A one-equation turbulence model for recirculating flows

A one-equation turbulence model which relies on the turbulent kinetic energy transport equation has been developed to predict the flow properties of the recirculating flows. The turbulent eddy-viscosity coefficient is computed from a recalibrated Bradshaw’s assumption that the constant a₁ = 0.31 is recalibrated to a function based on a set of direct numerical simulation (DNS) data. The values of dissipation of turbulent kinetic energy consist of the near-wall part and isotropic part, and the isotropic part involves the von Karman length scale as the turbulent length scale. The performance of the new model is evaluated by the results from DNS for fully developed turbulence channel flow with a wide range of Reynolds numbers. However, the computed result of the recirculating flow at the separated bubble of NACA4412 demonstrates that an increase is needed on the turbulent dissipation, and this leads to an advanced tuning on the self-adjusted function. The improved model predicts better results in both the non-equilibrium and equilibrium flows, e.g. channel flows, backward-facing step flow and hump in a channel.     

Fiber-optic beam shaper based on multimode interference

A new method of fiber-optic based beam shaping is investigated both numerically and experimentally. A cylindrically symmetric method of lines (MoLs) is developed to simulate the device. The device is fabricated by fusion splicing a predetermined length of multimode fiber (MMF) to a single-mode fiber. The multimode interference (MMI) effects create ring-shaped field profiles at certain positions inside the MMF. The shaped beam can be used in medical applications requiring particular irradiation patterns.     

Negative refraction of complex lattices of dielectric cylinders

Some photonic crystals (PCs) consisting of complex lattices of dielectric cylinders can have an effective refraction index (neff$n_{\mathrm{eff}}$) of −1. Subwavelength imaging by a slab of a honeycomb PC of dielectric cylinders with neff=−1$n_{\mathrm{eff}}=-1$ is investigated and an open resonator with a quality factor higher than 3000 is designed with the same PC. Air–PC interfaces with low reflection are also used for the slab lens and open resonator.     

Analytical analysis of anisotropic thermophoresis of a charged spheroidal colloid in aqueous media for extremely thin EDL cases

Thermophoresis of charged spheroids has been widely applied in biology and medical science. In this work, we report an analysis of the anisotropic thermophoresis of diluted spheroidal colloids in aqueous media for extremely thin EDL cases. Under the boundary layer approximation, we formulate the thermophoretic velocity, the thermophoretic force, and the thermodiffusion coefficient of a randomly dispersed spheroid. The parametric studies show that under the aforementioned conditions, the thermophoresis is anisotropic and its thermodiffusion coefficient should be considered as a vector, D _T. The thermodiffusion coefficient values and directions of D _T are strongly related to the aspect ratio and the angle θ between the externally applied temperature gradient and the particle's axis of revolution: The increasing aspect ratio enlarges the thermodiffusion coefficient value D_T of prolate (oblate) spheroids to a constant value when θ < 60° (θ > 45°), and it reduces D_T of prolate (oblate) spheroids to a constant value when θ > 60° (θ < 45°). The thermodiffusion coefficient direction of both prolate and oblate spheroids deviates slightly from −∇T_∞ for a small aspect ratio, and such deviation becomes serious for a large aspect ratio.     

Direct immobilization of iodine-loaded silver-coated silica gel with silicate glass powders at low temperature

Journal of Radioanalytical and Nuclear Chemistry - To long-term immobilization of secondary iodine-waste, iodine loaded silver-coated silica-gel (AgIs), glass-powder was used to directly solidify...     

二维金属有机框架材料的合成及电催化应用

二维金属有机框架材料(MOFs)由于具备高比表面积、 多孔性以及丰富的活性位点等优异特性而受到广泛关注, 并且在电催化领域展现出巨大的应用潜力. 研究者们已在二维MOFs的可控制备与电催化性能调控方面取得许多突破性进展, 显示出相关研究对开发高性能电催化剂的关键作用. 本文总结了二维MOFs的自上而下和自下而上合成策略以及二维MOFs衍生物的典型合成方法, 概述了二维MOFs在各尺度下的电催化性能调控策略, 并介绍了各种合成方法和调控策略在电催化中的应用. 最后讨论了该领域面临的挑战, 并对未来的发展方向进行了展望.     

ABC三嵌段共聚物胶束从多间隔结构到多核结构转变的Monte Carlo模拟

采用Monte Carlo模拟方法研究了疏水-亲水-疏水(H-P-H)型ABC三嵌段共聚物在B嵌段的选择性溶剂中的自组装行为. 模拟结果表明, 通过调节A嵌段和C嵌段的疏水性和二者之间的不相容性, 体系中可以形成多种形貌各异的胶束. 根据胶束中疏水核结构的特点, 这些胶束大体上可以被分为多核型胶束和多间隔型胶束两种类型. 通过增强疏水嵌段的疏水性或降低A嵌段和C嵌段间的不相容性, H-P-H型ABC三嵌段共聚物胶束能够发生从多核型胶束向多间隔型胶束的转变. 进一步分析胶束中聚合物的链构象等微观结构信息发现, A嵌段和C嵌段间的排斥作用和疏水作用之间存在竞争关系, 而这种竞争关系是影响体系中形成多核型胶束还是多间隔型胶束的决定性因素.     

理论研究晶体场效应和电荷转移效应对Co2+的2p电子X射线L2,3吸收边光谱的影响

运用多重态计算方法研究了在正八面体对称性的晶体场中Co²⁺离子的2p电子X射线L_2,3吸收边光谱, 研究了Co²⁺离子和周围的配位离子之间的正八面体(O_h)晶体场效应和相应的电荷转移效应对于吸收光谱的影响. 系统讨论了在多重态计算中起作用的所有物理参数对CoO和CoCl₂的X射线吸收光谱特性的特定影响及其物理机制. 将计算得出的光谱数据和同样具有O_h对称性结构Co²⁺离子的CoO和CoCl₂实验光谱数据进行了对比, 在实验光谱数据中发现的特征被确定为来自不同自旋态, 并且光谱强度的变化与晶体场的强度相关, 揭示了其中包含的电荷转移效应. 本文为低对称性复杂系统的多重态计算提供了一个基础的参考标准, 可以适用于含有钴元素或其它过渡金属的复杂体系的X射线吸收光谱的理论计算.     

哌啶并[2,3-b]哌嗪类衍生物的设计、合成及其抗血小板聚集活性研究

以2,3-二氨基吡啶和2,3-丁二酮为起始原料,经环化、催化氢化和亲核取代反应合成了10个新型哌啶并[2,3-b]哌嗪类衍生物(3a~3j),其结构经¹H NMR、¹³C NMR和HR-MS确证。体外抗血小板聚集活性研究表明,化合物3d、3e、3g、3h和3j具有一定的抗血小板聚集作用,其中化合物3h(IC₅₀=1.24mmol/L)的活性显著优于母体化合物川芎嗪(IC₅₀=3.96mmol/L)和阳性药物阿司匹林(IC₅₀=2.41mmol/L)。     

Synthesis of carrageenan coated silver nanoparticles by an easy green method and their characterization and antimicrobial activities

The aim of the present work was to synthesize carrageenan coated silver nanoparticles (CA–AgNPs) using carrageenan as reducing and stabilizing agent. For this purpose, 10 mL of 0.35% (w/v) carrageenan solution was mixed with 10 mL AgNO₃ solution at different concentrations (1, 5 and 10 mM), and the resulting mixture was stirred at 100 °C at high speed for 2 h. The formation of CA–AgNPs was proven with the surface plasmon peaks observed at approximately 420 nm. The sizes and zeta potentials of CA–AgNPs were determined by Zeta-Sizer. Negative zeta potentials of CA–AgNPs indicated that the obtained AgNPs were stable. With scanning electron microscope (SEM) and transmission electron microscope analysis, it was seen that CA–AgNPs have spherical structure. According to the energy dispersion spectrometer analysis based on SEM images, it was observed that the samples were elementally composed of carbon, oxygen, sulfur, potassium and silver. The chemical structures of CA–AgNPs were determined by Fourier transform infrared spectroscopy, and it was proved that the carbonyl and OH groups of carrageenan were involved in formation and stabilizing of AgNPs, respectively. According to thermal gravimetric analysis, it has been observed that CA–AgNPs were thermally more stable than pure carrageenan. Antibacterial activity of CA–AgNPs against gram-positive and gram-negative bacteria was investigated with agar well diffusion and liquid test. It has been observed that CA–AgNPs synthesized with 1 mM AgNO₃ did not have an antibacterial activity on Escherichia coli and Staphylococcus aureus. Inhibition zones of varying diameters were observed in the 5 mM and 10 mM S-AgNPs groups. The synthesized CA–AgNPs (5 and 10 mM) have the capacity to be used in wound dressing materials or topical agents applied to burns and wounds due to their antibacterial effects and stability.