Synthesis of Flexible Elastomeric Polyurethane Films with High Elasticity and Evaluation of Their Structural Permanency

Flexible elastomeric polyurethane (EPU) films were synthesized by ultraviolet (UV) curing of thermoplastic polyurethanes (TPUs) through the reaction among poly (oxytetramethylene) diol (PTMO), isophorone diisocyanate (IPDI), cis-2-butene-1,4-diol (cis-BDO), and 1,6-hexanediol diacrylate (HDDA). In order to improve elasticity and structural permanency in the synthesized TPUs, cross-linking reaction involving unsaturated groups of chain extender (cis-BDO) and reactive diluent (HDDA) using 27 and 41 seconds of UV radiation is introduced. Investigation of structure and mechanical properties was performed using FTIR, GPC, and tensile tests. Stress-strain behavior showed that Young's moduli of EPUs were in the range of 0.2 to 0.4 MPa, which is evidence for high flexibility. Three times of repeated loading on one sample up to 100% strain with 10 min intervals for its recovery showed that considerable structural change didn't occur under these conditions and all observed permanent sets vanished within a time not exceeding 10 min.     

一种多孔配位聚合物的氢键协同客体响应

由硝酸锌、 吡唑-3,5-二羧酸（H₃pzdc）和2-氨基对苯二甲酸（H₂abdc）在溶剂热条件下反应得到一种多孔配位聚合物(Me₂NH₂)[Zn₂(pzdc)(abdc)]·H₂O·DMF(1·g), 其中Me₂NH₂⁺由溶剂N,N-二甲基甲酰胺（DMF）水解得到, 1可视为平行排列的平整带状{Zn₂(pzdc)}⁺链被abdc^2-柱子交错支撑而成的三维多孔框架. 通过脱附/吸附溶剂分子, 中心对称的配位聚合物1·g可以可逆转变成手性的(Me₂NH₂)[Zn₂(pzdc)(abdc)](1′). 单晶结构分析表明, 在客体响应过程中, 基于框架、 抗衡离子和客体分子之间的氢键协作与竞争, 抗衡离子发生了显著的移动 和转动, 导致{Zn₂(pzdc)}⁺链扭曲和转动, 伴随着超过10%的晶胞体积和孔洞率变化. 气体吸附测试表明, 化合物1'对N₂和CO₂存在不同的结构响应行为.     

Flexibility across and flexibility within: The domain of integer addition and subtraction

To better understand the role that flexibility plays in students’ success on integer addition and subtraction problems, we examined students’ flexibility when solving open number sentences. We define flexibility as the degree to which a learner uses more than one strategy to solve a single task when prompted, as well as the degree to which a learner changes strategies when solving a range of tasks to accommodate task differences. We introduce the categorizations of flexibility within and flexibility across to distinguish these two ways of operationalizing flexibility. We examined flexibility and performance within and among three groups of students — 2nd and 4th graders who had negative numbers in their numerical domains, 7th graders, and college-track 11th graders. Profiles of five students are shared to provide insight in relation to the quantitative findings.     

Designing coarse-grain reconfigurable architectures by inlining flexibility into custom arithmetic data-paths

This paper introduces a design technique for coarse-grained reconfigurable architectures targeting digital signal processing (DSP) applications. The design procedure is analyzed in detail and an area-time-power efficient reconfigurable kernel architecture is presented. The proposed technique inlines flexibility into custom carry-save (CS) arithmetic datapaths exploiting a stable and canonical interconnection scheme. The canonical interconnection is revealed by a transformation, called uniformity transformation, imposed on the basic architectures of CS-multipliers and CS-chain-adders/subtractors. Experimental results including quantitative and qualitative comparisons with existing reconfigurable arithmetic cores and exploration results of the proposed reconfigurable architecture are provided.     

一种提高大型可分区服务器柔软性的方案

文章针对大型可分区服务器的资源配置和管理缺乏柔软性的现象，提出了一种基于分区技术的资源配置和资源重组的方案。该方案解决了大型可分区服务器的资源最大化利用率问题和资源调整的柔软性问题。文章给出了分区资源配置和调整的方案．该方案已应用于某一基于大型可分区服务器的虚拟操作管理系统．该管理系统已经投入使用，取得了良好的效果。     

A novel method of preparing of glass capillary columns: Low-temperature plasma etching and polymerization

A novel method is described for the preparation of stable glass capillary columns (glass open tubular columns), including the etching and formation of a polymer film on the inner glass capillary surfaces. The approach used here is based on low-temperature plasma etching and polymerization. Under the influence of a field of radio frequency discharge, low pressure gases of fluoric compounds, introduced into the glass capillary tube, generate excited fluorine radicals which etch the inner surface. The plasma of organosilicone monomer in the glass capillary yields a uniform polymerized film on the inner surface. The resultant material functions as a good stationary phase for glass capillary gas chromatography (GC²). The inner surfaces treated with such a plasma, can be studied by means of a scanning electron microscope (SEM). The flexibility of this method permits the use of various stationary phases and surface modification.     

Shallow Flows Over a Permeable Medium: The Hydrodynamics of Submerged Aquatic Canopies

Aquatic flow over a submerged vegetation canopy is a ubiquitous example of flow adjacent to a permeable medium. Aquatic canopy flows, however, have two important distinguishing features. Firstly, submerged vegetation typically grows in shallow regions. Consequently, the roughness sublayer, the region where the drag length scale of the canopy is dynamically important, can often encompass the entire flow depth. In such shallow flows, vortices generated by the inflectional velocity profile are the dominant mixing mechanism. Vertical transport across the canopy–water interface occurs over a narrow frequency range centered around f _v (the frequency of vortex passage), with the vortices responsible for more than three-quarters of the interfacial flux. Secondly, submerged canopies are typically flexible, coupling the motion of the fluid and canopy. Importantly, flexible canopies can exhibit a coherent waving (the monami) in response to vortex passage. This waving reduces canopy drag, allowing greater in-canopy velocities and turbulent stresses. As a result, the waving of an experimental canopy reduces the canopy residence time by a factor of four. Finally, the length required for the set-up and full development of mixing-layer-type canopy flow is investigated. This distance, which scales upon the drag length scale, can be of the same order as the length of the canopy. In several flows adjacent to permeable media (such as urban canopies and reef systems), patchiness of the medium is common such that the fully developed condition may not be representative of the flow as a whole.     

Mechanical properties of kirigami phosphorene via molecular dynamics simulation

The newly discovered two-dimensional phosphorene suffers low stretchability which limits its application in flexible devices. Herein we employ kirigami technique to overcome this limitation. Molecular dynamics simulation is employed to investigate the mechanical properties of kirigami-phosphorene under shear and tensile loadings. Our simulation results show that loading type, intrinsic structural anisotropy, and the height of middle cuts are three key factors that govern the mechanical response of kirigami-phosphorene. Under the tensile loading along the armchair direction, phosphorene exhibits a considerable increase in its tensile strain. By contrast, phosphorene is too weak to stand any structural modification induced by kirigami in the zigzag direction. Under shear loading, there is merely no improvement in the shear properties of kirigami-phosphorene. Our results demonstrate the prospective applications of kirigami-phosphorene along the armchair direction in modern wearable, and stretchable electronics and optoelectronics devices.     

Underlying principle of efficient propulsion in flexible plunging foils

Passive flexibility was found to enhance propulsive efficiency in swimming animals.In this study,we numerically investigate the roles of structural resonance and hydrodynamic wake resonance in optimizing efficiency of a flexible plunging foil.The results indicates that（1）optimal efficiency is not necessarily achieved when the driving frequency matches the structural eigenfrequency;（2）optimal efficiency always occurs when the driving frequency matches the wake resonant frequency of the time averaged velocity profile.Thus,the underlying principle of efficient propulsion in flexible plunging foil is the hydrodynamic wake resonance,rather than the structural resonance.In addition,we also found that whether the efficiency can be optimized at the structural resonant point depends on the strength of the leading edge vortex relative to that of the trailing edge vortex.The result of this work provides new insights into the role of passive flexibility in flapping-based propulsion.     

Conductive Film with Flexible and Stretchable Capability for Sensor Application and Stealth Information Transmission

Flexible and wearable strain sensors for human-computer interaction, health monitoring, and soft robotics have drawn widespread attention to promising applications in the next generation of artificial intelligence devices. However, conventional semiconductor sensors are difficult to meet the requirements of flexibility and stretchability. Here, we reported a kind of novel and simple sensor based on layer-by-layer(LBL) method. Carbon nanotubes (CNTs) layer provides high ductility and stability in the process of tension sensing, while silver layer provides low initial resistance and fast reflecting in the process of tension sensing. LBL method ensures the uniformity of the conductive layer. The sensor has superior sheet resistance of 9.44Ω/sq., high elongation at break of 104%. For sensing capability, the sensor has wide reflecting range of 60%, high gauge factor (GF) of 1000 up to 60%strain, fast reflecting time of 165 ms. Excellent reliability and stability have also been verified. It is also worth mentioning that the entire process does not require any expensive equipments, complicated processes or harsh experimental conditions. The above features provide an idea for large-scale application of flexible stretchable sensors.