Two Colour Photoflow Chemistry for Macromolecular Design

We report a photochemical flow setup that exploits λ‐orthogonal reactions using two different colours of light (λ₁=350 nm and λ₂=410 nm) in sequential on‐line irradiation steps. Critically, both photochemically reactive units (a visible‐light reactive chalcone and a UV‐activated photo‐caged diene) are present in the reaction mixture. We demonstrate the power of two colour photoflow by the wavelength‐selective end group modification of photo‐caged polymer end groups and the subsequent polymer ring closure driven by a [2+2] cycloaddition. Importantly, we evidence that the high energy gate does not induce the visible light reaction of the chalcone, which attests the true λ‐orthogonal nature of the flow reaction system. For the first time, this study opens the realm of photoflow reactions to λ‐orthogonal photochemistry.     

混沌时间序列多步自适应预测方法

针对混沌时间序列局域自适应预测方法在多步预测中预测器系数无法调节的问题，根据混沌时间序列的短期可预测性及自适应算法的自适应跟踪混沌运动轨迹的特点，提出了混沌时间序列多步自适应预测方法.仿真结果表明，此方法的多步预测性能明显好于局域自适应预测方法的多步预测性能. 关键词： 多步自适应预测方法 局域自适应预测方法 混沌时间序列     

扩散方程区域分解的多步算法

利用分数步法进行内边界值的多步计算,改进二维扩散方程的区域分解算法,形成新的并行算法,放宽稳定性条件.其中采用分数步空间大步长离散格式计算内边界点值.算法精度与隐格式相当.与改进前相比,稳定性条件放宽了q倍(g为两个相邻时间步之间执行分数步内边界值计算的次数).利用离散极值原理,严格证明了算法的收敛性.在并行机上进行数...     

Autoionization spectra of Sm atom

Spectra of autoionizing states of the Sm atom in an energy region between 45948.9 cm-1 and 46943.6 cm-1 are systematically investigated by a three-color multi-step resonant excitation scheme with three different excitation paths.The three intermediate states,4f 66s7s 7F3,4f 66s7s 7F4,and 4f 66s7s 9F5 are employed for the three paths,respectively.Based on precise calibration of wavelength,the level energies of 112 autoionizing states are determined with the line widths and the relative line intensities of the related transitions.The possible influence of configuration interaction on the line shape of autoionizing state is also discussed.In addition,a unique value of J,the total angular momentum,is assigned to all detected states by comparing the three spectra obtained with the different excitation paths.     

分子筛的酸处理对Mo/HZSM-5催化甲烷无氧芳构化反应性能的影响

 采用HNO3溶液对HZSM-5分子筛进行预处理,并以处理后的分子筛为载体制备了Mo/HZSM-5 催化剂. 结果表明,改性的Mo/HZSM-5催化剂在甲烷无氧脱氢芳构化反应中表现出很好的稳定性,显著地抑制了积炭物种在催化剂表面的形成. SEM,XRD和1H MAS NMR等表征结果表明,酸处理在一定程度上降低了HZSM-5分子筛的结晶度,使部分Al物种脱离骨架结构,迁移到骨架外形成新的表面Al羟基,从而使HZSM-5分子筛上B酸中心的数目明显减少. 未经改性的Mo/HZSM-5催化剂表面,平均每个晶胞中有1.12个B酸位,而改性的Mo/HZSM-5催化剂表面,平均每个晶胞中仅有0.88个B酸位. 这表明过多的酸性位存留在催化剂上会引起积炭的生成,降低催化剂的稳定性.     

天然沸石同晶取代制备钛丝光沸石

以优质的天然丝光沸石为原料,采用液固相置换反应,经多步"脱铝-补钛"的方式,制备了含钛的丝光沸石.运用X射线粉末衍射(XRD)、紫外可见光谱(UV-Vis)、X射线光电子能谱(XPS)以及ICP等手段对制备的钛丝光沸石进行了表征,结果表明钛已成为天然丝光沸石的骨架元素.多步脱铝-补钛的方式可有效调控骨架钛的含量和避免骨架外钛物种的生成.     

渐近非扩展映象的多步迭代

建立了渐近非扩展映象族的多步迭代格式的几个强收敛结果，所得结果扩展并改进了Xu和Noor等人的最新结果．     

液固相同晶取代法制备Sn-NaY催化环己酮Baeyer-Villiger氧化

以微孔分子筛NaY为载体,SnCl_4·5H_2O为锡源,通过液固相同晶取代法制备催化材料Sn-NaY,研究了脱铝预处理和焙烧两个因素对制备Sn-NaY的影响.采用FT-IR、UV-Vis、XRD、N_2物理吸附、ICP、NH_3-TPD、吡啶红外、激光拉曼等手段对催化材料进行了表征.结果表明:对载体进行脱铝预处理有利于分子筛在催化剂制备过程中保持良好的骨架结构,焙烧有利于进入分子筛骨架中的Sn(Ⅳ)与硅羟基成键,从而形成有催化活性的四配位的Sn(Ⅳ),而空气氛围下焙烧容易产生骨架外SnO_2物种.Sn-NaY催化环己酮Baeyer-Villiger氧化结果表明,在环己酮0.03 mol,n(H_2O_2)∶n(酮)=1.5∶1,0.35 g催化剂,15 mL乙腈,70℃反应24 h的工艺条件下,N_2氛围焙烧的同晶取代脱铝催化剂性能最好,环己酮的转化率可达44%,己内酯的选择性为62%.     

Recent advances in methods for numerical solution of O.D.E. initial value problems

This is a review paper which describes recent advances in numerical methods and computer codes for solving initial value problems of ordinary differential equations. Particular emphasis is placed upon stiff systems.     

Investigation of antibacterial and cytotoxic potential of phenolics derived from Cistus incanus L. by means of thin-layer chromatography-direct bioautography and cytotoxicity assay

Cistus incanus L. (hairy rockrose) is a medicinal plant which belongs to the Cistaceae family and the Cistus genus, with a well established position in traditional medicine of the Mediterranean basin and the Middle East. It was the aim of this study to compare antibacterial activity of the phenolics derived from fourteen C. incanus samples of different origin (Turkey, Albania, Greece, and an unknown geographical location) obtained as herbal teas from a local market of diet supplements. This activity was assessed with the use of thin-layer chromatography–direct bioautography (TLC-DB) applied to crude extracts against the Gram negative naturally luminescent marine bacterium Aliivibrio fischeri and the Gram positive soil bacterium Bacillus subtilis as the test microorganisms. It was established that in spite of different origin of the investigated herbal samples, in qualitative terms their antibacterial activity was closely comparable and more strongly pronounced against the Gram positive than the Gram negative bacterium. Crude extract originating from one herbal specimen labelled A3 (sample no. 3 from Albania) underwent selective multi-step extraction of the phenolics, dividing them into six fractions (I to VI) that expectedly contain flavonoid aglycons, free phenolic acids, non-polar flavonoid glycosides, polar flavonoid glycosides, and phenolic acids obtained through the acidic and basic hydrolysis from the respective glycosides. Antibacterial activity of each A3 fraction was then assessed with the use of the same TLC-DB approach and it was established that the strongest effect was exerted by fractions I and II (flavonoid aglycons and free phenolic acids). Moreover, cytotoxic assay was performed for the crude C. incanus extracts against the human colon adenocarcinoma cells and a moderate yet well measurable cytotoxic effect was observed with all investigated C. incanus samples. In analogy to antibacterial activity, also in this case cytotoxic potential of all investigated crude C. incanus extracts was similar.