Facile route for preparation of silver nanoparticle-coated precipitated silica

In this research, a facile route was used to prepare silver nanoparticle-coated precipitated silica using sodium silicate, a cheap precursor. Precipitated silica (PS) was synthesized by dropping 8% H₂SO₄ into a mixed solution of sodium silicate 24% (Na₂O·3.4SiO₂) and NaCl 4%; under constant stirring. The precipitated silica was then modified by simultaneous addition of 3-aminopropyltriethoxysilane (3-APTES) and 8% H₂SO₄. The resulting material was aged at 80 °C for 1 h to produce amino-functionalized precipitated silica (AFPS). Silver nanoparticle-coated precipitated silica (Ag-NPS) was synthesized by adding silver nitrate (AgNO₃). The synthesis procedure also involved mixing for 2 h and dropping 0.05 M sodium borohydride (NaBH₄). The final products, namely, PS, AFPS, and Ag-NPS were characterized using BET analyzer, FE-SEM, TEM and XRD. Silver nanoparticles with an average size ranging from 18 to 25 nm were found mostly coated on the exterior layer of the precipitated silica. The synthesis method reported in this work is facile and might be used for large-scale industrial production of inexpensive Ag-NPS.     

The influence of TiO2 nanoparticle incorporation on surface potential decay of corona-resistant polyimide nanocomposite films

PI nanocomposite films containing surface modified nanoparticles by employing silane coupling agent were prepared using in-situ dispersion polymerization process. The surface potential decay measurements on films were investigated over the different negative corona-charged voltages and times in a controlled environment where temperature and relative humidity were kept at 21 °C and 45%, respectively. There is a significant change in the surface potential decay characteristics after nano-fillers were introduced into polyimide. The surface potential decay pattern depends also on the amount of nano-fillers. The possible surface potential decay and corona resistance mechanisms responsible for the observed phenomena were discussed.     

高压下AlN的电子结构和光学性质

运用密度泛函理论体系下的平面波赝势(PWP)和广义梯度近似(GGA)方法,利用第一性原理计算了不同压强下六方纤锌矿结构AlN晶体的晶格常数、总能量、电子态密度、能带结构、光反射系数与吸收系数。通过比较能带结构的变化行为,得出 AlN在16.7Gpa附近存在等结构相变,即由直接带隙结构转变为间接带隙结构。同时,结合高压下的态密度分布图和能级移动情况,分析了AlN在高压下的光学性质,吸收谱有向高能端移动(蓝移) 的趋势。     

基于改进光谱特征拟合算法的高光谱数据矿物信息提取

根据光谱特征拟合算法在实际应用中存在的问题,介绍一种改进光谱特征拟合算法,该算法综合常规的特征拟合处理和地物光谱吸收特征参量约束为一体,能更细致地进行高光谱数据地物信息提取.实验基于不同空间分辨率和信噪比的高光谱数据,编程实现改进光谱特征拟合算法对实验区的白云母、方解石、绿泥石等蚀变矿物信息提取,与常规光谱特征拟合和光谱角制图处理结果的比较分析发现改进算法在矿物混淆区分、信息提取精细度上均得到提高,有较强的实用性.     

Researches on Thermal Decomposition Kinetics of Composite Modified Double-base Propellants

The thermal decomposition kinetics of composite modified double‐base (CMDB) propellants with a series of contents of hexogeon (RDX) was investigated by using parameters of T_eo, T_i, T_p, T_f, T_b, T_a, E, lg A and ΔH, which were obtained from using a CDR‐4P differential scanning calorimeter (DSC) and Perkin‐Elmer Pyris 1 thermogravimetric analyzer (TG) analyses with heating rates of 5, 10, 15 and 20 K/min. Reliable activation energy was calculated using Flynn‐Wall‐Ozawa method before analyzing the thermal decomposition mechanism. TG‐DTG curves were treated with Malek method in order to obtain the reaction mechanisms. The obtained results show that the thermal decomposition mechanisms with the conversion from 0.2 to 0.4 was f(α)?1/2α, and with the conversion from 0.5 to 0.7 was f(α)?(1/4)(1?α)[?ln(1?α)]^?3.     

Flavonoid glycosides from Chromolaena odorata leaves and their in vitro cytotoxic activity

Two new flavonoid glycosides, (1, 2), and eleven known compounds, (3-13), were isolated from from a 70% EtOH extract of the leaves of Chromolaena odorata (Asteraceae). Their structures were elucidated by 1D and 2D NMR spectroscopic interpretation as well as by chemical studies. The newly isolated compounds were tested in vitro for their cytotoxic activities against the LLC and HL-60 cancer cell lines. Compound 1 showed cytotoxicity against LLC and HL-60 cancer cell lines with IC(50) values of 28.2 and 11.6 μM, respectively. Compound 2 exhibited significant cytotoxic activity in the inhibition of HL-60 cancer cell lines with IC(50) value of 10.8 μM.     

Determination of the surface acidity of a free-base corrole in a self-assembled monolayer

Mixed self-assembled monolayers (SAMs) containing a corrole moiety have been prepared to examine their electrochemical properties and surface acidity, with the eventual goal of biosensor development. Mixed SAMs consisting of 6-mercapto-hexanol (6-MHO) and 8-amino-1-octanethiol (8-AOT) in varying ratios were modified with a free-base corrole and characterized via Osteryoung square-wave voltammetry and contact angle measurements. The surface acidity of the free-base corrole was determined using an electrochemical titration method, with pK _a values established at 6.4 when using Fe(CN) ₆ ^4? /Fe(CN) ₆ ^3? as a redox probe and at 6.7 when using iodide, and assigned to the CorH₄ ⁺ ? CorH₃ + H⁺ equilibrium.     

基于Ⅲ-V与Ⅱ-Ⅵ族半导体材料色散特性的高灵敏度慢光干涉仪

分析了Ⅲ-V与Ⅱ-Ⅵ族半导体材料的光学特性,证明半导体慢光介质不但可以提高干涉仪的光谱灵敏度,而且可以获得远大于气体慢光介质的工作光谱范围.实验证明,基于慢光介质GaAs的干涉仪光谱灵敏度相对于传统的干涉仪提高约3.2倍.     

基于Ⅲ-Ⅴ与Ⅱ-Ⅵ族半导体材料色散特性的高灵敏度慢光干涉仪

分析了Ⅲ-Ⅴ与Ⅱ-Ⅵ族半导体材料的光学特性,证明半导体慢光介质不但可以提高干涉仪的光谱灵敏度,而且可以获得远大于气体慢光介质的工作光谱范围.实验证明,基于慢光介质GaAs的干涉仪光谱灵敏度相对于传统的干涉仪提高约3.2倍. 关键词： 干涉仪 非线性光学 Ⅲ-Ⅴ与Ⅱ-Ⅵ族半导体材料     

Optical polariton properties in ZnSe-based planar and pillar structured microcavities

Strong coupling is demonstrated in monolithic ZnSe-based microcavities. Under nonresonant excitation the polariton dispersion has been investigated in dependence on the photon-exciton detuning for different excitation densities at low temperatures. For zero detuning indications of a polariton lasing threshold are observed like a k-space and energy dispersion narrowing of the lower polariton branch with increasing excitation density. Furthermore, it is observed that this effect is hampered for measurements at negative detunings as a result of the less effective polariton relaxation to the ground state. Latter results in the formation of a discrete polariton distribution at finite k values as known for the polariton bottleneck. In order to investigate the influence of a three-dimensional optical confinement on the polariton relaxation, pillar structured microcavities were fabricated. The formation of discrete polariton states in the k-space distribution is observed. Furthermore, indications for a softening of the k-conservation arising from the structural confinement are found leading to a more effective polariton relaxation. This process would be beneficial for the realization of efficient polariton lasing processes.