Recoil momentum spectroscopy of highly charged ion collisions on magneto-optically trapped Na

We have used a cold ( T<1 mK), laser-cooled target of Na atoms confined in a magneto-optical trap to study electron capture processes during highly charged ion-sodium atom collisions at keV energies. Momentum distributions of target ions were determined by employing time-of-flight and position sensitive detection of the Na ions, produced during the collisions and extracted by a weak electric field. In this way impact parameter sensitive information about multielectron capture processes is obtained.     

毛细管离子色谱-串联质谱法测定热纤梭杆菌发酵液中的低相对分子质量有机酸

建立了一种测定热纤梭杆菌发酵液中的低相对分子质量有机酸的毛细管离子色谱-串联质谱方法。探索优化了色谱和质谱的检测条件,在最佳分析条件下同时检测8种有机酸。离子色谱以KOH水溶液作为流动相进行梯度洗脱;用IonSwift MAX-100毛细管柱进行分离;在喷雾电压为3.0 kV、喷雾气压强为2 000 kPa、成源温度为275℃的条件下,选择离子监测(SIM)模式下运行质谱。结果表明,柠檬酸和异柠檬酸两种同分异构体能够得到很好的分离,8种有机酸在一定浓度范围内具有良好的线性关系,相对标准偏差为1.45%~5.99%,相关系数为0.9696~0.9986,平均加标回收率为89.0%~110.0%,8种有机酸的检出限为0.01~0.50 mg/L。该方法进样量少,灵敏度高,重现性好,能够满足实际样品的检测要求,可用于嗜热厌氧菌发酵液中低分子量有机酸的测定。     

Strong isotope effects on the charge transfer in slow collisions of He2+ with atomic hydrogen, deuterium, and tritium

Probabilities and cross sections for charge transfer by He2+ impact on atomic hydrogen (H), deuterium (D), and tritium (T) at low collision energies are calculated. The results are obtained using an ab initio theory, which solves the time-dependent Schr?dinger equation. For the H target, excellent agreement is achieved between the present and previous results. Differences by orders of magnitude are observed between the cross sections for H, D, and T. A method is introduced to separate the contributions of charge-transfer mechanisms due to radial and rotational coupling. The large differences observed for H, D, and T are attributed to isotope effects in the rotational coupling mechanism.     

Fluorescence Properties of Porphyrin Dimers Incorporating an Anhydride Linker

IntroductionOligomeric porphyrins play a number of criticalbiological roles in many processes, such as energytransfer and electron transfer, molecular binding, mul-tielectron redox catalysis and light harvest[1,2]. Amongthe arrays of covalently linked por…     

离子色谱法同时测定胞外培养液中的有机酸与核苷酸

建立了一种利用阴离子交换色谱柱分离,抑制型电导检测器同时测定乳酸、丙酸、丙酮酸、苹果酸、磷酸二羟丙酮、柠檬酸、异柠檬酸7种有机酸和单磷酸核苷酸(AMP)、双磷酸核苷酸(ADP)、三磷酸核苷酸(ATP)3种核苷酸的方法。采用IonPacAS11-HC阴离子交换柱,KOH梯度洗脱,流速1.00mL/min,柱温30℃,进样体积25μL。方法的相对标准偏差为0.39%～4.69%,线性相关系数为0.9906～0.9996,加标回收率为80.71%～94.02%,方法可用于嗜热厌氧菌胞外培养液中有机酸和核苷酸的同时测定。     

可视化传感阵列对乌龙茶等级的快速识别研究

以金属二聚体卟啉,席夫碱过渡金属配合物和特异性染料为敏感材料,结合溶胶凝胶技术构建了一种新型可视化传感器阵列系统,对9种不同产地不同等级的乌龙茶进行了检测。采用主成分分析,聚类分析技术和欧式距离对检测结果进行分析。该传感阵列系统可以对乌龙茶的产地和等级实现准确的可视化识别与分类,检测耗时为3 min。通过主成分分析获得的前2个主成分所代表的乌龙茶63.6%的信息量即可以实现不同等级茶叶区分。9种乌龙茶的平行实验数据均能100%准确区分,且等级相同产地相同的样本优先聚成一簇。研究结果表明所构建的可视化阵列传感器是一种能快速准确区分乌龙茶等级与产地的方法,在实时快速检测茶叶品质方面有潜在的应用价值。     

纳米金-卟啉复合传感阵列快速识别肺癌患者呼气中的有机小分子

合成了小粒径纳米金作为卟啉保护剂,以纳米金-卟啉化合物和p H指示剂共同构建6×6传感阵列,将其用于可视化检测12种肺癌患者呼出气体中的有机小分子(OSMs),设置了3个浓度梯度且每个样品重复5次.实验结果显示,纳米金的引入可显著提高阵列的稳定性和灵敏度;聚类分析结果表明,5次平行实验的结果优先聚为一簇,结构相似的目标物随后聚在一起;差谱图显示该方法对不同种类、不同浓度的OSMs具有良好的定性及半定量分析能力.该方法可快速识别OSMs且具有肺癌筛查的潜在应用前景.     

Implementation Aspects of 3D Lattice-BGK: Boundaries, Accuracy, and a New Fast Relaxation Method

In many realistic fluid-dynamical simulations the specification of the boundary conditions, the error sources, and the number of time steps to reach a steady state are important practical considerations. In this paper we study these issues in the case of the lattice-BGK model. The objective is to present a comprehensive overview of some pitfalls and shortcomings of the lattice-BGK method and to introduce some new ideas useful in practical simulations. We begin with an evaluation of the widely used bounce-back boundary condition in staircase geometries by simulating flow in an inclined tube. It is shown that the bounce-back scheme is first-order accurate in space when the location of the non-slip wall is assumed to be at the boundary nodes. Moreover, for a specific inclination angle of 45 degrees, the scheme is found to be second-order accurate when the location of the non-slip velocity is fitted halfway between the last fluid nodes and the first solid nodes. The error as a function of the relaxation parameter is in that case qualitatively similar to that of flat walls. Next, a comparison of simulations of fluid flow by means of pressure boundaries and by means of body force is presented. A good agreement between these two boundary conditions has been found in the creeping-flow regime. For higher Reynolds numbers differences have been found that are probably caused by problems associated with the pressure boundaries. Furthermore, two widely used 3D models, namelyD₃Q₁₅andD₃Q₁₉, are analysed. It is shown that theD₃Q₁₅model may induce artificial checkerboard invariants due to the connectivity of the lattice. Finally, a new iterative method, which significantly reduces the saturation time, is presented and validated on different benchmark problems.     

Synthetic studies with the brevicidine and laterocidine lipopeptide antibiotics including analogues with enhanced properties and in vivo efficacy

Brevicidine and laterocidine are two recently discovered lipopeptide antibiotics with promising antibacterial activity. Possessing a macrocyclic core, multiple positive charges, and a lipidated N-terminus, these lipopeptides exhibit potent and selective activity against Gram-negative pathogens, including polymyxin-resistant isolates. Given the low amounts of brevicidine and laterocidine accessible by fermentation of the producing microorganisms, synthetic routes to these lipopeptides present an attractive alternative. We here report the convenient solid-phase syntheses of both brevicidine and laterocidine and confirm their potent anti-Gram-negative activities. The synthetic routes developed also provide convenient access to novel structural analogues of both brevicidine and laterocidine that display improved hydrolytic stability while maintaining potent antibacterial activity in both in vitro assays and in vivo infection models.

Convenient solid-phase approaches are described for the synthesis of brevicidine and laterocidine. Also reported are novel analogues including a laterocidine variant with enhanced hydrolytic stability and potent in vivo antibacterial activity.