Residue analysis of melamine in milk products by micellar electrokinetic capillary chromatography with amperometric detection

A high-performance micellar electrokinetic capillary chromatography with amperometric detection (MECC–AD) method for the fast determination of melamine (MM), occasionally used to increase the apparent protein content of milk products, has been developed. Method development involved optimisation of the working electrode, the running buffer system and acidity, the concentration of sodium dodecyl sulphate (SDS), the separation voltage, the applied potential and the sample injection time. Under the optimum conditions, MM can be well separated from its co-existing interferences in real-world samples within 9 min at the separation voltage of 20 kV in a 8 mmol/L SDS/20 mmol/L H₃BO₃–Na₂B₄O₇ running buffer (pH 7.4). Satisfactory recovery (83.3–105.5%), repeatability of the peak current (3.2%) and migration time (3.8%), and the limit of detection (2.1 × 10⁻⁶ g/mL) for the method were achieved. This proposed procedure has been successfully used for the determination of MM in milk products.     

氯化铵低温热处理制备空心碳纳米笼及其机理研究

碳纳米笼(CNC)的应用很广泛,但原始CNC具有金属核心,必须去除该核心才能得到空心CNC。采用氯化铵低温热处理原始CNC,再用水过滤得到空心产品。结果表明,这是一种很好的纯化方法。同时深入研究了该方法的机理,提出一种解释:氯化铵分解产物扩散进CNC后与金属核心反应,产物以气态形式扩散出CNC,最终消耗掉金属核心。     

Backward simulation of the probability of a trace particle reaching a given region

This paper describes the solution of the backward-type Kolmogorov equation (backward method) as an alternative to the forward method to determine the probability (P) of a trace particle reaching a given region within a time τ, which is of interest in groundwater contamination investigation, such as pollution monitoring and controlling. The backward-type Kolmogorov equation describing P was theoretically derived under the assumption that the divergence of the velocity field is zero. We here verify that this assumption is unnecessary and therefore the equation can be used in general cases when various recharge/discharge sources in the flow equation are considered. The backward method is validated by comparing its results with that from the forward method. We find that boundary conditions must be properly imposed in the backward method in order to obtain the same results as from the forward method. The backward method is much more efficient than the forward method.     

均匀化热处理对牙科烤瓷无钯高金合金组织性能的影响

研究了均匀化热处理对一种无钯牙科高金烤瓷合金组织性能的影响,对其进行了950℃保温30min的均匀化处理,然后快速在冰水混合物中淬火,并对之做了一系列测试分析.实验结果显示合金在均匀化热处理后,组织显著均匀化,硬度显著降低.淬火后的合金仍为α1和α2两相组织,但富铂的α2相颗粒的量比铸态组织明显减少,颗粒的尺寸也有所减小,SEM下观察有很强的立体感.作者认为合金高温淬火后仍为两相组织,而非单一均匀相,主要与热处理温度和材料的固态相变温度相距较近有关.     

Single-walled Carbon Nanotubes Regularly Aligned in Channels of Zeolite Single Crystal

We report the synthesis of single-wall carbon nanotubes (SWCNs) formed in 1-nm-sized channels of zeolite crystal by pyrolysis of tripropylamine molecules. The SWCNs are mono-sized and parallelly aligned along the crystal direction. In the present paper, we report the polarized Raman spectra measured for the wellaligned SWCNs, which gives us information about structural symmetry. Electrical transport properties of the SWNTs are measured in the temperature range of 0.3 K ～ 300 K. The conductivity of the SWCNs is monotonically decreased with decreasing temperature. The observed temperature dependence of zero-field conductance, In(σ) ～ 1/√T, could be explained well in terms of electron localization caused by imperfections and impurities in the nanotubes.     

Superplastic deformation of a heat-resistant Al–Cu–Mg–Ag–Mn alloy

The superplastic behavior and deformation mechanism of a heat-resistant Al–Cu–Mg–Ag–Mn alloy prepared by ingot metallurgy was investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. It is shown that the Al–Cu–Mg–Ag–Mn alloy shows good superplastic properties at temperatures higher than 450 °C and strain rates lower than 10^?2 s^?1. A maximum elongation-to-failure of 320% was observed at 500 °C and 5 × 10^?4 s^?1, where the corresponding strain rate sensitivity index m is 0.58 and the flow stress σ is 5.7 MPa. Microstructure studies revealed that the observed superplastic behavior resulted from severe grain elongation rather than grain boundary sliding. It is suggested that this phenomenon may provide a new concept for developing superplastic materials.     

CdSe四脚状纳米晶粒的光荧光研究

采用高温微乳液的化学方法,在溶液中合成了高产率的CdSe四脚状纳米晶粒。高分辨透射电镜(HRTEM)分析结果表明,CdSe四脚状纳米晶粒是由1个立方的核心和4个六方的臂所组成。研究了该四脚晶粒的变激发功率光荧光(PL)谱和变温的PL谱,分析发现低温时四脚晶粒的光荧光主要来自于被表面缺陷所局域的激子的辐射复合,而随着温度升高,束缚激子被热激发,室温时光荧光主要来自于自由激子的贡献。CdSe纳米量子点的退局域化温度比四脚纳米晶粒的高,而12K时CdSe纳米量子点的局域化能量比四脚纳米晶粒的也大得多,并对这一现象作了解释。     

高钙粘性飞灰对SCR催化剂的影响分析

为预测液态排渣炉产生的高钙粘性飞灰对选择性催化还原(SCR)催化剂的影响,通过分析烟气中飞灰浓度、粒度分布及成分组成,同时于电厂烟道中进行催化剂小样测试,表明高钙飞灰中的活性CaO与SO3的化学反应产物及粘性细灰在催化剂表面的沉积是影响催化剂活性的主要原因。对此,提出采用高效吹灰器、提高烟气流速等改善催化剂表面清洁状况的措施。     

Genome-Wide Identification and Analysis of the VQ Motif-Containing Protein Family in Chinese Cabbage (Brassica rapa L. ssp. Pekinensis)

Previous studies have showed that the VQ motif–containing proteins in Arabidopsis thaliana and Oryza sativa play an important role in plant growth, development, and stress responses. However, little is known about the functions of the VQ genes in Brassica rapa (Chinese cabbage). In this study, we performed genome-wide identification, characterization, and expression analysis of the VQ genes in Chinese cabbage, especially under adverse environment. We identified 57 VQ genes and classified them into seven subgroups (I–VII), which were dispersedly distributed on chromosomes 1 to 10. The expansion of these genes mainly contributed to segmental and tandem duplication. Fifty-four VQ genes contained no introns and 50 VQ proteins were less than 300 amino acids in length. Quantitative real-time PCR showed that the VQ genes were differentially expressed in various tissues and during different abiotic stresses and plant hormone treatments. This study provides a comprehensive overview of Chinese cabbage VQ genes and will benefit the molecular breeding for resistance to stresses and disease, as well as further studies on the biological functions of the VQ proteins.