Proceedings of the Eindhoven FASTAR Days 2004 : Eindhoven, The Netherlands, September 3-4, 2004

The Eindhoven FASTAR Days (EFD) 2004 were organized by the Software Construction group of the Department of Mathematics and Computer Science at the Technische Universiteit Eindhoven. On September 3rd and 4th 2004, over thirty participants|hailing from the Czech Republic, Finland, France, The Netherlands, Poland and South Africa|gathered at the Department to attend the EFD. The EFD were organized in connection with the research on finite automata by the FASTAR Research Group, which is centered in Eindhoven and at the University of Pretoria, South Africa. FASTAR (Finite Automata Systems|Theoretical and Applied Research) is an in- ternational research group that aims to lead in all areas related to finite state systems. The work in FASTAR includes both core and applied parts of this field. The EFD therefore focused on the field of finite automata, with an emphasis on practical aspects and applications. Eighteen presentations, mostly on subjects within this field, were given, by researchers as well as students from participating universities and industrial research facilities. This report contains the proceedings of the conference, in the form of papers for twelve of the presentations at the EFD. Most of them were initially reviewed and distributed as handouts during the EFD. After the EFD took place, the papers were revised for publication in these proceedings. We would like to thank the participants for their attendance and presentations, making the EFD 2004 as successful as they were. Based on this success, it is our intention to make the EFD into a recurring event. Eindhoven, December 2004 Loek Cleophas Bruce W. Watso

Ultrafast Spectroscopic Studies of Solution-Processing Organic Photovoltaic Materials and Devices

Organic solar cells (OSCs) have potential applications in wearable electronics as well as in-door and building-integrated photovoltaics, owing to features such as low-temperature processing, light weight and flexibility, and synthetic versatility. Due to the development of new materials systems with unique optoelectronic properties, a breakthrough in the OSC performance has been achieved. However, knowledge of the underlying mechanism still lags behind. Such understanding is essential for further development of organic photovoltaics. The needed comprehensive investigation mainly comes from studying the carrier dynamics on promising OSC systems. To this aim, the used tool kits, ultrafast spectroscopic methods, are the subject of this thesis. First three chapters of the thesis present the general paradigm of photoconversion in OSCs and outlines the key models used to describe their photovoltaic performance. The ability of OSCs to generate electrical current in response to absorbing sunlight greatly differs, depending on materials and the following device fabrication methods. In the device operation, the performance is related to the conversion efficiency from molecular excited states into charge carriers. Chapter 2 presents a historical review of different material combination, device architecture and key processes relevant for solar cell performance. This leads to the key questions that this thesis addresses: which molecular properties are most important for photoconversion in OSCs? How much energy is required to convert from molecular excited states to free charges? What are the optimal preparation procedure and microstructure of OSC devices? Chapter 3 gives an overview of spectroscopic tools used to address these questions. Chapters 4 to 8 target above questions in application to different material systems, from the ‘classical’ broadly studied polythiophene-fullerene blends to the high-performance OSC devices based on non-fullerene acceptors (NFAs). Firstly, the rate of exciton dissociation is studied in state-of-the-art organic blends with NFAs. The charge generation is found to be slow (ps), in sharp contrast with the ultrafast timescales in traditional blends based on fullerene acceptors. Secondly, a new technique is developed, namely temperature-dependent pump-push photocurrent spectroscopy, which is able to measure the strength of interaction between charges in working OSCs. This technique is applied to research which factors govern the dissociation of molecular excited states in fullerene-based blends. Thirdly, recombination processes are studied using a set of ultrafast techniques, focusing on their effect on device performance, and the dependence on processing conditions and used materials. Finally, a new method ‘via sequential deposition’ is demonstrated for fabrication of efficient NFA-based devices. We discuss the properties of OSCs fabricated by this method and the potential for its commercialisation.China Scholarship Council (No. 201503170255

Psychophysics, Gestalts and Games

International audienceMany psychophysical studies are dedicated to the evaluation of the human gestalt detection on dot or Gabor patterns, and to model its dependence on the pattern and background parameters. Nevertheless, even for these constrained percepts, psychophysics have not yet reached the challenging prediction stage, where human detection would be quantitatively predicted by a (generic) model. On the other hand, Computer Vision has attempted at defining automatic detection thresholds. This chapter sketches a procedure to confront these two methodologies inspired in gestaltism. Using a computational quantitative version of the non-accidentalness principle, we raise the possibility that the psychophysical and the (older) gestaltist setups, both applicable on dot or Gabor patterns, find a useful complement in a Turing test. In our perceptual Turing test, human performance is compared by the scientist to the detection result given by a computer. This confrontation permits to revive the abandoned method of gestaltic games. We sketch the elaboration of such a game, where the subjects of the experiment are confronted to an alignment detection algorithm, and are invited to draw examples that will fool it. We show that in that way a more precise definition of the alignment gestalt and of its computational formulation seems to emerge. Detection algorithms might also be relevant to more classic psychophysical setups, where they can again play the role of a Turing test. To a visual experiment where subjects were invited to detect alignments in Gabor patterns, we associated a single function measuring the alignment detectability in the form of a number of false alarms (NFA). The first results indicate that the values of the NFA, as a function of all simulation parameters, are highly correlated to the human detection. This fact, that we intend to support by further experiments , might end up confirming that human alignment detection is the result of a single mechanism

Registration of histology and magnetic resonance imaging of the brain

Combining histology and non-invasive imaging has been attracting the attention of the medical imaging community for a long time, due to its potential to correlate macroscopic information with the underlying microscopic properties of tissues. Histology is an invasive procedure that disrupts the spatial arrangement of the tissue components but enables visualisation and characterisation at a cellular level. In contrast, macroscopic imaging allows non-invasive acquisition of volumetric information but does not provide any microscopic details. Through the establishment of spatial correspondences obtained via image registration, it is possible to compare micro- and macroscopic information and to recover the original histological arrangement in three dimensions. In this thesis, I present: (i) a survey of the literature relative to methods for histology reconstruction with and without the help of 3D medical imaging; (ii) a graph-theoretic method for histology volume reconstruction from sets of 2D sections, without external information; (iii) a method for multimodal 2D linear registration between histology and MRI based on partial matching of shape-informative boundaries

Lattice Boltzmann Methods for Partial Differential Equations

Lattice Boltzmann methods provide a robust and highly scalable numerical technique in modern computational fluid dynamics. Besides the discretization procedure, the relaxation principles form the basis of any lattice Boltzmann scheme and render the method a bottom-up approach, which obstructs its development for approximating broad classes of partial differential equations. This work introduces a novel coherent mathematical path to jointly approach the topics of constructability, stability, and limit consistency for lattice Boltzmann methods. A new constructive ansatz for lattice Boltzmann equations is introduced, which highlights the concept of relaxation in a top-down procedure starting at the targeted partial differential equation. Modular convergence proofs are used at each step to identify the key ingredients of relaxation frequencies, equilibria, and moment bases in the ansatz, which determine linear and nonlinear stability as well as consistency orders of relaxation and space-time discretization. For the latter, conventional techniques are employed and extended to determine the impact of the kinetic limit at the very foundation of lattice Boltzmann methods. To computationally analyze nonlinear stability, extensive numerical tests are enabled by combining the intrinsic parallelizability of lattice Boltzmann methods with the platform-agnostic and scalable open-source framework OpenLB. Through upscaling the number and quality of computations, large variations in the parameter spaces of classical benchmark problems are considered for the exploratory indication of methodological insights. Finally, the introduced mathematical and computational techniques are applied for the proposal and analysis of new lattice Boltzmann methods. Based on stabilized relaxation, limit consistent discretizations, and consistent temporal filters, novel numerical schemes are developed for approximating initial value problems and initial boundary value problems as well as coupled systems thereof. In particular, lattice Boltzmann methods are proposed and analyzed for temporal large eddy simulation, for simulating homogenized nonstationary fluid flow through porous media, for binary fluid flow simulations with higher order free energy models, and for the combination with Monte Carlo sampling to approximate statistical solutions of the incompressible Euler equations in three dimensions

Understanding the Optical and Photophysical Properties of Organic and Hybrid Macromolecules and Polymers for Solar Cell Application

Organic solar cell materials represent a better sustainable alternative relative to inorganic materials in terms of lower cost, ease of large-scale processing, better absorptivity, ease of tunability, and unique flexibility so as to be used on different kinds of surfaces. With the knowledge of the fundamental molecular structure of an organic solar cell material, scientists and engineers can predict the electronic and optically-excited properties. Hence, understanding the structure-property-function relationships is paramount in optimizing the solar cell device performance. This thesis is structured into two sections. The first section focuses on electron acceptors in the active layer of bulk heterojunction (BHJ) device architectures, and the second section discuses organic and hybrid electron donors. In the first section, the optical and photophysical properties of several structural variations of a special class of non-fullerene acceptor compound – perylene diimide (PDI), are described in substantive details with a number of studies. In the active layer, this material functions as the electron acceptor, and acts in tandem as an excellent light-harvester. The first study on intramolecular singlet exciton fission (iSEF) in PDI trimers – the generation of two triplet charges from one photogenerated singlet, seeks to elucidate the important structural features required to obtain high yield triplet formation as a result of multiexciton generation and subsequent separation in multichromophoric PDI systems. Time-resolved spectroscopic measurements were used to show how the flexibility of the π-bridge connections in these multichromophoric PDI systems, strongly affect the triplet yield and triplet formation rate. The results obtained showed that the weak electronic coupling observed in the twisted PDI trimer is necessary to activate iSEF in multichromophoric systems. The next chapter is about the effect of ring-fusion on the optically-excited properties of N-annulated thiophene π-bridged PDI dimers. The results of this study show that ring-fusion favors ultrafast photoinduced intramolecular charge transfer (CT) and opens up the triplet excited state deactivation pathway that was absent in the unfused dimer. The triplets were formed via spin-orbit CT intersystem crossing pathway owing to the strong electronic coupling present in the fused-ring thiophene π-bridged dimer. The final chapter about PDIs involves two analogous positional isomers, exhibiting twisted vs planar geometries. The results confirm an efficient and faster intramolecular CT mechanism (symmetry-breaking) taking place in the planar PDI dimer, leading to better device performance despite strong aggregation effects. The second section involves the electron-donating portion of the active layer of BHJ devices. For donor polymers, the influence of furan vs thiophene π-bridge heterocycles and linear vs bulky sidechains on the optical properties of donor–π-bridge–acceptor polymers, was investigated. The results showed that the furan π-bridge polymer displayed better solar absorptivity and showed a more planar polymeric backbone that correlated to better CT and longer excitonic lifetimes. Also, the linear sidechain polymers showed improved solution-processability leading to better photophysical properties, like longer fluorescence lifetime, relative to the bulky sidechain polymers in BHJs. The final chapter of this dissertation covers three structural variations (Cube, Half and Corner) of hybrid silsesquioxanes, functionalized with donor chromophore(s) at the edge(s) of the cage unit. Improved excitation energy transport and ultrafast CT was observed in the Cube compound relative to the Half and Corner systems attributed to strong electronic coupling. A detailed summary of this dissertation alongside a set of molecular geometry guidelines for structure-function relationships and future direction, was provided.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/167973/1/kizmadu_1.pd