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Chips die voelen: Volledig geïntegreerde bio-geïnspireerde elektronische huidsystemen
No full textTactile sensing is fundamental yet underestimated means for humans and robots to interact with the physical environment. Neuromorphic skin, which mimics the behavior and mechanical properties of the human tactile perception proves to be a more power-efficient approach. Previous research on neuromorphic skin, guided by mimicking simple receptive fields of monkeys, rely on a coarse sensor spatial resolution (>1mm) and a 1:1 sensor-to-neuron connection. Mimicking complex receptive fields in human skins, containing multiple highly-sensitive zones, however requires sub-mm sensor spatial resolution with many-to-one sensor-to-neuron connections. Quick estimates yield a required 10x density improvement of sensors over current state of the art. This increased sensor and consequently readout density requirement requires novel low-power, area-efficient readout while integrated on a flexible substrate.status: Accepte
Who punishes the government? Income-based disparities in economic voting
No full textEconomic voting theory posits that electoral outcomes are influenced by economic performance: voters reward incumbent parties when the economy performs well and punish them when economic conditions deteriorate. Traditionally, this theory assumes that voters react uniformly to economic conditions. However, this study challenges that notion by exploring how income groups differ in holding incumbents accountable. We hypothesize that lower-income voters who are more vulnerable to economic downturns, and higher-income voters, insulated from personal financial risk but with more available assets, will react differently when economic conditions change. Through analyzing multilevel models based on the Comparative Study of Electoral Systems (CSES), we find that higher-income voters give more weight to economic evaluations when punishing or rewarding incumbent parties. Our results underscore voter heterogeneity in economic voting, suggesting that incumbents may disproportionately respond to the interests of wealthier voters.status: Publishe
Fracture-related infection: op weg naar diagnostische uniformiteit en geoptimaliseerde behandelingsstrategieën
No full textPart 1: Diagnosis In 2018, the consensus definition for fracture-related infection (FRI) has been introduced. The FRI consensus definition consists of a combination of clinical, radiological, blood, and microbiological parameters in order to diagnose infections in injured patients who sustained a fracture. The newly proposed definition is gradually acknowledged and implemented worldwide. An important next step will be to establish prospectively whether the FRI consensus definition is truly a valid construct to define infection after fracture treatment. Therefore, a prospective study will be conducted evaluating surgical wounds after fracture management (Chapter 1). Furthermore, I already performed an international multicenter study comparing the FRI consensus definition with the Centers for Disease Control and Prevention (CDC) Surgical Site Infection criteria (SSI) in order to assess the value of both definitions in diagnosing infections after operative fracture treatment (Chapter 2). Part 2: Treatment FRI treatment can be challenging with regard to involvement of comorbidities, medication, infection site, soft tissue status, extent of infection, implants used, and resistance of microorganisms. For some patients one-stage reoperation with irrigation and debridement followed by systemic antibiotic treatment is sufficient to treat the infection. Unfortunately, many patients need multiple debridement operations to control the infection. A randomized controlled trial will be performed to investigate whether the application of local antibiotics reduces the chance of persistent and recurrent infection (Chapter 3). Extensive debridement of all dead tissue is often associated with formation of a bone and soft tissue defect (dead space). Proper dead space management (i.e with bone void fillers) is important to control bacterial colonization and promote bone healing. However, methods used for dead space management vary widely. A cross-sectional study will be performed to evaluate currently used treatment strategies and associated success rates in terms of bone and soft tissue healing and eradication of the infection (Chapter 4). Part 3: Outcome To evaluate the current antibiotic treatment protocols, I already performed a multicenter retrospective study evaluating the relationship between the antibiotic regime and the risk on recurrence of infection after surgical treatment of FRI (Chapter 5). A recent systematic review showed that approximately 7-11% of the patients with FRI suffers from recurrent infections (2). However, these findings were based on studies that did not use a standardized definition for FRI and outcome. Therefore, a multicenter retrospective cohort study will be performed to evaluate the clinical outcome of patients after FRI treatment (Chapter 6).status: Accepte
Numerieke analyse in ruimten van vaste-rang tensoren en andere Riemannse variëteiten
No full textWe consider the geometry of low-rank tensors in two different ways. First, we look at the Lie group action induced by changes of basis in each mode. We show that this action is transitive under suitable restrictions on the sets of
- tensors with fixed canonical polyadic rank,
- tensors with fixed tensor train rank,
- tensors with fixed multilinear rank.
This induces a homogeneous smooth manifold structure.
We explore a few natural applications of this structure. Most importantly, it induces a so-called canonical Riemannian metric on the aforementioned sets. Geodesics are then induced by horizontal geodesics on the change-of-basis Lie group, which is a product of general linear groups. Using a known expression for geodesics on the general linear group, along with a clever choice of representative where the horizontal space has a particular rank structure, we derive an expression for geodesics on low-rank tensors. Importantly, these can then be evaluated efficiently using ideas from the theory of exponential integrators.
We further classify the manifolds that have an important additional property, namely those that are reductive. This property implies that the manifold is Riemannian-homogeneous, meaning that changes of basis are isometries, and has implications for so-called Lie integrators.
Secondly, we continue the work of Lars Swijsen on the Riemannian geometry of rank-1 tensors as an embedded submanifold of Euclidean space. By identifying the metric locally as a warped product, we are able to derive the exponential and logarithmic maps. We are moreover able to put this manifold in a more general context. There is a one-parameter family of metrics, obtained from tweaking a parameter in the warping function of the warped product. It includes the Euclidean, but also some other interesting geometries. In particular, some of these are geodesically connected, meaning that any pair of points can be connected by a geodesic. This property is important in, for example, consensus aggregation, where we want to find the rank-1 tensor that best represents the average of a set of many rank-1 tensors.
We then consider the general problem of how to approximate a map into a Riemannian manifold. Many established approximation schemes follow a general pullback-approximate-pushforward template. We relate their accuracy to the geometry of the target manifold by showing that if one uses the exponential and logarithmic maps to pull back and push forward to and from the tangent space, then it is possible to bound the approximation error on the manifold in terms of the linear approximation on the tangent space and a lower bound on the sectional curvature. It turns out that for many manifolds that appear organically in numerical analysis, we have explicit expressions for the exponential and logarithmic maps, and there are often global lower curvature bounds as well. Numerical experiments and a natural application to Krylov subspace recycling are presented.
Our analysis uses Toponogov's theorem, a classic result from Riemannian comparison theory about geodesic triangles. The idea is that one can construct such a triangle where one corner is the true function value and another corner is the approximated value. Having constructed the correct comparison triangle, the analysis is straightforward.
If the exponential and logarithmic maps are not known for a manifold, one can use a so-called retraction, which is a map that agrees with the exponential to first order. We discuss how it is possible to use our framework to think about the approximation error when retracting. Typically, this will overestimate the error. Numerical experiments confirm that there is practically no difference in the errors between exponentiating and retracting.
Everything numerical is implemented in Julia, and the source code is available. The low-rank tensor geometries and the rank-1 warped product geometries are all contributed to the popular library Manifolds.jl. There is also a separate package, ManiFactor.jl, published to demo the process of approximating maps into Riemannian manifolds via this pullback-approximate-pushforward techniquestatus: Accepte
Geïntegreerde microfabricage en metrologie met behulp van ruimtelijke lichtmodulatoren
No full textMicro- and nanostructures play a central role in modern photonic technologies by governing light-matter interactions, with broad applications in optics, photonics, biosensing, security labeling, and information storage. The fabrication and optical characterization of such structures remain challenging, as they typically require high-precision, specialized, and costly equipment.
This research develops a unified, programmable optical framework both the fabrication and characterization of micro- and nanostructures using spatial light modulators. A digital micromirror device (DMD) enables the generation of arbitrarily tailored optical fields with high spatial precision for maskless microfabrication, where the light distribution directly determines the resulting structures. In parallel, a phase-only liquid-crystal spatial light modulator (LC-SLM) is used to impose designed phase profiles to generate structured light beams for optical metrology. This approach provides high flexibility, precision, and cost efficiency compared to conventional methods.
The platform is applied to the fabrication of diffraction gratings, structural color elements, responsive optical sensors, and chiral assemblies. The chiral structures of interest are investigated using structured light carrying orbital angular momentum, revealing enantiomer-specific optical responses beyond conventional circular dichroism. Overall, this work highlights the potential of programmable light fields to simplify and unify the fabrication and optical analysis of advanced photonic structures, with applications in sensing, security, and photonic technologies.status: Accepte
Model-ordereductie gebaseerd op rationale interpolatie voor digitale tweelingen: Adaptive-Anderson-Antoulas voor tijdsdomein-data en niet-lineaire systemen
No full textThe main goal of this PhD project is the development of parametric model order reduction methods for the efficient evaluation of the models involved in the estimation process of Digital Twins for high-dynamic mechatronic systems. The desired reduced model will be able to undergo reconfigurations over the state and parameter space, in a trade-off between accuracy and computational load. The focus will be set on the transformation of expensive flexible multibody and nonlinear finite element models into lower cost parameterized counterparts which are sufficiently small and have an ordinary differential equation structure for effective inclusion in a single-step estimation framework.status: Publishe
Onderzoek naar de werkingsmechanismen van hoogwaardige structurele materialen tijdens de anaerobe vergisting van kaaswei-afvalwater
No full textAnaerobic digestion (AD) is an environmentally friendly and universally applicable microbial process for treating wastewater with high organic content, such as cheese whey wastewater. During the AD process, a functionally diverse microbial community converts complex organic matter into biogas, which is one of the cleanest renewable energy carriers, containing methane and carbon dioxide. Microbial communities with different functions play their respective roles in four stages, including hydrolysis, acidogenesis, acetogenesis, and methanogenesis, using the products of previous stages as substrates to contribute to a stable and collaborative micro-ecosystem, especially in the anaerobic granular sludge system. In this process, effective cooperation and suitable environmental conditions, such as pH, temperature, and alkalinity, determine the stability of the anaerobic system and the efficiency of methane production. Generally, high-concentration organic wastewaters such as cheese whey wastewater result in the production of high levels of intermediate metabolites, e.g., volatile fatty acids, which leads to decreased pH and inhibited metabolic activity of methanogens. In the case of an unfavorable environment for methanogens and disordered microbial cooperation, two problems will occur: a long lag phase, which means a long recovery time of methane production from inhibition, and low methane production.
Advanced structural materials (ASMs) such as biochar with advanced properties have been proven to be a potential additive to improve the efficiency of methane production in the anaerobic system. Several mechanisms of these ASMs, such as pH regulation, colonization, and electron transfer, were proposed to play roles in the improvement of the anaerobic process. However, the systematic understanding of the mechanisms and the relationship between the characterization of ASMs and the mechanisms are not yet fully clear in functional material-assisted anaerobic systems. This makes selecting and synthesizing ASMs with specific characterization challenging in the anaerobic system with specific wastewater.
In this thesis, several ASMs with different characteristics were selected and synthesized as additives in AD fed with cheese whey wastewater. The effects and mechanisms of action of these ASMs were investigated by analyzing the characterization of ASMs and biological processes. The results showed that the roles of three mechanisms, including pH regulation, colonization, and electron transfer, were confirmed in the anaerobic process with pinewood biochar or magnetite biochar. ASMs increased pH from about 5 to 7, which was beneficial to the growth of methanogens, through increasing the alkalinity by releasing alkaline ions such as Ca and Mg. Due to the larger specific surface area (SSA) and porous structure, the colonization of microorganisms in biochar or magnetite biochar was observed by scanning electron microscopy, enriching the top 20 bacteria, such as Clostridium, Desulfotomaculum, Oxobacter, Saccharicrinis, and Ornatilinea, selected based on relative abundance. Bacteria associated with direct interspecies electron transfer (DIET) are enriched in biochar or magnetite biochar due to their electrical conductivity and oxygen-containing functional groups, which can enhance DIET and thus increase methane production. Based on this research, we further clarified the roles of three mechanisms, namely pH regulation, microbial colonization, and DIET, in shortening the lag phase and enhancing methane production by synthesizing ASMs with specific characterizations, such as alkalinity, SSA, and electrical conductivity. The addition of alkaline ASMs helped to increase the alkalinity around the microorganisms and thus increased the local pH, which was crucial in shortening the lag phase. MOF reduced the pH of the surrounding anaerobic medium through the protons released by its acidic group (such as carboxyl) during the anaerobic process, resulting in a prolonged lag phase. For methane production, geopolymer derived from biochar with higher EC (42.78 mS/cm) and appropriate SSA (17.71 m²/g) increased methane yield by enhancing DIET between syntrophic bacteria and methanogens at 1.00 g/L. The MOF with both electrical conductivity and proton conductivity increased methane production by up to 48% by enhancing proton-electron coupling transfer between syntrophic bacteria and methanogens. However, the larger SSA (77.78 m²/g) of acacia biochar decreased the methane yield due to over-colonization at 1.00 g/L. Among all ASMs, 1.00 g/L of low-cost geopolymers derived from waste (e.g., fly ash, pinewood, and sludge powder) achieved the optimum potential, with a 30% reduction in lag phase and a 35% increase in methane production compared to the control without ASMs.
A valorisation plan exploring contract research for geopolymer-assisted AD technology obtained from this thesis in collaboration with external partners was developed to achieve the 35 billion cubic meters (bcm) goal by 2030 in the REPowerEU plan. This technology can be used to improve the AD of wastewater in the secondary treatment stage of conventional wastewater treatment processes in new and upgraded anaerobic plants. In 2027, geopolymer-assisted AD systems are estimated to increase 6.62 bcm of biomethane and 9.00 trillion euros of economic benefits in wastewater treatment plants. In total, this thesis has guiding significance for the selection of ASMs, the exploration of promotion mechanisms, and valorisation plan of ASMs-assisted anaerobic systems.status: Publishe
Direction-of-Arrival Data Association for Wildlife Acoustic Localization
No full textEstimating the position of animals over time provides useful additional information for understanding animal behavior and for ecology studies in general. A common approach for this task is to deploy microphone arrays (nodes) and use the acoustic signals to estimate the direction of arrival (DOA) of the sound source. DOAs from different nodes are then intersected to find the source's position. However, when multiple sources are active, the DOA association problem (AP) arises as it becomes unclear which DOAs correspond to the same source. This problem is further exacerbated in bioacoustical scenarios where large distances increase the error in the DOA estimates, and sounds often overlap in both time and frequency. In this paper, we propose a method to tackle the DOA AP in such challenging environments. In particular, we beamform to each of the estimated DOAs and extract features that characterize each of the detected sources, then, we associate features from different nodes based on their similarity, resulting in groups of DOAs that belong to the same source. Preliminary simulations suggest the potential of the proposed method for scenarios with missed detections and unknown number of sources, even when the number of microphones available at each node is limited.status: Publishe
Nieuwe geheugentopologieën mogelijk gemaakt door IGZO in de BEOL en FeRAM-onderzoek voor DRAM-toepassingen
No full textRecently, DRAM has faced challenges in two key areas: the sustainability of device scaling and the need to address the demands of emerging applications such as artificial intelligence (AI) and high-performance computing (HPC), which differ significantly from traditional domains like PCs, servers, mobile devices, graphics, and commodity systems.
First, in process nodes below 20nm, the scaling ratio of the technology feature size (F), of DRAM has decreased to below 20%, a significant slowdown compared to the ∼30% scaling ratio achieved in earlier technology nodes (>20nm).
Second, with the advent of the AI era, the 'memory wall' has emerged as a critical bottleneck for AI and machine learning (ML) applications. Since Ousterhout's analysis in 1990 [Ousterhout, 1990], memory bandwidth has been identified as the primary hardware issue, failing to keep pace with the rapid increases in CPU bandwidth [McKee, 2004, Wulf and McKee, 1995].
This doctoral research addresses these challenges by exploring three key directions.
• 2T0C-IGZO: Improvement of noise immunity at the storage node.
• 2T0C-IGZO: High-density and low-power read operation enabled by the proposed HSA circuit.
• FeRAM: Design Space Exploration as a DRAM Alternative.
These findings demonstrate how materials and architectural innovations can address the scaling limitations of DRAM, paving the way for high-density, energy-efficient memory solutions tailored to the demands of modern AI and HPC applications.status: Publishe
The dynamic approach to knowability
No full textThe Church-Fitch paradox of knowability is an argument from the knowability thesis (namely the thesis that all truths are possibly known) to the omniscience thesis (namely the thesis that all truths are known). In response, Van Benthem (2004) and others have investigated a dynamic concept of knowability. This leads to a reformulated and restricted version of the knowability thesis. I argue, however, that this concept is non-factive (i.e. not truth-entailing), whereas 'knowable' is factive. Holliday (2018) has proposed a new dynamic concept of knowability, which comes with its own reformulated and restricted knowability thesis. I argue that, in contradistinction to the old dynamic concept, the new dynamic concept is factive (with one modification and one qualification). However, the new framework, when combined with certain epistemological theses, introduces a problem concerning the sources of new knowledge. I investigate several variations on Holliday's framework. Each variation, however, either preserves the original problems regarding the sources of new knowledge or introduces new ones, such as dynamically possible omniscience or inescapable ignorance.sponsorship: Fonds Wetenschappelijk Onderzoek|G088219Nstatus: Published onlin