Experimental analysis of nonlinear resonances in piezoelectric plates with geometric nonlinearities

Piezoelectric devices with integrated actuation and sensing capabilities are often used for the development of electromechanical systems. The present paper addresses experimentally the nonlinear dynamics of a fully integrated circular piezoelectric thin structure, with piezoelectric patches used for actuation and other for sensing. A phase-locked loop control system is used to measure the resonant periodic response of the system under harmonic forcing, in both its stable and unstable parts. The single-mode response around a symmetric resonance as well as the coupled response around an asymmetric resonance, involving two companion modes in 1:1 internal resonance, is accurately measured. For the latter, a particular location of the patches and additional signal processing is proposed to spatially discriminate the response of each companion mode. In addition to a hardening behavior associated with geometric nonlinearities of the plate, a softening behavior predominant at low actuation amplitudes is observed, resulting from the material piezoelectric nonlinearities.

     

Modelling and speciation of nitrogen oxides in engines

The present study extends the Nitrogen Oxide Relaxation Approach (NORA [Vervisch et al., Combust. Flame 158 (2011) 1480–1490]) for NO_x modelling in engines by introducing alternative chemical routes to the thermal pathway as well as a speciation of nitrogen oxides into nitrogen monoxide (NO), nitrogen dioxide (NO₂) and nitrous oxide (N₂O). Perturbations of equilibrium state are considered to identify nitrogen oxide reactivity in various mixture and thermodynamic conditions. A common Intrinsic Low-Dimensional Manifold (ILDM) is identified for NO and NO₂, while nitrous oxides appear to stay in near-equilibrium state for any in-cylinder conditions. The relaxations back towards the equilibrium state after the perturbations are analysed to extract the characteristic times of relaxation, an image of the species reactivity. Tabulation of equilibrium mass fractions and characteristic relaxation times as a function of mixture and thermodynamic conditions allows nitrogen oxide modelling to be performed for internal combustion engines at very low computational cost through idealised ILDMs that are independent of the combustion ones. Results show the accuracy of the modelling approach for nitrogen oxide emissions of a Diesel engine at part and full load.     

A green route to enantioenriched (S)-arylalkyl carbinols by deracemization via combined lipase alkaline-hydrolysis/Mitsunobu esterification

Herein we report results of the chemoenzymatic deracemization of a range of secondary benzylic acetates 1a–9a via a sequence of hydrolysis with CAL-B lipase in non-conventional media, combined with esterification of the recovered alcohol according to the Mitsunobu protocol following an enzymatic kinetic resolution (KR). The KR of racemic acetates 1a–9a via an enzymatic hydrolysis, with CAL-B lipase and Na₂CO₃, in non-aqueous media was optimized and gave high selectivities (E ? 200) at good conversions (C >49%) for all of the substrates studied. This method competes well with the traditional one performed in a phosphate buffer solution. The deracemization using Mitsunobu inversion gave the (S)-acetates in moderate to excellent enantiomeric excess 75% < ee < 99%, in acceptable isolated yields 70% < yield < 89%, and with some variations according to the acetate structure.     

One‐Step Double Covalent Functionalization of Reduced Graphene Oxide with Xanthates and Peroxides

Radical functionalization of reduced graphene oxide has been achieved by reaction with a xanthate in the presence of peroxide as a radical initiator. X‐ray photoelectron spectroscopy, bulk elemental analyses, and thermogravimetric analyses showed that the xanthate grafting is covalent and efficient. The synthesis and use of seven xanthates and three peroxides showed that the highest grafting yield is obtained when xanthate and peroxide are introduced in stoichiometric amounts. It also revealed that the peroxide used as radical initiator is grafted at the graphenic surface during the functionalization. The method presented in this contribution therefore allows bifunctionalized reduced graphene oxide samples to be easily obtained in one single step. This method leads to undamaged graphene sheets with higher dispersibility than the pristine sample.