A Hybrid Method Using HAVOK Analysis and Machine Learning for Predicting Chaotic Time Series

The prediction of chaotic time series systems has remained a challenging problem in recent decades. A hybrid method using Hankel Alternative View Of Koopman (HAVOK) analysis and machine learning (HAVOK-ML) is developed to predict chaotic time series. HAVOK-ML simulates the time series by reconstructing a closed linear model so as to achieve the purpose of prediction. It decomposes chaotic dynamics into intermittently forced linear systems by HAVOK analysis and estimates the external intermittently forcing term using machine learning. The prediction performance evaluations confirm that the proposed method has superior forecasting skills compared with existing prediction methods.     

Design of diamond-shape photonic crystal fiber polarization filter based on surface plasma resonance effect

A novel plasmonic polarization filter based on the diamond-shape photonic crystal fiber(PCF) is proposed. The resonant coupling characteristics of the PCF polarization filter are investigated by the full-vector finite-element method. By optimizing the geometric parameters of the PCF, when the fiber length is 5 mm, the polarization filter has a bandwidth of 990 nm and an extinction ratio(ER) of lower than -20 dB. Moreover, a single wavelength polarization filter can also be achieved, along with an ER of -279.78 dB at wavelength 1.55 μm. It is believed that the proposed PCF polarization filter will be very useful in laser and optical communication systems.     

Molecular simulation of water behaviors on crystal faces of hydroxyapatite

The water behavior on (001) and (100) crystal faces of hydroxyapatite (HAP) were studied using molecular dynamics (MD) simulations. The study showed that the water molecules between the HAP faces were under conditions of strong electrical field and high pressure, and hence formed 2–3 well-organized water layers on the crystal surfaces. These structured water layers had ice-like features. Compared with the crystallographic [100] direction of HAP, the polarity along the [001] direction was stronger, which resulted in more structured water layers on the surface. The interaction of water molecules with the calcium and phosphate sites at the HAP-water interface was also studied. The results indicated the multiple pathways of water adsorption onto the HAP surfaces. This study revealed the formation and the detailed structure of water layers on HAP surfaces and suggested that the interfacial water played an important role in stabilizing the HAP particles in aqueous solutions. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(8): 1392–1400 (in Chinese)     

超高效液相色谱法同时测定蜂胶中的12种活性成分

采用超高效液相色谱法同时测定了蜂胶中类黄酮、阿魏酸、咖啡酸苯乙酯等12种活性成分。蜂胶样品用甲醇稀释,超声波提取,样液过滤后以Acquity BEH C18柱(100 mm×2.1 mm,1.7 μm)为分离柱,0.4%磷酸水溶液和甲醇为流动相,梯度洗脱,采用二极管阵列检测器检测。整个分离过程在9.5 min内完成。以加标蜂胶样品做添加回收测定,12种化合物的回收率为90.1%～104.3%,相对标准偏差为2.12%～4.90%。该方法为评价蜂胶质量提供了一种新的检测方法,已应用于实际蜂胶样品的测定。     

通过C(sp3)-H键活化构建C-P键合成氨基膦酸酯类化合物

氨基膦酸酯及其衍生物是一种重要的有机化合物,因其具有抗菌、抗真菌、酶抑制剂和催化抗体活性而广泛应于药物化学和农业化学。通过C(sp3)-H键活化构建C-P键的方法是合成氨基膦酸酯衍生物重要方法之一。本文以过渡金属体系和非金属体系进行分类,介绍了近年来通过C(sp3)-H键活化方法构建C-P键合成氨基膦酸酯类化合物的研究进展。     

侧链结构对磺化聚芳醚性能及微观形貌的影响

比较了3种主链结构相同而侧链结构不同的磺化聚芳醚(SPAE)材料的性能. 分析了侧链结构对聚合物的吸水、 溶胀及质子传导行为的影响. 结果表明, 在相同的离子交换容量(IEC)条件下, 具有柔顺脂肪族侧链的聚芳醚材料具有较高的质子传导率. 其原因是由于柔顺的脂肪族侧链比刚性的芳香族侧链更易运动, 有利于侧链末端磺酸基团的聚集, 进而形成离子簇. 3种聚合物微观形貌的分析结果表明, 含柔顺侧链结构的聚合物薄膜具有更大的质子传输通道, 其结果与聚合物的宏观吸水和传导现象相吻合.     

过渡金属(Mo,Fe,Co和Ni)基催化剂在电催化还原二氧化碳还原中应用

近年来,全球二氧化碳排放量逐年增加, 对人们赖以生存的生态环境已造成严重威胁, 因此将二氧化碳转化成高附加值的化学品和燃料受到前所未有的广泛关注. 与目前已开发的转化技术(如热催化和光催化等)相比, 电催化二氧化碳转化技术具有稳定的效率?可控的选择性?简单的反应单元和巨大的工业应用潜力, 是一种更为理想的转化技术之一. 从反应动力学来看, 目前的催化剂仍难以克服反应过程中高的能量屏障以及迟缓的反应速度. 另一方面, 电催化二氧化碳转化包含多个质子和电子的耦合过程, 反应过程包含多种路径, 反应产物往往是混合物. 在此背景下, 如何发展高催化效率和高选择性电催化剂成为目前研究的焦点. 在众多的电催化剂中, 贵金属及其合金展现出较高的电催化二氧化碳还原活性, 但储量小的缺点限制了其大规模的工业应用. 铜基材料可以把二氧化碳转化为附加值更高的产品. 然而, 铜基材料仍难以克服选择性差?失活严重和效率低等缺点. 作为一种更廉价的材料, 碳基催化剂具有价廉?比表面积大?导电性好?化学性质稳定以及优异的机械性能等优点在电催化二氧化碳还原中得到了广泛的研究. 然而, 单纯的碳催化剂对于二氧化碳分子活化以及吸附反应中间体能力较低, 导致了碳基材料催化电催化二氧化碳还原活性以及选择性较低. 因此, 开发出可实际应用的高效率和高选择性非贵金属电极材料是当前该技术研究中亟待解决的关键科学问题.过渡金属基化合物在能源转化中展现出巨大的应用潜力. 过渡金属价电子在d轨道, 而d轨道邻近费米能级, d轨道电子填充的变化使得d轨道中心与费米能级相对位置发生变化, 进而展现出多种催化活性. 电催化二氧化碳还原是一个多电子和质子耦合过程, 催化剂的本征活性由其表面电子结构决定. 在此背景下, 过渡金属基化合物价层电子轨道的多变性使其成为提高电催化二氧化碳还原效率和选择性的理想催化剂. 对于电催化二氧化碳还原, 不同中间体的标度关系是制约反应总效率的关键因素. N?rskov等研究发现, MoS2, MoSe2和Ni掺杂 MoS2催化剂上存在不同种类的活性位点. 不同的活性位点可以分别吸附反应中间体并使中间体的吸附过程相对独立, 从而有效打断中间体的标度关系. 2014,Salehi-Khojin等成功把MoS2应用在高效电催化二氧化碳还原中. 边缘Mo原子d带电子靠近费米能级的特性使其具有更高的电催化活性. 其它研究工作者通过引入掺杂物质, 进一步提高了MoS2的电催化二氧化碳还原性能. Fe位点在理论上虽然具有很高的电催化二氧化碳转化活性, 然而目前铁基催化剂的研究相对较少. Co基材料也可用于电催化二氧化碳转化.2016年, Xie等首次制备无机Co基材料用于电催化二氧化碳还原. 部分氧化的钴可以促进速控步骤反应进程, 进而降低整体反应的过电势. 基于此, 制备了超薄的Co3O4片层, 发现价电子轨道中心更靠近费米能级时, 电极材料展现出更高的催化活性. 进一步研究发现氧空穴的存在也可以减小速控步骤的能量屏障. 此外, Ni基材料也被证明具有高的催化二氧化碳转化活性. 目前这些研究工作对如何构建高性能电极材料在理论上给出了指导方向, 并且联系实验证明了方法的可行性. 受到这些工作的启发, 未来可将有巨大潜力的过渡金属基化合物化合物, 例如过渡金属氮化物?过渡金属磷化物?过渡金属碳化物和过渡金属硼化物等, 作为电催化剂研究其二氧化碳还原催化性能. 另外, 就目前的研究来看, 将二氧化碳有效地还原到特定的产物仍存在巨大的挑战. 如何优化过渡金属(Mo, Fe, Co和Ni)基催化剂价层d轨道结构, 促进反应中间体吸附过程, 将是解决催化活性和选择性这一科学问题的关键.     

UPLC-ELSD Determination of 1-Octacosanol in Raw Material and Health Products

Determination of the levels of 1-octacosanol is important in food stuff for the study of its pharmacological activities and health benefits. In this study, a novel, simple and fast internal standard method for the non-derivatization ultra-performance liquid chromatographic determination of 1-octacosanol in raw materials and health products was developed and validated based on evaporative light scattering detection. The linearity (r ² > 0.998), recovery (99.1–100.2%, RSD <2.7%), intra- and inter-day precision (RSD <3.8%), limit of detection (1.0 mg/L), limit of quantification (2.2 mg/L) of the 1-octacosanol were determined. The method was successfully applied to nine real 1-octacosanol products. The results of analyses had close agreement with the labeled claims of 1-octacosanol content in these products. Compared with the classical gas chromatography method, the developed method was simpler, faster and more environmentally friendly due to avoiding any derivatization step. This protocol represents a rapid and feasible method for quality control of 1-octacosanol products.

     

Identification and molecular characterization of a novel flavin-free NADPH preferred azoreductase encoded by <Emphasis Type="Italic">azoB</Emphasis> in <Emphasis Type="Italic">Pigmentiphaga kullae</Emphasis> K24

Background  

Microbial degradation of azo dyes is commonly initiated by the reduction of the azo bond(s) by a group of NADH or NADPH dependant azoreductases with many requiring flavin as a cofactor. In this study, we report the identification of a novel flavin-free NADPH preferred azoreductase encoded by azoB in Pigmentiphaga kullae K24.     

Poly(N‐vinylcarbazole) chemically modified graphene oxide

A new soluble donor‐acceptor type poly(N‐vinylcarbazole)‐covalently functionalized graphene oxide (GO‐PVK) has been synthesized by reaction of DDAT (S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐aceticacid)trithiocarbonate)‐PVK with GO‐toluene‐2,4‐diisocynate. The incorporation of sufficient amount of PVK chains makes the modified GO nanosheets readily dispersible in organic solvents. The resulting material exhibits an enhanced solubility of 10 mg/mL in organic solvents. Covalent grafting of PVK onto the edge and surface of GO nanosheets did not change the carbazole absorption in the ultraviolet region, but substantially reduced the absorption intensity of GO in the visible region. The intensity of the emission band of GO‐PVK at 437 nm was a little bit quenched when compared with that of DDAT‐PVK, suggesting intramolecular quenching from PVK to GO. Such intramolecular quenching process may involve energy or electron transfer between the excited singlet states of the PVK moiety and the GO moiety. The HOMO/LUMO values and the energy bandgap of GO‐PVK experimentally estimated by the onset of the redox potentials are ?5.60, ?3.58, and 2.02 eV, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2642–2649, 2010