evelyne kolb - Academia.edu (original) (raw)

Papers by evelyne kolb

Physical review, May 1, 1995

Physical Review Letters, 1993

Journal of Applied Physics, 1996

Inverse giant magnetoresistance (GMR) is obtained in multilayers alternating two ferromagnetic la... more Inverse giant magnetoresistance (GMR) is obtained in multilayers alternating two ferromagnetic layers F1 and F2 with different asymmetry of spin scattering, α1≳1 and α2<1. This is clearly demonstrated in the simple spin-valve system with perpendicular magnetization Fe1−xVx/Au/Co. With respect to Fe, the FeV alloys with x=0.18 and 0.29 exhibit an inversion of the spin scattering coefficients (αFe≳1, αFeV<1) due to the change of the densities of states at the Fermi level. The inverse MR of FeV/Au/Co is studied as a function of FeV layer thickness and temperature and compared to calculations based on the Camley–Barnas model. The data show that the inverse GMR is due to the bulk scattering within the FeV layer, which coexists with a substantial interface scattering favoring normal GMR.

HAL (Le Centre pour la Communication Scientifique Directe), 2006

Bulletin of the American Physical Society, 2015

Submitted for the DFD15 Meeting of The American Physical Society Reconfiguration of a flexible fi... more Submitted for the DFD15 Meeting of The American Physical Society Reconfiguration of a flexible fiber immersed in a 2D dense granular flow close to the jamming transition EVELYNE KOLB1, NICOLAS ALGARRA, DAMIEN VANDEMBROUCQ, PMMH, ESPCI, ARNAUD LAZARUS2, IJLRA, UPMC — We propose a new fluid/structure interaction in the unusual case of a dense granular medium flowing against an elastic fibre acting as a flexible intruder. We experimentally studied the deflection of a mylar flexible beam clamped at one side, the other free side facing a 2D granular flow in a horizontal cell moving at a constant velocity. We investigated the reconfiguration of the fibre as a function of the fibre’s rigidity and of the granular packing fraction close but below the jamming in 2D. Imposing the fibre geometry like its length or thickness sets the critical buckling force the fibre is able to resist if it was not supported by lateral grains, while increasing the granular packing fraction might laterally consol...

Plant and Soil, Jun 16, 2012

The mechanical and topological properties of a soil like the global porosity and the distribution... more The mechanical and topological properties of a soil like the global porosity and the distribution of void sizes greatly affect the development of a plant root, which in turn affects the shoot development. In particular, plant roots growing in heterogeneous medium like sandy soils or cracked substrates have to adapt their morphology and exert radial forces depending on the pore size in which they penetrate. We propose a model experiment in which a pivot root (chick-pea seeds) of millimetric diameter has to grow in a size-controlled gap δ (δ ranging 0.5-2.3 mm) between two photoelastic grains. By time-lapse imaging, we continuously monitored the root growth and the development of optical fringes in the photoelastic neighbouring grains when the root enters the gap. Thus we measured simultaneously and in situ the root morphological changes (length and diameter growth rates, circumnutation) as well as the radial forces the root exerts. Radial forces were increasing in relation with gap constriction and experiment duration but a levelling of the force was not observed, even after 5 days and for narrow gaps. The inferred mechanical stress was consistent with the turgor pressure of compressed cells. Therefore our setup could be a basis for testing mechanical models of cellular growth.

Physical Biology, Nov 16, 2017

Plant root system development is highly modulated by the physical properties of the soil and espe... more Plant root system development is highly modulated by the physical properties of the soil and especially by its mechanical resistance to penetration. The interplay between the mechanical stresses exerted by the soil and root growth is of particular interest for many communities, in agronomy and soil science as well as in biomechanics and plant morphogenesis. In contrast to aerial organs, roots apices must exert a growth pressure to penetrate strong soils and reorient their growth trajectory to cope with obstacles like stones or hardpans or to follow the tortuous paths of the soil porosity. In this review, we present the main macroscopic investigations of soil-root physical interactions in the field and combine them with simple mechanistic modeling derived from model experiments at the scale of the individual root apex.

Journal of the Royal Society Interface, Aug 1, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License Plant root growth against a mechanical obstacle: the early growth response of a maize root facing an axial resistance is consistent with the Lockhart model

arXiv (Cornell University), Apr 4, 2022

Plant root growth is dramatically reduced in compacted soils, affecting the growth of the whole p... more Plant root growth is dramatically reduced in compacted soils, affecting the growth of the whole plant. Through a model experiment coupling force and kinematics measurements, we probed the force-growth relationship of a primary root contacting a stiff resisting obstacle, that mimics the strongest soil impedance variation encountered by a growing root. The growth of maize roots just emerging from a corseting agarose gel and contacting a force sensor (acting as an obstacle) was monitored by time-lapse imaging simultaneously to the force.

HAL (Le Centre pour la Communication Scientifique Directe), 2005

ABSTRACT: There is clearly a link missing between the macroscopic mechanical behavior of a granul... more ABSTRACT: There is clearly a link missing between the macroscopic mechanical behavior of a granular medium (flow properties, elastic versus plastic range) and microscopic parameters such as individual mechanical properties and local geometrical organizations ...

Journal of Applied Physics, 1997

ABSTRACT

Experiments of penetration of a cylindrical intruder inside a bidimensional dense and disordered ... more Experiments of penetration of a cylindrical intruder inside a bidimensional dense and disordered granular media were reported recently showing the jamming / unjamming transition. In the present work, we perform molecular dynamics simulations with the same geometry in order to assess both kinematic and static features of jamming / unjamming transition. We study the statistics of the particles velocities at the neighborhood of the intruder to evince that both experiments and simulations present the same qualitative behavior. We observe that the probability density functions (PDF) of velocities deviate from Gaussian depending on the packing fraction of the granular assembly. In order to quantify these deviations we consider a q-Gaussian (Tsallis) function to fit the PDF's. The q-value can be an indication of the presence of long range correlations along the system. We compare the fitted PDF's obtained with those obtained using the stretched exponential, and sketch some conclusions concerning the nature of the correlations along a granular confined flow.

Le Centre pour la Communication Scientifique Directe - HAL - Inria, Oct 1, 2019

Cornell University - arXiv, Apr 4, 2022

Mechanical characterizations of plant roots are of primary importance in geophysics and engineeri... more Mechanical characterizations of plant roots are of primary importance in geophysics and engineering science for implementing mechanical models for the stability of root reinforcedsoils, as well as in agronomy and soil science for understanding the penetration of roots in soils and optimizing crop. Yet the mechanical properties of plant roots depend on their water content, which can drastically evolve with drying or flooding of the external soil. The present work deals with the determination of the longitudinal Young's modulus of single nonlignified plant roots, chick-peas (Cicer arietinum L.), tested in compression along their root axis for different external environments: in controlled conditions of natural drying in air or in a osmotic solution of mannitol at the isotonic concentration where no water exchange occurs between the root and the external solution. We submitted the chick-pea radicles to successive mechanical compression cycles separated by rest periods to follow the time evolution of the root mechanical properties in drying and non-drying environments. Control experiments on non-drying roots placed in isotonic osmotic solutions showed no evolution of the root's Young's modulus whose value was around 2 MPa. On the contrary, the experiments performed in air exhibited a dramatic increase of the root's Young's modulus with the drying time, sometimes by a factor of 35. Moreover, the Young's modulus in these cases was observed to scale as a decaying power-law with the root's cross-section measured at different times of drying. We interpreted our results in the framework of the mechanics of cellular foams.

Root growth and development are highly modulated by soil conditions which influence its mechanica... more Root growth and development are highly modulated by soil conditions which influence its mechanical impedance i.e. the soil resistance to root penetration. Root cap cells surrounded by the mucilage they secrete are the firsts to encounter obstacles during soil exploration, and are known to sense and integrate environmental cues, making the root cap a relevant candidate as mechanoperception site. We thus investigated in this study a putative implication of the root cap in the sensing and in the response to mechanical impedance. We developed two-Layer-Phytagel media in which an increase in mechanical impedance was generated by a lower harder layer covered by an upper softer layer. Root growth and trajectory of primary roots of Arabidopsis thaliana seedlings were investigated using image analysis. In response to the contact with the harder layer, the roots rapidly bent allowing the reorientation of root primary growth. The root bending was associated with an inhibition of root growth ra...

EPJ Web of Conferences, 2021

We describe the deformations of a 2D elastic structure (beam, rod or filament) subjected to rando... more We describe the deformations of a 2D elastic structure (beam, rod or filament) subjected to randomly distributed local orthogonal forces. The fiber is in quasistatic equilibrium condition when a given force distribution is acting on it. To analyze the effects of force fluctuations on the observed configurations, we study the behavior of the bending moment at the origin and the filament curvature, as a function of nominal values of the local mean forces and small, moderate and large fluctuations around them.