Analytical method of predicating the instabilities of a micro arch-shaped beam under electrostatic loading

An arch-shaped beam with different configurations under electrostatic loading experiences either the direct pull-in instability or the snap-through first and then the pull-in instability. When the pull-in instability occurs, the system collides with the electrode and adheres to it, which usually causes the system failure. When the snap-through instability occurs, the system experiences a discontinuous displacement to flip over without colliding with the electrode. The snap-through instability is an ideal actuation mechanism because of the following reasons: (1) after snap-through the system regains the stability and capability of withstanding further loading; (2) the system flips back when the loading is reduced, i.e. the system can be used repetitively; and (3) when approaching snap-through instability the system effective stiffness reduces toward zero, which leads to a fast flipping-over response. To differentiate these two types of instability responses for an arch-shaped beam is vital for the actuator design. For an arch-shaped beam under electrostatic loading, the nonlinear terms of the mid-plane stretching and the electrostatic loading make the analytical solution extremely difficult if not impossible and the related numerical solution is rather complex. Using the one mode expansion approximation and the truncation of the higher-order terms of the Taylor series, we present an analytical solution here. However, the one mode approximation and the truncation error of the Taylor series can cause serious error in the solution. Therefore, an error-compensating mechanism is also proposed. The analytical results are compared with both the experimental data and the numerical multi-mode analysis. The analytical method presented here offers a simple yet efficient solution approach by retaining good accuracy to analyze the instability of an arch-shaped beam under electrostatic loading.

Fe/Nb多层膜中离子辐照效应研究(英文)

采用磁控溅射技术在Si衬底上沉积Si/[Fe(10 nm)/Nb(4 nm)/Fe(4 nm)/Nb(4 nm)]2/ [Fe(4nm)/Nb(4 nm)]4多层膜。用2 MeV的Xe离子在室温下辐照多层膜。采用俄歇深度剖析、X射线衍射和振动样品磁强计分析辐照引起的多层膜元素分布、结构及磁性变化。AES深度剖析谱显示当辐照注量达到1 .0×1014ions/cm2时,多层膜界面两侧元素开始混合;当辐照注量达到2 .0×1016ions/cm2时,多层膜层状结构消失,Fe层与Nb层几乎完全混合。XRD谱显示,当辐照注量达到1 .0×1014ions/cm2时, Nb的衍射峰和Fe的各衍射峰的峰位相对于标准卡片向小角方向偏移,这说明辐照引起Nb基和Fe基FeNb固溶体相的形成;当辐照注量大于1 .0×1015ions/cm2时,辐照引起非晶相的出现。VSM测试显示,多层膜的磁性随着结构的变化而变化。在此实验基础上,对离子辐照引起界面混合现象的机理进行了探讨。

不同剂量率X射线辐照对小鼠免疫系统的影响

目的检测经相同剂量不同剂量率X射线照射的BalB/C小鼠外周血淋巴细胞周期及胸腺和脾脏指数。方法18只BalB/c小鼠随机分为对照组(control),低剂量率照射组(20cGy/min)和高剂量率照射组(300cGy/min),每组6只。低剂量组和高剂量组采用剂量率分别为20cGy/min和300cGy/min的1GyX射线对小鼠进行全身照射,24h后取血及器官,用流式细胞仪检测外周血淋巴细胞的周期变化,用称量的方法得到胸腺和脾脏指数。结果高剂量率辐射时,小鼠外周血淋巴细胞的损伤较低剂量时大,而且对雄性鼠的影响大于雌性;同时,胸腺和脾脏指数变化也随着剂量率的增大而减小。结论低剂量率的照射对小鼠外周血淋巴细胞、胸腺和脾脏的影响较高剂量率辐射小;雌性鼠的辐射耐受能力较雄性强。