Modulation of Uptake and Reactivity of Nitrogen Dioxide in Metal-Organic Framework Materials

We report the modulation of reactivity of nitrogen dioxide (NO₂) in a charged metal–organic framework (MOF) material, MFM-305-CH₃ in which unbound N-centres are methylated and the cationic charge counter-balanced by Cl⁻ ions in the pores. Uptake of NO₂ into MFM-305-CH₃ leads to reaction between NO₂ and Cl⁻ to give nitrosyl chloride (NOCl) and NO₃⁻ anions. A high dynamic uptake of 6.58 mmol g⁻¹ at 298 K is observed for MFM-305-CH₃ as measured using a flow of 500 ppm NO₂ in He. In contrast, the analogous neutral material, MFM-305, shows a much lower uptake of 2.38 mmol g⁻¹. The binding domains and reactivity of adsorbed NO₂ molecules within MFM-305-CH₃ and MFM-305 have been probed using in situ synchrotron X-ray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, high-field solid-state nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants.     

The determination of silicon in airborne particulate matter by XRF and LA-ICP-MS

This study reports the analysis of Si in airborne particulate matter by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) as well as X-ray fluorescence (XRF). It was found that Si concentration in airborne particulates collected on PTFE-membrane filters could be accurately determined with a laser beam operated at 160 mJ free running mode, 6.5 mm defocusing distance and 0.8 l/min carrier gas flow rate during the LA-ICP-MS measurement. Standard filters prepared by NIST SRM 1648 urban particulates were used for both XRF and LA-ICP-MS not only to establish the calibration curves of Si, but also to examine the proposed method's effectiveness. The capability of applying both methods for natural sample analysis was also examined. Particulate loaded filter samples collected from a heavily polluted metropolitan area of Kaoshiung, Taiwan were initially measured by XRF, then by LA-ICP-MS. An intercomparison between them was thus performed. As a result, both XRF and LA-ICP-MS proved to be the valid analytical methods for directly determining Si concentrations in airborne particulates on PTFE membrane filters.     

几种不同产地高岭土的漫反射傅里叶红外光谱分析

分别采用压片法与漫反射法测得几种不同产地高岭土的红外吸收谱图,解析了各高岭土的结构特征与吸收峰值的关系,发现利用漫反射傅里叶红外光谱技术,经K-M函数校正的红外谱图较压片法灵敏度高,也更准确,解析更简单;依据对高频区3700～3600cm-1波数段高岭石OH基特征吸收峰的吸收情况,可快速判断高岭石结晶度,结果与X射线衍射技术所测Hinckley指数(Hi)一致。     

Osher Flux with Entropy Fix for Two-Dimensional Euler Equations

We compare in this paper the properties of Osher flux with O-variant and P-variant (Osher-O flux and Osher-P flux) in finite volume methods for the two-dimensional Euler equations and propose an entropy fix technique to improve their robustness. We consider both first-order and second-order reconstructions. For inviscid hypersonic flow past a circular cylinder, we observe different problems for different schemes: a first-order Osher-O scheme on quadrangular grids yields a carbuncle shock, while a first-order Osher-P scheme results in a dislocation shock for high Mach number cases. In addition, a second-order Osher scheme can also yield a carbuncle shock or be unstable. To improve the robustness of these schemes we propose an entropy fix technique, and then present numerical results to show the effectiveness of the proposed method. In addition, the influence of grid aspects ratio, relative shock position to the grid and Mach number on shock stability are tested. Viscous heating problem and double Mach reflection problem are simulated to test the influence of the entropy fix on contact resolution and boundary layer resolution.     

基于Pancharatnam-Berry相位和动力学相位调控纵向光子自旋霍尔效应

提出了一种基于Pancharatnam-Berry相位和动力学相位操控纵向光子自旋霍尔效应的方法.理论分析表明:当光场通过一个由Pancharatnam-Berry相位透镜和动力学相位透镜构成的透镜组时,透镜组会存在两个自旋相关的焦点.首先,当左旋和右旋圆偏振光通过微结构相位延迟为π的Pancharatnam-Berry相位透镜时,由于Pancharatnam-Berry相位的自旋相关性,两个圆偏振分量会获得符号相反的Pancharatnam-Berry相位而导致其中一个被聚焦而另一个发散.然后,在Pancharatnam-Berry相位透镜后再插入普通透镜引入动力学相位调制,由于动力学相位是自旋无关,使得这一透镜组,可以在合适的条件下使不同自旋态的光子分别聚焦于纵向上不同焦点处.纵向自旋分裂由两透镜焦距及间距共同决定,因此可以通过改变两个透镜的焦距及其间距获得任意的纵向自旋分裂值.最后,搭建了一套实验装置,所得实验结果与理论结果一致.     

Test of the gravitational inverse square law at millimeter ranges

We report a new test of the gravitational inverse square law at millimeter ranges by using a dual-modulation torsion pendulum. An I-shaped symmetric pendulum and I-shaped symmetric attractors were adopted to realize a null experimental design. The non-Newtonian force between two macroscopic tungsten plates is measured at separations ranging down to 0.4 mm, and the validity of the null experimental design was checked by non-null Newtonian gravity measurements. We find no deviations from the Newtonian inverse square law with 95% confidence level, and this work establishes the most stringent constraints on non-Newtonian interaction in the ranges from 0.7 to 5.0 mm, and a factor of 8 improvement is achieved at the length scale of several millimeters.     

一流课程建设背景下大学物理线上线下混合课程的建设与实践

大学物理课程是高校理工科专业学生非常重要的一门必修公共基础课,一流本科课程建设对大学物理教学提出了新的要求.本文从教学内容、教学方法、教学手段、考核方式等方面探索了实施大学物理混合式教学较为有效的策略和方法,以期为物理学科一流课程建设助力.     

Determination of the half-life of 184gRe and the isomeric ratio of 184m,gRe induced by D-T neutrons

The isomeric ratio of ^{184m, g}Re and the half-life of ^184gRe were measured in the ¹⁸⁵Re (n, 2n) ¹⁸⁴Re reaction at 14.8 MeV, and the uncertainty was discussed in detail. The measurements were performed using the activation method implemented for a rhenium sample using the K-400 neutron generator at the Chinese Academy of Engineering Physics (CAEP). Isomeric state and ground state nuclei of ¹⁸⁴Re were identified by their γ-ray spectra. To eliminate the effect of the γ-ray emitted from the isomer on the counting of the ground state characteristic peaks, the isomeric ratio of ^{184m, g}Re was calculated to be 0.29 ± 0.11 according to the neutron activation cross-section formula. This result is consistent with previous data within the uncertainty and can be used to determine parameters that characterize the dependence of the level density on the excitation energy and angular momentum. Through exponential function fitting and a detailed discussion of the uncertainty evaluation, the half-life of ^184gRe was determined as 35.43 ± 0.16 d, which is consistent with the currently recommended value; however, the uncertainty assessment of the latter was barely documented. In addition, this study indicates that the half-life of the ground state can be obtained by eliminating the contamination of γ-rays emitted from the isomer, which provides the possibility of determining the half-lives of nuclides containing isomers.     

The Number of Limit Cycles in a Class of Piecewise Polynomial Systems

In this paper, we pay attention to the number of limit cycles for a class of piecewise smooth near-Hamiltonian systems. By using the expression of the first order Melnikov function and some known results about Chebyshev systems, we study upper bound of the number of limit cycles in Hopf bifurcation and Poincar\''{e} bifurcation respectively.