Facile synthesis of uniform hollow hematite sub-micro spheres with controllable shell thickness

A simple method was developed to prepare the uniform hematite hollow submicro-spheres with controllable structure and different diameter based on monodisperse poly(styrene-co-acrylic acid) [P(St-co-AA)] particles. The structure and formation mechanism of the hollow spheres were investigated in detail. The control mechanism of shell thickness was also discussed. The results indicated that the shell thickness and coarseness of the synthesized core-shell hematite hollow spheres could be tuned simply by the surface carboxyl content of the P(St-co-AA) particles. This method provided a new approach for the structure control in the preparation of hollow spheres. A Brunauer-Emmett-Teller (BET) test shows that the prepared hollow spheres have large surface areas which were decreased along with the increase of the diameter. The magnetic properties of the as-obtained hematite hollow spheres were investigated. The result showed that the coercivity and saturated magnetization were increased along with the increase of the shell thickness, and the remanent magnetization was increased along with the decrease of the diameter.     

基于CFD方法的阵风响应与阵风减缓研究

通过设计舵面的同期运动,可以达到缓解飞行器遭遇阵风时引起的非定常气动力与力矩干扰的目的。文章通过引入"网格速度"模拟阵风条件,求解非定常欧拉方程实现了翼型阵风响应的数值模拟;并通过动态嵌套网格方法研究了舵面运动时的阵风减缓效果。首先采用该方法对NACA0006翼型迎角阶跃型阵风的气动力响应进行了计算,计算结果与理论结果、文献计算结果吻合良好。进一步对NLR两段翼型在迎角阶跃型、One-m inus-cosine型阵风做用下的气动力响应过程进行了数值模拟,对襟翼运动时的阵风减载效果进行了分析,并研究比较了襟翼运动参数对阵风减缓的影响。结果表明:通过合理设计舵面运动方式,可以很好抑制阵风引起的非定常气动干扰。     

Photocatalytic performance of TiO<Subscript>2</Subscript> thin films connected with Cu micro-grid

Aiming at reducing the recombination of photo-induced carriers in semiconductor photocatalytic process, we prepared TiO₂ thin film with its surface modified by a connected Cu micro-grid via a microsphere lithography strategy, which showed higher photocatalytic activity than the pure TiO₂ film. The improvement of photocatalytic activity of Cu micro-grid to the TiO₂ film is due to the charge carrier separation and electron transfer by the conducting metal grid. The photocatalytic activity was improved as metal loading increased, which obtained the best performance at a certain loading amount, and then decreased at higher loading amount. This phenomenon was attributed to the metal’s bulk effect which could be explained by the relationship between the energetic positions and the metal cluster size. Supported by the National Natural Science Foundation of China (Grant Nos. 50672003, 50872005) and the National Basic Research Program of China (“973” Project) (Grant No. 2007CB613302) and the Fok Ying Tong Education Foundation (Grant No. 111050)     

Penumbral imaging and numerical evaluation of large area source neutron imaging system

The fusion neutron penumbral imaging system Monte Carlo model was established. The transfer functions of the two discrete units in the neutron source were obtained in two situations: Imaging in geometrical near-optical and real situation. The spatial resolutions of the imaging system in two situations were evaluated and compared. The penumbral images of four units in the source were obtained by means of 2-dimensional (2D) convolution and Monte Carlo simulation. The penumbral images were reconstructed with the same method of filter. The same results were confirmed. The encoding essence of penumbral imaging was revealed. With MCNP(Monte Carlo N-particle) simulation, the neutron penumbral images of the large area source (200 μm×200 μm) on scintillation fiber array were obtained. The improved Wiener filter method was used to reconstruct the penumbral image and the source image was obtained. The results agree with the preset neutron source image. The feasibility of the neutron imaging system was verified. Supported by the NSAF Joint Fund set up by NSFC and CAEP (Grant No. 10576022)     

Requirement of ultra-high voltage GIS arrester to voltage gradient of metal-oxide varistor

The surge arrester with excellent protection characteristics would decrease the overvoltage level ap- plied on the power apparatus to reduce their insulation levels and manufacturing bottleneck. The arrester for the 1000-kV ultra-high voltage ac power transmission system is designed as tank-type structure. The field-circuit combination numerical method combining the three-dimensional finite element method with circuit is proposed to analyze the potential distribution of GIS arrester. By comparing several design schemes, the most effective method to improve the potential distribution along the varistor column is to increase the voltage gradient of the ZnO varistor. Synthesizing several influential factors, the suitable voltage gradient of ZnO varistor should be controlled to 435 V/mm, and the resulted nonuniform degree of the potential distribution along the varistor column inside the GIS arrester would be controlled smaller than 10%. The result in this paper provides the fundamental technical index for the study of the high voltage gradient ZnO varistors.     

Multi-channel micro neural probe fabricated with SOI

Silicon-on-insulator(SOI) substrate is widely used in micro-electro-mechanical systems(MEMS).With the buried oxide layer of SOI acting as an etching stop,silicon based micro neural probe can be fabri-cated with improved uniformity and manufacturability.A seven-record-site neural probe was formed by inductive-coupled plasma(ICP) dry etching of an SOI substrate.The thickness of the probe is 15 μm.The shaft of the probe has dimensions of 3 mm×100 μm×15 μm with typical area of the record site of 78.5 μm2.The im...     

Growth of Ag nanocrystals on multiwalled carbon nanotubes and Ag-carbon nanotube interaction

The experimental investigations on the interaction between Ag-nanocrystal particles (Ag-NCPs) and carbon nanotubes (CNTs) in Ag-nanocrystal particles/carbon nanotubes (Ag-NCPs/CNTs) hybrid structures were reported. The growth of Ag-NCPs on multiwalled carbon nanotubes (MWCNTs) was carried out by thermal evaporation deposition. High-resolution transmission electron microscopy and X-ray diffraction analyses revealed that Ag-NCPs had the crystal lattice feature of face-centered cube (fcc). The growth of Ag-NCPs on MWCNTs induced the cross-section deformation of MWCNT. The experimental results also showed that the synthesized Ag-NCPs/CNTs hybrid structure appeared as quasi-one dimensional nanowires containing the Ag-NCP/CNT hetero-junction. There was local cross-section deformation on MWCNTs at the interface of hetero-junction. These results involve the important topic about fundamental and practical studies for structure of MNCPs on CNTs and also find clues to further research of Ag nanocrystal growing on MWCNTs and related Ag-CNT interaction.     

Composite silicone rubber of high piezoresistance repeatability filled with nanoparticles

The ruthenium oxide nanoparticles with size less than 20 nm were fabricated by annealing the metallic ruthenium nanoparticles in air, which were synthesized by using the thermal reduction in the polyol solution. The rutile structure of the ruthenium oxide was proved by using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The oxide has good electron conductivity. The surface of the ruthenium oxide was modified by a vinyl silane coupling agent. The assembling of the silane to the oxide surface was proved by Infrared (IR) absorption spectroscopy. By mixing the nanoparticles with poly(methylvinylsiloxane) (PMVS) silicone rubber, a composite filled with dispersive conducting phase was fabricated. The temperature dependent conductivity shows that the electron transportation through composite is mainly dominated by tunneling. The measurement of piezoresistance shows that the composite at low strain has high piezoresistance repeatability. The 3D reconstruction images of the composite filled with carbon black or ruthenium oxide show that the aggregation of the nanoparticles differs much for two composites. The narrow distribution range of the particle size was thought to be the main factor for the high piezoresistance recurrence.     

采用磁选和重选回收废旧电路板中的金属

采用磁选和重选联合工艺回收废旧印刷电路板中Fe、Cu、Al、Pb、Zn、Sn和Ni等金属。结果表明,采用干法磁选工艺,可回收的铁磁性物质约占废旧电路板质量分数的8．23％,重液分选可使金属与非金属有效分离,采用磁选和重选联合工艺可使Fe、Cu、Pb、Zn、Ni和Sn的回收率分别达到约100％、80％、65％、75％、88％和56％。     

压电陶瓷在声速测量中的应用

本文论述了压电陶瓷在声速测量中的应用,阐述了几种测量超声波波速的方法。