Iterative control approach to high-speed force-distance curve measurement using AFM: time-dependent response of PDMS example

Force-distance curve measurements using atomic force microscope (AFM) has been widely used in a broad range of areas. However, currently force-curve measurements are hampered the its low speed of AFM. In this article, a novel inversion-based iterative control technique is proposed to dramatically increase the speed of force-curve measurements. Experimental results are presented to show that by using the proposed control technique, the speed of force-curve measurements can be increased by over 80 times--with no loss of spatial resolution--on a commercial AFM platform and with a standard cantilever. High-speed force curve measurements using this control technique are utilized to quantitatively study the time-dependent elastic modulus of poly(dimethylsiloxane) (PDMS). The force-curves employ a broad spectrum of push-in (load) rates, spanning two-order differences. The elastic modulus measured at low-speed compares well with the value obtained from dynamic mechanical analysis (DMA) test, and the value of the elastic modulus increases as the push-in rate increases, signifying that a faster external deformation rate transitions the viscoelastic response of PDMS from that of a rubbery material toward a glassy one.     

非接触式电压相量测量算法

同步相量测量技术为电网动态安全监测提供了数据基础,非接触式电压传感技术具备安全、便捷、成本低的优势,有利于测量装置实现海量布点。现有非接触式电测量的缺陷在于复杂电压经探头传变后二次侧输出电压发生畸变,难以还原一次侧电压相量。为解决电压畸变问题,文中提出了一种对带内信号分频计算的相量测量算法。首先对探头输出电压进行预处理,滤除带外信号与噪声,随后采用矩阵束法计算带内信号频率,以此构建信号模型进行时域拟合求解带内信号相量,最后将带内信号相量还原至一次侧后合成得到综合相量。仿真结果表明,所提方法能够利用探头二次侧输出电压采样值计算一次侧电压相量。实验数据显示所提方法的幅值测量误差小于4.5%,相位误差小于1°,频率误差小于0.04 Hz,频率变化率误差小于4 Hz/s。     

基于FPGA的多通道雷达数据回放系统设计

为解决雷达实时信号处理功能及性能有效验证问题,文中设计并实现了一种宽窄带一体化、多通道雷达数据回放系统。该系统按雷达工作的时序和数据率将雷达回波数据发送至实时信号处理系统,从而对目标跟踪场景进行复现,实现雷达实时信号处理功能及性能的有效验证。系统硬件平台由磁盘阵列服务器与两块PCIe光纤板组成。基于Xilinx系列产品,结合系统特点对PCIe DMA控制流程及响应机制做进一步调整,实现了服务器到光纤板的雷达回波数据高速批量传输。根据雷达工作机制及回波数据结构,设计FPGA回放控制状态机及相关功能模块,严格按照雷达工作的时序和数据率使雷达回波数据由光纤板传输至实时处理系统。分别设计软件同步控制方法和硬件同步控制方法,保证多板卡数据回放的同步性。测试结果表明,该系统实现了宽、窄带雷达回波数据的板间同步回放,各数据类型分别支持6路并行数据通道,数据回放峰值速率可达1 920 MB·s^-1。文中系统可依托雷达原有硬件平台实现,无需增设板卡和线缆,具有良好的集成性与通用性,目前已被应用于某多功能相控阵雷达中。     

InPBi薄膜材料的结构性能和光学性能研究

室温下,InPBi表现出强而宽的光致发光光谱,其宽光谱特性来自于材料中的PIn反位深能级和与Bi相关的深能级。该特性使得InPBi有希望应用于制备光学相干层析扫描系统中的超辐射光源。文章利用透射电子显微镜和三维原子探针研究了InPBi薄膜材料的结构性能,发现Bi原子在InPBi薄膜中的分布极不均匀,在InPBi/InP界面出现了Bi的富集区,从该区域沿[001]方向出现了Bi的纳米面,此纳米面位于(110)平面上。这种Bi原子的富集分布阻碍了PIn反位参与的载流子复合过程,对InPBi的光学性能有显著的影响。研究结果可为制造光学相干层析扫描系统的超辐射发光二极管提供一定的理论基础。     

Writing with Fluid: Structuring Hydrogels with Micrometer Precision by AFM in Combination with Nanofluidics

Hydrogels have many applications in biomedical surface modification and tissue engineering. However, the structuring of hydrogels after their formation represents still a major challenge, in particular due to their softness. Here, a novel approach is presented that is based on the combination of atomic force microscopy (AFM) and nanofluidics, also referred to as FluidFM technology. Its applicability is demonstrated for supramolecular hydrogel films that are prepared from low‐molecular weight hydrogelators, such as derivates of 1,3,5‐benzene tricarboxamides (BTAs). BTA films can be dissolved selectively by ejecting alkaline solution through the aperture of a hollow AFM‐cantilever connected to a nanofluidic controller. The AFM‐based force control is essential in preventing mechanical destruction of the hydrogels. The resulting “chemical writing” process is studied in detail and the influence of various parameters, such as applied pressure and time, is validated. It is demonstrated that the achievable structuring precision is primarily limited by diffusion and the aperture dimensions. Recently, various additive techniques have been presented to pattern hydrogels. The here‐presented subtractive approach can not only be applied to structure hydrogels from the large class of reversibly formed gels with superior resolution but would also allow for the selective loading of the hydrogels with active substances or nanoparticles.     

Elemental partitioning,lattice misfit and creep behaviour of Cr containing γ′ strengthened Co base superalloys

Novel Cr containing Co-Al-W base superalloys were studied by atom probe tomography and neutron diffraction. Cr is found to predominantly partition to the γ matrix and decrease partitioning of W to γ′. Furthermore, Cr significantly enhances the γ′ volume fraction, decreases the γ/γ′ lattice misfit and deteriorates the creep resistance. Addition of Ni to the Cr containing alloys affects partitioning of W and Al, further decreases the lattice misfit and results in the formation of irregularly shaped precipitates. Al, W and Cr tend to occupy the ‘B'sublattice in the γ′-A₃B phase (L1₂ type), while Co and Ni reside in the ‘A' sublattice.     

接触触发式探头结构优化设计

设计了一种适用于微纳米三坐标测量机的高灵敏度接触触发式探头。介绍了该探头的结构和原理,建立了探头的灵敏度模型和刚度模型,依据三维方向等灵敏度和等刚度的原则,利用最优化方法得出了探头结构参数的最优解。对探头的刚度进行了仿真验证;分别对探头的刚度、分辨率以及稳定性进行了实验测试。实验结果表明:该探头在三维方向上的刚度均小于1 mN/μm,且近似相等;分辨率高于50 nm;当环境温度的波动范围小于±0.025℃时,探头在1.3 h内的漂移量为20nm。     

获取界面响应不可测数据的频响探针关键技术研究

目的针对传统逆子结构理论在求解过程中界面响应难以实测的问题,提出一种利用频响探针技术来获取该界面响应的关键技术。方法首先基于该频响探针的动力学微分方程,从理论上推导了该频响探针技术的理论公式,然后对建立的二级单点刚性耦合系统进行了有限元数值验证,将利用频响探针技术预测得到的难测原点频响函数与有限元计算值进行比较,并将该预测值代入逆子结构理论公式中,得到了部件频响函数的预测值,将该预测值与有限元计算值进行了对比验证。结果预测值与有限元计算值高度吻合,验证了该理论的准确性。结论该频响探针关键技术在获取界面响应不可测数据方面,有很好的应用价值。     

基于连续压导探针的炸药爆速和临界直径测试方法?

临界直径是确定炸药合理装药直径、预防炸药拒爆和不完全爆轰的重要指标,对炸药性能提高和高效利用有着十分重要的意义。设计了一种连续压导探针和楔形装药装置,在对炸药爆速进行测试的同时,利用炸药在临界直径不完全爆轰的特征,通过寻找爆轰波传播的拐点确定炸药临界直径。试验结果表明:装药密度为0.9g/cm3的铵油炸药爆速为3 261 m/s,临界直径为12.5 mm。提供了一种可同时测得炸药爆速和临界直径的方法,该方法简单,试验费用低,对炸药参数测试具有一定的指导意义。     

超音速条件下基于CFD的压力探针校准特性数值模拟

对超音速条件下倒角型总压探针的校准特性进行了数值模拟研究,并对影响校准特性的关键影响量进行了分析,得到了总压系数随着位置、压力、总温、马赫数几个关键参数的变化规律。数值模拟结果和实验结果进行了对比,二者较为接近。研究结果表明,安装位置的选择对倒角总压探针总压系数影响较大,探针的安装位置越接近风洞上游,总压系数绝对值越小;倒角型总压探针总压系数的绝对值随温度和压力的升高而减小,随马赫数的升高而增大。