Viscosity critical behaviour at the gel point in a 3d lattice model

Within a recently introduced model based on the bond-fluctuation dynamics we study the viscoelastic behaviour of a polymer solution at the gelation threshold. We here present the results of the numerical simulation of the model on a cubic lattice: the percolation transition, the diffusion properties and the time autocorrelation functions have been studied. From both the diffusion coefficients and the relaxation times critical behaviour a critical exponent k for the viscosity coefficient has been extracted: the two results are comparable within the errors and are in close agreement with the Rouse model prediction and with some experimental results. In the critical region below the transition threshold the time autocorrelation functions show a long time tail which is well fitted by a stretched exponential decay.Comment: 14 pag., RevTex, 9 figure

Induced and endogenous acoustic oscillations in granular faults

The frictional properties of disordered systems are affected by external perturbations. These perturbations usually weaken the system by reducing the macroscopic friction coefficient. This friction reduction is of particular interest in the case of disordered systems composed of granular particles confined between two plates, as this is a simple model of seismic fault. Indeed, in the geophysical context frictional weakening could explain the unexpected weakness of some faults, as well as earthquake remote triggering. In this manuscript we review recent results concerning the response of confined granular systems to external perturbations, considering the different mechanisms by which the perturbation could weaken a system, the relevance of the frictional reduction to earthquakes, as well as discussing the intriguing scenario whereby the weakening is not monotonic in the perturbation frequency, so that a re-entrant transition is observed, as the system first enters a fluidized state and then returns to a frictional state.Comment: 15 pages, 12 figure

A Geometrical Interpretation of Hyperscaling Breaking in the Ising Model

In random percolation one finds that the mean field regime above the upper critical dimension can simply be explained through the coexistence of infinite percolating clusters at the critical point. Because of the mapping between percolation and critical behaviour in the Ising model, one might check whether the breakdown of hyperscaling in the Ising model can also be intepreted as due to an infinite multiplicity of percolating Fortuin-Kasteleyn clusters at the critical temperature T_c. Preliminary results suggest that the scenario is much more involved than expected due to the fact that the percolation variables behave differently on the two sides of T_c.Comment: Lattice2002(spin

Complex viscosity behavior and cluster formation in attractive colloidal systems

The increase of the viscosity, which is observed in attractive colloidal systems by varying the temperature or the volume fraction, can be related to the formation of structures due to particle aggregation. In particular we have studied the non trivial dependence of the viscosity from the temperature and the volume fraction in the copolymer-micellar system L64. The comparison of the experimental data with the results of numerical simulations in a simple model for gelation phenomena suggests that this intriguing behavior can be explained in terms of cluster formation and that this picture can be quite generally extended to other attractive colloidal systems.Comment: 5 pages, 4 figure

Percolation in high dimensions is not understood

The number of spanning clusters in four to nine dimensions does not fully follow the expected size dependence for random percolation.Comment: 9-dimensional data and more points for large lattices added; statistics improved, text expanded, table of exponents inserte

Hegelians on the Slopes of Vesuvius: A Transnational Study in the Intellectual History of Naples, 1799-1861

This thesis examines the reception, circulation and revision of Hegel’s thought, most notably his philosophy of history, in Neapolitan intellectual history during the Risorgimento, approached from a transnational perspective. In particular, attention will focus on five inter-related themes: (i) the complex set of intellectual exchanges and encounters enabling the penetration and popularisation of Hegel’s philosophy in Naples; (ii) the ongoing revision, taking place during the early decades of the nineteenth century, of Giambattista Vico’s historicism via debates that ultimately deployed an image of the Neapolitan thinker as a theorist of historical time, on the one hand, and the proponent of an idealist account of it, on the other; (iii) the amalgamation of a Hegelian notion of absolute historical development and Vichian historicism taking place in the southern capital’s private schools of philosophy, enabling historians to view Neapolitan Hegelianism as the result of a broad transnational encounter, yet closely rooted in local contexts and debates; (iv) the ways in which, in response to ongoing experiences of political change, most notably the 1848 Revolution and the emancipation of the Italian peninsula, Neapolitan Hegelianism was systematically deployed in support of – and in opposition to – different strands of Risorgimento political thought: it came to support, in fact, a form of democratic constitutionalism reminiscent of the Jacobin ideas informing the Neapolitan Revolution of 1799, in direct opposition to moderate Piedmontese liberalism; and (v) the shaping of a transnational cosmopolitan sensitivity among Neapolitan Hegelians, ultimately merging the political ambitions connected with the emancipation and unification of Italy with the negotiation of a vantage point for the country in the intellectual and philosophical lives of modern European nations

Correlations and Omori law in Spamming

The most costly and annoying characteristic of the e-mail communication system is the large number of unsolicited commercial e-mails, known as spams, that are continuously received. Via the investigation of the statistical properties of the spam delivering intertimes, we show that spams delivered to a given recipient are time correlated: if the intertime between two consecutive spams is small (large), then the next spam will most probably arrive after a small (large) intertime. Spam temporal correlations are reproduced by a numerical model based on the random superposition of spam sequences, each one described by the Omori law. This and other experimental findings suggest that statistical approaches may be used to infer how spammers operate.Comment: Europhysics Letters, to appea