Gesamtliste aus der Hochschulbibliographie

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Sachs, Sebastian; Ratz, Manuel; Mäder, Patrick; König, Jörg; Cierpka, Christian
Particle detection and size recognition based on defocused particle images: a comparison of a deterministic algorithm and a deep neural network. - In: Experiments in fluids, ISSN 1432-1114, Bd. 64 (2023), 2, 21, S. 1-16

The systematic manipulation of components of multimodal particle solutions is a key for the design of modern industrial products and pharmaceuticals with highly customized properties. In order to optimize innovative particle separation devices on microfluidic scales, a particle size recognition with simultaneous volumetric position determination is essential. In the present study, the astigmatism particle tracking velocimetry is extended by a deterministic algorithm and a deep neural network (DNN) to include size classification of particles of multimodal size distribution. Without any adaptation of the existing measurement setup, a reliable classification of bimodal particle solutions in the size range of 1.14 μm–5.03 μm is demonstrated with a precision of up to 99.9 %. Concurrently, the high detection rate of the particles, suspended in a laminar fluid flow, is quantified by a recall of 99.0 %. By extracting particle images from the experimentally acquired images and placing them on a synthetic background, semi-synthetic images with consistent ground truth are generated. These contain labeled overlapping particle images that are correctly detected and classified by the DNN. The study is complemented by employing the presented algorithms for simultaneous size recognition of up to four particle species with a particle diameter in between 1.14 μm and 5.03 μm. With the very high precision of up to 99.3 % at a recall of 94.8 %, the applicability to classify multimodal particle mixtures even in dense solutions is confirmed. The present contribution thus paves the way for quantitative evaluation of microfluidic separation and mixing processes.



https://doi.org/10.1007/s00348-023-03574-2
Xu, Changfan; Dong, Yulian; Shen, Yonglong; Zhao, Huaping; Li, Liqiang; Shao, Guosheng; Lei, Yong
Fundamental understanding of nonaqueous and hybrid Na-CO2 batteries: challenges and perspectives. - In: Small, ISSN 1613-6829, Bd. 0 (2023), 0, 2206445, S. 1-30

Alkali metal-CO2 batteries, which combine CO2 recycling with energy conversion and storage, are a promising way to address the energy crisis and global warming. Unfortunately, the limited cycle life, poor reversibility, and low energy efficiency of these batteries have hindered their commercialization. Li-CO2 battery systems have been intensively researched in these aspects over the past few years, however, the exploration of Na-CO2 batteries is still in its infancy. To improve the development of Na-CO2 batteries, one must have a full picture of the chemistry and electrochemistry controlling the operation of Na-CO2 batteries and a full understanding of the correlation between cell configurations and functionality therein. Here, recent advances in CO2 chemical and electrochemical mechanisms on nonaqueous Na-CO2 batteries and hybrid Na-CO2 batteries (including O2-involved Na-O2/CO2 batteries) are reviewed in-depth and comprehensively. Following this, the primary issues and challenges in various battery components are identified, and the design strategies for the interfacial structure of Na anodes, electrolyte properties, and cathode materials are explored, along with the correlations between cell configurations, functional materials, and comprehensive performances are established. Finally, the prospects and directions for rationally constructing Na-CO2 battery materials are foreseen.



https://doi.org/10.1002/smll.202206445
Philipp, Friedrich;
Relatively bounded perturbations of J-non-negative operators. - In: Complex analysis and operator theory, ISSN 1661-8262, Bd. 17 (2023), 1, 14, insges. 30 S.

We improve known perturbation results for self-adjoint operators in Hilbert spaces and prove spectral enclosures for diagonally dominant J-self-adjoint operator matrices. These are used in the proof of the central result, a perturbation theorem for J-non-negative operators. The results are applied to singular indefinite Sturm-Liouville operators with Lp-potentials. Known bounds on the non-real eigenvalues of such operators are improved.



https://doi.org/10.1007/s11785-022-01263-2
Hörsch, Florian; Szigeti, Zoltán
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
Alver, Füsun; Sarısakalo&bovko;glu, Aynur
Communication science in Türkiye: how communication research and education developed over the years. - In: Publizistik, ISSN 1862-2569, (2023), insges. 20 S.

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
Schulte, Julian; Nissen, Volker
Sensitivity analysis of combinatorial optimization problems using evolutionary bilevel optimization and data mining. - In: Annals of mathematics and artificial intelligence, ISSN 1573-7470, Bd. 0 (2023), 0, insges. 20 S.

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
Lee, Dae Gwan; Philipp, Friedrich; Voigtlaender, Felix
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
Großmann, Max; Bohm, Sebastian; Heyder, Stefan; Schwarzburg, Klaus; Kleinschmidt, Peter; Runge, Erich; Hannappel, Thomas
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
Schlag, Leslie; Isaac, Nishchay Angel; Hossain, Mohammad M.; Hess, Anna-Lena; Wolz, Benedikt C.; Reiprich, Johannes; Ziegler, Mario; Pezoldt, Jörg; Jacobs, Heiko O.
Self-aligning metallic vertical interconnect access formation through microlensing gas phase electrodeposition controlling airgap and morphology. - In: Advanced electronic materials, ISSN 2199-160X, Bd. 9 (2023), 1, 2200838, S. 1-8

This publication reports self-aligning metallic via microlensing gas phase electrodeposition formation. Key operational parameters to fabricate vertical ruthenium and rhodium interconnects (via) with a diameter of 100 nm are discussed. Moreover, airgaps are implemented during the deposition process, which utilizes spark discharge to generate a flux of charged nanoparticles. An inert gas flow transports the nanoparticles through a reactor chamber close to the target substrate. The substrate uses a pre-patterned resist with openings to a silicon/silicon dioxide/metal stack to direct the deposition of the nanoparticles to form localized self-aligning vertical interconnects. Five process parameters were identified, which impact the morphology and conductance of the resulting interconnects: spark discharge power, gas flow rate, microlens via dimensions, substrate surface potential, and in situ flash lamp power. This parameter set enables a controlled adjustment of the via interconnect morphology and its minimum feature size. Gas flow rate in combination with spark discharge power contribute significantly to the morphology of the interconnect. Spark power and microlens via dimensions have the largest influence on the surface potential of the insulating resist cover, which enables a localized microlensing gas phase electrodeposition of a via with a controlled ratio between conducting diameter and airgap.



https://doi.org/10.1002/aelm.202200838
Hasieber, Michael; Wenz, Felix; Grätzel, Michael; Lenard, James Andrew; Matthes, Sebastian; Bergmann, Jean Pierre
A systematic analysis of maximum tolerable tool wear in friction stir welding. - In: Welding in the world, ISSN 1878-6669, Bd. 0 (2022), 0, insges. 15 S.

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