Solvent mediated interactions between model colloids and interfaces: A microscopic approach

We determine the solvent mediated contribution to the effective potentials for model colloidal or nano- particles dispersed in a binary solvent that exhibits fluid-fluid phase separation. Using a simple density functional theory we calculate the density profiles of both solvent species in the presence of the `colloids', which are treated as external potentials, and determine the solvent mediated (SM) potentials. Specifically, we calculate SM potentials between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface, and (iii) a colloid and a planar wall with an adsorbed wetting film. We consider three different types of colloidal particles: colloid A which prefers the bulk solvent phase rich in species 2, colloid C which prefers the solvent phase rich in species 1, and `neutral' colloid B which has no strong preference for either phase, i.e. the free energies to insert the colloid into either of the coexisting bulk phases are almost equal. When a colloid which has a preference for one of the two solvent phases is inserted into the disfavored phase at statepoints close to coexistence a thick adsorbed `wetting' film of the preferred phase may form around the colloids. The presence of the adsorbed film has a profound influence on the form of the SM potentials.Comment: 17 Pages, 13 Figures. Accepted for publication in Journal of Chemical Physic

Interfacial and wetting properties of a binary point Yukawa fluid

We investigate the interfacial phase behavior of a binary fluid mixture composed of repulsive point Yukawa particles. Using a simple approximation for the Helmholtz free energy functional, which yields the random phase approximation (RPA) for the pair direct correlation functions, we calculate the equilibrium fluid density profiles of the two species of particles adsorbed at a planar wall. We show that for a particular choice (repulsive exponential) of the wall potentials and the fluid pair-potential parameters, the Euler-Lagrange equations for the equilibrium fluid density profiles may be transformed into a single ordinary differential equation and the profiles obtained by a simple quadrature. For certain other choices of the fluid pair-potential parameters fluid-fluid phase separation of the bulk fluid is observed. We find that when such a mixture is exposed to a planar hard-wall, the fluid exhibits complete wetting on the species 2 poor side of the binodal, i.e. we observe a thick film of fluid rich in species 2 adsorbed at the hard-wall. The thickness of the wetting film grows logarithmically with the concentration difference between the fluid state-point and the binodal and is proportional to the bulk correlation length of the intruding (wetting) fluid phase. However, for state points on the binodal that are further from the critical point, we find there is no thick wetting film. We determine the accompanying line of first-order (pre-wetting) surface phase transitions which separate a thin and thick adsorbed film. We show that for some other choices of repulsive wall potentials the pre-wetting line is still present, but its location and extent in the phase diagram is strongly dependent on the wall-fluid interaction parameters.Comment: 11 pages, 7 figures. Accepted for publication in Journal of Chemical Physic

Vertex Sparsifiers: New Results from Old Techniques

Given a capacitated graph $G = (V,E)$ and a set of terminals $K \subseteq V$, how should we produce a graph $H$ only on the terminals $K$ so that every (multicommodity) flow between the terminals in $G$ could be supported in $H$ with low congestion, and vice versa? (Such a graph $H$ is called a flow-sparsifier for $G$.) What if we want $H$ to be a "simple" graph? What if we allow $H$ to be a convex combination of simple graphs? Improving on results of Moitra [FOCS 2009] and Leighton and Moitra [STOC 2010], we give efficient algorithms for constructing: (a) a flow-sparsifier $H$ that maintains congestion up to a factor of $O(\log k/\log \log k)$, where $k = |K|$, (b) a convex combination of trees over the terminals $K$ that maintains congestion up to a factor of $O(\log k)$, and (c) for a planar graph $G$, a convex combination of planar graphs that maintains congestion up to a constant factor. This requires us to give a new algorithm for the 0-extension problem, the first one in which the preimages of each terminal are connected in $G$. Moreover, this result extends to minor-closed families of graphs. Our improved bounds immediately imply improved approximation guarantees for several terminal-based cut and ordering problems.Comment: An extended abstract appears in the 13th International Workshop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX), 2010. Final version to appear in SIAM J. Computin

Powder Epoxy for One-Shot Cure, Out-of-Autoclave Applications: Lap Shear Strength and Z-Pinning Study

Large composite structures manufactured out-of-autoclave require the assembly and bonding of multiple parts. A one-shot cure manufacturing method is demonstrated using powder epoxy. Lap shear plates were manufactured from powder epoxy and glass fiber-reinforced plastic with four different bonding cases were assessed: secondary bonding using standard adhesive film, secondary bonding using powder epoxy, co-curing, and co-curing plus a novel Z-pinning method. This work investigates the lap shear strength of the four cases in accordance with ISO 4587:2003. Damage mechanisms and fracture behavior were explored using digital image correlation (DIC) and scanning electron microscopy (SEM), respectively. VTFA400 adhesive had a load at break 24.8% lower than secondary bonding using powder epoxy. Co-curing increased the load at break by 7.8% compared to powder epoxy secondary bonding, with the co-cured and pinned joint resulting in a 45.4% increase. In the co-cured and co-cured plus pinned cases, DIC indicated premature failure due to resin spew. SEM indicated shear failure of resin areas and a large amount of fiber pullout in both these cases, with pinning delaying fracture phenomena resulting in increased lap joint strength. This highlights the potential of powder epoxy for the co-curing of large composite structures out-of-autoclave

In vitro growth factor-induced bio engineering of mature articular cartilage

Articular cartilage maturation is the postnatal development process that adapts joint surfaces to their site-specific biomechanical demands. Maturation involves gross morphological changes that occur through a process of synchronised growth and resorption of cartilage and generally ends at sexual maturity. The inability to induce maturation in biomaterial constructs designed for cartilage repair has been cited as a major cause for their failure in producing persistent cell-based repair of joint lesions. The combination of growth factors FGF2 and TGFβ1 induces accelerated articular cartilage maturation in vitro such that many molecular and morphological characteristics of tissue maturation are observable. We hypothesised that experimental growth factor-induced maturation of immature cartilage would result in a biophysical and biochemical composition consistent with a mature phenotype. Using native immature and mature cartilage as reference, we observed that growth factor-treated immature cartilages displayed increased nano-compressive stiffness, decreased surface adhesion, decreased water content, increased collagen content and smoother surfaces, correlating with a convergence to the mature cartilage phenotype. Furthermore, increased gene expression of surface structural protein collagen type I in growth factor-treated explants compared to reference cartilages demonstrates that they are still in the dynamic phase of the postnatal developmental transition. These data provide a basis for understanding the regulation of postnatal maturation of articular cartilage and the application of growth factor-induced maturation in vitro and in vivo in order to repair and regenerate cartilage defects

Mainstreaming domestic and gender-based violence into sociology and the criminology of violence

Sociological and criminological views of domestic and gender-based violencegenerally either dismiss it as not worthy of consideration, or focus on specificgroups of offenders and victims (male youth gangs, partner violence victims). Inthis paper, we take a holistic approach to violence, extending the definition fromthat commonly in use to encompass domestic violence and sexual violence. Weoperationalize that definition by using data from the latest sweep of the CrimeSurvey for England and Wales. By so doing, we identify that violence is currentlyunder-measured and ubiquitous; that it is gendered, and that other forms of violence (family violence, acquaintance violence against women) are equally ofconcern. We argue that violence studies are an important form of activity forsociologists

Mapping Hansard Impression Management Strategies through Time and Space

Impolite behaviour is thought to be easier to investigate than polite or politic behaviour in diachronic contexts, because of attracting more evaluative comment. But an approach based on such metapragmatic commentary can miss a lot of facework strategies in contexts such as the UK parliament (modern and historical). In this paper, I draw on Historic Hansard datasets (1812–2003) to demonstrate how a (semi)automatic method involving contiguous searches of two-to-four features can better reveal the nuances of these MPs’ facework strategies than a focus on metapragmatic terms has afforded hitherto. The (semi)automatic method uses the recently created Historic Thesaurus Semantic Tagger (HTST) to search for meaning constellations (Archer and Malory 2017). Meaning constellations relating to facework are made up of sequences of semantic fields and/or parts-of-speech which, when organised in certain ways, achieve im/politeness, politic behaviour, strategic ambiguity, a combination of face enhancement and face threat, etc. This paper discusses a number of these meaning constellations, with a particular focus on those which engage in both face enhancement and face aggravation simultaneously (whilst nonetheless avoiding the label, “unparliamentary language”)