2,192 research outputs found
The buffered chemostat with non-monotonic response functions
We study how a particular spatial structure with a buffer impacts the number
of equilibria and their stability in the chemostat model. We show that the
occurrence of a buffer can allow a species to persist or on the opposite to go
extinct, depending on the characteristics of the buffer. For non-monotonic
response functions, we characterize the buffered configurations that make the
chemostat dynamics globally asymptotically stable, while this is not possible
with single, serial or parallel vessels of the same total volume and input
flow. These results are illustrated with the Haldane kinetic function.Comment: 9th IFAC Symposium on Nonlinear Control Systems (NOLCOS 2013),
Toulouse : France (2013
A modeling approach of the chemostat
Population dynamics and in particular microbial population dynamics, though
they are complex but also intrinsically discrete and random, are conventionally
represented as deterministic differential equations systems. We propose to
revisit this approach by complementing these classic formalisms by stochastic
formalisms and to explain the links between these representations in terms of
mathematical analysis but also in terms of modeling and numerical simulations.
We illustrate this approach on the model of chemostat.Comment: arXiv admin note: substantial text overlap with arXiv:1308.241
Minimal-time bioremediation of natural water resources
We study minimal time strategies for the treatment of pollution of large
volumes, such as lakes or natural reservoirs, with the help of an autonomous
bioreactor. The control consists in feeding the bioreactor from the resource,
the clean output returning to the resource with the same flow rate. We first
characterize the optimal policies among constant and feedback controls, under
the assumption of a uniform concentration in the resource. In a second part, we
study the influence of an inhomogeneity in the resource, considering two
measurements points. With the help of the Maximum Principle, we show that the
optimal control law is non-monotonic and terminates with a constant phase,
contrary to the homogeneous case for which the optimal flow rate is decreasing
with time. This study allows the decision makers to identify situations for
which the benefit of using non-constant flow rates is significant
Why does wurtzite form in nanowires of III-V zinc-blende semiconductors?
We develop a nucleation-based model to explain the formation of the wurtzite
(WZ) crystalline phase during the vapor-liquid-solid growth of free-standing
nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires,
nucleation generally occurs at the outer edge of the solid/liquid interface
(the triple phase line) rather than elsewhere at the solid/liquid interface. In
the present case, this entails major differences between ZB and WZ nuclei.
Depending on the pertinent interface energies, WZ nucleation is favored at high
liquid supersaturation. This explains our systematic observation of ZB during
the early stages of nanowire growth.Comment: 4 pages with 4 figures Submitted to Physical Review Letter
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