Finite Element Modelling of Micro-cantilevers Used as Chemical Sensors

Nowadays, silicon micro-cantilevers with different geometrical shapes are widely used as micro-electro-mechanical systems and, more recently, as force sensor probes in atomic force microscopy (AFM). During the last ten years, several applications, which include these AFM micrometer-sized cantilevers as mass probes in microbalances or as chemical sensors in chemical micro-system devices, were developed. In the case of complex shapes of cantilevers, where the cross-section is not constant along the cantilever length (case of “V-shaped” micro-cantilevers), their resonant frequencies can not be analytically calculated. Firstly, in order to validate the accuracy of our FEM approach, we carried out a comparison between analytical, experimental and FEM-computed values of the resonant frequencies for homogenous rectangular shaped micro-cantilevers. Then, we performed a modeling of silicon beams coated with a thin sensitive layer (50 nm of Gold). To precisely calculate the resonant frequencies of these multilayer-cantilevers, the influence of the mesh parameters on the calculated frequencies was strongly investigated. Secondly, the sensitivity of different “V-shaped” silicon cantilevers was estimated, as a function of their geometrical dimensions and of their mechanical parameters (Young modulus, density). The resonant frequencies of uncoated cantilevers were calculated and compared with the values experimentally determined. Then, a similar approach was employed to predict the sensitivities of such cantilevers recovered with a sensitive layer

Atomic Force Microscopy: A Promising Tool for Deciphering the Pathogenic Mechanisms of Fungi in Cystic Fibrosis

During the past decades, atomic force microscopy (AFM) has emerged as a powerful tool in microbiology. Although most of the works concerned bacteria, AFM also permitted major breakthroughs in the understanding of physiology and pathogenic mechanisms of some fungal species associated with cystic fibrosis. Complementary to electron microscopies, AFM offers unprecedented insights to visualize the cell wall architecture and components through three-dimensional imaging with nanometer resolution and to follow their dynamic changes during cell growth and division or following the exposure to drugs and chemicals. Besides imaging, force spectroscopy with piconewton sensitivity provides a direct means to decipher the forces governing cell-cell and cell-substrate interactions, but also to quantify specific and non-specific interactions between cell surface components at the single-molecule level. This nanotool explores new ways for a better understanding of the structures and functions of the cell surface components and therefore may be useful to elucidate the role of these components in the host-pathogen interactions as well as in the complex interplay between bacteria and fungi in the lung microbiome

Self-assembly of proteins into a three-dimensional multilayer system: investigation of the surface of the human fungal pathogen Aspergillus fumigatus.

Hydrophobins are small surface active proteins that fulfil a wide spectrum of functions in fungal growth and development. The human fungal pathogen Aspergillus fumigatus expresses RodA hydrophobins that self-assemble on the outer conidial surface into tightly organized nanorods known as rodlets. AFM investigation of the conidial surface allows us to evidence that RodA hydrophobins self-assemble into rodlets through bilayers. Within bilayers, hydrophilic domains of hydrophobins point inward, thus making a hydrophilic core, while hydrophobic domains point outward. AFM measurements reveal that several rodlet bilayers are present on the conidial surface thus showing that proteins self-assemble into a complex three-dimensional multilayer system. The self-assembly of RodA hydrophobins into rodlets results from attractive interactions between stacked β-sheets, which conduct to a final linear cross-β spine structure. A Monte Carlo simulation shows that anisotropic interactions are the main driving forces leading the hydrophobins to self-assemble into parallel rodlets, which are further structured in nanodomains. Taken together, these findings allow us to propose a mechanism, which conducts RodA hydrophobins to a highly ordered rodlet structure. The mechanism of hydrophobin assembly into rodlets offers new prospects for the development of more efficient strategies leading to disruption of rodlet formation allowing a rapid detection of the fungus by the immune system

Applying Model Based Techniques for Early Safety Evaluation of an Automotive Architecture in Compliance with the ISO 26262 Standard

International audienceIn 2011, the automotive industry introduced the application of a standardized process for functional safety-related development of automotive electronic products. The related international standard, ISO 26262 functional safety for road vehicles, has high demands on process documentation and analysis. Within an engineering context this challenges the tremendous increase of complexity for modern automotive systems and high productivity demands for industrial competiveness purpose. Model based development techniques based on an Architecture Description Language (ADL) has been identified as the best candidate to manage the system complexity and the related safety analysis with the benefit of formal description and capabilities for test automation. The proposed concept relies on the definition of a compositional error modeling approach tightly coupled with the system architecture model, capable to analyze the software and hardware architectures and implementations. This paper explains the results of the language extension based on the EAST-ADL and AUTOSAR domain model in terms of early safety evaluation of an automotive architecture, automating the qualitative and quantitative assessment of road vehicle products as claimed by the application of the ISO 26262

Mechanical properties of nanotubes of polyelectrolyte multilayers

The elastic properties of nanotubes fabricated by layer-by-layer (LbL) assembly of polyelectrolytes in the nanopores of polycarbonate track-etched membranes have been investigated by resonant contact Atomic Force Microscopy (AFM), for nanotube diameters in the range of 100 to 200 nm. The elastic modulus of the nanotubes was computed from the resonance frequencies of a cantilever resting on freely suspended LbL nanotubes. An average value of 115MPa was found in air for Young's modulus of these nanostructures, well below the values reported for dry, flat multilayers, but in the range of values reported for water-swollen flat multilayers. These low values are most probably due to the lower degree of ionic cross-linking of LbL nanotubes and their consequently higher water content in air, resulting from the peculiar mode of growth of nanoconfined polyelectrolyte multilayers

What’s new on physiology and virulence factors of Scedosporium apiospermum ?

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Effects of radiative heat transfer on the structure of turbulent supersonic channel flow

International audienceThe interaction between turbulence in a minimal supersonic channel and radiative heat transfer is studied using large-eddy simulation. The working fluid is pure water vapour with temperature-dependent specific heats and molecular transport coefficients. Its line spectra properties are represented with a statistical narrow-band correlated-k model. A grey gas model is also tested. The parallel no-slip channel walls are treated as black surfaces concerning thermal radiation and are kept at a constant temperature of 1000 K. Simulations have been performed for different optical thicknesses (based on the Planck mean absorption coefficient) and different Mach numbers. Results for the mean flow variables, Reynolds stresses and certain terms of their transport equations indicate that thermal radiation effects counteract compressibility (Mach number) effects. An analysis of the total energy balance reveals the importance of radiative heat transfer, compared to the turbulent and mean molecular heat transport