关键词： Robust control   mechanical systems   orbital stabilisation   disturbance attenuation   actuator dynamics  

摘要： Robust periodic motion generation is developed for a class of mechanical systems with actuator dynamics. The virtual constraint (VC) approach is first refined under incomplete state measurements and it is then extended to the case where the actuator dynamics are brought into play for avoiding limitations in the system performance. The extended VC approach is subsequently coupled to the nonlinear synthesis to yield the robust output feedback periodic motion generation for mechanical systems of underactuation degree one, driven by electrical motors with their own dynamics. The effectiveness of the proposed synthesis is supported in the numerical study made for a cart-pendulum testbed.

关键词： 海洋平台   上部组块   动力特性   振动响应   模态分析  

摘要： 海洋平台上部组块机械设备动力响应评估是保障其结构安全和设备平稳运行的重要手段。针对某海洋平台复产方案中新增空压机和增压机的振动问题,制定了海洋平台上部组块机械设备振动评估技术流程,采用ANSYS软件建立该平台上部组块有限元模型,基于提出的分析流程,计算得到平台结构的自振特性。分析了平台结构的位移响应频谱,在修井和防窜两种作业条件下,分别对平台增压机和空压机不同组合工况下的振动响应进行评估。研究结果表明:增压机和空压机的激振频率均远离平台自振频率,不会引发共振;平台结构在不同工况下的振动速度和振动加速度均满足规范要求,复产设计方案可行;平台最大响应工况为增压机与空压机B组合同时运行,实际工作时,建议以空压机B为备用设备。研究结果可为海洋平台复产计划的顺利实施提供技术保障。

关键词： 心脏骤停   心肺复苏   机械通气   血气指标   血流动力学   生存率  

摘要： 目的观察早期机械通气在心肺复苏患者中的应用效果,评价其对患者血气指标及血流动力学的影响。方法选择本院2017年2月~2019年3月收治的心脏骤停(CA)患者60例为本次研究对象,根据插管成功时机不同将其分为对照组与观察组,对照组为CA发生5 min后插管成功,观察组在5 min内插管成功,对比两组患者心肺复苏时间、复苏成功率、复苏后血气指标、血流动力学指标及7 d生存率。结果复苏效果:观察组复苏成功率为24.00%,明显高于对照组的6.67%,观察组复苏时间明显短于对照组,差异有统计学意义(P<0.05);血气指标情况:观察组复苏后血乳酸(BLA)含量、二氧化碳分压(PaCO2)低于对照组,酸碱值(pH)、动脉血氧分压(PaO2)高于对照组,差异有统计学意义(P<0.05);血流动力学:观察组心率(HR)、平均动脉压(MAP)数据与对照组比较,差异无统计学意义(P>0.05);7 d生存率:观察组7 d生存率为10.00%,高于对照组的3.33%,但差异无统计学意义(P>0.05)。结论早期机械通气在心肺复苏患者中应用效果肯定,能够有效改善患者血气指标,提升7 d生存率。

关键词： 自主创新   课程改革   教学方法   实践  

摘要： 动力机械仿真课程具有很强的实践性、创新性、综合性特征,重庆交通大学为满足企业对自主创新人才的需求,在本科能动专业中尝试开设动力机械仿真课程。从教学效果来看,取得了较好的效果,学生展现出很强的学习欲,提升了学生主动学习的热情,培养了学生的科研实践与自主创新意识与能力。该课程的开设,有利于培养出适应企业需求的具有自主创新意识与实践能力的应用型能动专业人才。

关键词： 工程机械液压系统   动力匹配   控制技术  

摘要： 目前工程机械液压动力系统的优化及匹配是通过技术与理论相互结合的高级系统功能实现的。随着国内机电一体化的快速发展,机械液压系统动力匹配控制技术的技术水平也随之提升。本文主要围绕工程机械液压系统动力匹配与控制技术进行分析,以供参考。

关键词： 2D material   Bonded graphene ribbon   Mechanical properties   Molecular dynamics simulation   Uniaxial test  

摘要： The mechanical properties of bonded graphene ribbon were evaluated via uniaxial tensile tests by molecular dynamics simulations. For an ideal/pristine few-layered graphene ribbon, the interlayer superlubrication leads to easily relative sliding between neighboring layers. When the layers in the ribbon are sewn by collision with high speed fullerenes from both sides, a new two-dimensional material is fabricated. A part of bonds in the original graphene layers are broken, and new bonds are generated to connect the neighboring layers at the impacted areas. The in-plane mechanical properties, e.g., Young's modulus, maximal engineering strain (which demonstrates deformability), deformation energy (which illustrates structural stiffness) and the maximal stress (which describes strength), of the newly fabricated defective ribbon are different from the original ideal ribbon. By comparison with the ideal ribbon, the changes of the mechanical properties were demonstrated. Meanwhile, temperature effect on the changes of properties was also discussed for potential application of the new two-dimensional material. In brief, the maximal strain slightly depends on temperature and loading speed. The defective ribbon breaks in tension failure mode when stretched along x/zigzag direction, but in shear failure mode when stretched along y/armchair direction. The Young's modulus reduces 10%-12%, but, the maximal strain reduces more than 50% when compared with the ideal ribbon.

关键词： 边界元法   机械臂   伺服动力  

摘要： 机械臂因其智能化与高精度广泛应用于各行各业中。针对机械臂因机电耦合极易造成控制精度低的问题,本文基于边界元法的高精度交流机械臂伺服动力特性分析,将转子磁链定向矢量控制子系统应用于机械臂伺服传动系统中,转子磁链定向矢量控制子系统选取齿轮传动控制机械臂传动,转子磁链定向矢量控制子系统选取RV减速机与谐波减速机控制机械臂关节运动,利用机械臂伺服传动系统中的三环控制子系统控制机械臂的稳定运行。将机械臂伺服传动系统应用于6自由度柔性机械臂中,选取边界元法分析该机械臂动力特性,通过机械臂中梁元件弯曲震动动态基本解获取梁单元于纵向和扭转方向边界控制方程,将不同方向的边界控制方程依据梁元件各方向的震动特点组合,获取机械臂动力学方程,依据动力学方程分析高精度交流机械臂伺服动力特性。通过以上方法获取机械臂动力学方程,通过动力学速度跟踪以及位置跟踪结果验证伺服传动系统的伺服特性,采用该伺服传动系统的机械臂关节结束运动时位置波动极小,波动范围与稳态误差小于18"以及1.5′;该方法分析高精度交流机械臂伺服动力特性结果相对误差均在0.05%以内,验证基于伺服传动系统的高精度交流机械臂伺服特性,以及该方法分析高精度交流机械臂伺服动力特性的准确性。

关键词： Mechanical properties   Polymers  

摘要： The mechanical properties of rubber nanocomposites are believed to relate to the chain dynamics at the filler interface. Here, we tackle this hypothesis by combining traditional rheological measurements with our published results obtained by a modern technique of interfacial sensitive spectroscopy (Macromolecules 51:2180-2186, 2018). The complex shear modulus (G*) for silica (SiO2) nanoparticles filled with uncross-linked styrene-butadiene rubber (SBR) was studied as a function of the strain amplitude and temperature. In the case of the composite with a higher SiO2 fraction, G* remarkably decreased with increasing strain amplitude, known as the Payne effect. This phenomenon has been explained by the breakage of the filler network formed in the composite. Postulating that the G* difference between strain amplitudes of 0.1 and 20% (Delta G*) is a signature of the extent of how the filler network is broken, Delta G* was plotted against temperature. The decrement of Delta G* with increasing temperature changed at 340 K. This temperature coincided with the temperature at which the chains in direct contact with the filler surface start to structurally relax. This coincidence was also observed for the SiO2-filled uncross-linked polyisoprene composite. Our results make it clear that the aforementioned hypothesis is likely for SiO2-filled uncross-linked rubber composites.

关键词： Silk hydrogels   HRP-mediated crosslinking   Tyramine substitution   Gelatin composite hydrogels   Cyclic RGD peptide   Cell encapsulation  

摘要： Silk fibroin (SF) was enzymatically crosslinked with tyramine-substituted silk fibroin (SF-TA) or gelatin (G-TA) to fabricate hybrid hydrogels with tunable gelation kinetics, mechanical properties and bioactivity. Horseradish peroxidase (HRP)/hydrogen peroxide (H2O2) mediated crosslinking of SF in physiological buffers results in slow gelation and limited mechanical properties. Moreover, SF lacks cell attachment sequences, leading to poor cell material interactions. These shortcomings can limit the uses of enzymatically crosslinked silk hydrogels in injectable tissue fillings, 3D bioprinting or cell microencapsulation, where rapid gelation and high bioactivity are desired. Here SF/SF-TA and SF/G-TA composite hydrogels were characterized for hydrogel properties and the influence of conjugated cyclic arginine-glycine-aspartic acid (RGD) peptide or G-TA content on bioactivity was explored. Both SF-TA and G-TA significantly increased gelation kinetics, improved mechanical properties and delayed enzymatic degradation in a concentration-dependent manner. beta-Sheet formation and hydrogel stiffening were accelerated by SF-TA content but delayed by G-TA. Both cyclic RGD and G-TA significantly improved morphology and metabolic activity of human mesenchymal stem cells (hMSCs) cultured on or encapsulated in composite hydrogels. The hydrogel formulations introduced in this study provide improved control of gel formation and properties, along with biocompatible systems that can be utilized in tissue engineering and cell delivery applications.

关键词： Dental materials   Ceramics   Yttria stabilized tetragonal zirconia   Biaxial flexural strength  

摘要： This study aimed to evaluate the effects of low temperature degradation (LTD) on commercial dental zirconias (conventional and high-translucent - HT) with different microstructures, as well as on their mechanical properties and t-m phase transformation. The amount of monoclinic zirconia in different depths was quantified using X-ray diffraction (XRD) with different anode tubes (Cr, Co and Cu). XRD was also used to measure the residual stress of the materials at 0 h, 26 h and 140 h aging times. Vickers microhardness and biaxial flexural strength tests were performed. Data were subjected to two-way ANOVA and Tukey's post-hoc test, both with alpha = 0.05 for means comparisons. Weibull parameters were calculated and compared based on the overlapping of confidence intervals (CI = 95%). HT Zirconia presented smaller grain sizes and had a higher rate of t-m transformation over time. The microstructure of the conventional zirconia showed an expressive increase of the grain size and consequently greater morphological variation with the LTD. The non-aged samples (control) did not present any residual stress and the aged ones presented compression stress, All zirconia showed a residual stress increase with the increase of LTD time, but the conventional one showed a decrease after 140 h. HT zirconia showed no significant change in flexural strength over LTD time, but the conventional one showed a strength decrease after 140 h (681.78 +/- 121.18 MPa). Vickers hardness decreased for all zirconia samples after 26 h. The mechanics of LTD is significantly altered in different zirconia microstructures. Zirconias with smaller grains are more prone to t-m phase transformation, but present lower variation of residual stress, while larger grains zirconias have a lower surface area and therefore a more pronounced increase in stress over LTD time. Stress values close to the maximum compression stress generates ejection of the zirconia grains, producing defects and causing reduction of the