Overview
Welcome to the PhD Seminar in Mathematics at RICAM.
The seminar is intended for PhD students in mathematics at RICAM and JKU Linz, offering a forum to present their research, exchange ideas, engage in academic discussions with colleagues, and prepare for their PhD defenses.
The seminar is held on Mondays, twice a month, from 2:00 PM to 3:00 PM.
Schedule
This schedule is for the Winter Semester 2025-2026:
| Date | Speaker |
|---|---|
| Mon 20.10.2025 | Fatima Hasanova |
| Mon 03.11.2025 | Philipp Carsten Hornung |
| Mon 17.11.2025 | Michalis Kokkinos |
| Mon 01.12.2025 | Michael Winkler |
| Mon 15.12.2025 | Yildiz Oruklu |
| Mon 12.01.2026 | Luca Pasini |
| Mon 26.01.2026 | Jan-Michael Holzinger |
Former Seminars
Date: January 26, 2026
Speaker: Jan-Michael Holzinger
Title: Construction of Hadamard matrices via Legendre pairs
Description: Hadamard matrices are central objects in combinatorics with applications in coding theory and cryptography, yet their existence is not fully understood. This talk presents construction methods based on Legendre pairs, sequences with prescribed periodic autocorrelation properties. We review how binary Legendre pairs yield Hadamard matrices of order \(2\ell+ 2\) and explain why unresolved Hadamard orders correspond to open cases for binary pairs. We then extend the framework to quaternary (complex) Hadamard matrices and quaternary Legendre pairs. The talk concludes with a short discussion of constructions for odd and even lengths, highlighting recent progress using compression techniques.
References:
Cohn (1965); Fletcher–Gysin–Seberry (2001); Kotsireas–Winterhof (2024); Kotsireas et al. (2023); Jedwab–Pender (2025).
Bio: I am a Senior Lecturer at Johannes Kepler University (JKU) Linz, affiliated with the Department for STEM (MINT) Didactics, where I teach mathematics primarily in the Artificial Intelligence program and in Teacher Education Studies (Mathematics). In addition, I am a PhD student at JKU, supervised by Arne Winterhof (first supervisor) and Christoph Koutschan (second supervisor), both at RICAM, with a research focus on Hadamard matrices. Outside my academic work, I enjoy spending time with my family and friends. Few things compare to watching the sunrise from a mountaintop after a hike with close friends.
Date: January 12, 2026
Speaker: Luca Pasini
Title: Mathematical Modelling of Cardiac Pathologies and Treatments
Description: Cardiovascular diseases are the leading cause of death worldwide, accounting for nearly one-third of all fatalities [1]. This statistic has driven extensive research efforts to find effective solutions. In this context, advances in computational modeling have introduced "in silico" approaches as powerful tools to complement and enhance traditional experimental pipelines [2].
In this talk, we explore the application of mathematical modeling to the study of two distinct cardiac diseases: Cardiac Allograft Vasculopathy (CAV) and cardiac arrhythmias.
CAV represents a major cause of late graft failure in heart transplant recipients [3]. To investigate the mechanisms underlying this pathology, a multiscale computational framework has been developed, integrating cellular and tissue level analyses. In particular, the model focuses on lymphocyte transport, which is described by a convection–diffusion equation to simulate lymphocyte migration within the bloodstream.Cardiac arrhythmias, on the other hand, are associated with irregular heart rhythms and are commonly treated through catheter-based ablation prcedures. Among the available techniques, Pulsed Field Ablation (PFA) has recently emerged as a promising approach to improve treatment efficacy and safety [4]. The goal of my PhD project is to develop a time-dependent mathematical model that simulates the ablation process and reproduces the cardiac tissue response using the bidomain equations.
References:
[1] Rebecca C. Woodruff et al. “Trends in Cardiovascular Disease Mortality Rates and Excess Deaths, 2010–2022”. In: American Journal of Preventive Medicine 66 (4 Apr. 2024), pp. 582–589. ISSN: 18732607. DOI: 10.1016/j.amepre.2023.11.009.
[2] Anna Corti et al. Multiscale Computational Modeling of Vascular Adaptation: A Systems Biology Approach Using Agent-Based Models. Nov. 2021. DOI: 10.3389/fbioe.2021.744560.
[3] Jordan S. Pober et al. Cardiac allograft vasculopathy: Current review and future research directions. Nov. 2021. DOI: 10.1093/cvr/cvab259.
[4] Chun Julian et al. “State-of-the-art pulsed field ablation for cardiac arrhythmias: ongoing evolution and future perspective”. In: Europace 26 (6 June 2024). ISSN: 15322092. DOI: 10.1093/europace/euae134.
Bio: I am originally from Turin, where I completed my entire educational background, earning both my Bachelor’s and Master’s degrees in Biomedical Engineering at the Politecnico di Torino. During my Master’s thesis, I moved to Houston, Texas (USA), where I spent nine months developing a computational multiscale model to investigate Cardiac Allograft Vasculopathy.
Since September, I have joined the Mathematical Methods in Medicine and Life Sciences group under the supervision of Argyrios Petras, focusing on the computational modeling of Pulsed Field Ablation (PFA) and its effects on cardiac tissue.
Outside the lab, I enjoy spending time outdoors, especially climbing and mountain adventures. With the Alps so close to Linz, I’m happy to keep pursuing this passion.
Date: December 15, 2025
Speaker: Yildiz Oruklu
Title: Layer Adapted Time of Flight Calculation using Interpolation for Medical Ultrasound Imaging
Description: Medical ultrasound images are frequently reconstructed using simplifying assumptions regarding acoustic wave propagation. A prevalent assumption is that sound speed is uniform across the imaging medium. However, different tissue types posess varying sound speeds, which leads to image distortions and defocusing. This talk introduces a precise and computationally efficient method for ultrasonic ray tracing in layered media. We present a geometrical acoustics based algorithm that corrects aberrations in layered media using a modified time-of-flight (ToF) calculation additionally considering sound speed variations and the resulting refraction effects [1]. The focusing delays, required for the calculation of the ultimate image, are corrected using accurate ToF results obtained from a nonlinear system of the equations, which was derived using geometrical acoustics. Our interpolation method extends traditional bilinear interpolation by using annular sector area ratios to establish generalized barycentric coordinates, facilitating effective interpolation over smoothly curved geometries. When compared to ground truth time-of-flight values, our method consistently achieves errors small enough to be negligible when applied in image reconstruction. This result demonstrates that our method makes a step towards improved real-time aberration correction in ultrasound imaging
References:
[1] S. Hackl, S. Hubmer, and R. Ramlau. A geometrical acoustics based focusing algorithm for layered media in medical ultrasound, oct 2025
Bio: Yildiz Oruklu is a PhD researcher at the Johann Radon Institute for Computational and Applied Mathematics (RICAM), working within the Christian Doppler Laboratory for Mathematical Modeling and Simulation of Ultrasound in Medicine (MaMSi). Her research focuses on inverse problems and computational imaging, in particular on tomographic reconstruction, mollifier methods, and the Linear Functional Strategy (LFS). She is currently developing and analyzing algorithms for ultrasound time-of-flight modeling and limited-angle CT reconstruction.
Date: December 1, 2025
Speaker: Michael Winkler
Title: On the generalized homotopy approach in multiobjective optimization
Description: The Pareto curve of a multicriteria optimization problem can be interpreted as a zero curve of the homotopy map which is derived from the scalarization of the underlying vector-valued objective. Numerically tracing the homotopy curve thus allows for an efficient computation of candidates for Pareto optimal points. The conventional approach however fails in connecting the sections of different curvature of a nonconvex Pareto curve. Generalizing the homotopy map and introducing a (varying) local parametrization vector enables tracing the curve past inflection points. We present preliminary numerical results for benchmark problems and current challenges.
Bio: I am a PhD student at RICAM supervised by Peter Gangl. My (work-related) research interests are topology optimization, numerical methods in optimization and continuation methods. In my abundant spare time as a PhD student I enjoy going for a run, playing music, drinking coffee, going for a beer, drinking more coffee and watching the stars at night (because I cannot fall asleep due to too much coffee).
Date: November 17, 2025
Speaker: Michalis Kokkinos
Title: Elementary methods and the sum-product problem
Description: In this talk we are planning to explore how elementary methods are used in Additive Combinatorics to produce strong results regarding the growth of some sets. We will start by introducing the sum-product problem, which says that either the set of all distinct pairwise sums or the set of all distinct pairwise products determined by a finite set of real (or even complex) numbers must be almost as big as possible. A beautiful elementary argument of Solymosi will be presented, that improved the previous world record on the exponent of the sum-product problem significantly. We will proceed by investigating how the elementary method of "squeezing" is used to produce strong results about the growth of other sets of real numbers.
Bio: I am now a second-year PhD student at the Institute of Algebra, under the supervision of Oliver Roche-Newton. I moved to Austria after completing my studies in the United Kingdom, at the University of Manchester and the University of Oxford. I am fascinated by number theory, particularly Additive Combinatorics, where I focus on sum-product estimates and discrete geometry. When I’m not in the office, you can usually find me at the gym or travelling.
Date: November 3, 2025
Speaker: Philipp Carsten Hornung (University of Copenhagen, Sweden)
Title: Mean-field approximations in insurance
Description: When modelling the insurance liabilities of an individual, which is part of a group of dependent individuals, the calculation of said liabilities leads to a computationally challenging many-body problem. However, by adopting a mean-field approach, this many-body problem can be approximated by a non-linear one-body problem.
In this talk, we focus on insurance liabilities modelled as (conditional) expectations of functionals of an underlying jump process. The many-body problem corresponds to solving a high-dimensional system of coupled linear integro-differential equations, while the non-linear one-body problem corresponds to solving a low-dimensional system of non-linear integro-differential equations. Under certain regularity assumptions we show that the insurance liability, modelled as either unconditional or conditional expectation, converges to its mean-field approximation as the number of individuals in the group goes to infinity. Additionally, we examine examples from both life- and non-life insurance.
Bio: I am a third-year PhD student at the University of Copenhagen, currently visiting Associate Professor Dr. Sascha Desmettre. My field of study is actuarial mathematics, and my research interests include design of pension products and multistate modelling.
Date: October 20, 2025
Location: Room 416-2, at RICAM
Speaker: Fatima Hasanova
Title: Isogeometric multigrid methods for the biharmonic equation on multi-patch domains
Description: In this talk, we explore the development and analysis of multigrid solvers for biharmonic equations discretized using isogeometric analysis (IGA). Our focus lies on handling C¹-smooth multi-patch domains, which can be used for fourth-order partial differential equations (PDEs). Such problems arise in simulations of structural properties of thin plates and shell structures, discretized with multi-patch spline parameterizations.
Following the works [1] and [3], we consider analysis-suitable G¹multi-patch parametrizations that ensure C¹-smooth discretizations. Building on the robust multigrid framework introduced in [4], we investigate efficient two-level refinement relations and analyze the block structures of smoothing matrices to improve computational performance. Moreover, we aim to extend the methodology to C¹-smooth constructions over arbitrary multi-patch surfaces as discussed in [2].
Through numerical experiments on a two-patch domain, we aim to compare the performance of different multigrid solver setups. Additionally, we examine how the underlying spline parameterization influences convergence of the solver.
REFERENCES
[1] A. Collin, G. Sangalli, T. Takacs, Analysis-suitable G¹ multi-patch parametrizations for C¹ isogeometric spaces, Computer Aided Geometric Design, 47 (2016) 93–113.
[2] A. Farahat et al., Isogeometric analysis with C¹-smooth functions over multi-patch surfaces, Computer Methods in Applied Mechanics and Engineering, 403, Part A (2023) 115706.
[3] M. Kapl, G. Sangalli, T. Takacs, Dimension and basis construction for analysis-suitable G¹ two-patch parameterizations, Computer Aided Geometric Design, 52–53 (2017) 75–89.
[4] J. Sogn, S. Takacs, Robust multigrid solvers for the biharmonic problem in isogeometric analysis, Computers & Mathematics with Applications, 77, Issue 1 (2019) 105–124.
Bio: I am a second-year PhD student at RICAM in the Geometry in Simulations group, working under the supervision of Dr. Thomas Takacs. My research interests include the biharmonic equation, Kirchhoff–Love plate theory, isogeometric analysis, and the multigrid method. In my spare time, I enjoy reading, doing yoga, and listening to music.
Former Seminars (winter semester 2024-2025)
Date: January 13, 2025
Speaker: Corinna Perchtold (JKU)
Title: Precipitation and mortality modeling in Austria
Description: In this talk, I will provide a brief introduction to the field of Spatial Statistics. Following this, I will focus on precipitation modeling in Austria. Specifically, I will present a spatio-temporal generalised additive model to investigate whether precipitation patterns have changed over two 10-year periods within the last 50 years. The analysis includes three scenarios: monthly mean precipitation, monthly maximum precipitation, and the maximum length of a dry spell per month. These are modeled using gamma, blended generalised extreme value, and negative binomial distributions, respectively. By comparing the periods 2013–2022 and 1973–1982, I will highlight changes in precipitation patterns based on the model outputs. To conclude, I will offer an outlook on mortality modeling in Austria. This will introduce a different type of spatial data and new challenges in the field of statistical modeling.
Bio: My name is Corinna. I am a fourth year PhD student at the Institute of Stochastics at JKU. My research interests are about statistical modeling, data analysis, etc. in any kind of applied field. My favorite spots at the university, aside from my green office, are LUI, where I enjoy meeting up with friends, and the gym.
Date: December 16, 2024
Speakers: Argyrios Petras and Sumaia Saad Eddin
Title: Plans for the Summer and Winter Semesters 2025
Download: Presentation slides
Date: December 2, 2024
Speaker: Lukas Weissinger (RICAM)
Title: Singular Value and Frame Decomposition-based Reconstruction for Atmospheric Tomography
Description: Atmospheric tomography, the problem of reconstructing atmospheric turbulence profiles from wavefront sensor measurements, is an integral part of many adaptive optics systems used for enhancing the image quality of ground-based telescopes. Singular-value and frame decompositions of the underlying atmospheric tomography operator can reveal useful analytical information on this inverse problem, as well as serve as the basis of efficient numerical reconstruction algorithms. In this talk, we extend existing singular value decompositions to more realistic Sobolev settings including weighted inner products, and derive an explicit representation of a frame-based (approximate) solution operator. These investigations form the basis of efficient numerical solution methods, which we analyze via numerical simulations for the challenging, real-world Adaptive Optics system of the Extremely Large Telescope using the entirely MATLAB-based simulation tool MOST.
Bio: I am a third-year PhD-student in the Transfer Group, under the supervision of Prof. Ramlau. My research interests include imaging sciences, regularization theory and numerical realizations of regularization methods. In my free time I like playing hockey, concerts, cooking and enjoying nature.
Date: November 18, 2024
Speaker: Devika Khurana (JKU)
Title: First-passage time of SDEs to time-varying thresholds and its applications
Description: First-passage time is a fundamental concept in stochastic processes, representing the time it takes for a process to reach a specified threshold for the first time. Often considering a time-varying threshold is essential for accurately modeling the system, as it provides a more accurate and adaptable framework. With this talk, I am going to present an exact simulation method, that has been developed for constant thresholds and detail our extension to time-varying thresholds. Further, I present two applications using this method to simulate (i) spike times of a neuron and (ii) price of barrier options in finance.
Bio: I am a PhD student at Institute of Stochastics, working under supervision of Prof. Dr. Evelyn Buckwar. My research interests include first-passage time, stochastic differential equations and numerical analysis. In my spare time I enjoy cooking, listening to music and spending quality time with my friends and family.
Date: November 4, 2024
Speaker: Michael Winkler (RICAM)
Title: Continuation methods for higher-order density-based topology optimization
Description: We aim to solve a topology optimization problem where the distribution of material in the design domain is represented by a density function.
To obtain candidates for local minima, we want to solve the first order optimality system via Newton's method. This requires the initial guess to be sufficiently close to the a priori unknown solution. Introducing a stepsize rule often allows for less restrictions on the initial guess while still preserving convergence. In topology optimization one typically encounters nonconvex problems where this approach might fail. We therefore opt for a homotopy (continuation) approach which was first introduced in the 1980s and is based on solving a sequence of parameterized problems to approach the solution of the original problem.
We show preliminary numerical results and current challenges.
Bio: I am a PhD student at RICAM supervised by Peter Gangl. My (work-related) research interests are topology optimization, numerical methods in optimization and continuation methods. In my abundant spare time as a PhD student I enjoy going for a run, playing music, drinking coffee, going for a beer, drinking more coffee and watching the stars at night (because I cannot fall asleep due to too much coffee).
Date: October 21, 2024
Speaker: Amira Meddah (JKU)
Title: Stochastic Hybrid Dynamical Systems for Simulating Low-Grade Glioma Evolution
Description: Gliomas stand out as the most common and aggressive type of brain tumours, characterised by their rapid cell growth and invasive behaviour into adjacent brain tissue. In this work, we present a comprehensive study of glioma progression through several mathematical models that capture both microscopic and macroscopic levels, providing insights into their progression dynamics.
Bio: I am a PhD student at the Stochastic Institute, under the supervision of Professor Evelyn Buckwar. My research focuses on modelling and simulating the growth and invasion of gliomas (a type of brain tumours). Originally from Tunisia, I enjoy watching anime and spending quality time with friends and family over good meals. I am also an enthusiastic escape room participant, enjoying the challenge and puzzle-solving they offer.
Date: October 7, 2024
Speaker: Stefan Tyoler (RICAM)
Title: Adaptive mesh refinement with non-matching Isogeometric multi-patch domains
Description: In 2008, Tom Hughes et al. introduced the concept of Isogeometric Analysis (IgA) with the goal of utilizing B-splines to unify design (CAD) and numerical analysis. Another advantage of employing B-splines is the enhanced smoothness in the approximation of numerical solutions. In this talk, we discuss arising challenges by combining the concept of IgA with local mesh refinement, which is crucial in the approximation of solutions of reduced regularity. Specifically, we discuss the treatment of emerging hanging nodes and introduce an efficient domain decomposition solver.
Bio: I am a PhD student in the group "Computational methods for PDE's" under the supervision of Stefan Takacs from the NuMa Institute of JKU. The topic of my PhD is the efficient implementation of a local mesh refinement strategy in the context of multi-patch Isogeometric Analysis (IgA). I am 28 years old and I was born here in Linz. In my freetime I like to go hiking or skiing in the mountains (obviously) and also bouldering or playing videogames at home :-).
Date: September 23, 2024
Speaker: Minha Anees (RICAM)
Title: Enhancing the efficacy of radiofrequency ablation: developing in-silico human model for improved treatment outcomes.
Description: Radiofrequency ablation (RFA) is a minimally invasive procedure used to treat abnormal electrical signals that cause cardiac arrhythmias. During RFA, the tip electrode of a catheter delivers radiofrequency current at a frequency of 500 kHz. This electrical current flows through the resistive volume, which includes myocardial tissue and blood, and reaches a dispersive patch positioned on the patient’s skin, typically on the back or thigh. In this talk, I will present the development of highly realistic in-silico model of human patient, integrating both anatomy and physiology to enhance the efficacy of the RFA procedure, with the goal of improving treatment outcomes and optimizing procedural parameters.
Bio: I am a PhD student supervised by Argrios Petras and co-supervised by Luca Gerardo-Giorda. My research focuses on mathematical modelling, particularly in radio frequency ablation (RFA), using imaging data. My interests include developing models that simulate the physical processes involved in RFA, with the goal of improving accuracy and outcomes in medical treatments.
Date: September 9, 2024
Speaker: Yisen Wang (RICAM)
Title: WZ-Pair in Combinatorial Identities
Description: Wilf-Zeilberger pairs are fundamental in the algorithmic theory of Wilf and Zeilberger for computer-generated proofs of combinatorial identities. In this talk, we will introduce how it works to prove some known identities and also helps to discover new identities. It interests us that the universal structure of WZ-pairs in the summation case as well as the differential case.
Bio: I am a PhD student co-supervised by Christoph Koutschan (RICAM, Austria) and Shaoshi Chen (AMSS, China). My research interests are symbolic computation (symbolic integration and summation) and combinatorics (Wilf-Zeilberger method).
Contact
If you have any questions or need further information, please feel free to reach out to us at
Email: sumaia.saad-eddin(at)ricam.oeaw.ac.atorargyrios.petras(at)ricam.oeaw.ac.at
Office: Room 409, or Room 431: (RICAM, SP2, 4th floor).
We look forward to your participation!
Organizers: Sumaia Saad Eddin and Argyrios Petras