基于视觉的桥梁挠度测量方法与研究进展

挠度是评估桥梁承载能力和健康状态最直观的指标。近20年来,基于计算机视觉的桥梁挠度测量方法凭借其非接触式、快速简易安装等优点,被逐步应用于实际测量中。本文从测量原理、测量方式和影响因素3个方面出发,介绍了当前基于视觉的桥梁挠度测量方法与研究进展。在测量原理方面,从相机标定、三维立体视觉、摄影测量、特征检测与匹配4个方面进行了介绍。在测量方式方面,介绍了单相机二维测量、双相机三维测量、基于摄影测量的准静态测量和位移传递串联相机网络多点动态测量。在影响因素方面,介绍了相机自身因素、标定因素、算法因素和环境因素4个方面对测量结果的影响,并总结了目前国内外的研究成果。最后对基于视觉的桥梁挠度测量技术的未来发展趋势做出了展望。     

锂离子电池的电化学阻抗谱分析

电化学阻抗谱(EIS)是研究电极/电解质界面发生的电化学过程的最有力工具之一,广泛应用于研究锂离子在锂离子电池嵌合物电极活性材料中的嵌入和脱出过程。本文从分析嵌合物电极的EIS谱特征入手,探讨了电化学阻抗谱中各时间常数的归属问题,重点讨论了与锂离子嵌脱过程相关的动力学参数,如电荷传递电阻、活性材料的电子电阻、扩散以及锂离子扩散迁移通过固体电解质相界面膜(SEI膜)的电阻等,对电极极化电位和温度的依赖关系。     

高效液相色谱-串联质谱法测定葱中5种双酰肼农药残留

建立了同时分析葱中5种双酰肼农药的高效液相色谱-串联质谱方法。样品经乙腈高速匀浆提取,盐析后浓缩,弗罗里硅土柱色谱净化,采用液相色谱-串联质谱分析5种化合物。质谱分析采用电喷雾电离,正离子扫描,多反应监测模式。对双酰肼农药主要碎片的裂解方式进行了剖析。实验证明,柱净化后无明显的基质效应,样品中添加0.002～0.2 mg/kg的5种双酰肼,其回收率为72.6%～95.5%,相对标准偏差(n=5)小于15%;检出限为0.5 μg/kg,定量限为2 μg/kg。该方法提取效果好,具有良好的灵敏度、回收率和重复性。     

Salt-dependent DNA-DNA spacings in intact bacteriophage λ reflect relative importance of DNA self-repulsion and bending energies

Using solution synchrotron x-ray scattering, we measure the variation of DNA-DNA d spacings in bacteriophage λ with mono-, di-, and polyvalent salt concentrations, for wild-type [48.5×10(3) base pairs (bp)] and short-genome-mutant (37.8 kbp) strains. From the decrease in d spacings with increasing salt, we deduce the relative contributions of DNA self-repulsion and bending to the energetics of packaged phage genomes. We quantify the DNA-DNA interaction energies within the intact phage by combining the measured d spacings in the capsid with measurements of osmotic pressure in DNA assemblies under the same salt conditions in bulk solution. In the commonly used Tris-Mg buffer, the DNA-DNA interaction energies inside the phage capsids are shown to be about 1kT/bp, an order of magnitude larger than the bending energies.     

Exploring the potentiality of future standard candles and standard sirens to detect cosmic opacity

In this work, we explore the potentiality of future gravitational wave (GW) and Type Ia supernovae (SNe Ia) measurements to detect cosmic opacity by comparing the opacity-free luminosity distance (LD) of GW events with the opacity-dependent LD of SNe Ia observations. The GW data are simulated from the future measurements of the ground-based Einstein Telescope (ET) and the space-borne Deci-Herz Interferometer Gravitational wave Observatory (DECIGO). The SNe Ia data are simulated from the observations of the Wide Field Infrared Survey Telescope (WFIRST) that will be collected over the next few decades. A binning method is adopted to match the GW data with the SNe Ia data at the same redshift z with a selection criterion \begin{document}$ |\Delta z|<0.005$\end{document}, and most of the available data from the GW measurements is employed to detect cosmic opacity due to improvements in the distribution of the future SNe Ia observations. Results show that the uncertainties of the constraints on cosmic opacity can be reduced to \begin{document}$ \sigma_{\epsilon}\sim 0.0041$\end{document} and 0.0014 at the \begin{document}$ 1\sigma$\end{document} confidence level (CL) for 1000 data points from the ET and DECIGO measurements, respectively. Compared with the allowable limits of intergalactic opacity obtained from quasar continuum observations, these future astronomical observations can be used to verify the cosmic opacity. In this way, GW and SNe Ia measurements can be used as important and effective tools to detect cosmic opacity in the future.     

Li3PO4‐Coated LiNi0.5Mn1.5O4: A Stable High‐Voltage Cathode Material for Lithium‐Ion Batteries

LiNi_0.5Mn_1.5O₄ is regarded as a promising cathode material to increase the energy density of lithium‐ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li₃PO₄ on LiNi_0.5Mn_1.5O₄ to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ is prepared by a solid‐state reaction and noncoated LiNi_0.5Mn_1.5O₄ is prepared by the same method as a control. The materials are fully characterized by XRD, FT‐IR, and high‐resolution TEM. TEM shows that the Li₃PO₄ layer (<6 nm) is successfully coated on the LiNi_0.5Mn_1.5O₄ primary particles. XRD and FT‐IR reveal that the synthesized Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ has a cubic spinel structure with a space group of Fd$\bar 3$ m, whereas noncoated LiNi_0.5Mn_1.5O₄ shows a cubic spinel structure with a space group of P4₃32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ shows dramatically enhanced cycling performance compared with noncoated LiNi_0.5Mn_1.5O₄.     

The dependence of high-order harmonic generation on the laser frequency and inter-nuclear distance from multi-atom molecular ions

High-order harmonic generation from one-dimensional (1D) multi-atom molecular ions in an ultra-short laser field is theoretically investigated. The dynamics of the electron in a linearly polarized intense laserfield is analyzed in terms of 1D Schr(o)dinger equation with the Crank-Nicolson algorithm. The dependence of high-order harmonics on the laser frequency and the inter-nuclear distance is discussed. It is found that the optimum range of inter-nuclear distance should be changed to get extended harmonic generation for different laser frequency, and the lower frequency laser pulse is favorable to higher order harmonic generation as the inter-nuclear distance increases.     

阿基米德序半群的链的若干刻画

本文首先引入了一个序半群$S$的准素模糊理想的概念,通过序半群$S$上的一些二元关系以及它的理想的模糊根给出了该序半群是阿基米德序子半群的半格的一些刻画.进一步地借助于序半群$S$的模糊子集对该序半群是阿基米德序子半群的半格进行了刻画.尤其是通过序半群的模糊素根定理证明了序半群$S$是阿基米德序子半群的链当且仅当$S$是阿基米德序子半群的半格且$S$的所有弱完全素模糊理想关于模糊集的包含关系构成链.     

Electron beam emission from a diamond-amplifier cathode

The diamond amplifier (DA) is a new device for generating high-current, high-brightness electron beams. Our transmission-mode tests show that, with single-crystal, high-purity diamonds, the peak current density is greater than 400 mA/mm2, while its average density can be more than 100 mA/mm2. The gain of the primary electrons easily exceeds 200, and is independent of their density within the practical range of DA applications. We observed the electron emission. The maximum emission gain measured was 40, and the bunch charge was 50 pC/0.5 mm2. There was a 35% probability of the emission of an electron from the hydrogenated surface in our tests. We identified a mechanism of slow charging of the diamond due to thermal ionization of surface states that cancels the applied field within it. We also demonstrated that a hydrogenated diamond is extremely robust.     

超声波-微波法制备NiW/Al2O3加氢脱硫催化剂

 采用一次浸渍技术制备了NiW/Al2O3加氢脱硫(HDS)催化剂,在制备过程中采用超声波处理浸渍液,采用微波进行样品干燥. 以噻吩为模型化合物,在微反装置上评价了该催化剂的加氢脱硫活性. 使用X射线光电子能谱和透射电镜等表征手段研究了催化剂的表面状态和物化性. 结果表明,使用超声波及微波技术制备的NiW/Al2O3催化剂具有较高的加氢脱硫活性,催化剂的活性组分较易硫化,可生成更多的硫化物种参与反应. 催化剂中硫化态钨的表面原子浓度较高,从而使硫化态钨物种保持较高的表面分散度,有利于增加活性中心的数目. 该催化剂的活性中心结构具有较多配位不饱和的边缘位和棱边位,因而具有较高的加氢脱硫活性.