Lifetime of dynamic heterogeneity in strong and fragile kinetically constrained spin models

Kinetically constrained spin models are schematic coarse-grained models for the glass transition which represent an efficient theoretical tool to study detailed spatio-temporal aspects of dynamic heterogeneity in supercooled liquids. Here, we study how spatially correlated dynamic domains evolve with time and compare our results to various experimental and numerical investigations. We find that strong and fragile models yield different results. In particular, the lifetime of dynamic heterogeneity remains constant and roughly equal to the alpha relaxation time in strong models, while it increases more rapidly in fragile models when the glass transition is approached.Comment: Submitted to the proceedings of the 6th EPS Liquid Matter Conference, Utrecht 2-6 July 200

Multiple Functionality in Nanotube Transistors

Calculations of quantum transport in a carbon nanotube transistor show that such a device offers unique functionality. It can operate as a ballistic field-effect transistor, with excellent characteristics even when scaled to 10 nm dimensions. At larger gate voltages, channel inversion leads to resonant tunneling through an electrostatically defined nanoscale quantum dot. Thus the transistor becomes a gated resonant tunelling device, with negative differential resistance at a tunable threshold. For the dimensions considered here, the device operates in the Coulomb blockade regime, even at room temperature.Comment: To appear in Phys. Rev. Let

Negative differential resistance in nanotube devices

Carbon nanotube junctions are predicted to exhibit negative differential resistance, with very high peak-to-valley current ratios even at room temperature. We treat both nanotube p-n junctions and undoped metal-nanotube-metal junctions, calculating quantum transport through the self-consistent potential within a tight-binding approximation. The undoped junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Following microscopic motion in a two dimensional glass-forming binary fluid

The dynamics of a binary mixture of large and small discs are studied at temperatures approaching the glass transition using an analysis based on the topology of the Voronoi polygon surrounding each atom. At higher temperatures we find that dynamics is dominated by fluid-like motion that involves particles entering and exiting the nearest-neighbour shells of nearby particles. As the temperature is lowered, the rate of topological moves decreases and motion becomes localised to regions of mixed pentagons and heptagons. In addition we find that in the low temperature state particles may translate significant distances without undergoing changes in their nearest neig hbour shell. These results have implications for dynamical heterogeneities in glass forming liquids.Comment: 12 pages, 7 figure

O Protestantismo Brasileiro. Estudo de Eclesiologia e de História Social (IV)

(Primeiro Parágrafo do Artigo)O problema das relações entre Igrejas missionárias e Igrejas de missões, haveria de apresentar-se, certamente às demais denominações protestantes do Brasil

O Protestantismo Brasileiro. Estudo de Eclesiologia e de História Social (III)

(Primeiro Parágrafo do Artigo)O Protestantismo brasileiro se mostrara assim vitorioso, nas provações a que havia sido submetido

O Protestantismo Brasileiro. Estudo de Eclesiologia e de História Social (VI)

(Primeiro Parágrafo do Artigo)Chegamos, assim, às imediações de 1930, data que se  considera geralmente , na história geral e na história do Brasil, como o início do período atual

O Protestantismo Brasileiro. Estudo de Eclesiologia e de História Social (V)

(Primeiro Parágrafo do Artigo)A questão nacional, que as Igrejas brasileiras haviam proposto às Missões estrangeiras, iria apresentar-se agora também a elas, uma vez tornadas missionárias

O Protestantismo brasileito. Estudo de eclesiologia e de história social (conslusão)

(Primeiro Parágrafo do Artigo)Os problemas eclesiásticos e as discussões teológicas que examinamos agora, correspondem a um estado de maturidades das zonas geográficas e sociais mais antigas do protestantismo brasileiro