脉冲型介电电泳颗粒特异性分离的数值仿真研究

通过数值仿真研究了直径分别为3μm、5μm、10μm的聚苯乙烯微球在脉冲型介电电泳作用下的动态分离过程,结果表明:通过合理地调整流速、脉冲周期、电压幅值可以实现对颗粒混合物的特异性分离;在背景流速为30μm/s 时,得到了在单步内提取中等粒径(直径5μm)颗粒的参数区间(电势6~7.5V,脉冲周期1.5~2.6s).同时,进一步研究了其它条件不变时,占空比和电极非对称率对提取中等粒径颗粒的影响,结果表明:随着周期的增加,提取颗粒所需的占空比相应地增加;而随着电极非对称率的增加,DEP力的强度逐渐增加,提取颗粒所需的周期也相应增加.仿真结果与实验及已有分析解符合较好,为器件的系统设计和优化器件提供了依据.     

Investigation on the combustion efficiency and residual of nitrocellulose–alcohol humectant mixtures

To have an insight into the fire properties of nitrocellulose–isopropanol and –ethanol mixtures, the experimental data in previous work are further extracted and analyzed carefully. Generally, the effective heats of combustion of the two samples characterized by both the peak and mean heat release rates decrease with the increasing external irradiance levels. The combustion efficiencies characterized by the ratio of carbon dioxide (CO₂) to carbon monoxide (CO), regardless of the maximum and mean values, also show the similar decreasing tendency, exhibiting a lower combustion efficiency at elevated external radiation. With respect to the X-ray photoelectron spectroscopy results, the two nitrocellulose–alcohol mixtures appear to yield the similar species of combustion residuals, but slightly different in the atomic concentrations, which may be due to the differences in the alcohol humectant and nitrogen content in nitrocellulose substrate. These findings are expected to provide further understanding of fire properties of nitrocellulose–alcohol mixtures and help with fire investigation of such type of fires.

     

Spectroscopic studies of a BINAM-based sensor: Highly selective fluorescent recognition of lysine in water solution through a nucleophilic substitution reaction

A BINAM-based compound (R)-1 is found to show significant fluorescence enhancement in the presence of Lys in aqueous solution (1%DMF). This probe achieves highly selective fluorescent recognition of Lys even in the presence of other natural amino acids. It can be used as a sensitive as well as selective fluorescent probe for Lys. The mechanism for the interaction of (R)-1 with Lys was studied by NMR and HRMS.     

临界半线性波动方程解的有限时间破裂

研究了带临界指标的半线性波动方程u_tt-Δu=（1+|x|²）^α|u|^p小初值Cauchy问题解的破裂,证明了该问题在p=p_c（n）时不存在整体解.     

W/O液滴绕流微柱阵列的数值模拟研究

基于COMSOL Multiphysics 4.1层流两相流模型,通过数值模拟研究了连续相流速一定的情况下大接触角(?=160°)的油包水(W/O)液滴绕流微柱阵列的二维运动。通过相场方法考虑表面张力的影响,实现对油-水界面的追踪,获得了W/O液滴的运动状态,重点考查了液滴尺寸对运动特性的影响。模拟结果表明,初始尺寸不同的液滴变形后,长度上存在差异,但厚度基本一致,尺寸介于100?m~150?m液滴的运动速度与液滴尺寸无关。进一步研究了利用尖楔对液滴进行分割的过程,发现液滴脱离末端微柱时,其垂向位置高度与液滴尺寸密切相关,呈先线性增加后趋于定值的特点,利用这一预定位功能及尖楔结构可以获得尺寸可控的均匀子液滴。数值方法与已有实验结果基本一致,且可以很好地表现W/O液滴与微柱的相互作用,揭示液滴的流动细节和运动规律,为设计更为复杂的液滴微流控芯片提供了支撑。     

The influence of pre-stressing on breakdown characteristics in liquid silicone rubber

Liquid silicone rubber (LSR) has increasingly been used as one kind of inner insulating material. Studies of space charge and its effect during pre-stressing and breakdown (BD) process in LSR were carried out. DC electrical breakdown field (BDF) of LSR specimens before and after DC electrical pre-stressing was measured. The space charge characteristics of LSR specimens under different DC electrical pre-stressing fields and that during the BD processes were measured by a pulsed electro-acoustic (PEA) method. It was found that the amount of homo space charges near electrodes increases obviously as a rising electric field is applied. Whether the polarity of BDF is the same as that of the pre-stressing field or not, the DC BDF of pre-stressed specimens is higher than that of specimens without pre-stressing. However, the pre-stressing does not show monotone and saturation effects, as generally occurs in the literature. In hetero BD experiments for example, with an increasing pre-stressing field, the DC BDF first increases up to 14.5% at the pre-stressing field of 25 kV/mm and then decreases. The influence of pre-stressing on the BD processes in LSR are discussed. The relationship between space charge and the DC BDF was related to the microstructure of nano-silica and LSR molecules.     

Facile synthesis of ternary AgInS2 nanowires and their self-assembly of fingerprint-like nanostructures

Nanowires (NWs) and self-assemble nanostructures made of chalcogenide semiconductor nanocrystals (NCs) are of great interests to the fundamental studies and practical applications. In this study, we reported a seeded-mediated growth of AgInS₂ NWs and their intriguing self-assembly nanostructures with fingerprint-like shape. The key to the formation and self-assembly of AgInS₂ NWs was the presence of In-S species that was a type of molecular metal chalcogenide complexes, serving as specific inorganic ligands for the growth of NWs and cross-linker molecules for the self-assembly of fingerprint-like nanostructures. Systematic studies were carried out to investigate the reaction factors, including the thermodynamics, amount and type of In precursors, and 1-dodecanethiol usage, to the success of the desired products.     

Studies on synthesis and characterization of waterborne polyurethane from epigallocatechin-3-gallate

A novel waterborne polyurethane (PU), based on (-)-epigallocatechin-3-gallate (EGCG) that contains phenolic hydroxyl group, was successfully synthesized and characterized. The structural study of PU based on EGCG through FT-IR confirmed the incorporation of EGCG into the chain of PU. The results of X-ray diffraction (XRD) showed that the introduction of EGCG changed the crystallization behavior of the pure waterborne PU. Thermogravimetric analysis (TGA) results indicated that the PU samples exhibited improved thermal decomposition temperature. The degree of phase segregation of modified PU was confirmed by Scanning electron microscope (SEM) analysis. The physical and biodegradable properties of modified PU indicated a comprehensive performance.     

CO2 Reduction Mechanism on the Cu2O(110) Surface: A First-Principles Study

Cu₂O is an attractive catalyst for the selective reduction of CO₂ to methanol. However, the mechanism of the reaction and the role of the Cu species in different oxidation states are not well understood yet. In this work, by first-principles calculations, we investigate the mechanism of the reaction on the Cu₂O(110) surface, which is the most selective for methanol, in different degrees of reduction: ideal surface, slightly reduced surface (SRS), and partially reduced surface (PRS). The most favorable reaction pathways on the three surfaces were identified. We found that Cu(I) on the ideal surface is not capable of chemisorbing CO₂, but surface oxygen serves as the active site which selectively converts CO₂ to CH₃OH with a limiting potential of −0.77 V. The Cu(0) on the SRS and PRS promotes the adsorption and reduction of CO₂, while the removal of the residue O* becomes potential/rate limiting with a more negative limiting potential than the ideal surface. The SRS is selective to methanol while the PRS becomes selective to methane. The result suggests that the key to high methanol selectivity is to avoid the reduction of Cu(I), which provides a new strategy for the design of more efficient catalysts for selective CO₂ reduction to methanol.