Melting of icosahedral gold nanoclusters from molecular dynamics simulations

Molecular dynamics simulations show that gold clusters with about 600--3000 atoms crystallize into a Mackay icosahedron upon cooling from the liquid. A detailed surface analysis shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temperature. This softening is found to be due to the increasing mobility of vertex and edge atoms with temperature, which leads to inter-layer and intra-layer diffusion, and a shrinkage of the average facet size, so that the average shape of the cluster is nearly spherical at melting.Comment: 40 pages, 27 figure

Bent surface free energy differences from simulation

We present a calculation of the change of free energy of a solid surface upon bending of the solid. It is based on extracting the surface stress through a molecular dynamics simulation of a bent slab by using a generalized stress theorem formula, and subsequent integration of the stress with respect to strain as a function of bending curvature. The method is exemplified by obtaining and comparing free energy changes with curvature of various reconstructed Au(001) surfaces.Comment: 14 pages, 2 figures, accepted for publication in Surface Science (ECOSS-19

A distributed system for microelectronic algorithms

Microelectronics tools tend to consume large amounts of memory and processor time. When circuit size outgrows the resources available on a station, its time for a scalable tool architecture. Applied to design rule checking of jlattened masks, this distributed; object-oriented architecture summons together the power of small, cheap desktop computers. The distributed system enables processing of larger circuits, assigning distinct parts of the problem to each machine. Larger circuits can be tested and testing time reduced as more computers are aggregated to the process

Theoretical study of Ga-based nanowires and the interaction of Ga with single-wall carbon nanotubes

Gallium displays physical properties which can make it a potential element to produce metallic nanowires and high-conducting interconnects in nanoelectronics. Using first-principles pseudopotential plane method we showed that Ga can form stable metallic linear and zigzag monatomic chain structures. The interaction between individual Ga atom and single-wall carbon nanotube (SWNT) leads to a chemisorption bond involving charge transfer. Doping of SWNT with Ga atom gives rise to donor states. Owing to a significant interaction between individual Ga atom and SWNT, continuous Ga coverage of the tube can be achieved. Ga nanowires produced by the coating of carbon nanotube templates are found to be stable and high conducting.Comment: 8 pages, 8 figure

Tachyon Vacuum Solution in Open String Field Theory with Constant B Field

We show that Schnabl's tachyon vacuum solution is an exact solution of the equation of motion of Witten's open bosonic string field theory in the background of constant antisymmetric two-form field. The action computed at the vacuum solution is given by the Dirac-Born-Infeld factor multiplied to that without the antisymmetric tensor field.Comment: 8 page

Roughening of close-packed singular surfaces

An upper bound to the roughening temperature of a close-packed singular surface, fcc Al (111), is obtained via free energy calculations based on thermodynamic integration using the embedded-atom interaction model. Roughening of Al (111) is predicted to occur at around 890 K, well below bulk melting (933 K), and it should therefore be observable, save for possible kinetic hindering.Comment: RevTeX 4 pages, embedded figure

Time-localized projectors in String Field Theory with E-field

We extend the analysis of hep-th/0409063 to the case of a constant electric field turned on the worldvolume and on a transverse direction of a D-brane. We show that time localization is still obtained by inverting the discrete eigenvalues of the lump solution. The lifetime of the unstable soliton is shown to depend on two free parameters: the b-parameter and the value of the electric field. As a by-product, we construct the normalized diagonal basis of the star algebra in $B_{\mu\nu}$-field background.Comment: 27 +1 pages, v2: references added, typos correcte

Um sistema distribuído para algoritmos de microeletrônica

Microelectronics tools tend to consume large amounts of memoly and processor time. When circuit size outgrows the resources available on a station, its time for a scalable tool architectllre. Applied to design rule checking of flattened masks, this distributed; object-oriented architecture summons together the power of small, cheap desktop computers. The distributed system enables processing of larger circuits, assigning distinct parts of the problem to each machine. Larger circuits can be tested and testing time reduced as more computers are aggregated to the process.Ferramentas de Microeletrônica tendem a consumir grandes quantidades de memória e tempo de processador. Quando o tamanho de circuito supera os recursos disponível em uma estação, surge a necessidade de uma arquitetura de ferramenta de escalável. Esta arquitetura distribuída orientada a objeto foi aplicada para conferir regras de máscaras planas, congregando o processamento de computadores de mesa pequenos baratos. O sistema distribuído habilita o processamento de circuitos maiores e aloca partes distintas do problema a cada máquina. Circuitos maiores podem ser testados agregando-se maior número de computadores que possibilitam maior uso de recursos e podem reduzir o tempo de processamento

First principles simulations of liquid Fe-S under Earth's core conditions

First principles electronic structure calculations, based upon density functional theory within the generalized gradient approximation and ultra-soft Vanderbilt pseudopotentials, have been used to simulate a liquid alloy of iron and sulfur at Earth's core conditions. We have used a sulfur concentration of $\approx 12$wt, in line with the maximum recent estimates of the sulfur abundance in the Earth's outer core. The analysis of the structural, dynamical and electronic structure properties has been used to report on the effect of the sulfur impurities on the behavior of the liquid. Although pure sulfur is known to form chains in the liquid phase, we have not found any tendency towards polymerization in our liquid simulation. Rather, a net S-S repulsion is evident, and we propose an explanation for this effect in terms of the electronic structure. The inspection of the dynamical properties of the system suggests that the sulfur impurities have a negligible effect on the viscosity of Earth's liquid core.Comment: 24 pages (including 8 figures