三自由度并联机构设计及优化

根据PPR支链的特性,分析并联机构的运动原理,设计出PPR驱动链的机械结构,拟定3-PPR并联平台的整体设计方案,优化并联机构和确定运动平台的具体结构设计,对运动台进行自由度分析,对于重要零件的结构用有限元进行分析.设计出的平面3-PPR并联机构,可以通过3个驱动的输入完成平面内的三轴运动,并能进行各种定位台动作;相比串联平面机构,该机构存在累积误差为0、刚性高、定位精度高、动作灵活、结构简单、制造成本低等优点,并克服了一般用于精密定位的3-PRP并联平台运动高度耦合、运动学解法复杂等难点;该机构具有较高的分辨率和简便的控制性能,能满足FPD设备领域对精密对位系统的迫切需求.     

中低速磁浮防侧滚装置轻量化设计

防侧滚装置是中低速磁浮车辆悬浮架的关键部件.首先针对悬挂中置式悬浮架的防侧滚装置进行了3种工况下的静力学分析,由计算结果发现当前防侧滚装置的片梁结构具有进一步优化的空间.通过拓扑优化计算得到改进后的防侧滚片梁结构,并对新结构进行静强度校核,校核结果表明新结构满足设计要求,且相比原结构单个防侧滚片梁减重约26.5％,一定程度上达到了轻量化设计目标.     

Cell evolution and compressive properties of styrene–butadiene–styrene toughened and calcium carbonate reinforced polystyrene extrusion foams with supercritical carbon dioxide

Polystyrene (PS) foams have been used in various fields, whereas its broader application is limited by its low mechanical strength and brittle features. In this study, styrene–butadiene–styrene (SBS) and calcium carbonate (CaCO₃) nanoparticles were melt‐blended with PS and extrusion‐foamed with supercritical carbon dioxide as a blowing agent to simultaneously toughen and reinforce PS foams. Under the same foaming conditions, the addition of SBS and CaCO₃ was shown to have a significant influence on the cell structure and the compressive properties of the composite foams. We found that the cell structure evolution was highly correlated with the system viscosity. When the rubbery‐phase SBS content was 20%, the cell diameter decreased by 20.7%, and the compressive modulus was enhanced by 289.5%. With the further addition of 5% rigid CaCO₃ nanoparticles, the cell diameter was further reduced by 72.2% and the compressive modulus was improved by 379.2%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43508.     

Circulating Organ-Specific MicroRNAs Serve as Biomarkers in Organ-Specific Diseases: Implications for Organ Allo- and Xeno-Transplantation

Different cell types possess different miRNA expression profiles, and cell/tissue/organ-specific miRNAs (or profiles) indicate different diseases. Circulating miRNA is either actively secreted by living cells or passively released during cell death. Circulating cell/tissue/organ-specific miRNA may serve as a non-invasive biomarker for allo- or xeno-transplantation to monitor organ survival and immune rejection. In this review, we summarize the proof of concept that circulating organ-specific miRNAs serve as non-invasive biomarkers for a wide spectrum of clinical organ-specific manifestations such as liver-related disease, heart-related disease, kidney-related disease, and lung-related disease. Furthermore, we summarize how circulating organ-specific miRNAs may have advantages over conventional methods for monitoring immune rejection in organ transplantation. Finally, we discuss the implications and challenges of applying miRNA to monitor organ survival and immune rejection in allo- or xeno-transplantation.     

激光成形修复Inconel 625合金的工艺特性和组织研究

对激光成形修复Inconel 625合金的工艺特性以及不同区域的组织进行了研究。结果表明:激光成形修复Inconed625合金的工艺范围较宽;激光功率主要影响单道修复层的宽度;扫描速度对单道修复层的尺寸影响较为显著,而送粉率的影响较小。基材的相组成包括γ(Ni-Cr)基体相、大尺寸(约10μm)块状MC型碳化物(M为Nb和Ti)、沿晶界析出的小尺寸(约0.5μm)块状MC型碳化物以及不规则形状的Laves相。修复区组织为呈外延生长的柱状枝晶,相组成为γ基体相、沿枝晶界析出的Laves相以及少量MC型碳化物。层与层界面处Laves相析出急剧增加形成层间过渡区。     

高含水率有机质河道底泥压缩性状试验研究

河道底泥的压缩性状是影响河道底泥环保疏浚设计及处置的一个关键因素,采集了4条河道的底泥,针对4种城市河道底泥和过氧化氢处理的底泥开展了一系列物理和压缩试验,研究河道底泥的压缩性状,探讨有机质含量对河道底泥压缩性状的影响规律。试验结果表明,河道底泥的有机质含量变化范围大,河道底泥的压缩性状与底泥的物理性状密切相关,与无机质土类似,初始孔隙比和液限孔隙比是河道底泥压缩性状的两个关键控制因素。有机质对底泥压缩性状的影响可以归结于液限孔隙比的改变,有机质含量主要影响河道底泥的液限和比重,进而导致河道底泥重塑屈服应力σ_(yr)~′和压缩性状发生改变。有机质含量越高,液限孔隙比越大,压缩指数越大,呈现出的压缩性越高。     

Design of a europium-activated lithium-silicate cyan phosphor via cation substitution

Lithium-containing silicates have been considered as a considerable alternative for luminescent materials. In this study, a novel cyan-emitting phosphor, Na₃LiHf₂Si₃O₁₂: Eu²⁺, was successfully synthesized via cationic substitution with Na₄Hf₂Si₃O₁₂: Eu²⁺ as the initial model. The crystal structure, morphology, and luminescence performance of Na_4-xLi_xHf₂Si₃O₁₂: Eu²⁺ were investigated in detail. The substitution of Li⁺ for Na⁺ site causes a significant blue-shift of the emission band in the range of 550–500 nm and a smaller full width at half maximum. As a result, a cyan phosphor Na₃LiHf₂Si₃O₁₂: Eu²⁺ that can be effectively excited by near-ultraviolet and high-energy beams is obtained. The mechanism of emission regulation was proposed based on the transformation of crystal structure and luminescence performance. In addition, the thermal quenching and cathodoluminescence behaviors were also studied. The results show that cation substitution is an effective method to design new lithium-containing silicate phosphors.     

高原机车悬挂方案对车辆振动特性的影响

针对青藏铁路冻土带路基下沉问题,为了实现高原机车转向架低动力作用,基于车辆多体系统动力学理论,建立了两种不同悬挂方案的高原机车动力学模型,研究了不同一、二系悬挂刚度比μ对车体、构架以及轮轨垂向振动的影响。发现一、二系悬挂刚度比在0.5~3范围内变化时,轮轨垂向力和构架垂向振动加速度增大了11.24%和12.2%,车体平稳性指标和垂向加速度分别减小了11.3%和15%,并分析了高原线路上两种悬挂方案机车动力学特性。计算结果表明,选择刚度较大的二系悬挂,虽然一定程度上恶化车体平稳性指标,但较小的一系刚度在中低速范围内,能够降低由轨道不平顺引起轮轨垂向冲击,显著抑制了对轨下部分损伤较大的低频振动,减小运行过程中机车对轨下部分的损害。     

Real-time cutting tool state recognition approach based on machining features in NC machining process of complex structural parts

Cutting tool state recognition plays an important role in ensuring the quality and efficiency of NC machining of complex structural parts, and it is quite especial and challengeable for complex structural parts with single-piece or small-batch production. In order to address this issue, this paper presents a real-time recognition approach of cutting tool state based on machining features. The sensitive parameters of monitored cutting force signals for different machining features are automatically extracted, and are associated with machining features in real time. A K-Means clustering algorithm is used to automatically classify the cutting tool states based on machining features, where the sensitive parameters of the monitoring signals together with the geometric and process information of machining features are used to construct the input vector of the K-Means clustering model. The experiment results show that the accuracy of the approach is above 95% and the approach can solve the real-time recognition of cutting tool states for complex structural parts with single-piece and small-batch production.     

UV混杂固化硅氧烷改性水性PUA/邻甲酚醛环氧树脂的制备

制备了水性邻甲酚醛环氧树脂(o-CFER)和聚氨酯丙烯酸酯(PUA),研究了γ-缩水甘油醚氧丙基三甲氧基硅烷偶联剂KH560对紫外光-阳离子混杂固化PUA/o-CFER热固性树脂热性能的影响,并用动态力学谱仪和热重分析仪进行了表征。结果表明:PUA/o-CFER体系相容性很好,KH560用量占总质量的6%时,PUA/o-CFER热固性树脂的玻璃化转变温度达125.9℃;当KH560用量占总质量的8%时,PUA/o-CFER热固性树脂热降解所需活化能最高为41.41 kJ/mol,反应级数为1.54;固化后树脂涂膜的硬度达4 H,冲击强度达50 kg·cm,并具有良好的附着力。