Gesamtliste aus der Hochschulbibliographie

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Li, Zirui; Faheem, Faizan; Husung, Stephan
Collaborative Model-based Systems Engineering using Dataspaces and SysML v2. - In: Systems, ISSN 2079-8954, Bd. 12 (2024), 1, 18, S. 1-22

Collaborative Model-based Systems Engineering between companies is becoming increasingly important. The utilization of the modeling possibilities of the standard language SysML v2 and the multilateral data exchange via Dataspaces open new possibilities for efficient collaboration. Based on systemic approaches, a modeling concept for decomposing the system into sub-systems is developed as a basis for the exchange. In addition, based on the analysis of collaboration processes in the context of Systems Engineering, an architectural approach with a SysML editor and Dataspace for the exchange is elaborated. The architecture is implemented on the basis of open-source solutions. The investigations are based on an application example from precision engineering. The potential and challenges are discussed.



https://doi.org/10.3390/systems12010018
Käufer, Theo; Cierpka, Christian
Volumetric Lagrangian temperature and velocity measurements with thermochromic liquid crystals. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 3, 035301, S. 1-11

We propose a Lagrangian method for simultaneous, volumetric temperature and velocity measurements. As tracer particles for both quantities, we employ encapsulated thermochromic liquid crystals (TLCs). We discuss the challenges arising from color imaging of small particles and present measurements in an equilateral hexagonal-shaped convection cell of height h = 60 mm and distance between the parallel side walls w = 10^4 mm, which corresponds to an aspect ratio Γ = 1.73. As fluid, we use a water-glycerol mixture to match the density of the TLC particles. We propose a densely-connected neural network, trained on calibration data, to predict the temperature for individual particles based on their particle image and position in the color camera images, which achieves uncertainties below 0.2 K over a temperature range of 3 K. We use Shake-the-Box to determine the 3D position and velocity of the particles and couple it with our temperature measurement approach. We validate our approach by adjusting a stable temperature stratification and comparing our measured temperatures with the theoretical results. Finally, we apply our approach to thermal convection at Rayleigh number Ra = 3.4 × 10^7 and Prandtl number Pr = 10.6. We can visualize detaching plumes in individual temperature and convective heat transfer snapshots. Furthermore, we demonstrate that our approach allows us to compute statistics of the convective heat transfer and briefly validate our results against the literature.



https://doi.org/10.1088/1361-6501/ad16d1
Rakhimov, Damir; Haardt, Martin
Analytical performance assessment of 2-D Tensor ESPRIT in terms of physical parameters. - In: IEEE open journal of signal processing, ISSN 2644-1322, Bd. 5 (2024), S. 122-131

In this paper, we present an analytical performance assessment of 2-D Tensor ESPRIT in terms of physical parameters. We show that the error in the r -mode depends only on two components, irrespective of the dimensionality of the problem. We obtain analytical expressions in closed form for the mean squared error (MSE) in each dimension as a function of the signal-to-noise (SNR) ratio, the array steering matrices, the number of antennas, the number of snapshots, the selection matrices, and the signal correlation. The derived expressions allow a better understanding of the difference in performance between the tensor and the matrix versions of the ESPRIT algorithm. The simulation results confirm the coincidence between the presented analytical expression and the curves obtained via Monte Carlo trials. We analyze the behavior of each of the two error components in different scenarios.



https://doi.org/10.1109/OJSP.2023.3337729
Engemann, Thomas; Ispas, Adriana; Bund, Andreas
Electrochemical reduction of tantalum and titanium halides in 1-butyl-1-methylpyrrolidinium bis (trifluoromethyl-sulfonyl)imide and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ionic liquids. - In: Journal of solid state electrochemistry, ISSN 1433-0768, Bd. 28 (2024), 5, S. 1557-1570

The electrodeposition of tantalum-titanium–based films using different tantalum and titanium halides was investigated in two ionic liquids, namely, 1-butyl-1-methylpyrrolidinium bis (trifluoromethyl-sulfonyl)imide ([BMP][TFSI]) and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([BMP][OTf]). Cyclic voltammetry was used to analyse the electrochemistry of the electrolytes and potentiostatic deposition was performed to evaluate the feasibility of electrodepositing tantalum-titanium–based layers. Both the metal salts and the ionic liquid influenced the electrochemical reduction of the tantalum and titanium halides significantly. While titanium halides considerably retarded the reduction of tantalum pentahalides and inhibited electrodeposition in many electrolytes, an electrolyte composition from which tantalum and titanium-containing layers could be deposited was identified. Specifically, in TaBr5 and TiBr4 in [BMP][TFSI], TiBr4 did not inhibit the deposition of tantalum and titanium was co-deposited itself by a three-step reduction mechanism as confirmed by cyclic voltammetry and energy-dispersive X-ray spectroscopy. Furthermore, [BMP][TFSI] led to smoother and more compact deposits.



https://doi.org/10.1007/s10008-023-05773-7
Huang, Tianbai; Kupfer, Stephan; Geitner, Robert; Gräfe, Stefanie
Computational modelling and mechanistic insight into light-driven CO dissociation of square-planar rhodium(I) complexes. - In: ChemPhotoChem, ISSN 2367-0932, Bd. 8 (2024), 5, e202300219, S. 1-13

The activation step of Vaska-type Rh(I) complexes, such as the photocleavage of the Rh‑CO bond, plays an important role in the subsequent C-H activation. To elucidate the details of the photochemistry of Vaska-type Rh(I) complexes, such as trans-Rh(PMe3)2(CO)(Cl), we here present a computationally derived picture as obtained at the density functional level of theory (DFT) in combination with multireference wavefunction-based methods. We have identified that the photocleavage of CO proceeds via the metal-centered excited state, which is populated through intersystem crossing (ISC) from the dipole-allowed excited state S1. Moreover, the present study unraveled the reasons for the low C-H activation efficiency when using Rh featuring the bidentate ligand 1,2-bis(dimethylphosphino)ethane (dmpe), namely due to its unfavorable photochemical properties, i.e., the small driving force for light-induced CO loss and the fast deactivation of 3MC state back to the singlet ground state. In this study, we provide theoretical insight into mechanistic details underlying the light-induced CO dissociation process, for Rh complexes featuring PMe3 and dmpe ligands.



https://doi.org/10.1002/cptc.202300219
Schmidt, Leander; Schricker, Klaus; Diegel, Christian; Sachs, Florian; Bergmann, Jean Pierre; Knauer, Andrea; Romanus, Henry; Requardt, Herwig; Chen, Yunhui; Rack, Alexander
Effect of partial and global shielding on surface-driven phenomena in keyhole mode laser beam welding. - In: Welding in the world, ISSN 1878-6669, Bd. 68 (2024), 6, S. 1353-1374

Partial shielding by means of local gas supply has proven to be very effective in reducing spatter. Besides the effect of gas-induced dynamic pressure, the shielding of oxygen is also highly relevant for melt pool dynamics and spatter formation due to the growth of oxides and the influence on surface tension. Therefore, this paper addresses the effect of local supplied argon on oxide growth and seam topography during keyhole mode laser beam welding of high-alloy steel AISI 304. To determine the shielding quality, the results are compared to laser beam welding in a global argon atmosphere. The topography of the upper weld seams was analyzed by scanning electron microscopy (SEM). An X-ray microanalysis (EDX) in line scan modus was performed to determine and to locate the elements which are covering the specimen surface. The chemical state of the found elements was quantified by X-ray photoelectron spectroscopy (XPS). In a last step, high-speed synchrotron X-ray imaging was performed to separate the effect of the gas-induced pressure and the gas-induced shielding on keyhole geometry. The results show that a local supply of argon contributes to a significant difference in oxide growth, affecting melt pool convection and weld seam geometry. It was further shown that the effect of gas flows at low flow rates is primarily because of oxygen shielding, as no significant difference in keyhole geometry was found by high-speed synchrotron X-ray imaging.



https://doi.org/10.1007/s40194-023-01627-y
Freisinger, Elena; Unfried, Matthias; Schneider, Sabrina
The AI-augmented crowd: how human crowdvoters adopt AI (or not). - In: The journal of product innovation management, ISSN 1540-5885, Bd. 41 (2024), 4, S. 865-889

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/jpim.12708
Vasilyan, Suren; Rogge, Norbert; Preißler, Hannes; Starkloff, Michael; Schubert, Marco; Fröhlich, Thomas
Adaptation of metrology-grade ac current source in velocity mode of Planck-Balance 2: direct referencing induced voltages with ac quantum voltage standard. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 1, 015026, S. 1-11

The adaptation of developed metrology-grade ac current source (MCS) to the velocity mode of measurements of the Planck-Balance 2 as a means for generating ac mechanical oscillations is presented. The universality in operating with the MCS unit especially practical for the Planck-Balance setup for frequencies of 0.1 Hz-20 Hz (including but not limited to the negligence of a broader range of 0.01 Hz up to several hundred Hz) and for amplitudes of up to 10 mA with 16 (offset with 14)-bit effective resolution is demonstrated. MCS allows generating complex ac waveform signals as waveform synthesizers by adding to the original signal an extra five independent harmonic components, each of which with an adjustable resolution of 10 ns for phase and 16-bit for amplitude. Additionally, the MCS is supported by an external clock at 10 MHz frequency which serves also as a common reference time base for the comparison between the direct output signal of MCS, or of the induced voltage in the coil of the Planck-Balance resulting due to the applied current by MCS, with the ac quantum voltage standard at the required accuracy levels.



https://doi.org/10.1088/1361-6501/ad006c
Xu, Changfan; Qiu, Jiajia; Dong, Yulian; Li, Yueliang; Shen, Yonglong; Zhao, Huaping; Kaiser, Ute; Shao, Guosheng; Lei, Yong
Dual-functional electrode promoting dendrite-free and CO2 utilization enabled high-reversible symmetric Na-CO2 batteries. - In: Energy & Environmental Materials, ISSN 2575-0356, Bd. 7 (2024), 3, e12626, S. 1-10

Sodium-carbon dioxide (Na-CO2) batteries are regarded as promising energy storage technologies because of their impressive theoretical energy density and CO2 reutilization, but their practical applications are restricted by uncontrollable sodium dendrite growth and poor electrochemical kinetics of CO2 cathode. Constructing suitable multifunctional electrodes for dendrite-free anodes and kinetics-enhanced CO2 cathodes is considered one of the most important ways to advance the practical application of Na-CO2 batteries. Herein, RuO2 nanoparticles encapsulated in carbon paper (RuCP) are rationally designed and employed as both Na anode host and CO2 cathode in Na-CO2 batteries. The outstanding sodiophilicity and high catalytic activity of RuCP electrodes can simultaneously contribute to homogenous Na+ distribution and dendrite-free sodium structure at the anode, as well as strengthen discharge and charge kinetics at the cathode. The morphological evolution confirmed the uniform deposition of Na on RuCP anode with dense and flat interfaces, delivering enhanced Coulombic efficiency of 99.5% and cycling stability near 1500 cycles. Meanwhile, Na-CO2 batteries with RuCP cathode demonstrated excellent cycling stability (>350 cycles). Significantly, implementation of a dendrite-free RuCPNa anode and catalytic-site-rich RuCP cathode allowed for the construction of a symmetric Na-CO2 battery with long-duration cyclability, offering inspiration for extensive practical uses of Na-CO2 batteries.



https://doi.org/10.1002/eem2.12626
Spetzler, Benjamin; Abdel, Dilara; Schwierz, Frank; Ziegler, Martin; Farrell, Patricio
The role of vacancy dynamics in two-dimensional memristive devices. - In: Advanced electronic materials, ISSN 2199-160X, Bd. 10 (2024), 1, 2300635, S. 1-18

Two-dimensional layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of defect dynamics in the switching process of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. It explains the distinct features of the device characteristics observed experimentally, including fundamentally different device behavior previously thought to originate from multiple mechanisms. Key influence factors are identified and discussed with a fully coupled and dynamic charge transport model for electrons, holes, and ionic point defects, including image-charge-induced Schottky barrier lowering (SBL). Thermal effects and local Joule heating are considered by coupling the transient heat transfer equation to the electronic properties. The model is validated with hysteresis and pulse measurements for various lateral 2D MoS2-based devices, strongly corroborating the relevance of vacancy dynamics in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications.



https://doi.org/10.1002/aelm.202300635