bluuebunny/crossref_metadata_2025_split huggingface dataset:
Explicit Polynomial Trefftz-DG Method for Space-Time Elasto-Acoustics
Authors: Barucq H. , Calandra H. , Diaz J. , Shishenina E. 
Published: August 2020

AbstractThe popularity of Discontinuous Galerkin (DG) methods has increased during the last years in particular with easy access to high performance computers. DG approximations gather different interesting features such as high-order accuracy, hp-adaptivity, easy parallelization but have the disadvantage of requiring a high number of degrees of freedom. DG methods are thus known to use higher computational burden and herein, we investigate the possibility of reducing it by employing an appropriate set of basis functions. We then solve the first-order elasto-acoustic wave problem in a space-time Trefftz-DG space. We use a space-time mesh with space-time polynomial basis functions. The space-time variational formulation reduces then to surface integrals set only on the skeleton of the mesh. However, the solution of the problem requires inverting a sparse matrix whose size could be very large when addressing realistic geophysical problems. A direct implementation of the Trefftz-DG formulation creates thus extra cost as compared to that of standard DG formulation where the space and time integrations are performed one by one after another. We then propose an approximate formulation which amounts to inverting the block-diagonal component of the Trefftz-DG matrix. We then end up with an explicit representation of the wavefield which is stable provided a CFL condition is satisfied.
New Preconditioners for Semi-linear PDE-Constrained Optimal Control in Annular Geometries
Authors: Christiansen Lasse Hjuler , Jørgensen John Bagterp 
Published: August 2020

AbstractOptimization problems that are constrained by partial differential equations (PDEs) often pose significant computational challenges to black-box optimization algorithms. This is particular the case for non-linear problems that typically rely on multi-query solution of large-scale linearized subsystems. In this regard, this paper proposes a customized solution strategy for a class of semi-linear PDE-constrained optimization problems in annular domains. At its core, the strategy relies on a collection of new Poisson-like preconditioners that are based on boundary-adapted spectral Galerkin methods. The preconditioners are matrix-free and scale linearly with the problem size. To establish proof-of-concept, a case study solves a benchmark control problem for various model parameters. The results show that the preconditioners lead to fast solution strategies that outperform conventional direct approaches.
Model Reduction by Separation of Variables: A Comparison Between Hierarchical Model Reduction and Proper Generalized Decomposition
Authors: Perotto Simona , Carlino Michele Giuliano , Ballarin Francesco 
Published: August 2020

AbstractHierarchical Model reduction and Proper Generalized Decomposition both exploit separation of variables to perform a model reduction. After setting the basics, we exemplify these techniques on some standard elliptic problems to highlight pros and cons of the two procedures, both from a methodological and a numerical viewpoint.
A First Meshless Approach to Simulation of the Elastic Behaviour of the Diaphragm
Authors: Cacciani Nicola , Larsson Elisabeth , Lauro Alberto , Meggiolaro Marco , Scatto Alessio , Tominec Igor , Villard Pierre-Frédéric 
Published: August 2020

AbstractThe diaphragm is the main muscle that regulates the human respiration. When a patient is put under controlled mechanical ventilation, the diaphragm is exposed to forces that damage the muscle function. The long-term aim of this work is to study this process through numerical simulation. Here, we take the first steps in developing a meshless numerical simulation method for the diaphragm. We describe how the diaphragm geometry can be extracted from medical images, and then be used in the meshless method. We show that for a thin volume like the diaphragm, the resolution of the thin dimension is highly relevant for the accuracy of the approximation, and we also show that the method converges for a test case, where realistic displacements are used as boundary conditions.
Multiwavelet Troubled-Cell Indication: A Comparison of Utilizing Theory Versus Outlier Detection
Authors: Vuik Mathea J. 
Published: August 2020

AbstractThis article discusses the effectiveness of the theoretical detection of troubled cells using multiwavelet approaches for the discontinuous Galerkin method and compares them with a statistical approach that uses boxplots. This is an important study in order to understand in which regime these tools are valid. Troubled cells are regions in the domain where a shock or discontinuity has developed, leading to spurious oscillations in the numerical approximation. One option for improving the numerical treatment near these artifacts is through the application of a limiter. The elements where such treatment is necessary are referred to as troubled cells. In this article, a new multiwavelet troubled-cell indicator is formed using the cancelation property (Dahmen, J Comput Appl Math 128:133–185, 2001) and the derived thresholding technique (Gerhard et al., J Sci Comput 62:25–52, 2015). We show that the new detector based on the cancelation property is very accurate in asymptotic regimes (very fine meshes). For coarser meshes, it might be better to use a different indicator, such as the ones that were designed by Vuik and Ryan (J Comput Phys 270:138–160, 2014; SIAM J Sci Comput 38:A84–A104, 2016).
An Anisotropic p-Adaptation Multigrid Scheme for Discontinuous Galerkin Methods
Authors: Rueda-Ramírez Andrés M. , Rubio Gonzalo , Ferrer Esteban , Valero Eusebio 
Published: August 2020

AbstractIn this work, we present an anisotropic p-adaptation multigrid algorithm for discontinuous Galerkin methods for steady-state problems that uses a p-multigrid scheme both as a solver and as an anisotropic error estimator. To achieve this, we develop a new anisotropic truncation error estimator based on the tau-estimation method, that can be evaluated inside the multigrid cycle with a negligible extra cost. The new error estimator is cheaper to evaluate and more accurate than previous versions of the tau-estimation procedure. In our technique, a non-converged solution in a reference mesh is used to estimate the truncation error with the multigrid scheme for different combinations of polynomial orders in different directions inside every element, and the mesh is adapted accordingly to target a desired truncation error threshold. The accuracy and computational cost of the proposed p-anisotropic adaptation algorithm is tested for the steady viscous flow past a NACA0012 airfoil. A speed-up of 16 can be achieved in the proposed numerical example compared with the uniformly refined simulation without multigrid.
Non-conforming Elements in Nek5000: Pressure Preconditioning and Parallel Performance
Authors: Peplinski A. , Offermans N. , Fischer P. F. , Schlatter P. 
Published: August 2020

AbstractAdaptive mesh refinement (AMR) is an important component of modern numerical solvers, as it allows to control the computational error during the simulation, increasing the reliability of the numerical modelling and giving the possibility to study a broad range of different phenomena even without knowing the physics a priori. In this work we present selected aspects of the implementation and parallel performance of a newh-type AMR framework developed for the high-order CFD solverNek5000; the development was done within the ExaFLOW EU project. We utilise in this case the natural domain decomposition inherent to the spectral element method (SEM), which constitutes the main source of parallelism and provides meshing flexibility that can be exploited in AMR. We use standard libraries for parallel mesh management (p4est) and partitioning (ParMetis) and focus on developing efficient preconditioners for the pressure problem solved on non-conforming meshes. Two different approaches are considered: an additive overlapping Schwarz and a hybrid Schwarz-multigrid method. The strong scaling is shown on the example of the simulation of the turbulent flow around a NACA4412 wing section atRe = 200, 000.
Sparse Approximation of Multivariate Functions from Small Datasets Via Weighted Orthogonal Matching Pursuit
Authors: Adcock Ben , Brugiapaglia Simone 
Published: August 2020

AbstractWe show the potential of greedy recovery strategies for the sparse approximation of multivariate functions from a small dataset of pointwise evaluations by considering an extension of the orthogonal matching pursuit to the setting of weighted sparsity. The proposed recovery strategy is based on a formal derivation of the greedy index selection rule. Numerical experiments show that the proposed weighted orthogonal matching pursuit algorithm is able to reach accuracy levels similar to those of weightedℓ1minimization programs while considerably improving the computational efficiency for small values of the sparsity level.
An Adaptive Error Inhibiting Block One-Step Method for Ordinary Differential Equations
Authors: Gu Jiaxi , Jung Jae-Hun 
Published: August 2020

AbstractAn explicit error inhibiting block one-step method was developed by Ditkowski and Gottlieb in 2017. It is motivated by a class of one-step methods described in Shampine and Watts (Math Comp 23:731–740, 1969), which takes initial s step values to generate the next s step values at each step. The error inhibiting method shares the form of the diagonally implicit multistage integration method of type 3 introduced in Butcher (Appl Numer Math 11:347–363, 1993). With the explicit error inhibiting scheme, the convergence of the global error is one order higher than that of the local truncation error, while in general the global error decays with the same order as the local truncation error. In this work, we improve the explicit error inhibiting block one-step method in order to further enhance the convergence and accuracy of the method. The main idea is to adopt the radial basis functions as a reconstruction basis replacing the polynomial basis. The numerical results confirm that the proposed method is efficient in providing enhanced order of accuracy.
Pirate Narratives and the Colonial Atlantic
Authors: Ganser Alexandra 
Published: August 2020

AbstractThis chapter examines the transformation of the Caribbean pirate into a colonial agent on the one hand and an enemy for Puritan society on the other around 1700. It begins with an analysis of Exquemelin’s Buccaneers of America (1678), which inspired a series of ethnographic narratives about the New World by former ‘pirates’ at the time (e.g., William Dampier, Basil Ringrose, Bartholomew Sharp, Lionel Wafer), written as evidence of their authors’ gradual transformation into scientists. They adopted the discourse of science and helped legitimize colonial plunder—material and symbolic—as beneficial to the European ‘empire of knowledge’. The second part focuses on gallows narratives and anti-piratical sermons in Puritan New England, which articulated piracy as sinful, devilish, and destructive for the community. Public executions of pirates and the sermons and broadsides produced for these events used the figure of the pirate as an Other against whom to produce and renew third-generation Puritan social cohesion. Cotton Mather’s and other ministers’ comments on piracy are read as a response to the perception of collective crisis of Puritan society.
Introduction: From Fundamentals to Advances in Crowdfunding Research and Practice
Authors: Shneor Rotem , Zhao Liang , Flåten Bjørn-Tore 
Published: August 2020

AbstractThe chapter introduces the phenomenon of crowdfunding while presenting its definition and main manifestations in recent years. It then discusses the roles played by the various parties to a crowdfunding transaction, as well as the benefits each may gain from such engagement. Overall, it argues for a win-win situation, where all parties become better off from involvement in a responsible crowdfunding engagement. Furthermore, the chapter highlights the process dimension of crowdfunding, as represented through a series of three main stages, which are further specified into a seven sub-stage model. Each stage in the process depends on successful completion of the stage preceding it and relates to concrete activities and considerations that should be taken at different points in time. The chapter concludes with a review of the chapter contributions included in this book and highlights their main contributions.
The FinTech Industry: Crowdfunding in Context
Authors: Griffiths Paul 
Published: August 2020

AbstractThis chapter presents how the financial services sector, especially banking, was a driver for ICT development in the last quarter of the twentieth century and early years of this century. But several phenomena happened on technological, social, and financial fronts in the second half of the last decade that led banks to ‘get their eyes off the ball’ and open the window for a whole new industrial sector to emerge, FinTech. This chapter analyses the phenomenon with the objective of answering: Why did FinTech emerge as an industrial sector, independent of banking? How is the FinTech industry organized and where does crowdfunding fit in? The chapter identifies three external forces that acted upon the banking system and created the conditions for the FinTech sector to emerge. It also looks at the FinTech sector from an industrial organization perspective and proposes a framework connecting financial services functionality and technological applications.
Crowdfunding in China: Turmoil of Global Leadership
Authors: Zhao Liang , Li Yuanqing 
Published: August 2020

AbstractThis chapter offers a comprehensive review and explanation of crowdfunding in China. It first extensively describes the status of crowdfunding in China by presenting the market facts, insights, and current regulations of the four main crowdfunding models (reward-based, equity-based, loan-based, and donation-based) respectively. Next, through a detailed up-to-date literature review of the key literature of Chinese crowdfunding, three main research streams are summarized and discussed covering success drivers, comparative studies of Chinese versus other contexts of crowdfunding practice, and applications of crowdfunding for creative and sustainability projects. Finally, both practical and research implications are presented together with the challenges and future research directions on crowdfunding in China.
Crowdfunding Sustainability
Authors: Maehle Natalia , Otte Pia Piroschka , Drozdova Natalia 
Published: August 2020

AbstractThe chapter focuses on using crowdfunding for financing sustainable projects, that is projects aiming to extend their goal beyond market success and provide benefit to the larger part of society. The chapter discusses the definition and dimensions of sustainable development and sustainable entrepreneurship and provides an overview of the existing literature on crowdfunding of sustainable projects. The authors also review four European sustainability-oriented crowdfunding platforms representing different crowdfunding models. This review reveals that sustainable projects have rather high success rates in crowdfunding and may address all the three dimensions of sustainable development. However, environmental dimension gets the most attention. All the crowdfunding models are relevant for sustainable projects; yet, Loan-based crowdfunding seems to have the highest success rates. Moreover, focus on a particular dimension of sustainability may influence the choice of the crowdfunding model.
Civic Crowdfunding: Four Perspectives on the Definition of Civic Crowdfunding
Authors: Wenzlaff Karsten 
Published: August 2020

AbstractCivic Crowdfunding describes campaigns which aim to create a semi-public good. Unlike other crowdfunding practices, civic crowdfunding creates benefits for people outside of the group of supporters as well. This chapter analyses the literature on civic crowdfunding and proposes to view this increasing field of practice through four perspectives: the project, the supporter, the project owner, and the platform. The chapter argues that the platform is central to understanding the self-positioning of projects, supporters, and project owners within civic crowdfunding.
Crowdfunding Models, Strategies, and Choices Between Them
Authors: Shneor Rotem 
Published: August 2020

AbstractThe growing popularity of crowdfunding is manifested through the proliferation of thousands of platforms globally. The current chapter presents an elaborate, up-to-date, and detailed typology of crowdfunding models currently in use, as well as their main characteristics. Furthermore, it suggests some of the first frameworks developed for guiding prospective fundraisers in choosing between models. Each of the frameworks is designed for a different type of fundraiser, including model choice heuristics for organizations and consumers. The chapter concludes with some suggestions for further research and implications for practice.
Crowdfunding Education: Objectives, Content, Pedagogy, and Assessment
Authors: Shneor Rotem , Flåten Bjørn-Tore 
Published: August 2020

AbstractDespite its rapid growth, little attention has been given to education and training in crowdfunding. Such training is important for ensuring the healthy and ethical development of the crowdfunding industry by educating the public about the challenges and risks as well as the merits and benefits of crowdfunding. While many may have heard the term ‘crowdfunding’, it often remains poorly understood by the larger public. Hence, this chapter argues the need for crowdfunding dedicated education programmes, while presenting a concrete course programme based on the Crowdfunding Lab developed at the University of Agder in Norway. The Crowdfunding Lab is to our knowledge one of the first university courses being offered and will thus provide unique insight. The course objectives, content, pedagogy, and assessment procedures are discussed, and opportunities for further developments are outlined. This chapter concludes with implications for educators, as well as with relevant suggestions for research.
Reward-Based Crowdfunding Research and Practice
Authors: Zhao Liang , Ryu Sunghan 
Published: August 2020

AbstractThis chapter offers a review of reward-based crowdfunding. Based on a concrete framework, this chapter extensively explains the definition, mechanisms, and unique aspects of reward-based crowdfunding. To better understand the status of reward-based crowdfunding from a global perspective, the development and regional characteristics of it in different crowdfunding markets are presented and discussed in this chapter. In addition, through a comprehensive literature review of key reward-based crowdfunding research, two main research streams of reward-based crowdfunding (success drivers and contributor behaviour) are summarized. Lastly, this chapter also sheds light on the implications of reward-based crowdfunding for practice and research, as well as mentions its potential contributions and limitations.
Lernzielorientierte Kurse
Authors: Derr Katja , Mechelke-Schwede Edith , Weigel Miriam 
Published: August 2020

ZusammenfassungDie Struktur des mathematischen Curriculums des optes-Vorkurses (siehe Kapitel 13) findet sich im Aufbau und der Anordnung der Lerninhalte wieder. Jedes mathematische Themengebiet ist einem ILIAS-Kurs zugeordnet. Die Lerninhalte dieses Kurses wiederum wurden zu Lernzielen zusammengefasst, die den Lernenden helfen, sich im Vorkurs zurechtzufinden.
E-Tutoring
Authors: Mersch André , Seibt Alina 
Published: August 2020

ZusammenfassungE-Learning bietet zahlreiche Möglichkeiten, die Präsenzlehre inhaltlich und didaktisch anzureichern und damit die Studienbedingungen zu verbessern. In der Praxis fehlt den Lehrenden jedoch oftmals der zeitliche Spielraum, um entsprechende Angebote zu erstellen. Das Konzept des E-Tutorings schafft hier Entlastung: E-Tutor* innen unterstützen Lehrende beim Einsatz digitaler Medien in der Gestaltung von Lehr-, Lern- und Prüfungsprozessen.
Nachhaltige Softwareentwicklungen im Verbundprojekt optes
Authors: Kunkel Matthias , Samoila Oliver 
Published: August 2020

ZusammenfassungIn Forschungs- und Entwicklungsprojekten mit E-Learning-Bezug wird gerne Open-Source-Software eingesetzt, weil diese leicht und kostengünstig Anpassungen an spezifische Projektanforderungen erlaubt. Diesem Vorteil an Flexibilität steht jedoch ein gravierender Nachteil gegenüber. Durch das individuelle Anpassen der Software kann diese nicht mehr ohne Weiteres auf neue Versionen aktualisiert werden.
Umgang mit Heterogenität – Das Konzept der A-/B-Kurse
Authors: Shayanfar Nikta , Weigand Hans-Georg 
Published: August 2020

ZusammenfassungDurch die zahlreichen Wege zur Erlangung einer Hochschulzugangsberechtigung hat die Heterogenität bei Studienanfänger*innen an den Hochschulen zugenommen (z. B. Biehler et al. 2010 oder Leuders et al. 2017). Neben der grundlegenden Aufarbeitung der Schulmathematik und der spezifischen Vorbereitung der Schulabgänger*innen auf die Studieneingangsphase stellt der Umgang mit der Heterogenität eine zusätzliche Herausforderung bei der Durchführung eines Brückenkurses wie etwa demjenigen von optes dar.
Adaptives Üben, adaptive Aufgabentrainings, Modelle grundlegenden Wissens und Könnens
Authors: Götz Gerhard , Hamich Myriam , Pinkernell Guido , Schönwälder David , Ullrich Daniel , Wankerl Sebastian 
Published: August 2020

ZusammenfassungDas Üben hat in der grundlegenden Konzeption der optes-Kurse einen hohen Stellenwert. Die angehenden Studierenden müssen nicht nur über mathematische Kenntnisse, Fähigkeiten und Fertigkeiten verfügen, sondern diese auch zielgerichtet anwenden können. Für die Konzeption ist auch relevant, dass viele der behandelten mathematischen Themengebiete bereits aus der Schule bekannt sind.
A new mechanical calibration strategy for U-channel extrusions
Authors: Raknes Christian Arne , Ma Jun , Welo Torgeir , Paulsen Frode 
Published: August 2020

AbstractThe extrusion process of aluminum profiles introduces dimensional variations commonly exceeding the dimensional tolerance requirements for fit-up and assembly when using automated welding processes in the automotive industry. Improving dimensional accuracy of extrusions is challenging from both a technical and economical point of view. However, an alternative technical approach is to introduce fast and simple downstream processes, such as mechanical calibration, to achieve components or products with improved dimensional characteristics. In this paper, a new mechanical calibration strategy is proposed based on the principle of combining transversal stretching and local bending. The strategy is tested on a U-channel extrusion—which is a particularly challenging geometry for extrusions concerning dimensional accuracy. The overall objective is to improve gap opening variations on U-channels compared with as-extruded dimensional capabilities, especially in the case of alloys that are water quenched to obtain high strength and ductility. The study is also intended to serve as basis for future optimization of the mechanical calibration process. An experimental platform and die/tool system was developed, and finite element simulation was used as a research tool to re-produce and better understand the calibration process, thus further analyzing the mechanisms and deformation characteristics important to dimensional accuracy. The experimental results show that the mechanical calibration strategy has good potential to improve the dimensional accuracy of gap openings of U-channels by 90%. The study demonstrates that as-extruded profiles with tolerance limits exceeding the requirements of the final component can effectively be calibrated with the proposed method and hence used in high-volume manufacturing.