The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Manuel K Rausch - One of the best experts on this subject based on the ideXlab platform.
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an augmented iterative method for identifying a stress free Reference Configuration in image based biomechanical modeling
Journal of Biomechanics, 2017Co-Authors: Manuel K Rausch, Martin Genet, Jay D HumphreyAbstract:Continued advances in computational power and methods have enabled image-based biomechanical modeling to become an important tool in basic science, diagnostic and therapeutic medicine, and medical device design. One of the many challenges of this approach, however, is identification of a stress-free Reference Configuration based on in vivo images of loaded and often prestrained or residually stressed soft tissues and organs. Fortunately, iterative methods have been proposed to solve this inverse problem, among them Sellier's method. This method is particularly appealing because it is easy to implement, convergences reasonably fast, and can be coupled to nearly any finite element package. By means of several practical examples, however, we demonstrate that in its original formulation Sellier's method is not optimally fast and may not converge for problems with large deformations. Fortunately, we can also show that a simple, inexpensive augmentation of Sellier's method based on Aitken's delta-squared process can not only ensure convergence but also significantly accelerate the method.
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An augmented iterative method for identifying a stress-free Reference Configuration in image-based biomechanical modeling
Journal of Biomechanics, 2017Co-Authors: Manuel K Rausch, Martin Genet, Jay D HumphreyAbstract:Continuing advances in computational power and methods have enabled image-based biomechanical modeling to become a crucial tool in basic science, diagnostic and therapeutic medicine, and medical device design. One of the many challenges of this approach, however, is the identification of a stress-free Reference Configuration based on in vivo images of loaded and often prestressed or residually stressed soft tissues and organs. Fortunately, iterative methods have been proposed to solve this inverse problem, among them Sellier’s method. This method is particularly appealing for it is easy to implement, convergences reasonably fast, and can be coupled to nearly any finite element package. However, by means of several practical examples, we demonstrate that in its original formulation Sellier’s method is not optimally fast and may not converge for problems with large deformations. Fortunately, we can also show that a simple, inexpensive augmentation of Sellier’s method based on Aitken’s delta-squared process can not only ensure convergence but also significantly accelerate the method.
Jay D Humphrey - One of the best experts on this subject based on the ideXlab platform.
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an augmented iterative method for identifying a stress free Reference Configuration in image based biomechanical modeling
Journal of Biomechanics, 2017Co-Authors: Manuel K Rausch, Martin Genet, Jay D HumphreyAbstract:Continued advances in computational power and methods have enabled image-based biomechanical modeling to become an important tool in basic science, diagnostic and therapeutic medicine, and medical device design. One of the many challenges of this approach, however, is identification of a stress-free Reference Configuration based on in vivo images of loaded and often prestrained or residually stressed soft tissues and organs. Fortunately, iterative methods have been proposed to solve this inverse problem, among them Sellier's method. This method is particularly appealing because it is easy to implement, convergences reasonably fast, and can be coupled to nearly any finite element package. By means of several practical examples, however, we demonstrate that in its original formulation Sellier's method is not optimally fast and may not converge for problems with large deformations. Fortunately, we can also show that a simple, inexpensive augmentation of Sellier's method based on Aitken's delta-squared process can not only ensure convergence but also significantly accelerate the method.
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An augmented iterative method for identifying a stress-free Reference Configuration in image-based biomechanical modeling
Journal of Biomechanics, 2017Co-Authors: Manuel K Rausch, Martin Genet, Jay D HumphreyAbstract:Continuing advances in computational power and methods have enabled image-based biomechanical modeling to become a crucial tool in basic science, diagnostic and therapeutic medicine, and medical device design. One of the many challenges of this approach, however, is the identification of a stress-free Reference Configuration based on in vivo images of loaded and often prestressed or residually stressed soft tissues and organs. Fortunately, iterative methods have been proposed to solve this inverse problem, among them Sellier’s method. This method is particularly appealing for it is easy to implement, convergences reasonably fast, and can be coupled to nearly any finite element package. However, by means of several practical examples, we demonstrate that in its original formulation Sellier’s method is not optimally fast and may not converge for problems with large deformations. Fortunately, we can also show that a simple, inexpensive augmentation of Sellier’s method based on Aitken’s delta-squared process can not only ensure convergence but also significantly accelerate the method.
Christel M. Marian - One of the best experts on this subject based on the ideXlab platform.
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Intersystem-crossing and phosphorescence rates in fac-IrIII(ppy)3: A theoretical study involving multi-Reference Configuration interaction wavefunctions
The Journal of chemical physics, 2015Co-Authors: Martin Kleinschmidt, Christoph Van Wüllen, Christel M. MarianAbstract:We have employed combined density functional theory and multi-Reference Configuration interaction methods including spin–orbit coupling (SOC) effects to investigate the photophysics of the green phosphorescent emitter fac-tris-(2-phenylpyridine)iridium (fac-Ir(ppy)3). A critical evaluation of our quantum chemical approaches shows that a perturbational treatment of SOC is the method of choice for computing the UV/Vis spectrum of this heavy transition metal complex while multi-Reference spin–orbit Configuration interaction is preferable for calculating the phosphorescence rates. The particular choice of the spin–orbit interaction operator is found to be of minor importance. Intersystem crossing (ISC) rates have been determined by Fourier transformation of the time correlation function of the transition including Dushinsky rotations. In the electronic ground state, fac-Ir(ppy)3 is C3 symmetric. The calculated UV/Vis spectrum is in excellent agreement with experiment. The effect of SOC is particularly pronoun...
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The UV/Vis Spectrum of Potassium Heptacyanovanadate(III): A Theoretical Multi-Reference Configuration Interaction Study Combined with Low-Temperature Experiments
European Journal of Inorganic Chemistry, 2006Co-Authors: Volker Schmid, Rolf Linder, Christel M. MarianAbstract:The electronic spectrum of K4[V(CN)7] has been calculated by means of a combined quantum chemical density functional and multi-Reference Configuration interaction scheme. In addition to the states known so far, our calculations predict the existence of two low-lying triplet electronic states with excitation energies of 13600 and 13700 cm–1, respectively. Both result from d d excitations in the slightly distorted pentagonal-bipyramidal ligand field. To validate these theoretical results we measured a UV/Vis spectrum at low temperatures. In the wavelength range between 800 and 500 nm we observed a broad band with vibrational substructure (peak positions: 13661, 14450, 15243, 16051, and 16807 cm–1). The origin transition at 13661 cm–1 is in excellent agreement with our theoretical predictions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Stéphane Avril - One of the best experts on this subject based on the ideXlab platform.
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Patient-specific stress analyses in the ascending thoracic aorta using a finite-element implementation of the constrained mixture theory
Biomechanics and Modeling in Mechanobiology, 2017Co-Authors: S. Jamaleddin Mousavi, Stéphane AvrilAbstract:It is now a rather common approach to perform patient-specific stress analyses of arterial walls using finite-element models reconstructed from gated medical images. However this requires to compute for every Gauss point the deformation gradient between the current Configuration and a stressfree Reference Configuration. It is technically difficult to define such a Reference Configuration and there is actually no guarantee that a stressfree Configuration is physically attainable due to the presence of internal stresses in unloaded soft tissues. An alternative framework was proposed by Bellini et al., 2014. It consists of computing the deformation gradients between the current Configuration and a prestressed Reference Configuration. We present here the first finite-element results based on this concept using the Abaqus software. The Reference Configuration is set arbitrarily to the in vivo average geometry of the artery, which is obtained from gated medical images and is assumed to be mechanobiologically homeostatic. For every Gauss point, the stress is split additively into the contributions of each individual load-bearing constituent of the tissue, namely elastin, collagen, smooth muscle cells. Each constituent is assigned an independent prestretch in the Reference Configuration, named the deposition stretch. The outstanding advantage of the present approach is that it simultaneously computes the in situ stresses existing in the Reference Configuration and predicts the residual stresses that occur after removing the different loadings applied onto the artery (pressure and axial load). As a proof of concept, we applied it on an ideal thick-wall cylinder and showed that the obtained results were consistent with corresponding experimental and analytical results of well-known literature. In addition, we developed a patient-specific model of a human ascending thoracic aneurys-mal aorta and demonstrated the utility in predicting the wall stress distribution in vivo under the effects of physiological pressure. Finally we simulated the whole process preceding traditional in vitro uniaxial tensile testing of arteries, including excision from the body, radial cutting, flattening and subsequent tensile loading, showing how this process may impact the final mechanical properties derived from these in vitro tests.
C. David Sherrill - One of the best experts on this subject based on the ideXlab platform.
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General-order single- and multi-Reference Configuration interaction and coupled-cluster theory: Symmetric dissociation of water
Chemical Physics Letters, 2005Co-Authors: Micah L. Abrams, C. David SherrillAbstract:Abstract We present a determinant-based method used to formulate many-body wave functions and energy expectation values of any quantum chemical model which can be written in terms of second-quantized operators. The method is used to apply single- and multi-Reference Configuration interaction and coupled-cluster theories, with restricted Hartree–Fock (RHF), unrestricted Hartree–Fock (UHF), and complete-active-space self-consistent-field (CASSCF) orbitals, to the symmetric dissociation of water. Results from unrestricted state-selective multi-Reference coupled-cluster theory are presented for the first time.
