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Elastic Membrane (elastic + membrane)
Selected AbstractsImproving realism of a surgery simulator: linear anisotropic elasticity, complex interactions and force extrapolationCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3 2002Guillaume Picinbono Abstract In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. The goal of this simulator is to provide a realistic training test bed to perform laparoscopic procedures. Therefore, its main functionality is to simulate the action of virtual laparoscopic surgical instruments for deforming and cutting tridimensional anatomical models. Throughout this paper, we present the general features of this simulator including the implementation of several biomechanical models and the integration of two force-feedback devices in the simulation platform. More precisely, we describe three new important developments that improve the overall realism of our simulator. First, we have developed biomechanical models, based on linear elasticity and finite element theory, that include the notion of anisotropic deformation. Indeed, we have generalized the linear elastic behaviour of anatomical models to ,transversally isotropic' materials, i.e. materials having a different behaviour in a given direction. We have also added to the volumetric model an external elastic membrane representing the ,liver capsule', a rather stiff skin surrounding the liver, which creates a kind of ,surface anisotropy'. Second, we have developed new contact models between surgical instruments and soft tissue models. For instance, after detecting a contact with an instrument, we define specific boundary constraints on deformable models to represent various forms of interactions with a surgical tool, such as sliding, gripping, cutting or burning. In addition, we compute the reaction forces that should be felt by the user manipulating the force-feedback devices. The last improvement is related to the problem of haptic rendering. Currently, we are able to achieve a simulation frequency of 25,Hz (visual real time) with anatomical models of complex geometry and behaviour. But to achieve a good haptic feedback requires a frequency update of applied forces typically above 300,Hz (haptic real time). Thus, we propose a force extrapolation algorithm in order to reach haptic real time. Copyright © 2002 John Wiley & Sons, Ltd. [source] Numerical simulation of viscous flow interaction with an elastic membraneINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2008Lisa A. Matthews Abstract A numerical fluid,structure interaction model is developed for the analysis of viscous flow over elastic membrane structures. The Navier,Stokes equations are discretized on a moving body-fitted unstructured triangular grid using the finite volume method, taking into account grid non-orthogonality, and implementing the SIMPLE algorithm for pressure solution, power law implicit differencing and Rhie,Chow explicit mass flux interpolations. The membrane is discretized as a set of links that coincide with a subset of the fluid mesh edges. A new model is introduced to distribute local and global elastic effects to aid stability of the structure model and damping effects are also included. A pseudo-structural approach using a balance of mesh edge spring tensions and cell internal pressures controls the motion of fluid mesh nodes based on the displacements of the membrane. Following initial validation, the model is applied to the case of a two-dimensional membrane pinned at both ends at an angle of attack of 4° to the oncoming flow, at a Reynolds number based on the chord length of 4 × 103. A series of tests on membranes of different elastic stiffness investigates their unsteady movements over time. The membranes of higher elastic stiffness adopt a stable equilibrium shape, while the membrane of lowest elastic stiffness demonstrates unstable interactions between its inflated shape and the resulting unsteady wake. These unstable effects are shown to be significantly magnified by the flexible nature of the membrane compared with a rigid surface of the same average shape. Copyright © 2007 John Wiley & Sons, Ltd. [source] Mechanical Response of Single Plant Cells to Cell Poking: A Numerical Simulation ModelJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 6 2006Rong Wang Abstract Cell poking is an experimental technique that is widely used to study the mechanical properties of plant cells. A full understanding of the mechanical responses of plant cells to poking force is helpful for experimental work. The aim of this study was to numerically investigate the stress distribution of the cell wall, cell turgor, and deformation of plant cells in response to applied poking force. Furthermore, the locations damaged during poking were analyzed. The model simulates cell poking, with the cell treated as a spherical, homogeneous, isotropic elastic membrane, filled with incompressible, highly viscous liquid. Equilibrium equations for the contact region and the non-contact regions were determined by using membrane theory. The boundary conditions and continuity conditions for the solution of the problem were found. The force-deformation curve, turgor pressure and tension of the cell wall under cell poking conditions were obtained. The tension of the cell wall circumference was larger than that of the meridian. In general, maximal stress occurred at the equator around. When cell deformation increased to a certain level, the tension at the poker tip exceeded that of the equator. Breakage of the cell wall may start from the equator or the poker tip, depending on the deformation. A nonlinear model is suitable for estimating turgor, stress, and stiffness, and numerical simulation is a powerful method for determining plant cell mechanical properties. (Managing editor: Wei Wang) [source] An autopsy case of Fabry disease with neuropathological investigation of the pathogenesis of associated dementiaNEUROPATHOLOGY, Issue 5 2008Riki Okeda The pathogenesis of dementia associated with Fabry disease was examined neuropathologically in an autopsy case. The patient was a 47-year-old computer programmer who developed renal failure at the age of 36, necessitating peritoneal dialysis, and thereafter suffered in succession episodic pulmonary congestion, bradyacusia, heart failure, and dementia, before dying of acute myocardial infarction. MRI of the brain demonstrated leuko-araiosis. The CNS parenchyma showed widespread segmental hydropic swelling of axons in the bilateral cerebral and cerebellar deep white matter in addition to neuronal ballooning due to glycolipid storage in a few restricted nuclei and multiple tiny lacunae. Hydropic axonal swelling was also sparsely distributed in the pyramidal tract, pedunculus cerebellaris superior and brachium colliculi inferioris, but wallerian degeneration of these tracts was absent. Additional features included angiopathy of the subarachnoidal arteries due to Fabry disease, such as medial thickening resulting from glycolipid deposition in smooth muscle cells (SMCs) and adventitial fibrosis with lymphocytic infiltration, together with widespread subtotal or total replacement of medial SMCs by fibrosis, associated with prominent intimal fibrous thickening and undulation of the internal elastic membrane of medium-sized (1000,100 ,m diameter) arteries. The findings in this case suggest that axonopathic leukoencephalopathy due to multisegmental hydropic swelling of axons in the bilateral cerebral deep white matter is responsible for the dementia associated with Fabry disease, and may be caused by ischemia resulting from widespread narrowing and stiffening of medium-sized subarachnoidal arteries and progressive heart failure. [source] Reproducibility of coronary lumen, plaque, and vessel wall reconstruction and of endothelial shear stress measurements in vivo in humansCATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 1 2003Ahmet U. Coskun PhD Abstract The purpose of this study was to assess the reproducibility of an in vivo methodology to reconstruct the lumen, plaque, and external elastic membrane (EEM) of coronary arteries and estimate endothelial shear stress (ESS). Ten coronary arteries without significant stenoses (five native and five stented arteries) were investigated. The 3D lumen and EEM boundaries of each coronary artery were determined by fusing end-diastolic intravascular ultrasound images with biplane coronary angiograms. Coronary flow was measured. Computational fluid dynamics was used to calculate local ESS. Complete data acquisition was then repeated. Analysis was performed on each data set in a blinded manner. The intertest correlation coefficients for all arteries for the two measurements of lumen radius, EEM radius, plaque thickness, and ESS were r = 0.96, 0.96, 0.94, 0.91, respectively (all P values < 0.0001). The 3D anatomy and ESS of human coronary arteries can be reproducibly estimated in vivo. This methodology provides a tool to examine the effect of ESS on atherogenesis, remodeling, and restenosis; the contribution of arterial remodeling and plaque growth to changes in the lumen; and the impact of new therapies. Catheter Cardiovasc Interv 2003;60:67,78. © 2003 Wiley,Liss, Inc. [source] | ||||||||||