Simulation verschiedener Hull-Zellen-Geometrien, Teil 2 - Erweiterung der Simulationsmodelle mittels 3D. - In: Galvanotechnik, ISSN 0016-4232, Bd. 113 (2022), 5, S. 575-585
Distortion of electric field homogeneity between two thin toroidal electrodes by a dielectric sphere. - In: Serbian journal of electrical engineering, ISSN 2217-7183, Bd. 19 (2022), 1, S. 45-56
We assess the influence of a radius and a relative permittivity of an isotropic dielectric sphere on electric field homogeneity. The homogenous electric field is generated using two thin toroidal electrodes, charged by equal charges of opposite signs. The Poisson equation is solved by a method of separation of variables. Increase in a relative permittivity of the sphere and in its radius, produces more distortions of the electric field homogeneity.
https://doi.org/10.2298/SJEE2201045M
Analysis of biomechanical and biochemical markers of rat muscle soleus fatigue processes development during long-term use of C60 fullerene and N-acetylcysteine. - In: Nanomaterials, ISSN 2079-4991, Bd. 12 (2022), 9, 1552, S. 1-15
The development of an effective therapy aimed at restoring muscle dysfunctions in clinical and sports medicine, as well as optimizing working activity in general remains an urgent task today. Modern nanobiotechnologies are able to solve many clinical and social health problems, in particular, they offer new therapeutic approaches using biocompatible and bioavailable nanostructures with specific bioactivity. Therefore, the nanosized carbon molecule, C60 fullerene, as a powerful antioxidant, is very attractive. In this study, a comparative analysis of the dynamic of muscle soleus fatigue processes in rats was conducted using 50 Hz stimulation for 5 s with three consistent pools after intraperitoneal administration of the following antioxidants: C60 fullerene (a daily dose of 1 mg/kg one hour prior to the start of the experiment) and N-acetylcysteine (NAC; a daily dose of 150 mg/kg one hour prior to the start of the experiment) during five days. Changes in the integrated power of muscle contraction, levels of the maximum and minimum contraction force generation, time of reduction of the contraction force by 50% of its maximum value, achievement of the maximum force response, and delay of the beginning of a single contraction force response were analyzed as biomechanical markers of fatigue processes. Levels of creatinine, creatine phosphokinase, lactate, and lactate dehydrogenase, as well as pro- and antioxidant balance (thiobarbituric acid reactive substances, hydrogen peroxide, reduced glutathione, and catalase activity) in the blood of rats were analyzed as biochemical markers of fatigue processes. The obtained data indicate that applied therapeutic drugs have the most significant effects on the 2nd and especially the 3rd stimulation pools. Thus, the application of C60 fullerene has a (50-80)% stronger effect on the resumption of muscle biomechanics after the beginning of fatigue than NAC on the first day of the experiment. There is a clear trend toward a positive change in all studied biochemical parameters by about (12-15)% after therapeutic administration of NAC and by (20-25)% after using C60 fullerene throughout the experiment. These findings demonstrate the promise of using C60 fullerenes as potential therapeutic nanoagents that can reduce or adjust the pathological conditions of the muscular system that occur during fatigue processes in skeletal muscles.
https://doi.org/10.3390/nano12091552
A novel covariance model for MIMO sensing systems and its identification from measurements. - In: Signal processing, Bd. 197 (2022), 108542
A novel model for the covariance matrix of sampled observations by multiple-input-multiple-output (MIMO) sensing systems with parallel receiver channels will be presented. The model is of shifted Kronecker structure and accounts for two mutually independent noise processes: a coloured and a white one. The maximum-likelihood (ML) estimator is applied to identify this covariance model from observations. The ML estimator gives rise to a non-convex optimisation problem. Since no closed-form solution is available, an iterative, space-alternating Gauss-Newton algorithm is proposed to solve the optimisation problem. This approach repeatedly requires the evaluation of the ML cost function. Since the cost function composes of the inverse and determinant of the covariance matrix, its evaluation can be memory exhaustive, numerically unstable and computationally complex. A computational method is developed to overcome these issues, using the simultaneous matrix diagonalisation and exploiting the properties of the Kronecker product. Measurements by a MIMO radar are used to identify the covariance model and to demonstrate its benefits. The identified covariance model is used to whiten the measurements. The whitening reduces interfering, noise-like components, which enhances the signal-to-interference ratio and hence facilitates the target detection.
https://doi.org/10.1016/j.sigpro.2022.108542
Effect of fullerene C60 thermal and tribomechanical loading on Raman signals. - In: Diamond and related materials, ISSN 0925-9635, Bd. 126 (2022), 109036, S. 1-14
Fullerene C60 powder was loaded by 1 N normal force and exposed to sliding under different frequencies for 15 min. It is shown that the velocity of the sliding movement determines the stability of the fullerene C60 powder. At slow velocity of movement with a frequency of 1 Hz under 1 N normal force, the fullerene C60 structure remains undamaged after 15 min sliding. On the contrary, high sliding velocities of 10 Hz and 50 Hz affected fragmentation of the fullerene C60, which resulted in a reduction of the coefficient of friction (COF). During sliding with 1 Hz, the friction reached the highest level with an average COF of 0.59 ± 0.03. The faster relative motion under 1 N normal force gave a lower average COF with 0.39 ± 0.03. The initial fullerene C60 powder formed a thick compressed layer in the tribomechanical loaded zone. As proven by Raman spectroscopy, operating the tribomechanical sliding test at 50 Hz stimulated the re-attraction of fresh C60 fullerene island onto the fragmented layer from outside of the loaded powder regions. The COF was increasing again up to 0.44 ± 0.04 for 1 N normal force and 50 Hz frequency. The fragmentation and decomposition of fullerene C60 with increasing sliding velocity is attributed to thermal heating up during fast relative movement. Raman spectra of the tribomechanical loaded fullerene C60 are compared with Raman spectra from slowly heated up C60 in air and with Raman spectra of laser irradiated fullerene C60.
https://doi.org/10.1016/j.diamond.2022.109036
Individually optimized multi-channel tDCS for targeting somatosensory cortex. - In: Clinical neurophysiology, ISSN 1872-8952, Bd. 134 (2022), S. 9-26
Objective - Transcranial direct current stimulation (tDCS) is a non-invasive neuro-modulation technique that delivers current through the scalp by a pair of patch electrodes (2-Patch). This study proposes a new multi-channel tDCS (mc-tDCS) optimization method, the distributed constrained maximum intensity (D-CMI) approach. For targeting the P20/N20 somatosensory source at Brodmann area 3b, an integrated combined magnetoencephalography (MEG) and electroencephalography (EEG) source analysis is used with individualized skull conductivity calibrated realistic head modeling. - Methods - Simulated electric fields (EF) for our new D-CMI method and the already known maximum intensity (MI), alternating direction method of multipliers (ADMM) and 2-Patch methods were produced and compared for the individualized P20/N20 somatosensory target for 10 subjects. - Results - D-CMI and MI showed highest intensities parallel to the P20/N20 target compared to ADMM and 2-Patch, with ADMM achieving highest focality. D-CMI showed a slight reduction in intensity compared to MI while reducing side effects and skin level sensations by current distribution over multiple stimulation electrodes. - Conclusion - Individualized D-CMI montages are preferred for our follow up somatosensory experiment to provide a good balance between high current intensities at the target and reduced side effects and skin sensations. - Significance - An integrated combined MEG and EEG source analysis with D-CMI montages for mc-tDCS stimulation potentially can improve control, reproducibility and reduce sensitivity differences between sham and real stimulations.
https://doi.org/10.1016/j.clinph.2021.10.016
Reverse numerical simulation of kinetic parameters from acidic copper Hull cell deposition. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Bd. 169 (2022), 5, 052501
Hull cell depositions are industrially used to monitor electrolytes and study the influence of additives. By combining the Hull cell deposition and a numerical simulation based on the boundary element method via a curve-fitting approach allows to obtain kinetic parameters (e.g. transfer coefficient, exchange current density) and assessing the effects of additives without losing the visual information and the opportunity to get the structural and physical properties of the metal deposition (reverse determination). In an acidic copper electrolyte, an additive based on polyethylene glycol decreases the effective exchange current density, by up to two orders of magnitude, while the transfer coefficient is hardly influenced. By adding another additive based on bis-(3-sulfopropyl)disulphide, the effect is counteracted and increases in dependence on the ratio of both additives. The combined approach enables obtaining more information about visual and structural effects and the deposition kinetics from one experimental analysis.
https://doi.org/10.1149/1945-7111/ac694c
Size dependent properties of reactive materials. - In: Inorganics, ISSN 2304-6740, Bd. 10 (2022), 4, 56, S. 1-19
The nature of the self-sustained reaction of reactive materials is dependent on the physical, thermal, and mechanical properties of the reacting materials. These properties behave differently at the nano scale. Low-dimensional nanomaterials have various unusual size dependent transport properties. In this review, we summarize the theoretical and experimental reports on the size effect on melting temperature, heat capacity, reaction enthalpy, and surface energy of the materials at nano scale because nanomaterials possess a significant change in large specific surface area and surface effect than the bulk materials. According to the theoretical analysis of size dependent thermodynamic properties, such as melting temperature, cohesive energy, thermal conductivity and specific heat capacity of metallic nanoparticles and ultra-thin layers varies linearly with the reciprocal of the critical dimension. The result of this scaling relation on the material properties can affect the self-sustained reaction behavior in reactive materials. Resultant, powder compacts show lower reaction propagation velocities than bilayer system, if the particle size of the reactants and the void density is decreased an increase of the reaction propagation velocity due to an enhanced heat transfer in reactive materials can be achieved. Standard theories describing the properties of reactive material systems do not include size effects.
https://doi.org/10.3390/inorganics10040056
The effect of meninges on the electric fields in TES and TMS. Numerical modeling with adaptive mesh refinement. - In: Brain stimulation, ISSN 1876-4754, Bd. 15 (2022), 3, S. 654-663
Background - When modeling transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS) in the brain, the meninges - dura, arachnoid, and pia mater - are often neglected due to high computational costs. - Objective - We investigate the impact of the meningeal layers on the cortical electric field in TES and TMS while considering the headreco segmentation as the base model. - Method - We use T1/T2 MRI data from 16 subjects and apply the boundary element fast multipole method with adaptive mesh refinement, which enables us to accurately solve this problem and establish method convergence at reasonable computational cost. We compare electric fields in the presence and absence of various meninges for two brain areas (M1HAND and DLPFC) and for several distinct TES and TMS setups. - Results - Maximum electric fields in the cortex for focal TES consistently increase by approximately 30% on average when the meninges are present in the CSF volume. Their effect on the maximum field can be emulated by reducing the CSF conductivity from 1.65 S/m to approximately 0.85 S/m. In stark contrast to that, the TMS electric fields in the cortex are only weakly affected by the meningeal layers and slightly (∼6%) decrease on average when the meninges are included. - Conclusion - Our results quantify the influence of the meninges on the cortical TES and TMS electric fields. Both focal TES and TMS results are very consistent. The focal TES results are also in a good agreement with a prior relevant study. The solver and the mesh generator for the meningeal layers (compatible with SimNIBS) are available online.
https://doi.org/10.1016/j.brs.2022.04.009
Metal oxide semiconducting nanomaterials for air quality gas sensors: operating principles, performance, and synthesis techniques. - In: Microchimica acta, ISSN 1436-5073, Bd. 189 (2022), 5, 196, S. 1-22
To meet requirements in air quality monitoring, sensors are required that can measure the concentration of gaseous pollutants at concentrations down to the ppb and ppt levels, while at the same time they exhibiting high sensitivity, selectivity, and short response/recovery times. Among the different sensor types, those employing metal oxide semiconductors (MOSs) offer great promises as they can be manufactured in easy/inexpensive ways, and designed to measure the concentration of a wide range of target gases. MOS sensors rely on the adsorption of target gas molecules on the surface of the sensing material and the consequent capturing of electrons from the conduction band that in turn affects their conductivity. Despite their simplicity and ease of manufacturing, MOS gas sensors are restricted by high limits of detection (LOD; which are typically in the ppm range) as well as poor sensitivity and selectivity. LOD and sensitivity can in principle be addressed by nanostructuring the MOSs, thereby increasing their porosity and surface-to-volume ratio, whereas selectivity can be tailored through their chemical composition. In this paper we provide a critical review of the available techniques for nanostructuring MOSs using chemiresistive materials, and discuss how these can be used to attribute desired properties to the end gas sensors. We start by describing the operating principles of chemiresistive sensors, and key material properties that define their performance. The main part of the paper focuses on the available methods for synthesizing nanostructured MOSs for use in gas sensors. We close by addressing the current needs and provide perspectives for improving sensor performance in ways that can fulfill requirements for air quality monitoring.
https://doi.org/10.1007/s00604-022-05254-0