9,787 research outputs found
Field-control, phase-transitions, and life's emergence
Instances of critical-like characteristics in living systems at each
organizational level as well as the spontaneous emergence of computation
(Langton), indicate the relevance of self-organized criticality (SOC). But
extrapolating complex bio-systems to life's origins, brings up a paradox: how
could simple organics--lacking the 'soft matter' response properties of today's
bio-molecules--have dissipated energy from primordial reactions in a controlled
manner for their 'ordering'? Nevertheless, a causal link of life's macroscopic
irreversible dynamics to the microscopic reversible laws of statistical
mechanics is indicated via the 'functional-takeover' of a soft magnetic
scaffold by organics (c.f. Cairns-Smith's 'crystal-scaffold'). A
field-controlled structure offers a mechanism for bootstrapping--bottom-up
assembly with top-down control: its super-paramagnetic components obey
reversible dynamics, but its dissipation of H-field energy for aggregation
breaks time-reversal symmetry. The responsive adjustments of the controlled
(host) mineral system to environmental changes would bring about mutual
coupling between random organic sets supported by it; here the generation of
long-range correlations within organic (guest) networks could include SOC-like
mechanisms. And, such cooperative adjustments enable the selection of the
functional configuration by altering the inorganic network's capacity to assist
a spontaneous process. A non-equilibrium dynamics could now drive the
kinetically-oriented system towards a series of phase-transitions with
appropriate organic replacements 'taking-over' its functions.Comment: 54 pages, pdf fil
The mechano-chemistry of cytoskeletal force generation
In this communication, we propose a model to study the non-equilibrium
process by which actin stress fibers develop force in contractile cells. The
emphasis here is on the non-equilibrium thermodynamics, which is necessary to
address the mechanics as well as the chemistry of dynamic cell contractility.
In this setting we are able to develop a framework that relates (a) the
dynamics of force generation within the cell and (b) the cell response to
external stimuli to the chemical processes occurring within the cell, as well
as to the mechanics of linkage between the stress fibers, focal adhesions and
extra-cellular matrix.Comment: 22 pages, 6 figures, 1 table, accepted in Biomechanics and Modeling
in Mechanobiolog
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