The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Nicolas Vauchelet - One of the best experts on this subject based on the ideXlab platform.
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traveling wave solution of the hele shaw Model of tumor growth with nutrient
Mathematical Models and Methods in Applied Sciences, 2014Co-Authors: Nicolas Vauchelet, Benoit Perthame, Min TangAbstract:Several mathematical Models of tumor growth are now commonly used to explain medical observations and predict cancer evolution based on images. These Models incorporate mechanical laws for tissue compression combined with rules for nutrients availability which can differ depending on the situation under consideration, in vivo or in vitro. Numerical solutions exhibit, as expected from medical observations, a proliferative rim and a necrotic core. However, their precise profiles are rather complex, both in one and two dimensions. We study a simple free Boundary Model formed of a Hele–Shaw equation for the cell number density coupled to a diffusion equation for a nutrient. We can prove that a traveling wave solution exists with a healthy region separated from the progressing tumor by a sharp front (the free Boundary) while the transition to the necrotic core is smoother. Remarkable is the pressure distribution which vanishes at the Boundary of the proliferative rim with a vanishing derivative at the transition point to the necrotic core.
Benoit Perthame - One of the best experts on this subject based on the ideXlab platform.
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traveling wave solution of the hele shaw Model of tumor growth with nutrient
Mathematical Models and Methods in Applied Sciences, 2014Co-Authors: Nicolas Vauchelet, Benoit Perthame, Min TangAbstract:Several mathematical Models of tumor growth are now commonly used to explain medical observations and predict cancer evolution based on images. These Models incorporate mechanical laws for tissue compression combined with rules for nutrients availability which can differ depending on the situation under consideration, in vivo or in vitro. Numerical solutions exhibit, as expected from medical observations, a proliferative rim and a necrotic core. However, their precise profiles are rather complex, both in one and two dimensions. We study a simple free Boundary Model formed of a Hele–Shaw equation for the cell number density coupled to a diffusion equation for a nutrient. We can prove that a traveling wave solution exists with a healthy region separated from the progressing tumor by a sharp front (the free Boundary) while the transition to the necrotic core is smoother. Remarkable is the pressure distribution which vanishes at the Boundary of the proliferative rim with a vanishing derivative at the transition point to the necrotic core.
Boyce E Griffith - One of the best experts on this subject based on the ideXlab platform.
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image based immersed Boundary Model of the aortic root
Medical Engineering & Physics, 2017Co-Authors: Ali Hasan, Ebrahim M Kolahdouz, Andinet Enquobahrie, Thomas G Caranasos, John P Vavalle, Boyce E GriffithAbstract:Each year, approximately 300,000 heart valve repair or replacement procedures are performed worldwide, including approximately 70,000 aortic valve replacement surgeries in the United States alone. Computational platforms for simulating cardiovascular devices such as prosthetic heart valves promise to improve device design and assist in treatment planning, including patient-specific device selection. This paper describes progress in constructing anatomically and physiologically realistic immersed Boundary (IB) Models of the dynamics of the aortic root and ascending aorta. This work builds on earlier IB Models of fluid-structure interaction (FSI) in the aortic root, which previously achieved realistic hemodynamics over multiple cardiac cycles, but which also were limited to simplified aortic geometries and idealized descriptions of the biomechanics of the aortic valve cusps. By contrast, the Model described herein uses an anatomical geometry reconstructed from patient-specific computed tomography angiography (CTA) data, and employs a description of the elasticity of the aortic valve leaflets based on a fiber-reinforced constitutive Model fit to experimental tensile test data. The resulting Model generates physiological pressures in both systole and diastole, and yields realistic cardiac output and stroke volume at physiological Reynolds numbers. Contact between the valve leaflets during diastole is handled automatically by the IB method, yielding a fully competent valve Model that supports a physiological diastolic pressure load without regurgitation. Numerical tests show that the Model is able to resolve the leaflet biomechanics in diastole and early systole at practical grid spacings. The Model is also used to examine differences in the mechanics and fluid dynamics yielded by fresh valve leaflets and glutaraldehyde-fixed leaflets similar to those used in bioprosthetic heart valves. Although there are large differences in the leaflet deformations during diastole, the differences in the open configurations of the valve Models are relatively small, and nearly identical hemodynamics are obtained in all cases considered.
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image based immersed Boundary Model of the aortic root
arXiv: Medical Physics, 2017Co-Authors: Ali Hasan, Ebrahim M Kolahdouz, Andinet Enquobahrie, Thomas G Caranasos, John P Vavalle, Boyce E GriffithAbstract:Each year, approximately 300,000 heart valve repair or replacement procedures are performed worldwide, including approximately 70,000 aortic valve replacement surgeries in the United States alone. This paper describes progress in constructing anatomically and physiologically realistic immersed Boundary (IB) Models of the dynamics of the aortic root and ascending aorta. This work builds on earlier IB Models of fluid-structure interaction (FSI) in the aortic root, which previously achieved realistic hemodynamics over multiple cardiac cycles, but which also were limited to simplified aortic geometries and idealized descriptions of the biomechanics of the aortic valve cusps. By contrast, the Model described herein uses an anatomical geometry reconstructed from patient-specific computed tomography angiography (CTA) data, and employs a description of the elasticity of the aortic valve leaflets based on a fiber-reinforced constitutive Model fit to experimental tensile test data. Numerical tests show that the Model is able to resolve the leaflet biomechanics in diastole and early systole at practical grid spacings. The Model is also used to examine differences in the mechanics and fluid dynamics yielded by fresh valve leaflets and glutaraldehyde-fixed leaflets similar to those used in bioprosthetic heart valves. Although there are large differences in the leaflet deformations during diastole, the differences in the open configurations of the valve Models are relatively small, and nearly identical hemodynamics are obtained in all cases considered.
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immersed Boundary Model of aortic heart valve dynamics with physiological driving and loading conditions
arXiv: Computational Engineering Finance and Science, 2017Co-Authors: Boyce E GriffithAbstract:The immersed Boundary (IB) method is a mathematical and numerical framework for problems of fluid-structure interaction, treating the particular case in which an elastic structure is immersed in a viscous incompressible fluid. The IB approach to such problems is to describe the elasticity of the immersed structure in Lagrangian form, and to describe the momentum, viscosity, and incompressibility of the coupled fluid-structure system in Eulerian form. Interaction between Lagrangian and Eulerian variables is mediated by integral equations with Dirac delta function kernels. The IB method provides a unified formulation for fluid-structure interaction Models involving both thin elastic boundaries and also thick viscoelastic bodies. In this work, we describe the application of an adaptive, staggered-grid version of the IB method to the three-dimensional simulation of the fluid dynamics of the aortic heart valve. Our Model describes the thin leaflets of the aortic valve as immersed elastic boundaries, and describes the wall of the aortic root as a thick, semi-rigid elastic structure. A physiological left-ventricular pressure waveform is used to drive flow through the Model valve, and dynamic pressure loading conditions are provided by a reduced (zero-dimensional) circulation Model that has been fit to clinical data. We use this Model and method to simulate aortic valve dynamics over multiple cardiac cycles. The Model is shown to approach rapidly a periodic steady state in which physiological cardiac output is obtained at physiological pressures. These realistic flow rates are not specified in the Model, however. Instead, they emerge from the fluid-structure interaction simulation.
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immersed Boundary Model of aortic heart valve dynamics with physiological driving and loading conditions
International Journal for Numerical Methods in Biomedical Engineering, 2012Co-Authors: Boyce E GriffithAbstract:SUMMARY The immersed Boundary (IB) method is a mathematical and numerical framework for problems of fluid–structure interaction, treating the particular case in which an elastic structure is immersed in a viscous incompressible fluid. The IB approach to such problems is to describe the elasticity of the immersed structure in Lagrangian form, and to describe the momentum, viscosity, and incompressibility of the coupled fluid–structure system in Eulerian form. Interaction between Lagrangian and Eulerian variables is mediated by integral equations with Dirac delta function kernels. The IB method provides a unified formulation for fluid–structure interaction Models involving both thin elastic boundaries and also thick viscoelastic bodies. In this work, we describe the application of an adaptive, staggered-grid version of the IB method to the three-dimensional simulation of the fluid dynamics of the aortic heart valve. Our Model describes the thin leaflets of the aortic valve as immersed elastic boundaries, and describes the wall of the aortic root as a thick, semi-rigid elastic structure. A physiological left-ventricular pressure waveform is used to drive flow through the Model valve, and dynamic pressure loading conditions are provided by a reduced (zero-dimensional) circulation Model that has been fit to clinical data. We use this Model and method to simulate aortic valve dynamics over multiple cardiac cycles. The Model is shown to approach rapidly a periodic steady state in which physiological cardiac output is obtained at physiological pressures. These realistic flow rates are not specified in the Model, however. Instead, they emerge from the fluid–structure interaction simulation. Copyright © 2011 John Wiley & Sons, Ltd.
Shinobu Yoshimura - One of the best experts on this subject based on the ideXlab platform.
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A novel ghost cell Boundary Model for the explicit moving particle simulation method in two dimensions
Computational Mechanics, 2020Co-Authors: Zumei Zheng, Guangtao Duan, Naoto Mitsume, Shunhua Chen, Shinobu YoshimuraAbstract:The moving particle simulation (MPS) method has proved to be an effective technique to Model fluid flows with free surfaces. However, it still remains a challenging task to treat the wall Boundary problem with complicated geometries accurately and robustly. The purpose of this work is to propose a two-dimensional ghost cell Boundary Model for the explicit MPS method to achieve this end. The appeal of the novel Model lies in providing an easy and natural treatment for the wall Boundary of complicated shapes. On one hand, the wall Boundary can be easily represented by using ghost cells of different sizes or shapes (e.g. triangles and quadrilaterals in two dimensions), and ghost cells are constructed in the pre-processing phase. On the other hand, the particle-cell interaction can be Modeled by an integral version of the MPS Model that requires the specific area of each cell, while the particle-particle interaction near wall Boundary is still handled by the conventional version of the MPS Model via assuming that each particle takes the same area. In this manner, the particle-cell interaction is Modeled naturally. Two numerical examples, i.e. the hydrostatic and dam break tests, are performed to validate the effectiveness of the proposed Model, where the effects of the distribution of ghost cells are also numerically investigated. Finally, a numerical case considering a star-shaped obstacle in dam break flows is carried out to demonstrate the capacity of the novel Model in dealing with the wall Boundary problem with complicated geometries.
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parallel analysis system for fluid structure interaction with free surfaces using adventure_solid and lexadv_emps
2016Co-Authors: Naoto Mitsume, Shinobu Yoshimura, Tomonori Yamada, Kohei MurotaniAbstract:In this chapter, we present a parallel analysis system for fluid–structure interaction (FSI) analysis with free-surfaces. It is based on a method that uses the moving-particle semi-implicit/simulation (MPS) method for flow computations and the finite element (FE) method for structural computations. The MPS-FE method is an efficient and robust approach for FSI problems involving free-surface flow. To develop the system presented herein, we use two existing open-source software modules: ADVENTURE_ Solid, a large-scale FE solver for structural computations; and LexADV_ EMPS, a library for large-scale MPS computations for free-surface flow. The explicitly represented polygon (ERP) wall Boundary Model employed in LexADV_ EMPS is accurate and stable, and it expresses wall boundaries as a set of arbitrarily shaped triangular polygons with appropriately imposed Boundary conditions. Thus, when the ERP is used, in both the fluid and the structure computations, the fluid–structure interfaces are matched, and therefore, preprocessing of the data for FSI analysis is greatly facilitated. We demonstrate the applicability of the developed system by solving a dam-break problem with an elastic obstacle.
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Explicitly represented polygon wall Boundary Model for the explicit MPS method
Computational Particle Mechanics, 2015Co-Authors: Naoto Mitsume, Shinobu Yoshimura, Kohei Murotani, Tomonori YamadaAbstract:This study presents an accurate and robust Boundary Model, the explicitly represented polygon (ERP) wall Boundary Model, to treat arbitrarily shaped wall boundaries in the explicit moving particle simulation (E-MPS) method, which is a mesh-free particle method for strong form partial differential equations. The ERP Model expresses wall boundaries as polygons, which are explicitly represented without using the distance function. These are derived so that for viscous fluids, and with less computational cost, they satisfy the Neumann Boundary condition for the pressure and the slip/no-slip condition on the wall surface. The proposed Model is verified and validated by comparing computed results with the theoretical solution, results obtained by other Models, and experimental results. Two simulations with complex Boundary movements are conducted to demonstrate the applicability of the E-MPS method to the ERP Model.
Rolf Brendel - One of the best experts on this subject based on the ideXlab platform.
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loss analysis of n type passivated emitter rear totally diffused back junction silicon solar cells with efficiencies up to 21 2
IEEE Journal of Photovoltaics, 2016Co-Authors: Bianca Lim, Till Brendemuhl, Thorsten Dullweber, Rolf BrendelAbstract:In this work, we present screen-printed n-type passivated emitter rear totally diffused (n-PERT) back-junction (BJ) silicon solar cells with efficiencies up to 21.2% on total area of 239 cm2. The process sequence is based on that of p-type passivated emitter and rear cells (p-PERC), adding only a boron diffusion at the beginning. We reduce the recombination at the homogeneous phosphorus-doped front surface field by a wet-chemical etch-back of 10–20 nm and apply an advanced five-busbar layout on the front side to increase the energy conversion efficiency. We simulate the performance of the n-PERT BJ solar cell using the conductive Boundary Model and perform a synergistic efficiency gain analysis to identify the main limitations of our n-PERT BJ solar cells. We observe the biggest gain of 0.72% absolute after eliminating recombination at the P-doped front surface field and find that reducing recombination in general is most important for further improving our n-PERT BJ solar cells.