科创中国

The existing researches on singularity of parallel mechanism are mostly limited to the property and regularity of singularity locus and there is no further research into the geometric relationship between uncontrolled kinematic screw and parallel mechanism in singularity.A 3UPS-S parallel mechanism is presented which fulfils 3-DOF in rotation.The regularity of nutation angle singularity is analyzed based on the Jacobian matrix,and the singularity surface of 3UPS-S parallel mechanisms is obtained.By applying the concept of reciprocal product in screw theory,the singular kinematic screw is derived when 3UPS-S parallel mechanism is in singularity.The geometric relationship between singular kinematic screw and singular configuration of 3UPS-S parallel mechanism is investigated by using programs in MATLAB.It is revealed that there are two kinds of situation.Firstly,the three limbs of 3UPS-S parallel mechanism intersect the singular kinematic screw in space simultaneously;Secondly,two limbs cross the singular kinematic screw while the third limb parallels with that screw.It is concluded that the nutation angle singularity of 3UPS-S parallel mechanism belongs to the singular linear complexes.This paper sheds light into and clarifies the geometric relationship between singular kinematic screw and singular configuration of 3UPS-S parallel mechanism.

The 3D inverse design method,which methodology is far superior to the conventional design method that based on geometrical description,is gradually applied in pump blade design.However,no complete description about the method is outlined.Also,there are no general rules available to set the two important input parameters,blade loading distribution and stacking condition.In this sense,the basic theory and the mechanism why the design method can suppress the formation of secondary flow are summarized.And also,several typical pump design cases with different specific speeds ranging from centrifugal pump to axial pump are surveyed.The results indicates that,for centrifugal pump and mixed pump or turbine,the ratio of blade loading on the hub to that on the shroud is more than unit in the fore part of the blade,whereas in the aft part,the ratio is decreased to satisfy the same wrap angle for hub and shroud.And the choice of blade loading type depends on the balancing of efficiency and cavitation.If the cavitation is more weighted,the better choice is aft-loaded,otherwise,the fore-loaded or mid-loaded is preferable to improve the efficiency.The stacking condition,which is an auxiliary to suppress the secondary flow,can have great effect on the jet-wake outflow and the operation range for pump.Ultimately,how to link the design method to modern optimization techniques is illustrated.With the know-how design methodology and the know-how systematic optimization approach,the application of optimization design is promising for engineering.This paper summarizes the 3D inverse design method systematically.

In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via compensating the parasitic error, but few research the multi-dimensional flexure mechanisms. A general design principle and method for high-precision flexure mechanisms based on the parasitic-motion compensation is presented, and the proposed method can compensate the parasitic rotation in company with translation, or the parasitic translation in company with rotation, or both. The crucial step for the method is that the parasitic motion of a flexure mechanism is formulated and evaluated in terms of its compliance. The overall compliance matrix of a general flexure mechanism is formulated by using screw theory firstly, then the criteria for the parasitic motions is introduced by analyzing the characteristics of the resultant compliance matrix as well as with aid of the concept of instantaneous rotation center. Subsequently, a compliance-based compensation approach for reducing parasitic-motion is addressed as the most important part. The design principles and procedure are further discussed to help with improving the accuracy of flexure mechanisms, and case studies are provided to illustrate this method. Finally, an analytical verification is provided to demonstrate that the symmetry design philosophy widely used in flexure design can effectively improve accuracy in terms of the proposed method. The proposed compensation method can be well used to diminish the parasitic-motion of multi-dimensional flexure mechanisms.

In the prediction of active vibration isolation performance,control force requirements were ignored in previous work.This may limit the realization of theoretically predicted isolation performance if control force of large magnitude cannot be supplied by actuators.The behavior of a feed-forward active isolation system subjected to actuator output constraints is investigated.Distributed parameter models are developed to analyze the system response,and to produce a transfer matrix for the design of an integrated passive-active isolation system.Cost functions comprising a combination of the vibration transmission energy and the sum of the squared control forces are proposed.The example system considered is a rigid body connected to a simply supported plate via two passive-active isolation mounts.Vertical and transverse forces as well as a rotational moment are applied at the rigid body,and resonances excited in elastic mounts and the supporting plate are analyzed.The overall isolation performance is evaluated by numerical simulation.The simulation results are then compared with those obtained using unconstrained control strategies.In addition,the effects of waves in elastic mounts are analyzed.It is shown that the control strategies which rely on unconstrained actuator outputs may give substantial power transmission reductions over a wide frequency range,but also require large control force amplitudes to control excited vibration modes of the system.Expected power transmission reductions for modified control strategies that incorporate constrained actuator outputs are considerably less than typical reductions with unconstrained actuator outputs.In the frequency range in which rigid body modes are present,the control strategies can only achieve 5–10 dB power transmission reduction,when control forces are constrained to be the same order of the magnitude as the primary vertical force.The resonances of the elastic mounts result in a notable increase of power transmission in high frequency range and cannot be attenuated by active control.The investigation provides a guideline for design and evaluation of active vibration isolation systems.

在介绍物流企业及其文化竞争力建设的基础上,运用模糊矩阵分析法构建物流企业文化竞争力的评价指标体系,探讨我国物流企业文化竞争力建设的主要措施,以期为我国物流企业文化竞争力建设提供一定参考.

背景:Notch信号通路在多种人类恶性肿瘤的发生、发展中起关键作用.研究显示Notch与NF-κB信号通路之间的交互作用可促进胰腺癌进展.目的:明确Notch信号通路对胰腺癌侵袭性的影响及其可能机制.方法:体外培养人胰腺癌细胞株BxPC3,以Notch-1 siRNA下调其Notch-1表达,同时设置转染对照siRNA的阴性对照组和不予siRNA干扰的空白对照组.以Transwell细胞侵袭实验观察各组BxPC3细胞的侵袭能力,电泳迁移率变动分析(EMSA)检测NF-κB活性,蛋白质印迹法检测Notch-1、NF-κB p65、血管内皮生长因子(VEGF)、基质金属蛋白酶-9(MMP-9)蛋白表达.结果:经Notch-1 siRNA干扰、Notch-1表达下调的BxPC3细胞,Transwell细胞侵袭实验穿膜细胞数较空白对照组和阴性对照组显著减少(26.5±1.3对78.5±2.4和76.7 ±2.2,P<0.01),NF-κB活性显著降低(P<0.01),NF-κB p65、VEGF、MMP-9蛋白表达显著下调(P<0.05).结论:Notch-1可通过激活NF-κB促进其下游基因VEGF、MMP-9表达,由此增强胰腺癌的侵袭性.