21,396 research outputs found
Quantifying the entropic cost of cellular growth control
We quantify the amount of regulation required to control growth in living
cells by a Maximum Entropy approach to the space of underlying metabolic states
described by genome-scale models. Results obtained for E. coli and human cells
are consistent with experiments and point to different regulatory strategies by
which growth can be fostered or repressed. Moreover we explicitly connect the
`inverse temperature' that controls MaxEnt distributions to the growth
dynamics, showing that the initial size of a colony may be crucial in
determining how an exponentially growing population organizes the phenotypic
space.Comment: 3 page
Theory of controlled quantum dynamics
We introduce a general formalism, based on the stochastic formulation of
quantum mechanics, to obtain localized quasi-classical wave packets as
dynamically controlled systems, for arbitrary anharmonic potentials. The
control is in general linear, and it amounts to introduce additional quadratic
and linear time-dependent terms to the given potential. In this way one can
construct for general systems either coherent packets moving with constant
dispersion, or dynamically squeezed packets whose spreading remains bounded for
all times. In the standard operatorial framework our scheme corresponds to a
suitable generalization of the displacement and scaling operators that generate
the coherent and squeezed states of the harmonic oscillator.Comment: LaTeX, A4wide, 28 pages, no figures. To appear in J. Phys. A: Math.
Gen., April 199
Quantitative constraint-based computational model of tumor-to-stroma coupling via lactate shuttle
Cancer cells utilize large amounts of ATP to sustain growth, relying primarily on non-oxidative,
fermentative pathways for its production. In many types of cancers this leads, even in the presence
of oxygen, to the secretion of carbon equivalents (usually in the form of lactate) in the cell’s
surroundings, a feature known as the Warburg effect. While the molecular basis of this phenomenon
are still to be elucidated, it is clear that the spilling of energy resources contributes to creating a
peculiar microenvironment for tumors, possibly characterized by a degree of toxicity. This suggests
that mechanisms for recycling the fermentation products (e.g. a lactate shuttle) may be active,
effectively inducing a mutually beneficial metabolic coupling between aberrant and non-aberrant
cells. Here we analyze this scenario through a large-scale in silico metabolic model of interacting
human cells. By going beyond the cell-autonomous description, we show that elementary physico-
chemical constraints indeed favor the establishment of such a coupling under very broad conditions.
The characterization we obtained by tuning the aberrant cell’s demand for ATP, amino-acids and
fatty acids and/or the imbalance in nutrient partitioning provides quantitative support to the idea
that synergistic multi-cell effects play a central role in cancer sustainmen
Decaying dark energy in light of the latest cosmological dataset
Decaying Dark Energy models modify the background evolution of the most
common observables, such as the Hubble function, the luminosity distance and
the Cosmic Microwave Background temperature-redshift scaling relation. We use
the most recent observationally-determined datasets, including Supernovae Type
Ia and Gamma Ray Bursts data, along with and Cosmic Microwave Background
temperature versus data and the reduced Cosmic Microwave Background
parameters, to improve the previous constraints on these models. We perform a
Monte Carlo Markov Chain analysis to constrain the parameter space, on the
basis of two distinct methods. In view of the first method, the Hubble constant
and the matter density are left to vary freely. In this case, our results are
compatible with previous analyses associated with decaying Dark Energy models,
as well as with the most recent description of the cosmological background. In
view of the second method, we set the Hubble constant and the matter density to
their best fit values obtained by the {\it Planck} satellite, reducing the
parameter space to two dimensions, and improving the existent constraints on
the model's parameters. Our results suggest that the accelerated expansion of
the Universe is well described by the cosmological constant, and we argue that
forthcoming observations will play a determinant role to constrain/rule out
decaying Dark Energy.Comment: 15 pages, 3 figure, 2 table. Accepted in the Special Issue
"Cosmological Inflation, Dark Matter and Dark Energy" on Symmetry Journa
Dynamics of multi-frequency minority games
The dynamics of minority games with agents trading on different time scales
is studied via dynamical mean-field theory. We analyze the case where the
agents' decision-making process is deterministic and its stochastic
generalization with finite heterogeneous learning rates. In each case, we
characterize the macroscopic properties of the steady states resulting from
different frequency and learning rate distributions and calculate the
corresponding phase diagrams. Finally, the different roles played by regular
and occasional traders, as well as their impact on the system's global
efficiency, are discussed.Comment: 9 pages, 5 figure
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