Timo Tiihonen

University of Jyväskylä | JYU · Faculty of Information Technology

Background: Temporal principal component analysis (tPCA) has been widely used to extract eventrelated potentials (ERPs) at group level of multiple subjects ERP data and it assumes that the underlying factor loading is fixed across participants. However, such assumption may fail to work if latency and phase for one ERP vary considerably across parti...

Industry 4.0 and Smart Manufacturing are associated with the Cyber-Physical-Social Systems populated and controlled by the Collective Intelligence (human and artificial). They are an important component of Critical Infrastructure and they are essential for the functioning of a society and economy. Hybrid Threats nowadays target critical infrastruct...

The cover shows a DNA‐encoded biosensor based on a Fluorescence Resonance Energy Transfer (FRET) technique named PaxTS. The biosensor consists of an LD12 domain, an LIM1234 domain, a nano‐spring and a pair of fluorescent proteins to convert the tension across paxillin to FRET efficiency in living cells, indicating that there exists a force transmis...

Paxillin is a potential participant in direct intracellular force transmission, which is considered as the foundation of cells sensing and responding to the extracellular environment. However, the detection of tension across paxillin has not been achieved due to lacking microsized tools. Herein, a paxillin tension sensor (PaxTs) based on the Fluore...

Information retrieval (IR) is known facilitator of changes ongoing in human society and vice versa. This is due to the fact that IR is a key component of the digital ecosystems, where both information providers and information consumers collaboratively address their problems with the use of technologies. Organization and design of such ecosystems d...

Temporal principal component analysis (t-PCA) has been widely used to extract event-related potentials (ERPs) at the group level of multiple subjects' ERP data. The t-PCA is, however, poorly employed to isolate ERPs from single-trial data of an individual subject. Additionally, the effects of varied trial numbers on the yields of t-PCA have not bee...

Let us consider a system and let us assume that we have some theoretical knowledge (or at least reasonable assumptions) about its behaviour. Such knowledge typically includes being aware of the underlying phenomena and recognizing the entities that describe these phenomena and their interactions. Yet, we do not necessary need to know formulae for e...

In practical applications the “complete” model, i.e., a model that contains all features that the experts in the application domain consider important, is often quite complicated and difficult to analyse mathematically. A straightforward numerical realization is often costly and may give very little qualitative understanding of the situation. It is...

Helium filled carnival balloons take off easily and can fly long distances. How high can they rise? Can they be of concern to airplanes? Now you might say that this latter question sounds a bit artificial and naive. However, helium balloons are regularly sent to the upper atmosphere for observing weather data. When designing and controlling such me...

Researchers have to operate in an increasingly competitive environment in which funding is becoming a scarce resource. Funding agencies are unable to experiment with their allocation policies since even small changes can have dramatic effects on academia. We present a Proposal-Evaluation-Grant System (PEGS) which allows us to simulate different res...

This book provides a thorough introduction to the challenge of applying mathematics in real-world scenarios. Modelling tasks rarely involve well-defined categories, and they often require multidisciplinary input from mathematics, physics, computer sciences, or engineering. In keeping with this spirit of modelling, the book includes a wealth of cros...

For the first time, we systemically analyze the influence of magneto-thermo-electromechanical effects on the band structure calculations by using the fully coupled model. We focus on three different types of quantum dots (QDs): (a) ferroelectric, (b) piezomagnetic, and (c) magnetoelectric, with and without wetting layers (WLs). We demonstrate that...

Dedicated to Professor P. Neittaanmäki on His 60th Birthday Series: Computational Methods in Applied Sciences, Vol. 27 Repin, Sergey; Tiihonen, Timo; Tuovinen, Tero (Eds.)

We quantify the influence of coupled electromechanical effects on the band structure calculations of wurtzite AlN/GaN quantum dots with wetting layers (WLs). Based on a strain dependent fully coupled 8-band k·p method, we computed eigenvalues and wavefunctions of electrons in quantum dots with WLs of different aspect ratios. These computed eigenval...

This paper focuses on finite element error analysis for problems involving both conductive and radiative heat transfers. The radiative heat exchange is modeled with a nonlinear and nonlocal term that also makes the problem non-monotone. The continuous problem has a maximum principle which suggests the use of inverse monotone discretizations. We als...

The shape optimization of an elastic body in contact with a rigid surface is considered. An existence result for optimal shapes as well as a numerical realization are stated. From several numerical results it can be seen that minimizing the total potential energy of the system leads to an even distribution of contact forces on the contact boundary,...

The optimal shape design of a two dimensional body on a rigid foundation is analyzed. The problem is how to find the boundary part of the body where the unilateral boundary conditions are assumed in such a way that a certain energy integral (total potential energy, for example) will be minimized. It is assumed that the material of the body is elast...

We study the well-posedness of a class of models describing heat transfer by conduction and radiation. For that purpose we propose an abstract mathematical framework that allows us to prove existence, uniqueness and the comparison principle for the weak solution with minimal or almost minimal a priori assumptions for the data. The theory covers dif...

In this paper we consider numerical methods for stationary free boundary problems. We start by analysing systematically different shape optimization formulations of a model problem and show how the optimality conditions relate to construction of trial type methods. Shape sensitivity analysis of the free boundary leads also to the so-called total li...

In this work we analyse a model for radiative heat transfer in materials that are conductive, grey and semitransparent. Such materials are for example glass, silicon, water and several gases. The most important feature of the model is the non-local interaction due to exchange of radiation. This, together with non-linearity arising from the well-kno...

We consider a free boundary problem where the free boundary is an interface between two subdomains. Our problem admits several formulations of different character:a non-smooth variational problem, a 'shape variational' problem or a shape optimization problem of the least squares type. Our goal is to analyze the different variants based on shape opt...

We consider the problem of deriving finite element error estimates in smooth domains. We propose to decompose the approximation error into two parts, a geometric part and a finite element part, by introducing an auxiliary problem defined in a polynomial domain approximating the original smooth domain. Some techniques to estimate the geometric part...

The use of finite elements in smooth domains leads naturally to polyhedral or piecewise polynomial approximations of the boundary. Hence the approximation error consists of two parts, geometric part and finite element part. We propose to exploit this decomposition in the error analysis by introducing an auxiliary problem defined in a polygonal doma...

We have developed a detailed mathematical model and numerical simulation tools based on the streamline upwind/Petrov-Galerkin (SUPG) finite element formulation for the Czochralski silicon crystal growth. In this paper we consider the mathematical modeling and numerical simulation of the time-dependent melt flow and temperature field in a rotational...

We introduce briefly some nonlocal models for heat transfer in conducting and radiating media. The goal is to give an idea of the general mathematical structure and related existence results for such models.

We consider both stationary and time-dependent heat equations for a non-convex body or a collection of disjoint conducting bodies with Stefan-Boltzmann radiation conditions on the surface. The main novelty of the resulting problem is the non-locality of the boundary condition due to self-illuminating radiation on the surface. Moreover, th...

We consider the stationary heat equation for a non-convex body with Stefan–Boltzmann radiation condition on the surface. The main virtue of the resulting problem is non-locality of the boundary condition. Moreover, the problem is non-linear and in the general case also non-coercive and non-monotone. We show that the boundary value problem has a max...

. In this work we analyse a model for radiative heat transfer in materials that are conductive, gray and semitransparent. Such materials are for example glass, silicon, water and several gases. The most important feature of the model is the non-local interaction due to exchange of radiation. This, together with non-linearity arising from the well-k...

In this work we consider the problem of determining the free surface for a stationary flow of inviscid fluid. We introduce several different formulations for the problem and study the numerical methods suggested by different formulations. The formulations to be studied include 'shape variational principles' where free boundary is sought after as a...

In this work we consider the problem of determining the free surface for a stationary flow of inviscid fluid. We introduce several different formulations for the problem and study the numerical methods suggested by different formulations. The formulations to be studied include 'shape variational principles' where free boundary is sought after as a...

We consider both stationary and time dependent heat equation for a non-convex body or a collection of disjoint conductive bodies with Stefan-Boltzmann radiation condition on the surface. The main virtue of the resulting problem is non-locality of the boundary condition due to self-illuminating radiation on the surface. Moreover, the problem is non-...

We consider both stationary and time dependent heat equation for a non-convex body or a collection of disjoint conductive bodies with Stefan-Boltzmann radiation condition on the surface. The main virtue of the resulting problem is non-locality of the boundary condition due to self-illuminating radiation on the surface. Moreover, the problem is non-...

. In this work we consider different formulations for a free boundary problem and analyze the related numerical methods. In particular, we formulate various shape optimization problems that are weak forms of a free boundary problem and analyze their properties using the tools of 'shape calculus'. The main result is that it is possible to influence...

In this work we consider different formulations for a free boundary problem and analyze the related numerical methods. In particular, we formulate various shape optimization problems that are weak forms of a free boundary problem and analyze their properties using the tools of 'shape calculus'. The main result is that it is possible to influence th...

In the photocopying and laser printing the ink is usually fixed to paper by using a hot fuser roll. During rolling the paper temperature rises and moisture level decreases. We present a mathematical model for coupled heat and mass transfer under rolling conditions. The water in the paper is assumed to be completely bound to the fibre framework so t...

We consider thermal deformations of transversally inhomogenous elastic plates. Thin plate equations are derived as limits of full three-dimensional models both in the linear as well as in the non-linear case with appropriate convergence proofs. In the non-linear case also the corresponding von Kármán equations are formulated. It is obtained that th...

We consider the trial methods for solving steady state free boundary problems. For two test examples (electrochemical machining and continuous casting) we discuss the convergence of a fixed point method. Moreover, using the techniques of shape optimization we introduce a modification of the method, which gives us superlinear convergence rate. This...

We propose a new incremental method for solving time dependent free boundary problems. In this work we consider the so-called quasi-steady flows, i.e. flows that are so slow that the inertial effects can be ignored but where the domain of the flow is non-cylindrical in time. Moreover, the shape of the fluid varies according to the flow velocity whi...

We consider the problem of controlling the coincidence set in connection with an obstacle problem. We shall transform the obtained optimal shape design problem into a boundary control problem with Dirichlet boundary conditions.

We propose a new incremental method for solving time dependent free boundary problems. In this work we consider the so-called quasi-steady flows, i.e. flows that are so slow that the inertia! effects can be ignored but where the domain of the flow is non-cylindrical in time. Moreover, the shape of the fluid varies according to the flow velocity whi...

In the first part we give a general existence theorem and a regularization method for an optimal control problem where the control is a domain in R**n and where the system is governed by a state relation which includes differential equations as well as inequalities. In the second part applications for optimal shape design problems governed by the D...

We consider the problem of controlling the solution of a finite element model using the nodal co-ordinates as control variables. The main emphasis is on the study of the applicability of the domain deformation method for different element types. The results are applied to a simple problem of finite element grid optimization.

In this paper we shall study dierent solution strategies for abstract form of free boundary problems. Using the tools of shape calculus we analyse dierent solution

We consider simulation of a fluid flow in a channel whose outflow boundary consists of a regular array of small identical tubes. We derive a model where the tube array is replaced by a homogeneous effective medium, the properties of which can be determined by solving a local problem in one tube. The method is applied to Stokes equations, laminar Na...

We consider the Stefan problem for a non-convex body or a collection of disjoint conductive bodies with Stefan-Boltzmann radiation condition on the surface. The main virtue of the resulting problem is nonlocality of the boundary condition due to self-illuminating radiation on the surface. Moreover, the problem is nonlinear non-monotone and in the g...