Science for policy: the need for a Commission for Science

There is growing interest in the use of scientific research for informing public policy (Gluckman, 2011). Science has shown itself increasingly able to make predictions of catastrophic harms many decades in advance, as well as suggesting ways in which these harms may be avoided. Scientific methodologies are now also being drawn on in many other areas of policy. Randomised controlled trials (RCT) and related statistical and experimental techniques are starting to be used to evaluate the effectiveness of existing policy and to experiment with the development of new policies, for instance (Pearce and Raman, 2014)

Surface Melting and Breakup of Metal Nanowires: Theory and Molecular Dynamics Simulations

We consider the surface melting of metal nanowires by solving a phenomenological two-parabola Landau model and by conducting molecular dynamics simulations of nickel and aluminium nanowires. The model suggests that surface melting will precede bulk melting when the spreading parameter $\Delta \gamma$ for the melt in contact with the solid surface is positive (i.e. if the melt wets or partially wets the surface) and the wire is sufficiently thick, as is the case for planar surfaces and sufficiently large nanoparticles. Surface melting does not occur if $\Delta \gamma$ is negative. We test this model, which assumes the surface energies of the wire are isotropic, using molecular dynamics simulations. For nickel, we observe the onset of anisotropic surface melting associated with each of the two surface facets present, but this gives way to uniform surface melting and the solid melts radially until the solid core eventually breaks up. For aluminium, while we observe complete surface melting of one facet, the lowest energy surface remains partially dry even up to the point where the melt completely penetrates the solid core.Comment: 11 pages, 13 figures, article submission preprin

Surface-reconstructed Icosahedral Structures for Lead Clusters

We describe a new family of icosahedral structures for lead clusters. In general, structures in this family contain a Mackay icosahedral core with a reconstructed two-shell outer-layer. This family includes the anti-Mackay icosahedra, which have have a Mackay icosahedral core but with most of the surface atoms in hexagonal close-packed positions. Using a many-body glue potential for lead, we identify two icosahedral structures in this family which have the lowest energies of any known structure in the size range from 900 to 15000 lead atoms. We show that these structures are stabilized by a feature of the many-body glue part of the interatomic potential.Comment: 9 pages, 8 figure

Elucidating the Mechanism of Iron‐Catalyzed Graphitization:The First Observation of Homogeneous Solid‐State Catalysis

Carbon is a critical material for existing and emerging energy applications and there is considerable global effort in generating sustainable carbons. A particularly promising area is iron‐catalyzed graphitization, which is the conversion of organic matter to graphitic carbon nanostructures by an iron catalyst. In this paper, it is reported that iron‐catalyzed graphitization occurs via a new type of mechanism that is called homogeneous solid‐state catalysis. Dark field in situ transmission electron microscopy is used to demonstrate that crystalline iron nanoparticles “burrow” through amorphous carbon to generate multiwalled graphitic nanotubes. The process is remarkably fast, particularly given the solid phase of the catalyst, and in situ synchrotron X‐ray diffraction is used to demonstrate that graphitization is complete within a few minutes

Single-copy nuclear genes resolve the phylogeny of the holometabolous insects

Background: Evolutionary relationships among the 11 extant orders of insects that undergo complete metamorphosis, called Holometabola, remain either unresolved or contentious, but are extremely important as a context for accurate comparative biology of insect model organisms. The most phylogenetically enigmatic holometabolan insects are Strepsiptera or twisted wing parasites, whose evolutionary relationship to any other insect order is unconfirmed. They have been controversially proposed as the closest relatives of the flies, based on rDNA, and a possible homeotic transformation in the common ancestor of both groups that would make the reduced forewings of Strepsiptera homologous to the reduced hindwings of Diptera. Here we present evidence from nucleotide sequences of six single-copy nuclear protein coding genes used to reconstruct phylogenetic relationships and estimate evolutionary divergence times for all holometabolan orders. Results: Our results strongly support Hymenoptera as the earliest branching holometabolan lineage, the monophyly of the extant orders, including the fleas, and traditionally recognized groupings of Neuropteroidea and Mecopterida. Most significantly, we find strong support for a close relationship between Coleoptera (beetles) and Strepsiptera, a previously proposed, but analytically controversial relationship. Exploratory analyses reveal that this relationship cannot be explained by long-branch attraction or other systematic biases. Bayesian divergence times analysis, with reference to specific fossil constraints, places the origin of Holometabola in the Carboniferous (355 Ma), a date significantly older than previous paleontological and morphological phylogenetic reconstructions. The origin and diversification of most extant insect orders began in the Triassic, but flourished in the Jurassic, with multiple adaptive radiations producing the astounding diversity of insect species for which these groups are so well known. Conclusion: These findings provide the most complete evolutionary framework for future comparative studies on holometabolous model organisms and contribute strong evidence for the resolution of the 'Strepsiptera problem', a long-standing and hotly debated issue in insect phylogenetics

Nanowire Melting Modes during the Solid-Liquid Phase Transition: Theory and Molecular Dynamics Simulations

Molecular dynamics simulation have shown that after initial surface melting, nanowires can melt via two mechanisms: an interface front moves towards the wire centre; the growth of an instability at the interface can cause the solid to pinch-off and breakup. By perturbing a capillary fluctuation model describing the interface kinetics, we show when each mechanism is preferred and compare the results to molecular dynamics simulation. A Plateau-Rayleigh-type of instability is found, and suggests longer nanowires will melt via a instability mechanism, whereas in shorter nanowires the melting front will move closer to the centre before the solid pinch-off can initiate. Simulations support this theory; preferred modes that destabilise the interface are proportional to the wire length, with longer nanowires preferring to pinch-off and melt; shorter wires have a more stable interface close to their melting temperature, and prefer to melt via an interface front that moves towards the wire centre.Comment: 6 pages, 7 figure

Effective slip length of nanoscale mixed-slip surfaces

We present an approximate relation for the effective slip length for flows overmixed-slip surfaces with patterning at the nanoscale, whose minimumslip length is greater than the pattern length scale. doi:10.1017/S144618110900017

Tunable nanopatterns via the constrained dewetting of polymer brushes

Coarse-grained molecular dynamics simulations were used to investigate the morphology and dynamics of nanopatterns formed by grafted polymer brushes on a nonadsorbing substrate as a result of constrained dewetting. As a good solvent is made to gradually evaporate, polymer brushes with low to moderate grafting density collapse into discrete nanosized aggregates, with different types of nanopatterns possible, including pancake micelles and holey layers. The type of pattern, the size and number of features, and their dynamics depend on the grafting density of the polymer brush and amount of good solvent adsorbed. The final pattern morphology depends primarily on the total amount of material adsorbed to the surface, including both polymer and solvent. This result suggests the possibility for the use of polymer brushes as surfaces with reversibly tunable nanopatterns