Photolithographically patterned smart hydrogel based bilayer actuators

We describe the fabrication of photopatterned actuators, composed of stimuli-responsive hydrogel bilayers made from N-isopropyl-acrylamide (NIPAm), acrylic acid (AAc), and poly-ethylene oxide diacrylate (PEODA). The hydrogels were deposited by spin coating and casting and were patterned by non-contact photolithography. We investigated the swelling behavior of the individual photopatterned hydrogels in aqueous solutions of varying pH and ionic strength (IS). By combining materials with optimal swelling responses, bilayer structures were triggered via changes in pH and IS to actuate into three dimensional (3D) structures. We also used these hydrogel bilayers as hinges to actuate integrated structures composed of rigid polymeric SU-8 panels, patterned to resemble the shape of a Venus Flytrap. This system provides a straightforward way to design and fabricate actuator hinges composed entirely of polymers.     

Environmental studies of smart/self-healing coating system for steel

Smart/self-healing micro-capsulated inhibitor incorporated in epoxy primer before painting on a steel surface was evaluated for its corrosion protection effectiveness on exposure to ASTM D 5894 electrolyte in laboratory and natural tropical sea-shore environment. The “healant” inhibitor was industrial custom-made and non-chromate organic-based microcapsules which were mixed into the primer before applying a polyurethane topcoat layer on steel surface. The results indicate that the active components in ruptured embedded inhibitor microcapsules were released into an inflicted scribe primer and topcoat film on steel surface on exposure to inhibit development of an electrochemical cell. Undamaged surface film of the test and control specimens exposed in the environments demonstrated excellent corrosion-inhibition performance as reflected by both visual inspection and electrochemical impedance spectroscopy experimental data. The results obtained on the performance of self-healing inhibitors should provide an understanding of the fundamental material-property relationships of smart inhibitor coatings. And, thus, should facilitate the development of optimized paint compositions in order to extend the useful service life of steel-infrastructure applications.     

簇团开发理论和实践

本文旨在对簇团开发理论的发展和实践做出较为客观的介绍和评价。文章首先阐释了簇团发展理论产生的时代背景,重点分析了产生簇团开发理论的历史渊源——＂美国梦＂文化、＂城市蔓延＂争论、传统社区复兴思想和环境保护思想。文章的第二部分探讨了簇团开发理论的内涵及实践,内容包括了簇团开发模式、簇团开发法案和簇团开发实践。在簇团开发实践中结合伊州的草场口社区开发实例,剖析了簇团发展理论的具体指导原则、分项标准、开发时序和实际效果。最后,文章对簇团发展理论的一些不足和问题、及对我国规划工作的可能借鉴意义做出了有选择性的总结。     

“新城市主义”与“精明增长”理论进展与评述

第二次世界大战后,美国城市向郊区的无序蔓延带来了许多负面影响.针对"城市蔓延"问题,"新城市主义"和"精明增长"理论应运而生.控制城市蔓延、实现紧凑式发展、采取公交导向的发展模式、设定城市增长边界是二者的理论共识,但这两种理论因对空间分布和种族问题以及对区域性的忽略而使其自身也存在不足.将这两种理论借鉴至中国,则体现为:强化城市土地的集约利用,倡导生态设计,倡导公交优先,提倡建立公众参与机制.     

IMS客户端认证过程研究

IMS客户端基于IMS网络,是目前网络技术研究的前沿和热点。IMS客户端是最终用户享受IMS技术带来的诸多成果的最直接的表现方式。IMS客户端不同于传统的SIP客户端,其主要区别之一是其更安全的认证机制,它实现了网络与客户端的双重鉴权,从而使使用更加安全可靠。本文通过对已有的终端注册过程进行分析,现场测试保证了数据的真实性和相关理论方法的有效可行性,使读者能够进一步了解其鉴权的过程。为以后的开发者提供参考。     

智能血液监测器的设计及其应用

阐述了血液监测器原理,并对其结构从理论上进行了分析.介绍了一种应用于血液净化设备的血液监测传感器,临床中检测患者上机与下机过程中血液体外循环管路内血液和生理盐水的变化情况,并及时发出警告,提示医护人员及时处置,以有效增强治疗安全;采用红外传感器发射、接收组件进行非接触式检测,并借助单片机技术进行数据采集与状态识别.     

An equivalent single-layer model for magnetoelectroelastic multilayered plate dynamics

An equivalent single-layer model for the dynamic analysis of magnetoelectroelastic laminated plates is presented. The electric and magnetic fields are assumed to be quasi-static and the first-order shear deformation theory is used. The formulation of the model provides for a preliminary fulfillment of the electro-magnetic governing equations, which allows to determine the electric and magnetic potential as functions of the mechanical variables. Then, by using this result, the equations of motion are written leading to the problem governing equations. They involve the same terms of the elastic dynamic problem weighted by effective stiffness coefficients, which take the magneto-electro-mechanical couplings into account. Additional terms, exclusively arising in force of the piezoelectric and piezomagnetic behavior, appear. The electromagnetic inputs are treated as equivalent external distributed axial forces and bending moments. Free and forced vibrations solutions for simply-supported plates are presented to validate the model by comparing the present results with benchmark solutions found in the literature.     

Coupled efficient layerwise and smeared third order theories for vibration of smart piezolaminated cylindrical shells

The improved third order zigzag theory and its smeared counterpart (without the zigzag effect), recently developed by the authors for static analysis of piezoelectric laminated cylindrical shells, are extended to dynamics. The piezoelectric layers are considered as radially polarized to make use of the extension actuation mechanism that is best suited for effective actuation and sensing. The zigzag theory accounts for the layerwise variation of inplane displacements and includes the transverse normal extensibility under electric field, and also satisfies the conditions on transverse shear stresses at the layer interfaces and at the inner and outer surfaces of the shell. Yet, the number of primary displacement variables is only five, same as its smeared counterpart. The two theories are critically assessed for their accuracy by direct comparison with the three dimensional piezoelasticity solutions for free and forced vibration response of simply supported smart angle-ply infinite-length and cross-ply finite-length shells, with a variety of heterogeneous composite and sandwich laminates. It is shown that the zigzag theory, in spite of being computationally efficient, is very accurate even for shells with highly inhomogeneous laminates. In contrast, the smeared third order theory is grossly inadequate for smart shells made of inhomogeneous composite and sandwich substrates.     

Sensing of damage and healing in three-dimensional braided composites with vascular channels

With the rise of composite materials as replacements for traditional monolithic materials comes an increase in demand for multifunctionality. Prior studies have demonstrated the ability of an embedded, electrically percolating carbon nanotube network to respond electrically to the onset and progression of damage in composite structures. We build upon this work by incorporating healing functionality into braided composites through the use of a hollow channel resin delivery system. This study demonstrates the ability of a carbon nanotube network to sense crack filling during resin injection, thus providing the scientific basis required for sensing healing in advanced composites. With practical application in mind, a two-part healant system is employed in this study. Two methods for qualitatively assessing healing are employed and compared; these include elastic modulus/strain energy recovery and FTIR spectroscopy.     

Use of a surface-mounted chirped fibre Bragg grating sensor to monitor delamination growth in a double-cantilever beam test

A surface-mounted chirped fibre Bragg grating (CFBG) sensor has been used for the first time to monitor delamination growth within a composite material (a transparent, unidirectionally reinforced glass fibre/epoxy resin double-cantilever beam (DCB) specimen). The specimens were tested using a constant displacement rate, with the delamination length being measured using complementary techniques: (i) in situ photography, (ii) surface-mounted strain gauges, and (iii) the surface-mounted CFBG sensors. The unidirectionally reinforced DCB specimens showed characteristics typical of such material which complicate the curvature of the beams, i.e. the development of extensive fibre bridging and pronounced R-curve behaviour. To validate the interpretation of the CFBG reflected spectrum, the experimentally determined strains from the surface-mounted strain gauges have been used, together with in situ photographs of the position of the delamination front. Using the CFBG sensor technique, the delamination length was measured to within about 4 mm over the 60 mm sensor length.