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At least 667 records · Page 37Linked to original sources
PubMed2000

Topological evolution of dynamical networks: global criticality from local dynamics.

We evolve network topology of an asymmetrically connected threshold network by a simple local rewiring rule: quiet nodes grow links, active nodes lose links. This leads to convergence of the average connectivity of the network towards the critical value K(c) = 2 in the limit of large system size N. How this principle could generate self-organization in natural complex systems is discussed for two examples: neural networks and regulatory networks in the genome.

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PubMed2000

Rheological evidence for a dynamical crossover in polymer melts via nonequilibrium molecular dynamics

A certain "critical" molecular weight controls rheological properties of the multibead finitely extensible nonlinear elastic (FENE) chain model polymer melt. The rheological crossover manifests itself in a change of power law behavior for the viscous properties at a critical number of beads per chain N(c) = 100+/-10. This finding confirms a newly proposed relationship between dimensionless critical weight, characteristic length, and flexibility which we obtain as a side result. Results further suggest that the entanglement molecular weight N(e) for the flexible FENE chain model could be comparable in size or even larger than its critical molecular weight N(c).

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PubMed2006

Experimental and quantum dynamical study on an asymmetric insertion reaction: state-to-state dynamics of O(1D) + HD(1Sigmag+, v' = 0, j' = 0)-->OH(Pi, v", N") + D(2S).

Quantum-state-resolved differential cross sections of the O((1)D) + HD --> OH + D reaction at the collision energy of 7.11 kJ/mol has been determined experimentally and theoretically. The results of the time-dependent wave-packet calculations are overall in good agreement with the crossed beam scattering data, providing a benchmark example of an asymmetric insertion reaction at the state-to-state scattering level. The good agreement between experiment and theory suggests that the underlying ground potential energy surface is generally correct and that the nonadiabatic effect involving the electronic excited pathway is apparently small in this system.

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PubMed2004

Dynamics of simple liquids at heterogeneous surfaces: molecular-dynamics simulations and hydrodynamic description.

In this paper we consider the effect of surface heterogeneity on the slippage of fluid, using two complementary approaches. First, MD simulations of a corrugated hydrophobic surface have been performed. A dewetting transition, leading to a super-hydrophobic state, is observed for pressure below a "capillary" pressure. Conversely, a very large slippage of the fluid on this composite interface is found in this super-hydrophobic state. Second, we propose a macroscopic estimate of the effective slip length on the basis of continuum hydrodynamics, in order to rationalize the previous MD results. This calculation allows to estimate the effect of a heterogeneous slip length pattern at the composite interface. Comparison between the two approaches shows that they are in good agreement at low pressure, but highlights the role of the exact shape of the liquid-vapor interface at higher pressure. These results confirm that small variations in the roughness of a surface can lead to huge differences in the slip effect. On the basis of these results, we propose some guidelines to design highly slippery surfaces, motivated by potential applications in microfluidics.

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