熔融制样-X射线荧光光谱法测定硅铁中硅磷锰铝钙铬

熔融制样-X射线荧光光谱法(XRF)测定硅铁合金样品,需重点解决样品前处理中合金样品侵蚀铂-黄坩埚的难题。硅铁样品以四硼酸锂-碳酸锂预氧化剂在石墨垫底瓷坩埚中高温预氧化熔融后,再将熔融物转移至铂-黄坩埚中,用四硼酸锂熔融制成玻璃熔片,实现了熔融制样-X射线荧光光谱法对硅铁合金中硅、磷、锰、铝、钙、铬的测定。实验讨论了预氧化熔融的熔剂体系及氧化方法、试样与熔剂的稀释比,结果表明,试样与熔剂以1∶35的稀释比,以10滴300g/L碘化钾溶液为脱模剂,在1100℃熔融30min,熔融制得的玻璃片均匀、透明、无气泡,符合测定要求。用具有浓度梯度的系列硅铁有证标准样品制作校准曲线,各待测元素校准曲线的线性相关系数均大于0.9995。方法应用于硅铁合金实际样品中硅、磷、锰、铝、钙、铬的测定, 结果的相对标准偏差(RSD,n=11)在0.1%~5.8%之间;正确度试验表明,硅铁标准样品的测定结果与认定值相符,硅铁实际样品的测定结果与国家标准方法测定值一致,能满足常规分析要求。     

High strain rate compressive response of the Cf/SiC composite

Carbon fiber reinforced ceramic owns the properties of lightweight, high fracture toughness, excellent shock resistance, and thus overcomes ceramic's brittleness. The researches on the advanced structure of astronautics, marine have exclusively evaluated the quasi-static mechanical response of carbon fiber reinforced ceramics, while few investigations are available in the open literature regarding elastodynamics. This paper reports the dynamic compressive responses of a carbon fiber reinforced silicon carbide (C_f/SiC) composite (CFCMC) tested by the material test system 801 machine (MTS) and the split Hopkinson pressure bar (SHPB). These tests were to determine the rate dependent compression response and high strain rate failure mechanism of the C_f/SiC composite in in-plane and out-plane directions. The in-plane compressive strain rates are from 0.001 to 2200?s^?1, and that of the out-plane direction are from 0.001 to 2400?s^?1. The compressive stress-strain curves show the C_f/SiC composite has a property of strain rate sensitivity in both directions while under high strain rate loadings. Its compressive stiffness, compressive stress, and corresponding strain are also strain rate sensitive. The compressive damage morphologies after high strain rate impacting show different failure modes for each loading direction. This study provides knowledge about elastodynamics of fiber-reinforced ceramics and extends their design criterion with a reliable evaluation while applying in the scenario of loading high strain rate.     

基体稀释或基体匹配石墨炉原子吸收光谱法测定土壤样品中铅和镉

用石墨炉原子吸收光谱法测定土壤样品中Pb和Cd时,有时候直接按照方法标准GB/T 17141—1997操作,测定结果不能满足质控要求。研究结果表明,目标元素系列标准溶液中,分别含和不含土壤基体元素Na、Mg、Al、Si、Fe、Ca等元素混合成分时,校准曲线斜率明显不同。为减小基体效应的影响,基于文献调研和实验结果,对上述方法标准实验步骤进行了下列改进:(1)取相同体积实际样品消解液混合后,定量加入到用于建立校准曲线的系列标准溶液中,用于基体匹配;(2)对消解液进行适度稀释,仍采用标准溶液建立校准曲线。用4个土壤标样和土壤样品加标测定结果对改进后的方法进行了验证,结果表明,基体稀释法测定Pb的回收率范围分别为90.4%~114%;测定低含量Cd时,回收率范围为84.1%~125%。基体匹配法测定Pb和Cd的回收率范围分别为93.0%~105%和102%~119%,基本满足土壤样品中重金属回收率为80%~120%的质控要求。样品中痕量镉在测定下限附近时,应严格控制稀释倍数,或采用基体匹配法测定。改进后的操作步骤适合日常检测工作中大批量土壤样品中Pb和Cd的准确测定。     

电感耦合等离子体原子发射光谱法测定土壤中8种组分

为满足土地质量调查的需求,实现土壤中多组分的同时消解及准确测定,提高大批量样品的分析效率,建立了土壤样品经高压密闭消解后,采用电感耦合等离子体原子发射光谱法(ICP-AES)测定K₂O、Na₂O、CaO、MgO、Ba、Mn、Cu、Zn的方法。通过对消解体系、酸用量、消解温度等方面的考察,确定最佳实验条件;并对待测液中共存元素Al、Fe的干扰进行探讨,两者均不干扰测定。各组分校准曲线线性相关系数均大于0.999;检出限为0.01~10μg/g。实验方法用于测定土壤标准样品GBW07385、GBW07386、GBW07388中K₂O、Na₂O、CaO、MgO、Ba、Mn、Cu、Zn,测定结果的相对标准偏差(RSD,n=12)为1.1%~4.3%,相对误差RE为-4.0%~4.6%。采用实验方法对土壤实际样品中K₂O、Na₂O、CaO、MgO、Ba、Mn、Cu、Zn进行测定,结果的RSD(n=6)为1.2%~4.6%;并与地矿行业标准方法DZ/T 0279.2—2016测定结果进行比对,测得结果基本一致。     

Effects of Environments on the Noise of Atomic Force Microscopy Cantilevers

环境对原子力显微镜悬臂噪声的影响

句宏宇 张松 崔树勋

（西南交通大学 生命科学与工程学院 材料先进技术教育部重点实验室，四川 成都 610031）

创新点说明：

1）发现了原子力显微镜（AFM）在高真空环境中具有非常小的噪声；

2）发现了AFM在液体环境中的噪声与液体粘度和悬臂运动速率之间的关系。

研究目的：

得到AFM的噪声和使用环境、悬臂种类以及仪器参数设置之间的关系，找出减小AFM噪声的有效方法。

研究方法：

模拟基于AFM的单分子力谱实验过程，通过计算AFM在高真空、大气和不同粘度液体环境中不同运动速率下力信号数值的标准差（即噪声大小），分析AFM噪声的影响因素。

研究结果：

1）V形悬臂在高真空环境中具有非常小的噪声，在大气环境中噪声有微小增大，在液体环境中噪声显著增大；

2）AFM具有较低的系统噪声，且系统噪声大小和悬臂到基底的距离相关；

3）随着悬臂运动速率的增加，V形悬臂在不同粘度液体环境中的噪声表现出相似的增大趋势。且液体黏度越大，噪声随速率增大的趋势越显著；

4）相同环境中矩形悬臂的噪声小于V形悬臂的噪声。

结论：

1）高真空环境中AFM具有较小的噪声和较高的分辨率，是进行单分子力谱实验的理想环境；

2） 在液体环境中为了获得较高的信噪比，应尽可能地减小悬臂的运动速率和液体粘度。

关键词：原子力显微镜；悬臂；噪声；高真空；粘度

     

Deacylation of Calcium-Dependent Antibiotics from Streptomyces violaceoruber in Co-culture with Streptomyces sp. MG7-G1

When Streptomyces violaceoruber grows together with Streptomyces sp. MG7-G1, it reacts with strongly induced droplet production on its aerial mycelium. Initially the metabolite profile of droplets from S. violaceoruber in co-culture with Streptomyces sp. MG7-G1 was compared to samples from S. violaceoruber in single-culture by using high-performance liquid chromatography-mass spectrometry (HPLC-MS). Then, the exudate from agar plates of co-cultures and single cultures (after freezing and thawing) was also analysed. Several compounds were only observed when S. violaceoruber was grown in co-culture. Based on their high-resolution ESI mass spectra and their comparable retention times to the calcium-dependent antibiotics (CDAs) produced by S. violaceoruber, the new compounds were suspected to be deacylated calcium-dependent antibiotics (daCDAs), lacking the 2,3-epoxyhexanoyl residue of CDAs. This was verified by detailed analysis of the MS/MS spectra of the daCDAs in comparison to the CDAs. The major CDA compounds present in calcium ion-supplemented agar medium of co-cultures were daCDAs, thus suggesting that Streptomyces sp. MG7-G1 expresses a deacylase that degrades CDAs.     

氮酮与薄荷醇联用对5-氟尿嘧啶的促透作用

目的：以5-氟尿嘧啶（5-FU）为模型药物，对氮酮和薄荷醇的促透特性进行比较，并探讨两种促透剂合用时的促透效果。方法：在离体透皮实验装置上进行透皮试验，由浓度计算累积透过量，运用倍量法对氮酮与薄荷醇联用的效果进行评价。结果： 浓度为0.25%、0.50%、1.00%、2.00%的氮酮对5-FU均有促透作用，与空白对照组相比，差异具有统计学意义（P<0.01）；浓度为0.25%、0.50%、1.00%、2.00%的薄荷醇对5-FU也有明显的促透作用，与空白对照相比，差异具有统计学意义（P<0.01）；用倍量法对两种药物联用的作用进行评价分析时，二者联用未显示有协同作用。结论：氮酮和薄荷醇对（5-FU）均有促透作用，但二者以相同浓度合用时，未有明显的协同作用。     

What is a crystal to the new chemical crystallographer,after that first,automated structure analysis?

This educational review postulates the importance of maintaining an adequate level of crystallographic education among structure-dependent scientists whose interests are not primarily in crystallography, at a time when automation and validation have made it possible to obtain high-quality structure analyses in many cases with a minimum of crystallographic background. The topics addressed are intended to form a second round of crystallographic education for a novice user whose first round involved hands-on experience with structure solution and an introduction to elementary concepts. The specific topics, chosen for their relevance as basic knowledge and their lack of emphasis in many formal treatments, are (1) crystallographic reference frames and the utility of the reciprocal cell in geometrical calculations; (2) the relationship between the two concepts that constitute our model of the crystal, namely the unit cell and the lattice; (3) the manner in which an atom is represented in concept and in practice; (4) the importance of interleaved symmetry elements required by the presence of additional symmetry on a lattice; (5) the harnessing of the natural properties of the crystalline state for the potential manipulation of properties of synthetic crystals; and (6) useful terminology for navigating a crystal structure.     

HPLC-Q-TOF MS法研究3种银杏双黄酮成分的质谱裂解途径

本研究采用高效液相色谱-串联四极杆飞行时间质谱(HPLC-Q-TOF MS)在负离子模式下分析3种银杏双黄酮(7-去甲基银杏双黄酮、金松双黄酮、异银杏双黄酮)的质谱裂解途径。结果表明,3种化合物具有相似的裂解途径,均易丢失CH 3OH和CO 2,且该类成分在Ⅰ—C环和Ⅱ—C环发生多种Retro-Diels-Alder(RDA)裂解,可进一步失去取代基,得到相应的特征碎片离子。该结论可为银杏双黄酮类的结构鉴定提供依据。