Nanoscale flexoelectric energy harvesting

One of the most tantalizing applications of piezoelectricity is to harvest energy from ambient mechanical vibrations for powering micro and nano devices. However, piezoelectricity is restricted only to certain materials and is severely compromised at high temperatures. In this article, we examine in detail, the possibility of using the phenomenon of flexoelectricity for energy harvesting. The flexoelectric effect is universally present in all dielectrics and exhibits a strong scaling with size. Using a simple beam-based paradigmatical design, we theoretically and computationally examine flexoelectric energy harvesting under harmonic mechanical excitation. We find that the output power density and conversion efficiency increase significantly when the beam thickness reduces from micro to nanoscale and flexoelectricity-based energy harvesting can be a viable alternative to piezoelectrics. Specifically, the conversion efficiency in flexoelectric transduction at sub-micron thickness levels is observed to increase by two orders of magnitude as the thickness is reduced by an order of magnitude. The flexoelectric energy harvester works even for a single layer beam with a symmetric cross section which is not possible in piezoelectric energy harvesting. Our results also pave the way for exploration of high temperature energy harvesting since unlike piezoelectricity, flexoelectricity persists well beyond the Curie temperatures of the high electromechanical coupling ferroelectrics that are often used.     

Transmission loss of periodically stiffened laminate composite panels: shear deformation and in-plane interaction effects

This paper investigates the transmission loss of symmetric and asymmetric laminate composite panels periodically reinforced by composite stiffeners. A comprehensive model based on periodic structure theory is developed. First order shear deformation theory is used and the coupling of the in-plane motion of the panel with its out-of-plane motion is taken into account. Stiffeners interact with the panel through three forces (two in-plane, one out-of-plane) and a torsion moment. Three types of cross sections are investigated for the composite stiffeners: I-shaped, C-shaped, and omega-shaped cross-sections. The model is validated numerically by comparison with the finite element/boundary element method. Experimental validations are also conducted. In both cases, excellent agreement is obtained. Numerical results show that the in-plane coupling effect is increased by increasing the panel thickness and the stiffener's eccentricity. The in-plane coupling effect is also found to increase with frequency.     

Spectral discretization of the vorticity, velocity and pressure formulation of the Navier–Stokes equations

We consider the Navier–Stokes equations in a two- or three-dimensional domain provided with non standard boundary conditions which involve the normal component of the velocity and the tangential components of the vorticity. We write a variational formulation of this problem with three independent unknowns, the vorticity, the velocity and the pressure, and prove the existence of a solution for this problem. Next we propose a discretization by spectral methods which relies on this formulation. In the two-dimensional case, we prove quasi-optimal error estimates for the three unknowns. We conclude with some numerical experiments.

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Résumé Nous considérons les équations de Navier–Stokes dans un domaine biou tri-dimensionnel, munies de conditions aux limites non usuelles portant sur la composante normale de la vitesse et la ou les composantes tangentielles du tourbillon. Nous écrivons une formulation variationnelle de ce problème qui comporte trois inconnues indépendantes: le tourbillon, la vitesse et la pression. Nous prouvons que ce problème admet au moins une solution. Nous proposons une discrétisation par méthodes spectrales construite à partir de cette formulation. Dans le cas bidimensionnel, nous établissons des majorations quasi-optimales de l'erreur pour les trois inconnues. Nous concluons par quelques expériences numériques.

     

Design of a highly efficient catalyst for the oxaziridinium-mediated epoxidation of olefins by Oxone

2,3,3-Trimethyl-7-nitro-3,4-dihydroisoquinolinium tetrafluoroborate is a highly efficient catalyst for the oxaziridinium-mediated epoxidation of a variety of olefins, including monosubstituted ones.     

Selective modification of oleuropein,a multifunctional bioactive natural product

Oleuropein is the major phenolic compound extracted from olive leaves and it is also present in olive fruits and virgin olive oil. It has already demonstrated a wide range of pharmacological activities, but new derivatives have to be designed in order to obtain useful Structure–Activity Relationships for this family of products, as well as new analogs with improved and/or different biological properties. However, taking into account the multiple OH groups (catechol and sugar) present in oleuropein, the selective modification of this natural product is a challenging problem. In this paper, we present an efficient strategy allowing the selective modification at the primary alcohol position of this natural product. Using appropriate protection/deprotection sequences, we prepared by hemisynthesis several triazoles linked to the oleuropein core, as representative examples for the development of such an approach.     

Biological Activities Evaluation of Enantiopure Isoxazolidine Derivatives: In Vitro,In Vivo and In Silico Studies

Applied Biochemistry and Biotechnology - A series of enantiopure isoxazolidines (3a–c) were synthesized by 1,3-dipolar cycloaddition between a (−)-menthone-derived nitrone and various...     

Synthesis, Crystal Structure and Characterization of a New Dabcodiium Hexaaquacobalt(II) Bis(Selenate), (C6H14N2)[Co(H2O)6](SeO4)2

Abstract  

The new hybrid material, cobalt selenate templated by 1,4-diazabicyclo[2.2.2]octane (abbreviated dabco), has been synthesised by the slow evaporation method at room temperature. Its crystal structure was investigated using single crystal X-ray diffraction data. It crystallises in the monoclinic system (space group P2₁/c) with the following unit-cell parameters: a = 12.9169(2) ?, b = 11.9101(2) ?, c = 12.4951(2) ?, β = 108.484(1)°, V = 1823.10(5) ?³ and Z = 4. The supramolecular structure of (C₆H₁₄N₂)[Co(H₂O)₆](SeO₄)₂ consists of isolated [Co(H₂O)]²⁺ and (C₆H₁₄N₂)²⁺ cations and (SeO₄)²⁻ anions linked together by three dimensional hydrogen-bond network. The infrared spectroscopy confirmed the presence of these different entities. The thermal behaviour of the precursor, studied by thermodiffractometry and thermogravimetric analyses, indicates that its decomposition proceeds through three stages giving rise to the cobalt oxide.     

Flexible all-plastic mirrors for the THz range

We present a simple and cheap approach to fabricate large-area stop-band filters and mirrors for the THz range. This approach extends the well-known concept of dielectric mirrors to the far infrared. We use alternating layers of different polymer materials with a typical thickness of several tens of micrometers to build a flexible all-plastic mirror. The structures are characterized by THz time-domain spectroscopy. The experimental results are in good agreement with transfer-matrix simulations. Received: 28 September 2001 / Accepted: 4 October 2001 / Published online: 20 December 2001     

Error bounds in high-order Sobolev norms for POD expansions of parameterized transient temperatures

In this work, we analyze the convergence of the POD expansion for the solution to the heat conduction parameterized with respect to the thermal conductivity coefficient. We obtain error bounds for the POD approximation in high-order norms in space that assure an exponential rate of convergence, uniformly with respect to the parameter whenever it remains within a compact set of positive numbers. We present some numerical tests that confirm this theoretical accuracy.     

Phase transitions and vibrational study of Rb2SeO4·Te(OH)6 and Rb1.12(NH4)0.88SO4·Te(OH)6

Calorimetry, conductivity, IR and Raman studies of the two ionic-protonic conductors Rb₂SeO₄·Te(OH)₆ (RbSeTe) and Rb_1.12(NH₄)_0.88SO₄·Te(OH)₆ (RNST) have been recorded and analyzed. These compounds crystallize in the monoclinic system, the space groups being, respectively, P2₁/c and P2₁/a for (RbSeTe) and (RNST) with four formula units in their unit cells.

The main feature of these atomic arrangements is the coexistence of two independent and different types of anions in the unit cell, connected by hydrogen bonds, which insure the cohesion of the crystalline edifice. Differential scanning calorimetry traces show three peaks for both the materials, corresponding to three phase transitions, at 430, 470 and 493 K for RbSeTe and at 418, 458 and 483?K for RNST.

A sudden surge in the temperature dependence of conductivity confirms the presence of the third transition, which is characterized by a high conductivity. The Raman spectra of these two materials were investigated in the range 295–600?K and IR spectra achieved at room temperature between 10 and 4000?cm^?1, confirm the presence of the phase transitions and show that anionic groups coexist independently in the same crystal.