Tracking differential interference contrast diffraction line images with nanometre sensitivity

This paper presents a computer vision framework for detecting and tracking diffraction images of linear structures in differential interference contrast (DIC) microscopy. The tracker can resolve image displacements of 1/10 of a pixel despite the weak and orientation-dependent contrast in DIC, as well as the variable blur in such image data caused by vertical specimen movement. In our high numerical aperture, high magnification microscope set-up, this resolution corresponds to 5 nm in object space. In video DIC similar resolution has been reported hitherto only for rotationally symmetric targets such as bead images. The tracker was developed for measuring deflections of clamped microtubules with a freely moving second end. By analysing the thermal fluctuations of such microtubules it was possible to derive their elasticity.   The paper describes a filtering scheme for the detection and localization of DIC diffraction line images which represent loci of microtubules. For tracking the movements of the extracted lines we adopted the sum of squared (brightness) differences algorithm from computer vision. The analysis of the fluctuation measurements demonstrates the high sensitivity of this tracking technique in quantifying positional and orientational changes. We derived that the theoretical limit in tracking displacements of such diffraction line images is 1.25 nm, four times below the experimentally verified sensitivity. This indicates that the proposed tracker is still suboptimal. Nevertheless, the tracking precision was sufficient to reveal subtle deviations in the distribution of microtubule deflection from free diffusion. They were induced by pivotal points and multiple positions of relaxation. Also, the results suggest that there were defects in the polymer structure which caused very small but significant bends in the microtubule axis.     

Magnetism in Si1 − xMnx diluted magnetic semiconductor thin films

We have studied the electrical and magnetic properties of p-type semiconductor thin films of Si_1 − xMn_x/Si (x = 0.036 and 0.05) grown by molecular beam epitaxy. Experimental results reveal that the resistivity of the samples decreases gradually with increasing measurement temperature, which can be described well by Mott's variable-range-hopping model. All the samples exhibit the ferromagnetic ordering above room temperature. Among these samples, Si_0.95Mn_0.05 has a higher hole density and magnetization. This indicates an enhancement of hole-mediated ferromagnetic exchange interactions when the Mn-doping concentration is increased.     

Effect of Heat‐Moisture Treatment on Structural and Thermal Properties of Rice Starches Differing in Amylose Content

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat‐moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat‐moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A‐type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short‐range molecular order to amorphous (RSA) of heat‐moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V‐amylose‐lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (T_o) but decreased the gelatinization enthalpy (ΔH) of rice starches. A broad gelatinization temperature range (T_c‐T_o) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT₂₇ (HMT at 27% moisture level). Additionally the (T_c‐T_o) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.     

LiF enhanced nucleation of the low temperature microcrystalline silicon prepared by plasma enhanced chemical vapour deposition

A 15-nm lithium fluoride (LiF) thin film evaporated on glass substrate is shown to enhance the nucleation of microcrystalline Si grown by plasma enhanced chemical vapour deposition at the amorphous/microcrystalline boundary conditions. The effect is more pronounced at low substrate temperatures, nucleation density being 10 times higher at ∼ 80 °C. The effect is ascribed to the ionic chemical nature of LiF, the low work function material used in organic electronic devices, and we propose its use for micro patterning crystalline Si regions in otherwise amorphous Si film.     

基于小波包的气门故障诊断

本文利用小波包将信号按任意时频分辨率（满足测不准原则）分解到不同频段的特点,论述了小波包特征提取的方法。利用这一特性对柴油机气门间隙和漏气故障进行了诊断,取得了满意的结果。     

等离子脉冲电机的冲击传动系统的分析研究

等离子电机是一种新型、瞬时而高功率的特种电机,由于该同的能源来自于机械能向有的瞬时转换,所以系统的冲击问题成为一个不可避免而又致关重要的问题。本文应用了机电模拟的思想,通过电枢回路方程,求得电流、电压随时间变化曲线,从而找到惯量J的选取方法,导出了转速及转矩随时间变化方程式。本文从静态和动态二方面对系统进行受力分析和计算。通过对系统固有频率的计算,措出了避开固有频率的方法,最后从波动学角度,对系统的应力波作了浅显的讨论。根据分析计算,建议采用电磁离合器作为解决冲击问题的手段。     

原位合成MoSi_2-SiC复合材料的高温强化

采用高温压缩实验研究了不同体积分数 ＳｉＣ含量对原位合成 ＭｏＳｉ２—ＳｉＣ复合材料在 １０００－１４００℃ 的屈服强度及流变应力的影响结果表明,与单－ ＭｏＳｉ２材料相比,复合材料的高温强度随 ＳｉＣ含量的增加而明显提高．高温屈服强度 σｙ和第二相 ＳｉＣ粒子间距λＳ服从σＹ＝σ０＋ｋλＳ－１／２关系式结合组织结构的研究结果对其相间障碍强化的高温强化机制进行了初步探讨．     

熔敷金属力学性能人工神经网络预测法的应用

在实测样本的基础上,用人工神经网络建立了熔敷金属力学性能的预测模型。该模型预测的结果同实验值之间有很好的对应关系。利用该模型研究了杂质元素S,P,O,N和合金元素C,Mn,Ti对熔敷金属低温韧性的影响,并采用正交实验的方法得出了较佳的熔敷金属化学成分。本文的研究为熔敷金属力学性能的设计和控制提供了有效的途径。     

双曲屋面钢结构制作安装施工技术

清华大学综合体育中心屋盖为双曲弧面拱顶,屋面钢骨架为三维空间曲线结构.施工中采取将超长双曲弓形空腹梁在地面拼接、整榀安装,并把三维空间构件分解成平面构件与实测尺寸相结合等措施,保证了安装进度与质量.     

越南河内还剑湖历史地区的保护与再开发——趋向场所精神的保护

本论文建议通过保护世界历史与自然遗产,再生场所的记忆和复兴经济活力来保护还剑湖历史地区的内在精神,提出将现有建成的历史环境分成不同层次－－这些层次体现了残民地和后殖民地时期的设计理念和经济政治条件,然后通过设计导则对其进行保护。在这些设计导则的基础上,提出了还剑湖历史地区的整体保护规划。