Investigation of performance variations due to the amplitude of group-delay ripple in chirped fiber Bragg gratings

We measure the system impacts due to the amplitude of group-delay (GD) ripple in single and cascaded chirped fiber Bragg gratings (CFBGs). Signals with smaller pulse width result in smaller performance variation at the same data rate. A 65-ps peak-to-peak GD ripple induces 0.9, 1.7, and 2.7 dB maximum penalties for 10, 20, and 40-Gb/s, respectively. We also find that cascading gratings with random ripple causes much less degradation than cascading gratings with the same ripple profile.     

β-Si3N4增强MoSi2基复合材料的组织与性能

利用放电等离子烧结法(SPS)制备了不同体积分数β-Si3N4增韧的MoSi2复合材料,研究了β-Si3N4颗粒对MoSi2基复合材料显微组织和力学性能的影响,初步探讨了β-Si3N4颗粒对MoSi2增韧的机理.结果表明:在MoSi2基体中加入β-Si3N4颗粒,能细化基体组织,改善力学性能;随着β-Si3N4体积分数的增加,复合材料的显微硬度和断裂韧性先增后减,20%β-Si3N4/MoSi2复合材料的显微硬度与断裂韧性分别比MoSi2提高了31.7%与62.9%,增韧补强效果显著;β-Si3N4的强韧化机理为细晶强化.     

Preparation and high-temperature performance of HfC-based nanocomposites derived from precursor with Hf-(O,N) bonds

A novel precursor was synthesized by reacting hafnium chloride with dicyandiamide and dimethylformamide. The precursor was characterized via FT-IR and NMR, as well as TG. Subsequently, the precursor was annealed in Ar over a range of temperatures from 1000 °C to 2000 °C, and the microstructural evolution of the ceramics was investigated by XRD, XPS, and TEM. The results show that the carbothermal reduction of the precursor starts at 1150 °C and the ceramic yields at 1500 °C reach 44.6 wt%. The obtained powders exhibit a uniform distribution and are composed of N-doped HfC and graphite. The N-doped structure postponed the oxidation of the HfC(N) ceramics. The HfC(N) ceramics were first oxidized to yield HfO₂, carbon, and nitrogen, and then the carbon was oxidized with the evolution of CO₂. The presented synthesis method is believed to be applicable to the preparation of other high-performance ceramics.     

Fabrication of Mg-doped ZnO nanofibers with high purities and tailored band gaps

The tailored doping levels towards the band gap tunability are one of the challenges to push forward the potential application of one-dimensional (1D) ZnO nanostructures in the opto/electric nanodevices. In present work, we reported the exploration of Mg-doped ZnO nanofibers via electrospinning of polyvinylpyrrolidone (PVP), Zn(CH₃COO)₂ (ZnAc) and Mg(CH₃COO)₂ (MgAc), followed by calcination in air. The resultant products were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), and X-ray photoelectron spectroscopy (XPS). The optical measurements (UV–vis) of the Mg-doped ZnO nanofibers suggested that the optical band gaps of the ZnO nanofibers could be tuned from 3.33 to 3.40 eV as a function of the Mg doing levels. This tunability of the band gap of ZnO nanofibers with an intentional impurity could eventually be useful for optoelectronic applications.     

载荷对含Cr碳膜摩擦磨损性能影响研究

用闭合场非平衡磁控溅射技术制备了高硬度含Cr碳膜。分别用压入法和划痕法测定了薄膜的结合强度。薄膜厚度用球坑法表征。用显微硬度计测定了薄膜的努氏硬度。在不同载荷条件下,用Ball-on-disc球盘磨损试验机研究了薄膜的摩擦系数、比磨损率的变化规律。分析讨论了载荷对含Cr碳膜摩擦磨损性能的影响。结果发现：随着载荷的提高,对磨钢球时薄膜的摩擦系数呈下降趋势．对磨损轨迹和对磨球磨损表面的扫描电镜（SEM）观察发现存在转移膜现象。对磨球磨损表面的EDX分析结果进一步证明了转移膜的存在。文中还对含Cr碳膜磨损机理进行了分析和讨论。用闭合场非平衡磁控溅射技术制备了高硬度含Cr碳膜。分别用压入法和划痕法测定了薄膜的结合强度。薄膜厚度用球坑法表征。用显微硬度计测定了薄膜的努氏硬度。在不同载荷条件下,用Ball-on-disc球盘磨损试验机研究了薄膜的摩擦系数、比磨损率的变化规律。分析讨论了载荷对含Cr碳膜摩擦磨损性能的影响。结果发现：随着载荷的提高,对磨钢球时薄膜的摩擦系数呈下降趋势．对磨损轨迹和对磨球磨损表面的扫描电镜（SEM）观察发现存在转移膜现象。对磨球磨损表面的EDX分析结果进一步证明了转移膜的存在。文中还对含Cr碳膜磨损机理进行了分析和讨论。     

Effect of denucleating glass composition on undercooling of Fe83Ga17 alloy melts

Adopting glass fluxing combined with superheating cycling method, the undercooling and its stability of Fe₈₃Ga₁₇ alloy melts were investigated using different kinds of denucleating glass: B₂O₃, 90% NaSiCa + 10% B₂O₃ (simplified as Na–Si–Ca–Al–B) and 70% Na–Si–Ca–Al–B + 30% Na₂B₇O₄. The results showed that different glass has different denucleating mechanism. The purification of B₂O₃ glass is only a physical process, by which the stable bulk undercooling cannot be obtained during superheating–cooling cycles. While taking Na–Si–Ca–Al–B glass as purifying agent, its denucleating mechanism is a comprehensively physicochemical process. But the stability of undercooling is still undesirable because of the separation between melt and glass during cooling process in superheating cycling. A stable bulk undercooling can be obtained by physicochemical denucleating process in the case of 70% Na–Si–Ca–Al–B + 30% Na₂B₇O₄ molten glass owing to its suitable viscosity.     

A nanocomposite of dual-phase Fe/TiCN wrapped in nitrogen-doped carbon with magnetic and dielectric characters for superior microwave absorption

A careful approach to the optimization of magnetic and dielectric losses in nanomaterials can improve the electromagnetic wave absorption loss performance for certain microwave absorption applications. In this study we prepared dual core (Fe/TiCN) coated with nitrogen (N) doped carbon shell nanocomposite by arc-discharge method under mix atmospheres of working gases and with varying elemental compositions. Among all nanocomposites, (Fe/TiC_0.7N_0.3)@N–C dual-core@ N- doped shell nanocomposite exhibits enhanced microwave absorption. Owing to the novel dual-core@ N-doped shell structure and numerous defects induced by doping N in carbon shells, an improved dielectric relaxation in composite is observed and the minimum reflection loss was reached −44.36 dB at 5.3 GHz for 4.8 mm thickness.     

放电等离子烧结工艺制备Ni60B镍基自熔合金

采用放电等离子烧结技术制备了KF-Ni60B镍基自熔合金,通过硬度、密度测试,研究了烧结温度、保温时间和烧结压力对烧结体性能的影响,并对烧结工艺进行了优化.结果表明:烧结温度对该合金性能的影响最大,烧结压力和时间的影响次之;在65 MPa压力下,经870℃烧结15 min的Ni60B自熔合金性能最佳,硬度为64.22 ...     

A novel bilayer film material composed of polyaniline and poly(methylene blue)

Electrically conducting polyaniline(PAn)/poly(methylene blue)(PMB) bilayer film was prepared by electrochemical polymerization of methylene blue on the PAn-coated Pt working electrode. The bilayer film electrode exhibits higher electrocatalytic activity towards oxidation of methanol than PAn electrode and PMB electrode in neutral and alkaline solutions. FTIR spectroscopy reveals PAn-unit is a main unit in the structure of the bilayer film. In addition, the PAn/PMB bilayer film has also been characterized by scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS), respectively.     

合金成分与制备工艺对Nd-Fe-B铸片显微组织的影响

在工业生产线上,选择不同条件下制备的Nd-Fe-B合金铸片,分析了成分设计、浇注工艺以及铸片厚度对Nd-Fe-B合金铸片显微组织的影响.成分设计中较高的重稀土元素含量增大熔液结晶时的过冷度,使铸片显微组织中产生较多细小等轴晶.当平均厚度为0.3～0.4mm时,铸片具有较好的显微组织,即主相以片状晶方式沿垂直贴辊面的方向生长,富Nd相呈薄层状均匀分布在主相内部及晶界处,薄层间距约为3～5μm;厚度偏大时,在铸片自由面附近存在少量α-Fe相,而厚度偏小时,其显微组织中富Nd相薄层间距偏小,仅为2μm左右.合适的浇注工艺可以获得理想的铸片显微组织,浇注温度偏低导致细小等轴晶出现,而且浇注温度偏低和熔液浇注速度偏慢均不利于片状晶生长.