膜流动电位测试中Ag-AgCl电极的制备及稳定性研究

膜的动电特性研究中,往往采用流动电位方法。该方法中,Ag-Ag Cl测试电极的质量是影响测试准确性的关键要素。本文采用正交试验设计和方差分析,着重考察电解法制备Ag-Ag Cl电极过程中,电流强度(I)、氯化时间(t)、电解质溶液浓度(CHCl)、电极来源(n)、烘烤温度(T)、活化电极溶液浓度(CKCl)等因素对Ag-Ag Cl电极稳定性的影响。得到Ag-Ag Cl电极的最优制备参数为:电流密度3.0m A/cm2,氯化时间50min,盐酸浓度0.1mol·L-1,烘烤温度120℃,活化电极溶液(KCl)浓度0.001mol·L-1;最显著影响因素为电极来源,显著影响因素为氯化时间和烘烤温度。对最优条件组合下制备的AgAg Cl电极,进行了稳定性实验,结果表明:制备的电极具有较好的稳定性,24h内电极电位漂移量小于0.10mv,7天内电极电位漂移量小于0.2mv;在聚偏氟乙烯中空纤维超滤膜流动电位测试中,流动电位与流动压差具有良好的线性和可重复性,回归曲线R20.99,变化规律符合Helmholtz-Smoluehowski公式,可以较好满足膜的流动电位测试要求。     

Multiscale expansions in discrete world

In this paper, we show the attainability of KdV equation from some types of nonlinear Schrödinger equation by using multiscale expansions discretely. The power of this manageable method is confirmed by applying it to two selected nonlinear Schrödinger evolution equations. This approach can also be applied to other nonlinear discrete evolution equations. All the computations have been made with Maple computer packet program.     

Silicon‐containing trifunctional and tetrafunctional cyanate esters: Synthesis,cure kinetics,and network properties

The synthesis and physical properties of new silicon‐containing polyfunctional cyanate ester monomers methyl[tris(4‐cyanatophenyl)]silane and tetrakis(4‐cyanatophenyl)silane, as well as polycyanurate networks formed from these monomers are reported. The higher crosslinking functionality compared to di(cyanate ester) monomers enables much higher ultimate glass transition temperatures to be obtained as a result of thermal cyclotrimerization. The ability to reach complete conversion is greatly enhanced by cocure of the new monomers with di(cyanate ester) monomers such as 1,1‐bis(4‐cyanatophenyl)ethane. The presence of silicon in these polycyanurate networks imparts improved resistance to rapid oxidation at elevated temperatures, resulting in char yields as high as 70% under nitrogen and 56% in air in the best‐performing networks. The water uptake in the silicon‐containing networks examined is 4–6 wt % after 96 h of immersion at 85 °C, considerably higher than both carbon‐containing and/or di(cyanate ester) analogs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 767–779     

Amine catalysis in phosphoryl transfer from 2,4-dinitrophenyl phosphate in aprotic and protic solvents

Reactions of tetra-n-butylammonium 2,4-dinitrophenyl hydrogen phosphate, (ArPH)^?(R₄N)⁺, in aprotic and protic solvents, in the absence and in the presence of alcohols or water, ROH, are compared with analogous reactions of the salt in the presence of hindered and unhindered amines, e.g. diisopropylethyl amine and quinuclidine. Similar studies are performed with the acid, ArPH₂, in the presence of variable amounts of amines. The release of phenol and the fate of the phosphorus compounds are followed by ¹H and ³¹P NMR spectrometry. In the absence of free unhindered amine, reactions of the monoanion are relatively slow, sensitive to steric hindrance in the alcohol, and incapable of producing t-butyl phosphate from t-butanol; reactions of the dianion are relatively fast, insensitive to steric hindrance in the alcohol, and produce t-butyl phosphate. In the presence of free unhindered amine, reactions of the monoanion are relatively fast but still sensitive to steric hindrance in the alcohol, and hence do not produce t-butyl phosphate. The intermediate CH(CH₂CH₂)₃⁺NP(O)(OH)O^? is detected in the presence of quinuclidine. Reactions of the dianion in the presence of unhindered amines are analogous to those observed in the presence of hindered amines. The uncatalyzed and the nucleophilic amine-catalyzed reactions of the monoanion are assumed to proceed via oxyphosphorane, P(5), intermediates. The dianion reactions, which are not susceptible to nucleophilic catalysis, are assumed to proceed via the monomeric metaphosphate ion intermediate, PO₃^?. Significant effects related to solvent properties are observed in these reactions.     

示波器观测动态磁滞回线实验中曲线描绘浅析

给出了示波器观测铁磁材料物质磁滞回线的基本原理,针对实验中常见的错误,介绍了如何选取合理的数据并快速描绘磁滞回线的技巧。     

Electrocyclic [1,5] hydrogen shift in the thermal elimination kinetics of phenyl acetate and p-tolyl acetate in the gas phase: a density functional theory study

The kinetics and mechanisms of thermal decomposition of phenyl acetate and p-tolyl acetate in the gas phase were studied by means of electronic structure calculations using density functional theory methods: B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), B3PW91/6-31G(d,p), B3PW91/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBE/6-31G(d,p) and PBE/6-31++G(d,p). Two possible mechanisms have been considered: mechanism A is a stepwise process involving electrocyclic [1,5] hydrogen shift to eliminate ketene through concerted six-membered cyclic transition-state structure, followed by tautomerisation of cyclohexadienone or by 4-methyl cyclohexadienone intermediate to give the corresponding phenol. Mechanism B is a one-step concerted [1,3] hydrogen shift through a four-membered cyclic transition-state geometry, to produce ketene and phenol or p-cresol. Theoretical calculations showed reasonable agreement with experimental activation parameters when using the Perdew, Burke and Ernserhof (PBE)functional, through the stepwise [1,5] hydrogen-shift mechanism. For mechanism B, large deviation for the entropy of activation was observed. No experimental data were available for p-tolyl acetate; however, theoretical calculations showed similar results to phenyl acetate, thus supporting the stepwise mechanism for both phenyl acetate and p-tolyl acetate.     

Effect of trabecular bone material properties on ultrasonic backscattering signals

In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed. The backscatter coefficient （BSC） and integrated backscatter coefficient （IBC） were numerically investigated for varying trabecular bone material properties, including density, Lame coefficients, viscosities, and resistance coefficients. The results show that the BSC is a complex function of trabecular bone density, and the IBC increases as density increases. The BSC and IBC increase with the first and second Lame coefficients. While not very sensitive to the second viscosity of the trabeculae, the BSC and IBC decrease as the first viscosity and resistance coefficients increase. The results demonstrate that, in addition to bone mineral density （BMD） and microarchitecture, trabecular material properties significantly influence ultrasonic backseattering signals in cancellous bones. This research furthers the understanding of ultrasonic backscattering in cancellous bones and the characterization of cancellous bone status.     

Tension trapping of carbonyl ylides facilitated by a change in polymer backbone

Epoxidized polybutadiene and epoxidized polynorbornene were subjected to pulsed ultrasound in the presence of small molecules capable of being trapped by carbonyl ylides. When epoxidized polybutadiene was sonicated, there was no observable small molecule addition to the polymer. Concurrently, no appreciable isomerization (cis to trans epoxide) was observed, indicating that the epoxide rings along the backbone are not mechanically active under the experimental conditions employed. In contrast, when epoxidized polynorbornene was subjected to the same conditions, both addition of ylide trapping reagents and net isomerization of cis to trans epoxide were observed. The results demonstrate the mechanical activity of epoxides, show that mechanophore activity is determined not only by the functional group but also the polymer backbone in which it is embedded, and facilitate a characterization of the reactivity of the ring-opened dialkyl epoxide.     

Medlar (<Emphasis Type="Italic">Achras Sapota</Emphasis> L.) as Oral Contrast Agent for MRI of the Gastrointestinal Tract

Magnetic resonance imaging (MRI) of the gastrointestinal (GI) tract is still limited due to the lack of widely available oral contrast agents (OCA). The availability of OCA for MRI of the GI tract is a necessity; different fruits might be implemented as OCA in order to solve this need throughout the year. The objective of this study is to present an alternative fruit as a clinical OCA for MRI of the GI tract, Achras sapota L. (common medlar). Both physical and chemical characterization of the medlar was performed. It was also tested in situ and in vivo as an OCA for MRI of the GI tract. Results showed that this fruit had a diamagnetic behavior, although it has enough iron, manganese and copper to contrast the GI tract in T ₁- and T ₂-weighted images. Thus we conclude that the medlar fruit has shown a potential as an OCA in GI evaluation by MRI, so it can be considered as an alternative in complementation of natural OCA.