Adhesive interactions of geckos with wet and dry fluoropolymer substrates

Fluorinated substrates like Teflon^® (poly(tetrafluoroethylene); PTFE) are well known for their role in creating non-stick surfaces. We showed previously that even geckos, which can stick to most surfaces under a wide variety of conditions, slip on PTFE. Surprisingly, however, geckos can stick reasonably well to PTFE if it is wet. In an effort to explain this effect, we have turned our attention to the role of substrate surface energy and roughness when shear adhesion occurs in media other than air. In this study, we removed the roughness component inherent to commercially available PTFE and tested geckos on relatively smooth wet and dry fluoropolymer substrates. We found that roughness had very little effect on shear adhesion in air or in water and that the level of fluorination was most important for shear adhesion, particularly in air. Surface energy calculations of the two fluorinated substrates and one control substrate using the Tabor–Winterton approximation and the Young–Dupré equation were used to determine the interfacial energy of the substrates. Using these interfacial energies we estimated the ratio of wet and dry normal adhesion for geckos clinging to the three substrates. Consistent with the results for rough PTFE, our predictions show a qualitative trend in shear adhesion based on fluorination, and the quantitative experimental differences highlight the unusually low shear adhesion of geckos on dry smooth fluorinated substrates, which is not captured by surface energy calculations. Our work has implications for bioinspired design of synthetics that can preferentially stick in water but not in air.     

织物纤维干湿态压缩成型特性

对干态和湿态两种工况下的碳纤维和玻璃纤维织物进行了压缩成型特性实验,利用黏弹性理论模型,分析了上述两种工况下压缩、应力松弛和回弹阶段的黏弹性曲线和黏弹性模型参数。通过分析两种工况下织物纱线压缩成型3个阶段的变形机制,阐述了产生上述差异的原因。结果表明,对于织物压缩阶段,当达到相同的最大成型压力时,湿态织物的成型厚度比干态的成型厚度略大。湿态织物的压缩时间比干态的压缩时间短,且织物规格越小,相差时间越少。湿态织物压缩阶段的时间常数小于干态织物对应值。对于织物应力松弛和回弹阶段,介质较少渗入织物间隙,织物变形过程基本相同,织物在两种工况下的成型厚度差值与回弹厚度差值十分接近。因此,湿态下织物的回弹厚度比干态下的回弹厚度略大。应力松弛和回弹阶段的时间常数基本相同。上述研究结果对纤维增强树脂基复合材料的成型工艺具有了一定的指导意义。      

Novel ejector model for performance evaluation on both dry and wet vapors ejectors

A novel ejector model is proposed for the performance evaluation on ejectors with both dry and wet vapor working fluids at critical operating mode. A simple linear function is defined in order to approach the real velocity distribution inside the ejector. Mass flow rates of the primary flow and secondary flow are derived by integrating the velocity function at the inlet section of the mixing chamber. By considering the flow characteristics of the critical-mode operating ejector, the developed model contains only one energy conservation equation and is independent of the flow in the mixing chamber and the diffuser. Experimental data from different ejector geometries and various operation conditions reported earlier are used to verify the effectiveness of the new model. Results show that the model has a good performance in predicting the mass flow rates and the entrainment ratio for both dry and wet vapor ejectors.     

液体设备的流程和配置选择

简介液体设备的流程选择方法和理由,并结合3000m3/h液体设备,分析在液体设备中选择国产压缩机与膨胀机的合理性。     

汽车零部件检测生产线控制终端设计

针对汽车零部件检测生产线效率低,以及数据传递速度慢和信息掌握延时等问题,研究设计了一款用于汽车零部件检测生产线的新型控制终端.终端以嵌入式ARM芯片Cortex-A9为控制核心;采用Android操作系统,Linux作为内核,搭建应用程序开发平台;集成了射频识别模块、实时定位模块和无线通信模块等,实现了控制终端数据采集传输、身份识别、实时定位和无线通信等功能.     

铜基复合材料干湿条件下的摩擦学行为

采用粉末冶金技术制备铜基复合材料,在制动压力0. 5～1. 2 MPa 范围内,通过定速摩擦试验机研究了干、湿条件下,速度、压力与材料摩擦磨损性能的关系,结果表明:影响摩擦磨损性能的重要因素在于载荷性质和第三体状态。在干摩擦条件下,处于低摩擦速度范围时,摩擦力的静载荷性质使第三体呈疏松状态,这增加了微凸体间的啮合程度而使摩擦系数处于较高值。随第三体致密性增加,其润滑作用增强,微凸体间的机械啮合程度减弱,使材料的摩擦系数和磨损量降低。在高速摩擦时,微凸体间的冲击作用使处于摩擦表层的硬质颗粒容易发生粉碎性破损而弥散分布,这强化了表面强度而使摩擦系数有所增加。摩擦压力对高速摩擦性能影响明显,原因在于高负荷加剧了摩擦面的变形和损伤程度。湿摩擦条件下,水膜的润滑和流动具有降低摩擦系数和增加磨损率的作用主要体现在低速低压条件下。在高摩擦速度和高压力条件下,水分的高温蒸发与离心作用明显,破坏了水膜的存在条件,从而使材料的摩擦磨损性能与干摩擦状态相近。      

稳定高产黄酮的水母雪莲细胞系的建立

利用60Co-γ射线照射、高温诱变和紫外光线照射等手段诱变雪莲愈伤组织,结果表明:剂量为40Gy的60Co-γ射线照射原始雪莲细胞系RP-1得到的IRP-5细胞系,黄酮含量可从细胞干重的4.34%提高至6%.分别采用温度和紫外光线等手段诱变IRP-5细胞系得到的细胞系TIP-33和UIP-17,相应的黄酮含量可提高至10.1%和8.8%.用上述三种诱变方法处理原始雪莲细胞系,获得了一株稳定高产雪莲细胞系TUIP-8,黄酮含量大于12%,比天然植株高20～30倍,连续传代培养100代,细胞的培养密度和黄酮含量一直维持在20g(干重)/L和12%～14%左右.考察了温度对TUIP-8细胞悬浮培养的影响,该细胞系可以在20～30℃环境中生长,最适培养温度范围为20～25℃.     

Comparison of the wet and dry fatigue properties of all ceramic crowns

The purpose of this paper was to investigate the influence of fatigue on the fracture strength of In ceram, optimal pressable ceramic (OPCTM) and IPS Empress in both wet and dry environments. Twenty-six crown shapes 8 mm in diameter and 8.5 mm in height were fabricated for each ceramic system. For each ceramic system, ten specimens were tested for fracture strength without fatiguing. The second group was submitted to a fatigue and fracture test in a dry (eight specimens) and a third group in a wet (eight specimens) environment using an Instron testing machine. The results were statistically analysed using a Mann–Whitney test. The results indicated that: (i) the fracture strength for In ceram was significantly stronger than OPCTM and IPS Empress (p<0.05) – no difference was found between OPCTM and IPS Empress; (ii) fatiguing and fracture testing showed a significant decrease in the fracture strength for In ceram and IPS Empress in the wet environment and no difference was found in the dry environment – no difference was found for OPCTM; and (iii) when fatigued in a dry environment, In ceram crown shapes were significantly stronger than OPCTM and IPS Empress (p<0.05) – the same statistical differences were found when fatigued in a wet environment.     

Nano-scale sliding contact deformation behaviour of enamel under wet and dry conditions

The abrasion response of cross sectional areas of enamel was studied by sliding a rounded diamond conical nano-indenter tip across the surface. The nano-indenter tip (radius ~1,200 nm) was scanned over a specific squared area with a load of 400 μN. Two different environments were chosen: Hank’s balanced salt solution (HBSS) and atmospheric laboratory condition. SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy) were used to characterize the final abraded areas. In addition, single scratches with linear incremented load were performed. The normal load and displacement data were utilized in a complementary manner to support the proposed deformation mechanisms. Greater orientation dependence for the case of the single scratches in relation to the abrasion tests was found. The latter results are discussed in terms of plastic deformation effects. The abrasion mechanisms were found to be the same for both wet and dry measurements and similar to that described in a previous study (Guidoni et al., Wear 266:60–68, 2009; Guidoni, Nano-scale mechanical and tribological properties of mineralized tissues. PhD. Montan University Leoben, Leoben, Austria, 2008). However, scratch deformation under fluid measurements shows greater recovery effects and abrasion resistance.