High performance shape memory polyurethane synthesized with high molecular weight polyol as the soft segment

Shape memory polyurethanes (SMPUs) are typically synthesized using polyols of low molecular weight (MW~2,000 g/mol) as it is believed that the high density of cross-links in these low molecular weight polyols are essential for high mechanical strength and good shape memory effect. In this study, polyethylene glycol (PEG-6000) with MW ~6000 g/mol as the soft segment and diisocyanate as the hard segment were used to synthesize SMPUs, and the results were compared with the SMPUs with polycaprolactone PCL-2000. The study revealed that although the PEG-6000-based SMPUs have lower maximum elongations at break (425%) and recovery stresses than those of PCL-based SMPUs, they have much better recovery ratios (up to 98%) and shape fixity (up to 95%), hence better shape memory effect. Furthermore, PEG-based SMPUs showed a much shorter actuation time of < 10 s for up to 90% shape recovery compared to typical actuation times of tens of seconds to a few minutes for common SMPUs, demonstrated their great potential for applications in microsystems and other engineering components

Analysis of strip footings on fibre reinforced slopes with the aid of Particle Image Velocimetry (PIV)

YesThis paper provides results of a comprehensive investigation into the use of waste carpet fibres for reinforcement of clay soil slopes. The interaction between laboratory scale model slopes made of fibre reinforced clay soil and surface strip footing load was examined. Results for the influence of two variables namely fibre content and distance between the footing edge and the crest of the slope are presented and discussed. Particle Image Velocimetry (PIV) technique was employed to study the deformation of the slope under the surface loading. The front side of the tank was made of a thick Perspex glass to facilitate taking accurate images during the loading stage. To study the stress induced in the slope under footing pressure, excess pore-water pressure and total stress increase were measured at predetermined locations within the slope. The results showed that fibre reinforcement increased the bearing resistance of the model slope significantly. For instance, inclusion of 5% waste carpet fibre increased the bearing pressure by 145% at 10% settlement ratio.The post-print of this article will be released for public view when the version of record has been published by ASCE

Two characterisations of accessible quasi-transitive graphs

We prove two characterisations of accessibility of locally finite quasi-transitive connected graphs. First, we prove that any such graph $G$ is accessible if and only if its set of separations of finite order is an ${\rm Aut}(G)$-finitely generated semiring. The second characterisation says that $G$ is accessible if and only if every process of splittings in terms of tree amalgamations stops after finitely many steps.Comment: 15 page

Splitting groups with cubic Cayley graphs of connectivity two

A group $G$ splits over a subgroup $C$ if $G$ is either a free product with amalgamation $A \underset{C}{\ast} B$ or an HNN-extension $G=A \underset{C}{\ast} (t)$. We invoke Bass-Serre theory and classify all infinite groups which admit cubic Cayley graphs of connectivity two in terms of splittings over a subgroup

Civil Society, Everyday Life and the Possibilities for Development Studies

Civil society is one of the most contentious terms in political thought. There is considerable, and highly significant, difference between academic debate about the meaning of ‘civil society’ and the way the term is mobilized in international development discourse. In particular, narratives of civil society in international development are often dominated by reference to organizational descriptions and measurability. But I would like to suggest here that the term should be reclaimed as a way of giving meaning to the stories of the everyday lives of the people who create, shape and embody civil society. Used in this way, the idea of civil society can be understood as intersecting emotions, discourses and practices and can add to the body of scholarly work that nurtures and values everyday life as a lens through which to view wider social processes. Paying attention to the everyday life of civil society may have implications for that way the civil society is engaged with academically, and also has the potential to refresh how civil society is thought about in development practice

On vertex-transitive graphs with a unique hamiltonian cycle

A graph is said to be uniquely hamiltonian if it has a unique hamiltonian cycle. For a natural extension of this concept to infinite graphs, we find all uniquely hamiltonian vertex-transitive graphs with finitely many ends, and also discuss some examples with infinitely many ends. In particular, we show each nonabelian free group $F_n$ has a Cayley graph of degree $2n + 2$ that has a unique hamiltonian circle. (A weaker statement had been conjectured by A. Georgakopoulos.) Furthermore, we prove that these Cayley graphs of $F_n$ are outerplanar