1,923 research outputs found
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 (VII)
(Primeiro Artigo do Parágrafo)
Dos problemas do corpo protestante, passemos ao das Igrejas, e, em primeiro lugar, ao mais antigo: o de suas relações com as missões estrangeiras
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
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