Controlling Assembly of Mixed Thiol Monolayers on Silver Nanoparticles to Tune Their Surface Properties

Modifying the surfaces of metal nanoparticles with self-assembled monolayers of functionalized thiols provides a simple and direct method to alter their surface properties. Mixed self-assembled monolayers can extend this approach since, in principle, the surfaces can be tuned by altering the proportion of each modifier that is adsorbed. However, this works best if the composition and microstructure of the monolayers can be controlled. Here, we have modified preprepared silver colloids with binary mixtures of thiols at varying concentrations and modifier ratios. Surface-enhanced Raman spectroscopy was then used to determine the effect of altering these parameters on the composition of the resulting mixed monolayers. The data could be explained using a new model based on a modified competitive Langmuir approach. It was found that the composition of the mixed monolayer only reflected the ratio of modifiers in the feedstock when the total amount of modifier was sufficient for approximately one monolayer coverage. At higher modifier concentrations the thermodynamically favored modifier dominated, but working at near monolayer concentrations allowed the surface composition to be controlled by changing the ratios of modifiers. Finally, a positively charged porphyrin probe molecule was used to investigate the microstructure of the mixed monolayers, i.e., homogeneous versus domains. In this case the modifier domains were found to be <2 nm.

Biological efficacy of electroless-deposited silver on plasma activated polyurethane

Silver coating of catheters has been shown to have inhibitory effects on bacterial growth and adhesion to catheter surfaces. In this study, plasma-modification was used to enhance the adhesion of an electroless silver coating on polyurethane. Both the antibacterial and antiadhesive properties of these coatings were investigated. Bacterial growth was inhibited in cultures exposed to silver-treated polyurethane compared to unmodified polyurethane. Higher growth inhibition was observed for polyurethane surfaces with lower silver coverage. Bacterial adhesion was completely inhibited on all silver-coated surfaces.

Animal group forces resulting from predator avoidance and competition minimization

A new model to explain animal spacing, based on a trade-off between foraging efficiency and predation risk, is derived from biological principles. The model is able to explain not only the general tendency for animal groups to form, but some of the attributes of real groups. These include the independence of mean animal spacing from group population, the observed variation of animal spacing with resource availability and also with the probability of predation, and the decline in group stability with group size. The appearance of "neutral zones" within which animals are not motivated to adjust their relative positions is also explained. The model assumes that animals try to minimize a cost potential combining the loss of intake rate due to foraging interference and the risk from exposure to predators. The cost potential describes a hypothetical field giving rise to apparent attractive and repulsive forces between animals. Biologically based functions are given for the decline in interference cost and increase in the cost of predation risk with increasing animal separation. Predation risk is calculated from the probabilities of predator attack and predator detection as they vary with distance. Using example functions for these probabilities and foraging interference, we calculate the minimum cost potential for regular lattice arrangements of animals before generalizing to finite-sized groups and random arrangements of animals, showing optimal geometries in each case and describing how potentials vary with animal spacing. (C) 1999 Academic Press.</p>

"The End." A winner of the 2012 "15 Minutes of Fame" competition. Authors: Lyon, E. Publication date: 2012

A winner of the 2012 "15 Minutes of Fame" competition.

The machinist landscape:Land Art Generator Initiative (Competition)

THE MACHINIST LANDSCAPE: AN ENTROPIC GRID OF VARIANCE
‘By drawing a diagram, a ground plan of a house, a street plan to the location of a site, or a topographic map, one draws a “logical two dimensional picture”. A “logical picture” differs from a natural or realistic picture in that it rarely looks like the thing it stands for.’
A Provisional Theory of Non-Sites, Robert Smithson (1968)

Between design and ground there are variances, deviations and gaps. These exist as physical interstices between what is conceptualised and what is realised; and they reveal moments in the design process that resist the reconciliation of people and their environment (McHarg 1963). The Machinist Landscape interrogates the significance of these variances through the contrasting processes of coppice and photovoltaic energy. It builds on the potential of these gaps, and in doing so proposes that these spaces of variance can reveal the complexity of relationships between consumption and remediation, design and nature.
Fresh Kills Park, and in particular the draft master plan (2006), offers a framework to explore this artificial construct. Central to the Machinist Landscape is the analysis of the landfill gas collection system, planned on a notional 200ft grid. Variations are revealed between this diagrammatic grid measure and that which has been constructed on the site. These variances between the abstract and the real offer the Machinist Landscape a powerful space of enquiry. Are these gaps a result of unexpected conditions below ground, topographic nuances or natural phenomena? Does this space of difference, between what is planned and what is constructed, have the potential to redefine the dynamic processes and relations with the land?
The Machinist Landscape is structured through this space of variance with an ‘entropic grid’, the under-storey of which hosts a carefully managed system of short-rotation coppice (SRC). The coppice, a medieval practice related to energy, product, and space, operates on theoretical and programmatic levels. It is planted along a structure of linear bunds, stabilized through coppice pole retaining structures and enriched with nutrients from coppice produced bio-char. Above the coppice is built an upper-storey of photovoltaic (PV); its structures fabricated from the coppiced timber and the PV produced with graphene from coppice charcoal processes.

Asymmetric information without common priors: an indirect evolutionary analysis of quantity competition

The common prior assumption justifies private beliefs as posterior probabilities when updating a common prior based on individual information. We dispose of the common prior assumption for a homogeneous oligopoly market with uncertain costs and firms entertaining arbitrary priors about other firms' cost-type. We show that true prior beliefs can not be evolutionarily stable when truly expected profit measures (reproductive) success.