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Decaestecker E.,Catholic University of Leuven | De Gersem H.,Wave Group | Michalakis Y.,IRD Montpellier | Raeymaekers J.A.M.,Catholic University of Leuven | Raeymaekers J.A.M.,University of Basel
Ecology Letters | Year: 2013

An increase in biological diversity leads to a greater stability of ecosystem properties. For host-parasite interactions, this is illustrated by the 'dilution effect': a negative correlation between host biodiversity and disease risk. We show that a similar mechanism might stabilise host-parasite dynamics at a lower level of diversity, i.e. at the level of genetic diversity within host species. A long-term time shift experiment, based on a historical reconstruction of a Daphnia-parasite coevolution, reveals infectivity cycles with more stable amplitude in experienced than in naive hosts. Coevolutionary models incorporating an increase in host allelic diversity over time explain the detected asymmetry. The accumulation of resistance alleles creates an opportunity for the host to stabilise Red Queen dynamics. It leads to a larger arsenal enhancing the host performance in its coevolution with the parasite in which 'it takes all the running both antagonists can do to keep in the same place'. © 2013 John Wiley & Sons Ltd/CNRS.

Teppati V.,Polytechnic University of Turin | Bolognesi C.R.,Wave Group
IEEE Transactions on Instrumentation and Measurement | Year: 2012

In this paper, a thorough evaluation of calibration residual uncertainty of on-wafer load-pull systems at millimeterwave frequencies, with actual comparisons between real-time and non-real-time load-pull systems, is reported for the first time. Two figures of merit for uncertainty evaluation are taken into account, showing the differences between the two methodologies. In the case of non-real-time systems, based on a simulation tool developed for the purpose, typical values of uncertainties to be expected at millimeter-wave frequencies are shown. Finally, a methodology to reduce calibration residual uncertainty of nonreal- time load-pull measurements, based on the optimization of a thru load-pull map, is for the first time introduced, and its effects on actual measurements of microwave HBTs at 40 GHz are shown. © 2012 IEEE.

Delrue S.,Wave Group | Van Den Abeele K.,Wave Group
Ultrasonics | Year: 2012

Early stage delaminations in composite materials tend to be closed at rest. Inspection with traditional linear ultrasonic techniques generally fails to diagnose and locate such imperfections. However, if undetected and left untreated, incipient defects may gradually grow within the material and eventually lead to failure of the component. Kissing bonds or clapping contacts inherently demand a non-linear diagnostic method, applying a finite excitation amplitude that is able to overcome an activation threshold to open and close the contact. In order to obtain a better understanding and analysis of the macroscopic non-linear behavior that can be observed at the component level, we developed and investigated the results of a finite element model for a composite material containing a single circular delamination. The model makes use of local node splitting and the non-linear constitutive behavior is implemented by means of spring-damper elements at the delamination interface. The results of this parametric study allow a better insight in the behavior of the excited delamination in experimental conditions, including the appearance of localized subharmonics and harmonics of the excitation frequency. Based on the developed model, two different detection and localization techniques (using either a single frequency or a sweep excitation) were demonstrated to determine position, shape, depth and orientation of one or multiple delaminations. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.

Torrent D.,Wave Group | Sanchez-Dehesa J.,Wave Group
Physical Review Letters | Year: 2010

This Letter reports physical realization of acoustic metamaterials with anisotropic mass density. These metamaterials consist of a superlattice of two fluidlike components radially periodic. Several structures are spectroscopically characterized at large wavelengths (homogenization limit) by studying the acoustic resonances existing in the circular cavity where they are embedded. This characterization method allows us to extract the diagonal components of the sound speed tensor. Analytical expressions describing the anisotropic behavior as a function of the corrugation parameter are also developed and their predictions are in agreement with measurements. © 2010 The American Physical Society.

De Gersem H.,Wave Group
IEEE Transactions on Magnetics | Year: 2010

The performance of a magnetic brake is calculated by a cross-sectional model where stator and air gap are discretized by finite elements, whereas the nonlinear ferromagnetic rotor is discretized by spectral elements, in order to guarantee a sufficient resolution of the thin eddy-current layers. © 2006 IEEE.

Torrent D.,Wave Group | Sanchez-Dehesa J.,Wave Group
New Journal of Physics | Year: 2010

Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sánchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

This article describes a brief review of recent research advances in chiral liquid crystals (CLCs) for laser applications. The CLC molecules have an intrinsic capability to spontaneously organize supramolecular helical assemblages consisting of liquid crystalline layers through their helical twisting power. Such CLC supramolecular helical structures can be regarded as one-dimensional photonic crystals (PhCs). Owing to their supramolecular helical structures, the CLCs show negative birefringence along the helical axis. Selective reflection of circularly polarized light is the most unique and important optical property in order to generate internal distributed feedback effect for optically-excited laser emission. When a fluorescent dye is embedded in the CLC medium, optical excitation gives rise to stimulated laser emission peak(s) at the band edge(s) and/or within the CLC selective reflection. Furthermore, the optically-excited laser emission peaks can be controlled by external stimuli through the self-organization of CLC molecules. This review introduces the research background of CLCs carried out on the PhC realm, and highlights intriguing precedents of various CLC materials for laser applications. It would be greatly advantageous to fabricate active CLC laser devices by controlling the supramolecular helical structures. Taking account of the peculiar features, we can envisage that a wide variety of supramolecular helical structures of CLC materials will play leading roles in next-generation optoelectronic molecular devices. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Published online in Wiley InterScience DOI 10.1002/tcr.201000013Recent developments of chiral liquid crystals (CLCs) that can be used for a wide variety of laser applications are discussed. Liquid crystal compounds with molecular chirality have an intrinsic capability to self-organize the supramolecular helical assemblages, which are 1D periodic structures possessing characteristic optical properties. Tailoring the CLC materials and device structures enables a variety of applications in next-generation molecular optoelectronic devices. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Furumi S.,Wave Group | Fudouzi H.,Wave Group | Sawada T.,Wave Group
Laser and Photonics Reviews | Year: 2010

We present an overview of recent developments in the fabrication and uses of colloidal crystals (CCs) for photonics and laser applications. Microparticles with a diameter in the range from 10nm to 10μm often have an intrinsic capability to spontaneously organize themselves from a colloidal suspension into 3D lattice structures. Such highly ordered 3D architectures of microparticles are called colloidal crystals (CCs). The CC structures have received tremendous attention as one of the facile and high-throughput fabrication techniques of photonic crystals (PCs). We introduce here interesting precedents not only of diverse techniques of high-quality CC structures, but also of their versatile applications in optical sensors responding to various external stimuli. This review also highlights a new potential use of the CCs as low-threshold laser devices. We believe that a wide variety of CC architectures will play leading roles in the next generation of optoelectronic devices. © 2010 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wave Group | Date: 2014-01-23

An applique is provided that is attached to the outer surface of a product. The applique comprises a decorative piece including an upper surface with a design element digitally printed thereon and an opposite lower surface attached to the product.

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