The water clock of Proteus mirabilis paces colony periodic and synchronous swarming

For decades, the origin of the concentric ring pattern of bacterial swarming colonies has puzzled microbiologists. Thanks to _in situ_ and real time infrared microspectroscopy and the brilliance of the infrared beam at SOLEIL synchrotron, we demonstrate here that _Proteus mirabilis_ swarming is paced by a periodic variation of the water activity at colony's edge. This periodic variation originates a phase transition within the extracellular matrix water H bond network which switches on and off the exopolysaccharides viscoelasticity and, consequently, the ability of bacterial cells to swarm. A dynamic behaviour emerges from the global properties of the multicellular entity which here relies on the ability of the bacterial cells to tune exoproducts synthesis in order to undergo sharp transitions above/below a given water activity threshold

Identification of damaged zone in composite materials using displacement field measurements

This work presents an identification strategy of local elastic properties of orthotropic carbon-epoxy laminates for aviation industry. Based on global and local stages of study, this methodology uses the Finite Element Model Updating (FEMU) method as identification technique with simulated kinematic fields corresponding to tensile test response. The aim of this paper is to predict the spatial variation of elastic plane properties and to deduce the localization of damaged zones

Universal behaviour of a wave chaos based electromagnetic reverberation chamber

In this article, we present a numerical investigation of three-dimensional electromagnetic Sinai-like cavities. We computed around 600 eigenmodes for two different geometries: a parallelepipedic cavity with one half- sphere on one wall and a parallelepipedic cavity with one half-sphere and two spherical caps on three adjacent walls. We show that the statistical requirements of a well operating reverberation chamber are better satisfied in the more complex geometry without a mechanical mode-stirrer/tuner. This is to the fact that our proposed cavities exhibit spatial and spectral statistical behaviours very close to those predicted by random matrix theory. More specifically, we show that in the range of frequency corresponding to the first few hundred modes, the suppression of non-generic modes (regarding their spatial statistics) can be achieved by reducing drastically the amount of parallel walls. Finally, we compare the influence of losses on the statistical complex response of the field inside a parallelepipedic and a chaotic cavity. We demonstrate that, in a chaotic cavity without any stirring process, the low frequency limit of a well operating reverberation chamber can be significantly reduced under the usual values obtained in mode-stirred reverberation chambers

3D printing for cyclonic spray chambers in ICP spectrometry

International audienceAdditive manufacturing (AM) or 3D-printing is an increasingly widespread technique which is often described as a source for rapid prototyping whereas it is a manufacturing process in itself. It is a new tool for instrumental research laboratories which can now easily manufacture by themselves a large variety of devices. This article describes its application to ICP introduction system spray chambers. We undertake to print and study cyclone spray chambers by combining and comparing for the first time 3 different AM processes, 5 materials and 8 designs. The analytical performances of these spray chambers are compared with commercial glass and PFA chambers in terms of signal intensity, stability, oxide ratio, LOD and wash-out time. LODs measured with polymer printed chambers are in the range or even outperform those measured with the glass chamber even though 3D-printed chambers provide lower results in terms of sensitivity than glass. Compared to PFA chambers, the printed chambers are superior in terms of LOD. At low temperature, the printed chambers' efficiency depends on both AM process and manufacturing material. SLA and FDM printers give lower results in terms of sensitivity but not in LOD than the Polyjet printer. This study also illustrates the influence of the inner shape of the side arm nebulizer and confirms the importance of a free aerosol recirculation current around the nebulizer tip. Transfer tube efficiency is also questioned; it is found to be weakly detrimental to the sensitivity to light elements but shows no influence on heavy ones as well as on the stability or oxide ratio, whatever the element

Non destructive investigation of defects in composite structures by three infrared thermographic techniques

This paper investigates full-field measurement techniques based on Infrared Thermography for Non Destructive Testing (NDT) applications on composite materials. Three methods have been implemented and the paper intends to characterize and compare their defect detection limit and related specific application fields. Various composites have been considered in this study, namely laminates and sandwich structures, in order to address many important issues of performance assessment for the aviation industry

Non destructive investigation of defects in composite structures by fullfield measurement methods

This paper presents different interests of non destructive full-field measurement. More precisely, it focuses on the characterization and the comparison of the X-ray tomography and two methods of infrared thermography in order to define the defect detection limits and to precise the specific application fields for each technique on multi-layered and sandwich composite structures. The obtained results are qualitatively and quantitatively analyzed

Study of a reverberation chamber shape inspired from chaotic cavities

International audienceUsing the knowledge gained from the wave chaos theory, we present a simple modification of the shape of a reverberation chamber (RC) consisting in inserting a metallic hemisphere on a cavity wall. The presented simulation results show a significant improvement of the field statistical properties, and this without resorting to a mode stirrer

Global and local identification on composte material

One of the main challenges in composite design and development is to be able to compute the damage state at any point of a composite structure during a complex loading. In this context, knowledge of the spatial distribution of the material elastic properties provides a quantitative estimation of the damage level and localization. The work presented here intends to access to such distribution through the association of kinematic fields and finite element model updating method. Such iterative technique has many interesting advantages for structural analysis and industrial requirements, including the numerical framework, the ability to explore complex shapes and loads and a treatment based on surface measurement without any assumption on volume distribution