330 research outputs found
On the power spectrum of magnetization noise
Understanding the power spectrum of the magnetization noise is a long
standing problem. While earlier work considered superposition of 'elementary'
jumps, without reference to the underlying physics, recent approaches relate
the properties of the noise with the critical dynamics of domain walls. In
particular, a new derivation of the power spectrum exponent has been proposed
for the random-field Ising model. We apply this approach to experimental data,
showing its validity and limitations.Comment: 8 pages, 3 .eps figures (elsart.cls style required
Comment on: "Roughness of Interfacial Crack Fronts: Stress-Weighted Percolation in the Damage Zone"
This is a comment on J. Schmittbuhl, A. Hansen, and G. G. Batrouni, Phys.
Rev. Lett. 90, 045505 (2003). They offer a reply, in turn.Comment: 1 page, 1 figur
Avalanche precursors of failure in hierarchical fuse networks
We study precursors of failure in hierarchical random fuse network models
which can be considered as idealizations of hierarchical (bio)materials where
fibrous assemblies are held together by multi-level (hierarchical) cross-links.
When such structures are loaded towards failure, the patterns of precursory
avalanche activity exhibit generic scale invariance: Irrespective of load,
precursor activity is characterized by power-law avalanche size distributions
without apparent cut-off, with power-law exponents that decrease continuously
with increasing load. This failure behavior and the ensuing super-rough crack
morphology differ significantly from the findings in non-hierarchical
structures
Barkhausen noise from zigzag domain walls
We investigate the Barkhausen noise in ferromagnetic thin films with zigzag
domain walls. We use a cellular automaton model that describes the motion of a
zigzag domain wall in an impure ferromagnetic quasi-two dimensional sample with
in-plane uniaxial magnetization at zero temperature, driven by an external
magnetic field. The main ingredients of this model are the dipolar spin-spin
interactions and the anisotropy energy. A power law behavior with a cutoff is
found for the probability distributions of size, duration and correlation
length of the Barkhausen avalanches, and the critical exponents are in
agreement with the available experiments. The link between the size and the
duration of the avalanches is analyzed too, and a power law behavior is found
for the average size of an avalanche as a function of its duration.Comment: 11 pages, 12 figure
Deblocking of interacting particle assemblies: from pinning to jamming
A wide variety of interacting particle assemblies driven by an external force
are characterized by a transition between a blocked and a moving phase. The
origin of this deblocking transition can be traced back to the presence of
either external quenched disorder, or of internal constraints. The first case
belongs to the realm of the depinning transition, which, for example, is
relevant for flux-lines in type II superconductors and other elastic systems
moving in a random medium. The second case is usually included within the
so-called jamming scenario observed, for instance, in many glassy materials as
well as in plastically deforming crystals. Here we review some aspects of the
rich phenomenology observed in interacting particle models. In particular, we
discuss front depinning, observed when particles are injected inside a random
medium from the boundary, elastic and plastic depinning in particle assemblies
driven by external forces, and the rheology of systems close to the jamming
transition. We emphasize similarities and differences in these phenomena.Comment: 20 pages, 8 figures, submitted for a special issue of the Brazilian
Journal of Physics entitled: Statistical Mechanics of Irreversible Stochastic
Models - I
Protein accumulation in the endoplasmic reticulum as a non-equilibrium phase transition
Several neurological disorders are associated with the aggregation of
aberrant proteins, often localized in intracellular organelles such as the
endoplasmic reticulum. Here we study protein aggregation kinetics by mean-field
reactions and three dimensional Monte carlo simulations of diffusion-limited
aggregation of linear polymers in a confined space, representing the
endoplasmic reticulum. By tuning the rates of protein production and
degradation, we show that the system undergoes a non-equilibrium phase
transition from a physiological phase with little or no polymer accumulation to
a pathological phase characterized by persistent polymerization. A combination
of external factors accumulating during the lifetime of a patient can thus
slightly modify the phase transition control parameters, tipping the balance
from a long symptomless lag phase to an accelerated pathological development.
The model can be successfully used to interpret experimental data on
amyloid-\b{eta} clearance from the central nervous system
Explaining the dynamics of tumor aggressiveness : at the crossroads between biology, artificial intelligence and complex systems
Facing metastasis is the most pressing challenge of cancer research. In this review, we discuss recent advances in understanding phenotypic plasticity of cancer cells, highlighting the kinetics of cancer stem cell and the role of the epithelial mesenchymal transition for metastasis. It appears that the tumor micro-environment plays a crucial role in triggering phenotypic transitions, as we illustrate discussing the challenges posed by macrophages and cancer associated fibroblasts. To disentangle the complexity of environmentally induced phenotypic transitions, there is a growing need for novel advanced algorithms as those proposed in our recent work combining single cell data analysis and numerical simulations of gene regulatory networks. We conclude discussing recent developments in artificial intelligence and its applications to personalized cancer treatment
Dynamic hysteresis in Finemet thin films
We performed a series of dynamic hysteresis measurements on three series of
Finemet films with composition FeCuNbSiB, using
both the longitudinal magneto-optical Kerr effect (MOKE) and the inductive
fluxometric method. The MOKE dynamic hysteresis loops show a more marked
variability with the frequency than the inductive ones, while both measurements
show a similar dependence on the square root of frequency. We analyze these
results in the frame of a simple domain wall depinning model, which accounts
for the general behavior of the data.Comment: 3 pages, 3 figure
Barkhausen Noise and Critical Scaling in the Demagnetization Curve
The demagnetization curve, or initial magnetization curve, is studied by
examining the embedded Barkhausen noise using the non-equilibrium, zero
temperature random-field Ising model. The demagnetization curve is found to
reflect the critical point seen as the system's disorder is changed. Critical
scaling is found for avalanche sizes and the size and number of spanning
avalanches. The critical exponents are derived from those related to the
saturation loop and subloops. Finally, the behavior in the presence of long
range demagnetizing fields is discussed. Results are presented for simulations
of up to one million spins.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
- …