Spatiotemporal phase slip patterns for visual evoked potentials, covert object naming tasks, and insight moments extracted from 256 channel EEG recordings. - In: Frontiers in integrative neuroscience, ISSN 1662-5145, Bd. 17 (2023), 1087976, S. 01-20
Phase slips arise from state transitions of the coordinated activity of cortical neurons which can be extracted from the EEG data. The phase slip rates (PSRs) were studied from the high-density (256 channel) EEG data, sampled at 16.384 kHz, of five adult subjects during covert visual object naming tasks. Artifact-free data from 29 trials were averaged for each subject. The analysis was performed to look for phase slips in the theta (4-7 Hz), alpha (7-12 Hz), beta (12-30 Hz), and low gamma (30-49 Hz) bands. The phase was calculated with the Hilbert transform, then unwrapped and detrended to look for phase slip rates in a 1.0 ms wide stepping window with a step size of 0.06 ms. The spatiotemporal plots of the PSRs were made by using a montage layout of 256 equidistant electrode positions. The spatiotemporal profiles of EEG and PSRs during the stimulus and the first second of the post-stimulus period were examined in detail to study the visual evoked potentials and different stages of visual object recognition in the visual, language, and memory areas. It was found that the activity areas of PSRs were different as compared with EEG activity areas during the stimulus and post-stimulus periods. Different stages of the insight moments during the covert object naming tasks were examined from PSRs and it was found to be about 512 ± 21 ms for the ‘Eureka’ moment. Overall, these results indicate that information about the cortical phase transitions can be derived from the measured EEG data and can be used in a complementary fashion to study the cognitive behavior of the brain.
https://doi.org/10.3389/fnint.2023.1087976
Editorial: Functional assessments of the ocular circulation. - In: Frontiers in medicine, ISSN 2296-858X, Bd. 10 (2023), 1222022, S. 01-04
https://doi.org/10.3389/fmed.2023.1222022
Unsteady inherent convective mixing in thermal-energy-storage systems during standby periods. - In: PRX energy, Bd. 2 (2023), 4, 043001, S. 043001-1-043001-17
Recent studies on the flow phenomena in stratified thermal-energy-storage (TES) systems have shown that heat conduction from the hot upper fluid layer through the vertical tank sidewall into the lower cold fluid layer leads to counterdirected wall jets adjacent to the vertical sidewalls. It was shown that these phenomena destroyed half of the total exergy content in less than a tenth of the storage time constant of a 2-m3 stratified TES system. This paper investigates short-term fluctuations of the wall jets since these fluctuations can potentially mix the hot and cold zones of the thermal stratification that are separated by the thermocline region. Using particle-image velocimetry measurements in two regions of a TES model experiment (near-wall region and far-field region) and analyzing the frequency content of the velocity fields revealed characteristic oscillations for different regions. In the near-wall region, observed fluctuations agreed well with an adjusted boundary layer frequency from the literature, showing that the wall jet is transitioning from laminar to turbulent flow. In the far-field region, the oscillations are related to the Brunt-Väisälä frequency. It is shown that the fluctuations from the boundaries of the thermocline region are most dominant and propagate into deeper regions of the thermocline. A comparison to data from the large-scale test facility for thermal energy storage in molten salt at the German Aerospace Center in Cologne showed good agreement. The consensus between the two experiments proves firstly that a small-scale model experiment with water as a storage liquid can be used to analyze the physical phenomena of large-scale molten salt storage facilities and secondly that these fluctuations are relevant for exergy destruction in real-scale TES.
https://doi.org/10.1103/PRXEnergy.2.043001
Visible-light-assisted donor-acceptor-Stenhouse-adduct-based reversible photoswitching on a laser-structurable OrmoComp substrate. - In: ACS applied polymer materials, ISSN 2637-6105, Bd. 5 (2023), 10, S. 8631-8640
Laser-assisted nanolithography of commercially available photoresists is offering a limitless designing opportunity in the micro- and nanostructuring of 3D organotypic cell culture scaffolds. Among them, chemically functionalized OrmoComp has shown promising improvement in cell adhesion that paves the way to assemble cellular entities on a desirable geometry. Establishing a photoswitchable chemistry on the OrmoComp surface may offer an additional degree of freedom to manipulate the surface chemistry locally and selectively. We have established the methods for functionalization of the photopolymerized OrmoComp surface with visible-light-switchable donor-acceptor Stenhouse adducts. Unlike other polymers, a photopolymerized OrmoComp surface appears to be optimal for reversible photothermal switching, offering the possibility to influence surface properties like absorption and hydrophilicity tremendously. Light-assisted chemical modulation between colored triene-2-ol and colorless cyclopentenone can be achieved to a size region as narrow as 20 μm. Thermal reversion to the original triene-2-ol state can be analyzed spectroscopically and observed with the naked eye.
https://doi.org/10.1021/acsapm.3c01766
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
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
Gate-tunable hysteresis response of field effect transistor based on sulfurized Mo. - In: AIP Advances, ISSN 2158-3226, Bd. 13 (2023), 9, 095224, S. 095224-1-095224-7
Hysteresis effects and their tuning with electric fields and light were studied in thin film molybdenum disulfide transistors fabricated from sulfurized molybdenum films. The influence of the back-gate voltage bias, voltage sweep range, illumination, and AlOx encapsulation on the hysteresis effect of the back-gated field effect transistors was studied and quantified. This study revealed the distinctive contribution of MoS2 surface, MoS2/SiO2 interface defects and their associated traps as primary sources of of hysteresis.
https://doi.org/10.1063/5.0165868
Temporal resolution of acoustic process emissions for monitoring joint gap formation in laser beam butt welding. - In: Applied Sciences, ISSN 2076-3417, Bd. 13 (2023), 18, 10548, S. 1-17
With the increasing power and speed of laser welding, in-process monitoring has become even more crucial to ensure process stability and weld quality. Due to its low cost and installation flexibility, acoustic process monitoring is a promising method and has demonstrated its effectiveness. Although its feasibility has been the focus of existing studies, the temporal resolution of acoustic emissions (AE) has not yet been addressed despite its utmost importance for realizing real-time systems. Aiming to provide a benchmark for further development, this study investigates the relationship between duration and informativeness of AE signals during high-power (3.5 kW) and high-speed (12 m/min) laser beam butt welding. Specifically, the informativeness of AE signals is evaluated based on the accuracy of detecting and quantifying joint gaps for various time windows of signals, yielding numerical comparison. The obtained results show that signals can be shortened up to a certain point without sacrificing their informativeness, encouraging the optimization of the signal duration. Our results also suggest that large gaps (>0.3 mm) induce unique signal characteristics in AE, which are clearly identifiable from 1 ms signal segments, equivalent to 0.2 mm weld seam.
https://doi.org/10.3390/app131810548
Research progress of solid electrolyte interphase for sodium metal anodes. - In: The chemical engineering journal, ISSN 1873-3212, Bd. 475 (2023), 146227
Inhomogeneous and fragile solid electrolyte interphase (SEI) leads to poor battery cycle life and safety hazards, which is a key challenge that limits the practical application of low-cost sodium metal anodes. Although sodium metal batteries based on non-aqueous liquid and solid electrolytes have made great progress in terms of interfacial chemistry and SEI regulation strategies, the relevant evaluation of SEI from the perspective of the electrolyte is not well understood. This paper reviews the formation mechanism, physicochemical properties, and failure mechanism of SEI at the interface between the sodium metal and the liquid/solid electrolyte, focusing on poor stability, compatibility, interfacial ion transport problems, and influencing factors. Recent advances in SEI regulation are summarized in terms of electrolytes, artificial interphases, and electrode engineering to achieve ideal electrochemical reversibility. The effectiveness of the SEI engineering strategies was evaluated based on a comprehensive review of the interfacial stability in different electrolyte systems. Finally, the challenges associated with rational interface design for long-lasting sodium metal batteries are discussed, along with promising avenues for the same.
https://doi.org/10.1016/j.cej.2023.146227
High-purity graphene and carbon nanohorns prepared by base-acid treated waste tires carbon via direct current arc plasma. - In: Environmental research, ISSN 1096-0953, Volume 238 (2023), part 1, 117071
As the accumulation of waste tires continues to rise year by year, effectively managing and recycling these discarded materials has become an urgent global challenge. Among various potential solutions, pyrolysis stands out due to its superior environmental compatibility and remarkable efficiency in transforming waste tires into valuable products. Thus, it is considered the most potential method for disposing these tires. In this work, waste tire powder is pyrolyzed at 560 ˚C to yield pyrolysis carbon black, and meanwhile, the purification effects of base-acid solutions on pyrolysis carbon black are discussed. High-purity few-layer graphene flakes and carbon nanohorns are synthesized by a direct current arc plasma with H2 and N2 as buffer gases and high-purity pyrolysis carbon black as raw material. Under an H2 atmosphere, hydrogen effectively terminates the suspended carbon bonds, preventing the formation of closed structures and facilitating the expansion of graphene sheets. During the preparation of carbon nanohorns, the nitrogen atoms rapidly bond with carbon atoms, forming essential C-N bonds. This nitrogen doping promotes the formation of carbon-based five-membered and seven-membered rings and makes the graphite lamellar change in the direction of towards negative curvature. Consequently, such change facilitates the formation of conical structures, ultimately yielding the coveted carbon nanohorns. This work not only provides an economical raw material for efficient large-scale synthesis of few-layer graphene and carbon nanohorns but also broadens the intrinsic worth of pyrolysis carbon black, which is beneficial to improving the recycling value of waste tires.
https://doi.org/10.1016/j.envres.2023.117071