On the complexity of finding well-balanced orientations with upper bounds on the out-degrees. - In: Journal of combinatorial optimization, ISSN 1573-2886, Bd. 45 (2023), 1, 30, S. 1-14
https://doi.org/10.1007/s10878-022-00962-y
Communication science in Türkiye: how communication research and education developed over the years. - In: Publizistik, ISSN 1862-2569, Bd. 68 (2023), 1, S. 89-108
In Türkiye, communication science falls under the category of social sciences and is regarded as an interdisciplinary scientific field focused on empirical research. The field is influenced by communication science developments of the West in terms of developing theories and methodology, and it faces challenges when it comes to the systematisation of theories and research methods created by different research traditions; their critical evaluation, development, and the failure to put theories to practical use. In order to ascertain the present condition of the field, this article explores the institutionalisation of communication science at universities and its potential tendencies as an academic field of study, its research trends, and the characteristics of communication science studies.
https://doi.org/10.1007/s11616-022-00766-4
Sensitivity analysis of combinatorial optimization problems using evolutionary bilevel optimization and data mining. - In: Annals of mathematics and artificial intelligence, ISSN 1573-7470, Bd. 91 (2023), 2/3, S. 309-328
Sensitivity analysis in general deals with the question of how changes in input data of a model affect its output data. In the context of optimization problems, such an analysis could, for instance, address how changes in capacity constraints affect the optimal solution value. Although well established in the domain of linear programming, sensitivity analysis approaches for combinatorial optimization problems are model-specific, limited in scope and not applicable to practical optimization problems. To overcome these limitations, Schulte et al. developed the concept of bilevel innovization. By using evolutionary bilevel optimization in combination with data mining and visualization techniques, bilevel innovization provides decision-makers with deeper insights into the behavior of the optimization model and supports decision-making related to model building and configuration. Originally introduced in the field of evolutionary computation, most recently bilevel innovization has been proposed as an approach to sensitivity analysis for combinatorial problems in general. Based on previous work on bilevel innovization, our paper illustrates this concept as a tool for sensitivity analysis by providing a comprehensive analysis of the generalized assignment problem. Furthermore, it is investigated how different algorithms for solving the combinatorial problem affect the insights gained by the sensitivity analysis, thus evaluating the robustness and reliability of the sensitivity analysis results.
https://doi.org/10.1007/s10472-022-09827-w
A note on the invertibility of the Gabor frame operator on certain modulation spaces. - In: The journal of Fourier analysis and applications, ISSN 1531-5851, Bd. 29 (2023), 1, 3, S. 1-20
We consider Gabor frames generated by a general lattice and a window function that belongs to one of the following spaces: the Sobolev space $$V_1 = H^1(\mathbb {R}^d)$$, the weighted $$L^2$$-space $$V_2 = L_{1 + |x|}^2(\mathbb {R}^d)$$, and the space $$V_3 = \mathbb {H}^1(\mathbb {R}^d) = V_1 \cap V_2$$consisting of all functions with finite uncertainty product; all these spaces can be described as modulation spaces with respect to suitable weighted $$L^2$$spaces. In all cases, we prove that the space of Bessel vectors in $$V_j$$is mapped bijectively onto itself by the Gabor frame operator. As a consequence, if the window function belongs to one of the three spaces, then the canonical dual window also belongs to the same space. In fact, the result not only applies to frames, but also to frame sequences.
https://doi.org/10.1007/s00041-022-09980-0
A systematic analysis of maximum tolerable tool wear in friction stir welding. - In: Welding in the world, ISSN 1878-6669, Bd. 67 (2023), 2, S. 325-339
Friction stir welding (FSW) is a solid-state joining process with a wide range of applications in the E-mobility, automotive, aerospace and energy industries. However, FSW is subjected to specific challenges including comparatively high process forces and high requirements on the clamping technique as well as tool wear resulting from the tool-workpiece interaction and thermo-mechanical stresses. Geometric-related tool wear can cause premature tool failure, process instabilities or weld seam irregularities. Therefore, tool wear in general, wear limits and tool life are essential factors for the efficient and sustainable implementation of friction stir welding. Against this background, this study analysed areas of significant tool wear on the shoulder and probe as a function of process temperature, weld seam length and weld seam quality. This provided functional correlations for determining limiting conditions on maximum tolerable tool wear. Geometrical deviations of the tool, induced by wear, were detected experimentally at different measuring points on the probe and shoulder and varying weld seam length. The investigations were carried out using a force-controlled robotized welding setup in which AA-6060-T66 sheets with a thickness of 5 mm were joined by weld seams up to 500 m in length. To identify the maximum tolerable tool wear, the weld seam properties were determined by visual and metallographic inspections and by tensile tests at 50-m intervals on the weld seam. It was shown that a 50% reduction in rotational speed (lower temperatures) resulted in less wear and thus in an increase of tool life of up to 150%. In addition, it was shown that the shoulder, like the probe, was also subject to significant wear. These results can be incorporated into FSW maintenance schedules to maximize tool life and minimize scrap rates.
https://doi.org/10.1007/s40194-022-01407-0
Relative genericity of controllablity and stabilizability for differential-algebraic systems. - In: Mathematics of control, signals, and systems, ISSN 1435-568X, Bd. 35 (2023), 1, S. 45-76
https://doi.org/10.1007/s00498-022-00332-3
Progrediente pigmentierte Fundusläsion nach 23 Jahren - therapieren oder beobachten?. - In: Die Ophthalmologie, ISSN 2731-7218, Bd. 120 (2023), 8, S. 851-856
https://doi.org/10.1007/s00347-022-01729-w
The computational turn in online mental health research: a systematic review. - In: New media & society, ISSN 1461-7315, Bd. 25 (2023), 10, S. 2781-2799
Digital trace data and computational methods are increasingly being used by researchers to study mental health phenomena (i.e. psychopathology and well-being) in social media. Computer-assisted mental health research is not simply a continuation of previous studies, but rather raises ethical, conceptual and methodological issues that are critical to behavioural science but have not yet been systematically explored. Based on a systematic review of n = 147 studies, we reveal a multidisciplinary field of research that has grown immensely since 2010, spanning the humanities, social sciences, and engineering. We find that a substantial majority of studies in our sample lack a standardized form of ethical consideration, focus on specific constructs and have a rather narrow focus on specific social media platforms. Based on our findings, we discuss how computational elements have influenced mental health research, highlight academic gaps and suggest promising directions for future studies.
https://doi.org/10.1177/14614448221122212
Generalized modeling of photoluminescence transients. - In: Physica status solidi, ISSN 1521-3951, Bd. 260 (2023), 1, 2200339, S. 1-12
Time-resolved photoluminescence (TRPL) measurements and the extraction of meaningful parameters involve four key ingredients: a suitable sample such as a semiconductor double heterostructure, a state-of-the-art measurement setup, a kinetic model appropriate for the description of the sample behavior, and a general analysis method to extract the model parameters of interest from the measured TRPL transients. Until now, the last ingredient is limited to single curve fits, which are mostly based on simple models and least-squares fits. These are often insufficient for the parameter extraction in real-world applications. The goal of this article is to give the community a universal method for the analysis of TRPL measurements, which accounts for the Poisson distribution of photon counting events. The method can be used to fit multiple TRPL transients simultaneously using general kinematic models, but should also be used for single transient fits. To demonstrate this approach, multiple TRPL transients of a GaAs/AlGaAs heterostructure are fitted simultaneously using coupled rate equations. It is shown that the simultaneous fits of several TRPL traces supplemented by systematic error estimations allow for a more meaningful and more robust parameter determination. The statistical methods also quantify the quality of the description by the underlying physical model.
https://doi.org/10.1002/pssb.202200339
Recent developments and future prospects of transition metal compounds as electrode materials for potassium-ion hybrid capacitors. - In: Advanced Materials Technologies, ISSN 2365-709X, Bd. 8 (2023), 3, 2200515, insges. 18 S.
Potassium-ion hybrid capacitors (PIHCs) have attracted considerable attention as emerging electrochemical energy storage devices for simultaneously achieving high energy and power density, which the key to success is the development of compatible electrode materials for both battery-type anode and capacitive cathode. Among numerous electrode materials, transition metal compounds (including oxides, chalcogenide, carbides, and nitrides) show great potential owing to their high theoretical capacity to achieve high energy density, but their sluggish reaction kinetics restrict the attainable power density. Hence, in the last few years, different strategies are proposed to improve the performance of transition metal compounds as electrode materials for PIHCs, and significant progress is achieved. Herein, this review outlines recent advances of employing transition metal compounds as electrode materials for PIHCs. The performance and challenges of different transition metal compounds are discussed in detail. Finally, the future prospects of practical applications of transition metal compounds in PIHCs are briefly discussed.
https://doi.org/10.1002/admt.202200515