18,929 research outputs found
Dynamic model for failures in biological systems
A dynamic model for failures in biological organisms is proposed and studied
both analytically and numerically. Each cell in the organism becomes dead under
sufficiently strong stress, and is then allowed to be healed with some
probability. It is found that unlike the case of no healing, the organism in
general does not completely break down even in the presence of noise. Revealed
is the characteristic time evolution that the system tends to resist the stress
longer than the system without healing, followed by sudden breakdown with some
fraction of cells surviving. When the noise is weak, the critical stress beyond
which the system breaks down increases rapidly as the healing parameter is
raised from zero, indicative of the importance of healing in biological
systems.Comment: To appear in Europhys. Let
Velocity selection problem for combined motion of melting and solidification fronts
We discuss a free boundary problem for two moving solid-liquid interfaces
that strongly interact via the diffusion field in the liquid layer between
them. This problem arises in the context of liquid film migration (LFM) during
the partial melting of solid alloys. In the LFM mechanism the system chooses a
more efficient kinetic path which is controlled by diffusion in the liquid
film, whereas the process with only one melting front would be controlled by
the very slow diffusion in the mother solid phase. The relatively weak
coherency strain energy is the effective driving force for LFM. As in the
classical dendritic growth problems, also in this case an exact family of
steady-state solutions with two parabolic fronts and an arbitrary velocity
exists if capillary effects are neglected. We develop a velocity selection
theory for this problem, including anisotropic surface tension effects. The
strong diffusion interaction and coherency strain effects in the solid near the
melting front lead to substantial changes compared to classical dendritic
growth.Comment: submitted to PR
Magnetoelectric Effects on Composite Nano Granular Films
Employing a new experimental technique to measure magnetoelectric response
functions, we have measured the magnetoelectric effect in composite films of
nano granular metallic iron in anatase titanium dioxide at temperatures below
50 K. A magnetoelectric resistance is defined as the ratio of a transverse
voltage to bias current as a function of the magnetic field. In contrast to the
anomalous Hall resistance measured above 50 K, the magnetoelectic resistance
below 50 K is significantly larger and exhibits an even symmetry with respect
to magnetic field reversal . The measurement technique required
attached electrodes in the plane of the film composite in order to measure
voltage as a function of bias current and external magnetic field. To our
knowledge, the composite films are unique in terms of showing magnetoelectric
effects at low temperatures, 50 K, and anomalous Hall effects at high
temperatures, 50 K.Comment: ReVTeX, 2 figures, 3 page
Anomalous kinetics of attractive reactions
We investigate the kinetics of reaction with the local attractive
interaction between opposite species in one spatial dimension. The attractive
interaction leads to isotropic diffusions inside segregated single species
domains, and accelerates the reactions of opposite species at the domain
boundaries. At equal initial densities of and , we analytically and
numerically show that the density of particles (), the size of domains
(), the distance between the closest neighbor of same species
(), and the distance between adjacent opposite species ()
scale in time as , , and respectively. These dynamical exponents form a new
universality class distinguished from the class of uniformly driven systems of
hard-core particles.Comment: 4 pages, 4 figure
Dynamic model of fiber bundles
A realistic continuous-time dynamics for fiber bundles is introduced and
studied both analytically and numerically. The equation of motion reproduces
known stationary-state results in the deterministic limit while the system
under non-vanishing stress always breaks down in the presence of noise.
Revealed in particular is the characteristic time evolution that the system
tends to resist the stress for considerable time, followed by sudden complete
rupture. The critical stress beyond which the complete rupture emerges is also
obtained
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