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Publication Surface stability of nonlinear magnetoelastic solids(Wiley, 2007-12) Ottenio, M.; Destrade, Michel; Ogden, R.W.; WileyThe present paper proposes to identify surface stability when a magnetoelastic half-space is subjected to a pure homogeneous pre-deformation and to a magnetic field normal to its (plane) boundary. Clearly, the aim is to find the critical stretch ratio beyond which surface instabilities may develop, or in other words, to establish a bifurcation criterion based on the incremental static solution of the boundary value problem. We want to analyse how the presence of a coupling between magnetism and nonlinear elasticity modify the conditions of stability.Publication Onde de Love Piézoacoustique(2006-04-24) Collet, Bernard; Destrade, Michel; |~|Une sélection de résultats analytiques et numériques concernant la propagation d'ondes planes harmoniques guidées dans un bicouche piézoélectrique est présentée. L'étude effectuée concerne les modes transverses horizontaux (ondes de Love). L analyse repose sur l utilisation du formalisme de Stroh associé a la notion d impédance d interface. Les courbes de dispersion et les amplitudes des champs continus sont donnés et brievement commentés.Publication Wireless communicative stent for follow-up of abdominal aortic aneurysm,(IEEE, 2006) Destrade, Michel; IEEE; |~|An abdominal aortic aneurysm (AAA) is a dilatation of the aorta at the abdominal level, which rupture is a life threatening complication. Recent treatment of AAA consists in endovascular treatment with covered stent grafts. Despite improving devices, this treatment is still associated with close to 25% of failure related to persisting pressure into the excluded aneurismal sac. The follow-up becomes thus crucial and demands frequent examinations (CT-scan, IRM) which are not so liable given the complications. In order to evaluate the post-operative period of an AAA treatment, we designed a communicative stent, comprising of an integrated pressure sensor. This paper presents the conception of a communicative sensor, the elaboration of a numerical model, and the development of an experimental testbench constituting the aortic flux across an AAA and allowing the optimization and validation of the measurement principle.Publication A note about waves in dissipative and dispersive solids(World Scientific, 2008) Destrade, Michel; Saccomandi, Giuseppe; |~|We study shear waves propagating in a special viscoelastic model proposed first by Fosdick and Yu in 1996. We deduce an asymptotic approximation which reduces the full balance equations to a system of evolution equations which are a vectorial generalization of the Modified KDV-Burger equation. In such a way we show that the model takes into account not only dissipative effects but also dispersive effects.Publication Waves and vibrations in a solid of second grade(World Scientific, 2006) Destrade, Michel; Saccomandi, Giuseppe; |~|We study the viscoelastic second grade solid, for which the constitutive equation consists in the sum of a purely elastic part and a viscoelastic part; this latter part is specified by two microstructural coefficients α1 and α2, in addition to the usual Newtonian viscosity ν. We show via some exact solutions that such solids may describe some interesting dispersive effects. The solutions under investigation belong to special classes of standing waves and of circularly-polarized finite-amplitude waves.Publication Mechanical properties of excised human skin(Springer Verlag, 2010) Ni Annaidh, Aisling; Ottenio, M.; Bruyere, K.; Destrade, Michel; Gilchrist, Michael D.; Springer; |~|6201984|~|In this study we have investigated in influence of location, gender and orientation on the deformation characteristics of 55 samples of human excised skin. Uniaxial tensile tests were carried out at a strain rate of 0.012s-1 on excised human skin from the back. The deformation characteristics of skin (Ultimate Tensile Strength (P<0.0001), Failure Strain (P=0.0177), Young s Modulus (P<0.0076), Initial Slope (P=0.0375) and Strain Energy (P=0.0101)) were found to be dependent upon the orientation of specimens with respect to the Langer s Lines. The location of specimens on the back was also found to have a significant effect on the Ultimate Tensile Strength (P =0.0002), the Young s Modulus (P=0.0017) and the Strain Energy (P=0.005).Publication ENDOCOM: Abdominal aortic aneurysm test bench for in vitro simulation(IEEE, 2007) Destrade, Michel; |~|1267880|~|An abdominal aortic aneurysm (AAA) is a dilatation of the aorta at the abdominal level, whose rupture is a life threatening complication. Recent treatment procedures of AAA consists in endovascular treatment with covered stent grafts. Despite improving design of these devices, this treatment is still associated with close to 25% of failure, due to persisting pressure into the excluded aneurysmal sac. The follow-up becomes thus crucial and demands frequent examinations (CT- scan, IRM) which are not so liable given the complications. In order to evaluate the post-operative period of an AAA treatment, we designed a communicative stent, comprising of an integrated pressure sensor. This paper presents the conception of a communicative sensor, the elaboration of a numerical model, and the development of an experimental testbench reproducing the aortic flux across an AAA and allowing the optimization and validation of the measurement principle.Publication Finite-amplitude Love waves in a pre-stressed neo-Hookean material(2008) Destrade, Michel; Rodrigues Ferreira, Elizabete; Boulanger, Philippe; |~|In the context of the non-linear elasticity theory we consider a model for compressible solids called compressible neoHookean material . We show how (exact) finite-amplitude inhomogeneous plane wave solutions and finite-amplitude unattenuated solutions can combine to form a finite-amplitude Love wave. Also, we investigate the special case when the interface between the layer and the substrate is in a principal plane of the pre-strain.Publication Experimental characterisation of neural tissue at collision speeds(International Research Council on Biomechanics of Injury (IRCOBI), 2012) Destrade, Michel; Rashid, Bader; Gilchrist, Michael; |~|IRCSET|~|Mechanical characterisation of brain tissue at high loading velocities is particularly important for modelling Traumatic Brain Injury (TBI). During severe impact conditions, brain tissue experiences a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue at these strains and strain rates is of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. In this research, we describe the design and operation of a High Rate Tension Device (HRTD) that has been used for tensile tests on freshly harvested specimens of porcine neural tissue at speeds corresponding to a maximum strain rate of 90/s. We investigate the effects of inhomogeneous deformation of the tissue during tension by quasi-static tests (strain rate 0.01/s) and dynamic tests (strain rate 90/s). Based on a combined experimental and computational analysis, brain specimens of aspect ratio (diameter/thickness) S = 10/10 or lower (10/12, 10/13) are considered suitable for minimising the effects of inhomogeneous deformation during tension tests.The Ogden material parameters were derived from the experimental data both at quasi-static conditions (mu=440 Pa and alpha=-4.8 at 0.01/s strain rate) and dynamic conditions (mu=4238 Pa and alpha=2.8 at 90/s strain rate) by performing an inverse finite element analysis to model all experimental data. These material parameters will prove useful for the nonlinear analysis of brain tissue.Publication Strain rate effects on the failure characteristics of excised human skin(The 9th International Conference on the Mechanics of Time Dependent Materials, 2014) Destrade, Michel; |~|Skin is a complex, multi-layered material which exhibits non-linear, anisotropic and viscoelastic behaviour. Its structure is complex and can be broadly divided into three main layers: the epidermis, the dermis and hypodermis. The thickest of these layers, the dermis, consists of strong stiff collagen fibres which govern many of the mechanical properties of human skin. The mechanical properties of skin are important for a number of applications including surgery, dermatology, impact biomechanics and forensic science. Many studies in the literature use human skin substitutes such as pigskin or silicone, and in vitro tests on human skin are particularly rare. The objective of this study is to determine the strain rate effects on the failure characteristics of excised human skin considering both the rate dependency and anisotropic nature of skin.Publication Partition functions and chiral algebras.(American Mathematical Society, 2007-05) Tuite, Michael P.; |~|We discuss recent work of the authors concerning correlation functions and partition functions for free bosons/fermions and the b-c or ghost system. We compare and contrast the nature of the 1-point functions at genus 1, and explain how one may understand the free boson partition function at genus 2 via vertex operators and sewing complex tori.Publication The bosonic vertex operator algebra on a genus g Riemann surface(2011-08) Tuite, Michael P.; Zuevsky, Alexander; |~|We discuss the partition function for the Heisenberg vertex operator algebra on a genus g Riemann surface formed by sewing handles to a Riemann sphere. In particular, it is shown how the partition can be computed by means of the MacMahon Master Theorem from classical combinatorics.Publication Hyperelastic and viscoelastic properties of brain tissue in tension(ASME, 2012) Destrade, Michel; Gilchrist, Michael D.; |~|IRCSET|~|Mechanical characterization of brain tissue at high loading velocities is particularly important for modelling Traumatic Brain Injury (TBI). During severe impact conditions, brain tissue experiences a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue at these strains and strain rates is thus of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. In this research, uniaxial tensile tests at strain rates of 30, 60 and 90/s up to 30% strain and stress relaxation tests in tension at various strain magnitudes (10% - 60%) with an average rise time of 24 ms were performed. The brain tissue showed a stiffer response with increasing strain rates, showing that hyperelastic models are not adequate and that viscoelastic models are required. Specifically, the tensile engineering stress at 30% strain was 3.1 ± 0.49 kPa, 4.3 ± 0.86 kPa, 6.5 ± 0.76 kPa (mean ± SD) at strain rates of 30, 60 and 90/s, respectively. The Prony parameters were estimated from the relaxation data. Numerical simulations were performed using a one-term Ogden model to analyze hyperelastic and viscoelastic behavior of brain tissue up to 30% strain. The material parameters obtained in this study will help to develop biofidelic human brain finite element models, which subsequently can be used to predict brain injuries under impact conditions.Publication Semi-nonnegative matrix factorization with global statistical consistency for collaborative filtering(2009) Yang, Haixuan; |~|[no abstract available]Publication Learning with Consistency between Inductive Functions and Kernels(2009) Yang, Haixuan; |~|[no abstract available]Publication Characteristic classes of complexified bundles(Summer School in Algebraic Topology: Sheaf theoretic methods in the theory of characteristic classes, 2007) Rahm, Alexander D.; |~|We examine the topological characteristic cohomology classes of complexified vector bundles . In particular, all the classes coming from real vector bundles are computed. We use characteristic classes with the ax-ioms of Milnor and StasheffPublication NHDC and PHDC: Non-propagating and propagating heat diffusion classifiers(12th International Conference on Neural Information Processing, 2005) Yang, Haixuan; |~|Abstract - By imitating the way that heat flows in a medium with a geometric structure, we propose two novel classification algorithms, Non-propagating Heat Diffusion Classifier (NHDC) and Propagating Heat Diffusion Classifier (PHDC). In NHDC, an unlabelled data is classified into the class that diffuses the most heat to the unlabelled data after one local diffusion from time 0 to a small time period, while in PHDC, an unlabelled data is classified into the class that diffuses the most heat to the unlabelled data in the propagating effect of the heat flow from time 0 to time t, which means that in PHDC, the heat diffuses infinitely many times from time 0 and each time period is infinitely small. In other words, we measure the similarity between an unlabelled data and a class by the heat amount that the unlabelled data receives from the set of labelled data in the class, and then classify the unlabelled data into the class with the most similarity. Unlike the traditional method, in which the heat kernel is applied to a kernel-based classifier we employ the heat kernel to construct the classifier directly; moreover, instead of imitating the way that the heat flows along a linear or nonlinear manifold, we let the heat flow along a graph formed by the k-nearest neighbors. An important and special feature in both NHDC and PHDC is that the kernel is not symmetric. We show theoretically that PWA (Parzen Window Approach when the window function is a multivariate normal kernel) and KNN are actually special cases of NHDC model, and that PHDC has the ability to approximate NHDC. Experiments show that NHDC performs better than PWA and KNN in prediction accuracy, and that PHDC performs better than NHDC. I.Publication A point-distribution index and its application to sensor-grouping in wireless sensor networks(ACM, 2006) Yang, Haixuan; |~|We propose [i], a novel index for evaluation of point-distribution. [i] is the minimum distance etween each pair of points normalized by the average distance between each pair of points. We find that a set of points that achieve a maximum value of [i] result in a honeycomb structure.Publication Predictive random graph ranking on the web(2006) Yang, Haixuan; |~|The incomplete information about the Web structure causes inaccurate results of various ranking algorithms. In this paper, we propose a solution to this problem by formulating a new framework called, Predictive Random Graph Ranking, in which we generate a random graph based on the known information about the Web structure. The random graph can be considered as the predicted Web structure, on which ranking algorithm are expected to be improved in accuracy. For this purpose, we extend some current ranking algorithms from a static graph to a random graph. Experimental results show that the Predictive Random Graph Ranking framework can improve the accuracy of the ranking algorithms such as PageRank, Common Neighbor, and Jaccard's Coefficient.Publication Diffusionrank: a possible penicillin for web spamming(2007) Yang, Haixuan; |~|While the PageRank algorithm has proven to be very effective for ranking Web pages, the rank scores of Web pages can be manipulated. To handle the manipulation problem and to cast a new insight on the Web structure, we propose a ranking algorithm called DiffusionRank. DiffusionRank is motivated by the heat diffusion phenomena, which can be connected to Web ranking because the activities flow on the Web can be imagined as heat flow, the link from a page to another can be treated as the pipe of an air-conditioner, and heat flow can embody the structure of the underlying Web graph.