10,167 research outputs found
Absorbing phase transition in a conserved lattice gas with random neighbor particle hopping
A conserved lattice gas with random neighbor hopping of active particles is
introduced which exhibits a continuous phase transition from an active state to
an absorbing non-active state. Since the randomness of the particle hopping
breaks long range spatial correlations our model mimics the mean-field scaling
behavior of the recently introduced new universality class of absorbing phase
transitions with a conserved field. The critical exponent of the order
parameter is derived within a simple approximation. The results are compared
with those of simulations and field theoretical approaches.Comment: 5 pages, 3 figures, accepted for publication in J. Phys.
Sph propagation modelling of an earthflow from southern italy
Natural slopes in clayey soils are often affected by failures which may cause the onset of landslides of the flow type travelling large distances and damaging buildings and major infrastructures. Particularly, the so-called earthflows pose challenging tasks for the individuation and forecasting of the remobilized masses; as a consequence, the mathematical modelling of the propagation stage allows enhancing the understanding of earthflows in order to obtain reliable assessments of run-out distances and displaced soil volumes. This paper deals with the reactivations of Montaguto earthflow (Southern Italy) occurred from 1998 to 2009 that are simulated, through the depth-integrated “GeoFlow-SPH” model, thanks to the availability of a detailed data-set. The achieved results provide a satisfactory agreement with the in-situ information and outline how a change of the rheology of the mobilized masses can affect the whole phenomenon
Spectral distortion of cosmic background radiation by scattering on hot electrons. Exact calculations
The spectral distortion of the cosmic background radiation produced by the
inverse Compton scattering on hot electrons in clusters of galaxies (thermal
Sunyaev-Zeldovich effect) is calculated for arbitrary optical depth and
electron temperature. The distortion is found by a numerical solution of the
exact Boltzmann equation for the photon distribution function. In the limit of
small optical depth and low electron temperature our results confirm the
previous analyses. In the opposite limits, our method is the only one that
permits to make accurate calculations.Comment: 18 pages, 7 figures, to be published in Ap
Collective versus hub activation of epidemic phases on networks
We consider a general criterion to discern the nature of the threshold in
epidemic models on scale-free (SF) networks. Comparing the epidemic lifespan of
the nodes with largest degrees with the infection time between them, we propose
a general dual scenario, in which the epidemic transition is either ruled by a
hub activation process, leading to a null threshold in the thermodynamic limit,
or given by a collective activation process, corresponding to a standard phase
transition with a finite threshold. We validate the proposed criterion applying
it to different epidemic models, with waning immunity or heterogeneous
infection rates in both synthetic and real SF networks. In particular, a waning
immunity, irrespective of its strength, leads to collective activation with
finite threshold in scale-free networks with large exponent, at odds with
canonical theoretical approaches.Comment: Revised version accepted for publication in PR
Phase transitions with infinitely many absorbing states in complex networks
We instigate the properties of the threshold contact process (TCP), a process
showing an absorbing-state phase transition with infinitely many absorbing
states, on random complex networks. The finite size scaling exponents
characterizing the transition are obtained in a heterogeneous mean field (HMF)
approximation and compared with extensive simulations, particularly in the case
of heterogeneous scale-free networks. We observe that the TCP exhibits the same
critical properties as the contact process (CP), which undergoes an
absorbing-state phase transition to a single absorbing state. The accordance
among the critical exponents of different models and networks leads to
conjecture that the critical behavior of the contact process in a HMF theory is
a universal feature of absorbing state phase transitions in complex networks,
depending only on the locality of the interactions and independent of the
number of absorbing states. The conditions for the applicability of the
conjecture are discussed considering a parallel with the
susceptible-infected-susceptible epidemic spreading model, which in fact
belongs to a different universality class in complex networks.Comment: 9 pages, 6 figures to appear in Phys Rev
Percolation and Epidemic Thresholds in Clustered Networks
We develop a theoretical approach to percolation in random clustered
networks. We find that, although clustering in scale-free networks can strongly
affect some percolation properties, such as the size and the resilience of the
giant connected component, it cannot restore a finite percolation threshold. In
turn, this implies the absence of an epidemic threshold in this class of
networks extending, thus, this result to a wide variety of real scale-free
networks which shows a high level of transitivity. Our findings are in good
agreement with numerical simulations.Comment: 4 Pages and 3 Figures. Final version to appear in PR
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