Heterogeneous ice nucleation on silver-iodide-like surfaces

We attempt to simulate the heterogeneous nucleation of ice at model silver-iodide surfaces and find relatively facile ice nucleation and growth at the Ag+ termi nated basal face, but never see nucleation at the I- terminated basal face or the prism and normal faces. Water molecules strongly adsorb onto the Ag+ terminate d face to give a well-ordered hexagonal ice-like bilayer that then acts as a template for further ice growth.Comment: 2 pages, 1 figur

A FLAT RATE TAX: IMPACTS ON REPRESENTATIVE HOG AND GRAIN FARMS

This paper focuses on identifying shifts in the tax burden within agriculture associated with various flat tax proposals by comparing their effects on farms with different enterprise combinations, resource bases, and financial characteristics. In general, the flat tax imposes higher average tax burdens on small farms and yields a tax cut from ERTA laws for large farms even when the tax base is broadened.Agricultural Finance, Livestock Production/Industries, Public Economics,

Close-Packing of Clusters: Application to Al_100

The lowest energy configurations of close-packed clusters up to N=110 atoms with stacking faults are studied using the Monte Carlo method with Metropolis algorithm. Two types of contact interactions, a pair-potential and a many-atom interaction, are used. Enhanced stability is shown for N=12, 26, 38, 50, 59, 61, 68, 75, 79, 86, 100 and 102, of which only the sizes 38, 75, 79, 86, and 102 are pure FCC clusters, the others having stacking faults. A connection between the model potential and density functional calculations is studied in the case of Al_100. The density functional calculations are consistent with the experimental fact that there exist epitaxially grown FCC clusters starting from relatively small cluster sizes. Calculations also show that several other close-packed motifs existwith comparable total energies.Comment: 9 pages, 7 figure

The structure of binary Lennard-Jones clusters: The effects of atomic size ratio

We introduce a global optimization approach for binary clusters that for a given cluster size is able to directly search for the structure and composition that has the greatest stability. We apply this approach to binary Lennard-Jones clusters, where the strength of the interactions between the two atom types is the same, but where the atoms have different sizes. We map out how the most stable structure depends on the cluster size and the atomic size ratio for clusters with up to 100 atoms and up to 30% difference in atom size. A substantial portion of this parameter space is occupied by structures that are polytetrahedral, both those that are polyicosahedral and those that involve disclination lines. Such structures involve substantial strains for one-component Lennard-Jones clusters, but can be stabilized by the different-sized atoms in the binary clusters. These structures often have a `core-shell' geometry, where the larger atoms are on the surface, and the smaller atoms are in the core.Comment: 13 pages, 9 figure

Self-assembly of two-dimensional binary quasicrystals: A possible route to a DNA quasicrystal

We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta- and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm `star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms. We explore several possible design strategies and conclude that DNA star tiles that are designed to interact with one another in a specific but not overly constrained way could potentially be used to construct soft quasicrystals in experiment. We verify that such star tiles can form stable dodecagonal motifs using oxDNA, a realistic coarse-grained model of DNA