scholarly journals Critical Pressure of Intramural Delamination in Aortic Dissection

2021 ◽  
Author(s):  
Ehsan Ban ◽  
Cristina Cavinato ◽  
Jay D Humphrey
Keyword(s):  
Aortic Dissection ◽  
Phase Field ◽  
Computational Models ◽  
Additional Data ◽  
Analytical Models ◽  
Characteristic Energy ◽  
Element Simulation ◽  
Mechanical Factors ◽  
Experimental Findings ◽  
Classical Experiment

Computational models of aortic dissection can provide novel insights into possible mechanisms by which this potentially lethal condition develops and propagates. We present results from a phase-field based finite element simulation of a classical experiment that had not previously been understood. Initial simulations agreed qualitatively and quantitatively with the experimental findings, but because of the complexity of the boundary value problem it was still difficult to build intuition. Hence, simplified analytical models were extended to gain further insight. Together, the simplified models and phase-field simulations revealed a power-law-based relation between the pressure required to initiate an intramural tear and key geometric and mechanical factors - area of the initial insult, stiffness of the wall, and characteristic energy of tearing. The degree of axial stretch and luminal pressure similarly influenced the value of the tearing pressure, which was ~70 kPa for a healthy aorta having a sub-millimeter-sized initial insult but even lower for larger tear sizes. Finally, the simulations showed that the direction a tear propagates can be altered by focal regions of weakening or strengthening, which can drive the tear towards the lumen (re-entry) or adventitia (rupture). Additional data are needed, however, on aortas having different predisposing disease conditions.

Analytical Computational Models for Relationship between Ultimate Bending Moment of Concrete Segments and Axial Force

2020 ◽  
Vol 853 ◽  
pp. 177-181
Author(s):  
Zhi Yun Wang ◽  
Shou Ju Li
Keyword(s):  
Numerical Simulation ◽  
Computational Model ◽  
Axial Force ◽  
Computational Models ◽  
Plane Deformation ◽  
Bending Moment ◽  
Analytical Models ◽  
Bending Moments ◽  
Axial Forces ◽  
Practical Engineering

Concrete segments are widely used to support soil and water loadings in shield-excavated tunnels. Concrete segments burden simultaneously to the loadings of bending moments and axial forces. Based on plane deformation assumption of material mechanics, in which plane section before bending remains plane after bending, ultimate bending moment model is proposed to compute ultimate bearing capacity of concrete segments. Ultimate bending moments of concrete segments computed by analytical models agree well with numerical simulation results by FEM. The accuracy of proposed analytical computational model for ultimate bending moment of concrete segments is numerically verified. The analytical computational model and numerical simulation for a practical engineering case indicate that the ultimate bending moment of concrete segments increases with increase of axial force on concrete segment in the case of large eccentricity compressive state.

Biomechanics of the Lumbar Disc

1997 ◽  
Vol 01 (02) ◽  
pp. 81-94 ◽  
Author(s):  
V. K. Goel ◽  
N. M. Grosland ◽  
J. Scifert
Keyword(s):  
Morphological Changes ◽  
Imaging Techniques ◽  
Lumbar Disc ◽  
Analytical Models ◽  
Clinical Observations ◽  
Disc Bulge ◽  
Mechanical Factors ◽  
Methods Analytical

The human disc and the facets work in unison to transmit loads across a lumbar motion segment. For this reason, if one component is affected by the degenerative process, the other follows. Modern imaging techniques and clinical observations have adequately delineated morphological changes in the spinal structures, while in vitro biomechanical studies have revealed that repetitive complex loads may lead to loosening of spinal structures, annular tears, and herniated discs. In addition to such experimental methods, analytical models have been able to explain the role of mechanical factors in producing disc degeneration and herniation. Furthermore, these techniques are applicable to investigating various surgical stabilization procedures. From a biomechanical perspective, surgical procedures such as discectomy are effective in reducing pain due to a decrease in disc bulge following surgery. Excessive instability across the disc, however, may require the use of bone grafts, cages or other types of interbody spacers to restore disc height. Efforts are currently underway to restore disc mechanics via an artificial disc. The following review is aimed at outlining the role of mechanical foctors in both inducing and stabilizing the degenerated/herniated intervertebral disc.

A phase-field study of domain dynamics in ferroelectric BCT-BZT system

MRS Advances ◽  
2016 ◽  
Vol 1 (40) ◽  
pp. 2783-2788 ◽  
Author(s):  
Soumya Bandyopadhyay ◽  
Tushar Jogi ◽  
Kumaraswamy Miriyala ◽  
Ranjith Ramadurai ◽  
Saswata Bhattacharyya
Keyword(s):  
Free Energy ◽  
Phase Field ◽  
Three Dimensional ◽  
Phase Field Model ◽  
Ginzburg Landau ◽  
Equimolar Composition ◽  
Electrical Boundary Conditions ◽  
Experimental Findings ◽  
Domain Dynamics ◽  
Three Dimensional Simulations

ABSTRACTWe present a thermodynamically consistent phase-field model describing the free energy of perovskite-based BCT-BZT solid solution containing an intermediate morphotropic phase boundaries. The Landau coefficients are derived as functions of composition of zirconium. The electrostrictive and elastic constants are appropriately chosen from experimental findings. The resulting Landau free energy is constructed to describe the stable polarization states as a function of composition. The evolution of the polarization order parameters at a particular composition is described by a set of time-dependent Ginzburg-Landau (TDGL) equations. Additionally, we solve Poisson’s equation and mechanical equilibrium equation to account for the ferroelectric/ferroelastic interactions. We have performed two dimensional and three-dimensional simulations with appropriate electrical boundary conditions to study the effect of external electric field on domain dynamics in BCT-BZT system at the equimolar composition.

scholarly journals From predicting to analyzing HIV-1 resistance to broadly neutralizing antibodies

2015 ◽  
Author(s):  
Anna Feldmann ◽  
Nico Pfeifer
Keyword(s):  
Neutralizing Antibodies ◽  
Computational Models ◽  
Prediction Models ◽  
Scale Up ◽  
Test Sequence ◽  
Broadly Neutralizing Antibodies ◽  
Subtype B ◽  
Envelope Sequence ◽  
Experimental Findings ◽  
Hiv 1

Treatment with broadly neutralizing antibodies (bNAbs) has recently proven effective against HIV-1 infections in humanized mice, non-human primates, and humans. For optimal treatment, susceptibility of the patient's viral strains to a particular bNAb has to be ensured. Since no computational approaches are so far available, susceptibility can only be tested in expensive and time-consuming neutralization experiments. Here, we present well-performing computational models (AUC up to 0.84) that can predict HIV-1 resistance to bNAbs given the envelope sequence of the virus. Having learnt important binding sites of the bNAbs from the envelope sequence, the models are also biologically meaningful and useful for epitope recognition. Additional to the prediction result, we provide a motif logo that displays the contribution of the pivotal residues of the test sequence to the prediction. As our prediction models are based on non-linear kernels, we introduce a new visualization technique to improve the model interpretability. Moreover, we confirmed previous experimental findings that there is a trend towards antibody resistance for the subtype B population of the virus. While previous experiments considered rather small and selected cohorts, we were able to show a similar trend for the global HIV-1 population comprising all major subtypes by predicting the neutralization sensitivity for around 36,000 HIV-1 sequences - a scale-up which is very difficult to achieve in an experimental setting.

scholarly journals Local mechanical stimuli shape tissue growth in vertebrate joint morphogenesis

2021 ◽  
Author(s):  
Ester Comellas ◽  
Johanna E Farkas ◽  
Giona Kleinberg ◽  
Katlyn Lloyd ◽  
Thomas Mueller ◽  
...  
Keyword(s):  
Computational Models ◽  
Element Model ◽  
Light Sheet ◽  
Tissue Growth ◽  
Mechanical Stimuli ◽  
Local Tissue ◽  
Pressure Dynamics ◽  
Sense And Respond ◽  
Poroelastic Model ◽  
Experimental Findings

The correct formation of synovial joints is essential for proper motion throughout life. Movement-induced forces are critical to creating correctly shaped joints, but it is unclear how cells sense and respond to these mechanical cues. To determine how mechanical stimuli drive joint morphogenesis, we combined experiments on regenerating axolotl forelimbs with a poroelastic model of bone rudiment growth. Animals either regrew forelimbs normally (control) or were injected with a TRPV4 agonist to impair chondrocyte mechanosensitivity during joint morphogenesis. We quantified growth and shape in regrown humeri from whole mount light sheet fluorescence images of the regenerated limbs. Results revealed statistically significant differences in morphology and cell proliferation between the two groups, indicating that mechanical stimuli play a role in the shaping of the joint. Local tissue growth in our finite element model was dictated by a biological contribution, proportional to chondrocyte density, and a mechanical one, driven by fluid pore pressure dynamics. Computational predictions agreed with experimental outcomes, suggesting that interstitial pressure might promote local tissue growth. Predictive computational models informed by experimental findings allow us to explore potential physical mechanisms and regulatory dynamics involved in tissue growth to advance our understanding of the mechanobiology of joint morphogenesis.

The Development of Multi-Directional Spatially Reinforced Material Structural Theory

2018 ◽  
Vol 284 ◽  
pp. 146-151 ◽  
Author(s):  
I.V. Magnitsky ◽  
F.R. Odinabekov ◽  
E.S. Sergeeva
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Elastic Properties ◽  
Simulation Models ◽  
Material Model ◽  
Analytical Models ◽  
Structural Components ◽  
Reinforced Composite ◽  
Element Simulation ◽  
Reinforced Composite Material

Finite-element simulation of the spatially reinforced composite material elastic properties is performed. The simulation models are built in two steps: first, a 4DL-reinforced material model simulating a perfect matrix/rod contact is built; second, an improved simulation model is developed, taking into account the possibility of separation between the composite components. Comparison is made between the results obtained numerically and those based on the existing analytical models. With these finite-element simulation models, it is possible to estimate the required composite elastic properties to be used when designing structural components based on those materials.

scholarly journals Finite element simulation of pressure-loaded phase-field fractures

Meccanica ◽  
2017 ◽  
Vol 53 (6) ◽  
pp. 1513-1545 ◽  
Author(s):  
N. Singh ◽  
C. V. Verhoosel ◽  
E. H. van Brummelen
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Phase Field ◽  
Element Simulation

A Computational Study of a Period of Infant Object-Concept Development

Perception ◽  
1980 ◽  
Vol 9 (2) ◽  
pp. 125-150 ◽  
Author(s):  
Slava Prazdny
Keyword(s):  
Computer Program ◽  
Computational Models ◽  
Computational Study ◽  
Concept Development ◽  
External Object ◽  
Object Concept ◽  
The World ◽  
Experimental Findings ◽  
The Way

Piaget has distinguished a number of distinct stages in the development of the concept of an enduring external object during infancy. I present a theory of a class of behaviours at one of these stages embodied in a working computer program. The behaviour of this program matches a class of perceptual behaviours of infants between about twelve and twenty weeks of age in a number of experimental situations studied by Bower. The theory argues that these behaviours are a result of the interaction between the perceptual and conceptual levels of the system, and the way in which conflicts between competing descriptions of an object are resolved. I locate the cause of several features of the behaviours in the procedures for managing the changing representation of the world, and the system's way of treating transitions between the states of an object (for example, moving to stationary). The basic conceptual primitives of the analysis are objects and events, not motion and place, as argued by Bower, or the infant's previous activity, as argued by Piaget. I argue that adequate explanations of experimental findings such as these require the construction of fairly detailed computational models.

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