Friction and wear behaviours of surface densified powder metallurgy Fe–2Cu–0.6C material

Surface rolling was employed to fabricate a densified layer on a powder metallurgy (PM) Fe–2Cu–0.6C piece. A densified surface layer with a depth of 335?μm and a surface hardness of 330?HV_0.1 was obtained, in which the lamellar spacing of pearlite and grain size of ferrite were refined. Friction and wear behaviours of the surface densified material were studied. Results indicated that friction coefficient of the rolled material decreased as the load increased, which was lower than that of the un-rolled material. Wear volumes were lower than that of the un-rolled material, which increased as the load increased. Wear loss was caused by flake spalling and grooves, and the wear mechanism mainly was abrasive wear. The surface densified layer with higher hardness and lower porosity can hinder the cracks initiation and propagation on the surface and under the surface, which enhance the wear resistance of the PM material.     

Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

Amphiphilic TiO₂ nanotube arrays (TiO₂ NTs) were fabricated through electrochemical oxidation of Ti in solution containing H₃PO₄ and NaF. Scanning electron microscopic analysis shows that the as-prepared TiO₂ NTs have an average pore diameter of 100 nm and a wall thickness of 15 nm. The electrochemical oxidation of Ti can be divided into four stages. In the first stage, when the potential is very low, oxygen formation and Ti dissolution are the major reactions. The second stage corresponds to a slightly higher potential, but less than 2.5 V. In this stage, the formation of TiO₂ film occurs. When the potential is increased to the even higher range from 2.5 V to 6 V, the TiO₂ film dissolves and nanoporous surface structure is generated. This is the third stage. Further increase of the potential enters stage four. The high potentials cause the self-organization of the nanostructure and allow the formation of well-aligned TiO₂ NTs. We also found that the change in surface condition of Ti by annealing heat treatment affects the film dissolution kinetics. As compared with TiO₂ thin film, the TiO2 NTs show higher photocatalytic activity on decomposing Rhodamine B. The surface of the TiO₂ NTs can be wetted by both water and oil. Such an amphiphilic property comes from the capillary effect of the nanochannel structure of the TiO₂ NTs. Because of the amphiphilic property and the photocatalytic activity, we conclude that the TiO₂ NTs have the capability of self-cleaning.     

Epoxy Ring Opening Phase Transfer as a General Route to Water Dispersible Superparamagnetic Fe3O4 Nanoparticles and Their Application as Positive MRI Contrast Agents

A novel and efficient method to produce water dispersible superparamagnetic Fe₃O₄ nanoparticles is described. Nanoparticles prepared by non‐hydrolytic organic phase methods are subsequently functionalized with (3‐glycidyloxypropyl)trimethoxysilane, a linker that prevents aggregation and is available for subsequent coupling reactions with a wide range of polymers and biomolecules. Ring opening coupling reactions were used to coat the epoxy‐functionalized magnetite nanoparticles with aminated polymers (polyetheramines) or small molecules (arginine). The resulting nanoparticles, with hydrodynamic size of 13 nm, are found to be very stable over extended periods in water or PBS due to the presence of a dense stabilizer layer covalently anchored to the surface. Exceptionally high spin‐lattice relaxivity, r₁, values of 17 s^?1 mM^?1, and low r₂/r₁ ratios of 3.3–3.8 were exhibited in the clinical MRI frequency range, irrespective of the molecule selected for nanoparticle stabilization. As a result the dispersions are excellent candidates for incorporation into multi‐functional assemblies or for use as positive contrast agent for MRI.     

用均匀圆阵实现宽频段来波信号频率和二维角估计

本文提出了一种在DFT波束空间实时估计入射到均匀圆阵(UCA)上宽频段(1～18GHz)信号的频率、方位角和仰角的方法。该方法可在时间欠采样条件下实现频率无模糊估计,在空间欠采样条件下,用整数搜索法实现方位角和仰角无模糊估计,且频率、方位角和仰角估计可自动配对。模拟频率间接估计算法的估计方差比直接估计算法的方差要小2～3个数量级。仿真实验表明了算法是有效的。     

用于大功率半导体激光器的新型焊料

在大功率半导体激光器列阵及叠阵的组装中,焊料的选择是极其关键的,因为焊料直接参与对激光器的导电、导热激光器所需的电流全部从焊料通过,而半导体激光器列阵或叠阵工作时电流是很大的,可达50A～100A。同时半导体激光器工作时产生的热量非常大,如焊料的导热性不好,由于电流的热效应,就会在焊料上产生巨大的热量,使焊料熔化。文中研制了一种新型的焊料,这种焊料在两层铟之间蒸镀几层金,焊料由钨/镍/金/铟/铜等多层金属构成。利用这种焊料研制出脉冲功率达100W的半导体激光器列阵。     

替代衬底上的碲镉汞长波器件暗电流机理

基于暗电流模型,通过变温I-V分析长波器件(截止波长为9~10μm)的暗电流机理和主导机制.实验对比了不同衬底、不同成结方式、不同掺杂异质结构与暗电流成分的相关性.结果表明,对于B+离子注入的平面结汞空位n~+-on-p结构,替代衬底上的碲镉汞(HgCdTe)器件零偏阻抗(R0)在80 K以上与碲锌镉(CdZnTe)基碲镉汞器件结阻抗性能相当.但替代衬底上的HgCdTe因结区内较高的位错,使得从80 K开始缺陷辅助隧穿电流(I_(tat))超过产生复合电流(I_(g-r)),成为暗电流的主要成分.与平面n~+-on-p器件相比,采用原位掺杂组分异质结结构(DLHJ)的p~+-on-n台面器件,因吸收层为n型,少子迁移率较低,能够有效抑制器件的扩散电流.80 K下截止波长9.6μm,中心距30μm,替代衬底上的p~+-on-n台面器件品质参数(R0A)为38Ω·cm2,零偏阻抗较n-on-p结构的CdZnTe基碲镉汞器件高约15倍.但替代衬底上的p+-on-n台面器件仍受体内缺陷影响,在60 K以下较高的Itat成为暗电流主导成分,其R0A相比CdZnTe基n~+-on-p的HgCdTe差了一个数量级.     

红外焦平面阵列非均匀性及校正分析

大规模红外焦平面阵列器件固有的非均匀性,严重地制约着红外成像系统的性能,这 是其应用中必须解决的一个关键问题。本文详尽地分析了产生非均匀性的各种因素,并对其校正原理进行了阐述,最后给出了基于参考源校正算法的仿真结果。     

一种微透镜阵列的研制

介绍一种利用表面张力的作用、以光纤作材料、用分离的自聚焦透镜制作微透镜阵型的方法，这种方法具有制作工艺简单、无须昂贵设备等优点，用此方法实际制作了具有良好连续面型的微透镜阵列，并对制作的微透镜阵列进行了测试，效果较好。     

矩形波导窄边倾斜缝隙天线阵的设计

介绍了一种矩形波导窄边斜缝泰勒线阵设计的方法.简要阐述了矩形波导窄边缝隙天线阵列的相关理论,并使用HFSS软件对单个缝隙结构,无限阵列环境下缝隙单元的导纳参数进行数值仿真.然后按照仿真获得的等效谐振电导曲线,运用泰勒线元法综合求出非谐振式48元波导窄边缝隙线阵,并对整个线阵进行了仿真和实测.仿真和实测结果表明,该天线阵列具有低副瓣、宽带宽、高增益等特点,并且实测结果与仿真吻合良好.