Distribution of Platinum and Palladium between Dissolved,Nanoparticulate, and Microparticulate Fractions of Road Dust

Ageing processes of vehicle catalytic converters inevitably lead to the release of Pt and Pd into the environment, road dust being the main sink. Though Pt and Pd are contained in catalytic converters in nanoparticulate metallic form, under environmental conditions, they can be transformed into toxic dissolved species. In the present work, the distribution of Pt and Pd between dissolved, nanoparticulate, and microparticulate fractions of Moscow road dust is assessed. The total concentrations of Pt and Pd in dust vary in the ranges 9–142 ng (mean 35) and 155–456 (mean 235) ng g⁻¹, respectively. The nanoparticulate and dissolved species of Pt and Pd in dust were studied using single particle inductively coupled plasma mass spectrometry. The median sizes of nanoparticulate Pt and Pd were 7 and 13 nm, respectively. The nanoparticulate fraction of Pt and Pd in Moscow dust is only about 1.6–1.8%. The average contents of dissolved fraction of Pt and Pd are 10.4% and 4.1%, respectively. The major fractions of Pt and Pd (88–94%) in road dust are associated with microparticles. Although the microparticulate fractions of Pt and Pd are relatively stable, they may become dissolved under changing environmental conditions and, hence, transformed into toxic species.     

Dielectric Loss and Electrical Conductivity Behaviors of Epoxy Composites Containing Semiconducting ZnO Varistor Particles

Polymer nanodielectrics render a great material platform for exhibiting the intrinsic nature of incorporated particles, particularly semiconducting types, and their interfaces with the polymer matrix. Incorporating the oxide fillers with higher loading percentages (>40 vol%) encounters particular challenges in terms of dispersion, homogeneous distribution, and porosity from the process. This work investigated the dielectric loss and electrical conduction behaviors of composites containing semiconducting ZnO varistor particles of various concentrations using the epoxy impregnation method. The ZnO varistor particles increased the dielectric permittivity, loss, and electrical conductivity of the epoxy composites into three different regimes (0–50 vol%, 50–70 vol%, 70–100 vol%), particularly under an electric bias field or at higher temperatures. For lower loading fractions below 50 vol%, the dielectric responses are dominated by the insulating epoxy matrix. When loading fractions are between 50 and 70 vol%, the dielectric and electric responses are mostly associated with the semiconducting interfaces of ZnO varistor particles and ZnO–epoxy. At above 70 vol%, the apparent increase in the dielectric loss and conductivity is primarily associated with the conducting ZnO core forming the interconnected channels of electric conduction. The foam-agent-assisted ZnO varistor particle framework appears to be a better way of fabricating composites of filler loading above 80 vol%. A physical model using an equivalent capacitor, diode, and resistor in the epoxy composites was proposed to explain the different property behaviors.     

A Collection of Molecular Fingerprints of Single Aerosol Particles in Air for Potential Identification and Detection Using Optical Trapping-Raman Spectroscopy

Characterization, identification, and detection of aerosol particles in their native atmospheric states remain a challenge. Recently, optical trapping-Raman spectroscopy (OT-RS) has been developed and demonstrated for characterization of single, airborne particles. Such particles in different chemical groups have been characterized by OT-RS in recent years and many more are being studied. In this work, we collected single-particle Raman spectra measured using the OT-RS technique and began construction of a library of OT-RS fingerprints that may be used as a reference for potential detection and identification of aerosol particles in the atmosphere. We collected OT-RS fingerprints of aerosol particles from eight different categories including carbons, bioaerosols (pollens, fungi, vitamins, spores), dusts, biological warfare agent surrogates, etc. Among the eight categories, spectral fingerprints of six groups of aerosol particles have been published previously and two other groups are new. We also discussed challenges, limitations, and advantages of using single-particle optical trapping-Raman spectroscopy for aerosol-particle characterization, identification, and detection.     

2013年诺贝尔物理学奖获得者——彼得·希格斯

彼得·希格斯(Peter Higgs)是英国著名的理论物理学家,因是希格斯机制的主要贡献人之一及以其名字命名的希格斯粒子而闻名于世。彼得·希格斯与弗朗索瓦·恩格勒(Francois Englert)共同获得了2013年诺贝尔物理学奖。文章简要介绍了彼得·希格斯的生平,希格斯机制的提出以及希格斯粒子命名的由来。此外,文章还简要回顾了希格斯粒子的发现过程。     

探索上帝粒子与质量起源

欧洲大型强子对撞机(LHC) 上发现的125 GeV新希格斯粒子可能成为标准模型预期的“上帝粒子”。这一革命性发现开启了探索宇宙中一切基本粒子质量起源的新时代,成为21世纪粒子物理学的转折点。文章着重介绍：(1) 探寻上帝粒子的重大科学意义;(2) 探索质量起源的历史,以及为什么牛顿力学和爱因斯坦相对论均未解决质量起源问题;(3) 神秘的真空与希格斯机制;(4) 上帝粒子是如何提出的和怎样在LHC上发现的;(5) 展望21世纪质量起源的探索与新物理定律的革命。     

基于正交超声驻波场的粒子运动建模和控制

为了获得具有均匀的倒金字塔表面微结构的多晶硅,提出了一种新腐蚀加工方法。通过建立一个相互正交的超声驻波场,来协助硅的化学侵蚀并改善其对光的吸收能力。首先对硅片表面结构进行一些比较,在二维上建立网格状的数学模型。然后建立网格中粒子运动的控制理论模型,并进行仿真验证。最后设计实验用于检验超声驻波对粒子的运动控制效果。多晶硅侵蚀结果说明将超声驻波应用在网格化微加工上是可行、可靠的。     

等离子体融断开关磁场Hall渗透机制的模拟研究

利用自行研制的2-1/2维全电磁柱坐标粒子模拟程序对等离子体融断开关磁场渗透机制进行了模拟研究。模拟结果表明在磁场Hall渗透机制特征长度远远小于等离子体离子的无碰撞趋肤深度的条件下,等离子体内部磁场渗透过程主要由电子流体运动的Hall项来控制。对于等离子体空间分布存在较大的密度梯度的物理问题,必须考虑二维空间特性对磁场渗透速度的影响。在磁场已渗透经过的等离子体区域中,等离子体呈现非电中性,离子受静电场的作用会加速运动到达阴极,最终形成真空鞘层。     

武威重离子治癌装置高能束线的准直安装

武威重离子治癌装置高能线爬升段上下跨度约为18 m,由于超大超重元件的悬空安装和狭小的安装空间及通视条件不足,使得就位时磁铁的位置及角度与地面做标定时不同,给准直安装工作带来了挑战。借助于激光跟踪仪和三维控制网,通过多重坐标转换,探索了一种新的方法,消除了爬升段磁铁调节时角度带来的偏差,有效提高了准直安装的工作效率,使得最后所有的磁铁安装各向安装误差均控制在0.10 mm以内,其结果优于该装置的精度要求,为整体安装进度提前提供了有力保证。     

Monodisperse polystyrene microspheres prepared by dispersion polymerization with microwave irradiation

Monodisperse polystyrene microspheres with diameters of 200–500 nm were prepared by dispersion polymerization with microwave irradiation with poly(N‐vinylpyrrolidone) as a steric stabilizer and 2,2′‐azobisisobutyronitrile as a radical initiator in an ethanol/water medium. The morphology, size, and size distribution of the polystyrene microspheres were characterized with transmission electron microscopy and photon correlation spectroscopy, and the formed films of the polystyrene dispersions were characterized with atomic force microscopy. The effects of the monomer concentration, stabilizer concentration, and initiator concentration on the size and size distribution of the polystyrene microspheres were investigated. The polystyrene microspheres prepared by dispersion polymerization with microwave irradiation were smaller, more uniform, and steadier than those obtained with conventional heating. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2368‐2376, 2005     

Recording of PIV images on photothermoplastic plates

In this paper we explore the possibility of utilizing commercially available photothermoplastic plates as recording support in Particle Image Velocimetry (PIV), to allow real time analysis of recorded data. An experimental apparatus has been developed which allows holographic recording and reconstruction of simulated PIV images. We show that double exposed photothermoplastic plates can successfully be analysed provided that a suitable recording/reconstruction scheme is used.