Comparison of Wavelets for Adaptive Mesh Refinement

In the field of Scientific Computing there is a big focus on solving time dependent Partial Differential Equations (PDEs) as efficiently and fast as possible. In order to do so, the PDE is discretized and solved on a mesh at every time step. Adaptive mesh refinement is used to develop a mesh at every time step which is sparse and which results in an accurate approximation to the solution. Interpolating wavelets are successfully used in adaptive mesh refinement (AMR). A detailed comparison of two wavelets for AMR is done on different data sets: Donoho’s interpolating wavelet and a lifted version (also called second generation wavelets) of Donoho’s interpolating wavelet. Moreover, various ways of handling the boundaries are considered. An algorithm to construct the meshes using wavelets is tested and optimized. Donoho’s interpolating wavelet with lower order boundary stencil implementation appears to be the most accurate, whilst resulting in very high compression compared to the original mesh. Furthermore, adapting the algorithm which constructs the meshes such that it adds more points for very irregular shapes, turns out to be valuable for solutions with fast changing features. For one such PDE, Donoho’s interpolating wavelet keeps less than 5% of the points whilst having an error smaller than 10􀀀4, in other words a sparsification of 20 times. Lastly, an improvement on the inverse transform during the adaptive mesh refinement leads to promising results.Numerical Analysi

Stakeholder inclusive design for sustainable port development

It is being increasingly recognized that sustainable port development requires an integrated planning approach which includes working with nature, a stakeholder inclusive design and co-creation of values, as well as an adaptive design that can cope with future uncertainties without losing its functionality. The multi-disciplinary character of port design whereby engineering, ecological, economic and governance aspects are integrated, makes the implementation of this approach very challenging. Not surprisingly, concrete examples of port projects incorporating and demonstrating these principles are rare. This paper proposes that pilot case studies would go a long way towards the acceptance and implementation of the approach. It discusses the desirable characteristics of pilot studies (with opportunities for creating economic value), which could establish the effectiveness of this approach for sustainable port design. The ongoing UDW project "Integrated and Sustainable Port Development in Ghana" funded by NWO-WOTRO exemplifies such an inclusive pilot study and represents a significant step in bringing about a paradigm shift from a traditional approach to port development, to a stakeholder inclusive integrated approach for sustainable port development.Policy AnalysisRivers, Ports, Waterways and Dredging Engineerin

The mobile museum guide: Artwork recognition with eigenpaintings and SURF

This paper investigates the performance of eigenpaintings, SURF and a combination of both methods in a query-bypicture system dedicated to artwork images. For this purpose a database containing photographs of 17 artworks was created. These photos were taken by visitors of the exhibition \u93The VUB Art Collection \u96 On Display and in Your Hand\u94 using the camera of a mobile phone. The resulting images present several challenging aspects, including reflections, different light conditions, variations in perspective viewing conditions etc. Experiments show that the method based on eigenpaintings classifies 85% of the artworks correctly and the method based on SURF 84%. The combined classifier shows an accuracy of 88%

Classification of link-breaking and link-creation updating rules in susceptible-infected-susceptible epidemics on adaptive networks

In the classical susceptible-infected-susceptible (SIS) model, a disease or infection spreads over a given, mostly fixed graph. However, in many real complex networks, the topology of the underlying graph can change due to the influence of the dynamical process. In this paper, besides the spreading process, the network adaptively changes its topology based on the states of the nodes in the network. An entire class of link-breaking and link-creation mechanisms, which we name Generalized Adaptive SIS (G-ASIS), is presented and analyzed. For each instance of G-ASIS using the complete graph as initial network, the relation between the epidemic threshold and the effective link-breaking rate is determined to be linear, constant, or unknown. Additionally, we show that there exist link-breaking and link-creation mechanisms for which the metastable state does not exist. We confirm our theoretical results with several numerical simulations.Network Architectures and ServicesMathematical Physic

Static Unified Inelastic Model: pre- and post-yield dislocation-mediated deformation

Modelling dislocation glide over the initial part of a stress–strain curve of metals received little attention up to now. However, dislocation glide is essential to ones understanding of the fundamental relationship between inelastic deformation and the evolution of the dislocation network structure. Therefore, we present a model of dislocation-driven deformation under static loading conditions. We reproduce repeated cyclic uniaxial tensile tests on Interstitial-Free and Low-Alloy steels. The elastic mechanical behaviour is described by isotropic linear elasticity, pre-yield anelastic mechanical behaviour by a dislocation bow-out model with dissipation, and the post-yield evolution of dislocation network structure by a statistical storage model. We hypothesise that when the local anelastic compliance is lower than the global plastic compliance, deformation is mechanically recoverable, and vice versa. This hypothesis is corroborated with the classical Taylor relation. We report the relation between stable and unstable dislocation glide using this prototypical modelling framework. We find four structural variables, that are based on dislocation physics, to describe the stress–strain curve: total dislocation density, average dislocation segment length, dislocation junction formation rate, and average dislocation junction length. Firstly, we quantify the dislocation network evolution during uniaxial monotonic loading, and verify work-hardening by dislocation junction formation and a Taylor-type equation for flow. Finally, we present a semi-empirical relation for the evolution of the dislocation network structure. Which allows us to: refine the physical interpretation of the Taylor relationship, and rationalise experimental observations on apparent modulus degradation by thermomechanical processing. Both these findings circumvent the limitations of current, physics-based hardening models.Team Erik OffermanTeam Jilt Sietsm

Nucleation Sites in the Static Recrystallization of a Hot-Deformed Ni-30 Pct Fe Austenite Model Alloy

In the present study, the nucleation of static recrystallization (SRX) in austenite after hot deformation is experimentally analyzed using a Ni-30 pct Fe model alloy. In agreement with the predictions by current models, nucleation rate exhibits a strong peak, early during SRX. Whereas such an early peak is explained by current models by the saturation of nucleation sites, this condition is far from reached, even after the peak declines. In addition, triple-junction and grain-boundary sites are shown to make a quantitatively similar contribution to nucleation. However, for a given boundary between deformed grains, nucleation predominantly starts at one of the triple junctions. Triple-junction nucleation initiates by strain-induced boundary migration of the nucleus (bulging) along one of the boundaries at the junction. Annealing twin boundaries contribute negligibly to nucleation through their grain-boundary sites. By contrast, their junctions with the boundaries of the parent grains do play a relevant role. The earlier nucleation at the triple junctions is attributed to the higher dislocation density observed around them, and the energy of the boundary consumed by the bulge. Both the maximum and average number of nuclei formed per boundary between deformed grains increase with increasing boundary length.Team Erik OffermanTeam Jilt SietsmaTeam Joris Di

Extracting Learning Performance Indicators from Digital Learning Environments

In the last decades, there has been a steady adoption of digital online platforms as learning environments applied to all levels of education. This increasing adoption forces a transition in educational resources which has further been accelerated by the recent pandemic, leading to an almost complete online-only learning environment in some cases. The aim of this paper is to outline the methodology involved in setting up a framework for mapping course-specific data based on student activity to standard learning indicators, which will serve as an input to performance prediction algorithms. The process involves systematically surveying, capturing, and categorising the vast range of data available in digital learning platforms. The data are collected from two sample courses and distilled into five dimensions represented by the generic learning indicators: prior knowledge, preparation, participation, interaction, and performance. The data is weighted based on course development and teaching member’s perspectives to account for course-wise variations. The framework established will allow portability of prediction algorithms between courses and provide a means for meaningful and directed learner formative feedback. Two courses, both bachelor-level and worth 5 European Credits (ECs), that use several online learning platforms in their teaching tools have been chosen in this study to explore the nature and range of student interaction data available, accessible, and usable in a course. The first course is Electromagnetics II at Eindhoven University of Technology, and the second course is Electronics at Delft University of Technology. Both Universities are located in the Netherlands. This work is in the scope of a broader study to use such learning indicators with predictive algorithms to provide a prognosis on individual student performance. The findings in this paper will enable the realization of student performance prediction at a very early stage in the course.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic

Long-eccentricity regulated climate control on fluvial incision and aggradation in the Palaeocene of north-eastern Montana (USA)

Aggradation and fluvial incision controlled by downstream base-level changes at timescales of 10 to 500 kyr is incorporated in classic sequence stratigraphic models. However, upstream climate control on sediment supply and discharge variability causes fluvial incision and aggradation as well. Orbital forcing often regulates climate change at 10 to 500 kyr timescales while tectonic processes such as flexural (un)loading exert a dominant control at timescales longer than 500 kyr. It remains challenging to attribute fluvial incision and aggradation to upstream or downstream processes or disentangle allogenic from autogenic forcing, because time control is mostly limited in fluvial successions. The Palaeocene outcrops of the fluvial Lebo Shale Member in north-eastern Montana (Williston Basin, USA) constitute an exception. This study uses a distinctive tephra layer and two geomagnetic polarity reversals to create a 15 km long chronostratigraphic framework based on the correlation of twelve sections. Three aggradation–incision sequences are identified with durations of approximately 400 kyr, suggesting a relation with long-eccentricity. This age control further reveals that incision occurred during the approach of – or during – a 405 kyr long-eccentricity minimum. A long-term relaxation of the hydrological cycle related to such an orbital phasing potentially exerts an upstream climate control on river incision. Upstream, an expanding vegetation cover is expected because of an increasingly constant moisture supply to source areas. Entrapping by vegetation led to a significantly reduced sediment supply relative to discharge, especially at times of low evapotranspiration. Hence, high discharges resulted in incision. This study assesses the long-eccentricity regulated climate control on fluvial aggradation and incision in a new aggradation–incision sequence model.Applied Geolog

Predicting time-resolved electrophysiological brain networks from structural eigenmodes

How temporal modulations in functional interactions are shaped by the underlying anatomical connections remains an open question. Here, we analyse the role of structural eigenmodes, in the formation and dissolution of temporally evolving functional brain networks using resting-state magnetoencephalography and diffusion magnetic resonance imaging data at the individual subject level. Our results show that even at short timescales, phase and amplitude connectivity can partly be expressed by structural eigenmodes, but hardly by direct structural connections. Albeit a stronger relationship was found between structural eigenmodes and time-resolved amplitude connectivity. Time-resolved connectivity for both phase and amplitude was mostly characterised by a stationary process, superimposed with very brief periods that showed deviations from this stationary process. For these brief periods, dynamic network states were extracted that showed different expressions of eigenmodes. Furthermore, the eigenmode expression was related to overall cognitive performance and co-occurred with fluctuations in community structure of functional networks. These results implicate that ongoing time-resolved resting-state networks, even at short timescales, can to some extent be understood in terms of activation and deactivation of structural eigenmodes and that these eigenmodes play a role in the dynamic integration and segregation of information across the cortex, subserving cognitive functions.Network Architectures and Service