Infrared spectroscopy in the gas and liquid phase from first principle molecular dynamics simulations - Application to small peptides

International audienceWe discuss the applicability of finite temperature Car-Parrinello molecular dynamics simulations for the calculation of infrared spectra of complex molecular systems, either in the gas phase or in the condensed phase, taking examples from the infrared spectroscopy of N-methylacetamide and small peptides. Band assignments for the simulation is still challenging and we introduce here a general method for obtaining effective normal modes of molecular systems from Molecular Dynamics simulations. The effective normal modes are defined as linear combination of internal coordinates such that the power spectra of these modes are as localized as possible in frequency. We further define band intensities for these modes from different levels of approximation of the infrared spectrum. Applications of this approach for assigning infrared bands from first-principle molecular dynamics simulations are presented for N-methylacetamide in gas phase and in solution, for the gas phase alanine dipeptide and the gas phase octa-alanine peptide

Self-actuated Polymeric Valve for Autonomous Sensing and Mixing

We present an autonomously operated microvalve array for chemical sensing and mixing, which gains the actuation energy from a chemical reaction on the valve structure. An 8-μm-thick flapper valve made in SU-8 is coated with stress-loaded Al on one side and Ti on the other side. The metal films keep the flapper in a flat, stress-balanced closed position. Upon contact with an analyte composed of a NaOH solution the Al film is etched from the valve surface unbalancing the surface stress and bending the flapper. A deflection of up to 45 μm is observed allowing for effective release of a green marker from a reservoir. Calculations reveal that valve operation with stress originating from biochemical processes will require considerable enhancement of the actuation efficiency

UM-CRT : Un modèle de canal semi-déterministe pour les VANETs

National audienceLe choix d'un modèle de canal efficace pour la simulation des VANETs (Vehicular Ad-hoc NETworks) est difficile. Avec un modèle de canal purement déterministe les simulations sont réalistes mais prennent un temps très long, voire prohibitif. Dans le cas d'un modèle purement statistique, les simulations sont rapides mais le réalisme obtenu est limité. Dans ce papier nous proposons UM-CRT, un modèle de canal semi- déterministe basé sur un simulateur 3D déterministe de canal et sur le modèle statistique géométrique de canal SCME-UM (Spatial Channel Model Extended - Urban Micro). Nous avons intégré ce modèle dans le simulateur de réseaux NS-2 et montré qu'il fournit des résultats proches de ceux du modèle déterministe en un temps très nettement réduit