Biomedical subjects

Vittoria Colizza

Publications and source records attributed to Vittoria Colizza.

3 recordsLinked to original sources

PubMed2004

Network structures from selection principles.

We present an analysis of the topologies of a class of networks which are optimal in terms of the requirements of having as short a route as possible between any two nodes while yet keeping the congestion in the network as low as possible. Strikingly, we find a variety of distinct topologies and novel phase transitions between them on varying the number of links per node. Our results suggest that the emergence of the topologies observed in nature may arise both from growth mechanisms and the interplay of dynamical mechanisms with a selection process.

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PubMed2002

Fluctuation-dissipation ratio for compacting granular media.

In this paper we investigate the possibility of a dynamical definition of an effective temperature for compacting granular media in the framework of the fluctuation-dissipation (FD) relations. We have studied two paradigmatic models for the compaction of granular media, which consider particles diffusing on a lattice, with either geometrical (tetris model) or dynamical (Kob-Andersen model) constraints. Idealized compaction without gravity has been implemented for the tetris model, and compaction with a preferential direction imposed by gravity has been studied for both models. In the ideal case of an homogeneous compaction, the obtained FD ratio is clearly shown to be in agreement with the prediction of Edwards' measure at various densities. Similar results are obtained with gravity only when the homogeneity of the bulk is imposed. In this case the FD ratio obtained dynamically for horizontal displacements and mobility and from Edwards' measure coincide. Finally, we propose experimental tests for the validity of the Edwards' construction through the comparison of various types of dynamical measurements.

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PubMed2002

Definition of temperature in dense granular media.

In this paper we report the measurement of a pseudotemperature for compacting granular media on the basis of the fluctuation-dissipation relations in the aging dynamics of a model system. From the violation of the fluctuation-dissipation theorem emerges an effective temperature (a dynamical temperature T(dyn)) whose value depends on the particle density. We compare the results for T(dyn) at several densities with the values of Edwards' compactivity at the corresponding densities [S. F. Edwards, in Granular Matter: An Interdisciplinary Approach, edited by A. Mehta (Springer-Verlag, New York, 1994) and references therein]. It turns out that the dynamical temperature and Edwards' compactivity coincide on a large range of densities, opening in this way the door to experimental checks as well as theoretical constructions.

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