Divisibility Graphs: Graphs representing modular multiplications

E-print/Working paper (in press)

The mod 2 cohomology rings of congruence subgroups in the Bianchi groups

E-print/Working paper (in press)

We provide new tools for the calculation of the torsion in the cohomology of congruence subgroups in the Bianchi groups : An algorithm for finding particularly useful fundamental domains, and an analysis ... [more ▼]

We provide new tools for the calculation of the torsion in the cohomology of congruence subgroups in the Bianchi groups : An algorithm for finding particularly useful fundamental domains, and an analysis of the equivariant spectral sequence combined with torsion subcomplex reduction. [less ▲]

Teacher-Student Relationships and Student Outcomes: A Systematic Review of Meta-Analyses and Second-Order Meta-Analysis

E-print/Working paper (2023)

Teacher-student relationships (TSRs) play a vital role in establishing a positive school climate and promoting positive student outcomes. Several meta-analyses have suggested significant associations ... [more ▼]

Teacher-student relationships (TSRs) play a vital role in establishing a positive school climate and promoting positive student outcomes. Several meta-analyses have suggested significant associations between TSRs and, for example, academic achievement, a lack of disruptive behavior, school engagement, peer relationships, motivation, executive functions, and general well-being. However, these meta-analyses have differed substantially in TSR-outcome relationships, moderators, and quality, thus complicating the interpretation of these findings. In this preregistered systematic review of meta-analyses plus original second-order meta-analyses (SOMAs), we aimed to (a) synthesize the meta-analytic evidence on relationships between TSRs and student outcomes, (b) map influential moderators of these relationships, and (c) assess the methodological quality of the meta-analyses. We synthesized over 70 years of educational research in 24 meta-analyses encompassing a total of 116 effect sizes based on more than 2 million prekindergarten and K-12 students. We conducted several three-level SOMAs and found that TSRs had similar strong significant relationships with eight clusters of outcomes: academic achievement, academic emotions, appropriate student behavior, behavior problems, executive functions and self-control, motivation, school belonging and engagement, and student well-being. Age, gender, and informant (student-, peer-, or teacher-assessments) were the most frequently examined moderators in prior research, and our moderator analyses suggested student grade level and social minority status as moderators. We further found large differences in quality between the meta-analyses, and these differences were not associated with the TSR-outcome relationships. These results map the field of TSR research; present their relationships, moderators, and meta-analytic quality; and show how TSRs can contribute to improving outcomes in students via relationship building. Future research should follow meta-analytic open science procedures to improve quality and reproducibility. [less ▲]

Investigating Preservice Teachers’ Attitudes Toward Lesbian, Gay, and Bisexual Students in Luxembourg

E-print/Working paper (2023)

Lesbian, gay, and bisexual (LGB) students face victimization in multiple contexts, including the educational context. Here, teachers can serve as an important resource for LGB students. However, teachers ... [more ▼]

Lesbian, gay, and bisexual (LGB) students face victimization in multiple contexts, including the educational context. Here, teachers can serve as an important resource for LGB students. However, teachers who are prejudiced against students from sexual minorities might not be able to fulfill this role. Accordingly, it is important to find out more about teachers' attitudes and their correlates, as such information can provide starting points for sensitization interventions in teacher education programs, which have the potential to improve the situation of LGB students in the school setting. In the present preregistered questionnaire study, we investigated the attitudes of 138 preservice teachers from the University of Luxembourg toward LGB students and tried to identify predictors of teachers’ attitudes. Results suggested that Luxembourgish preservice teachers hold mostly positive attitudes toward LGB students. Using correlation and multiple regression analyses, we identified the frequency of participants’ contact with LGB people in family or friend networks, hypergendering tendencies, sexual orientation, and religiosity as reliable predictors of attitudes toward LGB students. Age, gender, and right-wing conservatism did not reliably predict preservice teachers’ attitudes in the regression models. Our findings thus offer support for intergroup contact theory and have implications for teacher education in Luxembourg. [less ▲]

Reconfigurable Intelligent Surfaces Enhanced NOMA D2D Communications Underlaying UAV Networks

E-print/Working paper (2023)

Device-to-device (D2D) communications offers high spectral efficiency, low energy consumption and transmission latency. However, one of the main limitations of D2D communications is co-channel ... [more ▼]

Device-to-device (D2D) communications offers high spectral efficiency, low energy consumption and transmission latency. However, one of the main limitations of D2D communications is co-channel interference from underlaying wireless system. Reconfigurable intelligent surfaces (RIS) is a promising technology because it can manipulate the electromagnetic waves in their environment to overcome interference and enhance wireless communications. This paper considers RIS enhanced D2D communications underlaying unmanned aerial vehicle (UAV) networks with non-orthogonal multiple access (NOMA). The objective is to maximize the sum rate of NOMA D2D communications by optimizing the power budget of D2D transmitter, NOMA power allocation coefficients of D2D receivers and passive beamforming of RIS while guaranteeing the quality of services of UAV user. Due to non-convexity, the optimization problem is intractable and challenging to handle. Therefore, it is solved in two parts using alternating optimization. Simulation results unviel the performance of the proposed RIS enhanced D2D communications scheme. Results demonstrate that the proposed scheme ach [less ▲]

NOMA-Based Backscatter Communications: Fundamentals, Applications, and Advancements

E-print/Working paper (2023)

Developing wireless communication technologies is an ongoing process to satisfy the requirements of new applications and the increasing proliferation of interconnected devices. Using non-orthogonal ... [more ▼]

Developing wireless communication technologies is an ongoing process to satisfy the requirements of new applications and the increasing proliferation of interconnected devices. Using non-orthogonal multiple access (NOMA) and backscatter communication (BC) has surfaced as an advantageous approach for enhancing energy efficiency (EE), maximizing sum rates, ensuring security, and optimizing resource allocation. NOMA permits multiple users to share time and frequency resources even without the requirement of antenna arrays, whereas BC employs ambient RF signals for low-power communication. By integrating the advantages of NOMA and BC, NOMA-based BC provides a solution for future energy-efficient and low-power networks. Despite its potential, there is a lack of a comprehensive overview of NOMA-BC, necessitating a systematic survey that covers its principles, applications, challenges, and future directions. This survey aims to bridge the gap by exploring NOMA-BC within B5G and 6G networks. We delve into its technical aspects, performance optimization techniques, and real-world applications to enhance understanding and knowledge. First, we cover topics such as enhancing EE, maximizing the sum rates, ensuring security, and optimizing resource allocation. Our primary goal is to provide researchers and practitioners with valuable insights that enable them to grasp the capabilities and benefits of NOMA-BC. To achieve this, we comprehensively analyze various schemes' performance by presenting detailed summary tables. These analyses cover a range of scenarios, methods, and objectives, focusing on emerging B5G technologies such as reconfigurable intelligent surfaces (RIS), visible light communication (VLC), and unmanned aerial vehicle (UAV) communication. By examining NOMA-BC's effectiveness within these contexts, we aim to provide a holistic view of its potential and applicability in diverse technological domains. Moreover, our survey identifies and discusses open research challenges and proposes future directions to guide researchers toward unexplored areas and facilitate advancements in NOMA-BC. [less ▲]

RIS-Assisted Energy-Efficient LEO Satellite Communications with NOMA

E-print/Working paper (2023)

This paper proposes an energy-efficient RIS-assisted downlink NOMA communication for LEO satellite networks. The proposed framework simultaneously optimizes the transmit power of ground terminals of the ... [more ▼]

This paper proposes an energy-efficient RIS-assisted downlink NOMA communication for LEO satellite networks. The proposed framework simultaneously optimizes the transmit power of ground terminals of the LEO satellite and the passive beamforming of RIS while ensuring the quality of services. Due to the nature of the considered system and optimization variables, the energy efficiency maximization problem is non-convex. In practice, obtaining the optimal solution for such problems is very challenging. Therefore, we adopt alternating optimization methods to handle the joint optimization in two steps. In step 1, for any given phase shift vector, we calculate satellite transmit power towards each ground terminal using the Lagrangian dual method. Then, in step 2, given the transmit power, we design passive beamforming for RIS by solving the semi-definite programming. We also compare our solution with a benchmark framework having a fixed phase shift design and a conventional NOMA framework without involving RIS. Numerical results show that the proposed optimization framework achieves 21.47% and 54.9% higher energy efficiency compared to the benchmark and conventional frameworks. [less ▲]

Motile bacteria leverage bioconvection for eco-physiological benefits in a natural aquatic environment

E-print/Working paper (2023)

Bioconvection, the active self-sustaining transport phenomenon triggered by the accumulation of motile microbes under competing physico-chemical cues, has been long studied, with recent reports suggesting ... [more ▼]

Bioconvection, the active self-sustaining transport phenomenon triggered by the accumulation of motile microbes under competing physico-chemical cues, has been long studied, with recent reports suggesting its role in driving ecologically-relevant fluid flows. Yet, how this collective behaviour impacts the ecophysiology of swimming microbes remains unexplored. Here, through physicochemical profiles and physiological characterizations analysis of the permanently stratified meromictic Lake Cadagno, we characterize the community structure of a dense layer of anaerobic phototrophic sulfur bacteria, and report that the associated physico-chemical conditions engender bioconvection when bulk of the motile purple sulfur bacterium Chromatium okenii synchronize their movement against the gravity direction. The combination of flow cytometry and fluorescent in situ hybridization (FISH) techniques uncover the eco-physiological effects resulting from bioconvection, and simultaneous measurements using dialysis bags and 14C radioisotope, allowed us to quantify in situ the diurnal and nocturnal CO2 fixation activity of the three co-existing species in the bacterial layer. The results provide a direct measure of the cellular fitness, with comparative transcriptomics data - of C. okenii populations present in regions of bioconvection vis-a-vis populations in bioconvection-free regions - indicating the transcripts potentially involved in the bioconvection process. This work provides direct evidence of the impact of bioconvection on C. okenii metabolism, and highlights the functional role of bioconvection in enhancing the metabolic advantage of C. okenii relative to other microbial species inhabiting the microbial layer. [less ▲]

Balancing education and engagement. A suggested co-design process for historical game development

E-print/Working paper (2023)

Physical Activity, Dietary Consumption and Weight Status of school aged children

E-print/Working paper (2023)

Key findings: Boys are more physically active than girls. Girls consume vegetables daily more frequently than boys. Prevalence of overweight and obesity is higher for boys than for girls.

OPTWIN: Drift identification with optimal sub-windows

E-print/Working paper (2023)

Online Learning (OL) is a field of research that is increasingly gaining attention both in academia and industry. One of the main challenges of OL is the inherent presence of concept drifts, which are ... [more ▼]

Online Learning (OL) is a field of research that is increasingly gaining attention both in academia and industry. One of the main challenges of OL is the inherent presence of concept drifts, which are commonly defined as unforeseeable changes in the statistical properties of an incoming data stream over time. The detection of concept drifts typically involves analyzing the error rates produced by an underlying OL algorithm in order to identify if a concept drift occurred or not, such that the OL algorithm can adapt accordingly. Current concept-drift detectors perform very well, i.e., with low false negative rates, but they still tend to exhibit high false positive rates in the concept-drift detection. This may impact the performance of the learner and result in an undue amount of computational resources spent on retraining a model that actually still performs within its expected range. In this paper, we propose OPTWIN, our “OPTimal WINdow” concept drift detector. OPTWIN uses a sliding window of events over an incoming data stream to track the errors of an OL algorithm. The novelty of OPTWIN is to consider both the means and the variances of the error rates produced by a learner in order to split the sliding window into two provably optimal subwindows, such that the split occurs at the earliest event at which a statistically significant difference according to either the 𝑡- or the 𝑓 -tests occurred. We assessed OPTWIN over the MOA framework, using ADWIN, DDM, EDDM, STEPD and ECDD as baselines over 7 synthetic and real-world datasets, and in the presence of both sudden and gradual concept drifts. In our experiments, we show that OPTWIN surpasses the F1-score of the baselines in a statistically significant manner while maintaining a lower detection delay and saving up to 21% of time spent on retraining the models. [less ▲]

Optimal Timing of Carbon-Capture Policies Among Di erent Countries Under Markovian Competition

E-print/Working paper (2023)

Carbon capture and storage (CCS) is considered one of the most important and efficient tools in fighting against greenhouse gas emissions. Countries differ in terms of the level CCS processes implemented ... [more ▼]

Carbon capture and storage (CCS) is considered one of the most important and efficient tools in fighting against greenhouse gas emissions. Countries differ in terms of the level CCS processes implemented, with the main barrier to CCS adoption being its high cost. This paper introduces a differential game model with heterogeneous countries to investigate the optimal timing for countries to initiate CCS projects, taking into account CCS costs. We show that (i) the thresholds for the triggering of CCS projects depend not only on one's own CCS costs but also those of others, in addition to the pollution damage costs; (ii) the optimal timing for different countries to initiate their CCS projects is the moment when their threshold level of pollution stock is reached; (iii) countries are more inclined to free-ride by both reducing pollutant emissions and deploying CCS when pollution damage costs are symmetric rather than asymmetric; finally, (iv) we provide sufficient conditions under which some countries never deploy CCS even though they bear the same pollution damage as the others. [less ▲]

Strategic Considerations of Critical Mineral Depletion and Recycling Under Markovian Competition

E-print/Working paper (2023)

With the exhaustion of non-renewable resources and the increasing importance of critical materials for the transition to clean technology, recycling is being called into action. Fulfilling demand for ... [more ▼]

With the exhaustion of non-renewable resources and the increasing importance of critical materials for the transition to clean technology, recycling is being called into action. Fulfilling demand for critical minerals involves challenges such as supply chain disruption, resource depletion and positive minimum demand, however. Under Markovian competition between an exporting cartel and an importing country, we demonstrate that (i) if both virgin and recyclable resources are abundant, multiple subgame perfect Markovian Nash equilibria arise; (ii) if the exporting cartel can choose which Nash equilibrium to follow, when the cost of exploiting the non-renewable resource is sufficiently high, stopping the supply of virgin resource to the market is the Nash equilibrium; (iii) the consequence of this choice is that when the recyclable resource is exhausted, there is no Nash equilibrium anymore, although there remains virgin resource to exploit. [less ▲]

Temperature and Joint Time Use

E-print/Working paper (2023)

We combine exogenous variation in temperature at the county-day level in the U.S. with daily time use data to examine the effect of temperature on joint time use. We show that low temperatures reduce time ... [more ▼]

We combine exogenous variation in temperature at the county-day level in the U.S. with daily time use data to examine the effect of temperature on joint time use. We show that low temperatures reduce time spent with friends but increase time spent with family. Conversely, high temperatures increase time alone but reduce time with family. We also provide evidence of the effect of temperature on joint time use being location-dependent. We rationalize this finding using a model in which the chosen time allocation is the outcome of a dual-self decision process with an indoor and an outdoor self. The two selves have different tastes for time alone, time with family, and time with friends. Weather conditions can change the influence of each self, and thereby the corresponding preferences for joint time use. We test the predictions of the model empirically by drawing on methods from the household economics literature. The test results support the hypothesis that weather affects joint time use insofar it affects where the activities take place. [less ▲]

Going Further: Flatness at the Rescue of Early Stopping for Adversarial Example Transferability

E-print/Working paper (2023)

Transferability is the property of adversarial examples to be misclassified by other models than the surrogate model for which they were crafted. Previous research has shown that transferability is ... [more ▼]

Transferability is the property of adversarial examples to be misclassified by other models than the surrogate model for which they were crafted. Previous research has shown that transferability is substantially increased when the training of the surrogate model has been early stopped. A common hypothesis to explain this is that the later training epochs are when models learn the non-robust features that adversarial attacks exploit. Hence, an early stopped model is more robust (hence, a better surrogate) than fully trained models. We demonstrate that the reasons why early stopping improves transferability lie in the side effects it has on the learning dynamics of the model. We first show that early stopping benefits transferability even on models learning from data with non-robust features. We then establish links between transferability and the exploration of the loss landscape in the parameter space, on which early stopping has an inherent effect. More precisely, we observe that transferability peaks when the learning rate decays, which is also the time at which the sharpness of the loss significantly drops. This leads us to propose RFN, a new approach for transferability that minimizes loss sharpness during training in order to maximize transferability. We show that by searching for large flat neighborhoods, RFN always improves over early stopping (by up to 47 points of transferability rate) and is competitive to (if not better than) strong state-of-the-art baselines. [less ▲]

Accurate long-read sequencing identified GBA variants as a major genetic risk factor in the Luxembourg Parkinson\textquoterights study 2023.03.29.23287880

E-print/Working paper (2023)

Heterozygous variants in the glucocerebrosidase GBA gene are an increasingly recognized risk factor for Parkinson's disease (PD). Due to the pseudogene GBAP1 that shares 96\% sequence homology with the ... [more ▼]

Heterozygous variants in the glucocerebrosidase GBA gene are an increasingly recognized risk factor for Parkinson's disease (PD). Due to the pseudogene GBAP1 that shares 96\% sequence homology with the GBA coding region, accurate variant calling by array-based or short-read sequencing methods remains a major challenge in understanding the genetic landscape of GBA-related PD. We established a novel long-read sequencing technology for assessing the full length of the GBA gene. We used subsequent regression models for genotype-phenotype analyses. We sequenced 752 patients with parkinsonism and 806 healthy controls of the Luxembourg Parkinson's study. All GBA variants identified showed a 100% true positive rate by Sanger validation. We found 12% of unrelated PD patients carrying GBA variants. Three novel variants of unknown significance (VUS) were identified. Using a structure-based approach, we defined a potential risk prediction method for VUS. This study describes the full landscape of GBA-related parkinsonism in Luxembourg, showing a high prevalence of GBA variants as the major genetic risk for PD. Our approach provides an important advancement for highly accurate GBA variant calling, which is essential for providing access to emerging causative therapies for GBA carriers. [less ▲]

Forensic DNA Phenotyping: a review on SNP panels, genotyping techniques, and prediction models

E-print/Working paper (2023)

In the past few years, forensic DNA phenotyping (FDP) has attracted a strong interest in the forensic research. Among the increasing publications, many have focused on testing the available panels to ... [more ▼]

In the past few years, forensic DNA phenotyping (FDP) has attracted a strong interest in the forensic research. Among the increasing publications, many have focused on testing the available panels to infer biogeographical ancestry (BGA) on less represented populations and understanding the genetic mechanisms underlying externally visible characteristics (EVC). However, there are currently no publications that gather all the existing panels limited to FDP and discuss the main technical limitations of the technique. In this review, we performed a bibliographic search in Scopus database of FDP-related literature, which resulted in a total of 48, 43 and 15 panels for BGA, EVC and both BGA and EVC inference, respectively. Here we provide a list of commercial and non-commercial FDP panels and the FDP limitations regarding the lack of harmonization in terms of terminology (i.e., categorization and measurement of traits) and reporting, the lack of genetic knowledge and environment influence to select markers and develop panels, and the debate surrounding the selection of genotyping technologies and prediction models and algorithms. In conclusion, this review aims to be an updated guide and to present an overview of the current FDP-related literature. [less ▲]

MAgNET: A Graph U-Net Architecture for Mesh-Based Simulations

E-print/Working paper (2023)

In many cutting-edge applications, high-fidelity computational models prove too slow to be practical and are thus replaced by much faster surrogate models. Recently, deep learning techniques have become ... [more ▼]

In many cutting-edge applications, high-fidelity computational models prove too slow to be practical and are thus replaced by much faster surrogate models. Recently, deep learning techniques have become increasingly important in accelerating such predictions. However, they tend to falter when faced with larger and more complex problems. Therefore, this work introduces MAgNET: Multi-channel Aggregation Network, a novel geometric deep learning framework designed to operate on large-dimensional data of arbitrary structure (graph data). MAgNET is built upon the MAg (Multichannel Aggregation) operation, which generalizes the concept of multi-channel local operations in convolutional neural networks to arbitrary non-grid inputs. The MAg layers are interleaved with the proposed novel graph pooling/unpooling operations to form a graph U-Net architecture that is robust and can handle arbitrary complex meshes, efficiently performing supervised learning on large- dimensional graph-structured data. We demonstrate the predictive capabilities of MAgNET for several non-linear finite element simulations and provide open-source datasets and codes to facilitate future research. [less ▲]

Wavelet-Type Expansion of Generalized Hermite Processes with rate of convergence

E-print/Working paper (2023)

Wavelet-type random series representations of the well-known Fractional Brownian Motion (FBM) and many other related stochastic processes and fields have started to be introduced since more than two ... [more ▼]

Wavelet-type random series representations of the well-known Fractional Brownian Motion (FBM) and many other related stochastic processes and fields have started to be introduced since more than two decades. Such representations provide natural frameworks for approximating almost surely and uniformly rough sample paths at different scales and for study of various aspects of their complex erratic behavior. Hermite process of an arbitrary integer order d, which extends FBM, is a paradigmatic example of a stochastic process belonging to the dth Wiener chaos. It was introduced very long time ago, yet many of its properties are still unknown when d ≥ 3. In a paper published in 2004, Pipiras raised the problem to know whether wavelet-type random series representations with a well-localized smooth scaling function, reminiscent to those for FBM due to Meyer, Sellan and Taqqu, can be obtained for a Hermite process of any order d. He solved it in this same paper in the particular case d = 2 in which the Hermite process is called the Rosenblatt process. Yet, the problem remains unsolved in the general case d ≥ 3. The main goal of our article is to solve it, not only for usual Hermite processes but also for generalizations of them. Another important goal of our article is to derive almost sure uniform estimates of the errors related with approximations of such processes by scaling functions parts of their wavelet-type random series representations. [less ▲]

Multiple Access in Constellation Domain by Non-Coherent Massive MIMO

E-print/Working paper (2023)

Multiple access is the base for increasing the capacity in multi-user communication networks. However, the growing demand for higher data rates and the number of users who requires communication services ... [more ▼]

Multiple access is the base for increasing the capacity in multi-user communication networks. However, the growing demand for higher data rates and the number of users who requires communication services has led to the scarcity of orthogonal resources in current wireless communications. On the other hand, integrating the satellite within terrestrial networks as an initiative of 3GPP since its Release 15 entails the need for new forms of multiple access between terrestrial and non-terrestrial users. This paper studies constellation schemes as a new domain to enhance the state-of-the-art multiple-access techniques for future communication technologies employing non-coherent communications with massive MIMO. In addition, we propose a hybrid model between the classic access methods such as Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA), the emerging models of non-orthogonal multiple access (NOMA) and the proposed domain of the constellation based on non-coherent massive multiple-input multiple-output (MIMO) schemes. This model is discussed for different scenarios in satellite communications that help increase the system's capacity and avoid interference between terrestrial and non-terrestrial users. [less ▲]

The Next Generation EU (NGEU) as a catalyst for the promotion of the international role of the euro

E-print/Working paper (2023)

Recent developments in the global arena such as the COVID-19 pandemic and stresses in energy markets, made it clear that it is critical for the EU to ensure its strategic autonomy in the macroeconomic ... [more ▼]

Recent developments in the global arena such as the COVID-19 pandemic and stresses in energy markets, made it clear that it is critical for the EU to ensure its strategic autonomy in the macroeconomic field. Strengthening the international role of the euro is one of the key elements in this regard. Through timely analysis of the changes stemming from the establishment of the Next Generation EU (NGEU), we seek to understand to what extent the NGEU can serve as a catalyst for the promotion of the international role of the euro. While it is implausible that the euro will overcome the primacy of the US dollar, we center our analysis around the transformation of the EU’s presence in capital markets. Following massive issuances of green bonds under the NGEU, the EU became the largest issuer of green bonds and has the potential to progress from a small supranational issuer to a sovereign size issuer. This means that the pool of highly rated euro-denominated safe assets will expand significantly. That is where we focus our analysis and where we see the opportunity of the NGEU for unlashing the potential of the euro and boosting its international role. [less ▲]

On the pointwise regularity of the Multifractional Brownian Motion and some extensions

E-print/Working paper (2023)

We study the pointwise regularity of the Multifractional Brownian Motion and in particular, we get the existence of slow points. It shows that a non self-similar process can still enjoy this property. We ... [more ▼]

We study the pointwise regularity of the Multifractional Brownian Motion and in particular, we get the existence of slow points. It shows that a non self-similar process can still enjoy this property. We also consider various extensions of our results in the aim of requesting a weaker regularity assumption for the Hurst function without altering the regularity of the process. [less ▲]

Planktonic Active Matter

E-print/Working paper (2023)

Planktonic active matter represents an emergent system spanning different scales: individual, population and community; and complexity arising from sub-cellular and cellular to collective and ecosystem ... [more ▼]

Planktonic active matter represents an emergent system spanning different scales: individual, population and community; and complexity arising from sub-cellular and cellular to collective and ecosystem scale dynamics. This cross-scale active matter system responds to a range of abiotic (temperature, fluid flow and light conditions) and biotic factors (nutrients, pH, secondary metabolites) characteristic to the relevant ecosystems they are part of. Active modulation of cell phenotypes, including morphology, motility, and intracellular organization enable planktonic microbes to dynamically interact with other individuals and species; and adapt - often rapidly - to the changes in their environment. In this chapter, I discuss both traditional and contemporary approaches to study the dynamics of this multi-scale active matter system from a mechanistic standpoint, with specific references to their local settings and their ability to actively tune the behaviour and physiology, and the emergent structures and functions they elicit under natural ecological constraints as well as due to the shifting climatic trends. [less ▲]

Historian cultures – the epistemology and methodology of history in the digital age - CulturHist

E-print/Working paper (2023)

CulturHist has its sights particularly on the community of researchers, who have done little to make the results and suggestions offered by the digital humanities their own. We want to focus the ... [more ▼]

CulturHist has its sights particularly on the community of researchers, who have done little to make the results and suggestions offered by the digital humanities their own. We want to focus the discussion on a cross cutting issue: the link to archives, as the raw material for writing an account of the past. The habit of working digitally of those historians who do not nowadays verbalise their computer practices is now widespread and is bolstered by policies aimed at making many digitised document collections available online. For example, a search using the Internet Archive wayback machine developed by a not-for-profit company which archives the Web, shows that, in January 2002, Gallica, the digital library of the Bibliothèque Nationale de France (National Library of France), reported having 80 000 documents online, as compared to a little over 5.8 million on 4 September 2019. These days, it is possible to carry out international historical investigations without being in physical contact with a document, as was demonstrated as far back as 2011 by the Data mining with criminal intent project (Cohen et al.). This means that researchers often become data managers (Cartier et al.). Most researchers now practise these habits, and there is an urgent need to analyse them and adapt initial and further training in history in order to help students and historians grasp how ways of writing history are being changed. [less ▲]

Closed-End Funds and Discount Control Mechanisms

E-print/Working paper (2023)

The discount control mechanisms that closed-end funds often choose to adopt before IPO are supposedly implemented to narrow the difference between share price and net asset value. We find evidence that ... [more ▼]

The discount control mechanisms that closed-end funds often choose to adopt before IPO are supposedly implemented to narrow the difference between share price and net asset value. We find evidence that non-discretionary discount control mechanisms such as mandatory continuation votes serve as costly signals of information to reveal higher fund quality to investors. Rents of the skill signaled through the announcement of such policies accrue to managers rather than investors as differences in skill are revealed through growing assets under management rather than risk- adjusted performance. [less ▲]

“The last new novel”: Strategies of Reader-Navigation in Reviews of Fiction Published in the Athenaeum, the Saturday Review and Household Words, 1850-59.

E-print/Working paper (2023)

Cardiovascular risk prediction - a systems medicine approach

E-print/Working paper (2023)

Background Guidelines for the prevention of cardiovascular disease (CVD) have recommended the assessment of the total CVD risk by risk scores. Current risk algorithms are low in sensitivity and ... [more ▼]

Background Guidelines for the prevention of cardiovascular disease (CVD) have recommended the assessment of the total CVD risk by risk scores. Current risk algorithms are low in sensitivity and specificity and they have not incorporated emerging risk markers for CVD. We suggest that CVD risk assessment can be still improved. We have developed a long-term risk prediction model of cardiovascular mortality in patients with stable coronary artery disease (CAD) based on newly available machine learning and on an extended dataset of new biomarkers.Methods 2953 participants of the Ludwigshafen Risk and Cardiovascular Health (LURIC) study were included. 184 laboratory and 21 demographic markers were ranked according to their contribution to risk of cardiovascular (CV) mortality using different data mining approaches. A self-learning bioinformatics workflow, including seven different machine learning algorithms, was developed for CV risk prediction. The study population was stratified into patients with and without significant CAD. Thereby, significant CAD was defined as a lumen narrowing of 50 or more in at least one of the coronary segments or a history of definite myocardial infarction. The machine learning models in both subpopulations were compared with established CV risk assessment tools.Results After a follow-up of 10 years, 603 (20.4%) patients died of cardiovascular causes. 95% patients without CAD deceased within ten years and 247 (13.2 %) patients with CAD within 5 years. Overall and in patients without CAD, NT-proBNP (N-terminal pro B-type natriuretic peptide), TnT (Troponin T), estimated cystatin c based GFR (glomerular filtration rate) and age were the highest ranked predictors, while in patients with CAD, NT-proBNP, GFR, CT-proAVP (C-terminal pro arginine vasopressin) and TNT were highest predictive. In the comparison with the FRS, PROCAM and ESC risk scores, the machine learning workflow produced more accurate and robust CV mortality prediction in patients without CAD. Equivalent CV risk prediction was obtained in the CAD subpopulation in comparison with the Marschner risk score. Overall, the existing algorithms in general tend to assign more patients into the medium risk groups, while the machine learning algorithms tend to have a clearer risk/no risk assignment. The framework is available upon request.Conclusion We have developed a fully automated and self-validating computational framework of machine learning techniques using an extensive database of clinical, routinely and non-routinely measured laboratory data. Our framework predicts long-term CV mortality at least as accurate as existing CVD risk scores. A combination of four highly ranked biomarkers and the random forest approach showed the best predictive results. Moreover, a dynamic computational model has several advantages over static CVD risk prediction tools: it is freeware, transparent, variable, transferable and expandable to any population, types of events and time frames. [less ▲]

REACHING BEYOND THE ACQUIRER-TARGET DYAD IN M&A – LINKAGES TO EXTERNAL KNOWLEDGE SOURCES AND TARGET FIRM VALUATION

E-print/Working paper (2023)

From methylation to myelination: epigenomic and transcriptomic profiling of chronic inactive demyelinated multiple sclerosis lesions 2023.01.12.523740

E-print/Working paper (2023)

Introduction In the progressive phase of multiple sclerosis (MS), the hampered differentiation capacity of oligodendrocyte precursor cells (OPCs) eventually results in remyelination failure. We have ... [more ▼]

Introduction In the progressive phase of multiple sclerosis (MS), the hampered differentiation capacity of oligodendrocyte precursor cells (OPCs) eventually results in remyelination failure. We have previously shown that DNA methylation of Id2/Id4 is highly involved in OPC differentiation and remyelination. In this study, we took an unbiased approach by determining genome-wide DNA methylation patterns within chronically demyelinated MS lesions and investigated how certain epigenetic signatures relate to OPC differentiation capacity.Methods We compared genome-wide DNA methylation and transcriptional profiles between chronically demyelinated MS lesions and matched normal-appearing white matter (NAWM), making use of post-mortem brain tissue (n=9/group). DNA methylation differences that inversely correlated with mRNA expression of their corresponding genes were validated for their cell-type specificity in laser-captured OPCs using pyrosequencing. The CRISPR-dCas9-DNMT3a/TET1 system was used to epigenetically edit human-iPSC-derived oligodendrocytes to assess the effect on cellular differentiation.Results Our data show hypermethylation of CpGs within genes that cluster in gene ontologies related to myelination and axon ensheathment. Cell type-specific validation indicates a region-dependent hypermethylation of MBP, encoding for myelin basic protein, in OPCs obtained from white matter lesions compared to NAWM-derived OPCs. By altering the DNA methylation state of specific CpGs within the promotor region of MBP, using epigenetic editing, we show that cellular differentiation can be bidirectionally manipulated using the CRISPR-dCas9-DNMT3a/TET1 system in vitro.Conclusion Our data indicate that OPCs within chronically demyelinated MS lesions acquire an inhibitory phenotype, which translates into hypermethylation of crucial myelination related genes. Altering the epigenetic status of MBP can restore the differentiation capacity of OPCs and possibly boost (re)myelination.Competing Interest StatementThe authors have declared no competing interest. [less ▲]

What can inform us about the arrival of daily extreme stock market events?

E-print/Working paper (2023)

The Impact of the Johnson-Reed Act on Filipino Labor Market Outcomes

E-print/Working paper (2023)

Immigration restrictions to the US are rather modern policies. One of the most significant policy changes, the Johnson-Reed Act of 1924, drastically limited the number of new immigrants per year ... [more ▼]

Immigration restrictions to the US are rather modern policies. One of the most significant policy changes, the Johnson-Reed Act of 1924, drastically limited the number of new immigrants per year, especially from Asia. In combination with the Emergency Quota Act of 1921, immigration per country was capped at 2 percent of the respective population in the 1890 census. In this paper, I examine to what extent immigration restrictions affected labor market outcomes of prior migration cohorts. Using decennial census data, I apply a difference-in-difference estimation, considering that restrictions initially did not impact the Philippines, then a US territory. My findings indicate that initial immigration restrictions affected exempted Filipinos, highlighting the impact of competition on their economic assimilation. Relative to other migrants, labor force participation and employment rates of Filipinos increased while their log income scores declined. This finding corroborates previous studies that emphasize the relevance of substitutability among immigrant cohorts. Individual panel data analysis partially supports the findings in the cross-sectional evaluation. [less ▲]

Interaction of mitochondrial polygenic score and environmental factors in LRRK2 p.Gly2019Ser parkinsonism 2023.01.02.23284113

E-print/Working paper (2023)

The objective of our study was to investigate the impact of the mitochondrial polygenic score (MGS) and lifestyle/environmental data on age at onset in LRRK2 p.Gly2019Ser parkinsonism (LRRK2-PD) and ... [more ▼]

The objective of our study was to investigate the impact of the mitochondrial polygenic score (MGS) and lifestyle/environmental data on age at onset in LRRK2 p.Gly2019Ser parkinsonism (LRRK2-PD) and idiopathic Parkinson\textquoterights disease (iPD).In this study, we included N=486 patients with LRRK2-PD and N=9259 patients with iPD from AMP-PD, Fox Insight, and a Tunisian Arab-Berber founder population. Genotyping data was utilized to perform the MGS analysis, using 14 Single Nucleotide Polymorphisms (SNPs) from genes causally associated with mitochondrial function and PD risk. Additionally, lifestyle and environmental data were obtained from the PD risk factor questionnaire (PD-RFQ). Correlation analyses and linear regression models were used to assess the relationship between MGS, lifestyle/environment, and AAO.We observed that higher MGS was associated with earlier AAO in patients with LRRK2-PD (p=4.0\texttimes10-4, β=-0.18) but not in patients with iPD. A correlation between MGS and AAO was visibly stronger in European ancestry LRRK2-PD patients (p=0.01, r=-0.16) than in Tunisian Arab-Berber patients (p=0.44, r=-0.05). We found that the MGS interacted with coffee (p=0.03, β=-0.38) and caffeinated soda consumption (p=0.03, β=-0.37) in LRRK2-PD and with caffeine soda consumption (p=0.047, β=-0.22) and pesticide exposure (p=0.02, β=-0.37) in iPD. Thus, patients with a high MGS had an earlier AAO only if they consumed caffeine or were exposed to pesticides.The MGS related to mitochondrial function was associated with AAO in LRRK2-PD but not iPD with an ethnic-specific effect. Caffeine consumption or pesticide exposure interacted with MGS to predict PD AAO. Our study suggests gene-environment interactions as modifiers of AAO in LRRK2-PD.Competing Interest StatementCK serves as a medical advisor to Centogene and Retromer Therapeutics and received speaking honoraria from Desitin. The remaining authors declare no conflict of interest.Funding StatementThis project was supported by the DFG RU ProtectMove (DFG FOR2488), the Michael J. Fox Foundation (MJFF-021227 \& MJFF-019271), and the Else Kroener-Fresenius-Stiftung.Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:Ethical permission was given by the Ethical Committee of the Institut National de Neurologie and certified by the Ministry of Health, Tunisia.I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.YesData sharing is not applicable to this article as no new data were created or analysed in this study. Data used in the preparation of this manuscript were obtained from the Fox Insight database (https://foxinsight-info.michaeljfox.org/insight/explore/insight.jsp) on 18/10/2020. For up-to-date information on the study, visit https://foxinsight-info.michaeljfox.org/insight/explore/insight.jsp. Data used in the preparation of this article were obtained from the Accelerating Medicine Partnership (AMP) Parkinson\textquoterights Disease (AMP PD) Knowledge Platform. For up-to-date information on the study, visit https://www.amp-pd.org. [less ▲]

Acquisition Experience and the Winner’s Curse in Corporate Acquisitions

E-print/Working paper (2023)

A Reissner-Mindlin plate formulation using symmetric Hu-Zhang elements via polytopal transformations

E-print/Working paper (2023)

In this work we develop new finite element discretisations of the shear-deformable Reissner--Mindlin plate problem based on the Hellinger-Reissner principle of symmetric stresses. Specifically, we use ... [more ▼]

In this work we develop new finite element discretisations of the shear-deformable Reissner--Mindlin plate problem based on the Hellinger-Reissner principle of symmetric stresses. Specifically, we use conforming Hu-Zhang elements to discretise the bending moments in the space of symmetric square integrable fields with a square integrable divergence. The latter results in highly accurate approximations of the bending moments M and in the rotation field being in the discontinuous Lebesgue space , such that the Kirchhoff-Love constraint can be satisfied for t tending to zero. In order to preserve optimal convergence rates across all variables for the case t tending to zero, we present an extension of the formulation using Raviart-Thomas elements for the shear stress. We prove existence and uniqueness in the continuous setting and rely on exact complexes for inheritance of well-posedness in the discrete setting. This work introduces an efficient construction of the Hu-Zhang base functions on the reference element via the polytopal template methodology and Legendre polynomials, making it applicable to hp-FEM. The base functions on the reference element are then mapped to the physical element using novel polytopal transformations, which are suitable also for curved geometries. The robustness of the formulations and the construction of the Hu-Zhang element are tested for shear-locking, curved geometries and an L-shaped domain with a singularity in the bending moments. Further, we compare the performance of the novel formulations with the primal-, MITC- and recently introduced TDNNS methods. [less ▲]

Looking ahead: after web (archives)?

E-print/Working paper (2023)

In-Work Poverty: Is the EU Up to the Challenge?

E-print/Working paper (2023)

Covariant Riesz transform on differential forms for 1<p\leq2

E-print/Working paper (2022)

Distributionally robust optimal allocation with costly verification

E-print/Working paper (2022)

Is Bitcoin a better safe-haven asset for individual investors than Gold? – Evidence from sanctioned Russia

E-print/Working paper (2022)

Extensive research on safe-haven assets has been conducted in the literature. An important finding is that safe-haven assets are frequently used by institutional investors, such as pension funds and ... [more ▼]

Extensive research on safe-haven assets has been conducted in the literature. An important finding is that safe-haven assets are frequently used by institutional investors, such as pension funds and investment banks, to ride out high volatility. However, the issue of whether individual investors can benefit from it during a financial crisis has not been adequately addressed. Using the case of sanctioned Russia, we attempt to study whether Bitcoin as a decentralized asset can play a more useful role than gold to protect individual investors when the majority of safe-haven assets are restricted from transactions. Our main results show that both assets exhibit intraday weak safe-haven properties against the ruble. However, gold saw a waning trend compared with its historical performance, whereas Bitcoin’s capability increased during this period. Further sentiment analysis demonstrates Russian investors’ positive attitudes regarding Bitcoin boosting its price in response to the ruble’s depreciation. The return on gold is more likely to be impacted by international investors who are concerned about global uncertainties. [less ▲]

The Zoom City: Working From Home, Urban Productivity and Land Use

E-print/Working paper (2022)

Who will benefit and who will lose from a permanent increase in working from home (WFH)? This paper investigates the impact of WFH on cities of different sizes, highlights the dangers of too much WFH, and ... [more ▼]

Who will benefit and who will lose from a permanent increase in working from home (WFH)? This paper investigates the impact of WFH on cities of different sizes, highlights the dangers of too much WFH, and discusses aspects of the disagreement between workers and firms. Our results suggest that WFH raises urban productivity and average wages only in large cities. We also study the optimal fraction of WFH and show that workers-residents have incentives to adopt an inefficiently high WFH scheme. The implementation of remote work in the short run---at fixed rents and wages---implies higher benefits for long-distance commuters and lower benefits or even losses for short-distance ones. It also implies benefits for some firms and losses for others, which potentially explains the low prevalence of WFH before the pandemic. Finally, we show that advances in digital technology, which increase the productivity of remote workers, lead to increased welfare benefits. A calibration exercise for the average and the largest European capital cities sheds more light on the impact of WFH on cities of different sizes. [less ▲]

FastCycle: A Message Sharing Framework for Modular Automated Driving Systems

E-print/Working paper (2022)

Automated Driving Systems (ADS) have rapidly evolved in recent years and their architecture becomes sophisticated. Ensuring robustness, reliability and safety of performance is particularly important. The ... [more ▼]

Automated Driving Systems (ADS) have rapidly evolved in recent years and their architecture becomes sophisticated. Ensuring robustness, reliability and safety of performance is particularly important. The main challenge in building an ADS is the ability to meet certain stringent performance requirements in terms of both making safe operational decisions and finishing processing in real-time. Middlewares play a crucial role to handle these requirements in ADS. The way middlewares share data between the different system components has a direct impact on the overall performance, particularly the latency overhead. To this end, this paper presents FastCycle as a lightweight multi-threaded zero-copy messaging broker to meet the requirements of a high fidelity ADS in terms of modularity, real-time performance and security. We discuss the architecture and the main features of the proposed framework. Evaluation of the proposed framework based on standard metrics in comparison with popular middlewares used in robotics and automated driving shows the improved performance of our framework. The implementation of FastCycle and the associated comparisons with other frameworks are open sourced. [less ▲]

#Discover Life on Mars with a Rover - Didaktischer Kommentar

E-print/Working paper (2022)

Forecasting of a complex microbial community using meta-omics

E-print/Working paper (2022)

Microbial communities are complex assemblages whose dynamics are shaped by abiotic and biotic factors. A major challenge concerns correctly forecasting the community behaviour in the future. In this ... [more ▼]

Microbial communities are complex assemblages whose dynamics are shaped by abiotic and biotic factors. A major challenge concerns correctly forecasting the community behaviour in the future. In this context, communities in biological wastewater treatment plants (BWWTPs) represent excellent model systems, because forecasting them is required to ultimately control and operate the plants in a sustainable manner. Here, we forecast the microbial community from the water-air interface of the anaerobic tank of a BWWTP via longitudinal meta-omics (metagenomics, metatranscriptomics and metaproteomics) data covering 14 months at weekly intervals. We extracted all the available time-dependent information, summarised it in 17 temporal signals (explaining 91.1 of the temporal variance) and linked them over time to rebuild the sequence of ecological phenomena behind the community dynamics. We forecasted the signals over the following five years and tested the predictions with 21 extra samples. We were able to correctly forecast five signals accounting for 22.5 of the time-dependent information in the system and generate mechanistic predictions on the ecological events in the community (e.g. a predation cycle involving bacteria, viruses and amoebas). Through the forecasting of the 17 signals and the environmental variables readings we reconstructed the gene abundance and expression for the following 5 years, showing a nearly perfect trend prediction (coefficient of determination >= 0.97) for the first 2 years. The study demonstrates the maturity of microbial ecology to forecast composition and gene expression of open microbial ecosystems using year-spanning interactions between community cycles and environmental parameters. [less ▲]

Second Order Bismut formulae and applications to Neumann semigroups on manifolds

E-print/Working paper (2022)

Optimal coalition splitting with heterogenous strategies

E-print/Working paper (2022)

We consider a group of players initially members of a coalition managing cooperatively a public bad, in this case, the stock of pollution. Countries are technologically heterogeneous but the pollution ... [more ▼]

We consider a group of players initially members of a coalition managing cooperatively a public bad, in this case, the stock of pollution. Countries are technologically heterogeneous but the pollution damage is uniform. We essentially attempt to characterize the conditions under which a country may eventually split and when it splits within an infinite horizon multi-stage differential game. In contrast to the existing literature, we do not assume that after splitting, the splitting player and the remaining coalition will adopt Markovian strategies. Instead, we assume that the latter will remain committed to the collective control of pollution and play open-loop, while the splitting player plays Markovian. Within a full linear-quadratic model, we characterize the optimal strategies. We later compare with the outcomes of the case where the splitting player and the remaining coalition play both Markovian. We highlight several interesting results in terms of the implications for long- term pollution levels and the duration of coalitions with heterogeneous strategies. [less ▲]

The geometric data on the boundary of convex subsets of hyperbolic manifolds

E-print/Working paper (2022)

Let $N$ be a geodesically convex subset in a convex co-compact hyperbolic manifold $M$ with incompressible boundary. We assume that each boundary component of $N$ is either a boundary component of ... [more ▼]

Let $N$ be a geodesically convex subset in a convex co-compact hyperbolic manifold $M$ with incompressible boundary. We assume that each boundary component of $N$ is either a boundary component of $\partial_\infty M$, or a smooth, locally convex surface in $M$. We show that $N$ is uniquely determined by the boundary data defined by the conformal structure on the boundary components at infinity, and by either the induced metric or the third fundamental form on the boundary components which are locally convex surfaces. We also describe the possible boundary data. This provides an extension of both the hyperbolic Weyl problem and the Ahlfors-Bers Theorem. Using this statement for quasifuchsian manifolds, we obtain existence results for similar questions for convex domains $\Omega\subset \HH^3$ which meets the boundary at infinity $\partial_{\infty}\HH^3$ either along a quasicircle or along a quasidisk. The boundary data then includes either the induced metric or the third fundamental form in $\HH^3$, but also an additional ``gluing'' data between different components of the boundary, either in $\HH^3$ or in $\partial_\infty\HH^3$. [less ▲]

EU acts without binding legal force producing binding legal effects at the national level: Enforcement of ESA soft law in the Czech Republic

E-print/Working paper (2022)

The European Supervisory Authorities (ESAs) are empowered, by their founding regulations, to adopt guidelines and recommendations “with a view to establishing consistent, efficient and effective ... [more ▼]

The European Supervisory Authorities (ESAs) are empowered, by their founding regulations, to adopt guidelines and recommendations “with a view to establishing consistent, efficient and effective supervisory practices within the ESFS, and to ensuring the common, uniform and consistent application of Union law”. These acts can be considered genuine EU soft law since they lack the binding legal force. However, they remain perfectly non-binding only at the EU level and in the relation between the ESAs and the national competent authorities (NCAs). Although the NCAs have a duty “to make every effort to comply” with such soft law, they keep a certain leeway to decide whether they eventually comply or not. Nonetheless, the situation is different in case of financial institutions under their supervision. Formally, the EU regulations attribute to them also only a duty “to make every effort to comply”. However, once the NCA decides to comply and effectively enforces the compliance from financial institutions, the latter have a very limited, or even no leeway to decide about the compliance. Within the complex regulatory system, the NCA metamorphosis from a normtaker into an effective norm-enforcer who is capable to determine what effects the ESA soft law have at the national level. This paper focuses on the life of ESA soft law in the Czech Republic. It examines the role and power of the Czech NCA (the Czech National Bank, CNB) in the light of the legislative framework and other domestic binding legal rules. It takes into consideration the real enforcement strategy and practices of the CNB to show that, in the hands of the CNB, ESA guidelines and recommendations become acts, which produce binding legal effects upon financial institutions. Based on this observation, the paper raises questions about the proper control of ESA soft law and potential remedies. [less ▲]

Data Viz Superpowers - Didaktischer Kommentar

E-print/Working paper (2022)

Integration of external biomass reactions into existing metabolic models

E-print/Working paper (2022)

Currently, seven biomass objective functions have been defined in human metabolic reconstructions. The integration of published biomass reactions into alternative models can contribute to the prediction ... [more ▼]

Currently, seven biomass objective functions have been defined in human metabolic reconstructions. The integration of published biomass reactions into alternative models can contribute to the prediction power of the model. Thus, in this work, we present a workflow to integrate reactions and biomass functions originating from several genome-scale reconstructions into models other than their home models. Additionally, a benchmark to identify the biomass that confers the highest prediction accuracy in terms of gene essentiality and growth predictions is provided. [less ▲]

Local Verlet buffer approach for broad-phase interaction detection in Discrete Element Method

E-print/Working paper (2022)

The Extended Discrete Element Method (XDEM) is an innovative numerical simulation technique that extends the dynamics of granular materials known as Discrete Element Method (DEM) by additional properties ... [more ▼]

The Extended Discrete Element Method (XDEM) is an innovative numerical simulation technique that extends the dynamics of granular materials known as Discrete Element Method (DEM) by additional properties such as the thermodynamic state, stress/strain for each particle. Such DEM simulations used by industries to set up their experimental processes are complexes and heavy in computation time. At each time step, those simulations generate a list of interacting particles and this phase is one of the most computationally expensive parts of a DEM simulation. The Verlet buffer method, initially introduced in Molecular Dynamic (MD) (and also used in DEM), allows keeping the interaction list for many time steps by extending each particle neighbourhood by a certain extension range, and thus broadening the interaction list. The method relies on the temporal coherency of DEM, which guarantees that no particles move erratically from one time step to the next. In the classical approach, all the particles have their neighbourhood extended by the same value which leads to suboptimal performances in simulations where different flow regimes coexist. Additionally, and unlike in MD, there is no comprehensive study analysing the different parameters that affect the performance of the Verlet buffer method in DEM. In this work, we propose a new method for the dynamic update of the neighbour list that depends on the particles individual displacement and define a particle-specific extension range based on the local flow regime. The interaction list is analysed throughout the simulation based on the particle's displacement allowing a flexible update according to the flow regime conditions. We evaluate the influence of the Verlet extension range on the execution time through different test cases and analyse empirically the extension range value giving the best performance. [less ▲]