27,561 research outputs found
Knowing one's place: a free-energy approach to pattern regulation.
Understanding how organisms establish their form during embryogenesis and regeneration represents a major knowledge gap in biological pattern formation. It has been recently suggested that morphogenesis could be understood in terms of cellular information processing and the ability of cell groups to model shape. Here, we offer a proof of principle that self-assembly is an emergent property of cells that share a common (genetic and epigenetic) model of organismal form. This behaviour is formulated in terms of variational free-energy minimization-of the sort that has been used to explain action and perception in neuroscience. In brief, casting the minimization of thermodynamic free energy in terms of variational free energy allows one to interpret (the dynamics of) a system as inferring the causes of its inputs-and acting to resolve uncertainty about those causes. This novel perspective on the coordination of migration and differentiation of cells suggests an interpretation of genetic codes as parametrizing a generative model-predicting the signals sensed by cells in the target morphology-and epigenetic processes as the subsequent inversion of that model. This theoretical formulation may complement bottom-up strategies-that currently focus on molecular pathways-with (constructivist) top-down approaches that have proved themselves in neuroscience and cybernetics
Gluon density in nuclei
In this talk we present our detail study ( theory and numbers) [1] on the
shadowing corrections to the gluon structure functions for nuclei. Starting
from rather contraversial information on the nucleon structure function which
is originated by the recent HERA data, we develop the Glauber approach for the
gluon density in a nucleus based on Mueller formula [2] and estimate the value
of the shadowing corrections in this case. Than we calculate the first
corrections to the Glauber approach and show that these corrections are big.
Based on this practical observation we suggest the new evolution equation which
takes into account the shadowing corrections and solve it. We hope to convince
you that the new evolution equation gives a good theoretical tool to treat the
shadowing corrections for the gluons density in a nucleus and, therefore, it is
able to provide the theoretically reliable initial conditions for the time
evolution of the nucleus - nucleus cascade.Comment: Talk at RHIC'96, 43 pages, 23 figure
Refractory porcelain enamel passive-thermal-control coating for high-temperature superalloys
Study was conducted to match thermal expansion coefficients thereby preventing enamels from cracking. Report discusses various enamel coatings that are applied to two different high-temperature superalloys. Study may be of interest to manufacturers of chemical equipment, furnaces, and metal components intended for high-temperature applications
Coulomb Glasses: A Comparison Between Mean Field and Monte Carlo Results
Recently a local mean field theory for both eqilibrium and transport
properties of the Coulomb glass was proposed [A. Amir et al., Phys. Rev. B 77,
165207 (2008); 80, 245214 (2009)]. We compare the predictions of this theory to
the results of dynamic Monte Carlo simulations. In a thermal equilibrium state
we compare the density of states and the occupation probabilities. We also
study the transition rates between different states and find that the mean
field rates underestimate a certain class of important transitions. We propose
modified rates to be used in the mean field approach which take into account
correlations at the minimal level in the sense that transitions are only to
take place from an occupied to an empty site. We show that this modification
accounts for most of the difference between the mean field and Monte Carlo
rates. The linear response conductance is shown to exhibit the Efros-Shklovskii
behaviour in both the mean field and Monte Carlo approaches, but the mean field
method strongly underestimates the current at low temperatures. When using the
modified rates better agreement is achieved
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