3,233 research outputs found
Elastic response of filamentous networks with compliant crosslinks
Experiments have shown that elasticity of disordered filamentous networks
with compliant crosslinks is very different from networks with rigid
crosslinks. Here, we model and analyze filamentous networks as a collection of
randomly oriented rigid filaments connected to each other by flexible
crosslinks that are modeled as worm-like chains. For relatively large
extensions we allow for enthalpic stretching of crosslinks' backbones. We show
that for sufficiently high crosslink density, the network linear elastic
response is affine on the scale of the filaments' length. The nonlinear regime
can become highly nonaffine and is characterized by a divergence of the elastic
modulus at finite strain. In contrast to the prior predictions, we do not find
an asymptotic regime in which the differential elastic modulus scales linearly
with the stress, although an approximate linear dependence can be seen in a
transition from entropic to enthalpic regimes. We discuss our results in light
of the recent experiments.Comment: 10 pages, 11 figure
An Investigation into the Variation of the Haemoglobin Level in Women with Special Reference to Menstruation and Pregnancy
The original purpose of this investigation was to find out whether there was any variation in the haemogloblin level before the onset of the menstrual flow (Group A), and during pregnancy (Group B). In the first part of the investigation 45 unmarried women were examined, and in the second part 486 pregnant women were examined. In Group A, each woman was examined on a number of occassions. In Group B, single readings were taken in the case of 424 women, and two or more readings in the case of 62 women. The total number of observations made in Group A. was 953, and in Group B. was 604. During the course of the investigation various other points of interest emerged, and re dealt with in the text
Stress relaxation in F-actin solutions by severing
Networks of filamentous actin (F-actin) are important for the mechanics of
most animal cells. These cytoskeletal networks are highly dynamic, with a
variety of actin-associated proteins that control cross-linking, polymerization
and force generation in the cytoskeleton. Inspired by recent rheological
experiments on reconstituted solutions of dynamic actin filaments, we report a
theoretical model that describes stress relaxation behavior of these solutions
in the presence of severing proteins. We show that depending on the kinetic
rates of assembly, disassembly, and severing, one can observe both
length-dependent and length-independent relaxation behavior
Driven diffusive systems with mutually interactive Langmuir kinetics
We investigate the simple one-dimensional driven model, the totally
asymmetric exclusion process, coupled to mutually interactive Langmuir
kinetics. This model is motivated by recent studies on clustering of motor
proteins on microtubules. In the proposed model, the attachment and detachment
rates of a particle are modified depending upon the occupancy of neighbouring
sites. We first obtain continuum mean-field equations and in certain limiting
cases obtain analytic solutions. We show how mutual interactions increase
(decrease) the effects of boundaries on the phase behavior of the model. We
perform Monte Carlo simulations and demonstrate that our analytical
approximations are in good agreement with the numerics over a wide range of
model parameters. We present phase diagrams over a selective range of
parameters.Comment: 9 pages, 8 Figure
Active biopolymer networks generate scale-free but euclidean clusters
We report analytical and numerical modelling of active elastic networks,
motivated by experiments on crosslinked actin networks contracted by myosin
motors. Within a broad range of parameters, the motor-driven collapse of active
elastic networks leads to a critical state. We show that this state is
qualitatively different from that of the random percolation model.
Intriguingly, it possesses both euclidean and scale-free structure with Fisher
exponent smaller than . Remarkably, an indistinguishable Fisher exponent and
the same euclidean structure is obtained at the critical point of the random
percolation model after absorbing all enclaves into their surrounding clusters.
We propose that in the experiment the enclaves are absorbed due to steric
interactions of network elements. We model the network collapse, taking into
account the steric interactions. The model shows how the system robustly drives
itself towards the critical point of the random percolation model with absorbed
enclaves, in agreement with the experiment.Comment: 6 pages, 7 figure
Actively stressed marginal networks
We study the effects of motor-generated stresses in disordered three
dimensional fiber networks using a combination of a mean-field, effective
medium theory, scaling analysis and a computational model. We find that motor
activity controls the elasticity in an anomalous fashion close to the point of
marginal stability by coupling to critical network fluctuations. We also show
that motor stresses can stabilize initially floppy networks, extending the
range of critical behavior to a broad regime of network connectivities below
the marginal point. Away from this regime, or at high stress, motors give rise
to a linear increase in stiffness with stress. Finally, we demonstrate that our
results are captured by a simple, constitutive scaling relation highlighting
the important role of non-affine strain fluctuations as a susceptibility to
motor stress.Comment: 8 pages, 4 figure
Investigation of the Coupling Potential by means of S-matrix Inversion
We investigate the inelastic coupling interaction by studying its effect on
the elastic scattering potential as determined by inverting the elastic
scattering -matrix. We first address the effect upon the real and imaginary
elastic potentials of including excited states of the target nucleus. We then
investigate the effect of a recently introduced novel coupling potential which
has been remarkably successful in reproducing the experimental data for the
C+C, C+Mg and O+Si reactions over a
wide range of energies. This coupling potential has the effect of deepening the
real elastic potential in the surface region, thereby explaining a common
feature of many phenomenological potentials. It is suggested that one can
relate this deepening to the super-deformed state of the compound nucleus,
Mg.Comment: 12 pages with 3 figure
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