Monodispersed ZnSe colloidal microspheres: preparation, characterization, and their 2D arrays

Uniform and monodispersed ZnSe colloidal microspheres were prepared via a hot injection route by using trioctylamine as solvent and with a relatively higher concentration of the monomer precursors. The size of the colloidal ZnSe spheres was tuned from 138 to 629 nm by varying the concentration of the precursors, and the size increased linearly with the concentration of Zinc oleate in the range from 0.05 to 0.10 kg/L with the molar ratio of Zn to Se of 0.5. The colloidal microspheres were well characterized by SEM, TEM, HRTEM, EDS, UV-vis, and PL techniques. Detailed examination confirmed that the colloidal microspheres were formed by the in-situ aggregation of ZnSe nanoparticles. Furthermore, the 2D ordered assembly of the ZnSe microspheres was realized via a simple vertical precipitation technique. Due to the high refractive index and absence of absorption in the visible region, the monodispersed ZnSe colloidal microspheres could be potential building blocks to construct photonic band gap crystals and other functional devices.     

在无单位元下体现零模

本文用Horn函子刻划阿丁环．     

非线性组合动态传播率模型与我国COVID-19疫情分析和预测

针对传统的流行性传染病学中基本传染数R0难以准确估计以及单一模型预测精度低的缺陷,利用组合动态传播率替换基本传染数R0,提出基于支持向量回归的非线性时变传播率模型并对我国COVID-19疫情进行分析和预测.首先,计算动态传播率的离散值;其次,使用多项式函数、指数函数、双曲函数和幂函数分别对动态传播率的离散值进行拟合并基...     

The Existence of Almost Periodic Solutions of Second Order Neutral Differential Equations with Piecewise Constant Argument

51.Intr0ducti0nInthispaper,weconsidertheexistenceofalmostperiodicsoluti0nsforthefoll0wingneutralfunctionaldifferentialebuationwithpiecewiseconstantargument:wherep,qarenonzeroconstants,p(t)lsanalmostper1odicfunctlon,g:RXRXR-Risanalm0stperiodicfunctionintanduniformlyonRXR,andL.jstandsforthegreatest-integerfunction.Notethatforanyintegern,if2n-10)andtheequations(1),(2)areadvanced(orretardedrespectively).Differentialequationswithpiecewiseconstantar…     

一类泛圈图

本文证明了如果 Ｇ 是 ２ 连通无爪图, Ｇ 不是圈,ｎ＝ ｜ Ｖ（ Ｇ）｜≥９, Ｇ 的每个导出子图 Ａ都满足φ（ａ１,ａ２ ）,且 Ｇ 中不含同构于 Ｚ＋２ 的导出子图,则 Ｇ是泛圈图     

纳米半导体表面光诱导电子传递动力学——以4oxoTEMPO为电子受体TiO_2表面光还原效率的ESR研究

以４氧２ ,２ ,６ ,６四甲基哌啶酮（４ｏｘｏ２ ,２ ,６ ,６ ,ｔｅｔｒａｍｅｔｈｙｌ１ｐｉｐｅｒｄｉｎｙｌｏｘｙ 简称４ｏｘｏＴＥＭＰＯ） 作为电子受体,利用消自旋（Ｓｐｉｎ ｃｏｕｎｔｅｒａｃｔｉｏｎ） 的ＥＳＲ 方法,定量研究了ＴｉＯ２ 纳米半导体表面光诱导电子传递动力学,确定了ＴｉＯ２ 纳米半导体表面光还原速率方程和反应动力学常数．结果发现,在本实验体系中,ＴｉＯ２ 纳米半导体表面光还原对于底物是零级反应,而对于ＴｉＯ２ 则为一级反应,所测得的反应动力学常数能定量地表示ＴｉＯ２ 纳米半导体表面的光还原效率．不同波长光照及相异ｐＨ 值对ＴｉＯ２ 纳米半导体表面光还原速率有不同程度的影响．     

茶叶中重金属浸出规律的研究

采用火焰原子吸收光谱法测定了红茶和绿茶中铅、铜、锌的含量。考察了浸泡次数、浸泡温度和浸泡时间对铅、铜、锌3种金属元素浸出率的影响。结果表明,茶叶中铅、铜、锌的浸出率随浸泡次数的增多而减少,随浸泡温度的升高而增大,30min前随浸泡时间延长而增加。     

溶胶-凝胶法制备Ce3+掺杂纳米SiO2材料光致发光研究

通过溶胶-凝胶技术制备了掺杂Ce^3＋离子的纳米SiO2材料,并经较低温度下煅烧,研究其光致发光（PL）性能。X射线衍射（XRD）及透射电子显微镜（TEM）测试结果表明该纳米材料具有非晶态结构,颗粒尺寸为20～30nm。对其光致发光谱的测定显示：经450℃低温煅烧,未掺杂SiO2样品的光致发光谱明显为多峰的宽带结构,而微量Ce^3＋掺杂的样品在230nm激发下存在着唯一的一个很强的、主峰位于346nm左右的紫外发光峰,与未掺杂SiO2及Cu^2＋掺杂SiO2样品的比较表明该发光峰并非常见的Ce^3＋离子的d-f跃迁产生的特征发光带,而是起源于SiO2中的某种本征缺陷中心。通过不同煅烧温度以及不同Ce^3＋离子掺杂量对346nm发光峰强度的影响,讨论该发光峰起源可能的结构模型。     

Fe/nanoporous carbon hybrid derived from metal–organic framework for highly effective microwave absorption

A novel Fe/nanoporous carbon (Fe/NPC) composite was synthesized via Fe₃O₄ nanoparticles coating in metal–organic framework. The pyrolysis conditions are carefully optimized, and the effects of pyrolysis temperature on electromagnetic parameters have been systematically analyzed. Among these candidates, the Fe/NPC composite pyrolyzed at 800 °C (Fe/NPC‐800) shows the eminent microwave absorption due to interface polarization and well matched characteristic impedance. The results indicate that the effective reflection loss absorption bandwidth of Fe/NPC‐800 reaches 5.6 GHz (12.4–18 GHz) with a thickness of 1.8 mm. It provides an exciting clue for the fabrication of lightweight and highly effective microwave absorbers in the future.     

Enhanced Metal–Semiconductor Interaction for Photocatalytic Hydrogen-Evolution Reaction

The selective immobilization of noble metals right at the place where photogenerated electrons migrate through the photodeposition approach is a unique strategy to load cocatalysts on semiconductors for solar hydrogen production. However, a poor metal–semiconductor interaction is often formed, which not only hinders the interfacial charge transfer, but also results in the easy aggregation and shedding of cocatalysts during photocatalytic reactions. Herein, it is demonstrated that the photodeposited ultrafine metals, such as nanosized Au, can be well stabilized on TiO₂ nanocrystallines without sintering by employing a sacrificial carbon coating annealing strategy to strengthen the metal-support interaction. Benefiting from the improved interfacial contact between Au and TiO₂ for fast charge transfer and the well-preserved size-dependent catalytic behavior of Au nanoparticles toward hydrogen evolution reaction, the annealed Au/TiO₂ exhibits a significant enhanced activity toward photocatalytic H₂ production with good durability.