Functionalized AFM probes for force spectroscopy: eigenmodes shape and stiffness calibration through thermal noise measurements

The functionalization of an Atomic Force Microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response ? And more important for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques? In this article, the influence of a colloidal mass loading on the eigenmodes shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without a bead attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry. The focused beam from the interferometer probes the cantilever at different positions and the spatial shapes of the modes are determined up to the fifth resonance, without external excitation. The results clearly demonstrate that the first eigenmode almost doesn't change by mass loading. However the oscillation behavior of higher resonances present a marked difference: with a particle glued at its extremity, the nodes of the mode are displaced towards the free end of the cantilever. These results are compared to an analytical model taking into account the mass and the inertial moment of the load in an Euler-Bernoulli framework, where the normalization of the eigenmodes is explicitly worked out in order to allow a quantitative prediction of the thermal noise amplitude of each mode. A good agreement between the experimental results and the analytical model is demonstrated, allowing a clean calibration of the probe stiffness

Euclid in a Taxicab: Sparse Blind Deconvolution with Smoothed l1/l2 Regularization

The l1/l2 ratio regularization function has shown good performance for retrieving sparse signals in a number of recent works, in the context of blind deconvolution. Indeed, it benefits from a scale invariance property much desirable in the blind context. However, the l1/l2 function raises some difficulties when solving the nonconvex and nonsmooth minimization problems resulting from the use of such a penalty term in current restoration methods. In this paper, we propose a new penalty based on a smooth approximation to the l1/l2 function. In addition, we develop a proximal-based algorithm to solve variational problems involving this function and we derive theoretical convergence results. We demonstrate the effectiveness of our method through a comparison with a recent alternating optimization strategy dealing with the exact l1/l2 term, on an application to seismic data blind deconvolution.Comment: 5 page

Steady and unsteady shear flows of a viscoplastic fluid in a cylindrical Couette cell

Abstract Yield stress fluid flows in Couette cells have been widely studied in the last decades for their intriguingly exhibiting phenomena. In this paper, we use a {PIV} technique to investigate the axisymmetric flow and rheological properties of a Carbopol gel in a relatively wide cylindrical Couette device. Carbopol gel is known to exhibit viscoplastic behavior and is often described using a Herschel–Bulkley law, which is characterized by a plastic yield stress τ y and a shear-dependent nonlinear viscosity. In some cases, the elasticity of the material has to be accounted for to understand the whole dynamics of the system, in particular for unsteady flows as observed in the present study. Two set of experiments are conducted here in order to highlight these different rheological behaviors and the resulting dynamics: (i) a steady shear configuration and (ii) an unsteady shear configuration, in which the angular velocity of the inner cylinder is either constant or time dependent ( sin profile), respectively. In the steady configuration, a simple optimization model, based on the Herschel–Bulkley law, is developed to extract the rheological parameters of the viscoplastic contribution of the gel from the steady velocity fields. Results are shown to be in good agreements with rheological parameters obtained from a standard rheometer. On the other hand, the elastic contribution of the material is highlighted in the unsteady shear configuration, for which a spatio-temporal transition between solid-elastic and fluid behaviors is observed. Different models are proposed to describe the dynamics of the unsteady flow. First, quasi-steady state models allow to predict both the fluid shear zone close to the inner cylinder and the elastic deformation of the material as long as their contributions can be decoupled in space and in time. For more complex dynamics, i.e. when the flow becomes strongly unsteady, an elasto-viscoplastic model is developed to describe the flow dynamics. It is shown to quantitatively reproduce the experimental measurements. Finally, an elastic wave model is derived to describe an elastic front propagating from the inner cylinder to the outer one, and observed at every half forcing period. The front velocity is thus shown to scale on the phase velocity of an elastic wave in a deformable solid

Intensification of Ester Production in a Continuous Reactor

Numerous continuous intensified reactors are now accessible on the market that offer enhanced thermal performances in a continuous reactor. Such reactors are then particularly suited to fast and highly exothermic reactions. In this paper, the ability to also manage a slow and equilibrated system, the methyl acetate esterification reaction, on condition of intensification in terms of design and operating conditions is presented. To achieve this purpose, a new kinetics model has been developed and validated from experiments carried out in a lab scale batch reactor. Implemented in a simulation framework, this model leads to an intensified design of the reactor and the associated operating conditions. All this intensification methodology has been supported and validated by experimental studies

CREATION ET EXPERIMENTATION DE VARIETES DE POMMES ADAPTEES A L’AGRICULTURE BIOLOGIQUE

Our apple breeding program is based entirely on the results of our work to safeguard, evaluate and valorize the rich heritage of apple tree genetic resources in our regions. Since 1975, no fewer than 1800 introductions have been collected in our collections and, taking into account duplicates, errors and synonyms, this represents a total of about 850 distinct cultivars. These are systematically evaluated in experimental orchards that do not undergo any treatment. Some cultivars that are highlighted for their high level of resistance to the main diseases as well as for their agronomic and quality characteristics of trees and fruits are used as parents. Our priorities are mainly focused on the expansion of the apple's genetic base, polygenic resistance to the main diseases (scab, powdery mildew, canker) and a whole series of characteristics present in certain old and peasant varieties such as long natural conservation, rusticity, robustness, frugality, nitrogen efficiency, tree architecture and the nutritional qualities and properties of the fruit. These parents are then crossed with varieties, often more commercial, which offer advantages in terms of speed of fruiting, yield, flesh quality and tree architecture. The current plant breeding program is based on extensive methodological work that has been developed specifically to select materials with partial disease resistance that express good potential for adaptation to simple and 'low-input' crop conditions. About sixty elite selections from our work are currently being tested in organic farming and are compared with 48 other new commercial varieties in order to look for varietal alternatives that are much better adapted to organic production than those currently being grown. Partial results of about twenty selections and varieties are presented, including results relating to the sustainability of a panel of varieties carrying the Vf gene

Modélisation de l'association entre l'insatisfaction conjugale et les problèmes comportementaux chez des enfants d'âge préscolaire

Ce projet vise l’approfondissement de l’association longitudinale réciproque entre l’insatisfaction conjugale des parents ainsi que les problèmes de comportement extériorisés et intériorisés des enfants entre l’âge de deux ans et cinq ans. Les participants de cette étude (n = 1997 pour les mères, n = 1616 pour les pères) proviennent de l’Étude longitudinale du développement des enfants du Québec (ÉLDEQ) dans le cadre de laquelle plus de 2000 enfants québécois ont été suivis de façon longitudinale. Les difficultés de comportement des enfants et la satisfaction conjugale des pères et des mères ont été mesurées de façon répétée alors que les enfants avaient en moyenne deux ans, trois ans, quatre ans et cinq ans à l’aide de questionnaires complétés par les parents. Les résultats montrent une association concomitante et bidirectionnelle entre l’insatisfaction conjugale et les problèmes de comportement extériorisés et intériorisés des enfants. Ces résultats s'ajoutent au très petit bassin d'observations empiriques sur le rapport bidirectionnel entre l’insatisfaction conjugale et les problèmes comportementaux de l'enfant