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Geförderte OA-Publikationen mit Erscheinungsjahr 2020

Anzahl der Treffer: 64
Erstellt: Fri, 26 Feb 2021 23:33:38 +0100 in 0.0406 sec


Schweser, Thomas; Stiebitz, Michael;
Partitions of hypergraphs under variable degeneracy constraints. - In: Journal of graph theory. - New York, NY [u.a.] : Wiley, ISSN 1097-0118, Bd. 96 (2021), 1, S. 7-33

https://doi.org/10.1002/jgt.22575
Song, Xinya; Cai, Hui; Jiang, Teng; Sennewald, Tom; Kircheis, Jan; Schlegel, Steffen; Noris, L.; Benzetta, Y.; Westermann, Dirk;
Research on performance of real-time simulation based on inverter-dominated power grid. - In: IEEE access : practical research, open solutions.. - New York, NY : IEEE, ISSN 2169-3536, Bd. 9 (2021), S. 1137-1153

https://doi.org/10.1109/ACCESS.2020.3016177
Eichfelder, Gabriele; Warnow, Leo;
Proximity measures based on KKT points for constrained multi-objective optimization. - In: Journal of global optimization. - Dordrecht [u.a.] : Springer Science + Business Media B.V, ISSN 1573-2916, (2020), insges. 24 S.
- Published: 08 December 2020

An important aspect of optimization algorithms, for instance evolutionary algorithms, are termination criteria that measure the proximity of the found solution to the optimal solution set. A frequently used approach is the numerical verification of necessary optimality conditions such as the Karush-Kuhn-Tucker (KKT) conditions. In this paper, we present a proximity measure which characterizes the violation of the KKT conditions. It can be computed easily and is continuous in every efficient solution. Hence, it can be used as an indicator for the proximity of a certain point to the set of efficient (Edgeworth-Pareto-minimal) solutions and is well suited for algorithmic use due to its continuity properties. This is especially useful within evolutionary algorithms for candidate selection and termination, which we also illustrate numerically for some test problems.



https://doi.org/10.1007/s10898-020-00971-3
Köhler, Tobias; Grätzel, Michael; Bergmann, Jean Pierre;
Influence of different Ni coatings on the long-term behavior of ultrasonic welded EN AW 1370 cable/EN CW 004A arrestor dissimilar joints. - In: Welding in the world. - Berlin : Springer, ISSN 1878-6669, (2020), insges. 12 S.
- Published: 23 November 2020

The increasing demand for energy-efficient vehicles requires suitable methods for cost and weight reduction. This can be achieved by the replacement of copper by aluminum, in particular for the on-board power systems. However, the complete substitution is restricted by the mechanical and physical material properties of aluminum as well as challenges in the aluminum copper interface. The challenges concern the corrosion vulnerability and the occurrence of brittle intermetallic compounds (IMC) which can negatively influence the mechanical properties and the electrical conductivity. Therefore, current investigations focus on the one hand on the realization of dissimilar aluminum copper joints by suitable joining technologies, like ultrasonic welding, and on the other hand on the assurance of a sufficient prevention against harmful corrosion effects. In cases where the joint cannot be protected against corrosion by sealing, nickel coatings can be used to protect the joint. In the present study, the influence of electroless, electroplated, and sulfamate nickel coatings was investigated regarding the long-term stability. The joints were performed as industry-related arrester connections, consisting of EN AW 1370 cables and EN CW 004A terminals. The samples were exposed to corrosive as well as electrical, thermal, and mechanical stress tests according to current standards and regulations.



https://doi.org/10.1007/s40194-020-01030-x
Hunold, Alexander; Machts, René; Haueisen, Jens;
Head phantoms for bioelectromagnetic applications: a material study. - In: Biomedical engineering online. - London : BioMed Central, ISSN 1475-925X, Bd. 19 (2020), 87, S. 1-14

Assessments of source reconstruction procedures in electroencephalography and computations of transcranial electrical stimulation profiles require verification and validation with the help of ground truth configurations as implemented by physical head phantoms. For these phantoms, synthetic materials are needed, which are mechanically and electrochemically stable and possess conductivity values similar to the modeled human head tissues. Three-compartment head models comprise a scalp layer with a conductivity range of 0.137 S/m to 2.1 S/m, a skull layer with conductivity values between 0.066 S/m and 0.00275 S/m, and an intracranial volume with an often-used average conductivity value of 0.33 S/m. To establish a realistically shaped physical head phantom with a well-defined volume conduction configuration, we here characterize the electrical conductivity of synthetic materials for modeling head compartments. We analyzed agarose hydrogel, gypsum, and sodium chloride (NaCl) solution as surrogate materials for scalp, skull, and intracranial volume. We measured the impedance of all materials when immersed in NaCl solution using a four-electrode setup. The measured impedance values were used to calculate the electrical conductivity values of each material. Further, the conductivities in the longitudinal and transverse directions of reed sticks immersed in NaCl solution were measured to test their suitability for mimicking the anisotropic conductivity of white matter tracts.



https://doi.org/10.1186/s12938-020-00830-y
Budzinski, Oliver; Gänßle, Sophia; Stöhr, Annika;
The proposal of a 10th amendment of German competition law: interventionism or laissez-faire? :
Der Entwurf zur 10. GWB Novelle: Interventionismus oder Laissez-faire?. - In: List Forum für Wirtschafts- und Finanzpolitik. - [Berlin] : Springer Gabler, ISSN 2364-3943, Bd. 46 (2020), 2, S. 157-184

https://doi.org/10.1007/s41025-020-00204-1
Rochyadi-Reetz, Mira; Budiono, Olivia Deskarina; Wolling, Jens;
Regularity of a crisis: media framing of the 2015 transboundary haze issue in Indonesia, Singapore, and Malaysia. - In: Jurnal Komunikasi. - Bangi : Universiti Kebangsaan Malaysia, ISSN 0128-1496, Bd. 36 (2020), 2, S. 415-433
- Richtiger Name des Verfassers: Olivia Deskarina Budiono

The problem of the haze caused by huge forest fires persists as an annual transboundary problem for Indonesia and the rest of Southeast Asia. In 2015, the problem was worse than ever before, affecting many countries in the Association of Southeast Asian Nations (ASEAN) and causing respiratory ailments for more than half a million Indonesians. This study explores the media framing of the haze problem in Indonesia from June to December 2015. Using Entmans framing approach, it investigates how media outlets from Indonesia, Malaysia, and Singapore covered the crisis. Articles from six online media outlets published in these three countries were analysed. Using cluster analysis, this research identified three frames as follows: (1) crisis frame, (2) immediate action frame, and (3) regular problem frame. The first cluster/frame consists of articles giving high salience to all problems and causes of the forest fires provoking the haze. In contrast, the second frame mostly ignores causes and problems and focuses almost exclusively on the need for immediate action. The third frame, which represents more than 60% of the articles, covers the haze problem as a regular issue without emphasizing prominently either the different aspects of the problem itself or its causes and solutions. Further results show that the media in Singapore and Malaysia used the crisis frame more often than the media in Indonesia.



https://doi.org/10.17576/JKMJC-2020-3602-25
Boeck, Thomas; Sanjari, Seyed Loghman; Becker, Tatiana;
Parametric instability of a magnetic pendulum in the presence of a vibrating conducting plate. - In: Nonlinear dynamics : an international journal of nonlinear dynamics and chaos in engineering systems.. - Dordrecht [u.a.] : Springer Science + Business Media B.V, ISSN 1573-269X, Bd. 102 (2020), 4, S. 2039-2056

A pendulum with an attached permanent magnet swinging in the vicinity of a conductor is a typical experiment for the demonstration of electromagnetic braking and Lenz law of induction. When the conductor itself moves, it can transfer energy to the pendulum. An exact analytical model of such an electromagnetic interaction is possible for a flat conducting plate. The eddy currents induced in the plate by a moving magnetic dipole and the resulting force and torque are known analytically in the quasistatic limit, i.e., when the magnetic diffusivity is sufficiently high to ensure an equilibrium of magnetic field advection and diffusion. This allows us to study a simple pendulum with a magnetic dipole moment in the presence of a horizontal plate oscillating in vertical direction. Equilibrium of the pendulum in the vertical position can be realized in three cases considered, i.e., when the magnetic moment is parallel to the rotation axis, or otherwise, its projection onto the plane of motion is either horizontal or vertical. The stability problem is described by a differential equation of Mathieu type with a damping term. Instability is only possible when the vibration amplitude and the distance between plate and magnet satisfy certain constraints related to the simultaneous excitation and damping effects of the plate. The nonlinear motion is studied numerically for the case when the magnetic moment and rotation axis are parallel. Chaotic behavior is found when the eigenfrequency is sufficiently small compared to the excitation frequency. The plate oscillation typically has a stabilizing effect on the inverted pendulum.



https://doi.org/10.1007/s11071-020-06054-y
Angermeier, Sebastian; Karcher, Christian;
Model-based condenser fan speed optimization of vapor compression systems. - In: Energies : open-access journal of related scientific research, technology development and studies in policy and management.. - Basel : MDPI, ISSN 1996-1073, Volume 13 (2020), issue 22, 6012, Seite 1-26

Vapor compression systems (VCS) cover a wide range of applications and consume large amounts of energy. In this context, previous research identified the optimization of the condenser fans speed as a promising measure to improve the energy efficiency of VCS. The present paper introduces a steady-state modeling approach of an air-cooled VCS to predict the ideal condenser fan speed. The model consists of a hybrid characterization of the main components of a VCS and the optimization problem is formulated as minimizing the total energy consumption by respectively adjusting the condenser fan and compressor speed. In contrast to optimization strategies found in the literature, the proposed model does not relay on algorithms, but provides a single optimization term to predict the ideal fan speed. A detailed experimental validation demonstrates the feasibility of the model approach and further suggests that the ideal condenser fan speed can be calculated with sufficient precision, assuming constant evaporating pressure, compressor efficiency, subcooling, and superheating, respectively. In addition, a control strategy based on the developed model is presented, which is able to drive the VCS to its optimal operation. Therefore, the study provides a crucial input for set-point optimization and steady-state modeling of air-cooled vapor compression systems.



https://doi.org/10.3390/en13226012
Chehreh, Abootorab; Grätzel, Michael; Bergmann, Jean Pierre; Walther, Frank;
Fatigue behavior of conventional and stationary shoulder friction stir welded EN AW-5754 aluminum alloy using load increase method. - In: Metals : open access journal.. - Basel : MDPI, ISSN 2075-4701, Volume 10 (2020), issue 11, 1510, Seite 1-11

https://doi.org/10.3390/met10111510