Molecular dynamics study of anisotropic shock responses in oriented α-quartz single crystal

Journal of Materials Science - This paper presents an investigation aimed at understanding the shock wave propagation response of oriented α-quartz single crystals by using molecular dynamics...     

毛细管区带电泳-间接紫外检测法测定婴儿配方奶粉中的胆碱

目的建立毛细管区带电泳-间接紫外检测法测定婴儿配方奶粉中胆碱含量的新方法。方法用5 mmol/L乙酸提取婴儿配方奶粉样品中的胆碱,涡旋混匀、9000 r/min离心,上清液经0.45μm醋酸纤维素滤膜过滤后进样。用未涂覆熔融石英毛细管75μm×70 cm(有效长度:60 cm)作为分离柱。以10 mmol/L磷酸二氢钠+20 mmol/L磷酸+7 mmol/L 4-甲基咪唑为分离缓冲体系。分离电压为28 k V,进样压力及时间为0.5 psi、10 s,检测波长为214 nm。结果胆碱的校正峰面积与质量浓度在8.7~86.8 mg/L范围内间线性关系良好,相关系数为0.9997、检出限为2.6 mg/L、定量限为8.7 mg/L,方法的日内和日间精密度分别为1.9%和3.9%(n=7)。3个质量浓度添加水平的平均加标回收率分别为98.8%、95.2%及97.6%,相应RSD分别为0.8%、0.9%及0.6%(n=5)。用本法分析了10件婴儿配方奶粉样品,均获满意结果。结论本方法简单、无需有机溶剂,适用于婴儿配方奶粉中胆碱的常规检测。     

Effect of annealing atmosphere on the structure and dielectric properties of unfilled tungsten bronze ceramics Ba4PrFe0.5Nb9.5O30

Unfilled tungsten bronze ceramics with the nominal formula Ba₄PrFe_0.5Nb_9.5O₃₀ were synthesized via the standard solid-state sintering route, and the effects of oxygen vacancies on the dielectric and electrical properties were investigated in addition to the structure. Room-temperature X-ray diffraction showed that the N₂-annealed sample had the largest cell volume. Low-temperature spectrum showed that N₂ annealing rendered the dielectric constant and dielectric loss more frequency dispersive, whereas O₂ annealing inhibited the frequency dispersion. The dc conductivity of all the samples originated from the electrons produced in the second ionization of oxygen vacancies and was most likely controlled by a mixed conduction mechanism of the electron and oxygen-vacancy ions. The N₂-annealed sample has the highest dc conductivity owing to its high concentration of oxygen vacancies. The broadening of the Raman lines and the decrease of Raman intensity for the N₂-annealed sample originated from a significant structural disorder. X-ray photoelectron spectra demonstrated that the increased oxygen vacancies caused by the change of valences of Fe and Pr ions contributed to the structural disorder.     

乌鲁木齐机场多普勒天气雷达故障统计分析

文章针对乌鲁木齐机场多普勒天气雷达(以下简称ADWR)2009~2019年发生的故障次数、故障分布以及备件更换情况,逐年统计故障率,深入分析了ADWR系统性能,总结出运行维护中的经验,就如何更好地提高雷达业务运行指标提出建议,以提高ADWR雷达的维护、维修能力,建立有针对性的备件管理,为科学的业务运行管理提供依据。     

起重机自重应力对安全评估中应力测试实验结果的影响

应力测试是起重机安全评估中必须进行的一项检测。目前在安全评估工作中常采用应变电测法来采集起重机工作过程中的应力时程数据,由于该方法只能采集到结构由于载荷变化产生的应力,而无法采集到结构因自重产生的应力,导致应力测试无法获取结构的完整应力。利用起重机金属结构自重应力在总应力中占有的权重,分析其对应力测试实验结果的影响大小,试验结果表明在危险截面自重应力大小占总应力大小可达60%,此时不考虑自重应力进行结构安全性的判定是不全面的。可考虑利用仿真技术获取自重应力[1,2],从而使得安全评估应力测试实验结论更加准确。     

Dispersive-Solid-Phase Extraction Cleanup Integrated to Dispersive Liquid-Liquid Microextraction Based on Solidification of Floating Organic Droplet for Determination of Organochlorine Pesticides in Vegetables

A simple and rapid method applying acetonitrile extraction, dispersive-solid-phase extraction (d-SPE) cleanup, and dispersive liquid-liquid microextraction based on solidification of floating organic droplet (DLLME-SFO) was developed for determination of organochlorine pesticides in vegetables. In order to simplify operation, d-SPE cleanup was integrated to DLLME-SFO concentration procedure, and a protection device for glass tube was applied to achieving high-speed centrifugation. The comparison study between the integrated d-SPE and normal d-SPE showed that the former could shorten the sample preparation time without decrease of cleanup efficiency. Subsequently, the necessity of using a high-centrifugation speed (more than 8603 g) for complete separation of the d-SPE sorbents, water phase, and organic phase was confirmed through turbidity analysis. The recoveries of the proposed method ranged from 77.2 to 112.5%, and the relative standard deviations were less than 15%. The limits of detection were in the range of 0.45 ~ 1.33 μg kg^?1, while the limits of quantitation were from 1.35 to 3.99 μg kg^?1, respectively. Finally, the method was successfully applied to analyze real vegetable samples.     

Preparation and properties of Eu and Dy co-doped strontium aluminate long afterglow nanomaterials

The long afterglow nanomaterials of strontium aluminate co-doped by Eu and Dy have been synthesized by co-precipitation combined hydrothermal method. The effects of hydrothermal time, calcination time, pH value, the amount of aluminum nitrate, activator, co-activator and flux H₃BO₃ on the fluorescence properties of the product were investigated by means of single factor optimization experiment. Then the orthogonal experiment was employed to obtain the optimal synthesis conditions that are as follows: n_Dy/n_Eu = 2.5, t_c = 2.5?h, n_Eu/n_Sr = 0.02, t_h = 8?h. Subsequently, the optimal synthesis conditions were verified by three repeated experiments, and the obtained products were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and fluorescence spectrometer. The results showed that the synthesized target products all were the mixed crystal phase of SrAl₂O₄ and Sr₄Al_l4O₂₅. The particles presented regular spherical-like with size ~ 100?nm. The dopants Eu and Dy were confirmed existed in the SrAl₂O₄ powders. The fluorescence and afterglow data of the target products were better than that in the orthogonal experiment scheme. The primary emission spectra band was in the range of 400–600?nm with characteristic peak located at ~ 460?nm corresponding to the transitions of Eu²⁺ ions from 4f⁶5d→4f⁷, and the blue light can be observed by naked eyes. The similar fast-decaying and slow-decaying processes were displayed in all the afterglow curves, and the initial afterglow brightness of the target product is apparently higher than that of products synthesized by the orthogonal experiment. The synthesized target products, which show excellent long afterglow performance, present a great application prospects in the aspects of ceramics, plastics, arts and crafts, ink and coating.     

新疆发酵驼乳中分解植酸盐酵母菌的筛选及鉴定

为发掘和保护新疆牧区传统发酵驼乳中潜在益生酵母菌资源，从新疆伊犁地区不同牧区采集12份传统发酵驼乳样品，通过酵母浸出粉胨葡萄糖（YPD）培养基分离酵母菌，通过富含植酸二钾的培养基初筛及降解植酸盐能力的测定从中筛选可降解植酸盐的酵母菌，通过形态观察、生理生化试验及5.8S rDNA ITS1/ITS4区域序列同源性分析进行菌种鉴定，并测定其耐酸及耐胆盐性能。结果表明，筛选出11株可分解植酸盐的酵母菌，鉴定8株为库德毕赤酵母（Pichia kudriavzevii），2株为白地霉（Geotrichum candidum），1株为乳酸克鲁维酵母（Kluyveromyces lactis），其中库德毕赤酵母菌BJ9-12在模拟胃液和模拟肠液中的存活率分别为87.79%和81.50%，耐酸及耐胆盐性能较好，且培养48 h时分解植酸盐的透明圈直径达到3.45 cm，在发酵食品中具有良好的应用潜力。     

北沙参乙醇分级多糖的理化性质及抗氧化活性研究

采用水提醇沉法分级纯化得到4种北沙参多糖(GLP-30、GLP-50、GLP-70、GLP-剩余),采用傅里叶变换红外光谱、高效液相色谱、凝胶渗透色谱、扫描电镜以及差示扫描量热—热重分析等进行分析,并测定其抗氧化活性。结果表明:4种北沙参多糖均具有多糖的典型基团,但差示扫描量热结果相差较大;各多糖组分分子量随乙醇浓度的增加而降低;不同组分间的多糖得率及单糖含量有一定差异,其中GLP-50得率(5.43%)和半乳糖醛酸含量(2.03%)最高,蛋白含量(7.66%)较高,具有最高的保油性,在清除DPPH自由基和羟基自由基中表现出最高的抗氧化能力。乙醇分级沉淀的方法可用于分级纯化北沙参多糖组分,其中50%乙醇更适宜沉淀制备北沙参多糖,且所得多糖抗氧化性较强。