Fluid–structure interaction modeling and simulation of transcatheter heart valves

Bioprosthetic heart valves (BHVs) are prostheses fabricated from xenograft biomaterials for treating valvular disease. While these devices have mechanical and blood flow characteristics similar to the native valves, the durability remains limited to 10-15 years with device failure continues to result from leaflet structural deterioration mediated by fatigue and tissue mineralization. Improving BHV design remains an important clinical goal and represents a unique cardiovascular engineering challenge. Transcatheter heart valves (THVs) have emerged as a minimally invasive alternative to surgical bioprosthetic heart valves therapy. THVs offer advantages such as less postoperative pain, faster rehabilitation, and better pressure gradients. However, issues such as paravalvular leakage, leaflet fatigue, and valve migration limit the widespread use of THV in the younger population, especially due to the lack of data concerning its long-term performance and durability. The friction force and the radial force between THV frames and the surrounding anatomy are important indicators for the safe anchoring. Thus, in-vitro measurement of these forces is vital for pre-operative planning of transcatheter aortic valve replacement (TAVR) procedures. There is a profound need to develop a general understanding of heart valve mechanism through novel simulation technologies that take advantage of fluid–structure interactions (FSI). In this work, a framework for modeling BHVs using recently proposed isogeometric analysis based parametric design platform and immersogeometric FSI analysis is presented. Due to the complex motion of the heart valve leaflets, the blood flow domain undergoes large deformations, including changes of topology. The FSI simulations are carried out using our hybrid arbitrary Lagrangian--Eulerian/immersogeometric methodology, which allows us to efficiently perform a computation that combines a boundary-fitted, deforming-mesh treatment of the artery with a non-boundary-fitted treatment of the leaflets. The development of modeling and simulation of full THV is integrated with the immersogeometric FSI analysis. With an effective material model considering the collagen fibers network of heart valve leaflets, and a novel method for the THV frame isogeometric design and simulation, a biomechanically rigorous and physiologically realistic computational FSI framework is carried out to study the interaction between THVs and aortic wall. From the computed friction force analysis, the anchoring ability of THVs is estimated, which is a valuable information for clinical planning and decision making of TAVR

A Novel Self-Intersection Penalty Term for Statistical Body Shape Models and Its Applications in 3D Pose Estimation

Statistical body shape models are widely used in 3D pose estimation due to their low-dimensional parameters representation. However, it is difficult to avoid self-intersection between body parts accurately. Motivated by this fact, we proposed a novel self-intersection penalty term for statistical body shape models applied in 3D pose estimation. To avoid the trouble of computing self-intersection for complex surfaces like the body meshes, the gradient of our proposed self-intersection penalty term is manually derived from the perspective of geometry. First, the self-intersection penalty term is defined as the volume of the self-intersection region. To calculate the partial derivatives with respect to the coordinates of the vertices, we employed detection rays to divide vertices of statistical body shape models into different groups depending on whether the vertex is in the region of self-intersection. Second, the partial derivatives could be easily derived by the normal vectors of neighboring triangles of the vertices. Finally, this penalty term could be applied in gradient-based optimization algorithms to remove the self-intersection of triangular meshes without using any approximation. Qualitative and quantitative evaluations were conducted to demonstrate the effectiveness and generality of our proposed method compared with previous approaches. The experimental results show that our proposed penalty term can avoid self-intersection to exclude unreasonable predictions and improves the accuracy of 3D pose estimation indirectly. Further more, the proposed method could be employed universally in triangular mesh based 3D reconstruction

Post-Newtonian Approximation of Teleparallel Gravity Coupled with a Scalar Field

We use the parameterized post-Newtonian (PPN) formalism to explore the weak field approximation of teleparallel gravity non-minimally coupling to a scalar field $\phi$, with arbitrary coupling function $\omega(\phi)$ and potential $V(\phi)$. We find that all the PPN parameters are identical to general relativity (GR), which makes this class of theories compatible with the Solar System experiments. This feature also makes the theories quite different from the scalar-tensor theories, which might be subject to stringent constraints on the parameter space, or need some screening mechanisms to pass the Solar System experimental constraints.Comment: 15 pages, revtex4; v2: discussions added, Nucl. Phys. B in press; v3: published versio

Systematic study of proton radioactivity of spherical proton emitters within various versions of proximity potential formalisms

In this work we present a systematic study of the proton radioactivity half-lives of spherical proton emitters within the Coulomb and proximity potential model. We investigate 28 different versions of the proximity potential formalisms developed for the description of proton radioactivity, $\mathcal{\alpha}$ decay and heavy particle radioactivity. It is found that 21 of them are not suitable to deal with the proton radioactivity, because the classical turning points $r_{\text{in}}$ cannot be obtained due to the fact that the depth of the total interaction potential between the emitted proton and the daughter nucleus is above the proton radioactivity energy. Among the other 7 versions of the proximity potential formalisms, it is Guo2013 which gives the lowest rms deviation in the description of the experimental half-lives of the known spherical proton emitters. We use this proximity potential formalism to predict the proton radioactivity half-lives of 13 spherical proton emitters, whose proton radioactivity is energetically allowed or observed but not yet quantified, within a factor of 3.71.Comment: 10 pages, 5 figures. This paper has been accepted by The European Physical Journal A (in press 2019

CCFL: Computationally Customized Federated Learning

Federated learning (FL) is a method to train model with distributed data from numerous participants such as IoT devices. It inherently assumes a uniform capacity among participants. However, participants have diverse computational resources in practice due to different conditions such as different energy budgets or executing parallel unrelated tasks. It is necessary to reduce the computation overhead for participants with inefficient computational resources, otherwise they would be unable to finish the full training process. To address the computation heterogeneity, in this paper we propose a strategy for estimating local models without computationally intensive iterations. Based on it, we propose Computationally Customized Federated Learning (CCFL), which allows each participant to determine whether to perform conventional local training or model estimation in each round based on its current computational resources. Both theoretical analysis and exhaustive experiments indicate that CCFL has the same convergence rate as FedAvg without resource constraints. Furthermore, CCFL can be viewed of a computation-efficient extension of FedAvg that retains model performance while considerably reducing computation overhead