Computational surface partial differential equations

Surface partial differential equations model several natural phenomena; for example in uid mechanics, cell biology and material science. The domain of the equations can often have complex and changing morphology. This implies analytic techniques are unavailable, hence numerical methods are required. The aim of this thesis is to design and analyse three methods for solving different problems with surface partial differential equations at their core. First, we define a new finite element method for numerically approximating solutions of partial differential equations in a bulk region coupled to surface partial differential equations posed on the boundary of this domain. The key idea is to take a polyhedral approximation of the bulk region consisting of a union of simplices, and to use piecewise polynomial boundary faces as an approximation of the surface and solve using isoparametric finite element spaces. We study this method in the context of a model elliptic problem. The main result in this chapter is an optimal order error estimate which is confirmed in numerical experiments. Second, we use the evolving surface finite element method to solve a Cahn- Hilliard equation on an evolving surface with prescribed velocity. We start by deriving the equation using a conservation law and appropriate transport formulae and provide the necessary functional analytic setting. The finite element method relies on evolving an initial triangulation by moving the nodes according to the prescribed velocity. We go on to show a rigorous well-posedness result for the continuous equations by showing convergence, along a subsequence, of the finite element scheme. We conclude the chapter by deriving error estimates and present various numerical examples. Finally, we stray from surface finite element method to consider new unfitted finite element methods for surface partial differential equations. The idea is to use a fixed bulk triangulation and approximate the surface using a discrete approximation of the distance function. We describe and analyse two methods using a sharp interface and narrow band approximation of the surface for a Poisson equation. Error estimates are described and numerical computations indicate very good convergence and stability properties

Coupled bulk-surface free boundary problems arising from a mathematical model of receptor-ligand dynamics

We consider a coupled bulk-surface system of partial differential equations with nonlinear coupling modelling receptor-ligand dynamics. The model arises as a simplification of a mathematical model for the reaction between cell surface resident receptors and ligands present in the extra-cellular medium. We prove the existence and uniqueness of solutions. We also consider a number of biologically relevant asymptotic limits of the model. We prove convergence to limiting problems which take the form of free boundary problems posed on the cell surface. We also report on numerical simulations illustrating convergence to one of the limiting problems as well as the spatio-temporal distributions of the receptors and ligands in a realistic geometry

Evolving surface finite element method for the Cahn-Hilliard equation

We use the evolving surface finite element method to solve a Cahn- Hilliard equation on an evolving surface with prescribed velocity. We start by deriving the equation using a conservation law and appropriate transport for- mulae and provide the necessary functional analytic setting. The finite element method relies on evolving an initial triangulation by moving the nodes according to the prescribed velocity. We go on to show a rigorous well-posedness result for the continuous equations by showing convergence, along a subse- quence, of the finite element scheme. We conclude the paper by deriving error estimates and present various numerical examples

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

SpaceTeamSat1 Preliminary Design Document: Ground Station and Radio Communication

Preliminary design document (PDD) for the ground station (GS) and radio communication of the CubeSat mission SpaceTeamSat1 (STS1) of the TU Wien Space Team (TUST). It gives an overview of the architecture and operation of the GS as well as the RF communication protocol. Moreover, the document serves as a base for the preliminary design review (PDR)

Coupled bulk-surface free boundary problems arising from a mathematical model of receptor-ligand dynamics

We consider a coupled bulk-surface system of partial differential equations with nonlinear coupling modeling receptor-ligand dynamics. The model arises as a simplification of a mathematical model for the reaction between cell surface resident receptors and ligands present in the extracellular medium. We prove the existence and uniqueness of solutions. We also consider a number of biologically relevant asymptotic limits of the model. We prove convergence to limiting problems which take the form of free boundary problems posed on the cell surface. We also report on numerical simulations illustrating convergence to one of the limiting problems as well as the spatiotemporal distributions of the receptors and ligands in a realistic geometry

Cerebral white matter hyperintensities indicate severity and progression of coronary artery calcification

Abstract Cerebral white matter hyperintensities (WMH) have been associated with subclinical atherosclerosis including coronary artery calcification (CAC). However, previous studies on this association are limited by only cross-sectional analysis. We aimed to explore the relationship between WMH and CAC in elderly individuals both cross-sectionally and longitudinally. The study population consisted of elderly stroke- and dementia-free participants from the community-based Austrian Stroke Prevention Family Study (ASPFS). WMH volume and CAC levels (via Agatston score) were analyzed at baseline and after a 6-year follow-up period. Of 324 study participants (median age: 68 years), 115 underwent follow-up. Baseline WMH volume (median: 4.1 cm3) positively correlated with baseline CAC levels in multivariable analysis correcting for common vascular risk factors (p = 0.010). While baseline CAC levels were not predictive for WMH progression (p = 0.447), baseline WMH volume was associated CAC progression (median Agatston score progression: 27) in multivariable analysis (ß = 66.3 ± 22.3 [per cm3], p = 0.004). Ten of 11 participants (91%) with severe WMH (Fazekas Scale: 3) at baseline showed significant CAC progression > 100 during follow-up. In this community-based cohort of elderly individuals, WMH were associated with CAC and predictive of its progression over a 6-year follow-up. Screening for coronary artery disease might be considered in people with more severe WMH