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Scientific context

Tree stems increase in diameter through cyclic formation of wood by a thin layer of undifferentiated stem cells, the cambium, which lies between the bark and the mature wood. The mechanical state of the cambium is very peculiar since it is a soft tissue compressed between two harder ones. In spite of that, cambium stem cells are able to divide, enlarge and finally differentiate into wood fibers and vessels, thanks to their osmotic pressure which counters the stress imposed by the bark. Nevertheless, the equilibrium of forces acting upon the cambium and the bark is poorly understood. Moreover, a current hypothesis assumes that the mechanical stress field does not only limit growth but also acts as a signal interpreted by stem cells to orient their division plane. It would explain the very ordered arrangement of cells in cambium and wood. Despite their potential significance, the mechanical aspects of wood formation have been scarcely addressed. Mathematical models are lacking to estimate the stress field in the cambium and investigate its effect on tissue growth and patterning. It is one of the aims of the CEMACam project (Computations and Experiments
on the MechAnics of Cambium), lead by research units PIAF (Clermont-Ferrand), LMGC (Montpellier) and RDP (Lyon).

The candidate will contribute to the development of a model of wood formation coupling mechanical and hydric aspects. Based on her/his choice, one of the two following lines of investigation will be explored:

•  modeling tissues using continuum mechanics and the finite elements method;
•  modeling tissues explicitly as cellular structures.

In both cases, the required computational and software tools are already available. During the internship, a first model will be developed and used to quantitatively investigate the role of mechanical stress and strain in wood formation and tissue patterning.

Expected skills

The candidate should have a training in mathematical, mechanical or biophysical modeling. No prior knowledge of the finite element method is required (although it would be an advantage). A strong interest for interdisciplinarity is expected.

Location :

PIAF, INRAE Clermont-Ferrand (site de Crouël) and visits at RDP (ENS Lyon)

The internship period can be agreed upon depending on your master requirements.
This internship can be followed by a PhD thesis, whose funding is already secured.

Contacts :

• Félix Hartmann : felix.hartmann@inrae.fr (+33 4 43 76 14 44)
• Christophe Godin : christophe.godin@inria.fr (+33 4 72 72 88 26)