The effect of DC voltage pre-stress on breakdown voltage of air under composite DC & LI voltage and test circuit: design and application. - In: Energies, ISSN 1996-1073, Bd. 15 (2022), 4, 1353, S. 1-23
The use of HVDC systems is increasing in number due to technological innovations, increasing power capacity and increasing customer demand. The characteristics of insulation systems under composite DC and LI voltage must be examined and clarified. In this study, firstly, experimental circuits were designed to generate and measure composite DC and LI high voltage using a simulation program. The coupling elements used were chosen according to simulation results. Afterward, experimental circuits were established in the laboratory according to the simulation results of the designed experimental circuit. Then, breakdown voltages under composite DC and LI voltage for less uniform and non-uniform electric fields were measured with four different electrode systems for positive and negative DC voltage pre-stresses with different amplitudes. The 50% breakdown voltage was calculated using the least-squares method. Finally, 3D models were created for the electrode systems used in the experiments using the finite element method. The efficiency factors of electrode systems calculated with the FEM results were correlated with the experimental breakdown voltage results. Thus, the breakdown behavior of air under bipolar and unipolar composite voltages (CV) was investigated. In conclusion, the experimental results showed that very fast polarity change in bipolar CV causes higher electrical stress compared to unipolar CV.
https://doi.org/10.3390/en15041353
fastmat: efficient linear transforms in Python. - In: SoftwareX, ISSN 2352-7110, Bd. 18 (2022), 101013, S. 1-8
Scientific computing requires handling large linear models, which are often composed of structured matrices. With increasing model size, dense representations quickly become infeasible to compute or store. Matrix-free implementations are suited to mitigate this problem at the expense of additional implementation overhead, which complicates research and development effort by months, when applied to practical research problems. Fastmat is a framework for handling large structured matrices by offering an easy-to-use abstraction model. It allows for the expression of matrix-free linear operators in a mathematically intuitive way, while retaining their benefits in computation performance and memory efficiency. A built-in hierarchical unit-test system boosts debugging productivity and run-time execution path optimization improves the performance of highly-structured operators. The architecture is completed with an interface for abstractly describing algorithms that apply such matrix-free linear operators, while maintaining clear separation of their respective implementation levels. Fastmat achieves establishing a close relationship between implementation code and the actual mathematical notation of a given problem, promoting readable, portable and re-usable scientific code.
https://doi.org/10.1016/j.softx.2022.101013
Multispectral imaging flow cytometry with spatially and spectrally resolving snapshot-mosaic cameras for the characterization and classification of bioparticles. - In: Micromachines, ISSN 2072-666X, Bd. 13 (2022), 2, 238, S. 1-12
https://doi.org/10.3390/mi13020238
A high-density 256-channel cap for dry electroencephalography. - In: Human brain mapping, ISSN 1097-0193, Bd. 43 (2022), 4, S. 1295-1308
High-density electroencephalography (HD-EEG) is currently limited to laboratory environments since state-of-the-art electrode caps require skilled staff and extensive preparation. We propose and evaluate a 256-channel cap with dry multipin electrodes for HD-EEG. We describe the designs of the dry electrodes made from polyurethane and coated with Ag/AgCl. We compare in a study with 30 volunteers the novel dry HD-EEG cap to a conventional gel-based cap for electrode-skin impedances, resting state EEG, and visual evoked potentials (VEP). We perform wearing tests with eight electrodes mimicking cap applications on real human and artificial skin. Average impedances below 900 k[Ohm] for 252 out of 256 dry electrodes enables recording with state-of-the-art EEG amplifiers. For the dry EEG cap, we obtained a channel reliability of 84% and a reduction of the preparation time of 69%. After exclusion of an average of 16% (dry) and 3% (gel-based) bad channels, resting state EEG, alpha activity, and pattern reversal VEP can be recorded with less than 5% significant differences in all compared signal characteristics metrics. Volunteers reported wearing comfort of 3.6 ± 1.5 and 4.0 ± 1.8 for the dry and 2.5 ± 1.0 and 3.0 ± 1.1 for the gel-based cap prior and after the EEG recordings, respectively (scale 1-10). Wearing tests indicated that up to 3,200 applications are possible for the dry electrodes. The 256-channel HD-EEG dry electrode cap overcomes the principal limitations of HD-EEG regarding preparation complexity and allows rapid application by not medically trained persons, enabling new use cases for HD-EEG.
https://doi.org/10.1002/hbm.25721
Detection of liver dysfunction using a wearable electronic nose system based on semiconductor metal oxide sensors. - In: Biosensors, ISSN 2079-6374, Bd. 12 (2022), 2, 70, S. 1-15
https://doi.org/10.3390/bios12020070
Selective metallization of polymers: surface activation of polybutylene terephthalate (PBT) assisted by picosecond laser pulses. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 24 (2022), 4, 2100933, S. 1-15
https://doi.org/10.1002/adem.202100933
Efficient organic solar cells enabled by simple non-fused electron donors with low synthetic complexity. - In: Small, ISSN 1613-6829, Bd. 18 (2022), 3, 2104623, insges. 10 S.
https://doi.org/10.1002/smll.202104623
Ferrimagnetic large single domain iron oxide nanoparticles for hyperthermia applications. - In: Nanomaterials, ISSN 2079-4991, Bd. 12 (2022), 3, 343, S. 1-12
This paper describes the preparation and obtained magnetic properties of large single domain iron oxide nanoparticles. Such ferrimagnetic particles are particularly interesting for diagnostic and therapeutic applications in medicine or (bio)technology. The particles were prepared by a modified oxidation method of non-magnetic precursors following the green rust synthesis and characterized regarding their structural and magnetic properties. For increasing preparation temperatures (5 to 85 ˚C), an increasing particle size in the range of 30 to 60 nm is observed. Magnetic measurements confirm a single domain ferrimagnetic behavior with a mean saturation magnetization of ca. 90 Am2/kg and a size-dependent coercivity in the range of 6 to 15 kA/m. The samples show a specific absorption rate (SAR) of up to 600 W/g, which is promising for magnetic hyperthermia application. For particle preparation temperatures above 45 ˚C, a non-magnetic impurity phase occurs besides the magnetic iron oxides that results in a reduced net saturation magnetization.
https://doi.org/10.3390/nano12030343
A comprehensive survey on cooperative intersection management for heterogeneous connected vehicles. - In: IEEE access, ISSN 2169-3536, Bd. 10 (2022), S. 7937-7972
https://doi.org/10.1109/ACCESS.2022.3142450
Effect of SiO2 interlayer thickness in Au/SiO2/Si multilayer systems on Si sources and the formation of Au-based nanostructures. - In: Advanced materials interfaces, ISSN 2196-7350, Bd. 9 (2022), 2, 2101493, insges. 9 S.
Si sources involved in the growth of Au-SiOx nanostructures are investigated through the rapid thermal annealing of gold thin films on SiO2/Si substrates with various SiO2 layer thicknesses (3, 25, 100, 500 nm) in a reducing atmosphere. This method reveals three Si sources whose involvement depends on the thickness of the SiO2 layers, i.e., Si diffusion from the substrate, and SiO from SiO2 decomposition and from Si active oxidation. Increasing thicknesses of the SiO2 layer hampers the Si diffusion and the decomposition of regions of the SiO2 layer, which decreases the concentrations of discovered regions weakening the Si active oxidation. These discovered regions appear in systems with a SiO2 layer of 25 or 100 nm, while they are absent for a 500 nm layer. Furthermore, Au-SiOx nanostructures of different shapes form in each system. Both behaviors indicate that the influence and transport mechanisms of the different Si sources are largely dependent on the thicknesses of the SiO2 layers and that they control the evolution of the Au-SiOx nanostructures. A clear understanding of the relationship between these thicknesses and the possible Si sources and their roles in the evolution of the nanostructures makes the tailored fabrication of nanostructures possible.
https://doi.org/10.1002/admi.202101493