Gesamtliste aus der Hochschulbibliographie

Anzahl der Treffer: 464
Erstellt: Wed, 27 Mar 2024 23:38:05 +0100 in 0.1511 sec


Tayyab, Umais; Kumar, Ashish; Petry, Hans-Peter; Asghar, Muhammad Ehtisham; Hein, Matthias
Dual-band nested circularly polarized antenna array for 5G automotive satellite communications. - In: Applied Sciences, ISSN 2076-3417, Bd. 13 (2023), 21, 11915, S. 1-15

Currently, 5G low-earth orbit satellite communications offer enhanced wireless coverage beyond the reach of 5G terrestrial networks, with important implications, particularly for automated and connected vehicles. Such wireless automotive mass-market applications demand well-designed compact user equipment antenna terminals offering non-terrestrial jointly with terrestrial communications. The antenna should be low-profile, conformal, and meet specific parameter values for gain and operational frequency bandwidth, tailored to the intended applications, in line with the aesthetic design requirements of passenger cars. This work presents an original concept for a dual-band nested circularly polarized automotive user terminal that operates at the S-band frequencies around 3.5 GHz and Ka-band frequencies around 28 GHz, namely within the 5G new-radio bands n78 and n257, respectively. The proposed terminal is designed to be integrated into the plastic components of a passenger vehicle. The arrays consist of 2 × 2 aperture-coupled corner-truncated microstrip slot patch antenna elements for the n78 band and of 4 × 4 single-layer edge-truncated microstrip circular slot patch antenna elements for the n257 band. The embedded arrays offer, across the two bands, respectively, 9.9 and 13.7 dBi measured realized gain and 3-dB axial ratio bandwidths of 100 and 1500 MHz for the n78 and n257 bands along the broadside direction. Detailed link budget calculations anticipate uplink data rates of 21 and 6 Mbit/s, respectively, deeming it suitable for various automotive mobility and Internet-of-Things applications.



https://doi.org/10.3390/app132111915
Mohammadkarimi, Shiva; Neitzel, Benedikt; Lang, Maximilian; Puch, Florian
Investigation of the fiber length and the mechanical properties of waste recycled from continuous glass fiber-reinforced polypropylene. - In: Recycling, ISSN 2313-4321, Bd. 8 (2023), 6, 82, S. 1-20

This paper explores the mechanical recycling of continuous fiber-reinforced thermoplastics (CFRTPs) waste into injection molded products, focusing on the influence of recycling parameters on fiber length and mechanical properties. CFRTPs are gaining attention for their promising attributes, including weight-specific mechanical properties, short cycle times, storability, and recyclability, making them suitable for diverse applications. However, as CFRTP production rates rise, recycling strategies become crucial for sustainability. This study investigates the processability of CFRTP waste, defines size reduction conditions, and evaluates the impact of various compounding parameters such as temperature, screw speed, and fiber volume content during extrusion. The research findings indicate that higher screw speeds lead to fiber length reduction, whereas elevated temperatures result in longer fibers. Increased fiber volume intensifies interactions, resulting in shorter lengths. Additionally, the study examines the influence of injection molding parameters such as back pressure, screw speed, and initial fiber length on the resulting fiber length and mechanical properties of injection molded specimens, emphasizing the need for precise parameter control to optimize performance in recycled CFRTPs. Key findings are that increasing the initial fiber length from 260 μm to 455 μm results in an average fiber length after injection molding of 225 μm and 341 μm, respectively. This implies that longer initial fibers are more prone to breakage. Regarding the mechanical properties, increasing back pressure from 20 bar to 60 bar results in a reduction in Young’s modulus of approximately 40 MPa. Higher screw speed also reduces modulus by approximately 70 MPa due to intensified fiber-screw interactions. However, back pressure and screw speed have neutral effects on the tensile strength and the elongation at break.



https://doi.org/10.3390/recycling8060082
Hoffmann, Matthias K.; Gulakala, Rutwik; Mühlenhoff, Julian; Ding, Zhaoheng; Sattel, Thomas; Stoffel, Marcus; Flaßkamp, Kathrin
Data augmentation for design of concentric tube continuum robots by generative adversarial networks. - In: Proceedings in applied mathematics and mechanics, ISSN 1617-7061, Bd. 23 (2023), 4, e202300278, S. 1-7

Concentric tube continuum robots are a promising type of robot for various medical applications. Their application in neurosurgery poses challenging requirements for design and control that can be addressed by physics-informed data-based approaches. A prerequisite to data-based modeling is an informative, rich data set. However, limited access to experimental data raises interest in partially or entirely synthetic data sets. In this contribution, we study the application of generative adversarial networks (GANs) for data augmentation in a data-based design process of such robots. We propose a GAN framework suitable for curve-fitting to generate synthetic trajectories of robots along with their corresponding control parameters. Our evaluation shows that the GANs can efficiently produce meaningful synthetic trajectories and control parameter pairs that show a good agreement with simulated trajectories.



https://doi.org/10.1002/pamm.202300278
¸Sen, Gök¸cen Devlet; Schaller, Manuel; Worthmann, Karl
Stage-cost design for optimal and model predictive control of linear port-Hamiltonian systems: energy efficiency and robustness. - In: Proceedings in applied mathematics and mechanics, ISSN 1617-7061, Bd. 23 (2023), 4, e202300296, S. 1-9

We consider singular optimal control of port-Hamiltonian systems with minimal energy supply. We investigate the robustness of different stage-cost designs w.r.t. time discretization and show that alternative formulations that are equivalent in continuous time, differ strongly in view of discretization. Furthermore, we consider the impact of additional quadratic control regularization and demonstrate that this leads to a considerable increase in energy consumption. Then, we extend our results to the tracking problem within model predictive control and show that the intrinsic but singular choice of the cost functional as the supplied energy leads to a substantial improvement of the closed-loop performance.



https://doi.org/10.1002/pamm.202300296
Sachs, Sebastian; Schmidt, Hagen; Cierpka, Christian; König, Jörg
On the behavior of prolate spheroids in a standing surface acoustic wave field. - In: Microfluidics and nanofluidics, ISSN 1613-4990, Bd. 27 (2023), 12, 81, S. 1-19

The active manipulation of particle and cell trajectories in fluids by high-frequency standing surface acoustic waves (sSAW) allows to separate particles and cells systematically depending on their size and acoustic contrast. However, process technologies and biomedical applications usually operate with non-spherical particles, for which the prediction of acoustic forces is highly challenging and remains a subject of ongoing research. In this study, the dynamical behavior of prolate spheroids exposed to a three-dimensional acoustic field with multiple pressure nodes along the channel width is examined. Optical measurements reveal an alignment of the particles orthogonal to the pressure nodes of the sSAW, which has not been reported in literature so far. The dynamical behavior of the particles is analyzed under controlled initial conditions for various motion patterns by imposing a phase shift on the sSAW. To gain detailed understanding of the particle dynamics, a three-dimensional numerical model is developed to predict the acoustic force and torque acting on a prolate spheroid. Considering the acoustically induced streaming around the particle, the numerical results are in excellent agreement with experimental findings. Using the proposed numerical model, a dependence of the acoustic force on the particle shape is found in relation to the acoustic impedance of the channel ceiling. Hence, the numerical model presented herein promises high progress for the design of separation devices utilizing sSAW, exploiting an additional separation criterion based on the particle shape.



https://doi.org/10.1007/s10404-023-02690-z
Warsito, Indhika Fauzhan; Komosar, Milana; Bernhard, Maria Anne; Fiedler, Patrique; Haueisen, Jens
Flower electrodes for comfortable dry electroencephalography. - In: Scientific reports, ISSN 2045-2322, Bd. 13 (2023), 16589, S. 1-15

Dry electroencephalography (EEG) electrodes provide rapid, gel-free, and easy EEG preparation, but with limited wearing comfort. We propose a novel dry electrode comprising multiple tilted pins in a flower-like arrangement. The novel Flower electrode increases wearing comfort and contact area while maintaining ease of use. In a study with 20 volunteers, we compare the performance of a novel 64-channel dry Flower electrode cap to a commercial dry Multipin electrode cap in sitting and supine positions. The wearing comfort of the Flower cap was rated as significantly improved both in sitting and supine positions. The channel reliability and average impedances of both electrode systems were comparable. Averaged VEP components showed no considerable differences in global field power amplitude and latency, as well as in signal-to-noise ratio and topography. No considerable differences were found in the power spectral density of the resting state EEGs between 1 and 40 Hz. Overall, our findings provide evidence for equivalent channel reliability and signal characteristics of the compared cap systems in the sitting and supine positions. The reliability, signal quality, and significantly improved wearing comfort of the Flower electrode allow new fields of applications for dry EEG in long-term monitoring, sensitive populations, and recording in supine position.



https://doi.org/10.1038/s41598-023-42732-8
Schatz, David; Roßberg, Michael; Schäfer, Günter
Evaluating statistical disclosure attacks and countermeasures for anonymous voice calls. - In: ARES 23, (2023), 22, insges. 10 S.

Assuming a threat model of a global observer, statistical disclosure attacks have been proposed to efficiently de-anonymize communication relationships in text-based mix networks over time. It is commonly assumed that such attacks are also able to disclose call relationships in anonymous communication networks (ACNs) that support voice calls. One straightforward countermeasure is to expect users to permanently send and receive packets that mimic a Voice over IP (VoIP) call. However, this is not practical in real world scenarios, like on mobile devices. In this article, we adapt one specific statistical disclosure attack (Z-SDA-MD) to voice calls and quantitatively study less resource-intensive countermeasures. As base countermeasure, we evaluate a round-based communication model, corresponding to a timed mix. A simulation study of this scenario shows that the Z-SDA-MD is not well suited for a general disclosure of call relationships because of too many false positives. Nevertheless, the attack is able to correctly identify the most frequent relationships. Still, the accuracy in that regard may significantly be decreased by increasing the duration of one round, by decoupling actions (call setup and teardown) of caller and callee by a random number of rounds, and by occasional fake calls to a fixed set of “fake friends”. Overall, our study shows that anonymous voice calls may be implemented with an acceptable trade-off between anonymity, call setup time, and bandwidth overhead.



https://doi.org/10.1145/3600160.3600186
Fischer, Daniel; Sauerwein, Clemens; Werchan, Martin; Stelzer, Dirk
An exploratory study on the use of threat intelligence sharing platforms in Germany, Austria and Switzerland. - In: ARES 23, (2023), 30, insges. 7 S.

Threat intelligence sharing is a promising solution to enhance knowledge and situational awareness of the rapidly growing number of emerging cyber threats. Accordingly, there are a variety of platforms on the security solutions market that enable the efficient and targeted exchange of threat intelligence across organisations. Unfortunately, very little is known so far about the dissemination and use of these platforms from the end-user perspective. To address this issue, we conducted an exploratory study on the use of threat intelligence sharing platforms in Germany, Austria and Switzerland. For this purpose, we surveyed 69 security and IT experts from large companies, federal authorities and public universities in autumn 2022. Our findings show, among other things, a growing interest in threat intelligence sharing platforms and their value to information security processes.



https://doi.org/10.1145/3600160.3600185
Eichler, Stefan; Arnim, Mareike; Brätz, Oliver; Hildebrand, Jörg; Gericke, Andreas; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth-Michael
Heat management and tensile strength of 3 mm mixed and matched connections of butt joints of S355J2+N, S460MC and S700MC. - In: ce/papers, ISSN 2509-7075, Bd. 6 (2023), 3/4, S. 1476-1482

High-strength structural steels are beneficial in terms of the sustainability of constructions due to the possible reduction of weight and overall material needs. Nevertheless, high-strength steels have a smaller processing parameter range in regarding the specific heat input and resulting cooling rate. Especially the cooling time t8/5 characterizing the time span to cool down from 800 to 500 ˚C is an important indicator. Single layer butt-welded gas metal arc welding (GMAW) connections of 3 mm plates between normal strength (S355J2+N, S460MC) and high-strength steels (S700MC) as well as matched connections (S460MC, S700MC) are carried out. Hereby, the influence of the energy input, melting rate, joint preparation, filler metal (matching and undermatching) and backing methods are observed. Spatially resolved IR-thermal observation shows variations within the welds of up to 50 % in the cooling time t8/5 depending on those parameters. These fluctuations lead to significant changes of the microstructure within the melting and heat-affected zone. UCI hardness mappings show the softening and microstructural change within these zones. Those soft zones can be the region of failure for butt welded connections as shown by transverse tensile tests with spatially resolved optical strain measurements. The results obtained can be used to define more precise welding procedures of these types of connections and also are used to develop design rules for mixed connections made of normal strength and high-strength steel.



https://doi.org/10.1002/cepa.2265
Stoll, Eckhard; Breide, Stephan; Göring, Steve; Raake, Alexander
Automatic camera selection, shot size, and video editing in theater multi-camera recordings. - In: IEEE access, ISSN 2169-3536, Bd. 11 (2023), S. 96673-96692

In a non-professional environment, multi-camera recordings of theater performances or other stage shows are difficult to realize, because amateurs are usually untrained in camera work and in using a vision mixing desk that mixes multiple cameras. This can be remedied by a production process with high-resolution cameras where recordings of image sections from long shots or medium-long shots are manually or automatically cropped in post-production. For this purpose, Gandhi et al. presented a single-camera system (referred to as Gandhi Recording System in the paper) that obtains close-ups from a high-resolution recording from the central perspective. The proposed system in this paper referred to as “Proposed Recording System” extends the method to four perspectives based on a Reference Recording System from professional TV theater recordings from the Ohnsorg Theater. Rules for camera selection, image cropping, and montage are derived from the Reference Recording System in this paper. For this purpose, body and pose recognition software is used and the stage action is reconstructed from the recordings into the stage set. Speakers are recognized by detecting lip movements and speaker changes are identified using audio diarization software. The Proposed Recording System proposed in this paper is practically instantiated on a school theater recording made by laymen using four 4K cameras. An automatic editing script is generated that outputs a montage of a scene. The principles can also be adapted for other recording situations with an audience, such as lectures, interviews, discussions, talk shows, gala events, award ceremonies, and the like. More than 70 % of test persons confirm in an online study the added value of the perspective diversity of four cameras of the Proposed Recording System versus the single-camera method of Gandhi et al.



https://doi.org/10.1109/ACCESS.2023.3311256