一个二次多项式混沌系统的均匀化及其熵分析

利用已有理论给出了一个二次多项式混沌系统,证明了该系统与Tent映射拓扑共轭,给出了该混沌系统的概率密度函数;并根据此概率密度函数,得到了轨道均匀分布的反三角函数映射;对均匀化前后的混沌系统在不同参数下产生序列的信息熵、Kolmogorov熵、离散熵的特性进行了分析,结果显示均匀化后产生的混沌序列混沌程度不改变且具有更好的均匀性.     

正交相Fe2(MoO4)3的制备与表征及其负膨胀行为的第一性原理研究

采用水热合成法制备出Fe₂(MoO₄)₃样品, 并用高温X-射线衍射、热重和差示扫描量热同步热分析仪对其进行表征, 发现样品在510 ℃附近发生低温单斜相和高温正交相之间的可逆相变, 且正交相表现出负膨胀特征. 采用第一性原理计算了正交相Fe₂(MoO₄)₃ 的原子、电子结构以及声子谱、声子态密度, 并和可获得的实验结果进行了系统的比较. 结果显示正交相Fe₂(MoO₄)₃中MoO₄四面体较之FeO₆八面体具有更强的刚性. 发现最低频的光学支处具有最负的格林乃森(Grüneisen)系数, MoO₄四面体和FeO₆ 八面体相连的桥氧原子的横向振动、FeO₆八面体柔性扭曲转动以及MoO₄四面体的刚性翻转共同导致了Fe₂(MoO₄)₃负膨胀现象的发生.     

液滴撞击液膜过程的格子Boltzmann方法模拟

本文采用格子Boltzmann方法对液滴撞击液膜过程进行了研究, 主要考察了雷诺数(Re)、韦伯数(We)、相对液膜厚度 (h) 以及表面张力 (σ) 等物理参数对界面运动过程的影响. 首先, 随着Re数和We数的增加, 可以明显观察到液滴撞击液膜过程中形成的皇冠状水花以及卷吸现象; 当Re数较大时, 液体会发生飞溅, 由液体飞溅形成的小液滴则会继续下落, 并与液膜再次发生碰撞. 其次, 当相对液膜厚度较小时, 液滴撞击液膜并最终导致液膜断裂; 然而随着相对液膜厚度的增大, 尽管撞击过程溅起的液体会越来越多, 但是液膜并不会发生断裂. 再次, 随着表面张力的增大, 界面变形阻力增大, 撞击过程中产生的界面形变也逐渐减弱. 最后还发现皇冠(由液滴溅起形成)半径r 随时间满足r/(2R) ≈ α√Ut/(2R), 这一结果与已有结论是一致的.     

Enhanced stability of ZnTPPS by polymeric gold nanoparticles in acidic aqueous solutions

Novel kind of core-shell corona complex micelles were prepared, which enhanced both the hydrolytic stability and the photostability of water-soluble zinc tetrakis(4-sulfonatophenyl) porphyrin (ZnTPPS) in acidic aqueous solutions. The core-shell gold nanoparticles (AuNPS) were synthesized by reducing HAuCl₄ and di-thioester terminated block copolymer, poly(Nisopropylacrylamide)-block-poly(4-vinylpyridine) (PNIPAM-b-P4VP). The complex micelles with gold core, P4VP/ZnTPPS shell and PNIPAM corona were formed by simple mixing of gold nanoparticles and ZnTPPS. The photochemical properties of the complex micelles were studied by UV–Visiblespectroscopy and fluorescence spectroscopy. The results showed trapping of ZnTPPS in the positively charged micellar shell that effectively prevented demetallation of the ZnTPPS that would occur in acidic aqueous solutions. Furthermore, with appropriate concentration of gold nanoparticles, ZnTPPS in the complex micelle had excellent photostability by suppression of generation of reactive oxygen species (ROS). The enhanced stability of ZnTPPS in acidic aqueous media could be extensively used for photocatalysis and in solar cells.     

How does a CC double bond cleave in the gas phase? Fragmentation of protonated ketotifen in mass spectrometry

In the literature, it is reported that the protonated ketotifen mainly undergoes C?C double bond cleavage in electrospray ionization tandem mass spectrometry (ESI‐MS/MS); however, there is no explanation on the mechanism of this fragmentation reaction. Therefore, we carried out a combined experimental and theoretical study on this interesting fragmentation reaction. The fragmentation of protonated ketotifen (m/z 310) always generated a dominant fragment ion at m/z 96 in different electrospray ionization mass spectrometers (ion trap, triple quadrupole and linear trap quadrupole (LTQ)‐orbitrap). The mechanism of the generation of this product ion (m/z 96) through the C?C double bond cleavage was proposed to be a sequential hydrogen migration process (including proton transfer, continuous two‐step 1,2‐hydride transfer and ion‐neutral complex‐mediated hydride transfer). This mechanism was supported by density functional theory (DFT) calculations and a deuterium labeling experiment. DFT calculations also showed that the formation of the product ion m/z 96 was most favorable in terms of energy. This study provides a reasonable explanation for the fragmentation of protonated ketotifen in ESI‐MS/MS, and the fragmentation mechanism is suitable to explain other C?C double bond cleavage reactions in mass spectrometry. Copyright © 2016 John Wiley & Sons, Ltd.     

A Sensitive Electrochemical Sensor Based on Solution Polymerized Molecularly Imprinted Polymers for Procaine Detection

A sensitive and selective method for the determination of procaine hydrochloride using molecularly imprinted polymers (MIPs) modified glassy carbon electrodes was developed. The MIPs were prepared by solution polymerization using procaine hydrochloride as the template molecules and acrylic acid (AA) and vinyltriethoxysilane (WD‐20) as the functional monomer and cross‐linking agent, respectively. A film was formed on the surface of the glassy carbon electrodes and later cross‐linked with ethanol as solvent. Next, these electrodes were employed to detect procaine hydrochloride by differential pulse voltammetry (DPV). Under the optimized conditions, good linearity (correlation coefficient of 0.9986) was observed between the oxidation peak current and the concentration of procaine hydrochloride in the range of 4.0×10^?8 to 2.4×10^?5 M in a pH 7.0 0.04 M phosphate buffer solution, and the detection limit (S/N=3) was 1.02×10^?8 M. In addition, the stability and reproducibility of the sensors were satisfactory. Moreover, the concentration of procaine hydrochloride in human blood serum samples was detected, and its recoveries ranged from 97.5 % to 106.4 % with RSD less than 2.15 %. These results suggest that the prepared molecularly imprinted electrochemical sensors can be used for the determination of procaine in clinical studies.     

Iodine-promoted direct sulfenylation of 2,3-dihydroimidazo[2,1-b]thiazoles with disulfides

A novel and facile method for the direct sulfenylation of 2,3-dihydroimidazo[2,1-b]thiazoles with disulfides has been developed. The transformation is promoted by iodine under metal-free conditions, providing the corresponding products in moderate to good yields.     

A study of the interaction between polyvinylpyrrolidone and gemini surfactant G12-3-12 by NMR

The interaction between a water-soluble polymer polyvinylpyrrolidone (PVP) and a gemini surfactant N,N'-didodecyl-N,N,N',N'-tetramethyl-N,N'-propanediyl-diammonium dibromide (G12-3-12) was investigated by means of NMR in a D₂O solution at 298 K. The critical micelle concentration (СMC), critical aggregation concentration (СAC) and adsorption reached the saturated concentration (C2) were confirmed by chemical shift and self-diffusion coefficients, respectively. The results of the relaxation time ratio (T_R = T₂/T₁) of G12-3-12 show that the motion of the ionic head N⁺–CH₃^* proton (G6) is seriously restricted, and thus, it can be proved that the cationic head groups are situated in the hydrophilic layer of the micelle. The size of the mixed-aggregates in the G12-3-12/PVP solution is larger than pure G12-3-12 micelles according to self-diffusion coefficients, indicating that the G12-3-12 and PVP has formed mixed micelles, and ionic heads N⁺–CH₃^* become more tightly packed in the hydrophilic layer of the micelle shell. On the other hand, strong cross peaks, such as G1-P2, G1-P3, and G2-P3, appear in the 2D nuclear Overhauser enhancement spectroscopy (2D NOESY) spectra of the G12-3-12/PVP system, further indicating that the interaction sites are located between the hydrophobic tail of G12-3-12 and PVP ring.     

Self-sacrificial template method to MnO2 microspheres as highly efficient electrocatalyst for oxygen evolution reaction

Journal of Solid State Electrochemistry - ε-MnO2 microspheres have been synthesized using a self-sacrificial template method by annealing MnCO3 microspheres. The transformation process from...     

Hybrid porous Ni(OH)2-MnO2 nanosheets/plasma-grafted MWCNTs for boosted supercapacitor performance

The utilization of nickel hydroxide and manganese dioxide solely as high-performance supercapacitive materials is hindered by their low capacitance retention and electrical conductivity. As Ni(OH)₂ and MnO₂ give a synergistic effect, porous Ni(OH)₂-MnO₂ nanosheets with a thickness of 9 nm are successfully grown on carbon fiber (CF) via a single-step hydrothermal co-deposition method. Multi-walled carbon nanotubes (CNT) are grafted with maleic anhydride (MA) through plasma-grafted process, followed by thiol-ene reaction to synthesize CNT-MA−S (CMS) to increase their aqueous dispersion behavior. The electrochemical properties of Ni(OH)₂-MnO₂ are further enhanced by dip-coating CMS on nanosheets. The composition and morphology of CMS and Ni(OH)₂-MnO₂ nanosheets are characterized using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), electron spectroscopy for chemical analysis (ESCA), transmission electron microscopy (TEM), thermogravimetric analyses (TGA), nuclear magnetic resonance (NMR), and Raman spectroscopy. The electrochemical characteristics of fabricated electrodes are analyzed using cyclic voltammetry and chronopotentiometry methods. CF−Ni(OH)₂-MnO₂/CMS electrode is successfully synthesized without using any binder, exhibited ultrahigh specific capacitance (2049 F g⁻¹ at a current density of 1 A g⁻¹), and excellent capacitance retention (>80 %) at 2 A g⁻¹ charge/discharge rate after 5000 cycles.