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.

     

Protein/polysaccharide complexes and coacervates in food systems

Since the pioneering work of Bungenberg de Jong and co-workers on gelatin-acacia gum complex coacervation in the 1920-40s, protein/polysaccharide complexes and coacervates have received increasing research interest in order to broaden the possible food applications. This review focuses on the main research streams followed in this field during the last 12 years regarding: i) the parameters influencing the formation of complexes and coacervates in protein-polysaccharide systems; ii) the characterization of the kinetics of phase separation and multi-scale structure of the complexes and coacervates; and iii) the investigation of the functional properties of complexes and coacervates in food applications. This latter section encompasses various technological aspects, namely: the viscosifying and gelling ability, the foaming and emulsifying ability and finally, the stabilization and release of bioactives or sensitive compounds.     

Enzyme-catalyzed polyester synthesis in organic medium: Ring-chain equilibrium

Enzyme-catalyzed synthesis of aliphatic, unsaturated and semi-aromatic polyesters from methyl diesters and diols was carried out in toluene at 60°C in the presence of supported lipases. Whatever the monomer structure, rings were formed concurrently to linear chains excepted when dimethyl fumarate was used. The yield of rings depends on several parameters such as the monomer structure and the initial concentration of the reactive functions and strongly influences the average molar masses of the unfractionated samples. For aliphatic, unsaturated and semi-aromatic polyesters, the molar cyclization equilibrium constants (K) were determined and it would appear that the molar distribution of the ringed species obeys Jacobson-Stockmayer equation: LnK = LnB − 5/2 Lnn, where B and n represent a constant and the number of monomer units of each type in the ring, respectively.     

Q(γ-H2AX), an analysis method for partial-body radiation exposure using γ-H2AX in nonhuman primate lymphocytes

We previously used the γ-H2AX assay as a biodosimeter for total-body-irradiation (TBI) exposure (γ-rays) in a rhesus macaque (Macaca mulatta) model. Utilizing peripheral blood lymphocytes and plucked hairs, we obtained statistically significant γ-H2AX responses days after total-body exposure to 1-8.5 Gy ((60)Co γ-rays at 55 cGy min(-1)). Here, we introduce a partial-body exposure analysis method, Q(γ-H2AX), which is based on the number of γ-H2AX foci per damaged cells as evident by having one or more γ-H2AX foci per cell. Results from the rhesus monkey - TBI study were used to establish Q(γ-H2AX) dose-response calibration curves to assess acute partial-body exposures. γ-H2AX foci were detected in plucked hairs for several days after in vivo irradiation demonstrating this assay's utility for dose assessment in various body regions. The quantitation of γ-H2AX may provide a robust biodosimeter for analyzing partial body exposures to ionizing radiation in humans.     

Active Mamyshev regenerator

In this contribution, we numerically and experimentally investigate the extension of the so-called Mamyshev regenerator with the implementation of an additional Raman gain. We evaluate the potential efficiency and advantages of this new active Mamyshev regenerator at 40 Gbps and we highlight a strong reduction of the working power as well as a large improvement of the available output power.     

Convenient grafting through approach for the preparation of stealth polymeric blood pool magnetic resonance imaging contrast agents

New hydrosoluble magnetic resonance imaging (MRI) macrocontrast agents are synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization of poly(ethylene oxide) methyl ether acrylate (PEOMA) with an acrylamide bearing a ligand for gadolinium, followed by the complexation of Gd³⁺. This convenient and simple grafting through approach leads to macrocontrast agents with a high relaxivity at high frequency that is imparted by the restricted tumbling of the Gd³⁺ complex caused by its attachment to the polymer backbone. Importantly a very low protein adsorption is also evidenced by the hemolytic CH50 test. It is the result of the poly(ethylene oxide) (PEO) brush that efficiently hides the gadolinium complex and renders it stealth to the proteins of the immune system. Improved contrast and long blood circulating properties are thus expected for these macrocontrast agents. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Maximum and Minimum Principles for Radionuclide Transport Calculations in Geological Radioactive Waste Repository: Comparison Between a Mixed Hybrid Finite Element Method and Finite Volume Element discretizations

In the context of high-level radioactive waste repository simulations, specific waste repository system properties require the use of a highly heterogeneous and anisotropic diffusion tensors. Classical finite volume or mixed hybrid finite element schemes produce non-physical negative concentrations and therefore are unsuitable for simulations which couple transport and chemical reactivity models. In this article, the authors use a new finite volume scheme satisfying a minimum and maximum principle to solve the transport equations and demonstrate that this scheme avoids the negative concentration values generated by other schemes.     

Genealogy of Shocks in Burgers Turbulence¶with White Noise Initial Velocity

As time passes, the shocks of the solution of the inviscid Burgers equation aggregate. We characterize, in the case of white noise initial velocity, the stochastic fragmentation process obtained when time runs backwards. In other words, we specify the law of the genealogy of the shocks of the Burgers turbulence with white noise initial velocity. Received: 5 September 2000 / Accepted: 29 May 2001     

Kinetics and electron spin resonance study of the radical polymerization of n‐butyl acrylate mediated by a nitroxide precursor: C‐phenyl‐N‐tert‐butylnitrone

The C‐phenyl‐N‐tert‐butylnitrone/azobisisobutyronitrile pair is able to impart control to the radical polymerization of n‐butyl acrylate as long as a two‐step process is implemented, that is, the prereaction of the nitrone and the initiator in toluene at 85 °C for 4 h followed by the addition and polymerization of n‐butyl acrylate at 110 °C. The structure of the in situ formed nitroxide has been established from kinetic and electron spin resonance data. The key parameters (the dissociation rate constant, combination rate constant, and equilibrium constant) that govern the process have been evaluated. The equilibrium constant between the dormant and active species is close to 1.6 × 10^?12 mol L^?1 at 110 °C. The dissociation rate constant and the activation energy for the C? ON bond homolysis are 1.9 × 10^?3 s^?1 and 122 ± 15 kJ mol^?1, respectively. The rate constant of recombination between the propagating radical and the nitroxide is as high as 1.2 × 10⁹ L mol^?1 s^?1. Finally, well‐defined poly(n‐butyl acrylate)‐b‐polystyrene block copolymers have been successfully prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6299–6311, 2006