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271.
The corrosion of printed circuit boards can be effectively prevented with a polyurethane conformal coating. In this study, the protective performance of PU coating was investigated systematically through electrochemical measurements and simulated exposure/immersion tests. Some fungi tests were also included. All experimental results show that a polyurethane coating effectively inhibits corrosion on printed circuit boards. The optimal thickness of the coating film should be about 60 μm. Long-term exposure tests showed that this coating material could preserve the reliability of the investigated printed circuit boards for more than 400 days in a 90% relative humidity environment at 25°C. 相似文献
272.
The polarographic behaviour of dithiodiacetic acid and that of U(VI) in a solution containing dithiodiacetic acid as complexing agent have been investigated. For the dithiodiacetic acid system, two waves appear over the pH range studied. The prewave is kinetic in nature and the mainwave is diffusion-controlled. However, as U(VI) is added into the dithiodiacetic acid system, the polarogram changes due to the existence of a complex. The current-potential curve of the first wave is not the normal S shape. This is due to the superposition of the first wave of the ligand and the wave due to the reduction of the U(VI) in the complex to U(V). The second wave is due to the reduction of the complex The first wave is an adsorption-controlled current and the second wave is partly diffusion-controlled and partly adsorption-controlled. We propose an electrode reaction mechanism for both systems and the complex species. The dissociation constant of the complex HASSAUO+2 is found to be of the order of 10?4. 相似文献
273.
274.
We describe the syntheses of 6, 8-di-tert-butyl-, 7, 9-di-tert-butyl., 6,7-di-n-propyl and 8, 9-di-n-propyl-O-spirodienonelactone from 3, 5-di-tert-butylcatechol and 3, 4-di-n-propylcatechol. 相似文献
275.
A solid-phase microextraction (SPME) device was used as a time-weighted average sampler for n-valeraldehyde. The SPME device was first modified to improve the wearer's acceptance as a passive sampler. Then a poly(dimethylsiloxane)-divinylbenzene fiber was used and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was loaded onto the fiber. Vapors of known concentrations around the threshold limit values time-weighted average of n-valeraldehyde and specific relative humidities (RHs) were generated by syringe pumps in a dynamic generation system. n-Valeraldehyde vapors in gas bags were also generated. An exposure chamber was designed to allow measurement of face velocities, temperatures, exposing vapor concentrations, and RHs. Gas chromatography with flame ionization detection was used for sample analysis. The appropriate adsorption time for SPME coating PFBHA was determined to be 2 min and the desorption time for oxime formed after sampling was optimized to be 2 min. The experimental sampling constant was found to be (3.86+/-0.13) x 10(-2) cm3/min and face velocity was not expect to have effect on the sampler. 相似文献
276.
You WK So SH Lee H Park SY Yoon MR Chang SI Kim HK Joe YA Hong YK Chung SI 《Experimental & molecular medicine》1999,31(4):197-202
Endostatin, a carboxyl-terminal fragment of collagen XVIII is known as an anti-angiogenic agent, that specifically inhibits the proliferation of endothelial cell and the growth of several primary tumor. We report here the purification and characterization of the recombinant murine endostatin (rmEndostatin) which was expressed in a prokaryotic expression system. This rmEndostatin has similar physiochemical properties of yeast-produced recombinant endostatin, and it also specifically inhibits the proliferation and migration of bovine capillary endothelial cells stimulated by basic fibroblast growth factor. The biological activity of rmEndostatin was also shown by its anti-angiogenic ability on the chorioallantoic membrane of chick embryo in vivo. In this article, we demonstrate the refolding and purification of rmEndostatin, expressed using E. coli system, to a biologically active and soluble form. In addition, these results confirm the activity of endostatin as a potent anti-angiogenic agent. 相似文献
277.
In the enantioselective esterification of racemic naproxen with 4(2-hydroxyethyl) morpholine by Lipase MY in organic solvents,
a productivity improvement of the desired (S)-naproxen ester from 0.42 to 0.72 mM at the reaction time of 130 h was observed,
when the surfactantbis (2-ethylhexyl) sodium sulfosuccinate (AOT) was added in the reaction mixture. The presence of a small amount of exogenously
added water dramatically activated the enzyme in AOT/cyclohexane-reversed micelles. Desorption of the surfactant molecule
from the enzyme mass and solubilization of the enzyme into reversed micelles were used to elucidate an existing maximum of
the initial rate of (S)-naproxen synthesis with the water content. Moreover, the effects of alcohol and surfactant concentration
on the enzyme activity are reported. 相似文献
278.
<正> 苯乙烯(简称St)-4(甲基丙烯酸)2,2,6,6-四甲基哌啶醇酯(简称MTMP)共聚物(简称PDS)是七十年代发展起来的一种新型高效光稳剂。本文用IR研究了一系列自由基聚合的PDS共聚物,找出了MTMP对序列结构敏感的吸收峰,发现MTMP的1152.5厘米~(-1)峰位置与三单元序列分布F_(SMS)值有一定线性关系,还对通过测量MTMP羰基伸缩振动ν_(C=O)峰位置来计算二单元序列分布P_(mm)的关系进行了讨论。 相似文献
279.
Xiu Ling ZHANG Wei Min GONG* Bin DAI Chang Hou LIU Plasma Chemistry Laboratory Dalian University of Technology Dalian Center of Analysis Dalian Institute of Light Industry Dalian 《中国化学快报》2002,(2)
The oxidative coupling of methane (OCM) to C2 hydrocarbons using carbon dioxide as oxidant is an attractive process from environmental point of view. Only a few research papers reported for it1-3. In general, the yield of C2 hydrocarbons was about 6%. This indicated that the method of catalytic activation was unfavorable to the reaction. It is necessary for us to find a new method in order to activate reaction and improve C2 hydrocarbon yield. Non-equilibrium plasma is a cold plasma in… 相似文献
280.
Reciprocal derivative constant-current stripping analysis (RD-CCSA) is based on the measurement of dt/dE converted from a derivative signal, dE/dt, vs. electrode potential (E) during the stripping of analyte under galvanostatic conditions from a mercury-film electrode after preconcentration. The potential transient signal (E-t) in normal chronopotentiometric stripping analysis (CPSA) is converted in RD-CCSA into a stripping peak (dT/dE)(p) the height of which is proportional to the bulk concentration of analyte in solution. The theory of RD-CCSA has been derived, and validated by the good correlation obtained between the theory and experimental data. Compared with normal CPSA, RD-CCSA is more sensitive and has higher resolution. The detection limit for cadmium is 6 x 10(-10)M. Simultaneous determination of Cd(2+), In(3+), and Tl(+) (for which the differences between the stripping peak potentials are 58 and 50 mV, respectively) which is impossible for normal CPSA, voltammetry or differential pulse polarography, has become possible with RD-CCSA. 相似文献