Tyre rubber friction on a rough road

One of the most challenging aspects of vehicle dynamics is accurate modelling of the tyre-road interface. Forces between the tyre and road need to be accurately represented in simulation. This is challenging over rough roads since the friction changes along the road due to large surface asperities.The Heinrich/Klüppel friction coefficient estimation model has been implemented on smooth roads in the past. However, this study investigates the applicability of using this model over a rough but hard terrain, such as Belgian paving or cobblestones. The model is based on physical properties that can be determined mathematically or experimentally. The study includes detailed terrain topography and the difference between the top and bottom topography is used to determine the radially averaged PSD. Emphasis is placed on finding and implementing the flash temperature in a practical manner that could also be used in further studies.An experimental setup is built to validate the model. The experimental friction coefficient is compared to the friction coefficient calculated using the Heinrich/Klüppel model. The relative percentage error difference between experimental and friction model results is found to be less than 10% on a smooth concrete road and 20% on a rough road (concrete Belgian paving).     

超快扫描量热技术表征高分子结晶动力学

高分子结晶行为是高分子材料加工过程研究的热点,因为高分子组分和加工工艺控制着高分子结晶及其产物性能。差示扫描量热仪(DSC)是研究高分子结晶动力学常规手段。但是,普通DSC所能达到的最快降温速率一般无法抑制较快的样品结晶,结晶行为将在等温结晶动力学测试之前发生,因此可进行等温结晶的研究温度范围局限于较低结晶过冷度的高温区域。近年来,具有超快速升降温扫描速率和精准控温的快速扫描芯片量热仪(FSC,其商业化版本Flash DSC 1)得到了广泛应用。FSC可以抑制高分子样品在升降温过程中的结晶成核,避免对之后的结晶动力学测试产生影响。因此FSC技术将高分子结晶动力学的研究温度区间延伸至具有较大过冷度的低温区,加深了我们对高分子结晶成核机理以及高分子工业加工过程的理解。本文首先介绍了由初级成核方程描述的高分子结晶动力学原理,初级成核自由能位垒(?G~*)和扩散活化能位垒(?U)分别控制了高低温区的结晶动力学。我们还总结了FSC技术的发展,包括氮化硅薄膜芯片技术、快速扫描量热仪、商业化Flash DSC 1在不同高分子结晶熔融行为研究中的应用。然后介绍表征高分子等温结晶动力学的方法,其中包括样品制备、质量估算、消除热历史、临界扫描速率的确定等,并举例介绍FSC在高分子结晶动力学研究中的应用,涵盖高分子总结晶动力学、结晶成核动力学、高分子焓松弛对结晶成核的影响、FSC联用技术等方面。应用举例中对应形貌和结晶信息,分析了通过FSC测试得到的结晶成核动力学特点。另外通过比较不同结构特点的高分子,总结了我们对结晶动力学行为的基本理解。总之,FSC技术是一种能够提供相转变动力学和热力学信息的高效工具,特别是应用于分析只能在快速扫描中得到的样品结构变化信息。同时我们希望本文能够帮助读者考虑超快扫描量热技术在其他材料研究上的应用,包括合金、药物、生物大分子等。     

基于约束共轭梯度的高能闪光照相3维重建算法

 针对高能闪光照相系统成像信噪比低的特点,提出了3维约束共轭梯度算法,该算法基于3维重建理论来重建方程,利用约束共轭梯度法迭代求图像重建的最优解。数值模拟结果表明：采用3维约束共轭梯度算法能有效改善高能闪光照相重建图像轴线噪声大的问题,是一种具有很高抗噪能力的闪光照相图像重建算法。     

高能闪光X射线二极管设计与模拟

 为了研制出便携式的具有较高性能的高能闪光X射线系统,需要发展新型紧凑型的高能闪光X射线二极管,要求其体积小,能工作在较高电压下。简要介绍了冷阴极X射线二极管的结构和工作原理;阐述了二极管绝缘结构设计原则,设计了一种新型的紧凑型轴向绝缘结构的X射线二极管;在高压端和地电极之间采用绝缘环和金属均压环交替叠加进行轴向绝缘,有利于减小二次电子发射几率,降低绝缘体表面爬电几率,缩短轴向绝缘距离。二极管工作电压为1 MV,轴向绝缘距离约260 mm,结合ANSYS数值模拟软件进行了静电场数值计算。二极管轴向绝缘区最大工作场强为95 kV/cm,各阳极三相点最大场强为26 kV/cm。计算结果表明：二极管的工作场强低于真空闪络场强;所有三相点的工作场强均满足绝缘要求。     

Studies on the ZrO/W(100) surface by means of low-energy electron diffraction and X-ray photoelectron spectroscopy

The low work-function ZrO/W(100) surface was examined with the aim of understanding the reducing mechanism of the work function. Low-energy electron diffraction (LEED) was employed to analyze the surface atomic arrangement, and X-ray photoelectron spectroscopy (XPS) was used to identify the surface chemical condition. The ZrO/W(100) surface was made as follows: (i) around three monolayers of Zr were deposited on a clean W(100) surface, (ii) the sample was heat treated in an oxygen ambience of 1.3x10⁻⁵ Pa for several tens of minutes at 1500 K, and (iii) the sample was flash heated at 2000 K in ultrahigh vacuum (UHV). During heat treatment in O₂, the deposited Zr was oxidized to ZrO₂, and the LEED pattern formed was p(2×1). The work function increased to 5.3 eV. Subsequent flash heating in UHV changed the p(2×1) LEED pattern into a c(4×2) pattern, and transformed ZrO₂ into the so-called Zr–O complex, the oxidized level of which is between ZrO₂ and metallic Zr. A drastic decrease in the work function to 2.7 eV ensued. The angular dependence of XPS showed that the Zr–O complex segregated within a few monolayers at the surface.     

A laser flash photolysis, matrix isolation, and DFT investigation of (η-C6H5Y)Cr(CO)3 (Y = NH2, OCH3, H, CHO, or CO2CH3)

The quantum yield for arene displacement from (η⁶-C₆H₅Y)Cr(CO)₃ was measured in 1,1,2-trifluorotrichloroethane (Y = NH₂, OCH₃, H, CHO, or CO₂CH₃). Values of 0.24, 0.27, 0.15, 0.17, and 0.32 were obtained respectively (λ_exc. = 355 nm). These values are significantly higher than those measured for photoinduced arene loss in hydrocarbon solvents using the same excitation wavelength. Laser flash photolysis of (η⁶-C₆H₅Y)Cr(CO)₃ in 1,1,2-trifluorotrichloroethane (λ_exc. = 355 nm) resulted in the rapid formation (<10 ns) of Cr(CO)₆. Matrix isolation experiments on (η⁶-C₆H₅Y)Cr(CO)₃ (Y = H or CHO) at 12 K in CH₄ or CO-doped CH₄ matrixes using monochromatic irradiation confirmed the presence of two discrete excited states, one leading to CO-loss and the other to arene-loss. The results correlate with the calculated electron drift in the excited state derived from density functional theory and time dependent density functional theory calculations.     

Study on volatility and flash point of the pseudo binary mixtures of sunflower-based biodiesel + methylcyclohexane

The transesterification of sunflower seed oil was carried out in supercritical ethanol without using any catalyst to produce biodiesel. In the present work, methylcyclohexane was added to enhance the vapor pressure of biodiesel. The vapor pressures of mixtures of biodiesel + methylcyclohexane as a function of temperature were measured by comparative ebulliometry with an inclined ebulliometer. The vapor pressures versus composition at different temperatures were obtained. Experimental data of vapor pressures and equilibrium temperatures were correlated by the Antoine equation. A mathematical model was used to predict the flash point of the pseudo binary mixtures. With the regular solution theory, the predictive flash point displays agreement with the experimental data obtained by closed cup test.     

利用反向投影的flash场景自适应视频编码算法

针对闪光造成的光照变化会导致视频帧之间巨大的强度差异问题,提出利用反向投影的flash场景自适应视频编码算法。根据直方图差异提取闪光和非闪光帧,相应地为每个帧分配适当的编码类型,并在加权预测(WP)参数集确定中采用运动向量导数,通过反向投影保证flash场景的全局一致性。实验结果表明,相比其他几种加权预测算法,本文算法在峰值信噪比(PSNR)及计算复杂度方面获得了更加优越的编码性能。     

一台基于串级二极管技术的高强度脉冲硬X射线源

介绍了利用串级二极管产生高强度脉冲硬X射线的方法及其辐射场参数。以“闪光二号”加速器为平台,通过适应性改造,产生快前沿电压脉冲;研制了两级阻抗1 Ω串级二极管,通过串联分压降低二极管端电压、各级二极管电子束独立打靶在空间叠加形成高强度均匀辐射场。解决了悬浮电极绝缘支撑、二极管阴极均匀发射等技术难题,实现了串级二极管的稳定工作。在总电压约700 kV、电流约310 kA条件下,X射线平均能量87 keV,500 cm²上的平均能注量36 mJ/cm²,剂量均匀性（最大值比最小值）达到2∶1。     

Multifunctional nanocomposites based on tetraethylenepentamine-modified graphene oxide/epoxy

Composites based on epoxy/graphene were investigated for thermal-mechanical performance. Initially, few-layer graphene oxide (GO) was modified with tetraethylenepentamine (GO-TEPA) in a reaction assisted by microwave radiation. GO and GO-TEPA samples were characterized for their structure and morphology. Composites containing 0.1, 0.3 and 0.5 wt.% of GO and GO-TEPA were prepared, and the effect of fillers on the morphology of cryofractured regions of epoxy matrix was observed through electron microscopy images. Dynamic mechanical thermal analysis (DMA) tests revealed increases of approximately 20 °C in glass transition. Moreover, when compared to neat polymer, composites containing 0.5 wt.% of GO-TEPA gained up to 103% in thermal conductivity (obtained by flash laser). Finally, nanoindentation analyses showed increases of 72% in Young's modulus and 143% in hardness for the same sample. The system is characterized as multifunctional nanocomposites because of the simultaneous gains in thermal and mechanical properties. The best results of the multifunctional composites were strongly associated with the chemical modification of the GO by TEPA.