PCS was estimated as 2.3 mM. 相似文献
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