A non-invasive learning branch to capture leaf-image attention for tree species classification

Multimedia Tools and Applications - Tree species classification is a necessary and challenging task for both multimedia technique and forestry engineering. Continuous developments in multimedia and...     

超厚板TC4钛合金电子束焊接接头应力腐蚀敏感性

针对100 mm超厚板TC4钛合金电子束焊接接头，采用慢应变速率拉伸方法评价接头在人造海水中的应力腐蚀敏感性，分析接头的显微组织和断口形貌，对接头的腐蚀机制进行研究. 结果表明，室温条件下应变速率为ε=1×10-6 s-1时，母材在海水中未表现出应力腐蚀敏感性；焊缝上部、中部和下部具有轻微应力腐蚀敏感性. 焊缝在海水中发生阳极溶解，产生氢吸附，导致裂纹的萌生. 同时氢扩散诱导α'相界及α'相内发生位错塞积，进而使裂纹在更低的应力水平下发生扩展.     

Tunable microwave absorption properties of nickel-carbon nanofibers prepared by electrospinning

The nickel-carbon nanofibers (Ni-C NFs) were fabricated by the electrospinning of poly(vinyl alcohol) (PVA) and nickel acetate tetrahydrate (NiAc) solution precursor with succedent PVA pyrolyzation and calcination process. The microwave absorption performance and electromagnetic (EM) parameters of the NFs were researched over the frequency range of 2.0–18.0?GHz. Both the impedance matching and EM wave absorption properties of the Ni-C NFs were improved by changing the carbonization temperature. The effect of graphitization degree on reflection loss (RL) and the possible loss mechanisms were directly displayed in the comparative study of each sample. The optimal RL value of ??44.9?dB and an effective frequency bandwidth of 3.0?GHz under a thickness of 3.0?mm can be reached by a sample calcined at 650?°C. These lightweight Ni-C NFs composites can be promising candidates for EM wave absorbers due to the combination of multiple loss mechanisms, nano-size effect and good impedance matching between Ni nanoparticles and CNFs.     

不同类型催化剂对异丁烯齐聚反应过程的影响

采用固定床反应器分别探究了三类催化剂（固体磷酸催化剂、酸性阳离子交换树脂催化剂以及分子筛催化剂）对异丁烯齐聚过程的影响。实验结果表明：固体磷酸催化剂适用于C₈烯烃的生产，酸性阳离子树脂催化剂及改性的分子筛催化剂（Hβ）适合生产C₁₂烯烃。异丁烯齐聚产物C₈～C₁₆（清洁燃料油）因无芳烃、无硫，在石化工业中具有非常广泛的应用潜力；由三种类催化剂的评价结果来看，C₈～C₁₆的选择性最高时均能接近100%，但是固体磷酸催化剂和酸性阳离子树脂催化剂的异丁烯原料转化率比Hβ分子筛催化剂低，Hβ催化作用下异丁烯转化率可以达到88%。     

表面改性对蛭石流延浆料性能的影响

蛭石是一种具有层状硅酸盐结构的非金属矿物,具有良好的抗氧化性和压缩回弹性,是制备耐高温密封材料的优质原料.论文采用流延法进行材料成型加工,以硬脂酸和硅烷偶联剂A-151为改性剂,考察表面改性对蛭石流延浆料分散稳定性和流变性能的影响.结果表明,硬脂酸改性效果优于硅烷偶联剂A-151,当硬脂酸用量为2％时,高温膨胀蛭石粉体接触角为83°,改性效果显著,球磨制浆的RSH最大为79.2％,分散稳定性较好,浆料流动性最佳,流延坯带表面平整、均匀.     

基于多线结构光的弱纹理物体形貌测量方法

大多数现有的主流结构光测量装置在被测物体的表面上投射单条激光,通过移动装置实现物体表面的扫描重建。为了实现物体表面的在线快速重建,将多线结构光和双目立体视觉理论相结合,设计了一种新的三维测量方法。提出了一种结合形态滤波和Zhang-Suen细化算法的光条骨架提取方法和基于光条序列关系的光条匹配算法,并通过极线约束实现光条上特征点的精确匹配。通过实验验证了方法的有效性,相对误差在3%以内。     

Experimental and numerical investigation of sands and Geldart A biomass co-fluidization

This article investigated the fluidization of sands and small Geldart A biomass mixtures. The mixture fluidized like Geldart A type particles with a uniform bed expansion regime before bubbling. The video recorded color distance between pure sands and sands–biomass mixtures was used to estimate the sands–biomass mixing. The coarse-grained computational fluid dynamics–discrete element method with a hybrid drag model which couples the Syamlal–O'Brien drag and a filtered drag can capture the mixing while the simulation with Gidaspow drag predicted a segregated bed. The simulations were further validated with experimental measured pressure drops. The time averaged pressure drop equals the weight of the bed material, however, its fluctuation is about three times of the bed material fluctuation.     

基于CFD技术优化50 L发酵罐内气体分布器

通过CFD模拟技术对50L通气搅拌发酵罐内不同气体分布器的传质混合效果进行气液双相流模拟。首先对发酵罐自带气体分布器进行流场模拟,针对模拟结果提出两种改进气体分布器。结果表明:双层环形气体分布器表现出一种较理想的混合传质效果,为此类发酵罐的优化和放大提供一种有效的技术手段。     

A hybrid material-point spheropolygon-element method for solid and granular material interaction

Capturing the interaction between objects that have an extreme difference in Young's modulus or geometrical scale is a highly challenging topic for numerical simulation. One of the fundamental questions is how to build an accurate multiscale method with optimal computational efficiency. In this work, we develop a material-point-spheropolygon discrete element method (MPM-SDEM). Our approach fully couples the material point method (MPM) and the spheropolygon discrete element method (SDEM) through the exchange of contact force information. It combines the advantage of MPM for accurately simulating elastoplastic continuum materials and the high efficiency of DEM for calculating the Newtonian dynamics of discrete near-rigid objects. The MPM-SDEM framework is demonstrated with an explicit time integration scheme. Its accuracy and efficiency are further analyzed against the analytical and experimental data. Results demonstrate this method could accurately capture the contact force and momentum exchange between materials while maintaining favorable computational stability and efficiency. Our framework exhibits great potential in the analysis of multi-scale, multi-physics phenomena.     

Achieving C/CuO microfiber composites with efficient microwave absorbing performance at low thickness

Journal of Materials Science: Materials in Electronics - The carbon fibers with low density still face significant microwave absorbing application issues due to their high dielectric constant....