36 research outputs found
Dynamical correlations in the escape strategy of Influenza A virus
The evolutionary dynamics of human Influenza A virus presents a challenging
theoretical problem. An extremely high mutation rate allows the virus to
escape, at each epidemic season, the host immune protection elicited by
previous infections. At the same time, at each given epidemic season a single
quasi-species, that is a set of closely related strains, is observed. A
non-trivial relation between the genetic (i.e., at the sequence level) and the
antigenic (i.e., related to the host immune response) distances can shed light
into this puzzle. In this paper we introduce a model in which, in accordance
with experimental observations, a simple interaction rule based on spatial
correlations among point mutations dynamically defines an immunity space in the
space of sequences. We investigate the static and dynamic structure of this
space and we discuss how it affects the dynamics of the virus-host interaction.
Interestingly we observe a staggered time structure in the virus evolution as
in the real Influenza evolutionary dynamics.Comment: 14 pages, 5 figures; main paper for the supplementary info in
arXiv:1303.595
Loss separation for dynamic hysteresis in magnetic thin films
We develop a theory for dynamic hysteresis in ferromagnetic thin films, on
the basis of the phenomenological principle of loss separation. We observe
that, remarkably, the theory of loss separation, originally derived for bulk
metallic materials, is applicable to disordered magnetic systems under fairly
general conditions regardless of the particular damping mechanism. We confirm
our theory both by numerical simulations of a driven random--field Ising model,
and by re--examining several experimental data reported in the literature on
dynamic hysteresis in thin films. All the experiments examined and the
simulations find a natural interpretation in terms of loss separation. The
power losses dependence on the driving field rate predicted by our theory fits
satisfactorily all the data in the entire frequency range, thus reconciling the
apparent lack of universality observed in different materials.Comment: 4 pages, 6 figure
Phase transitions in a disordered system in and out of equilibrium
The equilibrium and non--equilibrium disorder induced phase transitions are
compared in the random-field Ising model (RFIM). We identify in the
demagnetized state (DS) the correct non-equilibrium hysteretic counterpart of
the T=0 ground state (GS), and present evidence of universality. Numerical
simulations in d=3 indicate that exponents and scaling functions coincide,
while the location of the critical point differs, as corroborated by exact
results for the Bethe lattice. These results are of relevance for optimization,
and for the generic question of universality in the presence of disorder.Comment: Accepted for publication in Phys. Rev. Let
The average shape of a fluctuation: universality in excursions of stochastic processes
We study the average shape of a fluctuation of a time series x(t), that is
the average value _T before x(t) first returns, at time T, to its
initial value x(0). For large classes of stochastic processes we find that a
scaling law of the form _T = T^\alpha f(t/T) is obeyed. The
scaling function f(s) is to a large extent independent of the details of the
single increment distribution, while it encodes relevant statistical
information on the presence and nature of temporal correlations in the process.
We discuss the relevance of these results for Barkhausen noise in magnetic
systems.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let