NMR and DFT studies on persistent carbocations derived from benzo[kl]xanthene,dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran,and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran in superacidic media

Persistent carbocations generated by the protonation of hetero‐polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene ( 1 ), dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran ( 2 ), and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran ( 3 ) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO₃H‐SbF₅ (4:1)/SO₂ClF and 3 in FSO₃H‐SbF₅ (1:1)/SO₂ClF ionized to 1aH⁺ with protonation at C(4) and to 3aH⁺ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH⁺ and 3aH⁺ were the most stable protonated carbocations and that 2 should ionize to 2aH⁺ with protonation at C(6). According to the changes in ¹³C chemical shifts (Δδ¹³C), the positive charge was delocalized into the naphthalene unit for 1aH⁺ , into one benzo[b,d]furan unit for 2aH⁺ , and into one benzo[b,d]furan unit for 3aH⁺ . Copyright © 2015 John Wiley & Sons, Ltd.     

Reproducibility of the gadolinium concentration measurements and of the fitting parameters of the vascular input function in the superior sagittal sinus in a patient population

It is widely recognised that the measurement of the arterial input function (AIF) is a key issue and a major source of errors in the pharmacokinetic modelling of dynamic, contrast-enhanced magnetic resonance imaging (DCE-MRI) data, and the modality of the AIF determination is still a matter of debate. In this study we addressed the problem of the intrinsic variability of the AIF within the imaged volume of a DCE-MRI scan by systematically investigating the change in the concentration of contrast agent over time and the fit parameters of the derived vascular input function (VIF) obtained from the superior sagittal sinus (SSS) of a patient population that was scanned longitudinally during treatment for high grade glioma. From a total of 82 scanning sessions, we compared the results obtained with three different DCE-MRI protocols and between two different fitting functions. We applied a correction algorithm to the measured concentration-time curves to minimize the effect of the low temporal resolution on the VIF, and investigated the effect of this algorithm on the reproducibility. Finally, where possible, we compared the signal obtained in the SSS to the signal obtained in the middle cerebral artery. We found a good intrapatient reproducibility of both the measured gadolinium concentrations and VIF parameters, and that the variation of the parameters due to slice location within a patient was significantly lower than the intra patient variation. Intrapatient, interscan differences were significantly less marked than inter-patient differences showing a good intraclass correlation coefficient. We did encounter a MRI protocol dependence of the VIF fitting parameters. The correction algorithm significantly improved the reproducibility of the fitting parameters. These results support the idea that the use of a patient specific measured AIF, not necessarily averaged over a large volume, offers a significant benefit with respect to an external AIF or a measured cohort average AIF.     

Investigation of Simulated Trading — A multi agent based trading system for optimization purposes

Some years ago, Bachem, Hochstättler, and Malich proposed a heuristic algorithm called Simulated Trading for the optimization of vehicle routing problems. Computational agents place buy-orders and sell-orders for customers to be handled at a virtual financial market, the prices of the orders depending on the costs of inserting the customer in the tour or for his removal. According to a proposed rule set, the financial market creates a buy-and-sell graph for the various orders in the order book, intending to optimize the overall system. Here I present a thorough investigation for the application of this algorithm to the traveling salesman problem.     

安息香笼化合物光化学反应的时间分辨红外光谱

采用时间分辨红外吸收光谱方法,研究了邻甲基苯甲酸安息香酯在266 nm激光作用下发生的光化学反应,并考察了溶剂对反应过程的影响. 从瞬态红外光谱上观察到了邻甲基苯甲酸和苯甲酰自由基及苯偶酰,提供了直接的光谱证据证明了脱保护反应及C-C=O处均裂反应的发生. 通过对比溶剂中不同水含量下均裂反应中间体及邻甲基苯甲酸的产率,发现水含量在溶剂中的增加能促进脱保护反应的发生.     

分散橙3掺杂聚合物薄膜的全光极化特性及其驰豫过程研究

利用旋涂法制备了分散橙3（DO3）/PMMA主客体掺杂薄膜,对其吸收谱、厚度和折射率进行了测量,并采用全光极化的方法对薄膜的二阶非线性光学特性进行了研究。实验结果表明,随着厚度的增加其二阶非线性先增强后减弱,d33最大值约为0.827×10-2pm/V。对极化饱和后的驰豫情况进行了分析,发现不同厚度薄膜的驰豫时间不同,这是由于薄膜中偶氮含量和厚度的不同,分子间的相互作用对顺反异构逆过程的快慢有较大的影响。     

Nb掺杂影响NiTi金属间化合物电子结构的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了Nb元素掺杂对B2构型NiTi金属间化合物电子结构的影响.点缺陷生成能的计算结果表明,Nb原子掺杂后,NiTi中产生Ni原子和Ti原子空位和反位点缺陷所需要的能量均明显升高;态密度计算结果表明,Nb原子掺杂后与临近原子发生了明显的s-s, p-p和d-d电子相互作用,增加了与临近原子之间的电荷密度,有利于Nb与合金原子的成键.这些由Nb掺杂所导致的NiTi电子结构和键合特征的变化均有利于促进Nb与合金原子的相互作用,在一定程 关键词： NiTi金属间化合物 点缺陷 电子结构 第一性原理计算     

弹性波通过一维复合材料系统的透射性质

提出了不同结构的一维弹性波复合材料系统模型,包括一维周期结构声子晶体、标准Fibonacci准周期结构声子晶体、广义Fibonacci准周期结构声子晶体以及完全无序结构的复合材料系统. 采用模式匹配理论法,数值计算了弹性波通过一维复合材料系统的透射系数. 计算结果表明,利用特殊的准周期结构声子晶体可获得比周期结构声子晶体更宽的带隙范围,准周期结构排列的复合材料系统相当于在周期结构中引入了缺陷体一样,带隙内出现了丰富的局域模式. 对弹性波/声波在复合材料系统中局域态性质的研究有助于弹性波/声波滤波器、导波器 关键词： 弹性波复合材料 局域化     

碳纳米管-硅纳米线复合结构的形成和热稳定性

通过分子动力学方法模拟了在碳纳米管内填充一定数目的半导体元素硅形成碳纳米管-硅纳米线复合结构的过程,并采用Lindemann指数研究了这种复合结构的热稳定性．计算结果表明,当考虑碳纳米管和硅纳米线轴向方向的周期性边界条件之后,在C（13,0）和C （14,0）碳纳米管内能够形成亚稳结构的硅纳米线Si₁₆NW和Si₂₀NW,从而获得一种碳纳米管-硅纳米线的新型复合结构．通过计算这种复合结构的Lindemann指数,可以看到由于碳纳米管的保护作用,碳纳米管包裹的硅纳 关键词： 复合结构 纳米线 碳纳米管 分子动力学     

开槽前扩孔及复合角对气膜冷却的影响

本文对开槽前扩孔及在此基础上加30°、45°和60°不同角度复合角的气膜冷却结构进行了数值模拟,计算了指定冷却壁面的温度场分布以及冷却效率.结果表明:引入复合角后,能够改善冷却气膜在壁面的横向分布,复合角越大,气膜分布越均匀.在高吹风比下,复合角结构能够产生较大的气膜覆盖范围和较好的冷却效果.     

基于实时操作系统的光电稳定自适应模糊PI复合控制方法研究

针对经典稳定控制理论存在超调与快速性之间难以调和的矛盾,建立了稳定控制系统数学模型,采用自适应模糊实现控制的快速性,用PI保证系统的稳态精度,以误差为模糊控制的输入,设计一种实用的自适应模糊和PI复合控制系统,并在基于VxWorks实时操作系统的数字平台上得以实现.仿真和试验表明:设计的新型自适应模糊PI复合控制系统超调量为0,调节时间约8 ms,带宽约29 Hz.