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31.
A kinetic method is proposed for the simultaneous determination of europium(II) and cerium(III), based on their inductive action on the Cr(VI)-iodide redox reaction in weak acidic medium. The reaction rate was followed by the stopped-flow spectrophotometric technique using starch-iodine complex as indicator. The method can be used for the determination of europium and cerium after reduction with zinc metal powder in the concentration ranges 0–2.1 and 0–1.8 g/ml, respectively. The detection limits are 0.015 g/ml Eu and 0.010 g/ml Ce. 100 to 1000 times higher concentrations of other rare earth metal ions and Th4+, Al3+, Mn2+, Hg2+, Co2+, Ni2+, Cu2+, Pb2+ do not interfere. The method is applied to the determination of europium and cerium in a synthetic sample and in barium yttrium fluoride fluorescent material, with relative standard deviation of about 4%. 相似文献
32.
In this study,the preparation of a new kind of magnetic and luminescent Fe3O4/CdTe nanocomposites was demonstrated. Superparamagnetic Fe3O4 nanoparticles were first synthesized by hydrothermal coprecipitation of ferric and ferrous ions,followed by the modification of their surfaces with tetramethylammonium hydroxide(TMAOH) and the chemical activation with aspartic acid.The surface-modified Fe3O4 nanoparticles were then covalently coated with CdTe quantum dots(QDs),which were modified with mercaptoacetic acid(MPA),to form the Fe3O4/CdTe magnetic and luminescent nanocomposites through the coordination of the amino groups on the surfaces of Fe3O4 and the carboxyl groups on CdTe QDs.The structure and properties of as-synthesized nanocomposites were characterized.It was indicated that the nanocomposites possessed structure with an average diameter of 40- 50 nm,yellow-green emission feature and room temperature ferro-magnetism.Both the fluorescence and UV-vis absorption spectra of the nanocomposites showed a blue shift comparing with those of CdTe QDs.The mechanism of the blue shift was presented.The nanocomposites retained the ferromagnetic property with a saturation magnetization of 8.9 emu/g. 相似文献
33.
采用盐酸为介质,以顺序注射-氢化物发生原子荧光法测定生产用水中的锑含量.通过正交实验确定了仪器工作参数,研究了介质浓度、KBH4浓度、硫脲一抗坏血酸加入量等因素对测定结果的影响,探讨了共存离子的干扰.在选定的最佳实验条件下,方法的检出限为0.011ng/mL,线性范围0~8ng/mL,相对标准偏差为2.78%~6.20%,加标回收率为91.0%~99.1%.该方法操作简便,灵敏度高,准确度好,与微波消解法相比较,两者无显著性差异. 相似文献
34.
Dynamics of laser-induced cavitation bubbles on different wedge-shaped propelled surfaces, including 30°-surfaces, 90°-surfaces and 180°-surfaces, were investigated for laser propulsion in water environment by means of an optical beam deflection method. The expansion of the bubble on the three kinds of surfaces was simulated numerically. The pressure fields on the inner side of the surfaces and the energy that the propelled surfaces received from the expanding bubble were investigated numerically. For the three kinds of surfaces, the collapse times of the nonspherical bubbles were all less than the Rayleigh collapse time of the spherical bubble. The bubble on a narrow-shaped surface grew faster in a certain direction, which indicates that the propelling force was concentrated spatially and temporally. However, the most narrow-shaped surface did not get the most propelling energy. The repetition rate and spatial array density of the laser pulse cannot be too high, because of the scattering effect of the bubble. As a result of the laser plasma shielding and bubble scattering, high pulse energy does not necessarily result in a high propelling force. The narrow-shaped surfaces experienced higher shock damage, and emitted stronger noise. 相似文献
35.
HV-4B型碳硫分析仪的故障及维修 总被引:2,自引:0,他引:2
介绍HV-4B型碳硫分析低度的常见故障、故障产生的原因及排除方法。 相似文献
36.
《Current Opinion in Colloid & Interface Science》2001,6(5-6):516-518
37.
Patch near-field acoustic holography (NAH) coupled with an array of sound intensity probes allows separating the sound field incident on a surface from the one radiated by the surface itself. Although the measurement principle has been successfully used to separate the noise source contribution from disturbing sources and/or noise reflections, the method accuracy has not been investigated in the literature. We describe the results of experiments meant to evaluate the uncertainty in the identification of noise radiated by vibrating panels with different absorption characteristics in presence of an incident acoustic radiation using the statistically optimized near-field acoustic holography. Measurement errors were evaluated through tests performed in controlled acoustic conditions. Results evidenced that the measurement uncertainty depends on the accuracy of the microphone array positioning and on the incident sound field. These conclusions were in agreement with the results obtained by simulations in the phase of instrument optimization. 相似文献
38.
考虑了带特征的Mass形式的自守L函数的零点密度估计问题.证明了L(s,fχ)的零点密度估计具有下面的形式:∑χN(σ,T,χ)(qT)A(σ)(1-σ)+ε. 相似文献
39.
Four factors three level face centered central composite response surface design was employed in this study to investigate and optimize the effect of process variables (liquid-solid (LS) ratio (10:1–20:1 ml/g), pH (1−2), sonication time (15–30 min) and extraction temperature (50–70 °C)) on the maximum extraction yield of pectin from waste Artocarpus heterophyllus (Jackfruit) peel by ultrasound assisted extraction method. Numerical optimization method was adapted in this study and the following optimal condition was obtained as follows: Liquid-solid ratio of 15:1 ml/g, pH of 1.6, sonication time of 24 min and temperature of 60 °C. The optimal condition was validated through experiments and the observed value was interrelated with predicted value. 相似文献
40.