小时滞梯度系统的动力学行为

该文研究下列具有小时滞的一般非线性梯度型发展方程_tu+Au=f(u(t),u(t-τ)).证明了当时间趋于无穷大时,时滞方程的每一个有界解将收敛于某一个平衡点,只要时滞足够小,这意味着时滞系统的行为非常类似非时滞系统.这里的方法主要是基于梯度系统不变集的Morse结构和发展方程的几何理论.这个结果的证明分两步完成:首先,在梯度系统和有限个孤立平衡点的假设下,证明了一定存在一个足够小的时滞使得时滞方程的任一个有界解将会最终进入并停留在某一个平衡点的邻域里面;其次,在双曲平衡点的假设下,运用指数二分性和一系列的估计,证明了一定存在ε0和足够小的τ0使得任一个落于某个平衡点ε-邻域内的解最终收敛于该平衡点,当时间趋于无穷大时.     

Studies on the Thermodynamic and Kinetic Properties of the Reactions of Ti+ with Sulfur Transfer Reagent SCO Along the C═S Bond Activation Branch at 200–1200K

Theoretical studies on the thermodynamic and kinetic properties of the reactions of Ti⁺ with sulfur transfer reagent SCO via the C═S bond activation pathway have been carried on using DFT/B3LYP method, general statistical thermodynamics, and Eyring transition state theory with Wigner correction. The relevant reactions include reaction 1 ⁴ Ti⁺+¹SCO → ⁴ IM ₁ → ⁴ TS ₁ → ⁴ IM ₂ → ⁴ TiS⁺+ ¹ CO, and reaction 2 ⁴Ti⁺+¹SCO →⁴IM₁→ CP →²IM₂→²TiS⁺+¹CO in which the spin multiplicity changes from the quartet state to the doublet state in the crossing region. It is concluded that the increase of the temperature is favored to the reaction 1 process, since the equilibrium constants (K) rises from 0.566 × 10[P]-9 at 200 K to 0.109 × 10⁰ at 1200 K, and the reaction rate constant (k) from 0.222 × 10⁰ s[P]-1 at 200 K to 0.540 × 10 ¹¹ s[P]-1 at 1200 K. Moreover, reaction 1 is endothermic, and non-spontaneous in the way the entropy increases, while reaction 2 is exothermic and spontaneous in the way their entropy decreases. The reaction path 2 is the energetically favorable channel, and its thermodynamic data change not largely with the rise of temperature.     

Nitroxide‐mediated Living Radical Polymerization of Styrene with Fluorescent Initiator

A fluorescence method was used for determination of marked chain ends in polystyrene samples prepared by 4‐substituted TEMPO type nitroxide‐mediated living free radical polymerization of styrene. 2,2,6,6‐Tetramethyl‐1‐(1‐phenylethoxy)‐piperidin‐4‐yl‐4‐pyren‐1‐ylbutanoate (PYNOR) was prepared and used as an unimolecular initiator bearing pyrene as a fluorescence mark on mediating nitroxide fragment. The bulk polymerization of styrene at 120°C, in the presence of new unimolecular initiator, was a typical nitroxide mediated living radical polymerization. For comparison, two different molar ratios of initiator and monomer (1∶400 and 1∶1000 initiator ‐ monomer [I:M]) were used for polymerization. When I:M=1∶400, the obtained polydispersity was 1.12 and maximum molecular weight 27,000 g/mol was obtained at 62% conversion. For ratio 1∶1000, slightly higher polydispersity was obtained ?1.26 and the molecular weight was 53,000 g/mol at 70% conversion. The content of the polystyrene chains bearing mediating nitroxide fragment was determined by fluorescence spectroscopy. The intensity of pyrene fluorescence decreased as the molar mass, and the conversion increased as well. The extent of the incorporation of chromophore at propagating chain end or “livingness” of polymerization decreased despite the fact that the polydispersity did not change. The extent of side reaction leading to broadening of polydispersity is suppressed due to the high viscosity of the system at higher conversion. A low extent of “livingness” will have a very negative effect on possible preparation of block copolymers.     

A Novel Fission Process in Mini-emulsion RAFT Polymerization: Shell Crosslinked Nanoparticles as a Model

Shell crosslinked nanoparticles, prepared from copolymerization of styrene and disulfide crosslinker, using poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) as stabilizer and macroinitiator, exhibited a special fission behavior during the mini-emulsion RAFT polymerization process.     

The role of the solvation shell decomposition of alkali metal ions in their selective complexation by resorcinarene and its cavitand

2-Methylresorcinarene and its methylene-bridged cavitand derivative as host compounds were investigated in selective complexation of alkali metal ions as guests in methanol media by photoluminescence measurements. These host molecules possess either flexible (2-methylresorcinarene) or rigid (cavitand) molecular skeleton. The Benesi–Hildebrand method and the van't Hoff theory have been applied to determine the stability constants and the thermodynamic parameters, respectively. Considerable interactions between 2-methylresorcinarene and Li⁺ or Na⁺ ions have been observed while the rigid cavitand derivative can interact only with K⁺ or Cs⁺ ions. Neither the complexes of 2-methylresorcinarene with K⁺ or Cs⁺ nor those of the cavitand derivative with Li⁺ or Na⁺ ions are stable at room temperature in methanol media. Quantum-chemical investigations justified that only solvated Li⁺ and Na⁺ ions can form stable complexes with 2-methylresorcinarene while unsolvated K⁺ and Cs⁺ ions form stable complexes with the methylene-bridged cavitand. These results highlight that the stability of the guest solvation shell and its size could play a key role in the selectivity behaviour of host molecules.     

A UFLC‐MS/MS method with a switching ionization mode for simultaneous quantitation of polygalaxanthone III,four ginsenosides and tumulosic acid in rat plasma: application to a comparative pharmacokinetic study in normal and Alzheimer's disease rats

A fast, sensitive and reliable ultra fast liquid chromatography‐tandem mass spectrometry (UFLC‐MS/MS) method has been developed and validated for simultaneous quantitation of polygalaxanthone III (POL), ginsenoside Rb1 (GRb1), ginsenoside Rd (GRd), ginsenoside Re (GRe), ginsenoside Rg1 (GRg1) and tumulosic acid (TUM) in rat plasma after oral administration of Kai‐Xin‐San, which plays an important role for the treatment of Alzheimer's disease (AD). The plasma samples were extracted by liquid–liquid extraction using ethyl acetate–isopropanol (1:1, v/v) with salidrdoside as internal standard (IS). Good chromatographic separation was achieved using gradient elution with the mobile phase consisting of methanol and 0.01% acetic acid in water. The tandem mass spectrometric detection was performed in multiple reaction monitoring mode on 4000Q UFLC‐MS/MS system with turbo ion spray source in a negative and positive switching ionization mode. The lower limits of quantification were 0.2–1.5 ng/ml for all the analytes. Both intra‐day and inter‐day precision and accuracy of analytes were well within acceptance criteria (±15%). The mean absolute extraction recoveries of analytes and IS from rat plasma were all more than 60.0%. The validated method has been successfully applied to comparing pharmacokinetic profiles of analytes in normal and AD rat plasma. The results indicated that no significant differences in pharmacokinetic parameters of GRe, GRg1 and TUM were observed between the two groups, while the absorption of POL and GRd in AD group were significantly higher than those in normal group; moreover, the GRb1 absorbed more rapidly in model group. The different characters of pharmacokinetics might be caused by pharmacological effects of the analytes. Copyright © 2013 John Wiley & Sons, Ltd.     

Synergistic effects between silicon-containing flame retardant and potassium-4-(phenylsulfonyl)benzenesulfonate (KSS) on flame retardancy and thermal degradation of PC

A novel flame retardant (PSiN), containing silicon and nitrogen, was synthesized using N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH-602) and diphenylsilanediol through solution polycondesation and it was used together with potassium-4-(phenylsulfonyl)benzenesulfonate (KSS) to prepare a flame-retardant system for polycarbonate (PC). The structure and thermal property of PSiN were characterized by Fourier transform infrared spectroscopy (FTIR), ¹HNMR and thermogravimetric analysis (TG) tests. Flammability and thermal behaviors of PC/KSS/PSiN systems were estimated by limited oxygen index (LOI), cone calorimeter, vertical burning test (UL-94), and TG tests. The results showed that the flame retardancy and char residues of PC/KSS system were improved with the addition of PSiN. When 1 mass% PSiN and 0.5 mass% KSS were incorporated, the LOI value of PC was found to be 46, and class V-0 of the UL-94 test. Moreover, both the heat release rate and the total heat release of PC/KSS/1 mass% PSiN decreased compared with those of PC and PC/KSS systems. The microstructures observed by scanning electron microscopy and FTIR indicated that the surface of the char for PC/KSS/PSiN system hold a more cohesive and denser char structure when compared with the pure PC and PC/KSS system.     

Improved electrochemical performance of nano-crystalline Li2FeSiO4/C cathode material prepared by the optimization of sintering temperature

Li₂FeSiO₄/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li₂FeSiO₄/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li₂FeSiO₄ nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li₂FeSiO₄/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA?h g^?1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li₂FeSiO₄/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.     

含巯基/二硫键聚合物生物材料

含巯基/二硫键聚合物生物材料具有多种良好的性能,作为药物、基因等的释放载体在生物医学领域具有广泛的应用前景。随着基因工程和组织工程的发展,含巯基/二硫键聚合物生物材料的可生物降解性得到高度重视,而怎样改善其降解性能成为限制其应用的关键因素。由于二硫键在细胞外环境里保持稳定,在细胞溶质的还原环境中容易发生断裂,因此在制备新型基因、药物等释放载体上,二硫键充当了重要的角色,它的引入为聚合物生物材料的生物降解性能的设计与改善提供了一条重要的途径。本综述重点以聚合物水凝胶、聚合物微胶束、囊泡等为例,从巯基/烯的光聚合反应、Michael加成反应、氧化还原反应的角度,介绍了巯基/烯在聚合物中形成二硫键的不同途径的研究进展,并详细论述了基因载体、蛋白质载体、小分子药物载体三种还原敏感型材料的制备、表面修饰和改性的进展情况,进一步强调含巯基/二硫键聚合物生物材料的研究在生物医学领域应用的重要性。     

固相萃取–超高效液相色谱三重四级杆质谱联用法测定水中四环素、土霉素及罗红霉素

建立了固相萃取–超高效液相色谱三重四级杆质谱联用法同时测定水中的罗红霉素、四环素和土霉素残留。水样经过固相萃取纯化、富集,液质联用分析,采用甲酸溶液和乙腈作为流动相,在5 min内完成对3种目标化合物的分析,3种目标化合物的方法检出限介于0.08~0.35 ng/L之间,测定结果的相对标准偏差为1.4%~5.6%,空白样品和实际样品的加标回收率分别为82.5%~114%,71.5%~126%。