Selective switching of individual multipole resonances in single dielectric nanoparticles

Following Mie theory, nanoparticles made of a high‐refractive‐index dielectric, such as silicon, exhibit a resonator‐like behavior and very rich resonance spectra. Which electric or magnetic particle mode is excited depends on the wavelength, the refractive‐index contrast relative to the environment, and the geometry of the nanoparticle itself. In addition, the spatial structure of the impinging light field plays a major role in the excitation of the nanoparticle resonances. Here, it is shown that, by tailoring the excitation field, individual multipole resonances can be selectively addressed while suppressing the excitation of other particle modes. This enables a detailed study of selected individual resonances without interference by the other modes.

     

高中化学竞赛中电子效应和空间效应考点分析——以近年全国化学奥林匹克竞赛试题为例

电子效应和空间效应是有机化学的基础,近年来,这部分知识在全国化学奥林匹克竞赛中的考查比例处于上升趋势。因此,以近年全国化学奥林匹克竞赛试题为例,详细说明电子效应和空间效应在竞赛中的考点,帮助辅导化学竞赛的教师和参加化学竞赛的考生了解该部分知识需要达到的教学标准和掌握层次。     

Diffusiophoresis in suspensions of highly charged soft particles

Diffusiophoresis phenomenon of aoft particles suspended in binary electrolyte solutions is explored theoretically in this study based on the spherical cell model, focusing on the chemiphoresis component in absence of diffusion potential. Both the electrostatic and hydrodynamic aspects of the boundary confinement, or steric effect, due to the presence of neighboring particles are examined extensively under various electrokinetic conditions. Significant local extrema are found in mobility profiles expressed as functions of the Debye length in general, synchronized with the strength of the motion-inducing double layer polarization. Moreover, a seemingly peculiar phenomenon is observed that the soft particles may move faster in more concentrated suspensions. The competition between the simultaneous enhancement of the motion-inducing electric driving force and the motion-retarding hydrodynamic drag force from the boundary confinement effect of the neighboring particles is found to be responsible for it. The above findings are also demonstrated experimentally in a very recent study on the diffusiophoretic motion of soft particles through porous collagen hydrogels. The results presented here are useful in various practical applications of soft particles like drug delivery.     

Sn-Al-β分子筛酸性在葡萄糖转化反应中作用的固体NMR研究

制备了一系列具有不同酸性质的β分子筛催化剂, 通过固体核磁共振(NMR)探针分子技术对其酸性质进行了表征, 并考察了其催化葡萄糖转化为乙酰丙酸甲酯的性能. 吸附三甲基磷的³¹P NMR实验结果表明, 含有骨架Sn以及Al原子的Sn-Al-β催化剂同时具有Br?nsted与Lewis酸性. 通过2-¹³C-丙酮探针分子区分出 3种酸强度的Br?nsted酸位, 其中一种酸强度接近“超强酸”, 可能是由于空间邻近的Br?nsted酸位和Lewis酸位发生协同作用产生的. 葡萄糖转化为乙酰丙酸甲酯的催化反应结果表明, 相比于分别只含有Lewis酸位和Br?nsted酸位的Sn-β和Al-β样品以及两者的物理混合样品, Sn-Al-β分子筛催化剂具有高催化活性与产物选择性, 这主要是由于Br?nsted酸位和Lewis酸位的协同作用产生了强Br?nsted酸位, 这种强Br?nsted酸位进一步导致了更高的催化活性.     

A hybrid nanofluid analysis near a parabolic stretched surface

Two dimensional incompressible steady viscous nano-fluid flow with the impacts of heat generation and porous medium is examined numerically. For this objective Ti₆Al₄v are taken as nano-particles dispersed in different base fluids such as methanol, engine oil and water. Basically in this study we will compare three different nano-fluids to assess their flow behaviour and thermal performance. The flow model is developed under certain assumptions. The two dimensional non-linear PDEs are converted into non-linear ODEs with suitable transformation. The numerical procedure is adopted to find the results by using Bvp4c technique in MATLAB. Moreover, graphs are generated for various parameters against the temperature and velocity profiles. The fluid behaviour for different parameter is examined on velocity and temperature profile. It is depicted that for high values of volume fraction and curvature parameter nano-particles leads to high velocity and temperature profile. Moreover, velocity profile decreases for permeability parameter, while temperature profile enhances for heat generation parameter. The influence of Nusselt number and skin friction also assessed. The model of entropy generation is also presented.     

A two-point calibration method for quantifying organic binary mixtures using secondary ion mass spectrometry in the presence of matrix effects

Quantification of the composition of binary mixtures in secondary ion mass spectrometry (SIMS) is required in the analyses of technological materials from organic electronics to drug delivery systems. In some instances, it is found that there is a linear dependence between the composition, expressed as a ratio of component volumes, and the secondary ion intensities, expressed as a ratio of intensities of ions from each component. However, this ideal relationship fails in the presence of matrix effects and linearity is observed only over small compositional ranges, particularly in the dilute limits. In this paper, we assess an empirical method, which introduces a power law dependence between the intensity ratio and the volume fraction ratio. A previously published physical model of the organic matrix effect is employed to test the limits of the method and a mixed system of 3,3′-bis(9-carbazolyl) biphenyl and tris(2-phenylpyridinato)iridium (III) is used to demonstrate the method. This paper introduces a two-point calibration, which determines both the exponent in the power law and the sensitivity factor for the conversion of ion intensity ratio into volume fraction ratio. We demonstrate that this provides significantly improved accuracy, compared with a one-point calibration, over a wide compositional range in SIMS quantification and with a weak dependence on matrix effects. Because the method enables the use of clearly identifiable secondary ions for quantitative purposes and mitigates commonly observed matrix effects in organic materials, the two-point calibration method could be of significant benefit to SIMS analysts.     

The Surface Analysis Working Group at the Consultative Committee for Amount of Substance,Metrology in Chemistry and Biology: A successful initiative by Martin Seah

Dr Martin Seah, NPL, was the initiator, founder, and first chairman of the Surface Analysis Working Group (SAWG) at the Consultative Committee for Amount of Substance, Metrology in Chemistry and Biology (CCQM) at the Bureau International des Poids et Mesures (BIPM), the international organization established by the Metre Convention. This tribute letter summarizes his achievements during his chairmanship and his long-running impact on the successful work of the group after his retirement.     

Response surface methodology for optimization of heavy metal removal by magnetic biosorbent made from anaerobic sludge

In this study, optimum conditions for adsorption of heavy metals such as Cu²⁺, Cd²⁺ and Pb²⁺ onto a low-cost, magnetically modified-alkali conditioned anaerobically digested sludge (MADS) adsorbent were obtained. Response Surface Methodology (RSM) incorporating Central Composite Design (CCD) of experiments was applied to optimize four independent process variables. Statistical analysis was executed by ANOVA and the quadratic model developed had regression coefficients of 0.959, 0.957 and 0.95 for Cu²⁺, Cd²⁺ and Pb²⁺, respectively. The independent variables such as pH, time and initial concentration positively influenced adsorption capacity, q_e, whereas the value of q_e decreased with an increase in MADS dosage. Model validation experiments for optimization of adsorption process showed comparable results with predicted values. The adsorption capacity of MADS adsorbent at optimum conditions found through RSM analysis was 29.721 mg L^?1, 28.551 mg L^?1 and 28.601 mg L^?1 for Cu²⁺, Cd²⁺ and Pb²⁺ respectively.     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

聚合物材料表面化学镀铜的前处理研究进展

聚合物材料表面金属化在通讯、电子、航空航天领域具有重要应用. 化学镀铜是聚合物材料表面金属化的主要技术之一. 聚合物材料表面的前处理直接影响化学镀铜层的结合力及镀层平整度. 本综述详细介绍非导电聚合物材料的种类、组成以及性能, 并概述其表面化学镀铜前处理的研究进展.