高效率小型化行波管的二次谐波抑制

以罗埃大信号理论为基础，利用两节螺距具有正负变化的双跳变输出电路对提高宽带行波管效率的二次谐波抑制问题进行了模拟。对输出电路的跳变位置和跳变螺距进行了详细研究。模拟与测试结果证明：采用双跳变输出线路，在低频端二次谐波受到很大抑制，正向基波分量得到明显增强，在宽频带(6—18GHz)范围内，获得了均衡的饱和功率输出。     

连续40 W 808 nm量子阱线阵二极管激光封装技术

研究了高功率二极管激光 (LD)封装中的铟焊料蒸镀工艺和回流焊工艺对芯片焊接状态的影响。在数值模拟和实验研究的基础上 ,优化了冷却器结构设计 ,研制出具有热阻低、压降小的铜微通道液体冷却器 ,可以满足热耗散功率大于 6 0W的二极管激光器散热冷却需要。通过封装实验得到输出功率 40W ,波长 80 8nm ,谱线半高宽<2nm ,电光效率近 40 %的连续线阵二极管激光器。用该激光器进行了抽运Nd∶YAG固体激光实验 ,在抽运功率为 40W时 ,获得 11 8W单横模固体激光输出 ,光 光效率约为 30 %。     

提高无线传感器网络信息安全的时间反演技术

近年来无线传感器网络被广泛应用于三维立体监测、分布式监测、目标跟踪、空间探索、随机分布测量等领域.由于无线传感器网络在军事上的特殊用途,如敌情侦察、兵力监控及其它的特殊用途,使其信息传输的安全性研究得到广泛关注.通过引入一种新技术——时间反演(TR,Time Reversal)技术,来降低信号在空间与时间上被非法检测到的概率.时间反演技术使得信号只有在特定的时间和特定的空间内才可以被检测出来,而超出这个范围信号很难被检测出来,从而提高了无线传感器网络的信息安全.     

Brazing Al2O3 to sintered Fe-Ni-Co alloys

Active metal brazing has been widely used to join ceramics to metals, as sound joints are usually achieved in a single step process without special equipment. However, residual stresses may be a potential problem especially upon joining ceramics to alloys with relatively high thermal expansion coefficients. This work investigates the brazing behavior of Alumina (Al₂O₃) to a sintered Fe-Ni-Co alloy, specially designed to match its coefficient of thermal expansion to that of the ceramic counterpart. The results indicate the presence of an interfacial zone whose microstructure depends on the filler alloy employed. A relationship was established between the microstructure of the interface and the flexural strength of the joints.     

钛合金平板电子束焊接残余应力的小孔法测量

采用小孔法对TC11平板真空电子束焊接接头的残余应力进行了测量,结果发现,其残余应力为以纵向残余应力为主的单向拉伸应力状态,横向残余应力数值较小,同时还将测量结果与有限元结果进行对比分析,证明了有限元模型的合理性和可靠性。     

Diffusion bonding of an aluminium-lithium alloy (AA8090) using aluminium-copper alloy interlayers

Diffusion bonds have been produced between sheets of an Al-Li-Cu-Mg-Zr alloy using aluminium-4% copper vapour deposited metallic interlayers. Microstructural changes occurred both in the parent alloy and in the bond interface after diffusion bonding cycles and post-bonding heat treatments were analysed. Different metallographic techniques (light microscopy, scanning and transmission electron microscopy) have been used. Diffusion bonding trials were carried out using the same alloy (AA8090), both in non-superplastic (T6) and superplastic conditions. Differences in their behaviours in relation to diffusion bonding were observed.     

Effects of thermal annealing on the optical characteristics of k -na + waveguides

We present a systematic study of the changes induced in the refractive-index profile of different sets of K -Na + ion-exchanged waveguides on soda-lime and BK7 substrates because of thermal annealing in the presence or absence of salt vapors. The concentration of potassium is recovered by secondary ion mass spectrometry, and the propagation losses are measured by means of the three-prism configuration.     

Ferromagnetic resonance study of structural relaxation and crystallization of the Metglas 2826A amorphous alloy

The ferromagnetic resonance technique was used to study the ageing behaviour of the metallic glass Fe₃₂Ni₃₆Cr₁₄P₁₂B₆ (Metglas 2826A). The peak-to-peak linewidth was measured for several isothermal annealing times in the temperature range 350 to 375° C. After an initial decrease, attributed to structural relaxation, the linewidth increases linearly with the transformed fraction of the first crystallization phase. For 0.05 <f< 0.50, the transformed fraction,f, as a function of time,t, satisfies the Avrami equation with the exponentn being between 1.58 and 1.71. The activation energy for the first crystallization phase is estimated from the times to reach 5 to 40% transformation to be 306 kJ mol^–1. The experimental results suggest that the second phase of crystallization begins when the transformed fraction of the first phase is of the order of 50%.     

Slurry sampling in serum blood for mercury determination by CV-AFS

The heavy metal mercury (Hg) is a neurotoxin known to have a serious health impact even at relatively low concentrations. A slurry method was developed for the sensitive and precise determination of mercury in human serum blood samples by cold vapor generation coupled to atomic fluorescence spectrometry (CV-AFS). All variables related to the slurry formation were studied. The optimal hydrochloric concentration and tin(II) chloride concentration for CV generation were evaluated. Calibration within the range 0.1-10 microg L(-1) Hg was performed with the standard addition method, and compared with an external calibration. Additionally, the reliability of the results obtained was evaluated by analyzing mercury in the same samples, but submitted to microwave-assisted digestion method. The limit of detection was calculated as 25 ng L(-1) and the relative standard deviation was 3.9% at levels around of 0.4 microg L(-1)Hg.