@inproceedings{19899,
abstract = {{Most existing robot formation problems seek a target formation of a certain
minimal and, thus, efficient structure. Examples include the Gathering
and the Chain-Formation problem. In this work, we study formation problems that
try to reach a maximal structure, supporting for example an efficient
coverage in exploration scenarios. A recent example is the NASA Shapeshifter
project, which describes how the robots form a relay chain along which gathered
data from extraterrestrial cave explorations may be sent to a home base.
As a first step towards understanding such maximization tasks, we introduce
and study the Max-Chain-Formation problem, where $n$ robots are ordered along a
winding, potentially self-intersecting chain and must form a connected,
straight line of maximal length connecting its two endpoints. We propose and
analyze strategies in a discrete and in a continuous time model. In the
discrete case, we give a complete analysis if all robots are initially
collinear, showing that the worst-case time to reach an
$\varepsilon$-approximation is upper bounded by $\mathcal{O}(n^2 \cdot \log
(n/\varepsilon))$ and lower bounded by $\Omega(n^2 \cdot~\log
(1/\varepsilon))$. If one endpoint of the chain remains stationary, this result
can be extended to the non-collinear case. If both endpoints move, we identify
a family of instances whose runtime is unbounded. For the continuous model, we
give a strategy with an optimal runtime bound of $\Theta(n)$. Avoiding an
unbounded runtime similar to the discrete case relies crucially on a
counter-intuitive aspect of the strategy: slowing down the endpoints while all
other robots move at full speed. Surprisingly, we can show that a similar trick
does not work in the discrete model.}},
author = {{Castenow, Jannik and Kling, Peter and Knollmann, Till and Meyer auf der Heide, Friedhelm}},
booktitle = {{Stabilization, Safety, and Security of Distributed Systems - 22nd International Symposium, SSS 2020, Austin, Texas, USA, November 18-21, 2020, Proceedings}},
editor = {{Devismes , Stéphane and Mittal, Neeraj }},
isbn = {{978-3-030-64347-8}},
pages = {{65--80}},
publisher = {{Springer}},
title = {{{A Discrete and Continuous Study of the Max-Chain-Formation Problem – Slow Down to Speed Up}}},
doi = {{10.1007/978-3-030-64348-5_6}},
volume = {{12514}},
year = {{2020}},
}
@article{19938,
abstract = {{We show that symplectic integrators preserve bifurcations of Hamiltonian boundary value problems and that nonsymplectic integrators do not. We provide a universal description of the breaking of umbilic bifurcations by nonysmplectic integrators. We discover extra structure induced from certain types of boundary value problems, including classical Dirichlet problems, that is useful to locate bifurcations. Geodesics connecting two points are an example of a Hamiltonian boundary value problem, and we introduce the jet-RATTLE method, a symplectic integrator that easily computes geodesics and their bifurcations. Finally, we study the periodic pitchfork bifurcation, a codimension-1 bifurcation arising in integrable Hamiltonian systems. It is not preserved by either symplectic on nonsymplectic integrators, but in some circumstances symplecticity greatly reduces the error. }},
author = {{McLachlan, Robert I and Offen, Christian}},
journal = {{Foundations of Computational Mathematics}},
number = {{6}},
pages = {{1363--1400}},
title = {{{Preservation of Bifurcations of Hamiltonian Boundary Value Problems Under Discretisation}}},
doi = {{10.1007/s10208-020-09454-z}},
volume = {{20}},
year = {{2020}},
}
@article{19939,
author = {{Kreusser, Lisa Maria and McLachlan, Robert I and Offen, Christian}},
issn = {{0951-7715}},
journal = {{Nonlinearity}},
number = {{5}},
pages = {{2335--2363}},
title = {{{Detection of high codimensional bifurcations in variational PDEs}}},
doi = {{10.1088/1361-6544/ab7293}},
volume = {{33}},
year = {{2020}},
}
@phdthesis{19947,
abstract = {{Ordinary differential equations (ODEs) and partial differential equations (PDEs) arise
in most scientific disciplines that make use of mathematical techniques. As exact solutions are in general not computable, numerical methods are used to obtain approximate
solutions. In order to draw valid conclusions from numerical computations, it is crucial
to understand which qualitative aspects numerical solutions have in common with the
exact solution. Symplecticity is a subtle notion that is related to a rich family of geometric properties of Hamiltonian systems. While the effects of preserving symplecticity
under discretisation on long-term behaviour of motions is classically well known, in this
thesis
(a) the role of symplecticity for the bifurcation behaviour of solutions to Hamiltonian
boundary value problems is explained. In parameter dependent systems at a bifurcation
point the solution set to a boundary value problem changes qualitatively. Bifurcation
problems are systematically translated into the framework of classical catastrophe theory. It is proved that existing classification results in catastrophe theory apply to
persistent bifurcations of Hamiltonian boundary value problems. Further results for
symmetric settings are derived.
(b) It is proved that to preserve generic bifurcations under discretisation it is necessary and sufficient to preserve the symplectic structure of the problem.
(c) The catastrophe theory framework for Hamiltonian ODEs is extended to PDEs
with variational structure. Recognition equations for A-series singularities for functionals on Banach spaces are derived and used in a numerical example to locate high-codimensional bifurcations.
(d) The potential of symplectic integration for infinite-dimensional Lie-Poisson systems (Burgers’ equation, KdV, fluid equations, . . . ) using Clebsch variables is analysed.
It is shown that the advantages of symplectic integration can outweigh the disadvantages of integrating over a larger phase space introduced by a Clebsch representation.
(e) Finally, the preservation of variational structure of symmetric solutions in multisymplectic PDEs by multisymplectic integrators on the example of (phase-rotating)
travelling waves in the nonlinear wave equation is discussed.}},
author = {{Offen, Christian}},
publisher = {{Massey University}},
title = {{{Analysis of Hamiltonian boundary value problems and symplectic integration}}},
year = {{2020}},
}
@inproceedings{19953,
abstract = {{Current GNN architectures use a vertex neighborhood aggregation scheme, which limits their discriminative power to that of the 1-dimensional Weisfeiler-Lehman (WL) graph isomorphism test. Here, we propose a novel graph convolution operator that is based on the 2-dimensional WL test. We formally show that the resulting 2-WL-GNN architecture is more discriminative than existing GNN approaches. This theoretical result is complemented by experimental studies using synthetic and real data. On multiple common graph classification benchmarks, we demonstrate that the proposed model is competitive with state-of-the-art graph kernels and GNNs.}},
author = {{Damke, Clemens and Melnikov, Vitaly and Hüllermeier, Eyke}},
booktitle = {{Proceedings of the 12th Asian Conference on Machine Learning (ACML 2020)}},
editor = {{Jialin Pan, Sinno and Sugiyama, Masashi}},
keywords = {{graph neural networks, Weisfeiler-Lehman test, cycle detection}},
location = {{Bangkok, Thailand}},
pages = {{49--64}},
publisher = {{PMLR}},
title = {{{A Novel Higher-order Weisfeiler-Lehman Graph Convolution}}},
volume = {{129}},
year = {{2020}},
}
@inproceedings{19965,
author = {{Grabo, Matti and Acar, Emre and Kenig, Eugeny}},
location = {{Cologne}},
title = {{{Modeling of a Latent Heat Storage System Consisting of Encapsulated PCM- Elements}}},
year = {{2020}},
}
@article{19973,
abstract = {{As a result of lightweight design, increased use is being made of high-strength steel and aluminium in car bodies. Self-piercing riveting is an established technique for joining these materials. The dissimilar properties of the two materials have led to a number of different rivet geometries in the past. Each rivet geometry fulfils the requirements of the materials within a limited range. In the present investigation, an improved rivet geometry is developed, which permits the reliable joining of two material combinations that could only be joined by two different rivet geometries up until now. Material combination 1 consists of high-strength steel on both sides, while material combination 2 comprises aluminium on the punch side and high-strength steel on the die side. The material flow and the stress and strain conditions prevailing during the joining process are analysed by means of numerical simulation. The rivet geometry is then improved step-by-step on the basis of this analysis. Finally, the improved rivet geometry is manufactured and the findings of the investigation are verified in experimental joining tests.}},
author = {{Uhe, Benedikt and Kuball, Clara-Maria and Merklein, Marion and Meschut, Gerson}},
journal = {{Production Engineering}},
keywords = {{Self-piercing riveting, Joining technology, Rivet geometry, Multi-material design, High-strength steel, Aluminium}},
pages = {{417--423}},
title = {{{Improvement of a rivet geometry for the self-piercing riveting of high-strength steel and multi-material joints}}},
doi = {{10.1007/s11740-020-00973-w}},
volume = {{14}},
year = {{2020}},
}
@proceedings{19974,
abstract = {{Due to the trend towards lightweight design in car body development mechanical joining technologies become increasingly important. These techniques allow for the joining of dissimilar materials and thus enable multi-material design, while thermic joining methods reach their limits. Semi-tubular self-piercing riveting is an important mechanical joining technology. The rivet production, however, is costly and time-consuming, as the process consists of several process steps including the heat treatment and coating of the rivets in order to achieve an adequate strength and corrosion resistance. The use of high nitrogen steel as rivet material leads to the possibility of reducing process steps and hence increasing the efficiency of the process. However, the high tool loads being expected due to the high strain hardening of the material are a major challenge during the rivet production. Thus, there is a need for appropriate forming strategies, such as the manufacturing of the rivets at elevated temperatures. Prior investigations led to the conclusion that forming already at 200 °C results in a distinct reduction of the yield strength. To create a deeper understanding of the forming behaviour of high nitrogen steel at elevated temperatures, compression tests were conducted in a temperature range between room temperature and 200 °C. The determined true stress – true strain curves are the basis for the further process and tool design of the rivet production. Another key factor for the rivet manufacturing at elevated temperatures is the influence of the process temperature on the tribological conditions. For this reason, ring compression tests at room temperature and 200 °C are carried out. The friction factors are determined on the basis of calibration curves resulting from the numerical analysis of the ring compression process. The investigations indicate that the friction factor at 200 °C is significantly higher compared to room temperature. This essential fact has to be taken into account for the process and tool design for the rivet production using high nitrogen steel.}},
editor = {{Kuball, Clara-Maria and Jung, R and Uhe, Benedikt and Meschut, Gerson and Merklein, Marion}},
keywords = {{High nitrogen steel, Self-piercing riveting, Joining by forming, Bulk forming, Strain hardening}},
title = {{{Influence of the process temperature on the forming behaviour and the friction during bulk forming of high nitrogen steel}}},
doi = {{10.1016/j.jajp.2020.100023}},
volume = {{1}},
year = {{2020}},
}
@proceedings{19976,
abstract = {{The aim to reduce pollutant emission has led to a trend towards lightweight construction in car body development during the last years. As a consequence of the resulting need for multi-material design, mechanical joining technologies become increasingly important. Mechanical joining allows for the combination of dissimilar materials, while thermic joining techniques reach their limits. Self-piercing riveting enables the joining of dissimilar materials by using semi-tubular rivets as mechanical fasteners. The rivet production, however, is costly and time-consuming, as the rivets generally have to be hardened, tempered and coated after forming, in order to achieve an adequate strength and corrosion resistance. A promising approach to improve the efficiency of the rivet manufacturing is the use of high-strength high nitrogen steel as rivet material because these additional process steps would not be necessary anymore. As a result of the comparatively high nitrogen content, such steels have various beneficial properties like higher strength, good ductility and improved corrosion resistance. By cold bulk forming of high nitrogen steels high-strength parts can be manufactured due to the strengthening which is caused by the high strain hardening. However, high tool loads thereby have to be expected and are a major challenge during the production process. Consequently, there is a need for appropriate forming strategies. This paper presents key aspects concerning the process design for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel. The aim is to produce the rivets in several forming stages without intermediate heat treatment between the single stages. Due to the high strain hardening of the material, a two stage forming concept will be investigated. Cup-backward extrusion is chosen as the first process step in order to form the rivet shank without forming the rivet foot. Thus, the strain hardening effects in the area of the rivet foot are minimized and the tool loads during the following process step can be reduced. During the second and final forming stage the detailed geometry of the rivet foot and the rivet head is formed. In this context, the effect of different variations, for example concerning the final geometry of the rivet foot, on the tool load is investigated using multistage numerical analysis. Furthermore, the influence of the process temperature on occurring stresses is analysed. Based on the results of the investigations, an adequate forming strategy and a tool concept for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel are presented.}},
editor = {{Kuball, Clara-Maria and Uhe, Benedikt and Meschut, Gerson and Merklein, Marion}},
keywords = {{high nitrogen steel, self-piercing riveting, joining by forming, bulk forming, tool design}},
pages = {{280--285}},
title = {{{Process design for the forming of semi-tubular self-piercing rivets made of high nitrogen steel}}},
doi = {{10.1016/j.promfg.2020.08.052}},
volume = {{50}},
year = {{2020}},
}
@misc{19999,
author = {{Mayer, Stefan}},
publisher = {{Universität Paderborn}},
title = {{{Optimierung von JMCTest beim Testen von Inter Method Contracts}}},
year = {{2020}},
}
@inproceedings{20116,
author = {{Nouri, Zahra and Wachsmuth, Henning and Engels, Gregor}},
booktitle = {{Proceedings of COLING 2020, the 28th International Conference on Computational Linguistics}},
location = {{Barcelona, Spain}},
pages = {{6264--6276}},
title = {{{Mining Crowdsourcing Problems from Discussion Forums of Workers}}},
year = {{2020}},
}
@inproceedings{20122,
author = {{El Baff, Roxanne and Al-Khatib, Khalid and Stein, Benno and Wachsmuth, Henning}},
booktitle = {{Third Workshop on Computational Modeling of People's Opinions, Personality, and Emotions in Social Media (PEOPLES 2020)}},
pages = {{29--40}},
title = {{{Persuasiveness of News Editorials depending on Ideology and Personality}}},
year = {{2020}},
}
@inbook{20123,
author = {{Herzig, Bardo and Martin, Alexander and Klar, Tilman-Mathies}},
booktitle = {{Deutsch Digital. Band 1 Theorie (2. Aufl.)}},
editor = {{Knopf, Julia and Abraham, Ulf}},
isbn = {{978-3-8340-2048-2}},
pages = {{108--135}},
title = {{{Mobile Medien – Medienpädagogische und technische Grundlagen, Potential für den Deutschunterricht und Beispiele.}}},
year = {{2020}},
}
@techreport{20131,
author = {{Kundisch, Dennis and Beverungen, Daniel}},
pages = {{22--26}},
title = {{{Als Wirtschaftsinformatiker die digitale Transformation in Organisationen gestalten}}},
year = {{2020}},
}
@inproceedings{20139,
author = {{Spliethöver, Maximilian and Wachsmuth, Henning}},
booktitle = {{Proceedings of the 7th Workshop on Argument Mining (ArgMining 2020)}},
pages = {{76--87}},
title = {{{Argument from Old Man's View: Assessing Social Bias in Argumentation}}},
year = {{2020}},
}
@inproceedings{20140,
author = {{Dorsch, Jonas and Wachsmuth, Henning}},
booktitle = {{Proceedings of the 7th Workshop on Argument Mining (ArgMining 2020)}},
pages = {{19--29}},
title = {{{Semi-Supervised Cleansing of Web Argument Corpora}}},
year = {{2020}},
}
@inproceedings{20141,
author = {{Heindorf, Stefan and Scholten, Yan and Wachsmuth, Henning and Ngonga Ngomo, Axel-Cyrille and Potthast, Martin}},
booktitle = {{Proceedings of the 28th ACM International Conference on Information and Knowledge Management (CIKM 2020)}},
pages = {{3023--3030}},
title = {{{CauseNet: Towards a Causality Graph Extracted from the Web}}},
doi = {{10.1145/3340531.3412763}},
year = {{2020}},
}
@techreport{20145,
abstract = {{Der Karosseriebau ist zunehmend durch die Verwendung unterschiedlicher Werkstoffe in Mischbauweise gekennzeichnet, was zu einem Einsatz von mechanischen Fügeverfahren geführt hat. Hieraus resultieren die Zielsetzungen, die mechanischen Fügeverfahren in ihrer Effizienz und ihren Einsatzbereichen zu erweitern, sowie die Anzahl der Experimente zu reduzieren und Entwicklungszyklen zu verkürzen. Dies erfolgt mit Unterstützung der numerischen Simulation. Neben der Beschreibung des plastischen Verhaltens gilt es auch, das Schädigungsverhalten abzubilden.
Der Fügeprozess bzw. die Fügerichtung erfolgt senkrecht zur Blechoberfläche und führt somit zu einem dreidimensionalen Zustand der Fügelemente. Hieraus leitet sich die Herausforderung ab, das Werkstoffversagen in Abhängigkeit der Beanspruchungssituation zu beschreiben. Ein einfacher Ansatz zur Abbildung des Durchdringens ist ein geometrisches Trennkriterium.
Ein solches Kriterium basiert i.d.R. auf einem experimentell beobachteten Verhalten und ist somit nicht prognosefähig für Variationen bzgl. Werkzeugkonfigurationen, Blechdicken- und Werkstoffgüten-Kombinationen. In diesem Projekt wird das Schädigungsmodell GISSMO (Generalized Incremental Stress State dependent damage Model) verwendet, um die Entwicklung der duktilen Schädigung zu beschreiben und den Bruchbeginn während des Stanzniet- und Schneidclinchens vorherzusagen.
Der Spannungszustand während der Prozesssimulation wird untersucht und die verschiedenen Schädigungsproben werden experimentell erprobt, um die Versagenskurven zu charakterisieren. Die Versagenskurven werden im Schädigungsmodell GISSMO definiert. Um die Genauigkeit des Modells zu gewährleisten, wird die Verifizierung des Modells durch die Simulation von Schädigungsproben mit dem Schädigungsmodell durchgeführt.
Zur Validierung des Modells wird die Simulation des Fügeprozesses mit dem Schädigungsmodell durchgeführt und die Ergebnisse von Simulation und Experiment verglichen. Darüber hinaus werden Sensitivitätsanalysen durchgeführt, um die Einflüsse der Fertigungsprozesse, der Lackierung und des Diskretisierungsgrades auf das Schädigungsverhalten des Materials zu identifizieren.
Das IGF-Vorhaben „Methodenentwicklung zur Schädigungsmodellierung für die numerische Prozesssimulation mechanischer Fügeverfahren" der Forschungsvereinigung EFB e.V. wurde unter der Fördernummer AiF 19452N über die Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF) im Rahmen des Programms zur Förderung der Industriellen Gemeinschaftsforschung (IGF) vom Bundesministerium für Wirtschaft und Energie aufgrund eines Beschlusses des Deutschen Bundestages gefördert. Der Abschlussbericht ist als EFB-Forschungsbericht Nr. 527 erschienen und bei der EFB-Geschäftsstelle und im Buchhandel erhältlich.}},
author = {{Otroshi, Mortaza and Meschut, Gerson}},
isbn = {{978-3-86776-582-4}},
pages = {{182}},
publisher = {{Europäische Forschungsgesellschaft für Blechverarbeitung e.V.}},
title = {{{Methodenentwicklung zur Schädigungsmodellierung für die numerische Prozesssimulation mechanischer Fügeverfahren}}},
year = {{2020}},
}
@inproceedings{20146,
abstract = {{Joining technology is regarded as a key technology for reducing energy consumption and CO2 imitation as well as the use of innovative materials and development of new, resource-saving products. Punch riveting is a widely used and established joining process in many sectors. The white and brown goods, electrical engineering, construction and, in particular, the automotive industry are some of the sectors mentioned here.
Since the design and assessment of punch rivet components with regard to structural durability can only be carried out experimentally using prototypes due to a lack of experience and calculation concepts, the improvement of this uneconomical and time-consuming procedure is the goal of this contribution.
Therefore, a numerical simulation and design method for cyclically loads punched riveted joints shall be introduced. This concept shall be based on the notch strain concept.
The following steps are necessary to achieve the goal shown above:
Tensile tests on all materials involved in the joint for determination of tensile strength and quasi-static stress-strain curves
Estimation of the cyclic material properties from the tensile strength in order to obtain the strain-life curve and the cyclic stress-strain curve
Estimation of mean stress sensitivity from the tensile strength to conduct an amplitude transformation for variable amplitude loadings.
Execution of a 2D forming simulation of the joining process to determine the geometry and the stresses and degrees of deformation present in the connection
Transferring the results of the forming simulation into a static-mechanical load simulation for determining the relation between the external load and the elastic-plastic strain at the critical point
Estimation of the service life by means of the damage parameter Wöhler curves calculated from the strain-life curve
In order to verify the simulation and calculation method, service life investigations have been carried out on punched riveted components under constant and variable amplitude load.
The test results, as well as the workflow through the fatigue assessment and its accuracy in estimation the fatigue life will be shown in this contribution.}},
author = {{Masendorf, Lukas and Wächter, Michael and Horstmann, Stephan and Otroshi, Mortaza and Esderts, Alfons and Meschut, Gerson}},
isbn = {{978-3-9820591-0-5}},
keywords = {{punch rivet, notch strain conept, structural durability}},
location = {{Darmstadt, Germany}},
publisher = {{Deutscher Verband für Materialforschung und -prüfung e.V.}},
title = {{{Linear damage accumulation of self-pierce riveted joints}}},
year = {{2020}},
}
@article{20156,
author = {{Schapeler, Timon and Philipp Höpker, Jan and Bartley, Tim}},
issn = {{1094-4087}},
journal = {{Optics Express}},
title = {{{Quantum detector tomography of a 2×2 multi-pixel array of superconducting nanowire single photon detectors}}},
doi = {{10.1364/oe.404285}},
year = {{2020}},
}