TY - GEN
AB - Many problems in science and engineering require the efficient numerical
approximation of integrals, a particularly important application being the
numerical solution of initial value problems for differential equations. For
complex systems, an equidistant discretization is often inadvisable, as it
either results in prohibitively large errors or computational effort. To this
end, adaptive schemes have been developed that rely on error estimators based
on Taylor series expansions. While these estimators a) rely on strong
smoothness assumptions and b) may still result in erroneous steps for complex
systems (and thus require step rejection mechanisms), we here propose a
data-driven time stepping scheme based on machine learning, and more
specifically on reinforcement learning (RL) and meta-learning. First, one or
several (in the case of non-smooth or hybrid systems) base learners are trained
using RL. Then, a meta-learner is trained which (depending on the system state)
selects the base learner that appears to be optimal for the current situation.
Several examples including both smooth and non-smooth problems demonstrate the
superior performance of our approach over state-of-the-art numerical schemes.
The code is available under https://github.com/lueckem/quadrature-ML.
AU - Dellnitz, Michael
AU - Hüllermeier, Eyke
AU - Lücke, Marvin
AU - Ober-Blöbaum, Sina
AU - Offen, Christian
AU - Peitz, Sebastian
AU - Pfannschmidt, Karlson
ID - 21600
T2 - arXiv:2104.03562
TI - Efficient time stepping for numerical integration using reinforcement learning
ER -
TY - JOUR
AB - It is a challenging task to identify the objectives on which a certain decision was based, in particular if several, potentially conflicting criteria are equally important and a continuous set of optimal compromise decisions exists. This task can be understood as the inverse problem of multiobjective optimization, where the goal is to find the objective function vector of a given Pareto set. To this end, we present a method to construct the objective function vector of an unconstrained multiobjective optimization problem (MOP) such that the Pareto critical set contains a given set of data points with prescribed KKT multipliers. If such an MOP can not be found, then the method instead produces an MOP whose Pareto critical set is at least close to the data points. The key idea is to consider the objective function vector in the multiobjective KKT conditions as variable and then search for the objectives that minimize the Euclidean norm of the resulting system of equations. By expressing the objectives in a finite-dimensional basis, we transform this problem into a homogeneous, linear system of equations that can be solved efficiently. Potential applications of this approach include the identification of objectives (both from clean and noisy data) and the construction of surrogate models for expensive MOPs.
AU - Gebken, Bennet
AU - Peitz, Sebastian
ID - 16295
JF - Journal of Global Optimization
TI - Inverse multiobjective optimization: Inferring decision criteria from data
VL - 80
ER -
TY - JOUR
AB - Secret sharing is a well-established cryptographic primitive for storing highly sensitive information like encryption keys for encoded data. It describes the problem of splitting a secret into different shares, without revealing any information to its shareholders. Here, we demonstrate an all-optical solution for secret sharing based on metasurface holography. In our concept, metasurface holograms are used as spatially separable shares that carry encrypted messages in the form of holographic images. Two of these shares can be recombined by bringing them close together. Light passing through this stack of metasurfaces accumulates the phase shift of both holograms and optically reconstructs the secret with high fidelity. In addition, the hologram generated by each single metasurface can uniquely identify its shareholder. Furthermore, we demonstrate that the inherent translational alignment sensitivity between two stacked metasurface holograms can be used for spatial multiplexing, which can be further extended to realize optical rulers.
AU - Georgi, Philip
AU - Wei, Qunshuo
AU - Sain, Basudeb
AU - Schlickriede, Christian
AU - Wang, Yongtian
AU - Huang, Lingling
AU - Zentgraf, Thomas
ID - 21631
IS - 16
JF - Science Advances
SN - 2375-2548
TI - Optical secret sharing with cascaded metasurface holography
VL - 7
ER -
TY - CONF
AB - Several methods, including order analysis, wavelet analysis and empirical mode decomposition have been proposed and successfully employed for the health state estimation of technical systems operating under varying conditions. However, where information such as the speed of rotating machinery, component specifications or other domain-specific information is unavailable, such methods are often infeasible. Thus, this paper investigates the application of classical time-domain features, features from the medical field and novel features from the highly comparative time-series analysis (HCTSA) package, for the health state estimation of rotating machinery operating under varying conditions. Furthermore, several feature selection methods are investigated to identify features as viable health indicators for the diagnostics and prognostics of technical systems. As a case study, the presented methods are evaluated on real-world and experimentally acquired vibration data of bearings operating under varying speed. The results show that the selected features can successfully be employed as health indicators for technical systems operating under varying conditions.
AU - Aimiyekagbon, Osarenren Kennedy
AU - Bender, Amelie
AU - Sextro, Walter
ID - 22507
KW - Wind turbine diagnostics
KW - bearing diagnostics
KW - non-stationary operating conditions
KW - varying operating conditions
KW - feature extraction
KW - feature selection
KW - fault detection
KW - failure detection
T2 - Proceedings of the Seventeenth International Conference on Condition Monitoring and Asset Management (CM 2021)
TI - On the applicability of time series features as health indicators for technical systems operating under varying conditions
ER -
TY - JOUR
AU - Friedrich, Christoph
AU - Blügel, Stefan
AU - Schindlmayr, Arno
ID - 22761
IS - 3
JF - Physical Review B
SN - 2469-9950
TI - Erratum: Efficient implementation of the GW approximation within the all-electron FLAPW method [Phys. Rev. B 81, 125102 (2010)]
VL - 104
ER -
TY - GEN
AB - The Koopman operator has become an essential tool for data-driven approximation of dynamical (control) systems in recent years, e.g., via extended dynamic mode decomposition. Despite its popularity, convergence results and, in particular, error bounds are still quite scarce. In this paper, we derive probabilistic bounds for the approximation error and the prediction error depending on the number of training data points; for both ordinary and stochastic differential equations. Moreover, we extend our analysis to nonlinear control-affine systems using either ergodic trajectories or i.i.d.
samples. Here, we exploit the linearity of the Koopman generator to obtain a bilinear system and, thus, circumvent the curse of dimensionality since we do not autonomize the system by augmenting the state by the control inputs. To the
best of our knowledge, this is the first finite-data error analysis in the stochastic and/or control setting. Finally, we demonstrate the effectiveness of the proposed approach by comparing it with state-of-the-art techniques showing its superiority whenever state and control are coupled.
AU - Nüske, Feliks
AU - Peitz, Sebastian
AU - Philipp, Friedrich
AU - Schaller, Manuel
AU - Worthmann, Karl
ID - 23428
T2 - arXiv:2108.07102
TI - Finite-data error bounds for Koopman-based prediction and control
ER -
TY - CONF
AU - Kucklick, Jan-Peter
AU - Müller, Jennifer
AU - Beverungen, Daniel
AU - Müller, Oliver
ID - 22514
T2 - European Conference on Information Systems
TI - Quantifying the Impact of Location Data for Real Estate Appraisal – A GIS-based Deep Learning Approach
ER -
TY - JOUR
AB - Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe-Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.
AU - Schmidt, Falko
AU - Kozub, Agnieszka L.
AU - Gerstmann, Uwe
AU - Schmidt, Wolf Gero
AU - Schindlmayr, Arno
ID - 21946
IS - 5
JF - Crystals
TI - Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response
VL - 11
ER -
TY - CONF
AB - This paper deals with a novel method for the online fitting of a microscopic traffic simulation model to the current state of a real world traffic area. The traffic state estimation is based on limited data of different measurement sources and guarantees general accordance of reality and simulation in terms of multimodal road traffic counts and vehicle speeds. The research is embedded in the challenge of improving the traffic by controlling the traffic light systems (TLS) of the examined area. Therefore, the current traffic state and the predicted route choices of individual road users are the matter of interest. The concept is generally transferable to any road traffic system. To give an impression of the accuracy and potential of the approach, the validation and first application results are presented.
AU - Malena, Kevin
AU - Link, Christopher
AU - Mertin, Sven
AU - Gausemeier, Sandra
AU - Trächtler, Ansgar
ID - 24166
SN - 978-1-7281-7584-3
T2 - 2021 IEEE Transportation Electrification Conference & Expo (ITEC)
TI - Validation of an Online State Estimation Concept for Microscopic Traffic Simulations◆
ER -
TY - CONF
AU - zur Heiden, Philipp
AU - Priefer, Jennifer
ED - Breitner, Michael H.
ED - Lehnhoff, Sebastian
ED - Nieße, Astrid
ED - Staudt, Philipp
ED - Weinhardt, Christof
ED - Werth, Oliver
ID - 24534
T2 - Pre-Conference 16th International Congress on Wirtschaftsinformatik at Universität Duisburg-Essen
TI - Transitioning to Condition-Based Maintenance on the Distribution Grid: Deriving Design Principles from a Qualitative Study
ER -
TY - JOUR
AB - Microstructure transformation due to thermo-mechanical processing have an acute effect the macroscopic properties of low carbon steels. This effect includes visco-plastic deformation and phase transformations. Hot forming processes such as press hardening are particularly affected. Most engineering applications require a combination of high strength and sufficient residual ductility, which can be achieved by the development of graded microstructures. In the present work, the evolution of phase transformations is investigated by linking experiments and simulations to produce graded microstructures. For this purpose, an extended material model is proposed to represent the evolution of phase transformations under inhomogeneous heating and cooling strategies. On the experimental side, phase transformations are identified during thermo-mechanical treatment of flat steel specimens using digital image correlation and thermal imaging. Based on the experimental results, the material parameters are identified, and the simulation model is validated. On the numerical side an algorithm for the finite-element simulation of phase transformations in low carbon steels is proposed. The evolution of phase transformations is presented for the simulation of tensile specimen employing the finite-element-method.
AU - Westermann, Hendrik
AU - Reitz, Alexander
AU - Mahnken, Rolf
AU - Schaper, Mirko
AU - Grydin, Olexandr
ID - 23795
JF - steel research international
KW - phase transformations
KW - graded microstructure
KW - low carbon steel
KW - thermo-mechanical treatment
KW - digital image correlation
SN - 1611-3683
TI - Microstructure transformations in a press hardening steel during tailored thermo‐mechanical processing
ER -
TY - JOUR
AU - Reitz, Alexander
AU - Grydin, Olexandr
AU - Schaper, Mirko
ID - 23803
JF - Materials Data for Smart Forming Technologies
TI - Characterization of phase transformations during graded thermo- mechanical treatment of steel 22MnB5 by means of optical methods
ER -
TY - JOUR
AB - AbstractQuantum well (QW) heterostructures have been extensively used for the realization of a wide range of optical and electronic devices. Exploiting their potential for further improvement and development requires a fundamental understanding of their electronic structure. So far, the most commonly used experimental techniques for this purpose have been all-optical spectroscopy methods that, however, are generally averaging in momentum space. Additional information can be gained by angle-resolved photoelectron spectroscopy (ARPES), which measures the electronic structure with momentum resolution. Here we report on the use of extremely low-energy ARPES (photon energy ~ 7 eV) to increase depth sensitivity and access buried QW states, located at 3 nm and 6 nm below the surface of cubic-GaN/AlN and GaAs/AlGaAs heterostructures, respectively. We find that the QW states in cubic-GaN/AlN can indeed be observed, but not their energy dispersion, because of the high surface roughness. The GaAs/AlGaAs QW states, on the other hand, are buried too deep to be detected by extremely low-energy ARPES. Since the sample surface is much flatter, the ARPES spectra of the GaAs/AlGaAs show distinct features in momentum space, which can be reconducted to the band structure of the topmost surface layer of the QW structure. Our results provide important information about the samples’ properties required to perform extremely low-energy ARPES experiments on electronic states buried in semiconductor heterostructures.
AU - Hajlaoui, Mahdi
AU - Ponzoni, Stefano
AU - Deppe, Michael
AU - Henksmeier, Tobias
AU - As, Donat Josef
AU - Reuter, Dirk
AU - Zentgraf, Thomas
AU - Springholz, Gunther
AU - Schneider, Claus Michael
AU - Cramm, Stefan
AU - Cinchetti, Mirko
ID - 25227
JF - Scientific Reports
SN - 2045-2322
TI - Extremely low-energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/AlGaAs heterostructures
VL - 11
ER -
TY - CONF
AU - Syed, Shahbaz
AU - Al-Khatib, Khalid
AU - Alshomary, Milad
AU - Wachsmuth, Henning
AU - Potthast, Martin
ID - 22158
T2 - Proceedings of the Joint Conference of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (ACL-IJCNLP 2021): Findings
TI - Generating Informative Conclusions for Argumentative Texts
ER -
TY - JOUR
AB - AbstractIn order to reduce fuel consumption and thus pollutant emissions, the automotive industry is increasingly developing lightweight construction concepts that are accompanied by an increasing usage of aluminum materials. Due to poor weldability of aluminum in combination with other materials, mechanical joining methods such as clinching were developed and established in series production. In order to predict the relevant characteristics of clinched joints and to ensure the reliability of the process, it is simulated numerically during product development processes. In this regard, the predictive accuracy of the simulated process highly depends on the implemented friction model. In particular, the frictional behavior between the sheet metals as well as between the sheet metal and clinching tools has a significant impact on the geometrical formation of the clinched joint. No testing methods exist that can sufficiently investigate the frictional behavior in sheet materials, especially under high interface pressures, different relative velocities, and long friction paths, while allowing a decoupled consideration of the test parameters. This paper describes the development of further testing concepts based on a proven tribo-torsion test method for determining friction coefficients between sheet metal materials for the simulation of clinching processes. For this purpose, the correlation of interface pressure and the relative velocity between aluminum and steel sheet material in clinching processes is investigated using numerical simulation. Based on these findings, the developed concepts focus on determining friction coefficients at interface pressures of the above materials, yield stress, as well as the reproduction of the occurring friction conditions between sheet metal materials and tool surfaces in clinching processes using tool substitutes. Furthermore, wear investigations between sheet metal material and tool surface were carried out in the friction tests with subsequent EDX analyses of the frictioned tool surfaces. The developed method also allows an optical deformation measurement of the sheet metal material specimen by means of digital image correlation (DIC). Based on a methodological approach, the test setups and the test systems used are explained, and the functionality of the concepts is proven by experimental tests using different sheet metal materials.
AU - Böhnke, Max
AU - Rossel, Moritz Sebastian
AU - Bielak, Christian Roman
AU - Bobbert, Mathias
AU - Meschut, Gerson
ID - 25556
JF - The International Journal of Advanced Manufacturing Technology
SN - 0268-3768
TI - Concept development of a method for identifying friction coefficients for the numerical simulation of clinching processes
ER -
TY - CONF
AU - Pollmeier, Pascal
AU - Fechner, Sabine
ED - Habig, Sebastian
ID - 26718
T2 - Naturwissenschaftlicher Unterricht und Lehrerbildung im Umbruch?
TI - Erweiterung des epistemologischen Verständnisses durch Konfrontation mit anomalen Daten.
ER -
TY - GEN
AB - We study the complexity of problems solvable in deterministic polynomial time
with access to an NP or Quantum Merlin-Arthur (QMA)-oracle, such as $P^{NP}$
and $P^{QMA}$, respectively. The former allows one to classify problems more
finely than the Polynomial-Time Hierarchy (PH), whereas the latter
characterizes physically motivated problems such as Approximate Simulation
(APX-SIM) [Ambainis, CCC 2014]. In this area, a central role has been played by
the classes $P^{NP[\log]}$ and $P^{QMA[\log]}$, defined identically to $P^{NP}$
and $P^{QMA}$, except that only logarithmically many oracle queries are
allowed. Here, [Gottlob, FOCS 1993] showed that if the adaptive queries made by
a $P^{NP}$ machine have a "query graph" which is a tree, then this computation
can be simulated in $P^{NP[\log]}$.
In this work, we first show that for any verification class
$C\in\{NP,MA,QCMA,QMA,QMA(2),NEXP,QMA_{\exp}\}$, any $P^C$ machine with a query
graph of "separator number" $s$ can be simulated using deterministic time
$\exp(s\log n)$ and $s\log n$ queries to a $C$-oracle. When $s\in O(1)$ (which
includes the case of $O(1)$-treewidth, and thus also of trees), this gives an
upper bound of $P^{C[\log]}$, and when $s\in O(\log^k(n))$, this yields bound
$QP^{C[\log^{k+1}]}$ (QP meaning quasi-polynomial time). We next show how to
combine Gottlob's "admissible-weighting function" framework with the
"flag-qubit" framework of [Watson, Bausch, Gharibian, 2020], obtaining a
unified approach for embedding $P^C$ computations directly into APX-SIM
instances in a black-box fashion. Finally, we formalize a simple no-go
statement about polynomials (c.f. [Krentel, STOC 1986]): Given a multi-linear
polynomial $p$ specified via an arithmetic circuit, if one can "weakly
compress" $p$ so that its optimal value requires $m$ bits to represent, then
$P^{NP}$ can be decided with only $m$ queries to an NP-oracle.
AU - Gharibian, Sevag
AU - Rudolph, Dorian
ID - 27160
T2 - To appear in 13th Innovations in Theoretical Computer Science (ITCS 2022)
TI - On polynomially many queries to NP or QMA oracles
ER -
TY - JOUR
AB - Due to the lack of established real-world benchmark suites for static taint analyses of Android applications, evaluations of these analyses are often restricted and hard to compare. Even in evaluations that do use real-world apps, details about the ground truth in those apps are rarely documented, which makes it difficult to compare and reproduce the results. To push Android taint analysis research forward, this paper thus recommends criteria for constructing real-world benchmark suites for this specific domain, and presents TaintBench, the first real-world malware benchmark suite with documented taint flows. TaintBench benchmark apps include taint flows with complex structures, and addresses static challenges that are commonly agreed on by the community. Together with the TaintBench suite, we introduce the TaintBench framework, whose goal is to simplify real-world benchmarking of Android taint analyses. First, a usability test shows that the framework improves experts’ performance and perceived usability when documenting and inspecting taint flows. Second, experiments using TaintBench reveal new insights for the taint analysis tools Amandroid and FlowDroid: (i) They are less effective on real-world malware apps than on synthetic benchmark apps. (ii) Predefined lists of sources and sinks heavily impact the tools’ accuracy. (iii) Surprisingly, up-to-date versions of both tools are less accurate than their predecessors.
AU - Luo, Linghui
AU - Pauck, Felix
AU - Piskachev, Goran
AU - Benz, Manuel
AU - Pashchenko, Ivan
AU - Mory, Martin
AU - Bodden, Eric
AU - Hermann, Ben
AU - Massacci, Fabio
ID - 27045
JF - Empirical Software Engineering
SN - 1382-3256
TI - TaintBench: Automatic real-world malware benchmarking of Android taint analyses
ER -
TY - JOUR
AB - ZusammenfassungLehrkräftekooperation wird generell eine positive Bedeutung in Bezug auf Schul- und Unterrichtsentwicklung zugeschrieben. Dabei sind empirische Belege für eine positive Wirksamkeit nach wie vor kaum vorhanden, es gibt sogar Befunde zu ‚negativen‘ Konsequenzen von Lehrkräftekooperation. Um diese Widersprüchlichkeit zu klären, wurde in der vorliegenden Arbeit Kooperation nicht als Instrument bzw. als Technik betrachtet, sondern als soziale Praxis verstanden, in der eigenlogisches, kollektiv-implizites Wissen (re)produziert wird (Community of Practice). Parallel dazu wurde ein praxeologisches Kompetenzverständnis (Praxiskompetenz) eingeführt, das wesentlich auf die Praxeologie Pierre Bourdieus zurückgeht und den Zusammenhang zwischen Lehrkräftekooperation als Community of Practice und kollektiv strukturierter, individueller Kompetenz theoretisch verdeutlicht. Die empirischen Befunde, welche mittels der Dokumentarischen Methode generiert wurden, verweisen auf die Bedeutung unterschiedlicher Relationslogiken (Nicht-Passung, Entfaltung, Herausforderung) für das ‚Lernen‘ von oder innerhalb von Praxiskompetenz(en) und damit auch auf die Wichtigkeit einer grundlegend kollektiv gerahmten Perspektive auf Lehrkräftekooperation. Vor diesem Hintergrund ist ein allzu positiver Blick auf Lehrkräftekooperationsprozesse kritisch zu betrachten.
AU - Bloh, Thiemo
ID - 27881
JF - Zeitschrift für Bildungsforschung
SN - 2190-6890
TI - Entwicklung von Praxiskompetenz durch Kooperationsprozesse von Lehrkräften
ER -
TY - GEN
AB - As in almost every other branch of science, the major advances in data
science and machine learning have also resulted in significant improvements
regarding the modeling and simulation of nonlinear dynamical systems. It is
nowadays possible to make accurate medium to long-term predictions of highly
complex systems such as the weather, the dynamics within a nuclear fusion
reactor, of disease models or the stock market in a very efficient manner. In
many cases, predictive methods are advertised to ultimately be useful for
control, as the control of high-dimensional nonlinear systems is an engineering
grand challenge with huge potential in areas such as clean and efficient energy
production, or the development of advanced medical devices. However, the
question of how to use a predictive model for control is often left unanswered
due to the associated challenges, namely a significantly higher system
complexity, the requirement of much larger data sets and an increased and often
problem-specific modeling effort. To solve these issues, we present a universal
framework (which we call QuaSiModO:
Quantization-Simulation-Modeling-Optimization) to transform arbitrary
predictive models into control systems and use them for feedback control. The
advantages of our approach are a linear increase in data requirements with
respect to the control dimension, performance guarantees that rely exclusively
on the accuracy of the predictive model, and only little prior knowledge
requirements in control theory to solve complex control problems. In particular
the latter point is of key importance to enable a large number of researchers
and practitioners to exploit the ever increasing capabilities of predictive
models for control in a straight-forward and systematic fashion.
AU - Peitz, Sebastian
AU - Bieker, Katharina
ID - 21199
T2 - arXiv:2102.04722
TI - On the Universal Transformation of Data-Driven Models to Control Systems
ER -