微剪切应力传感器的加工工艺

提出了一种感测单元不直接接触流场的微剪切应力传感器结构,详细阐述了其感测单元MEMS制作工艺。采用热氧化硅掩膜方法解决了硅深刻蚀的选择比问题;优化后的硅深刻蚀工艺参数：刻蚀功率1600 W、低频(LF)功率100 W,SF6流量360 cm3/min,C4F8流量300 cm3/min,O2流量300 cm3/min。采用Cr/Au掩膜,30 ℃恒温低浓度HF溶液解决了玻璃浅槽腐蚀深度控制问题;喷淋腐蚀和基片旋转等措施提高了玻璃浅槽腐蚀表面质量。采用上述MEMS工艺制作了微剪切应力传感器样品,样品测试结果表明：弹性悬梁长度和宽度误差均在2 m以内、玻璃浅槽深度误差在0.03 m以内、静态电容误差在0.2 pF以内,满足了设计要求。     

基于剪应力检测的石英微结构及其陀螺效应研究

为了简化石英陀螺结构侧壁上的电极图形,设计了一种基于剪应力检测Coriolis力的新型石英微结构.通过对剪应力检测方案的分析,微结构侧壁电极的极性单一,采用锥度为15°的锥形梁结构作为敏感梁的设计可以增大敏感梁的检测灵敏度.通过各项异性湿法腐蚀z切石英片的方法制造了微结构样件.测试表明样件的驱动频率约为5.6kHz,大气下的品质因子在5000以上.输出信号频谱的谱线存在Coriolis力信号,验证了设计思想的正确性。     

传感器电解质材料热膨胀性能和热稳定性变化规律研究

以ZrO2固体电解质材料为例,研究氧传感器电解质材料原子振动特点和热膨胀系数及其热稳定性随温度和时间的变化规律,探讨原子非简谐振动的影响。结果表明：原子振动的频率、阻尼系数,在简谐近似下为常数,在考虑到非简谐效应后随温度升高而增大;原子平均位移和热膨胀系数在简谐近似下为零,在考虑到非简谐效应后随温度升高而增大,随的时间的增长而减小;热膨胀性能稳定性温度系数随温度的升高而减小,随时间的增长而增大,即使用时间越长,材料的热膨胀性能稳定性越低;温度越高,热膨胀性能越稳定;非简谐情况下的原子振动的频率、阻尼系数和热膨胀系数与简谐近似下的差值随温度的升高而增大,即温度越高,非简谐效应越显著。     

Initial damage induced by thermal residual stress and microscopic failure analysis of carbon-fiber reinforced composite under shear loading

In order to study the mechanical properties and the progressive failure process of composite under shear loading, a representative volume element (RVE) of fiber random distribution was established, with two dominant damage mechanisms – matrix plastic deformation and interfacial debonding – included in the simulation by the extended Drucker–Prager model and cohesive zone model, respectively. Also, a temperature-dependent RVE has been set up to analyze the influence of thermal residual stress. The simulation results clearly reveal the damage process of the composites and the interactions of different damage mechanisms. It can be concluded that the in-plane shear fracture initiates as interfacial debonding and evolves as a result of interactions between interfacial debonding and matrix plastic deformation. The progressive damage process and final failure mode of in-plane shear model which are based on constitute are very consistent with the observed result under scanning electron microscopy of V-notched rail shear test. Also, a transverse shear model was established as contrast in order to comprehensively understand the mechanical properties of composite materials under shear loading, and the progressive damage process and final failure mode of composite under transverse shear loading were researched. Thermal residual stress changes the damage initiation locations and damage evolution path and causes significant decreases in the strength and fracture strain.     

A continuum thermal stress theory for crystals based on interatomic potentials

This paper presents a new continuum thermal stress theory for crystals based on interatomic potentials.The effect of finite temperature is taken into account via a harmonic model.An EAM potential for copper is adopted in this paper and verified by computing the effect of the temperature on the specific heat,coefficient of thermal expansion and lattice constant.Then we calculate the elastic constants of copper at finite temperature.The calculation results are in good agreement with experimental data.The thermal stress theory is applied to an anisotropic crystal graphite,in which the Brenner potential is employed.Temperature dependence of the thermodynamic properties,lattice constants and thermal strains for graphite is calculated.The calculation results are also in good agreement with experimental data.     

Stable 85Rb micro vapour cells: fabrication based on anodic bonding and application in chip-scale atomic clocks

We describe the microfabrication of 85 Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb.Under controlled conditions,the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm 3 internal volumes during the cell sealing process.At an ambient temperature of 90 C the optical absorption resonance of 85 Rb D1 transition with proper broadening and the corresponding coherent population trapping (CPT) resonance,with a signal contrast of 1.5% and linewidth of about 1.7 kHz,have been detected.The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status.In addition,the physics package of chip-scale atomic clock (CSAC) based on the cell was realized.The measured frequency stability of the physics package can reach to 2.1×10 10 at one second when the cell was heated to 100 C which proved that the cell has the quality to be used in portable and battery-operated devices.     

Effects of residual stress and interfacial frictional shear stress on interfacial debonding at notch-tip in two-dimensional unidirectional composite

A calculation method based on the shear lag approach was presented to get an approximate estimate of influences of residual stresses and frictional shear stress at the debonded interface on the interfacial debonding behavior at the notch-tip along fiber direction in two-dimensional unidirectional double-edge-notched composites. With this method, the energy release rate for initiation and growth of debonding as a function of composite stress were calculated for some examples. The calculation results showed in outline how much the tensile and compressive residual stresses in the matrix and fiber along fiber direction, respectively, act to hasten the initiation and growth of the debonding when the final cut element in the notch is matrix, while they act to retard them when the final cut element is fiber, and how much the frictional shear stress at the debonded interface reduces the growth rate of the debonding.     

空间光学遥感器环境适应性设计与试验研究

为适应空间光学遥感技术的迅速发展及对空间光学遥感器需求的不断增长,在追求高高空间分辨率、高光谱分辨率、高辐射分辨率性能及轻量化的同时,必须考虑空间光学遥感器对恶劣的发射运载力学环境及在轨真空热环境的适应性问题。本文概述了国内外空间光学遥感器环境适应性设计的现状与进展,阐述了空间环境因素对空间光学遥感器性能的影响,尤其是在力学及真空热环境作用下的环境效应,探讨了环境效应的作用机理;在对任务需求和环境效应分析的基础上,提出了空间光学遥感器环境适应性设计的要求、准则以及适应性设计要点。在空间光学遥感器设计的早期设计阶段,统筹考虑对未来可能遇到的各种环境的适应性问题,并开展以质量特性、动力学特性及热光学特性为主的适应性设计分析迭代。在工程实施阶段,进行相应的特征试验以及环境模拟试验,实地考核空间光学遥感器的力学及热光学特性以及在各种模拟环境条件下功能和性能的有效性和正确性,确保对未来各种恶劣环境条的适应性。本文对设计分析迭代过程中以及试验过程中对环境适应性的评价方法及其相关的地面试验内容和方法也进行了论述。     

真空热蒸发生长CdX(X=S,Te)纳米线研究性实验

将一维纳米结构的气—液—固生长机制与大学材料物理实验真空热蒸发镀膜结合,设计了生长半导体纳米线的研究性实验.利用金属铋或锡作为催化剂,真空热蒸发生长了CdS,CdTe等半导体纳米线.纳米线产物形貌均匀,并可实现选择性生长.     

Regulation of shear stress on rolling behaviors of HL-60 cells on P-selectin

Circulating leukocytes in trafficking to the inflammatory sites, will be first tether to, and then roll on the vascular surface. This event is mediated through specific interaction of P-selectin and P-selectin glycoprotein ligand-1(PSGL-1), and regulated by hemodynamics. Poor data were reported in understanding P-selectin-mediated rolling. With the flow chamber technique, we herein observed HL-60 cell rolling on P-selectin with or without 3% Ficoll at various wall shear stresses from 0.05 to 0.4 dyn/cm2. The results demonstrated that force rather than transport regulated the rolling, similar to rolling on L- and E-selectin. The rolling was accelerated quickly by an increasing force below the optimal shear threshold of 0.15 dyn/cm2 first and then followed by a slowly decelerating phase starting at the optimum, showing a catch-slip transition and serving as a mechanism for the rolling. The catch-slip transition was completely reflected to the tether lifetime and other rolling parameters, such as the mean and fractional stop time. The narrow catch bond regime stabilized the rolling quickly, through steeply increasing fractional stop time to a plateau of about 0.85. Data presented here suggest that the low shear stress threshold serves as a mechanism for most cell rolling events through P-selectin.     

Initiation of vacuum breakdown and failure mechanism of the carbon nanotube during thermal field emission

The carbon nanotube(CNT)-based materials can be used as vacuum device cathodes. Owing to the excellent field emission properties of CNT, it has great potentials in the applications of an explosive field emission cathode. The falling off of CNT from the substrate, which frequently appears in experiments, restricts its application. In addition, the onset time of vacuum breakdown limits the performance of the high-power explosive-emission-cathode-based diode. In this paper, the characteristics of the CNT, electric field strength, contact resistance and the kind of substrate material are varied to study the parameter effects on the onset time of vacuum breakdown and failure mechanism of the CNT by using the finite element method.     

基于黑体辐射感温薄膜的瞬态高温传感器的设计

针对瞬态高温的测量难题,采用辐射式测温技术和接触式测温技术有机结合的方法,设计了由黑体辐射温度敏感体、圆柱状高强度金属外壳以及壳内信号调理电路构成的瞬态高温测量装置。通过对感温薄膜特殊材料的恰当选取以及整体结构的合理设计,并利用ANSYS软件对其黑体感温薄膜进行了瞬态高温热传导分析。分析表明,施加的温度载荷为2 000 ℃、2 500 ℃、3 000 ℃时,此温度传感器响应时间分别为487.001 s、545.001 s、590.001 s,能够克服传统瞬态温度传感器体积大、响应慢、安装不方便以及易受恶劣环境因素影响等不足,在测温技术领域具有良好的应用价值。     

Miniature optical fiber current sensor based on a graphene membrane

The unique electronic and mechanical properties, of graphene make it an ideal material for nanoelectromechanical system (NEMS) applications. Here, a miniature optical fiber current sensor based on a quasistatic graphene NEMS with a graphene membrane covering the hole on a pre‐etched fiber tip and two gold electrodes on opposite sides of the tip has been demonstrated. The sensor overcomes the shortcomings of conventional optical fiber current sensors based on thermal effects, such as relatively low sensitivity, long response time, and huge device size; it has simultaneously a high sensitivity of 2.2 × 10⁵ nm/A², a short response time of ∼0.25 s and a compact device size of ∼15 μm, and has found practical application. Using a smaller graphene membrane with better quality can reduce the response time to submillisecond levels with a more precise measurement system. The sensor presented in this paper may pave the way for the practical usage of optical fiber current sensors based on thermal effects.

     

Microstreaming velocity field and shear stress created by an oscillating encapsulated microbubble near a cell membrane

Sonoporation mediated by microbubbles is being extensively studied as a promising technology to facilitate gene/drug delivery to cells. However, the theoretical study regarding the mechanisms involved in sonoporation is still in its infancy. Microstreaming generated by pulsating microbubble near the cell membrane is regarded as one of the most important mechanisms in the sonoporation process. Here, based on an encapsulated microbubble dynamic model with considering nonlinear rheological effects of both shell elasticity and viscosity, the microstreaming velocity field and shear stress generated by an oscillating microbubble near the cell membrane are theoretically simulated. Some factors that might affect the behaviors of microstreaming are thoroughly investigated, including the distance between the bubble center and cell membrane (d), shell elasticity (χ), and shell viscosity (κ). The results show that (i) the presence of cell membrane can result in asymmetric microstreaming velocity field, while the constrained effect of the membrane wall decays with increasing the bubble-cell distance; (ii) the bubble resonance frequency increases with the increase in d and χ, and the decrease in κ, although it is more dominated by the variation of shell elasticity; and (iii) the maximal microstreaming shear stress on the cell membrane increases rapidly with reducing the d, χ, and κ. The results suggest that microbubbles with softer and less viscous shell materials might be preferred to achieve more efficient sonoporation outcomes, and it is better to have bubbles located in the immediate vicinity of the cell membrane.     

Finite-element analysis on performance and shear stress of cemented tungsten carbide anvils used in the China-type cubic-anvil high-pressure apparatus

Stress distribution in cemented tungsten carbide (WC) anvils is of primary interest in high pressure research, but is very difficult to determine experimentally. We have performed finite-element simulations to study the performance and the shear stress distribution of WC anvils used in the China-type cubic-anvil high pressure apparatus (SPD-6×2000). Our results show that in order to avoid failure cracks in high-stress areas, the maximum shear stress should be lower than 3.17 GPa for the WC anvils (8% cobalt). The simulations have been verified by high-pressure experiments. Our method of analyzing stress distribution helps in evaluating the ability of WC anvils, and would aid in designing a new anvil to enhance performance.     

基于LabVIEW的低温及真空测量系统设计

低温真空环境下超导材料的热物性参数测量是低温工程学的基础性研究内容。为了提高超导磁体热物性参数数据采集的实时性、连续性及准确性,同时实现多仪器和多数据采集的整合,设计了基于LabVIEW虚拟仪器系统的低温及真空数据采集系统,进行了相关的实验。通过对实验所采集数据的分析可知,基于LabVIEW虚拟仪器的低温真空测量系统具有稳定性好,数据采集连续、直观、准确的特点,为获得低温和真空参数的准确测量提供了一种新方法。     

Molecular dynamics study of thermal stress and heat propagation in tungsten under thermal shock

Using molecular dynamics （MD） simulation, we study the thermal shock behavior of tungsten （W）, which has been used for the plasma facing material （PFM） of tokamaks. The thermo-elastic stress wave, corresponding to the collective displacement of atoms, is analyzed with the Lagrangian atomic stress method, of which the reliability is also analyzed. The stress wave velocity corresponds to the speed of sound in the material, which is not dependent on the thermal shock energy. The peak pressure of a normal stress wave increases with the increase of thermal shock energy. We analyze the temperature evolution of the thermal shock region according to the Fourier transformation. It can be seen that the “obvious” velocity of heat propagation is less than the velocity of the stress wave; further, that the thermo-elastic stress wave may contribute little to the transport of kinetic energy. The heat propagation can be described properly by the heat conduction equation. These results may be useful for understanding the process of the thermal shock of tungsten.     

基于紫外刻写相移光栅的温度应力同时测量传感器

传统光纤光栅传感器存在温度应力交叉敏感的问题,无法同时测量被测物体的温度应力变化情况.针对这种情况,提出一种新型的利用紫外光刻写相移光栅的方法,在刻写光栅前用电极放电的方法去除掉极小一段光纤的光敏性,使光纤原有的均匀周期分布状态被破坏,从而形成相移光栅,并对其进行理论分析.此种相移光栅的透射光谱存在2个明显的谐振峰,利...     

Co-registration of the distribution of wall shear stress and 140 complex plaques of the aorta

Previous studies provide evidence that atherosclerosis develops in vascular regions exposed to low wall shear stress (WSS) and high oscillatory shear index (OSI). 4D flow MRI was analyzed in 70 stroke patients with complex plaques (≥ 4 mm thickness, ulcerated or superimposed thrombi) and in 12 young healthy volunteers. The segmental distribution of peak systolic WSS_systole and OSI was quantified in analysis planes positioned directly at the location of 140 complex plaques found in the 70 patients. In addition, WSS_systole and OSI were evaluated in 8 standard analysis planes distributed along the aorta. Complex plaques were predominantly found at the inner curvature of the aortic arch and of the descending aorta. High OSI was co-located with the segments mostly affected by complex plaque while WSS_systole demonstrated a homogenous distribution. In standard analysis planes, patients demonstrated significantly (p < 0.01) altered distribution of wall parameters compared to volunteers (reduced WSS_systole in 91% of aortic wall segments, increased OSI in 48% of segments). OSI distribution was asymmetric with higher values at the inner curvature of the aorta. While WSS and OSI showed expected changes in patients compared to healthy controls, their distribution pattern at complex plaques indicated a more complex and heterogeneous relationship than previously anticipated.     

基于XRD的镀锌钝化膜残余应力试验研究

利用XRD技术测试了镀锌钝化膜结合界面的残余应力，同时通过电解抛光法检测了其厚度方向残余应力的分布规律，分析了残余应力对镀锌钝化膜结合强度的影响. 试验结果表明，镀锌钝化膜的残余应力均表现为压应力，并随着基体表面残余应力的增大而减小；钝化膜在2—10μm厚度方向的残应力为-274.5—-428.3MPa，其应力为梯度分布；镀锌钝化膜与基体的界面结合强度与其残余应力成反比，减小薄膜残余应力，有利于提高镀锌钝化膜与基体的结合强度. 关键词： X射线衍射法(XRD) 镀锌钝化膜 结合强度 残余应力