Spectral separation of evoked and spontaneous cortical activity, Part 2: Somatosensory high frequency oscillations. - In: Biomedical signal processing and control, ISSN 1746-8108, Volume 95, part A (2024), article 106456, S. 1-8
N-Interval Fourier Analysis (N-FTA) allows for simultaneous spectral assessment of evoked and spontaneous activity in the frequency domain. We applied this method to signals following peripheral electrical nerve stimulation and performed analysis of cortical somatosensory evoked potentials within the 400 to 750 Hz band. For median nerve stimulation, data from eleven volunteers were analyzed. For tibial nerve stimulation, three subjects were investigated. For both stimulation sites, evoked high frequency oscillations (HFOs) components were identified. Furthermore, two kinds of background HFO activity were detected in sham stimulation trials. Spectral component models were applied for quantifying signal properties. Evoked spectral components reflected HFOs being time-locked to the stimulus. The detected spectral components were distributed over the entire investigated spectral band. Their spectral amplitude was close to the limit of the resolution of N-FTA. The experimentally observed spectral amplitude were in quantitative agreement with a model using a Morlet morphology. Within the HFO band, a flat noise floor was observed. Spontaneous physiological background activity contributes significantly to the spectral amplitude. This random activity is the dominant source of interference when extracting evoked HFOs. Within the HFO band, narrow spectral peaks in background activity were detected – both for real and sham stimulation. In the data sampled at 9.6 kHz, such peaks were observed in all recordings. For the 5.0 kHz sampling rate, these peaks were visible in about half of the recordings, and their amplitude was reduced. Based on a mathematical model, these peaks may be generated by organized spontaneous HFO activity producing a stable background wave.
https://doi.org/10.1016/j.bspc.2024.106456
Development of an indirect measurement method for the Contact Tube to Workpiece Distance (CTDW) in the Direct Energy Deposition - Arc (DED-ARC) process for different arc types. - In: Journal of advanced joining processes, ISSN 2666-3309, Bd. 9 (2024), 100228, S. 1-9
During the layer-by-layer build-up in the Direct Energy Deposition (DED) - Arc additive manufacturing (AM) process, the distance between the contact tube and the workpiece, effectively the welded layer, changes. Since the weld paths are predefined by the path planning software, a constant Contact Tube to Workpiece Distance (CTWD) and weld bead height is assumed. However, even small changes in geometry, such as crossovers of weld paths, result in higher weld beads than assumed. Similarly, an incorrectly assumed bead height as input to the path planning will result in a change in the CTWD. The sum of the deviations of the real weld geometries from the assumed ones in the path planning can greatly influence the CTWD. This implies that the dimensional accuracy may be significantly compromised. This research presents an approach for a general indirect measurement method using the welding current to obtain the CTWD during the actual welding process. A real-time process control method is implemented and validated using the mechanically controlled short arc and the pulsed arc process. Varying process parameters are used to validate the general applicability for a specific material. For the mechanically controlled short arc process, the model underestimates the measured CTWD by a mean error of 3.4 mm. The pulse process is overestimated by a mean error of 2.2 mm. The standard deviation for the pulse process with 1.3 mm is slightly smaller than for the short arc process with 1.7 mm.
https://doi.org/10.1016/j.jajp.2024.100228
A deep learning approach to explore the association of age-related macular degeneration polygenic risk score with retinal optical coherence tomography: a preliminary study. - In: Acta ophthalmologica, ISSN 1755-3768, Bd. 0 (2024), 0, S. 1-11
Purpose: Age-related macular degeneration (AMD) is a complex eye disorder affecting millions worldwide. This article uses deep learning techniques to investigate the relationship between AMD, genetics and optical coherence tomography (OCT) scans. Methods: The cohort consisted of 332 patients, of which 235 were diagnosed with AMD and 97 were controls with no signs of AMD. The genome-wide association studies summary statistics utilized to establish the polygenic risk score (PRS) in relation to AMD were derived from the GERA European study. A PRS estimation based on OCT volumes for both eyes was performed using a proprietary convolutional neural network (CNN) model supported by machine learning models. The method's performance was assessed using numerical evaluation metrics, and the Grad-CAM technique was used to evaluate the results by visualizing the features learned by the model. Results: The best results were obtained with the CNN and the Extra Tree regressor (MAE = 0.55, MSE = 0.49, RMSE = 0.70, R2 = 0.34). Extending the feature vector with additional information on AMD diagnosis, age and smoking history improved the results slightly, with mainly AMD diagnosis used by the model (MAE = 0.54, MSE = 0.44, RMSE = 0.66, R2 = 0.42). Grad-CAM heatmap evaluation showed that the model decisions rely on retinal morphology factors relevant to AMD diagnosis. Conclusion: The developed method allows an efficient PRS estimation from OCT images. A new technique for analysing the association of OCT images with PRS of AMD, using a deep learning approach, may provide an opportunity to discover new associations between genotype-based AMD risk and retinal morphology.
https://doi.org/10.1111/aos.16710
Comparison of Reinforcement Learning and Model Predictive Control for automated generation of optimal control for dynamic systems within a design space exploration framework. - In: International journal of automotive engineering, ISSN 2185-0992, Bd. 15 (2024), 1, S. 19-26
This work provides a study of methods for the automated derivation of control strategies for over-actuated systems. For this purpose, Reinforcement Learning (RL) and Model Predictive Control (MPC) approximating the solution of the Optimal Control Problem (OCP) are compared using the example of an over-actuated vehicle model executing an ISO Double Lane Change (DLC). This exemplary driving maneuver is chosen due to its critical vehicle dynamics for the comparison of algorithms in terms of control performance and possible automation within a design space exploration framework. The algorithms show reasonable control results for the goal of this study, although there are differences in terms of driving stability. While Model Predictive Control first requires the optimization of the trajectory, which should then be optimally tracked, RL may combine both in one step. In addition, manual effort required to adapt the OCP problem to new design variants for solving it with RL and MPC is evaluated and assessed with respect to its automation. As a result of this study, an Actor-Critic Reinforcement Learning method is recommended for the automated derivation of control strategies in the context of a design space exploration.
https://doi.org/10.20485/jsaeijae.15.1_19
The strength of uncoated and coated ultra-thin flexible glass under cyclic load. - In: AIMS Materials Science, ISSN 2372-0484, Bd. 11 (2024), 2, S. 343-368
Ultra-thin flexible glass with thicknesses of 100 µm or below is a substrate in the fields of optics, electronics, and semiconductors. Its brittleness is challenging in production processes like physical vapor deposition processes, especially in roll-to-roll production. In many cases, multiple geometric deformations take place and each step, like coating or cutting, influences the glass strength. By now, the relation between the strength of ultra-thin glass under quasi-static conditions and its strength under cyclic load has not been studied. Moreover, the effect of coatings has not been investigated. Both aspects are crucial to design reliable production processes. Therefore, the strength of ultra-thin glass under cyclic load was studied for uncoated and coated substrates. Two coating types were investigated: a single indium tin oxide film and a seven-layer antireflective layer stack. The coatings significantly influence the strength of the underlying glass in both test modes. The barrier properties, thin film stress, and the morphology/crystalline structure are identified as the major characteristics influencing the strength.
https://doi.org/10.3934/matersci.2024019
Investigation of the cooperative-effects of Lewis- and Brønstedt acids in homogeneously catalyzed OME fuel synthesis by inline-NMR monitoring. - In: RSC Advances, ISSN 2046-2069, Bd. 14 (2024), 21, S. 14942-14948
Via inline-nuclear magnetic resonance measurements, the homogeneously catalyzed poly(oxymethylene dimethyl ether) fuel synthesis using trioxane and dimethoxy methane is investigated. Besides the Brønsted acid (BA) catalyst triflic acid (TfOH) different metal halides are studied as Lewis-acidic (LA) catalysts. Among the used LAs, MgCl2, the weakest based on electronegativity, reveals the highest catalytical activity. Additionally, the influence of the concentration of BA and LA is investigated. An increase in BA concentration leads to an exponential increase of the reaction rate, while increasing the concentration of the LA leads to a volcano plot with its optimum at a LA : BA ratio of 1 : 3. The influence of the LA on the electron density of the intermediate formaldehyde is concluded as the main factor for this behavior.
https://doi.org/10.1039/D4RA00744A
Nanocalorimetry of nanoscaled Ni/Al multilayer films: on the methodology to determine reaction kinetics for highly reactive films. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2302279, S. 1-10
Free-standing Ni/Al multilayer films with a planar morphology, a bilayer thickness of 20 nm, and an average composition of Ni50Al50 (at%) deposited by direct current magnetron sputtering are investigated by nanocalorimetry and conventional calorimetry. Both the novel fast differential scanning calorimeter (FDSC) Flash DSC 2+ from Mettler-Toledo (MT) and conventional calorimeter MT DSC 3 are used to cover a range of heating rates from 0.1 to 10^4 K s^−1. A quantitative kinetic study of the interdiffusion and phase reaction sequence is performed via a Kissinger analysis covering five orders of magnitude of heating rates. Using the calorimetric data, the derived apparent activation energies suggest monotonic reaction kinetics over the entire range of heating rates applied. To correct the thermal lag at the highest heating rates with the FDSC for nonadhered free-standing films, a new methodology for its correction is used. Overall, this work extends the application of commercial FDSC to nonadhered films.
https://doi.org/10.1002/adem.202302279
Hexagonal ferrites for self-biasing circulators integrated in LTCC microwave modules. - In: Materials research bulletin, Bd. 178 (2024), 112878, S. 1-8
Next-generation microwave LTCC modules for satellite communication systems require the integration of passive components including circulators to manipulate electromagnetic signals at high frequency. Substituted M-type hexagonal ferrites (Ba/Sr)ScxFe12−xO19 are applied as self-biasing microwave magnetic materials at frequencies of about 30 GHz. The ferrites are integrated into LTCC multilayer devices as sintered drop-in bulk samples. Sintered ferrites with preferential orientation of grains were fabricated by compaction of powders in a magnetic field and sintering at 1300 ˚C. Alternatively, screen-printed ferrite films were dried in an external magnetic field, and cofired at 900 ˚C. The magnetic texture of the ferrites is characterized using XRD, EBSD, and magnetic measurements. Integrated Y-type circulators were tested and exhibit non-reciprocal behavior. This indicates that hexagonal ferrites are promising candidates for self-biasing circulators embedded in LTCC microwave modules operating at Ka-band frequencies at around 30 GHz.
https://doi.org/10.1016/j.materresbull.2024.112878
Correlation of rare earth coordination and spectral properties in Er3+ doped Na2O-Al2O3-SiO2 glasses with different Al2O3 concentrations by molecular dynamics simulations. - In: Journal of luminescence, ISSN 0022-2313, Bd. 273 (2024), 120676, S. 1-9
The molecular structure of Er2O3 doped Na2O-Al2O3-SiO2 glasses with varying Na2O/Al2O3 ratios is explored via molecular dynamics (MD) simulations using the so-called inherent structure sampling method, which allows the calculation of a large number of local structures of low concentration, as needed to determine the surrounding of low concentration dopants. General structural parameters, including radial distribution functions, coordination numbers and interatomic distances of all network forming and network modifying ions are reported. However, in this work, special attention is devoted to the effect of Al2O3 concentration on the local surrounding of the doped Er3+ ions. It is shown that the Er atoms coordinate 5-6 oxygen ions in their first coordination sphere in the investigated glasses. The Er-O coordination number increases monotonically with increasing Al2O3 concentration and decreasing Na2O/Al2O3 ratio. It is found that the Er atoms are preferably connected to non-bridging oxygen atoms (NBO) in all glasses, even in the peraluminous composition. Additionally, the MD simulation results are compared to the glasses spectral properties that were already investigated in detail by Tanabe and Hanada. The increasing Er-NBO coordination number derived by MD simulations could be correlated with the increased peak splitting of the Er3+ absorption peaks reported by Tanabe and Hanada. Furthermore, a correlation between the Judd-Ofelt parameters published by Tanabe and Hanada and the Er3+ coordination in the glass structure is discussed. It is shown that the Er-O coordination increases with increasing Ω2 parameter as the Al2O3 concentration increases in the glass composition. A correlation of the average overall Er-O coordination number with the symmetry of the local Er site is proposed.
https://doi.org/10.1016/j.jlumin.2024.120676
Impact of single-melamine tautomerization on the excitation of molecular vibrations in inelastic electron tunneling spectroscopy. - In: Nano letters, ISSN 1530-6992, Bd. 0 (2024), 0, insges. 7 S.
Vibrational quanta of melamine and its tautomer are analyzed at the single-molecule level on Cu(100) with inelastic electron tunneling spectroscopy. The on-surface tautomerization gives rise to markedly different low-energy vibrational spectra of the isomers, as evidenced by a shift in mode energies and a variation in inelastic cross sections. Spatially resolved spectroscopy reveals the maximum signal strength on an orbital nodal plane, excluding resonant inelastic tunneling as the mechanism underlying the quantum excitations. Decreasing the probe-molecule separation down to the formation of a chemical bond between the melamine amino group and the Cu apex atom of the tip leads to a quenched vibrational spectrum with different excitation energies. Density functional and electron transport calculations reproduce the experimental findings and show that the shift in the quantum energies applies to internal molecular bending modes. The simulations moreover suggest that the bond formation represents an efficient manner of tautomerizing the molecule.
https://doi.org/10.1021/acs.nanolett.4c00904