Investigation into time dependant degradation and atmospheric conditions on the wettability of nylon 6,6 which has undergone CO2 laser surface modification

Modification of the wettability of polymers has been demonstrated previously; however, it is known that the wettability modifications of these materials can degrade or vary over time. This can be seen to be crucial from a commercial point of view as this would indicate that a shelf-life has to be established. But at the same time, atmospheric parameters may affect the contact angle and must therefore be accounted for as a control variable in any long-term study of wettability. In this study four CO2 laser patterned nylon 6,6 samples with differing topographical patterns and one as-received sample were analysed over a 30 week period whilst stored in ambient air. By obtaining the characteristic contact angle every two weeks it was found that the contact angle varied erratically before ultimately increasing for all samples after the 30 weeks. White light interferometry analysis determined that the laser patterning gave rise to peak heights of up to 3 μm with roughness parameters Ra and Sa of up to 0.305 and 0.408 μm, respectively. X-ray photoelectron spectroscopy found that surface oxygen content increased by up to 7 %At. It was identified that there was a significant correlation between changes in barometric air pressure and contact angle, highlighting the need for further study to determine if this is a dominant factor

Approaches to inform redevelopment of brownfield sites: an example from the Leeds area of the West Yorkshire coalfield, UK

Government-led regeneration schemes and policies encouraging the use of brownfield land present a challenge, particularly in coalfield areas. Coalfields have typically experienced multiple phases of development and can be susceptible to a suite of problematic ground conditions that may be rooted in the near-surface geology or result from anthropogenic activity. Such problems, related to the nature of void backfill, undermined and unstable ground and the presence of contaminated land in the near-surface, may deter investment in the very areas earmarked for redevelopment. An understanding of previous developments within coalfields is required to identify potential geological hazards, so that regeneration proposals include measures that address these issues. Public records of landfill and site investigations, and minerals exploration including opencast mine plans can reveal the distribution, thickness and high-level descriptions of fill materials, although the coverage of data typically precludes a comprehensive analysis of entire cities. The best way to show the spatial distribution of fill materials is currently as a two dimensional national/regional scale dataset. Depending on the distribution of data points, however, 3D modelling can be possible, which is much more detailed and accurate. Focusing on the heavily urbanised county of West Yorkshire in northern England, the assessment of opencast coal mining on the landscape and benefits of quantifying the impact are discussed. We demonstrate how certain types of publicly available data allow a greater understanding of the interaction between human activity and natural superficial and bedrock geology. If successful, this approach can help lessen the impact of delays and increased financial costs caused by unforeseen ground conditions

Interaction of CO2 laser-modified nylon with osteoblast cells in relation to wettability

It has been amply demonstrated previously that CO2 lasers hold the ability to surface modify various polymers. In addition, it has been observed that these surface enhancements can augment the biomimetic nature of the laser irradiated materials. This research has employed a CO2 laser marker to produce trench and hatch topographical patterns with peak heights of around 1 μm on the surface of nylon 6,6. The patterns generated have been analysed using white light interferometery, optical microscopy and X-ray photoelectron spectroscopy was employed to determine the surface oxygen content. Contact angle measurements were used to characterize each sample in terms of wettability. Generally, it was seen that as a result of laser processing the contact angle, surface roughness and surface oxygen content increased whilst the apparent polar and total surface energies decreased. The increase in contact angle and reduction in surface energy components was found to be on account of a mixed intermediate state wetting regime owing to the change in roughness due to the induced topographical patterns. To determine the biomimetic nature of the modified and as-received control samples each one was seeded with 2×104 cells/ml normal human osteoblast cells and observed after periods of 24 hours and 4 days using optical microscopy and SEM to determine mean cell cover densities and variations in cell morphology. In addition a haeymocytometer was used to show that the cell count for the laser patterned samples had increased by up to a factor of 1.5 compared to the as-received control sample after 4 days of incubation. Significantly, it was determined that all laser-induced patterns gave rise to better cell response in comparison to the as-received control sample studied due to increased preferential cell growth on those surfaces with increased surface roughness

Quasistatic Scale-free Networks

A network is formed using the $N$ sites of an one-dimensional lattice in the shape of a ring as nodes and each node with the initial degree $k_{in}=2$. $N$ links are then introduced to this network, each link starts from a distinct node, the other end being connected to any other node with degree $k$ randomly selected with an attachment probability proportional to $k^{\alpha}$. Tuning the control parameter $\alpha$ we observe a transition where the average degree of the largest node $$ changes its variation from $N^0$ to $N$ at a specific transition point of $\alpha_c$. The network is scale-free i.e., the nodal degree distribution has a power law decay for $\alpha \ge \alpha_c$.Comment: 4 pages, 5 figure

Modulated Scale-free Network in the Euclidean Space

A random network is grown by introducing at unit rate randomly selected nodes on the Euclidean space. A node is randomly connected to its $i$-th predecessor of degree $k_i$ with a directed link of length $\ell$ using a probability proportional to $k_i \ell^{\alpha}$. Our numerical study indicates that the network is Scale-free for all values of $\alpha > \alpha_c$ and the degree distribution decays stretched exponentially for the other values of $\alpha$. The link length distribution follows a power law: $D(\ell) \sim \ell^{\delta}$ where $\delta$ is calculated exactly for the whole range of values of $\alpha$.Comment: 4 pages, 4 figures. To be published in Physical Review

Scale free networks from a Hamiltonian dynamics

Contrary to many recent models of growing networks, we present a model with fixed number of nodes and links, where it is introduced a dynamics favoring the formation of links between nodes with degree of connectivity as different as possible. By applying a local rewiring move, the network reaches equilibrium states assuming broad degree distributions, which have a power law form in an intermediate range of the parameters used. Interestingly, in the same range we find non-trivial hierarchical clustering.Comment: 4 pages, revtex4, 5 figures. v2: corrected statements about equilibriu

Evidence for explosive silicic volcanism on the Moon from the extended distribution of thorium near the Compton-Belkovich Volcanic Complex

We reconstruct the abundance of thorium near the Compton-Belkovich Volcanic Complex on the Moon, using data from the Lunar Prospector Gamma Ray Spectrometer. We enhance the resolution via a pixon image reconstruction technique and find that the thorium is distributed over a larger (40km × 75 km) area than the (25km × 35 km) high-albedo region normally associated with Compton-Belkovich. Our reconstructions show that inside this region, the thorium concentration is 14–26ppm. We also find additional thorium, spread up to 300km eastward of the complex at ∼2 ppm. The thorium must have been deposited during the formation of the volcanic complex, because subsequent lateral transport mechanisms, such as small impacts, are unable to move sufficient material. The morphology of the feature is consistent with pyroclastic dispersal, and we conclude that the present distribution of thorium was likely created by the explosive eruption of silicic magma

Synthesising Novel Movements through Latent Space Modulation of Scalable Control Policies

We propose a novel methodology for learning and synthesising whole classes of high dimensional movements from a limited set of demonstrated examples that satisfy some underlying ’latent’ low dimensional task constraints. We employ non-linear dimensionality reduction to extract a canonical latent space that captures some of the essential topology of the unobserved task space. In this latent space, we identify suitable parametrisation of movements with control policies such that they are easily modulated to generate novel movements from the same class and are robust to perturbations. We evaluate our method on controlled simulation experiments with simple robots (reaching and periodic movement tasks) as well as on a data set of very high-dimensional human (punching) movements.We verify that we can generate a continuum of new movements from the demonstrated class from only a few examples in both robotic and human data

Axion-like particles as ultra high energy cosmic rays?

If Ultra High Energy Cosmic Rays (UHECRs) with E>4 10^{19} eV originate from BL Lacertae at cosmological distances as suggested by recent studies, the absence of the GZK cutoff can not be reconciled with Standard-Model particle properties. Axions would escape the GZK cutoff, but even the coherent conversion and back-conversion between photons and axions in large-scale magnetic fields is not enough to produce the required flux. However, one may construct models of other novel (pseudo)scalar neutral particles with properties that would allow for sufficient rates of particle production in the source and shower production in the atmosphere to explain the observations. As an explicit example for such particles we consider SUSY models with light sgoldstinos.Comment: 5 pages, 2 postscript figures, ref. adde