Electrospun crosslinked poly(acrylic acid) fiber constructs: towards a synthetic model of the cortical layer of nerve

In an attempt to mimic properties of the polyanionic nanofibrous cortical layer (ectoplasm) of nerve, tube‐shaped poly(acrylic acid) (PAA) nanofiber constructs were prepared via electrospinning. The influence of processing parameters on the morphology of the electrospun PAA nanofibers was systematically investigated. Smooth and uniform PAA nanofibers with average fiber diameter of 820 nm were produced at a concentration of 4 wt% with a flow rate of 0.8 mL h^?1 when a high voltage of 15 kV was applied. Water‐stable PAA nanofibers were obtained by thermally crosslinking PAA with ethylene glycol. The resulting tubes were neutralized to the sodium polyacrylate form and were shown to undergo reversible and abrupt length changes upon titration with CaCl₂ followed by titration with sodium citrate. The sharpness of the length transition was found to be highly dependent upon the bathing NaCl concentration and the operation temperature. It is suggested that electrospun PAA may be a promising candidate as a key element of an abiotic macromolecular mimic of selected properties of axons. © 2014 Society of Chemical Industry     

Synthesis and evaluation of the thermal properties of biosourced poly(ether)ureas and copoly(ether)ureas from 1,4:3,6‐dianhydrohexitols

A new series of poly(ether)ureas were prepared by solution polyaddition of three diamines based on 1,4:3,6‐dianhydrohexitols with three types of diisocyanate. The corresponding poly(ether)ureas were obtained with high yields. They were characterized by various analytical techniques (NMR, TGA and differential thermal analysis, DSC). NMR spectroscopy allowed us to confirm structure type and to optimize reaction conditions and DSC proved the high thermal properties of the products obtained (T_g and T_m in the range 126 ? 158 °C and 235 ? 330 °C respectively). Then, copoly(ether)ureas partially based on commercial diamines were synthesized in order to reduce polymer cost and tune their thermal behaviour. The reactivity of both diamines was evaluated by their incorporation in the polymer by means of NMR spectra. Then their thermal properties were compared with fully commercial diamine based polyureas by DSC studies. © 2014 Society of Chemical Industry     

Improved direct inverse tracking control of a piezoelectric tube scanner for high-speed AFM imaging

For a piezoelectric tube scanner (PTS), this paper proposes an improved direct inverse tracking control algorithm and apply it to an atomic force microscope (AFM) to accomplish high-speed scanning tasks. That is, to enhance the high-speed tracking control performance of a PTS, an improved direct inverse rate-dependent Prandtl–Ishlinskii (P–I) model is firstly constructed, which includes a polynomial module to eliminate the structure nonlinearity. Based on the model, a practical feedforward control law is then designed to implement high-speed tracking control for a high-frequency trajectory with strong robustness, which presents the advantages of high-speed response, simple structure and convenient implementation. Subsequently, the designed feedforward law is combined with a feedback component, and the combined control strategy is employed in an AFM to accomplish fast imaging tasks. Numerous experimental results are then collected, which convincingly demonstrate the superior performance of the proposed practical model/control scheme.     

Real-time administration of tool sharing and best matching to enhance assembly lines balanceability and flexibility

Collaboration has been found in previous studies on the design of assembly lines to be a useful mechanism. In this study, the focus is on a collaborative assembly (CA) framework, inspired by the design principles of CCT, the Collaborative Control Theory, to improve balanceability and flexibility of assembly lines through tool sharing (TS) among idle and bottleneck workstations. TS is widely practiced in advanced assembly facilities to reduce cost and improve consistency and standardization in assembly and in assembly-and-test utilities, relying often on real time control. The framework developed here addresses the systems design aspect of Mechatronics, covering the planning, execution, and control mechanisms. Planning includes assembly line balancing (ALB) and initial TS decisions, made continually by solving a bi-objective mixed-integer program (BOMIP). A collaborative multi-agent system (CMAS) enhanced with a TS-best matching (BM) protocol is developed to execute the plan, control the process, and modify the TS decisions, considering dynamic changes in the system’s operations. Experiments show that the new CA framework significantly outperforms classic approaches (i.e., ALB without TS-BM) in terms of cycle time, utilization of tools, and balanceability. In addition, the control mechanism is proven to augment the line’s flexibility against the inherent uncertainties of assembly processes, compared to the previously developed static CA frameworks.     

高路堤预应力锚索桩板墙承载特性分析

以昆明—曼谷国际公路k70路堤加固工程为背景,采用原位测试方法,完成了不同工况下预应力锚索桩板墙承载特性的现场试验。通过观测结构位移、土压力、桩身内力以及锚索预应力等,系统分析了预应力锚索桩板墙的受力特性与力学行为。锚索桩板墙对高路堤的加固效果显著,填筑初期结构位移随填土高度线性增加,锚索施工后增速有所减缓;初始填筑阶段,抗滑桩变形以刚性倾斜为主,随着锚索张拉和桩后填土不断增高桩身产生了较为明显的弯曲变形。作用在抗滑桩后的土压力大致呈三角形分布,板后土压力大致呈抛物线型分布;相同埋深条件下作用在抗滑桩上的土压力明显大于挡板,原因在于相邻抗滑桩间产生了明显的土拱效应,下部相邻抗滑桩间的土拱效应更强;与解析解的对比结果表明,实测最大桩后土压力与滑坡推力接近,远小于被动土压力;实测板后土压力与主动土压力接近,工程设计中可选取Rankine主动土压力作为挡板的设计荷载,在不利位置采取增大板厚等措施避免挡板发生破坏。采用弹性弯曲梁理论对锚索桩板墙内力计算的结果与实测结果基本一致。张拉锁定初期锚索预应力损失较大,约为设计荷载的10%,后期锚索预应力逐渐趋于稳定,锚索预应力长期损失约为设计荷载值的12%~15%。     

Reverse iodine transfer polymerization of vinyl acetate and vinyl benzoate: synthesis and characterization of homo‐ and copolymers

Homo‐ and copolymers of vinyl esters including vinyl acetate (VAc) and vinyl benzoate (VBz) were synthesized via the reverse iodine transfer radical polymerization technique. Polymerization was carried out in the presence of iodine as the in situ generator of the transfer agent and 2,2′‐azobis(isobutyronitrile) as the initiator at 70 °C. Reverse iodine transfer radical homopolymerization of VAc and VBz led to conversions of 76 and 57%, number‐average molecular weights of 8266 and 9814 g mol^?1 and molecular weight distributions of 1.58 and 1.49, respectively. The microstructure of the synthesized polymers was investigated in detail using gel permeation chromatography, ¹H NMR, ¹³C NMR and distortionless enhancement of polarization transfer (135° decoupler pulse) techniques. Relatively narrow molecular weight distribution and controlled and predictable trend of molecular weight versus conversion were observed for the synthesized polymers, showing that reverse iodine transfer radical homo‐ and copolymerization of VAc and VBz proceeded with controlled characteristics. Results of molecular weight and its distribution along with the ¹H NMR spectra recorded for homo‐ and copolymers indicated that side reactions can occur during the course of polymerization with a significant contribution when VAc, even in a small amount, was present in the reaction mixture. This can result in polymer chains with aldehyde dead end and broadening of the molecular weight distribution. © 2015 Society of Chemical Industry     

某340矫直机上辊快开机构裂纹原因分析及预防措施

340管线矫直机是太原重工成熟产品,在国内占有较大市场,并出口印度、印尼、缅甸、埃及等国际市场。出口印度矫直机在质保期内出现主缸裂纹问题,为探明问题原因并杜绝类似情况发生,快开机构设计静强度分析、疲劳强度分析及生产加工过程等方面探查裂纹原因并提出几点预防措施。     

基于DSP的电子行走辅助系统的设计与实现

为帮助视障者独立行走，基于DSP设计一套电子行走辅助系统。介绍系统的功能和基本结构，详细描述各模块的硬件设计和系统软件工作流程。该系统以实时图像处理为基础，能够完全脱离 PC机实现视频图像的采集、处理和语音提示等功能，帮助视障碍者独立行走。该系统具有小巧、便携、使用方便的特点，与传统助盲设备相比提高了导盲精度，与大型电子盲道或全球定位系统相比节省了成本，实验验证了其有效性。     

Elastic behaviour and failure mechanism in epoxy syntactic foams: The effect of glass microballoon volume fractions

A representative elementary volume (REV) in epoxy syntactic foams was generated to incorporate randomly distributed glass microballoons that followed a log-normal size distribution. Finite element modelling of the REV foam was developed and experimentally validated to investigate the elastic behaviour and failure mechanism in the foams with different microballoon volume fractions (V). The localised stresses concentrate in various zones within the foam, and can cause the vertical splitting fracture of microballoons and the micro-crack formation in the matrix. Dependent on the microballoon volume fraction, micro-cracks can propagate to join adjacent micro-cracks and voids left by fractured microballoons, and finally develop into a macro-crack either in the preferred longitudinal (for low V) or diagonal (for high V) directions. This is consistent with the macroscopic observations of the fracture process in the foam specimens. It was also found that elastic characteristics of the foam vary with microballoon volume fractions.     

Effect of microstructure on the fatigue crack growth behaviour of a near-α Ti alloy

Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure.